FR2458557A1 - PROCESS FOR THE DISSOLUTION OF CELLULOSE IN ORGANIC SOLVENTS CONTAINING A QUANTITY OF LOWERED FORMALDEHYDE AND SOLUTIONS THUS OBTAINED - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR THE PREPARATION OF SOLUTIONS OF CELLULOSE DERIVATIVES IN ORGANIC SOLVENTS, SOLUTIONS FROM WHICH ONE CAN FORM SHAPED OBJECTS IN REGENERATED CELLULOSE BY PRECIPITATION OF THE CELLULOSE DERIVATIVE AND REGENERATION OF THE SOLVENT AND WHICH COMPONENTS IN CONTACT OF CELLULOSE WITH PARAFORMALDEHYDE AND A SOLVENT CHOSEN FROM DIMETHYLACETALDEHYDE, DIMETHYLFORMAMIDE AND N-METHYLPYRROLIDONE UNDER CONDITIONS SUCH AS AMOUNTS OF FORMALDEHYDE CORULEROSE MOSQUELLO-MOO-DEHYDE CORULOSE-MOISTURO-CHROUCIDANT A 13. CELLULOSE DISSOLUTION OCCURS IN THE ABSENCE OF AMOUNTS OF WATER GREATER THAN 0.15 AT TEMPERATURES AT OR OVER 135C.

Description

PROCESS FOR THE DISSOLUTION OF CELLULOSE IN SOLVENTS

  ORGANICS CONTAINING A QUANTITY OF LOWERED FORMALDEHYDE

The Applicant has described in its patent application

FR 79 08268 filed on April 2, 1979 a process for the preparation

  ration of solutions of cellulose derivatives, called ha-

usually "methylol derivatives" 'even if their chemical structure

  that exact is not entirely certain, in organic solvents, particularly dimethylformamide (DMF), dimethylacetamide (DMAC) and N-methylpyrrolidone. Said methods essentially consist in bringing the cellulose into contact with the paraformaldehyde and with the solvent at

  high temperatures, formaldehyde to cell ratios

  lulose being such that the molar ratio of the CH2O units to the anhydroglucosidic units of the cellulose is at least

  minus 13. The cellulose derivative can be precipitated and reg-

  emerge cellulose from these solutions which leads to the formation of shaped objects, for example filaments,

  provided that the mo-

formaldehyde in the solution by degassing or by

  very means to significantly lower the ratio of these reasons

on the anhydroglucosidic units of cellulose, (this report

port will be called in the following for the sake of brevity "report

port CH2O / cellulose ") up to a value even as low as 3. Under these conditions, objects made of regenerated cellulose can be produced from these solutions using

  suitable coagulation and regeneration baths.

  We have found now and this is the object of the pre-

It is an invention that solutions of the type mentioned above can be prepared in which the CH 2 O / cellulose ratios are, even from the start, lower than those which are

believed necessary until now, and we can reach values

their as low as 8. This obviously constitutes a pro-

considerable sandstone since the need for

  formal recovery and purification operations

  dehyde. The method according to the invention is characterized in that the cellulose is dissolved in the 2. the paraformaldehyde / solvent system in the presence of quantities

  of paraformaldehyde corresponding to molar ratios

tives CH 2 O / anhydroglucosidic cellulose units clearly lower than 13 and preferably not significantly higher than 8, at temperatures not lower than

  1350C in the absence of water quantities greater than 0.15%.

  The solutions obtained are threadable, that is to say

that they can be coagulated with simultaneous or ul-

  cellulose by the same methods as those which are adapted to the solutions prepared with contents

  into higher CH2O units and which were then degassed.

Preferably, the solutions are also submitted according to the in-

vention before spinning to a treatment for the reduction of the formaldehyde content which as we said can be

decreased for example to a CH O / cellulose ratio of

about 3. Methods have been described for such spinning by

example in patent applications FR 79 19500 of July 27,

  let 1979 and FR 80 09286 of April 24, 1980 in the name of the Deman-

  deresse. The preferred solvent for carrying out the process according to the invention is dimethylacetamide (DMAC). However we

  can also use DMF and N-methylpyrrolidone.

  The DMAC used must be substantially free of acetic acid and have a water content which is not

  greater than 0.15%, preferably 0.10%.

  The amounts of solvent used are such that the concentration of cellulose in the final solution is

between 5 and 15%.

The duration of the cell dissolution operation

  lose depends on the speed of heating, agitation and

the temperature and is between 20 minutes and 2 hours.

Preferred temperatures are between 1351C and WC. The invention will be better understood by the examples

following non-limiting.

EXAMPLE I

  40.5 parts of a pre-hydrolyzed cellulose obtained by the sulphate method (degree of polymerization DP about 500) dried in an air circulation oven are mixed

  for one hour with 63 parts of commercial paraformaldehyde

cial (purity greater than 95%) and with 370 parts of distilled DMAC (water content not greater than 0.1%) in a

  reactor completely lined and fitted with efficient agitation

that's. The reactor head is preheated to around 160WC

  to prevent deposition of sublimed paraformaldehyde and heating

  then fe the mixture with stirring. After 10 minutes the temperature

  the reaction reaches 1250C.

For 20 minutes, the temperature rises from 1250C to 150WC and this temperature is maintained for another few minutes. At this time, the dissolution is complete and the reactor is opened after slowly bringing the pressure to ambient pressure. The temperature at this time is -1200C and it is kept at the same level throughout

the time required to degas formaldehyde, i.e.

say for about 20 minutes.

  A final solution is thus obtained containing 10% of cellulose with a degree of polymerization (DP) of 370 and with 6.3% of formaldehyde. The quantities of reagents used show that the solution was initially prepared with a CH2O / cellulose ratio of approximately 8. In this text

  all parts and percentages are by weight.

EXAMPLE II

40.5 parts of a pre-hydrolyzed cellulose prepared by the sulphate method (DP approximately 500) dried in an air circulation oven for one hour are mixed with 63 parts of commercial paraformaldehyde (purity greater than 95%) and with 380 parts of distilled N-methylpyrrolidone

  (water content not more than 0.1%) in a combined reactor

  fully jacketed with effective agitation. We pre-

  heats the reactor head to 1600C to prevent condensation

  tion of sublimed paraformaldehyde and the mixture is then heated with stirring. After approximately 10 minutes, the temperature of the mixture reaches 125WC and in the following 20 minutes it rises from 125 to 1500C and it is maintained at this value

for another 30 minutes.

At this time, the dissolution is complete.

  The reactor is opened after having reduced its pressure

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4.

  at ambient pressure. At this time, the temperature is maintained.

  reaction temperature between 115 and 1200C and the gas is degassed

  residual formaldehyde in about 20 minutes.

  A final solution containing approximately 10% cellulose and 6.1% formaldehyde is obtained from which cellulose films with a DP of approximately 380 can be obtained by precipitating the cellulose, for example by

  an ammonia bath having a concentration of 5%.

EXAMPLE III

  40.5 parts of a pre-mixed cellulose are mixed

hydrolyzed obtained by the sulphate method (DP about 500) dried in an air circulation oven for one hour with 78.5 parts of a commercial paraformaldehyde

  (purity greater than 95%) and with 370 parts of DMF available

  tilled (water content not more than 0.1%) in a reac-

completely jacketed with effective agitation.

The reactor head is preheated to prevent deposition of sublimed formaldehyde and the mixture is then heated with stirring. After 10 minutes, the temperature of the mixture reaches 125WC. In 20 minutes, the temperature rises from 125 to 1500C,

  temperature which is maintained for 30 minutes.

At this time, the dissolution is complete and the reaction is opened.

tor after slowly reducing the pressure to ambient pressure at a temperature of about 1200C. The excess formaldehyde is degassed for approximately 15 minutes until a final solution containing approximately% of cellulose is obtained with a DP of approximately 350 and a content of

8% formaldehyde.

  As goes without saying and as it already follows from the foregoing, the invention is in no way limited to those of its embodiments and of application which have

been more specifically contemplated; she embraces it

milk all variants.

,

Claims (8)

  1. Process for the preparation of de-   riveted of cellulose in organic solvents from   which can be produced from shaped cellulose generated by precipitation of the cellulose derivative and reg-   cellulose generation, process comprising bringing into contact   tact of cellulose with paraformaldehyde and the organic solvent at an elevated temperature and in which the solvent is chosen from dimethylacetamide (DMAC), dimethylfor-   mamide and N-methylpyrrolidone, characterized in that corresponding quantities of formaldehyde are used to molar ratios of the CH 20 units to the cell units lose anhydroglucosidic less than 13 and that the dissolu- tion of cellulose takes place in the absence of quantities of water   greater than 0.15%, at temperatures that are not in- below 1350C.   2. Method according to claim 1, characterized in that the molar ratio of the CH2O units on the anhydroglucosidic patterns is greater than about 8. 3. Method according to claim 1, characterized in that the dissolution of the cellulose is carried out   temperatures reaching values higher than 1500C. 4. Method according to claim 1, characterized   by the fact that we treat the solution to reduce the t- neur in formaldehyde up to a value corresponding to a CH2O / cellulose ratio which is not less than 3.   5. Method according to claim 1, characterized   by the fact that the solvent is dimethylacetamide.   6. Method according to claim 5, characterized in that the dimethylacetamide is devoid of acid   acetic and has a water content which is not higher than less than 0.1%.   7. Method according to claim 1, characterized in that an amount of solvent is used such that a final solution is obtained having a content of cellulose between 5 and 15%.   8. Solutions of cellulose derivatives, characteristic   sed by the fact that they are prepared by the se-   according to one of claims 1 to 7.