Calculation of the kinetics of degradation of alkali cellulose under variable temperature

Conclusions It is possible to calculate the kinetics of alkali cellulose degradation at a variable temperature from a nomogram.A good agreement of the results of calculating degree of polymerization from the nomogram is found with results from the empirical equation.Translated from Khimicheskie Volokna, No. 3, pp. 34–35, May–June, 1983.     

Thermal degradation of cellulose model compounds in inert atmosphere

Thermal degradation of cellulose model compounds was studied using thermogravimetry (TG), electric spin resonance (ESR) spectroscopy, and gas chromatography–mass spectrometry (GS–MS). The molecular weight of samples did not influence the activation energy of gasification. In the case of catalytic influence of NaOH on cellulose thermolysis formation of gaseous products in the temperature range 250–350°C increased and a greater amount of residue was formed at 350–400°C compared to noncatalytic thermolysis. Residues of compounds with hemiacetal groups showed higher concentration of unpaired electrons than residues obtained from models with the blocked hemiacetal group.     

Fabrication of alkali cellulose

Sheet cellulose is mercerized in two stages. In the first stage, 4-6-fold swelling of the cellulose takes place for 30–60 sec, and the alkali penetrating the swollen sheet is depleted due to chemical binding of NaOH. In the second stage, which lasts for 1–2 h, diffusion leveling of the concentrations takes place, and the amount of chemically bound NaOH increases by 10–15%. In the continuous method of sheet mercerization, treatment with alkali lasts for 30–60 sec, and to ensure the required amount of chemically bound NaOH, its concentration in the working solution is increased by 10–20%. Bulk mercerization, where cellulose filaments with a cross section of 0.03 mm are accessible to the alkali, takes place in 1–5 sec, since the diffusion stage is almost absent in this case. The continuous method of mercerization of cellulose in bulk includes the positive aspects of the process conducted in a VA unit and in UNM-30 continuous mercerization units and is free of their drawbacks. All-Russian Scientific-Research Institute of Fibres, Mytishchi. Translated fromKhimicheskie Volokna, No. 2, pp. 11–15, March–April, 2000.     

Effect of cellulose crystallinity on the progress of thermal oxidative degradation of paper

Dynamic differential scanning calorimetry (DSC) using paper samples of different compositions has evidenced varying degrees of endothermic activity prior to the exothermic, oxidative decomposition of cellulose under static air. Whereas cotton cellulose papers displayed a significant endothermic activity, wood‐pulp papers showed a much less pronounced effect or no activity at all. DSC measurements using microcrystalline cellulose submitted to different extents of milling indicated that the observed endotherm is related to the degree of crystallinity of cellulose. Crystallinity decrease is accompanied by a decrease in the area of the endothermic peak. Thermal disruption of cellulose crystalline domains is therefore believed to be the reason for the appearance of an endotherm in the thermograms of paper. The higher degree of crystallinity of cotton cellulose in comparison to wood‐pulp cellulose accounts for the more pronounced endothermic activity observed for cotton papers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 61–66, 2000     

New mathematical model on the thermal degradation of industrial plastisols

The thermal degradation of some plastisols [poly(vinyl chloride) and plasticizer mixtures] normally used in the toy industry was studied using a nonisothermal thermogravimetric technique. Some kinetic parameters such as activation energies are calculated according to some methods reported in the literature. A mathematical model based on considerations of the plasticizer amount was proposed to foresee the thermal degradation behavior of plastisols mostly used in the toy industry. Activation energies calculated according to the proposed model agree reasonably well with experimental results in a broad range of plastisol composition. © 1996 John Wiley & Sons, Inc.     

Phase transitions in mercerization and alkali distribution in alkali cellulose

Conclusions Problems of stoichiometry and of the depth of the phase transition in mercerizing with NaOH solutions of various concentrations have been examined from the position of formation of an additive compound (inclusion compound) of sodium hydroxide and cellulose.An estimate has been made of the alkali and water contents in regions of alkali celluloses having different order of structural elements, and a method has been indicated for calculating optimum concentrations of the mercerizing solution.Conclusions about the presence of optimum concentrations at the end of the phase transition region have been confirmed by data on the structure of the xanthate and filterability of the viscose.Performing the mercerization of celluloses with NaOH solutions whose concentrations correspond to regions adjoining the phase transition region will afford an opportunity to prepare spinning solutions with good filterability and with a reduced consumption of carbon disulfide.Translated from Khimicheskie Volokna, No. 1, pp. 5–9, January–February, 1988.     

Role of the polymer substrate in oxidative degradation of natural and synthetic dyes on flax cellulose

The “protective” function of the polymer substrate in oxidative treatments of linen cloth was revealed. It was found that the stability of the chromophore structure of direct and active dyes on flax cellulose in both acid and basic medium is much higher than in aqueous solution and printing composition. The “protective” effect of the polymer in oxidative degradation of flax cellulose natural dyes is manifested to a lesser degree due to the effective destruction of cellulose dye satellites in conditions of discharge printing of grey linen. Ivanovo State University of Chemical Engineering. Translated fromKhimicheskie Volokna, No. 2, pp. 47–50, March–April, 2000.     

Thermal degradation of cellulose and cellulose esters

Cellulose, cellulose diacetate (CDA), cellulose triacetate (CTA), cellulose nitrate (CN), and cellulose phosphate (CP) were subjected to dynamic thermogravimetry in nitrogen and air. The thermostability of the cellulose and its esters was estimated, taking into account the values of initial thermal degradation temperature T_d, the temperature at the maximum degradation rate T_dm, and char yield at 400°C. The results show that these polymers may be arranged in the following order of increasing thermostability: CN < CP < regenerated cellulose < filter cotton < CDA < CTA. The activation energy (E), order (n), and frequency factor (Z) of their degradation reactions were obtained following the Friedman, Chang, Coats–Redfern, Freeman–Carroll, and Kissinger methods. The dependence of T_d, T_dm, E, n, Ln Z, and char yield at 400°C on molecular weight and test atmosphere is also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:293–304, 1998     

A kinetic study of ultrasonic degradation of carboxymethyl cellulose

In this study, the effect of power of ultrasound, temperature, and concentration of carboxymethyl cellulose (CMC) solution on the rate of ultrasonic degradation were investigated, and a kinetic model based on viscometry data was used to calculate the rate constants in different conditions. To investigation of effect of ultrasonic power on the degradation of CMC, the power of ultrasound was increased and observed that the viscosity of the CMC solution was decreased with an increase in the power of ultrasound, but the extent of the degradation in a constant power was found to decrease with an increase in concentration or temperature. The ultrasonic degradation of CMC solutions was carried out at different temperatures to investigate the effect of the temperature on the rate of degradation. The calculated rate constants indicated that the degradation rate of the CMC solutions decreased as the temperature increased. The degraded CMCs were characterized by gel permeation chromatography, and average molecular weights of ultrasonicated CMCs were compared in different reaction conditions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Studies on the mechanical degradation of cellulose

The mechanical degradation by high-speed stirring of cellulose in dilute n-butanol suspensions was investigated on six different samples with degrees of polymerization (DP) between 300 and 7500. The degrees of polymerization were determined viscosimetrically in CuEn (copper ethylendiamine complex) at different times of mechanical action. The distributions of the DP were measured on the polymer-analogous nitrates by size exclusion chromatography (HPSEC) in THF. The investigations reveal that only high-molecular-weight cellulose undergoes degradation, whereas celluloses with a starting DP₀ < 3000 remain undegraded. In the case of degradation the decrease of the DP with time is exponential, reaching a “limiting” DP (DP_∞) of about 3200 which does not diminish further. The narrowing with degradation time of the distributions of DP of the degraded samples allows to assume that the bonds splitting by the action of mechanical forces are the so-called “weak links” present in high-molecular-weight cellulose. The course of the nonuniformity U with decreasing DP, could be confirmed by mathematical derivation of the relationship between U and the degree of degradation DP₀/DP_t, considering the scission of only “weak links”.