Proceedings of the Polymer Processing Society 26th Annual Meeting ~ PPS-26 ~ July 4-8, 2010 Banff (Canada) STRETCHING HIGH MELT STRENGTH POLYPROPYLENE (HMSPP) W. L. Oliani 1* , D. F. Parra 1 , L.F. C. P. Lima 1 , H. F. R. Ferreto 1 and A. B. Lugao 1 1 Instituto de Pesquisas Energéticas e Nucleares, IPEN - CNEN/SP Av. Professor Lineu Prestes 2242, Pinheiros, 05508-000, Sao Paulo, SP - Brazil washoliani@usp.br Abstract – The use of traditional polypropylene resins in blow film processes has been prevented due to their poor melt strength and bubble instability. To overcome these deficiencies is necessary to improve the melt strength since it is known that opportunities exist for the use of a high melt strength polypropylene resin in blown film process. This work aims to study the HMSPP films obtained by gamma radiation under acetylene, after uniaxial expantion. The thin films were stretched at 170 °C using an Instron machine. Film surface morphology and the thermal properties at HMSPP stretched were analised using atomic force microscopy (AFM), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results showed some evidences of fibrillar structures containing crystallites and gel formation. Preferred orientations of crystals that develop stretching polypropylene samples are observed Introduction The use of traditional polypropylene resins in blown film processes has been prevented due to their poor melt strength and bubble instability. Improvement of the melt strength by radiation processing is an opportunity for a high melt strength polypropylene resin use (application) in blown film (Oliani et al, 2010). The primary process in the interaction of radiation with polymers is the formation of excited species leading to the breakdown of chemical bonds and to free radicals formation. The produced radicals can react, resulting in crosslinking or chain scission (Zhang et al, 1999, Stojanovic et al, 2005). Isotactic polypropylene (iPP) undergoes crosslinking and extensive main chain scissions when submitted to irradiation. Particularly in presence of acetylene, the simultaneous irradiation of PP is able to control chain scission and to produce grafting in radiation induced long-chain branching. The grafted PP further reacts with PP radicals resulting in branching and crosslinking (Yoshiga et al, 2009, Cheng et al, 2010). The PP grade having low MFI values tends to have longer molecular chains and higher average molecular weight which form more molecular entanglements in the polymer melt. These polymers with a greater degree of molecular entanglements tend to have a higher resistance to extensional deformation yielding a higher melt strength (Muke et al, 2001). In recent study, were investigated the deformation induced changes in the structure of iPP films during uniaxial stretching at three different temperatures (room temperature, 60 and 160 °C). The role of chain entanglement in the interlamellar amorphous region plays an important role affecting the structure. At low temperatures, as the chain mobility is relatively low, tie chains from entanglements may initiate the fragmentation of lamellar crystals upon stretching, forming oriented mesomorphic iPP phase with extended-chain conformation. At high temperatures, as the chain mobility is relatively high, tensile deformation can lead to chain disentanglement allowing the formation of more folded-chain crystals from coiled segments (Zuo et al, 2007). In important study of microstructure of iPP (Dasari, 2003), the evolution during tensile deformation was examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM), as a function of strain rate. Although both AFM and SEM are similar in lateral resolution, AFM has superior vertical resolution, and provides quantitative evaluation of surface topographical characteristics. The excellent resolution of AFM to describe surface topography has opened new opportunities to study surface deformation in polymeric materials (Dasari et al, 2003, Dvir et al, 2006, Koike and Cakmak, 2006, Hosier et al, 2004). Many authors have investigated the structure and morphological properties of stretched polypropylene films (Tabatabaei et al, 2009) and the influence of molecular orientation on the crosslinking behavior iPP