Chemical treatments of bamboo to modify its moisture absorption and adhesion to vinyl ester resin in humid environment

Moisture absorption is a major concern in the case of natural fibers used as reinforcement in structural composites. Bamboo strip as a kind of natural material has been used to reinforce vinyl ester resin, in this study. The moisture absorption behavior of the bamboo strips and their adhesion to vinyl ester resin at different levels of relative humidity (RH) during specimen fabrication are investigated. To improve moisture resistance and the adhesion to vinyl ester resin under high RH conditions, the bamboo strips are subject to different chemical treatments, that is with alkaline, pre-alkaline and acetic anhydride, pre-alkaline and potassium permanganate, and pre-alkaline and silane. The study of the equilibrium moisture content of modified bamboo strips shows that it is slightly increased by alkaline treatment, while it is reduced by the other three methods, especially by acetylation due to its well-known esterification. The interfacial shear strength (IFSS) by pull-out test is greatly improved after the modification and it decreases steadily as the fabrication RH levels increase for both untreated and treated samples. At high level RH (80% RH), IFSS is almost negligible except acetylated specimens. Results indicate that the severe negative impact on the IFSS by fabrication RH levels is not so considerable if the bamboo strips are subjected to acetylation as pretreatment. The interlaminar shear strength values based on short-beam shear test of unidirection bamboo strip mats/vinyl ester resin composites are well consistent with IFSS data.