Chemical finishing can be defined as the use of chemicals to achieve a desired fabric property. Chemical finishing also referred to as ‘Wet’ finishing, includes processes that change the chemical composition of the fabrics that they are applied to. Typically chemical finishing takes place after dyeing or printing, but before fabrics are made into garments or other textile articles. However many chemical finishes can also be successfully applied to yarns or garments.
Chemical finishes can be durable, i.e., undergo repeated launderings or dry cleanings without losing effectiveness, or non-durable, i.e., intended when only temporary properties are needed or when the finished textile typically is not washed or dry cleaned, for example some technical textiles. In nearly all cases, the chemical finish is a solution or emulsion of the active chemical in water. Use of organic solvents to apply chemical finishes is restricted to special applications owing to the expense and the real or possible toxicity and flammability of the solvents employed. The actual method of finish application depends on the particular chemicals and fabrics involved and the machinery available.
The proper formulation of chemical finishes requires consideration of several important factors: the type of textile being treated (fibre and construction); the performance requirements of the finish (extent of effect and durability); the cost to benefit ratio; restrictions imposed on the process by availability of machinery, procedure requirements, environmental considerations; and compatibility of different formula components as well as the interaction of the finishing effects.
To bring all these parameters to an acceptable compromise is not easy, even for a single purpose finish. but usually several types of finishes are combined for economical reasons mostly in one bath. this is often the hardest challenge of chemical finishing. first all components of the finish bath must be compatible. Precipitation of anionic with cationic products have to be avoided. the emulsion stability of different products may be reduced by product interactions. more difficult is often the second hurdle, the compatibility of the primary and secondary effects of the different types of finishes that are being combined:
- Some effects are similar or assist each other, for example silicone elastomers cause water repellency, softeners bring about antistatic effects and antistatic finishes can be softening.
- Some effects are obviously contradictory, for example hydrophobic finishes and hydrophilic antistatic finishes, or stiffening and elastomeric finishes, or stiffening and softening finishes.
- Other types of finishes typically reduce the main effect of a finish type, for example the flame retardant effect is decreased by nearly all other types of chemical finishes as they add flammable components to the fabric.
- Fortunately true antagonistic effects are rare, but true synergistic effects are also rare, where the resulting effect of a combination is greater than the sum of the single effects of the combined products. Examples of both cases are different types of flame retardants.
Thus the finisher is glad when the combined products do not interfere, neither in the finishing bath nor on the fabric., with all their different effects, but this usually is the exception rather than the rule.
The discussion of the interaction of the primary effects of the combined products can be expanded to their secondary effects, the desired and the undesired ones. Obviously this task quickly approaches confusion. It is not surprising that successful chemical finishing is sometimes thought of as being nearly magical.
the above table gives some of the general requirements expected of a chemical finish. As can be seen, they can be quite daunting. One future challenge for chemical finishing is the ever increasing concern over environmental and ecological issues. Traditional chemistries and manufacturing methods must be changed and modified to meet the new realities of our modern world.
Thus it is not surprising that an expert system was developed (TEXPERTO from Clariant), where the experience of many finishing experts is combined in a software program that enables less experienced finishers to create successful recipes interactively with a computer. This computer-aided generation of recipes starts with detailed detailed questions about the textile article to be finished, followed by a profile of requirements for the chemical finish. Included are questions concerning restrictions, for example cost limits, available machinery, process steps and environmental limitations. This expert system incorporates most of the different requirements and factors that have to be considered when formulating a demanding finishing recipe.
This recipe formulation is not only a challenge but also a charming task. For those finishers, who have the knowledge and some experience, chemical finishing is an inspiring and fascinating job, where the interaction of chemical understanding, technical grasp, textile feeling, and an instinct for market trends leads to considerable success and increased value (both in the worth of the finished fabric and in the esteem of the finish designer).
IMPORTANCE OF CHEMICAL FINISHING
Chemical finishing has always been an important component of textile processing, but in recent years the trend to high tech products has increased the interest and use of chemical finishes. As the use of high performance textiles has grown, the need for chemical finishes to provide the fabric properties required in these special applications has grown accordingly.
The amount of textile chemical auxiliaries sold and used globally in one year is estimated to be about one-tenth of the world’s fibre production. With fibre production currently at 60 million tonnes, about 6 million tonnes of chemical auxiliaries are consumed. About 40% of textile auxiliaries are used in finishing, the largest percentage usage of all textile chemicals, followed by dyeing and printing auxiliaries and pretreatment chemicals. Within the textile finishing group, the product breakdown based on TEGEWA is given as a survey in Fig. below and given in more detail in table below. Softeners are clearly the most important individual product group. In terms of value, the repellent group is the leader with the highest ratio of cost per amount. This reflects the relatively high cost of the fluorochemical subgroup of repellents.