Injection Molding Material Selection Guide 2

PP (Polypropylene) — The Top Choice for Lightweight and Versatile Applications

Definition & Properties
Polypropylene (PP) is a semi-crystalline thermoplastic with excellent chemical resistance, low density, and fatigue durability. It is widely used for producing custom plastic parts and in various plastic parts manufacturing projects due to its cost-effectiveness and ease of processing.

Typical Applications

• Consumer Products & Packaging: PP is ideal for products with living hinges, such as flip-top bottle caps and reusable containers, which can withstand hundreds of thousands of open-close cycles.

• automotive injection: PP is commonly used in dashboards, door panels, and bumper liners. It is favored by many automotive component manufacturers for its lightweight properties, which contribute to overall vehicle weight reduction and fuel efficiency.

• medical device injection molding: With good biocompatibility and chemical resistance, PP is used in disposable syringes, medical containers, and housing for diagnostic equipment in various medical molding and medical injection molding companies.

• injection moulding large parts: Due to its high melt flow index, PP is ideal for large-volume molds like industrial bins and logistics pallets, frequently used by industrial molding corp where impact resistance is critical.

Considerations
PP exhibits relatively high shrinkage (1.5%–2.5%) during molding, so mold design must compensate for potential warpage or deformation. It can withstand temperatures up to 100°C and is highly recyclable—making it a preferred choice for environmentally conscious moulding maker operations.

PE (Polyethylene) — Excellent Impact Resistance and Chemical Durability

Definition & Properties
Polyethylene comes in two common forms: HDPE and LDPE. It features great mechanical flexibility and chemical resistance, making it a staple for injection mold inc projects that involve chemical storage or transfer.

Typical Applications

• Chemical containers, oil bottles, detergent packaging

• automotive injection: Fuel system tubing and mudguard components

• medical injection molding: IV bottles and sampling tubes

• custom plastic parts: Agricultural drippers, cable jackets

• injection moulding large parts: Trash bins and fluid tanks

Considerations
PE has high molding shrinkage (1.5%–4%), requiring careful mold cooling design. While cost-effective, it offers limited dimensional precision for high-tolerance parts.

PET (Polyethylene Terephthalate) — High Strength and Optical Clarity

Definition & Properties
PET is a transparent engineering plastic with excellent dimensional stability, gas barrier properties, and surface hardness. It is commonly used in visually critical custom plastic parts and medical device plastic molding.

Typical Applications

• Bottle preforms for beverages, oils, and cleaning agents

• medical molding: Transparent housings and drug containers

• automotive injection: Sensor enclosures and optical bases

• Premium injection mold inc parts requiring both strength and appearance

Considerations
Due to high moisture absorption, PET must be dried below 0.02% moisture content before molding. Mold surfaces must be highly polished to ensure transparency.

PA (Polyamide/Nylon) — High Strength and Wear Resistance for Engineering Use

Definition & Properties
PA6 and PA66 are the most common nylons, offering excellent strength, self-lubrication, and abrasion resistance. They are ideal for functional plastic parts manufacturing requiring load-bearing capability.

Typical Applications

• automotive injection: Gears, bearing washers, fan blades

• medical molding: High-strength support arms, surgical tool grips

• custom plastic parts: Connectors for industrial machinery and moving components

• Frequently chosen by moulding maker for structural development

Considerations
PA absorbs moisture readily and must be thoroughly dried before molding. Poor drying results in bubbles and internal stress. Uniform cooling is essential for dimensional accuracy.

PC (Polycarbonate) — Exceptional Impact Strength and Flame Retardancy

Definition & Properties
PC is an amorphous engineering plastic known for its high impact resistance and optical clarity. Naturally flame-retardant (V-2 rating), it is widely used in medical device injection molding and automotive injection.

Typical Applications

• Electronic device covers and LED light enclosures

• medical plastic molding: Transparent shields for disposable medical devices

• automotive injection: Light covers, control panel windows, dashboard lenses

• Optical-grade parts for high-end injection mold inc projects

Considerations
Drying is critical (below 0.03% moisture). It has low shrinkage but is sensitive to internal stress. A hot runner system is recommended to optimize flow.

PS (Polystyrene) — Cost-Efficient with Excellent Surface Finish

Definition & Properties
PS is a low-cost plastic with excellent processability and high surface gloss. It is suitable for medium-to-low-end custom plastic parts and aesthetic housings.

Typical Applications

• Disposable cutlery, blister packaging for medications

• medical device injection molding: Petri dishes, syringe covers

• injection moulding large parts: Lightweight appliance casings

• Consumer electronics housings

Considerations
PS is brittle and has low impact resistance. HIPS (High Impact Polystyrene) is recommended for parts requiring durability.

Comprehensive Selection Advice — Key Considerations for moulding maker

1. Functional Matching: For chemical resistance and fatigue durability, choose PP. For transparent, durable products, PC is preferred. For cost-sensitive projects, PS is a good option.

2. Process Compatibility: PE and PET require strict moisture control and advanced tooling. PA needs intensive drying—ideal for experienced moulding maker setups.

3. Cost vs. Performance: PP and PS are cost-effective. PC and PA are more expensive but offer superior performance.

4. Post-processing and Sustainability: All six materials are recyclable. PP and PE offer the highest reuse potential, aligning with sustainable manufacturing goals.
    If you want to know other materials such as：PVDF, PCTFE, UHMWPE, PSU, PFA, and PPS  please click to view another article:“Injection Molding Plastics Comparison”
   
   

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