Bio-based pulp internal sizing agent for producing molded pulp product with high water resistance and preparation method of bio-based pulp internal sizing agent

Abstract

The invention relates to a bio-based pulp internal sizing agent for producing a molded pulp product with high water resistance and a preparation method of the bio-based pulp internal sizing agent. The bio-based pulp internal sizing agent for producing the molded pulp product with high water resistance is prepared from the following raw materials: cationic starch, rosin emulsion, polyvinyl alcohol, silica sol, polyaluminum chloride and water. The invention also provides a preparation method of the bio-based pulp internal sizing agent for producing the high-water-resistance paper pulp molded product, which comprises the following steps: adding cationic starch into water, heating, gelatinizing and cooling to obtain cationic starch gelatinized liquid; adding polyvinyl alcohol into water, heating and cooling to obtain a polyvinyl alcohol aqueous solution; and mixing the cationic starch gelatinization liquid with the rosin emulsion, sequentially adding a polyvinyl alcohol aqueous solution, silica sol and polyaluminum chloride, and uniformly mixing to obtain the bio-based pulp internal sizing agent for producing the high-water-resistance paper pulp molded product. The technical problem that in a neutral slurry sizing environment, a high-water-resistance paper pulp molded product cannot be produced by adopting a bio-based internal sizing agent is solved.

Description

Technical Field

[0001] The invention relates to the technical field of chemicals for papermaking, and in particular to a bio-based internal sizing agent for producing highly water-resistant pulp molded products and a preparation method thereof. Background Art

[0002] With the release of various policies on plastic pollution control in my country, new restrictions on the use of plastic products in various industries have been proposed, and the control of the use of plastic products in industries such as food, catering, express delivery and industrial product inner packaging has been further strengthened. In particular, non-degradable disposable foamed plastic lunch boxes and tableware and industrial product inner packaging will be banned nationwide. At the same time, pulp produced from plant fibers as raw materials, as a degradable and renewable resource, has become an important substitute for plastics. Food packaging boxes, tableware and industrial product inner packaging made of pulp molded products have begun to appear in large numbers on the market. However, ordinary pulp molded products will quickly soften and deform after being immersed in water, and even leak. For industries such as tableware and industrial product inner packaging that require water resistance, they cannot meet their use requirements. Therefore, it is particularly important to process and treat pulp molded products for water resistance.

[0003] In the current production of pulp molded products, the processing method to improve the water resistance of products is to apply sizing during the production process. There are two specific production methods, one is called surface sizing and the other is called internal sizing. Surface sizing is to use synthetic latex, organic polymer solid coating or film as raw materials, through coating, laminating or hot pressing process, to add a layer of colloid isolation layer on the surface of the already formed pulp molded products to play the role of isolation and water resistance. At present, the colloid isolation layer used in pulp molded products is mainly paraffin and polyethylene. The pulp molded products made by this method are essentially a composite paper product formed by a plastic glue layer attached to its surface. The large-scale use of this composite paper product will still bring plastic pollution and will be banned one after another; internal sizing is to add a sizing agent that can reduce the surface free energy and thus reduce the adhesion of paper surface fibers to water in the slurry before the pulp molded products are formed. At present, the main chemical synthetic sizing agent used in the production of water-resistant pulp molded products is a reactive alkyl ketene dimer (AKD) compounded as the main component. This is a neutral sizing agent, which is basically consistent with the sizing environment of pulp molding plastics, and is therefore widely used in the field of pulp molding production. However, alkyl ketene dimer will further polymerize during the hot pressing process of pulp molded product production to generate alkyl ketene polymers that are difficult to degrade, causing white pollution. At the same time, alkyl ketene dimer remaining in pulp molded products and white water is also likely to cause water pollution and even affect human health. With the implementation of the "plastic ban", pulp molded products produced using alkyl ketene dimer as the main component of the sizing agent have begun to be unacceptable to the market. Summary of the invention

[0004] The purpose of the present invention is to provide a bio-based internal sizing agent for producing highly water-resistant pulp molded products and a preparation method thereof, so as to solve the problem that the existing internal sizing agent contains alkyl ketene dimer, thereby polluting the environment and affecting human health.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following raw materials, measured in parts by weight: 2 to 3 parts by weight of cationic starch, 40 to 60 parts by weight of rosin emulsion, 1 to 2 parts by weight of polyvinyl alcohol, 0.5 to 2 parts by weight of silica sol, 1 to 2 parts by weight of polyaluminium chloride and 15 to 70 parts by weight of water.

[0007] Preferably, the cationic substitution degree of the loose cationic starch is 0.3% to 0.5%.

[0008] Preferably, the solid content of the rosin emulsion is 30% to 40wt%.

[0009] Preferably, the solid content of the silica sol is 20-30 wt % and the pH value is 7-9.

[0010] Preferably, the following raw materials are included, by weight: 2.3-2.8 parts by weight of cationic starch, 45-55 parts by weight of rosin emulsion, 1.2-1.8 parts by weight of polyvinyl alcohol, 0.6-1.8 parts by weight of silica sol, and 1.2-1.8 parts by weight of polyaluminium chloride.

[0011] Preferably, the following raw materials are included, by weight: 2.5 parts by weight of cationic starch, 50 parts by weight of rosin emulsion, 1.5 parts by weight of polyvinyl alcohol, 1.2 parts by weight of silica sol, and 1.5 parts by weight of polyaluminium chloride.

[0012] The present invention also provides a method for preparing the bio-based internal sizing agent for producing highly water-resistant pulp molded products according to the present invention, comprising the following steps:

[0013] Adding cationic starch into water, heating for gelatinization, and cooling to obtain cationic starch gelatinized liquid;

[0014] Adding polyvinyl alcohol into water, heating to dissolve, and cooling to obtain a polyvinyl alcohol aqueous solution;

[0015] Cationic starch gelatinized liquid and rosin emulsion are mixed, and then polyvinyl alcohol aqueous solution, silica sol and polyaluminium chloride are added in sequence and mixed evenly to obtain a bio-based internal sizing agent for producing highly water-resistant pulp moulding products.

[0016] Preferably, the cationic starch is added into water, the concentration of the cationic starch is 6% to 20wt%, heated to 85°C to fully gelatinize the cationic starch, and then cooled to room temperature to obtain a cationic starch gelatinized liquid;

[0017] Preferably, polyvinyl alcohol is added into water with a concentration of 8% to 12 wt%, heated to 95° C. to fully dissolve the polyvinyl alcohol, and then cooled to room temperature to obtain a polyvinyl alcohol aqueous solution.

[0018] Beneficial effects of the present invention:

[0019] The bio-based internal sizing agent for producing highly water-resistant pulp molded products of the present invention uses natural, biodegradable cationic starch, rosin emulsion and polyvinyl alcohol as main raw materials, and does not contain chemical synthetic substances such as alkyl ketene dimer that are easy to cause white pollution. At the same time, no toxic and harmful substances are added to the raw materials, which prevents the generation and release of toxic and harmful substances and effectively avoids pollution to the environment. Starch, rosin and polyvinyl alcohol all have the advantages of abundant sources, biodegradability, no plastic pollution and low price, which provides favorable guarantees for the industrial production of bio-based internal sizing agents.

[0020] The preparation method of the bio-based in-slurry sizing agent for producing highly water-resistant pulp molded products of the present invention comprises the following steps: firstly mixing the cationic starch gelatinized liquid with the rosin emulsion to form a cationic complex, then successively adding a polyvinyl alcohol aqueous solution and a silica sol to form a protective layer, and finally adding polyaluminium chloride to mix, thereby avoiding the precipitation effect of the direct mixing of the polyaluminium chloride and the rosin emulsion to damage the stability of the rosin emulsion. By utilizing the affinity of the cationic complex in the present invention with the fibers with anionic characteristics in the slurry used for pulp molding production, the sizing agent is adsorbed onto the pulp fibers, and then by utilizing the bridging and precipitation effects of the polyaluminium chloride, the cationic complex is further precipitated and attached to the pulp fibers by adding the polyaluminium chloride of the in-slurry sizing agent, thereby achieving the purpose of reducing the surface free energy of the fibers. Finally, by utilizing the hydrolysis cross-linking property of the silica sol and the film-forming property of the polyvinyl alcohol, the surface strength and stiffness of the pulp molded product are further improved, thereby further effectively improving the water resistance of the pulp molded product. The pulp molded products produced by the present invention have high strength, stable molding, and water resistance far higher than the traditional pulp molded products and the requirements for water resistance in the pulp molded product standards formulated by the state and the industry. They are highly water-resistant pulp molded products and are particularly suitable for the requirements of the catering, ocean shipping and other industries for highly water-resistant pulp molded products. They also have the advantages of simple process operation and low production cost, and have more industrial production value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1The present invention is a process flow chart for preparing a bio-based in-pulp sizing agent for highly water-resistant pulp molded products. DETAILED DESCRIPTION

[0022] The following will describe the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0023] Example 1

[0024] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0025] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0026] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0027] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0028] Example 2

[0029] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0030] S1, adding 2 kg of starch with a cationic substitution degree of 0.5% and 11 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0031] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0032] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0033] Example 3

[0034] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0035] S1, adding 3 kg of starch with a cationic substitution degree of 0.3% and 17 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0036] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0037] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0038] Example 4

[0039] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0040] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0041] S2, adding 1 kg of polyvinyl alcohol and 9 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0042] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0043] Example 5

[0044] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0045] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0046] S2, adding 2 kg of polyvinyl alcohol and 18 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0047] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0048] Example 6

[0049] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0050] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0051] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0052] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 40 kg of rosin emulsion with a solid content of 40 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0053] Example 7

[0054] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0055] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0056] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0057] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 60 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0058] Example 8

[0059] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0060] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0061] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0062] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 0.5 kg of silica sol with a solid content of 30 wt% and a pH of 9 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0063] Example 9

[0064] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0065] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0066] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0067] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 2 kg of silica sol with a solid content of 20 wt% and a pH of 7. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0068] Example 10

[0069] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0070] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0071] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0072] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0073] Embodiment 11

[0074] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0075] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0076] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0077] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 2 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0078] Example 12

[0079] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0080] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 10 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0081] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0082] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0083] Example 13

[0084] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0085] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 39 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0086] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0087] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0088] Embodiment 14

[0089] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0090] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0091] S2, adding 1.5 kg of polyvinyl alcohol and 17 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0092] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0093] Embodiment 15

[0094] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0095] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0096] S2, adding 1.5 kg of polyvinyl alcohol and 11 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0097] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0098] Comparative Example 1

[0099] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0100] S1. Add 1 kg of starch with a cationic substitution degree of 0.5% and 6 kg of water into a reaction container, stir and disperse, heat to 85° C. to fully gelatinize the cationic starch, and then cool to room temperature to obtain a cationic starch gelatinized liquid;

[0101] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0102] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0103] Comparative Example 2

[0104] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0105] S1, adding 4 kg of starch with a cationic substitution degree of 0.3% and 23 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0106] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0107] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0108] Comparative Example 3

[0109] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0110] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0111] S2, adding 0.5 kg of polyvinyl alcohol and 4.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0112] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0113] Comparative Example 4

[0114] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0115] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0116] S2, adding 3 kg of polyvinyl alcohol and 27 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0117] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0118] Comparative Example 5

[0119] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0120] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0121] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0122] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 30 kg of rosin emulsion with a solid content of 40 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0123] Comparative Example 6

[0124] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0125] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0126] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0127] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 70 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0128] Comparative Example 7

[0129] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0130] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0131] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0132] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 0.3 kg of silica sol with a solid content of 30 wt% and a pH of 9 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0133] Comparative Example 8

[0134] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0135] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0136] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0137] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 3 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0138] Comparative Example 9

[0139] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0140] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0141] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0142] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 0.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0143] Comparative Example 10

[0144] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0145] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0146] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0147] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 3 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0148] Comparative Example 11

[0149] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0150] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 7.5 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0151] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0152] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0153] Comparative Example 12

[0154] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0155] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 47 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0156] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0157] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0158] Comparative Example 13

[0159] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0160] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0161] S2, adding 1.5 kg of polyvinyl alcohol and 23 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0162] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0163] Comparative Example 14

[0164] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0165] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0166] S2, adding 1.5 kg of polyvinyl alcohol and 8.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0167] S3. Mix the cationic starch gelatinized liquid obtained in S1 with 50 kg of rosin emulsion with a solid content of 30 wt%. After mixing evenly, add the polyvinyl alcohol aqueous solution obtained in S2 and mix. After mixing evenly, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 and mix. After mixing evenly, finally add 1.5 kg of polyaluminium chloride and mix. After mixing evenly, a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products is obtained.

[0168] Comparative Example 15

[0169] A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products comprises the following steps:

[0170] S1, adding 2.5 kg of starch with a cationic substitution degree of 0.5% and 14 kg of water into a reaction container, stirring and dispersing, heating to 85° C. to fully gelatinize the cationic starch, and then cooling to room temperature to obtain a cationic starch gelatinized liquid;

[0171] S2, adding 1.5 kg of polyvinyl alcohol and 13.5 kg of water into a reaction container, heating to 95° C. under stirring to completely dissolve the polyvinyl alcohol, and then cooling to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0172] S3. Mix the cationic starch gelatinized liquid obtained in S1 and the polyvinyl alcohol aqueous solution obtained in S2, add 1.2 kg of silica sol with a solid content of 20 wt% and a pH of 7 after mixing evenly, add 50 kg of rosin emulsion with a solid content of 30 wt% after mixing evenly, finally add 1.5 kg of polyaluminium chloride to obtain a bio-based in-slurry sizing agent for producing highly water-resistant pulp moulding products.

[0173] Analytical Testing

[0174] The bio-based in-pulp sizing agent for producing highly water-resistant pulp molded products prepared in Examples 1 to 15, and the sizing agent products prepared in Control Examples 1 to 15, were used in the production of pulp molded products. The amount added was the average amount commonly added in the industry, that is, 5% of the sizing agent relative to absolute dry pulp (white water was not recycled). The apparent properties and the water resistance of the obtained pulp molded products were tested (the water resistance test method was carried out in accordance with BB / T0045-2021 "Pulp Molded Products Industrial Packaging" and GB / T36787-2018 "Pulp Molded Tableware"). The performance indicators are shown in Table 1.

[0175] Table 1 Sizing agents prepared in Examples 1 to 15 and Comparative Examples 1 to 15 and energy indexes of the prepared pulp molded paper

[0176]

[0177]

[0178] Note: The water resistance and water leakage indicators listed in the table are implemented using the test methods specified in the BB / T0045-2021 "Pulp Molded Products Industrial Packaging" and GB / T36787-2018 "Pulp Molded Tableware" standards respectively.

[0179] From the data analysis in Table 1 above, it can be seen that the in-slurry sizing agent for producing highly water-resistant pulp molded products obtained by using Examples 1 to 15 of the present invention has good properties, and the various performance difference indicators of the produced pulp molded products far exceed the relevant technical indicators specified in BB / T0045-2021 "Pulp Molded Products Industrial Packaging" and GB / T36787-2018 "Pulp Molded Tableware", and meet the requirements of industries such as catering and ocean transport packaging for high water resistance of pulp molded products. The sizing agent obtained in Example 1 has the best comprehensive performance and cost performance. In Control Example 1, due to the small amount of cationic starch used, the water resistance is significantly reduced. In Control Example 2, due to the large amount of cationic starch used, the in-slurry sizing agent is thick, the dispersibility is poor, and the water resistance is also reduced. In Control Example 3, due to the small amount of polyvinyl alcohol used, the water resistance is significantly reduced. In Control Example 4, due to the excessive amount of polyvinyl alcohol used, the obtained sizing agent in the slurry is thick and has coagulation phenomenon, which affects the use. In Control Example 5, due to the small amount of rosin emulsion used, the water resistance is significantly reduced. In Control Example 6, due to the excessive amount of rosin emulsion used, the obtained sizing agent in the slurry is thick and has coagulation phenomenon. In Control Example 7, due to the small amount of silica sol added, the water resistance is significantly reduced. In Control Example 8, due to the excessive amount of silica sol added, the obtained sizing agent emulsion is destroyed and is in the form of a clear liquid, and the water resistance is also significantly reduced. In Control Example 9, due to the small amount of polyaluminium chloride added, the water resistance is significantly reduced. In Control Example 10, due to the excessive amount of polyaluminium chloride added, the obtained sizing agent in the slurry is thick and has coagulation phenomenon. In Control Example 11, the concentration of starch during gelatinization was too high, resulting in the gelatinized liquid being too thick, causing the prepared in-slurry sizing agent to coagulate, affecting its normal use. In Control Example 12, the concentration of starch during gelatinization was too low, resulting in the gelatinized liquid being too thin, and the prepared in-slurry sizing agent was in the form of a clear liquid, and its water resistance was also significantly reduced. In Control Example 13, because the concentration of polyvinyl alcohol was too low when it was dissolved, the prepared in-slurry sizing agent had a stratification phenomenon. In Control Example 14, because the concentration of polyvinyl alcohol was too high when it was dissolved, the prepared in-slurry sizing agent was too thick and coagulated, affecting its normal use. In Control Example 15, the mixing order of the materials was changed, making it impossible to prepare a stable in-slurry sizing agent. The above control examples prove that in the preparation method of the in-slurry sizing agent for producing highly water-resistant pulp molded products of the present invention, the ratio among cationic starch, rosin emulsion, polyvinyl alcohol, silica sol and polyaluminium chloride, the gelatinization concentration of cationic starch, the dissolution concentration of polyvinyl alcohol and the order of ingredients are all important parameters affecting the performance of the in-slurry sizing agent.

[0180] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or change made by a person skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A bio-based internal sizing agent for producing highly water-resistant pulp molded products, characterized in that: The invention comprises the following raw materials by weight: 2-3 parts by weight of cationic starch, 40-60 parts by weight of rosin emulsion, 1-2 parts by weight of polyvinyl alcohol, 0.5-2 parts by weight of silica sol, 1-2 parts by weight of polyaluminium chloride and 15-70 parts by weight of water.

2. The bio-based internal sizing agent for producing highly water-resistant pulp molded products according to claim 1, characterized in that: The cationic substitution degree of the loose cationic starch is 0.3% to 0.5%.

3. The bio-based internal sizing agent for producing highly water-resistant pulp molded products according to claim 1, characterized in that: The solid content of the rosin emulsion is 30% to 40wt%.

4. The bio-based internal sizing agent for producing highly water-resistant pulp molded products according to claim 1, characterized in that: The solid content of the silica sol is 20-30 wt %, and the pH value is 7-9.

5. The bio-based internal sizing agent for producing highly water-resistant pulp molded products according to claim 2, characterized in that: By weight, it includes the following raw materials: 2.3-2.8 parts by weight of cationic starch, 45-55 parts by weight of rosin emulsion, 1.2-1.8 parts by weight of polyvinyl alcohol, 0.6-1.8 parts by weight of silica sol, and 1.2-1.8 parts by weight of polyaluminium chloride.

6. The bio-based internal sizing agent for producing highly water-resistant pulp molded products according to claim 4, characterized in that: The following raw materials are included by weight: 2.5 parts by weight of cationic starch, 50 parts by weight of rosin emulsion, 1.5 parts by weight of polyvinyl alcohol, 1.2 parts by weight of silica sol, and 1.5 parts by weight of polyaluminium chloride.

7. A method for preparing a bio-based internal sizing agent for producing highly water-resistant pulp molded products according to any one of claims 1 to 5, characterized in that: The following steps are involved: Adding cationic starch into water, heating for gelatinization, and cooling to obtain cationic starch gelatinized liquid; Adding polyvinyl alcohol into water, heating to dissolve, and cooling to obtain a polyvinyl alcohol aqueous solution; Cationic starch gelatinized liquid and rosin emulsion are mixed, and then polyvinyl alcohol aqueous solution, silica sol and polyaluminium chloride are added in sequence and mixed evenly to obtain a bio-based internal sizing agent for producing highly water-resistant pulp moulding products.

8. The preparation method according to claim 7, characterized in that: The method comprises adding cationic starch into water with a concentration of 6-20 wt %, heating the water to 85° C. to fully gelatinize the cationic starch, and then cooling the water to room temperature to obtain a cationic starch gelatinized liquid.

9. The preparation method according to claim 7, characterized in that: The polyvinyl alcohol is added into water with a concentration of 8-12 wt %, heated to 95° C. to fully dissolve the polyvinyl alcohol, and then cooled to room temperature to obtain a polyvinyl alcohol aqueous solution.

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