Textiles review: manufactured regenerated fibers

The final part of my textiles review covers regenerated fibers. I imagine my textiles reviews are not as exciting to read as are my normal blog entries, but writing them was quite helpful to me. The test was yesterday. I found it easy. I am sorry if you do not care for these reviews, but I plan to write more of them next time a test rolls around. Fortunately that will not be for a while, so I may now return to my normal irreverent blogging.

Manufactured fibers are formed into fibers from chemical compounds. They do not exist in fiber form without human intervention. Manufactured fibers may be regenerated or synthetic. Regenerated fibers are produced from naturally occurring polymers that do not occur naturally as fibers. Regenerated fibers are made from cellulose (plant) or protein (plant or animal). Synthetic fibers are made from polymers that do not occur naturally.

The Federal Trade Commission gives fibers generic names based on fiber chemistry. Manufacturers may also use trade names for the fibers they produce.

Fiber production
The process of producing a manufactured fiber is called spinning. Whether fibers are regenerated or synthetic, the spinning process is the same. The only significant differences occur in the production of the solution from which the fiber is made. Raw materials are made into a spinning solution (dope) by dissolving them in chemicals. I do not have the necessary knowledge of chemistry to understand the solution production process, and information about that process is not taught in my class, so I will speak of it no more. Fiber manufacture follows three steps:
1. Prepare a dope or melt
2. Extrude the dope or melt through a spinneret to form a fiber
3. Solidify the fiber by coagulation, evaporation, or cooling.

The spinneret is like a showerhead through which the dope is forced. The size and shape of the holes in the spinneret determine the size and shape of the fiber.

Manufactured fibers may be used in filament or staple form. Filament yarn is made by twisting filament fibers together. Filament tow is a rope of thousands of untwisted filament fibers. It is cut to make staple fibers. The fibers may be crimped.

There are three basic methods of fiber spinning:
Wet spinning: Raw material is dissolved by chemicals to produce a dope. The fiber is spun into a chemical bath where it solidifies. Wet spinning is the oldest and most complex method of fiber manufacture. The solvent and chemical bath are hazardous materials that must be recovered. Wet spinning can be used to produce acrylic, lyocell, rayon, and spandex. Wet spinning is rarely used.

Dry spinning: Resin solids are dissolved by chemicals to produce a dope. The fiber is spun into warm air where evaporation of the solvent causes the fiber to cool and solidify. The solvent must be recovered, but without the chemical bath there are fewer hazardous materials than in wet spinning. Dry spinning can be used to produce acetate, acrylic, modacrylic, and spandex.

Melt spinning: Resin solids are melted to produce a dope. The fiber is spun into air where it cools and solidifies. It is the cheapest method of fiber production, and there are no solvents to be recovered. It can be used to produce nylon, olefin, polyester, and saran. Regenerated fibers are not produced by melt spinning.

Fiber modifications
Every step of the fiber manufacture process can be precisely controlled to produce uniform fibers with specific characteristics.

Spinneret modifications: The size and shape of spinneret holes can be adjusted to produce fibers with specific dimensions. Hollow fibers may be created by adding gas forming compounds to the dope, by injecting air into the fiber as it forms, or by altering the shape of the spinneret hole. Hollow fibers are good insulators.

Molecular structure and crystallinity modifications: The molecular structure and the degree of crystallinity of a fiber contribute to its properties. These can be altered in the manufacture process by a controlled stretching of the fiber after it exits the spinneret or by selecting specific compounds used to produce the polymers. High tenacity fibers may be produced by stretching the fibers to line up the molecules and /or by chemical modification of the polymer to increase the degree of polymerization. I am not really sure what that all means. I never liked organic chemistry. The molecules are too big. I prefer physics where all the really exciting stuff happens in spaces smaller than an atomic nucleus.

Dope additives: Chemicals may be added to the dope to alter the fiber’s properties. Dyes may be added to color a fiber. Solution dyed fibers retain color better than fibers dyed after they are produced. Dye-accepting chemicals may be added to make a fiber more dyeable. Whiteners may be added to make fibers look whiter and resist yellowing. Delusterants may be added to reduce a fiber’s luster.

Modifications in fiber spinning: Crimp may be added to manufactured fibers by altering the way the fiber cools and solidifies. Filament fibers can be cut to create staple fibers.

Bicomponent fibers: Two polymers may be combined in a single fiber. Bilateral fibers are spun with two polymers side by side. Core-sheath fibers have one polymer encircled by another. The different polymers may react differently to heat and moisture, or each may have specific characteristics that are desired in the finished fiber.

Regenerated fibers
Regenerated fibers are produced from naturally occurring polymers that do not occur naturally as fibers. Cellulose and protein may be uses to produce regenerated fibers.

Rayon, lyocell, acetate, bamboo, and PLA are regenerated cellulosic fibers.

Azlon is the generic name for all regenerated protein fibers.

Rayon
Rayon was the first manufactured fiber. The earliest form of rayon was invented in 1846, but it was highly explosive. Commercial production of viscose rayon began in the U.S. in 1911. Rayon is produced with the wet spinning method.

There are three types of rayon: Viscose rayon, cuprammonium (cupra), and high wet modulus (HWM) rayon. Viscose was the first type of rayon commercially produced, and HWM is the newest. Cupra is sold with the trade name Bemberg®. HWM is sold with the generic name polynosic and the trade name ModalTM.

Physical structure of rayon
Rayon can be either staple or filament. The fiber has lengthwise lines called striations. It has a serrated or indented circular cross section. This is caused by the fiber collapsing in on itself during coagulation from loss of the solvent. Cupra and HWM have a rounder cross section than viscose.

Properties of rayon
Aesthetics: Rayon can be produced to look like cotton, flax, wool, and silk.

Durability: Rayon is a low tenacity fiber that loses up to 50% of its strength when wet. HWM rayon is stronger than cupra, and cupra is stronger than viscose. Viscose has a breaking elongation of 8% to 14%. HWM rayon has a breaking elongation of 9% to 18%. Rayon may be permanently damaged by water.

Comfort: Rayon has a soft, smooth hand. It is highly absorbent, a good conductor of heat, and it does not build up a static charge.

Appearance retention: Rayon has low resiliency and dimensional stability. Viscose rayon may stretch or shrink. HWM rayon has better dimensional stability; it is less likely to stretch or shrink.

Care: Viscose rayon should be dry-cleaned. Cupra and HWM rayon may be machine washable; read the care label. Rayon is resistant to heat and may be ironed with high temperatures. Rayon may be damaged by silverfish and mildew, so it should be stored dry.

Environmental impact: Most rayon is produced from wood pulp. The fiber is biodegradable, but it cannot degrade if it is placed in a landfill. The wet spinning process uses large quantities of chemicals that may contribute to air and water pollution. Cupra is no longer produced in the U.S. because manufacturers were unable to comply with water and air quality requirements.

Lyocell
Lyocell was introduced in the early 1990s. It was originally sold as a type of rayon, but it differs from rayon enough that it now has a separate generic classification. Lyocell is sold with the trade name Tencel®

Physical structure of lyocell
Lyocell fibers can be staple or filament. The fibers have a smooth surface and round cross section.

Properties of lyocell
Aesthetics: The luster, drape, and texture of lyocell can be varied. Lyocell imitates the aesthetics of the natural cellulosic fibers, but it most closely resembles cotton. Lyocell fibers may pill.

Durability: Lyocell is the strongest regenerated cellulosic fiber. Its breaking tenacity is 4.8 to 5.0 g/d dry and 4.2 to 4.6 g/d wet. Lyocell has good abrasion resistance and poor elongation.

Comfort: Lyocell has a soft, smooth hand. It resembles cotton. It has excellent absorbency and poor thermal retention.

Appearance retention: Lyocell has moderate resiliency; it wrinkles, but not as badly as rayon. Lyocell has moderate dimensional stability. It may shrink, but not too badly.

Care: Lyocell may be machine washed on gentle cycle or dry cleaned. Read the care label. It may be ironed with high heat. It may be damaged by mildew and insects.

Environmental impact: Lyocell is produced with the wet spinning method, but the solvents are recycled so hazardous waste is not produced. The chemicals used to produce lyocell are less harmful than those used to produce rayon. Lyocell is biodegradable, but if it is placed in a landfill it will not degrade.

Acetate
Acetate was introduced in the U.S. in 1924

Physical properties of acetate
Acetate fibers can be staple or filament. Acetate typically has a lobular cross-sectional shape and lengthwise striations, but the shape of the fiber can be altered in the spinning process. Acetate is thermoplastic; it melts in high heat. Acetate dissolves in acetone.

Properties of acetate
Aesthetics: The aesthetic properties of acetate are excellent. It has high luster, good drape, and smooth hand and texture. It is often used to make fabrics for which good appearance is more important that durability and ease of care.

Durability: Acetate is not a durable fiber. Its dry breaking tenacity is 1.2 to 1.4 g/d, and it is slightly weaker when wet. Acetate has low abrasion resistance and elongation. Acetate is resistant to mildew and moths.

Comfort: Acetate has a smooth, soft, but slightly clammy hand. It has moderate absorbency. It builds up a static charge. It is a moderate insulator.

Appearance retention: Acetate has poor appearance retention. It has poor resiliency and elastic recovery, and moderate dimensional stability. It may shrink. Acetate may experience fume fading – its color changes. This may be prevented with solution dyeing.

Care: Acetate should be dry-cleaned. It melts at high temperatures, so it may only be ironed on low heat.

Other regenerated fibers
Bamboo is a type of rayon that uses bamboo as the source of cellulose. It contains no bamboo fibers. In the past few years bamboo has been marketed as an environmentally friendly fabric, but the claims were unsubstantiated. The FTC has recently taken action against manufactures of bamboo rayon barring them from making deceptive claims about the fabric. The FTC does not recognize “bamboo” as a generic name for bamboo based rayon.

PLA (polylactic acid) is a regenerated cellulosic fiber made from cornstarch. The FTC approved it as a generic fiber in 2002. It is sold with the trade name Ingo®. We had some PLA in lab. It seems great. I would like to find some of it to play with.

SoySilk® is a type of azlon. It is made from a soy protein that is a waste product of the tofu manufacturing process. Yummy. It is a durable fiber with a soft hand, great drape, good colorfastness, excellent absorbency, good comfort, and good thermal retention. We had some SoySilk® in lab too. I liked it a lot. If it isn't too expensive I want to use it to make a shirt.

Silk Latte® is a type of azlon made from milk protein. It is similar to SoySilk® but slightly less durable.