多壁碳纳米管-环氧树脂纳米复合材料的γ-射线固化行为

通过γ-射线辐射固化制备了多壁碳纳米管-环氧树脂复合材料.采用索氏提取法、傅里叶变换红外光谱(FT-IR)和差示扫描量热法(DSC)测试了多壁碳纳米管-环氧树脂复合体系的凝胶含量、转化率及热流曲线等固化动力学参数.采用扫描电子显微镜(SEM)表征了复合材料的微观组织.结果表明:通过γ-射线辐射固化的复合体系的凝胶含量随着辐射剂量、光引发剂含量的增加而增加;由于多壁碳纳米管对活性反应中心的影响,转化率随着多壁碳纳米管加入量的增加呈先下降,后增加的趋势.复合体系中多壁碳纳米管含量较高时易发生团聚,团聚会对复合体系的固化行为产生一定影响.     

固化条件对环氧树脂/丙烯酸酯橡胶共混体系结构与性能的影响

利用丙烯酸酯橡胶(ACM)提高热固性环氧树脂(EP)的韧性,系统研究共混体系固化条件对材料结构和性能的影响.研究表明,固化前环氧树脂与丙烯酸酯橡胶在整个组成范围内为均相体系,固化过程中两组份分子量不断增大,部分组成环氧树脂/丙烯酸酯橡胶共混体系(80/20及50/50)发生反应诱导相分离现象(RIPS).在发生反应诱导相分离的体系中,分相后的环氧树脂和丙烯酸酯橡胶两相彼此包含对方的组分,是一种不彻底的相分离.同时,固化后材料的结构与性能强烈依赖于所用固化条件(包括固化时间、固化温度及固化剂含量等).因此,可以通过调节体系固化条件实现对环氧树脂/丙烯酸酯橡胶共混体系结构和性能的调控.     

环氧树脂/氧化石墨纳米复合物的等温固化行为研究

用示差扫描分析仪(DSC)研究了氧化石墨(GO)对N,N,N',N'-四缩水甘油基-4,4'-二氨基二苯基甲烷环氧树脂(TGDDM)/4,4'-二氨基二苯基砜(DDS)体系的等温固化反应的影响,用X射线光电子能谱仪(XPS)和傅里叶变换红外光谱仪(FTIR)研究了GO上存在的官能团及其对TGDDM/DDS体系固化行为的影响,用热失重分析仪(TGA)研究了天然石墨和GO的热力学稳定性.XPS、FTIR和TGA结果表明,GO上存在的大量羟基、羧基、环氧基等官能团能够影响环氧树脂的固化行为.DSC研究发现,环氧树脂/氧化石墨纳米复合物的固化反应属于自催化类型,随着GO含量的增加,达到最大反应速率的时间不断减小,初始反应速率不断增大,这说明GO对环氧树脂的固化反应有促进作用.Kamal模型计算得到的结果表明,随着GO含量的增加自催化反应初期阶段表观活化能E1先减小再增大,而自催化反应结束后表观活化能E2略微减小.经Kamal模型扩散控制函数修正后,整个固化过程中拟合得到的结果与实验数据相当吻合.以上结果说明,少量的GO对TGDDM/DDS体系的固化反应起着催化作用.     

温度效应对氟链封端聚醚酰亚胺改性环氧树脂相分离的影响

用差示扫描量热仪(DSC)、扫描电镜(SEM)和时间分辨光散射(TRLS)比较了全氟碳链封端和苯环封端聚醚酰亚胺改性环氧树脂在不同温度下的相分离.结果表明,与P-blend相比,F-blend的固化速度和相分离速度较慢,诱导期和相结构固定时间推迟,相间距较小.升高温度,相间距因相分离速度加快而增大,同时由于全氟碳链端基引起的差异减小.因此,通过改变固化温度和聚醚酰亚胺的端基来降低聚醚酰亚胺的表面能,可以在一定程度上调控反应诱导相分离体系的相结构,并获得相间距较小的双连续结构.     

PAA对PLA流变性能和热性能的影响

通过熔融共混法制备了一系列的PLA/PAA共混物,考察了PLA/PAA共混体系的流变行为和热性能(结晶行为和热降解行为).FTIR测试结果证实PLA与PAA分子链之间形成了氢键网络.动态剪切流变测试和DSC测试均表明共混体系的流变行为和冷结晶行为会随着PAA含量的改变而改变,这可能是由于PLA与PAA的氢键作用受到PAA含量的影响.另外,DSC测试证实共混体系中的氢键网络还会受到试样热历史的影响.当PAA含量较低(低于5 wt%)时,PLA/PAA共混体系中PAA与PLA熔体两相的相分离不严重,使得PAA与PLA分子链能够较大限度地接触而形成较强的氢键作用,因而可以明显减缓增塑作用对黏度降低的影响.     

热塑性聚醚酰亚胺改性四官能度环氧树脂的相分离研究──固化剂用量的影响

以DSC、TRLS和SEM等方法研究了固化剂DDS用量对苯端基聚醚酰亚胺(P-PEI)改性4,4'-二氨基二苯甲烷四缩水甘油环氧树脂(TGDDM)体系的固化速率及相结构的影响.结果表明,20phrP-PEI改性环氧体系在150℃固化时,随DDS量增加,固化反应速率增大,相分离时间提前,形成了不同的相结构,解释了DDS量对粘接剪切强度的影响.     

高性能环氧树脂/碳纳米管复合物的热分析研究

用差示扫描量热仪(DSC)、热失重分析仪(TGA)和动态力学热分析仪(DMTA)研究了多壁碳纳米管(MWNTs)/高性能4,4′-二氨基二苯甲烷四缩水甘油环氧树脂(TGDDM)/4,4′-二氨基二苯基砜(DDS)复合物的热性能.Kissinger和Flynn-Wall-Ozawa的非等温固化动力学研究发现,随着MWNTs含量的增加,复合物固化反应的活化能先减小后增大.TGA研究表明,MWNTs的添加对环氧树脂热稳定性影响很小.碳纳米管填充到TGDDM/DDS体系后,复合物的储存模量随着MWNTs含量的增加而增大,而玻璃化温度却随之减小.     

橡胶改性环氧树脂的固化诱导相分离

研究了一种新型的液体橡胶ZR与环氧树脂的固化反应诱导相分离过程,分别通过时间分辨的激光光散射、光学显微镜研究了两相结构的发展,并用DSC跟踪该体系的固化动力学。结果表明,该固化反应经历了不稳相分离过程(spindodal decomposition),固化动力学过程与相分离过程有强烈的依赖性,固化速度越快,橡胶相尺寸越大;并且当环氧固化反应转化率达80％时,橡胶相结构基本得以固定,最终得到双连续结构。     

聚醚酰亚胺改性TGDDM环氧树脂的相分离研究

合成了不同化学结构的聚醚酰亚胺(PEI)并用于4,4′-二氨基二苯甲烷四缩水甘油醚(TGDDM)环氧树脂的增韧改性,以DSC,TRLS和SEM等方法研究了体系相分离过程中相容性和熔融粘度对相分离过程和结构的影响,对固化反应诱导相分离中相结构的控制提出初步的看法.     

原位法制备纳米银修饰碳纳米管环氧导电复合材料

将碳纳米管(CNTs)和乙酸银同时引入到环氧树脂-咪唑固化体系中,在固化过程中原位热降解银-咪唑复合物生成纳米银修饰碳纳米管,差示扫描量热仪(DSC)表明改性碳纳米管对环氧固化有一定的促进作用.采用X-射线衍射(XRD)表征了乙酸银和咪唑配合物[Ag(2E4MZ)2]Ac的结构,并提出了原位降解生成纳米银的机理.XRD结果表明,单独的乙酸银-咪唑配合物热降解生成的纳米银粒径为21-24nm,而配合物在环氧基体中生成的纳米银粒径为11-13nm.添加80%(质量分数)片状微米银粉制备的纳米银/碳纳米管环氧导电复合材料其体积电阻率低达9×10-5Ω·cm.当纳米银和碳纳米管质量比为80:20时,复合材料导电性和剪切强度达到最佳;采用扫描电镜(SEM)表征了复合材料的形貌结构.     

Phase separation,porous structure,and cure kinetics in aliphatic epoxy resin containing hyperbranched polyester

Thermosetting blends of an aliphatic epoxy resin and a hydroxyl‐functionalized hyperbranched polymer (HBP), aliphatic hyperbranched polyester Boltorn H40, were prepared using 4,4′‐diaminodiphenylmethane (DDM) as the curing agent. The phase behavior and morphology of the DDM‐cured epoxy/HBP blends with HBP content up to 40 wt % were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The cured epoxy/HBP blends are immiscible and exhibit two separate glass transitions, as revealed by DMA. The SEM observation showed that there exist two phases in the cured blends, which is an epoxy‐rich phase and an HBP‐rich phase, which is responsible for the two separate glass transitions. The phase morphology was observed to be dependent on the blend composition. For the blends with HBP content up to 10 wt %, discrete HBP domains are dispersed in the continuous cured epoxy matrix, whereas the cured blend with 40 wt % HBP exhibits a combined morphology of connected globules and bicontinuous phase structure. Porous epoxy thermosets with continuous open structures on the order of 100–300 nm were formed after the HBP‐rich phase was extracted with solvent from the cured blend with 40 wt % HBP. The DSC study showed that the curing rate is not obviously affected in the epoxy/HBP blends with HBP content up to 40 wt %. The activation energy values obtained are not remarkably changed in the blends; the addition of HBP to epoxy resin thus does not change the mechanism of cure reaction of epoxy resin with DDM. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 889–899, 2006     

原位制备PEI/SiO2复合材料及其改性环氧树脂的研究

在N,N-二甲基乙酰胺/四氢呋喃(DMAc/THF)混合溶剂中,在正硅酸乙酯(TEOS)存在条件下,通过溶胶-凝胶法原位制备了聚醚酰亚胺(PEI)/SiO2复合材料.在该复合材料中,当SiO2含量低于20 wt％时,透射电镜(TEM)和扫描电镜(SEM)的观察表明,SiO2纳米粒子可以均匀分散,粒径可在80～300 n...     

Studies on the Phase Separation of Poly(Ether Imide)‐Modified Cyanate Ester Resin

Abstract

A high temperature thermosetting bisphenol‐A dicyanate (BADCy) was blended with a novel thermoplastic poly(ether imide) (PEI) at various composition. The phase separation behavior during isothermal curing was studied by differential scanning calorimeter (DSC), time‐resolved light scattering (TRLS), scanning electron microscopy (SEM), and rheological measurements. The results suggested that the phase structure changed from separated phase, via co‐continuous phase, to phase inversion with the increase of the PEI content. The curing conversion of BADCy was slightly affected by the composition in the blend and the curing rate was decreased with the increase of PEI content. The co‐continuous phase morphology was attributed to a spinodal decomposition. The initial concentration of PEI had an effect on the rheological behavior during phase separation. It was found by tensile test that the blend with 15 wt.% PEI had higher tensile strength and elongation at break than that without PEI.     

Phase separation during synthesis of polyetherimide/epoxy semi-IPNs

The phase separation behavior and the morphology of polyetherimide (PEI)-modified diglycidyl ether of bisphenol A (DGEBA) epoxy resin were studied using scanning electron microscopy and light scattering. Reaction kinetics, cloud point and onset of gelation were determined by differential scanning calorimeter, optical microscope and physica rheometer, respectively. The mixture of partially cured epoxy and PEI showed bimodal upper critical solution temperature (UCST) behavior. For PEI content smaller than 10 wt%, the blends exhibited a sea-island morphology formed via nucleation and a growth mechanism. Above 25 wt% PEI content, the phase separation proceeded via a spinodal decomposition mechanism and a nodular structure was formed. With PEI content between 15 and 20 wt%, dual phase morphology was observed. This morphology was formed via primary spinodal decomposition and secondary phase separation within the dispersed phases and the matrix phases formed by the primary phase separation. This morphology was presumed to be formed in the reaction-induced phase separation mechanism with the mixture showing bimodal UCST behavior. The curing temperature had an effect on the final morphology, and the modulus of PEI-modified epoxy was influenced by the phase separation.     

Thermal and mechanical properties of a dendritic hydroxyl‐functional hyperbranched polymer and tetrafunctional epoxy resin blends

Blends of a tetrafunctional epoxy resin, tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM), and a hydroxyl‐functionalized hyperbranched polymer (HBP), aliphatic hyperbranched polyester Boltorn H40, were prepared using 3,3′‐diaminodiphenyl sulfone (DDS) as curing agent. The phase behavior and morphology of the DDS‐cured epoxy/HBP blends with HBP content up to 30 phr were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The phase behavior and morphology of the DDS‐cured epoxy/HBP blends were observed to be dependent on the blend composition. Blends with HBP content from 10 to 30 phr, show a particulate morphology where discrete HBP‐rich particles are dispersed in the continuous cured epoxy‐rich matrix. The cured blends with 15 and 20 phr exhibit a bimodal particle size distribution whereas the cured blend with 30 phr HBP demonstrates a monomodal particle size distribution. Mechanical measurements show that at a concentration range of 0–30 phr addition, the HBP is able to almost double the fracture toughness of the unmodified TGDDM epoxy resin. FTIR displays the formation of hydrogen bonding between the epoxy network and the HBP modifier. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 417–424, 2010     

Thermoplastic modification of monomeric and partially polymerized Bisphenol A dicyanate ester

Bisphenol A dicyanate ester (BADCy) was modified with different amounts of an engineering thermoplastic, polysulfone (PS) to improve impact strength of the parent resin. Differential scanning calorimetry of the blends suggested that addition of PS widens the curing exotherm of the BADCy considerably. FTIR of cured neat resins indicated total conversion of cyanate functional groups into triazine rings by cyclotrimerization. The cured neat resins showed phase separated morphology with cyanate ester as the continuous phase. The modified resins were shown to have better thermal, hygrothermal and impact strength properties. However, when glass fiber reinforced composites were made using partially polymerized BADCy and PS, very little or no phase separation in the resin was noticed. Flexural and impact strength measurement of composites showed that PS modification has compromised the flexural properties and only retained the impact strength of the parent resin containing composite. This study thus suggests that improvements realized in thermoplastic modification of monomeric BADCy are not directly transferable to composites using a partially prepolymerized BADCy.     

Synthesis and characterisation of epoxy-novolac/bismaleimide networks

Epoxy-novolac resin was modified with 1,1^′-(methylenedi-4,1-phenylene) bismaleimide (BMI), and cured with an aromatic amine. Cure behaviour of these blends was studied using differential scanning calorimetry (DSC). The thermograms indicated a unimodal exothermic peak for blends containing lower percentage of BMI. The cured blends showed much higher glass transition temperatures than that of the unmodified epoxy. Thermal stability of the cured epoxy resin was also improved with BMI addition. A homogeneous structure (with no phase separation) of the blends was confirmed both by DSC analysis and scanning electron microscopy (SEM).     

POLYESTERIMIDE-MODIFIED BISMALEIMIDE RESINS. I. EFFECT OF POLYESTERIMI DE CONTENT

ABSTRACT

A novel polyesterimide (PEsI-M) was used to improve toughness of bismaleimide (BMI) resin composed of bis(4-maleimidediphenyl) methane (BDM) and O,O′-diallyl bisphenol A (DBA). Morphologies of modified resins changed from spherical particles to inverted phase structures, depending on PEsI-M's content based on the observation of scanning electronic microscopy (SEM). PEsI-M was an effective morphology modifier so that loading of 12 pbw resulted in a diverted phase structure. Dynamic mechanical analysis (DMA), rheometrics mechanical spectroscopy (RMS) and differential scanning calorimetry (DSC) were respectively used to investigate the dynamic mechanical behavior, and the gelation time and the curing extent of unmodified and modified BMI resins. The fairly uniform morphology in 15 pbw PEsI-M modified system cured at 180°C suggests that the phase separation might take place via a spinodal decomposition mechanism. The fracture energy (G _IC ) increased with the increase of PEsI-M content in the modified system. G _IC of 15 pbw PEsI-M modified system was 0.63 times larger than that of the unmodified BMI resin.     

Phase behavior and morphology in epoxy resin/poly(L-lactide) blends. Comparison with epoxy resin/poly(L,D-lactide) blends

Thermoset/thermoplastic blends were prepared with epoxy–aromatic diamine mixtures and poly(L-lactide) (PLLA), as semicrystalline thermoplastic, in concentrations ranging from 4 to 25 wt.%. In some cases, poly(L,D-lactide) (PDLLA), an amorphous thermoplastic, was used instead for comparative purposes. Diglycidyl ether of bisphenol-A (DGEBA) was employed as epoxy resin and 4,4′-diaminodiphenylmethane (DDM) as curing agent. Phase behavior and morphology were studied during curing at 140 °C. Initially, all blends were homogeneous; however, the curing reaction of the epoxy resin caused a liquid–liquid phase separation. A co-continuous morphology was formed at the beginning of the phase separation in all the considered blend compositions. Blends evolved to a particle/matrix structure or to a phase-inverted structure depending on the initial blend composition. At 140 °C, crystallization only occurred in blends with 16 and 25 wt.% PLLA. This crystallization originates changes in the surface of the epoxy-rich droplets developed with the phase separation.