A plastic’s impact resistance is its toughness, its ability to withstand sudden force without breaking apart. This is a crucial property for any material that will be subjected to mechanical stress, harsh weather conditions, or rough handling.
Plastics have a unique nature, meaning they react to an impact in a way that’s part solid and part liquid. Like a solid, they can be strong, elastic, and hold their shape. However, they also possess a fluid-like quality that allows them to flex and flow under stress, particularly when the temperature changes. This hybrid behavior differs significantly from that of metals, ceramics, or glass, and it can be a challenging adjustment for manufacturers new to working with impact resistant plastics.
When Need Use Impact Resistant Plastics?
Auto industry: You’ll find impact-resistant plastics in critical parts of your car, like bumpers, dashboards, and door panels, where they provide essential scratch resistant protection and lasting durability.
Construction: Impact-resistant plastics are perfect for the construction industry. Their durability makes them ideal for withstanding the demands of window profiles, pipes, and architectural glazing.
Electronics: In the electronics industry, impact resistant plastics act as protective shells and packaging to shield delicate components.
Packaging: To keep your food safe from bumps and drops, many food containers and packages are made with tough, impact-resistant materials.
Sports: Tough, impact-resistant plastics are what make sports equipment like helmets, face shields, and protective goggles so effective at preventing injuries
Medical facilities: To keep patients and medical staff safe, many medical devices are made from tough, impact-resistant plastics that can withstand daily use and abuse.
Common Impact Resistant Plastics
A material’s impact resistance is its ability to withstand a sudden blow, a crucial property for many products. This is measured in a lab using standardized tests, such as the Notched IZOD (a pendulum strike) and the Gardner Impact (a weight drop). The final score indicates the amount of force required to crack the material, so a higher number signifies a more durable, scratch-resistant plastic.
Here are a few impact resistant plastics known for their excellent impact resistance:
Acrylonitrile Butadiene Styrene (ABS)
ABS plastic (Acrylonitrile Butadiene Styrene) is a popular plastic known for being both strong and easy to manufacture. Its chemical resistance properties come from its three components: acrylonitrile and styrene for strength and rigidity, and butadiene for dimensional stability and impact resistance. Thanks to this durability and adaptability, it’s the go-to material for many automotive parts, consumer electronics, and household items.
ABS plastic is a standout material thanks to its well-rounded features:
Durability: It offers excellent impact strength and good heat resistance to elevated temperatures.
Workability: It’s relatively easy to machine and is compatible with injection molding, extrusion, and 3D printing for complex designs.
Resilience: It behaves reasonably well when exposed to many chemicals.
Aesthetics: It can be easily colored and finished, making it attractive to people.
This combination of strength, toughness, and manufacturing makes ABS the right material.
High-Density Polyethylene (HDPE)
HDPE (High-Density Polyethylene) is a workhorse plastic known for its strength, durability, and resistance to chemicals. You’ll find it everywhere: in packaging, construction, and plumbing, to name a few.
Its real-world advantages are pretty impressive. HDPE is lightweight yet tough enough to withstand impacts and harsh weather conditions. It doesn’t absorb water and can withstand moisture and sun exposure without falling apart, making it ideal for both outdoor and underground pipes. It’s also a great electrical insulator and, crucially, 100% recyclable.
In short, its blend of flexibility, ruggedness, and versatility makes HDPE a valuable plastic.
Polyamide-imide (PAI)
Polyamideimides (PAI) are top-tier, high-performance thermoplastics known for their incredible heat resistance. As part of the thermoplastic polyimide family, PAI stands out for its unique combination of valuable properties.
It offers exceptional toughness, stiffness, and resistance to warping (creep), all while maintaining a low rate of thermal expansion to keep its shape. When modified with materials like graphite or PTFE, it becomes a super-abrasion-resistant material with an extremely low friction coefficient, even without the use of lubrication.
Remarkably, PAI retains its high mechanical strength and hardness from extremely low temperatures to its glass transition temperature of 280°C. This means PAI components won’t lose their properties or performance, even when subjected to intense, continuous heat.
High Impact Polystyrene (HIPS)
HIPS plastic is the quarterback of the polymer world. It’s incredibly tough, standing up to high impacts and repeated stress without wearing out. It offers a great balance of stiffness, so it won’t bend when you need it to be rigid, and a light weight that makes it easy to work with. This makes it a sturdy and reliable choice for parts that require long-lasting performance.
You’ll find HIPS everywhere, in consumer products, electronics, automotive parts such as gas tanks, and various types of industrial machinery. It’s also a favorite in 3D printing for support structures. Because it’s certified as food-safe, it’s perfect for food storage items, from the liners in coffee cups to refrigerator interiors.
The downsides? HIPS isn’t the most eco-friendly option, as it’s slow to biodegrade and rarely economical to recycle. It’s also highly flammable and doesn’t withstand exposure to certain chemicals and solvents.
Key Spec:
Notched IZOD Impact: 50.0 – 350.0 j/m²
Factors Affecting the Impact Resistance of Plastic
Chemical makeup
HDPE, ABS, and polycarbonate are prized for their ability to withstand impacts. This durability is thanks to their geometry, which shows tightly packed molecules and strong molecular bonds.
Temperature
You know how a rubber band stretches when warm but can snap if it’s frozen. Similarly, many impact resistant plastics become brittle in the cold but are more flexible in high temperatures.
UV light exposure
Like our skin, resistant plastic get damaged by extreme conditions over time. UV rays weaken it, making it prone to breaking from impact.
Cut of the plastic
Sharp corners weaken the plastic, making it more likely to crack or break under stress.
Design Considerations for Impact Resistance in Plastic Parts
Sharp corners weaken the plastic, making it more likely to crack or break under stress.
Radius
For optimal results, set the corner radius to between 0.9 and 1.2 times the part’s nominal thickness.
Thickness of the wall
Maintaining even wall thickness is key. It minimizes the risk of warping and other defects that drive up the price.
Draft
Draft is the slight angle on a part’s walls that lets it slide cleanly out of the mold. Always aim for at least 1-2 degrees of taper, and add more if the design is complex.
A product’s impact resistance hinges on two key choices: selecting a rugged plastic and designing the part to optimize its toughness.