The PhD thesis of Maiju Hietala published in late 2012 studied the processing of biocomposite materials using twin-screw extrusion technique. The doctoral thesis was made in collaboration with Luleå University of Technology, Sweden, resulting in doctoral degrees from both universities.
Biocomposites are materials in which natural fibres are used instead of synthetic fibres to reinforce plastic matrices making them more environmentally friendly than the traditional composites. As Finland and Sweden have plenty of forests and forest industry, devising novel wood-based materials remains an important issue.
Due to cost issues, wood flour consisting of very small wood particles is typically used in the manufacturing of composite materials, though wood fibres with higher length-to-diameter ratios would improve the strength of the material more. The results of Maiju Hietala’s PhD thesis show that the separation of individual fibres from the wood chips in a single extrusion process step is possible enabling the use of cheaper raw materials. The use of larger wood particles as a raw material in wood-plastic composites enables their use e.g. as an eco-friendly replacement of impregnated wood in outdoor building, such as terrace decking.
Currently the preparation techniques of bionanocomposites are time consuming and usually only small amounts of material can be produced. Thus the use of extrusion technique in the manufacturing of bionanocomposites would be a great benefit, but the hydrophilic nature and aggregation tendency of nanocellulose cause challenges. In Maiju Hietala’s PhD thesis, a method for the production of thermoplastic starch-cellulose nanofibre composites using extrusion is presented. The studied nano-scale reinforcement materials make it possible to obtain unique material properties.
Last updated: 20.6.2013