Fibrous Yarns Research Articles

Overlap Model for Chemical Vapor Infiltration of Fibrous Yarns

Attention is focused on fabrication of fiber‐reinforced ceramic composites by chemical vapor infiltration. A model is proposed for infiltration of a cylindrical fiber bundle, or yarn strand, comprised in turn of small cylindrical fibers. Along any cross section perpendicular to the yarn axis, the centers of the fibers are assumed to be randomly distributed throughout the cross‐sectional area without fiber overlap. As infiltration/densification proceeds, growth is assumed to occur via sequential deposition of uniform layers such that the fiber‐matrix composite consists of growing cylinders whose edges eventually overlap. Based on the random overlap model, expressions for key time‐dependent properties are developed for both the reaction‐limited case and for cases with significant diffusional limitations. An analytical solution to the resulting equations is obtained for the reactionlimited case whereas numerical solutions are required for the diffusion‐limited case. The effects of geometric, kinetic, and diffusional parameters on the infiltration dynamics are explored.

Graft copolymers of cellulose and vinylic ketones. I. Preparation of poly(methyl vinyl ketone)–cotton cellulose copolymers

The graft copolymerization reaction of methyl vinyl ketone from several solvents with fibrous cotton cellulose, preirradiated to a dosage of 5.2 × 1019 eV/g with γ-radiation from 60Co, was investigated. Solvents included water, methanol, N,N-dimethyl formamide, and several combinations of these solvents. From water a maximum yield of copolymer product was obtained after 2 hr at 25°C. The addition of methanol to aqueous solutions of methyl vinyl ketone, in all concentrations, inhibited the graft copolymerization reaction. The addition of a small amount of N,N-dimethylformamide to aqueous solutions of the monomer increased the rate of the copolymerization reaction; however, the addition of large amounts of N,N-dimethylformamide to these solutions also inhibited the reaction. From solutions of methanol or N,N-dimethylformamide and monomer, little or no copolymerization of monomer with irradiated cellulose occurred. The copolymer products exhibited a strong infrared absorption band at 5.85 μ which is characteristic of the CO group of the grafted poly(methyl vinyl ketone). Fibrous copolymer yarns exhibited increased yarn number and decreased breaking strength and average stiffness, as compared with unmodified cotton yarns.

Fibrous glass for electrical insulation

Development of fibrous glass yarn has provided a new insulating material that will withstand high operating temperatures for use in electrical machines