Chemical Structure
Linear aliphatic diols with terminal hydroxyl groups supply the structural flexibility required in polyester resin synthesis for packaging adhesives. When reacted with dicarboxylic acids or diisocyanates, 1 6 hexanediol forms linear chains that improve impact strength in polyurethane laminating adhesives. The six-carbon alkane chain imparts low glass transition temperatures to the cured resin network.
This chemical structure bounds the thermal stability of the cured adhesive, beyond which thermal degradation of the ester linkages occurs.
Hydrolytic Resistance
Ester linkages derived from primary diols exhibit varying rates of moisture degradation depending on hydrocarbon chain length. In laminating adhesives used for flexible packaging, 1 6 hexanediol creates hydrophobic segments that impede water penetration into the bond line. Retaining bond strength under humid storage conditions prevents delamination in foil and film combinations.
Curing Behavior
Reactivity during polyurethane prepolymer synthesis depends on the accessibility of primary hydroxyl groups. Hydroxyl groups situated at the terminal positions of 1 6 hexanediol react rapidly with aliphatic or aromatic diisocyanates under mild heat. Controlled addition rates during prepolymer production prevent gelation while achieving the targeted hydroxyl number.
High conversion rates ensure minimal unreacted monomer remains in the dry adhesive layer applied to flexible packaging films. Complete reaction eliminates migratory low molecular weight species that could contaminate food contact surfaces.
