Orientated CNT‐polypropylene nanocomposite films made from extruded monofilaments

In this study, a method for making an orientated polymer nanocomposite film was developed. Melt‐drawn nanocomposite monofilaments of isotactic polypropylene and acicular nanofillers, i.e. carbon nanotubes (CNT) or vapor grown carbon nanofibers (VGCF), were prepared and characterized from the aspect of polymer chain orientation, mechanical properties, and overall morphology. A marked improvement in mechanical properties was observed as a function of the addition of CNT, increasing draw down ratio (DDR) and annealing. Nanocomposite films were prepared from drawn monofilaments by hot‐pressing under low pressure in order to maintain the orientation of the monofilaments. Wide angle X‐ray diffraction showed a high degree of residual orientation in the films. Electron microscopy (high‐resolution scanning electron microscopy, transmission electron microscopy) unexpectedly revealed that the CNT‐matrix interface is amorphous. However, differential scanning calorimetry found no measurable influence of the CNT on the overall crystallinity as determined by the enthalpy of melting of the matrix. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Morphological studies on extruded films and filaments of polypropylene

In the present work, an attempt has been made to study the development of morphology during extrusion and uniaxial stretching of polypropylene (PP) films and filaments at corresponding conditions. Dies for extrusion of films and filaments were designed to achieve similar extrusion velocity and shear rates. Orientation in films and fibers of PP produced from these dies was determined by birefringence and wide-angle X-ray diffraction (WAXD). The degree of crystallinity was determined by density and WAXD. The superstructure developed during extrusion was studied in films by small-angle light scattering. It was inferred that films and fibers prepared under similar conditions would produce similar morphology. Hence, films can be characterized by optical techniques when it is difficult to study fibers. © 1994 John Wiley & Sons, Inc.     

Self‐reinforced polypropylene/LCP extruded strands and their moldings

Polypropylenes (PP) of various molecular weights were mixed with a thermotropic liquid crystal polymer (LCP) and strands were prepared by extrusion and stretching. The strands were subsequently pelletized and then injection molded at temperatures below the melting point of LCP. The mechanical properties and the morphology of the strands and injection‐molded specimens were investigated as a function of draw ratio, LCP concentration, and PP molecular weight. The results for strands show that an increase in the draw ratio, LCP concentration and matrix molecular weight in general enhance the modulus and tensile strength. However, the tensile properties of injection‐molded specimens are found to be reduced compared with those of the original strands, in particular at high LCP concentration. The morphology of LCP changes from spherical or ellipsoidal droplets to elongated fibrils in the strands as the draw ratio increases, but this aligned LCP fibrillar morphology was not transferred to the injection‐molded specimens because of the disorientation of fibrils during injection molding. Compatibilization of PP/LCP blends was also studied by using various polymers. Maleic anhydride and acrylic acid modified PPs improved the tensile properties modestly, but maleic anhydride modified EPDM reduced the tensile properties.     

Co‐extruded polymeric films for gas separation membranes

In recent years, gas separation has become an important step in many production process streams and part of final products. Through the use of melt co‐extrusion and subsequent orientation methods, gas separation membranes were produced entirely without the use of solvents, upon which current methods are highly dependent. Symmetric three layer membranes were produced using poly(ether‐block‐amide) (PEBA) copolymers, which serve as a selective material that exhibits a high CO₂ permeability relative to O₂. Thin layers of PEBA are supported by a polypropylene (PP) layer that is made porous through the use of two methods: (1) inorganic fillers or (2) crystal phase transformation. Two membrane systems, PEBA/(PP + CaCO₃) and PEBA/β‐PP, maintained a high CO₂/O₂ selectivity while exhibiting reduced permeability. Incorporation of an annealing step either before or after orientation improves the membrane gas flux by 50 to 100%. The improvement in gas flux was a result of either elimination of strain induced crystallinity, which increases the selective layer permeability, or improvement of the PP crystal structure, which may increase pore size in the porous support layer. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39765.     

Mechanical performance of re‐extruded and aged graphene/polypropylene nanocomposites

In the present research polypropylene/expanded graphite (PP/ExpG) and polypropylene/graphene nanoplatelet (PP/GNP) composites were prepared by melt blending and their morphology and tensile properties were investigated. Although both reinforcements improved the elastic modulus of PP, PP/GNP composite presented better dispersion of the nanofiller in the polymer matrix and it was selected for further re‐extrusion and ageing experiments. The re‐extrusion affected the content of crystal phases of PP in pure PP and in its nanocomposite with GNP and increased their elastic modulus. The ageing of one and five times re‐extruded PP caused an increase of the β‐crystal phase and the formation of voids in the cross‐section. GNPs seem to protect the PP matrix from ageing as in Fourier transform IR spectra of PP/GNP nanocomposite, both one and five times extruded, the peak corresponding to carbonyl degradation products of PP was barely visible. The tensile properties of aged nanocomposites, one and five times re‐extruded, were similar to those of the corresponding non‐aged composites, whereas in aged PP the tensile strength and strain decreased significantly compared to non‐aged PP. The anti‐ageing effect of graphene can prolong the life of the PP matrix. © 2017 Society of Chemical Industry     

Zeolite A‐polypropylene and silver‐zeolite A‐polypropylene composite films for antibacterial and breathable applications

Polypropylene (PP) composite films were successfully prepared using melt blending by directly mixing PP pellets with zeolite A or silver‐zeolite A powder and then blowing. All the prepared films were characterized in terms of their physical, mechanical, optical, and gas permeability properties. The structure of each composite film was similar to that of the pure PP film. The crystallinity and glossy quality of the composite films were increased by the addition of silver, zeolite, and maleic anhydride grafted PP (PP‐g ‐MA). The composite PP film with zeolite A and PP‐g ‐MA exhibited a level of oxygen and carbon dioxide permeation (6438 and 15,087 cc m^?2 day^?1 atm^?1, respectively). Finally, all the films were evaluated for their antibacterial activity and fruit packaging applications. Silver‐zeolite A‐PP composite films exhibited a bactericidal activity of 79% against Staphylococcus aureus and 52% against Escherichia coli , while the zeolite A‐PP film could extend the shelf‐life of bananas for over a week. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45450.     

Air‐hole properties of calcite‐filled polypropylene copolymer films

This work was designed to study the effects of inorganic calcite powder on structurally different copolymer [poly(propylene‐co‐ethylene)] and terpolymer [poly (propylene‐co‐ethylene‐co‐1‐butene)] matrices and the possibility of making a suitable porous composite film. The yield stress of the composites did not improve, but the modulus increased gradually with the filler loading. The theoretical and experimental modulus and yield stress of the composites provided evidence of filler and polymer adhesion behavior. The impact strength showed little enhancement up to a 20 wt % loading for the poly(propylene‐co‐ethylene‐co‐1‐butene) system. The number‐average, weight‐average, and z‐average air‐hole diameters were compared with respect to the draw ratio as well as the calcite loading. The morphology of a micromechanically deformed composite, studied with an image analyzer, revealed that the aspect ratio and area of the air holes increased linearly as a function of the draw ratio, but the change in the aspect ratio upon filler loading was not remarkable. A suitable loading of a filler up to 30 wt % was good for controlling the porosity in the composite films. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The role of filler type in the photo‐oxidation behaviour of micro‐ and nano‐filled polypropylene

The rising interest in polymer nanocomposites leads also to an increasing concern for their photo‐oxidation resistance. The main properties and photo‐oxidation behaviour of polypropylene‐based microcomposites and nanocomposites were investigated. The results show that the use of nanosized calcium carbonate may lead to a higher photo‐oxidation rate than that of pristine polypropylene, in a way that is comparable to organo‐modified nanoclays. It is also observed that nanosized calcium carbonate causes higher photodegradation rates than microsized calcium carbonate. The main reasons for the increased photo‐oxidation rates when using organo‐modified nanoclays include the presence of iron ions, the degradation of the organo‐modifier and the formation of acidic sites on nanoclay layers, while in the case of calcium carbonate the main reasons are related to the achieved morphology and structure. The presence of calcium carbonate, especially when nanosized, significantly modifies the distribution of photo‐oxidation products in comparison to clay‐filled nanocomposites. Copyright © 2011 Society of Chemical Industry     

Preparation of extruded melt‐mixed polypropylene/montmorillonite nanocomposites with inline monitoring

This article advances the use of an inline optical detector to monitor the disaggregation of the montmorillonite (MMT) clay tactoids during the preparation of polypropylene (PP)/MMT nanocomposites via polymer melt compounding. During the exfoliation of the tactoids their size are reduced below the minimum particle size to produce light extinction and so, the signal of the inline detector reduces as the nanosize composite is formed. The measurement is done at the transient state with the MMT clay added as a pulse with constant weight into the PP extrusion melt flow and followed by the optical detector. The data comes out as the common residence time distribution curves having its maximum intensity related to the tactoids average particle size, keeping all other variables constants. The light extinction was measured for composites with different clays (Cloisite® 15A, 30B, Na⁺, and Sintered 20A) using the same PP grafted with maleic anhydride compatibilizer. The dissaglomeration/exfoliation efficiency increases as: ‘‘Sintered 20A’’ < ‘‘Na+ clay’’ < ‘‘organo‐modified clay’’ < ‘‘organo‐modified clay + compatibilizer’’. The best result is obtained using Cloisite® 15A and Cloisite® 20A following the expected reduction of the particle size obtained during a nanocomposite melt processing. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Preparation and characterization of nano/micro‐calcium carbonate particles/polypropylene composites

A new kind of polypropylene (PP)/CaCO₃ composites was prepared on a twin screw extruder with the nanoparticle content of 5 wt % and the 2500 mesh microparticle content of 15 wt %. The mechanical property of four different samples [pure PP (1) , PP filled with 15 wt % microCaCO₃ particle composites (2) , PP filled with 5 wt % nanoCaCO₃ particle composites (3) and PP filled with micro/nano‐CaCO₃ complex size particle composites (4) ] was investigated through tensile tests, notched Izod impact tests and SEM. The results indicated that the sample 4 had the best mechanical property. The proofs of SEM showed that the high impact energy could lead to debonding and creating microcavitation between the nanoparticle and polymer interface if the polymer was filled with the nanoparticles. This process could absorb a lot of mechanical failure energy, but too much mechanical failure energy would lead to the enlargement of microcavitation and the destruction of the composites in sample 3 . In sample 4 , the microparticle could be used to prevent the enlargement of microcavitation in the matrix polymer under the higher impact failure energy. In this article, the model of the impacting failure process of micro/nanoCaCO₃/PP composites was established. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of initial mixing methods on melt‐extruded single‐walled carbon nanotube–polypropylene nanocomposites

We report the first direct comparison of melt‐extruded polypropylene–single‐walled carbon nanotube (PP/SWNT) nanocomposites prepared by three different initial mixing methods. The standard deviation of the G‐band intensity obtained using Raman mapping was found to be the best measure of dispersion uniformity in the extruded composites, and dispersion uniformity was found to generally correlate with rheological and thermal properties. For all three initial mixing methods, both unmodified and sidewall‐functionalized purified SWNTs were evaluated. Surprisingly, in all cases, dodecylated SWNTs prepared using the reductive alkylation method were less uniformly dispersed in the final composite than the unmodified SWNTs. The simplest process, dry blending, resulted in poor nanotube dispersion and only polymer crystallization was significantly affected by the presence of the nanotubes. A slightly more complex rotary evaporation process resulted in significantly more uniform dispersion and significant changes in rheological properties, polymer crystallization, and thermal stability. The most elaborate process tested, hot coagulation, enabled the most uniform dispersion and the greatest change in properties but also resulted in some polymer degradation. POLYM. ENG. SCI., 50:1831–1842, 2010. © 2010 Society of Plastics Engineers     

Matting films prepared from waterborne acrylic/micro‐SiO2 blends

Acrylic resin/micro‐SiO₂/polymethyl urea (AC/SiO₂/PMU) composites were prepared by physical blends of acrylic resin latex (AC), polymethyl urea resin (PMU), and modified SiO₂. The effects of SiO₂ and PMU content in the hybrid composites morphology and physical properties were investigated in detail using transmission electron microscopy (TEM), UV‐Vis spectrometry (UV‐Vis), scanning electron microscope (SEM), thermogravimetric analysis (TGA), and contact angle measurement. The results showed that introduction of SiO₂ into AC composites could increase the viscosity which caused by gelation and agglomeration of SiO₂. The TEM, SEM images, and TGA results indicated that hybrid membranes have phase separation. During the film formation process, a high number of PMU and SiO₂ particles of an appropriate size were stranded on the surface of the film to form matting surface. These results highlight the sensitivity of the gloss to the polymer morphology and surface. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41707.     

Melt‐electrospun fibers obtained from polypropylene/poly(ethylene‐co‐vinyl alcohol)/polypropylene three‐layer films

Production of polypropylene (PP) nanofibers below 1 μm in average diameter is difficult with conventional melt‐spinning. A nozzle‐free melt‐type electrospinning (M‐ESP) system with a line‐like CO₂ laser beam melting device were used to produce PP nanofibers. To achieve the purpose, core [poly(ethylene‐co‐vinyl alcohol) (EVOH)]–clad (PP) nanofibers (average diameter, 0.88 μm) were fabricated from PP/EVOH/PP three‐layer films using the M‐ESP. The core–clad structure was formed by a wrapping phenomenon caused by the difference in the melt flow rates (MFRs) of PP and EVOH melts. Hollow PP nanofibers were obtained from the core–clad nanofibers by extraction of EVOH. Nanofiber diameter and hollow wall thickness could be altered by changing the MFR of the PP melt. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46393.     

Oxygen transfer in co‐extruded multilayer active films for food packaging

Oxygen scavenger applications in flexible food packaging are still limited due to the difficulty to ensure scavenging activity during storage and throughout the product shelf life. To avoid fast inactivation of the scavenger, multilayer active structures can be realized by inserting the active layer between two or more inert layers. In this work, an unsteady‐state 1D reaction‐diffusion mass transfer model was developed for predicting and optimizing the barrier‐to‐oxygen performance and the physical configurations of the co‐extruded multilayer active films. The film configuration was a three‐layers structure composed of polyethylene terephthalate (PET) as external inert layers, and PET with a polymeric oxygen scavenger as the core reactive layer. Scavenging activity of the multilayer film increased with the reactive layer thickness. Oxygen absorption reaction at short times decreased proportionally with the thickness of the external layers. The most appropriate combinations of inert‐to‐active film thickness were studied and analyzed. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Fast space charge behavior in heat‐treated polypropylene films

In this study, the characterization of the short‐circuit current within hundreds of nanoseconds is proposed to study the effect of heat treatment on fast space charge behavior in the polarized biaxially oriented polypropylene (BOPP) films. The BOPP films were cooled either quickly or slowly during the sample preparation. The damped oscillating feature was found in the short‐circuit current of all the polarized film samples, but the periods of the oscillating current for the samples prepared by fast cooling rate decrease faster. Bipolar space charge injection in the polarized BOPP films was observed by the thermal pulse (TP) measurement. The variation feature of the short‐circuit current was considered to be associated with the varying fast space charge behavior, which depended on the varying structural traps modified by the heat treatment during the sample preparation. The sample subjected to fast cooling process was with relatively shallow trap level revealed by the thermally stimulated current method, which led to higher mobility of the escaping charge in the sample. The TP measurements were utilized to analyze space charge features in the polarized BOPP films. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42235.     

Enhanced dielectric performances of polypropylene films via polarity adjustment by maleic anhydride‐grafted polypropylene

Maleic anhydride‐grafted polypropylene (MA‐g ‐PP) was hybridized with pure PP to form hybrid films with the aim to enhance the dielectric performances of the PP film via polarity adjustment. The changes of microstructure and crystallinity of PP matrix by MA‐g ‐PP incorporation were studied, and the polarity change was identified by the surface wettability. The dielectric behaviors of the hybrid films were explored. Increasing polarity of PP film leads to increase in dielectric constant but decrease in breakdown strength, and a balance is achieved in 10 vol % MA‐g ‐PP/PP hybrid film, with the maximum discharge energy density reaching 1.96 J cm^?3 and charge–discharge efficiency as high as 96%. The ultralow loss is attributed to the dense and homogeneous microstructure together with increased crystallinity induced by incorporation of MA‐g ‐PP. These PP‐based films with increased polarity not only show enhanced dielectric performances but also provide a type of matrix that would be compatible with polar fillers to further increase dielectric properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45029.     

Oxo‐biodegradability of high‐density polyethylene films containing limited amount of isotactic polypropylene

Limited amount of isotactic polypropylene (iPP) is added to high‐density polyethylene (HDPE) containing 1% w/w an oxo‐biodegradable additive and extruded and converted to films. The films are put under UV irradiation for different periods of time. Irradiation of the films for 6 weeks imposes remarkable effects on viscosity average molecular weight (M_v) and carbonyl index (CI) of them. M_v decreases from 3.4 × 10⁵ to 4.7 × 10⁴ g mol^?1 for neat HDPE films; from 3.1 × 10⁵ to 3.3 × 10⁴ g mol^?1 for the films containing oxo compound, and from 1.5 × 10⁵ to 2.6 × 10⁴ g mol^?1 for the films containing oxo compound and 1% w/w iPP. Carbonyl index of the neat HDPE films increases from 4 to 8.7 while for the sample containing only the oxo compound it increases from 4.5 to 7.3 and for the sample containing both oxo compound and iPP it decreases from 12.0 to 8.8. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) indicate more cracks and uniform degradation in the samples containing iPP and oxo compound. Thermogravimetric analysis (TGA/DTG) of the samples shows that the samples containing iPP and oxo compound have lower decomposition temperature after UV irradiation. Finally, it can be said that the presence of iPP in HDPE matrix containing oxo compound can improve HDPE oxo‐biodegradablity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45843.     

On the differences in micro‐deformation mechanism between isotactic polypropylene and β‐nucleated isotactic polypropylene as revealed by the confocal laser scanning microscopy

To understand the toughness enhancement of β‐nucleated isotactic polypropylene (iPP) in comparison with iPP, the differences in the micro‐deformation mechanisms between the neat iPP and β‐nucleated iPP were visualized using the confocal laser scanning microscopy (CLSM). Structure of the α‐ and β‐spherulites situated close to the tip of the sharp starter crack has been investigated during tensile deformation in the viewing field of the CLSM. In the α‐spherulite of the neat iPP, highly localized inter‐ and intra‐spherulitic micro‐shear bands have been observed. In the β‐nucleated iPP, relatively uniform distribution of diffuse shear bands has been observed in the β‐phase, while the α‐phase remained relatively undeformed exhibiting only narrow intra‐spherulitic shear bands in the direction perpendicular to the loading direction. Delocalization of plastic deformation into diffuse shear bands in β‐nucleated iPP can explain its enhanced crack resistance compared with the neat iPP exhibiting highly localized shear banding. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Polylactide/nano‐ and micro‐scale silica composite films. II. Melting behavior and cold crystallization

Nonisothermal crystallization of polylactide (PLA)/silica composites prepared by (i) directly blending the PLA with nanoscale colloidal silica sol and by (ii) a sol–gel process are studied by differential scanning calorimeter (DSC) at various heating rates. Samples quenched from the molten state exhibited two melting endotherms (T_ml and T_mh) due to melt‐recrystallization during the DSC scans. Lower heating rate and the presence of silica particles generate a lower peak intensity ratio of T_ml /T_mh. The nonisothermal crystallization kinetics is analyzed by modified Avrami model, Ozawa model, and Liu‐Mo models. The modified Avrami and Liu‐Mo models successfully described the nonisothermal cold crystallization processes, but Ozawa is inapplicable. The nucleation constant (K_g) is calculated by modified Lauritzen‐Hoffman equation and the activation energy by Augis‐Bennett, Kissinger, and Takhor models. These calculated parameters indicate consistently that the nanoscale silica particles seem to form more heterogeneous nucleation to increase crystallization, but microscale one form hindrance to retard crystallization. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Functionalization of industrial polypropylene films via the swift‐heavy‐ion‐induced grafting of glycidyl methacrylate

Swift‐silver‐ion irradiation was explored as a means of forming chemically active sites on the surface of biaxially oriented polypropylene films. The active species, formed in air, was used to induce the graft copolymerization of glycidyl methacrylate in an aqueous solution. The surface structure, crystallinity, morphology, and hydrophilicity of the grafted samples were characterized with Fourier transform infrared, UV, wide‐angle X‐ray diffraction, scanning electron microscopy, and contact‐angle measurements. Glycidyl methacrylate could be grafted onto biaxially oriented polypropylene after swift‐heavy‐ion irradiation without an additional initiator. The contact angle of the modified films decreased with the grafting percentage of glycidyl methacrylate on the polypropylene. The swift silver ions induced significant grafting only in small regions (i.e., the latent tracks) of the polymer. Furthermore, as the fluence of swift heavy ions increased beyond an optimum value, the overlapping of the latent tracks reduced the grafting yield. The observed findings could be very useful in developing an initiator‐free grafting system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007