The tensile strength and inter-laminar shear strength of carbon fiber-resin composites comprised of matrix resins of different tensile moduli ranging from 4.74MN/m² to 1170MN/m² were measured, and the effect of matrix resin properties on the effective tensile strength of carbon fibers in carbon fiber-resin composite strands was investigated. The inter-laminar shear strength changed in the range from 13.3MN/m² to 98.8MN/m² in correspondence with the tensile modulus of matrix resin. It was observed that the inter-laminar shear fracture occurred at the interface between fiber and resin when the matrix resin was sufficiently stiff. On the other hand, when the stiffness of the matrix resin was low, the inter-laminar shear fracture occurred in the matrix resin. The effective fiber strength in the composite strands varied in the range from 1.78GN/m² to 2.94GN/m², and it tended to increase with increasing tensile modulus of matrix resin. From the results of the observation of fracture surface, the fracture mechanism of the composite strands was considered in relation with the matrix resin properties. When the matrix resin is stiff enough, the effective fiber strength of the composite strands depends on the strength at the interface between fiber and resin. In contrast, when the matrix resin becomes soft, the effective fiber strength is governed by the shear modulus of matrix resin.

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Tubes of high density polyethylene were drawn with a conical mandrel. The changes of the draw ratios on the mandrel in the longitudinal direction of the tubes (the machine direction, MD) and in the hoop direction (the transverse direction, TD) were measured. The change of the draw ratio in the TD, λ₂, is almost completely determined by the diameter and shape of the mandrel. At the early stage of mandrel drawing, the draw ratio in the MD, λ₁, decreased with increasing λ₂ and then suddenly began to increase. Namely, dλ₁/dλ₂ was negative at first, and then it became positive. In almost all regions of dλ₁/dλ₂>0, d²λ₁/dλ₂² was negative.

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The biaxial stretching mode of thin-walled plastic tube over a conical mandrel was discussed by using a hypothetical stress-draw ratio relation. The results of these calculations show that, when the change of stress in the longitudinal direction (the machine direction, MD) after the yielding point is small, the draw ratio in the MD, λ₁, increases abruptly immediately after the yielding point of the tube in the MD. These results support the conclusions of the previous paper¹⁾.

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Polyethylene terephthalate copolymers were prepared by substitutions with adipic acid up to 30 mol% for the purpose of producing processable polyester fibers easily weight-reduced by alkali.
Melting temperature, glass transition temperature and cold crystallization temperature measured by DTA for the melt-quenched samples decreased with increasing comonomer (adipic acid) content. Density and crystallinity of the hot-pressed films increased with increasing comonomer content. As the comonomer content increased, the rate constant of dissolution of the copolymer measured by hydrolysis in 10% NaOH aqueous solution at 80°C increased up to the comonomer content of 5 mol%, decreased up to 10 mol%, and then increased up to 30 mol%. This irregular change was also observed for the rate constant of disperse dye absorption measured by dyeing at 80°C. By the copolymerization, the tensile elongation of the hot-pressed films decreased for the copolymers with the comonomer content of 5 and 10 mol% and increased remarkably for that with 30 mol% as compared with polyethylene terephthalate. Heat resistance estimated by TG was little affected by the copolymerization.

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In the previous paper we reported that the rate constant of dissolution by alkali hydrolysis of polyethylene terephthalate copolymers prepared by substitutions with adipic acid up to 30 mol% increased with increasing comonomer content up to 5 mol%, decreased up to 10 mol%, and then increased up to 30 mol%.
It was found in this study that the irregular change of the rate constant mentioned above was intensified by increasing the alkali concentration from 2% to 20%, and by increasing the temperature from 60°C to 90°C. The apparent activation energy for the dissolution decreased with increasing comonomer content up to 10 mol% and then increased up to 30 mol%.

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Nylon 6 was dyed in aqueous solution of p-aminoazobenzene (pAAB) at temperatures ranging from 51°C to 99°C and pressures up to 2.5 kbar. The adsorption isotherms were found to be linear under the pressures and the partition coefficient K increased with increasing pressure. The pressure dependence of K was analysed and discussed in terms of ΔV° as obtained by where R, T and P are the gas constant, the absolute temperature and the pressure, respectively, and ΔV° is the difference in the partial molar volumes of pAAB in solution and in the amorphous phase of nylon 6. ΔV° was found to be independent of temperature within the experimental error, the average value being -5.5cm³/mol. Referring to the reported data on ΔV°, the above result suggests that the pAAB molecule was adsorbed on nylon 6 by a force corresponding to “1.5 hydrogen bonds”.

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