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Absh-act:The electrical conductivity of carbon black filled ethylene-vinyl acetate copolymer was measured as a function of carbon and vinyl acetate (VAc) content. For the composites whose matrices contain less than 32 wt % of VAc content, a sharp break point of the relation between carbon content and conductivity was observed. The conductivity jumps as much as ten orders of magnitude at the break point. The critical carbon content corresponding to the break point can essentially be predicted by our previous model. This model was derived under certain assumptions, the most important of which is that when the interfacial excess energy introduced by carbon particles into the polymer matrix reaches a "universal value", Ag*, the carbon particles begin to coagulate so as to avoid any further increase of energy and to form networks which facilitate electrical conduction. On the other hand, for the composites whose matrices contain more than 32 wt % of VAc content, a sharp break of the relation between the carbon content and conductivity cannot be observed and conductivity increases continuously with increasing VAc content. In this region of VAc content, carbon particles were dispersed well in the VAc rich matrices. This is because the presence of polar groups in a VAc component enhances its bonding to conductive fillers. In this case, the interfacial excess energy, Ag, seems to be the case Ag <_ 0. Better dispersibility of fillers in this region of VAc content can be shown from an electron micrograph (TEM).

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The effect on water on mechanical properties of collagen films has been studied. The S‐shaped sorption isotherm is separated into an adsorption curve C1 and a solution curve C2. From the C2 curve, a value of 0.8 is calculated for the Flory‐Huggins interaction parameter χ1. The dynamic shear modulus G′, loss modulus G″, and loss tangent tan δ determined as functions of water content indicate two dispersions at low and at high water content. The region of water content from about 0.05 to 0.1 g/g, G′ decreases suddenly, G″ has a peak, and tan δ increases, corresponds to the region where the C2 component of sorption becomes detectable. Another dispersion occurs at water contents above 0.2 g/g. A composite curve can be obtained by shifting stress‐relaxation curves obtained at different humidities along the log time axis. When only the C2 component of sorbed water is taken into account, the shift factor ac is explained by a relation of Fujita and Kishimotos' based on free‐volume theory. Shift factor for the relaxation curves of wool fibers, except for an initial part at times of less than 1 sec, are described by the same equation. The parameter β in the equation has the same value of 0.16 for both collagen and wool.

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