Which is stronger abs or polypropylene

10 common plastics in the injection molding process

Nowadays, a large number of commercial products made of plastics and engineering resins are brought into the market. In order to achieve the perfect performance, either appearance or functionality of the plastic product, the selection of the right material is a crucial factor.

Thanks to LUSHI's many years of experience in plastics technology and injection molding processes, we have a deep understanding of the chemical and mechanical properties of different plastics, which enables us to offer customers an exact solution during product development.

In the following, 10 common plastics used in the injection molding process are presented:


ABS (acrylonitrile butadiene styrene)

Chemical and mechanical properties

ABS is synthesized from three chemical monomers: acrylonitrile, butadiene, and styrene. Each monomer has different properties: acrylonitrile has high strength, heat resistance and chemical resistance. Butadiene has toughness and impact resistance. Styrene is easy to process, has a high gloss and high strength. From a morphological point of view, ABS is an amorphous material. Polymerization of the three monomers yielded a two-phase terpolymer, one continuous phase consisting of styrene-acrylonitrile and the other consisting of dispersed polybutadiene rubber. The properties 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 bring hundreds of ABS materials with different quality and different properties on the market, such as impact resistance from medium to high, surface finish from low to high and different deformation rate. ABS has super easy processability, good appearance, low creep and excellent dimensional stability as well as high impact resistance.

Application examples:

Automotive industry (dashboards, hubcaps, mirror cases), food processors, lawn mowers, telephone boxes, keypads, housing parts

Processing in the injection molding process:

Pre-drying temperature: 80 ° C - 90 ° C
Pre-drying time: 2-4 hours
Mass temperature range: 210 ° C - 240 ° C
Mold temperature: 25 ° C - 70 ° C
Injection pressure: 500 - 1000bar
Injection speed: medium to high

More information on ABS plastic


PBT (polybutylene terephthalate)

Chemical and mechanical properties

PBT is one of the hardest engineering thermoplastics, a semi-crystalline material with very good chemical stability, mechanical strength, electrical insulation properties and thermal stability. PBT has excellent stability under different environments. PBT has weak hygroscopic properties. The tensile strength of normal PBT is 50 MPa and can be up to 170 MPa with the addition of glass fiber. With a high proportion of glass fiber, the material becomes brittle. The crystallization of PBT takes place very quickly, which leads to uneven cooling, which results in bending deformations. In the case of material with glass additives, the shrinkage in the direction of flow can be reduced. The shrinkage of general materials is between 1.5% and 2.8%. PBT with 30% glass fiber shrinks between 0.3% and 1.6%. Both the melting point (225 ° C) and the high temperature deformation are lower than with PET materials. In addition, the softening temperature is around 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.

Application examples:

Household appliances (kitchen knives, vacuum cleaner elements, electric fans, hair dryers, coffee goods), automotive industry (body parts, hubcaps, door and window parts)

Processing in the injection molding process:

Pre-drying temperature: 120 ° C-150 ° C
Pre-drying time: 2-4 hours
Melt temperature range: 225 ° C - 275 ° C
Mold temperature: 40 ° C - 60 ° C
Injection pressure: medium to 1500bar
Injection speed: as fast as possible

More information on PBT plastic


PC (polycarbonate)

Chemical and mechanical properties

PC plastic is a non-crystalline engineering resin with particularly good impact strength, heat resistance, high gloss, bacteria resistance, flame retardancy and pollution resistance. The impact resistance of PC plastic is quite high, as is the shrinkage rate is low, generally 0.1% ~ 0.2%. Because of its low flow property, PC is difficult in the injection molding process. When choosing PC plastic, final expectations of the product should be used as a benchmark. If the plastic part requires high impact strength, PC with a low flow rate is used, otherwise PC with a high flow rate is used to optimize the injection molding process.

Application examples:

Electrical devices (computer components, connectors), household appliances (food processors, refrigerated drawers), front and rear lights, vehicle dashboards.

Processing in the injection molding process:

Pre-drying temperature: 100 ° C-200 ° C
Pre-drying time: 3-4 hours
Mass temperature range: 260 ° C - 340 ° C
Mold temperature: 70 ° C - 120 ° C
Injection pressure: as high as possible
Injection speed: low with a small nozzle, otherwise high

Further information on PC plastic


PE-HD (high density polyethylene)

Chemical and mechanical properties

The high crystallinity of PE-HD leads to its high density, tensile strength, high temperature deformation, viscosity and chemical stability. PE-HD has a low impact strength. The properties of PH-HD mainly depend on the density and the molecular weight distribution. PE-HD has a good flow property MFR between 0.1 and 28. The higher the molecular weight, the worse the flow property of PH-HD, but the better the impact resistance. PE-HD is susceptible to stress cracks in the environment. Cracks can be reduced by using the material with lower flow properties to reduce internal stresses.

Application examples:

Fridge containers, storage containers, household dishes, sealing lids

Processing in the injection molding process:

Pre-drying: No drying required
Melt temperature range: 220 ° C - 260 ° C
Mold temperature: 50 ° C - 95 ° C
Injection pressure: 700 - 1050bar
Injection speed: high

Further information on PE-HD plastic


PMMA (polymethyl methacrylate)

Chemical and mechanical properties

PMMA has excellent optical properties and weather resistance as well as good impact strength. The transmission for white light is up to 92%. PMMA products have very little birefringence, which is particularly suitable for the production of DVDs and lenses. Stress cracks can occur with increasing load over a long period of time.

Application examples:

Automotive industry (signaling devices, dashboards), pharmaceutical industry (blood storage containers), lenses, consumer goods (drinking cups, stationery)

Processing in the injection molding process:

Pre-drying temperature: 90 ° C
Pre-drying time: 2-4 hours
Melt temperature range: 240 ° C - 270 ° C
Mold temperature: 35 ° C - 70 ° C
Injection pressure: medium
Injection speed: medium

Further information on PMMA plastic


PP (polypropylene)

Chemical and mechanical properties

PP-polypropylene is a semi-crystalline resin. It is harder than PE and has a higher melting point. Because homopolymer PP is very brittle at temperatures above 0 ° C, many PP resins are added with an additional 1% to 4% ethylene or even more. PP copolymer has a lower heat resistance (10 ° C), low transparency, low gloss and low rigidity, but has higher 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 resin has good surface rigidity and scratch resistance. In general, PP is mechanically modified by adding glass fibers, metal additives or thermoplastic rubber. The fluidity MFR ranges from 1 to 40. For materials with the same MFR, the PP copolymer is stronger than the homopolymer type. Due to the crystallization, the shrinkage of PP is quite high, generally 1% to 2.5%. The shrinkage uniformity is much better than PE-HD. By adding 30% glass additives, the shrinkage can be reduced to 0.7%. Both homopolymer and copolymer materials have excellent resistance to moisture absorption, acid and alkali corrosion, and dissolution.

Application examples:

Automotive industry (mainly use of PP with metal additives: fenders, ventilation pipes, fans), storage and transport containers, suction systems, ventilation pipes of the dryer, frames and covers for washing machines

Processing in the injection molding process:

Pre-drying: No drying required
Mass temperature range: 220 ° C - 275 ° C
Mold temperature: 40 ° C - 80 ° C
Injection pressure: medium to 1800bar
Injection speed: general

More information on PP plastic


PS (polystyrene)

Chemical and mechanical properties

Most PS are transparent amorphous materials. PS has very good geometric and thermal stability, good optical transmission and electrical insulation properties. It can withstand water and inorganic acids, but can be attacked and deformed by strong oxidizing acids such as concentrated sulfuric acid. The typical shrinkage is between 0.4 and 0.7%.

Application examples:

Packaging, furniture, household goods (dishes, trays), transparent containers, light diffusers, insulating films.

Processing in the injection molding process:

Pre-drying temperature: 80 ° C
Pre-drying time: 2-3 hours
Mass temperature range: 180 ° C - 280 ° C
Mold temperature: 40 ° C - 50 ° C
Injection pressure: 200 - 600bar

Further information on PS plastic


PVC (polyvinyl chloride)

Chemical and mechanical properties

PVC is one of the most commonly used plastics. PVC is often spiked with stabilizers, lubricants, processing aids, dyes, whipping agents, and other additives in actual use. PVC is non-flammable, high-strength, weather-resistant and contains excellent geometric stability. PVC is very resistant to oxidizing agents, reducing agents and strong acids. However, it can be corroded by concentrated oxidizing acids such as concentrated sulfuric acid and concentrated nitric acid and is not suitable for use with aromatic and chlorinated hydrocarbons. The melting temperature of PVC during processing is a very important process parameter. If this parameter is not properly controlled, the problem of degradation arises. The flow properties of PVC are quite poor, with a high molecular weight it is more difficult to process (usually lubricants are added to improve the flow properties). Basically, low molecular weight PVC resin is used in processing. The shrinkage of PVC is quite small between 0.2% to 0.6%.

Application examples:

Water supply pipe, wall panels, housings, packaging

Processing in the injection molding process:

Pre-drying: No drying required
Mass temperature range: 185 ° C - 205 ° C
Mold temperature: 20 ° C - 50 ° C
Injection pressure: up to 1500bar
Injection speed: medium to high

More information on PVC plastic


SAN (styrene-acrylonitrile copolymers)

Chemical and mechanical properties

SAN is a hard, transparent material. The styrene component makes SAN hard, transparent and easy to process, the acrylic component makes SA chemically and thermally stable. SAN has strong load-bearing capacity, chemical resistance, thermal deformation resistance and geometric stability. Adding fiberglass additives to SAN can increase strength and resistance to thermal deformation, and decrease the coefficient of thermal expansion. The Vicat softening temperature of SA is about 11 ° C. The deformation temperature under load is approx. 10 ° C. The SAN contraction rate of 7% is approx. 0.3 to 0.7%.

Application examples:

Electrical appliances (sockets, housings), household goods (kitchen appliances, refrigerator, TV tables), automotive industry (headlight boxes, reflectors, dashboards), household goods (dishes, food knives), cosmetic packaging

Processing in the injection molding process:

Pre-drying temperature: 80 ° C
Pre-drying time: 2-4 hours
Mass temperature range: 200 ° C - 270 ° C
Mold temperature: 40 ° C - 80 ° C
Injection pressure: 350 - 1300bar
Injection speed: high

More information on SAN plastic


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 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 materials and do not easily absorb moisture. The high degree of crystallinity of POM leads to a relatively high shrinkage, which can be up to 2% to 3.5%. There are different shrink rates for different reinforced materials.

Application examples:

Gears and bearings, pipe valves, pump housings, lawn equipment

Processing in the injection molding process:

Pre-drying: No drying required
Mass temperature range: 190 ° C - 230 ° C
Mold temperature: 80 ° C - 105 ° C
Injection pressure: 700 - 1200bar
Injection speed: medium to high

Further information on POM plastic