Dentin collagen is a major component of the hybrid layer, and its stability may have a great impact on the properties of adhesive interfaces. We tested the hypothesis that the use of tannic acid (TA), a collagen cross-linking agent, may affect the mechanical properties and stability of the dentin matrix. The present study evaluated the effects of different concentrations of TA on the modulus of elasticity and enzymatic degradation of dentin matrix. Hence, the effect of TA pre-treatment on resin-dentin bond strength was assessed with the use of two bonding systems. Sound human molars were used and prepared according to each experimental design. The use of TA affected the properties of demineralized dentin by increasing its stiffness. TA treatment inhi bited the effect of collagenase digestion on dentin matrix, particularly for 10%TA and 20%TA. The TA-dentin matrix complex resulted in improved bond strength for both adhesive systems.

ABSTRACT:High strength polyethylene fiber (Toyobo, Dyneema® fiber: hereinafter abbreviated to DF) has a negative thermal expansion coefficient. Relation between fiber structure and thermal strain of DF used as reinforcement of DF reinforced plastic (DFRP) for cryogenic use was investigated. The crystallinities and orientation angles of several kinds of polyethylene fibers having different modulus from 15 to 134Gpa (herein after abbreviated to DFs) were measured by NMR and X-ray. We obtained the parameters of the mechanical series-parallel model composed of crystal and amorphous by crystallinity and modulus. Thermal expansion coefficients of DFs were estimated by mechanical seriesparallel model. All DFs having different modulus showed negative thermal expansion coefficients in the temperature range from 180 to 300K, and absolute values of those markedly increased by increasing tensile modulus of DF. The estimated thermal expansion coefficients showed negative values, and thermal strains showed a similar curve to observed ones mostly. Average thermal expansion coefficients in the temperature range from 180 to 300K estimated by mechanical model agreed with the observed ones.

High strength polyethylene fiber (Toyobo, Dyneema 1 fiber, hereinafter abbreviated to DF) used as reinforcement of fiber-reinforced plastics for cryogenic use has a high thermal conductivity. To understand the thermal conductivity of DF, the relation between fiber structure and thermal conductivity of several kinds of polyethylene fibers having different modulus from 15 to 134 GPa (hereinafter abbreviated to DFs) was investigated. The mechanical series-parallel model composed of crystal and amorphous was applied to DFs for thermal conductivity. This mechanical model was obtained by crystallinity and crystal orientation angle measured by solid state NMR and X-ray. Thermal conductivity of DF in fiber direction was dominated by that of the continuous crystal region. The thermal conductivity of the continuous crystal part estimated by the mechanical model increases from 16 to 900 mw/cmK by the increasing temperature from 10 to 150K, and thermal diffusivity of the continuous crystal part was estimated to about 100 mm 2 /s, which is almost temperature independent. The phonon mean free path of the continuous crystal region of DF obtained by thermal diffusivity is almost temperature independent and its value about 200 Å . With the aforementioned, the mechanical series-parallel model composed of crystal and amorphous regions could be applied to DFs for thermal conductivity. V V C 2005 Wiley Periodicals, Inc.

ABSTRACT:To understand the influence on the thermal conductivity by the length of the molecular chain in the polymer fiber, the thermal conductivity and thermal diffusivity of ramie fibers and those irradiated by ␥ rays, which induced molecular chain scission of cellulose, were investigated in a range of low temperatures. The degrees of polymerization, crystallinities, and orientation angles of ramie fibers and those irradiated by ␥ rays (␥-ray treatment) were measured by the solution viscosity method, solid-state NMR, and X-ray diffraction. Only the degree of polymerization decreased with the ␥-ray treatment, and the crystallinities and orientation angles were almost independent of the ␥-ray treatment. The thermal conductivities of the ramie fibers with and without ␥-ray treatments decreased with decreasing temperature. The thermal diffusivities of the ramie fibers and those irradiated by ␥ rays were almost constant from 250 to 100 K, increased slightly with the temperature decreasing from 100 to 50 K, and increased rapidly with the temperature decreasing below 50 K. The thermal conductivity and thermal diffusivity of the ramie fibers decreased with the ␥-ray treatment. The mean free path of the phonon in the ramie fibers was reduced by the ␥-ray treatment. This decrease of the thermal diffusivity and thermal conductivity was explained by the reduction of the mean free path of the phonon by molecular chain scission with ␥ rays.