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Role of Anti-creasing agents/Lubricants in Textile Wet-Processing

With the evolution of high turbulence, high torque dyeing equipment, increased attention has been given to the lubricants employed in textile wet processing. Even before the advent of modern equipment, lubricants have been used and sometimes misused in the prevention of crease marks and chaffing of knitted goods during processing.

Because jet/overflow machines transport the fabric in rope form, creases are inevitable, but if the creases are rapidly and continuously moved they do not become permanent. When dyeing at longer liquor ratios this shifting in position of the folds is easier than under short liquor ratio processing conditions. Inside the jet nozzle the surface of the fabric becomes subject to stress and friction between fabric and fabric or between fabric and metal, resulting in a more fibrillated surface, abrasion marks, or permanent fibre damage.

Creasing may result from:
·  an inadequate prepare (relaxation/bulking of fabric may not be complete or may have occurred too quickly);
·  quality of goods (a tight construction, high twist yarns, dense weight per sq.m.);
·  poor suitability of machine (folds not moved);
·  too heavy a batch of fabric;
·  incorrect loading (twisted rope, knotted or poorly sewn ends with no opportunity to balloon);
·  incorrect process (heating, cooling rates too rapid);
·  lustre – stationary fabric sitting on hot metal of machine under pressure giving a glazed mark.

To avoid fabric creasing the first steps should be to follow some simple rules to avoid the above problems and then an anti-crease lubricant should be used to influence the fibre-to-fibre friction, and fibre-to-metal friction only as an extra insurance against creasing and abrasion faults. The  formation of creases and many other undesired phenomena can be avoided by reduction of friction.

The basic requirement of an anti-creasing agent in wet processing is that it should form a thin, uniform protective coating around the fiber to lower the surface friction and flexural rigidity, thus minimizing the formation of durable creases during high temperature wet-processing. Thus, it has become increasingly important to select chemistries of anti-creasing agents/lubricants with discernment.

While the natural derivatives like animal fats and vegetable oils still constitute an appreciable share of the market, synthetic types have gained acceptance and are especially useful in niche applications.

In a broad general sense, natural lubricants enhance or promote fiber-to-fiber lubricity by lowering the coefficient of friction between the fiber and itself and fiber and metal. Whereas, the area of synthetic lubricants is limitless because of the variations due to the ever increasing availability of novel starting materials. These lubricants differ not only by chemistry, but also by their effect on the substrate. Unlike the natural based chemistries, the synthetics tend to influence fiber-to-metal and metal-to-metal friction rather than the fiber-to-fiber type.

In this article, the synthetic chemistries are subdivided into three; acrylics/acrylamides, emulsified paraffinic oils/waxes and modified silicones.

The acrylic/acrylamide synthetic lubricants have several characteristics that make them a much broader and deeper class upon initial inspection. They generally have excellent solubility properties while promoting a perceived lubricity by increasing laminarity unlike many of the natural types. Beginning with vinyl terminated monomers, the polymers/copolymers can be grown to various molecular weight ranges which affect solubility, rinsibility and lubricity.

Generally, acrylic acid and acrylamide are the monomers of choice for the polymer scientist. Acrylic esters offer latitude for incorporating other functionalities along the polymer backbones. It is critical to control the size and rate of the polymerization and the range of the molecular weight distribution. Use of the acrylic acid monomer imparts a degree of anionicity to the final polymer. Acrylic esters allow for the degree of anionicity to be modified. Physical properties, depending on the alkyl group of the ester, are altered. Matlube UCA is an acrylic copolymer, especially recommended where high stability to electrolyte (required in dye-baths) and to alkaline conditions (required in scouring baths) is a necessity. It is therefore particularly suitable for the preparation, and dyeing of cotton and its blends.

Acrylamide monomers result in added stability to the polymer, especially in an acidic medium where the amido group is partially protonated and the polymer can behave somewhat cationically by taking on a partial positive charge. From relatively neutral pH medium, polyacrylamide behaves like a nonionic species in its compatibility with other products. We at Matex, have studied the behaviour of monomers and have successfully developed Matlube CA based on acrylamide chemistry.

clip_image002Perhaps the broadest range of synthetic lubricants are those formulated from paraffinic hydrocarbons. This chemistry is quite resistant oxidation and color degradation. A side branch of paraffinic hydrocarbons is polyethylene.

Abrasion and chafing marks may result from:

  • too high a machine speed;
  • stationary fabric in a running machine,
  • caused by poor wetting, knots and tangles in the fabric,
  • poor operating practice e.g. whilst sewing ends;
  • overloading the machine, leading to mechanical friction;
  • rough patches in the machine.

Such chafe marks may exaggerate creasing, by dyeing a different shade on the abraded edge of the crease. Making a scratch with something metal on a prepared cotton knitted fabric, and then dyeing with a reactive phthalocyanine turquoise and a yellow can demonstrate this. The area on which the scratch was made will dye to a deeper, bluer shade than the rest of the fabric. This is because damaged cotton will dye darker with a phthalocyanine blue dye. This can clearly be seen under the microscope.

Matlube DBL is distinguished from other wet-processing lubricants in having very useful emulsifying properties for oils and waxes which may be present on the fabric or on the walls of the machine. These properties help to avoid reprocessing as a result of spots and stains on the fabric, as well as reducing or eliminating creases and abrasion damage. Moreover it is highly stable in alkaline conditions, in presence of electrolytes as well as high temperatures upto 130°C. Hence it can be used for cotton, polyestser and its blends.

Polyethylene based products do promote fiber-to-fiber Iubricity, but due to their durability and hydrophobicity, they are primarily employed for yarn lubricants and sewing lubricants. Their rinsibilities can be quite inferior to less substantive lubricants.

clip_image004The perfect winding control of modern winding systems now permits the further processing of yarn packages directly after dyeing, thus making it possible to eliminate rewinding in most cases. However this presupposes that the yarn after dyeing is finished with an effective lubricant. In this case, Matlube YLW is applied as lubricant in the last rinsing bath after dyeing.

Benefits of Polyethylene based lubricants :

  • Improves abrasion resistance properties
  • Imparts good gliding effects and an excellent soft handle to the yarn
  • Makes hard waxing or oiling the yarn unnecessary
  • Retains the strength of the yarn
  • It does not affect the shade or fastness properties of dyed yarn
  • Causes no thermo-migration when polyester fibers are dyed with disperse dyes
  • Causes no yellowing of yarn, hence no effect on whiteness of optically brightened yarn
  • Reduces fibre-metal friction, thus facilitating further operations such as twisting, rewinding, weaving and knitting

Sewability of the fabric is the property by virtue of which it gives resistance to the penetration force of the needle of sewing machine. Thus lower the resistance it offers better is the sewability. Any fabric either it is woven or knitted has to undergo tremendous forces during stitching at garment stage which may result in rupture of fabric construction at the point of contact of needle & fabric. This rupture is also termed as sewing damage. In order to reduce this friction, it is required to use an appropriate sewability improver.

clip_image006Matlube SEW furnishes the fiber with smooth and sliding properties. It decreases the inter-friction between fibers and avoids the abrasion damage of the fibers by the metal surface of the needle. It eases needle penetration considerably when needling non-woven and felts. Facilitates making-up operations too.

Modified silicones also play a vital role as thread lubricants. They have practically no affinity or substantivity towards the substrate while providing adequate lubricity. Advantage of silicones over paraffin based lubricant is that is moisture free. Hence can be applied easily by lick roll method. It provides uniform distribution over the entire thread surface. Matlube LRT is a modified silicone that provides the thread with low friction characteristics. Thus it facilitates winding and re-winding operations.

Very rarely are all the characteristics embodied in one single product. Variations in substrates, processing equipment, bath conditions etc. leads to the requirement of an appropriate lubricant.

If anyone has any feedback or input regarding the published news, please contact: info@textiletoday.com.bd

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