Effects of Prepolymer on the Cooking-resistant Properties of Solvent-free Polyurethane Adhesives

A series of polyurethane prepolymers were designed and synthesized as isocyanate-terminated component for the final product: two-component solvent-free polyurethane adhesives. Structural characterization using infrared and ¹H NMR spectroscopies confirmed the structure of the designed prepolymers. The effect of the isocyanate mass fraction (ω_NCO) of the prepolymer, molecular weight of polyols and ratio R (molar ratio of –OH to –NCO in adhesives) on viscosity and cooking resistance of the polyurethane adhesives were investigated by a variable-control method. The results show that in the case of ω_NCO=17%, the prepolymer has a low viscosity, and the prepared adhesive has a higher peel force after boiling treatment. For a constant value of ω_NCO, as the molecular weight of the polyol decreases, the viscosity of the prepolymer increases, so does the peel force of the polyurethane adhesive before and after boiling. With polyols molecular weight of 1609 g/mol, ω_NCO of 17% and R of 2.5, the peel force of retort cast polypropylene (RCPP) layer before and after boiling is as high as 6.30 N and 4.37 N, respectively. A series of polyurethane adhesives were prepared by mixing this prepolymer with different B components, meeting the requirements in standard GB/T41168-2021 for cooking resistance requirements of aluminum plastic composite film.