Elongational Flow Field Research Articles

Scalable In-situ Microfibrillar dielectric films: Achieving exceptional energy density and efficiency

It is a formidable challenge to develop a feasible strategy for the scalable fabrication of all-organic dielectrics with simultaneous improvements in both discharged energy density (Ud) and efficiency (η). Herein, an innovative technology of “melting extrusion-hot stretching-quenching” was put forward for the large-scale preparation of all-organic polymer dielectric films, where polymethyl methacrylate (PMMA) was miscible with polyvinylidene fluoride (PVDF) to form single dispersed phase in the polypropylene (PP) matrix and in-situ transformed into microfibrils with the aid of elongational flow field. Thereby, a simultaneous enhancement in the dielectric constant and breakdown strength was achieved and the as-prepared PP-based all-polymer dielectric film exhibited an unprecedented ultrahigh Ud of 9.6 J cm−3 and an exceptional η of 90.9 %. Experimental verification and computational simulation confirmed that the formation of highly oriented PMMA/PVDF microfibrils and well-aligned interfaces are constructive to enhancing breakdown strength by suppressing electric field distortion. The highly oriented dipoles in PVDF and PMMA, coupled with the eliminated ferroelectric behavior of PVDF, synergistically contributed to the heightened Ud and η. The approach presented in this work opens up a promising avenue for the large-scale production of all-organic capacitor films with enhanced Ud and η, heralding a new era of advanced dielectric materials.

Enhanced carbon black exfoliation through elongational flows for faster and higher value-added rubber recycling

The recycling of rubber featuring intricate three-dimensional crosslinked networks necessitates the application of cutting-edge technology and specialized machinery. In this study, the rubber was recycled by mechanochemistry under elongational flow field. The crosslink bonds in the rubber were rapidly broken through the high extension of molecular chains, without the need for additives or additional refinements. At 200 °C, the waste rubber is devulcanized in only 2 min so that the sol molecular weight reached an impressive 3.3 × 104 g/mol, and the mechanical properties of the reclaimed rubber were significantly enhanced, reaching a tensile strength of 17.44 MPa. The elongational flow field devulcanizes the waste rubber while simultaneously achieving rapid refinement of rubber particles and exfoliating the carbon black from the crosslinked network. These making reclaimed rubber forms a micro-nano microstructure in natural rubber (NR), which makes particle reinforcement of the NR-matrix. Faster and high-value-added rubber recycling achieved successfully through elongational flows.

Experimental study on the continuous preparation of high‐performance thermal conductivity CNTs/EG/SSBR composite based on the shear and elongation flow fields with the assistance of the silanization reaction

AbstractA self‐developed Serial Rubber Continuous Mixing Device (SRCMD) based on the shear and elongation flow fields was adopted to continuously prepare the carbon nanotubes (CNTs)/expanded graphite (EG)/Solution‐polymerized styrene butadiene rubber (SSBR) composite. Meanwhile, the silanization reaction between the Silica and Si69 was introduced to improve the performance of the CNTs/EG/SSBR composite. When comparing the sample prepared using the two‐stage mixing process based on the shear flow field in the internal mixer, the continuously prepared CNTs/EG/SSBR composite with 3 wt% CNTs and 15 wt% EG demonstrates a higher thermal conductivity of 1.32 W/m·K. At the same time, it exhibits significant advantages in terms of mechanical properties, processability and dispersion rating. In addition, the mechanism for the continuous preparation of CNTs/EG/SSBR composite was revealed through visual experiments. This study aims to achieve the real continuous production of high‐performance thermally conductive polymer composites to meet the urgent demand for thermal conductivity materials in 5G technology.Highlights Real continuous preparation of CNTs/EG/SSBR composite was realized. The silanization index of 92.26% between Silica and Si69 was achieved. Good silanization promotes the construction of thermal conductivity networks. High‐performance CNTs/EG/SSBR composite with low Payne effect was obtained.

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Establishment of dynamic prediction model on morphology development of polypropylene/polyamide 6 blends under in-situ fibrillation flow

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.

Work distribution of a colloid in an elongational flow field and under Ornstein-Uhlenbeck noise.

The study of thermodynamic properties of microscopic systems, such as a colloid in a fluid, has been of great interest to researchers since the discovery of the fluctuation theorem and associated laws of stochastic thermodynamics. However, most of these studies confine themselves to systems where effective fluctuations acting on the colloid are in the form of delta-correlated Gaussian white noise (GWN). In this study, instead, we look into the work distribution function when a colloid trapped in a harmonic potential moves from one position to another in a fluid medium with an elongational flow field where the effective fluctuations are given by the Ornstein-Uhlenbeck noise, a type of colored noise. We use path integrals to calculate this distribution function and compare and contrast its properties to the case with GWN. We find that the work distribution function turns out to be non-Gaussian as a result of the elongational flow field but continues to obey the fluctuation theorem in both types of noise. Further, we also look into the effects of the various system parameters on the behavior of work fluctuations and find that although the distribution tends to broaden with increasing noise intensity, increased correlation in fluctuations acts to oppose this effect. Additionally, the system is found to consume heat from the surroundings at early times and dissipate it into the media at later times. This study, therefore, is a step towards gaining a better understanding of the thermodynamic properties of colloidal systems under nonlinear complex flows that also display correlated fluctuations.

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

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

Strengthening-toughening pure poly(lactic acid) with ultra-transparency through increasing mesophase promoted by elongational flow field

Poly(lactic acid) (PLA), as a biodegradable material, finds wide applications in packaging, automotive, and biological industries. However, achieving high strength, toughness, ultra-transparency, and heat resistance simultaneously in pure PLA through continuous one-step manufacturing remains a significant challenge. In this study, we addressed this challenge by utilizing the eccentric rotor extruder (ERE) in combination with cooling rolls to manufacture PLA sheets with outstanding mechanical performance. The ERE's elongational flow field combined with the cooling roller's weak stretching action induced orientation in the PLA molecular chains and promoted the formation of more mesophase, significantly improving mechanical properties. When the extrusion-stretch ratio (λ) value was 3.5, the tensile yield strength, Young's modulus, and elongation at break of ERE-fabricated samples ER-3.5 reached 86.2 MPa, 1777 MPa, and 57.9 %, respectively. Compared to the SE-3.5 samples manufactured with traditional methods, the increases were 38.8 %, 25.8 %, and 9.4 times, respectively. Additionally, the ERE manufactured samples maintained ultra-transparency and high heat resistance, making them suitable for food packaging, biomedicine, and other related fields. This methodology provides an efficient industrial-scale approach for manufacturing neat, biodegradable PLA with outstanding mechanical performance and ultra-transparency.

Generation of Tough Poly(glycolic acid) (PGA)/Poly(butylene succinate-co-butylene adipate) (PBSA) Films with High Gas Barrier Performance through In situ Nanofibrillation of PBSA under an Elongational Flow Field

Generation of Tough Poly(glycolic acid) (PGA)/Poly(butylene succinate-co-butylene adipate) (PBSA) Films with High Gas Barrier Performance through In situ Nanofibrillation of PBSA under an Elongational Flow Field

Investigation the effect of processing condition and dispersed phase content on rheology–morphology relationship in polypropylene/polyethylene terephthalate microfibrillar composite

AbstractMorphological evolutions during the production of microfibrillar composites can be investigated by considering two main steps: (1) the melt blending in the extruder and (2) the drawing process. Deformation, coalescence and break‐up of dispersed phase droplets under shear and elongational flow fields applied in these two main steps lead to the formation of fibrillar morphology. Therefore, it can be stated that the fibrillar morphology is controlled by dispersed phase content, rheological and interfacial properties of the components as well as dispersed phase domains relaxation. In this study, the effect of dispersed phase content on the morphology of the polypropylene/polyethylene terephthalate microfibrillar composite was investigated. Also, three following processing parameters were considered to evaluate the kinetics of in‐situ formation of the microfibrils: Extruder die temperature, water bath temperature and the drawing path length. Linear and nonlinear rheological tests were used as an efficient tool to investigate the rheology–morphology relationship. Among the processing parameters studied, the drawing path length and die temperature had the most and least effect on microfibrillar morphology, respectively. By increasing the drawing path length from 20 to 30 cm, the break‐up of the fibrils and non‐uniformity in the cross section of the fibrils caused a weaker strain recovery after stress removal and also a rapid reduction of stress after cessation of steady shear flow field. Increasing the die temperature has a similar but weaker effect on the final morphology. The rheological results in the linear viscoelastic range all indicated the formation of a physical network of microfibrils within the matrix.

Constructing synergistically strengthening-toughening 3D network bundle structures by stereocomplex crystals for manufacturing high-performance thermoplastic polyurethane nanofibers reinforced poly(lactic acid) composites

As one of the most promising biodegradable materials, poly(lactic acid) (PLA) is seriously restricted by its notorious inherent brittleness and weak heat distortion resistance. In this work, a novel and simple methodology is proposed using an eccentric rotor extruder (ERE) with a predominantly elongational flow field to manufacture high-performance engineered poly(L-lactic acid)/poly(D-lactic acid)/thermoplastic polyurethane nanofiber composites on an industrial scale. The oriented tough TPU nanofibers (TNFs), rigid integrated PLA hybrid crystals and their good interface compatibility produce a strengthening-toughening bundle structure. When the PDLA content reached 3 wt%, the bundle structures interlinked with each other to form a strengthening-toughening 3D network. This resulted in a high-performance engineered 80L/5D/15T nanofiber composite with super toughness of 74.1 kJ/m2, high strength of 47.3 MPa and superior Young's modulus of 1378 MPa, which are 28.6 times, 85% and 92.7%, respectively, compared with neat PLLA. Compared with those published literatures, the 80L/5D/15T nanofiber composite not only possesses super toughness (more than 28 times) but also maintains good strength (maintain 85%), additionally good heat distortion resistance was also obtained. The performance of 80L/5D/15T nanofiber composite was significantly superior in comparison with biodegradable plastics as well as petroleum-based non-degradable general-purpose plastics and engineering plastics, demonstrating its enormous potential as a substitute structural material in harsh environments. It is believed that the novel and industrial scale methodology opens new perspectives for manufacturing other high-performance engineered biodegradable materials.

Efficient fabrication of low-density polyethylene/polyethylene oxide/carbon nanotubes films with robust shape stability and photothermal property for thermal management and afterheat utilization

The smart energy absorption and storage properties make the phase change materials the ideal candidate for solar thermal conversion and afterheat utilization. Applying the vane extruder (VE) coupled with a single-layer blown film die, a fast and efficient one-step method is proposed for the successive and mass production of LDPE/PEO/CNTs (PPCs) nanocomposite films. Benefiting from the volumetric elongational flow field provided by the VE, the CNTs are uniformly dispersed in the matrix and a co-continuous network is formed, thereby the thermal conductivity and tensile strength of the PPCs film are effectively improved. The melting enthalpy of PPC0.02 film is 110 J g−1 and tensile strength is 3.308 MPa. Furthermore, the PPCs films maintain stable phase change temperature and robust chemical properties after 150 thermal cycles. The temperature of the simulated greenhouse can be controlled within the range that is conducive to crop growth when the PPCs film is applied to its roof. This can be ascribed to the sufficient light-to-thermal conversion capability and thermal conductivity of the PPCs film. The PPCs film with sufficient shape stability and leakage resistance can be an excellent candidate for harvesting and recycling solar and heat energy sources.

A novel PLA/P(3HB-co-4HB)/MWCNT composite featuring enhanced mechanical properties and excellent thermal stability based on elongational rheology

Simple melt blending is the most frequently-used strategy to obtain high-performance PLA composites. However, the thermosensitive PLA displays the defects of poor thermostability, high brittleness and low heat deformation temperature (HDT) in traditional melt-plasticizing equipment based on shear flow field (SFF). In this work, PLA/P(3HB-co-4HB) blends were fabricated via melt blending technology based on the melt plasticization equipment of elongational flow field (EFF) and SFF. Subsequently, Multi-Walled Carbon Nanotube (MWCNT) was introduced into PLA/P(3HB-co-4HB) blends to prepare PLA/P(3HB-co-4HB)/MWCNT high-performance alloy in an eccentric rotor extruder based on EFF. The periodic compression and release of the EFF on the melt promoted P(3HB-co-4HB) in-situ fiberization and formed special microstructure, which greatly enhanced the mechanical properties, HDT, thermal stability and crystallization perfection of PLA. The tensile strength, Young's modulus, elongation at break, impact strength and HDT of the blend containing 20 wt% P(3HB-co-4HB) under EFF were 8.7%, 22.5%, 80.9%, 62.5% and 14.8% higher than those under SFF, respectively. In addition, MWCNT was induced to disperse into P(3HB-co-4HB) phase by EFF, and played a ‘bridge’ role in PLA and P(3HB-co-4HB), thereby obtaining PLA/P(3HB-co-4HB)/MWCNT high-performance alloy with stronger comprehensive performance. The fabricated PLA/P(3HB-co-4HB)/MWCNT alloy provides a reference for preparing biopolymers under EFF and broadens the potential application value of PLA/P(3HB-co-4HB).

High orientation structure in UHMWPE/BN composites continuously obtained by elongational flow field leading to superior thermal conductivity

AbstractUltra‐high‐molecular‐weight polyethylene/boron nitride (BN) composites have been continuously prepared successfully by eccentric rotor extruder (ERE) based on elongational flow. Optical microscopy (OM), scanning electron microscopy (SEM), x‐ray diffraction (XRD), thermal conductivity test, heat‐dissipation test, and tensile test were performed to investigate the orientation structure, thermal conductivity, mechanical properties, and insulation properties. The orientation factor and thermal conductivity of the composites prepared by ERE were 79.3 and 3.75 W·m−1·K−1, which were much higher than those of composites prepared with a torque mixer (14.7 and 2.73 W·m−1·K−1, respectively). OM and SEM showed that the BN sheets were in contact inside the composites and formed an efficient thermal conductivity network. Besides, the composites prepared by ERE had satisfactory mechanical and insulation properties (>1013 Ω·cm). This study provides experimental and theoretical guidance for industrial preparation of polymer/layered‐filler functional composites.

Solvation-Free Fabrication of PEO/LiTFSI/SiO2 Composite Electrolyte Membranes with High Ionic Conductivity Based on a Novel Elongational Flow Field

Solvation-Free Fabrication of PEO/LiTFSI/SiO₂ Composite Electrolyte Membranes with High Ionic Conductivity Based on a Novel Elongational Flow Field

Toughening and reinforcing waste polypropylene with POE/nano‐SiO2 under elongational flow

AbstractDue to the white pollution, the recycling of waste plastics has attracted more and more attention. In this research, waste polypropylene/Ethylene‐octene elastomer/nano‐SiO2 composites (wPP/POE/SiO2) were melt‐blended using an Eccentric Rotor Extruder (ERE) dominated by elongational flow field and a Torque Rheometer (TR) dominated by shear flow field, respectively. The micromorphology, mechanical, crystallization, thermal and rheological properties of wPP/POE/SiO2 blends were studied. Compared to the blends fabricated by TR, the wPP/POE/SiO2 blends with different compositions fabricated by ERE showed higher tensile strength, flexural strength, and modulus. Particularly, without sacrificing the tensile strength, the notched impact strength of the wPP/POE/SiO2 blends fabricated by ERE increased to 13.53 kJ/m2, a factor of 3 times larger than that of neat wPP. The enhancement of impact strength of the wPP/POE/SiO2 blends fabricated by ERE could be ascribed to the good dispersion of POE under elongational flow and the increase of PP crystallinity. The finding from this work provides an efficient way to recycle wPP.

Elongational Flow Field Processed Ultrahigh Molecular Weight Polyethylene/Polypropylene Blends with Distinct Interlayer Phase for Enhanced Tribological Properties.

Herein, we produced a series of ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blends by elongational-flow-field dominated eccentric rotor extruder (ERE) and shear-flow-field dominated twin screw extruder (TSE) respectively and presented a detailed comparative study on microstructures and tribological properties of UHMWPE/PP by different processing modes. Compared with the shear flow field in TSE, the elongational flow field in ERE facilitates the dispersion of PP in the UHMWPE matrix and promotes the interdiffusion of UHMWPE and PP molecular chains. For the first time, we discovered the presence of the interlayer phase in blends with different processing modes by using Raman mapping inspection. The elongational flow field introduces strong interaction to enable excellent compatibility of UHMWPE and PP and induces more pronounced interlayer phase with respect to the shear flow field, eventually endowing UHMWPE/PP with improved wear resistance. The optimized UHMWPE/PP (85/15) blend processed by ERE displayed higher tensile strength (25.3 MPa), higher elongation at break (341.77%) and lower wear loss of ERE-85/15 (1.5 mg) compared to the blend created by TSE. By systematically investigating the microstructures and mechanical properties of blends, we found that with increased content of PP, the wear mechanism of blends varies from abrasive wear, fatigue wear, to adhesion wear as the dominant mechanism for two processing modes.

Phase transformation and dielectric properties of polyvinylidene fluoride/organic‐montmorillonite nanocomposites fabricated under elongational flow field

AbstractCompounding montmorillonite (MMT) with polymorphic polyvinylidene fluoride (PVDF) by melt intercalation method can induce the crystal phase transformation of PVDF, which is of great significance to obtain the electroactive PVDF. In this research, PVDF/Organic‐Montmorillonite (OMMT) nanocomposites were prepared by a novel vane mixer, which was dominated by the elongational flow field in the whole plasticizing. The dispersion of OMMT, the crystal phase transformation of PVDF, and the resulting properties of nanocomposites were experimentally studied. The results of TEM and WAXD evidenced that homogeneous dispersion and desirable intercalation structure of OMMT were formed in the PVDF matrix under the effect of the elongational flow field. WAXD, FTIR, and DSC tests demonstrated that large amounts of β‐phase of PVDF was formed due to the introduction of OMMT. The intercalation structure of OMMT and the crystal transformation of PVDF increased the dielectric constant and piezoelectric properties of nanocomposites, while the dielectric loss still maintained at a very low level. Finally, the effect of unique ''double‐layer peeling'' mechanism of OMMT on the properties of nanocomposites was discussed.

Tuning wettability and mechanical property of polylactide composite films with in-situ nanofibrils of poly(butylene adipate-co-terephthalate)

The poor hydrophobicity and toughness of polylactide (PLA) films make it difficult to meet the requirements of barrier, printing and moisture-proof material. How to improve the two drawbacks of PLA simultaneously is a daunting challenge at present. In this work, we introduce poly (butylene adipate-co-terephthalate) (PBAT) as a second flexible phase into PLA matrix and concomitantly impose intensive elongational flow by two-stage drawing. Under the elongational flow field, the PLA/PBAT film can form the oriented structure combining in-situ nanofibrils with oriented lamellae, exhibiting excellent stiffness-toughness balance. Then surface treatment via moderate alkaline etching makes the micro/nano structure expose on the surface, which can effectively improve the hydrophobicity of the surface. We further investigates the influence of blend composition, drawing ratio and etching time on the oriented structure, mechanical and wetting properties. It is found that the PLA/PBAT film with the weight ratio of 70/30, low draw ratio of 2.7 and etching time of 24 h has the optimal properties, which possesses Young's modulus of 2.53 GPa, yield strength of 51.9 MPa, elongation of break of 131.8% and water contact angle of 131.8°. It is noteworthy that the film can mainly keep original mechanical after surface treatment. This work could offer a facile and effective method to fabricate the green PLA based film with good mechanical properties and hydrophobicity in a large scale.

Rheological rationalization of in situ nanofibrillar structure development: Tailoring of nanohybrid shish-kebab superstructures of poly (lactic acid) crystalline phase

The key rheological parameters for in situ development of poly (butylene terephthalate) nanofibrils (PBT NFs) in poly (lactic acid) (PLA) matrix using a tuned melt spinning process were studied. Observation of ellipsoidal PBT domains oriented along a short die was attributed to a low interfacial tension between the blend constituents and fulfilled melt rheological criteria for fibrillation in a simple shear flow. The stability of the deformed droplets under the shear and elongational flows was studied by comparing the droplet breakup time and residence time in each flow field. It was demonstrated that the deformed droplets (ellipses) with an increased robust interface underwent coalescence through pinch-off in the subsequent elongational flow field, and transformed to the nanofibrils with an average diameter comparable to the gyration radius (Rg) of PLA chains. In the fabricated isotropic in situ nanofibrillar composites (NFCs), a random orientation of 2D nanohybrid shish-kebab (NHSK) superstructure was observed as a result of the orthogonal pattern of melt crystallized PLA nanodomains on the PBT NFs surface. The NHSK superstructure established in quiescent bulk through mechanism of geometric confinement (soft epitaxy) enabled us to tailor the crystalline morphology via annealing temperature. In a constant nanofibril content, increasing the isothermal temperature (Tiso) up to 114 °C led to an increase in the kebabs length and interlocking of the adjacent superstructures. A transition to spherulitic crystal morphology was observed due to further temperature increase (Tiso≥117 °C). The observed transition indicated that at higher Tiso, the fewer raw nuclei, which were initiated by soft epitaxy mechanism of PLA chain segments on the PBT NFs at the early stage of nucleation, could conduct self-nucleation and 3D lateral growth. The Avrami model was found to be applicable for interpreting variations of crystallite morphology, crystallization rate, and nucleation mechanisms with PBT NF content and isotherm temperature.