PP

Polypropylene (PP) shares similar characteristics with polyethylene (PE) but is harder and more heat-resistant. 

It is the second most commonly used plastic in the world. 

While the density of polypropylene varies with the type of filler used, pure PP is the least dense commodity plastic.

Advantages and Disadvantages of PP

Polypropylene plastic offers good chemical resistance and maintains its shape after twisting or bending. 

PP also has a high melting point and does not degrade when exposed to moisture or water. 

Injection-molded polypro (sometimes referred to as this plastic) can also be recycled up to four times. 

Additionally, recycled PP can be blended with other plastic materials.

Injection-molded polypropylene degrades under ultraviolet light and is highly flammable. A

t temperatures above 100°C (212°F), it dissolves into aromatic hydrocarbons harmful to human health, such as benzene and toluene. 

Due to its difficulty in bonding, PP is hard to color; however, pigments can be added to color the material.

Applications and Grades of PP

Injection-molded polypropylene has various consumer, commercial, and industrial applications. 

Examples include children's toys, storage containers, sports equipment, packaging, appliances, and power tool bodies.

PP plastics can be filled with glass fiber to improve dimensional stability, stiffness, strength, and resistance to warping. 

Grades include high crystalline polypropylene (HcPP), which has higher rigidity than ordinary polypropylene.

PS

Polystyrene (PS) is a commodity plastic with two basic types for injection molding: ● General Polystyrene (GPPS) ● High-Impact Polystyrene (HIPS)

GPPS is brittle and has lower dimensional stability than HIPS, which is compounded with polybutadiene rubber to enhance its material properties. 

GPPS also has glass-like transparency, while HIPS is opaque. Both types of polystyrene are highly suitable for injection molding as they have predictable and uniform shrinkage rates.

Advantages and Disadvantages of PS

PS plastics are inexpensive, lightweight, and resistant to moisture and bacterial growth. 

They also have excellent resistance to gamma radiation, making them suitable for disinfecting medical equipment. 

Injection-molded polystyrene also has good chemical resistance to dilute acids and alkalis.

Polystyrene is flammable, degrades under ultraviolet light, and is susceptible to erosion by hydrocarbon solvents such as benzene and kerosene. 

Because it is brittle, GPPS is prone to cracking. While injection-molded polystyrene is recyclable, it is not biodegradable.

Applications and Grades of PS

Polystyrene is used in medical, optical, electrical, and electronic applications. 

Due to its higher impact strength, HIPS is often used with appliances and equipment. 

Injection-molded GPPS is used for plastic toys, boxes, containers, and trays. 

Polystyrene can be filled with glass to increase strength or copolymerized with acrylic to improve transparency and enhance chemical and UV stability.

TPE

Thermoplastic Elastomer (TPE) or Thermoplastic Rubber (TPR) is a blend of rubber and plastic materials. 

While TPE has rubber-like characteristics and performance, its processing is similar to that of plastics. 

The elasticity of TPR is one reason it attracts designers and engineers. 

TPE is also recyclable, with the ability to be recycled up to six times. Additionally, other recycled materials can be mixed to produce TPE.

Advantages and Disadvantages of TPE

Thermoplastic elastomers can stretch to moderate elongations and almost return to their original shape after releasing the stress. 

TPEs also have shorter molding cycles, support secondary molding options, and are easier to mold and cheaper than liquid silicone rubber (LSR).

However, TPE is prone to creep under continuous stress, a tendency for solid materials to permanently deform. 

This material also tends to lose its rubber properties at higher temperatures and is much more expensive than other injection molding materials.

Applications and Grades of TPE

Injection-molded TPE is used in footwear, medical devices, automotive parts, and pet products. 

Automotive applications include wind and rain seals and shock and dust covers. Medical applications include breathing tubes, valves, catheters, and ventilation masks.

TPU

Thermoplastic polyurethane (TPU) is a thermoplastic elastomer (TPE).

Like other TPEs, TPU has rubber-like elasticity; however, injection-molded TPU has higher hardness and can be used as a substitute for hard rubber. 

TPU is often chosen over TPE because it is better suited for extreme temperatures and chemical resistance. On the other hand, TPE is softer and more flexible.

Advantages and Disadvantages of TPU 

Compared to other TPEs, TPU has higher abrasion resistance, chemical resistance, oil, grease, and high-temperature performance. 

Injection-molded thermoplastic polyurethane also has good load-bearing capacity and is suitable for materials exposed to ozone environments.

TPU may be too hard or lack the desired flexibility for some injection molding parts. 

Thermoplastic polyurethane also tends to be more expensive and requires drying before processing. 

Because some grades have a short shelf life, injection molders may have to dispose of them before use.

Applications and Grades of TPU 

Injection-molded TPU is used in footwear, gaskets, wheels, and sports equipment. 

Applications also include housings or covers for electronics and medical devices.

 In medical applications, TPU is sometimes used instead of polyvinyl chloride (PVC), a plastic that can cause skin irritation. 

Thermoplastic polyurethane has commercial, medical, and industrial grades. 

TPU materials are mainly divided into three categories: polyester, polyether, and polycaprolactone