Research Article Received: 11 October 2011 Revised: 6 March 2012 Accepted: 27 March 2012 Published online in Wiley Online Library: (wileyonlinelibrary.com) DOI 10.1002/pi.4338 Oxygen permeability, electron spin resonance, differential scanning calorimetry and positron annihilation lifetime spectroscopy studies of uniaxially deformed linear low-density polyethylene film Damir Klepac, a Mario ˇ Sˇ cetar, b Mia Kurek, b Peter E. Mallon, c Adriaan S. Luyt, d Kata Gali´ c b and Sre´ cko Vali´ c a,e* Abstract Linear low-density polyethylene (PE-LLD) films were mechanically deformed at room temperature in both parallel and perpendicular directions to their initial orientation obtained during the manufacturing process. The degree of deformation λ, defined as λ = l/l 0 , l and l 0 being the length of the deformed and relaxed samples, respectively, was varied from 1.0 to 2.0. Oxygen transport was investigated by a manometric method and the results were correlated with differential scanning calorimetry and positron annihilation lifetime spectroscopy measurements in order to investigate the contribution of various factors that influence the permeability of deformed PE-LLD films. An electron spin resonance spin-probe method was employed to determine the influence of uniaxial deformation on the chain segmental mobility in the amorphous phase. The results show that the deformation process reduces oxygen permeability and diffusion coefficients. It was found that the reduction is a combined effect of an increased crystallinity and reduced fractional free volume. The decrease of the chain segmental mobility with deformation plays an important role in the gas diffusion mechanism. c  2012 Society of Chemical Industry Keywords: polyethylene; uniaxial deformation; gas permeability; ESR – spin probe; PALS INTRODUCTION Linear low-density polyethylene (PE-LLD) is the most widely used polymeric material in the food packaging industry, largely because of its special physical properties such as high barrier resistance against gases and water vapor, high tear strength and toughness, excellent environmental stress cracking resistance, and also improved processability compared with conventional low- density polyethylene (PE-LD). However, its main disadvantage is that films made of PE-LLD can be easily deformed by application of mechanical force, even at room temperature. Such deformation is likely to occur during transportation and handling of packed food and affect the barrier properties of PE-LLD. In turn, this could lead to possible food degradation caused by an increase in oxygen permeability. Hence understanding the gas diffusion process in deformed polymer materials is of vital importance for the food packaging industry. It is well known that gas permeation through undeformed polymer films is described by the solution – diffusion mechanism. 1,2 In the drawn films, one would also expect other mechanisms of permeation, such as the mass flow through holes type of mechanism. 3 However, Villaluenga et al. 4 showed that the main transport mechanism in parallel and perpendicularly drawn PE- LLD films is also of the solution–diffusion type. This mechanism involves dissolution of the gas in the film matrix at the higher concentration side, molecular diffusion of the gas through the film driven by a concentration gradient and evaporation of the gas from the other surface. 5 The second step of the process, i.e. diffusion, is much slower compared with others, so it is considered as the rate-limiting step in gas transport across a film. Solid-state NMR spectroscopy revealed that the semicrystalline polyethylene is composed of crystalline, amorphous and intermediate regions. 6 It is known, however, that the sorption and diffusion phenomena ∗ Correspondence to: Sre´ cko Vali´ c, Department of Chemistry and Biochemistry, School of Medicine, University of Rijeka, Bra´ ce Branchetta 20, HR-51000 Rijeka, Croatia. E-mail: valics@medri.hr a Department of Chemistry and Biochemistry, School of Medicine, University of Rijeka, Bra´ ce Branchetta 20, HR-51000 Rijeka, Croatia b Faculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6, HR-10000 Zagreb, Croatia c Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa d Department of Chemistry, University of the Free State (Qwaqwa Campus), Private Bag X13, Phuthaditjhaba 9866, South Africa e Rudjer Boˇ skovi´ c Institute, Bijeniˇ cka 54, HR-10000 Zagreb, Croatia Polym Int (2012) www.soci.org c  2012 Society of Chemical Industry