Oxidation of Various Kraft Lignins with a Bacterial Laccase Enzyme

Modification of kraft lignin (KL), traditionally uses harsh and energy-demanding physical and chemical processes. In this study, the potential of the bacterial laccase CotA (spore coating protein A) for oxidation of KL under mild conditions was assessed. Thereby, the efficiency of CotA to oxidize both softwood and hardwood KL of varying purity at alkaline conditions was examined. For the respective type of wood, the highest oxidation activity by CotA was determined for the medium ash content softwood KL (MA_S) and the medium ash content hardwood KL (MA_H), respectively. By an up to 95% decrease in fluorescence and up to 65% in phenol content coupling of the structural lignin units was indicated. These results correlated with an increase in viscosity and molecular weight, which increased nearly 2 and 20-fold for MA_H and about 1.3 and 6.0-fold for MA_S, respectively. Thus, this study confirms that the CotA laccase can oxidize a variety of KL at alkaline conditions, while the origin and purity of KL were found to have a major impact on the efficiency of oxidation. Under the herein tested conditions, it was observed that the MA_H KL showed the highest susceptibility to CotA oxidation when compared to the other hardwood KLs and the softwood KLs. Therefore, this could be a viable method to produce sustainable resins and adhesives.     

A study on flexural properties of carbon-basalt/epoxy hybrid composites

The objective of this research is to investigate the performances of the carbon-basalt/epoxy hybrid composites under flexural loading. In this work, the hybrid composites were manufactured by the vacuum assisted resin transfer molding (VARTM) process. The variations of flexural strength and modulus of the hybrid composite according to the number of basalt fabric were investigated, and we obtained the expression to calculate their mechanical properties. In the study of flexural properties for the hybrid composites with different stacking sequence of the reinforcements, we knew that their properties strongly depend on the reinforcing position of carbon and basalt fabric.