Biodegradable plastics offer green alternative

Edited by the Engineeringtalk editorial team Mar 20, 2003

The biodegradable properties of polyvinyl alcohol make it ideal in the creation of thermoplastics for the production of environmentally acceptable disposable parts.

The biodegradable properties of polyvinyl alcohol (PVOH) particularly as it comes into contact with water, have been known for a number of years.

Commercially viable volumes of compostable polymer material based on it however, have only recently become available in a workable dry pellet form and of consistent quality.

The 'rediscovery' as a thermoplastic has high potential for the production of environmentally acceptable disposable parts.

Toolcraft Plastics of Swindon, in conjunction with material developers PVAXX, has been trialling both biodegradable and biocompostable materials, to establish the mould conditions for high product quality and cost economy.

By definition, the biodegradable material will ultimately break down into carbon dioxide, water and biomass within a specific time.

As compostable it must also contain no toxic materials, the break down time must be less than 12 weeks, and the resulting compost must not impede plant growth.

Toolcraft has wide experience with moulding engineering plastics including some of the lesser used materials and unusual fillers, and the results of tests on the four injection moulding grades of biodegradable materials tried have been startling.

With the high standards of production quality control, Toolcraft was able to run them on existing production lines and equipment, achieving mould times as low as 50% of runs with standard materials, whilst retaining a high quality of finished product.

These polymer materials have been shown to be similar to conventional polymers in both thermal characteristics and many mechanical parameters, including flexural modulus, tensile and impact strength.

Other product qualities include optimum viscosity and melt flow, the absence of static buildup, and have nontoxic, safe-to-handle qualities and first-rate print adhesion and weldability.

The net result of trials at Toolcraft is substantially lower parts cost with all the advantages of the familiar engineering plastics.

The crucial property of the material, however, is its unique capacity to biodegrade and compost into nontoxic residues.

The injection moulding materials trialled by Toolcraft degrade when coming into contact with water, the rate of degradation being temperature dependant, that is, faster degradation in hot water.

This property gives the materials the ability to provide a major contribution to the fundamental ecological issue in the disposal of plastics with a significant impact on the problems posed by materials with an indefinite lifespan.

These biodegradable and compostable polymers have received European safety approval for food contact, further extending their value.

All materials trailed to date accept a full range of colours.

Most importantly the degradation period, which can be adjusted by grade choice and coatings, commences only when the part comes into contact with moisture.

Other moulded applications currently being evaluated include golf tees, garment hangers and medical disposables.

Some materials include mouldable sheets that could enhance Toolcraft's range of industrial storage trays.

Although most materials tested worked well in conventional tools, Toolcraft's experience in the design and running of mould tools and a tool room in-house proved invaluable throughout the trials.

Toolcraft are now able to work most biodegradable materials with confidence.