Method for preparing polyurethane microcapsule shell by means of direct crosslinking of cellulose and polyisocyanate

Abstract

A method for preparing a polyurethane microcapsule shell by means of direct crosslinking of cellulose and a polyisocyanate. A rigid polyurethane structure shell having high-density carbamate groups is generated thereby, and the direct crosslinking method improves the stability of a microcapsule and makes the product quality more reliable.

Description

A method for preparing polyurethane microcapsule shells by direct crosslinking of cellulose and polyisocyanate Technical Field

[0001] The invention belongs to the field of material science and engineering technology, and particularly relates to a method for preparing a polyurethane microcapsule shell by directly cross-linking cellulose and polyisocyanate. Background Art

[0002] Microencapsulation technology involves encapsulating substances in tiny capsules to preserve their stability and performance. Initially applied in the pharmaceutical field, microencapsulation technology was used to control drug release and improve drug stability. With the continuous development of technology, microencapsulation technology has been gradually applied to a variety of fields, including food, cosmetics, coatings, rubber, plastics, and ceramics.

[0003] Microcapsules are composed of an outer shell and a core material. According to the properties of the microcapsules and the shell formation mechanism, the structural design methods of microcapsules can be divided into three categories: physical and mechanical methods, phase separation methods, and polymerization reaction methods. Currently, the commonly used polymerization reaction methods are mainly in-situ polymerization and interfacial polymerization. In the in-situ polymerization method, an aqueous solution of a polymer monomer is mixed with an oil phase solution of a core monomer, and an emulsifier is added and stirred at high speed to form an emulsion. The reaction between the polymer monomers is then controlled by changing the temperature or pH value so that it solidifies on the surface of the droplet to form a wall material. However, this method has higher requirements for the polymer monomers that form the wall material, and it also requires more stringent experimental conditions to be controlled. The higher the requirements for experimental conditions, the more difficult the preparation process may be. In comparison, the interfacial polymerization method is simpler.

[0004] Interfacial polymerization involves mixing an oil-phase solution of the core material and polymer monomer A with an aqueous solution, adding an emulsifier, and stirring at high speed to form an emulsion. Once the emulsion stabilizes, a reactive monomer B soluble in the aqueous phase is added. These two polymer monomers polymerize at the water-oil interface, relying on their highly reactive molecules, to form a shell that encapsulates the core material, thus producing microcapsules. Interfacial polymerization is suitable for preparing liquid-encapsulated microcapsules. The method is relatively simple, and the resulting microcapsules have good density. However, while interfacial polymerization can effectively prepare liquid-encapsulated microcapsules with good density, a key factor influencing product performance during the preparation process is the dispersion state. For example, stirring speed, viscosity, and the type and amount of emulsifiers and stabilizers can significantly influence the particle size distribution and wall thickness of the microcapsules. This requires strict control of various parameters during operation, otherwise unstable product quality may result.

[0005] Summary of the Invention

[0006] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0007] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0008] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing polyurethane microcapsule shells by directly cross-linking cellulose and polyisocyanate.

[0009] In order to solve the above technical problems, the present invention provides the following technical solution: a method for preparing a polyurethane microcapsule shell by direct crosslinking of cellulose and polyisocyanate, comprising:

[0010] The cellulose crystals are mixed with deionized water to prepare an aqueous phase;

[0011] N,N-dimethylaniline, toluene and polyisocyanate are mixed evenly as the oil phase;

[0012] Pour the oil phase into the water phase and stir for 20 min to form an emulsion;

[0013] The emulsion is heated and stirred, then allowed to stand for 2 hours, cooled to room temperature, filtered, washed, filtered again, and dried to obtain the polyurethane microcapsule shell.

[0014] As a preferred embodiment of the method of the present invention, the polyisocyanate is one of polymethylene polyphenyl isocyanate, toluene diisocyanate and isophorone diisocyanate.

[0015] As a preferred embodiment of the method of the present invention, the mass ratio of the cellulose crystals to the polyisocyanate is 1.05:8.

[0016] As a preferred embodiment of the method of the present invention, the mass ratio of the N,N-dimethylaniline, toluene and polyisocyanate is 3:9:4.

[0017] As a preferred embodiment of the method of the present invention, the volume ratio of the water phase to the oil phase is 4:1.

[0018] As a preferred embodiment of the method of the present invention, the stirring is performed for 20 minutes at a stirring rate of 1300 r / min.

[0019] As a preferred embodiment of the method of the present invention, the emulsion is heated and stirred, wherein the heating temperature is 70-80°C.

[0020] As a preferred embodiment of the method of the present invention, the heating and stirring process has a stirring rate of 200 r / min and a stirring time of 15 min.

[0021] Another object of the present invention is to overcome the deficiencies in the prior art and provide a polyurethane microcapsule shell prepared by direct cross-linking of cellulose and polyisocyanate.

[0022] Another object of the present invention is to overcome the deficiencies in the prior art and provide an application of a polyurethane microcapsule shell prepared by direct cross-linking of cellulose and polyisocyanate.

[0023] Beneficial effects of the present invention:

[0024] (1) The present invention proposes a method for preparing a polyurethane microcapsule shell by directly cross-linking nanocrystalline cellulose with polyisocyanate, which generates a rigid polyurethane structure shell with a high density of carbamate groups. This direct cross-linking method increases the stability of the microcapsules and makes the product quality more reliable.

[0025] (2) Amphiphilicity and wettability of cellulose: The crystalline edges of cellulose chains form a “hydrophobic face” that facilitates its adsorption at the oil / water interface. This enables cellulose to stabilize emulsion droplets and promote particle repulsion, resulting in dense cellulose accumulation on the droplet surface, which helps form uniform and stable microcapsules.

[0026] (3) Heating to initiate cross-linking: Heating the mixture to 70-80°C can initiate a cross-linking reaction between the hydroxyl groups of cellulose and the isocyanate groups of the polyisocyanate. Heating eliminates steric factors, improves the reactivity of the isocyanate groups, and promotes the diffusion of the polyisocyanate to the reaction sites, which helps to form a uniform and stable polyurethane microcapsule shell. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0028] FIG1 is a schematic diagram of the shell-forming reaction of the polyurethane microcapsules of the present invention.

[0029] FIG2 is a SEM image of the polyurethane microcapsule shell of the present invention.

[0030] FIG3 is a particle size distribution diagram of the polyurethane microcapsule shell prepared in the present invention. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0032] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0033] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0034] The manufacturers and specifications (purity) of the chemical reagents used in preparing the polyurethane microcapsule shell samples in the method of the present invention are shown in Table 1.

[0035] Table 1

[0036] The models and manufacturers of the main experimental instruments used to prepare the polyurethane microcapsule shell samples in the method of the present invention are shown in Table 2.

[0037] Table 2

[0038] Example 1

[0039] This embodiment provides a method for preparing a polyurethane microcapsule shell directly cross-linked with nanocrystalline cellulose and polyisocyanate, comprising the following steps:

[0040] (1) Preparation of aqueous phase

[0041] Add 150-200 mL of deionized water to a 500 mL beaker, weigh 1.05 g of cellulose crystals using an electronic balance, mix them in the deionized water, and stir them magnetically at 500 rpm for 5 minutes at room temperature to ensure thorough mixing.

[0042] (2) Preparation of emulsion

[0043] Take 6 mL of N, N-dimethylaniline (TMA) and mix it with 40 mL of toluene, add 8 g of polymethylene polyphenyl isocyanate (PMDI), and stir evenly as the oil phase;

[0044] The oil phase was poured into the water phase with a volume ratio of 4:1 between the water phase and the oil phase. The mixture was mechanically stirred at 1300 r / min for 20 minutes at room temperature to form an emulsion.

[0045] (3) Preparation of microcapsule shell

[0046] The prepared emulsion was stirred in a constant temperature magnetic stirrer at 75°C and 200 r / min for 15 minutes, and then allowed to stand in a constant temperature water bath at 75°C for 2 hours to complete the reaction.

[0047] (4) Washing and drying

[0048] After the sample is cooled to room temperature, it is vacuum filtered, washed with deionized water 5 to 6 times, filtered again, and dried at room temperature for 48 hours to obtain a sample.

[0049] The principle of the polyurethane microcapsule shell formation reaction in this embodiment is shown in Figure 1. In the traditional interfacial polycondensation reaction, the PU capsule shell is formed according to the moving boundary mechanism, which prompts the polyol molecules to diffuse from the aqueous phase to the oil phase, where they react with the isocyanate. In the NCC / PU capsule, the PU shell is formed by the diffusion of PMDI.

[0050] The dried sample was examined using a scanning electron microscope (SEM), and the resulting SEM image is shown in Figure 2. The capsules are dispersed, not aggregated, and have an intact shell. The capsule morphology originates from the initially formed emulsion droplets, resulting in their predominantly spherical shape. However, some capsules exhibit inward curvature, which may be related to the evaporation of toluene after shell cross-linking. The NCC / PU capsules have a smooth, uniform shell, which is due to the dense packing of NCC at the oil / water interface and its further uniform cross-linking with PMDI.

[0051] Capsule size was calibrated using an electron microscope and sample calculations were performed using sampling software. The results showed the formation of non-aggregated capsules with an average size of 18.6 μm and a smooth, uniform shell thickness of 450 nm. The particle size distribution curve, plotted using Origin software, is shown in Figure 3. The figure shows that the prepared samples exhibit a unimodal particle size distribution with a concentrated distribution between 10 and 40 μm. The capsules are relatively small in size and have a concentrated volume distribution, indicating the high quality of the resulting capsule shells.

[0052] Example 2

[0053] The difference between this embodiment and embodiment 1 is that the temperature in step (3) is replaced with 70° C., and the remaining steps are the same as those in embodiment 1. The microcapsules prepared in this embodiment are similar to those in embodiment 1.

[0054] Example 3

[0055] The difference between this embodiment and embodiment 1 is that the temperature in step (3) is replaced with 80° C., and the remaining steps are the same as those in embodiment 1. The microcapsules prepared in this embodiment are similar to those in embodiment 1.

[0056] Comparative Example 1

[0057] The difference between this comparative example and Example 1 is that the temperature in step (3) is replaced with 50°C, and the remaining steps are the same as Example 1. However, due to the low stirring temperature, the cross-linking reaction is insufficient, resulting in a decreased capsule forming rate and poor quality of the formed capsules.

[0058] Comparative Example 2

[0059] The difference between this comparative example and Example 1 is that the temperature in step (3) is replaced with 100° C., and the remaining steps are the same as Example 1. However, due to the excessively high stirring temperature, part of the reactants volatilized, resulting in poor quality of the formed capsules.

[0060] Comparative Example 3

[0061] This comparative example differs from Example 1 in that N,N-dimethylaniline was not added in step (2). Instead, 8 g of polymethylene polyphenyl isocyanate (PMDI) was added to 46 mL of toluene and stirred uniformly to form the oil phase. The remaining steps were the same as in Example 1. Due to the omission of N,N-dimethylaniline, the crosslinking reaction was incomplete, resulting in an uneven microcapsule shell.

[0062] Comparative Example 4

[0063] This comparative example differs from Example 1 in that N,N-dimethylaniline in step (2) is replaced with 1,3-diethylbenzene, and the remaining steps are the same as Example 1. However, since 1,3-diethylbenzene fails to act as a catalyst, the crosslinking reaction is incomplete, and the resulting microcapsule shell is not round.

[0064] Comparative Example 5

[0065] This comparative example differs from Example 1 in that the volume ratio of the aqueous phase to the oil phase is changed to 2:1, and the remaining steps are the same as in Example 1. However, due to the reduced volume ratio of the aqueous phase compared to Example 1, the emulsion droplets are not fully formed, resulting in a large emulsion droplet volume and partial adhesion. The resulting capsules are large in size and have poor dispersibility.

[0066] Comparative Example 6

[0067] The difference between this comparative example and Example 1 is that the volume ratio of the water phase to the oil phase is changed to 6:1, and the remaining steps are the same as Example 1. However, due to the excessively large volume proportion of the water phase, the emulsion droplet formation effect is poor, and the resulting capsules are not shelled.

[0068] Comparative Example 7

[0069] This comparative example differs from Example 1 in that the mass ratio of cellulose crystals to polyisocyanate is 1:16, and the remaining steps are the same as Example 1. However, due to the low cellulose content, the cellulose accumulation on the surface of the emulsion droplets is not dense, the crosslinking reaction is not sufficient, the microcapsule shell formation is incomplete, and the quality is poor.

[0070] Comparative Example 8

[0071] This comparative example differs from Example 1 in that the mass ratio of cellulose crystals to polyisocyanate is 1:4, and the remaining steps are the same as Example 1. However, due to the high cellulose content, the cellulose accumulation on the surface of the emulsion droplets is too dense, resulting in a rough and very thick capsule shell and poor capsule quality.

[0072] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, and all of these should be included in the scope of the present invention.

Claims

1. A method for preparing a polyurethane microcapsule shell by direct crosslinking of cellulose and polyisocyanate, characterized in that: include, The cellulose crystals are mixed with deionized water to prepare an aqueous phase; N,N-dimethylaniline, toluene and polyisocyanate are mixed evenly as the oil phase; Pour the oil phase into the water phase and stir for 20 min to form an emulsion; The emulsion is heated and stirred, then allowed to stand for 2 hours, cooled to room temperature, filtered, washed, filtered again, and dried to obtain the polyurethane microcapsule shell.

2. The method according to claim 1, wherein: The polyisocyanate is one of polymethylene polyphenyl isocyanate, toluene diisocyanate and isophorone diisocyanate.

3. The method according to claim 1, wherein: The mass ratio of the cellulose crystals to the polyisocyanate is 1.05:

8.

4. The method according to claim 1, wherein: The mass ratio of the N,N-dimethylaniline, toluene and polyisocyanate is 3:9:

4.

5. The method according to claim 1, wherein: The volume ratio of the water phase to the oil phase is 4:

1.

6. The method according to claim 5, wherein: The stirring was carried out for 20 minutes, wherein the stirring rate was 1300 r / min.

7. The method according to claim 1, wherein: The emulsion is heated and stirred, wherein the heating temperature is 70-80°C.

8. The method according to claim 1, wherein: The heating and stirring process has a stirring rate of 200 r / min and a stirring time of 15 min.

9. A polyurethane microcapsule shell prepared by the method according to any one of claims 1 to 8.

10. Use of the polyurethane microcapsule shell as claimed in claim 9.

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