Study of Polypropylene Morphology Obtained from Blown and Cast Film Processes: Initial Morphology Requirements for Making Porous Membrane by Stretching (original) (raw)
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Polymers
In this study, block and random copolymers of polypropylene–ethylene are selected to prepare porous membranes through the melt extrusion-annealing-uniaxial stretching technique (MEAUS), at a constant draw ratio. In some cases, these copolymers were blended with a homopolymer grade. The variation of temperature in the stages of extrusion, annealing and uniaxial strain was analysed. Several characterisation techniques were employed to study this influence. The crystalline orientation was analysed by polarised infrared spectroscopy (FT-IR), and crystalline features were studied by differential scanning calorimetry (DSC). The thermal stability of the membranes was checked by thermogravimetric analysis (TGA). Tensile tests were performed to ascertain the stiffness and ductility of the produced samples. The results were correlated with the porous morphology, global porosity, and permeability to air. A close relationship was found between crystalline characteristics, porous morphology and ...
Polymer, 2009
Cast films of a high molecular weight linear polypropylene (L-PP) were prepared by extrusion followed by stretching using a chill roll. An air knife was employed to supply air to the film surface right at the exit of the die. The effects of air cooling conditions, chill roll temperature, and draw ratio on the crystalline orientation, morphology, mechanical and tear properties of the PP cast films were investigated. The crystallinity and crystal size distribution of the films were studied using differential scanning calorimetry (DSC). It was found that air blowing on the films contributed significantly to the uniformity of the lamellar structure. The orientation of crystalline and amorphous phases was measured using wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR). The amount of lamellae formation and long period spacing were obtained via small angle X-ray scattering (SAXS). The results showed that air cooling and the cast roll temperature have a crucial role on the orientation and amount of lamellae formation of the cast films, which was also confirmed from scanning electron microscopy (SEM) images of the films. Tensile properties and tear resistance of the cast films in machine and transverse directions (MD and TD, respectively) were evaluated. Significant increases of the Young modulus, yield stress, tensile strength, and tensile toughness along MD and drastic decreases of elongation at break along TD were observed for films subjected to air blowing. Morphological pictograms are proposed to represent the molecular structure of the films obtained without and upon applying air cooling for different chill roll temperatures. Finally, microporous membranes were prepared from annealed and stretched films to illustrate the effect of the PP cast film microstructure on the morphology and permeability of membranes. The observations of SEM surface images and water vapor transmission rate of the membranes showed higher pore density, uniform pore size, and superior permeability for the ones obtained from the precursor films prepared under controlled air cooling.
Polymer, 2005
This work reports the flat sheet membrane preparation from syndiotactic polypropylene (sPP) by thermally induced phase separation (TIPS) process. sPP obtained by polymerization using metallocene catalysts and isotactic polypropylene (iPP) also obtained via metallocene catalysis with similar molecular weight were used. The phase diagrams of sPP and iPP with diphenylether as diluent were obtained. The properties of three representative membranes from sPP and three from iPP, prepared using different PP concentrations were evaluated with respect to membrane pore structure, gas flow, liquid displacement (bubble point), and water permeability. Two selected membranes, one from sPP and one from iPP were analysed with regard to polypropylene bulk morphology (X-ray diffraction) and mechanical properties (tensile strength). Under the same formation conditions, membranes with less inter-connected pores and less porous surface were obtained from sPP compared with iPP. Overall, lower permeabilities had been found for the sPP membranes, which were attributed to the difference in pore morphology. The differences between sPP and iPP were also discussed in terms of different driving forces for liquid-liquid demixing as deduced from the phase diagrams. The X-ray analysis had shown that the sPP membranes had a higher amorphous phase content than that in iPP, and the mechanical test had revealed a pronounced ductile behaviour for sPP samples. These results helped to explain the lower permeabilities of the sPP membranes, and their pressuredependency. q
Stretching High Melt Strength Polypropylene (HMSPP)
The use of traditional polypropylene resins in blow film processes has been prevented due to their poor melt strength and bubble instability. To overcome these deficiencies is necessary to improve the melt strength since it is known that opportunities exist for the use of a high melt strength polypropylene resin in blown film process. This work aims to study the HMSPP films obtained by gamma radiation under acetylene, after uniaxial expantion. The thin films were stretched at 170 °C using an Instron machine. Film surface morphology and the thermal properties at HMSPP stretched were analised using atomic force microscopy (AFM), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results showed some evidences of fibrillar structures containing crystallites and gel formation. Preferred orientations of crystals that develop stretching polypropylene samples are observed
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Polymer-Plastics Technology and Materials, 2019
The objective of this research was to investigate process limits and properties of porous tapes obtained by solid-phase die-drawing of talc-filled polypropylene to a thickness of 1 mm, which is low for this process. Two different composites with different talc particle size distributions were drawn under similar conditions and the development of porosity with increasing linear draw ratio was more gradual in the drawn product with smaller mean particle size, leading to greater mechanical strength even at a final porosity level matching that in the other drawn material. The morphology of the drawn products was examined to explain these trends.