Polymer Composites Research Articles

Ultratough, Robustness, and Reprocessable Thermoset Epoxy Resins Synergistically Enhanced by Hierarchical Coordination Interactions and Dynamic Covalent Networks

AbstractEpoxy resins, ubiquitous and indispensable thermosetting material in various industries, suffer from the resistance to crack initiation, poor ductility, and irreparable permanent cross‐linked network, which hinder their utilization in high‐performance applications and are detrimental to the development of a sustainable economy. However, achieving the trade‐off between toughness, robustness, and reprocessability of epoxy resins remains a formidable challenge. Herein, an epoxy resin that combines ultratoughness, robustness, and reprocessability by incorporating a hierarchical crosslink structure embedded in a transesterification network is reported. The construction of hierarchical coordination structures facilitates formation of dense nano‐hard domains, enabling enhancement of both strength and toughness at multilength scales. As a result, the epoxy resin, integrating covalent adaptable networks with sacrificial non‐covalent networks, exhibits exceptional elongation at break (280%), modulus (1.8 GPa), stress at break (56.3 MPa), and tensile toughness (142 MJ m−3), showcasing its excellent endurance and ability to undergo multiple reprocessability. The application of this epoxy resin in carbon fiber‐reinforced polymer composites further underscores its potential as the resulting HCEV‐CFRPs exhibit unprecedented tensile properties and facilitate multiple non‐destructive recycling of high‐value carbon fiber under mild conditions. This research provides novel design principles for recyclable and high‐performance materials that combine strength and toughness.

Study of mechanical and electrical properties through positron annihilation spectroscopy for ethylene-propylene-diene rubber biocomposites with treated wheat husk fibers

The positron annihilation lifetime (PAL) spectroscopy characteristics of ethylene-propylene-diene monomer rubber (EPDM) composites reinforced with treated wheat husk fibers (WHFs) were investigated for the first time. PAL spectroscopy is employed to study the free volume of polymers. The use of lignocellulosic materials as reinforcement in polymeric composites has gained attention due to their low cost, availability, and eco-friendliness. In this study, the impact of the loading concentration on the interfacial adhesion between the EPDM matrix and WHFs is quantified, along with the evaluation of swelling measurement and tensile properties. Additionally, the nanoscopic properties derived from PAL spectroscopy correlate with the composites’ macroscopic properties. In addition, the dielectric properties of the investigated samples have been studied, and their conductivity has been calculated. To determine the conduction mechanism within these samples and how it is affected by the addition of WHF, the change in electrical conductivity with the frequency of the external electric field applied to the samples was studied, and from this, the conduction mechanism was determined, and the barrier height value was calculated. The experimental results provide insights into the relationship between the structure and properties of EPDM-WHF biocomposites, offering valuable knowledge for developing sustainable and high-performance materials.

Organic polymer composite with inorganic SiO2 particles for mechanical robustness and self-cleaning anti-reflective coatings

Anti-reflective coatings prepared from SiO2 nanoparticles have excellent anti-reflective properties, but the coating's poor mechanical properties and low self-cleaning performance limit its practical application. In this work, SiO2 nanoparticles were modified into hydrophobic particles using surface modification, and then organic polymer were added as a binder to formulate SiO2 sols, which were coated onto a glass substrate to form a anti-reflective coating. The coating can enable the glass substrate to achieve a transmittance of 99.1 % at 580 nm, and it can increase the average transmittance of the glass substrate from 89.6 % to 96.2 % in the 400–1100 nm band. In addition, the coatings prepared from hydrophobic SiO2 nanoparticles composite organic polymers have a water contact angle of 136°, resulting in good self-cleaning properties. The organic polymers can connect the SiO2 nanoparticles together, increasing the mechanical properties of the coating. This multifunctional anti-reflective coating with high transmittance, good mechanical properties and self-cleaning is beneficial in many applications, such as photovoltaic glass, architectural glass, displays and more.

Chemistry of Reduced Graphene Oxide: Implications for the Electrophysical Properties of Segregated Graphene-Polymer Composites.

Conductive polymer composites (CPCs) with nanocarbon fillers are at the high end of modern materials science, advancing current electronic applications. Herein, we establish the interplay between the chemistry and electrophysical properties of reduced graphene oxide (rGO), separately and as a filler for CPCs with the segregated structure conferred by the chemical composition of the initial graphene oxide (GO). A set of experimental methods, namely X-ray photoelectron spectroscopy (XPS), ultraviolet-visible spectroscopy, van der Paw and temperature-dependent sheet resistance measurements, along with dielectric spectroscopy, are employed to thoroughly examine the derived materials. The alterations in the composition of oxygen groups along with their beneficial effect on nitrogen doping upon GO reduction by hydrazine are tracked with the help of XPS. The slight defectiveness of the graphene network is found to boost the conductivity of the material due to facilitating the impact of the nitrogen lone-pair electrons in charge transport. In turn, a sharp drop in material conductivity is indicated upon further disruption of the π-conjugated network, predominantly governing the charge transport. Particularly, the transition from the Mott variable hopping transport mechanism to the Efros-Shklovsky one is signified. Finally, the impact of rGO chemistry and physics on the electrophysical properties of CPCs with the segregated structure is evaluated. Taken together, our results give a hint at how GO chemistry manifests the properties of rGO and the CPC derived from it, offering compelling opportunities for their practical applications.

Polylactide-Based Polymer Composites with Rice Husk Filler

In this work, composites made of polylactide (PLA) and filled with alkali-pretreated rice husk (RH) were investigated. Composites containing 20, 30, and 40 wt.% of RH were synthesized. It was shown that alkaline treatment, along with the change in crystal lattice, led to an increase in the content of non-crystalline parts and the volume of intercrystalline spaces, and the internal surface of the cellulose fiber increased, which resulted in improved adhesion of the fiber with the matrix. The addition of rice husk to the PLA matrix led to an increase in the flexural modulus, which increased to 2881 MPa for the PLA/RH (80/20 wt.%) and 3034 MPa for the PLA/RH (70/30 wt.%) composites and lowered the peak load stress by approximately 43% for the composite with 20 wt.% RH and 56% for the composite with 30 wt.% RH. The reduction in the degree of PLA crystallinity allows macromolecules to move more freely in amorphous regions, which has a positive effect on increasing the flexibility of materials in general. The optimal formulation is a composite consisting of 30% RH and 70% PLA matrix.

Application of Natural (Plant) Fibers Particularly Hemp Fiber as Reinforcement in Hybrid Polymer Composites - Part III. Investigations of Physical and Mechanical Properties of Composites Reinforced with Hemp Fibers

ABSTRACT The article is the third part of a multi-directional analysis of the possibilities, advisability and validity of using natural plant fibers (NPFs) as a reinforcement for polymer structural composites that can be used in the shipbuilding industry in Poland. As a result of the analysis of macroeconomic indicators and natural and non-natural factors regarding NPFs, a representative selection of hemp (Cannabis sativa L.) was made as the raw material to be used to reinforce these composites. Methods and test results are presented enabling comparison of the physical and mechanical properties of the new pro-ecological construction material–hemp fiber reinforced polymer (HFRP), reinforced with fabric made of unmodified and chemically modified hemp fibers.

Boron nitride: The key material in polymer composites for electromobility

AbstractDespite the continuous development and improvement of many technologies and multifunctional materials for the electric powertrain (ePowertrain) for electric vehicles, there are still technical issues and challenges to address such as thermal management in batteries, electric motors, and power electronic devices, as most of their failures are due to poor thermal management. Consequently, conventional engineering polymer materials already used must be replaced since most of them have low thermal conductivity and are therefore limited in performance for thermal management applications. A key solution is to develop highly thermally conductive polymer composites that combine other features, such as flame‐retardant, electrical insulation, and mechanical and barrier properties, by incorporating fillers into the polymer matrix. This approach has attracted intensive research efforts. In this review, we first examine the key drivers, trends, and solutions of the ePowertrain segment, emphasizing thermal management. Second, special attention is given to the state‐of‐the‐art boron nitride (BN) polymer composites with current or potential applications in the automotive industry, especially, in batteries, electric motors, and power electronics. Third, analysis and prediction of thermal properties of BN polymer composites by finite element simulation are presented. Finally, outlooks for future research in this field are highlighted.Highlights Thermal management of batteries, electric motors and power electronics, using BN polymer composites, optimizes the functionality of electric vehicles. Cross‐linked polymers with BNNSs provide resins for high power motors, film capacitors, and Li‐metal battery electrolytes for electric vehicles. Mathematical modeling and life cycle analysis can predict trends and research gaps in ePowertrain applications.

Recent advances in responsive liquid crystal elastomer‐contained fibrous composites

AbstractResponsive polymers can react to surrounding environments by changing their physical and/or chemical properties. Among them, liquid crystal elastomers (LCEs) have emerged as one of the important branches in the field of applied polymer science due to their significant advantages in flexible mechanics and shape memory. Manufacturing LCE fibers with a large specific surface area and functional fillers has become a research hotspot in recent years. This type of LCE‐contained fibrous composite (LCEF) exhibits not only extremely high response sensitivity but also excellent axial mechanical strength and a high degree of deformation freedom. In this paper, we provide a bird's eye view of recent developments in LCEF, including structural designs, synthesis and forming methods, mechanical response principles and modes. Furthermore, we discuss recent advances of LCEF in artificial muscles, smart textiles, biomimetic systems, intelligent soft machines, followed by challenges and possible routes in fabrications and applications of LCEF. At the end, we aim to provide a perspective for an emerging field of stimulus‐responsive polymeric fiber composites.

Thermosetting boron-nitride-filled polybutadiene composites with enhanced thermal conductivity and good dielectric properties

Low dielectric materials with high heat dissipation, low dielectric constant (Dk), and dielectric loss (Df) are urgently needed to address the issues of signal cross-talk and heat accumulation arising from the rapid development of modern communication technology and the integration of microelectronics. Polyolefins, as hydrocarbon polymers, have shown significant potential due to their excellent low dielectric properties. However, their low polarity and flexible structures limit their thermal conductivity and thermomechanical properties. In this study, we developed a method to prepare thermosetting polybutadiene composites with enhanced thermal conductivity and good dielectric performance by modifying hexagonal boron nitride (h-BN) and hydroxyl-terminated polybutadiene (HTPB) with thermally cross-linkable benzocyclobutene (BCB) groups. The properties of the resulting composites were tailored by varying the filler content. With 30 wt% of the BCB-modified filler, the composite (HB-30) displayed excellent dielectric properties (Dk = 2.70; Df = 1.67 × 10−3 @10 GHz). Meanwhile, it exhibited a thermal conductivity of 0.615 W/mK at 35 °C, which was 7.1 times that of pristine HTPB. It also showed significantly enhanced mechanical properties and thermal stability with a storage modulus of 2.7 GPa and a glass transition temperature (Tg) of 208.5 °C. This method proved effective for preparing polymer composites with enhanced thermal conductivity, heat resistance, mechanical properties and good dielectric properties, making them suitable for high-frequency communication applications.

One-pot fabrication of bio-inspired shape-morphing bilayer structures

Soft bilayer structures capable of shape morphing in response to external stimuli have been commonly adopted in the design of soft robots, flexible electronics and many other smart systems. However, existing methods to fabricate such structures generally require multiple steps and may end up a weak interface between the two layers. Here, we report a one-pot fabrication strategy to generate elastomer-based shape-morphing bilayer structures with a seamless interface. Our strategy leverages on a recently developed bioinspired polymer-NaCl particle composite system which can undergo significant osmotic swelling in water. Bilayer structures are readily formed after the precipitation of NaCl particles in liquid polymers under gravity and the crosslinking of the polymers. The shape-morphing behavior of the fabricated bilayer structures can be well controlled by tuning the particle precipitation kinetics, NaCl content, and crosslinking level of the polymer matrix. More importantly, the bilayer structures fabricated using this strategy exhibit more complex shape-morphing responses than typical bilayer structures. Considering the wide applicability of NaCl particle-induced osmotic swelling of polymer composites, our one-pot bilayer formation strategy will greatly benefit many shape-morphing applications with a simplified fabrication workflow and enhanced configurational versatility.

Front Cover

The cover image is based on the Article Percolation behavior and sensing performance of polypropylene‐based conductive polymer composites under compressive strains and temperature by Zhi Wu et al., https://doi.org/10.1002/pol.20230894. Image Credit: Zhi Wu. Percolation behavior and sensing performance of polypropylene‐based conductive polymer composites filled with carbon black and multi‐walled carbon nanotubes (CB/PP, CB/MWCNTs/PP) are comparatively investigated. Under different compressive strains and temperatures, CB/MWCNTs/PP exhibits better conductivity and cyclic sensing properties owing to MWCNTs working as “bridges” between CBs. This is shown in the cover image by first author Zhi Wu. image

In Situ Alloying Enabled by Active Liquid Metal Filler for Self‐Healing Composite Polymer Electrolytes

AbstractSolid inorganics, known for kinetically inhibiting polymer crystallization and enhancing ionic conductivity, have attracted significant attention in solid polymer electrolytes. However, current composite polymer electrolytes (CPEs) are still facing challenges in Li metal batteries, falling short of inhibiting severe dendritic growth and resulting in very limited cycling life. This study introduces Ga62.5In21.5Sn16 (Galinstan) liquid metal (LM) as an active liquid alternative to conventional passive solid fillers, aiming at realizing self‐healing protection against dendrite problems. Compared to solid inorganics, for example silica, LM droplets could more significantly reduce polymer crystallinity and enhance Li‐ion conductivity due to their liquid nature, especially at temperatures below the polymer melting point. More importantly, LMs are unraveled as dynamic chemical traps, which are capable of blocking and consuming lithium dendrites upon contact via in situ alloying during battery operation and further inhibiting dendritic growth due to the lower deposition energy barrier of the formed Li‐LM alloy. As a proof of concept, by strategically designing an asymmetric CPE with the active LM filling, a solid‐state Li/LiFePO4 battery achieves promising full‐cell functionality with notable rate performance and stable cycle life. This active filler‐mediated self‐healing approach could bring new insights into the battery design in versatile solid‐state systems.

In Situ Alloying Enabled by Active Liquid Metal Filler for Self-Healing Composite Polymer Electrolytes.

Solid inorganics, known for kinetically inhibiting polymer crystallization and enhancing ionic conductivity, have attracted significant attention in solid polymer electrolytes. However, current composite polymer electrolytes (CPEs) are still facing challenges in Li metal batteries, falling short of inhibiting severe dendritic growth and resulting in very limited cycling life. This study introduces Ga62.5In21.5Sn16 (Galinstan) liquid metal (LM) as an active liquid alternative to conventional passive solid fillers, aiming at realizing self-healing protection against dendrite problems. Compared to solid inorganics, for example silica, LM droplets could more significantly reduce polymer crystallinity and enhance Li-ion conductivity due to their liquid nature, especially at temperatures below the polymer melting point. More importantly, LMs are unraveled as dynamic chemical traps, which are capable of blocking and consuming lithium dendrites upon contact via in situ alloying during battery operation and further inhibiting dendritic growth due to the lower deposition energy barrier of the formed Li-LM alloy. As a proof of concept, by strategically designing an asymmetric CPE with the active LM filling, a solid-state Li/LiFePO4 battery achieves promising full-cell functionality with notable rate performance and stable cycle life. This active filler-mediated self-healing approach could bring new insights into the battery design in versatile solid-state systems.

Influence of brown algae filler and process parameters on the surface roughness and MRR of jute fiber polymeric composite machined by abrasive water jet

Traditional manufacturing of polymeric composite leads to delamination. Implementing abrasive water jet machining (AWJM) presents a sustainable solution for shaping the polymeric composites, thereby eliminating the need to dispose of chemically contaminated waste. Brown microalgae, commonly found in aquatic environments, serve as viable additives for enhancing the properties of polymeric composites. This study entails the polymeric composite reinforced with jute fiber fabricated by modulating the weight percentages of brown algae powder by 0, 3, and 6 wt.% utilizing the hand layup procedure. The composites were formed and subsequently subjected to drilling by AWJ machining filled with brown algae. The experimental investigation was done to analyze the effect of AWJ parameters: water jet pressure (WJP), traverse speed (TS), and stand-off distance (SoD)—on the material removal rate (MRR) and average surface roughness ( Ra). Orthogonal Array L27 experimental results revealed that polymeric composite reinforced with jute fiber containing 3 wt.% of brown algae exhibited the highest MRR, with an increase of up to 12% compared to other samples. Additionally, these composites demonstrated a significant reduction in surface roughness, reaching up to 8% when compared to alternative samples. Utilizing the Taguchi-based ANOVA method facilitated a systematic exploration and identification of influential factors impacting both MRR and Ra in AWJ machining. Notably, the WJP and SoD emerged as key factors significantly influencing both MRR and Ra.

Progress on the Sound Absorption of Viscoelastic Damping Porous Polymer Composites.

Porous polymer composites (PPC) have developed rapidly recently, which are widely used in various industrial fields. Viscoelastic damping is an important behavior of porous polymer composites, and it can determine the sound absorption for noise reduction applications. This review has mainly covered the viscoelastic damping and sound absorption of porous polymer composites. Different fabrication approaches of porous polymer composites are gathered. The mechanism of viscoelastic damping behavior is described, and also the sound absorption properties. Followed by the introduction of enhanced sound absorption of viscoelastic damping porous polymer composites, including the incorporation of fillers, microstructures modification, combination with nanofibrous materials, and multilayer configuration, etc. The incorporated fillers can effectively adjust the interfacial area in composites, and obtain desired bonding conditions. Microstructures modification is an effective tool to improve the morphologies of both polymer matrix and fillers, which can be achieved by chemical treatment and surface coating. The combination with lightweight nanofibrous layer can increase the low frequency absorption. The configuration of multilayer composites can improve both acoustical and mechanical properties for engineering applications. It is hoped that this comprehensive review is benefit for the promising development of porous polymer composites in related fields.

Numerical Investigation of Polymer-based Biomaterials for Artificial Hip Joint with Diverse Boundary Conditions

Background: Hip suffering is a serious concern for human health, which may be caused by arthritis, accidents, and childhood disorders; hence, man-made joints are the only option for restoring the function of natural hips and ensuring a comfortable life. To design an effective hip joint is a challenging task; there are myriads of novel designs continuously patented over the last two decades. Methods: The finite element approach was utilized in this extensive investigation to assess selfmated polymer-based biomaterials (PTFE, UHMWPE, and PEEK) with different boundary conditions. The numerical analysis was performed to find the stress intensity and deflection of the femoral head and the acetabular components; the evaluation was done critically with a 10-node quadratic tetrahedron element and different mesh intensities. Results: The detailed outcome showcases that the bare PEEK mated GO-PEEK has good load resistance and is affected by minimum stress and deflection, which is quantified at 20.89% less than the PTFE with GO-PEEK (M3) combination. This stress and deflection are quite higher than those of metal implants (Ti6Al4V) but comparatively more prominent materials for human cortical bone. Conclusion: This investigation proved the polymer-on-polymer combination effectively eliminates stress shielding and metal ion emission, reducing revision surgery and elevating implant longevity. Therefore, it was identified that PEEK-based polymer composites are the best-suited alternative substance for hip repair applications.

A Novel Super-Toughness and Self-Healing Solid Polymer Electrolyte for Solid Sodium Metal Batteries.

Solid sodium metal batteries (SSMBs) offer an alternative promising power source for electrochemical energy storage due to their high energy density and high safety. However, the inherent sodium dendrite growth and poor mechanical properties of electrolytes seriously limit their application. Herein, a network structure composed of polyethylene oxide-based composite polymer electrolyte (CPE) is designed with liquid metal nanoparticles (LM) for SSMBs, in which LM can move in the solid electrolyte with the electric field driven. This effect can facilitate the inactivated sodium return to the metal sodium anode, and alloy with dendrites at the same time, which is beneficial for inhibiting the growth of dendrites. The symmetric cell with the CPE containing LM achieves good cyclic stability of more than 1800 and 800h at 0.1 and 0.2mAcm-2, respectively. The energy density of the pouch battery can reach 230Whkg-1. In sum, LM presents great potential to be employed as a performance reinforcement filler for CPEs, which paves the way for achieving high-performance SSMBs.

Assessing the external atmospheric input of microplastics: Two strategies based on polymer composition and aging characteristics

Microplastics (MPs) can be transported over long distances in the environment, hence, distinguishing between MPs generated locally and those introduced from external sources is necessary for regional MP pollution management. In this study, MPs pollution in the dust of Siziwang banner (Sizi), a sparsely populated area on the Mongolian Plateau, and Hohhot, a city with large populations, was observed. The high proportion of small MPs in Sizi (<25 μm), combined with the fact that most air masses reaching the area have undergone long-distance transport, supports the presence of external input through atmosphere. Based on the significantly different composition distributions and surface characteristics of the small sized MPs in Sizi and Hohhot, a composition-based Bray-Curtis similarity index (Comp-BCs) and a carbonyl index-based BCs index (CI-BCs) were established. Contributions of the external MPs input to small MPs in Sizi were estimated as 23–36 %, indicating that the role of atmospheric input on MPs pollution in sparsely populated areas should not be overlooked.

Pinewood biochar antistatic polymer composites: an investigation of electrical, mechanical, rheological and thermal properties

ABSTRACT This study investigates the practical applications of biochar as an innovative and sustainable conductive filler in composite materials. Utilizing the conventional melt-blending method, we prepared conductive pinewood biochar-filled poly(lactic acid)/poly(butylene adipate-co-terephthalate) (PLA/PBAT) composites and systematically examined their electrical, mechanical, rheological and thermal properties. Our results reveal a significant enhancement of electrical and mechanical properties upon the inclusion of conductive pinewood biochar in the PLA/PBAT matrix. With the addition of 10 wt% of conductive pinewood biochar, the average surface resistivity of the composites decreased by three orders of magnitude, measuring 4.86 × 10 10 Ω / sq , which meets the antistatic requirements for polymer composites. Additionally, the average tensile strength of the biochar filler composites improved by 53% with an addition of just 1 wt% of biochar.

Performance of glass epoxy composites under combined effect of in‐plane fiber waviness with circular cutout through tensile test, and image processing technique

AbstractPresent study comprehensively explores the phenomenon of in‐plane fiber waviness in glass/epoxy fiber reinforced polymer (GFRP) composites. Utilizing a pioneering technique that employs a semi‐circular bar to induce controlled fiber waviness, coupled with image processing using OpenCV library in Python coding for precise measurement and analysis of in‐plane fiber waviness. This defect is commonly found in components fabricated with fiber‐reinforced composites. During the process of manufacturing fibers may deviate from their intended orientation due to process variables or resin flow dynamics. Understanding in‐plane fiber waviness is crucial due to its impact on mechanical properties of composites. It is essential for optimizing manufacturing processes and ensuring enhanced structural performance in diverse engineering applications through analysis of strength and failure mechanism. A novel study was conducted by introducing a circular cutout within the fiber waviness region to investigate the combined effect of multiple defects. The experimental tensile test reveals that as waviness ratio (WR) increases a significant decrease in its tensile strength and vice versa. The study incorporates scanning electron microscopy (SEM) image analysis to examine composite failure. By advancing the understanding of in‐plane fiber waviness and its implications, this research significantly contributes to ongoing efforts in composite design and optimization.Highlights Adopting a cutting‐edge method to create controlled fiber waviness that makes use of a semi‐circular bar. Image processing with Python code that makes use of the OpenCV package to precisely measure and analyze in‐plane fiber waviness. A new investigation was carried out to examine the combined effect of multiple flaws by creating a circular cutout within the fiber waviness zone.