What Are Olefin Fibers?
Although olefin monofilaments have been manufactured for specialized industrial applications since 1949, the widespread use of olefin fibers for a variety of textile products dates to the 1960s. These fibers are often called polyolefins, but the FTC specifies the generic name olefin. According to the FTC, an olefin fiber is a manufactured fiber in which the fiber-forming substance is any long-chain synthetic polymer composed of at least 85 percent by weight of ethylene, propylene, or other olefin units. Chemists also use the term olefin to refer to the monomer as well as the polyolefins described here. Polyolefin plastics in many forms are widely used in products such as supermarket bags, yogurt pots, detergent bottles, and many other household items, and many people recognize them through recycle symbols #2, #4, and #5. Their low density and moisture resistance help explain why they are used in both everyday plastics and technical textiles.
Main Types of Olefin Fibers
Two major categories of olefin fibers exist. One is polypropylene; the other is polyethylene. Of the two, polypropylene is used far more extensively for textiles and constitutes the larger share of olefin fibers in use today, primarily because of its higher thermal stability. Worldwide the production of olefin fibers has increased significantly. They have gone from fourth among the synthetic fibers in the 1980s to second today after polyester, and much of the growth is attributable to the extensive use of polypropylene in nonwovens.
Polypropylene Fibers
Manufacture
Propylene, the starting material for polypropylene, is produced during the refining of petroleum for gasoline. Production of the polymer has largely been the purview of the chemical divisions of the large oil companies, which have a ready supply of propylene for polymerization. This is also the case for polyethylene.
In the polymerization step, specialized catalysts are used to produce polymer molecules that are capable of crystallizing when formed into fibers. Two chemists, Karl Ziegler and Giulio Natta, won a Nobel Prize in 1963 for developing the catalyst system. A newer catalyst, the metallocene system, is now also used by several producers. The metallocene system produces purer polymers that are more uniform in size. After polymerization, the polymer is extruded and cut into pellets, which are shipped as resin to fiber or film producers.
Polypropylene may be melt spun into fiber filaments for subsequent conversion to yarns, or laid down in a fiber web to form a nonwoven fabric. Another form, fibrillated fibers, can be created by first extruding a film of polypropylene. The film is then either stretched and split or slit and drawn into a network of fibers. This flexibility makes polypropylene especially useful in both textile and nonwoven production.
The polyolefin supply chain differs from that of most other manufactured fibers. Instead of one firm making the polymer and the fiber, polypropylene fiber manufacturing plants buy their resin from a large chemical supplier. Hence, they have lower capital investment than do vertically organized manufacturers and so tend to be smaller in scale. Because polypropylene fibers are difficult to dye, it is easier to add pigment colors during spinning, and there is an economic incentive for smaller runs of differently colored fibers. Additives to alter fiber properties such as light or flame resistance may be either put in before spinning or incorporated into the polymer resin at the polymerization stage.
Molecular Structure
The polypropylene molecule has methyl groups (—CH3) on every other carbon in the polymer backbone. For high crystallinity, and optimum fiber properties, the methyl groups are all on one side. This configuration is called isotactic, for iso, meaning uniform, and tactic, meaning arrangement or order. Both catalyst systems produce this polymer arrangement that allows tight chain packing and crystalline areas. Within the fiber the polymer chains assume a three-dimensional helical configuration.
Properties of Polypropylene Fibers
Physical Properties
- Shape: In microscopic appearance melt-spun polypropylene fibers may have any of several cross-sectional configurations, depending on the shape of the holes of the spinneret used in extruding the fibers. Under the microscope, the surfaces of polypropylene fibers appear to be smooth; however, under the greater magnification of electron microscopy, pigmented fibers may have protuberances along the fiber surface that are thought to be either clumps of pigment particles or part of the fiber structure. The properties of the melt-spun fibers and fibrillated fibers differ somewhat. The denier range of melt-spun fibers is greater than is that of fibrillated fibers. Fibrillated fibers have a branchlike structure that may eliminate the need to add texture to the fiber. Also, fiber-to-fiber interlocking is better in fibrillated films, but fiber length is not so uniform, and fibrillated fibers are less regular in shape than melt-spun fibers. They are often flat rather than round.
- Specific Gravity: The density of polypropylene is especially low. Its specific gravity is 0.92, or less than that of water. As a result, olefin fabrics float on water when they are washed. The low density of polypropylene also is related to the relatively low cost of olefin fiber; a small weight of raw materials can be used to produce a large volume of fiber.
- Color: Because polypropylene fibers are hard to dye, pigments are usually added to the melted polymer before the fibers are spun. Unpigmented fibers, which are clear, are used in many nonwoven products.
Mechanical Properties
- Strength: Polypropylene fibers can vary in tenacity, ranging from 2.5 to 5.5 g/d depending on the amount of stretching the fiber undergoes after extrusion. End use dictates this, with higher strength required for ropes and other industrial products. Olefin fibers are generally weaker than equivalent nylon or polyester fibers but are still strong enough to be used in applications where strength is important, such as ropes.
- Modulus: Polypropylene fibers have low initial resistance to stretch, compared to cotton and polyester. This is due to the helical form of the polymer, which straightens when the fiber is stretched.
- Elongation and Recovery: The elastic recovery of polypropylene fibers is excellent. They will stretch a moderate amount before breaking. High-strength polypropylenes for industrial uses have lower elongation.
- Resilience: The resilience of polypropylene is lower than nylon and polyester, and carpet made from the fiber will have a higher tendency to mat. Newer variants of polypropylene, however, have better resilience.
Chemical Properties
- Absorbency: Polypropylene is almost completely nonabsorbent. This low absorbency makes it difficult to dye but gives the fiber exceptional resistance to waterborne soil and stains. Grease and oil do stain polypropylene fabrics, and because they are oleophilic, stains may be difficult to remove. Depending on their construction, olefin fabrics have good wickability, enabling them to transport liquid moisture away from the body.
- Electrical Conductivity: The electrical conductivity of polypropylene is poor. Its low absorbency contributes to problems of static electricity buildup, although finishes used in the spinning and processing of the fiber can overcome this problem in the finished product.
- Effect of Heat and Combustibility: The melting point of polypropylene is low: 330°F. While this may be an advantage during production, where lower heat is required for melt spinning, it can be a problem in product use. Hot bacon fat dropped on olefin carpets will melt fibers. Hot dryers and heaters can also affect them. Olefins are combustible and melt as they burn. They produce a sooty smoke. Some flame-resistant polypropylenes are available.
- Chemical Reactivity: Polypropylene’s resistance to bases and to acids is very good. This chemical resistance, combined with low moisture absorbency, has spurred its use in protective clothing and implanted medical devices. Some organic solvents used in dry cleaning may affect the fabrics adversely. Home laundering is preferable to dry cleaning in the care of polypropylene fabrics.
Environmental and Other Properties
- Environmental Properties: Mold, mildew, and insects do not attack olefins. Age has no appreciable effect, but sunlight can significantly deteriorate the fabric. This property can be altered by incorporation of ultraviolet stabilizers in the polymer melt before spinning.
- Dimensional Stability: The wet dimensional stability of polypropylene is good because of the fiber’s low moisture absorbency. Its low melting point, however, makes it susceptible to thermal shrinkage at temperatures above 250°F.
- Abrasion Resistance: Polypropylene fibers have moderate abrasion resistance, lower than polyester and nylon.
Uses of Polypropylene Fibers
Nonwovens and Hygiene Products
Polypropylene is the fiber of choice for many nonwovens, from industrial filters to parts of disposable diapers. The easy processability of the polymer makes it ideal for forming nonwovens directly by melt spinning. In addition, the fiber is inexpensive and light weight. Polypropylene nonwovens for filters and wipes can be given an electrical charge to enhance their ability to attract dust and dirt particles. As diaper liners, they wick moisture away from the skin to the inner absorbent layer of the diaper. This combination of low cost, light weight, and versatility is a major reason polypropylene has expanded in hygiene and filtration products.
Industrial Uses and Geotextiles
Other industrial applications of polypropylene include ropes, cordage, netting, and bagging. Nonwoven olefin geotextile materials are used in road construction and in other engineering projects. Polypropylene geotextiles are placed under the soil or roadbeds, where their strength and chemical resistance are advantages and they will not be degraded by light. They are also used in erosion-control systems. Ropes and cords made from polypropylene are light weight, water resistant, and can be very strong when higher-tenacity fibers are used.
Carpets, Upholstery, and Apparel
Another significant use for polypropylene is in carpets. It has virtually replaced jute in carpet backing because of its resistance to microorganisms. This is a large use of fibrillated fibers. Being nonabsorbent and having good weather resistance, polypropylene can be made into carpets that will withstand exposure to outdoor conditions in areas where sunlight is not intense or prolonged. However, without ultraviolet light stabilizers, such carpets will deteriorate in climates such as those of the American Southwest. When polypropylene is used for traditional indoor carpets, soil- and waterborne stain resistance are exceptional, and the carpets have good lightfastness and resistance to moths. A drawback has been its lower resilience, which can affect the stability of the carpet pile.
For many years upholstery fabric manufacturers made extensive use of polypropylene in a variety of fabrics including velvets. Stain resistance was a particular advantage. Changes in home furnishing fashions, as well as other expanding markets such as nonwovens, have resulted in a decline in the amount of polypropylene used in upholstery. It is still often seen in contract and office furniture, though.
Although industrial and home furnishings areas are the major outlets for polypropylene fiber, it is also an apparel fiber. It enjoys a good proportion of the market for activewear products because of its excellent wicking qualities, transmitting moisture to the outer surface and reducing the cold, clammy feeling next to the skin. Use in other apparel fabrics is limited. Fine-denier filament polyolefin is difficult to produce as high-quality filament yarn, although research in this area continues. Staple fiber yarns are more easily produced, and most apparel is made from staple yarns. Because the polymer must be colored before it is extruded, polypropylene has the advantage of excellent colorfastness but the disadvantage that decisions about color must be made long before the fabrication of final products. Given the structure of the olefin industry today, however, with its smaller, more flexible manufacturers and the quick-response ability of most of the textile supply chain, opportunities for specialty and fashion-oriented apparel products are increasing.
Insulation and Protective Materials
Polypropylene fibers are also being used as insulation materials for gloves, footwear, and apparel. Fine olefin and polyester fibers are made into a nonwoven batting that the manufacturer, 3M, calls Thinsulate®. The batting provides good insulation because the high surface area and low density of the material trap air. The fine size and light weight of the fibers contribute to warmth without excessive bulk or weight. DuPont manufactures Tyvek®, a nonwoven polyolefin for use in barrier garments such as clean suits, protective garments for toxic waste cleanup, and the like. One of the major advantages of the fiber is the low cost of production.
Care Procedures
Polypropylene carpet and upholstery fabrics are relatively carefree, and great strides in improving stain resistance have been made. For most of these fabrics, stains can be wiped off with a damp cloth. Routine vacuuming and periodic shampooing will help to maintain and preserve both appearance and durability. Garments and other items can be laundered at moderate temperatures. The fiber, however, is heat sensitive at about 250°F. Most dryers do not exceed temperatures of 180°F to 190°F, so drying at low temperatures is permissible; however, line drying may be preferable as it generally eliminates any need for pressing. Hot irons will damage these fabrics, so only cool iron temperatures should be used for pressing. Polypropylene fibers are affected by some dry-cleaning fluids. Care labels should be checked carefully as blends of polypropylene with other fibers may require special care. Many polypropylene nonwoven fabrics are used in disposable products that are designed for one or a few uses for sanitary or durability reasons. Procedures for caring for these products are, therefore, not an issue.
Polyethylene Fibers
Manufacture and Structure
Polyethylene shares many qualities with polypropylene and exhibits some differences, including a lower melting point and some tendency to be deformed if stretched more than 10 percent. Melt-spun polyethylene has not been a textile fiber of major importance; the polymer has been used mostly for plastic films and packing materials. The plastic bags used by so many are usually made of polyethylene.
In the late 1960s, high-strength polyethylene fibers were developed using the gel-spinning process. The fibers are stretched to a great length while in the gel state, resulting in a nearly perfect alignment of the polymer chains. This high degree of crystallinity and orientation confer extremely high strength to the fibers. Indeed, they are among the strongest fibers known: fifteen times stronger than steel on a strength-to-weight ratio and more than twice the strength of the para-aramids. The modulus of gel-spun polyethylene fibers is likewise exceedingly high relative to other fibers, and these polyethylene fibers are less brittle. They resist moisture, chemicals, and ultraviolet light and are light weight. Disadvantages are a low melting point (300°F, or 147°C) and, for some varieties of the fiber, a tendency to creep, or elongate, under load over a long period of time.
Properties and Uses
Products for which these fibers are being used include ropes, cables, cut-resistant gloves, backpacks, ballistic vests and helmets, surgical sutures, and a wide range of fiber composite materials for industry. Spectra® polyethylene fibers are produced by Honeywell, and Dyneema® is manufactured by DSM.
Conclusion
Olefin fibers remain important due to their low density, minimal moisture absorbency, chemical resistance, and efficient processing. Polypropylene dominates everyday textiles and nonwovens, while gel-spun polyethylene is used in high-performance applications where strength-to-weight ratio is critical. Together, these fibers offer a balance of cost, functionality, and performance, ensuring their continued relevance across both industrial and consumer textile sectors.
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor to Wikipedia.
