Cotton, cellulose from linters

The manufacture of cellulose acetate involves the acetylation of cellulose from cotton linters or wood pulp by acetic anhydride and acetic acid. Production started about 30 years ago, and early products that were developed include safety photographic films, airplane dopes, and acetate fabrics. It is now also produced in the form of sheeting, rods, and tubes and is widely used as a molding compound. 

Alkali cellulose from cotton linters or wood pulp, usually prepared in a way similar to the first step in the viscose process (see Section 9.7), is used as raw material. Alkylation is carried out by using alkyl chlorides. The reaction proceeds according to the SN2 mechanism (bimolecular nucleophilic substitution) ... 

Cellulose UF membranes are used in applications where low fouling characteristics are required. Cellulose has a very regular structure and is able to form strong intermolecular hydrogen bonds between the several hydroxy groups. As a result, cellulose is practically insoluble in almost all solvents. The only exceptions are dilute solutions in DM Ac or NMP with addition of lithium chloride. Cellulose membranes are prepared by methods that basically involve precipitation from a solution of chemically modified native cellulose (from cotton linters, etc.). Until some years ago the three main methods were based on cellophane, cuprophane and cuenophane. 

Cellulosics. CeUulosic adhesives are obtained by modification of cellulose [9004-34-6] (qv) which comes from cotton linters and wood pulp. Cellulose can be nitrated to provide cellulose nitrate [9004-70-0] which is soluble in organic solvents. When cellulose nitrate is dissolved in amyl acetate [628-63-7] for example, a general purpose solvent-based adhesive which is both waterproof and flexible is formed. Cellulose esterification leads to materials such as cellulose acetate [9004-35-7], which has been used as a pressure-sensitive adhesive tape backing. Cellulose can also be ethoxylated, providing hydroxyethylceUulose which is useful as a thickening agent for poly(vinyl acetate) emulsion adhesives. Etherification leads to materials such as methylceUulose [9004-67-5] which are soluble in water and can be modified with glyceral [56-81-5] to produce adhesives used as wallpaper paste (see Cellulose esters Cellulose ethers). 

R wPrior to World War II, CN was produced mainly from cotton linters because of their higher degree of purity (alpha cellulose >98%). The high purity linters allowed a higher yield and better quaUty product compared to those obtained from less pure wood pulps or other cellulose sources. The development of highly purified chemical-grade wood pulps has allowed this material to be used in the same manner as are linters. 

All unfractionated cellulose triacetate samples and high molecular weight fractions showed a shoulder on the high molecular weight side of the GPC distribution. Material Isolated from this region was found to be highly enriched in mannose and xylose, attributed to the presence of a hemicellu-lose derivative. Cellulose triacetate from cotton linters did not show this behavior. 

C.G.Dunkle, PATR 1100(1941 )(Purification of NC from cotton linters) 134)G.L.Richter, OSRD Rpt 71 (l94l)(Wood cellulose nitrates for munitions) 135)A.Kraus, NC 12, 63 4(1941) ... 

XSemi-plant scale purification of NC from cotton linters) 143)H.A.Aaronson, PATR 1187(1942)(Prepn props of NC of high-nitrogen content) 144)R.W.Scharf, PATR 1190(1942) (Semi-plant scale purification of NC by ethanol) 145)R.O.Carter, Jr, et al, OSRD Rpt 1385(1943) (Mechanism of gelatinization soln of fibrous NC in non-aqueous solvents) 146)G.Petitpas, MSCE 30, 243-7(1943) CA 40, 7614-15(1946) (Nitration of cellulose in mixts of HNC>3 O contg compds) MSCE 30, 248-56(1943) CA 40,... 

Speed of nitration gelatinization of NC) 147)F. Vogel, PATR 1233(1943)(Semi -plant scale purification of NC from cotton linters) 148)H.A.Aaronson, PATR 1331(1943) (Nitration of cellulose with N2Og by the Stein Hall Co process) 149)A.Stettbacher, Protar 9, 212-18, 233 42(1943) CA 38, 4445(1944)... 

Dialysis is a simple clean-up or purification process to remove unwanted low-molecular-weight compounds from solutions. The dialysis membrane consists of regenerated cellulose prepared from cotton linters by the viscose process. In addition to water, the membrane also contains glycerol and small amounts of sulfur compounds, which are removed during preparation of the tubing prior to use. 

A purified form of cellulose, obtained from cotton linters or wood pulp, is reacted with sodium hydroxide solution to produce a swollen alkali cellulose that is chemically more reactive than untreated cellulose. The alkali cellulose is then treated with chloromethane and propylene oxide to produce methyl hydroxypropyl ethers of cellulose. The fibrous reaction product is then purified and ground to a fine, uniform powder or granules. 

The role of CBMs may not be entirely passive, although thermodynamics ensure that any interaction has to be stoichiometric rather than catalytic. An isolated CBM 2a, originally from a Cellulomonas fimi endoglucanase, formed the usual (3-sandwich, but, in solution, when unconstrained by an attached catalytic domain, dimerised." This CBM liberated small particles from cotton linters but not bacterial microcrystalline cellulose the same behaviour was shown by the holoenzyme which had been inactivated with the appropriate Withers inactivator." " However, another CBM 2a, from Cellvibrio japonicus, was rigorously shown to act only by increasing substrate proximity." ... 

Wood Paper Cellulosic separators are made from cotton linters or craft pulp and generally coated with phenolic resin for acid resistance and strength Comparatively large pore size and relatively high electrical resistance... 

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. 

The preparation of dialdehydocellulose from microcrystalline cellulose and cotton linters has been compared for a variety of reaction conditions. Microcrystalline cellulose was shown to be more reactive, and under optimal... 

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. 

Up until about 1940, the use of chemical cellulose derived from wood was restricted mainly to the manufacture of regenerated cellulose whilst cotton linters were preferred as the source of cellulose for making cellulose derivatives. At this time, production of chemical cellulose from the two sources was approximately equal. Over the past 30 years the yearly production of chemical cellulose from wood has grown until it now accounts for over 95% of the total. The reasons for this growth are based on price stability, uniformity of product and continued improvement in quality. 

In this equation, 1 (20 = 18°) shows amorphous cellulose intensity and I g (20 = 22.5°) represents intensity of crystalline cellulose [63]. For instance, the degree of crystallinity for CNC from cotton linter was more than cotton Enters [136], while this characteristic for NFC from sugarcane bagasse was 36% [63]. Fourier Transform Infrared Spectrometer (FTIR) is an instrument for studying the change of the functional groups... 

Table I. Fitting the C4 region of spectra recorded at 7.05 T on cellulose isolated from cotton linters...

NOTE The results of a non-linear least squares fitting of the C4 region of the CP/MAS C-NMR spectrum recorded on cellulose isolated from cotton linters by HCl(aq) hydrolysis (Reproduced with permission from reference 16. Copyright 1999). 

Additionally, there are cellulose casings, made from cotton linters collagen casings, made from a collagen source, such as the corium layer of beef hide and plastic netting made of polyethylene threads. 

---