Warp Sizing – An Industry Problem!
Formaldehyde modified resins were introduced to the apparel market in the 1950’s. These finishes imparted a no-wrinkle character to cotton fabric and promised relief from the tedious job of ironing apparel. Preliminary marketing studies on the concept was an immediate and huge success. Optimism for this new market potential turned out to be premature. Apparel finished with these materials fulfilled the Durable Press promise but failed miserably in durability. Formaldehyde based resins converted cotton fiber into a brittle rod structure unable to withstand the rigors of the wash-and-wear cycle. The potential of this huge market was in jeopardy.
Introduction of Dacron® polyester fiber blended with cotton (P/C) served to provide a solution to the lack of durability of permanent-press fabric. Petroleum based Dacron® is impervious to formaldehyde-resin and provided an acceptable durability in high Dacron®/cotton apparel. No-wrinkle performance was dramatically reduced but was a minor concern to those freed from the chore of ironing. The market potential was returned to life, and production of P/C fabric turned over to weaving mills.
For over 200 years the accepted abrasion resistant barrier for cotton yarn was natural starch and derivatives. The chemistry of carbohydrate starch and cellulosic cotton was compatible and provided natural adhesion of the starch film on warp yarn to resist loom abrasion. With a majority Dacron® fiber in the warp, there were no sites for starch to adhere to the synthetic fiber surface. Size formulations based on starch were quickly shed to the surrounding environment in weaving. A high level of demand existed, but economical production of P/C fabric for resin finishing was not possible. Panic became a standard atmosphere in USA weaving mills. Potential chemical additives that had any promise of binding starch to P/C yarn were trialed with no success.
In desperation, a trial was initiated with polyvinyl alcohol. The material had been initially produced in Germany in 1924 and introduced to the USA around 1935. Evaluation of PVA in warp sizing area was not a logical choice. PVA formed a strong film, but the pendent hydroxyl functionality that provided water dispersibility and adhesion to fiber was the same as starch. Desperation was at a level where logic was not a factor in attempts to solve the problem. It was a surprise when the PVA film did not shed from the yarn on the loom. PVA provided a very strong barrier film which encapsulated P/C yarn to minimize loom abrasion. The film was so strong that initial trials of PVA provided a sized yarn sheet so strong that yarn ruptured at the bust section during separation to individual sized yarn. This problem was moderated by diluting PVA film strength with starch to weaken the size film. Addition of starch to the formulation also moderated the shock of the cost difference between starch and PVA. (At the time, starch was $0.045/lb and PVA $0.35/lb).
PVA/starch combinations now dominate materials providing surface barrier protection in spun yarn weaving. Warp size formulations have now progressed to variations of the following components based on loom and fabric style:
- Polyvinyl Alcohol &/or Synthetic Polymer
- Modified Starch
- Other synthetic adhesion/film modifier
Acceptance of synthetic polymers represents the most significant advance in surface protection since starch coatings were adopted to minimize abrasion on warp yarn. Synthetic polymers and the advances that size technicians have developed have been outstanding but are not the major cause of concern for the stagnation that is now firmly established in warp sizing. The root of the problem has been an acceptance that further progress in weaving efficiencies based in the sizing process is no longer a realistic objective. Chemical materials to provide abrasion resistant surface barriers are now formulated to meet budgeted costs rather than improving performance levels. This situation does not encourage research or expenditure for improvement in either mills or by chemical suppliers.
Complacency has not been a characteristic normally associated with the textile industry but has now found a home in warp sizing.
John Callow Lark, PhD