Polypropylene, fibrillated

The specimens of soil with fibres and cement or cactus pulp as a binder were subjected to bending, abrasion, erosion and water absorption. Sisal fibres 40-50 mm long and polypropylene fibrillated fibres 20 mm long were... 

The film is fibrillated mechanically by mbbing or bmshing. Immiscible polymers, such as polyethylene or polystyrene (PS), may be added to polypropylene to promote fibrillation. Many common fiber-texturing techniques such as stuffer-box, false-twist, or knife-edge treatments improve the textile characteristics of slit-film fibers. 

Fibrillated tape, again particularly successful with polypropylene, in which oriented film is stretched so much that fibrillation occurs. 

An important application for polypropylene is film tape. This is made by slitting unoriented film (cast or blown) into tapes 2 or 3.5 mm wide and stretching under heat about seven-fold. With cast film the orientation is more completely monoaxial and there is a tendency for the film to split along its length (fibrillate). Tubular film does not self-split so easily and also has a somewhat softer feel. Such tapes may be woven into sacks and these have... 

Effects were similar with the two polypropylenes as matrix. Nevertheless, as in our earlier studies f44], the in situ fibrillation was more pronounced for the more viscous PP (VB1950K) and this PP grade was selected for the additional experiments. 

Since the glass mat supplies sufficient stiffness, high backweb thickness was no longer needed These fleeces are made of organic fibers (polyester and polypropylene, as well as so-called synthetic pulp , i.e., fibrillated polypropylene) on paper machines. 

Significantly different seemed intiaUy the crystal morphology of polyethylene, polybutene-1, polypropylene, polystyrene, poly(4-methyl pen-tene-1), and polyisoprene polymerized with varying solvents and at varying temperatures (114, 123). Discrete hollow particles with a fibrous texture could be observed. The fibrils had an appearance similar to polyethylene crystallized from solution sheared by rapid stirring (118). A closer analysis of this similarity was carried out by Wikjord and Manley (124), Keller and Willmouth (117), and Ingram and Schindler (125) for polyethylene. 

Synthetic wood-pulp separators (SWP). So-called synthetic wood-pulp (SWP) separators are used widely in Japan for automotive batteries. These are fleeces made from fibrillated polyethylene or polypropylene and small amounts of additional fibres (e.g., polyester fibres) sometimes, the fleeces are also filled with silica. The organic sheets are laminated with a glass mat, which serves to stabilize the positive active-material [39]. 

The smaller the fiber diameter used in the prefilter, the greater the surface area for adsorption of particles and the better the retention of small particles. In the sixties, asbestos fibers were recognized as the best prefilter media. The individual fibrils were smaller than 0.01 ju and they had a positive zeta potential. However, when it was suspected that asbestos fibers presented a health hazard, fine diameter glass and synthetic polymer fibers were substituted. Unfortunately, neither media equals the performance of asbestos. Glass fibers are available in the finest diameters, but some users are fearful they may represent a similar health hazard. The trend has been to use polypropylene or polyester fiber prefilters. Melt blown or spun-bonded fibers are available in diameters near 1 ju. Multilayers of these media with appropriate calendering have resulted in surprisingly efficient prefilters. 

In the special case of branched polyethylene, the elastic modulus at 45° to the fiber axis is exceptionally small this means that shear compliance along the fiber axis is very high (16). Such deformation involves reversible shearing displacement of adjacent fibrils. Since a similarly high shear compliance does not occur with linear polyethylene and isotactic polypropylene, the difference may be attributable to the substantial difference in draw ratio (4.5 in branched, 20 in linear polyethylene and propylene) which results in proportionately shorter microfibrils and fibrils in the former. The shorter the microfibril, the shorter the fibril and the smaller the surface-to-cross section ratio and hence the smaller the resistance to shear displacement. 

Woven mesh of fibrillated polypropylene film that allows water permeation but prevents the ingress of fine soil particles. 

B. Wanno, J. Samran, and S. Bualek-Limcharoen. Effect of melt viscosity of polypropylene on fibrillation of thermotropic liquid crystalline polymer in in situ composite film. Rheol. Acta, 39 311-319, 2000. 

Table 3.1 presents the worldwide production of polyolefin fibers in 1996 2002, according to Fiber Organon [1]. In 2002, the total production of polyolefin fibers grew to 5.913 million tons (MT). The annual rate of growth was 2% as compared to 8% for polyester, 6.4% for PAN, and 4.4%i for polyamides. The production of polypropylene fibers, excluding fibrillated fibers, reached 3.99 MT in 2002 and 4.20 MT in 2003. About 70% of its production was in filament yarn and 30%i in staple. As Table 3.1 also shows the portion of polypropylene filaments increased from 40.4%i in 1996 to 45.5%i in 2002, while fibers from fibrillating film decreased from 35.2 to 32.5%i. The portion of ST remained steady at 22.1%. 

The productivity of polypropylene in West Europe increased from 1.70 MT in 1999 to 1.80 MT in 2002, while it increased from 1.35 to 1.85 MT in 2002 in the United States. After 25 years of developmental efforts, China became the second largest producer of polypropylene after the United States. Its production of polypropylene fibers, excluding fibrillated fibers, was 561 KT. The productivity share was 165%i for China and 22.5% for the United States. The growth was fastest in the Middle East and Africa. In the Middle East, the production of polypropylene grew from 0.75 MT in 2000 to 1.95 MT in 2001 due to new investments by Saudi Arabia. The consumption of polypropylene in the Asia Pacific region increased by 10% in 2000 and 5% in 2001, thus draining the export capacity from Saudi and Iran. 

Polypropylene fibers are produced by a larger variety of processes than other melt-spun fabrics. At one end of the range, the long air-quench process produces high-quality multifilament yarns, and, at the other end, fibrillating slit film produces coarser fibers. The success of the lower-cost polypropylene slit-film fiber is due to the lower price of the polypropylene resin and the unique adaptability of polypropylene to the less expensive slit-fibn fibrillation process. The water-quench process for monofilament has long been an established technique... 

The formation of the fibril is a eonsequence of dispersed phase deformation and orientation correlating with the viscous force and interfacial tension between the dispersed phase and the matrix [236,237]. For good fibrillation to be achieved, the viscosity of dispersed phase should be lower than that of the matrix (i.e., / = rjd/ mtemperature dependence of p of PS to PP is shown in Figure 3.68. Experimental results showed that p is less than 1 above 210°C and reduces to about 0.5. This indicates that polystyrene is able to form the fibrils in polypropylene matrix when the processing temperature is over 210°C, but finds it difficult below 210°C [239]. 

Polypropylene film fiber is becoming of great commercial interest in many applications such as carpeting and woven sacks. It consists of an extruded film that is slit along the machine direction into narrow, fiber-like ribbons. These ribbons are then woven to make strong fabrics, nets, and sacks. Low-density polyethylene (LDPE) is sometimes blended with PP in slit film applications in order to reduce fibrillation and improve processability. 

The tubular-film process is unsuitable for polymers with a very low melt strength such as polyethylene terephthalate. It is also not suitable for polypropylene films for packaging because the films are too crystalline, opaque and brittle due to too slow cooling. However, these films are often used as a precursor for fibrillated film fibres. 

Coarse products suitable for the manufacture of baler twines, ropes and hawsers are made by flat film extrusion, water-bath quenching, air-oven stretching and optionally annealing thick film strips. The oriented strips are twisted and coarse fibrillation then occurs spontaneously. These polypropylene twines and ropes are stronger than ropes of sisal or manilla... 

It is also possible to obtain crimped fibres by the split-fibre technology in a different way. If a laminated film is produced by extruding the raw material or raw materials in such a way that the layers display during stretching stress-strain curves which do not coincide, then a spontaneous crimp can be obtained immediately after fibrillation without additional thermal treatments of the fibres. It is, of course, necessary that the layers adhere well to each other. If both layers consist of polypropylene or copolymers of propylene, this is no problem. However, if different polymers are used, the adhesion is usually insufficient. 

Bicomponent films can also be made from two different polymers if sufficient adhesion between the layers can be achieved to prevent delamination during stretching and fibrillation. Mehta has pointed out that bicomponent films can be made from polypropylene and low density polyethylene. After stretching and fibrillation the fibres look like ordinary split fibres but on heating they develop a spiral crimp with the LDPE on the inside. These fibres have the important advantage that a carded fleece, when needle-punched and exposed to temperatures above the melting... 

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