CN106381758B

CN106381758B - Application of carboxymethyl chitin as retention and drainage aid

Info

Publication number: CN106381758B
Application number: CN201610893733.1A
Authority: CN
Inventors: 由耀辉; 孙绪兵; 雷光东; 马静; 黄辉; 曹锟
Original assignee: Neijiang Normal University
Current assignee: Neijiang Normal University
Priority date: 2016-10-13
Filing date: 2016-10-13
Publication date: 2020-04-07
Anticipated expiration: 2036-10-13
Also published as: CN106381758A

Abstract

The invention relates to a papermaking auxiliary agent, and particularly discloses application of carboxymethyl chitin as a retention and drainage aid. The invention also discloses a retention and drainage aid system consisting of carboxymethyl chitin and polyaluminium chloride, which is found to have excellent retention and drainage-aid performance. And the retention and drainage aiding effects of the two reagents in the system are different according to different adding sequences of the two reagents. The invention has the advantages that: 1) the carboxymethyl chitin is applied to the retention and filtration aid for the first time, so that the retention and filtration aid which has good retention and filtration aid effects, is renewable, has low cost and is suitable for acidic and neutral papermaking is obtained; 2) provides a retention and drainage aid system consisting of carboxymethyl chitin and polyaluminium chloride, and the system has excellent retention and drainage-aid performance.

Description

Application of carboxymethyl chitin as retention and drainage aid

Technical Field

The invention relates to a papermaking process, in particular to a papermaking auxiliary agent.

Background

The retention and drainage aid is the most important process aid in the wet part of papermaking, and mainly has the main functions of improving the net-surfing retention rate during the filtering of paper pulp, having excellent retention effect on fine fibers and fillers, enhancing the drainability of the paper pulp and reducing the dewatering energy consumption in the processes of forming, squeezing and drying the wet paper. This is usually achieved by adding a certain amount of retention and drainage aids to the papermaking equipment during the papermaking process. During papermaking, paper pulp is dispersed in water and conveyed to papermaking equipment, and during papermaking, retention and filtration aids are added, and then water is filtered to form and dry, so that paper is finally obtained.

Currently used retention and drainage aids can be classified into three major categories, namely inorganic polymers (alum, etc.), natural organic polymers (cationic starch, etc.), synthetic organic polymers (cationic polyacrylamide, etc.).

But the retention and drainage aiding effect of alum is poor. Cationic starch as retention and drainage aid has obvious disadvantages: large addition amount, pasting during use, complex operation, short storage life and undesirable use effect. The cationic polyacrylamide is a petrochemical material and has the defects of non-regeneration, difficult biodegradation and the like.

The patent document with publication number CN1415409A discloses a retention and drainage aid, which is a composite retention and drainage aid compounded by cationic polyacrylamide and chitosan, mainly using chitosan as a linear high molecular polymer, wherein the molecular chain contains stronger cationic groups (primary amino groups), and the charge neutralization capacity between the chitosan and anionic fibers and fillers is stronger, and the retention and drainage-aid performance of the chitosan mainly depends on the cationic property of the chitosan. However, chitosan is only soluble in water and exhibits cationic property under weak acid condition, and is difficult to be applied to neutral paper making, so that the use of chitosan is greatly limited.

The renewable resource macromolecule comes from biomass generated by solar energy, the renewable resource macromolecule is inexhaustible and renewable, and the research and utilization of the renewable resource macromolecule are the conversion, utilization and research of ecological resources and energy, Chitin (CH) is (1-4) -glycosidic bond-N-acetyl-2-deoxy- β -D-glucose, is rich in natural stock and is mostly prepared from shells of crustaceans.

Carboxymethyl chitin is a derivative of chitin after carboxymethylation. The chitosan not only keeps the excellent biological characteristics of the chitosan, but also has water solubility, and no relevant report that the carboxymethyl chitosan is used as a retention and drainage aid for papermaking is found at present. The carboxymethyl chitin can be synthesized by using chitin as a raw material and sodium chloroacetate as an etherifying agent, and the carboxymethyl chitin with different degrees of substitution can be synthesized by changing the addition amount of the sodium chloroacetate.

Disclosure of Invention

The inventor finds that the carboxymethyl chitin has good retention and drainage effects through experiments, can be used as a retention and drainage aid, and researches the retention and drainage aid performance of the carboxymethyl chitin.

Carboxymethyl chitin and chitosan, a derivative of chitin (chitosan is subjected to deacetylation reaction to expose a large amount of primary amino groups to form chitosan), have obvious physicochemical property differences, and the application of chitosan to retention and drainage aids has been reported at present (for example, patent document with publication number CN 1415409A); however, the mechanism of action of carboxymethylchitin is quite different from that of chitosan: (1) carboxymethyl chitin does not undergo deacetylation reaction, and compared with chitosan, carboxymethyl chitin does not have primary amino group and does not have cationic property, so that charge neutralization capacity of carboxymethyl chitin is very weak (carboxymethyl chitin is negatively charged, and a negatively charged substance is not added into paper pulp as a drainage and retention aid according to general experience, because fibers and fine components in the paper pulp are also negatively charged, and the fibers and the fine components are mutually repelled due to the addition of a negatively charged reagent, electrostatic repulsion is enhanced, retention rate is reduced), and a retention and drainage aid mechanism mainly depends on bridging flocculation; when bridging flocculation occurs, polymer molecules are adsorbed on particles or fibers in a cyclic form, the unadsorbed part extends into the solution, and bridging flocculation occurs when the unadsorbed part extends out of an electric double layer and is adsorbed on another particle. Thus, the retention rate is improved. (2) The water solubility of carboxymethyl chitin depends on the introduction of hydrophilic carboxymethyl groups on hydroxyl sites and can be adapted to neutral conditions, whereas chitosan can only be dissolved in weak acid conditions and exhibits cationic properties.

The invention also discloses a retention and drainage aid system comprising the carboxymethyl chitin.

More preferably, the retention and drainage aid system consists of carboxymethyl chitin and polyaluminium chloride. The inventor finds that the carboxymethyl chitin lacks cationic property, and the cationic property can be compensated by adopting polyaluminium chloride. Polyaluminium chloride is an inorganic polymer and will carry a certain amount of positive charge at the moment of addition to the paper stock system. The carboxymethyl chitin is added to form floccules which are cut off, then the polyaluminium chloride is added, a patch-shaped structure with positive charges is formed on the surface of the particles through the attraction of positive and negative charges, and fine particles are connected on longer fibers in a bridging mode, so that a unique floccule structure is formed, the retention rate is improved, and meanwhile, the polyaluminium chloride is hydrolyzed into colloidal aluminium hydroxide, so that the flocculation effect is further enhanced, and the retention rate is improved.

The carboxyl introduced into the carboxymethyl chitin has strong coordination crosslinking capacity with certain metal salt, and the inventor finds that polyaluminium chloride can be matched with the carboxyl through experiments to further crosslink and increase the molecular weight of the carboxyl, so that the increase of the molecular weight of the high molecular polymer can undoubtedly further enhance the bridging flocculation capacity of the carboxyl, and obtain better effect.

As a further improvement of the above scheme, wherein the degree of substitution of carboxymethyl chitin is 0.6. The inventor finds out through experiments that: the substitution degree of the carboxymethyl chitin is increased, the flocculation effect of the carboxymethyl chitin is improved, and the retention and drainage effects are improved.

The invention also discloses a papermaking method, which is characterized by comprising the following steps: during the papermaking process, a retention and drainage aid system consisting of carboxymethyl chitin and polyaluminium chloride is added into papermaking equipment as a retention and drainage aid.

More preferably, the retention and drainage aid system is added in the following manner: firstly adding carboxymethyl chitin and then adding polyaluminium chloride.

More preferably, the amount of polyaluminium chloride added is 0.2-0.7%, preferably 0.5% of the dry weight of the pulp.

The invention has the beneficial effects that: 1) the carboxymethyl chitin is applied to the retention and filtration aid for the first time, so that the retention and filtration aid which has good retention and filtration aid effects, is renewable, has low cost and can be dissolved in neutral pulp liquid is obtained; 2) provides a retention and drainage aid system consisting of carboxymethyl chitin and polyaluminium chloride, and the system has excellent retention and drainage-aid performance.

Drawings

Figure 1 is the carboxymethyl chitin retention aid effect.

FIG. 2 shows the filter aid effect of carboxymethyl chitin.

FIG. 3 is a graph showing the effect of the amount of added polyaluminum chloride on retention.

FIG. 4 shows the retention effect of the carboxymethyl chitin/polyaluminium chloride retention and drainage aid system.

FIG. 5 shows the drainage aid effect of carboxymethyl chitin/polyaluminium chloride retention and drainage aid system.

FIG. 6 shows the effect of the order of addition of carboxymethyl chitin and polyaluminium chloride on retention.

FIG. 7 is a scanning electron micrograph of the pulp.

Description of the drawings: in the above figures, carboxymethyl chitin is denoted by CCH, and polyaluminium chloride is denoted by PAC.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

Description of the drawings: the following percentages are by weight unless otherwise specified.

80g of paper pulp (containing 30 percent of oven dry paper pulp) is weighed and put into a cellulose standard fluffer, tap water is added, and after the paper pulp is soaked for 4 hours, fluffing is carried out for 25 minutes, thus obtaining the paper pulp with the pulp concentration of 1.2 percent.

The first embodiment is as follows:

weighing a proper amount of paper pulp with the pulp concentration of 1.2 percent, diluting the paper pulp with tap water to be 0.2 percent of paper pulp, adding 30 percent of kaolin (relative to the dry weight of the paper pulp), stirring the paper pulp for 30s at 300rpm, adding different predetermined amounts of carboxymethyl chitin with the substitution degree of 0.4 (relative to the dry weight of the paper pulp), stirring the paper pulp for 30s at 300rpm, draining, and uniformly mixing the filtrate.

Example two:

weighing a proper amount of paper pulp with the pulp concentration of 1.2 percent, diluting the paper pulp with tap water to be 0.2 percent of paper pulp, adding 30 percent of kaolin (relative to the dry weight of the paper pulp), stirring the paper pulp for 30s at 300rpm, adding different predetermined amounts of carboxymethyl chitin with the substitution degree of 0.5 (relative to the dry weight of the paper pulp), stirring the paper pulp for 30s at 300rpm, draining, and uniformly mixing the filtrate.

Example three:

weighing a proper amount of paper pulp with the pulp concentration of 1.2 percent, diluting the paper pulp with tap water to be 0.2 percent of paper pulp, adding 30 percent of kaolin (relative to the dry weight of the paper pulp), stirring the paper pulp for 30s at 300rpm, adding different predetermined amounts of carboxymethyl chitin with the substitution degree of 0.6 (relative to the dry weight of the paper pulp), stirring the paper pulp for 30s at 300rpm, draining, and uniformly mixing the filtrate.

Determination of retention Performance:

retention properties are characterized by the retention of kaolin. The determination method comprises the following steps: about 10mL of the filtrate was collected, and the absorbance at 550nm was measured. Different amounts of kaolin are weighed to prepare suspensions, and the absorbance of the suspensions is measured at 550nm, so that a standard curve y is 1.552x + 0.0079. The filler retention was calculated as follows:

wherein: y is absorbance;

x is the mass of kaolin in the filtrate, g;

m-mass of added kaolin, g.

FIG. 1 shows the retention effect of carboxymethyl chitin. As shown in fig. 1, with the addition of carboxymethyl chitin, the retention increases first and then decreases. When the addition amount of the carboxymethyl chitin with the degree of substitution of 0.6 is 0.7%, the retention rate reaches the maximum value, is 70.9%, and is improved by 35.4% compared with the retention rate without any addition agent. When the addition amount of the carboxymethyl chitin with the degree of substitution of 0.5 is 0.5%, the retention rate reaches the maximum value, and is 65.1%. When the addition amount of the carboxymethyl chitin with the degree of substitution of 0.4 is 0.5%, the retention rate reaches the maximum value, and is 60.4%. As can be seen from fig. 1, the degree of substitution is increased, and the retention aid effect of carboxymethyl chitin is better.

Retention of fine components in the pulp is by two mechanisms: mechanical entrapment and colloidal flocculation. Wherein the main part is colloid flocculation, which comprises coagulation and flocculation. The carboxymethyl chitin is a high molecular polymer and can play a role in bridging flocculation as a retention and drainage aid. When bridging flocculation occurs, polymer molecules are adsorbed on particles or fibers in a cyclic form, the unadsorbed part extends into the solution, and bridging flocculation occurs when the unadsorbed part extends out of an electric double layer and is adsorbed on another particle. Thus, the retention rate is improved. However, the carboxymethyl chitin is added too much, so that the retention and drainage effects are deteriorated. This is because carboxymethyl chitin is negatively charged, and fibers and fine components in the pulp are also negatively charged, and they repel each other, so that the electrostatic repulsion is enhanced and the retention rate is lowered.

And (3) measuring the filter aid performance:

drainage aid performance is characterized by freeness. It is generally believed that the lower the freeness, the better the drainage performance. The beating degree is measured according to the relevant national standard (GB/T3332-.

FIG. 2 shows the effect of carboxymethyl chitin in assisting filtration. As shown in fig. 2, with the addition of carboxymethyl chitin, the freeness increased first and then decreased. When the addition amount of the carboxymethyl chitin with the degree of substitution of 0.6 is 0.5%, the beating degree reaches the minimum value, namely 23 DEG SR, and is reduced by 10 DEG SR compared with the beating degree without any auxiliary agent. When the addition amount of the carboxymethyl chitin with the degree of substitution of 0.5 is 0.3 percent, the beating degree reaches the minimum value and is 24 DEG SR. When the addition amount of the carboxymethyl chitin with the degree of substitution of 0.4 is 0.3%, the beating degree reaches the minimum value, and is 27 DEG SR. From fig. 2, the degree of substitution is increased, and the filter aid effect of carboxymethyl chitin is better. The carboxymethyl chitin can promote flocculation between the fiber and the filler, reduce the specific surface area of the fiber and the filler, form a large flocculent and accelerate the dehydration speed.

Example four:

weighing a proper amount of pulp with the pulp concentration of 1.2 percent, diluting the pulp with tap water to be 0.2 percent of pulp, adding 30 percent of kaolin (relative to the dry weight of the pulp), stirring the pulp for 30s at 300rpm, adding different preset amounts of polyaluminium chloride (relative to the dry weight of the pulp), stirring the pulp for 30s at 300rpm, draining, and uniformly mixing the filtrate.

FIG. 3 is a graph showing the effect of the amount of added polyaluminum chloride on retention. As can be seen from FIG. 3, when the added amount of the polyaluminium chloride is 0.8%, the retention rate reaches the maximum value, which is 50.9%, and compared with the retention rate without any addition agent, the retention rate is only increased by 15.4%, which indicates that the retention and drainage-aid effect of the polyaluminium chloride single system is poor. In addition, a binary system is constructed by selecting 0.8 percent of polyaluminium chloride and the carboxymethyl chitin, and the retention and filtration aid effects of the binary system are not improved compared with that of a single carboxymethyl chitin system. This is probably because the amount of polyaluminium chloride added is too large. The inventor obtains through experiments that when the adding amount of the polyaluminium chloride is 0.2-0.7%, the polyaluminium chloride has a good synergistic effect on a single carboxymethyl chitin system, and when the adding amount is 0.5%, the effect is more prominent. For the carboxymethyl chitin/polyaluminium chloride binary system of the present invention, the amount of polyaluminium chloride added is preferably 0.5%.

Example five:

weighing a proper amount of paper pulp with the pulp concentration of 1.2 percent, diluting the paper pulp with tap water to be 0.2 percent of paper pulp, adding 30 percent of kaolin (relative to the dry weight of the paper pulp), stirring the paper pulp for 30s at 300rpm, adding different predetermined amounts of carboxymethyl chitin with the substitution degree of 0.6 (relative to the dry weight of the paper pulp), stirring the paper pulp for 30s at 300rpm, adding 0.5 percent of polyaluminium chloride (relative to the dry weight of the paper pulp), stirring the paper pulp for 30s at 300rpm, draining, and uniformly mixing the filtrate.

FIG. 4 shows the retention aid effect of the binary system carboxymethyl chitin/polyaluminium chloride. As shown in fig. 4, the amount of carboxymethyl chitin added increases, with the retention increasing first and then decreasing. When the addition amount of the carboxymethyl chitin is 0.7%, the retention rate reaches the maximum value of 79.5%. The retention rate is improved by 8.6 percent compared with a single carboxymethyl chitin system, is improved by 33.3 percent compared with a single polyaluminium chloride system, and is improved by 44 percent compared with the retention rate without adding any auxiliary agent. From fig. 4, the carboxymethyl chitin/polyaluminium chloride binary system has better retention effect than the carboxymethyl chitin single system.

FIG. 5 shows the filter aid effect of carboxymethyl chitin/polyaluminium chloride binary system. As shown in fig. 5, with the addition of carboxymethyl chitin, the freeness decreased first and then increased. When the addition amount of the carboxymethyl chitin is 0.3 percent, the beating degree reaches the minimum value, namely 22 DEG SR. The beating degree is reduced by 1 DEG SR compared with that of a single carboxymethyl chitin system, and is reduced by 11 DEG SR compared with that of the single carboxymethyl chitin system without adding any auxiliary agent. From fig. 5, the filtration-aiding effect of the carboxymethyl chitin/polyaluminium chloride binary system is better than that of the carboxymethyl chitin single system.

Example six:

this example illustrates the effect of the order of reagent addition on retention and drainage performance.

Weighing a proper amount of paper pulp with the pulp concentration of 1.2 percent, diluting the paper pulp with tap water to be 0.2 percent of paper pulp, adding 30 percent of kaolin (relative to the dry weight of the paper pulp), stirring the paper pulp for 30s at 300rpm, adding 0.5 percent of polyaluminium chloride (relative to the dry weight of the paper pulp), stirring the paper pulp for 30s at 300rpm, adding 0.7 percent (relative to the dry weight of the paper pulp) of carboxymethyl chitin with the substitution degree of 0.6, stirring the paper pulp for 30s at 300rpm, draining, and uniformly mixing the filtrate.

Example seven:

Weighing a proper amount of paper pulp with the pulp concentration of 1.2 percent, diluting the paper pulp with tap water to be 0.2 percent of paper pulp, adding 30 percent of kaolin (relative to the dry weight of the paper pulp), stirring for 30s at 300rpm, adding 0.7 percent (relative to the dry weight of the paper pulp) of carboxymethyl chitin with the substitution degree of 0.6, and stirring for 30s at 300 rpm; 0.5% polyaluminium chloride (dry weight of pulp) was added, stirred at 300rpm for 30s, filtered and the filtrate was mixed well.

FIG. 6 shows the effect of the order of addition of carboxymethyl chitin and polyaluminium chloride on retention. As shown in fig. 6, the order of adding carboxymethyl chitin and polyaluminium chloride increases the retention rate compared to the blank, but the effect of adding carboxymethyl chitin and polyaluminium chloride first (example seven) is better than that of adding polyaluminium chloride and then carboxymethyl chitin (example six). This is probably because adding carboxymethyl chitin and then adding polyaluminium chloride more easily forms a network floccule structure with the pulp fiber, thereby improving the retention effect.

FIG. 7 is a scanning electron micrograph of the pulp. FIG. 7(a) is a scanning electron micrograph of pure pulp, which is very clean on pulp fibers. FIG. 7(b) shows that only kaolin is added, and that many flocks are adsorbed on the fiber, the flocks are not uniformly distributed, and the size of the flocks is larger. FIG. 7(c) shows that carboxymethyl chitin (the amount of carboxymethyl chitin is 0.7%) is added as a retention and drainage aid, and that the size of the flocs adsorbed on the fibers is reduced and the flocs are uniformly distributed. Fig. 7(d) shows that carboxymethyl chitin is added first and then polyaluminium chloride (the amount of carboxymethyl chitin is 0.7%, and the amount of polyaluminium chloride is 0.5%) is added as a retention and drainage aid, and that the size of flocs is greatly reduced, and the flocs with larger sizes are almost not generated and are distributed more uniformly.

From FIG. 7, flocculation occurred between filler particles in the pulp without the addition of the aid. When the carboxymethyl chitin is used alone, the flocculation forms are flocculation among filler particles and bridging flocculation among the filler particles and fiber components. In a binary system of carboxymethyl chitin/polyaluminium chloride, after the carboxymethyl chitin is added, a large floccule is cut into small floccules, and after the polyaluminium chloride is added, the small floccules react with the large floccules to form a micro floccule with smaller size and more compactness.

Claims

1. The application of carboxymethyl chitin as retention and drainage aid comprises the following steps: adding a retention and drainage aid system in the papermaking process, wherein the retention and drainage aid system comprises carboxymethyl chitin; the corresponding addition amount of the carboxymethyl chitin under different degrees of substitution is as follows: when the substitution degree of the carboxymethyl chitin is 0.4 or 0.5, the addition amount of the carboxymethyl chitin is 0.5 percent of the dry weight of the paper pulp; when the substitution degree of the carboxymethyl chitin is 0.6, the addition amount of the carboxymethyl chitin is 0.7 percent of the dry weight of the paper pulp.

2. The use of carboxymethyl chitin as a retention and drainage aid according to claim 1, characterized in that: the retention and drainage aid system consists of carboxymethyl chitin and polyaluminium chloride.

3. The use of carboxymethyl chitin as retention and drainage aid according to claim 2, characterized in that: the retention and drainage aid system is added in the following mode: firstly adding carboxymethyl chitin and then adding polyaluminium chloride.

4. Use of carboxymethyl chitin as a retention and drainage aid according to claim 2 or 3, characterized in that: wherein the adding amount of the polyaluminium chloride is 0.2 to 0.7 percent of the dry weight of the paper pulp.

5. Use of carboxymethyl chitin as a retention and drainage aid according to claim 2 or 3, characterized in that: wherein the added amount of the polyaluminium chloride is 0.5% of the dry weight of the pulp.