Sewing Threads and Their Technical Applications

Types, Properties and Uses of Sewing Threads

Md. Jasimuddin Mandal
Govt. College of Engineering and Textile Technology,
Serampore, India.
Email ID: jasimmandal@gmail.com

Sewing Thread:
According to the definition given by ASTM, sewing thread is a flexible, small diameter yarn or strand usually treated with a surface coating, lubricant or both, intended to be used to stitch one or more pieces of material or an object to a material. It may be defined as smooth, evenly spun, hard-twisted ply yarn, treated by a special finishing process to make it resistant to stresses in its passage through the eye of a needle and through material involved in seaming and stitching operations.

Sewing threads are used in garments, upholstery, air-supported fabric structures and geotextiles to join different components by forming a seam. The primary function of a seam is to provide uniform stress transfer from one piece of fabric to another, thus preserving the overall integrity of the fabric assembly.

Threads for the high temperature applications are required to withstand and hold the seams secure in their position in extreme temperature conditions between 260ºC-1100ºC. Threads are usually made from glass, carbon, polytetrafluoroethylene, steel and aramid fibers. Polyesters, Polypropylene, Nylon 6, Nylon 66, are widely used for low temperature applications such as car upholstery, leather industry, packing like cement and fertilizer bags. Medical sutures are used for wound closure and are specially design and sterilized to fulfill the end applications.

Seam can be formed by the following techniques:

• Mechanical: stapling, sewing.
• Physical: welding or heat-setting.
• Chemical: by means of resins.

The formation of seams by physical and chemical methods is restricted to a few specialized applications, as these processes tend to alter certain properties of the textile material. Among mechanical sewing techniques, sewing maintains its prevailing position by virtue of its simplicity, sophisticated and economical production methods and the controllable elasticity of the seam produced.

Essential Properties Required for Sewing Threads:
Industrial sewing techniques make specific and often very exacting demands on the threads involved in the sewing process. The sewability of sewing threads is of major importance, having a very profound effect on seam quality and production costs. The sewing and the seam performance of a sewing thread are largely influenced by the material to be sewn, the sewing technique and the end-use for which the sewn material is intended.

These requirements can be defined as:

1. The ability of the sewing thread to meet the functional requirements of producing the desired seam effectively.
2. The ability of the sewing thread to provide the desired aesthetics and serviceability in the seam.
3. The cost of sewing thread and that associated with producing the desired seam.

The different important properties required by a sewing thread are discussed below:

1. Needle thread must pass freely through the small eye of the needle; consequently they must be uniform, knot-free, non-torque and fault free.

2. Tensile strength/breaking strength is one of the essential properties of the thread. It must be capable of withstanding several kinetic/lateral movements during sewing. The strength of the sewing thread must be higher than that of the fabric so that the thread does not rupture during use. During sewing at high speeds, the needle thread is subjected to repeated tensile stresses at very high rates. The thread also comes under the influence of heat, bending, pressures, torsion and wearing. The value of these stresses depends on the sewing speed, machine settings and the thread used. The stresses created within the thread have a negative effect on the processing and functional characteristics of the thread, and there is significant reduction in the thread strength after sewing.

This is a function of the dynamic and thermal loading of the thread and is influenced by the thread frictional properties, thread tensioning during sewing, needle size, stitch length and number of fabric layers in the seam. The thread should therefore possess adequate strength and elongation in order to perform satisfactorily during sewing and in seam.

3. For good performance in a sewing machine moderate to low extension-at-break of the thread is usually preferred. Needle thread with different elongation-at-break has been found to behave quite differently during stitch formation. The determinants of success of sewing a thread with certain elongation per cent without any problem the machine setting and special properties of the sewing thread itself.

4. The elasticity of the sewing thread must be uniform along its length in order to enable equal length stitches to be formed, and it must closely match the elasticity of the fabric being sewn; otherwise either seam thread fracture, or tearing of the adjacent fabric may arise during garment use. Clearly, the requirements of woven and knitted fabrics will be different.

5. The forces that are developed in the sewing thread are mostly due to the friction between the thread and machine parts, the most severe action taking place between:

• The thread and the needle.
• The thread and the fabric being sewn.

A controlled level of both static and dynamic friction is required; this must not be too high, which could cause lack of thread control. High static friction values are necessary to allow the stitches to lock and prevent “run-back” of seams. Spun threads are particularly good in this respect when compared with filament thread. The worst is the monofilament threads. The frictional properties are affected by lubrication. The factors that influence the frictional properties are:

• Uniform application of lubricating agents.
• Adhesion of the finishing agent on the thread.

The quantity and quality of finishes are very important. Special finishes like silicone compounds have been found to exhibit clear advantage over standard paraffin wax.

6. Good abrasion resistance is essential for good sewing performance. The thread is under tension condition, especially when the stitch is being set. The thread must be resilient enough to return to shape after the distortions, and then must maintain its physical properties to provide good performance in the seam after the sewing process is complete. Nylon and polyester offer the best resistance to abrasion.

7. Good resistance to heat is a very important requirement of a sewing thread. The temperature reached by the sewing needle during sewing very much depends on:

• The nature of the fabric to be sewn (density, thickness, finish)
• The speed of the sewing machine
• The type of needle used (size, shape, surface finish)
• Size and finish of the sewing thread.

The needle temperature is especially critical for fabrics and sewing threads of thermoplastic fibers, where it may exceed their melting temperature. Needle heating causes sewing thread breakage, cross-thread, skipped stitches, seam damage and physical damage to the needle.

Various studies show that the sewing thread influences the needle temperature significantly. Its movement through the needle reduces the needle temperature by an average of 21- 45%, the amount of reduction depends on the sewing condition and the structure, fineness and composition of sewing thread.

Lubrication of sewing thread with a mixture of wax, emulsions with synthetic resins, and silicon based products may minimize heat generation, and the fibers surface of spun yarns may be an advantage in that a thin layer of the surrounding air will move with the thread and promote needle cooling.

8. The hairiness of sewing thread also affects the appearance of the seam. Sewing threads for decorative seams are singed, squeezed and gloss-brushed.

9. The final direction of twist insertion may be important to enable the stitch forming mechanism of the sewing machine to perform correctly; most sewing machine require Z twist, but there are a few where performance is better with S twist.

10. Color fastness is a general requirement for sewing thread. It is important that the selected shade retain its color throughout the life of the garment. Two aspects of fastness are important:

• The thread must not change color.
• The thread must not stain any material adjacent to the seam.

11. Low shrinkage during washing and ironing is required. Shrinkage due to fiber swelling causes seams to pucker, especially if the fabric exhibits less shrinkage than threads. Synthetic threads suffer less from this problem than cotton threads owing to their much lower moisture absorbency; however they are liable to residual shrinkage problems if unsuitable manufacturing processes are employed. Synthetic threads can suffer from the problem of thermal shrinkage during ironing but this difficulty can be solved by the use of high temperature setting, which stabilizes the thread at temperature above those normally encountered during the ironing process.

The sewing threads should possess better evenness and should contain minimal number of knots, faults and neps, etc. Thread should have very low level of imperfections and classimat faults.

12. Good luster in the thread improves appearance of the seam.

13. Threads must be uniformly dyed in a good match to the materials being sewn and also the dyed thread should have properties like colorfastness to washing, light, perspiration, and sublimation.

14. The ability of the thread to perform efficiently in the sewing machine is defined sewability. It can be assessed by the number of breaks that occur during the sewing of a certain number of stitches. However, owing to the generation of needle heat in high-speed sewing, the threads could be damaged without breaking. The long knot-free evenner yarns in case of rotor and air-jet can give better sewability.

15. The characteristics of properly constructed seam are strength, elasticity, durability, stability and appearance. The relative importance of these qualities is determined by the end-use of the sewn product. The factors that govern these properties are seam and stitch type, thread strength and elasticity, stitches per unit length of seam, thread tension, seam efficiency of the material. The hairiness of sewing thread is important to decide seam appearance. The shrinkage potential of the thread and hence the seam is also major importance for proper seam appearance. The serviceability of a garment depends not only on the quality of the fabric but also on that of the seam. The seam quality is measured by stitching parameters of the threads and seam parameters such as size, slippage and strength.

The failure of seam produced by traverse loading can generally be classified as: Type I: the failure due to thread breakage, Type II: the failure due to fabric breakage, Seam breakage: the failure due to the slippage of cloth yarns at right angle to the seam.

Seam slippage is the most probable cause for seam failure that leads to garment rejection in wear. The durability of a seam depends largely on its strength and its relationship with elasticity of the material. It is measured in terms of seam efficiency, where Seam Efficiency = (Seam tensile strength/fabric tensile strength) x 100, generally ranges between 85 to 90%. The minimum loop strength correlates well with the stitch breaking strength. Further resistance to abrasion and wear of the seam during everyday use, including laundering is also essential for the longer seam.

16. Seam puckering can be defined as a differential shrinkage occurring along the line of a seam and is mainly caused due to seam instability, due to high tension imposed during sewing. Though currently available threads have a certain amount of controlled elasticity and elongation they get over-stretched when the sewing tensions are high. During relaxation the thread recovers its original length, thus gathering up the seam. Threads for use in apparel are also required to have good stability to laundering, ironing and other treatments since differential shrinkage between the sewing thread and the fabric of a garment can cause puckering.

Further, Seam pucker can be determined by measuring the differences in fabric and seam thickness under a constant compressive load. The seam-thickness strain is calculated by using the formula:

Thickness strain (%) = (seam thickness – 2 x fabric thickness) x 100 / 2x fabric thickness

Functions of Various Machines in Sewing Thread Manufacturing Process:

Yarn singeing:
Sewing thread must be singed to ensure that the projecting fibers do not interfere with downstream processing. Percentage of singeing can be achieved varied by varying the yarn collection speed. Hair removal efficiency at singeing machine is normally 30 – 50%. Flame temperature is around 800°C. Singeing is mainly done in Cotton Sewing Threads.

Features:

1. The heart of the machine – the burner, serves to singe reliably the projecting fibers of yarn running through at high speed, without inflicting burns on yarn itself. There is a choice between the gas burner and the electric burner. Gas burner is widely used. The gas burner consumes about 55 gm of natural, propane or butane gas an hour, depending on singeing rate and yarn type.
2. Speed: 300-1200 m/min.

Hank to cone winding:

• Conversion of hank in to cone of suitable weight
• Waxing for reducing co-efficient of friction in sewing thread.

Features of new machines:

• Twin Input Rollers: At the front of the head are the twin-input rollers, set to a fixed speed but proportional to the winding speed. The main functions of this unit are to eliminate unwanted tensions prior to yarn entering waxing unit.
• The speed of machine ranging from 400-700 rpm, with possible traverse from150-200 mm.

Polishing:
Some threads for special end uses like leather industries, bag stitching, kite flying are treated with starch, softeners, whitener, etc on this machine. Cooked starch is mixed with other chemicals and different recipes are made for different qualities depending on the end uses.

Main objectives of polishing are:

• Extra ordinary smooth surface
• Thread becomes round
• Stiffness increases
• Increase in tensile strength (7-10%).

Cross winding and lubrication:

• Winding in various types of sewing thread packages like cone, cop , tube, ball, vicone and spool.
• Threads are treated with special waxes for achieving best workability during sewing operation.
• Lick roller lubrication is applied on industrial sewing thread where thread has to run on high speed sewing machine; the basic ingredient of the most of the lubricants is parafin wax. Although silicones are also used because of their stability to heat and various additives are also included to give some special properties.

Geometry of Packages:
Threads are wound in many forms. Small length spools are employed in retail store distribution, whereas somewhat larger spools are used to a limited extent industrially. Some of the very fine soft threads are wound on cones, very coarse soft threads are in skein form, but the largest proportion by far is wound on the one headed tube with base or straight tubes.

These packages in some instances are put on a weight basis; however, the larger percentage is marked on a length basis. Ready-wound bobbins in a number of styles to accommodate the various sewing machines employed are also available. Cross winding threads are generally laid in with traverse ratio 1: 6 (one double traverse = six spindle revolution) and 1: 4 for coarser counts.

The following types of packages are used in sewing threads (with commonly used dimensions).

Spool:
Spools are small flanged plastic or wooden bobbins; they are both with tapered (so-called Diabolo spools) and straight flanges. Mainly parallel winding (because side unwinding is easy) is done. Cross-windings are also possible on the spools. They contain relatively short length of 100-500 meter thread. The length of traverse on spool is 2.9-3.8 cm.

End uses: Upholstery, footwear, leather goods manufacturing, and in hand sewing operations.

Cop:
Cops are small cylindrical flangeless spools, with precision cross winding. They are mostly made of paper and plastic. They are of two types, small Cop (Tube) and medium Cop (Cop). The lack of flanges facilitates regular off winding on industrial sewing machines although their small diameter makes them less well suited to the faster thread take off machines. Smaller Cops are popular make-up in fashion trades, where a variety of shades are used and production runs for any one color or style of garments. The length of thread wound ranges from 100-2000 m on small cop and 400-4000 m on cop. The length of traverse on small cop is 5 – 6.3 cm and on cop is10 cm.

End uses: Kite flying, Upholstery, ready-made garment, tailoring, hosiery, umbrella, and shoe stitching.

Cone:
This is self-supporting, cross wound conical package. It is easier to withdraw yarn over end from a cone than from a cheese and because of this, cone is more widely used. They contain relatively long lengths 1000-25000m with length of traverse ranging from 10-15 cm. They give trouble free thread unwinding at intermittent or continuous high speeds. Cones are the most economical packages for conventional sewing threads in situations where thread consumption is high and production runs are long.

End uses: Readymade garment, tailoring, hosiery, leather stitching, Upholstery, shoe stitching, denim, embroidery, and kite flying.

Vicone or King spool:
Vicones are parallel tubes or low angled cones with an additional base in the form of a raised flange, which may incorporate a small tip. The build of vicone depends on the exact conformity of the taper with the angle of vicone’s base. Coarse yarns require a large traverse for the taper — fine yarn a small one. They contain lengths of 1000-5000 m with length of traverse 6.5-9 cm.

End uses: Embroidery, core-spun, and filament threads.

Prewound Bobbin:
Prewound bobbins are precision parallel wound thread package designed to replace metal bobbins on a variety of lock stitch machines.

Skein:
A very small hank of soft twisted plied thread (around 8 m) of coarse count is parallel wound with the help rotating flyer, which withdraws the thread from the supply package cone.

End uses: Embroidery.

Ball:
A typical ball like structure, wound with the help of four types of different winding. They are: Rough base winding, form winding, surface layer winding, and circumference winding. The initial winding provides firmness at the base. Next winding process makes space for placing the identification ticket. The third stage of winding provides firm gripping of the ticket. The last stage of winding makes a band over the ball, which retains its shape. An easy unwinding of thread is possible.

End uses: Embroidery, fishing net and bag closing.

Cocoon:
Cocoons are self-supporting i.e. center-less thread package specially designed for the insertion in the shuttle of multi needle quilting and some types of embroidery. Cocoons are used in the shuttle of multi needle quilting and some types of embroidery machines.

Different Types of Winding System:

Precision winding:

• Constant winding ratio
• Winding angle reduces with increasing diameter
• No pattern areas
• Good off-winding characteristics
• High package density

Step precision or digicone winding:

• Almost constant winding angle
• The wind ratio is reduced in steps
• Combines the advantage of random and precision winding
• No pattern areas
• Higher consistent package density
• Perfect unwinding characteristics
• Straight sided packages

Random winding:

• Winding angle is kept constant since the winding ratio reduces with increasing diameter
• Stable packages
• Even density

Pineapple winding:

• Winding traverse reduces to produce packages with tapered edges
• Required for filament winding operations
• All three types of winding applicable

Parallel winding:

• Very high package density
• Thread vertical to package axis
• Relatively short lengths of thread
• Suitable for side unwinding
• No pattern areas 5,6

Ball winding:

• Very easy unwinding
• Winding takes place in 4 stages:
  1. Rough base winding
  2. Form winding
  3. Surface layer winding
  4. Circumferencial winding

Skein winding:

• Easy unwinding
• Very small parallel strand of soft twisted thread.

Different Types of Sewing Threads:
Usually, sewing threads are manufactured from either natural or man made fibers in either staple or filament form. A broad classification of different types of sewing threads is given below:

PTFE coated fiberglass sewing threads:
PTFE coated fiberglass sewing threads is made from continuous filament yarns, resulting in a strong, chemical resistant textile sewing thread. Uniform PTFE coating completely encapsulates the thread, enhancing resistance to build-up of contaminates and repelling attack by most acids and alkalis. Smooth PTFE coating enhances the flexibility of the fiberglass yarn, making it suitable for many industrial applications and minimizing the tendency to kink, strip-back or break like other very high temperature threads. PTFE coated fiberglass can be categorized according to the temperature range i.e. S2 Grade Fiberglass, E Grade Fiberglass, Beta Grade Fiberglass These threads offer high temperature resistance, high strength, chemical resistance and suitable for temperatures up to 538°C to maximum of 760°C.

Applications:

1. Aerospace: Randomness, thermal shields, micrometeorite debris shields, ceramic-matrix, Composites, metal-matrix composites, polymer-matrix composites.
2. Industrial: Furnace linings, galvanized steel furnaces, porcelain furnaces, furnace zone dividers, door seals, tube seals, gaskets, expansion joints sealing and insulating products, safety clothing and gloves.

Alumina-silica sewing threads:
Alumina-silica yarn is made up of thousands of filaments, giving it excellent flexibility and stability for transformation into textiles, without the aid of other organic or metal fibers. A boron-free alumina-silica fiber that is composed of Al₂O₃ 72% and SiO₂ 28%, Table1 which is commonly known as a representative stable metal oxide material. It is a polycrystalline filament whose crystal type is gamma alumina and amorphous silica with a fine filament diameter of 7 micron. Textile properties include good chemical resistance, thermal shock resistance up to 1200ºC and superior insulation properties. They are also corrosion-resistant and do not absorb moisture. Filaments are inherently colorless, but can be colored with inorganic pigment red, black and blue. Pigments are stable up to 700/800°C.

Table 1: Thread specifications

Applications:
High temperature textiles, safety spray shields, braided sleeving, insulation jackets thermal insulation pads, high temperature gaskets, kiln seals, welding blankets, heat shields.

Carbon fiber sewing threads:
Carbon fibers are the closest to asbestos in a number of properties. Each carbon filament thread is a bundle of many thousand carbon filaments. A single such filament is a thin tube with a diameter of 5–8 micrometers and consists almost exclusively of carbon. Carbon fiber gives high strength and temperature resistance (up to 1100ºC) properties.

Table 2: Thread specifications

Application: Sports cars, super bikes, aerospace, marine.

Kevlar sewing threads:
These threads are schappe spun meta-aramid sewing thread. Threads made of Kevlar retain much of their strength at high temperatures, they can help the seams and tape edges stay sealed and keep out flames. Kevlar threads have excellent strength (Table 3) and good thermal stability retaining a high percentage of room temperature properties at temperatures up to 300°C. It does not melt, or support combustion, but will oxidize to a cinder at 400 – 430°C. Offer other properties like low thermal conductivity, will not burn or smolder, will not stretch or shrink high strength-to-weight ratio, resistant to sparks and welding spatter, superior resistance to abrasion, resistant to most chemicals, excellent flexibility up to 300°C.

Table 3: Thread specifications

Applications: Safety clothes, pilot’s overalls, defense uniforms, low flammability textiles

Nomex sewing threads:
These threads are schappe-spun meta-aramid sewing thread. Mainly used to over lock the fabrications (prevent fraying at edges), Nomex thread is known for its ‘flame resistant properties, and is used extensively in protective textiles. Nomex does not melt and has extremely low flammability. At temperatures above 371°C, the fiber degrades to a char. Nomex has excellent resistance to chemicals, low thermal conductivity, non-combustible, dimensionally stable at elevated temperature, high strength-to-weight ratio, resistant to abrasion, good dielectric properties, resistant to acids and alkalis, excellent flexibility.

Table 4: Thread specifications

Applications: Protective clothing and gloves for firefighters, industrial filtration felts, smoke curtains for naval vessels, protective clothing for petrochemical workers, heat insulation tape for sleeving, aviator and racecar driver uniforms, thermal insulation felts and batts.

Stainless steel spun yarn with PTFE or cotton:
For High Temp products required to go above 550°C, this thread is used as the main reinforcing stitch. It has excellent resistance to high temperatures up to 800°C. For cotton coated thread the cotton burns off at relatively low temperatures to leave the stainless steel thread as the main reinforcing material. Typical thread with diameter of 0.035mm gives tensile strength of 925-1100 Mpa with 30% elongation to break.

Table 5: Thread composition

Applications: Heat shield curtains and high temperature textiles.

Poly propylene sewing thread:
Polypropylene fiber have some good inherent characteristics such as high tensile strength, high chemical and abrasion resistance, weather resistance, neutrality to odors, dirt repellence, no tendency to pilling and rot resistance. Polypropylene fibers have limitation of melting temperature which is 165-170ºC. These threads can be applied for technical textiles where they are not subjected to the high temperatures. High Tenacity Polypropylene twisted yarn is also available in raw white or mass-dyed colors on industrial cones, king spools or metered bobbins for sewing threads and technical applications.

Applications: Inherent hydrophobicity makes them ideal sewing threads for fertilizer bags, Geotextiles, cement bags, Upholstery, filtration, packaging, bulk container and furnishing industry.

Nylon 6 bonded or non-bonded continuous filaments sewing threads:
These threads are made up of 100% continuous Nylon 6 (Polyamide 6) yarn of high tenacity. Nylon 6 threads have very good elastic recovery at low stresses they recover almost 100%. Nylon 6 shows high resistance to alkali, and weak acids. Nylon 6 gives high abrasion resistance.

Applications: This type of threads can be used for leather shoes, uppers, leather garments, footwear, wallet, sports goods, gloves, bags, light leather goods, mattresses, upholstery, automobile seats, industrial filters, carpets, parachutes, airbags etc.

Nylon 6, 6 bonded or non-bonded continuous filament threads:
Polyamide 6.6 is semi crystalline polyamide and excels in applications where high strength, impact resistance and toughness are required. Bonded is made from 100% Continuous Polyamide 6, 6 high tenacity yarns. Thread after twisting and dyeing (as required) is coated with specially formulated Bonding finish.

Advantages of the bonded threads are:

1. Excellent performance of multi-directional sewing operation as the plies stays together, due to the bonding of plies.
2. Exceptionally high abrasion resistance due to coating of specially formulated bonding chemical.
3. High Melting point of above 260° C, thus preventing thread melting at needle eye while sewing.
4. Low stretch and excellent recovery properties resulting in very neat seams.

Applications: Ladies shoe uppers, Shoe lining where decorative work is important rather than strength.

Polyester bonded, non bonded continuous filament thread:
Polyester has good tenacity, very good elastic recovery, stable at quite high temperatures, hydrophobic nature, resistance to acids and alkali make polyester ideal member for the sewing threads. Pre stabilized 100% continuous filament polyester with specially formulated bonding chemical finishes gives excellent performance on multidirectional machines and automatic machines as the plies do not open during sewing. Bonding also provides very high resistance to abrasion due to protective bonding chemical coating.

Applications: Ladies shoe uppers, shoe lining, leather garments, footwear, wallet, sports goods, gloves, bags, light leather goods, mattresses, upholstery, automobile seats, industrial filters, carpets, parachutes, zips, stitching of leather goods, ornamental stitching of leather shoes, saddlery, tarpaulin, tents, jeephoods, safety belts etc.

Polished polyester / cotton core spun sewing thread:
These threads are made from high tenacity polyester filament covered with cotton during spinning. After spinning special chemical treatment and process are given to give it an extremely smooth surface and bright luster. These threads give very high resistance to heat due to heat cover. Threads give strength of high tenacity polyester with softness and feel of cotton, combine with very good luster due to the Special Polishing Treatment.

Applications: This type of threads are used where decoration is required leather jackets, coats, wallets, belts, garment linen, leather jackets, gloves, handbags, leg guards, all types of leather goods, raincoats, umbrellas, brushed shoe uppers etc. higher counts are generally preferred.

100% spun polyester sewing thread:
These threads are made from high tenacity Spun Polyester Yarn. Thread is highly supple, rot proof, UV Resistant, waxed, and polished. Micromolecular lubrication is given for very smooth high speed sewing operation.

Applications: Highly suitable for foot ball, basket ball, sole stitching, saddlery etc.

High tenacity lubricated polyester braids:
These are thick threads and can be used for heavy functional, decorative seams. Performance in any condition, high speed or different materials is granted by the special structure and lubrication, imparting a good gliding and needle cooling. Can be used on all heavy sewing machines for shoe soles, rand, automatic units, two needles. The primary use is for coarse functional seams and decorations by heavy stitching machines.

PTFE sewing threads:
Filter bags, cartridges, and other sewn filter media are exposed to extreme temperatures chemicals, abrasives, and, occasionally, moist environments, for extended periods. These conditions degrade the filter media and thread, and the thread often gives out first. In some cases the thread is not appropriate for the application, or it simply wears out from chemical, temperature, or abrasive attack before the filter media. Sewing thread, made from 100 percent expanded PTFE and engineered specifically for the demands of filtration applications, withstands exposure to chemicals, high temperatures, abrasives, and moist environments. These threads are manufactured by the paste extrusion process, PTFE resin is processed into membrane, tape, and fibers by combining extrusion and thermal elongation processes. Known as expanded PTFE shortened to ePTFE materials.

The extrusion process typically delivers much better tensile performance (up to 4g/d), with lower shrinkage (3–5 percent).

Advantages of the PTFE threads:

1. Chemically inert to acids, caustics, solvents and hydrocarbons (0-14pH)
2. Temperature resistant from -350ºF to 550ºF (-212ºC to 288ºC)
3. Non contaminating – will not shed or cause contamination
4. Low shrinkage at high temperatures
5. Non-aging
6. Unaffected by moist environments

TENARA® sewing thread is a long-lasting thread which enhances the life of the outdoor and marine products in which it is used. Conventional seam threads on awnings and other outdoor fabric products suffer from exposure to wind and weather. After a few years they can become brittle and break. Ordinary polyester threads break down over time due to exposure to UV sunlight, cleaning agents, saltwater and extreme weather. Resistance to sunlight is a key requirement for high quality outdoor products.

These sewing threads maintain their strength even after regular exposure to UV sunlight. Remain flexible even in extreme of temperature or frost. It gives outdoor fabric products the kind of strength that withstands severe weather conditions – even after years of exposure. PTFE is unaffected by acids, alkaline solutions and cleaning chemicals. Due to its chemical.

Characteristics it is highly suitable for use in manufacturing processes involving contact with aggressive media. High resistance to UV rays, chemical and atmospheric agents. Up to 15 Years threads remains unaffected by the U.V. Radiation.

Applications:
PTFE thread can improve the performance of a variety of products where seam life and integrity are of the utmost importance. This thread will not break down due to exposure to the elements, and therefore it is ideally suited for use in a variety of outdoor and marine fabric applications like Protective fabrics, sails, boat-covers, cabriolet, Awning, umbrellas, Artificial turf installation, hunting blinds, Gliders, Marine Bimini tops, Swimming pool covers, Hot air and weather balloons, Convertible tops, Gliders etc.

Surgical sutures:
Surgical sutures are one of the most commonly used devices for wound closure and tissue approximation. In the US, approximately 50 million open surgical procedures a year are performed requiring the use of sutures. Surgical sutures can be broadly classified as absorbable and non absorbable sutures depending on the material used for the manufacturing.

Absorbable sutures:
Absorbable sutures are made of materials which are broken down in tissue after a given period of time, which depending on the material can be from ten days to eight weeks. They are used therefore in many of the internal tissues of the body. In most cases, three weeks is sufficient for the wound to close firmly.

The suture is not needed any more, and the fact that it disappears is an advantage, as there is no foreign material left inside the body and no need for the patient to have the sutures removed. Absorbable sutures were originally made of the intestines of sheep, the so called catgut. However, the major part of the absorbable sutures used are now made of synthetic polymer fibers, which may be braided or monofilament; these offer numerous advantages over gut sutures, notably ease of handling, low cost, low tissue reaction, consistent performance and guaranteed non-toxicity. In Europe and Japan, gut sutures have been banned due to concerns over bovine spongiform encephalopathy (mad-cow disease). Occasionally, absorbable sutures can cause inflammation and be rejected by the body rather than absorbed.

Some typical absorbable synthetic sutures are as follows:

1. PGA (polyglycolic acid, multifilament)
2. PGA Quick (short term absorbable braid)
3. PGLA (Polyglycolide-co-L-lactide) braid
4. PDO (polydioxanone, monofilament)

These sutures provide advantages such as high initial tensile strength, guaranteed holding power through the critical wound healing period. Smooth passage through tissue, easy handling, and excellent knotting ability, secure knot tying.

Non-absorbable sutures:
There are several materials used for non-absorbable sutures. The most common is a natural fiber, silk, which undergoes a special manufacturing process to make it adequate for its use in surgery. Other non-absorbable sutures are made of artificial fibers, like polypropylene, polyester or nylon; these may or may not have coatings to enhance their performance characteristics. Finally, stainless steel wires are commonly used in orthopedic surgery and for sternal closure in cardiac surgery.

Chitin’s properties as a flexible and strong material make it favorable as surgical thread. Its biodegradability means it wears away with time as the wound heals. Moreover, chitin has some unusual properties that accelerate healing of wounds in humans.

Non-absorbable suture threads are as below:

1. Silk braided, untreated, waxed, siliconed
2. Polyester braided, untreated, waxed, siliconed and teflon coated
3. Nylon monofilament
4. Polypropylene monofilament
5. Norefil (PVDF-polyvinylidefluoride) monofilament
6. Linen
7. Steel wire

Soluble sewing threads:
Synthetic polycarbonate threads and polycarbonate threads has been developed to replace conventional basting or tacking threads and is use to stitch the material in usual manner finished products are treated with dry cleaning solvent, when agitated, reduce thread cohesion until fracture is initiated and the broken fragments are shaken away from the fabric. These threads can be used to for Tacking thread for sanitary laundry bags, sewing fabrics with long stitches like tarpaulin, before sewing to hold it in position and then after sewing removed by dissolving them.

Fusible sewing threads:
Fusible threads are made up of the two components one component of the thread has lower melting point in comparison to the other component. These threads are made up of a fusible bonding fiber which is twisted with a normally melting polyester or polyamide supporting fiber. When exposed to heat the fusible adhesive component of the thread, which due to its low melting temperature is only used as lower thread, melts and forms an adhesive bond while the supporting fiber remains unchanged to form a stitched seam with the top thread. Fusible threads are manufactured in various counts from 45 to 1100 dtex and are available with melting points of 85°C and 140°C.

Application: Leather industry, upholstery, seat belts

Conclusion:
Sewing thread is a critical component in terms of the overall quality and appearance of textile structure besides impacting productivity. Sewing threads are intensively made of polyesters, polypropylene, Nylon6, Nylon66, with bonding treatments and lubricating use for automobiles, leathers, packing industry. Medical sutures have very good prospectus and they are generally made up of synthetic yarns. New suture threads are also being developed to better respond to particular surgical needs. Heat resistant sewing threads from Kevlar, Glass, Nomex are specially designed to meet their end use requirements.

These threads have excellent sewability with other desirable properties like resistance to chemical, light weight etc are useful for industrial applications while carbon and steel sewing threads offers slow speed sewing with high tensile strength. Growing demand for the safety legislations open up the wide market for the heat resistant threads in spite of their high cost.

The sewing thread is of considerable importance, playing a major role in retaining the fabric appearance, look, and life of the garment in the long run, even though it usually represents much less than 1% by mass of a garment.

Nowadays, a numerous variety of sewing threads are available in the market due to diverse demands from the sewing industry, increasing use of different types of fibers in the garment industry and expanding application of textile materials in various fields like apparels, technical applications as well. Better understanding of the sewing process and its requirements as obtained through studies by modern instrumentation techniques has also greatly contributed to the development of new threads. It is also very much required and appreciable to have different types of sewing threads, which can suit various applications, since various end-uses demand specific property requirements.

It is beyond anybody’s doubt that the success of garment manufacturing process mainly depends upon the operation of sewing, though a very better quality of fabric is selected for the garment manufacturing process. Again, the sewing threads play a vital role in the success of sewing operation, since a wrong thread may ruin a very high quality fabric and even a best sewing machine used for the sewing, and the whole process will fail. It can add to waste of both time and money. Hence, it is very much imperative to select a right type of sewing thread which can suit one’s requirements exactly. This is possible by the correct understanding of the type of fiber used to manufacture, manufacturing processing sequence and properties of different types of sewing threads existing on earth, which was touched upon in this technical article to a greater extent.

References:

1. Processing and properties of sewing threads published on Indian textile journal on August,2009.
2. J O Ukponmwan, A Mukhopadhyay and K N Chatterjee: Sewing Threads, Textile Progress, The Textile Institute, Volume 30, No. 3 /4, pp 1.
3. S D Pai, V G Munshi and A V Ukidue: Cotton and Synthetic Sewing Thread — I, The Indian Textile Journal, August 1984, pp 63-75.
4. Pradip V Mehta, and Satish K Bharadwaj: Managing Quality in the Apparel Industry, National Institute of Fashion Technology, New Delhi, India, New Age Publihers, 1998.
5. K R Salhotra, P K Hari and G Sundaresan: Sewing Thread Properties, Textile Asia, September 1994, pp 46-57.
6. www.threadsindia.com
7. P.W. Harrison; Sewing threads; Textile progress, 2000; Vol. 30, Number3/4, 1-93

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Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.

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