Durable flame-retardant treatments based on a vinyl phosphonate oligomer or Thps were applied to cotton, cotton/polyester, cotton/wool, and cotton/polyester/wool medium-weight twill fabrics. The treatments were applied by either a pad, dry, cure process or a two-step procedure consisting of a pad, dry, cure application of DMDHEU followed by a Thps-NH 3 cure process. Flammability of the treated fabrics was evaluated by a number of tests, including burning rate, vertical char length, oxygen index, and a flame-extinguishment test. Physical properties were determined by standard tests to measure breaking strength, wrinkle recovery, stiffness, durablepress rating and shrinkage due to laundering. Cotton/wool blend fabrics treated with Thps-urea-TM M had the best flame-retardant properties. B
SynopsisMedium weight twill fabrics constructed from cotton and cotton blended with polyester and/or wool were analyzed under nitrogen by three thermoanalytical techniques. Fabrics were tested both before and after treatment with [tetrakis(hydroxymethyl)phosphonium] sulfate (THPS), urea, and trimethylolmelamine. The presence of all fibers was distinguishable in differential scanning calorimetric analysis (DSC) of untreated fabrics; the relative positions of the endothermic, decomposition peak temperatures were only slightly changed. After flame-retardant (FR) treatment, the blended cotton and wool fibers were altered. Both fibers decomposed as exotherms during DSC analysis. These data supported earlier microscopical, X-ray evidence that wool fibers were actually reacting with the FR treatment. The two DSC peaks for polyester polymer melting and decomposing remained unaffected by either blending with other fibers or the presence of the FR finish on the fabric. There was excellent agreement between DSC peak temperatures and the temperature of maximum rate of weight loss obtained from thermogravimetric analysis (TGA). Blending cotton with either of these fibers increased the residue measured after TGA. The increased residue correlated with increased flame resistance as measured by the 45" angle, edge-ignition burning rate test.
Treating cotton textile fabrics with phosphorus-containing flame retardant finishes reduces the flammability of the fabrics. The presence of fibers other than cotton in blended fabrics changes the burning rates and char lengths of the fabrics, as well as the nature of the resultant chars. To better understand the relationship of blended fibers during burning, and the response of each fiber to heat, scanning electron microscopy was used to study structures of blended cotton/polyester and cotton/ wool fabrics, and of individual fibers, both before and after exposure to flames. In blended fabrics, changes in physical structures of polyester and wool were observed before those in cotton. Chars of blended fabrics were more stable than those from either fiber alone, because the charred cotton formed a network onto which the melted polyester and wool could flow. These melts in turn protected and strengthened the cotton residue.Visual examination of fabrics exposed to heat gives information on the response of both fibers and fabrics to increasing temperatures. Scanning electron microscopy (SEM) provides a means for examination at magnifications great enough to see changes in indi-vidual fiber structures, and has been used to study chars of cotton fabrics that had been treated with various flame retardant (FR) agents [3,4,6,7]. Natural and synthetic fibers respond differently to flame retardants and to heat, and thus have different
Three cotton printcloth fabrics treated for flame resistance with THPOH-NHx, oxidized and nonoxidixed, were studied by light microscopy and by transmission (TEM) and scanning (SEM) electron microscopy. Chars of the treated fabrics were also examined. Staining with Acid Blue I and examination by light microscopy provided a semicluantitative assessment of penetration of nonoxidized THPOH-NHa into yarns and fibers, but was less effective with the oxidized sample. SEM observations indicated polymer build-up on fabric surfaces. Deposits of polymer between fibers were usually heavier around the periphery of the yarn. Laundering removed surface deposits but oxidized samples laundered 50 times were still flame resistant, TEM of ultrathin cross sections showed that no major structural change had occurred in the treated fibers. Both SEM and TEM of fiher char sections indicated that the fibers had become shells on burning.Residue patterns left by treated fiber sections after microincineration suggested that the laulymer had completely penetrated the fibers.
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