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Value-added Conversion of Waste Cooking Oil, Post-consumer PET Bottles and Soybean
Meal into Biodiesel and Polyurethane Products
THESIS
Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in
the Graduate School of The Ohio State University
By
Yu Dang
Graduate Program in Food, Agricultural & Biological Engineering
The Ohio State University
2016
Master's Examination Committee:
Dr. Scott A. Shearer, Advisor
Dr. Katrina Cornish, Co-Advisor
Dr. Jianjun Guan
Dr. Rudolph G. Buchheit
Copyrighted by
Yu Dang
2016
Abstract
Biodiesel is an environmentally friendly alternative to petroleum diesel. It is
biodegradable, nontoxic and has lower greenhouse gas emission profiles compared to
petroleum diesel. Polyurethane (PU) products such as PU foams and PU coatings are
widely used in many aspects of our life. Traditionally, the PU industry is heavily
petroleum dependent because both the feedstocks - isocyanates and polyols - are
petrochemical products. Bio-based PU products became a very promising research field
due to concerns about the environment and the depletion of petroleum resources.
Waste cooking oil (WCO), which is abundantly available and about 2 or 3 times
cheaper than virgin vegetable oil, is considered a good source for production of biodiesel.
Also, post-consumer PET bottles contribute a large volume fraction in the solid waste
stream and their non-biodegradability has caused concern. In this study, a sustainable
process of value-added utilization of wastes, specifically WCO and post-consumer PET
bottles for the production of biodiesel and PU foams, respectively, was developed. WCO
collected from campus cafeteria was firstly converted into biodiesel, which can be used
as vehicle fuel. Then crude glycerol (CG), a byproduct of the above biodiesel process,
was incorporated into the glycolysis process of post-consumer PET bottles collected from
campus to produce polyols. Thirdly, PU foams were synthesized through the reaction of
the above produced polyols with isocyanate in the presence of catalysts and other
additives. The characterization of the produced biodiesel demonstrated that its properties
ii
meet the specification of the biodiesel standard. The effect of CG loading on the
properties of polyols and PU foams were investigated. With the increase of CG loading
from 0% -15%, the hydroxyl value increased from 478 mg KOH/g to 592 mg KOH/g.
This is most likely due to the high hydroxyl value of glycerol (1829 mg KOH/g). The PU
foams produced showed density of 46.03-47.66 kg/m3 and compressive strength of 235.9
to 299.9 kPa, which are comparable to some petroleum-based analogs. A mass balance
and a cost analysis for the conversion of WCO and waste PET into biodiesel and PU
foams indicate potential economic viability of the developed process.
Soybean meal (SM) is the soy protein residue after the extraction of oil from
soybeans. With its high protein content, SM has the potential to become one of the
feedstocks for PU production. In this study, a novel way was developed to produce UVcurable PU acrylate coatings from SM. High oleic SM was hydrolyzed by dilute acid to
amino acid oligomers, then a hydroxyl-terminated PU oligomer was synthesized through
a non-isocyanate pathway: i) amination of the amino acid oligomers with ethylene
diamine to produce amino-terminated compound; ii) amidation of the amino-terminated
compound was reacted with ethylene carbonate. Functionalization of hydroxylterminated PU oligomers was achieved by esterification and acrylation reactions to
produce PU acrylate oligomers. PU acrylate oligomers were then formulated with
multifunctional monomer and photo initiator to form a PU coating under UV light. The
PU oligomer after esterification showed a hydroxyl value of 223 mg KOH/g and
viscosity around 6.1 Pa·s at 10.9 1/s shear rate. The UV-cured coating showed higher
tensile strength (approximately 18.2 MPa) and modulus (approximately 450.1 MPa), and
iii
lower elongation at break (approximately 4.5%) compared to other PU acrylate coatings
reported in literature, which might due to hydrogen bonding between amino acid and
urethane bond and enhanced cross-linking density with the incorporation of oleic acid in
esterification reaction.
In summary, the value-added conversion of WCO, post-consumer PET bottles and
SM into Biodiesel and PU products (i.e. PU foams and coatings) have been successfully
developed in this study. All the parameters of biodiesel produced from WCO meet the
requirements in the ASTM D6751 standard. The PU foams showed good compressive
strength and insulation properties and have potential application as construction
materials. The PU coatings also showed promising mechanical properties and good
thermal stability.
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This document is dedicated to my family.
v
Acknowledgments
I would like to say thank my advisor, Dr. Scott Shearer, and my co-advisor Dr.
Katrina Cornish for their support, encouragement and guidance to me. I also would like
to thank Dr. Rudolph Buchheit and Dr. Jianjun Guan for their time and effort as my
committee members. Furthermore, I want to thank Mrs. Candy McBride and Mrs. Peggy
Christman for their administrative support, Mrs. Mary Wicks for proofreading and
providing useful suggestions to my papers and proposals, and Mr. Michael Klingman for
his technical support on my research.
My appreciation also goes to Dr. Fuqing Xu, Dr. Feng Wang, Dr. Xumeng Ge,
Dr. Chun Chang, Ms. Juliana Vasco Correa, Mrs. Danping Jiang, Mrs. Xiaoying Zhao,
Mr. Lu Zhang Mr. Johnathon Sheets and many more for their help and friendship. I
would give my special thanks to Dr. Xiaolan Luo who gave me lots of advice and help on
my research, Dr. Mark Soucek and Dr. Zhouying He from The University of Akron for
their help and support on my project. I also want to thank Ms. Kathryn Lawson and Mr.
Josh Borgemenke for their support on the courses I took in Columbus. Lastly, I would
like to thank my family, my boyfriend Kyle Smith and my beloved friends Wenna Chen,
Fang Qiu, Rao Fu and Yuli Fan for their constant encouragement and understanding to
me through the two years of my graduate study and for always believe in me and support
my choices.
vi
Vita
1991................................................................Born, Chengdu, Sichuan, China
2014................................................................B.S. Polymer Materials and Engineering,
Sichuan University, China
2014 to present ..............................................Graduate Teaching Associate, Department
of Food, Agricultural and Biological
Engineering, The Ohio State University
Publications
1.
Shi, Y., Huang, G., Liu, Y., Qu, Y., Zhang, D., Dang, Y. Synthesis and thermal
properties of novel room temperature vulcanized (RTV) silicone rubber containing POSS
units in polysioxane main chains. Journal of Polymer Research (2013) 20:245, DOI:
10.1007/s10965-013-0245-y
2.
Dang, Y., Luo, X., Wang, F., Li, Y. Value-Added Conversion of Waste Cooking
Oil and Post-consumer PET Bottles into Biodiesel and Polyurethane Foams. Waste
Management (2016) 52:360-6, DOI: 10.1016/j.wasman.2016.03.054
vii
Fields of Study
Major Field: Food, Agricultural & Biological Engineering
viii
Table of Contents
Abstract ............................................................................................................................... ii
Acknowledgments.............................................................................................................. vi
Vita.................................................................................................................................... vii
Table of Contents ............................................................................................................... ix
List of Tables ................................................................................................................... xiii
List of Figures .................................................................................................................. xiv
Chapter 1: Introduction ...................................................................................................... 1
1.1
Background .............................................................................................................. 1
1.2
Research hypothesis ................................................................................................. 4
1.3
Research objectives .................................................................................................. 4
Chapter 2: Literature review ............................................................................................... 6
2.1 Introduction ................................................................................................................... 6
2.2 Polyols and PUs from CG ............................................................................................. 7
2.2.1 Polyols and PUs from direct conversion of CG ..................................................... 7
2.2.2 Polyols and PUs from CG based liquefaction of lignocellulosic biomass ........... 10
ix
2.3 Polyols and PUs from glycolyzation of PET .............................................................. 12
2.4 polyols and PUs from protein based feedstocks ......................................................... 15
2.4.1 Introduction of different types of protein feedstocks ........................................... 15
2.4.2. Polyols from protein feedstocks .......................................................................... 17
2.4.3 PUs of protein feedstocks ..................................................................................... 19
Chapter 3 Value-Added Conversion of Waste Cooking Oil and Post-consumer PET
Bottles into Biodiesel and Polyurethane Foams ............................................................... 22
3.1 Introduction ................................................................................................................. 22
3.2 Experimental ............................................................................................................... 24
3.2.1 Materials ............................................................................................................... 24
3.2.2 Characterization of WCO ..................................................................................... 25
3.2.3 Production of biodiesel from WCO ..................................................................... 26
3.2.4 Characterization of biodiesel and CG from biodiesel production ........................ 26
3.2.5 Synthesis of polyols ............................................................................................. 27
3.2.6 Characterization of polyols .................................................................................. 27
3.2.7 Synthesis of PU foams ......................................................................................... 28
3.2.8 Characterization of PU foams .............................................................................. 28
3.3 Results and Discussion ............................................................................................... 29
3.3.1 Properties of biodiesel and CG from WCO ......................................................... 29
x
3.3.2 Properties of polyols............................................................................................. 30
3.3.3 Performance of PU foams .................................................................................... 32
3.3.4 Structural characterization.................................................................................... 35
3.3.5 Mass balance and cost analyses of the process from WCO and waste PET to
biodiesel and PU foams ................................................................................................. 36
3.4 Conclusion .................................................................................................................. 39
Chapter 4 Value-added Conversion of soybean meal into UV-curable polyurethane
acrylate coatings................................................................................................................ 40
4.1 Introduction ................................................................................................................. 41
4.2 Materials and methods ................................................................................................ 41
4.2.1 Materials ............................................................................................................... 41
4.2.2 Measurements....................................................................................................... 42
4.2.3 Synthesis of glutamic acid based hydroxyl terminated PU oligomer .................. 43
4.2.4 Synthesis of SM based polyol .............................................................................. 43
4.2.5 Preparation of UV cured PU coating.................................................................... 48
4.3 Results and discussion ................................................................................................ 48
4.3.1 Model compound glutamic acid based polyol...................................................... 48
4.3.2 SM-based polyol .................................................................................................. 50
4.3.3 Properties of the coating film ............................................................................... 51
xi
4.3.3.1 Mechanical properties.................................................................................... 51
4.3.3.2 Thermal properties ......................................................................................... 52
4.4 Conclusions ................................................................................................................. 54
Chapter 5 Conclusions and Suggestions for Future Research .......................................... 55
5.1 Conclusions ................................................................................................................. 55
5.2 Suggestions for Future Research ................................................................................ 56
References ......................................................................................................................... 57
xii
List of Tables
Table 1 PU foam production formula ............................................................................... 28
Table 2 Properties of biodiesel sample compared to ASTM D6751 standard .................. 30
Table 3 Properties of polyols from PET and CG .............................................................. 32
Table 4 Foaming characteristics of PU foams .................................................................. 33
Table 5 Breakdown of biodiesel production costs in dollars per liter .............................. 37
Table 6 Breakdown of PU foam production costs in dollars per kilogram ...................... 37
Table 7 Amine, acid and hydroxyl value of Glu and SM derived oligomers ................... 50
Table 8 Mechanical properties of SM-based PU acrylate coating .................................... 52
Table 9 Thermal properties of SM-based PU acrylate coating ......................................... 53
xiii
List of Figures
Figure 1 Reactions involved in the thermochemical conversion of CG for the production
of polyols (Li et al., 2015) .................................................................................................. 9
Figure 2 Modification of protein with PEG and cyanuric chloride for the production of
polyol (Li et al., 2015) ...................................................................................................... 18
Figure 3 Modification of protein with ethylene diamine and ethylene carbonate for the
production of polyol (Li et al., 2015) ................................................................................ 19
Figure 4 The process diagram for value-added conversion of WCO and post-consumer
PET bottles into biodiesel and PU foams ......................................................................... 24
Figure 5 Mass balance analysis for the production of biodiesel and PU foams from WCO
and post-consumer PET bottles ........................................................................................ 24
Figure 6 Compressive strength, density, and thermal conductivity of PU foams............. 34
Figure 7 FT-IR spectra of PET, DEG, CG, Pol-9, and PUF-9 ......................................... 36
Figure 8 Process diagram for the conversion of SM into UV-cured PU acrylate coating 41
Figure 9 Synthesis route of hydroxyl-terminated PU oligomer ........................................ 46
Figure 10 Synthesis route of PUOFA and PUAO ............................................................ 47
Figure 11 FT-IR spectra of (A) Glu-ED-EC, (B) Glu-ED, and (C) Glu ........................... 48
Figure 12 Viscosity as a function of shear rate of SM-PUOFA and SM-ED-EC............. 51
Figure 13 TGA and DTA curves of UV-cured PU acrylate coating................................. 53
xiv
Chapter 1: Introduction
1.1
Background
Biodiesel is a promising alternative to fossil fuels. The production of biodiesel involves a
transesterification reaction of renewable feedstocks, such as vegetable oils and animal fat,
with alcohol. It is biodegradable and nontoxic, and has lower greenhouse gas emissions
than petroleum diesel, so is environmentally beneficial (Ma and Hanna, 1999). The
limitations to extensive commercialization of biodiesel are high manufacturing cost and
competition for vegetable oil with food consumption. Waste cooking oil (WCO), which is
abundantly available and about 2.5-3.0 times cheaper than virgin vegetable oils
(Demirbas, 2009), can considerably reduce biodiesel production cost. It is estimated that
an average of 10 kilograms of total waste grease per person are produced annually in the
U.S. (Wiltsee, 1998).
Crude glycerol (CG) is a major byproduct generated during biodiesel production.
Basically, the production of every 10 kg of biodiesel yields approximately 1 kg of CG
(Kongjao et al., 2010). Depending on the feedstock, the process and the post-treatment
methods used, CG contains various impurities such as free fatty acids (FFAs), alcohols,
water, salts, and soap and has a low value (approximately $0.11/kg) (Johnson and Taconi,
2007). The refining of CG to pure glycerol is an important value-added processing step
because glycerol is a versatile platform chemical in the industries of foods and beverages,
1
pharmaceuticals, cosmetics, textiles, etc. However, refining processes are costly
(approximately $0.44/kg (Werpy et al., 2004)), especially for small- and medium-sized
biodiesel plants (Pachauri and He, 2006). CG has become a potential financial and
environmental liability for biodiesel producers (Johnson and Taconi, 2007). Many studies
have been conducted to develop both chemical and biological processes for value-added
conversion of CG (Johnson and Taconi, 2007; Pachauri and He, 2006; Pagliaro et al.,
2007; Yang et al., 2012). Examples of products derived from CG include: 1,3propanediol (Mu et al., 2006; Oh et al., 2008), citric acid (Rywińska and Rymowicz,
2010), hydrogen (Sabourin-Provost and Hallenbeck, 2009), poly(hydroxyalkanoates)
(Mothes et al., 2007), succinic acid (Scholten et al., 2009), polyols, and polyurethane
(PU) foams (Hu et al., 2012; Luo et al., 2013).
Poly (ethylene terephthalate) (PET) is a semi-crystalline thermoplastic material widely
used in the manufacture of fibers, films and food packaging materials-mainly bottles.
Although waste PET materials do not create a direct hazard to the environment, its
substantial fraction by volume in the waste stream and its high resistance to atmospheric
and biological agents has led to concerns over its environmental pollution (Paszun and
Spychaj, 1997; Sinha et al., 2010). Recycling and reprocessing PET can serve as a way to
reduce solid waste and also contribute to the conservation of raw petrochemical products
and energy. Chemical recycling is one of the most attractive techniques of recycling PET
waste as it can depolymerize PET to generate feedstocks for the production of highly
valuable polymers (Sinha et al., 2010). Chemical recycling of PET can be divided by the
type of chemical agents used: hydrolysis of PET is carried out in alkaline solution or
2
concentrated acid (Paszun and Spychaj, 1997); glycolysis of PET is carried out in
glycols, most frequently ethylene glycol (Baliga and Wong, 1989), diethylene glycol
(Pardal and Tersac, 2006), propylene glycol(Vaidya and Nadkarni, 1987) or dipropylene
glycol (Vaidya and Nadkarni, 1988); methanolysis of PET is carried out in methanol
(Kishimoto et al., 1999; Yang et al., 2002).
Soybeans are widely grown as an industrial crop cultivated for oil and protein. Soybeans
account for 55% global oilseed production and 90% U.S. oilseed production (Cromwell,
2011). In the U.S., about 70% of soybean oil goes to human consumption; about 22%
goes to the production of biodiesel, and the remainder to other uses, including the
production of coatings, inks, lubricants, soy polyols and other industrial products.
Soybean meal (SM) is the soy protein residue after oil extraction, for each ton of crude
soybean oil, about 4.5 tons of SM is produced (Watchararuji et al., 2008). SM has long
been considered an excellent supplemental protein source in diets for livestock and
poultry because of its high content (44% to 49%) of digestible protein. Recently, soybased plastics, adhesives, films and coatings are being considered in agricultural
equipment, marine infrastructure, automobiles and civil engineering (Kumar et al., 2002).
However, the low mechanical properties and weak water resistance of soy protein has
hindered expansion of its industrial use. Nowadays, most SM is used as animal feed
(96.49%), and only a small portion (3.29%)is refined to flour, concentrates or isolates
suitable for human consumption, and an even smaller amount (0.22%) of SM is used
industrial applications, such as fibers, adhesives, and paper coatings (United Soybean
Board, 2015).
3
PUs are versatile polymeric materials and can be used in many aspects of modern life.
Due to the large variety of their isocyanate and polyol feedstocks, PUs can be easily
tailored for wide applications, such as foams, coatings, adhesives, constructional
materials, fibers, paddings, paints, elastomers and synthetic skins. Traditionally, the PU
industry is heavily petroleum dependent because isocyanates and polyols are both
petrochemical products. With the growing awareness of the need to find alternatives to
petroleum resources, the demand for green or bio-based PUs is increasing. Different
renewable feedstocks have been studied for the production of bio-based polyols and PU,
including vegetable oils and their derivatives, lignocellulosic biomass, and protein based
feedstocks (Li et al., 2015).
In this study, we developed a sustainable process for value-added conversion of WCO
and post-consumer PET bottles into biodiesel and PU foams, and a process for the
production of UV-cured PU acrylate coatings from SM, respectively. The properties of
the produced biodiesel, polyols, PU foams and PU acrylate coatings were evaluated. The
effects of CG loading on properties of polyols and the resulting PU foam also were
investigated. A mass balance and a cost analysis for the conversion of WCO and waste
PET to biodiesel and PU foams are discussed.
1.2
Research hypothesis
The central hypothesis of this study is that CG, post-consumer PET materials and SM can
be can be effectively utilized for the production of polyols and PU products with
commercially-acceptable properties and production costs.
1.3
Research objectives
4
1)
Produce biodiesel and PU foams from WCO and post-consumer PET bottles,
investigate the effect of CG loading on the properties of polyols and PU foams, conduct
mass balance and cost analysis of the whole process. (Chapter 3)
2)
Prepare UV-cured PU acrylate coatings from SM and evaluate their mechanical
properties and thermal properties. (Chapter 4)
5
Chapter 2: Literature review
2.1 Introduction
Polyol generally refers to compounds that contain two or more reactive hydroxyl
groups in one molecule. Polyols used in polyurethane (PU) manufacture are divided into
two groups based on their structure. The first group is monomeric polyols with low
molecular weight (Mw), such as: propylene glycol, ethylene glycol, dipropylene glycol,
diethylene glycol, 1, 4 butanediol, triethanolamine, glycerol, and others. These polyols
are often used as chain extenders and crosslinkers in PU production. The second group is
polymeric polyols, i.e. polyols that are low Mw polymers with terminal hydroxyl groups.
Most common polymeric polyols used in the PU industry are polyether and polyester
polyols (Ionescu, 2005). By controlling the functionality of the initiator and the degree of
polymerization, a wide range of polyols are commercially available for various types of
PU applications. Generally, polyols with high functionality (3.0-8.0), low molecular
weight (150-1000 g/mol), and high hydroxyl value (250-1000 mg KOH/g) are used for
the production of rigid foams and high performance coatings, while polyols with low
functionality (2.0-3.0), higher molecular weight (1000-6500 g/mol), and low hydroxyl
value are used for the production of flexible foams and elastomers (Fink, 2005; Szycher,
1999).
6
Currently, the PU industry is heavily depended on petroleum derivatives, because
most commercial polyols and isocyanates are petrochemical products. Recently, concern
over the depletion of petroleum has led to the development of bio-based polyols and PUs
from renewable sources. Three major sources for producing bio-based polyols include:
vegetable oils and their derivatives, lignocellulosic biomass and protein-based feedstocks
(Li et al., 2015).
Vegetable oils, such as palm oil, soybean oil, rapeseed oil, and sunflower seed oil,
and their derivatives have been widely used for the production of polyols and PUs. The
pathways for the production of polyols from vegetable oils are: (1) epoxidation and
oxirane ring-opening, (2) hydroformylation and hydrogenation, (3) ozonolysis, (4) thiolene coupling, and (5) transesterification/ amidation (Li et al., 2015). The polyols and PUs
prepared from vegetable oils have comparable properties to petroleum-based analogs.
However, polyols and PUs made from vegetable oils and their derivatives still face
challenges including technical barriers and high cost. It is also worth noting that the
production of polyols and PUs from vegetable oils will compete with food supplies and
biodiesel production.
Value-added conversion of biodiesel industry byproducts such as crude glycerol
(CG) and soybean meal (SM) into biobased polyols and PU products has the potential to
improve the economics of biodiesel production as well as the sustainability of the polyol
and PU industry.
2.2 Polyols and PUs from CG
2.2.1 Polyols and PUs from direct conversion of CG
7
Direct utilization of CG to produce bio-based polyols and PU foams has been
reported. Hoong et al. (Hoong et al., 2011) produced polyglycerol from CG. The
preferred CG composition from biodiesel industry was: 60 to 90% glycerol, 10 to 25%
methanol and 10 to 15% soap. The process steps included (a) thermal dehydration
reaction of CG to polyglycerol at 270ºC for 3 to 5 hours, soap in CG could act as a
catalyst in this step, (b) acidification of the crude product with phosphoric acid at 5090ºC, (c) centrifugation to separate the fatty acid and salt from the product. However, the
properties of the polyglycerol produced through this process, such as hydroxyl values,
were not tested, and the feasibility of using polyglycerol for the production of PU
materials was not investigated. Thermochemical conversion of CG for polyols was also
reported (Hu et al., 2015; Li et al., 2014; Luo et al., 2013). The reactions involved in the
thermochemical conversion are mainly (1) acidification of soap using sulfuric acid, (2)
esterification of glycerol and fatty acids, (3) transesterification of glycerol and fatty acid
methyl esters (FAME) (Figure 1) (Li et al., 2015). The reaction parameters, such as
sulfuric acid loading, reaction temperature and reaction time, were investigated by Luo et
al. (Luo et al., 2013). It was discovered that the preferred reaction conditions for the CG
used in the study (composition: 22.9% glycerol, 10.9% methanol, 18.2% water, 26.2%
soap, 21.3% FAMEs, 1.0% FFAs, and 1.2% glycerides) were 200ºC, 90 min and 3%
sulfuric acid loading. Hu et al. (Hu et al., 2015) also investigated the effect of soap
content in CG on polyol production. Their study showed that at higher soap levels,
FAMEs were converted more rapidly than at low levels due to the intensified emulsifying
and/or catalytic effects of soap. However, it is worth noting that high residual soap
8
content in the polyols is unfavorable for PU production. Therefore, after balancing these
two contradictory effects of soap, they concluded that the preferred soap content was
6.6%, and the polyol produced at 190ºC and 120 min had low FFA (< 1%) and FAME
(ca. 2.5%) contents.
Figure 1 Reactions involved in the thermochemical conversion of CG for the production
of polyols (Li et al., 2015)
Polyols produced from CG have been used to make PU foams and waterborne PU
coatings. PU foams using polyol produced from CG (acid value 5.02 ± 0.03mg KOH/g,
hydroxyl value 481± 10 mg KOH/g) and polymeric methylene-4,4’-diphenyl
9
diisocyanate (pMDI) (Luo et al., 2013) had a compressive strength of 184.5 kPa and a
density of 43.0 kg/m3, both of which are comparable to petroleum based and vegetable oil
based analogs (Li et al., 2015; Luo et al., 2013). Waterborne PU coatings derived from
CG-based polyols had higher glass transition temperatures (Tg) (66-81 ºC) than coatings
from soybean oil-based polyol due to higher functionality (fn: 4.7) and higher hydroxyl
number (378 mg KOH/g) of the CG-based polyols. The waterborne PU coatings from
CG-based polyol also had similar thermal degradation properties as vegetable-oil based
PU coatings, excellent adhesion properties and low flexibility (Hu et al., 2015).
2.2.2 Polyols and PUs from CG based liquefaction of lignocellulosic biomass
Lignocellulosic biomass refers to the dry matter in plants, and is the world’s most
abundant renewable biomass feedstock. The main structural units in lignocellulosic
biomass are carbohydrate polymers (30-35% cellulose, 15-35% hemicellulose), and
aromatic polymers (20-35% lignin), all of which are highly functionalized materials rich
in hydroxyl groups, making them promising candidate for bio-based polyol production.
Currently, polyols from lignocellulosic biomass are mainly produced by two
technologies: (1) oxypropylation and (2) liquefaction. The oxypropylation of
lignocellulosic biomass is a polymerization process that grafts oligo (propylene oxide) or
propylene oxide onto macromolecular structures of lignocellulosic biomass. The reaction
often requires KOH as catalyst and is often carried out under high pressure (650-1820
kPa) and high temperature (100-200 ºC) (Evtiouguina et al., 2000; Li et al., 2015). The
polyols produced from oxypropylation process is a mixture containing oxypropylated
10
biomass, poly propylene oxide, and some unreacted or partially oxypropylated biomass,
and usually can be directly used in the production of PU materials (Aniceto et al., 2012).
Liquefaction of lignocellulosic biomass is the degradation and decomposition
processes of biomass into smaller molecules by polyhydric alcohols via solvolytic
reactions. The liquefaction process is often conducted at elevated temperatures (150-250
ºC) under atmospheric pressure, and can be either acid- or base-catalyzed. Polyols
produced via liquefaction of lignocellulosic biomass are a mixture of different
compounds rich in hydroxyl groups and can be used directly in the preparation of PU
foams (Yan et al., 2008), adhesives (Juhaida et al., 2010; Lee and Lin, 2008) and films
(Kurimoto et al., 2001).
A variety of lignocellulosic biomasses such as wood, wheat straw, corn bran and
cornstalks have been studied for production of polyols by either oxypropylation or
liquefaction.
Currently, almost all liquefaction solvents are expensive petroleum-derived
polyhydric alcohols, such as polyethylene glycol, ethylene glycol, glycerol and ethylene
carbonate. Typically, 5-6.25 g solvent/g biomass is needed to obtain high-quality polyols.
Because of its potential to reduce the high cost of solvent and increase the sustainability
of the biomass liquefaction process, CG from the biodiesel industry has also been studied
as an alternative biomass liquefaction solvent for polyol production. The effects of
reaction temperature, reaction time, sulfuric acid loading and biomass loading on the
liquefaction process of soybean straw have been evaluated (Hu et al., 2012). With an
increase in reaction temperature from 120 to 240 ºC, the biomass conversion rate
11
increased from 15% to 50%, the viscosity of the polyol increased from 36 to higher than
100 Pa·s, the polyol hydroxyl and acid value decreased from approximately 635 to 533
mg KOH/g and from 23 to 2.7 mg KOH/g, respectively. Increasing reaction time from 45
to 360 min increased the biomass conversion ratio from 46% to 75%. The optimal
loading of sulfuric acid as catalyst was between 3% and 5%, and optimal biomass loading
was between 10% and 15%. This study showed that liquefaction temperature, reaction
time, and acid loading had significant effects on the density of the PU foams (p <0.05),
while liquefaction temperature, reaction time and biomass loading had significant effects
on the compressive strength of the PU foams (p <0.05). Despite the slightly lower
biomass liquefaction efficiency, the polyols and PU foams produced exhibited properties
comparable to those prepared from conventional petroleum solvent based liquefaction
processes (Hu et al., 2012). A two-step sequential CG-based liquefaction of
lignocellulosic biomass (corn stover) also was developed (Hu and Li, 2014). The first
step, acid-catalyzed liquefaction, was highly effective in liquefying biomass, which
helped enhance biomass conversion rate; the second step, base-catalyzed liquefaction,
featured extensive condensation reactions, increased the molecular weight of the
produced polyol and decreased its acid number. The PU foams produced using polyol
from the two-step liquefaction process showed higher compressive strength than those of
PU foams produced from only acid- or base-catalyzed biomass liquefaction process, and
are excellent thermal insulation materials due to their low thermal conductivity (Hu and
Li, 2014).
2.3 Polyols and PUs from glycolyzation of PET
12
PET is semi-crystalline thermoplastic polyester that has been widely used in the
manufacture of apparel fibers, disposable soft-drink bottles, and photographic films (Mir
et al., 2012). This has caused environmental concerns due to large number of postconsumer PET products, especially bottles and containers. Although PET products are
non-toxic and do not create a direct hazard to the environment, they have high resistance
to atmospheric and biological agents, and have a high volume fraction in solid waste
streams. Chemical recycling of PET materials have many advantages over land filling of
such non-biodegradable material: (1) consumption of waste materials by converting them
into new useful materials, (2) conversion of a non-biodegradable polymer into a
biodegradable one (Mir et al., 2012). Among many PET chemolysis processes, such as
hydrolysis (Paszun and Spychaj, 1997), alcoholysis (Kishimoto et al., 1999; Yang et al.,
2002), glycolysis (Baliga and Wong, 1989; Pardal and Tersac, 2006; Vaidya and
Nadkarni, 1987), aminolysis (Shukla and Harad, 2006), and ammonolysis (Blackmon et
al., 1990), glycolysis using various glycols is most popular. During the glycolysis
reaction, PET polymer is depolymerized by glycols, which break the ester linkages and
replace them with hydroxyl groups in the presence of trans-esterification catalysts
(mainly metal acetates). The effects of reaction conditions, such as type of glycol used,
glycolysis time, glycolysis temperature, catalyst concentration, and glycol concentration
on the glycolysis process of PET, have been studied (Chen et al., 2001; Pardal and
Tersac, 2006). Glycolysis of PET by diethylene glycol (DEG), dipropylene glycol (DPG)
and glycerol (Gly) was studied at 220 ºC without catalyst and at 190 ºC with titanium
(IV) n-butoxide by Pardal and Tersac (Pardal and Tersac, 2006). It was found that the
13
order of reactivity for uncatalyzed glycolysis at 220 ºC is: DEG ≫ Gly ≫ DPG, while the
order of reactivity for catalyzed reactions is DEG > DPG ≫ Gly. DEG showed the best
reactivity in both reaction conditions and allows low molecular mass oligomers to be
obtained quickly. A 23 factorial experiment studied the main, two-factor interaction and
three-factor interaction effect of glycolysis temperature, glycolysis time, and the amount
of catalyst (cobalt acetate) on the glycolysis of recycled postconsumer soft-drink PET
bottles. The sequence of main effects on the glycolysis conversion of PET was found to
be: catalysis concentration > glycolysis temperature > glycolysis time (Chen et al., 2001).
Luo and Li (Luo and Li, 2014) reported for the first time the utilization of CG in the
recycling process of waste PET to produce polyols. In their study, post-consumer PET
was first glycolyzed by DEG, the obtained PET oligomer was then further reacted with
pretreated CG at different weight ratios. They concluded that increasing weight ratio of
CG to PET and DEG, lead to polyols with decreased molecular weights and viscosities,
and increased hydroxyl numbers. Polyols prepared using CG as the sole glycolysis agent
showed slightly higher acid values than those of polyols prepared from DEG and CG
(Luo and Li, 2014). Chaudhary et al (Chaudhary et al., 2013) reported micro-wave
assisted glycolysis of PET for preparation of polyester polyols, and they discovered that
the reaction time required for glycolysis using microwave (about 30 min) is significantly
shorter than conventional thermal glycolytic processes (8-9 h for the same level of
depolymerization).
The polyols produced from recycled PET have been used to produce PU foams
and coatings. Vitkauskiene et al. (Vitkauskiene et al., 2011) synthesized polyurethane14
polyisocyanurate (PU-PIR) foams from a series of aromatic polyester polyols from
glycolysis of PET waste using DEG. In their study, glycerol, adipic acid, polypropylene
glycol and hexanediol also were tested as functional additives in the glycolysis process.
PU-PIR foams based on PET-waste-derived polyols had high isocyanurate yield (67%90%), high closed cell content (more than 94%), and excellent mechanical properties
exceeding those of typical PU-PIR foams. They also discovered that the incorporation of
glycerol as a functional additive decreased isocyanurate yield, core density, and tensile
strength but increased elongation at break, while the incorporation of adipic acid acted
vice versa (Vitkauskiene et al., 2011). Kathalewar et al. (Kathalewar et al., 2013)
glycolyzed post-consumer PET using neopentyl glycol and prepared PU coatings from
the glycolyzed oligomers. The coatings showed excellent gloss and chemical resistance,
good hardness and thermal stability, but poor impact resistance due to the brittle nature of
the films (Kathalewar et al., 2013).
2.4 polyols and PUs from protein based feedstocks
2.4.1 Introduction of different types of protein feedstocks
Proteins are large macromolecules (polypeptides) formed by linking many αamino acids via amide bonds (peptide bonds). The presence of many functional groups,
such as amino (-NH2) groups, carboxyl (-COOH) groups, hydroxyl (-OH) groups and
disulfide (-S-S-) groups (Schulz and Schirmer, 1979), makes protein a promising material
for the production of bio-based polymeric materials. Feedstocks that contain high protein
content are also abundant in nature, including soybean protein products, such as soy
flour, defatted SM, soy protein concentrates, and soy protein isolates (Kumar et al.,
15
2002a). Each of the soybean protein products have different protein content and are used
to produce different protein products in the food industry. Soy flour has a protein content
ranging from 40-60% (Kumar et al., 2002a) and is used as a source material for soymilk,
tofu and other specialty foods (Singh et al., 2008). SM has a protein content ranging from
10-90%, and is often used as animal feed (United Soybean Board, 2015). Soy protein
concentrates contain about 60-70% protein (Kumar et al., 2002a), and are used in bakery
products, baby foods, cereals and milk replaces (Singh et al., 2008). Soy protein isolates
have the highest protein content (80-90%) (Kumar et al., 2002a) and are often used as
poultry and meat protein replacements (Singh et al., 2008). Corn is another high volume
protein source, with products such as corn gluten meal, corn gluten feed, distillers dried
grains (DDG), and distillers dried grains with solubles (DDGS). Corn gluten meal has the
highest protein content (65%), corn gluten feed has about 23% protein content, and
DDGS has about 27% protein content. Zein, a functional prolamine protein, can be
produced from corn gluten meal and has been used in the production of plastics, coatings,
inks, chewing gum, adhesive and fibers (Anderson and Lamsa, 2011). A third source,
wheat gluten, generally contains about 75-85% protein and has been successfully utilized
for the production of bio-based plastics (Domenek et al., 2004). Fourthly, algal biomass,
which can be classified into macroalgal and microalgal biomass, following the extraction
of oil for the production of biodiesel, has a protein content of about 48%. In order to
improve the economics of algae oil based biodiesel, value-added conversion of algae
biomass residue including the production of methane through anaerobic digestion has
been developed (Chisti, 2007).
16
2.4.2. Polyols from protein feedstocks
Two methods are mainly used for the production of polyols from protein
feedstocks: (1) modification of proteins into polyols, (2) liquefaction of proteins. The
modification of proteins have been achieved via the addition reaction with polyethylene
glycol (PEG)-aldehyde, or the substitution reaction with cyanuric chloride-modified PEG
(Figure 2) (Li et al., 2015). Oxypropylation of hydrolysate of SM mixed with sucrose
based polyol has been reported to produce polyols (Narayan et al., 2014). The derived
polyol obtained from oxypropylation had a hydroxyl value of 442 mg KOH/g, an amine
value of 102 mg KOH/g and a water content lower that 0.2% (Narayan et al., 2014).
Algal protein-based polyols have been produced through reactions of algal hydrolysate
with ethylene diamine and ethylene carbonate (Figure 3) (Kumar et al., 2014a). The
polyols obtained showed a hydroxyl value of 422 mg KOH/g, an acid value of 3 mg
KOH/g, and an amine value of 26 mg KOH/g (Kumar et al., 2014a).
17
Figure 2 Modification of protein with PEG and cyanuric chloride for the production of
polyol (Li et al., 2015)
18
Figure 3 Modification of protein with ethylene diamine and ethylene carbonate for the
production of polyol (Li et al., 2015)
Liquefaction also has been shown to be effective in generating protein-based
feedstocks for polyol production. Liquefaction of DDG under atmospheric pressure in
ethylene carbonate with sulfuric acid as catalyst was most successful using a liquefaction
solvent/DDG ratio of 4, liquefaction temperature of 160 ºC, liquefaction time of 2 h, and
sulfuric acid loading of 3 wt% (Yu et al., 2008).
2.4.3 PUs of protein feedstocks
PU foams, coatings/films, and composites/plastics have been successfully
prepared based on protein feedstocks. Both algae polyol and SM polyol were used in
19
combination with other polyols to prepare PU foams. The most noticeable property of
foams formulated with algae-based polyol and SM based polyol was the self-catalytic
property due to the presence of tertiary amine groups in their protein structures. This was
confirmed by shorter cream time, gel time, rise time, and tack-free time compared to
reference foam samples from commercial polyols. Both algae- and SM-based foams
showed similar physical properties to reference foams (Kumar et al., 2014b; Narayan et
al., 2014).
Soy protein has significant potential for the production of coatings and films due
to its good biocompatibility, biodegradability, and processability (Song et al., 2011).
However, poor water resistance and brittleness of soy protein-based films has limited
their use in industrial applications. Various modification methods have been studied
including denaturation and cleavage of proteins, crosslinking, enzyme modification,
plasticization, and blending with other polymers (Kumar et al., 2002b; Tong et al., 2015).
Among these methods, blending is the most popular and useful one (Li et al., 2015). Liu
et al. (Liu et al., 2008) have successfully prepared blended films from hydrophobic castor
oil-based PU and p-phenylene diamine soy protein (PDSP), and the blended films
combined good mechanical properties with optical transmittance. It was discovered that
PDSP exhibited good miscibility with PU with its content varying from 10 to 80 wt%,
and PDSP and PU had strong hydrogen bond and chemical cross-linking interactions.
With the increase of PU content, the blend films showed increased elongation at break,
thermal stability, and water resistance and decreased tensile strength and Young’s
modulus (Liu et al., 2008). Waterborne PU (WPU) was used to modify soy protein isolate
20
(SPI) to improve the flexibility and water resistance of the soy protein films (Tian et al.,
2010). The blended films exhibited good compatibility due to strong hydrogen bonding
interactions between the SPI and WPU. Not only did the blended film have improved
flexibility and water resistance, the incorporation of WPU also enhanced the mechanical
properties of the blend films in water, leading to the applications suited to wet conditions
(Tian et al., 2010).
PU composites/plastics are the materials that combine PU and other constituent
materials with different physical or chemical properties. PU composites/plastics
containing protein feedstocks have been reported in which a series of protein composites
from 30 to 50 wt% PU prepolymer (PUP) with soy dreg (SD), soy whole flour (SWF),
and soy protein isolate (SPI) were compression-molded at 120 ºC(Chen et al., 2003). The
results in this study indicated that the protein component in the soy products plays an
important role in the enhancement of adhesivity, processability and biodegradability of
the composites. It is also possible to obtain different materials, from plastic to elastomer,
by changing the type of soy protein product and the content of PUP (Chen et al., 2003).
Zein-based PUs were synthesized by chemical modification of zein protein with
isocyanates (phenyl isocyanate (PI) and n-hexyl isocyanate (HI)) and diisocyanates
(isophorone diisocyanate (IPDI) and methylenediphenyl 4,4’-diisocyanate (MDI)) (Sessa
et al., 2013). Moisture uptake decreased with isocyanate and diisocyanate modifications,
indicating improved waster resistance of zein-based PU polymers compared to pure zein
polymers. The authors suggested potential applications of zein-based PUs in bioplastics,
floor coating, and printing ink (Sessa et al., 2013).
21
Chapter 3 Value-Added Conversion of Waste Cooking Oil and Post-consumer PET
Bottles into Biodiesel and Polyurethane Foams
Value-added utilization of waste cooking oil (WCO) and post-consumer PET
bottles for the production of biodiesel and polyurethane (PU) foams was developed.
WCO collected from campus cafeteria was firstly converted into biodiesel, and then
crude glycerol (CG), a byproduct of the above biodiesel process, was incorporated into
the glycolysis process of post-consumer PET bottles to produce polyols. PU foams were
synthesized from the above produced polyols. The characterization of the produced
biodiesel demonstrated that its properties meet the specification of biodiesel standard.
The effect of CG loading on the properties of polyols and PU foams were investigated.
All the polyols showed satisfactory properties for the production of rigid PU foams which
had performance comparable to those of some petroleum-based analogs. A mass balance
and a cost analysis for the conversion of WCO and post-consumer PET into biodiesel and
PU foams were also discussed. This study demonstrated the potential of WCO and PET
waste for the production of value-added products.
3.1 Introduction
Biodiesel (fatty acid ester) produced by transesterification of renewable
feedstocks such as vegetable oils and animal fats with alcohol, has been widely
22
considered as an alternative to petroleum diesel. However, the commercialization of
biodiesel is mainly limited by its high manufacturing cost (Camobreco et al., 1998;
Meher et al., 2006). WCO, as a cheaper alternative than virgin vegetable oil, can largely
reduce the biodiesel production cost. The production of biodiesel from WCO is mainly
performed under the catalysis of alkalis, acids, or enzymes, with alkaline catalysts such as
NaOH, KOH, and NaOCH3 being most commonly used due to their higher reaction rate
than acid and enzymatic catalysts. CG is a byproduct of the biodiesel production process.
It has the potential to be converted into value-added products through biological or
chemical reactions. Chemical recycling of PET can depolymerize PET to generate
feedstocks for the production of highly valuable polymers (Sinha et al., 2010). In this
chapter, value-added conversion of WCO and post-consumer PET bottles into biodiesel
and PU foams was successfully developed (Figure 4). The biodiesel production from
WCO and the glycolyzation of post-consumer PET were integrated by CG. The
properties of the produced value-added products, i.e. biodiesel, polyols, and PU foams,
were characterized to examine the feasibility of designed process. The effects of CG
loading polyols and PU foams were investigated. Mass balance and a preliminary cost
analysis for this process were discussed.
23
Figure 4 The process diagram for value-added conversion of WCO and post-consumer
PET bottles into biodiesel and PU foams
Figure 5 Mass balance analysis for the production of biodiesel and PU foams from WCO
and post-consumer PET bottles
3.2 Experimental
3.2.1 Materials
WCO and post-consumer PET water bottles were collected from the cafeteria in
Ohio State Agricultural Technical Institute (Wooster, OH) and from the recycle center at
the Ohio Agricultural Research and Development Center (Wooster, OH). After the
24
removal of polyethylene caps and polypropylene labels, the collected PET bottles were
washed, dried, and cut into small pieces (5 × 30 mm) using a HSM Shredstar BS10CS
shredder (Downingtown, PA). DEG, glycerol, and 0.1 mol/L and 10.0 mol/L NaOH
solution were purchased from Fisher Scientific (Pittsburgh, PA). Ethanol and
Tetrahydrofuran (THF) as high performance liquid chromatography (HPLC) grade were
purchased from Pharmco-AAPER (Shelbyville, KY). Titanium isopropoxide,
HYDRANAL-Composite 5, HYDRANAL-Water Standard 10.0 and HYDRANALMethanol Rapid for Karl Fischer titration; glycerin, monoolein, diolein, triolein,
butanetriol, tricaprin and N-Methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA) for
the quantitative analysis of total monoglycerides and free/total glycerol in biodiesel,
were purchased from Sigma-Aldrich (St. Louis, MO). Standard polystyrene samples were
purchased from Agilent Technologies (Santa Clara, CA). Polycat 5, polycat 8, and Dabco
DC5357 used in foaming process were obtained from Air Products & Chemicals, Inc.
(Allentown, PA). Polymeric methylene-4,4´-diphenyl diisocyanate (pMDI) was obtained
from Bayer Material Science (Pittsburgh, PA). Chemicals were reagent grade, except
those specifically mentioned.
3.2.2 Characterization of WCO
To determine whether any pretreatment was needed, the water and FFA contents
of WCO were determined prior to transesterification for biodiesel production. The water
content was measured by Mettler Toledo volumetric Karl Fisher compact titrator V20
(Mettler Toledo, Columbus, OH) was 0.1%. The FFA content was 0.53%, measured in
accordance with AOCS Ca 5a-40.
25
3.2.3 Production of biodiesel from WCO
Due to the low water and FFA contents, the transesterification of WCO was
carried out in a one-step alkali-catalyzed process for the production of biodiesel. 1,500 g
WCO, 300 mL methanol, and 9.15 g KOH (7.5 g for catalyst and 1.65 g for neutralizing
the FFA) were charged into a 2.5-L glass reactor equipped with a magnetic stirring bar
(Banani et al., 2014). The mixture was stirred for 2h at 37 °C, and then settled overnight.
The crude biodiesel located in the upper layer was washed three times with deionized
water to remove residues of catalysts and glycerol, and dried by rotary evaporation to
yield biodiesel. The CG in the bottom layer also was collected for subsequent
applications to produce polyols from PET waste. The residual methanol in the glycerol
was removed by evaporation. Other common impurities of CG such as water, soap an
salts (Yang et al., 2012) might still exist.
3.2.4 Characterization of biodiesel and CG from biodiesel production
The density of biodiesel samples were determined by measuring their masses in
fixed volume. Dynamic viscosity was measured by a Brookfield DV-II+Pro Viscometer
(Brookfield, Middleboro, MA) at 40°C and converted to kinematic viscosity by dividing
the dynamic viscosity by the fluid mass density. Water contents of biodiesel and CG were
determined using a volumetric Karl Fisher compact titrator V20 (Mettler Toledo,
Columbus, OH). The glycerol and methanol contents in CG were determined using a
Shimazu LC-20 AB HPLC system (Shimadzu, Columbia, MD) equipped with a RID-10A
refractive index detector and a Phenomenex RFQ- Fast Fruit H+ (8%) column. The
mobile phase was 0.005 N H2SO4 aqueous solution, which ran at 60°C with a flow rate of
26
0.6 mL/min. The monoglyceride and free/total glycerol contents in the biodiesel were
measured according to ASTM D6584-13 by gas chromatography (GC) using a Shimadzu
GC-2010 plus GC system (Shimadzu, Columbia, MD) equipped with a flame ionization
detector (FID). The results were compared to requirements for biodiesel listed in ASTM
D6751-15a.
3.2.5 Synthesis of polyols
Polyols were prepared by PET glycolysis in the presence of DEG and CG as a
trifunctional additive. Glycolysis was carried out at 230°C for 4 h in a 500 mL three-neck
round bottom flask equipped with a magnetic stirring bar, condenser, thermometer, and
nitrogen inlet. Titanium isopropoxide (0.5 wt.% of PET) was added as a catalyst (Luo
and Li, 2014). The molar ratio of PET to DEG was kept constant at 1:2 to investigate the
effect of CG loading on the properties of polyols. The CG loading varied from 0% to 5%,
9% and 15% based on the total weight of PET, DEG or CG.
3.2.6 Characterization of polyols
Both hydroxyl and acid numbers of polyols were determined following ASTM
D4272-05D and ASTM D4662-08. The viscosities of polyols were determined in
accordance with ASTM D4878-08 using a Brookfield DV-II+Pro Viscometer
(Brookfield, Middleboro, MA) at 25°C. The average molecular weights and molecular
weight distributions of polyols were determined by gel permeation chromatography
(GPC) analysis in THF at 35°C with an elution rate of 1.0 mL/min using a Shimadzu LC20 AB GPC system (Shimadzu, Columbia, MD) equipped with a RID-10A refractive
index detector, a SPD-M20A prominence photodiode array detector, and a Waters
27
styragel HR1 column (7.8 × 300 mm). Polystyrene standard samples were used to
calibrate the GPC column.
3.2.7 Synthesis of PU foams
PU foams from the above obtained polyols were prepared according to our
previous study (Hu et al., 2012). Polyols, catalysts, a surfactant, and a blowing reagent
(water) were mixed by rapid stirring using a hand mixer for 10-15 s in a 250 mL plastic
cup to achieve homogeneous mixing. Pre-weighed pMDI with an isocyanate index of 110
was then quickly added and vigorously mixed for 5 s. The mixture was poured into a
square wood box (11cm × 11cm × 11cm) with aluminum foil lining and left to rise at
room temperature. The cream time, rising time, and tack free time were recorded
according to ASTM D7487-13. PU foams were allowed to cure at room temperature for
24 h before the thermal conductivity test, and for 1 week before density and compressive
strength tests. The formula used for the PU foam preparation is shown in Table 1.
Table 1 PU foam production formula
Ingredients
Parts by weight
PET-based polyols
100
Catalyst-Polycat 5
1.26
Catalyst-Polycat 8
0.84
Surfactant-DABCO DC5357
2.5
Blowing agent-Water
3
Equivalent weight for
pMDI
isocyanate index of 110
3.2.8 Characterization of PU foams
28
The thermal conductivity of PU foams was measured by a Lasercomp FOX 314
heat flow meter (Lasercomp, Saugus, MA) according to ASTM C518. The compressive
strength parallels to the foam rise direction were measured following ASTM D1621-10
using Instron 3366 (Instron, Norwood, MA). The PU foam density was measured
following ASTM D1622M-14. Fourier transform infrared (FT-IR) spectroscopy for PET,
CG, DEG, polyols and PU foams were obtained from PerkinElmer Spectrum 2 IR
spectrometers (Perkin Elmer, Waltham, MA).
3.3 Results and Discussion
3.3.1 Properties of biodiesel and CG from WCO
As shown in Table 2, all measured parameters, including viscosity, water content,
monoglyceride, and free and total glycerol of biodiesel produced from WCO, meet the
requirements in ASTM D6751 standard. Compared to parameters reported for biodiesel
produced from different sources of feedstock, such as beef tallow (free glycerol: 0.01%,
total glycerol 0.33%, and monoglycerides: 0.13%) (da Cunha et al., 2009) and WCO with
high content of FFA (free glycerol: 0.08% and total glycerol: 0.21%) (Meng et al., 2008),
the biodiesel produced in this study had lower contents of free/total glycerol and
monoglycerides. This indicates that complete transesterification between WCO and
methanol occurred in the study. The post-treatment of crude biodiesel (separation and
water washing) produced high-quality biodiesel.
29
Table 2 Properties of biodiesel sample compared to ASTM D6751 standard
Kinematic Viscosity
(mm2/s, 40°C)
Water content
(% in volume)
<0.050
ASTM D6751 1.9-6.0
5.5
0.049
Biodiesel
Note: a Below detection level (0.0001%)
Monoglycerides
(wt %)
Free glycerol
(wt %)
Total glycerol
(wt %)
<0.40
0.06
<0.02
BDLa
<0.240
0.206
The produced CG after evaporation of methanol contains 84.46% glycerol, 2.64%
water, and 4.03 % residual methanol. Compared to the CG collected from a WCO
biodiesel plant (glycerol content 27.31-30.25%, water content 5.10-8.20%) (Kongjao et
al., 2010), CG collected in this study had a much higher glycerol content and lower water
content. This difference could be attributed to the different feedstocks and the processes
used for biodiesel production. Moreover, the CG has significantly different composition
from the one previously used for the production of PET-based polyols (Luo and Li, 2014)
and may produce polyols and PU foams with different properties.
3.3.2 Properties of polyols
Polyols were synthesized by the glycolysis of PET with DEG in the presence of
different loadings of CG (0%, 5%, 9%, and 15%). The acid values of all polyols were
below 0.6 mg KOH/g (Table 3), which fell within the maximum acidity (around 2 mg
KOH/g) acceptable for polyester polyols (Ionescu, 2005). With CG content increasing
from 0 to 15%, the hydroxyl number of the derived polyols increased by 23.8%. This is
most likely due to the high hydroxyl number of glycerol (1829 mg KOH/g). Similar
results have also been observed for the PET-based polyols produced previously (Luo and
Li, 2014). In that study, as CG contains 22.9% of glycerol, the actual glycerol contents in
the reaction mixture were 6.87% and 11.45% at CG loadings of 30% and 50%,
30
respectively. Compared to polyols produced in the previous study with similar glycerol
content, the polyols in this study had higher hydroxyl numbers (Table 3), and were more
favorable for the production of rigid PU foams. The difference in hydroxyl number
between the polyols obtained in the previous study and this study was mainly caused by
the impurities in CG. The high contents of impurities such as fatty acid esters, soap and
fatty acids in CG used for the production of PET-based polyols in the previous study
participated in reactions and consumed hydroxyl groups, resulting in low hydroxyl
numbers (Luo and Li, 2014). It was also observed that the dynamic viscosity and the
molecular weight of polyols increased from 819.4 to 1511.5 cP and from 738 to 806 (Mn),
respectively, as the CG loading increased from 0 to 15% (Table 3). This is possibly
caused by the participation of glycerol in glycolysis of PET. Glycerol has been widely
used as a crosslinker in polymeric material production, and could compete with DEG in
the depolymerization of PET for the formation of cross-linking structures, resulting in
increased molecular weights of the glycolyzed PET polyols. Furthermore, the glycolyzed
PET with increased cross-linking structures can cause more entanglement, resulting in
increased viscosity. Due to the high purity of CG, polyols yields above than 92% were
obtained under all conditions. Polyols in this study showed lower viscosity, higher
molecular weight and yield, and increased hydroxyl number compared to polyol
produced previously (Luo and Li, 2014). It concluded that the composition of CG has a
significant impact on polyol properties, which could affect PU foam performance.
31
Table 3 Properties of polyols from PET and CG
Polyolsa
Pol-0
CG
loadingb
(wt%)
0
Pol-5
5
4.22
0.34±0.03
526.3±5.1
1022.0±4.0
96.6
754
989
1.31
Pol-9
9
7.60
0.40±0.05
548.9±15.1
1104.5±18.5
96.3
791
1044
1.31
Pol-15
15
12.69
0.52±0.03
591.5±9.8
1511.5±9.5
92.9
806
1035
1.29
d
30
6.87
0.18±0.05
282.6±1.6
4994±21
68.2
763
1132
1.48
50
11.45
0.22±0.01
374.6±4.2
1810±3
68.2
671
931
1.39
Pol-A
Pol-B
d
Glycerol
contentc
(wt%)
0
Acid #
(mg
KOH/g)
0.28±0.01
OH #
(mg
KOH/g)
477.9±7.6
Viscosity
(cP, 25°C)
Yield
(wt%)
Mn
(Da)
Mw
(Da)
Mw/Mn
819.4±6.0
97.4
738
980
1.33
a
Note: For all polyols, the PET to DEG molar ratio was kept at 1:2;
b
CG loading=mass(CG)/mass(CG+PET+DEG);
c
Glycerol content=mass(glycerol)/mass(CG+PET+DEG);
d
Polyols produced in previous study(Luo and Li, 2014).
3.3.3 Performance of PU foams
PU foams (PUF-x) were produced by the polymerization of the above prepared
PET-based polyols (Pol-x) and polymeric methylene-4,4’-diphenyl diisocyanate (pMDI)
using polycat 5 and polycat 8 as catalysts, Dabco DC5357 as a surfactant, and water as a
blowing agent. As shown in Table 4, the cream time, rise time and tack free time of PU
foams increased as CG loading increased in the preparation of PET-based polyols. In
general, the cream time and rise time are related to the expansion rate, while the tack free
time is used for the characterization of gelation rate (Hu et al., 2002). As a result, the PU
foams showed slower expansion rate and gelation rate with the increase of CG loading.
This was most likely related to the increase of secondary hydroxyl groups from glycerol
and the increased viscosity of the polyols. Water content in CG might also affect the
foaming characteristics of PU foams. According to Chen et al. (Chen et al., n.d.), the
cream time, rise time and tack free time of the PU foam increase with the increase of
32
water used in the formulation. As the CG loading increasing from 0 to 15%, the water
content in CG as an impurity also increased, thus resulting in increased water in polyols
even the formulation remained the same for four foams with different CG loadings.
Moreover, with an increase of hydroxyl number of polyols, the required amount of pMDI
increased under the same isocyanate index, and thus slightly longer time might be needed
for well-mixing.
Table 4 Foaming characteristics of PU foams
PU
foams
PUF-0
Cream
time (s)
8-10
Rise time
(s)
14-16
Tack free
time (s)
13-15
PUF-5
10-12
19-21
18-20
PUF-9
16-18
23-25
20-22
PUF-15
16-18
24-25
24-25
33
330
Compressive strength (kPa)
310
60
Compressive strength
Density
55
Thermal conductivity
290
50
270
250
45
230
40
210
190
35
Density (kg/m3)
Thermal conductivity (mW·m-1·K-1)
350
170
150
30
PUF-0
PUF-5
PUF-9
PUF-15
Figure 6 Compressive strength, density, and thermal conductivity of PU foams
The compressive strength, density and thermal conductivity of the PU foams
made from PET-based polyols are shown in Figure 6. CG loading had little impact on the
density of the foams but significantly influenced their compressive strength and thermal
conductivity.
All the foams produced showed similar densities ranging from 46.03 to 47.66
kg/m3. With increasing CG loading from 0 to 15%, the compressive strength increased
from 235.9 to 299.9 kPa. This could be explained by the increased cross-linking
structures of polyols and the resulting PU foams due to the trifunctional characteristics of
glycerol. Compared to PU foams made from polyols from PET and other CG sample
(Luo and Li, 2014), PU foams in this study showed much higher compressive strengths
34
due to the higher hydroxyl number of polyols. Moreover, the presence of very low
content fatty acid chains from impurities of CG also contributed to the improvement of
compressive strength perhaps because the dangling fatty acid chains in PU structures
could generate plasticizing effect. It further indicated that the composition of CG
influences properties of PU foams. In addition, the compressive strength of PU foams
were superior over that (compressive strength of 220 kPa) of a commercial analog for
construction applications (Demharter, 1998). Thermal conductivity of PU foams
decreased from 38.7 to 33.3 mW·m-1·k-1 with the increase of CG loading from 0 to 9%,
after which it increased to 40.8 mW·m-1·k-1 at CG loading of 15% (Figure 6). Most of the
PU foams showed thermal conductivities comparable to those of conventional rigid PU
foams (38 mW·m-1·k-1) (Kacperski and Spychaj, 1999) and commercial EPS foams (37
mW·m-1·k-1) (Zarr and Pintar, 2012). PU foams with 9% of CG loading had the best
insulation properties.
3.3.4 Structural characterization
The FT-IR spectra of PET, DEG, CG, a representative polyol (pol-9), and the
resulting foam are presented in Figure 7. In the spectra of DEG and CG, characteristic
hydroxyl stretching at 3200-3400 cm-1 was observed, along with absorption bands related
to C–H of alkyl groups at 2850-3000 cm-1. Small peaks at 1570cm-1 and 1740 cm-1 in the
spectrum of CG indicate the presence of some amount of impurities: the small band at
around 1570 cm-1 represents the COO- of soap, while the small band at 1740cm-1 is
evidence of C=O of fatty acids and their esters (Kongjao et al., 2010). An absorption
band at 1714 cm-1 due to ester stretching is present in the spectrum of polyol as a result of
35
glycolysis of PET (Chaudhary et al., 2013). This peak is also present in the spectrum of
PET. The absorption bands of polyol at 3200-3400 cm-1 and 2850-3000 cm-1 are similar
to the absorption band in the spectra of DEG and CG, representing hydroxyl groups and
C–H of alkyl groups in the polyol. The spectrum of the PU foam showed the presence of
several characteristic urethane bands: –N–H stretching at 3304cm-1, C=O stretching at
1707cm-1, C–O stretching at 1217cm-1, and C-N stretching of carbamate group at
1595cm-1, and N-H bending at 1511cm-1 (Čuk et al., 2015; Mishra et al., 2009).
1714
PET
3200-3400
Transmittance (%)
DEG
2850-3000
CG
1740
1570
Pol-9
PUF-9
1595
3304
4000
3500
3000
1707 1511 1217
2500
2000
Wavenumber (cm-1)
1500
1000
500
Figure 7 FT-IR spectra of PET, DEG, CG, Pol-9, and PUF-9
3.3.5 Mass balance and cost analyses of the process from WCO and waste PET to
biodiesel and PU foams
36
Table 5 Breakdown of biodiesel production costs in dollars per liter
Costs for 50 L of Biodiesela($)
WCO
9.38
Methanol
2.16
Potassium hydroxide
0.28
Electricity
0.17
Water
0.02
Total
12.00
Unit cost ($/L)
0.24
b
WCO price: approximately $200/ton(Zhang et al., 2003)
b
Table 6 Breakdown of PU foam production costs in dollars per kilogram
Costs for 50kg of PU foamsa ($)
Recycled PET flakes*
2.92
CG (from biodiesel process)
0.28
DEG
4.80
TPP
0.14
Electricity
10.65
Nitrogen gas
0.74
Water
0.01
pMDI
49.49
Polycat 5
1.11
Polycat 8
0.43
DABCO DC 5357
2.72
Total
73.29
Polyol unit cost ($/kg)
1.17
Foam Unit cost($/kg)
1.47
*Recycled PET flakes market price: approximately $0.40/kg
a
Unless specified, chemical prices are from http://www.icis.com,
http://www.alibaba.com, http://www.zauba.com.
During biodiesel production, the cost of raw materials, especially vegetable oil, is
the biggest contributing factor for the overall operating cost. Hass et al. (Haas et al.,
2006) designed a model to calculate the annual operating costs for a 3.87 ×107 L/year
biodiesel production facility. In their analysis, biodiesel production cost is around
$567/ton, in which soybean oil itself constitutes 90.2%. WCO is usually sold at $200/ton
(Zhang et al., 2003), which is much cheaper than the price of virgin canola oil ($500/ton)
37
(Zhang et al., 2003) and virgin soybean oil ($520/ton) (Haas et al., 2006). Together with
other fats such as beef tallows, waste greases have the potential of producing 3.5 billion
liters of biodiesel per year (Nelson et al., 1994). Based on the mass balance analysis
shown in Figure 5, the estimated cost for biodiesel produced from WCO is around
$0.24/L (Table 5), which is about half the price of biodiesel produced under similar
process using virgin vegetable oil as a feedstock [30].
The market price for PU foam production is about $2.2-4.4/kg, which is
significantly dependent on the cost of polyol. Table 6 shows the estimated cost for the
production of polyols and PU foams from PET and CG with a loading of 15%. The
production cost of polyol is $1.17/kg, less than half of the average price of
petrochemical-based polyol ($2.69/kg) (Nikje and Garmarudi, 2010). Besides the cost for
pMDI, the main contributing factors for the overall production cost of PU foam are the
cost of DEG and electricity, and the production cost of PU foam can be as low as
$1.48/kg. During the cost analysis, 50L biodiesel and 50kg PU foams were chosen to
represent the scale of typical lab size production. The mass balance and preliminary cost
analyses for biodiesel and PU foams production indicate a very competitive production
cost advantage of the presented process in the comparison with biodiesel from virgin
vegetable oil and polyols and PU foams from petroleum. Incorporating biodiesel
byproduct into PET recycling for PU foams production appears a promising application.
Furthermore, the comprehensive utilization of waste into value-added products can
improve the sustainability of the PU foams industry and help enhance competitiveness of
biodiesel as a sustainable energy source against petroleum diesel.
38
3.4 Conclusion
A sustainable process for value-added conversion of WCO and post-consumer
PET bottles into biodiesel and PU foams was developed successfully. CG, a byproduct of
the biodiesel production from WCO, can be effectively used as a functional additive
during the glycolysis of post-consumer PET bottles with DEG for the production of
polyols with properties suitable for rigid PU foam applications. CG composition affects
the properties of polyols and PU foams. With the increase of CG loading from 0 to 15%,
polyols showed increased hydroxyl numbers, viscosities, and molecular weights, and the
resulting PU foams presented increased compressive strength while at similar densities.
Best insulation properties were was obtained from PET-based polyol prepared with 9%
CG. The PU foams also showed physical performance comparable to those of some of
petroleum-based analogs. A preliminarily mass balance and cost analyses indicated the
potential of economic viability of this process. Overall, this sustainable process
effectively combined biodiesel production from WCO with recycling of post-consumer
PET bottles for PU foam production, and is promising for converting them into valueadded products for industrial uses.
39
Chapter 4 Value-added Conversion of soybean meal into UV-curable polyurethane
acrylate coatings
In this study, a novel way has been developed to produce UV-curable polyurethane (PU)
acrylate coatings from soybean meal (SM). High oleic SM was hydrolyzed by dilute acid
to amino acid oligomers, then a hydroxyl-terminated PU oligomer was synthesized
through a non-isocyanate method: i) amination of the amino acid oligomers with ethylene
diamine to produce amino-terminated compound; ii) amidation of the amino-terminated
compound was achieved with ethylene carbonate. Functionalization of hydroxylterminated PU oligomers was achieved by esterification and acrylation reactions to
produce PU acrylate oligomers. PU acrylate oligomers were then formulated with
multifunctional monomer and photo initiator to form a PU coating under UV light. Pure
glutamic acid (Glu) was used as a model compound to verify the feasibility of the
process. The hydroxyl number, acid number and chemical structures of both PU acrylate
oligomers derived from Glu and SM were determined. The thermal and mechanical
properties, such as tensile strength, modulus, glass transition temperature and degradation
temperature, of UV-cured PU acrylate coatings from SM were characterized. The
diagram for this process is shown in Figure 8.
40
Figure 8 Process diagram for the conversion of SM into UV-cured PU acrylate coating
4.1 Introduction
SM is the soy protein residue after oil extraction, and has long been considered a
promising feedstock for the production of bio-based polymer materials due to its high
protein content.
UV radiation curing has been widely used in the production of PU coatings. The
main advantages of using UV radiation are: very high polymerization rates, low energy
input compared with traditional thermal cured coatings, and no or low volatile organic
compounds (VOCs) (Decker and Decker, 2002; Decker, 1998, 1996). A UV-curable PU
coating formulation is mainly composed of a PU oligomer, a multifunctional monomer
that acts as a reactive diluent to adjust formulation viscosity, and a photoinitiator.
4.2 Materials and methods
4.2.1 Materials
High oleic SM was provided by Cargill Inc. (Sidney, OH). After receiving the
SM, its protein content was determined to be 51.06% by the Kjeldahl method. Glutamic
acid, sodium hydroxide solution, oleic acid, hydroxyethyl acrylate (HEA), isophorone
diisocyanate (IPDI), phenolphthalein, imidazole and methyl ethyl ketone were obtained
41
from Fisher Scientific (Pittsburgh, PA). Ethylene diamine, ethylene carbonate,
hexanediol diacrylate (HDDA), 1-hydroxy-cyclohexyl-phenylketone (Irgacure 184),
bromophenol blue, and phthalic anhydride were obtained from Sigma-Aldrich (St. Louis,
MO). Pyridine, ethanol and hydrochloric acid were obtained from Pharmco-AAPER
(Shelbyville, KY). Dibutyltin dilaurate (DBTDL) was obtained from Pfaltz & Bauer, Inc.,
(Waterbury, CT).
4.2.2 Measurements
Fourier transformed infrared spectroscopy (FT-IR) analyses were performed on a
PerkinElmer spectrum Two IR spectrometer (PerkinElmer, MA), and all samples were
scanned from 4000 to 400 cm-1 with a resolution of 4 cm-1.Thermal properties of UVcured PU acrylate coatings were investigated by differential scanning calorimetry (DSC)
(TA Instruments Q20, TA Instruments, New Castle, DE). Each measurement was
performed in three cycles at a rate of 10 °C/min under nitrogen atmosphere. The samples
were first heated from 40 to 200 °C to eliminate the thermal history, then cooled to −50
°C and held for 3 min, and heated again to 200 °C. The glass transition temperature (Tg)
was determined based on the third cycle. Thermal degradation behaviors of UV-cured PU
acrylate coatings were evaluated by thermogravimetric analysis (TGA), which was
performed under nitrogen atmosphere at a heating rate of 20 °C/min from 50 to 700 °C
using a TA Instruments Q50 thermogravimetric analyzer. Both DSC and TGA data
analyses were conducted using a TA Universal Analysis 2000. Pencil hardness of the
coatings cured on iron plates was determined in accordance with ASTM D3363-05.
42
Tensile strength, modulus and elongation at break of the films were measured using an
Instron 3366 tensiometer (Instron, Norwood, MA) at room temperature.
4.2.3 Synthesis of glutamic acid based hydroxyl terminated PU oligomer
Glutamic acid (Glu) was chosen as a model amino acid because it commonly has
the highest abundance among amino acids in soybean (Berk, 1992). The synthesis from
Glu to amino terminated compound and hydroxyl terminated compound is illustrated in
Figure 9. Glu (14.71g, 0.1mol) , excess ED (36.06g, 0.6mol) and DBTDL (0.51g, 1wt%)
were added to a 250-ml round bottom flask equipped with a magnetic stirrer, a three-way
adapter, a condenser, a vacuum adapter, a receiving flask and a thermometer . The system
was raised to 105°C and reacted for 6 hours to yield amino-terminated compound (GluED). Unreacted ED was distilled out at the end of the reaction for reuse.
Glu-ED obtained from the previous step was first dissolved in ethanol. Since
unreacted Glu is insoluble in ethanol, it was simple to separate Glu-ED with unreacted
Glu by centrifuge followed with filtration. The Glu-ED thus obtained (24.52g, amine
value equals to 465.5 mg KOH/g) was reacted with EC (17.91g, 0.203mol) with ethanol
as solvent in a 250-ml three-neck flask equipped with a magnetic stirrer, a condenser and
a thermometer. The ratio of the total amine value equivalents to the total carbonate
equivalents was kept close to 1. The reaction was carried out at 70°C for 2 hours to
produce hydroxyl-terminated PU oligomer (Glu-ED-EC).
4.2.4 Synthesis of SM based polyol
100g SM (51.06% protein) and 300 ml 60% (v/v) aqueous ethanol solution was
added to a round bottom flask equipped with a magnetic stirrer. After constant stirring for
43
1 hour under room temperature, the slurry was filtered under vacuum and the wet SM
was dried in 40ºC oven overnight. 80.32g SM without soluble carbohydrates was
obtained.
The hydrolysis of SM was carried out in a 500-ml three neck flask, equipped with
a magnetic stirrer, a condenser, a thermometer and a N2 inlet, under atmosphere pressure
with constant stirring. About 50g ethanol extracted SM and 200 ml 2N HCl was added to
the flask and heated to 100ºC in an oil bath with constant stirring. The temperature was
held constant for 24 hours of reaction time. After reaction, the solution was cooled to
room temperature and centrifuged at 1000 rpm for 10 min. The supernatant was decanted
and neutralized using 10M NaOH to a pH 6 and then the solvent was evaporated using a
rotary evaporator at 50-70ºC.
SM-ED, SM-ED-EC were synthesized using the same procedure as the syntheses
of Glu-ED and Glu-ED-EC. SM-ED-EC (10 g, hydroxyl value=478.6 mg KOH/g,
contains 0.085mol hydroxyl groups) and oleic acid (11.99g, 0.043mol) (the molar ratio of
hydroxyl groups to carboxyl groups is 2:1) were added to a three-necked flask equipped
with a magnetic stirrer, condenser and thermometer. The temperature was held constant
at 130ºC under vacuum for 20 hours of reaction time (Figure 10).
In order to react with 10g SM-PUOFA (hydroxyl number = 222.5mg KOH/g,
contains 0.04mol hydroxyl groups), IPDI-HEA derivative was first synthesized. 8.30
IPDI (0.04mol) and 0.22 ml DBTDL were placed in a three-necked flask equipped with
magnetic stirrer, a dropping funnel with a drying tube, a thermometer and a nitrogen
inlet. The flask was placed to a previously heated oil bath. The reaction mixture was
44
stirred at 35 ºC while 4.17 ml 2-HEA (0.04mol) was dripped into the flask. After the
dripping was finished, the reaction mixture was stirred until the absorption peak of OH
group (3500 cm-1) in FT-IR had disappeared. After that, 10g SM-PUOFA was dissolved
in 20ml methyl ethyl ketone (MEK) and added to the flask. The reaction mixture was
stirred at 75 ºC until the absorption peak of NCO groups (2267cm-1) in FT-IR had
disappeared. The solvent was then evaporated (Figure 10).
45
O
O
HO
NH2
OH
NH2
O
NH2
(ethylenediamine)
Amination
O
NH2
N
H
O
NH2
N
H
NH2
O
O
(ethylene carbonate)
Amidation
HO
H
N
O
O
O
N
H
O
N
H
HN
H
N
O
O
O
O
urethane bond
OH
46
Glutamic acid
(Represent amino acid oligiomers)
Amino-terminated compound
Hydroxyl-terminated polyurethane oligomer
Figure 9 Synthesis route of hydroxyl-terminated PU oligomer
46
OH
HO
H
N
O
O
O
N
H
O
N
H
HN
O
H
N
O
ROOH
(fatty acids)
OH
O
R
O
N
H
O
150 oC, vacuum
O
O
H
N
O
O
N
H
HN
O
H
N
O
R
O
O
O
O
O
OH
OH
Polyurethane oligomer-grafted fatty acid
Hydroxyl-terminated polyurethane oligomer
NCO
NCO
+
NCO
IPDI
OH
DBTDL
O
DBTDL
75 oC
O
35 oC
N
H
O
O
O
O
IPDI derivative
2-HEMA
47
O
R
O
H
N
O
O
O
N
H
O
N
H
HN
O
H
N
O
O
R
O
O
O
O
O
N
H
O
N
H
Polyurethane acrylate oligiomer
Figure 10 Synthesis route of PUOFA and PUAO
47
O
O
O
4.2.5 Preparation of UV cured PU coating
PUAO was first mixed with 20% hexanediol diacrylate (HDDA) and 4% Igracure
184, and then the mixture was coated on an iron plate by an applicator with a 6 mils
(152.4 μm) gap, and cured under UV light for 10 passes on a 5m/min conveyor.
4.3 Results and discussion
4.3.1 Model compound glutamic acid based polyol
(A)
1679
(B)
1255
1647
1548
(C)
1501
2000
1800
1600
1400
1200
1000
Figure 11 FT-IR spectra of (A) Glu-ED-EC, (B) Glu-ED, and (C) Glu
Figure 11 shows the FT-IR spectra of Glu-ED-EC, Glu-ED and Glu. The main
changes between Glu and Glu-ED were the appearance of new peaks at 1647cm-1 and
1255cm-1, corresponding to C=O deformation and C-O deformation of the amide groups;
the peak corresponding to N-H of the primary amine at 1501cm-1 was shifted to 1548cm-1
and is attributed to the transformation of amine into amide. The acid value of Glu-ED
48
(Table 7) indicates that most of the carboxylic groups were protected and converted to
amides. However, when comparing the experimental amine value to the theoretical value
(731.7 mg KOH/g), there is a 36.4% difference, which is 17% larger than data from
similar experiments (Kumar et al., 2014a). This might due to the chemical structure of
Glu. With carboxylic groups on both ends of the glutamic acid, when one side of
carboxylic group has reacted with ED, the steric hindrance for the carboxylic group on
the other side of Glu becomes larger; thus it becomes more difficult to ensure that both
carboxylic groups on Glu have reacted with ED.
The formation of urethane groups in Glu-ED-EC was confirmed by the
appearance of a peak corresponding to carbonyl stretching of the urethane groups at
1679cm-1. On the spectrum of Glu-ED-EC two small peaks at 1773 and 1805cm-1
corresponding to C=O stretching in EC can be observed, which indicate a small amount
of unreacted EC in Glu-ED-EC(Nyquist and Setyineri, 1991). The amine, acid and
hydroxyl values of Glu-ED-EC are shown in table 7. From the amine value we calculated
that the conversion rate of amines to hydroxyl terminated urethanes is around 83%, which
is 10% smaller than previously reported (Kumar et al., 2014b). This difference can also
be explained by larger steric hindrance of the amine groups in the middle of Glu-ED
chain.
49
Table 7 Amine, acid and hydroxyl value of Glu and SM derived oligomers
GluSM-
Glu-ED
Glu-ED-EC
SM-ED
SM-ED-EC
SM-PUOFA
Amine value (mg
KOH/g)
Acid value (mg KOH/g)
Hydroxyl value (mg
KOH/g)
465.5±19.3
79.4±0.29
533.4±9.4
98.2±1.2
-
59.8±3.2
37.3±1.5
24.8±0.4
22.6±1.6
1.5±0.5
402.6±15.2
478.6±9.6
222.5±10.9
4.3.2 SM-based polyol
The amine value, acid value and hydroxyl value of SM-ED, SM-ED-EC and SMPUOFA are summarized in Table 7. The SM-based polyol and its intermediate showed
similar values to the model Glu compound, which indicates that the amino acids from
hydrolyzed SM went through the same chemical reaction as the model compound.
50
60
SM-PUOFA
SM-ED-EC
Viscosity (Pa·s)
50
40
30
20
10
0
0
50
100
150
Shear rate (1/s)
200
250
300
Figure 12 Viscosity as a function of shear rate of SM-PUOFA and SM-ED-EC
As shown in Figure 12, after the esterification of SM-ED-EC with oleic acid, the
resultant SM-PUOFA showed decreased viscosity (at shear rate 10.9 1/s) from 41.2 Pa·s
to 6.1 Pa·s at 25ºC. The decrease in viscosity is evidence that oleic acid has successfully
reacted with SM-ED-EC and that the incorporation of oleic acid with long aliphatic chain
gave the SM-ED-EC oligomer chain more flexibility. Furthermore, the decrease in
viscosity will also be beneficial to the control of acrylation reaction following the
preparation of UV-curable PU coating. Both oligomers showed decreased viscosity with
increasing shear rate, demonstrating the shear thinning effect of non-Newtonian fluids.
4.3.3 Properties of the coating film
4.3.3.1 Mechanical properties
51
Mechanical properties of the SM-based PU acrylate coating are reported in Table
8. Compared to PU acrylate coatings reported by Gite et al. and Kim et al.(Gite et al.,
2010; Kim et al., 1996), the coating prepared in this study showed higher tensile strength
and modulus and lower elongation at break. Pencil hardness test also shows that the
coating film has the highest level of hardness. The results indicated that the coating
prepared in this study exhibited rigid and brittle mechanical properties. This may due to
possible hydrogen bonds between the N-H of the amide group and the C=O of another
amide, urethane carbonyl or the ether oxygen (Lu and Larock, 2008) and enhanced crosslinking density due to the additional double bonds in oleic acid.
Table 8 Mechanical properties of SM-based PU acrylate coating
SM-based PU acrylate
coating
PUA-1a
PUA-2a
PUA-3
Tensile strength
(MPa)
18.2±3.6
Modulus (MPa) Elongation at
break (%)
450.1±17.3
4.5±0.7
Pencil
hardness
9H
2.12
2.00
-
1.60
1.65
43.4
-
Note: a PU acrylate coatings prepared by Gite et al. (Gite et al., 2010)
b
PU acrylate coating prepared by Kim et al. (Kim et al., 1996)
4.3.3.2 Thermal properties
52
81
82
70
Figure 13 TGA and DTA curves of UV-cured PU acrylate coating
Table 9 Thermal properties of SM-based PU acrylate coating
SM-based PU
acrylate coating
TGA
T5 (ºC)
T50 (ºC)
203.2
350.2
Total weight
loss (%)
93.6
DSC
Tg (ºC)
84.4
Figure 13 shows the TGA and DTA curves of PU acrylate coating, it can be seen
that the coating showed a two-stage decomposition process. The first stage of weight loss
happened between 200-310 ºC is related to the decomposition of urethane groups existed
in PUAO from the reaction between SM-ED and ethylene carbonate and the reaction
between hydroxyl group in PUAO with isocyanate group in IPDI (Duquesne et al., 2001;
Tamami et al., 2004). The second stage of weight loss between 310-500 ºC reflects the
decomposition of urethane-acrylate terminal groups (Dzunuzovic et al., 2005; Gao et al.,
53
2011) and also the scission of oleic acid chains in the PU acrylate coating (Li et al., 2014;
Lu and Larock, 2008).
The decomposition temperatures at 5% and 50% weight loss and the glass
transition temperature (Tg) based on DSC measurements are summarized in Table 3. The
initial weight loss before 5% was mainly caused by the removal of uncured components
with low molecular weight. The glass transition temperature is higher than many PU
acrylate coatings reported (Xu and Shi, 2005; Xu et al., 2012), the Tg agrees well with the
coating’s rigid and brittle mechanical properties discussed previously.
4.4 Conclusions
UV-curable PU acrylate coatings derived from SM were successfully prepared
through a series of reactions, including amination, amidation, esterification and
acrylation. The feasibility of the process and the chemical structure of the oligomers was
studied using glutamic acid as the model compound. The oligomers prepared from SM
showed similar amine, acid and hydroxyl values as the oligomers prepared from model
compound. Compared with other PU acrylate coatings reported in literature, the UVcured PU acrylate coating prepared in this study showed higher Tg, tensile strength and
modulus, and lower elongation at break.
The high protein content in SM makes it a potential feedstock for amino acid
based polymers. The value-added conversion of soybean oil byproduct has the potential
to lower the price of biodiesel produced from soybean oil, and also lower the cost for
producing PU coatings. The developing of polymer from bio-based feedstocks also helps
reduce reliance on petrochemical feedstocks.
54
Chapter 5 Conclusions and Suggestions for Future Research
5.1 Conclusions
In the studies, value-added conversion of waste cooking oil (WCO), postconsumer PET bottles into biodiesel and polyurethane (PU) foams and value-added
conversion of soybean meal (SM) into PU coatings have been successfully developed and
evaluated.
The first study demonstrated that WCO is suitable feedstock for the production of
biodiesel and that crude glycerol (CG) can be effectively used as a functional additive
during the glycolysis of post-consumer PET bottles with DEG for the production of
polyols suited to rigid PU foam applications. Increasing CG loading from 0 to 15%,
increased polyol hydroxyl numbers, viscosities, and molecular weights, and the resulting
PU foams had increased compressive strength while having similar densities. Best
insulation was obtained from PET-based polyol prepared with 9% CG. A preliminarily
mass balance and cost analyses indicated the probable economic viability of this process.
The second study demonstrated that SM can be converted into polyol for the production
of UV-cured PU acrylate coatings. The feasibility of the process and the chemical
structure of the oligomers was studied using glutamic acid as the model compound. The
oligomers prepared from SM showed similar amine, acid and hydroxyl values to the
oligomers prepared from the Glu model compound. The UV-cured PU acrylate coating
55
prepared in this study showed good mechanical properties and thermal stability, with
higher Tg, tensile strength and modulus, and lower elongation at break than PU acrylate
coatings reported in literature.
5.2 Suggestions for Future Research
The preliminary cost analysis in chapter 3 included the market cost of
transportation and collection of WCO and recycled PET. However, the labor cost, facility
cost, and transportation cost for making biodiesel and PU foams are not included. A more
comprehensive techno-economic analysis or life cycle analysis is needed to better
analyze the feasibility of this process. What’s more, the varying composition of crude
glycerol could be a major barrier to the commercialization of this process. Future
research should focus on how to standardize or control the compositions of crude
glycerol to produce PU foams with stable qualities.
The produced PU acrylate coatings exhibit brittle, plastic-like properties, and
future research should focus on further modification of the product process to produce
PU coatings with improved elongation at break. Research should also be conducted on
the adhesion and water resistance properties of the coating, and to explore other SMbased PU products such as PU elastomers or plastics.
Lastly, we should investigate other processes for value-added conversion waste
materials into useful PU products. The value-added conversion of waste polymer
materials and biodiesel byproducts can enhance the cost-effectiveness of the biodiesel
and polymer industry, and also reduce the environmental impact of polymer materials.
56
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