Viscoelastic and surface properties of polymer complexes with fillers of different nature

Rheological and surface properties of polymer blends based on aqueous solutions of polyacryl-amide and polyvinyl alcohol were studied by viscometry and methods of penetration of a spherical indenter and detachment of a metal plate from a polymer body. The work of adhesion was examined in relation to the filler type and the time of formation of the polymer composites.     

Effect of ionizing radiation on the dynamic mechanical properties of an epoxy and a graphite fiber/epoxy composite

TGDDM/DDS epoxy and T300/NARMCO 5208 composite specimens were exposed to 0.5 MeV electrons to dose levels up to 10,000 Mrad, and the effects of radiation on the mechanical properties were characterized using dynamic mechanical analysis (DMA). In nominally cured specimens there remain unreacted epoxide groups because the epoxy system vitrifies during the cure, preventing additional reaction. DMA shows that ionizing radiation continues the reactions of epoxide groups. Also, the ultimate glass transition is shown to decrease monotonically with radiation dose. The room temperature elastic modulus of the epoxy increases slightly with radiation, but at temperatures exceeding 100°C there is a slight decrease with radiation. There is a dynamic loss phenomena associated with the composites, not seen in the epoxy, that is thought to be due to the interphase region between the fiber and the matrix.     

Improvement of PBO fiber surface and PBO/PPESK composite interface properties with air DBD plasma treatment

The interface of fibrous composites is a key factor to the whole properties of the composites. In this study, the effects of air dielectric barrier discharge (DBD) plasma discharge power density on surface properties of poly(p‐phenylene benzobisoxazole) (PBO) fiber and the interfacial adhesion of PBO fiber reinforced poly(phthalazinone ether sulfone ketone) (PPESK) composite were investigated by several characterization methods, including XPS, SEM, signal fiber tensile strength, interlaminar shear strength, and water absorption. After the air DBD plasma treatment at a power density of 41.4 W/cm³, XPS analysis showed that some polar functional groups were introduced on the PBO fiber surface, especially the emergence of a new oxygen‐containing group (?O–C = O group). SEM observations revealed that the air DBD plasma treatment had a great influence on surface morphologies of the PBO fiber, while the signal fiber tensile strength results showed only a small decline of 5.9% for the plasma‐treated fiber. Meanwhile, interlaminar shear strength value of PBO/PPESK composite was increased to 44.71 MPa by 34.5% and water absorption of the composite decreased from 0.46% for the untreated specimen to 0.27%. The results showed that the air DBD plasma treatment can effectively improve the properties of the PBO fiber surface and the PBO/PPESK composite interface. Results obtained from the above analyses also showed that both the fiber surface and the composite interface performance would be reduced when an undue plasma discharge power density was applied. Copyright © 2011 John Wiley & Sons, Ltd.     

The effect of surface modification with nitric acid on the mechanical and tribological properties of carbon fiber‐reinforced thermoplastic polyimide composite

Polyacrylamideacrylate (PAN)‐based carbon fibers were submitted to nitric acid oxidation treatments to improve the interfacial adhesion of the carbon fiber (CF)‐reinforced polyimide (CF/PI) composite. The carbon fiber surfaces were characterized by X‐ray photoelectron spectroscopy (XPS). Nitric acid oxidation not only affects the oxygen concentration but also produces an appreciable change in the nature of the chemical functions, namely the conversion of hydroxy‐type oxygen into carboxyl functions. Nitric acid oxidation treatment modifies the element constituting the fiber, the nitrogen concentration being about 1.2 times higher at the fiber external surface compared to the untreated one. The mechanical and tribological properties of the polymide (PI) composites reinforced by the carbon fibers treated with nitric acid oxidation were investigated. Results showed that the tensile strength of the CF/PI composites improved remarkably due to nitric acid treatment along with enhancement in friction and wear performance. Copyright © 2009 John Wiley & Sons, Ltd.     

Morphology and mechanical properties of extruded ribbons of LDPE/PA6 blends compatibilized with an ethylene-acrylic acid copolymer

Two grades of low density polyethylene (LDPE) were blended with polyamide-6 (PA) in the 75/25 and 25/75 wt/wt ratios and shaped into ribbons with a Brabender single screw extruder. An ethylene-acrylic acid copolymer (EAA) was used in the 2 phr concentration as a compatibilizer precursor (CP). The morphology of the ribbons and its evolution during high temperature annealing were investigated by scanning electron microscopy (SEM). The results confirmed that EAA does actually behave as a reactive compatibilizer for the LDPE/PA blends. In fact, in the presence of EAA, the interfacial adhesion is improved, the dispersion of the minor phase particles is enhanced and their tendency toward fibrillation is increased, especially for the blends with the higher molar mass LDPE grade. The mechanical properties of the latter blends were found to be considerably enhanced by the addition of EAA, whereas the improvement was relatively modest for the blends with the lower molar mass LDPE. The fracture properties of double end notched samples of the ribbons prepared with the blends containing the lower molar mass LDPE grade were also studied. It was shown that, despite of the increased interfacial adhesion caused by the presence of EAA, the latter plays a measurable positive effect on the fracture properties only for the blends with LDPE as the matrix.     

Theoretical study of the acid-base properties of the montmorillonite/electrolyte interface: influence of the surface heterogeneity and ionic strength on the potentiometric titration curves

The parallel shape of the potentiometric titration curves for montmorillonite suspension is explained using the surface complexation model and taking into account the surface heterogeneity. The homogeneous models give accurate predictions only if they assume unphysically large values of the equilibrium constants for the exchange process occurring on the basal plane. However, the assumption that the basal plane is energetically heterogeneous allows to fit the experimental data (reported by Avena and De Pauli [M. Avena, C.P. De Pauli, J. Colloid Interface Sci. 202 (1998) 195-204]) for reasonable values of exchange equilibrium constant equal to 1.26 (suggested by Fletcher and Sposito [P. Fletcher, G. Sposito, Clay Miner. 24 (1989) 375-391]). Moreover, we observed the typical behavior of point of zero net proton charge (pznpc) as a function of logarithm of the electrolyte concentration (log[C]). We showed that the slope of the linear dependence, pznpc=f(log[C]), is proportional to the number of isomorphic substitutions in the crystal phase, which was also observed in the experimental studies.     

Polyfunctional inorganic-organic hybrid materials: an unusual kind of NLO active layered mixed metal oxalates with tunable magnetic properties and very large second harmonic generation

Mixed M(II)/M(III) metal oxalates, as "stripes" connected through strong hydrogen bonding by para-dimethylaminobenzaldeide (DAMBA) and water, form an organic-inorganic 2D network that enables segregation in layers of the cationic organic NLO-phore trans-4-(4-dimethylaminostyryl)-1-methylpyridinium, [DAMS+]. The crystalline hybrid materials obtained have the general formula [DAMS]4[M2M'(C2O4)6].2DAMBA.2H2O (M = Rh, Fe, Cr; M' = Mn, Zn), and their overall three-dimensional packing is non-centrosymmetric and polar, therefore suitable for second harmonic generation (SHG). All the compounds investigated are characterized by an exceptional SHG activity, due both to the large molecular quadratic hyperpolarizability of [DAMS+] and to the efficiency of the crystalline network which organizes [DAMS+] into head-to-tail arranged J-type aggregates. The tunability of the pairs of metal ions allows exploiting also the magnetic functionality of the materials. Examples containing antiferro-, ferro-, and ferri-magnetic interactions (mediated by oxalato bridges) are obtained by coupling proper M(III) ions (Fe, Cr, Rh) with M(II) (Mn, Zn). This shed light on the role of weak next-nearest-neighbor interactions and main nearest-neighbor couplings along "stripes" of mixed M(II)/M(III) metal oxalates of the organic-inorganic 2D network, thus suggesting that these hybrid materials may display isotropic 1D magnetic properties along the mixed M(II)/M(III) metal oxalates "stripes".     

PET/R‐PP/PC blends by two‐stage reactive extrusion: effect of polypropylene reactively functionalized with an oxazoline group on morphology and mechanical properties

A series of PET/R‐PP/PC blends was studied in a chemical modification involving reactive extrusion with a ricinyl‐2‐oxazoline maleinate. The interfacial reaction between blend components were studied by the differential scanning calorimetry (DSC) and the scanning electron microscopy (SEM). The static tensile and flexural properties, and impact resistance response of the blends were tested. The phase morphology of the blends was of interpenetrating network (IPN) type according to SEM results. The blends offer excellent mechanical properties and improved impact strength as an effect of chemical reactions on reactive extrusion, even if PET waste and low PC contents (below 20%) have been used.     

The nature of the surface species formed on Au/TiO2 during the reaction of H2 and O2: an inelastic neutron scattering study

Inelastic neutron spectroscopy (INS) has been employed to identify surface species formed during the H2-O2 reaction on Au/TiO2 catalysts. Determination of the surface intermediates formed in this reaction is crucial to develop a mechanistic understanding for the direct vapor-phase propylene epoxidation reaction and synthesis of H2O2. Although the presence of intermediate hydroperoxo species (during these reactions) has been suggested in literature, it has never been demonstrated. Our studies provide direct evidence for the formation of surface hydroperoxo species during the H2-O2 reaction.     

Preparation and characterization of novel silk fibroin/2-(N,N-dimethylamino)ethyl methacrylate based composite hydrogels with enhanced mechanical properties for controlled release of cefixime

Hydrogels with improved mechanical properties have been particularly attractive for their applications in the biomedical area including wound healing. For this purpose, a series of novel composite hydrogels based on silk fibroin (SF) and 2-(N,N-dimethylamino) ethyl methacrylate (DMAEMA) were fabricated. The swelling and mechanical tests indicated that an optimum design of hydrogel was essential to provide a high degree of water uptake, higher tensile strength and elongation at break values. Here, the S40D60 was exhibited superior swelling and strong mechanical characteristics than all the other hydrogels with different compositions. Furthermore, it was observed that the cefixime was released from the formulation of S40D60 in a sustainable manner and the drug release rate can be controlled by pH of the dissolution medium. According to these findings, it is suggested that the optimal formulation of S40D60 would be effectively performed in situ drug therapy for wound healing.     

Recycled PP/EPDM/talc reinforced with bamboo fiber: Assessment of fiber and compatibilizer content on properties using factorial design

Thermoplastic composites reinforced with natural fibers have attracted the attention of many researchers, not only for environmental concerns, but also for economic reasons, recyclability, ease of processing, etc. One promising application is in the automotive industry due to their low cost and weight. This industry is increasingly pressured to produce vehicles that consume less fuel and are less polluting. Therefore, plastics reinforced with fibers are required to produce lighter parts to replace the much more abrasive glass fiber and mineral filled composites. One of the most widely used polymers in the automotive sector for manufacturing interior and exterior vehicle components is talc filled EPDM (ethylene-propylene-diene monomer) toughened polypropylene (PP). In this context, the aim of this study was to assess mechanical and thermal properties of bamboo fiber reinforced recycled talc filled PP/EPDM composites compatibilized with maleic anhydride grafted polypropylene (PP-g-MAH). Composites were prepared, according to a 2² factorial design with center point, in a Haake twin screw extruder with subsequent injection molding. Injected specimens were subjected to tensile, flexural, impact and fatigue testing. Morphological analyses were performed by scanning electron microscopy (SEM), and thermal analyses by thermogravimetry (TGA) and differential scanning calorimetry (DSC). Addition of bamboo fiber significantly increased tensile and bending strength, modulus and fatigue life, and decreased elongation at break and impact strength. On the other hand, addition of the compatibilizer had a positive effect only on tensile and flexural strength, and fatigue life whereas the effect was negative on elongation at break and impact strength. The addition of fiber and compatibilizer did not appreciably affect the matrix melting temperature, but slightly increased crystallization temperature and in some cases the degree of crystallinity.     

The reaction of tricarbon with acetylene: an ab initio/RRKM study of the potential energy surface and product branching ratios

Ab initio calculations of the potential energy surface for the C3(1Sigmag+)+C2H2(1Sigmag+) reaction have been performed at the RCCSD(T)/cc-pVQZ//B3LYP/6-311G(d,p) + ZPE[B3LYP/6-311G(d,p)] level with extrapolation to the complete basis set limit for key intermediates and products. These calculations have been followed by statistical calculations of reaction rate constants and product branching ratios. The results show the reaction to begin with the formation of the 3-(didehydrovinylidene)cyclopropene intermediate i1 or five-member ring isomer i7 with the entrance barriers of 7.6 and 13.8 kcal/mol, respectively. i1 rearranges to the other C5H2 isomers, including ethynylpropadienylidene i2, singlet pentadiynylidene i3, pentatetraenylidene i4, ethynylcyclopropenylidene i5, and four- and five-member ring structures i6, i7, and i8 by ring-closure and ring-opening processes and hydrogen migrations. i2, i3, and i4 lose a hydrogen atom to produce the most stable linear isomer of C5H with the overall reaction endothermicity of approximately 24 kcal/mol. H elimination from i5 leads to the formation of the cyclic C5H isomer, HC2C3, +H, 27 kcal/ mol above C3+C2H2. 1,1-H2 loss from i4 results in the linear pentacarbon C5+H2 products endothermic by 4 kcal/mol. The H elimination pathways occur without exit barriers, whereas the H2 loss from i4 proceeds via a tight transition state 26.4 kcal/mol above the reactants. The characteristic energy threshold for the reaction under single collision conditions is predicted be in the range of approximately 24 kcal/mol. Product branching ratios obtained by solving kinetic equations with individual rate constants calculated using RRKM and VTST theories for collision energies between 25 and 35 kcal/mol show that l-C5H+H are the dominant reaction products, whereas HC2C3+H and l-C5+H2 are minor products with branching ratios not exceeding 2.5% and 0.7%, respectively. The ethynylcyclopropenylidene isomer i5 is calculated to be the most stable C5H2 species, more favorable than triplet pentadiynylidene i3t by approximately 2 kcal/mol.     

ZnO nanoparticles as chain elasticity reducer and structural elasticity enhancer: Correlating the degradating role and localization of ZnO with the morphological and mechanical properties of PLA/PP/ZnO nanocomposite

The main purpose of this study was to investigate the effect of zinc oxide (ZnO) nanoparticles on the morphological, mechanical, thermal, and rheological properties of PLA/PP blend. In this regard, nanocomposites containing 1, 3, and 5 wt% of ZnO nanoparticles were prepared by melt mixing. In addition, three different mixing procedures were adopted to study their effects on the microstructure of nanocomposites. The rheological behaviors demonstrated a higher elasticity and less compatibility for two phases in the case of nanocomposites containing nanoparticles in harmony with the morphological observations. Accordingly, it was correlated to the elasticity originating from the interphase, anticipated coalescence of dispersed particles as a result of degradation of PLA chains triggered by ZnO nanoparticles (ZnO‐NPs) and also agglomeration of ZnO‐NPs depending on the content of nanoparticles and chosen mixing procedure. It was also found that mixing method puts a remarkable influence on the microstructure and rheological behavior of nanocomposites. Results of mechanical characterizations and thermogravimetric analysis (TGA) also confirmed the degradation induced by ZnO nanoparticles.     

Electropolishing of stainless steels in a choline chloride based ionic liquid: an electrochemical study with surface characterisation using SEM and atomic force microscopy

We have studied the anodic dissolution (electropolishing) of various stainless steel alloys in an ionic liquid comprising a 2 : 1 stoichiometric mix of ethylene glycol (EG) and choline chloride. We have used a combination of electrochemical and spectroscopic methods together with in situ liquid probe microscopy. We discuss the role and influence of the surface oxide passivation layer, characterized here by X-ray photoelectron spectroscopy (XPS) and linear sweep voltammetry, on the polishing process. We address the question of dealloying during the polish in order to contribute to our understanding of the viability of the ionic liquid as a replacement industrial electropolishing medium; the current commercial process uses a corrosive mixture of phosphoric and sulfuric acids. Also, we present data from ex situ and in situ liquid AFM studies giving both a qualitative and quantitative insight into the nature and scale of morphological changes at the steel surface during the polishing process.     

Polyester/organo‐graphite oxide composite: Effect of organically surface modified layered graphite on structure and physical properties of poly(ε‐caprolactone)

Silylated graphite oxide (sGO) was selected as suitable filler to improve the mechanical and electrical conductive properties of poly(ε‐caprolactone) (PCL). The composites of PCL and sGO were prepared by solution blending method. By modifying the surface of GO with silylation reagent (octyltrichlorosilane), the interlayer space of graphite oxide (GO) was increased and an excellent dispersion of the modified GO in the organic solvent and into the PCL matrix was achieved. The structures and physical properties of the sGO/PCL composites were characterized by the fourier transform infrared (FTIR), thermogravimetric analysis (TGA), wide angle X‐ray diffraction (WAXD) analysis, differential scanning calorimeter (DSC), tensile tests, dynamic mechanical analysis (DMA), and volume resistivity measurements. It indicated that the PCL/sGO composites formed an exfoliated structure from the WAXD study. The tensile strength and Young′s modulus of PCL increased with the addition of sGO. It was also found that a small amount of the sGO platelets in the composite could act as a nucleating agent and accelerated the crystallization of PCL. Further, the addition of the sGO platelets into the PCL matrix increased the volume electrical conductivity of PCL. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 294–301, 2010     

States of atoms and interatomic interactions in perovskite-like oxides: XXI. Effect of dopant nature on the magnetic properties of lanthanum manganites x (La1? y Y y )0.67Ca0.33MnO3-(1? x )La1? y Y y AlO3

A procedure of sol-gel synthesis was developed and solid solutions of lanthanum manganites doped with calcium and yttrium, containing 10 and 20% of yttrium, were obtained. The temperature and concentration dependences of the magnetic characteristics of the solid solutions were examined to reveal exchange interactions in the doped manganites and reasons for their different magnetic behavior. The properties of yttrium-substituted manganites vary nonmonotonically with increasing concentration of yttrium. Original Russian Text ? N.V. Chezhina. A.V. Fedorova, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 5, pp. 705–709. For communication XX, see [1].     

Structure and properties of star‐shaped solution‐polymerized styrene‐butadiene rubber and its co‐coagulated rubber filled with silica/carbon black‐I: morphological structure and mechanical properties

The morphological structure and mechanical properties of the star‐shaped solution‐polymerized styrene‐butadiene rubber (SSBR) and organically modified nanosilica powder/star‐shaped SSBR co‐coagulated rubber (N‐SSBR) both filled with silica/carbon black (CB) were studied. The results showed that, compared with SSBR, silica powder could be mixed into N‐SSBR much more rapidly, and N‐SSBR/SiO₂ nanocomposite had better filler‐dispersion and processability. N‐SSBR/SiO₂/CB vulcanizates displayed higher glass‐transition temperature and lower peak value of internal friction loss than SSBR/SiO₂/CB vulcanizates. In the N‐SSBR/SiO₂/CB vulcanizates, filler was dispersed in nano‐scale resulting in good mechanical properties. Composites filled with silica/CB doped filler exhibited more excellent mechanical properties than those filled with a single filler because of the better filler‐dispersion and stronger interfacial interaction with macromolecular chains. N‐SSBR/SiO₂/CB vulcanizates exhibited preferable performance in abrasion resistance and higher bound rubber content as the blending ratio of silica to CB was 20:30. Copyright © 2008 John Wiley & Sons, Ltd.