iPP Nanocomposites Research Articles

High-pressure crystallization of iPP nanocomposites with montmorillonite and carbon nanotubes

High pressure facilitates crystallization of isotactic polypropylene (iPP) in the orthorhombic γ-form, differing in structure and properties from the α-form, in which iPP crystallizes under common processing conditions. In the study, the effect of high pressure on crystallization of iPP nanocomposites was examined. The iPP nanocomposites with 1-5 wt.% of well dispersed either o-MMT (PP/MT) or MWCNT (PP/CN) were prepared by mixing molten iPP with the nanofillers. The nanocomposites and neat iPP were crystallized during cooling under pressures up to 300 MPa. Regardless of crystallization pressure, the crystallization temperatures were similar whereas the sizes of the polycrystalline aggregates were only slightly smaller in PP/MT compared to those of neat iPP. On the contrary, the presence of MWCNT elevated the crystallization temperature of PP/CN by 8-13 K compared to that of neat iPP, and strongly decreased the grain size. This evidenced the nucleating activity of MWCNT during high-pressure crystallization of iPP in the γ-form. The higher crystallization temperature allowed a larger portion of the polymer to crystallize in the γ-domain before the α-domain was reached. As a result, PP/CN, especially crystallized under 50-100 MPa, contained more γ-form than neat iPP and PP/MT.

Effect of Graphene Nanofibers on the Morphological, Structural, Thermal, Phase Transitions and Mechanical Characteristics in Metallocene iPP Based Nanocomposites

Several nanocomposites were prepared by extrusion from a commercial metallocene-type isotactic polypropylene (iPP) and different amounts of two types of graphene (G) nanofibers: ones with a high specific surface, named GHS, and the others with a low specific surface, labeled as GLS. The number of graphene layers was found to be around eight for GLS and about five in the GHS. Scanning electron microscopy (SEM) images of the resultant iPP nanocomposites showed a better homogeneity in the dispersion of the GLS nanofibers within the polymeric matrix compared with the distribution observed for the GHS ones. Crystallinity in the nanocomposites turned out to be dependent upon graphene content and upon thermal treatment applied during film preparation, the effect of the nature of the nanofiber being negligible. Graphene exerted a noticeable nucleating effect in the iPP crystallization. Furthermore, thermal stability was enlarged, shifting to higher temperatures, with increasing nanofiber amount. The mechanical response changed significantly with nanofiber type, along with its content, together with the thermal treatment applied to the nanocomposites. Features of nanofiber surface played a key role in the ultimate properties related to superficial and bulk stiffness.

Confinement of iPP crystallites within mesoporous SBA-15 channels in extruded iPP-SBA-15 nanocomposites studied by Small Angle X-ray scattering

The main objective of this research is the study of different nanocomposites based on isotactic polypropylene (iPP) and mesoporous SBA-15 silica prepared by melt extrusion, analyzing the possible effect of this filler on the polymorphic behavior of iPP and the eventual observation of confinement effects. Thus, simultaneous Small Angle X-ray Scattering/Wide Angle X-ray Diffraction (SAXS/WAXD) synchrotron experiments at variable temperature have been performed on several iPP nanocomposites with different contents of SBA-15 mesoporous particles. Real-time variable-temperature SAXS measurements turned out a very useful tool to analyze the confinement of iPP crystallites within SBA-15 channels, and also to determine the most probable long spacing of chains located outside the SBA-15 nanospaces. Importance of these structural features is assessed by changes in the mechanical response of the final materials, finding that the presence of mesoporous particles leads to a reinforcing effect and contribute to improve the final dimensional stability.

In situ polymerization of isotactic polypropylene sepiolite nanocomposites and its copolymers by metallocene catalysis

Isotactic Polypropylene (iPP)-sepiolite nanocomposites were prepared by in situ polymerization using nanoclays as support of the catalytic system. This study proposes a method of immobilization that considers the use of the density of the polar groups present on sepiolite surface, to fix the co-catalyst. In addition, the resulting polymerization process defines the reaction time as a variable which will provide a mechanism for controlling the productivity of the reaction, making possible the obtaining of a masterbatch which may be useful in increasing the PP-clay compatibility in melt blending processes. The results of the proposed method have allowed not only the additivation of polypropylene during the synthesis, but also the structure control in terms of stereo-specificity and molecular weight, improving its final properties. Furthermore, in an effort to improve the impact properties of the iPP matrix, iPP copolymers were synthesized with 1-olefins of different chain lengths as co-monomers. The influence of the amount of co-monomer, amount of filler and type of branching obtained on the final properties of iPP nanocomposites were studied.

Layered Double Hydroxide Nanoplatelets with Ultrahigh Specific Surface Area for Significantly Enhanced Crystallization Rate and Thermal Stability of Polypropylene

A facile method for the simultaneous delamination and the lateral size reduction of layered double hydroxides (LDH) is reported. This method directly resulted in the delaminated mesoporous LDH nanoplatelets (nanodot LDH) with the high specific surface area (lateral dimensions as low as 10–30 nm and featured a thickness of ∼1 nm). Such prepared LDH was used as fillers for isotactic polypropylene (iPP). For the purpose of comparison, LDH having different surface areas were also used as fillers for iPP. The incorporation of nanodot LDH showed a remarkable improvement in the polymer properties with only 1 wt % loading. The uniformly dispersed LDH particles have a significant effect on the nucleation ability, thermal stability, and mechanical properties of iPP. The nucleation ability of iPP in the presence of nanodot LDH is the best compared to other iPP nanocomposites reported using LDH as fillers in the literature. Furthermore, the microstructure of the iPP nanocomposites was systematically investigated at m...

Mechanical properties improvement of montmorillonite‐filled isotactic polypropylene nanocomposites by β‐modification

To investigate the effect of β‐crystallization on mechanical properties of isotactic polypropylene (iPP) nanocomposites, montmorillonite (MMT)‐filled α‐iPP and β‐iPP nanocomposites were prepared by MMT with α‐ and β‐nucleating surface, respectively. The polymorphic composition, mechanical properties and fracture morphologies of α‐MMT and β‐MMT filled iPP nanocomposites were compared and the exfoliation of MMT in the iPP matrix were investigated. It is found that the tensile modulus, yield strength, and flexural properties of β‐MMT filled iPP nanocomposites are higher than those of β‐iPP and the impact strength of β‐MMT filled iPP nanocomposites is higher than those of both β‐iPP and α‐iPP nanocomposites. The impact strength increases with increasing of the β‐crystal content. However, the β‐crystal content has little influence on the tensile and flexural properties of β‐MMT filled iPP nanocomposites. Compared with α‐MMT, the exfoliation of β‐MMT in iPP as well as interfacial adhesion between MMT and iPP are improved. POLYM. COMPOS., 38:E412–E420, 2017. © 2016 Society of Plastics Engineers

Development of multifunctional polymer nanocomposites with carbon-based hybrid nanostructures synthesized from ferrocene

This paper proposes the development of isotactic polypropylene (iPP) nanocomposites with magnetic carbon-based hybrid fillers, which contain magnetite, by melt mixing at 190°C. The carbon-based fillers such as carbon nanotubes (CNTs) were synthesized via chemical vapor deposition (CVD), using ferrocene as catalyst and precursor synthesis, and using silica (SiO2) or thermally reduced graphene oxide (TrGO) as support, obtaining SiO2/CNTMagnetite and TrGO/CNTMagnetite hybrid nanostructures, respectively. Mechanical, electrical and magnetic behaviors of the iPP nanocomposites with magnetic CNTs were evaluated; their performance against iPP composites with commercial CNTs was compared. The results show that the electrical conductivity of the iPP nanocomposites is not affected by the presence of magnetite, reaching a percolation threshold similar to that obtained in iPP nanocomposites with commercial CNTs. Likewise, the presence of CNTs with magnetic particles changes the diamagnetic nature of the polymeric matrix, transforming it into a ferromagnetic composite at low filler concentrations (2wt.%).

Non-isothermal crystallization kinetics of montmorillonite filled β-isotactic polypropylene nanocomposites

Montmorillonite filled isotactic polypropylene nanocomposites (iPP/MMT) generally form α-modification due to the heterogeneous α-nucleation of MMT for iPP crystallization. To obtain MMT filled β-iPP nanocomposites, MMT with β-nucleating surface (β-MMT) was prepared by supporting calcium pimelate (CaPA) as β-nucleator on the surface of MMT particles. The crystallization behavior, melting characteristics, and non-isothermal crystallization kinetics and crystallization activation energies of MMT and β-MMT filled iPP nanocomposites were studied by differential scanning calorimetry. It is found that the crystallization peak temperatures of β-MMT filled iPP nanocomposites were higher than those of β-iPP and MMT filled iPP nanocomposites, which indicated that the heterogeneous nucleation of β-MMT is stronger than that of MMT. Jeziorny and Mo methods were applicable to study the non-isothermal crystallization kinetics of iPP and its nanocomposites. Addition of CaPA, MMT and β-MMT can increase the crystallization rate. The crystallization activation energies were calculated by Friedman methods, and nucleating activities were calculated by Dobreva methods. It is indicated that β-nucleation decreased the crystallization activation energy of iPP, and the nucleating activity of β-MMT is higher than that of CaPA and MMT.

Functionalization of multi-walled carbon nanotubes (MWCNTs) with pimelic acid molecules: effect of linkage on β-crystal formation in an isotactic polypropylene (iPP) matrix

This work proposes an alternative method for the functionalization of MWCNT with molecules of pimelic acid (PA) using an ionic bridging linkage. This bridged linkage increases the amount of β-crystal in isotactic polypropylene (iPP) matrix compared to that obtained with chelating linkages of the same molecule. Evidence of a lateral bridge between the PA and MWCNT components was obtained from infrared spectra of the functionalized carbon nanotubes (MWCNT-f). This fact was confirmed by the absence of a characteristic infrared band at 1540 cm−1, which was attributed to a particular chelating form of the PA, known as calcium pimelate (MWCNT-PS). Furthermore, an increase in the thermal stability of the attached PA due to ionic linkage was observed using differential scanning calorimetry (DSC) and thermo-gravimetric analysis. iPP nanocomposites were prepared with these MWCNT-f, yielding an improvement in the induction of β-phase within the nanocomposites; this finding was further corroborated by DSC and wide-angle X-ray diffraction analysis (WAXD). The relative content of β-crystals reaches a value as high as 85.7 % at a loading of 0.45 w/w % MWCNT-f, resulting in an increase in impact strength and the glass transition temperature (Tg), while the storage modulus decreased. In addition, the evolution of the crystallization activation energy of the resulting nanocomposites was investigated. We correlate the energy requirements of the interactions between nucleating agents and the segments of iPP. The bridged form of the molecule was associated with an increased energy barrier during the crystallization process due to both the thermodynamic instability of the β-crystal and the higher amount of induced β-crystal relative to the amount promoted by the chelated form. In this article, we demonstrate how the linkage type between MWCNT and PA components can strongly influence the ability of this organic molecule to nucleate β-crystal and can impact the crystallization behavior in iPP nanocomposites.

Influence of different β-nucleating agent on crystallization behavior, morphology, and melting characteristic of multiwalled carbon nanotube-filled isotactic polypropylene nanocomposites

To obtain isotactic polypropylene (iPP) nanocomposites with high β-crystal content, TMB5, calcium pimelate and calcium pimelate supported on the surface of nano-CaCO3 were used as β-nucleating agent and MWCNT filled β-nucleated iPP nanocomposites were prepared. The effect of different β-nucleating agent and MWCNT on the crystallization behavior and morphology, melting characteristic and β-crystal content of β-nucleated iPP nanocomposites were investigated by DSC, XRD and POM. The results indicated that addition of MWCNT increased the crystallization temperature of iPP and MWCNT filled iPP nanocomposites mainly formed α-crystal. The β-nucleating agent can induce the formation of β-crystal in MWCNT filled iPP nanocomposites. The β-nucleating ability and β-crystal content in MWCNT filled β-nucleated iPP nanocomposites decreased with increasing MWCNT content and increased with increasing β-nucleating agent content due to the nucleation competition between MWCNT and β-nucleating agents. It is found that the calcium pimelate supported on the surface of inorganic particles as β-nucleating agent has stronger heterogeneous β-nucleation than calcium pimelate and TMB5. The MWCNT filled iPP nanocomposites with high β-crystal content can be obtained by supported β-nucleating agent. POLYM. COMPOS., 36:635–643, 2015. © 2014 Society of Plastics Engineers

A novel montmorillonite with β-nucleating surface for enhancing β-crystallization of isotactic polypropylene

Montmorillonite (MMT) generally has α-nucleating ability for isotactic polypropylene (iPP). A novel MMT with β-nucleating surface (β-MMT) supported by chemically calcium pimelate (CaA) was prepared through the chemical reaction between pimelic acid (HA) and calcium ion on the surface of MMT in the first time. Infrared spectrometry and thermogravimetric analysis confirmed the formation of CaA on the surface of MMT. The differential scanning calorimeter and X-ray diffraction illustrated that the iPP nanocomposites filled by MMT and β-MMT exhibit different heterogeneous nucleation. The heterogeneous nucleation of the prepared MMT surface has changed from α-nucleation into β-nucleation and a novel MMT with β-nucleating surface is obtained. Even, the heterogeneous β-nucleating ability of β-MMT is much stronger than that of CaA. Addition of MMT with β-nucleating surface into iPP matrix significantly increased the spherulite nuclei density and decreased the spherulite size, and can easily prepare the β-iPP nanocomposites with high relative β-phase content.

Polypropylene Nanocomposites Based on Synthetic Organic-Soluble Ag Nanocrystals with Prominent β-nucleating Effect: Quiescent Crystallization and Melting Behavior

Differential scanning calorimetry, x-ray diffraction, and polarized optical microscopy were used to investigate the quiescent crystallization and melting behavior of isotactic polypropylene (iPP) nanocomposites based on synthetic organic-soluble Ag nanocrystals (NCs). The effects of Ag loading and crystallization temperature on the crystallization behavior and crystalline structure were studied. The results showed that the synthetic Ag NCs as a novel effective β-crystal nucleating agent for iPP could promote the overall crystallinity, decrease the size of spherulites, and induce the formation of large amounts of β-crystals in the nanocomposites under quiescent crystallization. The relative content of β-crystals significantly increased with increasing Ag loading, and slightly increased with decreasing crystallization temperature. The quiescent crystallization kinetics was analyzed using the Avrami model. The results showed that the iPP nanocomposites with added Ag NCs had higher crystallization rate constant (k) and lower crystallization half-times (t1/2) as well as the Avrami exponent (n) than pure iPP, indicating that the presence of Ag NCs acted as heterogeneous nucleating sites and promoted the crystallization rate of iPP.

Effects of Carbon Black–Carbon Nanotube Complex Fillers on the Properties of Isotactic Polypropylene Nanocomposites

In this study, the reinforcing effects of carbon black (CB) and carbon nanotube (CNT) complex fillers on the properties of isotactic polypropylene (iPP) nanocomposites were investigated using various methods. The surface of the CNTs was modified using a linear alkyl chain in order to create a homogeneous CNT dispersion in the iPP matrix. When the CB content that was incorporated in the iPP matrix increased, the thermal and mechanical properties of the iPP/CB nanocomposites were enhanced. Additionally these enhancements in the properties were similarly induced by introducing a small amount of alkylated CNTs (a-CNTs). In contrast, the CB/a-CNT complex filler was more effective for the iPP nanocomposites than the CB or a-CNT single filler in terms of the thermal stability and the electrical properties. However, the mechanical properties of the CB/a-CNT complex filler incorporated iPP nanocomposites were poorer than the only a-CNT incorporated iPP nanocomposites. Additionally, the complex filler did not overcome the nucleation behavior of the a-CNTs in the re-crystallization of iPP.

Morphology, Crystallization Behavior, and Mechanical Properties of Isotactic Poly(propylene) Nanocomposites based on Organophilic Boehmites

AbstractiPP/organoboehmite nanocomposites were prepared to examine the influence of both boehmite crystallite size and organophilic boehmite modification on morphology development, thermal, and mechanical properties. Effective deagglomeration of the micrometer‐scaled organoboehmites was achieved, producing uniform dispersions of nanometer‐scaled boehmite crystallite assemblies within the iPP matrix. CS‐modified organoboehmites gave improved stiffness at the expense of elongation at break and impact strength. In contrast to CS, boehmites modified with OS2 lowered iPP crystallization (“anti‐nucleation effect”) without affecting crystal modification, affording iPP nanocomposites with significantly larger elongation at break and strain induced crystallization.magnified image

Isotactic Poly(propylene) Nanocomposites Based upon Boehmite Nanofillers

AbstractThe influence of boehmite crystallite sizes, varied between 10 and 60 nm, was studied with respect to the morphology development, crystallization behavior and mechanical properties of the boehmite‐based iPP nanocomposites. The nanometer‐scaled boehmites were formed during twin‐screw melt extrusion of iPP at 200 °C. Even in the absence of polymer compatibilizers, the boehmites, obtained from Sasol's process, enabled very effective deagglomeration and in‐situ dispersion of nanoboehmites. With increase in boehmite crystallite size it was possible to improve simultaneously stiffness and impact strength of iPP. As evidenced by means of DSC, POM and WAXS measurements, the deagglomerated nanoboehmites nucleated crystallization of poly(propylene)'s α‐modification.magnified image

Carbon Nanotube-Induced Changes of Crystal Growth In Polymer Films

AbstractIsotactic Polypropylene (iPP) nanocomposites with low concentrations of multiwall carbon nanotubes (CNTs) 0-1% were studied, using differential scanning calorimetry and Avrami analysis. The nanocomposites were isothermally crystallized at 135°C, in order to measure the effect of nanotubes on the kinetics of crystallization. In our study there is a great effect of the CNTs on the iPP crystallization kinetics. The Avrami analysis shows increase in the crystallization rate constant and constancy the Avrami exponent with increase of the CNTs concentration. The full width at half maximum (FWHM) of the heat flow exotherm and the peak time for crystallization (tp) change dramatically. For iPP, the carbon nanotubes serve as nucleation agents to speed up the crystallization process.

Physical Properties of Isotactic Poly(propylene)/Silver Nanocomposites: Dynamic Crystallization Behavior and Resultant Morphology

AbstractSummary: The presence of silver nanoparticles (0.01–5 wt.‐%) increased the crystallization temperature of isotactic poly(propylene) (iPP) (e.g., a 5 wt.‐% content increases the temperature by ca. 7 °C) and produced a sharper crystalline peak. It had little effect on the melt rheology of the nanocomposites. The shear‐induced crystallization behavior of iPP was accelerated with increasing Ag content and imposed frequency. In addition, the promoting effect of Ag nanoparticles on the overall crystallization behavior was more notable at 140 °C than at 130 °C. The wide‐angle X‐ray diffraction scans of iPP nanocomposites with 5 wt.‐% Ag crystallized at 130 °C clearly presented another peak at a 2θ value of 15.8°, which corresponded to a β‐form crystal. The nanocomposites with 5 wt.‐% Ag crystallized at 130 °C gave double melting peaks at 154 and 166 °C. On the other hand, the samples crystallized at 140 °C produced two melting peaks at 166 and 172 °C. The introduction of as much as 0.1 wt.‐% of Ag nanoparticles increased both the tensile strength and elongation at break, but subsequent further addition caused a decrease. In addition, iPP nanocomposites with more than 1 wt.‐% Ag exhibited a higher modulus than pure iPP.Time dependence of G′ of iPP and iPP/Ag nanocomposites at 130 °C at ω = 1 rad · s−1.magnified imageTime dependence of G′ of iPP and iPP/Ag nanocomposites at 130 °C at ω = 1 rad · s−1.