The effect of plasma treatment on flax fibres

In recent years, interest in using composites with natural fibres as reinforcement and/or filler has increased because of the advantages of natural fibres, such as low density, low cost, high mechanical properties, and biodegradability. Unmodified-hydrophilic natural fibres show poor compatibility with polymer matrix when they are used as reinforcement in polymer composites. Several methods of modifications of natural fibres, such as chemical and plasma modification of natural fibres have been performed to improve the interfacial compatibility of natural fibre and matrix, and also to decrease water absorption of fibres. The purpose of this study was to examine the effect of plasma treatment on Saskatchewan-grown oilseed flax fibre that can be used in biocomposites. For comparison, the fibres have also been chemically modified using sodium hydroxide and silane. A comparison has been made between the results from both cases. In this thesis, both plasma and chemically modified flax fibre are characterized to understand its crystallinity, color changes, mechanical properties, morphological changes, and thermal properties. Techniques such as X-ray diffraction (XRD), color test, tensile test, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and soft X - ray spectromicroscopy are used to study the structural changes of flax fibre after physical and chemical modifications. A fitting method with four Gaussian functions was used to determine crystallinity of cellulose. Results showed that the crystallinity of cellulose in modified (physical or chemical) fibres decreased. Chemical treatment did not improve the tensile strength nor the stiffness of the fibres. Morphological studies showed that the fibre surface changes in both treatments were significant, however, the surfaces of flax fibres exposed to the plasma were modified in the near-surface regions. There was no trace of lignin before and after chemical treatment except in the one-hour chemically treated fibres. The color of the fibres became lighter after chemical treatment. Chemical bonding between resin and fibre was observed in the untreated fibres, the one-hour chemically modified fibres and two-hour chemically modified fibres. Results of this research also showed that plasma treatment can be used as a surface modifying method for flax fibres, however there were some restrictions of utilizing the plasma modification method, e.g. sample size and non-uniformity of plasma gas