FR2570705A1 - PROCESS FOR PRECIPITATING CELLULOSE CARBAMATE - Google Patents

Abstract

THE PRESENT INVENTION RELATES TO A PROCESS FOR PRECIPITATING CELLULOSE CARBAMATE FROM AN ALKALI SOLUTION. THE SOLUTION IS CONTACT WITH A SOLUTION CONTAINING AN INORGANIC SALT, THANKS TO THE PRECIPITATED CELLULOSE CARBAMATE. THE CARBAMATE SOLUTION IS THREADED INTO A SOLUTION CONTAINING ONE OR MORE SELECTED INORGANIC SALTS IN THE GROUP CONSISTING OF CARBONATE, BICARBONATE, CHLORIDE, SULPHATE, SULPHITE AND BISULPHITE.

Description

Process for precipitating cellulose carbamate.

  The present invention relates to a method for

  precipitate cellulose carbamate from a solution

aqueous alkali.

  Cellulose carbamate is a derivative of alkali-soluble cellulose which is a compound of cellulose and isocyanic acid. It is possible

  to prepare a cell carbamate alkali solution

  lose which can be spun into fiber and in the form of film using a precipitation bath which precipitates the

  cellulose carbamate from the solution.

  As a precipitation bath, a solution contains

  sulfuric acid was used. Cellulose carbamate is stable under acidic conditions and is not

  therefore not broken down when precipitated. When-

  that the alkali solution of the carbamate is brought into contact

  with sulfuric acid, the cellulose carbamate pre-

  cipite and at the same time like sodium hydroxide is

  neutralized, sodium sulfate is formed.

  So the process of spinning the carbamate from cellu-

  lose produces sodium sulphate as a by-product, which due to its low price hinders the economy of the process. A

  another, more remarkable, disadvantage is that the acid neu-

  tralizes sodium hydroxide, which cannot be easily

  Lately returned to the process. Sodium hydroxide in-

  tervient for a significant part in the costs of ma-

  raw materials of the process. It would therefore be de-

  sirable to develop a precipitation process in which no undesirable by-product is formed. Such a precipitation process in which it would not be necessary to use a mineral acid at all and in which at least a substantial part of the sodium hydroxide could be economically recovered would be particularly desirable. However, the process must meet certain requirements with regard to the quality of the fiber or film. For example, the initial strength of the precipitating fiber must be sufficient for the product which is

  manufactured can tolerate mechanical stresses

  which it is subject to in processing. In the fabrica-

  tion of fibers, for example, stretching the fiber in the spinning step is essential to obtain the desired properties. As taught by the invention, it has been found that cellulose carbamate can be precipitated from an alkali solution satisfactorily, with respect to the manufacture of fibers or films, using a solution of precipitation which contains at the

  instead of classic sulfuric acid an inorganic salt.

  Therefore, a process is obtained from

  the teachings of the invention in which it is possi-

  ble to precipitate cellulose carbamate in a solution

  tion which does not contain any mineral acid at all. In the process of the invention also no salt is made as a by-product from which NaOH cannot be regenerated economically. Furthermore, according to the teachings

  of the invention, a process is obtained in which the hydro-

  sodium xyde used to dissolve carbamate can

  be easily retrieved and reused.

  The process of the invention for precipitating the car-

  cellulose bamate from an alkali solution is characterized in that precipitation is carried out in

  a solution containing an inorganic salt.

  The use of a salt solution as a precipitation bath allows the sodium hydroxide contained in

  the spinning solution to be recovered and reused. At the con-

  milking, when sulfuric acid is used, sodium hydroxide is transformed into sodium sulfate and a quan-

  equivalent tity must be introduced into the process.

  Sodium hydroxide explains an important part of

  raw material costs; therefore, it is pos-

  sible using the invention to significantly improve

O10 the economics of the process.

  Another essential advantage of the process

  vention is the possibility of easy recycling and recovery of chemicals. Particularly advantageous is then the use of carbonate solution since in this case, the recovery and recycling of the sodium hydroxide used to dissolve the carbamate can be

  choose advantageously. In principle, he was only born

  stop to ensure that the hydroxide content of so-

  dium in the precipitation bath does not become too high.

  This is achieved by the fact that an equivalent of sodium hydroxide

  dium is removed from the precipitation bath and used to prepare the cellulose carbamate solution. In principle,

  sodium carbonate is not consumed in the pro-

  yielded, nor used other salts in the process.

  In the process of the invention, the salts contained

  in the precipitation solution are inorganic salts.

  Almost all salts exhibit a precipitation effect at least to some extent, although the best results have been obtained using carbonates, bicarbonates, chlorides and sulfates. Salts

  acids also such as bisulfates can be used

  effectively read as precipitates. The best results

  states, concerning both the properties of fibers and the recovery of chemicals appear to be able

  be obtained when a carbonate, in particular carbon

  sodium nate, is used for said salt.

  The amount of salt required depends, for example, on the salt that is used and on its solubility properties at the temperatures employed. Too low a salt content means that the carbamate does not precipitate enough

  quickly, causing deterioration of mechanical properties.

  When sodium carbonate is used, the content

  salt property in the precipitation solution is 10-30% by weight, preferably above 20% by weight,

  most advantageously 25% by weight. When chlo-

  Rures are used as the salt, the appropriate chloride content in the precipitation solution is in the range of 1-30% by weight, preferably in the range of 20-30% by weight. When sulfates are used, the

  appropriate sulfate content in the precipitate solution

  tion is in the range of 1-30% by weight, more suitably in the range of 20-30% by weight. The amount

  salt is normally set to be such that the above

  pitation occurs quickly enough so that the fiber or film being produced can be

spun and stretched.

  In addition to an inorganic salt, the preci-

  pitation may also contain sodium hydroxide.

  The sodium hydroxide content should not become too high since the precipitability of the bath is then lowered. As a result, in a continuous process,

  it is necessary to continuously remove the sodium hydroxide

  dium at the same speed as that at which it enters at the same time as the spinning solution precipitates. It has been observed in the invention that the precipitation bath can contain sodium hydroxide up to 6% by weight, preferably at most 4% by weight, before the

precipitation is too altered.

  In the process of the invention, both fibers and films can be made from cellulose carbamate, by applying the processes and

  conventional means of the viscose process. When we do

  fiber brick, the carbamate solution is spun through dies in a precipitation bath, and when making films, the solution is expressed as

  through a slot-type nozzle in the precipitate bath

  tation. Since in the process of the invention no acid is used at all, less expensive materials

  can be used in equipment.

  In the process of the invention, the carbamate solution which is precipitated typically contains 4-15%

  by weight of cellulose carbamate, and the approximate viscosity

  required of the spinning solution is generally in the range of 550 Ns / m2. The appropriate concentration of sodium hydroxide is typically in the range of 5-12%

in weight.

  When the precipitation is over, the

  treatment of fibers or films, such as washing, drying and other steps, can be carried out using methods and means known per se in the art, which

  do not constitute objects of the present invention.

  The regeneration of the precipitation bath can

  be done in a number of different ways.

  Appropriate procedures have been described, for example in French patent applications filed on the same day as

  the present French patent application and claiming res-

  pectively the priorities of finan-

  dais N 843813 and 843814 by the same plaintiff.

  In the following examples, the method of the

  vention is illustrated in more detail. In the examples, the cellulose carbamate which was used had a content

  2.1% nitrogen and a DP of around 300.

  Solutions A-D were prepared from cellulose carbamate, their compositions being presented

  in table I below. The solutions were fil-

  very airy and deaerated by vacuum treatment. The solutions thus obtained were used in spinning experiments.

TABLE I

  Solution Content of Content Content of Carbon Content

  carbamate in NaOH in ZnO sodium cellulose nate

%%%%

A 7.1 9 -

B 6.5 9 0.9

C 6.5 9 -

D 6.8 9 - 2

E 7.4 9 1 -

Example 1.

  Solution E was spun at am-

  biante in a precipitation bath containing 8% sulfuric acid and 20% sodium sulfate. The spinning was carried out in a laboratory spinning apparatus having a

  nozzle at 100 holes of 50 μm in size. The characteristics

  physical ticks of the fiber thus obtained were as follows: titer 1, 1 dtex, resistance (air conditioning)

  2.2 cN / dtex, 8% elongation, and wet modulus 11.4 cN / tex.

Example 2.

  Solutions A-D were spun at room temperature in a laboratory spinning device having

  a nozzle with 100 holes of 50 vm of dimension. The owners

  precipitation solutions and characteristics

  fibers are obtained in the table

bleau II.

T A B L E A U II

  Solu- Carbamate ZnO Na2CO3 solution Pre- Characteristics of the fiber- tion cells of carbamate bamate lose-NaOH Na2C03 NaOH Temp. Title Resist- Allon- Wet management module (air

condi-

  % %%%%%% C dtex cN / dtex% cN / dtex

A 7.1 9 - - 22.5 0.1 20 2.1 2.1 8 9

A 7.1 9 - 20 - 20 2.3 1.9 9 4.7

B 6.5 9 0.9 - 20 - 20 1.5 2.0 8 6.4

  B 6.5 9 0.9 - 24 0.4 72 3.0 1.8 7 5.1

C 6.5 9 - 20 3.4 20 1.7 2.0 7 11.4

D 6.8 9 - 2 23 3 20 1.0 1.8 10 -

E 7.4 9 1 - 25 - 20 1.1 2.0 7 8.7

N n C)

2Z70705

  The test shows that with the process of the invention, results are obtained comparable to those obtained in the case of the product of Example 1, obtained by acid precipitation.

Example 3.

  A carbamate solution was prepared containing% by weight of cellulose carbamate and 9% by weight of NaOH. Precipitation occurred at 42-44 C in a laboratory spinning device similar to that of Examples 1 and 2. The precipitation bath contained 26% sodium chloride. The physical characteristics of the fiber obtained were as follows: count 2.7 dtex, strength 1.5 cN / dtex, elongation 7% and wet modulus

8.1 cN / dtex.

Example 4.

  A carbamate solution was prepared containing 7.4% by weight of cellulose carbamate and 10% by weight of sodium hydroxide. From the solution, we spun

  fiber using a spinning device of an ins-

  pilot plant, the die used having 100 holes

  vm of dimension. The spinning was done at the temple-

  rature in a precipitation bath containing% by weight of sodium bisulfate. The characteristics of the fibers obtained were as follows: 2.8 dtex titer, 2.1 cN / dtex strength, 4% elongation, and wet modulus

14 cN / dtex.

Example 5.

  A carbamate solution was prepared containing 6.5% by weight of cellulose carbamate and 9% by weight of NaOH and 0.9% by weight of ZnO. From the solution, fiber was spun at room temperature into a water solution, containing 15.4% by weight of Na2CO3 and 3.1% by weight of NaHCO 3. The characteristics of the fibers

  obtained were the following: title 0.99 dtex, resistance

  1.06 cN / dtex tance, 11% elongation and wet modulus

12.4 cN / dtex.

Example 6.

  A carbamate solution was prepared according to Example 5 and fiber was spun from the solution in a water solution containing 12.9% by weight of Na2CO3 and 4.4% by weight of NaHCO3. The characteristics of the fibers obtained were as follows: 0.99 dtex titer, resistance 0.86 cN / dtex, 7% elongation and wet modulus

12.5 cN / dtex.

Example 7.

  A cell carbamate solution was prepared

  lose containing 6.6% by weight of cellulose carbamate and 9% by weight of NaOH. From the solution, fiber was spun at room temperature into a water solution containing 7.0% NaHCO3. The characteristics of the fibers obtained were as follows: 1.08 dtex titer, 0.74 cN / dtex strength, 11% elongation and wet modulus

6.7 cN / dtex.

Claims (4)

  1. Process for precipitating cell carbamate   lose from an alkali solution, characterized in   that the solution is brought into contact with a solution   holding an inorganic salt, whereby the carbamate of cellulose precipitates.   2. Method according to claim 1, characterized   in that the carbamate solution is spun into a solution   tion containing one or more inorganic salts chosen from the group consisting of carbonate, bicarbonate,   chloride, sulfate, sulfite and bisulfite.   3. Method according to claim 1 or 2, charac-   terized in that the precipitation solution contains   sodium hydroxide in an amount of at most 0-6% by weight.   4. Method according to any one of the claims   above, characterized in that the precipitation solution contains sodium carbonate at a maximum of% by weight and sodium hydroxide at reason at most 6% by weight.