Influence of blocked polyisocyanate on the mechanical, thermal and interfacial properties of bamboo/hydroxyl-terminated polyurethane composites

Abstract

In this study, chemical modification of bamboo powder (BP)/hydroxyl-terminated polyurethane (HPU) composites obtained by hot press was investigated using blocked polyisocyanate synthesized from reaction of isophorone diisocyanate with 1,1,1-trimethylolpropane (TMP) followed by addition of methyl ethyl ketoxime (MEKO). The modified surface of MEKO-blocked polyisocyanate (M-bp)-treated BP/HPU composites was identified by Fourier transform infrared spectroscopy from the appearance of CO bands absorbance and the reduction in relative intensity of OH, with respect to bamboo. The effects of M-bp as a cross-linker on the properties of the products were studied. Mechanical testing results showed that the tensile and flexural properties of the composites were improved by addition of such a cross-linker. The morphology analysis revealed that the M-bp-modified composites exhibited better compatibility and homogeneous morphologies in comparison with the unmodified composites. Moreover, the thermogravimetric analysis demonstrated that thermal resistance of the composites was enhanced by addition of M-bp. The moisture absorption characteristics of the products were also studied and discussed, because it is a major influencing factor for natural fibre composites. The results showed that better water resistance of modified composites was obtained due to stronger interfacial adhesion. Based on the findings in this work, they all indicated that the chemical modification occurred by the cross-linking effect of M-bp, which induced the strong bonds among the composite components.