Boo Young Shin

Morphology and Rheology on the Blends of PLA/CMPS

The rheological behaviors and morphologies of polylactide (PLA) and chemically modified plasticized starch (CMPS) blends were investigated. For this study, oscillatory shear flow measurements of the PLA, CMPS and their blends were performed. A scanning electron microscope (SEM) study was also conducted on the extracted extrudates of the blends. The morphology of the blend changed in relation to the composition: sphere-shaped CMPS disperse/continuous PLA, rod-like deformed CMPS phase/continuous PLA, a co-continuous structure with bridged CMPS long rods and PLA dispersed/continuous CMPS. The composition of the phase inversion could be estimated and closely coincided from the observed morphology experimental results. The rheological behavior of the blends, from oscillatory measurements, was found to vary in relation to the composition, and reflected the morphologies of the blends. PLA showed Newtonian flow behavior, while CMPS showed strong shear thinning behavior. The relationships between the morphology and rheological properties were observed in detail.

Compatibilization of PLA/starch composite with electron beam irradiation in the presence of a reactive compatibilizer

The aim of this study is to improve the compatibility of poly (lactic acid) (PLA)/starch composite by electron beam irradiation in the presence of glycidyl methacrylate (GMA) as a reactive compatibilizer. Compatibilization process has been done by melt mixing the PLA/starch and GMA with a twin screw extruder and exposing the PLA/starch/GMA mixture to electron beam at room temperature. The exposure process was carried out to induce definite interfacial adhesion at the interface between PLA and starch through electron beam-initiated graft copolymerization by the medium of the GMA. To testify the effect of this compatibilization strategy, rheological, mechanical, and morphological properties of the composite were analyzed. The scanning electron micrographs of the cryofracture and tensile fracture surfaces of the composites revealed that the interfacial adhesion between PLA and starch was greatly improved by this strategy. Fourier transform infrared study confirmed the grafting reaction between PLA and starch. The reaction schemes were proposed to understand the reaction mechanisms at the interface.

Viscoelastic properties of PLA/PCL blends compatibilized with different methods

The aim of this study was to observe changes in the viscoelastic properties of PLA/PCL (80/20) blends produced using different compatibilization methods. Reactive extrusion and high-energy radiation methods were used for blend compatibilization. Storage and loss moduli, complex viscosity, transient stress relaxation modulus, and tan δ of blends were analyzed and blend morphologies were examined. All compatibilized PLA/PCL blends had smaller dispersed particle sizes than the non-compatibilized blend, and well compatibilized blends had finer morphologies than poorly compatibilized blends. Viscoelastic properties differentiated well compatibilized and poorly compatibilized blends. Well compatibilized blends had higher storage and loss moduli and complex viscosities than those calculated by the log-additive mixing rule due to strong interfacial adhesion, whereas poorly compatibilized blends showed negative deviations due to weak interfacial adhesion. Moreover, well compatibilized blends had much slower stress relaxation than poorly compatibilized blends and didn’t show tan δ plateau region caused by slippage at the interface between continuous and dispersed phases.