CHAPTER 1 INTRODUCTION

Transcription

1 CHAPTER 1 INTRODUCTION Finishing is the heart of textile processing. It is any process that is done to fiber, yarn, or fabric either before or after fabrication to change the appearance (what is seen), the hand (what is felt), or the performance (what the fabric does) (Kapolph and Langford, 1998). Fabric and other such materials undergo finishing operations with surface active materials to impart desired surface properties (Bajaj, 2002). In order to impart the required functional properties to the fiber or fabric, it is customary to subject the material to different types of physical and chemical treatments. It is the final processing of the cloth and its purpose is to make the fabric suitable for its intended end use. Textile finishes and finishing are classified in several ways. Usually categorized as aesthetic and functional finishes. The former modify the appearance and/or hand (feel) of fabric, while the latter improve the performance of a fabric under specific end use conditions. They are also categorized as chemical and mechanical finishes. These are also called wet finishing and dry finishing respectively. Finishes are also categorized by their degree of permanence. These finishes are called permanent, durable, semi-durable and temporary (Kapolph and Langford, 1998). In the case of textiles, finishing is accomplished through either the padding or the exhaust process. In both of these processes finishing compounds are transferred from aqueous solution phase to the fabric surface and then cured through the application of heat, leading to the desired surface finish. While the finishing compounds are transferred to the fabric through the physical entrapment in the padding process, the actual exhaustion of the compound from the solution phase on to the fabric is accomplished through specific adsorption in the exhaust process (Purohit, Somasundaran, and Kulkarni, 2006). Textile finishes are important because they help to improve the appearance; they also make the fabric more useful and suitable for an end (specific) use. Some functional or special finishes are applied to improve the performance of a fabric for some specific purpose, for example antibacterial, flame retardant, water absorbency and soil release activity. 1

2 Antibacterial: Microbes such as bacteria, viruses and fungi are present almost everywhere. Human beings have an immune system to protect against accumulation of microorganisms but material such as textiles can easily be colonized by high numbers of microbes or even decomposed by them. Textiles are carriers of microorganism such as pathogenic bacteria, odour generating bacteria, mould and fungi. Antimicrobials enhance the functionality and value of textile products by keeping the microorganism that cause odour and fiber degradation under control. The application of antimicrobial textile finishes includes a wide range of textile products for medical, textile, industrial, home furnishing and apparel sectors (Jaypriya and Bagyalaxmi, 2013). Bacteria, gram positive and gram negative, as well as fungi have been commonly found in textiles, including bedclothes and clothing. Many of these microorganisms are pathogens or opportunistic pathogens quite often related to nosocomial infections (Takai et al., 2002). Natural and synthetic fibers vary greatly in their response to microbial growth. Both may act as willing substrates but the mechanism in the two cases is very different. Natural fibers are easy objects for microbial attack because they retain water readily and microbial enzymes can readily hydrolyze their polymer linkages. Cotton, wool, jute and flex are reported to be most susceptible to microbial attack (Gupta and Bhaumik, 2007). Textile goods, especially those made from natural fibers, provide an excellent environment for microorganisms to grow, because of their large surface area and ability to retain moisture. A number of chemicals have been employed to impart antimicrobial activity to textile goods. These chemicals include inorganic salts, organometallics, phenols and thiophenols, onium salts, antibiotics, heterocyclics with anionic groups, nitro compounds, urea and related compounds, formaldehyde derivatives, and amines (Lim and Hudson, 2004). Many of these chemicals, however, are toxic to humans and do not easily degrade in the environment. Therefore, the development of non-toxic synthetic process for the preparation of biodegradable and biocompatible textiles with antimicrobial abilities, also known as antimicrobial-finished textile products is encouraged. These antimicrobial-finished 2

3 textile products usually contain inhibitory compounds such as silver, quaternary ammonium chloride, metals, aromatic, halogen compounds and chitosan (Kenawy, worley and Broughton, 2007; Alonso, et al., 2009). Chitosan, a natural biopolymer, has a combination of many unique properties such as antimicrobial activity with biodegradability, nontoxicity and cationic nature (Lim and Hudson, 2004). The textile industry continues to look for eco-friendly processes that substitute for toxic textile chemicals. In this point of view, chitosan is excellent as an eco-friendly textile chemical. Flame retardant: A flame resistance textile will not continue to support a flame once the source of ignition has been removed. Likewise, a glow resistance textile will not continue to glow when the source of ignition is removed; often, a fabric is flame resistant but not glow resistant. When both flame and glow resistances are exhibited, the product is said to be fire resistant. Several theories have been proposed to explain how flame retardants function; they include coating, gas, thermal, hydrogen bonding and catalytic dehydration of cellulose to carbon and water (Reeves and Drake, 2004). Cotton textiles are one of the admirable natural materials that have been extensively utilized in different productions (Das, Bakshi and Bhattacharya, 2014). Mercerization is a well-known treatment for enhancing certain physical properties of cotton fibers (Buschle-Diller and Zeronian, 1992). However, cotton fiber especially mercerized ones has the capacity of flammable (Ratnapandian et al., 2013). A large number of textiles and indoor adornments including curtains, carpets, wallpaper, and so on are all easy to burn (El-Tahlawy et al., 2008). The strong request for flame retardant fabrics has constantly developed during the past decades and has become a prompting demand (Zhao, 2010). For a long time, phosphorous compounds including N-methylol dimethylphosphono propionamide (MDPA) and tetrakishydroxymethyl phosphonium chloride (THPC) under the title of trade names Pyrovatex CP have been the most applicable approach to obtain durable flame retardant finishes for textiles. They are capable of forming cross-linked structures on the fiber or reacting 3

4 with the fiber (Schindler and Hauser, 2004; Yang and Wu, 2003). These compounds affect pyrolysis reaction, prevent the formation of levoglucosan and flammable volatiles, the formation of char and are used as flame retardant agents for cellulosic fibers (Cheng and Yang, 2009; Gaan and Sun, 2009). Water absorbency: Fabric structure can also influence hydrophilic properties due to mechanisms of moisture transport between fabrics. Moisture can remain in the fiber cross-sections, on the surface of the fibers, in the voids formed within a yarn by a plurality of fiber channels and in the voids caused by yarn crossovers in woven and knitted fabrics (Freddi, Mossotti and Innocenti, 2003). The clothing should take up the moisture from the skin as well as transmit it to the atmosphere. Higher hydrophilicity of a material is known for good absorption (Das et al., 2009). Hydrophilic fibers absorb higher number of water molecules and thus show higher moisture regain at a standard atmospheric condition. Regain of a blended material can be considered as a scale for quantifying hydrophilicity. Moisture regains and water absorbency of the material respectively determines how much water vapour or liquid water can be absorbed by the clothing material from the skin. Along with the absorption characteristic there are other moisture related properties which affect the thermo physiological clothing comfort, such as drying time, water vapour permeability and wicking property of the material. Human body perspires in two forms insensible (in vapour form) and sensible perspiration (in liquid form), and to be in a comfortable state, the clothing which will be worn should allow both the type of perspirations to transmit from the skin to the outer surface. Water vapour permeability determines breathability of the clothing material. The mechanism involved in water vapour transmission through fabric from the skin to the outer surface by diffusion and absorption desorption method (Das et al., 2007). In absorption transmission desorption method hygroscopic material acts as a sink, by absorbing the perspiration from the skin and water vapour get transmitted from it to the outer surface. It maintains a constant vapour concentration in the air immediately surrounding it (Das et al., 2009). 4

5 Soil release: Soiling generally means smearing or staining of a large surface of the fabric with dust or dirt and oil or grease or both. The problem of soiling is not a new one. Due to absorption and retention of soil, the whiteness and brightness of fabric is spoiled and it appears yellowish and dirty. Soil release finish is a chemical finish, due to application of this finish many desired properties like fabric absorbency, easy removal of stain from fabric, rise in the wicking action for better comfort in wear, easy in dry clean, good laundry durability and maintaining brightness after repeated laundering are obtained (Islam and Khan, 2013). A soil release finish does not prevent initial soiling, but it does enable deposited dirt to be easily removed in laundering. A soil repellent finish, on the other hand, keeps soil on the surface of the fabric so that it can be wiped off. Soil repellent finishes, consisting of a protective film on the surface of the fabric, appeared first in the market. Because some dirt eventually penetrated the protective film and become trapped in the fabric, a soil release system was developed which allowed deposited dirt to be washed away (Lunde and Janecek, 2010). Silicone finish: These days due to specific use and requirements of the consumers special purpose finishes are gaining importance of these antibacterial, flame retardant, water absorbency and soil release are some finishes which are very specific. Silicone finishes are widely recognized as the best materials for increasing the softness of fabrics, enhancing their aesthetic feel and imparting an excellent hand. They make fabrics more comfortable and more desirable to wear. Due to their outstanding specific property, as well as their higher effectiveness compared to conventional auxiliaries, silicone based textile finishing agents, are of enormous importance. Since many years, silicones have been used in the paint and cosmetic industry. Recently it has found extensive use in the textile industry also. Silicon (Si), chemical element with atomic no. 14 is extensively used for finishing of textiles. It is the eighth most common element in the universe by mass, but it very rarely occurs as the pure free element in nature. It is more widely distributed in dusts, sands and planetoids as various forms of silicon dioxide (silica) or silicates. 5

6 ( Main features of Silicone finish are very good softness, excellent fiber-fiber lubrication, substantive to fiber, good stretch and recovery, improved elasticity and resiliency, excellent drape, good durability, excellent sewability, exhaustible, very low yellowing (depending on type) etc. ( and Silicones have wide application in textile processing and finishing. They have been used as a premium finishing agents especially in the last few years as they offer durable, longer lasting, surface modifications to the fabric. The silicone emulsions are available in various particle sizes macro (milky, particle size nm), semi-micro (hazy, particle size nm) or micro (transparent, particle size below 40 nm) forms. The micro emulsions are mostly preferred due to their higher shear stability, but can only be obtained from amino silicones. Recently, the nano forms of silicone have been developed which have particle sizes < 10nm (Choudhury et al., 2012). Nano-silicone softeners penetrate the fabric inner structure more easily than others (Celik, Degirmenci, and Kaynak, 2010). Nano-emulsion softener improves the feel, softness and crease recovery to a higher extent compared to the conventional emulsion softener (Chattopadhyay and Vyas, 2009). Important textile fibers: Amongst textile fibers; cotton, wool and polyester are exclusively used along with cotton-polyester blend. Cotton is an important natural cellulosic fiber. Cotton fabric has excellent hand and its drapability is quite acceptable. Its low resiliency and poor recovery from deformation means that is wrinkles easily in both the dry and wet states and exhibits inferior crease retention. Starching of cotton improves these properties, but the effect is only temporary, and it is necessary to renew this finish after each laundering (Needles, 2011). Wool is regarded as a luxurious fiber because of superior characteristics such as the ability to be shaped by heat and moisture, good moisture absorption without feeling wet, excellent heat retention, and water repellency (Borghei et al., 2013). 6

7 Improvement of existing properties and the creation of new material properties are very important for the functionalization of textiles (Gowri et al., 2010). Polyester fiber, specifically poly (ethylene terephthalate) (PET), is the largest volume synthetic fiber produced worldwide (Jaffe and East, 2007). It is an inexpensive fiber with a unique set of desirable properties which have made it useful in a wide range of end-use applications. It possesses good strength and durability characteristics but exhibits moderate to poor recovery from stretching. The fiber is hydrophobic and non-absorbent without chemical modification. This lack of absorbency limits the comfort of polyester fabrics. Due to its hydrophobicity and high crystallinity, polyester is difficult to dye and special dyes and dying techniques must be used (Needles, 2011). Consumer generally accepts cotton-polyester textile fabrics. The selection of these fibers ensured sufficient comfort resulting mainly from the use of cotton fibers, as well as suitable mechanical properties such as the tensile strength characteristics of synthetic fibers (Walawska, Filipowska and Rybicki, 2003). Purpose of the study: Fabric finishing is the treatment given to textile materials to make them suitable for specific applications. After fabrics have been woven, they are usually washed, bleached, mercerized, dyed or printed. Their appearance is finally improved by finishing process. Increasing global competition in textiles has created many challenges for textile researches. The rapid growth in technical textiles and their end uses has generated many opportunities for the application of innovative finishes. Silicone finishes of high added value for fabrics are also greatly appreciated by a more demanding consumer market. Antimicrobial textiles with improved functionality find a variety of applications such as health and hygiene products, specially the garments worn close to the skin and several medical applications, such as infection control and barrier material. The field of flame retardancy has witnessed a vigorous development of new technologies and new products to meet the challenge of the needs of new industries, 7

8 such as computer, electronics and telecommunication industries. Flame retardants are also used in health care settings, hospital beds, and hospital curtains. As additional challenge is the growing awareness of environmental issues and the stiffening demands of consumer safety, which has been put forward by government and public agencies. New flame retardant systems are needed to meet the new product and market demand. Better water absorbency of fabric helps to absorb perspiration from the skin, which adds to the comfort factor and better dye ability of fabrics. Soil release finishes in fabric permit relatively easy removal of soils with ordinary home laundering. Other benefits arise from the use of soil release finishes in durable press fabrics because of their increased absorbency. These include: improved antistatic properties, improved fabric drapability and somewhat greater comfort in hot weather. Silicone products have been widely applied on textiles for various end uses. The primary applications of silicones in textile are fabric softening agents, fiber and thread lubricants, antifoaming agents, and antistatic agents (Drews, 2008). Ecological considerations now days, are becoming important factors in the selection of consumer goods, all over the world. The consumer s demand not only the right quality product, at right time but also with no harm to ecology during the manufacturer as well as in the use. Hence, there has been a constant desire to scientist and industrialist to explore and adopt the alternates; those are nonhazardous and eco-friendly. The use of silicones on textiles has been consequently increased due to environmental awareness. As textile processing is predominantly an aqueous process, silicones are likely to enter the environment via, waste water, either from scouring operations or through softener baths. Silicones have been extensively tested in both fresh and marine water and show no harmful effect on environment (Rajadhyaksha and Keskar, 2002). Thus, use of silicones in the textile industry will not cause any environment harm. Very few studies have been reported on use of silicone finish on textiles, through it is extensively used commercially by the paint and cosmetic industries. 8

9 Keeping in mind many valuable inherent properties and huge application potential of silicone, the objective of present study was focused on the application of silicone finishes to enhance the performance of textiles. Thus, in this study epoxy based silicone finishes were prepared and used for improving several properties such as anti-bacterial, flame retardancy, water absorbency and soil release. To fulfill the purpose of the study following objectives were framed. Objective of the study: 1. To study the general properties of various silicone finishes available for textile application on some important natural, manmade and blend fabrics. 2. To study the effect on special physical properties of silicone finishes when combined with property enhancing agents, for multi-functional effects - Silicone + antibacterial agent - Silicone + flame retardant agent - Silicone + water absorbency agent - Silicone + soil release agent. 3. To compare the results of epoxy based silicone finished fabric with nano silicone finished fabric. Delimitation of the study: Study was limited to widely use four fiber types i.e. cotton, wool, polyester and polyester/cotton blend fabrics. Study was also limited to the prepared epoxy based silicone finish in laboratory for enhancing four functional properties i.e. antibacterial, flame retardancy, water absorbency and soil release. 9