Thermal conductivity and thermal diffusivity analyses of low-density polyethylene composites reinforced with sisal, glass and intimately mixed sisal/glass fibres

The thermal conductivity and thermal diffusivity of sisal-reinforced polyet hylene (SRP), glass-reinforced polyethylene (GRP) and sisal/glass hybrid fi bre-reinforced polyethylene (GSRP) has been evaluated at cryogenic to high temperature (120-350 K). It has been observed that the variation of thermal conductivity with temperature is almost the same for LDPE and SRP containi ng perpendicularly oriented sisal fibres. The difference between the values of thermal conductivity shown by LDPE and GRP is greater than that of SRP and LDPE. The enhanced thermal conductivity of glass fibre is due to the pr esence of Fe2+ ions in the glass fibres. The linear variation in thermal co nductivity with fibre loading is explained with the help of a model suggest ed by Agari. The difference between the thermal conductivity properties in directions parallel and perpendicular to the applied Aux is a maximum for S RP owing to the anisotropic nature of sisal fibre. The difference is margin al for GRP on account of its isotropic nature. The position of GSRP is foun d to be intermediate. It can been observed that the variation of thermal di ffusivity with temperature is just opposite to that of thermal conductivity . This may be due to a reduction in the mean free path of phonons. An empir ical equation is derived to explain the variation in thermal conductivity a nd thermal diffusivity with temperature. (C) 2000 Elsevier Science Ltd. All rights reserved.