J. Silva 1 , M. Elias 2 , N. Lima 3 , S. Canevarolo 1 * 1 Department of Materials Engineering, Federal University of São Carlos, São Paulo, Brazil 2 Graduate Program in Materials Science and Engineering, Federal University of São Carlos, São Paulo, Brazil 3 Instituto de Pesquisas Energéticas e Nucleares, CCTM, São Paulo, Brazil Morphology in Multilayer Blown Films of Polypropylene and Ethylene-Octene Copolymer Blends In this work the microstructure of multilayer blown films con- sisting of a core layer placed between two external ones is studied. The core layer is a blend with 70 % (w/w) of a homo- polypropylene PP and 30 % of a metallocene-catalyzed ethy- lene-octene copolymer mEOC (LLDPE or VLDPE), whereas the external symmetrical layers are composed of LLDPE or they have the same composition as the core layer. The PP and PE crystalline phases formed during the film blowing were investigated by thermal analysis, mechanical properties, TEM morphology and X-ray diffraction pole figures. These films successfully combine the high mechanical strength of PP with the quasi-isotropic behavior of blown PE. Multilayer film containing PP/mEOC blends, particularly blends of PP70/LLDPE30, show better balanced tensile properties when compared at crossed directions. The presence of VLDPE in the blends shifts downwards the melting and crys- tallization temperatures and crystallinity of PP. X-Ray pole figures suggest the occurrence of epitaxial crystallization of the PE phase upon the PP crystals in these PP/mEOC blend films. 1 Introduction Polyolefins such as polypropylene (PP) and polyethylene (PE) are usually classified as commodities. These materials exhibit a good cost/benefit relation, being broadly used in the flexible packaging industry. A possible route to create films with better properties and/or lower cost than the films of one single materi- al, PP or PE, consists in combining both materials: PE, which is ductile at low temperatures, and PP that has a relatively high tensile strength. However, the poor compatibility between PP and PE and the low interfacial adhesion, resulting from the low surface free energy and lack of polar functional groups (Awaja et al., 2009), has hindered the commercial success of PP/PE films. Ethylene-propylene rubber (EPR) (Jancar et al., 1993; Moore, 1996; Nitta et al., 2005; Poelt et al., 2000), copolymer of ethylene-propylene-diene monomer (EPDM) (Bertin and Robin, 2002; Bhadane et al., 2006; Souza and Demarquette, 2002) and ethylene-vinyl acetate copolymer (EVA) (Huerta- Martinez et al., 2005; McEvoy and Krause, 1996) have been used to improve the compatibility and adhesion of PP/PE systems. Alternatively, in recent years, there has been increas- ing use of metallocene-catalyzed ethylene-a-olefin copolymers (mEC) to improve the melt and impact strength of PP (Chaffin et al., 2000a; b; Da Silva et al., 2002; McNally et al., 2002; Mohanty and Nayak, 2007; Premphet and Paecharoenchai, 2002; Rabinovitch et al., 2003; Yan et al., 2007). It seems that the more uniform branching and narrower molecular weight distributions obtained by the use of single-site catalysts can promote the adhesion and compatibility in PP/PE systems. In fact, although some authors have reported thermodynamical immiscibility between PP and mECs, most of the studies show enhanced interfacial adhesion and compatibility in these poly- meric systems (Chaffin et al., 2000a; b; Kukaleva et al., 2000a; b). Rana et al. (1998) studied blends of PP and metallo- cene-catalyzed ethylene-octene copolymer (mEOC). Notwith- standing the significant shift of PP crystallization peak toward low temperatures as the concentration of mEOC increases, the authors showed that PP and mEOC are thermodynamically im- miscible. Nevertheless, their work revealed the mechanical compatibility in the blends. McNally et al. (2002) observed partial miscibility of PP and mEOC provided that the concen- tration of the latter is low, i. e., 10 wt% or less. Moreover, they reported no alteration in PP crystallization peak maxima but a slight broadening which was attributed to the disruption of the PP crystal morphology by the mEOC. On the other hand, a pro- nounced increase of the PP crystallization temperature with in- creasing mEOC concentration (up to 30 wt%) was observed by Kukaleva et al. (2000a; b). The result was explained as being likely due to the increase of interfacial area that acts as a nucle- ating agent. The authors (Kukaleva et al., 2000a b) concluded that the studied PP/mEOC system is miscible at processing temperatures but immiscible in the solid state. Blends of PP SPECIAL ISSUE CONTRIBUTIONS Intern. Polymer Processing XXXIII (2018) 3 Ó Carl Hanser Verlag, Munich 345 * Mail address: Sebastião Canevarolo, DEMa – UFSCar, Department of Materials Engineering, Federal University of São Carlos, São Paulo 13565-905, Brazil E-mail: caneva@ufscar.br