Tomoyuki Yamamoto

Oxygen permeability and free volume hole size in ethylene-vinyl alcohol copolymer film: temperature and humidity dependence

Abstract Relationship between oxygen permeability and free volume hole size evaluated from ortho -positronium lifetime in ethylene–vinyl alcohol copolymer (EVOH) was studied as functions of temperature and relative humidity. As the relative humidity rises at room temperature, the permeability first decreases and then increases. This behavior is attributed to the effects of pore filling and plasticization by water molecules. Linear correlations are obtained on the plots of logarithmic permeability versus reciprocal free volume hole size for EVOH at different temperatures and humidities as well as for different polymers including EVOH at room temperature, suggesting that the free volume hole size plays a crucial role in the oxygen permeation in EVOH and other polymers.

Structure and orientational behaviour of polyurethane containing polydimethylsiloxane

Abstract The structure and orientational behaviour of polyurethanes containing polydimethylsiloxane in the main chain was investigated by means of infrared dichroism, small angle light scattering and differential scanning calorimetry. It was found that the introduction of polydimethylsiloxane in the main chain reduced the crystallization capability of the soft segments. Hard and soft segments are oriented positively on uniaxial stretching. The orientational behaviour of the hard segments is different from that for most segmented polyurethanes and poly(urethaneurea)s, in which hard segments show negative orientation at low elongation. The difference in orientational behaviour is discussed in terms of the capability of self-cohesion of hard segments.

Bulk and surface characterization of cellulose/poly(vinyl alcohol) blends by Fourier-transform infra-red spectroscopy

Abstract The miscibility and surface selectivity of cellulose/poly(vinyl alcohol) (PVA) blends were investigated by Fourier-transform infra-red ( FT i.r.) and attenuated total reflection ( FT i.r.-a.t.r.) spectroscopy. The blends were prepared in film form by casting mixed polymer solutions in a common solvent (dimethylsulphoxide-tetraethylammonium chloride) onto a glass plate and successively coagulating the solutions with ethanol. The dried films were optically clear irrespective of blend composition. The transmission FT i.r. measurements revealed that the crystallinity of each polymer component decreased with increasing content of the blending partner. These findings strongly suggest a certain level of miscibility of cellulose and PVA. The compositions of the film surfaces on the glass (substrate) side and the ethanol (coagulant) side were also examined by FT i.r.-a.t.r. via two methods: (1) a method using the ratio of the integrated area of an absorption peak centred at 897 cm −1 (cellulose) to that of a peak centred at 918 cm −1 (PVA); and (2) a least-squares curve-fitting method in the range 850 to 1200 cm −1 . The results obtained by both these methods lead to the conclusion that the concentration of PVA was higher than that of cellulose at the glass-side surface, whereas no selectivity was detected at the ethanol-side surface.

Free-volume study of ethylene - vinyl alcohol copolymer evaluated through positronium lifetime measurement

The free-volume, of size ranging from 0.2 to 0.4 nm in radius, in an ethylene-vinyl alcohol copolymer was estimated using positronium lifetime measurement to elucidate the dependence of oxygen permeability on the free-volume size and fraction, on the ethylene content and on the crystallinity. The permeability and the free-volume fraction with varying the ethylene content were well related and the relation was interpreted based on the free-volume theory near below and above the glass transition temperature. On the other hand, the crystallinity significantly influenced the fraction of the amorphous region, where the free-volume hole exists, along with a slight change of the free-volume size. The variation of the permeability with the crystalline degree cannot be explained from the averaged free-volume fraction estimated by the whole volume of the polymer, but the permeability correlated with the free-volume size apparently.