Linters degradation

HL linters, degraded by hydrolysis, wet-beaten, spray-dried 31 56... 

Cellulose (qv) is one of nature s most abundant stmctural materials, providing the primary framework of most plants. For industrial purposes cellulose is derived from two primary sources, cotton linters and wood pulp. Linters are derived from the machine by the same name used for removing the short fibers adhering to cotton seeds after ginning and consist essentially of pure cellulose (see Cotton). Wood (qv), on the other hand, contains 40—60% cellulose, which must be extracted by the chemical degradation of the wood stmcture. 

Acid anhydrides have been employed with, and without the use of a base catalyst. For example, acetates, propionates, butyrates, and their mixed esters, DS of 1 to ca. 3, have been obtained by reaction of activated cellulose with the corresponding anhydride, or two anhydrides, starting with the one with the smaller volume. In all cases, the distribution of both ester groups was almost statistic. Activation has been carried out by partial solvent distillation, and later by heat activation, under reduced pressure, of the native cellulose (bagasse, sisal), or the mercerized one (cotton linters). No catalyst has been employed the anhydride/AGU ratio was stoichiometric for microcrystalhne cellulose. Alternatively, 50% excess of anhydride (relative to targeted DS) has been employed for fibrous celluloses. In all cases, polymer degradation was minimum, and functionalization occurs preferentially at Ce ( C NMR spectroscopic analysis [52,56,57]). 

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. 

The initial rate of chain-length degradation AS/At, with S = 1/DP (Table II), increased, of course, with degradation temperature, both in the thermal and the thermohydrolytic treatments of the linters, but the Arrhenius energy of activation was much lower in thermohydrolysis. The difference in the rate between both kinds of treatment decreased significantly after a decrystallizing pretreatment of the linters with liquid... 

Table II. Initial Rate of Thermal and Thermohydrolytic Degradation of Linters...

Table V. Rate of Degradation of Linters in IN H2SC>4 at 80°C in Different Media...

Thus, further experiments were performed with two hydrolytically degraded linters powders subsequently disintegrated to different particle sizes (Filtrak, FNA and FND, VEB Spezialpapierfabrik Niederschlag, GDR), the lateral order of these samples being varied by liquid ammonia treatment or by mercerization with 18% aqueous NaOH. A posthydrolysis of these samples with aqueous acid (5% HC1, 2 hr, 100°C) resulted in changes in DP and in residue as indicated in Table IX and as to be expected from previous publications (11,16). 

Both papers used in this study were manufactured commercially. The newsprint was a typical groundwood sheet, and the rag paper was made from 100% cotton linters. The data in Table II show the properties of the two papers prior to accelerated degradation. 

Investigation of cotton linters, before and after thermal degradation in oxygen, showed no difference in the x-ray diffraction patterns. In... 

Depolymerization of cellulose fibers during irradiation is accompanied by a reduction in crystallinity, and, at high doses, extensive decomposition occurs. A dose of 5 X 10 equivalent roentgens brings about marked degradation and is sufficient to convert cotton linters into water-soluble materials. After irradiation, cellulose is more susceptible to acid hydrolysis and exhibits an after-effect. When irradiation is terminated, the intrinsic viscosity of cupriethylenediamine solutions of the irradiated cellulose continues to decrease. This behavior is initiated by oxygen and terminated by water. A similar effect is encountered with pectins after irradiation. 

Derivation Reacting cellulose (wood pulp or cotton linters) with acetic acid or acetic anhydride, with H2S04 catalyst. The cellulose is fully acetylated (three acetate groups per glucose unit), and at the same time the sulfuric acid causes appreciable degradation of the cellulose polymer so that the product contains only 200-300 glucose units per polymer chain. At this point in the process the cellulose acetate ordinarily is partially hydrolyzed by the addition... 

The principal commercial sources of chemical cellulose are purified cotton linters of about 99 per cent a-cellulose content and purified wood pulp of about 96 per cent cellulose content. Cellulose occurs in these materials as a fairly highly crystalline, high-molecular-weight polymer. It is in a fibrous form, which is insoluble in common reagents. Cellulose wUl not react to any significant d ee with acetic acid and will react with acetic anhydride without a catalyst only at very high temperatures, at which the cellulose is degraded. 

Koshizawa T (1960) Degradation of wood cellulose and cotton linters in phosphoric acid. Kami Pa Gikyoshi 14 455... 

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