Synthesis and characterization of new thermoplastic polyurethane adhesives containing rosin resin as an internal tackifier

Abstract

Three thermoplastic polyurethane elastomers (TPUs) were prepared using the prepolymer method. MDI (diphenylmethane-4,4′-diisocyanate) and the polyadipate of 1,4-butanediol (Mw = 2400) were reacted to produce a prepolymer containing unreacted isocyanate groups; chain extenders were different mixtures of 1,4-butanediol and a rosin resin (0-50%). The specific feature of this procedure was the introduction of a rosin resin as an internal tackifier to provide higher immediate adhesion to the TPUs. The new TPUs were characterized using gel permeation chromatography, wideangle X-ray diffraction, differential scanning calorimetry, stress-controlled rheology, and stress-strain measurements. The TPUs were used as raw materials to prepare solvent-based polyurethane adhesives, the adhesion properties of which were obtained from T-peel tests on PVC/polyurethane adhesive/PVC and leather/polyurethane adhesive/PVC joints. The addition of rosin resin as an internal tackifier contributed to the production of two types of hard segments, which affected the properties of the TPUs. Therefore, rosin resin as an internal tackifier produced an increase in the average molecular weight, an increase in the viscosity, and improved the rheological properties. The glass transtition temperature decreased if the TPUs contained rosin resin, due to a greater degree of incompatibility between the hard and soft segments. Consequently, slower kinetics of crystallization was obtained in the TPUs containing rosin resin. Depending on the amount of rosin resin in the TPU, different structures and properties were obtained. On the other hand, the immediate T-peel strength in all joints was improved if the TPU contained rosin resin.