Abstract
In this study, bio-based coatings were used for reducing water sorption of composites containing flame retardant treated natural fibres and phenolic resin. Two types of coatings; polyfurfuryl alcohol resin (PFA) and polyurethane (PU) were used on the composites and compared with a water resistant market product. Uncoated and coated samples were conditioned at 90 °C and relative humidity of 90% for three days and the relative moisture content and mechanical properties after conditioning were analysed. In addition, the changes in the weight loss of the conditioned samples were also investigated by thermogravimetric analysis. The moisture diffusion characteristics of coated laminates were also studied at room temperature under water immersion conditions. PFA coated samples showed better moisture resistance and mechanical performance than other bio-based coatings when subjected to long term environmental aging.
Highlights
The growing interest in using natural fibres as reinforcement in polymeric based composites is mainly due to their abundance, renewable origin, relatively high specific strength and modulus, light-weight, low cost and biodegradability when compared to glass fibres[1]
The authors reported that the water absorption decreased with increasing molar ratios of TMP or 1,4-CHDM which implied that the PU coatings were properly crosslinked, enabling them to reduce water uptake
Bio-based coatings were used as possible coatings to reduce moisture absorption as a result of environmental aging in flame retardant treated natural fibre phenolic reinforced composites
Summary
The growing interest in using natural fibres as reinforcement in polymeric based composites is mainly due to their abundance, renewable origin, relatively high specific strength and modulus, light-weight, low cost and biodegradability when compared to glass fibres[1]. Flame retardant treated flax fibre reinforced phenolic composites showed a decrease in the mechanical properties after the composites were exposed to environmental aging[25] In this case, the decrease was attributed to the moisture absorption of flax fibre and the hygroscopic nature of the applied flame retardant. In our approach, flame retardant treated flax fibre phenolic reinforced composites prepared by compression moulding were coated with polyfurfuryl alcohol and polyurethane as suitable bio-based coatings, and were compared with a water resistant market product This approach does not apply principles related to the coating techniques previously mentioned, but using renewable and sustainable hydrophobic polymer matrices as suitable protective coatings for natural fibre reinforced thermosetting matrix composite. The study shows that application of bio-based coatings especially PFA can significantly reduce moisture absorption of fibre reinforced composites and uphold their structural integrity when exposed to environmental conditions
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