Properties of a Good Sizing Material | Sizing Chemicals & Their Importance

Sizing is a complementary operation which is carried out on warps formed by spun yarns with insufficient tenacity or by continuous filament yarns with zero twist. In general, when sizing is necessary, the yarn is beam warped, therefore all beams corresponding to the beams are fed, as soon as warping is completed, to the sizing machine where they are assembled. Sizing consists of impregnating the yarn with particular substances which form on the yarn surface a film with the aim of improving yarn smoothness and tenacity during the subsequent weaving stage. Thanks to its improved tenacity and elasticity, the yarn can stand without problems the tensions and the rubbing caused by weaving.

Sizing Chemicals & Their Importance:
Film forming materials:
Starch is the oldest film forming material used in sizing of cellulosic fibers. It is also the most widely used in the world due to its low cost and ease of availability. In Pakistan, mostly maize starch is used, whereas, potato starch is more popular in Europe. 

PVA is the second largest film former used in sizing. It is mostly used on synthetic yarns such as polyester and poly/cotton blends. PVA coating is strong, abrasion resistant and can easily be desized in hot water. Its strength is greater than starch and also more flexible than most standard starches. PVA is less prone to setup in the size box compared to starches. PVA can form foam in the size box which is controlled with a deformer. PVA may be too strong for some sizing applications. In this case, some weaker film forming polymers such as starch are added to modify the mixture, which also reduces the cost, since PVA is more expensive than starch.

The most widely used size materials are starch and PVA. However, other size materials have been developed and used for specific purposes. Carboxymethyl cellulose (CMC) is produced from wood pulp and cotton lint and has good adhesion to cotton. 

Polyacrylic acid based sizes (polyacrylates and polyacrylamides) are used to size hydrophobic fibers and their blends such as nylon, acrylics, polyester, etc because of their good bonding.


Properties of a Good Sizing Material:

1. Environmentally safe.
2. Good film former.
3. Reasonable use economics.
4. Penetration of yarn bundle.
5. Elasticity.
6. Good film flexibility.
7. Good specific adhesion.
8. Good frictional properties.
9. Transparency.
10. Bacterial resistance.
11. Reasonable strength.
12. Controllable viscosity.
13. Water soluble or water dispersible.
14. Good hygroscopicity characteristics.
15. Uniformity.
16. Clean split at bust rods.
17. Improves weaving efficiencies.
18. No effect on drying.
19. Reasonable extensibility.
20. Recoverable and reusable
21. Low static propensity.
22. No skimming tendency.
23. Easily removed.
24. Easily prepared.
25. Lack of odor.
26. No beam blocking.
27. Compatible with other ingredients.
28. Good abrasion resistance.
29. Neutral pH.
30. High fold endurance.
31. Insensitive to high heat.
32. Low BOD.
33. No build up on dry cans.
34. Reduced shedding.
35. Rapid drying.
36. No re-deposition of size
37. Insensitive to changes in relative humidity.