Polypropylene Strapping Characteristics
Polypropylene (PP) - This polyolefin is readily formed by polymerizing propylene with suitable catalysts, generally aluminum alkyl and titanium tetrachloride. Polypropylene properties vary according to molecular weight, method of production, and the copolymers involved. Generally polypropylene has demonstrated certain advantages in improved strength, stiffness and higher temperature capability over polyethylene. Polypropylene has been very successfully applied to the forming of fibers due to its good specific strength which is why it is the single largest use of polypropylene. Polypropylene also happens to be one of the lightest plastics available with a density of 0.905 g/cm².
|Polypropylene (PP) was discovered in 1954 and grew a strong popularity very quickly. Because of extensive research, five main variations of Polypropylene have emerged as: homopolymers, impact (block) copolymers, random copolymers, rubber modified blends, and specialty copolymers.
Homopolymer Food Contact Acceptable, Good Processability
Copolymer Good Stiffness, Good Impact Resistance, High Flow, High Impact Resistance, High Stiffness , Chemically Coupled...
Household Goods, Containers, Appliances, Film, Electrical/Electronic Applications, Packaging, Automotive Interior Parts, General Purpose, Industrial Applications
- Degraded by UV
- Flammable, but retarded grades available
- Attacked by chlorinated solvents and aromatics
- Difficult to bond
- Several metals accelerate oxidative degrading
- Low temperature impact strength is poor
In general homopolymers (i.e. with only one type of monomer) can be used for housing, housewares, packaging, cassette holders and fibers, monofilaments and film tapes; copolymers (i.e. different monomers are involved) are prefered for all applications exposed to cold and they are widely used for pipes, containers, boat hulls, seat shells and automotive parts e.g. battery cases and bumpers.
Polypropylene can be manufactured to a high degree of purity to be used for the semiconductor industry. Its resistance to bacterial growth makes it suitable to be used in medical equipment. Polypropylene is used in most of our nonwoven fabrics such as rope used in a variety of industries, including fishing and agriculture. PP can be used for flexible packaging applications (e.g. yogurt containers, syrup bottles, straws, etc.), construction sector (e.g. drainage pipes, pumps, etc.), automotive sector, etc.
Polypropylene copolymer (PPC) grades are preferred for all applications exposed to cold conditions. These copolymers have better impact strength, maintained down to lower temperatures, than homopolymer at the expense of quite small reductions in other properties. Copolymer sheets are used extensively in Hygienic Lining Systems for wall and ceiling cladding. Hygienic, tough and impact resistant, it will stand repeated steam cleaning and is ideal in all food industry applications
Environmental issues and occupational health and safety issues
Plastics represents a 14 to 22% in volume of solid waste. It can be melted and recycled, making it a thermoplastic elastomer but the recycling degrade the properties. Another difficulty is the management of plastics that are difficult to separate from other materials for its recycling. On the other hand recycling can be a cost-effective possibility if we take into account the social cost of landfills as well as fees.
For more information on the disposal of plastics.
The use of PP does not have any remarkable effect from an occupational health and safety point of view, in terms of chemical toxicity. The manufacture of the polymer at high temperature can released irritating vapors to respiratory system and eyes. There is no known effect from chronic exposure to this product.
Polypropylene Strapping manufacture.
In the polypropylene strap processing, resin is loaded into a heated hopper fed into a heated screw chamber to facilitate the melting in the extruder. Since the presence of moisture does not affect the quality of strap, prior drying is not necessary. The resin is melted in the extruder in the temperature range of about 420F and quenched in water at a temperature of about 110F for an extrusion rate of about 8 metres per minute. The quenched strap is passed through the two stretching radiant heater ovens at a temperature of about 250F total stretching from 9 to 1 to 12 to 1, depending on the desired strength of the final strap. Since the crystallization of polypropylene is fast, and the crystallization rate is quite appreciable, even at the temperature of the quenching tank, the strap getting into the stretching section has sufficient strength for any stretching ratio. The radiant heater stretchings employed in connection with water quenching, as in this case, is due to the hydrophobic nature of polypropylene.