Research efforts on electromagnetic interference (EMI) shielding materials have begun to converge on green and sustainable biomass materials. These materials offer numerous advantages such as being lightweight, porous, and hierarchical. Due to their porous nature, interfacial compatibility, and electrical conductivity, biomass materials hold significant potential as EMI shielding materials. Despite concerted efforts on the EMI shielding of biomass materials have been reported, this research area is still relatively new compared to traditional EMI shielding materials. In particular, a more comprehensive study and summary of the factors influencing biomass EMI shielding materials including the pore structure adjustment, preparation process, and micro-control would be valuable. The preparation methods and characteristics of wood, bamboo, cellulose and lignin in EMI shielding field are critically discussed in this paper, and similar biomass EMI materials are summarized and analyzed. The composite methods and fillers of various biomass materials were reviewed. this paper also highlights the mechanism of EMI shielding as well as existing prospects and challenges for development trends in this field.
Agricultural crop-based lignin was utilized to modify phenol-formaldehyde (PF) resin to prepare fast curing biobased phenolic resins by copolymerization. Prior to the reaction, four types of demethylation reagents were used at atmospheric pressure to sever the methoxy bonds of lignin to increase its reactivity. The chemical and structural changes of the lignin molecule were analyzed using Fourier transform infrared (FT-IR) spectroscopy and 1H-NMR. The analytical results revealed that the methoxyl groups of lignin were transformed by the demethylation reagents into phenolic hydroxyl groups. FT-IR and liquid state 13C-NMR analysis revealed that lignin demethylated by Na2SO3 resulted in more phenolic-OH groups on the molecule and higher molecular reactivity. The influence of demethylation on the properties of biobased phenolic resin was also investigated. The increased quantity of hydroxyl groups resulting from lignin demethylation caused higher curing rate of the biobased phenolic resin. These results were confirmed by the improved bond strength and lower formaldehyde emissions of plywoods bonded with biobased phenolic resins.
19 February 2020 in ACS Sustainable Chemistry & Engineering