Thermal analysis of self-healing thermoplastic matrix nanocomposite from cyclic butylene terephthalate

This work is aimed to the development of a self-healing thermoplastic matrix nanocomposite, obtained through the ring-opening polymerization of cyclic butylene terephthalate (CBT) to polybutylene terephthalate (pCBT); a partial polymerization allows obtaining a mixture of CBT and pCBT, being the two materials characterized by a difference in the melting temperature of about 80 °C. Healing of the material requires heating to a temperature higher than melting of CBT, but lower than melting of pCBT; therefore, the molten CBT is able to weld the surfaces of the growing crack, thus restoring mechanical properties. The presence of solid pCBT allows retaining the geometry of the material. In order to produce a partially polymerized material, two different systems were studied: a first one with two catalysts, with different activation temperatures, and a second one with one single catalyst partially intercalated in nanoclay layers. Rheological analysis was used in order to study the viscosity evolution associated with the conversion of CBT to pCBT during thermal treatment. Differential scanning calorimetry (DSC) was used in order to measure the amount of unreacted CBT after processing, and to verify the further conversion of CBT to pCBT during healing. Also, DSC analysis highlighted the structural changes of pCBT crystallinity during healing. Flexural tests were performed on partially reacted pCBT samples, highlighting the relevant effect of the addition of nanoclay on the mechanical properties of the material. Adhesion tests performed after healing evidenced the efficacy of the proposed approach for development of self-healing thermoplastic polymers.