Effect of addition of boric acid on thermo-mechanical properties of microcrystalline cellulose/polyvinyl alcohol blend and applicability as wood adhesive

摘要

Although the wood adhesive uses cellulose as a cheap and bio-degradable reinforcing agent, the usage is restricted because of its inability to enhance tackiness and adhesion compared with conventional wood adhesives. In this study, microcrystalline cellulose (MCC) incorporated polyvinyl alcohol (PVA) was prepared by blending in water. The availability of free hydroxyl groups in MCC and PVA offers a site for further modification. To upgrade cellulose as a functional filler, crosslinking approach can be a possible solution. Here boric acid is investigated as a crosslinker to improve the mechanical and thermal properties of PVA/MCC blend. Various analytical methods were employed to quantify the effect of crosslinking namely viscosity measurement, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and water contact angle measurement. DSC result shows a shift in glass transition temperature with the increasing concentration of boric acid. From DMA results, the storage modulus at 100 degrees C doubled when 0.2 wt.% boric acid was added, compared to the blank sample. Additionally, the thermogram of tan delta exhibited a shift to higher temperatures with peak broadening on increasing boric acid concentration, which confirmed enhancements in thermo-mechanical properties. Moreover, crosslinking enhanced adhesive performance property. It was observed that the sample crosslinked with 0.2 wt.% boric acid showed the best result with two times increment in bonded tensile shear strength on wood substrate after 6 and 24 h of testing.