Thermal behavior of poly(lactic acid)-nanocomposite studied by near-infrared imaging based on roundtrip temperature scan.

The thermal behavior of poly(lactic acid) (PLA) was studied by near-infrared imaging to provide a molecular-level understanding of the physical improvement caused by nanoclay dispersion. A set of PLA samples, each having different nanoclay dispersion, was prepared under varying sonication time. Crystallinity variation of the polymer interacting with the nanoclay particles was analyzed by a roundtrip temperature scan below the melting temperature. Namely, the samples underwent heating and then cooling in the opposite way during the spectral measurement. The discrepancy of the spectral feature between the heating and the cooling indicated the development of the hysteresis associated with the cold crystallization of the PLA lamellae. The generation of the spectral residuals revealed the inner working mechanism of how the polymer structure undergoes variation depending on the presence of the clay particles and their dispersions. The sonication brings substantial dispersion of the nanoclay over the polymer matrix. The nanoclay particles then induce the additional development of the crystalline structure due to the molecular interaction between the PLA and nanoclay arising from the presence of enormous surface area, which in turn induces variation of mechanical strength to the polymer.

Measurement of speed of sound in poly(lactic acid)-clay composite.

We measured longitudinal speed of sound for matrix[poly(lactic acid)]-additive(clay particles) composite rectangular-solid specimen prepared by injection molding. It was found that the speed of sound measured in the direction along the longer side of the specimen was the highest at the middle of the specimen. This trend corresponded with that for crystallinity determined through differential scanning calorimetry (DSC). A cross section view of the specimen parallel to its longer side showed that there was a transverse flow trace of resin in the vicinity of the injection gate while the flow trace along the direction of the longer side spread wider as getting far from the gate toward the middle of the specimen. The high crystallinity appeared in the middle of the specimen was inferred to come from the promotion of crystallization by molecular orientation induced with the above flow trace parallel to the direction along the longer side of the specimen.

Determination of oxygen content in magnesium and its alloys by inert gas fusion-infrared absorptiometry.

A method for the determination of the oxygen content in magnesium and magnesium alloys has been developed. Inert gas fusion-infrared absorptiometry was modified by introducing a multistep heating process; a sample containing oxygen is fused with tin to form an eutectic mixture at 900°C in a graphite crucible, followed by a subsequent gradual temperature increase of up to 2000°C, which enables the evaporation of magnesium from the mixture, and subsequent solidification at the rim of the crucible. Residual tin including magnesium oxide remained at the bottom of the crucible. The oxygen in the tin is measured by a conventional inert gas fusion (IGF) method. From a comparison with the results of charged particle activation analysis, the IGF method is considered to be an attractive candidate for measuring the oxygen content in Mg and its alloys.