What Makes High Density Polyethylene Essential in Chemistry?
Whole world is under the threat of novel coronavirus or COVID-19. Governments and individuals are taking many measures to protect the nation and themselves, respectively. Even during this time of corona crisis, doctors are doing their duty diligently. You must have seen doctors wearing a special disposable suit during the treatment of a corona patient. You will be amazed to know that high density polyethylene or HDPE is one of the key ingredients of those special disposable suits. Not only this, if you look around, you will find at least five items composed of high density polyethylene or HDPE. Therefore, it becomes necessary for you to know about HDPE.
What is High Density Polyethylene?
High density polyethylene is a thermoplastic polymer whose monomer unit is ethylene. Ethylene or ethene (IUPAC name) is a hydrocarbon with the formula C2H4. High density polyethylene is also called PEHD (polyethylene high density), alkathene or polythene.
If any plastic material has a RIC (Resin Identification Code) - 2 written on it, then it means that plastic material is composed of HDPE. As RIC -2 stands for HDPE. High density polyethylene was discovered by Karl Ziegler of the Kaiser Wilhelm Institute in 1953. Karl Ziegler received the Nobel Prize for Chemistry in 1963. Soon, HDPE became the key raw ingredient for producing many materials. During World War -II, it was used in many vital military operations as critical insulating material, underwater cable coating etc. This made HDPE a very important resource during the WW – II. Due to its versatile uses, HDPE is still one of the largest volume polymers produced in the world. It still accounts over 34% of the global plastic market.
Production of High - Density Polyethylene
HDPE is generally produced by gas phase polymerization of ethylene. Under controlled conditions ‘cracking’ (A process of applying intense heat) is done by petroleum. Which leads to the production of ethylene gas. Now these ethylene molecules get polymerized and produce HDPE. After this HDPE goes through the process of separation and drying. It can also be produced by various catalytic processes such as Ziegler – Natta catalysis or Cr – silica catalysis.
What are the Properties of High - Density Polyethylene?
HDPE has numerous applications due to its unique properties. To understand its various uses in the industry, you need to know its properties first. Therefore, various properties of HDPE are listed below –
It can be molded again and again. Thus, it is a thermoplastic polymer.
It is well known for its high, strength to density ratio.
Its density is 940 kg/m3.
It has little branching in its structure.
It has stronger intermolecular forces and tensile strength than low density polyethylene.
Its melting point is 130.8℃.
Its temperature of crystallization is 111.9℃.
It is harder and more opaque than low density polyethylene.
It is resistant to many different solvents.
Its specific heat capacity is 1330 – 2400 J/kg – K
Its latent heat of fusion is 178.6 kJ/kg.
It shows chemical and electrical resistance.
It is able to resist lower temperatures than LDPE.
It is a strong and lightweight plastic polymer.
What are the Uses of High - Density Polyethylene?
All of the above stated desirable properties of high – density polyethylene make it suitable for numerous applications. Few applications of HDPE are listed below –
It is used to make disposable suits for various purposes.
It is applicable to make pipes which can be used for potable water and sewage water as well.
Its fibers can be spun into a rope.
It is used as house wrap to protect buildings.
Plastic envelopes which are generally used in mailing are made up of HDPE.
It is used in making chairs, stools, ice cube trays, bottles etc.
Bottle crates are composed of HDPE.
Many types of toys and playground equipment are made up of HDPE.
It is used to make milk jugs, jerrycans as it resists corrosion.
It is used in doormats.
It is a strong and long - lasting material so it is used in construction as well.
High density polyethylene is used in cutting boards.
High density polyethylene film is used in food packaging.
HDPE is used in wood plastic composites.
It is used in plastic surgery especially facial and rhinoplasty.
It is used in 3 – D printing filaments.
Food and beverage containers are composed of high density polyethylene.
HDPE is easily recyclable which makes it even more useful in today’s world. Recycled high – density polyethylene is almost as versatile as virgin or recently produced HDPE.
High – density polyethylene and low - density polyethylene, both are thermoplastic polymers of ethylene monomer unit. But differ in their various properties and have different uses.
Difference Between High – Density Polyethylene and Low – Density Polyethylene
This ends our coverage on the topic “High Density Polyethylene”. We hope you enjoyed learning and were able to grasp the concepts. We hope after reading this article you will be able to solve problems based on the topic. If you are looking for solutions to NCERT Textbook problems based on this topic, then log on to Vedantu website or download Vedantu Learning App. By doing so, you will be able to access free PDFs of NCERT Solutions as well as Revision notes, Mock Tests and much more.
FAQs on High Density Polyethylene Explained: Properties, Production & Uses
1. What is High-Density Polyethylene (HDPE)?
High-Density Polyethylene, commonly known as HDPE, is a thermoplastic polymer produced from the monomer ethylene. It is characterised by its linear molecular structure with minimal branching. This unbranched structure allows the polymer chains to pack closely together, which is the primary reason for its high density and strength. Its chemical formula is represented as (C₂H₄)n.
2. What are the key properties of High-Density Polyethylene (HDPE)?
HDPE is valued for its unique combination of properties, making it suitable for a wide range of applications. Key properties include:
- High Density: It has a density ranging from 0.941 to 0.965 g/cm³, making it stronger and more rigid than other forms of polyethylene.
- Excellent Chemical Resistance: It is highly resistant to many solvents, acids, and bases, which is why it's used for chemical containers.
- High Tensile Strength: It possesses a high strength-to-density ratio, making it durable and impact-resistant.
- High Melting Point: HDPE has a melting point of approximately 130-137 °C, allowing it to withstand higher temperatures than LDPE.
- Opacity: It is naturally milky white or opaque and has low permeability to gases and moisture.
3. How is HDPE produced on an industrial scale?
HDPE is produced through the addition polymerisation of ethylene (ethene) monomers. The process typically occurs at relatively low pressures (6–7 atm) and temperatures (60–70°C) in the presence of a specialised catalyst. The most common catalysts used are Ziegler-Natta catalysts (e.g., a mixture of titanium tetrachloride and triethylaluminium) or Phillips catalysts. These catalysts are crucial for directing the polymerisation to form long, linear chains with minimal branching, which defines the structure of HDPE.
4. What are some common uses and examples of HDPE in daily life?
Due to its strength, durability, and chemical resistance, HDPE is used in numerous everyday products. Common examples include:
- Packaging: Milk jugs, juice bottles, bottle caps, and containers for detergents, shampoos, and motor oil.
- Pipes and Tubing: Corrosion-resistant pipes for water mains, natural gas distribution, and agricultural irrigation.
- Household Goods: Cutting boards, plastic buckets, toys, and storage containers.
- Industrial Applications: Fuel tanks for vehicles, chemical-resistant lining, and plastic lumber.
5. How does the linear structure of HDPE give it a higher density and strength compared to LDPE?
The key difference lies in the molecular arrangement. HDPE has a linear structure with very few branches, allowing its long polymer chains to pack together tightly and in an orderly, crystalline fashion. This close packing increases the effectiveness of intermolecular forces (van der Waals forces) between the chains, resulting in a material that is denser, stronger, and more rigid. In contrast, Low-Density Polyethylene (LDPE) has a highly branched structure that prevents the chains from packing closely, leading to a less dense, more flexible material.
6. Why is HDPE considered a safe and suitable material for food and beverage containers?
HDPE is considered food-grade and safe for containers due to its high chemical stability and inertness. Its robust, non-porous surface is resistant to mould, mildew, and rotting. Most importantly, it has a very low risk of leaching, meaning it does not transfer harmful substances into the food or liquids it holds. This stability is maintained even when in contact with acidic or alkaline foods, making it a reliable choice for packaging products like milk, juice, and vinegar.
7. What makes HDPE a highly recyclable polymer, and how is it identified for recycling?
HDPE is highly recyclable because it is a thermoplastic. This means it can be melted down and remoulded into new products multiple times without significant degradation of its structural integrity. For identification in waste streams, HDPE products are marked with the Resin Identification Code (RIC) number 2, usually found inside a triangle of chasing arrows. This code helps recycling facilities sort it correctly, where it is often reprocessed into items like non-food bottles, plastic lumber, pipes, and outdoor furniture.
