BIOPLASTICS

This page concerns Bioplastics. In this case what is meant is biobased rather than biodegradable plastics.

Plastics are predominantly a by-product of oil, a diminishing resource; although fracking has opened up new sources.  Sustainability is an important concern in the 21st century, and polymer producers are no exception in exploring new, renewable sources of materials.

DEVELOPMENTS SO FAR

Initial developments have revolved around the use of corn derived or similar acids.  These have produced fairly basic plastics that in terms of cost have been able to compete with their oil derived equivalents.  However, there is the concern that the push towards plastics being produced from renewable sources, possibly driven by legislation in the future, will result in food crops being displaced.

A more recent solution has involved castor oil.  These plants can be harvested several times a year and have the added advantage that they can be grown in poor soil unsuited to food crops. A further plus is that the sebacic acid extracted from the plants can be used to manufacture engineering polymers, similar to nylon, which is a much more attractive proposition to polymer producers and end users alike.

These bioplastics can also offer other advantages over their traditional equivalents.  For example, polyamides absorb moisture but the bioplastic equivalent absorbs much less.  This makes it appealing to end users as an alternative to the traditional oil derived product.  At the moment these particular materials are still in the development phase and are not widely available.

WHAT IS AVAILABLE?

As with conventional polymers, bioplastics are not a single plastic material but a whole range offering different properties.  The most common materials to have biobased equivalents are polyethylene, polypropylene and polyester (PET).  A number of polymer producers are working on biobased polymers and one of the leading manufacturers in the field is DuPont.  Within their portfolio are RS (renewably sourced) versions  of Hytrel – a TPE with 35%-65% renewable content, Zytel (nylon) made with 20%-100% sebacic acid from castor oil plants and Sorona EP – a replacement for PBT with 20%-37% corn content.

Although the cost of these ‘greener’ plastics is coming down they still tend to be generally higher than their oil based equivalents and as a result demand is currently limited.  To put this in perspective, about 300m tonnes of plastics are produced a year of which biobased account for about 1m tonnes.  As costs of development are recovered and manufacturing processes are refined prices will fall further and then increased demand will also lead to economies of scale gains.

HOW GREEN ARE BIOPLASTICS?

There is evidence that bioplastics are not as green as may be thought.  1 kg of starch based polyethylene uses 500 gms of petroleum and consumes almost 80% of the energy required to manufacture traditional polyethylene.  Add this to the environmental cost of possible deforestation and food crop displacement and it can be seen that a viable alternative to oil based plastics may still be some way off.

Information about recycled plastics.