LIMA, J. C. C.; http://lattes.cnpq.br/0844586949765669; LIMA, Jéssica Camilla da Costa.
Résumé:
In order to overcome certain limitations of poly (lactic acid) (PLA) biopolymer, the
same was modified with poly (styrene / ethylene-butylene / styrene)(SEBS)
copolymer, and the effect of different content of this copolymer on the properties of
the blends, before and after heat treatment, was evaluated. The blends containing
5, 10, 15 and 20 wt% of SEBS were prepared by extrusion followed by injection
molding and characterized by rheological measurements, X-ray diffraction (XRD)
Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry
(DSC), dynamic mechanical thermal analysis (DMTA) and heat deflection
temperature (HDT). The results of torque rheometry indicated that the blends
exhibited increased stability compared to pure PLA. At low frequencies (oscillation
rheometer) PLA and PLA / SEBS blends containing 5 and 10% of SEBS exhibited a
Newtonian fluid behavior, and the blends containing 15 and 20% SEBS showed a
shear thinning behavior. It was also observed the presence two distinct arcs for all
blends, indicating that the SEBS and PLA phases are immiscible. It was also
observed that in the PLA / SEBS blends containing 15 and 20% SEBS, there is a
change in the slope of the curves. This change indicates that they begin to present
a pseudo-solid behavior. In the XRD patterns of the samples subjected to
annealing heat treatment a well-defined intense peak was observed for PLA
indicating its considerable crystallinity in the samples. The FTIR analysis pointed
out, by the presence of characteristic bands, that the PLA presented higher
crystallinity after the annealing heat treatment. The annealed samples showed
higher HDT values. There was a balance of mechanical properties, wherein the
elastic modulus and the tensile strength proved to be inversely proportional to the
content of the copolymer, while the elongation and tenacity were directly
proportional to this content. The addition of the copolymer caused a significant
increase in the impact strength for samples with and withoutheat treatment. The
SEM results showed that when the SEBS copolymer content was increased, an
increase in the average particle size of SEBS dispersed phase was observed,
probably due to the occurrence of coalescence. SEM results for samples after heat
treatment showed a decrease in average size of dispersed particles of SEBS,
which affected the mechanical properties. The blend studied in this paper
presented very attractive properties, and contains small amounts of the synthetic
9 copolymer. The developed material comes, in its most proportion, from renewable
sources, thus contributing to the environment.
