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Types of Biodegradable Plastics: Part 2

Types of Biodegradable Plastics: Part 2 March 28, 2019Leave a comment
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Biodegradable plastics can be biobased or fossil fuel based. New types of plastics have been produced in recent years to address the plastic pollution problem, by trying to shorten the time needed to degrade them, especially in natural conditions. However, not all the current biodegradable plastics have achieved this aim.

Definition of Biodegradable Plastics

Biodegradable plastics are those that can be degraded by microbial action to produce natural end products, like water and carbon dioxide, in a reasonable period. The time needed to decompose completely depends on the material, environmental conditions such as temperature and moisture, and location of decomposition.

Compostable plastics are those that biodegrade rapidly and turn into humus that is not contaminated by metals. Not all biodegradable plastics are compostable; only some are.

Materials must meet ASTM Specifications D6400 or D6868 to be called biodegradable and compostable on land, and meet ASTM D7081 specifications for marine environments. ASTM is a worldwide product standards group.

Biomass-Based Biodegradable Plastics

Biomass-based plastics are made of starch and cellulose obtained from crop residues as well as wood from trees.

Cellulose Acetate

Cellulose acetate (CA) is a synthetic product that is derived from cellulose that is found in each part of a plant. Cellulose is currently used from cotton, wood, and crop waste according to a 2015 scientific publication. This can be used to form molded solid plastics, cigarette filters, coatings, photographic-films, and filters. Cellophane is a biodegradable film produced from cellulose. There is ongoing new research to find new plastic films from waste crop and wood material that are water resistant and biodegradable according to Phys.

Biodegradability: Research shows that CA degrades and is reduced by 70% of its weight after 18 months in nature.

Starch

Starch is treated with heat, water, and plasticizers to produce a thermoplastic. To improve its strength, it is combined with fillers made of other materials. The primary sources of starch are maize, wheat, potato, and cassava. This plastic is used in packaging, bags, and agricultural mulch films, tableware, flower pots, and molded to make packaging and consumer goods. It is seen as an alternative for polystyrene (PS) according to the Food Packaging Forum. Starch is added to biobased and conventional plastics to make them more biodegradable.

Biodegradability: Starch-based plastics can be compostable or only biodegradable. Compostable variants require 90 days to degrade in industrial facilities, while the biodegradable ones require 100 days for 46% to degrade and up to two years to degrade completely.

Fossil Fuel Based Biodegradable Plastics

According to Bioplastics Guide, there are a few new fossil fuel plastics that can also be biodegradable. The most common ones are Polybutylene succinate (PBS), Polycaprolactone (PCL), polybutyrate adipate terephthalate (PBAT) and Polyvinyl alcohol (PVOH/PVA).

PBAT is a polymer that is produced from fossil fuel derivatives and is used sometimes in combination with starch. Efforts are on to produce this polymer from renewable sources. Bioplastics guide see it as a substitute for LDPE and HDPE. It is used to make garbage bags, wrapping films, disposable packaging and tableware (cups, dishes etc.). It is not only biodegradable but also compostable.

PCL is a synthetic polyester used to make compostable bags, in the medical application (sutures and fibers), as surface coatings, adhesives for shoes and leather, and stiffeners for shoes and orthopedic splints. Yeasts can decompose this plastic. More than 90% of films and 40% of foam made of this material can be degraded in 15 days.

PBS is a resin produced from fossil fuels or can also be biobased. It can be combined with other biobased polymers or fibers like jute to improve its quality. PBS is used to make food packaging, service ware, agricultural mulch sheets, plant pots, hygiene products like diapers, and fishing nets.

PVOH is a resin that can be used to make packaging films that can replace LDPE and HDPE. Its other important applications are as coatings and additives for paper and board production.

All four fossil fuel based plastics biodegrade in three months in industrial composting, in one year in backyard composting and in one to two years in soil/ landfills.

Recycling and Composting

Properties of the different biodegradable plastics must be kept in mind to treat them at the end of their life-cycle, cautions the Environmental Protection Agency (EPA).

EPA explains that biodegradable plastics should not be added to bins which recycle conventional plastics as they are made of different materials. This is true for both the biobased and the fossil fuel types.

Even though plastics are marked as biodegradable and compostable, many of them can degrade only in conditions available at commercial composting facilities; contact local recycling agencies for information on the nearest compost plant. Confirm that bags are compostable at home by following product instructions before adding them to the compost bins.

Recovery of material from biodegradable plastics is not possible through recycling, due to lack of facilities. Efficient segregation, collection, and degradation are necessary to take advantage of the biobased and biodegradable plastics. In its absence, most of the biodegradable plastics end up in landfills.

Link: Types of Biodegradable Plastics: Part 1

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