Syndiotactic Polypropylene Research Articles

Syndiotactic polypropylene-based elastomer as promising toughening agent for waste appliances-derived polypropylene

The rapid replacement of household appliances has generated a significant amount of waste appliances-derived polypropylene (WAPP), presenting a valuable resource for recycling. However, the long-term use and subsequent thermal processing of WAPP lead to its degradation, significantly impairing its toughness. Herein, syndiotactic polypropylene (sPP) as a novel toughening agent was investigated to achieve the efficient toughing of WAPP. The incorporation of 15 wt% of the sPP-based elastomer increased the impact strength of WAPP to 29.2 kJ/m2 (25 °C), which was 5.7 times that of the unmodified one and 1.9 times that modified with polyolefin elastomers (POE). This inspiring effect originates from the structural similarity between isotactic and syndiotactic polypropylene, which not only achieves a more uniform dispersion of the rubbery phase, but also creates micro voids between the phases due to the incompatibility of sPP and iPP, making it easier for shear bands to form. Further, the contradiction between rigidity and toughness is reconciled by introduction of talcum powder. This comprehensive investigation into the effects of the sPP-based toughening agent on the composite material's properties expands the potential applications of sPP and enhances our understanding of its toughening mechanisms.

Heating Rate Sensitive Polyethylene Terephthalate.

Smart materials react to external triggers by changing size, color, mechanical properties, or permeability. The next generation of smart materials will be able to not only recognize and react to external triggers but also to their dynamics. The only existing example of such a material is heating rate-sensitive polymorphous cross-linked syndiotactic polypropylene. This study presents a new principle of a heating rate-sensitive material on the example of cross-linked and fully amorphous quenchable semi-crystalline polyethylene terephthalate (x-PET). The x-PET is stretched to high elongation above its melting temperature and constrained quenched to a fully amorphous state. Then the polymer is heated to 120-170°C with different heating rates. Due to its heating-rate sensitivity, x-PET shrinks to different stabilized lengths dependent on the heating rate. The new length can be used to read out the heating rate and to specifically answer to this by mechanically switching a process. Detailed analytics of this process reveal that amorphous stretched x-PET is starting the retraction above Tg and simultaneously stopping it by crystallization. The different rates of these processes result in the heating rate sensitivity of x-PET.

The Effect of Chain Tacticity on the Thermal Energy Parameters of Isotactic and Syndiotactic Polypropylene

The thermal energy properties in any material affect the substance’s capacity to store or transfer heat. This study investigated the effect of the polymeric chains’ tacticity on the thermal properties of polypropylene related directly to the thermal power, i.e., the heat capacity and thermal conductivity. The study selected different commercial polypropylene groups with two steric modes: isotactic and syndiotactic. The aim is to determine the parameters: isotacticity index, degree of crystallinity, glass-transition temperature, melting point, heat capacity, and thermal conductivity. The data were collected using gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC). The results showed that methyl groups randomly distributed within the homo-polypropylene changed the overall content of meso diads, i.e., less isotacticity index. The differences between isotactic and syndiotactic polypropylene groups were 20-40% the degree of the crystallinity, 5-10°C the glass-transition temperature, and 10-20°C the melting point. Using suitable mathematical models, these parameters can be related directly to specific heat capacity and thermal conductivity.

Homogeneous Non-Metallocene Group 4 Metals Ligated with [N,N] Bidentate Ligand(s) for Olefin Polymerization.

The development of catalysts has significantly advanced the progress of polyolefin materials. In particular, group 4 (Ti, Zr, Hf) non-metallocene catalysts ligated with [N,N] bidentate ligand(s) have garnered increasing attention in the field of olefin polymerization due to their structurally stability and exceptional polymerization behaviors. Ligands containing nitrogen donors are diverse and at the core of many highly active catalysts. They mainly include amidine, guanidinato, diamine, and various N-heterocyclic ligands, which can be used to obtain a series of new polyolefin materials, such as ultrahigh molecular weight polyethylene (UHWMPE), olefin copolymers (ethylene/norbornene and ethylene/α-olefin) with high incorporations, and high isotactic or syndiotactic polypropylene after coordination with group 4 metals and activation by cocatalysts. Herein, we focus on the advancements and applications of this field over the past two decades, and introduce the catalyst precursors with [N,N] ligand(s), involving the effects of ligand structure, cocatalyst selection, and polymerization conditions on the catalytic activity and polymer properties.

The glass transition temperature investigation of polymers by molecular dynamic simulations

In this paper, the process of glass transition is studied, the theory of which is not fully developed. Computer modeling can be used to understand the theory of this phenomenon. The glass transition temperature is influenced by a large number of polymer parameters: cooling rate, pressure, presence of diluent, structural features, etc. We are considering a number of different polymers to test the ability of the pcff+ force field to determine the glass transition temperature. The effect of tactility, composition, pressure and the presence of a diluent on the glass transition temperature of polymers will be shown using molecular dynamics (MD) and pcff+ force-field modeling. The effect of tact was studied using the use of atactic, isotactic and syndiotactic poly(methyl methacrylate) and atactic, isotactic and syndiotactic polypropylene. The LAMMPS code integrated into the MedeA computing environment was used to simulate the molecular dynamics of polymers. The calculation of the glass transition temperature at different cooling rates is closely related to the balanced initial systems. Due to the inability of current atomistic simulations to achieve the required cooling rates, as in experiments, the gap was not sharp and quite obvious. The data obtained show that the pcf+ force field describes tactics quite effectively and gives differences in the glass transition temperature for different types of tact. For polymers diluted with CO2, the glass transition temperature decreases almost linearly, which is in good agreement with the experiment. As expected, the pressure increases the glass transition temperature. However, at high pressure, the slope fracture disappears, and the determination of Tg becomes extremely difficult. The simulated annealing process will be applied to a set of polymers to obtain graphs of the specific volume versus temperature and determine the glass transition temperature.

The Effect of Iron Content on the Thermodynamic Properties of Syndiotactic Polypropylene/Iron Composites

This study investigated the influence of iron concentration on the thermodynamic properties of syndiotactic polypropylene (sPP)/iron composites in the melt phase in a series of samples with varying iron content, ranging from 0 to 10% with a step of 2%. The HYSYS software was used to estimate molecular weight, critical temperature (Tc), critical volume (Vc), and eccentricity (Ec). The results showed that all these properties changed as the iron content varied. The findings of this study confirmed that iron concentration has an impact on the mechanical and chain dynamic (microscopic) properties of polymer composites.

The breakage of original crystallites determined small strain cavitation in syndiotactic polypropylene during step-cycle tensile deformation

The step-cycle tensile experiments were carried out on syndiotactic polypropylene to explore the crystallization and deformation temperature dependency of cavitation via the wide and small angle scattering X-ray techniques. The development of cavitation process exhibited a dependency on the original crystallites. The cavities appeared around the yield point could be healed after releasing the tensile force before a specific strain, while the ones occurred beyond this point are permanent. This phenomenon was in accord with the process of the recoverable lamellar thickness within one stretching and relaxation cycle. After reaching the critical point of fragmentation and recrystallization of lamellae, the growth rate of cavities started to decrease due to the destruction of the original crystallites. Moreover, the crystallites formed at higher crystallization temperature could be preserved to a larger strain and thus more intense cavitation could be expected. The high deformation temperature could weaken the intensity of cavitation, then, the weakest cavitation phenomenon was observed in the sample crystallized at low temperature but drawn at high temperature.

Crystallization with Nodular Aggregation near the Glass Transition Temperature for Syndiotactic Polypropylene

The isothermal crystallization from the melt state of syndiotactic polypropylene (sPP) has been studied by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and optical microscopy. The WAXD and SAXS results show the crystallization mechanism near the glass transition temperature in which the crystalline and mesomorphic nodules cover the entire sample with the formation of aggregation regions. For the SAXS analysis, the scattering function for the three-component system has been suggested. Furthermore, to analyze the growth kinetics of the aggregation region for sPP, the time-dependent structure factor combined with the homogeneous and inhomogeneous nucleation-and-growth kinetics has been suggested. The analysis shows that the growth kinetics of the aggregation region for sPP is the homogeneous nucleation-and-growth. The growth velocity of the aggregation region is a natural extrapolation of that of spherulite to the high supercooling region. These results might indicate that the crystallization with the nodular aggregation is a fundamental crystallization process near the glass transition temperature for polymers.

Construction of Helically Oriented Syndiotactic Polypropylene/Isotactic Polypropylene Composites for Medical Interventional Tubes via Rotation Extrusion

Medical tubes are important medical devices for interventional therapy. However, current tubes suffer from poor biocompatibility due to the heterogeneity of composites. In this study, we demonstrated a syndiotactic polypropylene (sPP)/isotactic polypropylene (iPP) composite tube with reinforced hoop strength and considerable biocompatibility. Taking advantage of the same backbone structure of PP, an iPP network was constructed in situ by rotation extrusion technology, which not only promoted interfacial crystallization but also increased the orientation degree in the hoop direction. As a result, the modulus of the iPP fiber-reinforced tubes reached 4.28 MPa/rad, which is about three times than that of the sPP tube. The biocompatibility of the as-prepared tube was evaluated in vitro and in vivo, and sPP/iPP had no impact on the cell shape or proliferation. This work overcomes the current bottleneck of a lack of composite materials for medical interventional tubes and simultaneously broadens the application of the sPP matrix.

İzo- ve Sindiyotaktik Polipropilenlerin Reolojik Davranışının Karşılaştırılması

The rheological behavior of iso- and syndiotactic polypropylenes (iPP and sPP) for two different temperatures of 175 and 190˚C at atmospheric pressure is analyzed employing the Yahsi-Dinc-Tav (YDT) non-Newtonian viscosity model. The predicted viscosity with shear rates of 0.093 to 93.91 s-1 on PPs is compared with the corresponding estimations from the Cross-like model. The obtained results from the YDT model deviate from the reported experimental observations with 1.041 for iPP and 1.86 for sPP. From the zero shear viscosity correlation to temperature- and vacancy fraction- dependent thermo-occupancy function, Yh = Yh(h, T), viscosity parameters were ascertained and associated with polymer tacticity. From the zero shear viscosity relation, an increase in Yh = Yh(h, T) function and hole fraction loss results in increased viscosity. The dependence of the derivative of logarithm of viscosity (viscoholibility) on vacancy fraction, as a function of pressure and temperature, h=h(P,T), procured from Simha-Somcynsky hole theory displays an exponentially decreasing behavior.

Aspects on the Relationship Between Tacticity and Thermal Properties of Isotactic and Syndiotactic Polypropylene

Aspects on the Relationship Between Tacticity and Thermal Properties of Isotactic and Syndiotactic Polypropylene

Toward a deep understanding of the difference between isotactic and syndiotactic polypropylene on the fire performance and degradation behavior

This work investigated the difference in flame retardancy and degradation behavior of polypropylene (PP) composites with different configurations. The piperazine pyrophosphate (PAPP) was combined with melamine polyphosphate (MPP) to construct an intumescent flame retardant system, before incorporating into the PP system by melt blending. It showed that by the introduction of equal amounts of flame retardant, isotactic polypropylene composites (iPP-IFR) can achieve better flame retardancy with a desirable UL-94 V-0 rating, whereas syndiotactic polypropylene (sPP-IFR) shows poor fire performance. Melt index tests show that sPP-IFR sample is easy to flow and prone to melt drops. Differential scanning calorimetry results show that iPP-IFR has a higher degree of crystallinity. The thermogravimetric infrared coupling results show that sPP-IFR produces more small molecule hydrocarbon gases during combustion, making the system more difficult to achieve satisfied flame retardancy. The burning properties of iPP-IFR have been proven to be somewhat better compared to that of sPP-IFR, and sPP is more difficult for flame retardant modification.

Point‐of‐need quantitative detection of trihalomethanes in environmental water samples using a highly sensitive and selective fiber‐based preconcentration system

AbstractDrinking water—a vital part of our ecosystem—is often exposed to contamination through industrialization. Halogenated compounds, for example, trihalomethanes (THMs), are among the most common contaminants, being by‐products of water chlorination/treatment. The carcinogenic and health effects of these compounds have motivated scientists to work on the accurate detection of THMs down to 80 ppb in treated water. Here, a superhydrophobic syndiotactic polypropylene (sPP) nanofiber mat is used to preconcentrate THMs in environmental water samples, and subsequently, detect them using a well‐known colorimetric reaction chemistry. The reaction chemistry yields a visible red/pink chromophore under visible light absorption. This reaction occurs when the preconcentrated THM becomes trapped in the liquid phase of the reaction chemistry, on the surface of the sPP fibers. This fiber mat is electrospun in a way which results in a large water contact angle >150°—allowing the working sensitivity of the reaction chemistry to be heightened and lowering the detection limit. The resulting color change can be analyzed via a simple quantitative color intensity analysis utilizing widely‐available software, measuring the THM content in water as low as 0.8 ppb. This cost‐effective and selective method was incorporated into a portable device, enabling on‐site users to evaluate the quality of drinking water.

Microwave-assisted foaming and sintering high-strength and antistatic polypropylene bead foams by constructing conductive 3D skeleton structure

Polypropylene (PP) bead foam parts, one of the most widely used automotive interiors, are traditionally welded by high-pressure steam, while their large inter-bead gaps result in the poor mechanical properties. Herein, syndiotactic polypropylene (sPP) powders, with low melting point, coated with carbon nanotubes (CNTs) were adopted as the microwave absorbing medium to weld the surface of expanded isotactic polypropylene (EiPP) beads, which were initially prepared by supercritical carbon dioxide (scCO2) foaming. Then, the modified EiPP (EiPP coated with CNTs@sPP powders, denoted as mEiPP) composite foams were successfully fabricated by microwave-assisted foaming and sintering. The obtained foam part consisted of porous iPP bead structure (body) and interconnected CNTs@sPP pathway (3D skeleton), which showed superior mechanical properties with tensile strength of 4.07 MPa and compressive strength of 4.64 MPa (10 % strain). Due to the conductive 3D skeleton, the requirements of antistatic PP bead foams could be sufficed with the lower CNTs loading.

Single-molecule study on the force-induced melting in syndiotactic polypropylene single crystals

Highly stereoregular syndiotactic polypropylene (s-PP) with high crystallinity and melting temperature has unique physical properties such as high impact resistance and transparency, which is closely related to the chain conformation and crystal structure of s-PP. However, the molecular mechanism underlying the mechanical properties remains unclear, because the complex amorphous-crystalline network and the diverse crystal structure limit the classical characterizations. Here, we investigate the single-molecule force-induced melting in the melt-prepared and solution-prepared s-PP single crystal by using atomic force microscopy (AFM)-based single molecule force spectroscopy (SMFS). Our results show that the mechanical stability slightly increases with the increase of crystal thickness and the crystal thickness also has a significant impact on the melting pathway. The comparison of the melting pathways of s-PP and isotactic polypropylene (i-PP) suggests that the syndiotactic structure and lower tacticity of s-PP will increase the chain friction during slide and therefore suppresses the αc relaxation in the crystal region. Moreover, the difference of the chain folding trajectory in sectors (100) and (010) shows no effect on the mechanical stability. However, the mechanical stability of form I structure was higher than that of form II.

Effect of Macro- and Microstructures on Catalytic Hydrogenolysis of Polyolefins

Polyethylenes of varying molecular weight and branch density, as well as polypropylenes of varying molecular weight and tacticity, were catalytically converted to lower-molecular-weight liquid products to showcase how these various properties in a mixed waste plastic stream could affect the final product. A Pt nanoparticle on a strontium titanate nanocuboid (Pt/STO) catalyst was used under solvent-free conditions in the presence of 170 psi of H2 at 300 °C for hydrogenolysis. The initial molecular weight of polyethylene was found to have a moderate effect on the yield to the final product (ranging from 55 wt% for Mn ∼ 7600 Da to 67 wt% for Mn ∼ 50,950 Da). The microstructure, defined as the length and density of branches in a polymer, of higher-molecular-weight polymers was the dominant factor in determining the yield (ranging from 67 wt% for Mn ∼ 50,950 Da for linear low-density polyethylene (LLDPE) with C2 branches to 97 wt% for Mn ∼ 38,850 Da for LLDPE with C6 branches). The same products (Mn = C29–C46, Đ = 1.1–1.6) and distribution of undesired light gases (C1–C4 ≈ 90 mol%, C5–C8 ≈ 10 mol%) are obtained from conversions of PE of varying molecular weight. The tacticity of polypropylene at a given molecular weight had a significant effect on the molecular weight of the final product, while not strongly affecting conversion. Hydrogenolysis of isotactic polypropylene (iPP) produced ≈C18 with a wider polydispersity (Đ ∼ 1.4) compared to the narrow ≈C64 (Đ ∼ 1.0) and ≈C54 (Đ ∼ 1.0) products from atactic (aPP) and syndiotactic (sPP) polypropylene, respectively. The stereochemistry of the methyl groups dictates the shape and structure of the polymer in the melt, which in turn affects how the hydrocarbon chain interacts with the catalyst surface, thereby impacting the number of C–C scissions. These results show how various characteristics such as the molecular weight and structure of a waste plastic stream could affect the final product.

Structure and Morphology of Crystalline Syndiotactic Polypropylene-Polyethylene Block Copolymers.

A study of the structure and morphology of diblock copolymers composed of crystallizable blocks of polyethylene (PE) and syndiotactic polypropylene (sPP) having different lengths is reported. In both analyzed samples, the PE block crystallizes first by cooling from the melt (at 130 °C) and the sPP block crystallizes after at a lower temperature. Small angle X-ray scattering (SAXS) recorded during cooling showed three correlation peaks at values of the scattering vector, q1 = 0.12 nm−1, q2 = 0.24 nm−1 and q3 = 0.4 nm−1, indicating development of a lamellar morphology, where lamellar domains of PE and sPP alternate, each domain containing stacks of crystalline lamellae of PE or sPP sandwiched by their own amorphous phase of PE or sPP. At temperatures higher than 120 °C, when only PE crystals are formed, the morphology is defined by the formation of stacks of PE lamellae (17 nm thick) alternating with amorphous layers and with a long period of nearly 52 nm. At lower temperatures, when crystals of sPP are also well-formed, the morphology is more complex. A model of the morphology at room temperature is proposed based on the correlation distances determined from the self-correlation functions extracted from the SAXS data. Lamellar domains of PE (41.5 nm thick) and sPP (8.2 nm thick) alternate, each domain containing stacks of crystalline lamellae sandwiched by their own amorphous phase, forming a global morphology having a total lamellar periodicity of 49.7 nm, characterized by alternating amorphous and crystalline layers, where the crystalline layers are alternatively made of stacks of PE lamellae (22 nm thick) and thinner sPP lamellae (only 3.5 nm thick).

In situ polymerisation of stereospecific propylene nanocomposites blends. Optimising mechanical properties

Isotactic (iPP) and syndiotactic (sPP) polypropylene composites and their blends containing different amounts of nanosepiolite as cocatalyst support were prepared via in-situ polymerisation using different metallocene catalysts to find out improvements in the mechanical properties in comparison with traditional PP nanocomposites obtained by melt.The results showed that the amount of nanoclay significantly affects the catalytic activity of the Cs-symmetry catalyst, obtaining nanocomposites with important microstructural changes: increased molecular weight and syndiotactic sections, narrower molecular weight distributions and increased crystallinity. The particular ordering of the crystalline sections of the sPP observed in the WAXS patterns was the main reason for the dramatic changes in the thermal and mechanical properties of the obtained nanocomposites. Although the nanocomposites obtained with catalyst mixtures maintained certain thermal properties of the iPP, these did not translate into improved mechanical properties due to the loss of crystallinity and the preference for the synthesis of syndiotactic configurations.

Surface tension and interfacial tension of polyolefins and polyolefin blends

AbstractThis paper focuses on the calculation of the interfacial tension of two systems: low‐density polyethylene with isotactic polypropylene and high‐density polyethylene with syndiotactic polypropylene. For this, three methods to measure the interfacial tension are compared: the use of Palierne's model, and Gramespacher and Meissner's model, both based on additional elasticity or long relaxation times brought by shape recovery of dispersed phase, and ab‐initio calculation, which requires the knowledge of the surface tension of the neat polymer measured at the same temperature. For that, a database collected from the literature is built in the first section of this paper, whether for the studied systems or for other systems of various olefinic homopolymers or copolymers with polypropylene. The results show the effectiveness of the Gramespacher and Meissner's model to calculate the interfacial tension of the studied systems for which the results were in agreement with ab‐initio calculation and Palierne's model. Extension of the ab‐initio calculation to olefinic copolymers was proposed.

Confined crystallization in the binary blends of diblock copolymers bearing stereoisomeric isotactic and syndiotactic polypropylene

The morphology and crystallization behavior of the binary blends of two crystalline-amorphous diblock copolymers bearing stereoisomeric crystalline blocks have been investigated. A polystyrene-block-isotactic polypropylene (S-iPP) and a polystyrene-block-syndiotactic polypropylene (S-sPP) were used to prepare a series of blends forming lamellar morphology. In the melt state, the PS blocks from these two diblock copolymers mixed intimately in the PS lamellar microdomains; meanwhile, the iPP and sPP blocks were found to form a miscible mixture in the PP domains. Under the effects of nanoscale confinement and the constraint imposed by the junction points, the iPP and sPP blocks exhibited the crystallization behavior greatly deviated from that in the neat diblock copolymers. A local demixing between a fraction of iPP and sPP chains was found to occur in the S-sPP-rich blend at low crystallization temperatures, which yielded the defective crystalline domains composed of alternately intervened iPP and sPP crystallites. This crystalline species displayed a significant depression of melting point located at the temperature around 10°C higher than the corresponding Tc due to an excess surface free energy at the interface between the alternately intervened iPP and sPP crystallites.