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2000 Volume 18 Issue 5
2000, 18(5): 389-396
Abstract:
Many bacteria have been found to synthesize a family of polyesters termed polyhydroxyalkanoate, abbreviated asPHA. Some interesting physical properties of PHAs such as piezoelectricity, non-linear optical activity, biocompatibility andbiodegradability offer promising applications in areas such as degradable packaging, tissue engineering and drag delivery.Over 90 PHAs with various structure variations have been reported and the number is still increasing. The mechanical property of PHAs changes from brittle to flexible to elastic,depending on the side-chainlength of PHA.Many attempts have been made to produce PHAs as biodegradable plastics using various microorganisms obtained from screening natural environments,genetic engineering and mutation.Due to the high production cost,PHAs still can not compete with the nondegradable plastics,such as polyethylene and polypropylene.Various processes have been developed using low cost raw materials for fermentation and an inorganic extraction process for PHA purification.However,a super PHA production strain may play the most critical role for any large-scale PHA production.Our recent study showed that PHA synthesis is a common phenomenon among bacteria inhabiting various locations,especially oil-contaminated soils.This is very important for finding a suitable bacterial strain for PHA production.In fact,PHA production strains capable of rapid growth and rapid PHA synthesis on cheap molasses substrate have been found on molasses contaminated soils.A combination of novel properties and lower cost will allow easier commercialization of PHA for many applications.
Many bacteria have been found to synthesize a family of polyesters termed polyhydroxyalkanoate, abbreviated asPHA. Some interesting physical properties of PHAs such as piezoelectricity, non-linear optical activity, biocompatibility andbiodegradability offer promising applications in areas such as degradable packaging, tissue engineering and drag delivery.Over 90 PHAs with various structure variations have been reported and the number is still increasing. The mechanical property of PHAs changes from brittle to flexible to elastic,depending on the side-chainlength of PHA.Many attempts have been made to produce PHAs as biodegradable plastics using various microorganisms obtained from screening natural environments,genetic engineering and mutation.Due to the high production cost,PHAs still can not compete with the nondegradable plastics,such as polyethylene and polypropylene.Various processes have been developed using low cost raw materials for fermentation and an inorganic extraction process for PHA purification.However,a super PHA production strain may play the most critical role for any large-scale PHA production.Our recent study showed that PHA synthesis is a common phenomenon among bacteria inhabiting various locations,especially oil-contaminated soils.This is very important for finding a suitable bacterial strain for PHA production.In fact,PHA production strains capable of rapid growth and rapid PHA synthesis on cheap molasses substrate have been found on molasses contaminated soils.A combination of novel properties and lower cost will allow easier commercialization of PHA for many applications.
2000, 18(5): 397-403
Abstract:
The effect of pan-milling on the rheological properties of high density polyethylene (HDPE) was studied. Aninnovative milling apparatus, viz. an inlaid pan-mill, was used. Melt indexer, capillary rheometer, Haake Rheocord 90 single-screw extruder and Brabender rheometer were used to evaluate the rheologieal properties of HDPE. HDPE with higher initialmolecular weight and larger particle size was easier to degrade under pan-milling stress, as indicated by the melt index.Pressure oscillation in capillary flow occurred at significantly higher shear stress and shear rate for milled HDPE than for unmilled HDPE.The apparent shear viscosity of HDPE decreased with increasing times of milling.After milling,the flow activation energy decreased and thus the sensitivity of viscosity to temperature was reduced.Die pressure and torque during single screw extrusion were reduced significantly after milling.Plasticizing time as measured in a Brabander mixer decreased markedly with increasing milling times.
The effect of pan-milling on the rheological properties of high density polyethylene (HDPE) was studied. Aninnovative milling apparatus, viz. an inlaid pan-mill, was used. Melt indexer, capillary rheometer, Haake Rheocord 90 single-screw extruder and Brabender rheometer were used to evaluate the rheologieal properties of HDPE. HDPE with higher initialmolecular weight and larger particle size was easier to degrade under pan-milling stress, as indicated by the melt index.Pressure oscillation in capillary flow occurred at significantly higher shear stress and shear rate for milled HDPE than for unmilled HDPE.The apparent shear viscosity of HDPE decreased with increasing times of milling.After milling,the flow activation energy decreased and thus the sensitivity of viscosity to temperature was reduced.Die pressure and torque during single screw extrusion were reduced significantly after milling.Plasticizing time as measured in a Brabander mixer decreased markedly with increasing milling times.
2000, 18(5): 405-412
Abstract:
Transesterification of poly(ethylene terephthalate) (PET) with poly(ε-caprolactone) (PCL) was investigated bymeans of NMR spectroscopy, extraction experiments, differential scanning calorimetry (DSC) and phase contrast microscopy(PCM). The 1H-NMR results show that transesterification takes place in the melt blends and leads to the formation of thePET-PCL copolyester with a chemical structure similar to ethylene terephthalate-ε-caprolactonc copolycster (TCL)synthesized directly from monomers.However,even in the blend that has been transesterified for 8 h,the random PET-PCL copolyester,PET-PCL copolyester with long PET or long PCL segments and the unreacted PET and PCL homopolymers may coexist.Due to the low mobility of PET and PCL chains and the high viscosity of the two macromolecules,the transesterification proceeds with difficulty.Furthermore,PET is incompatible with PCL,the transesterirication can only occur at the interface or in the interfacial region between two phases,and finally the reaction can only reach a local equilibrium.These results indicate that in fact the transesterification in the melt blend between two incompatible homopolymers could not lead to the formation of completely random or typical block copolyesters.
Transesterification of poly(ethylene terephthalate) (PET) with poly(ε-caprolactone) (PCL) was investigated bymeans of NMR spectroscopy, extraction experiments, differential scanning calorimetry (DSC) and phase contrast microscopy(PCM). The 1H-NMR results show that transesterification takes place in the melt blends and leads to the formation of thePET-PCL copolyester with a chemical structure similar to ethylene terephthalate-ε-caprolactonc copolycster (TCL)synthesized directly from monomers.However,even in the blend that has been transesterified for 8 h,the random PET-PCL copolyester,PET-PCL copolyester with long PET or long PCL segments and the unreacted PET and PCL homopolymers may coexist.Due to the low mobility of PET and PCL chains and the high viscosity of the two macromolecules,the transesterification proceeds with difficulty.Furthermore,PET is incompatible with PCL,the transesterirication can only occur at the interface or in the interfacial region between two phases,and finally the reaction can only reach a local equilibrium.These results indicate that in fact the transesterification in the melt blend between two incompatible homopolymers could not lead to the formation of completely random or typical block copolyesters.
2000, 18(5): 413-418
Abstract:
Graphite oxide, a pseudo-two-dimensional solid in bulk form, was synthesized from natural graphite powder byoxidization with KMnO44 in concentrated H24SO44. The poly(vinyl acetate)-intercalated graphite oxide nano-composite wasprepared by an in situ intercalative polymerization reaction, in which n-octanol-graphite oxide intercalation compounds werefirst obtained, vinyl acetate monomer was then dispersed into the interlayer of modified graphite oxide, followed by thermal polymerization of the monomer.It was experimentally shown that the c-axis space of poly(vinyl acetate)-intercalated graphite oxide was increased to 0.115 nm,which suggested there existed a monolayer of poly(vinyl acetate) chain between the layers of graphite oxide.The nanocomposite was also characterized with thermal analysis and FT-IR spectrometry.
Graphite oxide, a pseudo-two-dimensional solid in bulk form, was synthesized from natural graphite powder byoxidization with KMnO44 in concentrated H24SO44. The poly(vinyl acetate)-intercalated graphite oxide nano-composite wasprepared by an in situ intercalative polymerization reaction, in which n-octanol-graphite oxide intercalation compounds werefirst obtained, vinyl acetate monomer was then dispersed into the interlayer of modified graphite oxide, followed by thermal polymerization of the monomer.It was experimentally shown that the c-axis space of poly(vinyl acetate)-intercalated graphite oxide was increased to 0.115 nm,which suggested there existed a monolayer of poly(vinyl acetate) chain between the layers of graphite oxide.The nanocomposite was also characterized with thermal analysis and FT-IR spectrometry.
2000, 18(5): 419-422
Abstract:
The shape of unperturbed polymer chains was studied using the Monte Carlo technique on a tetrahedral lattice.The asphericity A, the ratios/and/ were calculated for different values of polymer chain length n,conformational energy ε (ε≥0) and temperature T. The asphericity A decreases with the increase of chain length and tends toreach its limiting value rapidly with the decrease of γ(γ=ε/kBT). For large n, A is about 0.525±0.005, the ratios22/12and 32>/L12 are about 2.7 and 12.0,respectively,and are almost independent of γ,but for short chains,they depend on γ.
The shape of unperturbed polymer chains was studied using the Monte Carlo technique on a tetrahedral lattice.The asphericity A, the ratios/and/ were calculated for different values of polymer chain length n,conformational energy ε (ε≥0) and temperature T. The asphericity A decreases with the increase of chain length and tends toreach its limiting value rapidly with the decrease of γ(γ=ε/kBT). For large n, A is about 0.525±0.005, the ratios22/12and 32>/L12 are about 2.7 and 12.0,respectively,and are almost independent of γ,but for short chains,they depend on γ.
2000, 18(5): 423-430
Abstract:
The complexation between styrene (St) and N-phenylmaleimide (PMI) was investigated by 1H-NMR spectroscopy,and the existence of a complex was proved. The equilibrium constant of St/PMI in chloroform at 50℃ was determined to be0.27. New elementary propagation reactions were proposed. On the basis of the propagation elementary reactions forcopolymerization with the participation of a charge-transfer complex (CTC), a method for measuring the reactivity ratios ispresented. Four reactivity ratios and relative reactivities of free monomer and CTC were obtained.They are γ21=0.012,γ1c=0.0030,γ2c=0.0034,and k1c/k12=11.34,k2c/k21=3.42
The complexation between styrene (St) and N-phenylmaleimide (PMI) was investigated by 1H-NMR spectroscopy,and the existence of a complex was proved. The equilibrium constant of St/PMI in chloroform at 50℃ was determined to be0.27. New elementary propagation reactions were proposed. On the basis of the propagation elementary reactions forcopolymerization with the participation of a charge-transfer complex (CTC), a method for measuring the reactivity ratios ispresented. Four reactivity ratios and relative reactivities of free monomer and CTC were obtained.They are γ21=0.012,γ1c=0.0030,γ2c=0.0034,and k1c/k12=11.34,k2c/k21=3.42
2000, 18(5): 431-435
Abstract:
In a polymerization model with low density polyethylene (LDPE) as the substrate and acrylic acid (AA) as themonomer, the performance of isopropylthioxanthone (ITX) in initiating surface photografting polymerization was evaluated.The results show that the reactivity of photopolymerization and photografting of ITX locate between benzophenone (BP) andbenzildimethylketal (BDK) for polymerization, BDK> ITX> BP; for surface grafting polymerization, BP> ITX>BDK.These results can be explained by a reaction mechanism of the inter-molecular or intra-molecular hydrogen abstraction reaction of ITX.
In a polymerization model with low density polyethylene (LDPE) as the substrate and acrylic acid (AA) as themonomer, the performance of isopropylthioxanthone (ITX) in initiating surface photografting polymerization was evaluated.The results show that the reactivity of photopolymerization and photografting of ITX locate between benzophenone (BP) andbenzildimethylketal (BDK) for polymerization, BDK> ITX> BP; for surface grafting polymerization, BP> ITX>BDK.These results can be explained by a reaction mechanism of the inter-molecular or intra-molecular hydrogen abstraction reaction of ITX.
2000, 18(5): 437-441
Abstract:
The morphology of polyvinyl chloride/polystyrene (PVC/PS) blend samples with different mass ratios, preparedby means of solution casting and melt mixing, have been successfully examined by electron microprobe analysis (EMP). Thisexperiment was performed in a scanning electron microscope attached to an energy dispersive X-ray analyzer. Differentialscanning calorimetry was also used to investigate the phase separation of the blends. The results show that PVC and PS are incompatible and the blends have sea-islands phase structures.Blends prepared via melt mixing have finer phase-dispersion than those prepared via solution casting.
The morphology of polyvinyl chloride/polystyrene (PVC/PS) blend samples with different mass ratios, preparedby means of solution casting and melt mixing, have been successfully examined by electron microprobe analysis (EMP). Thisexperiment was performed in a scanning electron microscope attached to an energy dispersive X-ray analyzer. Differentialscanning calorimetry was also used to investigate the phase separation of the blends. The results show that PVC and PS are incompatible and the blends have sea-islands phase structures.Blends prepared via melt mixing have finer phase-dispersion than those prepared via solution casting.
2000, 18(5): 443-447
Abstract:
Optically active copolyesters based on axially dissymmetric 1,1'-binaphthalene-2,2'-diyl units have been preparedand characterized by specific rotation, 13C-NMR and CD spectra. The results show that the rotation signs of tribasiccopolyesters or the mixture of corresponding homopolyesters obey a three dimensional quadrant pattern. The composition ofthe copolyesters was determined from 13C-NMR spectra to be triad sequence distributions and corresponding with the ratioby feed.
Optically active copolyesters based on axially dissymmetric 1,1'-binaphthalene-2,2'-diyl units have been preparedand characterized by specific rotation, 13C-NMR and CD spectra. The results show that the rotation signs of tribasiccopolyesters or the mixture of corresponding homopolyesters obey a three dimensional quadrant pattern. The composition ofthe copolyesters was determined from 13C-NMR spectra to be triad sequence distributions and corresponding with the ratioby feed.
2000, 18(5): 449-452
Abstract:
A new silazane oligomer containing cyclotrisilazane was synthesized by KH-catalyzed dehydro-coupling reactionsbetween diphenylsilane and 1,1,3,3,5,5-hexamethylcyclotrisilazane (D3N).
A new silazane oligomer containing cyclotrisilazane was synthesized by KH-catalyzed dehydro-coupling reactionsbetween diphenylsilane and 1,1,3,3,5,5-hexamethylcyclotrisilazane (D3N).
2000, 18(5): 453-457
Abstract:
Ladderlike polyhydroxypropylsilsesquioxane (HO-T) was synthesized by alcoholysis of ladderlike poly(3-propionyloxy-propyl)silsesquioxane. The HO-T was characterized by GPC, IR, NMR, DSC, TGA and X-ray diffractionmethods. Through hydrogen-bonding interaction, ladderlike polymer (HO-T) can form a supramolecular complex withsomewhat regular structure.
Ladderlike polyhydroxypropylsilsesquioxane (HO-T) was synthesized by alcoholysis of ladderlike poly(3-propionyloxy-propyl)silsesquioxane. The HO-T was characterized by GPC, IR, NMR, DSC, TGA and X-ray diffractionmethods. Through hydrogen-bonding interaction, ladderlike polymer (HO-T) can form a supramolecular complex withsomewhat regular structure.
2000, 18(5): 459-463
Abstract:
Ladderlike polychloropropylsilsesquioxane (CP-T) was first synthesized by "stepwise coupling polymerization".The molecular weight of CP-T is as high as 1.7×105. It is a tough, elastic reactive ladderlike polymer and has good heat-resistant and adhesive properties. CP-T can further react with many nucleophilic reagents to generate new ladderlike reactivepolysilsesquioxanes, which can be used as potential precursors in the synthesis of functional ladderlike polymers.
Ladderlike polychloropropylsilsesquioxane (CP-T) was first synthesized by "stepwise coupling polymerization".The molecular weight of CP-T is as high as 1.7×105. It is a tough, elastic reactive ladderlike polymer and has good heat-resistant and adhesive properties. CP-T can further react with many nucleophilic reagents to generate new ladderlike reactivepolysilsesquioxanes, which can be used as potential precursors in the synthesis of functional ladderlike polymers.
2000, 18(5): 465-468
Abstract:
The effect of self absorption on the ratio of excimer to monochromophore emission intensities, Ie/Im, has beenexplored by experimentally changing the solution layer thickness of the emission light path traversed in the solution in theright-angle geometry. The result shows that data obtained by front-face geometry are better than those obtained by right-angle geometry even after correction to zero solution thickness. The correction formula based on geometric optics given byTsai and Torkelson is not adequate.
The effect of self absorption on the ratio of excimer to monochromophore emission intensities, Ie/Im, has beenexplored by experimentally changing the solution layer thickness of the emission light path traversed in the solution in theright-angle geometry. The result shows that data obtained by front-face geometry are better than those obtained by right-angle geometry even after correction to zero solution thickness. The correction formula based on geometric optics given byTsai and Torkelson is not adequate.
2000, 18(5): 469-472
Abstract:
Mesoporous poly (styrene-co-maleic anhydride)/silica hybrid materials have been prepared. The synthesis wasachieved by the HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) and styrene-maleic anhydride copolymerin the presence of 3-aminopropyl triethoxysilane (APTES) as a coupling agent and citric acid as a nonsurfactant template orpore-forming agent, followed by ethanol extraction. Characterization results from nitrogen sorption isotherms and powder X-ray diffraction indicate the polymer-modified mesoporous materials with large specific surface areas(e.g. 900 m2/g) and pore volumes(e.g. 0.6cm3/g) could be prepared.As the citric acid concentration is increased,the specific surface areas,pore volumes and pore diameters of the hybrid materials increase.
Mesoporous poly (styrene-co-maleic anhydride)/silica hybrid materials have been prepared. The synthesis wasachieved by the HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) and styrene-maleic anhydride copolymerin the presence of 3-aminopropyl triethoxysilane (APTES) as a coupling agent and citric acid as a nonsurfactant template orpore-forming agent, followed by ethanol extraction. Characterization results from nitrogen sorption isotherms and powder X-ray diffraction indicate the polymer-modified mesoporous materials with large specific surface areas(e.g. 900 m2/g) and pore volumes(e.g. 0.6cm3/g) could be prepared.As the citric acid concentration is increased,the specific surface areas,pore volumes and pore diameters of the hybrid materials increase.
