Understanding Plastic Materials: Types, Properties & Selection Guide for Designers
- Bk Engineering
- 5 days ago
- 3 min read
Updated: 18 minutes ago
Table of Contents
Plastics play a huge role in product design and manufacturing, especially in industries like automotive, consumer goods, electronics, and packaging. In this blog, we’ll explore the different types of plastics, their properties, and how to choose the right plastic for your product.
Introduction to Understanding Plastic Materials
Plastics are synthetic materials made from polymers, which are long chains of molecules. They are widely used because they are lightweight, durable, moldable, and cost-effective. However, not all plastics are the same. Designers and engineers must understand plastic types and their properties before using them in a product.
Types of Plastics
Understanding Plastic Materials
generally classified into seven categories:
PET (Polyethylene Terephthalate) is commonly used in bottles and food containers. It’s lightweight, clear, and strong.
HDPE (High-Density Polyethylene) is used in pipes, detergent bottles, and toys. It’s stiff and resistant to impact and chemicals.
PVC (Polyvinyl Chloride) is found in pipes, medical devices, and wire insulation. It’s strong and durable, but not very flexible.
LDPE (Low-Density Polyethylene) is used in plastic bags and flexible containers. It’s softer and more flexible than HDPE.
PP (Polypropylene is Common in automotive interiors, food containers, and textiles. It’s resistant to fatigue and chemicals.
PS (Polystyrene)Also known as Styrofoam. Used in packaging and disposable items. It’s lightweight and cheap but brittle.
Miscellaneous (Other Plastics)Includes polycarbonate, fiberglass, nylon, acrylic (PMMA), and more. These offer special properties like high impact resistance, transparency, or flexibility.
Why Material Selection Matters
Choosing the right plastic is crucial, especially in automotive product design. Different parts serve different purposes, and materials must meet specific demands such as strength, flexibility, temperature resistance, and appearance.
For example, a car bumper must:
Absorb impact without cracking (flexible and tough)
Resist sunlight and weather (UV resistant)
Have a good surface finish and be paintable (aesthetic)
Key Plastic Properties
Here are important properties to consider during material selection:
1. Density
Mass per unit volume (g/cm³ or kg/m³)
Affects the part’s weight and cost
High density = heavier material
2. Melting Temperature
The range in which plastic melts
High-melting plastics are used in high-temperature areas
3. Mold Temperature
High mold temp = better flow of molten plastic = better quality
Low-flow plastics need more heat and cost to mold
4. Glass Transition Temperature
The temp where plastic shifts from hard to rubbery
Below this temp = brittle; above = flexible
5. Shrinkage
Plastics shrink as they cool in a mold
Important to account for the mold size
6. Tensile Strength
Resistance to breaking under pulling forces
High tensile strength = more durable parts
7. Impact Strength
Ability to resist sudden force without cracking
Essential for parts that face dynamic loads
8. UV Resistance
Protection from sun damage
Needed for exterior automotive components
9. Volume Resistivity
Resistance to electrical current
Important for electronics or insulation parts
10. Polymeric Structure
Amorphous plastics: flexible, transparent (e.g., acrylic)
Semi-crystalline plastics: stronger, opaque (e.g., nylon)
11. Water Absorption
Some plastics absorb water and swell
Measured after 24-hour water exposure
12. Heat Resistance
Important for engine parts or high-heat areas
13. Optical Nature
Transparent (see-through), translucent (blurry light), or opaque (no light)
14. Cost
Always consider the cost per volume for accurate estimates
Higher performance = higher cost
15. Chemical Resistance
Some plastics break down when exposed to chemicals
Must check compatibility with the environment
16. Welding Compatibility
Not all plastics can be welded together
Check compatibility charts before joining materials
Conclusion
Choosing the right plastic material is key to building durable, functional, and cost-effective products. Especially in automotive design, where parts face various physical, thermal, and chemical stresses, material knowledge is power.
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