Abstract
A poly(styrene-ran-methyl acrylate) (S-MA) (75/25 mol/mol), synthesized by surfactant-free emulsion copolymerization, was used as a compatibilizer for polystyrene-b-polybutadiene-b-polystyrene (SBS)-toughened polylactide (PLA) blends. Upon compatibilization, the blends exhibited a refined dispersed-phase morphology, a decreased crystallinity with an increase in their amorphous interphase, improved thermal stability possibly from the thicker, stronger interfaces insusceptible to thermal energy, a convergence of the maximum decomposition-rate temperatures, enhanced magnitude of complex viscosity, dynamic storage and loss moduli, a reduced ramification degree in the high-frequency terminal region of the Han plot, and an increased semicircle radius in the Cole–Cole plot due to the prolonged chain segmental relaxation times from increases in the thickness and chain entanglement degree of the interphase. When increasing the S-MA content from 0 to 3.0 wt %, the tensile properties of the blends improved considerably until 1.0 wt %, above which they then increased insignificantly, whereas the impact strength was maximized at an optimum S-MA content of ~1.0 wt %, hypothetically due to balanced effects of the medium-size SBS particles on the stabilization of preexisting crazes and the initiation of new crazes in the PLA matrix. These observations confirm that S-MA, a random copolymer first synthesized in our laboratory, acted as an effective compatibilizer for the PLA/SBS blends.
Highlights
Polylactide (PLA) has been extensively used in biomedical applications and plastics industry because it has many golden properties, such as degradability, biocompatibility, renewability, good mechanical properties [1,2,3]
The SBS dispersed phases appeared in the images as dark holes and bright spheroids, especially in the magnified images b, d, f, and h of images a, c, e, and g respectively, which was probably due to the “pull-out from the PLA matrix” and “break within the SBS phase itself” effects during the impact fracture of the specimens
SEM indicated that the impact-fractured surfaces of S-MA-compatibilized PLA/SBS blends displayed a more homogeneous, refined SBS dispersed-phase morphology than those of the uncompatibilized PLA/SBS blends
Summary
Polylactide (PLA) has been extensively used in biomedical applications and plastics industry because it has many golden properties, such as degradability, biocompatibility, renewability, good mechanical properties [1,2,3]. Polymers 2019, 11, 846 ethylene-vinyl acetate copolymer [12], poly(butylene succinate) (PBS) [13,14], high-density polyethylene (HDPE) [15], natural rubber [16], poly(ethylene oxide) [17], high-impact polystyrene (HIPS) [18], hydrogenated SBS [19], is an effective and economical approach to the improvement of the impact strength of PLA. Some researchers have used chemical methods to modify the polymer toughening agents of PLA, producing epoxidized PBD [4], glycidyl methacrylate (GMA)-grafted POE [7], PLA-b-PBS-b-PLA [14], PLA-b-polyethylene-b-PLA [20], etc. Ding et al [8] used PLA-poly(ethylene glycol)-PLA triblock copolymer as a compatibilizer to modify PLA/PBAT blends. Sikka et al [21] used poly(styrene-ran-methyl methacrylate) copolymers (S-MMAs) to modify a polystyrene (PS)/poly(methyl methacrylate) (PMMA) laminate interface; they found that the PS/PMMA modified with the
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