Properties modacrylics

Property Acrylic Modacrylic Nylon-6,6 Polyester Polyolefin Cotton Wool... 

Disperse dyes can be used to produce light to medium deep shades on acrylic and modacrylic fibers [96, p. 639], The dyeing mechanism and process correspond to those used on PES and CA fibers (see Section 4.12). However, dyeing can be performed below 100°C. Addition of carriers is not required. The good migration properties of disperse dyes result in problem-free level dyeing. 

Molecular weight characterization of modacrylic fibers is difficult because of the limited number of solvents available and inhomogeneties in composition between individual polymer chains that affect solution properties, particularly if the comonomers are ionic in character. Di-methylformamide and dimethylacetamide are suitable for measurement of molecular weight of polyacrylonitrile, but errors are introduced when copolymers are analyzed (126). Bortniak et al. (127) have analyzed modacrylic fibers quantitatively in microgram quantities by using pyrolysis gas chromatography. 

Typical physical and chemical properties of commercial modacrylic fibers have been published (125). Modacrylics are not affected by bleaches in the concentrations used for spot and stain removal (31). They are immune to attack by rot, mildew, bacteria, and insects such as moths and carpet beetles (125). Fungi may grow in dirt in an unlaundered Dynel fabric, but washing out the dirt removes the mildew with no effect on the fabric. 

Modacrylic fibers, like acrylic, require after-stretching and heat stabilization in order to develop the necessary properties. It is thought that the stretching is of the order of 900-1300 percent, and that, in a separate operation, shrinkage of about 15-25 percent is allowed during the time that the fibers are heat stabilized. 

The most successful approach for flame-retarding acrylic fibres is to copolymerise halogen-containing monomers into the fibre. These modacrylic fibres have excellent permanent flame retardancy and acceptable fibre properties. Some problems including reproducibility of dyeing gave rise to their substitution by flame-retardant modified polyester, for example for curtain fabrics and other decorative textiles. 

Providing flame retardancy for fibre blends has proved to be a difficult task. Fibre blends, especially blends of natural fibres with synthetic fibres, usually exhibit a flammability that is worse than that of either component alone. Natural fibres develop a great deal of char during pyrolysis, whereas synthetic fibres often melt and drip when heated. This combination of thermal properties in a fabric made from a fibre blend results in a situation where the melted synthetic material is held in the contact with the heat source by the charred natural fibre. The natural fibre char acts as a candle wick for the molten synthetic material, allowing it to bum readily. This can be demonstrated by the LOl values of cotton (18-19), polyester (20-21) and a 50/50 blend of both (LOl 18), indicating ahigher flammability of the blend as described later (Section 8.11). But a rare case of the opposite behaviour is also known (modacrylic fibres with LOl 33 and cotton in blends from 40-60 % can raise the LOl to 35). 

The modacrylic fibres have similar properties to those of acrylics and are flame resistant..Mostly this fibre is based on a 60/40 or 50/50 copolymer of acrylonitrile with vinylidine chloride (CH = CCy together with small proportion of ternary monomer to improve ionic dyeability or hydrophilicity. The better known modacrylic fibres have a ribbon-shaped or pea-nut shaped cross-section. One problem encountered with modacrylic fibre is loss of lustre at the boil [83, 84]. This fibre is used for apparel, home furnishing, wigs etc. 

Another property used to compare the flammability of textile fibers is the limiting oxygen index (LOI). This measurement quantity describes the minimum oxygen content (%) in nitrogen necessary to sustain candle-like burning. Values of LOI, considered a measure of the intrinsic flammability of a fiber, are listed in Table 12.28 in order of decreasing flammability. Acrylic fibers, it can be seen, are similar in flammability to cotton. Modacrylics, on the other hand, are somewhat less flammable than any of the synthetics, except 100% PVC, and are substantially less flammable than cotton and wool. 

A summary of the methods and equipment used for evaluating acrylic and modacrylic fiber properties in Table 12.31. 

Uses Copolymer intermediate for acrylic and modacrylic fibers resins and dispersions for paints, varnishes, inks, papers, adhesives, and glues aq. disp. for nonwoven fabrics, textiles, and paper cleaning and waxing prrxfs. plastics and syn. resins syn. mbber and latexes org. synthesis Properties APHA 10 max. clear liq. m.w. 86 sp.gr. 0.950 vise. 0.461 mPa s vapor pressure 91 mbar (20 C) f.p. - 75 C b.p. 80 C ( 1013 mbar) flash pt. (OC) 3 C ref. index 1.400 Precairtirm Highly flamm. 

Vinyl fibers are those man-made fibers spun from polymers or copolymers of substituted vinyl monomers and include vinyon, vinal, vinyon-vinal matrix (polychlal), saran, and polytetrafluoroethylene fibers. Acrylic, modacrylic and polyolefin—considered in Chapters 8 and 9—are also formed from vinyl monomers, but because of their wide usage and particular properties they are usually considered as separate classes of fibers. The vinyl fibers are generally specialty fibers due to their unique properties and uses. AH of these fibers have a polyethylene hydrocarbon backbone with substituted functional groups that determine the basic physical and chemical properties of the fiber. 

When the comonomer content exceeds 5%, certain properties of the fibers are largely modified and they are then called modacrylic fibers. 

The modacrylic fibers, like vinyon and unlike the acrylic fibers, have not become general purpose fibers. They can be dyed satisfactorily and thus are acceptable in many normal textile products but their nonflammability tends to place them in uses where that property is important, even vital. Blended... 

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