Structure and elastic properties of immiscible LDPE-PP blends: dependence on composition
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Structure and elastic properties of immiscible LDPE-PP blends: dependence on composition Julia S. Petronyuk, Olga V. Priadilova, Vadim M. Levin, Olga A. Ledneva, Anatolii A. Popov Institute of Biochemical Physics, Russian Academy of Sciences, 119991, 4 Kosygin St., Moscow, Russia
ABSTRACT Local elastic properties and microstructural features of low-density polyethylene-polypropylene (LDPE-PP) blends have been studied by microacoustical technique, differential scanning calorimetry and infrared spectroscopy. Focused ultrasonic beam of acoustic microscope has been employed to measure elastic wave velocities, bulk and shear elastic moduli and Poisson ratio. The experiments show that the mechanical properties of immiscible LDPE-PP blends are non-additivily changeable in relation to ones of primary gomopolymers. Maximum of the moduli values is achieved with small addition of LDPE to PP. Additional drawing of bipolymer shows essential increasing of orientation ability for PP chains in 5/95 – 10/90 % LDPE-PP compositions. DSC curves show no significant deviations in melting temperature and crystallinity degree for different compositions of PP and LDPE phases. Internal microstructure has been imaged for the blends by acoustic microscopy technique. It allows revealing dispersivity of components over the blend body. INTRODUCTION Mixing of the polymers leads to production of materials with positive properties omitting more expensive stages of the new polymer synthesis. Polyolefins are the main components of plastic wastes and scrapes [1] and their regeneration as a blend has a practical importance. One of the most extensively studied polyolefins are polyethylene and isotactic polypropylene. Many papers are devoted to investigations of the polyethylene-polypropylene blends [2-4]. Mechanical property of the blends and their relation to structural organization is one of the most attractive topic of consideration. Polymer mixing can lead to improvement of the properties [5]. Variation in properties depends on blend composition, morphology and interaction between phases as well as synthesis conditions [6,7]. A series of structure sensitive methods was used in this study – DSC, IR-spectroscopy and acoustic microscopy techniques (AM). In particular, modern ultrasound methods appear a valuable tool for the local elastic property characterization (compressive as well as shear elastic moduli) and monitoring of internal microorganization [8]. EXPERIMENTAL Material Isotactic polypropylene (PP) (Tm = 159.6 °C, χ = 47%, ρ = 0.9076g/cm3, Mw = 400 000, Mn = 150 000, Mw/Mn = 2.7) and polyethylene (PE) (Tm = 106.1 °C, χ = 22%, ρ = 0.9271g/cm3, Mw = 80 000, Mn = 30 000, Mw/Mn = 3) were the objects under investigation. The extrusion method of the blend preparation is described in [9]. Isotropic films have been fabricated by pressing with
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cellophane substrate at temperature of 190 oC with following quenching in water (0 oC). Thickness of PE-PP films was ~ 200 µm. Acoustic microscopy Methods of quantitative acoustic microscopy h
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