Nowadays, there are numerous commercial products made of plastic and technical resins on the market. In order to achieve the perfect performance, either in appearance or functionality, of the plastic products, the selection of the right resin is a crucial factor that should be considered before the product design as well as during the injection molding process.
LUSHI has rich experience of plastics technology and injection tooling manufacturing for more than 10 years. Our technical know-how and deep understanding of the chemical and mechanical properties of different plastics enable us to help our customers succeed with their projects.
In this article, we will talk about the 10 common plastic materials and their properties as well as their applications in the molding industry. They are ABS, PBT, PC,PE-HD, PMMA, PP, PS, PVC, SA, and POM.
ABS (Acrylonitrile-butadiene-styrene)
Chemical and mechanical properties
ABS is synthesized from three chemical monomers: acrylonitrile, butadiene, and styrene. Each monomer has different characteristics: acrylonitrile has high strength, thermal stability, and chemical stability; butadiene has toughness and impact resistance; and styrene has easy processing, high gloss, and high strength. From a morphological point of view, ABS is an amorphous material. The polymerization of the three monomers produced a terpolymer with two phases: one was a continuous phase of styrene-acrylonitrile, and the other was a polybutadiene rubber dispersed phase. The characteristics of ABS mainly depend on the ratio of the three monomers and the molecular structure in the two phases. This can have great flexibility in product design and thus produce hundreds of different-quality ABS materials on the market. These different quality materials provide different characteristics, such as impact resistance from medium to high, finish from low to high, and high temperature distortion characteristics. ABS plastic material has super easy processability, low creep, excellent dimensional stability, and high impact strength.
Applications
Automotive industry (dashboard, wheel cover, mirror box), food processor, lawn mower, phone case, keyboard.
Injection molding process condition
• Pre-drying temperature: 80°C - 90°C
• Pre-drying time: 2-4 hours
• Melt temperature range: 210°C - 240°C
• Tool temperaturer: 25°C - 70°C
• Injection pressure: 500 - 1000bar
• Injection speed: medium to hoch
PBT (polybutylene terephthalate)
Chemical and mechanical properties
PBT is one of the toughest engineering thermoplastic materials. It is a semi-crystalline material and has very good chemical stability, mechanical strength, electrical insulation properties, and thermal stability. These materials have good stability under a wide range of environmental conditions. PBT has weak hygroscopic properties. The tensile strength of the unreinforced PBT is 50 MPa, and the tensile strength of the glass additive PBT is 170 MPa. Too much glass additive will cause the material to become brittle. The crystallization of PBT is very rapid, which will cause bending deformation due to uneven cooling. For materials with glass additives, the shrinkage in the flow direction can be reduced, but the shrinkage in the vertical direction of the flow is basically the same as that of ordinary materials. The general material shrinkage is between 1.5% and 2.8%. Materials containing 30% glass additives shrink between 0.3% and 1.6%. Both the melting point (225 °C) and the high-temperature deformation temperature are lower than those of PET materials. The Vicat softening temperature is approximately 170 °C. Due to the high crystallization temperature of PBT, its viscosity is very low, and the processing time of plastic parts is generally shorter.
Applications
Household appliances (kitchen knives, vacuum cleaner elements, electric fans, hair dryers, coffee goods), Automotive (radiator grilles, body panels, wheel covers, door and window components, etc.)
Injection molding process condition
• Pre-drying temperature: 120°C-150°C
• Pre-drying time: 2-4 hours
• Melt temperature range: 225°C - 275°C
• Tool temperaturer: 40°C - 60°C
• Injection pressure: medium to 1500bar
• Injection speed: as quickly as possible
PC (Polycarbonate)
Chemical and mechanical properties
PC is a non-crystalline engineering material that has particularly good impact strength, thermal stability, gloss, bacterial resistance, flame retardant properties, and pollution resistance. The notched Izod impact strength of PC is very high, and the shrinkage rate is very low, generally 0.1% ~ 0.2%. PC has good mechanical properties but poor flow characteristics, so the injection molding process for this material is difficult. When choosing the quality of PC materials, the final expectations of the product should be used as a benchmark. If the plastic part requires high impact resistance, then use a low flow rate PC material; conversely, a high flow rate PC material can be used, which can optimize the injection molding process.
Applications
Electrical and commercial equipment (computer components, connectors, etc.), appliances (food processors, refrigerator drawers, etc.), transportation industry (The vehicle's front and rear lights, dashboard)
Injection molding process condition
• Pre-drying temperature: 100°C-200°C
• Pre-drying time: 3-4 hours
• Melt temperature range: 260°C - 340°C
• Tool temperaturer: 70°C - 120°C
• Injection pressure: as quickly as possible
• Injection speed: low if the nozzle is small, otherwise high
PE-HD (Polyethylene High Density)
Chemical and mechanical properties
The high crystallinity of PE-HD results in its high density, tensile strength, high distortion temperature, viscosity, and chemical stability. PE-HD is more resistant to penetration than PE-LD. PE-HD has low impact strength. The characteristics of PH-HD are mainly controlled by density and molecular weight distribution. The material has good flow characteristics, with an MFR between 0.1 and 28. The higher the molecular weight, the worse the flow characteristics of PH-LD, but the better the impact strength. PE-LD is a semi-crystalline material with a high shrinkage after molding, between 1.5% and 4%. PE-HD is prone to environmental stress cracking. Cracking can be reduced by using materials with very low flow characteristics to reduce internal stresses.
Applications
Refrigerator containers, storage containers, household kitchenware, sealed lids
Injection molding process condition
• Pre-drying: No drying required
• Melt temperature range: 220°C - 260°C
• Tool temperaturer: 50°C - 95°C
• Injection pressure: 700 - 1050bar
• Injection speed: hoch
PMMA (Polymethylmethacrylate)
Chemical and mechanical properties
PMMA has excellent optical and weather-resistant characteristics. The penetration of white light is up to 92%. PMMA products have very low birefringence, which is especially suitable for making video discs, etc. PMMA has room-temperature variation characteristics. With the increase in load and the increase in time, it can lead to the phenomenon of stress cracking. PHHA has better impact resistance.
Applications
Automotive industry (signal light equipment, instrument panels), pharmaceutical industry (blood storage containers), industrial applications (video discs, light diffusers), consumer goods (drink cups, stationery)
Injection molding process condition
• Pre-drying temperature: 90°C
• Pre-drying time: 2-4 hours
• Melt temperature range: 240°C - 270°C
• Tool temperaturer: 35°C - 70°C
• Injection pressure: medium
• Injection speed: medium
PP (Polypropylene)
Chemical and mechanical properties
PP is a semi-crystalline material. It is harder than PE and has a higher melting point. Because the temperature of homopolymer-type PP is higher than 0X and above, it is very brittle, so many commercial PP materials are random copolymers with T4% ethylene or clamp copolymers with higher ethylene content. Copolymer-type PP material has a lower heat distortion temperature (10 CTC), low transparency, low gloss, and low rigidity, but it has stronger impact strength. The strength of PP increases with increasing ethylene content. The Vicat softening temperature of PP is 15 °C. Due to its high crystallinity, this material has good surface stiffness and scratch resistance. PP does not suffer from environmental stress cracking. Generally, PP is modified by adding glass fibers, metal additives, or thermoplastic rubber. The flow rate (MFR) of PP ranges from 40 to 40. Low-MFR PP materials have better impact resistance but lower ductility. For materials of the same MFR, the copolymer type is stronger than the homopolymer type. Due to the crystallization, the shrinkage of PP is quite high, generally l.S. ~ 2.5%. The directional uniformity of the shrinkage is much better than that of materials such as PE-HD. Adding 30% of glass additives can reduce the shrinkage to 0.7%. Both homopolymer and copolymer materials have excellent resistance to moisture absorption, resistance to acid and alkali corrosion, and resistance to dissolution.
Applications
Automotive industry (mainly using PP with metal additives: fenders, ventilation pipes, fans), equipment (washer door gaskets, dryer ventilation pipes, washing machine frames and covers, refrigerator door gaskets)
Injection molding process condition
• Pre-drying: No drying required
• Melt temperature range: 220°C - 275°C
• Tool temperaturer: 40°C - 80°C
• Injection pressure: medium to 1800bar
• Injection speed: normal
PS (Polystyrene)
Chemical and mechanical properties
Most commercial PSs are transparent, amorphous materials. PS has very good geometric stability, thermal stability, optical transmission characteristics, electrical insulation characteristics, and a slight tendency to absorb moisture. It can resist water and diluted inorganic acids, but can be corroded by strong oxidizing acids, such as concentrated sulfuric acid, and can swell and deform in some organic solvents. Typical shrinkage is between 0.4 and 0.7%.
Applications
Product packaging, household goods (tableware, trays, etc.), electrical (transparent containers, light diffusers, insulation sheets, etc)
Injection molding process condition
• Pre-drying temperature: 80°C
• Pre-drying time: 2-3 hours
• Melt temperature range: 180°C - 280°C
• Tool temperaturer: 40°C - 50°C
• Injection pressure: 200 - 600bar
PVC (Polyvinylchlorid)
Chemical and mechanical properties
PVC is one of the most widely used plastic materials. PVC material is an amorphous material. PVC materials are often added with stabilizers, lubricants, auxiliary processing agents, colorants, impact agents, and other additives in actual use. PVC material has non-flammability, high strength, weather resistance, and excellent geometric stability. PVC is very resistant to oxidants, reducing agents, and strong acids. However, it can be corroded by concentrated oxidizing acids such as concentrated sulfuric acid and concentrated nitric acid, and it is not suitable for contact with aromatic and chlorinated hydrocarbons. The melting temperature of PVC during processing is a very important process parameter. If this parameter is improper, it will cause the problem of material decomposition. 5 The flow characteristics of PVC are quite poor, and its process range is very narrow. In particular, large-molecular-weight PVC materials are more difficult to process (usually lubricants are added to improve the flow characteristics). Therefore, low-molecular-weight PVC materials are usually used. The shrinkage of PVC is quite low, generally 0.2 ~ 0.6%.
Applications
Water supply pipes, house wall panels, commercial machine housings, electronics packaging, food packaging
Injection molding process condition
• Pre-drying: No drying required
• Melt temperature range: 185°C - 205°C
• Tool temperaturer: 20°C - 50°C
• Injection pressure: to 1500bar
• Injection speed: medium to high
SA (styrene-acrylonitrile copolymers)
Chemical and mechanical properties
SA is a hard, transparent material. The styrene component makes SA hard, transparent, and easy to process; the acrylic component makes SA chemically and thermally stable. SA has a strong load-bearing capacity, chemical resistance, thermal deformation resistance, and geometric stability. Adding glass fiber additives to SA can increase strength and resistance to thermal deformation and reduce the thermal expansion coefficient. The vicat softening temperature of SA is about 11 °C. The deflection temperature under load is about 10 °C. 7%。 The SA contraction rate is about 0.3 to 0.7%.
Applications
Electrical appliances (sockets, housings), household goods (kitchen appliances, refrigerator units, TV bases, cassette boxes), automotive industry (headlight boxes, reflective environments, dashboards), household goods (tableware, food knives), cosmetics packaging, etc.
Injection molding process condition
• Pre-drying temperature: 80°C
• Pre-drying time: 2-4 hours
• Melt temperature range: 200°C - 270°C
• Tool temperaturer: 40°C - 80°C
• Injection pressure: 350 - 1300bar
• Injection speed: high
POM (Polyoxymethylene)
Chemical and mechanical properties
POM is a tough and elastic material that has good creep resistance, geometric stability, and impact resistance even at low temperatures. POM has both homopolymer and copolymer materials. Homopolymer materials have good ductility and fatigue resistance, but they are not easy to process. Copolymer materials have good thermal and chemical stability and are easy to process. Both homopolymer and copolymer materials are crystalline and do not easily absorb moisture. P0M's high degree of crystallinity causes it to have a relatively high shrinkage, which can be as high as 2% to 3.5%. There are different shrinkage rates for different reinforced materials.
Applications
Gears and bearings, piping components (pipe valves, pump housings), lawn equipment.
Injection molding process condition
• Pre-drying: No drying required
• Melt temperature range: 190°C - 230°C
• Tool temperaturer: 80°C - 105°C
• Injection pressure:700 - 1200bar
• Injection speed: medium to hight