Densification of high-strength B4C-TiB2 composites fabricated by pulsed electric current sintering of TiC-B mixture

The densification and mechanical properties of B4C-TiB2 composites fabricated by reactive pulsed electric current sintering from a mixture of TiC and amorphous B powders were investigated. The excess of B was essential to remove the carbon produced by the reaction. The degassing process at 1900 degrees C before applying a 50 MPa external pressure greatly improved the densification of the composites. The B4C-41 vol% TiB2 composite obtained at the optimum condition had a high 3-point bending strength of 891 MPa, a Vickers hardness of 28 GPa and a fracture toughness of 4.4 MPa m(1/2), respectively. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Modification Methods’ Effects on the Characteristics of Carboxylated Cellulose Fibers: Carboxyl Group Introduction Method versus Physical Properties

Cotton fibers were modified by TEMPO oxidation, sodium periodate oxidation, and sodium chloroacetate etherification to obtain carboxylated cellulose fibers with similar carboxyl content (about 70 mmol/100 g). The characteristics of carboxylated cellulose fibers were analyzed by comparing the morphology, chemical structure, crystallinity, carboxyl content, yield, water retention value, degree of polymerization (DP), and cost. The results showed that etherification and oxidation are both important ways to introduce carboxyl groups into the molecular structure of cellulose. When the carboxyl group with similar content is introduced into cellulose, the three modification methods will encourage a certain degree of cellulose degradation. TEMPO oxidation and sodium periodate oxidation will degrade cellulose more obviously, whereas chloroacetate etherification can obtain a higher yield, DP, and lower cost

High-Performance Wet Adhesion of Wood with Chitosan

Strong adhesion is desirable when using wood with a wide range of moisture contents, but most of the existing adhesives face challenges in bonding wood under high-humidity conditions. Here, we report a simple strategy that involves the one-step dissolution of chitosan powder in acetic acid at room temperature, followed by direct use of the resulting chitosan slurry as an adhesive on dry/wet wood veneers. Mechanical interlocks and hydrogen bonds at cell wall interfaces provided strong adhesion. Moreover, heat treatment induced recrystallization and cross-linking of chitosan chains, resulting in a high cohesion. Meanwhile, heat treatment caused the acetylation reaction between the protonated amino groups (NH3+) of chitosan and acetate groups (CH3COO–) to produce hydrophobic acetyl groups. In addition, we prepared wooden products such as plywood (dry veneers) and wooden straws (wet veneers) using wood veneers with different moisture contents. The tensile shear strengths under 63 °C water and under boiling water of plywood were 1.12 and 0.81 MPa, respectively. The compressive strength of wooden straws is up to 35.32 MPa, which was higher than that of existing commercial straws (such as paper straws, polypropylene straws, and plastic straws). The chitosan wet adhesive showed good water resistance, high bonding strength, environmental degradability, and nontoxicity, thus providing a highly promising alternative to traditional wood composite adhesives