Specific Properties Flammability — Flame Retardants

Modifying Specific Properties Flammability - Flame Retardants 

Properties affected Ignitability. flame support/propagation. emission of smoke and fumes, smouldering/afterglow. 

Materials/characteristic.s Some inorganic fillers. Nitrogen-donors melamine compounds. Antimony compounds with halogen donors. Halogenated containing chlorine, bromine. Halogen-free systems aluminium trihydroxide (ATH), magnesium hydroxide, zinc borate. Intumescent systems phosphorus compounds. 

New developments Replacement of halogenated types reduction in emissions synergistic effect of combinations multi-functional systems combining two or more fire control functions. 

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Murphy, J. Modifying specific properties flammability-flame retardants. In Additives for Plastics, Handbooks, pp. 115-140. Elsevier Science Ltd., New York (2001)... 

Modifying Specific Properties Flammability - Flame Retardants 121 10.3.1 Chlorinated compounds... 

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. 

PVC-U formulations have low flammability due to the chlorine content. The addition of plasticiser in PVC-P formulations necessitates the use of flame retardant and smoke suppressant additives. These additives are known as functional fillers and a correct balance is necessary to achieve all the end-use specification requirements. They are predominately used in cable, conveyer belting and roofing membrane formulations to give resistance to fire initiation and propagation. It is also important to reduce dripping in a fire situation and that as little smoke as possible is generated. Antimony trioxide has been used extensively, usually in combination with phosphate ester plasticisers, giving excellent fire performance and mechanical properties. 

The relationship between other flammability characteristics and the polymer tendency for carbonization has also been studied 112-114). Flame retardant effectiveness of coke is, primarily, related to the reduced release of fuels into the gas-phase, and to the ability of the coke to undergo heterogeneous oxidation. Therefore, not only the composition is important but also the morphological structure, porosity, specific surface area and thermophysical properties of the carbonaceous residue115, U6). 

Specifically, PVC blends with polyethylene, polypropylene, or polystyrene could offer significant potential. PVC offers rigidity combined with flammability resistance. In essence, PVC offers the promise to be the lowest cost method to flame retard these polymers. The processing temperatures for the polyolefins and polystyrene are within the critical range for PVC. In fact, addition of the polyolefins to PVC should enhance its ability to be extruded and injected molded. PVC has been utilized in blends with functional styrenics (ABS and styrene-maleic anhydride co-and terpolymers) as well as PMMA offering the key advantage of improved flame resistance. Reactive extrusion concepts applied to PVC blends with polyolefins and polystyrene appear to be a facile method for compatibilization should the proper chemical modifications be found. He et al. [1997] noted the use of solid-state chlorinated polyethylene as a compatibilizer for PVC/LLDPE blends with a significant improvement in mechanical properties. A recent treatise [Datta and Lohse,... 

The flammability properties described earher show the potential in specific segments of the apparel market. PLA fabrics with no flame retardant treatments have passed the US tests 16 CFR1610, and have also achieved the standards specific for children s sleepwear, 16 CFR 1615 and 16 CFR 1616. 

The most commonly used specification for base materials is IPC-4101. This specification presents a classification scheme and specification sheets for the various materials in use. Table 6.2 summarizes the various materials by specification sheet number. Each specification sheet in IPC-4101 includes property requirements for that particular material type. As these specification sheets are updated periodically, it is recommended that the latest revision of this document be reviewed. This is particularly true in light of new requirements for materials that must be compatible with lead-free assembly.Table 6.2 is presented for reference only and is not all-inclusive. UL94 comments in Table 6.2 reference the minimum flammability requirements for that material. Materials may exceed these minimum ratings. Also note that where a non-halogen-based flame retardant is used, it is shown along with the resin system description. Definitions of the UL flammability ratings are given in Chap. 8. 

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