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CRYSTALLINE POLYMERS IN MULTILAYERED FILMS AND BLEND SYSTEMS

ZHANG, GUOJUN

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2014, Doctor of Philosophy, Case Western Reserve University, Macromolecular Science and Engineering.
Abstract CHAPTER 1: In this study, multilayer films of sPS-PPS (syndiotactic Polystyrene and Polyphenylene sulfide blend) against P4MP1 [Poly (4-Methylpentene-1)] with various compositions and layer thicknesses were prepared by a layer multiplying co-extrusion process. Incorporating the PPS into sPS layers before co-extrusion produced pores in the sPS layers upon a post-extrusion, uniaxial orientation. Confined crystallization of P4MP1 by sPS-PPS was examined before and after the uniaxial orientation. A melt and recrystallization method was employed to achieve the preferred in-plane orientation of P4MP1 crystals. This was characterized by the atomic force microscopy and x-ray spectroscopy. We found that with P4MP1 layer thickness smaller than 400 nm, a confinement effect will induce in-plane P4MP1 crystal orientation where the crystal c-axis is perpendicular to the film. This arrangement of crystals reduced oxygen’s tortuosity through the multilayer films. This conclusion was verified by increased oxygen permeability of the stretched-recrystallized multilayer films. CHAPTER 2: High-density polyethylene (HDPE) was co-extruded against high glassy transition temperature (Tg) polycarbonate (PC) to fabricate multilayer films. Melt and recrystallization experiments were conducted on these extruded films to study the effects of isothermal recrystallization temperature and layer thickness on HDPE lamellae orientation. WAXS and AFM were used to demonstrate lamellar morphology of HDPE layers. We report that HDPE lamellae show twisted morphology in 30 nm thin layers after confined crystallization at a high temperature (128 oC). It may be the first time that anyone has created such twisted lamellar morphology with HDPE in such a thin layer. Similar twisted morphology of HDPE was also observed when HDPE was co-extruded with another high Tg glassy polymer, polysulfone (PSF). Interestingly, the twisted HDPE lamellar morphology associated with an increased crystallinity improves both the oxygen and water vapor barrier properties of the multilayer films. CHAPTER 3: Confined crystallization of high-density polyethylene (HDPE) in multiplayer films is studied in this paper. A new cyclic olefin copolymer (COC), HP030, is co-extruded with HDPE by a layer multiplying technique. The number of layers and layer compositions are changed to study the effect of layer thickness on the crystalline morphology of the HDPE layers under confinement. Atomic force microscopy (AFM) is used to investigate the crystalline morphology of the HDPE layers. MOCON ((Minneapolis, MN, commercial instrument) units are employed to measure both oxygen permeability and water vapor transport rate (WVTR) of these co-extruded HDPE/HP030 multilayer films. We report that when the HDPE layer nominal thickness is about 290 nm in the HDPE/HP030 multilayer films, the HDPE layer effective gas barrier property is improved approximately 2 times for oxygen and 5 times for water vapor. This is the result of confined spherulite morphology of HDPE, which increases the tortuosity for gas to diffuse through the films. Similar phenomenon is found for polypropylene (PP), when PP is co-extruded against polycarbonate (PC). The same experiments as for HDPE are conducted to confirm that PP spherulites have been confined by PC in PP/PC multilayer films. We discover that the confined spherulites of PP improve its gas barrier properties as well. CHAPTER 4: Blends of linear low density polyethylene (LLDPE) and ethylene vinyl alcohol (EVOH) with different weight fractions are extruded to fabricate thin films. The extruded blend film morphology is investigated by atomic force microscopy (AFM). The extruded blend films have shown extended morphology along the extrusion direction (ED) and dispersed morphology along the transverse direction (TD). We report that due to this morphology, a two-dimensional (2-D) confined crystallization occurs. The EVOH has successfully confined the LLDPE from both film normal direction (ND) and transverse direction (TD) in this study. The confinement from ND results in an on-edge orientation of LLDPE, while the confinement from TD forces the on-edge oriented LLDPE crystals to further elongate along the extrusion direction (ED). This specific crystal orientation is different from one-dimensional (1-D) confined crystallization observed in multilayered films. Both wide angle X-ray scattering (WAXS) and small angle x-ray scattering (SAXS) are utilized to investigate the crystal orientations of LLDPE in the extruded blend films. Moreover, due to the morphology, the extruded blend films have shown high oxygen barrier properties, which make this material valuable in packaging applications. CHAPTER 5: The blend of linear low-density polyethylene (LLDPE) and ethylene vinyl alcohol (EVOH) with weight fraction of 50-50 is extruded by a multiplication extrusion system to fabricate thin films. Different numbers of multipliers are utilized to tailor the morphology of the extruded blend films. We found that as the number of multipliers increases, the blend film morphology transforms from an elongated and layer-like structure to the co-continuous structure and eventually becomes homogeneous. This is because during the multiplication process, the multipliers behave similar to static mixers that physically break the elongated and co-continuous like structure of LLDPE and EVOH into tiny domains. As the morphology evolves, the physical properties of the extruded blend films change dramatically. After the co-continuous and elongated morphology becomes homogenous, both the gas permeability and the transmission rate of these films increase. The tensile mechanical behaviors become isotropic at different deformation directions. Atomic force microscopy (AFM) and wide angle X-ray scattering (WAXS) are utilized to investigate the morphology and crystalline structure of the blend films. Oxygen gas permeability and water vapor transport rate (WVTR) of these blend films are measured by MOCON units. The transmission rate and mechanical properties are studied by the UV-vis and a mechanical tensile stretcher (MTS) respectively.
Eric Baer (Committee Chair)
203 p.

Recommended Citations

Citations

  • ZHANG, G. (2014). CRYSTALLINE POLYMERS IN MULTILAYERED FILMS AND BLEND SYSTEMS [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1404923073

    APA Style (7th edition)

  • ZHANG, GUOJUN. CRYSTALLINE POLYMERS IN MULTILAYERED FILMS AND BLEND SYSTEMS. 2014. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1404923073.

    MLA Style (8th edition)

  • ZHANG, GUOJUN. "CRYSTALLINE POLYMERS IN MULTILAYERED FILMS AND BLEND SYSTEMS." Doctoral dissertation, Case Western Reserve University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1404923073

    Chicago Manual of Style (17th edition)