Physical Prop Research Articles

Polyurea RIM-A Versatile High Performance Material

Polyurethane elastomers were the first products to find wide commercial use in the RIM process. Recently, the advent of a new chain extender, diethyltolu enediamine (DETDA), provided another class of commercially useful RIM elas tomers. These materials are best classified as polyurethane/urea elastomers. We have been working on the next logical step in this evolution: amine- terminated polyether resins with amine chain extenders. These are best classi fied as polyurea elastomers. Amine-terminated polyether resins, or polyether polyamines, can replace the polyol in a RIM formulation. These materials are much more reactive than pol yols, and their composition can be varied more easily than conventional RIM polyols. Thus, these products can be tailored to meet the performance require ments of a particular end use more easily than polyols. The use of amine-terminated polyether products in RIM applications brings a new dimension to the RIM process. Depending on the choice of amine termi nated polyether amine, one can formulate systems covering a broad range of properties from elastomeric materials to rigid materials. Elastomeric materials are made by having a small amount of hard segment in a block-copolymer in conjunction with a polyether diamine. These elasto meric materials can be more closely tailored to meet a specific physical prop erty by either adjusting the formulation or by adjusting the density of the polymer. Very rigid materials can also be made by increasing the amount of hard seg ment in the block-copolymer in conjunction with a polyether triamine. High levels of an aromatic diamine chain extender can be used with the polyether triamine.

Book Reviews : Methods of Experimental Physics: Volume 16, Part A: Molecular Structure and Dynamics, Part B: Crystal Structure and Morphology, Part D: Physical Prop erties. R. A. Fava, Ed. Academic Press, New York. 1980. Pt. A, $55.00; Pt. B, $45.00; Pt. C. $59.00

Book Reviews : Methods of Experimental Physics: Volume 16, Part A: Molecular Structure and Dynamics, Part B: Crystal Structure and Morphology, Part D: Physical Prop erties. R. A. Fava, Ed. Academic Press, New York. 1980. Pt. A, $55.00; Pt. B, $45.00; Pt. C. $59.00

Electro-Chemical Treeing in Ethylene-Propylene Rubber Compounds

A series of Ethylene-Propylene Diene (EPDM) compounds, designed to be transparent or translucent in nature, were formulated for the purpose of studying electro-chemical treeing, Systems were tested in sheet form for evaluation of physical properties and crosslinking behavior, and extruded under laboratory conditions over 14 AWG bare copper wire into thin wall mini-cables. Cables were then subjected to the Phelps Dodge Accelerated Treeing Test. All EPDM systems exhibited electro-chemical tree formation to some extent; trees originated at the site of contaminants and at the conductor. Treeing patterns observed are of similar appearance to those formed in Polyethylene and Crosslinked Polyethylene insulation. The nature of the EPDM systems, preparation techniques, physical prop erties and treeing effects are discussed. Results indicated that electro- chemical treeing is a phenomenon characteristic of both rubbery and semi crystalline polymeric materials.

The Effect of Low Doses of Co60 Gamma Radiation on Some Physical Properties and the Structure of Wool Fibers

It has been found that small doses of gamma radiation (0.5-10 Mrad) produce marked effects on some physical prop erties of wool. These effects are not readily detected by mechanical strength measurements on fibers, but are revealed by changes in the behavior of the wool when it is converted to the supercontracted quasi-rubbery state by treatment with LiBr solution. Kinetic studies of the initial supercontraction reaction indicate that irradiation produces a marked reduction in the activation, energy and increases the rate of the reaction. There is also a trend for the initial contractile force to increase and for the equilibrium length contraction to decrease at the higher radiation dose levels. Stress-strain measurements on supercontracted wool show that doses as low as 0.5 Mrad greatly reduce the number of effective cross links in the rubbery network, the effect being similar to that produced by complete removal of the normal disulfide cross links in wool by chemical treatments. There is also evidence of the rebuilding of stable linkages as the radiation dose is increased over a limited range, before bond breakage predominates at the higher dose levels where changes in mechanical strength properties begin to become noticeable. Measurements of the swelling of wool in formic acid give similar evidence of bond breakage and rebuilding processes in wool as it is irradiated. The results indicate that even small doses of gamma radiation break sufficient covalent bonds to make the crosslinked heptide chain structure more susceptible to the action of swelling and disordering agents. These small radiation-induced changes can be expected to affect properties of wool significant in absorption and penetration processes, such as those involved in dyeing, chemical modification, and grafting treatments of wool.

Factors Influencing the Dyeing of Acetate Fibers With Disperse Nonionic Dyes

A basic understanding of any textile dyeing process is concerned with those factors , which influence the distribution of dye molecules between an external phase, primarily aqueous, and the fiber phase. An adequate description of the factors affecting the dyeing of acetate fibers with the disperse dye class must include: 1. a detailed description of the dyes in terms of their chemical and physical prop erties and their behavior in the aqueous and fiber phases, 2. the influence of the degree of acetylation of the cellulose upon the dyeing rate and affinity for the disperse dyes, 3. the relationship of specific dye structure tp dyeability and colorfastness on secondary and tricellulose acetate, and 4. a discussion of the mechanism of accelerant or carrier dyeing as applied to cel- . lulose triacetate. White the data presented do not rigorously support either the solution dyeing or the site dyeing hypothesis, sufficient empirical observations are presented which will increase the control and economy of dyeing with the disperse dyes.