The effect of alkalization and fibre alignment on the mechanical and thermal properties of kenaf and hemp bast fibre composites: Part 1 – polyester resin matrix

Recently, the incorporation of lignocellulosic materials as reinforcing agents or as fillers in polymer composites has received an increased attention. Although natural fibres have a number of advantages over glass fibres, the strong polar character of their surface is a limiting factor, as compatibility with strongly apolar thermoplastic matrices is very low. Such problems of incompatibility may be overcome with fibre pre-treatments, which can enhance compatibility, albeit having a negative impact on the economics. In the present study, two fibre pre-treatment methods, acetylation and propionylation, were applied on flax, hemp and wood fibres. The effect of esterification between the acetyl/propionyl groups and the hydroxyl groups of the fibre was examined by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS), while its extent was assessed by titration. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the crystallinity and the surface morphology of the untreated and esterified fibres. The highest extent of the esterification reaction was achieved for the wood fibres due to their high lignin/hemicelluloses content. The two spectroscopic methods revealed that the fibre surface chemistry was altered after the treatments, as the results indicated that ester bonds are present on the fibre surface. The SEM results revealed that both treatments resulted in a removal of non-crystalline constituents of the fibres, possibly waxy substances, and alter the characteristics of the surface topography. It was also shown that the fibre crystallinity decreased slightly as a result of esterification.

A study of the effect of acetylation and propionylation surface treatments on natural fibres

Chemical modification of kenaf fibers

Present-day industry takes an interest in environment friendly materials, due to economic and ecological reasons. The use of natural materials in composite parts fits well into this picture: plant fibres that reinforce polymer matrices can replace glass fibres in many cases, although applications are often limited to non-structural parts. The poor interface in a non-treated natural fibre reinforced composite prevents the parts to be used to their full capacity. Consequently, this study concentrates on a simple but effective fibre treatment (i.e. alkalisation) that will enable a better adhesion between flax fibres and epoxy matrix. Parameters such as time and concentration are being optimised, in order to develop a continuous process for the treatment and resin impregnation of unidirectional flax fibre epoxy composites. This paper shows a clear improvement of the mechanical properties of the resulting material: e.g. a mild treatment in a 4% NaOH solution for 45 s will increase the transverse composite strength up to 30%.

Improving the properties of UD flax fibre reinforced composites by applying an alkaline fibre treatment

Mechanical properties of natural fibre reinforced polyester composites: Jowar, sisal and bamboo

Effect of wettability and ageing conditions on the physical and mechanical properties of uniaxially oriented jute-roving-reinforced polyester composites

Jose Roberto Morais d'Almeida

Papers

Effect of wettability and ageing conditions on the physical and mechanical properties of uniaxially oriented jute-roving-reinforced polyester composites