Flame retarded wool and blends

Within the area of flammability of all so-called conventional fibres, wool has the highest inherent non-flammability and so is particularly attractive for protective textile end-uses such as uniforms, coveralls, transport seatings and domestic and contract furnishings, where heavier fabrics may be used and the aesthetic character of wool may be marketed. Table 15.1 above shows it to have a relatively high LOI value of about 25 and a low flame temperature of about 680 0C.

Once again, char-promoting flame retardants are preferred, although bromine-containing, vapour phase-active surface treatments are effective. Horrocks (1986) has comprehensively reviewed developments in flame retardants for wool up to 1986 and very little has changed since that time. However, although considerable research has been undertaken into the use of functional phosphorus-based finishes, including the effectiveness of methylolated phosphonomides (e.g. Pyrovatex CP) (Hall and Shah, 1991), and substantive halogenated species like chlorendic, tetrabromophthalic anhydride (TBPA) and dibromo-maleic anhydrides and brominated salicylic acid derivatives, the most commonly used durable flame retardants are probably those based on Benisek's Zirpro (IWS) system (Horrocks, 1986). This treatment is applicable from the dyebath and has no obvious associated discoloration or affect on wool aesthetics.

The Zirpro process is based upon the exhaustion of negatively charged complexes of zirconium or titanium, usually as potassium hexafluorozirconate (K2ZrF6) or a mixture of this and potassium hexafluorotitanate (K2Ti F6), onto positively charged wool fibres under acidic conditions at a relatively low temperature of 60 0C. Application to wool is possible at any processing stage from loose fibre to fabric using exhaustion techniques either during or after dyeing; these have been fully reviewed and described elsewhere (Horrocks, 1986, 2003). The relatively low treatment temperature is an advantage because this limits the felting of wool and by maintaining a low pH (3), penetration is maximised and wash-fastness to as many as 50 washes at 40 0C or 50 dry cleaning cycles in perchloroethylene is achieved. The general simplicity of the whole process enables it to be used either concurrently with 1:1 premetallised and acid levelling dyes or after dyeing when applying acid milling reactive 1:2 premetallised and chrome dyes. Furthermore, Zirpro treatments are compatible with shrink-resist, insect-resistant and easy-care finishes.

It has been proposed that the Zirpro treatment enhances intumescent char formation (Benisek, 1971) although this view is not universally held (Beck et al., 1976). However, its effectiveness in protective fabrics to flame and heat at high heat fluxes, is associated with the intumescent fibrous char structures generated. Because of heavy metal effluent problems, there has been pressure to identify alternatives and limited interest remains in sulphation with ammonium sulphamate (Lewin and Mark, 1997) followed by curing at 180-200 0C in the presence of urea which can give a 50 hard water wash-durable finish for wool fabrics with little change in handle. While there has been concurrent interest in the use of intumescents (Horrocks and Davies, 2000) no commercial exploitation has taken place.

Wool blends pose different challenges, because of the complexity of wool on the one hand and the specificity of flame retardants with respect to each blend component fibre on the other. In the absence of any back-coating treatment, acceptable flame retardancy of Zirpro-treated blends is obtainable in 85/15 wool/polyester or polyamide combinations. Such fabrics are ideal for aircraft and other seatings as well as heavier fire protective clothing and uniforms. For lower wool contents in blends and without the possibility of using alternative FR treatments, flame retardancy can be maintained only if some of the Zirpro-treated wool is replaced by certain inherently flame retardant fibres, except for Trevira CS polyester where antagonistic effects have been noted (Benisek, 1981). Chlorine-containing fibres such as PVC and modacrylics are particularly effective in this respect.

End of Days Apocalypse

End of Days Apocalypse

This work on 2012 will attempt to note them allfrom the concepts andinvolvement by the authors of the Bible and its interpreters and theprophecies depicted in both the Hopi petroglyphs and the Mayan calendarto the prophetic uttering of such psychics, mediums, and prophets asNostradamus, Madame Blavatsky, Edgar Cayce, and Jean Dixon.

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