Introduction of several basic blown film raw materials

Raw material characteristics
Basic performance: melt flow rate density
Mechanical properties: Flexural strength, tensile strength at break, tensile strength at yield, environmental stress cracking resistance, impact strength, ultimate tensile strength, Rockwell hardness
Thermal performance: melting point, Vicat softening point, embrittlement temperature.

1. Polyethylene (PE)
(1) Performance and use
    Polyethylene is a typical thermoplastic, a flammable white powder that is odorless, tasteless and non-toxic. The polyethylene resins used for molding are waxy pellets that have been extruded and pelletized, and their appearance is milky white. The molecular weight of polyethylene is between 10,000 and 1 million, and those with a molecular weight of more than 1 million are ultra-high molecular weight polyethylene. The higher the molecular weight, the better its physical and mechanical properties, but as the molecular weight increases, the processing performance decreases. Therefore, the appropriate molecular weight and processing conditions should be selected according to the use situation. High molecular weight polyethylene is a processing structural material and load material, while low molecular weight polyethylene is only suitable for coating, polishing agent, lubricant and softener. The mechanical properties of polyethylene depend to a large extent on the molecular weight, degree of branching and crystallinity of the composite. The tensile strength of high-density polyethylene is 20-25MPa, while the tensile strength of low-density polyethylene is only 10-12MPa. The elongation of polyethylene mainly depends on the density, the density is high, the crystallinity is high, and its spreadability is poor. Polyethylene has excellent electrical insulation properties. Because it is a non-insulating material, its dielectric constant and dielectric loss are almost independent of temperature and frequency; it has good high-frequency performance and is suitable for manufacturing various high-frequency cables and submarine cables.

1. Low density polyethylene (LDPE)
(1) Performance

    The density range of low-density polyethylene is 0.910~0.925g/cm³. The molecular structure is a branched molecule with long and short branches on the main chain. There are about 50 or less ethyl, butyl or longer branches in the main chain per 1000 carbon atoms. Compared with high-density and medium-density polyethylene, it has lower crystallinity (55%-65%), lower softening point (108ºC～126ºC) and wider melt index (0.2～80g/10min) . Since the chemical structure of low-density polyethylene is similar to paraffinic hydrocarbons and does not contain polar groups, it has good chemical stability and corrosion resistance to acid, alkali and salt aqueous solutions. It has good electrical properties, low conductivity, low dielectric constant, low dielectric loss and high dielectric strength. However, low-density polyethylene has poor heat resistance and is not resistant to oxygen and light aging. Therefore, in order to improve its aging resistance, antioxidants and ultraviolet absorbers are usually added to the resin. Low-density polyethylene has good flexibility, extensibility and transparency, but its mechanical strength is lower than that of high-density polyethylene and linear low-density polyethylene

(2) Use
    Low-density polyethylene is mainly used to make films. Film products account for more than half of the total output of land-density polyethylene products, and are used for agricultural film and packaging of various food, textiles and industrial products. Low-density polyethylene has excellent electrical insulation properties and is commonly used as a coating material for wires and cables. Injection molded products include various toys, lid boxes, containers and so on. After being blended with high-density polyethylene, injection molding and hollow molding can be used to make pipes and containers.

2. High-density polyethylene (HDPE)
(1) Performance
    The high density of HDPE is 0.941~0.965g/cm³. The molecular structure is a linear structure with few branches, with only a few branches per 1000 carbon atoms on average. Compared with low-density polyethylene, high-density polyethylene has a crystallinity of 80% to 90%, high density, higher use temperature, greater hardness and mechanical strength, and good chemical resistance.
(2) Purpose
     The purpose of high-density polyethylene is different from that of low-density polyethylene. About 50% to 70% of low-density polyethylene is used to make films; while high-density polyethylene is mainly used to make hollow hard products, accounting for about 40% to 65% of total consumption. Specific uses include: blow molding to manufacture various bottles, cans and various industrial tanks, barrels and other containers; injection molding to manufacture various pots, barrels, baskets, baskets, baskets and other daily products, daily sundries and furniture, etc. ; Extrusion molding to manufacture all kinds of pipes, straps, fibers, monofilaments, etc. In addition, it can also be used to manufacture wire and cable coating materials and synthetic paper; after adding a large amount of inorganic calcium salt, it can also be used to manufacture calcium plastic packaging boxes, furniture, doors and windows, etc. Recently, high-density polyethylene is used to manufacture high-strength ultra-thin films, and packaging materials for food, agricultural and sideline products and textiles have developed rapidly.

3. Medium Density Polyethylene (MDPE)
(1) Performance
    The density is 0.926~0.940g/cm³, and the molecular structure is a linear polymer with a number of branches between high-density polyethylene and low-density ethylene. The crystallinity is 70%~75%, and the softening temperature is 110ºC~115ºC. In addition to the properties of both high and low density polyethylene, it also has excellent stress crack resistance, rigidity and heat resistance.
(2) Purpose
    It is most suitable for high-speed blow molding to manufacture bottles, high-speed automatic wrapping films, and various injection molded products and rotational molded products such as barrels and cans. It can also be used for wire and cable coating.

4. Linear Low Density Polyethylene (LLDPE)
(1) Performance

    The density of linear low-density polyethylene is 0.910～0.925g/cm³. Because the linear low-density polyethylene molecular side chain is short-branched, and the molecular structure is between linear high-density polyethylene and high-pressure low-density polyethylene with long-chain branches, its physical and mechanical properties are better than ordinary low-density polyethylene. Density polyethylene. In terms of mechanical properties, the tensile strength of linear low-density polyethylene is 50% to 70% higher than that of ordinary low-density and ethylene, the elongation is more than 50% higher, and the impact strength, puncture strength and low-temperature impact resistance are all lower than those of ordinary low-density polyethylene. Density polyethylene is good. In terms of physical properties, under the same density, the melting point of linear low-density polyethylene is higher than that of low-density polyethylene, and its use temperature range is wide. The allowable use temperature is 10ºC～15ºC higher than that of low-density polyethylene. 
(2) Purpose

    Linear low-density polyethylene can replace low-density polyethylene to make films, pipes, injection molded products, hollow blow molded containers, rotational molded products, and wire and cable coating materials. The mechanical properties of the obtained product are better than that of low-density polyethylene. Therefore, when manufacturing products with the same strength, linear low-density polyethylene products can be thinned.

Polypropylene (PP)

(1) Performance

    Polypropylene is light in weight, with a density of 0.90～0.91g/cm³, which is the lightest kind of general-purpose plastics. Polypropylene has excellent heat resistance. The long-term use temperature can reach 100ºC～120ºC, and the use temperature can reach 150ºC without load. Polypropylene is the only general-purpose plastic that can be boiled in water and can withstand a disinfection temperature of 135ºC. Therefore, pipes for transporting hot water can be manufactured. The low temperature resistance of polypropylene is not as good as polyethylene, and the catalytic temperature is -10ºC～-13ºC (polyethylene is -60ºC). Poor impact resistance at low temperature or even room temperature, and easy brittleness at low temperature is the main disadvantage of polypropylene. Polypropylene is a non-polar material with excellent chemical stability, and the higher the crystallinity, the better the chemical stability. Except for the corrosive effects of strengthening acids (such as fuming sulfuric acid and nitric acid), there is no solvent that can dissolve polypropylene at room temperature, but low molecular weight aliphatic hydrocarbons, aromatic hydrocarbons and chlorinated hydrocarbons can soften or soften it. Swelling effect. Its water absorption is very small, the water absorption rate is less than 0.01%. Polypropylene is susceptible to aging due to light, heat, and oxygen during molding and use. Polypropylene ages and becomes brittle after 12 days in the atmosphere, and it deteriorates after being placed indoors for 4 months. It is usually necessary to add ultraviolet absorbers, antioxidants, carbon black and zinc oxide to improve the weather resistance of polypropylene products. The mechanical strength, rigidity, and stress cracking resistance of polypropylene exceed that of high-density polyethylene, and it has outstanding extensibility and bending fatigue resistance. The living hinge made of it has undergone 70 million bending tests, and there is no trace of damage. Polypropylene has excellent electrical insulation properties, especially high-frequency insulation, high breakdown voltage strength, and low water absorption. It can be used as heat-resistant insulation materials for radios and televisions used at 120ºC.
(2) Purpose
    Polypropylene has excellent comprehensive properties and can be made into various products by injection molding, extrusion molding, and hollow molding. In these applications, injection molded products rank first, including household appliances, entertainment and sports goods, toys, etc.; automotive parts, such as battery shells, air-conditioning parts, radiator blades, etc.; hard packaging, such as medical scrubbers, Covers, cosmetic boxes; mechanical parts, such as washing tanks, agitators, and air pipes. Extrusion molding products include wires, cables, films, sheets, pipes and so on. The film is mainly used for packaging clothing, knitwear, food, cigarettes, etc. Hollow molded products include containers and bottles. Polypropylene fiber is divided into filament (monofilament, multifilament, bulked yarn) and staple fiber. Fiber can replace natural fibers such as cotton, hemp, silk and wool. Mainly used in the production of woven and knitted fabrics, such as carpets, sofas, strapping materials, ropes and woven bags, etc.