| The purpose of this work was to develop novel wood microfibre reinforced biocomposite films for packaging applications, and to understand fundamental mechanical and barrier properties of these composites.; A microfibre was defined as a fibre consisting of cellulosic chains having a diameter between 0.1 to 1 mum, with a minimum corresponding length of 2 to 20 mum. Microfibres were generated from bleached softwood kraft pulp by a combination of high shear refining in a PFI mill and crycrushing under liquid nitrogen, and subsequently isolated by filtering the resulting fibres through a screen of mesh size 60. The energy needed to generate microfibres by refining in the PFI mill was modelled using Rittinger's Law of comminution. It was predicted that the process of generating microfibres 1 mum in diameter from bleached kraft pulp by refining alone would consume about 103.3 MJ/kg.; The microfibres were dispersed in matrices of thermoplastic starch and polylactic acid (PLA) in conventional melt-mixing equipment. In view of the strong tendency of the microfibres to agglomerate due to hydrogen bonding, the microfibres were poured as dilute water suspension in molten starch polymer in a Brabender mixer. The resultant micro fibre-starch biocomposite was further added to molten PLA in the Brabender mixer to produce a microfibre-starch-PLA biocomposite. Best dispersion was obtained at a microfibre consistency of up to 0.2% for a flow rate of up to 3.25 ml/min of the suspension. Mechanical studies demonstrated that the tensile strength of the composites increased by about 10% with every percentage increase in microfibre loading, with a corresponding 50% increase in stiffness. Tensile studies with microfibre composite films cast with polyvinyl alcohol (PVA) indicated that the stiffness of the microfibres was about 126 GPa.; Diffusion studies demonstrated that the moisture barrier properties of the starch films increased substantially with microfibre loading, whereas there were indications of marginal improvement in oxygen moisture transmission with increased microfibre loading. Hence, improvement in tensile properties of the films by introducing the microfibres was achieved without adversely affecting their barrier properties to moisture and oxygen. |
