Bacterial cellulose coated 'hairy' sisal fibres for renewable hierarchical composites

摘要

Interest in new but renewable materials which are not only biodegradable but can compete with traditional engineering materials in terms of mechanical and physical performance is growing. Lightweight natural fibres offer the potential to replace conventional glass fibres in a wide range of composite applications, especially in automotive and packaging industries. They provide reinforcement to the polymeric matrices, with the added benefit of their price and their lower carbon footprint. Unfortunately, the major challenge of utilising cellulosic materials such as natural fibres in composite applications is their hydrophilic nature, high linear coefficient of thermal expansion (LCTE) and poor transverse properties. Due to the high LCTE of natural fibres, the residual stresses exerted on natural fibres by a polymer matrix after manufacturing will be lowered, leading to low interfacial shear stress between the polymer and reinforcement, as the interfacial shear stress is the product of residual stress and static coefficient of friction of the fibres. As a result, the compatibility between natural fibres and hydrophobic thermoplastics (for instance polylactic acid) is often poor. To overcome this challenge, nanocellulose can be coated onto the surface of natural fibres to bridge the gap between natural fibres and matrix. Here we present our progress in creating real "hairy" bacterial cellulose (BC) coated sisal fibres. To achieve this objective, different pre-treatments of the fibres, such as acetone, sodium hydroxide, were explored. The effect of surface treatments on the properties of the fibres was assessed. Sisal fibres were coated with bacterial cellulose by utilising the bacterial strain, Gluconacetobacter xylinus, who produces cellulose in both static and agitated culture conditions. By adding sisal fibres to the growth medium of the bacteria, BC coated fibres were obtained. Different inoculation times and culture conditions were tested and for each set of experiment, the fibre surface, their mechanical and tensile properties were characterised. Sisal fibres reinforced poly(lactic acid) (PLA) composites were prepared. The mechanical properties of the fibre reinforced composites will be assessed in terms of tensile properties and the fracture surface of the composites will be investigated by SEM to observe the interface between the fibres and the matrix.