Acrylic fibers surface treatment

When used as substitutes for asbestos fibers, plant fibers and manmade cellulose fibers show comparable characteristic values in a cement matrix, but at lower costs. As with plastic composites, these values are essentially dependent on the properties of the fiber and the adhesion between fiber and matrix. Distinctly higher values for strength and. stiffness of the composites can be achieved by a chemical modification of the fiber surface (acrylic and polystyrene treatment [74]), usually produced by the Hatschek-process 75-77J. Tests by Coutts et al. [76] and Coutts [77,78] on wood fiber cement (soft-, and hardwood fibers) show that already at a fiber content of 8-10 wt%, a maximum of strengthening is achieved (Fig. 22). 

Control of fiber friction is essential to the processing of fibers, and it is sometimes desirable to modify fiber surfaces for particular end-uses. Most fiber friction modifications are accomplished by coating the fibers with lubricants or finishes. In most cases, these are temporary treatments that are removed in final processing steps before sale of the finished good. In some cases, a more permanent treatment is desired, and chemical reactions are performed to attach different species to the fiber surface, e.g. siliconized slick finishes or rubber adhesion promoters. Polyester s lack of chemical bonding sites can be modified by surface treatments that generate free radicals, such as with corrosive chemicals (e.g. acrylic acid) or by ionic bombardment with plasma treatments. The broken molecular bonds produce more polar sites, thus providing increased surface wettability and reactivity. 

The commonly used separator material now is the surface treated polypropylene. The surface treatment helps in making the polypropylene permanently wettable. Surface treatments involve the grafting of a chemical such as acrylic acid to the base fibers to impart wettability and is accomplished using a variety of techniques such as UV or cobalt radiation. Another method of imparting wettability to the polypropylene is a sulfonation treatment where the base fiber material is exposed to fuming sulfuric acid. The separator surface is designed to be made hydrophilic to the electrolyte. 

From the above it appears clear that the moisture transport takes jdace at the surface of the fiber (solid-liquid interface). The capadty of water retenticm, on the other hand, appears to reside primarily in macrovcMds within the fiber. Actually, acrylic fibers with high water retention can be (Stained, accordii to a recent patent by spinning a fiber from a blend of an acrylic copt maer and a hqjdy soluble con ronent (e. g., glycerine), which later is washed out in the further treatment, leaving behind voids and capillaries which provide the water retention. 

Synthetic fibers do not contain natural impurities although there are added impurities such as sizing materials and oil stains. Therefore, their pretreatment process is simpler than other natural fibers. However, synthetic fibers such as polyester and acrylic have poor wettability, dyeability, and antistatic behavior. After plasma treatment, the fiber surface gets physically altered, and hydrophilic functional groups are introduced to the fiber surface, which improves the wettability of the fiber significantly. In recent years, many researchers have studied ways to modify polyester textile materials, and good results have been obtained (Morent et al., 2008). 

The half-life decay time of the treated acrylic samples is also shown in Table 3.12. Here, the plasma treatment has caused a drastic reduction in the half-decay time of the fibers. The half-decay time is found to decrease from 9.57 s for the untreated sample to 1.35 s for 3 min of plasma-treated sample. This result shows that the antistatic ability of acrylic fibers is drastically improved by plasma treatment. Surface wettability is directly related to surface energy, that is, more energetically stable surface results in... 

To improve the adhesion between natural fiber and polymer matrix, chemical modification of natural fibers was investigated by a number of researchers. The mechanism and utilization of selected chemical treatments is discussed in this section. There are many different methods to improve the interfacial adhesion between fiber and matrix by modifying fiber surface such as acetylation, benzoyla-tion, acrylation, permanganate, and isocyanate treatment. These treatments are described in detail by Kalia et al. [69]. 

To modify the fiber surface and its internal structure various treatments have been carried out, including alkalization, acetylation, acrylation, permanganate, cya-noethylation, and the use of silane coupling agents. In general, fiber treatments can increase interphase adhesion and also lead to penetration of the matrix resin into the fibers and influence the mechanical properties of fiber reinforced composites [33]. 

The nonwoven polyolefin fabric is used. The thickness of the separator is 100-200 pm, and the basis weight of the fiber is 50-80 g/m. The hydrophilicity is provided to the fiber surface of the separator with the sulfonation treatment, plasma treatment or acrylic acid graft polymerization treatment. 

When the above hardwood maple compound (except for the use of 30 phr wood fiber) was modified by sorption of CO2 in static experiments, all impact modifiers increased loss of gas to the atmosphere. This was less evident with crosslinked acrylic impact modifiers than with thermoplastic CPE. In practice, commercial compounds based on sodium bicarbonate or azodicarbonamide tend to use little or no impact modifier. They are, for example, not found in compositions described by Cope (Marley Mouldings) in a 1996 patent filing describing extmdable profiles. No surface treatment was described for the wood fiber used in the following compound, but it cannot be concluded that none was in use ... 

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