3. Results and discussion
3.1. Tensile strength and tensile-fractured surface morphology
Brittle fracture occurred for pure PLA and LBT-0 specimens
while stress whitening and necking phenomena (Fig. 1) were observed for all compatibilized blends samples during the cold drawing, the tensile strength showed a great dependance of TBT
concentration (Fig. 2). The pure PLA specimens give high tensile
strength of 58.4 MPa but low elongation at break of 2.3%. Since
PBAT has a low tensile strength (11.6 MPa) but a far higher elongation at break (811%) than pure PLA, the uncompatibilized PLA/PBAT
simple blends displays a substantial reduction by 39.7% in tensile
strength while a tremendous increase by almost twentyfold in
elongation at break. It should point out that the obtained value
of elongation at break is far lower than that reported in the previous study[8], which might be contributed to the different composition of the PLA matrix used. Zhang et al.[8] reported that the
elongation of the PLA/PBAT blend was tremendously increased
(>200%) even at 5% of PBAT and continuously increased with the
increasing in PBAT content. Dramatic improvement of elongation
at break is obtained for the compatibilized PLA/PBAT blends even
at 0.1% TBT incorporation, and the elongation at break increases
sustainedly with the further TBT loading level, and gives the values
of 298% in the case of 0.5% TBT loading. Similar ultimate strain was
also obtained for PLA/PCL blends using isocyannates-lysine
triisocyanate (LTI)[7]and dicumyl peroxide (DCP)[16]as reactive
processing agents. Previous study by Harada et al.[6]reported that
the ultimate strain in the presence of LTI was 270% higher than that
in the absence of LTI, and the maximum tensile strength gradually
decreased with the addition of LTI. Another work by Semba et al.
[16] also reported a significant increase of the ultimate tensile
strain at low DCP concentration, and yield point and ductile behavior under tensile test were observed for the PLA/PBAT blends with
low DCP contents. Nevertheless, the addition of the above reactive
processing agents into PLA/PBAT blends has improved the elongation but at the expense of the maximum tensile strength. In this
study, The tensile strength of the blends is enhanced by the incorporation of TBT albeit it is still lower than that of pure PLA. This
improvement might be attributed to the strong interaction produced by the occurrence of the transesterification between PLA
and PBAT in the presence of TBT during the melt compounding.
The tensile-fractured surface was observed using SEM, and the
corresponding micrographs are shown inFig. 3(bright particles
are PBAT). As compared to an apparent brittle surface for the
uncompatibilized PLA/PBAT blend, LBT-0.1 displays some coarse
surfaces in which some stubbly fibers are observed (Fig. 3b). By
contrast, the smooth surface disappears and a thoroughly rough
surface with threadlike fibers occurs for LBT-0.5 (Fig. 3c). This phenomena indicates that the interfacial adhesion between PLA and
PBAT be enhanced after the incorporation of TBT. Previous study
[13] have demonstrated that the PLA-g-PBAT copolymers are
formed through transesterification in the presence of TBT. Coltelli