Effects of binders on dimensional accuracy and mechanical properties of SiC particulates preforms fabricated by selective laser sintering

SiC preforms were produced by selective laser sintering and thermal treatment sintering at 700 °C for fabricating near-net-shape composites. The dimensional accuracy and mechanical properties were investigated. The results show that dimensional accuracy 98.42% of preforms was obtained. After sintering at 700 °C, the dimensional accuracy of preforms using the binder of epoxy resin was decreased obviously, but that using the binder of epoxy resin and NH₄H₂PO₄ was maintained. The tensile and bend strength of preforms using epoxy resin and NH₄H₂PO₄ as binder were higher than that using epoxy resin, and enough to support the external load. When the epoxy resin was decompounded at 700 °C, the reaction product of SiP₂O₇ phase can form an effective bonding for maintaining the dimensional accuracy and supporting mechanical properties of preforms by using the binder of epoxy resin and NH₄H₂PO₄.     

改性F-51/E-51环氧树脂水乳液研究

多官能度环氧树脂F-51与适量二乙醇胺反应,再与乙酸成盐得到一种水性环氧树脂,该树脂保留了较多的环氧基团,与胺类固化剂配合,可作为涂料或复合材料基体。此外,该改性树脂对其它环氧树脂有良好的乳化能力,用适量E-51环氧树脂与之混合,通过相转变法制备的水乳液稳定性好,固化膜综合性能良好,吸水率与溶剂型环氧体系相当。     

Optimum mixing ratio of epoxy for glass fiber reinforced composites with high thermal stability

The optimum condition of glass fiber/epoxy composites was investigated according to mixing ratio of two epoxy matrices. Novolac type epoxy and isocyanate modified epoxy were used as composites matrix. Based on chemical composition of mixing matrix, optimum mixing ratio of epoxy resins was obtained through FT-IR instrument. In order to investigate thermal stability and interface of epoxy resin, glass transition temperature was observed by DSC instrument, and static contact angle was measured by reflecting microscope. Change of IR peak and T_g was conformed according to different epoxy mixing ratios. After fabrication of glass fiber/epoxy composites, tensile, compression, and flexural properties were tested by UTM by room and high temperature. The composites exhibited best mechanical properties when epoxy mixing ratio was 1:1.     

Generation of thermal strains in GRP

The temperature dependence of the linear expansion coefficients in the longitudinal (α _l) and transverse directions \((\alpha _{t_1 } and \alpha _{t_2 } )\) of unidirectional glass fibre laminates and their matrix resins (α _m) has been studied. The results for the dry, fully post-cured polyester, epoxy resins and laminates have been found to be consistent with the predictions of the Schapery equations. An anomalous moisture phenomenon, in the form of a peak in theα _m (T)/T andα _t (T)/Tcurves for the polyester resin and laminates has been observed. A difference between \(\alpha _{t_1 }\) and \(\alpha _{t_2 }\) has been observed for partially cured polyester laminates, which is also perturbated in the presence of water. Both these moisture effects, which are not found in the epoxy specimens, are considered to result from a two-phase polyester matrix and the latter to continued curing below the softening point of the resin. These results have a considerable consequence on the magnitude of the thermal strains which develop in polyester composites.     

环氧树脂改性水性聚氨酯的合成研究

采用甲苯二异氰酸酯(TDI-80)、聚醚二醇(N220)、二羟甲基丙酸(DMPA)、环氧树脂和丙烯酸羟丙酯(HPA),合成了环氧改性的双键封端水性聚氨酯乳液.乳液由于含有不饱和双键而具有感光性能,故此乳液可用作水性紫外光固化涂料或胶粘剂的预聚物.实验结果表明,随着环氧树脂用量的增大,涂膜的硬度、耐水性、耐溶剂性及力学性能增强,但乳液外观和稳定性变差,故适宜的环氧树脂添加量为4%～8%.通过傅立叶变换红外光谱、粒径分析仪、凝胶渗透色谱(GPC)和透射电镜(TEM)等对乳液进行了表征.粒径分析仪分析显示,加入环氧树脂后,水性聚氨酯(WPU)分散体粒径增大,粒径分布变宽.凝胶渗透色谱分析表明环氧树脂改性水性聚氨酯提高了聚氨酯的分子量.     

自乳化水性环氧树脂的制备

采用聚醚醇二缩水甘油醚(PEGGE)、乙醇胺(MEA)及冰乙酸对双酚A环氧树脂(DGEBA)化学改性,在不需Lewis酸催化剂条件下制备低污染、高性能水性环氧树脂。首先,在物料摩尔比(MEA/PEGGE)2∶1,反应温度55℃,反应时间4h下,用PEGGE对MEA扩链合成MEA-PEGGE加成物;然后,在物料摩尔比(DGEBA/MEA-PEGGE)2∶1,反应温度65℃,反应时间5h下,用MEA-PEGGE加成物对DGEBA扩链,合成DGEBA-MEA-PEGGE加成物;再采用冰乙酸与DGE-BA-MEA-PEGGE加成物成盐,制备出具有良好水溶解分散性能的自乳化水性环氧树脂。该树脂涂膜性能优良,具有良好柔韧性和耐冲击性,改善了普通环氧树脂性能较脆的缺陷。     

Effects of 3D structure of silsesquioxane moieties on the thermal and optical properties of transparent epoxy/silsesquioxane hybrid materials

Transparent and colorless epoxy/silsesquioxane (SQ) hybrids were prepared by modifying bisphenol-A epoxy resin with two SQ type epoxy resins having different 3D structures, that is, double-decker SQ and cage SQ type epoxy resins. To compare these two hybrids, the cured resin modified with the imperfect ladder SQ epoxy resin was also prepared. The effects of the 3D-structure of the SQ moieties on the thermomechanical, optical and dielectric properties of the cured epoxy/SQ hybrids were investigated. Thus, the refractive index and dielectric constant of the hybrids significantly decreased with an increase in the contents of the SQ moieties. This is due to the introduction of Si atoms with a low atomic polarity and large intermolecular space that was estimated from the difference between the volume of the space surrounded by “Connolly surface” and the van der Waals volume of the SQ moieties. The glass transition temperature, T _g, also decreased with the introduction of the SQ moieties, due to the increase in the intermolecular space. Thus, it was concluded that the performance of the epoxy/SQ hybrids depends not only on the SiO_3/2 content, but also on the 3D structure of the SQ moieties.     

Vinylester/epoxy-based thermosets of interpenetrating network structure: An atomic force microscopic study

The morphology of vinylester (VE) and epoxy (EP) resins, and their combination (VE/EP at a ratio 1/1) was studied by atomic force microscopy (AFM). AFM scans taken on the ion-etched surface of EP showed a featureless homogeneous structure. On the other hand, VE exhibited a two-phase microgel, whereas VE/EP a two-phase interpenetrating network (IPN) structure. A vinylester-urethane hybrid resin (VEUH) showed also the formation of an IPN-like morphology. It was concluded that cross-reactions between the hydroxyl functionality of VE and additional functional groups, such as isocyanate in VEUH or epoxy in VE/EP combinations, strongly favour the IPN formation. AFM scans revealed the compaction of the IPN structure of VE/EP upon post-curing which was associated with a prominent increase in the glass transition temperature (T _g) according to dynamic-mechanical thermal analysis.     

Effect of nano Al pigment on the anti corrosive performance of waterborne epoxy coatings

This paper presents the results regarding the effect of nano aluminum powder pigment concentration on the protective properties of waterborne epoxy films in 3.5 wt pct NaCl solution. The anticorrosive performance of the coatings with 0.5, 1, and 3 wt pct pigments and none pigment were investigated using electrochemical impedance spectroscopy （EIS）, scanning electron microscopy （SEM） and Raman spectroscopy techniques. The results show that adding appropriate amount of nano-aluminium powder pigment can enhance the barrier properties of the epoxy coating, which is attributed to the surface effect of nanoparticles and the compatibility of the pigment with the waterborne epoxy coatings.     

高固低黏水性紫外光固化环氧丙烯酸酯的合成及性能

利用不同种类的稀释剂对环氧树脂进行降粘改性,而后与丙烯酸进行反应,合成得到具有光敏性的环氧丙烯酸酯,再用顺丁烯二酸酐对其接枝改性引入羧基,经有机碱中和成盐,得到可用于紫外光(UV)固化的高固低黏型水性环氧丙烯酸酯。讨论了反应温度、催化剂种类以及用量对反应的影响;测试了不同稀释剂对体系的降黏效果;并考察了固化漆膜的力学性能。结果表明:该光敏树脂具有固含量高、黏度低、固化速度快、固化后的涂膜硬度较高、对基材附着性好等特点。     

碳纤维/TiO2改性树脂复合材料的制备及力学性能

针对环氧树脂脆性大、与碳纤维形成的界面性能较差等问题,本文选用纳米TiO₂对5284环氧树脂进行改性,并以角联锁机织物为增强体制备了碳纤维/环氧树脂复合材料。使用FT-IR、旋转流变仪、表面张力仪等设备对TiO₂/环氧树脂进行表征,并研究了树脂改性对复合材料压缩与层间剪切性能的影响。研究表明:TiO₂的羟基与环氧树脂的环氧基和羟基发生了反应;经1wt.%TiO₂改性的树脂复数黏度为0.066 Pa·s,纤维与树脂间接触角为28.85°,浸润效果较好;相较于未改性复合材料,树脂改性的复合材料纵向压缩强度与模量分别提高了7.46%和11.03%,横向压缩强度与模量分别提高了6.99%和4.96%,纵向、横向的剪切强度分别提高了6.88%和4.65%。TiO₂改性环氧树脂提高了复合材料的承载能力,改善了界面结合强度。     

无溶剂环氧涂料的制备及涂层性能研究

为提高环氧涂料在受力和形变等动态环境下的性能,通过对环氧树脂和固化剂等基础材料的筛选、涂膜柔韧性能的改善和防腐蚀底漆配方的设计,研制一款无溶剂环氧树脂工业防腐蚀涂料。选取黏度较低的J51型环氧树脂以及与其成膜性好且漆膜力学性能优异的WH-31型环氧固化剂作为主要成膜物质,通过环氧活性稀释剂(SM80)进行增韧,当SM80与环氧树脂比例为1:7时,涂层柔韧性可达1mm且与碳钢板拉拔附着力可达12MPa。在此基础上进行无溶剂环氧铁红底漆研制,得到施工方便、力学性能优异、耐水性良好、耐碱性良好,耐盐雾可达1000h的工业防腐蚀底漆。     

Transparency and toughness characterization of epoxy resins modified with liquid chloroprene rubber

Transparent epoxy resins modified with liquid chloroprene rubber (LCR), containing in a category of rubber-toughened resin were found. Transparency and toughness characterization of the modified epoxy resins were investigated as a function of LCR content. Epoxy resins modified with 0–10 vol % LCR showed complete phase-separation microstructure. However, these modified resins were transparent, because the refractive index of LCR was compatible with that of the epoxy resin matrix at room temperature. On the other hand, it was observed that above 10 vol % LCR, a certain amount of LCR dissolved into the epoxy matrix. In this case, the glass transition temperature decreased with increasing LCR content. It was also found that the critical stress intensity factor, K _c, of the modified epoxy resins exhibited a maximum between 10 and 15 vol % LCR.     

Lignin/epoxy composites

This paper presents some possibilities for the use of lignin/epoxy resins in blends and composites with epoxy resins. A compatibility study was carried out by optical and electron microscopy, viscosimetric determinations and thermo-optical analysis in order to establish optimum synthesis conditions of molding mass (cast resins). Lignin/epoxy composites including various fillers (lead soap, alum earth, talc, chalk, sand, trihydrate aluminium oxide, glass fibers), plasticizer (dibutylphthalate and polyester C₆) and pigments (iron-oxide and titanium dioxide) have been obtained. Lignin/epoxy composites are characterized by good dielectric, mechanical and adhesive properties. These composite materials can be used in the electronics industry.     

Energy absorption capability of carbon nanotubes dispersed in resins under compressive high strain rate loading

The focus of the present study is on energy absorption capability (E_A) of carbon nanotubes (CNTs) dispersed in thermoset epoxy resin under compressive high strain rate loading. Toward this objective, high strain rate compressive behavior of multi-walled carbon nanotube (MWCNT) dispersed epoxy is investigated using a split Hopkinson pressure bar. The amount of MWCNT dispersion is varied up to 3% by weight. Calculation methodology for the evaluation of E_A of individual CNTs and CNTs dispersed in resins/composites is presented. Quantitative data on E_A of individual CNTs and CNTs dispersed in resins under quasi-static and high strain rate loading is given.     

Size reduction of WO3 nanoparticles by ultrasound irradiation and its applications in structural nanocomposites

The porous WO₃ (pore size 2–5 nm) nanoparticles were synthesized using a high intensity ultrasound irradiation of commercially available WO₃ nanoparticles (80 nm) in ethanol. The high resolution transmission electron microscopic (HRTEM) and X-ray studies indicated that the 2–5 nm uniform pores have been created in commercially available WO₃ nanoparticles without much changing the initial WO₃ nanoparticles (80 nm) sizes. The nanocomposites of WO₃/SC-15 epoxy were prepared by infusion of 1 wt.%, 2 wt.% and 3 wt.% of porous WO₃ nanoparticles into SC-15 epoxy resin by using a non-contact (Thinky) mixing technique. Finally the neat epoxy and nanocomposites were cured at room temperature for about 24 h in a plastic rectangular mold. The cured epoxy samples were removed and precisely cut into required dimensions and tested for their thermal and mechanical properties. The HRTEM and SEM studies indicated that the sonochemically modified porous WO₃ nanoparticles dispersed more uniformly over the entire volume of the epoxy (without any settlement or agglomeration) as compared to the unmodified WO₃/epoxy nanocomposites.     

Self-Compositing: A Efficient Method of Improving the Electrical Conductivity of Graphene Nanoplatelet/Thermosetting Resin Composites

Conductive composites based on thermosetting resins have broad applications in various fields. In this paper, a new self-compositing strategy is developed for improving the conductivity of graphene nanoplatelet/thermosetting resin composites by optimizing the transport channels. To implement this strategy, conventional graphene nanoplatelet/thermosetting resin is crushed into micron-sized composite powders, which are mixed with graphene nanoplatelets to form novel complex fillers to prepare the self-composited materials with thermosetting resins. A highly conductive compact graphene layer is formed on the surface of the crushed composite powders, while the addition of the micron-sized powder induces the orientation of graphene nanoplatelets in the resin matrix. Therefore, a highly conductive network is constructed inside the self-composited material, significantly enhancing the electrical conductivity. The composite materials based on epoxy resin, cyanate resin, and unsaturated polyester are prepared with this method, reflecting that the method is universal for preparing composites based on thermosetting resins. The highest electrical conductivity of the self-composited material based on unsaturated polyester is as high as 25.9 S m⁻¹. This self-compositing strategy is simple, efficient, and compatible with large-scale industrial production, thus it is a promising and general way to enhance the conductivity of thermosetting resin matrix composites.     

水性环氧耐核辐射涂料的制备

以环氧改性胺乳液为A组分,环氧树脂为B组分,制备了性能优异且环保的水性环氧耐核辐射涂料。研究了环氧改性胺乳液、耐核辐射颜填料及颜料体积浓度(PVC)等因素对涂料性能的影响。结果表明,采用环氧改性芳香胺为固化剂,配合功能性填料钛酸钾晶须制备的水性环氧耐核辐射涂料具有优良耐辐照性能及去污性能,经过8.5×105GY(累积剂量)辐照后漆膜完好,附着力良好。     

Service life assessment and moisture influence on bio-based thermosetting resins

In this study, three different types of bio-based resins are compared to a conventional oil-based epoxy in terms of moisture uptake, long-term properties and its influence of moisture and glass transition temperature, T _g. Moisture uptake is determined by means of gravimetric method, time temperature superposition (TTSP), and T _g data obtained in dynamic mechanical thermal analysis (DMTA). Moisture uptake show Fickian diffuison behavour for all resins, saturation level and diffusion coefficient however differ. The long-term properties is characterised by creep compliance master curves created by means of TTSP. The examined bio-based resins are compatible to the reference epoxy in term of stability up to 3–10 years. Comparison between master curves for virgin, wet, and dried material show that moisture present in the specimen increases creep rate, and that some of this increase remains after drying of samples. T _g measurements show that moisture inside the specimen decreases T _g; this is anticipated because of the plasticizing effect of water. The overall conclusions are that the bio-based resins of polyester, and epoxy type are comparable in performance with oil-based epoxy, LY556 and they can be used to develop high-performance composites.     

Improvements in mechanical and thermo-mechanical properties of e-glass/epoxy composites using amino functionalized MWCNTs

The prime objective of this work is to optimize the mechanical and thermo-mechanical properties of e-glass/epoxy composites by utilizing amino-functionalized multi-walled carbon nanotubes (MWCNTs–NH₂) through a combination of dispersion method. At first, 0.1–0.4 wt.% of MWCNT–NH₂ was integrated into SC-15 epoxy suspension using a combination of ultra-sonication and calendaring techniques. E-glass/epoxy nanocomposites were than fabricated at elevated temperature with the modified resin using hand layup and compression hot press. 3-Point flexural and dynamic mechanical analysis (DMA) results demonstrated a linearly increasing trend in properties from 0 to 0.3 wt.% loading. Micrographs of MWCNTs incorporated epoxy and e-glass/epoxy samples revealed uniform dispersion of MWCNTs in epoxy, good interfacial adhesion between CNTs and polymer, and improved interfacial bonding between fiber/matrix at 0.3 wt.% loading. An improved dispersion and hence an improved crosslink interaction between MWCNT–NH₂ and epoxy lead to the stronger shift of the mechanical and thermo-mechanical properties of the composites.