Materials

Harvesting bioplastics

Plastic – love it or loathe it, there’s no getting away from it in today’s society. Or is there? In recent years, a new crop of materials, similar in technical properties to their traditional counterparts yet completely biodegradable and compostable, has sprung up. Tony Breton digs up all you need to know about bioplastics

Harvesting bioplasticsWhen Alexander Parkes unveiled the first man-made plastic at the 1862 Great International Exhibition in London, it was heralded as a revolution. But only a few years later, high costs and low product quality meant the business failed. However, this clearly did not stop the plastics industry developing, and in the subsequent 50 years, the science of cracking natural gas and components of crude oil into monomers and subsequently polymers has been perfected. It is estimated that since World War II, over a billion tonnes of the many types of plastic have been produced and then discarded.

It is interesting then to note that the ‘bioplastics’ (for the purposes of this article bioplastics are those which are certified as biodegradable and compostable according to EN13432 and EN14995) industry appears to be mirroring its petro counterpart. The earliest bioplastics were invented around 1890, and in the 1920s Henry Ford, motivated to find a use for agricultural surpluses, developed plastics based on soybeans and even produced a prototype soy plastic car. But the advent of World War II and the ever-decreasing cost of petro plastics saw the end to this and many other projects.  

Since the 1980s, the increasing price of oil and a desire for a more sustainable approach to materials has led to a renaissance of the bioplastics industry and the development of a whole new breed of materials. Just as with the early days of the plastics industry, there have been a number of false dawns and failed companies but also an ever increasing number of successes, and the market for bioplastics is predicted to reach between two and four million tonnes by 2020. As these economies of scale are reached and if – as widely predicted – the cost of crude oil continues to rise, then it is likely that within a few years, one of the major barriers to the take up bioplastics, namely cost, will be eliminated.

There are two basic routes to produce bioplastic. Firstly, there is direct extraction from biomass that yields a series of natural polymer materials (cellulose, starch, proteins), fibres and vegetable oils that can then form the basis on which polymer materials and products can be developed. Alternatively, the renewable resources/biomass feedstock can be converted to
bio-monomers by fermentation or hydrolysis and then further converted by chemical synthesis to biodegradable polymers like polylactic acid (PLA). Bio-monomers can also be microbially transformed to biopolymers like the polyhydroxyalkanoates (PHA).

Using these techniques it is possible to make a whole range of products. Many readers will already be familiar with food waste caddy liners, carrier bags and packaging for fresh organic produce, but there have been a number of interesting recent product launches of particular interest here. Resource 57 included a list of the 10 most difficult household items to recycle, and whilst cat litter is not a current target application, four of the 10 have already been produced in a compostable format:

  • Compostable bubble wrap, padded envelopes, packaging chips and air pillows, typically made with a starch-based film or filler, have been on the market for a number of years.  
  • Citrus and other nets from Tenax Spa. The nets were used for the first time during the 2010 ‘Salone del Gusto’ festival in Italy for the packaging of the Slow Food Presidia, and received the award for the best packaging of the Presidia.
  • Toothpaste tubes from Tectubes for allVeggie in Sweden, which produces toothpaste made from natural substances.
  • Clingfilm from Silvex, which as well as being completely compostable is suitable for all foodstuffs, contains no plasticizers and is breathable, helping to evaporate any condensation that forms on warm food that is refrigerated. Additionally, it does not require a serrated edge to have a clean tear.

Megajoules consumed per kilogramme produced

Beyond these, it is now possible to get compostable crisp packets, long-life (two-year) coffee packaging, bread bags, meat and vegetable pads and much more.

When it comes to discussions on the merits of bioplastics, there are two areas of much debate: energy consumption and land use. Taking land use first and Italy as an example, in order to meet Italy’s total requirements for flexible plastics of around 1.5-2 million tonnes, just 70,000 hectares (ha) of corn and 600,000 ha of oleaginous non-food crops would be required. Considering that in Italy cultivatable land amounts to 15 million hectares, it is clear that bioplastics are not going to affect the food chain, and that through the development of new techniques and increased efficiencies could actually strengthen it.

In terms of the consumption of non-renewable energy to manufacture plastics and bioplastics, in the cradle-to-gate scenario, more often than not the production of bioplastics consumes less energy, as shown in the figure to the right. However, viewing such numbers in isolation should be done with extreme caution as they do not consider the final product, its complete lifecycle or the benefits such a product might have. In a number of current filmic applications, it is often necessary for the compostable film to be thicker than its petro counterpart, so more material will be used, thus potentially negating some of the environmental benefits. Yet this does not tell the whole story; for example, using compostable packaging to pack asparagus can extend the shelf life of the asparagus as the packaging’s inherent breathability slows down the development of fungi. So, in this instance the thicker film reduces waste but it is beyond the boundaries of a standard LCA to fully encompass this. Similarly, a compostable carrier bag might weigh a few grammes more than an HDPE bag, and the benefit gained from composting the film will be negligible. However, if that compostable carrier bag is filled with organic waste otherwise destined for landfill then the consequential benefit is greater.

A third point of debate is end-of-life treatment. A certified compostable product must compost in a commercial composting system in 12 weeks, typically much less time is required, and if certified under the new AfOR home composting scheme, it should take no longer than 12 months. As with petro plastics, if a clean material stream is collected then it is perfectly possible to mechanically recycle these materials. It is important to remember that most materials impede the recycling of others, so whether at a composting plant or recycling facility, purity of feedstock is essential. Trials have proven it possible to sort PLA bottles using infrared technology, but at the current level of market penetration it is not worth it for a MRF operator to make the additional investment. Sorting of mixed and food-contaminated film of any type is another area where the argument is raging and is often the bimonthly chip on Horatio’s shoulder. The public can’t do it and the MRFs can’t do it, so who can? In short, today, no one can. So, it may be that in the near term and until more sophisticated systems of identification are developed, the best route for such film of any origin is likely to be recovery.

The past decade has seen incredible developments in the field of biodegradable and compostable plastics based on renewable resources and these will continue apace long into the foreseeable future. End of life, identification and material sourcing are all important, but it is equally important to understand the additional environmental and commercial benefits such products can bring.