Comparison of Impact Resistance in Common Plastics

Impact resistance is a critical mechanical property of plastics, representing a material’s ability to withstand sudden external force without fracturing or undergoing plastic deformation. This performance directly influences the suitability of plastics for applications in automotive manufacturing, electronic packaging, transportation, and other sectors. The impact resistance of plastics is determined primarily by molecular structure, morphology, copolymerization, additives, and environmental temperature. This article compares the impact resistance of commonly used plastics—including PE, PP, PS, ABS, PVC, PC, and PA—based on widely recognized industry data, and provides insights for material selection.

1. High-Impact Plastics

High‑impact plastics typically achieve energy absorption through flexible molecular chains or copolymer modification, maintaining good toughness at both room and low temperatures.

Polycarbonate (PC)

PC is renowned for its exceptional impact resistance, attributed to flexible carbonate groups in its molecular chain that facilitate effective energy dissipation. Industry data shows that PC exhibits a notched Izod impact strength of 640–830 J/m². Even at −40°C, its impact strength remains above 80% of its room‑temperature value. This makes PC ideal for safety‑critical applications such as helmets, automotive glazing, and protective components.

Polyethylene (PE)

PE possesses high toughness due to its linear, unbranched molecular structure and high chain entanglement. LDPE, with more branching, exhibits superior impact absorption, with a notched impact strength exceeding 20 kJ/m². HDPE, having fewer branches and higher crystallinity, shows a lower but still respectable 5–10 kJ/m². A key advantage of PE is its excellent low‑temperature performance, with a embrittlement temperature below −50°C, making it suitable for cold‑storage packaging and low‑temperature piping.

Acrylonitrile-Butadiene-Styrene (ABS)

ABS combines a rigid SAN matrix with dispersed rubber particles that act as energy‑absorbing centers, effectively inhibiting crack propagation. Its notched Izod impact strength ranges from 123–454 J/m². ABS offers balanced toughness and processability, making it a common choice for electronic housings and automotive interior parts. While more cost‑effective than PC, its impact resistance decreases noticeably below −20°C.

2. Medium-Impact Plastics

Medium‑impact plastics are usually engineering or modified plastics that achieve improved toughness through copolymerization or small‑amount impact modifiers.

Polyamide (PA, Nylon)

PA exhibits a balance of rigidity and toughness due to hydrogen bonding between its molecular chains. Unreinforced PA has a notched impact strength of 53–85 J/m². Water absorption significantly enhances its toughness—improving impact strength by 30–50%—but reduces dimensional stability. Glass‑fiber reinforcement increases rigidity but slightly lowers impact strength, yet remains suitable for gears, bearings, and mechanical components.

Copolymer Polypropylene (PP)

PP’s impact resistance varies widely. Homopolymer PP, with high crystallinity, is relatively brittle, showing only 2–5 kJ/m². Copolymer PP, however, incorporates flexible ethylene segments, raising impact strength to 10–20 kJ/m². Blending with LLDPE can further improve toughness; at 70% LLDPE, impact strength can reach 37.5 kJ/m², a twenty‑fold increase over pure PP. PP is sensitive to temperature, with impact strength dropping to 50% of room‑temperature values at 0°C.

Rigid Polyvinyl Chloride (PVC)

Rigid PVC achieves medium impact resistance through small amounts of plasticizers or modifiers, with a typical notched impact strength of 30–40 kJ/m². Soft PVC, with higher plasticizer content, exhibits greater toughness but lower rigidity. Processing conditions significantly affect PVC’s impact performance; rapid cooling during injection molding can introduce internal stress and reduce toughness. It is commonly used in pipes, profiles, and packaging films.

3. Low-Impact Plastics

Low‑impact plastics typically have highly regular, rigid molecular structures, making them prone to brittle fracture under impact.

General-Purpose Polystyrene (GPS)

GPS features a rigid molecular structure with benzene rings, resulting in very low impact resistance—typically 10–80 J/m². It exhibits brittle behavior even at room temperature and is suitable only for non‑impact applications such as disposable tableware and decorative parts.

High-Impact Polystyrene (HIPS)

HIPS improves toughness by incorporating rubber particles, which increase energy absorption and raise impact strength to 50–150 J/m². This modification transforms GPS from brittle to tough, making HIPS suitable for appliance housings, toys, and general‑purpose components.

4. Factors Influencing Impact Resistance and Selection Guidelines

The impact resistance of plastics is primarily governed by molecular structure and modification methods. Flexible chains and branched structures, as seen in PE, enhance toughness. Incorporating elastomers—such as the rubber phase in ABS or PP/LLDPE blends—significantly improves impact performance. Temperature is another critical factor; most plastics become brittle at low temperatures, necessitating careful material selection for cold‑environment applications.

When choosing materials, engineers should prioritize performance and cost. High‑impact applications such as safety equipment and structural parts benefit from PC or ABS. Medium‑impact requirements, such as mechanical components and building materials, are well‑served by PA, copolymer PP, or rigid PVC. Low‑impact applications can use GPS. Additionally, processing conditions and environmental factors—such as PA’s water absorption and PP’s temperature sensitivity—must be considered to ensure optimal performance and cost‑effectiveness.