Structure and Performance of Carboxylic Styrene Butadiene Rubber/Citric Acid Composite Films

Fabrication of an Ultrastrong Formaldehyde-Free Wood Adhesive with an Organic-Inorganic Cross-Linking Network

The wood industry faces challenges in producing eco-friendly, high-performance, and formaldehyde-free adhesives. In this study, carboxylated styrene-butadiene rubber (XSBR) was blended with polyamidoamine-epichlorohydrin (PAE) resin, and a controlled amount of CaCO3 powder was incorporated to create an adhesive with exceptional strength. The resulting three-layer plywood demonstrated remarkable dry and wet shear strengths of 3.09 and 2.36 MPa, respectively, and of 2.27 MPa after boiling water tests, comparable to that of phenolic resins. Additionally, the adhesive exhibited strong adhesion across various materials including glass, metal, etc. This exceptional performance was due to two primary factors: (1) the high-density chemical cross-linking reaction and the physical entanglement between XSBR and PAE; (2) the organic-inorganic hybrid involving metal ion complexation developed by CaCO3, which fostered molecular chain connections and enhanced the adhesive-material interface. These findings offer valuable references for further research in the field of wood adhesives.

Shape-Memory Composites Based on Ionic Elastomers

Shape-memory polymers tend to present rigid behavior at ambient temperature, being unable to deform in this state. To obtain soft shape-memory elastomers, composites based on a commercial rubber crosslinked by both ionic and covalent bonds were developed, as these materials do not lose their elastomeric behavior below their transition (or activation) temperature (using ionic transition for such a purpose). The introduction of fillers, such as carbon black and multiwalled carbon nanotubes (MWCNTs), was studied and compared with the unfilled matrix. By adding contents above 10 phr of MWCNT, shape-memory properties were enhanced by 10%, achieving fixing and recovery ratios above 90% and a faster response. Moreover, by adding these fillers, the conductivity of the materials increased from ~10⁻¹¹ to ~10⁻⁴ S·cm⁻¹, allowing the possibility to activate the shape-memory effect with an electric current, based on the heating of the material by the Joule effect, achieving a fast and clean stimulus requiring only a current source of 50 V.