Bonding properties and crystallization kinetics of thermoplastic polyurethane adhesive

Resumo

The advantages of heterophasic thermoplastic polyurethanes (TPUs), such as their phase behavior and mechanical
properties, make these materials an important class of adhesives. Whereas the amorphous phase contributes
to good adhesion properties, the crystalline phase is responsible for the cohesive force of TPU adhesives.
This work investigates the performance of a polyester based TPU and its potential for being applied as
adhesive in the shoe industry. The TPU was formulated with three different additives. The crystallization
kinetics of the TPU was evaluated by Differential Scanning Calorimetry and the Avrami equation was used
to assess the influence of the additives on the geometry of crystal growth and nucleation conditions. It was
found that the additives had no effect on the nucleation process, whereas the polymer chains had reduced
mobility, mainly in the TPU comprising polyisocyanate ε-caprolactam. The best T-peel strength on a
poly(vinyl chloride) (PVC) substrate was determined for the TPU with polycarbodiimide, which improved
the adhesive bonding from 3.23 N/mm to 3.32 N/mm.
Key words: TPU, polyurethane, polycarbodiimide, adhesive, crystallinity.