Common Questions about Oxo-Biodegradable Plastic
Q1. What specific biodegradability claims does your industry make about oxo-degradable plastic?
Oxo-biodegradability is concerned with the biodegradation of the oxidatively degraded polymer in the open environment (cf hydro-biodegradable materials which are certified to compostable standards such as EN13432, ASTM D6400 which are specific to synthetic industrial composting conditions and therefore have defined timeframes.) Consequently our members claim that oxo-biodegradability occurs in any aerobic environment at a rate that is determined by the conditions of that natural aerobic environment, whereby the initiation period and degradation performance can be adjusted.
Q1a. Do these claims differ between manufacturers/brands?
OBPF members have a common stance as detailed in B1 above. Our relevant members have had their oxo-biodegradable additive formulations tested by independent facilities, in different polymer substrates in different aerobic conditions, i.e. soil, compost etc, to international standards and test guides.
Q2. Are there any environments in which oxo-degradable plastic does not biodegrade?
Oxo-biodegradation requires the presence of oxygen to produce the oxidative degradation and therefore these materials will not oxo-biodegrade in anaerobic environments, with the advantage that they will therefore not produce methane (a strong greenhouse gas) when subjected to these conditions.
Q3. Can you provide any test reports for oxo-degradable plastic that has undergone abiotic testing to BS 8472 (or equivalent) followed by biodegradation testing to ISO 17556?
The Research Group headed by Prof. Emo Chiellini conducted comprehensive investigation of different types and grades of polyethylene incorporating EPI’s TDPA™ (Totally Degradable Plastic Additive) and classified them as oxo-biodegradable, i.e. oxidative degradation followed by biodegradation of the oxidized materials in solid media (soil & compost) as per existing biodegradation standards ASTM 5388-98 or ASTM 5988-03 or EN-ISO 17556-04. The study by Prof. Emo Chiellini and his team were done in accordance with the principles in ASTM Standard Guide D6954-04 and the equivalent norm BS8472-11 and concluded that polyethylene incorporating TDPA are degradable by a combination of oxidation and molar mass reduction of the molecules followed by mechanical disintegration of the samples and ultimate environmental biodegradation (Ref. Pisa, June 2015.)
Note: The biodegradation testing performed in these standards (ASTM D6954-04 (2013) and BS8472-11) are identical to those which are required to be performed in the compostable standards EN13432 and ASTM D6400.
Q4. Do you believe the current standards and test methods sufficiently represent oxo-degradable plastic?
Current test standards, i.e. ASTM D6954, BS8472, provide framework and test methodologies to determine degradation, biodegradation and non-ecotoxicity of the oxo-biodegraded material. There are no standard specifications which provide a pass/fail criteria for oxo-biodegradability such as those available for industrial compostable plastics (ASTM D6400, EN13432, SPCR 141-4). This is due to the intrinsic difficulty of defining a natural environment.
Q5. Are there any future standards/test methods being developed?
OBPF members technically lead a work item at ASTM, WK49920, which is reviewing and refining ASTM D6954-04 (2013) to reflect the knowledge built up since first inception in 2004. There is also considerable discussion and work that the OBPF is involved with at ASTM to formulate agreed definitions for different aspects of the natural environment.
Q6. Do you have a preferred method for measuring biodegradation and why?
There are several standard test methods for determining the ultimate aerobic biodegradation in different modelled environments, i.e. ASTM D5338 / EN-ISO 14855 (biodegradation under compost conditions), ASTM D5988 / EN-ISO 17556 (biodegradation in soil)
These standards all rely upon the measurement of the amount of evolved CO2, through different techniques, to determine the ultimate degree of biodegradation.
These reflect conditions which may be found in the natural environment and give data on the potential rate and extent of biodegradation.