Manufacturing of compression and pressure garments
Most textile materials are made by weaving or knitting yarns together. Compression and pressure garments are mainly knits.
Knitted fabrics are divided into two basic types:
1) Warp knit fabrics
2) Weft knit fabrics
Knitting methods are divided in:
a) Circular knitting
b) Flat knitting
Warp knitting can get much more complicated depending on the application and its end-use requirements. All the Lymed products are made of flat knitted warp knit. Warp knit tends to have better ability to form compression and build tight curves into a garment. One of the big benefits is the fact that it doesn’t unravel. Flat knits can be made from thicker yarns, which results in a stiff fabric able to form greater compression. Flat knit garments are manufactured from a flat piece of fabric, which is then stitched together. These are usually made to measure for the individual patient.
Circular knit is made with a machine that knits the fabric in a continuous circle (tube). Most of the standard size compression socks are manufactured by using this technology to result a smooth, seamless product. Circular knitting has some challenges, like building a shape with tight curves into a garment because loops are hard to suddenly add or substract in circular knits. In flat knit the product must have one or more seams to manufacture a cylinder shaped product. Pressure garment materials also have some misconceived terms that are not based in textile industry. A good example is the term “flat weave”, which does not exist in compression and pressure materials.
Material effects in pressure and compression products
Material quality affects the product characteristics in a multitude of ways – eg. the composition, structure and density of the yarn its made of. The way how manufacturers use their respective materials to form compression and pressure determines the qualities of the end product. There are less rules in manufacturing standard size products. There is little to no information available on what are the parameters of pressure that the manufacturers use to make standard size products.
Most applicable raw materials in pressure garments are polyamide and elastane fibers, which are very flexible and have high recovery abilities. Polyamide was historically developed as a synthetic substitute for silk. It’s most known commercial name is Nylon. It is lightweight, drapes well, has low absorbency and dries quickly, and is resistant to dirt, chemicals and perspiration. One of the strongest man-made fiber, the use of polyamide can be found in apparel, home furnishings and outdoor equipment. Polyamide is extremely versatile and though it can stretch a lot, it quickly regains its original shape instead of bagging. It can be dyed in almost all colors and that is the reason why polyamide is also used to make clothes. It is a bit shiny and is very durable. It does not get damaged easily.
Elastane is a polyurethane that is formed into elastic fiber, known also as Lycra or Spandex. Its most important attribution is stretchability: elastane can be stretched repetitively over 500% without breaking and it still recovers to its original length. The long amorphous segments in elastane create the elastic properties and the short rigid segments provide the structure when the fiber is stretched and released. Elastane is soft, lightweight and abrasion resistant. Elastane is used where a high degree of permanent elasticity is required, as in tights, sportswear, swimwear and in woven and knitted fabrics. Adding elastane just for couple of percent makes fabrics more comfortable to wear. Elastane is always used in a blend with other fibers.
The property of material of returning to its original position after removing the external force is known elasticity. A body is known as elastic if its returns to its original shape and size after removal the external force. A measure of elasticity is called elastic recovery and it is expressed as a percentage. If a fiber returns to its original length from a specific amount of attenuation, it is said to have 100% elastic recovery at x-percent elongation. Elasticity of different fiber depends upon its chemical and physical structure like typed of molecular bonding and crystalline of fiber and under what condition stress was applied. It can be stretched to several times its length and rapidly revert to essentially its unstretched length when the tension is removed.
Elongation on an elastane yarn is much higher than on a more rigid yarn, like polyamide on Lymed fabric. When stretching a knit, the elastane yarn would practically never get to its limits of the elongation. This means, in most cases, that the elastane would not determine the ultimate elongation in the knit: determination is made by the rigid yarns in the fabric. Also, the construction of the knit has effect on the stretchability: looser the knit, stretchier the fabric.
Textile fibers contain crystalline and amorphous sections. In the crystalline section the molecules are highly organized and parallel with each other. This section makes the fiber strong and rigid. In the amorphous section the molecules are disorganized, which makes the section flexible. How elastic the fiber is, depends on the ratio of crystalline and amorphous sections- it’s called the orientation of the fiber. Orientation tells about the strength and the elasticity of the fiber.
Elastic limit is the greatest amount of stress that can be applied to the fiber without causing permanent deformation. Up to the elastic limit the material will return to its original shape and dimension. Value of intensity of stress corresponding to this limit force is called elastic limit of the material. Beyond the material’s elastic limit, material will start deform and this is known as plasticity.
It’s not just the raw materials of the knit that have effect on the compression garment’s functionality. There is no clear relationship between the material percentage, for example elastane percentage, and the wanted compression. Material properties such as knit construction, yarn thickness and Tex number of the yarn, also have an influence on the compression formation in the garment.
When evaluating the suitability of the material, it is important to pay attention to the ability of a material to recover to its original state. That makes up the actual compression and its “permanence”. More elastane content in a fabric does not mean that the fabric will have more stretch. By increasing the elastane content in the fabric, more resistance to stretch is created using the elastomeric material. More elastane means more powerful fabric.
Based on textile material alone, or even the amount of elastane in the fabric, it is nearly impossible to decide how the product performs, what is its resistance to pressure or how well it does its job. Also, the feel towards the skin plays a huge role; does the knit feel firm but soft at the same time. On a general note, it can be said that products, which have more seams, can be produced to fit better than a completely seamless product – regardless of the material. Seamless and one-seam products fit best in simple body parts without great variation in circumferences, such as arm sleeves.