Crystalline Phase Of Polypropylene Research Articles

Effect of Oxidation Temperature on the Crystalline Phase of Polypropylene in Composites with Single-Walled Carbon Nanotubes

Effect of Oxidation Temperature on the Crystalline Phase of Polypropylene in Composites with Single-Walled Carbon Nanotubes

Effect of Oxidation Temperature on the Crystalline Phase of Polypropylene in Composites with Single-Walled Carbon Nanotubes

The effect of thermal oxidation on the crystalline phase of polypropylene in composites with single-walled carbon nanotubes has been studied. The composites are synthesized in propylene bulk using a homogeneous catalytic system rac-Me2Si(2-Me-4PhInd)2ZrCl2, activated by methylaluminoxane. The effect of thermal oxidation on thermophysical characteristics (the heat of melting and the melting temperature) measured by DSC and changes occurring in the polymer investigated by IR spectroscopy is studied. Changes in the structure of PP during thermo-oxidative degradation are studied by DSC at 140 and 170°С, that is, before and after melting of the samples. It is shown that the oxidized PP in the composites possesses a higher degree of crystallinity and a more perfect structure than the pure PP. At 170°С the effect of thermo-oxidative stabilization is observed only at low filling degrees (up to 3 wt %), in agreement with the TGA data. An analysis of IR spectra demonstrates that the presence of nanotubes in PP‑based composites during oxidation slows down the formation of oxygen-containing groups in the polymer. The conclusion is made that carbon nanotubes inhibit the thermal oxidation of polypropylene in the composites.

Morphological Evolution and Damping Properties of Dynamically Vulcanized Butyl Rubber/Polypropylene Thermoplastic Elastomers.

We successfully prepared butyl rubber (IIR)/polypropylene (PP) thermoplastic vulcanizate (IIR/PP-TPV) for shock-absorption devices by dynamic vulcanization (DV) using octyl-phenolic resin as a vulcanizing agent and studied the morphological evolution and properties during DV. We found that the damping temperature region of the IIR/PP-TPV broadened with the disappearance of the glass transition temperature (Tg) in the PP phase, which is ascribed to the improvement of compatibility between the IIR and PP with increasing DV time. As DV progresses, the size of the dispersed IIR particles and the PP crystalline phase decreases, leading to the formation of a sea–island morphology. After four cycles of recycling, the retention rates of tensile strength and elongation at break of the IIR/PP-TPV reached 88% and 86%, respectively. The size of the IIR cross-linking particles in the IIR/PP-TPV becomes larger after melt recombination, and the continuous PP phase provides excellent recyclability. Significantly, the prepared IIR/PP-TPV exhibits excellent recyclability, high elasticity, and good damping property.

Non-isothermal crystallization kinetics of polypropylene/polytetrafluoroethylene fibrillated composites

Non-isothermal crystallization kinetics of polypropylene (PP)/polytetrafluoroethylene (PTFE) fibrillated composites is presented. In-situ fibrillated PP/PTFE-composites containing 1 and 3 wt% PTFE were prepared by melt compounding using a twin-screw extruder. The morphology and non-isothermal crystallization behavior of the composites were examined using scanning electron microscopy and differential scanning calorimetry, respectively. The Mo equation was used to analyze the kinetics of non-isothermal crystallization behavior. The PTFE created a three-dimensional (3-D) network. A low PTFE content promoted crystallization through fast nucleation, whereas a high PTFE content decreased the crystallization kinetics through hindering the crystal growth. These findings are all based on the Mo equation analysis. The activation energy and nucleation activity were also evaluated, and the way in which the PTFE nanofibers affected the crystallization was discussed in detail. Polarized optical microscopy images revealed that the size of PP spherulites decreased with the increase of PTFE content. Finally, the effect of PTFE on the crystalline phase of PP was investigated by wide angle X-ray diffraction.

Imparting External Stress-Free Two-Way Shape Memory Effect to Commodity Polyolefins by Manipulation of Their Hierarchical Structures.

Two simple methods are proposed to respectively impart external force-free reversible shape memory effect to commercial polyolefins: ultrahigh molecular weight polyethylene (UHMWPE) and polypropylene (PP). The key issues lie in the utilization of the partially entangled molecular chains of UHMWPE and the medium crystalline phases of PP as the reversible internal stress providers. The acquired reversible shape memory effect further proves to be applicable for assisting repeatedly self-healing of wider cracks. Compared to the conventional approaches, which used to introduce cross-linkages into the target materials, the present ones only need physical treatment, so that the valuable thermoplasticity of polyolefins is retained. This work can be regarded as an example of the concept "physically converting instead of chemically modifying" for the preparation of functional polymeric materials based on market available plastics.

Structure, mechanical and thermal properties of polypropylene based hybrid composites with banana fiber and fly ash

Polypropylene (PP)-Flyash (FA) composites containing natural banana fiber (NF) treated by Maleic anhydride and NaOH are reported here. Mechanical properties such asflexural modulus and impact strength were improved considerably which were maximum for 20% fly ash filled PP-NF treated composites. There is extensive nucleation of theα crystalline phase of PP in presence of the additives. This changed to mixed α phase with slight β content in presence of FA and treated NF as confirmed by XRD and DSC. The results on the mechanical properties have been explained on the basis of structure development of PP in presence of fly ash and treated NF. The results have also been analyzed with the help of different models for filled polymer composites and using rule of mixtures of two composites to form final ternary hybrid composite. Some agreement is found if a factor is introduced for redistribution of fibers due to added FA as third component. However, the synergistic behavior at certain composition can be explained on the basis of crystalline structure and nucleation due to the additives.

Crystallization behavior of polypropylene/graphene nanoplatelets composites

Interest in graphite fillers has grown since the separation of graphene from graphite by micromechanical cleavage. The object of the paper is to understand the influence of graphene nanoplatelets (GNPs) with different sizes on the crystallization behavior of a polyolefin matrix such as polypropylene (PP), after elaboration by melt mixing and compression molding. Composites with volume fractions of graphene nanoplatelets ranging from 0.3 to 2 vol% were prepared. The particle dispersion states in the composites were characterized at different scales using Scanning and Transmission Electron Microscopies (SEM and TEM). Polypropylene crystallization and orientation were investigated using optical microscopy, Differential Scanning Calorimetry (DSC) and X-ray diffraction. This paper discusses the strong acceleration of crystallization kinetics due to the presence of GNPs. The micrometric flake-shaped GNPs act as nucleating agent and induce an epitaxial growth of alpha (α) crystalline phase of PP. The nucleating effect is related to the surface of the particles available for heterogeneous nucleation. Radial spherulitic growths are observed from the smallest micrometric particles. The coarsest GNPs, easily oriented by flow, favor PP transcrystallinity, in such a way that (010) plane of PP is parallel to (001) plane of graphene nanoplatelets.

Antimicrobial Carvacrol-Containing Polypropylene Films: Composition, Structure and Function.

Significant research has been directed toward the incorporation of bioactive plant extracts or essential oils (EOs) into polymers to endow the latter with antimicrobial functionality. EOs offer a unique combination of having broad antimicrobial activity from a natural source, generally recognized as safe (GRAS) recognition in the US, and a volatile nature. However, their volatility also presents a major challenge in their incorporation into polymers by conventional high-temperature-processing techniques. Herein, antimicrobial polypropylene (PP) cast films were produced by incorporating carvacrol (a model EO) or carvacrol, loaded into halloysite nanotubes (HNTs), via melt compounding. We studied the composition-structure-property relationships in these systems, focusing on the effect of carvacrol on the composition of the films, the PP crystalline phase and its morphology and the films’ mechanical and antimicrobial properties. For the first time, molecular dynamics simulations were applied to reveal the complex interactions between the components of these carvacrol-containing systems. We show that strong molecular interactions between PP and carvacrol minimize the loss of this highly-volatile EO during high-temperature polymer processing, enabling semi-industrial scale production. The resulting films exhibit outstanding antimicrobial properties against model microorganisms (Escherichia coli and Alternaria alternata). The PP/(HNTs-carvacrol) nanocomposite films, containing the carvacrol-loaded HNTs, display a higher level of crystalline order, superior mechanical properties and prolonged release of carvacrol, in comparison to PP/carvacrol blends. These properties are ascribed to the role of HNTs in these nanocomposites and their effect on the PP matrix and retained carvacrol content.

Recycling polymeric waste from electronic and automotive sectors into value added products

The environmentally sustainable disposal and recycling of ever increasing volumes of electronic waste has become a global waste management issue. The addition of up to 25% polymeric waste PCBs (printed circuit boards) as fillers in polypropylene (PP) composites was partially successful: while the tensile modulus, flexural strength and flexural modulus of composites were enhanced, the tensile and impact strengths were found to decrease. As a lowering of impact strength can significantly limit the application of PP based composites, it is necessary to incorporate impact modifying polymers such as rubbery particles in the mix. We report on a novel investigation on the simultaneous utilization of electronic and automotive rubber waste as fillers in PP composites. These composites were prepared by using 25 wt.% polymeric PCB powder, up to 9% of ethylene propylene rubber (EPR), and PP: balance. The influence of EPR on the structural, thermal, mechanical and rheological properties of PP/PCB/ EPR composites was investigated. While the addition of EPR caused the nucleation of the β crystalline phase of PP, the onset temperature for thermal degradation was found to decrease by 8%. The tensile modulus and strength decreased by 16% and 19%, respectively; and the elongation at break increased by ~71%. The impact strength showed a maximum increase of ~18% at 7 wt.%–9 wt.% EPR content. Various rheological properties were found to be well within the range of processing limits. This novel eco-friendly approach could help utilize significant amounts of polymeric electronic and automotive waste for fabricating valuable polymer composites.

Viscoelastic, thermo-mechanical and environmental properties of composites based on polypropylene/poly(lactic acid) blend and copper modified nanoclay

Poly(lactic acid) (PLA)/polypropylene (PP) blends composites were prepared by incorporating 3 wt.% of copper modified montmorillonite (MMT-Cu2+), obtained using cation exchange in a CuSO4 solution, and 10 wt.% of polypropylene-graft-maleic anhydride (PP-g-MA) as a compatibilizer then varying the PLA content until 50 wt.%. These materials were subjected to several investigations such as X-rays diffraction, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and tensile and environmental tests. The DMTA analysis showed that the glassy PLA high stiffness and the PP crystalline phase compensate the decrease in the storage modulus occurring during the PP and PLA glass transitions, respectively. The variations of tan δ revealed no changes on the PP and PLA phases glass transitions temperatures which indicate the immiscibility of the two polymers, as supported by DSC analysis. Blends composites SEM micrographs stated the immiscibility of the system resulting in the poor adhesion of the PLA droplets to the PP matrix. Also, the blends composites exhibited intermediate tensile properties between those of PP and PLA. The incorporation of MMT-Cu2+ to the (50/50) PP/PLA blend accentuated its aptitude to water absorption and ensured an efficient antimicrobial activity over a satisfactorily long period of around six months.

A comparative study of the effect of different rigid fillers on the fracture and failure behavior of polypropylene based composites

Polypropylene (PP) composites with 5wt% of different rigid particles (Al2O3 nanoparticles, SiO2 nanoparticles, Clay (Cloisite 20A) nanoparticles or CaCO3 microparticles) were obtained by melt mixing. Composites with different CaCO3 content were also prepared. The effect of fillers, filler content and addition of maleic anhydride grafted PP (MAPP) on the composites fracture and failure behavior was investigated. For PP/CaCO3 composites, an increasing trend of stiffness with filler loading was found while a decreasing trend of strength, ductility and fracture toughness was observed. The addition of MAPP was beneficial and detrimental to strength and ductility, respectively mainly as a result of improved interfacial adhesion. For the composites with 5wt% of CaCO3 or Al2O3, no significant changes in tensile properties were found due to the presence of agglomerated particles. However, the PP/CaCO3 composite exhibited the best tensile behavior: the highest ductility while keeping the strength and stiffness of neat PP. In general, the composites with SiO2 or Clay, on the other hand, displayed worse tensile strength and ductility. These behaviors could be probably related to the filler ability as nucleating agent. In addition, although the incorporation of MAPP led to improved filler dispersion, it was damaging to the material fracture behavior for the composites with CaCO3, Al2O3 or Clay, as a result of a higher interfacial adhesion, the retardant effect of MAPP on PP nucleation and the lower molecular weight of the PP/MAPP blend. The PP/MAPP/SiO2 composite, on the other hand, showed slightly increased toughness respect to the composite without MAPP due to the beneficial concomitant effects of the presence of some amount of the β crystalline phase of PP and the better filler dispersion promoted by the coupling agent which favor multiple crazing. From modeling of strength, the effect of MAPP on filler dispersion and interfacial adhesion in the PP/CaCO3 composites was confirmed.

Correlations of mechanical properties and microstructural parameters in annealed drawn film of liquid crystalline polymer in situ reinforced PP

AbstractDrawn composite thin film based on thermotropic liquid crystalline polymer (TLCP) and polypropylene (PP) was annealed at 130 °C at different times. The influence of annealing time on microstructural and mechanical properties of the composite film has been studied. The correlation in mechanical properties and their microstructural parameters has also been investigated. X-Ray diffraction results reveal that the smectic mesophase transforms progressively into the monoclinic phase as annealing time is increased. Consequently, the true crystallinity (Xc), crystal thickness (L) as well as relative level of molecular orientation of PP crystalline phase in the annealed TLCP/PP films are increased significantly. Also, the TLCP fibrils have no influence on the microstructure of PP crystalline phase. The apparent crystallinity (Xc,a) of PP phase evaluated by DSC also increase significantly with annealing time. As a result, the increases of these microstructural parameters coupled with the reinforcement of TLCP fibrils could be contributed directly to the remarkable enhancement of mechanical properties of the annealed TLCP/PP film in both machine (MD) and transverse (TD) directions. The correlation of moduli with microstructural parameters (Xc, Xc,a and L) exhibits nonlinear relations. However, the relative level of molecular orientation is a more suitable parameter to correlate with the improvement of mechanical properties of the annealed TLCP/PP film. Finally, this work presents that the mechanical properties of the TLCP in situ reinforced thermoplastics can be significantly enhanced via a simple thermal treatment.

Preparation of degradable polypropylene by an addition of poly(ethylene oxide) microcapsule containing TiO 2. Part III: Effect of existence of calcium phosphate on biodegradation behavior

In this work, biodegradation behavior of a novel polypropylene (PP) composite containing a poly(ethylene oxide) (PEO)/modified TiO 2 microcapsule was studied with an oxo-biodegradation test combined with a photodegradation treatment (using a high-pressure mercury vapor lamp for 24 h of the irradiation at 30 °C in air) and a soil burial test (for 45 days of incubation at 20 °C). The modification of the TiO 2 was performed by the synthesis of octacalcium phosphate intercalated with succinic acid ion (OCPC). The existence of the microcapsule brought about higher PP photo- and biodegradation rates. In the photodegraded PP composite, active colonies of some microorganisms were observed. By comparing with the PP composite without the OCPC modification, it was found that the active behavior of the microorganisms was due to the inorganic phosphates, which were supplied by the dissolution of the OCPC during the photodegradation. In addition, the photodegraded parts in the composite were completely metabolized by the microorganisms. However, the microorganisms had the inability to metabolize other parts such as the PP crystalline phase.

Polymorphism in a metallocenic isotactic polypropylene as revealed by means of FTIR spectroscopy: Influence of the processing conditions

AbstractThe polymorphic structure in specimens of a metallocenic isotactic polypropylene, processed under different conditions, has been studied by means of wide‐angle X‐ray scattering (WAXS), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). The proportions of the different polymorphs have been evaluated, and the influence of the processing parameters (nucleating agents, cooling rate, and nature of the surface of the molds) has been analyzed. The combination of WAXS, DSC, and FTIR results confirms the adequacy of this last technique to obtain quantitative information about the competition between the crystalline phases of polypropylene. It has also been proved that the nature of the mold can enhance considerably the activity of beta‐nucleating agents. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Effect of carbon black addition and its phase selective distribution on the stress relaxation behavior of filled thermoplastic vulcanizates

AbstractThe long term mechanical behavior of thermoplastic vulcanizates (TPV) based on polypropylene (PP) and ethylene propylene diene terpolymer (EPDM) and different types and concentrations of carbon black (CB) has been characterized by means of stress relaxation experiments. Evaluation of the relaxation curves was carried out using the two‐component model allowing a division of the initial stress into different stress components which are caused by different networks available in TPV. The discussion focussed on the background of the stress components, which are originated by the CB addition, the non‐relaxing stress components σ, and σ, as well as the relaxing stress components ΔσCB(polymer‐layer) and ΔσCB(network). It was found that the concentration and type of CB as well as the phase specific CB distribution strongly affect the non‐relaxing and relaxing stress components. Up to a CB concentration of 9% in the EPDM phase the composite behaves as a thermo‐rheologically simple material because the impact of CB addition on the α‐relaxation of the crystalline PP phase is still negligible. A master curve was created by the horizontal shift of the relaxing stress curves ΔσComp(t) to a reference curve. At higher local CB loadings the additional relaxation processes induced by CB addition overlap with the α‐relaxation, thus, no master curve could be made in that case. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Morphology and crystalline properties of impact‐modified polypropylene blends

AbstractIsotactic polypropylene has been reactively blended with an ethylene‐octene copolymer so as to improve mechanical and rheological properties. Free radical polymerization of styrene and a multifunctional acrylate during melt extrusion has resulted in the formation of unique features in both amorphous and crystalline phases. Transmission electron microscopy images show that the elastomer domains are less than 200 nm in diameter, whereas grafting leads to the appearance of clusters of polymeric particles, ranging in size from several nanometers up to 200 nm. Differential scanning calorimetry (DSC) shows that grafting creates lamellar crystals that melt at much lower temperatures and recrystallize at much higher temperatures than binary blends. From wide angle X‐ray diffraction and DSC, grafting has been shown to limit the maximum crystal size and perfection, as well as broaden the size distribution of the crystals. Grafting causes significant changes in the α crystalline phase of polypropylene and promotes the formation of the β phase. Scanning electron microscopy reveals a unique cross‐hatch structure of small crystals in the reactive blend, with tangential and radial lamellae appearing as crosslinked material of about the same aspect ratio. Polarized light microscopy gives evidence that grafting and branching within this blend causes a gelation‐like recrystallization. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Effect of extender oils on the stress relaxation behavior of thermoplastic vulcanizates

The long term mechanical behavior of oil extended thermoplastic vulcanizates (TPV) based on polypropylene (PP) and acrylonitrile-butadiene rubber (NBR) has been characterized by means of stress relaxation experiments. The mor- phology of TPV and the phase specific oil distribution which depend on the content and type of oil as well as on the mixing regime have been characterized by means of Atomic Force Microscopy (AFM), Dynamic Mechanical Thermal Analysis (DMTA) and Differential Scanning Calorimetrie (DSC). The discussion of the stress relaxation behavior was carried out using the two-component model, which allows splitting the initial stress into two components: a thermal activated stress component and an athermal one. A master curve was created by shifting the relaxation curves vertically and horizontally towards the reference curve. The vertical shift factor bT is a function of the temperature dependence of the athermal stress components. It was found that the oil distribution strongly affects the athermal stress component which is related to the con- tribution of the structural changes, e.g. crystallinity of the PP phase and the average molecular weight between the cross- links of the NBR phase. From the temperature dependence of the horizontal shift factor aT the main viscoelastic relaxation process was determined as the α-relaxation process of the crystalline PP phase. It is not dependent on the polarity and con- tent of the oil as well as the mixing regime.

Influence of Phase Morphology on Molecular Mobility of Poly(propylene)‐(ethylene‐vinyl acetate) Copolymer Blends

AbstractThe dynamic mechanical and dielectric behaviours of Polypropylene (PP) and (Ethylene‐Vinyl Acetate) Copolymer (EVA) blends are reported as a function of the morphology. For EVA contents lower than 20%, blends show the two‐phase morphology characteristic of immiscible blends, with spherical EVA droplets finely dispersed in the PP matrix. After stretching in the molten state, the morphology of EVA fibers is observed. Mechanical Relaxation Spectroscopy display three relaxation processes: the EVA and PP α‐relaxations associated to the glass transitions and a β‐transition corresponding to a PP crystalline phase relaxation. The PP α‐relaxation shifts to higher temperatures when EVA presents a fiber morphology, corresponding to a decrease of PP chain mobility since it is hindered by the reinforcement effect of EVA fibers. Quite different results are obtained by DRS analysis. In blends containing EVA fibers, only one main relaxation associated to the EVA α‐transition is observed whereas one additional relaxation can be noticed in the blends containing EVA droplets. This new relaxation might be assigned to interfacial polarization effects, phenomena that are sometimes observed in heterogeneous polymer blends when a low content of one polar component is embedded in a non conductive matrix. In this case, the occurrence of a characteristic interfacial polarization relaxation appears to be correlated to the accessible experimental frequency.

INFLUENCE OF COMPATIBILIZATION TREATMENTS ON THE MECHANICAL PROPERTIES OF FIQUE FIBER REINFORCED POLYPROPYLENE COMPOSITES

Fique fibers reinforced polypropylene (PP) composites have been investigated for different fiber lengths and contents. Fiber/matrix interfacial adhesion has been modified by fiber treatments such as mercerization, esterification with maleic anhydride, and adding of an isocyanate compound. A copolymer of polypropylene with maleic anhydride has been employed as compatibilizer agent, by previous mixing with PP matrix. Both compatibilization ways improve fiber/matrix adhesion, as shown by changes of the free surface energy of fibers and also by SEM analysis. Addition of the compatibilizer agent leads to higher flexural properties than those obtained for composites where the fibers were treated. Dynamical mechanical properties of composites seem to indicate that movement in the crystalline PP phase, possibly occurring on the fiber/matrix interphase, takes place in between the glass transition and the melting temperatures of PP matrix.

Stratification processes in thermoplastic olefins monitored by step-scan photoacoustic FT-IR spectroscopy

In this study we utilized step-scan photoacoustic Fourier transform IR (SS-PA-FT-IR) spectroscopy to examine surface/interfacial properties of thermoplastic olefins (TPOs). This approach, combined with 2D FT-IR correlation analysis, allowed us to determine stratification processes in TPOs. These studies showed that the talc and polypropylene (PP) crystalline phase in TPO stratifies within the first 6–30 μm from the surface. Specifically, the PP crystalline phase exists at about 6.5 μm from the surface and its content diminishes at 7.1 μm, followed by reappearance around 11.3 μm, and becomes more prevalent upon approaching the bulk of TPO. Talc concentration levels show a similar pattern of change with depth across the interface, although absolute concentration levels differ from those of crystalline PP. These studies also demonstrated that SS-PA-FT-IR is a powerful tool in surface analysis, in particular for surface/interfacial analysis of multi-component polymeric systems.