Cellulose samples

In this study five cellulose samples of different crystallinities (10, 41, 63, 67, and 742) were treated to 10% by weight with H PO, H3BO3, and AlClo i O. These treated samples and untreated (control) samples were isothermally pyrolyzed under N2 at selected temperatures and the TGA data analyzed by four methods (0—, 1st-, and 2nd-order and Wilkinson s approximation) to obtain rates of mass loss. From these rates, activation energy (Efl), activation entropy (AS+) and enthalpy (AH+) values were obtained. Efl was also determined by the integral conversion method. 

Table II. Activation Parameters for Pyrolysis (Rate of Weight Loss) for Untreated Cellulose Samples Based on Data in Table I...

Figure 1. Arrhenius plot of the lst-order rates for the untreated cellulose samples ...

Cellulose pyrolysis kinetics, as measured by isothermal TGA mass loss, were statistically best fit using 1st- or 2nd-order for the untreated (control) samples and 2nd-order for the cellulose samples treated with three additives. Activation parameters obtained from the TGA data of the untreated samples suggest that the reaction mechanism proceeded through an ordered transition state. Sample crystallinity affected the rate constants, activation parameters, and char yields of the untreated cellulose samples. Various additives had different effects on the mass loss. For example, phosphoric acid and aluminum chloride probably increased the rate of dehydration, while boric acid may have inhibited levoglucosan... 

It is necessary to calibrate the 14C time scale for greater dating accuracy. However, the second-order variations are at least as important as the first-order constancy of atmospheric 14C. For example, they provide a record of prehistoric solar variations, changes in the Earth s dipole moment and an insight into the fate of C02 from fossil fuel combustion. Improved techniques are needed that will enable the precise measurement of small cellulose samples from single tree rings. The tandem accelerator mass spectrometer (TAMS) may fill this need. 

Table 5.3 Total heats of wetting (AHW°) of some cellulose samples.

Steele DF, Edge S, Tobyn MJ, Moreton RC, Staniforth JN. Adsorption of an amine drug onto microcrystalline cellulose and silicified microcrystalline cellulose samples. Drug Dev Ind Pharm 2003 29(4) 475 487,... 

Accessibility is the ratio between the portion of a cellulose sample which is accessible to a given reagent (such as Aca O,... 

Table I. Degrees of Polymerization of Cellulose Samples Obtained by Conventional Methods and by the New GPC Procedure...

Our experimental work started from the following original cellulose samples (a) acetate-grade, bleached cotton linters, DP 1800 (b) hot, refined, spruce, sulphite-dissolving pulp, machine dried, ca. 93% a-cellulose, DP — 750 (c) never-dried, normal, rayon-grade, beech sulphite pulp, ca. 90% a-cellulose, DP = 825 (d) commercial cellulose powders obtained by hydrolytic degradation and/or mechanical disintegration of cotton linters or spruce sulphite pulp. 

Table III. Chain-length Degradation of Different Cellulose Samples at 100°C in Aqueous Media...

Investigation of a cellulose sample that had been oxidized by aqueous chromic acid in the presence of sulfuric acid showed that most... 

Fig. 4 Left Fluorescence, MALLS (90°) and RI signals from a CCOA-labeled cellulose sample. Right Differential molecular weight distribution and degree of substitution of carbonyl groups (DSco) as calculated from the detector outputs...

Figure 1. Water retention of grafted and hydrolyzed cellulosic samples measured by method A2. Key MDC, dissolving pulp GP, greaseproof pulp EC, ethylcellu-lose and HEC, hydroxyethylcellulose.

The cellulose sample was generally treated according to the procedure described previously (9). In some experiments, the cellulose sample was treated with an aqueous solution of sodium hydroxide (17,6 %) for 2 h at room temperature and washed with water to neutrality for 24 h. The swollen sample was obtained after filtration. 

In the photosensitized experiments, the cellulose sample was treated with a solution of the initiator in acetone for 1 h at room temperature and the solvent evaporated in air. When this kind of adsorption was not possible, the initiator was dissolved in THF and added to the reactant medium. 

The percent grafting is considered (see discussion) as the weight increase of the dried cellulose sample after extraction. The percent homopolymer is calculated as the ratio weight of homopolymer over the weight of original monomer. 

As reported in literature (13) the irradiation of a cellulose sample at 254 nm results in glucosidic bond scission and C - H bond scission. Recent results in photosensitized experiments (15) show that the same behaviour can be obtained ... 

Materials. Commercial cotton (Pakistani cotton) cut into 5 mm length and Whatman cellulose powder CF-11 was used as cellulose samples after Soxhlet extraction with alcohol-benzene for 7 h. Wood meal (mainly 40 - 80 mesh) from Makanba (Betula Maximowicziana Regel) was used after washing with cold water. Methyl methacrylate and styrene were purified by the conventional methods. Other reagents used were analytical reagent grade. 

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