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2014 Volume 32 Issue 6
2014, 32(6): 675-680
doi: 10.1007/s10118-014-1455-4
Abstract:
The simple LBL technique was introduced to fabricate green nacre-like chatosan/montmorillonite (CHI/MMT) films. The results of SEM and XRD analysis demonstrate that the produced CHI/MMT composites films stacked densely together to bring out well-defined nacre-like brick-mortar structure. The nanoindentation technique is used to characterize the mechanical properties of the layered nanocomposite films, which show enhanced mechanical modulus (up to ~6.64 GPa) compared with the pure chitosan.
The simple LBL technique was introduced to fabricate green nacre-like chatosan/montmorillonite (CHI/MMT) films. The results of SEM and XRD analysis demonstrate that the produced CHI/MMT composites films stacked densely together to bring out well-defined nacre-like brick-mortar structure. The nanoindentation technique is used to characterize the mechanical properties of the layered nanocomposite films, which show enhanced mechanical modulus (up to ~6.64 GPa) compared with the pure chitosan.
2014, 32(6): 681-689
doi: 10.1007/s10118-014-1453-6
Abstract:
A long-term (about nine months) isothermal degradation experiment of two different commercial polylactide (PLA) samples used for food packaging was carried out at a relatively low temperature (423 K). Thermooxidative degradations of the same polymers were carried out in a thermogravimetric (TG) analyser, at higher temperatures (453 T 523 K), under isothermal heating conditions. The obtained set of experimental TG data was used to determine the apparent activation energy (Ea) of degradation through two isothermal kinetic methods. The results from long-term experiment evidenced considerable mass loss for both PLA samples in the investigated period, but the experimental data were not in agreement with those from the short-term degradations at higher temperatures, thus suggesting a different degradation kinetics, and, then a low reliability of the lifetime predictions for polymers in service or degradation forecasts for the end of their life based on experiments at higher temperatures.
A long-term (about nine months) isothermal degradation experiment of two different commercial polylactide (PLA) samples used for food packaging was carried out at a relatively low temperature (423 K). Thermooxidative degradations of the same polymers were carried out in a thermogravimetric (TG) analyser, at higher temperatures (453 T 523 K), under isothermal heating conditions. The obtained set of experimental TG data was used to determine the apparent activation energy (Ea) of degradation through two isothermal kinetic methods. The results from long-term experiment evidenced considerable mass loss for both PLA samples in the investigated period, but the experimental data were not in agreement with those from the short-term degradations at higher temperatures, thus suggesting a different degradation kinetics, and, then a low reliability of the lifetime predictions for polymers in service or degradation forecasts for the end of their life based on experiments at higher temperatures.
2014, 32(6): 690-702
doi: 10.1007/s10118-014-1450-9
Abstract:
In this work, a UV-Visible light controlled supramolecular system based on ethyl cellulose (EC) was constructed, combining the host-guest interaction of -cyclodextrin (-CD) group and trans-isomer of azobenzene (tAzo) group. To link -CD to the hydrophobic section, renewable EC was used as macroinitiator to initiate the polymerization of e-caprolactone (e-CL) to form biocompatible and biodegradable comb copolymer EC-g-PCL, and -CD was attached to the end of PCL side chain via click reaction. Meanwhile, hydrophilic PEG-tAzo was obtained by N,N'-dicyclohexylcarbodiimide (DCC) coupling. Then, the structures of the products were characterized by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). Subsequently, with the formation of inclusion complexes by -CD and tAzo groups, the obtained EC-g-PCL--CD/PEG-tAzo supramolecular system self-assembled in water with hydrophobic EC-g-PCL--CD as core and hydrophilic PEG-tAzo as shell. Furthermore, dynamic light scattering (DLS) and transmission electron microscopy (TEM) were utilized to investigate the particle size and size distribution, while NMR and UV-Vis spectra were applied to explore the UV-Vis ible light stimuli-responsiveness of the micelles.
In this work, a UV-Visible light controlled supramolecular system based on ethyl cellulose (EC) was constructed, combining the host-guest interaction of -cyclodextrin (-CD) group and trans-isomer of azobenzene (tAzo) group. To link -CD to the hydrophobic section, renewable EC was used as macroinitiator to initiate the polymerization of e-caprolactone (e-CL) to form biocompatible and biodegradable comb copolymer EC-g-PCL, and -CD was attached to the end of PCL side chain via click reaction. Meanwhile, hydrophilic PEG-tAzo was obtained by N,N'-dicyclohexylcarbodiimide (DCC) coupling. Then, the structures of the products were characterized by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). Subsequently, with the formation of inclusion complexes by -CD and tAzo groups, the obtained EC-g-PCL--CD/PEG-tAzo supramolecular system self-assembled in water with hydrophobic EC-g-PCL--CD as core and hydrophilic PEG-tAzo as shell. Furthermore, dynamic light scattering (DLS) and transmission electron microscopy (TEM) were utilized to investigate the particle size and size distribution, while NMR and UV-Vis spectra were applied to explore the UV-Vis ible light stimuli-responsiveness of the micelles.
2014, 32(6): 703-710
doi: 10.1007/s10118-014-1442-9
Abstract:
A constitutive model is constructed to consider the resin matrix post-yield softening and progressive hardening behaviors. A user-defined material mechanical behavior (UMAT) subroutine is created, then the non-linear three-dimensional finite element analysis on the tensile processes of multi-fiber composites is conducted. The approximate 45 shear bands emanating from the matrix crack tip are found, being coincided with the experimental observations. The shear stress on the adjacent intact fiber/matrix interface is strongly influenced by the shear band and thus the stress concentration factor (SCF) changes obviously in the adjacent fibers. The distinct stress redistribution in the adjacent intact fibers implies the significant effect of the shear bands on the progressive fiber fracture initiation. As the inter-fiber spacing increases, the peak value of the SCF in the adjacent intact fiber decreases, whereas the overload zone becomes wider. The research has provided a helpful tool to evaluate the failure of fiber composites and optimize the composite performance through the proper selection of resin matrix properties and fiber volume fraction.
A constitutive model is constructed to consider the resin matrix post-yield softening and progressive hardening behaviors. A user-defined material mechanical behavior (UMAT) subroutine is created, then the non-linear three-dimensional finite element analysis on the tensile processes of multi-fiber composites is conducted. The approximate 45 shear bands emanating from the matrix crack tip are found, being coincided with the experimental observations. The shear stress on the adjacent intact fiber/matrix interface is strongly influenced by the shear band and thus the stress concentration factor (SCF) changes obviously in the adjacent fibers. The distinct stress redistribution in the adjacent intact fibers implies the significant effect of the shear bands on the progressive fiber fracture initiation. As the inter-fiber spacing increases, the peak value of the SCF in the adjacent intact fiber decreases, whereas the overload zone becomes wider. The research has provided a helpful tool to evaluate the failure of fiber composites and optimize the composite performance through the proper selection of resin matrix properties and fiber volume fraction.
2014, 32(6): 711-717
doi: 10.1007/s10118-014-1424-y
Abstract:
Herein a facile and controllable heterocoagulation between polystyrene (PS) microspheres and multiwalled carbon nanotubes (MWCNTs) is introduced based on colloid thermodynamics. The MWCNTs play the role of steric stabilizer for stabilizing the metastable PS microspheres and thus immobilize spontaneously on the surface of PS microspheres. The synthesized MWCNTs-coated PS composite particles have been extensively characterized by scanning electron microscopy, transmission electron microscopy, thermogravimetry and Raman spectroscopy. The results indicate that the structure and morphology of the resultant MWCNTs-coated PS composite particles are significantly affected by the weight ratio of PS and MWNCTs and the amount of poly(vinylpyrrolidone) that is injected into PS dispersion before they are mixed with MWCNTs. Therefore, these composite particles have the potential to produce MWCNTs-based composite materials with controllable mass loading and dispersity of MWCNTs.
Herein a facile and controllable heterocoagulation between polystyrene (PS) microspheres and multiwalled carbon nanotubes (MWCNTs) is introduced based on colloid thermodynamics. The MWCNTs play the role of steric stabilizer for stabilizing the metastable PS microspheres and thus immobilize spontaneously on the surface of PS microspheres. The synthesized MWCNTs-coated PS composite particles have been extensively characterized by scanning electron microscopy, transmission electron microscopy, thermogravimetry and Raman spectroscopy. The results indicate that the structure and morphology of the resultant MWCNTs-coated PS composite particles are significantly affected by the weight ratio of PS and MWNCTs and the amount of poly(vinylpyrrolidone) that is injected into PS dispersion before they are mixed with MWCNTs. Therefore, these composite particles have the potential to produce MWCNTs-based composite materials with controllable mass loading and dispersity of MWCNTs.
2014, 32(6): 718-730
doi: 10.1007/s10118-014-1443-8
Abstract:
The morphology evolution and the corresponding linear viscoelastic behavior of the phase-separating polybutadiene (PB)/low vinyl content polyisoprene (LPI) blend have been investigated by phase contrast optical microscopy (PCOM), small-angle light scattering (SALS) and rheometry. Two kinds of structure evolutions and rheological responses have been observed. It is found that the co-continuous structure generally gives a power law behavior of the dynamic storage modulus versus frequency and the coarsening of co-continuous structure leads to a decrease of the storage modulus. For the droplet-matrix structure, a platform modulus is observed at the mediate frequencies, followed by the typical terminal relaxation behavior of storage modulus at the extremely low frequencies. The decreasing platform modulus and increasing terminal modulus with the growth of droplets are observed and can be well interpreted by the simplified Palierne model. The platform modulus and terminal modulus at a given frequency are found to be scalable with the phase separation time. Besides, the characteristic relaxation time and domain size of the droplets have been obtained by rheology. And it seems that the rheologically determined droplet dimensions are consistent with the ones determined by PCOM and SALS.
The morphology evolution and the corresponding linear viscoelastic behavior of the phase-separating polybutadiene (PB)/low vinyl content polyisoprene (LPI) blend have been investigated by phase contrast optical microscopy (PCOM), small-angle light scattering (SALS) and rheometry. Two kinds of structure evolutions and rheological responses have been observed. It is found that the co-continuous structure generally gives a power law behavior of the dynamic storage modulus versus frequency and the coarsening of co-continuous structure leads to a decrease of the storage modulus. For the droplet-matrix structure, a platform modulus is observed at the mediate frequencies, followed by the typical terminal relaxation behavior of storage modulus at the extremely low frequencies. The decreasing platform modulus and increasing terminal modulus with the growth of droplets are observed and can be well interpreted by the simplified Palierne model. The platform modulus and terminal modulus at a given frequency are found to be scalable with the phase separation time. Besides, the characteristic relaxation time and domain size of the droplets have been obtained by rheology. And it seems that the rheologically determined droplet dimensions are consistent with the ones determined by PCOM and SALS.
2014, 32(6): 731-742
doi: 10.1007/s10118-014-1448-3
Abstract:
Three-arm and four-arm star-like polybutadienes (PBds) were synthesized via the combination of living anionic polymerization and the click coupling method. Kinetic study showed that the click reaction between the azido group terminated PBd-t-N3 and the alkyne-containing multifunctional linking reagent was fast and highly efficient. All coupling reactions were fully accomplished within 40 min at 50 C in toluene in the presence of the reducing agent Cu(0), proven by 1H-NMR, FTIR and GPC measurements. For the coupling reactions between the PBd-t-N3 polymer and dialkyne-containing compound, the final conversion of the coupled PBd-PBd polymer was ca. 97.0%. When a PBd-t-N3 polymer was reacted with trialkyne-containing or tetraalkyne-containing compound, the conversion of three-arm or four-arm PBd was around 95.5% or 87.0%, respectively. Several factors influencing the coupling efficiency were studied, including the molecular weight of the initial PBd-t-N3, arm numbers and the molar ratio of the azido group to the alkynyl group. The results indicated that the conversion of the target products would be promoted when the molecular weight of the PBd-t-N3 was low and the molar ratio of the azido to alkynyl groups was close to 1.
Three-arm and four-arm star-like polybutadienes (PBds) were synthesized via the combination of living anionic polymerization and the click coupling method. Kinetic study showed that the click reaction between the azido group terminated PBd-t-N3 and the alkyne-containing multifunctional linking reagent was fast and highly efficient. All coupling reactions were fully accomplished within 40 min at 50 C in toluene in the presence of the reducing agent Cu(0), proven by 1H-NMR, FTIR and GPC measurements. For the coupling reactions between the PBd-t-N3 polymer and dialkyne-containing compound, the final conversion of the coupled PBd-PBd polymer was ca. 97.0%. When a PBd-t-N3 polymer was reacted with trialkyne-containing or tetraalkyne-containing compound, the conversion of three-arm or four-arm PBd was around 95.5% or 87.0%, respectively. Several factors influencing the coupling efficiency were studied, including the molecular weight of the initial PBd-t-N3, arm numbers and the molar ratio of the azido group to the alkynyl group. The results indicated that the conversion of the target products would be promoted when the molecular weight of the PBd-t-N3 was low and the molar ratio of the azido to alkynyl groups was close to 1.
2014, 32(6): 743-750
doi: 10.1007/s10118-014-1445-6
Abstract:
It is reported that alkali-metal borohydrides (MBH4, M = Li, Na and K) are efficient catalysts for ring opening polymerization (ROP) of -amino acid N-carboxyanhydrides (NCAs). Polypeptides are prepared in quantitative yields with relatively narrow molecular weight distributions (MWDs = 1.1~1.5) which depend on the reaction temperature. End groups of the produced polypeptide are studied in detail by MALDI-ToF MS, 1H-NMR, 13C-NMR, 1H-1H COSY and 1H-13C HMQC analyses. The results indicate that -hydroxy-w-aminotelechelic polypeptides are formed which are suitable for post-polymerization functionalization.
It is reported that alkali-metal borohydrides (MBH4, M = Li, Na and K) are efficient catalysts for ring opening polymerization (ROP) of -amino acid N-carboxyanhydrides (NCAs). Polypeptides are prepared in quantitative yields with relatively narrow molecular weight distributions (MWDs = 1.1~1.5) which depend on the reaction temperature. End groups of the produced polypeptide are studied in detail by MALDI-ToF MS, 1H-NMR, 13C-NMR, 1H-1H COSY and 1H-13C HMQC analyses. The results indicate that -hydroxy-w-aminotelechelic polypeptides are formed which are suitable for post-polymerization functionalization.
2014, 32(6): 751-757
doi: 10.1007/s10118-014-1444-7
Abstract:
A series of the copolymers of ethylene with 1-hexene (M1M9) synthesized by metallocene catalyst Et[Ind]2ZrCl2/MAO was studied by differential scanning calorimetry and successive self-nucleation and annealing (SSA) thermal fractionation. The distribution of methylene sequence length (MSL) in the different copolymers was determined using the SSA method. The comonomer contents of samples M4 and M5 are 2.04 mol% and 2.78 mol%, respectively. Both M4 and M5 have low comonomer content and their MSL distribution profiles exhibit a monotonous increase trend with their MSL. The longest MSL of M5 is 167, and its corresponding molar percent is 43.95%, which is higher than that of M4. Moreover, the melting temperature (Tm) of M5 is also higher than that of M4. The comonomer contents of samples M7, M8, and M9 are 8.73 mol%, 14.18 mol% and 15.05 mol%, respectively. M7, M8, and M9 have high comonomer contents, and their MSL distribution profiles display unimodality. M7 has a lower peak value of 33 and a narrow MSL distribution, resulting in a Tm lower than that of M8 and M9. The MSL and its distribution are also key points that influence the melting behavior of copolymers. Sometimes, MSL and its distribution of copolymers have a greater impact on it than the total comonomer contents, which is different from traditional views.
A series of the copolymers of ethylene with 1-hexene (M1M9) synthesized by metallocene catalyst Et[Ind]2ZrCl2/MAO was studied by differential scanning calorimetry and successive self-nucleation and annealing (SSA) thermal fractionation. The distribution of methylene sequence length (MSL) in the different copolymers was determined using the SSA method. The comonomer contents of samples M4 and M5 are 2.04 mol% and 2.78 mol%, respectively. Both M4 and M5 have low comonomer content and their MSL distribution profiles exhibit a monotonous increase trend with their MSL. The longest MSL of M5 is 167, and its corresponding molar percent is 43.95%, which is higher than that of M4. Moreover, the melting temperature (Tm) of M5 is also higher than that of M4. The comonomer contents of samples M7, M8, and M9 are 8.73 mol%, 14.18 mol% and 15.05 mol%, respectively. M7, M8, and M9 have high comonomer contents, and their MSL distribution profiles display unimodality. M7 has a lower peak value of 33 and a narrow MSL distribution, resulting in a Tm lower than that of M8 and M9. The MSL and its distribution are also key points that influence the melting behavior of copolymers. Sometimes, MSL and its distribution of copolymers have a greater impact on it than the total comonomer contents, which is different from traditional views.
2014, 32(6): 758-767
doi: 10.1007/s10118-014-1449-2
Abstract:
A series organosoluble and heterocyclic poly(ether-amide)s (PEA)s were synthesized from a new diamine containing pyridine moiety and four aliphatic-aromatic dicarboxylic acids by direct polycondensation reactions. Dicarboxilic acids 4a-4d containing ether groups were synthesized in two steps reactions. At first, dialdehydes 3a-3d were synthesized from four dibromo alkanes 1a-1d and 4-hydroxybenzaldehyde 2, then dicarboxilic acids 4a-4d were synthesized from dialdehydes 3a-3d and malonic acid in a solvent free reaction. On the other hand, the new diamine 8 containing pyridine ring was synthesized in two step reactions. The structures of synthesized monomers and polymers were provn by FTIR, NMR spectroscopy and elemental analysis. Also all of the above polymers were fully characterized by inherent viscosity, solubility tests, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The resulted PEAs have shown good inherent viscosities, solubility and thermal properties.
A series organosoluble and heterocyclic poly(ether-amide)s (PEA)s were synthesized from a new diamine containing pyridine moiety and four aliphatic-aromatic dicarboxylic acids by direct polycondensation reactions. Dicarboxilic acids 4a-4d containing ether groups were synthesized in two steps reactions. At first, dialdehydes 3a-3d were synthesized from four dibromo alkanes 1a-1d and 4-hydroxybenzaldehyde 2, then dicarboxilic acids 4a-4d were synthesized from dialdehydes 3a-3d and malonic acid in a solvent free reaction. On the other hand, the new diamine 8 containing pyridine ring was synthesized in two step reactions. The structures of synthesized monomers and polymers were provn by FTIR, NMR spectroscopy and elemental analysis. Also all of the above polymers were fully characterized by inherent viscosity, solubility tests, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The resulted PEAs have shown good inherent viscosities, solubility and thermal properties.
2014, 32(6): 768-777
doi: 10.1007/s10118-014-1425-x
Abstract:
From the self-assembly of the typical Salen-type Schiff-base ligand H2L and Zn(OAc)22H2O in the molar ratio of 1:1 or 1:2, the mononuclear [Zn(L)(H2O)] (1) or binuclear [Zn2(L)(OAc)2(H2O)] (2) are obtained, respectively. For both complexes 1 and 2, the unsaturated five-coordinate coordination environment to the catalytic active centers (Zn2+ ions) permits the monomer insertion for the effective solution copolymerization of cyclohexene oxide and maleic anhydride. All the solution copolymerizations afford poly(ester-co-ether)s, while lower catalyst and co-catalyst concentrations are helpful for the formation of alternating polyester. Of the three co-catalysts, 4-(dimethylamino)pyridine is found to be the most efficient, while an excess thereof is detrimental for chain growth of the copolymers.
From the self-assembly of the typical Salen-type Schiff-base ligand H2L and Zn(OAc)22H2O in the molar ratio of 1:1 or 1:2, the mononuclear [Zn(L)(H2O)] (1) or binuclear [Zn2(L)(OAc)2(H2O)] (2) are obtained, respectively. For both complexes 1 and 2, the unsaturated five-coordinate coordination environment to the catalytic active centers (Zn2+ ions) permits the monomer insertion for the effective solution copolymerization of cyclohexene oxide and maleic anhydride. All the solution copolymerizations afford poly(ester-co-ether)s, while lower catalyst and co-catalyst concentrations are helpful for the formation of alternating polyester. Of the three co-catalysts, 4-(dimethylamino)pyridine is found to be the most efficient, while an excess thereof is detrimental for chain growth of the copolymers.
2014, 32(6): 778-785
doi: 10.1007/s10118-014-1456-3
Abstract:
Spherical polyelectrolyte brushes (SPBs) with PS core and poly(acrylic acid) (PAA) brushes were prepared and analyzed by SAXS in this article. A radial electron density profile of SPB was brought up, which fits well with the SAXS result and shows a core-shell structure. The effect of pH on SPB form was represented by SAXS and it proves that the chains of SPB will stretch in response to increased pH owning to the increased electrostatic repulsion. SPBs immobilized with magnetic nanoparticles or bovine serum albumin (BSA) were prepared and analyzed by SAXS as well. SAXS could characterize the changes of electron density inside brushes of SPBs due to the immobilization of magnetic nanoparticles or BSA. This provides significant supports for further application of immobilized metal nanoparticles or proteins.
Spherical polyelectrolyte brushes (SPBs) with PS core and poly(acrylic acid) (PAA) brushes were prepared and analyzed by SAXS in this article. A radial electron density profile of SPB was brought up, which fits well with the SAXS result and shows a core-shell structure. The effect of pH on SPB form was represented by SAXS and it proves that the chains of SPB will stretch in response to increased pH owning to the increased electrostatic repulsion. SPBs immobilized with magnetic nanoparticles or bovine serum albumin (BSA) were prepared and analyzed by SAXS as well. SAXS could characterize the changes of electron density inside brushes of SPBs due to the immobilization of magnetic nanoparticles or BSA. This provides significant supports for further application of immobilized metal nanoparticles or proteins.
2014, 32(6): 786-792
doi: 10.1007/s10118-014-1452-7
Abstract:
A new strategy was developed to fabricate superhydrophobic nylon 6 nanofibers, in which the blend solutions of poly(dimethylsiloxane) (PDMS) prepolymer and nylon 6 was spun using an innovative solution blowing process, and then the PDMS prepolymer contianning nanofibers were cured to obtain PDMS/nylon 6 nanofiber mats. Morphology, surface composition, non-wetting property and protective performance were investigated. The results showed that the addition of PDMS prepolymer improved the spinnability of the spinning solutions, and the PDMS/nylon 6 nanofibers had smooth surfaces and diameters from 100 nm to 350 nm. The presence of PDMS effectively enhanced the hydrophobicity of the nanofiber mats, showing water contact angles of 132 to 161 for PDMS contents of 1 wt% to 3 wt%. The PDMS/nylon 6 mats also possessed excellent protective and transport properties. The results indicated the potential application of the novel nanofiber mats in protective clothing.
A new strategy was developed to fabricate superhydrophobic nylon 6 nanofibers, in which the blend solutions of poly(dimethylsiloxane) (PDMS) prepolymer and nylon 6 was spun using an innovative solution blowing process, and then the PDMS prepolymer contianning nanofibers were cured to obtain PDMS/nylon 6 nanofiber mats. Morphology, surface composition, non-wetting property and protective performance were investigated. The results showed that the addition of PDMS prepolymer improved the spinnability of the spinning solutions, and the PDMS/nylon 6 nanofibers had smooth surfaces and diameters from 100 nm to 350 nm. The presence of PDMS effectively enhanced the hydrophobicity of the nanofiber mats, showing water contact angles of 132 to 161 for PDMS contents of 1 wt% to 3 wt%. The PDMS/nylon 6 mats also possessed excellent protective and transport properties. The results indicated the potential application of the novel nanofiber mats in protective clothing.
2014, 32(6): 793-804
doi: 10.1007/s10118-014-1451-8
Abstract:
The relationship between the rheological properties of nylon-6,6 solutions and the morphology of their electrospun nanofibers was established. The viscosity of nylon-6,6 in formic acid (90%) was measured in the concentration range of 5 wt%-25 wt% using a programmable viscometer. Electrospinning of nylon-6,6 solutions was carried out under controlled parameters. The chemical structure, morphology and thermal properties of the obtained nanofibers were investigated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), respectively. Entanglement concentration (ce) was found to be 15 wt% and a power law relationship between specific viscosity and solution concentration was observed with exponents of 2.0 and 3.3 for semi-dilute unentangled (c ce) and semi-dilute entangled (c ce) regimes, respectively. The diameter and uniformity of the nanofibers were found to be dependent on the viscosity. Moreover, the average diameter of electrospun nanofibers was found to be dependent on zero shear rate viscosity and normalized concentration (c/ce) in a power law relationship with exponents of 0.298 and 0.816, respectively. For nylon-6,6 solutions, the entanglement concentration (ce = 15 wt%) provides the threshold viscosity required for the formation of a stable polymeric jet during electrospinning and producing uniform beadless fibers. For concentrations less than ce, beaded fibers with some irregularities are formed. DSC analysis showed an increase in crystallinity of all electrospun samples compared to original polymer. Furthermore, Based on FTIR spectroscopy, phase is dominant in electrospun nanofibers and minor amount of and phases is also available.
The relationship between the rheological properties of nylon-6,6 solutions and the morphology of their electrospun nanofibers was established. The viscosity of nylon-6,6 in formic acid (90%) was measured in the concentration range of 5 wt%-25 wt% using a programmable viscometer. Electrospinning of nylon-6,6 solutions was carried out under controlled parameters. The chemical structure, morphology and thermal properties of the obtained nanofibers were investigated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), respectively. Entanglement concentration (ce) was found to be 15 wt% and a power law relationship between specific viscosity and solution concentration was observed with exponents of 2.0 and 3.3 for semi-dilute unentangled (c ce) and semi-dilute entangled (c ce) regimes, respectively. The diameter and uniformity of the nanofibers were found to be dependent on the viscosity. Moreover, the average diameter of electrospun nanofibers was found to be dependent on zero shear rate viscosity and normalized concentration (c/ce) in a power law relationship with exponents of 0.298 and 0.816, respectively. For nylon-6,6 solutions, the entanglement concentration (ce = 15 wt%) provides the threshold viscosity required for the formation of a stable polymeric jet during electrospinning and producing uniform beadless fibers. For concentrations less than ce, beaded fibers with some irregularities are formed. DSC analysis showed an increase in crystallinity of all electrospun samples compared to original polymer. Furthermore, Based on FTIR spectroscopy, phase is dominant in electrospun nanofibers and minor amount of and phases is also available.
2014, 32(6): 805-816
doi: 10.1007/s10118-014-1454-5
Abstract:
The biodegradable porous composite scaffold, composed of poly(lactide-co-glycolide) (PLGA) and hydroxyapatite nanoparticles (n-HAP) surface-grafted with poly(L-lactide) (PLLA) (g-HAP) (g-HAP/PLGA), was fabricated using the solvent casting/particulate leaching method, and its in vivo degradation behavior was investigated by the intramuscular implantation in rabbits. The composite of un-grafted n-HAP/PLGA and neat PLGA were used as controls. The scaffolds had interconnected pore structures with average pore sizes between 137 m and 148 m and porosities between 83% and 86%. There was no significant difference in the pore size and porosity among the three scaffolds. Compared with n-HAP/PLGA, the thermo-degradation temperature (Tc) of g-HAP/PLGA decreased while its glass transition temperature (Tg) increased. The weight change, grey value analysis of radiographs and SEM observation showed that the composite scaffolds of g-HAP/PLGA and n-HAP/PLGA showed slower degradation and higher mineralization than the pure PLGA scaffold after the intramuscular implantation. The rapid degradation of PLGA, g-HAP/PLGA and n-HAP/PLGA occurred at 812 weeks, 1216 weeks and 1620 weeks, respectively. Compared with n-HAP/PLGA, g-HAP/PLGA showed an improved absorption and biomineralization property mostly because of its improved distribution of HAP nanoparticles. The levels of both calcium and phosphorous in serum and urine could be affected to some extent at 34 weeks after the implantation of g-HAP/PLGA, but the biochemical detection of serum AST, ALT, ALP, and GGT as well as BUN and CRE showed no obvious influence on the functions of liver and kidney.
The biodegradable porous composite scaffold, composed of poly(lactide-co-glycolide) (PLGA) and hydroxyapatite nanoparticles (n-HAP) surface-grafted with poly(L-lactide) (PLLA) (g-HAP) (g-HAP/PLGA), was fabricated using the solvent casting/particulate leaching method, and its in vivo degradation behavior was investigated by the intramuscular implantation in rabbits. The composite of un-grafted n-HAP/PLGA and neat PLGA were used as controls. The scaffolds had interconnected pore structures with average pore sizes between 137 m and 148 m and porosities between 83% and 86%. There was no significant difference in the pore size and porosity among the three scaffolds. Compared with n-HAP/PLGA, the thermo-degradation temperature (Tc) of g-HAP/PLGA decreased while its glass transition temperature (Tg) increased. The weight change, grey value analysis of radiographs and SEM observation showed that the composite scaffolds of g-HAP/PLGA and n-HAP/PLGA showed slower degradation and higher mineralization than the pure PLGA scaffold after the intramuscular implantation. The rapid degradation of PLGA, g-HAP/PLGA and n-HAP/PLGA occurred at 812 weeks, 1216 weeks and 1620 weeks, respectively. Compared with n-HAP/PLGA, g-HAP/PLGA showed an improved absorption and biomineralization property mostly because of its improved distribution of HAP nanoparticles. The levels of both calcium and phosphorous in serum and urine could be affected to some extent at 34 weeks after the implantation of g-HAP/PLGA, but the biochemical detection of serum AST, ALT, ALP, and GGT as well as BUN and CRE showed no obvious influence on the functions of liver and kidney.
