Effects of S/EB ratio on some properties of PLA/SEBS blends

Poly(lactic acid) (PLA)/styrene- b -(ethylene- co -butylene)- b -styrene (SEBS) blends were prepared by using two different SEBS polymers with different styrene to ethylene–butylene (S/EB) ratio. Polymer blends were prepared by high shear solution mixing and solvent-casted samples were compression moulded. PLA/SEBS blends with the ratio of 25/75, 50/50 and 75/25 were prepared and their morphological, mechanical, structural and thermal properties were evaluated. Scanning electron microscopy analysis showed that S/EB ratio was important in terms of morphology of the phase separation. While at lower S content, phase separation was mostly in the form of cylindrical channels, and at higher S ratio, copolymer dispersed in PLA in the form of random spherical particles and cylindrical channels. Although incorporation of SEBS led to decrease in tensile strength and increase in strain at break for both copolymers, higher S ratio resulted in higher strength and modulus. Thermal stability of PLA showed almost similar properties by addition of copolymers, regardless of the copolymer morphology. Fourier transform infrared spectroscopy and differential scanning calorimetry analyses showed the characteristic behaviour of the polymers. Blends did not show noticeable shift for glass transition temperature ( T g ) in terms of their SEBS component. However, T gPLA shifted to lower values and double peaks that are useful for understanding the melting behaviour of the system, turned into a single peak.