Acid hydrolysis linters

A recent modification of the hydrolysis-oxidation technique19 has produced strong support for the acid hydrolysis results already mentioned. In this instance samples of purified cotton linters were treated for varying times with boiling 2.5 N hydrochloric acid or with 2.5 N hydrochloric acid- 0.6 M ferric chloride. The latter was necessary where the hydrolysis extended over periods longer than 12 minutes and acted to hinder the formation of humic materials. By filtration and washing, a series of hydrocelluloses was obtained which corresponded to times of hydrolysis varying from 0 to 7 hours. 

The investigators also presented a comparison of data on crystallinity drawn from the literature. This tabulation clearly shows the wide variations which have been reported. At first sight the values just presented, particularly for linters, may seem to be inconsistent with acid hydrolysis estimates. However, it was recognized that swelling could increase the amorphous fraction to 50 or even 100 times the amount occurring in dry unswollen material and that determinations based on aqueous solutions such as acids involve considerably swollen material. Hencp, values obtained by the latter methods may be reasonably correct as implicitly defined by test conditions. 

The effect of ball milling on the dilute acid hydrolysis of cellulose is similar in many ways to the effect electron irradiation has on enhancing saccharification (18). In the case of cotton linters, for example, maximum irradiation lO d) resulted in a half life of hydrolysis of about 7 min... 

The relative influence of vibratory milling on the course of enzymatic and dilute acid hydrolysis of four cellulosic substrates was investigated. The four substrates—cotton linters, newsprint, Douglas fir, and red oak— were vacuum-dried and then milled for various time periods ranging up to 240 min. Assays were then made of rate and extent of hydrolysis, maximum yield of reducing sugar, and cellulose crystallinity. 

Vibratory milling also yields substantial increases in the rates of dilute acid hydrolysis of all four substrates nearly nine-fold for cotton linters and roughly five-fold for the three lignocelluloses. Increases in maximum sugar yields under simple batch conditions ranged from 60% to 140% over the yields for the unmilled materials. 

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. 

Figure 5. Effect of acid hydrolysis on the CP-MAS spectrum of cotton linters. A Original material, B subjected to 2.5N HCl for 30 min, and C a renormalized linear combination spectrum [4x(a-.72B)]. Spectrum A and B are normalized to the same total intensity.

Cotton linters have been subjected to acid hydrolysis for various times and the products converted into samples of cellulose tricarbanilate (weight-average mol. wt. 0.21—1.1 X 10 ).Measurements of the intrinsic viscosities of dilute solutions of the derivatives in p-dioxan and butanone showed that the environment is well displaced from the normal 0-state and is closer to that at the lower critical solution temperature (234 °C in / -dioxan). 

Fig. 7. Combined sulfur during preparation of cellulose acetate hydrolysis of sulfate and esters (6). Acetylation schedule A, mixer charged with linters and acetic acid B, minor portion of catalyst added C, began cooling to 18°C D, acetic anhydride added and continued cooling to 16°C E, significant portion...

Srichuwong, S., Isono, N., Mishima, T., Hisamatsu, M. (2005). Structure of linterized starch is related to X-ray diffraction pattern and susceptibility to acid and enzyme hydrolysis of starch granules. Int. J. Biol Macromol, 57,115-121. 

Most experiments were performed with cotton or cotton linters as highly crystalline celluloses. Table I shows conditions leading to complete dissolution. A minimum amount of an acid which forms a cellulose ester (sulfuric or trifluoromethylsulfuric acid) (Entries 5 7-14) is necessary for the reaction. The dissolution is accelerated by a temperature increase (Entries 10-12 13, 14) and leads to water-soluble cellulose acetate hydrogensulfate. Whereas this primary hydrolysis can be achieved within 1-5 min, the deesterification and complete hydrolysis of the soluble cellulose derivative proved to be much more difficult. This is in contrast to the generally accepted view that the main resistance to the hydrolysis of cellulose lies in the crystalline nature or low accessibility determining the heterogeneous first step of the reaction. 

Cellulose acetate (CA) is the acetic acid ester of cellulose. It is obtained by the action, under rigidly controlled conditions, of acetic acid anhydride on purified cellulose usually obtained from cotton linters. All three available hydroxyl groups in each glucose unit of the cellulose can be acetylated. However, in the material normally used for plastics, it is usual to acetylate fully and then to lower the acetylate value (expressed as acetic acid) to 52-56 percent by partial hydrolysis. When compounded with suitable plasticizers, this gives a tough thermoplastic material. Cellulose acetate is mainly an extrusion (film and sheet) material, but injection applications include premium toys, tool handles, appliance housings, shields, lenses, and eyeglass frames. 

Cellulose secondary acetate fibres are manufactured from cotton linters by steeping in glacial acetic acid and sulphuric acid-catalysed reaction with acetic anhydride. The reaction is exothermic and the final product in a maximum of 20 hours is cellulose triacetate, which is converted to secondary acetate by adding sufficient water. The hydrolysis is stopped when 1/6 of the acetate groups have been randomly changed to hydroxyl groups. The precipitated polymer flakes are dissoluted in acetone containing small amounts of water or alcohol. The chemical formula of cellulose triacetate and the diacetate fibre production chart are shown in Fig. 4.5. 

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