इस ब्लॉग की मुख्य भाषा हिंदी है | हिंदी माध्यम के छात्रों को वस्त्र विज्ञान की पाठ्य सामग्री हिंदी भाषा में सुलभ करने का यह मेरा प्रयास है | तदपि इसमें अंगरेजी भाषा की भी सामग्री का उपयोग किया है | यदि इसमें अपने अंचल की वस्त्र कला से परिचित कराना चाहते हैं तो आपका स्वागत है - मेल करें naiprerna@gmail.com
Wednesday, August 31, 2011
Nylon Fiber
1. INTRODUCTION
Nylon was the first truly synthetic fiber to be commercialized (1939). Nylon was developed in the 1930s by scientists at Du Pont, headed by an American chemist Wallace Hume Caruthers (1896-1937). It is a polyamide fiber, derived from a diamine and a dicarboxylic acid, because a variety of diamines and dicarboxylic acids can be produced, there are a very large number of polyamide materials available to produce nylon fibers. The two most common versions are nylon 66 (polyhexamethylene adiamide) and nylon 6 (Polycaprolactam, a cyclic nylon intermediate). Raw materials for these are variable and sources used commercially are benzene (from coke production or oil refining), furfural (from oat hulls or corn cobs) or 1,4-butadiene (from oil refining).
2. FIBER TYPES
Fiber types are produced commercially in various parts of the world. Nylon 66 has been preferred in North American markets, whereas nylon 6 is much more popular in Europe and elsewhere. Nylon is produced by melt spinning and is available in staple, tow, monofilament, and multi-filament form. The fiber has outstanding durability and excellent physical properties. Nylons are semi-crystalline polymers. The amide group -(-CO-NH-)- provides hydrogen bonding between polyamide chains, giving nylon high strength at elevated temperatures, toughness at low temperatures, combined with its other properties, such as stiffness, wear and abrasion resistance, low friction coefficient and good chemical resistance. These properties have made nylons the strongest of all man-made fibers in common use. Because nylons offer good mechanical and thermal properties, they are also a very important engineering thermoplastic. For example, 35% of total nylon produced is used in the automobile industry [2]. There are several commercial nylon products, such as nylon 6, 11, 12, 6/6, 6/10, 6/12, and so on. Of these, the most widely used nylon products in the textile industry are formed of nylon 6 and nylon 6/6. The others are mainly used in tubing extrusion, injection molding, and coatings of metal objects [3].
Nylon's outstanding characteristic in the textile industry is its versatility. It can be made strong enough to stand up under the punishment tire cords must endure, fine enough for sheer, high fashion hosiery, and light enough for parachute cloth and backpacker's tents. Nylon is used both alone and in blends with other fibers, where its chief contributions are strength and abrasion resistance. Nylon washes easily, dries quickly, needs little pressing, and holds its shape well since it neither shrinks nor stretches.
3. FIBER FORMATION
One of the most important factors in polymer processing is viscosity, which is a function of molecular weight. The number-average molecular weight of polymer suitable for textile fiber production ranges from 14,000 to 20,000. Since Polycaprolactam can be regarded at equilibrium as a polycondensation polymer, the number-average molecular weight alone is sufficient for its characterization. Two-step melt spinning, comprised of spinning and drawing, is considered to be the conventional method to manufacture nylon filaments. After melting, filtering, and deaerating, the molten polymer is extruded through a spinneret into a chamber where the melt solidifies into a filament form. At this stage, the filaments have little molecular orientation, and their slight birefringence is due to shear forces set up during extrusion. In order to achieve desirable properties through molecular orientation and crystallinity, the newly formed filaments must be drawn. Since the Tg of nylon is below room temperature, nylon can be cold drawn.Hot drawing is also frequently used. Nylon filaments are drawn approximately four times their initial length. The effect of drawing on birefringence, a measure of molecular anisotropy, can be seen in Table I. Also, the elastic modulus increases significantly with increasing orientation as shown in Table I. Other physical properties, such as density equilibrium, moisture sorption, tenacity and elongation-at-break, are also affected by drawing.
Table 1: Effect of Drawing on Birefringence and Elastic modulus
Draw Ratio
|
Birefringence
|
Elastic Modulus (GPa)
|
1
|
0.00832
|
1.97
|
2
|
0.03297
|
2.74
|
3
|
0.05523
|
3.70
|
4
|
0.05904
|
4.59
|
5
|
0.06381
|
5.77
|
60
|
0.06901
|
6.74
|
Rather than two-step spinning (extrusion) and drawing, a one-step, high-speed spinning process is being used increasingly. In high-speed spinning, filament windup speed relative to the extrusion speed is very high and orientation and crystallization occur in elongation flow along the spin line. When drawing as-spun fibers, the molecules are arranged randomly in amorphous regions and as folded chains in crystalline region .
In essence, cold drawing stretches chains in amorphous regions, but molecular folds are restricted and the molecules orient themselves along the fiber axis direction, resulting in enhanced orientation and high crystallinity. In the case of nylons, which have sheet-like crystal structures, drawing may enable the hydrogen-bonded polyamide sheets to slip past each other and form more oriented structure [4]. Hot drawing is a procedure using high temperature during drawing and annealing under restraint after drawing. Exposure to high temperature helps to increase the draw ratio, and higher moduli and tenacity can be achieved.. Ultra drawing of solidified crystalline material induces a high degree of chain extension, which leads to very high tensile strength and modulus. This results in a so-called high-performance fiber.A skin-core structure, mostly depending on spinning speed, is generally formed within melt-spun fibers. At a constant feeding rate, higher spinning speeds will produce more extended chains in the melt and form a finer filament. Therefore, the finer fiber usually has higher modulus and tenacity. Fine filament cannot be drawn as much as a coarse filament, because partial orientation on the outer parts of the filaments is formed when the molten fluid is drawn over the sides of the orifice. As a result, finer filaments have a greater proportion of 'skin' to bulk, i.e., better orientation has already been formed. Naturally, there is not much space for an improvement by cold drawing within fine filaments. The filaments become lustrous and strong.
4. RHEOLOGICAL BEHAVIOR
The melt viscosity of the polymer can be represented as a function of molecular weight by the relationship [5, 6]:
η=K (Mw) a
Where is the zero shear viscosity, Mw it the weight average molecular weight, K and an are constants dependent upon the polymer and temperature. In the case of nylons, the value of exponent a normally is in the range of 3.4-3.8.
It has long been known that moisture has a strong effect on the rheological behavior of nylons. Generally, high moisture levels cause degradation and foaming, and relatively low levels of moisture act as plasticizer in nylon 6 during melt processing. All nylons absorb moisture. The extent of moisture absorption depends on temperature, crystallinity, and humidity. Therefore, before processing of nylon resins, the polymer pellets must be dried to moisture levels below 0.2 wt%, in order to avoid bubble formation and significant polymer degradation during processing. A recent study [7] found that the drying temperatures used affect zero shear melt viscosity. The result is shown in
Table 2. Effect of Resin Drying Temperature on Zero Melt Viscosity
Drying Temperature (°C)*
|
Molecular Weight Exponent
|
50
|
3.8
|
110
|
4.6-5.4
|
5. NON-CONVENTIONAL SPINNING TECHNIQUES
Alternative to conventional melt spinning, various solution-spinning techniques have been introduced [8,9]. Solution spinning techniques (gel, wet, dry) enable the spinning of high molecular weight polyamides, leading to high tenacity filaments (tenacity 100cN/tex)[8]. As an innovation on fiber formation, new technologies producing micro fibers have been developed and reported [10]. Primarily direct spinning and mechanical and solvent splitting produce micro fibers. Electro spinning [11] represents another approach to fiber spinning, when electrical forces on polymer melt or solution surface overcome the surface tension and cause an ejection from an electrically charged jet. The diameter of the fibers produced by this technique is of the order of nanometers. Frequently, there are produced fibers that are electrically charged.
6. CRYSTALLINE STRUCTURE
Both nylon 6 and nylon 66 are semi-crystalline polymers. These linear aliphatic polyamides are able to crystallize mostly because of strong intermolecular hydrogen bonds through the amide groups (Figure. 3)[3], and because of Vander walls forces between the methylene chains. Since these unique structural and thermo-mechanical properties of nylons are dominated by the hydrogen bonds in these polyamides, quantum chemistry can be used to determine the hydrogen bond potential [3]. The left side of the figure shows hydrogen-bonding planes, and the right side shows the view down the chain axis. For the -form of nylon 6, adjacent chains are ant parallel and the hydrogen bonding is between adjacent chains within the same sheet (bisecting the CH2 angles). For the -form of nylon 6, the chains are parallel and the hydrogen bonding is between chains in adjacent sheets. . In nylon 66, the chains have no directions.
Mechanical, thermal and optical properties of fibers are strongly affected by orientation and crystallinity. Basically, higher fiber orientation and crystallinity will produce better properties. Crystallinity of nylons can be controlled by nucleation, i.e., seeding the molten polymer to produce uniform sized smaller spherulites. This results in increased tensile yield strength, flexural modulus, creep resistance, and hardness, but some loss in elongation and impact resistance. Another important benefit obtained from nucleation is decrease of setup time during processing [1].
7. DYEABILITY
The dyeing efficiency of nylon fibers is enhanced due to the end groups -COOH and -NH2, which exhibit polar and hydrophilic characteristics. Dye diffusion into fibers is closely related to the rate of dyeing, level of dyeing through dye migration, wet fastness properties of dyes, etc. It is generally believed that dye diffusivity is independent on dye concentration, with some exception. T. Shibusawa [12] studied the diffusion of most disperse dyes on nylon 6 and found that the actual diffusivity on nylon 6 fibers is not always independent on dye concentration. Kim et al. [13] have reported that both dyeing rate and dye saturation of 1,4 -diaminoanthraquinone (1,4-DAA) were improved considerably in the presence of didodecyldimethlammonium bromide (DDDMAB). The amount of DDDMAB adsorbed on nylon 6 fiber is roughly 20 times higher than that a conventional dispersing agent. This suggests that there might be fairly strong interaction between DDDMAB and the fiber by virtue of electrostatic and hydrophobic interactions. There have been many attempts to improve nylon's dyeability or at least to point out the factors and mechanisms acting in nylon dyeing. It has been shown that acrylonitrile and styrene radiation grafting on the polymer could improve the dyeability of nylon [15]. Another approach to higher dyeability of nylon 6 is by copolymerization [16]. In this case, the dyeability can be improved at the expense of a decrease of specific viscosity and of heat and hydrolysis resistance. Other treatments, such as plasma etching [17] and superheated steaming [18] have proved to decrease nylon dyeability. In the former treatment, outer structures, not normally susceptible to dyes, are etched away whereas the crystalline phases inside the fiber are not as much affected. Superheated steaming of the fibers leads to higher shrinkage and to higher crystallinity and crystal size, which contribute to decrease dyeability.
8. DEGRADATION
The -COOH and -NH2 end-groups in nylons are sensitive to light, heat, oxygen, acids and alkali. When exposed to elevated temperatures, unmodified nylons undergo molecular weigh degradation, which results in loss of mechanical properties. The degradation is highly time/temperature dependent. By adding heat stabilizer, nylon can be used at elevated temperature for long-term performance. Exposure to UV light results in degradation nylon over an extended period of time, it appears that adding carbon black can reduce the radiation degradation. Nylons are chemical resistance to hydrocarbons, aromatic and strong acids, bases, and phenols attack aliphatic solvents, but them. They also are gradually attacked hydrolytically by hot water. Newly developed sulfonation of nylon 6 fiber [19] by 2,5 dichlorobenzene sulfonyl chloride (DSBC) has a great effect on the heat and chemical stability of the fibers. It reported that the modified fiber is non-melting up to 1000oC, and does not burn when put it in direct flame (but chars without losing fiber form). It does not dissolve in formic acid and concentrated mineral acid. Its glass transition temperature is about 500oC.
9. PROPERTIES OF NYLON 66
-Tenacity-elongation at break ranges from 8.8g/d-18% to 4.3 g/d-45%. Its tensile strength is higher than that of wool, silk, rayon, or cotton.
- 100% elastic under 8% of extension
-Specific gravity of 1.14
-Melting point of 263oC
-Extremely chemically stable
-No mildew or bacterial effects
-4 - 4.5% of moisture regain
-Degraded by light as natural fibers
-Permanent set by heat and steam
-Abrasion resistant
-Lustrous- Nylon fibers have the luster of silk
-Easy to wash
-Can be pre colored or dyed in wide range of colors; dyes are applied to the molten mass of nylon or to the yarn or finished fabric.
-Resilient
-Filament yarn provides smooth, soft, long lasting fabrics
-Spun yarn lend fabrics light weight and warmth
10. PROPERTIES OF NYLON 6
The main difference between nylon 6 and nylon 6,6 is nylon 6 has a much lower melting point than nylon 66. This is a serious disadvantage, as garments made from it must be ironed with considerable care.
11. NONWOVENS USAGE
The fiber has outstanding durability and excellent physical properties. Like PET fiber, it has a high melting point, which conveys good high- temperature performance. The fiber is more water sensitive than PET; despite this fact, nylon is not considered a comfortable fiber in contact with the skin. Its toughness makes it a major fiber of choice in carpets, including needle punched floor-covering products. Because of its relatively high cost, nylon has somewhat limited use in nonwoven products. It is used as a blending fiber in some cases, because it conveys excellent tear strength. The resiliency and wrinkle recovery performance of a nonwoven produced from nylon is not as excellent as that from PET fiber.
12. WORLD CONSUMPTION OF NYLON FIBER IN NONWOVENS 1998- 2007
It is forecasted that global consumption of nonwoven may reach 3.7 million tons by 2005 and 4 million tones by 2007.Consumption of manmade fiber was about 8.1% of all Textile fibers in 1998.In 2005 it is expected to reach 10% and 10.4 % by 2007.In certain applications, the performance of nylon fiber is hard to beat. However, because of its higher cost, it is used in specialized applications where its performance can justify the increased cost. It is used as a blending fiber in some cases, because it conveys excellent tear strength. The resiliency and wrinkle recovery performance of a nonwoven produced from nylon is not as excellent as that from PET fiber. This polymer is used in moderate quantities, because it is more expensive than polyester, polypropylene, or rayon. Some particular applications are as follows:
· It can be mostly found in garment interlinings and wipes where it supplies strength and resilience.
· In Ni/H and Ni/Cd batteries, nylon fibers are used as Nonwovens separators.
· Nylon fibers are used for the manufacture of split table-pie fibers. These fibers find application in high performance wipes, synthetic suede, heat insulators, battery separators and specialty papers.
· Nonwovens developed from nylon are found in automotive products, athletic wear and conveyor belts.
REFERENCES
[1]. P. G. Galanty, and G. A. Bujtas, “Modern Plastics Encyclopedia” '92, pp 23-30 McGraw Hill 1992
[2]. P. Meplestor, “Modern Plastics”, 74, Jan., 66 (1997)
[3]. S. Dasgupta, W.B.hammond, and W.A. Goddard III, J. Am. Chem. Soc. 118,12291-12301, (1996)
[4] A. B. Thompson Fiber structure Edited by J. W. Hearle and R. H. Peters, Butterworth & Co. Ltd. and the Textile Institute pp 499 (1963)
Tuesday, June 14, 2011
Colour
https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B-mFGz_i1PaTNjExMGQ0MWQtMGU4NS00YTViLTk1NzgtYTNmMDM2ZDkwM2M3&hl=en_US
Thursday, May 5, 2011
Tea fiber
Tea fiber is a kind of new fiber developed by Qingdao Meidu Textile Co., Ltd.. It is high-end functional fiber firstly developed at home and abroad, and reaches the international advanced level. It is antibacterial and odor resistant viscose fiber made from natural tea pigment, tea polyphenols and catechins which are extracted from tea.
Tea fiber is natually antibacterial, odor resistant, moisture absorption and breathable. The bacteriostasis rate and bactericidal rate on staphylococcus aureus and escherichia coli have reached or exceeded the standard of China, US and Japan.
The natural green tea antimicrobial agent uniformly distributes in the tea fiber, thus it can improve the microcirculation of human body after the long-term contact with skin. The textile products made by the fiber are anti-radiation and anti-ultraviolet.
Tea fiber and its products are naturally toasted almond colored, which will not cause pollution and are harmless to human body.
Tea fiber is believed to have a bright future
Tea fiber is natually antibacterial, odor resistant, moisture absorption and breathable. The bacteriostasis rate and bactericidal rate on staphylococcus aureus and escherichia coli have reached or exceeded the standard of China, US and Japan.
The natural green tea antimicrobial agent uniformly distributes in the tea fiber, thus it can improve the microcirculation of human body after the long-term contact with skin. The textile products made by the fiber are anti-radiation and anti-ultraviolet.
Tea fiber and its products are naturally toasted almond colored, which will not cause pollution and are harmless to human body.
Tea fiber is believed to have a bright future
Tuesday, March 8, 2011
Eco -textile and eco labeling of textile
Banned amines are the chemicals which are released from some of the azo dyes on reductive clevage. Following is the list of amines banned by Germany.
· 4-Amino biphenyl (CAS-No.:92-67-1)
· Benzidine (CAS-No.:92-87-5)
· 4-Chlor-o-toluidine(CAS-No.95-69-2)
· 2-Naphthylamine (CAS-No.:91-59-8)
· p-Chloroaniline(CAS-No.106-47-8)
· 2,4-Diaminoanisole(CAS-No.615-05-4)
· 4,4'-Diamino diphenyl methane (CAS No.:101-77-9)
· 3,3'-Dichloro benzidine (CAS-No.:91-94-1)
· 3,3'-Dimethoxy benzidine(CAS-No.:119-90-4)
· 3,3'-Dimethyl benzidine(CAS-No.:119-93-7)
· 3,3'-Dimethyl-4,4'-diamino diphenyl methane (CAS-No.:838-88-0)
· p-Cresidine (CAS-No.:120-71-8)
· 4,4'-Methylene-bis-(2-chloraniline) (CAS No.:101-14-4)
· 4,4'-Oxydianiline (CAS-No.:101-80-4)
· 4,4'-Thiodianiline (CAS-No.:139-65-1)
· o-Toluidine(CAS-No.:95-53-4)
· 2,4-Diamino toluene(CAS-No.:95-80-7)
· 2,4,5-Trimethyl aniline (CAS-No.:137-17-7)
· o-aminoazotoluene (CAS-No.:97-56-3)
· 2-amino-4-nitrotoluene (CAS No.:99-55-8)
· p-amino azo benzene
· 2-methoxy aniline
These are suspected to be carcinogenic and are being banned.
Apart from Germany, Netherlands has also banned the presence of these amines and this is applicable to clothing, bed linen and footwear. As per the latest information received, the European Commission has circulated a working document relating to the restrictions on the marketing and use of dangerous substances and preparation (azo dyes), for the consideration of the European parliament and the Council. The draft proposal aims to restrict the use of 22 amines in textiles and leather articles.
In order to promote the concept of eco-friendly textiles, a comprehensive system of eco labels is advocated by European and other Western countries. For the purpose of issuing eco labels, certain norms/criteria are stipulated in respect of textile products, on the basis of Cradle-to-Grave approach. i.e. These criteria are developed on analysing the product's entire life cycle commencing with extraction of raw materials, progressing through the stages of production, distribution and utilisation and disposal after use. The norms are also referred to as Eco Standards. By and large, these standards are voluntary in nature.
While formulating eco-norms for the issuance of eco labels, at present the use of 7 different classes of chemicals in textile production and processing are taken into consideration. These are:
· Formaldehyde
· Toxic pesticides
· Pentachlorophenol (PCP)
· Heavy metal traces
· Azo dyes which release carcinogenic amines
· Halogen carriers
· Chlorine Bleaching
The eco standards stipulated by (i) MST, the German Textile Association, (ii) OTN 100,the famous OEKOTEX Institute from Austria, (iii) Clean fashion and (iv) Steilmann, the two private eco-label issuing organisations in Germany are popular in European countries. In addition to the four eco labels specified above, a number of private and national labels are operating in Europe. In some cases these labels are used solely as a marketing instrument and have little factual and technical substance. In the face of the proliferation of eco labels, the Coordination Committee for the Textiles Industries in the EEC (COMITEXTIL), supports a single European label. Further, it is learnt that the European Union is finalizing the criteria for a common "European Community Eco label" (EC-Eco label) after taking into consideration the criteria specified by other eco labels.
The Government of India has also evolved eco standards for the eco labeling of the textile items in consultation with the Indian Textile Trade and Industry. The criteria for the environmentally friendly textiles including Cotton, Woolen, Man-made, Jute and Silk products was notified in the Gazette on October 8, 1996 by Ministry of Environment and Forests. The eco labeling of textiles notified in the Gazette is a voluntary scheme. This scheme aims at distinguishing through the agency of Eco-Mark, any product which is made, used or disposed of in a way that significantly reduces the adverse effect, it would otherwise have on the environment. The Earthen Pot is being used as the logo of this scheme.
A comparison of the norms/criteria stipulated for eco parameters in the popular eco labels operating in Europe and in the Indian Eco Mark Scheme for textiles are as under:
| S. No | Eco Parameter | Criteria/Norms stipulated in ppm | ||||||||||||||||||||||||||||||||||||||||||||||||||
| M.S.T | OTN 100 | Clean Fashion | Steil-mann | COMIT-EXTIL | Indian Eco Label | |||||||||||||||||||||||||||||||||||||||||||||||
| Formaldehyde (i) Baby Clothing (ii) Close to skin (iii) Outer wear | 20 75 300 | 20 75 300 | 20 75 300 | 50 300 500 | 20 75 300 | 20 75 300 | ||||||||||||||||||||||||||||||||||||||||||||||
| | Toxic Pesticides | 1 | 5 | 1 | 1 | 0.1 to 1 | 1 | |||||||||||||||||||||||||||||||||||||||||||||
| | Pentachlorophenol | 0.5 | -- | 0.5 | Ban | 0.05 to 0.5 | 0.5 | |||||||||||||||||||||||||||||||||||||||||||||
| | Heavy Metals (i) Arsenic (ii) Lead (iii) Cadmium (iv) Mercury (v) Copper (vi) Chromium (vii) Cobalt (viii) Zinc (ix) Nickel | 0.001 to 0.01 0.004 to 0.04 0.0005 to 0.005 0.0001 to 0.1 0.3 to 100.0 1 to 2
| ||||||||||||||||||||||||||||||||||||||||||||||||||
Accreditation is a formal recognition that a Testing /Calibration Laboratory is competent to carry out specific test/s. Such an accreditation is granted only after the accrediting body ( Govt. /non Govt. body or any third party) is satisfied with a particular laboratory seeking Accreditation. In India, the National Accreditation Board for Testing and Calibration Laboratories (NABL) is accrediting the laboratories. Apart from this there are a number of accrediting bodies operating at international level including A2LA (American Association for Laboratory Accreditation, USA) and RvA (Raad Voor Accreditate), Dutch Accreditation Council, Netherlands.
Textiles Committee Laboratories, Mumbai is accredited by Raad Voor Accreditate, the Dutch Accreditation Council, Netherlands and National Accreditation Board For Testing and Calibration Laboratories (NABL) on the basis of its compliance to the relevant criteria which are based on ISO /IEC Guide 25 and EN-45001. This is the first Textile Laboratory in India accredited by a reputed Accreditation Board from abroad.
Q-4. What are the advantages of testing of textiles in an accredited laboratory ?
In an accredited laboratory, a documented Quality System is implemented and its effectiveness is assured. Consequently, the test reports/certificates issued by the laboratory is readily accepted by the trade, industry and exporters. The testing services rendered by the laboratory is qualitatively better than a non-accredited laboratory due to the following reasons :
· The accuracy, repeatability and reproducibility of the test results are assured;
· Qualified and trained man power is employed for the testing various parameters;
· Standard and validated methods only are used for testing;
· The accuracy and precision of the equipments used is ascertained by periodical calibration using devices traceable to National Standards; and,
· The testing of various parameters is carried out under conditions which does not affect the accuracy and precision of the test results.
State the list of dyes banned by Government of India?The Ministry of Environment and Forests, Government of India has prohibited the handling of benzidine based dyes vide the notification published in the Gazette in January, 1990. As per this notification, handling of all the 42 benzidine based dyes are prohibited from 1993 onwards. These are related to banned amines.The Ministry of Environment and Forests has further prohibited the handling of 70 more azo dyes which came under the banned category as per the notification published in the Gazette on 26th March, 1997. Thus, the Ministry of Environment and Forests has prohibited the handling of 42+70=112 dyes which are capable of releasing any of the harmful amines.
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