Among synthetic fibers, acrylics occupy a unique position as the closest man-made alternative to wool. Their soft hand, bulk, and resistance to sunlight have kept them relevant across apparel, home furnishing, and industrial applications for decades. Though their share of world fiber production has declined from 15 percent in 1982 to around 5 percent by 2002, they remain widely manufactured across Asia and continue to serve end uses where wool-like character is desired at a lower cost.
What Are Acrylic Fibers?
Acrylics are copolymers of acrylonitrile and another material incorporated into the polymer chain. The basic acrylonitrile unit is (—CH₂—CH—) | CN.
The FTC differentiates between two types of acrylic fibers by the amount of acrylonitrile in the polymer. Acrylic is defined as “a manufactured fiber in which the fiber-forming substance is any long-chain synthetic polymer composed of at least 85 percent by weight of acrylonitrile units.” Modacrylic is “a manufactured fiber in which the fiber-forming substance is any synthetic polymer composed of less than 85 percent but at least 35 percent by weight of acrylonitrile units.”
One hundred percent acrylonitrile fibers, referred to as PAN (for polyacrylonitrile), are produced for limited industrial uses. Note, however, that PAN is commonly used in Europe as an abbreviation for acrylic fibers in general.
History and Commercial Development
Although polyacrylonitrile, the polymer of which acrylic fibers are composed, had been synthesized earlier, it could not be melt spun because it tends to decompose before it melts. Suitable solvents for the polymer were not found until the 1940s.
A number of different fiber producers had been working independently to develop and patent processes for spinning fibers from the acrylonitrile polymer, each proceeding along somewhat different lines. As a result, seven separate production processes were patented: six using wet spinning and one using dry spinning. The second synthetic fiber to be produced commercially by DuPont, Orlon acrylic fiber, entered production in 1950. Monsanto entered the acrylic field in 1952 with Acrilan acrylic, and American Cyanamid introduced Creslan acrylic in 1958. None of these fibers are produced any longer.
Manufacturing has since moved from the United States and Europe to China, Taiwan, and India. The only acrylic manufacturer remaining in the United States is Sterling Fibers, which makes Creslan and Cresloft. A number of companies in Japan, China, and Taiwan produce acrylic fibers, including Toraylon by Toray and Vonnel by Mitsubishi.
Manufacturing of Acrylic Fibers
Manufacturing of acrylic fibers starts with synthesis of the polymer from acrylonitrile and other monomers, which make up less than 15 percent of the polymer. Producers select the comonomers for their different processes to enhance both the solubility of the polymer and the dyeability of the fibers. PAN polymers have no comonomer added.
After the acrylic polymer is synthesized, it is dissolved in an appropriate solvent to create the solution for spinning. Both dry and wet spinning methods are used for manufacturing acrylics. For wet spinning, the polymer is dissolved in dimethylformamide (DMF) or dimethyl acetamide (DMAc) and spun into a bath of water and a low concentration of the solvent. DMF is the solvent used for dry spinning because it has a lower ignition point than DMAc and, therefore, less energy is needed to evaporate it in the spinning chamber.
Freshly spun acrylic fibers are porous, often retaining some of the solvent, and as a result have very little orientation. Dye is readily absorbed in this state, and “gel dyeing” processes have been used to color the fiber. The fibers must be drawn to develop the orientation and crystalline structure desired. Drawing takes place in a bath of hot water where the filaments are stretched between two rollers. After drawing, the fibers are then washed to remove any residual solvent, crimped, and cut into staple lengths. A final step is heat-setting the fibers in a relaxed state using steam. If they are not relaxed, the fibers will have a high degree of latent shrinkage, which could affect their performance in textile products.
A recent development is the production of acrylic filament fibers using a dry-jet wet spinning process similar to that for lyocell. The vast majority of acrylic, however, is still produced and sold as staple fibers.
To a great extent, the properties of acrylic fibers are dependent on the processing conditions employed.
Molecular Structure
In PAN fibers, made of 100 percent acrylonitrile, the polymer chains pack together closely, forming a highly crystalline structure. The resulting fibers are very strong but also extremely brittle, making them unacceptable for most processing and uses. They have, however, found an important use as a starting material for producing carbon fibers.
For other acrylics, the inclusion of other monomers in the acrylonitrile polymer interrupts the regular packing of the polymer molecules and reduces the brittleness of the fiber. As a result, the molecular structure is moderately crystalline and can be controlled by the spinning process and subsequent drawing of the fiber. Different producers use different comonomers, resulting in some variation of fiber properties and processing.
Properties of Acrylic Fibers
Physical Properties
- Shape: Wet-spun acrylic fibers can have cross sections varying from approximately round to bean shaped. Dry-spun fibers generally have a dog-bone shape. The nonround shapes are produced during spinning by formation of an outer “skin” before the inner core of the fibers solidifies. When the core solidifies, it shrinks and the skin collapses against it. The effect is more pronounced in dry-spun fibers, resulting in the dog-bone rather than the bean-shaped cross section. Indentations or deviations from the round show up as wide, lengthwise markings in the longitudinal view of the fiber.
- Luster: Acrylics are usually delustered with titanium dioxide, and the crimp that is imparted after spinning further decreases the apparent luster. The new filament acrylic fibers have a high luster to make them more like silk.
- Specific Gravity: Specific gravity ranges from 1.14 to 1.19, making acrylic yarns and fabrics lightweight. Voids in the fibers make them less dense than other fibers such as polyester and cotton.
Mechanical Properties
- Strength: Standard breaking tenacities of acrylic fibers are reported as ranging from 2.0 to 3.6 g/d. The fibers are relatively weak and are, therefore, not appropriate for end uses requiring high strength. Because acrylic is not very absorbent, however, its strength is not appreciably lower when the fiber is wet. PAN fibers, with their high crystallinity, are stronger.
- Modulus: The range of moduli for acrylic fibers is moderate to low, making them compatible with a number of other fibers, such as wool and nylon, and they are often seen in blends.
- Elongation and Recovery: Acrylics stretch fairly easily and will extend up to 25 percent before breaking. The degree of elongation depends on the amount of drawing the fiber has undergone. The elastic recovery of acrylic fibers varies from one trademarked fiber to another. In general, however, it is lower than that for most other synthetics.
- Resilience: Acrylic has lower wrinkle resistance than nylon or polyester, which is why it is found more commonly in knitted fabrics, which resist wrinkling better. Crimped fibers and bulked yarns enhance compressional and bending recovery.
Chemical Properties
- Absorbency and Moisture Regain: The moisture absorption of acrylics is low, ranging from regains of 1.0 to 2.5 percent. This is an important comfort aspect in which acrylics differ significantly from wool, but can be compensated for by nonround fiber shapes that prevent close packing of fibers in yarns and allow moisture to move along fibers and away from the body.
- Electrical Conductivity: The low electrical conductivity of acrylics is related to their low moisture absorption. Antistatic finishes may be added to fibers to eliminate static electricity buildup.
- Effect of Heat and Combustibility: Acrylics do not exhibit typical melting points, but rather tend to decompose over a wide temperature range and eventually char to a brittle residue. Untreated acrylic fibers ignite and burn, leaving a hard, black bead residue at the edge of the fabric. Fibers shrink in steam but can be safely ironed at 300°F. Exposure to high, dry heat causes yellowing or further darkening of the fibers.
- Chemical Reactivity: Acrylics are very resistant to acids, except to nitric acid, in which they dissolve. Resistance to bases is good. Solvents used in commercial dry cleaning do not affect the fiber adversely, and most acrylics are not harmed by household bleaches.
Environmental Properties
- Resistance to Microorganisms: Mildew, microorganisms, and moths will not harm acrylic fibers.
- Resistance to Environmental Conditions: Resistance to sunlight ranges from very good to excellent. This characteristic, which is superior to polyester and nylon, has promoted the use of acrylics in awnings and outdoor furniture. Age has no detrimental effect on fabric strength.
Other Properties
- Dimensional Stability: Because of the fiber’s low moisture absorbency, acrylic fabrics generally have good dimensional stability. They do, however, relax under hot, moist conditions. This property is used in manufacturing of some acrylic yarns where stretched fibers are subjected to steam to relax them and develop bulk. The degree of stretch and relaxation varies among the different acrylics produced, and therefore, instructions on care labels should be followed carefully in laundering. For example, some fabrics are manufactured from specially crimped fibers that require machine drying after laundering to restore the crimp. If hung wet on a line, some of these fabrics may stretch out of shape.
- Abrasion Resistance: The abrasion resistance of acrylics is somewhat lower than that of other synthetics.
Bicomponent Acrylic Fibers and Yarns
Acrylic fibers may be made in bicomponent varieties. Bicomponent acrylic fibers are created by extruding two different types of acrylic material together as one fiber from the spinneret. Each has somewhat different shrinkage properties, and when the fiber is subjected to heat and moisture during processing, one polymer shrinks more than the other and produces a permanent spiral crimp, similar to that in wool. The crimp provides increased bulk and resilience. Bicomponent acrylics are most often used in knitted goods such as sweaters and socks.
Care instructions provided with bicomponent acrylic fibers often indicate that they must be laundered and tumble dried. During laundering the fibers swell, relieving tensions placed on the fibers during use, and the tumble drying is necessary to return fibers to their crimped and bulked shapes. Because line drying will not produce the same results, consumers should be sure to follow care instructions.
Bicomponent yarns can also be constructed by combining two acrylic fibers with different shrinkage properties. High-shrinkage fibers that have not been steam relaxed are blended with those that have had the steam after-treatment. When the blended yarn is subjected to wet heat, the high-shrinkage fibers will shrink, bulking up the structure and increasing its softness.
Specialty Acrylics and Trademarks
Specialty acrylics have expanded the range of what the fiber can do. Sterling Fibers’ Conductrol incorporates electrically conducting carbon into the acrylic structure. Tafel Parclean, produced by Mitsubishi, is an antimicrobial fiber, while Silpalon is a filament acrylic made by Mitsubishi for women’s knitwear. Producers can add antimicrobial and antistatic properties during manufacturing of the fibers, the latter being particularly important for the use of acrylics in carpets and rugs.
End Uses of Acrylic Fibers
Acrylic fibers have found a market in areas where wool has traditionally been used. Their mechanical properties are similar to wool: low strength and modulus, high elongation, and moderate recovery. These properties make acrylic a good fiber for sweaters, suits, coats, and socks. Acrylic does not, however, have the high moisture absorbency of wool and so does not display the comfort characteristics associated with absorbent fibers. Crimp, which is natural in wool, can be imparted to acrylic for high bulk and resilience.
Acrylic fibers are fabricated into woven and knitted fabric constructions in a variety of textures and weights appropriate for different end uses. They are often blended with other fibers, particularly wool. Their wool-like hand and bulk combined with easy-care characteristics make them popular for use in sweaters, fleece fabrics, hand-knitting yarns, and blankets. Their bulk also makes them appropriate for socks, where they can provide both warmth and cushioning for the feet.
Resistance to degradation by sunlight leads to use of acrylics in drapery and upholstery fabrics, and increasingly in outdoor products such as awnings and furniture. Not only is their light resistance an advantage, but also their low moisture absorbency helps to protect the fabrics under a variety of weather conditions. Industrial uses of acrylic include insulation as a replacement for asbestos and reinforcement for concrete and stucco structures.
Care Procedures
Different acrylic fibers may vary in their care requirements. For this reason, it is especially important to follow care labels on these fabrics. In general, acrylic fabrics can be laundered and dry-cleaned. They do not shrink in laundering but may be sensitive to heat, so when machine drying is recommended for acrylic products, low heat settings should be used and fabrics should be removed from the dryer immediately after tumbling. Pressing temperatures should not exceed 250°F to 300°F.
Conclusion
Acrylic fibers have carved out a durable niche in the textile industry by offering a practical, lower-cost alternative to wool across a wide range of applications. Their combination of wool-like bulk and hand, strong resistance to sunlight, and ease of care has kept them relevant in both apparel and outdoor end uses, even as global production has shifted away from traditional manufacturing centers. The development of bicomponent varieties and specialty fibers with antimicrobial and conducting properties shows that the category continues to evolve. As manufacturing techniques improve and performance requirements grow more demanding, acrylic fibers are likely to find new applications while continuing to serve the markets they have long held.