Wisdom For Polyethylene vol.1
1. About 4 kinds of polyethylene
2023-12-21
(1) High-pressure low-density polyethylene (LDPE)
It is the most standard polyethylene and is commonly referred to as a plastic bag material.
It is clear, flexible, and has excellent tear strength and tensile strength, and is widely used for applications ranging from food packaging to drum liner bags.
It is clear, flexible, and has excellent tear strength and tensile strength, and is widely used for applications ranging from food packaging to drum liner bags.
(2) Linear short-chain branched polyethylene (LLDPE)
This polyethylene is difficult to distinguish from LDPE above. Even our expert operators have trouble identifying them.
IR analysis or differential scanning calorimetry (DSC) is necessary for identification. However, the manufacturing process at the polyethylene resin stage differs from that of high-pressure low-density polyethylene (LDPE).
As the polymerization process of ethylene is ionic polymerization, we have determined that some properties are close to those of medium- to low-pressure high-density polyethylene (HDPE). This is because it is designed to have many short molecular chains by copolymerizing small amounts of C-4LL (butene-1), C-6LL (hexene-1), and C-8LL (octene-1) as comonomers, depending on the type of hydrocarbon during polymerization, in order to replicate the properties of high-pressure low-density polyethylene (LDPE).
Common LLDPE is mostly of the C-4LL type. LLDPE has historically been a newer polyethylene with better sealing performance and physical strength than LDPE.
IR analysis or differential scanning calorimetry (DSC) is necessary for identification. However, the manufacturing process at the polyethylene resin stage differs from that of high-pressure low-density polyethylene (LDPE).
As the polymerization process of ethylene is ionic polymerization, we have determined that some properties are close to those of medium- to low-pressure high-density polyethylene (HDPE). This is because it is designed to have many short molecular chains by copolymerizing small amounts of C-4LL (butene-1), C-6LL (hexene-1), and C-8LL (octene-1) as comonomers, depending on the type of hydrocarbon during polymerization, in order to replicate the properties of high-pressure low-density polyethylene (LDPE).
Common LLDPE is mostly of the C-4LL type. LLDPE has historically been a newer polyethylene with better sealing performance and physical strength than LDPE.
(3) Medium- to low-pressure high-density polyethylene (HDPE)
A typical application is supermarket shopping bags. These bags are extremely thin, ranging from 15 μm to 25 μm.
They are made with an opalescent (titania) colorant, but even without colorant, they are stronger than LDPE and therefore used as ultra-thin films (10 μm to 30 μm).
Also, when the thickness is 50 μm or 100 μm, it is used only for special applications because it lacks flexibility and smoothness.
Tensile strength is excellent compared to LDPE, but it has strong longitudinal (Y-axis) orientation and weak tear strength. Once a cut is made in the film, it tears easily.
They are made with an opalescent (titania) colorant, but even without colorant, they are stronger than LDPE and therefore used as ultra-thin films (10 μm to 30 μm).
Also, when the thickness is 50 μm or 100 μm, it is used only for special applications because it lacks flexibility and smoothness.
Tensile strength is excellent compared to LDPE, but it has strong longitudinal (Y-axis) orientation and weak tear strength. Once a cut is made in the film, it tears easily.
(4) Metallocene-catalyzed linear short-chain branched polyethylene (LLDPE)
This is a type of LLDPE that has recently emerged and is polymerized with a metallocene catalyst.
It has a much narrower molecular weight distribution compared to conventional catalysts (Ziegler–Natta catalysts) and a uniform distribution of comonomers.
Therefore, it is a polyethylene with excellent tearing, tensile, adhesion, and pinhole resistance properties.
On the other hand, when we measured the tensile strength, the film was so strong that the machine reached its maximum load without breaking.
Because its mechanical strength is high, it allows for thickness reduction (gauge down), which means it can be considered an environmentally friendly material for the future.
It has a much narrower molecular weight distribution compared to conventional catalysts (Ziegler–Natta catalysts) and a uniform distribution of comonomers.
Therefore, it is a polyethylene with excellent tearing, tensile, adhesion, and pinhole resistance properties.
On the other hand, when we measured the tensile strength, the film was so strong that the machine reached its maximum load without breaking.
Because its mechanical strength is high, it allows for thickness reduction (gauge down), which means it can be considered an environmentally friendly material for the future.
Figure 1: Major Types of Polyethylene
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2. List of Polyethylene Analysis Methods