Reaction mechanism and rheological properties of polypropylene irradiated under various atmospheres Ademar B. LugaÄo a, *, Beatriz Hutzler b , Telmo Ojeda c , Shinichi Tokumoto c , Richard Siemens d , Keizo Makuuchi e , Anna.-Lucia C.H. Villavicencio a a Institute for Energy and Nuclear Research, IPEN, Sao Paulo, Brazil b EMBRARAD, Jurubatuba, Sao Paulo, Brazil c OPP, Polo PetroquõÂmico de Triunfo, R. Gde. do Sul, Brazil d IBM Almaden Research Center, CA, USA e Takasaki Radiation Chemistry Research Establishment, Takasaki, Gunma, 370-12, Japan Abstract It is well-known that the melt-strength properties of a polymer increases with molecular weight and with long chain branching due to the increase in the entanglement level. This study is a contribution for the understanding of the following points: Ð the role of branching, crosslinking and degradation on melt strength properties; Ð the mechanism and the kinetics of PP irradiation with time of irradiation and the importance of double bond formation. The results showed that degradation was the major reaction in the initial step of irradiation no matter the atmosphere and or antioxidant. However, double bond formation increased the production of branching and crosslinking reactions. Double bond formation had no eect on the crystallization kinetics, on the other hand, long chain branching had a marked eect on the crystallization temperature. # 2000 Elsevier Science Ltd. All rights reserved. 1. Introduction PP suers from low melt strength, i.e., the melted PP does not exhibit an increase in resistance to stretch- ing during elongation. It is well-known that the melt- strength properties of a polymer increases with molecu- lar weight and with long chain branching due to the increase in the entanglement level. The production of long-chain branching in PP by irradiation in oxygen free atmosphere is already claimed (US Patent 4,916,198, 1990; US Patent 5,414,027, 1995). The ir- radiation of PP in the presence of polyfunctional monomers to improve the elongational viscosity was studied by Yoshi et al. (1986a). This study is a contri- bution for the understanding of the following points: Ð The eect of radiolysis products on the kinetics of crystallization Ð DSC studies on the eects of ir- radiation on PP have been performed when infor- mation about the changes in morphology are sought (Bus®eld and O'Donnell 1979; Avrami, 1940). More- over, the nucleating eects of HMSPP (high melt strength polypropylene) alone or mixed with others polymers are well-known and the crystallization pro- Radiation Physics and Chemistry 57 (2000) 389±392 0969-806X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0969-806X(99)00473-9 www.elsevier.com/locate/radphyschem * Corresponding author. Tel: +55-11-8169382; fax: +55-11- 8169325. E-mail address: ablugao@net.ipen.br (A.B. LugaÄo).