Acrylic fibers tensile properties

We presently report on a broad search for specific acrylic carbon fiber precursors, which should be stabilized in short time (less than one hour), and yet would give carbon fibers with satisfactory tensile properties. In planning the chemistry of such precursors, it was necessary to take into account the chemical reactions and physical processes going on during the heat treatment. 

The abrasion resistance of cellulose acetate is lower compared with that of other fibers. Abrasion resistance was measured by the wet-flex abrasion determined with the Stoll Abrasion Tester. Abrasion resistance of several fibers was rated in the following decreasing order nylon, polyester fiber, acrylic fiber, wool, cotton, viscose rayon, and acetate. It was suggested that the abrasion resistance of fabrics is related to the strength and the recovery properties of fibers. The fact that acetate is not a particularly strong fiber probably accounts in part for its inferior abrasion resistance. Heat-treated cellulose triacetate fabrics have both higher tensile strength and abrasion resistance than secondary acetate fabrics for the conditions of dry, wet, and hot wet (80°C) [53,63]. 

PAN by use of gel-spinning or other techniques to create a completely extended chain. Their estimate, based on a comparison of the rod-like PAN conformation with helical chain conformations of other polymers, is that the maximum tensile modulus of atactic PAN would be about 55 GPa. They conclude that PAN with ultrahigh modulus cannot be made by gel spinning, or by any other means, due to the intrinsic chain properties. It is proposed that the strong intramolecular nitrile repulsions that cause the PAN to adopt a rod-like, semiextended conformation do not allow the chain to unravel completely from its semiex-tended conformation. Attempts to develop gel-spinning processes in acrylic fibers are discussed in Section 12.5.4. 

The sustained commercial success of acrylic fibers over the past 50 years can be attributed largely to their desirable balance of properties. Apparel goods and carpets made from acrylics have appealed to the consumer because they are aesthetically pleasing in comfort and appearance, easy to care for, and reasonably durable. The physical properties of the fiber are by no means remarkable and some obvious deficiencies such as a poor hot-wet strength and only modest tensile strength and abrasion resistance have prevented penetration of acrylic into some markets. 

Lyocell tibers have been explored in blends. Chang et al. [141] prepared Lyocell based blends. Poly(vinyl alcohol) (PVA), poly(vinyl alcohol-co-ethylene) (EVOH), and poly(acrylic acid-co-maleic acid) (PAM) were used as fillers in blends with lyocell produced through solution blending. The results showed that blends with PVA exhibit the best tensile properties. Thus, Lyocell fibers have recently been used as reinforcement for thermoplastic fiber composites. 

Nytril fibers are made up of polymers containing at least 85% vinyli-dene dinitrile units, which appear at least every other unit in the polymer chain. The comonomer used in Nytril synthesis is vinyl acetate. The two monomers are polymerized in benzene using peroxide catalyst. The polymer is precipitated, washed, and dissolved in ], ] -dimethyl formamide and then passed through a spinneret into an aqueous coagulating bath to form Nytril fibers. The properties of the Nytril fiber are similar to the other acrylic fibers. The fiber possesses moderate tensile, regain, and thermal properties. The fiber is chemical and sunlight resistant but is as flammable as cellulosic fibers. Darvan Nytril fibers were produced in the U.S. until 1961. 

In Chapter 3, mechanical properties of glass fiber-reinforced polypropylene are improved by addition of a coupling agent. Likewise, the in situ generation of modified polypropylene by grafting acrylic acid onto the polymer backbone in the Nichols and Kheradi investigation yields enhanced tensile strength compared with unfilled polypropylene and uncoupled composite (Fig. 10.2). 

Glass fiber reinforced composites based on epoxy-acrylate modified UPRs were studied [228]. The authors showed that UPRs, endcapped with acrylate groups and diluted with reactive multifunctional acrylic and allylic monomers in the presence of a photoinitiator, can be photocrosslinked with UV radiation as glass fiber laminates in a rapid process. It was found that the physical properties of the photo-crosslinked laminates are well correlated with the molecular weight of the polyester, the amount of multifunctional monomer added, and the glass fiber content. A greater improvement of the tensile and flexural properties of the photocured products was observed for multifunctional acrylate or acrylether monomers added to the UPR (Table 31) than for allylic monomers. 

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