Effects of Fibre Loading and Additives on the Properties of Rubberwood-Polypropylene Composites

The three parts study utilised rubberwood, polypropylene and additives in which rubberwood and polypropylene was melt blended, compressed and moulded prior to preparation of test samples. Samples were tested using ASTM standards, except for water absorption where British Standard was adopted. Spectroscopic analyses of Fourier Transform Infra-red spectroscopy (FTIR), Dynamic Mechanical Analysis (DMA) and Scanning Electron Microscopy (SEM) were carried out on the RWPC. For Part A the appearance of RWPC with 0.5mm fibre size was darker than 1-2mm fibre size RWPC. When additives were added, the colours of all the RWPC generally became darker. The water absorption (p<0.01), hardness and mechanical strength of the WPC were significantly affected using the addition of fibre. Without maleated polypropylene (MAP), the coupling agent, the fibres behave as standard fillers. With MAP the resultant RWPC gave significantly enhanced strength properties (tensile, flexural, Izod) for RWPC containing 40 to 60% fibre loading. The enhancement was significantly (p<0.05) stronger for 1-2mm fibre size. In Part B1 the higher molecular weight maleated polypropylene (PMAP) have higher mechanical strength (p<0.05) than the lower molecular weight MAP. The reactive additive (RA) different functionality used in Part B2 for RWPC after the polypropylene had been irradiated gave proportional increase in mechanical strength as the functionality increase. For di-functionality EBYCYL 600 (OLI), the presence of acrylates and epoxy gave different reaction mechanism leading to significantly (p<0.01) improved RWPC performance. For irradiated RWPC, reduction of mechanical strength upon ageing in 2-ethylhexanol acrylate (EHA), hexanediol diacrylate (HDDA) and OLI were attributed to de-polymerisation of the PP polymer caused by trapped radicals. Non-irradiated RWPC did not exhibit any de-polymerisation over a period of 24 months. The DMA data showed the presence of reactive material in irradiated RWPC. The presence of exothermic peak accounted through the increase of storage modulus (E’), was proportional to the molecular weight of the RA used. The FTIR spectra also clearly indicate the presence of interaction of different rigidity for PP, rubberwood, untreated and treated RWPC. SEM images gave clear indication of the interaction changes for untreated versus treated RWPC.

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