Bio-Based Hyperbranched Toughener From Tannic Acid and Its Enhanced Solvent-Free Epoxy Resin with High Performance

It is essential to design economic and efficient tougheners to prepare high-performance epoxy resin;however,this has remained a huge challenge.Herein,an eco-friendly,low-cost,and facile-fabricated bio-based hyperbranched toughener,carboxylic acid-functionalized tannic acid(CATA),was successfully prepared and applicated to the preparation of solvent-free epoxy resins.The mechanical performance,morphology,structural characterization,and thermal characterization of toughened epoxy resin system were studied.The toughened epoxy resin system with only 1.0wt%CATA reached the highest impact strength,111%higher than the neat epoxy resin system.Notably,the tensile strength and elongation at break of toughened epoxy resin systems increased moderately with increasing CATA loading.Nonphase-separated hybrids with significant toughening effect were obtained.Additionally,the thermal stabilities of toughened epoxy resin systems decreased with increasing CATA loading.This study provides an eco-friendly,cost-effective,and facile approach for the preparation of high-performance,solvent-free epoxy resins with potential for practical applications in sealing integrated circuits and electrical devices fields.

Facile Synthesis of a Novel Bio-Based P-N Containing Flame Retardant for Effectively Reducing the Fire Hazards of Epoxy Resin

In this work,a bio-based flame retardant(Cy-HEDP)was synthesized from cytosine and HEDP through a facile salt-forming reaction and embedded into epoxy matrix to improve the flame retardancy and smoke suppression performance.The product Cy-HEDP was well characterized by FTIR,^(1)H and^(31)P NMR and SEM tests.On the basis of the results,by adding 15 wt%Cy-HEDP,the EP15 can pass UL-94 V-0 rating,and the total smoke production(TSP)as well as total heat release(THR)can be decreased by 61.05%(from 22.61 to 8.7 m^(2)/m^(2))and 39.44%(from 103.19 to 62.50 MJ/m^(2))in comparison to the unfilled EP,reflecting the attenuated smoke toxicity and impeded heat generation.According to the analysis results of residual char,it can be concluded that Cy-HEDP possessed the ability to promote the formation of continuous and dense char layers,which would be a physical barrier to insulate oxygen and prevent heat feedback during the combustion of EP.This work provide inspiration towards developing bio-based flame retardant,probably extending the prospects to other polymeric material system.

Recyclable bio-based epoxy resin thermoset polymer from wood for circular economy

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.

PROMOTION EFFECT OF MELAMINE ON FLAME RETARDANCY OF EPOXY RESINS CONTAINING CAGED BICYCLIC PHOSPHATE

Caged bicyclic phosphate （CBP） and its dimelamine salt （PDS） were synthesized and added to epoxy resins to obtain the flame retarded epoxy resin composites. The flammability of the composites was characterized by the limiting oxygen index （LOI） and cone calorimeter tests. The LOI values of flame retarded composites increase consistently with the increase of flame retardant amounts, and they are almost the same when the loading of CBP is the same as that of PDS, although the phosphorus content of PDS is much lower than that of CBP. The total heat release increases in the order of CBP30/ER 〈 PDS30/ER 〈 PDS15/ER 〈 CBPI5/ER, whereas that of specific extinction area is CBP15/ER 〉 CBP30/ER 〉 PDS30/ER ≌ PDS15/ER. PDS exhibits more effective inhibition of oxidation of combustible gases. In the tests of thermogravimetric analyses （TG） and Fourier transform infrared spectroscopy （FT-IR）, it is found that the degradation of the composites is influenced greatly by the addition of flame retardants. By scanning electron microscopy （SEM）, a thick and tight char-layer is observed for PDS30/ER, resulting from the interaction of nitrogen species with phosphorus species. Therefore, the combination of CBP with melamine in the flame retarded system can improve the flame retardancy greatly.

Phosphorylated Salicylic Acid as Flame Retardant in Epoxy Resins and Composites

A novel,versatile flame retardant substructure based on phosphorylated salicylic acid(SCP)is described and used in the synthesis of new flame retardants for HexFlow
RTM6,a high-performance epoxy resin used in resin transfer molding processes as composite matrix.The starting material salicylic acid can be obtained from natural sources.SCP as reactive phosphorus chloride is converted with a novolak,a novolak containing 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide(DOPO)substituents or DOPO-hydroquinone to flame retardants with sufficient thermal stability and high char yield.Additionally,these flame retardants are soluble in the resin as well as react into the epoxy network.The determined thermal stability and glass transition temperatures of flame retarded neat resin samples as well as the interlaminar shear strength of corresponding carbon fiber reinforced composite materials showed the applicability of these flame retardants.Neat resin samples and composites were tested for their flammability by UL94 and/or flame-retardant performance by cone calorimetry.All tested flame retardants decrease the peak of heat release rate by up to 54%for neat resin samples.A combination of DOPO and SCP in one flame retardant shows synergistic effects in char formation and the mode of action adapts to neat resin or fiber-reinforced samples,so there is efficient flame retardancy in both cases.Therefore,a tailoring of SCP based flame retardants is possible.Additionally,these flame retardants efficiently reduce fiber degradation during combustion of carbon fiber-reinforced epoxy resins as observed by scanning electron microscopy and energy dispersive X-ray spectroscopy.

Study on the Effect of Carboxyl Terminated Butadiene Acrylonitrile (CTBN) Copolymer Concentration on the Decomposition Kinetics Parameters of Blends of Glycidyl Epoxy and Non-Glycidyl Epoxy Resin

The degradation of the epoxy system was studied for the prepared six blend samples with the incorporation of 0 wt% - 25 wt% carboxyl terminated butadiene acrylonitrile (CTBN) copolymer, on a dynamic basis using Thermo gravimetric analysis (TGA) technique under a nitrogen atmosphere. The blends were prepared by physical mixing and were cured with diamine. The degradation of each sample followed second-order degradation kinetics, which was calculated by Coats-Redfern equation using best-fit analysis. This was further confirmed by linear regression analysis. The validity of data was checked by t-test statistical analysis. From this value of reaction order, activation energy (E), and pre-exponential factor (Z) were calculated. It was found that the activation energy increased with the addition of liquid elastomer.

Unleashing the Power of Bio-based Thermotropic Liquid Crystal Modifiers:Toughening and Reinforcing Petroleum-based Epoxy Resin without Compromising Other Properties

Toughening the petroleum-based epoxy resin blends with bio-based modifiers without compromising their modulus,mechanical strength,and other properties is still a big challenge in view of the sustainability.In this study,a bio-based liquid crystal epoxy resin(THMT-E P)with an s-triazine ring structure was utilized to modify a petroleum-based bisphenol A epoxy resin(E51)with 4,4'-diaminodiphenylsulfone(DDS)as a curing agent,and the blended systems were evaluated for their thermal stability,mechanical properties,and flame retardancy.The results showed that the impact strength of the blended system initially increased and then decreased with the increase in THMT-EP content,and it reached the a maximum value of 26.5 kJ/m^(2)when the THMT-EP content was 5%,which was 31.2%higher than that of E51/DDS.Notably,the flexural strength,modulus,and glass transition tem perature of the blended system were all simultaneously improved with the addition of THMT-EP.At the same time,the addition of THMT-EP enhanced the flame retardancy of the system by increasing the char yield at 700℃and decreasing the peak heat release rate and total heat release rate.This work paves the way for a more sustainable improvement in the comprehensive performance of epoxy resin.

Characterization of Electrical Tree Degradation of Epoxy Resin under Thermal and Temperature Stresses by Photoelastic Effect

Epoxy resin is widely used in the support,insulation,and packaging components of electrical equipment owing to their excellent insulation,thermal,and mechanical properties.However,epoxy-resin insulation often suffers from thermal and mechanical stresses under extreme environmental conditions and a compact design,which can induce electrical tree degradation and insulation failure in electrical equipment.In this study,the photoelastic method is employed to investigate the thermal-mechanical coupling stress dependence of the electrical treeing behavior of epoxy resin.Typical electrical tree growth morphology and stress distribution were observed using the photoelastic method.The correlation between the tree length and overall accumulated damage with an increase in mechanical stress is determined.The results show that compressive stress retards the growth of electrical trees along the electric field,while tensile stress has accelerating effects.This proves that the presence of thermal stress can induce more severe accumulated damage.

Synthesis and properties of phosphorus-containing bio-based epoxy resin from itaconic acid

A phosphorus-containing bio-based epoxy resin(EADI)was synthesized from itaconic acid(IA)and 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide(DOPO).As a matrix,its cured epoxy network with methyl hexahydrophthalic anhydride(MHHPA)as the curing agent showed comparable glass-transition temperature and mechanical properties to diglycidyl ether in a bisphenol A(DGEBA)system as well as good flame retardancy with UL94 V-0 grade during a vertical burning test.As a reactive flame retardant,its flame-resistant effect on DGEBA/MHHPA system as well as its influence on the curing behavior and the thermal and mechanical properties of the modified epoxy resin were investigated.Results showed that after the introduction of EADI,not only were the flame retardancy determined by vertical burning test,LOI measurement,and thermogravimetric analysis significantly improved,but also the curing reactivity,glass transition temperature(T g),initial degradation temperature for 5%weight loss(T d(5%)),and flexural modulus of the cured system improved as well.EADI has great potential to be used as a green flame retardant in epoxy resin systems.

A Vanillin-Derived,DOPO-Contained Bisphenol as a Reactive Flame Retardant for High-Performance Epoxy Thermosets

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.

A bio-based epoxy resin derived from p-hydroxycinnamic acid with high mechanical properties and flame retardancy

Recent advances in epoxy resins have been forward to achieving high mechanical performance,thermal stability,and flame retardancy.However,seeking sustainable bio-based epoxy precursors and avoiding introduction of additional flame-retardant agents are still of increasing demand.Here we report the synthesis of p-hydroxycinnamic acid-derived epoxy monomer(HCA-EP)via a simple one-step reaction,and the HCA-EP can be cured with 4,4′-diaminodiphenylmethane(DDM)to prepare epoxy resins.Compared with the typical petroleum-based epoxy resin,bisphenol A epoxy resin,the HCA-EP-DDM shows a relatively high glass transition temperature(192.9℃)and impressive mechanical properties(tensile strength of 98.3 MPa and flexural strength of 158.9 MPa).Furthermore,the HCA-EP-DDM passes the V-1 flammability rating in UL-94 test and presents the limiting oxygen index of 32.6%.Notably,its char yield is as high as 31.6%under N_(2),and the peak heat rate release is 60%lower than that of bisphenol A epoxy resin.Such findings provide a simple way of using p-hydroxycinnamic acid instead of bisphenol A to construct high-performance bio-based thermosets.

On the Thermal Fatigue of a Room-Cured Neat Epoxy and Its Composite

An experimental investigation is conducted to evaluate the potential degradation in the mechanical properties of an epoxy resin and unidirectional glass fiber-reinforced epoxy (GFRE) as a result of exposure to fluctuating temperature. A commonly used room-cured epoxy resin and the GFRE are subjected to various numbers of thermal cycles (up to 1000 heating/cooling cycles). Mechanical tests are conducted to examine the influence of thermal cycles on the stiffness, ultimate strength and strain of the resin and its GFRE. The Fourier transform-Raman spectroscopy (FT-Raman) is conducted to investigate the influence of the thermal cycles on the resulting chemical changes and curing degree of the resin. In addition, the Differential Scanning Calorimetry (DSC) analysis is conducted to investigate the variation in the glass transition temperature (Tg) of the resin as a function of the applied thermal cycles.

可降解生物基含酯键环氧树脂的固化动力学研究

采用非等温差示扫描量热(DSC)法研究了可降解生物基含酯键环氧树脂固化动力学,分别建立了n级反应动力学模型、自催化模型以及结合n级反应和自催化模型的分段模型,并将模型预测值与实验数据进行了对比分析。结果表明,n级反应模型与实验曲线的偏差较大,自催化模型与实验曲线变化趋势基本一致,但仍然存在一定偏差,而结合两者的分段模型与实验曲线吻合较好,表明分段模型能更准确地描述该环氧树脂体系的固化反应过程,为其树脂基复合材料固化成型工艺条件优化提供理论指导。

生物基可降解环氧树脂及其可回收碳纤维复合材料的研究进展

环氧树脂是目前应用最为广泛的热固性树脂之一,其固化后会形成不溶、不熔的高度交联的三维网络结构,从而导致树脂及其碳纤维复合材料的降解困难而且难以再加工,造成了严重的资源浪费与环境污染。采用可再生生物质原料制备生物基可降解环氧树脂及其碳纤维复合材料,在缓解能源危机、减轻环境污染和实现资源再利用上具有重要意义。综述了生物基可降解环氧树脂及其可回收碳纤维复合材料的研究进展,主要包括含有热或化学不稳定键的可降解环氧树脂的合成、性能、降解机理及其碳纤维的无损回收,并总结了其优缺点。

一种具有优异本征阻燃性和可降解性的全生物基环氧树脂的制备及其性能

以香草醛(VAN)、酪胺(TA)及环氧氯丙烷(ECH)等为原料,制备了一种含有席夫碱结构的本征阻燃型环氧树脂(TA-VAN-EP)。通过傅里叶变换红外光谱和核磁共振氢谱对TA-VAN-EP的化学结构进行表征,测试分析了材料的固化行为、力学性能、热稳定性、阻燃性能和其他关键指标。结果表明,TA-VAN-EP为预期结构。与纯环氧树脂(EP)相比,TA-VAN-EP的力学性能显著提高,拉伸强度提升了82.0%,玻璃化转变温度(T_(g))从152℃提高到190℃。并且,TA-VAN-EP在UL94垂直燃烧测试中达到了V-1级,极限氧指数(LOI)从24.7%提高到了28.4%。此外,总热释放量(THR)、烟雾产生率(SPR)和总烟雾释放量(TSR)也大幅下降,显著提升了材料的阻燃性能。由于在结构中含有动态席夫碱结构,TA-VAN-EP在酸性条件下展现出良好的降解性能。

一种基于酯交换的可重塑成型白藜芦醇基环氧树脂

针对传统环氧树脂原料高度依赖石油资源和固化后难以回收利用的问题,开发一种生物基可回收环氧树脂。以白藜芦醇和琥珀酸酐为原料,基于两者间的酯化反应,在不添加溶剂的情况下,通过一步反应法制备一种生物基多元羧酸环氧树脂固化剂(CFR),并用CFR固化双酚F型环氧树脂。使用CFR固化的环氧树脂在室温下具有与商品化树脂相当的拉伸强度(79 MPa),玻璃化转变温度为101℃。由于酯键能在加热条件下进行可逆交换,CFR固化的环氧树脂可通过热压进行重塑成型,再次成型后环氧树脂的拉伸强度保持率可达99.2%。室温下,用CFR固化的环氧树脂35 min内可在NaOH水溶液(1 mol/L)中完全降解。固化后的环氧树脂在多种常规有机溶剂中表现出优良的耐溶剂性。

热固性酯类环氧/胺固化物的催化降解及循环利用研究

热固性环氧树脂的三维交联结构使其不溶不熔,回收困难。选择酯类环氧作为环氧基体,胺为固化剂进行固化,在常压下用乙二醇对固化物进行降解,研究了金属锌盐、有机碱等多种催化剂对环氧/胺固化物的催化降解效果及环氧降解产物的循环利用效果。结果表明:乙二醇可将环氧/胺固化物全部降解,使用质量分数5%的醋酸锌为催化剂,完全降解时间为365 min,与不加催化剂体系相比较,降解时间减少了135 min。降解物按照质量分数10%比例添加到原环氧/胺体系中,热稳定性保持良好,断裂伸长率提高了39%,拉伸强度略下降,但仍保持较高强度。催化剂能提高热固性环氧树脂的降解速度,降解物可按一定比例添加到原环氧/胺体系中实现循环利用。

Nucleophilic amino acids as a renewable alternative to petrochemically-derived amines in glycerol epoxy resins

The standard epoxy resin curing agents revealed are from unsustainable petroleum-based sources,which produce poisonous exhaust when cured.Amino acids,a bio-based epoxy curing agent with amino and carboxyl groups,are another potential curing agent.Water-soluble epoxy resins cured with lysine(Lys),glutamic acid(Glu),leucine(Leu),and serine(Ser)as amino acids were inves-tigated.The results showed that the water-soluble epoxy resin(glycerol epoxy resins,GER)was cured with Lys and Glu after reacting.Fourier transform infrared(FT-IR)spectroscopic analysis of the GER-Lys showed that the amino and carboxyl groups of Lys primarily reacted with the epoxy groups of GER.The elongation at break of Lys-cured GER(GER-Lys)cured at 70℃ with a molar ratio of 1꞉0.75 was 75.32%.The fact that elongations at break of GER-Lys(79.43%)were higher than those of GER-Glu(17.33%),respectively supports the decrease of crosslinking density by the amino acid-cured GER reaction.The potential of Lys and Glu alternatives for petrochemical amines is demonstrated and provides promising opportunities for industrial application.

催化剂对基于动态酯交换Vitrimers材料性能的影响

传统环氧树脂作为干式变压器、电压互感器和复合绝缘子等电工装备的主要原材料,有着良好的力学性能和电学性能,但是其固化后形成的交联网络难溶难熔。随着环氧树脂基电工装备运行年限的增长,大量退役设备的处理面临巨大的挑战。该文制备了基于酯交换的酸酐固化类玻璃化环氧树脂材料(Vitrimers),系统地研究了催化剂对树脂力学、电学、热学以及动态交换性能的影响规律,并使用醇类溶液探索其降解性能。研究结果显示,与传统环氧树脂相比,Vitrimers体系的断裂伸长率较高,表现出良好的韧性。在Vitrimers体系中以1,5,7-三叠氮双环(4.4.0)癸-5-烯(TBD)为催化剂的Vitrimers具有较佳的综合特性,在高温下表现出良好的应力弛豫特性,且能够在7h(190℃)全部溶解于乙二醇(EG)溶液中。该文研究结果表明,类玻璃化环氧树脂有较综合的力-热-电特性,能够快速溶解于降解溶液,有望用作电工装备的新型环保树脂基体。

交变载荷下绝缘拉杆用GFRP电树枝劣化特性

气体绝缘组合电器(gas insulated switchgear,GIS)现场调试或运行过程多次发生绝缘拉杆内部击穿问题,影响工程投运与设备可靠性,迫切需要探明故障机理。该文选取GIS断路器绝缘拉杆用玻璃纤维增强环氧树脂复合材料(glass fiber reinforced epoxy resin composite,GFRP)为研究对象,通过计算分、合闸下绝缘拉杆主应力分布特性,设置交变载荷下电树枝劣化实验条件,研究不同交变载荷对GFRP内电树枝生长特性影响规律。结果表明,相较于单一载荷,交变载荷条件下GFRP中电树枝生长速度加快,平均击穿时间降低,击穿概率增大。基于复合材料力学仿真发现交变载荷下GFRP内树脂-纤维界面处会出现较大的应力集中,局部应力损伤已达到失效的临界值。综上,交变载荷下绝缘拉杆纤维-树脂界面机械损伤与绝缘劣化交互演进是造成绝缘击穿的主要原因,也可作为试验考核与结构设计的改进依据。