Viscoelastic and thermal properties of polysulfide modified epoxy resin: The effect of modifier molecular weight

In this research two grades of polysulfide resin with low and high molecular weight (respectively G4 and G112) as reactive modifier was used to toughen epoxy resin. The effect of modifier molecular weight on impact resistance, thermal expansion coefficient, storage and loss modulus, decomposition temperature and adhesion properties of toughened epoxy was investigated. The impact strength and the thermal expansion coefficient (CTE) of epoxy resin was increased with increasing polysulfide but the G112 modified epoxy samples showed higher CTE values and impact resistance than those of modified with G4. Comparing of the same weight percent inclusion of G4 and G112 effect on decomposition temperature show that G4 modified epoxy resin has lower decomposition temperature than the G112 modified epoxy resin. Also addition of G112 up to 10 weight percent leads to higher bond strength with aluminum sheets. According to the DMTA graphs, glass transition temperature (Tg) of the modified epoxy was decreased with increasing polysulfide weight percent in composition. At the same time G4 modified epoxies have lower Tg and storage modulus than that of modified with G112.     

稀释剂对环氧树脂电子束辐射固化性能的影响

对分别加入4 种稀释剂的双酚A 环氧树脂和酚醛环氧树脂的电子束辐射固化性能进行了研究。分析了稀释剂种类及含量对环氧树脂体系辐射产物的固化度、固化均匀性、固化区域大小及其动态力学性能的影响规律。结果表明: 电子束固化环氧树脂体系中加入稀释剂后, 辐射产物的固化度、玻璃化转变温度及储能模量有所下降, 但固化均匀性得到提高; 加入稀释剂的环氧树脂电子束固化区域的厚度均小于未加稀释剂树脂, 而底面直径却大于未加稀释剂树脂; 随着树脂中实际稀释剂含量的增加, 电子束固化环氧树脂固化度逐渐降低, 固化层厚度减小, 固化区域的底面直径先增加后减小。      

环氧树脂/填料功能梯度材料的微波固化及其水声性能研究

以环氧树脂和蛭石粉为原料,采用微波固化制备了环氧树脂/蛭石粉水声功能梯度材料,研究了微波固化对试样的玻璃化转变温度、动态力学性能的影响,并着重对功能梯度材料的水下吸声性能进行了研究。研究表明,用微波固化制备功能梯度材料是可行的,微波固化对固化试样的玻璃化转变温度、动态力学性能影响不大,但能明显提高试样在低频区域的吸声性能。     

低粘度环氧树脂固化剂的合成和性能研究

按照不同配比合成两种低粘度环氧树脂固化剂802、804,再分别与市售环氧固化剂5505配制成两种不同的混合固化剂806、901。分别与环氧树脂制备成环氧树脂固化物,测试其力学性能和硬度。讨论了不同的固化剂对树脂固化物力学性能的影响。并讨论了固化剂用量对固化物力学性能的影响,得出最佳固化剂用量。     

端氨基树枝状大分子PAMAM/环氧树脂体系固化物的性能

以端氨基树枝状大分子PAMAM作为环氧树脂固化剂, 通过拉伸试验、 冲击试验、 DSC、 TGA研究了配比和固化温度对PAMAM与环氧树脂E-44的固化物性能的影响。 结果表明, 最佳固化温度为140℃, 但随着固化温度升高, 配比的影响表现出不同的规律: 80℃固化时, 最佳配比为0.47, 此时拉伸强度和冲击强度最佳, 玻璃化转变温度最高, 交联密度最大; 而在80℃以上固化时, 最佳配比逐渐向低配比方向移动, 140℃固化时, 最佳配比为0.28, 此时拉伸强度和冲击强度最佳, 玻璃化转变温度最高, 交联密度最大。固化物的密度和体积收缩率都是配比为0.47时最大, 而热稳定性都是配比为0.28时最佳。利用滴定法测定了固化物的固化度, 结果表明, 随着固化温度的升高, 低配比体系的固化度迅速提高并接近化学计量点配比体系的固化度。      

固体环氧树脂水分散体的制备和性能

用中等分子量的固体双酚A型环氧树脂ER-1和环氧乙烷/环氧丙烷的嵌段共聚物Lutrol F68合成了一种活性非离子型乳化剂F68-E,对乳化剂F68-E的结构以及合成过程进行了分析。用乳化剂F68-E对环氧树脂ER-1进行乳化,探讨了使用相反转法乳化时,乳化剂浓度、乳化温度和溶剂种类对环氧树脂水分散体的粒径和力学稳定性的影响。此外,将环氧树脂水分散体制成中温固化体系,对其干膜固化物进行了吸水率测试和动态热机械分析。结果表明,引入12%的乳化剂F68-E后,固化体系的吸水率由1.38%降至0.97%,玻璃化转变温度由102.5℃降至82.6℃。     

一种中温固化环氧树脂的研究

利用苯胺-甲醛与双氰胺反应得到了一种改性产物。相对于双氰胺, 它在环氧树脂和某种低沸点溶剂中有良好的溶解性。在促进剂作用下, 可以在125℃左右固化环氧树脂, 固化后的浇铸体有良好的力学性能和耐湿热性。用该树脂体系可湿法制作复合材料预浸布, 其玻璃布复合材料在力学性能和耐湿热性能上可达到国外同类产品的水平。      

含磷双环戊二烯酚醛固化剂的合成及固化环氧树脂的性能

合成了一种含磷酚醛型环氧树脂固化剂DCPD-DOPO,通过红外光谱和核磁共振谱对其化学结构进行了表征,采用凝胶渗透色谱测量了其相对分子质量。以DCPD-DOPO、苯酚型酚醛树脂(PF8020)或其复合物为固化剂,双酚A环氧树脂(DGEBA)为基料,制备了不同磷含量的阻燃环氧树脂。通过热重分析、差示扫描量热分析研究了环氧树脂固化物的热性能和阻燃性能;通过极限氧指数(LOI),垂直燃烧实验和锥形量热法研究了固化后环氧树脂固化物的燃烧特性。结果表明,DCPD-DOPO固化的环氧树脂的LOI可达31.6%,垂直燃烧性能达到UL94 V-0级,玻璃化转变温度(T_g)为133℃。采用DCPD-DOPO与PF8020复合物固化的环氧树脂的T_g提高到138℃以上,LOI值略有降低,但仍能通过UL 94V-0测试。DCPD-DOPO与PF8020添加DCPD-DOPO后,复合固化的环氧树脂的热释放速率峰值及总释热量较PF8020固化的环氧树脂大幅度降低。此外,还用Kissinger法对环氧树脂固化反应动力学进行了研究。     

Preparation of Microcellular Epoxy Foams through a Limited‐Foaming Process: A Contradiction with the Time–Temperature–Transformation Cure Diagram

3D cross‐linking networks are generated through chemical reactions between thermosetting epoxy resin and hardener during curing. The curing degree of epoxy material can be increased by increasing curing temperature and/or time. The epoxy material must then be fully cured through a postcuring process to optimize its material characteristics. Here, a limited‐foaming method is introduced for the preparation of microcellular epoxy foams (Lim‐foams) with improved cell morphology, high thermal expansion coefficient, and good compressive properties. Lim‐foams exhibit a lower glass transition temperature (T_g) and curing degree than epoxy foams fabricated through free‐foaming process (Fre‐foams). Surprisingly, however, the T_g of Lim‐foams is unaffected by postcuring temperature and time. This phenomenon, which is related to high gas pressure in the bubbles, contradicts that indicated by the time–temperature–transformation cure diagram. High bubble pressure promotes the movement of molecular chains under heating at low temperature and simultaneously suppresses the etherification cross‐linking reaction during post‐curing.     

Effects of compound curing agent on the thermo-mechanical properties and structure of epoxy asphalt

Epoxy asphalt curing system was prepared by sebacic acid compound with methyl-tetrahydrophthalic anhydride (MeTHPA) or Tung oil anhydride (TOA). Tensile strength, penetration, differential scanning calorimetry, dynamic mechanical thermal analysis, torn section microscopy photographs and scanning electron microscope analysis were utilised to investigate the mechanical properties, thermodynamic behaviour and micro-structure of epoxy asphalt curing systems under different curing agents. The results showed that in the presence of compound curing agent, the tensile strength and surface hardness of the epoxy asphalt curing system effectively improved, the induction period of the curing reaction decreased, the curing reaction mechanism turned to one-step reaction from two-step reaction, the Tg of asphalt phase and epoxy phase could simultaneously increase, and high-temperature damping performance also improved, but the particle size of asphalt dispersed in epoxy resin becomes uneven, while the curing system becomes semi-brittle from toughness. Compared to TOA, the effects of MeTHPA on such performance were more obvious.     

快速固化环氧树脂及其碳纤维/环氧复合材料性能

采用双酚A型环氧树脂（DGEBA）、改性咪唑（MIM）及改性脂肪胺（MAA）研制快速固化树脂体系。分别利用DSC和流变仪测试了树脂体系的固化特性与流变行为,优选了树脂配方。采用真空辅助树脂灌注工艺（VARIM）制备了快速成型的碳纤维/环氧复合材料层板,考察了层板的成型质量和力学性能,并与常规固化的层板性能进行了对比。结果表明：采用优选的树脂配方,120 ℃下树脂在5 min内固化度达95%,碳纤维/环氧复合材料层板成型固化时间可控制在13 min以内,固化度达95%以上,并且没有明显缺陷;与常规固化相比（固化时间大于2 h）,快速固化碳纤维/环氧复合材料层板的弯曲性能和耐热性能降低幅度较小。     

LTM树脂及其复合材料的初步研究

报告一种研制的低温固化高温使用树脂体系Xufyg-44。用它成型复合材料层压制件时,固化温度低于70 ℃,最终固化产物的玻璃化转变温度高于200 ℃,浇注体力学性能以及复合材料制件在整个固化周期中的尺寸稳定性良好。     

低粘度环氧树脂体系及其固化物性能的研究

为了满足环氧树脂在多种工艺中对低粘度的要求,使用了6002及618型两种普通双酚A型环氧树脂与低粘度XCT-802固化剂,设计出一种低粘度的环氧树脂体系,并对其粘度、固化物的力学性能等进行了表征。结果表明：该体系在常温下具有较长的适用期;在中温（80~C）条件下即可凝胶并固化,其固化物的力学性能优异。     

酚酞基聚醚酮/环氧树脂/氰酸酯半互穿聚合物的制备及性能

采用热熔法制备环氧树脂(EP)/氰酸酯树脂(CE)/酚酞基聚醚酮(PEK-C)半互穿网络聚合物。利用三点弯曲法测定了固化物的力学性能,通过动态力学分析(DMA)研究了固化物玻璃化转变温度(Tg)及储存模量变化规律;用扫描电镜(SEM)对断面进行了观察。结果表明,在Tg和弯曲性能基本保持不变的情况下,PEK-C能有效地改善固化物的韧性。当PEK-C的加入量为15%(质量分数,下同)时,断裂韧性KIC和GIC值可分别提高20%和50%,归功于此时固化物形成双连续相结构。但是随着PEK-C含量的增加,固化物初始分解温度略微下降,这可能与交联密度的少量降低有关。     

生物基没食子酸环氧树脂/纳米氧化锌抗菌涂层的制备与性能EI北大核心CSCD

以没食子酸为主要原料制备生物基没食子酸环氧树脂(GAER),将硅烷偶联剂KH550表面改性的纳米ZnO与GAER进行复合,以丁二酸酐为固化剂,制备KH550-nano-ZnO/GAER生物基复合涂层。对纳米ZnO改性前后微观结构的变化进行表征;采用示差扫描量热仪对丁二酸酐/GAER体系的固化过程进行研究,测试KH550-nano-ZnO的加入对GAER固化膜力学性能、热性能、动态力学性能以及抗菌性能的影响。结果表明:适量KH550-nano-ZnO的加入,可以增加GAER固化体系的玻璃化温度,提高涂层表面的抗冲击性,KH550-nano-ZnO含量的增加使得涂层的硬度增加,附着力下降,热稳定性增加。复合涂层的起始热失重温度(T5%)比纯GAER高12.6~15.4℃。当KH550-nano-ZnO含量为2%(质量分数)时,玻璃化转变温度与纯GAER树脂相比增加了30.7℃。KH550-nano-ZnO/GAER固化涂膜对大肠杆菌和金黄色葡萄球菌的抗菌率均达到99.99%。     

环氧乙烯基酯树脂固化工艺及性能研究

采用三种不同过氧化物为树脂基体固化剂,对环氧乙烯基树脂进行固化。测定不同固化剂含量在不同温度下树脂的凝胶时间,通过对制备的树脂浇注体进行拉伸实验测试,差示扫描量热（DSC）法研究了不同树脂固化体系的反应放热特性,采用扫描电镜（SEM）观察了不同固化剂在其最佳固化工艺下树脂浇注体的断面的表面形态。本文确定了不同体系树脂胶液的固化剂含量及固化工艺,得到拉伸性能良好的环氧乙烯基树脂浇注体。     

1,3,4-Oxadiazole epoxy resin-based liquid crystalline thermosets and their cure kinetics

Liquid crystalline thermosets were synthesized based on a difunctional liquid–crystal (LC) epoxy resin monomer, namely 2,5-bis(4-glycidyloxyphenyl)-1,3,4-oxadiazole with various tetrafunctional crosslinkers such as diaminodiphenyl methane, diaminodiphenyl sulfone, and diaminodiphenyl ether. The epoxy monomer was characterized by infrared and nuclear magnetic resonance spectroscopy. Cure kinetics of a stoichiometric mixture of epoxy monomer and diaminodiphenyl methane was investigated by differential scanning calorimetry (DSC) for specimens cured under various cure conditions. The nematic LC texture for the cured specimen was identified by polarized microscopy and confirmed by X-ray diffractometry. Phase diagram of cure time versus transition temperature was constructed based on the DSC data for epoxy/DDM system. The diagram displayed the changes of melting transition, isotropic transition, and glass transition temperatures as curing proceeds.     

Characterization of double network epoxies with tunable compositions

This article reports the processing and characterization of epoxy resins with near constant molar cross-link density prepared from sequentially reacted amine cross-linking agents. Stoichiometric blends of curing agents with compositions ranging from all polyetheramine to all diaminodiphenylsulfone (DDS) are reacted with an epoxy monomer in a staged curing procedure. The low reactivity of the aromatic amine permits the selective reaction of the aliphatic amine in the first stage. The residual aromatic amine and epoxide functionality are reacted in a second stage at higher temperature. Above approximately 50% DDS content the first stage produces sol glasses which have not reached the gel point. The glass transition temperatures of the partially cured networks decrease monotonically with increasing DDS content. The partially cured networks can be characterized thermally and mechanically above their respective glass transitions without significantly advancing the reaction of the residual DDS and epoxide functionality. The networks formed after the second stage of the cure exhibit thermal and mechanical properties intermediate between those of the two individual amine cured networks, according to composition. The blends do not show any evidence of phase separation across the entire composition range in either the partially cured or fully cured state.     

Improvement of the Compressive Strength of Carbon Fiber/Epoxy Composites via Microwave Curing

Microwave processing was used to cure the carbon fiber/epoxy composites and designed for improving the compressive strength of the materials. By controlling the power of microwave heating, vacuum bagged laminates were fabricated under one atmosphere pressure without arcing. The physical and mechanical properties of composites produced through vacuum bagging using microwave and thermal curing were compared and the multistep(2-step or 3-step) microwave curing process for improved compressive properties was established. The results indicated that microwave cured samples had somewhat differentiated molecular structure and showed slightly higher glass transition temperature. The 2-step process was found to be more conducive to the enhancement of the compressive strength than the 3-step process. A 39% cure cycle time reduction and a 22% compressive strength increment were achieved for the composites manufactured with microwave radiation. The improvement in specific compressive strength was attributed to better interfacial bonding between resin matrix and the fibers, which was also demonstrated via scanning electron microscopy analysis.     

Acrylonitrile-capped poly(propyleneimine) dendrimer curing agent for epoxy resins: Model-free isoconversional curing kinetics,thermal decomposition and mechanical properties

Acrylonitrile-modified aliphatic amine adducts are often used as curing agents for room-temperature epoxy formulations (coatings, adhesives, sealants, castings, etc.), yet the curing reaction and properties of resultant epoxy systems still remain less fundamentally understood. Herein we systematically investigate our newly-developed acrylonitrile-modified multifunctional polyamine curing agent for bisphenol A epoxy resin (DGEBA): an acrylonitrile-capped poly(propyleneimine) dendrimer (PAN4). The impact of the molecular structure of PAN4 and a controlled poly(propyleneimine) dendrimer (1.0GPPI) on the curing reactivity, reaction mechanisms, thermal stability, viscoelastic response and mechanical properties of the epoxy systems are highlighted. Differential scanning calorimetry (DSC) confirms DGEBA/PAN4 shows markedly lower reactivity and reaction exotherm than DGEBA/1.0GPPI, and the model-free isoconversional kinetic analysis reveals that DGEBA/PAN4 has the generally lower reaction activation energy. To be quantitative, the progress of the isothermal cure is predicted from the dynamic cure by using the Vyazovkin equation. The isothermal kinetic prediction shows that DGEBA/PAN4 requires about 10 times longer time to achieve the same conversion than DGEBA/1.0GPPI, which agrees with the experimentally observed much longer gel time of DGEBA/PAN4. Subsequently, dynamic mechanical analysis shows that PAN4 results in the cured epoxy network with the lower β- and glass-relaxation temperatures, crosslink density, relaxation activation energy, enthalpy, entropy, but the higher damping near room temperature than 1.0GPPI. Finally, thermogravimetric analysis (TGA) demonstrates cured DGEBA/PAN4 is thermally stable up to 200 °C, and mechanical property tests substantiate that PAN4 endows the cured epoxy with much higher impact and adhesion strengths than 1.0GPPI. Our data can provide a deeper insight into acrylonitrile-modified aliphatic amine curing agents from the two good model compounds (PAN4 and 1.0GPPI).