Design of self-healing biodegradable polymers

A biodegradable thermoplastic polymer has been formulated by solubilizing Murexide (M) salts in a commercial biodegradable vinyl alcohol copolymer (HVA). The Murexide has been employed as a self-healing filler with the aim to impart the auto-repair ability to the formulated material. Three different percentages (1, 3, and 5 mass%) of filler have been solubilized in HVA to evaluate the effect of the filler concentration on the thermal and self-healing properties of the resulting polymeric materials. The samples have been thermally characterized by Differential Scanning Calorimetry (DSC) and Thermogravimetric Analyses (TGA), while their self-healing ability has been evaluated through the estimation of the storage modulus recovery, measured by Dynamic Mechanical Analysis (DMA). The results of DSC analysis have highlighted that the increase of the amount of Murexide anticipates the thermal events such as glass transition, crystallization and melting. TGA measurements have evidenced that, although there is a reduction of thermal stability of the materials in the presence of a high concentration of M, the polymer still remains stable up to 270 °C. Healing efficiency higher than 80%, at a temperature beyond 60 °C, has been detected for the samples loaded with 3 and 5 mass% of Murexide, thus confirming the efficacy of this compound as an auto-repair agent and the relationship between the self-healing efficiency and its amount. For a temperature lower than 70 °C, the healing tests, carried out at different values of tensile deformation frequency, have highlighted a frequency-dependent healing efficiency. This dependence becomes negligible at higher temperatures for which the healing efficiency approaches the value of 100%.