Resin Backbone
Hydroxyl-terminated synthetic polymers produced by the esterification reaction between polyfunctional acids and glycols act as the principal flexible block in polyurethane laminating adhesives. A polyester polyol provides high tensile strength, outstanding abrasion resistance, and excellent adhesion to polar substrates like paper, board, and aluminum foil. The chemical structure of this polyol, particularly its ester linkages, governs the mechanical flexibility and the chemical resistance of the final packaging adhesive.
It is supplied in various molecular weights depending on the desired viscosity.
Hydrolysis Sensitivity
High susceptibility of the ester linkages to cleavage when exposed to warm, moist environments represents the primary limitation of these structures in long-term applications. When a polyester polyol is used in high-humidity packaging, it can undergo gradual hydrolytic degradation, resulting in a loss of bond strength. This process splits the polymer chains into smaller, acid-terminated fragments that can accelerate further degradation.
Consequently, these adhesives are often stabilized with moisture scavengers to extend the service life of the package.
Packaging Customization
Selecting the correct acid and glycol monomer during the synthesis stage allows manufacturers to adjust the glass transition temperature of the adhesive. This customization determines whether the cured film is suited for freezer packaging or high-temperature retort pouches.
