A study of global vs. local properties for maleic anhydride modified polypropylene nanocomposites

Nanoindentation of organomodified clay filled maleated polypropylene (MAPP) was investigated. The study aims to identify the relative increase in local stiffness in comparison to the increase in mechanical properties of the bulk in polypropylene-based nanocomposites. Such a study allows one to assess confined material property in addition to increased filler volume at the local scale. A mixture of highly intercalated and well exfoliated clay structures, when dispersed in MAPP matrix, was observed under transmission electron microscopy. The degree of exfoliation was found to increase with clay loading, which was attributed to the higher viscosity and mechanical shear forces during melt compounding. Instrumented indentation was performed on (1) clay aggregate supported by MAPP matrix, (2) clay-matrix boundary, and (3) the MAPP matrix. The clay aggregated region generally showed higher stiffness as compared to the matrix. And, the relative increase in indentation stiffness is substantially higher than the relative increase in tensile and compressive stiffnesses for clay reinforced systems. Polymer chain confinement and topological constraint appeared to be operative to enhance local stiffness in the clay aggregated region. Good correlation was, however, obtained between the change in macroscopic stiffness and the change in highly local indentation stiffness as a result of clay reinforcement.     

Metallocene‐based functionalized polyolefins as compatibilizers in polyolefin nanocomposites

This article reports a study of some functionalized polyolefins evaluated as compatibilizers in polyethylene nanocomposites. The functionalized polymers were prepared by direct metallocene‐mediated copolymerizations of ethylene and a functional comonomer. The prepared nanocomposites were evaluated for mechanical and barrier property enhancement. A good combination of mechanical and barrier properties was obtained with the metallocene‐based functionalized polyethylene. The toughness–stiffness balance was better than or comparable to that achieved with conventional functionalized polymers such as maleic anhydride grafted polyethylene. The results also indicated that these metallocene‐based functionalized polyolefins, when used as compatibilizers, could have relatively higher molar masses and lower functionality than those of conventional post‐reactor‐modified compatibilizers, and so the drawbacks associated with the latter could be avoided. Their inherent properties could also further improve the final nanocomposite properties. This was attributed to the more homogeneous nature of metallocene‐catalyzed polymers in comparison with post‐reactor‐modified products. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1094–1100, 2004     

Structure and properties of nanocomposites based on poly(butylene succinate) and organically modified montmorillonite

Poly(butylene succinate) and organically modified montmorillonite nanocomposites with there different compositions were prepared via melt blending in a twin‐screw extruder. The structure of the nanocomposites was studied with X‐ray diffraction and transmission electron microscopy, which revealed the formation of intercalated nanocomposites, regardless of the silicate loading. Dynamic mechanical analysis revealed a substantial increase in the storage modulus of the nanocomposites over the entire temperature range investigated. The tensile property measurements showed a relative increase in the stiffness with a simultaneous decrease in the yield strength in comparison with that of neat poly(butylene succinate). The oxygen gas barrier property of neat poly(butylene succinate) improved after nanocomposite preparation with organically modified montmorillonite. The effect of the layered‐silicate loading on the melt‐state linear viscoelastic behavior of the intercalated nanocomposites was also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 777–785, 2006     

"纳米内交联"耐高速聚氨酯新胶轮的研发

针对分散相尺寸和两相界面粘结这两个影响纳米复合材料性能的关键因素,运用“纳米内交联”技术,合成了聚氨酯纳米复合材料,生产出耐高速聚氨酯胶轮,与普通有机蒙脱土填充聚氨酯材料性能和其胶轮内生热的对比测试表明:“纳米内交联”耐高速聚氨酯纳米复合材料综合性能优异,阻尼性大幅度降低,从而大幅度降低了聚氨酯胶轮高速转动时的内生热,为解决长期困扰聚氨酯界的“聚氨酯高速转动内生热极大”的难题开辟了新路。     

Preparation of polypropylene/montmorillonite nanocomposites with an exfoliated structure by a designed route

Nanocomposites of polypropylene (PP) and montmorillonites (MMT) were prepared by solid‐phase grafting reactive organomontmorillonite (ROMT) and polar monomers onto powdered PP and melt‐blending granule PP with the master batches as PP/MMT grafting copolymers (PPMG). The structure and properties of the PP/MMT nanocomposites (PPMN) were investigated by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) patterns, transmission electron microscopy (TEM), dynamic mechanical analysis, differential scanning calorimetry, and thermogravimetric analysis. GPC showed that the numerical molecular weight and polydispersity of the graft copolymers of PPMG were approximately 4793 and 2.197, respectively. FTIR confirmed the solid‐phase graft copolymerization. XRD and TEM indicated the formation of the exfoliated, layered silicates (tactoids). The mole ratio of compound alkylammoniums and the exothermic enthalpy from solid‐phase graft copolymerization played key roles in the formation of tactoids. The optimum mole ratio of organophilic alkylammonium to reactive alkylammonium was 3 : 1. The mechanical and thermal properties increased with the contents of PPMG, and a preferable state was achieved at approximately 8 phr PPMG (parts of reagent per 100 parts of PP) because of the plastification of the exfoliated silicates and the graft copolymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3889–3899, 2006     

Synergic influence of a surfactant and ultrasonication on the preparation of soluble,conducting polydiphenylamine/silica‐nanoparticle composites

Conducting polydiphenylamine was used to encapsulate silica nanoparticles through the oxidative polymerization of diphenylamine in the presence of ultrasonic irradiation. The polymerization was performed in the presence of sodium lauryl sulfate as a surfactant. Experiments performed in the absence of ultrasound clearly demonstrated that the application of ultrasonication played multiple roles in the preparation of a composite of polydiphenylamine with silica nanoparticles. Ultrasonication dispersed the silica nanoparticles, converted sodium lauryl sulfate to lauryl alcohol, and augmented the dispersion of the silica‐nanoparticle/polydiphenylamine composite in an organic medium. Silica‐nanoparticle/polydiphenylamine composites were also prepared in the absence of ultrasound and/or sodium lauryl sulfate. The silica‐nanoparticle/polydiphenylamine composites were characterized with Fourier trans form infrared spectroscopy, ultraviolet–visible/near‐infrared spectroscopy, and thermogravimetric analysis. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3912–3918, 2006     

rGO-SnO2纳米复合物制备及室温下NH3气敏性能

采用沉淀-焙烧法制备了室温下对NH3具有高灵敏度和高选择性的rGO-SnO2纳米复合材料。利用X射线衍射（XRD），傅里叶红外光谱（FTIR），X射线光电子能谱（XPS），扫描电子显微镜（SEM），透射电子显微镜（TEM）和比表面积（BET）表征分析了纯SnO2与rGO(1.0%)-SnO2纳米复合物的属性。与纯SnO2相比，rGO(1.0%)-SnO2纳米复合物中SnO2晶体尺寸较小，约为6~20nm，比表面积更大，为33m2/g；rGO(1.0%)-SnO2纳米复合材料对0.01% NH3的灵敏度达到了49.6%，是相同NH3浓度下纯SnO2灵敏度的2.1倍，并且响应和恢复时间分别为21s和204s，比纯SnO2缩短了24s和10s，具有良好的重复性，选择性与稳定性；rGO(1.0%)-SnO2纳米复合材料优良的气敏性能是由rGO与SnO2产生的p-n异质结以及溶解的NH3电离出导电离子共同作用的结果。     

Chitosan/clay nanocomposite film preparation and characterization

Nanocomposites of chitosan and nanoclays (MMT‐Na⁺ and Cloisite 30B) were prepared by solvent casting. The structural properties, thermal behaviors, and mechanical properties were characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy, differential scanning calorimetry, thermogravimetry analyses, and an Instron universal testing machine. XRD and TEM results indicated that an exfoliated structure was formed with addition of small amounts of MMT‐Na⁺ to the chitosan matrix. Intercalation along with some exfoliation occurred with up to 5 wt % MMT‐Na⁺. Micro‐scale composite (tactoids) formed when Cloisite 30B was added to the chitosan matrix. Surface roughness increased with addition of a small amount of clay. Tensile strength of a chitosan film was enhanced and elongation‐at‐break decreased with addition of clay into the chitosan matrix. Melt behavior and thermal stability did not change significantly with addition of clays. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1684–1691, 2006     

Preparation and characterization of calcium carbonate/low‐density‐polyethylene nanocomposites

Calcium carbonate/low‐density‐polyethylene (LDPE) nanocomposites have been prepared by melting blend with twin‐screw extruder. The mechanical properties of composites and the dispersion of the nanoparticles were studied. The reinforcement mechanism was discussed. The results show that not only the tensile property but also the flexural modulus of the system have been evidently increased by the addition of calcium carbonate. The calcium carbonate particles have been dispersed in the matrix in the nanometer scale. The reinforcement mechanism of the calcium carbonate lies on that the calcium carbonate particles, acting as hetero‐nuclei, can induce higher crystallinity at the matrix‐particle interface compared to regions away from the interface. Consequently, in the process of the tensile test, the nanocomposites have better tensile yield strength. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Syndiotactic Polystyrene/Organoclay Nanocomposites: Synthesis via In Situ Coordination‐Insertion Polymerization and Preliminary Characterization

Summary: Syndiotactic polystyrene (sPS)/organophilic clay nanocomposites were obtained by in situ coordination‐insertion polymerization of styrene. Two cationic surfactants (alkylammonium and alkylphosphonium) were used for the intercalation of montmorillonite (MMT). For each organically modified clay, three protocols were performed using an MAO‐activated hemi‐metallocene catalyst, in order to compare the influence of experimental conditions on the composite microstructure and on its thermal stability. The microstructures of nanocomposites were investigated by wide angle X‐ray scattering and DSC. Partially exfoliated or intercalated materials were obtained in all cases and a decrease of crystallinity is observed. Thermal properties were also studied by DSC and thermogravimetric analysis. The presence of clay does not have a strong influence on the sPS thermal transitions but the thermal decomposition process of the material was slowed down in the presence of few organoclay percents, particularly in the degradation beginning. The influence of these two organically modified clays on the thermal stability of the material is discussed.

Gel and suspension formed from the combination of cloisite with toluene (left) and styrene (right), respectively.