Encyclopedia of Color Science and Technology

2016 Edition
| Editors: Ming Ronnier Luo

Finish, Textile

Reference work entry
DOI: https://doi.org/10.1007/978-1-4419-8071-7_154

Synonyms

Definition

Textile finishing can be defined as all processes (chemical and/or mechanical), employed subsequent to textile coloration which impart additional functionality/superior aesthetics to the textile material. Mostly, textile finishing is applied to fabrics (woven, knitted, nonwovens); however, textile finishes can also be applied to fibers and yarns.

Introduction

The primary objectives of textile finishing are to improve the aesthetic and functional properties of textiles. In a broader sense, “finishing” relates to all processes that fabrics might be subjected to subsequent to weaving, knitting, or nonwoven manufacturing processes. The term “finishing” could include fabric preparation (e.g., singeing, desizing, scouring, bleaching, optical brightening process, mercerization process, etc.) and coloration (dyeing and printing); indeed, the combination of these processes is sometimes referred to as “wet-finishing” processes [1]. Another school of thought refers to “finishing” as the final stage of fabric preparation with the objective to prepare the fabric for the consumer and that the term “finishing” concerns only fabric treatment other than fabric preparation and coloration. In this chapter, finishing subsequent to coloration will be discussed, in which context, it is important to check the compatibility of the finishing process with the treated substrate and the coloration process that has been previously implemented [2].

Classification

The conventional textile finishing methods can broadly be divided into two categories:
  1. (i)

    “Dry” or “mechanical” finishes

     
  2. (ii)

    “Wet” or “chemical” finishes

     

There are, however, finishing operations which combine mechanical and chemical finishes e.g., mercerization (the NaOH treatment of fabric on machines with or without tension).

“Dry” or “Mechanical” Finishes

The mechanical finishing of textiles may range from a simple drying operation to a complicated series of calendaring operations (Schreiner finisher). A few examples of the mechanical finishing of textile are discussed below.

Drying

It is well known that wet fabric can hold a large amount of water and that some of this held water can be easily removed by simple mechanical action. The efficiency of the process to mechanically remove the water from the fabric is vitally important from both cost and environmental points of view. High energy is required to evaporate the remaining water due to its high latent heat of evaporation. Machines such as mangles, centrifuges, and suction-slot machines are used in textile processing to remove water from fabric by mechanical means [3]. Drying machines are employed in textile processing with the purpose of removing the water that has not been removed by mechanical action. The majority of the dryers used in textile processing offer continuous throughput and a few examples of such machines are “hot flue”, “drum dryers”, “perforated drum dryers”, “tumble dryers”, etc. [1].

Calendering

In calendering, the fabric is passed between two heavy rollers. The rollers may vary in hardness, surface speed, and temperature. Fabric properties such as smoothness and luster can be improved using calendering [4]. Calender finishing can be of six types, namely, simple finishing or swizzing calendering, chasing calendering, friction calendering, Schreiner calendering, embossing calendering, and felt calendering. A few examples of calendering are discussed below.

Friction Calendering

The differential speed of the two rollers is carefully selected to produce effects such as “chintz.” The smooth metal roller normally rotates at a higher rate than the soft roller [1, 3]. Durable finishes (Everglaze) can be achieved using this method by adding a cross-linking agent [5].

Embossed Effects

In this technique, a fabric pattern is produced by calendering the fabric using an engraved heated metal roller and a soft roller [4]. To avoid slippage between the rollers, it is important to control the process accurately.

Schreiner Finishing

In “Schreinering,” fine lines engraved on a metal roller are transferred to the fabric. With appropriate fabric construction and by carefully engineering the line direction of the engraving, a soft lustrous handle can be achieved [3]. This treatment is used to give cotton fabric the appearance of silk [1]. Although the wash fastness of this effect is poor [1, 3], it increases the point-of-sale appeal [3].

Napping

Napping is a very effective way for imparting a soft handle to fabrics [6]. Fabrics of low-twist, staple fiber yarn can be used for napping [7]. The napping machine contains metal cards and the napping tool comprises rollers with curved metal wires [1] which pull the fiber ends to the surface of the fabric. One or both sides of the fabric can be napped [7].

Sanforizing

Fabrics contain internal tensions as a result of the various manufacturing processes employed, and a pretreatment is required to nullify this effect, since, otherwise, there is a possibility of significant shrinkage of garments during washing. Sanforizing is a controlled mechanical shrinkage process without the use of any chemicals. This treatment should be the last treatment that is applied to the fabric [1].

“Wet” or “Chemical” Finishes

Although chemical finishing has always been an important process for textiles, the demand for high-performance textiles has grown exponentially in recent years and, as a result, so has the demand for chemical finishing [8]. The majority of chemical finishes for textiles are additive, where the finishing treatment results in an increase in substrate mass through sorption or deposition of chemical compounds. However, some chemical finishing can be subtractive, in which the treatment results in the fiber substrate losing mass as a result of chemical degradation. While chemical finishing is mainly applied to fabric, it can also be applied to loose fibers, yarns, garments, etc. Based on the life-span of the finish on the textile substrate, textile finishing can also be classified as transient and durable finishing. The most important aspect in this regard is the resistance of the finish to domestic washing [9].

Application of Chemical Finishes

While the application and formulation of chemical finishes depends on several factors, the most important factors are the composition of the material being treated and the chemistry of the functional chemical. Interaction of the finishing effects, compatibility of different chemicals, and the environmental/green credentials of the process are other factors to consider.

If the functional chemical finishes displays high substantivity towards the substrate, then exhaust (immersion) application methods can be used and any of the textile dyeing machines employed for batchwise dyeing can be used for textile finishing. However, if the applied functional chemical has limited or low substantivity, then a continuous application method can be used. One such method is the pad-dry-cure method wherein the fabric is first immersed in a solution containing the functional chemical, followed by drying and finally “curing” to fix the finish within the fabric (Fig. 1).
Finish, Textile, Fig. 1

Schematic diagram of pad-dry cure operation

Chemical finishes can also be applied to textiles using modern application techniques such as exposure of the textile substrate to plasma employing either low pressure, low-temperature plasma, or atmospheric plasma. Plasma, which is considered as the fourth aggregation state of matter, can be described as a mixture of partially ionized gases in which the constituents are achieved by external energy addition. The main advantage of such plasma treatments are:
  • It consumes minimal chemicals compared to conventional finishing.

  • No costly drying process is required.

  • It is a surface treatment, so the bulk properties of the material are not affected.

  • High environmental compatibility.

Important Chemical Finishes

A few commercially important chemical finishes are discussed below. Other types of chemical finishes include, but are not limited to, antistatic finishes, soil release finishes, insect resist finishes, flame-retardant finishes, stain resist finishes, nonslip finishes, UV-protection finishes, finishing to improve color fastness, etc.

Softening Agents

Softeners are one of the most widely used chemicals in textile processing, and as the name suggests, the application of softeners dramatically improves the handle and perceived quality of a fabric. In textile processing, one of the most important functions of softeners is to counteract the harshness imparted by other finishes (e.g., easy care). Softeners are, however, also used extensively in domestic washing formulations.

Although the main effects of the softeners are at the surface of fibers, the small molecules can impart internal plasticization of the fibers by reducing the glass transition temperature (Tg) of the fibrous polymer [8]. Early softeners were based on waxes and oils although modern types can be divided into five categories, namely, cationic softeners, nonionic softeners, anionic softeners, reactive softeners, and amphoteric softeners [3].

Cationic softeners are the most important type of softener for both industrial and domestic applications. The positively charged ends of the cationic softeners orient themselves towards the negatively charged fibers (zeta potential), creating a new surface of hydrophobic carbon chains that are responsible for the excellent softening effect of cationic softeners [8]. Because of the positive charge, these softeners are substantive towards cellulosic fibers, and exhaust application of these finishes is widespread using conventional textile dyeing machines (e.g., winch, jet, beam) [3]. Cationic softeners are known to exacerbate the soiling propensity of fibers and to inhibit soil removal. Dimethyldistrearylammonium methosulfate is a good example of a popular cationic softener (Fig. 2). The use of silicone-based finishes in textile processing has grown steadily over the last 50 or so years [3]. Silicon-based cationic softeners provide a high degree of softness and a unique hand to fabrics. However, silicon softeners may contain variable amounts of siloxane oligomers, depending on the method of synthesis, which may be a cause of air pollution [8]. A popular range of silicon softeners are based on the weakly cationic amino functional siloxanes. Although these silicon compounds could potentially be applied from mild alkaline conditions, durability is improved by application at pH of 4.
Finish, Textile, Fig. 2

Dimethyldistrearylammonium methosulfate

Nonionic softeners are well known to perform multiple functions such as softeners, emulsifiers, stabilizers, extenders, and lubricants [3]. Paraffin waxes and similar materials are the most basic nonionic softeners. Molten polyethylene (Fig. 3) at high pressure can be air oxidized to secure hydrophilic characteristics (mainly carboxyl groups). High-quality, more stable products can be produced by emulsification in the presence of alkali. These products are stable to extreme pH conditions and can withstand the temperatures used for normal textile processing [8]. In recent years, polysiloxanes have gained importance as nonionic softeners (Fig. 4). Due to their limited substantivity, nonionic softeners, with very few exceptions, are normally applied by non-exhaust methods (e.g., padding) [3].
Finish, Textile, Fig. 3

Polyethylene

Finish, Textile, Fig. 4

Polydimethylsiloxane

Anionic softeners, due to the presence of the negative charge, are repelled from negatively charged fibers (e.g., cellulosic fibers) which leads to higher hydrophilicity [8]. These were among the first soft finishes to be used commercially and include long-chain alkyl sulfates, sulfonates, and succinates. Anionic softeners are used in specialized areas of application where the physiological activity is low, e.g., medical textiles. As the majority of fluorescent brightening agents are anionic, they are widely used in conjunction with anionic softeners for the resin finishing of white cellulosic fibers [3].

Reactive softeners contain functional groups capable of reacting with particular functional groups in some fibers [8] (e.g., the -OH group of cellulosic fibers). This type of finishing is permanent to washing due to the formation of covalent bonds between the softener and substrate. N-methylol derivatives of stearic acid amides and urea-substituted compounds are very successful as reactive softeners (Fig. 5) [3]. One example of a silicon-based reactive softener is given in Fig. 6, which is a modified siloxane and contains functional silanol groups. The silanol group could potentially be replaced by other functional groups such as amines or alcohols.
Finish, Textile, Fig. 5

N-methylol derivative (R: C17H35)

Finish, Textile, Fig. 6

Compound containing silanol group

Amphoteric softeners have limited textile applications but are very popular in personal care products (e.g., shampoo formulations) due to their low toxicity [3]. One example of an amphoteric softener is shown in Fig. 7.
Finish, Textile, Fig. 7

Alkyldimethylamine oxide softener (R: long alkyl chain)

Water and Oil-Repellent Finishes

There is a distinction between “water-repellent” and “waterproof” fabrics. Waterproofing is achieved, for example, by coating the fabric with rubber. Such a treated fabric will not only be impermeable to water but also most notably against air and perspiration; as such, “waterproof” fabrics are uncomfortable to wear. A water-repellent finish, on the other hand, remains permeable to air and is achieved by the application of hydrophobic chemicals to the fabric [1]. These types of “water-repellent” finishes are normally used for clothing and will be discussed in this chapter. As very few textiles are inherently water repellent but none are oil repellent, so an additional process must be added to display these properties.

If the internal cohesive interactions within a liquid are lower than the adhesive interactions operating between a solid surface and the liquid, then a drop of the liquid will spread on the solid surface. Based on this theory, repellent finishes (both oil and water) work on the principle of reducing the free energy of the fabric surface [8]. In this context, it should be mentioned that alongside the chemical composition of the material, the geometry of the textile surface also plays a significant role in the wettability of the textile [1]. It has long been recognized that superhydrophobic surfaces require a unique combination of two fundamental properties, namely, surface roughness and low surface energy [2]. The functional chemicals used to achieve water-repellent finishing significantly vary in their chemistry, their role being to reduce the surface energy of the fabric by adding lower surface energy chemical groups to the surface [3].

The chemicals traditionally used to achieve water repellence may be divided into a few groups: metal salts, soap/metal salts, wax, pyridinium-based finishes, organometallic complexes, N-methylol derivatives, silicone finishes, and fluorochemical finishes [3]. Among these, only fluorocarbon finishes are known to repel both oil and water [3, 12], whereas the other finishes can repel only water. Moreover, perfluorinated derivatives are effective at very low concentrations [1]. Polymeric fluorochemical finishes are typically acrylic or methacrylic polymers with perfluoro side chains. Silicon-based water repellents are also used (Fig. 8).
Finish, Textile, Fig. 8

Polydimethylsiloxane

Easy-Care and Durable Press Finishes

As the name suggests, “easy care” and “durable press” are applied to textiles to impart minimum care properties, mostly to cellulosic fibers and their blends with other fibers. Various terms have been used to describe this area, including easy care, easy-to-iron, no iron, crease resistant, wrinkle resistant, wrinkle free etc. However the technically correct term is “cellulosic anti-swelling” or “cellulosic cross-linking” finishes [8].

Cellulose (natural or regenerated) is a linear polymer formed by the condensation of β-d-glucopyranose that contains 1→4-glycosidic linkages. The presence of hydroxyl groups along each chain creates extensive H-bonding both between (intermolecular) and within (intramolecular) the chains. Formation of such intramolecular H-bonds imparts “stiffness” to the cellulose molecules by restricting movement of the 1,4-β-d-glucopyranose units. The -OH groups are also responsible for the hydrophilicity of cellulosic fibers; owing to the high density of the -OH groups, cellulosic fabrics shrink in water and crease upon drying. The main function of easy-care/durable press finishing is to overcome shrinkage and wrinkling by cross-linking the -OH groups.

Although finishing agents are unable to penetrate the crystalline regions of the fiber, the easy-care/durable press finish needs to be of small Mr and preferably high reactivity to enable it to penetrate the amorphous region of the fibers [3].

It was demonstrated in the late 1920s that thermosetting resins (e.g., phenol-formaldehyde, urea-formaldehyde) could impart crease resistance to cellulosic fabrics. Since then, numerous publication and patents have described novel cross-linking reagents based on urea-HCHO chemistry [4]. This original type of easy-care products (urea-HCHO resins) used to contain high free formaldehyde, e.g., dimethylolurea (DMU) which is prepared from an excess of HCHO (Fig. 9). These nonreactant types of finishes are only durable to washing temperatures up to 60 °C. Wash fastness can be improved by using reactive resins such as methoxymethylmelamines (Fig. 10).
Finish, Textile, Fig. 9

Dimethylolurea

Finish, Textile, Fig. 10

Methoxymethylmelamines (R=CH2OCH3, CH2OH)

The first cyclic urea-reactant finishing agent was dimethylol ethylene urea (DMEU) which displays poor fastness to chlorine bleaching and adversely affects the light fastness of the finished fabric (Fig. 11). Cyclic urea-based finishing agents, N,N’-dimethylol-4,5-dihyroxyethylene urea (DMDHEU), comprise ~90 % of the easy-care/durable press finish products that are available in the market [8] (Fig. 12). Due to the presence of two hydroxyl groups at the C-4 and C-5 positions, the reactivity of DMDHEU is low, and therefore, reaction requires a catalyst. Although DMDHEU-containing products contain >0.3 % free formaldehyde, the search for formaldehyde-free finishing agents has spanned several decades [3] due to the toxicological effects associated with formaldehyde. Textiles containing a high level of formaldehyde can give rise to eczema and allergic reactions; furthermore, HCHO is a suspected human carcinogen [8]. Expensive formaldehyde-free finishing agents such as N,N’-dimethyl-4,5-dihydroxyethylene urea (DMeDHEU) (Fig. 13) is used for textile processing. DMeDHEU is less reactive than DMDHEU and therefore requires a stronger catalyst and harsher reaction conditions for successful cross-linking with cellulosic fibers.
Finish, Textile, Fig. 11

Dihydroxymethyl ethylene urea

Finish, Textile, Fig. 12

N,N′-dimethylol-4,5-dihyroxyethylene

Finish, Textile, Fig. 13

N,N′-dimethyl-4,5-dihydroxyethylene urea

Antimicrobial Finishes

Antimicrobial finishes are used to inhibit the growth of or to destroy microscopic organisms [3]. This could be for hygiene purposes, i.e. to protect the user from pathogenic or odor-causing microorganisms or to protect the textile material itself from damage caused by mold, mildew, or rot-producing microorganisms. Formaldehyde is a widely used biocide and preservation product. As discussed in the previous section, the majority of easy-care/durable press finishes contain HCHO, and therefore, these finishes display a small antimicrobial effect. However, for effective antimicrobial action, specific chemical finishes are used. Traditional antimicrobial agents such as copper naphthenate, copper-8-quinolinate, and numerous organomercury compounds are strictly regulated because of their toxicity and potential for environmental damage [8].

A common antimicrobial agent extensively used for cellulosic material is polyhexamethylene biguanide (PHMB) which has long been used in applications such as cosmetics and swimming pools. Along with conventional textile applications, PHMB can also be used in the production of medical textiles. PHMB is cationic and therefore displays excellent durability on cellulosic material [3]. Triclosan (Fig. 14) is another antimicrobial agent that is used extensively in mouthwashes, toothpastes, deodorants, and on textiles. This is nontoxic to humans and used as durable antimicrobial finish on polyester and polyamide fibers and their blends with cotton and wool. Heavy metals such as silver, copper, and mercury can provide antimicrobial effect in the form of the metal or metallic salt. Antimicrobial high-performance textile fibers (e.g., polyester, nylon, etc.) can be produced that include nanoparticles of heavy metals (e.g., silver). Chitosan is a natural biodegradable polymer which is nontoxic and shows microbial resistant.
Finish, Textile, Fig. 14

2-(2,4-dichlorophenoxy)-5-chlorophenol

Conclusions

As a result of increasing demands for superior quality and functionality in textiles, the sophistication of textile finishes and finishing operations has increased. New types of finishing are being developed to provide novel effects such as fragrance finishes, well-being finishes, bionic finishes, as well as finishing for smart textiles, medical textiles etc. Parallel to the search for novel finishes, existing finishes (and application techniques) are constantly being scrutinized to ensure that processing is as efficient as possible from technical, economical, and ecological perspectives. Textile finishing can be expected to remain a highly valuable tool which can significantly enhance the value of the finished textile product.

Cross-References

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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  1. 1.School of DesignUniversity of LeedsLeedsUK