A New Perspective to Improve Warp Sizing

In the early 1800s, the introduction of the mechanical loom promised the potential of dramatically improved fabric production. However, the mechanical loom also introduced a level of abrasion on warp yarn that prevented this productivity potential. The abrasion problem was soon attacked by borrowing technology developed by the coatings industry. In coatings, surface protection was provided by the application of natural oils which crosslinked to form a permanent topical barrier. The concept provided the solution, but the woven fabric was not a candidate for a permanent abrasion barrier. Starch soon emerged as a suitable material to provide a transient abrasion-resistant barrier to protect warp yarn. This approach soon led to the development of the necessary machinery to apply an abrasion barrier and the concept was adopted by the industry.

During the next two centuries, significant improvements in coatings technology and materials have been adopted to accommodate continual changes in yarn composition, yarn formation, and loom technologies.  Warp sizes are now designed to meet the demands of each fabric style on a case-by-case basis.  Warp size suppliers and technicians have performed admirably in bridging continual changing technologies involved in the journey from fiber to fabric.  We now are more secure in gauging general rules of viscosity, penetration and overall size add-on levels for optimum weaving performance. Optimization of the sizing formulation is now paired with the variables from the slasher through the greige fabric.

Advances in the use of polymer/starch surface barriers now dominate spun yarn sizing.  Abrasion protection coupled with nearly 2 centuries of experience has achieved what is now regarded as the optimum in painting warp yarn.  Unfortunately, this experience has fostered an attitude of complacency to the potential for improving weaving performance utilizing chemicals in the size box.

The use of nanosize resins (oligomers) has now been evaluated as components in warp size formulations.  On a theoretical basis, and the barrier coatings approach, these materials provide little optimism for improvements in weaving.  Chemically, oligomer resins have the basic properties of higher molecular weight polymers of the same chemistry but are much too low in molecular weight for viable film formation.  Minor adhesion and plasticization of conventional barrier film formers became the primary hope for this new technology.  Initial trials with nanosize oligomers in conventional size formulations provided promising results in both adhesion and plasticization of the barrier coating.  In addition, incorporation of oligomer resins provided differences that were not readily explained.

1. Reduction in both warp and filling stops.

2. Fiber and size shed at both the slasher and looms were dramatically reduced.

3. Increased yardage of hard yarn on the loom beam.

These results did not neatly fit into the barrier concept of warp sizing.  Increased yardage on the loom beam logically indicated reduced size pick-up on warp yarn.  However, multiple desize analysis of hard yarn from trials and normal production were equivalent.  The repetition of these trials was consistent with the initial results.  Nanosize oligomer resins were clearly providing a mechanism to complement barrier coating film abrasion resistance.

Microscopic (60X) photos were utilized to determine any visual differences between standard and trial hard yarns. Yarns containing oligomer resin in the size formulation exhibit a smoother surface with less hard fiber disruption from the sheet break.  In addition, the examination of 60X photos of the sized yarn indicates a significant reduction in yarn core diameter. Sized yarn diameters exhibit near 20% reduction in comparison to normal formulation hard yarn at the same add-on.

Examination of 1040X magnification cross-sections of yarn prior to the size box provides an explanation of the function of nanosize resins within the yarn bundle. Vacant spaces between fibers in the bundle are micron or greater in diameter and volume.  Fibers in spun yarn systems are mildly anionic, natural or added, which maintain a repulsive force to keep fibers apart.  As the yarn is wet-out by water, huge numbers of millimicron oligomer resin particles penetrate and adhere to fiber surfaces. Repulsive forces existing between fibers are overwhelmed and the fiber surface is modified with nanosize particles.  These small resin molecules provide a like-like mutual attraction and allow fibers to be drawn closer together to partially reduce vacant spaces within the bundle.  Immediate compaction of the yarn bundle occurs upon wet-out.  A smaller yarn substrate is now available to host the barrier film.  The count of the yarn remains constant with a smaller diameter bundle.  An increase in the density of the yarn is attributed to improved fiber cohesion within the bundle.

Statamat and Uster evaluation of sized yarn at equivalent add-on provided revealing differences in properties of the sized yarns in both tensile and elongation. Although both Tensile & Elongation properties are affected, low-end values are the most important in weaving.  Low-end properties are improved and the coefficient of variation reduced to provide a more uniform hard yarn.  A particularly unusual benefit of fiber cohesion improvement has been in an average improvement in loss of elongation near 30% of conventionally sized yarn controls.

Years of experience with conventional size film formers have optimized penetration and encapsulation of the film barrier on yarn.  Add-on levels and film locations are controlled by the viscosity of high molecular weight film formers to minimize penetration and maintain the size coating.

Adequate abrasion resistance from the barrier coating is dependent upon the surface area that must be protected.  Sized yarn is a cylinder in which surface area is directly a function of the diameter of the cylinder.  The new yarn created by nanosize oligomer resins in the formulation allows a reduced total size add-on to prevent oversizing and embrittlement of the hard yarn1.

Oligomer resin effects on yarn are especially important in increasing low end tensile and elongation and reduction in coefficient of variation.  This effect produces a more uniform yarn substrate for subsequent steps in the weaving process.  Effects on yarn without warp size were determined through the addition of a small amount of oligomer product to the final rinse in a conventional mock dyeing procedure2.

Desize of greige fabric is accomplished utilizing conventional procedures at pH levels slightly above 7.

Demonstrated Benefits of Oligomer Resin in Warp Yarn to date:

1. Immediate compaction of the warp yarn.

2. Low end tensile and elongation improvement.

3. Coefficient of variation reduction.

4. Improved uniformity of the warp yarn.

5. Reduced use of conventional warp size film formers.

6. Reduced warp and filling stops.

7. Reduced size and fiber shed in slashing and weaving.

8. Reduced housekeeping in slashing and weaving room.

9. Improved fabric quality.

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