Cross-linked Network Structure Research Articles

Study on the performances of epoxy asphalt binders influenced by the dosage of epoxy resin and its application to steel bridge deck pavement

The concentration of epoxy resin can outstandingly affect the performance of hot-mixed epoxy asphalt binders. A standard measuring procedure of tensile performance for plastics is applied to investigate epoxy asphalt binders influenced by different dosages of epoxy. The rheological performances and microscope structure evolution process influenced by hot mixed epoxy dosage are investigated by dynamic shear rheometer and laser scanning confocal microscopy respectively. The consequences manifest that the flexibility and anti-rutting ability of epoxy asphalt binders is raised accompanied by raising the dosage of epoxy resin are founded by long time of creep, creep and recovery. Dynamic shear rheometer temperature scans showed that epoxy asphalt binders exhibited excellent thermal stability within the scope of -20 oC and 120oC, when the amount of epoxy resin is no less than 40%. It was observed by laser scanning confocal microscopy that the three-dimensional crosslinked network structure was gradually shaped when the epoxy resin concentration was no less than 40%. These experimental results demonstrated that the excellent performances of epoxy asphalt binders are obtained when the concentration of epoxy resin is no less than 40%. From the viewpoint of epoxy asphalt mixtures, the optimal mixture performances are acquired, when the concentration of epoxy resin is no less than 40%. Finally, when the concentration of epoxy resin is 40%, the excellent cost-performance of epoxy asphalt is obtained, which can be used in steel bridge deck pavement.

Facile synthesis of an acrylic acid-co-2-acrylamide-2-methylpropanesulfonic acid copolymer / polyvinylpyrrolidone semi-IPN hydrogel with excellent swelling and anti-leakage properties

Water scarcity becomes an increasingly serious problem for humankind due to climate change and population growth, especially the water leakage in arid and semi-arid areas. Hydrogel polymers show increasingly important roles on water resources utilization. A novel hydrogel copolymer, acrylic acid-co-2-acrylamide-2-methylpropanesulfonic acid copolymer / polyvinylpyrrolidone (P(AA-co-AMPS)/PVP) semi-interpenetrating network (semi-IPN) hydrogel, was designed and successfully synthesized via a facile one-pot free radical copolymerization method. The main parameters during the synthesis process were optimized, including relative contents of polymer monomers, cross-linking agent, initiator and neutralization agent. Physical characterizations demonstrate that, P(AA-co-AMPS)/PVP hydrogel shows porous three-dimensional network structure, including a crosslinked network structure in P(AA-co-AMPS) copolymers and their intermolecular hydrogen bonding interactions with linear PVP. The as-synthesized P(AA-co-AMPS)/PVP hydrogel not only can deliver superior water absorbing capability (up to 1689.95 g g−1) and good reswelling performance, but also shows excellent water anti-leakage performance when being composed with red clay, demonstrating its multi-role applications in future sustainable agriculture.

Microporous and functional group Co-designed polyesteramide membranes for efficient and broad-spectrum organic solvent nanofiltration

Organic solvent nanofiltration (OSN) is an emerging energy-efficient separations technology, which urgently requires easily processable OSN membranes with high selectivity and broad-spectrum organic solvent applicability to facilitate enhanced industrial applications. Herein, we describe the preparation of microporous polyesteramide (PEA) membranes through interfacial polymerization (IP) between amino-diphenol monomers and trimesoyl chloride (TMC) on a poly(ether ether ketone) (PEEK) support. The crosslinked network structures and large twisted monomers enhance the microporosity of PEA membranes, leading to a significant improvement in solvent permeance while maintaining high selectivity. The optimized PEA membrane demonstrates exceptional permeance for acetone (21.0 ​L ​m−2 ​h−1 bar−1) and methanol (14.3 ​L ​m−2 ​h−1·bar−1), with a molecular weight cut-off of 296 ​g ​mol−1. Additionally, the PEA/APH-diphenol membrane exhibits ultrafast permeance for the nonpolar solvent toluene (8.3 ​L ​m−2 ​h−1·bar−1), owing to the introduction of a large number of ester groups. Overall, PEA membranes prepared through the molecular-level structure design of IP monomers possess enormous industrial application potential owing to their high performance and broad-spectrum applications.

Phosphorus and nitrogen supramolecule for fabricating flame-retardant, transparent and robust polyvinyl alcohol film

Supramolecular flame retardants have attracted increasing attention recently due to their simple and eco-friendly preparation process. In this study, a novel flame retardant HEPFR was prepared using supramolecular self-assembly technology between piperazine and 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP). It was introduced into polyvinyl alcohol (PVA) matrix to form PVA/HEPFR composite film. Subsequently, the transparency, mechanical properties, thermal stability, and flame retardancy of PVA/HEPFR films were studied. Due to the hydrogen bonded cross-linked network structure between PVA and HEPFR, the mechanical properties of PVA/HEPFR films have been improved, while maintaining good transparency. With 10 wt% addition of HEPFR, PVA films can reach the VTM-0 level in UL-94 testing. And the limiting oxygen index can be increased from 18.5% of pure PVA to 26.5%. The peak heat release rate was reduced by 61.5%. The flame retardancy and thermal stability of PVA/HEPFR films have been greatly improved. This study provides a “one stone, three birds” strategy for preparing flame-retardant, transparent, and robust PVA film.

Cellulose hydrogels with high response sensitivity and mechanical adaptability for flexible strain sensor and triboelectric nanogenerator

Cellulose hydrogels are widely regarded as green and environmentally friendly flexible electronic materials. Herein, a novel multiple cross-linked cellulose hydrogel (MCC/SA20/MCC-g-P(AA-co-AM-AMPS)) with high sensitivity (gauge factor = 440, 670 %, 60 ms) and good mechanical adaptability was designed and prepared. The prepolymer (MCC-g-P(AA-co-AM-AMPS)) was introduced into the microcrystalline cellulose/sodium alginate (MCC/SA) hydrogel network to form a multiple cross-linked network structure, which effectively enhanced the tension and elasticity of the cross-linked network, and improved the mechanical adaptability and sensitivity of the hydrogel. Additionally, it was assembled as a strain sensor that can accurately identify and monitor various motion states of the human body. It was also assembled as a friction nanogenerator (TENG) that continuously generates a stable open circuit voltage (7.2 V) for self-powering small electronic devices. This study provides an effective and feasible strategy for cellulose hydrogels in flexible sensors for sports health monitoring, sustainable green energy harvesting, and self-powering applications for small electronic devices.

Development of urea-glyoxal resin wood adhesives with multiple crosslinking network structures using epoxy resin

To mitigate the potential risks posed to human health and the environment by formaldehyde emissions originating from formaldehyde-based adhesives, adopting low-toxicity and biodegradable glyoxal as an alternative to formaldehyde in the synthesis of amino resin adhesives represents a direct, convenient, and promising strategy. Urea-glyoxal (UG) resins represent the most minimalist category within the family of glyoxal-based wood adhesives. However, their widespread application is limited due to inferior adhesive properties and inadequate water resistance. In this study, we enhanced the bonding properties of urea-formaldehyde (UG) by formulating EPn-UG wood adhesive, which integrates UG resin with epoxy resin (EP). Structural characterization revealed successful incorporation of the epoxy backbone into the low molecular chain of the UG resin via ring-opening reactions between the epoxy groups and amino groups on the UG resin. Additionally, the EPn-UG adhesive exhibits a lower curing temperature and higher storage modulus. At an EP addition level of 5 %, the dry and wet strength of EP5-UG bonded plywood, measured after immersion in water at room temperature for 24 hours, were recorded as 1.65 and 1.02 MPa, respectively. This demonstrates a significant improvement of 34 % and 149 % compared to UG resin. Notably, the bonding strength exhibited a remarkable breakthrough from 0 to 0.61 MPa after immersion in water at 63°C for 3 hours. These findings suggest that the introduction of EP enhances the formation of a denser crosslinked network, effectively boosting both the bonding strength and water resistance of UG adhesives. This study presents a novel approach for investigating formaldehyde-free adhesives, further facilitating the industrial implementation of UG resin.

Dynamic covalent bonds of hemiacetals and acetals enables reprocessability and raw material recyclability of high performance cellulosic thermosetting resins

Despite covalent adaptable networks (CANs) imparting the reprocessing performance of crosslinked polymers, due to reversible bond exchange of the dynamic covalent bonds; it is still a huge challenge to design catalyst-free, fast reprocessing, controlled degradation and raw material recycling biomass base CANs. Here, for the first time, we prepared cellulose CANs base on hemiacetal and acetal bonds (ACCs) via aldehyde and hydroxyl reaction of the dialdehyde crosslinker with hydroxypropyl cellulose (HPC). By regulating the crosslink density and chemical structure of the crosslinked network, ACCs exhibit tunable thermal and mechanical properties. The crosslinked network structure of the ACCs benefits from the rapid bond exchange of the hemiacetal and acetal bonds at elevated temperatures, which allows for rapid stress relaxation and thus, superior reprocessing properties. In addition, it was found that the dynamic exchange of acetals in the ACCs is influenced by the chain length and flexibility of the crosslinker. Moreover, ACCs possess good degradation and cellulose feedstock recycling properties due to the acid sensitivity of the acetal bonds. This work provides an effective solution to the problems of resource waste caused by petroleum-based thermoset plastics.

Remarkably improved cycling stability of commercial micron-sized silicon enabled by a novel organic/inorganic hybrid binder

Silicon (Si) anode with ultra-high capacity and low cost are highly desirable for next-generation high-energy lithium-ion batteries, whereas suffers from severe volume change that causes rapid capacity decay upon lithiation/delithiation. The development of high-performance binders to alleviate volumetric expansion and maintain integrity of Si particles remains a significant challenge. Here, reported is a novel organic/inorganic hybrid binder composed of partial neutralized polyacrylic acid (PAAS) and sodium metaborate tetrahydrate (SMTH), which achieves in-situ crosslinking upon drying wafer electrodes. The robust crosslinked network structure with borate ester bonds is successfully attained, and can be modulated by changing the content of sodium metaborate. The strong covalent bond network endows the hybrid binder system with superior mechanical properties and powerful adhesion, which improve the contact and integrity of wafer silicon electrode by suppressing volume expansion and exfoliation, therefore facilitating Li-ion migration and enhancing electrochemical performance. The resulting commercial micro-silicon wafer electrode with PAAS/0.08SMTH binder remains a reversible specific capacity of 1670 mAh g−1 after 150 cycles at 300 mA g−1, largely superior to that prepared with the original PAAS binder because its reversible specific capacity was determined to be only 1046 mAh g−1 under identical conditions. The in-situ crosslinked 3D network structure provides a facile feasible way to improve the high-capacity anode materials for lithium-ion batteries.

Insight into low-grade natural Linze palygorskite for composite particles preparation towards efficient wastewater treatment

Natural clay possesses advantages such as low cost and high adsorption capacity, rendering it a promising adsorbent for wastewater treatment. In this work, low-grade Linze palygorskite (LZ), comprising 20.5% palygorskite, was utilized as a representative material to synthesize polyvinylformal-LZ (PVFM-LZ) composite particles through cross-linking polyvinyl alcohol (PVA) with formaldehyde. The raw material ratio of LZ and PVA was maintained at a high level of 20:1. Meanwhile, high-purity montmorillonite (Mt) and palygorskite (Pal) were employed as raw materials to prepare PVFM-Mt and PVFM-Pal using the same method, enabling comparative analysis with PVFM-LZ. PVFM-LZ exhibited a notable adsorption capacity of 101.92 mg·g−1 for methylene blue, which was comparable to that of PVFM-Mt and PVFM-Pal. What’s more, owing to the tightly cross-linked network structure formed by PVFM, PVFM-LZ demonstrated minimal loss (2.53%) and swelling (8.0%) rates in water, facilitating easy separation and promoting recyclability. Even after six cycles, its adsorption efficiency remained above 85%. The structure, physicochemical properties and adsorption performance of the three composite particles were meticulously examined before and after adsorption. Kinetic, thermodynamic and isotherm adsorption models revealed that PVFM-LZ exhibited spontaneous surface-controlled monolayer adsorption behavior. The possible adsorption mechanisms included electrostatic interactions, hydrogen bonding, and intermolecular forces. This work may provide an experience for the adsorption application of low-grade natural clay in composite engineering.

Enhancement of epoxy‐cyanate ester blends through staged curing‐induced nanophase separation strategy

AbstractEpoxy‐cyanate ester blends have attracted significant attention due to their unique synergistic properties and versatility in high‐performance applications. However, achieving precise control over the phase‐separated structures in these blends remains a challenge. In this work, we present a strategy for the preparation of epoxy‐cyanate ester blends with high‐performance through staged curing‐induced phase separation. By incorporating a thermally latent catalyst, 4‐ethyl‐2‐methylimidazole tetraphenylborate, into the epoxy‐anhydride‐cyanate system, the reactivity differences of multiple curing reactions within the blend were precisely controlled, thereby inducing the formation of well‐defined nanophase‐separated structures. The polymer systems prepared exhibit high mechanical properties and heat resistance, primarily due to the interpenetrating networks created by the epoxy‐anhydride‐cyanate ester and the formation of nanodomains induced by the staged curing process. Furthermore, epoxy‐cyanate ester blends demonstrate outstanding hygrothermal resistance due to the low polarity of the crosslinked network structure. This work provides new insights into regulating the microstructure of the thermosetting blends and expands the potential applications of these materials in fields requiring long‐term durability and reliability.

Effect of acylhydrazone self-healing agents with different structures on the properties of SBS modified asphalt waterproofing membrane

To prepare SBS modified asphalt (SMA) waterproofing membrane with excellent self-healing performance, in this paper, four self-healing agents (ASHA-A, ASHA-B, ASHA-C, ASHA-D) with acylhydrazone bonds and carbon-carbon double bonds (CC) were synthesized, and were used to prepare self-healing SMA waterproofing membranes (SSMA-A, SSMA-B, SSMA-C, SSMA-D). The effects of ASHAs with different structures on the structure, high and low temperature properties, joint peel strength and self-healing performance of SSMAs were investigated. The Fourier transform infrared spectroscopy and fluorescence microscope results showed that acylhydrazone bonds of ASHAs were introduced into the chains of SBS molecules, and the SBS in SSMAs occurred crosslinking through the CC of ASHAs and SBS, the crosslinked network structures of SBS in SSMA-C and SSMA-D were denser and more complete because ASHA-C and ASHA-D contained more CC involved in the crosslinking reaction. The softening point and low temperature flexibility of SSMAs were enhanced by the formation of the SBS crosslinked network structure, and the optimum dosage of ASHAs was 0.6%. The joint peel strength of SSMA-A, SSMA-B, SSMA-C and SSMA-D increased by 26.68%, 31.25%, 49.52% and 56.97% compared to SMA. The introduction of acylhydrazone bonds with reversible fracture and rearrangement significantly improved the crack self-healing performance of SMA, the impermeability times of SMA, SSMA-A, SSMA-B, SSMA-C and SSMA-D were 13.28 min, 37.29 min, 42.53 min, 53.34 min and 59.67 min after self-healing at 40℃ for 8 h, which indicated that ASHA-D with benzene ring and multiple CC had the best improvement in self-healing performance of SMA.

Degradable, anti-swelling, high-strength cellulosic hydrogels via salting-out and ionic coordination

Cellulosic hydrogels are widely used in various applications, as they are natural raw materials and have excellent degradability. However, their poor mechanical properties restrict their practical application. This study presents a facile approach for fabricating cellulosic hydrogels with high strength by synergistically utilizing salting-out and ionic coordination, thereby inducing the collapse and aggregation of cellulose chains to form a cross-linked network structure. Cellulosic hydrogels are prepared by soaking cellulose in an Al2(SO4)3 solution, which is both strong (compressive strength of up to 16.99 MPa) and tough (compressive toughness of up to 2.86 MJ/m3). The prepared cellulosic hydrogels exhibit resistance to swelling in different solutions and good biodegradability in soil. The cellulosic hydrogels are incorporated into strain sensors for human-motion monitoring by introducing AgNWs. Thus, the study offers a promising, simple, and scalable approach for preparing strong, degradable, and anti-swelling hydrogels using common biomass resources with considerable potential for various applications.

Three-Dimensional Cross-Linking Network Coating for the Flame Retardant of Bio-Based Polyamide 56 Fabric by Weak Bonds.

Weak bonds usually make macromolecules stronger; therefore, they are often used to enhance the mechanical strength of polymers. Not enough studies have been reported on the use of weak bonds in flame retardants. A water-soluble polyelectrolyte complex composed of polyethyleneimine (PEI), sodium tripolyphosphate (STPP) and melamine (MEL) was designed and utilized to treat bio-based polyamide 56 (PA56) by a simple three-step process. It was found that weak bonds cross-linked the three compounds to a 3D network structure with MEL on the surface of the coating under mild conditions. The thermal stability and flame retardancy of PA56 fabrics were improved by the controlled coating without losing their mechanical properties. After washing 50 times, PA56 still kept good flame retardancy. The cross-linking network structure of the flame retardant enhanced both the thermal stability and durability of the fabric. STPP acted as a catalyst for the breakage of the PA56 molecular chain, PEI facilitated the char formation and MEL released non-combustible gases. The synergistic effect of all compounds was exploited by using weak bonds. This simple method of developing structures with 3D cross-linking using weak bonds provides a new strategy for the preparation of low-cost and environmentally friendly flame retardants.

A tough, reversible and highly sensitive humidity actuator based on cellulose nanofiber films by intercalation modulated plasticization

Cellulose nanofiber was an ideal candidate for humidity actuators based on its wide availability, biocompatibility and excellent hydrophilicity. However, conventional cellulose nanofiber-based actuators faced challenges like poor water resistance, flexibility, and sensitivity. Herein, water-resistant, flexible, and highly sensitive cross-linked cellulose nanofibers (CCNF) single-layer humidity actuators with remarkable reversible humidity responsiveness were prepared by combining the green click chemistry modification and intercalation modulated plasticization (IMP). The incorporation of phenyl ring and the crosslinked network structure in CCNF films contributed to its improved water resistance and mechanical properties (with a stress increased from 85.9 ± 3.1 MPa to 141.2 ± 21.5 MPa). SEM analysis confirmed enhanced interlaminar sliding properties facilitated by IMP. This resulted in increased flexibility and toughness of CCNF films, with a strain of 11.5 % and toughness of 9.9 MJ/m3. These improvements efficiently enhanced humidity sensitivity for cellulose nanofiber, with a 4.8-fold increase in bending curvature and a response time of only 3.4 ± 0.1 s. Finally, the good humidity sensitivity of modified CNF can be easily imparted to carbon nanotubes (CNTs) via simple self-assembly method, thus leading to a high-performance humidity-responsive actuator. The click chemistry modification and IMP offer a new avenue to fabricate tough, reversible and highly sensitive humidity actuator based on cellulose nanofiber.

Preparation of a superior soy protein adhesive with high solid content by enzymatic hydrolysis combined with cross-linking modification

The production of traditional wood adhesives relies on petrochemical resources and puts enormous pressure on the ecosystem. Therefore, it is important to use bio-based soy protein adhesives to replace traditional adhesives. However, soy protein adhesives have the problems of low solid content, high viscosity and poor water resistance. In this study, we combined enzymatic hydrolysis with cross-linking modification to reduce the molecular mass of soy protein and increase the solid content of adhesive, constructed a uniform and tight covalent bond cross-linking network in the adhesive. Through this modification strategy, we prepared a soy protein adhesive with high solid content, suitable viscosity and excellent bonding strength. The results showed that compared with 0-SPI adhesive, the viscosity of 4-SPI-18/PA/TA adhesive decreased by 61.6%, reached 21899 mPa·s. Meanwhile, the residual rate of the adhesive increased by 18% (59%), the moisture absorption rate reduced by 7.8% to reach 3.8%. The dry/wet shear strength of modified adhesive increased by 56.1% (1.28 MPa) and 44.3% (0.88 MPa), respectively, and the tensile strain at break increased by 58.1% (14.84%). This is because enzymolysis improved its coating performance, and formed mechanical interlocking with wood. In addition, the amount of SPI increased, and more protein molecules participated in the cross-linking reaction, forming a more uniform and compact cross-linking network structure in the adhesive, effectively improving the bonding strength and toughness. This study provides a novel approach for the preparation of cleaning and tenacious adhesives, aiming to explore a green development model.

Effective decapsulation method for photovoltaic modules: Limonene-induced EVA controlled swelling under sonication and debonding mechanism analysis

Waste crystalline silicon (c-Si) solar cells are rich in metal resources. The detachment of ethylene-vinyl acetate (EVA) copolymer is a critical step in the recycling of end-of-life (EoL) c-Si photovoltaic (PV) modules, but a clean and high-efficiency adhesive removal method is absent. In this study, we presented a green solvent-based approach using limonene with ultrasound assistance for the efficient delamination of EVA from c-Si PV modules. By adjusting the concentration of limonene solution, the degree of swelling of EVA was effectively controlled, reducing the risk of battery damage caused by uneven swelling. The application of an ultrasonic physical field to the swelling system expedited the diffusion and penetration of the swelling agent between the EVA layers, while simultaneously supplying energy for the fracture of cross-linking bonds. Under the optimized laboratory-scale condition (70 °C, 0.5 h and 0.1 M limonene), complete separation of the glass and backsheet from the EVA bonding layer was achieved. The intact c-Si solar cells thus have the potential to be fully recovered in subsequent processes. FT-IR tests and density functional theory (DFT) simulations confirmed that under ultrasound conditions, limonene molecules selectively attacked crosslinking bridges and side chains of ethyl vinyl acetate in the EVA molecular chain. This induced the breakdown of the EVA crosslinked network structure, resulting in a reduction in adhesive strength and ultimately achieving interlayer separation in 20min. The findings of this study provide theoretical support and technical insights for the clean and efficient recycling of PV modules.

Durability and micromechanical properties of biochar in biochar-cement composites under marine environment

Integrating biochar into traditional construction materials presents a promising avenue to reduce carbon emissions from the construction industry. While recent research has focused on the performance of biochar-cement materials, limited attention is given to the durability of biochar in cementitious materials. This study investigated the alterations in the structural, chemical, and mechanical properties of biochar in the cementitious system and marine environment. The results showed an increased pore size in the biochar and a potential collapse of its structure after long-term exposure of biochar to an alkaline cement environment. The decline of the aromaticity, 23.8% increase in matrix defectiveness, and formation of organometallic complexes between Ca2+ and oxygen-containing functional groups of biochar indicated that its interactions with hydrated cement would lead to the changes in its chemical properties. The exposure of biochar to the simulated cement solution reduced its Young’s modulus from 3.81 GPa to 1.55 GPa and hardness from 0.70 GPa to 0.13 GPa possibly due to the collapse of the pore structure. The saponification reaction might disrupt the cross-linking network structure constructed by COOC and C–O–C in the biochar and release the fulvic-acid organics, causing a decrease in the short- and long-term rebound ratios by 5.6–25.6% and 5–17%, respectively. Biochar exposed to the simulated harsh environment (seawater) exhibited an increase in Young’s modulus and hardness by ∼40% compared to virgin biochar. The long-term rebound ratio reached 96.6–99.2% due to brucite, NaCl, and KCl deposition and filling, implying the potential advantage of biochar-cement composites for long-term durability in the marine environment. These findings contribute new insights to the assessment of mechanical performance and durability of biochar-cement composites in diverse environmental conditions.

Design and preparation of sulfur vulcanized polyamide 66 cross-linked nitrile butadiene rubber networked and its application in blending with graphene oxide

This study investigates the effect of a multiphase crosslinked network structure formed using a sulfur vulcanization system on the vulcanization, thermal stability, and mechanical and tribological properties of nitrile butadiene rubber/polyamide 66/graphene oxide (NBR/PA66/GO) composites. Differential scanning calorimetry and glass transition temperature (Tg) were used to evaluate thermal stability. Samples doped with 1 phr of sulfur (1S) have the best "residual carbon at 800 °C" and Tg. The surface morphology after friction wear was characterized using scanning electron microscopy and a 3D profilometer. The tensile and tear strengths of 1S increased by approximately 74 % and 39 %, respectively, compared to those of 0.5S. The coefficient of friction was reduced by approximately 61 % compared to that of 3S. Molecular dynamics simulations were used to explore the microscopic mechanism underlying the effect of the crosslinked structure of the composites on their properties. The NBR/PA66/GO composite exhibited the best 1S properties. However, when the sulfur content was higher, excessive cross-linking occurred, and the sulfide cross-linking network structure inside the matrix was damaged. This study also provides a viable strategy for the preparation of vulcanized rubber-plastic blend composites with potential for a wide range of industrial applications.

Toughing epoxy nanocomposites with Graphite-Nanocellulose layered framework

Epoxy nanocomposites hold immense promise for advanced high-performance applications in coatings, adhesives, and fiber-reinforced composite matrices. However, their widespread use is hindered by low fracture toughness, attributed to highly cross-linked network structure. Here, this study presents a synergistic manufacturing strategy combining ultrasonic graphite-nanocellulose assembly and bidirectional freeze casting to fabricate epoxy nanocomposites with remarkable layered architectures. Subsequent infiltration and curing with epoxy prepolymer produce nanocomposites exhibiting a fracture toughness 4.67 times higher than pure epoxy. Both experimental and theoretical analyses demonstrate the nanocomposite's superior crack propagation resistance, attributable to a range of synergistic toughening mechanisms. These include robust interfacial bonding and mechanical interlocking, which arise from fiber pull-out/flake fracture effects, effectively impeding crack growth. Additionally, the distinctive layered architecture promotes tortuous crack pathways, optimizing fracture energy dissipation. This work offers pivotal insights into structure–property relationships, paving the way for the design of next-generation nanocomposites with tailored, superior mechanical performance.

P/N/Si-rich and flexible coating imparting polypropylene excellent flame retardancy without compromising its inherent mechanical properties

In general, the addition of flame retardants may lead to the degradation of the mechanical properties of polymers, despite enhancing their flame retardancy. However, flame-retardant coatings have the potential to provide good flame resistance to polymers without compromising their inherent mechanical properties. In this study, we applied highly adhesive and flexible polysiloxane flame-retardant coatings (196 μm) to polypropylene, resulting in reductions of 74.9 %, 58.0 %, 80.0 %, and 56.4 % in peak heat release rate, peak smoke production rate, fire growth rate, and mass loss, respectively. By incorporating the lab-synthesized DOPO-modified polysiloxane (APID), the flame-retardant efficiency of ammonium polyphosphate (APP) was greatly enhanced. The primary film-forming agent, (3-aminopropyl) triethoxysilane (APTES), played a key role in maintaining the compatibility of APP and APID with the coating, as well as facilitating the formation of a robust SiOSi crosslinked network structure that strengthened the resulting char layer. The interactivity between the various components, including hydrogen bonds and crosslinked network structures, contributed to improved uniformity, thermal stability, and adhesion of the coatings. Moreover, the coatings exhibited resistance to ultraviolet radiation and water. Our findings suggest that highly flexible and adhesive flame-retardant coatings hold significant potential for applications in polymer protection. These promising results provide a viable pathway for improving the fire protection of polymers through the use of high-adhesive intumescent flame-retardant coatings.