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Poly Ethylene

Chemtrade Marketing, based in South Africa are import and export suppliers of PE.

The two most common types of polyethylene compounds are high density polyethylene (HDPE) and low density polyethylene (LDPE). Both compounds have very different physical properties. For example, while LDPE compounds have a melting point of 115º C, HDPE compounds melt at 135º C.

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WHAT IS POLYETHYLENE RESIN?

For the plastic packaging industry, polyethylene resin is commonly used. It is a type of thermoplastic used to manufacture bags, tubing, sheeting, stretch and shrink films.

It is also a flexible composite. Polyethylene, referred to as PE, is usually a mixture of polymers and ethylene. It has mechanical, thermal, chemical, electrical, and optical properties.

It absorbs almost no water, burns slowly and cannot be imprinted without pretreatment.

PE can become brittle when exposed to sunlight. To avoid this a UV stabilizer must be added.


Plastic containers, plastic bottles, plastic bags, and plastic toys; everywhere we look, we see plastic items.

Did you know that in 2012 alone, we managed to generate more than 32 million tons of plastic waste? Now, that is what most people would call a lot of plastic! Although plastic is composed of several different organic molecules, one in particular is called polyethylene. Polyethylene is an organic polymer made of several monomer subunits, and it is one popular compound. Before we address its popularity in industry, let's talk more about its structure.
 
WHY DOES POLY GET A BAD RAP?
It was synthesized by a chemist who prepared it by accident in 1898. Diazomethane was being investigated when a white waxy substance was created. This white waxy substance was again produced by applying extremely high pressure to a mixture of ethylene and benzaldehyde.
During the reaction, trace oxygen contamination was an issue, making it difficult to reproduce. Then in 1939 another chemist reproduced a high-pressure synthesis for polyethylene that became the basis for LDPE production. All this testing has led to a wide variety of many resins available including high performance resins that started in 2005.
High Density Polyethylene (HDPE)
High Density Polyethylene (HDPE) is a cost-effective thermoplastic with linear structure and no or low degree of branching. It is manufactured at low temperature (70-300°C) and pressure (10-80 bar) & derived from either:
• Modifying natural gas (a methane, ethane, propane mix) or
• The catalytic cracking of crude oil into gasoline 
HDPE is produced majorly using two techniques: Slurry Polymerization or Gas Phase Polymerization. 
High Density Polyethylene Molecular Structure
High density polyethylene is flexible, translucent/waxy, weather resistant, and displays toughness at very low temperatures. 
 
Properties of High Density Polyethylene
1. HDPE Melting point: 120-140°C
2. Density of HDPE: 0.93 to 0.97 g/cm3
3. High Density Polyethylene Chemical resistance:
    Excellent resistance to most solvents
    Very good resistance to alcohols, dilute acids and alkalis
    Moderate resistance to oils and greases
    Poor resistance to hydrocarbons (aliphatic, aromatic, halogenated)
4. Continuous temperature: -50°C to +60°C, Relatively stiff material with useful temperature capabilities
5. Higher tensile strength compared to other forms of polyethylene
6. Low cost polymer with good processability
7. Good low temperature resistance
8. Excellent electrical insulating properties
9. Very low water absorption
10. FDA compliant
Applications of High Density Polyethylene (HDPE)
Excellent combination of properties makes HDPE an ideal material in diverse applications across industries. It can be engineered according to the end use requirements.
Some of the major uses of high density polyethylene include:
1. Packaging Applications – High Density Polyethylene is used in several packaging applications including crates, trays, bottles for milk and fruit juices, caps for food packaging, jerry cans, drums, industrial bulk containers etc. In such applications HDPE provides the end product a reasonable impact strength.
2. Consumer Goods – Low cost and easy processability make HDPE a material of choice in several household/ consumer goods like garbage containers, housewares, ice boxes, toys etc.
3. Fibers and Textiles – Thanks to its high tensile strength, HDPE is widely used in ropes, fishing and sport nets, nets for agricultural use, Industrial and decorative fabrics, etc.
Other applications of HDPE include pipes and fittings (pipes for gas, water, sewage, drainage, sea outfalls, industrial application, cable protection, steel pipe coating, large inspection chambers and manholes for pipe sewage etc.) due to its excellent resistance to chemical and hydrolysis,  automotive – fuel tanks, wiring & cables – sheeting of energy, telecommunication cables. 
Low Density Polyethylene (LDPE)
Low Density Polyethylene (LDPE) is a semi-rigid and translucent polymer. Compared to HDPE, it has a higher degree of short and long side-chain branching. It is produced at high pressure (1000-3000 bar; 80-300°C) via free radical polymerization process.
The LDPE is composed of 4,000-40,000 carbon atoms, with many short branches. 
Two basic processes used for the production of low density polyethylene: stirred autoclave or tubular routes. The tubular reactor has been gaining preference over the autoclave route due to its higher ethylene conversion rates.
Low Density Polyethylene Structure
Properties of Low Density Polyethylene
1. LDPE Melting point: 105 to 115°C
2. Density of LDPE: 0.910–0.940 g/cm3
3. Chemical resistance of LDPE:  Good resistance to alcohols, dilute alkalis and acids and  Limited resistance to aliphatic and aromatic hydrocarbons, mineral oils, oxidizing agents and halogenated hydrocarbons .
4. Temperature resistance up to 80°C continuously and 95°C for shorter times.
5. Low cost polymer with good processability
6. High impact strength at low temperature, good weatherability
7. Excellent electrical insulating properties
8. Very low water absorption
9. FDA compliant
10. Transparent in thin film form
Applications of Low Density Polyethylene (LDPE)
Low Density Polyethylene (LDPE) uses majorly revolve around manufacturing containers, dispensing bottles, wash bottles, tubing, plastic bags for computer components, and various molded laboratory equipments. The most popular application of low density polyethylene is plastic bags. 
LDPE Applications
1. Packaging – Thanks to its low cost and good flexibility, LDPE is used in packaging industry for pharmaceutical and squeeze bottles, caps and closures, tamper evident, liners, trash bags, films for food packaging (frozen, dry goods, etc.), laminations etc.
2. Pipes and Fittings – Low Density Polyethylene is used to manufacture water pipes and hoses for the pipes and fittings industry due to Its plasticity and low water absorption.
Other applications include consumer goods - housewares, flexible toys, agricultural films, wiring & cables - sub-conductor insulators, cable jacketing.
Linear Low Density Polyethylene (LLDPE)
LLDPE is produced by polymerization of ethylene (or ethane monomer) with 1-butene and smaller amounts of 1-hexene and 1-octene, using Ziegler-Natta or metallocene catalysts. It is structurally similar to LDPE. 
The structure of LLDPE has a linear backbone with short, uniform branches (unlike longer branches of LDPE). These short branches are able slide against each other upon elongation without becoming entangled like LPDE.
In the present day scenario, Linear low density polyethylene (LLDPE) has been quite successful in replacing Low Density Polyethylene.
 
Properties of LLDPE
• Very flexible with high impact strength
• Translucent and natural milky color
• Excellent for mild and strong buffers, good chemical resistance
• Good water vapor and alcohol barrier properties
• Good stress crack and impact resistance
Applications of LLDPE: Suitable for a variety of film application such as general purpose film, stretch film, garment packaging, agricultural film, etc.
  
Benefits of Polyethylene Films 
• PE films burn to carbon dioxide and water with no residue. There are no toxic fumes or gases and no cinders produced in this process
• PE films contain no plasticizers and no heavy metals. They are physiologically harmless
• No odor pollution or wastewater are produced in the manufacture of PE films
How is PE Made?
Polyethylene is made by addition or radical polymerization of ethylene (olefin) monomers. 
Ziegler-Natta and Metallocene catalysts are used to carry out polymerization of polyethylene. 
How to Process PE Plastic?
Various forms of Polyethylene can be used in processes like injection molding, blow molding, extrusion and various film creation processes such as calendaring or blown film extrusion.
• High density polyethylene can be easily processed by injection molding, extrusion (tubes, blow and cast films, cables, etc.), blow molding and rotomolding. Being and ideal material for injection molding process, it is majorly used for batch and continuous production.
• The most common processing technique used for Low Density Polyethylene is extrusion (tubes, blow and cast films, cables...). Low Density Polyethylene can be processed by injection molding or rotomolding.

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