Biodegradable Plastics

Biodegradable plastics

BIODEGRADABLE PLASTICS Plastic bags have made our lives easier in many ways. Unfortunately, Unfortunately, they are often not disposed of properly. We see them blowing around in the streets and they often end up in streams and the oceans. These bags can be dangerous to animals, such as turtles, that ingest them or are strangled by them, especially in marine environments where plastic bags resemble jellyfish and other food items. One solution to this problem is to make degradable bags, such as those from starch. Starch, obtained from corn or potatoes, can be converted into lactic acid, which can be polymerized to the biodegradable plastic known as polylactide. Another solution is to add an ultraviolet-light absorber to make the material degrade when exposed to sunlight. Biodegradable plastics made with plant-based materials have been available for many years. Their high cost, however, has meant they have never replaced traditional non-degradable plastics in the mass market. The area of degradable polymers, products and definitions has evolved considerably over the last 20 years. In the most general sense and/or good judgment "biodegradable" means that a substance is able to be broken down into other substances, with a significant change of chemical structure, by the activities of living organisms and is therefore unlikely to persist in the environment. environment. With this definition, neither a time limit nor environmental conditions are prescribed and in this sagacity most materials could be classified as biodegradable. However, many materials will remain non-degraded in typical refuse conditions, such as a landfill, or will degrade to products with greater toxicity than the original material. Other terms that are of relevance here include photodegradable, where degradation results from the action of natural sunlight and disintegration, which is the falling apart into very small fragments of material caused by degradation processes. Now-a-days a biodegradable plastic would typically be defined as one in which degradation results from the action of naturally occurring micro-organisms such as bacteria, fungi and algae. There are ranges of standards for biodegradable plastics. The requirements vary from 60 to 90% decomposition of the material within 60 to 180 days of being placed in a standard environment - this may be either a composting situation or a landfill.

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A material that simply breaks up into smaller and tiny portions is no longer regarded as being biodegradable. Naturally occurring polymers include: polysaccharides e.g., starch from potatoes and corn, their derivatives, cellulose f rom marine crustaceans; proteins such as gelatin (collagen), casein (from milk), keratin (from silk and wool) and zein (from corn); polyesters such as poly hydroxyl alkanates formed by bacteria as food storage; lignin; shellac and natural rubber polylactic acid, jute, flux, silk, cotton can fall into the category of natural polymers where the monomer is produced by fermentation. The rate of degradation of each of these depends very much on their structural complexity, as well as the environmental conditions. While there are a number of biodegradable synthetic resins, including: polyalkylene esters, polylactic acid, polyamide esters, polyvinyl esters, polyvinyl acetate, polyvinyl alcohol, polyanhydrides. The materials mentioned here are those that exhibit degradation promoted by micro-organisms. This has often been coupled to a chemical or mechanical degradation step.

DEGRADABLE POLYMERS Degradability is the ability of materials to break down, by bacterial (biodegradable), thermal (oxidative) or ultraviolet (photodegradable) action. In order for degradable polymers to be made into functional plastic bags they must meet the following criteria [2]: Be able to be formed into film; Have adequate tensile strength and elongation; Have adequate puncture resistance; Have adequate tear resistance (not too splitty); and Generally possess properties that resemble low-density polyethylene (LDPE) or highdensity

polyethylene

(HDPE)

in

overall

physical

properties

and

rheological

characteristics.

Degradable plastics for bags are required to degrade rapidly at the end of their useful life while it is equally important that their mechanical properties remain essentially unchanged during use. There are three essential criteria for biodegradation of plastic bags [2]: They must disappear and leave no visible trace; This disintegration must occur in a reasonable timeframe (e.g. 3 months or 6 months); They must not leave behind any toxic residues.

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TYPES OF DEGRADABLE PLASTIC BAGS ± Degradable bags can be classified in two ways [2]: 1. According to the way that they degrade, for example whether they require the actions of microorganisms (i.e. are biodegradable), or whether they require heat, ultraviolet light, mechanical stress or water in order to break down; and 2. According to the materials they are manufactured from, for example whether they are made from natural starch polymers, from synthetic polymers or from a blend of a conventional polymer with an additive to facilitate degradation.

There are five different types of degradable polymers [2]:

Biodegradable polymers are those that are capable of undergoing decomposition into carbon dioxide, methane, water, inorganic compounds or biomass in which the predominant mechanism is the enzymatic action of micro-organisms that can be measured by standardized tests, in a specified time, reflecting available disposal conditions. Compostable polymers are those that are degradable under composting conditions. To meet this definition they must break down under the action of micro-organisms (bacteria, fungi, algae), achieve total mineralization (conversion into carbon dioxide, methane, water, inorganic compounds or biomass under aerobic conditions) and the mineralization rate must be high and compatible with the composting process. Oxo-biodegradable polymers are those that undergo controlled degradation through the incorporation of µprodegradant¶ additives (additives that can trigger and accelerate the degradation process). These polymers undergo accelerated oxidative define degradation initiated by natural daylight, heat and/or mechanical stress, and embrittle in the environment and erode under the influence of weathering. Photodegradable polymers are those that break down through the action of ultraviolet (UV) light, which degrades the chemical bond or link in the polymer or chemical structure of the plastic. This process can be assisted by the presence of UV-sensitive additives in the polymer. Water-soluble polymers are those that dissolve in water within a designated temperature range and then biodegrade in contact with microorganisms.

Out of these five types of degradable polymers paper gives emphasis on Biodegradable plastic in detail. The various kinds of biodegradable polymers & their compositon for the production of biodegradable plastic carry bags is discussed further. 3


BIODEGRADBLE POLYMERS The composition of biodegradable bags also varies, with the main categories being : Thermoplastic starch-based polymers made with at least 90% starch from renewable resources such as corn, potato, tapioca or wheat. Polyesters manufactured from hydrocarbons (oil or gas). All polyesters degrade eventually, with degradation rates ranging from weeks for aliphatic polyesters (e.g. polyhydroxyalkanoates) to decades for aromatic polyesters (e.g. PET). Starch-Polyester blends that mix thermoplastic starch with polyesters made from hydrocarbons. Following Table provides a list of the different types of degradable polymers. This table classifies polymers according to both degradation pathway and composition.

Polymer category, Degradation pathway Biodegradable starch-based polymers

Biodegradable Polyesters

Composition

From renewable or nonrenewable Resources

Thermoplastic starch derived from corn, potato or wheat, blended with additives (e.g. plasticizers) Thermoplastic starch derived from corn, potato or wheat, blended with polyester (PLA or PCL)

Mostly renewable

Starch component enewable, but hydrocarbonbased plastics and energy for agriculture are nonrenewable As above

Thermoplastic starch derived from tapioca, corn, potato or wheat, blended with polyethylene Thermoplastic starch derived from corn, As above blended with PVOH Polybutylene succinate (PBS) Non-renewabl e Poly (butylene succinate-co-adipate) (PBSA) Non-renewable copolymers Polybutyrate adipate terephthalate (PBAT)) Non-renewable Adipic acid aliphatic/aromatic copolyesters Non-renewable (AAC) Polylactic acid (PLA) Renewable Polycaprolactone (PCL) Non-renewable Polyhydroxy-butyrate-valerate) (PHB/V) Renewable

.

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COMPOSITION OF BIODEGRADABLE CARRY BAGS ± The composition for each polymer is based upon materials that would be required to perform as material for film blowing and application as shopping bags. The streamlined LCA utilises generic life cycle inventory data for each material and do not refer to specific commercial products on the market or from companies that manufacture each polymer.

Bag material

Composition

Assumptions made

Starch Polybutylene

50% - starch from maize

Adipic acid is manufactured

succinate/adipate

25% - 1,4- butanediol

from cyclohexane (40%) and

12.5% - succinic acid

(60%) nitric acid. Succinic

12.5% - adipic acid

acid is formed through the

(PBS/A)

(e.g.,Bionelle).

fermentation of corn-derived glucose. Starch

with

adipate

polybutylene

50% - starch from maize

1,4-butanediol

terephthalate

25% - 1,4- butanediol

either from natural gas or

12.5% - adipic acid

corn glucose.

(PBAT) (e.g.,Ecoflex)

is

derived

12.5% - terephthalate acid Starch-polyester blend

50% starch from maize

Maize growing based upon

(e.g. Mater-Bi)

50% polycaprolactone (PCL)

data

related

to

growing

maize in the Netherlands. PCL is produced from cyclohexanone

(95%)

and

aceticacid (5%). Starch-polyethylene

blend

(e.g.,Earthstrength)

30% starch from tapioca

Cassava

growing

based

70% high-density polyethylene

upon data related to growing cassava in the Netherlands.

Polyethylene+prodegradant

97% high density polyethylene

Additive modelled as stearic

(e.g., TDPA)

3% additive

acid and small amount of cobalt metal to represent the presence of cobalt stearate.

Polylactic acid (PLA)

100% polylactic acid

Based upon maize growing in the USA.

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In one of the recent invention[1] related to biodegradable plastic composition comprising rice powder and/or corn powder, which can be characterized in comprising 100 parts by weight of polyolefin matrix resin; 5 to 400 parts by weight of grain powder selected from the group consisting of rice powder, corn powder and mixture thereof. The biodegradable plastic composition according to the present invention can be manufactured in various forms such as injection molding product, sheet molding and blow molding product, which have excellent physical properties and product stability. The efficiency of waste disposable of the product manufactured with the composition can be remarkably improved since the rice powder or the corn powder contained in the composition can be degraded by microbes in the nature after a certain period. Therefore, the problems of soil, air, and sea pollution caused by burial or incineration of the wastes of conventional plastic molding product can be minimized. This invention provides a biodegradable plastic composition comprising 100 parts by weight of polyolefine matrix resin; and 5 to 400 parts by weight of grain powder selected from the group consisting of rice powder, corn powder and mixture thereof. The plastic composition according to the present invention preferably contains 0.1 to 10 parts by weight of polyvinyl alcohol as a biodegradation assistant to improve degradability of the composition and to prevent deterioration of the physical property caused by addition of the rice powder and/or the corn powder. Besides, 0.1 to 10 parts by weight of the coupling agent and 0.1 to 10 parts by weight of the plasticizer may be included to improve compatibility of the rice power and/or the corn powder with the matrix resin, and to improve simultaneously both physical properties and workability of the composition. The biodegradable plastic composition of the present invention comprises 5 to 400 parts by weight of the rice powder and/or the corn powder based on 100 parts by weight of the polyolefin matrix resin, preferably 30 to 80 parts by weight. For the matrix resin, various resins, such as polyolefin resin, ethylenevinylacetate resin which is the copolymer of polyethylene with vinylacetate, polystyrene, ABS resin can be used in consideration of the property of the product, and it is preferable to use polyolefin resin such as polyethylene and polypropylene. For the polyethylene resin, HDPE(High Density Polyethylene), LDPE(Low Density Polyethylene), LLDPE(Linear Low Density Polyethylene) etc., may be used alone or in the form of mixtures thereof, and it is preferable to use HDPE(High Density Polyethylene) considering the physical property of the product, and the mixture in the ratio of 100-50: 30-0:20-0 corresponding to HDPE:LDPE:LLDPE respectively can be used in consideration of formability of the product.

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Following table shows 9 different Embodiments and their contents employed for the production of biodegradable plastic. The unit of content of the component is parts by weight. Embodiment No. Component

1

2

3

4

5

6

7

8

9

Matrix resin

100

100

100

100

100

100

100

100

100

Rice powder

100

100

100

100

100

100

100

Corn powder

Anti-oxidant

1

1

1

1

Releasing agent

1

1

1

1

1

Polyvinylalcohol

5

5

5

5

5

5

5

Cacium stearate Polyethylene wax

5 5

Vinyltrimethoxy silane

1 1

1 1

5

50 100

50

1

1

1

1

5

5

5

5

5 2

Isopropyltriiso stearoyl titanate

2

Biodegradable plastic compositions according to above embodiments were injected using injection molder at the 55 condition of 180-190° C. and 500-600 psi to obtain samples of required thickness.

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PROCESS FLOW SEQUENCE FOR BIODEGRADABLE PLASTIC PRODUCTION-

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DURABILITY TEST FOR BIODEGRADABLE PLASTIC CARRY BAGSThere are various ASTM standard tests to determine the degree & rate of biodegradation of plastic materials. D5338 ± 98, D5526 ± 94, D6954 ± 04 are the three different ASTM tests to determine the biodegradability on exposure to controlled composting, accelerated landfill and by photoxidation & ecological impacts environment respectively. The purpose of these tests is discussed below in brief.

D5338 ± 98 This test method determines the degree and rate of aerobic biodegradation of plastic materials on exposure to a controlled-composting environment under laboratory conditions. This test method is designed to yield reproducible and repeatable test results under controlled conditions that resemble composting conditions. The test substances are exposed to an inoculum that is derived from compost from municipal solid waste. The aerobic composting takes place in an environment where temperature, aeration and humidity are closely monitored and controlled.

D5526 ± 94 This test method covers determination of the degree and rate of anaerobic biodegradation of plastic materials in an accelerated-landfill test environment. This test method is also designed to produce mixtures of household waste and plastic materials after different degrees of decomposition under conditions that resemble landfill conditions. The test materials are mixed with pretreated household waste and exposed to a methanogenic inoculum derived from anaerobic digesters operating only on pretreated household waste. The anaerobic decomposition occurs under dry (more than 30 % total solids) and static nonmixed conditions. The mixtures obtained after this test method can be used to assess the environmental and health risks of plastic materials that are degraded in a landfill.

D6954 ± 04 This guide provides a framework or road map to compare and rank the controlled laboratory rates of degradation and degree of physical property losses of polymers by thermal and photooxidation processes as well as the biodegradation and ecological impacts in defined applications and disposal environments after degradation. Disposal environments range from exposure in soil, landfill, and compost in which thermal oxidation may occur and land cover and agricultural use in which photooxidation may also occur. 9


REFERENCES-

1. Kyu-Teck Han, Jung-Hoon Choi, Ik-Soo, Chung United States Patent ³Bio- degradable plastic composition´, 2. Karli James, Tim Grant ³LCA of Degradable Plastic Bags´. 3. Sara Ellis, Sarah Kantner, Ada Saab, Mary Watson ³PLASTIC GROCERY BAGS: THE ECOLOGICAL FOOTPRINT´. 4. ExcelPlas Australia, Centre for Design (RMIT), and Nolan ITU, The impacts of degradable plastic bags in Australia. 2004, Final Report to Department of the Environment

and

Heritage,

Department

of

the

Environment

and

Heritage,

Commonwealth Government of Australia: Canberra. 5. D5338 ± 98 ³Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions´. 6. D5526 ± 94 ³Standard Test Method for Determining Anaerobic Biodegradation of Plastic Materials Under Accelerated Landfill Conditions´. 7. D6954 ± 04 ³Standard Guide for Exposing and Testing Plastics that Degrade in the Environment by a Combination of Oxidation and Biodegradation´.

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Biodegradable Plastics

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