Manufacturing Flax Fibre-Reinforced Polypropylene Composites by Hot-Pressing

Abstract

The renewable characteristic of natural fibres, such as flax, and the recyclable nature of thermoplastic polymers, such as polypropylene, provide an attractive eco-friendly quality to the resulting composite materials. Common methods for manufacturing natural fibre-reinforced thermoplastic composites, injection moulding and extrusion, tend to degrade the fibres during processing. Development of a simple manufacturing technique for these composites, that minimises fibre degradation, is the main objective of this study. Flax fibres were conditioned, cut into lengths ranging from 1 mm to 30 mm with scissors and a pelletiser, and shaped into randomly oriented mats using a drop feed tower. Polypropylene in sheet form, was added to the fibres to furnish polypropylene/flax/polypropylene sandwiches with a fibre mass fraction of 25%, which were then consolidated by the hot pressing technique. Tensile, flexural and impact properties of these composite sheets were determined as functions of fibre length and processing temperature.

Use of wet‐laid techniques to form flax‐polypropylene nonwovens as base substrates for eco‐friendly composites by using hot‐press molding

“…So that it is possible to use the wet‐laid process to obtain a good mixture with a base fiber (which will act as a reinforcement component) and a binder fiber (which will act as the embedding media to provide cohesion). These nonwovens could be the base materials for composite processing by hot‐press molding as the application of both pressure and temperature can melt the binder fiber to partially embed base fibers thus obtaining composite materials for potential use in technical applications such as automotive [29–32]. Although many binding fibers such as polypropylene, polyamides, polyethylene, etc., are petroleum‐based materials, the wet‐laid technique can be useful to obtain nonwovens characterized by high amounts of natural fibers (even higher than 90% wt%) with relatively low contents of binder fibers so that, leading to high renewable content materials with regard to conventional natural fiber composites obtained by extrusion or injection molding.…”

Effect of Compounding and Injection Molding on the Mechanical Properties of Flax Fiber Polypropylene Composites

“…The literature found on flax/PP composites refers mainly to two manufacturing routes, (i) mat technology, where non-woven flax mats are compression molded with PP to produce random natural fiber mat composites (NMTs) [2,5,6,18,22,[24][25][26] and (ii) the granule technology where flax fiber-reinforced PP granules are injection molded or extrusion compression molded (ECM) to produce mainly short-fiber-reinforced composites [17,24,[27][28][29][30][31][32][33]. Limited work is available on unidirectional and multidirectional flax/ PP composites [34], while very recently research is also looking into commingled yarn technology for flax/PP [35].…”

Life cycle assessment of wood-fibre-reinforced polypropylene composites

“…The length of the fibres varies from 1 to 4 mm, and applied when composite sheets are made, with no particular orientation or patterns. The composite preform can have three or five layers (Jolly and Jayaraman, 2006), depending on the thickness of the preform. In this study, 2-mm sheets are considered, therefore a three-layered structure is adopted, i.e.…”