环氧粉末涂料的固化动力学和固化工艺的研究

采用非等温示差扫描量热法(DSC)研究了E-12/双氰胺(固化剂)和E-12/双氰胺/2-甲基咪唑(促进剂)体系的固化反应动力学。采用Kissinger法和Crane公式对DSC数据进行处理,获得了固化反应动力学参数,应用热重分析(TGA)研究了固化产物的热稳定性。结果表明:双氰胺、2-甲基咪唑的最佳用量分别为环氧树脂质量的4%和0.4%,最佳固化条件为160℃/15min。E-12/双氰胺体系和E-12/双氰胺/2-甲基咪唑体系的表观活化能分别为105.12kJ/mol和70.62kJ/mol,固化反应级数n=0.92。起始分解温度约为410℃,促进剂2-甲基咪唑的加入对体系热稳定性没有影响。     

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。     

一种新型芳胺固化剂的性能研究

以双酚A为原料,通过硝化和还原反应制备2,2-二(3-氨基-4-羟基)苯基丙烷化合物(HAPP).以HAPP为固化剂,测定环氧树脂的凝胶特性,用DSC研究环氧树脂的固化反应,确定固化工艺条件,并用Kissinger及Ozawa方法分别计算得到该体系固化反应的表现活化能为42.30KJ//mol和46.68kJ/mol,固化反应级数为0.86.研究结果表明,HAPP在固化环氧树脂时具有自催化作用,因而固化反应活化能较低.与间苯二胺顺丁烯二酸酐和二氨基二苯基甲烷固化荆相比,由于HAPP的苯环上带有羟基且为刚性的分子结构,既降低了固化温度,又提高了力学性能.HAPP固化环氧树脂/芳纶纤维复合材料的层间剪切强度为34.1MPa,弯曲强度为375MPa,拉伸强度为380MPa.     

新型双马来酰亚胺改性环氧树脂体系性能研究

用含二氮杂萘联苯结构的双马来酰亚胺(DHPZ-BM I)与4,4'-二氨基二苯砜(DDS)为复合固化剂固化环氧树脂(E-51)。采用示差扫描量热仪(DSC)研究了该体系的固化反应动力学,求得固化反应表观活化能Ea=63.28 kJ/mol,碰撞因子A=1.55×106s-1,反应级数n=0.89,该体系与链延长型双马来酰亚胺PPEK-BM I(DP=15)/DDS/E-51体系的固化反应动力学数据几乎相同,证明二者的固化反应过程相同。采用热失重分析仪(TGA)分析研究了上述2种固化体系的热分解动力学,前者的热分解活化能达215.04 kJ/mol,为后者的1.5倍以上,说明DHPZ-BM I/DDS/E-51是1种热稳定性能良好的耐高温环氧树脂体系。     

耐高温环氧胶粘剂及其固化动力学研究

基于TGDDM环氧树脂和DDRS多官能环氧树脂,制得了3种耐高温环氧胶粘剂(J-1,J-2,J-3),并对其不同温度下的粘接强度进行了研究。研究结果表明,其200℃的拉伸剪切强度为15.6~18.6 MPa,耐热性能良好。采用J-3耐高温环氧胶粘剂为样品,利用DSC对其进行了固化动力学研究,采用Kissinger法计算出该环氧胶粘剂的表观活化能第1个峰Ea=69.8kJ/mol,第2个峰Ea=73.2kJ/mol;结合Crane公式求出该体系第1个峰的反应级数n=0.82,第2个峰的反应级数n=1.07。     

含氮杂环二胺固化双酚F环氧胶粘剂的研究

以1,2-二氢-2-(4-氨基苯基)-4-[4-(4-氨基苯氧基)-苯基]-二氮杂萘-1-酮(DHPZ-DA)为固化剂,采用示差扫描量热法(DSC),TGA,红外光谱及剪切强度测试研究了双酚F环氧树脂/DHPZ-DA粘接体系固化行为及耐热性。由Kissinger和Ozawa方法计算得到固化体系的表观活化能分别为80.1 kJ/mol和84.3kJ/mol。由Crane方程求得的表观反应级数为0.93。该胶粘剂体系Tg>200℃,当双酚F环氧树脂与DHPZ-DA固化剂的物质的量比为10∶4时,其室温剪切强度与150℃老化24 h后的剪切强度均大于12 MPa,表现出良好的耐热性。     

中温(110℃)固化—促进剂 D 的研究

<正> 一、引言中温固化结构胶粘剂作为铝合金——铝合金、铝合金——碳纤维复合材料的连接手段,在航天、航空结构件的应用日益广泛。中温固化结构胶粘剂已有廿多年的发展史了,其核心是固化体系。固化体系多以双氰胺(以下简称 Dicy)为潜伏型固化剂,以脲类、胍类为促进剂,于中温固化环氧树脂(多为缩水甘油醚型)。所用脲类有3—对—氯苯基—1,1—二甲基脲(以下简称氯脲)、二氯苯基—1,1—二甲基脲、硫脲、四甲基胍等。此外,还有化学改性 Dicy,如芳香二胺与 Dicy 的加成反应产物。也有     

含茚满结构二胺-E51环氧树脂固化反应动力学的研究

以5(6)-氨基-1-(4-氨基苯基)-1,3,3-三甲基茚满(PIDA)作为E51环氧树脂的新型固化剂,对比4,4′-二氨基二苯甲烷(DDM)、4,4′-二氨基二苯砜(DDS)两个固化剂与E51环氧树脂组成的不同体系,采用非等温差示扫描量热法,研究了其固化反应动力学。利用傅立叶红外光谱仪表征了固化材料的分子结构,采用Kissinger模型及Ozawa模型计算得到E51与PIDA体系的表观活化能分别为50.39 kJ/mol、54.89 kJ/mol。Crane模型计算得到E51与PIDA体系的反应级数为0.87。     

铅酸蓄电池用密封胶的性能及其固化动力学研究

采用自制的环氧树脂和改性多胺固化剂制备了铅酸蓄电池密封胶。通过示差扫描量热法(DSC)对该体系的固化过程进行了研究,利用Kissinger,Crane方程对其固化反应进行了动力学分析并测定了体系的粘接性能。结果表明:该体系反应活化能Ea为54.76 kJ/mol,频率因子A为1.66×107/s,固化反应级数n=0.898,固化工艺为25℃/24～48 h+60～70℃/1～2 h,密封胶固化后的剪切强度达5.5 MPa以上。经相关电池厂家验证,可满足蓄电池壳盖密封的要求。     

TDE-85/DICY/取代脲中温固化体系的固化动力学

采用DSC研究了以双氰胺/取代脲为潜伏型中温固化体系的三官能团环氧树脂TDE-85的固化反应动力学,探讨了反应机理并确定了最佳的固化工艺参数。结果表明,固化温度<140℃时,受扩散效应和双氰胺在环氧树脂中溶解速率的影响,体系的等温固化行为与自催化模型存在偏差;固化温度>150℃后,体系的等温固化行为可用自催化反应模型很好地描述,其表观活化能为86.33 kJ/mol,指前因子为2.68×1010,总反应级数(m+n)为2～3。综合变温DSC和等温DSC的实验结果,可确定体系的最佳固化工艺条件为:120℃下预固化1 h后再升温至150℃保温1 h。     

NMR Study of the Epoxy Crosslinking Reactions of N,N-Dimethyl-4-Chlorophenyl Urea

The crosslinking of one-part epoxy adhesives is a complex process involving reactions of dicyandiamide and any of a variety of accelerators with epoxide functional polymers. Variations in adhesive formulation and process affect the final properties of the adhesive bond. The reactions of N,N-dimethyl-4-chlorophenyl urea, an accelerator for one-part, dicyandiamide crosslinked epoxy adhesives has been studied with Carbon-13 NMR in model systems employing phenyl glycidyl ether as the epoxy. A complex reaction mixture was observed whose composition varied with epoxy-accelerator stoichiometry and reaction temperature.

NMR peaks having chemical shifts consistent with 2-N-(4-chlorophenyl)-4-phenoxymethyl oxazolidone, a quaternary amine terminated polyether and epoxy elimination products have been observed in reaction mixtures modeling adhesive formulations. The quaternary amine terminated polyether likely results from condensation of epoxy with the dimethyl amine that is formed from N,N-dimethyl-4-chlorophenyl urea under cure conditions. Of the three products observed, only the quaternary amine terminated polyether would afford crosslinks in the actual adhesive. The other two products would consume epoxide functionality without the concurrent formation of crosslinks. The relative amounts of these three products varied as a function of reaction temperature, suggesting that variations in process conditions may affect final properties of dicyandiamide-crosslinked epoxy adhesives that are accelerated with N,N-dimethyl-4-chlorophenyl urea.     

NMR Study of the Epoxy Crosslinking Reactions of N,N-Dimethyl-4-Chlorophenyl Urea

The crosslinking of one-part epoxy adhesives is a complex process involving reactions of dicyandiamide and any of a variety of accelerators with epoxide functional polymers. Variations in adhesive formulation and process affect the final properties of the adhesive bond. The reactions of N,N-dimethyl-4-chlorophenyl urea, an accelerator for one-part, dicyandiamide crosslinked epoxy adhesives has been studied with Carbon-13 NMR in model systems employing phenyl glycidyl ether as the epoxy. A complex reaction mixture was observed whose composition varied with epoxy-accelerator stoichiometry and reaction temperature.

NMR peaks having chemical shifts consistent with 2-N-(4-chlorophenyl)-4-phenoxymethyl oxazolidone, a quaternary amine terminated polyether and epoxy elimination products have been observed in reaction mixtures modeling adhesive formulations. The quaternary amine terminated polyether likely results from condensation of epoxy with the dimethyl amine that is formed from N,N-dimethyl-4-chlorophenyl urea under cure conditions. Of the three products observed, only the quaternary amine terminated polyether would afford crosslinks in the actual adhesive. The other two products would consume epoxide functionality without the concurrent formation of crosslinks. The relative amounts of these three products varied as a function of reaction temperature, suggesting that variations in process conditions may affect final properties of dicyandiamide-crosslinked epoxy adhesives that are accelerated with N,N-dimethyl-4-chlorophenyl urea.     

Curing behavior of dicyandiamide/epoxy resin system using different accelerators

Various amounts of dicyandiamide (Dicy), two grades of epoxy resins, i.e. Epiran 06 and Epikote 828, and three different accelerators including benzyl dimethyl amine (BDMA), 3-(4-chlorophenyl)-1,1-dimethyl urea (Monuron) and 2-methyl imidazole (Im) were used in curing of Dicy/epoxy resin system. Both of the used epoxy resins were based on diglycidyl ether of bisphenol A (DGEBA). The effects of type and concentration of accelerators on curing behavior were studied by differential scanning calorimetry (DSC) method in dynamic or non-isothermal mode. The optimum concentration of Dicy for curing of epoxy resins was obtained based on the glass transition temperature of the cured epoxy/Dicy formulations. The maximum glass transition temperature of 139 °C was obtained at the stoichiometric ratio of Dicy to epoxy of 0.65. The results showed that BDMA has a broader curing peak in DSC and starts the cure reaction earlier than the others. However, Monuron has a narrow curing reaction peak with good cure latency. The tensile properties of Dicy-cured Epiran 06 and Epikote 828 epoxy resins reinforced with chopped strand mat showed that these two epoxy resins have similar mechanical properties. For composites based on the Epiran 06 and Epikote 828 reinforced with 40 wt % glass chopped strand mat, tensile strength and modulus were 156 and 153.4 MPa and 11.6 and 12.4 GPa, respectively.     

13C‐NMR, 13C‐13C gCOSY,and ESI‐MS characterization of ether‐bridged condensation products in N,N′‐dimethylurea‐formaldehyde systems

The reaction of urea with formaldehyde is the basis for the production of urea‐formaldehyde (UF) resins which are widely applied in the wood industry. The presence of ether‐bridged condensation products in the UF resin reaction system is an open question in the literature. It is addressed in the present work. The N,N′‐dimethylurea‐formaldehyde model system was studied since it is chemically similar to the UF resin reaction system but allows for a simple elucidation of all reaction products. It was analyzed by ¹³C‐NMR spectroscopy and ESI‐MS. In corresponding NMR and MS spectra, peaks due to methoxymethylenebis(dimethyl)urea and its hemiformal were observed. ¹³C‐¹³C gCOSY analysis was conducted using labeled ¹³C‐formaldehyde. The correlation spectra showed evidence for an ether‐bridged compound and mass spectra exhibited peaks agreeing with labeled methoxymethylenebis(dimethyl)urea and its hemiformal. Methoxymethylenebis(dimethyl)urea was characterized in N,N′‐dimethylurea‐formaldehyde systems in acidic and slightly basic media. As urea is very similar to N,N′‐dimethylurea, the results of this work strengthen the assumption that ether‐bridged condensation products are likely to form in UF resins. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Dicyandiamide analysis and solubility in epoxy resins

A simple procedure is described for the rapid, quantitative analysis of dicyandiamide in epoxy resins and epoxy resin prepregs. High performance liquid chromatography is used to analyze for dicyandiamide and to investigate the solubility behavior of dicyandiamide and 3-(p-chlorophenyl)-1,1-dimethylurea (Monuron) in liquid epoxy resins. Solubility expressions and differential heats of solution are determined. The formation of soluble amine-epoxy reaction products and epoxy resin additives such as Monuron are found to enhance the solubility of dicyandiamide.     

A study on the properties of epoxy resin toughened by a liquid crystal‐type oligomer

A series of novel reactive toughening agents (LCEU_PPG) containing both a flexible spacer and rigid liquid crystalline unit were synthesized to modify the bisphenol epoxy resin/dicyandiamide curing system. The curing reactivity, apparent activation energy, curing mechanism, dynamic mechanical behavior, and impact strength of the modified system were systematically studied. Compared with the unmodified system, the results indicate that LCEU_PPG have greatly accelerated the curing reaction between epoxy resin and dicyandiamide, reduced the apparent activation energy of the curing reaction, enhanced the impact strength 3–7 times, and maintained high dynamic modulus and good thermal properties. In addition, SEM observation of the fracture surfaces showed a two‐phase microstructure in the modified systems. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 177–184, 1999     

芳香胺改性双氰胺固化环氧树脂反应动力学研究

通过示差扫描量热法分析(DSC)研究了芳香胺改性双氰胺/环氧树脂E-44体系的固化反应,并探讨了反应的机理。结果表明,芳香胺改性双氰胺对环氧树脂E-44具有较高的固化反应活性,反应表观活化能明显降低,固化反应可以在中温进行。其固化反应机理与未改性的双氰胺环氧体系不同。     

Aging and performance of structural film adhesives. IV. A modified epoxy with improved ambient temperature shelf life

It appears that improved latency in nitrile epoxy adhesives can be achieved by replacing the commonly used urea accelerator with one of much reduced solubility but similar chemical activity. A new, commercially available film adhesive claimed to possess a shelf life of 1 year at 22°C, excellent resistance to humidity prior to cure, and a service temperature range of ?55 to 120°C has been examined. Areas studied included characterization, cure kinetics, adhesive performance, and shelf life. Its composition was found to be a variant of the 120°C curing nitrile—epoxy systems using a urea-accelerated dicyandiamide cure. Two novel features were noted: the presence of bisphenol S and the urea 1,1'-p-phenylene-bis(3,3-dimethyl) urea. The relatively high shear strength found at elevated temperatures could be related to the adhesive's high T_g of 155°C resulting from the addition of bisphenol S and the improved room-temperature latency was due to the ultralow solubility of the urea accelerator. Good durability was obtained from aluminum joints prepared using a simple silane pretreatment. Aging experiments indicated a shelf life of at least 3 months at 23°C under both dry and wet conditions, and it is predicted that adhesives of this type of composition would be stable for at least 1 year at normal domestic refrigeration temperatures of 5–10°C. © 1993 John Wiley & Sons, Inc.