Plastics : Plastic material selection criteria for different applications

Material selection criteria are the key factors and requirements considered when choosing the most appropriate plastic material for a specific application or product.

Key selection criteria:

Mechanical properties:

• Tensile strength
• Impact resistance
• Flexural modulus
• Hardness
• Fatigue resistance

Tensile strength is the maximum stress a material can withstand while being stretched or pulled before breaking. 
Impact resistance is a material's ability to absorb energy during a sudden forceful collision without breaking. 
Flexural modulus measures how resistant a material is to bending under load. 
Fatigue resistance is a material's ability to withstand repeated cyclic loading without failing.

Example applications:

• High impact resistance for protective cases
• High tensile strength for load-bearing parts
• Flexibility for living hinges in bottle caps

Thermal properties:

• Heat deflection temperature
• Melting point
• Thermal expansion
• Thermal conductivity

Heat deflection temperature is the temperature at which a material starts to soften and bend under a specific load. It tells you when something will begin to deform due to heat and pressure.
Thermal expansion is how much a material changes in size when heated. Most materials expand (get bigger) when heated and contract (get smaller) when cooled.

Thermal conductivity is a material's ability to conduct or transfer heat.

Example applications:

• High heat resistance for automotive parts
• Low thermal expansion for precision components
• Heat conductivity for electronic housings

Chemical resistance:

• UV resistance
• Chemical compatibility
• Environmental stress cracking
• Oxidation resistance

Chemical compatibility is how well a material resists damage or degradation when exposed to various chemicals. It tells you which chemicals are safe or unsafe to use with the material.
Environmental stress cracking is when cracks form in a material due to both mechanical stress and exposure to certain chemicals or environments.
Oxidation resistance is how well a material resists reacting with oxygen, which can cause degradation like rusting in metals or breaking down of plastics. 

Example applications:

• UV resistant outdoor furniture
• Chemical resistant storage containers
• Weather resistant exterior parts

Processing requirements:

• Moldability
• Flow characteristics
• Cycle time
• Processing temperature
• Shrinkage

Moldability is how easily a material can be shaped in a mold to form parts. 
Flow characteristics describe how easily a melted material flows and moves during processing. 
Cycle time is how long it takes to complete one full manufacturing cycle, from starting to inject the material into the mold until the finished part can be removed.
Processing temperature is the temperature needed to properly melt and shape the material during manufacturing. It's the heat level required for good production.
Shrinkage is how much a part gets smaller as it cools and solidifies after molding. It's the difference between the mold size and the final part size.

Example applications:

• Easy-flow materials for complex molds
• Low-shrinkage materials for precision parts
• Fast-cycling materials for high-volume production

Cost considerations:

• Material cost
• Processing cost
• Tooling requirements
• Production volume
• Scrap rate

Scrap rate is the percentage of manufactured parts that must be rejected due to defects or quality issues. It measures how many parts end up as waste during production.

Example applications:

• Low-cost materials for disposable items
• High-performance materials for critical components
• Specialty materials for specific requirements

Environmental factors:

• Recyclability
• Biodegradability
• Carbon footprint
• Regulatory compliance

Example Applications:

• Recyclable packaging materials
• Biodegradable single-use items
• Food-grade materials for containers

Aesthetic requirements:

• Color options
• Surface finish
• Transparency
• Texture possibilities

Example applications:

• Clear materials for displays
• Colored materials for brand identity
• Textured materials for grip

Practical examples:

Water bottle selection criteria:

• Food safety compliance
• Clarity
• Impact resistance
• Cost-effectiveness Material Choice: PET

Outdoor furniture selection criteria:

• UV resistance
• Weather resistance
• Color stability
• Structural strength Material Choice: HDPE or PP with UV stabilizers

PET (Polyethylene Terephthalate) is a clear, strong plastic commonly used for beverage bottles and food containers. It's known for being lightweight, strong, and recyclable.
HDPE (High-Density Polyethylene) or PP (Polypropylene) with UV stabilizers are plastics that have special additives to protect them from breaking down in sunlight. 

The UV stabilizers help them maintain their strength and appearance when used outdoors.

Medical device housing selection criteria:

• Sterilization capability
• Chemical resistance
• Dimensional stability
• Regulatory compliance Material Choice: Medical grade PC or ABS

Medical grade PC (Polycarbonate) or ABS (Acrylonitrile Butadiene Styrene) are high-purity plastics specially manufactured to meet strict medical and healthcare standards. They are biocompatible, can be sterilized, and are safe for medical devices and equipment that come into contact with patients.

Automotive interior parts selection criteria:

• Heat resistance
• Impact strength
• UV stability
• Flame retardancy Material Choice: Modified PP or PA66

Modified PP (Polypropylene) or PA66 (Polyamide/Nylon 66) are plastics that have been enhanced with additives or chemical modifications to improve their properties. These modifications can make them stronger, more heat resistant, or better suited for specific applications compared to their standard versions.

Electronic enclosures selection criteria:

• Flame retardancy
• Dimensional stability
• Electrical properties
• Heat resistance Material Choice: FR-grade PC/ABS blend

FR-grade PC/ABS blend is a mixture of polycarbonate and ABS plastic that contains flame retardant additives. It's designed to resist catching fire or stop burning quickly if ignited, making it safer for electronics and other applications where fire safety is important.

Decision process:

• Define requirements
• List critical properties
• Evaluate material options
• Consider processing requirements
• Analyze costs
• Verify compliance
• Test and validate
• Make final selection

This systematic approach ensures the selected material meets all functional, economic, and regulatory requirements for the intended application.