Abstract

Composites of thermoplastics reinforced with natural fibres have been widely used in recent years. Natural fibres are considered as a greener substitute due to their advantages over conventional fibres such as low cost, low density, high availability, excellent mechanical properties, biodegradability and to be environmentally friendly. However, they present an important limitation, the weak interaction between fibres and matrix. Therefore, surface treatments on natural fibres are very common in order to increase wettability and surface energy and thus to promote good fibre-matrix adhesion. The objective of this work is to study adhesion between flax fibres, under different surface treatments, and LDPE matrix. Pull-out tests were carried out with flax fibres yarns treated with low pressure plasma, atmospheric pressure plasma torch,silane coating and different alkaline treatments as well as with untreated fibres.  Afterwards,  composites materials were manufactured using unidirectional flax fabric and LDPE in a hot plate press. Finally, mechanical properties of each composite material were evaluated by tensile tests using an universal test machine. In this way, a greater interaction between LDPE and flax fibres can be compared with the final properties.

Abstract

Through this study two different natural fibres composites were characterized from the point of view of decomposition kinetics comparing two kinetics models, Kissinger and Model Free Kinetics in order to estimate the lifetime of the composites. Composite materials were prepared with low density polyethylene as matrix and as reinforcements, plasma treated and untreated natural fibres with 20 and 30 wt.% of fibre content. Composites were manufactured using a rotor mixer and a hot plates press. Afterwards, thermogravimetric analysis was carried out for each material at six different rates with a coupled Mass Spectrometry device to identify detached elements in a specific temperature range. The influence of the low pressure plasma treatment, as well as the fibre type, was taken into account to evaluate the activation energy of the decomposition processes of each material. Besides, lifetime was estimated from the obtained decomposition energies and the Toop equation. It was found that plasma treatment does not have a meaningful influence on decomposition kinetics but, the main composition of the natural fibres is decisive in this aspect, giving rise to much longer lifetimes when the cellulose content of the fibre is higher.