Yukuo Nanzai

Decrease in bone strength of cadmium-treated young and old rats

A decrease in mechanical strength of bones was observed both in young and old rats for long periods of administration of cadmium. Young (3-week-old) female rats were given 0 (control), 5 and 10 ppm cadmium in drinking water, respectively, for 20 weeks. Old (18-month old) female rats were given 0 (control) and 40 ppm cadmium in drinking water, respectively, for 7 months. The compression strengths of bones of young rats which were given 10 ppm cadmium, and those of old rats which were given 40 ppm cadmium, significantly decreased at the distal end portion of femur. Cadmium contents in bones in the 10 ppm and 40 ppm groups were about 110 and 210 ng/g dry weight, respectively. The present result confirmed that cadmium has a lesional effect on the mechanical strength of bone at the concentration of 100–200 ng/g in dry weight of bone, for both young and old rats.

Decrease in the mechanical strength of bones of rats administered cadmium

The mechanical properties of the bones of young, adult and old rats administered various concentrations of cadmium were measured to prove the direct effect of cadmium on the bones of young rats. The young rats were divided into three subgroups, which were administered 0 (control), 5 and 10 ppm cadmium, respectively. The adult rats were subdivided into six groups, administered 0, 10, 20, 40, 80 and 160 ppm cadmium, respectively. The old rats were divided into three subgroups, which were administered 0, 80, and 160 ppm cadmium, respectively. The length of the administration was 4 weeks in every group. The decrease in the mechanical strengths of bones of young rats administered with cadmium was observed. On the other hand, no change in mechanical strength of bones was observed in the case of adult and old rats, administered up to 160 ppm cadmium. The correlation between the cadmium in bones and the decrease in the strength of the bone shows that cadmium directly affects the mechanical properties of bones of young rats.

Strain-induced liquid-like structures in glassy polymers

Abstract Experimental evidence verifying strain-induced isothermal structural transition of glassy polymers into liquid-like structures is presented for five amorphous polymers: polymethyl methacrylate, polystyrene, polycarbonate, polyvinyl chloride and styrene-acrylonitrile co-polymer. This transition presumably accelerates the relaxation and results in the non-linear viscoelasticity in glassy polymers. The evidence was derived by an application of the Eyring equation to the steady state of plastic flow in the polymers. In this analysis, a novel method of applying the Eyring equation was used, which provided numerical values of the activation enthalpy, ΔH , activation entropy, ΔS , and activation volume, v a , for each polymer as variables depending on strain-rate and temperature. Comparison of a unique functional relation between the rate factors ΔH and ΔS for the glass with a relation of ΔH vs. ΔS derived from the relaxation or dynamic viscoelastic data of the melt showed a good agreement for each polymer. Since the rate factors ΔH and ΔS are governed in quantity by the intermolecular interaction in the polymer system, this agreement led to a verification of the structural change of glassy polymers into liquid-like structures.

Decrease in compressive strength of the femoral bone in rats administered stannous chloride for a short period

Abstract The compressive strength of the entire femur of each rat, which was administered 0, 50, 150, 300, or 600 ppm of tin in the form of stannous chloride in drinking water, and commercial laboratory chow (contaminated with 52.4 ppm of tin) for 4 weeks, was measured in an Instron machine. The distal epiphysial compressive strength decreased significantly in the groups administered more than 300 ppm of tin. The present study demonstrates that inorganic tin has a toxic effect on the bone and suggests that the safe levels of tin is much lower than ever reported.

Variation of dynamic viscoelasticity during yielding and post-yield relaxation in a glassy polymer

Abstract A key factor causing the non-linear viscoelastic behaviors in largely deformed glassy polymers has been considered to be shear-induced structural change. To obtain further information on the molecular kinetics of the structural change, the dynamic viscoelastic properties of glassy polymethyl methacrylate were measured during its uniaxial elongation and subsequent relaxation processes. The dynamic data obtained in the yielding process showed that the structure of the quasi-equilibrium glass was successively changed into another stable one exhibiting much faster stress relaxation. in the post-yield relaxation process, on the other hand, the dynamic properties gradually reverted with time, presumably indicating structural recovery in the glass. Furthermore, some hardening mechanism was directly observed in a fully stress-relaxed state of the largely deformed glass.

Highly cooperative relaxation in glassy styrene-acrylonitrile copolymer induced by large deformation

Abstract Experimental data showing highly cooperative α-relaxation behavior at temperatures below the glass transition temperature, T g are presented for styrene-acrylonitrile copolymer. The highly cooperative α-relaxation kinetics, being otherwise latent at temperatures below T g , is probably activated to reveal itself in the state of steady plastic flow in the copolymer with the aid of high shear stress.

Study on nonlinear deformation mechanism in epoxy glass using birefringence

Two types of samples were prepared from the same epoxy precursor; one was cured with 4,4′-DDM to form a cross-linked molecular structure and the other was polymerized by aniline to form a linear molecular structure. After it was shown that the modified stress–optical rule is valid for the birefringence data of the samples, birefringence change was monitored during uniaxial elongation in the glassy state as well as in the rubbery state. The results were analyzed within the context of modified stress–optical rule to investigate the plastic deformation of epoxy glass. For the linear sample, rubbery stress increased after a yield point, while glassy stress remained almost constant. On the other hand, for the cross-linked sample, rubbery stress increased cooperatively with glassy stress from the beginning of elongation, and such cooperative increase in stresses continued after the strain passing an upper yield point.

Anisotropic structural evolution in poly(methyl methacrylate) aged under inelastic strain

Cylindrical specimens of fully annealed poly(methyl methacrylate) (PMMA) were simply sheared by twisting, up to an inelastic strain and left under the sheared condition for various periods. Subsequently, the specimens were sheared by twisting in the same direction or opposite to that of the inelastic pre-strain. The elastic modulus and yield stress for the aged specimens evaluated by twisting them in the same direction with the pre-strain increased monotonously with aging time, and their values were significantly higher than those of fully annealed specimens. Yet, when the specimens were twisted in the opposite direction to the pre-strain, their modulus and yield stress decreased with increasing time of aging at short aging time, and subsequently increased at long aging times. These results revealed a specific anisotropic structural evolution in PMMA aged under inelastic strain.

Dynamic Viscoelasticity of Ultrahigh-Molecular-Weight Polyethylene After Ethylene Oxide Gas or Gamma-Irradiated Sterilization

The static tensile test and dynamic viscoelastic measurement were carried out on samples of ultrahigh-molecular-weight polyethylene (UHMWPE) that were unsterilized, 2.5 Mrad gamma-irradiation sterilized in air, and ethylene oxide gas (EOG)-sterilized. The dynamic viscoelastic measurement was conducted over a temperature range of —150°C to 350°C using a dynamic mechanical spectrometer in tensile mode on a sample at an amplitude of 10 ltm, at a frequency of 0.5, 1, 2, 5, and 10 Hz. There were no significant differences among the static tensile data of the three types of samples, while there were some noticeable results with regard to the dynamic viscoelastic measurement. The value of loss tangent for the EOG sterilization samples was greater than those of the other samples over a temperature range from 100°C to 50°C. This indicates that the EOG molecules diffused into the UHMWPE. The value of loss tangent for the gamma-irradiated samples was less than those for the other samples at temperatures above the melting point. This indicates that some crosslinked structure may have taken place in the crystalline region. The loss tangent of the gamma-irradiated sample was influenced by strain frequency more significantly than those for the other samples at temperatures above the melting point. This indicates the presence of various crosslinked chains which reflect various relaxation time.

An extension of compensation effect for zero shear melt viscosity to non-newtonian flow in glassy polymers

Abstract The structural parameters in the Arrhenius equation of zero-shear viscosity for various equilibrium polymer melts were compared with those obtained from the non-Newtonian viscosity for non-equilibrium flowing glasses of the same polymers. The comparison led us to the conclusion that the linear equation between the structural parameters (which is called compensation effect) for zero-shear melt viscosity holds also for the non-Newtonian flow in glassy polymers. The shear rate dependence of viscosity in polymer liquids was calculated using the extended linear equation of the structural parameters. Based on the calculation we suggest that the shear thinning behavior at higher shear rates is also possible due solely to the structural change independent of the disentanglement or scission of polymer chains.