Peter Hauser
North Carolina State University

Introduction

Wet processing has been and will remain important to the textile industry in the future. However, economic forces, market demands, and environmental concerns will shape the direction that chemical development for wet processing will take.

General Trends

There are some clear trends apparent for chemical products destined for the textile wet processing industry.

Global competition is requiring textile chemicals at lower cost. One way to achieve this goal is to provide high solids concentrates. By reducing the amount of water to be shipped, transportation costs can be lowered, leading to lower cost products. One disadvantage of this approach is the necessarily higher cost per kilogram of the shipped product. Although the actual cost for use may be lower, the higher initial cost may be a deterrent to sales.

Another approach to lower chemical costs is to provide the chemicals in bulk or semi-bulk containers. In this way, the costs for drums and drum disposal are eliminated.

If the performance of a chemical product can be enhanced, then the amount of chemical needed for a specific property can be reduced. Using a more efficient chemical can lower the cost per use and since less chemical is being used, effluent problems can be minimized.

Combining several chemical auxiliaries into one product is another approach to lowering overall chemical costs. By reducing the number of individual products, shipping, storage, and disposal costs are significantly lowered.

Often, the use of a textile chemical involves generating undesirable side effects, such as foam and effluent problems. Overcoming these difficulties is costly in terms of additional chemical requirements and reduced productivity. One important requirement for competitive textile chemicals will be fewer problems during use.

The second significant trend for textile chemical products is the growing need to be environmentally friendly. Products that require less energy and water to perform their function will be preferred. Governments continue to restrict the use of various chemical products, requiring textile chemical suppliers to comply with a myriad of rules and regulations. Successful textile chemicals will need to provide desired performance with a minimum of pollution.

Preparation Chemicals

Chemicals used in preparing textiles for further wet processing often are considered as an uninteresting set of alkalis, enzymes, and detergents. However, significant technical advances have been made and are continuing to be made in this important area.

Combining two processes into one provides advantages in productivity and cost reduction. The bio-scouring process utilizes several different enzymes to catalyze the hydrolysis of warp sizes and the impurities found in cotton (Cognis). Amylases catalyze starch hydrolysis while pectases and lipases catalyze the hydrolysis of pectins and lipids, respectively. The majority of cotton impurities are located near the fiber surface and small amounts of cellulase may also be included to allow easier access for the enzymes.

Specialty surfactants have been developed that claim to allow the combining of desizing and scouring without the use of amylase enzymes (RAN Chemicals). These surfactants apparently are able to disperse and remove starch sizes in alkaline solutions.

In hydrogen peroxide bleaching, combining stabilizer, sequestrant, emulsifier and dispersant into one product can lead to higher productivity and lower overall costs (Boehme). Incorporating a biodegradable stabilizer into a hydrogen peroxide bleach bath reduces the load on waste treatment facilities (Clariant).

Alkyl phenol ethoxylates, although excellent surfactants, biodegrade to materials that are toxic to aquatic life. Many new textile chemicals have been reformulated to remove alkyl phenol products (BASF).

The increased use of Elastane fibers in textile apparel has led to the introduction of chemical auxiliaries specifically designed for use with this fiber. An oxidative, non-chlorine bleach is available for color reduction in denim garment processing (CHT).

New developments in preparation technology include the use of peroxide bleach activators to reduce the time and temperature associated with hydrogen peroxide bleaching [1-3]. In the bleach bath, peroxide activators form peracids which can bleach cotton more rapidly and at lower temperatures than hydrogen peroxide alone.

Two such activators, tetraacetylethylenediamine (TAED), I, and nonanoyloxy-benzene sulfonate (NOBS), II, have found limited use in textile preparation processes to date.

A new activator, N-[4-(triethylammoniomethyl)benzoyl] caprolactam chloride (TBCC), III, has been found to significantly reduce process times and temperatures while providing equivalent whiteness, absorbency, and less fiber damage.

Dyeing Auxiliaries

As with preparation chemicals, combining different dyeing auxiliaries into one product provides convenience, improved productivity, and lower transportation and storage costs. Examples of this trend include products that incorporate leveling agents, emulsifiers, dispersants, and trimer control agents into a single product for the disperse dyeing of polyester (BASF).

Another relatively recent innovation for improving the disperse dyeing of polyester is a process that utilizes selected dyes, buffering agents, and other auxiliaries to dye polyester under alkaline conditions (Dystar). The major advantage of this system is the reduction of trimer deposits since the deposits are hydrolyzed as they form by the alkaline bath.

One technology that is continuing to develop is the use of cationizing agents to form cationic cotton prior to dyeing [4-6]. Dyeing cationic cotton results in greater utilization of dye and higher color values. In addition, the strong dye-fiber interactions resulting from cationizing cotton allow dyeings with no added electrolytes and minimal rinsing and afterwashing.

A typical cationization process involves the reaction of 3-chloro-2-hydroxypropyl-trimethylammonium chloride (CHTAC) with alkali to form epoxypropyltrimethyl-ammonium chloride (EPTAC) which then reacts with cellulose to form cationic cotton (Dow Chemical).

The cationic sites on the modified cotton strongly attract anionic dye molecules, leading to the observed performance and process improvements.

Another developing technology for dyeing processes concerns real time concentration monitoring of dye bath components as well as time and temperature parameters [7-9]. The process uses the flow injection analysis technique to measure individual dye concentrations via spectroscopy (HuMetrix).

A diagram of the set up is shown below.

A portion of the dyebath is sampled continuously and pumped through a valve assembly. Periodically, the valve diverts some of the sample into a mixing chamber where it is diluted with the carrier solution and then passed through a spectrophotometer cell where the absorbance is measured. A computer compares the absorbance curve to previously determined standards and calculates the concentration of the individual dyes in real time. All dye classes can be measured with the system.

The ultimate goal of this system is to actually control the dyeing process, not just monitor it. The graphs below show how a tone-on-tone dyeing was achieved in a laboratory dyeing with acid dyes on nylon.

The graph on the left shows how uniformly the dyes exhausted to the fiber, while the graph on the right shows the actual dye concentrations in the dye bath. The three dye additions were made with pumps controlled by a computer program (HueMetrix).

Finishing Chemicals

In addition to lower cost in use and less adverse environmental impact, there are some emerging trends specific to finishing chemicals. The nature of chemical finishing allows for quicker responses to customer demands, so creativity and innovation are naturally more prevalent in this area of wet processing.

The constantly changing apparel market requires new fabric properties to stimulate consumer purchases. Chemical finishes that produce interesting and useful products are continually being developed and offered to the market.

The durability of chemical finishes is an important performance feature. Except for effects that are designed to be temporary, chemical finishes are expected to be durable throughout the useful life of the textile.

The traditional approach to application of chemical finishes is to employ the pad-dry-cure process. Often the fabric must be washed after curing to remove unreacted materials and then redried. This application method, although suitable for continuous processing, requires substantial capital investment and has significant energy demands. Chemical finishes that can be applied during the dyeing process or require less energy and water are being actively investigated.

Recent softener advancements include a silicone oil that is self-emulsifiable and 96% active (Clariant). This product reduces shipping and inventory costs and can be made into a useful emulsion in the mix room. A 100% active cationic non-silicone softener is available that allows the material to be added directly to dyeing machines without prior dilution or emulsification (CHT). A non-silicone nonionic hydrophilic softener has been offered that claims to provide a silicone feel (RAN Chemicals).

New flammability requirements for textiles have led to the use of intumescent chemistry in textile finishes (Amitech). Intumescent materials, used for many years in the paint and coatings industries, provide flame retardancy by forming a cohesive carbon foam when heated that insulates the treated textile from the flames’ heat. An intumescent finish is a mixture of a carbon source, dehydrating agent, blowing agent, and other additives included for specific properties.

Another fabric performance area that has recently been addressed is dust mite protection. These spider-like creatures thrive in the warm humid environment of bedding, eating the dead skin shed from the human body. By themselves they are harmless, but their waste products can cause severe allergic reactions in asthma sufferers. This problem can be controlled by frequent vacuuming of pillows and mattresses and the use of tightly woven fabrics treated with the appropriate insecticides.

“Bio-polishing” is the term for the use of cellulase enzymes to improve fabric appearance, reduce pilling, and soften fabric hand (Novozymes, Cognis). Cellulase enzymes catalyze the hydrolysis of the ß (1-4) ether linkage in cellulose. This treatment in combination with mechanical action removes short fibers from cellulose fabrics.

When solid materials melt, heat is absorbed from the environment (endothermic transition). When liquids solidify, heat is given off (exothermic transition). Materials that have melting points close to body temperature have been used to provide textiles with a finish that can moderate environmental temperature changes (Outlast). Microcapsules formed with these phase change materials in the interior of the capsules are applied to fabrics with appropriate binders. The graph below demonstrates the temperature moderating effect of phase change materials (PCM) on a roof membrane.

Finishes to combat body odors can function by several different mechanisms. Since the odors result from bacterial growth, they can be prevented from forming by the use of antimicrobial finishes, either “leaching” finishes that slowly release from the fabric to the environment or “bound” finishes that are firmly fixed to the fiber surface. Fabrics treated with antimicrobial finishes are subject to government regulations that vary from country to country.

Another mechanism for anti-odor finishes is to remove the odor molecules as they are formed. One approach is to incorporate cyclodextrins into a chemical finish (Clariant). Cyclodextrins have a unique molecular structure that forms a hydrophobic cavity with a hydrophilic exterior. The hydrophobic odor molecules become trapped in these cavities and are removed when the textile is laundered. A second approach is to take advantage of the fact that many odor molecules are organic acids. Applying a chemical finish that contains free amine groups will cause non-volatile amine salts, thereby removing the odor. In both of these approaches, the durability of the anti-odor effect depends on how well the odor absorbers are bound to the fabric.

A third mechanism for anti-odor finishes is to cover up the odors with fragrances. Cyclodextrin containing finishes can be used in this manner also. The fragrance molecules are placed into the cyclodextrin cavities before the textile is sold and are slowly released over time, providing a one time effect. Microcapsules containing fragrances can be applied to textiles with binders (Cognis). The microcapsules are designed to rupture as the textile is worn, releasing the fragrance.

One very interesting performance feature added to fabrics recently is self-cleaning. Two very different approaches to this feature are being investigated. One approach is to apply very fine particles of titanium dioxide to the fabric surface. Titanium dioxide absorbs ultraviolet light and generates oxygen free radicals that oxide organic soils allowing for their easy dispersal and removal by water only. This method has already been commercialized for window glass and exterior walls.

The second approach borrows an idea from nature. Lotus leaves repel water and are cleaned of soil by rain water alone. The surface of lotus leaves is covered with tiny hydrophobic particles. By forming similar structures on fiber surfaces, a fabric can be produced that can be cleaned by simply rinsing with water.

Several methods have been commercialized to provide fabrics with insect repelling properties. One process utilizes a repellent derived from chrysanthemums and attached durably to fabrics (Buzz Off). The other process incorporates the well known insect repellent DEET into microcapsules that are then applied with binders to fabrics (Cognis).

The concept of applying selected products to textiles for specific purposes has been applied to the area of cosmetics (Cognis). A variety of skin care products can be incorporated into microcapsules and applied with binders to textiles. Chemicals such as aloe, vitamin E, menthol, ginger, lavender, and capsicum can be encapsulated and promoted for their beneficial effects.

Since a textile is a material with a very high surface area, surface modifications of textiles can lead to products with interesting and unique properties. One method of modifying textile surfaces is to expose the textile to plasma. Plasmas are ionized gases containing high energy charged and uncharged species that can interact with fiber surfaces to induce etching, cleaning, polymer deposition, and surface energy changes. Plasmas can be produced by both vacuum (Europlasma) and atmospheric techniques (Dow Corning, Apjet). Batch processing systems using vacuum plasmas have been in commercial use for sometime and have been used to create modified textiles with special surface properties such as high water repellency and adhesion promotion. Commercial atmospheric plasma systems, which are suitable for continuous processing, are currently in development.

The use of chemical crosslinking agents to provide wrinkle resistance and shape retention in cellulosic fabrics is well established. Although acceptable performance can be achieved, loss of fabric strength loss and concern with formaldehyde release remain as problems with these finishes. Recent work [10] has identified a novel approach to cellulose stabilization without fabric strength loss or formaldehyde release. Cotton fabric that had been made anionic with sodium chloroacetate was able to be crosslinked with multivalent cationic compounds, while cationized cellulose was able to be crosslinked with multivalent anionic compounds. Improved wrinkle recovery and higher fabric strength were reported.

References

1) Gürsoy, N.C., A. El-Shafei, P.J. Hauser, and D. Hinks, “Cationic Bleach Activators for Improving Cotton Bleaching”, AATCC Review, 4(8). 37-40 (2004).

2) Gürsoy, N.C., S. Lim, D. Hinks, and P.J. Hauser, “Evaluation of Hydrogen Peroxide Bleaching with Cationic Bleach Activators in a Cold Pad-Batch Process”, Textile Research Journal, 74(11), 970-976 (2004).

3) Lim, S.H., J.J. Lee, D. Hinks, and P.J. Hauser, “Bleaching of cotton with activated peroxide systems”, Coloration Technology, 121(2), 89-95 (2005).

4) Hauser, P.J., “Reducing Pollution and Energy Requirements in Cotton Dyeing”, Textile Chemist and Colorist and American Dyestuff Reporter, 32(6), 44-48 (2000).

5) Hauser, P.J. and A.H. Tabba, “Improving the Environmental and Economic Aspects of Dyeing Cotton”, Coloration Technology, 117(5), 282-288 (2001).

6) Kanik M., and P.J. Hauser, “Ink-Jet Printing of Cationized Cotton Using Reactive Inks”, Coloration Technology, 119(4), 230-234 (2003).

7) Draper, S.L., K.R. Beck, and C.B. Smith, “On-Line Dyebath Monitoring by Sequential Injection Analysis”, AATCC Review, 1(1), 24-28 (2001).

8) Merritt, J. T., III, K. R. Beck, C. B. Smith, P. J. Hauser, and W. J. Jasper, " Determination of Indigo in Dyebaths by Flow Injection Analysis and Redox Titrations", AATCC Review, 1(4), 53-57, April 2001.

9) Draper, S.L., K.R. Beck, C.B. Smith, and P.J. Hauser, “Characterization of the Dyeing Behavior of Cationic Cotton with Direct Dyes”, AATCC Review, 2(10), 24-27(2002).

10) Hashem, M., P.J. Hauser and C.B. Smith, “Wrinkle Recovery for Cellulosic Fabric by Means of Ionic Crosslinking”, Textile Research Journal, 73(9), 762- 766 (2003).

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