Influence of Biobased Polyol Type On The Properties of Polyurethane Hotmelt Adhesives For Footwear Joints

Abstract

The implementation of a Circular Economy model, promoted by the increasingly stricter European policies, demands a comprehensive approach to resource efficiency. In this sense, polyurethanes, one of the most used polymers worldwide, are strongly dependent of non-renewable fossil resources. Thus, boosting the production of new polyurethanes / a new polyurethane based on more sustainable raw materials is crucial to move towards the footwear industry decarbonisation. INESCOP, aware of the footwear industry’s environmental impact, focuses on reducing or removing fossil-based raw materials and opts for eco-friendly ones. These sustainable raw materials provide polyurethane adhesives with additional beneficial non-toxicity and sustainable characteristics, without harming their properties during their useful life. Therefore, the aim of this study is to synthesise and characterise reactive hotmelt polyurethanes from biomass and CO2-based polyols as bioadhesives for the footwear industry. The influence of biobased polyols on the polyurethane structure, and therefore, on their final properties was analysed by different experimental techniques in order to assess their viability for the upper to sole bonding process.

Cleaner technologies to minimise the environmental footprint of the footwear bonding process

“…In addition, the softening point of conventional HMPUR adhesives is around 55°C and the new CO 2 -based adhesives had similar softening points. 53,54…”

“…The use of plasma, both low-pressure and atmospheric plasma, achieved in physically and chemically modifying the rubber surface so that the adhesion values obtained were comparable to those obtained with conventional roughening and halogenation treatment. 11,54 However, it was observed that the halogenation treatment for adhesive joints with HMPUR could be more effective due to the adhesion failures obtained. This is because the adhesion failures (shown in Figure 14) obtained in these joints correspond to a mixture of a failure with half of the sole material torn and the failure of adhesion to the sole material (50A2/50M2).…”

“…In addition, the softening point of conventional HMPUR adhesives is around 55°C and the new CO 2 -based adhesives had similar softening points. 53,54 Finally, the analysis of the effect of the incorporation of different amounts of CO 2 -based polyol on the final adhesive strength of the new adhesives was carried out by means of a T-peel test on the SBR leather/ rubber joints. The results of the T-peel strength after 72 h from joint formation as a function of the different amount of CO 2 -based polyol in the HMPUR adhesives are shown in Figure 7.…”