PE film or "PE" is a kind of thermoplastic and also happens to be the most common plastic. It accounts for approximately 34% of the entire plastics market. PE film has ideal physical properties, such as high ductility, high impact strength and very good chemical resistance. There are different types of PE film for different applications. High-density PE film has compactness and relatively high crystallinity, and can be used in harsh environments (such as construction). Low-density PE film is used for plastic bags and packaging.
The earliest record of polyethylene can be traced back to 1898. At this time, German chemist Hans von Pechmann accidentally made polyethylene while studying diazomethane. Diazomethane is not a preferred material for industrial applications because it is known to be very unstable.
In the United States in 1944, a company named Bakelite Corporation (a company headquartered in Texas) began large-scale commercial production of polyethylene under the license of the Imperial Chemical Industry Company. The discovery of catalysts in the 1950s to aid the polymerization process, which was crucial to the production of PE film, was an important milestone. These catalysts led to the production of high-density polyethylene throughout the 1950s, 1960s and 1970s.
PE film is made through a polymerization process. It all starts with the distillation of hydrocarbon fuels into distillates or lighter groups. These groups or monomers are then brought into contact with the catalyst to drive the polymerization process. The polymerization reaction is exothermic.
Today, coordination polymerization is the most commonly used method, involving metal chlorides and metal oxides. The most commonly used catalysts are called Ziegler-Natta catalysts and Phillips catalysts. PE film is sometimes produced by free radical polymerization. However, this method requires the use of high-voltage equipment. After making PE film, sometimes it is sometimes necessary to connect separate PE film parts together to make larger products. In this case, the following methods can be used to connect the PE film parts:
① Laser welding
② Ultrasonic welding
③ Hot gas welding
④ Hot Melt
⑤ Heat seal
Packaging: High-density PE film (HDPE) is used to manufacture common grocery boxes, trays and bottles. Bottle caps, cans and barrels are also made of HDPE. The high impact strength of HDPE makes it the material of choice for manufacturing such packaging products. Low-density polyethylene (LDPE) is used to make films, plastic bags, garbage bags and other food packaging materials. The advantage of LDPE lies in its low price and good physical flexibility.
l Pipes and fittings: PE film is widely used in the manufacture of various pipes and fittings. HDPE is used for coatings on gas pipes, water pipes, sewer pipes and steel pipes. HDPE has excellent chemical resistance and hydrolysis resistance, making it the material of choice for these applications. On the other hand, due to low water absorption and plasticity, LDPE is used to make water pipes and hoses.
l Electrical: PE film is a good insulator, used to make insulators for coaxial cables and cable sheaths.
l Medical: Certain types of PE film (such as ultra-high molecular weight polyethylene) have high toughness and are resistant to cuts and abrasion. It is also chemically resistant. Therefore, it is used to make artificial joints, knee replacements and hip replacements. It is also used to make certain parts of implants.
l Toys: One of the biggest applications of HDPE is toys. In fact, one third of all toys are made of HDPE. High tensile strength is one of the useful properties of HDPE.
l Consumer goods: trash cans, kitchen utensils, household goods, ice boxes, bowls, barrels, ketchup bottles, etc. are all made of PE film.
l Automobile: Automobile fuel tank is made of PE film (HDPE).
Polyethylene prototype using CNC, injection molding and 3D printer
① CNC machine tools. PE film is an excellent material for use with CNC machines. Due to its variants such as HDPE and LDPE, it appears in the form of sheets, rods and many other special shapes. Polyethylene works well in processes involving milling or lathes. It has satisfactory properties, such as good impact strength and toughness, which can be transformed into excellent machinability. The polyethylene used in CNC machines is usually black or white.
② 3D printing. PE film is currently not available in FDM, nor can it be used in any 3D printing process. Making 3D printed prototypes is considered a difficult material. Therefore, you must use CNC machines to manufacture PE film prototypes.
③ Injection Molding. PE film is a thermoplastic that can be used in injection molding machines because it can be reheated, melted and cooled without severe degradation. Usually, PE film is fed into an injection molding machine and heated to its melting
④ point. The liquid form is then injected into the mold to achieve the desired shape. The main advantages of using polyethylene in the injection molding process over other polymers are its low cost, easy recycling and strong impact strength, especially at low temperatures.