We are pleased to introduce the collection, 2022 Retrospective: Polymeric and Composite Materials. This collection aims to showcase original research and review-based papers on the most exciting developments of the past couple of years. The work presented here highlights the broad diversity of research performed across the section, and aims to put a spotlight on the main areas of interest. All research presented here seeks to display strong advances in theory, experiment, and methodology with applications to compelling problems. Authors are encouraged to showcase their most recent discoveries and to kickstart scientific discourse around them.

City University of Hong Kong

Nagoya University

Frontiers in Materials

Polymeric and Composite Materials

2022 Retrospective: Polymeric and Composite Materials

This collection of articles covers a range of Research Topics in polymeric and composite materials. Potential application areas covered include the development of construction materials, materials for efficient thermal management of electronic devices, polymer blends from biodegradable polymers, surface modification of nanoparticles for biomedical use, molding of two-dimensional (2D) woven CFRP into complex shapes, and transparent electrodes in organic solar cells.With demand for fly ash tending to exceed the supply for incorporation into construction materials for the building industry, <a href="https://doi.org/10.3389/fmats.2024.1267197">Liu et al.</a> studied the use of dactite powder to partially replace fly ash in the preparation of cementitious materials. The study found that the fineness of dacite powder is controlled by ball milling time, which affects the final performance. The authors also suggest an appropriate ratio of dactite powder to fly ash in the cement mixture, giving the best performance.In electronic devices, the development of new materials for thermal management is important. In particular, <a href="https://doi.org/10.3389/fmats.2021.817061">Kong et al.</a> developed a new composite system consisting of boron nitride nanosheets (BNNS) and cellulose nanofibers (CNFs). The BNNS were prepared by a water exfoliation method using the hexagonal boron nitride powder. The BNNS/CNF composite was then formed by a water filtration method similar to that used in the pulp industry; due to the 2D structure and in-plane compression of the BNNS, this composite has a very high in-plane thermal conductivity.The continued awareness of the environmental impact of petroleum-derived plastics has led to a real need for the development and use of naturally derived biodegradable materials such as polylactic acid (PLA). In order to overcome the inherent brittleness of PLA, the blending with a biodegradable elastomer such as poly (ε-caprolactone) (PCL) is a possible solution. <a href="https://doi.org/10.3389/fmats.2024.1377340">Negaresh et al.</a> have combined glycidyl methacrylate (GMA) and nanocalcium carbonate (NCC) to improve the poor compatibility between PLA and PCL in blends and enhance the interfacial interaction between PLA and PCL. Although GMA enhanced the elongation at break and Izod impacts the strength of the blend, NCC improved the tensile modulus and impact strength.Nanoparticles (NPs) with appropriate surface functionalization have found applications in the biomedical field; <a href="https://doi.org/10.3389/fmats.2022.878455">Sotoma</a> reviewed the literature on surface coatings of a number of nanoparticle types (nanodiamond, magnetic NPs, gold NPs, gold nanorods, and mesoporous silica) coated with hyperbranched polyglycerol (HPG) and polydopamine (PDA). Both HPG and PDA have low toxicity and could potentially reduce the inherent toxicity of NPs in biological systems. Their potential applications and hurdles to their development are also illustrated.When forming dry 2D woven CFRP fabrics into final 3D product shapes, knowledge of deformation and fiber orientation is important for understanding the performance of composite structures. <a href="https://doi.org/10.3389/fmats.2022.831820">Sun et al.</a> studied and compared dry fabric forming using a number of finite element-based modeling techniques and analytical solutions, and compared simulation results with experimental observations of two punch forming-geometries, i.e., hemispheric and tetrahedron.In organic solar cells, the development of transparent electrodes and hole transport layers requires transparency, conductivity, and stability; <a href="https://doi.org/10.3389/fmats.2022.860859">Sánchez Vergara et al.</a> studied hybrid films consisting of poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT: PSS) and hybrid films consisting of a seven-coordinated organotin (IV) complex modified with graphene. The optical properties of the hybrid films were investigated. The hybrid films were packaged into a complete solar cell structure (glass/ITO/PEDOT: PSS/graphene complex/BPhen/Ag) together with basophenanthroline (BPhen) as an electron transport layer, and their conductive behavior was discussed.RL: writing&#x2013;original draft and writing&#x2013;review and editing. PV: writing&#x2013;original draft and writing&#x2013;review and editing.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors, and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Editorial: 2022 retrospective: polymeric and composite materials

To expand the potential applications of polylactic acid (PLA), it is essential to incorporate a highly flexible polymer into the blend. Polycaprolactone (PCL) is an ideal choice due to its ductility and biodegradability. However, blending PLA with PCL resulted in weak mechanical properties. To address this issue, glycidyl methacrylate (GMA) and nano calcium carbonate (NCC) were introduced to enhance the adhesion at the interface between PLA and PCL. SEM images provided clear visual evidence of the impact of GMA and NCC on the morphology of the blend. Both components were effective in reducing the size of the dispersed PCL phase, shrinking it to approximately half the size of the original blend. Spectroscopic analysis revealed that GMA caused a reaction between its epoxy group and the hydroxyl and carboxyl groups of PLA and PCL. This reaction led to the formation of strong peaks in the 6.5 to 7.5 range in 1H NMR, as well as peaks at 76 and 139 ppm in 13C NMR. These findings were further corroborated by FT-IR, which demonstrated that NCC, despite its surface coating, did not create any new bonds. Rheological studies further demonstrated the positive effects of GMA and NCC. Both the storage modulus (G′) and complex viscosity (η*) of the blends increased, showing improved post-processing performance. Investigation into the shear-thinning behavior of the uncompatibilized blends revealed that NCC caused a significant decrease in complex viscosity at higher frequencies, indicating the disruption of the nanoparticle network. The power-law slope was measured to be 0.62. In contrast, the blend containing the compatibilizer demonstrated a moderate decrease in viscosity, with a power-law slope of 0.36. To analyze the behavior of the PLA/PCL blends in the presence of compatibilizers and nanoparticles at intermediate frequencies, the Palirene model was utilized. The superior integrity of the compatibilized blend was effectively demonstrated by the model, which showed enhanced stress transfer and phase relaxation.

To expand the potential applications of polylactic acid (PLA), it is essential to incorporate a highly flexible polymer into the blend. Polycaprolactone (PCL) is an ideal choice due to its ductility and biodegradability. However, blending PLA with PCL resulted in weak mechanical properties. To address this issue, glycidyl methacrylate (GMA) and nano calcium carbonate (NCC) were introduced to enhance the adhesion at the interface between PLA and PCL. SEM images provided clear visual evidence of the impact of GMA and NCC on the morphology of the blend. Both components were effective in reducing the size of the dispersed PCL phase, shrinking it to approximately half the size of the original blend. Spectroscopic analysis revealed that GMA caused a reaction between its epoxy group and the hydroxyl and carboxyl groups of PLA and PCL. This reaction led to the formation of strong peaks in the 6.5 to 7.5 range in 1H NMR, as well as peaks at 76 and 139 ppm in 13C NMR. These findings were further corroborated by FT-IR, which demonstrated that NCC, despite its surface coating, did not create any new bonds. Rheological studies further demonstrated the positive effects of GMA and NCC. Both the storage modulus (G′) and complex viscosity (η*) of the blends increased, showing improved post-processing performance. Investigation into the shear-thinning behavior of the uncompatibilized blends revealed that NCC caused a significant decrease in complex viscosity at higher frequencies, indicating the disruption of the nanoparticle network. The power-law slope was measured to be 0.62. In contrast, the blend containing the compatibilizer demonstrated a moderate decrease in viscosity, with a power-law slope of 0.36. To analyze the behavior of the PLA/PCL blends in the presence of compatibilizers and nanoparticles at intermediate frequencies, the Palirene model was utilized. The superior integrity of the compatibilized blend was effectively demonstrated by the model, which showed enhanced stress transfer and phase relaxation.

Poly(lactic acid)/ poly(ε-caprolactone) blends: the effect of nanocalcium carbonate and glycidyl methacrylate on interfacial characteristics

The hydration reaction of mass concrete seriously endangers the structural safety. At present, the concrete production relies excessively on fly ash due to hydration reaction. In view of the problem that the demand of fly ash exceeds the supply, this paper proposes to use dacite powder to partially replace fly ash as the raw material for preparing cementitious materials. Through comprehensive tests and microstructure tests, various properties of dacite powder and fly ash composite cementitious materials are studied. The results show that: 1. The dacite powder with a specific surface area of 650 m2/kg, a fineness of 15% under laser particle size and a ball-milling time of 1.0 h has the best performance. 2. It is advisable to mix dacite powder and fly ash. The total amount of dacite powder should not exceed 30% of the cementitious material. It has the best performance when the amount of dacite powder and fly ash is the same. 3. The alkali activity of aggregate can hardly be inhibited by mixing dacite powder alone. The recommended measures to inhibit the alkali activity of aggregate are: i) mixing more than 20% fly ash alone. ii) mixed with 25% dacite powder and more than 15% fly ash.

The hydration reaction of mass concrete seriously endangers the structural safety. At present, the concrete production relies excessively on fly ash due to hydration reaction. In view of the problem that the demand of fly ash exceeds the supply, this paper proposes to use dacite powder to partially replace fly ash as the raw material for preparing cementitious materials. Through comprehensive tests and microstructure tests, various properties of dacite powder and fly ash composite cementitious materials are studied. The results show that: 1. The dacite powder with a specific surface area of 650 m2/kg, a fineness of 15% under laser particle size and a ball-milling time of 1.0 h has the best performance. 2. It is advisable to mix dacite powder and fly ash. The total amount of dacite powder should not exceed 30% of the cementitious material. It has the best performance when the amount of dacite powder and fly ash is the same. 3. The alkali activity of aggregate can hardly be inhibited by mixing dacite powder alone. The recommended measures to inhibit the alkali activity of aggregate are: i) mixing more than 20% fly ash alone. ii) mixed with 25% dacite powder and more than 15% fly ash.

Study on microstructural and mechanical properties of cementitious materials composed of fly ash and dacite powder

Enhanced transparency, conductivity, and stability are some of the most important factors to consider in order to prepare transparent electrodes (TEs) and hole transport layer (HTL) for organic solar cells. In this study, the transparency, optical, and electrical behavior of hybrid films formed by poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) and heptacoordinated organotin (IV) complexes was improved by introducing graphene. The films were deposited by spin-coating and subsequently characterized by infrared and Raman spectroscopy, and by scanning electron microscopy (SEM) and atomic force microscopy (AFM). All the hybrid films transmitted more than 70% of light in the 600–1,000 nm wavelength region, and the optical band gap obtained is in the range of 2.64 and 3.09 eV. In addition, bathophenanthroline (BPhen) was introduced as an electron transport layer (ETL) in order to study the solar cell with complete architecture, conformed by glass/ITO/PEDOT:PSS-graphene-complex/BPhen/Ag. By incorporating the BPhen, the J–V curve current density values were increased, showing a conductivity change of as much as 2.1 × 10−4 S/cm, and under illuminated conditions a more pronounced J–V curve variation (as much as 2.5 × 101 A/cm2) was observed. In closing, the devices were subjected to accelerated lighting conditions to determine the stability and operating capacity of the solar cells. The electrical behavior of the devices changed. Within the first 2 h, the electrical behavior improved, where the organotin complex without a substituent (complex-a) device presents higher stability than the complex with the chloride substituent (complex-b) device due to the chloride radical interacting with the BPhen. However, the electrical behavior degraded after 4 h almost eight orders of magnitude in current density due to device films and interface degradation.

Enhanced transparency, conductivity, and stability are some of the most important factors to consider in order to prepare transparent electrodes (TEs) and hole transport layer (HTL) for organic solar cells. In this study, the transparency, optical, and electrical behavior of hybrid films formed by poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) and heptacoordinated organotin (IV) complexes was improved by introducing graphene. The films were deposited by spin-coating and subsequently characterized by infrared and Raman spectroscopy, and by scanning electron microscopy (SEM) and atomic force microscopy (AFM). All the hybrid films transmitted more than 70% of light in the 600–1,000&nbsp;nm wavelength region, and the optical band gap obtained is in the range of 2.64 and 3.09&nbsp;eV. In addition, bathophenanthroline (BPhen) was introduced as an electron transport layer (ETL) in order to study the solar cell with complete architecture, conformed by glass/ITO/PEDOT:PSS-graphene-complex/BPhen/Ag. By incorporating the BPhen, the J–V curve current density values were increased, showing a conductivity change of as much as 2.1 × 10−4&nbsp;S/cm, and under illuminated conditions a more pronounced J–V curve variation (as much as 2.5 × 101 A/cm2) was observed. In closing, the devices were subjected to accelerated lighting conditions to determine the stability and operating capacity of the solar cells. The electrical behavior of the devices changed. Within the first 2&nbsp;h, the electrical behavior improved, where the organotin complex without a substituent (complex-a) device presents higher stability than the complex with the chloride substituent (complex-b) device due to the chloride radical interacting with the BPhen. However, the electrical behavior degraded after 4&nbsp;h almost eight orders of magnitude in current density due to device films and interface degradation.

Improved Functionality of Poly(3,4-Ethylenedioxythiophene):Poly(Styrenesulfonate)/HeptaCoordinated Organotin Complex Films via Graphene Applied to Organic Solar Cell Fabrications

Nanoparticles play an active role in biomedical science due to their unique properties, which cannot be obtained from bulk materials. Therefore, understanding and controlling the physicochemical properties of nanoparticles are gaining increasing importance for their practical applications. Surface coating is an important technique that controls the physical properties of nanoparticles since the coating is the first part of the nanoparticle that is in contact with the environment. Additionally, the coating creates robust targeting, therapy, imaging, and sensing opportunities. This review first introduced two recently developed outstanding coatings, namely, hyperbranched polyglycerol and polydopamine, and the research achieved by the polyglycerol/polydopamine-coated nanoparticles was then highlighted.

Nanoparticles play an active role in biomedical science due to their unique properties, which cannot be obtained from bulk materials. Therefore, understanding and controlling the physicochemical properties of nanoparticles are gaining increasing importance for their practical applications. Surface coating is an important technique that controls the physical properties of nanoparticles since the coating is the first part of the nanoparticle that is in contact with the environment. Additionally, the coating creates robust targeting, therapy, imaging, and sensing opportunities. This review first introduced two recently developed outstanding coatings, namely, hyperbranched polyglycerol and polydopamine, and the research achieved by the polyglycerol/polydopamine-coated nanoparticles was then highlighted.

Polyglycerol/Polydopamine-Coated Nanoparticles for Biomedical Applications

In this study, four representative finite element (FE) based modelling techniques and an analytical solution for the prediction of 2D woven fabrics’ deformation during forming are compared back-to-back. Ordered from high to low fidelity they are: 1/a Multi-Filament (MF) method that sits between micro- and meso-scale that uses multiple beam element chains to represent each fibre yarn; 2/a meso-scale 3D representation (3D-Shell method) that uses 2D structural shell elements to model each fibre yarn; 3/a 2D continuum element approach that uses coincident membrane and shell elements with user defined material properties to capture the deformation response of textiles in an homogenised sense at the macro-scale; 4/pin-jointed net (PJN) models where the reinforcement directions are represented by extendable 1D elements, pin-jointed at the elements’ crossover points. These modelling approaches are systematically compared for identical forming processes with identical process and material parameters such as boundary conditions, weave architecture and tooling geometries. For completeness and to highlight the importance of considering inter-yarn and preform-to-tool interactions, a kinematic drape algorithm (based on geometrical mapping) is also considered. An attempt is made to visualise the overall modelling performance and computational cost of all representative modelling approaches by simplified metrics.

In this study, four representative finite element (FE) based modelling techniques and an analytical solution for the prediction of 2D woven fabrics&#x2019; deformation during forming are compared back-to-back. Ordered from high to low fidelity they are: 1/a Multi-Filament (MF) method that sits between micro- and meso-scale that uses multiple beam element chains to represent each fibre yarn; 2/a meso-scale 3D representation (3D-Shell method) that uses 2D structural shell elements to model each fibre yarn; 3/a 2D continuum element approach that uses coincident membrane and shell elements with user defined material properties to capture the deformation response of textiles in an homogenised sense at the macro-scale; 4/pin-jointed net (PJN) models where the reinforcement directions are represented by extendable 1D elements, pin-jointed at the elements&#x2019; crossover points. These modelling approaches are systematically compared for identical forming processes with identical process and material parameters such as boundary conditions, weave architecture and tooling geometries. For completeness and to highlight the importance of considering inter-yarn and preform-to-tool interactions, a kinematic drape algorithm (based on geometrical mapping) is also considered. An attempt is made to visualise the overall modelling performance and computational cost of all representative modelling approaches by simplified metrics.

Dry Textile Forming Simulations: A Benchmarking Exercise

A highly thermally conductive heat spreader for applications in electronic devices is becoming increasingly demanding, and therefore the removal of excess heat requires an efficient heat dissipating device. Boron nitride nanosheets (BNNSs) were prepared as thermally conductive fillers using hexagonal boron nitride (h-BN) powder as raw material by a water exfoliation method. A composite film was prepared by vacuum filtration using cellulose nanofibers (CNFs) as the substrate with an in-plane thermal conductivity (TC) of 82.4 W m−1 K−1, thermal conductivity enhancement increasing by 9,486% compared to pure cellulose film. Thus, CNF/BNNS composite films are promising as effective thermal interface materials (TIMs) in electronic devices and electronic component applications.

A highly thermally conductive heat spreader for applications in electronic devices is becoming increasingly demanding, and therefore the removal of excess heat requires an efficient heat dissipating device. Boron nitride nanosheets (BNNSs) were prepared as thermally conductive fillers using hexagonal boron nitride (h-BN) powder as raw material by a water exfoliation method. A composite film was prepared by vacuum filtration using cellulose nanofibers (CNFs) as the substrate with an in-plane thermal conductivity (TC) of 82.4&nbsp;W&nbsp;m−1&nbsp;K−1, thermal conductivity enhancement increasing by 9,486% compared to pure cellulose film. Thus, CNF/BNNS composite films are promising as effective thermal interface materials (TIMs) in electronic devices and electronic component applications.