Showing papers in "Journal of Polymer Research in 2014"

Isothermal crystallization behavior of β-nucleated isotactic polypropylene with different melt structures

Abstract: A previous work reported that the polymorphic crystallization behavior of isotactic polypropylene (iPP) can be efficiently tuned by the combination of controlling the melt structure (i.e., creation of an ordered structure by tuning the fusion temperature Tf by self-nucleation) and the addition of the α-/β-dual-selective nucleation agent (dual-selective β-NA, tradename WBG-II). In this study, we further investigated the impact of isothermal treatment on the polymorphic behavior and the isothermal crystallization kinetics of a β-iPP sample with different melt structures by differential scanning calorimetry (DSC). The results of isothermal crystallization kinetics study illustrated that as Tf decreased gradually from Region I to Region II and Region III, two sharp increases of the crystallization rate took place at the transition temperatures of Region II, showing that the enhancement of β-phase crystallization took place in a certain crystallization rate window. The calculation of the Avrami exponent n revealed that the two-dimensional growth of crystallites with instantaneous nucleation took place before and after the occurrence of the synergetic effect between the ordered structures and the dual-selective β-NA (when Tf ≥ 168 °C). Moreover, it was found that the occurrence of the synergetic effect in the fusion temperature range of Region II can evidently enhance the βc of the sample: by tuning the fusion temperature Tf and the isothermal crystallization temperature Tc, the relative percentage of β-phase (βc) of the single β-iPP sample with only 0.03 wt.% β-NA can be efficiently tuned in the wide βc range of 0 %–95.0 %; meanwhile, the sensitivity of βc to the isothermal crystallization temperature Tc was reduced.

Oxovanadium(IV) complexes with (ONNO)-chelating ligands as catalysts for ethylene homo- and copolymerization

Abstract: Oxovanadium(IV) complexes with (ONNO)-type tetradentate Schiff base ligands: salen, acacen, aceten, acetph (H2salen = N,N'-ethylenebis(salicylideneimine), H2aceten = N,N'-ethylenebis(2-hydroxyacetophenoneimine), H2acacen = N,N'-ethylenebis(acetylacetonimine), H 2 acetph = N ,N ' -phenylene-1,2-b is (2-hydroxyacetophenoneimine)), were the first time investi- gated in ethylene polymerization and ethylene/1-octene copo- lymerization processes. In general, all these complexes are moderately active precatalyst for ethylene polymerization up- on activation with EtAlCl2 and they give high molecular weight linear polyethylenes. Their activity in copolymeriza- tion was found relatively low. However, they yielded copoly- mers with high 1-octene incorporation even at low comono- mer concentrations in the feed. The catalytic performance in homo- and copolymerization was influenced by both the ligand structure and polymerization parameters (Al/ V molar ratio, polymerization temperature, comonomer feed concentration). In addition, the (VO(acacen)) was supported onto magnesium supports, and in the presence of various cocatalyst and at different reaction conditions it was screened as the catalyst of choice for ethylene homo- and copolymerization.

Electrospun polycaprolactone/ZnO nanocomposite membranes as biomaterials with antibacterial and cell adhesion properties

Abstract: In the present study we have investigated the effect of zinc oxide (ZnO) nanoparticles on the fiber diameter, fiber morphology, antibacterial activity, and enhanced cell prolifer- ation of the electrospun polycaprolactone (PCL) non-woven membrane. The effect of the ZnO nanoparticle concentration on the fiber diameter and fiber morphology was investigated using a scanning electron microscope (SEM). Fourier trans- form infraredspectroscopy(FT-IR)analysis was carried out to determine the nature of the interaction between the PCL and the ZnO nanoparticles. We also investigated the mechanical stability and antibacterial activity of the fabricated material. Interestingly, the membranes with ZnO nanoparticles showed enhanced mechanical stability, antibacterial properties, fibro- blast proliferation, and improved metabolic activity of the cells. Further, this is the first report regarding the ability of a biomaterial containing ZnO nanoparticles to enhance cell proliferation.

On the preparation and swelling properties of hydrogel nanocomposite based on Sodium alginate-g-Poly (acrylic acid-co-acrylamide)/Clinoptilolite and its application as slow release fertilizer

Abstract: A novel slow release fertilizer hydrogel nanocomposite was prepared via free radical polymerization of sodium alginate, acrylic acid, acrylamide, and clinoptilolite using N, N΄-methylene bisacrylamide as a crosslinker and ammonium persulfate as an initiator. Evidence of grafting and component interactions was obtained by a comparison of the Fourier transform infrared spectra of the initial substrates and hydrogel without clinoptilolite with that of the hydrogel nanocomposite containing clinoptilolite. The swelling behavior of both hydrogels in solutions of various pHs (2-12) and various saline solutions such as NaCl, KCl, CaCl2 and FeCl3 as well as swelling kinetics were investigated. Results showed that the swelling of hydrogels depends on the solution pH value. Also, the swelling of both hydrogels in all salt solutions is significantly lower than that of the values in distilled water. After those characterizations, the potential application was verified through sorption and fertilizer releasing from the hydrogel with and without clinoptilolite zeolite. The presence of the clinoptilolite zeolite in the hydrogel caused the system to liberate the nutrient in a more controlled manner than that with the neat hydrogel. The results of the fertilizer release of hydrogel nanocomposite were also encouraging in order to find applications in agriculture. Consequently, the good slow release fertilizer property as well as the good water adsorption capacity showed that this formulation is potentially viable to be used in agriculture as a nutrient carrier vehicle.

pH sensitive nanocomposite hydrogel beads based on carboxymethyl cellulose/layered double hydroxide as drug delivery systems

Abstract: In this paper new pH sensitive nanocomposite beads were prepared by the combination of layered double hydroxides (LDH) and carboxymethyl cellulose (CMC). Ibuprofen (IBU), as a model drug, was intercalated between LDH layers through the co-precipitation method. The synthesized LDH-IBU nanohybrids and nanocomposites beads were characterized using FTIR, XRD, and SEM. In vitro tests of drug delivery in conditions simulating the gastrointestinal tract were carried out to prove the effectiveness of this novel type of nanocomposite beads as a controlled drug delivery system (DDS). The drug release tests revealed a better protection against stomach pH and a controlled liberation in the intestinal tract conditions for new nanocomposite beads.

Preparation and properties of poly (vinylidene fluoride) membranes via the low temperature thermally induced phase separation method

Abstract: Tensile strength is of paramount importance to poly (vinylidene fluoride) (PVDF) membranes in expanding their industrial application. In this paper, porous PVDF membranes with higher tensile strength were prepared by the low temperature thermally induced phase separation (LT-TIPS) method. The effects of mixed diluents (MD) composition on the morphology, polymorphism, and tensile strength of such prepared flat sheet membranes were investigated. The competition of membrane formation mechanisms between the nonsolvent induced phase separation (NIPS) and TIPS was demonstrated by observing the membrane morphology in the LT-TIPS process. It was found that the tensile strength was improved by suppressing the formation of finger-like macrovoids and spherulitic morphologies through adjusting the composition of MD. PVDF crystallized into α phase for all the investigated cases, and as the MD became poorer, the total crystallinity increased slightly. Based on these experimental results, PVDF hollow fiber membranes were fabricated via LT-TIPS. The influences of MD composition and polymer concentration on the morphology, water permeability and tensile strength of the formed hollow fiber membranes were studied. The properties of optimized hollow fiber membranes associated with the surface and cross-section morphologies were promising and the performance can be further enhanced in future work.

Adsorption of lead ions using a modified lignin hydrogel

Abstract: Adsorbent composites comprising of bentonite/sodium lignosulfonate graft-polymerized with acrylamide and maleic anhydride (BLPAMA) were synthesized, characterized, and used to remove Pb2+ from aqueous solution with a large adsorption capacity. The fundamental adsorption behavior of the as-prepared BLPAMA was studied as a function of adsorbent dosage, initial pH, contact time, temperature, concentration of Pb2+, and additive electrolyte. Results showed that the adsorption of Pb2+ on BLPAMA was temperature-independent but strongly pH dependent. The Pb2+ adsorption kinetics was well described by a pseudo-second order model and the adsorption isotherms closely adhered to the Langmuir model, indicating a monolayer chemical adsorption. Thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy changes were also evaluated. Their values demonstrated that the adsorption of Pb2+ on BLPAMA was spontaneous and endothermic in nature. The competitive adsorption of Pb2+, Cu2+, Cd2+ and Zn2+ in their quaternary metal solution was investigated and the results showed that Pb2+ was preferably adsorbed on BLPAMA. TGA and SEM characterization proved that Pb2+ was adsorbed onto BLPAMA. FTIR and XPS analyses further revealed that the adsorption mechanism of Pb2+ on BLPAMA were mainly through chelation and ion exchange mechanism.

Antimicrobial alginate/PVA silver nanocomposite hydrogel, synthesis and characterization

Abstract: Superabsorbent hydrogel-silver nanocomposite based on poly(vinyl alcohol) (PVA) and sodium alginate (Na-Alg) was prepared using free radical polymerization in the presence of acrylamide (AAm) monomer. The reactions were conducted under normal atmospheric conditions, using ammonium persulfate (APS) as an initiator and methylene bisacrylamide (MBA) as a crosslinking agent. The effect of reaction parameters such as MBA, AAm, and APS concentration as well as Na-Alg/PVA weight ratio on the water absorbency and the gel content of the hydrogels were studied. Evidence of grafting was obtained by comparing the FT-IR spectra and the TGA of the initial substrates with that of the superabsorbent hydrogel. Furthermore, Ag nanoparticles were synthesized in a green synthesis process. Highly stable silver nanoparticles were obtained with the hydrogel networks as nanoreactor via in situ reduction of silver nitrate by using sodium borohydride as a reducing agent. The hydrogel silver nanocomposite was fully characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The effect of cross-link density, and Na-Alg/PVA weight ratio on the loading and the size of nanoparticles were studied. The antibacterial activity of the silver nanocomposite hydrogel was investigated as well.

Preparation of blend polyethersulfone/cellulose acetate/polyethylene glycol asymmetric membranes for oil–water separation

Abstract: Blend PES/CA hydrophilic membranes were prepared via a phase-inversion process for oil–water separation. PEG-400 was introduced into the polymer solution in order to enhance phase-inversion and produce high permeability membranes. A gas permeation test was conducted to estimate mean pore size and surface porosity of the membranes. The membranes were characterized in terms of morphology, overall porosity, water contact angle, water flux and hydraulic resistance. A cross-flow separation system was used to evaluate oil–water separation performance of the membranes. From FESEM examination, the prepared PES/CA membrane presented thinner outer skin layer, higher surface porosity with larger pore sizes. The outer surface water contact angle of the prepared membrane significantly decreased when CA was added into the polymer solution. The higher water flux of the PES/CA membrane was related to the higher hydrophilicity and larger pore sizes of the membrane. From oil–water separation test, the PES/CA membrane showed stable oil rejection of 88 % and water flux of 27 l/m2 s after 150 min of the operation. In conclusion, by controlling fabrication parameters a developed membrane structure with high hydrophilicity, high surface porosity and low resistance can be achieved to improve oil rejection and water productivity.

Collagen coated electrospun polycaprolactone (PCL) with titanium dioxide (TiO2) from an environmentally benign solvent: preliminary physico-chemical studies for skin substitute

Abstract: Fabrication of nanofibers with some biomaterials based on natural materials (collagen) through electrospinning is an important area for research. The effect of collagen coating on polycaprolactone (PCL) nanofiber surfaces was studied here. In this work, PCL nanofibers with titanium dioxide (TiO2) nanopowder were used for the development of active wound dressings. We used glacial acetic acid as an environmentally benign solvent. The prepared nanofibers were coated with collagen by soaking the scaffold in 10 mg/mL and 20 mg/ml collagen solution overnight. The samples produced were subjected to contact angle measurements, SEM, FTIR, and XRD, and mechanical strength was determined. Nanofibers in the range of 200–800 nm were produced. The other study confirmed the physical interaction between collagen and PCL. The hydrophilicity of PCL nanofibers was increased; this was confirmed by observing contact angle values. A hydrophilic surface on the scaffold is necessary for biomedical applications. FTIR have proved the presence of an amide group on the PCL structure that facilitates cell adhesion and proliferation. SEM images have clearly proved the formation of nanofibers as well as the attachment of collagen to PCL nanofibers. XRD has shown the crystalline nature of the PCL polymer. PCL can impart more mechanical strength, although incorporation of collagen has decreased the tensile strength to some extent.

In situ atom transfer radical polymerization of styrene to in-plane functionalize graphene nanolayers: grafting through hydroxyl groups

Abstract: Graphene oxide (GO) was modified with two different amounts of 3-(trimethoxysilyl)propyl methacrylate (MPS) by a silane coupling reaction. Atom transfer radical polymerization of styrene in the presence of different amounts of MPS-modified graphene was carried out to evaluate the effect of graphene loading along with the graft density on the properties of the products. Successful attachment of MPS on the surface of GO was evaluated using Fourier transform infrared spectroscopy. Expansion of graphene interlayers by oxidation and functionalization processes was evaluated using X-ray diffraction. The ordered and disordered crystal structure of carbon in pristine and surface modified graphenes was evaluated by Raman spectroscopy. Relaxation behavior of polystyrene chains in the presence of graphene layers and also effect of graft content on the chain confinement was studied using differential scanning calorimetry. High-density nanocomposites show much increase of Tg by addition of graphene content. Morphology of graphene nanolayers after modification processes was studied by scanning electron microscopy and also transmission electron microscopy. Flat and smooth morphology of graphene nanosheets was disturbed during the oxidation and functionalization processes and consequently wrinkled sheets with curvature were obtained.

Piezoelectric electrospun nanofibrous materials for self-powering wearable electronic textiles applications

Abstract: This research focuses on fabricating a one-step nano-generator based on electrospun nanofibrous materials for wearable electronics textiles applications. A nanofibrous structure from Poly (vinylidene fluoride), PVDF, was produced using electrospinning technique. Performances of these structures were evaluated by using X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM). Piezoelectric properties of fabricated composites also were evaluated on a self-made system as a function of frequency. Results showed that not only electrospinning process can effectively improve piezoelectric properties of nanofiber mats by changing the crystalline structure (e.g. create the β-phase) compared to PVDF film samples, but also the fibrous structure of these materials interestingly can be used in the wearable electronic textiles. By using a novel approach to fabricate the nanofiber layer along with incorporating the electrodes within the structure of the device, the electrical output was improved as high as 1 volt. These results imply promising applications for various wearable self-powered electrical devices and systems.

Synthesis and characterization of bio-based furanic polyesters

Abstract: Recent work in biomass-based furanic polyesters has shown that they deliver a good balance of sustainability advantage with improved performance and economics. In light of that research, completely renewable furanic polyesters with novel compositions and enhanced performance were synthesized using two different polymerization methods and characterized. These materials, based on ethylene glycol (PEF) and 1,4-Butanediol (PBF), exhibit thermal and structural properties similar to fossil-based poly (ethylene terephthalate) (PET), which is widely used in beverage packaging. Direct polycondensation method resulted in doubling the yield of polymer with properties identical to those of material synthesized using trans-esterification. PBF synthesized using our process has unique thermal properties (higher glass transition and lower melting temperature) that could result in lower costs and environmental impacts associated with the processing step. The other new polymer compositions were also well characterized for potential high-temperature applications. The biomass-based furanic polyesters are a potential sustainable alternative for petroleum-based PET in packaging applications.

Electrical power generation from piezoelectric electrospun nanofibers membranes: electrospinning parameters optimization and effect of membranes thickness on output electrical voltage

Abstract: Nanogenerators based on piezoelectric nanofibers capable to scavenging mechanical energy from the environment and converting into usable electrical energy. In this research work, the electrospinning parameters were optimized to produce randomly oriented uniform PVDF nanofiber mats without structural defects. Then, optimized nanofiber membranes with different thickness (110, 220, and 310 μm) were fabricated and their output voltages as a performance factor of the nanogenerator were measured. Results indicated that the nanogenerator based on piezoelectric nanofibers can generate voltage as high as several volts electrical outputs by applying mechanical impact. Finally, to investigate the effect of pure thickness on power harvesting efficiency, output voltages of samples were normalized to thickness. Results showed that in spite of the existed literature, increases in nanofiber membrane’s thickness can lead to decrease the output voltage of nanogenerator. These results imply promising applications for various wearable self-powered electrical devices within the clothing systems.

Beta-phase enhancement in polyvinylidene fluoride through filler addition: comparing cellulose with carbon nanotubes and clay

Abstract: The beta-phase in polyvinylidene fluoride (PVDF) is responsible for its ferro-, piezo- and pyroelectric properties, key for memory, sensing and actuation applications. Filler addition as a route to enhance the smart beta-phase in PVDF is presented in this study. PVDF composites with varying concentrations of microcrystalline cellulose, carbon nanotubes and kaolinite clay were prepared by solution-sonication method and subsequently cast into thin standing composite films. Crystallinity of PVDF and its composites were found to be similar. Phase evolution studies showed that addition of microcrystalline cellulose yields a beta-phase fraction comparable to carbon nanotubes and significantly higher than that of clay. The mechanism of interaction between microcrystalline cellulose and PVDF is also proposed.

Effect of thermal processing conditions on the structure and dielectric properties of PVDF films

Abstract: The effect of annealing and quenching tempera- tures on the crystallinity, β phase fraction and dielectric be- havior of poly (vinylidene fluoride) (PVDF) have been stud- ied. The crystallinity and β phase fraction of these films were evaluated using X-ray diffraction and FTIR techniques for different annealing and quenching temperatures. It is seen that the thermal processing conditions play a crucial role in deter- mining the dominant phase in PVDF. The β phase PVDF is the most desired phase for device applications such as sensors and actuators. Hence, the thermal processing conditions are optimized for obtaining β rich PVDF films. The β rich phase ofPVDFisobtainedfor filmswhichareannealedat80°Cand quenchedat 20 °C. The as-synthesized films for the optimized processing conditions was studied for their dielectric behavior and was found to exhibit dielectric constant as high as ~60.

Crystallization kinetics behavior, molecular interaction, and impact-induced morphological evolution of polypropylene/poly(ethylene-co-octene) blends: insight into toughening mechanism

Abstract: In this paper, SEM, POM, DSC, FTIR, polarized FTIR, and part-impact test were performed to investigate the effect of dispersed POE phase on crystallization kinetics behavior, molecular interaction, and impact-induced morphological evolution in polypropylene/poly(ethylene-co-octene) (PP/POE) blends. The main focus was to establish a systematic and deep toughening mechanism from microscopic molecular interaction to macroscopic deformation. The results showed that the existence of POE particles played the role of an obstacle during the crystallization process of a PP matrix, which could increase the growth path of PP lamellae or ordered PP molecules and reduce the growth space of spherulites, resulting in a slower spherulite growth rate and smaller spherulite size. This behavior was explained by a crystallization model. Most interestingly, a coated structure was formed in the interface, which was a transition state structure of molecules with different morphologies. The as-formed coated structure can be considered the origin of the cavitation effect and impact-induced morphology evolution of POE particles during the impact process. Moreover, micro-plastic deformation in PP/POE blends during the fracture process was a multi-stage mechanism, in which the POE content played a decisive role.

In situ grafted nanostructured ZnO/carboxymethyl cellulose nanocomposites for efficient delivery of curcumin to cancer

Abstract: In this present manuscript, zinc oxide (ZnO) nanoparticles embedded carboxymethyl cellulose (CMC) bionanocomposite were prepared by in situ grafting and the hydrophobic anticancer drug curcumin (Cur) was loaded into it. Structural, morphological, and physiochemical behavior of prepared curcumin-loaded CMC/ZnO nanocomposites (NCs) were characterized by FTIR, XRD, SEM, TEM, TGA, and DTA. The drug entrapment efficiency was evaluated and the in vitro efficacy as anticancer drug delivery vehicle was analyzed. The potential toxicity of curcumin-loaded ZnO/CMC NCs (Cur/ZnO/CMC NCs) was studied by using L929 and MA104 cell lines via MTT assay. The cellular uptake study of Cur/ZnO/CMC NCs by normal (L929) and cancer (MA104) cells carried out by using ethanol extraction and by FACS analysis has been reported. The results of this investigation demonstrate that the nanomatrix synthesized can effectively deliver the anticancer drug curcumin, and hence appears to be a promising nanoformulation for anticancer therapy and other biomedical applications.

From clay to graphene for polymer nanocomposites—a survey

Abstract: The development of aerospace and automotive industries requests lightweight, high-performance materials, and polymer nanocomposites are ideal candidates in this case, which is shown by the increasingly more publications in this research field over the past two decades. However, the performance of nanocomposite not only depend on the properties of their individual constituents, but on their morphology and surface characteristics of fillers as well. Selections of nanofillers geometries, e.g. particulate, fibrous or layered have a tremendous influence on the properties of nanocomposites and their processing methods. In this paper, we review the chronological works performed in the field of polymer nanocomposites, in particular epoxy nanocomposites reinforced with layered fillers, such as clay and graphene. Surprisingly layered fillers are commercially available and more cost-effective than nanoparticles and carbon nanofibres, and these make them to the most extensively studied fillers that can be geared toward future applications, particularly in large-scale polymer nanocomposite production.

Polysiloxane-based core-shell microspheres for toughening of epoxy resins

Abstract: We present a simple procedure for preparation of core shell poly(dimethylsiloxane)–epoxy microspheres (CPR) by suspension polymerisation route and demonstrate its potential as effective toughener for thermosetting epoxy resin. The curing of siloxane macromonomer was performed in the presence of platinum based hydrosilylation catalyst and the effect of reaction parameters on the dimensions of the polydimethylesiloxane (PDMS) based elastomeric microspheres was quantified, which could be varied from 90 to 216 μ. CPR were prepared by coating the PDMS core with epoxy resin in an additional step. Composites containing varying amounts of microspheres (3–10 % w/w) were prepared and the effect of their incorporation on quasi-static as well as dynamic properties of epoxy resin was evaluated. The glass transition temperature of the unmodified epoxy was unaltered on blending with elastomeric microspheres, which indicated its existence in a well separated phase. The presence of an epoxy coating on the silicone core led to improved dispersion in the epoxy matrix, which was evident from higher impact strength and fracture energies(GIC) as compared to its uncoated analogues. The charpy impact strength and GIC increased by 148 % and 70 % respectively on introduction of 5 % CPR. This was however accompanied with a reduction in the tensile modulus and strength of the base epoxy. Excellent agreement was found between the experimentally measured modulae and the predictions made on the basis of Halpin Tsai and Lewis-Neilson models. Post-mortem morphological studies of the fracture surfaces revealed the presence of spherical cavities which substantiate the role of rubber cavitation as the primary toughening mechanism in microsphere toughened epoxy composites.

Functionalized graphene oxide/polyimide nanocomposites as highly CO2-selective membranes

Abstract: The design of highly CO2-selective membranes by incorporating low amounts (0.25–0.75 wt%) of functionalized graphene oxide (F-GO) nanosheets (polyethylene glycol functionalized and aminated GOs) into an Ultem® 1000 polyetherimide (PEI) is presented. Structural and morphological analysis of the membranes by infrared spectroscopy, X-ray diffraction, differential scanning calorimetry and scanning electron microscopy revealed strong interfacial interactions between the F-GO nanosheets and PEI. The CO2/CH4 separation performance of the membranes was discussed in terms of filler-polymer interfacial interactions and free volume characteristics. The origins of free volume are proposed to be different for GO/PEI and F-GO/PEI membranes: free volume is mainly located at the GO-PEI interface of the GO/PEI membranes while distributed within interphase regions formed around the F-GO nanosheets in the F-GO/PEI ones. These different free volume localizations resulted in distinct gas separation properties of the membranes. The membranes containing aminated-GO showed outstanding CO2/CH4 selectivities up to 142, due to the activation of multi-permselectivity mechanism in the PEI membrane by addition of the aminated nanosheets. The promising potential of F-GOs in CO2 removal is highlighted by comparing the CO2/CH4 separation performance of the F-GO/PEI membranes with that of other nanocomposites of PEI.

Preparation of silica aerogel/polyurethane composites for the application of thermal insulation

Abstract: In this study, polyurethane was blended with silica aerogel to improve its thermal insulation property. The silica aerogel/polyurethane composite with a suitable composition 35/65 (v/v) has low thermal conductivity (0.13 W/m K) and a hydrophobic property (water contact angle of 95.6°). The pore size, pore distribution, and structure of silica aerogel (tetraethoxysilane-based) were studied to select the suitable silica aerogel for blending. The co-precursor method and the solvent exchange method were used to prepare the silica aerogel for comparison. Fourier Transform Infrared spectra confirmed that the co-precursor method created more Si-CH3 groups on the silica surface than solvent exchange method. The silica aerogel prepared by the co-precursor method had a thermal conductivity of 0.032 W/m K with a porosity of 97 %, and a water contact angle of 130°. This silica aerogel prepared was then used to blend with the polyurethane prepared by diisocyanate and poly (tetramethylene oxide), with 1,4-butanediol (1,4-BD) as the chain extender. Silica aerogel/polyurethane composites were formed as films of various compositions by the solvent casting method. Scanning electron microscopic (SEM) photographs revealed that the composites were uniform. The optimal composition of silica aerogel/polyurethane is 35/65 (v/v) with the water contact angle of 95.6° and the thermal conductivity 0.13 W/m K. The silica aerogel/polyurethane composites have no disadvantages of brittleness and hygroscopic property, and possess a low thermal conductivity property.

Electrodeposition of polyaniline-montmorrilonite nanocomposite coatings on 316L stainless steel for corrosion prevention

Abstract: The synthesis of polyaniline- montmorrilonite (MMT) nanocomposite coatings on 316L stainless steel (316L SS) surface has been investigated by using the galvanostatic method. The synthesized coatings were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), UV-visible absorption spectrometry and Scanning Electron Microscopy (SEM). The anticorrosion performances of polyaniline-MMT nanocomposite coatings were investigated in 0.5 M HCl medium by the potentiodynamic polarization technique and Electrochemical Impedance Spectroscopy (EIS). The corrosion rate of polyaniline-MMT nanocomposite coated 316L SS was found ∼540 times lower than bare 316L SS and potential corrosion increased from −0.386 V versus Ag/AgCl for uncoated 316L SS to −0.040 V versus Ag/AgCl for polyaniline-MMT nanocomposite coated 316L SS electrodes. Electrochemical measurements indicate that polyaniline-MMT nanocomposite coated have good inhibiting properties with mean efficiency of ~99.8 % at 0.75 mA cm−2 current density applied on 316L SS corrosion in acid media. The results of this study clearly ascertain that the polyaniline-MMT nanocomposite has an outstanding potential to protect 316L SS against corrosion in an acidic environment.

Viscoelastic properties correlations to morphological and mechanical response of HDPE/UHMWPE blends

Abstract: Melt-mixed and injection molded binary blends of high density polyethylene (HDPE)/ultra high molecular weight polyethylene (UHMWPE) were evaluated for their structural, thermal, rheological, morphological and mechanical attributes. X-ray diffraction (XRD) study has revealed the absence of any significant changes in the crystalline alignment/morphology of the two polyethylene components. Differential scanning calorimetry (DSC) studies revealed the increase in melting temperature, whereas the properties such as crystallization temperature and percentage crystallinity remained broadly unaffected. Dynamic rheological behavior revealed a transition from liquid like behavior (G′ G″) in the composition range of 20–30 wt% of UHMWPE. Scanning electron microscopy (SEM) of the cryo-fractured surface depicts two phase morphology along with very strong interface. The blending of UHMWPE with HDPE matrix has caused improvement in tensile, impact and flexural properties, whereas strain at break suffered a decrease. The analysis of tensile fractured surface morphology by SEM has proved to be useful in qualitatively understanding the underlying failure mechanisms. Eventually, a viscous-to-elastic transition in the rheological behavior has been observed and found to have a correspondence with structural, mechanical and morphological response in the similar composition window.

In situ chemical oxidative graft polymerization of thiophene derivatives from multi-walled carbon nanotubes

Abstract: We describe an effective route for the in situ chemical oxidative graft polymerization of thiophene derivatives from multi-walled carbon nanotubes (MWCNTs). To this goal, MWCNTs was carboxylated (MWCNTs-COOH) by conventional acid oxidation process, and then carboxylic groups were converted to acylchloride groups (MWCNTs-COCl) by treating of MWCNTs-COOH with thionyl chlorides. These acylchloride-functionalized MWCNTs were further reacted with 2-hydroxymethylthiophene (HMT) to produce thiophene-functionalized multi-walled carbon nanotubes (MWCNTs-T). Afterwards, the graft polymerization of 2,2’-bithiophene (BT), 3,4-ethylenedioxythiophene (EDOT), and 3-dodecylthiophene (DDT) monomers from MWCNTs-T was initiated by oxidized thiophene groups in the MWCNTs after addition of ferric chloride (FeCl3), an oxidative catalyst for polythiophene derivatives synthesis, and FeCl3-doped PBT, PEDOT, and PDDT was chemically grafted to the MWCNTs by oxidation polymerization. The chemical structures of all samples as representatives were characterized by Fourier transform infrared (FTIR) spectroscopy. The thermal properties of the MWCNTs-g-polythiophenes and their pure polymers were examined by thermogravimetric analysis (TGA). Moreover, direct and clear evidence of the PBT, PEDOT, and PDDT chemically grafted to the MWCNTs were obtained by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Synthesis of dual thermoresponsive and pH-sensitive hollow nanospheres by atom transfer radical polymerization

Abstract: A facile and effective approach was developed to fabricate dual temperature- and pH-sensitive hollow nanospheres utilizing an atom transfer radical polymerization (ATRP) method. To do this silica nanoparticles were used as primary cores that could be etched by an hydrofluoric (HF) aqueous solution. Due to uncontrolled ATRP of acrylic acid (AA) methyl acrylate (MA) was polymerized via surface-initiated ATRP (SI-ATRP) a and poly(2-hydroxyethyl methacrylate) (PHEMA) block was added via the same approach. To synthesize poly(AA-co-HEMA)-grafted silica nanoparticles polymethyl acrylate (PMA) chains were hydrolyzed to polyacrylic acid (PAA) using an aqueous NaOH solution. PAA segments were partially crosslinked via an esterification reaction of –COOH groups with 1,4-butanediol. Finally, poly(AA-co-HEMA) hollow nanospheres were fabricated by etching silica cores with an HF aqueous solution. The structure of the nanospheres was revealed by transmission electron microscopy (TEM). These hollow nanospheres consisting of poly(AA-co-HEMA) in their structure showed dual pH- and thermo-sensitive properties as measured by dynamic light scattering (DLS). The hydrodynamic diameter was measured as an affected parameter under different pH (3–12) and temperature (25–55 °C) conditions. Results showed that by decreasing pH or by increasing temperature the hydrodynamic diameter decreased and a lower critical solution temperature (LCST) point was observed.

Preparation of supramolecular corrosion-inhibiting nanocontainers for self-protective hybrid nanocomposite coatings

Abstract: Smart corrosion-inhibiting coatings generate or release an inhibitor only when demanded by the initiation of corrosion. Supramolecular nanocontainers of the α-cyclodextrin (α-CD) corrosion inhibitor were prepared by inclusion complex (IC) formation between α-CD and 2-mercaptobenzothiazole (MBT) or 2-mercaptobenzimidazole (MBI) under various conditions (at room temperature and under sonic energy). The structure of the supramolecular nanocontainers was characterized by hydrogen nuclear magnetic resonance (1H-NMR), x-ray diffraction (XRD), scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR). Supramolecular nanocontainer formation between MBT and MBI with α-CD in solid phase was emphasized by the significant differences between the 1H-NMR, FTIR and XRD spectra of the physical mixtures with respect to those of the complexes. The crystalline complexes adopted a head to head channel-type and cage conformation for α-CD/MBT and α-CD/MBI inclusion complexes, respectively.

Dynamic crystallization and melting behavior of β-nucleated isotactic polypropylene with different melt structures

Abstract: In the previous work, we reported that the β-selectivity, morphology and tensile behavior of isotactic polypropylene (iPP) can be efficiently tuned by the combination of controlling the melt structure status (namely, creation ordered structure by tuning the fusion temperature Tf) and the addition of β-nucleation agent (β-NA, tradename WBG-II, concentration 0.01 wt%), which was called “Ordered Structure Effect” (OSE). This study further investigates the dynamic crystallization and melting behavior of β-iPP with a different melt structure status by differential scanning calorimentry (DSC) and non-isothermal crystallization kinetics. The results revealed that under all the cooling rates studied (2, 5, 10, 20 and 40 °C/min), the crystallization temperature on the cooling curves increased gradually with the decrease of Tf; meanwhile, when the Tf was in the temperature range of 168–186 °C where the OSE occurs (defined as Region II), the crystallization activation energy ΔE was found to be evidently lower, compared with that when the Tf was higher than 186 °C or lower than 168 °C. The results of the subsequent heating showed that the occurrence of the OSE can be observed at all the cooling rates studied; the location of the Region II was constant when the cooling rate varied. Low cooling rate encouraged the formation of more β-phase triggered by OSE. Moreover, the role of OSE on the β-α recrystallization was comparatively studied by tuning the end temperature of recooling (Tend) after held at Tf, and it was found that the OSE encouraged the formation of β-phase with high thermal stability at the low temperature part of Region II, while enhancing the β-crystal with relatively low thermal stability at the high temperature part of Region II.

Understanding the effect of polymer crystallinity on the electrical conductivity of exfoliated graphite nanoplatelet/polylactic acid composite films

Abstract: Electrically conductive exfoliated graphite nanoplatelet (GNP) / polylactic acid (PLA) nanocomposite films were fabricated using a two-step, scalable melt compounding process. The effect of the polymer’s physical properties, such as crystallinity, on the mechanical and electrical properties of the composites were determined. The crystallization characteristics of PLA were altered significantly by altering the cooling rate during compression molding of the films. The crystallinity and crystal structure were investigated using differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and polarized optical microscopy (POM). The mechanical and electrical properties were also examined as a function of PLA’s crystallinity dictated by the cooling rate during compression molding. The electrical conductivity was examined using impedance spectroscopy. For the same GNP content, the crystallinity increases by ~40 % and electrical conductivity increases by ~3 orders of magnitude with decreased cooling rate indicating a strong correlation between polymer physical properties and electrical conductivity of the polymer composites. This mechanism can be utilized to tailor the electrical conductivity of a given filler/polymer system by tuning the physical properties of the polymer, without altering the fillers’ characteristics or the processing method, which is the common approach used.

TiO 2 and SiO 2 filled PTFE composites for microwave substrate applications

Abstract: TiO2 and SiO2 filled polytetrafluoroethylene (PTFE) composite substrates were fabricated for microwave circuit applications. The total content of TiO2 and SiO2 fillers was a fixed value of 55 wt%, and the content of TiO2 in the PTFE matrix varied from 1 wt% to 9 wt%. The influences of TiO2 filler loading on the microstructure, density, moisture absorption, microwave dielectric properties and coefficient of thermal expansion of filled PTFE composites were investigated. The distribution of filler was uniform throughout the PTFE matrix. The dielectric constant (e r) showed an increasing trend as the TiO2 content increased, while the dielectric loss (tanδ) decreased up to 5 wt% TiO2 filler loading and then slightly increased till 9 wt% TiO2 loading. Composites showed a similar trend of decreasing moisture absorption, and increasing linear coefficient of thermal expansion (CTE), density as the TiO2 filler content increased. Our results revealed that the TiO2 and SiO2 filled PTFE composites exhibited good dielectric properties (e r ~ 2.87, tanδ ~ 0.00075), acceptable moisture absorption (0.2 %), CTE (17 ppm/°C) and tensile strength (7.32 MPa) at filler loading of 5 wt% TiO2 and 50 wt% SiO2.