- 1 Fundamental Structural Features Of Yarn
- 2 1. Continuous Filament Structures
Fundamental Structural Features Of Yarn
The structural features of the yarn which have the influence on the physical and performance characteristics of yarn are-
- Volumetric density of yarn.
- Fiber segment length between points of entanglement.
- The mobility of fiber segment between points of entanglement.
These structural features are not easy to measure and to observe.
1. Volumetric Density
There is a lot of empty space is contained in all yarns, but the staple of textured filament yarns contains the airspace most.
A yarn is considered as dimensionally stable if the fiber packing density is remained some in the normal state and under low level of stress.
2. Fiber Segment Length Between Points Of Entanglement
The average fiber segment length between points of entanglement within a yarn structure is referred to as a fiber modular length.
In most of the yarns in which twist is the basic mechanism of entanglement, the average fiber or filament segment length between points of entanglement is related to the twisted geometry.
The orientation of the fiber segment length between points of entanglement with respect to the yarn axis is important but to a somewhat lesser extent.
3. The Mobility Of Fiber Segment Between Points Of Entanglement
- The mobility or freedom of movement and direction of movement of fibers segment relative to other fibers and fiber segment in the yarn plays a major role in yarn performance.
- Especially important is the lateral movement of fiber segment near the yarn surface on abrasion, snagging, pilling etc. in fabric structure.
- Yarn structures with minimum fiber segment mobility in both longitudinal, to yarn axis and cross-sectional to yarn axis is considered to be dimensionally stable.
These three are the fundamental structural features of yarn.
Yarn structural features depend mainly on the properties of constituent fibers and filaments and depend on characteristics of the fiber processing system.
Along with the generic (related parameters of fiber such as fiber friction resilience, modulus, extensibility, and elasticity) but most important fiber properties are length, fineness, crimp and cross-sectional shape.
Apart from fiber characteristics, the inherent characteristics of the processing system are fiber orientation and entanglement. Fiber orientation refers to the degree of linearity of the fibers or filaments in yarn and position of fiber or filament in relation to the yarn axis.
1. Continuous Filament Structures
While twisting multifilaments there is no any control on the tension or on the rate of feeding of individual filaments, due to which consequently a self-equalization tension phenomenon exist whereas in the individual filament exchange position easily among the various annular zones.
Filaments which are going to the outer layers of the yarn develop more tension and force itself towards the center of the yarn to relieve the tension and the filaments at the core of the under less tension so momentarily pushed to the yarn surface. This means that every filament is entangled periodically at both the surface and core of the yarns.
Continuous filament yarns with minimal twist or entanglement have a very long fiber segment length, between points of entanglement.
With the low twist, the filaments are free to spread and there is no definite or staple yarns cross-sectional shape or diameter filaments also can be pulled away individually from the main body and create the problem of snagging.
The yarns also tend to flatten out in fabric form and thereby makes possible a tremendous area of contact with any other surface, which is not desirable in most of the apparel applications. But on another hand, this also possess good linearity in filaments which is desirable for industrial applications.
More twist in the structure of the continuous filaments slightly decreases the degree of linearity of filament segment length in yarns, which leads to the reduction of strength.
This reduction in yarn strength occurs because of the more linear filaments are stained immediately on loading, whereas the less linear filaments tend to be straightened and then stained.
Increase in twist also reduces the length of filament segment between points of entanglement and thus reduce the tendency to spread out and snagging.
2. Textured Filament Structures
A continuous filament yarn that is textured into a high bulk yarn will contain a high degree of nonlinearity in its filaments, with a great amount of twist or entanglement.
Texturing essentially produces the high bulkiness in the yarns with no added extensibility in the yarns.
A continuous textured into a stretch yarns has a tremendous amount of filament nonlinearity, with minimal if any entanglement.
Moreover, the stretch yarns have little dimensional stability or structural integrity in either a tensile or compressive deformation.
3. Staple Yarns
The structure of staple spun yarns are an order of magnitude more complex than the structure of continuous filaments.
Although high-quality staple yarns may appear to be as uniform as filament yarn the closer examination would indicate the variation in the twist and randomly grouped fibers which are result in the thick and thin places along the length of the yarns.
Untwisting of the spun yarn structure indicates a more thorough and frequent tying-in of the fibers at the surface and at the cone layers than found in filaments.
Whereas low-quality staple spun yarn would show many localized complex fiber entanglements or hard spots known as neps that contained in the structure.
There is very high variation in the quality of staple yarns and uniformity of yarns because of the manner in which the fibers are processed during spinning.
Staple fibers are handled as a mass rather than an individual and therefore they tend to behave and to process in groups and subgroups.
Each staple fiber has two ends and that may cause to produce fuzz, hairiness, hook, buckle etc.
In the final process of staple spun yarn formation, a great amount of twist is superimposed onto the existing looser entanglement. This twist with the normal fibers migration pattern leads to very complex yarn structure.
While spinning the blend, an abnormal fiber migration may occur that is known as preferential radial migration or coring. In such case, one component is found at the core and another component at the surface of the yarns.
4. Non-Ring Spun Staple Yarns
Open-end yarns appear different than ring spun yarns on the surface. There is the rather important difference in the internal structure of the yarns especially in the fiber contiguity (assembly of the fibers which come together and entangle with each other).
The accumulation and entanglement mechanism in open-end spinning leads to more layering of the fibers or fibers segments into the specific annular zones in the yarns.
Whereas the migration of fibers from the surface to the core to the surface is found to be less than ring spun yarn.
The change in the internal structure of the open end yarns also reflects some effect on the performance characteristics.
Open-end yarns are more uniform in appearance and in linear density than ring spun yarns. Also, open-end yarns are somewhat more extensible, faller and softer.
But on the other hand, these yarns are not as strong as ring spun yarns.