Polymers: Polyolefins: Polyethylene, Poly Propylene And Polystyrene, Styrene Copolymers
Polyolefinsis family of polymers derived from a particular group of base materials known as olefins, are the world’s fastest growing polymer family. Polyolefins such as polyethylene (PE) and polypropylene (PP) are commodity plastics found in applications varying from house hold items such as grocery bags, containers, carpets, toys and appliances, to high tech products such as engineering plastics, industrial pipes, automotive parts, medial appliances and even prosthetic implants . Ethylene and propylene are monomers for polyethylene and polypropylene respectively. Global polyolefin market is likely to be 150 million tones by 2015 and 200 million tones by the year 2020. In India, the domestic polymer industry (like global industry) is dominated by polyolefins (polyethylene, polypropylene) . Market coverage of polyethylene, polypropylene is given in Table M-VIII 2.1.
Polystyrene is another important polyolefin and find wide application in manufacture of all sorts of packaging material. Styrene co-polymerised with acryloonitrile resulting in SAN polymer is characterized with high tensile strength than polystyrene. Another important styrene copolymer is Acrylonitrile Butadiene styrene (ABS) plastic find use in engineering plastic and is characterized with special mechanical properties.
Table M-VIII 2.1: Polyethylene/Polypropylene Market Coverage
Blown film with paper like quality, suitable for counter bags, carrier bags & wrapping films
Pipes PE-80/100 class, drinking water & gas pipes, waste pipes & sewer pipes their fitting etc.
Large BM grade
Universal container grade, vol. approx. 1,500lit;heating oil storage tanks, transport containers
Small BM grade
Disinfectant bottles, up to 2 lit, tubes for the cosmetics, containers from few ml up to 10 lit.
Stretched films and tapes for production of high strength knitted & woven sacks/bags/nets etc.
For transport and stacking crates, particularly bottle crates
Garment bags, grocery sacks, liner, blends, trash bags, cast like film diapers etc.
Large industrial parts used indoors, large industrial /agricultural tanks, shipping drums, toys etc.
House wares, crates, master batches, pails, food container etc.
Injection molding (Battery cases, crates, furniture,
house ware, luggage, sports/toys), Blow molding, Sheets, Tape/Raffia, FIBC,TQPP/BOPP films(food packaging, bottle labels etc. )
Extrusion coatings etc.
Thin walled injection moulding, low heat seal &
high transparency films, Blow moulding, packaging parts, automotive parts etc.
Automotive parts (bumper, exterior trims,
instrument panels, interior trims), Appliances, House wares, rigid packaging, thermoforming etc.
Table M-VIII 2.2: Characteristics of Polyolefin Catalyst
TiCl3, TiCl J MgCl2
CrO3 / SiO2
Late transition metalabsed
Ni, Pd, Co, Fe, with diimine, and other ligands
Molecular mass 200,000 – 500,000
Advantage: Low cost, excellent dielectric properties, moisture resistance, very good chemical resistance, available in food grade, processed by all thermoplastic methods.
Process Technology for Polyethylene: Several processes has been commercialised for the manufacture of polyethylene with varying densities. Various processes for manufacture of polyethylene are given in Table M-VIII 2.3.
Table M-VIII 2.3: Various Polyethylene Processes
Polymerisation in Fluidised bed
reactor using Ziegler Natta catalyst or Chromium catalyst
Temperature 75oC -110oC
Uses gas phase low pressure reactor.
Ziegler Natta catalyst
Comonomer hydrogen. Prepolymerisation in slurry loop reactor and fluidised bed reactor. Temperature 75oC -100oC
Polymerisation occurs in autoclave reactors or Tubular reactor
Polymeristion in Gas phase reactor
using Zigler natta catalyst
Phillips Co, LPE
Polymerisation takes place in an
isobutene slurry using very high activity properietry catalyst in loop reactor.
Low pressure polymerization in
fluidised bed reactor at 25kg/cm2 and 100oC
Polyethylene is produced by solution polymerization using ethylene gas and cyclohexane as solvent. Comonomer butane or Octane or both) Catalyst: Ziegle Natta catalyst