Woollen Spun Knitwear

Prior to finishing, woollen spun knitwear such as “Shetland” and “Lambswool”, has a rather lean and harsh handle, unattractive appearance and a high residual oil or total fatty matter content, i.e. typically in the region of 5-10% o.w.w. However, these are overcome, or improved, by “scouring” and “milling”.

The purpose of scouring is simply to remove or reduce the amount of residual oil, (<1.5% o.w.w. for garments carrying for example a Woolmark label), and milling is to improve both the appearance and handle of the product. This is achieved by the fact that during milling, which can be considered as a controlled method of washing, due to the mechanical action the yarn swells and begins to burst. This allows individual wool fibres to migrate to the surface, whilst at the same time the strains and tensions induced during manufacture (i.e. during the spinning and knitting stages, etc.), which are responsible for relaxation shrinkage, are released causing the knit structure to consolidate.

The resultant effect is that the garments have a characteristic “fuzzed” surface or milled finish, which is much more attractive, and a noticeable softer handle.

Finishing Procedures (Woollen Spun Knitwear)

The actual scouring and milling procedures adopted can vary considerably between companies. The reason for this is that in addition to the possibility that companies may have different types of machines, there are many other variables to consider. These include, for example:

• Degree of finish required on the garment
• Yarn type and its count and twist
• Type and amount of residual oil
• Colour (darker shades require longer milling times).
• Knit cover factor (Knitting density)

Typical finishing recipe (Woollen Spun Knitwear)

Generally, scouring and milling are carried out separately i.e. a two stage process, and a typical method is as follows:

• Scour:
  • Set bath at 40^oC
  • Add 3-6% detergent
  • L: R = 20-30: 1
  • Run 2-15 minutes (depending upon machine etc.)
  • Drain
  • Rinse in warm water at 40^oC
• Mill:
  • Set bath at 40oC
  • Add 1-3% non-ionic detergent
  • L: R = 20-30: 1
  • Run 2-40 minutes (depending upon machine etc.)
  • Drain
  • Rinse well
• Hydro:
  • As much water as possible should be removed in order to Reduce drying time.
• Tumble Drying:
  • It is important to establish a standard minimum time. Suggested temperature for medium to deep shades is 70- 90oC, whereas for paler shades and some mixture or multi-coloured garments, the temperature should not exceed 60oC.

Worsted Spun Knitwear

Unlike woollen spun knitwear, garments produced from worsted yarns only contain a minimal amount of residual oil, because only a small amount is added during yarn manufacture. Therefore, it is not essential to scour worsted spun garments, although it can be done.

The main objective in finishing worsted spun knitwear is to relax the garments, as with woollen spun knitwear, by releasing the strains and tensions and thereby removing the possibility of relaxation shrinkage occurring when the consumer first subjects the garment to washing.

The removal of the strains and tensions responsible for relaxation shrinkage can be done, in the case of worsted spun knitwear, by either “dry” finishing using steam, or by “wet” finishing, which involves a light aqueous scouring operation. In the latter case it is essential that garments are subjected to a very gentle scour to avoid any disturbance of the surface of the knit structure. The reason for this being that one of the main attributes of worsted spun knitwear is that it has a very clean, even surface with each knitted loop clearly seen. Any surface cover on worsted spun knitwear is regarded as unacceptable, and any fibres protruding from the surface can lead to the promotion of pilling during subsequent wear.

Finishing Procedures (Worsted spun wool knitwear)

As described earlier above worsted spun knitwear can either be “dry” finished or “wet” finished.

Dry Finishing simply involves blowing steam through the fabric while it is under minimal tension in order to relax it. The advantage of dry finishing is that in comparison to wet finishing, it is rapid and less expensive. The disadvantage is that it does not allow for the possibility of an anti-cockle treatment to be carried out, or much scope for further modification to the fabric handle i.e. application of a softener.

For dry finishing of knitted fabrics a number of purpose built finishing machines (Novakust, Bisio, Montirama etc.) are available. Although these machines are primarily designed to handle fabrics in roll form, such as those produced on circular knitting machines, certain manufacturers supply attachments to enable garment panels i.e. fully fashioned knitwear, to be finished. Alternatively, knitted panels can simply be dry finished on a press, by adopting the basic principle of blowing steam through the fabric to fully relax it, then pressing the fabric to set it in the relaxed state.

Wet Finishing of worsted spun wool knitwear involves a very gentle scour, almost a static soak, without any milling cycle. After the scour the garments are rinsed with clean water before hydro-extraction and tumble drying.

Typical Finishing Procedure (Worsted spun wool knitwear)

• Scour
  • Set bath at 40oC
  • 0.5-1.0 % Detergent (On weight of wool)
  • L: R 30:1
  • Run 2-5 min’s
  • Drain
  • Rinse well
• Hydro-extraction
  • As for woollen spun knitwear (2.2.1)
• Tumble drying
  • as for woollen spun knitwear (2.2.1)

Final Pressing

After the completion of the finishing operation the garments are given a final steam pressing to remove creases, ensure that the garments dimensions are correct and overall make them presentable for sale.

Although hand held irons are still used for this, the most effective is a flat steaming table (large enough for knitwear), which incorporates a vacuuming device.

A typical final pressing sequence for wool knitwear is

1. Place garment on steaming table
2. Apply steam (4 bar condensate free minimum) to make garments pliable.
3. Remove creases and crush marks and mould garments to shape
4. Check garment dimensions and readjust if necessary
5. Further steam to remove remaining stubborn creases and crush marks
6. Final check using tape measure of garment dimensions
7. Vacuum to remove moisture and cool the garment
8. Place carefully on a side table to allow garments to condition before packing.

Note: Although some stretching of the garments is required to both remove creases and to set the dimensions of the garment, excessive stretching (Recommend a maximum of 5%) should be avoided. Stretching of wool garments induces potential for relaxation shrinkage, and an excessive amount will lead to notable shrinkage of the garment by the consumer upon domestic laundering.