A comparative study of the thermal decomposition of cellulose and cellulose triacetate

Conclusions A comparative study has been made of the thermal decomposition of cellulose and of cellulose acetates having various degrees of polymerization, and also of specimens regenerated from nonaqueous solutions.The effect of the solvent on reducing the effective energy of activation of thermal decomposition on transition from the starting samples of cellulose and its derivatives to specimens regenerated from nonaqueous solutions has been revealed.It has been found that the degree of polymerization exerts no significant effect on the temperature of thermal decomposition.Translated from Khimicheskie Volokna, No. 4, pp. 28–29, July–August, 1986.     

Effects of solvent addition to acetylation medium on cellulose triacetate prepared from low-grade hardwood dissolving pulp

As cellulose triacetate was prepared from low-grade hardwood-dissolving pulp, a considerable amount of the insoluble residue was present in the acetylation medium of the acetic acid/acetic anhydride/sulfuric acid system, and it consisted mainly of cellulose triacetate (CTA) and xylan diacetate (XDA). As one of the remedies for reducing the insoluble residue, a solvent was added to the acetylation medium and the effects of the solvent addition on the amount of insoluble residue formed were studied. To do so, 17 different solvents were selected so as to cover a wide range of solubility parameters. The obtained results clearly indicated that the addition of the solvent affects the amount of insoluble residue and that, excluding dichloroacetic acid, nitromethane was effective for its reduction, but that neither methylene chloride nor nitroethane were in spite of their effectiveness for softwood-dissolving pulp, which would be due to the intrinsic properties of XDA on the solubility in the acetylation medium. A new acetylation system with such an appropriate solvent would, therefore, provide a clue as to an industrial usage of the low-grade hardwood-dissolving pulps for cellulose acetate production. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1445–1449, 1998     

Effect of cellulose acetate/cellulose triacetate ratio on reverse osmosis blend membrane performance

Surface functionalization and modification including the grafting process are effective approaches to improve and enhance the reverse osmosis (RO) membrane performance. This work is aimed to synthesize grafted/crosslinked cellulose acetate (CA)/cellulose triacetate (CTA) blend RO membranes using N-isopropylacrylamide (N-IPAAm) as a monomer and N,N-methylene bisacrylamide (MBAAm) as a crosslinker. The morphology of these membranes was analyzed by scanning electron microscopy and their surface roughness was characterized by atomic force microscopy. The performance of these membranes was evaluated through measuring two major parameters of salt rejection and water flux using RO unit at variable operating pressures. It was noted that the surface average roughness obviously decreased from 148 nm for the pure CA/CTA blend membrane with 2.5% CTA to 110 nm and 87 nm for the grafted N-IPAAm and grafted/crosslinked N-IPAAM/MBAAm/CA/CTA-RO membranes, respectively. Moreover, the contact angle decreased from 51.98° to 47.6° and 43.8° after the grafting and crosslinking process. The salt rejection of the grafted CA/CTA-RO membrane by 0.1% N-IPAAm produced the highest value of 98.12% and the water flux was 3.29 L/m²h at 10 bar.     

A study of rheological properties of cellulose diacetate in acetone solution at low and high shear rates

The rheological properties of cellulose diacetate (CDA) with different intrinsic viscosity (IV) and different concentration in acetone solutions were studied at low and high shear rates. The zero-shear viscosity increased and the structural index increased, when the IV of CDA was increased or the acetone solution concentration was increased. Evidence suggested that a sulfate structure may be forming. It is shown that the increase of hemicellulose and sulfur content is associated with an increase of chain entanglements between CDA molecules and the abnormal increase of solution zero-shear viscosity. At a high shear rate, the correlation curve between inlet pressure drop and solution concentration obtained by Bagley method analysis shows an inflection point, which appears to be the critical concentration at which the cellulose diacetate molecular chains in the solution form a long range entangled elastic network. After the concentration exceeds a certain range of above critical points, the entanglement of the molecular chains in the solution is significantly enhanced. The zero shear viscosity inflection point concentration calculated by the rheological curve with low shear velocity and the inlet pressure drop inflection point concentration calculated by the capillary rheological calculation have good consistency.     

三乙酸纤维素正渗透膜的制备与性能

以三乙酸纤维素（CTA）为膜材料,1,4-二氧六环、丙酮为溶剂,甲醇、乳酸为添加剂,采用相转换法制备了三乙酸纤维素正渗透膜。研究了不同1,4-二氧六环/丙酮配比、添加剂乳酸含量、挥发时间、膜厚度、热处理温度条件下正渗透膜性能的变化规律。研究表明,当采用纯水为原料液,0.56mol/L CaCl2为汲取液时,优化制备的CTA正渗透膜的水通量达到14.10L/(m2?h),溶质反扩散量为0.031mol/(m2?h);采用0.1mol/L NaCl为原料液,4mol/L葡萄糖为汲取液时,优化制备的CTA正渗透膜的水通量保持在5L/(m2?h)以上,对NaCl的截留率大于99%。CTA正渗透膜相比于HTI膜,具有较高的亲水性、水通量、截留率,稳定性更好。     

The cholesteric nature of cellulose triacetate solutions

Solutions of cellulose triacetate (CTA) in trifluoroacetic acid (TFA) become liquid crystalline above a certain critical concentration. Using the techniques of spectrophotometry, wide-angle light scattering and circular dichroism we have shown that the mesophase formed is cholesteric. We have measured its pitch, which depends on polymer concentration, and shown that the cholesteric structure is right-handed. Measurements of optical activity and the optical effects of shear and magnetic fields are also described and discussed.     

Pyroelectric behaviour of solution-grown cellulose acetate polymer films

The pyroelectric behaviour of cellulose acetate polymer films was studied in a vacuum of 10^?3 torr under a polarizing field strength range of 6.25 × 10⁵–50 × 10⁵ V/m and a polarizing temperature range of 304–406 K. The pyroelectric coefficient exhibited abnormal behaviour, starting initially on the negative side and then changing sign from negative to positive. Negative coefficients are believed to be due to dipolar orientation, whereas space charge polarization is responsible for positive pyroelectric coefficients.     

High‐quality cellulose triacetate prepared from bamboo dissolving pulp

Cellulose triacetate (CTA) was prepared from high‐grade bamboo dissolving pulp in general acetylation medium of acetic acid/acetic anhydride/sulfuric acid system. Despite its properties being improved compared with these of CTA prepared from viscose bamboo pulp, many insoluble residues still remained in its acetylation medium, which resulted in the decrease of the brightness and thermal stability of prepared CTA. Characterization of the insoluble residue indicated that its formation was associated with a higher content of xylan and ash in high‐grade bamboo pulp than in high‐grade hardwood pulp, in which insoluble residue was negligible. Because of the poor solubility of xylan diacetate (XDA) in acetylation medium, the insoluble residue formed through the aggregation of XDA and CTA by ultrastructural effects of the pulps during the precipitation of XDA. An addition to the good solvent of XDA, such as 1,2‐dichloroethane to acetylation medium of high‐grade bamboo pulp, could release the aggregation of XDA and CTA and dissolve the insoluble residue, which could lead to the improvement of the transmittance of reaction solution, as well as the properties of CTA prepared such as brightness and thermal stability. This study showed that high‐quality CTA could be prepared from high‐grade bamboo dissolving pulp in acetylation with an addition of solvent. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrical and structural properties of polyaniline/cellulose triacetate blend films

Polyaniline (PANI) has been blended with cellulose triacetate (CTA) to obtain both good mechanical properties and good electrical properties. The effects of PANI weight percentage on the optical, structural, morphological and electrical properties in the blend films of polyaniline and cellulose triacetate (PANI/CTA) have been investigated. The phenomenon of percolation was observed in these blend films. It is found that the electrical conductivity of the blend films increases with the increase of polyaniline content up to a value of 10⁻⁴ S cm⁻¹ at 84 weight percentage of PANI. The experimental percolation threshold of the dried blend films is obtained at 9.5 wt% of polyaniline. The values of Mott’s temperature, density of states at the Fermi level [N (E _f)], hopping distance (R _hop), and barrier height (W _hop) for PANI/CTA blend films are calculated. By applying Mott’s theory, it is found that the PANI/CTA blend films obey the three dimensional variable range hopping mechanism.     

Superior effect of TEMPO-oxidized cellulose nanofibrils (TOCNs) on the performance of cellulose triacetate (CTA) ultrafiltration membrane

Cellulose triacetate (CTA) ultrafiltration membranes were prepared via phase inversion technique using hydrophilic TEMPO-oxidized cellulose nanofibrils (TOCNs) as modifying agents. The permeation performance of the prepared membranes was evaluated in terms of pure water flux (Ji), protein rejection (Rm) and flux recovery ratio (FRR). Membrane surface morphology and cross-sectional structures were characterized by atomic-force microscopy (AFM) and scanning electron microscopy (SEM), respectively. XRD was performed in order to investigate the interactions between membrane components. Meanwhile, the effects of TOCN concentration on hydrophilicity of the membrane surface and mechanical properties were also examined. The experimental results indicated that CTA/TOCN composite membranes exhibit significant differences in surface properties and intrinsic properties due to the addition of TOCNs.     

Kinetics of acid catalysed degradation of cellulose triacetate in chloroalkane solvents: 1. Dichloromethane

The kinetics of degradation of cellulose triacetate in a dichloromethane-acetic anhydride mixture with perchloric or sulphuric acid catalyst was studied. Decrease in molecular weight with time was followed viscometrically using limiting viscosity numbers, calculated by a single-point method, and Mark-Houwink constants for the solvent mixture. Dependence of first-order rate constants on catalyst concentration and temperature was investigated and Arrhenius parameters, activation entropies and catalytic coefficients were obtained. A suggested reaction mechanism for degradation based on H⁺ and Ac⁺ (acetylium ion) acting as catalytic species is proposed.     

Studies on the composites of cellulose triacetate (prepared from sugar cane pulp) and gelatin

Sugarcane waste (bagasse) which is hitherto discarded as a waste at sugarcane parlors and jaggery units was recovered and cellulose triacetate (CTA) was prepared from the same, after isolation of cellulose. Using this CTA, CTA–gelatin composites were prepared. The materials prepared (i.e., sugarcane cellulose, CTA, CTA–gelatin composites) were characterized for their mechanical properties, water absorption capacity, infrared spectroscopy, and scanning electron microscopy. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 847–853, 2001     

Permeation behaviour in cellulose triacetate dense membrane during pervaporation separation of methanol/methyl tert-butyl ether mixture

The pervaporation separation of methanol/methyl tert-butyl ether through cellulose triacetate dense membranes has been carried out under different feed compositions, permeation temperatures and temperature cycles to investigate the permeation behaviour of the membrane during pervaporation process. The experimental data indicate that the plasticization effect has a decisive influence on pervaporation flux, permselectivity and permeation activation energy. The results show that the penetrants of different feeds are transported through the membrane by different pathways with the influence of plasticization effect at different temperatures. It has also been observed that plasticization had great effect on the membrane swelling and sorption selectivity. Furthermore, DSC results show that the membranes retain the influence of the plasticization effect after pervaporation separations are tested. © 2000 Society of Chemical Industry     

Novel crosslinked nonlinear optical materials based on cellulose diacetate

Preparation of second‐order nonlinear optical (NLO) materials based on cellulose diacetate and melamine derivatives was attempted. The NLO chromophore DR19 was incorporated into the crosslinking network resulting from the reaction of cellulose diacetate with trimethylolmelamine or hexamethylolmelamine. The poled and cured NLO materials exhibited electrooptic coefficient (r₁₃) values of 1.11 or 1.03 pm/V, respectively, at a laser wavelength of 1550 nm, a modulation frequency of 12.7 kHz. The r₁₃ values decreased to 80 or 81.5% of the initial values after 4 days. The laser transmission loss was 0.50 or 0.44 db. The crosslinking materials showed better temporal stability than that of host/guest type materials, and 73% of the initial r₁₃ value remained after keeping the NLO film at 100°C for 15 h. No evident weight loss was found below 250°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2832–2837, 2006     

Electrospinning of fluorescent fibers from CdSe/ZnS quantum dots in cellulose triacetate

Fluorescent cellulose triacetate (CTA) fibers were prepared by electrospinning solutions of CTA dissolved in an 8 : 2 v/v cosolvent system of methylene chloride (MC) and methanol (MeOH) which contained CdSe/ZnS quantum dots (QDs). The relatively low loading of colloidal nanoparticles was sufficient to impart fluorescence to the fibers but did not significantly alter fiber morphologies, which tended toward smooth surfaces with the occasional longitudinal feature. The fibers were birefringent due to the alignment of the polymer chains which occurred during electrospinning and had widths on the order of a hundred nanometers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

二醋酸纤维素的增塑改性及熔融纺丝研究

采用聚乙二醇(PEG)作为增塑剂,对二醋酸纤维素(CDA)共混改性并进行熔融纺丝,研究了改性后的CDA及其纤维的结构与性能。结果表明:经PEG改性后,CDA的结构及晶型没有变化,CDA的熔点降低,由220℃降至190℃,而热失重5%时的温度仍然为300～310℃;改性后的CDA纤维的断裂强度随PEG含量增加而降低,断裂伸长率则随之提高,适宜的PEG质量分数为25%;PEG的加入增加了CDA可稳定熔融纺丝的温度区间,提高了CDA的可纺性。     

Controlled grafting of cellulose diacetate

Cellulose diacetate (CDA) was acylated with 2-bromoisobutyryl bromide (BriBr) or with dichloroacetyl chloride (ClAcCl) giving polyfunctional macroinitiators for ATRP grafting of styrene (St), MMA and butyl acrylate (BuA). Under various reaction conditions, macroinitiators with variable degrees of functionalisation could be prepared. The macroinitiators with 2-bromoisobutyryl (BriB) groups were grafted with St or BuA, those with dichloroacetyl (ClAc) functions were used for graft copolymerization of MMA. Graft copolymers with chemically different grafts as well as tunable lengths and densities of grafts were synthesized in this way. Poly(CDA-g-St) and poly(CDA-g-MMA) were further used as macroinitiators of BuA polymerization, giving poly[CDA-g-(St-b-BuA)] and poly[CDA-g-(MMA-b-BuA)] graft copolymers with diblock grafts.     

Gel formation and liquid crystalline order in cellulose triacetate solutions

The formation of a liquid crystalline state of cellulose triacetate solution in trifluoroacetic acid was studied using optical microscopy, polarimetry and circular dichroism measurements. Below a critical concentration of $\text{34}\text{g}\text{100}\text{ml}$ a clear isotropic solution was formed. Solutions more concentrated than this were in the cholesteric liquid crystalline state. If water was added to the solution, a gel phase was formed if the polymer concentration was above a critical value. We interpret our observations in terms of the Pincus-de Gennes theory and show that the formation of liquid crystalline order involves both inter-and intramolecular forces.     

Supercritical carbon dioxide assisted preparation of conductive polypyrrole/cellulose diacetate composites

Supercritical carbon dioxide (SC‐CO₂) has been used to assist the preparation of conductive polypyrrole/cellulose diacetate (PPy/CDa) composites by in situ chemical oxidative polymerization. The morphology and conductivity of resulted composites were investigated with scanning electron microscopy and four‐probe method, respectively. With the assistance of strong swelling effect of SC‐CO₂, composite films were obtained with a macroscopically homogeneous structure and conductivity up to 10^?1 S cm^?1 order of magnitude. Increasing the pressure of SC‐CO₂ increased conductivity, while increasing the temperature decreased conductivity. For comparison, PPy/CDa composite was also prepared with conventional oxidative method in aqueous solution. From the viewpoint of conductivity and environmental protection, the SC‐CO₂ method showed its superiority over the conventional one. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4575–4580, 2006     

Ultrafine cellulose triacetate mats electrospun by using co‐solvent of DMSO/chloroform system

Cellulose triacetate (CTA) nanofiber nonwoven mats were continuously electrospun by using mixed solvent of DMSO/chloroform system. The size and morphology of CTA nanofibers were investigated. It was found that CTA fibers with diameters in the range of 98 nm–1.81 μm were obtained from 8 wt % CTA solutions in 1 : 1, 3 : 2, 2 : 1, 3 : 1, 5 : 1 and 7 : 1 (v/v) DMSO/chloroform. The average diameter of CTA nanofiber was decreased and size distribution was narrowed with increasing the DMSO content in the mixed solvent. Smooth and uniform nanofibers with mean diameters of about 260 nm could be obtained from a solution of CTA in the binary system DMSO/chloroform 5 : 1(v/v) at a polymer concentration of 8 wt %. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40373.