Mechanical and barrier properties of epoxy polymer filled with nanolayered silicate clay particles

The diglycidyl ether of bisphenol A (DGEBA) epoxy resin system filled with organo clay (OC) and unmodified clay (UC) were processed separately by two different curing agents. Triethylene tetramine (TETA) and Diaminodiphenyl methane (DDM) hardeners were used as curing agents. The nanocomposites were processed by shear mixing at different clay concentrations (1, 2, 3,5 and 10 wt%). The OC and UC were characterized by x-ray diffraction (XRD) technique. The morphology of the nanocomposites was obtained by XRD and Transmission Electron Microscopy (TEM). Bending and Impact tests conducted on these materials revealed that the organo clay filled epoxy resin showed good improvement in property over unmodified clay filled epoxy composites. The mass uptake of the nanocomposites was studied in the acid, base and water mediums. It is observed that the mass uptake in the acid medium is higher than in other mediums. The equilibrium mass uptake in all the mediums for nanocomposites was found to be lower compared to neat epoxy polymer system.     

Elastomeric epoxy nanocomposites: Nanostructure and properties

In polymer layered silicate nanocomposites, significant differences have been reported between the effects of the nano-reinforcement on rigid and elastomeric nanocomposites. In this paper, we have studied elastomeric nanocomposites based upon DGEBA epoxy resin filled with montmorillonite (MMT) and cured with a long-chain polyoxypropylene diamine, for comparison with analogous rigid nanocomposites. Ultrasonic mixing was used to disperse the MMT in the matrix to improve homogeneity and decrease the agglomerate size. Two different methods of nanocomposite preparation were used in which the MMT was first swollen with either the curing agent or the epoxy before the addition of, respectively, DGEBA or diamine. A better dispersion of the nanoclay in the matrix and a greater amount of intercalation occurred when the MMT was first swollen with the diamine. The effect of MMT concentrations up to 8 wt.% on the mechanical behaviour of the epoxy/MMT nanocomposites was investigated. It was found that the addition of MMT increased the tensile strength and modulus, although SAXS and TEM indicated that a significant fraction of the clay layers were not exfoliated. Nevertheless, the addition of the clay resulted in changes in the fracture surfaces, as indicated by SEM, consistent with the tensile results and indicative of toughening.     

二维和零维纳米材料协同增强的高性能纳米复合材料

将二维蒙脱土和零维纳米TiO_2共同复合到环氧树脂中,成功地制备出一种高性能有机蒙脱土/纳米TiO_2/环氧树脂复合材料。力学性能测试和热分析显示,该复合材料在拉伸模量、拉伸强度、弯曲模量、弯曲强度、缺口冲击强度、玻璃化转变温度、热分解温度上都明显优于纯环氧树脂,也优于有机蒙脱土/环氧树脂复合材料和纳米TiO_2/环氧树脂复合材料。XRD检测和透射电子显微镜观察显示,在有机蒙脱土/纳米TiO_2/环氧树脂复合材料中,蒙脱土被完全剥离为纳米单片,和纳米TiO_2交错分布于环氧树脂中。选择适宜的两种维度的纳米材料复合于聚合物中,是制备新型高性能复合材料的成功思路。     

Room temperature processing of epoxy-clay nanocomposites

Polymer/Clay nanocomposites consisting of an epoxy matrix filled with nanolayered silicate clay particles have been investigated. Recent and ongoing research has shown that dramatic enhancements can be achieved in mechanical and thermal properties by adding a small volume percent of clays. In the present work nanocomposites are processed by mechanical mixing of epoxy with organoclays and unmodified clays using a high speed electric shear mixer at room temperature. The addition of different organoclay wt% [1–3, 5 and 10] indicates good enhancement in hardness, dynamic mechanical properties, and also the molecular mobility of the polymer is reduced by the presence of the silicate layers, which in turn causes large stiffness improvements. X-ray diffraction (XRD) results show the intercalation/exfoliation of clays in the epoxy matrix. The influence of organoclay restricts the weight loss at varying temperatures. Experiments show improved elastic modulus for both modified and unmodified clays.     

反应型有机修饰剂对环氧树脂/粘土纳米复合材料热/机械性能的影响

使带有环氧基团的三缩水甘油基对氨基苯酚(TGPAP)分别与溴代正丁烷(BB)、2-溴乙醇(BE)反应,合成了反应型粘土有机修饰剂溴化(正定烷基)双环氧基(4-环氧醚基)铵(TGPAPB)和溴化(2-羟乙基)双环氧基(4-环氧醚基)铵(TGPAPE)。用这两种修饰剂改性粘土,分别制备出具有相同反应官能团但与环氧树脂的相容性略有不同的两种有机化粘土(B-Clay和E-Clay)。再用“粘土淤浆复合法”制备出两种环氧树脂/粘土纳米复合材料,研究了两种反应型有机修饰剂对纳米复合材料的结构和性能的影响。结果表明：带有羟基的E-Clay以高度无规剥离形式均匀分布在环氧树脂基体中;而B-Clay则形成了无规剥离/插层混合结构。两种粘土均参与固化反应在环氧树脂基体和粘土片层间产生了较强的界面作用力,从而显著提高了纳米复合材料的拉伸强度。粘土质量分数为3%的两种纳米复合材料,其拉伸强度分别达到32.4 MPa(E-Clay)和28.0 MPa(B-Clay),比对应的纯环氧树脂聚合物分别提高了76.47%和52.51%。同时,这两种纳米复合材料的玻璃化转变温度(T_g)也略有提高。     

Studies on the oxygen barrier and mechanical properties of low density polyethylene/organoclay nanocomposite films in the presence of ethylene vinyl acetate copolymer as a new type of compatibilizer

Nanocomposite films based on low density polyethylene (LDPE), containing of 2, 3, and 4 wt.% organoclay (OC) and ethylene vinyl acetate (EVA) copolymer as a new compatibilizer were prepared and characterized using rheological tests, X-ray diffraction, differential scanning calorimetry, oxygen permeation measurements, and tensile tests. There was no exfoliation or intercalation of the clay layers in the absence of EVA, while an obvious increase in d-spacing was observed when the samples were prepared with EVA present. This issue was reflected in the properties of nanocomposites. The oxygen barrier properties of the LDPE/EVA/OC film were significantly better than those of the LDPE/OC film. The average aspect ratio of clay platelets in nanocomposites was determined from permeability measurements and using Lape–Cussler model. In addition to barrier properties, the LDPE/EVA/OC film also had better elastic modulus than their counterparts without EVA. The modulus reinforcement of nanocomposites was studied using Halpin–Tsai equations, which are universally used for composites reinforced by flake-like or rod-like fillers.     

Effect of montmorillonite modification on mechanical properties of vulcanized natural rubber composites

Natural rubber-clay composites were prepared by direct polymer melt intercalation. Ca-montmorillonite Jelšovy Potok (JP; Slovakia) and Na-montmorillonite Kunipia-F (KU; Japan) were ion exchanged with octadecyltrimethylammonium (ODTMA) bromide and were used as aluminosilicate fillers. Silica Ultrasil VN3 was used in amount of 15 phr as conventional filler. The effect of clay or organoclay loading from 1 up to 10 phr on the mechanical properties was evaluated from the tensile tests (stress at break, strain at break and modulus M100). Organic modification resulted in an increase of toluene uptake degree for both fillers. While an addition of unmodified KU had no effect on tensile strength and deformation at break, a reinforcing effect was observed for the mixture containing 10 phr of unmodified JP. Both ODTMA modified fillers (KU and JP) exhibited substantial increase in tensile strength and deformation at break; JP proved to be more effective compared to KU also if modified with ODTMA. The highest stress at break and strain at break values for natural rubber composites were obtained with 15 phr of SiO₂ and 10 phr of montmorillonite; however, the effect of exchangeable cation was minor.     

环氧树脂/粘土纳米复合材料的制备与性能研究

研究了有机蒙脱土在环氧树脂中的插层和剥离行为,制备了两种环氧树脂/蒙脱土纳米复合材料并测试了其力学性能。实验结果表明,环氧树脂与有机土的相容性好,二者混合时环氧树脂很容易插入到粘土层间。使用经不同有机阳离子处理的两种有机蒙脱土,分别制得插层型和剥离型环氧/粘土纳米复合材料,力学性能结果表明,剥离型纳米复合材料的性能优于同组成的插层型纳米复合材料。     

Investigation of the mechanical properties of DGEBA-based epoxy resin with nanoclay additives

The present study investigated the effect of nanoclay additives on the mechanical properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The resin was cured with diethyltoluene diamine (DETDA) hardener and four material variations produced through the addition of four types of nanoclays, respectively. The nanocomposites were prepared by the in situ polymerisation method with the aid of mechanical shearing. The properties of the nanocomposites investigated included tensile modulus, tensile strength, tensile strain and fracture toughness (K_IC). It was observed that while the addition of nanoclay significantly increased the elastic modulus and fracture toughness of DGEBA epoxy resin, it also significantly reduced the failure strength and failure strain with increasing nanoclay level. Possible mechanisms for the improvement and degradation of these properties of the epoxy–clay nanocomposite materials are discussed.     

聚氨酯和蒙脱土协同增韧增强环氧树脂

采用聚合物互穿技术与原位插层聚合相结合的方法制备了有机蒙脱土修饰的环氧树脂/聚氨酯互穿网络纳米复合材料.傅立叶红外光谱,X射线衍射及透射电镜分析表明剥离或插层的蒙脱土片层表面羟基能与环氧树脂/聚氨酯基体发生交联反应,并且均匀分散在环氧树脂/聚氨酯基体中.力学性能测试结果表明聚氨酯,蒙脱土的加入同时增加了环氧树脂的拉伸强度和断裂韧性.扫描电镜分析表明聚氨酯和蒙脱土协同增韧增强环氧树脂的主要原因为剪切屈服和微裂纹增韧.     

Epoxy based nanocomposites with fully exfoliated unmodified clay: mechanical and thermal properties

The unmodified clay has been fully exfoliated in epoxy resin with the aid of a novel ultrafine full-vulcanized powdered rubber. Epoxy/rubber/clay nanocomposites with exfoliated morphology have been successfully prepared. The microstructures of the nanocomposites were characterized by means of X-ray diffraction and transmission electron microscopy. It was found that the unmodified clay was fully exfoliated and uniformly dispersed in the resulting nanocomposite. Characterizations of mechanical properties revealed that the impact strength of this special epoxy/rubber/clay nanocomposite increased up 107% over the neat epoxy resin. Thermal analyses showed that thermal stability of the nanocomposite was much better than that of epoxy nanocomposite based on organically modified clay.     

Modeling and mechanical performance of carbon nanotube/epoxy resin composites

The effect of multi-walled carbon nanotube (MWCNT) addition on mechanical properties of epoxy resin was investigated to obtain the tensile strength, compressive strength and Young’s modulus from load versus displacement graphs. The result shows that the tensile strength, compressive strength and Young’s modulus of epoxy resin were increased with the addition of MWCNT fillers. The significant improvements in tensile strength, compressive strength and Young’s modulus were obtained due to the excellent dispersion of MWCNT fillers in the epoxy resin. The dispersion of MWCNT fillers in epoxy resin was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis.Also, Halpin–Tsai model was modified by considering the average diameter of internal/external of multi-walled nanotube and orientation factor (α) to calculate the Young’s modulus of multi-walled carbon nanotubes (MWCNTs)/epoxy resin composite. There was a good correlation between the experimentally obtained Young’s modulus and modified Halpin–Tsai model.     

一种促进粘土在环氧树脂中剥离的方法研究

使用对环氧树脂的固化反应有促进作用的有机阳离子对粘土进行有机化处理，得到的有机土与环氧树脂混合后，尽管其层间距较小，层间容纳的环氧树脂较少，但由于催化作用使层间环氧树脂固化较快，结果在环氧的固化过程中粘土更易剥离，从而得到粘土剥离程度较高的环氧树脂／粘土纳米复合材料。这一研究为制备粘土剥离程度更高、性能更好的环氧／粘土纳米复合材料提供了有效的方法。     

Effect of processing parameters and clay volume fraction on the mechanical properties of epoxy-clay nanocomposites

The influence of processing parameters and particle volume fraction was experimentally studied for epoxy clay nanocomposites. Nanocomposites were prepared using onium ion surface modified montmorillonite (MMT) layered clay and epoxy resin (DEGBF). Two different techniques were used for dispersing the clay particles in the epoxy matrix, viz. high-speed shear dispersion and ultrasonic disruption. The volume fraction of clay particles was systematically varied from 0.5 to 6%, and mechanical properties, viz. flexural modulus and fracture toughness, were studied as a function of clay volume fraction and the processing technique. The flexural modulus was observed to increase monotonously with increase in volume fraction of clay particles, while, the fracture toughness showed an initial increase on addition of clay particles, but a subsequent decrease at higher clay volume fractions. In general, nanocomposites processed by shear mixing exhibited better mechanical properties as compared to those processed by ultrasonication. Investigation by X-ray diffraction (XRD) revealed exfoliated clay structure in most of the nanocomposites that were fabricated. Morphologies of the fracture surfaces of nanocomposites were studied using a scanning electron microscopy (SEM). Presence of river markings at low clay volume fractions provided evidence of extrinsic toughening taking place in an otherwise brittle epoxy.     

聚氨酯/蒙脱土纳米复合弹性体材料--(Ⅱ)结构及性能的表征

借助锥体磨的研磨剪切外力，将聚醚多元醇插层进入蒙脱土片层中，使其片层间距扩大并发生部分剥离，从而利用本体插层聚合法制备了综合性能优异的聚氨酯／蒙脱土纳米复合弹性体材料。当有机蒙脱土添加量仅为1％时，其拉伸强度比纯聚氨酯弹性体高30％．达到30．2MPa，断裂伸长率也略有增加。TGA及吸水实验分析表明聚氨酯／蒙脱土纳米复合材料有更高的热失重温度和更低的吸水率．研究了蒙脱土含量对聚氨酯／蒙脱土纳米复合材料各项性能的影响。     

Mode I interlaminar fracture behavior and mechanical properties of CFRPs with nanoclay-filled epoxy matrix

The mechanical properties and fracture behavior of nanocomposites and carbon fiber composites (CFRPs) containing organoclay in the epoxy matrix have been investigated. Morphological studies using TEM and XRD revealed that the clay particles within the epoxy resin were intercalated or orderly exfoliated. The organoclay brought about a significant improvement in flexural modulus, especially in the first few wt% of loading, and the improvement of flexural modulus was at the expense of a reduction in flexural strength. The quasi-static fracture toughness increased, whereas the impact fracture toughness dropped sharply with increasing the clay content.Flexural properties of CFRPs containing organoclay modified epoxy matrix generally followed the trend similar to the epoxy nanocomposite although the variation was much smaller for the CFRPs. Both the initiation and propagation values of mode I interlaminar fracture toughness of CFRP composites increased with increasing clay concentration. In particular, the propagation fracture toughness almost doubled with 7 wt% clay loading. A strong correlation was established between the fracture toughness of organoclay-modified epoxy matrix and the CFRP composite interlaminar fracture toughness.     

界面强度对柔性环氧树脂/粘土纳米复合材料热/力学性能的影响

先合成反应型BBDMP30-clay有机化粘土和非反应型CPDMP30-clay有机化粘土,然后以其为纳米增强体分别制备了两种界面强度不同的环氧树脂/粘土纳米复合材料。用透射电子显微镜(TEM)、拉伸实验表征这两种环氧树脂/粘土纳米复合材料并进行动态力学分析(DMA),研究了界面强度对其力学性能的影响。结果表明：这两种纳米复合材料具有几乎相同的无规剥离结构,反应型BBDMP30-clay比非反应型CPDMP30-clay能更有效地提高材料的热/机械性能。粘土质量分数为3.5%时BBDMP30-clay可使纳米复合材料的拉伸强度提高250%,而CPDMP30-clay只能使材料的拉伸强度提高190%。BBDMP30-clay使纳米复合材料的玻璃化转变温度(Tg)提高了6.5℃,而CPDMP30-clay只能使材料的Tg提高2.5℃。这些不同都可归因于这两种纳米复合材料界面强度的差异。     

Preparation and properties of nitrile rubber/montmorillonite nanocomposites via latex blending

The nitrile rubber (NBR)/unmodified montmorillonite (Na-MMT) clay nanocomposites were prepared by latex blending method followed by melt mixing of compounding ingredients by using two-roll mill. The X-ray diffraction (XRD) studies showed an increase in the basal spacing and broadening of peak corresponding to crystal structure of Na-MMT indicating the formation of intercalated/exfoliated clay layers in the NBR matrix. Increase in clay content of nanocomposite increased the XRD peak height due to the formation of many of clay tactoids at higher loading. The transmission electron microscopy (TEM) strengthened the XRD finding by showing the presence of intercalated/exfoliated morphology of clay platelets having good dispersion. The modulus and tensile properties of the nanocomposites were improved with addition of Na-MMT which is proportional to clay concentration. The retention of tensile properties of aged nanocomposites, with all clay concentration, was superior to either pure NBR and carbon black filled NBR composite. The dynamic mechanical analysis showed proportional increase in storage modulus analogous to Na-MMT loading at all the temperature ranges due to the confinement of polymer chains between the clay layers. Nanocomposites with different proportions of clay showed a decrease in tan δ_max peak height with a shift towards higher temperature indicating the reduction in the segmental mobility of polymer chain. A linear model was proposed to correlate the influence of Na-MMT content on storage modulus of nanocomposites. Differential scanning calorimetry indicated a linear increase in glass transition of nanocomposites which is proportional to clay loading. Thermogravimetric analysis revealed a small improvement in the thermal stability of nitrile rubber/clay nanocomposites.     

Environmental degradation of epoxy–organoclay nanocomposites due to UV exposure. Part I: Photo-degradation

The environmental degradation mechanisms of epoxy–organoclay nanocomposites due to accelerated UV and moisture exposure are studied. Various characterisation tools, including FTIR, SEM, XRD and XRF analyses, were used to evaluate the effects of clay content on the progressive changes in chemical element, topography and colour of the nanocomposite. It is found that microcracks started to appear on both the neat epoxy and nanocomposite surface after about 300 h of UV exposure. The nanocomposite exhibited thicker and shallower cracks with a less degree of discoloration than the neat epoxy due to the diffusion barrier characteristics of organoclay with high aspect ratio. The presence of transition metal ions along with low-molecular-weight organic modifiers in organoclay, however, accelerated the degradation of polymer, counterbalancing the above ameliorating barrier properties of clay. FTIR analysis indicated that photo-degradation generated carbonyl groups by chain scission and the rate was slightly higher for the nanocomposites than for the neat epoxy. While moisture further accelerated the photo-degradation process through the enhanced mobility of free radicals and ions, the organoclay could limit the deteriorating effect of moisture, resulting in much better overall resistance to photo-degradation in the presence of moisture for the nanocomposite than the neat epoxy.     

Mechanical,thermal and microstructural characteristics of cellulose fibre reinforced epoxy/organoclay nanocomposites

Epoxy nanocomposites reinforced with recycled cellulose fibres (RCFs) and organoclay platelets (30B) have been fabricated and investigated in terms of WAXS, TEM, mechanical properties and TGA. Results indicated that mechanical properties generally increased as a result of the addition of nanoclay into the epoxy matrix. The presence of RCF significantly enhanced flexural strength, fracture toughness, impact strength and impact toughness of the composites. However, the inclusion of 1 wt.% clay into RCF/epoxy composites considerably increased the impact strength and toughness. The presence of either nanoclay or RCF accelerated the thermal degradation of neat epoxy, but at high temperature, thermal stability was enhanced with increased char residue over neat resin. The failure micromechanisms and energy dissipative processes in these nanocomposites were discussed in terms of microstructural observations.