How to improve impact resistance?

Here's a breakdown of some key elements:

1. Material properties:

• Chain structure: Highly branched or cross-linked polymer structures offer more resistance to the propagation of cracks, preventing them from spreading and causing complete failure.
• Crystallinity: While it's often said that amorphous plastics are better at absorbing impact due to their disordered structure, this isn't a universal rule. Some amorphous polymers like PS and PMMA are actually quite brittle, while many semi-crystalline materials—such as POM, PBT, and PA6—can exhibit excellent impact resistance, especially when toughened or conditioned. Impact behavior depends more on the specific polymer chemistry, morphology, and additives than on crystallinity alone.
• Molecular weight: Generally, plastics with higher molecular weight have better impact resistance. This is because longer polymer chains can entangle with each other more effectively, creating a stronger network that resists force.

2. Temperature: Most plastics become more brittle at lower temperatures, leading to a decrease in impact resistance—especially when operating below their glass transition temperature (Tg), where molecular mobility is restricted. Conversely, some plastics may soften at higher temperatures (approaching or exceeding Tg or melting point), which can also reduce their ability to absorb impact and withstand force.

3. Reinforcements: Their effect is complex and can work in only some cases:

• With proper design: Short, well-dispersed fibers and rubber-toughened matrix can lead to a tougher composite
• With toughening agents: Combining reinforcements with elastomeric impact modifiers can offset the brittleness