Introduction. Light weighting are the key areas for the development of the new materials industries, while foaming is the main way to achieve the preparation of the lightweight polymers [1], [2], [3]. Polypropylene (PP) is one of the five major thermoplastic resins, and research on the green processing as well as the high-performance of PP foams have been a very important subject in the field of polymeric foaming [4], [5]. Nowadays, PP foams have been widely used in the area of automobiles...