Isotactic Polypropylene Matrix Research Articles

Isothermal crystallization of polyethylene droplets within the self-nucleated isotactic polypropylene matrix of a 70/30 iPP/PE immiscible blend via fast scanning chip calorimetry (FSC)

The escalating volume of waste related to polyolefins poses recycling challenges. Given the mixed composition of the post-consumer feedstock, studying blends of virgin polyolefins is a fruitful strategy to simulate such compositions. For the first time, this study investigates crystallization, self-nucleation (SN), and kinetics of a 70/30 iPP/PE blend, characterised by a "sea-island" morphology, using fast scanning calorimetry (FSC). Preliminary experiments on different chip sensors proved the technique's sensitivity and representativeness for polymer blends, even with minimal sample quantities. Application of the self-nucleation thermal protocol (employing fast scanning rates, from 500 to 1000 °C/s) to the iPP matrix phase revealed insights into the characteristic SN domains. The crystallization kinetics of PE-dispersed droplets within a SN iPP matrix was also investigated. Results indicate a 30 °C crystallization window for PE droplets within the self-nucleated iPP matrix, expanding the understanding of crystallization rates (up to four decades) compared to standard DSC measurements.

Microscopic investigation of the optical and morphological properties of iPP/TiO2 nanocomposite fibres using computed tomography technique.

In this article, the optical and structural properties of iPP/TiO2 nanocomposite fibres, considering three distinct extrusion speeds (25, 50 and 78 m/min) in addition to blank isotactic polypropylene samples were determined. Employing computed tomographic scans, localised optical defects in the nanocomposite fibres are unveiled, while refractive indices are examined by analysing transmitted intensity with incident light vibrating parallel and perpendicular to the fibre axis. The internal structure is further characterised through birefringence and density calculations. Mechanical properties, specifically stiffness, are probed by measuring elastic modulus values along the fibre. The investigation extends to the presence of TiO2 nanoparticles in the isotactic polypropylene matrix, inspecting their influence on the uniform morphology along and across the fibre. While the addition of TiO2 nanoparticles has many advantages, including enhanced properties, the study shows adverse effects on the morphological integrity of the fibres, particularly at higher extrusion rates. Micrographs are included to visually illustrate these findings, providing a comprehensive understanding of the complex interaction between extrusion rates, TiO2 nanoparticle incorporation, and the resulting optical and structural properties in iPP fibres.

Effect of Surface Properties of Nanoparticles on the Crystallization Behavior of Polypropylene/Polypropylene‐g‐Silica Nanocomposites

AbstractIn order to investigate the effect of surface properties of nanoparticles (NPs) on the crystallization behavior of nanocomposite, three kinds of silica (SiO2) NPs are dispersed in isotactic polypropylene (iPP) matrix by solution blending method. Specifically, the poor compatibility between inorganic bare SiO2 NPs and organic PP matrix triggers the formation of aggregates and induces the fractionated crystallization with two crystallization peaks at higher particle loading (Φ), i.e., main crystallization peak (MCP) and low temperature crystallization peak (LCP, always located at 124.0 °C). Once short PP chains (0.9 × 104 g mol−1) are grafted onto the surface of SiO2 NPs, the nanocomposites with all Φ only exhibit a single MCP which is attributed to the strong interfacial interaction. With the increase of grafting chain length (9 × 104 g mol−1), the more stretched conformation of grafting chains can provide numerous heterogeneous nucleation sites and significantly accelerate the crystallization rate of PP chains near the surface of SiO2 NPs, which lead to the formation of an extra high temperature crystallization peak (HCP, almost kept constant at 133.0 °C). The occurrence of various crystallization peaks implies that the surface properties of nanoparticles play a vital role in the nucleation ability of nanoparticles.

Effects of halloysite nanotubes modified by organic phosphate on the performance improvement for polypropylene

AbstractThe enhancement of halloysite nanotubes (HNT) for polymer mechanical performance is limited due to the poor compatibility with matrix. In this work, hydrophobic 2,2′‐methylene‐bis‐(4,6‐di‐tert‐butylphenyl) organic phosphate (MBP) with multiple methyl groups was firstly used for HNT compatibilization modification. The hydrophobicity transition of modified HNT (HNT‐M) and the dispersibility difference in isotactic polypropylene (iPP) matrix were distinguished by water contact angle and SEM analyses, respectively. In addition, the binding energy evaluated the interfacial interaction and compatibility with matrix before and after modification by molecular dynamic simulation. Correspondingly, the iPP performance was optimized after addition of HNT‐M. The onset decomposition temperature of system at 5% and 10% weight loss was increased by 7 and 11°C compared with neat iPP, respectively. Moreover, the flexural modulus and impact strength of iPP/HNT‐M system were 18.9% and 9.6% higher than neat iPP showing simultaneous enhancement. In addition, iPP/HNT‐M system crystallized begin at higher temperature showing enhanced crystallization ability. Furthermore, the faster crystallization process and more uniform spherulite size were obtained. As a result, the enhancement for iPP performance was obtained when the compatibility between HNT and matrix was improved through surface modification.

Reversible nucleation behavior of N, N′-dicyclohexylterephthalamide to polypropylene with the aid of polyamide 12

Through the hydrogen bonding between polyamide 12 (PA12) and N, N′-dicyclohexylterephthalamide (DCHT) nucleator, the intentionally controlled self-assembly of DCHT and the crystallization behavior of isotactic polypropylene (iPP) matrix are investigated. The introduction of PA12 could severely postpone the condensation of DCHT vapor in iPP matrix due to the reduced vapor concentration. As a result, the nucleating efficiency of DCHT at lower concentration for example iPP/PA12/0.05DCHT even failed at a relatively higher final heating temperature Tf. Such a failure of nucleating efficiency could be recoverable after a step-cycle treatment at lower Tf, where the sublimation of DCHT can hardly occur. The changes from a cluster-like structure to a network structure driven by hydrogen bonding between DCHT and PA12 could be a reason of nucleation failure and recovery. This means that the nucleating efficiency of DCHT and crystallization of iPP could be tuned by controlling the absorption and release of DCHT vapor at the surface of PA12 particles. For iPP/PA12/0.5DCHT with a higher concentration of DCHT, the absorption of PA12 could only reduce the DCHT vapor concentration in the iPP melt and thus, the dendrite structure of DCHT shows more and thinner branches, which results in better nucleating efficiency of DCHT than that in iPP/0.5DCHT.

Dynamic dielectric properties of isotactic polypropylene-g-maleic anhydride crosslinked by capped-end polyether diamine and filled with native or functionalized nano-graphite particles

Dynamic dielectric properties of an isotactic polypropylene matrix grafted with maleic anhydride (CA 100) and then crosslinked by polyether amine molecules and reinforced with different weight percentages of graphite nanoplatelets (GNPs), KNG180, were studied for the first time and compared to those obtained by DMA (Dynamic Mechanical Analysis). The main objective of this work was to investigate the reinforcement effect of GNPs focusing on the GNPs/matrix interfacial adhesion using dynamic dielectric relaxation spectroscopy in the frequency range from 0.1 Hz to 1 MHz and temperature range from 20 to 140 °C. The obtained interfacial polarization increments \({\Delta \varepsilon }_{\mathrm{MWS}}\) from MWS (Maxwell Wagners Sillars) relaxation showed a threshold value of 3% in weight of KNG180. This analysis suggests that interfacial compatibility between matrix and fillers in the case of nanocomposite KNG180 3 wt% is higher than those of other nanocomposites. A new plasma treatment was used to modify graphite nano-fillers to produce different types of nanocomposites. The 5 wt% plasma treated graphite nanocomposite shows a good dispersion of the nano-fillers but also a high value of \({\Delta \varepsilon }_{\mathrm{MWS}}\), which is an indication of high graphite/graphite interaction. This evolution could show that this material can be close to the formation of an electrical percolation network.

3D printing-enabled self-assembling β-nucleating agent alignment: Structural evolution and mechanical performances

Achieving good alignment of fillers within the composites is critical towards developing the high performance of the final 3D printed objects. Herein, flow-induced the alignment of self-assembling β-nucleating agent (SANAβ) within the isotactic polypropylene (iPP) matrix was achieved via fused deposition modeling (FDM) process. The influence of printing speed on the alignment of SANAβ, crystalline structure, and mechanical properties of FDM printed samples were investigated. Due to the converging nozzle effect, SANAβ fibers were fragmented from 26.13 μm to 9.98 μm in length, generating more oriented templates and further preferentially aligned along the printing direction to trigger the iPP crystallization. As a result, the crystal morphology of the printed sample was transformed from α-form to β-form hybrid shish-kebab structure. Highly oriented β-crystal was observed in iPP/SANAβ (FT) samples, as evidenced by 2D-WAXD. 2D-SAXS results revealed the formation of plenty of oriented lamellae in FT samples, which were arranged perpendicular and parallel to the printing direction. The aligned SANAβ also contributed to maintaining a high β-crystal content to overcome the shortcomings of rapid decrease of β-crystal for iPP at a high printing speed. Benefiting from this, with the increasing printing speed, compared with elongation at break of iPP samples decreased from 241.36% to 61.32%, those of FT sample increased dramatically from 305.07% to 390.23% but with a slight fade of less than 1% in the tensile strength. Additionally, the as-printed honeycomb array structure of FT sample presented superior energy absorption capacity and thus could function as loading-bear objects, highlighting the advantages of the alignment of self-reinforcing β-form hybrid shish-kebab.

Annealing induced high‐impact toughness of injection molded isotactic polypropylene filled with liquid‐phase exfoliated graphene

AbstractFavorable dispersibility of graphene (G) nanosheets in isotactic polypropylene (iPP) matrix is a keypoint that affects its toughening effect. In this work, a very low level of liquid‐phase exfoliated G was incorporated into iPP, and the iPP/G composite samples were further annealed at moderate temperature (120–140°C) for 3 h. It was found that liquid‐phase exfoliated G exhibits favorable dispersibility and efficient heterogeneous nucleation ability, significantly reducing the size of iPP spherulites. Characterization of the changes in microstructure of iPP and iPP/G composite upon annealing reveals that the presence of G promotes the perfection of crystalline structure and enhances dramatically the mobility of chain segments in the amorphous region of iPP during the annealing treatment. Moreover, the addition of this kind of well‐dispersed G may be favorable for the stabilization of β‐crystal during the injection molding process, and annealing at 120–140°C is also conducive to the formation of β‐crystal. A possible synergistic toughening mechanism of the incorporation of liquid‐phase exfoliated G and annealing treatment was put forward.

Formation of Knots of Carbon Nanotubes in Isotactic Polypropylene Matrix due to the Results of Small-Angle Neutron Scattering and Lattice Numerical Simulation

Formation of Knots of Carbon Nanotubes in Isotactic Polypropylene Matrix due to the Results of Small-Angle Neutron Scattering and Lattice Numerical Simulation

Engineered PP impact copolymers in a single reactor as efficient method for determining their structure and properties

Impact polypropylene (PP) copolymers (IPCs) are important materials for many commercial applications. These materials are usually synthetized through different methods involving two consecutive reactions in the same phase or in different phases. Here, a laboratory-scale synthesis method based on a sequential liquid- and gas-phase two-step process in a single reactor is developed. Propylene homopolymers and IPCs were synthesized with varying amounts of comonomers and hydrogen. The IPC materials obtained were fully characterized via analytical temperature rising elution fractionation (TREF), differential scanning calorimetry (DSC), 13C nuclear magnetic resonance (13C NMR), gel permeation chromatography with an infrared detector (GPC-IR5), Charpy impact, scanning electron microscopy (SEM), and cross-fractionation chromatography (CFC). The addition of only ethylene to the second step in the absence of hydrogen led to the creation of an ethylene-propylene (EP) copolymer with similar impact strength to that of a propylene homopolymer. The addition of hydrogen to the first step dramatically shortened the length of the PP chains and inhibited catalytic active centers that led to EP copolymer synthesis. This material exhibited very low molecular weight, low ethylene incorporation, and rubbery phases irregularly distributed along the isotactic polypropylene (iPP) matrix, resulting in the formation of an EP copolymer material with poor impact properties. IPCs synthesized without hydrogen and with a 50/50 (v/v) mixture of propylene/ethylene monomers in the second step enhance ethylene incorporation, facilitating adequate homogeneous and heterogeneous ethylene distribution and resulting in a high increment of amorphous ethylene-propylene-rubber (EPR) domains, which remarkably improves impact properties. Additionally, a criterion based on the ratio between EEE and EPE + PEP triads ranging between 1 and 2 was also established to predict the impact resistance of any heterophasic PP. Fractionation of the optimal sample provided a detailed understanding about the microstructure of this copolymer through the study of the molecular weight and composition of the fractions via GPC-IR, analytical TREF, and DSC measurements. Finally, the liquid–gas-phase two-step IPC material was compared, by means of SEM and CFC measurements, with synthesized IPC using liquid–liquid-phase two-step polymerization, and the results showed that the range of EP composition as well as ethylene distribution in the molar mass molecules of the IPCs was correlated to their mechanical behavior. This proves that crystalline families composed of high-molecular-weight EP copolymers in the liquid–gas-phase process can act as a compatibilizing agent between the iPP matrix and the elastomeric rubbery phase, allowing one to improve the impact resistance of the IPC, more so than that of IPCs obtained in the gas–gas and liquid–liquid phases. The results indicate that the synthesis of IPC resins in a single reactor is an efficient experimental method for fundamental research on IPCs.

A Morphology-Based Model to Describe the Low-Temperature Impact Behaviour of Rubber-Toughened Polypropylene.

The roles of the rubber particle size, the rubber particle size distribution and the constitutive behaviour of the isotactic polypropylene matrix have been studied by combining the Lazerri–Bucknall energy criterion for cavitation with the Van der Sanden–Meier–Tervoort ligament model adapted for impact conditions. It is concluded that an optimised morphology offers great potential to achieve enhanced mechanical properties with far less rubber and hence achieve a superior stiffness/toughness/processing balance.

The Effects of Geometry and Chemical Composition of Nanoparticles on The Fracture Toughness of iPP Nanocomposites

This research deals with possible hybrid effects in the fracture energy of hybrid nanocomposites while taking a critical approach toward the currently-prevailing engineering practice of applying classical composite micromechanics to nanocomposites. For this purpose, different nanoparticles were embedded in an isotactic polypropylene matrix. The particles had different geometries (fibrous and platelets) and different chemical structures (organic vapor grown carbon nanofibers (VGCF); graphene nanoplatelets (GNP); and inorganic nanoclays, SiO2 nanofibers, and ZrO2 nanofibers). Almost all the composite systems presented improvements in the fracture energy, whereas the iPP/VGCF/GNP presented a positive hybrid effect. The main conclusion was that each nanocomposite system should be analyzed individually according to the constituent properties; the quality of the dispersion; and, primarily, by the type of interaction between the particles and the matrix.

Melt-Mixed 3D Hierarchical Graphene/Polypropylene Nanocomposites with Low Electrical Percolation Threshold.

Graphene-based materials are a family of carbonaceous structures that can be produced using a variety of processes either from graphite or other precursors. These materials are typically a few layered sheets of graphene in the form of platelets and maintain some of the properties of pristine graphene (such as two-dimensional platelet shape, aspect ratio, and graphitic bonding). In this work we present melt mixed graphene-based polypropylene systems with significantly reduced percolation threshold. Traditionally melt-mixed systems suffer from poor dispersion that leads to high electrical percolation values. In contrast in our work, graphene was added into an isotactic polypropylene matrix, achieving an electrical percolation threshold of ~1 wt.%. This indicates that the filler dispersion process has been highly efficient, something that leads to the suppression of the β phase that have a strong influence on the crystallization behavior and subsequent thermal and mechanical performance. The electrical percolation values obtained are comparable with reported solution mixed systems, despite the use of simple melt mixing protocols and the lack of any pre or post-treatment of the final compositions. The latter is of particular importance as the preparation method used in this work is industrially relevant and is readily scalable.

Raman investigations on gamma irradiated iPP-VGCNF nanocomposites: The polymer's tale

Raman investigations on nanocomposites obtained by loading various amounts of vapor grown carbon nanofibers within an isotactic polypropylene matrix, and gamma irradiated in air, at various integral doses ranging between 0 and 27 kGy, are reported. The analysis is focused on the polymer's answers as revealed by Raman spectroscopy and investigate in detail the effect of ionizing radiation on the position of the Raman line originating from the polymer. The as-obtained data are correlated to the elastic features of the nanocomposites. A competition between gamma irradiation and loading by carbon nanofiber, resulting in the stretching of the polymeric matrix and revealed as a displacement of Raman lines towards smaller wavenumber is reported. It is concluded that side groups (CH3) are less affected by the loading with carbon nanofibers,

Kinetics of Crystallization and Thermal Degradation of an Isotactic Polypropylene Matrix Reinforced with Graphene/Glass-Fiber Filler.

Polypropylene composites reinforced with a filler mixture of graphene nanoplatelet-glass fiber were prepared by melt mixing, while conventional composites containing graphene nanoplatelet and glass fiber were prepared for comparative reasons. An extensive study of thermally stimulated processes such as crystallization, nucleation, and kinetics was carried out using Differential Scanning Calorimetry and Thermogravimetric Analysis. Moreover, effective activation energy and kinetic parameters of the thermal decomposition process were determined by applying Friedman’s isoconversional differential method and multivariate non-linear regression method. It was found that the graphene nanoplatelets act positively towards the increase in crystallization rate and nucleation phenomena under isothermal conditions due to their large surface area, inherent nucleation activity, and high filler content. Concerning the thermal degradation kinetics of polypropylene graphene nanoplatelets/glass fibers composites, a change in the decomposition mechanism of the matrix was found due to the presence of graphene nanoplatelets. The effect of graphene nanoplatelets dominates that of the glass fibers, leading to an overall improvement in performance.

Silanization of di-n-octyldichlorosilane as a route to improve the integration of titanium dioxide in polypropylene

In this work, a di-n-alkyldichlorosilane (di-n-octyldichlorosilane) was used as an agent to improve the integration of titanium dioxide particles into isotactic polypropylene (iPP) matrix. The thermal stability of the silane coating was studied to confirm the applicability of these particles under extrusion temperature; we found by infrared spectrometry and mass spectroscopy that silanization remains stable at temperatures around 400 °C. The non-isothermal analysis of the crystallization process, conducted by differential scanning calorimetry, showed a decrement in the energetic requirements to complete the process when we used the silanized particles and filled the iPP at 0.5% in mass. Also, these silanized particles demonstrate the capability to be a selective α nucleating agent in comparison with the neat TiO2 particles that showed a slight portion of β crystals according to the wide-angle X-ray diffraction analysis.

Effect of Cellulose Nanofiber (CNF) Surface Treatment on Cellular Structures and Mechanical Properties of Polypropylene/CNF Nanocomposite Foams via Core-Back Foam Injection Molding.

Herein, lightweight nanocomposite foams with expansion ratios ranging from 2–10-fold were fabricated using an isotactic polypropylene (iPP) matrix and cellulose nanofiber (CNF) as the reinforcing agent via core-back foam injection molding (FIM). Both the native and modified CNFs, including the different degrees of substitution (DS) of 0.2 and 0.4, were melt-prepared and used for producing the polypropylene (PP)/CNF composites. Foaming results revealed that the addition of CNF greatly improved the foamability of PP, reaching 2–3 orders of magnitude increases in cell density, in comparison to those of the neat iPP foams. Moreover, tensile test results showed that the incorporation of CNF increased the tensile modulus and yield stress of both solid and 2-fold foamed PP, and a greater reinforcing effect was achieved in composites containing modified CNF. In the compression test, PP/CNF composite foams prepared with a DS of 0.4 exhibited dramatic improvements in mechanical performance for 10-fold foams, in comparison to iPP, with increases in the elastic modulus and collapse stress of PP foams of 486% and 468%, respectively. These results demonstrate that CNF is extraordinarily helpful in enhancing the foamability of PP and reinforcing PP foams, which has importance for the development of lightweight polymer composite foams containing a natural nanofiber.

Influence on properties and phase structure of single gas-phase reactor made impact polypropylene copolymers

Impact polypropylene copolymers (IPC) are materials important for many commercial applications. These materials are usually synthetized by different methods involving two consecutive reactions: in liquid, gas or liquid-gas phase. This work presents a method of synthesis in a laboratory scale based on two sequential steps in only one reactor in gas phase. Variables such as H2 addition, reaction time, and composition during the second step were studied, and their influence on the formation of propylene-ethylene copolymer materials with different properties was analyzed. The IPC materials so obtained were characterized by analytical temperature rising elution fractionation (TREF), calorimetric methods (DSC), 13C nuclear magnetic resonance (13C NMR), gel permeation chromatography with an infrared detector (GPC-IR5), Charpy impact, and scanning electron microscopy (SEM).The isotactic polypropylene matrix (iPP) obtained in the first step of the gas-phase process displays spherical morphology and lower mean particle size than those obtained in the liquid-phase process, even though the polymer grains experimented a certain tendency to agglomerate.In particular, hydrogen addition caused a significant decline in the catalyst productivity and dramatically shortened the length of the propylene homopolymer chains. Similarly, the presence of hydrogen on the synthesis of ethylene-propylene copolymers was demonstrated to lead to materials with very low molecular weight, low ethylene incorporation, and rubbery phases irregularly distributed along the iPP matrix and therefore with poor impact properties.On the other hand, ethylene-propylene copolymers synthesized without hydrogen yielded a suitable combination of molecular weights and molecular weight distribution that can contribute to good polymer processing and were proven to incorporate adequate amounts of ethylene mainly randomly distributed into the iPP matrix. SEM measurements revealed that the amorphous rubbery phase was homogeneously dispersed in the iPP matrix, and the Charpy test allowed to rank these materials as IPC.Finally, fractionation of IPC materials by preparative TREF provided information about the microstructure formation. Subsequent studying of molecular weights and composition of the fractions by GPC-IR, analytical TREF, and DSC measurements based on the ethylene-propylene composition and ethylene distribution in the molar mass molecules was shown to enable the design of IPC materials. Additionally, the optimal IPC material was compared with the best IPC using liquid-phase polymerization, and the results showed that the range of ethylene-propylene composition, as well as the ethylene distribution in IPC molar mass molecules, correlated with IPC mechanical behavior.

“Improvement in the energy dissipation capacity of polypropylene composites through a surface modification of titanium dioxide particles with a dicarboxylic acid”

In this work, we modified commercial TiO2 nanoparticles using pimelic acid (PA) as an agent to improve interaction of titanium dioxide (TiO2) into an isotactic polypropylene (iPP) matrix. The chemical bond of PA at the TiO2 surface, allows a thermal and UV stabilization of PA molecules avoiding its decomposition in a process involving high temperature. As a consequence of an appropriate TiO2 integration into iPP, the results of the dynamical-mechanical analysis reveal that the iPP filled with modified particles (c-TiO2) dissipate around two times more energy than those with the non-modified particles (n-TiO2). A multi-frequency analysis of these composites also allowed us to estimate the apparent activation energy required to carry out the vitreous transition of these composites filled with c-TiO2, which shows that particles are effectively well integrated with the iPP. These results validate the surface modification as an appropriate strategy to improve both, coloring capacity of TiO2 and mechanical stress resistance of iPP measured as dissipated energy into the bulk of iPP with modified TiO2 particles.

Size Effect of Layered Double Hydroxide Platelets on the Crystallization Behavior of Isotactic Polypropylene.

Layered double hydroxide (LDH) platelets with nanosized and microsized level were synthesized and used as fillers in an isotactic polypropylene (PP) matrix. The nucleation and crystallization behavior of PP/LDH composites (denoted as 1-PPLx and 2-PPLx for composites containing nanosized and microsized LDH, respectively; x represents the mass percentage of LDH) was investigated by differential scanning calorimetry and polarized optical microscopy techniques. It is found that the crystallization temperature of PP/LDH composites is largely enhanced and the half crystallization time is reduced remarkably relative to pure PP, especially for 2-PPLx composite. The 2-PPLx composite exhibits stronger heterogeneous nucleating ability and faster crystallization rate than 1-PPLx samples with the same LDH loading. In addition, the crystallized PP/LDH composites possess significantly enhanced thermal stability, gas barrier, and flame-retardant properties relative to neat PP, which would show a broad application prospect in engineering plastics and packing industry.