Blendas de Poli (B-Hidroxibutirato) e Poli (Butileno-Adipatotereftalato) e seus compósitos com babaçu: efeito da composição e das condições de processamento

Abstract

This work deals with of poly (β-hydroxybutyrate) (PHB) and poly (butylene adipate terephthalate) (PBAT) blends as well as their composites with fibers extracted from the epicarp and mesocarp of babassu (Attalea sp.) The effect of processing conditions on the rheological, thermal and morphological properties of the composites as a function of load type and content was evaluated. PHB/ PBAT blends were processed in an internal mixer. They were characterized by torque rheometry and their crystallization and melting behavior were analyzed by differential scanning calorimetry (DSC). Composites having three different blends as the matrix and reinforced with 10 and 20 %wt. of the two kinds of fibrous loads were melt processed in an internal laboratory mixer and characterized by torque rheometry. Degradation rates, estimated by the reduction of the torque and molar mass during processing, were associated to blend composition as well as to the filler kind (epicarp or mesocarp) and content. Scanning electron microscopy was used to analyse the interface of the blends and composites, while optical microscopy was used to reveal the filler dispersion. DSC results showed that PBAT crystallizes completely during cooling while PHB and PHB/PBAT blends incompletely crystallized from the melt, the process achieving completion during the reheating step. These characteristics were independent of the heating rate and are the same for the pure polymers and for the blend with 50 %wt. of the PBAT. Pseudo-Avrami, Ozawa and Mo classical macrokinetic models were employed to describe the evolution of crystallization from the melt and it was found that none of the three classical kinetic models tested could accurately predict the experimental data for the blend. Some models can be used - as predictive tools - for pure components (Ozawa for PHB, Mo for PBAT) with a reduced validity range. The results of torque rheometry showed that PHB degraded faster during processing than PBAT and that the combination of PHB with PBAT provided significant protection against excessive degradation of PHB. Both the presence and level of the two types of filler increased the incipient degradation of the blend. The images obtained by optical microscopy (OM) showed uniform filler distribution in the matrix in all cases, without agglomerates. SEM of the fracture surface morphology indicated better matrix/fiber adhesion in mixtures rich in PHB and composites with babassu epicarp.