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2012 Volume 30 Issue 6
2012, 30(6): 777-785
doi: 10.1007/s10118-012-1172-9
Abstract:
Six dicarboxylic acids 3a-3f were synthesized by the reaction of 3,3',4,4'-benzophenonetetracarboxylic dianhydride 1 with L-aminoacids 2a-2f in a solution of glacial acetic acid/pyridine (Py) at refluxing temperature. Then six new poly(amide-imide)s PAIs were synthesized from the direct polycondensation reaction of [N,N'-(4,4'-carbonyldiphtaloyl)-bis-L-amino diacid]s with 1,5-bis(4-aminophenyl)penta-1,4-dien-3-one (APPD). The polymerization reactions produced a series of new optically active PAIs with high yield and good inherent viscosity. Also these PAIs are optically active and soluble in various organic solvents. These resulting new polymers can be used in column chromatography for the separation of enantiomeric mixtures. The resulted polymers were fully characterized by means of FTIR and 1H-NMR spectroscopy, elemental analyses, inherent viscosity measurements, solubility tests and thermogravimetric analysis (TGA).
Six dicarboxylic acids 3a-3f were synthesized by the reaction of 3,3',4,4'-benzophenonetetracarboxylic dianhydride 1 with L-aminoacids 2a-2f in a solution of glacial acetic acid/pyridine (Py) at refluxing temperature. Then six new poly(amide-imide)s PAIs were synthesized from the direct polycondensation reaction of [N,N'-(4,4'-carbonyldiphtaloyl)-bis-L-amino diacid]s with 1,5-bis(4-aminophenyl)penta-1,4-dien-3-one (APPD). The polymerization reactions produced a series of new optically active PAIs with high yield and good inherent viscosity. Also these PAIs are optically active and soluble in various organic solvents. These resulting new polymers can be used in column chromatography for the separation of enantiomeric mixtures. The resulted polymers were fully characterized by means of FTIR and 1H-NMR spectroscopy, elemental analyses, inherent viscosity measurements, solubility tests and thermogravimetric analysis (TGA).
2012, 30(6): 786-795
doi: 10.1007/s10118-012-1165-8
Abstract:
Orientation of copolymer polyacrylonitrile (PAN) chains during their deformation prior to stabilization and the further effect on the stabilization were investigated in detail. Results reveal that the orientation of PAN chains presents a saturation point of 69.51% when the deformation ratio reaches approximately 1.07, meanwhile the cyclization rather than the oxidation has a stronger dependence on the orientation of PAN chains during stabilization. The cyclization is facilitated that the cyclization degree is increasing while the activation energy is decreasing obviously as a consequence of the developing orientation of PAN fibers before the saturation point; however, it is restrained during the further deformation of PAN fibers after the point. The resulting carbon fibers obtained from the PAN fibers prepared at the saturation point possess the highest mechanical properties of 4.07 GPa in tensile strength and 249.0 GPa in tensile modulus.
Orientation of copolymer polyacrylonitrile (PAN) chains during their deformation prior to stabilization and the further effect on the stabilization were investigated in detail. Results reveal that the orientation of PAN chains presents a saturation point of 69.51% when the deformation ratio reaches approximately 1.07, meanwhile the cyclization rather than the oxidation has a stronger dependence on the orientation of PAN chains during stabilization. The cyclization is facilitated that the cyclization degree is increasing while the activation energy is decreasing obviously as a consequence of the developing orientation of PAN fibers before the saturation point; however, it is restrained during the further deformation of PAN fibers after the point. The resulting carbon fibers obtained from the PAN fibers prepared at the saturation point possess the highest mechanical properties of 4.07 GPa in tensile strength and 249.0 GPa in tensile modulus.
2012, 30(6): 796-807
doi: 10.1007/s10118-012-1176-5
Abstract:
Schiff base monomers [2-(4-bromobenzylideneamino)phenol and 2-(4-bromobenzylideneamino)-5-methylphenol] were synthesized by the condensation reaction of 4-bromobenzaldehyde with aromatic aminophenols. Then, the monomers were converted to their polyphenol derivatives by oxidative polycondensation reactions (OP) in an aqueous alkaline medium. The structures of the synthesized compounds were characterized by solubility tests, FT-IR, NMR, TG-DTA, DSC and SEC techniques. The HOMO-LUMO energy levels and electrochemical (Eg') and optical (Eg) band gaps were calculated from cyclic voltammetry (CV) and UV-Vis measurements, respectively. Cyclic voltammetry (CV) was used to determine the electrochemical oxidation-reduction characteristics. Optical properties were investigated by UV-Vis and fluorescence analyses. Solid state electrical conductivities were measured on polymer films by four point probe technique using a Keithley 2400 electrometer. The effects of electron-donating (―CH3) group at p-position of ―NH2 group in aminophenol on electrochemical and thermal properties were also discussed. Photoluminescence (PL) properties of the synthesized materials were determined in solution forms using different solvents. Fluorescence measurements were carried out in various concentrated solutions to determine the optimum concentrations to obtain the maximal PL intensities.
Schiff base monomers [2-(4-bromobenzylideneamino)phenol and 2-(4-bromobenzylideneamino)-5-methylphenol] were synthesized by the condensation reaction of 4-bromobenzaldehyde with aromatic aminophenols. Then, the monomers were converted to their polyphenol derivatives by oxidative polycondensation reactions (OP) in an aqueous alkaline medium. The structures of the synthesized compounds were characterized by solubility tests, FT-IR, NMR, TG-DTA, DSC and SEC techniques. The HOMO-LUMO energy levels and electrochemical (Eg') and optical (Eg) band gaps were calculated from cyclic voltammetry (CV) and UV-Vis measurements, respectively. Cyclic voltammetry (CV) was used to determine the electrochemical oxidation-reduction characteristics. Optical properties were investigated by UV-Vis and fluorescence analyses. Solid state electrical conductivities were measured on polymer films by four point probe technique using a Keithley 2400 electrometer. The effects of electron-donating (―CH3) group at p-position of ―NH2 group in aminophenol on electrochemical and thermal properties were also discussed. Photoluminescence (PL) properties of the synthesized materials were determined in solution forms using different solvents. Fluorescence measurements were carried out in various concentrated solutions to determine the optimum concentrations to obtain the maximal PL intensities.
2012, 30(6): 808-814
doi: 10.1007/s10118-012-1173-8
Abstract:
Organo-fly ash (OFA) was prepared with pretreated fly ash (FA) and hexadecyltrimethyl ammonium bromide (HDTMAB), and the composites composed of OFA and polyaniline were obtained by emulsion polymerization at different OFA weight ratios (2.0 wt%, 5.0 wt%, 10.0 wt%, 15.0 wt% and 20.0 wt%) in the presence of dodecylbenzenesulfonic acid as dopant and emulsifier. A polymerization procedure was supposed. The electrical conductivities of the composites were tested by the four-probe technique. The chemical structure and crystallinity of the composites were confirmed by FT-IR and X-ray diffraction, respectively. Morphologies of FA, OFA and the composites were observed by SEM. The element analysis was performed by energy dispersive spectrometry. The thermal stability of the composites was analyzed by TGA. The results showed that the electrical conductivity of the composites decreased with increasing the feed weight ratio of OFA, and the lowest value was 0.62 S/cm. HDTMAB and PAn were just adsorbed on the surface of FA and OFA, respectively according to the physical adsorption without destroying the crystalline structure of FA or OFA. The surface became smoother after organification of FA by using HDTMAB, and its content on FA surfaces was about 26.9 wt%. The core/shell structure of the composite was observed by SEM analysis. The composites showed a higher thermal stability than pure PAn by introduction of OFA into this polymerization system, the heat stability of PAn was increased by decreasing 31.8 wt% of weight loss after introducing 20 wt% of OFA.
Organo-fly ash (OFA) was prepared with pretreated fly ash (FA) and hexadecyltrimethyl ammonium bromide (HDTMAB), and the composites composed of OFA and polyaniline were obtained by emulsion polymerization at different OFA weight ratios (2.0 wt%, 5.0 wt%, 10.0 wt%, 15.0 wt% and 20.0 wt%) in the presence of dodecylbenzenesulfonic acid as dopant and emulsifier. A polymerization procedure was supposed. The electrical conductivities of the composites were tested by the four-probe technique. The chemical structure and crystallinity of the composites were confirmed by FT-IR and X-ray diffraction, respectively. Morphologies of FA, OFA and the composites were observed by SEM. The element analysis was performed by energy dispersive spectrometry. The thermal stability of the composites was analyzed by TGA. The results showed that the electrical conductivity of the composites decreased with increasing the feed weight ratio of OFA, and the lowest value was 0.62 S/cm. HDTMAB and PAn were just adsorbed on the surface of FA and OFA, respectively according to the physical adsorption without destroying the crystalline structure of FA or OFA. The surface became smoother after organification of FA by using HDTMAB, and its content on FA surfaces was about 26.9 wt%. The core/shell structure of the composite was observed by SEM analysis. The composites showed a higher thermal stability than pure PAn by introduction of OFA into this polymerization system, the heat stability of PAn was increased by decreasing 31.8 wt% of weight loss after introducing 20 wt% of OFA.
2012, 30(6): 815-823
doi: 10.1007/s10118-012-1188-1
Abstract:
An account of the experiments on preparing polystyrene (PS) nanocomposites through grafting the polymer onto organophilic montmorillonite is reported. Cloisite 20A was reacted with vinyltrichlorosilane to replace the edge hydroxyl groups of the clay with a vinyl moiety. Because the reaction may liberate HCl, it was performed in the presence of sodium hydrogencarbonate to prevent the exchange of quaternary alkylammonium cations with H+ ions. Only the silanol groups on the edge of the clay react with vinyltrichlorosilane. The radical polymerization of the product with styrene as a vinyl monomer leads to chemical grafting of PS onto the montmorillonite surface. The homopolymer formed during polymerization was separated from the grafted organoclay by Soxhlet extraction. Chemical grafting of the polymer onto Cloisite 20A was confirmed by infrared spectroscopy. The prepared nanocomposite materials and the grafted nano-particles were studied by XRD. Exfoliated nanocomposites may be obtained for 0.5 wt%-1 wt% clay content. The nanocomposites were studied by thermogravimertic analysis (TGA) dynamic thermal analysis (DTA) and dynamic mechanical analysis (DMTA).
An account of the experiments on preparing polystyrene (PS) nanocomposites through grafting the polymer onto organophilic montmorillonite is reported. Cloisite 20A was reacted with vinyltrichlorosilane to replace the edge hydroxyl groups of the clay with a vinyl moiety. Because the reaction may liberate HCl, it was performed in the presence of sodium hydrogencarbonate to prevent the exchange of quaternary alkylammonium cations with H+ ions. Only the silanol groups on the edge of the clay react with vinyltrichlorosilane. The radical polymerization of the product with styrene as a vinyl monomer leads to chemical grafting of PS onto the montmorillonite surface. The homopolymer formed during polymerization was separated from the grafted organoclay by Soxhlet extraction. Chemical grafting of the polymer onto Cloisite 20A was confirmed by infrared spectroscopy. The prepared nanocomposite materials and the grafted nano-particles were studied by XRD. Exfoliated nanocomposites may be obtained for 0.5 wt%-1 wt% clay content. The nanocomposites were studied by thermogravimertic analysis (TGA) dynamic thermal analysis (DTA) and dynamic mechanical analysis (DMTA).
2012, 30(6): 824-836
doi: 10.1007/s10118-012-1195-2
Abstract:
A new and efficient synthetic route to hydroxymethylated-3,4-ethylenedioxylthiophene (EDOT-MeOH) was developed by a simple four-step sequence, and its global yield was approximately 41.06%. The poly(hydroxymethylated-3,4-ethylenedioxylthiophene) (PEDOT-MeOH) film was electrosynthesized in aqueous sodium dodecylsulfate micellar solutions and characterized by different methods. The EDOT-MeOH possessed better water solubility, and lower onset oxidation potential than EDOT. The as-obtained PEDOT-MeOH film displayed good reversible redox activity, stability and capacitance properties in a monomer-free electrolyte, especially the good solubility of PEDOT-MeOH film in strong polar organic solvents such as dimethyl sulfoxide and tetrahydrofuran created a potential application in many different fields. Fluorescent spectra indicated that PEDOT-MeOH was a yellow-green-light-emitter with maximum emission at 568 nm. The as-formed PEDOT-MeOH film had good biocompatibility and was used for fabricating the electrochemical vitamin C biosensor. The proposed biosensor showed a linear range of 3 10-6 mol/L to 1.2 10-2 mol/L with the detection limit of 1 mol/L, a sensitivity of 95.6 A (mmol/L)-1 cm-2, and a current response time less than 10 s and a fairly good stability (The relative standard deviation was 0.43% for 20 successive assays, the proposed biosensor still retained 93.5% of bioactivity after 15 days storage. This result indicated that the prepared PEDOT-MeOH film as immobilization matrix of biologically-active species could be a promising candidate for the design and application of biosensor.
A new and efficient synthetic route to hydroxymethylated-3,4-ethylenedioxylthiophene (EDOT-MeOH) was developed by a simple four-step sequence, and its global yield was approximately 41.06%. The poly(hydroxymethylated-3,4-ethylenedioxylthiophene) (PEDOT-MeOH) film was electrosynthesized in aqueous sodium dodecylsulfate micellar solutions and characterized by different methods. The EDOT-MeOH possessed better water solubility, and lower onset oxidation potential than EDOT. The as-obtained PEDOT-MeOH film displayed good reversible redox activity, stability and capacitance properties in a monomer-free electrolyte, especially the good solubility of PEDOT-MeOH film in strong polar organic solvents such as dimethyl sulfoxide and tetrahydrofuran created a potential application in many different fields. Fluorescent spectra indicated that PEDOT-MeOH was a yellow-green-light-emitter with maximum emission at 568 nm. The as-formed PEDOT-MeOH film had good biocompatibility and was used for fabricating the electrochemical vitamin C biosensor. The proposed biosensor showed a linear range of 3 10-6 mol/L to 1.2 10-2 mol/L with the detection limit of 1 mol/L, a sensitivity of 95.6 A (mmol/L)-1 cm-2, and a current response time less than 10 s and a fairly good stability (The relative standard deviation was 0.43% for 20 successive assays, the proposed biosensor still retained 93.5% of bioactivity after 15 days storage. This result indicated that the prepared PEDOT-MeOH film as immobilization matrix of biologically-active species could be a promising candidate for the design and application of biosensor.
2012, 30(6): 837-844
doi: 10.1007/s10118-012-1194-3
Abstract:
Influence of crosslinking on physical properties of low density polyethylene was studied. The results indicated that, at low degrees of crosslinking, the network hardly affects the crystallinity, elastic modulus (E) and yielding stress while it improves the tensile strength and strain at break simultaneously. Tensile strength reaches a maximum of about 24 MPa at 1.5 phr dicumyl peroxide (DCP) then decreases to a constant value of about 18 MPa due to decrease of crystallinity. E reaches its maximum at 0.5 phr DCP corresponding to gel fraction of about 75% without marked change in crystallinity. The crosslinked polyethylene exhibits two yielding processes, and both yielding stresses approximately linearly depend on crystallinity.
Influence of crosslinking on physical properties of low density polyethylene was studied. The results indicated that, at low degrees of crosslinking, the network hardly affects the crystallinity, elastic modulus (E) and yielding stress while it improves the tensile strength and strain at break simultaneously. Tensile strength reaches a maximum of about 24 MPa at 1.5 phr dicumyl peroxide (DCP) then decreases to a constant value of about 18 MPa due to decrease of crystallinity. E reaches its maximum at 0.5 phr DCP corresponding to gel fraction of about 75% without marked change in crystallinity. The crosslinked polyethylene exhibits two yielding processes, and both yielding stresses approximately linearly depend on crystallinity.
2012, 30(6): 845-852
doi: 10.1007/s10118-012-1175-6
Abstract:
Waterborne polyurethane composites containing silica nanoparticles are synthesized successfully via the in situ polymerization. The structure, thermal stability, surface hardness, tensile strength, UV-Vis absorbance, dynamic mechanical properties and chemicals resistance of the resulting composites are investigated by FTIR, TEM, TGA, UV-Vis, DMA and chemicals soakage measurements. Results show that polyurethane molecules and silica nanoparticles are linked with covalent bonds. As a result, physical properties of polyurethane composites, such as thermal stability, surface hardness, weather and chemicals resistance are all improved when an appropriate concentration of silica nanoparticles are incorporated.
Waterborne polyurethane composites containing silica nanoparticles are synthesized successfully via the in situ polymerization. The structure, thermal stability, surface hardness, tensile strength, UV-Vis absorbance, dynamic mechanical properties and chemicals resistance of the resulting composites are investigated by FTIR, TEM, TGA, UV-Vis, DMA and chemicals soakage measurements. Results show that polyurethane molecules and silica nanoparticles are linked with covalent bonds. As a result, physical properties of polyurethane composites, such as thermal stability, surface hardness, weather and chemicals resistance are all improved when an appropriate concentration of silica nanoparticles are incorporated.
2012, 30(6): 853-864
doi: 10.1007/s10118-012-1185-4
Abstract:
Ethylene/propylene-random-copolymer (PPR)/clay nanocomposites were prepared by two-stage melt blending. Four types of compatibilizers, including an ethylene-octene copolymer grafted maleic anhydride (POE-g-MA) and three maleic-anhydride-grafted polypropylenes (PP-g-MA) with different melt flow indexes (MFI), were used to improve the dispersion of organic clay in matrix. On the other hand, the effects of organic montmorillonite (OMMT) content on the nanocomposite structure in terms of clay dispersion in PPR matrix, thermal behavior and tensile properties were also studied. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that the organic clay layers are mainly intercalated and partially exfoliated in the nanocomposites. Moreover, a PP-g-MA compatibilizer (compatibilizer B) having high MFI can greatly increase the interlayer spacing of the clay as compared with other compatibilizers. With the introduction of compatibilizer D (POE-g-MA), most of the clays are dispersed into the POE phase, and the shape of the dispersed OMMT appears elliptic, which differs from the strip of PP-g-MA. Compared with virgin PPR, the Youngs modulus of the nanocomposite evidently increases when a compatibilizer C (PP-g-MA) with medium MFI is used. For the nanocomposites with compatibilizer B and C, their crystallinities (Xc) increase as compared with that of the virgin PPR. Furthermore, the increase of OMMT loadings presents little effect on the melt temperature (Tm) of the PPR/OMMT nanocomposites, and slight effect on their crystallization temperature (Tc). Only compatibilizer B can lead to a marked increases in crystallinity and Tc of the nanocomposite when the OMMT content is 2 wt%.
Ethylene/propylene-random-copolymer (PPR)/clay nanocomposites were prepared by two-stage melt blending. Four types of compatibilizers, including an ethylene-octene copolymer grafted maleic anhydride (POE-g-MA) and three maleic-anhydride-grafted polypropylenes (PP-g-MA) with different melt flow indexes (MFI), were used to improve the dispersion of organic clay in matrix. On the other hand, the effects of organic montmorillonite (OMMT) content on the nanocomposite structure in terms of clay dispersion in PPR matrix, thermal behavior and tensile properties were also studied. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that the organic clay layers are mainly intercalated and partially exfoliated in the nanocomposites. Moreover, a PP-g-MA compatibilizer (compatibilizer B) having high MFI can greatly increase the interlayer spacing of the clay as compared with other compatibilizers. With the introduction of compatibilizer D (POE-g-MA), most of the clays are dispersed into the POE phase, and the shape of the dispersed OMMT appears elliptic, which differs from the strip of PP-g-MA. Compared with virgin PPR, the Youngs modulus of the nanocomposite evidently increases when a compatibilizer C (PP-g-MA) with medium MFI is used. For the nanocomposites with compatibilizer B and C, their crystallinities (Xc) increase as compared with that of the virgin PPR. Furthermore, the increase of OMMT loadings presents little effect on the melt temperature (Tm) of the PPR/OMMT nanocomposites, and slight effect on their crystallization temperature (Tc). Only compatibilizer B can lead to a marked increases in crystallinity and Tc of the nanocomposite when the OMMT content is 2 wt%.
2012, 30(6): 865-872
doi: 10.1007/s10118-012-1180-9
Abstract:
In order to achieve monodisperse particles with high content of antibacterial groups covalently bonded on surface, a bicationic viologen, N-hexyl-N'-(4-vinylbenzyl)-4,4'-bipyridinium bromide chloride (HVV) was devised as a surfmer in dispersion polymerization of styrene (St) using a mixture of methanol (or ethylene glycol) and water as media. Effects of content of HVV, its addition profile and composition of reaction media on particles size and incorporation of HVV moieties were mainly investigated. The attachment of silver and gold nanoparticles on particle surface under UV irradiation ascertained the surface-bonded HVV segments. SEM, TEM observations and XPS, zata potential measurements indicated that increase of initial HVV contents and addition of HVV (when polymerization had been performed for 3 h) led to grown particles and enhanced immobilization of HVV moieties. Using a mixture of ethylene glycol and water as reaction media, small particles (520-142 nm) with highly attached HVV moieties were prepared. Furthermore, antibacterial efficacy of the resultant particles against S. aureus was assayed, and particles with more HVV moieties anchored on surface demonstrated greater efficiency of antibacterial activity.
In order to achieve monodisperse particles with high content of antibacterial groups covalently bonded on surface, a bicationic viologen, N-hexyl-N'-(4-vinylbenzyl)-4,4'-bipyridinium bromide chloride (HVV) was devised as a surfmer in dispersion polymerization of styrene (St) using a mixture of methanol (or ethylene glycol) and water as media. Effects of content of HVV, its addition profile and composition of reaction media on particles size and incorporation of HVV moieties were mainly investigated. The attachment of silver and gold nanoparticles on particle surface under UV irradiation ascertained the surface-bonded HVV segments. SEM, TEM observations and XPS, zata potential measurements indicated that increase of initial HVV contents and addition of HVV (when polymerization had been performed for 3 h) led to grown particles and enhanced immobilization of HVV moieties. Using a mixture of ethylene glycol and water as reaction media, small particles (520-142 nm) with highly attached HVV moieties were prepared. Furthermore, antibacterial efficacy of the resultant particles against S. aureus was assayed, and particles with more HVV moieties anchored on surface demonstrated greater efficiency of antibacterial activity.
2012, 30(6): 873-878
doi: 10.1007/s10118-012-1186-3
Abstract:
A series of poly(N,N-diethylacrylamide-co-sodium acrylate) with a degree of crosslinking of 1 mol% have been prepared as thermosensitive superabsorbents for water. The critical swelling temperatures or the volume phase transition temperature (VPTT) and the water absorption capacity of the polymers can be modulated by varying the amount of sodium acrylate (0?60 mol%) in the copolymers. The water absorption and swelling properties of the different hydrogels have been studied as function of temperature. The crosslinked copolymers can absorb large amounts of water at ambient temperatures and dehydrate at higher temperatures with relative ease, making the absorbent materials thermally responsive and thus reusable. The water absorption capacity of the copolymers depends on the pH of the media as the acrylate monomer has a higher water absorption in its deprotonated state. Added urea in the media raises and sharpens the VPTT values of the copolymers containing sodium acrylate.
A series of poly(N,N-diethylacrylamide-co-sodium acrylate) with a degree of crosslinking of 1 mol% have been prepared as thermosensitive superabsorbents for water. The critical swelling temperatures or the volume phase transition temperature (VPTT) and the water absorption capacity of the polymers can be modulated by varying the amount of sodium acrylate (0?60 mol%) in the copolymers. The water absorption and swelling properties of the different hydrogels have been studied as function of temperature. The crosslinked copolymers can absorb large amounts of water at ambient temperatures and dehydrate at higher temperatures with relative ease, making the absorbent materials thermally responsive and thus reusable. The water absorption capacity of the copolymers depends on the pH of the media as the acrylate monomer has a higher water absorption in its deprotonated state. Added urea in the media raises and sharpens the VPTT values of the copolymers containing sodium acrylate.
2012, 30(6): 879-892
doi: 10.1007/s10118-012-1170-y
Abstract:
The effect of the different geometrical dimensionality of two dimensional graphene nanosheets (2D GNSs) and one dimensional carbon nanotubes (1D CNTs) on the non-isothermal crystallization of an ethylene-vinyl acetate (EVA) copolymer at high loading (5 wt%) was studied. Transmission electron microscopy indicated a homogeneous dispersion of GNSs and CNTs in EVA obtained by a solution dispersion process. Fourier-transform infrared spectroscopy and differential scanning calorimetry measurements showed that 1D CNTs and 2D GNSs acted as effective nucleating agents, with a noticeably increased onset crystallization temperature of EVA. A high weight fraction of nano-fillers slowed the overall crystallization rate of composites. At the same crystallization temperature, the crystallization behavior of GNS/EVA composites was slowed compared to that of the CNT/EVA ones owing to larger nucleus barrier and activation energy of diffusion. Dynamic mechanical relaxation and rheology behavior of CNT/EVA and GNS/EVA composites demonstrated that the planar structure of the GNSs had an intensively negative effect on EVA chain mobility due to interactions between nano-fillers and polymer chains, as well as spatial restriction.
The effect of the different geometrical dimensionality of two dimensional graphene nanosheets (2D GNSs) and one dimensional carbon nanotubes (1D CNTs) on the non-isothermal crystallization of an ethylene-vinyl acetate (EVA) copolymer at high loading (5 wt%) was studied. Transmission electron microscopy indicated a homogeneous dispersion of GNSs and CNTs in EVA obtained by a solution dispersion process. Fourier-transform infrared spectroscopy and differential scanning calorimetry measurements showed that 1D CNTs and 2D GNSs acted as effective nucleating agents, with a noticeably increased onset crystallization temperature of EVA. A high weight fraction of nano-fillers slowed the overall crystallization rate of composites. At the same crystallization temperature, the crystallization behavior of GNS/EVA composites was slowed compared to that of the CNT/EVA ones owing to larger nucleus barrier and activation energy of diffusion. Dynamic mechanical relaxation and rheology behavior of CNT/EVA and GNS/EVA composites demonstrated that the planar structure of the GNSs had an intensively negative effect on EVA chain mobility due to interactions between nano-fillers and polymer chains, as well as spatial restriction.
2012, 30(6): 893-899
doi: 10.1007/s10118-012-1181-8
Abstract:
The purpose of this research is to investigate the effects of the variously sulfated chitosans on lysozyme activity and structure. It was shown that the specific enzymatic activity of lysozyme remained almost similar to the native protein after being bound to 6-O-sulfated chitosan (6S-chitosan) and 3,6-O-sulfated chitosan (3,6S-chitosan), but decreased greatly after being bound to 2-N-6-O-sulfated chitosan (2,6S-chitosan). Meanwhile, among these sulfated chitosans, 2,6S-chitosan induced the greatest conformational change in lysozyme as indicated by the fluorescence spectra. These findings demonstrated that when sulfated chitosans of different structures bind to lysozyme, lysozyme undergoes conformational change of different magnitudes, which results in corresponding levels of lysozyme activity. Further study on the interaction of sulfated chitosans with lysozyme by surface plasmon resonance (SPR) suggested that their affinities might be determined by their molecular structures.
The purpose of this research is to investigate the effects of the variously sulfated chitosans on lysozyme activity and structure. It was shown that the specific enzymatic activity of lysozyme remained almost similar to the native protein after being bound to 6-O-sulfated chitosan (6S-chitosan) and 3,6-O-sulfated chitosan (3,6S-chitosan), but decreased greatly after being bound to 2-N-6-O-sulfated chitosan (2,6S-chitosan). Meanwhile, among these sulfated chitosans, 2,6S-chitosan induced the greatest conformational change in lysozyme as indicated by the fluorescence spectra. These findings demonstrated that when sulfated chitosans of different structures bind to lysozyme, lysozyme undergoes conformational change of different magnitudes, which results in corresponding levels of lysozyme activity. Further study on the interaction of sulfated chitosans with lysozyme by surface plasmon resonance (SPR) suggested that their affinities might be determined by their molecular structures.
2012, 30(6): 900-915
doi: 10.1007/s10118-012-1182-7
Abstract:
Glass transition behavior of hydrogen bonded polymer blends of poly(vinyl phenol) (PVPh) and poly(ethylene oxide) (PEO) is systematically investigated using normal differential scanning calorimetry (DSC) and recently developed multifrequency temperature-modulated DSC (TOPEM), in combination with Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) techniques, focusing on the effect of the PEO molecular weight on the spatial and dynamic heterogeneity. It is found, for the first time, that both the glass transition temperature (Tg) and activity energy (Ea) of the blends strongly depend on PEO molecular weight, and a common turning point, which separates the rapid and slow increasing regions, can be found. The interchain hydrogen bonding interactions, both determined by FTIR measurements and obtained from the Kwei equation, decrease with increasing PEO molecular weight, indicating a decrease of the componential miscibility. A series of parameters related to the microscopic spatial and dynamic heterogeneity, such as the activity energy, fragility, nonexponential factor and the size of cooperatively rearranging regions, are calculated from frequency dependency complex heat capacity measured using TOPEM. It is found that each of these parameters monotonically changes with increasing the PEO molecular weight during the glass transition process, demonstrating that hydrogen bonding interaction is the key factor in controlling the spatial and dynamic heterogeneity, thus the glass transition. NMR relaxation results reveal the existence of obvious phase separation large than 5 nm, implying that the cooperatively rearranging regions should be closely related to the interphase region between the two components. The above obtained origin and evolution of spatial and dynamic heterogeneity provide a new insight into the glass transition behavior of polymer blends.
Glass transition behavior of hydrogen bonded polymer blends of poly(vinyl phenol) (PVPh) and poly(ethylene oxide) (PEO) is systematically investigated using normal differential scanning calorimetry (DSC) and recently developed multifrequency temperature-modulated DSC (TOPEM), in combination with Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) techniques, focusing on the effect of the PEO molecular weight on the spatial and dynamic heterogeneity. It is found, for the first time, that both the glass transition temperature (Tg) and activity energy (Ea) of the blends strongly depend on PEO molecular weight, and a common turning point, which separates the rapid and slow increasing regions, can be found. The interchain hydrogen bonding interactions, both determined by FTIR measurements and obtained from the Kwei equation, decrease with increasing PEO molecular weight, indicating a decrease of the componential miscibility. A series of parameters related to the microscopic spatial and dynamic heterogeneity, such as the activity energy, fragility, nonexponential factor and the size of cooperatively rearranging regions, are calculated from frequency dependency complex heat capacity measured using TOPEM. It is found that each of these parameters monotonically changes with increasing the PEO molecular weight during the glass transition process, demonstrating that hydrogen bonding interaction is the key factor in controlling the spatial and dynamic heterogeneity, thus the glass transition. NMR relaxation results reveal the existence of obvious phase separation large than 5 nm, implying that the cooperatively rearranging regions should be closely related to the interphase region between the two components. The above obtained origin and evolution of spatial and dynamic heterogeneity provide a new insight into the glass transition behavior of polymer blends.
2012, 30(6): 916-922
doi: 10.1007/s10118-012-1191-6
Abstract:
PLLA/CA mixtures of different compositions were successfully electrospun to obtain composite nanofibrous membranes. The microstructures of the membrances changed from homogeneous to heterogeneous with the addition of CA, which was observed by FE-ESEM. The PLLA/CA fabric membranes were characterized by mechanical testing, DSC and contact angle measurements. The tensile stress of the composite ?brous membranes increased obviously with the increase of CA content. DSC results indicated that the CA component was the main factor for the changes of enthalpies in the composite ?bers. Contact angle measurements showed the hydrophilicity of the electrospun nanofiber membranes was improved with the addition of CA.
PLLA/CA mixtures of different compositions were successfully electrospun to obtain composite nanofibrous membranes. The microstructures of the membrances changed from homogeneous to heterogeneous with the addition of CA, which was observed by FE-ESEM. The PLLA/CA fabric membranes were characterized by mechanical testing, DSC and contact angle measurements. The tensile stress of the composite ?brous membranes increased obviously with the increase of CA content. DSC results indicated that the CA component was the main factor for the changes of enthalpies in the composite ?bers. Contact angle measurements showed the hydrophilicity of the electrospun nanofiber membranes was improved with the addition of CA.
