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

Long and random hemp and kenaf fibres were used in the as-received condition and alkalized with a 0.06 M NaOH solution. They were combined with polyester resin and hot-pressed to form natural fibre composites. The mechanical properties of the composites were measured to observe the effect of fibre alignment and alkalization. A general trend was observed whereby alkalized and long fibre composites gave higher flexural modulus and flexural strength compared with composites made from as-received fibres. Alkalized long kenaf–polyester composites possessed superior mechanical properties to alkalized long hemp–polyester composites. For the hemp–polyester composites a high flexural modulus and a high flexural strength are associated with a low work of fracture. Scanning electron microscopy micrographs of the treated hemp and kenaf fibres showed the absence of surface impurities which were present on the untreated fibres. Apparent density measurements on hemp and kenaf fibres did not show a significant change after alkalization with 0.06 M NaOH. Wide endothermic peaks present in differential thermal analysis thermograms for all of the composites indicated the presence of moisture which leads to inferior mechanical properties. Dynamic mechanical thermal analysis carried out on the polyester matrix composites showed that the alkalized fibre composites have higher E′ values corresponding to higher flexural moduli. Any correlation between fibre surface treatment and the work of fracture and tanδ of composites is less clear.