DE1178035B - Process for the production of chemically modified cellulosic material - Google Patents

Description

Process for the production of chemically modified cellulosic material The method according to the invention relates to the production of one for paper production or chemical processing of preferably suitable cellulose material Raw cotton linters.

After mechanical cleaning, the cotton linters have a degree of crystallization which roughly corresponds to that of wood pulp. The raw cotton linters must, however nor can a product be subjected to a dry cleaning process result, which is used for paper production and for the production of cellulose derivatives, z. B. cellulose acetate, sodium carboxymethyl cellulose, ethyl cellulose and the like. The chemical treatment of raw linters includes the digestion in Alkali leaching under pressure and that usually done with chlorine or a hypochlorite Bleaching.

The conditions to be used may vary depending on the contaminants to be removed and the physical state of the raw liner can be varied. Purification serves primarily the removal of wax, pectins and small amounts of staining Components that are distributed in or on the fibers, and at the same time the almost complete destruction of the impurities that are physically fine in the linters distributed, but not bound by them. In addition, the degree of degradation of the linters regulated here.

Though dry cleaning the cotton linters for making of a high quality product is essential, it has been found that the degree of crystallization of the cotton linters increased considerably during cleaning during the digestion of alkali.

The increased degree of crystallization is generally considered to be the cause viewed for their decreased chemical reactivity and their inability to to give paper of high strength under normal finishing conditions. It The aim was therefore to obtain purified cotton linters with a reduced degree of crystallization and modified morphology to improve chemical reactivity and to achieve the properties required for papermaking.

It has now been found that this increase in the degree of crystallization can be achieved thereby preventing or almost completely eliminating the fact that one is in front of or on Beginning of the alkali treatment on the anhydroglucose units ether substituents in added to such an amount that the chemically modified cotton linters in Alkali and water remain insoluble and the fiber structure of the raw, unmodified Keep cotton linters.

The ether substituents to be added are preferably those which are more hydrophilic or polar in nature. to these include the carboxyalkyl radicals, e.g. B. the carboxymethyl, Carboxyethyl radical and the like, either in the form of the free acid or in the form of an alkali metal salt, also oxyalkyl, sulfalkyl, z. B. the sulfethyl radical and the like., Either in the form of the acid or in the form of an alkali metal salt, and cyanoalkyl radicals, e.g. B. the cyanoethyl radical and the like.

The oxyalkyl substituents that are used according to the invention for chemical Modification of cotton linters that can be used include oxyethyl, oxypropyl, Oxybutyl and similar radicals and mixed oxyalkyl radicals, such as oxyethyl, oxypropyl and the like. The preferred substituent in practicing the invention is the oxyethyl radical.

The etherification takes place under those known for the cellulose etherification external conditions, but with a correspondingly small amount of etherifying agent.

Maintaining the alkali insolubility is necessary because the linters after etherification, this is usually done at high temperatures and pressures in the presence be subjected to digestion carried out by aqueous alkali. The alkali and Insolubility in water depends on the degree of substitution.

It has been found that it is expedient as a substituent in the oxyethyl radical is not to exceed a degree of substitution of about 0.5.

After mechanical cleaning, the cotton linters become ordinary a wetting or pre-soaking in aqueous alkali of a concentration of about 2 to 10 percent by weight. The purpose of the soft or meshing stage is the even distribution of the lye in the cotton linters. The pre-soak level is usually carried out under normal temperature and pressure conditions. A An excess of alkali is generally appropriate. After removing the excess Alkali lye is used to etherify the linters, e.g. B. by treatment with ethylene oxide.

Then the cotton linters are introduced into a decomposition vessel, where they with aqueous alkali, the concentration of which is about 1.5 to 4.5 percent by weight amounts to be treated. The digestion conditions, such as. B. time, temperature and Concentration of the alkali, must be adjusted in the usual suitable manner, the desired degree of purification and the desired degree of degradation of the cleaned Achieve linters. During the digestion, wetting agents can be added to the digestion liquid Small amounts are added to help remove impurities from the To facilitate cotton linters. The digestion can be used continuously a suitable system at temperatures up to 185 ° C and with treatment times be performed in no less than 10 minutes. If desired, the Digestion can also be carried out discontinuously by making vertical stationary or rotating ones Vessels used.

In the discontinuous process, the temperatures can be between 135 and 170 ° C and the duration varies between 2 and 6 hours. Generally recommends it is, both in the continuous and in the discontinuous digestion Use positive pressures.

After wetting the linters with caustic lye there is enough alkali available in order to reduce the reaction between the cotton linters and z. B. ethylene oxide to catalyze with addition of the oxyethyl substituent. With continuous The ethylene oxide must be used during the initial stages of the digestion process Cotton linters are implemented so that the treatment with ethylene oxide in the continuous digestion vessel before a substantial increase in the degree of crystallization z. B. in the first or the first two tubes one with eight to ten tubes equipped, continuously working digestion vessel is completed. The treatment of the cotton linters with ethylene oxide can also be done separately Stage, between the pre-soaking stage and the digestion.

The chemical modification by means of ethylene oxide can be carried out with normal Temperature and pressure conditions, but optionally also at somewhat elevated temperatures and pressing.

The chemically modified cotton linters become through the digestion freed from impurities, but retain a yellow-brown color and must be in the generally still be bleached. The bleaching processes used for this are the same the well-known and normally used to remove colored contaminants the cotton linters. The bleaching agents used are chlorine, hypochlorite, Chlorine dioxide, peroxide, permanganate and similar oxidizing agents are possible. The conditions, such as time, temperature, pH value, concentration tration of the bleach, etc., are the usual ones. The bleaching can be carried out in one or more stages with washing in between and filtering to remove the waste liquor.

After bleaching, the linters are washed and then dried.

The product according to the invention can be used in processes where cotton linters with improved strength properties are desired.

These properties are required in papermaking. aside from that The product according to the invention can be used where there is an improved reactivity the cotton linters are desired, e.g. B. in acetylation, ethylation, carboxymethylation and oxyethylation process for the production of cellulose derivatives from cotton linters, z. B. of acetylated oxyethyl cellulose, carboxymethyl-oxyäthylcellulose, Äthyloxyäthylcellulose, water-soluble oxyethyl cellulose and the like.

Example 1 The degree of crystallization was determined in a series of experiments different samples determined on the basis of X-ray diagrams. Samples were taken of 1. raw, mechanically cleaned "second-cut" cotton linters (cotton linters from the second pass with an average length of 2 mm), 2. mechanical Purified second-cut cotton linters after swelling in aqueous alkali, pressure digestion in aqueous alkali and bleaching with chlorine in the usual way and 3. of wood pulp of good chemical reactivity and satisfactory properties for papermaking.

Furthermore, the degree of crystallization of different types of cotton linters was determined determined that had been chemically modified according to the invention.

These chemically modified cotton samples were made by raw, mechanically cleaned "second-cut" cotton linters in aqueous alkali let go, with ethylene oxide with the addition of Oxyäthylubstituenten in various Degrees of substitution reacted, made a digestion with aqueous alkali, with chlorine bleached, washed and dried.

The degrees of crystallization of the various samples are shown in table 1 shown. In these and the following examples, the degree of substitution is indicated by S. G. designated.

Table I. Crystalline station Sample SG Degree Wood pulp .................. - 53 Raw liner ..................... - 54 Chemically cleaned linters .... - 65 0.017 58 Chemically modified and cleaned 0.054 60 Niges Linters .................. # 0.19 58 0.23 54 0.25 53 These data show that in practice the invention leads to a product whose degree of crystallization is substantially lower than that of cotton linters which have been treated by the usual mechanical and chemical cleaning processes.

Example 2 The advantage that can be achieved with the invention is evident from the data listed in Runs 1 to 10 of Table II. These attempts are to be regarded as pairs of experiments, so experiments 1 and 2 form the first pair. The experiments with odd digits were based on previously known ones Procedure performed by removing the cotton linters after dry cleaning were etherified. The trials with even numbers were carried out according to the present Invention executed by the cotton linters before their dry cleaning were etherified. The cellulose starting material consisted of in all experiments mechanically cleaned "second-cut" raw cotton linters (cotton linters from the second Passage with an average length of 2 mm). In the trials with odd The raw cotton linters were digested digits with aqueous alkali, with chlorine bleached, washed and dried. The resulting chemically cleaned cotton linters were then etherified to make the final paper base. In the trials with even numbers the raw cotton linters were soaked in aqueous alkali, etherified and then digested with aqueous alkali, bleached with chlorine, washed and dried to produce the final paper base. All products were at a consistency of 2.5% (neutral pH) in a Valley Dutchman refined with 0.56 kg with a base plate load of 6 kg. The refined samples have been using a Noble Wood hand scoop to achieve a Base weight of 18 kg (500 sheets 24 x 36) hand-scooped. The leaves were subsequently conditioned and according to standard TAPPI procedures (Technical Association of the Pulp and Paper Industry). The tests showed the strength of the leaves, expressed in the burst strength according to M u 11 e n, the tear strength according to E I m e n d o r f, the tensile strength and the folding strength or the kink resistance. The details are given in Table II.

Table II try 1 2 3 4 5 6 7 8 9 10 ornate, Paper base HEC *) HEC *) uPc *) HPC *) HBc *) HBC *) CEC *) CeC *) NacMc *) INacMc *) woll-Lintere Ethereal agent ethylene oxide propylene oxide butylene oxide acrylonitrile monochlorine none acetic acid SG ............ 0.20 0.20 0.03 0.05 0.03 0.01 0.01 0.01 0.02 0.02 unsubstituted performed Degree of crystallization,% ... 62 58 60 54 62 57 l 65 Burst resistance after Mullen, kg / cm2 ..... 2.43 3.05 2.19 2.54 1.75 2.26 2.03 2.53 1.89 2.00 1.26 Tensile strength according to Elmendorf. g / sheet 54 88 68 93 68 82 73 76 73 100 70 MIT fold strength, double, ASTM. D-643-43, B. 597 2945 208 1010 59 327 64 1200 85 232 23 Tensile strength, kg / cm ... 2.97 3.39 2.35 3.33 2.67 2.74 Grinding time in hours. 2.0 2.0 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 *) HEC = hydroxyethyl cellulose.

HPC = hydroxypropyl cellulose.

HBC = hydroxybutyl cellulose.

ClEC = carboxyethyl cellulose.

NaCMC = Na-carboxymethyl cellulose.

Example 3 The importance of the invention becomes even more apparent, if you achieved the cotton linters chemically modified by acetylation Compare the results with the results obtained with those cleaned in the usual way Cotton linters can be obtained using the same process. In experiment 1 were mechanically and chemically cleaned cotton linters that are used for acetylation Well-suited chemical cotton material apply, acetylated to the triacetate and investigated the solutions of the triacetate. In experiment 2, the chemical cotton replaced by chemically modified cotton linters, according to the invention by Oxyethylation of mechanically cleaned cotton linters with ethylene oxide before chemical Cleaning were made.

In the preparation of the various samples triacetate was used Acetylation process applied to fibers. 50 g each of the air-dried rehearse were soaked in 750 cc glacial acetic acid for 5 hours. From 650 cm of benzene and 300 cc Acetic anhydride, an acetylation mixture was prepared and cooled to 0 ° C. This mixture was placed in a vessel which contained 1.25 g of H2SO4 (96%).

After the acetylation mixture had been stirred, the The swollen sample is placed in the vessel and the temperature is reduced to 0 ° C for 30 minutes held. Acetylation took place while the vessel was at 30 ° C for 17 hours was shaken.

The fibrous triacetate was filtered and successively with benzene, Washed methanol and distilled water. The triacetate was by two Boiling in distilled water for one hour each and stabilized after Centrifuge dried at 105 ° C.

With a methylene chloride-ethyl alcohol mixture (85:15) were 15 weight percent Triacetate solutions produced and their falling ball viscosity, the Birefringence and the filterability is determined. The filterability of the solutions was determined by the Volume (ccm) of that at a given pressure until the flow of solution ceases measured solution passing through a certain filter medium. So the bigger it is Volume, the better the filterability.

The results of these determinations are shown in the table below specified.

Table 111 Ball drop filterable Double SG viscosity seek refraction in seconds (ccm) 5 - 45 to 60 23 to 30 66 to 94 2 0.16 81 12 236

Claims (1)

Claim: Process for the production of chemically modified cellulose material by opening up raw cotton linters with aqueous alkali at an elevated temperature and increased pressure and etherification, characterized in that the etherification before or at the beginning of the alkali treatment is carried out and that it is only so far is carried out that the fiber structure and the insolubility in alkali and water of the Raw cotton linters are retained. Considered publications: German Patent Specifications No. 493 585, 516461.