We use plastic products almost every day, and many people design items using plastics. However, few take the time to thoroughly understand the properties of the plastics they use, let alone what these properties mean or how they are measured.
To address this, we’ve taken the time to compile an overview of key plastic-related properties, including explanations of physical and mechanical properties, as well as the methods used to test them. With this information, you’ll no longer feel overwhelmed by the seemingly endless list of technical terms when designing products or reviewing material property sheets provided by suppliers.
Properties
Test Condition
Specification Document
Flexural Modulus
2.8mm/min
ASTM D790
Impact Strength of notched specimens
1/4" or 1/8"
ASTM D256
Rockwell Hardness
R-scale
ASTM D785
Heat deflection temperature
15.56kgf/cm
ASTM D645
Vicat Softening temperature
5Kg
ASTMD1525
1. Physical Properties of Plastics
Physical properties refer to the characteristics of plastics that can be observed or measured without changing the material’s composition. These properties play a significant role in determining how a plastic will perform in various environments and applications.
1. Density
Density is the mass per unit volume of a material. Plastics generally have lower densities compared to metals, making them lightweight and ideal for applications where weight reduction is critical.
For example, polypropylene (PP) has a density of around 0.9 g/cm³, while polyethylene (PE) ranges from 0.91 to 0.96 g/cm³.
2. Thermal Properties
Melting Point: The temperature at which a plastic transitions from a solid to a liquid state. For instance, ABS has a melting point of around 200°C, while polycarbonate (PC) melts at approximately 300°C.
Thermal Conductivity: Plastics are generally poor conductors of heat, which makes them excellent insulators.
Coefficient of Thermal Expansion (CTE): This measures how much a material expands or contracts with temperature changes. Plastics typically have higher CTEs than metals, which can lead to dimensional changes in varying temperatures.
3. Optical Properties
Some plastics, like polycarbonate and acrylic (PMMA), are transparent and have excellent light transmission properties, making them suitable for applications such as lenses, windows, and displays.
4. Electrical Properties
Plastics are excellent electrical insulators, which is why they are widely used in electrical and electronic components. Materials like PVC and PTFE (Teflon) are particularly valued for their insulating properties.
5. Chemical Resistance
Different plastics exhibit varying levels of resistance to chemicals, solvents, and environmental factors. For example, PTFE is highly resistant to most chemicals, while nylon may degrade when exposed to certain acids or bases.
2. Mechanical Properties of Plastics
Mechanical properties describe how a material responds to external forces such as tension, compression, impact, and wear. These properties are critical for ensuring that the final product can withstand the stresses it will encounter during use.
a. Tensile Strength
Tensile strength measures the maximum stress a material can withstand while being stretched or pulled before breaking. For example, polycarbonate has a high tensile strength of around 70 MPa, making it suitable for impact-resistant applications.
b. Flexural Strength
This property indicates a material’s ability to resist deformation under load. Plastics like PEEK (polyether ether ketone) have excellent flexural strength, making them ideal for structural components.
c. Impact Resistance
Impact resistance measures a material’s ability to absorb energy without fracturing. ABS and polycarbonate are known for their high impact resistance, which is why they are commonly used in automotive parts and protective gear.
d. Hardness
Hardness is the resistance of a material to surface indentation or scratching. Plastics like polypropylene are relatively soft, while materials like polycarbonate are harder and more scratch-resistant.
e. Elasticity and Plasticity
Elasticity: The ability of a material to return to its original shape after being deformed. Rubber-like materials such as thermoplastic elastomers (TPE) exhibit high elasticity.
Plasticity: The ability of a material to undergo permanent deformation without breaking. This property is essential for processes like injection molding, where the plastic is melted and reshaped.
f. Fatigue Resistance
Fatigue resistance refers to a material’s ability to withstand repeated stress cycles without failure. Plastics like nylon and PEEK are known for their excellent fatigue resistance, making them suitable for dynamic applications.
Why Understanding These Properties Matters
At our company, we leverage our deep understanding of plastic properties to:
Select the Right Material
By matching the material’s properties to the application’s requirements, we ensure optimal performance and longevity.
Optimize Design
Understanding mechanical properties helps us design parts that can withstand the intended stresses and strains.
Enhance Manufacturing Efficiency
Knowledge of physical properties like thermal behavior allows us to fine-tune our injection molding processes for better results.
Ensure Cost-Effectiveness
Choosing the right material and process reduces waste and minimizes production costs.