Isotactic Polypropylene Films Research Articles

Tensile mechanical behaviour of quenched and annealed isotactic polypropylene films over a wide range of strain rates

The tensile mechanical behaviour of quenched and annealed isotactic polypropylene (iPP) films has been analysed over a wide range of strain rates, i.e. from 10−3 to 3×10+2s−1. Evolution of mechanical properties of such films versus strain rate has been analysed through the microstructure. Thus, both the Young's modulus and the yield stress could be mainly controlled not only by the crystallinity ratio but also by the physical cross-linking degree of the amorphous phase induced by crystalline entities. For a given crystallinity ratio, the drawability of quenched and annealed iPP films is mainly controlled by the sum of the effects induced by both the physical cross-linking degree of the amorphous phase and the perfection degree of the crystalline phase. The increase in annealing temperature leads to the opposite evolution of these two microstructural parameters and then to opposite effects on the drawability of films. Changes in original microstructure of quenched films induced by drawing at various draw ratios and at various strain rates are also discussed.

Molecular Orientation Behavior with Drawing of Biaxially Stretched Film

Biaxially stretched poly (ethylene terephthalate) (PET), isotactic polypropylene (PE) and isotactic high density poly-propylene (HCPP) films have been characterized by crystallinity, dielectric constant, refractive index and birefringence. Anisotropy of refractive index by microwave for PET, PP and HCPP biaxially stretched films indicated higher value than refractive index by Abbe refractometer. We recognized good correlation between refractive indices by microwave and Abbe refractometer for biaxially stretched PET, PP and HCPP films, respectively.

Scanning force microscopy of oriented iso- and syndiotactic polypropylene films

Different scanning force microscopy (SFM) modes were applied for the examination of drawn films of isotactic and syndiotactic polypropylene, iPP and sPP. Uniaxially stretched films with a draw ratio λ=6 were studied at ambient conditions, and under water. In iPP films striated patterns of 40–50 nm in width, which are oriented along the stretching direction, exhibit shish-kebab morphology. The dominating nanoscale features are nanofibrils of 10–15 nm in width, and lamellar platelets, which are 40–50 nm in width and 30–35 nm in length. In many places lamellar platelets are closely packed, and they form periodical sequences with a repeat distance of 30–35 nm, which is consistent with thelong period. Similar and differing morphological features were found comparing the images of iPP and sPP films. Extended fibrillar patterns of sPP exhibit similar width in the 40–50 nm range, while the lamellar structure is more compact, and the platelets are less uniform in length than those in iPP. The length of lamellar platelets ranges from 30 to 60 nm, and they form local periodical patterns.

Corona-treated isotactic polypropylene films investigated by friction force microscopy

The effect of an excessive corona discharge treatment on polypropylene films has been investigated by friction force microscopy, an extension of atomic force microscopy. Friction force microscopy has been applied as a material specific analytical tool resulting in increased friction of morphological changes on the polymer surface, such as the formation of dropletlike protrusions. Shear experiments on the submicrometer scale provide information about the adhesive strength between the dropletlike protrusions and the bulk polymer surface. By applying lateral forces greater than 10−5 N, single protrusions, several hundred nanometers in size, have been tracked and sheared over the polymer bulk surface. This threshold has been quantified by a brief calculation of surface energies. Based on various information during measurements of the protrusion shape and properties, the droplets are assumed to be a product of frozen degradation products.

Formation and Spatial Statistics of Spherulitic Grain Pattern in Solidified Films of Isotactic Polypropylene

AbstractImage analysis and measurements on forimation and spatial statistics of spherulitic grain pattern in solidified films of a model polymer, isotactic polypropylene (iPP), have been carried out during in-situ observation experiments under isothermnl conditions. Topological correlations and geometrical distribution fuinctions of polymer grain sides and area are reported. Some topologically unstable configurations, such as multi-vertices, “T” type vertices and two sided grain (lens), have been found. Analysis by spatial tessellations shows that the tenWal evolution and spatial distributions of nuclei point patterns play a role in all of these microstructural properties.

Erratum to: Crystallinity of isotactic polypropylene films annealed from the quenched state

The names of the authors of this paper were omitted from the journal as published. The authors are R. NATALE, R. RUSSO and V. VITTORIA.

Structure of mesomorphic form of isotactic polypropylene

The structure of quenched isotactic polypropylene (iPP) films, including samples etched with fuming nitric acid (FNA), has been studied by infrared (IR) spectra, wide-angle x-ray diffraction (WAXD), small-angle x-ray scattering (SAXS), and differential scanning calorimetry (DSC) measurements. The changes of IR, SAXS, DSC, and WAXD results induced by annealing for etched samples have been compared with those for unetched ones. The IR absorbance spectrum of the quenched iPP etched by FNA did not change. In addition, the SAXS intensity did not increase when these samples were annealed, indicating that the total (IR) crystallinity (i.e., the content of chain segments in the helical conformations) of the etched samples does not increase. However, WAXD patterns of the samples changed in a manner similar to those of the unetched one, from the original two blurred diffraction peaks to the sharp crystal patterns of alpha-form iPP, suggesting that the mesomorphic (or liquid crystal-like) phase has reorganized to alpha-form crystals. It is concluded that the change of WAXD of quenched iPP films during annealing results mainly from transformation of order in the mesomorphic phase, rather than only from an increase of crystal size. In other words, mesomorphic-form iPP is not constituted by any known crystals (such as alpha or beta crystals) in small sizes; its WAXD pattern reflects truly the degree of order in the mesomorphic phase.

An atomic force microscopy study of corona-treated polypropylene films

The surfaces of corona-treated isotactic polypropylene films have been investigated by atomic force microscopy. The occurrence of droplets on the film surfaces is related to the energy dose of the corona discharge. The sizes of these droplets correlate with the corona dose. The loss of adhesive strength of self-adhered polypropylene films can be explained on the basis of morphology changes during corona treatment. A comparative study of uniaxial and biaxial polypropylene films is presented.

Characterization of orientation of one-way and two-way drawn isotactic polypropylene films

X-ray diffraction, Fourier Transform infra-red ( FTi.r.) spectroscopic and refractive index measurements have been utilized to characterize the state of molecular orientation in one-way and two-way (biaxially) drawn isotactic polypropylene (iPP) films. It is shown that the use of all three techniques leads to much greater confidence in the orientation averages deduced than can be obtained by using any two of the techniques. Orientation parameters in terms of 〈cos 2 θ〉 values in machine, transverse and normal directions have been evaluated and compared quantitatively for the different techniques. The results indicate that with one-way drawing the chain axes of both crystalline and amorphous regions orient towards the direction of drawing. The crystalline chains are more highly oriented than the amorphous chains and tend to orient towards the plane of the film, whereas the amorphous chains tend to be more uniaxially oriented towards the draw direction. In balanced, simultaneously two-way drawn films the crystalline chains are more highly oriented towards the plane of the film than the non-crystalline chains. For a sequentially, equibiaxially drawn iPP film, the orientations of the chain axes of both the crystalline and amorphous regions were found to be higher in the second draw (i.e. transverse) direction than in the first draw direction. The orientation of the crystalline chains was very close to the plane of the film, whereas the amorphous chains were almost uniaxially oriented with respect to the second draw direction. In all the films there is a strong tendency for the b-axes of the crystallites to align normal to the plane of the film.

Photo-oxidation of polypropylene under load

We have studied the photo-oxidation of isotactic polypropylene films under mechanical load. These films were either slightly or highly oriented, with or without photoprotecting agents. The oxidation reactions were followed by carbonyl index determinations from IR spectra. The results indicate that the oxidation rate can be related to mechanical load, polymer morphology and the intensity of the light source. In the earlier stages of the photo-oxidation, the static load can act as a protector against oxidation, in a similar manner to that observed with highly oriented samples.

Optical characterization of three‐dimensional surface and bulk anisotropy in high refractive index polymers

AbstractInterest in the development of polymeric materials for high temperature, electronic and microelectronic applications has led to an increasing number of new polymers. Many of these polymers have complex organic ring structures and semirigid backbones, characteristics that have posed some difficulties for structural analysis. The purpose of this paper is to test and compare two practical nondestructive optical techniques, polarized optical microscopy and polarized refractometry, for the determination of three‐dimensional surface and bulk anisotropy in these advanced materials. The optical techniques are first tested on a series of optically homogeneous uniaxially oriented isotactic polypropylene films and then applied to the analysis of high refractive index Kapton (PMDA‐ODA) polyimide films. The study includes a test of the validity of the compensator method, including the effect of fringe jumping, the use of polymer retarders, and the tilting technique of Stein.

Time Dependent Reactivity in the Post Irradiation Oxidation of Polypropylene

Abstract A kinetic model for the radiation induced oxidation of isotactic polypropylene film (38μ thick) has been developed which allows determination of the concentration profiles, rate constants and diffusion coefficients. The match with the experimental data is consistent with a distribution of reactivity that changes during the course of the reaction giving rise to time dependent fat? constants according to the Plonka's equation (k=ko (a-1). This equation can be rationalized within the framework of the random walk models under the assumption of temporal, geometric or energetic disorder. The origin and the characteristics of the reactivity distribution have been investigated by an ESR spectroscopy study of the degree of order and the molecular dynamics of the intermediate peroxy radicals.

Surface structure of polymers and their model compounds observed by atomic force microscopy

Results of atomic force microscopy (AFM) of normal alkanes, polyethylene, isotactic polypropylene and of a diblock copolymer are presented. Various types of surfaces - naturally and epitaxially grown on different substrates - have been examined from hundreds of nanometers down to the atomic scale. Surface morphology and molecular arrangement have been visualized in AFM images. Atomic-scale AFM images with some defects have been observed on lamellar surfaces of normal alkanes C 33H 68. Arrays of oriented polyethylene molecules have been revealed at the surface of thin polyethylene films, epitaxially crystallized on the (001) face of an anthracene single crystal. Contact faces of thin films of isotactic polypropylene (iPP), epitaxially crystallized on various substrates (i.e. benzoic acid, potassium salt of 4-chloro-benzoic acid or polyamide 11), show the lamellar structure as well as the methyl side-group pattern in the exposed iPP (010) planes. AFM offers the way to distinguish the crystalline modification as well as the molecular conformation (left- and right-handed helices). Also the morphology of a microphase-separated block copolymer, polystyrene-b-poly-(2-vinylpyridine) (PS/PVP), has been observed by AFM.

A Scale Effect in the Durability of Oriented Thin-Wide Polypropylene Films during Oxidation under Load: Fracture Model of Stressed Polypropylene Films

Abstract Studies have been made of the durability of oriented isotactic polypropylene (PP) films depending on their width during intensive oxidation (T = 130°C, P02 = 20 kPa) under load. As the specimen width decreases under low stresses, mean durability is determined thermooxidative destruction rate at the nucleation sites the scale effect takes place. The durability values are found to be discrete multiples of integers for narrow specimens. The conclusion is drawn that the difference in polymeric specimen durability is determined by the concentration of defect zones, rather than by the versatility of their nature. The model of oriented PP films fracture under low-load oxidation conditions is proposed. This model is based on the dependence of durability on a number of oxidation destruction centers which are similar in nature (in the initiation rate) and cause specimen fracture while growing and joining together.

Crystallinity of isotactic polypropylene films annealed from the quenched state

Quenched isotactic polypropylene films were annealed at 130, 140 and 155 °C for 24 h. The structural organization, after annealing, was analysed by wide-angle X-ray diffractograms (WAXD), differential scanning calorimetry (DSC), density and sorption of dichloromethane vapour at low activity. The comparison of the different methods used to obtain the crystallinity shows that, even at the highest annealing temperature, the transformation of the smectic phase into the monoclinic phase, is not complete. WAXD and DSC give the amount of monoclinic phase, whereas the amorphous fraction was derived from sorption of dichloromethane vapour at low activity. From the density, it was possible to derive the residual smectic fraction in the different samples. The results indicate that, at temperatures higher than 150 °C, there is an accelerated decrease of smectic phase and an accelerated increase in the crystal dimensions and perfection.

A scale effect in the durability of oriented narrow polypropylene films during oxidation under load. Fracture model of stressed polypropylene films

Studies have been made of the durability of oriented isotactic polypropylene (PP) films as a function of their width during intensive oxidation ( T = 130°, P O 2 = 20 kPa) under load. As the width of the specimen is decreased under low stresses, average durability was determined to be growing and the scale effect took place. The values of the durability are found to be discrete integers for narrow specimens. It is concluded that the difference in the durability of the polymeric specimen is determined by the concentration of defect zones, rather than by their nature. A model of fracture of oriented PP films under low-load conditions of oxidation is proposed. This model is based on the dependence of durability on the number of centres of the oxidative degradation that are similar in nature and cause the fracture of specimen during their growth and linking up.

Physicochemical changes in stabilized, orientated polypropylene films during the initial stages of thermal oxidation

AbstractOrientated, stabilized, isotactic polypropylene films have been oven‐aged at 130°C for times shorter than required for their embrittlement. The structural changes occurring during this induction period have been studied using tensile tensiometric, density, thermal analytical (DTA and TGA), and infrared spectrophotometric techniques. After an initially rapid annealing, films show similar time‐dependent changes in tensile, density‐derived crystalline and thermogravimetric behaviors. Comparison with vacuum‐aged sample properties shows that these changes reflect the effects of oxidative attack of polypropylene chains. Infrared examination shows that, even after the longest aging times studied and close to the induction period for embrittlement, the presence of oxidized chain groups is only just discernible. Oven aging reduces post‐fusion oxidative onset and maximum mass loss temperatures determined by TGA. Kinetic analysis demonstrates that the apparent activation energies and Arrhenius factors are reduced during aging as the post‐fusion oxidation mechanism becomes more complex. The results suggest that, during the induction period, changes in both physical and chemical structural features of orientated polypropylene occur which have possible importance in determining the lifetime of the polymer in use.

Oxygen permeation through films of polypropylene/hydrogenated oligocyclopentadiene blends

Oxygen permeation through films of isotactic polypropylene (iPP)/hydrogenated oligocyclopentadiene (HOCP) blends was studied as a function of the weight fraction of the two components and temperature. Increasing HOCP content lowers oxygen permeability and diffusivity through the films and increases the glass transition temperature of the polymer blends. Activation energies for permeation and diffusion processes were also measured. Annealing for 2 min at 100°C was shown to completely transform the smectic phase in the α-crystalline form and to induce a marked increase in oxygen permeability and diffusivity, especially in the blends, and a corresponding decrease in the activation parameters.

13C magnetic relaxation times in isotactic polypropylene

13C spin-lattice relaxation time, T 1, 13C and 1H spin-lattice relaxation times in the rotating frame, T 1ρ( 13 C) and T 1ρ( 1 H) , and the dipolar dephasing behaviour of methylene, methine and methyl carbons of annealed(monoclinic) and quenched(smectic) isotactic polypropylene films were measured using the CP/MAS method. Two T 1s were observed for methylene and methine carbons in the annealed and quenched samples but one T 1 for methyl carbons in both samples. T 1s for methylene and methine carbons in the annealed sample are longer than those in the quenched sample, whereas T 1 for methyl carbons is nearly the same for annealed and quenched samples. There is, however, a small but a definite difference between T 1 of upfield and downfield peaks of methyl carbons in the annealed sample: T 1 for the downfield peak is ca 15–20% shorter than that for the upfield peak. The carbon spin-lattice relaxation time in the rotating frame, T 1ρ( 13 C) , shows rather complicated manner; for the quenched sample, two T 1ρ( 13 C) s were obtained for all carbons but, for the annealed material, one T 1ρ( 13 C) was obtained for methine carbons and the downfield peaks of methylene and methyl carbons and two T 1ρ( 13 C) s were obtained for the upfield peaks of methylene and methyl carbons. For the proton spin-lattice relaxation time in the rotating frame, T 1ρ( 1 H) , two components were observed for all carbons of both samples. There is no large difference in the dipolar dephasing behaviour for annealed and quenched samples and the signal intensity decays as exp[-( t/ T′ 2) 2] for methylene and methyl carbons but as exp(- t/ T′ 2) for methyl carbons.

13C-NMR spectra of isotactic polypropylene film during stretching and shrinkage

The line-shape of 13C-NMR spectra of highly crystalline isotactic polypropylene film during stretching and subsequent shrinkage was investigated. Well-resolved splittings of the resonance peaks of methylene and methyl carbons before stretching disappear with increasing stretching ratio ( λ > 10) and recover, although incompletely, by the subsequent shrinkage. Structural properties such as crystallinity and d-spacings of (110) and (040) planes were also measured during stretching and shrinkage. The crystallinity decreases with increasing stretching ratio. When the sample of λ = 10 was shrunk, ca 60% of ΔX c was recovered, where ΔX c is the difference between crystallinity before and after stretching. The d-spacings of (110) and (040) planes slightly change during stretching and recover almost to the initial values as a result of the shrinkage.