Thermosets are indispensable to our daily life,but their crosslinked structures make them unable to be processed by the melt processing like thermoplastics,which greatly limits their shape designs and applications.Her...Thermosets are indispensable to our daily life,but their crosslinked structures make them unable to be processed by the melt processing like thermoplastics,which greatly limits their shape designs and applications.Herein,we address this challenge via an in situ self-growing strategy,i.e.utilizing the dynamic imidazole-urea moiety to suck up and integrate epoxy into the materials and making the thermoplastics grow in situ into thermosets.With this strategy,thermosets can be readily processed via hot-melt extrusion molding,including melt spinning and fused deposition modeling 3D printing.More importantly,this strategy simultaneously integrates the flexibility of polyurethane and the robustness of epoxy resin into the resulting thermosets,yielding a mechanical-reinforcing effect to make the material not only strong but also tough(toughness:99.3 MJ·m^(-3),tensile strength:38.8 MPa).Moreover,the crosslinking density and modulus of the as-prepared thermosets(from 34.1 MPa to613.7 MPa)can be readily tuned on demand by changing the growth index.Furthermore,these thermosets exhibited excellent thermal stability and chemical resistance.展开更多
Epoxy resin is widely used in electronic packaging due to its exceptional performance,particularly the low-temperature curable thiol/epoxy system,which effectively minimizes thermal damage to sensitive electronic comp...Epoxy resin is widely used in electronic packaging due to its exceptional performance,particularly the low-temperature curable thiol/epoxy system,which effectively minimizes thermal damage to sensitive electronic components.However,the majority of commercial thiol curing agents contain hydrolysable ester bonds and lack rigid structures,which induces most of thiol/epoxy systems still suffering from unsatisfactory heat resistance and hygrothermal resistance,significantly hindering their application in electronic packaging.In this study,we synthesized a tetrafunctional thiol compound,bis[3-(3-sulfanylpropyl)-4-(3-sulfanylpropoxy)phenyl]sulfone(TMBPS)with rigid and ester-free structures to replace traditional commercial thiol curing agents,pentaerythritol tetra(3-mercaptopropionate)(PETMP).Compared to the PETMP/epoxy system,the TMBPS/epoxy system exhibited superior comprehensive properties.The rigid structures of bisphenol S-type tetrathiol enhanced the heat resistance and mechanical properties of TMBPS/epoxy resin cured products,outperforming those of PETMP/epoxy resin cured products.Notably,the glass transition temperature of TMBPS/epoxy resin cured products was 74.2℃which was 11.8°C higher than that of PETMP cured products.Moreover,the ester-free structure in TMBPS contributed to its enhanced resistance to chemicals and hygrothermal conditions.After undergoing 1000 h of hightemperature and high-humidity aging,the tensile strength and adhesion strength of TMBPS-cured products were 73.33 MPa and 3.39 MPa,respectively exceeding 100%and 40%of their initial values,while PETMP-cured products exhibited a complete loss of both tensile strength and adhesion strength.This study provides a strategy for obtaining thermosetting polymers that can be cured at low temperatures and exhibit excellent comprehensive properties.展开更多
A glass fiber(GF)/polydicyclopentadiene(PDCPD)composite impact simulation model was established based on LS-DYNA(the finite element analysis software peroduced by Livermore Software Technology Corporation)simulation.A...A glass fiber(GF)/polydicyclopentadiene(PDCPD)composite impact simulation model was established based on LS-DYNA(the finite element analysis software peroduced by Livermore Software Technology Corporation)simulation.An optimal ply thickness of the composite GF/PDCPD was determined as 3.0 mm,and thus the final intrusion depth was controlled within 8.8 mm,meeting the performance standards for battery electric vehicle protection materials.A comparative analysis of failure modes during impacts was conducted for composites GF/PDCPD,GF/polypropylene(PP)and GF/polyamide(PA).The results indicated that GF/PDCPD exhibited compressive failure modes and ductile fractures,resulting in smaller damage areas.In contrast,GF/PP and GF/PA showed fiber fracture failures,leading to larger damage areas.The molding process and impact resistance of GF/PDCPD were investigated.By comparing the impact performance of GF/PDCPD with that of GF/PP and GF/PA,it was concluded that GF/PDCPD demonstrated superior performance and better alignment with the performance standards of battery electric vehicle protective materials.The predictability and accuracy of LS-DYNA simulation was verified,providing a theoretical foundation for further in-depth research.展开更多
Epoxy resin,characterized by prominent mechanical and electric-insulation properties,is the preferred material for packaging power electronic devices.Unfortunately,the efficient recycling and reuse of epoxy materials ...Epoxy resin,characterized by prominent mechanical and electric-insulation properties,is the preferred material for packaging power electronic devices.Unfortunately,the efficient recycling and reuse of epoxy materials with thermally cross-linked molecular structures has become a daunting challenge.Here,we propose an economical and operable recycling strategy to regenerate waste epoxy resin into a high-performance material.Different particle size of waste epoxy micro-spheres(100–600μm)with core-shell structure is obtained through simple mechanical crushing and boron nitride surface treatment.By using smattering epoxy monomer as an adhesive,an eco-friendly composite material with a“brick-wall structure”can be formed.The continuous boron nitride pathway with efficient thermal conductivity endows eco-friendly composite materials with a preeminent thermal conductivity of 3.71 W m^(−1)K^(−1) at a low content of 8.5 vol%h-BN,superior to pure epoxy resin(0.21 W m^(−1)K^(−1)).The composite,after secondary recycling and reuse,still maintains a thermal conductivity of 2.12 W m^(−1)K^(−1) and has mechanical and insulation properties comparable to the new epoxy resin(energy storage modulus of 2326.3 MPa and breakdown strength of 40.18 kV mm^(−1)).This strategy expands the sustainable application prospects of thermosetting polymers,offering extremely high economic and environmental value.展开更多
The use of CO_(2) as monomer to synthesize polymer materials is an important and potential applications topic from the viewpoint of green and sustainable chemistry.A new kind of CO_(2)-based polyurea(PUa)was synthesiz...The use of CO_(2) as monomer to synthesize polymer materials is an important and potential applications topic from the viewpoint of green and sustainable chemistry.A new kind of CO_(2)-based polyurea(PUa)was synthesized by polycondensation of CO_(2) with 4,7,10-trioxa-1,13-tridecanediamine and tris(2-aminoethyl)amine(TAEA).TAEA was used as cross-link reagent.The mechanical properties of PUa were significantly improved by inserted the crosslink agent of TAEA.The formed slight cross-linked PUa exhibited excellent mechanical properties with tensile strength of 26.8 MPa,elongation at break of 34%and Young’s modulus of 351 MPa.Moreover,it could be remolded for 3 times without obvious change in the mechanical properties,which are ascribed to the hydrogen bonding interaction among the main chains and the slight cross-linked structure.In addition,the synthesized CO_(2)-based PUa is of outstanding thermal performance with an initial decomposition temperature above 300℃,besides it is tolerance for a variety of organic solvents.展开更多
Due to their extraordinary durability and thermal stability,Epoxy Resin Thermosets(ERTs)are essential in various industries.However,their poor recyclability leads to unacceptable environmental pollution.In this study,...Due to their extraordinary durability and thermal stability,Epoxy Resin Thermosets(ERTs)are essential in various industries.However,their poor recyclability leads to unacceptable environmental pollution.In this study,Wu et al.successfully synthesized a completely bio-based ERT using lignocellulose-derived building blocks which exhibit outstanding thermal and mechanical properties.Remarkably,these bio-materials degrade via methanolysis without the need of any catalyst,presenting a smart and cost-effective recycling strategy.Furthermore,this approach could be employed for fabricating reusable composites comprising glass fiber and plant fiber,thereby expanding its applications in sustainable transportation,coatings,paints or biomedical devices.展开更多
Stiffened thermosetting composite panels were fabricated with co-curing processing.In the co-curing processing,the temperature distribution in the composite panels was nonuniform.An investigation into the threedimensi...Stiffened thermosetting composite panels were fabricated with co-curing processing.In the co-curing processing,the temperature distribution in the composite panels was nonuniform.An investigation into the threedimensional cure simulation of T-shape stiffened thermosetting composite panels was presented.Flexible tools and locating tools were considered in the cure simulation.Temperature distribution in the composites was predicted as a function of the autoclave temperature history.A nonlinear transient heat transfer finite element model was developed to simulate the curing process of stiffened thermosetting composite panels.And a simulation example was presented to demonstrate the use of the present finite element procedure for analyzing composite curing process.The glass/polyester structure was investigated to provide insight into the nonuniform cure process and the effect of flexible tools and locating tools on temperature distribution.Temperature gradient in the intersection between the skin and the flange was shown to be strongly dependent on the structure of the flexible tools and the thickness of the skin.展开更多
Quest for bio-based halogen-free green flame retardant has attracted many concerns in recent years.Herein a reactive functional flame retardant containing phosphorus VDP is synthesized from vanillin,9,10-dihydro-9-oxa...Quest for bio-based halogen-free green flame retardant has attracted many concerns in recent years.Herein a reactive functional flame retardant containing phosphorus VDP is synthesized from vanillin,9,10-dihydro-9-oxa-10-phosphophene-10-oxide(DOPO)and phenol via a facile way.VDP is characterized with^(1)H NMR,^(31)P NMR,FTIR and Time of Flight Mass Spectrometry,and used as a new reactive flame retardant for bisphenol epoxy thermosets.Thermogravimetry analysis shows that when the VDP loading is only 0.5P%(based on phosphorus content),the residue increases from 14.2%to 21.1%at 750℃ in N_(2)compare with neat DGEBA.Correspondingly,the limit oxygen index increased to 29.6%,and flame retardancy reaches UL-94 V0 grade.Micro combustion calorimetry(MCC)and cone calorimetry analyses demonstrate that VDP can significantly lower flammability of the epoxy thermoset.With only 0.5P%of VDP,the heat release rate,total heat release rate and smoke production are reduced markedly.At the same time,the mechanical properties of the modified epoxy thermosets are also improved.The impact strength increases by 34%and the flexural strength increased by 23%,with 1.5P%of VDP.In short,VDP not only improves the flame retardancy,but also improves the mechanical properties of the epoxy thermosets.展开更多
A series of Diels-Alder reaction cross-linked thermosets with recyclability and healability were prepared from furan-containing aromatic polyamide and bismaleimides with different chemical structures.The structures of...A series of Diels-Alder reaction cross-linked thermosets with recyclability and healability were prepared from furan-containing aromatic polyamide and bismaleimides with different chemical structures.The structures of synthesized bismaleimides were confirmed by 1 H nuclear magnetic resonance(1 H-NMR)spectroscopy;their reversible cross-linking with the furanic polyamide was further detected by 1 H-NMR technique and sol-gel transition behavior.The dynamic mechanical analysis and tensile test revealed the variable thermal and mechanical properties of thermosets cross-linked by different bismaleimides and with different molar ratios of maleimide group to furan group(Ima/fur).The tensile test also demonstrated that the better recyclability and solvent-assisted healability of thermosets cross-linked could be achieved by more flexible bismaleimides.This work is expected to provide valuable information for design of recyclable and healable high-performance thermosets with desired properties.展开更多
Two kinds of difunctionalized isosorbide derivatives containing norbornene groups were designed and synthesized by a facile one-step reaction under mild conditions.~1H NMR spectroscopy confirmed the chemical compositi...Two kinds of difunctionalized isosorbide derivatives containing norbornene groups were designed and synthesized by a facile one-step reaction under mild conditions.~1H NMR spectroscopy confirmed the chemical composition and differential scanning calorimetry（DSC） revealed the distinct curing behaviors between conventional petroleum-based dicyclopentadiene（DCPD） and synthesized renewable isosorbided-based monomer（ISN）. In contrast to DCPD, ISN was low viscous liquid at room temperature and had even higher reactivity to perform ring-opening metathesis polymerization（ROMP） in the presence of Grubbs＇ catalyst. Due to the presence of flexible and elastic Si–C long chains, the cured poly（ISN） thermosets not only had good mechanical properties but also exhibited much higher storage modulus at the rubbery state in comparison with traditional poly（DCPD）.展开更多
The low-velocity impact response and infrared radiation characteristics of composites have rarely been focused on simultaneously.This study aims to investigate the low-velocity impact response and infrared radiation c...The low-velocity impact response and infrared radiation characteristics of composites have rarely been focused on simultaneously.This study aims to investigate the low-velocity impact response and infrared radiation characteristics of the glass fiber reinforced thermoplastic polypropylene and carbon fiber reinforced thermosetting epoxy resin laminates wildly used in the aircraft industry.The impact tests were conducted at five energy levels.Characterization parameters such as impact load,displacement,and absorbed energy were measured.The damage evolution and damage modes of the laminates were analyzed through active and passive thermography,ultrasonic C-scan,and optical microscope.The results indicate that Thermosets(TS)laminates exhibit better impact resistance,while Thermoplastics(TP)laminates show higher delamination ductility,and the maximum contact force of TP laminates is much smaller than that of the TS laminates under lowvelocity impacts,but the low bending stiffness and low ductility of the TP matrix cause the difference in energy absorption level between the two not significant.The temperature characteristic changes of passive infrared thermography heat maps could characterize the damage mode of the laminates.The correlation between the heat maps and the impact characteristic curves is explained;the fluctuation of the impact characteristic curves is directly related to the hot spot characteristics changes of the heat maps.More frequent curve fluctuations correspond to a larger and brighter hot spot on the heat map,which peaks at the maximum impact load after the impact force versus time curve fluctuation cutoff point,the maximum center displacement of the impact force versus displacement curve,and the maximum absorbed energy of the absorbed energy versus time curve.展开更多
In this work,apigenin was chosen as a raw material to synthesize a novel epoxy monomer(DGEA),while the bio-based epoxy resin was further obtained after curing with 4,4’-diaminodiphenylmethane(DDM).The control samples...In this work,apigenin was chosen as a raw material to synthesize a novel epoxy monomer(DGEA),while the bio-based epoxy resin was further obtained after curing with 4,4’-diaminodiphenylmethane(DDM).The control samples were prepared by curing diglycidyl ether of bisphenol A(DGEBA)with DDM.The non-isothermal differential scanning calorimeter(DSC)method was utilized to further investigate the curing behavior and curing kinetics of the DGEA/DDM system.Despite no flame retardant active elements,the DGEA/DDM thermoset still exhibited exceptional anti-flammability.Specifically,the DGEA/DDM thermoset reached a V-0 rating in the UL-94 test and owned a high limiting oxygen index(LOI)value of 37.0%,while DGEBA/DDM resins were consumed completely in the vertical combustion test with a low LOI of 23.0%.Furthermore,the microscale combustion calorimetry(MCC)results manifested that compared with DGEBA/DDM resins,both PHRR and THR values of the DGEA/DDM resins were dropped by 84.0%and 57.6%,respectively.Additionally,the DGEA/DDM resin also presented higher storage modulus and tensile strength compared with DGEBA/DDM one.Particularly,in contrast with that of the cured DGEBA/DDM one(156℃),the DGEA/DDM thermoset displayed an extremely high glass transition temperature(232℃).This study breaks new ground on how to produce biobased monomers with aromatic structures and achieve high-performance thermosetting polymers.展开更多
The development of efficient green flame retardants is an important way to realize more sustainable epoxy thermosets and downstream materials.In this work,a monoepoxide is synthesized through O-glycidylation of eugeno...The development of efficient green flame retardants is an important way to realize more sustainable epoxy thermosets and downstream materials.In this work,a monoepoxide is synthesized through O-glycidylation of eugenol,and then reacted with DOPO(9,10-dihydro-9-oxa-10-phosphophenanthrene-10-oxide)to obtain a new bio-based flame retardant,DOPO-GE.DOPO-GE is blended with a bisphenol A epoxy prepolymer exhibiting good compatibility and DDS(4,4′-diaminodiphenylsulfone)is used as the curing agent to afford epoxy thermosets.Although DOPO-GE leads to the reduced glass transition temperature of the thermosets,the storage modulus increases considerably.The DOPO-GE-modified thermosets exhibit the high thermal stability with the onset thermal decomposition temperature in nitrogen and air exceeding 300℃.When the phosphorus content in the thermoset is 1.0%,the residual yield of the thermosets at 750℃ in nitrogen increases from 13.9%to 30.6%,due to the increased charring ability.More interestingly,when the phosphorus content is only 0.5%,the limiting oxygen index is as high as 30.3%with UL94 V0 achieved.Cone calorimeter results reveals the significantly decreased heat release rate,total heat release,mass loss and total smoke production.Furthermore,DOPO-GE can notably improve the flexural strength,flexural modulus and fracture toughness,whereas the shear and impact strength are reduced to varied extents.In short,DOPO-GE can be obtained via a facile way,and shows the good flame-retardant effect on the epoxy thermosets with an application potential.展开更多
Thermosetting materials are widely used as encapsulation in the electrical packaging to protect the core electronic components from external force, moisture, dust, and other factors. However, the spreading and curing ...Thermosetting materials are widely used as encapsulation in the electrical packaging to protect the core electronic components from external force, moisture, dust, and other factors. However, the spreading and curing behaviors of such kind of fluid on a heated surface have been rarely explored. In this study, we experimentally and numerically investigated the spreading and curing behaviors of the silicone(OE6550 A/B, which is widely used in the light-emitting diode packaging) droplet with diameter of ~2.2 mm on a heated surface with temperature ranging from 25 ℃ to 250 ℃. For the experiments, we established a setup with high-speed camera and heating unit to capture the fast spreading process of the silicone droplet on the heated surface. For the numerical simulation, we built a viscosity model of the silicone by using the Kiuna’s model and combined the viscosity model with the Volume of Fluid(VOF) model by the User Defined Function(UDF) method. The results show that the surface temperature significantly affected the spreading behaviors of the silicone droplet since it determines the temperature and viscosity distribution inside the droplet. For surface temperature varied from 25 ℃ to 250 ℃, the final contact radius changed from ~2.95 mm to ~1.78 mm and the total spreading time changed from ~511 s to ~0.15 s. By further analyzing the viscosity evolution of the droplet, we found that the decreasing of the total spreading time was caused by the decrease of the viscosity under high surface temperature at initial spreading stage, while the reduction of the final contact radius was caused by the curing of the precursor film. This study supplies a strategy to tuning the spreading and curing behavior of silicone by imposing high surface temperature, which is of great importance to the electronic packaging.展开更多
Thermosetting acrylic coatings were prepared by using carboxyl acid group-containing acrylic oligomer and curing with titanium-oxo-clusters which were first pre-hydrolyzed from titanium n-butoxide.The curing ability o...Thermosetting acrylic coatings were prepared by using carboxyl acid group-containing acrylic oligomer and curing with titanium-oxo-clusters which were first pre-hydrolyzed from titanium n-butoxide.The curing ability of the titanium-oxo-cluster was examined using a microdielectric analytical(DEA)curing monitor,Fourier transformed infrared spectroscopy(FTIR),and Soxhlet extraction experiments,and the properties of the resulted coatings were investigated with pendulum hardness tester,dynamic mechanical analysis(DMA),thermogravimetric analysis(TGA)and ultraviolet-visible spectrometer.The effect of titania-oxo-cluster in leading acrylic oligomers to form thermosetting acrylic coatings was confirmed.An increasing pendulum hardness and modulus of acrylic coatings with increasing titania content was observed, which resulted from the increment of crosslinking degree rather than of the titania content.The thermosetting acrylic/titania coatings also showed better thermal stability and higher UV-blocking properties than those coatings using organic curing agent.展开更多
Biomass-derived dynamic covalent thermoset has been considered as a promising solution to the high dependence on fossil resources and the difficulty in recyclability after curing of conventional bisphenol A epoxy resi...Biomass-derived dynamic covalent thermoset has been considered as a promising solution to the high dependence on fossil resources and the difficulty in recyclability after curing of conventional bisphenol A epoxy resins.However,the design and preparation of a dynamic covalent biobased epoxy thermoset with both comparable thermal and mechanical performances to bisphenol A epoxy resins and reprocessibility remains a significant challenge.Herein,based on imine chemistry,a novel Schiff base-containing dynamic covalent epoxy thermoset was facilely fabricated from biobased protocatechualdehyde and synthetic siloxane diamine.Due to the more reactive epoxides in the epoxy monomer than in bisphenol A epoxy oligomer,the thermoset exhibited a high cross-linking density,resulting in high thermal stability and glass transition temperature.The rigid aromatic Schiff base moieties endowed the thermoset with excellent mechanical properties:Thanks to the plasticization of the flexible siloxane,the thermoset displayed high impact strength.Meanwhile,owing to the high segmental mobility,the fast exchange of imine bonds was guaranteed;and the thermoset was able to be recycled through reprocessing.Taking these features,this work provided great potential for designing and preparing sustainable substitutes for bisphenol A epoxy resins in the high-performance applications.展开更多
Recently developed low fluorine containing polymers are advanced materials which confer advantageous properties to surfaces at a lower cost than conventional fluoropolymers (like PTFE), and are also more easily proces...Recently developed low fluorine containing polymers are advanced materials which confer advantageous properties to surfaces at a lower cost than conventional fluoropolymers (like PTFE), and are also more easily processable. Fluoropolymer surfaces are characterized by a low surface energy, high oleo and hydrophobicity, low coefficients of friction, among many other properties. This makes them desired materials in microelectronics, antifogging, antifouling and medical applications, to name a few. Fluorinated compounds are not easily coupled with macromolecules or common organic systems, and great efforts are made to compatibilize fluorinated species with hydrocarbon polymers. In this work, two chemical routes were explored in order to incorporate perfluorinated alkyl chains in an epoxy-amine based thermoset. On one side, a perfluoroalkyl thiolated molecule was used as a stabilizing ligand for silver nanoparticles, which were incorporated in the matrix polymer. On the other hand, fluorinated chains containing epoxy functionalities, were used as the matrix modifier. In the first case, fluorinated chains covering the nanoparticles, were mixed with the matrix, while in the second case, the fluoroalkyl chains were chemically linked to the network. Fluorine migration to the air—polymer interface was confirmed by X-Ray photoelectron spectroscopy (XPS). The materials hydrophobicity was then studied in terms of their contact angle with water (CA), as a function of the surface composition and the topography. Scanning electron microscopy (SEM) and atomic force microscopy (AFM), operated in moderate and light tapping modes, were used to morphologically describe the surfaces. An exhaustive surface analysis was made in order to explain the different hydrophobicity grades found.展开更多
The consumption ofthermoset resins as building polymers is approximately over one million tone word wide. The thermoset resins are proven construction materials for the technical and highly demanding applications of t...The consumption ofthermoset resins as building polymers is approximately over one million tone word wide. The thermoset resins are proven construction materials for the technical and highly demanding applications of the transportation, electrical and building part industry. Heat stability, high thermal, low shrinkage, excellent mechanical properties are typical for their type of polymers. Above applications in addition to the mechanical properties also require good flame retardants of the materials. Undertaken activities refer to official draft, laws and legal recommendations in UE states. This paper presents positive effect of reduced flammability of thermoset resins （unsaturated polyester and epoxy resins） thanks to the use of nanocomposites containing multi-ingredient halogen-flee flame retardants which combine conventional phosphorus/nitrogen modifiers interacting with nanofillers （oMMT （organomodified montmorillonite）, EG （expandable graphite）, graphene, GO （graphene oxide）, nSi （nanosilica））.展开更多
Carbon brushes with a resin binder were prepared according to an industrial process and the effects of the molding pressure, grains size and cure temperature on the properties of brush samples were discussed. The resu...Carbon brushes with a resin binder were prepared according to an industrial process and the effects of the molding pressure, grains size and cure temperature on the properties of brush samples were discussed. The results show that the bulk density, bending strength and Rockwell hardness increase, while resistivity decreases with increasing molding pressure. Cure temperature has much more influence on the properties of brushes than molding pressure and grains size. Isothermal differential scanning calorimetry(DSC) was used to estimate the degree of cure of resin binder and a novel method of using the true density to measure the degree of cure of resin binder was presented and discussed briefly. Based on optimal process parameters carbon brushes were manufactured, durability tests for brushes were carried out on an alternate current motor and scanning electron microscope(SEM) was adopted to observe the morphology of worn surface of brushes. The results show that a luster oxide film can be formed on the surface of brushes and their service life reaches 380 h.展开更多
基金financially supported by the Natural Science Foundation of Zhejiang Province(No.LQ24B040004)。
文摘Thermosets are indispensable to our daily life,but their crosslinked structures make them unable to be processed by the melt processing like thermoplastics,which greatly limits their shape designs and applications.Herein,we address this challenge via an in situ self-growing strategy,i.e.utilizing the dynamic imidazole-urea moiety to suck up and integrate epoxy into the materials and making the thermoplastics grow in situ into thermosets.With this strategy,thermosets can be readily processed via hot-melt extrusion molding,including melt spinning and fused deposition modeling 3D printing.More importantly,this strategy simultaneously integrates the flexibility of polyurethane and the robustness of epoxy resin into the resulting thermosets,yielding a mechanical-reinforcing effect to make the material not only strong but also tough(toughness:99.3 MJ·m^(-3),tensile strength:38.8 MPa).Moreover,the crosslinking density and modulus of the as-prepared thermosets(from 34.1 MPa to613.7 MPa)can be readily tuned on demand by changing the growth index.Furthermore,these thermosets exhibited excellent thermal stability and chemical resistance.
基金the support of the Science and Technology Commission of Shanghai Municipality(STCSM,No.20dz1203600)the Experimental Center of Materials Science and Engineering in Tongji University。
文摘Epoxy resin is widely used in electronic packaging due to its exceptional performance,particularly the low-temperature curable thiol/epoxy system,which effectively minimizes thermal damage to sensitive electronic components.However,the majority of commercial thiol curing agents contain hydrolysable ester bonds and lack rigid structures,which induces most of thiol/epoxy systems still suffering from unsatisfactory heat resistance and hygrothermal resistance,significantly hindering their application in electronic packaging.In this study,we synthesized a tetrafunctional thiol compound,bis[3-(3-sulfanylpropyl)-4-(3-sulfanylpropoxy)phenyl]sulfone(TMBPS)with rigid and ester-free structures to replace traditional commercial thiol curing agents,pentaerythritol tetra(3-mercaptopropionate)(PETMP).Compared to the PETMP/epoxy system,the TMBPS/epoxy system exhibited superior comprehensive properties.The rigid structures of bisphenol S-type tetrathiol enhanced the heat resistance and mechanical properties of TMBPS/epoxy resin cured products,outperforming those of PETMP/epoxy resin cured products.Notably,the glass transition temperature of TMBPS/epoxy resin cured products was 74.2℃which was 11.8°C higher than that of PETMP cured products.Moreover,the ester-free structure in TMBPS contributed to its enhanced resistance to chemicals and hygrothermal conditions.After undergoing 1000 h of hightemperature and high-humidity aging,the tensile strength and adhesion strength of TMBPS-cured products were 73.33 MPa and 3.39 MPa,respectively exceeding 100%and 40%of their initial values,while PETMP-cured products exhibited a complete loss of both tensile strength and adhesion strength.This study provides a strategy for obtaining thermosetting polymers that can be cured at low temperatures and exhibit excellent comprehensive properties.
文摘A glass fiber(GF)/polydicyclopentadiene(PDCPD)composite impact simulation model was established based on LS-DYNA(the finite element analysis software peroduced by Livermore Software Technology Corporation)simulation.An optimal ply thickness of the composite GF/PDCPD was determined as 3.0 mm,and thus the final intrusion depth was controlled within 8.8 mm,meeting the performance standards for battery electric vehicle protection materials.A comparative analysis of failure modes during impacts was conducted for composites GF/PDCPD,GF/polypropylene(PP)and GF/polyamide(PA).The results indicated that GF/PDCPD exhibited compressive failure modes and ductile fractures,resulting in smaller damage areas.In contrast,GF/PP and GF/PA showed fiber fracture failures,leading to larger damage areas.The molding process and impact resistance of GF/PDCPD were investigated.By comparing the impact performance of GF/PDCPD with that of GF/PP and GF/PA,it was concluded that GF/PDCPD demonstrated superior performance and better alignment with the performance standards of battery electric vehicle protective materials.The predictability and accuracy of LS-DYNA simulation was verified,providing a theoretical foundation for further in-depth research.
基金supported by the National Natural Science Foundation of China(Nos.51977084 and 52307025).
文摘Epoxy resin,characterized by prominent mechanical and electric-insulation properties,is the preferred material for packaging power electronic devices.Unfortunately,the efficient recycling and reuse of epoxy materials with thermally cross-linked molecular structures has become a daunting challenge.Here,we propose an economical and operable recycling strategy to regenerate waste epoxy resin into a high-performance material.Different particle size of waste epoxy micro-spheres(100–600μm)with core-shell structure is obtained through simple mechanical crushing and boron nitride surface treatment.By using smattering epoxy monomer as an adhesive,an eco-friendly composite material with a“brick-wall structure”can be formed.The continuous boron nitride pathway with efficient thermal conductivity endows eco-friendly composite materials with a preeminent thermal conductivity of 3.71 W m^(−1)K^(−1) at a low content of 8.5 vol%h-BN,superior to pure epoxy resin(0.21 W m^(−1)K^(−1)).The composite,after secondary recycling and reuse,still maintains a thermal conductivity of 2.12 W m^(−1)K^(−1) and has mechanical and insulation properties comparable to the new epoxy resin(energy storage modulus of 2326.3 MPa and breakdown strength of 40.18 kV mm^(−1)).This strategy expands the sustainable application prospects of thermosetting polymers,offering extremely high economic and environmental value.
文摘The use of CO_(2) as monomer to synthesize polymer materials is an important and potential applications topic from the viewpoint of green and sustainable chemistry.A new kind of CO_(2)-based polyurea(PUa)was synthesized by polycondensation of CO_(2) with 4,7,10-trioxa-1,13-tridecanediamine and tris(2-aminoethyl)amine(TAEA).TAEA was used as cross-link reagent.The mechanical properties of PUa were significantly improved by inserted the crosslink agent of TAEA.The formed slight cross-linked PUa exhibited excellent mechanical properties with tensile strength of 26.8 MPa,elongation at break of 34%and Young’s modulus of 351 MPa.Moreover,it could be remolded for 3 times without obvious change in the mechanical properties,which are ascribed to the hydrogen bonding interaction among the main chains and the slight cross-linked structure.In addition,the synthesized CO_(2)-based PUa is of outstanding thermal performance with an initial decomposition temperature above 300℃,besides it is tolerance for a variety of organic solvents.
基金the foundational support by the Fundamental Research Funds for the Central Universities(BLX202132)the foundational support by the Beijing Youth Talent Funding Program-Visiting program for young foreign scholars(Q2023043)IIT(BHU)Varanasi.
文摘Due to their extraordinary durability and thermal stability,Epoxy Resin Thermosets(ERTs)are essential in various industries.However,their poor recyclability leads to unacceptable environmental pollution.In this study,Wu et al.successfully synthesized a completely bio-based ERT using lignocellulose-derived building blocks which exhibit outstanding thermal and mechanical properties.Remarkably,these bio-materials degrade via methanolysis without the need of any catalyst,presenting a smart and cost-effective recycling strategy.Furthermore,this approach could be employed for fabricating reusable composites comprising glass fiber and plant fiber,thereby expanding its applications in sustainable transportation,coatings,paints or biomedical devices.
文摘Stiffened thermosetting composite panels were fabricated with co-curing processing.In the co-curing processing,the temperature distribution in the composite panels was nonuniform.An investigation into the threedimensional cure simulation of T-shape stiffened thermosetting composite panels was presented.Flexible tools and locating tools were considered in the cure simulation.Temperature distribution in the composites was predicted as a function of the autoclave temperature history.A nonlinear transient heat transfer finite element model was developed to simulate the curing process of stiffened thermosetting composite panels.And a simulation example was presented to demonstrate the use of the present finite element procedure for analyzing composite curing process.The glass/polyester structure was investigated to provide insight into the nonuniform cure process and the effect of flexible tools and locating tools on temperature distribution.Temperature gradient in the intersection between the skin and the flange was shown to be strongly dependent on the structure of the flexible tools and the thickness of the skin.
基金This work is supported by the National Natural Science Foundation of China(NSFC)under the agreements of 21875131 and 21773150The Natural Science Basic Research Plan in Shaanxi Province of China(2020JM-283)the Fundamental Research Funds for the Central Universities(GK202003044 and GK201902014)are also acknowledged for partial support。
文摘Quest for bio-based halogen-free green flame retardant has attracted many concerns in recent years.Herein a reactive functional flame retardant containing phosphorus VDP is synthesized from vanillin,9,10-dihydro-9-oxa-10-phosphophene-10-oxide(DOPO)and phenol via a facile way.VDP is characterized with^(1)H NMR,^(31)P NMR,FTIR and Time of Flight Mass Spectrometry,and used as a new reactive flame retardant for bisphenol epoxy thermosets.Thermogravimetry analysis shows that when the VDP loading is only 0.5P%(based on phosphorus content),the residue increases from 14.2%to 21.1%at 750℃ in N_(2)compare with neat DGEBA.Correspondingly,the limit oxygen index increased to 29.6%,and flame retardancy reaches UL-94 V0 grade.Micro combustion calorimetry(MCC)and cone calorimetry analyses demonstrate that VDP can significantly lower flammability of the epoxy thermoset.With only 0.5P%of VDP,the heat release rate,total heat release rate and smoke production are reduced markedly.At the same time,the mechanical properties of the modified epoxy thermosets are also improved.The impact strength increases by 34%and the flexural strength increased by 23%,with 1.5P%of VDP.In short,VDP not only improves the flame retardancy,but also improves the mechanical properties of the epoxy thermosets.
基金financially supported by the National Natural Science Foundation of China (No. 51473031)the Natural Science Foundation of Shanghai (No. 17ZR1401100)the doctoral innovation foundation (No. CUSF-DH-D-2017037)
文摘A series of Diels-Alder reaction cross-linked thermosets with recyclability and healability were prepared from furan-containing aromatic polyamide and bismaleimides with different chemical structures.The structures of synthesized bismaleimides were confirmed by 1 H nuclear magnetic resonance(1 H-NMR)spectroscopy;their reversible cross-linking with the furanic polyamide was further detected by 1 H-NMR technique and sol-gel transition behavior.The dynamic mechanical analysis and tensile test revealed the variable thermal and mechanical properties of thermosets cross-linked by different bismaleimides and with different molar ratios of maleimide group to furan group(Ima/fur).The tensile test also demonstrated that the better recyclability and solvent-assisted healability of thermosets cross-linked could be achieved by more flexible bismaleimides.This work is expected to provide valuable information for design of recyclable and healable high-performance thermosets with desired properties.
基金National Natural Science Foundation of China (No. 51503181)Foundation of Educational Committee of Zhejiang Province of China (No. Y201225071)Ningbo Natural Science Foundation of China (Nos. 2013A610135, 2015A610092, 2015A610100) for financial support
文摘Two kinds of difunctionalized isosorbide derivatives containing norbornene groups were designed and synthesized by a facile one-step reaction under mild conditions.~1H NMR spectroscopy confirmed the chemical composition and differential scanning calorimetry（DSC） revealed the distinct curing behaviors between conventional petroleum-based dicyclopentadiene（DCPD） and synthesized renewable isosorbided-based monomer（ISN）. In contrast to DCPD, ISN was low viscous liquid at room temperature and had even higher reactivity to perform ring-opening metathesis polymerization（ROMP） in the presence of Grubbs＇ catalyst. Due to the presence of flexible and elastic Si–C long chains, the cured poly（ISN） thermosets not only had good mechanical properties but also exhibited much higher storage modulus at the rubbery state in comparison with traditional poly（DCPD）.
基金the Major Research Plan of the National Natural Science Foundation of China (No. 92060106)the National Natural Science Foundation of China (No. 52075541)+1 种基金the China Postdoctoral Science Foundation (No. 2019M650262)the Natural Science Foundation of Shaanxi Province, China (No. 2020JM-354)
文摘The low-velocity impact response and infrared radiation characteristics of composites have rarely been focused on simultaneously.This study aims to investigate the low-velocity impact response and infrared radiation characteristics of the glass fiber reinforced thermoplastic polypropylene and carbon fiber reinforced thermosetting epoxy resin laminates wildly used in the aircraft industry.The impact tests were conducted at five energy levels.Characterization parameters such as impact load,displacement,and absorbed energy were measured.The damage evolution and damage modes of the laminates were analyzed through active and passive thermography,ultrasonic C-scan,and optical microscope.The results indicate that Thermosets(TS)laminates exhibit better impact resistance,while Thermoplastics(TP)laminates show higher delamination ductility,and the maximum contact force of TP laminates is much smaller than that of the TS laminates under lowvelocity impacts,but the low bending stiffness and low ductility of the TP matrix cause the difference in energy absorption level between the two not significant.The temperature characteristic changes of passive infrared thermography heat maps could characterize the damage mode of the laminates.The correlation between the heat maps and the impact characteristic curves is explained;the fluctuation of the impact characteristic curves is directly related to the hot spot characteristics changes of the heat maps.More frequent curve fluctuations correspond to a larger and brighter hot spot on the heat map,which peaks at the maximum impact load after the impact force versus time curve fluctuation cutoff point,the maximum center displacement of the impact force versus displacement curve,and the maximum absorbed energy of the absorbed energy versus time curve.
基金financially supported by the National Natural Science Foundation of China(Nos.22075265 and 22050410269)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2021459)。
文摘In this work,apigenin was chosen as a raw material to synthesize a novel epoxy monomer(DGEA),while the bio-based epoxy resin was further obtained after curing with 4,4’-diaminodiphenylmethane(DDM).The control samples were prepared by curing diglycidyl ether of bisphenol A(DGEBA)with DDM.The non-isothermal differential scanning calorimeter(DSC)method was utilized to further investigate the curing behavior and curing kinetics of the DGEA/DDM system.Despite no flame retardant active elements,the DGEA/DDM thermoset still exhibited exceptional anti-flammability.Specifically,the DGEA/DDM thermoset reached a V-0 rating in the UL-94 test and owned a high limiting oxygen index(LOI)value of 37.0%,while DGEBA/DDM resins were consumed completely in the vertical combustion test with a low LOI of 23.0%.Furthermore,the microscale combustion calorimetry(MCC)results manifested that compared with DGEBA/DDM resins,both PHRR and THR values of the DGEA/DDM resins were dropped by 84.0%and 57.6%,respectively.Additionally,the DGEA/DDM resin also presented higher storage modulus and tensile strength compared with DGEBA/DDM one.Particularly,in contrast with that of the cured DGEBA/DDM one(156℃),the DGEA/DDM thermoset displayed an extremely high glass transition temperature(232℃).This study breaks new ground on how to produce biobased monomers with aromatic structures and achieve high-performance thermosetting polymers.
基金The authors acknowledge the support from the National Natural Science Foundation of China(21875131 and 21773150)the Natural Science Basic Research Plan in Shaanxi Province of China(2020JM-283)the Fundamental Research Funds for the Central Universities(GK202003044 and GK201902014).
文摘The development of efficient green flame retardants is an important way to realize more sustainable epoxy thermosets and downstream materials.In this work,a monoepoxide is synthesized through O-glycidylation of eugenol,and then reacted with DOPO(9,10-dihydro-9-oxa-10-phosphophenanthrene-10-oxide)to obtain a new bio-based flame retardant,DOPO-GE.DOPO-GE is blended with a bisphenol A epoxy prepolymer exhibiting good compatibility and DDS(4,4′-diaminodiphenylsulfone)is used as the curing agent to afford epoxy thermosets.Although DOPO-GE leads to the reduced glass transition temperature of the thermosets,the storage modulus increases considerably.The DOPO-GE-modified thermosets exhibit the high thermal stability with the onset thermal decomposition temperature in nitrogen and air exceeding 300℃.When the phosphorus content in the thermoset is 1.0%,the residual yield of the thermosets at 750℃ in nitrogen increases from 13.9%to 30.6%,due to the increased charring ability.More interestingly,when the phosphorus content is only 0.5%,the limiting oxygen index is as high as 30.3%with UL94 V0 achieved.Cone calorimeter results reveals the significantly decreased heat release rate,total heat release,mass loss and total smoke production.Furthermore,DOPO-GE can notably improve the flexural strength,flexural modulus and fracture toughness,whereas the shear and impact strength are reduced to varied extents.In short,DOPO-GE can be obtained via a facile way,and shows the good flame-retardant effect on the epoxy thermosets with an application potential.
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.51606074,51625601,and 51576078)the Ministry of Science and Technology of the People’s Republic of China(Grant No.2017YFE0100600)the Creative Research Groups Funding of Hubei Province(Grant No.2018CFA001)
文摘Thermosetting materials are widely used as encapsulation in the electrical packaging to protect the core electronic components from external force, moisture, dust, and other factors. However, the spreading and curing behaviors of such kind of fluid on a heated surface have been rarely explored. In this study, we experimentally and numerically investigated the spreading and curing behaviors of the silicone(OE6550 A/B, which is widely used in the light-emitting diode packaging) droplet with diameter of ~2.2 mm on a heated surface with temperature ranging from 25 ℃ to 250 ℃. For the experiments, we established a setup with high-speed camera and heating unit to capture the fast spreading process of the silicone droplet on the heated surface. For the numerical simulation, we built a viscosity model of the silicone by using the Kiuna’s model and combined the viscosity model with the Volume of Fluid(VOF) model by the User Defined Function(UDF) method. The results show that the surface temperature significantly affected the spreading behaviors of the silicone droplet since it determines the temperature and viscosity distribution inside the droplet. For surface temperature varied from 25 ℃ to 250 ℃, the final contact radius changed from ~2.95 mm to ~1.78 mm and the total spreading time changed from ~511 s to ~0.15 s. By further analyzing the viscosity evolution of the droplet, we found that the decreasing of the total spreading time was caused by the decrease of the viscosity under high surface temperature at initial spreading stage, while the reduction of the final contact radius was caused by the curing of the precursor film. This study supplies a strategy to tuning the spreading and curing behavior of silicone by imposing high surface temperature, which is of great importance to the electronic packaging.
基金supported by the National Natural Science Foundation of China(No.20774023)Shanghai Leading Academic Discipline Project(No.B113).
文摘Thermosetting acrylic coatings were prepared by using carboxyl acid group-containing acrylic oligomer and curing with titanium-oxo-clusters which were first pre-hydrolyzed from titanium n-butoxide.The curing ability of the titanium-oxo-cluster was examined using a microdielectric analytical(DEA)curing monitor,Fourier transformed infrared spectroscopy(FTIR),and Soxhlet extraction experiments,and the properties of the resulted coatings were investigated with pendulum hardness tester,dynamic mechanical analysis(DMA),thermogravimetric analysis(TGA)and ultraviolet-visible spectrometer.The effect of titania-oxo-cluster in leading acrylic oligomers to form thermosetting acrylic coatings was confirmed.An increasing pendulum hardness and modulus of acrylic coatings with increasing titania content was observed, which resulted from the increment of crosslinking degree rather than of the titania content.The thermosetting acrylic/titania coatings also showed better thermal stability and higher UV-blocking properties than those coatings using organic curing agent.
基金the National Science Foundation of China(Nos.51822304,51773137)the 111 Project(No.B20001)Fundamental Research Funds for the Central Universities are sincerely acknowledged。
文摘Biomass-derived dynamic covalent thermoset has been considered as a promising solution to the high dependence on fossil resources and the difficulty in recyclability after curing of conventional bisphenol A epoxy resins.However,the design and preparation of a dynamic covalent biobased epoxy thermoset with both comparable thermal and mechanical performances to bisphenol A epoxy resins and reprocessibility remains a significant challenge.Herein,based on imine chemistry,a novel Schiff base-containing dynamic covalent epoxy thermoset was facilely fabricated from biobased protocatechualdehyde and synthetic siloxane diamine.Due to the more reactive epoxides in the epoxy monomer than in bisphenol A epoxy oligomer,the thermoset exhibited a high cross-linking density,resulting in high thermal stability and glass transition temperature.The rigid aromatic Schiff base moieties endowed the thermoset with excellent mechanical properties:Thanks to the plasticization of the flexible siloxane,the thermoset displayed high impact strength.Meanwhile,owing to the high segmental mobility,the fast exchange of imine bonds was guaranteed;and the thermoset was able to be recycled through reprocessing.Taking these features,this work provided great potential for designing and preparing sustainable substitutes for bisphenol A epoxy resins in the high-performance applications.
文摘Recently developed low fluorine containing polymers are advanced materials which confer advantageous properties to surfaces at a lower cost than conventional fluoropolymers (like PTFE), and are also more easily processable. Fluoropolymer surfaces are characterized by a low surface energy, high oleo and hydrophobicity, low coefficients of friction, among many other properties. This makes them desired materials in microelectronics, antifogging, antifouling and medical applications, to name a few. Fluorinated compounds are not easily coupled with macromolecules or common organic systems, and great efforts are made to compatibilize fluorinated species with hydrocarbon polymers. In this work, two chemical routes were explored in order to incorporate perfluorinated alkyl chains in an epoxy-amine based thermoset. On one side, a perfluoroalkyl thiolated molecule was used as a stabilizing ligand for silver nanoparticles, which were incorporated in the matrix polymer. On the other hand, fluorinated chains containing epoxy functionalities, were used as the matrix modifier. In the first case, fluorinated chains covering the nanoparticles, were mixed with the matrix, while in the second case, the fluoroalkyl chains were chemically linked to the network. Fluorine migration to the air—polymer interface was confirmed by X-Ray photoelectron spectroscopy (XPS). The materials hydrophobicity was then studied in terms of their contact angle with water (CA), as a function of the surface composition and the topography. Scanning electron microscopy (SEM) and atomic force microscopy (AFM), operated in moderate and light tapping modes, were used to morphologically describe the surfaces. An exhaustive surface analysis was made in order to explain the different hydrophobicity grades found.
文摘The consumption ofthermoset resins as building polymers is approximately over one million tone word wide. The thermoset resins are proven construction materials for the technical and highly demanding applications of the transportation, electrical and building part industry. Heat stability, high thermal, low shrinkage, excellent mechanical properties are typical for their type of polymers. Above applications in addition to the mechanical properties also require good flame retardants of the materials. Undertaken activities refer to official draft, laws and legal recommendations in UE states. This paper presents positive effect of reduced flammability of thermoset resins （unsaturated polyester and epoxy resins） thanks to the use of nanocomposites containing multi-ingredient halogen-flee flame retardants which combine conventional phosphorus/nitrogen modifiers interacting with nanofillers （oMMT （organomodified montmorillonite）, EG （expandable graphite）, graphene, GO （graphene oxide）, nSi （nanosilica））.
基金Project(59972009) supported by the National Natural Science Foundation of China
文摘Carbon brushes with a resin binder were prepared according to an industrial process and the effects of the molding pressure, grains size and cure temperature on the properties of brush samples were discussed. The results show that the bulk density, bending strength and Rockwell hardness increase, while resistivity decreases with increasing molding pressure. Cure temperature has much more influence on the properties of brushes than molding pressure and grains size. Isothermal differential scanning calorimetry(DSC) was used to estimate the degree of cure of resin binder and a novel method of using the true density to measure the degree of cure of resin binder was presented and discussed briefly. Based on optimal process parameters carbon brushes were manufactured, durability tests for brushes were carried out on an alternate current motor and scanning electron microscope(SEM) was adopted to observe the morphology of worn surface of brushes. The results show that a luster oxide film can be formed on the surface of brushes and their service life reaches 380 h.
基金Acknowledgements： The authors would like to express their appreciation to the National Natural Science Foundation of China （No. 50373008） and Key Project of Heilongjiang Province of China （No. GC04A216）.
