What is LDPE?
Low-density Polyethylene or LDPE belongs to the Polyethylene branch of thermoplastics. It is soft, lightweight, tough, and flexible in its nature. The thermoplastic material is also known for having low-temperature compatibility and good corrosion resistance. The polymer also boasts good chemical properties and impact resistance which makes it easy to fabricate or process. It has a melting point of 110°C.
Their names themselves can figure out the major difference between LDPE and HDPE. HDPE has a higher density than LDPE, which means that the former has more mass than its volume.
It is more branched out in its structure rather than being in perfect rows, and that is the reason for its low-density/volume, thus is often used in applications where structural strength and stiffness are an important requirement.
How is LDPE Made?
Like other thermoplastics, the polyethylene monomer is derived from using a process called polymerization where small molecules called “fractions” are removed, and some of them are transformed into desired thermoplastic.
Presently, two methods are widely used for LDPE production – stirred autoclave or tubular routes. However, the later methods are gaining popularity currently because of their high ethylene conversion ratio.
From that, LDPE plastic is extracted from gaseous ethylene under very high pressure and high temperatures(up to 350 °C) with the catalyst oxide initiators in the presence. It is the first polyethylene to be priced, even before HDPE.
The process creates a polymer structure with both long and short branches, the polymer with shorter branches in Low-density polyethylene.
LDPE Properties –
Low-Density polyethylene comes with a wide range of properties. There are several differences in high-density polyethylene and low-density polyethylene properties, but some similar applications. Below are the main attributes:
- Great resistance to alcohols, acids, and dilute alkalis
- Fantastic electrical insulating properties
- Meager water absorption
- High impact strength at low temperature
- Decent weatherability
- Good processability as compared to price (inexpensive)
- Density: 0.910–0.940 g/cm3
- Meager resistance to mineral oils, halogenated and aromatic hydrocarbons, and oxidizing agents
- Normal temperature resistance – 80°C continuously and 95°C for shorter times.
Comparison: Low-density polyethylene and High-Density Polyethylene Properties:
|Flexural Modulus||0.245 – 0.335 GPa||
0.75 – 1.575 GPa`
|Elongation of Break||200 – 600 %||500 – 700 %|
|Elongation at Yield||13 – 17%||15 %|
|Hardness Rockwell M||1||1|
|Hardness Shore D||40 – 50||60 – 70|
|Stiffness||0.245 – 0.335 GPa||
0.75 – 1.575 GPa
|Strength at break||10 – 20 MPa||30 – 40 MPa|
|Strength at Yield||10 – 15 MPa||25 – 30 MPa|
|Toughness at Room Temperature||999 J/m||20 – 220 J/m|
|Aromatic Hydrocabrons @20°C||Non-satisfactory||
|Aromatic Hydrocarbons in hot conditions||Non-satisfactory||Non-satisfactory|
|Ammonium hydroxide @ diluted, 20°C||Good||Good|
|Ammonium hydroxide @ diluted, 60°C||Good||Good|
|Chlorinated solvents @ 20°C||Non-satisfactory||
|Ethanol @ 96%, 20°C||Non-satisfactory||Good|
|Kerosene @ 20°C||Non-satisfactory||Good|
|Methanol @ 100%, 20°C||Good||Good|
|Dielectric Strength||16 – 28 kV/mm||17 – 24 kV/mm|
|Dissipation Factor||3 – 4 x 10-4||3 – 20 x 10-4|
|Arc Resistance||130 – 160 sec||100 – 180 sec|
|Volume Resistivity||16 – 18 x 1015 Ohm.cm||
16 – 18 x 1015 Ohm.cm
|Gloss||35 – 97 %||5 – 120 %|
|Haze||1.3 – 27.5 %||6 %|
|Density||0.917 – 0.94 g/cm3||
0.94 – 0.97 g/cm3
|Glass Transition Temperature||-110°C||-110°C|
- The processing attribute at low temperatures makes LDPE’s applications limited as they can’t be processed at higher temperatures.
- High permeability towards gases, especially carbon dioxide
- Meager UV resistance
- Susceptible to stress cracking
- Highly flammable
Lightweight plastics are extremely useful, let alone LDPE plastics. It is mainly used for pricing wash bottles, shopping bags, containers, dispensing bottles, tubings, computer components, etc. Here are some of the major applications:
- Packaging Applications: Pertaining to LDPE material’s inexpensiveness and good flexibility, it is extensively used in packaging applications for both consumer and industrial divisions – lunch boxes, squeeze bottles, pharmaceutical packaging, liners, trash bags, liners, laminations, food packaging films, etc.
- Consumer Goods: Agriculture films used for packaging and storing all sorts of agriculture products, flexible and lightweight toys, housewares, etc.
- Pipes & Fittings: Low water absorption and lightweight properties make LDPE the go-to thermoplastic for water-related applications. Example – water pipes, hoses, etc.
- Wires & Cables: Good electrical properties make low-density polyethylene a prime choice for manufacturing cable jacketing & coatings and sub-consumer insulators.
Is LDPE Toxic?
The plastic recycling code of LDPE is #4. It does not contain BPA but is susceptible to leaching estrogenic chemicals. It is recyclable plastic. However, recycling is not as common and easy compared to other thermoplastics as you read earlier in the applications that it 100% safe for human consumption.
Additionally, it’s not compostable, and a low-density polyethylene particle may take thousands of years to degrade.
Processing of LDPE –
- The crystallization tendency holds significant importance in the process.
- Specifically, for injection molding, the speed of molding material should be higher, and injection pressure should be lower.
- Processing temperature – 160° to 220°C
- High shrinkage rate is susceptible
The Future of LDPE Plastic –
According to a study conducted by Mordor Intelligence, the global LDPE market reached a capacity of 22 million tons in 2020, and it is going to exhibit a CAGR of 3% from 2021-2026.
The numbers will obviously be affected because of the Covid-19 pandemic because of a sharp drop in revenues for instruction and packaging industries, which are the largest LDPE consumers. But, there is a piece of good news, the e-commerce and healthcare sectors have shown impressive even during the pandemic.
Asia-pacific was the largest LDPE plastic processing and consuming region with almost 30% market share. Countries like China, Japan, and India are witnessing rapid growth in the packaging and construction sectors(Even being in the midst of a pandemic).
As of writing this piece, a Covid-19 vaccine has been discovered by scientists, and people have started to come out, go to work, and trying to make things normal, so the severe damage caused by the pandemic might be short-lived.
With the rapid economic recovery in the Asia-Pacific region with growth in packaging and construction verticals, the LDPE market momentum will be stable until the end of the forecast period.
1. Can I mix HDPE and LDPE?
Ans. Unlike other polymers, HDPE and LDEP are miscible. They can be recycled together. However, their structural design is drastically different from each other, so it’s better to separate them.
2. Can you weld LDPE to HDPE?
Ans. The essential rule about polyethylene is that you can weld low to high but not high to low. Meaning an LDPE rod can easily be welded inside an HDPE sheet, but not vice versa. The reason s very simple The higher the density, the more difficult it is to break down the components to weld. If the parts cannot be broken down at the same rate, they cannot weld together correctly.
3. What are the 7 types of plastics?
Ans. The Basics On 7 Common Types of Plastics are:
1) Polyethylene Terephthalate (PET or PETE)
2) High-Density Polyethylene (HDPE)
3) Polyvinyl Chloride (PVC or Vinyl)
4) Low-Density Polyethylene (LDPE)
5) Polypropylene (PP)
6) Polystyrene (PS or Styrofoam)
4. What to Choose LDPE or PET bottles?
Ans. Hands down, PET is the best material for manufacturing all types of bottles, but sometimes using LDPE bottles makes more sense. LDPE is a more squeezable material making dispensing sauces, honey, creams, condiments, and syrups. It is also better at withstanding colder temperatures than PET.
5. What is the difference between LDPE and LLDPE?
Ans. LDPE is a homopolymer constituted by ethylene monomers. LLDPE is a copolymer of ethylene and another longer olefin integrated to improve properties such as tensile strength to harsh environments.
Suggested Read –
- When Was Plastic Invented? | The History of Plastics
- How is Plastic made? A Simple and Detailed Explanation.
- 7 Best UV Resistant Plastics For Outdoor Applications
- 6 Best Plastic Molding Techniques | A Complete Analysis
- Top 10 Plastic Bottle Manufacturers in USA
- Top 10 Plastic Injection Molding Companies In United States
- What is Anionic Polymerization? An In-Depth Analysis
- Step Growth vs Chain Growth Polymerization
Final Thoughts –
Finally, I would like to say that LDPE is a very useful thermoplastic that can help you cut costs and boost your profits. Kindly share your reviews and something you feel I’ve missed in the post in the comment section.