**2. Microbial degradation of fibers**

Textiles are easily attacked by microorganisms, which means that they quickly become damaged. Microorganisms pose a threat to textile materials at all stages of their production – from the obtaining of raw material (for example on plantations), through to the transportation and storage of the raw material and of the finished product.

Microbial degradation of fabrics depends primarily on their chemical composition. Fabrics of natural origin are particularly susceptible to attack by microorganisms.

The decomposition of natural plant-based fibres caused by the presence of fungi was known as early as 1926–1928, and was described by Smith and Morris. Research into the mechanism of the decomposition of such fibres by microorganisms has continued for 80 years (Zyska, 1977). The main component of plant fibres is **cellulose**. The content of cellulose depends on the type of fibre – in cotton it reaches 94%, in linen fabric around 80%, and in others from 63% to 77% (jute, sisal, hemp). Cellulose is a polysaccharide composed of molecules of βglucose linked by 1,4-β-glycoside bonds. The number of glucose molecules in a chain ranges from 7 to 10 thousand. Chains may be arranged in parallel, forming a crystalline structure, or tangled to form an amorphous structure. Cellulose is broken down by microorganisms through a process of enzymatic hydrolysis. This mechanism involves a multistage decomposition of cellulose to glucose, brought about successively by the enzymes 1,4-endoβ-D-glucan cellobiohydrolase (EC 3.2.1.91) (also called exoglucanase, cellobiohydrolase), endo-1-4-β-D-glucan glucanohydrolase (EC 3.2.1.4) (endoglucanase, β-glucanase) and glucohydrolase of β-D-glucosides (EC 3.2.1.21) (cellobiose, β-glucosidase) (Evans, 1996; Jeffries, 1987; Szostak-Kot, 2005).

The intensity of cellulose decomposition is indicated by the appearance of differently coloured stains on fabrics (carotenes, anthraquinones, excreted by the microorganisms), reduction in the degree of polymerization, breakage of the fibre structure and reduction in tearing strength. In extreme cases the cellulose may decompose completely.

Plant fibres also contain small quantities (up to 10%) of such compounds as hemicellulose and lignin, which give the fibres rigidity, and pectins, which act as a kind of glue. Many microorganisms are capable of producing enzymes which decompose hemicelluloses and pectins (xylanase, galactosidase, mannosidase, glucuronidase, pectinesterase, glycosidase and others) (Bujak & Targoński, 1990; Szostak-Kot, 2005). Lignin is the least rapidly decomposed component of plants, because of its structure – phenylpropane compounds are linked by ether and carbon bonds and are very resistant to enzymatic decomposition. In spite of this there are certain species of fungi and bacteria which are capable of decomposing lignin (*Chaetomium, Paeciliomyces, Fusarium, Nocardia, Streptomyces, Pseudomonas, Arthrobacter* and others) (Szostak-Kot, 2005; Targoński & Bujak 1991).

The rate of decomposition of natural plant-based fibres depends on their chemical composition. Among cellulose-based fibres, the slowest to decompose is jute (35% non-

A separate issue is the protection of finished textile materials against biodegradation through proper storage, and possibly the use of an appropriate process of disinfection which can effectively eliminate microorganisms without affecting the material's strength

Textiles are easily attacked by microorganisms, which means that they quickly become damaged. Microorganisms pose a threat to textile materials at all stages of their production – from the obtaining of raw material (for example on plantations), through to the

Microbial degradation of fabrics depends primarily on their chemical composition. Fabrics

The decomposition of natural plant-based fibres caused by the presence of fungi was known as early as 1926–1928, and was described by Smith and Morris. Research into the mechanism of the decomposition of such fibres by microorganisms has continued for 80 years (Zyska, 1977). The main component of plant fibres is **cellulose**. The content of cellulose depends on the type of fibre – in cotton it reaches 94%, in linen fabric around 80%, and in others from 63% to 77% (jute, sisal, hemp). Cellulose is a polysaccharide composed of molecules of βglucose linked by 1,4-β-glycoside bonds. The number of glucose molecules in a chain ranges from 7 to 10 thousand. Chains may be arranged in parallel, forming a crystalline structure, or tangled to form an amorphous structure. Cellulose is broken down by microorganisms through a process of enzymatic hydrolysis. This mechanism involves a multistage decomposition of cellulose to glucose, brought about successively by the enzymes 1,4-endoβ-D-glucan cellobiohydrolase (EC 3.2.1.91) (also called exoglucanase, cellobiohydrolase), endo-1-4-β-D-glucan glucanohydrolase (EC 3.2.1.4) (endoglucanase, β-glucanase) and glucohydrolase of β-D-glucosides (EC 3.2.1.21) (cellobiose, β-glucosidase) (Evans, 1996;

The intensity of cellulose decomposition is indicated by the appearance of differently coloured stains on fabrics (carotenes, anthraquinones, excreted by the microorganisms), reduction in the degree of polymerization, breakage of the fibre structure and reduction in

Plant fibres also contain small quantities (up to 10%) of such compounds as hemicellulose and lignin, which give the fibres rigidity, and pectins, which act as a kind of glue. Many microorganisms are capable of producing enzymes which decompose hemicelluloses and pectins (xylanase, galactosidase, mannosidase, glucuronidase, pectinesterase, glycosidase and others) (Bujak & Targoński, 1990; Szostak-Kot, 2005). Lignin is the least rapidly decomposed component of plants, because of its structure – phenylpropane compounds are linked by ether and carbon bonds and are very resistant to enzymatic decomposition. In spite of this there are certain species of fungi and bacteria which are capable of decomposing lignin (*Chaetomium, Paeciliomyces, Fusarium, Nocardia, Streptomyces, Pseudomonas, Arthrobacter*

The rate of decomposition of natural plant-based fibres depends on their chemical composition. Among cellulose-based fibres, the slowest to decompose is jute (35% non-

tearing strength. In extreme cases the cellulose may decompose completely.

and others) (Szostak-Kot, 2005; Targoński & Bujak 1991).

transportation and storage of the raw material and of the finished product.

of natural origin are particularly susceptible to attack by microorganisms.

properties.

**2. Microbial degradation of fibers** 

Jeffries, 1987; Szostak-Kot, 2005).

cellulose substances, including 25% lignin) (Basu & Ghose, 1962; Szostak-Kot, 2005). The rate also depends on many other factors: apart from environmental factors and the type of microorganisms, there is also an effect from thickness, type of weave, degree of crystallinity (amorphous cellulose is more easily degraded) and degree of orientation (namely the angle made by the fibrils with the long axis of the fibre – highly oriented fibres are less susceptible to biodeterioration) (Pedersen et al., 1992; Salerno-Kochan & Szostak-Kotowa, 2001; Szostak-Kot, 2005; Tyndal, 1992).

Artificial cellulose fibres include regenerated fibres (rayon) and cellulose acetate. Rayon usually has a lower degree of crystallinity, polymerization and ordering than cotton. It is also highly hygroscopic (its capacity to absorb water in normal conditions is 9.8–13%), which is a reason for its common use in making woven and knitted fabrics and as an additive to natural and synthetic fibre products. Its rate of microbiological decomposition is comparable to that of cotton. Cellulose acetate is produced by the acetylation of cellulose with acetic anhydride, as a result of which the product has a maximal degree of acetylation, and the fibre becomes more resistant to microbiological decomposition than cellulose (Buchanan et al., 1993, Buschle-Diller et al., 1994; Salerno-Kochan & Szostak-Kotowa, 2001; Szostak-Kot, 2005).

**Wool** is characterized by high strength, thermal insulation properties and hygroscopicity (it can absorb 50% moisture without feeling wet). Chemically, wool is built from three types of keratins: low-sulphur, high-sulphur and high-tyrosine. Low-sulphur keratins primarily are linked with each other and to proteins of the matrix by numerous bonds – sulphide bridges, covalent bonds and hydrogen bonds, and in the presence of water also hydrophobic bonds. Due to the presence of these bonds and the network structure of wool, it is resistant to stretching and tearing and to environmental factors, including enzymatic degradation.

The biodeterioration of woollen fabrics involves microorganisms with mainly proteolytic and keratinolytic enzymes. So far 299 species of fungus with keratinolytic properties have been described, of which 107 are pathogenic to humans (Błyskal, 2009). Decomposition of a woollen fabric proceeds by way of deamination, sulphitolysis and proteolysis (Kunert, 1992, 2000). The first stage involves the splitting of disulphide bridges, which are the source of keratin's resistant strength. This is followed by the enzymatic decomposition of proteins by proteolytic enzymes (proteases) into oligopeptides, and these are then broken down by peptidases into amino acids, which are used in metabolic processes of oxidative deamination with the release of ammonia (Gochel et al., 1992; Kunert, 1989; Szostak-Kot, 2005). Characteristic symptoms of the microbiological decomposition of wool include the variously coloured stains on the fabric surface, a distinctive smell (in anaerobic conditions H2S is produced), and loss of stretching strength.

During the technological process the woollen raw material is subjected to mechanical, chemical and photochemical action, which increases the susceptibility of the fibres to biodegradation. Many problems have been reported and described resulting from the development of microorganisms on woollen textiles, for example when carpets are in storage (Gochel et al., 1992; Hoare, 1968; Simpson, 1987). In favourable conditions of temperature (37°C) and humidity of the material (25–75%), the number of fungi may increase to as much as 109 CFU/1g of wool over 20 days (Zyska, 2001).

Microbial Degradation of Woven Fabrics and Protection Against Biodegradation 271

**Polyester** fibres are produced from large-molecule compounds with repeating ester bonds in the main chain. The type most commonly used in the textile industry is poly(ethyl terephthalate) (PET), while among aliphatic polyesters polylactic acid (PLA) is beginning to take on great importance. Polyester fibres containing terephthalate are resistant to microbiological decomposition, although in research into the effect of soil microflora such fabric displayed changes in fibre structure, which may indicate the possibility of biodegradation over a long period (Salerno-Kochan & Szostak-Kotowa, 1997). The processes of decomposition of PLA may involve enzymes such as proteinase K (Li & Vert, 1995).

**Polyacrylonitrile** fibres are produced from polyacrylonitrile, or else are copolymers of acrylonitrile with other monomers containing groups capable of reacting with reactive dyes. These fibres have high resistance to atmospheric effects, a pleasant feel, good strength and resistance to chemical and biological agents. Polyacrylonitrile, as well as dipolymers and terpolymers of acrylonitrile, are resistant to microbiological decomposition, although at high air relative humidity (90%) mould attack on the surface of polyacrylonitrile has been

Biodeterioration of fabrics is mainly caused by filamentous fungi, and to a lesser extent by bacteria. Microorganisms capable of degrading natural and artificial fibres are listed in Table

The rate of microbiological decomposition of fabrics is affected by environmental factors such as air relative humidity, temperature, light, and the properties of the fabrics, chiefly their chemical composition, fibre structure, density and thickness of weave, and the type of

**High humidity** in a fabric is the most important factor affecting the development of microorganisms. The absorption of water by a fabric depends, among other things, on its hygroscopicity and porosity. A level of fabric relative humidity above 65% increases fibre swelling and favours the development of microorganisms, particularly moulds, on the fabric. The development of bacteria requires a high fabric relative humidity, above 95% (Szostak-Kot, 2009). At the **temperature** used for fabric storage (20–35°C) many microorganisms develop on the fabrics, and the range within which microorganisms

All fibres are sensitive to photo-oxidation caused by **light radiation** (particularly ultraviolet and infrared). Ultraviolet radiation in cellulose fibres, such as cotton, causes breakage of the cellulose chain and leads to its decomposition. Wool and silk are also susceptible to photochemical degradation, particularly in the presence of oxygen – for example the photodegradation of fibroin in silk occurs as a result of the breakage of hydrogen bonds and oxidation of tyrosine. Biodegradation of silk may be favoured by prior photodegradation under the action of ultraviolet (Sionkowska & Planecka, 2011). The action of infrared radiation on textile material causes overheating of the surface and leads to many physicochemical changes. Light, increased temperature and atmospheric impurities additionally speed up the process of ageing, and in such conditions fabrics may also be

develop is significantly greater (4–50°C, excluding extremophilic microorganisms).

more sensitive to attack by microorganisms (Szostak-Kot, 2009).

**3. Conditions favourable for biodegradation of fibres and fabrics** 

substances used in the finishing of the unwoven fabric (Szostak-Kot, 2005).

described (Zyska, 2001).

1. (based on a survey of the literature).

Natural **silk** is a fibre produced from the cocoon shell of the mulberry silkworm. Silk is characterized by high strength, elasticity, thermal insulation properties and hygroscopicity (in natural conditions silk contains approximately 11% moisture, and it can have a moisture content of 30% without feeling wet).

Raw silk consists of protein fibres – fibroins – stuck together with the protein sericin. The chains are linked by disulphide bridges, which give the fibre its strength; there are also hydrogen bonds within and between molecules. This polypeptide has a crystalline structure, and around 90% of it consists of four amino acids: alanine, glycine, serine and tyrosine. Textile manufacturers formerly used raw silk, which was resistant to the damaging action of light (chiefly ultraviolet) and was stronger, although the fabric yellowed with time. Fabrics are now made from degummed silk (with the sericin removed) – this material does not yellow under the action of light, and is more resistant to microbiological decomposition (Becker et al., 1995; Kaplan et al., 1994; Szostak-Kot, 2005). Microorganisms probably assimilate sericin more easily than fibroin. The decomposition of sericin involves mainly proteolytic enzymes of microorganisms (Forlani et al., 2000). In vitro tests have also confirmed the degradation of fibroin by protease (Horan et al., 2005).

Synthetic fibres are obtained by means of polymerization. The most commonly used types are polyamide, polyester, polyurethane and polyacrylonitrile fabrics. Synthetic fabrics are resistant to biodeterioration as a rule, and if the process occurs, it is a long-lasting one.

**Synthetic fibres** which have undergone a process of biodegradation become less resistant to stretching (by as much as 20–30%), undergo swelling (increase in diameter by up to 20%), and change colour due to microbially produced dyes and acidic products which react with the dyes present in the fabrics (Zyska, 2001)..

Mechanisms of biodegradation involve physical damage to fibres and chemical decomposition due to numerous metabolites produced by microorganisms (ammonia, nitrates, hydrogen sulphide, organic acids) or by an enzymatic route (activity of lipases, esterases, proteases, ureases) (Lucas et al., 2008).

**Polyamide** fibres contain amide groups in the main chain of their macromolecules. Greatest interest is shown in aliphatic polyamides, and among them, polyamide 6 (Steelon, Perlon) and polyamide 6.6 (Nylon). Polyamides are resistant to microbiological decomposition, although research is carried out using various strains of microorganisms which contribute to that process. It has been found that some bacterial and fungal oxidases and hydrolases (for example manganase peroxidase from white rot Basidiomycetes) decompose aliphatic polyamides, leading to their depolymerisation (Friedrich et al., 2007; Lucas et al., 2008).

In the textile industry there are two types of **polyurethane** fibres used: high-crystalline types with a linear structure, and highly elastic segmental fibres of the Spandex type. Highcrystalline fibres have a similar structure to polyamides, and display high rigidity. The highly elastic type of fibres contain a minimum of 85% polyurethane polymer with a segmental structure. This fibre has a very large extension at rupture, colour permanence, and resistance to radiation and ageing. Microbial degradation of polyurethanes occurs by way of chemical hydrolysis, as a result of the extracellular action of esterase enzymes (Akutsu et al., 1998; Allen et al., 1990; Ruiz et al., 1999).

Natural **silk** is a fibre produced from the cocoon shell of the mulberry silkworm. Silk is characterized by high strength, elasticity, thermal insulation properties and hygroscopicity (in natural conditions silk contains approximately 11% moisture, and it can have a moisture

Raw silk consists of protein fibres – fibroins – stuck together with the protein sericin. The chains are linked by disulphide bridges, which give the fibre its strength; there are also hydrogen bonds within and between molecules. This polypeptide has a crystalline structure, and around 90% of it consists of four amino acids: alanine, glycine, serine and tyrosine. Textile manufacturers formerly used raw silk, which was resistant to the damaging action of light (chiefly ultraviolet) and was stronger, although the fabric yellowed with time. Fabrics are now made from degummed silk (with the sericin removed) – this material does not yellow under the action of light, and is more resistant to microbiological decomposition (Becker et al., 1995; Kaplan et al., 1994; Szostak-Kot, 2005). Microorganisms probably assimilate sericin more easily than fibroin. The decomposition of sericin involves mainly proteolytic enzymes of microorganisms (Forlani et al., 2000). In vitro tests have also

Synthetic fibres are obtained by means of polymerization. The most commonly used types are polyamide, polyester, polyurethane and polyacrylonitrile fabrics. Synthetic fabrics are resistant to biodeterioration as a rule, and if the process occurs, it is a long-lasting one.

**Synthetic fibres** which have undergone a process of biodegradation become less resistant to stretching (by as much as 20–30%), undergo swelling (increase in diameter by up to 20%), and change colour due to microbially produced dyes and acidic products which react with

Mechanisms of biodegradation involve physical damage to fibres and chemical decomposition due to numerous metabolites produced by microorganisms (ammonia, nitrates, hydrogen sulphide, organic acids) or by an enzymatic route (activity of lipases,

**Polyamide** fibres contain amide groups in the main chain of their macromolecules. Greatest interest is shown in aliphatic polyamides, and among them, polyamide 6 (Steelon, Perlon) and polyamide 6.6 (Nylon). Polyamides are resistant to microbiological decomposition, although research is carried out using various strains of microorganisms which contribute to that process. It has been found that some bacterial and fungal oxidases and hydrolases (for example manganase peroxidase from white rot Basidiomycetes) decompose aliphatic polyamides, leading to their depolymerisation (Friedrich et al., 2007; Lucas et al., 2008).

In the textile industry there are two types of **polyurethane** fibres used: high-crystalline types with a linear structure, and highly elastic segmental fibres of the Spandex type. Highcrystalline fibres have a similar structure to polyamides, and display high rigidity. The highly elastic type of fibres contain a minimum of 85% polyurethane polymer with a segmental structure. This fibre has a very large extension at rupture, colour permanence, and resistance to radiation and ageing. Microbial degradation of polyurethanes occurs by way of chemical hydrolysis, as a result of the extracellular action of esterase enzymes

confirmed the degradation of fibroin by protease (Horan et al., 2005).

content of 30% without feeling wet).

the dyes present in the fabrics (Zyska, 2001)..

esterases, proteases, ureases) (Lucas et al., 2008).

(Akutsu et al., 1998; Allen et al., 1990; Ruiz et al., 1999).

**Polyester** fibres are produced from large-molecule compounds with repeating ester bonds in the main chain. The type most commonly used in the textile industry is poly(ethyl terephthalate) (PET), while among aliphatic polyesters polylactic acid (PLA) is beginning to take on great importance. Polyester fibres containing terephthalate are resistant to microbiological decomposition, although in research into the effect of soil microflora such fabric displayed changes in fibre structure, which may indicate the possibility of biodegradation over a long period (Salerno-Kochan & Szostak-Kotowa, 1997). The processes of decomposition of PLA may involve enzymes such as proteinase K (Li & Vert, 1995).

**Polyacrylonitrile** fibres are produced from polyacrylonitrile, or else are copolymers of acrylonitrile with other monomers containing groups capable of reacting with reactive dyes. These fibres have high resistance to atmospheric effects, a pleasant feel, good strength and resistance to chemical and biological agents. Polyacrylonitrile, as well as dipolymers and terpolymers of acrylonitrile, are resistant to microbiological decomposition, although at high air relative humidity (90%) mould attack on the surface of polyacrylonitrile has been described (Zyska, 2001).

Biodeterioration of fabrics is mainly caused by filamentous fungi, and to a lesser extent by bacteria. Microorganisms capable of degrading natural and artificial fibres are listed in Table 1. (based on a survey of the literature).
