Development of fore resistant wood-substituted composites from polybenzoxazine alloys

Abstract

This research aims to develop a fire resistant wood-substituted composite from matrices based on polymer alloys between benzoxazine resin and phenolic novolac resin and to use hevea brasiliensis woodflour as a filler. Polybenzoxazine (BA- a), polymer based on phenolic resin, possesses some outstanding properties such as its ease of synthesis, no by-products released from the curing process, low A-stage viscosity, near-zero shrinkage, low water absorption, and high thermal stability. Whereas the benefits of phenolic novolac resin are high compatibility with wood, outstanding fire resistance, no toxic by-product from burning, and its low cost. The objectives of this work are to investigate the effects of the benzoxazine/phenolic novolac alloy (BP) composition on fire resistant, thermal, significant mechanical and physical properties for making the wood-substituted composites. The experimental results reveal that phenolic novolac resin can substantially reduce the curing temperature of the neat benzoxazine resin as seen from the shift of the curing peak maximum temperature in the DSC thermogram. The value of a limiting oxygen index (LOI) at 70% by weight of woodflour is raised from 22.7 in BA-a to about 24.0 in BP55. The rate of burning reduce from 18.5 mm/min in the BA-a to about 15 mm/min in the BP55 with 70% by weight of woodflour. Moreover, the wood composite is self-extinguishable in the BP82 with 50% by weight of woodflour. However the LOI decreased while the rate of burning increased with increasing wood content (LOI and the rate of burning of woodflour are 21 and 42.8 mm/min respectively). The degradation temperature (at 5% weight loss) rapid increase from 271°C in the BA-a to 277°C in the BP82 and also up to 279°C in the BP55 with 70% by weight of woodflour. Moreover, the degradation temperature decreases with increasing of woodflour (the degradation temperature of hevea brasilliensis woodflour is 265°C which less than both of used resins). The char yield (at 850°C) in nitrogen atmosphere, by analysis from TGA, rapid up from 32.4% in the BA-a to 35.5% in the BP82 and raise to 36% in the BP55 at the 70% by weight of woodflour and decrease with increasing woodflour content (the char yield of hevea brasilliensis woodflour is 14.43%). The optimum composition of polymer alloys is BP82 since it shows excellent characteristics over the alloys prepared from other benzoxazine/phenolic novolac ratio. For the flexural modulus of system in the BP82 at 70% by weight of woodflour is about 6.38 GPa. The wood composites in the BP82 at the woodflour content of 70% by weight rendered a wood-substituted composite systems of suitable fire-resistant characteristics for potential as a construction material.