Diaminodiphenyl Methane Research Articles

Preparation and Characterization of Epoxy-Based Composite Materials Reinforced with Graphene Oxide

In this study, modified graphene oxide (GO) with γ-APS silane coupling agent before being dispersed into an epoxy/4,4’-diamino diphenyl methane matrix to prepare a composite material using the bar-coating technique. The modified GO materials with the γ-APS silane (GOS) were characterized by infrared spectrum, Zeta potential, and TG/DSC thermal analysis. The amount of silane grafted on the GO is ~ 3.3 wt.%; the Zeta potential value shifted from the negative to the positive region was observed on the surface potential distribution diagram. Scanning electron microscopy, DSC thermal analysis, and dielectric constant were used to characterize the obtained composite epoxy/GO material properties. The results show that graphene oxide, after modification with γ-APS silane agent, has good dispersion ability in the epoxy resin matrix. Composite material epoxy/GOS presented a high dielectric constant value (εaverage = 6.19, at 1 kHz), increasing thermal stability, which is a suitable material promising for future applications.

Biomass-derived epoxy resin and its application for high-performance natural fiber composites

The development of bio-based materials with superior comprehensive properties from biomass resources remains a significant challenge, providing an alternative to conventional petroleum-based materials. This study explores the lignin-derived vanillyl alcohol epoxy (VAE) resin-containing mono and di (m&d) epoxy structure as an adhesive to develop environment-friendly natural fiber-reinforced composites to reduce the carbon footprint. The synthesized m&dVAE containing mono and di-epoxidized (m&d) aromatic rings, when cured with 4, 4´-diaminodiphenyl methane (DDM) hardener, exhibits higher record tensile strength ∼124.0 ± 8.43 MPa and tensile modulus ∼2.88 ± 0.35 GPa compared to a commercial petroleum-based epoxy, diglycidyl ether bisphenol A (DGEBA) thermoset. Additionally, it demonstrated higher adhesion shear strength (∼19.16 ± 0.58 MPa) with cellulose nanofibers film than DGEBA. Moreover, fabricated green composite possesses excellent flexural strength of ∼203.72 ± 2.08 MPa and stiffness of ∼11.58 ± 0.38 GPa than the petroleum-based thermoset composite. The composite’s fracture surface morphology shows that the resin and fibers have good interfacial adhesion. Notably, the sustainable composite showed good hydrophobicity and an excellent heat-resistant index of 144.4°C. The m&dVAE resin can be an alternative to petroleum-based resins as an adhesive, and its environment-friendly sustainable composite could be a promising candidate to replace synthetic materials for high-performance structural applications.

A novel flame retardant epoxy thermoset based on renewable honokiol and furfuryl alcohol

In this study, honokiol epoxy resin was directly functionalized by bio-based material honokiol, which was combined with furfuryl alcohol-derived flame retardant by Diels-Alder reaction to prepare bio-based epoxy cross-linking system. After curing with 4,4′-diaminodiphenyl methane, HE1/FP0.5/DDM (121.37 °C) offered higher glass transition temperature than EP/DDM (91.75 °C). Meanwhile, the HE1/FP0.5/DDM exhibited excellent thermal stability and flame retardancy compared to EP/DDM. The char residue of HE1/FP0.5/DDM was obviously increased from 12.8% (EP/DDM) to 35.6% at 700 °C. Notably, the HE1/FP0.5/DDM achieved a limiting oxygen index value of 37.4% and UL-94 V-0 rating. Cone calorimeter demonstrated that the peak heat release rate, total heat release and fire growth rate of HE1/FP0.5/DDM were 400.29 kW/m2, 33.45 MJ/m2 and 4.40 kW/m2·s, reduced by 57.47%, 63.39% and 41.1% compared with EP/DDM, respectively. The satisfactory flame retardancy and smoke suppression were attributed to the flame-retardant function of FP in the condensed and gas phases. Thus, this work not only provided a simple but also eco-friendly approach to achieve flame retardant thermosets from honokiol to replace bisphenol A epoxy.

Constructing and characterizing various multi-component crosslinked epoxy resins based on molecular dynamics simulations with a curing reaction model

Epoxy resins are extensively used as the matrix for carbon-fiber-reinforced plastic (CFRP) in commercial airplanes due to their outstanding thermomechanical properties. Until now, few researchers have simulated multicomponent epoxy resins. In this work, the impact of stoichiometric variations in the base resins in the Di Glycidyl Ether of Bisphenol A (DGEBA)/Tetra Glycidyl Diamino Diphenyl Methane (TGDDM)/4,4′-Diamino Diphenyl Sulfone (4,4′-DDS) system on the curing process and thermomechanical properties is investigated. When the proportions of each component are comparable, the curing process is primarily determined initially by the component with a lower activation energy and subsequently by the component with a relatively greater quantity during the high conversion rate stage. Furthermore, a higher proportion of TGDDM in the DGEBA/TGDDM/4,4′-DDS system results in an increased number of ring structures, which in turn leads to enhanced thermomechanical properties. Our Python-LAMMPS algorithm can be further developed for designing new multi-component epoxy resin materials.

Fully aminated rigid‐rod aromatic polyamide efficiently reinforces tetraglycidyl diamino diphenyl methane epoxy resin and its carbon fiber composite

AbstractTetraglycidyl diamino diphenyl methane (TGDDM) and its carbon fiber composite are widely studied and used because of their heat resistance and high performance. In order to obtain efficient reinforcing effects in a simple manner, we adopt the idea of molecular composite—uniformly dispersing the rigid‐rod macromolecules in the TGDDM matrix. Herein, we prepared fully aminated‐poly(p‐phenylene terephthalamide) by direct polycondensation and hydrogenation reduction as the reinforcing agent. The fully aminated‐PPTA is distributed uniformly in the cross‐linked epoxy resin (EP) network by chemical bonds, and achieves efficient reinforcement. With the addition of only 0.5 wt% fully aminated‐PPTA, the tensile strength and Young's modulus of EP are improved to 127.7 ± 7.4 MPa (+28%) and 3.36 ± 0.15 GPa (+44%); the flexural strength and modulus are improved to 209.6 ± 9.4 MPa (+42%) and 3.70 ± 0.14 GPa (+37%); the notch impact strength is improved by 32%. Crucially, the heat resistance of EP almost remains unchanged. Furthermore, the flexural properties and interlaminar shear strength of the carbon fiber composite are also comprehensively increased. Compared with other modified fillers, the fully aminated‐PPTA is simple to prepare and blend, and is an efficient reinforcing agent for TGDDM and its carbon fiber composite benefitting from its rigid‐rod main chain and amino side groups.Highlights Molecular composite can achieve excellent strengthen and toughen effects. Fully aminated‐PPTA is embedded uniformly in EP network by chemical bonds. TGDDM is effectively reinforced without deteriorated heat resistance. Fully aminated‐PPTA is also a comprehensive reinforcement for EP/CF composite.

Environment-friendly, high-performance cellulose nanofiber-vanillin epoxy nanocomposite with excellent mechanical, thermal insulation and UV shielding properties

With the increased demand for biobased epoxy thermosets as an alternative to petroleum-based materials in various fields, developing environment-friendly and high-performance natural fiber-biobased epoxy nanocomposites is crucial for industrial applications. Herein, an environment-friendly nanocomposite is reported by introducing cellulose nanofiber (CNF) in situ interaction with lignin-derived vanillin epoxy (VE) monomer and 4, 4´-diaminodiphenyl methane (DDM) hardener that serves as a multifunctional platform. The CNF-VE nanocomposite is fabricated by simply dispersing the CNF suspension to the VE and DDM hardener solution through the in-situ reaction, and its mechanical properties and thermal insulation behavior, wettability, chemical resistance, and optical properties are evaluated with the CNF weight percent variation. The well-dispersed CNF-VE nanocomposite exhibited high tensile strength (∼127.78 ± 3.99 MPa) and strain-at-break (∼16.49 ± 0.61 %), haziness (∼50 %) and UV-shielding properties. The in situ loading of CNF forms covalent crosslinking with the VE and favors improving the mechanical properties along with the homogeneous dispersion of CNF. The CNF-VE nanocomposite also shows lower thermal conductivity (0.26 Wm−1K−1) than glass. The environment-friendly and high-performance nanocomposite provides multiple platforms and can be used for building materials.

Fracture behavior of high‐performance carbon fiber composites toughened by reactive polyetherimide

AbstractCarbon fiber‐reinforced epoxy composites (CFECs) continue to grow in demand for aerospace, mass transportation, electric vehicle, and energy efficient architecture due to their lightweight, high strength, and high modulus. However, CFECs are susceptible to delamination upon impact which can lead to premature structural failure. This paper investigates the interlaminar fracture toughness of unidirectional CFECs based on reactive polyetherimide (rPEI) modified multifunctional epoxy matrix system. The matrices were cured formulations of tetraglycidyl diamino diphenyl methane, triglycidyl para‐amino phenol, rPEI having different molecular weights (MW) and diaminodiphenyl sulfone. Multi‐phase morphologies were observed from the resin castings and CFECs containing different MW rPEI modifiers. Results show that the mode I fracture toughness (GIC) of the rPEI‐toughened CFECs can be increased by as much as 150% over the unmodified CFECs based on the MW and type of phase morphology that promotes crack‐bridging mechanism. In addition, rPEI‐modified CFECs exhibit better property retention (~80% of GIC) after prolonged solvent exposure.Highlights A processing‐structure–property relationship based on CFECs is established. The amine‐terminated rPEI facilitates the formation of a strong bonding. The molecular weight effect of rPEI on the phase morphology was investigated. The rPEI enhances the interlaminar fracture toughness of the composites. The rPEI particle bridging is found to be responsible for the toughening effect.

High Performance Shape Memory Epoxy Syntactic Foam Composites as Lost Circulation Material in Deep Drilling

AbstractLost circulation is a critical issue in drilling. This work reports the investigations on shape memory epoxy polymers (SMEPs) with high switching temperatures, and good thermal, mechanical and shape memory properties for plugging in deep drilling. The SMEPs are produced by curing diglycidyl ether of bisphenol A (DGEBA) and castor oil glycidyl ether (COGE) with a flexible poly(oxypropylene) diamine (D230) and a rigid 4, 4′ ‐diaminodiphenyl methane (DDM). Increasing D230 contents or using COGE, glass transition temperature (Tg, 93–163 °C, DMA analyses) and crosslink density of SMEPs are reduced, shape recovery rate is increased, while tensile strength, elongation at break and impact strength are improved. Further, shape memory epoxy syntactic foams (SMEFs) with high‐temperature adhesion are developed by introducing polymer microspheres into SMEPs. The SMEFs have compression ratio of 52–58%, and expansion ratio of 100% by adding 2% wt. microspheres. They retain the Tg and thermal stability of SMEPs, and show a delayed, slower recovery than SMEPs. Long fracture plugging experiments exhibit that a pressure‐bearing capability of 8.99–9.81 MPa is achieved with SMEFs in sealing fracture slots at a high temperature.

Design of low-consumption epoxy resin porous plugging material via emulsification-curing method

Since the higher cost of epoxy resin, its application in reservoir plugging at high temperature and high salinity was seriously restricted. Herein, the expensive epoxy resin was used as the supporting skeleton to provide the mechanical strength required for plugging, while water was introduced via emulsification - curing method in the closed non-connected pores to reduce the material consumption. The curing kinetics of epoxy resin was studied using differential scanning calorimetry (DSC). On this basis, the high temperature stability and dynamic gel time of the epoxy resin emulsion were examined, and the microstructure and mechanical properties of the cured material were tested. Firstly, in the shear rate range of 10–100 s−1, the viscosity of epoxy resin emulsion was less than 1200 mPa·s under the condition of 20 ℃, meanwhile, the viscosity value was less than 100 mPa·s in high temperature environment of the reservoir (120 ℃), which meets the demand of mixing and injection. Secondly, in the W/O emulsion state, the curing reaction rate was accelerated. However, when the curing agent 4,4′-methylenebis[2,6-diethyl]aniline (DTD) is used instead of 3,3′-diethyl-4,4′-diaminodiphenyl methane (DEDDM), utilizing steric effect of double ethyl group, the thickening time is extended from 55 to 60 min to 110–120 min. Finally, after curing the epoxy resin emulsion, although mostly occupied by pore water (fw=50%), the increase in the curing degree made the elastic modulus increase from 0.017 MPa to 3.220 MPa compared with the pure epoxy resin, and the uniaxial compressive strength can reach 25.14 MPa.This design method can reduce the material consumption of epoxy resin by 30–35% while controlling leakage, providing an effective way for the construction of plugging materials in high temperature (120 ℃) and high salinity (21.81 ×104 mg/L) environment.

Fabrication of Lightweight Polyimide Foams with Exceptional Mechanical and Thermal Properties.

Lightweight polyimide foams (PIFs) with exceptional thermal resistance and compressive properties arefabricated by heating polyester ammonium salts (PEASs) which areprepared by copolymerizing 4, 4'-diaminobenzanilide (DABA), 4, 4'-diaminodiphenyl methane (MDA) and 3, 3', 4, 4'-benzophenone tetracarboxylic dianhydride (BTDA). Hydrogen bonds areformed between CONH and CO in the PI chains due to the addition of DABA and the melt viscosity of PEAS precursors increase with increasing content of DABA, which isadvantageous to bind the foaming gases for cell expansion. The expansion ratio of PEAS precursors isincreased from 633% to 1133% when the molar ratio of MDA/DABA ischanged from 10:0 to 6:4. The compressive strength and modulus of PIFM9D1 (i.e., the molar ratio of MDA/DABA is9:1, foam density: 120.8 kg m-3 ) reach as high as 0.59 and 15.0MPa, respectively. The PIFs possess prominent thermal performance with the initial thermal degradation temperatures (under both nitrogen and air atmosphere) and glass transition temperatures (as assessed by DSC and DMA) exceeding 511 and 292°C, respectively. The thermal conductivity of PIFs islower than 0.049 W m-1 K-1 , which exhibits promising applications for serving as high-temperature thermal insulation materials in the fields of aerospace, marine, and nuclear sectors among others.

The Effect of Flame-Retardant Additives DDM-DOPO and Graphene on Flame Propagation over Glass-Fiber-Reinforced Epoxy Resin under the Influence of External Thermal Radiation.

The flammability of various materials used in industry is an important issue in the modern world. This work is devoted to the study of the effect of flame retardants, graphene and DDM-DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-4,4'-diamino-diphenyl methane), on the flammability of glass-fiber-reinforced epoxy resin (GFRER). Samples were made without additives and with additives of fire retardants: graphene and DDM-DOPO in various proportions. To study the flammability of the samples, standard flammability tests were carried out, such as thermogravimetric analysis, the limiting oxygen index (LOI) test, and cone calorimetry. In addition, in order to test the effectiveness of fire retardants under real fire conditions, for the first time, the thermal structure of downward flame propagation over GFRER composites was measured using thin thermocouples. For the first time, the measured thermal structure of the flame was compared with the results of numerical simulations of flame propagation over GFRER.

Adhesion Improvement of Bio‐Based Epoxy in Environmentally Friendly and High‐Performance Natural Fiber‐Reinforced Composites

AbstractDeveloping robust bio‐based epoxy against petroleum‐derived epoxy is necessary for environmentally friendly and high‐performance natural fiber‐reinforced composites. A bio‐based vanillin epoxy (VE) is synthesized from the lignin‐derived vanillin, and a thermoset resin is prepared after mixing it with a 4,4′‐diaminodiphenyl methane (DDM) hardener. Further, it is infused in high‐cellulose‐containing alkali‐treated jute fiber (TJF) mats through a simple approach to enhance the adhesion between the VE‐DDM and TJF. Bio‐based VE‐DDM resin shows better compatibility with TJF than petroleum‐derived bisphenol A diglycidyl ether (DGEBA) epoxy. The bio‐based VE‐DDM/TJF composite demonstrates the Tgis ≈165 °C, tensile strength is ≈83.12 ± 3.80 MPa, and Young's modulus is ≈2.86 ± 0.10 GPa with excellent flexural strength (138.72 ± 3.81 MPa) and flexural modulus (8.01 ± 0.11 GPa). It also shows merits regarding hydrophobicity, reduced water absorption ability, durability, and chemical resistance in an acidic medium. The natural fiber‐reinforced VE composites pave the way to produce environmentally friendly and high‐performance composites for structural applications.

Study on materials composition and process parameters of polyurethane-modified asphalt synthesized in-situ by the one-shot process

To improve the performance of ordinary road asphalt, and overcome the problems of poor thermal storage stability, easy segregation, and high preparation temperature of polymer-modified asphalt such as SBS (styrene–butadienestyrene block copolymer) or rubber powder. Polyurethane-modified asphalt (PUMA) was synthesized in-situ by the one-shot process with varying dosages of polyurethane (PU) raw materials (2.86 wt% ∼ 11.94 wt%) and isocyanate index R (–NCO/–OH) values (2, 3, 5, and 7) for a total of 12 samples, in this study. The material composition, development time, and modification mechanism of PUMA were analyzed using the approach of “macro performance + micro mechanism”. Firstly, the conventional properties, rotational viscosity, and rheological properties of PUMA samples were evaluated and compared to virgin asphalt. Secondly, under the optimal material composition scheme, the conventional performance and thermal storage stability differences between MOCA (3, 3′ -dichloro-4,4′ -diamino diphenyl methane) and BDO (1,4-butanediol) were compared. Comparing the performance of PUMA during the development times of 0 to 12 h, the oven temperature is 105 °C. Fourier transform infrared spectroscopy (FTIR) and fluorescence microscopy (FM) were used to analyze the chemical structure and spatial structure of PU in asphalt. The results indicate that: 1) the higher the R (–NCO/–OH), the higher the asphalt's high-temperature performance, elastic recovery performance, and viscosity, but the lower its low-temperature performance. 2) Under the same R (–NCO/–OH) condition, the increase in PU has little effect on the preceding performance. 3) MOCA is marginally superior to BDO in terms of high-temperature performance, whereas BDO has greater advantages in terms of low-temperature performance; compatibility is comparable. 4) At 105 °C, the performance continued to improve for 0 to 5 h, but after 5 to 12 h, the improvement was no longer noticeable. 5) Due to the reaction of the isocyanate group with the polyol and the active group in the asphalt, functional groups such as carbamate and urea are directly synthesized in the asphalt, allowing the PU molecular chain to expand and form a network structure within the asphalt. This procedure modifies the performance of the virgin asphalt. These findings not only improve our understanding of the effect of optimal material composition and development time on the properties of PUMA, but they also provide direction for future research.

4,4−Diaminodiphenyl methane functionalized reduced graphene oxide/CoFe−layered double hydroxide obtained by in−situ hydrothermal as a high−performance absorber

The self−assembly among different two−dimensional materials could effectively improve the self−stacking effect and promote repeated reflection and refraction of incident electromagnetic wave (EMW). The polarization effect caused by the heterogeneous contact also helps the attenuation of EMW. In this study, the in−situ hydrothermal approach was used to effectively fabricate petal−like CoFe−layered double hydroxide sheets (CoFe−LDH) grown on reduced graphene oxide (RGO) functionalized by 4,4−diaminodiphenyl methane (DDM). The microwave absorption properties of DDM−functionalized RGO/CoFe−layered double hydroxide composites (DDM−RGO/LDH) were investigated. When the loading of DDM−RGO is 40.0 ​mg, the reflection loss reached −60.0 ​dB at 5.28 ​GHz, resulting in great EMW absorption performance. The effective absorption bandwidth at 2.00 ​mm is 5.28 ​GHz. The results show that DDM−RGO/LDH has a wide microwave absorption bandwidth and strong absorption capability, thus could be applied as an advanced EMW absorbing material.

Mechanical properties of reactive polyetherimide-modified tetrafunctional epoxy systems

Highly crosslinked multifunctional epoxy resins are commonly brittle. Thermoplastic toughening agents have been used to improve the fracture toughness of crosslinked epoxy resins. However, toughness improvement is limited due to poor interfacial adhesion between epoxy matrix and thermoplastic toughener. Furthermore, it is desired that toughness improvements should not come at the expense of other properties, including modulus, thermal properties and processability. In this work, amine functionalized reactive polyetherimide (rPEI) having two different molecular weights and loading levels were incorporated in tetraglycidyl-4, 4′-diaminodiphenyl methane (TGDDM) epoxy resin to study the structure-property relationship, including effects of reaction-induced phase separation on fracture toughness. Results demonstrate that the phase morphologies of rPEI in an epoxy resin can be drastically affected by the functionality, molecular weight and loading levels of rPEI. The mode-I fracture toughness (KIC) of rPEI-toughened epoxy is increased by up to 140% versus untoughened epoxy control. An investigation into the fracture mechanisms of rPEI-toughened TGDDM epoxy showed evidence of rPEI particle bridging as one of the key mechanisms of toughening. Our work further demonstrated that the rPEI-toughened TGDDM epoxy maintained both high modulus and high Tg, rendering it suitable for a wide range of applications.

Vanillin-based liquid crystalline polyimine thermosets and their composites for recyclable thermal management application

The development of bio-based thermosets with favorable mechanical properties, high glass transition temperature (Tg), and recyclability for thermal management applications remains a huge challenge. In this study, a trifunctional aldehydes monomer was prepared from vanillin followed by curing with two kinds of diamine for novel polyimine networks. The results showed that the polyimine networks cured with 4,4′-diaminodiphenyl methane demonstrated the liquid crystalline polyimine thermosets with a high Tg of 193 °C, a high tensile strength up to 84 MPa, and excellent thermal stability (the values of degradation temperature for 5 wt% weight loss, Td5 = 373 °C), while the polyimine networks cured with 4,4′-methylenebis(cyclohexylamine) demonstrated amorphous polyimine thermosets with inferior mechanical and thermos-physical performances, due to the crosslinked liquid crystal structure, the rigid benzene ring and the π-π stacking effect of the former. Furthermore, the polyimine nanocomposites were constructed by incorporating graphene nanoplatelets (GnPs) into these bio-based thermosets. With only 8 wt% GnPs, the nanocomposites showed a remarkable thermal conductivity of 1.8 W m−1 K−1. Interestingly, both the polyimine networks and their composites demonstrated complete recyclability in mild acid conditions owing to the existence of dynamical Schiff-base structures. The bio-based polyimines and nanocomposites reported here offer various advantages, including high mechanical properties and Tg, excellent thermal stability, remarkable thermal conductivity, and recyclability, which provides a new direction for the development of high-performance base composite networks.

Curing behavior, mechanical, and flame‐retardant properties of epoxy‐based composites filled by expandable graphite and ammonium polyphosphate

AbstractIn this study, 4,4′‐Diaminodiphenyl methane (DDM) was exploited as hardener for diglycidyl ether of daidzein (DGED) and epoxy resin mixture (E‐D). The composites were produced by blending with different contents of ammonium polyphosphate (APP) and expandable graphite (EG) into E‐D resin, named E‐D/A‐E composites. Firstly, E‐D/A‐E blends were analyzed by Fourier transform infrared spectroscopy and DSC to evaluate their curing behavior. The TGA was performed on the E‐D/A‐E composites to analyze their thermal stability, and the thermal properties of the composites were enhanced by adding APP‐EG (A‐E) flame retardants. The mechanical properties and the fractured surfaces of the E‐D/A‐E composites were studied by tensile, impact tests and scanning electron microscopy. Finally, through torch burning test, limiting oxygen index (LOI), vertical burning (UL‐94) and micro‐calorimetry tests, the influence of A‐E flame retardants contents on flammability of composites were evaluated. The results showed that the UL‐94 V‐0 rating was obtained for the E‐D/A‐E composites and the composites exhibited a self‐extinguishing phenomenon. When A‐E flame retardants content reached 9.1 wt%, the LOI value reached 34.5%, and total heat release (Total HR) was reduced by 20.2% compared with E‐D/A‐E 1.

Effect of bio-based derived epoxy resin on interfacial adhesion of cellulose film and applicability towards natural jute fiber-reinforced composites

This paper reports a bio-based vanillin-derived epoxy (VDE) resin for bio-based natural fiber-reinforced composites. VDE monomer was synthesized, and curing agents, namely, 4,4´-diaminodiphenyl methane (DDM) and isophorone diamine, were used. The prepared VDE resins with various curing parameters were characterized using FTIR, NMR, tensile test, bending test and water contact angle. Further, the interfacial adhesion feasibility of VDE resins on cellulose film was studied through the single-lap shear joint examination and compared with a commercial epoxy, DGEBA. The VDE-DDM resin exhibited excellent interfacial adhesion with cellulose than VDE-IPDA and DGEBA-DDM resins. The cured VDE-DDM thermoset showed a tensile strength of 86.0 ± 6.5 MPa, thermal stability of 241.0 °C at Td5%, and an elastic modulus of 2.9 ± 0.3 GPa, which is better than the commercial epoxy resin. Besides, the developed VDE-DDM resin was used to fabricate treated-jute fiber (TJF)-reinforced composites. The bio-based VDE-DDM/TJF composite's flexural strength was higher than the commercial epoxy resin composite, DGEBA-DDM/TJF. Furthermore, the phosphorus moiety of the VDE-DDM resin endows flame retardancy to the VDE-DDM/TJF composite during combustion. Overall, the appealing properties of bio-based VDE-DDM/TJF composite render environment-friendly and high-performance structural applications.

Molecular-scale investigation on relationship between thermal conductivity and the structure of crosslinked epoxy resin

Epoxy resins are widely used as matrix resins in many fields due to their excellent physical and mechanical properties. However, their low thermal conductivities restrict their applications, especially in electronic packaging. In this work, nonequilibrium molecular dynamics (NEMD) simulations were used to investigate the relationship between thermal conductivity and epoxy resin structure. Three systems, diglycidyl ether of bisphenol A (DGEBA)/4,4’-diamino diphenyl sulfone (4,4’-DDS), DGEBA/diethylene triamine (DETA), and tetraglycidyl diamino diphenyl methane (TGDDM)/4,4’-DDS, were simulated based on our previous crosslinking algorithm. The thermal conductivity of DGEBA/4,4’-DDS increased with the degree of crosslinking, which is due to increases in new thermal pathways through crosslinking bonds. The sequence of thermal conductivities was found to be TGDDM/4,4’-DDS > DGEBA/DETA > DGEBA/4,4’-DDS which was quantitatively validated with our experimental measurements, consistent with the sequence of crosslink density. To explore the microscopic mechanism governing thermal conductivity, separate heat transfer modes were investigated, revealing that the thermal conductivity contribution of bonded interactions dominates over that of non-bonded interactions for all three systems. This finding verifies that introducing crosslinking bonds dominantly contributes to higher thermal conductivity in epoxy materials. Our research provides suggestions for large scale manufacture of higher thermal conductive epoxy resins.

Versatile levulinic acid-derived dynamic covalent thermosets enabled by in situ generated imine and multiple hydrogen bonds

Bio-based dynamic covalent thermosets have attracted extensive attention as they are expected to break conventional thermosets' reliance on fossil resources and address the recycling issue after disposal. However, there has always been a contradiction between using bio-based feedstocks and possessing high properties, as well as a conflict between high performance and rapid recycling (reprocessing and degradation). In this work, a simple approach was developed to prepare bio-based thermosets with high performance, rapid reprocessing, high flame retardancy, and antibacterial properties enabled by in-situ generated dynamic covalent imine (Schiff base) bonds and multiple hydrogen bonds. The levulinic acid epoxy (ELA) was successfully synthesized and cured with 2-(4-aminophenyl)-1H-benzimidazol-5-amine (BIA) containing benzimidazole structures. The high concentration of Schiff bases and multiple hydrogen bonds of ELA-BIA endowed it with high glass transition temperature and mechanical properties, as well as satisfactory catalyst-free malleability, rapid reprocessing and repairing. Furthermore, due to the combined effect of the in-situ Schiff base and benzimidazole structure, ELA-BIA exhibited excellent condensed phase char formation ability, resulting in intrinsic flame retardancy with a limiting oxygen index of 33.8 % and a UL-94 V-0 rating, both of which were significantly higher than 4, 4′-diaminodiphenyl methane (DDM) cured ELA or DDM cured bisphenol A epoxy. Moreover, the Schiff bases bonded in the networks provided 100 % of the intrinsic antibacterial rates. This work provides a feasible and simple strategy for the preparation of high-performance and versatile bio-based dynamic covalent thermosets.