Synthesis, characterization and applications of ethylene vinylalcohol copolymers Citation for published version (APA): Ketels, H. H. T. M. (1989). Synthesis, characterization and applications of ethylene vinylalcohol copolymers. Technische Universiteit Eindhoven. https://doi.org/10.6100/IR316591 DOI: 10.6100/IR316591 Document status and date: Published: 01/01/1989 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. 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Tels, voor een commissie aangewezen door het College van Dekanen in het openbaar te verdedigen op dinsdag 12 september 1989 te 16.00 uur door Hendrikus Hubertus Theodoor Maria Ketels geboren te Tegelen druk. wrbr'O dlss~rt:atn::idrukkerq. helmand Dit proefschrift is goedgekeurd door de promotoren: Prof. Dr. P.J. Lemstra Prof. Dr. Ir. H.E.H. Meijer en de copromotor: Dr. G.P.M. van der Velden CONTENTS CHAPTER 1 INTRODUCTION 1.1 EVOH copolymers 1.2 Permeability of polymers 2 1.3 Factors influencing permeability 5 1.4 Background of the present investigation 7 1.4.1 EVOH copolymers used as harrier resins 7 1.4.2 EVOH copolymers for fiber production 10 1.5 Aim of the present investigation 11 1.6 Survey of thesis 11 1.7 References 14 CHAPTER 2 SYNTHESIS OF EVOH COPOL YMERS 2.1 Introduetion 15 2.2 Copolymerization of ethylene and vinylacetate 16 2.3 Experimental 21 2.3.1 Principle of operation 21 2.3.2 Apparatus 21 2.3.3 Copolymerization process 24 2.3.4 Characterization techniques 25 2.4 Results and discussion 26 2.4.1 Ethylene content 26 2.4.2 Molecular weight 27 2.5 Conclusions 29 2.6 References 31 CHAPTER3 MICROSTRUCIURE OF EVOH COPOL YMERS AS STUDlED BY 1H AND 13C NMR 3.1 Introduetion 33 3.2 Experimental 34 3.2.1 Materials 34 3.2.2 NMR measurements 34 3.3 Results and discussion 35 3.3.1 1H NMR 35 3.3.2 13C NMR 43 3.4 Conclusions 51 3.5 References 53 CHAPTER4 EVOH/NYWN-6 BLENDS 4.1 Introduetion 55 4.2 Experimental 56 4.2.1 Materials 56 4.2.2 Films 56 4.2.3 Characterization techniques 56 4.3 Results and discussion 58 4.3.1 Extrusion blending of EVOH and Nylon-6 58 4.3.2 Barrier properties of EVOH/Nylon-6 films 59 ii 4.3.3 Miscibility of EVOH and Nylon-6 61 4.3.4 Mechanical properties of EVOH/Nylon-6 films 64 4.3.5 Transmission Electron Microscopy 65 4.3.6 Solid State 13C NMR 66 4.3.6.1 Chemica! shifts 66 4.3.6.2 Spin lattice relaxation times 69 4.4 Conclusions 72 4.5 References 73 CHAPTER 5 EVOH/PET AND EVOH/PE BLENDS 5.1 Introduetion 75 5.2 Experimental 80 5.2.1 Materials 80 5.2.2 Blends and films 81 5.2.3 Irradiation 83 5.2.4 Morphology 83 5.3 Results and discussion 83 5.3.1 Stratified pellets 83 5.3.2 Compatibilizers 84 5.3.3 Irradiation 86 5.3.4 Films 87 5.4 Conclusions 92 5.5 References 94 111 CHAPTER6 PREPARATION AND CHARACfERIZATION OF SOLUTION (GEL-SPUN) EVOH FIBERS 6.1 Introduetion 95 6.2 Experimental 96 6.2.1 Materials 96 6.2.2 Fiber-spinning/drawing 96 6.2.3 Characterization techniques 97 6.3 Results and discussion 97 6.3.1 Synthesis of EVOH copolymers 97 6.3.2 Properties of EVOH fibers 98 6.3.3 Development of Young's modulus as a function of draw ratio .À 99 6.4 Conclusions 102 6.5 References 103 APPENDIX Al Introduetion 105 A2 Experimental 105 A.2.1 Materials 105 A.2.2 NMR measurements 106 A3 Results and discussion 106 A4 Conclusions 114 A5 References 115 iv SUMMARY 117 SAMENVATTING 121 CURRICULUM VITAE 125 V CHAPTER 1 INTRODUeTION 1.1 EVOH copolymers Copolymerization represents one of the most powerfut tools in tailoring polymer systems to meet specific engineering needs and sametimes extends the range of 1 3 utility of monomers that would otherwise be of Iimited value • • Ethylene vinylalcohol copolymers are paradigmatic in this respect. The pure homopolymer polyvinylalcohol (PVOH) possesses intrinsic limitations concerning processability and moisture sensitivity. The abundance of -OH side groups promotes the absorption of water, resulting in a deterioration of physical and mechanica! properties, and moreover degradation occurs during processing via the melt. At relative low humidities however, the pure homopolymer PVOH possesses interesting properties. The -OH side group is relatively smalt and consequently PVOH is crystallizable, despite its atactic character, into a distorted monoclinic version of the polyethylene structure. Due to its crystal­ linity, but notably due to the high glass transition temperature Tg (approx. 80 oe at 0 % relative humidity (R.H.)), PVOH possesses excellent harrier properties (low permeability) against gases like oxygen (02) and carbon dioxide (C02), at low relative humidities. The similarity of PVOH and polyethylene with respect to the crystal structure stimulated research efforts to produce high-strength/high-modulus fibers similar to developments based on polyethylene Iike melt-spinning and/or 4 solution-spinning/ultra-drawing • Developments in using PVOH as harrier film and high-performance fibers have only been partly succesfull, mainly as a consequence of the moisture sensitivity and lack of processability. A salution to this problem could be the incorporation of ethylene in the PVOH chain which results in the EVOH copolymer. On a technological scale, PVOH is produced via complete hydralysis (methanolysis) of polyvinylacetate (PVA). Direct synthesis from the corresponding monoroer "vinylalcohol" is impossible since this species exists in its more stable, tautomerie, keto-form: acetaldehyde. It is well known that ethylene and vinylacelate copolymerize readily into a copolymer, ethylene vinylacelate (EVA) copolymer, in which the ethylene and vinylacetate units are arranged at random along the molecule. Hydralysis of these EVA copolymers results in ethylene vinylalcohol (EVOH). The hydrapbobic ethylene segments willlower the moisture sensitivity. EVOH copolymers are quite unique because they are co-crystallizable over the 5 whole composition range • This results in a, relatively, smalt decrease of melting temperature and crystallinity of the EVOH copolymers with changing composition. Moreover, the T 1 of EVOH copolymers decreases, in comparison with PVOH, only slightly with increasing ethylene content (e.g. Tg EVOH (44 mole% ethylene) = 65 oe at 0% R.H.). The decomposition temperature of the EVOH copolymers is, in contrast to PVOH, above the melting point and consequently melt processing is possible. A disadvantage of EVOH copolymers is their brittleness due to their relative low molar mass as will be discussed in chapter 2. In this thesis the possibilities of EVOH copolymers for the production of fibers and fortheuse as a harrier resin will be investigated. For a better understanding of the harrier properties of polymers in general, some introductory remarks about the permeability of polymers are given in the next section. 1.2 Penneability of p«)}ymers The process of permeation through non-porous polymers is generally explained 6 in terros of the solution-diffusion model • This model postulates that the permeation of a gas through a polymer film occurs in three stages: 1 sorption of the penetrant in the surface of the polymer, ~ diffusion through the polymer 2 and l desorption from the other face. The permeability P is a combination of the diffusivity D of the gas dissolved in the polymer and its concentration gradient, which in turn is proportional to the gas solubility Sin the polymer. Above the glass transition temperature T1 of the polymerjpenetrant system the solubility of gases usually obeys Henry's law and the sorption isotherm shows a linear dependenee of concentration C versus pressure p: S = C/p (I) Since the solubility of gases in rubbery polymers is sufficiently small ( < 0.2 o/o) the concentration dependenee of D is negligible.