Non-isothermal cure kinetics of aerogel/epoxy composites using differential scanning calorimetry

ABSTRACT

The present work determines the non-isothermal cure parameters of aerogel/epoxy samples along with the effect of a wetting agent. The cure parameters were calculated using Kissinger and isoconversional methods after which the reaction was modeled with the Sestak–Berggren equation. It is seen that the composites had higher activation energy and frequency factor values compared to the pure resin, and similarities in cure parameters between the aerogel/epoxy composites with and without the wetting agent were seen. Hence, the former’s use is advocated due to its positive influence on the resin–aerogel interface without sacrificing the cure parameters.     

Cure kinetics of epoxy resin used for advanced composites

The cure kinetics of an epoxy resin used for the preparation of advanced polymeric composite structures was studied by isothermal differential scanning calorimetry (DSC). A series of isothermal DSC runs provided information about the kinetics of cure over a wide temperature range. According to the heat evolution behavior during the curing process, several influencing factors of isothermal curing reactions were evaluated. The results showed that the isothermal kinetic reaction of this epoxy resin followed an autocatalytic kinetic mechanism. In the latter reaction stage, the curing reaction became controlled mainly by diffusion. Cure rate was then modeled using a modified Kamal autocatalytic model that accounts for the shift from a chemically controlled reaction to a diffusion‐controlled reaction. The model parameters were determined by a nonlinear multiple regression method. Copyright © 2004 Society of Chemical Industry     

Thermal analysis of curing process of epoxy prepreg

The curing process of epoxy prepreg was studied by means of differential scanning calorimetry analysis. The dynamic, isothermal, and combinations of dynamic and isothermal measurements were done over selected temperature ranges and isothermal cure temperatures. The heats of reaction for dynamic and isothermal cure were determined. The results show that the heat of the isothermal‐cure reaction increased with the increment of temperature. The degree of cure was calculated from the heat of the isothermal‐cure reaction. The complete cure reaction could be achieved at 220°C within a very short cure time. The changes of cure rate with time were given for the studied isothermal cure temperatures. To simulate the relationship between the cure rate and degree of cure, the autocatalytic model was used and the four parameters were calculated. Except in the late stage of the cure reaction, the model agrees well with the experimental data, especially at high temperatures. To account for the effect of diffusion on the cure rate, a diffusion factor was introduced into the model. The modified model greatly improved the predicted data at the late stage of cure reaction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1074–1083, 2002     

新型含磷环氧树脂的合成及其反应动力学研究

将9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO)与邻甲酚醛环氧树脂进行加成反应制得了含磷环氧树脂,并用FT-IR和NMR对其结构进行了表征,确认了该含磷环氧树脂的结构。采用DSC分析方法研究了DOPO与邻甲酚醛环氧树脂的反应动力学,得到两者反应的表观活化能Eα为53.457kJ/mol,反应级数n为0.93。     

DSC study on the effect of cure reagents on the lignin base epoxy cure reaction

The cure reactions of liquid lignin base epoxy resin (LEPL) with three different curing agents, viz., methylhexahydrophthalic anhydride, maleic anhydride, and 2‐methyl‐4‐methylimidazole (EMI‐2,4), were investigated by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry. Cure kinetics was evaluated using the multiple heating rate Kissinger method. The reactivities of the three curing agents were compared based on kinetics results obtained by DSC. FTIR spectra of these curing systems were also studied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

环氧树脂/苯乙烯-马来酸酐共聚物体系固化动力学研究

用示差扫描量热仪(DSC)对环氧树脂/苯乙烯-马来酸酐共聚物/甲基咪唑体系的固化反应过程进行了分析,并用Kissinger和Ozawa方法分别求得固化反应的表观活化能ΔE为58.27 kJ/mol和64.93 kJ/mol;根据Crane理论计算得到该体系的固化反应级数n=0.85,为该环氧树脂体系的固化工艺确定提供理论依据。     

二氧化硅粉体改性E—Si／CE固化动力学的研究

采用非等温差示扫描量热法（DSC）研究了纳米二氧化硅（SiO2）和微米SiO2的混合粉体改性环氧基硅烷（E—Si）／氰酸酯（CE）树脂体系固化动力学;用Kissinger、Crane和Ozawa法确定固化动力学参数。结果表明,Kissinger式求得的表观活化能为66．09kJ／mol;Ozawa法求得的表观活化能为7001kJ／mol;根据Crane理论计算该体系的固化反应级数为0.89。计算了不同升温速率所对应的不同温度的频率因子和反应速率常数;求得了改性体系的固化工艺参数：凝胶温度130．74℃、固化温度160．96℃和后处理温度199.16℃,确定了体系的最佳固化工艺。与E—Si／CE体系对比表明,SiO2的加入可以降低E—Si／CE体系的活化能,使其固化能在较低温度下进行。     

Dielectric cure determination of a thermosetting epoxy composite prepreg

Evaluation of degree of cure (DoC) of a glass reinforced epoxy composite prepreg used for manufacturing of printed circuit board (PCB) is an intensive issue because of its practical importance and cost reduction in industry. Typical techniques such as differential scanning calorimetry (DSC) and fourier transform infrared spectroscopy (FTIR) are destructive and require curing a material during a chosen time, quenching the sample to stop cure before performing analysis. Thus, it is necessary to remove the temperature influence on the determination of DoC. In this study, the feasibility of nondestructive dielectric sensing method as an in situ DoC measuring technique through cure monitoring of prepreg is presented, where a vacuum packing configuration has been established so as for the prepreg to evaluate accurately the DoC in a quenched state at an ambient temperature. The optimal curing condition to get the fully cured state of a prepreg material is determined by the dielectric cure monitoring based on the behavior of ion viscosity. The temperature effect compensated DoC of prepreg is correlated and compared with that evaluated by DSC and FTIR. The correlated DoC with ion viscosity has identified the curing behavior of prepreg by determining cure kinetic parameters. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44707.     

环氧树脂微胶囊合成及其反应动力学

将环氧树脂E-51分散在水中形成稳定的乳液,使用三乙烯四胺固化剂,在环氧树脂液滴表面形成交联结构作为环氧树脂微胶囊囊壁,这种微胶囊为环氧树脂复合材料的科学研究和工程应用提供了无界面差异囊壁的研究模型。采用扫描电子显微镜（SEM）和光学显微镜（OM）分析了乳化剂种类及用量、反应温度和搅拌速率等工艺条件对这种微胶囊的形成过程、表面形貌、粒径大小及分布和壁厚的影响。采用红外光谱（FTIR）研究了环氧树脂微胶囊的化学结构。当合成条件为乳化剂Tween 80浓度为1%,固化剂三乙烯四胺浓度为2.5%,反应温度90℃,搅拌速度600～1000 r·min^-1,合成的环氧树脂微胶囊形状规整,表面光滑致密,平均粒径为103 μm,囊芯含量为44.65%,壁厚为5 μm。研究三乙烯四胺固化剂中伯胺和仲胺的反应速率常数和活化能等反应动力学参数,定量分析环氧树脂-三乙烯四胺的化学反应中伯胺和仲胺的反应活性差异。     

环氧灌封料固化反应动力学及其性能研究

采用非等温示差扫描量热法(DSC)研究了环氧树脂(E-51)/甲基四氢苯酐/DMP-30/球形SiO2体系的固化反应动力学,采用Kissinger法和Crane公式对体系的DSC数据进行了处理,获得了固化反应动力学参数,确定了固化工艺。同时通过力学性能和热性能测试研究了球形SiO2添加量对复合材料性能的影响。结果表明,SiO2质量分数为10%的体系其起始固化温度为109.7℃,峰顶固化温度为134.8℃,终止固化温度为154.3℃;较好的固化工艺为100℃/2 h+140℃/2 h+160℃/2 h。该体系反应级数n=0.917,表观活化能Ea=78.52 kJ/mol。当SiO2添加量为30%时,其弯曲强度达到最大值97 MPa,同时热分解温度达到最大值332℃,试样热膨胀系数也明显降低。     

Studies on the cure kinetics and networks properties of neat and polydimethylsioxane modified tetrafunctional epoxy resins

The cure kinetics of tetrafunctional epoxy resins with three different backbone structures and their modification by polydimethylsioxane (PDMS) were studied by means of differential scanning calorimetry with dynamic approach. The development of epoxy networks was characterized by dynamic viscoelastic measurements. Results showed that all the epoxy resins obeyed the autocatalytic reaction mechanism with a reaction order of about 3. Epoxy resin with softer aliphatic backbone demonstrated a higher cure reactivity and stronger tendency towards autocatalysis, as well as lower crosslinking density. The PDMS‐modified epoxy resins showed higher early cure reactivity and a lower crosslinking density due to the plasticization and restriction effect of the dispersed PDMS phase, respectively. Based on cure kinetics and dynamic viscoelastic results, the α_m was found to be an effective precursor for describing the developing of epoxy networks during the course of cure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of external electric field on morphologies and properties of the cured epoxy and epoxy/acrylate systems

In this article, the influences of the external electric field exerted to the curing epoxy and epoxy/acrylate systems on their cured microstructures and macroscopic performances were investigated by means of morphological investigation and some characteristic analyses. Epoxy and epoxy/acrylate (an interpenetrating polymer network) systems were subjected to the action of the alternating electric field during the curing process. The changes in the nanolamellae microstructure in the cured epoxy and the nanoellipsoid microstructure in the cured epoxy/acrylate systems resulting from the electric field treatment were observed using atomic force microscopy. Dynamic mechanical analysis showed that the external electric field treatment made the low and high relaxation peaks shift to the lower and higher temperatures, respectively. Thermogravimetric analysis implied that the curing reactions of the epoxy systems with the aid of the external electric field resulted in some negative influences on their thermal stability. The dielectric measurements demonstrated that the electrical properties of the epoxy system for vacuum pressure impregnation insulation of the high-voltage electric machines could be much improved with the aid of the external electric field. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

新型环氧树脂胶粘剂的固化动力学研究

在不同升温速率下采用非等温差示扫描量热（DSC）技术对一种新型改性环氧树脂胶粘剂的固化反应过程进行了跟踪,并利用Kissinger、crane方程以及Arrhenius方程对该固化反应进行了动力学分析。结果表明,该固化反应的活化能为59.18kJ／mol,反应级数为0．89;结合Dsc谱图确定其固化工艺为130℃／1h＋150℃／2h＋175℃／3h。     

环氧树脂固化反应动力学研究及其活性增韧

采用动态DSC法跟踪环氧树脂E-51／固化剂5784体系的反应历程,确定固化温度,利用Kissinger方程和Crane方程对固化反应动力学进行分析,通过红外分析确定聚硫橡胶的增韧方式,研究不同聚硫橡胶用量列固化产物力学性能的影响,采用扫描电镜分析试样断口形貌。研究结果表明：该固化体系的动力学参数为表观活化能△E=63．946kJ／mol,指前因子Ak=1．90×10^5,反应能级n=0．91,聚硫橡胶增韧环氧树脂通过化学键合来实现,并且效果明显。     

DSC法研究聚异氰酸酯／环氧树脂胶粘剂的固化反应动力学及固化工艺

采用差示扫描量热法(DSC)研究了聚异氰酸酯／环氧树脂的固化过程,研究了不同配比对固化反应的影晌,固化度与固化温度的关系,计算了固化反应表观活化能和反应级数,确定了聚异瓤酸酯／环氧树脂胶粘剂的固化工艺。结果表明:胶粘剂中固化剂的含量对环氧树脂的固化反应过程有显著的影响,随着聚异氰酸酯的增加,固化放热量增加。当聚异氰酸酯的含量达到1．2份时,固化反应放热量达到最大值;不同升温速率下,体系固化温度有很大差异,随着升温速率的提高,固化温度增加。通过动力学计算得到体系最佳固化温度为108℃,固化时间为6-8h,固化体系的活化能为43．31kJ／mol,反应级数为1．17。     

Investigation of the reaction mechanism of different epoxy resins using a phosphorus‐based hardener

In this work, the fundamental kinetic and structure/property information for a novel phosphorus‐based hardener, bis(4‐aminophenoxy) phosphonate is cured with a range of common epoxy resins such as diglycidyl ether of bisphenol A, tri glycidyl p‐amino phenol and tetra glycidyl diamino diphenyl methane (TGDDM) at various cure temperatures. The rate coefficients k₁ and k₂ for the primary and secondary amine epoxide addition reactions, respectively, were determined and were found to exhibit a positive substitution effect for the TGAP and TGDDM epoxy resins. Etherification or internal cyclization were shown to be important at higher levels of cure conversion, with these reactions being more significant for the TGAP/BAPP system. Some basic structure/property relationships were established between the glass transition temperature (T_g) and epoxide conversion. The master curve obtained for the superimposition of the various cure temperatures for each epoxy demonstrated the independence of the cure mechanism with temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99:3288–3299, 2006     

Analysis of the cure of epoxy based layered silicate nanocomposites: Reaction kinetics and nanostructure development

The cure reaction kinetics of epoxy resin, with organically modified montmorillonite loadings of up to 20 wt % and with stoichiometric conditions, has been studied by differential scanning calorimetry with a view to understanding further the fabrication of epoxy‐based polymer layered silicate nanocomposites. The kinetic analysis of isothermal and nonisothermal cure shows that the autocatalytic model is the more appropriate to describe the kinetics of these reactions, and it is observed that a dominant effect of the montmorillonite is to catalyze the curing reaction. However, it was not possible to model the reactions over the whole range of degrees of conversion, in particular for nonisothermal cure. This attributed to the complexity of the reactions, and especially to the occurrence of etherification by cationic homopolymerization catalyzed by the onium ion of the organically modified montmorillonite. The homopolymerization reaction results in an excess of diamine in the system, and hence in practice the reaction is off stoichiometric, which leads to a reduction in both the heat of cure and the glass transition temperature as the montmorillonite content increases. Small angle X‐ray scattering of the cured nanocomposites shows that an exfoliated nanostructure is obtained in nonisothermal cure at slow heating rates, whereas for nonisothermal cure at faster heating rates, as well as for isothermal cure at 70°C and 100°C, a certain amount of exfoliation is accompanied by the growth of d‐spacings of 1.4 nm and 1.8 nm for dynamic and isothermal cure, respectively, smaller than the d‐spacings of the modified clay before intercalation of the resin. A similar nanostructure, consisting of extensive exfoliation accompanied by a strong scattering at distances less than the d‐spacing of the modified clay, is also found for resin/clay mixtures, before the addition of any crosslinking agent, which have been preconditioned by storage for long times at room temperature. The development of these nanostructures is attributed to the presence of clay agglomerations in the original resin/clay mixtures and highlights the importance of the quality of the dispersion of the clay in the resin in respect of achieving a homogeneous exfoliated nanostructure in the cured nanocomposite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Cure kinetics of biphenyl epoxy resin system using latent catalysts

The investigation of the cure kinetics of a biphenyl epoxy–phenol resin system with different kinds of latent catalysts was performed by differential scanning calorimetry using an isothermal approach. All kinetic parameters of the curing reaction including the reaction order, activation energy, and rate constant were calculated and reported. The results indicated that the curing reaction of the biphenyl epoxy resin system in this experiment proceeded through an autocatalytic kinetic mechanism, irrespective of the kind of catalyst. The epoxy resin system with acid/diazabicycloundecene (DBU) salt as the latent catalyst showed a second overall reaction order; however, a third reaction order was represented for microencapsulated triphenylphosphine (TPP). The storage stability tests for these systems were performed, and a good shelf life was observed in the epoxy resin system with pyromellitic acid/DBU salt, trimellitic acid/DBU salt, and microencapsulated TPP as the latent catalyst. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2711–2720, 2001     

Dynamic cure kinetics of epoxy resins using an amine‐containing borate as a latent hardener

An amine‐containing borate (labeled NBD) was obtained by a one‐step esterification using neopentyl glycol, boric acid and N,N‐dimethylethanolamine (DMEA) as reactants, and nuclear magnetic resonance as well as Fourier transform infrared (FTIR) measurements were used to characterize its chemical structure. The thermally latent curing properties of NBD were confirmed by differential scanning calorimetry (DSC), FTIR and gelation time results. The cure processes of bisphenol A diglycidyl ether epoxy resins (E51) using NBD as a latent hardener in comparison with a common hardener, DMEA, were studied by DSC measurements. The Avrami and Arrhenius methods as well as the Horowitz‐Metzger method were used to calculate kinetic parameters. These methods also revealed a transition at which the cure reaction mechanism showed a marked change and provided the apparent activation energy E_a associated with the cure reaction at different reaction stages. Copyright © 2012 Society of Chemical Industry     

Blends of epoxy resins and polyphenylene oxide as processing aids and toughening agents 2: Curing kinetics,rheology, structure and properties

The curing behaviour, chemorheology, morphology and dynamic mechanical properties of epoxy ? polyphenylene oxide (PPO) blends were investigated over a wide range of compositions. Two bisphenol A based di‐epoxides ? pure and oligomeric DGEBA ? were used and their cure with primary, tertiary and quaternary amines was studied. 4,4′‐methylenebis(3‐chloro‐2,6‐diethylaniline) (MCDEA) showed high levels of cure and gave the highest exotherm peak temperature, and so was chosen for blending studies. Similarly pure DGEBA was selected for blending due to its slower reaction rate because of the absence of accelerating hydroxyl groups. For the PPO:DGEBA340/MCDEA system, the reaction rate was reduced with increasing PPO content due to a dilution effect but the heat of reaction were not significantly affected. The rheological behaviour during cure indicated that phase separation occurred prior to gelation, followed by vitrification. The times for phase separation, gelation and vitrification increased with higher PPO levels due to a reduction in the rate of polymerization. Dynamic mechanical thermal analysis of PPO:DGEBA340/MCDEA clearly showed two glass transitions due to the presence of phase separated regions where the lower T_g corresponded to an epoxy‐rich phase and the higher T_g represented the PPO‐rich phase. SEM observations of the cured PPO:DGEBA340/MCDEA blends revealed PPO particles in an epoxy matrix for blends with 10 wt% PPO, co‐continuous morphology for the blend with 30 wt% PPO and epoxy‐rich particles dispersed in a PPO‐rich matrix for 40wt% and more PPO. © 2014 Society of Chemical Industry