Mechanism of Thermal Decomposition of Lignin

Differential thermal analysis studies of milled wood lignin and lignin carbohydrate complex at different heating rates showed three exothermic peaks. The heating rate is the factor that affects their sharpness and position. The peaks are sharp at low heating rates. Infrared spectra and scanning electron micrographs of the pyrolyzed lignin residues show that aliphatic scission of the lignin molecule at the onset of pyrolysis and progressive carbonization of the surface are the principal features of degradation; there is no intermediate compound formed during the pyrolysis

OPTIMIZING LIGHT-CURED COMPOSITE PROPERTIES WITH CAMPHROQUINONE AND BUTYLHYDROXYTOLUENE COMBINATIONS

poster abstractPolymerization shrinkage is an inherent property in dental composite that has major effects on its clinical performance. Many strategies on minimizing the shrinkage have been explored in the past. Here we propose that, by op-timizing the dose combinations of photoinitiator and polymerization inhibitor, we can effectively reduce the polymerization shrinkage stress without sacri-ficing the mechanical properties of dental composite. The objective of this study therefore was to investigate the effects of a common photoinitiator, camphroquinone (CQ), and inhibitor, butylhydroxytoluene (BHT), at clinical-ly-relevant concentration combinations on the shrinkage properties and me-chanical properties of light-cured composite. Samples were prepared by mix-ing bisphenol-A-glycidyl methacrylate, urethane dimethacrylate, and tetraethyleneglycol dimethacrylate at a 1:1:1 ratio. Borosilicate glass fillers constituted 70% of the resin weight. Sixteen groups of resin composite were prepared from the combination of four CQ (0.1%, 0.5%, 1.0%, and 1.5%) and four BHT (0.0%, 0.5%, 1.0%, and 1.5%) levels. Six properties were tested, including Flexural strength (FS) flexural modulus (FM), degree of conversion (DC), contraction stress (CS), stress rate (SR), and gel point (GP). The effects of CQ and BHT combinations on each of these properties were evaluated using two-way analysis of variance (ANOVA). Groups with low CQ and BHT showed moderate values for FS, FM, SR and CS with DC around 70%. Increasing the BHT concentration caused a decrease in SR, CS, DC and an increase in GP values. Increasing the CQ content gave a steady increase in values for FS and FM. Notable, in CQ=1.5% group, increasing BHT from 0 to 1.5% result in a statistically significant decrease in polymeri-zation shrinkage stress (p<0.05) while maintain the same mechanical prop-erties. In this project, we successfully demonstrated that the polymerization shrinkage of resin composite can be tailored through CQ and BHT combina-tions with high CQ and high BHT showing the most promising results

Studies on the Mechanism of Flame Retardation in Wood

Two lignins, of different carbohydrate content, were pyrolyzed before and after treatment with inorganic salts. Lignin that is relatively free of carbohydrate was inert to the salts: its DTA curve did not change. The DTA curve of lignin associated with about 50% carbohydrate showed a shift of the exothermic peak io a higher temperature and the appearance ofa new exotherm; lithium chloride was the most effective salt in causing this shift. The results support the chemical theory of flame retardation