Showing papers in "Polymer Bulletin in 2013"

Thermoviscosifying polymer used for enhanced oil recovery: rheological behaviors and core flooding test

Abstract: Polymer flooding represents one of the most efficient processes to enhance oil recovery, but the poor thermostability and salt tolerance of the currently used water-soluble polymers impeded their use in high temperature and salinity oil reservoirs. Thermoviscosifying polymers (TVPs) whose viscosity increases upon increasing temperature and salinity may overcome the deficiencies of most water-soluble polymers. A novel TVP was studied in comparison with traditional partially hydrolyzed polyacrylamide (HPAM) in synthetic brine regarding their rheological behaviors and core flooding experiments under simulated high temperature and salinity oil reservoir conditions (T: 85 °C, and total salinity: 32,868 mg/L, [Ca2+] + [Mg2+]: 873 mg/L). It was found that with increasing temperature, both apparent viscosity and elastic modulus of the TVP polymer solution increase, while those of the HPAM solutions decrease. Such a difference is attributed to their microstructures formed in aqueous solution, which were observed by cryogenic transmission electron microscopy. Core flow tests at equal conditions showed an oil recovery factor of 13.5 % for the TVP solution versus only 2.1 % for the HPAM solution.

Kinetic study of Diels–Alder reaction involving in maleimide–furan compounds and linear polyurethane

Abstract: Linear polyurethane was synthesized by Diels–Alder (DA) reaction between a polyurethane prepolymer end-capped with furan rings (MPF) and bismaleimide (BMI). The polymerization kinetics were studied following a preliminary kinetic study of the DA reaction between furfuryl alcohol (FA) and BMI compounds by attenuated total reflection infrared, ultraviolet–visible and in situ 1H NMR spectroscopies, where in situ 1H NMR spectroscopy was selected as the analytical method of choice to study the DA reaction between MPF and BMI. The results showed that the reaction followed second-order kinetics, and the most beneficial experimental conditions to maximize conversion were identified.

Dynamic mechanical properties of high density polyethylene and teak wood flour composites

Abstract: The dynamic mechanical properties of high density polyethylene (HDPE) and teak wood flour (TWF) composites at varying volume fraction (Φ f) of TWF from 0.00 to 0.32 have been studied. In HDPE/TWF composites, storage modulus (E′) decreased at Φ f = 0.05, then increases with Φ f; however, values were lower than HDPE up to Φ f = 0.16, due to a pseudolubricating effect of filler. Loss modulus (E″) values were higher than HDPE in β and α relaxation regions while in γ relaxation region values were marginally equal to HDPE. Tan δ value decreases with Φ f which may be due to enhanced amorphization and decreased crystallinity of HDPE. In presence of maleic anhydride grafted HDPE (HDPE-g-MAH), E′ values were lower than HDPE/TWF composites. In HDPE/TWF/HDPE-g-MAH, E″ were slightly higher than HDPE/TWF due to slippage of HDPE chains facilitated by the extent of degradation of coupling agent. Tan δ were higher for both systems than the rule of mixture.

Synthesis of kappa -carrageenan-g-poly(acrylamide)/sepiolite nanocomposite hydrogels and adsorption of cationic dye

Abstract: In this study, nanocomposite hydrogels from grafting of acrylamide onto kappa-carrageenan biopolymer were prepared in the presence of sepiolite clay. Methylenebisacrylamide and ammonium persulfate were used as cross-linker and initiator, respectively. The sepiolite nanoclay was introduced into hydrogel matrix without any chemical treatment. The structure of nanocomposites was investigated by FTIR, SEM, TEM, and TGA techniques. The TEM image showed that sepiolite exists as individual needle’s shape. The swelling of hydrogels were studied in distilled water, salt solutions, and various pHs. The obtained nanocomposites were evaluated to remove of cationic crystal violet (CV) dye from water. The kinetic and isotherm of adsorption of dye onto nanocomposites were studied and analyzed according to kinetic and isotherm models. The results showed that the pseudo-second-order adsorption kinetic was predominated for the adsorption of CV onto nanocomposites. The experimental equilibrated adsorption capacity of nanocomposites was analyzed using Freundlich and Langmuir isotherm models. The results corroborated that the experimental data fit the Langmuir isotherm the best. By varying the pH of initial dye solution, while the clay-free hydrogel showed relatively pH-independent adsorption behavior, the nanocomposites depicted pH-dependent adsorption.

An improved method for preparing glutaraldehyde cross-linked chitosan–poly(vinyl alcohol) microparticles

Abstract: The features of microparticles, as size, surface structure, and morphology, depend, mainly, on the methodology used for their preparation. Emulsion polymerization techniques are undoubtedly among the most widespread. However, the use of toxic, volatile organic solvents represents a major disadvantage, namely, because of environmental issues. In this study, we prepared glutaraldehyde cross-linked chitosan–poly(vinyl alcohol) microparticles by an improved water-in-oil emulsion technique using corn oil as organic phase. The application of this polymeric blend as microparticle is scarcely investigated. As resulting of the procedure here presented, spherical and smooth surface microparticles were obtained, with mean diameter of 16 μm. The cross-linking reaction between the aldehyde and the amino or the hydroxyl groups formed either an imine (Schiff’s base) or an acetal bond, respectively, as analyzed by infrared spectroscopy. The microparticles here described did not present cytotoxic potential. Accordingly, this study can find promising and successful application in biotechnology.

Removal of methylene blue from aqueous solution by sorption on lignocellulose-g-poly(acrylic acid)/montmorillonite three-dimensional cross-linked polymeric network hydrogels

Abstract: Batch lignocellulose-g-poly(acrylic acid)/montmorillonite (LNC-g-PAA/MMT) hydrogel nanocomposites were applied as adsorbents. The nanocomposites were characterized by FTIR, XRD, SEM, and TEM. The results showed that montmorillonite (MMT) could react with the monomers and change the structure of polymeric network of the traditional superabsorbent materials, an exfoliated structure was formed in the nanocomposites. The effect of process parameters such as MMT content (wt%), contact time (t), initial concentration of dye solution (C0), adsorption temperature (T), and pH value (pH) of the dye solution for the removal of methylene blue (MB) from aqueous solution were also studied. The results showed that the adsorption capacity for MB increased with increasing contact time, initial dye concentration, and pH value, but decreased with increasing MMT content and temperature. The adsorption kinetics were better described by the pseudo-second-order equation, and their adsorption isotherms were better fitted for the langmuir equation. By introducing 20 wt% MMT into LNC-g-PAA polymeric network, the obtaining hydrogel composite showed the high adsorption capacity 1994.38 mg/g and economic advantage for MB. The desorption studies revealed that the composite provided the potential for regeneration and reuse after MB dye adsorption, which implied that the composite could be regarded as a potential adsorbent for cationic dye MB removal in a wastewater treatment process.

Effect of SiO2 and nanoclay on the properties of wood polymer nanocomposite

Abstract: Wood polymer composite (WPC) were developed by using solution blended high density polyethylene, low density polyethylene, polypropylene, poly(vinyl chloride), Phragmites karka wood flour and polyethylene-co-glycidyl methacrylate. The effect of addition of nanoclay and SiO2 on the properties of the composite was examined. X-ray diffractrometry and transmission electron microscopy were used to study the distribution of silicate layers and SiO2 nanopowder in the composite. The improvement in miscibility among the polymers and WPC was studied by scanning electron microscopy. Fourier transform infrared spectroscopy study revealed the interaction between polymer, wood, clay and SiO2. WPC treated with 3 wt% each of clay and SiO2 showed an excellent improvement in mechanical properties, thermal and flame retarding properties. Water uptake of WPC was found to decrease on incorporation of nanoclay and SiO2 in WPC.

Crystallization of poly(lactic acid) accelerated by cyclodextrin complex as nucleating agent

Abstract: Poly(lactic acid) (PLA) is a well-known biodegradable and biocompatible polyester with intrinsically slow crystallization rate. To extend its applications to the field where heat resistance is required, increasing the crystallization rate of the material becomes critical. In this note, the nucleation effect of supramolecular inclusion complex (IC), organized by non-covalent interactions through threading α-cyclodextrin molecules onto PLA chains, on the crystallization of PLA was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy. The formation of IC was confirmed by wide-angle X-ray diffraction and DSC measurements. It was found that the presence of PLA-IC significantly promoted the crystallization of PLA from both the non-isothermal and isothermal crystallization experiments. The nucleation mechanism was also discussed to some extent.

Electrospinning of poly (3-hydroxybutyric acid) and gelatin blended thin films: fabrication, characterization, and application in skin regeneration

Abstract: A tissue engineering scaffold should mimic the structure and biological function of native extracellular matrix proteins. Electrospinning is a simple and versatile method to produce ultrathin fibers for tissue engineering. Blended submicron fibers of poly (3-hydroxybutyric acid) and gelatin were electrospun using 1,1,1,3,3,3 hexafluoro-2-propanol as solvent. Cross linking of fibers was achieved using glutaraldehyde, and the resultant fibers were tested and analyzed using scanning electron microscopy (SEM), differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, and Fourier transformed infrared spectroscopy (FTIR).The fibers were found to exhibit good tensile strength. Degradation studies were performed and analyzed using SEM and FTIR and proved the stability of fibers for tissue engineering applications. The fibrous scaffold supported the growth and rapid proliferation of human dermal fibroblasts and keratinocytes with normal morphology, thus proving its reliability in using it as a potential scaffold for skin regeneration.

Synthesis and characterization of polyurethane/titanium dioxide nanocomposites obtained by in situ polymerization

Abstract: The development of new polymeric and polymeric based materials is fundamental to meet the market demands. This work aims the synthesis and characterization of polyurethane/titanium dioxide nanocomposite, using low cost commercial raw materials. Nanocomposites were synthesized by in situ polymerization reactions in which titanium dioxide were added in the following proportions, by weight, in relation to the mass obtained from the pure polymer: 0.5, 1.0, 2.0, 3.0, 5.0, 7.0, and 10.0 %. These reactions were based in poli (e-caprolactone) and 1,6-diisocyanatohexane. The materials were characterized by infrared spectroscopy Fourier transform, scanning electron microscopy, differential scanning calorimetry analysis, thermogravimetric analysis, dynamic mechanical thermal analysis, and UV–Vis spectroscopy. Based on the obtained results it was concluded that the nanocomposites synthesized by in situ polymerization presented, in general, thermal properties (degradation temperature) and mechanical properties higher than the pure polymer.

Conductivities enhancement of poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) transparent electrodes with diol additives

Abstract: High conductivity, good stability, and high transmittance in the visible region are the three essential requirements for the polymer electrodes used in the optoelectronic devices. It was found that with addition of diols, such as ethylene glycol, diethylene glycol, or poly(ethylene glycol) (PEG), to the poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS) emulsion before spin-coating could increase dramatically the conductivities of the resultant PEDOT:PSS thin films from 1 to 90 S cm−1 while maintain the optical transparency of the modified thin films. With up to −2.4 V potential applied, the PEDOT:PSS with PEG 200 additive does not show obvious color change, indicating its good electrochemical stability as polymer electrode. Detailed studies on the structures and morphologies of these modified PEDOT:PSS thin films, in comparison to that of PEDOT:PSS without additives were carried out using AFM, Raman, and FTIR to investigate the underlying mechanisms.

Study on the mechanical and morphological properties of toughened polypropylene blends for automobile bumpers

Abstract: Studies on the use of polyolefin elastomer (POE) and high density polyethylene (HDPE) for toughening polypropylene (PP) to meet the demands of automobile bumpers were conducted. The effect of the basic resin, POE and the influences of the POE amount and HDPE doses on the mechanical properties of the blended composites were discussed. The morphology of impact fracture sections were characterized by scanning electron microscopy (SEM) while the crystalline properties were investigated by DSC. The effect of the composites’ morphology on mechanical properties was also discussed. Results showed that POE could improve the impact strength of PP while the use of HDPE had obvious effects on synergistic toughening. SEM images and DSC data analysis testified to the relationship between morphology, crystallinity and the mechanical properties.

Thermal and mechanical properties of nano-titanium dioxide-doped polyvinyl alcohol

Abstract: Organic polymers exhibit poor thermal stability and inferior mechanical properties. Significant improvement in mechanical and thermal properties of polymers can be achieved by homogeneous distribution of inorganic materials preferably in nano size. In this study, these properties of polyvinyl alcohol were found to improve by addition of nano-titanium dioxide. Microwave irradiation method was used to prepare nano-titanium dioxide and doped in polyvinyl alcohol matrix to formulate the composite film. The spectral and morphological characterizations of the composites were carried out by the conventional techniques. Various mechanical properties were determined by Tinus Oisen universal testing machine. Thermal gravimetric analysis and differential scanning calorimetry were used for studying the thermal properties of the composites. Shift in decomposition temperature of polyvinyl alcohol indicated the enhanced thermal stability of polyvinyl alcohol. The composite also exhibited significant improvement in all the mechanical properties.

Synergistic effect of nanoTiO2 and nanoclay on mechanical, flame retardancy, UV stability, and antibacterial properties of wood polymer composites

Abstract: Wood–polymer nanocomposite (WPNC) based on styrene–acrylonitrile copolymer (SAN), γ-trimethoxy silyl propyl methacrylate-modified TiO2 nanoparticles, and nanoclay was prepared by impregnation. The flexural, tensile, and flame-retardant properties were improved. UV stability was evaluated by photo-induced weight loss, FTIR, loss in mechanical properties, and scanning electron microscopy. The results showed that UV stability was maximum for wood sample treated with SAN/TiO2 (0.5 %)/nanoclay (0.5 %). The presence of TiO2 nanoparticles in WPNC-exhibited antibacterial activity.

Thermal and dynamic mechanical properties of bio-based poly(furfuryl alcohol)/sisal whiskers nanocomposites

Abstract: In this study, bio-based nanocomposites of sisal whiskers-reinforced poly(furfuryl alcohol) (PFA) were prepared using an in situ polymerization method. Furfuryl alcohol (FA), which is a derived renewable monomer, was used to serve first as a solvent to disperse the whiskers and later as a monomeric precursor to produce PFA. Sisal whiskers were prepared via acid hydrolysis, which was followed by freeze-drying and re-dispersion of the dried whiskers in FA by sonication for 20 min. The polymerization process was catalysed using citric acid, which is also a renewable carboxylic acid found in citrus fruits. The effect of increased sisal whiskers loading on the thermal and dynamic mechanical properties of the nanocomposites was investigated using thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The TGA results showed slightly higher thermal stability for the nanocomposite samples compared to neat PFA. The DMA results showed that the incorporation of sisal whiskers imparts significant enhancement in the storage modulus of the PFA matrix. Moreover, the intensity of the tan δ peak at ~75 °C for the nanocomposites was remarkably reduced compared to that of neat PFA.

Enzymatic synthesis of poly(ε-caprolactone): thermal properties, recovery, and reuse of lipase B from Candida antarctica immobilized on macroporous acrylic resin particles

Abstract: Candida is a genus of yeast, and lipase B isolated from Candida antarctica (CALB) has been utilized as a biocatalyst for the synthesis of a variety of organic compounds including polyesters and polylactones. Among the various immobilization media reported in the literature, the porous acrylic resin utilized in Novozym-435 has been widely studied. Here, we report the enzyme recovery and reuse for the synthesis of poly(e-caprolactone) in toluene at 70 °C for 4 h per cycle for up to 10 reaction cycles, which consistently resulted in polymers with a weight-average molecular weight, M w , of ~50,000 g mol−1 and a polydispersity index of ~1.4. In addition, the thermal properties of the resin particles used in Novozym-435, with and without the enzyme, were evaluated by TGA and DSC analysis. The effect of mechanical agitation on the enzyme stability, recovery, and reuse was also discussed. These results may have significance to enzymatic polymer synthesis as well as to the enzyme immobilization on acrylic resins and other matrices.

Removal of methyl orange from aqueous solutions with poly(acrylic acid-co-acrylamide) superabsorbent resin

Abstract: Poly(acrylic acid-co-acrylamide) (P(AA-co-AM) superabsorbent resin was prepared by solution polymerization of acrylic acid (AA) and acrylamide (AM) using ammonium persulfate (APS) as an initiator and N,N′-methylenebisacrylamide (MBA) as a cross linker. P(AA-co-AM) was used for the removal methyl orange (MO) from aqueous solutions. Factors influencing the adsorption capacity, such as adsorption time, initial concentration of MO, dosage of the superabsorbent resin, pH value and ionic strength, were investigated in detail. It was found that P(AA-co-AM) was effective to remove MO from its aqueous solutions. The equilibrium adsorption capacity was 394.6 mg/g at room temperature as the initial concentration of MO was 3000 mg/L. The mechanism of the adsorption process was also speculated. Study on the equilibrium adsorption isotherms showed that the adsorption was in accordance with both Langmuir and Freundlich model. Further study of the adsorption kinetics showed that the adsorption process was consistent with the Pseudo second-order kinetic model.

Compatibility of waste rubber powder/polystyrene blends by the addition of styrene grafted styrene butadiene rubber copolymer: effect on morphology and properties

Abstract: Waste rubber powder/polystyrene (WRP/PS) blends with different weight ratio were prepared with styrene grafted styrene butadiene rubber copolymer (PS-g-SBR) as a compatibilizer. The graft copolymer of PS-g-SBR was synthesized by emulsion polymerization method and confirmed through Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC). The copolymer at different weight ratio was subsequently added into the blends. The effects of weight ratio of WRP/PS and compatibilizer loading on mechanical properties were investigated. PS/WRP blends in a weight ratio of 80/20 showed higher impact strength. Moreover, the impact strength of the blend materials increased with the addition of SBR-g-PS, however, decreased at a high loading of the copolymer. The morphology and thermal properties of WRP/PS blends were examined by DSC, scanning electron microscopy (SEM), thermogravimetry (TG). DSC indicated that compared with PS/WRP blend, the glass transition temperature (Tg) of PS matrix phase in PS/WRP/SBR-g-PS blend shifted to low temperature because of the formation of chemical crosslinks or boundary layer between PS and WRP, and the Tg of WRP phase of both the PS/WRP and PS/WRP/SBR-g-PS blends did not appear. SEM results showed that interfacial adhesion in the blends with the PS-g-SBR copolymer was improved. The morphology was a typical continuous–discontinuous structure. PS and WRP presented continuous phase and discontinuous phase, respectively, indicating the moderate interface adhesion between WRP and PS matrix. TG illustrated that the onset of degradation temperature in the PS/WRP/PS-g-SBR blend decreased slightly by contrast with PS/WRP blend and the degradation of PS/WRP blends with and without SBR-g-PS was completed about at the same values.

Nanoindentation study of individual cellulose nanowhisker-reinforced PVA electrospun fiber

Abstract: Electrospun poly(vinyl alcohol) (PVA) fiber and its composites have been widely studied recently. However, most physical properties reported in literature are measured from a nanofiber web. In this study, for the first time, the mechanical properties of individual electrospun fiber, rather than fiber web, of cellulose nanowhisker-reinforced poly(vinyl alcohol) was studied using nanoindentation technique. The modulus is 2.1 GPa for a pure PVA electrospun fiber, and 7.6 GPa for 20.0 wt% cellulose nanowhisker-reinforced PVA electrospun fiber, respectively. The modulus of PVA/cellulose nanowhisker electrospun fibers increases linearly with increasing loading ratio of cellulose nanowhiskers up to 20.0 wt%. The experimental results were compared with that calculated using isotropic and longitudinal Halpin–Tsai models. The modules of the cellulose nanowhiskers are 60–80 % higher than the isotropic model predictions but lower than longitudinal model prediction, suggesting the nanowhiskers are partially aligned to the electrospun fiber direction.

Facile preparation of poly(ε-caprolactone)/Fe 3 O 4 @graphene oxide superparamagnetic nanocomposites

Abstract: The main goal in this work was to prepare and characterize a kind of novel superparamagnetic poly(e-caprolactone)/Fe3O4@graphene oxide (PCL/Fe3O4@GO) nanocomposites via facile in situ polymerization. Fabrication procedure included two steps: (1) GO nanosheets were decorated with Fe3O4 nanoparticles by an inverse co-precipitation method, which resulted in the production of the magnetite/GO hybrid nanoparticles (Fe3O4@GO); (2) incorporation of Fe3O4@GO into PCL matrix through in situ polymerization afforded the magnetic nanocomposites (PCL/Fe3O4@GO). The microstructure, morphology, crystallization properties, thermal stability and magnetization properties of nanocomposites were investigated with various techniques in detail. Results of wide-angle X-ray diffraction showed that the incorporation of the Fe3O4@GO nanoparticles did not affect the crystal structure of PCL. Images of field emission scanning electron microscope and transmission electron microscopy showed Fe3O4@GO nanoparticles evenly spread over PCL/Fe3O4@GO nanocomposites. Differential scanning calorimeter and polar optical microscopy showed that the crystallization temperature increased and the spherulites size decreased by the presence of Fe3O4@GO nanoparticles in the nanocomposites due to the heterogeneous nucleation effect. Thermogravimetric analysis indicated that the addition of Fe3O4@GO nanoparticles reduced the thermal stability of PCL in the nanocomposites. The superparamagnetic behavior of the PCL/Fe3O4@GO nanocomposites was testified by the superconducting quantum interference device magnetometer analysis. The obtained superparamagnetic nanocomposites present potential applications in tissue engineering and targeted drug delivery.

Electrospinning of polyvinylalcohol–polycaprolactone composite scaffolds for tissue engineering applications

Abstract: Random nanofibrous composite scaffolds of PVA/PCL bilayer were fabricated by electrospinning method. The bilayer nanofibrous scaffolds were subjected to detailed structural, morphological, chemical, and thermal analysis using XRD, SEM, FTIR, and DSC. Morphological investigations revealed that the prepared nanofibers have uniform morphology and the average fiber diameters for bilayer samples A, B, and C are 203, 252, and 244 nm, respectively. The obtained scaffolds have a porous structure with porosity of 77, 89.2, and 78.3 % for bilayer samples A, B, and C, respectively. FTIR analysis ensured complete evaporation of solvent and formation of non-interactive bilayers. Biocompatibility of the membranes was investigated by studying the adhesion of mouse NIH 3T3 fibroblasts for 72 h, and its enhanced adhesion and proliferation proved its mettle as a potential scaffold for tissue engineering applications.

The synthesis of shape-controlled polypyrrole/graphene and the study of its capacitance properties

Abstract: Polypyrrole (PPy)/graphene nainocomposite was prepared by methyl orange (MO) reactive template. By changing the amount of MO, the morphology of PPy can be controlled to range from nanoparticle to nanowire. Transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction results demonstrated that the composites were successfully synthesized. The different morphologies of PPy/graphene nanocomposites had certain effects on the supercapacitor performance. The experimental results showed that the capacitance of PPy (nanoparticle)/graphene was higher than that of PPy (nanowire)/graphene. As a model, PPy (nanoparticle)/graphene was used to construct a supercapacitor. By changing the amount of pyrrole monomer, the performance of the supercapacitor prepared from different PPy content was studied in detail.

Effect of H12MDI isomer composition on mechanical and physico-chemical properties of polyurethanes based on amorphous and semicrystalline soft segments

Abstract: Two series of segmented thermoplastic polyurethanes were synthesized having 33 wt % hard segment based on 4,4′-dicyclohexyl methane diisocyanate with different trans–trans isomer contents and 1,3-propanediol chain extender. The soft segments were based on poly(hexamethylene–pentamethylene carbonate)diol and poly(butylene sebacate)diol, amorphous and semicrystalline polyol, respectively. 4,4′-Dicyclohexyl methane diisocyanate with different trans–trans isomer contents were obtained by fractional crystallization of commercial diisocyanate and were characterized by differential scanning calorimetry and nuclear magnetic resonance spectroscopy. 4,4′-Dicyclohexyl methane diisocyanate trans–trans isomer lead to some interesting properties in the synthesized polyurethanes, due to the more ordered hard domains formed by packing of trans–trans 4,4′-dicyclohexyl methane diisocyanate. Thereby, as 4,4′-dicyclohexyl methane diisocyanate trans–trans isomer content increased, a better phase separated structure was observed.

Crystallization behaviors and foaming properties of diatomite-filled polypropylene composites

Abstract: The non-isothermal crystallization kinetics and foaming properties of polypropylene (PP) filled with various contents of diatomite were investigated. The results showed that the diatomite had strong effects on the PP crystallization kinetics, which significantly increased the crystallization temperature and reduced crystallite size. These were attributed to the nucleation effect of the diatomite particles and the complex interface properties between the PP chains and diatomite particles. Non-isothermal crystallization can be well described by the Mo’s method. The non-isothermal crystallization activation energy calculated by the Kissinger’s method increased with increased content of diatomite. The foamed PP composites, in particular, the PP composites filled with 10 wt% diatomite had better cell morphology ascribed to the facilitated crystallization and increased polymer melt strength compared with the foamed pure PP.

Enhanced swelling and responsive properties of an alginate-based superabsorbent hydrogel by sodium p-styrenesulfonate and attapulgite nanorods

Abstract: In this work, a series of sodium alginate-g-poly(sodium acrylate-co-sodium p-styrenesulfonate)/attapulgite (NaAlg-g-poly(NaA-co-NaSS)/APT) superabsorbent composites were prepared by graft copolymerization using N,N’-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate as an initiator. Fourier transform infrared spectroscopy revealed that NaA and NaSS had been grafted onto NaAlg, and APT participated in polymerization reaction through reactive –OH groups. The introduction of proper amount of NaSS and APT induced the improved surface morphology, swelling capacity, and swelling rate. Moreover, the swelling behaviors of the superabsorbent composites were remarkably influenced by various salt medium, pH buffer solutions and organic solvents, and especially an intriguing swelling–deswelling behavior was observed with altering water/organic solvent ratio.

Effect of crosslinkers on size and temperature sensitivity of poly( N -isopropylacrylamide) microgels

Abstract: In this work, we study the effect of crosslinkers on the size and swelling properties of temperature sensitive N-isopropylacrylamide (NIPAAm) microgels produced by dispersion polymerization. The crosslinkers studied were N,N′-methylenebisacrylamide (MBA), ethylene glycol dimethacrylate (EGDMA) an 3,9-divinyl-2,4,8,10-tetra-oxaspiro[5.5] undecane (DVA). The type of crosslinker had a major impact on the size and swelling behavior, although the proportion of crosslinker used in each case was low (maximum 5 mol%). The effect can be related to the hydrophilic/hydrophobic characteristics of the crosslinkers. DVA produces smaller hydrogels with reduced swelling ratio, MBA produces bigger microgels with higher swelling ratio, while EGDMA results in an intermediate behavior. With increasing amount of crosslinker used in the synthesis, the extent of the swelling ratio decreases for DVA and EGDMA crosslinked microgels, while increases for MBA crosslinked microgels. There is also a slight effect on the critical transition temperature (T c) of the microgels from 30 °C (DVA) to 34 °C (MBA) as observed in copolymers of NIPAAm with hydrophilic or hydrophobic comonomers.

Synthesis and characterization of graft copolymer of sodium alginate and poly(itaconic acid) by the redox system

Abstract: In this study, grafting of itaconic acid (IA) onto sodium alginate (NaAlg) using cerium(IV) ammonium nitrate/nitric acid (CAN/HNO3) as redox system was carried out by free radical polymerization. The structures of the grafted copolymers (NaAlg-g-PIA) were characterized by ATR-FTIR spectroscopy, NMR spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The reaction conditions for maximum grafting were optimized by varying the reaction time, temperature, percentage of sodium alginate, monomer, initiator, and nitric acid concentrations. The optimum reaction conditions were obtained with reaction time of 5 h, reaction temperature of 30 °C, IA concentration of 0.92 M, CAN concentration of 1.368 × 10−1 M, HNO3 concentration of 0.094 M and percentage of NaAlg 0.5 g/dL. The solubility test of NaAlg-g-PIA was also investigated using solvents. The results indicate that prepared graft copolymer was non-soluble in the various solvents, while it was soluble only in saturated solution of NaOH and promising as an adsorbent.

Formation of stable crystalline connecting bridges during the fabrication of polypropylene microporous membrane

Abstract: The influence of hot stretching ratio and stretching temperature on the connecting bridge structure formed during the fabrication of polypropylene microporous membrane was studied It was found that with the increase of stretching ratio to 200 % under temperature of 130 °C, bridge length was increased Under the stretching ratio of 100 %, the main melting peak became wider, whereas similar phenomenon could not be seen under temperature of 110 °C Under the ratio of 200 % and temperature of 130 °C, strong bridge structure lead to appearance of small shoulder on the right of main melting peak Compared with that only through cold stretching, more connecting bridges were initiated during hot stretching The unrestrained tie chains due to the chain disentanglement under high temperature, which were not involved in the annealing crystallization and cold stretching, could be stretched and crystallized into bridges At the same time, some chains could also be pulled out from the initial lamellae All these contributed to the increase of bridge number During hot stretching, the broken bridges merged with other stable bridges and some bridges adhere to each other, resulting in the formation of stable bridges, which will be helpful to the stabilization of pore structure

Synthesis and characterization of poly(benzimidazolium) membranes for anion exchange membrane fuel cells

Abstract: Poly(dimethyl benzimidazolium) iodides were synthesized from polybenzimidazole derivatives by permethylation. They were easily changed to OH−, CO3 2− and HCO3 − ion conducting electrolytes by immersing in 1 M of KOH, K2CO3 and KHCO3. Properties of polymers were changed by the ion exchange process. The anion conducting membranes showed tough and flexible properties. The water uptake, ion exchange capacity and conductivity varied depending on the counter anions. One of the poly(dimethyl benzimidazolium) carbonate membranes, Me-DAB-OBBA-carbonate showed the highest water uptake (59 %) as well as ion conductivity (33.74 mS/cm at 80 °C), and could be a good candidate for an anion exchange membrane for anion exchange membrane fuel cells.

Novel blend microspheres of poly(vinyl alcohol) and succinyl chitosan for controlled release of nifedipine

Abstract: Water-soluble succinyl chitosan (SCS) was synthesized by reacting succinic anhydride with –OH and –NH2 reactive groups of chitosan (CS). The blend hydrogel microspheres were prepared from SCS with poly(vinyl alcohol) (PVA) by water-in-oil (w/o) emulsion cross-linking using glutaraldehyde (GA) as the cross-linking agent. Nifedipine (NFD), an antihypertensive drug having a plasma half-life of 2 h, was encapsulated giving encapsulation efficiency up to 92 % and its release was extended up to 12 h. Scanning electron microscopy (SEM) confirmed the spherical nature and smooth surfaces of the microspheres, while Fourier transform infrared spectroscopy (FTIR) confirmed succinylation of CS and chemical stability of NFD in the matrix. Thermogravimetry (TGA) and differential scanning calorimetry (DSC) characterized the SCS and the blend hydrogel microspheres. X-ray diffraction (XRD) and DSC were also used to study the crystalline or amorphous nature of NFD. Swelling and in vitro release experiments performed in pH 1.2 and 7.4 buffer media showed a dependence of blend composition, extent of cross-linking and pH of the media. The mechanism of drug release as analyzed by an empirical equation, suggested non-Fickian trends.