What are the differences in thermal deformation between plastic types under load?

When plastics are subjected to both mechanical load and elevated temperatures, their deformation behavior varies significantly based on material composition and properties. The key differentiating factors include heat deflection temperature (HDT), coefficient of thermal expansion (CTE), and creep resistance.

Amorphous thermoplastics like polystyrene (PS) and polycarbonate (PC) typically exhibit lower HDT values (around 70-130°C) and more pronounced thermal expansion under load. Semi-crystalline materials such as nylon (PA) and polypropylene (PP) demonstrate higher HDT (up to 200°C for reinforced grades) and better load-bearing capacity at elevated temperatures due to their ordered molecular structure.

The coefficient of thermal expansion also varies substantially - PTFE has one of the highest CTE values at approximately 135×10⁻⁶/°C, while mineral-filled composites can reduce expansion by up to 50%. Creep deformation, the time-dependent strain under constant load, differs markedly between materials. Acetal (POM) shows excellent creep resistance, while polyethylene exhibits significant cold flow under sustained loading.

Glass reinforcement dramatically improves thermal performance, with glass-filled nylon achieving HDT values exceeding 200°C. Understanding these differences is crucial for design engineers selecting materials for applications experiencing both mechanical stress and thermal cycling, such as automotive components, electronic housings, and industrial parts operating in varied environmental conditions.