US2275805A - Preparation of cellulose nitrate from wood pulp - Google Patents

Description

Patented Mar. 10, 1942 ED STATES P EN EQ-FFLCE PREPARATION F crtwtosr .NJ M woonPlJLt-i John L. Patterson, Rochester; N. -Y.', assignor to Eastman-Kodak Company,. Rochester, N. Y., a 1 corpora o of New J rsey 4 Claims. (01. 2. 05223) This invention relates to the incorporation of not more than equal parts of nitrated cotton with nitrated wood pulp composed of thin pieces prior to the washing and dehydrating operations to increase itsyield, and improve its handlingqualities.

It has been recognized that nitrated wood pulp due probably to its physical makeup is susceptible to losses upon washing and dehydrating subsequent to the nitration step". Consequently nitrating processes have almost invariably employed cotton linters as the starting material particularly in the preparation of the low viscosity cel-' lulose nitrates.

In the preparation of cellulose nitrate, the product, after the nitration'step, is usually thoroughly washed with water to free it of any trace of the nitrating acid. This washing is usually accompanied by an elevated temperatureiandagitation such as stirring. With nitrated woodpulp composed of thin hits, the material is badly disintegrated or'broken up with the result that 'a high loss in yield is experienced. Also in the de hydration treatment in which the water is removed by treatment of the cellulose nitrate with alcohol, such as butyl alcohol, nitrated wood pulp forms a mass in the centrifuge in which the dehydration occurs which is susceptibleto channelling thus cutting down the efiiciency of the dehydration treatment.

One object of my invention is to-provide a method in the making of cellulose nitrate from wood pulp in the form of thin pieces in which losses during treatment are minimized and in which efficient dehydration is accomplished. Other objects will appear herein.

I have found that loss of nitrated wood pulp in the form of thin pieces in its washing may be minimized and uniform and efiicient dehydration of the nitrate accomplished by mixing with the nitrated wood pulp prior to its washing and dehydration, some but not more than equal parts and preferably -30% of nitrated cotton (preferably as nitrated linters). This problem cannot be satisfactorily solved by mixing cotton linters and the wood pulp together and then nitrating due to the difference in reactivity to nitration of these two forms of cellulose and the non-uniformity of the product obtained. The result obtained by blending the nitrated wood pulp and nitrated cotton is superior to that which would be expected by merely averaging the properties of the nitrated pulp and the nitrated linters. For example on the basis of loss of cellulose nitrate in ing th fol owin resu ts ha e .b e oba tained.

Perc nt loss of nit ate upo was All nitrated pulp 10.8 nitrated pulp, 25% nitrated cotton linters L 1.3 All nitrated cotton -linter s 1.0 s'w h t a mino -p oport on o ni te e t r he l swes redu ed alm s to th t ed when t e ee l l se t t commie F f 1 nitrated cotton linters was washed.

' The nitra wobd ru e to h eh y te t n is p a i tha retense y n r t aj thi pi ces or milea h as have th aes o le s W QQQl'inch, such as pbtained by tearing or are high." It is to the prevention of these losses that my invention is directed. Wood pulp. to which m e nti n is dapte is t t hi h' a be obtained on the market in the form of sheets of paper thinness. which weigh approximately 1 lb. per 1 0.0sq. it. This sheet is torn or cut into small pieces usually of irregular shape prior to the nitration to facilitate its treatment.

,It is preferred in carrying out my invention to first 'pump the nitrated cotton in a stream of water to the washer followed by pumping the nitrated wood pulp therein in the same manner and mixing the two materials at this point. In this way the nitrated cotton being firstff orms a layer thru which the water from the nitratedv pulp passes. Thusthe nitrated linters act as a bed to rev t o Q 'nitr ed wood l n h n therum e Wate i drain d ofi from th m s The at $1l l i h n st i zed W a by boiling in' water. pulp and cotton is stirred sufiiciently to form a complete and uniform blend. The nitrated cotton appears to act as a buffer to prevent undue break-up of the nitrated pulp and to retain any fines which break 01f therefrom.

After stabilization the blends may be pumped to storage tanks in the form of a slurry such as of 2-5% concentration, particularly if its dehydration cannot be carried out at that time. In carrying out the dehydration the slurry is introduced into a rotating centrifuge basket whereby the water is thrown off forming a cake made up of the blend of nitrated linters and nitrated pulp. This cake is so constituted that a dehydrating agent used flows thru the cake a t t et mall' iees g cellulose nitrate The mixture of nitrated.

evenly and efficiently. Any suitable dehydrating agent may be employed such as a lower aliphatic alcohol. Butyl alcohol has been found to be quite satisfactory for this purpose.

The effect of the nitrated cotton linters in a mass of nitrated pulp is out of all proportion to the percentage of nitrated cotton linters introduced. For example whereas treatment of 2 lbs.

of nitrated pulp with a gallon of alcohol would' only lower the percentage: of water present in the centrifuge cake to app oximately 35%, treatment of 2 lbs. of a mixture consisting of 90% nitrated pulp and nitrated cotton lowered the percentage of water present in the centrifuge cake, under the same conditions, to approximately 27%. Using 2 gals. of alcohol the moisture content of the mass of all nitrated pulp is only reduced to approximately 32%. The addition of a greater percentage of nitrated cotton linters increases the efiectiveness of the dehydration treatment, other things being equal.

My invention is particularly suitable where the wood pulp which is nitrated is in the form of shreds. One type of wood pulp which may be used is that in which the wood pulp which is nitrated is in the form of cuttings having dimensions of approximately 1"x%" and with paper thickness (.0003 to .0004 inch thick) and has an alpha cellulose content of at least 90%.

As an illustration of the beneficent efiect of blending nitrated cotton with nitrated pulp, nitrated cotton linters were pumped in a stream of Water to the washing machine and nitrated wood pulp made from thin pieces of wood pulp, was pumped to the washingmachine in the same manner, the blend being made up (dry weight) of 30% nitrated cotton linters and 70% nitrated pulp. The pumping water was drained ofi and the mass was then boiled with water to stabilize it. i It was also stirred during the stabilization to thoroughly and uniformly mix the nitrated linters and wood pulp. The blended mass was then pumped into a rotating centrifuge basket, whereby the water was thrown off and the blend formed a cake made up of nitrated pulp bits held apart by the fibrous nitrated liners.

Butyl alcohol was then run thru the cake in the rotating centrifuge basket until substantial dehydration had been accomplished. The yield of nitrated pulp was 133%. The yield of nitrated wood pulp is approximately 115% under similar conditions providing no nitrated linters are blended therewith. The yield is based upon the original cellulose as 100%.

In another example carried out in the same way except that the blend was made up of 31% nitrated cotton linters and 69% nitrated pulp the yield of nitrated pulp was 136% as compared to th yield without blending of 115%.

. the nitrogen content range should be so strictly limited, it is to the nitrated pulps within this range that my invention is particularly directed. As little as 1% of nitrated cotton will be helpful altho usually an amount at least 5% of the total amount of cellulose nitrate should be employed to effectively increase the yield.

- My invention is broadly directed to the incorporation of nitrated cotton in general with nitrated wood pulp made from thin pieces of wood pulp in the refining of cellulose nitrate. It is desirable that the nitrated cotton be easily separable. As cotton linters are ordinarily in a form in which they may be readily separated so that they can, when nitrated, be uniformly distributed" in the mass of nitrated wood pulp, their use in nitrated form in the present invention is preferred. Any nitrated cotton which is in an easily separable form however, is suitable for use in my invention. It is preferred to use nitrated cotton in a loosely separated form such as is obtained where the cotton is put thru a picker or other separating machine prior to its nitration.

I claim:

1. In the refining of nitrated wood pulp made from thin pieces of wood pulp, the step which comprises mixing 1-50%v (based on the weight of the mixture) of nitrated cotton therewith prior to at least one of the refining steps.

2. In the refining of nitrated wood pulp made from thin pieces of wood pulp in which the nitrated pulp is washed the step which comprises mixing 1-50% (based on the weight of the mixture) of nitrated cotton, with the nitrated pulp prior to the washing step.

3. In the refining of nitrated wood pulp made from thin pieces of wood pulp in which the nitrated pulp is washed, stabilized and dehydrated, the step which comprises mixing 20-30% (based on the total weight of cellulose nitrate) of nitrated cotton linters therewith prior to at least one of the refining steps.

4. In the refining of nitrated wood pulp made from wood pulp cuttings having a thickness of .0003.0004 inch, the step which comprises mixing 20-30% (based on the total weight of the cellulose) of nitrated cotton loosely separated therewith prior to a refining step.

JOHN L. PATTERSON.