Controlling tackiness of shape memory polyurethanes for textile applications

Tackiness is an important parameter to take into account in order to obtain new materials with the desired properties for textile applications. Among these new materials, shape memory polymers (SMPs) are earning high interest due to the immense possibilities to apply them in different technological applications. Moreover, in order to expand the applications of these materials to biomedicine, the recovery temperature of the shape memory effect (T-trans) should be close to the human's body temperature. Amorphous shape memory polyurethanes (SMPUs) are good candidates because they have all the required properties, and is possible to modify the glass transition temperature (T-g) that acts as T-trans by varying the hard to soft segment ratio. Furthermore, usually a well known stoichiometric ratio, NCO/OH = 1 is used providing excellent properties to SMPUs. Nevertheless, this stoichiometry usually generates tacky raw materials that obviously cannot be used in some applications such as biomedicals or textile industry. Therefore, control the tackiness of a SMPU during its synthesis is a critical step and may be decisive for its final application. In this study, we demonstrate that the tackiness of SMPUs, which seems directly related to free hydroxyl groups, could be easily controlled during the synthesis by changing the stoichiometric proportion of the different reagents, that is, the NCO/OH ratio. With this purpose, the same SMPU has been synthesized and characterized with three different NCO/OH ratios (1, 1.05 and 1.1), evaluating not only the changes in the stickiness of the sample but also in other properties such as the shape memory effect.