Compostable Plastics

World Centric® compostable plastic cups and containers are made from a bio-based plastic derived from renewable plants. Chemically, this material is known as PLA, or Poly Lactic Acid, which can be derived from a variety of plant-based starches.

Benefits

• Made from plants instead of petrochemicals from fossil fuels
• Manufacturing uses less energy and creates fewer greenhouse gas emissions
• Freezer safe
• Certified to break down in a commercial composting facility in 3 – 6 months¹

Limitations

• May be mistaken for traditional plastic by consumers
• Cannot handle hot foods or liquids
• Needs to be stored at temperatures below 110°F, away from hot surfaces and direct sunlight
• Not suitable for home composting
• Not accepted at many commercial composting facilities

Overview

Compostable Plastics are a new generation of plastics which are biodegradable through composting. They are derived generally from renewable raw materials like starch (e.g. corn, potato, tapioca etc), cellulose, soy protein, lactic acid etc., are not hazardous/toxic in production and decompose back into carbon dioxide, water, biomass etc. when composted. Some compostable plastics may not be derived from renewable materials, but instead derived made from petroleum or made by bacteria through a process of microbial fermentation.

Currently, there are a number of different compostable plastics resins available in the market and the number is growing every day. The most commonly used raw material for making the compostable plastics is corn starch, which is converted into a polymer with similar properties as normal plastic products. Other compostable resins are available made from potato starch, soybean protein, cellulose and as well from petroleum and petroleum by products. It is counter intuitive to think that compostable resins could be derived from petroleum, when all normal plastic products are derived from petroleum and are non compostable. However, there are certified compostable resins available in the market, derived from petroleum and the field of compostable plastics is constantly evolving with new materials and technologies being worked on and being brought to market. There is even research underway to make compostable plastics from carbon dioxide.

Properties

The compostable resins for the most part mimic plastic properties, and different resins have different properties related to heat resistance, tensile strength, impact resistance, MVTR, oxygen barrier etc. One of the main compostable resin PLA, for example has a heat resistance of only 110F, while other compostable resins can have a much higher heat resistance.

Biodegradability & Compostability

Bioplastics can take different length of times to totally compost, based on the material and are meant to be composted in a commercial composting facility, where higher composting temperatures can be reached and is between 90-180 days. Most existing international standards require biodegradation of 60% within 180 days along with certain other criteria for the resin or product to be called compostable. It is important to make the distinction between degradable, biodegradable and compostable. These terms are often (incorrectly) used interchangeably.

• Compostable Plastic is plastic which is "capable of undergoing biological decomposition in a compost site as part of an available program, such that the plastic is not visually distinguishable and breaks down to carbon dioxide, water, inorganic compounds, and biomass, at a rate consistent with known compostable materials (e.g. cellulose). and leaves no toxic residue." American Society for Testing & Materials (ASTM). In order for a plastic to be called compostable, three criteria need to be met:
  • Biodegrade - break down into carbon dioxide, water, biomass at the same rate as cellulose (paper).
  • Disintegrate - the material is indistinguishable in the compost, that it is not visible and needs to be screened out.
  • Eco-toxicity - the biodegradation does not produce any toxic material and the compost can support plant growth.
• Biodegradable Plastic is plastic which will degrade from the action of naturally occurring microorganism, such as bacteria, fungi etc. over a period of time. Note, that there is no requirement for leaving "no toxic residue", and as well as no requirement for the time it needs to take to biodegrade.
• Degradable Plastic is plastic which will undergo a significant change in its chemical structure under specific environmental conditions resulting in a loss of some properties. Please note that there is no requirement that the plastic has to be degrade from the action of "naturally occurring microorganism" or any of the other criteria required for compostable plastics.

A plastic therefore may be degradable but not biodegradable or it may be biodegradable but not compostable (that is, it breaks down too slowly to be called compostable or leaves toxic residue).

Estimated Composting Times

The rate of biodegradation for different compostable products is dependent upon the composition and thickness of the material as well as composting conditions. Commercial composting facilities grind the materials, turn over the piles and reach high temperatures, thus reducing the amount of time it takes to compost and, is thus, the recommended method for composting these products. Home composting rates are slower and can vary, depending on how frequently the pile is turned over, the moisture and material content and the temperature. Composting utensils at home is not recommended, due to their thickness and they may not break down for few years. Similarly, PLA products are not recommended to be composted at home.

Standards

There are currently few international organizations which have established standards and testing methods for compostability, namely:

• American Society for Testing and Materials - ASTM-6400-99
• European Standardization Committee (CEN) -EN13432
• International Standards Organization (ISO) -ISO14855 (only for biodegradation)
• German Institute for Standardization (DIN) -DIN V49000

The ASTM, CEN and DIN standards specify the criteria for biodegradation, disintegration and eco-toxicity for a plastic to be called compostable.

• Biodegradability is determined by measuring the amount of CO2 produced over a certain time period by the biodegrading plastic. The standards require 60% conversion of carbon into carbon dioxide within 180 days for resins made from single polymer and 90% conversion of carbon into carbon dioxide for co-polymers or polymer mixes.
• Disintegration is measured by sieving the material to determine the biodegraded size and less than 10% should remain on a 2mm screen within 120 days.
• Eco toxicity is measured by having concentrations of heavy metals below the limits set by the standards and by testing plant growth by mixing the compost with soil in different concentrations and comparing it with controlled compost.