Dimensional stability of regenerated cellulose film in relation to orientations of crystalline and noncrystalline phases

The dimensional stability of regenerated cellulose film on swelling with water is discussed in relation to the biaxial orientation of the two kinds of structural units, cellulose II crystallites and noncrystalline chain segments, and their anisotropic swelling (anisotropic absorption of water). Considerable dimensional stability in the plane of the film but enormous instability of thickness on swelling in water of some commercial cellophanes is qualitatively interpreted in terms of the planar orientation of crystal (101) planes along the film surface and the orientation of the noncrystalline chain segments parallel to the film surface. The dimensional changes on swelling from the completely dry state to 10% moisture regain were further interpreted quantitatively in terms of the degrees of biaxial orientation of the two kinds of structural units and their degrees of anisotropic swelling by modifying the Hermans monophase model for crystalline and noncrystalline biphase structures. The following degrees of anisotropic swelling of the structural units were thus obtained: q_{c, [101]} = 0.40%, q_{c, [101 ]} = ?0.33%, and q_a = 2.42%.     

Dynamic study of the noncrystalline phase of 13C-labeled polyethylene by variable-temperature 13C CP/MAS NMR spectroscopy

The ¹³C spin-lattice relaxation times T₁ of ¹³C-labeled polyethylene crystallized under different conditions were measured at temperatures from ?120 to 44°C by variable-temperature solid-state high-resolution ¹³C nuclear magnetic resonance (NMR) spectroscopy, in order to determine accurately the dynamics of the noncrystalline region of the polymer. From these results, it was found that the T₁ minimum for the CH₂ carbons in the noncrystalline region of solution-crystallized polyethylene with high crystallinity appears at higher temperature by about 20°C than that of melt-quenched polyethylene with low crystallinity. This means that the molecular motion of the CH₂ carbons in the noncrystalline regions is more constrained at a given temperature in the material of higher crystallinity. Furthermore, dynamics of the noncrystalline region is discussed in terms of the ¹³C dipolar dephasing times.     

Rheo-optical studies on the deformation mechanism of semicrystalline polymers. XIV. Alpha and beta mechanical dispersions of spherulitic high-density polyethylene and the dynamic orientation distribution function of crystallites

The dynamic tensile deformation mechanism of spherulitic high-density polyethylene was investigated by dynamic x-ray diffraction at various temperatures and frequencies in order to assign the α and β mechanical dispersions explicity. The uniaxial orientation distribution function q(ζ_j,0) of the jth crystal plane and its dynamic response Δq′_j(ζ_j,0) in phase with dynamic strain were observed for the (110), (200), (210) and (020) crystal planes. Then the orientation distribution function w(ζ,0,η) of crystallites (crystal grains) and its dynamic response Δw′(ζ,0,η), also in phase with the dynamic strain, were determined by a mathematical transformation procedure proposed by Roe and Krigbaum on the basis of the Legendre addition theorem. The temperature and frequency dependences of w′(ζ,0,η) were analyzed in terms of the model parameters for dynamic spherulite deformation combining affine orientation of crystal lamellae with several types of preferential reorientation of the crystal grains within the orienting lamellae. The following assignments are made: (i) The α mechanical dispersion must be assigned to the dynamic orientation dispersion of crystal grains within the crystal lamellae, involving two types of preferential rotations of the grains about their own crystal b and a axes. The rotation about the b axis is associated with lamellar detwisting, mostly in the equatorial zone of uniaxially deformed spherulites; the rotation about the a axis is associated with intralamellar shearing, mostly in the polar zone of the spherulites. Thus both rotations are intralamellar grain-boundary phenomena. (ii) The β mechanical dispersion must be assigned to the dynamic orientation dispersion of the crystal lamellae behaving as rigid bodies. It is not accompanied by reorientation of the crystal grains, but is associated with orientation dispersion of noncrystalline material between the lamellae. Thus it is an interlamellar grain-boundary phenomena.     

Quantitative structural characterization of the melting behavior of isotactic polypropylene

The melting behavior of restrained isotactic polypropylene fibers is examined quantitatively in terms of the influence the anisotropic structural state of the polymer has on the observed properties. Two endotherm peaks are observed to occur in some of the samples. The formation and location of the multiple peaks are determined by the orientation of the noncrystalline chains, and is independent of the fabrication path used to achieve that orientation. Above a certain minimum orientation of the noncrystalline chains, multiple endotherm peak formation occurs. The high-temperature endotherm (T_2M) extrapolates to an ultimate melting point for fully oriented noncrystalline chains of 220°C, while the lower-temperature endotherm (T_1M) extrapolates to an ultimate melting point of 185°C. Noncrystalline chain orientation influences the endotherm temperature through its changing configurational entropy. It is shown quantitatively that the noncrystalline polymer must be considered as plastically deformed, since rubber elasticity theory is not followed as predicted. The melting behavior of isothermally crystallized samples are also reported to further elucidate the nature of the observed endotherms.     

Infrared studies of drawn polyethylene. II. Orientation behavior of highly drawn linear and ethyl-branched polyethylene

Infrared dichroism is employed to study the orientation of chain molecules in linear and ethyl-branched polyethylene in the crystalline and noncrystalline regions during drawing and subsequent annealing. A crystalline (1894 cm^?1) and a noncrystalline (1368 cm^?1) band, as well as the bands at 909 cm^?1 and 1375 cm^?1 resulting from vinyl endgroups and methyl endgroups and sidegroups, are studied. For these bands relative orientation functions are derived and compared as a function of draw ratio and annealing temperature. It is shown that the relative orientation functions as derived from the dichroism of the noncrystalline, vinyl and methyl bands follow the same curve while the orientation function for the crystalline bands does not. These results support a two-phase model for partially crystalline polyethylene and additionally favor segregation of the endgroups and sidegroups in the noncrystalline component during crystallization. It is further shown that shrinkage occurs at the temperature at which the noncrystalline chain molecules start to disorient. From the dichroism of the methyl groups in ethyl-branched polyethylene, a value for the mean orientation of the noncrystalline chain molecules is calculated. We obtain for the orientation function of the noncrystalline regions at highest draw ratios (λ = 15–20), f = 0.35–0.57, while the chain molecules in the crystallites are nearly perfectly oriented (f ≈ 1.0). On the assumption that the noncrystalline component consists of folds, tie molecules, and chain ends, the different contributions of these components to the overall orientation are estimated. From these the relative number of CH₂ groups incorporated into folds, tie molecules, and cilia can be derived. Further, on the basis of a simple structural model, the relative number of chains on the crystal surface contributing to the different noncrystalline components and their average length are estimated.     

High-resolution solid-state 13C NMR study of ethylcellulose films

Ethylcellulose films cast from concentrated solutions of chloroform, benzene, and carbon tetrachloride were subjected to the NMR relaxation measurements including ¹H spin-lattice relaxation time (T_1H), rotating-frame ¹H spin-lattice relaxation time (T_1ρH), and ¹³C spin-lattice relaxation time (T_1C). The values of T_1ρH for carbons in the glucose units of ethyl-cellulose were of the same order of magnitude as those reported for the crystalline and noncrystalline regions of ramie cellulose. The values of T_1C for unsubstituted C2, C3 carbons were smaller than those for the corresponding carbons in the noncrystalline region of native celluloses. The T_1C values for unsubstituted C2, C3, and substituted C6 carbons showed a small but definite dependence on the solvent from which the films were cast. © 1993 John Wiley & Sons, Inc.     

CP/MAS 13C NMR analyses of hydrogen bonding and the chain conformation in the crystalline and noncrystalline regions for poly(vinyl alcohol) films

The chain conformation and hydrogen bonding in the crystalline and noncrystalline regions have been characterized for atactic poly(vinyl alcohol) (PVA) films prepared under different conditions by CP/MAS ¹³C NMR analyses developed recently. The CH resonance lines of the crystalline and noncrystalline components split in different ways, depending significantly on casting solvents and annealing. These lines are found to be successfully resolved into 3–7 constituent lines by the least‐squares curve fitting. In this analysis, nine lines with different chemical shifts are prepared as elementary lines for the curve fitting by assuming the upfield shifts due to the γ‐gauche effect and the downfield shifts due to the formation of the intramolecular hydrogen bonds. The integrated intensities of the constituent lines thus obtained are also interpreted in terms of statistical calculations, assuming the random distribution of the trans and gauche conformations along PVA chains and the statistical distribution of the intramolecular and intermolecular hydrogen bonds between appropriate adjacent OH groups. On the basis of probabilities f_t and f_a for the trans conformation and the intramolecular hydrogen bond obtained through these analyses, the effects of casting solvents and annealing are discussed for both crystalline and noncrystalline components. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1–9, 2000     

Structure and crystallization of sub-elementary fibrils of bacterial cellulose isolated by using a fluorescent brightening agent

The structure and crystallization of carefully isolated sub-elementary fibrils (SEFs) of bacterial cellulose have been investigated using TEM, WAXD, and high-resolution solid-state ¹³C NMR. The addition of a suitable amount of fluorescent brightener (FB) to the incubation medium of Acetobacter xylinum effectively suppressed the aggregation of the SEFs into the microfibrils, as previously reported. However, this study confirmed for the first time that serious structural change in the SEFs occurs during the removal of excess FB by washing with buffer solutions having pH values higher than 6 or with the alkaline aqueous solution that was frequently used in previous studies. In contrast, the isolation of unmodified SEFs was successfully performed by utilizing a washing protocol employing pH 7 citrate–phosphate buffer solution containing 1% sodium dodecyl sulfate. High-resolution solid-state ¹³C NMR and WAXD measurements revealed that the SEFs thus isolated are in the noncrystalline state in which the pyranose rings of the almost parallel cellulose chains appear to be stacked on each other. The respective CH₂OH groups of the SEFs adopt the gt conformation instead of the tg conformation found in cellulose I _α and I _β crystals, and undergo significantly enhanced molecular motion in the absence of intermolecular hydrogen bonding associated with these groups. The main chains are also subject to rapid motional fluctuations while maintaining the parallel orientation of the respective chains, indicating that the SEFs have a liquid crystal-like structure with high molecular mobility. Moreover, the SEFs crystallize into cellulose I _β when the FB molecules that may adhere to the surface of the SEFs are removed by extraction with boiling 70 v/v% ethanol and 0.1N NaOH aqueous solution. On the basis of these results, the crystallization of the SEFs into the I _α and I _β forms is discussed, including the possible formation of the crystalline-noncrystalline periodic structure in native cellulose.     

General description of optical dichroic orientation factors for relating optical anisotropy of bulk polymer to orientation of structural units

The relationship between the optical anisotropy of high polymeric materials in bulk and the orientation of structural units within the materials was described in general by using several types of mean values of the orientation distribution function of three Eulerian angles, i.e., the orientation factors, under some assumptions about the symmetry of the function being applicable for the most of the industrial products. A newly defined biaxial orientation factor, F_θηⁱ = 〈sin² θ_j cos 2η_j〉, where θ_j and η_j are the polar and azimuthal angles of the jth axis within the structural unit with respect to the bulk axes, may relate the biaxial orientation of the structural units to the dichroic orientation factors, which are measurable optical anisotropic indices of the bulk materials. Some applications of the results to the birefringence and infrared and dye dichroism are also discussed.     

Approximate solution of the autocatalytic hydrolysis of cellulose

Depolymerization of cellulose in homogeneous acidic medium is analyzed on the basis of autocatalytic model of hydrolysis with a positive feedback of acid production from the degraded biopolymer. The normalized number of scissions per cellulose chain, S(t)/n° = 1 − C(t)/C₀, follows a sigmoid behavior with reaction time t, and the cellulose concentration C(t) decreases exponentially with a linear and cubic time dependence, C(t) = C₀exp[−at − bt ³], where a and b are model parameters easier determined from data analysis.     

Structure of native and regenerated cellulose as revealed by proton NMR analysis

Differences in fiber structure between cotton and cuprammonium rayon are studied by a refined broad-line proton NMR analysis of samples swollen with deuterated dimethyl sulfoxide, which has no effect on the spectra but enhances differences in molecular mobility between crystalline and noncrystalline regions. The spectra obtained are decomposed into four components: broad, medium, narrow, and extremely narrow. These components are identified as contributions, respectively, from crystalline and rigid noncrystalline (frozen glassy) material, a noncrystalline glassy component exhibiting local segmental motion, a noncrystalline rubbery component exhibiting liquidlike molecular motion, and protons included in DMSO-d₆ as an impurity. The mass fraction of the narrow component in cotton was about 0.01, whereas it was as high as 0.18 in cuprammonium rayon. It is concluded that even in the swollen state, native cellulose is devoid of a liquidlike mobile component, but regenerated cellulose contains a considerable amount of a noncrystalline component involving liquidlike segmental motion of molecules.     

Component analysis of proton NMR spectra of linear polyethylene in the α-transition temperature range and phase distribution

Broad-line ¹H NMR spectra of linear polyethylene at temperatures in the α-transition range can be analyzed in terms of contributions from the crystalline and noncrystalline components provided molecular motion in the crystalline region is adequately considered. The spectrum of solid n-C₃₂H₆₆ or n-C₄₄H₉₀ prior to melting is used to take account of the contribution of the crystalline region of the polymer to molecular motions. The temperature dependence of the component distribution in the polymer is briefly discussed for a wide range of temperatures, together with previously reported results at low temperatures. The noncrystalline component is in a rigid glassy state at very low temperatures but with rising temperature it transforms to a mobile glassy state with restricted molecular motion, and transforms partially to the rubbery state at high temperature. The crystalline component remains rigid at low temperature, but some molecular motion is associated with it at higher temperatures in the α-transition range.     

Preferential uniplanar orientation mechanism of the (101) crystal plane of regenerated cellulose

The molecular orientation behavior of regenerated cellulose, in both crystalline and noncrystalline phases, was investigated quantitatively under various conditions during coagulation-regeneration from viscose solution and during drying of the resulting gel film. It was concluded that the stronger the tensions which arise parallel to the film surface during coagulation-regeneration and drying of the gel film, the more prominent become the uniplanar orientation of the (101) crystal plane and planar orientations of the crystal b axis and noncrystalline chain segments, all parallel to the film surface and associated with considerable distortion and disintegration of the regenerated crystal. This conclusion suggests an orientation mechanism of the cellulose II crystal, namely, rotation of the crystal around the U_{(101 )} axis associated with slippage of the (101) crystal plane, the most highly hydrated and most readily dislocated plane, in the direction of the tension, which is also parallel to the surface of the film. The behavior of this type of uniplanar orientation of the (101) crystal plane is characterized semiquantitatively by comparing observed distributions of the orientation of crystallographic axes with those calculated on the basis of a relatively simple model for crystal orientation.     

Excluded volume study of a sulfonate-containing polyelectrolyte in salt solutions

Chain characteristics of a linear sulfonate-containing homopolymer, sodium poly(3-methacryloyloxypropane-1-sulfonate), in aqueous salt solutions (ionic strength, C_s = 0.01N to 5N NaCl) have been investigated by light scattering and intrinsic viscosity. The molecular weight (M?_w)–viscosity relation can be well described by the Mark–Houwink and the Stockmayer–Fixman equations. The coil is highly expanded even in the most concentrated NaCl solution (6N), and no 1:1 electrolyte was found to precipitate this polymer. A linear relation was observed between the viscosity expansion factor, α^3η, and (M?_w/C_s)^1/2. Examination of the data in terms of theories for excluded volume and hydrodynamic interaction suggests that the coil experiences dominant hydrodynamic interaction, corresponding to a nondraining coil, and the second virial coefficient and coil expansion at high C^s can be correlated by the Flory–Krigbaum–Orofino equation. Results for this polymer are compared with those for other polyelectrolytes, and are discussed in terms of chain structure, flexibility, and hydrophobicity.     

The Radical Anions of N,N′-Dicyanoquinone Diimines,a New Class of Electron Acceptors

The radical anions of 12 N,N′-dicyanoquinone diimines, a new class of electron acceptors, hace been characterized by their hyperfine data with the use of ESR and ENDOR spectroscopy. The largest coupling constant (0.30–0.45 mT), due to the two ¹⁴N nuclei in the exocyclic positions, gives rise to a conspicuous broadening of the peripheral ESR lines by an incomplete averaging of the hyperfine anisotropy. The most plausible interpretation of the experimental results for the radical anions of N,N′-dicyano- 1,4-benzoquinone diimine ( 1 ) and N,N′-Dicyano-9,10-anthraquinone diimine ( 9 ) is in terms of both ‘syn’- and ‘anti’-configurations contributing to the ESR and ENDOR spectra and having equal proton- and ¹⁴N-coupling constants. The π-spin distribution in the radical anions of N,N′-dicyanoquinone diimines is compared with those in the analogous ions of tetracyanoquinodimethanes and quinones.     

Integrity basis approach to the elastic free energy functional of liquid crystals

Using the method integrity basis, the most general SO(3)-invariant free energy density up to all powers in _xβ and up to second order in Q_xβ,y is established. The method provides all analytically independent elastic modes for nematics and cholesterics in the form of 33 so-called, irreducible invariants. Interestingly, among the irreducible invariants there are only three chiral terms (i.e. linear in Q_δ,β,y ). They give rise locally to three independent helix modes in chiral, biaxial liquid crystals. This conclusion generalizes results of Trebin and Govers and Vertogen and contradicts a statement of Pleiner and Brandt, according to which only one twist term is supposed to exist. The most general free energy expansion can be written as sum of 39 additive invariants, which are multiplied by arbitrary polynomials in TrQ² and TrQ³.     

Properties of cellulose acetate in solution. I. Light scattering,osmometry, and viscometry on dilute solutions

Light-scattering, osmotic pressure, and viscometric studies on fractions of cellulose acetate (degree of substitution 2.45) in three solvents are described. The data yield the dependence of the mean-square radius of gyration 〈s²〉, the second virial coefficient Γ₂, and the intrinsic viscosity [η] on molecular weight M and temperature. The results are interpreted to show that excluded volume effects on 〈s²〉 are negligible, even though Γ₂ is large and dΓ₂/dT is positive. The large experimental value of d In [η]/d In M is interpreted in terms of partial draining effects. Data on 〈s₂〉 and [η] for other cellulose esters in the literature are similarly interpreted. Significant aggregation found in solutions of cellulose acetate in many solvents is discussed.     

Multiaxial deformations of end‐linked poly(dimethylsiloxane) networks. III. Effect of entanglement density on strain‐energy density function

Strain‐energy density functions (W) of end‐linked polydimethylsiloxane (PDMS) networks with different entanglement densities were estimated as a function of the first and second invariants I₁ and I₂ of Green's deformation tensor on the basis of the quasi‐equilibrium biaxial stress‐strain data. Entanglement densities in the PDMS networks were controlled by varying the precursor PDMS concentration (?₀) in end‐linking. The deduced functional form of W [W = C₁₀(I₁ ? 3) + C₀₁(I₂ ? 3) + C₁₁(I₁ ? 3)(I₂ ? 3) + C₂₀(I₁ ? 3)² + C₀₂(I₂ ? 3)²] is independent of the degree of dilution at network preparation. The contribution of each term in I₁ and I₂ to total energy depends on whether the precursor PDMS solution before end‐linking belongs to the concentrated regime ?₀ > ?_c where many entanglement couplings of precursor chains exist or the moderately concentrated regime ?₀ < ?_c where pronounced entanglement couplings of precursor chains are absent. These results suggest that the rubber elasticity of the end‐linked networks is significantly influenced by the entangled state of precursor chains before end‐linking, and the extra terms in the estimated W that are absent in the prediction of the classical rubber elasticity theories [W = C (I₁ ? 3)] mainly originate from the effect of trapped entanglements. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2780–2790, 2002     

Solutions of cellulose in DMAc + LiCl: migration of the solute in an electrical field

For solutions of cellulose (Solucell, M_w=230 kg mol^–1) in the mixed solvent DMAc (N,N-dimethylacetamide) + LiCl, it is demonstrated by means of an electrolysis cell, subdivided into six compartments, that cellulose migrates to the anode. This observation is interpreted in terms of a field-induced opening of associations between the [DMAc]_xLi⁺ complex and the [cellulose]Cl^– complex. This understanding is corroborated by the observed changes in the positions of the menisci in the electrode compartments of the electrolysis cell. Contrary to expectations, the rate of cellulose transport does not depend on its molar mass, at least under the present conditions.