Search Results (76)

This study investigates the effect of chemical modification of xylite—a fraction derived from Polish lignite—using succinic anhydride (SA) on the morphology and mechanical performance of isotactic polypropylene (iPP) composites. Xylite was incorporated at loadings of 1, 10, and 25 wt% and in two particle size ranges (40–63 µm and 63–125 µm), with and without SA (0.5 and 2 wt%). The composites were characterized by wide-angle X-ray scattering (WAXS), Fourier-transform infrared spectroscopy (FTIR), and tensile testing to evaluate crystallinity (X_c), β-phase content (k_β), and mechanical properties. Unmodified xylite reduced crystallinity (X_c down to ~37%) and significantly decreased ductility, with elongation at break strongly negatively correlated with filler content (r ≈ −0.68), indicating poor dispersion and weak interfacial adhesion. In contrast, SA addition (0.5–2 wt%) partially restored crystallinity (up to ~48%) and increased stiffness (Young’s modulus up to 2120 MPa), while altering β-phase content. FTIR analysis indicated reduced intermolecular hydrogen bonding between xylite surface hydroxyl groups in the presence of SA, consistent with interfacial chemical interactions, likely via esterification. The β-phase content showed a moderate positive correlation with xylite loading (r = +0.43) and a negative correlation with elongation at break (r = −0.46), suggesting that excessive β-phase formation may reduce toughness. Larger particles (63–125 µm) provided slightly improved elongation at break and stiffness. Overall, SA acts as both a compatibilizer and a morphology-directing agent, enabling precise control of the stiffness–ductility balance and crystalline structure in iPP/xylite composites. These results establish chemically modified lignite-derived fillers as a viable strategy for engineering cost-efficient polyolefin materials with tunable structure–property relationships, offering strong potential for scalable industrial implementation. Full article

This study investigated mechanical properties of composite materials consisting of an isotactic polypropylene (iPP) matrix reinforced with whisker-like fillers: carbon nanofibers (CBNF) and wollastonite (WN). We strove to develop mechanical models specifically for predicting yield stress and fracture toughness. Experimentally obtained results validated findings obtained using the proposed models. Regarding the elastic modulus, data suggest that conventional rules of mixture, typically used for glass fiber-reinforced polymers, remain applicable, indicating that filler addition enhances stiffness in a predictable manner. However, yield stress and fracture toughness exhibited distinct behaviors. Results revealed that these properties are governed predominantly by shear yielding of the iPP matrix rather than reinforcement effect of the fillers. Despite the presence of whiskers, the overall yield and fracture mechanisms depend heavily on the matrix’s plastic deformation and energy dissipation. The constructed models consistently explain these findings, supporting quantitative evaluation of the matrix’s contribution. These results emphasize that developing high-performance iPP composites requires knowledge of the intrinsic ductile properties of the matrix alongside filler selection and dispersion. Full article

An accurate prediction of the final properties of injection-molded semi-crystalline parts requires models that capture crystallization kinetics during processing. This work presents two practical strategies to incorporate experimentally derived crystallization behaviors into Autodesk Moldflow, addressing cases where kinetics differ from the software’s native Avrami–Hoffman–Lauritzen formulation. We apply these methods to isotactic polypropylene (iPP T30G) displaying heterogeneous nucleation with a low-temperature plateau, and to polyoxymethylene (POM) exhibiting combined heterogeneous and homogeneous nucleation. The parameters for Moldflow were obtained by matching isothermal half-crystallization times (t_0.5) and by tuning flow-induced nucleation terms. Validation against isothermal and non-isothermal injection tests shows agreement between calculated and expected crystallinity evolution and reproduces measured spherulite diameters. Full article

Isotactic polypropylene (iPP), solidified under high-pressure in the orthorhombic γ-form, can exhibit enhanced mechanical properties compared to iPP crystallized in the common monoclinic α-form under atmospheric pressure. The aim of the study was to enhance the mechanical performance of injection-molded iPP and its nanocomposite containing 5 wt% of multiwall carbon nanotubes (MWCNTs) through high-pressure processing, which induced the formation of the γ-phase. Initially, the materials were crystallized in a high-pressure cell. To simulate the conditions during molding, crystallization was carried out by pressurizing the molten polymer to 250 MPa. For comparison, crystallization was also performed during cooling under 200 MPa and 1.4 MPa. Subsequently, the injection molding was conducted under optimized conditions, under pressure of 250 MPa, to promote the formation of the γ-phase, and, for comparison, under 20 MPa, to favor the α-phase formation. The injection-molded nanocomposite crystallized in the γ-form, tested in compression, exhibited an elastic modulus, yield stress, and stress at break higher by approx. 50%, 35% and 40–50%, respectively, compared to injection-molded neat iPP solidified predominantly in the α-form. These results demonstrate that substantial improvements in mechanical performance can be achieved through the incorporation of MWCNTs into iPP and the optimization of high-pressure injection-molding conditions. Full article

Nanofibers, as nucleating agents, can significantly alter the nucleation and growth dynamics of polymer crystallization, thereby modulating the morphology and structure of crystals to enhance mechanical performance of the materials. In this study, the effects of nanofibrillar nucleating agent 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol (DMDBS) content, melting temperature, and injection speed on the crystallization behavior and mechanical performance of isotactic polypropylene (iPP) were systematically investigated. The incorporation of DMDBS significantly increased the number of iPP nuclei, reduced crystal size and raised the onset crystallization temperature by approximately 11 °C. Concurrently, the tensile strength and elastic modulus of injection-molded iPP samples improved by 15% and 55%, respectively. However, a rise in the melting temperature led to a decrease in the crystallinity, tensile strength, elastic modulus, and impact strength of both neat iPP and iPP/DMDBS samples. With the increase in injection speed, the tensile strength and elastic modulus of iPP/DMDBS samples increased. During the crystallization process, DMDBS crystallizes prior to the iPP melt, forming the nanofibrillar network that effectively reduced the energy barrier for iPP crystal nucleation. Furthermore, under the influence of shear forces during processing, the presence of these nanofibrillar networks promoted the formation of oriented crystalline structures, which in turn contributed to the enhanced tensile strength and elastic modulus observed in iPP samples. Full article

Superhydrophobic and superoleophilic nanofibrous or microfibrous membranes are regarded as ideal oil/water separation materials owing to their controllable porosity, superior separation efficiency, and ease of operation. However, developing efficient, scalable, and environmentally friendly strategies for fabricating such membranes remains a significant challenge. In this study, isotactic polypropylene (iPP) fibrous membranes with morphologies ranging from ellipsoidal stacking to microfiber stacking were successfully fabricated via a multistage stretching extrusion and leaching process using in situ microfibrillar composites (MFCs). The results establish a significant relationship between microfiber morphology and membrane oil adsorption performance. Compared with membranes formed from high-aspect-ratio microfibers, those comprising short microfibers feature larger pores and a more open structure, which enhances their oil adsorption capacity. Among the fabricated membranes, the iPP membrane with an ellipsoidal stacking morphology exhibits optimal performance, achieving a porosity of 65% and demonstrating both hydrophobicity and superoleophilicity, with a silicone oil adsorption capacity of up to 312.5%. Furthermore, this membrane shows excellent reusability and stability over ten adsorption–desorption cycles using chloroform. This study presents a novel approach leveraging in situ microfibrillar composites to prepare high-performance oil/water separation membranes in this study, underscoring their considerable promise for practical use. Full article

To improve the mechanical property and foamability of linear structured isotactic polypropylene (iPP), a second phase of polyamide11 (PA11) was introduced to the iPP matrix, and a low contented PP-g-MAH was added to adjust their compatibility. As a result, a high impact strength of 8.43 kJ/m² (a 118% increase compared to that of iPP) and an elongation at break of 465.87% (a 130% increase compared to that of iPP) of the compounded iPP/20PA11/10PP-g-MAH were achieved, which was attributed to the PA11 being well distributed in the iPP matrix and to the compatibility enhancement by PP-g-MAH. Depending on a suitable material formulation and a bath foaming strategic design, microcellular cells with an average size from 204.8 to 5.9 μm and a cell density from 6.0 × 10⁶ to 6.5 × 10⁹ cells/cm³ were obtained. Due to the significant enhancement of melt strength by partially melted crystals, combined with the synergistic effect of PA11, a quiet high expansion ratio of up to 37.9 was achieved. These manufactured foams have potential applications in packaging, thermal insulation, and other industrial fields. Full article

Polypropylene (PP), with its good physical, thermal, and mechanical properties and excellent processing capabilities, has become one of the most used synthetic polymers. It is known that the overall properties of semicrystalline polymers, including PP, are governed by morphology, which is influenced by the crystallization behavior of the polymer under specific conditions. The most important industrial PP remains the isotactic one, and it has been studied extensively for its polymorphic characteristics and crystallization behavior for over half a century. Due to its regular chain structure, isotactic polypropylene (iPP) belongs to the group of polymers with a high tendency for crystallization. The rapid quenching of molten iPP fails to produce a completely amorphous polymer but leads to an intermediate crystalline order. On the other hand, slow cooling yields a material with high crystalline content. The processing conditions that occur in practice and industry are between these two extremes and, in some cases, are even very close. Therefore, the study of limits in processability and the impact of extreme preparation conditions on morphology, structure, thermal, and mechanical properties fills a gap in the current understanding of how the processing conditions of iPP can be used to design the desired properties for specific applications and is in the focus of this research. The first set of samples (Q samples) was obtained by rapid quenching, while the second was prepared by very slow cooling from the melt to room temperature (SC samples). Testing of samples was performed by optical microscopy (OM), scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic dielectric spectroscopy (DDS), and mechanical measurements. Characterization revealed that slowly cooled samples exhibited a significantly higher degree of crystallinity and larger crystallites (χ ≥ 55% and L₍₁₁₀₎ ≈ 20 nm), compared to quenched samples (χ < 30%, L₍₁₁₀₎ ≤ 3 nm). Mechanical testing showed a drastic contrast: quenched samples exhibited elongation at break > 500%, while slowly cooled samples broke below 15%, reflecting their brittle behavior. For the first time, DDS is applied to investigate molecular mobility differences between processing-dependent structural forms, specifically the mesomorphic (smectic) and α-monoclinic forms. In slowly cooled samples, α relaxation exhibited both enhanced intensity and an upward temperature shift, indicating stronger structural constraints due to a much higher crystalline phase content and significantly larger crystallite size, respectively. These findings provide novel insights into the structure–property–processing relationship, which is crucial for industrial applications. Full article

The ecological aspect of substituting synthetic materials with natural materials is of great interest nowadays. This paper examines the percentage of lignocellulose-based fillers that can be added to a synthetic polymer matrix to ensure the resulting biocomposite maintains its dielectric properties. Biocomposites were made from isotactic polypropylene (iPP) and various proportions (20%, 30%, and 40%) of oats, rye, wheat, and barley bran and granules from corn cobs using a Brabender plastograph and a hydraulic hot press. From a morphological analysis, it was noted that the particles were well incorporated into the polymer matrix. The frequency-dependent behavior of the dielectric properties was analyzed across a frequency range from 30 Hz to 60 kHz at a room temperature of 23 °C and 35% relative humidity. The obtained results showed that the incorporation of biomasses into the iPP matrix increased the values of the dielectric properties across the entire measured frequency range. The samples with wheat showed the most stable values of the dielectric parameters with frequency changes, for all three concentrations. A linear regression analysis showed a very high coefficient of determination (R² = 0.997) between the effective dielectric permeability and filler concentration at 30 Hz for the samples with wheat. Furthermore, the biocomposite iPP/20% wheat showed a desirable balance of dielectric properties for electronic applications. The results showed that biocomposites obtained by adding cheap lignocellulose-based biomass, such as bran or granules from corn cobs, to a synthetic polymer matrix have a great potential for use as electrically insulating materials because their dielectric parameters are comparable to those of standard insulating materials. Full article

This paper elucidates the consecutive chain transfer reaction, initially to (p-vinylphenyl) methyl dichlorosilane (or (p-vinylbenzyl) methyl dichlorosilane), followed by hydrogen, during metallocene-catalyzed propylene polymerization by an isospecific metallocene catalyst (i.e., rac-dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride, I)/ activated with methylaluminoxane (MAO), rendering a catalytic access styryldichlorosilane capped isotactic polypropylenes (iPP). The PP molecular weight is inversely related to the molar ratio of [(p-vinylphenyl) methyl dichlorosilane]/[propylene] and [(p-vinylbenzyl) methyl dichlorosilane]/[propylene]. Every polypropylene chain formed presents a terminal (p-vinylphenyl) methyl dichlorosilane (or (p-vinylbenzyl) methyl dichlorosilane) unit. Hydrogen enhances the concentration of the starting arm polymer for the subsequent synthesis of the star polymer by increasing the incorporation of the chain terminal group. In order to create star polymers with isotactic polypropylene(iPP) as the arm and a siloxane cross-linking structure as the core, the terminal dichlorosilane iPP unit can work up (with water) to create cyclic siloxane oligomer interlinkages between iPP chains. Full article

This study investigates the correlation between the crystallinity and mechanical properties of calendered isotactic polypropylene (iPP) foils, focusing on the influence of haul-off speed and additive type. Two groups of iPP foils produced on an industrial scale were compared: (i) foils containing 10 wt.% recycled PP at haul-off speeds of 2 and 10 m/min; and (ii) foils with different additives (neat PP, 10 wt.% recycled PP, and PP random copolymer) at a constant haul-off speed of 10 m/min. All foils exhibited a pronounced skin–core structure, with the inner surface showing higher crystallinity (up to 10%) due to slower cooling rates, as determined by Flash Differential Scanning Calorimetry (Flash DSC). Nanoindentation tests correlated these differences in crystallinity with variations in the hardness and elastic modulus across the cross-section of the foil. Higher haul-off speeds (10 m/min) resulted in increased crystallinity, a higher elastic modulus and higher hardness. Polarized optical microscopy (POM) confirmed the morphological differences and highlighted the presence of highly oriented skin layers and stratified crystalline structures. These findings emphasize the significant influence of processing conditions, such as hauling speed and the addition of recycled polypropylene or a random copolymer, on the mechanical and optical properties of iPP foils. This comprehensive approach to characterizing complex structure–property relationships is valuable for optimizing the production and performance of polypropylene-based packaging foils on an industrial scale. Full article

The electron donors (ED) in Ziegler–Natta (Z-N) catalysis are classified as internal electron donors (IED) and external electron donors (EED), and both IED and EED are indispensable components for enhancing the catalytic reactivity and regulating the stereoregularity of polyolefinic materials in a typical industrial Z-N catalytic process. With the intensive research on ED, the Z-N catalyst performances have experienced successive progress in the last few decades. Polypropylenes (PP) as a commodity polyolefin material, especially the isotactic PP (iPP), are produced in multi-billion pounds per annum by utilization of the various IED- and EED-assisted Z-N catalysts systems. In the course of developing Z-N catalysts, the ED constitutes a key component of the content and represents a significant area of future research. In this review, we introduced a concise overview of the functions of IEDs in the generations of Z-N catalyst systems and the widely used IED types (A total of 11 different types of IEDs are encompassed within this study) that have been developed so far. In addition, we focused on the coordination modes of different IEDs in the MgCl₂-supported Z-N catalyst system and analyzed the effects of different types of IEDs on the PP isotacticity, regioselectivity, hydrogen sensitivity, and briefly introduced the application of environmentally friendly rosinate and salicylate IEDs. Full article

Polypropylene (PP) is regarded as a recyclable material for high-voltage direct current (HVDC) cable insulation due to its high melting point and electrical resistivity. This work focuses on the effect of the β-nucleating agent content on the electrical tree growth characteristics in isotactic PP (iPP) insulation. The results demonstrate that adding β-nucleating agents promotes the growth of β-crystals while limiting the α-crystal content. The crystallinity improves with the reduction in the average size of spherulites due to the addition of a β-nucleating agent with 0.1 wt% content. Electrical tree experiments show that the electrical tree growth rate declines as the nucleating agent content rises from 0 to 0.1 wt%. Meanwhile, the expansion coefficient increases with higher nucleating agent content. Continuous increases in the nucleate agent content result in the upward growth rate of electrical trees. When the nucleating agent content is below 0.1 wt%, the α–β-crystal interface introduced by the agent suppresses carrier migration and limits impact ionization, leading to the slower growth rate of the electrical tree. Further addition of the nucleate agent induces a β–β-crystal interface with weak coupling in carriers. It is concluded that β-nucleating agent-modified PP with 0.1 wt% content has potential application in HVDC cable insulation. Full article

Moisture has been a crucial problem during the operation of cable systems. When we are faced with polypropylene (PP)-based insulation for the development of cable systems, there are few reports on the effects of water intrusion on the electrical performances of PP. In this study, the water absorption characteristics of isotactic PP (iPP) and atactic PP (aPP), as well as their effects on volume resistivity and relative permittivity, were investigated. The structure evolution during the water absorption process of the two PPs was also compared via infrared spectra and X-ray diffraction analyses. The results show that both of the two PPs show a saturation of water absorption at ~216 h, even though there are structural differences. And water intrusion into bulk could increase the interplanar spacing of iPP while decreasing the interplanar spacing of aPP. Moreover, with the increase in water absorption, the volume resistivity of the two PPs show a decreasing trend while the relative permittivity presents an increasing behavior, which shows an almost linear correlation. Full article

This study investigates the potential for recycling fishing rope waste from the Magdalen Islands, Canada, into sustainable wall cladding panels, addressing both environmental concerns and waste management challenges. A comprehensive characterization of the fishing ropes was conducted using various analytical techniques to assess their suitability for recycling. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) identified polyethylene (PE) and isotactic polypropylene (iPP) as the main polymers present in the ropes, with a composition of approximately 25% PE and 75% PP. The effects of photodegradation were evaluated through carbonyl index analysis, differential scanning calorimetry (DSC), tensile testing, and gel permeation chromatography (GPC). The results showed reduced crystallinity, a 20% decrease in tensile strength, and lower molecular weights due to environmental exposure in comparison with unused ropes. However, melt flow rate (MFR) measurements aligned with virgin HDPE and PP values used in rope manufacturing, indicating suitable processability for recycling. Panels produced from recycled fishing ropes exhibited lower flexural and impact properties compared to commercial alternatives due to the presence of mineral contaminants and voids in the panels as revealed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). This comprehensive investigation provides valuable insights into the potential repurposing of fishing rope waste, contributing to the development of sustainable waste management strategies for coastal communities. Full article