Login In
2014 Volume 32 Issue 2
2014, 32(2): 123-129
doi: 10.1007/s10118-014-1395-z
Abstract:
A kind of fibrous clay, palygorskite (PAL), was used as the sole stabilizer in suspension polymerization without the using of any other stabilizer usually used, especially polymeric stabilizers. In order to improve the compatibility with the organic monomer, PAL nano fibers were organically modified with silane coupling agent methacryloxypropyltrimethoxysilane (MPS). Transmission electron microscopy (TEM) and Fourier-transform infrared (FTIR) spectroscopy results show that the hydrolyzed MPS was attached onto PAL surface through Si―O―Si bonds formation without morphology change of PAL. At a loading amount of PAL to monomer as low as 0.36 wt%, effective stabilization could be achieved. After suspension polymerization, spherical poly(methyl methacrylate) (PMMA) particles were obtained. Scanning electron microscopy (SEM) analysis on both the outer surface and the inner cracked surface of the spherical PMMA particles indicates that the PAL particles reside on the surface of the PMMA spheres. The densely stacked PAL together with attached silane coupling agent stabilized the droplets throughout the suspension polymerization.
A kind of fibrous clay, palygorskite (PAL), was used as the sole stabilizer in suspension polymerization without the using of any other stabilizer usually used, especially polymeric stabilizers. In order to improve the compatibility with the organic monomer, PAL nano fibers were organically modified with silane coupling agent methacryloxypropyltrimethoxysilane (MPS). Transmission electron microscopy (TEM) and Fourier-transform infrared (FTIR) spectroscopy results show that the hydrolyzed MPS was attached onto PAL surface through Si―O―Si bonds formation without morphology change of PAL. At a loading amount of PAL to monomer as low as 0.36 wt%, effective stabilization could be achieved. After suspension polymerization, spherical poly(methyl methacrylate) (PMMA) particles were obtained. Scanning electron microscopy (SEM) analysis on both the outer surface and the inner cracked surface of the spherical PMMA particles indicates that the PAL particles reside on the surface of the PMMA spheres. The densely stacked PAL together with attached silane coupling agent stabilized the droplets throughout the suspension polymerization.
2014, 32(2): 130-136
doi: 10.1007/s10118-014-1396-y
Abstract:
Poly(3-(2-methoxyphenyl)thiophene) (PMP-Th) nanowires were fabricated using porous anodic alumina (PAA) as template through electrochemical polymerization by cyclic voltammetry. The control on the size of nanowires was confirmed by electron microscopy. The results indicated that the luminescence spectra of PMP-Th nanowires in PAA nanochannels were blue-shifted and emission intensity was enhanced compared to the emission of the PMP-Th film. Moreover, the luminescent spectra of PMP-Th nanowires were size dependent, which may result from the change in the degree of confinement of nanowires in PAA. Frster energy transfer from PAA to PMP-Th molecules is considered to be responsible for the enhancement of luminescence from PMP-Th nanowires in PAA. The results show that the emission properties of polymers with nanostructures can be tuned by controlling their size.
Poly(3-(2-methoxyphenyl)thiophene) (PMP-Th) nanowires were fabricated using porous anodic alumina (PAA) as template through electrochemical polymerization by cyclic voltammetry. The control on the size of nanowires was confirmed by electron microscopy. The results indicated that the luminescence spectra of PMP-Th nanowires in PAA nanochannels were blue-shifted and emission intensity was enhanced compared to the emission of the PMP-Th film. Moreover, the luminescent spectra of PMP-Th nanowires were size dependent, which may result from the change in the degree of confinement of nanowires in PAA. Frster energy transfer from PAA to PMP-Th molecules is considered to be responsible for the enhancement of luminescence from PMP-Th nanowires in PAA. The results show that the emission properties of polymers with nanostructures can be tuned by controlling their size.
2014, 32(2): 137-142
doi: 10.1007/s10118-014-1381-5
Abstract:
Ethylene polymerization was carried out by immobilization of rac-ethylenebis(1-indenyl)zirconium dichloride (Et(Ind)2ZrCl2) and rac-dimethylsilylbis(1-indenyl)zirconium dichloride (Me2Si(Ind)2ZrCl2) preactivated with methylaluminoxane (MAO) on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 ℃ and 70 ℃ for Me2Si(Ind)2ZrCl2/MAO and Et(Ind)2ZrCl2/MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 ℃ for both catalysts systems. The melting points of the produced polyethylene were about 130 ℃, which could be attributed to the linear structure of HDPE.
Ethylene polymerization was carried out by immobilization of rac-ethylenebis(1-indenyl)zirconium dichloride (Et(Ind)2ZrCl2) and rac-dimethylsilylbis(1-indenyl)zirconium dichloride (Me2Si(Ind)2ZrCl2) preactivated with methylaluminoxane (MAO) on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 ℃ and 70 ℃ for Me2Si(Ind)2ZrCl2/MAO and Et(Ind)2ZrCl2/MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 ℃ for both catalysts systems. The melting points of the produced polyethylene were about 130 ℃, which could be attributed to the linear structure of HDPE.
2014, 32(2): 143-150
doi: 10.1007/s10118-014-1371-7
Abstract:
Porous PVDF blend membranes with good hydrophilicity and a symmetric structure were prepared by the phase inversion method using amphiphilic brush-like copolymers, P(MMA-r-PEGMA), as hydrophilic additive and triethylphosphate (TEP) as solvent. P(MMA-r-PEGMA) was synthesized by radical polymerization in TEP. Then the obtained amphiphilic copolymer solution was mixed with PVDF and TEP to prepare the dope solution. The effects of P(MMA-r-PEGMA) content and coagulation composition on membrane morphologies were investigated using scanning electron microscopy (SEM). The results demonstrated that, even blended with amphiphilic copolymers, a symmetric structure can be formed. Hollow fiber membranes with a mainly symmetric structure were also fabricated. The dry hollow fiber membranes showed good hydrophilicity, high flux and good rejection performance because of their hydrophilic surface and pores wall.
Porous PVDF blend membranes with good hydrophilicity and a symmetric structure were prepared by the phase inversion method using amphiphilic brush-like copolymers, P(MMA-r-PEGMA), as hydrophilic additive and triethylphosphate (TEP) as solvent. P(MMA-r-PEGMA) was synthesized by radical polymerization in TEP. Then the obtained amphiphilic copolymer solution was mixed with PVDF and TEP to prepare the dope solution. The effects of P(MMA-r-PEGMA) content and coagulation composition on membrane morphologies were investigated using scanning electron microscopy (SEM). The results demonstrated that, even blended with amphiphilic copolymers, a symmetric structure can be formed. Hollow fiber membranes with a mainly symmetric structure were also fabricated. The dry hollow fiber membranes showed good hydrophilicity, high flux and good rejection performance because of their hydrophilic surface and pores wall.
2014, 32(2): 151-162
doi: 10.1007/s10118-014-1394-0
Abstract:
A novel series of polyphosphazene-graft-polystyrene (PP-g-PS) copolymers were successfully prepared by atom transfer radical polymerization (ATRP) of styrene monomers and brominated poly(bis(4-methylphenoxy)phosphazene) macroinitiator. The graft density and the graft length could be regulated by changing the bromination degree of the macroinitiator and the ATRP reaction time, respectively. The PP-g-PS copolymers readily underwent a regioselective sulfonation reaction, which occurred preferentially at the polystyrene sites, producing the sulfonated PP-g-PS copolymers with a range of ion exchange capacities. The resulting sulfonated PP-g-PS membranes prepared by solution casting showed high water uptake, low water swelling and considerable proton conductivity. They also exhibited good oxidative stability and high resistance to methanol crossover. Morphological studies of the membranes by transmission electron microscopy showed clear nanophase-separated structures resulted from hydrophobic polyphosphazene backbone and hydrophilic polystyrene sulfonic acid segments, indicating the formation of proton transferring tunnels. Therefore, these sulfonated copolymers may be candidate materials for proton exchange membranes in direct methanol fuel cell (DMFC) applications.
A novel series of polyphosphazene-graft-polystyrene (PP-g-PS) copolymers were successfully prepared by atom transfer radical polymerization (ATRP) of styrene monomers and brominated poly(bis(4-methylphenoxy)phosphazene) macroinitiator. The graft density and the graft length could be regulated by changing the bromination degree of the macroinitiator and the ATRP reaction time, respectively. The PP-g-PS copolymers readily underwent a regioselective sulfonation reaction, which occurred preferentially at the polystyrene sites, producing the sulfonated PP-g-PS copolymers with a range of ion exchange capacities. The resulting sulfonated PP-g-PS membranes prepared by solution casting showed high water uptake, low water swelling and considerable proton conductivity. They also exhibited good oxidative stability and high resistance to methanol crossover. Morphological studies of the membranes by transmission electron microscopy showed clear nanophase-separated structures resulted from hydrophobic polyphosphazene backbone and hydrophilic polystyrene sulfonic acid segments, indicating the formation of proton transferring tunnels. Therefore, these sulfonated copolymers may be candidate materials for proton exchange membranes in direct methanol fuel cell (DMFC) applications.
2014, 32(2): 163-168
doi: 10.1007/s10118-014-1385-1
Abstract:
A new type of polymerizable ionic liquid (IL) 1-(3-aminobenzyl)-3-methylimidazolium chloride (AMIC) was synthesized to obtain a novel polymer salt poly(1-(3-aminobenzyl)-3-methylimidazolium chloride) (PAMIC). The AMIC was structurally characterized by mass spectrometry and Fourier transform infrared spectrometry (FTIR). The structure, morphology and properties of PAMIC were investigated by FTIR, ultraviolet visible absorption spectra (UV-Vis), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), conductivity measurement and thermo-gravimetric analysis (TGA). The PAMIC was spherulitic with an average diameter of about 50 nm and showed high conductivity and excellent thermal stability.
A new type of polymerizable ionic liquid (IL) 1-(3-aminobenzyl)-3-methylimidazolium chloride (AMIC) was synthesized to obtain a novel polymer salt poly(1-(3-aminobenzyl)-3-methylimidazolium chloride) (PAMIC). The AMIC was structurally characterized by mass spectrometry and Fourier transform infrared spectrometry (FTIR). The structure, morphology and properties of PAMIC were investigated by FTIR, ultraviolet visible absorption spectra (UV-Vis), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), conductivity measurement and thermo-gravimetric analysis (TGA). The PAMIC was spherulitic with an average diameter of about 50 nm and showed high conductivity and excellent thermal stability.
2014, 32(2): 169-176
doi: 10.1007/s10118-014-1386-0
Abstract:
The freshly prepared water-wet amidoximated bacterial cellulose (Am-BC) serves as an effective nanoreactor to synthesis zinc oxide nanoparticles by in situ polyol method. The obtained ZnO/Am-BC nanocomposites have been characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The influence of the zinc acetate concentration on the morphologies and size of ZnO nanoparticles and the possible formation mechanism were discussed. The results indicated that uniform ZnO nanoparticles were homogeneously anchored on the Am-BC nanofibers through strong interaction between the hydroxyl and amino groups of Am-BC and ZnO nanoparticles. The loading content of ZnO nanoparticles is higher using Am-BC as a template than using the unmodified bacterial cellulose. The resultant nanocomposite synthesized at 0.05 wt% shows a high photocatalytic activity (92%) in the degradation of methyl orange.
The freshly prepared water-wet amidoximated bacterial cellulose (Am-BC) serves as an effective nanoreactor to synthesis zinc oxide nanoparticles by in situ polyol method. The obtained ZnO/Am-BC nanocomposites have been characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The influence of the zinc acetate concentration on the morphologies and size of ZnO nanoparticles and the possible formation mechanism were discussed. The results indicated that uniform ZnO nanoparticles were homogeneously anchored on the Am-BC nanofibers through strong interaction between the hydroxyl and amino groups of Am-BC and ZnO nanoparticles. The loading content of ZnO nanoparticles is higher using Am-BC as a template than using the unmodified bacterial cellulose. The resultant nanocomposite synthesized at 0.05 wt% shows a high photocatalytic activity (92%) in the degradation of methyl orange.
2014, 32(2): 177-186
doi: 10.1007/s10118-014-1387-z
Abstract:
Three-layer core/shell latex particles with various shell crosslinking level and shell thickness were prepared by multistep emulsion polymerization, and the hollow latex particles with different morphologies were then obtained after alkali post-treatment. Influences of divinyl benzene (DVB) content and the core/shell mass ratio on emulsion polymerization and particle morphology were investigated. Results showed that with the increase of DVB content, the percentage of total amount of ―COOH on the particle surface and free in aqueous phase (PSFa) decreased, and the morphology of the post-treated particles underwent evolution from cracked, intact hollow to deficient swelling structure. Decreasing the core/shell mass ratio could not only make more carboxyl groups encapsulated by the shell, but also increase the shell resistance to the swelling of the core. The uniform hollow latex particles with intact morphology were obtained when the DVB content was 3.54 wt% and the core/shell mass ratio was 1/6.
Three-layer core/shell latex particles with various shell crosslinking level and shell thickness were prepared by multistep emulsion polymerization, and the hollow latex particles with different morphologies were then obtained after alkali post-treatment. Influences of divinyl benzene (DVB) content and the core/shell mass ratio on emulsion polymerization and particle morphology were investigated. Results showed that with the increase of DVB content, the percentage of total amount of ―COOH on the particle surface and free in aqueous phase (PSFa) decreased, and the morphology of the post-treated particles underwent evolution from cracked, intact hollow to deficient swelling structure. Decreasing the core/shell mass ratio could not only make more carboxyl groups encapsulated by the shell, but also increase the shell resistance to the swelling of the core. The uniform hollow latex particles with intact morphology were obtained when the DVB content was 3.54 wt% and the core/shell mass ratio was 1/6.
2014, 32(2): 187-196
doi: 10.1007/s10118-014-1393-1
Abstract:
Two polyborosiloxanes (PBSis) with char yield up to 74.13% at 800 ℃ were synthesized by the direct polycondensation of boric acid with phenyltrimethoxysilane in diglyme. The PBSis were characterized by gel permeation chromatography, IR spectroscopy as well as 1H-, 29Si- and 11B-NMR. PBSi modified phenol-formaldehyde resins (PBSi/PFs) were prepared at different PBSi/PF mass ratios and were cured at 150 ℃. The PBSi/PFs were characterized by IR spectroscopy, scanning electron microscopy, thermogravimetric analysis and tensile test. The results revealed that the cured PBSi/PFs had sea-island morphology and higher char yield than the common PF. PBSi/PF blend with PBSi/PF mass ratio of 0.4:1 had char yield up to 70.83% at 800 ℃. The PBSi/PFs had tensile strength similar to PF. The ceramization of PBSi/PFs was also studied. The silicon boron oxycarbide (SiBOC) ceramics formed were characterized by IR spectroscopy and elemental analysis. This method provided a valuable way to prepare easily shapeable polymer blends as ceramic precursors.
Two polyborosiloxanes (PBSis) with char yield up to 74.13% at 800 ℃ were synthesized by the direct polycondensation of boric acid with phenyltrimethoxysilane in diglyme. The PBSis were characterized by gel permeation chromatography, IR spectroscopy as well as 1H-, 29Si- and 11B-NMR. PBSi modified phenol-formaldehyde resins (PBSi/PFs) were prepared at different PBSi/PF mass ratios and were cured at 150 ℃. The PBSi/PFs were characterized by IR spectroscopy, scanning electron microscopy, thermogravimetric analysis and tensile test. The results revealed that the cured PBSi/PFs had sea-island morphology and higher char yield than the common PF. PBSi/PF blend with PBSi/PF mass ratio of 0.4:1 had char yield up to 70.83% at 800 ℃. The PBSi/PFs had tensile strength similar to PF. The ceramization of PBSi/PFs was also studied. The silicon boron oxycarbide (SiBOC) ceramics formed were characterized by IR spectroscopy and elemental analysis. This method provided a valuable way to prepare easily shapeable polymer blends as ceramic precursors.
2014, 32(2): 197-208
doi: 10.1007/s10118-014-1392-2
Abstract:
The curing behavior of diglycidyl ether of bisphenol-A (DGEBA) with different phosphorus containing diamide-diimide-tetraamines (DADITAs) was studied by DSC. Eight DADITAs of varying structures were synthesized by reacting 1 mole of pyromellitic anhydride (PMDA)/3,3'-benzophenone tetracarboxylic dianhydride (BTDA)/1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA)/4,4'-oxydiphthalic anhydride (ODPA) with 2 mole of L-tryptophan (T) in a mixture of acetic acid and pyridine (3:2 V/V) followed by activaton with thionyl chloride and then condensation with excess of phosphorus containing triamines tris(3-aminophenyl) phosphine (TAP) and tris(3-aminophenyl) phosphine oxide (TAPO). DADITAs obtained by reacting PMDA/BTDA/NTDA/ODPA with L-tryptophan followed by condensation with TAP/TAPO were designated as PTAP, PTAPO, BTAP, BTAPO, NTAP, NTAPO, OTAP and OTAPO respectively. The structural characterization of synthesized DADITAs was done by FTIR, 1H-NMR, 13C-NMR, 31P-NMR spectroscopic techniques and elemental analysis. Thermal stability of the isothermally cured epoxy was investigated using dynamic thermogravimetry analysis. The glass transition temperature (Tg) was highest in DGEBA cured using PTAP. All epoxy thermosets exhibited excellent flame retardancy, moderate changes in Tg and thermal stability. Due to presence of phosphorus in curing agents, all epoxy resin systems met the UL-94 V-0 classification and the limiting oxygen index (LOI) reached up to 38.5, probably because of the nitrogen-phosphorus synergistic effect.
The curing behavior of diglycidyl ether of bisphenol-A (DGEBA) with different phosphorus containing diamide-diimide-tetraamines (DADITAs) was studied by DSC. Eight DADITAs of varying structures were synthesized by reacting 1 mole of pyromellitic anhydride (PMDA)/3,3'-benzophenone tetracarboxylic dianhydride (BTDA)/1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA)/4,4'-oxydiphthalic anhydride (ODPA) with 2 mole of L-tryptophan (T) in a mixture of acetic acid and pyridine (3:2 V/V) followed by activaton with thionyl chloride and then condensation with excess of phosphorus containing triamines tris(3-aminophenyl) phosphine (TAP) and tris(3-aminophenyl) phosphine oxide (TAPO). DADITAs obtained by reacting PMDA/BTDA/NTDA/ODPA with L-tryptophan followed by condensation with TAP/TAPO were designated as PTAP, PTAPO, BTAP, BTAPO, NTAP, NTAPO, OTAP and OTAPO respectively. The structural characterization of synthesized DADITAs was done by FTIR, 1H-NMR, 13C-NMR, 31P-NMR spectroscopic techniques and elemental analysis. Thermal stability of the isothermally cured epoxy was investigated using dynamic thermogravimetry analysis. The glass transition temperature (Tg) was highest in DGEBA cured using PTAP. All epoxy thermosets exhibited excellent flame retardancy, moderate changes in Tg and thermal stability. Due to presence of phosphorus in curing agents, all epoxy resin systems met the UL-94 V-0 classification and the limiting oxygen index (LOI) reached up to 38.5, probably because of the nitrogen-phosphorus synergistic effect.
2014, 32(2): 209-217
doi: 10.1007/s10118-014-1388-y
Abstract:
Intrinsic viscosities for a given polyelectrolyte in salt free and low-salt solvents reported in literatures are normally not comparable, because of inadequate valuation procedures. This article describes a theoretically justified reliable method, which is free of any model assumptions: The so called Wolf plot (logarithm of the relative viscosity as a function of polymer concentration) enables the unequivocal determination of intrinsic viscosities for all kinds of macromolecules, irrespective of whether they are chain molecules of different architecture or globular polymers, whether they are charged or uncharged. The validation of the method was examined by evaluation of the viscosities of a polyelectrolyte, some uncharged polymers of different architectures, uncharged polymer blends, and some literature data.
Intrinsic viscosities for a given polyelectrolyte in salt free and low-salt solvents reported in literatures are normally not comparable, because of inadequate valuation procedures. This article describes a theoretically justified reliable method, which is free of any model assumptions: The so called Wolf plot (logarithm of the relative viscosity as a function of polymer concentration) enables the unequivocal determination of intrinsic viscosities for all kinds of macromolecules, irrespective of whether they are chain molecules of different architecture or globular polymers, whether they are charged or uncharged. The validation of the method was examined by evaluation of the viscosities of a polyelectrolyte, some uncharged polymers of different architectures, uncharged polymer blends, and some literature data.
2014, 32(2): 218-229
doi: 10.1007/s10118-014-1402-4
Abstract:
Nanocomposites of polyaniline (PANI) and the macrocycle thiacalix[4]arene tetra sulfonate (TCAS) were successfully synthesized in feed ratios of 1:0.25, 1:0.50 and 1:0.75 by three prevail synthetic methods, i.e. in situ polymerization, emulsion polymerization and solution casting technique. The structures of the nanocomposites were confirmed by FTIR, UV-Vis, XRD, SEM, and TEM techniques. The conductivity was measured by a four probe method. The conductivity was recorded to be as high as 10510-2 Scm-1 for the nanocomposite with a nanometer size structure and homogeneously distributed morphology. The electroactivity of the nanocomposites was approved by cyclic voltammetry (CV) and impedance spectroscopy technique (EIS). The antioxidant ability and thermal property of the composites were further studied. Preliminary studies have evidenced the production of conductive nanocomposites with good thermal property and relatively good solubility in N-methyl 2-pyrrolidone (NMP), with the antioxidant activity reaching up to 80%.
Nanocomposites of polyaniline (PANI) and the macrocycle thiacalix[4]arene tetra sulfonate (TCAS) were successfully synthesized in feed ratios of 1:0.25, 1:0.50 and 1:0.75 by three prevail synthetic methods, i.e. in situ polymerization, emulsion polymerization and solution casting technique. The structures of the nanocomposites were confirmed by FTIR, UV-Vis, XRD, SEM, and TEM techniques. The conductivity was measured by a four probe method. The conductivity was recorded to be as high as 10510-2 Scm-1 for the nanocomposite with a nanometer size structure and homogeneously distributed morphology. The electroactivity of the nanocomposites was approved by cyclic voltammetry (CV) and impedance spectroscopy technique (EIS). The antioxidant ability and thermal property of the composites were further studied. Preliminary studies have evidenced the production of conductive nanocomposites with good thermal property and relatively good solubility in N-methyl 2-pyrrolidone (NMP), with the antioxidant activity reaching up to 80%.
2014, 32(2): 230-235
doi: 10.1007/s10118-014-1372-6
Abstract:
The hydrothermal aging of poly(ethylene terephthalate) (PET) was investigated at 70-95 ℃. A new method to investigate the hydrolysis degree of PET by Fourier transform infrared spectroscopy (FTIR) was proposed. The spectra during the hydrothermal aging were measured using attenuated total reflection accessory (ATR). Peak resolving of carbonyl regions was performed, and the ratio of two groups of bands representing carboxylic acids and esters respectively were calculated to show the hydrolysis degree of ester groups in PET. The acid/ester ratio shows exactly the same trend as the average chain scission number per unit mass at various temperatures and thus can be used as a parameter to characterize the hydrolysis and random chain scission of PET. This method related to the hydrolysis mechanism directly, is simple, fast and convenient compared to the traditional methods such as viscometry, end-group titration and size exclusion chromatography (SEC). It may also be useful in hydrolysis characterization of other polyesters.
The hydrothermal aging of poly(ethylene terephthalate) (PET) was investigated at 70-95 ℃. A new method to investigate the hydrolysis degree of PET by Fourier transform infrared spectroscopy (FTIR) was proposed. The spectra during the hydrothermal aging were measured using attenuated total reflection accessory (ATR). Peak resolving of carbonyl regions was performed, and the ratio of two groups of bands representing carboxylic acids and esters respectively were calculated to show the hydrolysis degree of ester groups in PET. The acid/ester ratio shows exactly the same trend as the average chain scission number per unit mass at various temperatures and thus can be used as a parameter to characterize the hydrolysis and random chain scission of PET. This method related to the hydrolysis mechanism directly, is simple, fast and convenient compared to the traditional methods such as viscometry, end-group titration and size exclusion chromatography (SEC). It may also be useful in hydrolysis characterization of other polyesters.
2014, 32(2): 236-244
doi: 10.1007/s10118-014-1373-5
Abstract:
In this study a series of chemically crosslinked chitosan/poly(ethylene glycol) (CS/PEG) composite membranes were prepared with PEG as a crosslinking reagent other than an additional blend. First, carboxyl-capped poly(ethylene glycol) (HOOC-PEG-COOH) was synthesized. Dense CS/PEG composite membranes were then prepared by casting/evaporation of CS and HOOC-PEG-COOH mixture in acetic acid solution. Chitosan was chemically crosslinked due to the amidation between the carboxyl in HOOC-PEG-COOH and the amino in chitosan under heating, as confirmed by FTIR analysis. The hydrophilicity, water-resistance and mechanical properties of pure and crosslinked chitosan membranes were characterized, respectively. The results of water contact angle and water absorption showed that the hydrophilicity of chitosan membranes could be significantly improved, while no significant difference of weight loss between pure chitosan membranes and crosslinked ones was detected, indicating that composite membranes with amidation crosslinking possess excellent water resistanance ability. Moreover, the tensile strength of chitosan membranes could be significantly enhanced with the addition of certain amount of HOOC-PEG-COOH crosslinker, while the elongation at break didn't degrade at the same time. Additionally, the results of swelling behaviors in water at different pH suggested that the composite membranes were pH sensitive.
In this study a series of chemically crosslinked chitosan/poly(ethylene glycol) (CS/PEG) composite membranes were prepared with PEG as a crosslinking reagent other than an additional blend. First, carboxyl-capped poly(ethylene glycol) (HOOC-PEG-COOH) was synthesized. Dense CS/PEG composite membranes were then prepared by casting/evaporation of CS and HOOC-PEG-COOH mixture in acetic acid solution. Chitosan was chemically crosslinked due to the amidation between the carboxyl in HOOC-PEG-COOH and the amino in chitosan under heating, as confirmed by FTIR analysis. The hydrophilicity, water-resistance and mechanical properties of pure and crosslinked chitosan membranes were characterized, respectively. The results of water contact angle and water absorption showed that the hydrophilicity of chitosan membranes could be significantly improved, while no significant difference of weight loss between pure chitosan membranes and crosslinked ones was detected, indicating that composite membranes with amidation crosslinking possess excellent water resistanance ability. Moreover, the tensile strength of chitosan membranes could be significantly enhanced with the addition of certain amount of HOOC-PEG-COOH crosslinker, while the elongation at break didn't degrade at the same time. Additionally, the results of swelling behaviors in water at different pH suggested that the composite membranes were pH sensitive.
2014, 32(2): 245-254
doi: 10.1007/s10118-014-1397-x
Abstract:
The combined effects of stretching and single-walled carbon nanotubes (SWCNTs) on crystalline structure and mechanical properties were systematically investigated in melt-spun polypropylene (PP) fibers prepared at two different draw ratios. The dispersion, alignment of the SWCNT bundles and interfacial crystalline structure in the composite fibers are significantly influenced by the stretching force during the melt spinning. The nanohybrid shish kebab (NHSK) superstructure where extended PP chains and aligned SWCNT bundle as hybrid shish and PP lamellae as kebab has been successfully obtained in the composite fibers prepared at the high draw ratio and the related formation mechanism is discussed based on the results of morphological observations and 2d-SAXS patterns. Large improvement in tensile strength and modulus has been realized at the high draw ratio due to the enhanced orientation and dispersion of SWCNT bundles as well as the formation of NHSK.
The combined effects of stretching and single-walled carbon nanotubes (SWCNTs) on crystalline structure and mechanical properties were systematically investigated in melt-spun polypropylene (PP) fibers prepared at two different draw ratios. The dispersion, alignment of the SWCNT bundles and interfacial crystalline structure in the composite fibers are significantly influenced by the stretching force during the melt spinning. The nanohybrid shish kebab (NHSK) superstructure where extended PP chains and aligned SWCNT bundle as hybrid shish and PP lamellae as kebab has been successfully obtained in the composite fibers prepared at the high draw ratio and the related formation mechanism is discussed based on the results of morphological observations and 2d-SAXS patterns. Large improvement in tensile strength and modulus has been realized at the high draw ratio due to the enhanced orientation and dispersion of SWCNT bundles as well as the formation of NHSK.
