New finishing technologies for textiles

Introduction

In the last few years, demand for protective garments, particularly those designed to provide protection

against microbes, chemicals, pesticides and pollutants has been on the rise. Well established finishing

methods based primarily on chemical treatments have so far been used to impart such finishes. When

chemical coatings are used, they close all the pores in the fabric and make it impenetrable to all foreign

elements. These coatings, though effective, suffer from problems like adding weight and bulkiness,

making the fabric harsh but most importantly making the fabric non breathable and therefore

uncomfortable to wear. Such garments have been shown to impair user performance and there are safety

issues relating to their use as well as disposal. Scientists therefore, continue to look for alternate agents

and technologies which are eco friendly, durable, cost effective and do not adversely affect the comfort

characteristics of a garment while providing optimum protection and efficiency.

This paper discusses some innovative technologies which have the potential to revolutionalise the field of

textile finishing in the years to come. These technologies include immobilization of enzymes, Layer by

layer (LBL) assemblies, nanotechnology applications and use of plasma for textile surface

functionalisation. All these technologies are distinct from conventional finishes in that they impart

special functionalities to textile surfaces by bringing about modifications at micro or nano level, without

affecting the bulk properties. Special one sided effects or multifunctional effects can be created which

cannot not be obtained with traditional methods. Some of these technologies have been tested and

validated at lab scale, but most are still in research stages. As advances and developments in these areas

of finishing continue to unfold, they will increasingly be used to produce smart, intelligent and interactive

textiles of the future. As the following paragraphs show, the future of research in textile finishing is

undoubtedly based on assimilation of different sciences such as nano technology, physics, biotechnology

and biology.

Enzyme immobilisation

Enzymatic processes provide an effective non polluting alternative to conventional chemical finishing

treatments because they can operate under mild conditions, are substrate specific, non toxic,

biodegradable and do not produce any harmful by products. They can be produced on an industrial scale

by simple biotechnological methods. Matt Schwausch, 2010 Because of these reasons, enzymes have long

been used in textile wet processing. Enzymatic desizing, bio scouring, bleaching, bio washing and bio-

polishing of cotton are well established commercial technologies. Transesterification of cotton by

proteinase subtilisin has been reported, Ying Zhang (2010). In protein fibres, proteases have been used

extensively for shrinkproofing of wool and adding other functionalities to the fibre, Cai, Shao-Bo; (2011),

163(1), 112-126. Multifunctional wool fabrics with antioxidant, antibacterial and water repellent properties could be

produced by grafting alkyl gallates through laccase catalysed reaction, Gaffar Hossain (2010), 67(3-4), 231-235.

Desizing of silk with proteases has also been studied extensively Shen, J (2010).

More recently research has been conducted on treatment of synthetic fibres with enzymes. Several studies

have been reported on treatment of polyesters with cutinases and esterases to impart hydrophilicity and

antistat properties to them El-Bendary, Magda A (2010. Treatment of nylon with amidase and polyacrylonitrile

with nitrilase has also been reported. Teresa Matama, 2007 , Matama, T.; Cavaco-Paulo, A (2010).

The focus of this paper is not on such processes where enzyme is used as a finishing agent, but rather on

an innovative technology, which can be used to impart long term functionalisation to textile surfaces.

This technique is one where active enzymes are attached or ‘immobilized’ on textile substrates to impart

special properties to textile surface Qiang Wang (2009) 32:633–639, N. A. Ibrahim, (2007). As compared to free

enzymes, immobilized enzymes are permanently attached to the textile, thereby functionalising its

surface. Thus, while the free enzyme is lost after the first use, the immobilized enzyme continues to

catalyse the intended reactions again and again. This helps to reduce the enzyme cost, while at the same

time providing a permanently bio active textile surface. In biochemical procedures, immobilization is one

of the main methods used to stabilize free enzymes and is well established, but on textiles it is a more

challenging process which is still in initial stages of research. E. N. Danial, 2010, pp. 3120- 3125. ,

M. M. Elnashar, www.sciyo.com , 2010. Magdy M. M. Elnashar, 2010, 1, 61-77.

Enzyme immobilization can be used to impart durable antimicrobial and wound healing properties, stain

resistance, self cleaning and self decontamination properties to textiles. In addition, enzymes can be used

as triggers to impart bioresponsive properties to medical use textiles containing specific elements

susceptible to modification by these biocatalysts. Thus controlled release of functional molecules such as

drugs, antimicrobial substances or perfumes from materials can be achieved. Wehrschuetz-Sigl, E (2010),

The applicability and efficiency of enzyme based processes is determined by the nature of enzyme, the

physicochemical properties of textile substrate, method of immobilization, enzyme stability in the

polymeric environment and most importantly, its surface availability and accessibility. I Banerjee, 2011,

M. Tasso 2009.

Methods of enzyme immobilization

The five traditional methods of immobilisation of enzymes are adsorption, covalent bonding,

encapsulation and crosslinking. Magdy M, 2010.

i) Adsorption

This process consists of treating the substrate with enzyme under suitable conditions of pH and ionic

strength, followed by incubation. Though the process is quick, easy and cheap it is not suitable for textile

finishing as the enzyme is held only by weak forces of attraction and will leach out of the textile as soon

as it is put in water.

ii) Covalent bonding

In this process, covalent bond is formed between the enzyme and textile. This is most appropriate for

textile finishing as it is a strong linkage that will provide a permanent bonding between the functional

groups present on the textile and the amino acid residues of the enzyme. The reaction could be based on

formation of isourea linkage, diazo linkage, peptide bond or an alkylation reaction T. Xie, 2009. The

process is complex as several steps may be involved in forming a covalent bond. Depending on the

physic-chemical characteristics of the respective fibre and enzyme, either the fibre or enzyme or both may

have to be chemically modified or pretreated in order to impart suitable functionalities needed for

covalent bond formation to occur.

iii) Entrapment

In biochemical procedures, enzymes can be trapped in the lattice structure of a gel for immobilization.

The porosity of the gel structure has to be controlled so as to prevent enzyme leakage while allowing free

activity of enzyme. On textile fibres, use of polyelectrolyte multilayer films have been used to trap

enzymes. Singh,et al. 2004, propose a process for development of polyethylenimine films containing

organophosphorus hydrolases on cotton. A layer by layer deposition sequence was used to develop a

smart cotton fabric capable of decontaminating organophosphorus based pesticides and nerve agents. The

fabric has possibilities for use in civilian and military applications. Y Lee, 2003, M Onda, 2000, F

Caruso,2000 also report development of polyelectrolyte multilayers (PEMs) by layer by layer electrostatic

adsorption of oppositely charged polyelectrolytes for encapsulation of enzymes. These aqueous

polyelectrolyte solutions can be chemically tuned to create an environment conducive to the preservation

of enzyme function and stability.

iv) Encapsulation

Enzymes can be encapsulated inside a polymeric membrane, such as that of nylon or cellulose nitrate to

form micro or nano capsules which can then be applied to textile by a coating method. Amount of loading

or the rate of diffusion of enzyme are important parameters that need to be controlled in this process.

Encapsulation is a preferred method of applying special finishes to textiles.

v) Enzyme crosslinking

In this process, the enzyme molecules are cross linked with each other to form a large 3D complex

structure which is durably attached to the substrate. Enzyme crosslinking can either be based on physical

or chemical bonds. While bi- or multifunctional agents such as glutaraldehyde or bicarboxylic acid can be

used for chemical crosslinking, polyamines, phosphates, polyethyleneimine etc. can be used to crosslink

with physical bonds. Crosslinking is often used with the other methods of immobilization to enhance the

bonding process. The disadvantage of this process lies in that the formation of a 3D structure in textile

makes the fabric harsh and brittle and sometimes even the activity of enzyme may be impaired by self

crosslinking.

Besides these conventional biochemical procedures, several new technologies for enzyme immobilization

have been proposed. These include use of single enzyme nanoparticles, where each molecule of enzyme

is protectively enclosed in a nano capsule for enhanced stability and high activity. Yan et al. (2006).

Other techniques involve use of enzymes, microwave irradiation and ionic liquids for immobilization

which have been discussed in detail by Magdy in an excellent review. Magdy, 2010.

Parameters of enzyme immobilization

1) Enzyme selection: Hundreds of enzymes are available in nature. Therefore the first step in

enzyme immobilization relates to the selection of enzyme. Enzyme selection depends primarily

on the type of functionality desired such as self cleaning, antimicrobial or detoxification etc.

Weina Li, 2011

2) Method of immobilization: Once an enzyme with the suitable functionality has been selected, next

consideration is the process of its attachment to the selected substrate. This depends on the

physical and chemical properties of the textile, the desired efficiency of activity and enzyme

loading, end use of the treated fabric and so on. Immobilised enzyme may exhibit different

properties depending upon the method of immobilization. Loss in biological activity and enzyme

stability should be minimum. S. M. Olsen,2007 . Based on these considerations, a suitable

method of immobilization has to be selected.

3) Modification of enzyme or substrate: Based on the method selected, the fabric and/or the enzyme

may have to be suitably modified to allow the bonding to occur. For example, for chemical

bonding, the substrate should have adequate number of functional groups to bind with the

enzyme. The nature of functional groups should allow formation of durable bonds, like covalent,

co-ordinate or electrovalent so that the treatment is durable to washing and abrasion etc. Enzymes

can also be modified. Method of modification of enzyme and substrate has to be chosen carefully.

Enzyme efficiency and stability should not be affected.

4) Enzyme loading : Effective loading concentration would be determined by the nature of

functionality desired. Process for obtaining optimum enzyme loading in each case needs to be

developed.

5) Enzyme retention and durability: Durability is the final and critical process consideration. During

manufacturing and use, a garment is subjected to severe mechanical, abrasive and laundering

activities. The immobilized enzyme should retain its activity and be durable to stresses

experienced during use. Important losses of biological activity appear during drying and in the

first months of storage of immobilized preparations. Special treatments or processes for attaining

higher extent of fixation along with better retained activity need to be developed. N. A. Ibrahim,

M. Gouda, 2007, Matt Schwausch, 2010; Ying Zhang (2010)

Applications of enzyme immobilization on textiles

Wool

Wang et al, 2008 report the immobilization of lysozyme (5g/l, 400C, pH7, 6h) on wool which had been

pretreated with glutaraldehyde ( 0.2%,250C, 6h). Lysozyme was fixed with the help of covalent bonds. As

lysozyme is a known antimicrobial agent, treated wool showed good antimicrobial effect against S.

aureus. Qiang Wang , (2009).

Cotton

Belov et al. immobilized proteolytic enzymes trypsin, lysozyme and lysoamidase on cotton wool and

dressings for treatment of burn and other wounds. They found that immobilized enzymes were much

more effective in healing wounds as compared to free enzymes. A. A. Belov, 2008

Ibrahim et al, 2007 optimised the parameters for immobilization of alpha amylase, alkaline pectinase

and laccase enzymes on modified cotton to make it antimicrobial. Cotton crosslinked with BTCA and

post activated could bind with the enzyme with the help of ionic interactions. In another case, pre -

aminated cotton was chelated with Cu to form co-ordinate bonds with the enzyme. In each case the

antimicrobial property was found to be durable for up to 30 washes. N. A. Ibrahim, (2007)

Chemically modified papain enzyme was immobilized on activated cotton fabric by a two step method.

Thermal stability and resistance to alkali and washing detergent of immobilized modified enzyme was

improved considerably after immobilization. Xue, Yong (2010).

Synthetics

Li et al. report a comparative study on properties of lipase immobilized by six different methods on

synthetic nonwoven fabrics and a woven silk cotton fabric. Hydrophobic treatment based on polydimetyl

siloxane was found to be most effective. Weina Li, 2011

Enzyme immobilization has the potential to become a major textile finishing technology. However

several challenges must be resolved before their full practical applicability can be exploited.

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