Thermoplastic polyurethane-based polycarbonate diol hot melt adhesives: The effect of hard-soft segment ratio on adhesion properties

Polycarbonate-based thermoplastic polyurethane elastomers (PCD-TPUs) were synthesized from polyhexamethylene carbonate diol, 4,4-diphenylmethane diisocyanate and 1,4 butanediol, intended for adhesive applications. The chemical structure, thermal transition temperature, phase separation morphology, mechanical properties, and adhesion properties were studied to elucidate the structure-properties relationship of PCD-TPUs as a function of hard segment content. The phase separation behavior was described as a shift of the glass transition temperature and the dimension size of the hard domain. It was found that the higher hard segment fraction led to a lower degree of phase separation as well as a reduction in tensile strength and elongation at break. The hydrogen bonding characteristic of PCD-TPUs was investigated by FTIR. The presence of free hydrogen bonded PCD-TPUs benefits the higher peel strength since it promotes hydrogen bonding interaction with the substrate. The peel strength was obtained from PCD-TPUs/stainless steel joint. The adhesion properties of the adhesive system were strongly influenced by the soft segment. These results can establish the possibility of designing new formulations for hot melt adhesive.