Chapter 11
Flame-Retardant Latices for Nonwoven Products
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 27, 2018 | https://pubs.acs.org Publication Date: May 9, 1990 | doi: 10.1021/bk-1990-0425.ch011
P. A. Mango and M. E. Yannich Air Products and Chemicals, Inc., Allentown, PA 18195
Nonwoven products ranging from medical disposables to automotive fabrics are required to meet specific flammability standards. These fabrics are generally composed of cellulosic and/or synthetic fibers which are flammable. Additionally, polymer coatings are applied to the fabric to impart properties such as strength, abrasion resistance and overall binding. It is the purpose of this paper to describe the various polymer coatings commonly used in the nonwovens' industry and their effect on flammability of the substrates. Additionally, the effect of flame retardant additives, commonly used in latex formulations, will be discussed. As nonwovens penetrate more markets traditionally held by other materials, the need for flame retardancy is frequently encountered. In hospitals, nurses' caps, surgeon's masks, surgical drapes and insulation gowns are required to meet flammability standards. In automobiles, nonwoven carpets, high loft padding and fiberfill must meet federal and industry flammability standards. In building materials, nonwoven drapes, blinds, wall coverings, air filters, and furniture fiberfill are all subject to local flammability ordinances. These are a few of the applications that the nonwovens' manufacturer must establish an effective flame retardant product for. Air Products, a manufacture of latex binders, has completed a comprehensive study of flame retardants for latex binder systems. This study evaluates the inherent flammability of the major polymer types used as nonwovens binders. In addition, 18 of the most common flame retardants from several classes of materials were evaluated on polyester and rayon substrates. Two of the most widely recognized and stringent small scale tests, the NFPA 701 vertical burn test and the MVSS-302 horizontal burn test, are employed to measure flame retardancy of a latex binder-flame retardant system. Quantitative results of the study indicate clear-cut choices of latex binders for flame retardant nonwoven substrates, as well as the most effective binder-flame retardant combinations available. Latex Binders Used in Flame Retardant Nonwovens There are several polymer systems widely employed as nonwoven binders: acrylics ethylene-vinyl chloride copolymers (EVCL) vinyl acetate-ethylene copolymers (VAE) polyvinyl chloride and copolymers (PVC) styrene-butadiene copolymer (SBR) polyvinyl acetate homopolymers (PVAC) 0097-6156/90A)425-0145$06.00/0 © 1990 American Chemical Society
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
146
FIRE AND POLYMERS
Each is used to some degree in nonwovens requiring flame retardancy, even though some actually impart flammability where others are inherently flame retardant. Table I summarizes the characteristics of some representative polymers widely used on rayon and polyester nonwoven substrates. Table II further identifies binder physical and chemical properties. Each binder was evaluated for its inherent flame retardancy on polyester and rayon as well as its flame retardancy in combination with commonly available flame retardants.
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 27, 2018 | https://pubs.acs.org Publication Date: May 9, 1990 | doi: 10.1021/bk-1990-0425.ch011
Flame Retardants for Nonwovens There are literally hundreds of flame retardants commercially available for nonwoven polyester and rayon. These can be subdivided into durable and nondurable. In this paper, non-durable means water soluble in room temperature water. Durable means able to withstand at least five washes in hot water with detergent. Flame retardants with performance somewhere in between, often called semi-durable, were not utilized in this study. Table III is a compilation of the flame retardants included in the study. Compositions include: • • • •
halogen containing compounds (with or without antimony) phosphorus containing compounds hydrated compounds other inorganic salts
The different classes of chemicals act in different ways to inhibit combustion. Prior to combustion of a nonwoven, several stages(l) occur: • • • •
substrate temperature elevated by heating decomposition of substrate evaporation of decomposition products oxidation
Each class of flame retardant attacks the combustion process at different stages. For example, the hydrated compounds (alumina trihydrate, sodium silicate) contain bound water which is released upon heating and acts to reduce the temperature of the substrate. The phosphorus containing compounds(2) are thought to decompose to phosphoric acids which form stable nonvolatile products preventing libration of flammable materials. These are sometimes called solid phase flame retardants. A third mechanism for stopping combustion is to retard oxidation. So called vapor phase flame retardants, primarily the halogenated compounds with or without antimony, decompose to form free radicals which react with flammable matter. Without antimony, hydrogen halides are the precursor species; with antimony, antimony trihalide is the precursor. Hydrogen halides alone form noncombustible gases which oxygen starve the oxidation, act as a heat sink, and interfere with the free radical chain reaction. Antimony trihalides volatilize and are stronger inhibitors of the same free radical reaction. Because fire retardant mechanisms are not fully understood, this study developed empirical data - no correlation to or elucidation of mechanism was attempted. Flame Retardant Test Pertinent to Nonwovens There are many flame retardant tests used with some frequency for nonwovens. This study uses two of the most widely utilized and stringent tests: NFPA-701, a vertical flame test and MVSS-302, a horizontal test.
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
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