Polymer/clay nanocomposites as VOC barrier materials and coatings

The transport properties of select volatile organic compounds were measured in polyurethane/clay nanocomposite barrier membranes as a function of clay content. The nanocomposites were fabricated by two different processing methods involving stirring and sonication of the clay particles. The concentration of Cloisite^® 30B in the nanocomposite was varied from 0 to 50 wt%. Characterization of membrane transport properties was achieved via a gravimetric sorption method. Material-phase diffusivity coefficients (D) decreased with increasing Cloisite^® concentration, while changes in the material/VOC partition coefficients (K) depended on the molecular interactions of the VOCs with the membrane material.     

Caffeine Molecular Imprinted Microgel Spheres by Precipitation Polymerization

Imprinted uniform microgel spheres were prepared by precipitation polymerization. Acetonitrile was used as the dilute solvent with MAA as the monomer, EDMA as the crosslinker and caffeine as the print molecule. Comparison of caffeine adsorption on molecular imprinted and blank microgel spheres was made. Langmuir model was used to fit the adsorption data. It was found that the caffeine imprinted microgel spheres show specific binding sites to the target molecules. A binding study of caffeine on imprinted microgel spheres was made by Scatchard analysis; the dissociation constants (K_D) and the maximum binding capacity were K_D= 1.84×10⁻⁴mol/L,Q _max = 16.98 μmol/g for high affinity binding site and K_D=1.33×l0⁻³ mol/L, Q_max=46.84 μmol/g for lower affinity binding site, respectively This microgel spheres can be useful affinity adsorbents in further applications.     

Online Particle Size Measurement in Microgel Particle Suspensions: Principles and Data Analysis

If a gelled system is subjected to shearing or the concentration of reactive components is low, microgel particles are formed. Since labile microgel particles with high water capacities can often be found in food systems, and as they are important for the textural properties, particle size measurement is relevant for fundamental research and control of industrial processes. A chord length measurement system was tested for online particle sizing.     

Interface-tuned epoxy/clay nanocomposites

Though interface has been known for a critical role in determining the properties of conventional composites, its role in polymer nanocomposites is still fragmented and in its infancy. This study synthesized a series of epoxy/clay nanocomposites with different interface strength by using three types of modifiers: ethanolamine (denoted ETH), Jeffamine^® M2070 (M27) and Jeffamine^® XTJ502 (XTJ). XTJ created a strong interface between clay layers and matrix because it bridged the layers with matrix by a chemical reaction as proved by Fourier transform infrared spectroscopy; M27 produced an intermediate interface strength due to the molecular entanglement between grafted M27 chains and matrix molecules; the interface made by ETH was weak because neither chemical bridging nor molecular entanglement was involved. The studies of mechanical and thermal properties and morphology at a wide range of magnification show that the strong interface promoted the highest level of exfoliation and dispersion of clay layers, and achieved the most increment in Young’s modulus, fracture toughness and glass transition temperature (T_g) of matrix. With ∼1.3 wt% clay, the critical strain energy release rate G_1c of neat epoxy improved from 179.0 to 384.7 J/m, 115% improvement and T_g enhanced from 93.7 to 99.7 °C, 6.4% improvement.     

无皂乳液聚合制备含氟温敏型微凝胶

在微波辐射下,采用无皂乳液聚合方法,制备了稳定的含氟N-异丙基丙烯酰胺(FA-NIPAAm)温度敏感型微凝胶乳液.利用FT-IR表征了微凝胶的化学组成;采用激光光散射粒度仪(PCS)研究了微凝胶粒径在不同温度的变化,测定了微凝胶的低临界溶解温度(LCST);用透射电子显微镜(TEM)观察了微凝胶的形貌;考察了微凝胶乳液...     

薄层扫描法测定核—壳型微交联聚苯乙烯微粒中线性组分的含量

本文用薄层扫描法测定了微交联核—壳结构聚苯乙烯（ＰＳ）微粒中线性ＰＳ分子的含量。０．２～１．６×１０－６ｇ的点样量，薄层扫描峰面积与样品量呈良好的线性关系，可直接由峰面积计算线性分子的含量。     

环氧树脂/粘土纳米复合材料的研究

采用原位插层聚合法制备环氧树脂／粘土纳米复合材料，用X衍射（XRD），红外光谱（FTIR），差示扫描量热法（DSC），扫描电镜（SEM）对有机化蒙脱土（OMMT）和环氧树脂／粘土纳米复合材料进行测试与表征，结果表明，与纯环氧树脂固化物相比，环氧树脂／粘土纳米复合材料的力学，热学性能有较大的改善和提高。     

Effect of clay modifiers on the morphology and physical properties of thermoplastic polyurethane/clay nanocomposites

Thermoplastic polyurethanes (TPUs)/clay nanocomposites were prepared via melt processing using the ester type and the ether type TPUs and three differently modified organoclays (denoted as C30B, C25A and C15A) as well as pristine montmorillonite (PM). XRD and TEM results showed that the addition of C30B with hydroxyl group led to the nearly exfoliated structures in both TPUs. In the case of C25A and C15A clays, partially intercalated nanocomposites were obtained in both TPUs, where C25A showed better dispersion than C15A. Natural clay (PM) was not effectively dispersed in both TPUs. The tensile properties of nanocomposites with C30B were better than ones with the other clays. Higher tensile properties were obtained for ester type TPU than ether type TPU nanocomposites with all clays tested. Although the improvement in tensile properties decreased after the second extrusion of the nanocomposites, properties of the nanocomposite after first melt processing were still good enough for practical applications. Morphological changes induced by the addition of clays were analyzed using FTIR, DSC and rheological test results. Some clays were observed to cause demixing of hard and soft segments in the nanocomposites and location of clays in either soft segment or hard segment domains was also studied.     

Fully exfoliated nanocomposite from polypyrrole graft copolymer/clay

Exfoliated polypyrrole graft copolymer/clay nanocomposites were prepared by in situ polymerization of pyrrole onto pre-exfoliated water-soluble poly(styrenesulfonic acid-co-pyrrolylmethyl styrene) (P(SSA-co-PMS))/clay nanocomposite or by simple blending of poly(styrenesulfonic acid-g-pyrrole) (PSSA-g-PPY) with clay. As the clay content in PSSA-g-PPY/clay nanocomposite increases, the conductivity of PSSA-g-PPY/clay nanocomposite decreases. Thermal de-doping temperature shifts to higher temperature as the clay content in PSSA-g-PPY/clay nanocomposite increases.     

Effect of clay on the morphology and properties of PMMA/poly(styrene-co-acrylonitrile)/clay nanocomposites prepared by melt mixing

Nanocomposites of blends of polymethylmethacrylate (PMMA) and poly(styrene-co-acrylonitrile) (SAN) with natural and organically modified montmorillonite clays (Cloisite^®25A and Cloisite^®15A) were prepared by melt mixing in a twin-screw extruder and the effect of clay on the phase separation morphology and physical properties of nanocomposites was investigated. Multi-pass samples were; those extruded once (one-pass), twice (two-pass) and three times (three-pass). Dispersion of clays in the matrix polymers was investigated using XRD and TEM. Interestingly enough, the clays were observed to be mainly located at the boundaries of PMMA and SAN for most of the nanocomposites. As the number of pass increased, the phase-separated domain size became larger for nanocomposites of PMMA/SAN containing PM, while nanocomposites with clay 25A or 15A showed less degree of growth in domain size in the TEM pictures. Viscosities of the continuous phase and separated domains, and the compatibilizing effect of clays were discussed as the probable explanations for these observations. These were supported by the rheological properties measurements, where the nanocomposites with clay 25A or 15A showed the higher complex viscosities than those of PM and also showed some shear thinning behavior. DSC and TGA analyses were also conducted.     

Polymer/layered clay nanocomposites: 2 polyurethane nanocomposites

A kind of novel polyurethane/Na⁺-montmorillonite nanocomposites has been synthesised using modified 4,4′-di-phenymethylate diisocyanate (M-MDI), modified polyether polyol (MPP) and Na⁺-montmorillonite (layered clay). Here, MPP was used as a swelling agent to treat the layered clay. Experimental results indicated that with increasing the amount of layered clay, the strength and strain-at-break increased. The storage modulus below the glass transition temperature of the soft segments in the polyurethane was increased by more than 350%. With increased loading of layered clay, the thermal conductivity decreased slightly rather than increased. This finding will provide valuable information for polyurethane industry.     

The effect of clay on the thermal degradation of polyamide 6 in polyamide 6/clay nanocomposites

The degradation pathway of polyamide 6/clay nanocomposites was studied as a function of clay content. Well-dispersed polymer-clay nanocomposites can be easily obtained by simple melt blending between organically-modified clays and polyamide 6. Polyamide 6-clay nanocomposites exhibit a large reduction in the peak heat release rate, 60%, measured by cone calorimetry. There are no significant differences in the evolved products during thermal degradation of polyamide 6 and polyamide 6/clay nanocomposites in terms of composition and functionality. The main degradation pathway of polyamide 6 is aminolysis and/or acidolysis, primarily through an intra-chain reaction, producing ε-carprolactam, which is the monomer of polyamide 6. As the clay loading is increased, the relative quantity of ε-carprolactam in the evolved products decreases and the viscosity of the soluble solid residues increases. It is thought that inter-chain reactions become significant in the presence of clay because the degrading polymer chains are trapped in the gallery space of the clay during thermal degradation.     

Micro- and nano-structure in polypropylene/clay nanocomposites

Polypropylene (PP)/clay nanocomposites prepared by melt blending using different clays and coupling agents based on maleic anhydride-grafted PP (MA-PP) were studied. Clay dispersion using field emission gun scanning electron microscope (FEG-SEM) and transmission electron microscopy (TEM), and PP matrix morphology were characterized. Clay dispersion was improved in the presence of MA-PP, as shown by the higher particles surface density (number of particles/mm²) at all micro-, sub-micro- and nano-levels. The PP spherulite diameter was affected by both the presence of MA-PP and clay dispersion. Clay intercalation, characterized by both complementary X-ray diffraction (XRD) and TEM, was greatly influenced by the characteristics of MA-PP. The use of low molecular weight (M_w) MA-PP led to a good and uniform intercalation but with no further possibility to exfoliation. The use of higher M_w MA-PP led to a heterogeneous intercalation with signs of exfoliation. The crystallization behavior of nanocomposites was studied by differential scanning calorimetry (DSC). When fine clay dispersion was achieved with MA-PP, clay-nucleating effect was limited and lower crystallization temperature and rates were observed. It was also shown by wide angle X-ray diffraction (WAXD) that clay induced some orientation of α-phase PP crystallites.     

Preparation and crystalline morphology of biodegradable starch/clay nanocomposites

An organically modified clay (o-clay) and a pristine clay (p-clay) were used to prepare biodegradable thermoplastic starch (TPS)/clay nanocomposites by melt processing. The gelatinization behaviour of starch with glycerol/H₂O was investigated and the gelatinized temperature (T_gel) was determined using a polarized optical microscopy (POM) equipped with a hot stage. The morphologies of gelatinized starch and extruded starch were revealed by scanning electron microscopy (SEM). Thermal stabilities of starch/clay nanocomposites were evaluated under N₂ atmosphere using thermogravimetric analysis (TGA). Transparent films of starch/clay hybrids were fabricated by hot pressing. Intercalation of starch into clay galleries and crystalline structure of starch were investigated using X-ray diffraction (XRD). It was found that the increase in d-spacing of organically modified clay was due to starch molecular intercalation while the increase in d-spacing of pristine clay was mostly caused by glycerol intercalation because of the narrow valid d-spacing of pristine clay and special ring-like monomer of starch. The mechanism of starch intercalation in clay galleries was discussed.     

Unique clay orientation in the injection-molded bar of isotactic polypropylene/clay nanocomposite

In this article, the injection-molded bars of isotactic polypropylene/organoclay nanocomposite with different clay contents have been obtained via dynamic packing injection molding (DPIM). The oriented microstructure including layered nanoparticles and PP lamellae has been inspected through 2D-WAXS analyses along the sample thickness of the molded bars. Depending on the clay content and sample thickness, various oriented clay structures with nanoparticles uniplanar-axially oriented parallel to the surface of molded bar, or partially tumbled around the flow axis of the molded bar, or even a random orientation, could be observed. The observed orientation behavior of nanoparticles could be temporarily elucidated as the results of the sensitive response of layered nanoparticles to shear deformation and the structural recovery of clay network assisted by the electrostatic attraction existing between adjacent nanoplatelets.     

Effects of different kinds of clay and different vinyl acetate content on the morphology and properties of EVA/clay nanocomposites

A series of EVA/clay nanocomposites and microcomposites have been prepared via melt-blending. Using four kinds of EVA with different vinyl acetate (VA) contents: 28, 40, 50 and 80 wt%, and four kinds of clay: three are organophilic clay (OMMT) and one unfunctionalized clay (Na-MMT), the effects of different VA content of EVA and the kinds of the clay on the morphology and properties of EVA/clay nanocomposites were systematically investigated. In previous studies, there are only two distinct nanostructures to distinguish polymer/clay nanocomposites: the intercalated and the exfoliated. But in this paper, we proposed a new nanostructure—‘the wedged’ to describe the dispersion degree of clay in nanocomposites, it means the sheets of clay were partly wedged by the chains of polymer. The wedged, the intercalated and the partially exfoliated structures of EVA/clay nanocomposites were characterized by X-ray diffraction (XRD) and by high-resolution transmission electron microscopy (HRTEM). The enhanced storage modulus of EVA/clay nanocomposites was characterized by dynamic mechanical thermal analysis (DMTA). The enhanced degree in the storage modulus of the OMMT on EVA/clay nanocomposites with the partially exfoliated and intercalated structure is much higher than that with wedged structure, and that with the higher VA content is higher than that with the lower. The thermal stabilities of EVA/clay nanocomposites were also studied by thermal gravimetric analysis (TGA).     

Effect of tethering chemistry of cationic surfactants on clay exfoliation, electrospinning and diameter of PMMA/clay nanocomposite fibers

We examine the influence of tethering chemistry of cationic surfactants on exfoliation of montmorillonite (MMT) clay dispersed in methyl methacrylate (MMA) followed by in-situ polymerization to form poly(methyl methacrylate) (PMMA) nanocomposites, the effect of exfoliation and clay loading on the rheology of polymer/clay dispersions in dimethyl formamide, and the diameters of nanocomposite fibers formed from these dispersions by electrospinning. Incorporation of an additional reactive tethering group of methacryl functionality significantly improves the intercalation and exfoliation of clays in both in-situ polymerized PMMA nanocomposites and the corresponding electrospun fibers. The proper surfactant chemistry also increases the dispersion stability, extensional viscosity, extent of strain hardening and thus the electrospinnablity of the nanocomposite dispersions, especially at low nanocomposite concentrations. The degree of the enhancement in electrospinnability by clays with proper tethering chemistry is at least the same as or greater than that obtained with three times higher loading level of clay particles without proper tethering chemistry in the nanocomposites. These results suggest a new strategy to produce smaller diameter fibers from very dilute polymer solutions, which are otherwise not electrospinnable, by incorporating a small amount of well-exfoliated clays.     

Three-dimensional electrochemical microfabrication of n-GaAs using l-cystine as a scavenger

The confined etchant layer technique (CELT) was used to fabricate complex three-dimensional (3D) microstructures on gallium arsenide (n-GaAs). The design of an appropriate chemical etching system is needed in order to realize successful microfabrication. In this study, Br₂ was electro-generated at the mold surface and used as an efficient etchant for n-GaAs. The use of l-cystine as a scavenger to replace the toxic scavenger H₃A_SO₃ was explored. The resolution of the fabricated microstructure depended strongly on the composition of the electrolyte, and especially on the concentration ratio between l-cystine and KBr. A well-defined and polished Pt micro-cylindrical electrode with a diameter of ∼50 μm was employed as one kind of mold for CELT. By inspecting the deviation of the sizes of the etching spots from the real diameter of the microelectrode, the thickness of confined etchant layer (CEL) can be estimated and thus the composition of electrolyte can be optimized for better etching precision. By choosing an appropriate concentration ratio between l-cystine and KBr, complex microstructures were fabricated successfully on n-GaAs. The etched patterns on n-GaAs were approximately negative copies of the mold, and the precision of duplication could easily reach the submicrometer scale, which was better than that achieved with H₃A_SO₃. The experimental results indicated that l-cystine is a good scavenger for microfabrication on n-GaAs by CELT. This technique avoids severe pollution of the environment, which will help to extend its future application in industry.     

Properties of novel epoxy/clay nanocomposites prepared with a reactive phosphorus-containing organoclay

In this study, a reactive phosphorus-containing organoclay (RPC) was successfully prepared through the cationic exchange reaction of sodium montomorillonite clay with hexyltriphenylphosphonium bromide and surface modification by grafting it with glycidyloxypropyltrimethoxy silane. It is characterized using X-ray diffraction (XRD) and Fourier transform IR (FTIR) measurements. A series of novel epoxy/clay nanocomposites (ERPC) was then prepared with a selected epoxy resin and varying amounts of RPC. The results of XRD and TEM of the nanocomposites showed that the RPC particles were well dispersed in the epoxy matrix with a highly exfoliated structure due to the presence of the reactive epoxide group of RPC. The as-prepared epoxy/RPC nanocomposites (ERPC) were thermally stable up to 388 °C. Thermal stability was increased by increasing the RPC content as indicated by the corresponding activation energies (E_a) and the integral procedural decomposition temperatures (IPDT). Furthermore, the storage modulus in the glass state of the nanocomposites was dramatically increased with the increase in RPC content. In addition, the large increment of limiting oxygen index (LOI) which was 11 units higher than that of the neat epoxy indicates that an extraordinary enhancement of flame retardancy was obtained from the nanocomposite containing 5 wt% of RPC.     

Influence of clay exfoliation on the physical properties of montmorillonite/polyethylene composites

Melt compounding was used to prepare conventional composites of montmorillonite clay and polyethylene (PE) as well as nanocomposites of exfoliated montmorillonite platelets dispersed in a maleated polyethylene (PE-g-MAn) matrix. The extent of clay platelet exfoliation in the PE-g-MAn nanocomposites was confirmed by X-ray diffraction and resulted in a significant reduction of the degree of crystallinity and increased polymer crystallization rates. Studies of non-isothermal crystallization kinetics suggested that the exfoliated clay promotes heterogeneous nucleation and two-dimensional crystallite growth.PE/clay composites behaved in a similar manner as conventional macrocomposites, exhibiting modest increases in their rheological properties and Young's modulus. Conversely, the nanoscale dimensions of the dispersed clay platelets in the nanocomposites led to significantly increased viscous and elastic properties and improved stiffness. This was attributed to the high surface area between the polymer matrix and the exfoliated clay, which resulted in enhanced phase adhesion.