Fast realization of high-strength, repeatable, damp-heat resistant bamboo-strip scarf bonding joints via hot-melt adhesives

Abstract

Bamboo, which has excellent mechanical strength, is an ideal raw material for manufacturing high-performance bio-composites. However, due to a lack of fast, high-strength lengthening technology for bamboo units, the large-scale, mechanized, continuous production of bamboo woven materials has not been fully developed. In this work, bamboo strips (BS) with 0.5 mm thickness were used as a basic unit to prepare lengthened bamboo strips with the scarf jointing method. The effects of scarf jointed angles and hot-melt adhesive type on the scarf bonding performance were systematically investigated. The tensile strength of BS scarf joints appears to increase as the scarf joint angle decrease. Scarf joints prepared with low-cost thermoplastic polyurethane (TPU) film outperform those prepared with reactive polyurethane (PUR) or ethylene vinyl acetate copolymer (EVA) hot-melt adhesives in terms of maximum tensile strength (197.9 MPa), secondary repeated bonding performance, and damp-heat aging resistance, where tensile strength of 136 MPa was retained after a 120 h cycle aging test. Specimens bonded with PUR adhesive are resistant to damp-heat aging, but show unsatisfactory secondary repeated bonding performance. The tensile strength and damp-heat aging resistance of EVA bonded specimens are unacceptable due to an unreliable bonding interface. We developed a facile solution for high-strength BS lengthening with repeated bonding and damp-heat resistant characteristics, which may provide technical support for the large-scale, mechanized manufacturing of bamboo-based composites.