Isotactic Polypropylene Films Research Articles

Stepwise crystallization method combining isotactic polypropylene-based plastic waste film to prepare high-performance polypropylene random copolymer

Upcycling of waste plastic film is increasingly important at the background of energy shortage and environmental crisis. However, direct reuse of the waste plastics as reworked material inevitably downgrades the mechanical properties. Herein, a stepwise crystallization method was used to enable the recycling of waste isotactic polypropylene (iPP) film value-added in iPP-based homocomposites. In detail, the effect of β-nucleating agent (β-NA) and iPP on crystallization behaviors of polypropylene random copolymer (PPR) was investigated at first. The stepwise crystallization procedure was further introduced to promote the β-crystallization of PPR/iPP/β-NA composites in which the crystal structures, polymorph compositions and phase morphologies were systematically researched. At last, impact behaviors of PPR/iPP/β-NA composites were characterized and a penitential toughening mechanism was proposed. It was found that the stepwise crystallization boosted β-crystallization and growth of rubbery phase during the isothermal procedure, resulting in an increase of relative β-crystal content and low temperature impact toughness from 0 % and 2.02 kJ/m2 of neat PPR to 33.4 % and 3.06 kJ/m2 of PPR/iPP/β-NA composites. This work provides a simple, implementable, and effective method for the recycling of waste iPP films and the low-temperature toughening of PPR.

Morphological transformation of extruded isotactic polypropylene film from the Mesophase to α-form crystals

The morphological transformation of extruded polypropylene (PP) films from the mesophase to α-form crystals has been investigated. Extruded PP films prepared by quenching had the mesophase morphology with a nearly-random orientation of the molecular chains. The mesophase structure of the quenched PP films completely transformed to α-form crystals by annealing at 100 °C accompanied by enhancement of the molecular orientation along the machining direction (MD). Moreover, the annealed films expanded and shrank by approximately 0.5% along the MD and transverse direction (TD), respectively. The unusual expansion behavior during annealing suggests that a small amount of oriented molecular chains formed in the extruded film, and the oriented chains acted as a nucleating agent. Consequently, the molecular orientation along the MD was enhanced owing to the morphological transformation. The oriented chains also acted as nucleating agent during tensile deformation, resulting in a significant improvement of strength in the MD stretching.

Determining the maximum melting temperature of polymer crystals from a change in morphology of dewetting rims

Dewetting experiments on molten spherulites, previously grown at Tc = 120 °C in thin films of isotactic polypropylene (iPP), revealed two kinds of instabilities of the dewetting rims, namely a fingering instability and a fracture instability for dewetting temperatures Ts above and below ca. 165 °C, respectively. For Ts ≥ 165 °C, the dynamics of growing dewetting holes on slippery substrates was governed by viscous dissipation, causing undulations leading to a fingering instability of the rims. However, for 160 °C < Ts < 165 °C, the dewetting rims exhibited a fracture instability, which was related to the release of elastic energy stored in the rim. From the dewetting dynamics of the molten polymers, we derived the non-equilibrium viscosity ηnon-equ(Ts) and equilibrated viscosity ηequ(Ts) as a function of Ts. The values of ηnon-equ(Ts) were significantly larger than ηequ(Ts), with differences decreasing for increasing Ts. Interestingly, extrapolation of ηnon-equ(Ts) to the cross-over point ηnon-equ = ηequ yielded Ts,cross ≈ 166 °C. We relate Ts,cross with the maximum melting temperature of crystalline domains which existed within iPP spherulites. Below Ts,cross, not all crystallites were molten and the melt contained crystalline seeds. Above Ts,cross, the melt was homogeneous and free of any seeds. Our approach opens up a new possibility for determining the maximum melting temperature of polymer crystals.

Visualization of small-angle X-ray scattering datasets and processing-structure mapping of isotactic polypropylene films by machine learning

With the rapid development of the synchrotron radiation X-ray characterization techniques, the preprocessing of large small-angle X-ray scattering (SAXS) datasets and the data mining become urgent requirements for researchers. In this work, we apply the variational autoencoder (VAE) and the conditional variational autoencoder (cVAE) to visualize a large SAXS dataset of hard-elastic isotactic polypropylene (iPP) films in 2- and 1-dimensional latent spaces. The low-dimensional representations enable us to capture key features of the dataset rapidly, such as the similarity among SAXS patterns and the structural evolution trends. The preprocessing of the dataset points out the further direction of data analysis so that researchers can focus on the most valued regions in the dataset. Then, we develop a hybrid VAE-multilayer perceptron (MLP) neural network to realize the processing-structure mapping of iPP films. The robustness of the hybrid VAE-MLP network is verified. Finally, SAXS patterns in the temperature-strain space are generated, which allows us to explore the processing parameter space not involved by previous experiments. These capabilities indicate that the developed machine-learning methods are valuable artificial intelligence toolset to assist in the preprocessing of large-scale SAXS datasets and the establishment of comprehensive processing-structure relationship of hard-elastic iPP films.

Improvement of polymer adhesion by designing the interface layer

Polymer adhesion with inorganic materials is a key technology for realizing the diversification of materials. When a polymer contacts with inorganic materials, a layer containing strongly- and loosely-adsorbed chains is formed at the surface. The former and latter are chains that adopt mainly train and loop/tail conformations, respectively. To improve the interfacial adhesion, it is of pivotal importance to control the interaction between loosely-adsorbed chains, which are in part directly attached to the solid surface, and bulk free chains. We here succeeded in increasing the interfacial strength by chemically cross-linking them. Polymer chains were attached to the surface of a silicon wafer and then a film of isotactic polypropylene or polyamide 6 was mounted on it to produce our model system. As loosely-adsorbed chains have photo-cross-linkable moieties, the polyolefin or engineering plastic film could be strongly adhered to the silicon wafer via the adsorbed layer. On the other hand, the film could be easily detached from the wafer having loosely-adsorbed chains without photo-cross-linkable groups. Our facile idea that loosely-adsorbed interfacial chains chemically bond to the polymer bulk shows promise for the design and construction of not only interfacial adhesion but also composite materials.

Method for hidden marking of transparent polypropylene film

Objectives. To quantitatively describe the thermochromic properties of films of isotactic polypropylene, a large-tonnage polymer widely used in the production of flexible packaging for goods and foodstuffs, as well as substantiate the possibility of covert labeling of transparent packaging.Methods. Differential scanning calorimetry, polarization photometry, infrared Fourier spectrometry, gravimetry, temperature control, physical and mechanical strength testing.Results. The identified thermochromic effect of dichroism in polarized light on industrial samples of transparent biaxially oriented film of isotactic polypropylene was studied. A change in the phase composition of the film-forming composition during short-term heating during marking was established. The absence of heat shrinkage and change in transparency in non-polarized light was shown, which provides the possibility of hidden recording of information and its contrast manifestation in a passing light stream at a certain arrangement of light filters.Conclusions. The causes and optimal conditions of the thermochromic effect are established. It is proposed to use local contact heat treatment of a polypropylene film for covert recording of information and marking of product packaging in order to protect against counterfeiting.

Synthesis of Anion Electrolyte Membrane through Radiation-induced Graft Polymerization of Poly(4-vinylbenzyl chloride) onto Isotactic Polypropylene Film

Radiation grafting, a widely used process for preparing different functional materials, allows the facile amalgamation of desirable properties from two or more polymers without altering the inherent properties of the base substrate. In this study, an anion electrolyte membrane (AEM) was successfully prepared through radiation grafting of poly(vinylbenzyl chloride) (PVBC) from isotactic polypropylene (iPP) film using gamma-ray irradiation. It was shown that the amount of grafted PVBC increased with increasing absorbed dose, which yielded iPP-g-PVBC with 127% degree of grafting at 50 kGy. The iPP-g-PVBC was reacted with aqueous trimethylamine hydrochloride solution to introduce quaternary ammonium ions, thereby producing the AEM membrane in chloride form (iPP-g-PVBC-TMA-Cl), which was further reacted with potassium hydroxide (KOH) to convert it into hydroxide form (iPP-g-PVBC-TMA-OH). The pristine, grafted and functionalized iPP films were characterized using attenuated total reflectance – Fourier transform infrared spectrometer, thermogravimetric analyzer and scanning electron microscopy – energy dispersive X-ray spectrometer. The effect of degree of grafting on the ionic conductivity, ion exchange capacity and water uptake were evaluated in both AEM’s chloride and hydroxide forms. Results showed that a higher degree of grafting films achieved higher ionic conductivity, ion exchange capacity and water uptake for both chloride and hydroxide forms. The synthesized AEM with a degree of grafting of 70% (IEC = 1.87 meq/g) obtained a conductivity of 129.34 mS/cm, which is higher than the AEMs reported in previous works.

Specific deformation behavior of isotactic polypropylene films under a multiaxial stress field.

The specific deformation behavior of crystalline polymer films, namely unoriented crystallized isotactic polypropylene (it PP) films, was investigated under a multiaxial stress field. Changes in the aggregation structure of the films were investigated during the bulge deformation process using in situ small-angle X-ray scattering, wide-angle X-ray diffraction (WAXD) measurements, and polarized high-speed-camera observations. The films had a thickness of approximately 10 μm. The it PP films were fixed at the hole of a plate, then bulge deformation was applied using N2 or He gas pressure, and stress-strain curves were then calculated from the applied pressure and bulge height. Yielding was observed in the stress-strain curves. Below the yield point, in situ WAXD measurements revealed that the crystal lattice expanded isotropically at the center, edge, and bottom of the bulge hole. Above the yield point, a craze started to form slightly near the center, and crazes formed in various directions with a further increase in strain, while the crystal lattice expanded uniaxially along the circumference at the edge and bottom. Crazes oriented in various directions merged and lost birefringence, indicating a change to the isotropic orientation. The different directions of the crazes indicated several directions of stress. In other words, even if multiaxial deformation is applied to a crystalline it PP film, the string-shaped crystalline polymer chain structure produces local anisotropic uniaxial stress.

Elasticity investigation of thin cellular structure films for piezoelectric sensors

PurposeThis paper aims to present the details of isotactic polypropylene (it-PP) films with a cellular structure (air-cavities) dedicated to pressure sensors. The polymer composites (thin films enriched with 5 and 10 wt% of mineral fillers as Sillikolloid P 87 and glass beads) should exhibit suitable structural elasticity within specific stress ranges. After the deformation force is removed, the sensor material must completely restore its original shape and size.Design/methodology/approachEstimating the stiffness tensor element (C33) for polymer films (nonpolar space-charge electrets) by broadband resonance ultrasound spectroscopy is a relatively simple method of determining the safe stress range generated in thin pressure sensors. Therefore, ultrasonic and piezoelectric studies were carried out on four composite it-PP films. First, the longitudinal velocity (vL) of ultrasonic waves passing through the it-PP film in the z-direction (thickness) was evaluated from the ω-position of mechanical resonance of the so-called insertion loss function. In turn, the d33 coefficient was calculated from accumulated piezoelectric charge density response to mechanical stress.FindingsResearch is at an early stage; however, it can be seen that the mechanical orientation of the it-PP film improves its piezoelectric properties. Moreover, the three-year electric charge stability of the it-PP film seems promising.Originality/valueUltrasonic spectroscopy can be successfully handled as a validation method in the small-lot production of polymer films with the air-cavities structure intended for pressure sensors. The structural repeatability of polymer films is strongly related to a homogeneous distribution of the electric charge on the electret surface.

Environmental degradation and formation of secondary microplastics from packaging material: A polypropylene film case study

A model study on isotactic polypropylene (iPP) films as commonly used in packaging was performed for simulating the process of microplastics formation from large-scale objects like littered packaging material,. Accelerated ultraviolet (UV) ageing in a Xenotest device resulted in chemical degradation and oxidation of the polymer, together with fragmentation into sub-mm particles, within less than 48 h. Combining the results with an independent Arrhenius study allowed an estimate of the lifetime until sub-mm particle formation between 9 months and 3.2 years, depending on location and climate. The findings offer a possible explanation for the mass loss at the lower end of the particle size distribution of environmental microplastics and the divergence between input estimates and actually detected amounts of microplastics.

Markedly improved photo-oxidation stability of α form isotactic polypropylene with nodular morphology

Photo-oxidation degradation behaviors of isotactic polypropylene (iPP) films with different crystalline morphology were investigated by artificially accelerated aging test. The α form iPP with nodular morphology was obtained by quenching the melt and subsequent annealing process, and its photo-oxidation degradation behavior was compared with that of the melt-crystallized α form iPP sample. Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), X-ray scattering, dynamic mechanical analysis (DMA) and atomic force microscopy (AFM) were utilized to characterize the microstructural variations of these two kinds of iPP films during photo-oxidation degradation process. The results showed that iPP film of nodular morphology exhibits improved photo-oxidation stability compared with that of lamellar and spherulitic structure. UV-Vis spectra and O2 diffusivity test of unexposed and aged samples demonstrated that the iPP film of nodular morphology has higher transparency and lower O2 diffusivity than that of lamellar morphology. Combining the microstructural analysis and surface morphology observation, the improved photo-oxidation stability of “nodular” iPP was correlated with its higher UV light transparency, lower O2 diffusion coefficient as well as the slower segmental mobility in the amorphous phase.

Preparation of isotactic polypropylene (iPP) films with different top and bottom surface parts via solution cast method using decahydronaphthalene as the diluent

ABSTRACT iPP films with different top and bottom surface parts were prepared via solution cast method. The structure and mechanism of iPP films prepared using this method were analyzed. When the evaporation temperature was not enough to form a homogeneous film, a top surface part was formed due to thermally induced phase separation (TIPS) and the crystallization, a bottom surface part was created due to the adsorption of carrier and both these parts were temperature sensitive. When the evaporation temperature was 60°C, particles with lotus leaf structure appeared in the top surface part, resulting in a quasi superhydrophobic surface.

Physical supercritical fluid deposition of polymer films: controlling the crystallinity with pressure

The self-assembly of isotactic polypropylene films from supercritical n-pentane was studied. The effects of solution thermodynamics and fluid mechanics were reported.

Stretch-induced structural evolution of pre-oriented isotactic polypropylene films: An in-situ synchrotron radiation SAXS/WAXS study

In-situ small- and wide-angle X-ray scattering (SAXS/WAXS) is employed to study the stretch-induced structural evolutions of four different pre-oriented isotactic polypropylene (iPP) cast films during uniaxial stretching at room temperature. The mechanical properties and structural evolutions show distinct features with the improvement in orientation of initial structure. For low-oriented films, the tensile stress induces the amorphization of lamellar crystals parallel to stretching direction, while the shear stress triggers the shearing of lamellar stacks at other angles through crystal slipping. For high-oriented films, the elastic deformation mode dominates as the normals of all lamellae are along stretching direction. Under tensile stress, micro-buckling or bending replaces the lamellar shearing to trigger the initial deformation instability of crystals. And stress-induced amorphization of lamellar crystals might also occur at large strains in the strain hardening zone. This study uncovers the different structural evolution roads of low- and high-oriented films, which will aid to deepen the understanding of the orientation effects on the deformation mechanisms of other semi-crystalline polymers.

Transcrystallinity in maize tissues/polypropylene composites: First focus of the heterogeneous nucleation and growth stages versus tissue type

The improvement of cellulosic biomass‐polymer composites needs to evaluate what occurs at the biomass‐matrix interface during crystallization. Different well‐defined maize tissues were obtained by original dry fractionation processes, without chemical treatment. Their morphological features were identified by optical and scanning electron microscopies. For each type of tissue, a small fragment was sandwiched between two films of isotactic polypropylene. The composite was subjected to quiescent isothermal conditions, followed in‐situ by polarized optical microscopy. Focus of the heterogeneous nucleation at the surface of maize tissues showed that in all cases, more or less numerous semi‐crystalline entities originated from the tissue surface, indicating a moderate nucleating activity. Different crystallization behaviors were observed as a function of the tissue. Growth rates of surface layers were generally higher that the growth rates of bulk spherulites. The differences were small, but significant. They were discussed within the frame of kinetic theory of growth.

Влияние модификации изотактического полипропилена на его транспортные свойства

Модификацией промышленных полимеров можно создать материалы с определенным набором эксплуатационных свойств. В данной работе проведена модификация структуры пленок изотактического полипропилена марки 01030 (ПП) путем обработки их жидкими алканами с увеличивающимся числом атомов углерода (гексан, гептан, н-нонан), которая приводит к увеличению сорбции и проницаемости воды в процессе первапорации. Эксперименты проводили по четырем маршрутам, как при изучении набухания ПП, так и при первапорации. Показано, что при проведении эксперимента по маршруту № 1 с увеличением числа атомов углерода в молекуле алкана степень набухания ПП растет, а величина плотности первапорационного потока падает. При модификации пленок ПП алканами по маршрутам №№ 3-4 происходит рост подвижности сегментов макромолекулярных цепей и увеличение расстояний между ними. При десорбции алканов образовавшаяся структура, по-видимому, сохраняется. После полного удаления ранее растворенного вещества (гексан и гептан) остаются «пустоты», через которые проникает вода (маршрут № 3) и наблюдается рост равновесной степени набухания ПП, а н-нонан полностью не удаляется, поэтому вода не может проникнуть в ПП. Аналогичное поведение наблюдается и при первапорации воды по маршруту №3. В случае маршрута № 4, когда десорбцию алканов не проводили, вода выталкивает алканы из полимера и проникает вслед за ними в пленку по образовавшимся каналам. С повышением температуры в изучаемом интервале плотность потока алканов возрастает (для гексана в 5 раз). Увеличение плотности потока воды после модификации происходит для всех изучаемых алканов, но она уменьшается при переходе от гексана к н-нонану. Показано, что в маршруте № 2 происходит поверхностная модификация пленки, в маршрутах № 3 и № 4 − объемная модификация. Таким образом, модификация полимерных пленок с использованием гидрофобных веществ приводит к увеличению сорбции и проницаемости гидрофильных веществ (воды).

High-velocity stretching of polyolefin tapes

Stretched polyolefin films and tapes are used in many packaging applications, such as BigBags. Stretching is elongation of polymer tapes in one direction, resulting in improved mechanical properties. Both, amorphous and crystalline polymers are in principle stretchable but linear, unbranched macromolecules are highly stretchable. Hence, the stretchability of e.g. branched low density polyethylene (PE-LD) is lower than of high-density polyethylene (PE-HD). Basic requirements for stretching of thermoplastics are known, but correlations between material parameters and stretching behaviour are scarce. Moreover, stretching of polymers is usually studied with tensile tests at stretching velocities much lower (1–500 mm/min) than in industrial processes (400–1000 mm/s), while results from high-velocity stretching tests or on production machines have not been published as of yet. We investigated high-velocity (800 mm/s) stretching of PE-LD, PE-HD and isotactic polypropylene films and tapes and which stretching parameters resulted in maximum mechanical properties. It was found that sample geometry, temperature, and the degree of stretching have a significant influence on the properties of stretched tapes, e.g. higher stretching temperature resulted in higher mechanical properties and orientation of crystallites. Furthermore, about 80% of the maximum stretching degree resulted in maximum mechanical properties.

Preparation, Structure, and Properties of an Isotactic Polypropylene Film with Ultrahigh Content, Ordered, and Continuous β-Transcrystallinity

β-Transcrystallinity (β-TC) of polypropylene (PP) is a novel kind of crystal that is of significant importance. Owing to the low content, discontinuity, and random distribution of β-TC obtained by ...

Rheology of polymer multilayers: Slip in shear, hardening in extension

The nonlinear rheology of multilayer stacks of alternating isotactic polypropylene (PP) and polyethylene (PE) films with N layers was measured in shear and uniaxial extension. We show that the force to extend N − 1 interfaces can lead to strain hardening. We studied three PE/PP pairs: a Ziegler–Natta catalyzed pair and two metallocene pairs, one with high density PE and one with linear low density PE. Interfacial tension was measured on matrix/droplet blends of each pair using small amplitude oscillatory shear measurements fitted with the Palierne model. Multilayer coextrusion was used to fabricate bilayers and sheets with hundreds of layers for each polyolefin pair. Under shear deformation, disentangling of chains in the N − 1 interfaces led to a decrease in the overall shear viscosity, which is interpreted as an interfacial slip velocity and is in agreement with previous studies on multilayer films. Under extensional flows, the multilayers exhibited an increased transient extensional viscosity (tensile stress growth coefficient, η E , M +) and pronounced strain hardening, even when the constituent homopolymers exhibited no strain hardening behavior. A model based on a force summation was developed to predict this behavior with interfacial tension as a fitting parameter; the extracted interfacial tensions agreed reasonably well with those from the Palierne model. The “slip in shear” and “hardening in extension” behaviors highlight the role of interfacial polymer physics during rheological measurements and polymer processing.

Self-Purification of Isotactic Polypropylene Films from Unknown Impregnated Impurities

Commercial films of stereoregular isotactic polypropylene (PP) are the objects of the study. The aim of the work is to substantiate the mechanism of the previously observed weight loss of the PP films as a result of consequtive sorption of hydrophobic and hydrophilic substances, while considering PP as a combination of hydrophobic and hydrophilic localized and delocalized sorbents. A variable sequence of the processes of sorption of probe molecules with different polarities is used as an investigation method, while only an analytical balance serves as a research instrument. It is shown that the weight loss of PP films during the sorption of a hydrophilic substance (water) after their preliminary swelling in a hydrophobic sorbate (hexane) containing a small amount of native water is caused by complexation of water molecules with hydrophilic impurities. As a result, a reverse flow of these complexes out of the polymer occurs along the transport channels that arise during its swelling in the hydrophobic sorbate (hexane).