Isotactic Polypropylene Films Research Articles

Direct Comparison of Crystal Nucleation Activity of PCL on Patterned Substrates

A sample containing different regions with poly(e-caprolactone) (PCL), oriented polyethylene (PE), and oriented isotactic polypropylene (iPP) films in contact with glass slide has been prepared to be observed in the same view field in an optical microscope and the crystallization of PCL in different regions during cooling from 80 °C down to room temperature at a rate of 1 °C·min−1 was studied. The results showed that the crystallization of PCL started first at the PE surface and then at the iPP surface, while its bulk crystallization occured much later. This indicates that though both PE and iPP are active in nucleating PCL, the nucleation ability of PE is stronger than that of iPP. This was due to a better lattice matching between PCL and PE than that between PCL and iPP. Moreover, since lattice matching existed between every (hk0) lattice planes of both PCL and PE but only between the (100)PCL and (010)iPP lattice planes, the uniaxial orientation feature of the used PE and iPP films resulted in the existence of much more active nucleation sites of PCL on PE than on iPP. This led to the fact that the nucleation density of PCL at PE surface was so high that the crystallization of PCL at PE surface took place in a way like the film developing process with PCL microcrystallites happened everywhere with crystallization proceeding simultaneously. On the other hand, even though iPP also enhanced the nucleation density of PCL evidently, the crystallization of PCL at iPP surface included still a nucleation and crystal growth processes similar to that of its bulk crystallization.

Direct Evaluation of Local Dynamic Viscoelastic Properties of Isotactic Polypropylene Films Based on a Dynamic μ-Beam X-ray Diffraction Method.

The local mechanical properties of crystalline polymer were evaluated using synchrotron radiation X-ray diffraction with 10 μm lateral resolution. A nonoriented isotactic polypropylene (iPP) film with isolated spherulites in a crystallized matrix was used as a model sample. In situ wide-angle X-ray diffraction (WAXD) measurement was performed on the iPP film using a microbeam synchrotron radiation X-ray under sinusoidal strain. The lattice spacing of the crystal planes increased and decreased in response to the applied sinusoidal strain. Local dynamic viscoelastic functions (dynamic storage and loss moduli (E' and E″)) were calculated at room temperature from the relationship between the calculated applied stress and the response strain obtained by dynamic μ-beam WAXD measurement inside and outside of the spherulites. The E' values inside and outside of spherulite obtained from the change in spacing of the (110) plane were 1.8 and 1.1 GPa, respectively. Furthermore, the E' value inside of spherulite obtained from the change in spacing of the (1̅13) plane was 6.0 GPa. These values can be explained by the deformation of crystallite, which depends on the direction of crystal planes. The results obtained here revealed that synchrotron radiation X-ray diffraction measurement gives not only structural information but also the local mechanical properties of the materials E'.

Adapting a Capillary Rheometer for Research on Polymer Melt Interfaces

Interfaces between immiscible polymers are widely known to be the origin of premature failure in multilayers and blends. Developing a small-scale, continuous method to fabricate interfaces from polymer melts with short contact times to simulate industrial coextrusion is critical for assessing new materials, polymeric systems, and processing conditions. Here we develop a miniature coextrusion die that can be fitted to a twin bore capillary rheometer for precise temperature and contact time control from 4.4 to 440 s. The design of the feedblock, stacker, manifold, and land zones was optimized via flow simulation software to allow bilayer coextrusion with minimal (<10%) edge distortions. Bilayer films of isotactic polypropylene (iPP) and polyethylene (PE) were produced using 90% less material than a lab-scale continuous multilayer coextrusion device, and the interfacial adhesion was in excellent agreement with iPP/PE bilayers produced using a continuous coextrusion technique for a range of PE molecular archi...

Stress-induced microphase separation of interlamellar amorphous phase in hard-elastic isotactic polypropylene film

Lamellar stacks, arranged alternatively with hard crystal and soft amorphous nano-layers, are the basic building units to determine the intrinsic mechanical properties of semi-crystalline polymeric materials. The mechanical instability of hard-elastic isotactic polypropylene (iPP) films with highly parallel lamellar stacks is studied with in-situ synchrotron radiation small- and wide-angle X-ray scattering (SAXS/WAXS) techniques during cyclic tensile deformation. Unexpectedly, the micro-strain, deduced from the relative variation of lamellar periodicity, shows an accelerated increase at the onset of instability and reaches values larger than the corresponding macro-strain after yield, during which no irreversible plastic destruction of crystal is observed. Combining the unpredictable increase of long period and other structural information obtained with in-situ SAXS/WAXS measurements, we propose that stress-induced microphase separation of interlamellar amorphous phase is responsible for the yield behavior and the hyperelasticity of hard-elastic iPP films, which stems from the heterogeneous distribution of tie chain/trapped entanglement in interlamellar amorphous nano-layers. This reversible stress-induced non-equilibrium phase transition of interlamellar amorphous phase is different from current plastic deformation models with crystal destruction in semi-crystalline polymers but in line with the nearly 100% elastic recovery ratio of hard-elastic films.

Structural Evolution of Hard-Elastic Isotactic Polypropylene Film during Uniaxial Tensile Deformation: The Effect of Temperature

The effects of temperature on the nonlinear mechanical behaviors of hard-elastic isotactic polypropylene films are systematically studied with in-situ ultrafast synchrotron radiation small- and wide-angle X-ray scattering techniques (SAXS/WAXS) during uniaxial tensile deformation at temperatures from 30 to 160 °C. Based on the mechanical behaviors and structural evolutions in strain–temperature two-dimensional space, three temperature regions (I, II, and III) are clearly defined with the α relaxation temperature (Tα ≈ 80 °C) and the onset of melting temperature (Tonset ≈ 135 °C) as boundaries, where different mechanisms dominate the nonlinear deformations after yield. In region I, microstrain in lamellar stacks em obtains an accelerated increase after yield and reaches a value significantly larger than corresponding macrostrain e, during which neither slipping, melting, nor cavitation occurs. We propose stress-induced microphase separation of interlamellar amorphous to be responsible to the hyperelastic b...

Oxidative degradation and morphological properties of gamma‐irradiated isotactic polypropylene films

Isotactic polypropylene (iPP) films of 25 μm thickness were subjected to gamma-ray irradiation for different doses (30, 60, 90 and 100 kGy) at ambient atmosphere and both molecular modifications and surface properties have been investigated by Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM), respectively. The occurrence of the oxidation process is identified and quantified by the FTIR. In addition, it is found that the carbonyl index increases with the absorbed dose which confirms that the irradiation process induces the diffusion of the oxygen into the iPP matrix. The AFM image (for virgin and higher dose irradiated samples) showed a dramatic change in the surface topography. The gamma radiation induces the formation of the nanostructured iPP surface. The roughness of the polymer surface, measured by AFM, increases after gamma irradiation. These results revealed that the oxidative degradation may be correlated with the morphological properties.

Evaluation of thermal degradation in isotactic polypropylene films used in power capacitors

Power capacitors are widely used by electric power utilities in electrical systems to improve power quality for their consumers. However, problems with physical installation, ambient temperature and electrical disturbances can raise the internal operating temperature above the ideal designed for the component, which can accelerate the degradation of the dielectric material. Since polypropylene film is the main part of the capacitor dielectric system, it is important to know about the effects of thermal aging on the physicochemical properties of the material. This work presents results of physical–chemical characterization tests of thermal aged isotactic polypropylene (iPP) film used in power capacitors. Tensile strength tests, dynamic mechanical thermal analysis, differential scanning calorimetry, X-ray diffraction (WAXS) and dielectric strength were performed. The results showed that the thermal aging causes morphological changes and reduction in the dielectric breakdown voltage of the iPP film.

Structure and Properties of β Nucleated Polypropylene Film Prepared by Tubular Water Quench Process

ABSTRACTβ-Nucleated isotactic polypropylene (iPP) films were prepared by tubular quench process. The stretching of the film during the process resulted in the formation of different polymorphs in nucleated iPP, whereas meso phase alone resulted in unnucleated iPP. The process conditions determine the formation of β crystals transforming into α crystals on stretching. The crystalline content and β phase decrease as the stretching speed increases. The β nucleated film samples are found to have voided surface. The degree of crystallinity and crystalline content define physical properties of the film.

Role of type and content of nanoparticles on certain dielectric characteristics of polypropylene nanocomposites

In practical power apparatus, the insulation under high electrical stress is exposed to recurrent partial discharge pulses, and the utility of the insulation is largely determined by its resistance to aging by partial discharges. The occurrence of partial discharges is largely governed by a combination of the applied field and the space charges that are generated due to these discharges. Since the space charge profile generated by a time-varying voltage and, thus, the resultant field would be much different from that of a constant ac voltage, this work investigates how the partial discharge characteristics, the resulting erosion, and remnant breakdown strength change when samples are aged with a step voltage profile. Since incorporation of nanofillers in controlled quantities is known to alter the space charge formation and transportation, this work also focuses on understanding the effect of incorporation of different quantities of natural (cloisite 20 A° natural montmorillonite clay) and synthetic (tetrasilisic fluro mica) nanofillers into a pure polypropylene matrix on its partial discharge characteristics and the resulting effect when aged under the application of step voltages. Isotactic polypropylene films with different filler concentrations of natural and synthetic nanofillers were aged. The cumulative effect of the partial discharge behavior was investigated through analysis of the erosion depth produced by these pulses on sample surface and remnant breakdown strengths of aged samples. Results indicate that maximum partial discharge magnitudes become prominently lower in nanofilled samples as compared to that of base polypropylene only when the applied voltage is beyond a certain level. Up to that voltage, the average discharge magnitude is significantly lower in samples whose filler content is below a percolation threshold, but above that voltage, the average magnitude depends on the aspect ratio of the nanofillers. Partial discharge resistance and characteristic breakdown strength increases with increase in filler content in both types of nanofilled samples, but excessive filler content is not effective in enhancing these parameters.

Investigation on the Tensile Behavior and Morphology Evolution of Isotactic Polypropylene Films Polymerized with Different Ziegler-Natta Catalysts

Stereodefect distribution is very important in determining the morphology and properties of isotactic polypropylene (iPP). In this study, two iPPs (PP-A and PP-B) with different uniformities of stereodefect distribution were prepared. The tensile behavior and morphology evolution of their cast films were studied. The morphology study of the cast films showed that compared with PP-B, PP-A with less uniform distribution of stereodefects has smaller spherulites and spheruilitic boundaries and higher degree of crystallinity. In uniaxial tensile measurements, PP-A exhibited higher yield strength and lower elongation at break. When strain was 500%, PP-A exhibits totally transparent appearance and highly oriented structures without cavities, whereas PP-B shows opaque appearance and mass of both nanometer- and micrometer-sized cavities. Moreover, calculation of rigid amorphous fraction (RAF) indicated that PP-B cast film has a higher amount of RAF, which might be the reason for the different morphology evolutions and tensile behaviors of the samples.

Three dimensional molecular orientation of isotactic polypropylene films under biaxial deformation at higher temperatures

We investigated the in-situ molecular orientation behavior of isotactic polypropylene (iPP) films under simultaneous and sequential biaxial deformation by polarized infrared spectroscopy at near melting temperature. The three-dimensional orientation functions in two stretching directions (in-plane of the film specimen) and its thickness directions were obtained from the dichroic ratios of two bands with different transition moments. Equi-biaxial stretching was found to cause iPP chains in both crystalline and amorphous regions to rotate towards the stretching plane. However, under sequential biaxial elongation, the iPP chains in both regions first oriented towards the first stretching direction and then rotated to the second stretching direction during the second stretching process.

Structure effect of thin film polypropylene view by dielectric spectroscopy and X‐ray diffraction: Application to dry type power capacitors

ABSTRACTThis work reports on the relationship between structure and dielectric properties of biaxially oriented polypropylene. The morphology of semicrystalline bioriented isotactic polypropylene films is investigated using wide angle X‐ray diffraction and Polarized Optical Microscopy. A β‐orthorhombic structure, with a crystallinity ratio of about 46%, and “Crater” morphology of the β‐form is identified. Dielectric properties are measured by Broadband Dielectric Spectroscopy over a wide temperature range (−150 to 125°C). Since the dissipation factor of the PP is very low, special care was taken to obtain valid data. Two main relaxation processes are observed: a α‐relaxation peak associated to the glass transition temperature (Tg) at temperature about −7°C, and a broad β*‐relaxation at about −60°C, partly attributed to CH orientation. The variation of the dissipation factor versus sample thickness (from 3.8 to 11.8 µm) is correlated and partly explained by the increase of crystallinity ratio and lamella size at larger thicknesses. It comes out that the thinnest film seems perfectly meet the application requesting, namely lowest dissipation factor and highest permittivity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42602.

The spatial correlation between crystalline and amorphous orientations of isotactic polypropylene during plastic deformation: An in situ observation with FTIR imaging

On the basis of research method in FTIR imaging, we made a heterogeneous thin film of isotactic polypropylene (iPP) that contains a few large spherulites (∼150 μm) which are surrounded by small spherulites (∼15 μm) for tensile testing. The evolution processes of crystalline and amorphous orientations of iPP are monitored with its characteristic peaks at 998 and 973 cm−1, respectively. By introducing the correlation images, the analysis demonstrates the relationships between the orientation evolutions of crystalline and amorphous phases in a space of 250 μm × 250 μm detecting area. During the plastic deformation, crystalline orientation is higher than amorphous orientation outside the large spherulite, while that is opposite inside the region. In addition, the evolutions of crystalline and amorphous orientations almost keep a positive correlation.

In-situ FTIR imaging on the plastic deformation of iPP thin films

The plastic deformation behavior of isotactic polypropylene (iPP) film is studied with in-situ Fourier transformation infrared microspectroscopic imaging (FTIRI). During uniaxial tensile test, spatial distributions of crystallinity and orientations are obtained in necking region (NR), transition front (TF) and non-necking region (NNR). A low valley of crystallinity exists at TF, while both NNR and NR have crystallinities at a high plateau. This provides a direct evidence of deformation-induced melting–recrystallization mechanism of plastic deformation. The non-monotonic evolution of amorphous orientation from NR, TF to NNR further supports the occurrence of deformation-induced melting–recrystallization. The decrease of amorphous orientation behind TF is attributed to recrystallization.

Viscoelastic Computational Modeling of Extruded Micro-textured Polymeric Films

The feasibility of the production of reduced-coefficient-of-friction micro-textured polymeric films by continuous extrusion using micro-patterned dies made by nonconventional meso-scale micromachining methods has been reported in our previous study [1]. During continuous manufacturing of such polymeric films, the viscoelastic effects of polymeric melts (e.g., die swell) lead to a film micro-texture that is different from the micro-patterned die. Thus, computational studies based on viscoelastic models solved by finite elements methods (FEM) were conducted to predict the die micro-geometries that develop desirable micro-texture shapes. ANSYS Polyflow® was used in conjunction with Cross and Giesekus models to predict the pressure drop and shape/die- swell of isotactic polypropylene films for a rectangular-semicircular micro-pattern. An isothermal, 3-parameter Cross model led to accurate estimation of the pressure drop through the dies, but led to poor estimations of the dimensions of the extrudate. In contrast, a unimodal Giesekus model resulted in over-prediction of the pressure drop (∼ two-fold), but led to accurate prediction of the extrudate shape and size (within an error of 15%) due to the incorporation of viscoelastic effects.

Continuously extruded micro‐textured polypropylene films

The continuous extrusion of micro‐textured isotactic polypropylene (i‐PP) film and its tribological properties are reported. As analyzed by scanning electron microscopy, a rectangular‐semicircular micro‐patterned die successfully produced extruded cast‐films with hill‐like micro‐texture. Such films displayed static and kinetic coefficients of friction (COFs and COFk) values of 0.247 ± 0.028 and 0.245 ± 0.003, respectively, for a steel fixture sliding along the micro‐texture of the film. The equivalent COFs and COFk values for non‐textured (NT) films were 0.369 ± 0.036 and 0.340 ± 0.024, respectively, confirming that textured films displayed a reduction in COF of about 30%. For textured and NT films sliding on textured films, the COFk values were even lower at 0.161 ± 0.013 and 0.113 ± 0.004, which represents about 20–40% reduction as compared with that for the NT‐NT counterparts. Films coated with a silicone lubricant displayed COFs and COFk values of 0.334 ± 0.042 and 0.099 ± 0.012, respectively, for NT films sliding over lubricated NT films, and 0.426 ± 0.031 and 0.063 ± 0.006, respectively, for textured films sliding over lubricated textured films. The COFk values for textured/non‐lubricated films approach those of NT/lubricated films, indicating that micro‐textured polypropylene films may be used in environmentally sensitive applications where lubricants and fluorinated additives may not be used for reducing friction. POLYM. ENG. SCI., 54:2147–2154, 2014. © 2013 Society of Plastics Engineers

Effects of annealing on structure and deformation mechanism of isotactic polypropylene film with row‐nucleated lamellar structure

ABSTRACTThe effects of annealing on structure and deformation mechanism of isotactic polypropylene films with row‐nucleated lamellar structure were investigated. The microstructure developments of the lamellar structure and amorphous during annealing were detected by differential scanning calorimeter and Fourier transform infrared. As annealing went on, the “core–shell sandwich” lamellar structure was proposed to explain the unique tensile property and the microstructure changes of the annealed films. The recrystallized lamellar structure improved the ability of slipping resistance of original lamellar structure during stretching. Microporous membranes were produced through melt extrusion/annealing/uniaxial stretching way. The uniformities of micropore structure of microporous membranes were improved as the annealing time increased for the annealed films. As the “core–shell sandwich” structure developed during annealing, the shapes and diameters of micropore structure were getting more uniform. The annealing time for annealed films improved the water vapor transmission of the microporous membranes, indicating the increased interconnectivity of the pore structure. The pore dimensions of the microporous membranes measured by mercury porosimetry increased with the annealing time for annealed films. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1659–1666, 2013

Improved thermal oxidation stability of polypropylene films in the presence of β-nucleating agent

Thermal oxidation behavior of isotactic polypropylene (PP) films with and without nucleating agent was investigated at 100 °C in air. The crystal form of PP was modified with a specific aryl amide derivative as β-nucleating agent (β-NA). Fourier transform infrared spectroscopy (FTIR), polarized optical microscopy (POM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile tests were performed to determine the extent of chemical degradation and the variations of microstructure of the two kinds of PP films during thermal oxidation. It was found that the mechanism of thermal oxidation of PP films was not changed in the presence of β-NA, but the time to initiation and the rate of oxidation both declined. Moreover, during the thermal oxidation aging, the melting temperature of neat PP significantly decreased while only a slight decrease of the melting temperature occurred for β-PP. Overall, the investigation indicated that the thermal oxidative stability of β-PP was higher than that of neat PP. The underlying mechanism was further analyzed by considering the change in the physical structure, especially the crystalline and the amorphous structure, of PP in the presence of β-NA.

Molecular Orientation Behavior of Isotactic Polypropylene Films under Uniaxial and Biaxial Deformation at Elevated Temperatures

Abstract In-situ molecular orientation behavior of isotactic polypropylene films prepared by quenching at 0°C was investigated under uniaxial and biaxial extension at elevated temperatures. Both the retardation value of film and the stress were simultaneously measured during stretching. The stress required to deform films depended on the stretching temperature, but the retardation was nearly independent of temperature.

Stimuli-responsive membranes through peroxidation radiation-induced grafting of 2-hydroxyethyl methacrylate (2-HEMA) onto isotactic polypropylene film (IPP)

Stimuli-responsive membranes were prepared by peroxidation radiation-induced grafting of 2-hydroxyethyl methacrylate (2-HEMA) onto IPP. The radioactive isotope 60Co was used as the source of gamma radiation. A plausible mechanism of grafting has been proposed. Using this method, the degree of grafting and morphology could be controlled through the variation of reaction parameters such as total dose, inhibitor concentration, monomer concentration, reaction time, reaction temperature and solvents. Maximum percentage of grafting (210 %) was obtained at total radiation dose of 20 kGy. The graft copolymerization reaction was carried out for 3 h with 20 v/v% of the monomer (2-HEMA) in methanol at 85 °C using 0.06 wt% of FeCl3 as inhibitor. The chemical structures of grafted membranes were characterized by Fourier transform infrared spectroscopy (FTIR) which indicates that HEMA has been grafted onto IPP. The atomic force microscopy (AFM), scanning electron microscopy (SEM) techniques were used to assess the morphological characterization of the membranes, revealing the roughness of the surface. These membranes were investigated for their swelling behavior. pH-sensitivity and the dyeability of the grafted and ungrafted membranes have also been studied.