Content1. What are high-density polyethylene bags?
1.1 What is high-density polyethylene (HDPE)?2. Low-density vs. high-density bags
2.1 The difference between high-density bags and low-density bags
2.2 Similarities between LDPE and HDPE
2.3 Advantages and disadvantages of HDPE & LDPE
2.4 Application of HDPE & LDPE3. How to buy high-density polyethylene bags?
What are high-density polyethylene bags?
Polyethylene is the raw material for making plastic bags. Obviously, the main component of polyethylene plastic is polyethylene. Its raw material ethylene mainly comes from petroleum cracking, which belongs to petrochemical products. Polyethylene plastic bags are mainly divided into linear low-density polyethylene plastic bags, low-density polyethylene plastic bags (LDPE), and high-density polyethylene bags.
HDPE plastic bags, also known as high-density polyethylene bags, are economical thermoplastic polymers. It has a linear structure with little to no degree of branching. They are manufactured at low temperatures of 70°C to 300°C and pressures of 10 to 80bar. They are obtained by catalytic cracking of crude oil into gasoline or by modifying natural gas, such as ethane, methane, or propane blends.
There are generally seven types of plastics, each consisting of a unique combination of resins. These different types are easily identified on plastic containers because of the triangular arrow mark with a number in the middle. HDPE, known as plastic No.2, is usually created by utilizing two different techniques
Slurry polymerization - Monomer polymerization in a dispersed monomer particle structure.
Gas-phase polymerization - Monomer polymerization in a fluidized bed reactor with a structure of vaporized monomers, fluidized catalysts, and polymer particles.
The plastic material of HDPE plastic bags has strong resistance characteristics that make it the preferred choice for packaging solutions such as plastic bags, garbage bags, laundry bags, grocery bags, etc. Thanks to its extreme impact strength, it ensures that the goods are also protected on the inside. This makes HDPE plastic bags suitable for a variety of industries, not just one. The main features of HDPE plastic bags are as follows.
a. Low cost, lightweight, transparent and durable.
b. Resistant to alcohol, alkalis, diluted acids, grease, and liquids such as water.
c. Highly flexible making it malleable and easily molded into a variety of shapes and sizes.
d. Industrial grade, NSF, FDA, and USDA approved.
They are also used in the production of a wide variety of products such as cling film and film, flexible packaging materials, food bags, and injection molded parts.
What is high-density polyethylene (HDPE)?
High-density Polyethylene (HDPE)
is essentially a white powder or granular product. Features are as follows.
a. Non-toxic, tasteless, crystallinity is 80%～90%. Softening point is 125 to 135℃. During use, the temperature can reach 100℃.
b. Better hardness, tensile strength, and creep than low-density polyethylene.
c. Better abrasion resistance, electrical insulation, toughness, and cold resistance.
d. Good chemical stability, insoluble in any organic solvent at room temperature. Resistant to alkalis, acids, and various salts.
e. Low permeability of the film to water vapor and air, and low water absorption.
f. Poor aging resistance, environmental stress cracking resistance is not as good as low-density polyethylene, especially thermal oxidation will degrade its performance, so the resin must add antioxidants and UV absorbers to improve this aspect of deficiencies.
g. High-density polyethylene film has a lower heat deflection temperature under stress, so attention should be paid when applying it.
High-density polyethylene resins can be molded into plastic products by injection, extrusion, rotational molding, and blow molding. Injection molding can be used to mold various types of containers, industrial parts, medical products, toys, shells, corks, and shrouds. Blow molding can be used to mold various hollow containers, ultra-thin films, etc. Extrusion molding can be used to form pipes, strapping, monofilaments, stretch strips, wire, cable sheaths, etc. In addition, we can also mold decorative panels for construction, shutters, synthetic wood, synthetic paper, synthetic film, and molded calcium-plastic products.
Low-pressure polyethylene bags
are polyethylene (PE) plastic bags
. It is made up of repeating -CH2-units connected. The properties of polyethylene depend on its polymerization method, which is the addition polymerization of ethylene (CH2=CH2). High-density polyethylene (HDPE) is produced by Ziegler-Natta polymerization under moderate pressure (15-30 atm) catalytic conditions of organic compounds. Polyethylene molecules polymerized under such conditions are linear and have long molecular chains with molecular weights up to several hundred thousand. In the case of free radical polymerization under high pressure (100-300 MPa), high temperature (190-210C), and peroxide catalytic conditions, low-density polyethylene (LDPE) is produced, which is a branched structure.
The common types of high-density polyethylene bags
on the market are sponge bags, HDPE garbage bags, HDPE shopping bags, rolled HDPE bags used in supermarkets, HDPE biogas bags, etc.
Low-density vs. high-density bags
High-pressure bags and low-pressure bags are both types of plastic bags, made of PE polyethylene. Low-pressure bags are made of high-density polyethylene and are mainly characterized by being hard, very good to the touch, opaque, and unbreakable. At the same time, it has high stability, good dimensional stability, high heat resistance and mechanical strength, a high-water vapor barrier, and poor transparency. High-pressure plastic bags are made of low-density polyethylene, the main characteristics are soft, good transparency, feel sticky, easy to wear, and low strength. It has low crystallinity and softening point, good flexibility and elongation, and impact resistance.
The difference between high-density bags and low-density bags
a. The chemical symbol of a high-pressure bag is LDPE, also known as low-density polyethylene; the chemical symbol of a low-pressure bag is HDPE, also known as high-density polyethylene.
b. High-pressure plastic bags have many characteristics that are superior to low-pressure bags, but because of their softness, high-pressure plastic bags are much thicker than low-pressure bags, so they require more material than low-pressure plastic bags. Therefore, the price of high-pressure plastic bags will be a little higher.
c. When the plastic bags are stretched by hand, the white marks appear on the low-pressure material, while the high-pressure material has no white marks.
d. High-pressure bags have a certain degree of glossy appearance, soft and smooth to the touch, soft sound when rubbed, and very small sound; elongation, and toughness are better. High-pressure bag transparency is higher, many higher-grade portable plastic bags raw materials, industrial products packaging, such as packaging box liner bags, instrumentation dustproof heavy, supermarkets sold in the fresh film are made of high-pressure material. Low-pressure bags do not look glossy, feel rough, sound when rubbed than high-pressure bags, very good tensile strength; much higher hardness than high-pressure plastic bags. It is widely used in supermarket shopping bags and vegetable market shopping bags.
Similarities between LDPE and HDPE
LDPE and HDPE, because they are formed from the same basic polymerized ethylene molecules, share many common characteristics. Some of them are as follows.
a. Light weight of the material.
b. Tensile strengths ranging from 0.20 to 0.40 N/mm².
c. High impact strength.
d. Chemical resistance.
e. Resistant to water vapor and weathering.
g. Low manufacturing and fabrication costs.
Advantages and disadvantages of HDPE & LDPE
d. Generally strong and stiff
e. Resistance against various elements
f. Highly flexible
g. Industrial grade – FDA, NSF, and USDA approved
d. Good electrical insulation
e. May be processed as transparent
f. Flexibility – Easy to process and mold
|Disadvantages||a. Possibility of breaking under stress|
b. Little to no UV resistance
c. Increased risk of mold decreasing in size
|a. Higher probability of breaking under stress
b. Little to no UV resistance
c. Ineffective in extremely high or low temperatures
Application of HDPE & LDPE
a. Since LDPE and HDPE have many applications, some industries use them together. These industries include medical devices, packaging, and life sciences.
b. Because of its strength and ability to withstand high temperatures, HDPE is often used in plastic laboratory bottles and medical waste containers. Medical and surgical instruments, such as catheters and medical tubing, also benefit from HDPE's resistance to cracking and radiation. LDPE is flexible and tough and is widely used as a low-cost and durable material for many cleanroom applications.
c. HDPE is easy and inexpensive to process and is often used in the production of plastic packaging. It can form a strong barrier with chemical stability, which means it is ideal for bottles and containers, especially for industrial and household chemicals. LDPD is often used in the packaging when heat sealing is required, such as in the film. LDPE polyethylene bags are strong, act as a moisture barrier, and are translucent.
d. Because both LDPE and HDPE are non-toxic, maintain a high degree of fracture resistance, and are non-contaminating (when extruded using only virgin resins and no surfactants), they are often used to protect life science and medical products. HDPE is used for products that require higher impact strength protection, chemical resistance, and heat resistance.
How to buy high-density polyethylene bags?
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