Iranian polymer journal
Volume:20 Issue: 5, 2011

Open-cellular elastomeric nanocomposite foams were obtained by polymerizationof water-in-oil high internal phase emulsions (HIPEs) containing 2-ethylhexylacrylate, styrene, divinylbenzene, and organo-modified montmorillonite(org-MMT)s. The effects of various org-MMT contents on the emulsion viscosityand microcellular structure and mechanical properties of the resulting elastomericfoams were investigated. The results showed that the incorporation of modified clay(organoclay) led to lower emulsion torque value, approximately to a characteristic valueof the emulsion viscosity. Scanning electron microscopy (SEM) micrographs revealedthat the presence of modified clays, 1-5% (by weight), considerably influenced themicrostructure of the copolymer solid foam. For instance, the introduction of 1% (byweight) organoclay (Cloisite® 15A) decreased the mean void diameter from 5.47 to4.45 μm and the intercellular pore size from 1.39 to 0.86 μm. At above this content oforganoclay, the mean void diameter and intercellular pore size increased. Thepresence of organoclay may influence the separation phase behaviour within the polymerizingmonomeric organic phase and it may act as a co-surfactant to vary the sizesof voids and intercellular pores. X-Ray diffraction (XRD) patterns and transmissionelectron microscopy (TEM) micrographs showed an intercalated nanocompositestructure for the elastomeric composite foams containing Cloisite® 30B organoclay.TEM Micrographs showed that less hydrophobic Cloisite® 30B organoclay tends to belocated at the interface between aqueous and organic phases of emulsion, while incase of more hydrophobic organoclay, i.e., Cloisite® 15A, it finds its position away fromthe interface; inside the continuous organic phase of concentrated emulsion.Surprisingly, adding the organoclays to the emulsions lowers the compressivemechanical properties of the reinforced solid rubbery foams compared with thecopolymer foam without any reinforcement. On the whole significant improvement onthe compression set was observed.

Poly(vinyl alcohol) (PVA)/hydrotalcite (HT) composite nanofibres were preparedby electrospinning. First HT was pretreated by sodium dodecyl benzenesulphonate (SDBS) in order to improve its dispersability and stability in PVA. Themorphological structure and mechanical properties of the nanofibres were investigatedby scanning electron microscopy, transmission electron microscopy, X-ray diffractionanalysis, Fourier transform infrared spectroscopy and appropriate mechanical tests. Itis believed that because of good compatibility in weak acidic condition, PVA/HTsolution could be made into nanofibres with uniform fibre diameter. The structural studyshowed that some of the molecular chains of PVA are inserted into HT layers, allowingHT with wider layer spacing for more PVA chains to be situated between the layers,which led to better combination of PVA and HT. Also with the treated-HTjoined in, the intensity and position of crystalline absorption of PVA at 1140 cm-1showed no noticeable change, indicating HT did not undermine the crystallization ofPVA. In addition, the mechanical tests results showed that adding HT can improve tensilestrength of the PVA matrix.

In recent years it has been shown that electrically conducting polymers such aspolyaniline (PANI) in integrated coating applications are able to protect steel fromcorrosion due to formation of passive oxide layer on the metal surface. In this report,we present the comparative corrosion protection performance of the coatingscontaining nanopolyaniline and polyaniline/TiO2 nanocomposites (PTC) on carbonsteel in epoxy binder. The PANI was prepared by emulsion polymerization method ofaniline using ammonium persulphate. The synthesized polymers were characterized byFTIR, X-ray diffraction (XRD) and the particle size and surface morphology wereanalyzed by transmission electron microscopy technique. The corrosion protectionperformance of the coatings was evaluated by weight loss measurement in differentcorrosive media for 960 h and surface morphology was examined by scanning electronmicroscopy. Furthermore, immersion test was carried out in an aqueous solution ofNaCl for 720 h and corrosion of the panels was monitored by visual inspection. Thewater adsorption in the prepared coatings was also studied. In our study, it wasobserved that the PANI/TiO2 in epoxy coating showed better physico-mechanicalproperties as compared to nano-PANI containing coatings. The PANI/TiO2 could beuseful as an adhesion promoter and corrosion inhibitor.

Polypropylene-clay nanocomposites were prepared in solution and followed by amelt mixing process. The nanocomposites were prepared for 5% (by weight)organoclay with varying amounts of two oxidized polypropylene waxes (OPPWs)as compatibilizer. The clay dispersion was analyzed by X-ray diffraction (XRD),transmission electron microscopy and melt rheology technique. The extent ofintercalation in clay platelets was quantified by XRD analysis based on interactionsbetween OPPW and clay layers. A maximum of ca. 10% increase in clay basalspacing was observed. It was revealed that the degree of clay intercalation in solutiontechnique varies by the polarity of OPPW. In subsequent melt mixing process, the claydispersion was evaluated by XRD which correlated well with the variations of storagemoduli at low frequency region and displayed a pseudo solid-like behaviour. Therheological measurements also showed higher dispersion of clay platelets in PP matrixin the presence of OPPW. The increase in storage moduli especially at low frequencyregion implied that there were stronger interactions between Cloisite® 15A organoclaysand polymer chains when OPPW is present. The TEM images mainly suggested tocom-patibilizing effect of OPPW in clay intercalation. In spite of low mechanicalproperties of OPPW, the DMTA showed the highest modulus of glassy region innanocomposites with maximum OPPW content. These findings agreed well with eachother in co-intercalation effect of OPPW in PP nanocomposites.

Alarge number of studies using cone calorimeter have shown that nanoparticlesin even small quantities improve flammability resistance by reducing heatrelease and mass loss rate significantly. In recent years, nanoclay has beenincreasingly used as an alternative to traditional fire retardants to improve the strengthand fire retardancy of polymeric materials. They have distinct advantages overtraditional fillers in terms of production, amount of required additive of only 2-10% comparedto 20-70%. The objectives of this work were the numerical and experimentalevaluations of the flammability of the polymeric composite and nanocompositematerials under the external radiation heat flux. The theoretical modelling of mass lossand heat release rate based on conservation equations of mass and energy were thenconfirmed by the experimental data of cone calorimetry test. Running the computerprogramme and cone calorimeter, at 8×104 W/m2 external radiation heat flux condition,there were lower heat release rate of 30-50% and a lower mass loss of 20-40% fornanocomposites in comparison with composite counterparts. Nanocomposite samplesshowed excellent potential as thermal protection system because upon pyrolysis, theorganic-inorganic nanostructure in reinforcing the polymer can be converted into auniform ceramic layer which may lead to significantly higher resistance to oxidation andmechanical erosion compared to simple composites. Formation of this ceramic layer onchar formed from the pyrolysis of the nanocomposite at high temperature not onlyenhances the char mechanical strength, but also acts as secondary protection layer toprotect the lower remaining nanocomposite.

Cellulose/carbonated hydroxyapatite (CHA) nanocomposites were successfullyprepared in ionic liquid by microwave-assisted method and were characterizedby X-ray powder diffraction, thermogravimetric analysis, Fourier transforminfrared spectrometry and scanning electron microscopy. Ionic liquid acts simultaneouslyas a solvent and a microwave absorber for the synthesis of cellulose/CHAnanocomposites. The cellulose in nanocomposites displayed cellulose type II crystallinestructure. The XRD and FTIR results confirmed the products as cellulose/CHAnanocomposites. The SEM and TEM results indicated that the aggregated CHAnanorods were observed in the cellulose matrix. The effects of cellulose concentrationsand heating methods on the products were also investigated. The density of nanocompositeswas increased with higher cellulose concentration. Cellulose/CHA nanocompositeswith rough surface were formed in ionic liquid by microwave-assisted method,in contrast to the cellulose/HA nanocomposites with flake-like cellulose and rod-like HAprepared in N,N-dimethylacetamide by the microwave heating. A good example ofcombining green chemistry and functional materials, the microwave-assisted ionicliquid method for the synthesis of cellulose/CHA nanocomposites is capable to achievethe full product within 30 min. This method is fast, environmentally friendly and suitablefor the large-scale production of cellulose-based nanocomposites with minimalenvironmental impact. This nanocomposite is a very promising candidate in applicationof bioactive materials

One of the most serious problems encountered in poly(vinyl chloride) (PVC)processing is due to low thermal stability of the PVC. In this work, the presenceof organoclay and low density polyethylene (LDPE) of variable contents werestudied in relation to the thermal degradation of PVC. The samples were preparedusing an internal mixer with (10, 20 and 30 phr) LDPE and (1, 3, 5 and 7 phr) nanoclayat 180ºC and 45 rpm of rotor speed. The morphology of nanoclay was evaluated byX-ray diffraction and transmission electron microscopy. Thermal degradation wastracked by polyene and carbonyl indices using Fourier transform infrared and thermalgravimetric analysis. The results revealed that exfoliation morphology was obtained at1 and 3 phr concentrations of nanoclay and the intercalation morphology was observedat higher nanoparticle concentration. The addition of LDPE had no significant effect onthe dispersion status of nanoparticles. The lowest polyene and carbonyl indices wererelated to 1 phr concentration of nanoclay. TGA Results showed that the onsettemperature of degradation shifted to higher temperature due to the presence ofnanoparticles and LDPE and the highest shift was attributed to the sample containing1 phr of nanoclay and 10 phr of LDPE. Mechanical properties of the samples showeddirect correlations with nanoclay and LDPE contents and thermal degradation of PVC.The mechanisms for the prevention of thermal degradation reaction of PVC by LDPEand nanoparticle are proposed and discussed.

Adescriptive and historical account with experimental evidence is provided for theproduction feasibility of micro- and nanofibrils from structured-fibres usingexisting technologies. Blends of 6.25% polypropylene, 87.5% nylon 6 and 6.25%polypropylene grafted with maleic anhydride as compatibilizer (N6/PP-g-MAH/PP)were spun into continuous filaments yarns using a melt spinning unit (pilot plant) at thespeed of 2000 m/min. The yarn samples were drawn in a drawing unit with draw ratiosof 1.3 and 2.6. Samples were treated with formic acid (98%) to dissolve the nyloncomponent that forms the matrix of the bi-constituent filaments. Different analyticaltechniques including polarizing microscopy, scanning electron microscopy, FTIRspectroscopy, differential scanning calorimetry and wide angle X-ray diffraction wereused to examine the filaments and fibrils. It is shown that by existing technology it ispossible to produce polyblend filaments from two rather incompatible polymers, whilethe extraction of polypropylene micro and nanofibrils is possible either by decantationor Soxhlet using formic acid as solvent for nylon 6. The extracted fibrils were partiallycrystalline having melting temperature close to neat polypropylene. The fibrils havediameters less than one micrometer, down to less than 100 nm. By examining thefibrils, it was found that fibrils are partially crystalline with considerable molecularorientation.

The reduction in burst release of a new drug nanocarrier system was achieved byionic gelation of nanoparticles made of chitosan and tripolyphosphate. Capabilityof calcium alginate for reinforcement of the chitosan-tripolyphosphate nanoparticlematrix was studied. Bovine serum albumin (BSA) was loaded into nanoparticlesas a model drug. The final particle size, polydispersity index, entrapment efficiency andthe release rate of BSA were optimized in relation to variations in parameters such assodium alginate concentration, theoretical loading of BSA and degree of deacetylationof chitosan. It was found that increases in sodium alginate concentration resulted insmaller particle size, higher polydispersity index, lower entrapment efficiency and lowerrelease rate of BSA. The same parametric changes were observed for the theoreticalloading of BSA, with the exception of drug release which was followed by higher rate.Nanoparticles of chitosan-tripolyphosphate with a high degree of deacetylation led toproduction of smaller particle size, higher polydispersity index and entrapmentefficiency, and a faster drug-release profile. The experimental data of this studyrevealed that burst release decreased significantly in reinforced chitosan-tripolyphosphatenanoparticles.