Cliff Top View On Understanding Biodegradability of Bio Plastics
Introduction
As we demand more from products we inadvertently run the risk of increasing stress on our eco system in how we deal with the waste generated from these demands. Take plastic with its impact and volume of use in our daily lives. If you open your fridge door and take a count of all the items that are packaged in plastic, you will simply find the results staggering. Go one step further and list all the items in your house that are made from plastic, you will now get the scenes of the sheer scale of how much plastic we have in our lives.
Plastic is a part of our lives and our dependability on it grows every day but unfortunately it is with us forever as it’s difficult to dispose off in an environmentally friendly way. We now have a new generation of Eco Plastics derived from natural sources as in feed crops. Understanding how we can proactively use these new Bio Plastic’s is important but understanding how we can dispose of them is even greater. UZETworld is introducing to the market through its own direct marketing and that of its client base Bio products made from Natural Plastic that meet with the highest standards and broadest signature of biodegradability.
Degradability versus Biodegradability
Biodegradability relates to the degradation of materials through a biological route eg bacteria, enzymes, fungi; this may be through an aerobic or anaerobic mechanism. Composting is a specific approach to the biodegradation of plastics and other organic waste materials which uses aerobic mechanism to convert the carbon to carbon dioxide. Waste water treatment (eg sewage systems).
Anaerobic digestion converts the carbon to methane gas, which can then be used as a fuel source (biogas). Plastics can also be degraded through oxidative mechanisms involving heat or light in the presence of oxygen. There is specific ASTM specification relating to the photodegradable for hycone, ring pull closures.
Ox biodegradable falls into this category of “degradable plastics”. To date there is no recognized test protocol available to validate the efficacy of these material claims.
Hot Composting
This is the current main approach to certify biodegradable plastic items. The specifications are ASTM D6400, EN 13432 (food packaging), EN 14995 (non food packaging) and ISO 17088 (under development). The specification has a number of components, all which need to be met for a product to be certified.
Complete biodegradation (ASTM D5338) – conversion or organic carbon to carbon dioxide (60% for homopolymers, 90% for copolymers and blends); 180 days or less for ASTM D6400 and 90 days for EN13432. Mechanical disintegration (thickness related) : <10% on xx sieve after 90 – 180 days. Compost quality/ecotoxicity – no change in growth rate for cress and/or barley. Regulated heavy metal content <50% EPA (USA, Canada)
Why Hot Composting?
Municipal collection and handling program that allows for compost to be cycled in an efficient manner. Typically has a 7-10 day period where the materials are kept at 55-70C and high humidity, followed by the remaining period where the temperature slowly decays to ambient (retained by critical mass, regular turning and biological activity).
Essential for some biodegradable plastics systems that require hot hydrolytic breakdown of the polymer before microbial degradation can take place. Also essential for elimination of toxic organisms from degraded food waste which could influence compost quality. However hot composting is fairly limited and requires a critical mass of collection to be economically effective. Often yard waste is added to provide critical mass and nutrients for degradation. There is a need for a more environmentally flexible degradation process – home composting
Cold Composting / Soil Burial
ASTM D5338 / ISO 14855 used to measure the biological decomposition within ASTM D6400 uses an elevated temperature to measure respirometry rate.
The same procedure can be used under ambient conditions to measure O2 uptake or CO2 release and also the same procedure can be used with a change in microbial activity to simulate cold composting, soil burial or aquatic environments (removal of fungal species). This can provide indicative information on the rate of biodegradation under “domestic conditions, ”Currently there is no reproducible quantitative mechanical disintegration test
ASTM D7081 Marine Degradation Specification
Relates to materials that are denser than seawater. Mandates compliance to ASTM D6400. Biodegradability is carried out according to ASTM D6691 or ASTM D6692 – lower temperature and microbial concentration.
Mechanical disintegration carried out in seawater at 30C. Ecotoxicity involves aquatic species eg daphnia with the same heavy metal constraints.
Photodegradable
Photodegradable means that a product is degradable when exposed to sunlight. This term is most commonly used on plastic products such as trash bags and agricultural mulch film, and is often accompanied by the phrase "Will break down into small pieces if left uncovered in
Photodegradable plastics are supposed to disintegrate into small pieces when exposed to sunlight (manufacturers add a sun-sensitive component to the plastic to trigger degradation). But sustainability requires that a degradable materials break down completely by natural processes so that the basic building blocks can be used again by nature to make a new life form. Plastics made from petrochemicals are not a product of nature and cannot be broken down by natural processes. Therefore, despite how small the pieces of plastic may become, they are not and cannot be biodegradable.
Understanding the biodegradation process gives you the ability to make an informed choice. Bio based biomass sustainable solutions and products are the future, which can be engineered into everyday products.