Overview
AS 4736 “Biodegradable Plastics – Biodegradable Plastics suitable for composting or other biological treatments” is the standard developed by Standards Australia to regulate controlled composting degradable materials entering the Australian market.
This standard is based on the European standard EN 13432, in addition to the ecotoxicological performance requirements of earthworm ecotoxicological detection.
Specific requirements are as follows:
A chemical restriction: set minimum levels of organic matter, heavy metals and fluorine for controlled compost materials;
B biodegradability: it is stipulated that more than 90% of controllable composting materials must be eventually converted into carbon dioxide, water and minerals in the longest months under aerobic composting;
C Disintegration performance: it is stipulated that the degradable materials in controllable composting must disintegrate into more than 90% fragments that can pass through 22mm screen in maximum 12 weeks under aerobic composting condition;
D Ecotoxicological performance: selected plants can achieve more than 90% of the original survival rate and biological traits after the introduction of compost decomposition materials of controlled composting degradation materials, and at the same time, earthworms can achieve more than 90% of the original survival rate and biological traits after the introduction of compost decomposition materials of controlled composting degradation materials.
Australian Standard 4736:2006 Biodegradable plastics- Biodegradable plastics suitable for composting and other microbial treatmentgoverns the identification and performance expectations of bioplastic materials in Australia.
In summary, AS 4736 requires demonstration of a product’s characteristics and performance under the following tests:
Characterization
Biodegradability (aerobic only)
Disintegration
Compost quality, ecotoxicology (plants), ecotoxicology (earthworms)
Recognizability
Characterization
Characterization is the determination of the various constituents of the test material. This is seen as important to ensure that no harmful (toxic, hazardous) compounds are released into the environment.
AS 4736-2006 requires that the test material is identified and characterized prior to testing as follows:
The information on and identification of each constituent of the plastic (e.g. thickness) shall be determined or obtained, and recorded.
The volatile solids content of the plastic shall be determined and recorded. The plastic shall contain a minimum of 50% of volatile solids.
The presence of heavy metals and other toxic and hazardous substances shall be determined and recorded. The concentration of any component present in a plastic material shall not exceed the value specified in the Standard.
The organic carbon content and total dry solids of the plastic shall be determined and recorded.
The thickness of the plastic shall be determined and recorded.
The colour constituents of the plastic shall be determined and recorded
Characterization is the determination of the various constituents of the test material.
Biodegradability (aerobic)
This process involves determining the alteration of the chemical structure of the test material brought about by biological action, resulting in the transformation of the test material into various compounds including CO2 and methane (CH4). The limit value for biodegradation is based on conversion of the carbon of the test material into carbon dioxide and biomass. The details of calculation depend on the test and analytical methods used. The overarching standard on which this requirement of AS 4736-2006 is based is ISO 14855 which outlines the appropriate methods for determining aerobic biodegradability.
AS 4736-2006 requires that test samples are not subjected to conditions that will accelerate biodegradation prior to testing. The period of application of the test shall be a maximum of 6 months, within which the test material shall degrade at least 90% w/w (dry weight) in total or of the maximum degradation of a suitable reference substance.
Disintegration
Disintegration in AS 4736-2006 is defined as the physical falling apart into minute fragments of the test material. Any product to be labelled a biodegradable plastic under Australian Standards® must disintegrate by over 90% into fragments < 2 mm in size in a 12 week pilot-scale composting bin under aerobic conditions. The disintegration test of the Test Material is performed under defined and standardized composting conditions and includes a control treatment with both test series replicated in duplicate. The test material is tested in a form and thickness comparable to that for its intended use. The test material used in the following disintegration experiment was a 130 μm plastic film.
Note: Due to the nature of the disintegration test, the test results cannot differentiate between biodegradation and abiotic disintegration in this post Quality and Ecotoxicology (Plants and Earthworms)
Any toxic effect of the test material in compost can have an adverse effect on biological organisms such as plants and animals that inhabit soil (e.g. earthworms). It is therefore necessary to assess any such affects on representatives of these species due to the presence of residues from the test material in compost.
Following the disintegration test, a number of parameters are measured on the compost with and without the addition of the test material (i.e. volumetric weight, total dry solids, volatile solids etc).Earthworm and plant ecotoxicology tests are then conducted on the compost in the following manner:
The earthworm eco-toxicity test follows that outlined in AS 4736-2006 and ASTM E1676-04. The species used is Eisenia fetida, a lumbricid earthworm (redworm). The standard 14-day toxicity test is applied. For successful completion of the earthworm eco-toxicity assay, a difference of less than 10% in the morbidity and mean weight of surviving worms must be found between the compost containing the test material and the control compost (without test material).
The plant ecotoxicity test is conducted using two higher plant species recommended by the OECD guideline 208 and follows the test outlined in AS 4736-2006.The compost produced from the disintegration test with and without the addition of the test materialis used to assess germination rate and plant biomass. Each replicate from the disintegration testis tested at two concentrations, 25% and 50% (m/m or v/v) of compost (mixed with the control compost from the disintegration tests). Each replicate from the disintegration test is used here to provide biologically independent replicates of the disintegration process.For successful completion of the plant eco-toxicity assay, the germination rate and the plant biomass of the compost containing the test material of both plant species should be more than 90% of those from the corresponding negative control compost.
Recognizability
Recognizability in AS 4736-2006 is concerned with ensuring that the bioplastic product is sufficiently labelled/branded that the end user recognizes that it is a biodegradable or compostable product and uses and disposes of the product in an appropriate manner.
Polylactic acid (PLA) is a new type of biodegradable material, which is made of starch from renewable plant resources (such as corn). It can replace PP and mix with wheat straw fiber, which has reached the standard of complete degradation AS4736. However, the cost of using PLA is very high, estimated to be more than three times that of PP.
Post time: Mar-22-2022