Kink bands in bast fibres and their effects on mechanical properties

Abstract

Low fibre strength has always been a disadvantage of natural fibres when used as composite reinforcement. Mechanical treatments are commonly used to separate the technical fibres from stems. These mechanical treatments are known to cause defects in the fibres. The effect of defects on the strength of individual fibres having undergone varying degrees of mechanical treatment was investigated. Potential damage to the cell wall polymers was investigated by estimating changes in their degree polymerisation. A technique which measures the viscosity of a solution of fibre and gives an indirect measure of the degree of polymerisation, was used. As expected, it was found that mechanical processing decreased tensile strength and elastic modulus. Viscosity measurements indicated that mechanical damage does not cause scission of cellulose chains. However, a clear decrease in viscosity following acid hydrolysis was seen, indicating that the damage regions in the fibre are more susceptible to chemical attack.