Effects of the hydroxyl value of polyol in rigid polyurethane foams

Rigid polyurethane foams (RPUFs) have been fabricated from crude MDI (CMDI) and polypropylene glycols (PPGs) of various hydroxyl values (OHVs) of 300–600 with an environmentally friendly blowing agent (HFC 365mfc). The closed cell content, compression strength, and dimensional stability of the foam increased with increase in the OHV due to the increased crosslink density, which was evidenced from the increased glass transition temperature (Tg). The cream time, gel time, tack‐free time, and density of the foam showed a minimum at 500OHV. The decrease and increase around the minimum were, respectively, interpreted in terms of increased mixture mobility and extensive allophanate crosslinks, which retard gelling as well as foaming reactions. The thermal conductivity also showed a small minimum at 500OHV.