Showing papers in "Polymer Bulletin in 2011"

The concept of materials brittleness and its applications

Abstract: Brittleness is a significant property considered in product design and the research and development of materials. However, for a long time the methods to determine brittleness have been largely “hand-waving” arguments or else circumferential properties—in other words describing numerous properties related to brittleness but not actually quantifying brittleness itself. We have defined brittleness of polymeric materials quantitatively with applications to multiple areas. Relationships between brittleness and both tribology and mechanics have been discovered and are described. Moreover, the definition has been applied in the development of multilayer composite materials; structural integrity of the composites decreases with increasing brittleness. Other applications and the fact that toughness is not an inverse of brittleness are also discussed.

Removal of cationic dyes from aqueous solutions with poly ( N -isopropylacrylamide- co -itaconic acid) hydrogels

Abstract: In this study, N-isopropylacrylamide-based temperature and pH-sensitive hydrogels were synthesized by free radical polymerization for removal of cationic dyes from aqueous solutions. For this purpose, N-isopropylacrylamide was copolymerized with various amounts of sodium salt of itaconic acid in the presence of crosslinking agent (N,N-methylene bisacrylamide). The chemical structures of hydrogels were characterized by FT-IR analysis. In order to investigate swelling properties of the hydrogels, water absorption (swelling) and shrinking (deswelling) kinetics, the equilibrium swelling ratios in water and different pH buffer solutions, and the temperature dependent swelling ratios were determined. Then, their adsorption properties such as adsorption capacities, kinetics, isotherms were investigated in case of their usage in removal of Safranine T (ST), Brilliant Green (BG), and Brilliant Cresyl Blue (BCB) aqueous solutions. According to adsorbed dye amount, the adsorption capacities are followed the order BG > ST ≅ BCB. In addition, the results indicated that the pseudo-second-order kinetic model fitted better than the data obtained from pseudo-first-order model for the adsorption of all dyes onto hydrogels. Furthermore, according to effect of the initial dye concentration findings, it is concluded that, Freundlich isotherm explains the adsorption better than Langmuir isotherm.

A novel benzoxazine monomer with methacrylate functionality and its thermally curable (co)polymers

Abstract: Benzoxazine monomer with methacrylate functionality, namely 2-(2-(2H-benzo[e][1,3]oxazin-3(4H)-yl)ethoxy) ethyl methacrylate (BEM) was synthesized by simple esterification reaction of hydroxyl containing benzoxazine (B–OH) with methacryloyl chloride, and characterized. BEM was then copolymerized with styrene in 1:4 mol ratio by free radical polymerization using 2,2′-azobis(isobutyronitrile) (AIBN) as initiator. The structure, chemical composition, and molecular weight characteristics of the resulting copolymer were confirmed by FT-IR, 1H-NMR spectroscopy, and GPC, respectively. The curing behavior and thermal properties of both monomer and copolymer were also studied by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA).

Thermal and electrical properties of carbon nanotubes based polysulfone nanocomposites

Abstract: Carbon nanotubes (CNTs)-reinforced polysulfone (PSU) nanocomposites were prepared through solution mixing of PSU and different weight percent of multi-walled carbon nanotubes (MWCNTs). Thermal properties of nanocomposites were characterized using thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA studies revealed an increase in thermal stability of the PSU/MWCNTs nanocomposites, which is due to the hindrance of the nanodispered carbon nanotubes to the thermal transfer in nanocomposites and also due to higher thermal stability of CNTs. Morphological properties of nanocomposites were characterized by high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscope (FESEM). The influence of CNTs loading on electrical properties of PSU/MWCNTs nanocomposites was studied by the measurement of AC and DC resistivity. Dielectric study of nanocomposites was carried out at different frequencies (10 Hz–1 MHz) by using LCR meter. An increase in dielectric constant and dielectric loss was observed with increase in CNTs content, which is due to the interfacial polarization between conducting CNTs and PSU.

Effect of different amounts of surfactant on characteristics of nanoencapsulated phase-change materials

Abstract: Phase-change nanocapsule particles are successfully synthesized by the two-step miniemulsion polymerization method. Urea–formaldehyde resin is used as the shell material. Hexadecane is used as the core material. The particle size distribution and the surface morphology of nanocapsules are characterized by laser particle size analyzer, optical and scanning electron microscopy. The thermal properties are investigated by differential scanning calorimeter. The effects of the amounts of surfactant (AS) on the properties of prepared nanocapsules are also investigated. The results indicated that the nanocapsules have smooth surface and the mean particle size is about 270 nm; nano-structure of capsules has not changed dramatically after being heated at 100 °C for 72 h; The phase-change enthalpy of nanocapsules increases from 114.6 to 143.7 J/g with the increasing of the AS, but the mean particle diameter decreases from 285 to 253 nm; The degree of undercooling of hexadecane decreases about average 94% after being encapsulated in capsules.

Removal of heavy metals from aqueous solution by poly(acrylamide-co-acrylic acid) modified with porous materials

Abstract: In this study, a series of poly acrylamide-co-acrylic acid/NaY zeolite, poly acrylamide-co-acrylic acid/MCM-41, and poly acrylamide-co-acrylic acid/clinoptilolite nanocomposites were synthesized. These materials were characterized by using FT-IR spectroscopy, XRD, TGA, and SEM. Removal capacity of Pb(II) and Cd(II) ions in aqueous solutions by using these nanocomposites was investigated with controlled time, initial metal ions concentration, pH values, adsorbent content, and temperature by using atomic absorption spectrometry. Results show that these nanocomposites have further adsorption related to NaY, MCM-41, and clinoptilolite. Poly(AAm-co-AAc)/NaY, poly(AAm-co-AAc)/MCM-41, and poly(AAm-co-AAc)/clinoptilolite exhibit superior Pb(II) (about 90–99%) and Cd(II) (about 88–98%) adsorption behavior at room temperature and the poly(AAm-co-AAc)/NaY nanocomposite had the best adsorption behavior. Finally, the equilibrium removal performance of the composites is analyzed according to the Langmuir and Freundlich adsorption isotherm model that shows result fitted to Langmuir model and have monolayer adsorption.

Effect of emulsifier on poly(urea–formaldehyde) microencapsulation of tetrachloroethylene

Abstract: Microcapsules containing tetrachloroethylene as an internal phase were prepared by in situ polymerization of urea–formaldehyde (UF) without prepolymerization The effects of different emulsifiers on the process of microencapsulation and morphology of microcapsules were investigated The results show that the emulsifier gum arabic (GA) can effectively slow down the deposition rate of resin onto the oil/water interface, which can lead to smooth and compact surface of microcapsules The surface activity of GA was also enhanced by complex formation of gum arabic and sodium dodecyl benzene sulfonate The microcapsules represent good thermal and barrier property as a result of the formation of capsule wall with compact microstructure

Crystallization morphology and crystallization kinetics of poly(lactic acid): effect of N -Aminophthalimide as nucleating agent

Abstract: The effect of N-Aminophthalimide compound (NA-S) as nucleating agent on crystallization behavior and morphology of poly(lactic acid) was studied. With polarized optical microscope (POM), the unique phenomena of nucleation and epitaxial crystallization of PLA/NA-S system were observed. Dynamic morphology of crystallization was also studied by POM to investigate the relationship between growth behavior of PLA and nucleating agent. Isothermal and non-isothermal crystallization behavior of PLA were studied by differential scan calorimeter (DSC). When nucleating agent was added, a new peak appeared in wide angle X-ray diffraction (WAXD) compared with pure PLA, indicating the nucleating effect of NA-S on crystallization of PLA. All the results indicate that the nucleating agent of NA-S shows obvious nucleating effect on isothermal crystallization above 120 °C and in non-isothermal crystallization after it is added in PLA, that is, the induction crystallization time is reduced, the crystallization rate and nucleation density of PLA are increased.

Thermal properties and degradation characteristics of polylactide, linear low density polyethylene, and their blends

Abstract: Melt blending of linear low density polyethylene (LLDPE) and polylactide (PLLA) was performed in an extrusion mixer with post extrusion blown film attachment with and without compatibilizer-grafted low density polyethylene maleic anhydride. The blend compositions were optimized for tensile properties as per ASTM D 882-91. Based on this, LLDPE 80 (80 wt% LLDPE & 20 wt% PLLA) and M-g-L 80/4 (80 wt% LLDPE, 20 wt% PLLA and 4 parts compatibilizer per hundred parts of resin) were found to be an optimum composition. FTIR reveals that the presence of compatibilizer shifts carbonyl peak hence some increase in interaction between LLDPE and PLLA. Morphological characteristics of the fracture surface of with and without compatibilizer blends were examined by scanning electron microscopy. It shows that use of compatibilizer enhances the dispersions of PLLA in LLDPE matrix. Thermogravimetric (TG) analysis of blends shows the M-g-L 80/4 blend has higher thermal stability among studied blends. The degradation study under different pH of soil compost gives that in alkaline condition and the presence of compatibilizer was favorable for degradation. This blend may be used for packaging application.

Characterization of thermo-sensitive hydrogels based on poly(N-isopropylacrylamide)/hyaluronic acid

Abstract: In this study, an hydrogel was synthesized from the monomer N-isopropylacrylamide (NIPA), generating the poly(N-isopropylacrylamide) (PNIPA) and other formulations were synthesized in the presence of 1, 2, and 3% hyaluronic acid (HA) for obtain an interpenetrating polymer network. For all the obtained hydrogels, the thermo-sensitive response was studied since the lower critical solution temperature (LCST) and was analyzed by differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and oscillatory rheology at constant frequency as a function of temperature. The LCST transition temperature (Tt onset) was found between 34.4 and 35.5 °C. By scanning electron microscopy (SEM) PNIPA-HA formulations showed a porous morphology. The applicability of the hydrogels as injectable and non-toxic materials was verified, respectively, by rheology results and by cytotoxicity studies through an in vitro test of cell hemolysis on blood agar.

Hydrogel nanocomposite sorbents for removal of basic dyes

Abstract: Hydrogel nanocomposites having high amount of functional group, enhanced swelling ability, and improved mechanical properties were prepared for removal of basic dyes from aqueous solutions. Acrylamide (AAM) and itaconic acid sodium salt (IANa) were polymerized using polyethyleneglycol (400) diacrylate as crosslinker in the presence of montmorillonite (MMT). The products were characterized by swelling degree, total basic group content, XRD analysis, and FTIR spectroscopy. It was observed that MMT addition increased the itaconic acid gelation. The incorporation of low amount of MMT into the hydrogel structure increased also swelling degree. The products were used as adsorbent for removal of brilliant cresyl blue (BCB) from aqueous solutions. It was observed that the adsorption of BCB onto the nanocomposite completed in 30 min. It was found that the adsorption kinetics followed a pseudo-second-order kinetic model. Equilibrium isotherm of nanocomposite was analyzed using Freundlich and Langmuir isotherms. It was seen that the Langmuir isotherm model fit the adsorption data. These hydrogel nanocomposites have been shown to have the potential to be used as novel, fast-responsive and high capacity adsorbent materials for the removal of cationic dyes which is a serious problem, especially in textile industry.

Water resistance and thermal stability of hybrid lignocellulosic filler–PVC composites

Abstract: In this study, composites based on polyvinyl chloride (PVC), pulp fiber (PF), and wood flour (WF) were made by injection molding. The effects of two variable factors, namely the filler form and filler loading level, on the composite physical properties were examined. The result clearly showed that the major part of water absorption was due to water absorption of PF. It was found that the water absorption in the lignocellulosic material base composites is significantly higher than the neat PVC. Besides, the water absorption increased sharply with increasing cellulosic filler loadings in the composites. In case of hybrid composites, the rate of water uptake correlated with percentage weight of WF, lower WF (higher PF) loadings in composites exhibit higher rate of absorption. The higher onset of degradation temperature indicates the improved thermal stability of the samples. In other words, the result clearly illustrates that the thermal property of the composites increases after using PF and further increases after addition of WF.

Enhanced interfacial interaction for effective reinforcement of poly(vinyl alcohol) nanocomposites at low loading of graphene

Abstract: The graphene/poly(vinyl alcohol) (PVA) nancomposites with homogeneous dispersion of the nanosheet and enhanced nanofiller–matrix interfacial interaction were fabricated via water blending partially reduced graphene oxide and PVA. The nanocomposites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetry. The graphene nanosheets were fully exfoliated in the PVA matrix and a new covalent linkage was formed between graphene and PVA matrix. Uncommon to conventional method, the enhanced interfacial adhesion resulted from covalent interaction and hydrogen bondings between graphene and PVA backbone. The mechanical and thermal properties of the nanocomposites were significantly improved at low graphene loadings. An 116% increase in tensile strength and a 19 °C improvement of onset thermal degradation temperature were achieved by the addition of only 0.8 wt% graphene.

Antifouling ability of polyethylene glycol of different molecular weights grafted onto polyester surfaces by cold plasma

Abstract: Different molecular weights of polyethylene glycol (PEG, MW 200, 400, 600, 2000, and 4600) were grafted onto silicon tetrachloride (SiCl4) plasma functionalized polyethylene terephthalate (PET) surfaces. Dramatic increase of the C–O peak in the C1s high-resolution spectra determined by electron spectroscopy for chemical analysis suggests that PEG was successfully grafted. PEG-grafted PET showed significant inhibition of attachment and biofilm formation by Salmonella enterica sv. Typhimurium compared to unmodified PET. The antifouling ability of PEG-grafted PET surfaces was affected by the molecular weight of PEG and PEG2000 was the most effective. Both PEG600- and PEG2000-grafted PET also significantly inhibited biofilm formation by Listeria monocytogenes. Stability tests showed that over 2-month storage under ambient conditions PEG2000-grafted PET demonstrated reduced antifouling ability, but still significantly reduced biofilm formation by S. enterica sv. Typhimurium.

Soluble polyimides based on a novel pyridine-containing diamine m,p-PAPP and various aromatic dianhydrides

Abstract: A novel pyridine-containing aromatic diamine monomer, 4-phenyl-2,6-bis[3-(4-aminophenoxy)phenyl]pyridine (m,p-PAPP), was successfully synthesized by a modified Chichibabin reaction of benzaldehyde and a substituted acetophenone, 3-(4-nitrophenoxy)acetophenone (m,p-NPAP), followed by a reduction of the resulting dinitro compound 4-phenyl-2,6-bis[3-(4-nitrophenoxy)phenyl]pyridine (m,p-PNPP) with Pd/C and hydrazine monohydrate. The aromatic diamine was employed to synthesize a series of pyridine-containing polyimides (PIs) by polycondensation with various aromatic dianhydrides in N,N-dimethylformamide (DMF) via the conventional two-step method, and further thermal or chemical imidization forming PIs. The inherent viscosities of the resulting poly(amic acid)s and PIs were 0.59–0.73 and 0.56–0.68 dL/g; most of the PIs obtained by chemical imidization were readily soluble in common organic solvents such as DMF, N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), etc. Meanwhile, strong and flexible PI films were obtained, which had good thermal stability, with the glass transition temperature (Tg) of 204.5–237.4 °C and the temperature at 10% weight loss of 527.7–552.0 °C in nitrogen atmosphere, as well as outstanding mechanical properties with tensile strengths of 88.6–90.4 MPa, a tensile moduli of 1.04–1.56 GPa, and elongations at break of 7.2–8.7%. The PI films also were found to possess low water uptake of 0.89–0.98%.

Poly(lactic acid) blends with desired end-use properties by addition of thermoplastic polyester elastomer and MDI

Abstract: The disadvantages of the poor mechanical properties of polylactic acid (PLA) limit its ability to be used in a wide number of applications. Melt blending of PLA and thermoplastic polyester elastomer (TPEE) has been performed in an effort to toughen the PLA without significant losses in modulus and ultimate tensile strength. In order to enhance the compatibility of PLA and TPEE, a diisocyanate compound was used as a reactive modifier. The thermal and mechanical properties, miscibility and phase morphologies of the blends were investigated. A blend of PLA and TPEE with a modifier does not lead to an important drop in tensile strength and modulus whereas the elongation at break is characterized by a significant increase (above 300%), compared with that of neat PLA and PLA/TPEE. The blends of PLA/TPEE/Modifier were found by thermal and fractured surface analysis to be an immiscible system with the addition of a modifier. However, the relative ductility of PLA/TPEE/Modifier is 34 times higher than that of neat PLA. The brittle fracture of neat PLA was transformed into a ductile fracture by the addition of a modifier.

Poly(hydroxybutyrate-co-hydroxyvalerate) microspheres loaded with atrazine herbicide: screening of conditions for preparation, physico-chemical characterization, and in vitro release studies

Abstract: Due to their widespread use in agriculture as well as in urban areas, agricultural chemicals are globally some of the most commonly encountered substances in waters. The objective of this study is to develop (including preparation and characterization) a new modified release system for the herbicide atrazine, employing poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) microspheres. The microspheres were prepared by the emulsification/solvent evaporation method, emulsifying an organic phase (atrazine and PHBV dissolved in chloroform) into an aqueous phase containing polyvinyl alcohol (PVA) as surfactant, under stirring, and then evaporating the solvent. A 24-1 fractional factorial design, investigating the influence of four variables at two levels, was performed to obtain formulations with optimized association efficiencies. There was a greater dependence of association efficiency on PVA concentration (negative) and the mass of polymer (positive) with lesser influence of both stirring speed and organic phase volume. The size of the particles was assessed using scanning electron microscopy, which showed that the particles were rough-surfaced spheres. The results obtained are promising, since the formulations presented encapsulation efficiency near 25% and the release kinetics profile of atrazine was altered when it was encapsulated in the microparticles, indicating that these systems may be efficient in reducing the environmental impact caused by the herbicide, hence making it safer to use.

Fabrication and characterization of silica modified polyimide–zeolite mixed matrix membranes for gas separation properties

Abstract: In this study, new monomers having silica groups were synthesized as an intermediate for the preparation of poly(imide siloxane)-zeolite 4A and 13X mixed matrix membranes (MMMs). The effects of membrane preparation steps, zeolite loading, precursor’s composition, and pore size of zeolite on the gas separation performance of these mixed matrix membranes were studied. The new diamine monomer was prepared from 3,5-diaminobenzoic acid (3,5-DABA), 3-aminopropyltrimethoxysilane (3-APTMS), and zeolite 4A and zeolite 13X in N-methyl-2-pyrollidone (NMP) at 180 °C. Poly(imide siloxane)-zeolite 4A and 13X MMMs were synthesized from pyromellitic dianhydride (PMDA) and 4,4-oxydianiline (ODA) in NMP using a two-step thermal imidization. SEM images of the MMMs show the interface between polymer and zeolite phases getting closer when surface modified zeolite is used. The increase in glass transition temperature (Tg) confirms the polymer chain becoming more rigid induced by the presence of zeolite. The experimental results indicated that a higher zeolite loading resulted in a decrease in gas permeability and an increase in gas pair selectivity. In terms of O2 and N2 permeance and ideal selectivity, the separation performances of poly(imide siloxane)-zeolite MMMs were related to the zeolite type and zeolite pore dimension.

Enhanced adsorption properties of interpenetrating polymer network hydrogels for heavy metal ion removal

Abstract: In this study, sequential interpenetrating polymer network (IPN) hydrogels based on poly(polyethylene glycol diacrylate) poly(PEGDA) and poly(methacrylic acid) (PMAA) were prepared with enhanced adsorption properties for heavy metal ion removal. The swelling behavior and mechanical property of the IPN hydrogels were characterized. It was found that swelling ratio increased, and mechanical strength decreased with the PMAA content in the IPN. The IPN hydrogels were used to remove heavy metal ions from aqueous solution under the non-competitive condition. The effects of pH values of the feed solution at the range of 3–5 and PMAA content in the IPN on the adsorption capacity were investigated. The results indicated that the adsorption capacity of the IPN hydrogels increased with the pH values and PMAA content in the IPN. Furthermore, the synergistic complexation of metal ions with two polymer networks in the IPN was found in the adsorption studies. Regeneration studies suggested that metal rebinding capacity of the IPN hydrogels did not change significantly through repeated applications compared with the first run. It was concluded that the poly(PEGDA)/PMAA hydrogels could be used as fast-responsive, high capacity, and renewable sorbent materials in heavy metal removing processes.

Study on properties of nanocomposites based on HDPE, LDPE, PP, PVC, wood and clay

Abstract: Wood polymer nanocomposite (WPC) was prepared by solution blending of high density polyethylene, low density polyethylene, polypropylene and polyvinyl chloride (1:1:1:0.5) with wood flour and nanoclay. Xylene and tetrahydrofuran were used as solvent and the ratio was optimized at 70:30. TEM study revealed better dispersion of silicate layers in WPC loaded with 3 wt% of clay. WPC loaded with 3 wt% nanoclay exhibited higher thermal stability compared to WPC loaded with 1 and 5 wt% clay. The storage and loss modulus were found to enhance on incorporation of clay to WPC. The damping peak was found to be lowered by the addition of clay to WPC. Limiting oxygen index value increased due to incorporation of nanoclay. WPCs were subjected to exposure to cellulase producing Bacillus sp. and it showed the growth of bacteria as revealed by SEM study. Mechanical properties of WPC decreased due to degradation by bacteria. Water vapour uptake of WPC decreased due to addition of nanoclay.

Comparison of succinylation methods for bacterial cellulose and adsorption capacities of bacterial cellulose derivatives for Cu2+ ion

Abstract: Bacterial cellulose (BC) was homogenously modified with succinic anhydride in N,N-dimethylacetamide/LiCl in the presence of triethylamine and heterogeneously in pyridine in the presence of 4-dimethylaminopyridine. FTIR, XRD, 13C CP MAS NMR, SEM were used to characterize BC and succinylated bacterial cellulose (SBC). For homogeneous modification, the degree of substitution (DS) of SBC differs from 0.21 to 1.45 with the variation of the adding amount of succinic anhydrate, temperature, reaction time, and the amount of triethylamine. DS and XRD profiles reveal that heterogenous reaction mainly happens on the surface of BC membrane. The adsorption capacity and mechanism of Cu2+ onto BC and SBC were investigated. The result shows the adsorption is affected by the morphology and the DS of adsorbents.

Synthesis and solution properties of novel comb-shaped acrylamide copolymers

Abstract: An amphiphilic macro-monomer of allyl polyoxyethylene-12 ether with butyl-end group (AE12B) was synthesized, and its chemical structure was characterized. AE12B and the other two macro-monomers with different hydrophobic and hydrophilic groups were copolymerized with acrylamide to prepare the novel comb-shaped acrylamide copolymer (CPAM) through aqueous free radical polymerization. The solution properties of CPAM with different side-chain lengths were studied and compared with those of partially hydrolyzed polyacrylamide (HPAM). The experimental results show that the obtained CPAM, compared to HPAM, exhibited a dramatic enhancement in the heat- and salt-resistant properties. In addition, the increase of the side-chain length and the amount of hydrophobic groups in the side-chain improved the thickening properties of CPAM solution under high temperature and high mineralization conditions. Among the investigated macro-monomers, AE12B was optimized for the enhanced thickening properties of the CPAM solution.

Metathesis of renewable products: degradation of natural rubber via cross-metathesis with β-pinene using Ru-alkylidene catalysts

Abstract: Renewable β-pinene and natural rubber (NR) were used in the cross-metathesis reactions for the synthesis of terpene-terminated oligomers. The metathesis was carried out under solvent-free conditions using the second generation Grubbs catalyst (I). Isolated yields of oligomers were high and ranged between 80 and 90%. It was shown that the molecular weights of products may be changed in a wide range by controlling the ratio of β-pinene to NR. The formation of β-pinene and NR cross-metathesis products during chain transfer was confirmed using a model reaction of β-pinene with (Z)-3-methyl-2-pentene.

Mechanical and thermal characterization of cis -polyisoprene and trans -polyisoprene blends

Abstract: Measurements of mechanical and thermal transport properties have been made on the blends of cis-polyisoprene (CPI) and trans-polyisoprene (TPI) prepared by a solution casting method. Characterization of these blends has been done using wide angle X-ray scattering. Thermo-mechanical, mechanical, and thermal transport properties have been determined employing dynamic mechanical analyzer (DMA) and transient plane source. Storage modulus and tan δ as determined from DMA have been found to increase and decrease with the increase in TPI content, respectively. Mechanical properties such as Young’s modulus and tensile strength, as determined from strain–stress behavior of CPI/TPI blends, have been found to increase with increasing TPI content. This increase in properties has been explained on the basis of the crosslink density, calculated using theory of rubber elasticity. Thermal transport properties such as thermal conductivity, thermal diffusivity, and volumetric heat capacity are higher for all the three blends as compared to their pure components.

Synthesis and properties of cationic polyurethane-fluorinated acrylic hybrid latexes by emulsifier-free emulsion polymerization and the solvent-free method

Abstract: A series of cationic polyurethane-fluorinated acrylic hybrid latex (PUFA) have been synthesized by solvent-free method. In the method, vinyl monomers acted as dilution agent and the polyurethane (PU) having quaternary ammonium groups acted as macromolecular emulsifier without using any other solvent and surfactant. The structure and properties of PUFA were characterized by Fourier transform infrared spectroscopy (FT-IR), F19 nuclear magnetic resonance (F19 NMR), particle size distribution (PSD) analysis, transmission electron microscopy (TEM), contact angle (CA), surface free energy analysis, scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometry (EDS), and thermogravimetric (TG) analysis. The FT-IR, F19 NMR, and EDS confirmed that the FA monomer had been introduced into the chain of the PUFA hybrid polymer. The PSD analysis indicated the particles of PUFA were smaller than corresponding pure PU dispersion and narrower in particle size distribution. The CA and surface free energy analysis proved the PUFA hybrid latex film with fluorine possessed higher contact angle and lower surface free energy in contrast with the film without fluorine. The FPUA films exhibited good surface property which could be enhanced at higher annealing temperature. The EDS of PUFA confirmed the fluorine enrichment on the surface of PUFA. TG analysis suggested the PUFA hybrid latex film had a better thermal stability than pure PU.

pH-responsive swelling behavior, elasticity and molecular characteristics of poly(N,N-dimethylaminoethyl methacrylate) gels at various initial monomer concentrations

Abstract: The equilibrium swelling degree and the modulus of elasticity of pH-responsive poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) gels prepared at various initial monomer concentrations were investigated both in buffer solutions and in aqueous salt solutions. As pH of the solution is increased, PDMAEMA gels first remain in the swollen state up to pH 7.7, then exhibit pH-sensitive phase transitions at 8.0 in which PDMAEMA gels attain a collapsed state. The swelling kinetic measurements of PDMAEMA gels showed that pH sensitivity of PDMAEMA is quite stable and the swelling process is reproducible in accordance with pH changing. The swelling behavior of PDMAEMA gels was analyzed by Flory-Rehner theory and the results were combined by the results of compression measurements to calculate the molecular characteristics of gels. The resulting pH-responsive PDMAEMA gels were elastic and displayed good swelling behavior both in buffer solutions and in aqueous salt solutions, therefore, they can be used as a kind of carrying material in drug delivery systems.

Methacrylate-based ionic liquid: radical polymerization/copolymerization with methyl methacrylate and evaluation of molecular weight of the obtained homopolymers

Abstract: Azobisisobutyronitlite (AIBN)-induced free radical polymerization of a methacrylate-based ionic liquid monomer, 1-(2-methacryloxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (Met-IL) was carried out in a common organic solvent, N,N-dimethylformamide (DMF), and an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMImTFSI). The molecular weight of the obtained poly(Met-IL) was evaluated by transforming it to non-ionic poly(methyl methacrylate) with hydrolysis of the imidazolium-salt-substituted pendant ester groups and methyl esterification. Radical copolymerization with methyl methacrylate (MMA) was also carried out in both DMF and EMImTFSI. Analysis of copolymer composition revealed that the reactivity of Met-IL was lower than that of MMA in both DMF and EMImTFSI solutions.

Preparation and evaluation of O-carboxymethyl chitosan/cyclodextrin nanoparticles as hydrophobic drug delivery carriers

Abstract: In present study, novel composite nanocarriers comprised of O-carboxymethyl chitosan/β-cyclodextrin (O-CMC/β-CD) nanoparticles (NPS) were prepared and used to improve the bioavailability of hydrophobic drugs. Ibuprofen (IBU) was selected as a model drug and chitosan/β-CD (CS/β-CD) NPS were also prepared as control. The prepared NPS were characterized by FT-IR spectroscopy and X-ray diffraction. IBU entrapment of up to 93.25 ± 2.89% was obtained as determined by UV spectrophotometer. The NPS were spherical in shape with average particle sizes of 166 nm. The in vitro release studies were performed in simulated gastric medium (pH 1.2) and simulated intestinal medium (pH 6.8). The release rate of IBU from the O-CMC/β-CD NPS was slower than CS/β-CD NPS in simulated gastric medium. However, the converse tendency was observed in simulated intestinal medium. These results suggested that O-CMC/β-CD NPS were more suitable for the oral delivery of hydrophobic drugs compared with the CS/β-CD NPS.

Immobilization horseradish peroxidase on amine-functionalized glycidyl methacrylate-g-poly(ethylene terephthalate) fibers for use in azo dye decolorization

Abstract: Activated fibers were used as a new support material for the immobilization of horseradish peroxidase (HRP). Poly(ethylene terephthalate) (PET) fibers were grafted with glycidyl methacrylate (GMA) using benzoyl peroxide (Bz2O2) as initiator. 1,6-diaminohexane (HMDA) was then covalently attached to this GMA grafted PET fibers. HMDA-GMA-g-PET fibers were activated with glutaraldehyde and HRP was successfully immobilized. Both on the free HRP and the immobilized HRP activities, pH, temperature, thermal stability, and reusability were investigated. Both free enzyme and immobilized enzyme were used in a batch process for the degradation of azo dye. About 98% of azo dye removal was observed with immobilized HRP, while 79% of azo dye removal was found with the free HRP. 45 min of the contact time is sufficient for the maximum azo dye removal. The HRP immobilized on modified PET fibers were very effective for removal of azo dye from aqueous solutions.

Nanocomposites of PLA/PP blends based on sepiolite

Abstract: In the present study, the effectiveness of four polymers grafted with maleic anhydride used as compatibilizers in blends with poly(lactic acid) and its composites with sepiolite as matrices was evaluated in terms of transmission and scanning electron microscopy, oscillatory shear flow and tensile properties. Two polypropylenes were used as dispersed phases in the blends prepared in a corotating twin-screw extruder. Results showed that the compatibilized blends prepared without clay have higher susceptibility to isothermal degradation and higher tensile toughness than those prepared with sepiolite. The blend with the grafted metallocene polyethylene as compatibilizer exhibited the highest tensile toughness. The composites based on polyblends with polypropylene displayed lower tensile strength and Young’s modulus values, increased values of elongation at break, tensile toughness, complex viscosity, and storage modulus compared to those of the nanocomposite of PLA. These results are related to the clay dispersion, to the type of morphology of the different blends, to the grafting degree of the compatibilizers, and to the migration of the sepiolite toward the PP interface.