Biomaterials - a natural choice?

There remains much mystification regarding biomaterials. Two widespread misconceptions are that all biodegradable materials are derived from sustainable crops and that all biodegradable materials will be compostable. Unfortunately neither is true. There are several fossil fuel plastics that easily biodegrade. Furthermore, in order to be classified as biodegradable according to EN:13432, it is necessary for aerobic composting of the material to result in disintegration so that 90 per cent of the mass can pass through a 2mm sieve within 12 weeks.

Biodegradable certification – a misnomer?

This gives a misleading reading – it is possible for a thin film to be manufactured from a compostable biomaterial and that will be classified as biodegradable. However, a brick made from the same material probably won’t compost within the timeframe and thus will not be classified accordingly. Equally a PE material containing metallic salts that permits degradation over four years or so will also not comply. Let’s consider all biomaterials in turn.

PLA: polylactic acid

This is manufactured from sugars that are mostly starch-derived from American corn that has, for other reasons, been genetically-modified (GM). The GM is destroyed during fermentation, so there is none in the final product, but it is difficult to convince someone that is totally opposed to the GM concept. PLA is a clear, brittle material that has similar aesthetics to PET and can thus become mixed up in the recycling and wreck the PET recycled material. PLA does not have a good gas barrier and has a low melting point, although development work is currently being undertaken to rectify that characteristic. PLA can only be composted in commercial high-temperature composting units.

Aliphatic polyesters

These are fossil fuel-derived materials that will easily biodegrade, being generally added to other materials such as starch or PLA to produce useful materials. Both thin films and thermoformed containers can be produced, being generally garden-compostable.

Starch

This is often added to other materials – it cannot be used alone to manufacture thin packaging materials, as it is brittle. However, there are a few companies making pressed and ‘baked’ trays from starch, designed for very short-term use. It is claimed that the Australian company Plantic has developed a starch-based water-soluble material that is thermoformable.

Cellulose

One of the original plastic films, made from paper pulp. This is very sustainable but not compostable, until recently. Innovia Films has recently launched NatureFlex, which they claim is a compostable cellulose film. The downside is that it tends to wrinkle when moist. Garden-compostable grades are also available.

Paper/board

This is manufactured from a totally renewable crop and is biodegradable. However, it takes about four times the power and water to manufacture and distribute than plastic film, also being generally less durable.

Sugarcane

Sugarcane is the basic raw material for many commodities, including ethanol and alcohol production. The dried remains, bagasse, have a high cellulose content and are suitable for the manufacturing of shallow containers. It is not a transparent material and difficult to make into deep containers, but remains a good compostable material.

Palm leaf

Containers made from palm leaves were first introduced into the UK in the 90s. They are made from the cut palm leaves that would have been traditionally burned as waste. Palm leaves are easily garden-compostable, yet susceptible to moisture absorbance and going soft.

PHA/PHB

Polyhydroxyalkanoates (PHA) and Polyhydroxybutyrate (PHB) are polyester materials manufactured by feeding bacteria on starch, which are harvested when ready. This material is in its infancy, but one to watch. The materials have not yet been developed as clear materials, but they are highly versatile and thermoformable. Garden-compostable and even marine biodegradable, these products are plastics of the future.

PVOH

Polyvinylalcohol (PVOH) is a fossil fuel plastic that is water-soluble. It is most commonly used as a water-soluble covering for dishwasher capsules.

Calcium carbonate (chalk)

This has become an important, increasingly used, filler material. CaCO3 is not compostable. However, it is a soil component and can thus be successfully added to compostable materials to give bulk, where required.

Hybrid materials

Such hybrids as starch mixed with PP or PE are increasingly being used. These are not compostable or even recyclable, but the replacement of fossil fuel plastic with starch is leading many companies to view hybrids as a halfway house, especially as contaminated food trays are likely go to landfill, rather than being recycled.

Adhesives

When designing an overall bio package, adhesives are often missed out. However, biodegradable adhesives are available, manufactured from sugars, starch or polycaprolactone, a biodegradable fossil fuel plastic.

Applying common sense

There are many routes to bio/sustainable packaging, and increasing numbers of consumers are demanding to see them in use, but they are not the experts. The most important requirement is that a material must be fit for purpose. The carbon footprint of a sustainable crop material that uses lots of energy to manufacture may be less environmentally-responsible than utilising a fossil fuel-based plastic in an location where there is a good collection and recycling system already in practice.

E-mail: Terry Robins on terry@trpacksolutions.com