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Thermoplastic vulcanizate (TPV) with fascinating high elasticity has been received the ongoing research attention in the application of sealing system for the engineering machine. However, there still exists one factor, the plastic strain of plastic matrix adjacent to rubber particles in equatorial direction, which has greatly inhibited the resilience improvement of TPV. Traditional in-situ online experiments could not accurately obtain and quantify the stress-strain evolution behavior of heterogeneous rubber-plastic materials, crucial for resilience. Herein, one kind of TPV based on polyamide thermoplastic elastomer (TPAE) and ethylene-propylene-diene monomer (EPDM) with outstanding rebound resilience has been fabricated via introducing the interfacial compatibilization reaction and reinforcing particles during the melt-reactive blending. One three-dimensional representative volume element (3D-RVE) model has been established to analyze the deformation mechanism of such designed TPV in this work compared with that for TPV based on polypropylene (PP) and EPDM. By analyzing the forces on the RVE mesh units, it could reveal that the TPAE matrix exhibited more uniform stress transfer behavior at the thin ligament, and the recovery behavior of TPV matrix mainly occurred at the thin ligament. This work would provide important value for the preparation of new high elastic TPV materials from a microscopic level. [Display omitted] • A TPV with excellent resilience was prepared by melt blending with interfacial compatibilization and nano filler, offering 39% higher resilience than EPDM/PP TPV. • A 3D-RVE model of TPAE-based TPV was established to analyze the deformation mechanism compared to PP/EPDM-based TPV. • The stress-strain evolution and plastic strain inhibition of this TPV can be quantified, potentially improving on traditional methods. [ABSTRACT FROM AUTHOR]

Although calcium pimelate (CaPim) is recognized as an efficient β-nucleating agent for polypropylene with nucleating ability solely for the β-phase, it was found to induce less β-phase in polypropylene random copolymer (PPR) compared to polypropylene homopolymer (PPH). Generally, this reduction is attributed to unfavorable β-growth. Besides growth, here, nucleation behavior was also investigated in detail. With nucleation barrier determined through fractionated crystallization, the relative β-nuclei proportion induced by CaPim was calculated to be 96.6 % for PPH and 79.1 % for PPR with 7.3 mol% ethylene inserted. This fewer β-nuclei induction may be linked to a decreased proportion of isometric sequences exceeding the critical length required for β-nucleation. As expected, the relative growth rate of the β- to α-phase (G β / G α) is lower in PPR indicating unfavorable β-growth. These results indicate that diminished β-nuclei induction and subsequent unfavorable β-growth jointly result in less β-phase induction in PPR. Less β-phase induction in PPR arises from the combined effect of fewer β-nuclei induced by CaPim during the nucleation stage and the subsequent unfavorable β-growth. [Display omitted] • CaPim induces less β-phase in PPR than in PPH. • Lower I β / I value indicates fewer nuclei induction by CaPim in PPR. • I β / I value is associated with the isometric sequence distribution of PP resins. • Lower G β / G α value indicate unfavorable β-growth in PPR. • Fewer β-nuclei induction and unfavorable β-growth result in less β-phase in PPR. [ABSTRACT FROM AUTHOR]

For microstructure characterization of polyolefin by separation-based techniques with infrared detector, either 1,2-dichlorobenzene (o-DCB) or 1,2,4-trichlorobenzene (TCB) is commonly selected as a dissolution solvent and mobile phase. Herein, we studied the effects of o-DCB and TCB on the comonomer detection and chemical composition distribution (CCD) by crystallization elution fractionation (CEF) with a filter-based IR detector. We first compared the detector sensitivity on methyl group content or short chain branching (SCB) in polyethylene-co-butene with varied sample concentrations in o-DCB and TCB. TCB demonstrated superior comonomer detection in the IR detector with a single linear calibration across a wide range of sample concentrations. In contrast, o-DCB displayed stronger concentration dependent methyl group response, requiring a more complex equation in the calibration. Furthermore, o-DCB provided better separation of comonomer distribution with less peak broadening and co-crystallization effects, as observed with various polyolefins, including high density polyethylene (HDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), and ethylene-propylene copolymer (EP). [Display omitted] • Solvent selection (o-DCB or TCB) influences comonomer detection sensitivity, which can be addressed by a modified calibration. • o-DCB offers better separation of the comonomer distribution with minimal peak broadening and co-crystallization effects. • Solvent choice (o-DCB vs. TCB) significantly affects PP peak temperature in CCD analysis, unlike PE. [ABSTRACT FROM AUTHOR]

Polyolefins, such as polyethylene and polypropylene, are low-surface-energy materials that are poorly adhesive owing to weak van der Waals (VDW) forces. While physical bonding offers an attractive alternative to conventional VDW-based adhesion, the development of adhesion methods based on this mechanism requires an understanding of the fracture mechanism of adhesive interfaces. Herein, we reveal the fracture mechanism associated with "nailing adhesion," in which two polymers are tightly bound physically by needle-like polyolefin crystals at a polyurethane/polyolefin adhesive interface. The mechanism was directly observed by transmission electron microscopy using the modified copper-grid technique. The peel strength and fracture mechanism depended on the polyolefin type (polyethylene or polypropylene). During crack growth at the adhesive interface, needle-like polyethylene crystals deform and finally break, whereas needle-like polypropylene crystals snap with crazing. The deformation of needle-like polyethylene crystals enhances peel strength more than the crazing and snapping of needle-like polypropylene crystals. [Display omitted] • Needle-like polyolefin crystals physically bind two polymers via nailing adhesion. • Fracture at the adhesion interface was directly observed by TEM. • Polyethylene crystals deform, whereas polypropylene crystals snap with crazing. • Deformation of needle-like crystals enhances peel strength by energy dissipation. [ABSTRACT FROM AUTHOR]

Polyolefinic thermoplastic vulcanizates (TPVs) composed of iPP (isotactic polypropylene) and crosslinked EPDM (ethylene-propylene-diene rubber) prepared by dynamic vulcanization process exhibit rubber domains dispersed in the iPP matrix, even though the EPDM component is the major component. Here we proposed a kinetic nonequilibrium constitutive equation that considers the transition of the mechanical nature from plasto-rigid deformation to rubbery deformation during uniaxial extension to explore the origin of the thermoplastic elastomer behavior of TPV (thermoplastic vulcanizate) materials. Fitting of the constitutive equation to the experimental stress‒strain curves quantitatively revealed the critical transition point of the mechanical properties. The transition shifted to higher strains with decreasing EPDM content. In situ wide-angle X-ray diffraction profiles monitored during the uniaxial extension confirmed the mechanical transition process. [Display omitted] • A nonequilibrium constitutive equation is analyzed for tensile behavior of TPV. • Mechanical transition is determined by in situ wide-angle X-ray diffraction. • Morphological feature under tension was identified by Takayanagi model. [ABSTRACT FROM AUTHOR]

The shear-induced crystallization of polypropylene (PP) in immiscible blends with poly(methyl methacrylate) (PMMA) was studied using three types of PMMA samples with different molecular weights. The addition of low-molecular-weight PMMA greatly enhanced the shear-induced crystallization of PP. Because the low-molecular-weight PMMA had low viscosity at high temperatures, the PMMA droplets dispersed in the PP were deformed in the flow direction and subsequently turned fibrous. As the temperature decreased, the viscosity of PMMA increased greatly prior to PP crystallization. Consequently, the deformed PMMA dispersions were hardly deformed further in the molten PP. It provided excess stress for PP in the flow direction, leading to a large Rouse-Weissenberg number. They thereby accelerated shear-induced crystallization of the PP. Because of the pronounced shear-induced crystallization, the orientation of the PP chains, which causes high rigidity, was greatly enhanced. [Display omitted] • PMMA with low molecular weight promoted shear-induced crystallization of PP. • Deformed PMMA droplets solidified during cooling and acted as rigid fibers. • Because of pronounced shear-induced crystallization, PP orientation was enhanced. • PMMA with high molecular weight barely affected shear-induced crystallization of PP. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) films have been widely used in medical, electronics, and construction fields due to their low cost and excellent comprehensive properties. However, the poor low-temperature toughness of PP films restricts its further applications in extreme cold environments. Here, the nacre-inspired 8-, 32-, 128-, and 512-layer PP/SEBS-based films were constructed via our multilayer blown systems. Compared to the conventional blended films, 128-layer films showed significant improvement under the low-temperature conditions, i.e., 160 %, 150 %, and 136 % in impact toughness, tear toughness, and elongation at break, respectively. The high toughening efficiency of the multilayer films is because of the nacre-inspired multilayer structures, which can develop the multi-stage propagation of the damage behavior such as craze and plastic deformation to dissipate much energy when mechanically broken. Since nacre-inspired PP/SEBS-based multilayer films show high efficiency in low-temperature toughening, this work may provide a possible solution to improving the low-temperature mechanical properties of PP films or even other types of polymeric films. [Display omitted] • PP/SEBS-based microlayer films up to 512 layers with a thickness of 140 μm were fabricated. • Excellent low-temperature toughening efficiency were achieved. • An industrial feasibility for large-scale production of high-toughness PP/SEBS-based films were provided. [ABSTRACT FROM AUTHOR]

Plant fiber reinforced composite has broad industrial application prospects, and has the trend of gradually replacing traditional materials, but there are also problems such as not obvious advantages of lightweight and poor toughness. In this paper, alkali modified bamboo fiber reinforced polypropylene (BF/PP) composite was prepared by supercritical foam injection molding. The effect of fiber content on the formability of BF/PP composite was studied. Furthermore, the strength and toughness of BF/PP composites were balanced by blending Ethylene Propylene Diene Monomer (EPDM) elastomers with different content under the optimal fiber content of 20 %. The physical and mechanical properties of BF/PP composites were studied. The results showed that the addition of bamboo fiber improved the structure of the cell and significantly enhanced the mechanical properties of the composite. The addition of elastomer EPDM effectively alleviates the problem of poor toughness and brittle fracture of bamboo fiber composites. The foam material density decreased by about 15 %, the addition of bamboo fiber brought the maximum 57.37 % tensile strength and 79.96 % flexural strength improvement to the polypropylene matrix. When the EPDM content was 10 %, the foaming effect of the material was the best, and the impact toughness increased by 34.42 % compared with pure polypropylene. This study expands the application prospect of the bamboo fiber reinforced polypropylene microcellular foam materials. [Display omitted] • The fiber was completely pretreated and chemically modified. • Physical microcellular foaming technology was adopted. • Effects of different fiber and EPDM content on composites. • Comprehensive performance assessment, including physical properties, mechanical properties and microstructure analysis. • The strengthening mechanism of bamboo fiber and EPDM on the properties of composites was described. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • 70/30 PP/PE blend crystallization investigated by fast scanning calorimetry (FSC). • FSC represents a suitable technique for polymer blends with phase dispersion at the micro level. • The self-nucleation of PP matrix at 100-1000 °C/s allows separation of PE and PP during melting. • 30 °C crystallization window for PE droplets in the self-nucleated iPP matrix could be explored. [ABSTRACT FROM AUTHOR]

Polyolefin (PO) blends are difficult to separate due to density and chemical structure similarities. The associated waste treatment in the context of mechanical recycling is therefore complicated by the establishment of multi-phase morphologies that are not yet fully understood. In the present work, a high density polyethylene (HDPE) with a very high melt flow index (MFI) and a polypropylene (PP) with a very low MFI are deliberately mingled to better understand the full spectrum of morphological variations for PO blending. The linkage with the control over injection mold-based mechanical properties such as tensile strength, elasticity modulus, elongation at break, and impact strength is made. This is done supported by the connecting of experimental analyses at different scales, including (i) the molecular scale via size exclusion chromatography and Fourier transform infrared spectroscopy (FTIR), and (ii) the meso-scale via scanning electron and polarized light microscopy as well as differential scanning calorimetry, including a differentiation between the bulk and surface region. Emphasis is both on blends processed once and re-processed either once, twice or three times. For the single processing, it is demonstrated that in most cases a droplet morphology is obtained, with smaller droplets in case HDPE is the minor component and with a dominance of HDPE at the surface even for 60% PP, due to a better HDPE flowability. It is further shown that the scission of PP chains and crosslinking of HDPE chains respectively facilitates and inhibits crystallization, at least if meso-scale -mixing as more evident during re-processing is not taking over. It is also highlighted that the properties of PP can be enhanced by adding up to 10 wt% HDPE, acting as a filler, and that the (ideally) reprocessed blends remain suitable for application. [Display omitted] • Morphological variations of polyolefin blends with large MFI differences for its components. • More molecular scale degradation but also more macro-scale mixing upon reprocessing. • Analysis at both surface and in bulk region to identify morphological gradients. • Optimized mechanical properties based on composition. • Guidelines on analysis of stability blends in view of mechanical recycling $. [ABSTRACT FROM AUTHOR]

Olefin block copolymer is one class of promising high-end material that has the potential to combine the performance advantages of individual blocks. In this work, a series of isotactic polypropylene (i PP)-based diblock copolymers was designed and synthesized by coordinative chain transfer polymerization using a dimethyl(pyridylamido)hafnium/[Ph 3 C][B(C 6 F 5) 4 ]/Al i Bu 3 catalytic system. The prepared diblock copolymers were composed of the regular i PP segments and the propylene/1,5-hexadiene (1,5-HD) random segments. The incorporated 1,5-HD existed exclusively as methylene-1,3-cyclopentane units in the polymer chains, because of the complete cyclization selectivity of the employed dimethyl(pyridylamido)hafnium catalyst. These block copolymers possessed high melting temperatures over 158 °C. Moreover, the block copolymers exhibited remarkably improved mechanical properties with respect to i PP, which could be systematically tuned by adjusting the content of 1,5-HD. In the 1,5-HD content range of 3.4–11.0 mol%, the block copolymers exhibited both high yield stress and high elongations at break. The copolymerization approach of block copolymers provided an effective method to achieve the strength-ductility balance of i PP-based copolymers. [Display omitted] • The isotactic polypropylene-based block copolymers consist of hard and soft blocks. • The 1,5-hexadiene incorporated in the soft blocks underwent the complete cyclization. • The i PP-based block copolymers exhibit both high yield strength and elongation at break. [ABSTRACT FROM AUTHOR]

Compared with traditional injection foaming, co-injection foaming serves as a method to prepare products with high-quality surfaces and enhanced mechanical properties, demonstrating excellent technical advantages and economic benefits. The effects of high-density polyethylene (HDPE) content, foaming agent content, melting temperature of core material, and nano-organic montmorillonite (OMMT) content on the cell structure, mechanical properties, and crystallization behavior of isotactic polypropylene (iPP)/HDPE composite foam prepared by co-injection foaming were systematically studied. At a foaming agent content of 2 wt.%, HDPE content of 30 wt.%, OMMT content of 3 wt.%, and the melting temperature of core material of 190 °C, the composite foam exhibited a cell size measuring 85 μm, a cell density of 2.5 × 105 cells/cm3, a tensile strength of 25.8 MPa, and an impact strength of 12.5 kJ/m2. The addition of HDPE reduced the crystallinity of iPP matrix, while enhancing the solubility of carbon dioxide within the matrix. The non-miscible interface between HDPE and iPP helped reduce the energy barrier for cell nucleation. Furthermore, the introduction of OMMT as a nucleating agent in iPP/HDPE composite material dramatically decreased the energy barrier for cell nucleation. These synergistic effects result in foam with the smaller cell size and the higher cell density, exhibiting excellent comprehensive mechanical properties. This work provides a feasible method for preparing composite foam with excellent comprehensive performance. [Display omitted] • The addition of HDPE reduced the crystallinity of iPP matrix, while enhancing the solubility of CO 2 within the matrix. • The non-miscible interface between HDPE and iPP helped reduce the energy barrier of cell nucleation. • The introduction of OMMT in iPP/HDPE composite material dramatically reduced the energy barrier of cell nucleation. [ABSTRACT FROM AUTHOR]

The distinctive oil gelation characteristics of styrene-ethylene-butylene-styrene (SEBS) thermoplastic elastomers were utilized for successful oil spill remediation with a range of different oils. Porous non-woven SEBS mat was fabricated via melt blown processing using a twin-screw extruder with customized blow die. After conducting rotational and capillary rheology investigations, a heightened melt-blowing temperature (300 °C) was applied to achieve an elevated melt flow index of SEBS for the melt-blowing process. Under optimized blowing parameters, a non-woven fabric was obtained consisting of fine fibers featuring an average fiber diameter of 20 μm. The material and oil absorption properties of the engineered SEBS fabric were compared to polypropylene (PP) nonwovens, a widely used material for oil spill mitigation that relies solely on adsorption and capillary forces to separate and immobilize spilled oil. SEBS nonwovens exhibited outstanding absorption and gelation properties for both crude petroleum and mineral transformer oil. Notably, SEBS demonstrated the ability to immobilize oil even under head pressure and at saturation, surpassing the capabilities of PP nonwovens (average fiber diameter 12 μm). This showcases a more efficient and cleaner method for remediating oil spills by effectively separating oil from water through absorption. [Display omitted] • Synchronous pyrolysis and activation transform PET bottles to functional carbon. • The pyrolysis and activation parameters dictate the yield and porosity of the activated carbon. • The surface area and surface charge levels of the activated carbon determines the adsorption potential. • The activated carbon's dye adsorption efficiency can be tuned by adjusting the wastewater pH. [ABSTRACT FROM AUTHOR]

Weak interfaces can impede crack propagation in rigid natural materials containing small amounts of organic compounds. Inspired from this, we start from the core-shell structured isotactic propylene (iPP)/polypropylene random copolymers (PPR) homocomposites and construct serval kinds of interfaces to study the toughening mechanisms by applying the crystallization epitaxies of PPR on iPP. Through molecular chain diffusion and crystallization epitaxy, derived models from microscopic core-shell structured crystals in the homocomposites to macroscopic layer-by-layer assemblies with different interfaces are established to magnify the role that each layer plays during crack initiation and propagation. As a result, the ductile β-PP interface can decrease crack tip strength so that a further step of crack initiation is triggered in the composite laminates with a fold of fracture energy consumption compared to the laminates with weak or rigid interfaces. At last, we come back to the core-shell structured homocomposites and toughen them with an improve in impact toughness from ∼10.8 to ∼18.2 kJ/m2 by manipulating the content of ductile interfaces. This work provides a novel research routine and a new toughening mechanism toward the toughening of PP and can be extended to study the fracture mechanisms of other toughening systems with core-shell structures. [Display omitted] • Layer-by-layer assemblies were established to study the crack initiation and propagation of core-shell structured crystals. • Ductile β-PP interface can decrease crack tip strength for a further step of crack initiation. • The manipulation on weak interfaces can improve the impact strength of PPR/iPP/β-NA composites from ∼10.8 to ∼18.2 kJ/m2. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) membrane with low porosity and poor hydrophilicity limits the performance of lithium-ion batteries. In mechanism, the function of amorphous structure of precursor film on microporous structure of PP membrane is yet unknown. In this work, the porous and hydrophilic PP/reduced hydroxyl-modified polypropylene (PPrOH) membrane was fabricated by blending esterified-PPOH firstly and then hydrolyzing to introduce the hydrogen bond in amorphous region and avoid phase separation. The results showed that the hydrogen bond was successfully introduced into the amorphous region of PP/PPrOH film and led to an increase of physical crosslinking points. Therefore, a large region of microphase separation emerged in the PP/PPrOH membrane after cold stretching, which resulted in a 45.6 % increase of porosity at maximum compared to the PP membrane. Besides, the hydrophilicity of PP/PPrOH membrane was improved with the blend content exceeding 10 wt%. Eventually, the lithium-ion conductivity of PP/PPrOH-10 membrane enhanced by 37.5 % over the base PP membrane. This work provides a novel perspective for preparing hydrophilic PP membrane with high porosity. [Display omitted] • Introducing hydrogen bond in amorphous of PP film by melt blending with PPrOH. • Hydrogen crosslinking in amorphous results in more region of microphase separation at stretching. • Addition of PPrOH increases porosity by 45.6 % and enhances lithium-ion conductivity by 37.5 % compared to PP membrane. • Crosslinking density in amorphous is positively correlated with porosity of membrane. [ABSTRACT FROM AUTHOR]

The utilization of recycled waste plastics presents a promising opportunity for the development of filament for fused filament fabrication (FFF). This approach holds the potential to effectively conserve resources, mitigate solid waste generation, and contribute to the reduction of greenhouse gas emissions. The present study involves the processing of recycled polypropylene (rPP) into filaments with the purpose of manufacturing 3D printed components and the effects of the processing parameters on the properties of the printed parts. The selection of manufacturing parameters for 3D printing of rPP relies on the material-specific characteristic values, including glass transition temperature, melting temperature, viscosity, etc. More importantly, a novel methodology with the self-diffusion coefficient by applying the real-time cooling rate of rPP was devised to determine the total accumulated diffusion, which enables the prediction of mechanical performance by considering the local thermal conditions during material bonding between individual strands and different layers. The finding of the study indicates that the specimen fabricated by using elevated temperature and minimal time interval, which correlates with a high total accumulated diffusion, exhibited enhanced mechanical properties between the strands those are comparable to properties of the injection-molded virgin polypropylene. [Display omitted] • Effects of the processing parameters on the performance of filament fabricated rPP were studied. • Novel methodology of the self-diffusion coefficient was applied for exploring the mechanical performance of printed rPP. • The mechanical performance increased with increasing the total accumulated diffusion. • rPP performs on par with injection-molding level. [ABSTRACT FROM AUTHOR]

The results of studies of optical properties in UV, visible and IR spectral regions, and radiation resistance of nanocomposites based on polypropylene modified with nanoparticles of oxide compounds (ZrO 2 , Al 2 O 3 , SiO 2 , MgO, TiO 2 , ZnO) are presented. Diffuse reflectance spectra were recorded under 2 ∙ 10−6 torr vacuum before and after electron irradiation (in situ, Е = 30 keV, F = 2 ∙ 1016 cm−2). According to research findings, modification of polypropylene with nanoparticles leads to an increase in radiation resistance, which depends on the structure of the nanopowders, their size and specific surface area. The SiO 2 nanopowder, characterized by its amorphous nature, the largest specific surface area, and the smallest particle size, stands as the most effective modifier for enhancing radiation resistance. The IR-Fourier spectra of electron-irradiated samples are similar to the original spectra. A slight decrease in transmission across all characteristic bands compared to the non-irradiated samples indicates minor structural changes as a result of irradiation. [Display omitted] • Modification of polypropylene (PP) with oxide nanoparticles was carried out. • Modification makes it possible to increase the radiation resistance of the optical properties of PP. • Mechanisms for such an increase in stability upon irradiation of PP by modification with nanoparticles have been proposed. • The best modifier was selected to increase the radiation resistance of the optical properties of PP. [ABSTRACT FROM AUTHOR]

The cavitation behavior of polypropylene-silica (PP-silica) and high density polyethylene-silica (HDPE-silica) composites with varying silica content during uniaxial tension was investigated via in situ X-ray techniques. The introduction of silica was found to significantly influence the mechanical properties of the materials. Small-angle X-ray scattering (SAXS) was employed to determine the cavitation onset strain and to observe the evolution of cavity structures. Through model fitting, the size evolution of nanoscale cavities at the onset of cavitation was quantitatively characterized. Scanning electron microscopy (SEM) was utilized to examine the morphology before and after stretching, revealing that cavity structures primarily resulted from internal defects in the polymer matrix and interfacial debonding between silica and the polymer. The long axis of the nanoscale cavities at the onset of cavitation was perpendicular to the tensile direction, and further deformation led to the coalescence into micron-sized cavities with the long axis parallel to the tensile direction. Wide-angle X-ray scattering (WAXS) was used to characterize the microscale deformation process of crystals, showing that during stretching, the lamellae reoriented with the angle between their normal direction and the tensile direction gradually decreasing. Several sets of transition strains representing the plastic deformation were used to compare the microscale and macroscale deformation, elucidating the sequence and differentiation between crystal plastic deformation, cavitation, and yield in the two polymer materials. Intriguingly, both PP-silica and HDPE-silica composites exhibited optimal silica additions and initial structural parameters for regulating cavitation behavior. These findings offer significant guidance for the control of internal structures in porous separators in industrial production. [Display omitted] • Cavitation in stretched polymer-silica composites was studied by in-situ SAXS/WAXS. • Cavitation within the polymer matrix and interface debonded was strongly affected by silica. • Cavity evolution starting from nanoscale and advancing to microscale was unveiled. [ABSTRACT FROM AUTHOR]

The impact of flow on semi-crystalline polymer transformation is crucial, influencing crystallization kinetics, final structure, and part properties. In injection molding, a commonly used polymer transformation process, molten polymers undergo intense shear flow fields. These conditions alter crystallization and morphology, leading to morphologies distinct from quiescent crystallization and thus to peculiar material properties in the final product. The highly non-linear nature of flow-induced crystallization poses scientific challenges, and a comprehensive predictive modeling approach is still lacking. Experimental work has focused on understanding morphological development during stress-induced crystallization, varying temperature, velocity, and shear time, along with rheo-optical measurements. This study investigates the effects of shear flow on isotactic polypropylene (iPP) using a Multi-Pass Rheometer (MPR), aiming to understand the relationship between processing conditions and final polymer morphology. The MPR reproduces flow conditions encountered during injection molding and enables the study of shear-induced crystallization kinetics. Experiments at 138 °C with varying shear rate and time are monitored on-line by using birefringence measurements. Optical microscopy images reveal a morphological transition based on shear conditions. [Display omitted] • Flow significantly affects semicrystalline polymer crystallization kinetics, impacting solidification history and final part properties. • A device mimicking injection molding shear rates, offering real-time birefringence data on crystallinity changes was adopted. • Longer shear times and higher shear rates accelerate crystallinity evolution due to increased nucleation. • The applied model for flow-induced crystallization model aligns with experimental birefringence data. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Evolution of phase morphology of nascent IPC upon melting is described. • Formation process of the core-shell structure is revealed. • PP in the matrix is not encapsulated into the disperse phase in melt processing. [ABSTRACT FROM AUTHOR]

In this work, the morphology development of polypropylene (PP)/polyamide 6 (PA6) blends was thoroughly investigated under in-situ fibrillation process, including shear mixing flow and uniaxial elongational flow. By establishing rheological constitutive model based on Trouton Rules, the shear and elongational rheological characteristic parameters of PP and PA6 were obtained for the establishment of the prediction model. In the shear mixing process, different screw speed was applied to evaluate the effects of the shear flow on PA6 original particle size in PP/PA6 blends. In the uniaxial stretching process, the elongational flow field characteristics were obtained through solving dynamic equation with Fourth-order Runge-Kutta method. And the evolution of PA6 droplets in obtained elongational flow field characteristics was analyzed by combining SEM results of PP/PA6 in situ fibrillar composites and theorical parameters of the deformation and breakup of the droplets (the reduced capillary number Ca*). Finally, based on force balance theory, the dynamic model of morphology development of PA6 dispersed phase in PP matrix was defined under the whole in situ fibrillation process. By comparing with experimental values, it was found that the established model was supposed to be able to predict the phase morphology development of polymer droplets well when the original particle size was smaller, and when the original particle size was larger, the coalescence between the droplets should be further considered. [Display omitted] • The polymer phase morphology is developed from spherical to fibrillar under the in-situ fibrillation technique. • The flow field characteristics of the uniaxial elongational flow is solved with four-order Runge-Kutta methods. • The dynamic prediction model describing the phase morphology evolution is established under the whole in situ fibrillation process. • At relatively smaller original particle size, the prediction model fits well with the experimental results. [ABSTRACT FROM AUTHOR]

Isotactic polypropylene (iPP) composites filled with electrospun isotactic polystyrene (iPS) fibers were prepared through solution blending by sonication in a nonsolvent water bath. After optimal sonication treatments, the entangled and surface-fused iPS fibers in the nonwoven fabrics were disentangled and separated to facilitate better dispersion in the as-prepared composites. Composites with different fiber concentrations (0.01, 0.1, and 1 wt%) subjected to various thermal treatments were characterized using DSC, POM, and simultaneous WAXD/SAXS. The effects of cooling rates and crystallization temperatures on the formation of β -form crystals and lamellar morphology were extensively studied. Results showed that electrospun iPS fibers are novel β -nucleating agent towards iPP to enhance crystallization rate. A β -form content of ∼50% was achieved at a fiber concentration of 0.1 wt%, and the β -form content increased with increasing cooling rate. Under isothermal crystallization, the maximum β -form content was found at 120 °C, lying between the T αβ and T βα ; the former is associated with α -to- β and the latter is relevant to the β -to- α crystal transformation due to the difference in the growth rates of both α and β phases. This finding is consistent with POM observations, revealing that a transcrystalline layer of dense α -form nuclei is first induced at the iPS fiber surface for initial crystal growth, followed by α -to- β bifurcation growth to develop highly birefringent β -form crystals. The average lamellar thickness derived from SAXS results is dependent on the supercooling degree, as well as on the relative content of α/β crystals developed in the composites. Image 1 • Electrospun iPS fibers are found to be dual-nucleating agent for iPP to produce both the α and β phases. • A β -form content of ∼50% is achieved at a fiber concentration of 0.1 wt%. [ABSTRACT FROM AUTHOR]

Interfacial effects can significantly perturb the properties of nanocomposites. Modification of filler surfaces can improve filler dispersion and compatibilize the polymer-filler interface, leading to property enhancements relative to composites made with unmodified filler. Here, we have isolated the effect of interactions between matrix polymer and polymer-grafted nanoparticles (PGNs) from dispersion quality and studied how the interactions affect the properties of polypropylene (PP)/halloysite nanotube hybrids in the absence of entanglements between matrix PP and grafted PP. We prepared PP hybrids with pristine halloysite nanotubes (p-HNT) or PP-grafted halloysite nanotubes (PP-g-HNT) up to 10 wt% filler using melt mixing or solid-state shear pulverization (SSSP). For melt-mixed samples, PGN-type filler yields better property enhancement than pristine filler, consistent with the combination of improved dispersion and polymer-filler interactions. As shown by microscopy and rheology, hybrids prepared by SSSP with p-HNT and PP-g-HNT fillers have very similar, high levels of dispersion, eliminating dispersion quality as a factor in property improvements. In comparison with well-dispersed PP/p-HNT nanocomposites at the same filler level, well-dispersed PP/PP-g-HNT nanocomposites prepared by SSSP exhibit enhanced tensile strength but the same values within error of Young's modulus and elongation at break when there is no entanglement between matrix polymer and grafted chains. Notably, at the same filler level, well-dispersed PP/PP-g-HNT nanocomposites exhibit higher crystallization rate and nucleation efficiency (NE) that is 2.5–4.5 times higher than well-dispersed PP/p-HNT hybrids. The impact of grafted PP chains on NE is so strong that at the same filler level but with worse dispersion, PP/PP-g-HNT hybrids made by melt mixing exhibit NE values 2.1 to 3.4 times higher than well-dispersed PP/p-HNT nanocomposites made by SSSP. Image 1 • PP hybrids with pristine or polymer-grafted nanoparticles (PGNs) were made by SSSP. • Similar, high levels of dispersion were achieved regardless of filler modification. • Effects of nanofiller-polymer matrix interactions were isolated from dispersion. • Nanocomposites with PGNs exhibit better tensile strength and crystallization rate. • Young's modulus, ductility, and crystallinity are independent of filler modification. [ABSTRACT FROM AUTHOR]

In this work, for the first time, the effect of graphene oxide on the photodegradation behaviour of polypropylene-graphene oxide nanocomposites is presented. The graphene oxide was characterised, and AFM images show that the GO can be classified as multilayer-GO (mGO). Based on previous work, two new methods were used, liquid-phase feeding (LPF) and solid-solid deposition (SSD), to insert pre-exfoliated mGO into the polymer matrix. Moreover, the morphology and structure of the nanocomposites were analysed using an optical microscope, rheological and dynamic mechanical analysis, x-ray diffraction, and differential scanning calorimetry. The results show that stacked layers are obtained, especially for the SSD method, since it decreases the nanocomposites viscosity, mostly due to the self-lubricity of mGO layers. Finally, the photodegradation behaviour was investigated and revealed that mGO plays an important role, with a factor of three increase regarding photodegradation resistance, when compared to pure polypropylene. Image 1086 • The LPF method shows smaller particle sizes compared to the SSD method. • Shear viscosity of nanocomposites decreases due to the intrinsic self-lubricity of mGO. • DMA show the mGO particles are localised in the amorphous region, preferentially. • The mGO particles delay the photo-oxidative process by the screen mechanism. • A stabilization factor of three times is observed for the nanocomposites. [ABSTRACT FROM AUTHOR]

How the reduction of macromolecular entanglements in two polypropylenes affects their rheology and mechanical properties, as well as their isothermal and non-isothermal crystallization has been investigated. In the partially disentangled polymers, lower values of viscosity were observed. The mechanical test in compression showed that strain hardening was slower in partially disentangled polymer. However, the crystallization was faster when the polypropylene had a reduced density of entanglements. In the second part of the experiments, it was investigated how quickly entanglements are re-established in the partially disentangled polymer subjected to annealing in the melt. The time of re-entangling was longer if the polypropylene was less entangled, there was a lower annealing temperature, or the polymer had a higher molecular weight. It turned out that the times of re-entangling measured in three different experiments varied significantly. This time was 60–150 min during crystallization studies, 120–180 min during the mechanical properties studies and well above 120 min in rheological researches. The reason for this is the different dependence of the individual properties of polypropylene on the degree of macromolecular entanglement. Image 1 • Reduction of macromolecular entanglements leads to changes in PP properties. • Rheology, mechanical properties and crystallization depends on entanglements. • Annealing of PP leads to reconstruction of the equilibrium network of entanglements. • Time of re-entangling increases when the polymer is less entangled. • The determined re-entangling time depends on the type of experiment performed. [ABSTRACT FROM AUTHOR]

In this article, the content of β crystals in polypropylene (PP) cast films was adjusted by annealing treatment. Subsequently, the effect of the content β crystals on the pore structures and the porosity of PP microporous membranes was investigated. It was found that annealing could improve the long period of lamella stacking and the lamellar thickness, without altering the crystalline morphology and orientation of cast films. The microporous membranes with high porosity and uniform pores and pore-size distribution could be obtained by biaxial stretching. Interestingly, the pore structures of these microporous membranes were quite different. The sample composed of β transcrystals (β-TCs) have only a few or no obvious connecting bridge structures in microporous membranes. However, the sample composed of pure α transcrystals (α-TCs) had a large number of connecting bridge structures, as well as the pores distribution and pore-size distribution were also uniform. These results indicated that the pore structures of microporous membranes could be adjusted by the content of β crystals in PP cast films and homogeneous microporous membranes could also be obtained by biaxial stretching other crystalline forms of PP materials. It afforded a new insight to obtain PP microporous membranes with excellent performance. Image 1 • Having a similar on orientation and crystalline morphologies, samples with different β crystals contents could be obtained by annealing treatments. • The microporous membranes with more uniform pores and pore-size distribution could be obtained by biaxial stretching the annealed sample. • The pore structures of microporous membranes could be adjusted by the content of β crystals in PP cast films. [ABSTRACT FROM AUTHOR]

The effects of tacticity and molecular weight (MW) of isotactic polypropylene (iPP) on crystallization kinetic and crystal morphology were investigated by in-situ isothermal crystallization using simultaneous synchrotron small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM) techniques. Several quantitative parameters were extracted and analyzed in details. It was found that tacticity notably influenced the rate of nuclei seeding, where the high-tacticity iPP sample exhibited a faster nucleation rate. However, tacticity affected only slightly on the crystallization and normalized spherulite-growth rates. Inversely, the MW strongly influenced the crystal lamellar morphology, in which the amorphous layer thickness (L a) was found to be larger in high-MW iPP than that in low-MW iPP. These findings indicated the behavior of "tapering" in the lamellar width during crystal growth, where tacticity and MW both played a role in this process. Image 1 • Tapering in lamellar width of polypropylene is evidenced, for the first time. • Both molecular weight (MW) and tacticity play the role on the tapering process. • Tacticity strongly influences the crystallization kinetic, while MW notably affects the lamellar morphology. [ABSTRACT FROM AUTHOR]

Abstract Based on Takayanagi's two-phase model and the brittle-ductile transition equations, we established a relation between the composite modulus E c and related parameters including modifier modulus E d , modifier content φ , modifier particle size d and interparticle distance ID , which determined the stiffness and toughness of the composite toughened with one phase modifier particle. From this relation, we can quantitatively study how the composite modulus depends on E d , φ , d , and ID at the critical brittle-ductile transition point, and thereby can give the theoretic guidance for designing the composite with balanced toughness and rigidity by optimizing these parameters. The results show that lower critical interparticle distance (ID c) leads to a great loss of the stiffness for rubber or elastomer toughened polymer composites. This is a main reason that the high impact polypropylene (HIPP) composites with high stiffness is more difficult to be obtained. Graphical abstract Image 1 Highlights • The relation between the composite modulus and related parameters was established. • Lower ID c leads to a great loss of the stiffness for toughened polymer composites. • An effective way to obtain the HIPP composites with high stiffness was proposed. [ABSTRACT FROM AUTHOR]

Joining different parts is one of the crucial components of designing/engineering of materials. Presently, the current energy efficient low weight automotive and aerospace components consist of a different class of materials, such as metals, polymers, ceramics, etc. Joining these components remains a challenge. Here, we demonstrate metal (aluminum) and polymer (Polypropylene, pp) joining using mechanical friction. The detailed characterization clearly demonstrates that atomically locked interfaces are formed in such joining and no chemical bonds are formed during the joining. Also, a waterproof and strong interface is formed in such a process. Fully atomistic molecular dynamics simulations were also carried out in order to further gain insights on the joining process. Image 1074976 • Demonstrate that mechanical friction can be utilized to form atomically locked interface joints between two different materials (metal and polymer). • Atomically locked interfaces formed in such joining result in a waterproof and strong interface. • The tensile and bend tests confirm the resistance to fracture due to the interlocking morphology, which exists at macro level and extends all the way to the atomic scale. • Fully atomistic molecular dynamics simulations to further gain insights on the joining process. [ABSTRACT FROM AUTHOR]

The property of ultrahigh molecular weight polyethylene (UHMWPE)-based materials are significantly dependent on the morphology and phase behavior evolution subjected to extensional-shear coupled flow fields. In this study, we utilize polypropylene (PP)/UHMWPE blends as model and present a combination of numerical simulation and experimental study on their association behavior under extensional-shear coupled flow field. In terms of simulation, combined molecular dynamics (MD) and dissipative particle dynamics (DPD) method are applied, where two kinds of extensional-shear coupled flow fields are produced, named as coupledⅠand coupled Ⅱ. In response to coupled Ⅰ, shear-stretched alignment of PP chains is observed at shear rate of γ ˙ = 0.01, followed by a quick disordering transition with increasing the shear rates and a final phase-separation at shear rate of γ ˙ = 0.1. When subjected to coupled Ⅱ, the weak segregation start to connect with the adjacent ones, giving a homogeneous phase when further increasing the applied pressure. The presence of pressure-driven flow helps in bridging different chains, causing the percolating polymer network reinforcement. Besides, experimental studies by means of Raman spectroscopy, Raman mapping and rheological measurement are compared with the above simulations. It confirms that it is more efficiently broken for melted drops under an extensional dominated coupled flow than those under a shear dominated coupled flow, in which an effective lubricating phase forms, leading to the induced miscibility in polymer blends and reduction in storage modulus and viscosity. These experimental findings are consistent with simulation results. Image 1 • In response to couple Ⅰ, a final phase separation take place with varying the shear rates. • As imposed by couple Ⅱ, a homogeneous phase can be obtained when further increasing the applied driving pressure. • The obtained results from simulations are in good agreement with these experimental findings. • It forms an effective lubricating phase for the benefit to the viscosity reduction. [ABSTRACT FROM AUTHOR]

Abstract Large strain cavitation induced stress whitening was observed in propylene-butene-1 copolymer during stretching by means of ultra-small angle X-ray scattering technique. The critical stress for initiating this cavitation depended on the stretching temperature (T s). A constant critical stress was found below T s of 125 °C while the stress started to increase above 125 °C. This peculiar cavitation performance presented in propylene-butene-1 copolymer was supposed to be associated with the melting of unstable crystallites before deformation. Such unstable crystallites were normally composed of chains with co-units or short length. At the strain just before whitening, chains from those melted crystallites could recrystallize wholly into oriented crystallites as the copolymer was stretched below 125 °C while they remained molten when the sample was deformed above 125 °C. Thus, different highly oriented amorphous networks were created below and above 125 °C in copolymer, resulting in different critical stresses for large strain cavitation since this cavitation is determined by the fracture of such oriented amorphous network. Graphical abstract Image 1 Highlights • The stretching temperature can affect the critical stress of initiating the large strain cavitation in PP copolymer. • Critical stress for triggering such cavitation kept constant below 125 °C while it increased above 125 °C. • The melting of unstable crystallites caused different critical stresses of large strain cavitation in PP copolymer. [ABSTRACT FROM AUTHOR]

Abstract In this study, multi-scale micro/nano fibers membrane based on polypropylene and polystyrene were successfully fabricated by one-step melt-blown technique for high performance air filtration. The incompatibility of the used polymers made the viscosity of blended melt fluctuate continuously, resulting in the remarkable diameter difference occurred in prepared fibers. The micro-scale fibers acted as skeleton supports which could improve the permeability of melt-blown nonwovens, and the nano-scale fibers acted as connection props which could increase the surface area/volume ratio to improve the filtration performance by simply varying the composition of precursor solutions. And the obtained nonwovens showed the enhanced filtration efficiency and reduced pressure drop simultaneously, which included high air filtration efficiency of 99.87%, a low pressure drop of 37.73 Pa and a satisfactory quality factor of 0.18 Pa-1. The successful preparation of micro/nano fibers by the simple one-step method may develop novel filtration and separation materials to reduce air pollution. Graphical abstract Image 10 Highlights • Multi-scale micro/nano fibers membrane are prepared by melt-blown technique. • The formation principle was attributed to different directional "tug of war". • Membrane showed enhanced filtration efficiency and reduced pressure drop. • Filtration efficiency of 99.87% and pressure drop of 37.73 Pa can be obtained. [ABSTRACT FROM AUTHOR]

Abstract Ductile functionalized polypropylene is of great interest in multi-layer composites development. A capped-end triblock polyether diamine (H 2 N-PO 2 -TMO 9 -PO 3 -NH 2) was used as a linker of two different maleated isotactic polypropylenes (iPP -g- MAH, at 1 and 3 wt%) by twin-screw reactive extrusion. The molecular architecture, the semi-crystalline microstructure and the mechanical properties of the resulting polymers were analysed as a function of the molar ratio of NH 2 :MAH (0:1, 0.33:1, 0.5:1, 0.66:1, 1:1, 1.5:1, 2:1). At the molecular scale, the chemically modified polymers were characterized by FTIR and by the determination of gel content following the ASTM D2765-84 standard method. Differential Scanning Calorimetry, Wide Angle X-rays Scattering and Self Successive Auto-nucleation techniques showed the impact of the crosslinking: a decrease of the melting temperature as compared with the unmodified iPP -g- MAH polymer, as well as a decrease of the crystallinity ratio for the iPP -g- MAH at 3 wt% of MAH. Interestingly, Dynamic Mechanical Analysis and video-controlled uniaxial tensile tests showed that the polymers obtained in stoichiometric NH 2 :MAH molar ratio exhibit the best mechanical properties enlightened by a switch from brittle to ductile mechanical behaviour with few differences between the two iPP -g- MAH. Graphical abstract A slight crosslinking enables maleated isotactic polypropylenes to switch from brittle to ductile mechanical behavior with higher resilience than the most conventional one. Image 1 Highlights • A capped-end triblock polyetherdiamine is used as a linker of different iPP- g -MAH by twin-screw reactive extrusion. • The three-dimensional networks are characterized by FTIR and by the determination of gel content. • The semi-crystalline microstructure is thermally described applying the Self-Successive Auto nucleation technique. • A switch from brittle to ductile mechanical properties is observed studying the intrinsic true mechanical behaviours. [ABSTRACT FROM AUTHOR]

Abstract Calculating the effective elastic properties of semi-crystalline polymers is challenging due to a pronounced phase stiffness contrast, complex micro-structures and extreme anisotropies of the crystalline phases. To estimate the effective Young modulus of isotactic polypropylene depending on the crystallinity, we construct complex and simple homogenization schemes that unify the micro-scale interaction mechanisms that have been identified by Bartenev and Valishin [4], Bédoui et al. [5], Parenteau et al. [38]. This is achieved by a two-step homogenization approach, namely a local laminate stiffness that is then subjected to orientation averaging. The resulting estimates show good agreement to experimental results. They further suggest that the relatively high effective stiffness of isotactic polypropylene when compared to polyethylene may in part be a result of the stronger lateral confinement effect on the laminate level. Graphical abstract Image 1 Highlights • An ad-hoc homogenization scheme for the elasticity of iPP is presented. • Laminate orientation averages are calculated. • The ellipsoidal-inclusion approach is critically discussed. • The lateral confinement effect contributes to the high stiffness of iPP. [ABSTRACT FROM AUTHOR]

Abstract We report herein new biocomposites prepared from thermally treated oyster shell powder (TTOSP) and modified polypropylene (PP). Untreated and heat-treated OSP are examined to determine which of them is more effective as a bactericidal agent that can be incorporated into a modified PP to prepare biocomposites. The results of TGA and SEM indicate poor compatibility between PP and biocomposites containing more than 0.5 wt% TTOSP. A quantitative analysis reveals that TTOSP can impart antibacterial activity. MTT assay tests on the biocomposites reveal that the relative growth rates of L929 fibroblast cells increase with the TTOSP content, indicating that the biocomposites exhibit no cytotoxicity. The results from this study suggest that a TTOSP content of as low as 0.5 wt% is sufficient to improve the thermostability and tensile property of PP. Graphical abstract Image 1 Highlights • Thermally treated oyster shell powder (TTOSP) has never been reported to impart antibacterial properties to polymers. • This is the first report that indicates TTOSP could promote the bioactivity of polymers. • TTOSP could substantially improve the themostability and mechanical properties of biocomposites. • TTOSP as potential additives and antibacterial agents for polymer industries. [ABSTRACT FROM AUTHOR]

Abstract Accelerating shear-induced crystallization and enhancing crystal orientation of isotactic-polypropylene (iPP) via controlling the morphology of N,N′-dicyclohexyl-2,6-naphthalene dicarboxamide (NJS) is reported here. By adjusting the final heating temperature, NJS crystallizes into dotlike, needlelike, and treelike morphologies. Due to the selective absorption, longer polymer chains are anchored on the surface of NJS, leading to a lower viscosity of the composite than pure iPP. Since that anchoring points will inhibit the relaxation of oriented polymer chains after shear ceases, the shear-induced crystallization kinetics of the composite is greatly accelerated compared with pure iPP. As the morphology of NJS changes from dotlike to treelike, the crystallization induction time decreases further from 620 s to 250 s. Additionally, the branches of the treelike NJS will be detached from the tree upon the shear flow and orient themselves in the shear direction, which endows a highest degree of crystal orientation of the composites with treelike NJS. Graphical abstract Image 1 Highlights • Due to the selective absorption, longer polymer chains are anchored on the surface of NJS. • The anchoring points inhibit the relaxation of polymer chains, which accelerate greatly the crystallization kinetics. • The detachment and orientation of NJS branches from the tree upon shear flow benefits the crystal orientation. [ABSTRACT FROM AUTHOR]

Abstract In the preparation of polypropylene (PP)-based nanocomposites, grafting end-functionalized PP to nano-sized fillers is a promising strategy to alleviate the compatibility and interfacial problems at once, while poor synthetic efficiency for the end-functionalized PP and its grafting has been a major issue to be addressed. Here, we synthesized functionalized PP with one or less silicon methoxy groups per chain by means of direct copolymerization using a Ziegler-Natta catalyst, and utilized it as a reactive matrix in melt-mixing with spherical SiO 2 nanoparticles. In addition to its synthetic advantage, the introduction of a trace amount of reactive functional groups delivered several profitable consequences to the nanocomposites that are typical for end-functionalized PP, such as improved dispersion, dramatically accelerated crystallization, and mechanical reinforcements. Graphical abstract Image 1 Highlights • A trace amount of reactive groups was introduced into PP by copolymerization. • The functionalized PP as a reactive matrix was in-situ grafted to SiO 2 nanoparticles. • The functionalized PP behaved like an end-functionalized PP in the nanocomposites. [ABSTRACT FROM AUTHOR]

It is well accepted that thermoplastic vulcanizate (TPV) combine the appealing recyclability of thermoplastics with the mechanical robustness when compared to traditional rubbers. However, the compatibility between heterogeneous materials has a significant impact on the high-performance TPV. This work demonstrates a novel representative volume element (RVE) model via the cohesive zone model for TPV based on polypropylene (PP)/ethylene propylene diene monomer (EPDM) blends. Considering the material characteristics, both the elastic and elastic-plastic interface types have been employed to establish this RVE model. The model indicates that the elastic-plastic interface model could provide a better description for the mechanical behavior of this TPV. Finally, a bivariate partial dependence plot for TPV has been obtained via the simulation result, illustrating the influence mechanism between the interface structure-properties for TPV. Moreover, the universality of this impact mechanism was validated in a PA6/EPDM-based TPV system. This work could provide a theoretical foundation for optimizing interface compatibility and implementing controllable performance for TPV. [Display omitted] • This work introduces a novel RVE model for TPV, based on PP/EPDM blends and employing the cohesive zone model. • The RVE model includes elastic and elastic-plastic interfaces, highlighting their impact on high-performance TPV. • The elastic-plastic interface model proves to be more accurate in describing the mechanical behavior of TPV. • A bivariate plot elucidates TPV's structure-properties link, aiding material behavior understanding. • The research provides a theoretical basis for optimizing interface compatibility and achieving controllable TPV performance. [ABSTRACT FROM AUTHOR]

Despite the maturity of the technology, processing of fiber-reinforced thermoplastic materials remains challenging, and difficulties in processability often result in material formulations with high modulus and strength, yet rather poor ductility compared to the pure polymer matrix. To gain fundamental insight into the deformation mechanisms present in such materials, the complexity of the system is step-wise increased; first, the effect of the most commonly applied adhesion enhancement, the addition of MAH-g-PP compatibilizer, on the bulk properties is assessed. The small-strain tensile properties, i.e., modulus and yield stress, appear to be only marginally affected by the addition of such compatibilization agent, however, the strain-at-break is strongly reduced, even before the addition of the fiber reinforcement. Subsequently, using in-situ X-ray characterization methods upon tensile deformation, the time evolution of crystal structure and lamellar morphology is determined, and at first glance the compatibilizer addition appears to better preserve the crystalline structure. The onset of local failure (cavitation) is quantified at the interface of a single glass fiber. By increasing the adhesive interaction between fiber and matrix the stress concentration at the interface is increased, leading to an acceleration in void formation followed by unstable growth, which in turn strongly embrittles the composite. By the addition of various selective nucleating agents, it is demonstrated that the role of local phase composition and morphology on the deformation kinetics and subsequent failure mechanisms is much more pronounced than the increased adhesion between fiber and matrix by compatibilization or sizing effects. These findings may specify a new route towards tougher fiber-reinforced composites with reduced complexity in the material formulation. [Display omitted] • The mechanical performance of a composite grade iPP is systematically assessed. • With the addition of MAH-g-PP compatibilizer, the cavitation is more severe. • By the addition of a single fiber, strain is localized at the interface region. • Increased adhesion by sizing leads to accelerated cavitation and brittle fracture. • In β -phase polypropylene, despite extreme voiding the brittle fracture is suppressed. [ABSTRACT FROM AUTHOR]

The effects of magnesium maleate (MgMA) and maleic anhydride (MAH) on the interfacial interaction and the shape memory properties of ethylene propylene diene monomer (EPDM) and polypropylene (PP) thermoplastic vulcanizate (TPV) with sea island structure prepared by dynamic vulcanization were investigated in this study. PP matrix could maintain the temporary shape of TPVs and the crosslinked EPDM phase supplied stress to drive the deformed shape recovery during the shape memory process. MgMA and MAH grafted on PP and EPDM chains verified by FTIR, DMA and SEM, which improved the interfacial compatibility of EPDM and PP and enhanced the efficiency of stress transfer in the shape memory process. The shape fixity ratio (R f) and shape recovery ratio (R r) of TPVs compatibilized by MgMA and MAH were almost above 80%. The shape memory property and the mechanical performance of TPVs were all improved compared to that of the sample without compatibilization. [Display omitted] • We produced an ethylene propylene diene monomer and polypropylene thermoplastic vulcanizate by dynamic vulcanization. • The TPV was compatibilized by magnesium maleate (MgMA) and maleic anhydride (MAH) with good shape memory performance. • The shape fixity ratio (R f) and shape recovery ratio (R r) of compatibilized TPVs were almost above 80%. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • The cavitation behavior of sPP is linked to the original crystallites. • The cavities produced in sPP could be healed at early deformation stage. • The development of cavities in sPP began to slow down beyond the critical point C. [ABSTRACT FROM AUTHOR]

Isotactic polypropylene (iPP) sheets were subjected to low-energy falling-weight impacts under various conditions. The elastic energy recovered during unloading gradually increases with increasing impact energy and reaches a fixed value, while the dissipated energy during the impact test increases monotonically. Whereas higher impact energy and repeated impacts result in enhanced whitening in an iPP sheet, the load–displacement curve is unaffected by impact repetition. The stress–strain curves of the impact-damaged iPP specimens indicate that these specimens retain high ductility irrespective of the impact energy and number of impacts. In addition, the striker impact did not affect the crystalline lattice of the original iPP. The impact damage solely induces the decrease in yield stress, suggesting impact in the crystalline phase. The yield stress gradually decreases with increasing impact energy and number of repetitions owing to accumulation of impact damage in the crystalline phase. The yield stress reaches a constant value after several repeated impacts, where the asymptotic value decreases with the impact energy. Because the drop of the yield stress increases with the impact energy, it is suggested that preferential fracture in the lamellar crystals takes place owing to fluctuation in the strength. Impact-induced voids with a size of approximately twice the long period are found by in-situ small-angle X-ray scattering. Partial fragmentation of the lamellar crystal into lamellar cluster units is suggested to be the microscopic origin of the impact damage. [Display omitted] • FWIM damage was highlighted by in-situ small-angle X-ray scattering during tensile stretching. • Although the impact damage leads to significant decrease of the yield stress, the damaged specimen retains high ductility. • Partial fragmentation into lamellar cluster units is suggested to be the microscopic origin of the impact damage. [ABSTRACT FROM AUTHOR]

Abstract This work presents an ultrasonic-assisted approach for fast impregnation of thermoset and thermoplastic polymers including solvent-free epoxy resins, polydimethylsiloxane resins, and polypropylene into multi-walled carbon nanotube (MWCNT) nanopapers to prepare nanocomposites or prepregs with high loading (>20 wt%) of well-dispersed MWCNTs, not achievable by the conventional compounding or resin transfer molding methods. The approach involves making MWCNTs into macroscopic paper-like sheets (also called "nanopapers") via a dispersion-filtration method and then impregnating the mesoporous nanopapers with polymeric resins using an ultrasonic infiltration method to form a prepreg or nanocomposite. The formed nanocomposites revealed an excellent combination of mechanical strength, sand erosion and scratch resistance, electrical and thermal properties, and good processing flexibility. Highlights • A cost-effective, scalable, and environmentally friendly process for CNT nanopaper production via filtration was developed. • An ultrasonic infiltration method was developed to infiltrate resins into CNT nanopapers to make prepreg nanotapes. • The composites showed improved abrasion/scratch resistance, heat release, EMI shielding, and processing flexibility. • The prepreg has potential uses in automotive, sporting goods, mobile electronics, wind energy, and aerospace markets. [ABSTRACT FROM AUTHOR]

Abstract This work describes the important effects of microstructural features on crystalline structure, mechanical behavior and molten state response for poly (propylene- co -1-pentene- co -1-heptene) terpolymers. The study was carried out in a wide range of compositions, varying the 1-pentene/1-heptene ratio and the thermal history applied. Molecular features, as propylene sequences and compositional triads, allow predicting the material behavior. Moreover, rheological response has demonstrated the influence of molecular weight, comonomer content and short-chain branches on the properties. The flow activation energy can justify the importance of the material density over the whole spectrum of properties. Graphical abstract Image 1 Highlights • A complex polymorphic behavior is exhibited by poly(propylene- co -1-pentene- co -1-heptene) terpolymers. • Overall content in comonomers and ratio between the 1-pentene and 1-heptene comonomers become key molecular parameters. • Development of trigonal polymorph leads to unusual relationships of crystallinity and mechanical magnitudes on composition. • Changes in mobility promote an increase of flow activation energy with the comonomer content. [ABSTRACT FROM AUTHOR]

Abstract The fixation stage of cellular structure during polymer foaming process is difficult to control due to difficult removing of internal heat, especially for crystalline polymers such as polypropylene (PP). In order to control cellular structure in the fixation stage, we established an universal method by introducing water as an in-situ internal cooling agent during the foaming process of PP. Particularly, hydrophilic fillers were added into the high melt flow index polypropylene (HMI-PP) with poor foaming ability to study the effect of adsorbed water on the foaming process of PP/filler composites during sc-CO 2 batch foaming process. Compared to pure HMI-PP, HMI-PP/hydrophilic filler composites showed increased adsorption amount for water and melt viscosity. The water within the composites played a key role in the foaming process, which not only served as a physical foaming agent to increase the volume expansion ratio of PP composite foam, but also showed the function of rapid cooling foam proved by thermal imaging technology. As a result, the presence of some hydrophilic fillers within HMI-PP matrix significantly improved the foaming properties of HMI-PP, including preventing internal bubble collapse and significantly increasing the volume expansion ratio of the foam. The applicability of this method was validated using other PP materials besides HMI-PP, including high molecular weight PP (HMW-PP), high melt strength PP (HMS-PP). Graphical abstract Image Highlights • The presence of hydrophilic fillers enhanced adsorption amount of water in PP/filler composites. • Adsorbed water served as both in-situ cooling agent and foaming co-agent during CO 2 batch foaming process. • The in-situ cooling effect of adsorbed water in PP composites provides an efficient method to control cellular structure. [ABSTRACT FROM AUTHOR]

Abstract Exerting high shear force and adding compatilizer are two different methods used for regulating the size of dispersed phase of polymer blends. Nevertheless, the comparison of the effect of the high shear force and adding compatilizer on the phase morphologyies and properties is less studied, not to mention the synergistic effect. In this work, the incompatible PP/PLA binary blends with large polarity differences were prepared using high-shear processing, compared with the effect of adding ethylene-(methyl acrylate)-(glycidyl methacrylate) (EMA-GMA) as reactive compatibilizer for PP/PLA blends. It was found that adding compatilizer under relative low shear force was more efficient on improving the interface, showing blurred boundaries, compared with the reduction of the dispersed phase size under high shear force without compatilizer. As a result, the blends with the compatilizer presented a higher elongation at break; yet the yield strength of the binary blends prepared under high shear force was higher than that of the ternary blends. Furthermore, the synergistic effect of adding compatibilizer and high shear force was limited, which could be attributed to the fact that the degree of reactive compatibilization had already reached saturation under the rotation speed of 100 rpm due to the high efficiency of EMA-GMA. Graphical abstract Image 1 Highlights • The comparison of the effect of the high shear force and adding compatilizer is systematically studied. • The size of the PLA dispersed droplets decreases significantly under high rotation speed and relatively low temperature. • The PP/PLA binary blends prepared using high-shear processing show higher yield strength and lower toughness. [ABSTRACT FROM AUTHOR]

Abstract Lamellar stack in semicrystalline polymers composed of alternatively arranged lamellar crystal and amorphous layers is one of the typical hard-soft laminated nano-composites. Considering the Poisson contraction effects during uniaxial tensile deformation along the normal direction of layers, microbuckling instability of lamellar stacks is first proposed as a new deformation mechanism to trigger the nonlinear mechanical behaviors in semicrystalline polymers. Based on the non-equilibrium process of crystallization and experimental observations, a three-phase structure with lamellar stack (crystal and interlamellar amorphous) and the amorphous matrix is proposed as a deformation unit in semicrystalline polymers. Based on the three-phase model and the proposition of buckling with shear mode, we deduce the theoretical critical strain for the sinusoidal microbuckling through linear stability analysis method. Taking hard-elastic isotactic polypropylene as an example, the theoretically calculated critical strain is in a good agreement with the experimental critical strain at temperatures below α relaxation temperature T α. These results suggest that elastic microbuckling is indeed a possible mechanism to trigger the nonlinear instability, which is different from current plastic deformation models with crystal destruction around yield in semicrystalline polymers. Graphical abstract Image 1 Highlights • Microbuckling is first proposed as a possibility to trigger nonlinear instability in semicrystalline polymer. • Linear stability analysis is used to calculate theoretical critical strain for microbuckling. • A perfect agreement between experimental and theoretical critical strain of microbuckling is obtained. [ABSTRACT FROM AUTHOR]

Abstract Crystallization kinetics of polypropylene (PP) nucleated with sorbitol-type nucleating agents was studied with fast differential scanning calorimety (FDSC) at high supercooling and correlated to the optical characteristics of mold injected parts. FDSC was used for determination of the critical cooling rate for occurrence of non-isothermal crystallization and the time to maximum crystallization rate during isothermal crystallization after rapid cooling. The nucleating agents studied were 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS) and 1,2,3-tridesoxy-4,6:5,7-bis- O -[(4-propylphenyl) methylene]-nonitol (TBPMN). In contrast to particulate nucleating agents, where the number of particles determines the number of heterogeneous nuclei, sorbitol-type nucleating agents self-assemble a nano-fibrillar super-structure by phase separation of sorbitol-type molecules that were previously dissolved in the polymer melt. An approach is proposed to describe the efficiency of nucleating agents self-assembly. In combination with haze data two different crystallization mechanisms are identified, which are interpreted as three-dimensional spherulitic crystallization at high haze and one-dimensional (rod or shish-kebab-like) crystallization at low haze. Graphical abstract Image 1 Highlights • Crystallization kinetics of polypropylene with sorbitol-based nucleating agents. • Results of Fast DSC measurements correlate with optical properties. • Introduction of an approach to describe the nucleating efficiency by Fast DSC. • Measurement of a structural transformation driven by nucleating agent content. • Nucleating efficiency and haze correlate for parts produced by injection molding. [ABSTRACT FROM AUTHOR]

Addition of a β-nucleating agent (β-NA) is the most effective method of preparing β-nucleated isotactic polypropylene (β-iPP); however, the poor dispersion and agglomeration of β-NAs limit nucleation efficiency. To solve this problem, a self-dispersing β-NA strategy was developed based on in situ preparation of β-NA (instead of pre-addition) during the processing of iPP. Zinc adipate (ZnAA), a typical β-NA, was chosen; self-dispersed ZnAA (ZnAA(IS)) was prepared in situ from its reaction precursors adipic acid (AA) and zinc oxide (ZnO) during extrusion of iPP. In situ preparation of ZnAA(IS) led to a significantly higher nucleation efficiency than pre-addition of ZnAA. The β-crystal content ( k β value) of nucleated iPP prepared with ZnAA(IS) reached 0.99, significantly higher than iPP prepared with ZnAA. Moreover, the impact strength of 0.1 wt % ZnAA(IS)/iPP composites was nearly 5.3-fold higher than neat iPP with a net gain in reinforcement (157%) compared to pre-addition of ZnAA. To explain these phenomena, we proposed mechanism for the self-dispersion of β-NA in the context of in situ generation of β-NA during iPP processing; the mechanism was confirmed by Fourier Transform Infrared Spectroscopy (FTIR), Polarized Optical Microscopy (POM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) data. Therefore, this strategy and method of preparing β-NA in situ offers unique advantages that will advance the production and application of β-iPP. Furthermore, this strategy could potentially be extended to solve issues of poor dispersion and agglomeration for other additives. [ABSTRACT FROM AUTHOR]