A New Strategy to Exfoliate Silicone Rubber/Clay Nanocomposites

Summary: A new strategy was developed to prepare disorderly exfoliated nanocomposites, in which a soft siloxane surfactant with a weight‐average molecular weight ( ) of 1 900 was adopted to modify the clay. The modified clay slurry was then mixed with silicone rubber by hand, and exfoliation was achieved. The proposed mechanism thereof was verified by TEM and XRD. The physical entanglement of the soft siloxane surfactant plays a vital role in the diffusion and intercalation of the matrix molecules during the compounding of the slurry‐polymer mixture. This simple method is applicable to other silicone‐based materials reinforced by clay.

TEM micrograph of silicone rubber/clay‐sil nanocomposite.     

聚酰胺/粘土纳米复合材料

聚酰胺／粘土纳米复合材料是一种新型的有机－无机纳米复合材料。在无机物含量远少于常规填充复合材料的情况下就可以具有较好的力学性能、阻隔性能等,热稳定性能也显著提高,并具有阻燃性和各向异性。是一种性能优异的、具有广泛应用前途的纳米复合材料。综述了该纳米复合材料的制备、性能和应用前景等。     

Acrylic,Elastomeric, Particle‐Dispersed Epoxy‐Clay Hybrid Nanocomposites: Mechanical Properties

Summary: Nanocomposites were formulated by curing a sonicated mixture of epoxy resin, C18 clay, and acrylic rubber dispersants. At 5.5 phr (parts per hundred) organoclay loading and a rubber concentration of 15 phr, the tensile‐failure strain of the nanocomposite was found to be higher than that of epoxy nanocomposite, rubber‐dispersed epoxy, and pristine epoxy. A plausible mechanism for improvement of the failure strain of nanocomposites is proposed.

Stress strain curves of filled and unfilled epoxy specimen.     

粘土中金属组分对粘土胶热降解的影响

天然橡胶;粘土中金属组分对粘土胶热降解的影响     

Influence of Liquid Isoprene Rubber on Strain Softening of Carbon Black Filled Isoprene Rubber Nanocomposites

The reinforcement of rubbers by nanoparticles is always accompanied with enhanced dissipation of mechanical energy upon large deformations. Methods for solving the contradiction between improving reinforcement and reducing energy dissipation for rubber nanocomposites have not been well developed. Herein carbon black(CB) filled isoprene rubber(IR)/liquid isoprene rubber(LR) blend nanocomposites with similar crosslink density(ν_e) are prepared and influence of LR on the strain softening ...     

Exfoliated Polylactide/Clay Nanocomposites by In‐Situ Coordination–Insertion Polymerization

Poly(L ‐lactide)/layered aluminosilicate nanocomposites were synthesized in bulk by ring‐opening polymerization in the presence of two organo‐modified montmorillonites. When the organo‐modifier consisted of an ammonium cation bearing primary hydroxyl groups, polymerization was initiated by the alcohol functions after adequate activation. The growing polymer chains were directly “grafted” onto the clay surface through the hydroxyl‐functionalized ammonium cations yielding exfoliated nanocomposites with enhanced thermal stability.

TEM image of a fully exfoliated Cloisite®30B‐based nanocomposite, showing delamination of the silicate layers.     

Effect of the Brush Structure on the Degradation Mechanism of Polystyrene–Clay Nanocomposites

Summary: Pyrolysis‐GC‐MS and TGA‐FT‐IR methods have been used to perform a comparative degradation study of polystyrene and a polystyrene–clay composite. An abnormally high yield of α‐methylstyrene has been detected for the composite. This and other differences in degradation products have been explained by enhanced intermolecular interaction of the grafted PS chains, forming a brush structure. A conceptual model of the process has been suggested.

GC pyrograms of virgin PS (A) and PS–clay composite (B) pyrolyzed at 500 °C (1: styrene; 2: 2,4‐diphenylbut‐1‐ene; 2′: dimer derivatives; 3: 2,4,6‐triphenylhex‐1‐ene; 3′: trimer derivatives; 4: α‐methylstyrene).     

Mechanical Properties and Phase Transition of High Clay Content Clay/Poly(N-isopropylacrylamide) Nanocomposite Hydrogel

Summary: A series of high clay content Clay-S/PNIPAAm nanocomposite hydrogels (S-N gels) has been successfully prepared by in situ polymerization. Their mechanical properties and phase transition behavior has been systematically investigated. It was found that S-N gels show high tensile strength, high elongation at break, fast stress relaxation, high hysteresis, and poor resilience, which may be ascribed to the hydrophilicity and flexibility of PNIPAAm chains. It was also concluded that the macroscopic phase transition behavior of S-N gels depend on the ratio of Segments II (thermosensitive segments) to Segments I (non-thermosensitive segments).     

Tailoring the Thermal Conductivity of Rubber Nanocomposites by Inorganic Systems: Opportunities and Challenges for Their Application in Tires Formulation

The development of effective thermally conductive rubber nanocomposites for heat management represents a tricky point for several modern technologies, ranging from electronic devices to the tire industry. Since rubber materials generally exhibit poor thermal transfer, the addition of high loadings of different carbon-based or inorganic thermally conductive fillers is mandatory to achieve satisfactory heat dissipation performance. However, this dramatically alters the mechanical behavior of the final materials, representing a real limitation to their application. Moreover, upon fillers’ incorporation into the polymer matrix, interfacial thermal resistance arises due to differences between the phonon spectra and scattering at the hybrid interface between the phases. Thus, a suitable filler functionalization is required to avoid discontinuities in the thermal transfer. In this challenging scenario, the present review aims at summarizing the most recent efforts to improve the thermal conductivity of rubber nanocomposites by exploiting, in particular, inorganic and hybrid filler systems, focusing on those that may guarantee a viable transfer of lab-scale formulations to technological applicable solutions. The intrinsic relationship among the filler’s loading, structure, morphology, and interfacial features and the heat transfer in the rubber matrix will be explored in depth, with the ambition of providing some methodological tools for a more profitable design of thermally conductive rubber nanocomposites, especially those for the formulation of tires.     

Micromechanical models of young's modulus of NR/organoclay nanocomposites

Small strain Young's moduli of natural rubber (NR)/organoclay nanocomposites were estimated using the Guth–Gold, Halpin–Tsai (HT), and Krieger–Dougherty (KD) models, and compared with experimental measurements of NR vulcanizates containing organo‐montmorillonite (OM) or organo‐sepiolite (OS). To account for the effect on modulus of the NR matrix of the vulcanization‐active modifier in the organoclay, a matrix modulus correction (MMC) term was derived from the vulcanization parameters of the nanocomposites. The KD model gave a better empirical fit with the experimental data than the Guth–Gold model, with both giving good agreement with particle shape factors estimated from transmission electron microscope (TEM) images. The HT model gave the best fit with experiment for both types of nanocomposite, and use of the MMC term meant that the empirical shape factor was sufficiently close to that estimated from TEM images that the model could potentially be used to accurately predict the Young's moduli of NR/OM and NR/OS nanocomposites. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1621–1627, 2011     

Free Volume of Montmorillonite/Styrene‐Butadiene Rubber Nanocomposites Estimated by Positron Annihilation Lifetime Spectroscopy

Summary: The size and concentration of free‐volume holes of two kinds of montmorillonite (MMT)/styrene‐butadiene rubber (SBR) nanocomposites were investigated by positron annihilation lifetime spectroscopy (PALS). Strong interfacial interaction caused an apparent reduction of the free‐volume fraction of rubber probably by depressing the formation of free‐volume holes in the interfacial region. Interfacial interaction in MMT/SBR nanocomposites was weaker than that in SBR filled with carbon black.

Dependence of normalized o‐Ps intensity of four kinds of composites on filler volume fraction.     

Features,Questions and Future Challenges in Layered Silicates Clay Nanocomposites with Semicrystalline Polymer Matrices

The present features review article discusses the crystallisation of the polymer matrix when containing silicate layers. The accent is put on nylons (polyamides) and poly(ethylene oxide) as typical hydrophilic polymers and, poly(propylene) from the hydrophobic group. The effects of the clay, either intercalated or exfoliated, on the crystallisation behaviour of the matrix are highlighted. In addition, the crucial aspects of the semicrystalline morphology of the matrix in the presence of the clay platelets are also debated. The overall crystallisation rate is reported to slow down for most of the crystallisable polymer matrices on account of a retarding growth effect exerted by the clay platelets. As far as the location of the exfoliated clay platelets in the polymer matrix is concerned, they are assumed to be rejected from the crystalline phase in the interspherulitic space.

     

High‐Performance Exfoliated Poly(propylene)/Clay Nanocomposites by In Situ Polymerization with a Novel Z–N/Clay Compound Catalyst

Highly exfoliated poly(propylene) (PP)/clay nanocomposites with obvious improvements in both the tensile strength and toughness have been prepared by a novel TiCl₄/MgCl₂/imidazolium‐modified montmorillonite (IOHMMT) compound catalysts. Through this approach, in situ propylene polymerization can actually take place between the silicate layers and lead not only to PP with a high isotacticity and molecular weight, but also to a highly exfoliated structure even at high clay content levels (as high as 19 wt.‐%).

     

Effects of Annealing on the Migration Behavior of PA6/Clay Nanocomposites

Summary: Migration of clay to the surface of nylon 6‐organically modified clay is investigated. The effect of annealing time and temperature on the migration of the clay is reported. Attenuated total reflectance FT‐IR spectrometry, X‐ray diffraction, and high‐resolution electronic microscopy are used in this study. The results obtained indicate that migration occurs predominantly in the samples with exfoliated structure. Migration increases in the temperature range of 250–275 °C. A further increase in temperature decreases the extent of migration. Migration increases with time at 250 °C. Annealing in the presence of oxygen decreases migration. It is suggested that the extent of migration depends on the concentration of the surfactant and the polymer in the exfoliated particles.

High‐resolution electronic microscopy image of an exfoliated nylon‐6/clay sample in which migration has occurred.     

Controlling the Deintercalation in Hydrogenated Nitrile Rubber (HNBR)/Organo‐Montmorillonite Nanocomposites by Curing with Peroxide

Summary: The effect of peroxide vulcanization on organoclay dispersion in hydrogenated nitrile rubber (HNBR)/organo‐montmorillonite (organo‐MMT) nanocomposites was investigated. Three types of organoclays were tested, one containing a primary amine and two bearing quaternary intercalants. In contrast to sulfur vulcanization, which in combination with primary amine intercalants produced a confined/deintercalated clay structure, the peroxide curing yielded well‐ordered intercalated nanocomposites. The tensile mechanical performance and oxygen permeability of the HNBR nanocomposites were determined.

Oxygen permeability coefficient ratio for the different HNBR films tested at 0 and 60% relative humidity (i.e., dry and wet conditions, respectively).     

Characterization of HDPE /Polyamide 6/ Nanocomposites Using Scanning-and Transmission Electron Microscopy

Summary: Preparation and morphology of high density polyethylene (HDPE)/ polyamide 6 (PA 6)/modified clay nanocomposites were studied. The ability of PA 6 in dispersing clays was used to prepare modified delaminated clays, which were then mixed with HDPE. Mixing was performed using melt processing in a torque rheometer equipped with roller rotors. After etching the materials with boiling toluene and formic acid at room temperature, the morphology was examined by SEM analyses, showing that the PA 6 formed the continuous phase and HDPE the dispersed phase. X-ray diffraction patterns show that the (001) peak of the clay is dramatically decreased and shifted to lower angles, indicating that intercalated/exfoliated nanocomposites are obtained. TEM analyses confirmed the typical structure of exfoliated nanocomposites. A scheme for the mechanism of exfoliation and/or intercalation of these HDPE /PA 6/ /organoclay nanocomposites is proposed.     

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。