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Photocatalytic Effect of Zinc Oxide (ZnO) Nanorods on the
Decomposition of Plastics Recovered from Cebu City, Philippines
A research proposal
Presented to Ms. Sherry P. Ramayla
Mentor for Asia Pacific Economic Cooperation (APEC)
Cyber-mentoring Research Program
February 2014
1.1 Background of the Study
1.2 Objectives of the Study
1.3 Significance of the Study
1.4 Scope and Limitations
1.5 Definition of Terms
2.1 Biodegradable Plastics
2.2 Degradation of Plastics
2.3 Photocatalysis and Semiconductors
2.4 Seawater: Importance and Degradation Capability
2.5 Related Studies
3.1 Research Design
3.2 Preparation of Samples
3.3 Experimentation
3.4 Weight Loss Analysis
3.5 Statistical Analysis
1.1 Research Background
Plastics are composed of long chains of molecules containing carbon. Because of
their molecular stability, plastics do not easily break down or decompose into simpler
components. As a result, plastics create a solid waste problem. (Quina, 2009)
According to a survey conducted by the NRDC (National Resource Defense
Council), plastic accounts for 60-80% of marine litter. So much plastic is thrown into the
sea that marine animals and plants are already at risk, coastlines are polluted, and the
health of the people is at risk.
Each year, an estimated 500 billion to one trillion plastic bags are consumed
worldwide - meaning over a million plastic bags are used each minute. Majority of plastic
bags end up in landfills but some are found in bodies of water where hundreds of aquatic
animals die each year for eating discarded plastics often mistaken for food.
To solve the solid waste crisis created by plastic pollution, scientists developed
the biodegradable plastics that will decompose due to the enzymatic reaction by
microorganism present in the soil or by UV rays emitted by the sun. Biodegradable
plastics are plastics that will decompose in natural aerobic (composting) and anaerobic
(landfills) environment. Biodegrading of plastics can be achieved by letting the
microorganisms in the soil or other environment suitable for biodegrading to degrade the
plastic by enzymatic reaction (Blanco et al, 2009).
Scientists are incorporating starch molecules into some plastic resins during the
manufacturing process. These plastics are biodegradable starch-based polymers. It is
composed of thermoplastic starch blended with polyester or additives (James and Grant,
2003). When these plastics are discarded, microorganisms such as bacteria and fungi will
eat the starch molecules. This causes the polymer molecules to break apart, allowing
plastics to decompose (Richardson, 2007).
A normal biodegradable plastic can decompose in about three to six months
which is a lot quicker than a normal synthetic plastic which takes several hundred years
to decompose. But most biodegradable plastics are not environmental friendly as they
seem. Some are made with organic pollutants that are present in the synthetic plastic.
(Jack Serle, Focus).
Biodegradable plastics have many kinds. One example is Oxo-biodegradable
plastics. These plastics are engineered to degrade and totally fragment in 90 to 120 days
and 60% mineralize/biodegradable further 12 to 24 months after disposal. EcoDegradable
products are engineered for disposal in a landfill and under these conditions will degrade
and fragment at a slower rate (12 to 18 months) (
These days, many stores and establishments are releasing biodegradable plastics
as packaging of their products. Sometimes, consumers take the sign biodegradable
embedded on the plastic as a sign that they can dispose the garbage everywhere. Even
though they are biodegradable, it will still take a long time to degrade them completely.
And due to the massive production of plastics, there will be more plastics disposed by the
time it degrades. This study may contribute in lessening of the plastic population caused
by this problem with the help of technology.
1.2 Objectives of the Study
First of all, this research aims to determine the degradation rates of the
biodegradable plastics and the non-biodegradable plastic from four identified stores in
Cebu City. It also aims to reduce the plastic pollution present in many aquatic
environments not just in Cebu but all around the world .With the use of seawater and
Zinc Oxide, a semiconductor, we can see if we can address this severe threat to help save
the environment as a whole.
This study specifically aims to:
Measure the change in weight of the plastic bag as an indicator of its degredation;
Identify the effect on the plastics witht the presence and absence of the following
variables: Zinc Oxide semiconductor and light in the plastic samples in a seawater
based condition; and
Compare and contrast the weight loss of the four plastic samples every 5 days for
2 months of experimentation.
1.3 Significance of the Study
Nowadays, many shops, market and malls use plastics, which are mostly non
biodegradable, to carry the goods and things customers bought from their stores. People
stopped using carts and wagons because plastics are lightweight but can carry many
objects inside dry and safe. Though there are biodegradable plastics used, this might
probably give a wrong impression to the consumer that these plastics can degrade
anywhere and they can dispose it anytime they want.
Today, hundreds of millions of malls and vendor shops have been established to
meet up the increasing population's demand. And with that also comes the increasing
usage of plastics. Plastics are commonly thrown into landfills on which they are recycled
but a number of them get thrown in the sewers, canals and drainages which lead to the
seas and rivers. This may harm the organisms that lives there and eventually causes
humans, who eat the products of the sea, a big trouble. (Blanco et al, 2009).
This is where the significance of this study applies. This research allows
modernization to be used against the harmful effects of plastics. With the use of Zinc
Oxide and other cheaper semiconductors, there can be a massive deterioration of plastics
that have been thrown into aquatic areas thus, reducing pollution and keeping the,
environment, marine inhabitants and humans safe.
1.3 Scope and Limitation of the Study
The study will be conducted within the Philippine Science High School - Central
Visayas Campus premises and kept in the same environmental conditions with the school
premises itself.
The study only focuses the plastics gathered from 4 major malls and stores in
Cebu City, Philippines. The stores of the Biodegradable Plastics are as follows: SM City
Cebu, Metro Gaisano - Cebu, and National Bookstore Mango Ave. Branch, Cebu City.
And the non biodegradable plastic will be collected from Carbon Market, Cebu City.
Each sample will only have five replicates.
This research aims only to determine the degradation of the plastics through their
weight loss under the conditions stated in the methodology
The plastics' weight loss will be compared based on the data gathered from the
experiment with the use of the standard statistical tools stated in the methodology.
The experimentation will take place for 2 months (exactly 60 days). From March
1, 2014 - April 30, 2014. Weighing of the samples will be held on a five day interval.
1.4 Definition of Terms
Biodegradable Plastic - A β€œbiodegradable” plastic is a plastic that has the ability
to break down, safely and relatively quickly, by biological means, into the raw materials
of nature where it is made of and disappear into the environment.
Degredation - Decomposition of a compound by stages, exhibiting well-defined
intermediate products.
Organic Pollutants - Organic pollutants are organic substances that emit
pollutants into the atmosphere.
Photocatalysis - the alteration of the rate of a chemical reaction by light or other
electromagnetic radiation.
Plastics - polymeric material that has the capability of being molded or shaped,
usually by the application of heat and pressure. This property of plasticity, often found in
combination with other special properties such as low density, low electrical
conductivity, transparency, and toughness, allows plastics to be made into a great variety
of products.
Polyethylene Plastic - A polymerized ethylene resin, used especially for
containers, kitchenware, and tubing, or in the form of films and sheets for packaging.
Replicate - an exact copy of something.
UV Ray - also known as Ultraviolet Ray, It is an Invisible light ray with a
wavelength shorter than that of visible light but longer than that of x rays. Commonly
produced from the sun
2.1 Biodegradable Plastics
Biodegradable plastics are one of the most significant improvements in helping
the environment from pollution. These kinds of plastics can degrade easily chemically or
physically. Unlike the other kinds of plastics like Polyethylene Terephthalate or
Polyvinyl Chloride, biodegradable plastics degrade faster. (Blanco et al, 2009).
Biodegradable plastics came from renewable sources. Chemical companies
nowadays are now utilizing annual plants and modern technology to produce these types
of plastics. For some time, agricultural materials have been considered as an alternate
feedstock and source of energy for plastic production (
Many shopping bags are polyethylene or non-biodegradable but scientists had
developed biodegradable shopping bags that are composed of starch derived from corn,
potato, or wheat blended with polyester (polylactic acid) (James and Grant 2003).
Traditional polymers made from petroleum-based materials are slowly being replaced by
plastics produced from renewable sources such as corn in some food and grocery
applications (
Scientists incorporate starch molecules into some plastics resins during
manufacturing process. These plastics are biodegradable starch-based polymers. The
starch makes these kinds of plastics biodegradable because bacteria and fungi use starch
as carbon source ( It is composed of thermoplastic starch blended
with polyester or additives (James and Grant, 2003). When these plastics are discarded,
microorganisms such as bacteria and fungi eat the starch molecules. This causes the
polymer molecules to break apart, allowing the plastic to decompose (Richardson, 2007).
Some biodegradable plastics are based on chemical synthesis (i.e. polyglycolic
acid, polylactic acid, polyaprolactone, and polyvinyl alcohol). Other biodegradable
plastics are products of microbial fermentation such as polyesters and neutral
polysaccharide or prepared from modified natural sources like cellulose, starch, chitin, or
soy protein (Lenz and Marchessault, 2004).
According to the report made by James and Grant (2003), the composition of
degradable plastic bags varies. It could be Thermoplastic starch-based polymers which
are made up at least 90% starch from corn, potato or wheat. Another composition of this
kind of plastic is polyester which is manufactured from hydrocarbons. The last category
is starch-polyester blend that is mixture of thermoplastic starch and polyester made from
2.2 Degradation of Plastics
The degradation of plastics begins as soon as the polymer is synthesized, and is
increased by residual stresses left by molding processes. This can be followed by
exposure to light (especially UV), humidity, oxygen, heat, bacteria, and stress. (Blanco et
al, 2009).
There are two types of plastic degradation: physical and chemical, and both are
closely inter-connected. Physical degradation can involve environmental stress cracking
and plasticizer migration and loss. Chemical reactions include oxidation and hydrolysis,
and is a problem affecting the cellulose esters (cellulose nitrate and cellulose acetate),
which emit acidic degradation products. If not removed, these catalyze further reactions
and eventually cause serious crazing and total destruction of the object. If degrading
cellulose esters are not isolated, the acidic fumes will infect similar objects stored close
by and initiate degradation. (Katz,1995).
2.3 Photocatalysis and Semiconductors
The term "photocatalysis" is still the subject of some debate. It is argued that the
idea of a photocatalysed reaction is fundamentally incorrect, since it implies that, in the
reaction, light is acting as a catalyst, whereas it always acts as a reactant which is
consumed in the chemical process. In reality the term "photocatalysis" is in widespread
use and is here to stay; it is not meant to, nor should it ever be used to, imply catalysis by
light, but rather the "acceleration of a photoreaction by the presence of a catalyst". (Mills
et al, 1997)
In a solid, the electrons occupy energy bands as a consequence of the extended
bonding network. In a semiconductor, the highest occupied and lowest unoccupied
energy bands are separated by a bandgap. Activation of a semiconductor photocatalyst is
achieved through the absorption of a photon of ultra-bandgap energy which results in the
promotion of an electron, e-, from the valence band into the conduction band with the
concomitant generation of a hole. (Mills et al, 1993)
To simplify things up, according to Kameyama (n.d.), Photocatalyst is a lightactivated catalyst. When a photocatalyst material is exposed to light, it absorbs photon
energy and causes various chemical reactions. Metal complexes and semiconductors
catalyst are recognized as photocatalyst materials.
It has been recognized that there are many reactions which can be promoted by
light activated solids which are not consumed in the overall reaction. Such solids are
often reffered to as photocatalyst, photosensitisers and are invariably known as
semiconductors (Mills, 1982). Semiconductor photocatalysis often leads to partial or
complete mineralization of organic pollutants. Upon irradiation with UV/visible light,
semiconductors catalyze redox reactions in presence of air/O2 and water. (Dutta et al,
According to Janotti et al (2009), ZnO is a very promising material for
semiconductor device applications. It has a direct and wide band gap in the near-UV
spectral region, and a large free-exciton binding energy so that excitonic emission
processes can persist at or even above room temperature. ZnO crystallizes in the wurtzite
structure, the same as GaN, but, in contrast, ZnO is available as large bulk single crystals.
2.4 Seawater: Importance and Degradation Capability
Almost anything can be found in seawater. This includes dissolved materials from
Earth's crust as well as materials released from organisms. The most important
components of seawater that influence life forms are salinity, temperature, dissolved
gases (mostly oxygen and carbon dioxide), nutrients, and pH.
In the past decades, a great deal of attention has been focused on evaluating the
various methods for the biodegration of polymers, ranging from immersing them in
seawater to evaluating them in the controlled laboratory. (Trishul et al, 2009) It is
because of the mineral ascended from the Earth's crust and mixed with the seawater like
nitrogen (N), phosphorous (P), and potassium (K), silica and iron (Fe) that enables
seawater to degrade polymers. Also, dissolved gases like oxygen (O2), and Carbon
Dioxide (CO2) is undeniably a factor why seawater is able to degrade. Bacteria like and
other microorganisms also aid in the degradation capability of the seawater because they
are able to degrade organic molecules such as starch present in the plastics.
2.5 Related Researches
A research is done by Pantoja et al (2011) which is about the response of the
coastal ocean influenced by two river discharges and inputs of photosynthetically derived
organic carbon product of upwelling, was evaluated by estimating rates of microbial
hydrolysis of macromolecules with the goal of estimating the potential degradation
capability of the coastal ecosystem off central Chile.
Brandl and Puchner (1992) found out that plastic good made from poly 3hydrozyalkanoates (PHA) are degraded in an aquatic ecosystem under normal in situ
conditions. The plastic bottles were placed 20 cm above the sediment surface. The
experiment was done in Lake Lugano, Switzerland.
An investigatory project related to biodegradability plastic was conducted by
Philippine Science High School - Western Visayas Campus. They identified the effects of
different types of substrates on the same plastic bag. They were able to find out that
different substrates, compost, loam, tap water, and seawater, have different effects on its
biodegradability (Biyo and Temelo, 2008).
Composting was also used in the study made by Johnson et al, (1993) on the
degradation of degradable starch-polyethylene plastics in a compost environment. They
have tested the biodegradability through the change in a molecular weight by hightemperature gel permeation chromatography. They have found out that plastics films
placed in the interior compost row showed little degradation compared to the plastic films
placed in the exterior row.
Another study was done by Blanco et al 2011 in Philippine Science High School Central Visayas Campus which is about degrading the plastics in the air for 100 days.
They hanged the plastic strips in the air and measured it ever 20 days. The results showed
that the air in the study area proves that it areal degradation can quicken up the
decomposition of both biodegradable and non-biodegradable plastics than a non-aerobic
mean of decompising.
Another study was conducted by Wellfair (2008) to investigate the degradation
rates of two conventional plastics, one degradable form Tesco and non-biodegradable
from Sainsbury's. Several samples of each type of plastic were placed into designated
marine environment. Six environment were included namely, saltwater, freshwater, mud,
sand, and dark salt water (to simulate deeper ocean environment) to allow a broad scope
of different environment. The researcher of this study concluded that all the different
samples were capable of degradation, even the non-degradable plastics from Sainsbury's.
However, polyethylene samples degraded very poorly in environments with no light, seen
comparatively in the difference saltwater and darkness. This further showed that samples
require access to UV radiation as an energy source to trigger chemical breakdown of the
polymers and to help facilitate in the overall degradation of plastic.
Chapter 3
3.1 Research Design
This study is an experimental research. There will be 4 plastics bags from
different stores in Cebu City that will be used in the experiment: 3 biodegradable plastics
and one polyethylene plastic. In each plastic, five replicates will be made. The films will
be submerged in a seawater based condition to be conducted at Philippine Science High
School - Central Visayas Campus, Talaytay, Argao, Cebu.
3.2 Preparation of Samples
Three biodegradable plastics and one non-biodegradable plastic will be collected
from 4 different stores in Cebu City, Philippines. The plastics will be cut into strips and
must not exceed 1 gram in weight. The dimension of the plastic strips will be 150 cm. by
50 cm. For the seawater that will be used, it will be gathered from 3 different places
located in southeastern Cebu namely: Argao, Dalaguete and Boljoon (2 gallons each) to
balance out the salinity. Filtering will be done with the use of 2 layers of cloth to remove
unwanted particles. Three rectangular glass containers will be used for the experiment.
The filtered seawater collected (6 gallons in all) will be mixed and be equally
distributed to 3 containers labeled with "with Semiconductors and light", "with light" and
"without semiconductors and light". All three containers will be placed under room
temperature (25 ˚c) and will be exposed to sunlight during the day and to flourescent
light during night time except for the container labeled with "without semiconductors and
light" which will be covered by a black garbage bag to prevent the light from coming in.
1gram of ZnO or Zinc Oxide will be mixed with the seawater inside the container
labeled "with semiconductors and light ". Five replicates of plastic per sample will be
placed in each containers . Therefore, there will be 20 plastics per box. Every sample of
plastics will be tied together to and will be numbered to avoid errors.
3.3 Experimentation
3 water pumps will be assigned to each container to enable the semiconductor to
circulate around the container and also to balance out its effect. Starting March 1, 2014
the experimentation will begin. The containers will be covered with cloth so as to prevent
small particles to contaminate the experiment. Every 5 days, the plastic trips will be
removed and will be air dried for about 3 hours. Afterwards, the samples will be checked
for unwanted particles and will be weighted with the use of an analytical balance. The
plastics will be returned after being weighted. The experimentation will end at April 30,
3.4 Weight Loss Analysis
After the weight of each of the plastic films is taken in every checking day,
degradation rates for the plastic will be calculated. The degradation rates of each brand
will be computed using the formula derived from the research done by Blanco et al
(March 2011).
(1)π‘Ÿπ‘Žπ‘‘π‘’π‘‘π‘’π‘”π‘Ÿπ‘’π‘‘π‘Žπ‘‘π‘–π‘œπ‘› = βˆ’
βˆ†π‘šπ‘Žπ‘ π‘ π‘π‘™π‘Žπ‘ π‘‘π‘–π‘
π‘šπ‘Žπ‘ π‘ π‘“π‘–π‘›π‘Žπ‘™ βˆ’ π‘šπ‘Žπ‘ π‘ π‘–π‘›π‘–π‘‘π‘–π‘Žπ‘™
π‘‘π‘–π‘šπ‘’π‘“π‘–π‘›π‘Žπ‘™ βˆ’ π‘‘π‘–π‘šπ‘’π‘–π‘›π‘–π‘‘π‘–π‘Žπ‘™
The average degradation will be determined for each brand of biodegradable
plastic. Pictures will be taken. Graph of the change of mass of each biodegradable plastic
per day will be made.
3.5 Statistical Analysis
To compare the degradation rates of the 4 different brands of plastics bags, OneWay ANOVA (Analysis Variance) will be used as a statistical tool in Statistical Package
for Socila Sciences 16.0 (SPSS). The One-Way ANOVA calculates the level of
significance between brands of biodegradable plastics. Tukey's HSD will also be
obtained to compare the difference between any two mean scores against HSD. The
formulas below will be used for the calculation of mean square (MS), the ratio of two
variances or F ratio (F), and honestly significant difference (HSD). (Blanco et al, 2009).
(2) 𝑀𝑆 =
Where MS = mean square;
SS = sum of squares
Df = degrees of freedom
βˆ‘(π‘₯ βˆ’ 𝑑)2
X = any raw score
T = total mean for all groups combined
N = number pf scores in any group
(3)𝐹 =
Where F = F ratio
MSbetween = between-groups mean square
MSwithin = within-groups mean square
𝑀𝑆 π‘€π‘–π‘‘β„Žπ‘–π‘›
(4)𝐻𝑆𝐷 = π‘žβˆš
𝑁 π‘”π‘Ÿπ‘œπ‘’π‘
Where HSD = honestly significant difference
Q = table value at a given level of significance for the total number of group
means being
MSwithin = within-groups mean square (obtained from the analysis variance)
Ngroup = number of subjects in each group
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