One of the most used thermoplastics globally is Polyethylene, and it is commonly used in various items such as plastic bags, soft drink bottles, and even water bottles. Polyethylene can also be segmented into many other smaller groups based on its structure, whereby each structure has its characteristics catered for use in certain situations.
The two most common types of Polyethylene include:
1. High-Density Polyethylene (HDPE)
HDPE Plastic Bags, also known as High-Density Polyethylene, are affordable thermoplastic polymers with a straight structure with little to no degree of branching. It is manufactured at low temperatures ranging from 70ºC to 300°C and pressures ranging from 10 to 80 bar. It is obtained through the catalytic cracking of crude oil into gasoline or modifying natural gases such as ethane, methane, or propane mix.
There are seven general types of plastic, each of which comprises a unique combination of resins. These various types are easily identified on the plastic containers marked by triangular arrows with numbers in the middle. Known as the number 2 plastic, HDPE is generally created by utilising two different techniques:
- Slurry Polymerisation – Polymerisation of monomers in the structure of dispersed monomer particles
- Gas-Phase Polymerisation – Polymerisation of monomers in the structure of a vaporised monomer, fluidised catalyst, and polymer particles in a fluidised bed reactor
HDPE Plastic Bags have a strong resistance feature in their plastic material, making them the preferred choice for packaging solutions such as plastic, garbage, laundry, grocery bags, and many more. Due to its extreme impact strength, it ensures that goods are protected on the inside as well. This allows HDPE Plastic Bags to be suitable for various industries rather than just one.
HDPE Plastic Bags key features consist of it being:
- Low-cost, lightweight, transparent & largely durable
- Resistant against alcohols, diluted acids, alkalis, grease & liquids such as water
- Highly flexible, making it malleable and easily moulded into various shapes and sizes
- Industrial-grade, FDA, NSF, and USDA-approved
They are also widely used in producing a variety of products like plastic wrap and film, flexible packaging material, grocery bags, and injection molded parts.
2. Low-Density Polyethylene (LDPE)
LDPE Plastic Bags, also known as Low-Density Polyethylene (LDPE), is a soft and flexible polymer. It has a lower density, strength, and temperature resistance than HDPE plastics.
The polybag structure features a higher degree of short and long side-chain branching, produced at a high pressure of 1000 to 3000 bar and a low temperature of 80ºC to 300°C. This manufacturing process is known as “Free Radical Polymerisation,” and it is a type of chain-growth polymerisation in which the polymer takes shape due to continuous additions of unsaturated monomer molecules to an active, free radical centre.
LDPE plastic bag is a suitable polymer with excellent processability. It has a high impact strength at low temperatures, as well as chemical resistance, weather resistance, excellent electrical insulator, low water absorption, meets FDA regulations, and is transparent in thin foil film.
LDPE Plastic Bags key features consist of it being:
- Lightweight, low-cost and weatherproof
- Largely flexible, making it malleable and easily moulded into various shapes & sizes
- Resistant against chemicals such as alcohols, dilute acids, and alkalis
- Protected against other elements including moisture, dust, dirt, oil, and grease
- An excellent electrical insulator
- FDA approved
Overall, LDPE Plastic Bags are segmented and ranked fourth among plastics. Its primary use is in film applications, and some everyday products include food plastic bags, shrink wrap, and stretch film. Due to their physical properties, LDPE Plastic Bags have exceptional resistance to chemicals such as alcohols, dilute alkalis, acids, and other elements containing moisture, dust, dirt, oil, and grease. Furthermore, it is FDA-approved, making it safe for contact with perishable food items.
There are also many other packaging solutions for food products. These include products such as desiccants, oxygen absorbers, and ethylene absorbers which can extend the shelf life of food products while preserving their freshness and quality.
HDPE vs. LDPE – Pros and Cons
Overall, both HDPE and LDPE Plastic Bags have beneficial overlapping characteristics, one of which they have in common is having high chemical resistance. However, both HDPE and LDPE Plastic Bags have pros and cons due to their distinct material properties, influencing their usefulness in various applications. To learn more about HDPE and LDPE Plastic Bags, click here!