Gas Permeability of Uniaxially Deformed Polyethylene and Polypropylene Films

1. Iw In Gas Permeability of Uniaxially DeformedPolyethylene and Polypropylene Films D. Klepac1, K. Galić2, S. Valić1,3 1 School of Medicine, University of Rijeka, Braće Branchetta 20, HR-51000 Rijeka, Croatia 2 Faculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6, HR-10000 Zagreb, Croatia 3 Rudjer Bošković Institute, Bijenička 54, HR-10000 Zagreb, Croatia dklepac@medri.hr Results Objective • influence of the parallel and perpendicular uniaxial deformation on the gas permeability of polyethylene and polypropylene films • correlation of the permeability measurements with those obtained by ESR and DSC l = degree of deformation l = deformed sample length (cm) l0 = initial sample length (cm) q = permeance unit (cm3 m-2 d-1 bar-1) Materials Figure 1. Gas permeability of deformed a) polyethylene, b) polypropylene Xc = degree of crystallinity (%) ΔHf = heat of fusion (J g-1) ΔHf,th = theoretical heat of fusion of 100% crystalline polymer (J g-1) Methods • electron spin resonance (ESR) - spin probe method • differential scanning calorimetry (DSC) • manometric method • the mean values of three independent measurements were calculated for DSC and manometric measurements Figure 2. Degree of crystallinity of deformed a) polyethylene, b) polypropylene Figure 4. ESR spectra of a) non-deformed, b) perpendicularly and c) parallelly deformed PE. ESR spin probe 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl • 1 wt.% of spin probe was incorporated in PE samples by swelling the samples in the toluene probe solution at 60 °C; solvent was removed and samples were annealed at 60 °C for 48 hours • ESR measurements were preformed in the temperature range from -100 ºC to 120 ºC Tg = glass transition temperature (K) Figure 5. Temperature dependence of the outer extrema (2Azz) of ESR spectra for non-deformed, parallelly deformed and perpendicularly deformed PE. Figure 3. ESR spectra of non-deformed polyethylene in the temperature range from -100 ºC to 120 ºC References • L.S. Somlai, R.Y.F. Liu, L.M. Landoll, A. Hiltner, E. Baer, Effect of orientation on the free volume and oxygen transport of a polypropylene copolymer, J. Polym. Sci. Pol. Phys. 43 (2005) 1230-1243. • J.P.G. Villaluenga, B. Seoane, Influence of drawing on gas transport mechanism in LLDPE films, Polymer 39 (1998) 3955-3965. • Z. Hlouškova, J. Tino, I. Chodak, Study of PE-based composites by the spin-probe method, Eur. Polym. J. 30 (1994) 175-178. • manometric measurements show the increased permeability of parallelly and perpendicularly deformed PP and of perpendicularly deformed PE. Only a slight decrease in permeability of parallelly deformed PE has been measured. • DSC measurements indicate slight increase of the crystallinity for both parallelly and perpendicularly deformed PE and for parallelly deformed PP. A small decrease of the crystallinity in perpendicularly deformed PP has been observed. • ESR spectra indicate that the probe motions are hindered by deformation. The higher amount of the broad component (lower In/Iw) in deformed samples can be attributed to the anisotropy of the probe motion and dynamic restrictions induced by the deformation of free volume holes. • T5mT increases for 8 °C when PE film is parallelly deformed with l = 1.48. Conclusions • For PP samples containing around 40% of crystalline phase, the change of the crystalline phase amount seems to have a moderate influence on the film permeability. The increase of permeability should be therefore related to the changes in the size and shape of the free volume holes induced by external deformation. • The deformation of PE leads to the lower change in the permeability than in the PP. The change in permeability seems to be governed mostly by the amount of the crystalline phase.