Synthesis of polymeric isocyanate microcapsules via interfacial polymerization and their characterisation using spectroscopy and microscopy techniques

Abstract

Wood adhesives are holding a key in improving the efficiency of using raw materials in the wood-based panel industry and in durability of the panels during their life in service. Massive progress has been made on research and development of wood adhesives over the past century, but many important challenges are still remaining. In this study, an alternative cross-linker for wood adhesives named microcapsules polymeric 4,4 methane diphenyl isocyanate (M-pMDI) were synthesized at different conditions via interfacial polymerization, and were characterized using spectroscopy and microscopy techniques. Three factors were taken into account to examine the characteristics of M-pMDI, namely isocyanate content, microencapsulation temperature, and microencapsulation agitation rate. Attenuated total reflectance Fourier transform infrared spectroscopy revealed that the isocyanate (-N=C=O) groups of pMDI at 2,250 cm−1 disappeared after microencapsulation due to the reaction of pMDI and ethylene glycol to form urethane (-R-NH-C=O-) linkages at 1,650 cm−1 as microcapsules shell. Digital microscopy and micro confocal raman imaging hyperspectral spectroscopy confirmed the formation of microcapsules and urethane shell. The results showed that concentration of isocyanate remarkably affected the yield of M-pMDI, while microencapsulation temperature and agitation speed influence the formation of microcapsules itself. Prel-liminary investigation using ATR-FTIR spectroscopy confirmed that free–NCO groups could be released by applying pressure. This study suggested that a combination of 5 mL of pMDI, 60°C of microencapsulation temperature, and 600 rpm of microencapsulation agitation speed could produce M-pMDI with high yield as an alternative cross-linker for wood adhesives in the future.