Biological degradation after exposure to sunlight or heatMany synthetic polymers are normally resistant to oxidation and biodegradation as commercial products thanks to the use of antioxidants and stabilisers. They are also resistant to hydrolysis but can be made oxo-biodegradable by adding so-called pro-degradants. In that way they are degraded by a chain reaction with a free radical mechanism including the oxygen of the air.
The primary degradation products are hydro peroxides that can in turn be degraded either thermolytically or photolytically. This leads to chain scission and build-up of low molecular oxidation products like carboxylic acids, alcohols and ketones, which are suitable for microorganisms for bioassimilation.
Abiotic (without microorganisms) degradation
The lifetime of a polymeric material is mainly determined by the oxygen sensitivity of the material. This in turn depends on the chemical and physical properties of the material.
Development of biodegradable materials always includes a compromise between physical properties that are good enough for the product to work well and a quick and predictable degradation in nature. This means that it is important to know for how long a product is going to work under normal usage conditions but also after how long time the waste will be degraded enough in a given environment so that the degraded material can be metabolised by microorganisms.
Sunlight and heat
Degradation in heat by thermooxidation is performed at elevated temperatures in dry or moist air depending on expected usage. Degradation in sunlight by photooxidation is tested using artificial weatherability tests in which a test object is subjected to the influence of artificial sunlight and/or moist air and/orsimulated rain. Effects of exposure are evaluated using for example mechanical tests like SEC (Size Exclusion Chromatography) and/or IR (infra red spectroscopy) measurements. The measurements give information about how the molecular weight and degree of oxidation changes with time for differentmaterials.
Materials degradable through a combination of abiotic oxidation and biological metabolism.
A test according to ASTM D 6954 or SPCR 141 appendix 4 can show whether a material or product like for instance plastic film for farming and/or golf items are first degraded abiotically in a given environment for a specified time and that the degraded material can be metabolised in soil or compost to a high degree.