Thin Polypropylene Films Research Articles

Oriented crystallization and mechanical properties of polypropylene nucleated on fibrillated polytetrafluoroethylene scaffolds

It is known that friction deposited polytetrafluoroethylene (PTFE) layers are able to nucleate crystallization of thin films of isotactic polypropylene (iPP). In order to investigate the influence of PTFE on the crystallization behavior and morphology of iPP in bulk, PTFE-particles of two different sizes in various concentrations were melt-blended with iPP and subsequently processed by injection molding. For one size of particles, high resolution scanning electron microscopy (HR-SEM) showed the presence of a PTFE scaffold consisting of highly fibrillated PTFE particles. With X-ray diffraction (WAXD) pole-figures, it was evidenced that, after melting and recrystallization of the iPP matrix, a strongly oriented crystallization of iPP on this PTFE scaffold takes place (quiescent crystallization conditions). With WAXD it was also shown that under processing conditions, PTFE acts as a nucleating agent for iPP and that PTFE strongly enhances the formation of processing induced morphologies. Impact and tensile performance of the mixtures were measured. Both the strain energy release rate (GI) and the E-modulus were found to increase upon introducing PTFE in iPP. POLYM. ENG. SCI., 45:458-468, 2005.

Covalent immobilization of polypropylene thin films

This article describes a simple and versatile approach to the covalent attachment of ultrathin polypropylene films on silicon wafers. The immobilization was accomplished by way of the C–H insertion reaction of perfluorophenyl nitrenes generated by thermolysis or photolysis of perfluorophenyl azides. Covalently immobilized thin films of crystalline and amorphous polypropylene and an elastomeric copolymer of polypropylene were successfully fabricated. Patterned polypropylene films were also delineated.

Numerical and Physical Modeling of Polymer Crystallization

Abstract Crystallization of thin polypropylene films was performed in isothermal, constant cooling-rate and mixed conditions. The experiments were first analyzed using the classical procedures based on simplified forms (Avrami, Ozawa) of the general Kolmogoroff-Avrami-Evans (KAE) theory. These analyses, which can be applied over an unusually wide transformation range, show that the crystallizations are actually 2 D. Then, a procedure has been established for the determination of the nucleation and growth parameters involved in the theoretical model presented in the first paper of this series. These parameters have been introduced into the model in order to predict the crystallization behavior in isothermal, constant-cooling-rate and mixed-conditions: transformed fraction, number of activated nuclei, final size distribution of semi-crystalline entities. A very good agreement is generally found between predictions and experimental results.

Determination of film thickness and refractive index by interferometry

The interference fringes formed in an air wedge and those based on the theory of two-beam interference such as the Pluta microscope and Michelson interferometer are utilized for estimating the thickness and/or refractive index of transparent polypropylene thin films. The theories of the methods are presented, and their applications to measurement of film thickness and refractive index are given. The accuracy of the measured film thickness and refractive index is calculated. The three interference methods proved that they could be transformed into valuable technological tools. The study established that, estimation of the thickness of thin films by the air wedge interference method is more simple and more accurate than the others. Films not more than 50 μm thickness are recommended in the Pluta interference microscope.

Controlled grafting of N-isoproply acrylamide brushes onto self-standing isotactic polypropylene thin films: surface initiated atom transfer radical polymerization

Surface initiated atom transfer radical polymerization (ATRP) technique using CuBr/CuBr 2/bpy complex is employed to graft N-isopropyl acrylamide (NIPAA) brushes onto ‘self-standing’ isotactic polypropylene (iPP) film surface via iPP-Br macro-initiator. The successful accomplishment of surface grafting is understood from the UV–Vis, ATR-FTIR, XPS, SEM analysis and contact angle measurements of the modified samples. The ability to control the degree of grafting of NIPAA brushes reaffirms the elegance of the surface initiated ATRP technique to develop tailor-made polymer surfaces. The LCST nature of the NIPAA brushes would introduce stimuli responsive character onto the surface of the iPP films used for various specialty applications, especially for biomedical purposes.

Resonance absorption of coherent infrared radiation by thin polypropylene films and its technological applications

Tunable CO 2 and non-tunable CO 2 lasers were used for the irradiation of thin polypropylene films. The wavelength of the IR radiation was adjusted in such a way that it coincided exactly with the absorbance peak in the spectrum of the polypropylene pattern. In this way, conditions of resonance absorption of IR radiation by polymer films were produced. Strong thermal effects in PP were observed under irradiation at the resonance wavelength. The threshold value of IR power, which causes thermal phenomena in irradiated films was established. We pulled films exposed to established threshold values with a constant speed in the plane normal to the laser beam. Highly developed relief and thin traces were formed depending on the pulling speed. Traces with a width smaller than the wavelength of the incident laser beam were obtained. The IR spectra of irradiated PP films were studied with a FTIR spectrometer. Changes in the spectra of PP films were established using correlation analysis of spectral data. The phenomenon could be applied for obtaining highly developed surface relief, storage of information in polymer films and welding of polymer materials.

Combinatorial Approach for Studying the Effects of 4-Biphenyl Carboxylic Acid on Polypropylene Films

The crystallization behavior of thin polypropylene films with and without 4-biphenyl carboxylic acid as a nucleating agent was investigated using high-throughput methodology in conjunction with optical microscopy. The high-throughput approach involves the use of thin films cast with a gradient in thickness, placed on a hot stage possessing a temperature gradient orthogonal to the thickness gradient. This system is used to study the effect of the nucleating agent on the morphology at different temperature and film thickness combinations. The addition of the nucleating agent, upon annealing and undercooling, results in spherulite formation 10−15 °C higher than neat crystallization temperatures and spherulite sizes an order of magnitude smaller than those of neat polypropylene. 4-Biphenyl carboxylic acid can have a significant effect on the morphology of thin polypropylene films.

Spectroscopic and thermal studies of gamma irradiated polypropylene polymer

Thin films of polypropylene have been irradiated with different doses of gamma radiation from a 60Co source. IR, UV-VIS spectra of this polymer before and after irradiation have been recorded and from the spectral data some modifications in the properties have been investigated. The spectra indicated that polypropylene film was oxidised at the dose of 106 Gy. Due to the removal of additives, total destruction of the polymer takes place at this dose. Isotactic arrangement of the polymer is no longer present after irradiation. Growth of carbon cluster takes place above a gamma dose of 102 Gy. Thermal stability of the polymer changes due to irradiation and the polymer seems to decompose in four different steps at the highest dose of 106 Gy.

Energy loss straggling of energetic 1H and 2H ions crossing polypropylene foils

An indirect transmission method as nuclear technique in precise measurement of energy loss straggling in polymer foils is presented. The details of experimental procedures related to the combination of Rutherford backscattering spectrometry and transmission technique are described. Advantages of the application of such a method in energy straggling experiments are discussed. The energy loss straggling measurements have been performed in the energy range of 900–3000 keV for protons and deuterons in thin films of polypropylene. The obtained values of energy straggling are compared to those deduced from Bohr and Bethe–Livingston theoretical predictions. This comparison was made by using Bragg’s rule as model of calculation over the investigated energy range.

Monte Carlo simulation on the glass transition of free-standing atactic polypropylene thin films on a high coordination lattice

A recently developed high coordination lattice based Monte Carlo method is applied to investigate the glass transition of free-standing atactic polypropylene thin films. In this method the short-range interactions are described by a rotational isomeric state model and the long-range interactions are obtained from a discretized form of a Lennard-Jones function. Simulations of five thin films of C150H302 with thickness of 20–100 Å at Tg are performed by a stepwise cooling from the melts to the glass states. The temperature dependence of the thickness of the thin films is obtained from the fitting of the density profile by a hyperbolic function. The glass transition temperatures of the thin films are evaluated from the change in thermal expansion coefficients at Tg. The Tg decreases as the films become thinner. For all but the thinnest film, 1/Tg is inversely proportional to the thickness of the film. The proportionality constant is within the range cited in experimental studies of other systems. The depression of the glass transition temperature arises mainly from the fast dynamics in the surface region.

Far-infrared laser measurement of the refractive index of polypropylene.

The refractive index of polypropylene in the far infrared (FIR) is measured by means of a suitably modified laser of a FIR spectrometer. When thin polypropylene films of 12.7-microm nominal thickness are introduced in the optical cavity of a laser at the Brewster angle, the radiation ceases because of the change in the optical path of the laser beam. This change is measured from the displacement of one of the laser mirrors, which is necessary to restore the laser resonance. The refractive index of polypropylene is deduced from this measurement and from the film thickness, as obtained from an independent measurement based in pycnometry. The value obtained for the refractive index is 1.492(15) for the wavelengths between 118.834 and 251.140 microm, for a polypropylene film of 12.71(2)-microm thickness and 0.9049(7) g/cm3 density.

Deformation Mechanisms of Polymer Thin Films by Simultaneous Kinetic Measurement of Microscopic Infrared Dichroism and Macroscopic Stress. Part III: Influence of Morphology on Molecular Orientation of Isotactic Polypropylene Films Subjected to Uniaxial Stretching

Molecular orientations of the crystalline and the amorphous phases are studied in relation to morphology using an instrument constructed for simultaneous kinetic measurement of microscopic infrared (MicIR) dichroism from a pre-determined sampling area and macroscopic stress of isotactic polypropylene (iPP) thin film uniaxially stretched at a constant strain rate at room temperature. The morphology imposes important influences on profiles of MicIR dichroism as a function of stretching time and also on a relationship between the orientation functions, fc and f am, of the crystalline and the amorphous phases. Linear relationships between fc and fam are found for the local areas without giant spherulite inclusions when f am<0.3~0.4, suggesting the harmonious developments of amorphous chain deformation and lamellar orientation during the necking propagation. The proportionality constant between fc and fam is not universal but is strongly dependent on the morphology of the surrounding area where the local area under examination is located. The linear relationship between fc and fam is completely invalidated for describing the relationship between the amorphous chain deformation and the lamellar orientation inside the spherulites, which reveals that the deformation mechanism in the spherulite is different from that in the microcrystalline region.

Creep crack growth characteristics of polypropylene film at various temperatures

Creep crack growth rates were measured using centrally cracked tension specimens of thin polypropylene film at various temperatures and stress levels. The creep crack growth rates were correlated with the stress intensity factor. The experimental results showed that there is the region of the minimum constant crack growth rate which occupies more than 75% of the total creep failure life. This steady or constant creep crack growth rate depends on the test temperature and the initial stress intensity factor. The constant creep crack growth rate characteristics were analyzed on the basis of the Arrhenius type thermally activated process. It is found that creep crack growth behavior is closely related to the crack tip opening displacement and the creep zone size.

Adhesion properties of aluminium-metallized/ammonia plasma-treated polypropylene: Spectroscopic analysis (XPS, EXES) of the aluminium/polypropylene interface

The purpose of this work was to investigate the influence of a low-pressure, low-frequency ammonia plasma treatment on the wettability of polypropylene (PP) thin films and its consequences on the adhesion properties of such treated films to thermally evaporated aluminium coatings. The wettability was determined by contact angle measurements while the adherence was evaluated by a U-Peel test especially suited to thin flexible substrates with thin metallic layers. Furthermore, an image processing system was used to measure the percentage of the peeled-off metal. Measurements carried out on NH3 plasma-treated PP films revealed a sharp increase in the wettability and in the adhesion properties for treatment times as short as 1s. Electron-induced X-ray emission spectroscopy and X-ray photoelectron spectroscopy showed the formation of new chemical bonds at Al/NH3 plasma-treated PP film interfaces. The new types of bonds have been characterized by well-defined chemical states (C–NHx, CO–NH, Al–N–C) in the N 1s (and C 1s) spectra. The interfacial complexes Al–N–C and Al–N–CO are formed by the NH3 plasma treatment which creates at the PP surface active sites (N(C–NHx) and N(CO–NH)) which react with the evaporated aluminium atoms. These interfacial bonds play an important role in the enhancement of the metal/polymer adhesion.

A novel photoadditive for polyolefin photostabilization: hindered amine light stabilizer

Hindered-amine light stabilizers were surface anchored to polyethylene and polypropylene thin films by: i) direct photo-grafting of 1,2,2,6,6-pentamethyl piperidinyl-4-acrylate onto the surface and ii) by reacting of 1,2,2,6,6-pentamethyl-4-piperidinol with succinic anhydride functionalized polyolefin surface. The samples were exposed to UV irradiation in air and the oxidative-degradation of the polymers was studied with FT-IR spectroscopy. The photo-stability of surface anchored Hindered-amine stabilizers (HAS) was compared with films stabilized with commercial HAS by melt blending. The results of the study evince superiority of surface anchored HAS over that of melt blended polyolefins.

Cavitation during isothermal crystallization of isotactic polypropylene

Cavitation during isothermal crystallization of thin films of isotactic polypropylene was investigated systematically by light microscopy. Cavitation results from the negative pressure buildup due to density change during crystallization in the pockets of melts occluded by impinging spherulites. The morphology of such areas was also studied by SEM. The value of the negative pressure at the moment of cavitation was calculated from the drop of the spherulite growth rate. It was shown that the process of cavitation and the value of the negative pressure causing cavitation depend on the crystallization temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2439–2448, 2001

High-speed laser welding of plastic films

Laser welding of plastic materials has a large field of applications in the packaging industry provided that it can compete, in quality and productivity, with currently used industrial methods. Welding of white and transparent thin films of polypropylene and polyethylene of low and high density at high speeds of 20 m s −1 using a CO 2 laser has been studied experimentally.` The weld process has been characterised by the specific energy required for each thickness, kind of plastic and the resistance of the weld seam. The influence of the dimensions of the laser beam spot on weld strength has also been analysed.

Effect of negative pressure on melting behavior of spherulites in thin films of several crystalline polymers

The melting behavior of spherulites in thin films of isotactic polypropylene, poly(ethylene oxide), poly(methylene oxide), and poly(ethylene adipate) crystallized isothermally at various temperatures has been studied by polarized light microscopy. The local increase of melting temperature in regions surrounding cavities and multiple boundary points, dependent on the crystallization temperature, was observed in all studied polymers. In pockets of occluded melt an arising negative pressure lowers an equilibrium melting temperature; hence, decreases an undercooling, which results in the increase of lamellae thickness and their melting temperature. The elevation of melting temperature and the negative pressure buildup depend on the polymer and the crystallization temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1380–1385, 1999

Lattice imaging in melt crystallized polypropylene thin films

Melt crystallized isotactic polypropylene thin films of thickness between 30 and 100 nm have been investigated by high-resolution transmission electron microscopy at room temperature. The c-axis projection of the 2*31 helices and their packing in the lattice were clearly visible in flat-on lamellae of the α-phase following reconstruction from the components of the image Fourier transform corresponding to the (110) and (040) lattice planes, and the image power spectra also indicated contributions from (130) and (060) relfections, corresponding to a line resolution of about 0.35 nm. These results are discussed in terms of Bloch wave calculations based on the generally accepted structure for the α-phase. Attempts to obtain lattice images of the β-phase in isotactic polypropylene and melt crystallized syndiotactic polypropylene under similar operating conditions are also briefly discussed, although these provided relatively little structural information.

Development of high-resolution vacuum crystal spectrometer in a compact helical system and large helical device

A vacuum crystal spectrometer that covers a wavelength range of 1.0–2.5 nm has been developed to observe light (oxygen) and heavy (titanium and iron) impurities for large helical device (LHD) diagnostics. A Johann-type spectrometer (2 R = 60 cm and 3 m, RAP crystal, 2 d = 2.612 nm) was constructed and installed in a compact helical system (CHS). The O VII resonance line was successfully observed through a thin (3.3 μm t) polypropylene film, although the metallic impurity lines were not seen. In the case of a crystal with 2 R = 3 m, however, the spectral resolution λ/Δλ was limited to 440, whereas the replacement by the crystal with 2R = 60 cm improved the resolution to 610. The result is discussed with regard to the quality of the bent crystal.