Saturday, March 7, 2015

Fiber Blends[1-2]
Art Resource

Marie-Therese Wisniowski

This is the thirty-seventh post in the "Art Resource" series, specifically aimed to construct an appropriate knowledge base in order to develop an artistic voice in ArtCloth.

Other posts in this series are:
Glossary of Terms
Units Used in Dyeing and Printing of Fabrics
Occupational, Health & Safety
A Brief History of Color
The Nature of Color
Psychology of Color
Color Schemes
The Naming of Colors
The Munsell Color Classification System
Methuen Color Index and Classification System
The CIE System
Pantone - A Modern Color Classification System
Optical Properties of Fiber Materials
General Properties of Fiber Polymers and Fibers - Part I
General Properties of Fiber Polymers and Fibers - Part II
General Properties of Fiber Polymers and Fibers - Part III
General Properties of Fiber Polymers and Fibers - Part IV
General Properties of Fiber Polymers and Fibers - Part V
Protein Fibers - Wool
Protein Fibers - Speciality Hair Fibers
Protein Fibers - Silk
Protein Fibers - Wool versus Silk
Timelines of Fabrics, Dyes and Other Stuff
Cellulosic Fibers (Natural) - Cotton
Cellulosic Fibers (Natural) - Linen
Other Natural Cellulosic Fibers
General Overview of Man-Made Fibers
Man-Made Cellulosic Fibers - Viscose
Man-Made Cellulosic Fibers - Esters
Man-Made Synthetic Fibers - Nylon
Man-Made Synthetic Fibers - Polyester
Man-Made Synthetic Fibers - Acrylic and Modacrylic
Man-Made Synthetic Fibers - Olefins
Man-Made Synthetic Fibers - Elastomers
Man-Made Synthetic Fibers - Mineral Fibers
Man Made Fibers - Other Textile Fibers
From Fiber To Yarn: Overview - Part I
From Fiber to Yarn: Overview - Part II
Melt-Spun Fibers
Characteristics of Filament Yarn
Yarn Classification
Direct Spun Yarns
Textured Filament Yarns
Fabric Construction - Felt
Fabric Construction - Nonwoven Fabrics
A Fashion Data Base
Fiber Construction - Leather
Fabric Construction - Films
Glossary of Colors, Dyes, Inks, Pigments and Resins
Fabric Construction – Foams and Poromeric Material
Glossary of Fabrics, Fibers, Finishes, Garments and Yarns
Weaving and the Loom
Similarities and Differences in Woven Fabrics
The Three Basic Weaves - Plain Weave (Part I)
The Three Basic Weaves - Plain Weave (Part II)
The Three Basic Weaves - Twill Weave
The Three Basic Weaves - Satin Weave
Figured Weaves - Leno Weave
Figured Weaves – Piqué Weave
Figured Fabrics
Glossary of Art, Artists, Art Motifs and Art Movements

The Glossary of Terms, Timelines of Fabrics, Dyes and Other Stuff, A Fashion Data Base, Glossary of Colors, Dyes, Inks, Pigments and Resins, Glossary of Fabrics, Fibers, Finishes, Garments and Yarns and Glossary of Art, Artists, Art Motifs and Art Movements have been updated in order to better inform your art practice.

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Different fibers may be blended into one yarn. Filaments may be mixed before twisting; staple fibers may be combined at different stages in the spinning process.

A blended yarn or fabric combines the characteristics of its component fibers or filaments, and so blending can be used to modify performance in a number of different areas. For example, cotton and wool are often blended with nylon and polyester to improve durability; an expensive fiber such as cashmere or mohair is blended with a cheaper fiber such as wool to give an expensive handle for a fraction of the cost; fibers with different dye affinities are blended to give subtle color effects in piece-dyed fabrics.

Reasons for Blending Fibers
Blending of fibers is done for several reasons:
(i) To obtain cross-dyed effects or to create new colour effects such as heather. For example, when fibers with unlike dye affinity are blended together and then piece-dyed.
(ii) To improve spinning, weaving and finishing efficiency for uniformity of product. For example, as with self blends of natural fibers in order to improve their uniformity.
(iii) To obtain better texture, hand or fabric appearance. A small amount of a specialty wool may be used to give a buttery or slick hand to the whole fabrics - or a small amount of rayon may give luster and softness to a cotton fabric. Fibers with different shrinkage properties are blended to produce bulky and lofty fabrics or fur-like fabrics with guard hairs.
(iv) For economic reasons. Expensive fibers can be extended by blending them with cheaper more plentiful fibers. This use may be misleading to the consumer especially when the expensive fiber is used sparingly but is advertised on the tag in large print (e.g. CASHMERE and wool blend).
(v) To produce fabrics with better performance. This is perhaps the major reason for blending. In end uses where durability is very important, nylon or polyester blended with wool or cotton provide strength and resistance to abrasion, while the cotton and wool look is maintained. A classic example is durable-press garments where 100% cotton fabrics are not as durable as polyester/cotton blends.

In the above chart some fiber properties are rated. Notice that each fiber is deficient in one or more important properties. Hence, different blends are used in order to make up for some of these deficiencies.
Courtesy of reference [2].

Blending is a complicated and expensive process, but it makes it possible to build in a combination of properties that are permanent. Not only are blends used for better functionality of fabrics, but they are also used for beauty of appearance and to create a better fabric handle.

Properties of Some Blended Fibers
The properties of different yarns and fabrics depend on the component fibers and on the yarn structure.

The different fibers in yarns may be combined in a number of ways. If blending takes place early such as during processing (e.g. during opening) it results in a more intimate and uniform blend. The coarser fiber will yield to the fabric its characteristic touch and handle, masking the effects of any fine and costlier fibers in the blend. If fibers of the same diameter but different stiffness or rigidity are blended, the stiffer fiber, because it resists twisting will remain on the outside of the yarn, and so will dictate the handle characteristics of the fabric. Some spinning processes (e.g. Coverspun) are specifically designed to give a non-uniform distribution of the component fibers. Hence, in this case, each fiber in a 50:50 blend may not contribute equally to the final yarn or fabric properties. In practice, it is therefore very difficult to predict exactly what the characteristics of the blend will be.

Different blend types in a fiber.
Courtesy of reference [1].

Viyella - a non-uniform blend of cotton and wool.
Note: The wool fibers being coarser than the cotton, end up on the outside of the yarn, giving a wool handle to the fabric, which launders like cotton.
Courtesy of reference [1].

Blending of fibers is now commonplace in clothing. For example, polyesters have a low affinity for water, since they are hydrophobic. However, because of the absence of water in the fiber polymer system, polyesters cannot dissipate static electricity build, which attracts oily and greasy particles, causing soiling that is difficult to remove. The fiber is resilient and crease-resistant, but tends to feel uncomfortable on hot days, since it cannot absorb perspiration well. An approach in overcoming this uncomfortable feel on hot days is to highly twist the yarn, but with a loosely woven structure. However, the most practical solution is to blend polyester with cotton. The poly/cotton blends have been a success in apparel manufacture (and not only from a cost view point). The mixtures of cotton, and polyester fibres of similar diameter to the cotton fiber, are also crimped with the polyester fibres and are then cut into staple lengths to match the cotton staple that is in the blend.

In blends of polyester and cotton, the cotton fibers provide a crisp, cool handle and the comfort of moisture absorbency. Polyester gives the blend excellent crease recovery and drip-dry properties. However, the major problem with such a blend is pilling. The polyester fibers are stronger than the cotton fibers, and with abrasion during use, will break. They cannot fall away from the fabric since they are “tied down” by strong fibers of polyester. Pill resistant polyester cotton blends have been developed, which entails just weakening the polyester fibers to a similar strength to the cotton fibers.

Polymer blending creates the possibility of a whole new class of fibers called - multipolymer fiber.

Blend Levels
For a specific end-use,a blend of fibers that complement each other (see above) will give a more satisfactory all-round performance than a 100% fiber fabric. In his article, "Fiber Translation in Blends", M.J. Caplan used the following example to show that a blend will yield a fabric with intermediate values. He took two fibers labelled A and B, each of which could be used to make a similar fabric, and measured five performance properties of each of these 100% fabrics. He then redacted the performance properties of a 50-50% blend by averaging the values of each fabric in the blend. For example, for performance property 1 fabric A had say a 12 level performance whereas fabric B had a 4 level performance. Hence the 50-50% blend would be predicted to have: (12+4)/2 = 8 level performance.

Hypothetical properties of a 100% fabric A and B and their predicted value for a 50-50% blend. Courtesy of reference [2].

The higher the level of performance the greater its utility. For example, say property 1 was resistant to abrasion and fabric A was polyester and fabric B was cotton, then it would be predicted that a 50-50% blend of polyester and cotton blend yields a fabric that was less resistant to abrasion than polyester (level 12) but twice as much resistance to abrasion than a fabric made from cotton only (level 8 compared to level 4).

Whilst this is a simplistic exercise, in reality blends behave in far more complex manner. For example, a very small amount of nylon (15%) improves the strength of wool, but 60% nylon is needed to improve the strength of rayon. More importantly, there are other properties that need to be considered. Improving the strength of a fabric may be desirable, but is it the be all and end all of the exercise. For example, the blended fabric may be strong but if its handle is slippery on the skin, would you feel comfortable wearing it as an under garment? Perhaps not!

Blending Methods
Blending can be done at any stage prior to the spinning operation. Blending can be done during opening-picking, drawing and roving. One of the disadvantages of direct spinning is that blending cannot be done before the sliver is formed.

The earlier the fibers are blended in processing the better the blend.

Cross-section of yarn showing the location of the fibers in the blend.
Courtesy of reference [2].

The above sketch shows a cross section of yarn A, in which fibers were blended in the opening, and yarn B, a yarn in which fibers were blended at the roving stage.

Variations occur from spot to spot in the yarn and also from inside to outside. Long, fine fibers tend to move to the centre of a yarn, while coarse, shorter fibers migrate to the periphery of the yarn - see C in the diagram above. The older methods of blending involve much hand labor.

Opening Picking
In one method, several bales of fiber are laid around the picker and an armful from each bale are fed alternatively into the machine. Another method is called sandwich blending. The desired amounts of each fiber are weighed out and a layer of each is spread over the preceding layer to build up a sandwich composed of many layers. Vertical sections are taken through the sandwich and fed into the picker. See sketch below.

Sandwich blending of wool.
Courtesy of reference [2].

Feeder blending is an automatic process in which each type of fiber is fed to a mixing apron from individual hoppers (see diagram below).

Feeder blends.
Courtesy of reference [2].

Blending on the Drawing Frame
When the physical properties of two fibers differ, it is not always practical to blend them before carding, so they are picked and carded separately and then blended in the drawing frame. The problem of mixed wastes is eliminated with this process.

Blending on the Roving and Spinning Frame
Both these operations combine fiber strands to reduce size and increased amount of twist until the final size and twist are achieved. The primary purpose at this stage is to blend for a particular hue.

[1] A Fritz and J. Cant, Consumer Textiles, Oxford University Press, Melbourne (1986).

[2] N. Hollen and J. Saddler, Textiles, 3rd Edition, Collier-Macmillan Ltd., London (1968).

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