Selecting Engineering Plastics for Injection Molding - Practical Guide 2025

Introduction to Material Selection

Plastic material selection is one of the most critical stages in injection molding process design. The right material choice determines not only the final part properties but also processing parameters, production costs, and the durability of the finished product. Modern plastics processing offers dozens of different material groups, each delivering unique combinations of mechanical, thermal, and chemical properties.

This guide provides comprehensive information on injection molding materials, their classification, processing parameters, and selection criteria. Whether you're producing consumer packaging, automotive components, or precision medical parts, this article delivers the essential knowledge for optimal material decisions.

What Is Engineering Material Selection?

Engineering material selection is a systematic process of analyzing application requirements and matching the right plastic that meets all functional, economic, and processing criteria. This involves understanding both the material properties and the specifics of the injection molding process as well as the end-use conditions of the finished part.

Proper plastic material selection considers a range of factors: mechanicaloads, operating temperature range, chemical exposure, aesthetic requirements, industry standards, and economic aspects. Modern engineering plastics offer a wide spectrum of options—from low-cost commodity materials to highly specialized polymers with exceptional properties.

Types of Injection Molding Plastics

The injection molding materials market offers dozens of different thermoplastics. In industrial practice, 10-12 main plastic families are most commonly used, divided into three categories: standard, engineering, and high-performance. Each category features distinct levels of mechanical and thermal properties as well as price.

Standard Plastics (PP, PE, PS)

Standard plastics account for about 70% of global thermoplastic consumption in injection molding. They offer good processability, low cost, and a wide range of applications.

Polypropylene (PP)

• Processing temperature - 200-280°C, low mold temperature 20-80°C
• Mechanical properties - good flexural strength, fatigue resistance
• Chemical resistance - acids, bases, organic solvents
• Applications - food packaging, automotive parts, furniture
• Approximate price - 1,2-1,8 EUR/kg

Polyethylene (PE-HD, PE-LD)

• Processing temperature - 180-280°C, excellent flow
• Mechanical properties - flexibility, impact resistance at low temperatures
• Chemical resistance - excellent resistance to most chemicals
• Applications - containers, pipes, films, tanks
• Approximate price - 1,0-1,6 EUR/kg

Polystyrene (PS, HIPS)

• Processing temperature - 180-260°C, easy processing
• Mechanical properties - rigidity, transparency (PS), impact resistance (HIPS)
• Applications - disposable packaging, electronics housings, toys
• Approximate price - 1,3-1,9 EUR/kg

Engineering Plastics (ABS, PC, PA, POM)

Engineering plastics offer significantly better mechanical and thermal properties than standard materials. They are used in applications requiring high strength, dimensional stability, and resistance to elevated temperatures.

Acrylonitrile-butadiene-styrene (ABS)

• Processing temperature - 220-270°C, mold temperature 50-80°C
• Mechanical properties - excellent impact strength, rigidity, good surface finish
• Service temperature - up to 85°C continuous load
• Applications - device housings, instrument panels, LEGO bricks
• Approximate price - 2,0-3,0 EUR/kg

Polycarbonate (PC)

• Processing temperature - 280-320°C, requires drying <0,02% moisture
• Mechanical properties - highest impact strength, optical transparency
• Service temperature - up to 135°C continuous load
• Applications - lenses, protective covers, medical components
• Approximate price - 3,5-5,0 EUR/kg

Polyamide (PA6, PA66)

• Processing temperature - PA6: 230-280°C, PA66: 260-300°C
• Mechanical properties - excellent strength, wear resistance
• Drying requirements - critical <0,1% moisture, hygroscopic
• Applications - gears, bearings, automotive structural parts
• Approximate price - 2,8-4,5 EUR/kg

Polyoxymethylene (POM, acetal)

• Processing temperature - 190-230°C, narrow processing window
• Mechanical properties - high rigidity, low friction, dimensional stability
• Applications - precision parts, clock mechanisms, zippers
• Approximate price - 2,5-3,8 EUR/kg

Thermoplastic Elastomers (TPE, TPU)

• Processing temperature - 180-230°C, depending on hardness
• Mechanical properties - rubber-like flexibility, reprocessable
• Applications - grips, seals, soft-touch components
• Approximate price - 3,0-8,0 EUR/kg

High-Performance Plastics (PEEK, PPS)

High-performance plastics are an elite group of polymers with exceptional thermal and mechanical properties. They are used in the most demanding industrial applications where standard materials fall short.

Polyetheretherketone (PEEK)

• Processing temperature - 360-400°C, requires specialized equipment
• Service temperature - up to 250°C continuous load
• Mechanical properties - highest strength in its class
• Chemical resistance - virtually universal
• Applications - aerospace, medical, oil & gas industry
• Approximate price - 80-120 EUR/kg

Polyphenylene sulfide (PPS)

• Processing temperature - 310-350°C
• Service temperature - up to 200°C continuous load
• Mechanical properties - rigidity, dimensional stability
• Chemical resistance - acids, bases, solvents
• Applications - under-hood parts, electrical components
• Indicative price - 12-25 EUR/kg

Key processing parameters

Proper processing parameters are essential for producing high-quality molded parts. Each material requires a specific set of injection molding machine settings.

1. Barrel temperature (°C)

The plasticizing barrel temperature must be matched to the material's rheological properties. Too low a temperature causes incomplete melting and increased internal stresses. Too high a temperature leads to thermal degradation of the material.

Typical temperature ranges:

• PP: 200-280°C
• ABS: 220-270°C
• PC: 280-320°C
• PA: 230-300°C
• PEEK: 360-400°C

2. Mold temperature (°C)

Injection mold temperature affects surface quality, dimensional stability, and cycle time. Amorphous materials (PC, ABS) require higher mold temperatures of 60-120°C for better surface finish. Semi-crystalline materials (PP, PA, POM) need controlled cooling for optimal crystallinity.

3. Injection pressure (MPa)

Injection pressure must be sufficient to fill the mold cavity. Higher pressure is required for thin walls and long flow paths.

Typical pressure values:

• PE: 70-120 MPa
• PP: 80-130 MPa
• ABS: 100-150 MPa
• PC: 120-180 MPa
• PA: 100-160 MPa

4. Injection speed (mm/s)

Injection speed affects mold filling and molecular orientation. Shear-sensitive materials (PC, POM) require moderate speeds. Low-viscosity materials (PP, PE) tolerate high speeds. Typically: 20-200 mm/s depending on geometry and material.

5. Holding pressure (MPa)

Holding pressure compensates for material shrinkage during solidification. It should be 40-80% of injection pressure.

High-shrinkage materials:

• PP: 1.5-2%
• PA: 0.8-1.5%

Low-shrinkage materials:

• PC: 0.5-0.7%
• ABS: 0.4-0.7%

6. Cooling time (s)

Cooling time accounts for 50-70% of total cycle time. It depends on wall thickness, mold temperature, and material thermal properties. Rule of thumb: cooling time = (wall thickness)² x material factor.

Material factors:

• PP: 2.5
• PC: 3.5
• PA: 3.0

7. Drying requirements

Hygroscopic materials (PA, PC, PET, PBT) require drying before processing. Improper drying causes hydrolysis defects and degraded mechanical properties.

Typical drying parameters:

• PA: 80°C for 4-6h to <0.1% moisture
• PC: 120°C for 3-4h to <0.02% moisture
• PET: 160°C for 4-6h to <0.005% moisture

Material selection criteria

Selecting the right injection molding material requires systematic analysis of technical and economic factors.

1. Mechanical properties

• Tensile strength - PP: 25-40 MPa, ABS: 40-55 MPa, PA: 70-85 MPa, PEEK: 90-100 MPa
• Modulus of elasticity - material stiffness, from 1000 MPa (PP) to 4000 MPa (PEEK)
• Impact strength - impact resistance, critical for PC and ABS
• Fatigue resistance - important for dynamically loaded parts

2. Thermal properties

• HDT (heat deflection temperature) - maximum service temperature
• Coefficient of thermal expansion - dimensional stability across temperature changes
• Thermal conductivity - heat dissipation from the part
• Flammability - UL94 classification, V-0 requirements for electronics

3. Chemical resistance

• Service environment - exposure to oils, fuels, solvents
• PP and PE - excellent resistance to most chemicals
• PA - sensitive to strong acids and oxidizers
• PC - sensitive to aromatic solvents and bases
• PEEK and PPS - virtually universal chemical resistance

4. Industry requirements and certifications

• Food contact - FDA, EU 10/2011, migration certificates
• Medical applications - USP Class VI, ISO 10993, biocompatibility
• Automotive - PPAP, IATF 16949, VDA
• Electronics - UL94, RoHS, REACH

5. Economic aspects

• Raw material price - from 1 EUR/kg (PE) to 120 EUR/kg (PEEK)
• Processability - cycle time, energy consumption
• Tooling costs - abrasive materials require hardened steel molds
• TCO (Total Cost of Ownership) - total cost of ownership over the product lifecycle

Industry applications

Injection molding materials are used across virtually every industry sector. Material selection is closely tied to industry specifics and end-product requirements.

Automotive industry

Automotive is the largest consumer of engineering plastics.

Common materials:

• Talc-filled PP - bumpers, interior parts
• PA-GF - under-hood parts up to 150°C
• ABS/PC - instrument panels
• POM - mechanical components
• PBT-GF - electrical connectors

Requirements:

• Temperature resistance -40 to +120°C
• UV resistance
• IATF 16949 compliance

Medical industry

The medical sector demands the highest purity and biocompatibility materials.

Common plastics:

• PC - medical device housings
• Medical-grade PP - syringes, packaging
• PEEK - implants, surgical instruments
• TPE - seals, soft components

Requirements:

• FDA certifications
• USP Class VI
• ISO 10993
• Sterilizability

Electronics and appliances

The electronics industry primarily uses:

Common materials:

• ABS - housings, decorative parts
• PC - transparent parts, LED lenses
• PA-GF - structural components
• PBT - connectors, sockets

Requirements:

• V-0 flammability per UL94
• RoHS and REACH compliance
• ESD (antistatic or conductive materials)

Packaging

The packaging sector accounts for over 40% of global plastics consumption.

Common materials:

• PP - food packaging, closures
• HDPE - containers, bottles
• PET - preforms, transparent packaging
• PS - disposable packaging

Requirements:

• Food contact certifications
• Barrier properties
• Recyclability

Aerospace and defense industry

The most demanding applications use high-performance plastics:

Common materials:

• PEEK - structural parts, seals
• PPS - engine components
• PI - high-temperature insulation

Requirements:

• Temperature resistance up to 250°C
• Low coefficient of friction
• Radiation resistance

Compatibility with Tederic machines

Tederic injection molding machines are designed to process a wide range of thermoplastics. Modern control systems and precise plasticizing units ensure optimal conditions for every material type.

Plasticizing Barrel Configuration

• Standard Screw (L/D 22:1) - PP, PE, PS, ABS - universal applications
• Barrier Screw (L/D 24:1) - engineering materials PA, PC, POM
• Mixing Screw - glass fiber reinforced plastics
• Screw Tips - special tips for shear-sensitive materials

Tederic Temperature Control System

• Heating Zones - 5-7 s zones with individual control ±1°C
• Temperature Profile - customizable gradient for each material
• Real-Time Monitoring - melt temperature sensors at nozzle outlet
• Process Alarms - automatic detection of deviations from set parameters

Injection Precision for Demanding Materials

• All-Electric Tederic NEO Injection Molding Machines - ideal for precision-demanding PC, PA, POM ±0,1%
• Holding Pressure Control - multi-stage profiles to minimize stresses
• Injection Speed - programmable profiles up to 500 mm/s
• Decompression - adjustable for materials with varying viscosities

Material Storage and Preparation

Proper storage and preparation of plastics is critical for final product quality and injection molding process efficiency.

Pellet Storage Conditions:

• Temperature - 15-25°C, avoid temperature fluctuations
• Relative Humidity - <50% for hygroscopic materials
• UV Protection - store in original packaging or opaque containers
• Cleanliness - avoid contamination, dust, contact with chemicals
• Stock Rotation - FIFO (First In, First Out) principle

Material Drying Procedures:

• PA (polyamide) - 80°C for 4-6 hours, target moisture <0,1%
• PC (polycarbonate) - 120°C for 3-4 hours, target moisture <0,02%
• PET (polyethylene terephthalate) - 160°C for 4-6 hours, target moisture <0,005%
• PBT - 120°C for 4 hours, target moisture <0,04%
• ABS - 80°C for 2-4 hours (optional, recommended)

Dryer Types:

• Convection Dryers - basic, for non-hygroscopic materials
• Desiccant Dryers - required for PA, PC, PET
• Vacuum Dryers - most efficient, shorter drying times
• Central Systems - for large plants, automatic distribution

Raw Material Quality Control:

• Moisture Measurement - hygrometers, moisture analyzers (gravimetric method)
• MFI Control - melt flow index
• Visual Analysis - color, contaminants, lumps
• Documentation - material certificates, batch numbers, expiration dates

Summary

Plastic Material Selection is a fundamental stage in injection molding process design, determining the success of the entire production venture. Proper material selection impacts final product properties, process efficiency, production costs, and end-customer satisfaction.

Key Takeaways from the Guide:

• Material Classification - standard plastics (PP, PE, PS), engineering (ABS, PC, PA, POM) and high-performance (PEEK, PPS) differ in properties and cost by up to 100x
• Processing Parameters - barrel temperature from 180°C (PE) to 400°C (PEEK) requires precise control for each material
• Drying Requirements - hygroscopic materials (PA, PC, PET) require mandatory drying to moisture <0,1% before processing
• Selection Criteria - mechanical, thermal, chemical properties, industry certifications and economic aspects must be analyzed comprehensively
• Machine Compatibility - modern Tederic injection molding machines offer full configurability for all thermoplastic types
• Material Storage - storage conditions and preparation procedures directly impact final quality
• Specialized Industries - automotive, medical and aerospace require certified materials and strict quality control

Proper material selection is an investment in quality, efficiency and competitiveness. Systematic analysis of application requirements and thorough understanding of available plastic properties helps avoid costly errors and maximize final product value.

If you need support in material selection or are looking for an injection molding machine tailored to specific processing requirements, contact the TEDESolutions experts. As an authorized Tederic partner, we offer comprehensive technical advice, optimal machine configuration selection, and training on processing various plastic types.

Check out our articles on injection molding machines, production cycle optimization and injection molding defect identification.