The wood powder of Cryptomeria japonica (Japanese cedar) was liquefied in phenol, with H 2 SO 4 and HCl as a catalyst. The liquefied wood was used to prepare the liquefied wood-based novolak phenol formaldehyde (PF) resins by reacting with formalin. Furthermore, novolak PF resins were mixed with wood flour, hexamethylenetetramine, zinc stearate as filler, curing agent, and lubricating agent, respectively, and hotpressed under 180 or 200 C for 5 or 10 min to manufacture moldings. The results showed that physicomechanical properties of moldings were influenced by the hotpressing condition. The molding made with hot-pressing temperature of 200 C for 10 min had a higher curing degree, dimensional stability, and internal bonding strength. The thermal analysis indicated that using a hotpressing temperature of 180 C was not sufficient for the liquefied wood-based novolak PF resins to completely cure.
Novolak-type phenol-formaldehyde (PF) resins with solution form were prepared by reacting phenol-liquefied Cryptomeria japonica (Japanese cedar) wood with formalin in the presence of methanol. Wood powders of Albizzia falcate (Malacca albizzia) impregnated with these resins were air dried followed by an oven-dried at 60 C. DSC analysis showed the PF resin existing in wood powders could be melted, and could be cured if hexamine was mixed and heated at high temperature. Compressionmolded plates made with PF resin impregnated woods had a high degree of curing reaction. However, compressionmolded plates hot-pressed at 180 C for 8 min or 200 C for 5 min had better internal bonding strength and dimensional stability than others. Premixing hexamine with PF resin and impregnating into wood powders simultaneously could enhance the reactivity of PF resin, but it was not useful for improving the properties of compression-molded plates.
Dendrocalamus latiflorus Munro (ma bamboo) was liquefied in phenol or in polyethylene glycol/glycerol cosolvent, with H 2 SO 4 as a catalyst. The liquefied bamboo was reacted with bisphenol-A and epichlorohydrin to prepare copolymer epoxy resins. The thermal properties of resins during and after curing were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The results showed that a novel epoxy resin can be prepared by copolymerizing liquefied bamboo with bisphenol-A and epichlorohydrin in a two-step process. DSC analysis showed that the copolymer epoxy resins prepared with phenol-liquefied bamboo had a curing behavior similar to that of neat epoxy resin, even when 50% of the bisphenol-A was replaced with liquefied bamboo. However, the reactivity of copolymer epoxy resins prepared with polyhydric alcohol-liquefied bamboo decreased as the substitution amount of liquefied bamboo increased. DMA showed that the storage modulus and tan d of cured copolymer epoxy resins decreased as the amount of substituted liquefied bamboo increased.
Reactive polyurethane hot-melt resin (moisture-cured reactive polyurethane, PUR) could successfully be prepared from poly(tetramethylene ether) glycol (PTMG), castor oil and dimethylglyoxime (DMG) by one or two-stage synthesis. Fourier-transform infrared spectroscopy (FTIR) analysis showed that the synthesis resins belonged to NCO-capped castor oil-based polyurethane. The thermal behaviors of the cured PUR were analyzed by differential scanning calorimeter (DSC) and dynamic mechanical analyzer (DMA) instruments. The results showed that the cured resin provided remeltable properties under the dosages of 3 wt% DMG. Furthermore, the phenomenon could be proved by FTIR analysis according to the characteristic absorption peak of NCO groups after the cured resin was heated. Comparing different syntheses, the resin prepared by one-stage synthesis showed random distribution of DMG with PUR structure and that prepared by two-stage synthesis had distribution of DMG with branching structure in the prepolymer. The former obtained lower remeltable temperatures from 90 to 130 °C than the latter temperatures, which had temperatures above 125 °C. The tensile test showed that all of the PUR films exhibited typical tough behavior. Thus, the cured resin with DMG dosages of 3 wt% provided remeltable and mechanical properties at the same time. Overall, the crosslinking density and numbers of dynamic bonds should be kept in balance for preparation of remeltable PUR.
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