Behavior of cellulose in NaOH/Urea aqueous solution characterized by light scattering and viscometry

Cellulose was dissolved in 6 wt % NaOH/4 wt % urea aqueous solution, which was proven by a ¹³C NMR spectrum to be a direct solvent of cellulose rather than a derivative aqueous solution system. Dilute solution behavior of cellulose in a NaOH/urea aqueous solution system was examined by laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 6 wt % NaOH/4 wt % urea aqueous solution at 25 °C was [η] = 2.45 × 10^?2 weight‐average molecular weight (M_w)^0.815 (mL g^?1) in the M_w region from 3.2 × 10⁴ to 12.9 × 10⁴. The persistence length (q), molar mass per unit contour length (M_L), and characteristic ratio (C_∞) of cellulose in the dilute solution were 6.0 nm, 350 nm^?1, and 20.9, respectively, which agreed with the Yamakawa–Fujii theory of the wormlike chain. The results indicated that the cellulose molecules exist as semiflexible chains in the aqueous solution and were more extended than in cadoxen. This work provided a novel, simple, and nonpollution solvent system that can be used to investigate the dilute solution properties and molecular weight of cellulose. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 347–353, 2004     

Dissolution and regeneration of cellulose in NaOH/thiourea aqueous solution

A novel cellulose solvent, 1.5 M NaOH/0.65 M thiourea aqueous solution, was used to dissolve cotton linters having a molecular weight of 10.1 × 10⁴ to prepare cellulose solution. Regenerated cellulose (RC) films were obtained from the cellulose solution by coagulating with sulfuric acid (H₂SO₄) aqueous solution with a concentration from 2 to 30 wt %. Solubility of cellulose, structure, and mechanical properties of the RC films were examined by infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, ¹³C NMR, and tensile tests. ¹³C NMR analysis indicated that the novel solvent of cellulose is a nonderivative aqueous solution system. The presence of thiourea enhanced significantly the solubility of cellulose in NaOH aqueous solution and reduced the formation of cellulose gel; as a result, thiourea prevented the association between cellulose molecules, leading to the solvation of cellulose. The RC film obtained by coagulating with 5 wt % H₂SO₄ aqueous solution for 5 min exhibited higher mechanical properties than that with other H₂SO₄ concentrations and a homogenous porous structure with a mean pore size of 186 nm for free surface in the wet state. The RC film plasticized with 10% glycerin for 5 min had a tensile strength of 107 MPa and breaking elongation of 10%, and about 1% glycerin in the RC film plays an important role in the enhancement of the mechanical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1521–1529, 2002     

Effects of temperature and molecular weight on dissolution of cellulose in NaOH/urea aqueous solution

Dissolution of cellulose having different viscosity-average molecular weight (M _η ) in 7 wt%NaOH/12 wt%urea aqueous solution at temperature from 60 to −12.6°C was investigated with optical microscope, viscosity measurements and wide X-ray diffraction (WXRD). The solubility (S_a) of cellulose in NaOH/urea aqueous solution strongly depended on the temperature, and molecular weight. Their S_a values increased with a decrease in temperature, and cellulose having M _η below 10.0 × 10⁴ could be dissolved completely in NaOH/urea aqueous solution pre-cooled to −12.6°C. The activation energy of dissolution (E_a,s) of the cellulose dissolution was a negative value, suggesting that the cellulose solution state had lower enthalpy than the solid cellulose. The cellulose concentration in this system increased with a decrease of M _η to achieve about 8 wt% for M _η of 3.1 × 10⁴. Moreover, cellulose having 12.7 × 10⁴ could be dissolved completely in the solvent pre-cooled to −12.6°C as its crystallinity (χ _c) decreased from 0.62 to 0.53. We could improve the solubility of cellulose in NaOH/urea aqueous system by changing M _η , χ _c and temperature. In addition, the zero-shear viscosity (η ₀ ) at 0°C for the 4 wt% cellulose solution increased rapidly with an increase of M _η , as a result of the enhancement of the aggregation and entanglement for the relatively long chains.     

Hydrogen-bond-induced inclusion complex in aqueous cellulose/LiOH/urea solution at low temperature.

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.     

Rapid dissolution of cellulose in LiOH/urea and NaOH/urea aqueous solutions

Rapid dissolution of cellulose in LiOH/urea and NaOH/urea aqueous solutions was studied systematically. The dissolution behavior and solubility of cellulose were evaluated by using (13)C NMR, optical microscopy, wide-angle X-ray diffraction (WAXD), FT-IR spectroscopy, DSC, and viscometry. The experiment results revealed that cellulose having viscosity-average molecular weight ((overline) M eta) of 11.4 x 104 and 37.2 x 104 could be dissolved, respectively, in 7% NaOH/12% urea and 4.2% LiOH/12% urea aqueous solutions pre-cooled to -10 degrees C within 2 min, whereas all of them could not be dissolved in KOH/urea aqueous solution. The dissolution power of the solvent systems was in the order of LiOH/urea > NaOH/urea > KOH/urea aqueous solution. The results from DSC and (13)C NMR indicated that LiOH/urea and NaOH/urea aqueous solutions as non-derivatizing solvents broke the intra- and inter-molecular hydrogen bonding of cellulose and prevented the approach toward each other of the cellulose molecules, leading to the good dispersion of cellulose to form an actual solution.     

Entanglement properties of cellulose and amylose in an ionic liquid

Concentrated solutions of cellulose and amylose were prepared with an ionic liquid 1‐butyl‐3‐methylimidazolium chloride (BmimCl), which was chosen as a good solvent for these polysaccharides. Dynamic viscoelasticity of the concentrated solutions was examined to obtain the molecular weight between entanglements, M_e. The value of M_e in the molten state (M_e,melt), a material constant that reflecting the entanglement properties, was determined for cellulose and amylose by extrapolating M_e to the “melt.” A marked difference in M_e,melt was found: 3.2 × 10³ for cellulose and 2.5 × 10⁴ for amylose. The value of M_e,melt for cellulose, which is composed of β‐(1,4) bonding of D ‐glucose units, is very close to those for polysaccharides with a random‐coil conformation such as agarose and gellan in BmimCl. The much larger M_e,melt for amylose can be attributed to the helical nature of the amylose chain, α‐(1,4)‐linked D ‐glucose units. The effect of concentration on the zero‐shear viscosity for the solutions of cellulose and amylose was also examined. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Rheological properties of poly(lactides). Effect of molecular weight and temperature on the viscoelasticity of poly(l‐lactic acid)

The dynamic viscoelastic behavior of Poly(l‐lactic acid) (PLLA), with molecular weights ranging from 2,000 to 360,000, have been studied over a broad range of reduced frequencies (approximately 1 × 10⁻³ s⁻¹ to 1 × 10³ s⁻¹), using time–temperature superposition principle. Melts are shown to have a critical molecular weight, M_c, of approximately 16,000 g/mol, and an entanglement density of 0.16 mmol/cm³ (at 25°C). PLLA polymers are noted to require substantially larger molecular weights in order to display similar melt viscoelastic behavior, at a given temperature, as that for conventional non‐biodegradable polymers such as polystyrene. The reason for this deviation is suspected to be due to steric hindrance, resulting from excessive coil expansion or other tertiary chain interactions. PLLA melts show a dependence of η₀ on chain length to the 4.0 power (M), whilst J is independent of M_W in the terminal region. Low molecular weight PLLA (∼ 40,000) shows Newtonian‐like behavior at shear rates typical of those achieved during film extrusion. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1803–1814, 1999     

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

A water‐soluble sample (TM4b), extracted from sclerotia of Pleurotus tuberregium, was analyzed using elemental analysis, one‐ and two‐dimensional ¹H and ¹³C 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 (〈S²〉) on weight–average molecular weight (M_w) for TM4b in the M_w range from 1.89 × 10⁴ to 2.58 × 10⁶ were found to be [η] = 0.21M and 〈S²〉 = 3.63M. 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. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2546–2554, 2007     

Effects of molecular weight of nitrocellulose on structure and properties of polyurethane/nitrocellulose IPNs

Semi‐interpenetrating polymer network (semi‐IPN) coatings were prepared by using castor oil‐based polyurethane (PU) and nitrocellulose (NC) with various viscosity‐average molecular weights (M_η) from 6 × 10⁴ to 42 × 10⁴, and coated on a regenerated cellulose (RC) film to obtain water‐resistant film. The PU/NC coatings and coated films, which were cured at 80°C for 5 min and 2 min, respectively, were investigated by infrared (IR) and ultraviolet (UV) spectroscopy, X‐ray diffraction, swelling test, strength test, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The results show that the crosslink densities of the PU/NC semi‐IPNs were smaller than that of pure PU, and decreased with the decrease of M_η of nitrocellulose (NC M_η), indicating NC molecules cohered intimately with PU, and hindered the PU network formation. The physical and mechanical properties of the films coated with PU/NC coatings were significantly improved. With the increase of NC M_η, the strength and thermal stability of the coated films increased, but the pliability, water resistivity, and optical transmission decreased slowly. The PU/NC coating with low NC M_η more readily penetrated into the RC film, and reacted with cellulose, resulting in a strong interfacial bonding and dense surface caused by intimate blend of PU/NC in the coated films. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1623–1631, 1999     

Rheological Behaviors in the Regimes from Dilute to Concentrated in Cellulose Solutions Dissolved at Low Temperature

Cellulose was dissolved rapidly in 9.5 wt.‐% NaOH/4.5 wt.‐% thiourea aqueous solution pre‐cooled to ?5 °C to prepare cellulose solution with different concentrations. The rheological properties of the cellulose solutions in wide concentration regimes from dilute (0.008 wt.‐%) to concentrated (4.0 wt.‐%) at 25 °C were investigated. On the basis of data from the steady‐shear flow test, the critical overlap (c*), the entanglement (c_e) and the gel (c_g) concentrations of the cellulose solution at 25 °C were determined, respectively, to be 0.10 wt.‐%, 0.53 wt.‐% and 2.50 wt.‐%, in accordance with the results of storage modulus (G′) versus c by dynamic test. Moreover, the Cox‐Merz deviation at relatively low concentrations was in good agreement with the micro‐gel particles in dilute regime. As the cellulose concentration increased, a homogeneous 3‐dimensional network formed in the cellulose solution in the concentrated regime, and further increasing of the concentration led to micro‐phase separation as determined by the time‐temperature superposition (tTS). So far, this complex cellulose solution has been successfully described by the concentration regime theory for the first time, and the relatively molecular morphologies in each regime have been determined, providing useful information for the applications of the cellulose solution systems.

     

Synthesis of O‐(2,3‐dihydroxypropyl) cellulose in NaOH/urea aqueous solution: As a precursor for introducing “necklace‐like” structure

O‐(2,3‐dihydroxypropyl) cellulose (DHPC) samples were synthesized by etherification of cellulose with glycidol (GLY) in a NaOH/urea aqueous solution system under different reaction conditions, so that they had different degrees of ether substitution (DS) in both the overall and regional distributions. The characterization was made by NMR spectroscopy in order to clarify the effects of the molar ratio of in‐fed GLY to anhydroglucose unit and of the reaction temperature not only on the total and regional DSs but also on the molar substitution (MS_dhp) for the multireactive dihydroxypropyl group. The evaluation of MS_dhp was performed after complete propionylation of each DHPC sample. Determination of molecular weights was also conducted on the propionylated DHPCs by GPC analysis. As a preliminary extension, butyralization of DHPC was undertaken in aqueous solution by using p‐toluenesulfonic acid as catalyst together with butyraldehyde (BuA). Two‐dimensional NMR (¹H–¹³C gHSQC) spectra measurements revealed that the products contained butyral groups, owing to dehydration‐cyclization between the BuA‐carbonyl and the duplicate hydroxyls in the side chain of DHPC. Such butyral derivatives of cellulose are expected to be a promising functional material parallel or superior to poly(vinyl butyral) available for safety glass interlayers, etc. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3590–3597     

Dynamic light scattering studies of atactic and syndiotactic poly(methyl methacrylate)s in dilute theta solution

The present article considers the coil‐to‐globule transition behavior of atactic and syndiotactic poly(methyl methacrylates), (PMMA) in their theta solvent, n‐butyl chloride (nBuCl). Changes in Rh in these polymers with temperature in dilute theta solutions were investigated by dynamic light scattering. The hydrodynamic size of atactic PMMA (a‐PMMA‐1) in nBuCl (M_w: 2.55 × 10⁶ g/mol) decreases to 61% of that in the unperturbed state at 13.0°C. Atactic PMMA (a‐PMMA‐2) with higher molecular weight (M_w: 3.3 × 10⁶ g/mol) shows higher contraction in the same theta solvent (α_η = R_h(T)/R_h (θ) = 0.44) at a lower temperature, 7.25°C. Although syndiotactic PMMA (s‐PMMA) has lower molecular weight than that of atactic samples (M_w: 1.2 × 10⁶), a comparable chain collapse was observed (α_η = 0.63) at 9.0°C. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2253–2260, 1999     

Dilute solutions of poly(vinyl alcohol) derived from vinyl trifluoroacetate

The dilute-solution behavior of poly(vinyl alcohol) (PVA_VTFA), derived from vinyl trifluoroacetate, in water-dimethylsulfoxide (DMSO) mixtures was investigated. With solvent mixtures ranging from 10 to 20 vol % DMSO, the relation between the reduced viscosity η_sp/C and the polymer concentration C was linear for polymer concentrations above 0.2 g/dL, whereas in solutions in mixed solvents of other compositions the dependence was linear for polymer concentrations above 0.1 g/dL. The relation between the intrinsic viscosity [η] obtained for aqueous solutions of PVA_VTFA and the molecular weight M estimated from viscosity measurements in solutions of poly(vinyl acetate) (PVA_VTFA), obtained by acetylation of PVA_VTFA, was given by [η] = 7.34 × 10^?4 M^0.63. The value of [η] was greatest for the solvent mixture with 10 vol % DMSO and smallest for about 50 vol % DMSO, and Huggins constants k were smallest and greatest for these two cases, respectively. The turbidity of the solutions of low-molecular-weight PVA_VTFA, was higher than that of high-molecular-weight PVA_VTFA up to 30 vol % DMSO, and the reverse relation held for 40-70 vol % DMSO.     

Rapid dissolution of spruce cellulose in H<Subscript>2</Subscript>SO<Subscript>4</Subscript> aqueous solution at low temperature

Dissolution of cellulose is the key challenge in its applications. It has been discovered that spruce cellulose with high molecular weight (4.10 × 10⁵ g mol^?1) can be dissolved in 64 wt% H₂SO₄ aqueous solution at low temperature within 2 min, and the cellulose concentration in solution can reach as high as 5 % (w/v). FT-IR spectra and XRD spectra proved that it is a direct solvent for cellulose rather than a derivative aqueous solution system. The cold H₂SO₄ aqueous solution broke the hydrogen bonds among cellulose molecules and the low temperature dramatically slowed down the hydrolysis, which led to the dissolution of cellulose. The resultant cellulose solution was relatively stable, and the molecular weight of cellulose only slightly decreased after storage at ?20 °C for 1 h. Due to the high molecular weight of cellulose, cellulose solution could form regenerated films with good mechanical properties and transparency at low concentration (2 % w/v). This work has not only provided the new evidence of cellulose dissolution which facilitated the development of cellulose solvent, but also suggested a convenient way to directly transfer cellulose with high molecular weight into materials without structure modifications.     

Ionic interaction behavior and facilitated olefin transport in poly(n‐vinyl pyrrolidone):Silver triflate electrolytes; Effect of molecular weight

Interactions of cation/anion and cation/polymer in poly(N‐vinyl pyrrolidone) (PVP):silver triflate (AgCF₃SO₃) electrolytes with different weight‐average molecular weights (M_w's) of 1 × 10⁶ (1 M), 3.6 × 10⁵ (360 K), 4 × 10⁴ (40 K), and 1 × 10⁴ (10 K) have been studied with IR and Raman spectroscopies. According to the change of the C?O peak, coordination of silver ions by C?O in a low M_w (10 or 40 K) PVP matrix tend to be always thermodynamically favorable than high M_w (1 M or 360 K) PVP, demonstrating that the polymer matrix of low M_w dissolves silver salts more effectively. In addition, silver cations interact with both larger SO and smaller CF₃ to form ion pairs, and the former interaction is stronger than the latter in a monomer or low M_w polymer matrix (40 K, 10 K), as demonstrated by theoretical ab initio calculation or experimental spectroscopy, respectively. However, CF₃ interacts more favorably with silver cation than SO in high M_w (1 M and 360 K) PVP, which is ascribed to the steric effect of the bulky SO anion by highly entangled polymer chains. Despite the superior dissolving property of the low M_w polymer matrix, the membranes consisting of low M_w PVP and AgCF₃SO₃ exhibited poor separation performance for propylene/propane mixtures in comparison with those of high M_w, presumably because of the poor mechanical property for membrane formation in low M_w PVP. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1813–1820, 2002     

Relaxation dynamics of salt‐free polyelectrolyte solutions using flow birefringence and rheometry

Relaxation dynamics of salt‐free, aqueous solutions of sodium poly(styrene sulfonate) (NaPSS) were investigated by mechanical rheometry and flow birefringence measurements. Two semidilute concentration regimes were studied in detail for a range of polymer molecular weights. At solution concentrations c < 10 mg mL, limiting shear viscosity η₀ was found to scale with molecular weight and concentration as η₀ ∼ c^0.5M_w over nearly two decades in concentration. At higher solution concentrations, c > 10 mg mL, a change in viscosity scaling was observed η₀ ∼ c^1.5M, consistent with a change from simple Rouse dynamics for unentangled polyions to near‐perfect reptation dynamics for entangled chains. Characteristic relaxation times τ deduced from shear stress and birefringence relaxation measurements following start‐up of steady shearing at high rates reveal very different physics. For c < 10 mg mL, both methods yield τ ∼ c^−0.42M and τ ∼ c⁰M for c > 10 mg mL. Curiously, the concentration scalings seen in both regimes are consistent with theoretical expectations for salt‐free polyelectrolyte solutions undergoing Rouse and reptation dynamics, respectively, but the molecular weight scalings are not. Based on earlier light scattering studies using salt‐free NaPSS solutions, we contend that the unusual relaxation behavior is likely due to aggregation and/or coupled polyion diffusion. Simultaneous stress and birefringence measurements suggest that in concentrated solution, NaPSS aggregates are likely well permeated by solvent, supporting a loose collective of aggregated chains rather than the dense polymer aggregates previously supposed. Nonetheless, polyion aggregates of either variety cannot account for the inverse dependence of relaxation time on polymer molecular weight for c < 10 mg mL. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 825–835, 1999     

Synthesis and characterization of a poly(N‐isopropylacrylamide) with β‐cyclodextrin as pendant groups

A novel linear poly(N‐isopropylacrylamide) (PNIPA) with β‐cylodextrin (β‐CD) moiety (PNIPA‐β‐CD) was synthesized by the conjugation of β‐CD carrying amino groups (EDA‐β‐CD) onto PNIPA with epoxy groups (P(NIPA‐co‐GMA), M_n = 3.86 × 10⁴), and the related reaction conditions are investigated. PNIPA‐β‐CD was characterized by means of IR, NMR and UV spectroscopes, element analysis, and differential scanning calorimetry (DSC). The number‐average molecular weight (M_n) and the β‐CD content of the obtained PNIPA‐β‐CD are 4.87 × 10⁴ and 18.8 wt %, respectively. PNIPA‐β‐CD can not only respond to temperature stimuli but also include guest molecules. Lower critical solution temperature (LCST) of aqueous PNIPA‐β‐CD solution is similar to that of PNIPA. The association constant (K_a) for PNIPA‐β‐CD with methyl orange (MO) is 2.4 × 10³ L mol^?1 at pH 1.4, which is comparable to that of EDA‐β‐CD (K_a = 2.9 × 10³ L mol^?1). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3516–3524, 2005     

Solution characterization of the novel organometallic polymer poly(ferrocenyldimethylsilane)

A series of four well‐defined poly(ferrocenyldimethylsilane) (PFS) samples spanning a molecular weight range of approximately 10,000–100,000 g mol⁻¹ was synthesized by the living anionic polymerization of dimethyl[1]silaferrocenophane initiated with n‐BuLi. The polymers possessed narrow polydispersities and were used to characterize the solution behavior of PFS in tetrahydrofuran (THF). The weight‐average molecular weights (M_w ) of the polymers were determined by low‐angle laser light scattering (LALLS), conventional gel permeation chromatography (GPC), and GPC equipped with a triple detector (refractive index, light scattering, and viscosity). The molecular weight calculated by conventional GPC, with polystyrene standards, underestimated the true value in comparison with LALLS and GPC with the triple detection system. The Mark–Houwink parameter a for PFS in THF was 0.62 (k = 2.5 × 10⁻⁴), which is indicative of fairly marginal polymer–solvent interactions. The scaling exponent between the radius of gyration and M_w was 0.54, also consistent with marginal polymer–solvent interactions for PFS in THF. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3032–3041, 2000     

Third virial coefficient of polystyrene in benzene

Second virial coefficients A₂ and third virial coefficients A₃ for benzene solutions of ten polystyrene fractions ranging in weight-average molecular weight M_w from 10⁴ to 2 × 10⁷ at 25°C were determined by light scattering. The third coefficient is represented approximately by A₃ = 8.0 × 10^?6 M mol g^?3 cm⁶ for M_w above 10⁵. In this molecular weight region, the factor g defined by A₃/AM_w/ This trend of g is consistent with predictions of early two-parameter theories but not with those of renormalization group theories. In particular, quantitative agreement is observed between the present experiments (for M_w ? 2 × 10⁵) and the mean-field two-parameter theory of Stockmayer and Casassa.     

Structure and properties of blend membranes prepared from cellulose and alginate in NaOH/urea aqueous solution

Regenerated cellulose (RC)/alginic acid (AL) blend membranes were satisfactorily prepared from 6 wt % NaOH/4 wt % urea aqueous solution by coagulating with 5 wt % CaCl₂ aqueous solution, and then treated with 3 wt % HCl. Morphology, crystallinity, mechanical properties, and thermal stability of the membranes were investigated by scanning electron microscopy (SEM), IR and UV spectroscopes, X‐ray diffraction, tensile tests, and thermogravimetric analysis (TGA). The RC/AL blends were miscible in all weight ratios of cellulose to alginate. The membranes have homogeneous mesh structures, and the mesh sizes of the blend membranes (200–2000 nm) significantly increased with increasing alginate content. The crystalline state of the AL membrane prepared from 6 wt % NaOH/4 wt % urea aqueous solution was broken completely, and the crystallinity of the blend membranes decreased with an increase of AL. Comparing with AL membranes, the tensile strength and breaking elongation of the blend membranes were obviously improved in dry and wet states. Therefore, the RC/AL blends offer a promising way of alginate as separate and functional materials used in the wet state. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 451–458, 2001