28 Apr 2008 (Updated 12 Jun 2013)


Biopolymers

Dr Markus A Meier and Miriam Wehrli on reducing carbon footprints with biopolymers.

Sustainability is a key challenge in our modern and environmentally aware society, and even more in the centre of interest with recent initiatives from big retailers and brand owners.

Reducing carbon footprint is the main focus, particularly in the packaging market – and, in this regard, biopolymers are consistently in the spotlight.

What are biopolymers?

Terms like 'biodegradability', 'compostability' and so forth often lead to confusion, and consumers often don't know how to deal with these new features, which makes them unsure of the real benefits of biopolymers. Generally, polymers can be divided into four different groups depending on their source and their ability to degrade in a certain environment.

The majority of standard plastics such as Polyethylene (PE) and Polypropylene (PP) are non-(bio-)degradable and are based on fossil resources. Some others, such as Polycaprolactone (PCL), are (bio-)degradable even though they're made of fossil raw materials, and there are different so-called 'oxodegradable' additives on the market that trigger degradation of non-degradable petroleum-based polymers and allow them to degrade. This could be an interesting option for some very specific applications where degradation is the key functionality and not driven by sustainability. Examples are mulch films in agriculture or, potentially, shopping bags.

Presently, the term ‘biopolymers’ is often associated with biodegradable and bio-based polymers. The most prominent example is Polylactic acid (PLA), which is presently supposed to be the most prevalent biopolymer on the market. However, biopolymers refer only to plastics that are based on renewable resources and are therefore not necessarily related to biodegradability. For instance, sugar-based PE is considered a biopolymer even though it's not biodegradable.

Do we need biodegradable polymers?

Biodegradability is an attribute that's often associated with environmental friendliness, but on the other hand also with instability of the polymer and low performance. Currently, biodegradability is frequently used as a marketing tool, though not all aspects of biodegradability are known and therefore hardly foreseeable (eg impact of degradation products).

Already, we're confronted with headlines pointing to the rising prices for corn tortillas in Mexico due to the increasing demand of bio-resources causing corn shortages. Feed stock and farmland for biopolymers are in competition with biofuels as well as land capacity, which could be used to feed people.

The benefits of biopolymers capable of being chemically recycled rather than composted are therefore obvious. Collecting industrial and post-consumer waste of polylactic acid (PLA), for instance, and converting it back to lactic acid by depolymerization results again in a purified base material for the polylactic acid production. In doing so, corn production, corn wet milling and fermentation could be avoided, and leading to an overall reduction of costs and energy consumption.

Biodegradability should rather be regarded as functionality for some specific applications than being directly linked with biopolymers. Furthermore, when considering the high efforts presently made to improve the mechanical and technical properties of biopolymers, future biopolymer solutions will most probably end up losing the biodegradability at the expense of strength. In essence, the development of bio-based polymers should target a polymer which is recyclable rather than biodegradable.

Carbon footprint

In this context, the main driver for biopolymers on the market turns out to be the fact that they're based on renewable raw materials. This is presumably linked with the increasing pressure to reduce the environmental impact of products, and furthermore to comply with internal sustainability commitments.

Biopolymer resin producers especially enhance their life cycle studies by purchasing renewable energy credits, but this option is certainly independent of the polymer produced.

For the time being, Ciba’s market analysis in collaboration with Pira International and life cycle assessment (LCA) studies of biopolymers in cooperation with the Swiss Federal Institute of Technology (ETH Zurich) show neither clear advantages nor disadvantages of biopolymers compared with traditional mineral, oil-based polymers.

As processing, use, collection and even waste management (except composting) don't show significant difference, and are comparable for all kind of polymers in terms of energy demand and greenhouse gas emissions, a fully greenhouse-gas-neutral option can only be achieved by using renewable resources. Even if 100% recycling could be feasible, traditional plastics would still need crude oil as a feed stock and therefore release net CO2 to the atmosphere.

The long-term vision for a sustainable solution points to biopolymers that are 100% recyclable. If this is considered unfeasible, then at least incineration with heat recovery should be the option and not composting, in which, neither energy nor base material can be recovered (destroying value).

Kompogas – anaerobic digestion

One exception from the above statement, and therefore an additional end-of-life option for some biodegradable polymers, could be anaerobic digestion. In contrast to composting, the material breakdown occurs in the absence of oxygen and therefore produces carbon dioxide and methane instead of carbon dioxide and water.

Moreover, anaerobic digestion is a renewable energy source because the methane and carbon-dioxide-rich biogas, which is produced during the process, is suitable for energy production, helping replace fossil fuels. The Swiss company Kompogas is producing CO2-neutral energy from biogenous household waste with this method.

Additionally, the nutrient-rich solids left after digestion can be used as fertiliser. However, the quality of compost obtained from (bio-)degraded packaging waste is questionable.

Hence, the issue of not being able to reuse base material, as in the case of recycling, will still remain. Furthermore, many biodegradable polymers, including PLA, are not (yet) suitable for anaerobic digestion. Nevertheless, this could be an attractive end-of-life alternative for several very specific applications where biodegradability implicates additional functionality and value.

Role of raw material suppliers

Ciba continuously strives for superior performance and is committed to contribute to long-term sustainable development. Regarding biopolymers simply as a new type of polymer on the market, Ciba is committed to learn more about these new materials.

The company is capitalising on its expertise in polymers, colorants and additives to support the development of biopolymers by improving their technical performance through additives, focusing on testing compatibility with polymers and recycling rather than biodegradability.

Beyond the interests in the embryonic biopolymer market, Ciba offers a wide range of sustainable solutions for plastics and paper/paperboard packaging. Consequently, the company’s contribution to sustainable packaging will not only concentrate on additives and colorants for biopolymers, but also include strength solutions which allow significant light-weighing of packaging as well as improvement of recycled resin performance.

There will be no standard solution eliminating all present and future concerns. Rather, the point is to find individual ways to change general attitudes and develop technologies to balance environmental, economic and social aspects of sustainability in order to ensure the same quality of life also for future generations.

By Dr Markus A Meier and Miriam Wehrli