Title : "GABA-functionalized carbon nanotubes to improve compatibility, dispersion and mechanical properties of PHBV nanocomposites"
Poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, is a biodegradable and biocompatible polyester with the potential to be used as a substitute for conventional thermoplastics. However, PHBV is brittle and has low mechanical properties, which hinder its use for applications that require superior properties. One alternative is the incorporation of nanoparticles into matrices to improve their characteristics. One of the most used nanoparticles is carbon nanotube (CNT), which has remarkable mechanical and electrical properties. The addition of nanoparticles into polymer matrices changes its characteristics, including mechanical and thermal. In this work, CNTs were covalently functionalized with gamma-aminobutyric acid (CNT-GB). The functionalization was confirmed by infrared spectroscopy and X-ray photoelectron spectroscopy. Nanocomposites with 0.5 wt% of CNT and CNT-GB were prepared and evaluated by impact strength, scanning electron microscopy of the fracture surface, Shore D hardness and the crystallization kinetics was studied. The impact strength was reduced by about 12% after the introduction of CNT into PHBV; however, when CNT-GB was added, the impact strength was not harmed. Meanwhile, the impact fracture surface, which presented fragile morphology for PHBV and PHBV/CNT, became ductile for PHBV/CNT-GB, suggesting a strong interaction between CNT-GB and PHBV, and improved dispersion. The improved dispersion could be confirmed by Shore D hardness and by the crystallization activation energy (Ea) value. Shore D hardness was increased by about 4% for PHBV/CNT-GB nanocomposite, compared to PHBV. The non-isothermal crystallization kinetics was analyzed using the isoconversional method. The kinetics study showed negative activation energy for all samples, indicating that the crystallization increases as the temperature decreases. The addition of CNT, functionalized or not, reduced the value of Ea when comparing with pure PHBV. The hypothesis is that CNTs act as heterogeneous nucleating agents, accelerating the crystallization process. CNT-GB presented the better dispersion into the PHBV matrix, resulting in the lower value of Ea.