Polyolefins are high molecular weight hydrocarbons and represent almost two-thirds of the major commodity thermoplastics used worldwide. These are the only plastics that weigh less than water. When ethylene is polymerized the result is polyethylene having relatively straight polymer chains. From main chain varying degree of branching can takes place to provide different molecular structures.
General Characteristics:
They are low cost polymers have excellent chemical resistance (resistant to alkalis and oxidising acids, good solvent resistance below 60 °C), very good processablity, very low water absorption, excellent electrical insulating properties and are FDA compliant. Generally all polyolefins are nonpolar, nonporous have low-energy surface that is not receptive to inks, and lacquers without special oxidative pretreatment. They can become brittle from oxidation, are susceptible to stress cracking, exhibit Poor UV light and Gamma radiation resistance, has low heat resistance and very difficult to high-frequency welding and joining.
They are usually processed by Extrusion, Blow, Injection and Rotational moulding,
Thermoforming and Calendaring methods. All Polyolefins are also well suited to recycling which is an important consideration in today's environment conscious world. Let us study the members of Polyethylene family and how they differ from each other:
LDPE has most excessive long branching. This causes the low density to have a less compact molecular structure which is what makes it less dense.
Density
0.910 – 0.925 g/cm3
Melting Temperature
98 - 115°C
Glass Transition temperature
-110°C
Max/ Min continuous Service temperature
60 – 75°C/ - 70°C
Processing Temperature
160 - 210°C
Strength:
They are glossy, flexible, translucent with a waxy feel and show high impact strength at low temperature.
Limitations:
are highly flammable, low strength, stiffness and low maximum service temperature, high gas permeability particularly carbon dioxide.
Applications:
Pharmaceutical and squeeze bottles, caps and closures, tamper evident liners, trash bags, films for food packaging (frozen, dry goods..), agriculture pipes and hoses, lamination, coatings.
LLDPE has significant numbers of short branches. Because of this it's chains are able slide against each other upon elongation giving it better properties than LDPE.
Density
0.91 - 0.94 g/cm3
Melting Temperature
130-137°C
Glass transition temperature
-110 °C
Max / Min continuous Service temperature
90 - 110 °C/- 70 °C
Processing Temperature
180 - 260 °C
Strength: Exhibits higher Tensile, Impact strength and Puncture resistance versus conventional LDPE, improved flex life, low warpage, improved stress-crack resistance and lower thickness films can be blown
Limitations: high mould shrinkage, narrower heat seal temperature range and difficult to process than LDPE
Applications: Bags and pouches, films and liners, Pipes & Fittings, Wiring & Cables, Water pipes, Cable jacketing, able insulators, overhead tanks,
has densities between 0.890 and 0.915 Applications include disposable gloves, Shrink packages, vacuum cleaner hoses, tuning, bottles, shrink wrap, diaper film liners, and other health care products
has extremely long chains, with molecular weight numbering in the millions (usually 2to 6 million), at least 10 times of HDPE. High MW leads to high degree of physical entanglements above Tmelt (130 C or 266F), the material behaves in a rubber-like molecule rather than fluid-like manner causing processing troubles due to extremely high viscosities. Thus is processed by ram extrusion and compression moulding.
Density
0.928-0.941 g/cm3
Max/Min continuous Service temperature
67-82°C/-30°C
Strength:
Excellent abrasion resistance and toughness, high impact strength, ESCR and chemical resistance with the low coefficient of friction, Gamma/ UV Light resistance, UHMWPE yields a self-lubricating, non-stick surface.
Limitations:
Not melt processable, higher cost than PE
Applications:
Used in variety of applications like Pump parts, seals, lining of bunkers, silos, chemical tanks, chemical handling equipment, Truck bed linings, Bearings, Belt wipers, Star wheels, Timing screws, prosthetic wear surfaces, gears, Guide rails, Chain guides, Hopper/chute linings, Bumpers, Bushings, Wear plates, Sprockets, butcher-block cutting surfaces, other industrial applications.
Is an economical material that offers a combination of outstanding physical, chemical, mechanical, thermal and electrical properties which is not found in any other thermoplastic.
Density
0.90-0.91cm3
Melting Temperature
165 °C
Glass transition temperature
-10 °C
Max/ Min continuous Service temperature
100 - 110 °C/ -20 To -10°C
Processing Temperature
190 - 300 °C
Polypropylenes are available either as homopolymers or block co-polymers.
Homopolymers are high strength and stiff but become brittle at low temperatures.
Block co-polymers have ethylene blended-in to improve the low temperature performance but they have less clarity and gloss. The higher the ethylene content the softer and tougher the material becomes.
Random copolymers with lower ethylene content and a slightly different structure exhibit lower melting point, greater flexibility or enhanced clarity (transparency)
The properties of polypropylene can be altered by the addition of fillers like talc or glass fibres. The addition of talc provides improved rigidity but results in lower impact strength and reduced resistance to long term heat ageing. Glass fibres provide good rigidity, improved impact resistance, a good resistance to creep and better environmental stress cracking resistance.
Strength:
Low Cost, Processable by all methods, Excellent aesthetic properties, easy to fabricate, Low coefficient of triction, stiff, light weight with good tensile, Exural impact strength, Excellent electrical insulation, Good fatique resistance, Exclent moisture resistance, Excellent strength, Aurocavable. Very good chemical resistance, low moisture absorption, Because of its inherent flexiblity Itis loballysuited to integral hinges used for flip flop closures, compass box.
Limitations:
High thermal expansion, UV degradation, poor weathering resistance, subject to attack by chlorinated solvents and aromatics, Difficulty to bond or paint, oxidizes readily, flammable
Applications:
from crates and bins, through housewares, washing machine drums and plumbing fittings, to automotive applications such as bumpers and dashboards, Chemical and plating tanks, Orthotics and prosthetics, Film, Containers, Appliances, Packaging, Electrical/Electronic, furniture, paint pails, industrial products, Medical products, others
Is a thermoplastic polymer of methyl pentene monomer units. Its properties are reasonably similar to those of other polyolefins, although it is more brittle and more gas permeable.
Density
0.835-0.84 g/cm3
Melting Temperature
220°C to 240°0.
Processing Temperature
+ or - 300°C
Processed by Blow, Injection and Extrusion process
Properties:
Transparent crystalline material, rigid, tough, lightweight, highly permeable to gases, excellent heat and chemical resistance, autoclavable, very low surface tension, excellent electrical insulator, low dielectric properties and release qualities, strong hydrolysis and vapour resistance, Very low density, Low water absorption, Exceptional acoustical properties, High melting point and Vicat softening point, FDA compliant,
Limitations:
Attacked by oxidizing agents, hydrogen carbon and chlorinate solvents, Poor UV resistance and quite flammable, expensive then polyolefins
Applications:
Medical and laboratory equipments, syringes, lamp covers radar applications, encapsulation, microwave food packaging, release paper for synthetic leather, Release Films, Mandrels, Cosmetic caps and tubes, Heat resistant non-woven, ultrasonic transducer heads.
Popularly known as EVA is the copolymer of ethylene and vinyl acetate. Polymer is highly flexible, compatible with many other polymers and additives and is easy to process. The weight percent of vinyl acetate usually varies from 8 to 35% and higher the VA content more is the flexibility. EVA has little or no odour and is competitive with rubber and vinyl products in many electrical applications.
Density
0.926 - 0.950 g/cm3
Melting Temperature
55°C- 100°C (varying VA %)
Max / Min continuous Service temperature
45 - 65°C/-60°C
Processing Temperature
150 - 220°C
Processed by conventional thermoplastic or by rubber processing techniques
Properties:
Tough, transparent to semi-opaque material with relatively low upper working temperatures (65°C), Flexible (rubbery), Resilient, Crack resistant, good low temperature flexibility(-70°C), good chemical resistance, high friction coefficient, ESCR, good UV resistance. EVA is softer, clearer and more permeable than LDPE.
Limitations:
Poor heat resistance, reduced barrier properties and creep compared to LDPE, Attacked by polar solvents, hydrocarbons, oxidants and strong acids
Applications:
EVAs are leading polymers for hot-melt manufacturing fulfilling various requirements in packaging, bookbinding or label sticking. Widely used for handle grips, flexible tubing, shock absorber in sports shoes for shoe soles, flexible packaging, shrink wrap, auto bumper pads, flexible toys, ice cube trays, bicycle saddles, barrel bungs, railway sleeper pads, baby bottle teats, teethers, refrigerator door gaskets, sealant layer in multilayer films others. The foam is also commonly used as padding in equipment for various sports such as ski boots, hockey & boxing. EVA is used in biomedical engineering applications such as drug delivery device used within the body. While the EVA is not biodegradable within the body, it is quite inert and causes little or no reaction following implantation.
EVOH copolymers are highly crystalline, and their properties are highly dependent on the relative concentration of the co-monomers, ethylene and vinyl alcohol.
Generally speaking, as the ethylene content increases, the gas barrier properties decreases, the moisture barrier properties improve, and the resins are processed more easily.
Density
1.1-1.2 g/cm3
Melting Temperature
170 °C - 220°C
Glass transition temperature
15-70 °C
Max continuous Service temperature
80 - 100 °C
When melt temperature exceeds 250°C the polymer may decompose.
EVOH is hydrophilic, absorbs significant moisture when exposed to humid conditions, leading to an increase in its oxygen permeability. Pellets should be dried at 90-110°C for 2-3 h in such case.
EVOH is typically processed by Extrusion and also blow moulding process.
Properties:
Outstanding barrier to gases - oxygen, nitrogen, carbon dioxide and helium, odours and aromas, good printability & weathering resistance, adhesion with polyamides. Excellent resistance to greases, chlorinated solvents, esters, alcohols & hydrocarbons, suitable for transparent applications and FDA compliant.
Limitations:
Sensitive to moisture, Moderate heat resistance, attacked by acids and oxidants, Poor adhesion to most polymers, a tie-layer is generally needed properties highly depend on ethylene to vinyl alcohol concentrations
Applications:
co-extruded or laminated as a thin layer between cardboard, foil or other plastics, Multilayer rigid and flexible food packaging of sauces, edible oils and juices for improved shelf life, Tubes for cosmetic, packaging processed meats, bag in box and cereal. Bottles for pesticides and agrochemicals, in auto-motive fuel systems to control emissions of hydro-carbons from fuel lines and tanks
It has minimal branching of its' polymer chains and thus stronger intermolecular forces. It is more rigid, opaque and has higher tensile strength then LDPE, LLDPE.
Density
0.941-0.965 g/cm3
Melting Temperature
130-137 °C
Glass transition temperature
110°C
Max/ Min continuous Service temperature
70-80 °C/-70°C
Processing Temperature
190 - 280 °C
Strength:
Good processablity, excellent chemical resistance and Electrical insulation properties
Limitations:
Stress Cracking susceptible, high mould shrinkage, poor UV light resistance, Low stiffness than PP
Application:
Packaging Films, bags, Agriculture films, Pipes and hoses. Geotextiles, bottles and containers, cans, caps and closures, household plastic products, Large drums, crates, gas pipes, crates, woven sacks, auto fuel tanks, Orthotics and prosthetics others.
It has a little less branching then the HDPE. It is less notch sensitive then HDPE and has better stress cracking resistance. It has a density range of 0.926 - 0.940 g/cm3
XLPE is high density polyethylene which has covalent bonds connecting its polymer chains thus forming 3-dimensional polymers with high molecular weights. The cross linking is achieved generally by addition of small amounts of organic peroxides, provides superior stress cracking, improved toughness, stiffness, chemical and heat resistance, good low temperature resistance and insulating properties compared to the HDPE.
Density
0.915-1.4 g/cm
Max continuous Service temperature
110 - 130 °C
Processing Temperature
~ 190°C
Processed generally by Extrusion process and also Rotational Moulding
Applications:
Extruded products like Pipes, Films (shrink wrap film in particular) Electrical wire and cable insulation
Also known as 'Vinyl' is one of the most versatile and one of the least expensive polymer made of 57% chlorine (derived from industrial grade salt) and 43% carbon (derived predominantly from oil / gas via ethylene). It is less dependent than other polymers on crude oil or natural gas, which is non-renewable, and hence can be regarded as a natural resource saving plastic.
The polymer cannot be used in its natural state, but compounding it offers enormous range of properties from rigid products (window frames) to flexible son material (sheets, pipes, hoses) and this ability of being used in either the rigid or son (plasticised) forms doubles the market for this exceptionally safe material. There are more compounding recipes for PVC than for any other polymer.
PVC compounds can be extruded, injection, compression or Blow moulded or calendared to give variety of products, either rigid or flexible depending on the amount and type of plasticizers used.
Processing: Drying before processing is highly recommended, moisture rate should be lower than 0.3%
PVC is sensitive to the heat and on thermal decomposition evolves HCI gas hence suitable stabilizers are to be used during processing
For Moulding Melt temperature should lie between 170 and 210°C. Mould temperatures of 20 to 60°C are more suitable. Mould shrinkage lie between 0.2 and 0.5%.Screw with an L/D ratio of 15 to 18 is recommended.
For Extrusion temperatures are 10-20°C below injection moulding temperatures in order to avoid premature thermal degradation.
Is strong, good combination of stiffness and impact strength, has excellent solvent stress cracking resistance, weatherproof, flame resistant with good overal mechanical properties, better chemical resistance than plasticized PVC, good dimensional stability at room temperature, Low cost, good electrical insulation and vapour barrier properties, FDA Compliant.
Density
1.35 - 1.5 g/cm3
Glass transition temperature
60 - 100 °C
Max / Min continuous Service temperature
50 - 80 °C/-10-1 °C
Limitations: Difficult to process, Low continuous service temperature of 50°C, tends to degrade at high temperatures, Becomes brittle at 5°C (without impact modifiers and/or processing aids), Limited solvent stress cracking resistance, Some plasticized materials are susceptible to microbiological attack and staining, High specific gravity for plastic material.
Applications:
Building: Waste water pipes & fittings, grating covers, guttering, roofing sheets, sanitary installations, window frames, fencing fascia boards.
Electrical : Insulation pipes, panels, electricity distribution boxes, switches, telephone and plug housings, battery terminals.
Is easier to process than rigid PVC, Low cost, soft, flexible and transparent, good resistance to UV, Flexible, high ratio of strength to weight, Good resistance to acids, alkalis, oils and many corrosive inorganic chemicals, Good electrical insulation properties, Non-flammable, used in medical applications.
Density
1.3-1.7 g/cm3
Glass transition temperature
-50 to -5°C
Max/Min continuous Service temperature
50-80°C/-40 to -5°C
Limitations:
Properties can change with time, due to plasticizer migration, tends to degrade at high temperatures, Non suitable for food contact with some plasticizers, Lower chemical resistance than rigid PVC.
Applications:
PVC is the main material used for blood bags, gloves and medical tubing saving countless lives.
Electricals: Cable and wire insulation, plugs, cable jackets, sockets, cable heads and distributors.
Engineering: Gaskets, stuffing boxes, pipes, hoses, coatings, and protective caps for pipes.
Building: Seals for windows and doors, swimming bath linings, floor coverings, doorstops, garden hoses, wire coverings
Others: Shoe soles, divers masks, car body seals, ski sunglasses, toys, tablecloths, boots, cases. Cling film, inflatable dinghies, balls, handbags, book covers, office equipment, artificial leather seats.
Possesses the same outstanding chemical resistance of PVC, but offers superior performance to PVC in applications where higher heat resistance is required.
Although more difficult than PVC, CPVC can be thermo-welded, chemically bonded, Superior corrosion resistance, better UV resistance, high pressure resistance (3 bars at 90°C), Inert to most mineral acids, bases and salts, as well as aliphatic hydrocarbons,
Self-extinguishing and relatively low smoke generation
Density
1.5 - 1.55 g/cm3
Glass transition temperature
100-110 °C
Max continuous Service temperature
80-100 °C
Limitations:
Poor impact resistance, Opaque, Poor resistance to aromatic solvents, ketones and esters, High cost, compared with PVC.
Application:
Construction industry pipes and fittings, sewage pipes, Tanks, hoods, Pipes for chemicals, Agriculture, Automotives Thrust washers, Digital copier and printer components.
Is a highly effective barrier coating polymer that is produced by the polymerisation of a vinylidene chloride monomer with other monomers such as acrylic esters and unsaturated carboxyl groups. PVDC homopolymers are difficult to fabricate, so only
PVDC copolymers have commercial importance.
Density
1.6-1.75 g/cm°
Glass transition temperature
-15 °C
Max continuous Service temperature
70-90°C
PVDC is procesed by sheet or film extrusion, co-extrusion and coating applications.
PVDC homopolymer has melting point of 198-205°C and decomposes at around
210°C, making it difficult to process, while copolymers of PVDC have lower Tm of about 140-175°C, making melt processing feasible. However, because of narrow range of feasible processing temperatures for PVDC, its coextrusion with polymers that require high processing temperatures such as nylon 6 (260-290°C) and PET
(280-310°C) and others becomes difficult.
Strengths:
Excellent transparency, outstanding chemical resistance, Excellent barrier to gas, high fats, vapour, odours, oils and greases which extend the shelf life and conservation of foods, FDA compliant, good sealability, easily printable, Suitable for transparent applications, outstanding heat sealing properties help materials such as paper, cellophane and other plastics.
Limitations:
Toxicity of its combustion smoke, Poor UV resistance
Applications:
Films for food packaging of confectionary, dehydrated foods, dairy products, sausages, meat, smoked fish, and dried products such as herbs, spices tea and coffee, Pharmaceutical blister packaging, Films for thermal insulation, sensitive electronics.