ExtruCO2

Development of a Low-temperature Processing Method for the Production of Natural Long-fibre Filled Polypropylene Sheet for Automotive Applications

Technology developed by one of the consortium partners has shown that traditional plastics processing equipment can be modified to allow for liquid CO2 to be used as a processing aid that allows for processing at lower temperatures. However, this technology is a high-pressure and high-shear process, unsuitable for the processing of shear- and thermally-sensitive natural fibres.

ExtruCO2 aimed to develop the necessary extrusion and mixing technologies to allow for the low-temperature processing of natural fi bre fi lled polypropylene (using liquid CO2 as a processing aid) to produce a non-woven polypropylene sheet suitable for thermoforming automotive applications.

The main objectives were:

• To produce a sheet material based on renewable resources with improved recyclability as well as mechanical and thermal properties than those currently on the market.
• To develop innovative technologies for low-damage sheet production.
• To remove the need for expensive and environmentally harmful chemical treatment of natural fibres.

Organisational Information

Budget: €1.3M
Funding: €700k
Start Date: February 2004
Finish Date: May 2006
Duration (in months): 28
Lead Partner (Co-ordinator): Smithers Rapra, UK

Participants

• AIMPLAS, Spain
• Aspin Engineering Ltd, UK
• Candea Industrias Plásticas SA, Spain
• Carcoustics España SA, Spain
• ESP Plastics Ltd, UK
• Hemcore Ltd, UK
• Kenaf Eco Fibers Italia SpA, Italy
• Plásticos Flome SL, Spain
• Sivel Ltd, Bulgaria
• Whitaker Technical Plastics, UK

Results – What happened next?

The project demonstrated conclusively the plasticisation effect of supercritical CO2, which has, in turn, enabled the development of a sheet extrusion process to manufacture polypropylene natural fibre composites at temperatures below 200ºC. In this respect, both the prototype pre-competitive process and product have been realised: these provide additional opportunities to expand the remit of natural fi bre products beyond the techniques that currently exist: mat technology etc.

The mechanical properties of the composites produced are in line with the requirements of the automotive industry. Charpy impact properties greater than 25 kJ m-2 have been obtained and tensile modulus values greater than other types of organic fi llers have also been achieved.

With respect to competitor materials currently available as pre-compounded feedstocks, the properties of the products developed are superior and the cost comparison quite promising.

The environmental credentials of the product have been reviewed by undertaking recycling studies. Again, the results are promising, with trials indicating that up to 50% w/w of recyclate can be reincorporated without deterioration in mechanical properties. This feature will again help support the economics of the ExtruCO2 process.