Revival in “Age of the Environment”
Polypropylene fiber is attracting attention in this “age of the environment.”Demands for polypropylene fiber are expanding because it is the synthetic fiber friendliest to the environment. While major synthetic fibers such as polyester fiber, nylon fiber and acrylic fiber suffer from their structural over-supply, a minor polypropylene fiber has come into the limelight.
Fiber Gentle to Earth
Light Environmental Burden
Polypropylene fiber was invented and industrialized in Italy in the 1950s. With subsequent commercialization in many other countries, it created a sensation around the world as a “dream fiber” or the “ultimate synthetic fiber.” This is because of high evaluations: (1) polypropylene fiber has the small specific gravity of 0.91 and is lightest among synthetic fibers, (2) it possesses high tensile strength, and (3) its material (propylene) costs are lowest. Polypropylene fiber is made by melt-spinning polypropylene. Polypropylene is obtained by the polymerization of propylene monomer. Propylene is a byproduct when refining oil and it is separated from naphtha compounds.
Polypropylene fiber, however, failed to spread for apparel applications and anticipations of polypropylene fiber withered rapidly because of its drawbacks of being unable to be dyed and being less heat-resistant, in addition to an insufficient resistance to light. As a minor fiber even among synthetic fibers, polypropylene fiber managed to find meager applications only in industrial applications. Polypropylene itself is a versatile material for films and resins, but the scale of its production for fibers is small; even including spunbonded nonwoven fabrics.
This polypropylene fiber, however, has become a favorite in the era in connection with environmental issues. The contributing factors are as follows: (1) Polypropylene fiber hardly generates harmful substances when burned because it consists of only carbon and hydrogen; (2) Recycling is very easy because its molecular structure is simple; and (3) It has a sufficient tensile strength despite of it being the lightest fiber with the specific gravity of 0.91. To summarize, polypropylene fiber has been reevaluated as the “most kind synthetic fiber to the global environment” with a light environmental burden. Furthermore, its physical properties of “being unable to absorb water whatsoever” and of being “highly stain-resistant” are being reviewed from a new angle.
Being exceptionally small, the scale of its production stands no comparison with polyester fiber. The expansion of equipment, however, is under way in response to the growth of demands. Further contributing factors are technological developments such as the impartment of functional properties and the expansion of fiber variations, in addition to cost performance. Moreover, the development of new applications has made good progress.
Polypropylene Staple Fiber
From Industrial to Even Apparel Applications
Inquiries for polypropylene staple fiber for industrial material applications have increased for the past several years. For example, 100% spun polypropylene sheets (olefin-resin-coated woven fabrics made of spun polypropylene yarn) hardly generate injurious substances through disposal by burning. Furthermore, recycling is very easy because they are 100% polypropylene sheets. In other words, a light environmental load characterizes 100% spun polypropylene sheets.
Moreover, polypropylene fiber is light and floats on water because of its specific gravity of 0.91. Consequently, 100% spun polypropylene sheets achieved 60% lighter weight and easy handling operations, as compared with conventional polyvinyl chloride (PVC)-coated sheets (the base cloth being spun polyester woven fabrics). At the same time, an excellent resistance to cold characterizes it and their fabrics were not hardened even under the condition of a temperature as low as 30-40 deg C below zero.
Spun polypropylene sheets also offer an excellent thermal processing properties such as with heat– sealing in the sewing process. In addition, the recovery of used spun polypropylene sheets for recycling has been made possible.
As a material with a small environmental impact, polypropylene staple fiber has found its broadening applications not only for bag and upholstery fabrics, but also it has attained evaluations as a material for separators of secondary cells. This is one of the ways of doing environment business.
For example, separators in nickel-hydrogen cells for hybrid cars with both engines and motors employ polypropylene fiber. New markets are being developed for nickel-hydrogen cells including electrically-driven scooters and an emergency power supply for optical fiber cables. It is highly anticipated that these developments will achieve good results.
Finally, polypropylene staple fiber is going to develop apparel applications, in addition to nonwoven fabrics for industrial material applications and for sanitary materials such as paper diapers. For example, the marketing of materials for sports underwear made from 100% spun polypropylene yarn or 70% polypropylene/30% acrylic blended yarn has already begun. This material is characterized by non-water/moisture absorbing quality, low heat conductivity and an excellent warmth-retaining property.
Polypropylene Filament Yarn
From Carpets to New Applications
Polypropylene filament yarn is primarily used for carpets such as tile carpets and option mats for automobiles. The market has given approval to the development of products such as fine-denier yarn and the impartment of functional properties, in addition to cost performance.
Furthermore, producers have made a major announcement of the advantage of “being an environment-friendly material” through the utilization of its simple molecular structure and the ease of recycling in the development of new applications.
For example, office chairs made from all polypropylene materials have made an appearance as a new application. These chairs employ polypropylene resin as aggregate and polypropylene filament woven fabrics as upholstery.
The automotive upholstery application is also hopeful. A shift to polypropylene resins is in progress for door-trim boards and interior panels. Since car interior materials are exposed to direct sunlight, the conventional polypropylene fiber with poor resistance to light has drawbacks, but a highly light-resistant type polypropylene filament yam has been developed. Consequently, integrated recycling has been made available by the use of this type of polypropylene filament yam fabric in combination with resins, as is the case with office chairs. Automotive producers have taken an increasing interest in polypropylene interior fabrics.
In the building sector, polypropylene filament yam has been increasingly employed for sealing nets. This will replace conventional nylon and polyester filament yarns. This reflects evaluations given to the advantages of polypropylene filament yam such as lightweight and non-water absorbing qualities (and the resulting dimensional stability). In addition, there is great anticipation for harmony with the urban landscape because a high degree of color development has been made available by spun– dyeing.
The development of demands for nursing care products is also progressing through the utilization of physical properties such as having the lightest weight among fibers (its specific gravity is lighter than water), non-water absorbing quality and an excellent resistance to stains.
Copyright Osaka Senken Ltd. Jun 2001
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