Mechanical properties of natural-fibre-mat-reinforced thermoplastics based on flax fibres and polypropylene.

Thermoplastic composites based on flax fibres and a polypropylene (PP) matrix were manufactured using (i) a film-stacking method based on random fibre mats and (ii) a paper making process based on chopped fibres. The influence of fibre length and fibre content on stiffness, strength and impact strength of these so-called natural-fibre-mat-reinforced thermoplastics (NMTs) is reported and compared with data for glass-mat-reinforced thermoplastics (GMTs), including the influence of the use of maleic-anhydride grafted PP for improved interfacial adhesion. In addition some preliminary data on the influence of fibre diameter on composite stiffness and strength is reported. The data is compared with the existing micro-mechanical models for strength and stiffness. A good agreement was found between theory and experiment in case of stiffness whereas in the case of strength the experimental values fall well below the theoretical predictions. Results indicated that NMTs are of interest for low-cost engineering applications and can compete with commercial GMTs when a high stiffness per unit weight is desirable. Results also indicated that future research towards significant improvements in tensile and impact strength of these types of composites should focus on the optimisation of fibre strength rather than interfacial bond strength

Thermoplastic composites based on biopolymers and natural fibres

The objective of the present research is to utilise the advantages offered by renewable resources for the development of biodegradable composite materials. Two types of biocomposites using flax fibres as a reinforcement and poly[(R)-3-hydroxyalkanoates] (PHA) as a biodegradable polymer matrix were manufactured: First, natural-fibre-mat-reinforced thermoplastics (NMTs) using a compression moulding method and needle-punched nonwoven flax fibre mats and secondly, injection moulding compounds based on short flax fibres. The influence of fibre content and processing method on the tensile and impact properties of these composites was studied. Results indicated that the addition of (cheap) flax fibre to poly(3-hydroxybutyrate) (PHB) could be advantageous as far as cost-performance of these materials is concerned. For example, the addition of flax fibres to the relatively brittle PHB matrix offers the chance to obtain cheaper products together with improved toughness, while retaining biodegradability of the resulting polymer composites. Especially in the case of relatively long fibres as in the case of NMTs the improvement in impact resistance is significant. Regarding the influence of processing method it was observed that, with the exception of impact resistance, injection moulded samples possessed similar properties to NMT samples, indicating that for some applications injection moulding might be advantageous over NMT because of the more versatile production process

A study on the trans-crystallisation behaviour of flax fibre reinforced polypropylene composites and effect on mechanical properties

The effect of flax fiber reinforcement on crystn. behavior of polypropylene (PP) was investigated using a hot-stage optical microscope. To follow the crystn. kinetics, cooling rate and crystn. temps. were varied. Flax fibers with different processing history e.g. green flax, Duralin flax, alkali and silane treated flax were used for investigation. The effect of fiber treatment on crystn. behavior was obsd. Finally the effect of trans-crystallinity on the interfacial shear strength in micro-composites was studied by fiber pull-out metho

Thermoplastic composites based on biopolymers and natural fibres

The objective of the present research is to utilise the advantages offered by renewable resources for the development of biodegradable composite materials. Two types of biocomposites using flax fibres as a reinforcement and poly[(R)-3-hydroxyalkanoates] (PHA) as a biodegradable polymer matrix were manufactured: First, natural-fibre-mat-reinforced thermoplastics (NMTs) using a compression moulding method and needle-punched nonwoven flax fibre mats and secondly, injection moulding compounds based on short flax fibres. The influence of fibre content and processing method on the tensile and impact properties of these composites was studied. Results indicated that the addition of (cheap) flax fibre to poly(3-hydroxybutyrate) (PHB) could be advantageous as far as cost-performance of these materials is concerned. For example, the addition of flax fibres to the relatively brittle PHB matrix offers the chance to obtain cheaper products together with improved toughness, while retaining biodegradability of the resulting polymer composites. Especially in the case of relatively long fibres as in the case of NMTs the improvement in impact resistance is significant. Regarding the influence of processing method it was observed that, with the exception of impact resistance, injection moulded samples possessed similar properties to NMT samples, indicating that for some applications injection moulding might be advantageous over NMT because of the more versatile production process