Orientation Of Molecular Chains Research Articles

Mechanism of the performance difference and effect of blow‐up ratio parameters on biodegradable poly (butyleneadipate‐co‐terephthalate)/polylactide composite mulch films

AbstractThe development and application of biodegradable mulching film is an efficient way to solve the “white pollution” of farmland. In the actual production, we found that the mulch film produced by different processing technology with the same formula showed quite different application properties. Here, the poly (butyleneadipate‐co‐terephthalate)/polylactide (PBAT/PLA) composite films with two die/screw diameters and eight blow‐up ratio were prepared by extrusion blowing. Results showed increasing blow‐up ratio can significantly improve the tensile strength at the transverse direction. In addition, the optical and water vapor barrier performances of the PBAT/PLA composite films were slightly effected. With the increasing of blow‐up ratio, the transverse molecular chain orientation of the polymer increases, resulting in changes in mechanical performance. This work can contribute to better understand the relationship between the performance and the manufacturing parameters of the biodegradable mulching films and foster the end‐user confidence in the eco‐friendly biodegradable mulch films.Highlights Eight PBAT/PLA mulch films with different blow‐up ratios were obtained. The properties of PBAT/PLA mulch films were mainly affected by blow‐up ratio. The relation between performance and manufacturing parameters was clarified. Die and screw diameter have no significant effect on film properties.

Insights into multi-scale structural evolution and dielectric response of poly(methyl acrylate) under pre-strain: A simulation study.

The structural evolution of dielectric elastomer induced by pre-strain is a complex, multi-scale process that poses a significant challenge to a deep understanding of the effect of pre-strain. Through simulation results, we identify the variation in the dielectric constant and multi-scale (electronic structure, molecular chain conformation, and aggregation structure) response of poly(methyl acrylate). As the pre-strain increases, the dielectric constant initially rises (below 200% pre-strain) and then declines (above 200% pre-strain). Analysis of the charge distribution, surface electrostatic potential, HOMO-LUMO bandgap, and electron density differences reveal that adjusting chain conformation appropriately could enhance polarity domain and electron polarization. The correlation between permittivity and segment dynamics of deformed molecules is explored, encompassing segment orientation, mean shift displacement, and diffusion coefficient. Following molecular chain orientation, the kinematic capability of the chain segment improves, which leads to an increase in the number and activity of effective dipoles and the enhancement of orientation polarization. Excessive stretching restricts the polymer molecular chain mechanically, reducing the number and activity of effective dipoles and negatively impacting electron polarization. The permittivity transitions from isotropic to anisotropic behavior when the system is subjected to strain. This study provides an interesting solution for research on multiscale responses and intrinsic mechanisms of pre-strain.

Mesoscopic Simulation on Centrifugal Melt Electrospinning of Polyetherimide and Polyarylethernitrile

Polyetherimide (PEI) and polyarylethernitrile (PEN) are high–performance materials for various applications. By optimizing their fiber morphology, their performance can be further enhanced, leading to an expanded range of applications in carbon fiber composites. However, developing processes for stable and efficient fiber production remains challenging. This research aims to simulate the preparation of high–performance ultrafine PEI or PEN fibers using electrospinning. A mesoscopic simulation model for centrifugal melt electrospinning was constructed to compare and analyze the changes in molecular chain orientation, unfolding, fiber diameter, and fiber yield under high-voltage electrostatic fields. The simulation results showed that temperature and electric field force had a particular impact on the diameter and yield of PEI and PEN fibers. Changes in rotational speed had negligible effects on both PEI and PEN fibers. Additionally, due to their different molecular structures, PEI and PEN, which have different chain lengths, exhibit varied spinning trends. This study established a mesoscopic dynamic foundation for producing high-performance ultrafine fibers and provided theoretical guidance for future electrospinning experiments.

Bonding of rubber to steel: Effects of hydroxyl‑terminated polybutadiene on the adhesion of waterborne polyurethane adhesives

Rubber as a substrate exhibits very different surface physical and chemical characteristics from steel. It still remains challenging to achieve a complete interface stripping of steel while maintaining double-sided adhesion between rubber and steel. Hydroxyl-terminated polybutadiene (HTPB) possesses remarkable low-temperature flexibility that contributes to migration and orientation of molecular chains, and contains abundant C = C bonds that facilitate cross-linking reaction. In this work, the hydroxyethyl acrylate (HEA)-terminated waterborne polyurethane (WPUH) adhesive was prepared by introducing HTPB into polyurethane backbone. The impact of HTPB on the properties of WPUH adhesive was investigated by changing HTPB/poly(tetramethylene ether) glycol (PTMG) molar ratio. The reasons for such change were studied focusing on the structure and bonding mechanism of WPUH adhesive. When rubber and steel were bonded together by WPUH adhesive, the rubber would induce non-polar HTPB segments to approach the bonding interface while the steel would attract the polar carbamate groups to its surface. The adhesion was strengthened by the interfacial interaction once WPUH adhesive wetted two substrates. In addition, the 1,2-isomer C = C bonds of HTPB could undergo free radical polymerization with HEA to form a cross-linked network, which improved the cohesion. This study provides a feasible strategy for achieving the goal of effectively bonding rubber-to-steel without residual adhesive stripping.

Multifunctional Nano‐Conductive Hydrogels With High Mechanical Strength, Toughness and Fatigue Resistance as Self‐Powered Wearable Sensors and Deep Learning‐Assisted Recognition System

AbstractHigh mechanical strength, toughness, and fatigue resistance are essential to improve the reliability of conductive hydrogels for self‐powered sensing. However, achieving mutually exclusive properties simultaneously remains challenging. Hence, a novel directed interlocking strategy based on topological network structure and mechanical training is proposed to construct tough hydrogels by optimizing the network structure and modulating the orientation of molecular chains. Combining Zn2+ crosslinked cellulose nanofibers (CNFs) and a polyacrylamide‐poly(vinyl alcohol) double‐network, the unique interlocked‐network structure exhibits an enhanced toughening effect due to hydrogen bonding and metal‐ligand interactions. The aligned nanocrystalline domains achieved by training further contribute to an increase in the toughness and fatigue thresholds. This innovative approach synergistically enhances the mechanical properties of the nano‐conductive hydrogel, achieving a maximum tensile strength of 4.98 MPa and a toughness of 48 MJ m−3. Notably, the CNFs template with anchored polyaniline, when oriented through mechanical training, forms a unique directional conductive pathway, which significantly enhances the power output performance. Besides, a motion recognition system based on a self‐powered sensing device is designed with the assistance of deep learning techniques to accurately identify human motion behaviors. This work showcases a potentially transformative flexible electronic material for self‐powered sensing systems and intelligent recognition systems.

Synergistic Enhancement of Biaxial Stretching and Multilayer Composites in All-Solid-State Polymer Electrolytes.

As an important component of lithium-ion batteries, all-solid-state electrolytes should possess high ionic conductivity, excellent flexibility, and relatively high mechanical strength. All-solid-state polymer electrolytes (ASSPEs) based on polymers seem to be able to meet these requirements. However, pure ASSPEs have relatively low ionic conductivity, and the addition of inorganic fillers such as lithium salts will reduce their flexibility and mechanical strength. To address the above issues, in this paper, the solvent-free method was used to prepare a poly(vinylidenefluoride-co-hexafluoropropylene)/lithium bis(trifluoromethanesulfonyl) imide/poly(ethylene oxide) all-solid-state polymer electrolyte, which was then subjected to 4 × 4 magnification synchronous bidirectional stretching. Subsequently, it was multilayered with PEO-based composite polymer electrolytes to obtain multilayered composite polymer electrolytes (MCPEs). Bidirectional stretching provides superior in-plane and out-of-plane mechanical properties to MCPEs by inducing molecular chain orientation, which suppresses the growth of lithium dendrites. Concurrently, it facilitates the formation of the β-crystal form of PVDF-HFP, thereby weakening the ion solvation effect and reducing the lithium-ion migration energy barrier. Multilayered compounding improves the interfacial contact between MCPEs and electrodes, thereby reducing the interfacial impedance. Experiments have demonstrated that the MCPEs prepared in this paper exhibit high ionic conductivity at room temperature (1.83 × 10-4 S cm-1), low interfacial resistance (547 Ω cm-2), excellent mechanical properties (26 MPa), and excellent cycling rate performance (a capacity retention rate of 90% after 110 cycles at 0.1 C), which can meet the performance requirements of lithium-ion batteries for ASSPEs.

Wet-Spinning Carbon Nanotube/Shape Memory Polymer Composite Fibers with High Actuation Stress and Predesigned Shape Change.

Actuators based on shape memory polymers and composites incorporating nanomaterial additives have been extensively studied; achieving both high output stress and precise shape change by low-cost, scalable methods is a long-term-desired yet challenging task. Here, conventional polymers (polyurea) and carbon nanotube (CNT) fillers are combined to fabricate reinforced composite fibers with exceptional actuation performance, by a wet-spinning method amenable for continuous production. It is found that a thermal-induced shrinkage step could obtain densified strong fibers, and the presence of CNTs effectively promotes the tensile orientation of polymer molecular chains, leading to much improved mechanical properties. Consequently, the CNT/ polyurea composite fibers exhibit stresses as high as 33MPa within 0.36 s during thermal actuation, and stresses up to 22MPa upon electrical stimulation enabled by the built-in conductive CNT networks. Utilizing the flexible thin fibers, various shape change behavior are also demonstrated including the conversion between different structures/curvatures, and recovery of predefined simple patterns. This high-performance composite fibers, capable of both thermal and electrical actuation and produced by low-cost materials and fabrication process, may find many potential applications in wearable devices, robotics, and biomedical areas.

Role of Annealing with Electric Field Toward Improvement of Ferroelectric and Electroactive Properties of PVDF Copolymer and Terpolymer Thin Films.

The present study elucidates the role of annealing with electric field on lamellar crystalline structure and molecular orientation of polymer chains in ferroelectric copolymer (P(VDF-TrFE)) and ferroelectric terpolymer (P(VDF-TrFE-CFE)) spin-coated thin films. The ferroelectric polymer thin films annealed under an electric field support the growth of nanostructure with an "edge-on" lamellar crystalline structure having in-plane molecular chain orientation. The poled P(VDF-TrFE) thin films have higher remnant polarization (Pr) ≈6.2µCcm-2 and saturation polarization (Ps) ≈8.2µCcm-2 at an applied electric field of 250 MV/m compared to unpoled thin films having Pr ≈4.7 and Ps ≈6.2µCcm-2. Also, poled P(VDF-TrFE) thin films show lower coercive field (Ec) ≈94 MV/m compared to an unpoled thin film having Ec ≈105 MV/m. Similarly, poled PVDF-TrFE-CFE thin film shows better ferroelectric properties having Pr ≈0.4 and Ps ≈5.7µCcm-2 at an applied electric field of 200 MVm-1 compared to unpoled thin films having Pr ≈0.4 and Ps ≈4.1µCcm-2. The storage energy efficiency of unpoled and poled P(VDF-TrFE-CFE) thin films is measured to be ≈75% and 80%. Annealing of ferroelectric P(VDF-TrFE) polymer thin films under an electric field demonstrates improved ferroelectric and electroactive properties.

Preparation and properties of phosphorus-containing thermotropic liquid crystal copolyester fibers with excellent flame retardance and mechanical property

In order to acquire polymeric fibers have both excellent flame retardance and mechanical properties, high molecular weight phosphorus-containing liquid crystal copolyesters derived from 6-hydroxy-2-naphthenic acid (HNA), terephthalic acid (TA) and 10-(2,5-dihydroxypheny)-10-hydro-9-oxa-10-phospha phenanthrene-10-oxide (DOPO-HQ) were synthesized via “one-pot” melt polymerization, and then the fibers were obtained by melt spinning method. The structure and property of the copolyesters were studied elaborately by experimental characterization technique and molecular simulation method. Shear shinning behavior was observed from rheology measurement, indicating that the copolyesters had excellent melt fluidity and spinnability. The rigidity of molecular chain was efficiently improved by the phosphorus-containing monomer DOPO-HQ and naphthalene HNA units which could be reflected by the molecular simulation results as well as high Tg values. The flame retardant mechanism of the phosphorus-containing flame retardant copolyester was systematically studied via limiting oxygen index (LOI), vertical burning (UL-94) test, cone calorimetry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the copolyesters exhibit synergistic flame retardant mechanism of gas phase and condensed phase. Meanwhile, mechanical property of the as-spun fibers could be significantly improved by increasing the spinneret draw ratio (SDR) attributed to high molecular chain orientation. The maximum tensile strength of the as-spun fiber was 0.77 GPa observed for P-HNA60P20 at a relatively low SDR of 29. It was shown the unique combination of good thermal stability, spinnability as well as mechanical and flame retardant properties of the copolyesters would make them could be used as high-performance flame retardant materials.

Effect of Chain Orientation on Coupling of Optical and Mechanical Anisotropies of Polymer Films

Polymer films have broad applications in different industries with specific requirements for their optical and mechanical properties. In mass production, processing conditions during film formation that apply forces and motions in various directions to the film tend to manifest preferred molecular chain orientation in the film microstructure, which unavoidably produces optical and mechanical anisotropies. In this paper, we investigate the effect of such macromolecular orientations on the optical and mechanical anisotropies of several polymer films, including polystyrene, poly(methyl methacrylate), poly(ethylene terephthalate), poly(ethylene naphthalate), poly(ether ether ketone), poly(ether sulfones), poly(ethylene chlorotrifluoroethylene), poly(phenylsulfone), and polycarbonate, at temperatures well below their respective glass transitions (Tg). The film mechanical responses, including elasticity, yielding, and post-yield behaviors, were obtained for the in- and out-of-plane directions utilizing tensile and nanoindentation testing methods, respectively. In addition, the net chain orientation within the films was evaluated by birefringence through analyzing the film optical refractive indices, which were verified and complemented by wide-angle X-ray scattering (WAXS) measurements. The results reveal a considerable quantitative correlation between the birefringence and the degree of elastic anisotropy and a qualitative correlation between the chain orientation and the film post-yield tensile instability (necking). These observations corroborate the interrelationship between the microstructure of polymer films and their optical and mechanical properties. In addition, they emphasize that process conditions can be selected to tune the optical and mechanical anisotropies to best serve the material performance in specific devices. We also propose an empirical equation to approximate the out-of-plane film stiffness based upon the optical and in-plane mechanical properties.

Enhanced melt flow UHMWPE/HDPE blends melt spinning and performance study

AbstractThe extremely low melt flowability of ultra‐high molecular weight polyethylene (UHMWPE) is the primary obstacle to its melt processing. Particularly in melt spinning processes, the extremely high molecular weight of UHMWPE and the density of entangled molecular chains severely limit its production efficiency and monofilament performance. This study investigates the effect of flow modifiers on the melt spinning process of UHMWPE/HDPE blends, focusing on CaSt2, PEG, and CaSt2/silicone powder composite additives, and their impact on the standard tensile samples and monofilament tensile properties of UHMWPE/HDPE. The mechanism of additive influence on the tensile properties of UHMWPE/HDPE blends is analyzed through tensile strength testing, thermal analysis, and microscopic morphology observation. The results show that in standard tensile samples, CaSt2 or CaSt2/silicone powder composite additives can enhance the crystallinity of the blend, thereby improving its tensile strength. Conversely, adding PEG significantly reduces the crystallinity and tensile strength of the blend. The maximum tensile strength of CaSt2‐modified UHMWPE/HDPE monofilament is 1236.61 MPa. This enhancement is attributed to the lubricating effect of CaSt2, which simultaneously assists the molecular chains in the amorphous region, and the reorientation of the stress‐induced molten lamellar structure under tension, greatly promoting the formation of straight‐chain crystals in the monofilament. During hot drawing, PEG inhibits the formation of straight‐chain crystals in the monofilament, resulting in a 3.06% decrease in maximum crystallinity compared with standard tensile samples. When CaSt2 is combined with silicone powder, the additives tend to aggregate during hot drawing, and these larger aggregate particles hinder the orientation of molecular chains along the drawing direction, resulting in a 30.75% decrease in maximum tensile strength of the monofilament compared with the standard tensile samples.Highlights The tensile property of UHMWPE/HDPE blends modified with additives was discussed. Analytical techniques including DSC, SEM, and tensile strength tests were used. The maximum tensile strength of the monofilament can reach up to 1236.61 MPa. UHMWPE/HDPE/CaSt2 = 60/40/0.5 exhibits the best tensile property.

A clean, simple, and efficient method for preparing vibration-reducing low-carbon bamboo building materials with high strength

Large-format bamboo panels prepared by bamboo flattening are adhesive-free and retain the natural structure of bamboo, making them ideal materials for interior architecture. However, due to poor dimensional stability and vibration-reducing properties, flattened bamboo easily deforms and vibrates when applied to building walls and floors due to ambient humidity changes or external excitation, impacting both comfort and structural safety. In this work, a clean, efficient, and simple densification process for flattened bamboo is developed to prepare low-carbon bamboo building materials with enhanced vibration reduction. The results indicated that the densification process reduced the vibration intensity of the flattened bamboo under excitation, changed its vibrational modes, avoided low-frequency resonance, and improved its vibration reduction and suppression properties. The dynamic stiffness of the densified bamboo increased to 3.23–3.63 times, while the root mean square (RMS) and transfer function value decreased by 20.84 % and 62.5 %, respectively. The MOE (16.2 GPa) and MOR (276 MPa) increased to 2.73 times and 2.22 times, respectively. The densified bamboo met the dimensional stability requirements of the GB/T 18102–2020 building material standards. Compared with damping, the increased stiffness played the primary role in improving the vibration-reducing properties of densified bamboo. The hydrothermal mechanical treatment changed the structure and composition. From a macroscopic perspective, the gradient structure of the vascular bundles and parenchyma cells was gradually plasticized and homogenized, compacting large capillary pores and channels such as those in parenchyma cells, vessels, and sieve tubes. On a microscopic level, defects such as pits, intercellular spaces, and micropores were filled, and microfibrils between the middle lamellae were tightly stacked, forming a mechanically-interlocked structure. At the molecular scale, there was an increase in the crystallinity and orientation of cellulose molecular chains, accompanied by an increase in hydrogen bond density. The densified bamboo developed in this study shows good application potential for vibration-reduction structures such as buildings and rail transit.

Effect of Aggregation Structure on Capacitive Energy Storage in Conducting Polymer Films.

Conducting polymers (CPs), a significant class of electrochemical capacitor electrode materials, exhibit exceptional capacitive energy storage performance in aqueous electrolytes. Current research primarily concentrates on enhancing the electrical conductivity and capacitive performance of CPs via molecular design and structural control. However, the absence of a comprehensive understanding of the impact of molecular chain spatial order on ion/electron transport and capacitive performance impedes the development and optimization of advanced electrode materials. Here, a solvent treatment strategy is employed to modulate the molecular chain spatial order of PEDOT : PSS films. The results of electrochemical performance tests and Grazing Incidence Wide Angle X-ray Scattering (GIWAXS) show that Poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonic acid) (PEDOT : PSS) films with both face-on and edge-on orientations exhibit exceptional electronic conductivity and ion diffusion efficiency, with capacitive performance 1.33 times higher than that of PEDOT : PSS films with only edge-on orientation. Consequently, molecular chain orientations conducive to charge transport not only enhance inter-chain coupling, but also effectively reduce ion transport resistance, enabling efficient capacitive energy storage. This research provides novel insights for the design and development of higher performance CPs-based electrode materials.

Effect of pulsation elongational stress on the structure and properties of preparing self-reinforced sheets

A vane-type melt pulsation pumping device induces molecular chain orientation in HDPE melts via pulsating stretch-compression, enabling self-reinforced sheet extrusion. Experiments assess the impact of varying device temperature and rotational speed on the mechanical properties and microstructure of extruded sheets. The results show that the orientation of the samples can be preliminarily verified by heating test. SEM analysis reveals closely aligned HDPE crystal regions along the extrusion direction following pulsating elongational stress. 2D-WAXD analysis demonstrates a shift in diffraction intensity where it diminishes in the meridional direction and intensifies in the equatorial plane, resulting in a maximum orientation index of 0.683, an increase of 16.6% compared to direct extrusion. When the temperature of the melt pulsation pumping device is set to 180°C and the shaft speed is set to 30 rpm, the tensile strength of the sheets in the extrusion direction reached a maximum value of 66.37 MPa, surpassing that of directly extruded samples by 42.7% and that of compression-molded samples by 90%. In summary, this research realizes the self-reinforced and efficient continuous extrusion of single-component HDPE sheets through a simple device and process, which is of great significance for convenient recycling and environmental protection.

Customizing superior surface insulation properties of polymeric dielectric via in-plane molecular chain orientation

Surface flashover is a common breakdown phenomenon on material surfaces for which surface charge migration property, determined by surface composition and molecular chain structure, is crucial. Precise modulation of charge migration property by simple and efficient methods to improve surface flashover voltage is the goal in industry. Here, in-plane molecular chain orientation (MCO) modulation by uniaxial stretching was proposed to achieve this goal and investigate the intrinsic mechanism of charge migration on flashover. Flashover voltage and accompanying leakage current, performed with electrodes oriented at varying angles to the MCO direction, show a consistent trend, which skillfully reveals that the facilitated charge migration is favorable for improving flashover voltage. When the stretching ratio is 3.5, the flashover voltage along the stretching direction (SD) increases by up to 48.7%, while the in-plane minimum flashover voltage remains essentially unchanged with the change in stretching ratio. Molecular chain segment motion properties along different directions further elucidate that the surprising improvement of flashover voltage along SD is primarily due to the MCO that promotes intra-chain charge migration. This work provides a new perspective on anti-flashover modification of polymeric dielectric and will promote the development of surface flashover mechanisms.

Molecular chain orientation and mechanical properties of hydrogenated nitrile-butadiene rubbers with different acrylonitrile content and crosslink density

A study of the thermal and mechanical properties, as well as the molecular chain orientation of sulfur-vulcanized hydrogenated nitrile-butadiene rubber (HNBR) with acrylonitrile (ACN) content of 34 and 36 wt% and different crosslink density is presented. The objective is to establish the relationships between structural changes during stretching and the tensile and elastic behavior of HNBR having different chain microstructure. The (vulcanized) HNBR samples are amorphous at room temperature with glass transition temperatures that increase with increasing ACN content and crosslink density. The samples do not exhibit strain-induced crystallization. Stretching at room temperature only induces orientation of the amorphous segments along the stretching direction, which contributes to improved tensile strength, strain-hardening, and toughness, while preserving excellent elastic recovery of the rubbers. Precise correlations are established between the degree of orientation of the amorphous chain and the deformation in the framework of the affine deformation model of rubber elasticity.

Bending of polymer films: a method for obtaining a compressive modulus of thin films.

Due to the advent of various foldable electric devices, it is becoming increasingly important to understand the bending properties of film materials. Bending of isotropic materials may be trivial if elastic deformation is small within a range of linear elasticity, which is often the case for bending. However, bending of polymer films, often used in recent foldable devices, may not be the case. Polymer films are frequently fabricated with stretching, which induces anisotropic orientation of molecular chains. In addition, there are many studies on bimodulus materials, which suggest the importance of the difference in tensile and compressive elastic moduli, i.e., the importance of elastic asymmetry, considering that bending involves compression and extension. In this study, we extended the standard linear elastic theory to include elastic anisotropy and elastic asymmetry and developed a method for obtaining compressive moduli of films, which cannot be obtained by a simple compression test because thin films under compression buckle at small strains. Our method is based on a bending test combined with a uniaxial tension test, which allows the measurement of Poisson's ratio in addition to Young's modulus, which are both anisotropic and asymmetric. To test our theory and method, we further performed experiments on biaxially stretched poly(ethylene terephthalate) (PET) films. As a result, we found non-negligible anisotropy in Poisson's ratio and non-negligible asymmetry (bimodulus) in tensile and compressive moduli. We further justify our framework by demonstrating a clear data collapse to show agreement between experiment and theory, clarifying limitations. Our results suggest the importance of elastic anisotropy and elastic asymmetry in bending of industrial films and give fundamental knowledge on this subject, which would be useful for applications. Such applications include the control of the position of the neutral plane and precise measurements of elastic moduli and Poisson's ratio, which are crucial, e.g., for the development of tough flexible electric devices and for the structural designs using compliant mechanisms.

Effects of different types of functionalized polypropylenes on the tensile strength of short carbon fiber-reinforced polypropylene composites

In this study, the effects of various functionalized polypropylenes (PPs) with different types and contents of functional groups and crystallinities on the tensile strength of short carbon fiber (SCF)-reinforced plastics (SCFRPs) prepared by injection molding were evaluated. The tensile strengths of SCFRPs were significantly influenced by interfacial adhesion. The types and contents of functional groups introduced into functionalized PP were the dominant factors impacting the development of interfacial adhesion. In particular, near the surface where SCF and PP were highly oriented in parallel, functionalized PP with more functional groups added to side chains exhibited higher interfacial adhesion than that with fewer functional groups. These results suggested that PP molecular chain orientations resulting from the shear flow of injection molding were among the key factors affecting the interfacial adhesion of the PP matrix.

Effect of ultrasonic-assisted on the bonding properties of hot-pressing molded polybutylene terephthalate/aluminum alloy composite

ABSTRACT The mechanical properties and structure of polybutylene terephthalate (PBT)/aluminum (Al) composite prepared by ultrasonic-assisted hot-pressing were analyzed, and the influence of ultrasonic-assisted on the bonding properties of PBT/Al composite was studied. The experimental results showed that under the optimal ultrasonic-assisted conditions, the tensile shear strength of the PBT/Al composite reached 26.55 MPa, which was 22.18% higher than that of the PBT/Al composite without ultrasonic-assisted (21.73 MPa). Scanning electron microscopy (SEM) showed that during the hot-pressing process, ultrasonic-assisted promoted the embedding of PBT in the anodic oxide pores on the surface of Al, forming a stronger mechanical interlocking structure. X-ray diffraction (XRD) showed that ultrasonic-assisted did not change the crystal type of PBT, but the shear effect of ultrasound affected the arrangement and orientation of molecular chains in the PBT melt, resulting in changes in crystallinity. X-ray photoelectron spectroscopy (XPS) showed that ultrasonic-assisted did not generate new chemical bonds during the hot-pressing process. Therefore, during the hot-pressing process, ultrasonic-assisted promoted the embedding of PBT in the anodic oxide pores on the surface of Al, enhanced the mechanical interlocking effect between PBT and Al, and improved the tensile shear strength of the PBT/Al composite.

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.