Showing papers in "Journal of Macromolecular Science, Part B in 2011"

Influence of Crosslink Density on Mechanical Properties of Natural Rubber Vulcanizates

Abstract: Crosslink density is an important structural parameter for cured rubber. Natural rubber (NR) vulcanizates with different crosslink densities were obtained through using different sulfur and accelerator amounts and different accelerator types. The crosslink density was characterized by an 1 H-NMR technique and its influence on mechanical properties, such as Shore A hardness, 300% modulus, tensile strength, and elongation at break, of NR vulcanizates was investigated. The results showed that both the sulfur amount and the accelerator type and amount had an influence on the crosslink density of the NR networks. The relationship between total crosslink density and mechanical properties was also studied. The results, by changing either the sulfur or the accelerator amount, showed that tensile strength of NR vulcanizates reached maximum value when the total crosslink density was around 13.5 × 10−5 mol/cm3, equivalently the average molecular weight of the intercrosslink chains (Mc) was around 7000 g/mol. The max...

Tuning of Lower Critical Solution Temperature (LCST) of Poly(N-Isopropylacrylamide-co-Acrylic acid) Hydrogels

Abstract: Temperature-responsive hydrogel with a lower critical solution temperature (LCST) close to human body temperature was prepared. Crosslinked N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) copolymer networks were synthesized at various monomer ratios in the presence of ammonium persulfate (APS), N,N′-methylenebisacrylamide (NMBA) and N,N,N′,N′-tetramethylethylenediamine (TEMED) via a redox polymerization method. The resulting hydrogels possessed thermo- and pH-responsive characteristics. They were characterized in terms of swelling ratio, volume change, water uptake and diffusivity, water vapor uptake and diffusivity, and phase transition temperature. The water liquid and vapor diffusion coefficients for all the synthesized hydrogels were higher than the literature data, implying higher rates for drug release. The LCST of the hydrogel increased with higher AAc content in the copolymer. The gel containing 1.8% AAc exhibited an LCST similar to human body temperature, demonstrating a potential use in dr...

Electrospinning of Poly(Hydroxybutyrate-co-hydroxyvalerate) Fibrous Scaffolds for Tissue Engineering Applications: Effects of Electrospinning Parameters and Solution Properties

Abstract: Electrospinning, a technology capable of fabricating ultrafine fibers (microfibers and nanofibers), has been investigated by various research groups for the production of fibrous biopolymer membranes for potential medical applications. In this study, poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), a natural, biocompatible, and biodegradable polymer, was successfully electrospun to form nonwoven fibrous mats. The effects of different electrospinning parameters (solution feeding rate, applied voltage, working distance and needle size) and polymer solution properties (concentration, viscosity and conductivity) on fiber diameter and morphology were systematically studied and causes for these effects are discussed. The formation of beaded fibers was investigated and the mechanism presented. It was shown that by varying electrospinning parameters within the processing window that was determined in this study, the diameter of electrospun PHBV fibers could be adjusted from a few hundred nanometers to a few micro...

pH-Sensitive Poly(Vinyl Alcohol)/Sodium Carboxymethylcellulose Hydrogel Beads for Drug Delivery

Abstract: A series of pH-sensitive hydrogel beads were prepared composed of poly(vinyl alcohol) (PVA) and sodium carboxymethylcellulose (CMC) by using Fe3+ crosslinking and freeze-thawing (FT) cycle techniques. The mixed solution of CMC and PVA was firstly crosslinked with Fe3+ to form beads and then subjected to freezing-thawing cycles for further crosslinking. The formation of hydrogel was confirmed by Fourier transform infrared spectroscopy (FTIR). The gelling rate in ferric solution and the swelling and pH-senstive properties of the hydrogel beads were investigated. The encapsulation efficiency and in-vitro release properties of beads were also evaluated using Bovine serum albumin as model drug. The pH sensitivity and the release rate increased with increasing CMC content. These results suggest that the PVA/CMC hgdrogel beads should be useful as pH-sensitive drug delivery systems for bioactive agents.

Influence of the Polymer/Inorganic Filler Interface on the Mechanical, Thermal, and Flame Retardant Properties of Polypropylene/Magnesium Hydroxide Composites

Abstract: The relationship between the interface structure and the macroscopic properties of composites composed of isotactic polypropylene (iPP) and magnesium hydroxide (MH) was investigated with a focus on mechanical properties, thermal stability, and flame retardancy. Surface treatment of MH was carried out using dodecanoic acid (DA) and dodecylphosphate (DP), both of which interacted with MH to form submonolayer coverages. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed that both organic reagents adhere to the MH surface via ionic interactions. Even low amounts of organic reagents on the MH surface were sufficient to improve the mechanical, thermal, and flame retardant properties of the composites. The incorporation of 1.8 wt% of DP in (70/30) iPP/MH-DP composite decreased the peak heat release rate (PkHRR) to 39% compared with that of neat iPP. Since the effects of DA with the same dodecyl chains were not significant, it is concluded that the phosphate groups ...

Effect of Jet Swell and Jet Stretch on the Structure of Wet-Spun Polyacrylonitrile Fiber

Abstract: The jet swell effect in the wet spinning of polyacrylonitrile (PAN) fiber was studied by optical microscopy and the jet swell ratio was obtained through directly measuring the diameter of the freely extruded fibers. For reflecting the actual drawing situation of the fibers in the coagulation process, the jet stretches were then corrected from the apparent values to the true values, and their effect on the cross-sectional morphology, internal structure, and orientation of the wet-spun PAN fibers was studied by optical microscopy, scanning electron microscopy, and X-ray diffraction, respectively. The results showed that jet stretch plays an important role in eliminating the adverse effects caused by the jet swell effect and affects the fiber structure; PAN fibers of uniform denier, dense and homogenous structure, and high orientation can only be obtained at a suitable jet stretch.

Investigation on the Tribological Properties of POM Modified by Nano-PTFE

Abstract: The tribological properties of polyoxymethylene (POM) modified by nano-polytetrafluorethylene (nano-PTFE) were investigated by a block-on-ring wear tester. For comparison, modified POM with micro-polytetrafluoroethylene (micro-PTFE) was also studied. The modified POM with a much lower concentration of nano-PTFE showed the similar tribological properties compared with POM modified by micro-PTFE. The friction coefficient decreased with the increase of nano-PTFE, while the wear rate showed the lowest value when the concentration of nano-PTFE was 2%. Scanning electron microscope (SEM) micrographs revealed that transfer films played an important role in the friction process. The transfer films decreased and stabilized the friction coefficient. Comparing to POM/2%nano-PTFE, when the concentration of nano-PTFE reached 4%, the mechanical properties decreased significantly, possibly due to poor dispersion of nano-PTFE.

A Study on Effect of Waviness on Mechanical Properties of Multi-Walled Carbon Nanotube/Epoxy Composites Using Modified Halpin–Tsai Theory

Abstract: In order to improve the precision in prediction of mechanical properties of multi-walled carbon nanotubes (MWNTs)/epoxy composites, the effect of waviness of nanotubes is considered by applying a correction factor to a modified Halpin–Tsai equation Data validation was carried out through the comparison of theoretical data with real mechanical test results obtained by the authors and in the literature Tensile tests of various weight percents (wt%) of MWNT/epoxy composites were carried out to obtain the mechanical properties of MWNT/epoxy composites Applicability of the proposed modification of Halpin–Tsai equation was endorsed by the experimental results and was found to be more accurate in comparison with results obtained from the same equation without considering the waviness effect

Crystallization and Thermal Conductivity of CaCO3 Nanoparticle Filled Polypropylene

Abstract: Isotactic polypropylene (IPP) and calcium carbonate (CaCO3) nanocomposites were prepared by melt extrusion in a twinscrew extruder. The effect of CaCO3 nanoparticles on the crystallization and thermal conductivity (TC) of PP was studied by thermal analysis (DSC) and thermal conductivity analysis (TCA). The introduction of CaCO3 nanoparticles resulted in an increase in crystallinity. The incorporation of this nanoparticle (up to 15 phr) caused a significant increase of TC of PP, especially for larger filler content. Several models were used for prediction of TC of the nanocomposites. The experimental results had a good correlation with the Ce Wen Nan Model.

Synthesis and Aqueous Solution Properties of a Novel NonIonic, Amphiphilic Comb-Type Polyacrylamide

Abstract: Nowadays comb-type polyacrylamides are deemed to be the most promising oil-displacing agent in the field of enhanced oil recovery (EOR). We describe the synthesis of a nonionic, amphiphilic macromer (OPAE) with acrylic acid (AA) and t-octylphenoxypolyoxyehylene (OP) by an esterification reaction. The macromer was then copolymerized with acrylamide (AM) under a free radical initiator system and a comb-type modified polyacrylamide (MPAM) was obtained. The structures of OPAE and the MPAM were characterized by Fourier transform infrared (FTIR), 1H nuclear magnetic resonance (NMR) and dynamic laser light scattering. In order to compare with partially hydrolyzed polyacrylamide (HPAM), the aqueous solution of the MPAM had a higher apparent viscosity, especially in brine. We suggest that the reason was that the branched chains enhanced the rigidity of the MPAM, and made the molecules have a larger hydrodynamic radius, especially in brine, endowing the copolymer with excellent salt tolerance.

A New Equation between Surface Tensions and Solubility Parameters without Molar Volume Parameters Simultaneously Fitting Polymers and Solvents

Abstract: Both surface tension and solubility parameter are decided by molecular interactions. There are several empirical equations describing their connection. However, at least two limitations exist for them: polymers cannot be treated and only apolar or weakly polar solvents can be fitted. We found when only the dispersive properties were considered, for 37 solvents and 22 polymers, a linear relationship exists between γ d and γ/δ2/3 d , fitted by a new equation. Compared with the previous equations, the value of the new equation is that most solvents and common polymers could be treated simultaneously. This equation will be of value for estimating the accuracy of reported surface tension data or solubility parameters of polymers.

Synthetic Aliphatic Biodegradable Poly(Butylene Succinate)/MWNT Nanocomposite Foams and Their Physical Characteristics

Abstract: Synthetic aliphatic biodegradable poly(butylene succinate) (PBS) nanocomposites with multiwalled carbon nanotube (MWNT) were investigated to study the effects of the preparation method and MWNTs on physical characteristics of biodegradable polymer nanocomposite foams. PBS nanocomposites were prepared by the solution blending and melt mixing methods. Nanocomposites of PBS/MWNT were also prepared by the SOAM method, where the solution-blended nanocomposites were further mixed in the melt state. The dispersion of MWNTs in the PBS matrix was characterized by FT-Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), and field-emission transmission electron microscopy (FE-TEM). The mechanical and thermal properties of the PBS nanocomposites were measured using a universal test machine (UTM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Nanocomposite foams with high-density closed cells were prepared by using a chemical blowing agent (CBA) that acted as a cell...

Dynamic Rheological Behavior of HDPE/UHMWPE Blends

Abstract: The rheological behaviors of high-density polyethylene (HDPE)/ultra-high molecular weight polyethylene (UHMWPE) blends prepared by melt blending and solution blending were studied. The results showed that the rheological parameters (G′, G ″, and η*) of both types of blends increased gradually with increasing fraction of UHMWPE, while the tanδ decreased correspondingly. Comparing blends with the same UHMWPE content, all G′, G ″, and η* values of solution blends were higher, and the tanδ of the solution blends were remarkably lower than those of the melt blends. Combined with the scanning electron microscopy (SEM) observations, it was proved that, because of its very high melt viscosity, the UHMWPE chain is difficult to diffuse and be distributed well in the HDPE matrix by melt blending, resulting in a two-phase-like morphology. On the other hand, the blends prepared by the solution blending showed a homogeneous distribution of UHMWPE in the HDPE matrix. In addition, the state of aggregation of the UHMWPE i...

Effect of Malonic Acid Treatment on Crystal Structure, Melting Behavior, Morphology, and Mechanical Properties of Isotactic Polypropylene/Nano-CaCO3 Composites

Abstract: The influence of malonic acid (MA) treatment of nano-calcium carbonate (CaCO3) on the crystallization, morphology, and mechanical properties of isotactic polypropylene (iPP)/nano-CaCO3 composites have been studied. The results of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and polarized light microscopy (PLM) show that untreated nano-CaCO3 facilitates the formation of α phase, while MA treated nano-CaCO3 increases the relative content of β phase of iPP dramatically. The results of scanning electron microscopy (SEM) show that MA treated nano-CaCO3 has better dispersion in the matrix than the untreated one. The toughness of PP/MA treated nano-CaCO3 composite is improved drastically. When 2.5 wt% MA treated nano-CaCO3 is added, the Izod notched impact strength reaches its maximum, which is 2.89 times greater than that of the pure iPP.

Preparation and Mechanical and Tribological Properties of High-Density Polyethylene/Hydroxyapatite Nanocomposites

Abstract: High-density polyethylene (HDPE) nanocomposites reinforced with hydroxyapatite nanorods (nHA) were fabricated by means of extrusion and injection molding. The thermal, mechanical, and dry sliding wear properties of HDPE-based nanocomposites filled with nHA loadings up to 20 wt% were investigated. The results of mechanical property characterization showed that nHA additions improved the hardness, elastic modulus, and yield strength of HDPE at the expense of its tensile ductility and impact strength. Thermogravimetric analysis and heat deflection temperature measurements revealed that nHA fillers are very effective to enhance the thermal stability of HDPE. The wear behavior of HDPE/nHA nanocomposites was studied using a pin-on-disk tribometer. nHA fillers of a large aspect ratio improved the wear resistance of HDPE substantially because of their load-bearing effect and the formation of a continuous transfer film on the steel counterface.

Mechanical Properties and Morphology of Polylactide Composites with Acrylic Impact Modifier

Abstract: Polylactide (PLA) composites with acrylic impact modifier BPM, i.e., PLA/BPM composites, were produced by the melt blending method. The effects of BPM on the thermal properties, melting behaviors, and dynamic mechanical properties of the PLA/BPMs were investigated by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. Tensile strength, flexural strength, and modulus of the injection molded specimens were measured by an Instron tensile machine. The influence of BPM on the impact strength of injection molded PLA/BPM composites was examined using an impact tester. The morphology of cryofractured surfaces and fracture surfaces of the composites after the tensile and impact testing was also investigated using scanning electron microscope. The test results show that the composites with BPM possess better flexibility when compared with neat PLA. However, the notched Izod impact strength showed improvement only when the BPM content was higher than 15 wt%.

Study of PEO—PPO—PEO Copolymers Conformational Changes: Viscosity and Dynamic Light Scattering Measurements

Abstract: The self-assembly behaviour of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly (ethylene oxide) copolymers, (EO)13(PO)30(EO)13 (Pluronic L64), and (EO)70 (PO)30(EO)70 (Pluronic F68) in water and in p-xylene has been elucidated by using viscosity and dynamic light scattering measurements to investigate the effects of hydrophilic chains length on their conformational changes. The viscosity measurements were performed for a range of temperature varying from 27°C to 60°C and concentration from 4 to 60 mg/ml. The variation of the viscosity and the conformational changes in aqueous solution depends on the kinds of interactions and the balance between excluded volume effects and hydrophobic interactions. Some dynamic light scattering measurements were also performed at room temperature for the same range of concentration to provide more information on the micellar structures in aqueous and organic solution.

Effectiveness of Maleic Anhydride Grafted EPDM Rubber (EPDM-g-MAH) as Compatibilizer in NR/Organoclay Nanocomposites Prepared by Melt Compounding

Abstract: The effectiveness of maleic anhydride grafted ethylene propylene diene monomer rubber (EPDM-g-MAH) as an interfacial compatibilizer in enhancing the extent of interaction between natural rubber (NR) matrix and organoclay (OC) nanolayers, and also the eventually developed microstructure during a melt mixing process, has been evaluated as an alternative material to be used in place of commonly used epoxidized NR with 50 mol % epoxidation (ENR50). The latter usually weakens the processability of the final compound. The curing behavior, rheological, and dynamic mechanical properties of the prepared nanocomposites have been evaluated. Microstructural characterizations revealed better interfacial compatibilization by EPDM-g-MAH than ENR50, which is attributed to the lower polarity of the EPDM-g-MAH and hence more affinity for the NR matrix to be diffused onto the galleries of OC. This was confirmed with transmission electron microscopy (TEM) examination and higher elasticity exhibited by the unvulcanized NR/OC/...

Design and Fabrication of Artificial Skin: Chitosan and Gelatin Immobilization on Silicone by Poly Acrylic Acid Graft Using a Plasma Surface Modification Method

Abstract: Acrylic acid (AAc) was grafted onto the surfaces of polydimethylsiloxane (PDMS) films using a two-step oxygen plasma treatment. The first step of this method included oxygen plasma pretreatment of the PDMS films, immersion in AAc, and drying. The second step was carried out by plasma polymerization of the preadsorbed reactive AAc on the surfaces of the dried pretreated films. Then chitosan and gelatin were immobilized onto the poly(acrylic acid) grafted silicone through covalent bonding. The films were characterized by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and water contact angle measurements. Fibroblast cells (L929) were cultured onto the chitosan- and gelatin-immobilized poly(acrylic acid)-grafted silicone and poly(acrylic acid)-grafted silicone films. It was observed that the chitosan- and gelatin-immobilized surfaces showed significant cell growth in comparison with poly(acrylic acid)-grafted silicone samples. It seems that chitosan- and gelatin-immobilized sur...

Effect of Modified Nano-Silica on the Reinforcement of Styrene Butadiene Rubber Composites

Abstract: The performance of styrene butadiene rubber (SBR) composites filled with nano-silica has been improved by surface modification of the nano-silica using silane coupling agents. The dispersion of nano-silica in SBR rubber and the bonding force of nano-silica with SBR were significantly improved, and the physical and mechanical properties of the vulcanized rubber were greatly improved. The results showed Si69 (bis-(γ- triethoxysilylpropyl)-tetrasulfide) was the best modifier among the six silane coupling agents used in the experiments, and its optimum amount was 12% (wt) of nano-silica.

Structure and Shape Memory Properties of Polyurethane Copolymers Having Urethane Chains as Soft Segments

Abstract: Shape memory polyurethanes are usually fabricated with low-molecular weight polyols through a two-step copolymerization, which often results in difficulty attaining both desired shape memory switch temperature and optimal thermomechanical properties. Here we present a series of shape memory polyurethane copolymers having urethane chains as soft segments. The structure and shape memory properties of copolymers were investigated with differential scanning calorimetry, dynamic mechanical analysis, small angle x-ray scattering, and thermomechanical tests. Increasing the length of the urethane soft segments enhanced phase separation, while it brought little change to the glass transition temperature (T g). Based on the urethane soft segments, some rigid chain extenders could be readily introduced into the backbone of copolymers, resulting in better phase separation. All polyurethane copolymers exhibited more than 90% of shape recovery. The shape recovery of the materials was proved to be inversely proportional...

Effect of carbon nanotubes on the mechanical properties of polypropylene/wood flour composites: reinforcement mechanism

Abstract: Maleic anhydride grafted polypropylene (PP-g-MA) was employed as the compatibilizer and carbon nanotubes (CNTs) or hydroxylated CNTs as reinforcements for polypropylene/wood flour composites. The results showed that when the PP-g-MA loading level was 10 wt%, the bending strength, tensile strength, Izod notched impact strength, and elongation at break of PP-wood composites were enhanced by 85% (66.3 MPa), 93% (33.7 MPa), 5.8% (2.01 kJ/m2), and 64% (23%), respectively, relative to the uncompatibilized composites. The introduction of pristine CNTs only improved slightly the overall mechanical properties of the compatibilized composites due to poor interfacial compatibility. Unlike CNTs, incorporating hydroxylated CNTs (CNT-OH) could significantly improve all of the mechanical properties; for instance, at 0.5 wt% CNT-OH loading, the flexural strength and tensile strength reached 68.5 MPa, and 40.4 MPa about 6.6% higher than that for the composites with the same CNT loading. Furthermore, CNT-OH also remarkably...

Isothermal Crystallization Kinetics of Highly Filled Wood Plastic Composites: Effect of Wood Particles Content and Compatibilizer

Abstract: The isothermal crystallization behavior and crystal structure of the polypropylene (PP) component in wood plastic composites (WPC) with respect to wood particle content and maleic anhydride-grafted polypropylene (MAHPP) compatibilizer were studied by means of polarized optical microscopy, scanning electron microscopy, x-ray diffraction, and differential scanning calorimetry. It was found that under the experimental conditions of this research, the speed of crystallization of PP was faster in WPC with MAHPP than in composites without MAHPP. This is ascribed to the difference in undercooling due to the change in the equilibrium melting temperatures (T 0 m ) of the PP component in WPC due to the addition of wood flour and MAHPP compatibilizer. T 0 m decreased with the increase of wood particle content, and it decreased more severely with the addition of wood flour than the addition of compatibilizer. The half-crystallization time was the smallest in PP/wood composites, intermediate in PP/wood/compatibilizer ...

Flame Retardancy and Mechanical Properties of Ethylene-vinyl Acetate Rubber with Expandable Graphite/Ammonium Polyphosphate/Dipentaerythritol System

Abstract: Ethylene-vinyl acetate thermoset rubber (EVM) with high vinyl acetate content has been widely used in wires and cables for many years. However, the problem of melting drip and efficient flame retardance has not been effectively solved. The combination of expandable graphite (EG), ammonium polyphosphate (APP), and dipentaerythritol (DPER) as a flame retardant system for EVM rubber has been proven to be effective in preventing melting drip and improving flame retardance in this study. This is shown by limiting oxygen index (LOI) and vertical flammability (UL-94) tests. The thermal behavior of EVM treated with this instumescent-flame retardant (IFR) system was investigated by thermogravimetric analysis (TGA) experiments. The results indicated that the char residue of treated samples could reach up to 27.1% at 600°C, which is much higher than that of the untreated EVM. Scanning electron microscopy (SEM) micrographs of residue of treated and untreated EVM showed that the IFR system could promote formation of r...

Structure and Properties of Ultradrawn Polylactide/Thermoplastic Polyurethane Elastomer Blends

Abstract: Highly oriented self-reinforced 80/20 blends of polylactide (PLA)/thermoplastic polyurethane elastomer (TPU) were successfully fabricated through solid hot stretching technology. Different from the isotropic sample, stress rose rapidly in a low strain region, and exhibited strain hardening for the drawn samples of the PLA/TPU blend. Superior mechanical properties of the blend, with the notched Charpy impact strength 150 KJ/m2, and tensile strength 197 MPa, were achieved. With increasing hot stretch ratio, the storage modulus increased, the glass transition temperatures of the PLA-rich phase and TPU-rich phase in the blends moved to higher temperatures, and the melting temperature and crystallinity of the blend increased, indicating the stress-induced crystallization of the blend during drawing. The longitudinal fracture surfaces of the blends at different stretch ratios exhibited orderly arranged fibrillar bundle structure, which contributed to the significantly higher strength and toughness of the blend.

Preparation and Characterization of Gelatin–Poly(L-lactic) Acid/Poly(hydroxybutyrate-co-hydroxyvalerate) Composite Nanofibrous Scaffolds

Abstract: Poly(L-lactic) acid (PLLA) scaffolds, prepared by electrospinning technology, have been suggested for use in tissue engineering. They remain a challenge for application in biological fields due to PLLA's slow degradation and hydrophobic nature. We describe PLLA, PLLA/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), and PLLA/PHBV/gelatin (Gt) composite nanofiberous scaffolds (Gt–PLLA/PHBV) electrospun by changing the electrospinning technology. The morphologies and hydrophilicity of these fibers were characterized by scanning electron microscopy (SEM) and water contact angle measurement. The results showed that the addition of PHBV and Gt resulted in a decrease in the diameters and their distribution and greatly improved the hydrophilicity. The in-vitro degradation test indicated that GT–PLLA/PHBV composite scaffolds exhibited a faster degradation rate than PLLA and PLLA/PHBV scaffolds. Dermal fibroblasts viabilities on nanofibrous scaffolds were characterized by [3-(4, 5-dimethylthiazol-2-yl)-2, 5-dipheny...

Dielectric Relaxations and Structures of Nanoclay in Solution Cast Poly(Ethylene Oxide)– Montmorillonite Clay Nanocomposites

Abstract: The relative complex dielectric function, electric modulus and alternating current electrical conductivity spectra and complex impedance plane plots of aqueous solution cast poly(ethylene oxide)–montmorillonite clay (PEO–MMT) nanocomposite films were investigated over the frequency range 20 Hz to 1 MHz at ambient temperature The intercalated and exfoliated structures of nanoclay dispersed in PEO matrix were recognized by the significant change in real part of dielectric function with clay concentration in the range 0%–20 wt% The relaxation times corresponding to PEO chain segmental motion and ionic conduction relaxation processes were used to explore the interactions compatibility between PEO molecules and the dispersed MMT clay nanoplatelets and their effect on PEO chain dynamics Real part of conductivity spectra of these nanocomposites over five decades of frequency has nonlinear behavior, which is influenced by the MMT clay concentration The complex impedance plane plots confirm the bulk properties

Preparation and Properties of Polystyrene/Bacterial Cellulose Nanocomposites by In Situ Polymerization

Abstract: Polystyrene/bacterial cellulose (PS/BC) nanocomposites were prepared via in situ polymerization. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), themogravimetry (TG), and mechanical testing were employed to characterize the PS/BC nanocomposites. The polystyrene filled in the network of the BC and a lamellar structure was formed. The FTIR results show that no chemical reaction between PS and BC occurred during the polymerization. These composites showed good mechanical properties.

Poly(Butylene Terephthalate)/Single Wall Carbon Nanotubes Composite Nanofibers by Electrospinning

Abstract: Poly(buthylene terephthalate)(PBT)/single wall carbon nanotubes (SWCNTs) composite nanofibers were prepared by electrospinning. The effect of carbon nanotubes on the morphology, crystallization, and mechanical properties of the electrospun composite nanofibers were investigated by SEM, DSC, and tensile testing, respectively. SEM observations indicated that the presence of SWCNTs resulted in finer nanofibers for lower loading; however, a broader distribution, especially for the higher diameter ranges was found for nanofibers with higher amounts of carbon nanotubes. SWCNTs accelerated crystallization and acted as a nucleating agent; the degree of crystallinity increased with increasing content of SWCNTs, followed by a moderate decrease at higher content. Specific tensile strength and modulus of the PBT/SWCNTs composite nanofibers mats were higher than that of neat PBT nanofibers mat. However, the elongation at break of composite nanofibers mats was lower than that of the neat PBT nanofibers mat.

Effect of Silica and Silicone Oil on the Mechanical and Thermal Properties of Silicone Rubber

Abstract: The effect of three types of silicas with varied loading and the loading of hydroxyl terminated silicone oil on the mechanical and thermal properties of silicone rubbers (SRs) were investigated. Mechanical properties were affected by the silica loading because of the interaction between fillers and polymer and the filler dispersion. Fumed silica filled SRs showed higher tanδ, tensile strength, and elongation at break compared to those containing two types of precipitated silicas. With increasing silicone oil loading, the tensile strength, tear strength, hardness, and tanδ of SRs first increased and then decreased.