A biodegradable green environmental protection coating and a preparation method thereof

Abstract

This invention belongs to the field of biodegradable coatings and provides a method for preparing a biodegradable and environmentally friendly coating, comprising: mixing polycaprolactone diol and castor oil evenly, heating to 30-35°C, adding diisocyanate and a catalyst, heating to 80-85°C, reacting for 1.5-2 hours, then adding DMBA, a hydrophilic chain extender, and a catalyst to react again. After the reaction is complete, rotary evaporation is performed to obtain a polyurethane prepolymer; mixing a silane coupling agent and triethylamine evenly in water to obtain a mixture; mixing the polyurethane prepolymer and the mixture evenly, emulsifying with water to obtain a biodegradable polyester emulsion (WPU); and curing the biodegradable polyester emulsion (WPU) on a substrate to obtain the final product. This invention develops a high-strength biodegradable coating for surface modification of paper, giving it sufficient mechanical properties to meet the demand for replacing plastic products.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable coatings, and specifically relates to a biodegradable green and environmentally friendly coating and its preparation method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Plastics are macromolecules polymerized from monomers through addition or condensation polymerization. They have moderate resistance to deformation, falling between fibers and rubber, and are composed of synthetic resins and additives such as fillers, plasticizers, stabilizers, lubricants, and colorants. The large-scale use of plastics in the early days, coupled with the lack of an effective recycling system, led to "white pollution," a globally recognized environmental problem.

[0004] Replacing plastic with paper can reduce carbon emissions by reducing the use of fossil-based materials. However, paper-based materials are far less water-resistant and have lower mechanical properties than plastics. Therefore, paper needs to be chemically modified. However, the modified coating often cannot degrade on its own, which brings new environmental problems.

[0005] Polyester water-based emulsions have attracted much attention due to their wide adaptability to various films, excellent flexibility, and chemical resistance. The paper "Application Research of Polyurethane Emulsions in Paper Coating" discloses the application of a polyurethane prepolymer (imidazole-TDI-PEC600) emulsion synthesized from imidazole, toluene-2,4-diisocyanate, and polyethylene glycol (relative molecular mass 600) in paper coating, resulting in significant improvements in the paper's folding endurance, tear resistance, tensile strength, and other physical properties. The paper "Silane Coupling Agent Modified Waterborne Polyurethane Adhesives" discloses that introducing organosilicon (generally polysiloxanes with active end or side groups) into the polyurethane molecular chain can effectively improve the water resistance and heat resistance of the adhesive film. However, the poor compatibility between organosilicon and polyurethane leads to a decrease in the mechanical properties of the adhesive film. Using small-molecule silane coupling agents to modify waterborne polyurethane can increase compatibility and simultaneously improve the water resistance and heat resistance of the polyurethane adhesive film. However, the inventors discovered that the current biodegradable polyester emulsions still have room for improvement in enhancing paper strength. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a biodegradable, environmentally friendly coating. It uses biodegradable polycaprolactone diol and castor oil as raw materials, combined with small molecule compounds to prepare a synthetic polyester aqueous emulsion, and adds a silane coupling agent to further enhance strength. This coating is then used to modify the surface of paper, thereby improving paper strength.

[0007] Unlike existing technologies that introduce silane derivatives into the polyurethane molecular chain to improve the water and heat resistance of the film through moderate crosslinking, this invention improves paper strength by adding a mixed aqueous solution of silane coupling agent and triethylamine to a degradable material and co-emulsifying it with castor oil-based polyurethane prepolymer. Research has found that when silane coupling agent and triethylamine are added to water and co-emulsified with castor oil-based polyurethane prepolymer, the low surface energy of the siloxanes leads to surface enrichment. The silanol and alkoxy groups enriched on the surface readily form hydrogen bonds with hydroxyl groups on the fibers, acting as a link between distant fibers. This transforms the previously weak hydrogen bonds between fibers into stronger chemical bonds, resulting in a significant improvement in paper strength after modification.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] The first aspect of this invention provides a method for preparing a biodegradable, green, and environmentally friendly coating, comprising:

[0010] Polycaprolactone diol and castor oil are mixed evenly and heated to 30-35°C. Diisocyanate and catalyst are added and the temperature is raised to 80-85°C. The reaction is carried out for 1.5-2 hours. Then DMBA, hydrophilic chain extender and catalyst are added to carry out the reaction. After the reaction is completed, rotary evaporation is performed to obtain polyurethane prepolymer.

[0011] The silane coupling agent and triethylamine were mixed evenly in water to obtain a mixture.

[0012] The polyurethane prepolymer was mixed evenly with the mixture, and then emulsified with water to obtain a biodegradable polyester emulsion WPU.

[0013] The biodegradable polyester emulsion WPU is cured on a substrate to obtain the final product.

[0014] In a second aspect, the present invention provides a biodegradable, green, and environmentally friendly coating prepared by the above-described method.

[0015] A third aspect of the present invention provides the application of the above-mentioned biodegradable and environmentally friendly coating in improving paper strength.

[0016] Beneficial effects of the present invention

[0017] (1) The present invention develops a high-strength biodegradable coating to modify the surface of paper and give the paper sufficient mechanical properties to meet the needs of replacing plastic products.

[0018] (2) Unlike existing technologies that introduce silane derivatives into the polyurethane molecular chain to improve the water resistance and heat resistance of the film through moderate crosslinking, this invention adds a mixed aqueous solution of silane coupling agent and triethylamine to the degradation material and co-emulsifies it with castor oil-based polyurethane prepolymer to improve paper strength. Research found that when silane coupling agent and triethylamine are added to water and co-emulsified with castor oil-based polyurethane prepolymer, the low surface energy of the siloxanes leads to surface enrichment. The silanol alkoxy groups enriched on the surface readily form hydrogen bonds with the hydroxyl groups on the fibers, acting as a link between distant fibers. This transforms the originally weak hydrogen bonds between fibers into stronger chemical bonds, resulting in a significant improvement in paper strength after modification.

[0019] (3) The preparation method of the present invention is simple, practical and easy to promote. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 The effect of different polycaprolactone and castor oil contents on polyester strength;

[0022] Figure 2 The effect of different silane coupling agents on polyester strength. Detailed Implementation

[0023] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] A method for preparing a biodegradable, green, and environmentally friendly coating, comprising:

[0025] Polycaprolactone diol and castor oil are mixed evenly and heated to 30-35°C. Diisocyanate and catalyst are added and the temperature is raised to 80-85°C. The reaction is carried out for 1.5-2 hours. Then DMBA, hydrophilic chain extender and catalyst are added to carry out the reaction. After the reaction is completed, rotary evaporation is performed to obtain polyurethane prepolymer.

[0026] The silane coupling agent and triethylamine were mixed evenly in water to obtain a mixture.

[0027] The polyurethane prepolymer was mixed evenly with the mixture, and then emulsified with water to obtain a biodegradable polyester emulsion WPU.

[0028] The biodegradable polyester emulsion WPU is cured on a substrate to obtain the final product.

[0029] In some embodiments, the molar ratio of polycaprolactone to castor oil is 1–9:1–4.

[0030] In some embodiments, the molecular weight of the polycaprolactone is 2000 or 530.

[0031] In some embodiments, the amount of the silane coupling agent added is 3% to 6% of the total mass.

[0032] In some embodiments, the silane coupling agent is selected from at least one of KH-540, KH-550, KH-560, and KH-IC23.

[0033] In some embodiments, the chain extender is hydroquinone dihydroxyethyl ether (HQEE) or 1,4-butanediol (BDO).

[0034] In some embodiments, the diisocyanate is isophorone diisocyanate IPD or toluene diisocyanate TDI;

[0035] In some embodiments, the catalyst is dibutyltin dilaurate (DBTDL).

[0036] In some embodiments, DMPA is used instead of castor oil, and the catalyst is omitted.

[0037] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0038] In the following embodiments, the testing of the base paper and the coating were performed using testing methods commonly used in the art.

[0039] Example 1

[0040] A method for preparing a biodegradable, green, and environmentally friendly coating, comprising:

[0041] 1) Mix 6g of polycaprolactone (PCL (Mn = 2000)) and 24g of castor oil (CO) in a 1:4 ratio until homogeneous. Heat to 30°C, add 167g of isophorone diisocyanate (IPID) and 0.015g of dibutyltin dilaurate (DBTDL) dropwise, mix until homogeneous, heat to 80°C, and react for 2 hours. Then add 25g of acetone solution of N,N-dimethyl-N-butyl-N-methacrylate ammonium bromide (DMBA), 100g of 1,4-butanediol (BDO), and 0.01g of dibutyltin dilaurate (DBTDL), and react for 4 hours. Finally, rotary evaporate under vacuum at 45°C for 10 minutes to obtain polyurethane prepolymer.

[0042] 2) Mix 5% silane coupling agent KH-540 and 25g triethylamine in water until homogeneous to obtain a mixture;

[0043] 3) Mix the polyurethane prepolymer and the mixture evenly, adjust the speed of the emulsifier to 1200 rpm, and slowly add water while stirring the prepolymer at high speed. Stir at high speed for 1 hour to obtain biodegradable polyester emulsion WPU.

[0044] 4) The biodegradable polyester emulsion (WPU) is coated onto the base paper using a wire rod coating machine, with a single-layer coating weight of 8 g / m². 2 This results in a biodegradable, green, and environmentally friendly coating.

[0045] Example 2

[0046] The difference from Example 1 is that polycaprolactone (PCL) and castor oil (CO) were mixed in ratios of 9:1, 1:2, 1:6, and 1:9 respectively to prepare biodegradable polyester emulsions (WPU).

[0047] Example 3

[0048] The difference from Example 1 is that polycaprolactone (PCL (Mn = 500)) was chosen instead of PCL (Mn = 2000).

[0049] Example 4

[0050] The difference from Example 1 is that KH-550, KH-560, and KH-IC23 were selected as silane coupling agents to prepare biodegradable polyester emulsions (WPU), and the test results are as follows. Figure 2 As shown.

[0051] Example 5

[0052] The difference from Example 1 is that the silane coupling agent is added during the formation of the prepolymer, as follows:

[0053] 1) Mix 6g of polycaprolactone (PCL (Mn=2000)) and 24g of castor oil (CO) in a 1:4 ratio until homogeneous. Heat to 30℃, add 167g of isophorone diisocyanate (IPID) and 0.015g of dibutyltin dilaurate (DBTDL) dropwise, mix until homogeneous, heat to 80℃ and react for 2h. Then add 25g of N,N-dimethyl-N-butyl-N-methacrylate ammonium bromide (DMBA) in acetone, 100g of 1,4-butanediol (BDO) and 0.01g of dibutyltin dilaurate (DBTDL), react for 4h, add 5% silane coupling agent KH-540, react for 10min, and then rotary evaporate under vacuum at 45℃ for 10min to obtain polyurethane prepolymer.

[0054] 2) Mix the polyurethane prepolymer with 25g of triethylamine evenly, adjust the speed of the emulsifier to 1200rpm, and slowly add water while stirring the prepolymer at high speed. Stir at high speed for 1 hour to obtain biodegradable polyester emulsion WPU.

[0055] Example 6

[0056] The difference from Example 1 is that hydroquinone dihydroxyethyl ether (HQEE) is used instead of 1,4-butanediol (BDO) as a chain extender, and KH-560 is used instead of KH-540 as a silane coupling agent, with an addition amount of 6%.

[0057] Experimental Example

[0058] The performance tests of the coatings prepared in the above embodiments were conducted, and the results are as follows:

[0059] To ensure biodegradability, this invention uses a combination of polycaprolactone and castor oil as raw materials. Examples 1-3 explore the molecular weight and segment ratio of the raw materials to improve coating strength.

[0060] As shown in Tables 1-2, Figure 1 As shown, this invention selects polycaprolactone with a molecular weight of 2000 and castor oil as reaction raw materials. Compared with polycaprolactone with a molecular weight of 500, the high molecular weight polycaprolactone provides better mechanical strength to the coating while ensuring a certain degree of toughness. In terms of controlling the chain segment ratio, through testing different chain segment ratios, it was found that when polycaprolactone and castor oil are combined in a molar ratio of 1:4, good strength is achieved while ensuring toughness.

[0061] Table 1. Mechanical properties of PCL with different molecular weights and different ratios to CO

[0062]

[0063] Table 2. Mechanical properties of PCL (Mn = 2000) and CO at different ratios

[0064]

[0065]

[0066] like Figure 2 As shown in Examples 1, 4, and 5, the present invention controls the type, dosage, and addition method of the silane coupling agent. The results show that: the selected silane coupling agent is KH-540, the addition amount is 5%, and the addition method is determined to be adding it to water together with the amine for co-emulsification. With the addition of the silane coupling agent, the paper strength is significantly improved compared to before.

[0067] As shown in Table 3, in Examples 1 and 6, the present invention investigated the effects of different silane coupling agent contents and different chain extenders on paper properties. The results showed that the combination of "KH-540+BDO" had better paper properties than "KH-560+HQEE".

[0068] Table 3. Characterization of paper properties with different silane coupling agent contents and different chain extenders

[0069]

[0070] Note: PU 1 has a PCL:CO ratio of 1:4, with 5% KH-540 added, BDO as the chain extender, and IPDI as the isocyanate supplier; PU 2 has a PCL:CO ratio of 1:4, with 6% KH-560 added, HQEE as the chain extender, and IPDI as the isocyanate supplier.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a biodegradable, green, and environmentally friendly coating, characterized in that, include: Polycaprolactone diol and castor oil are mixed evenly and heated to 30-35°C. Diisocyanate and catalyst are added and the temperature is raised to 80-85°C. The reaction is carried out for 1.5-2 hours. Then DMBA, hydrophilic chain extender and catalyst are added to carry out the reaction. After the reaction is completed, rotary evaporation is performed to obtain polyurethane prepolymer. The silane coupling agent and triethylamine were mixed evenly in water to obtain a mixture. The polyurethane prepolymer was mixed evenly with the mixture, and then emulsified with water to obtain a biodegradable polyester emulsion WPU. The biodegradable polyester emulsion WPU is cured on a substrate to obtain the product. The molar ratio of polycaprolactone to castor oil is 1:2, 1:4, or 1:6; the molecular weight of polycaprolactone is 2000. The amount of the silane coupling agent added is 5% to 6% of the total mass; The silane coupling agent is selected from at least one of KH-540, KH-550, KH-560, and KH-IC23; The chain extender is hydroquinone dihydroxyethyl ether (HQEE) or 1,4-butanediol (BDO).

2. The method for preparing the biodegradable green and environmentally friendly coating as described in claim 1, characterized in that, The diisocyanate is isophorone diisocyanate IPD or toluene diisocyanate TDI; Alternatively, the catalyst may be dibutyltin dilaurate (DBTDL).

3. The biodegradable, green, and environmentally friendly coating prepared by the method according to any one of claims 1-2.

4. The application of the biodegradable and environmentally friendly coating as described in claim 3 in improving paper strength.

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