Rathanawan Magaraphan

Preparation, structure, properties and thermal behavior of rigid-rod polyimide/montmorillonite nanocomposites

Polyimide/montmorillonite nanocomposites were prepared from solution of poly(amic acid) precursors and the dodecyl-montmorillonite (DMONT) using N-methyl-2-pyrrolidone as a solvent. The cured films of the rigid-rod polyimide/DMONT hybrids as characterized by FTIR, TEM and WAXD were exfoliated nanocomposites at low DMONT content (<1 wt.%) and partially exfoliated nanocomposites at high DMONT content (containing aggregates of DMONT). The nanocomposite showed optimum properties at 3 wt.% DMONT with low water absorption, improved mechanical strength and modulus, and high dielectric strength. The clay content significantly influences thermal behavior of the nanocomposite films, such as thermal expansion coefficient (CTE), glass transition and yielding temperatures of the rigid-rod and flexible polyimide nanocomposites. It was found that the rigid polyimide matrix gave a superior thermal behavior; i.e. lower CTE, higher glass transition and yielding temperatures than the flexible ones. Effect of DMONT content was significant at high temperature operation where a side reaction of dodecylamine and a poly(amic acid) should be aware to cause a reduction in degree of imidisation and glass transition temperature and the formation of silicate layer aggregates. High DMONT content nanocomposites (aggregates were formed) showed high yielding temperatures indicating the suppression of polymer flow by the rigidity of the clay. The flexible polyimide nanocomposites showed higher thermal deformation than the rigid ones. Moreover, the rigid polyimide nanocomposite with 9 wt.% DMONT showed a thermally reversible behavior indicating that the silicate layers efficiently suppressed the deformation of the rigid polyimide.

Development of Biodegradable Foamlike Materials Based on Casein and Sodium Montmorillonite Clay

Biodegradable foamlike materials based on a naturally occurring polymer (casein protein) and sodium montmorillonite clay (Na+ -MMT) were produced through a simple freeze-drying process. By utilizing DL-glyceraldehyde (GC) as a chemical cross-linking agent, the structural integrity of these new aerogels were remarkably improved when compared to those of the control system (without GC), with a minimal increase in the density from 0.11 to 0.12 g cm⁻³. The degree of perfection of the foamlike structures was another parameter that had a significant influence on the physical and thermal performances of the low density composites. The biodegradability of the aerogels was investigated in terms of the carbon dioxide (CO₂) evolution for up to 8 weeks in compost media under controlled conditions.

Preparation and characterization of polybenzoxazine-clay immiscible nanocomposite

Abstract An immiscible polymer-clay nanocomposite has been synthesized consisting of dispersed layers of organically modified montmorillonite (OMOM) in a polybenzoxazine matrix as shown by thermogravimetry, wide angle x-ray diffraction (WAXD), and transmission electron microscopy. Five small protonated amines showed high ion-exchangeability. The spacing of the silicate layers is strongly dependent on the size or molecular weight of the amine derivative and the solvent type. Binary solvents (5% mehthanol in toluene) exhibited superior ability to swell OMOM. Finally, WAXD results revealed that the silicate layer expansion of all polybenzoxazine-OMOM nanocomposites prepared from either melt or solution methods were similar, about 4 Å increment. This was correlated with TEM results showing the aggregation of silicate layers indicating that all prepared OMOM are immiscible with the polymer matrix. These results suggested that the compatibility between amine modifying agents and benzoxazine played the most important role for the characteristics of the nanocomposite.

MFI zeolite synthesis directly from silatrane via sol–gel process and microwave technique

Abstract Silatrane was synthesized from the reaction of SiO 2 and triethanolamine using ethylene glycol as solvent under N 2 atmosphere. The obtained silatrane complex was further used as a Si source for MFI zeolite synthesis. The effect of Na + , OH − , and tetrabutyl ammonium hydroxide (organic template) concentration in the reaction mixture was studied. The reaction temperature was varied using the microwave heating technique. The effect of aging the reaction mixture at room temperature for varying times was also investigated. The rate of MFI formation decreases with increasing Na + , decreasing OH − , or lower template concentration. Higher temperatures correlate to shorter aging and heating times. At fixed temperature, longer aging times lead to shorter heating times. It was found that a longer aging time is more important to achieve high crystallinity than the heating time.

Morphology study of MFI zeolite synthesized directly from silatrane and alumatrane via the sol–gel process and microwave heating

Silatrane and alumatrane were prepared via the oxide one-pot process, and used as precursors for synthesis of MFI. The effect on MFI morphology of tetra-butyl ammonium hydroxide (TBA) and tetra-propyl ammonium bromide (TPA) as organic templates was compared. The influence of aging time, and of the sodium and hydroxide content of alumatrane were also investigated. TPA shows better performance as a template for the MFI synthesis than TBA by decreasing aging and heating times. Different templates produce different morphologies and growth directions of MFI crystals due to the steric effect of the template molecule. Increase of alumatrane loading retards MFI crystal formation, but no significant effect is observed on varying sodium and hydroxide concentrations as previously found for pure silicate MFI.

Electrically conductive compounds of polycarbonate, liquid crystalline polymer, and multiwalled carbon nanotubes

A thermotropic liquid crystalline polymer (LCP) was blended with polycarbonate (PC) and multiwalled carbon nanotube (CNT) with the goal of improving electrical conductivity andmechanical properties over PC. The LCP was anticipated to produce fibrillar domains in PC and help improve the mechanical properties. The study was carried out using two grades of LCP--Vectra A950 (VA950) and Vectra V400P (V400P). The compounds contained 20wt% LCP and 0.5 to 15wt% CNT. The compounds were prepared by melt-blending in a twin-screw minicompounder and then injection molded using a mini-injection molder. The fibrillar domains of LCP were found only in the case of PC/VA950 blend. However, these fibrils turned into droplets in the presence of CNT. It was found that CNT preferentially remained inside the LCP domains as predicted fromthe value of spreading coefficient. The electrical conductivity showed the following order with the numbers in parenthesis representing the electrical percolation threshold of the compounds: PC/CNT (1%) > PC/VA950P/CNT (1%) > PC/V400P/CNT (3%). The storage modulus showed improvements with the addition of CNT and VA950.

pH-Sensitive PP/Clay Nanocomposites for Beverage Smart Packaging

The modification of clay by ion exchange reaction with cationic surfactants plays an important role in the greater interlayer spacing of Na-bentonite. Four types of quaternary alkyl ammonium ions, DO AM, DOEM, DCEM and DTDM, were introduced into the clay in order to investigate the effects of intercalation of the cationic surfactants. The organobentonites were characterized by XRD, FTIR and TGA. From WAXD patterns, DOEM-B exhibited the largest interlayer spacing, promissing the most suitable choice for producing PP/clay nanocomposites. The nanoclay composites incorporating pH indicator were melt compounding through a twin screw extruder using Surlynreg as a reactive compatibilizer. Subsequently, the nanoclay composites were fabricated into the sample sheet for pH-sensitive test.

Functionalized Porous Clay Heterostructure for Heavy Metal Adsorption from Wastewater

A wide variety of toxic metals and organic chemicals are discharged to the environment as industrial or laboratory wastes, causing serious water, air, and soil pollution. One of the interesting materials for using as the adsorbents to adsorb these pollutants in wastewater treatment is porous clay heterostructures (PCHs). These porous materials are obtained by the surfactant-directed assembly of mesostructured silica within clay layers. In the present work, the PCHs were synthesized within the galleries of Na-bentonite clay by the polymerization of tetraethoxysilane (TEOS) in surfactant templates (cetyltrimethylammonium ion and dodecylamine). These PCHs were functionalized with 3-mercaptopropyltrimethoxysilane (MPTMS) to obtain the MP-PCH utilizing as heavy metal adsorbent. According to N2 adsorption-desorption data, the results show that PCH has surface areas of 549.7 m2/g, an average pore diameter in the supermicropore to small mesopore range of 3.16 nm, and a pore volume of 0.45 cc/g, while MP-PCH shows pore parameters of 488.7 m2/g, 3.28 nm, and 0.48 cc/g, respectively. Moreover, the MP-PCH was investigated the adsorption properties which concerned with their function as adsorbents for aqueous solution. The results show that the adsorption capacity of MP-PCH was 0.22, 0.24, 0.50 , 0.48 and 0.11 mmol/g for Cd, Cu, Mn, Ni and Pb, respectively. They point out the potential for utilizing as the heavy metal adsorbents in wastewater treatment.

Admicellar Polymerization of Polystyrene on Natural Rubber Particles

Admicellar polymerization is a reaction for coating a thin-film of polymer on a surface. The process consists of the polymerization of the adsolubilized monomer in the hydrophobic regions of the surfactant bilayers that adsorbed on the substrate surface. In this research, the admicellar polymerization of polystyrene was carried out using micron to submicron size natural rubber particles as substrates. Cetyl trimethyl ammonium bromide (CTAB) was used to form the surfactant template. The adsorption isotherm of CTAB was determined in the absence and presence of salt. Styrene adsolubilization was found to increase with initial styrene concentration and in the presence of salt. The synthesized polystyrene in the molecular bilayer of micelles surrounding the natural rubber particles was characterized by optical microscope, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The observed morphology of the rubber particles after reaction was clearly two phases, a core-shell structure having the natural rubber core covered by the polystyrene shell. These core-shell particles were spheres and aggregated strongly in the emulsion. Effect of initiator type was investigated. The synthesized products showed core-shell morphology, which was still obtained after heating but after cooling phase inversion occurred and showed polystyrene-rich core and natural rubber-rich shell. Thin lamellar of both components was found in both polystyrene-rich core and natural rubber-rich shell making unique morphology and extended single transition of thermal decomposition. FTIR results show characteristic peaks of natural rubber and polystyrene and the absorbance of styrene increases with increasing styrene content. The TGA result showed that the decomposition temperatures of the products were altered by the amount of polystyrene.

High Internal Phase Emulsion Foams (HIPE) Filled with Organo-Bentonite: Hybrid Organic-Inorganic Porous Clay Heterostructures (HPCH) versus Organo-Modified Bentonite (MOD)

Organoclay derived from Na-bentonite can offer an alternative used as an inorganic filler for high internal phase emulsiom foams. Two types of organoclay, hybrid organic–inorganic porous clay heterostructures (HPCH), derived from organo–bentonite which prepared through surfactant–directed assembly of tetraethoxysilane (TEOS)/methyltetraethoxysilane (MTS) into galleries of the clay mineral, and organo-modified bentonite (MOD) treated with quaternary alkyl ammonium cation by ion exchange reaction, were used as a reinforcing agent for poly(divinylbenzene; DVB)polyHIPE foams in this study. Poly(DVB)polyHIPE foams filled with organo-bentonite (MOD and HPCH) loadings of 0, 1, 3, 5, and 10 wt% were successfully prepared using the HIPE technique. To study the effects of the organoclay on morphology, surface area, and mechanical properties of the prepared poly(DVB)polyHIPE foams, SEM, N2 adsorption-desorption, and a Lloyd Universal testing machine were employed. It was demonstrated that the addition of organo-bentonite (both MOD and HPCH) into PolyHIPE foams resulted in the enhancement of physical properties of the poly(DVB)polyHIPE foams. The incorporation of layered silicate in the polymer matrix were supported by SEM images, which shown that the roughness of the polymer wall surfaces appeared to increase due to the presence of organoclay. It was established that the use of organo–bentonite, both HPCH and MOD, as inorganic filler for poly(DVB)polyHIPE, has an effect on improving the surface area of the obtained materials. However, higher improvement in surface properties was achieved with poly(DVB)polyHIPE filled with HPCH when compared with poly(DVB)polyHIPE foams filled with MOD. This is because of the surface charateristic of the HPCH which is a combination of micro– and mesoporosity between each layered of silicates and gas molecules might be able to adsorbed into these porous structures. Mechanical properties of the filled poly(DVB)polyHIPE foams were found to improve when compared to the neat poly(DVB)polyHIPE. Highest Young’s modulus and compressive stress were observed at 5 wt% organoclay loading. It was clearly demonstrated in this study that the suitable content of