CN109535444B

CN109535444B - Bleaching process of hydroxyethyl cellulose

Info

Publication number: CN109535444B
Application number: CN201811454498.3A
Authority: CN
Inventors: 吴昊; 李永峰; 周能武; 吕玉山
Original assignee: Luzhou Beifang Cellulose Co ltd
Current assignee: Luzhou Beifang Cellulose Co ltd
Priority date: 2018-11-30
Filing date: 2018-11-30
Publication date: 2021-01-26
Anticipated expiration: 2038-11-30
Also published as: CN109535444A

Abstract

The invention relates to a bleaching process of hydroxyethyl cellulose, belonging to the technical field of cellulose and chemical materials. The invention solves the technical problems that the prior hydroxyethyl cellulose has poor bleaching effect and the viscosity is reduced more after bleaching. Dissolving flake caustic soda in a solvent in a reaction vessel, starting stirring, adding a stabilizer, adding hydroxyethyl cellulose after the stabilizer is dispersed and dissolved, adding hydrogen peroxide after the hydroxyethyl cellulose is dispersed, heating for bleaching, cooling after bleaching, neutralizing with acid until the pH value is 6.0-7.0, discharging, washing, centrifuging, drying and crushing to obtain a bleached product. The novel bleaching process is developed, has an obvious effect on bleaching hydroxyethyl cellulose, reduces the viscosity of the hydroxyethyl cellulose less, and plays a great role in promoting the quality improvement of daily chemicals and coating products.

Description

Bleaching process of hydroxyethyl cellulose

Technical Field

The invention belongs to the technical field of cellulose and chemical materials, and particularly relates to a bleaching process of hydroxyethyl cellulose.

Background

Hydroxyethyl cellulose (HEC) is nonionic cellulose single ether prepared from cotton fibers through processes of alkalization, ethylene oxide etherification and the like, and the HEC can be used as a coating agent, a binder, a cement and gypsum assistant, a thickening agent, a suspending agent, a medicinal auxiliary material, an antifogging agent, an oil well fracturing fluid, a gelling agent, a waterproof agent and the like due to the nonionic characteristic that the HEC does not react with positive ions and negative ions and has good compatibility, and is widely applied to the fields of coatings, petroleum, buildings, daily chemical industry, high polymer polymerization, textile industry and the like.

Due to the rapid development of paints and daily chemical products, the market not only requires excellent service performance, but also has strict requirements on the appearance, particularly the whiteness of high-end products for daily chemical and interior coatings is an important factor influencing the appearance, and the hydroxyethyl cellulose ether (HEC) serving as an important additive raw material has an important influence on the whiteness index of the paints and daily chemical products, so that the preparation of the HEC with the whiteness meeting the requirements of customers is very important. The method adopts hydrogen peroxide to bleach the yellow products in the production process, can improve the product quality and reduce the loss of waste materials in the production process.

The bleaching agent commonly used for bleaching the HEC comprises sodium hypochlorite and hydrogen peroxide, when the HEC is bleached by the sodium hypochlorite, the bleaching effect is poor, and the ash content and gel particles of a bleached product are increased. When the HEC is bleached by the hydrogen peroxide, the viscosity of the product is reduced greatly due to the strong oxidation effect of the hydrogen peroxide, so that the bleaching effect of the sodium hypochlorite and the hydrogen peroxide is poor, namely no effective process technology for bleaching the HEC product exists at present.

Disclosure of Invention

The invention solves the technical problems that the prior bleaching effect on hydroxyethyl cellulose is poor, and the viscosity is reduced more after bleaching.

The technical scheme for solving the problems is to provide a bleaching process of hydroxyethyl cellulose, which comprises the following steps:

dissolving flake caustic soda in a solvent in a reaction vessel, starting stirring, adding a stabilizer, adding hydroxyethyl cellulose after the stabilizer is dispersed and dissolved, adding hydrogen peroxide after the hydroxyethyl cellulose is dispersed, heating for bleaching, cooling after bleaching, neutralizing with acid until the pH value is 6.0-7.0, discharging, washing, centrifuging, drying and crushing to obtain a bleached product.

Wherein the mass ratio of the caustic soda flakes to the solvent is 0.1-0.4%, the mass ratio of the caustic soda flakes to the hydroxyethyl cellulose is 0.5-2.5%, and the mass ratio of the hydrogen peroxide to the hydroxyethyl cellulose is 2-10%.

Wherein the bleaching temperature is 45-75 ℃, and the bleaching time is 20-60 minutes.

Wherein the solvent is acetone.

Wherein the caustic soda flakes are solid sodium hydroxide and have the mass percentage of 98 percent.

Wherein the stabilizer is soluble magnesium salt, and the mass ratio of the soluble magnesium salt to the hydroxyethyl cellulose is 0.5-2%.

Preferably, the stabilizer is magnesium sulfate.

The invention has the beneficial effects that:

the invention develops a novel bleaching process, controls certain process parameters under the conditions of strong alkali, high temperature and the presence of a stabilizer, has obvious effect on bleaching hydroxyethyl cellulose, and reduces the viscosity of the bleached hydroxyethyl cellulose less.

Drawings

FIG. 1 is a comparison of hydroxyethyl cellulose before and after bleaching, where a is before bleaching and b is after bleaching.

Detailed Description

The hydrogen peroxide has a strong bleaching effect on the fiber, and the bleaching mechanism of the hydrogen peroxide has the following two statements:

1) earlier it was believed that the decomposition of hydrogen peroxide to produce nascent oxygen (O) has a bleaching effect on cellulose: h₂O₂→H₂O + (O); however, scientific research proves that nascent oxygen (O) can oxidize cellulose to cause damage particularly under strong alkali and high temperature, but has no definite evidence on how much bleaching effect is.

2) Widely cited at home and abroad is the argument of pette ney (Peter Nay) in germany: the hydrogen peroxide decomposition is believed to cause bleaching of the fibers by hydrogen peroxide ions HOO^-Since the main substance responsible for the oxidation of cellulose is the hydrogen peroxide radical HOO, the production of HOO is suppressed and HOO is caused to occur during the bleaching process^-The generation is stable, so that the cellulose can be prevented from being oxidized, and a good bleaching effect can be obtained. In aqueous solution, hydrogen peroxide dissociates to produce HOO^－I.e. H₂O₂→H⁺+HOO^－. Dissociation constant K in water₂₀＝1.78×10^－12From the above formula, HOO can be seen^－The amount of (A) increases with increasing pH of the solution, whereas bleaching is carried out under alkaline conditions. However, as the alkali concentration increases, hydrogen peroxide decomposes to generate excessive amounts of HOO and HO radicals, and the radicals have extremely high activity, and thus have a bleaching effect on cellulose, but the cellulose is easily damaged by excessive amounts of radicals. Therefore, effective stabilizers must be added to the bleach liquor to inhibit excess free radical generation due to catalytic decomposition while increasing HOO^－So as to prevent the HEC product from oxidative degradation and further play a good role in bleaching. HOO^－Has an oxidation reaction with the fiber pigmentBleaching, decoloring and removing impurities. The reaction formula is as follows:

based on the above analysis, the present invention provides a bleaching process for hydroxyethyl cellulose, which specifically comprises the following steps:

dissolving flake caustic soda in a solvent in a reaction vessel, starting stirring, adding a stabilizer A, adding hydroxyethyl cellulose after the stabilizer A is dispersed and dissolved, adding hydrogen peroxide after the hydroxyethyl cellulose is dispersed, heating to a certain temperature for bleaching, keeping the temperature and stirring for a certain time, cooling to 30 ℃, neutralizing with acid until the PH is 6.0-7.0, discharging, washing, centrifuging, drying and crushing to obtain a bleached product.

Wherein the bleaching temperature is 45-75 ℃, and the heat preservation time is 20-60 minutes.

Among them, acetone is preferred as the solvent.

Wherein, the flake caustic soda is preferably solid sodium hydroxide with the mass percentage of 98 percent.

Preferably, the stabilizer is magnesium sulfate.

The invention is also applicable to the bleaching of other cellulose derivatives.

The invention is further illustrated and described by the following examples.

The hydroxyethyl cellulose product selected in the examples was yellow in color, had a whiteness of 54, a viscosity of 493mpa.s (2%, 25 ℃, LVT), a hydrogen peroxide concentration of 27.5% (m/m), and the stabilizer used was magnesium sulfate.

Example 1

Weighing 560g of solvent and 0.56g of flake caustic soda, dissolving the flake caustic soda in the solvent in a reaction vessel, starting stirring, adding 0.5g of stabilizer, adding 100g of hydroxyethyl cellulose after the stabilizer is dispersed and dissolved, adding 2g of hydrogen peroxide after the hydroxyethyl cellulose is dispersed, heating to 45 ℃, preserving heat and stirring for 30 min. Cooling to 30 ℃, and neutralizing with acid until the PH value is 6.0-7.0. Washing with solvent after centrifugation, centrifuging, drying and crushing to obtain a bleached product PHEC-1, wherein the performance data of the obtained product is shown in Table 1. From example 1, the product whiteness increased from 54 to 64, 18.5% over before bleaching.

TABLE 1

Batch number	Whiteness degree	Viscosity (2%, 25 ℃, LVT) mpa.s
			HEC (before bleaching)	54	493
PHEC-1	64	489

Example 2

Weighing 560g of solvent and 1.12g of flake caustic soda, dissolving the flake caustic soda in the solvent in a reaction vessel, starting stirring, adding 1g of stabilizer, adding 100g of hydroxyethyl cellulose after the stabilizer is dispersed and dissolved, dispersing the hydroxyethyl cellulose, finally adding 6g of hydrogen peroxide, heating to 60 ℃, preserving heat and stirring for 30 min. Cooling to 30 ℃, and neutralizing with acid until the PH value is 6.0-7.0. Washing with solvent after centrifugation, centrifuging, drying and crushing to obtain the bleached product PHEC-2. The performance data of the resulting product is shown in Table 2, and the comparison before and after bleaching is shown in FIG. 1. From the data of example 2, it can be seen that the product whiteness increased from 54 to 78, and the product whiteness increased by 44.4%.

TABLE 2

Example 3

Weighing 560g of solvent and 2.24g of flake caustic soda, dissolving the flake caustic soda in the solvent in a reaction vessel, starting stirring, adding 2g of stabilizer, adding 100g of hydroxyethyl cellulose after the stabilizer is dispersed and dissolved, dispersing the hydroxyethyl cellulose, finally adding 8g of hydrogen peroxide, heating to 60 ℃, preserving heat and stirring for 30 min. Cooling to 30 ℃, and neutralizing with acid until the PH value is 6.0-7.0. Washing with solvent after centrifugation, centrifuging, drying and crushing to obtain a bleached product PHEC-3, wherein the performance data of the obtained product is shown in Table 3. From the data of example 3, it can be seen that the product whiteness increased from 54 to 77, and the product whiteness increased by 42.6%.

TABLE 3

Batch number	Whiteness degree	Viscosity (2%, 25 ℃, LVT) mpa.s
			HEC (before bleaching)	54	493
PHEC-3	77	386

Example 4

Weighing 560g of solvent and 2.24g of flake caustic soda, dissolving the flake caustic soda in the solvent in a reaction vessel, starting stirring, adding 100g of relatively yellow hydroxyethyl cellulose, dispersing the hydroxyethyl cellulose, finally adding 6g of hydrogen peroxide, heating to 60 ℃, preserving heat and stirring for 30 min. Cooling to 30 deg.C, and neutralizing with acid to pH of 6.0-7.0. Washing with solvent after centrifugation, centrifuging, drying and crushing to obtain the bleached product PHEC-4. Example 4 differs from example 3 in that example 4 has no added stabilizer. The performance data of the product obtained are shown in Table 4, and it is evident from example 4 that the whiteness of the product is improved by 7%, the product is still yellowish and the viscosity of the product is reduced more.

TABLE 4

Batch number	Whiteness degree	Viscosity (2%, 25 ℃, LVT) mpa.s
			HEC (before bleaching)	54	493
PHEC-4	58	36

Claims

1. The bleaching process of the hydroxyethyl cellulose is characterized by comprising the following steps: dissolving flake caustic soda in a solvent in a reaction vessel, starting stirring, adding a stabilizer, adding hydroxyethyl cellulose after the stabilizer is dispersed and dissolved, adding hydrogen peroxide after the hydroxyethyl cellulose is dispersed, heating for bleaching, cooling after bleaching, neutralizing with acid until the pH value is 6.0-7.0, discharging, washing, centrifuging, drying and crushing to obtain a bleached product; the mass ratio of the flake caustic soda to the solvent is 0.1-0.4%, the mass ratio of the flake caustic soda to the hydroxyethyl cellulose is 0.5-2.5%, and the mass ratio of the hydrogen peroxide to the hydroxyethyl cellulose is 2-10%; the bleaching temperature is 45-75 ℃, and the bleaching time is 20-60 minutes; the stabilizer is soluble magnesium salt, and the mass ratio of the soluble magnesium salt to the hydroxyethyl cellulose is 0.5-2%; the solvent is acetone.

2. The process of bleaching hydroxyethylcellulose according to claim 1, wherein: the flake caustic soda is solid sodium hydroxide and accounts for 98 percent by mass.

3. The process for bleaching hydroxyethylcellulose according to claim 1 or 2, characterized in that: the stabilizer is magnesium sulfate.