Polypropylene twines

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... 

This approach was adopted for a study of polypropylene used as the filler in the interstices between the cores of some types of three-phase power distribution cables. The cores consisted of a conductor with polymeric insulation and extruded screens which were in turn screened with copper tape. Polypropylene twine is used to pack the interstices as the cable is laid up and then the outer parts of the cable are applied later. Thus the polypropylene is in direct contact with the copper tape. 

We can manufacture fibers from a wide range of polymers. Polyamides, polyesters, and polypropylene can be woven or knitted into fabrics, ranging from those as coarse and strong as those used in back packs, luggage, and sails, to soft and highly flexible fabrics used in sweaters, shirts, and other apparel. Polymer filaments and yarns can be twisted or woven to make string, twine, cords, and ropes. 

Monofilament yarns consist of a single filament. The filament size is much larger than those found in multifilament yarn. Consequently, monofilament is relatively stiff and is used mainly for the production of rope and twine. Fiber size range is typically 75 to 5000 denier. Monofilament fiber is usually produced from polypropylene homopolymer with a relatively low melt flow index in the range 3.5 to 5.0 grams/10 min. 

Photo-biodegradable polyethylene using the above system was developed commercially for use in agriculture by D. Gilead of Plastopil Hazorea in Israel in collaboration with the author and is now widely used as Plastor in mulching films in Europe and Plastigone in the USA. It is also used in polypropylene baler twines as Cleanfields by AMBRACO in the USA, and in controlled release fertilisers as Nutri-cote by Chisso-Asahi Fertilizer Company in Japan. The biodegradation mechanism will be discussed below. 

As the name implies, single filaments are extruded the molten filaments are cooled and solidified in a water bath and then drawn. Typically, monofilaments are fairly large, being on the order of 250 dpf. Rope and twine are produced by twisting bundles of monofilament together. Polypropylene rope and twine are strong and moisture resistant, making them very useful in marine applications. 

Industrial applications of polyolefin fibers include woven and nonwoven geotextiles, agriculatural fabrics, construction sheeting, automobile fabrics, filtration media, rope/twine, woven bags, narrow-woven web and tapes, tents, and tarpaulins. Geosynthetic fabrics will continue to be a growing market for polypropylene nonwovens. 

Much polypropylene fiber is not spun, but produced from film. A film is blown, or cast on a chill roll, drawn 6-10 times and then fibrillated. There are numerous ways of slitting, fibrillating, and cutting. Split fiber finds applications in twines and ropes (as a replacement for sisal), cheap fabrics for bags and tarpaulins, and carpet backing (replacing jute). 

A comparatively recent development in the technique of monofilament production is based on extrusion of film which is subsequently slit and then processed in the same way as the conventional monofilaments. Tapes produced from slit film are used in many applications ranging from strapping, ropes and twines, to woven sacks and carpet backing. The main material here is polypropylene with some of the lighter tapes made in high density polyethylene. 

Both polythene (polyethylene) and polypropylene are made into twines that appear on casual inspection to be formed from fibres but closer observation reveals them to consist of slit and rolled films. There is in fact a limited number of plastics that can be drawn... 

In the USA photo-biodegradable polypropylene baler twines based on SG oxo-biodegradable PP have been used for 15 years and substantially replaced conventional PP slit films in hay wrapping and crop-protection netting. These are given a useful life of one year and this is followed by rapid disintegration and bioassimilation. 

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