Bioplastics – End-of-life options
The overall goal for bioplastic products at the end of their intended use is to ensure that the loop is closed, cycling the product back at the end of its life to be reutilized. The general preferred hierarchy of disposition at the end of product life is: reduce, reuse, recycle, compost.
The end-of-life options for bioplastics include
- Renewable energy recovery (incineration)
- Anaerobic digestion and
- Feedstock recovery
Bioplastics can be recycled but the recycling need to be done in separate streams. If degradable material enters the conventional plastics stream and fully degrades in the recycling process it may change the characteristics and specification of the conventional material it is mixed with. Also if it does not fully degrade it may continue to do so in the finished recycled product, leading to premature failure.
Though the sorting technology of bioplastics from conventional plastics is in existence, it is still in nascent stage and it will be feasible soon with the increase in commercial volumes to cover the investments required.
Renewable energy recovery (incineration)
Energy recovery from plastics is a practice followed globally due to the high amount of heat generated from it. Biodegradable plastics made from renewable resources, such as PLA—generally contain only carbon, oxygen, and hydrogen atoms, and specifically do not contain chlorine atoms. As they do not contain chlorine atoms, they do not produce dioxins during burning/incineration. Traditionally, bioplastics also do not have heavy-metal additives. So in general they can be safely incinerated, with no danger of releasing dioxins or heavy metals.
However, as biodegradability is the primary motive of bioplastics, energy recovery should be the least preferred end-of-life option as it has a very potential for other options such as recycling, compost and anaerobic digestion.
Feedstock recovery or Chemical recycling
During recycling, the bioplastic can not only be melted and made into granules again for a new application, but in some cases it can be broken back down into its starting chemical building block. For eg. Lactic acid can be recovered from PLA and can be again used to make PLA resin. This is also called chemical recycling.
One must have a clear understanding of the product that has been certified biodegradable or compostable and the clear difference between the two.
A compostable product is always biodegradable however, a biodegradable product is not always compostable.
- A compostable product must meet specific criteria in terms of:
- environmental conditions
- quality of compost produced
- Many bioplastic products are designed to be compostable. However, in many cases, this compostability will only occur in the tightly controlled conditions of industrial composting facilities.
- 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.
- There is no requirement for leaving “no toxic residue“, and as well as no requirement for the time it needs to take to biodegrade.
The method of using the waste from biodegradable plastics in bio-gasifiers and to convert it into useful methane is also practiced at a very small scale at present. The anaerobic digestion of bioplastics has a great scope if it is combined with compostability leading to more efficient waste management.