9—THE PROPERTIES OF AIR-TEXTURED CONTINUOUS FILAMENT YARNS

Abstract

A processing programme is outlined in which yarn pre-twist, applied air-pressure, and supply-yarn overfeed are systematically varied in the air-jet bulking process to investigate their effects on air-textured nylon 6.6 continuous-filament yarns.

Optical magnification of the air-textured yarns enables the average loop sizes and frequencies to be measured. The experimental results are shown to be in general agreement with a suggested mechanism of the process, which argues that the initial filament twist in the parent yarn redistributes itself as snarled loops and that the overfed yarn contributes to the size of such loops; the deflexion of filaments by air-drag forces is also shown to make a contribution to a looping effect, which can be estimated theoretically. Increasing the yam overfeed increases both the loop size and the loop frequency. Increasing the yam pre-twist decreases the loop size and increases the loop frequency. Increasing the air-pressure also decreases the loop size and increases the loop frequency. Experimental and theoretical results are in general agreement.

As would be expected, the only processing condition that effects a change in linear density is the overfeed, but all the processing conditions that have an effect on loop dimensions also have an effect on the change in volume, i.e., on the physical bulk. Overfeed is the greatest single contributor to physical bulk, since both loop size and loop frequency increase with overfeed, occluded air spaces being thereby created in yarn and fabric form; conversely, with varying twists and air-pressures, the effects of decreasing loop size and increasing loop frequency are to some extent self-balancing in their contribution to physical bulk.

It is shown how the various processing parameters affect the stability of air-textured yarns. Textured yams produced from parent yarns possessing small amounts of pre-twist have a high instability because of the lack of binding twist for securing the entangled structure. Increasing the overfeed greatly increases the number and size of loops, and this causes greater instability. Increases in the applied air-pressure also increase the yarn instability. Two new mechanical techniques have been devised to measure the yarn instability, and these have been found to be greatly superior to the stability-testing apparatus normally used, which has serious defects from the viewpoint of accuracy.

The tenacity of the air-textured yarns tends to decrease for increasing values of all the main processing variables considered. Increasing the yarn pre-twist tends to reduce the percentage elongation at break, but independent increases in the supply-yarn overfeed and the applied air-pressure both tend to increase this characteristic. These results are interpreted in the light of the bulking mechanism previously postulated.

KEY WORDS (SPECIFIC TERMS):

• AIR-JET-TEXTURED YARNS: AIR-JET-TEXTURING
• BULKING
• LOOP YARNS
• PRE-TWIST
• AIR-PRESSURE
• OVERFEED
• AIR-DRAG
• AIRSTREAMS
• NYLON 6.6
• LOOP SIZE
• LOOP FREQUENCY
• CORE DIAMETER
• YARN DIAMETER
• LINEAR DENSITY
• INSTABILITY
• BULK
• PACKAGE DENSITY
• BREAKING ELONGATION
• BREAKING STRENGTH
• STRESS-STRAIN CURVES
• TWIST
• INSTRON TENSILE TESTER (TN)
• DU PONT STABILITY TEST (TN)

KEY WORDS (BROADER TERMS):

• YARNS
• FILAMENT YARNS
• BULKED YARNS
• TEXTURED YARNS (FILAMENT)
• TEXTURING
• NYLON (POLYAMTDE FIBRES)
• MAN-MADE FIBRES
• YARN PROPERTIES
• MECHANICAL PROPERTIES
• PHYSICAL PROPERTIES (EXCLUDING MECHANICAL)