Cellulose Tricarbanilate Research Articles

Evaluation of Selected Cellulose Macromolecular Properties after Its Chemical Treatment Using Size Exclusion Chromatography.

This work evaluates the effect of using selected inorganic chemicals as the main components of waterborne wood preservative systems on the degradation of the cellulose constituent in wood from model samples. The polymeric properties of cellulose and the homogeneity of the degradation process primarily reflect very well the degree of cellulose deterioration. Whatman papers, as pure cellulose model samples, were impregnated with 10 different 5 wt% solutions of inorganic salts and distilled water and consequently subjected to wet-thermal accelerated aging (T = 85 °C, RH = 65%, for 30 days). The samples were then derivatized to cellulose tricarbanilates (CTCs) through two different procedures (by precipitation in a methanol-water mixture/by evaporation of pyridine from the reaction mixture) and finally analyzed using size exclusion chromatography (SEC). Chemically treated and aged cellulose samples showed different changes in the degree of polymerization (DP) and polydispersity (PD) in terms of untreated non-aged standard caused by different ongoing degradation reactions, such as dehydration, hydrolysis, oxidation, and crosslinking. In general, the lowest degradation rate after treatment by chemicals and after accelerated aging was observed in samples treated by borates, NaCl, and ZnSO4·7H2O. The greatest depolymerization after treatment and after accelerated aging was caused by sulphates containing NH4+, Cu2+, and Fe3+ cations, with aging by NH4Cl and (NH4)2HPO4-treated samples also leading to significant depolymerization. The higher DP values are linked to the precipitated method of CTC preparation, though not for chlorides and phosphates. PD is also generally higher in precipitated and aged samples and is heavily influenced by the presence of low molecular weight products. This paper brings new insights regarding the complex evaluation of the polymeric properties of degraded cellulose by considering all important factors affecting the sample and the analysis itself through the use of statistics. From the statistical point of view, the influences of all factors (solution, aging, method) and their interactions (except aging*method) on DP are statistically significant. The influence of the sample processing method used for analysis of the desired results becomes important mainly in practice. This work recommends the evaporation method for more accurate description of more degraded cellulose.

Evaluation of the dissolving ability of cellulosic pulps: investigation of a novel method using light scattering follow-up during classical cellulose carbanilation

Abstract The aim of the present study is to investigate the dissolving ability of a cellulosic substrate using a derivatization method, i.e. cellulose tricarbanilation and the follow-up by dynamic light scattering (DLS), for particle size measurement. The dissolving behavior of six commercial pulps, selected for their different nature and properties, were compared to the Fock test, and the analysis was completed by other methods for substrate characterization: crystallinity (XRD), DPv (in CuED), sugar analysis, molecular weight distribution (MWD) of cellulose by HPSEC-multidetectors (done on the cellulose tricarbanilates), and solubility in NaOH:urea:water. The proposed carbanilation/DLS method resulted practical and suitable for evaluating the dissolving ability of the different pulps – including hemicelluloses-containing kraft pulps – and allowed to discriminate the samples, contrary to the Fock test. Comparison and assessment of the relevance of the different methods are finally discussed.

Determination of Cellulose Degree of Polymerization in Historical Papers with High Lignin Content.

Determination of cellulose degree of polymerization (DP) is one of the most commonly used methods in paper degradation studies, performed either by a standardized method using viscometry (as average degree of polymerization (DPv)) or size-exclusion chromatography (SEC) (as weight average molecular mass (Mw)). Due to the insolubility of papers with high lignin content in cupriethylenediamine (CED), such as groundwood papers, viscometric determination is not possible; therefore, pretreatment is required to allow subsequent dissolution of the papers. In this study, the pretreatment of historical papers containing groundwood with sodium chlorite in acetic acid was investigated, which enables dissolution of the paper samples in CED and determination of the cellulose average degree of polymerization by viscometry (DPv). Kappa number was determined to estimate the lignin content in the papers. The suitability of SEC UV-VIS analysis for determination of Mw in papers with high lignin content had been verified before it was used as a comparative method for viscometry. Using SEC, changes in the weight average molecular mass (Mw) of cellulose tricarbanilate (CTC) derivative during delignification were evaluated. The results indicate that no significant depolymerization occurred in the selected samples under the studied delignification conditions, which was additionally confirmed with determination of monosaccharides by ion chromatography. The results of the Mw determinations by SEC and DPv by viscometry are in good correlation, justifying the use of viscometry after chlorite/acetic acid pretreatment to determine the cellulose average degree of polymerization in historical papers with high lignin content.

Towards determination of absolute molar mass of cellulose polymer by size exclusion chromatography with mulitple angle laser light scattering detection

The study focuses on determination of a set of crucial parameters for molar mass calculation of cellulose from the results of size exclusion chromatography coupled with multiple angle laser light scattering (MALLS) and differential refractive index (DRI) detectors. In the present work, cellulose has been derivatised to obtain cellulose tricarbanilate (CTC) soluble in tetrahydrofuran (THF). The parameters of Rayleigh scattering in the MALLS detector: refractive index increment (dn/dc) and second virial coefficient (A2) of CTC in THF were determined for laser wavelength 658nm. In order to avoid errors resulting from cellulose derivatisation by-products present in the CTC solution, the so called “on-line” method of measuring dn/dc and A2 was applied. Based on the A2 determination, its influence on cellulose molar mass calculations and cellulose molecular dimensions were critically assessed. The latter includes evaluation of artificially aged cellulose towards conceivable branching by conformation plot analysis.

SEC−MALS−QELS Study on the Molecular Conformation of Cellulose in LiCl/Amide Solutions

The SEC-MALS-QELS (size-exclusion chromatography equipped with multiangle light scattering and quasi-elastic light scattering detectors) method using lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) and LiCl/1,3-dimethyl-2-imidazolidinone (LiCl/DMI) as mobile phases was applied to cellulose and cellulose tricarbanilate (CTC) samples with various average degree of polymerization (DP) values. Molecular conformations of cellulose and CTC in the solvents were then discussed and compared on the basis of the relationships between the radii of gyration (R(g,z) or S(2)(z)(1/2)), the hydrodynamic radii (R(h,z)), and weight-average DP (DP(w)) or the contour lengths (L(w)). The Benoit-Doty theory for wormlike polymer chains was applied to the R(g) vs L(w) data obtained, and the theoretical curves with Kuhn segment lengths l(K) of around 18 nm were found to fit the data of both cellulose and CTC molecules in the solvents. It was concluded from the obtained results that both cellulose and CTC molecules have conformations essentially identical to each other in the solvents; they behave as typical semiflexible chains in good solvents.

Polymer‐Analogous Preparation of Cellulose Tricarbanilates: Mechanisms of Degradation in Dimethylsulfoxide

AbstractTwo cellulose samples were subject to treatment with phenylisocyanate (PhNCO), both in pyridine and in dimethylsulfoxide (DMSO). In each case, DMSO degraded cellulose in an extent depending on the derivatized cellulose. The formation of dimethylsulfonium ions was recognized as the cause leading to an oxidation of hydroxyl groups. This Pfitzner‐Moffatt type oxidation is dependent on carboxyl groups and therefore occurs most probably in their neighbourhood. It was deduced that formation of oxidised sections along the cellulose chains occurs containing either carbonyl and carboxyl groups in the same anhydroglucose unit (AGU) or singly oxidised AGUs in direct neighbourhood to each other. This leads to much facilitated eliminative degradation.

SANS studies of solutions and molecular composites prepared from cellulose tricarbanilate

We report on SANS measurements carried out on the instrument SANS1 (V4) at the BENSC facility on solutions and composites of cellulose tricarbanilate (CTC). This cellulose derivative exhibits lyotropic behaviour in methylacrylate (MA). The SANS data indicate that in the isotropic liquid state (up to 25% wt CTC in MA) the CTC chains behave like rods of mass per unit length (M/L). In the liquid crystalline (LC) phase (at and above 35% wt CTC in MA), the Q dependence varies from Q-1 to Q-4, probably as a result of self-assembling of the CTC chains. The general aim of our work is to prepare molecular composites, i.e. miscible blends of rigid-rod and flexible-coil polymers, from CTC solutions in polymerizable media. To establish the degree of homogeneity of the composites, we performed SANS measurements on UV-cured CTC/MA solutions. Here, we compare the SANS data of CTC/monomer solutions with those of the corresponding composites.

Powder and mechanical properties of microcrystalline cellulose with different degrees of polymerization.

This study investigated the influence of the degree of polymerization (DP) of cellulose materials (microcrystalline cellulose [MCC]) on some powder properties and the compression behavior of these materials. The DP was determined by measurements of viscosity (H). The weight average of molecular weight and the weight average of the different DPs were investigated after MCC was modified to cellulose tricarbanilate by light scattering measurements. The DP showed a remarkable influence on the physicochemical properties of the cellulose materials and, consequently, on the behavior of these materials during compression. MCC types with a high DP value showed greater water absorption than the types with a low DP value. No relevant relationship between the crystallinity index and the DP could be observed. DP 190 showed lower compactibility and compressibility parameters than DP 244 and 299. No significant differences could be observed between DP 244 and 299 when the same particle size fraction was compressed. Furthermore, the compressibility was increased by increasing the DP.

Lyotropic liquid crystalline cellulose derivatives in blends and molecular composites

Solutions of cellulose tricarbanilate (CTC) in methyl acrylate (MA) and methyl methacrylate (MMA) were prepared. The MA and MMA monomers were subsequently polymerised to produce a series of molecular composites, in which the amount of CTC and the degree of substitution (DS) of the tricarbanilate groups were varied. The CTC solutions were studied using polarised microscopy and indicated isotropic behaviour in solutions with a CTC concentration of less than 33 wt%. Solutions of 33–45 wt% CTC were found to have a nematic texture and a chiral nematic texture was detected on shearing of 45 wt% solutions. The mechanical properties and morphologies of the composites were investigated using dynamic mechanical thermal analysis (DMTA), tensile testing and scanning electron microscopy. Tensile testing measurements illustrated the reinforcing behaviour of the CTC on the composite, with the initial modulus increasing by up to 250% at 45 wt% CTC. Scanning electron microscope (SEM) micrographs for composites with <45 wt% CTC revealed a one-phase system. DMTA measurements indicated the existence of a double T g at DS of the tricarbanilate of less than 3, with a single T g for composites containing cellulose with degrees of carbanilate substitution equal to 3. The 45 wt% CTC composite showed a broad relaxation process at 350 K and another relaxation at higher temperature (490 K) corresponding to the glass transition of the CTC itself. This result, which is indicative of phase separation, is consistent with the SEM micrographs showing distinctive layered structures within the film.

Solution studies of cellulose tricarbanilates obtained in homogeneous phase

AbstractA number of cellulose samples was submitted to homogeneous phase carbanilation in dimethylacetamide/LiCl. The process is quantitative and leads to a completely substituted product, as verified by elemental analysis and UV spectroscopy. Tricarbanilated samples were characterized by viscometric and light‐scattering measurements in tetrahydrofuran. Our results are in good agreement with those reported in the literature, concerning products obtained in the heterogeneous phase. Gel permeation chromatography was performed for evaluating the molecular weight distribution of the parent cellulose, using both universal and linear calibration. The chromatographic technique is not adequate for samples exhibiting a high degree of polymerization. © 1995 John Wiley &amp; Sons, Inc.

Structure of cellulose in cuoxam

AbstractCuoxam ([CuII(NH3)4](OH)2) is a well known solvent for cellulose. Because of its deep blue colour, it has been used so far only for viscosity measurements. Direct light scattering measurements have not yet been reported in the literature.We carried out static and dynamic light scattering measurements in cuoxam using the blue wavelength of λ0 = 457.9 nm from an Argon ion laser. The measurements were involved with some difficulties mainly caused by colloidal particles of CuO and Cu(OH)2 which could be removed by direct centrifugation of the cells. Furthermore, the scattering intensity had to be corrected for extinction. The refractive index increment was taken from the literature.12 samples of different molecular weight and different origin were measured, and common power law behavior was found in a region up to about DPw = 1000 for both, the radius of gyration Rg and the hydrodynamic radius Rh, derived from the diffusion coefficient Dz. At higher degrees of polymerization characteristic deviations to lower radii occurred.These deviations are not caused by aggregation since the DPw's agreed with those from the cellulose tricarbanilates. The quantitative analysis of the radii and the angular dependence of the scattered light allowed determination of the chain stiffness. A Kuhn segment length of Ik = 25.6 (±6.2) nm and a characteristic ratio C∞ = 49.6 (±12.0) were derived. These values are close to those for cellulose‐tri‐carbanilate in dioxane.The reason for the increased stiffening is discussed on the basis of a special H‐bond model.

Pyridine‐catalyzed depolymerization of cellulose during carbanilation with phenylisocyanate in dimethylsulfoxide

AbstractCarbanilation reactions of cellulose samples (bleached cotton linters and Avicel) with phenylisocyanate in dimethylsulfoxide (DMSO) were carried out at 60°C in the presence of various pyridine derivatives. The molecular weight distributions of the resulting cellulose tricarbanilates (CTCs) were measured by high‐performance size exclusion chromatography. When pyridine or its derivatives were included in the reactions, the CTCs had reduced degree of polymerization (DP) values compared to those of CTCs prepared without the additives. The cellulose depolymerization was promoted by pyridines with electron‐donating substituents and was not favored by pyridines with electron‐withdrawing substituents nor with groups at positions ortho to the pyridine ring nitrogen atom. For the 3‐, 4‐, and 3,4‐ substituted pyridines, there was a linear relationship between log (weight‐average CTC DP) and the pKa (in water) of the pyridine derivative. For 2‐ and 2,6‐substituted pyridines, the DP–pKa relationships were different, probably because of steric effects of the different substituents ortho to the pyridine nitrogen atom. The optimum DMSO : pyridine solvent ratio for cellulose depolymerization during carbanilation in DMSO : pyridine mixtures was 3 : 1. All three components, phenylisocyanate, pyridine or its derivatives, and DMSO, are required for the depolymerization reaction. It is suggested that the depolymerization may be a consequence of cellulose oxidation by DMSO and/or cleavage of glucosidic bonds of partially carbanilated cellulose by reactions promoted by an enhanced solvent effect of DMSO.

Structure and phase behaviour of a lyotropic mesophase system: cellulose tricarbanilate-methyl acetoacetate

Solutions of cellulose tricarbanilate (CTC) in methyl acetoacetate (MAA) have been investigated and cholesteric mesophases found above a certain concentration. Structural features as well as the phase behaviour of this lyotropic liquid crystalline system were studied. The pitch of the helicoidal cholesteric structure P decreases with higher concentration c as Pαc −m with m = 2.3. The exponent can be correlated with the chain stiffness of the cellulosic molecule. The temperature behaviour of the pitch is in agreement with the theoretical considerations of others, if a left-handed helix conformation of a single cellulosic molecule is assumed. It can also be concluded that both steric and polar effects cause the formation of the mesophase. The thermally induced cholesteric-isotropic phase transition is a first-order transition. A two-phase region separates the anisotropic and isotropic phase ranges. The beginning of the transition as well as the clearing point are shifted to higher temperatures with increasing concentration. The resulting phase diagram is qualitatively best described by the lattice theory of Flory and Warner. The higher thermotropic effect as compared to the theory is correlated to a decrease in the Kuhn segment length. The enthalpy of the phase transition rises with increasing CTC concentration and can be explained by the disappearance of polymer-polymer interactions in favour of polymer-polymer contacts.

Molecular weight distribution of cellulose as its tricarbanilate by high performance size exclusion chromatography

AbstractCellulose tricarbanilates (CTCs) were prepared from a range of cellulose samples (cotton linters, wood pulps, Avicel, amorphous cellulose, and cellulose II) for molecular weight distribution (MWD) studies by high performance size exclusion chromatography (HPSEC). The HPSEC columns were calibrated using CTC standards with the aid of a microcomputer. CTCs were prepared by reaction of cellulose samples with phenylisocyanate in pyridine at 80°C. For some samples, e.g., cellulose II, activation with liquid ammonia and pyridine was necessary prior to reaction in pyridine. All samples tested were also derivatised in dimethylsulfoxide at 70°C, although for high molecular weight (MW) cellulose samples some MW reduction occurred in this solvent. Conditions were determined for optimum precipitation of CTCs in aqueous methanol without coprecipitation of low MW impurities.

Cellulose molecular weights determined by viscometry

AbstractThe equation suggested in the standard method SCAN C15:62 for the estimation of the degree of polymerization (DP) of a cellulose sample from its intrinsic viscosity ([η]) in cupriethylenediamine hydroxide (cuene) solution, P0.905 = 0.75 [η]/mL g−1, where P is an indeterminate average DP, is incorrect. Although differences between the experimental results from several laboratories need to be resolved, a tentative replacement (PV = 1.65 [η]) is suggested, based upon the pooled data and a conversion from the intrinsic viscosity of cellulose tricarbanilate (CTC) in tetrahydrofuran (THF) to that of cellulose in cuene. The treatment of statistical errors in Mark–Houwink–Sakurada parameters, and the nonlinearity of the log[η]−log Pv correlation are discussed.

Solution properties and chain conformation characteristics of cellulose tricarbanilate

AbstractFractions of two cellulose tricarbanilate samples were characterized by light‐scattering (weight‐average molecular weight, second virial coefficient, mean‐square radius of gyration), gel permeation chromatography (polydispersity index), and viscometry (intrinsic viscosity) in tetrahydrofuran and acetone. The intrinsic viscosity data were analyzed in terms of the theory developed for the continuous wormlike cylinder model, and the chain parameters (Kuhn statistical segment length λ−1, chain diameter d, and shift factor ML) were evaluated. The molecular‐weight dependence of the mean‐square radius of gyration in tetrahydrofuran was calculated for the Kratky—Porod chain model and compared with the experimental results. Data on the intrinsic viscosity and radii of gyration for other solvents at temperatures from 0 to 100°C were analyzed in the same way, and the effects of solvent and temperature on the statistical segment length were evaluated. Polymer—solvent interaction parameters were estimated from the second virial coefficients.

The effect of precipitation on the molecular weight distribution of cellulose tricarbanilate

AbstractThe effect of precipitation on the molecular weight distributions of cellulose tricarbanilate (CTC) samples prepared from α‐pulp, hydrolyzed α‐pulp, and Avicel was determined using size exclusion chromatography (SEC). Precipitation of the CTC samples in methanol resulted in the loss of a low molecular weight fraction accounting for 26% of the weight of the hydrolyzed α‐pulp, 20% of the Avicel, and 5% of the α‐pulp. Precipitation in a methanol/water mixture resulted in less fractionation; in this case, however, the reaction byproducts were also precipitated. These results indicate that the molecular weight distribution of precipitated CTC may not accurately reflect the molecular weight distribution of the original cellulose. SEC analysis of the nonvolatile products from the carbanilation reaction offers a simple method for determining the complete molecular weight distribution of this cellulose derivative.

Dilute‐Solution Dynamic Viscoelastic Properties of Cellulose Tricarbanilates

The frequency dependences of the storage and loss shear moduli, G′ and G″, of dilute solutions of three cellulose tricarbanilate fractions in tetraethylene glycol dimethyl ether were measured at 25.0°C by the Birnboim‐Schrag multiple‐lumped resonator. The frequency range was 100 to 5800 Hz and the concentration range 0.5 to 3 g/L. The weight‐average molecular weights were 0.4, 0.8, and 1.1×106. Intrinsic viscosities were determined by capillary viscosimetry. For interpretation of the results, the bead‐spring coil model and the Yamakawa‐Yoshizaki theory for the intrinsic viscosity of helical wormlike chains were modified to take into account a moderate degree of molecular weight heterogeneity with assumption of a Schulz‐Flory distribution. The viscoelastic data could be fitted by the bead‐spring model with the hydrodynamic interaction parameter h*=0.15 or 0.05 and Mw/Mn=1.3. From the intrinsic viscosities, the persistence length was calculated from the Yamakawa‐Yoshizaki theory as 10 nm for all three samples, much smaller than those of semiflexible rodlike molecules previously studied.

Dynamic light scattering from semidilute cellulose-tri-carbanilate solutions

A series of cellulose-tri-carbanilates (CTC) with a range of M w = 130 000 to 1 000 000 has been studied in dioxane at 20°C by static and dynamic light scattering. CTC is a semiflexible chain with a persistence length of 110 Å. In two cases ( M w = 130 000 and 1 000 000) a concentration region from dilute to 20c∗ was covered, where c∗ = 1 |η| is taken as the coil overlap concentration. Up to 3c∗ usual dilute solution behaviour was found. At about 3c∗ a sharp decrease in 1 M app [ = Kc R (q = 0)] and in the apparent diffusion coefficient D( c) (determined from the first cumulant of the time correlation function ( TCF)) was observed. Simultaneously, the mean square radius of gyration increases. Analysis of the TCF reveals two modes of motion: the mode which is fast, increases with c with an exponent of about 1.0 ± 0.1 and may be attributed to the cooperative diffusion coefficient of an entangled network. The other, which is slow, decreases with an exponent of about −2.6 ± 0.2 and thus is appreciably larger in value than −1.75 which is predicted for the self-diffusion of single chains. Master curves are obtained for M M app and D(c) D 0 as function of c c∗ . The observed behaviour indicates that there is no transient network formation. The results are, however, consistent with a model of entangled clusters existing in the region c∗ ⩽ c ⩽ 10c∗.

Conformational change studies by intrinsic viscosity of cellulose tricarbanilate as a function of temperature

The experimental variation of the intrinsic viscosity [η] as a function of temperature for various molecular weights of cellulose tricarbanilate in solution in dioxane displays a S-shaped character with two plateau regions, respectively at low and high temperatures. The use of the Yamakawa model leads to two distinct values for the chain stiffness q, one which may beo associated to a rather “rigid” conformation of the macromolecule (q=139 A), the other which may correspond to a rather “flexible” conformation (q = 84A).