iPP Phase Research Articles

The Impact of Regiodefects on the Melt-Memory of Isotactic Polypropylene.

The memory of crystalline phase in the melt of isotactic polypropylene (iPP) in regiodefective samples of iPP characterized by different concentrations regiodefects, constituted by secondary 2,1 propene units, is studied. The self-nucleation (SN) experiments have demonstrated that the presence of 2,1 regiodefects produces a strong memory of the crystalline phase in the melt that persists up to temperatures much higher than the melting temperature. The extension of the heterogeneous melt (domain II) containing self-nuclei increases with increasing the concentration of regiodefects. The higher the concentration of regiodefects the higher the temperature at which the self-nuclei are dissolved and the homogeneous melt is achieved. This demonstrates that a strong memory of the crystalline phase of iPP in the melt exists not only in copolymers with noncrystallizable bulky comonomeric units rejected from the crystals but even when small defects are largely included in the crystals.

Effect of Shear Stress during Processing on Structure, Morphology, and Properties of Isotactic Polypropylene Nucleated with Silsesquioxane-Based β-Nucleating Agent.

The study aimed to determine the influence of shear stress during real-life industrial processes such as compression molding and injection molding to different cavities on the crystallization of the isotactic polypropylene nucleated with a novel silsesquioxane-based β-nucleating agent. Octakis(N2,N6-dicyclohexyl-4-(3-(dimethylsiloxy)propyl)naphthalene-2,6-dicarboxamido)octasilsesquioxane (SF-B01) is a highly effective nucleating agent (NA) based on the hybrid organic-inorganic silsesquioxane cage. The samples containing various amounts of the silsesquioxane-based and commercial iPP β-nucleants (0.01-0.5 wt%) were prepared by compression molding and injection molding, including forming in the cavities with different thicknesses. The study of the thermal properties, morphology, and mechanical properties of iPP samples allows for obtaining comprehensive information about the efficiency of silsesquioxane-based NA in shearing conditions during the forming. As a reference sample, iPP nucleated by commercial β-NA (namely N2,N6-dicyclohexylnaphthalene-2,6-dicarboxamide, NU-100) was used. The static tensile test assessed the mechanical properties of pure and nucleated iPP samples formed in different shearing conditions. Variations of the β-nucleation efficiency of the silsesquioxane-based and commercial nucleating agents caused by shear forces accompanying the crystallization process during forming were evaluated by differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). The investigations of changes in the mechanism of interactions between silsesquioxane and commercial nucleating agents were supplemented by rheological analysis of crystallization. It was found that despite the differences in the chemical structure and solubility of the two nucleating agents, they influence the formation of the hexagonal iPP phase in a similar way, taking into consideration the shearing and cooling conditions.

Influence of Molecular Weight on the Nucleation and Growth of Different Crystal Forms in Isotactic Polypropylene: In Situ Synchrotron Microfocus X-Ray Scattering Combined with Fast-Scanning Chip Calorimetry Investigations

The molecular weight (Mw)-dependent formation of mesophase and the α phase of isotactic polypropylene (iPP) was explored by utilizing in situ synchrotron microfocus X-ray scattering measurements combined with a portable fast-scanning chip calorimetry (FSC) technique. A phase diagram illustrating the relationship between the lamellar long spacing (dac) and crystallization as well as melting temperatures of three iPP samples with different molecular weights suggests that a common crystallization line was shared by the mesophase of all three samples, whereas three different crystallization lines were observed for these iPP samples. Furthermore, unlike in the case of the α phase where the melting lines were significantly different from their crystallization lines, the melting line of the mesophase was found to overlap with its crystallization line. The results indicate that the crystallization of the α phase satisfied the multistage crystallization model in which an intermediate layer is suggested to be generated prior to the formation of native crystallites. The Mw-independent formation of the mesophase demonstrated that the nucleus size did not rely on the Mw of iPP because the final sizes of the mesophase were close to the initial nuclei sizes. The larger difference of the lamellar long spacing presented in the α phase of iPP with different Mw indicated that the growth from nuclei to crystallites was significantly influenced by the Mw.

The Friction of Structurally Modified Isotactic Polypropylene

The purpose of studies was to analyse an impact of heterogeneous nucleation of modified isotactic polypropylene (iPP) on its tribological properties. The iPP injection molded samples, produced by mold temperature of 20 and 70 °C, were modified with compositions of two nucleating agents (NA’s), DMDBS creating α-form and mixture of pimelic acid with calcium stearate (PACS) forming β–phase of iPP, with a total content 0.2 wt.% of NA’s. A polymorphic character of iPP, with both, monoclinic (α) and pseudo-hexagonal (β) crystalline structures, depending on the NA’s ratio, was verified. The morphology observation, DSC, hardness and tribological measurements as test in reciprocating motion with “pin on flat” method, were realized, followed by microscopic observation (confocal and SEM) of the friction patch track. It was found that Shore hardness rises along with DMBDS content, independent on mold temperature. The friction coefficient (COF) depends on NA’s content and forming temperature—for upper mold temperature (70 °C), its value is higher and more divergently related to NA’s composition, what is not the case by 20 °C mold temperature. The height of friction scratches and the width of patch tracks due to its plastic deformation, as detected by confocal microscopy, are related to heterogeneous nucleation modified structure of iPP.

Impact of order of catalytic ethylene and propylene polymerization on nanometer scale isotactic polypropylene‐polyethylene blend morphology in nascent heterophasic granules revealed by low voltage scanning electron microscopy and scanning transmission electron microscopy

AbstractNew heterophasic granules comprised of two high molecular weight semi‐crystalline components ‐ polyethylene (PE) and isotactic polypropylene (iPP) ‐ are prepared from a MgCl2 supported Zeigler‐Natta catalyst. The impact of order of monomer addition on granule morphology and extent of mixing of PE and iPP in these monomer‐to‐polymer scenarios are examined. In one polymerization propylene is followed by ethylene (iPP‐PE; 1), and in the second ethylene is followed by propylene (PE‐iPP; 2). Detailed morphological assessments were carried out on RuO4 stained sections of the nascent granules of these heterophasic products using low voltage scanning electron microscopy (LVSEM) and scanning transmission electron microscopy (STEM). In these side‐by‐side granule morphology comparisons, LVSEM, which has not been used for granule examinations, has proved to be invaluable, typically providing insights into phase morphology that STEM does not. Both polymerizations 1 and 2 result in intimate mixing of PE and iPP on the tens to hundreds of nanometer scale. However, morphological outcomes for 1 and 2 are markedly different. In the case of 1, comprising 31 wt% iPP and 69 wt% of PE (the second‐grown phase), a reticulated mesh network of PE is readily observed coursing through much of the first produced iPP globular and sub‐globular matrix. The PE fibrils that comprise this network are remarkably uniform in diameter; approximately 100–150 nm. This aspect of the morphology is consistent with a PE sheath encapsulating both iPP globules and sub‐globules commonly found in iPP homopolymer granules made with MgCl2 catalysts. This morphology is similar to that of the most extensively studied heterophasic granules, classic iPP‐ethylene‐propylene rubber (EPR) impact copolymer (ICP), where the second grown EPR fills in space between and around the iPP globules and sub‐globules. Thus, the dominant morphology of 1 is consistent with the often‐called pore‐filling model. Using the same catalyst and arriving at a similar global composition (65 wt% PE and 35 wt% iPP), sample 2 is produced through the reverse order of monomer addition. The dominant morphology for 2 cannot be explained by the pore‐filling model. Instead, LVSEM most clearly shows that the second grown iPP phase, is finely dispersed throughout the PE matrix (not outside it) as irregularly shaped inclusions that are nominally 100 to 400 nm in diameter, so the dominant morphology in 2 is consistent with the proposed but not previously observed core‐shell model. The STEM results for 2 also reveal the presence of primitive PE spherulites and organized PE lamellae in the granules; structures not found in 1 and apparently not reported before in polyethylene homopolymer granules. These structures form likely from heat released during ethylene polymerization in the first step in 2. In LVSEM, the PE and iPP phases provide different amplitude contrast (grayscale) that is useful for calibration. In the LVSEM images of both samples 1 and 2, non‐binary strong grayscale gradients are observed in many regions in the micrographs. These suggest, but do not yet prove, fine dispersion of some PE in the first formed iPP (1) as well as a fine dispersion, perhaps on the ~10 nm scale, of some iPP in the first formed PE (2). So even granules of 1 appear to have some hybrid quality; primarily pore‐filling, with some core‐shell result as well. Finally, in STEM images of both 1 and 2 well‐formed, long PE lamella provide occasional marked contrast (especially at boundaries) with nascent iPP, which exists in a microparacrystalline state (short, poorly formed crystals). Regardless of the morphological complexity, the exceedingly fine mixing of the two semi‐crystalline phases accomplished during dilation of the granules to accommodate each second produced crystallizable polymer offers the potential for utility of these heterophasic granules in materials design (grafting and cross‐coupling, for example).

Discovery of Polyolefin Granule Products That Can Be Deconstructed into Individual, Fully Separable Grains Provides New Insights into Grain Growth and Material Design

We have discovered a silica-supported metallocene catalyst that produces large, open, porous polyolefin granules that can be easily and quantitatively deconstructed into their constituent polyolefin grains (Gₚ) by lightly crushing any granule. Three such polymerization products have been examined as follows: two heterophasic, comprising isotactic polypropylene (iPP) and polyethylene (PE), and one monophasic, comprising iPP. Deconstruction of granules from each product was followed by quantitative examination by optical microscopy of hundreds of grains. These data have enabled the first statistically robust demonstrations of lognormal distributions of polymer grain size and sphericity. While the lognormal results are not surprising per se, they offer the first quantitative demonstration of such distributions, rather than the unimodal distribution used in physical models since the introduction of the multigrain model over 30 years ago. Three contributions to the lognormal size distribution of the polymer grains are identified: dominant among these is the distribution of simple spheroidal polymer grains. For these simplest of grains, we also give the special notation “primaries”. The two remaining more complex grain topologies are constructed from primaries. One of these topologies is created from two or more fused, or attached, polymer primaries. The third type of grain topology is constructed from three or more fused primaries where the primary aggregate contains at least one void within the grain. In all, the polymer grains range in average diameter from 40 to as large as 470 μm. The median Gₚ diameter measured for all grains in each of the three products ranges from 83 to 150 μm. Between 6 and 16% of polymer grains have optically detectable voids, and grains with voids have on average 40–100% larger diameters than both the aforementioned solid grains denoted primaries and fused primaries. A simple morphological model is proposed for the dispersion of size and shape observed. Based on the data and model, the smallest supported catalyst grain, from which the polymer primary is grown, is calculated independently for each polymer product. These are ∼4–7 nm in diameter, or within the range of basic SiO₂ building blocks reported or calculated for spray-dried silica. Polarized light microscopy examination of isolated spheroidal primaries shows that chains in the heterophasic products have a preferential orientation, with chains aligning more or less along the radius of each primary, whereas chains in the iPP product show no preferential orientation. The morphology, or texture, of iPP and high-density polyethylene (HDPE) in a polymer primary taken from one of the heterophasic granule products was examined by scanning transmission electron microscopy. This examination, together with another for a closely related heterophasic product made with the same catalyst, shows that these two normally immiscible polyolefins are dispersed or mixed via direct sequential polymerization on a ∼50-250 nm, and perhaps finer, scale. Thus, the results provide visual confirmation that, to accommodate the growth of the HDPE phase, the first-grown iPP phase fracture extends through the primary grains themselves as the grains expand with new polymer. We expect that the demonstration of nearly effortless quantitative production of small polyolefin spheres, potentially with controlled surface roughness, as well as the commingling of immiscible polyolefins achieved on this fine scale in the nascent granules, could spawn new creative opportunities for material design.

The crystallization and rheological behaviors of in situ microfibrillar isotactic polypropylene/polyamide 66 composites with a selective β‐nucleating agent distribution

AbstractIn situ microfibrillar composites (MFCs) with isotactic polypropylene (iPP) as matrix and β‐nucleating agents filled polyamide 66 (β‐PA66) as dispersed microfibrils were fabricated through multistage stretching extrusion technology. The simultaneous effects of β‐nucleating agents, shear‐flow and microfibrils on the crystallization and rheological behaviors of iPP were explored. Crystallization analysis demonstrated that the counteraction of shear flow and β‐nucleating agents resulted in the absence of β‐crystal in the as‐extruded MFCs. When the MFCs were annealed at 210°C for 10 min, the flow field was erased accompanied with the migration of β‐nucleating agents from PA66 phase to surface, which in turn inducing the formation of β crystal in the recrystallized samples. Shear rheological investigations suggested that the β‐NAs at interface mechanically integrated the PA66 and iPP phase thus improving the interfacial adhesion. These findings provided a potential way to solve the interfacial problems of MFCs.

In situ fibrillation of isotactic polypropylene in ethylene‐vinyl acetate: Toward enhanced rheological and mechanical properties

ABSTRACTIn situ microfibrillar reinforced composites with ethylene‐vinyl acetate (EVA) as matrix and isotactic polypropylene (iPP) as dispersed fibrils were successfully fabricated by multistage stretching extrusion with an assembly of laminating‐multiplying elements (LMEs). Four types of EVA with different apparent viscosity were utilized to study the influence of viscosity ratio on the morphology and mechanical properties of EVA/iPP in situ microfibrillar blends. The scanning electron micrographs revealed that the dividing–multiplying processes in LMEs could effectively transform the morphology of iPP phase into microfibrils and the morphology of iPP microfibrils strongly depended on the viscosity ratio. Higher viscosity ratio was favorable for formation of finer microfibrils with narrower diameter distribution. The morphology development of iPP with different viscosity ratio greatly affected the rheological and mechanical properties of EVA/iPP blends. The dynamic rheological results shown that the iPP microfibrils were helpful to increase the storage modulus and loss modulus. The tensile test indicated that the mechanical properties of EVA/iPP blends were controlled by the morphology of iPP phase and the polarity of EVA matrix. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47557.

Crystal structure: a way to control properties in cast films of polypropylene

The efficiency of the degree of cooling and shear-induced crystallization on the formation of different crystal polymorphs and morphology development of isotactic polypropylene (iPP) and random propylene–ethylene copolymer was analysed in cast films. Wide-angle X-ray scattering was applied to evaluate the crystal structure formed in films solidified at different chill roll temperatures (15, 40, and 70 °C) and throughputs of the line (60 and 120 kg/h). The crystal geometry and morphology were visualized by atomic force microscopy. For films generated at 15 °C or at large supercooling together with the nodular domain additional grained round-shaped structures composed of mesophase were detected on the film surface. Increase of the chill roll temperature or lower supercooling allowed formation of the monoclinic phase of iPP. Higher drawing rate triggered crystal formation preferably on the surface of films quenched at 15 °C. The crystal structure and morphology were correlated to selected optical and mechanical properties. At close-to-identical crystallinity, the crystal aspect ratio and film roughness play a major role in controlling the film transparency and stiffness.

Segregated polypropylene/cross-linked poly(ethylene-co-1-octene)/multi-walled carbon nanotube nanocomposites with low percolation threshold and dominated negative temperature coefficient effect: Towards electromagnetic interference shielding and thermistors

High-efficiently conductive networks have been well demonstrated to improve electrical properties of conductive polymer composites (CPCs). Here, a facile approach was introduced to control distribution of multi-walled carbon nanotubes (MWCNTs) in isotactic polypropylene/poly(ethylene-co-1-octene) blends (iPP/POE). The POE first melt-crosslinked by the addition of dicumyl peroxide, pulverized into small particles (40–60 meshes), then coated with iPP/MWCNTs composites, and finally compression molded to achieve the segregated iPP/POE/MWCNTs composites with MWCNTs confinedly dispersing in continuous iPP phase. This segregated structure could easily construct high-efficiently conductive networks, resulting in a low percolation threshold of 0.24 vol.%, high-performance electrical conductivity, and electromagnetic interference shielding effectiveness (EMI SE). For example, the EMI SE of ∼25 dB could be achieved in the segregated nanocomposites with 3.0 vol.% MWCNTs (thickness 1.2 mm) which reached the commercial requirement. Furthermore, the segregated samples also exhibited a relatively linear negative temperature coefficient (NTC) effect through wide temperature ranges of 45–120 °C and 150–190 °C because of anisotropic volume expansion effect caused by the segregated structure.

Mechanical and interfacial properties of compatibilized polyurethane blends

The effects of two different styrene‐ethylene/butylene‐styrene (SEBS; SEBS‐g‐MA) block copolymers as potential compatibilizers for thermoplastic polyurethane/isotactic polypropylene blends (TPU/iPP), at different composition were investigated. The compatibilizers involved are unfunctionalized SEBS and functionalized grades containing maleic anhydride grafted to the midblock (SEBS‐g‐MA). Compatibility of each TPU/iPP/SEBS and TPU/iPP/SEBS‐g‐MA polymer blend was compared investigating mechanical, morphological, thermal and interfacial properties. From the results of the interfacial surface free energy, SEBS‐g‐MA is optimal compatibilizer which located at the interface of TPU and iPP phase exhibited much better synergy and improved the compatibility between the TPU and iPP phase. Accordingly, TPU/iPP/SEBS‐g‐MA showed better mechanical properties (higher tensile strength, elongation at break, and E modulus) and finer and more stable morphologies that were clearly observed by scanning electron microscopy. The thermogravimetric analysis confirmed these results showing pronounced thermal stability by addition of functionalized compatibilizer. POLYM. ENG. SCI., 58:1911–1922, 2018. © 2017 Society of Plastics Engineers

Melt-Miscible Oxalamide Based Nucleating Agents and Their Nucleation Efficiency in Isotactic Polypropylene

In this study, the performance of three aliphatic oxalamide based compounds as nucleating agent (NA) for isotactic polypropylene (iPP) has been evaluated. The NAs evaluated in this study contain two oxalamide motifs that are connected through linking spacers with 2, 3, or 4 methylene units in between the oxalamide groups, while containing flexible hexyl end-groups on the outside. It is demonstrated that the onset of crystallization in the presence of these NAs under quiescent conditions, generally observed around 120–125 °C, is strongly dependent on both the crystallization conditions and NA concentration. Although these oxalamide compounds are only moderately effective under quiescent conditions, they show promise for use under industrially relevant processing conditions that require high cooling and shear rates: When the NA is forced to undergo shear-induced self-assembly and shear-alignment during cooling, the onset of crystallization of the iPP phase is observed in SAXS at temperatures up to 140 °C.

Enhanced mechanics in injection molded isotactic polypropylene/polypropylene random copolymer blends via introducing network-like crystal structure

The crystallization behavior, rheological behavior, mechanical properties and microstructures of injection molded isotactic polypropylene (iPP), polypropylene random copolymer (co-PP) and iPP/co-PP blends were investigated. Differential scanning calorimetry (DSC) and dynamic rheological analysis illustrated that iPP and co-PP were compatible in the blends and co-PP uniformly dispersed in the iPP phase. Polarizing optical microscope (POM) was adopted to observe the crystal size and morphology evolution. The results of mechanical properties and scanning electron microscopy (SEM) indicated that the crystal size of iPP in iPP/co-PP blends (10 wt% co-PP + 90 wt% iPP and 30 wt% co-PP + 70 wt% iPP) radically decreased after the incorporation of co-PP. During crystallization, the molecular chain segments of co-PP could penetrate iPP spherulites and form a network-like crystalline structure. The network-like crystal structure could effectively transmit stress and consume more energy to overcome intermolecular forces to resist stretching. In this way, the strength would improve to a certain degree. The impact fracture mechanism of iPP/co-PP blends is quasi ductile fracture by multiple crazes. Our work discovered that the blends containing 10 wt% and 30 wt% of co-PP exhibited prominent toughness and reinforcement.

Preparation and characterization of isotactic polypropylene/high‐density polyethylene/carbon black conductive films with strain‐sensing behavior

ABSTRACTNovel conductive films with a unique strain (ε)‐sensing behavior and based on a blend of isotactic polypropylene (iPP), high‐density polyethylene (HDPE), and carbon black (CB) were fabricated by an extrusion casting method. The morphology and ε‐sensing behavior of the films were investigated. Scanning electron microscope images showed that the oriented lamellae with a growing direction perpendicular to the extrusion direction were obtained in the HDPE phase and were accompanied by a cocontinuous structure of the iPP phase and HDPE/CB phase. The conductive percolation threshold (mc) and resistivity–ε behavior of the thin films are affected by the drawing ratio during the process of film preparation. The mc and electrical resistance of the iPP/HDPE/CB composite films increased with the drawing ratio. The gauge factor of the films within the elastic region decreased with increasing drawing ratio. Furthermore, the result of iPP/(HDPE/CB) 40/60 with a high drawing ratio shows that a reversible conductivity was obtained during the cyclic tensile testing (ε = 10%), but an irreversible conductivity makes the film fail during use at the applied ε values of up to 15%. This makes them good piezoresistive candidates for ε‐sensing materials. Moreover, a simple structural model was proposed to describe the reversible and irreversible phenomena in the electrical resistance behavior of the iPP/HDPE/CB films under tensile loading. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40686.

On the volume organisation of thermoplastic vulcanisates (TPVs) as revealed by scanning transmission electron microscopy (STEM) tomography

The phase organisation of thermoplastic vulcanisates (TPVs) has been analysed in detail by applying scanning transmission electron microscopy (STEM) tomography. High contrast between the crosslinked rubber (EPDM) and the isotactic polypropylene (iPP) phases has been achieved without staining the samples. STEM tomography at low-converge-angle conditions allows for the investigation of micrometre thick samples enabling analysis of dispersion and (possible) connectivity of the phases in the TPVs for ultra-large (>50 μm3) volumes. EPDM is dispersed in the iPP phase in a TPV with low EPDM content, whereas it forms a co-continuous phase in a TPV with high EPDM content. The latter could up to now not been demonstrated unambiguously and has impact on the rheological behaviour of the TPV. Moreover, it is demonstrated that zinc oxide and talc particles used as additives in the TPV formulation are located exclusively in the iPP phase of the TPV blend, which suggests that wetting of the solid particles by the relatively low viscous iPP phase during dynamic vulcanisation determines the location of these inorganic additives.

The effect of thermal history of polyamide 6 on the crystallization and melting behavior of β-nucleated polypropylene/polyamide 6 blends

It has been proved that the effect of amorphous polymer as the second component on the β-nucleating effect of β-nucleated isotactic polypropylene (iPP) blends was less than that of the crystalline polymers. We guess that it is the crystallinity of the second component that affects the β-nucleating effect. In order to prove this hypothesis, the blends of β-nucleated iPP and polyamide 6 (PA6) were prepared by melt compounding in this study. Cooling rate, crystallization temperature, crystallization time, annealing temperature and annealing time were used to control the crystallinity of PA6 phase, and the effect of PA6 crystallinity on the crystallization and melting behavior was studied, in turn its effect on the β-nucleating effect of iPP phase was explored. The results indicated that β crystal content markedly decreased with the increase of PA6 crystallinity, which proved that PA6 crystallinity controls the α-nucleating effect and suppresses the β-nucleating effect of the β-nucleating agent in the β-nucleated iPP blends, leading to a significant decrease in β crystal content. Therefore, decreasing the crystallinity of the second component in the β-nucleated iPP blends is a feasible method to weaken α-nucleating effect of the second component and an effective way to obtain β-nucleated iPP blend with high β crystal content.

IPP/CNTs Multifunctional Polymer Nanocomposite

ABSTRACTWe present a hybrid structure of Isotactic Polypropylene (iPP) nanocomposite with multiwall carbon nanotubes (MWCNTs). The polymer component contributes to the optical properties, flexibility and integrity of the polymer film while the carbon nanotubes change the thermal and mechanical stability, electrical and thermal conductivity and sensitivity. The multifunctional characteristics of this nanocomposite material are enhanced by anisotropic organization of the nanotubes and polymer through melt shearing which provides organization of the structural constituents at the molecular, nano, and micro length scales. This results in anisotropy of the macroscopic composite film properties parallel and perpendicular to the direction of shearing. On the molecular scale, the CNTs control the arrangement of the polymer molecules in a crystal lattice. On the nanometer scale, the CNTs couple to and align with the smectic normal of the liquid crystal phase of iPP. On the micron scale and larger, the secondary polymer crystal structure is rearranged due to the pinning of the polymer at the CNT surface to form fibrillar rather than spherulitic structures. These multi-scale rearrangements affect the optical, thermal, electrical, mechanical and chemical properties of the nanocomposite film. Our findings indicate that the CNTs under shear induce a novel anisotropy to the various thermo-physical properties of the iPP/CNTs films. We introduce an approach to extract the shear induced orientational order from the thermal conductivity of the dispersed CNTs. The index of refraction of the nanocomposites was also estimated via ellipsometry and was found to decrease slightly when CNTs were added and also showed shear induced anisotropy. The comparison between the results from the different experiments methods for probing induced anisotropy by melt shearing shows that orientation in iPP/CNTs nanocomposites induces anisotropy in multiple macroscopic properties.

Fabrication and morphology development of isotactic polypropylene nanofibers from isotactic polypropylene/polylactide blends

AbstractThe excellent characteristics of polymeric nanofibers with diameters less than 1 μm such as the enormous specific surface result in a dramatic increase in a variety of functional applications. In this article, polymer blends of isotactic polypropylene (iPP) and polylactide (PLA) were fabricated through a twin‐screw extruder. The extrudates were prepared at various processing conditions and the iPP nanofibers were obtained by removal of the PLA matrix from the drawn samples. The influences of drawing ratio, the processing temperature, and the blend ratio of iPP/PLA on the morphology development of iPP phase were investigated by scanning electron microscopy. It was found that the uniformed iPP nanofibers with averaged diameters less than 500 nm were fabricated by the suitable processing parameters. Otherwise, the processing immiscibility and rheological behavior of iPP/PLA blends were studied by means of dynamic mechanical analysis and capillary rheometer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effect of compounding procedure on morphology and crystallization behavior of isotactic polypropylene/high‐density polyethylene/carbon black ternary composites

The effect of compounding procedure on morphology and crystallization behavior of isotactic polypropylene/high‐density polyethylene/carbon black (iPP/HDPE/CB) composite was investigated. iPP/HDPE/CB composites were prepared by four compounding procedures (A: iPP + HDPE + CB; B: iPP/HDPE + CB; C: HDPE/CB + iPP; D: iPP/CB + HDPE). Scanning electron microscopy observation showed that CB particles are mainly distributed in HDPE in all composites, and the phase morphology of composites was obviously affected by a compounding procedure. The size of the HDPE/CB domains in the composites prepared by procedures A and D decreased with the increase in CB content, whereas that of HDPE/CB in the composites prepared by procedures B and C rarely changed with the increase in CB content. The crystallization behaviors of the composites were significantly affected by their phase morphology, which resulted from the variation of compounding procedure. The isothermal crystallization rate of iPP in the composites prepared by procedures A and D was obviously increased, which may originate from the small HDPE/CB droplets dispersed in the iPP phase. The non‐isothermal crystallization curves of composites prepared by procedure D represented two peaks because the iPP component in these composites had the fastest crystallization rate, whereas the curves of composites prepared by other compounding sequences only exhibited one peak. Moreover, the crystallinity of HDPE almost increased by one time with the incorporation of only 1 phr CB because the CB particles selectively located in the HDPE phase, and the crystallinity of HDPE decreased with the further increase of CB content because of the strong restriction of CB on the HDPE chains. Copyright © 2011 John Wiley & Sons, Ltd.

Effect of Malonic Acid Treatment on Crystal Structure, Melting Behavior, Morphology, and Mechanical Properties of Isotactic Polypropylene/Nano-CaCO3 Composites

The influence of malonic acid (MA) treatment of nano-calcium carbonate (CaCO3) on the crystallization, morphology, and mechanical properties of isotactic polypropylene (iPP)/nano-CaCO3 composites have been studied. The results of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and polarized light microscopy (PLM) show that untreated nano-CaCO3 facilitates the formation of α phase, while MA treated nano-CaCO3 increases the relative content of β phase of iPP dramatically. The results of scanning electron microscopy (SEM) show that MA treated nano-CaCO3 has better dispersion in the matrix than the untreated one. The toughness of PP/MA treated nano-CaCO3 composite is improved drastically. When 2.5 wt% MA treated nano-CaCO3 is added, the Izod notched impact strength reaches its maximum, which is 2.89 times greater than that of the pure iPP.