Polypropylene fibers, production processes

In summary, there is an impressive amount of research effort on various polypropylene fiber products. The developments of fine-denier spinning, dyeability modification, high fiber strength and modulus, and nanocomposites certainly appear inductive to further growth in market shares and value-in-use for propylene fibers. However, as with other synthetic fibers, the manufacturing process yield and cost, particularly spinning continuity, must not be adversely impacted by any new technology to be commercialized. This is clearly the key to the future success of polypropylene fibers. 

Improvements in melt spinning techniques and film filament processes have made polypropylene accessible for fiber production. Low-cost fibers made from polypropylene are replacing those made from sisal and jute. 

One of the most important developments in recent years has been the technology to extrude extremely fine filaments of less than 1.0 denier while maintaining all of the strength, uniformity, and processing characteristics expected by textile manufacturers and consumers. This product development began with the preparation of conjugated bicomponent filaments that were post-processed to split into ultrafine fibers. The process technology later matured and has been applied to polyesters, polyamides, polypropylene, and polyethylene and polyphenylene sulfide. 

Fiber finishes are normally added as lubricants or as antistats to the surface of fibers to facilitate fiber production and subsequent processing. Finishes are additives that may not achieve exactly what is intended. Low-molecular-weight mineral oils dissolve readily in polypropylene as do other materials added to the surface. It has been proposed that finishes may cause softening of the polymer surface [178], particularly at higher temperatures. Since polypropylene fibers are produced in colored form, the producer finish is not necessarily scoured off because it is for a dyeable fiber. The finish used by the fiber producer most frequently remains as part of the final product—for better or worse. Thus, the fiber finish must be considered not only as a processing aid but also as an additive. 

Corbiere-Nicollier et al. investigate transport pallets made of composites from China reed fiber used as a substitute for glass fiber [43]. The crucial factor of the assessment is the lifetime of the pallets the authors mention the need to optimize the process of fiber extraction in order to obtain a better material stiffness. For conventional pallets, a lifetime of 5 years is assumed. Environmental advantages for the transport pallets reinforced with China reed fiber are found if the pallet s lifetime is greater than 3 years. These advantages result from the substitution of the glass fiber production, from the reduction of polypropylene, and from the reduced weight of the pallet. For end-of-Ufe, incineration is the preferred option. 

In a process developed by DuPont [7, 42], nylon 6,6 carpet first is passed through dry processes consisting of a series of size reduction and separation steps. This provides a dry mix of 50-70% nylon, 15-25% polypropylene, and 15-20% latex, fillers, and dirt. Water is added in the second step where the shredded fiber is washed and separated using the density differences between the fillers, nylon, and polypropylene. Two product streams are obtained one 98% pure nylon and the other is 98% pure polypropylene. The recycled nylon is compounded with the virgin nylon at a ratio of 1 3 for making automotive parts. 

Figure 1.11 Fossil energy requirement for petrochemical polymers and PLA. The cross-hatched area of the bars represent the fossil energy used as chemical feedstock (i.e., fossil resource to build the polymer chain). The solid part of the bars represented the gross fossil energy used for the fuels and operation supplies used to drive the production processes. PC = polycarbonate HIPS = high-impact polystyrene GPPS = general purpose polystyrene LDPE = low-density polyethylene PET SSP = polyethylene terephthalate, solid-state polymerization (bottle grade) PP = polypropylene PET AM = polyethylene terepthalate, amorphous (fiber and film grade) ...

Pulp-like olefin fibers are produced by a high pressure spurting process developed by Hercules Inc. and Solvay, Inc. Polypropylene or polyethylene is dissolved in volatile solvents at high temperature and pressure. After the solution is released, the solvent is volatilised, and the polymer expands into a highly fluffed, pulp-like product. Additives are included to modify the surface characteristics of the pulp. Uses include felted fabrics, substitution in whole or in part for wood pulp in papermaking, and replacement of asbestos in reinforcing appHcations (56). 

Horticultural appHcations include use of greenhouse thermal screens, rowcrop and turf covers, conveyer belts to process agricultural products, and other similar items. High performance fibers are not normally used in these appHcations, but high strength fibers are preferable for conveyer belts. Environmentally inert low cost fibers such as polypropylene are used for many of the outdoor horticultural appHcations. 

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