What is the Most Common Thermoplastic?

Thermoforming is a special plastic processing method that processes thermoplastic sheets into various products. That is, the thermoplastic sheet is softened by heating and then pressure (vacuum or positive pressure) is used to make the thermoplastic sheet act on the surface of the mold to obtain a shape similar to the mold surface. After cooling and setting, the product of the desired shape is obtained through trimming.

Thermoforming is fast and uniform, has a short molding cycle and low mold costs. It is suitable for automation and long-term production. It is considered to be the lowest unit cost and most efficient processing method among plastic molding methods.

Thermoforming has developed rapidly since its emergence, especially with the continuous improvement of thermoforming processes and equipment and the intervention of computer simulation methods. Thermoforming has become the main processing method competing with injection molding and blow molding. This article will take you through the most common thermoplastic materials.

PE (Polyethylene)

Features

PE is the largest plastic variety in the world, and its current output accounts for about 1/3 of the total plastic output.

The appearance is milky white and has a waxy feel. Non-toxic, odorless, density 0.91-0.965g/cm³. The melting point of linear low density polyethylene(high-pressure) is 110-115°C, and the high melting point of high-density (low-pressure) polyethylene is in the range of 125-131°C.

It has excellent electrical insulation properties, chemical corrosion resistance, low temperature resistance and easy processing properties, but has poor heat resistance and aging resistance, and the surface is not easy to bond and print.

Strength, stiffness, hardness, and heat resistance are all lower than ordinary plastics.

Application

High-density polyethylene (low-pressure) can be used to make plastic pipes, plastic plates, plastic ropes, and parts with low load-bearing capacity, such as gears and bearing chips; low-density (high-pressure) polyethylene is often used to make plastic films, hoses, plastic bottles, and Insulated parts and coated cables in the electrical industry, and used in the medical devices.

PP (Polypropylene)

Features

Colorless, odorless and non-toxic. It looks like polyethylene, but is more transparent and lighter than polyethylene, with a density of about 0.91g/cm³. Does not absorb water, has good gloss and is easy to color.

The melting point is 160-176℃, it has good heat resistance and can be sterilized at temperatures above 100℃. Its low-temperature use temperature reaches -15°C, and it will become brittle when it is lower than -35°C.

It has excellent electrical insulation properties, good high-frequency insulation properties, and does not absorb water. The insulation properties are not affected by humidity. Chemical corrosion resistance, common acids, alkalis and organic solvents have almost no effect on it (mostly used in tableware). Aging resistance is worse than PE. However, it is easily depolymerized and aged under the action of oxygen, heat and light, so anti-aging agents must be added.

It has excellent mechanical properties, its bending fatigue resistance is better than other plastics, and its yield strength, tensile strength, compressive strength, hardness and elasticity are better than polyethylene. After directional stretching, polypropylene can be made into hinges, which have particularly high bending fatigue resistance.

Application

PP can be used to manufacture various packaging and barrier films, such as isolation films between metal and rubber protective layers in wires and cables, capacitor films, and various one- and two-way stretch packaging films.

Various modified PP can be used in automobile bumpers, woven tapes, thermoformed sheets, cotton roving tubes and low-voltage distribution boxes, etc.

PP can also be used to make various instrument cases with hinges, TV back covers, radio cassettes and various insulating parts in the electrical industry. PP can be made into high-temperature sterilization-resistant tableware, kitchen utensils, water filters, facial masks, etc. Pots, washing machines, biscuit boxes. PP film can be used as packaging materials and capacitor film. Polypropylene tear film can be used as wrapping materials, woven bags, etc.

PVC (Polyvinyl Chloride)

Features

The output of PVC ranks second after PE.

PVC resin is white or light yellow powder. The density of pure PVC is 1.4g/cm³. The density of PVC plastic parts with plasticizers and fillers added is generally in the range of 1.15-2.00g/cm³. It is in the glassy state within the temperature range of 0-80℃, in the elastic state between 80-175℃, and in the melting range of 175-190℃ (no obvious melting point in between). Brittleness can be decreased with the addition of plasticizers , which increases the mobility of amorphous chain segments to effectively lower the glass transition temperature.

PVC has good electrical insulation properties and can be used as low-frequency insulation material. Has good flame retardancy and chemical stability. However, polyvinyl chloride has poor thermal stability. Prolonged heating will cause decomposition, release hydrogen chloride gas, and cause discoloration of polyvinyl chloride. Its application temperature range is narrow, generally between -15-5°C. PVC has poor stability to light. Ultraviolet rays and oxygen in sunlight cause photooxidative degradation of PVC, reducing its softness and eventually embrittlement.

Has high mechanical strength. Rigid polyvinyl chloride does not contain or contains a small amount of plasticizers. It has good tensile, bending, compression and impact resistance properties and can be used alone as a structural material.

Application

Some toxic auxiliary materials such as plasticizers and anti-aging agents are added to PVC during the manufacturing process, so its products are generally not used to store food and medicine.

PVC is widely used in artificial leather, wallpaper, floor leather, flame-retardant conveyor belts and various protective coatings.

Modified PVC can be used in door and window profiles, flame-retardant cable materials, unidirectional stretch shrink films and flocked leather for packaging materials, etc.

Soft PVC plastic can be made into various films, sheets, pipes and other products with certain toughness and softness. It is widely used in packaging, rain gear, seedling film, daily necessities, toys, etc. It can also be used to make sheath insulation layers for wires and cables.

Rigid PVC is corrosion-resistant and can be made into various chemical-resistant pipes, pipe joints, containers, etc. Rigid PVC can also be used to extrude various rods, pipes, plates and profiles.

PS (Polystyrene)

Features

Polystyrene raw material is colorless and transparent granular material, odorless and non-toxic. The density is 1.05g/cm³ and the melting temperature is 140-180℃. The appearance of the product feels hard and brittle like glass. It is easy to bend but not easy to bend. It makes a metallic-like crisp sound when lightly thrown or knocked. Colorless and transparent, the light transmittance is as high as 80-92%, and the light transmittance is second only to PMMA. It is easy to color and can be made into various brightly colored products. Polystyrene is flammable and will ignite spontaneously without fire. It will soften and foam when burning. The flame will be orange-yellow with thick black smoke and the sweet aroma of styrene monomer.

Excellent electrical insulation properties. Resistant to acid and alkali corrosion, but not resistant to benzene, gasoline, chloroform, dichlorethylene, banana water and other organic solvents.

The mechanical properties are average and the impact resistance is poor. The components should not be subject to dynamic bending loads, and elastic clamps cannot be designed and manufactured.

Application

PS is mainly used in optical glass, instruments, lampshades, toothbrush handles, toys, instrument casings, camera parts, household appliance casings, electrical insulation parts, containers, toys, cultural supplies, shoe heels and bottle caps, etc.; PS foam plastic can be used as Sound insulation, heat insulation, shock-absorbing materials and fast food boxes, etc.; PS low-foaming plastic can replace wood to make furniture, etc.

At present, the output of PS is second only to PE, PVC, and PP, ranking fourth among general thermoplastics.

ABS (Acrylonitrile Butadiene Styrene)

Features

Acrylonitrile Butadiene Styrene ABS is a terpolymer made of three monomers: acrylonitrile-butadiene-styrene.

The appearance of ABS resin is light ivory and opaque. The products can be in various colors, bright and beautiful, non-toxic, odorless, and give people a tough, hard and rigid texture. The density of ABS plastic is about 1.05, has no obvious melting point, and the melting temperature is about 160°C. ABS is flammable and burns slowly. It continues to burn after being removed from the fire. The flame is yellow with black smoke. It softens and burns when burning, without dripping, and is accompanied by a smell similar to burning rubber.

ABS has good chemical stability and is almost unaffected by mineral and organic acids, alkalis and salts. It is insoluble in most alcohols and hydrocarbon solvents, but will soften and swell in long-term contact with hydrocarbons. It is soluble in ketones and aldehydes. , esters and chlorinated hydrocarbons. ABS has good heat resistance and cold resistance, a wide operating temperature range, and can be used for a long time at -40-100℃. Compared with other thermoplastics, ABS resin has a smaller thermal expansion coefficient.

Good comprehensive mechanical properties and good toughness are one of the outstanding characteristics of ABS. ABS has high impact strength and does not drop rapidly even at lower temperatures. Low creep and good dimensional stability as well as high impact strength.

Application

ABS has a wide performance range, large processing latitude, and a balanced price and performance, which makes it have a wide application market.

General-grade ABS has the characteristics of high gloss, impact resistance, and electroplatability, and is generally used in daily necessities such as home appliances and toys.

High-flow ABS is generally used for molding products such as large home appliances, motorcycle trailer shells, and thin-walled parts.

ABS with low flow characteristics is suitable for extruding sheets and pipe fittings. Generally used in refrigerator linings, suitcases, pipes and large containers.

Flame-retardant ABS is generally used in computer casings and accessories, electronic products, office machines and other products that need to meet the requirements of UL94 specifications.

Heat-resistant grade ABS is used for products suitable for high temperature requirements. Generally used in heating appliance casings, hair dryers, heaters and automotive components such as instrument panels.

PMMA – Polymethyl Methacrylate (Plexiglass, Acrylic)

Features

It is a colorless, transparent liquid with a special aroma at room temperature, with a boiling point of 100.6°C, a melting point of -48.2°C, and a density of 0.934g/cm³. Slightly soluble in ether and ethanol, easily soluble in aromatic hydrocarbons, esters, ethers, ketones and chlorinated hydrocarbon organic solvents. PMMA is the most important type of acrylic resin. It is often supplied in sheets, commonly known as organic glass and acrylic, but it is much lighter than inorganic glass and is impact-resistant and vibration-resistant. Optical properties: Polymethyl methacrylate is a rigid, colorless and transparent material with excellent optical properties, with a light transmittance of up to 92%, which is not only better than other transparent plastics, but also more than 10% higher than ordinary inorganic glass. Transmits most ultraviolet rays and some infrared rays.

PMMA is resistant to most washing liquids, dilute inorganic acids, alkali, salts and greases, but is not resistant to ketones, chlorinated hydrocarbons and aromatic hydrocarbons, and can be dissolved in many chlorinated hydrocarbons and aromatic hydrocarbons. After long-term exposure to sunlight, the transparency and color will change very little. PMMA has poor heat resistance and wear resistance.

It has good comprehensive mechanical properties and ranks among the best among general plastics. Its tensile, bending and compression strengths are higher than polyolefin, and also higher than polystyrene, polyvinyl chloride, etc. Its impact toughness is poor, but it is also better than polystyrene. It is not very strong, cannot withstand high stress, and easily cracks when drilling. PMMA’s threaded holes can also crack when tightened at room temperature. The surface hardness is poor and is easily scratched by hard objects. Special coating can improve it. The mechanical properties of PMMA plastic products are acceptable under short-term load. Under long-term use, the external stress the products bear must be very low, otherwise creep, silver streaks or surface cracking will occur. Excellent secondary processing performance.

Application

PMMA has excellent light transmittance and is widely used. It is used as canopies, windshields and string windows on aircraft, as transparent window glass in automobiles, skylights of large buildings (can prevent shattering), TV and radar screens, instruments and Equipment protective covers, instrument and instrument casings, optical lenses on telescopes and cameras, signs, light box advertisements, lampshades, etc.

There is a dazzling array of daily necessities made from PMMA, such as buttons made of pearlescent plexiglass. Various toys and lamps are also particularly beautiful because of the decorative effect of colored plexiglass.

PA (Polyamide)

Features

White to light yellow particles with low density. The density of different polyamides is between 1.01-1.16g/cm³. Melting temperature 178-225℃ (different grades).

Polyamide has good chemical resistance. At room temperature, polyamide is soluble in strong polar solvents, such as sulfuric acid, formic acid, glacial acetic acid, phenol, etc. Especially strong acids have corrosive effects on polyamide. Under room temperature and dry conditions, polyamide has good electrical properties, but they are significantly lower than those of polyethylene, polystyrene and other materials. Polyamide has good cold resistance. The high heat distortion temperature and maximum continuous use temperature of different polyamides are not too high. Polyamide is one of the most hygroscopic types of plastics.

PA is a typical hard and tough thermoplastic polymer. Its comprehensive mechanical properties are better than ordinary general-purpose plastics. It is tough, wear-resistant and fatigue-resistant, but it is extremely hygroscopic. PA6 has good elasticity, high impact strength and high water absorption. PA66 has high strength and good wear resistance. PA610 is similar to PA66, but less water absorbent and less rigid. PA1010 is translucent, has less water absorption and has better cold resistance.

Application

PA gears and polyformaldehyde gear mesh transmission have been widely used.

PA is a nylon plastic. It is tough, strong and good abrasion resistance. It is often used to make combs, toothbrushes, clothes hooks, fan ribs, mesh bag ropes, fruit packaging bags, etc. Non-toxic, but not in long-term contact with acids and alkalis.

PC (Polycarbonate)

Features

Polycarbonate is a transparent colorless or slightly yellow strong solid. Its transparency is second only to PMMA and PS. Its light transmittance can reach 89%. It is odorless and non-toxic. Its density is about 1.20g/cm³. It has good colorability and can Made into various colorful products. Polycarbonate can burn, but it burns slowly and extinguishes slowly after being removed from the fire. The flame is yellow and black smoke, the burning material melts and foams, and emits the smell of rotten fruits and vegetables.

Resistant to water at room temperature, dilute acids, oxidants, reducing agents, salts, oils, and aliphatic hydrocarbons, but not resistant to alkali, amines, ketones, lipids, and aromatic hydrocarbons. It also has good weather resistance, low water absorption, and can maintain good electrical properties in a wide temperature range.

PC has good comprehensive mechanical properties and electrical insulation properties, can maintain high mechanical strength in a wide temperature range, and is heat and cold resistant. Its outstanding features are particularly excellent impact resistance, creep resistance and dimensional stability, but poor fatigue resistance and wear resistance, high notch sensitivity, and prone to stress cracking.

Application

a. Used in the manufacturing of various accessories in electrical and electrical components applications.

b. Mechanical Applications Polycarbonate used in precision machinery and office equipment often needs to be reinforced with glass fibers. This type of material has high dimensional stability and modulus and can replace aluminum and steel.

c. Color-changing glasses used in medical and security applications to protect against gamma rays are made of polycarbonate. In addition, baby bottles, heat resistant medical equipment and various daily necessities made of polycarbonate are on the market.

In terms of security, its impact resistance is used to make bulletproof helmets.