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2010 Volume 28 Issue 4
2010, 28(4): 457-466
doi: 10.1007/s10118-010-9051-8
Abstract:
The effect of α phase nucleating agent (NA) 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS) on crystallization and physical properties of polypropylene/calcium carbonate (PP/CaCO3) composites has been comparatively investigated. Compared with binary PP/CaCO3 composites, in which CaCO3 exhibits weak heterogeneous nucleation, inconspicuous reinforcement and toughening effects for PP, the introduction of a few amounts of DMDBS induces a great increase of the degree of crystallinity. Largely improved tensile properties, fracture toughness at relatively higher temperature and heat deformation temperature (HDT) are observed for DMDBS nucleated PP/CaCO3 composites.
The effect of α phase nucleating agent (NA) 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS) on crystallization and physical properties of polypropylene/calcium carbonate (PP/CaCO3) composites has been comparatively investigated. Compared with binary PP/CaCO3 composites, in which CaCO3 exhibits weak heterogeneous nucleation, inconspicuous reinforcement and toughening effects for PP, the introduction of a few amounts of DMDBS induces a great increase of the degree of crystallinity. Largely improved tensile properties, fracture toughness at relatively higher temperature and heat deformation temperature (HDT) are observed for DMDBS nucleated PP/CaCO3 composites.
2010, 28(4): 467-473
Abstract:
Long chain semiaromatic polyamides were synthesized by the reactions of decanediamine with various aromatic diacids and characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H-NMR). The thermal behaviors were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The solubility, dynamic mechanical, physical and mechanical properties of the polyamides have also been investigated. The resultant polyamides have intrinsic viscosity ranging from 1.7 dL/g to 2.1 dL/g. Their melting temperatures range from 305°C to 343°C, and the glass transition temperatures fall in the range of 125–130°C. The tensile strength of the polyamides is above 100 MPa.
Long chain semiaromatic polyamides were synthesized by the reactions of decanediamine with various aromatic diacids and characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H-NMR). The thermal behaviors were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The solubility, dynamic mechanical, physical and mechanical properties of the polyamides have also been investigated. The resultant polyamides have intrinsic viscosity ranging from 1.7 dL/g to 2.1 dL/g. Their melting temperatures range from 305°C to 343°C, and the glass transition temperatures fall in the range of 125–130°C. The tensile strength of the polyamides is above 100 MPa.
2010, 28(4): 475-482
doi: 10.1007/s10118-010-9053-6
Abstract:
A series of butadiene-isoprene copolymers (BIR) with various compositions were synthesized with a neodymium-based catalyst system. The microstructure, composition and sequence of copolymers were characterized by FTIR and 13C-NMR spectroscopy. The crystallization behavior of the BIR copolymers was investigated by DSC analysis. The results demonstrate that the content of cis-1,4 configuration in both butadiene (Bd) and isoprene (Ip) units are around 98% when Bd content in feed (fBd) covering the range from 55.7 mol% to 96.0 mol%. The reactivity ratios of Bd and Ip were determined to be 1.40 and 0.48 respectively. The random copolymers of Bd and Ip show only one glass transition temperature (Tg) from -107.4°C to -80.5°C, which is dependent on the composition and fits nicely with Fox equation. The sequence distribution followed the first-order Markov statistical model. It is found that the copolymer chains with higher Bd content contain longer polybutadiene (PBd) segments, and the sequence length of PBd segments (NBd) exhibits great influence on the crystallization behavior of the copolymer. The copolymers with NBd ≥ 11.8 could crystallize at low temperatures -71°C to -43°C). The crystallization temperature and enthalpy values decreased gradually with decreasing NBd. The copolymers with NBd ≤ 7.9 are amorphous even at very low temperatures (0°C to-150°C) due to the short PBd segments.
A series of butadiene-isoprene copolymers (BIR) with various compositions were synthesized with a neodymium-based catalyst system. The microstructure, composition and sequence of copolymers were characterized by FTIR and 13C-NMR spectroscopy. The crystallization behavior of the BIR copolymers was investigated by DSC analysis. The results demonstrate that the content of cis-1,4 configuration in both butadiene (Bd) and isoprene (Ip) units are around 98% when Bd content in feed (fBd) covering the range from 55.7 mol% to 96.0 mol%. The reactivity ratios of Bd and Ip were determined to be 1.40 and 0.48 respectively. The random copolymers of Bd and Ip show only one glass transition temperature (Tg) from -107.4°C to -80.5°C, which is dependent on the composition and fits nicely with Fox equation. The sequence distribution followed the first-order Markov statistical model. It is found that the copolymer chains with higher Bd content contain longer polybutadiene (PBd) segments, and the sequence length of PBd segments (NBd) exhibits great influence on the crystallization behavior of the copolymer. The copolymers with NBd ≥ 11.8 could crystallize at low temperatures -71°C to -43°C). The crystallization temperature and enthalpy values decreased gradually with decreasing NBd. The copolymers with NBd ≤ 7.9 are amorphous even at very low temperatures (0°C to-150°C) due to the short PBd segments.
2010, 28(4): 483-497
doi: 10.1007/s10118-010-9058-1
Abstract:
An optimized and high-performance Monte Carlo simulation is developed to take thorough account of four different cases of termination in styrene ATRP. According to the simulation results, the bimolecular termination rate constant sharply drops throughout the polymerization when either chain-length dependency of termination rate constant, gel effect, or both together is applied to the simulation. In addition, as expected, the initiator is quickly decomposed at the early stages of the polymerization. The concentration of the catalyst in lower oxidation state decreases at first and then plateaus at higher conversion; furthermore, the steady concentration of MtnY/L in the polymerization is the highest when the chain-length-dependent diffusion-controlled termination rate constant is employed in the simulation. The rates of deactivation and chain end degradation reactions are also smaller in this case. Therefore, the fraction of dormant chains is higher throughout the reaction and consequently the portion of dead polymers decreases. Besides, molecular weight increases linearly with conversion; however, when neither gel effect nor chain-length dependency of termination rate constant is considered, the molecular weight deviates from linearity at the end of the reaction. The peak of chain length distribution shifts toward higher molecular weight too during the reaction. Finally, the molecular weight distribution broadens at higher conversion; however, the chain length distribution of polymers produced under conditions of applying chain-length-dependent diffusion-controlled termination rate constant is narrower.
An optimized and high-performance Monte Carlo simulation is developed to take thorough account of four different cases of termination in styrene ATRP. According to the simulation results, the bimolecular termination rate constant sharply drops throughout the polymerization when either chain-length dependency of termination rate constant, gel effect, or both together is applied to the simulation. In addition, as expected, the initiator is quickly decomposed at the early stages of the polymerization. The concentration of the catalyst in lower oxidation state decreases at first and then plateaus at higher conversion; furthermore, the steady concentration of MtnY/L in the polymerization is the highest when the chain-length-dependent diffusion-controlled termination rate constant is employed in the simulation. The rates of deactivation and chain end degradation reactions are also smaller in this case. Therefore, the fraction of dormant chains is higher throughout the reaction and consequently the portion of dead polymers decreases. Besides, molecular weight increases linearly with conversion; however, when neither gel effect nor chain-length dependency of termination rate constant is considered, the molecular weight deviates from linearity at the end of the reaction. The peak of chain length distribution shifts toward higher molecular weight too during the reaction. Finally, the molecular weight distribution broadens at higher conversion; however, the chain length distribution of polymers produced under conditions of applying chain-length-dependent diffusion-controlled termination rate constant is narrower.
2010, 28(4): 499-507
doi: 10.1007/s10118-010-9060-7
Abstract:
Hydroxyapatite/poly(L-lactide) (HA/PLLA) nanocomposites were prepared by the solvent mixing method. The isothermal crystallization behavior was studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results show that the crystallization behavior of HA/PLLA composites was strongly affected by the content of HA and crystallization temperature, and the addition of HA could promote nucleation and enhance the crystallization rate. When isothermal crystallization was carried out at 110°C, the HA/PLLA nanocomposite with 1% HA content crystallized most rapidly among all the composites and the half crystallization time was only 1.0 min. Banded spherulites were observed for the HA/PLLA composites, but no banded spherulites were seen in the crystals of PLLA under the same condition.
Hydroxyapatite/poly(L-lactide) (HA/PLLA) nanocomposites were prepared by the solvent mixing method. The isothermal crystallization behavior was studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results show that the crystallization behavior of HA/PLLA composites was strongly affected by the content of HA and crystallization temperature, and the addition of HA could promote nucleation and enhance the crystallization rate. When isothermal crystallization was carried out at 110°C, the HA/PLLA nanocomposite with 1% HA content crystallized most rapidly among all the composites and the half crystallization time was only 1.0 min. Banded spherulites were observed for the HA/PLLA composites, but no banded spherulites were seen in the crystals of PLLA under the same condition.
2010, 28(4): 509-515
Abstract:
Rare earth aryloxides substituted by various alkyl groups [Ln(OAr)3] such as methyl, isopropyl and tertbutyl, were used as single component catalysts to affect ring-opening polymerization of L-lactide (LLA). The catalytic activity, polymerization characteristics, polymerization kinetics and the mechanism were studied. It was found that the catalytic activity of rare earth aryloxides is influenced by both the structure and the number of alkyl groups on the phenyl ring. The stronger the electron-donation ability of the alkyl group, the higher the catalytic activity will be. An increase in the number of the substitute group will result in a higher catalytic activity. Lanthanum tris(2,4,6-tri-tert-butylphenolate) [La(OTTBP)3] exhibits the highest activity among all lanthanum aryloxides. According to the 1H-NMR data, it was proposed that the LLA polymerization proceeded via a coordination-insertion mechanism involving cleavage of acyl-oxygen bond of the lactide.
Rare earth aryloxides substituted by various alkyl groups [Ln(OAr)3] such as methyl, isopropyl and tertbutyl, were used as single component catalysts to affect ring-opening polymerization of L-lactide (LLA). The catalytic activity, polymerization characteristics, polymerization kinetics and the mechanism were studied. It was found that the catalytic activity of rare earth aryloxides is influenced by both the structure and the number of alkyl groups on the phenyl ring. The stronger the electron-donation ability of the alkyl group, the higher the catalytic activity will be. An increase in the number of the substitute group will result in a higher catalytic activity. Lanthanum tris(2,4,6-tri-tert-butylphenolate) [La(OTTBP)3] exhibits the highest activity among all lanthanum aryloxides. According to the 1H-NMR data, it was proposed that the LLA polymerization proceeded via a coordination-insertion mechanism involving cleavage of acyl-oxygen bond of the lactide.
2010, 28(4): 517-525
doi: 10.1007/s10118-010-9075-0
Abstract:
Six new optically active and flame-retardant poly(amide-imide)s PAIs 5a-5f containing phosphine oxide moiety as a flame-retardant unit in the main chain were synthesized from direct polycondensation reaction of six chiral N,N'-(pyromellitoyl)-bis-L-amino acid 3a-3f with bis(3-aminophenyl)phenyl phosphine oxide 4 in a medium consisting of N-methyl-2-pyrrolidone (NMP), triphenyl phosphite (TPP), calcium chloride (CaCl2) and pyridine. The polymerization reactions produced a series of optically active poly(amide-imide)s with good yield and good inherent viscosity of 0.34-0.70 dLg-1. The resulted polymers were fully characterized by means of FTIR and 1H-NMR spectroscopy, gel permeation chromatography (GPC), elemental analyses, inherent viscosity and solubility tests. Thermal properties and flame-retardant behavior of the PAIs 5a-5f were investigated using thermal gravimetric analysis (TGA and DTG) and limiting oxygen index (LOI). Data obtained by thermal analysis (TGA and DTG) revealed that these polymers showed good thermal stability. Furthermore, high char yield in TGA and good LOI values indicated that the resulting polymers were capable of exhibiting good flame retardant properties. N,N'-(pyromellitoyl)-bis-L-amino acids 3a-3f were prepared in quantitative yields by the condensation reaction of pyromellitic dianhydride (1,2,4,5-benzenetetracarboxylicacid-1,2,4,5-dianhydride) 1 with L-alanine 2a, L-valine 2b, L-leucine 2c, L-isoleucine 2d, L-phenyl alanine 2e and L-2-aminobutyric acid 2f in acetic acid solution.
Six new optically active and flame-retardant poly(amide-imide)s PAIs 5a-5f containing phosphine oxide moiety as a flame-retardant unit in the main chain were synthesized from direct polycondensation reaction of six chiral N,N'-(pyromellitoyl)-bis-L-amino acid 3a-3f with bis(3-aminophenyl)phenyl phosphine oxide 4 in a medium consisting of N-methyl-2-pyrrolidone (NMP), triphenyl phosphite (TPP), calcium chloride (CaCl2) and pyridine. The polymerization reactions produced a series of optically active poly(amide-imide)s with good yield and good inherent viscosity of 0.34-0.70 dLg-1. The resulted polymers were fully characterized by means of FTIR and 1H-NMR spectroscopy, gel permeation chromatography (GPC), elemental analyses, inherent viscosity and solubility tests. Thermal properties and flame-retardant behavior of the PAIs 5a-5f were investigated using thermal gravimetric analysis (TGA and DTG) and limiting oxygen index (LOI). Data obtained by thermal analysis (TGA and DTG) revealed that these polymers showed good thermal stability. Furthermore, high char yield in TGA and good LOI values indicated that the resulting polymers were capable of exhibiting good flame retardant properties. N,N'-(pyromellitoyl)-bis-L-amino acids 3a-3f were prepared in quantitative yields by the condensation reaction of pyromellitic dianhydride (1,2,4,5-benzenetetracarboxylicacid-1,2,4,5-dianhydride) 1 with L-alanine 2a, L-valine 2b, L-leucine 2c, L-isoleucine 2d, L-phenyl alanine 2e and L-2-aminobutyric acid 2f in acetic acid solution.
2010, 28(4): 527-535
Abstract:
Polyvinylidene fluoride (PVDF) hollow fiber membranes prepared from spinning solutions with different polyvinyl pyrrolidone (PVP) contents (1% and 5%) at different extrusion rates were obtained by wet/dry phase process keeping all other spinning parameters constant. In spinning these PVDF hollow fibers, dimethylacetamide (DMAc) and PVP were used as a solvent and an additive, respectively. Water was used as the inner coagulant. Dimethylformamide (DMF) and water (30/70) were used as the external coagulant. The performances of membranes were characterized in terms of water flux, solute rejection for the wet membranes. The structure and morphology of PVDF hollow fiber were examined by BET adsorption, dry/wet weight method and scanning electron microscopy (SEM). It is found that the increase in PVP content and extrusion rate of spinning solution can result in the increase of water flux and decrease of solute rejection. The improvements of interconnected porous structure and pore size are induced by shear-thinning behavior of spinning solution at high extrusion rates, which could result in the increase of water flux of hollow fiber membranes. The increase of extrusion rate also leads to the increase of membrane thickness due to the recovery effect of elastic property of polymer chains.
Polyvinylidene fluoride (PVDF) hollow fiber membranes prepared from spinning solutions with different polyvinyl pyrrolidone (PVP) contents (1% and 5%) at different extrusion rates were obtained by wet/dry phase process keeping all other spinning parameters constant. In spinning these PVDF hollow fibers, dimethylacetamide (DMAc) and PVP were used as a solvent and an additive, respectively. Water was used as the inner coagulant. Dimethylformamide (DMF) and water (30/70) were used as the external coagulant. The performances of membranes were characterized in terms of water flux, solute rejection for the wet membranes. The structure and morphology of PVDF hollow fiber were examined by BET adsorption, dry/wet weight method and scanning electron microscopy (SEM). It is found that the increase in PVP content and extrusion rate of spinning solution can result in the increase of water flux and decrease of solute rejection. The improvements of interconnected porous structure and pore size are induced by shear-thinning behavior of spinning solution at high extrusion rates, which could result in the increase of water flux of hollow fiber membranes. The increase of extrusion rate also leads to the increase of membrane thickness due to the recovery effect of elastic property of polymer chains.
2010, 28(4): 537-546
doi: 10.1007/s10118-010-9086-x
Abstract:
Poly(methylmetacrylate) (PMMA)/Y0.0025Si0.025Ba0.9725(Ti(0.9)Sn0.1)O3 (YBTS) composites were prepared at different weight ratios of YBTS (0 wt%, 5 wt%, 10 wt% and 20 wt% YBTS) in order to investigate effect of YBTS additions on the electrical and optical properties of PMMA host. The electrical properties (impedance, dielectric constant dielectric loss and AC conductivity) were studied in the frequency range 10 kHz-1 MHz and in temperature range 20-90oC. Upon increasing the contents of YBTS ceramic, we observed a reduction in the impedance and an increase in the dielectric constant, dielectric loss and AC conductivity of PMMA host. We also found that the relaxation process at high YBTS contents was due to relaxation in the ionic conductivity. The absorption coefficient (α) has been determined in the wavelength range 230-800 nm at room temperature for all YBTS-PMMA composites. Moreover, the addition of YBTS ceramic highly enhances the UV absorption of PMMA host especially below 300 nm. Addition of 20 wt% YBTS ceramic to PMMA host decreases the optical energy gap from 5 eV to 3.41 eV. Correlations between electrical, optical and SEM results are reported.
Poly(methylmetacrylate) (PMMA)/Y0.0025Si0.025Ba0.9725(Ti(0.9)Sn0.1)O3 (YBTS) composites were prepared at different weight ratios of YBTS (0 wt%, 5 wt%, 10 wt% and 20 wt% YBTS) in order to investigate effect of YBTS additions on the electrical and optical properties of PMMA host. The electrical properties (impedance, dielectric constant dielectric loss and AC conductivity) were studied in the frequency range 10 kHz-1 MHz and in temperature range 20-90oC. Upon increasing the contents of YBTS ceramic, we observed a reduction in the impedance and an increase in the dielectric constant, dielectric loss and AC conductivity of PMMA host. We also found that the relaxation process at high YBTS contents was due to relaxation in the ionic conductivity. The absorption coefficient (α) has been determined in the wavelength range 230-800 nm at room temperature for all YBTS-PMMA composites. Moreover, the addition of YBTS ceramic highly enhances the UV absorption of PMMA host especially below 300 nm. Addition of 20 wt% YBTS ceramic to PMMA host decreases the optical energy gap from 5 eV to 3.41 eV. Correlations between electrical, optical and SEM results are reported.
2010, 28(4): 547-554
doi: 10.1007/s10118-010-9082-1
Abstract:
The hydrophilicity of silicone hydrogels used as soft corneal contact lens plays an important role in wearing comfort. In order to enhance hydrophilicity and protein resistance, silicone hydrogel membranes were modified by atmospheric pressure glow discharge plasma (APGDP) induced surface graft polymerization of N-vinyl pyrrolidone (NVP) and poly(oligoethylene glycol methyl ether methacrylate) (PEGMA) in this paper. XPS analysis demonstrated the success of graft polymerization of NVP and PEGMA onto the surface of silicone hydrogel membranes. The hydrophilicity of silicone hydrogels was characterized by the measurement of water contact angle (WCA). The result showed that NVP grafted silicone hydrogel has the WCA of about 68° and PEGMA grafted silicone hydrogel has the lowest WCA of about 62°, while the pristine silicone hydrogel is hydrophobic with the WCA of about 103°. Protein resistance of silicone hydrogels was investigated by the method of bicinchoninic acid assay using bovine serum albumin (BSA) as a model. It’s found that the grafted silicone hydrogel has a significant improvement of protein resistance, and PEGMA grafting is more efficient for the reduction of protein adsorption than NVP grafting. The silicone hydrogel membranes grafted with NVP and PEGMA are good candidates of soft corneal contact lenses.
The hydrophilicity of silicone hydrogels used as soft corneal contact lens plays an important role in wearing comfort. In order to enhance hydrophilicity and protein resistance, silicone hydrogel membranes were modified by atmospheric pressure glow discharge plasma (APGDP) induced surface graft polymerization of N-vinyl pyrrolidone (NVP) and poly(oligoethylene glycol methyl ether methacrylate) (PEGMA) in this paper. XPS analysis demonstrated the success of graft polymerization of NVP and PEGMA onto the surface of silicone hydrogel membranes. The hydrophilicity of silicone hydrogels was characterized by the measurement of water contact angle (WCA). The result showed that NVP grafted silicone hydrogel has the WCA of about 68° and PEGMA grafted silicone hydrogel has the lowest WCA of about 62°, while the pristine silicone hydrogel is hydrophobic with the WCA of about 103°. Protein resistance of silicone hydrogels was investigated by the method of bicinchoninic acid assay using bovine serum albumin (BSA) as a model. It’s found that the grafted silicone hydrogel has a significant improvement of protein resistance, and PEGMA grafting is more efficient for the reduction of protein adsorption than NVP grafting. The silicone hydrogel membranes grafted with NVP and PEGMA are good candidates of soft corneal contact lenses.
2010, 28(4): 555-561
doi: 10.1007/s10118-010-9087-9
Abstract:
In an effort to develop biomaterials to meet guided tissue regeneration (GTR) standards for periodontal tissue recovery, a homogeneous and transparent chitosan (CS)/hydroxyapatite (HA) membrane with potential applications as GTR barrier in periodontal therapy has been prepared via in situ compositing. The membrane has been designed to have a smooth-rough asymmetric structure that meets the demand for GTR. Component and morphology of the membrane are characterized by XRD and SEM. It can be indicated that HA was in situ synthesized uniformly in the CS membrane. Mechanical experiments of the membranes with various HA contents show that their tensile strengths are adequate for periodontal therapy. Biological properties of the membrane have been performed by cell toxicity assays, hemolysis tests and animal experiments. Results indicate that the membrane has good biocompatibility and inductive effect for cell growth. Therefore this membrane can be potentially applied as GTR barrier membrane for periodontal tissue regeneration.
In an effort to develop biomaterials to meet guided tissue regeneration (GTR) standards for periodontal tissue recovery, a homogeneous and transparent chitosan (CS)/hydroxyapatite (HA) membrane with potential applications as GTR barrier in periodontal therapy has been prepared via in situ compositing. The membrane has been designed to have a smooth-rough asymmetric structure that meets the demand for GTR. Component and morphology of the membrane are characterized by XRD and SEM. It can be indicated that HA was in situ synthesized uniformly in the CS membrane. Mechanical experiments of the membranes with various HA contents show that their tensile strengths are adequate for periodontal therapy. Biological properties of the membrane have been performed by cell toxicity assays, hemolysis tests and animal experiments. Results indicate that the membrane has good biocompatibility and inductive effect for cell growth. Therefore this membrane can be potentially applied as GTR barrier membrane for periodontal tissue regeneration.
2010, 28(4): 563-571
doi: 10.1007/s10118-010-9095-9
Abstract:
Synergistic effects of layered double hydroxide (LDH) with intumescent flame retardanct (IFR) of phosphorus-nitrogen (NP) compound in the polypropylene/ethylene-propylene-diene/IFR/LDH (PP/EPDM/IFR/LDH) nanocomposites and related properties were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT) and thermo-gravimetric analysis (TGA). The XRD and TEM results show that the intercalated and/or exfoliated nanocomposites can be obtained by direct melt-intercalation of PP/EPDM into modified LDH and that LDH can promote the IFR additive NP to disperse more homogeneously in the polymer matrix. The SEM results provide positive evidence that more compact charred layers can be obtained from the PP/EPDM/NP/LDH sample than those from the PP/EPDM/LDH and PP/EPDM/NP samples during burning. The LOI and UL-94 rating tests show that the synergetic effects of LDH with NP can effectively increase the flame retardant properties of the PP/EPDM/NP/LDH samples. The data from the CCT and TGA tests indicate that the PP/EPDM/NP/LDH samples apparently decrease the HRR and MLR values and thus enhance the flame retardant properties and have better thermal stability than the PP/EPDM/LDH and PP/EPDM/NP samples.
Synergistic effects of layered double hydroxide (LDH) with intumescent flame retardanct (IFR) of phosphorus-nitrogen (NP) compound in the polypropylene/ethylene-propylene-diene/IFR/LDH (PP/EPDM/IFR/LDH) nanocomposites and related properties were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT) and thermo-gravimetric analysis (TGA). The XRD and TEM results show that the intercalated and/or exfoliated nanocomposites can be obtained by direct melt-intercalation of PP/EPDM into modified LDH and that LDH can promote the IFR additive NP to disperse more homogeneously in the polymer matrix. The SEM results provide positive evidence that more compact charred layers can be obtained from the PP/EPDM/NP/LDH sample than those from the PP/EPDM/LDH and PP/EPDM/NP samples during burning. The LOI and UL-94 rating tests show that the synergetic effects of LDH with NP can effectively increase the flame retardant properties of the PP/EPDM/NP/LDH samples. The data from the CCT and TGA tests indicate that the PP/EPDM/NP/LDH samples apparently decrease the HRR and MLR values and thus enhance the flame retardant properties and have better thermal stability than the PP/EPDM/LDH and PP/EPDM/NP samples.
2010, 28(4): 573-580
doi: 10.1007/s10118-010-9099-5
Abstract:
The hydrogel wound dressing based on polyvinyl alcohol (PVA) was prepared by the freezing-thawing cyclic method. The dehydration kinetics of prepared hydrogels was determined using the experimental method and mathematical modeling based on diffusion mechanism. The results show that the dehydration rate of PVA hydrogel wound dressing inversely depends on the hydrogel thickness as well as water content of the wound. On the other hand, the initial water content of hydrogel and the atmospheric humidity have little direct effect on the dehydration rate. The good agreement between experimental and mathematical modeling results in early stages of dehydration process shows that the predominate factor determining the dehydration of these wound dressings is diffusion.
The hydrogel wound dressing based on polyvinyl alcohol (PVA) was prepared by the freezing-thawing cyclic method. The dehydration kinetics of prepared hydrogels was determined using the experimental method and mathematical modeling based on diffusion mechanism. The results show that the dehydration rate of PVA hydrogel wound dressing inversely depends on the hydrogel thickness as well as water content of the wound. On the other hand, the initial water content of hydrogel and the atmospheric humidity have little direct effect on the dehydration rate. The good agreement between experimental and mathematical modeling results in early stages of dehydration process shows that the predominate factor determining the dehydration of these wound dressings is diffusion.
ANTIBACTERIAL POLY(D,L-LACTIDE) (PDLLA) FIBROUS MEMBRANES MODIFIED WITH QUATERNARY AMMONIUM MOIETIES
2010, 28(4): 581-588
doi: 10.1007/s10118-010-9094-x
Abstract:
Antibacterial poly(D,L-lactide) (PDLLA) fibrous membranes were developed via electrospinning, followed by surface modification which involved plasma pretreatment, UV-induced graft copolymerization of 4-vinylpyridine (4VP) and quaternization of the grafted pyridine groups with hexylbromide. The success of modification with quaternized pyridinium groups on the PDLLA fibrous membranes was ascertained by X-ray photoelectron spectroscopy (XPS). The antibacterial activities of these membranes were assessed against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). The PDLLA fibrous membranes modified with quaternized pyridinium groups showed antibacterial efficiency against both bacteria as high as 99.999%. The results demonstrated that the antibacterial activity was based on the interaction of the positive charge of pyridinium group and negatively charged cell membrane of bacteria, resulting in loss of membrane permeability and cell leakage.
Antibacterial poly(D,L-lactide) (PDLLA) fibrous membranes were developed via electrospinning, followed by surface modification which involved plasma pretreatment, UV-induced graft copolymerization of 4-vinylpyridine (4VP) and quaternization of the grafted pyridine groups with hexylbromide. The success of modification with quaternized pyridinium groups on the PDLLA fibrous membranes was ascertained by X-ray photoelectron spectroscopy (XPS). The antibacterial activities of these membranes were assessed against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). The PDLLA fibrous membranes modified with quaternized pyridinium groups showed antibacterial efficiency against both bacteria as high as 99.999%. The results demonstrated that the antibacterial activity was based on the interaction of the positive charge of pyridinium group and negatively charged cell membrane of bacteria, resulting in loss of membrane permeability and cell leakage.
2010, 28(4): 589-596
doi: 10.1007/s10118-010-9104-z
Abstract:
Five new optically active polyamides (PAs) 6a-6e were prepared by direct polycondensation reaction of 2-(1,3-isoindolinedione-2-yl)-glutaric acid 4 as a new chiral diacid with various aromatic diamines 5a-5e in a medium consisting of triphenyl phosphite (TPP), calcium chloride, pyridine (Py) and N-methyl-2-pyrrolidone (NMP). The polycondensation reaction produced a series of polyamids 6a-6e in quantitative yields with inherent viscosities of 0.26-0.39 dL/g. The resulting polymers were fully characterized by means of 1H-NMR, FT-IR spectroscopy, elemental analysis, inherent viscosity and specific rotation. Thermal properties of these polymers were investigated using thermal gravimetric analysis (TGA) and differential thermal gravimetry (DTG). Phthalimide rings as a bulky pendent group in the polymer chains disturb the interchain and intrachain interactions and make these PAs readily soluble in polar, aprotic solvents such as N,N-dimethyl acetamide (DMAc), N,N-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP) and sulfuric acid.
Five new optically active polyamides (PAs) 6a-6e were prepared by direct polycondensation reaction of 2-(1,3-isoindolinedione-2-yl)-glutaric acid 4 as a new chiral diacid with various aromatic diamines 5a-5e in a medium consisting of triphenyl phosphite (TPP), calcium chloride, pyridine (Py) and N-methyl-2-pyrrolidone (NMP). The polycondensation reaction produced a series of polyamids 6a-6e in quantitative yields with inherent viscosities of 0.26-0.39 dL/g. The resulting polymers were fully characterized by means of 1H-NMR, FT-IR spectroscopy, elemental analysis, inherent viscosity and specific rotation. Thermal properties of these polymers were investigated using thermal gravimetric analysis (TGA) and differential thermal gravimetry (DTG). Phthalimide rings as a bulky pendent group in the polymer chains disturb the interchain and intrachain interactions and make these PAs readily soluble in polar, aprotic solvents such as N,N-dimethyl acetamide (DMAc), N,N-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP) and sulfuric acid.
2010, 28(4): 597-605
doi: 10.1007/s10118-010-9083-0
Abstract:
Segmented block copolymer based on nylon6 (N6) and polyethylene oxide (PEO) with stochiometric ratio was synthesized via a two-step process. The first step represents end capping of N6 in the presence of adipic acid leading to carboxy terminated N6, and the second one is polycondensation of the latter product with PEO in the presence of catalyst and thermostabilizer to form a high molecular weight multi-block copolymer. Several methods were applied to characterize the synthesized copolymer such as Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, differential thermal analysis, differential scanning calorimetry, X-ray diffraction and atomic force microscopy. The obtained results confirmed the multi-block structure for copolymer with a very high degree of micro-phase separation. Atomic force microscopy micrographs indicated that the morphology was the dispersion of high stiffness nanostructured polyamide (PA) domains in the amorphous region of PEO matrix, which can be very important in their performance for membrane processes.
Segmented block copolymer based on nylon6 (N6) and polyethylene oxide (PEO) with stochiometric ratio was synthesized via a two-step process. The first step represents end capping of N6 in the presence of adipic acid leading to carboxy terminated N6, and the second one is polycondensation of the latter product with PEO in the presence of catalyst and thermostabilizer to form a high molecular weight multi-block copolymer. Several methods were applied to characterize the synthesized copolymer such as Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, differential thermal analysis, differential scanning calorimetry, X-ray diffraction and atomic force microscopy. The obtained results confirmed the multi-block structure for copolymer with a very high degree of micro-phase separation. Atomic force microscopy micrographs indicated that the morphology was the dispersion of high stiffness nanostructured polyamide (PA) domains in the amorphous region of PEO matrix, which can be very important in their performance for membrane processes.
2010, 28(4): 607-613
doi: 10.1007/s10118-010-9129-3
Abstract:
A new methacrylamide monomer, hexylamine methacrylamide (MAHA), was synthesized and used in polymerizations. The homopolymer of MAHA and its copolymers were synthesized by free radical polymerization techniques with N-isopropyl acrylamide (NIPAAm) in two different compositions. The quaternization of the homopolymer and copolymers were carried out using 1-bromopropane. The copolymers with NIPAAm and a low MAHA content showed temperature-responsive behavior in an aqueous environment. The lower critical solution temperatures (LCSTs) of these polymers varied between 32°C and 44°C. The LCSTs of quaternized copolymers were higher than those of neutral copolymers because they were more hydrophilic. The obtained homopolymers and copolymers were tested for antibacterial activities against S. aureus and E. coli. The quaternized water-soluble copolymers showed antibacterial activities against S. aureus. The quaternization resulted in the synthesis of both antibacterial and temperature-responsive copolymers.
A new methacrylamide monomer, hexylamine methacrylamide (MAHA), was synthesized and used in polymerizations. The homopolymer of MAHA and its copolymers were synthesized by free radical polymerization techniques with N-isopropyl acrylamide (NIPAAm) in two different compositions. The quaternization of the homopolymer and copolymers were carried out using 1-bromopropane. The copolymers with NIPAAm and a low MAHA content showed temperature-responsive behavior in an aqueous environment. The lower critical solution temperatures (LCSTs) of these polymers varied between 32°C and 44°C. The LCSTs of quaternized copolymers were higher than those of neutral copolymers because they were more hydrophilic. The obtained homopolymers and copolymers were tested for antibacterial activities against S. aureus and E. coli. The quaternized water-soluble copolymers showed antibacterial activities against S. aureus. The quaternization resulted in the synthesis of both antibacterial and temperature-responsive copolymers.
2010, 28(4): 615-624
doi: 10.1007/s10118-010-9111-0
Abstract:
This study investigated the influence of various organically modified montmorillonites (organoclays) on the structure and properties of rigid polyurethane foam (RPUF) nanocomposites. The organoclays were modified with cetyltrimethyl ammonium bromide (CTAB), methyl tallow bis(2-hydroxyethyl) quaternary ammonium chloride (MT2ETOH) and tris(hydroxymethyl)aminomethane (THMA) and denoted as CMMT, Cloisite 30B and OMMT, respectively. MT2ETOH and THMA contain hydroxyl groups, while THMA does not have long aliphatic tail in its molecule. X-ray diffraction and transmission electron microscopy show that OMMT and Cloisite 30B can be partially exfoliated in the RPUF nanocomposites because their intercalating agents MT2ETOH and THMA can react with isocyanate. However, CMMT modified with nonreactive CTAB is mainly intercalated in the RPUF matrices. At a relatively low filler content, the RPUF/CMMT composite foam has a higher specific compressive strength (the ratio of compressive strength against the apparent density of the foams), while at relatively high filler contents, RPUF/Cloisite 30B and RPUF/OMMT composites have higher specific compressive strengths, higher modulus and more uniform pore size than the RPUF/CMMT composite.
This study investigated the influence of various organically modified montmorillonites (organoclays) on the structure and properties of rigid polyurethane foam (RPUF) nanocomposites. The organoclays were modified with cetyltrimethyl ammonium bromide (CTAB), methyl tallow bis(2-hydroxyethyl) quaternary ammonium chloride (MT2ETOH) and tris(hydroxymethyl)aminomethane (THMA) and denoted as CMMT, Cloisite 30B and OMMT, respectively. MT2ETOH and THMA contain hydroxyl groups, while THMA does not have long aliphatic tail in its molecule. X-ray diffraction and transmission electron microscopy show that OMMT and Cloisite 30B can be partially exfoliated in the RPUF nanocomposites because their intercalating agents MT2ETOH and THMA can react with isocyanate. However, CMMT modified with nonreactive CTAB is mainly intercalated in the RPUF matrices. At a relatively low filler content, the RPUF/CMMT composite foam has a higher specific compressive strength (the ratio of compressive strength against the apparent density of the foams), while at relatively high filler contents, RPUF/Cloisite 30B and RPUF/OMMT composites have higher specific compressive strengths, higher modulus and more uniform pore size than the RPUF/CMMT composite.
2010, 28(4): 625-635
doi: 10.1007/s10118-010-9136-4
Abstract:
Ultra-fine silicalite-1 particles were modified with four kinds of chlorosilanes (dodecyltrichlorosilane, octyltrichlorosilane, hexadecyltrichlorosilane and octadecyltrichlorosilane) and characterized by FI-IR, TGA, contact angle measurements and BET analysis. It was found that the surface hydrophobicity of silicalite-1 particles was improved significantly as the alkyl group was strongly bonded to the particle surface. Modified silicalite-1 particles were incorporated into PDMS (poly(dimethylsiloxanediol)) membranes, which were applied for the pervaporation separation of ethanol/water mixtures. The effect of surface properties, zeolite loading and operation conditions on pervaporation performance of the membranes was investigated. The separation factor of PDMS membranes filled with modified silicalite-1 increased considerably compared with that filled with unmodified ones, and the total flux decreased with increasing zeolite loading. The solution and diffusion selectivity of hybrid membranes were also measured to explain the pervaporation properties of silicalite-1 filled PDMS membranes. It was found that modification of silicalite-1 with dodecyltrichlorosilane effectively improved the solution and diffusion selectivity of silicalite-1 filled PDMS membranes with high zeolite loading. This may be attributed to the high surface hydrophobicity of modified silicalite-1 and its good integration with PDMS membranes. Both the high separation factor and solution selectivity indicated that modification of silicalite-1 with chlorosilanes was an effective method to improve the selectivity of silicalite-1/PDMS hybrid membranes for ethanol.
Ultra-fine silicalite-1 particles were modified with four kinds of chlorosilanes (dodecyltrichlorosilane, octyltrichlorosilane, hexadecyltrichlorosilane and octadecyltrichlorosilane) and characterized by FI-IR, TGA, contact angle measurements and BET analysis. It was found that the surface hydrophobicity of silicalite-1 particles was improved significantly as the alkyl group was strongly bonded to the particle surface. Modified silicalite-1 particles were incorporated into PDMS (poly(dimethylsiloxanediol)) membranes, which were applied for the pervaporation separation of ethanol/water mixtures. The effect of surface properties, zeolite loading and operation conditions on pervaporation performance of the membranes was investigated. The separation factor of PDMS membranes filled with modified silicalite-1 increased considerably compared with that filled with unmodified ones, and the total flux decreased with increasing zeolite loading. The solution and diffusion selectivity of hybrid membranes were also measured to explain the pervaporation properties of silicalite-1 filled PDMS membranes. It was found that modification of silicalite-1 with dodecyltrichlorosilane effectively improved the solution and diffusion selectivity of silicalite-1 filled PDMS membranes with high zeolite loading. This may be attributed to the high surface hydrophobicity of modified silicalite-1 and its good integration with PDMS membranes. Both the high separation factor and solution selectivity indicated that modification of silicalite-1 with chlorosilanes was an effective method to improve the selectivity of silicalite-1/PDMS hybrid membranes for ethanol.
2010, 28(4): 637-645
doi: 10.1007/s10118-010-9123-9
Abstract:
Influences of lanthanum stearate (LaSt3) and calcium stearate/zinc stearate (Ca/Zn) stabilizers on stabilization efficiency of dibutyltin dilaurate (DBTDL) to polyvinyl chloride (PVC) in air were investigated. The results revealed that the stabilization effect of DBTDL could be achieved by the La/Sn stabilizers with a ratio of 8/2. Addition of DBTDL could enhance thermal property and reduce dynamic storage modulus (G’) at 180oC for PVC containing LaSt3 or Ca/Zn stabilizers. On the other hand, incorporation of LaSt3 did not influence the stabilization efficiency of DBTDL markedly; while addition of Ca/Zn stabilizers could significantly decrease thermal property for the DBTDL stabilized PVC. Furthermore, the effects of LaSt3 and Ca/Zn stabilizers on the stabilization efficiency of DBTDL were explained in the framework of ionization potential.
Influences of lanthanum stearate (LaSt3) and calcium stearate/zinc stearate (Ca/Zn) stabilizers on stabilization efficiency of dibutyltin dilaurate (DBTDL) to polyvinyl chloride (PVC) in air were investigated. The results revealed that the stabilization effect of DBTDL could be achieved by the La/Sn stabilizers with a ratio of 8/2. Addition of DBTDL could enhance thermal property and reduce dynamic storage modulus (G’) at 180oC for PVC containing LaSt3 or Ca/Zn stabilizers. On the other hand, incorporation of LaSt3 did not influence the stabilization efficiency of DBTDL markedly; while addition of Ca/Zn stabilizers could significantly decrease thermal property for the DBTDL stabilized PVC. Furthermore, the effects of LaSt3 and Ca/Zn stabilizers on the stabilization efficiency of DBTDL were explained in the framework of ionization potential.
2010, 28(4): 647-656
doi: 10.1007/s10118-010-9150-6
Abstract:
Blends of polystyrene (PS) and polypropylene (PP) were prepared through melt compounding. With an increase of PS content up to 30 wt%, the tensile strength of PP/PS blends increased from 37.4 MPa to 42.2 MPa, although the blends were widely regarded as immiscible. The DSC results showed that there’s slight decrease in melting temperature of PP, showing insufficient evidence for partial compatibility between PP and PS. Almost no variation of distinct characterization peaks were observed in FTIR spectra of PS/PP blends compared with those of neat PP and PS, indicating there is no chemical interactions between PP and PS. Since the morphology investigation showed a droplet structure as PS content was up to 30 wt%, the improvement of tensile strength could be simply considered as due to the reinforcing effect of dispersed rigid PS particles on the PP, combining with partial compatibility between them as evaluated by change of Cp at glass transition for both PS and PP. More interestingly, DSC and DMA results showed that the blending of PS and PP could lead to a substantial decrease of the glass transition temperature (Tg) of PP, and increase of Tg of PS. The annealing experiment was carried out to understand the change of Tg in PP/PS blends. It is believed that the compressive stress generated by the contracting PP should be the dominant mechanism for the Tg elevation of PS. On the other hand, the Tg decrease of PP is likely owing to the creation of a large amount free interface of PP and the dilatation of the PP phase resulting from the corresponding tension exerted by PS during cooling.
Blends of polystyrene (PS) and polypropylene (PP) were prepared through melt compounding. With an increase of PS content up to 30 wt%, the tensile strength of PP/PS blends increased from 37.4 MPa to 42.2 MPa, although the blends were widely regarded as immiscible. The DSC results showed that there’s slight decrease in melting temperature of PP, showing insufficient evidence for partial compatibility between PP and PS. Almost no variation of distinct characterization peaks were observed in FTIR spectra of PS/PP blends compared with those of neat PP and PS, indicating there is no chemical interactions between PP and PS. Since the morphology investigation showed a droplet structure as PS content was up to 30 wt%, the improvement of tensile strength could be simply considered as due to the reinforcing effect of dispersed rigid PS particles on the PP, combining with partial compatibility between them as evaluated by change of Cp at glass transition for both PS and PP. More interestingly, DSC and DMA results showed that the blending of PS and PP could lead to a substantial decrease of the glass transition temperature (Tg) of PP, and increase of Tg of PS. The annealing experiment was carried out to understand the change of Tg in PP/PS blends. It is believed that the compressive stress generated by the contracting PP should be the dominant mechanism for the Tg elevation of PS. On the other hand, the Tg decrease of PP is likely owing to the creation of a large amount free interface of PP and the dilatation of the PP phase resulting from the corresponding tension exerted by PS during cooling.
2010, 28(4): 657-666
doi: 10.1007/s10118-010-9174-y
Abstract:
The effect of pre-shear flow on the subsequent crystallization process of polymeric melt was investigated and a flow-induced crystallization (FIC) model based on the conformation tensor incorporating the pre-shear effect was proposed. The model is capable of predicting the overshoot phenomena of the stress and the flow-induced free energy change of the polymeric system at high pre-shear rates. Under the condition of flow, the increase in the activated nuclei number was contributed by the flow-induced free energy change, which showed an overwhelming effect on the nuclei formation during the pre-shear process at high shear rates. The half crystallization time (t1/2) of polypropylene (PP) as functions of pre-shear rate and pre-shear time at different crystallization temperatures was predicted and compared with the experiment data. Both numerical and experimental results showed that t1/2 of PP decreased dramatically when the flow started but leveled off at long times. It was found that two transformation stages in t1/2 existed within a wide range of shear rates. For the first stage where the melting polymer experienced a relatively weak shear flow, the acceleration of crystallization kinetics was mainly contributed by the steady value of free energy change while in the second stage for high shear rates, strong overshoot in flow-induced free energy change occurred and the crystallization kinetics was thus significantly enhanced. The overshoots in stress and flow-induced free energy change reflected an important role of flow on the primary nucleation especially when the flow was strong enough.
The effect of pre-shear flow on the subsequent crystallization process of polymeric melt was investigated and a flow-induced crystallization (FIC) model based on the conformation tensor incorporating the pre-shear effect was proposed. The model is capable of predicting the overshoot phenomena of the stress and the flow-induced free energy change of the polymeric system at high pre-shear rates. Under the condition of flow, the increase in the activated nuclei number was contributed by the flow-induced free energy change, which showed an overwhelming effect on the nuclei formation during the pre-shear process at high shear rates. The half crystallization time (t1/2) of polypropylene (PP) as functions of pre-shear rate and pre-shear time at different crystallization temperatures was predicted and compared with the experiment data. Both numerical and experimental results showed that t1/2 of PP decreased dramatically when the flow started but leveled off at long times. It was found that two transformation stages in t1/2 existed within a wide range of shear rates. For the first stage where the melting polymer experienced a relatively weak shear flow, the acceleration of crystallization kinetics was mainly contributed by the steady value of free energy change while in the second stage for high shear rates, strong overshoot in flow-induced free energy change occurred and the crystallization kinetics was thus significantly enhanced. The overshoots in stress and flow-induced free energy change reflected an important role of flow on the primary nucleation especially when the flow was strong enough.
