Takanobu Kawamura

Swelling behaviour of poly(butadiene) gels in liquid crystal solvents

The swelling behaviour of poly(butadiene) gels in four different nematogenic liquid crystalline (LC) solvents has been investigated as a function of temperature (T). Microscopy with crossed polarizers reveals that the nematic to isotropic phase transition temperature of the LC solvents inside the gels (TNI g) is slightly lower than that of the surrounding pure LC solvents (TNI o), but the degrees of depression in TNI g in each system are comparable regardless of the considerable differences in the degrees of equilibrium swelling (Q) at TNI g between the various systems. In general, Q in the isotropic phase is larger than that in the nematic phase, but a unique swelling behaviour of the gel is found in the vicinity of TNI due to the phase transition of the LC solvents. Q remains constant in the temperature range of TNI g ≤ T ≤ TNI o in which the phases of the LCs outside or inside the domain of the gels are different, namely, nematic and isotropic phase, respectively. In addition, a finite abrupt (discontinuous-like) change in Q is observed at around TNI. The gels swollen in the LCs, having an ability to interact with the crosslinking points via hydrogen bonding, show a significant thermal hysteresis for the temperature dependence of Q in the vicinity of TNI, while no discernible thermal hysteresis is observed for the gels in the LCs incapable of forming hydrogen bonds.

Biaxial Tensile Behavior of Rubber Vulcanizates: I. Silica and Gum Stocks

We have studied the strip biaxial tensile behavior of natural rubber vulcanizates filled with silica by the conventional milling method and by the in-situ silica filling method. The rapid increase of both stresses along the stretching and the fixed axes after the initial stretching was observed on samples filled with a conventional silica by the milling method. Low strain dependence of stresses in the successive strain regions was followed by the rapid increase of the stresses at the higher deformation region. On the other hand, we did not observe such behavior for the samples filled with silica generated in-situ in the rubber matrix before curing. The transmission electron microscopic measurements showed that a highly developed aggregated structure of silica particles was suggested in the conventional silica filled samples and just a simple aggregation was suggested in the case of the in-situ silica filled samples. The differences between samples reinforced with two different filling methods in low tensile region are mainly attributed to the aggregate structure of the silica particles dispersed in the rubbery matrix. We estimated the functional form of the strain energy density function for the samples filled with silica in intermediate and large deformation regions: W = C 10 (I 1 - 3) + C 01 (I 2 - 3) + C 20 (I 1 - 3) 2 The estimated W was found to reproduce the experimental stress-strain curves in intermediate and large deformation region. The relative contributions of three terms in the estimated W for the samples prepared by the in-situ method show the different dependence on the silica content from those of the samples containing silica mixed by the conventional method.

Characterization of molecular orientation under tensile deformation by near infrared spectroscopy

Abstract We present a novel method for characterizing orientation behavior of typical polyethylene (PE) materials such as HDPE, LLDPE, and LDPE. The chain orientation to the stretching direction was examined under uniaxial deformation by near infrared spectroscopy. Then we obtained directly the orientation function of PE chain axis (c-axis) from the CH stretching vibration of NIR spectra as a function of extension time or strain. We compared the present method with the conventional infrared IR method where the orientation function of PE c-axis (chain-axis) has been indirectly obtained from the b-and a-axis’s assuming the orthogonal crystal form by using the CH2 rocking vibrations in IR spectra

Influence of polymer morphology on photo-stability of polypropylene/SiO2 nanocomposites

Effect of polymer morphology on the photo-stability was studied for the nanocomposites of PP and SiO2. It was found from photo-degradation test that the composite without spherulite texture has less carbonyl group, indicating its higher photo-stability than that containing spherulites.