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The mechanical properties of bio-absorbable plastics, which is used as a bon fixation, change in the body because the plastics is hydrolyzed under the body environment. Theoretical prediction of the bio-degradation process will be useful for the medical application of these materials. Thus, a simple analytical model to predict hydrolytic characteristics of polymeric materials is necessary. In this study, several samples of poly(lactic acid) with different initial molecular weights, crystallinity and sample sizes were immersed in a phosphate buffered solution and the changes in the molecular weight and crystallinity were investigated. Theoretical analyses on the variation of these properties were performed and the results were compared with the experimental data. It is clarified that the theoretical results have successfully predicted the bio-degradation process of poly(lactic acid).

The effects of hydrophilicity and charge of the fiber surface on the formation of closely packed colloidal crystals on the fiber was investigated. Surface-treated polyester fiber was dip-coated with water suspension of uniform-sized silica particles. Hexagonal and square arrangements were observed for the particles deposited on the fiber surface by scanning electron microscopy (SEM). The crystallinity of deposited particles was estimated with the number ratio of arranged particles to all particles in the SEM image. Colloidal crystal with mainly hexagonal arrangement was formed on the fiber with high wettability irradiated with oxygen plasma. The crystallinity was increased and the ratio of hexagonal arrangement in the crystalline region was decreased with increasing the wettability of the plasma treated fiber surface. Colloidal crystal with mainly square arrangement was formed on the fiber with cationic charge derived from the amino groups induced with a sol-gel method using 3-aminopropyltriethoxysilane (APS). Crystallinity was decreased and ratio of square arrangement in the crystalline region was decreased with increasing the amount of amino group accompanying with decreasing the wettability on the APS treated fiber surface. [ABSTRACT FROM AUTHOR]

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Two kinds of cast films, mix-PLA(DOX) film and mix-PLA(CHL) film, were prepared with an equal-weight mixture of poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) by using 1,4-dioxane (DOX) or chloroform (CHL) as casting solvent, and it is clarified that mix-PLA(DOX) films are opaque, whereas mix-PLA(CHL) films are transparent. The relation between the transparency of these mix-PLA films and their morphology was studied by wide-angle X-ray diffraction, differential scanning calorimetry, and small-angle X-ray scattering. It is shown that the transparency does not depend on the crystallinity of sc-PLA, but on the macrostructure of the stereo-complex composed of PLLA and PDLA, sc-PLA, which is reflected in crystal size, lamella thickness and long period and their distribution. The transparency is lowered as the macrostructure becomes more disturbed or disordered. Moreover, it is shown that mix-PLA(CHL) films have good transmittance comparable to that of poly(methyl methacrylate) or polycarbonate and better thermal-resistance. [ABSTRACT FROM AUTHOR]

TiO2 doped poly vinylidene fluoride (PVDF) sheets were prepared by a solvent casting process. Both PVDF and TiO2 powders were dissolved in N-N dimethylformamide (DMF) solution and then spin-coated onto the Si or glass substrate. The flexible TiO2 doped PVDF sheets are transparent and have PVDF II-type crystallinity. The TiO2 particles distribute in the PVDF sheet with cohesion. Photocatalytic pigment degradation was observed when the sheet was irradiated by UV-light. After 840 hours UV-light irradiation, a significant change in XRD patterns and FT-IR spectra of the TiO2 doped PVDF sheets was not observed, however, the sheets became cloudy because a sub-micrometer surface roughness was formed due to local photocatalytic decomposition of the PVDF structure. As a result, the photocatalytic rate of the pigment decreased because of UV-light scattering. [ABSTRACT FROM AUTHOR]

Porous alumina samples were prepared by the sol-gel process using aluminum tri-sec-butoxide in the presence of D-(+)-glucose, D-(-)-ribose, or sucrose. The crystallinity and porosity of the alumina samples obtained were controlled by changing the amount of the sugar added and the calcination temperature. The less crystalline alumina samples exhibited a higher ability of sugar adsorption and a higher catalytic activity for the formose reaction. These observations indicate that lattice defects act as strong base sites. [ABSTRACT FROM AUTHOR]

We have investigated effects of the crystallinity (φc) of linear low-density polyethylene (LLDPE) and Ni content (CNi) on the electrical properties [the resistivity at room temperature (ρL) and positive temperature coefficient (PTC) effect of resistivity] of the LLDPE/Ni conductive polymer composites. The effect on ρL and PTC varied depending on φc and CNi even for samples with the same LLDPE (having the same melting-point). ρL decreased with increasing φc and/or CNi. Ni particles are localized in the amorphous matrix of LLDPE, and form the conductive paths. We concluded that many conductive paths are formed by increasing φc and/or CNi because the connection of Ni particles becomes tighter with increasing φc and/or CNi. The inflection-point temperature of the PTC curve (transition temperature of the PTC effect) of composites are 30 to 60°C lower than the melting-point of LLDPE when the φc of LLDPE is low. We clarified that the PTC effect appears from only a small cubical expansion of LLDPE even without melting of LLDPE. [ABSTRACT FROM AUTHOR]

The almost degraded silk fibers show deformed infrared spectra compared with that of reference silk fibers. In this report, the polarized micro infrared spectroscopy was used to clarify the reason for the deformation of spectrum. Since the polarized light is sensitive to the change in the secondary structure of fibroin molecules, the change in the crystallinity and the peak intensity ratio of spectrum of degraded silk fibers were evaluated. At first, the axis of single silk fiber was set parallel to the polarized light of 90°, and the spectra was measured successively by changing the angle of diamond cell until the final position of 0°, namely perpendicular to the axis of single silk fiber. As a result of the experiments, it was found that the crystallinity increases with progress in degradation. Furthermore, the crystallinity is higher in the direction for 90° compared with that for 0°. Furthermore, the peak intensity ratio, Amide I / Amide II, was adopted as the measure of degradation. The measured value was generally higher compared with that of reference silk fibers. The correlation between the crystallinity and Amide I / Amide II ratio was also investigated. [ABSTRACT FROM AUTHOR]

We investigated the changes in the amorphous structure and the effects on the mechanical properties of crystalline polymers caused by extracting petroleum resin in polyolefin/petroleum resin blends. Polyolefin and petroleum resin are miscible in the melt state, and melting point depression was observed in the crystalline blends. Pores were not observed in spite of the extraction of the petroleum resin from the crystalline blends, suggesting that the petroleum resin was extracted from the amorphous phase within the crystalline lamellae. Young's modulus, yield stress and yield strain decreased with increasing the petroleum resin extracted from the crystalline blends. The change in the mechanical properties may be attributed to the changes in the entanglement density and tie molecules in the amorphous phase. [ABSTRACT FROM AUTHOR]