Isotactic Polypropylene Films Research Articles

Laser Light and X-Ray Diffraction Studies of Oriented Isotactic Polypropylene (iPP) Prepared by Temperature Slope Crystallization

Isotactic polypropylene (iPP) film was melt-crystallized in a temperature gradient. The iPP film showed well oriented α- and β-crystalline textures along the gradient. The crystalline structure, phase transition boundary and lamellar twisting were examined by X-ray diffraction and laser light diffraction (LLD). On the α-β boundary, LLD shows a sharp streak perpendicular to the boundary, where the a-axis of the β-crystal is oriented perpendicular to the temperature gradient. Apart from the boundary, the a-axis of the β-crystal becomes parallel to the gradient. The β-crystal shows lamellar twisting with a pitch of 200 μm at room temperature. When heated the β-crystal, the lamellar distance of 295Å at room temperature decreases to 285Å at 80–100°C and then increases to more than 300Å above 120°C. During the heating, the value of the twist period increases from 200 to 210 μm at 90–100°C, and then to above 224 μm at 140°C. The increase of the twist period is related to the increasing crystalline thickness of the β-lamellae.

Study on the Bleeding Mechanism of Slip Agents in a Polypropylene Film using Molecular Dynamics

Abstract The bleeding (internal transport) process of additives in a polypropylene film under atmospheric pressure was investigated. The experimental results were explained more precisely by a new model assuming the two-step transport between the amorphous and crystalline regions. The diffusion coefficient of a higher fatty acid such as behenic acid (docosanoic acid) in isotactic polypropylene film and that of higher fatty acid amides such as erucamaide (13-cis-docosenamide) in ethylene copolymerized polypropylene film were determined at 40 and 50°C respectively. The difference between the diffusion coefficients of three slip agents in a polypropylene film at 50°C was explained using a molecular dynamics simulation in which self-association of the slip agent molecules by hydrogen bonding was considered.

The effect of additives on charge decay in electron-beam charged polypropylene films

The charge decay in isotactic polypropylene (i-PP) films of 50 µm thickness, containing three kinds of additives, namely a trisamide, a bisamide and a fluorinated compound, with concentrations in the range 0.004–1 wt% was studied. Compression molding was used to produce the films. The samples were either surface-charged by a corona method or volume-charged by mono-energetic electron beams of different energies, having penetration depths up to 6 µm. In all cases, surface potentials of about 200 V were chosen. After charging the films, the decay of the surface potential was studied either by an isothermal discharge method at 90 °C or by thermally stimulated discharge measurements. The results show a dependence of the decay rate on the kind of additive used, on additive concentration and on the energy of the injected charges. In particular, for samples with fluorinated additives, the stability of the surface potential decreases markedly with increasing electron energy, while such a dependence is very weak for samples containing the bisamide additive and does not exist at all for samples with the trisamide additive. These observations are tentatively explained by the radiation-induced generation of relatively mobile negative ions originating from the bisamide and fluorinated additives.

Effect of γ-dose rate on crystallinity and morphological changes of γ-sterilized biomedical polypropylene

The present work is aimed to study the changes in crystallinity and morphology of biomedical polyolefins after γ-sterilization. The isotactic polypropylene (iPP) films were sterilized by γ-radiation and the changes were characterized by differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and atomic force microscopy (AFM) techniques. The effect of dose rate on crystallinity changes also was focused. It was found that crystallinity and morphology significantly changed with γ-irradiation. There was an increase in crystallinity up to 10 kGy accompanied with decrease in viscosity and mechanical properties. The changes in crystallinity mainly depend on γ-irradiation dose and dose rate. The rise in crystallinity was attributed to chain scission and forming new perfect lamellae. However, the reduction was accompanied by occurrence of γ- and β-phases and crosslinking. Possible explanations for transitions in phases are also discussed based on our results.

Refractive index of corona-treated polypropylene films

The samples under investigation are 20??m thick isotactic polypropylene films corona treated at different corona polarities and grid voltages in a three-electrode system. In order to control the results of the applied treatment a combination of two refractive index (RI) measuring techniques (laser refractometry and spectrophotometry) is used to study RI dispersion in the spectral range 400?1000?nm. It is found that the surface RI was lower than the volume RI. After a corona treatment both surface and volume RI increase. The changes of the volume RI as compared to surface values are more influenced by the corona treatment conditions: the greater the grid potential, the bigger the volume RI.

MeV energy electron beam induced damage in isotactic polypropylene

A few thin films of isotactic polypropylene were irradiated with 6MeV energy electrons, in the fluence range from 5×1014 to 2×1015 electrons/cm2. The structural, optical and mechanical properties were characterized by techniques such as FTIR, UV–vis, XRD, SEM, hardness and contact angle measurements. The FTIR spectra indicate that C–H and C–C bonds are scissioned and an isotactic arrangement of chains is partially destroyed. Moreover, the new carbonyl groups (C=O) are observed, which signifies oxidation. The UV–vis spectra shows a red shift in the absorption edge from pristine value of 240 to 380nm, which corresponds to decrease in the optical band gap from 5.17 to 3.27eV. This is because of the formation of conjugated double bonds as well as carbonization. The crystalline properties were analysed using XRD and it shows no profound change. This result may attribute that the radiation-induced changes have probably occurred to a large extent in amorphous regions. However, surface morphology by SEM and contact angle measurements showed considerable surface roughening, which indicates an uneven evolution of gases from the surface. Interestingly, the surface hardness of the films was found to increase with fluence and it may be due to crosslinking and carbonization on the surface. Overall, in conclusion this study shows considerable modifications in the physicochemical properties of isotactic polypropylene irradiated by 6MeV energy pulsed electrons.

Photostability of isotactic polypropylene containing monoazo pigment

AbstractThe photodegradation of isotactic polypropylene (PP) films containing a monoazo pigment and hindered amine light stabilizers (HALS) has been undertaken. PP films were exposed to medium pressure mercury lamp radiation in the laboratory for periods of up to 8 weeks and the degree of degradation (oxidation/deterioration) was examined using FTIR spectroscopy and differential scanning calorimetry (DSC) as well as by measuring changes in the mechanical properties, contact angle, and density. The results of these measurements indicate that unstabilized PP films degraded after only 240‐h irradiation. By adding an organic pigment to PP films along with antioxidant and HALS, the photostability of PP films increased to the 1500‐h level. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Crystal morphology of rapidly cooled isotactic polypropylene: A comparative study by TEM and AFM

The morphology of crystals, formed at the surface and in the bulk of rapidly cooled and subsequently at elevated temperature annealed films of isotactic polypropylene (iPP) was analyzed by transmission electron microscopy (TEM) and by atomic force microscopy (AFM). Both techniques show a lamellar crystals after melt-crystallization at 12 K s-1, and a nodules after melt-crystallization at 750 K s-1. The morphology of crystals is independent on the position of the investigated film of thickness of 100 μm, suggesting (a) that the crystallization at the surface is not affected by the use of a glass substrate for preparation, and (b) that the temperature-gradient during primary crystallization is sufficiently small to ensure identical structure at the surface and in the bulk. AFM suggests a larger size of crystals than TEM, in particular if the absolute size of objects approaches the dimensions of the used tip of the AFM. If the absolute size of objects is distinctly larger, then AFM and TEM yield nearly identical dimensional information.

Thermosets as compatibilizers at the isotactic polypropylene film and thermomechanical pulp fiber interphase

The objective of this study was to improve interfacial adhesion properties at the interface of thermomechanical pulp (TMP) fiber and isotactic polypropylene (iPP) using thermoset adhesives such as phenol formaldehyde (PF) and urea formaldehyde (UF). This study also attempted to achieve fiber-to-fiber adhesion using thermoset adhesives before the molten iPP would flow into the fiber web. The fracture surfaces with thermoset adhesive showed identical differences in terms of fracture modes at the interface. An increased TMP fiber failure was observed with increased thermoset quantity at the interface. Using one percent resin content of weight fraction of TMP fiber handsheet, the tensile strength properties increased almost two fold higher than the strength of control samples. Additional adhesive contents of three and five percent showed gradual strength enhancement. However, the enhanced strength was statistically insignificant. UF resin showed slightly better strength performance over PF resin. This result may be caused by solid contents and additional pigments of resins.

100 MeV Ag7+ ion induced physicochemical changes in isotactic polypropylene

Thin films of isotactic polypropylene having 500μm thickness were irradiated with 100MeV Ag7+ ions at the fluences varying from 1011 to 5×1012ions/cm2. The properties such as chemical, optical, structural and surface morphology were characterized by techniques namely FTIR, UV–visible, photoluminescence, XRD, SEM and contact angle method. The FTIR spectra show the scissioning of C–H and C–C bonds, whereas, in photoluminescence, the intensities of the peaks at 440 and 480nm in emission spectra and at 236nm in excitation spectra observed to be decreased with increase in ion fluence. This may be due to the decomposition of luminescent centers. The UV–visible spectra also show a remarkable red shift from 218 to 367nm and the subsequent large reduction in the optical band gap from 5.37 to 3.39eV. This attributes to the carbonization or graphitization of polypropylene. On the contrary, the intensities of XRD peaks, particularly the peak due to 110 planes, shows sufficient enhancement which signifies overall increase in crystallinity. This ascribes to relief in the local strain on the crystallites due to scissioning of tie molecules in the amorphous zones. The contact angle has increased from 78° to 97° which reveals the absence of hydrophilic functional groups, carbonization and surface roughening. The result is also supported by SEM analysis.

Deformation-induced highly oriented and stable mesomorphic phase in quenched isotactic polypropylene

Changes of structure and morphology of quenched isotactic polypropylene (i-PP) film during tensile deformation at room temperature have been investigated by applying in situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. SAXS patterns show that the isotropic diffuse scattering peak in the initial quenched i-PP film disappears after the film experiences necking and a strong streak, which accompanies obvious film stress-whitening, appears when strain reaches 600% and above. Explanation to the former is the dropping of density contrast between amorphous and mesomorphic phases due to deformation and that to the latter is the formation of microfibrils and/or microvoids in the film. WAXD patterns indicate that i-PP chains in the mesomorphic phase become highly oriented along the drawing direction with the strain value more than 5% and the three-fold helical chain conformation keeps in the deformed mesomorphic phase. The mesomorphic structure in the initial quenched i-PP film does not transform into crystal phase although high orientation appears during tensile deformation and the highly oriented mesomorphic phase is considered to be quite stable. Thermal behaviors of the initial quenched i-PP and deformed i-PP with the strain value of 650% are examined by modulated differential scanning calorimetry (MDSC). MDSC results show that the highly oriented i-PP chains in deformed mesomorphic phase are stable, which brings about restriction to chain mobility and prohibits from phase transformation of mesophase to crystal phase in the temperature range normally measurable for the initial quenched i-PP. A model about tensile deformation of the quenched i-PP is outlined to distinctly illuminate the changes of structure and morphology in both the amorphous and mesomorphic phases.

The role of interlamellar chain entanglement in deformation-induced structure changes during uniaxial stretching of isotactic polypropylene

In-situ small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD) were carried out to investigate the deformation-induced structure changes of isotactic polypropylene (iPP) films during uniaxial stretching at varying temperatures (room temperature, 60°C and 160°C). From the WAXD data, mass fractions of amorphous, mesomorphic and crystal phases were estimated. Results indicate that at room temperature, the dominant structure change is the transformation of folded-chain crystal lamellae (monoclinic α-form) to oriented mesomorphic phase; while at high temperatures (>60°C); the dominant change is the transformation of amorphous phase to oriented folded-chain crystal lamellae. This behavior may be explained by the relative strength between the interlamellar entangled network of amorphous chains, which probably directly influence the tie chain distribution, and the surrounding crystal lamellae. It appears that during stretching at low temperatures, the interlamellar entanglement network is strong and can cause lamellar fragmentation, resulting in the formation of oriented mesomorphic phase. In contrast, during stretching at high temperatures, the chain disentanglement process dominates, resulting in the relaxation of restrained tie chains and the formation of more folded-chain lamellae.

Diffusivity of ethylene and propylene in atactic and isotactic polypropylene: Morphology effects and free‐volume simulations

AbstractDiffusion coefficients of propylene and ethylene through particles and films of isotactic polypropylene (iPP) as well as through films of atactic, completely amorphous, polypropylene have been measured by gravimetric experiments. iPP particles with relatively similar crystallinities but with different particle size distributions (PSD), and different origins have been used. They exhibited very different diffusion coefficients when the average radius of the PSD was used as the dimensional parameter of the diffusion process. However, films prepared with these particles and having similar crystallinities provided similar diffusion coefficients. The results are consistent with the idea of a multigrain structure in the particles, where the apparent (or experimental) diffusion coefficient is a consequence of the complex system formed by internal and external areas. The diffusion coefficient of the films, taken as the real diffusion magnitude, can be used in the calculation of the true diffusional radius of these multigrain particles. Experimental results of the diffusion coefficients have been reasonably well reproduced with the aid of the Vrentas‐Duda free volume model. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3871–3878, 2007

Chemiluminescence of isotactic polypropylene induced by photo‐oxidative degradation and natural weathering

AbstractThe analysis of the chemiluminescence (CL) kinetic parameters (induction time, oxidation rate, and activation energy) after the UV irradiation and outdoor exposure of isotactic polypropylene (i‐PP) films have been studied. The initial CL emission intensity increased with increasing photodegradation time of i‐PP films. On photodegradation, the activation energies were found to decrease linearly with time of UV‐irradiation and outdoor exposure. The slopes of these linear dependences were used to indicate the degree of photodegradation of the polymer and also for the characterization of the stabilizing effect of the additive. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4623–4629, 2006

Nanocomposites of isotactic polypropylene reinforced with rod-like cellulose whiskers

Nanocomposite films of isotactic polypropylene reinforced with cellulose whiskers highly dispersed with surfactant were prepared for the first time and compared with either bare or grafted aggregated whiskers. Films obtained by solvent casting from toluene were investigated by means of X-ray diffraction, differential scanning calorimetry, dynamic mechanical analysis and tensile testing. Evaluation of the crystallization behavior showed that the aggregated or surfactant-modified whiskers induced two crystalline forms (α and β) in the nanocomposites and also acted as nucleating agents for isotactic polypropylene. The linear mechanical properties above the glass–rubber transition were found to be drastically enhanced for all three of the nanocomposites as compared to the neat polypropylene matrix, and these effects were attributed to a mechanical coupling between the polypropylene crystallites and filler/filler interactions. For the mechanical experiments at large deformations, the quality of the whisker dispersion was found to play a major role. The nanocomposites obtained with the surfactant-modified whiskers exhibited enhanced ultimate properties when compared to the neat matrix or to the composites containing the other filler types.

Surface properties of plasma-modified polypropylene and propylene-hexene-1 copolymer films

The surface properties of polypropylene and propylene and hexene-1 copolymers synthesized on the rac-Me2SiInd2ZrCl2-polymethylalumoxane isocpecific metallocene system and the Ph2C(Cp)(Flu)ZrCl2-polymethylalumoxane syndiospecific system were studied. It was found that syndiotactic polypropylene films were less hydrophobic than isotactic polypropylene films, whereas the films of propylene and hexene-1 copolymers were less hydrophobic than the films of corresponding homopolymers. The hydrophobicity of samples decreased with the hexene-1 content of the copolymer. Treatment in a dc discharge resulted in noticeable surface hydrophilization in all of the test polymer samples. There is a correlation between the surface parameters and the density of surface charge induced in the polymers by dc discharge treatment.

Electret properties of biaxially stretched polypropylene films containing various additives

Isotactic polypropylene (i-PP) films containing additives such as the commercial α -nucleation agent NA11 and the anorganic filler particles CaCO3 and Al2O3 were biaxially stretched. As a result, the films assume a cellular morphology with oblong cavities extending in the direction of the film elongation. In the present study, stretched films of 50 µm thickness with additive concentrations of 0.05–10 mass per cent were charged with a corona method to potentials of 400 or 500 V. The stability of the charges was tested isothermally at temperatures of 90 and 120 °C and by means of thermally stimulated discharge (TSD) experiments. The isothermal measurements show, for the above additives with concentrations higher than about 0.3%, a reduction of the charge decay with increasing additive concentrations. Compared with reference films of pure PP, the potential decay of the films containing additive concentrations of 10% is significantly reduced. Correspondingly, the TSD measurements indicate a shift of the main discharge peak to higher temperatures up to the melting temperature. Generally, the voiding and thus the stability also increases with the stretching ratio. These improvements of the charge stability are attributed to the barrier effect of the cavities. The results are of interest with respect to the various applications of PP electrets, such as ferroelectret devices and air filters.

Rigidity of heat-treated oriented isotactic polypropylene

Uniaxially oriented commercial films of isotactic polypropylene were strained with ends keeping fixed and subjected to the heat treatment at temperatures from 50 to 200°C. The rigidity of annealed samples was characterized by the value of tangent modulus, Et, determined graphically at the initial portions of stress–strain curves. The structural changes in the samples were studied with the help of the IR and low-frequency Raman spectroscopies. The smallest Et values were obtained for the low-strained films, while the tangent moduli measured for highly strained samples exceeded the value for the original (untreated) film. The most prominent positive effect was achieved after annealing the samples at 90°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 6074–6080, 2006

Application of an interpenetrating network model to the necking in the microcrystalline region in four annealed isotactic polypropylene films subjected to uniaxial stretching at room temperature

The microscopic infrared dichroism, mesoscale deformation and macroscopic stress measurements are made on the microcrystalline region in four annealed isotactic polypropylene (iPP) thin films subjected to uniaxial stretching at room temperature. Results reveal that volume dilatation might occur during stretching and the necking causes the anisotropic shrinkage in the thickness and the width directions. The average orientation function f av and the true stress as a function of local draw ratio in the samples showing volume dilatation can be respectively overlapped onto those of the sample undergoing constant volume deformation. The pseudo-affine deformation is applicable for molecular orientation at f av<0.50 and the true stress–strain relationship on the mesoscale can be well described in the same region by the interpenetrating network model previously proposed for necking in the quenched iPP film. This model becomes invalid for deformations above f av=0.50 due to that plastic deformations in the crystalline phase, depending on the annealing time, start to play a major role.

Charge storage behavior of isotropic and biaxially‐oriented polypropylene films containing α‐ and β‐nucleating agents

AbstractA study on the influence of the crystal modification (α and β) of isotactic polypropylene (i‐PP) films on the resulting electret properties is presented. Two commercial nucleating agents, sodium 2,2′‐methylene‐bis(4,6‐di‐tert‐butylphenyl)‐phosphate (NA11) and N,N′‐dicyclo‐hexyl‐2,6‐naphthalene‐dicarbox‐amide (NU100), were employed in this investigation. Isothermal charge decay was measured at 90°C. In hot pressed isotropic polypropylene films, no significant differences in the charge storage properties were observed for α‐ and β‐nucleated specimens. In addition, the article presents the influence of the nucleating agents at different concentrations on the PP‐film morphology of biaxially stretched films with respect to electret features. It was possible to prepare elongated cavities with the virtually insoluble NA11 additive during stretching, even at concentrations below 0.3 wt %. These films displayed slightly improved electret properties in comparison to stretched neat PP films due to generated cavities acting as barriers for the drift of charges. Various draw ratios were also studied for i‐PP films with 0.15 wt % NA11. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 650–658, 2006