doctoralThesis
Blendas de Poli (B-Hidroxibutirato) e Poli (Butileno-Adipatotereftalato) e seus compósitos com babaçu: efeito da composição e das condições de processamento
Fecha
2019-02-19Registro en:
COSTA, Anna Raffaela de Matos. Blendas de Poli (B-Hidroxibutirato) e Poli (Butileno-Adipatotereftalato) e seus compósitos com babaçu: efeito da composição e das condições de processamento. 2019. 221f. Tese (Doutorado em Ciência e Engenharia de Materiais) - Centro de Ciências Exatas e da Terra, Universidade Federal do Rio Grande do Norte, Natal, 2019.
Autor
Costa, Anna Raffaela de Matos
Resumen
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.