A separable paper adhesive based on the starch―lignin composite.

Lignin was grafted onto starch main chain by free radical-initiated graft copolymerization and hyperbranched polyester H102 as dispersant to prepare a bio-based paper adhesive (Fig. 1). In the graphical abstract, a represents the structure of adhesives, b indicates the adhesiveness of adhesive to paper, c and d imply that only a trace of adhesive is dissolved when soaked in room temperature for 12 h. However, the adhesive is completely dissolved after the adhesive is shaken in hot water at 80 °C for 0.5 h. This indicates that the adhesive can be dissolved by heating and excluded by water during the waste paper recycling process, and does not affect the recovery of waste paper. The diagram of adhesion on cellulosic paper. (a) schematic diagram of adhesive structure; (b) the binding effect of adhesive on paper; (c) adhesives do not dissolve in cold water; (d) adhesives are dissolved in hot water. • The bio-based adhesive was prepared by lignin modified starch. • The adhesive stability was improved via using hyperbranched polyester as dispersant. • The bonding strength of the adhesive to paper is higher than cellulose itself. • The adhesive can be excluded by hot water without affecting the recovery of paper. One major defect in paper adhesives is that it is difficult to remove the adhesive in waste paper. These adhesives can easily adhere to paper-making equipment, which hampers recycling. Herein, the hyperbranched polyester H 102 is used to act as dispersant, and grafting copolymerization of lignin onto the starch backbone was carried out by initiation of free radicals to prepare a bio-based paper adhesive in water. The results show that the adhesive can achieve the best adhesion properties under m(H 2 O)/m(St) = 15:1, m(SLS)/m(St) = 0.15:1, m(APS)/m(St) = 0.02:1, and pH = 4 at 80 °C for 6 h. The addition of H 102 stabilizes the performance of the adhesive and extends the shelf life. The feasibility was verified by Fourier transform infrared spectroscopy (FT-IR), Ultraviolet-visible Spectrophotometry (UV–vis), Thermogravimetric analysis (TG), X-ray diffraction (XRD) and rheological property analysis. Moreover, the as-prepared adhesive can be dissolved in H 2 O by heating, which is beneficial to improve the recovery and recycling of waste paper compared with the traditional adhesives. [ABSTRACT FROM AUTHOR]