Chitosan used as a specific coupling agent to modify starch in preparation of adhesive film

To reduce the use of formaldehyde wood adhesives, a chemical modification of starch with chitosan was explored to prepare an adhesive film for plywood with good adhesive properties, low price, non-toxic, and convenient sizing. The effect of chitosan content of the adhesive film on the shear strength of plywood was studied. The modification mechanism and bonding mechanism of the film were analyzed by FTIR, XPS, XRD and SEM. The results showed that when the amount of chitosan was 30% of starch dry weight, the dry-wet shear strength of plywood met the requirements of Chinese national class II plywood (>= 0.80 MPa). FTIR and XPS analysis showed that -NH2 in the chitosan reacted with -COOH on starch and wood surface to form amide bond, which specifies the chitosan's role as a coupling agent. XRD and SEM analysis showed that the addition of chitosan disturbed the otherwise orderly arrangement of a starch structure. The structure of the attained modified film is mostly amorphous. Sizing in the form of a adhesive film solves the disadvantage of difficulty in sizing starch adhesive. Compared with commercial adhesives on the market, this adhesive film has the advantages of low price, wide source of raw materials, non-toxic, and is expected to be a good substitute for formaldehyde adhesives on the market. (C) 2020 Published by Elsevier Ltd.