PSAs are used in the manufacture of kinesiology patches intended for paramedical and sport activities. The removal of the current kinesiology patches is painful (particularly in hairy skins) and the current solutions are not satisfactory, there is a need to develop low-trauma PSAs. The strategy proposed in this study is the use of PSAs with high adhesion at body temperature (37 ºC), but reduced adhesion at 20 ºC. Thus, once the PSA is contacting the skin, the adhesion is produced; and upon cooling down to about 20 ºC or less, the adhesion is reduced and the PSA should be removed without pain.
The polyurethanes do not typically show PSA property because of their low tack and low peel adhesive strength. The addition of tackifiers, the compounding with other polymers and the use of crosslinking agents for obtaining polyurethane PSAs have been proposed. In this study, a novel approach for preparing polyurethane PSAs consisting in the design of the segmented structure of thermoplastic polyurethanes and the control of their degree of phase separation is proposed.
Thermoplastic polyurethanes (PUs) with PSA property were synthetized by reacting 4,4’-diphenylmethane diisocyanate (MDI) with 1,4-butanediol and mixtures of polypropylene glycols (PPGs) of different molecular weights (1000 and 2000 Da). Good tack at 37 ºC was obtained in PU PSAs prepared with PPG2000+PPG1000 mixtures containing 50 wt% or more PPG2000 and their PSA adhesion properties were related to their minor content of associated by hydrogen bond urethane groups and more important degree of phase separation; furthermore, they show reduced tack at 10 ºC, the tack was reversed by increasing the temperature. Furthermore, the PU PSAs followed Dahlquist criterion, had low glass transition temperatures, and adequate 180º peel strength.