1. PP Homopolymer
Homopolymer PP can be considered the most ‘basic’ grade of PP resin. This grade of PP resin is more rigid and has good resistance to high temperatures, making it particularly suitable for high-heat applications such as hot fill and microwave applications or steam sterilization applications. However, the tradeoff to this is lower impact resistance, particularly at low temperatures.
2. PP Random Copolymer
Random copolymer PP resins are created by modifying the PP polymer chain through the addition of random chains of ethylene among the PP units. Due to the presence of ethylene, the rigidity characteristic of homopolymer resins is somewhat sacrificed, however, this results in improved impact strength and a softer feel. Additional benefits to this include improved heat sealability, lower melting point, resistance to environmental stress cracking and improved clarity. Random Copolymer PP resins also exhibit good chemical resistance against most inorganic acids, alkalis and salts.
3. PP Impact Copolymer
Similar to random copolymers, impact (or block) copolymer PP resins are derived through copolymerization with ethylene, but with this grade the ethylene content is much higher. This results in a much tougher material with excellent impact strength even at low temperatures. For this reason, impact copolymer PP resins are particularly suitable for freezer and freezer-to-microwave applications.