阅读说明：本技术 一种小分子酸协同壳聚糖预处理过氧化氢漂白纸浆的方法 (Method for pretreating hydrogen peroxide bleaching paper pulp by virtue of micromolecule acid and chitosan ) 是由 万金泉 陈国政 马邕文 闫志成 于 2020-12-21 设计创作，主要内容包括：本发明公开了一种小分子酸协同壳聚糖预处理过氧化氢漂白纸浆的方法。该方法包括：向纸浆内加入小分子酸和壳聚糖,进行预处理,得到预处理后的纸浆；将预处理后的纸浆洗涤后,加入氧化氢、氢氧化钠、硅酸钠,进行过氧化氢漂白处理,得到过氧化氢漂白后的纸浆。小分子酸用量为绝干浆的1％-4％,壳聚糖用量为绝干浆的0.2％-0.5％。本发明提供的方法中,是在进行过氧化氢漂白前加入小分子酸作为金属离子的络合剂,且将脱乙酰度大于75％的壳聚糖作为金属离子的吸附载体。本发明在纸浆碱性过氧化氢漂白前加入小分子酸和壳聚糖能够提高过氧化氢的漂白效率,增加最终的成纸白度,且对纸张物理强度有一定的提升。(The invention discloses a method for pretreating hydrogen peroxide bleaching paper pulp by using micromolecular acid and chitosan. The method comprises the following steps: adding micromolecular acid and chitosan into the paper pulp, and carrying out pretreatment to obtain pretreated paper pulp; and washing the pretreated paper pulp, adding hydrogen oxide, sodium hydroxide and sodium silicate, and carrying out hydrogen peroxide bleaching treatment to obtain the paper pulp bleached by hydrogen peroxide. The dosage of the micromolecule acid is 1-4% of oven-dried pulp, and the dosage of the chitosan is 0.2-0.5% of oven-dried pulp. In the method provided by the invention, micromolecular acid is added as a complexing agent of metal ions before hydrogen peroxide bleaching, and chitosan with deacetylation degree of more than 75% is used as an adsorption carrier of the metal ions. According to the invention, the small molecular acid and chitosan are added before the alkaline hydrogen peroxide bleaching of the paper pulp, so that the bleaching efficiency of the hydrogen peroxide can be improved, the final whiteness of the paper is increased, and the physical strength of the paper is improved to a certain extent.)

1. A method for pretreating hydrogen peroxide bleaching paper pulp by small molecular acid and chitosan is characterized by comprising the following steps:

(1) bleaching pretreatment: adding micromolecular acid and chitosan into the paper pulp, uniformly mixing, and carrying out pretreatment to obtain pretreated paper pulp;

(2) hydrogen peroxide bleaching treatment: and (2) washing the pretreated paper pulp obtained in the step (1), adding hydrogen oxide, sodium hydroxide and sodium silicate, and carrying out hydrogen peroxide bleaching treatment to obtain the paper pulp bleached by hydrogen peroxide.

2. The method for pretreating hydrogen peroxide bleached pulp by using small molecular acid and chitosan according to claim 1, wherein the pulp obtained in the step (1) is sulfate pulp or waste paper deinking pulp; the waste paper deinking pulp is more than one of waste newspaper and magazine deinking pulp, waste corrugated board deinking pulp and office waste paper deinking pulp; the pulp concentration of the paper pulp is 5 wt% -15 wt%.

3. The method for pretreating hydrogen peroxide bleached pulp by using small molecular acid and chitosan together according to claim 1, wherein the small molecular acid in the step (1) is more than one of citric acid, acetic acid and formic acid; the mass of the micromolecular acid is 1-4 wt% of the absolute dry mass of the paper pulp.

4. The method for pretreating hydrogen peroxide bleached pulp by using small molecular acid and chitosan according to claim 1, wherein the deacetylation degree of the chitosan in the step (1) is 75-95%; the mass of the chitosan is 0.2 wt% -0.5 wt% of the oven-dried mass of the paper pulp.

5. The method for pretreating hydrogen peroxide bleached pulp by using small molecular acid and chitosan according to claim 1, wherein the temperature of the pretreatment in the step (1) is 40-70 ℃, and the time of the pretreatment is 20-60 min.

6. The method for pretreating hydrogen peroxide bleached pulp by using small molecular acid and chitosan according to claim 1, wherein the pulp concentration of the washed pulp in the step (2) is 10-30 wt%.

7. The method for pretreating hydrogen peroxide bleached pulp by using small molecular acid and chitosan according to claim 1, wherein the mass of the hydrogen peroxide in the step (2) is 3 wt% of the oven dry mass of the pulp.

8. The method for pretreating hydrogen peroxide bleached pulp by using small molecular acid and chitosan according to claim 1, wherein the mass of the sodium hydroxide in the step (2) is 1.5 wt% of the oven-dry mass of the pulp.

9. The method for pretreating hydrogen peroxide bleached pulp by using small molecular acid and chitosan according to claim 1, wherein the mass of the sodium silicate in the step (2) is 2 wt% of the oven-dry mass of the pulp.

10. The method for pretreating hydrogen peroxide bleached pulp by using small molecular acid and chitosan according to claim 1, wherein the temperature of the hydrogen peroxide bleaching treatment in the step (2) is 60-90 ℃, and the time of the hydrogen peroxide bleaching treatment is 1.5-3 h.

Technical Field

The invention belongs to the technical field of pulping and papermaking, and particularly relates to a method for pretreating hydrogen peroxide bleaching paper pulp by using micromolecule acid and chitosan.

Background

Due to the increasing shortage of papermaking fiber raw materials and the increasing public environmental awareness, the recycling of the plant fibers has important significance for relieving the shortage of raw materials and pollution of the papermaking industry in China due to the resource and energy conservation. With the lapse of time, the proportion of used paper pulp in the total consumption of paper pulp has increased year by year, and by 2018, the raw material with used paper as a core accounts for 62% of the total raw material. The waste corrugated paper and the waste newspaper are important raw materials for recycling the regenerated plant fiber for papermaking, the waste corrugated paper and the waste newspaper are recycled without pulping by cooking again, the energy consumption and pollution are greatly reduced, hydrogen peroxide bleaching is mainly adopted in the waste paper deinking pulp at present, and an alkaline or weakly alkaline environment is created by using sodium hydroxide, sodium silicate and the like while adding hydrogen peroxide in the hydrogen peroxide bleaching. As transition metal ions, adhesives, reinforcing agents, ash and the like carried by paper pulp and introduced in the recycling process can lead the ineffective decomposition of hydrogen peroxide to be aggravated, the bleaching efficiency of the hydrogen peroxide is deteriorated, the expected bleaching effect cannot be achieved, and the whiteness improvement caused by continuously adding the hydrogen peroxide is not obvious, a stabilizing agent, a chelating agent, an activating agent and the like are usually added in the bleaching process of the hydrogen peroxide to improve the bleaching efficiency of the hydrogen peroxide.

In the hydrogen peroxide bleaching, the most commonly used auxiliary agent for improving the efficiency is a chelating agent, and the chelating agent can be combined with transition metal ions to form a chelate with a stable annular structure, so that the invalid decomposition of hydrogen peroxide caused by metal ion catalysis can be effectively inhibited, and a colored compound and a metal ion-lignin compound can be prevented from being formed after the metal ions are absorbed by paper pulp, so that the whiteness of the paper pulp is obviously improved. At present, Ethylene Diamine Tetraacetic Acid (EDTA), Diethylene Triamine Pentaacetic Acid (DTPA), ethylene diamine tetramethylene phosphoric acid (EDTMPA), diethylene triamine pentamethyl phosphonic acid (DTPMPA) and the like are widely used in the hydrogen peroxide bleaching process, but the chelating agents belong to hardly degradable organic matters in water environment, chelated metal ions are transferred from solid matters to paper-making wastewater, on the other hand, the environmental pollution is increased, the chelating efficiency of most chelating agents in strong alkaline environment is greatly reduced, the PH of hydrogen peroxide bleaching is more than 10, and therefore the use of the chelating agents is under more and more doubt by people in recent years. Therefore, the finding of a green degradable substance to replace a chelating agent for improving the bleaching efficiency of hydrogen peroxide and improving the whiteness of paper has important significance.

Chitin is the second largest natural polysaccharide on the earth, chitosan generated through deacetylation contains a large number of hydroxyl and amino, the amino can be sufficiently close to the surface of fibers, the molecular weight of the chitosan has film forming capability, the chitosan has enough adhesive strength on the fibers and can bridge between the fibers, the hydroxyl on the molecule can be subjected to electrostatic bonding and hydrogen bonding with the fibers, the chitosan can be used as a reinforcing agent to be added into paper pulp, and the chitosan is proved to be a good metal chelating agent. However, chitosan has the problems of poor reinforcing effect, insolubility in water and the like under alkaline conditions, and the contact area between the chitosan and fibers is greatly reduced due to insolubility in water under alkaline conditions.

Hydroxyethylidene diphosphonic acid (HEDP) is used in the hydrogen peroxide bleaching stage of acacia kraft pulp by the sun, kohlrabi et al, and the HEDP is believed to be capable of stabilizing hydrogen peroxide and improving the hydrogen peroxide bleaching effect of pulp. See literature (Jingjianjiang et al, possibility discussion of use of hydroxyethylidene diphosphonic acid in chelating treatment of pulp bleaching process, paper manufacture in China, 32 (6): 7-10, (2013)). However, the amount of organic matters which are difficult to degrade in the bleaching waste liquid is still increased, and pressure is brought to the waste water treatment.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide a method for pretreating hydrogen peroxide bleaching paper pulp by using small molecular acid in cooperation with chitosan. The invention provides a method for pretreating hydrogen peroxide bleaching paper pulp by using micromolecule acid and chitosan, which is a method for improving the hydrogen peroxide bleaching efficiency of sulfate pulp and waste paper deinking pulp through pretreatment.

Aiming at the defects of the prior art of hydrogen peroxide bleaching, the invention provides a green and convenient hydrogen peroxide bleaching pretreatment method, which reduces the ineffective decomposition of hydrogen peroxide, thereby improving the hydrogen peroxide bleaching efficiency and the pulp whiteness, and simultaneously improving the physical strength of paper. The acidic environment created by the micromolecular acid can promote the dispersion of the chitosan in a pretreatment system, so that the fibers are fully contacted with the chitosan, and the micromolecular acid can also form a complex with metal ions, thereby reducing the concentration of the metal ions of the paper pulp to a certain extent and providing a sufficient theoretical basis for improving the bleaching efficiency of the hydrogen peroxide by replacing the traditional chelating agent with the pretreatment hydrogen peroxide bleaching of the micromolecular acid chitosan.

The purpose of the invention is realized by at least one of the following technical solutions.

The invention provides a method for pretreating hydrogen peroxide bleaching paper pulp by using micromolecule acid and chitosan in cooperation, which is characterized in that before alkaline hydrogen peroxide bleaching of the paper pulp, sulfate pulp or waste paper deinking pulp is pretreated by using the micromolecule acid and the chitosan in cooperation (the micromolecule acid and the chitosan are added before the hydrogen peroxide bleaching for pretreatment and then washing), and then alkaline hydrogen peroxide bleaching is carried out.

The method for pretreating hydrogen peroxide bleaching paper pulp by using micromolecule acid and chitosan, provided by the invention, comprises the following steps of:

(1) bleaching pretreatment: adding micromolecular acid and chitosan into the paper pulp, uniformly mixing, and carrying out pretreatment to obtain pretreated paper pulp;

(2) hydrogen peroxide bleaching treatment: and (2) washing the pretreated paper pulp obtained in the step (1), adding hydrogen oxide, sodium hydroxide and sodium silicate, and carrying out hydrogen peroxide bleaching treatment to obtain the paper pulp bleached by hydrogen peroxide.

Further, the pulp in the step (1) is sulfate pulp or waste paper deinking pulp; the waste paper deinking pulp is more than one of waste newspaper and magazine deinking pulp (ONP), waste corrugated cardboard deinking pulp (OCC) and office waste paper deinking pulp (MOW); the pulp concentration of the paper pulp is 5 wt% -15 wt%.

Further, the small molecular acid in the step (1) is more than one of citric acid, acetic acid, formic acid and the like; the mass of the micromolecular acid is 1-4 wt% of the absolute dry mass of the paper pulp.

Further, the deacetylation degree of the chitosan in the step (1) is 75-95%; the mass of the chitosan is 0.2 wt% -0.5 wt% of the oven-dried mass of the paper pulp.

Further, the temperature of the pretreatment in the step (1) is 40-70 ℃, and the time of the pretreatment is 20-60 min.

Preferably, the pretreatment temperature in the step (1) is 50-60 ℃.

Preferably, the pretreatment time in the step (1) is 30min-60 min.

Further, in the step (2), the pulp concentration of the washed pulp is 10 wt% to 30 wt%.

Preferably, in step (2), the pulp concentration of the washed pulp is 10 wt% to 15 wt%.

Preferably, the hydrogen peroxide, the sodium hydroxide and the sodium silicate are used in amounts of 3 wt%, 1.5 wt% and 2 wt%, respectively, based on the oven dry content of the pulp solution.

Further, the temperature of the hydrogen peroxide bleaching treatment in the step (2) is 60-90 ℃, and the time of the hydrogen peroxide bleaching treatment is 1.5-3 h.

Preferably, the time of the hydrogen peroxide bleaching treatment in the step (2) is 1.5-2.5 h.

Further preferably, the time of the hydrogen peroxide bleaching treatment in the step (2) is 120 min.

Preferably, the temperature of the hydrogen peroxide bleaching treatment in the step (2) is 70 ℃.

And (3) the paper pulp bleached by the hydrogen peroxide obtained in the step (2) can be made into sheets and then the whiteness, the tensile index, the tearing index and the burst index of the paper pulp are measured.

The paper pulp hydrogen peroxide bleaching pretreatment method uses micromolecular acid and chitosan as a metal ion complexing agent and an adsorbent in a pretreatment stage, replaces a chelation treatment stage of the traditional paper pulp hydrogen peroxide bleaching, and finally prepares the paper pulp fiber with good performance.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) according to the method provided by the invention, the hydrogen peroxide bleaching pretreatment of the sulfate pulp and the waste paper deinking pulp is carried out by utilizing the micromolecule acid and the chitosan, compared with the traditional acid treatment, the reaction condition is milder, and the acid environment created by the micromolecule acid well solves the problem that the chitosan with lower deacetylation degree is not easy to disperse in neutral and alkaline environments, and improves the adsorption efficiency of the chitosan on metal ions.

(2) Compared with the traditional chelation treatment, the method provided by the invention has the advantages that the used micromolecule acid and chitosan system are more easily biodegraded, and the environment-friendly characteristic is realized.

(3) According to the method provided by the invention, hydroxyl on the used chitosan molecule can be subjected to electrostatic bonding and hydrogen bonding with the fiber, the chitosan molecule is also a common pulp reinforcing agent, and the physical properties of the pretreated and bleached pulp are improved to a certain extent.

Detailed Description

The following examples are presented to further illustrate the practice of the invention, but the practice and protection of the invention is not limited thereto. It is noted that the processes described below, if not specifically described in detail, are all realizable or understandable by those skilled in the art with reference to the prior art. The reagents or apparatus used are not indicated to the manufacturer, and are considered to be conventional products available by commercial purchase.

Example 1

The method for pretreating OCC pulp by using citric acid and chitosan to bleach hydrogen peroxide in the embodiment comprises the following steps:

1) bleaching pretreatment stage (stage A)

In the bleaching pretreatment stage, citric acid and chitosan are used for pretreating unbleached old corrugated case board paper (OCC), wherein the whiteness of the unbleached old corrugated case board paper is 25.13% ISO, and specifically comprises the following steps: placing OCC paper pulp with the pulp concentration of 10 wt% into a polyethylene bag, adding citric acid and chitosan into the polyethylene bag to perform adsorption complexation on metal ions, wherein the dosage of the citric acid is 2% of the mass of the oven-dried pulp, the dosage of the chitosan with the deacetylation degree of 95% is 0.2% of the mass of the oven-dried pulp, the pretreatment temperature is 60 ℃, the pretreatment time is 20min, and the pulp in the polyethylene bag is kneaded every 20min to be fully contacted with the solution, so that the pretreated OCC paper pulp is obtained.

2) Hydrogen peroxide bleaching stage (P stage)

Washing the pretreated OCC paper pulp obtained in the step (1), and then adding hydrogen peroxide, sodium hydroxide and sodium silicate to perform subsequent hydrogen peroxide bleaching, specifically: putting pretreated OCC paper pulp with the pulp concentration of 10 wt% into a polyethylene bag, preheating to 70 ℃, adding 3% of hydrogen peroxide by mass of the oven-dry paper pulp, 1.5% of magnesium hydroxide by mass of the oven-dry paper pulp and 2% of sodium silicate by mass of the oven-dry paper pulp; bleaching at 70 deg.C for 120min, kneading the polyethylene bag every 30min to make the pulp fully contact with the solution to obtain bleached pulp (labeled A)_Lemon/shellP)。

3) The whiteness and the physical performance of the paper are detected by the bleached paper sheet (the whiteness is measured according to GB/T22880-2008; the tensile strength was determined according to GB/T12914-; burst strength was determined according to GB/T1539-2007).

Control experiment 1-1: the pulp obtained was marked as blank (P) as described in example 1, except that it was not subjected to a pretreatment stage, and the other conditions were the same.

Control experiments 1-2: the pulp obtained was marked A as described in example 1, except that no chitosan was added during the pretreatment stage, and the conditions were otherwise the same_{Lemon (fruit of lemon)}P。

Control experiments 1-3: the pulp obtained was marked A as described in example 1, except that no citric acid was added during the pretreatment stage, and the conditions were otherwise identical_ShellP。

Control experiments 1-4: the procedure is as in example 1 except that the pulp is pretreated with EDTA as chelating agent, no citric acid and chitosan are added, the conditions are the same, and the pulp obtained is marked Q_EDTAP。

The whiteness and physical properties of the pulp prepared in example 1 were measured, and the data of the results are shown in table 1.

TABLE 1

Note: the blank is a pulp bleached with hydrogen peroxide without pretreatment, Q_EDTAThe pulp was treated for chelation with EDTA.

The results of the testing of the OCC bleached pulp obtained in this example and the control experiment are shown in table 1 above: the data show that the citric acid and the chitosan are cooperatively used for chelating metal ions after OCC paper pulp pretreatment and then hydrogen peroxide bleaching is carried out, so that the whiteness of the paper pulp can be improved by 9.3%, the tensile index can be improved by 10.1%, and the burst index can be improved by 10.5%. The bleaching with hydrogen peroxide after the OCC paper pulp is pretreated by the citric acid can improve the whiteness of the paper pulp by 5.1 percent, slightly reduce the tensile index and improve the burst index by 4.3 percent. The whiteness of the paper pulp can be improved by 5.3 percent, the tensile index can be improved by 5.1 percent, and the burst index can be improved by 9.6 percent by carrying out hydrogen peroxide bleaching after the OCC paper pulp is pretreated by the chitosan. After the OCC paper pulp is chelated and pretreated by the EDTA, the whiteness of the paper pulp is improved by 5.6 percent, the tensile index is slightly reduced, and the burst index is improved by 3.5 percent. In summary, hydrogen peroxide bleaching after synergistic pretreatment of citric acid and chitosan, the optical and mechanical properties of OCC pulp are superior to those of pulp pretreated with only chitosan or only citric acid (A)_{Lemon (fruit of lemon)}P、A_ShellP) and is superior to hydrogen peroxide bleaching slurries (Q) using the traditional chelating agent EDTA_EDTAP)。

Example 2

The method for pretreating sulfate eucalyptus pulp by using acetic acid and chitosan for hydrogen peroxide bleaching comprises the following steps:

1) bleaching pretreatment stage (stage A)

In the bleaching pretreatment stage, acetic acid and chitosan are used for pretreating unbleached sulfate eucalyptus pulp, wherein the whiteness of the unbleached sulfate eucalyptus pulp is 40.09% ISO, and specifically comprises the following steps: filling unbleached sulfate eucalyptus pulp with the pulp concentration of 10 wt% into a polyethylene bag, adding acetic acid and chitosan into the polyethylene bag to adsorb and complex metal ions, wherein the dosage of the acetic acid is 2% of the mass of the oven-dried pulp, the dosage of the chitosan with the deacetylation degree of 95% is 0.2% of the mass of the oven-dried pulp, the pretreatment temperature is 60 ℃, the pretreatment time is 20min, and the pulp in the polyethylene bag is kneaded every 20min so that the pulp is fully contacted with the solution, so that the unbleached sulfate eucalyptus pulp after pretreatment is obtained.

2) Hydrogen peroxide bleaching stage (P stage)

Washing the pre-treated unbleached sulfate eucalyptus pulp obtained in the step (1), and adding hydrogen peroxide, sodium hydroxide and sodium silicate for subsequent hydrogen peroxide bleaching, specifically: after pre-treated unbleached sulfate eucalyptus pulp with the pulp concentration of 10 wt% is filled into a polyethylene bag and preheated to 70 ℃, the amount of hydrogen peroxide is 3% of the mass of the oven-dry pulp, the amount of sodium hydroxide is 1.5% of the mass of the oven-dry pulp, and the amount of sodium silicate is 2% of the mass of the oven-dry pulp; bleaching at 70 deg.C for 120min, kneading the polyethylene bag every 30min to make the pulp fully contact with the solution to obtain bleached pulp (labeled A)_{Second shell}P)。

3) And (5) detecting the whiteness and the physical property of the paper by using the bleached paper.

Control experiment 2-1: the pulp obtained was marked as blank (P) as described in example 2, except that it was not subjected to a pretreatment stage, and the other conditions were the same.

Control experiment 2-2: the pulp obtained was marked A as described in example 2, except that no chitosan was added during the pretreatment stage, and the conditions were otherwise the same_{Second step}P。

Control experiments 2-3: the pulp obtained was marked A as described in example 2, except that acetic acid was not added in the pretreatment stage, the conditions were otherwise the same_ShellP。

Control experiments 2-4: the procedure is as in example 2 except that the pulp is pretreated with EDTA as chelating agent, no citric acid and chitosan are added, the conditions are the same, and the pulp obtained is marked Q_EDTAP。

The whiteness and physical properties of the pulp prepared in example 2 were measured, and the data of the results are shown in table 2.

TABLE 2

Note: blank sampleFor pulps bleached with hydrogen peroxide only without pretreatment, Q_EDTAThe pulp was treated for chelation with EDTA.

The results of the kraft eucalyptus pulp bleaching test obtained in this example and the control are shown in table 2 above: the data show that the acetic acid and the chitosan are cooperatively used for carrying out hydrogen peroxide bleaching after chelating metal ions in the sulfate eucalyptus pulp pretreatment, so that the whiteness of the pulp can be improved by 10.4%, the tensile index can be improved by 10.2%, and the burst index can be improved by 10.3%. After the sulfate eucalyptus pulp is pretreated by acetic acid, hydrogen peroxide bleaching is carried out, so that the whiteness of the pulp is improved by 6.4 percent, the tensile index is slightly reduced, and the burst index is basically consistent with that of a blank sample. The method has the advantages that the sulfate eucalyptus pulp is pretreated by the chitosan and then is bleached by the hydrogen peroxide, so that the whiteness of the pulp is improved by 4.1 percent, the tensile index is improved by 4.8 percent, and the bursting index is basically consistent with that of a blank sample. After EDTA chelation pretreatment of the sulfate eucalyptus pulp, hydrogen peroxide bleaching is carried out, so that the whiteness of the pulp is improved by 9.5%, the tensile index is reduced by 5.3%, and the bursting index is basically consistent with that of a blank sample. In conclusion, the optical performance and mechanical performance of the sulfate eucalyptus pulp are better than those of the pulp pretreated by only using chitosan or only using acetic acid (A) after the hydrogen peroxide bleaching is carried out after the acetic acid and chitosan are pretreated cooperatively_{Second step}P、A_ShellP) and is superior to hydrogen peroxide bleaching slurries (Q) using the traditional chelating agent EDTA_EDTAP)。

Example 3

The method for pretreating ONP hydrogen peroxide bleaching by adopting formic acid and chitosan in cooperation comprises the following steps of:

1) bleaching pretreatment stage (stage A)

In the bleaching pretreatment stage, formic acid and chitosan are used for pretreating ONP pulp, and the whiteness of the unbleached ONP pulp is 49.17% ISO, which specifically comprises the following steps: filling unbleached ONP pulp with the pulp concentration of 5 wt% into a polyethylene bag, adding formic acid and chitosan into the polyethylene bag to adsorb and complex metal ions, wherein the amount of the formic acid is 1% of the mass of the oven-dried pulp, the amount of the chitosan with the deacetylation degree of 75% is 0.5% of the mass of the oven-dried pulp, the pretreatment temperature is 70 ℃, the pretreatment time is 60min, and the pulp in the polyethylene bag is kneaded every 20min to fully contact with the solution, so that the pretreated unbleached sulfate eucalyptus pulp is obtained.

2) Hydrogen peroxide bleaching stage (P stage)

Washing the pretreated unbleached ONP pulp obtained in the step (1), and then adding hydrogen peroxide, sodium hydroxide and sodium silicate to perform subsequent hydrogen peroxide bleaching, specifically: after pre-treated unbleached ONP pulp with the pulp concentration of 10 wt% is filled into a polyethylene bag and preheated to 90 ℃, the amount of hydrogen peroxide is 3% of the mass of the oven-dry paper pulp, the amount of sodium hydroxide is 1.5% of the mass of the oven-dry paper pulp, and the amount of sodium silicate is 2% of the mass of the oven-dry paper pulp; bleaching at 90 deg.C for 180min, kneading the polyethylene bag every 30min to make the pulp fully contact with the solution to obtain bleached pulp (labeled A P)₁)。

3) And (5) detecting the whiteness and the physical property of the paper by using the bleached paper.

Control experiment 3-1: the pulp obtained was marked as blank (P) as described in example 2, except that it was not subjected to a pretreatment stage, and the other conditions were the same.

Control experiment 3-2: as described in example 2, except that the amount of chitosan added in the pretreatment stage was 0.3% of the mass of the oven-dried pulp, the conditions were the same, and the pulp obtained was marked AP₂。

Control experiments 3-3: as described in example 2, except that formic acid was added in an amount of 4% by mass based on the mass of the completely dry pulp in the pretreatment stage, the conditions were the same, and the pulp obtained was designated as AP₃。

The whiteness and physical properties of the pulp prepared in example 3 were measured, and the data of the results are shown in table 3.

TABLE 3

Note: the blank is a pulp bleached with hydrogen peroxide alone without pretreatment.

The results of the bleaching tests on the ONP pulp obtained in this example and the control experiment are shown in table 3 above: data show formic acid andthe chitosan is synergistically used for chelating metal ions in the ONP pulp after pretreatment, and then hydrogen peroxide bleaching is carried out, so that the whiteness, the tensile index and the burst index of the pulp can be improved. After pretreatment under different conditions, AP₁、AP₂、AP₃The whiteness is respectively improved by 10.1 percent, 8.2 percent and 11.9 percent compared with the blank sample P, the tensile index is respectively improved by 21.0 percent, 15.6 percent and 14.0 percent compared with the blank sample P, and the burst index is respectively improved by 24.3 percent, 23.0 percent and 15.8 percent compared with the blank sample P. In conclusion, the optical performance and the mechanical performance of the ONP pulp are superior to those of the pulp without pretreatment by performing hydrogen peroxide bleaching after the synergistic pretreatment of the formic acid and the chitosan.

Example 4

The embodiment of the method for pretreating eucalyptus CTMP unbleached pulp by using acetic acid and chitosan and bleaching the pulp by using hydrogen peroxide comprises the following steps:

1) bleaching pretreatment stage (stage A)

In the bleaching pretreatment stage, acetic acid and chitosan are used for pretreating eucalyptus CTMP unbleached pulp, wherein the whiteness of the unbleached eucalyptus CTMP pulp is 52% ISO, and specifically comprises the following steps: putting unbleached eucalyptus CTMP pulp with the pulp concentration of 10 wt% into a polyethylene bag, adding acetic acid and chitosan into the polyethylene bag to adsorb and complex metal ions, wherein the dosage of the acetic acid is 2% of the mass of the oven-dried pulp, the dosage of the chitosan with the deacetylation degree of 80% is 0.5% of the mass of the oven-dried pulp, the pretreatment temperature is 70 ℃, the pretreatment time is 60min, and the pulp in the polyethylene bag is kneaded every 20min to be fully contacted with the solution, so that the pretreated unbleached sulfate eucalyptus pulp is obtained.

2) Hydrogen peroxide bleaching stage (P stage)

Washing the pretreated unbleached eucalyptus CTMP pulp obtained in the step (1), and adding hydrogen peroxide, sodium hydroxide and sodium silicate for subsequent hydrogen peroxide bleaching, wherein the steps are as follows: placing the unbleached eucalyptus CTMP pulp with the pulp concentration of 10 wt% and through pretreatment into a polyethylene bag, preheating to 90 ℃, adding 3% of hydrogen peroxide by mass of the oven-dry paper pulp, 1.5% of sodium hydroxide by mass of the oven-dry paper pulp and 2% of sodium silicate by mass of the oven-dry paper pulp; bleaching at 90 deg.C for 180min, kneading every 30minThe vinyl bag brought the pulp into intimate contact with the solution, resulting in a pulp that was bleached (labeled A P)₁)。

3) And (5) detecting the whiteness and the physical property of the paper by using the bleached paper.

Control experiment 4-1: the pulp obtained was marked as blank (P) as described in example 2, except that it was not subjected to a pretreatment stage, and the other conditions were the same.

Control experiment 4-2: the pulp obtained was labeled AP, as described in example 2, except that the pretreatment temperature in the pretreatment stage was 40 ℃ and the conditions were the same₂。

Control experiments 4-3: the pulp obtained was labeled AP, as described in example 2, except that the pretreatment time in the pretreatment stage was 40min, and the conditions were otherwise the same₃。

Control experiments 4-4: the pulp obtained was labeled AP, as described in example 2, except that the bleaching stage treatment temperature was 60 ℃ and the conditions were otherwise the same₄。

The whiteness and physical properties of the pulp prepared in example 4 were measured, and the data of the results are shown in table 4.

TABLE 4

Note: the blank is a pulp bleached with hydrogen peroxide alone without pretreatment.

The results of the eucalyptus CTMP pulp bleaching tests obtained in this example and the control experiment are shown in table 4 above: the data show that the formic acid and the chitosan are cooperatively used for carrying out hydrogen peroxide bleaching after chelating metal ions in the eucalyptus CTMP pulp pretreatment, and the whiteness, the tensile index and the burst index of the pulp can be improved. After pretreatment under different conditions, AP₁、AP₂、AP₃And AP₄The whiteness is respectively improved by 5.8%, 4.3% and 3.6% compared with the blank sample P, the tensile index is respectively improved by 9.8%, 2.8%, 6.3% and 7.7% compared with the blank sample P, and the burst index is respectively improved by 14.9%, 7.5%, 10.4% and 10.4% compared with the blank sample P. In conclusion, acetic acidAfter the pulp is pretreated with chitosan in a synergistic way, hydrogen peroxide bleaching is carried out, and the optical performance and the mechanical performance of the eucalyptus CTM pulp are superior to those of pulp without pretreatment.

The above examples are only preferred embodiments of the present invention, which are intended to be illustrative and not limiting, and those skilled in the art should understand that they can make various changes, substitutions and alterations without departing from the spirit and scope of the invention.