Structure and Performance
Polypropylene (PP) and polyethylene (PE) have very similar molecular structures, which results in many similar properties, particularly in their behavior in solutions and electrical characteristics. The presence of a methyl side group in the molecular structure of polypropylene significantly enhances its mechanical properties and thermal performance. However, this structural feature also makes polypropylene more susceptible to oxidative degradation when exposed to ultraviolet (UV) light and heat, resulting in relatively reduced chemical resistance.
Mechanical and Thermal
Polypropylene (PP) exhibits outstanding chemical stability and heat resistance. Its inherent properties are similar to those of high-density polyethylene (HDPE), but with slightly lower crystallinity, resulting in a generally translucent appearance and comparable hardness to HDPE. The properties of PP are mainly influenced by factors such as molecular weight and molecular weight distribution, crystallinity, the proportion of comonomers, and isotacticity.
Melting Point and Thermal Expansion
Polypropylene (PP) has a melting point range that is typically determined by differential scanning calorimetry (DSC) to find its peak temperature. Perfect isotactic PP has a melting point of 171°C, while commercial grades of PP typically have melting points ranging from 160°C to 166°C, depending on the proportion of atactic material and the degree of crystallinity. Syndiotactic polypropylene has a melting point of approximately 130°C and a crystallinity of around 30%.