Polyvinyl alcohol–cellulose blend wood adhesive modified by citric acid and its effect on physical, thermal, mechanical and performance properties

Exploitation of petrochemicals has reflected its negative impact environment. Quest for systems, which are environmentally benign and sustainable source, resulted in the exploration of biopolymers. Cellulose, being the most abundant biopolymer, has gained wide acceptance as it is a sustainable material and offers the possibilities for further modification. As adhesives play an integral role in construction and infrastructure sectors, the approach of incorporating earth abundant biopolymer reduces the dependency of petrochemicals and functions as a greener alternative. Hence, the present work investigates the applicability of microcrystalline cellulose (MCC)-incorporated polyvinyl alcohol (PVA) as a potential wood adhesive. To furthermore enhance the bond strength, chemical modification is engineered using citric acid, as a green cross-linker. Effect on physical, thermal and mechanical properties was studied by viscosity, pH, contact angle measurement, Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, pencil hardness test and ultimate stress of films. Various test results revealed the effect of cross-linking by citric acid at 0.3 wt.%. However, at 0.5 wt.%, sample showed predominant plasticizing nature, as it exceeded the optimum content. Introduction of citric acid in the blend exhibited drastic increase in the bond strength. The wood substrates bonded with the modified blend showed increment in lap shear bond strength by 56% and 123% for 0.3 and 0.5 wt.% citric acid, respectively, after 24 h of bonding. With the enhancement in physical, thermomechanical and performance properties, it was clearly evidenced by the effectiveness of citric acid, as a green additive for developing advanced wood adhesives based on PVA/MCC blend.