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Lignin, a byproduct from the chemical processing of lignocellulosic biomass, is a polyphenolic compound that has potential as a partial phenol substitute in phenolic adhesive formulations. In this study, HBr and HI were used as reagents to demethylate an alkali lignin (AL) to increase its hydroxyl content and thereby enhance its reactivity for the preparation of phenolic resins. Analyses by FT-IR, 1H-NMR and 2D-NMR(HSQC) demonstrated both a decrease in methoxyl groups and an increase in hydroxyl groups for each demethylated lignin (DL). In addition, the molar amounts of phenolic hydroxyls, determined by 1H-NMR, increased to 0.67 mmol/g for the HI-DL, and 0.64 mmol/g for the HBr-DL, from 0.52 mmol/g for the AL. These results showed that HI, a stronger nucleophilic reagent than HBr, provided a higher degree of AL demethylation. Lignin-containing resins, prepared by copolymerization, met the bonding strength standard for exterior plywood with DL used to replace as much as 50 wt.% of phenol. The increased hydroxyl contents resulting from the lignin demethylations also imparted faster cure times for the lignin-containing resins and lower formaldehyde emissions. Altogether, the stronger nucleophilicity of HI, compared to HBr, impacted the degree of lignin demethylation, and carried through to measurable differences the thermal properties and performance of the lignin-containing PF resins.

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Marine biofouling has brought a serious impact on human marine production and transportation activities. Applying antifouling coatings is an effective method to prevent marine biofouling. Here, we have conducted a...

Weathering products of silicate rocks are particularly useful for evaluating the continental chemical weathering on the Earth's surface and its mechanism. Clay mineralogy and major-element geochemistry of surface sediment samples collected in major rivers of Malay Peninsula and North Borneo in the tropical Southeast Asian region are used to study the present chemical weathering process and its controlling factors of tropical regions. The results indicate that the clay mineral assemblage in Malay Peninsula consists dominantly of kaolinite (average 80%) and minor illite (average 17%), almost without chlorite and smectite, whereas in North Borneo it consists mainly of illite and chlorite, with minor amounts of kaolinite (average 14%) and no smectite. Total contents of illite and chlorite in both Northwest and Northeast Borneo are 84% and 87%, respectively. Major-element geochemical results of both bulk and clay-fraction sediments show intensive chemical weathering degree for both areas. Relatively, the chemical weathering degree is gradually strengthened from Northeast Borneo, Northwest Borneo, to Malay Peninsula, and it is extremely intensive in Malay Peninsula. Our results indicate that, in the tropical Southeast Asian region exampled by Malay Peninsula and Borneo, climatic condition of tropical warm temperature and East Asian monsoon rainfall is the first-order controlling factor on the chemical weathering, resulting in intensive chemical weathering throughout tropical areas, and tectonic activity and lithology of parent rocks are subordinate factors, which still have an important impact on the weathering products, forming completely different clay mineral assemblages between Malay Peninsula and Borneo. clay minerals, major elements, fluvial sediments, chemical weathering, Malay Peninsula, Borneo Citation:Wang H, Liu Z F, Sathiamurthy E, et al. Chemical weathering in Malay Peninsula and North Borneo: Clay mineralogy and element geochemistry of river surface sediments.

The reasons, prevention, and control of loess disaster are of great concern in practice. In recent years, Xi’an city, China, has taken the leadership in large-scale construction of subway lines in the loess strata. To study the structural response of the tunnel in loess region under local hydrodynamic environment, an experimental testing in 1g as well as a numerical simulation were performed, in which the achieved results were verified and were found to be in good agreement. Furthermore, the results showed that when the water outlet point is above the lining, the overall stress of the lining is “peanut shell,” as the water pressure of the outlet point decreases, the tensile stress of the top and bottom of the lining increases, while the compressive stress on both sides decreases; the channel form of the flow to the lining changes with the variation of the position of the water outlet point. It is worth mentioning that in the process of water gushing, the closer to the water source, the greater surface subsidence is, and there is a positive correlation between water pressure and surface subsidence. This study is of significant benchmark for the construction, maintenance, and prevention of tunnel in loess strata under the influence of water environment.

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