Showing papers by "Lina Zhang published in 2007"

Multifilament Fibers Based on Dissolution of Cellulose in NaOH/Urea Aqueous Solution: Structure and Properties

Abstract: High-quality cellulose multifilaments are spun using a preliminary pilot apparatus, from the cellulose dope in an NaOH and urea aqueous solution precooled to -12 {sup o}C, by using a low-cost, simple, and environmentally friendly process. Small-angle X-ray scattering patterns indicate that the orientation of the multifilaments increase with a drawing process, leading to the improvement of their tensile strength.

Hydrogen‐Bond‐Induced Inclusion Complex in Aqueous Cellulose/LiOH/Urea Solution at Low Temperature

Abstract: It was puzzling that cellulose could be dissolved rapidly in 4.6 wt % LiOH/15 wt % urea aqueous solution precooled to -12 degrees C, whereas it could not be dissolved in the same solvent without prior cooling. To clarify this important phenomenon, the structure and physical properties of LiOH and urea in water as well as of cellulose in the aqueous LiOH/urea solution at different temperatures were investigated by means of laser light scattering, 13C NMR spectroscopy, differential scanning calorimetry, Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, and transmission electron microscopy (TEM). The results reveal that a hydrogen-bonded network structure between LiOH, urea, and water can occur, and that it becomes more stable with decreasing temperature. The LiOH hydrates cleave the chain packing of cellulose through the formation of new hydrogen bonds at low temperatures, which result in a relatively stable complex associated with LiOH, water clusters, and cellulose. A channel inclusion complex (IC) hosted by urea could encage the cellulose macromolecule in LiOH/urea solution with prior cooling and therefore provide a rationale for forming a good dispersion of cellulose. TEM observations, for the first time, showed the channel IC in dry form. The low-temperature step played an important role in shifting hydrogen bonds between cellulose and small molecules, leading to the dissolution of macromolecules in the aqueous solution.

Hydrogels Prepared from Unsubstituted Cellulose in NaOH/Urea Aqueous Solution

Abstract: Novel cellulose hydrogels were synthesized through a "one-step" method from cellulose, which was dissolved directly in NaOH/urea aqueous solution, by using epichlorohydrin as crosslinker. Structure and properties of the hydrogels were characterized by using SEM, NMR, and water absorption testing. The hydrogels are fully transparent and display macroporous inner structure. The equilibrium swelling ratios of the hydrogels in distilled water at 25 degrees C are in the range from 30 to 60 g H(2)O/g dry hydrogel. Moreover, the reswelling water uptake of the hydrogels could be achieved to more than 70% compared with their initial swelling states. This work provided a simple and fast method for preparing eco-friendly hydrogels from unsubstituted cellulose.

Influence of coagulation temperature on pore size and properties of cellulose membranes prepared from NaOH–urea aqueous solution

Abstract: The morphology and structure of the regenerated cellulose membranes prepared from its NaOH–urea aqueous solution by coagulating with 5 wt% H2SO4–10 wt% Na2SO4 aqueous solution with different temperatures and times were investigated. The pore size, water permeability and physical properties of the membranes were measured with scanning electron micrograph (SEM), wide X-ray diffraction (WXRD), Fourier transfer infrared spectroscopy (FTIR), flow rate method, and tensile testing. The SEM observation revealed that the structure and pore size of the membranes changed drastically as a function of the coagulation temperature. The membranes coagulated at lower temperatures tended to form the relatively small pore size than those at higher temperatures. On the contrary, the membranes coagulated at different times exhibited similar pore size. Interestingly, the mean pore size and water permeability of the membranes increased from 110 nm with standard deviation (SD) of 25 nm and 12 ml h−1 m−2 mmHg−1 respectively to 1,230 nm with SD of 180 nm and 43 ml h−1 m−2 mmHg−1 with an increase in coagulation temperature from 10 to 60°C. However, the membranes regenerated below 20°C exhibited the dense structure as well as good tensile strength and elongation at break. The result from FTIR and ultraviolet-visible (UV-vis) spectroscopy indicated that the relatively strong intermolecular hydrogen bonds exist in the cellulose membranes prepared at lower coagulation temperatures. This work provided a promising way to prepare cellulose materials with different pore sizes and physical properties by controlling the coagulation temperature.

Fabrication and Properties of Cellulose Hydrated Membrane with Unique Structure

Abstract: By employing a pre-gelation processing of cellulose solution, this work has presented a new method to prepare cellulose hydrated membranes in NaOH/thiourea aqueous solvent system. The morphology and structure of the hydrated membranes obtained at different pre-gelation temperatures were studied by scanning electron microscopy (SEM), wide-angle X-ray diffractometry (WAXD), and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The mechanical properties of the membranes were studied by tensile testing. Using a double-cell method, permeation of three model drugs (ceftazidine, cefazolin sodium, thiourea) through the hydrate membranes was determined in phosphate buffer solution at body-like temperature (37 °C). The results indicate that the membranes were packed densely by many hydrated nanospheres and exhibited good mechanical properties. At a relatively low pre-gelation temperature, the strain and the stress at break of the membranes are even up to 192% and 1.97 MPa, which are much larger than that of the hydrated membranes prepared by the general solution casting method. For the first time, the formation process of the hydrated membrane from gel state in water was investigated by ATR-FTIR spectrum, indicating a non-solvent-induced phase-separation mechanism.

Inclusion Complex Formation of Cellulose in NaOH–Thiourea Aqueous System at Low Temperature

Abstract: It is puzzling that cellulose could be dissolved rapidly in 9.5 wt.-% NaOH/4.5 wt.-% thiourea aqueous solution pre-cooled to - 5 °C, but it could not be dissolved in the same solvent mixture without prior cooling. To understand this phenomenon, changes in the structure and properties of NaOH and thiourea in water as well as solution behaviors of cellulose in the solvent at low temperatures were investigated by means of 13 C NMR, Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, transmission electron microscopy (TEM), and viscometry. The results indicated that an association of NaOH and thiourea in water through the hydrogen bonding strengthened with a decrease in temperature. The low temperature created a new hydrogen-bonded network structure associated with NaOH, thiourea, water cluster, and cellulose, leading to the cleaving of the close chain packing of cellulose. The results proved that a good dispersion of cellulose occurred at a low temperature as a result of the formation of an inclusion complex (IC) hosted by thiourea and NaOH, in which cellulose chain associated with NaOH hydrates as guest was encaged. IC could aggregate to form a sphere having a mean size of 60-160 nm. TEM observations, for the first time, revealed the shape and size of IC and its aggregate. The stability of the cellulose solution could be related to the thiourea IC.

Formation and Morphologies of Novel Self-Assembled Micelles from Chitosan Derivatives

Abstract: We successfully synthesized N-phthaloyl-carboxymethylchitosan (CMPhCh) from chitosan. CMPhCh could be self-assembled to form various morphologies of crew-cut micelle-like aggregates using a mixed solution of water and N,N-dimethylformamide (DMF). The results of scanning electron microscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS) revealed that the morphologies of the aggregates exhibited vesicles, vesicle-encapsulating vesicles, onion-like vesicles, and large compound micelles (LCM). Their morphologies were changed with varying the concentration of CMPhCh, the ratio of DMF in the mixture, and the self-assembly process. In relatively high CMPhCh concentration and content of DMF, CMPhCh was self-assembled to form the onion-like vesicles with a thin wall and 80-240 nm diameter. For the first time, TEM observation provided straightforward evidence of the onion-like vesicles prepared from natural polymer.

Influence of different amides as plasticizer on the properties of soy protein plastics

Abstract: A series of amide-plasticized soy protein isolate materials were prepared by hot compression-molding techniques at 140°C and 20 MPa. The plasticizing efficiency of amides was in the order of formamide > acetamide > acrylamide resulting from scanning electron microscopy, optical transmittance and differential scanning calorimetry. The results from torque rheology indicated that flowability and processability could be improved by adding amide as plasticizers. All of the sheets showed single glass transition temperature obtained by differential scanning calorimetry, indicating good compatibility between amide and soy protein. The water uptake of the plastics sheets and effects of moisture content on the thermal and mechanical properties were also investigated. The glass transition temperature and tensile strength decreased with an increase of moisture content in sheets. Formamide was considered as the best plasticizer of three amides because of the higher plasticizing efficiency and water resistance of SFm sheets. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Voltage-controlled variable light emissions from GaN codoped with Eu, Er, and Tm

Abstract: In this letter, a model to calculate the emission intensities of different rare-earth (RE) dopants in GaN is proposed based on the quantum collision theory and Judd-Ofelt approximation. The possible white light emission from Eu-, Er-, and Tm-codoped GaN is predicted according to the Commission International de I’Eclairage chromaticity diagram. Variable-wavelength emissions can be realized by adjusting the relative concentrations of different RE dopants in GaN and the bias voltage of the applied electric field. The availability of voltage-controlled light emissions and white light emission of the RE-doped GaN electroluminescent devices may have great potential for application in displays.

Molecular weight and chain conformation of amylopectin from rice starch

Abstract: By using laser light scattering (LS) and size exclusion chromatography combined LS, we have investigated the molecular weight and chain conformation of amylopectin from rice of India (II-b), japonica (IJ-b), and glutinous (IG-b) in dimethyl sulfoxide (DMSO) solution. The weight-average molecular weight (Mw) and radius of gyration (〈S2〉½) of amylopectin were determined to be 4.06 × 107 and 128.5 nm for India rice, 7.41 × 107 and 169.6 nm for japonica rice, 2.72 × 108 and 252.3 nm for glutinous rice, respectively. The 〈S2〉½ values were much lower than that of normal polymers, indicating a small molecular volume of amylopectin, as a result of highly branched structure. Ignoring the difference of degree of branching, approximated dependences of 〈S2〉½ and intrinsic viscosity ([η]) on Mw for amylopectin in DMSO at 25°C were estimated to be 〈S2〉½ = 0.30Mw0.35 (nm) and [η] = 0.331Mw0.41 (mL g−1) in the Mw range studied. Moreover, from the 〈S2〉½ values of numberless fractions obtained from many experimental points in the SEC chromatogram detected with LS, the dependence of 〈S2〉½ on Mw for the II-b sample was estimated also to be 〈S2〉½ = 0.34 Mw0.347, coinciding with the above results. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

A New Network Composite Material Based on Soy Dreg Modified with Polyurethane Prepolymer

Abstract: A series of biodegradable, soy-protein-based, composite materials was prepared by introducing castor-oil-based polyurethane prepolymer (PUP) into soy dreg (SD) without the addition of plasticizers, via extrusion and a compression-molding process. The effects of the NCO/OH molar ratio and the PUP content on the structure and properties of the resulting materials were studied by Fourier-transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, tensile testing, swelling experiments, and biodegradability testing. The results revealed that the -NCO group in the PUP played a vital role in improving the compatibility and elasticity, as a result of the formation of a cross-linking network structure with the -NH 2 , -NH, and -OH groups in SD containing protein and cellulose. Increasing the NCO/OH molar ratio to 2.0 resulted in an enhancement of the degree of cross-linking, leading to a higher tensile strength (24 MPa), glass-transition temperature (52°C) and water-resistivity of the composite materials. The unreacted SD also served as a filler in the cross-linked networks and enhanced the tensile strength of the composites. The biodegradation testing showed that the composites exhibited biodegradability under the condition of fungus culture.

Field-driven gel actuator with versatile long-range locomotion in air

Abstract: An approach to fabricate gel actuator using nonionic polymer gels and dielectric liquid pattern was developed. The actuator could be operated in air using a dc electric field and exhibited a rotation-slide complex motion on the horizontal and a snail-like or sliding motion on the slope with controlled path. The average rotational speed and the average climbing speed of the gel could reach 0.35rad∕s and 3.8mm∕s, respectively. The driving force of the gel originated from the electrohydrodynamic flow of the dielectric solvent inside and outside the gel induced by the ion-dragging mechanism under the electric field.

Fractionation and characterization of a protein–polysaccharide complex from Pleurotus tuberregium sclerotia

Abstract: A water-soluble sample (TM4b), extracted from sclerotia of Pleurotus tuberregium, was analyzed using elemental analysis, one- and two-dimensional 1 H and 1 3 C NMR. The results indicated that TM4b was protein-polysaccharide complex, and the polysaccharide moiety was hyperbranched β-D-glucan with residuals branched at C3, C2, C4, and C6 positions. A preparative size-exclusion chromatography (SEC) column combined with nonsolvent addition method was used to fractionate TM4b, and nine fractions were obtained. Solution properties of TM4b in 0.15 M aqueous NaCl were studied using static laser light scattering and viscometry at 25°C. The dependences of intrinsic viscosity ([η]) and radius of gyration ( z 1/2 ) on weight-average molecular weight (M w ) for TM4b in the M w range from 1.89 X 10 4 to 2.58 X 10 6 were found to be [η] = 0.21Mw 0.32±0.4 and z 1/2 = 3.63M w 0.21±0.02 . It indicated that TM4b existed as compact sphere conformation in the aqueous solution. Atomic force microscopy image further confirmed that the TM4b molecules exhibited globular shape in the solution. This work gave valuable information on fractionation and chain conformation characterization of the globular protein-polysaccharide complex.

Electrically induced linear locomotion of polymer gel in air

Abstract: A electromechanical gel, which could be driven in air by a DC electric field, was developed using poly(vinyl alcohol)/dimethylsulfoxide gel. When the applied electric field exceeds a certain threshold, the gel exhibited a continuous and linear crawling motion. The result indicated that, under the applied electric field of 275 V/mm, the maximum crawling velocity of the gel could reach v = 1.63 mm/s, which is about 80 times larger than that reported in earlier works. At a proper range of the driving time, the average crawling speed and crawling direction could be well controlled by the external electric field. Furthermore, some factors, which have influence on the critical driving electric field of the gel, such as the swelling degree of the gel and the apparent contact area between the gel and substrate, were studied. For the first time, a mechanism based on the strong electrostatic interaction between the external electric field and the charges accumulated in the gel–air and substrate–gel interfacial regions was put forward to explain the novel motion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1187–1197, 2007

Molecular weight and arm number of a star-shaped styrene–butadiene block copolymer synthesized on a pilot-vessel scale

Abstract: To improve the rheological properties and processability of industrial rubbers, star-shaped styrene–butadiene–styrene (SBS) block copolymers were synthesized and characterized in this work. Through the variation of the ratio of divinylbenzene to the diblock anion, a series of SBS samples with three to six arms were prepared. Multi-angle laser light scattering (MALLS) and size exclusion chromatography (SEC) combined with light scattering (LS) were used to determine the weight-average molecular weight (Mw), radius of gyration (〈S2〉1/2), arm number, and chain conformation. The results from MALLS indicated that the Mw values of the star-shaped SBS copolymers were 9.0, 13.0, 14.9, and 18.1 × 104, which corresponded to three, four, five, and six arms, respectively. There was a lot of Mw and 〈S2〉1/2 data for the many fractions in the SEC chromatograms of the SBS copolymers in tetrahydrofuran (THF) detected by LS, so the exponent of 〈S2〉1/2 = KMwα was determined to range from 0.59 to 0.30 for the samples having three to six arms. An analysis of the results revealed that the star SBS copolymers existed in a sphere conformation in THF, and their chain density increased with an increase in the arm number. The viscosity of the six-arm SBS copolymer was reduced significantly, compared with that of the SBS samples having three to five arms, when their Mw values were similar. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1853–1859, 2007

Long‐Range Self‐Governing Motion of Polymer Gel on a Gradiently Charged Insulating Substrate

Abstract: Herein, we report a special poly(vinyl alcohol)/dimethylsulfoxide (PVA/DMSO) gel electromechanical system with great self-governed capability. The system is operated in air by applying a noncontacted DC electric field. When the applied electric field exceeds a certain critical value, the gel exhibits fast and self-governing locomotion on the gradiently charged glass substrate. In contrast to field-controlled gel systems developed earlier, the crawling direction of the gel is independent of the direction of the applied electric field and can be actively controlled. The maximum crawling velocity can reach 3.22 mm s(-1), which is much larger than that of the actuators described earlier. Furthermore, some factors that influence the critical driving electric field and the average crawling speed of the gel were studied. The mechanism analysis indicates that, the self-governing linear motion of the gel is due to the spatially and temporally varying electrostatic interaction between the gel and the applied electric field in response to the gradient change of the charge density and the charge polarity on the substrate.