HDPE or high-density polyethylene is a colourless and odourless polyethylene thermoplastic. Known for its high strength-to-density ratio, HDPE is used as a major raw material in the manufacturing and processing industry. From safe food storage containers to high quality fuel tankers, there is a huge demand for HDPE in a wide range of applications.

HDPE is made from petroleum or semi-crystalline polyethylene products using a high intense process known as cracking. It involves production of ethylene gas which under controlled conditions are converted into a strong, highly resistant polymer. The resulting polymer is then processed through minute holes and gradually cut down to form what is called HDPE granules. There are various grades of HDPE available in the market and these are categorised based on their properties and industry specific requirements. Some of the commonly used HDPE grades include Polystone P5300, B5500, E5201, and F5400.

High-density polyethylene enjoys a position above conventional raw materials like steel, glass or even PVC tubes as it is considered to be safer and cost-efficient. Studies have shown that the recycling of an HDPE product involves less energy loss and cost than traditional methods of recycling practiced in the industry. Some of the key advantages of HDPE includes:

• Highly flexible and durable
• High strength-to-density ratio
• High temperature resistance
• Chemical and corrosion resistance
• No leak rate
• Recyclable and eco-friendly

Low density polyethylene is a thermoplastic made from the monomer called ethylene. It was first produced by Imperial Chemical Industries (ICI) in the 1930s and the process employed involves free radical polymerisation. A major concern with LDPE is the fact that only 5.7% of the material is actually recyclable, yet, it continues to be used widely as a common plastic due to its favourable properties.

LDPE varies generally by the level of flexibility, which differs according to the production process administered. The high density LDPE is the most rigid.

LDPE is a relatively stable plastic which appears semi-rigid and is known for its robustness, making it a high utility plastic. It is heat resistant and can withstand temperatures up to 85 degrees Celsius. Also, being chemically inert, it is highly resistant to a variety of alcohols, acids and bases. LDPE has a density range of 0.910–0.940 g/cm3. Aside from its toughness, it is also flexible and reacts only to strong oxidising agents and solvents.

• LDPE goes into the manufacturing of a large number of LDPE products:
• Packaging including food products – meat, bakery items, etc.
• Wrapping for towels and household utilities
• Packaging for liquid edibles such as milk cartons
• Storage – bags, trays, etc.
• In agriculture for greenhouse construction
• For insulation
• Industrial – chemical tank linings, pipes, etc.
• Electronics – hard disks, optical disks, etc.

Linear Low density polyethylene is a copolymer ethylene and an olefin such as 1-butene/1-hexene/4-methyl-1-pentene and 1-octene. The addition of the olefin in the polymerisation process adds strength and impact resistance to the end LLDPE product. This process is called free radical polymerisation. LLDPE resins occur in the form of odourless white granules. These can then be processed by extrusion, injection moulding and/or blow and cast film.

In recent times due to easy processing and its favourable properties, much of the LDPE market has moved to LLDPE.  However, LLDPE being inert to degradation, is considered an environmental hazard, even though it is often recycled into things such as lumber, floor tiles, trash bin and liners, landscaping ties, shipping envelopes, etc.

Both LDPE and LLDPE have more or less the same density, however LLDPE displays better impact and crack resistance than LDPE. Because of the linear linkages, LLDPE also exhibits a better appearance with enhanced gloss. However in its natural form, it has a poorer clarity or transparency. This allows for the production of thinner sheets without affecting the strength and resistant properties of the product.

LLDPE is very flexible, has higher tensile strength and under stress, it can elongate.  In addition, LLDPE is highly resistant to chemicals, can withstand punctures and has good electrical properties. However, with a lower capacity for heat sealing, it is not as easy to process as LDPE.  

Sometimes to make the most of appearance and strength, blends of LDPE and LLDPE granules are processed to make the finished product.

Polypropylene is a thermoplastic polymer resin of the composition of C3H6. It is a commonly used household and industrial plastic which is available in fiber-form or hardened plastic form. The versatility of forms and applications has made it one of the most widely used plastics today. The fact that it is recyclable and is being recycled in battery cases, paint cans, home storage, etc. makes it very popular.

Polypropylene due to its flexibility, occurs in two forms:

• Fiber
• Plastic

Polypropylene has favourable chemical characteristics as compared to other plastics, with a high melting point of 160 degrees Celsius, which makes it useful for long-term durability of plastic food containers. It has zero levels of the toxic component – Bisphenol (BPA), which makes it ideal for food packaging. It is chemically very resistant.

• Some of the important physical features, include:
• Translucent
• Water resistant
• Easily customisable
• Though less sturdy than polyethylene, it is still damage-resistant
• Light-weight
• Very flexible
• Good fatigue resistance
• Heat resistant

Specifically due to its higher melting point, Polypropylene has gained greater popularity than Polyethylene. Polypropylene is highly versatile and can be customized to make different things. Manufacturers can also add dye and colour to it without degrading the quality of the plastic. Being lightweight, inexpensive and non-toxic, it is often used in things people need every day.

Poly Vinyl Chloride Resin or PVC Resin as it is popularly called, is a thermoplastic Resin which can be softened on reheating. A common term for this commodity polymer is Vinyl. Often available in the form of a powder, PVC granules are highly resistant to oxidisation and degradation caused by atmospheric reaction.  In its raw form, it appears as a white powdery solid.

The composition of PVC is such that 57 % is chlorine and 43% is carbon. Since the process of deriving PVC Resin granules is rarely dependent on petroleum, it is considered as one of the more renewable plastics.

According to its appearance and flexibility, PVC is categorised into the following two categories:

• Rigid PVC: Use in construction
• Flexible PVC: The granules are made softer by the addition of plasticisers

PVC Resin is manufactured by the polymerisation of the vinyl chloride monomer. According to the method of polymerisation.

PVC Resin granules are characterised into four categories:

• Suspension PVC: This method is highly cost effective and about 80% of PVC Resin is produced via this method
• Emulsion PVC: This process produces finer particles and the product is mostly used in the manufacturing of plastisols
• Bulk-Polymerized PVC: In this method, no emulsifiers or additives are used. This helps to generate the purest form of PVC
• Co-Polymer PVC: This process is used for adding special properties to PVC by polymerising the granules along with other co-monomers. Vinyl flooring sheets come under this category

Ethylene-Vinyl Acetate is a Commodity Polymer that is a copolymer of Ethylene and Vinyl Acetate. EVA copolymer is classified into three categories according to Vinyl Acetate content present. The first type is EVA containing low VA percentage. This category of Ethylene-Vinyl Acetate is used as a Thermoplastics Material. The second type of EVA consists of 4% to 30% of VA and it is used as a Thermoplastic Ethylene-Vinyl Acetate. The third category of Ethylene-Vinyl Acetate consists of more than 40% VA and it is used as Ethylene-Vinyl Acetate Rubber. The process of manufacturing Ethylene-Vinyl Acetate involves a method wherein Ethylene and Vinyl Acetate are continuously polymerised. This continuous polymerisation is performed in a Polymerising Vessel. 

Usage

Ethylene-Vinyl Acetate has extensive applications in Biomedical Engineering where it is used as a Drug Delivery device. EVA is also known as Expanded Rubber or Foam Rubber. It is used as padding for sports equipment like Ski Boots, Bicycle Saddles, Hockey Pads, Gloves, helmets, etc. The Photovoltaics Industry also uses Ethylene-Vinyl Acetate as an Encapsulation Material for Crystalline Silicon Solar Cells. Other common uses of EVA include in Footwear Components, Flexible Hoses, Automobile Bumpers, Toys and Athletic Goods, Moulded Automotive Parts, Flexible Packaging, Films, etc. The Food Industry also uses Ethylene-Vinyl Acetate for various food packaging applications like Seafood and Meat Packaging, Beverage and Food Packaging Design, Dry Food, and Snack Packaging, Dairy and Cheese Packaging, Plastic Closures for Beverages, Vacuum Packaging, Barrier Shrink Bags, Case Ready Meat Packaging, etc.