Isotactic Polypropylene Research Articles

Ultra high density carbon fiber derived from isotactic polypropylene fiber without skin‐core structure

AbstractPolypropylene (PP)‐based carbon fibers were prepared by sulfonation process of isotactic PP fibers with concentrated sulfuric acid, followed by stress‐less carbonization under nitrogen atmosphere. The stabilization behaviors of PP fiber under different sulfonation temperatures and time were discussed. The carbonization behavior of the stabilized PP fibers under different carbonization temperatures, as well as the mechanical performance of the obtained carbon fibers were investigated. The results indicated that linear PP molecule were effectively converted into thermally stable structure at higher temperature (≥130°C) in short time (2 h) through sulfonation‐desulfonation reaction, among which ordered graphite structure has been formed prior to the carbonization process. Meanwhile, the carbon fibers were considerably densified by increasing the sulfonation temperature and carbonization temperature, and a bulk density of 1.96 g/cm3 was achieved. Moreover, the temperature and time of the sulfonation process as well as the temperature of the carbonization process were regulated, and carbon fibers with tensile strength of 262.3 MPa was obtained, which was superior to that of 208.1 MPa for the linear low density polyethylene‐based carbon fibers reported previously. Isotactic PP was proved to be a promising candidate to develop carbon fibers with tunable graphite structure and mechanical performance.

Flame retardancy in isotactic polypropylene modified with crystalline coordination polymers based on calcium, zinc or aluminum dimethyl phosphates

A novel variety of metal organophosphates (MOPs) coordination polymers: calcium bis(dimethyl phosphate) (CaDMP), zinc bis(dimethyl phosphate) (ZnDMP) and aluminum tris(dimethyl phosphate) was examined for the first time to act as potential flame retardants in isotactic polypropylene (iPP) materials and their flame-retarding activity compared with widely used commercial flame retarder ammonium polyphosphate (APP). All iPP composites containing 20 wt. % of MOPs as with APP achieve V-2 in the UL-94 test and LOI values even higher (25.5 vol. % for iPP/20 %CaDMP) than determined for APP-containing material accompanied by maintaining or slightly degrading mechanical properties. Also in mass loss calorimeter test (MLC) the MOPs demonstrated a positive effect on the fire response of the obtained composites leading to a reduced, in the case of ZnDMP, the peak of heat release rate (pHRR), total heat evolved (THE), average effective heat of combustion (avEHC), fire growth rate (FIGRA) by 57 %, 35 %, 29 %, 63 % respectively when compared with pure iPP. Moreover the detailed analysis of the solid and liquid pyrolysis products of MOPs was done via FTIR. The FTIR spectra and PRXD studies of the char residues after combustion indicated the formation of a solid, inorganic condensed phosphates and release of trimethyl phosphate (TMP) into the gas phase. Finally, the flame retardancy mechanism of MOPs was proposed based on results of MLC test and of the pyrolysis experiment. The gas phase activity of all three MOPs was confirmed by the decrease of avEHC most probably due to release of trimethyl phosphate (TMP) into flame, whereas, in particular ZnDMP acted strongly in the condensed phase by forming a intumescent, protective layer.

Phase morphology of nascent impact polypropylene copolymer and its evolution in the melt

In this study, the morphology of the nascent grains of a commercial impact polypropylene copolymer (IPC) and its evolution upon melting was investigated by atomic force microscopy (AFM) and atomic force microscopy-infrared (AFM-IR). The grains were found to be heterogeneous, about half translucent and the rest opaque, containing 12.2 and 2.0 wt% ethylene comonomer, respectively. The ethylene-propylene (EP) rubber in these two kinds of grains differed in content, but was of the same composition, filling the voids between isotactic polypropylene (iPP) subglobules in irregular long strips. Upon melting, the EP rubber strips were found to quickly break into smaller sections, and their shape became more regular, within which rigid cores started to appear. Then, disperse particles with clear core-shell structure were observed, and they grew slightly bigger at longer heating time. Both translucent and opaque grains went through the same morphology evolution process, resulting in core-shell particles of the same phase compositions as assessed by AFM-IR analysis. In addition, the translucent grains were mixed with 5 wt% of a deuterated PP in a twin-screw extruder, and the blend pellet was examined by AFM-IR, and the results showed that the deuterated species was abundant in the PP matrix and totally absent within the disperse particles, implying no encapsulation of the molecules from the matrix surrounding in the formation of the core-shell structure in the melt processing.

Morphology Distribution in Injection Molded Parts.

A more sustainable use of plastic parts makes it necessary to replace current plastic parts with recyclable components, also allowing the modulation of the part properties through the process. Injection molding is one of the most widely used technologies for obtaining rigid plastic parts, so it is crucial to understand how to tailor properties by adopting the correct processing conditions. One way is to perform annealing steps directly inside the mold: in-mold annealing improves the structural integrity and durability of the material, reduces defects, increases the resistance of parts against certain chemicals, reduces wear and tear, increases ductility, and lowers brittleness. In this work, several in-mold annealing steps were conducted, changing the mold temperature and annealing duration selected on the basis of the half crystallization time of the adopted isotactic polypropylene. The typical molded part morphology, composed of oriented layers at the surface, transition zones, and spherulitic core, is strongly affected by in-mold annealing. In particular, the thickness of the oriented layer, which forms in the early phase of the process, decreases, and the spherulites increase in size. Concerning mechanical behavior, the orientation degree mostly determines the elastic modulus value close to the surface, whereas the conditions under which crystallization occurs determine the modulus in the core.

Photooxidative degradation and fragmentation behaviors of oriented isotactic polypropylene

Photooxidative degradation and fragmentation behaviors of oriented isotactic polypropylene

Material extrusion of SEEPS blended isotactic PP for possible application as automotive bumper: Performance analysis through Finite Element Simulation

3D processing of isotactic polypropylene or PP based composites through material extrusion is evolving globally as an advanced product development tool for highly specialized sectors like aerospace, biomedicals and automobiles. Conversely, pristine PP shows a severe drawback of exhibiting higher warping compared to other thermoplastics following higher crystalline shrinkage. These have prohibited the wider acceptance of virgin PP in 3D processing for product development. The current investigation is primarily aimed to overcome these disadvantages through mixing with amorphous Poly (styrene-co-(ethylene-co-(ethylene-co-propylene)-co-styrene)) or SEEPS in various mass percentages starting from 10 wt% to 30 wt% in melt before printing. The target was to make a tougher PP with retention of its original strength by reducing the shrinkage; In addition, it is also aimed to predict the usability of such material by virtual testing as a potential alternative to pristine PP for constructing an automotive bumper, designed using an AutoCAD. The printed product (dumbbell) demonstrated a higher toughness and resistance to shrinkage than pristine PP but the tensile strength and modulus decreased significantly beyond 10 wt% loading of SEEPS. Parallelly, at 10 wt% loading, the tensile strength and toughness of the printed products were found to be superior than the compression molded sample. In addition, the printed sample at this loading also possessed lower specific heat (4.79 J/g °C) than the pristine one (5.83 J/g °C) and was more thermally stable (lower degradation rate) than both the pristine and the corresponding higher blend compositions. Due to partial similarity in chemical structure between SEEPS and PP, the former had produced autonomic compatibilization with PP and formed a partially miscible blend. A car bumper was designed from this blend composition (10 wt%) using AutoCAD and its resistances to withstand against the collision stress at high (60 km/h) and low (45 km/h) car speeds were evaluated and compared virtually through Finite Element Simulation (FES) with virgin PP. Due to advantageous properties like retention of tensile strength, higher toughness and thermal stability and lower specific heat, the 10 wt% composition exhibited lesser tendency towards failure by predicting higher deformation than virgin PP. Thus it was found suitable as a bumper material which can be prototyped/finally prepared using materials extrusion technique.

Effect of microstructure tuning by rapid heat cycle molding on the photodegradation behavior of isotactic polypropylene

AbstractRapid heat cycling molding (RHCM) is an injection molding technique that improves the product quality of isotactic polypropylene (iPP) by tuning the microstructure, but its effect on the photodegradation stability remains to be investigated. In this work, the effect of RHCM tuned microstructure on the photodegradation behavior of iPP was investigated and compared with conventional injection molding (CIM). Differential scanning calorimetry (DSC), x‐ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), atomic force microscopy (AFM), and shore durometer (D scale) were used to examine the photodegradation behavior of iPP samples. The results showed that RHCM increased the crystallinity, crystal size, and β‐crystal content of iPP samples. With the increase of photodegradation time, iPP samples injected with RHCM showed higher stability in terms of microstructure and surface quality. The relative changes in CI and Ra of RHCM90 were reduced by 48% and 40% after 800 h of UV irradiation, respectively. In addition, the combined results of dynamic mechanical analysis (DMA) and UV–visible absorption spectrum showed that RHCM promoted the development of crystalline structure and reduced the mobility of the surface chain segments as well as UV absorption coefficient. These combined effects contributed positively to its photodegradation stability.

Никельсодержащие нанокомпозиты на основе изотактического полипропилена и полиэтилена высокого давления

The effect of nanofiller (NF) additives containing nickel oxide nanoparticles stabilized by a polymer matrix of high pressure polyethylene (PE) obtained by the mechanochemical method on the structure and properties of metal-containing nanocomposites based on isotactic polypropylene (PP) and high pressure polyethylene(PE) using differential thermal (DTA) and X-ray phase (XRF) and SEM analyzes. The improvement of strength, deformation and rheological parameters, as well as thermal-oxidative stability of the obtained nanocomposites was revealed, which, apparently, is associated with the synergistic effect of interfacial interaction of nickel-containing nanoparticles in the PE matrix with the components of the PP/PE polymer composition. It is shown that nanocomposites based on PP/PE/NF can be processed both by pressing method and by injection molding and extrusion methods, which expands the scope of its application.

Helical polyamines.

Polymer microstructures rely on tacticity, yet exploration in polyamines has focused predominantly on atactic polymers. We introduce a method to synthesize a diverse library of ortho and para-cyanobenzenesulfonyl-activated-methyl aziridines using R, S, and racemic alaninol. Living anionic ring-opening polymerization of racemic sulfonyl aziridines yields soluble polymers, while enantiomerically-pure sulfonyl aziridines follow a dispersion polymerization with complete monomer conversion giving access to stereoblock copolymers. Removal of activation groups is achieved using dodecanethiol and tert-butylimino-tri(pyrrolidino)phosphorane to obtain isotactic or atactic linear polypropylene imines (LPPIs). High-purity L-PPIs are obtained in salt and neutral forms with high yields. Stereoblock copolymers of poly-R-block-S-polysulfonamides and respective polypropylene imine stereoblocks are synthesized, revealing helical structures in water influenced by the monomer type and sequence in CD spectroscopy. Molecular dynamics simulations confirm the helical nature of isotactic LPPIs in water. Bulk characterization demonstrates the first crystalline isotactic polyamines via spherulite growth in polarized light, atomic force microscopy and XRD analyses. In cell-transfection studies, the synthesized isotactic LPPIs exhibit lower toxicity and transfection efficiency than commercial hyperbranched polyethylene imine, with longer chains showing increased transfection efficiency. These isotactic polymers open avenues for complex macromolecular architectures with optically active polyamines akin to poly(amino acid)s but lacking hydrolytically cleavable amide links.

Triptycene as a scaffold in metallocene catalyzed olefin polymerization.

A set of metallocene olefin polymerization catalysts bearing triptycene moieties in either position 4-5 (complexes Ty1-Ty5) or in position 5-6 (complexes Ty6-Ty8) of the basic dimethylsilyl-bridged bis(indenyl) system has been tested in propene polymerization and in ethene/1-hexene copolymerization. Comparison of the results with QSPR (quantitative structure-property relationship) predictions not parametrized for these exotic ligand variations demonstrates that trends can still be identified by extrapolation. Interestingly, Ty7, upon suitable activation, provides a highly isotactic polypropylene with an exceptional amount of 2,1 regio-errors (8%). The previously developed QSPR type models successfully predicted the low regioselectivity of this catalyst, despite the fact that the catalyst structure differs significantly from the benchmark set.

Dynamical mechanical and impact strength behavior of 3D‐printing testing specimens manufactured by fused filament fabrication of isotactic polypropylene/functionalized titania nanotubes nanocomposites: Influence of β‐crystal promoting

AbstractThermomechanical and impact properties of isotactic polypropylene nanocomposites reinforced with titania nanotubes (TiNTs) at weight distributions of 0.5, 1, and 1.5 wt% were investigated. The goal of this study was to create a novel iPP‐based nanocomposite filament fused filament fabrication (FFF) with improved thermo‐mechanical and impact properties to enable the creation of more customized geometries. First, TiNTs were chemically functionalized with pimelic acid (PA) to promote the β‐crystalline phase using Ca as anchoring. FTIR results revealed the presence of new bands at 1575 and 1413 cm−1, which were attributed to the anchoring of the PA molecule on the TiNT surface. TEM images of the TiNTs confirmed its tubular morphology before and after the functionalization, while the SEM/EDS analysis showed the good dispersion of carbon which can only come from the organic molecule employed in the functionalization. The nano‐reinforcements were incorporated by extrusion generating a filament to produce 3D‐printed specimens. The efficacy of the modified reinforcement as a β‐crystalline phase promoter was evaluated by wide‐angle x‐ray diffraction. The nanocomposite with 1% modified TiNTs showed the highest β‐crystal promotion with a kβ‐index of 89% while the nanocomposites reinforced with unmodified TiNTs reached only 15%. Furthermore, the thermomechanical and impact properties were characterized by dynamic mechanical analysis and Izod. In the first, the storage modulus (E′) was higher than the raw iPP for all nanocomposites, with an increase of about 148% and 107%, while the nanocomposite with a high percentage of β‐crystal showed an increase of 183% in the impact strength properties. A shift of Tg to higher temperatures was attributed to better interfacial interactions polymer/nano‐reinforcement because of the functionalization. The modified nano‐reinforcement was able to generate a 3D‐printed nanocomposite with higher stiffness and impact strength properties than the raw iPP.

The genetics in polymers: Crystallization as a fingerprint of the molecular microstructure

Hidden details of the molecular structure of polymers can be revealed from the retro-analysis of the crystallization behavior. The way a polymer crystallizes and the selection of a specific polymorphic form upon crystallization contain all the information about the structure of macromolecules. The intriguing challenge is how to extract this information from the formed crystals. The key is the construction of a model and the availability of model systems of polymer crystallization based on the exploitation of the phenomena of polymorphism and isomorphism and on the understanding of how such phenomena are affected by the presence of microstructural defects. The explanatory case study of isotactic polypropylene (iPP) prepared with Ziegler-Natta catalysts is here described. iPP shows an intricate polymorphic behavior, which may be successfully exploited to build models of the crystallization behavior and reveal hidden details of the complex molecular structure dictated by the heterogenous multi-site Ziegler-Natta catalysts. A model of the crystallization behavior of iPP has been defined through deep analysis of the crystallization of iPP and its copolymers synthesized with soluble organometallic catalysts that produce a simple molecular structure with perfectly random distribution of defects. In these model systems the crystallization of the α and γ forms depend only on the average length of the regular propene sequences that, in turn, depends on the concentration of defects. A precise correlation between the amount of crystallized γ form and the average length of regular isotactic propene sequences is the basic of this model. This correlation can be used in more complex samples where the concentration of defects is not known or when the distribution of defects is not random as in Ziegler-Natta iPPs, as calibration curve to evaluate the length of regular propene sequences from the crystallization behavior by simply measuring the maximum amount of crystallized γ form. The retro-analysis of the crystallization behavior of iPP allows to disclose hidden aspects of the molecular structure of the extremely complex Ziegler-Natta polypropylene and provides evidence of the blocky structure of chains of iPP (and polyolefins in general) synthesized with Ziegler-Natta catalysts. This retro-analysis exploits the presence of polymorphism and is possible only for polymers that can crystallize in different polymorphic forms that exhibit thermodynamic stability and crystallization kinetics which depend on the molecular structure and, in particular, on the presence of defects.

Ratio between Random Coil Size and Crystalline Spacing Determines Mesophase Formation in Quenched Isotactic Polypropylene

Ratio between Random Coil Size and Crystalline Spacing Determines Mesophase Formation in Quenched Isotactic Polypropylene

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.

Thermal oxidation of blends of polypropylene and polyamide 6/66. Effect of inhibition

The thermal oxidation of the blends of isotactic polypropylene (PP) and mixed copolyamide PA6/66 has been studied in a wide range of compositions: 0, 5, 10, 20, 30, 40, 50 and 100 wt % PA6/66. Data obtained by differential scanning calorimetry (DSC) and FTIR indicate the immiscibility of two polymer phases in the blends. The melting enthalpy of mixtures is increased during oxidation that is explained by chemi-crystallization of PP under PP oxidation. PA6/66 component is found to retard the growth of PP enthalpy during PP oxidation. According to DSC data on the PP/PA6/66 blends in air, PA6/66 phase greatly enhances the oxidation onset temperature of the PP/PA6/66 blends thus indicating the improved thermal stability of new material. The oxygen consumption of the PP/PA6/66 blends at 130°C proceeds with a large oxidation induction time (OIT) which is increased with increase in PA6/66 content. After OIT is ended, a constant oxidation rate is established, which is characteristic of the autoxidation mechanism. Kinetic analysis of the thermal oxidation of the PP/PA6/66 blends was carried out on the base of two models of polyolefin autooxidation with hydroperoxide decomposition via the 1st or the 2nd order reaction. The both models were found to describe the experimental kinetic curves of the oxygen consumption. Two possible explanations of the inhibition of PP oxidation by PA6/66 phase are discussed. The migration of active radicals from the PP phase to the PA6/66 phase with their transformation into low-active PA6/66 radicals may be responsible for inhibition and an increase in OIT of PP. Another mechanism of OIT increase may be related with a change in the structure of the PP/PA6/66 blends depending on PA6/66 content.

Organic polymers revolution: Applications and formation strategies, and future perspectives

The history of organic polymers is a remarkable journey from the discovery of natural materials like rubber and silk to the development of sophisticated synthetic polymers that have transformed industries and modern life. This comprehensive review article presents a detailed account of the evolution of organic polymers. It begins with the early uses of natural polymers and explores key breakthroughs, including the invention of Bakelite, nylon, and neoprene. The theoretical foundations of polymer science, laid by Hermann Staudinger, are discussed, and the post-war surge in polymer development is examined, including the introduction of polyethylene, polypropylene, and PVC. Notable advances in polymer chemistry, such as isotactic polypropylene and silicone polymers, are highlighted. The article also delves into the development of high-performance polymers like Kevlar and carbon-based materials, offering insights into their applications. Moreover, it discusses the current trends in polymer science, emphasizing sustainability and biodegradability. As the world continues to rely on polymers for numerous applications, this review provides a historical perspective and a glimpse into the future of organic polymers, where innovations are expected to shape various aspects of technology, healthcare, and environmental protection.

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 evolution of stereoselective olefin polymerization modeling

We review the story of stereoselective 1-olefin polymerization with a focus on the production of isotactic polypropylene. Starting from the visionary modeling of early TiCl3 catalysts, this contribution will move to introduce briefly to the modeling of stereoselective propene polymerization by homogeneous catalysts and will conclude with an outlook on the type of modeling and techniques that will likely dominate the near future.

The Impact of Carbon Nanotube on the Thermal Properties of Polypropylene

This research paper investigates the effect of the addition of carbon nanotubes (0.5 and 1.0% by weight) on crystallisation procedure in isotactic polypropylene. The study found that the crystallisation temperature increased with increasing nanotube content, while the crystallisation of polymers did not substantially change. The critical cooling speed, at which PP does not crystalize, increases with the increase in carbon nanotube content. Using the critical cooling speed and nanotube content, a nucleation effectiveness parameter was developed, that is not dependent on the crystallisation temperature or the CNT load. The study also found that carbon nanotubes only speed up the development of α-phase in isothermal crystallisation experiments. The control fibers had a shrinkage of 27% to 160°C, while the shrinkage of the composite fibers was less than 5%. The melting temperature of PP and its nanocomposites was approximately 150 to 152°C. However, the values for the degree of crystallinity of the nanocomposites rose along with the CNT content.

Evolution of the Deformation‐ and Flow‐Induced Crystallization and Characterization of the Microstructure of a Single Spherulite, Lamella, and Chain of Isotactic Polypropylene

AbstractIsotactic polypropylene (iPP) is a frequently used polymer in industrial processing and scientific research, used as a model material. This review highlights some current and forefront issues in polymer science and engineering. This review alludes to classical deformation schemes to interpret the complicated deformation in isotactic polypropylene as a semicrystalline polymer. Also, due to the complex hierarchical structures of crystallized polymers, the progress on the multiscale and multistage microstructural evolution covering each deformation stage from the initiation of plasticity until failure is mainly concerned, particularly in terms of crystalline morphology changes. Specifically, the characterization of the microstructure evolution of a single spherulite, lamella, and chain of isotactic polypropylene will be emphasized and mentioned. Here, the authors are most interested in the results obtained from stretching (strain‐induced) orientation and crystallization studies accompanied by the in situ scattering and spectroscopy techniques offering a detection window from nano to micrometer scale, which should be able to reflect the microstructural changes at different length scales of interest. During polymer processing, the melts are frequently subjected to shear or/and elongation flow fields, producing flow‐induced molecular chain orientation in the melt. The oriented molecular chains crystallize differently than those encountered under quiescent conditions. Thus, orientation‐induced crystallization has long been an object of intense interest. A vast body of research is reported about the effects of preorientation on the crystallization of various polymers. Among them, iPP is most frequently studied since its diversified structure and morphology are very sensitive to changes in processing conditions and molecular parameters.