Alcohol (methanol or ethanol) and water showed synergistic effects on biomass direct liquefaction, and the 50 wt % co-solvent of either methanol-water or ethanol-water was found to be the most effective solvent for the liquefaction of eastern white pine sawdust. The 50 wt % aqueous alcohol at 300°C for 15 min produced a bio-oil yield at approximately 65 wt % and a biomass conversion of >95%. At a temperature higher than 300°C, conversion of bio-oil to char was significant by repolymerization. The Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) analyses of the obtained bio-oils confirmed the presence of primarily phenolic compounds and their derivatives (such as benzenes), followed by aldehyde, long-chain (and cyclic) ketone and alcohol, ester, organic acid, and ether compounds. Gel permeation chromatography (GPC) results suggested that hotcompressed ethanol as the liquefaction solvent favored lignin degradation into monomeric phenols. The X-ray diffraction (XRD) patterns of sawdust before and after the liquefaction displayed that the cellulosic structure of the feedstock was completely converted into amorphous carbon at around 300°C and into crystalline carbon at about 350°C.

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Phenolic bio-oil produced by the direct liquefaction of Eastern white pine (Pinus Strobus L.) sawdust in a hot-compressed ethanol-water (1:1 w/w) medium at 300 C was used to partially substitute for phenol in the synthesis of bio-oil-phenol-formaldehyde (BPF) resol resins. Bio-based resol resins with high levels of phenol substitution (up to 75 wt%) could be used as plywood adhesives because of the low molecular weights found for the phenolic bio-oil (weight-average molecular weight ¼ 1072 g/mol, numberaverage molecular weight ¼ 342 g/mol). The properties of the BPF resol resins were analyzed by differential scanning calorimetry, Fourier transform infrared spectroscopy, gel permeation chromatography, and thermogravimetric analysis. All of the experimental BPF resins possessed broad molecular weight distributions but had similar chemical/ thermal properties compared to a conventional phenolformaldehyde (PF) resol resin reference (or 0 wt % BPF resin). The BPFs exhibited the typical properties of a thermosetting PF resin, for example, an exothermic curing temperature of 140-150 C and an acceptable residual carbon yield of 48-72 wt % nonvolatile content at 700 C. The experimental BPFs were applied as adhesives in the assembly of plywood, and then, the dry/wet tensile strengths were evaluated. The tensile strengths of the dry plywood samples bonded with the BPF resins up to a high ratio value of 75 wt % bio-oil exceeded or were comparable to that of the conventional pure PF resin adhesive. All of the BPF-resin-bonded plywood samples gave wet tensile strengths comparable to those of the conventional PF adhesive.

One of the highest thermoresistant thermosetting resins ever studied so far, oligosilylarylnitrile resin, was investigated first in this study. Oligosilylarylnitrile was synthesized by lithium-reduced Wurtz-Fittig condensation reaction, and the prepared viscous resin exhibited moderate rheological behaviors while heated purely or together with 20% polysilazane as a cross-linking agent. The thermal curing temperatures were found by differential scanning calorimetry at 268 °C (pure) and 158 °C (with the polysilazane cross-linking agent), which is comparably close to that of polysilylarylacetylene resin (normally at 220-250 °C) but much lower than those of polyimide and phthalonitrile resins (normally >300 °C), indicating the admirable material processability of oligosilylnitrile. The cured oligosilylarylnitrile resins have extremely high thermal resistance, indicated by the results of thermogravimetric analysis (the mass residue at 800 °C is >90% under N) and dynamic mechanical analysis (the glass-transition temperature is >420 °C). The mechanical property of the oligosilylarylnitrile-matrixed silica-cloth reinforced laminate is comparably close to those of polyimide and phthalonitrile but much higher than that of polysilylarylacetylene, indicating the enviable thermal and mechanical properties of oligosilylnitrile. Thus, among the high-temperature resins ever studied so far, the oligosilylarylnitrile resin was found to have the almost best comprehensive characteristics of processability and properties.

ABSTRACT:In this article, propargyl functionalized novolac resins (PN resins), with varying propargyl contents and varying molecular weights, were synthesized conveniently. The structural characteristics were determined by 1 HNMR and FTIR methods. Thermal cure studies revealed that the uncatalyzed thermal cure was remarkably affected by propargyl extent, while it was hardly affected by molecular weight. The processability of the as-prepared PN resins was excellent as matrix of composite materials. The cure mechanism was complicated; postcure at high temperature was required to achieve entire crosslink formation. Both dynamic mechanical analysis and thermogravimetric analysis showed that the cured PN resins had substantially improved thermal mechanical properties and thermal stability in comparison to conventional cured phenolics. High propargyl extent was preferred for high thermal stability. The results show that PN resin is one of the ideal candidates for advanced composites matrices in thermostructural and ablative applications.