CS257613B1 - Method of synthetic rubber's latex coagulation - Google Patents

Abstract

Method of coagulation of synthetic rubber latex by addition of inorganic acid in the presence of an auxiliary coagulation agent based on collagen, which is an alkali metal salt of a hydroxymethyl derivative of hydrolyzed collagen. The auxiliary coagulation agent is stable even during prolonged storage

Description

The invention relates to a method of coagulation of synthetic rubber latex by the addition of an inorganic acid, optionally in a mixture with an inorganic salt, in particular by the addition of sulfuric acid and sodium chloride, in the presence of an auxiliary coagulant of a certain type.

Coagulation of synthetic latexes is currently most often carried out using a salt-acid system in a coagulation cascade, i.e. in a series of serially connected cylindrical coagulation vessels equipped with a stirrer. In the first phase, the so-called creaming of the latex occurs due to the added brine, accompanied by agglomeration of latex particles and release of the emulsifier into the dispersion phase.

In the next stage, the creamed latex is precipitated with acid.

A prerequisite for coagulation to proceed without obvious technological difficulties is to achieve a suitable size of coagulation slurry and perfect clarification of the waste coagulation serum with minimal consumption of salt and sulfuric acid. Too coarse slurry disrupts its continuous overflow to the next stage of the coagulation cascade and, conversely, if the slurry is too fine, an excessive amount of sediment is created in the next phase of the technological process, which is adversely affected, for example, by increasing sediment in screw devices and in dryers.

It is generally known that the size of the pulp can be influenced by changes in the electrolyte concentration in the cream, or in the coagulation serum. However, to achieve a sufficiently fine coagulation pulp and perfect clarification of the coagulation serum, it is necessary to dose a large amount of salt during the creaming process. Since the high concentration of salt in the waste serum during the coagulation of synthetic latexes has a negative impact on the environment, there is currently an effort to perform coagulation with reduced salt consumption, or in its absence.

If the coagulation of butadiene-styrene latexes is carried out only with sulfuric acid, i.e. without prior creaming with NaCl, its consumption during coagulation is excessively high, since in this case the acid serves not only to decompose resin and fatty acid salts, but also as an electrolyte, i.e. a coagulant and a clarifier. However, the coagulation slurry becomes increasingly sticky and sulfuric acid is more difficult to wash out. This has a negative impact on the modulus values and thermo-oxidative aging. Nevertheless, in this case, perfect clarification of the waste coagulation serum is not achieved even with a high acid dosage.

More complete clarification of coagulation serum while simultaneously reducing the size of coagulation debris can be achieved with reduced consumption of electrolytes, i.e., sodium chloride and sulfuric acid, in the presence of auxiliary coagulation agents.

Coagulation of synthetic rubber and latex, especially in the absence of sodium chloride or other similar salts, is therefore usually carried out using glue and acid.

A significant portion of the world's synthetic rubber production is produced in this way.

According to AO ČSSR 102 343, reducing the size of the coagulation slurry and thus reducing salt consumption can be achieved by carrying out the coagulation process in the presence of auxiliary coagulation agents, e.g. bone or skin glue. However, the use of glue to regulate the size of the slurry is made more difficult and sometimes completely impossible at higher latex temperatures, especially above 50 °C, because the waste coagulation serum is often insufficiently clarified, sometimes even cloudy.

To reduce salt consumption, it is known to use collagen hydrolysate with a molecular weight of around 2,000. In AO 1,065,424, the dosage of collagen hydrolysate with an average content of terminal carboxyl groups of 0.7 to 20% is recommended. However, it turns out that low-molecular collagen hydrolysates themselves are unsuitable for coagulation, because at very low molecular weights they do not contribute to the refinement of the size of the coagulation grit. Also the effectiveness of collagen hydrolysate in terms of sulfuric acid consumption when reducing their molecular weights.

Rubber Age 1965, 5, 73 states that the consumption of salt or glue in coagulation systems can be reduced by adding suitable polyamines, the application of which contributes to a more complete clarification of the waste coagulation serum.

However, due to their high price, polyamines are mainly only considered for technical use as by-products from the production of hexamethylenediamine, known under the trade name Amine 248. In countries where hexamethylenediamine production is not established, the advantageous properties of polyamines cannot usually be economically exploited.

It is also known from AO ČSSR 248 390 that coagulation of synthetic latexes can be carried out by using a mixture of gluten and its hydrolysates in a ratio of 1:20 to 6:1 as an auxiliary coagulation agent in the coagulation of latexes at temperatures above 50 °C, with a total amount of auxiliary coagulation agent in the range of 0.01 to 10 kg of the mixture based on 1 ton of synthetic rubber.

Gluten refers to water-soluble collagen contained in bone or skin glue.

Collagen hydrolysates with a molecular weight of less than 10,000 are designated as its hydrolysates. Hydrolysates with a molecular weight of less than 1,000, which mainly contain oligopeptides and alpha-amino acids, are designated here as low-molecular hydrolysates.

The ratio of both components in the coagulant can be used to advantageously change the properties of the coagulation system as needed. Increasing the ratio of glutin/glutin hydrolysate leads to a finer coagulation slurry. Reducing this ratio achieves a more complete clarification of the coagulation serum, especially in the case of low-molecular hydrolysates.

A common drawback of all substances prepared from natural sources is their easy susceptibility to putrefactive decomposition, which is accompanied by changes in their effectiveness and an adverse effect on the course of the coagulation process.

These disadvantages are eliminated by the method of coagulation of synthetic rubber latex by adding an inorganic acid, optionally in a mixture with an inorganic salt, in particular by adding sulfuric acid and sodium chloride, in the presence of an auxiliary coagulation agent based on collagen, consisting in the auxiliary coagulation agent being a salt of a hydroxymethyl derivative of hydrolyzed collagen of the general formula

R t I i

OíICH--ř-NH - CH - C+-O - M, r „ 'n . O where R is a side fragment in the unit of the amino acid molecule contained in collagen, n is 2 to 50 M is an alkali metal, especially sodium or potassium, or mixtures thereof with hydrolyzed collagen in a weight ratio of 90:1 to 1:90, preferably 10:1 to 5:1, while the amount of auxiliary coagulation agent is 0.01 to 10 kg per 1 ton of synteric rubber contained in the latex.

The salt of the hydroxymethyl derivative of hydrolyzed collagen may preferably be a product prepared by reacting formaldehyde with hydrolyzed collagen with a number average molecular weight of 200 to 5,000, using 0.2 to 5 moles of formaldehyde per 1 kg of hydrolyzed collagen depending on its content of terminal amine groups, and the reaction is carried out in an alkaline medium in the presence of hydroxides and/or alkali metal salts.

Derivatives of the above composition are generally known, but it is not known that they can be used as a coagulant agent. Their presence contributes to easier washing of sulfuric acid from the polymer during coagulation and therefore to improved thermo-oxidative stability of synthetic rubbers. Increasing the proportion of lower molecular weights contributes to clarification of waste coagulation serum, increasing the proportion of higher molecular weights results in a reduction in the size of the coagulation slurry and therefore easier flooding of the coagulation slurry. Compared to polyamines, their higher molecular weights allow coagulation with less intensive mixing.

Aqueous solutions of these salts are significantly more resistant to putrefactive decomposition and are as effective in terms of coagulation as the starting collagen hydrolysates used for their preparation.

The method according to the invention is further illustrated in more detail by examples of specific embodiments. Example 1 serves for comparative purposes.

Example 1

50 g of SBR 1500 butadiene-styrene latex with a dry matter content of 19.8% was weighed into a 150 ml glass beaker, which was heated to 65 °C. 2a mixing · 10% sulfuric acid was gradually added to the latex using a Radelkis OP 830 automatic burette at a rate of 2.5 ml/min. Mixing was carried out so that the sulfuric acid drops fell directly into the latex, not onto the coagulum that was forming.

The titration was interrupted as soon as spontaneous coagulation of the latex occurred in the entire volume while the waste coagulation serum was clarified. Perfectly clarified coagulation serum was not achieved in this experiment. The consumption of 10% sulfuric acid in the experiment carried out in this way was 40 ml, which corresponds to the consumption of 0.4 t I^SO^/t. Synthetic rubber (SK).

This example illustrates the fact that in the absence of an auxiliary coagulant, coagulation proceeds with a high consumption of sulfuric acid.

Example 2

The coagulant aid according to the invention was prepared as follows:

16 l of distilled water and 4 kg of bone glue were added to a stainless steel reactor with a volume of 20 l. The contents were gradually heated to a temperature of 95 °C. After reaching this temperature, 240 g of soda ash were added. Hydrolysis was carried out at a linear peripheral speed of the stirrer of 1.4 m/sec. The content of terminal amine groups and the number average of molecular weight values, hereinafter referred to as M _n ·

The calculated amount of formaldehyde added to the hydrolyzate solution for reaction with terminal primary amine groups, as well as other data obtained, are given in the attached Table No. 1.

The auxiliary coagulant according to the invention thus obtained was used in the coagulation of synthetic rubber latex according to Example 1.

The consumption of sulfuric acid during coagulation is considerably lower than during coagulation in the absence of an auxiliary coagulant and does not vary over a wide range of M^.

All prepared aqueous solutions of sodium salts of hydroxymethyl derivatives of hydrolyzed collagen showed significantly higher resistance to putrefactive decomposition, which was manifested by an extension of the shelf life without obvious signs of putrefactive decomposition.

With the decrease in molecular weight of these derivatives, an increased resistance of aqueous solutions to reduced temperatures was also noted. The freezing point, at M^ lower than 3,000, was around the freezing point of water.

It has been shown that aqueous solutions of hydroxymethyl derivatives of collagen can only be prepared if M _n is lower than 5,000. If it is higher, the hydrolysate gelates due to cross-linking reactions, so that the advantageous properties of hydroxymethyl derivatives, especially their long-term shelf life, cannot be used in the production of synthetic rubbers. This is especially true for skin glue, whose M _n is significantly higher than that of bone glue.

This example illustrates the positive effect of the present hydroxymethyl derivatives on coagulation and their resistance to putrefactive decomposition with a change in molecular weight over a wide range of molecular weights. At the same time, the molecular weight range of these derivatives for the preparation of aqueous solutions is defined.

Example 3

A significant influence of the molecular weight of the hydroxymethyl derivatives on the consumption of sulfuric acid during coagulation occurs only with large differences in molecular weights, as can be seen from the results obtained during the hydrolysis of bone glue with a molecular weight of 14,000 in the presence of 1% sodium hydroxide at temperatures of 130 °C after 2.5 hours of hydrolysis. The amounts of formaldehyde used and the results are given in Table 2. In the case of bone glue, in addition to formaldehyde, soda ash was added in an amount of 0.000 1 g/g dry matter of hydrolyzed collagen. It is obvious that the somewhat increased consumption of acid with a decrease in M _n of the hydroxymethyl derivatives brings significant advantages in the field of storage stability of the solutions.

Example 4

This example illustrates the effect of the molecular weight of hydroxymethyl derivatives on the size of the coagulant pulp.

Coagulation of SBR latex was carried out with the addition of sodium salts of hydroxymethyl derivatives of mixtures with different ratios of bone glue and its hydrolysate.

The coagulation device consisted of a vessel of $ 220 mm and a capacity of 12 1. The stirrer was equipped with a pair of blades measuring 70 x 30 mm, which were inclined at an angle of 45° to the axis and two pairs of knives measuring 80 x 30 mm. The stirrer speed was 1,350 min

To 3,000 ml of latex, with a dry matter content of 20%, heated to 65 °C, was added, with stirring, 30 ml of a 10% solution of a mixture of hydroxymethyl derivatives of bone glue and its hydrolysate. The latex with this mixture was dosed in 165 ml increments simultaneously with 6 ml of 10% р^SO^, with stirring, into coagulation serum, heated to 65 °C, with the following composition:

400 ml of distilled water 120 ml of 10% H ₂ SO ₄ ml of 10% solution of a mixture of hydroxymethyl derivatives

The number _of bone glues was 6,500 and its hydrolysate was 690.

The molecular weights of mixtures with different bone glue contents, the necessary doses of formaldehyde for the preparation of their hydroxymethyl derivatives, and the particle sizes of the coagulation pulp obtained when using them are given in Table 3.

Example 5

The influence of hydroxymethyl derivatives in terms of their minimum consumption during coagulation of butadiene-styrene latexes was obtained by titration of 50 g of latexes (20% dry matter) of the SBR 1,500 type, containing various amounts of the auxiliary coagulant, 10% sulfuric acid, at 65 °C.

The experiments used sodium salts of hydroxymethyl derivatives of hydrolyzed hand glue with a number average molecular weight M^ = 3,115, which were prepared by adding 0.009 63 g of formaldehyde per 1 g of dry matter of the hydrolyzate of the indicated molecular weight. The results obtained are summarized in Table 4.

From the results of this example, it can be seen that the amount of dosed hydroxymethyl derivatives prepared from hydrolysate based on hand glue significantly affects the consumption of sulfuric acid during coagulation. Dosing the agent above a certain limit, in this case at amounts higher than 4 kg/t SK, no longer leads to a significant reduction in sulfuric acid consumption, although coagulation can still be carried out under these conditions.

Example 6

The use of small amounts of auxiliary coagulation agent near the lower limit of the proposed range is evident from coagulation carried out under operating conditions in a coagulation cascade with reduced salt consumption. The example also illustrates the possibility of using hydroxymethyl derivatives in combination with collagen hydrolysates.

3

20 m/h of latex type SBR 1,500, 2.4 m/h of saturated brine (26%), and 100 l/h of a 1% aqueous solution of auxiliary coagulation agent, which are sodium salts of hydroxymethyl derivatives of hydrolyzed collagen and with a number average molecular weight M = 808, flow into the first stirred vessel. n

A mixture of 20% bone glue and 80% collagen hydrolysate with 700 was used as the starting material. 4.3 kg of 37% formaldehyde/t dry weight of the auxiliary agent was added to this mixture, i.e. 10 times less compared to the amount calculated according to the content of terminal amine groups. The latex mixture flows into a second stirred coagulation vessel, into which 20 kg t^SO^/h is dosed together with the return serum.

In terms of overflow, the coagulation trough in the second vessel was of optimal size, with the waste coagulation serum being completely clear and the coagulum drying well. Before dosing the auxiliary coagulation agent, it was necessary to dose saturated brine in an amount of 3.2 m/h.

Example 7

In experiments carried out in a similar manner as in Example 1, except that the coagulation temperature was increased to 95°C, a significant effect of temperature on the consumption of sodium salts of hydroxymethyl derivatives of hydrolyzed collagen was found. By increasing the temperature of the coagulation medium from 65°C to 95°C, the consumption of the dry substance of the agent decreased when using the same amount of sulfuric acid (20 kg/t of synthetic rubber) from 0.6 to 0.25 ml of 10% auxiliary coagulant per 50 ml of latex.

Example 8

After adding 2.5 ml of sulfuric acid with a concentration of 10% to 50 kg of SBR latex with a dry matter of 20%, a part of the polymer precipitated from the latex at 65 °C. After that, a 1% solution of sodium salt of hydroxymethyl derivatives of hydrolyzed collagen with M = 3,115 was gradually added until the coagulation serum was completely clarified. The total consumption of 1% reagent was 3.66 ml.

In another experiment, 10 ml of sulfuric acid (10%) was added to the latex at the same temperature, i.e. 4 times more than in the first experiment. The total consumption of 1% auxiliary coagulation agent required for complete clarification was 1.6 ml. This fact shows the possibility of reducing the consumption of auxiliary coagulation agent in the case of mixing latex with return serum, in which the sulfuric acid concentration is higher than in the coagulation vessel. Therefore, it is appropriate to mix latex with acidified return serum in mixers of various designs.

Table 1

Hydrolysis time (h> 0 1 4 8 10 15 20 ^With n 6,500 4,970 4 227 3 555 3,115 2,350 1,960 Concentration of terminal amine groups Uimol/q) 154 201 237 281 321 426,511 Addition of formaldehyde 100 i <9 ^/k 5> 37 % 4.61 12.5 6.04 16.3 7.09 19.2 8.44 22.9 9.63 26.0 12.77 15.3 34.5 41.4 Consumption of 10% sulfuric acid during coagulation (ml/50 q latex) 2.30 2.36 2.45 2.40 2.40 2.33 2.47 Amount of auxiliary 10% coagulant (ml/50 g hatex) 0.25 0.25 0.25 0.25 0.25 0.25 0.25 Storage life of 20% aqueous solutions of collagen hydrolysates (days) 2 5 5 6 7 7 10 Storage life of 20% aqueous solutions of sodium salts of hydroxymethyl derivatives (days) 10 30 32 35 37 40 40 Table 2 Hyarolysis time_.{hl_ __ _ . 0 . 2 _x 5 ^With n 14,000 900 Concentration of terminal amine groups (mol/q) _____Stares.. 1,111.1 Formaldehyde addition 100 % 2.14 33.3 (g/kg) dosed: 37 % 5.79 90 Consumption of 10% sulfuric acid for coagulation of 50 g latex (ml/50 q latex) _____lUá _____á _x 0_ Shelf life (days) 2 350 Resistance to low temperatures up to + 18° C - 1 °C Table 3 Glue content (% by weight) 8 .15 20 30 40 ^M n (q/mol.) 768 808 052 942 1,074 Formaldehyde addition (q/kq of mixture) 39.1 31.7 35.2 31.8 27.9

Evaluation of particle size of the crushed large pieces have broken into crushed lumps with particles of compact size approx. approx. approx. approx. coagulum .30 mm 25 mm 20 mm 15 mm

Claims (2)

SUBJECT OF THE INVENTION A method for coagulating a synthetic rubber latex by adding an inorganic acid, optionally in admixture with an inorganic salt, in particular sulfuric acid and sodium chloride, in the presence of a collagen-based coagulating agent, characterized in that the coagulating co-agent is a hydroxymethyl derivative of hydrolyzed collagen. formulas R AND OHCH ₂ * - f - NH - CH - C 1 - O - M, Where R is a side fragment in the unit of the amino acid molecule contained in collagen, n is 2 to 50 and M is an alkali metal, especially sodium or potassium, or a mixture thereof with hydrolyzed collagen in a weight ratio of 90: 1 to 1:90, preferably 10: 1 to 5: 1, wherein the amount of coagulating agent is 0.01 to 10 kg per 1 ton of synthetic rubber contained in the latex. 2. The synthetic rubber latex coagulation method of claim 1, wherein the hydroxymethyl derivative of hydrolyzed collagen is a product obtainable by reacting formaldehyde with hydrolyzed collagen having a number average molecular weight of 200-5000 using 0.2-5 moles of formaldehyde per mol. 1 kg of hydrolyzed collagen, depending on its content of terminal amine groups and reaction, is carried out in an alkaline environment in the presence of alkali metal hydroxides and / or salts.