Yu-Ching Lai

The compatible and mechanical properties of biodegradable poly(Lactic Acid)/ethylene glycidyl methacrylate copolymer blends

The Fourier transform infrared results suggest that the carboxylic acid groups of poly(lactic acid) (PLA) molecules react with the epoxy groups of molecules of Ethylene Glycidyl Methacrylate Copolymer (EGMC) during the reactive extrusion processes of PLAxEGMCy specimens. The tensile and tear strength values of PLAxEGMCy blown-film specimens in machine and transverse directions improve significantly, and reach their maximal values as their EGMC contents approach an optimum value of 6 wt.%. The melt shear viscosity values of PLAxEGMCy resins, measured at varying shear rates, are significantly higher than those of the PLA resin, and increase consistently with their EGMC contents. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) of PLA and PLAxEGMCy specimens reveal that the percentage crystallinity, peak melting temperature, and onset re-crystallization temperature values of PLAxEGMCy specimens reduce gradually as their EGMC contents increase. In contrast, the glass transition temperatures of PLAxEGMCy specimens increase gradually in conjunction with their EGMC contents. Demarcated porous morphology with several connected fungi-decomposed cavities was found on the surfaces of the PLAxEGMCy specimens after being buried for specific amounts of time, in which the sizes of the fungi-decomposed cavities found on the surfaces of buried PLAxEGMCy specimens reduce significantly as their EGMC contents increase. Further DMA and morphological analysis of PLAxEGMCy specimens reveal that the EGMC molecules are compatible with PLA molecules at EGMC contents equal to or less than 2 wt.% because no phase-separated EGMC droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLAxEGMCy specimens, respectively. The possible reasons for these remarkable properties of the PLA/EGMC specimens are proposed in this study.

Structures and Mechanical Properties of Polyurethane/Clay Composites Prepared by Different Pre-mixing Procedures

A novel method for preparing polyurethane/nano-clay composites was used in this study. The nano-clay was pre-mixed with the various components, such as diphenylmethane diisocyanate (MDI), 2,2-bis(hydroxymethyl) propionic acid (DMPA) or polytetramethyleneglycol (PTMG), of polyurethane (PU) polymer to prepare the composites. The PU/clay composites prepared by this method revealed that the values of the tensile strength at break, the elongation at break, the modulus and the surface roughness for the composite prepared from the pre-mixture of clay and PTMG (PU/clay-PTMG composite) were higher than those for the composite prepared from the pre-mixture of clay and MDI (PU/clay-MDI composite), the composite prepared from the pre-mixture of clay and DMPA (PU/clay-DMPA composite) and PU. The thickness of the crystals for PU/clay-MDI and PU/clay-DMPA composites was larger than that for PU and PU/clay-PTMG; whereas the layer distance of the crystals for PU/clay-MDI and PU/clay-DMPA composites was smaller than those for PU and PU/clay-PTMG. The values of glass transition temperature (Tg) of soft and hard segments were in the order of PU/clay-MDI > PU/clay-DMPA > PU > PU/clay-PTMG. Among the three PU/clay composites prepared by the pre-mixing procedure, PU/clay-MDI and PU/clay-DMPA composites showed significant gathering of the nano-clay in the PU matrix. A possible mechanism of the structural changes under tensile stress was speculated to explain the reason for the higher tensile strength and elongation at break of PU/clay-PTMG composite. The pre-mixing of clay-PTMG was a good procedure for the manufacture of the PU/clay composite, which had higher values of tensile strength and elongation at break.