Pad-dry-cure process

Another modification of this process was reported in 1988 (84). In this process, a precondensate of THPC and urea, plus excess urea, are neutralized to a pH of about 5.7, and the buffer salt is added. The fabric is then given a standard pad-dry-cure process followed by oxidation and laundering. The principal advantage of this modification is a reduction in both formaldehyde vapors and phosphine-like odors released during processing (84). 

THPC—Amide—PoIy(vinyI bromide) Finish. A flame retardant based on THPC—amide plus poly(vinyl bromide) [25951-54-6] (143) has been reported suitable for use on 35/65, and perhaps on 50/50, polyester—cotton blends. It is appUed by the pad-dry-cure process, with curing at 150°C for about 3 min. A typical formulation contains 20% THPC, 3% disodium hydrogen phosphate, 6% urea, 3% trimethylolglycouril [496-46-8] and 12% poly(vinyl bromide) soUds. Approximately 20% add-on is required to impart flame retardancy to a 168 g/m 35/65 polyester—cotton fabric. Treated fabrics passed the FF 3-71 test. However, as far as can be determined, poly(vinyl bromide) is no longer commercially available. 

After application of the chemical finish, the fabric must be dried and if necessary, the finish must be fixed to the fibre surface, usually by additional heating in a curing step. A schematic diagram of a pad-dry-cure process is... 

Pad-dry-cure process. Reproduced from Cotton Dyeing and Finishing a technical guide, 1997, pi 52, courtesy of Cotton Incorporated, Cary, NC. 

Although inorganic salts can provide excellent flame-retardant properties for cellulose, reasonable laundering durability must be incorporated into any finish destined for apparel use. The most successful durable flame retardants for cellulose are based on phosphorous- and nitrogen-containing chemical systems that can react with the fibre or form crosslinked structures on the fibre. The key ingredient of one of these finishes is tetrakis(hydroxymethyl)phosphonium chloride (THPC), made from phosphine, formaldehyde and hydrochloric acid (Fig. 8.11). THPC reacts with urea to form an insoluble structure on cellulose in a pad-dry-cure process (Fig. 8.12). 

Pretreatment of cotton with polyacrylamide enhances the possibility of dyeing cotton at neutral pH with various commercial reactive dyes. Such pretreatment, as applied through pad-dry-cure process, brings about some chemical changes in the treated fabric. 

In smart polymer applications in textiles, PCMs and colour change polymers mostly take the form of microcapsules. A microcapsule is an intermediate state which is added to solutions, fibres, films and nonwovens to incorporated a smart function into the textile. These materials may be incorpated into textiles by printing, coating and dyeing. For printing and coating, the materials are microencapsulated first and then coated or printed onto the fabric surface by common methods such as the pad-dry-cure process. 

We have also examined the interactions of SMPU treatment with a traditional DMDHEU easy-care finishing method and a LA pre-treatment. The results indicate a strrface grafting of SMPU on cotton fibers, and a model of interaction between SMPU and DMDHEU/LA treatments has been proposed accordingly. During the pad-dry-cure process, an SMPU layer forms on cotton fibers. The SMPU layer acts as a gas-permeable layer, which can remember the original shape upon the first deformation at a high temperature (which occurs at the curing process). However, the DMDHEU and LA do react with cellulose at a microscopic level. 

Stearamidomethylpyridinium chloride is applied to cellulosic fabrics by a pad-dry-cure process. A buffer, usually sodium acetate, is added to prevent tendering of the fabric by the HCl formed. Pyridine liberated during the reaction has an unpleasant odor, and the fabric has to be scoured after the cure. 

Figure 14.1 The pad-dry-cure process for the wet-finishing of textile materials.

Eabric can be cross-linked either in the dry or the wet state. If fabric is cross-linked in the dry state, smoothness returns on tumble drying. By contrast, if fabric is cross-linked in the wet state, smoothness is achieved byline-drying the fabric. This concept has been demonstrated using formaldehyde in pad—dry—cure or wet cure processes (eq. 2) (29). 

Except for certain dyeing procedures, there are three basic steps involved in most dyeing and finishing processes application of the color or finish, predrying to remove the excess water, and curing to fix or chemically cross-link the dyestuff or finish, respectively. This procedure is commonly referred to as a pad-dry-cure operation. 

The SMPU solution prepared was used directly in solution form, and was prepared by mixing 80 g of SMPU solution with IL of water. The process employed was the traditional pad-dty-cure process, whereby the cotton fabric is immersed into the finishing solution on a padding machine (Rapid 354) arrd padded twice between two mbber rollers at a pressme of 3 MPa. After the padding process, the wet pick-up of the fabric was about 75% (based on a completely dry sample). It was subsequently dried at 80°C for two minutes, before being cured at 120°C for three mirmtes. 

The standard conventional finishing process has been modified to suit the purposes for different fabrics and garments. Eor example, tubular knits are frequently handled using specialized equipment to control tension and to get adequate padding. Some tubular knits are subjected to wet-on-wet padding, dried and cured in large dmm dryers, and steam-treated to achieve a relaxed and nondistorted knit. 

Fluoropolymer repellent finishes are applied by padding, spraying, or exhaust. Generally, the fabric is padded, dried at 120-180°C, and cured for 1-3 min at 150-182°C. The coapplied adjuvants and resins may require the fabric to be process washed and dried at 150-175°C. Fluorochemicals (e.g., CH2=CH-COO(CH2)2C8Fn) [149] have been applied to fabrics by plasma coating as well. 

Ammonia—Gas-Cured Flame Retardants. The first flame-retardant process based on curing with ammonia gas, ie, THPC—amide—NH, consisted of padding cotton with a solution containing THPC, TMM, and urea. The fabric was dried and then cured with either gaseous ammonia or ammonium hydroxide (96). There was Httle or no reaction with cellulose. A very stable polymer was deposited in situ in the cellulose matrix. Because the fire-retardant finish did not actually react with the cellulose matrix, there was generally Httle loss in fabric strength. However, the finish was very effective and quite durable to laundering. 

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