Showing papers in "Journal of Applied Polymer Science in 2008"

Improving mechanical performance of injection molded PLA by controlling crystallinity

Abstract: Currently, use of poly(lactic acid) (PLA) for injection molded articles is limited for commercial applications because PLA has a slow crystallization rate when compared with many other thermoplastics as well as standard injection molding cycle times. The overall crystallization rate and final crystallinity of PLA were controlled by the addition of physical nucleating agents as well as optimization of injection molding processing conditions. Talc and ethylene bis-stearamide (EBS) nucleating agents both showed dramatic increases in crystallization rate and final crystalline content as indicated by isothermal and nonisothermal crystallization measurements. Isothermal crystallization half-times were found to decrease nearly 65-fold by the addition of only 2% talc. Process changes also had a significant effect on the final crystallinity of molded neat PLA, which was shown to increase from 5 to 42%. The combination of nucleating agents and process optimization not only resulted in an increase in final injection molded crystallinity level, but also allowed for a decreased processing time. An increase of over 30°C in the heat distortion temperature and improved strength and modulus by upwards of 25% were achieved through these material and process changes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Novel superabsorbent cellulose-based hydrogels crosslinked with citric acid

Abstract: This work is focused on the preparation of new environmentally friendly hydrogels derived from cellulose and hence originating from renewable resources and characterized by biodegradable properties. Two cellulose derivatives, sodium carboxymethylcellulose (CMCNa) and hydroxyethylcellulose (HEC), were used for superabsorbent hydrogel preparation. Citric acid (CA), a crosslinking agent able to overcome toxicity and costs associated with other crosslinking reagents, was selected in a heat activated reaction. Differential scanning calorimeter (DSC), fourier transform infrared spectroscopy (FTIR), and swelling measurements were performed during the reaction progress to investigate the CA reactivity with each of the polymers. Also, CMCNa/HEC polymer mixtures (3/1 w/w) crosslinked with CA were investigated and compared with previous results. Finally, a possible reaction mechanism was proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of foam density on the properties of water blown rigid polyurethane foam

Abstract: Density is an important parameter that influences the properties and performances of rigid polyurethane foam (PUF). Rigid PUF with different densities were prepared by varying the amount of distilled water as blowing agent. This investigation reports the mechanical, morphological, water absorption, thermal conductivity, and thermal behavior of rigid PUF varying with the density, which controls the foam architecture. The density of the PUF decreased from 116 to 42 kg/m3 with an increase in the amount of water from 0.1 to 3.0 parts per hundred polyol by weight (phr), respectively. It was found that the mechanical properties of the PUFs changed with the foam density. The results of water absorption of the PUFs showed that water absorption increased with decrease in density, due to increase in the cell size and decrease in the cell-wall thickness. The thermal conductivity measurements showed that the thermal conductivity decreased with increase in density. It was due to the decrease in cell size. The thermal analysis of the PUFs shows that the glass transition temperature increases with the decrease in foam density, but the thermal stability decreases with the decrease in foam density. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Ignition, combustion, toxicity, and fire retardancy of polyurethane foams: A comprehensive review

Abstract: This review provides insight into the ignition, combustion, smoke, toxicity, and fire-retardant performance of flexible and rigid polyurethane foams. This review also covers various additive and reactive fire-retardant approaches adopted to render polyurethane foams fire-retardant. Literature sources are mostly technical publications, patents, and books published since 1961. It has been found by different workers that polyurethane foams are easily ignitable and highly flammable, support combustion, and burn quite rapidly. They are therefore required to be fire-retardant for different applications. Polyurethane foams during combustion produce a large quantity of vision-obscuring smoke. The toxicity of the combustion products is much higher than that of many other manmade polymers because of the high concentrations of hydrogen cyanide and carbon monoxide. Polyurethane foams have been rendered fire-retardant by the incorporation of phosphorus-containing compounds, halogen-containing compounds, nitrogen-containing additives, silicone-containing products, and miscellaneous organic and inorganic additives. Some heat-resistant groups such as carbodiimide-, isocyanurate-, and nitrogen-containing heterocycles formed with polyurethane foams also render urethane foams fire-retardant. Fire-retardant additives reduce the flammability, smoke level, and toxicity of polyurethane foams with some degradation in other characteristics. It can be concluded that despite many significant attempts, no commercial solution to the fire retardancy of polyurethane foams without some loss of physical and mechanical properties is available.

Physicochemical characterization and antioxidant activity of quercetin-loaded chitosan nanoparticles

Abstract: Quercetin is an abundant flavonoid in food plants with numerous biological activities and widely used as a potent antioxidant. Being sparingly soluble in water and subject to degradation in aqueous intestinal fluids, the absorption of quercetin is limited upon oral administration. In the present study, chitosan nanoparticles and quercetin-loaded nanoparticles were prepared based on the ionic gelation of chitosan with tripolyphosphate anions. The encapsulation of quercetin in the chitosan nanoparticles were confirmed by differential scanning calorimetry, X-ray powder diffractometry, Fourier transformed infrared spectroscopy, ultraviolet-visible spectrum, and fluorescence spectrum. The morphology of the nanoparticles was characterized by atomic force microscopy. The antioxidant activity of the quercetin-nanoparticles was also evaluated in vitro by two different methods (free radical scavenging activity test and reducing power test), which indicates that inclusion of quercetin in chitosan nanopaticles may be useful in improving the bioavailabilty of quercetin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Green composites reinforced with hemp nanocrystals in plasticized starch

Abstract: New nanocomposite films were prepared from a mixed suspension of hemp cellulose nanocrystals (HCNs) and thermoplastic starch, or plasticized starch (PS), by the casting and evaporating method. The morphology, thermal behavior, mechanical properties, and water sensitivity of the films were investigated by means of scanning electron microscopy, wide-angle X-ray diffraction, differential scanning calorimetry, tensile testing, contact angle measurements, and water absorption. The results indicate that the cellulose nanocrystals dispersed in the PS matrix homogeneously and resulted in an increase in the glass-transition temperature ascribed to the fact that the flexibility of the starch molecular chains in the starch-rich phase was reduced because of the strong intermolecular interactions between the starch and stiff HCNs. The films exhibited significant increases in the tensile strength and Young's modulus, from 3.9 to 11.5 MPa and from 31.9 to 823.9 MPa, respectively, with increasing HCN content from 0 to 30 wt %. In addition to the improvement in mechanical properties, the incorporation of HCNs into the PS matrix also led to a decrease in the water sensitivity of the final composite materials. Therefore, the HCNs played an important role in improving the mechanical properties and water resistance of the starch-based material. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of crystallization temperature on crystal modifications and crystallization kinetics of poly(L-lactide)

Abstract: The crystalline structure of poly(L-lactide) (PLLA) have been found to quite depend on the crystallization temperatures (Tcs), especially in the range of 100−120°C, which is usually used as the crystallization temperature for the industrial process of PLLA. The analysis of wide-angle X-ray diffraction and Fourier transformed infrared spectroscopy revealed that 110°C is a critical temperature for PLLA crystallization. At Tc < 110°C and Tc ≥ 110°C, the α′ and α crystals were mainly produced, respectively. Besides, the structural feature of the α′-form was illustrated, and it was found that the α′-form has the larger unit cell dimension than that of the α-form. Moreover, the crystallization kinetics of the α′ and α crystals are different, resulting in the discontinuousness of the curves of spherulite radius growth rate (G) versus Tc and the half time in the melt-crystallization (t1/2) versus Tc investigated by Polarized optical microscope and Differential scanning calorimetry, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Polyethylene/boron nitride composites for space radiation shielding

Abstract: Composites made with boron might be absorbers of low energy neutrons, and could be used for structural materials for spacecraft. Polyethylene/boron nitride composites were fabricated using conventional polymer processing techniques, and were evaluated for mechanical and radiation shielding properties. The boron nitride powder surfaces were also functionalized to improve interfacial adhesion. Addition of neat boron nitride to an injection molding grade HDPE increased the tensile modulus from 588 to 735 MPa with 15 vol % filler. The bonding of a trifunctional alkoxysilane to the powder surface prior to processing increases the composite modulus to 856 MPa at the same loading. Scanning electron microscopy of fracture surfaces verified that the silane-treated powders had improved adhesion at the filler/polymer interface. Radiation shielding measurements of a 2 wt % boron nitride composite were improved over those of the neat polyethylene. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of fiber length on processing and properties of extruded wood-fiber/HDPE composites

Abstract: Fiber length and distribution play important roles in the processing and mechanical performance of fiber-based products such as paper and fiberboard. In the case of wood–plastic composites (WPC), the production of WPC with long fibers has been neglected, because they are difficult to handle with current production equipment. This study provides a better understanding of the effect of fiber length on WPC processing and properties. The objectives of this study were therefore to determine the role of fiber length in the formation process and property development of WPC. Three chemithermomechanical pulps (CTMP) with different lengths, distributions, and length-to-diameter ratios (L/D) were obtained by mechanical refining. Length, shape, and distribution were characterized using a fiber quality analyzer (FQA). The rheometer torque properties of high-density polyethylene (HDPE) filled with the pulps at different loads were studied. Variations in fiber load and length distribution resulted in significant variations in melting properties and torque characteristics. Composites from the three length distributions were successfully processed using extrusion. Physical and mechanical properties of the obtained composites varied with both length distribution and additive type. Mechanical properties increased with increasing fiber length, whereas performance in water immersion tests decreased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Thermal and dynamic mechanical behavior of bionanocomposites: Fumed silica nanoparticles dispersed in poly(vinyl pyrrolidone), chitosan, and poly(vinyl alcohol)

Abstract: Various bionanocomposites were prepared by dispersing fumed silica (SiO2) nanoparticles in bio- compatible polymers like poly(vinyl pyrrolidone) (PVP), chitosan (Chi), or poly(vinyl alcohol) (PVA). For the biona- nocomposites preparation, a solvent evaporation method was followed. SEM micrographs verified fine dispersion of silica nanoparticles in all used polymer matrices of compo- sites with low silica content. Sufficient interactions between the functional groups of the polymers and the surface hydroxyl groups of SiO2 were revealed by FTIR measurements. These interactions favored fine dispersion of silica. Mechanical properties such as tensile strength and Young's modulus substantially increased with increas- ing the silica content in the bionanocomposites. Thermog- ravimetric analysis (TGA) showed that the polymer matrices were stabilized against thermal decomposition with the addition of fumed silica due to shielding effect, because for all bionanocomposites the temperature, corre- sponding to the maximum decomposition rate, progres- sively shifted to higher values with increasing the silica content. Finally, dynamic thermomechanical analysis (DMA) tests showed that for Chi/SiO2 and PVA/SiO2 nanocomposites the temperature of b-relaxation observed in tand curves, corresponding to the glass transition tem- perature Tg, shifted to higher values with increasing the SiO2 content. This fact indicates that because of the reported interactions, a nanoparticle/matrix interphase was formed in the surroundings of the filler, where the macromolecules showed limited segmental mobility. V C 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 1739-1749, 2008

Lignins as Macromonomers for Polyurethane Synthesis: A Comparative Study on Hydroxyl Group Determination

Abstract: The hydroxyl group contents of four technical lignins [Indulin AT (Meadwestvaco), Alcell (Repap), Curan 27-11P (Borregaard LignoTech), and Sarkanda (Granit SA)] were investigated in view of their valorization as polyols in polyurethane synthesis. The different hydroxyl group contents were determined by the following methods: titration and 1H-NMR, 13C-NMR, and 31P-NMR spectroscopy. The titration method chosen was on the basis of a standard method commonly used to characterize commercial polyols for polyurethanes synthesis. The values of the total and phenolic hydroxyl contents determined by the different techniques were found to be in good agreement. For the total hydroxyl contents, coefficients of variation of 5.6% (Alcell), 3.2% (Indulin AT), 2.3% (Sarkanda), and 6.2% (Curan 27-11P) were established. For the phenolic hydroxyl contents, a good correlation was observed between data obtained from 31P-NMR and 13C-NMR for all lignin samples, except for the Sarkanda lignin, for which a relatively high coefficient of variation (12.6%) was found. For softwood lignins (Indulin AT and Curan 27-11P), the phenolic hydroxyl content determined by 1H-NMR was always lower than that deduced from 31P-NMR and 13C-NMR spectroscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Soy‐based polyurethanes by nonisocyanate route

Abstract: Polyurethanes by a nonisocyanate route were prepared by reacting carbonated soybean oil with different diamines. The effect of amine structure and carbonate to amine ratio on polyurethane structure and mechanical, physical, and swelling properties was studied. The reactants 1,2-ethylenediamine, 1,4-butylenediamine, and 1,6-hexamethylenediamine were used with the carbonate to amine ratio of 1 : 0.5, 1 : 1, and 1 : 2. It was found that along with urethane formation, the amine group reacted with ester groups to form amides. All amines produced elastomeric polyurethanes with glass transitions between 0 and 40°C and hardness between 40 and 90 Shore A. The reaction of epoxidized soybean oil with carbon dioxide was optimized resulting in complete conversion of epoxy to cyclic carbonate groups ending in polyurethanes with higher crosslinking density and much higher tensile strength than previously reported for similar polyurethanes. Swelling in toluene and water depended on crosslinking density and the polarity of polyurethane networks controlled by the cyclic carbonate-to-amine-ratio. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Characterization of polyvinyl alcohol/gelatin blend hydrogel films for biomedical applications

Abstract: In the present investigation, attempt was made to prepare blend hydrogel by esterification of polyvinyl alcohol with gelatin. The blend hydrogel was further converted into films by the conventional solution-casting method. These films were characterized by FTIR, DSC, and X-ray diffraction studies. The refractive index and viscosity of different composition of the blends were measured in the solution phase of the material. The mechanical properties of the blend films were measured by tensile test. Swelling behavior of the blend hydrogel was also studied. The FTIR spectrum of the blend film indicated complete esterification of the free carboxylic group of gelatin. The DSC results indicate that the addition of gelatin with PVA changes the thermal behavior like melting temperature of PVA, which may be due to the miscibility of PVA with gelatin. The interaction of gelatin with PVA molecule changes the crystallite parameters and the degree of crystallinity. The crystallinity of the blend film was mainly due to gelatin. The comparison of viscosity indicated an increase in the segment density within the molecular coil. The results revealed the changes observed in the properties of the gel, and it enhances the gel formation at viscoelastic phase of the material. The blend film had sufficient strength and water-holding capacity. The results obtained indicated that the blend film could be used for various biomedical applications such as wound dressing and drug-delivery systems. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Poly(lactic acid)‐based biocomposites reinforced with kenaf fibers

Abstract: Biodegradable thermoplastic-based compo- sites reinforced with kenaf fibers were prepared and char- acterized. Poly(lactic acid) (PLA) was selected as polymeric matrix. To improve PLA/fibers adhesion, low amount of a proper reactive coupling agent, obtained by grafting ma- leic anhydride onto PLA, was added during matrix/fibers melt mixing. Compared with uncompatibilized composites,

Materials selection and residual solvent retention in biodegradable electrospun fibers

Abstract: Electrospun tissue engineering scaffolds pro- vide mechanical support to seeded cells that populate the structure while depositing specific extracellular matrix com- ponents. The potent sterilizing agent 1,1,1,3,3,3-hexafluoro- 2-propanol (HFIP) is often used in electrospinning investi- gations involving biologically-derived polymers. Surpris- ingly, there has been no study of solvent retention versus composition even though materials selection should influ- ence organic solvent content. We developed a method quantifying HFIP retention following electrospinning of gel- atin, polycaprolactone (PCL), and PCL-gelatin blends using electro-spray mass spectroscopy. The acetone content of ace- tone-spun PCL was also established. Pure gelatin fiber con- tained as much as 1600 ppm of HFIP. In contrast, little ace- tone or HFIP was detected in 100% PCL. Gelatin clearly has a greater affinity for HFIP than PCL and materials selection has a strong influence on the amount of retained solvent. Vacuum 1 heat treatment at 37 and 458C reduced (HFIP) to 10 and 5.6 ppm, respectively, levels having no demon- strated effects on mammalian cell viability. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 107: 1547-1554, 2008

On the electrospinning of poly(vinyl alcohol) nanofiber mats: A revisit

Abstract: Electrospinning was used to fabricate mats of poly(vinyl alcohol) (PVA; Mw = 72,000 Da, degree of hydrolysis ≈ 97.5–99.5) nanofibers from PVA solutions in reverse osmotic water. The effects of solution concentration, applied electrical potential, sonication, and collection distance on morphological appearance and diameters of the as-spun fiber mats as well as those of the individual fibers were carefully investigated mainly by scanning electron microscopy. The effect of the distance from the center of the as-spun fiber mat on morphological appearance and diameters of the as-spun fibers was also investigated. The mechanical integrity of some as-spun PVA fiber mats was also investigated. At all concentrations and applied electrical potentials investigated, the average diameters of the as-spun PVA fibers ranged between 85 and 647 nm. The use of sonication to prepare a PVA solution caused the viscosity of the solution to decrease; hence, the observed decrease in the average diameters of the as-spun fibers and the average diameters of the as-spun fibers were practically the same throughout the as-spun fiber mat. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Thermal and Mechanical Properties of a Poly(ε-caprolactone)/Graphite Oxide Composite

Abstract: The effect of graphite oxide (GO) as the enforcing filler on the properties of poly(ϵ-caprolactone) (PCL) was investigated in this study. Through the introduction of GO, the Young's modulus of PCL was increased from 340 to 1000 MPa, and the tensile strength of PCL was increased from 15 to 26 MPa. Furthermore, the interlayer distance of GO (0.6 nm) was found to expand to 1.1 nm in the PCL/GO composite, which indicated the intercalation of the PCL chain into the GO layers. Because of this intercalation structure of the PCL/GO composite, GO showed a higher reinforcing effect than graphite on the mechanical properties of PCL. The intercalation should have enabled much effective load transfer in the PCL/GO composites. Moreover, GO showed a nucleating effect toward the crystallization of PCL, as the nonisothermal crystallization peak temperature shifted from 25°C for pure PCL to about 34°C for the PCL/GO composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Polymer nanocomposites based on needle‐like sepiolite clays: Effect of functionalized polymers on the dispersion of nanofiller, crystallinity, and mechanical properties

Abstract: Polypropylene (PP)/sepiolite (Sep) nanocomposites are prepared by melt compounding in a mini-extruder apparatus. The often used maleic anhydride-modified polypropylene (PP-g-MA) is compared with two custom-made functionalized polymers, PP-acid and the di-block copolymer PP-PEO, with respect to the filler dispersion and filler reinforcement efficiency. For that purpose, morphological and mechanical studies are carried out by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and mechanical tensile tests. In addition, the nanocomposites are characterized by wide-angle X-ray scattering (WAXS) and differential scanning calorimetric (DSC) techniques, to assess the effect of the nanofiller on the crystalline structure of the PP matrix nano-filler. The use of PP-PEO and PP-acid resulted in a better nanofiller dispersion compared with traditional PP-g-MA-modified systems. Sepiolite acts as nucleating agent for the crystallization of PP and seems to lead to an orientation of the α-phase crystals. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Preparation and application of silver nanoparticles on silk for imparting antimicrobial properties

Abstract: Silver nanoparticles were produced by a chemical reduction method that reduced silver nitrate with reducing agents such as hydrazine and glucose The silver nanoparticles were characterized with transmission electron microscope, scanning electron microscope, and optical microscope The effects of process parameters such as the stirring speed, temperature, type of reducing agent, and dispersing agent on the particle size were studied The particle size decreased with an increase in the stirring speed and a decrease in the process temperature Smaller particles were formed when the silver nitrate was reduced by glucose versus those that were formed by reduction with hydrazine Silver nanoparticles with average sizes of 10 and 35 nm, produced by reduction with hydrazine at 5 and 40°C, were applied to silk by an exhaust method Silk fabrics treated with 40 ppm silver hydrosol produced at 5°C and 60 ppm silver hydrosol produced at 40°C showed 100% antimicrobial activity against the gram-positive bacterium Staphylococcus aureus The durability of the antimicrobial property of the treated silk fabric to washing was also examined and is presented © 2008 Wiley Periodicals, Inc J Appl Polym Sci, 2008

Effect of Expandable Graphite on the Properties of Intumescent Flame-Retardant Polyurethane Foam

Abstract: Water-blown rigid polyurethane foam (PUF) with two different particle sizes (180 and 300 μm) of expandable graphite (EG) as a flame-retardant additive were prepared, and the effects on the mechanical, morphological, water absorption, thermal conductivity, thermal, and flame-retardant properties were studied. In this investigation, EG content was varied from 5 to 50 php by weight. The mechanical properties of PUF decreased with increasing EG loading in both cases. The water absorption of the PUF increased with an increase in the EG loading mainly because of the collapse of foam cells, as evidenced from the scanning electron microscopy pictures. The thermal conductivity of the EG-filled PUF showed that the insulation properties decreased with EG loading. The flame-retardant properties (limiting oxygen index and char yield measurement) of the PUF improved with increasing EG loading. PUF filled with the higher particle size EG showed better mechanical properties and fire-retardant properties than the PUF filled with the lower particle size EG. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Environmentally friendly mixed tannin/lignin wood resins

Abstract: We obtained lignin-based wood adhesives satisfying the requirements of relevant international standards for the manufacture of wood particleboard. These were based on two different low-molecular-mass lignins. These lignin-based wood adhesives did not use any formaldehyde in their formulation; formaldehyde was substituted with a nonvolatile nontoxic aldehyde, namely, glyoxal. The last formaldehyde present, contributed by a fortifying synthetic phenol–formaldehyde resin, was also eliminated by the substitution of the phenol–formaldehyde resin with a natural, vegetable polyflavonoid tannin extract to which no aldehyde was added. This substitution brought the total content of natural material up to 80 wt % of the total adhesive. The adhesives yielded good internal bond strength results of the panels, enough to pass relevant international standard specifications for interior-grade panels. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Evaluating cell wall structure and composition of developing cotton fibers using Fourier transform infrared spectroscopy and thermogravimetric analysis

Abstract: Universal attenuated total reflectance Fourier transform infrared (UATR-FTIR) spectroscopy and thermogravimetric analysis (TGA) were used to investigate the structural changes of cotton (Gossypium hirsutum L.) fibers as a function of developmental programming. The presence of noncellulosic compounds (wax, protein, hemicelluloses, pectic substances, amino acids, etc.) was evident from FTIR spectra of fibers at 10, 14, 17, and 20 dpa (day postanthesis). The vibration corresponding to the noncellulosic compounds disappeared at 36 dpa. Furthermore, independent TGA analysis supported the results obtained with FTIR, showing that the transition from primary cell wall synthesis to secondary cell wall synthesis occurs at or around 20 dpa. This study is the first to report on the use of the UATR-FTIR and TGA to elucidate structural changes during cotton fiber development. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Antibacterial effects of a new dental acrylic resin containing silver nanoparticles

Abstract: The addition of silver nanoparticles (Ag NPs) to an acrylic resin rendered a dental composite that exhibited strong antibacterial activity against Escherichia coli and showed rather improved mechanical properties. Such antibacterial effects were mainly attributed to the release of silver ions upon immersion of the composite in water, which appeared to be fairly nontoxic to humans. Furthermore, an acrylic liquid was used as a new reducing agent for the conversion of silver ions into pure elemental Ag NPs in quantitative yields. The structure, morphology, average size, and size distribution of the as-prepared Ag NPs were determined by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, which confirmed the fabrication of rather dispersed, face-centered cubic nanoparticles with a mean average diameter of 38 nm. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Synthesis and properties of starch‐graft‐acrylic acid/Na‐montmorillonite superabsorbent nanocomposite hydrogels

Abstract: The graft copolymerization of acrylic acid (AA) onto starch was carried out with monomer/starch weight ratio = 1.5. Cerium ammonium nitrate (CAN) and N,N′-methylenebis acrylamide (NMBA) were used as initiator and crosslink agent, respectively. Na-montmorillonite was used as nanoparticles. Starch-graft-acrylic acid/Na-MMT (S-g-AA/MMT) nanocomposite hydrogels were characterized by X-ray diffraction (XRD) and FTIR analysis. The effect of Na-MMT content in nanocomposite hydrogels on the swelling behavior was investigated. Increasing the Na-MMT/monomers ratio up to 1% causes an increment in water absorbency, which indicates that Na-MMT can improve the ability of water absorbency but further increase of Na-MMT causes a decrease in water absorbency. In addition, we describe the removal of safranine T from aqueous solutions using S-g-AA/MMT nanocomposite hydrogels. Effects of various parameters such as treatment time, initial dye concentration, and amount of the Na-MMT were investigated. The Freundlich equations were used to fit the equilibrium isotherms. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Electrospun Nanofibers from Crosslinked Poly(vinyl alcohol) and Its Filtration Efficiency

Abstract: Nanoscaled crosslinked poly(vinyl alcohol) PVA fibers were prepared by electrospinning This study described its electrospinning process, structure, and filtration applications The fibers were found to be efficiently crosslinked by maleic acid Vitriolic acid was used as a catalyst activator during crosslinking Scanning electron micrograph and differential scanning calorimetric techniques as well as infrared reflection–absorption spectroscopy (FTIR) were employed to characterize the morphology and structure of crosslinking of PVA fibers, PVA fibers as well as PVA powder Moreover, the filtration properties of crosslinked PVA nanofibers were tested During the experiments, crosslinked PVA nanofibers layers with different area weight were placed on the spunbond or meltblown sublayers The result shows that the filtration efficiency increases sharply when crosslinked PVA nanofibers layers were added to the sublayers © 2008 Wiley Periodicals, Inc J Appl Polym Sci, 2008

Environment-Friendly Soy Flour-Based Resins Without Formaldehyde

Abstract: Glyoxalated soy flour adhesives for wood particleboard added with a much smaller proportion of glyoxalated lignin or tannin and without any addition of either formaldehyde or formaldehyde-based resin are shown to yield results satisfying the relevant standard specifications for interior wood boards. Adhesive resin formulations in which the total content of natural material is either 70 or 80% of the total resin solids content gave good results. The resins comprising 70% by weight of natural material can be used in a much lower proportion on wood chips and can afford pressing times fast enough to be significant under industrial panel pressing conditions. The best formulation of all the ones tried was the one based on glyoxalated precooked soy flour (SG), to which a condensed tannin was added in water solution and a polymeric isocyanate (pMDI), where the proportions of the components SG/T/pMDI was 54/16/30 by weight. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Improvement of conductivity of electrochemically synthesized polyaniline

Abstract: The electrochemical polymerization of aqueous solution of aniline and HCl was carried out in a single compartment electrochemical cell. After 2 h of the polymerization reaction, polarity of the electrodes was reversed and kept for 1 h. By this process the conductivity of the polyaniline (PAni) formed was found to increase dramatically from 1.1 × 10−4 to 3.0 × 10−1 S/cm. The PAni samples obtained both by reversing the polarity (“PANI-R”) and without reversing the polarity (“PANI”) were characterized by the infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), ultraviolet spectroscopy (UV), Hall effect experiment, X-ray analysis (XRD) and scanning electron microscope (SEM). The results show that the increase in the conductivity of PAni through the reversion of polarity is due to the partial reduction of over oxidized sample giving more emeraldine base and hence more polaron formation with increased charge carrier density and its mobility. The degree of crystallinity and the crystallite size is decreased marginally and the d-spacing is increased marginally due to this reduction. The PAni behaves like a p-type semiconductor that means the majority current carriers are holes. A plausible reduction mechanism due to reversal of polarity during electrochemical polymerization is also proposed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Fabrication, Structure, and Properties of Chitin Whisker-Reinforced Alginate Nanocomposite Fibers

Abstract: Calcium alginate yarn (30 fibers) and cal- cium alginate nanocomposite yarn (30 fibers) containing 0.05-2.00% w/w chitin whiskers were both prepared by wet spinning process. The whiskers were prepared by acid hydrolysis of chitin from shrimp shells. The average length and width of the whiskers were 343 and 46 nm, with the aspect ratio being � 7.5. Incorporation of a low amount of the whiskers in the nanocomposite fibers improved both the mechanical and the thermal properties of the fibers significantly, possibly a result of the specific interactions, i.e., hydrogen bonding and electrostatic interactions, between the alginate molecules and the homogeneously dispersed chitin whiskers. Biodegrada- tion of the calcium alginate fibers and the nanocomposite fibers was tested in Tris-HCl buffer solution and the same buffer solution that contained lysozyme. The addi- tion of the chitin whiskers in the nanocomposites fibers accelerated the biodegradation process of the fibers in the presence of lysozyme, whereas the presence of Ca 2þ ions in the Tris-HCl buffer solution helped to improve the te- nacity of both the alginate and the nanocomposite fibers. V C 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 890-899, 2008

Formation of a bicontinuous structure membrane of polyvinylidene fluoride in diphenyl carbonate diluent via thermally induced phase separation

Abstract: Diphenyl carbonate was used as a diluent to prepare microporous polyvinylidene fluoride (PVDF) membrane via thermally induced phase-separation method. The liquid–liquid phase-separation phenomenon was found in PVDF/diphenyl carbonate system during the thermally induced phase-separation process. The monotectic point of this system appeared at a high polymer concentration approximately 56 wt %. This suggested that PVDF membrane with a bicontinuous or cellular structure could be obtained when the PVDF concentration was less than this point value. The effects of polymer concentration and quenching temperature on the membrane structure, porosity, and tensile strength were also investigated. The results showed that low polymer concentration and high quenching temperature led to a large pore size membrane. The tensile strength of the membrane increased with increase in the polymer concentration, but the porosity of the membrane decreased. On condition that the PVDF concentration was higher than 60 wt %, only polymer crystallization occurred and a typical compact spherulitic structure was obtained. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Adsorption of Heavy Metal Ions from Aqueous Solution Onto Chitosan Entrapped CM-Cellulose Hydrogels Synthesized by Irradiation

Abstract: The application of novel environment-conscious hydrogels as an adsorbent for heavy metal ions adsorption from aqueous solutions was examined. Chitosan was blended with highly concentrated carboxymethylated cellulose (CM-cellulose) solution to form CM-cellulose/chitosan physical hydrogels, which were crosslinked by additionless irradiation technique. The adsorptive properties of the blend hydrogels against some divalent heavy metal ions were investigated by batch adsorption method. It was found that the addition of chitosan increased the crosslinking degree and the adsorption capacity of the blend hydrogels. As a typical example, experimental data of Cu(II) ion were exploited for kinetic and isothermal evaluations. Copper adsorption process was found to be initially transport-controlled, and its adsorption isotherm can be fitted well into the Langmuir equation. Cu(II) adsorption mechanism can be viewed as the complexation of the Cu(II) with carboxyl groups and amino groups on the CM-cellulose/chitosan gel during the adsorption. From these preliminary evaluations, it is possible to conclude that the CM-cellulose/chitosan blend hydrogels have great potential for applications in water treatment for the removal of heavy metal ions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008