Natural hemp fiber reinforced polybenzoxazine composites: Curing behavior, mechanical and thermal properties

The short length hemp fibers treated with 5% NaOH (THF) were sandwiched in bisphenol A-aniline based benzoxazine (BA-a) to form the resin-fiber-resin composite. The effects of fluctuating fiber volume on the curing behavior, mechanical, thermomechanical, and thermal properties of the resulted composites were studied through fourier transform infrared (FTIR), differential scanning calorimetry (DSC), dynamic mechanical analyzer (DMA), thermogravimetric analysis (TGA), and scanning electron microscope (SEM). The results confirmed that the rich -OH groups on THF can promote the ring-opening of oxazines at lower curing temperature, and improve the adhesion between fiber and matrix. In addition, an increase of 185% in impact strength, 1.3 GPa in flexural modulus, and 109% in tensile strength was recorded for 25 vol% THF content cured composites. The slight diminution in thermal stability was observed as THF content increased, at 25 vol% THF content, weight loss temperature (T5%) and char yield at 800 °C (Yc) were 11 °C, and 0.4% lower than pristine poly(BA-a), respectively.