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HDPE vs. LDPE - Differences and Similarities in Plastic Production and Recycling
HDPE vs. LDPE - Differences and Similarities in Plastic Production and Recycling
Why do producers choose polyethylene (PE) to manufacture plastic products over other polymers? Over the years, it has become a common type of plastic due to its several advantages in the market. For instance, it has a lower cost than other polymers, is highly resistant to electricity and chemicals, and has valuable properties such as being moldable, flexible, and impact-resistant, making it efficient in every plastic production process.
PE is divided into different types or branches according to their molecular and structural differences. Each type achieves distinct application requirements. In this article, we will briefly explain the differences and similarities between the two main types of PE, high-density polyethylene (HDPE) and low-density polyethylene (LDPE), alongside some suggestions on recommended applications for each.
HDPE - Strength and Resistance
HDPE is a thermoplastic polymer used to produce durable plastic parts and products. Its molecular structure has little branching, meaning it has excellent resistance and hardness while being lightweight. Its toughness is not only in its physical properties but also in its molecules, enabling it to have a high melting point that helps this material to keep its original form until very high and low temperatures. All these properties have made HDPE one of the most popular plastic materials for different applications, which we will discuss in this article.
When using HDPE to produce plastic film, it is easy for producers to commercialize their final products thanks to its properties. HDPE allows producers to easily print their company’s logo or product information on top of the plastic film, increasing their product’s value while creating a stronger position in the market.
Overview of HDPE’s Properties
| Properties | Description |
|---|---|
|
Density |
0.93 – 0.97 g/cm3 |
|
Melting Point |
Between 120°C to 130°C |
|
Flexibility |
More rigid and tougher due to its linear structure |
|
Appearance |
Opaque and translucent (depending on its thickness) |
LDPE - The Flexible Plastic
LDPE is a thermoplastic polymer mostly known for being lightweight and flexible thanks to its low density, just like its name describes. This last property is the one that makes LDPE different from HDPE. While high-density polyethylene molecules hardly have any branches, low-density polyethylene is made up of a highly branched structure, giving it a semi-crystalline and low-density structure.
In contrast with HDPE, known for being rigid and resistant, LDPE is more malleable than high-density polyethylene, hence its popularity in plastic bag production. LDPE is also characterized as having a translucent and transparent appearance, although this might highly depend on its thickness. Its high resistance to humidity, chemicals, and electricity expands the innumerable ways LDPE can be valuable in plastic production.
Overview of LDPE’s Properties
| Properties | Description |
|---|---|
|
Density |
0.910 – 0.940 g/cm3 |
|
Melting Point |
Between 106°C to 115°C |
|
Flexibility |
More flexible due to its branched structure |
|
Appearance |
Translucent and transparent (depending on its thickness) |
Production and Applications
Both LDPE and HDPE are used for blown film extrusion. In the plastic film industry, LDPE and HDPE are sometimes suitable substitutes for each other, but this strongly depends on the producer’s objectives. Some questions like “How will the plastic film be used?” and “How flexible should it be?” are examples of the matters a producer has to keep in mind before starting a plastic film production.
Plastic film producers may decide which material to use for production according to their application requirements since they offer different advantages.
HDPE Applications
As we have mentioned earlier, HDPE is more resistant than LDPE. This is why plastic producers might prioritize applying HDPE when producing rigid materials in different manufacturing processes such as injection molding, blow molding, and 3D printing. HDPE is widely applied in the manufacturing of plastic containers and bottles, as well as in the production of irrigation pipes, toys, playground equipment, and outdoor furniture such as chairs and tables.
HDPE is the preferred choice for plastic film applications that require high resistance to punctures or tears and to be able to pack heavy items within it. Some HDPE applications in the plastic film market include:
- Heavy-duty bags
- T-shirt bags
- Construction film
- Courier bags (shipping envelopes)
Most of these applications involve two or three plastic film layers, mostly known as co-extrusion. POLYSTAR offers AB and ABA co-extrusion blown film machines, which consist of 2 extruders to produce plastic films with two layers (AB) and three layers (ABA). In the following pictures, you may find a brief comparison between both plastic film layer structures.
-
__24C129pJAq.png "Layer structure of an AB blown film machine")
(Layer structure of an AB blown film machine)
-
__24C12KoXsW.png "Layer structure of an ABA blown film machine")
(Layer structure of an ABA blown film machine)
LDPE Applications
LDPE, just like HDPE, is used to manufacture many different plastic products. Its appearance and flexibility open its opportunities since it finds its way into the plastic market to accomplish many purposes, such as plastic computer components, bendable pipes, medical and laboratory sterilized equipment, and squeezable containers. Even though these products might sound different from one another, the truth is that they all share similar properties, such as flexibility, transparency, moisture, and chemical resistance.
LDPE plastic films also share these same properties. Producers who wish to bring new, resistant, flexible, and transparent products to the market tend to choose LDPE over HDPE. Even though LDPE and HDPE may be used to produce the same or similar plastic products, LDPE dominates the plastic film and packaging market to protect other products. LDPE has a low heat resistance and melting point, making it an excellent material for heat-sealing packaging applications. It is suitable for the following plastic film applications:
POLYSTAR’s cost-effective monolayer blown-film machines Star-X and Duo-X are the perfect choice for manufacturing these products. These machines allow producers to achieve higher production efficiency while having the opportunity to cover the most demanded film sizes in the market (from 200mm up to 2000mm, depending on the model). Additionally, we offer customization options and optional devices to all our blown film machines to help our customers achieve the requirements and objectives they are looking for.
Recycling HDPE and LDPE - Are They Different?
Each plastic material has its different properties. You may identify a product’s material according to its recycling code written on its label. If you are familiar with these codes, you might know that HDPE and LDPE are classified under different numbers, as shown in the picture above. They share the same recycling process, for they are both thermoplastics. Nevertheless, recyclers must be aware when recycling low-density polyethylene products due to its stickiness and low melting point.
POLYSTAR offers the most optimal solution for recycling these two materials in the same machine! Our recycling machines process several HDPE and LDPE post-industrial waste. For instance, POLYSTAR Repro Flex’s cutter compactor is suitable for recycling plastic film, film scraps, and garbage bags, among other materials. If you want to recycle hard plastic bottles, plastic lumps, or film rolls, our shredder-integrated recycling machine, Repro-One, is the adequate solution! Additionally, if you have any HDPE or LDPE post-consumer waste, Repro-Flex Plus is the machine you are looking for!
Conclusion
(POLYSTAR provides simple recycling solutions)
Polyethylene can be classified into two main types according to their molecular structure: High-Density polyethylene and Low-density polyethylene.
Even though their applications might be somewhat similar, the reasons why a producer might choose one over the other will strongly depend on the product’s purposes. For instance, if a producer is looking for a much more flexible and translucent material suitable for packaging, then LDPE would be recommended for his production. On the other hand, if a producer wants a more rigid and resistant product, he might consider HDPE rather than LDPE.
HDPE and LDPE are labeled under different recycling codes, but their recycling process is very similar because they are both thermoplastics. For this reason, some recyclers might choose to recycle them separately. However, POLYSTAR offers you the most efficient and cost-effective recycling machines!
If you wish to know more about HDPE and LDPE plastic film production or recycling, contact POLYSTAR’s experienced sales team! We are here to provide any information and advice regarding your needs and requirements.