Influência do uso de plastificante nas propriedades térmicas e mecânicas de nanocompósitos de POLI (Hidroxibutirato-CO-Hidroxivalerato)

Abstract

The aim of this work was to evaluate the influence of the addition of a plasticizer – triethyl citrate (TEC) – on the thermal and mechanical properties of biodegradable polymer nanocomposites based on poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV). The nanocomposites were obtained using 3 wt% of different phyllosilicates – unmodified montmorillonite (MMT), organically modified montmorillonite (OMMT), and halloysite (HNT) – and 10 wt% of TEC by melt mixing. The exudation and solvent extraction tests, together with scanning electron microscopy (SEM), suggested a good compatibility between TEC and PHBV. The morphological analysis by SEM identified some agglomerated structures in the systems containing MMT. This result was confirmed by X-ray energy dispersive spectroscopy (EDS). For the other samples, the results of SEM/EDS and X-ray diffraction (XRD) suggested a homogeneous distribution of nanoparticles within the PHBV matrix, mainly in the presence of TEC. XRD results also indicated that the addition of nanoparticles and plasticizer did not change the crystalline structure of PHBV. The differential scanning calorimetry (DSC) indicated a reduction in the melting temperature of the samples compared to the neat PHBV. The crystallization temperature increased for the nanocomposites without TEC and for the PHBV/TEC/HNT system. This can be attributed to the nucleating effect of the clays. Moreover, the nanocomposites were more crystalline than the neat PHBV. Dynamic mechanical analysis (DMA) results confirmed the plasticizing effect by the reduction of the glass transition temperature (Tg) of all samples containing TEC. It was observed a general increase in the impact strength. However, this was dependent on the degree of dispersion of nanoparticles in the polymer matrix. The set of results revealed the potential of HNT when compared to MMT. In general, the plasticized nanocomposites exhibited better processing characteristics and mechanical performance, which makes the plasticizing an alternative to facilitate the use of this polymer in various industrial applications.