Preparation and properties of EPDM–clay hybrids

Volume Dependence of Hydrogen Diffusion for Sorption and Desorption Processes in Cylindrical-Shaped Polymers

In the actual application of gas transport properties under high pressure, the important factors are sample size dependence and permeation efficiency, related to gas sorption. With a modified volumetric analysis technique, we firstly measured the overall diffusion properties and equilibrium times for reaching the saturation of hydrogen content in both hydrogen sorption and desorption processes. The measured parameters of total uptake (C_∞), total desorbed content (C₀), diffusion coefficient in sorption (D_s), diffusion coefficient in desorption (D_d), sorption equilibrium time (t_s) and desorption equilibrium time (t_d) of hydrogen in two polymers were determined relative to the diameter and thickness of the cylindrical-shaped polymers in the two processes. C_∞ and C₀ did not demonstrate an appreciable volume dependence for all polymers. The identical values of C_∞ and C₀ indicate the reversibility between sorption and desorption, which is interpreted by the occurrence of physisorption by sorbed hydrogen molecules. However, the measured diffusivity of the polymers was found to be increased with increasing thickness above 5 mm. Moreover, the larger D_d values measured in the desorption process compared to D_s may be attributed to an increased amorphous phase and volume swelling caused by increased hydrogen voids and polymer chain scission after decompression. The t_s and t_d were found to be linearly proportional to the square of the thickness above an aspect ratio of 3.7, which was consistent with the numerical simulations based on the solution of Fick's law. This finding could be used to predict the t_s in a polymer without any measurement, depending on the sample size.

Thermostable water reservoirs in the interlayer space of a sodium hectorite clay through the intercalation of γ-aminopropyl(dimethyl)ethoxysilane in toluene

Treatment of Na⁺-based hectorite LAPONITE® (LAP) and of Na⁺-montmorillonite (MMT) with a homologous series of γ-aminopropyl(methyl)_x(ethoxy)_ysilanes (x + y = 3, y > 0) in toluene was studied by means of thermogravimetric analysis coupled with mass spectrometry, infrared spectroscopy, ²⁹Si and ²³Na solid-state nuclear magnetic resonance spectroscopy and powder X-ray diffraction. The triethoxy silane (APTS) exclusively grafts on the clays' edges as branched oligomers whereas both the monoethoxy silane (APMS) and the diethoxy silane (APDS) are also intercalated, the latter as linear oligomers. Intercalation of APMS varies for MMT and LAP: MMT hosts the smallest amounts of the silanes with marginal increase of the basal distance and no stabilization of water. On the contrary, LAP accommodates the largest amount of guests in the form of monomeric APMS which yields the largest increase of the basal distance and stabilizes water up to 200 °C when APMS dimerizes. APMS stabilization is attributed to intramolecular Si-O-H-NH₂ hydrogen bonds and the hydrophobic geminal methyl groups together with the trimethylene sides of the cyclic monomers are thought to compartmentalize the hydrated sodium sites. The high temperature release of water from APMS@LAP is discussed in the light of potentially triggered interphase degradation in composite materials for recycling purposes.

Preparation and Characteristics of a Novel Silicone Rubber Nanocomposite Based on Organophilic Montmorillonite

Novel room-temperature-vulcanized silicone rubber (RTV-SR)/organic montmorillonite (OMMT) nanocomposites were prepared by a solution intercalation process. Di(2-oxyethyl)-12 alkane- 3 methyl-amine chloride was used as the intercalation agent to treat Na°-montmorillonite and form a new kind of OMMT. Four types of RTV-SR/OMMT composites were synthesized with different amounts of OMMT. Properties such as tensile strength, differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) were measured and compared. A combination of Fourier transform infrared spectroscopy (FT-IR), wide angle X-ray diffraction (WAXD) and transmission electronic microscopy (TEM) studies showed that RTV-SR/OMMT composites were on the nanometer scale and the presence of OMMT interfered with the segmented structure of RTV-SR, due to the reaction between the monomer and the intercalation agent. Results showed that the RTV-SR system with 10 phr OMMT has the best physical and mechanical properties due to the exfoliation of OMMT and the resultant nano-effect on the system

Novel synergistic combinations of amphiphilic fatty acid derivatives for high-performance rubber–organoclay nanocomposites

Synergistic binary combinations of fatty acid derivatives have remarkably enhanced the performance of a rubber–organoclay nanocomposite.

Properties of vulcanized polyisoprene rubber composites filled with opalized white tuff and precipitated silica

Opalized white tuff (OWT) with 40 μm average particle size and 39.3 m²/g specific surface area has been introduced into polyisoprene rubber (NR). Their reinforcing effects were evaluated by comparisons with those from precipitated silica (PSi). The cure characteristic, apparent activation energy of cross-link (E_ac) and reversion (E_ar), and mechanical properties of a variety of composites based on these rubbers were studied. This was done using vulcanization techniques, mechanical testing, and scanning electron microscopy (SEM). The results showed that OWT can greatly improve the vulcanizing process by shortening the time of optimum cure (t_c90) and the scorch time (t_s2) of cross-linked rubber composites, which improves production efficiency and operational security. The rubber composites filled with 50 phr of OWT were found to have good mechanical and elastomeric properties. The tensile strengths of the NR/OWT composites are close to those of NR/PSi composites, but the tear strength and modulus are not as good as the corresponding properties of those containing precipitated silica. Morphology results revealed that the OWT is poorly dispersed in the rubber matrix. According to that, the lower interactions between OWT and polyisoprene rubber macromolecules are obtained, but similar mechanical properties of NR/OWT (100/50) rubber composites compared with NR/PSi (100/50) rubber composites are resulted.

Preparation and Properties of EPDM/NBR/Organoclay Nanocomposites

In this research work, three different types of nano-composites based on EPDM/NBR blend (70/30 wt.%) have been prepared: one type including Cloisite 20A in EPDM phase, the other one containing Cloisite 30B in NBR phase and the third type consisting of Cloisite 20A in EPDM and Cloisite 30B in NBR phases simultaneously (called EN-xAB). XRD and TEM techniques showed intercalated or exfoliated structures for all types of nano-composites. According to SEM results, the most roughness of the surface was observed at EN-xAB nano-composites. Cure characteristics of the samples showed that the lowest scorch and cure time and highest crosslink density was devoted to EN-xAB samples. Comparison of mechanical properties of the nano-composites showed that the best properties were found in the samples consisted of both types of organo-clays simultaneously.

Synthesis and characterization of cationic surfactants in the preparation of organobentonite and study their effectiveness on the properties of styrene-butadiene rubber/bentonite composites

Two cationic surfactants ( N-isopropyl- N, N-dimethyldodecan-1-aminium bromide (S1) and N-isopropyl- N, N-dimethylhexadecan-1-aminium bromide (S2)) are synthesized. The chemical structure of the synthesized surfactants was confirmed by Fourier transform infrared (FTIR) and 1H Nuclear magnetic resonance spectroscopy. Critical micelle concentration (CMC) of the synthesized cationic surfactants was determined. CMC decreased with increasing alkyl chain length. Organobentonites are prepared using cationic surfactants (S1 and S2) and characterized by x-ray diffraction (XRD), FTIR spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy. Results of XRD, FTIR, SEM and TGA showed that the surfactants were intercalated into the interlamellar space of bentonite. Organobentonites fillers were added to styrene-butadiene rubber and cured by conventional vulcanization system. The filler loading was varied from 0 to 10 parts per hundred parts of rubber (phr). The compounds were characterized with respect to their curing characteristics and mechanical properties. The vulcanization rate and torque value of the organobentonites compounds are sensibly higher than the unmodified bentonite compound.

MONTMORILLONITE-REINFORCED NATURAL RUBBER NANOCOMPOSITES THROUGH EMULSION STABILIZATION–DESTABILIZATION METHOD

A nanoplatelet of montmorillonite (MMT) was incorporated in the natural rubber (NR) matrix at a high loading content using a newly developed stabilization–destabilization process in the colloid states. Examination of the surface charge of the colloid drops by zeta potential measurement led to the identification of the stable and unstable conditions of the colloid mixture as well as each colloid system as a function of pH. The stabilized mixture of the MMT and NR colloids was subsequently destabilized by changing the pH of the mixture to achieve a well-dispersed and intercalated NR/MMT precipitate. The resulting NR/MMT nanocomposites provided an exfoliated MMT morphology up to 25 phr, and the mechanical properties and aging tolerance of the resulting nanocomposite vulcanizates were substantially enhanced by the incorporated MMT nanofillers. The developed stabilization–destabilization methodology ensured a highly loaded MMT rubber composite system, which could be used to obtain high performance NR/MMT nanocomposite systems with ease without using high-shear processing techniques.