• Kristian, Salminen
• Lappalainen, Timo
• Prakash, Baranivignesh
• Nikinmaa, Miika
• Asikainen, Jaakko
• Immonen, Kirsi

Abstract

Replacing plastic fibers with wood fibers in thermoplastic polymer matrix is one of the pathways to manufacture carbon-neutral biocomposites. It is known that fibers improve the mechanical properties of composites. However, due to harsh processing conditions in the current technologies including extrusion and moulding, the fiber length in the final composite is significantly shorter. Therefore, we coupled foam forming technology with thermoforming to produce biocomposites with impressive mechanical properties that exceeded the current wood-based thermoplastic composites found in the literature. During foam-forming, the fiber length in the final composite was maintained irrespective of initial fiber consistency and fiber length. Experiments were carried out in both lab and pilot scale. In lab, experiments were mainly carried out to understand the effect of raw material composition on strength properties. Pilot trials were carried out to demonstrate the scalability and to understand the effect of processing conditions to generate floc free web with long fibers. The foam-forming consistency ranged from 0.12% to 3 %, which was a significant increase compared to water-forming process. Initially, foam sheets with varying grammages in the range of 42 g/m2 to 393 g/m2 were produced in the pilot machine. The dried foam sheets were then stacked to achieve grammage of 1200 g/m2 followed by thermoforming at 180ºC and 6.2 bar. Foam sheets were made using the following raw materials: a) 1.7 dTex Tencel fiber with the length above 10 mm as long fibers, b) 2 mm wood pulp as short fibers, and c) BiCo fibers comprising polypropylene core and polyethylene sheath or LDPE powder as thermoplastic fibers. The effect of fiber type, proportion of long fibers and fiber length on uniformity, strength and mouldability were studied. Visual assessments indicated that the sheet uniformity was good with improved fiber bundle disintegration and reduced flocs even with 20 mm long Tencel fibers. Moulding properties were highly dependent on the proportion of fiber, fiber type, amount of thermoplastics, basis weight, density and the ratio of wood to plastic fibers. In summary, the results indicated that the foam-forming technology enables the manufacturing of long fiber biocomposites with visual and strength properties suitable for packaging, furniture, and automotive applications.

Topics

• density
• impedance spectroscopy
• Carbon
• experiment
• extrusion
• strength
• composite
• wood
• thermoplastic