The flammability is a property of almost every fabric that is characterized differently for different fabric. Cellulose (cotton, rayon) burns readily with after glow and formation of char, while wood support combustion only with difficulty. Synthetic fibers burn and melt readily. After combustion, the polymer may burst into flames, melt, shrink or char. The role of flame retardant is to inhibit the formation of combustible products. Inherent flame retardant fibers are also now made. Eg:- Nomex, Kevlar, Kymol, etc.

Most of the non-durable flame-retardants for textiles inorganic salts or hydrates such as Borax, ammonium chloride or aluminum oxide trihydrate. Phosphorus containing flame-retardants usually have functional groups that are phosphates or a phosphamide – trade name PyroVotex CR — both applied to cotton fabrics
by pad-dry-cure process.

THPC Finishes

There are a number of components of THPC, Tetrekis (Hydroxymethyl) Phosphonium Chloride, and their application methods that have been used for flame retardant finishing of cotton fabrics. Prominent among these are the following:

• THPC + Methylol Melamine +Urea, Heat

• THPC + Methylol Melamine + Urea, Heat-cure

• THPC + Methylol Melamine + Partially Heat – cure – partially NH3 cure

• THPC + NaOH, NH3 cure.

• THPC + NaOH + Amide, Partially Heat cure-Partially NH3 cure

Recipe and Composition

Ammonium sulphate acts as the flame retardant and does not affect the hand of the treated fabric. Boric acid acts as the stabilizer and protects the treated material against discoloration and tendering during exposure to high temperature.

Composition of the general flame retardant finish using THPC is :

Effect of THPC Finishes on the Properties of Cotton Fabric

Some THPC flame-retardants and their effect on properties of cotton are as:

Durability of THPC finish

The finish composition for padding chosen for the study is given in the table. While preparing the padding liquor, firstly urea and tri-ethanol amine are added to water and to this mixture are added THPC, sodium sulphite and lastly ammonium sulphate just prior to padding. Cotton fabric is padded to a pick-up of 100%, dried at 1050C and then passed through infrared oven heated to 3700C for fabric to get dwell time of 11 sec. The sample is subsequently scoured in rope form in an aqueous solution containing 0.2% soda ash and 0.2% non-ionic detergent, rinsed, softened with 0.5% of a cationic type softener and finally dried at 1050C. The finished fabric is tested for all-important parameters and the results obtained are as:-

Test results of flame retardant finished fabric :

The THPC treated fabric showed durable flame retardant properties and retention of tensile properties. However, the treated fabric, although turned slightly stiffer, showed an excellent hand.

THPC With Low Decomposition Point Flame Retardants

Cotton fabrics, flame retardant treated with nitro-methylol-phosphorus resin systems, such as the one with THPC, but still showing after flaming deficiency, can be made fully flame retardant by incorporating low decomposition point flame retardants in the treatment. Examples of low decomposition point flame-retardants are:

· Polymers such as polyvinyl sulphone

· Homopolymers or copolymers of diallyl phosphate, tri-allyl phosphate, diallyl phophite and diallyl cyanoethyl phosphonate.

· Substantially neutral hydrocarbon alcohol polyesters of polyphosphonitrillic halides such as (PNCl2)3-4 and the like.

· Organic phosphates such as phenyl dimorpholine phosphate, tricresyl phosphate and tri(2-ethyl hexyl) phosphate.

Nitrilomethylol-phosphorus resins such as the one formed with THPC on cellulose have relatively high decomposition points. At 15% resin add-on level on 8-ounce cotton twill when heated at 3150C in air, only scorching takes place in 60 sec without any noticeable decomposition or char. Only when heated at about 3500C for 40 sec, decomposition starts.

Flame retardants with low decomposition points, decomposes and char at temperatures below 3000C in less than 30 secs. Out of these, the referred ones for combining with THPC are polymerizable hydrocarbon alcohol phosphates and the substantially neutral hydrocarbon alcohol polyesters of polyphosphononitrile halides.

Method to regain tear strength of cotton fabric lost during THPC flame retardant finishing

An ideal flame retardant finish, while conferring flame retardant property to cotton fabrics should not adversely affect its soft feel and its wear durability. Most of the THPC based flame-retardants finishes adversely affect the feel and strength of cotton fabrics resulting in stiffness and an appreciable fall in the tear strength. These properties, being very important for apparel fabrics, the author’s Stannate phosphate flame retardant process incorporates additives to adequately counter the adverse effect on the useful physical properties of cotton fabrics. In the past there were a few attempts to achieve, i.e., to improve the desirable physical properties of cotton fabrics after flame retardant treatment with THPC compositions.

Biodegradability and related environmental requirements of flame retardant finishes

The untreated cotton fabric decomposes with cellulase within 48 hrs. Biodegrading action of cellulase is slow in the phosphorylated fabrics, attributed to the inhibiting effect of phosphoric group hindering cellulose accessibility. Bit addition of 1 mg/ml of pancreatic in the form of lyophilized pancreatic juice to the biodegrading agent system initiates rapid and complete bio-degradation of the phosphorylated cotton. This action could be due to hydrolysis of the phosphoric ester link to cellulose for cellulase to act on. The overall results show that flame retardant finished fabric is biodegradable.

Ideal environmentally friendly finishes including flame retardant finishes should be non-toxic, non-dermatitic, non-mutagenic and non-tetragenic to humans. The importance of these environmental requirements in flame retardant finishes is stressed as follows:

· The flame retardant finished fabrics should not contain or release formaldehyde, as it is a skin irritant.

· On disposal, it should bio-degrade or be capable of being incinerated to form harmless break down products

· It should not be toxic to plants, animals or micro organisms, particularly those operating in waste water treatment facilities.

· Its manufacture and application should not consume large quantities of natural resources nor of energy.

· Its use should not produce any eco-toxicological problems and could impart only minimum pollution to land, air and water.

Thus summing up these, it is mentioned that an ideal flame retardant finish should be effective at low add-on levels and at low cost levels with only minimum release of any toxic gases, resistant and particulates during the pyrolysis and combustion stages.

Although at present there are not much flame retardants present available with all ideal attributes, the phosphorylated finish appears as a promising one.

Team S&A