Showing papers in "Journal of Applied Polymer Science in 2007"

Injection-molded short hemp fiber/glass fiber-reinforced polypropylene hybrid composites—Mechanical, water absorption and thermal properties

Abstract: Natural fiber-based thermoplastic composites are generally lower in strength performance compared to thermoset composites. However, they have the advantage of design flexibility and recycling possibilities. Hybridization with small amounts of synthetic fibers makes these natural fiber composites more suitable for technical applications such as automotive interior parts. Hemp fiber is one of the important lignocellulosic bast fiber and has been used as reinforcement for industrial applications. This study focused on the performance of injection-molded short hemp fiber and hemp/glass fiber hybrid polypropylene composites. Results showed that hybridization with glass fiber enhanced the performance properties. A value of 101 MPa for flexural strength and 5.5 GPa for the flexural modulus is achieved from a hybrid composite containing 25 wt % of hemp and 15 wt % of glass. Notched Izod impact strength of the hybrid composites exhibited great enhancement (34%). Analysis of fiber length distribution in the composite and fracture surface was performed to study the fiber breakage and fracture mechanism. Thermal properties and resistance to water absorption properties of the hemp fiber composites were improved by hybridization with glass fibers. Overall studies indicated that the short hemp/glass fiber hybrid polypropylene composites are promising candidates for structural applications where high stiffness and thermal resistance is required. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2432–2441, 2007

Synthesis and characterization of core-shell SiO2 nanoparticles/poly(3-aminophenylboronic acid) composites

Abstract: SiO2/Poly(3-aminophenylboronic acid) (PAPBA) composites were synthesized under different experimental conditions, using ultrasonic irradiation method. Polymerization was carried out in the presence of sodium fluoride and D-fructose to anchor 3-aminophenylboronic acid groups on to SiO2 surface. The SiO2/PAPBA nanocomposite prepared by NaF and D-fructose in the polymerization medium was found to show different morphology, electrical properties, thermal behavior and structural characterization in comparison to the nanocomposites prepared under other conditions. Ultrasonic irradiation minimizes the aggregation of nanosilica and promotes anchoring of PAPBA units over SiO2 surface. The morphology of PAPBA/ SiO2 nanocomposite was investigated by using transmission electron microscopy, UV-visible spectroscopy; thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray diffraction analysis were used for characterization. Transmission electron microscope of the nanocomposites observation shows that SiO2/PAPBA composite, prepared with D-fructose and NaF under ultrasonication has a core–shell morphology. The thermal and crystalline properties of core-shell SiO2/PAPBA nanocomposite was prepared via ultrasonication method is different from the SiO2/PAPBA nanocomposite prepared via conventional stirring method, in which SiO2 nanoparticles are submerged in PAPBA. Conductivity of the composite prepared via ultrasonication shows around 0.2 S/cm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2743–2750, 2007

Investigation on process parameters of electrospinning system through orthogonal experimental design

Abstract: Electrospinning is a very simple and versa- tile method of creating polymer-based high-functional and high-performance nanofibers. But most of the investiga- tions are not systematic and describe the electrospinning process without quantitative accuracy. Inconsistent and even opposite results have been reported, which has hin- dered the consistent interpretation of the experiments. Or- thogonal experimental method was used to investigate qualitative and quantitative correlations between fiber characteristics (diameters and morphologies) and the pro- cessing and materials parameters. Uniform fibers can be obtained without any beads by proper selection of the processing parameters, and a lower glass transition tem- perature was observed for electrospun fibers than that of native polymer. Results of statistical analysis showed that significant influences were observed for polymer molecular weight and solution concentration on fiber diameters, and there were significant effects of polymer molecular weight, solution concentration, and solvent system on fiber mor- phologies. Meanwhile, solution concentration and polymer molecular weight, and polymer molecular weight and sol- vent system had obvious interaction effects. Regression analysis revealed quantitative relations of fiber diameters and beads percent, that is, Y1 ¼ 72.8X1 � 8.1X2 þ 138.8, Y2 ¼� 3.2X1 þ 0.4X2 þ 60.5, where Y1 is fiber diameter (nm), Y2 beads percent (%), X1 solution concentration (%, w/w), and X2 polymer molecular weight (kDa). Validation test showed that the experimental values of fiber size and beads percent were in good agreement with the calculated ones. Based on these results, optimal conditions could be obtained for predetermined diameters and morphologies

Structure and Properties of Cellulose Nanocomposite Films Containing Melamine Formaldehyde

Abstract: Films of high Young's modulus and low density are of interest for application as loudspeaker membranes. In the present study nanocomposite films were prepared from microfibrillated cellulose (MFC) ...

Enhanced thermal conductivity of boron nitride epoxy‐matrix composite through multi‐modal particle size mixing

Abstract: Castable particulate-filled epoxy resins exhibiting excellent thermal conductivity have been prepared using hexagonal boron nitride (hBN) and cubic boron nitride (cBN) as fillers. The thermal conductivity of boron nitride filled epoxy matrix composites was enhanced up to 217% through silane surface treatment of fillers and multi-modal particle size mixing (two different hBN particle sizes and one cBN particle size) prior to fabricating the composite. The measurements and interpretation of the curing kinetics of anhydride cured epoxies as continuous matrix, loaded with BN having multi-modal particle size distribution, as heat conductive fillers, are highlighted. This study evidences the importance of surface engineering and multi-modal mixing distribution applied in inorganic fillered epoxy-matrix composite. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Effect of the particle size of Al2O3 on the properties of filled heat‐conductive silicone rubber

Abstract: An elastomeric thermal pad with a thermal conductivity of 1.45 W/m K, needed for the heat dissipation of microelectronics, was obtained with hybrid alumina of different particle sizes as a filler and silicone rubber (vinyl-end-blocked polymethylsiloxane) as the matrix. The effects of the amount, particle size, and mixing mass ratio of the filler particles on the thermal conductivity and mechanical properties of silicone rubber were investigated. The results indicated that the thermal conductivity of the rubber filled with larger particles was superior to that of the rubber filled with the smaller grain size, and the rubber incorporated with a mixture of hybrid particles at a preferable mass ratio exhibited higher thermal conductivity than the rubber for which a filler with only a single particle size was used. In addition, the surface treatment of the hybrid filler with 3-methacryloyloxypropyltrimethoxysilane could increase the thermal conductivity of the composite rubber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1312–1318, 2007

Increased impact strength of biodegradable poly(lactic acid)/poly(butylene succinate) blend composites by using isocyanate as a reactive processing agent

Abstract: Poly(lactic acid) (PLA) blended with poly(butylene succinate) (PBS) was prepared in the presence of lysine triisocyanate (LTI) by using a twin-screw extruder and injection molding machine. The physical properties, rheological behavior, compatibility, and morphology were investigated by using a tensile test, a Charpy impact test, melt mass-flow rate (MFR) measurements, size exclusion chromatography (SEC), and laser scanning confocal microscopy (LSCM). The impact strength of PLA/PBS(90/10 wt %) blend composite was about 18 kJ/m2 in the absence of LTI, and it increased to 50–70 kJ/m2 in the presence of LTI at 0.5 wt %. The MFR value of PLA/PBS(90/10 wt %) decreased from 25 g/10 min at 200°C in the absence of LTI to approximately 3 g/10 min in the presence of LTI. These results imply that isocyanate groups of LTI reacted with both terminal hydroxyl or carboxyl groups of the polymers. Spherical particles at 1 μm were observed by using LSCM in the presence of LTI. These results indicate that the LTI is a useful reactive processing agent to increase the compatibility of PLA/PBS blend composites to increase the impact strength of PLA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Preparation and antibacterial effects of PVA‐PVP hydrogels containing silver nanoparticles

Abstract: The poly(vinyl alcohol)/ poly(N-vinyl pyrrolidone) (PVA-PVP) hydrogels containing silver nanoparticles were prepared by repeated freezing-thawing treatment. The silver content in the solid composition was in the range of 0.1-1.0 wt %, the silver particle size was from 20 to 100 nm, and the weight ratio of PVA to PVP was 70 : 30. The influence of silver nanoparticles on the properties of PVA-PVP matrix was investigated by differential scanning calorimeter, infrared spectroscopy and UV-vis spectroscopy, using PVA-PVP films containing silver particles as a model. The morphology of freeze-dried PVA-PVP hydrogel matrix and dispersion of the silver nanoparticles in the matrix was examined by scanning electron microscopy. It was found that a three-dimensional structure was formed during the process of freezing-thawing treatment and no serious aggregation of the silver nanoparticles occurred. Water absorption properties, release of silver ions from the hydrogels and the antibacterial effects of the hydrogels against Escherichia coli and Staphylococcus aureus were examined too. It was proved that the nanosilver-containing hydrogels had an excellent antibacterial ability.

Composites of poly(L‐lactide) with hemp fibers: Morphology and thermal and mechanical properties

Abstract: Composites of poly(L-lactide) (PLA) with hemp fibers (Cannabis sativa), prepared by batch mixing and plasticized with poly(ethylene glycol) (PEG; weight-average molecular weight = 600 g/mol), were examined by polarized optical microscopy, scanning electron microscopy, wide-angle X-ray scattering, differential scanning calorimetry, thermogravimetric analysis, and mechanical tests. The properties of both fully amorphous and semicrystalline samples of PLA/hemp and PLA–PEG/hemp composites were analyzed as a function of the fiber amount. The cold-crystallization kinetics of PLA in amorphous composites were investigated under isothermal conditions within the range of 70–130°C. For PLA/hemp samples, the bulk crystallization rate displayed a maximum near 110°C, whereas for plasticized samples, a higher and almost constant crystallization rate was observed over the entire temperature range, independently of the hemp amount. The kinetics were then analyzed on the basis of the Avrami model. The effect of fibers on the growth morphology of PLA spherulites, as well as the influence of the plasticizer on the melting behavior of PLA crystals and their reorganization during heating, was also examined. The thermogravimetric analysis of the composites, carried out in both nitrogen and air, showed that the degradation process of fiber-filled systems started earlier than that of plain PLA, independently of the presence of the plasticizer. Mechanical tests showed that the modulus of elasticity of the composites markedly increased with the hemp content, reaching 5.2 GPa in the case of crystallized PLA reinforced with 20 wt % hemp, whereas the elongation and stress at break decreased with an increasing amount of fiber for all examined systems. Plasticization with PEG did not improve the tensile properties of the composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 255–268, 2007

Electrospinning of cellulose‐based nanofibers

Abstract: Cellulose derivatives of carboxymethyl cellulose sodium salt (CMC), hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), and enzymatically treated cellulose have been electrospun, and the microstructure of the resulting nanofibers has been analyzed by scanning electron microscopy (SEM). Before electrospinning, the solutions were characterized by viscometry and surface tension measurements, and the results were correlated with spinnability. Four different CMC derivatives, varying in molecular weight (Mw), degree of substitution (DS), and substitution pattern, have been electrospun in mixtures with poly(ethylene oxide) (PEO), and nanofibers of various characteristics have formed. The CMC-based nanostructures, i.e., the nonwoven sheet and individual nanofibers, proved to be independent of Mw and DS but largely dependent on the substitution pattern. The nonwoven sheets varied in homogeneity, and beads appeared on the individual fibers. Depending on the chemical nature of the CMC, the extraction of PEO resulted in pure CMC nanostructures of varying appearance, indicating that the distribution of PEO and CMC in the nanofibers also varied. Two different HPMC derivatives, varying in DS, were electrospun into nanofibers. Homogeneous nonwoven sheets based on nanofibers of similar appearance are formed, independent of the substitution content of the HPMC sample. Preliminary fibers were obtained from enzymatically treated cellulose in a solvent system based on lithium chloride dissolved in dimethyl acetamide (LiCl: DMAc). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1473–1482, 2007

A novel method for porosity measurement of various surface layers of nanofibers mat using image analysis for tissue engineering applications

Abstract: Research in polymer nanofibers has undergone significant progress in the last decade. One of the main driving force for this progress is the increasing use of these polymer nanofibers for tissue engineering. Adequate porosity and surface area are widely recognized as important parameters in the design of scaffolds for tissue engineering and therefore measurement of porosity is very important. Previous methods such as mercury measurement, indirect method, the porosity measurement based on density of nanofibers do not measure the porosity of various surface layers. The goal of this study is measurement of porosity of various surface layers of scaffold. Image analysis was used for this purpose. SEM images of nanofibers mat were converted to binary images using different thresholds and porosity of scaffold was measured in various layers. On the basis of the results of our study, this method can be applied to porosity measurement of various surface layers of nanofibers mat. The results showed that porosity of various surface layers is related to the number of layers of nanofibers mat. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Pyrolysis of epoxy resins and fire behavior of epoxy resin composites flame‐retarded with 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide additives

Abstract: The pyrolysis of an epoxy resin and the fire behavior of corresponding carbon fiber-reinforced composites, both flame-retarded with either 10-ethyl-9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide or 1,3,5-tris[2-(9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide-10-)ethyl]1, 3,5-triazine-2,4,6(1H,3H,5H)-trione, are investigated The different fire retardancy mechanisms are discussed, and their influence on the fire properties assessed, in particular for flammability (limiting oxygen index, UL 94) and developing fires (cone calorimeter with different external heat fluxes of 35, 50, and 70 kW m−2) Adding the flame retardants containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide affects the fire behavior by both condensed phase and gas phase mechanisms Interactions between the additives and the epoxy resin result in a change in the decomposition pathways and an increased char formation The release of phosphorous products results in significant flame inhibition The fire properties achieved are thus interesting with respect to industrial exploration © 2007 Wiley Periodicals, Inc J Appl Polym Sci 104: 2260–2269, 2007

Nucleating agent for poly(L‐lactic acid)—An optimization of chemical structure of hydrazide compound for advanced nucleation ability

Abstract: A series of compounds having hydrazide groups was prepared and evaluated as nucleating agent for poly(L-lactic acid) by differential scanning calorimetry. Hydrazide compounds derived from benzoic acid, 2-hydroxybenzoic acid, 3-tert-butylbenzoic acid, and 2-aminobenzoic acid, where two of hydrazide compounds connected by four methylene chain were evaluated in series. Benzoylhydrazide type was found to be more effective on the enhancement of crystallization of poly(L-lactic acid). Effects of connecting length of methylene chain numbers between two of benzoylhydrazide on the nucleation ability were also evaluated. Benzoylhydrazide-type compound having 10 methylenes, that is, decamethylenedicarboxylic dibenzoylhydrazide demonstrated excellent nucleation ability, and the resulted crystallization temperature and enthalpy of PLA with the compound of 1 wt % loading were 131°C and 46 J g−1. The achieved crystallization temperature and enthalpy were over 10°C and over 10 J g−1 higher than PLA with conventional nucleating agents, such as talc and ethylenebis (12-hydroxystearylamide). Thus, the improvement in processability, productivity, and heat resistance of PLA is suggested to be achieved by using decamethylenedicarboxylic dibenzoylhydrazide as a nucleating agent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 198–203, 2007

Influence of Nanoclay on Properties of HDPE/Wood Composites

Abstract: Composites based on high density polyeth- ylene (HDPE), pine flour, and organic clay were made by melt compounding and then injection molding. The influ- ence of clay on crystallization behavior, mechanical proper- ties, water absorption, and thermal stability of HDPE/pine composites was investigated. The HDPE/pine composites containing exfoliated clay were made by a two-step melt compounding procedure with the aid of a maleated polyeth- ylene (MAPE). The use of 2% clay decreased the crystalliza- tion temperature (Tc), crystallization rate, and the crystallin- ity level of the HDPE/pine composites, but did not change the crystalline thickness. When 2% MAPE was added, the crystallization rate increased, but the crystallinity level was further lowered. The flexural and tensile strength of HDPE/ pine composites increased about 20 and 24%, respectively, with addition of 1% clay, but then decreased slightly as the clay content increased to 3%. The tensile modulus and ten- sile elongation were also increased with the addition of 1% clay. The impact strength was lowered about 7% by 1% clay, but did not decrease further as more clay was added. The MAPE improved the state of dispersion in the composites. Moisture content and thickness swelling of the HDPE/pine composites was reduced by the clay, but the clay did not improve the composite thermal stability. 2007 Wiley Peri-

Lignin‐based polycondensation resins for wood adhesives

Abstract: Lignin-based wood adhesives are obtained that satisfy the requirements of relevant international standards for the manufacture of exterior-grade wood particleboard. Formulations based on low molecular mass lignin and presenting an increase in the relative proportion of reactive points yield better results than the higher molecular mass lignin used in the past. These lignins allow a higher proportion of hydroxymethylation during preparation of methylolated lignins. These lignin-based adhesives also yield acceptable results at particleboard pressing times that are sufficiently low to be of industrial significance. Lignin-based wood adhesives, in which a nonvolatile nontoxic aldehyde (glyoxal) is substituted for formaldehyde in their preparation, are prepared and tested for application to wood panels such as particleboard. The adhesives yield good internal bond strength results for the panels, which are good enough to comfortably pass relevant international standard specifications for exterior-grade panels. The adhesives also show sufficient reactivity to yield panels in press times comparable to that of formaldehyde-based commercial adhesives. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1690–1699, 2007

Isothermal cold crystallization kinetics of polylactide/nucleating agents

Abstract: The isothermal cold crystallization kinetics of polylactide (PLA)/nucleating agents (CaCO3, TiO2, and BaSO4, content from 0.5–2.0 wt %) was investigated by differential scanning calorimetry in the temperature range of 120–124°C. With blending nucleating agents, the crystallinity of PLA had a maximum crystallinity of 14.9%. Crystallization rate decreased with increasing crystallization temperature in the researched content range. The crystallization rate followed the Avrami equation with the exponent n around 4.5. From Lauritzen–Hoffman equation, the nucleation parameter Kg was estimated. And from the value of Kg, regime II crystallization behavior can be concluded. Then the lateral and fold surface free energy were calculated from Kg. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 310–317, 2007

Crosslinked poly(vinyl alcohol) and starch composite films. II. Physicomechanical, thermal properties and swelling studies

Abstract: Poly(vinyl alcohol) (PVA) was blended with 10, 20, 30, 40, and 50 wt % of starch with and without crosslinking by solution casting process. The solution-casted films were dried and tested for physicomechanical properties like tensile strength, tensile elongation, tensile modulus, tear and burst strengths, density, and thermal analysis by differential scanning calorimetry (DSC). These PVA/starch films were further characterized for moisture content; solubility resistance in water, 5% acetic acid, 50% ethanol, and sunflower oil; and swelling characteristics in 50% ethanol and sunflower oil. The crosslinked PVA/starch composite films show significant improvement in tensile strength, tensile modulus, tear and burst strengths, and solubility resistance over the uncrosslinked films. Between the crosslinked and uncrosslinked films, the uncrosslinked films have higher tensile elongation, moisture content, moisture absorption, and swelling over the crosslinked films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 909–916, 2007

Electrochemical synthesis of polyaniline and its comparison with chemically synthesized polyaniline

Abstract: The synthesis of polyaniline (PAni) powder was carried out from 0.15M of aniline and 1M of HCl in distilled water at room temperature in a single compartment electrochemical cell. The PAni was again synthesized chemically keeping the composition and temperature same as electrochemical process but adding equimolar amount of ammonium peroxydisulfate as an oxidizing agent. Then the PAni obtained from these two methods were characterized by the conductivity, solubility, X-ray, FTIR, TGA, UV, and SEM, and compared. Result shows that the electrochemically synthesized PAni (ECS-PAni) has somewhat lower conductivity, higher solubility, more benzenoid rings than quinoid rings, lower crystallinity, higher band energy, and higher particle size than that of chemically synthesized PAni (CS-PAni). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1900–1904, 2007

Novel electrically conductive and ferromagnetic composites of poly(aniline‐co‐aminonaphthalenesulfonic acid) with iron oxide nanoparticles: Synthesis and characterization

Abstract: Nanocomposites of iron oxide (Fe3O4) with a sulfonated polyaniline, poly(aniline-co-aminonaphthalenesulfonic acid) [SPAN(ANSA)], were synthesized through chemical oxidative copolymerization of aniline and 5-amino-2-naphthalenesulfonic acid/1-amino-5-naphthalenesulfonic acid in the presence of Fe3O4 nanoparticles. The nanocomposites [Fe3O4/SPAN(ANSA)-NCs] were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, elemental analysis, UV–visible spectroscopy, thermogravimetric analysis (TGA), superconductor quantum interference device (SQUID), and electrical conductivity measurements. The TEM images reveal that nanocrystalline Fe3O4 particles were homogeneously incorporated within the polymer matrix with the sizes in the range of 10–15 nm. XRD pattern reveals that pure Fe3O4 particles are having spinel structure, and nanocomposites are more crystalline in comparison to pristine polymers. Differential thermogravimetric (DTG) curves obtained through TGA informs that polymer chains in the composites have better thermal stability than that of the pristine copolymers. FTIR spectra provide information on the structure of the composites. The conductivity of the nanocomposites (∼ 0.5 S cm−1) is higher than that of pristine PANI (∼ 10−3 S cm−1). The charge transport behavior of the composites is explained through temperature difference of conductivity. The temperature dependence of conductivity fits with the quasi-1D variable range hopping (quasi-1D VRH) model. SQUID analysis reveals that the composites show ferromagnetic behavior at room temperature. The maximum saturation magnetization of the composite is 9.7 emu g−1. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Shape‐memory behavior of thermally stimulated polyurethane for medical applications

Abstract: Shape memory polymers (SMPs) have been of great interest because of their ability to be thermally actuated to recover a predetermined shape. Medical applications in clot extracting devices and stents are especially promising. We investigated the thermomechanical properties of a series of Mitsubishi SMPs for potential application as medical devices. Glass transition temperatures and moduli were measured by differential scanning calorimetry and dynamic mechanical analysis. Tensile tests were performed with 20 and 100% maximum strains, at 37 and 80°C, which are respectively, body temperature and actuation temperature. Glass transitions are in a favorable range for use in the body (35–75°C), with high glassy and rubbery shear moduli in the range of 800 and 2 MPa respectively. Constrained stress–strain recovery cycles showed very low hysteresis after three cycles, which is important to know for preconditioning of the material to ensure identical properties during applications. Isothermal free recovery tests showed shape recoveries above 94% for MP5510 thermoset SMP cured at different temperatures. One material exhibited a shape fixity of 99% and a shape recovery of 85% at 80°C over one thermomechanical cycle. These polyurethanes appear particularly well suited for medical applications in deployment devices such as stents or clot extractors. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3882–3892, 2007

Study of electrospinning of sodium alginate, blended solutions of sodium alginate/poly(vinyl alcohol) and sodium alginate/poly(ethylene oxide)

Abstract: Alginate is an interesting natural biopolymer for many of its merits and good biological properties. This paper investigates the electrospinning of sodium alginate (NaAlg), NaAlg/PVA- and NaAlg/PEO- blended systems. It was found in this research that although NaAlg can easily be dissolved in water, the aqueous NaAlg solution could not be electrospun into ultrafine nanofibers. To overcome the poor electrospinnability of NaAlg solution, synthetic polymers such as PEO and PVA solutions were blended with NaAlg solution to improve its spinnability. The SEM images of electrospun nanofibers showed that the alginate (2%, w/v)–PVA (8%, w/v) blended system in the volume ratio of 70 : 30 and the alginate (2%, w/v)–PEO (8% w/v) blended system in the volume ratio of 50 : 50 could be electrospun into finest and uniform nanofibers with average diameters of 118.3 nm (diameter distribution, 75.8–204 nm) and 99.1 nm (diameter distribution, 71–122 nm), respectively. Rheological studies showed a strong dependence of spinnability and fiber morphology on solution viscosity and thus on the alginate-to-synthetic polymer (PVA or PEO) blend ratios. FTIR studies indicate that there are the hydrogen bonding interactions due to the ether oxygen of PEO (or the hydroxyl groups of PVA) and the hydroxyl groups of NaAlg. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Electrospinning and crosslinking of zein nanofiber mats

Abstract: Electrospinning processing can be applied to fabricate fibrous polymer mats composed of fibers whose diameters range from several microns down to 100 nm or less. In this article, we describe how electrospinning was used to produce zein nanofiber mats and combined with crosslinking to improve the mechanical properties of the as-spun mats. Aqueous ethanol solutions of zein were electrospun, and nanoparticles, nanofiber mats, or ribbonlike nanofiber mats were obtained. The effects of the electrospinning solvent and zein concentration on the morphology of the as-spun nanofiber mats were investigated by scanning electron microscopy. The results showed that the morphologies of the electrospun products exhibited a zein-dependent concentration. Optimizing conditions for zein produced nanofibers with a diameter of about 500 nm with fewer beads or ribbonlike nanofibers with a diameter of approximately 1–6 μm. Zein nanofiber mats were crosslinked by hexamethylene diisocyanate (HDI). The tensile strength of the crosslinked electrospun zein nanofiber mats was increased significantly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:380–385, 2007

Comparison of the Effectiveness of Four Different Crosslinking Agents with Hyaluronic Acid Hydrogel Films for Tissue-Culture Applications

Abstract: Received 23 October 2006; accepted 13 December 2006DOI 10.1002/app.25993Published online 5 March 2007 in Wiley InterScience (www.interscience.wiley.com).ABSTRACT: The effectiveness of four different reagents,glutaraldehyde (GTA), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), poly(ethyelene glycol) diglycidylether (EX 810), and divinyl sulfone (DVS) as crosslinkersfor cast hyaluronic acid (HA) films has been evaluated.Films were prepared by casting from solution and exposedto solutions of the crosslinkers in acetone–water solution.Swelling in water and in phosphate buffered saline (PBS)was then used to assess the effectiveness of the cross-linkers. GTA-crosslinked films were found to be of lowstability compared with those treated with EDC, EX 810,and DVS. Results suggest that instability in GTA-cross-linked materials arises in part from residual acid catalyst.The effects of polymer molecular weight are not uniform.With GTA-crosslinked film produced from higher molecu-lar weight HA swells more, and this is attributed toreduced diffusion of the crosslinker, but with EDC, theopposite effect is observed, implying some additional mo-lecular weight dependent mechanism. Differential scan-ning calorimetry and dynamic mechanical thermal analysisresults suggest that there are no significant structural dif-ference between the gels for each crosslinker system andonly the crosslink density and moisture content alters thetransitions.

Mechanical properties of epoxy networks based on DGEBA and aliphatic amines

Abstract: The mechanical properties of epoxy networks based on diglycidyl ether of bisphenol A epoxy resin cured with various linear aliphatic amines, such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and cyclic amines such as 1-(2-aminoethyl)piperazine and isophorone diamine, were studied. General characteristics such as Tg, density, and packing density, were determined and related to the structure and funcionality of the curing agent. Dynamic mechanical spectra were used to study both the α and β relaxations. Tensile and the flexural tests were used to determine the Young's and flexural modulus, and fracture strength all in the glassy state. Furthermore, linear elastic fracture mechanics was used to determine KIC. As a rule, isophorone diamine network presented the higher tensile and flexure modulus while 1-(2-aminoethyl)piperazine gave the highest toughness properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Synthesis and properties of flame‐retardant epoxy resins based on DOPO and one of its analog DPPO

Abstract: Two phosphorus-containing heterocyclic flame retardants -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 2,8-dimethyl-phenoxaphosphin-10-oxide (DPPO) - and their derivatives were characterized and incorporated in the backbone of epoxy novolac to obtain flame-retardant epoxy resins. The structures and spectroscopic data including high-resolution mass spectroscopy of these flame retardants were determined. Flame-retardant epoxy resins with a phosphorus content of up to 2% based on heterocyclic DOPO and DPPO were cured with 4,4′-diaminodiphenylmethane (DDM), and their features were examined by UL 94, LOI, and DSC. In this manner, high-performance polymers with glass transition temperatures around 190°C and the UL 94 rating V0 were obtained. These polymers were compared with epoxy resins incorporating diphenyl phosphite and diphenyl phosphate, which are nonheterocyclic and do not pass the UL 94 test up to 2% phosphorus. DPPO has a similar flame retardancy like the commercially available DOPO. Furthermore, to explain the difference in the efficiency of the tested flame retardants, key experiments for the determination of the active species during the flame-retarding process were performed and the PO radical was identified. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007.

Effect of zinc oxide nanoparticles as cure activator on the properties of natural rubber and nitrile rubber

Abstract: Zinc oxide (ZnO) nanoparticles were synthesized by homogeneous precipitation and calcination method and were then characterized by transmission electron microscopy and X-ray diffraction analysis. Synthesized ZnO was found to have no impurity and had a dimension ranging from 30–70 nm with an average of 50 nm. The effect of these ZnO nanoparticles as cure activator was studied for the first time in natural rubber (NR) and nitrile rubber (NBR) and compared with conventional rubber grade ZnO with special reference to mechanical and dynamic mechanical properties. From the rheograph, the maximum torque value was found to increase for both NR and NBR compounds containing ZnO nanoparticles. ZnO nanoparticles were found to be more uniformly dispersed in the rubber matrix in comparison with the conventional rubber grade ZnO as evident from scanning electron microscopy/X-ray dot mapping analysis. The tensile strength was observed to improve by 80% for NR when ZnO nanoparticles were used as cure activator instead of conventional rubber grade ZnO. An improvement of 70% was observed in the case of NBR. The glass transition temperature (Tg) showed a positive shift by 6°C for both NR and NBR nanocomposites, which indicated an increase in crosslinking density. The swelling ratio was found to decrease in the case of both NR and NBR, and volume fraction of rubber in swollen gel was observed to increase, which supported the improvement in mechanical and dynamic mechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Effect of different salts on electrospinning of polyacrylonitrile (PAN) polymer solution

Abstract: Electrospinning is a relatively simple method to produce submicron fibers from solutions of different polymers and polymer blends. If the solution is absolutely insulating, or the applied voltage is not high enough that electrostatic force cannot overcome the surface tension, then no fiber can be produced by electrospinning; however, if some salt is added in the solution, the problem can be overcome. The effect of different salts on electrospinning of polyacrlonitrile (PAN) polymer solution was investigated in this article. The various inorganic salts used in this work include LiCl, NaNO3, NaCl, and CaCl2.The results show that when the salts were added, respectively, into different concentrations of PAN solution, the order of conductant was LiCl > NaNO3 > CaCl2 > NaCl > no salt added. Viscosity and shearing strength of electrospinning solutions are slightly affected by the adding of salts and mainly affected by the changes in concentration of PAN electrospinning solutions. The diameter of nanofibers electrospun by solutions with different salts size down as follows: LiCl > NaNO3 > CaCl2 > NaCl. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3865–3870, 2007

Cotton fabric surface modification for improved UV radiation protection using sol–gel process

Abstract: In this study, lightweight 100% cotton fab­ ric was successfully modified by the sol-gel process to impart high ultraviolet radiation (UVR) scattering property to the fabric surface. Active ingredients were tetraethyl orthotitanate (Ti(OCH2CH3)4) and tetraethyl orthosilicate (Si(OCH2CH3)4)' The cotton fabric was padded with the nanosol solution, dried at 60'C, and cured at 150°C. Scan­ ning electron microscopy showed continuous and uniform film on the fiber surface. Excellent UVR scattering was obtained with all treated fabrics. Increasing titania content

Electrospinning of keratin/poly(ethylene oxide)blend nanofibers

Abstract: Research on the electrospinning of nanofibers has increased in recent years because of the number of potential applications in different areas, ranging from technical textiles (e.g., filters, composite reinforcements, and protective fabrics) to biomedical commodities and devices such as bandages, membranes, bioactive surfaces, and porous substrates for tissue engineering, for which biocompatible polymers play an essential role. In this work, wool keratin/poly(ethylene oxide) nanofibers were electrospun from aqueous solutions of polymer blends under different operating conditions. The filaments were characterized with scanning electron microscopy, Fourier transform infrared, and differential scanning calorimetry analyses and compared with films of the same materials produced via casting with the aim of investigating structural changes due to the electrospinning process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 863–870, 2007

Poly(lactide) nanofibers produced by a melt‐electrospinning system with a laser melting device

Abstract: A new melt-electrospinning system equipped with a CO2-laser melting device was developed. Rod-like samples were prepared from poly(lactide) pellets, and then fibers were produced from the samples using the new system. The effects of producing conditions on the fiber diameter were investigated. Furthermore, the physical properties of the fibers were investigated. The following conclusions were obtained: (i) in a special case, fibers having an average fiber diameter smaller than 1 μm could be obtained using the system developed; (ii) the fiber diameter could be decreased with increased laser output power, but the physical properties of the fibers such as the melting point and the molecular weight were decreased; and (iii) the electrospun fibers exhibited an amorphous state, and the annealed fibers exhibited an isotropic crystal orientation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1640–1645, 2007