Knitted fabric shrinkage causes and preventive measures

Knitted fabrics are inevitably subject to the following conditions during dyeing and printing production as well as during weaving production:
1. hot and humid environments for dyeing and printing processes;
2. efforts have been made to create conditions in the dyeing and printing production of knitted fabrics to make knitted fabrics in less tension, no tension, however, so far knitted fabrics in the processing of the production process is not possible to completely avoid tension. Tension exists so that the fabric longitudinal stretch, fabric density has been reduced, the fabric deformation;
3. Knitted fabrics are dried away from the steady state;
4. Knitwear yarn processing, knitting process also exists latent tension.
Due to the existence of the above conditions, will bring to the knitted fabric caused by shrinkage potential of a series of problems. Specific performance:
1. As the dyeing and finishing process is in a hot and humid state, the water molecules enter the amorphous zone of the fibre, which reduces the force between the molecular chains. At this time, under the action of external forces, the molecular chain segment displacement, so that the fibre elongation. If dried in this elongated state, hydrogen bonds are formed in the new position between the molecular chains of the fibre, and the elongated part of the fibre fails to retract to its original state. The stability of deformation in this hot and humid state is unstable. 2.
2. Knitted fabrics are made of loops of yarns, which have the most stable structural form. If the knitted fabric is in a stable structural state, it is in a dimensionally stable state and does not shrink when exposed to water. However, in the actual production process, the fabric, especially in the longitudinal direction of the fabric by a large repeated stretching effect, resulting in plastic deformation of yarn fibres, longitudinal elongation of the fabric, the width becomes narrower, the coil transfer, the fabric structure away from the fabric stable state. This state is unstable, in the appropriate conditions, there is a tendency to return to the original stable state.
3. knitted fabrics in the elongation of the drying condition, the surface seems to be stable, but in fact this "stability" is temporary.
4. Knitted fabric yarn processing, fabric knitting process by the stretch, the effect of tension with latent tension, the same will cause the yarn fibre retraction.
In summary, the causes of shrinkage of knitted fabrics:
1. The return of fibre deformation in the state of moisture and heat. Cotton knitted fabrics in the relaxed state of washing, water molecules can be produced to destroy the new hydrogen bonding, so that the internal stress relaxation, the elongation of the part of the retraction that is produced by shrinkage.
2. Knitted fabric deformation recovery. Knitted fabric structure away from the fabric stability state, in the case of wet washing, fibre plasticity enhancement, response force has been strengthened to produce the deformation of the response, elongation retraction, cotton knitted fabrics shrinkage and return to the original stable state, which is caused by cotton knitted fabrics shrinkage of the main reasons.
3. Fibre moisture absorption, yarn diameter increases, resulting in yarn shrinkage, resulting in shrinkage. Yarn diameter increases to cause the length of the yarn to shorten, resulting in fabric shrinkage (including length and width), density increases.
The above mentioned are the basic reasons for shrinkage of knitted fabrics. As for knitted fabrics in different circumstances, the impact of shrinkage factors and shrinkage, such as: different fibre composition of knitted fabrics, different tissue structure of knitted fabrics, different dyeing and finishing processes and equipment, whether the fabric after mercerising, stentering, pre-shrinkage treatment, and so on, is still to be practiced, explored, summed up, perfected and improved.

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