熔融插层法制备聚乳酸/蒙脱土纳米复合材料的研究进展

综述了使用熔融插层法制备聚乳酸（PLA）/蒙脱土（MMT）纳米复合材料及其表征与性能的研究进展。研究表明,对MMT进行有机改性,可以增大MMT片层间距,使PLA/MMT形成剥离和插层的结构,同时有效地提高PLA/MMT复合材料的性能。随着MMT含量的增加,MMT片层粒子容易形成团簇,不利于结构分散以及性能提高;由于MMT片层粒子在PLA基体中良好分散,形成剥离/插层的结构,有利于抑制PLA分子链运动,从而提高了PLA的韧性、热稳定性、气体阻透性能;MMT片层粒子作为二维异向成核剂,可以提高复合材料的结晶度和结晶速率;分散的MMT片层粒子形成了一种空间连接结构,大大提高了复合材料的熔体强度,有利于拓宽其加工窗口;同时MMT结构中的末端羟基可以增加复合材料的生物降解速率。     

硫化方法对橡胶/黏土纳米复合材料黏土片层分散状态的影响

通过熔体插层法以及常压硫化法制备了橡胶/黏土纳米复合材料,并与模压硫化法制备的复合材料进行了对比,研究了硫化方法对橡胶/黏土纳米复合材料微观分散状态的影响。结果表明:采用熔体插层法制备的橡胶/黏土混合物,其受限状态的橡胶大分子链在高温、高压条件下,在黏土片层之间处于一种热力学不稳定状态;模压处理会对橡胶/黏土混合物的分散状态产生不利影响。透射电子显微镜和X光衍射分析表明,采用模压硫化、常压硫化得到的丁基橡胶或丁苯橡胶/黏土纳米复合材料中黏土片层的微观分散状态不同;排除压力的影响,常压硫化有利于提高橡胶/黏土纳米复合材料中黏土片层的分散程度。     

聚丙烯/黏土纳米复合材料制备的影响因素

综述了原料性能、加工设备和加工工艺对于聚丙烯/黏土纳米复合材料制备过程的重要影响。原料性能方面,当前的研究表明,聚丙烯的分子结构参数、黏土性能、相容剂性能对复合材料的结构与性能具有重要影响。均聚聚丙烯和共聚聚丙烯的相对分子质量越小,越有利于得到"插层结构"的复合材料;而相对分子质量越大,越不利于高分子链进入黏土层间,但一旦进入层间却有利于片层分离,得到"剥离结构"的复合材料。黏土的有机化处理和处理后黏土的阳离子交换能力越大越有利于"插层"和"剥离"的进行。相容剂马来酸酐接枝聚丙烯(PP-g-MAH)的相对分子质量和接枝率对于"插层结构"和"剥离结构"的获得均有影响,低相对分子质量、高接枝率的 PP-g-MAH 有利于"插层结构"的获得,而高相对分子质量、低接枝率的 PP-g-MAH 有利于部分"剥离结构"的获得;加工设备方面,当前的研究表明,双螺杆挤出机依然是制备聚丙烯纳米复合材料的重要选择,而且高剪切速率的螺杆有利于得到"剥离结构"的复合材料,但是过高的剪切速率和物料在螺杆内的较长停留时间却不利于"剥离结构"的稳定。此外,在双螺杆挤出机上增加电熔融管,通过其产生的电场可以得到"剥离结构"的复合材料;加工工艺...     

聚氯乙烯/水滑石纳米复合材料热稳定性和燃烧烟密度的研究

采用十一烯酸根插层水滑石存在下的氯乙烯悬浮聚合聚氯乙烯（PVC）／水滑石纳米复合材料，研究了纳米复合材料的结构及纳米水滑石含量对复合材料热稳定性和燃烧烟密度的影响。发现原位聚合中部分氯乙烯与插层十一烯酸共聚，可实现聚合物插层；复合材料中水滑石部分剥离，分散尺寸小；随着纳米水滑石含量增加，复合材料的热失重温度和热变色时间增加，热稳定性提高；纳米水滑石对PVC具有显著的抑烟作用，当纳米水滑石含量为1．25％（质量分数）时，最大燃烧烟密度减小40％。     

PP/黏土纳米复合材料的结构与性能

采用熔体插层法制备聚丙烯（PP）/有机黏土（OMMT）纳米复合材料。XRD和TEM的测试结果表明,采用熔体插层法制备的PP/OMMT复合材料是剥离型纳米复合材料。力学性能实验结果表明,相容剂的加入提高了PP与OMMT之间的相互作用,使其各项力学性能都得到了提高;PP/OMMT纳米复合材料的各项力学性能在有机黏土含量较小的情况下,就可以有较大幅度的提高;与纯PP相比,相容剂含量为10 phr、有机黏土用量为1 phr的聚丙烯基纳米复合材料具有最好的各项力学性能。     

聚合物/粘土纳米复合材料的研究进展

综述了聚合物/粘土纳米复合材料的制备、表征和性能。粘土经相容剂修饰成为有机土,层间距增大,层间微环境由亲水变为亲油,从而利于聚合物的插层。聚合物插层导致粘土片层剥离并分散于聚合物基体中,得到的聚合物/粘土纳米复合材料的机械和物理性能比原来的聚合物材料有了显著的提高。     

天然橡胶／有机粘土纳米复合材料的制备与表征

自从丰田中心率先研究出了尼龙6／有机粘土纳米复合材料之后，聚合物／层状硅酸盐纳米复合材料引起了很多高分子科学家的关注。纳米复合材料就是一些无机填料以纳米级均匀分散在高聚物基体中形成的复合材料。粘土片层被聚合物插层或剥离可形成聚合物／粘土纳米复合材料。     

宽峰聚乙烯／蒙脱土纳米复合材料的制备与性能研究

制备出两种氢调敏感性的不同的催化剂，然后按照不同的比例混合，通过原位聚合法制备了宽峰聚乙烯纳米复合材料，分别表征和测定了其微观结构、分子结构参数和力学性能。结果表明：蒙脱土片层在乙烯聚合过程中发生了插层及剥离，以单片层或几层共存的形式纳米级分散于聚乙烯基体中；聚合物相对分子质量呈宽峰分布（Mw／Mn=7．23）；在熔体流动速率相近的情况下，复合材料的断裂伸长率提高到900％以上，拉伸强度达到40MPa。     

不同亚微观形态的聚丙烯/蒙脱土纳米复合材料的研究

通过控制不同的工艺条件，利用双螺杆挤出插层法制备出两种不同微观结构的聚丙烯／蒙脱土纳米复合材料。利用透射电子显做镜观察发现．分别制备出了插层型和半插层型聚丙烯／蒙脱土纳米复合材料，半插层型结构的材料中有机土分散更均匀，尺度更小。对两种纳米复合材料的物理性能测试表明，插层型纳米复合材料的缺口冲击强度提高幅度最大，同时耐热性并没有降低；半剥离型纳米复合材料的熔体质量流动速率降低幅度最大，屈服强度、弹性模量、耐热性提高幅度最大，缺口冲击强度略小于插层型。     

相容剂对聚丙烯/纳米黏土复合材料抗熔垂性能影响的研究

在双螺杆挤出机上制备了相容剂马来酸酐接枝聚丙烯(PP-g-MAH)改性的聚丙烯(PP)纳米黏土复合材料。通过XRD测试和杭熔垂性能测试研究了PP-g-MAH对复合材料杭熔垂性能的影响。研究表明:PP-g-MAH的性能和用量对复合材料的插层结构有一定影响,进而影响到复合材料的杭熔垂性能.其中,采用熔体流动辣率小、接枝率低的PP-g-MAH所得到的纳米黏土复合材料的杭熔垂性能相对较奸,但PP-g-MAH的含量不宜过高。插层结构的黏土片层的层间距与复合材料杭熔垂性能存在一定关联,PP纳米黏土复合材料中存在最利于材料杭熔垂性能捍高的插层结构,层间距为2. 90-3. 10 nm的插层结构对应的复合材料的杭熔垂能力较好     

A novel strategy for nanoclay exfoliation in thermoset polyimide nanocomposite systems

A novel method of nanoclay exfoliation in the synthesis of nanocomposites of PMR type thermoset resins was investigated. The method involves nanoclay intercalation by lower molecular weight PMR monomer prior to dispersion in primary, higher molecular weight PMR resin and resin curing to obtain the final composites. The resultant mechanical and thermal properties were evaluated as functions of clay type, degree of clay exfoliation, and clay intercalation strategies. It was found that sonication of clay at the time of intercalation by lower molecular weight PMR resin helps to achieve higher degree of exfoliation. In addition, clays obtained from ion exchange with a 50:50 mixture of N-[4(4-aminobenzyl)phenyl]-5-norborene-2,3-dicarboximide (APND), and dodecylamine (C12) showed better exfoliation than Cloisite^® 30B clay. The resultant nanocomposites show higher thermal stability and higher tensile modulus.     

Processing–structure–properties relationships of mechanically and thermally enhanced smectite/epoxy nanocomposites

Mechanically reinforced and thermally enhanced smectite/epoxy nanocomposites were synthesized using “direct” (without solvent) and “solvent” processing techniques. The molecular dispersion of smectite clay in the epoxy resin was investigated for its role in the rheology, structure formation, and properties of nanocomposites. The effects of three types of organic modifiers on the dispersion structure were compared. The use of solvent during processing assists in the enhancement of clay exfoliation. Rheology was used as a method to compare the degree of clay delamination in the resin matrix, as well as to estimate the suspension structure. The critical volume fraction (Φ*) and maximal packaging of smectites were determined and used for prediction of the viscosity. The qualitative changes in the nanostructure of suspensions above Φ*, due to flocculation of exfoliated clay layers, were compared with the alteration of the properties of nanocomposites, related to the structure formation and morphology. The curing kinetics were found to depend on both the organic modifier and solvent, but the extent of curing was roughly equivalent for the pure epoxy resin and the nanocomposites. The structure of the nanocomposites, either intercalated or exfoliated, produced by the direct processing technique was controlled by the organic modifier. By using solvent processing, the effect of the solvent dominates that of the organic modifier, presumably leading to exfoliated nanocomposites. The mechanical and thermal properties are strongly enhanced above the Φ* of smectites, and they are significantly dependent on the type of nanocomposite structure and the use of solvent. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2499–2510, 2005     

Quantification of clay dispersion in nanocomposites of styrenic polymers

Polymer‐clay nanocomposites are materials with many interesting structures, properties, and potential applications. Microstructural evaluation of a nanocomposite is not an easy task, as clay may form hierarchical structures which may look different when observed at various magnifications under a microscope, and also as the concepts of “intercalation” and “exfoliation” are not self‐sufficient to describe its morphology. In this work polymer‐clay nanocomposites of polystyrene and two styrene‐containing block copolymers (styrene‐butadiene‐styrene and styrene‐ethylene/butylene‐styrene) were prepared using three different techniques. Clay dispersion was evaluated by a recently developed microscopy image analysis procedure, combining the analysis of optical and transmission electron micrographs, and the characterization was complemented by X‐ray diffraction and rheological measurements. The results showed better clay dispersion for both block copolymers nanocomposites, mainly due to their molecular architectures. Moreover, the techniques which showed the best results involved mixing the materials in a solvent medium. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Morphological influence on mechanical characterization of ethylene‐vinyl acetate copolymer–clay nanocomposites

Ethylene‐vinyl acetate copolymer (EVA)/montmorillonite (MMT) clay nanocomposites with varying degree of intercalation and exfoliation have been prepared using direct melt blending techniques with various degrees of polarity (9, 18, and 28 wt% vinyl acetate [VA]) and two different types of clay modification. Morphological characterization using wide‐angle X‐ray scattering (WAXS) and transmission electron microscopy (TEM) have indicated/confirmed the presence of intercalation and/or a combination of intercalation and exfoliation existing in the nanocomposites. The effects of these (simple intercalation or mixed intercalation/exfoliation) states and the effect of changing matrix polarity (by changing VA wt% content) on the nanocomposite mechanical behavior were studied. There is sufficient evidence from the mechanical studies that 1) the presence of nanoclay can simultaneously improve modulus and strength of the nanocomposites, and 2) the mechanical properties are a combined function of the clay concentration and the nanocomposite morphology (due to the VA wt% and presence of clay). It is shown here that interrelation between the VA wt% content and the clay exfoliation affects the mechanical properties in a way that has a positive and increasing slope with increasing loading of clay. It is shown that a clear understanding of the nanocomposite mechanical properties can be obtained from its morphological analysis. POLYM. ENG. SCI., 45:889–897, 2005. © 2005 Society of Plastics Engineers     

Morphology and rheological behavior of polylactic acid/clay nanocomposites

The investigated rheological properties of polylactic acid (PLA)/clay nanocomposite are important to understand the effect of organically modified layered silicates (OMLS) (clay) on processing as well as the change in viscoelastic properties due to polymer filler interaction. The time sweep result revealed that the thermal stability improved with addition of nanoclay due to the formation of percolating network structure. It was also supported by multi wave ramp test. The frequency sweep analysis showed that the dynamic moduli increased with addition of nanoclay. Viscoelastic spectra (DMTA) showed an increase of the storage and loss moduli with the increase in the clay content. Wide angle X‐ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to determine the degree of intercalation, or exfoliation and nanostructure level of clay dispersion on PLA nanocomposites. XRD data demonstrated complete exfoliation at lower nanoclay content. On increasing the nanoclay content, exfoliated and partially intercalated structures were obtained. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Thermomechanical and electrical characterization of epoxy‐organoclay nanocomposites

The effect of amount of clay content on the thermomechanical and electrical properties of epoxy/organoclay nanocomposites is investigated in the present research. An organoclay, cloisite 30B (C30B), was dispersed in the epoxy resin and was cured with an amine curing agent. The morphology of the nanocomposite examined by X‐ray diffraction shows exfoliation for nanocomposites with lesser clay content and intercalation for nanocomposites with higher clay content. The storage modulus (E′) of the nanocomposites increases monotonously with the increase in the amount of clay. The short time alternating current breakdown strength of the nanocomposites increases by the addition of C30B up to a certain clay content and then show a decrease. The space charge measured by pulsed electroacoustic method shows that the nanocomposite accumulate a very less amount of space charge and the charge decay in the nanocomposites are quicker than in the pure polymer. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Comparative effect of metallocene and Ziegler‐Natta polypropylene on the exfoliation of montmorillonite and hectorite clays to obtain nanocomposites

The present study was carried out on the effect of molecular weight and polydispersity of polypropylene (PP) obtained via Ziegler‐Natta or metallocene catalysis on the formation of nanocomposites with montmorillonite and mineral and synthetic hectorite. The formation of the nanocomposites was achieved by the melt‐mix method. X‐ray diffraction, transmission electron microscopy, and analysis of mechanical properties showed that, using PP obtained via metallocene catalysis (polydispersity ～ 2), it is possible to achieve improved formation of nanocomposites compared with PP obtained via Ziegler‐Natta catalysis (polydispersity ～ 4). It was also found that the molecular weight of the PP affects the tendency toward clay exfoliation and consequently the properties of the nanocomposites. Montmorillonite type clay was evaluated at 1%, 3%, and 5% by weight in the nanocomposite. The nanocomposite with 1 wt % clay was found to have better mechanical properties compared with the nanocomposite containing 3 wt % and 5 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 698–706, 2007     

Diffusion behavior of water and sulfuric acid in epoxy/organoclay nanocomposites

The research on polymer‐layered silicate nanocomposites is currently an expanding field of study because they often exhibit a wide range of improved properties over their unmodified starting polymers. Epoxy/organoclay nanocomposites have been prepared by intercalating epoxy into the organoclay montmorillonite. The intercalation and/or exfoliation of the clay within the nanocomposite were monitored using X‐ray diffraction and transmission electron microscopy. Diffusion was studied through epoxy samples containing up to 10 phr of organically treated montmorillonite following the gravity method. The water and sulfuric acid diffusion within the epoxy‐based nanocomposites were evaluated in terms of diffusivity, weight change and penetration depth of the sulfuric acid element S as function of immersion time and immersion temperature. An investigation of the resistance of epoxy nanocomposite to a corrosive environment by immersion into sulfuric acid at elevated temperature was performed. The effect of the degree of exfoliation of the clay on moisture barrier effect and corrosion resistance is specifically studied. The data has been compared to those obtained from the neat epoxy resin to evaluate the diffusion properties of the nanocomposites. It was found that the diffusion of water and that of acid do not obey Fick's law, and that the higher the organoclay content the higher weight change was obtained. The presence of the organoclay enhanced the diffusivity and delayed the penetration of the sulfuric acid. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

PE/Clay Nanocomposite with Bimodal Molecular Weight Distribution Produced Via In-Situ Polymerization

A Ti-based Ziegler–Natta catalyst supported on the clay was used for producing the polyethylene/clay nanocomposites through in situ polymerization. This catalyst showed high activity in the ethylene polymerization. The two-step polymerization approach, i.e. in the presence and absence of hydrogen, was laid out to broaden the molecular weight distribution of the polyethylene/clay nanocomposite. The molecular weights and molecular weight distribution of the nanocomposites were characterized by the gel permeation chromatography. It was found that the molecular weight distribution was remarkably widened towards bimodal distribution by using the above mentioned approach. The thermal properties of the produced nanocomposites were studied by differential scanning calorimetry and thermal gravimetric analysis. The microstructure of the resulting bimodal polyethylene/clay nanocomposite was investigated by X-ray diffraction and transmission electron microscopy. The thermal gravimetric analysis indicated an improved thermal stability of the produced nanocomposites. In addition, the studies proved the nanocomposite formation with the exfoliated structure of the clay in the polyethylene matrix.     

Characterization of nanoclay orientation in polymer nanocomposite film by small-angle X-ray scattering

The orientation distribution of layer-shaped nanoclays (e.g. organoclays and pristine clays) dispersed in a polymer matrix is an important parameter to control the properties of polymer nanocomposites. In this study, we demonstrate that the use of multi-directional 2-D small-angle X-ray scattering (SAXS) can quantitatively describe the orientation distribution of organoclays (e.g. Cloisite C20A) in melt-pressed nanocomposite films, containing ethylene-vinyl acetate (EVA) copolymers as polymer matrices. Different weight fractions of organoclays were used to alter the orientation profile of nanocomposite films, in which the dispersion and morphology of organoclays were also characterized by complementary 2-D and 3-D transmission electron microscopy (TEM). All nanocomposites exhibited mixed intercalation/exfoliation clay morphology, where the intercalated structure possessed partial orientation parallel to the in-plane direction of the film. The higher content of the clay loading showed a higher clay orientation. A simple analytical scheme for SAXS data analysis to determine the orientation parameter (P₂) was demonstrated, the results of which are in agreement with the gas permeation properties of the nanocomposite films.