Characterization of polypropylene/layered silicate nanocomposites prepared by single-step method

The extent of organo-modified clay (C93A) platelets dispersion in polymer matrix and crystallization and melting behavior of iPP-based nanocomposites prepared by a single-step melt-mixing method were investigated by wide-angle X-ray diffraction (WAXD), transmission (TEM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). WAXD patterns revealed exfoliated structure of nanocomposites containing 1 wt% clay, and mixed intercalated/exfoliated structure at higher concentration of nanoclay. The isothermal crystallization proceeds faster in the matrix polymer (iPP/PP-g-MA) than in nanocomposite samples. The results obtained for T _m ^o suggest that the presence of nanoclay has induced a perfection of the formed crystals. The presence of C93A particles in PP leads to increase in crystallization peak temperature implying nucleating ability of clay particles, which was more pronounced in exfoliated than in mixed intercalated/exfoliated system.     

Electrical characterization of poly(ethylene oxide)–clay nanocomposites prepared by microwave irradiation

Poly(ethylene oxide) (PEO)–clay (montmorillonite, hectorite, and laponite) nanocomposites were prepared by a melting intercalation procedure induced by microwave irradiation. The influence of parameters such as the time of irradiation, power, amount and relative ratio of the reagents, and relative humidity was investigated. X-ray diffraction, differential scanning calorimetry, elemental microanalysis, Fourier transform infrared, and scanning electron microscopy techniques were applied to characterize the resulting nanocomposites. Techniques involving impedance spectroscopy, thermoelectric power, and electrical polarization in the solid state were used to characterize the electrical properties of the nanocomposites. The electrical behavior of these PEO–silicate nanocomposites, including those containing an excess of alkaline metal salts in comparison with that of similar systems prepared by alternative procedures such as direct intercalation from polymer solutions or melting intercalation, was also examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3249–3263, 2003     

聚氧化乙烯/蒙脱土纳米嵌入化合物的制备与结构表征

利用溶液法和熔融法制备聚氧化乙烯(PEO)/蒙脱土纳米嵌入化合物,用XRD、IR和DSC等测试手段对嵌入化合物进行了表征.嵌入的PEO分子同蒙脱土晶层中的Na⁺生成PEO-Na⁺络合物,嵌入化合物具有一定的耐溶剂萃取性,PEO分子以单层螺旋构象排列于蒙脱土的晶层中.PEO分子在蒙脱土层间运动受到限制,致使嵌入化合物的结晶熔融峰减弱.     

Thermal and mechanical properties of syndiotactic polystyrene/organoclay nanocomposites with different microstructures

The fabrication of syndiotactic polystyrene (sPS)/organoclay nanocomposite was conducted via a stepwise mixing process with poly(styrene‐co‐vinyloxazolin) (OPS), that is, melt intercalation of OPS into organoclay followed by blending with sPS. The microstructure of nanocomposite mainly depended on the arrangement type of the organic modifier in clay gallery. When organoclays that have a lateral bilayer arrangement were used, an exfoliated structure was obtained, whereas an intercalated structure was obtained when organoclay with a paraffinic monolayer arrangement were used. The thermal and mechanical properties of sPS nanocomposites were investigated in relation to their microstructures. From the thermograms of nonisothermal crystallization and melting, nanocomposites exhibited an enhanced overall crystallization rate but had less reduced crystallinity than a matrix polymer. Clay layers dispersed in a matrix polymer may serve as a nucleating agent and hinder the crystal growth of polymer chains. As a comparison of the two nanocomposites with different microstructures, because of the high degree of dispersion of its clay layer the exfoliated nanocomposite exhibited a faster crystallization rate and a lower degree of crystallinity than the intercalated one. Nanocomposites exhibited higher mechanical properties, such as strength and stiffness, than the matrix polymer as observed in the dynamic mechanical analysis and tensile tests. Exfoliated nanocomposites showed more enhanced mechanical properties than intercalated ones because of the uniformly dispersed clay layers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1685–1693, 2004     

Biodegradable Nanocomposites Based on the Polyester Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) and Layered Silicate or Expanded Graphite

Novel nanocomposites based on the biodegradable polymer poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHx) and layered fillers, specifically layered silicate (clay25A) and expanded graphite (EG), were prepared by melt intercalation. The dispersion of the fillers in the PHBHx was characterized by wide‐angle X‐ray diffraction (WAXD) and transmission electron microscopy (TEM). The effects of the fillers on the polymer structure, thermal stability and mechanical properties of the nanocomposites were also studied, by differential scanning calorimetry, thermogravimetric analysis, and strain‐stress measurements in elongation, respectively. The WAXD and TEM results showed that the clay25A and EG was exfoliated into well‐dispersed sheets in the polymer matrix, especially when the filler concentration were relatively low. This gave rise to considerable improvements in Young's modulus, and resulted in increases in the thermal degradation. It should be possible to convert the EG dispersions obtained thus far to ones yielding filler‐filler networks that show electrical conductivity.     

Saturation ratio of poly(ethylene oxide) to silicate in melt intercalated nanocomposites

Melt intercalation has been found to be a very successful approach for preparation of polymer-clay nanocomposites. An aspect of this area that has been little investigated is the amount of polymer required to fill the interlayer galleries of the clay. This paper reports experiments which determine the amount of poly(ethylene oxide) (PEO) required to saturate the spacing between montmorillonite (MMT) or organically-modified bentonite (B34) layers. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to determine the saturation ratios of PEO to silicates, which are then compared to theoretical calculations. The deduced saturation ratio of PEO to MMT is 28:72, and PEO to B34 15:85 by XRD and DSC, whilst ratios of PEO to MMT of 21:79 and PEO to B34 10:90 were obtained via TGA. The density of intercalated PEO in the silicate galleries is estimated to be 0.82 g/cm³, which suggests that PEO in the silicate galleries is far less efficiently packed than in the amorphous region of the bulk polymer.     

Poly(vinylidene fluoride)/clay nanocomposites prepared by melt intercalation: Crystallization and dynamic mechanical behavior studies

The preparation and properties of poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported for the first time. PVDF/clay nanocomposites were prepared by melt intercalation with organophilic clay. The composites were characterized with X‐ray diffraction, differential scanning calorimetry, and dynamic mechanical analysis. X‐ray diffraction results indicated intercalation of the polymer into the interlayer spacing. PVDF in the nanocomposites crystallized in the β form. Differential scanning calorimetry nonisothermal curves showed an increase in the melting and crystallization temperatures along with a decrease in crystallinity, as evidenced by the melting and crystallization peaks. Isothermal crystallization studies showed an enhanced rate of crystallization with the addition of clay, as evidenced by a reduction in the crystallization time. Dynamic mechanical analysis indicated significant improvements in the storage modulus over a temperature range of ?100 to 150 °C. The tan δ peak signifying the glass‐transition temperature of PVDF shifted to higher temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1682–1689, 2002     

铜离子配位下的聚氧乙烯受限结晶行为研究——缺陷引起的熔点下降

利用铜离子(Cu2+)对聚氧乙烯(PEO)的配位作用所形成的对分子链运动的束缚,研究了链段受限下PEO的结晶和熔融行为.首先利用宽频介电松弛谱(BDS)对受限条件下PEO的松弛行为进行表征,结果表明,加入铜离子后PEO的β-过程和γ-过程的特征松弛时间都变长,说明PEO的链段协同运动和主链扭转运动都变得更加困难;松弛时间为评价受限程度提供了定量的依据.DSC的测试结果表明,受限条件下PEO的玻璃化转变温度(Tg)升高,同时出现冷结晶现象,说明Cu2+配位作用确实对PEO的链段运动产生了束缚作用;同时PEO的结晶度和熔点都随着铜离子含量的提高而降低.WAXD结果表明,CuBr2在共混物中没有发生结晶,同时PEO的晶型没有发生改变.利用AFM进一步研究了PEO/CuBr2共混物薄膜的结晶形貌,发现在不同Cu2+含量的共混物中PEO都形成伸直链晶体,片晶厚度没有变化,说明熔点的降低并非是片晶厚度变化所导致.但是AFM的结果却显示螺位错晶体的数量随着Cu2+含量的提高明显增加.可以认为,在Cu2+配位受限下的PEO体系中,晶体缺陷应是引起熔点下降的主要原因,和金属等其它晶体材料的情况有着类似效应.     

Dielectric and conductivity studies of 90 MeV O7+ ion irradiated poly(ethylene oxide)/montmorillonite based ion conductor

In the present work effect of 90 MeV O⁷⁺ ions with five different fluences on poly(ethylene oxide) (PEO)/Na⁺-montmorillonite (MMT) nanocomposites has been investigated. PEO/MMT nanocomposites were synthesized by solution intercalation technique. With the increase in irradiation fluence, gallery spacing of MMT increases in the composite and an exfoliated nanostructure is obtained at the fluence of 5?×?10¹² ions/cm² as revealed by X-ray diffraction results. Highest room temperature ionic conductivity of 4.2?×?10^?6?S?cm^?1 was found for the fluence 5?×?10¹² ions/cm², while the conductivity for unirradiated polymer electrolyte was found to be 7.5?×?10^-8?S?cm^?1. The increase in intercalation of PEO chains inside the galleries of MMT results in the increase in interaction between Na⁺ cation and oxygen heteroatom leading to the increase in ionic conductivity of the composites. Surface morphology and interactions among the various constituents in the nanocomposites at different fluence have been examined by scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The appearance of peak for each fluence in the loss tangent suggests the presence of relaxing dipoles in the polymer nanocomposite electrolyte films. With the increase in ion fluence the peak shifts towards higher frequency side, suggesting decrease in the relaxation time.     

插层聚合聚丙烯-蒙脱土纳米复合材料的微观结构形态

使用偏光显微镜，扫描电镜，透射电镜和广角X射线衍射法研究了插层聚合法制备的聚丙烯－蒙脱土（PP－MMT）纳米复合材料的微观结构和形态发展。结果表明，随着插层聚合反应的进行，较大的初级MMT粒子逐渐剥离成较小的次级粒子。次级粒子由2－20片的单个MMT片层组成，其层间充满了PP分子链。提出了插层聚合过程中PP－MMT复合材料的形态发展模型。另外，MMT的加入对PP的球晶形态也有重要影响，PP完整的球晶随MMT的加入逐渐变小和趋于扭曲甚至破坏。     

Effect of the vibration shear flow field in capillary dynamic rheometer on the crystallization behavior of polypropylene

The self-made capillary dynamic rheometer was adopted to study the relationship between the crystallization behavior of isotactic polypropylene (iPP) and the vibration shear conditions, namely, vibration amplitude and vibration frequency. The crystalline structure of iPP under different vibration conditions was characterized by using differential scanning calorimeter (DSC) and wide-angle X-ray diffractometer (WAXD) techniques. The samples extruded under vibration shear conditions had a higher melting temperature (from DSC). A new shoulder-shape peak appeared at ca. 162 °C under low frequency or low amplitude conditions, which was engulfed by the main melting peak with the increase of the vibration amplitude or frequency. This was probably an indication that more perfect crystals had formed [Polym Eng Sci 38 (1998) 1-20]. The WAXD demonstrated that crystalline form of iPP extruded was not changed but the average crystalline size decreased, according to the Scherrer formula [Analytical methods of polymer materials, China Petrochemical Press, Beijing, 1997]. This proved a large increase in the number of small crystals.     

Relaxations of confined chains in polymer nanocomposites: Glass transition properties of poly(ethylene oxide) intercalated in montmorillonite

The relaxation behavior of poly(ethylene oxide) (PEO), intercalated in montmorillonite, a naturally occurring mica-type silicate, was studied by differential scanning calorimetry (DSC) and thermally stimulated dielectric depolarization (or thermally stimulated current, TSC). The materials were synthesized by melt or solution-mediated intercalation. In both intercalates, the PEO chains were confined to ca. 0.8-nm galleries between the silicate layers. The solution intercalate contained a fraction of unintercalated PEO chains which exhibited a weak and depressed PEO melting endotherm in DSC. In contrast, the melt intercalate was “starved” such that almost all the PEO chains were effectively intercalated. For these melt intercalates, no thermal events were detected by DSC. TSC thermal sampling technique was used to examine the glass transition regions and to estimate the extent of cooperativity of chain motions. The motions of the intercalated PEO chains are inherently noncooperative relative to the cooperative T_g motions in the amorphous portion of the bulk polymer. This is presumably due to the strong confining effect of the silicate layers on the relaxations of the intercalated polymer. © 1997 John Wiley & Sons, Inc.     

Effect of a silicate filler on the crystal morphology of poly(trimethylene terephthalate)/clay nanocomposites

A series of intercalated poly(trimethylene terephthalate) (PTT)/clay nanocomposites were prepared in a twin‐screw extruder by the melt mixing of PTT with either quaternary or ternary ammonium salt‐modified clays. The morphology and structure, along with the crystallization and melting behavior, and the dynamic mechanical behavior of the composites were characterized by X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry, and dynamic mechanical thermal analysis. The results showed that the PTT chains could undergo center‐mass transport from the polymer melt into the silicate galleries successfully during the blending and extrusion process. More coherent stacking of the silicate layers was reserved at higher clay concentrations and shorter blend times. Compared with conventionally compounded composites, the nanoscale‐dispersed organophilic clays were more effective as crystal nucleation agents. The influence of the nanosilicates on the crystallization and melting behavior of PTT became distinct when the concentration of clay was around 3 wt %. The changes in the crystallization behavior of the polymer/clay nanocomposites depended not only on the size of the silicates but also on the intrinsic crystallization characteristics of the polymers. The resulting nanocomposites showed an increase in the dynamic modulus of PTT and a decrease in the relaxation intensity (both in loss modulus and loss tangent magnitude). © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2275–2289, 2003     

Influence of degree of intercalation on the crystal growth kinetics of poly[(butylene succinate)-co-adipate] nanocomposites

The influence of the degree of intercalation of polymer chains in the two dimensional silicate galleries on the crystallization behavior of poly[(butylene succinate)-co-adipate] (PBSA) is being reported on. The nanocomposites were prepared by melt-blending of PBSA and organically modified montmorillonite (OMMT) in a batch-mixer. Two different types of commercially available OMMTs, with different extents of miscibility of organic modifiers with PBSA, were used, leading to highly delaminated and stacked/intercalated nanocomposite structures as revealed by X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) observations. The non-isothermal crystallization behavior of PBSA and the nanocomposite samples were studied by differential scanning calorimetry (DSC). Crystal growth kinetics studies showed that when silicate layers are highly delaminated into the PBSA matrix, nucleation behaviors decreased significantly, relative to the stacked/intercalated silicate layers. These observations indicate that the overall crystal growth kinetics retard in delaminated nanocomposites, opposed to increasing in the case of stacked/intercalated nanocomposites. Polarized optical microscopy (POM) observations and light scattering studies indicate that PBSA spherulites are fairly large and more perfectly grown in the case of delaminated nanocomposites, relative to the pure PBSA matrix. The effect of high levels of dispersion of silicate layers in the PBSA matrix on cold crystallization behavior was also studied.     

Dual bimodal polyethylene prepared by intercalated silicate with nickel diimine complex

The ethylene polymerization was catalyzed by the intercalated montmorillonite with the nickel complex, [ArN?C(Me)? C(Me)?NAr]NiBr₂ (Ar = 2,6‐C₆H₃ (i‐Pr)₂). Polymer with low melting point and high molecular weight was produced at the early stage of polymerization followed by formation of polymer with high melting point and low molecular weight. It is proposed that the gallery of silicate lowers the propagation rate of polymerization and frequency of “chain walking” process of nickel complex anchored inside the gallery, which produces polymer with low molecular weight and low branching, whereas the nickel complex immobilized on the surface of silicate generates polymer with high molecular weight and high branching. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5506–5511, 2005     

Multiple melting behavior of isotactic polypropylene and poly(propylene-co-ethylene) after stepwise isothermal crystallization

The multiple melting behavior of several commercial resins of isotactic polypropylene (iPP) and random copolymer, poly(propylene-co-ethylene) (PPE), after stepwise isothermal crystallization (SIC) were studied by differential scanning calorimeter and wide-angle X-ray diffraction (WAXD). For iPP samples, three typical melting endotherms appeared after SIC process when heating rate was lower than 10 °C/min. The WAXD experiments proved that only α-form crystal was formed during SIC process and no transition from α1- to α2-form occurred during heating process. Heating rate dependence for each endotherm was discussed and it was concluded that there were only two major crystals with different thermal stability. For the PPE sample, more melting endotherms appeared after stepwise isothermal crystallization. The introduction of ethylene comonomer in isotactic propylene backbone further decreased the regularity of molecular chain, and the short isotactic propylene sequences could crystallize into γ-form crystal having a low melting temperature whereas the long sequences crystallized into α-form crystal having high melting temperature.     

Isothermal crystallization of layered silicate/starch-polycaprolactone blend nanocomposites

The isothermal crystallization behavior of layered silicate/starch-polycaprolactone blend nanocomposites was studied by means of differential scanning calorimetry (DSC) measurements. The theoretical melting point was higher for the matrix than for nanocomposites. At low clay concentration, the induction time decreased and the overall crystallization rate increased acting as nucleating agent whereas at higher concentrations became retardants. Classical Avrami equation was used to analyze the crystallization kinetic of these materials. n values suggested that clay not only affected the crystallization rate but also influenced the mechanism of crystals growth. An Arrhenius type equation was used for the rate constant (k). Models correctly reproduced the experimental data.     

Montmorillonite-poly(ethylene oxide) nanocomposites: interlayer alkali metal behavior

Clay-PEO nanocomposites can have large electrical conductivities that make them potential electrolyte materials for rechargeable lithium batteries, but the origin of these large conductivities, especially for Li-containing materials, is poorly understood. This paper presents X-ray diffraction (XRD), TGA-DTA, and (7)Li and (23)Na NMR data for PEO nanocomposites made with natural (SWy-1) and synthetic (MNTS) montmorillonite clays that provide new insight into interlayer structure. An increase in basal d(001)-spacings demonstrates successful intercalation of PEO in all samples, and X-ray line narrowing shows that this intercalation improves the layer stacking order. The basal spacings of 17.9-19.4 A are consistent with a helical or bilayer structure of PEO in the interlayer. TGA-DTA provides quantitative results for the hydration state of the nanocomposites, demonstrates PEO intercalation, and shows that the composites prepared from the synthetic montmorillonite are less stable than those made with SWy-1. (7)Li NMR shows that the nearest neighbor hydration state of Li(+) is unaffected by PEO intercalation and suggests weak interaction of Li(+) with PEO. (23)Na NMR shows that PEO intercalation results in the conversion of the multiple Na(+) hydration states observed for the pristine clay into inner sphere sites most likely formed through coordination with the basal oxygens of the clay. These differences between lithium and sodium suggested that tighter binding of the Na to the clay may be the origin of the conductivity of Li-montmorillonite-PEO nanocomposites being as much as 2 orders of magnitude larger than those of Na-montmorillonite-PEO nanocomposites. The results confirm the idea that polymer oxygen atoms do not participate in sequestering the exchangeable cations and agree with the jump process for cation migration advanced by Kuppa and Manias (Kuppa, V.; Manias, E. Chem. Mater. 2002, 14, 2171).     

苯乙烯-氧乙烯-苯乙烯三嵌段聚合物的受限结晶行为的反气相分析

 采用反气相法研究了苯乙烯 氧乙烯 苯乙烯三嵌段结晶聚合物 (PS PEO PS)的结晶熔融相变 ,测定了PS PEO PS的结晶度、熔点以及熔程 ,探讨了正构烷烃探针分子的碳链长度对测定结果的影响。研究结果表明 :PS PEO PS的微相分离对PEO链段的结晶行为有较大的影响 ,其晶体结构中存在由多种不完善PEO结晶和PS非结晶构成的中间层 ;正构烷烃探针分子的碳链长度对测定PS PEO PS的熔点和熔程无影响 ,但对结晶度测定和PEO结晶熔融相变的检测影响较大 ,所测得PS PEO PS的结晶度随正构烷烃探针分子碳链的增长而降低。     

Degradable polyoctamethylene suberate/clay nanocomposites. Crystallization studies by DSC and simultaneous SAXS/WAXD synchrotron radiation

Several organo-modified montmorillonites were studied to prepare nanocomposites of polyoctamethylene suberate, a biodegradable polyester. Mixtures were analyzed by conventional powder X-ray diffraction and transmission electron microscopy techniques. C30B clay was effective in rendering an intercalated structure with rather variable silicate layer spacing. The hydroxyl groups of the organo-modifier may allow the establishment of good interactions with the polar carbonyl groups of the studied polyester. A slight decrease in thermal stability was detected when the modified clay was incorporated into the polymer matrix. Isothermal and nonisothermal crystallization kinetics were studied by DSC and results compared with those for the neat polyester. The overall crystallization rate determined by calorimetric methods depends on the nucleation density and the crystal growth rate, which were independently evaluated by means of optical microscopy. Crystallization and morphological features were also analyzed by simultaneous SAXS/WAXD measurements made at a selected crystallization temperature and cooling rate under both isothermal and nonisothermal conditions, respectively.