Coconut fiber modified polyurea material and preparation method thereof

Abstract

The invention provides a coconut fiber modified polyurea material and a preparation method thereof, and relates to the technical field of polyurea materials. According to the invention, a polyurea matrix is modified by using the alkali-modified coconut fibers, so that the surface energy of the polyurea material is effectively reduced, the hydrophobic property of the polyurea material is improved, and meanwhile, the tensile strength and the elongation at break are also remarkably improved.

Description

Technical Field

[0001] The present invention provides a polyurea material modified by coconut shell fiber and a preparation method thereof, belonging to the technical field of polyurea materials. Background Art

[0002] Polyurea has excellent mechanical properties, outstanding corrosion resistance, and good plasticity, so it is widely used in fields such as aerospace, wind power generation, and building materials. However, its inherent defects limit its further application in some fields. For example, it has insufficient toughness and shows high brittleness after curing. Although polyurea materials have high strength and modulus, their toughness is relatively poor. When subjected to external forces, polyurea materials are prone to brittle fracture and lack sufficient deformation ability to absorb and disperse energy. Currently, the insulating coatings applied in the field of local insulation have certain requirements for toughness, and there are certain deficiencies in the current commercial applications of polyurea. At the same time, polyurea materials usually show high brittleness after curing, which makes them prone to cracks and damage when subjected to impact or vibration.

[0003] Research has found that as a reinforcing material incorporated into composite materials, plant fibers have demonstrated excellent capabilities. They can not only significantly improve the mechanical properties of the matrix material, including key indicators such as strength, toughness, and durability, but also endow the matrix material with a series of new properties and functions that it originally did not possess, greatly enriching the properties of the matrix material and thus opening up a broader space for the application of the matrix material. For example, by incorporating plant fibers into an epoxy resin matrix, on the basis of maintaining the excellent mechanical properties of polyurea, the reinforcing characteristics of plant fibers can be fully utilized to effectively improve the problem of insufficient toughness of the composite material.

[0004] Therefore, it has high feasibility and research prospects to use plant fibers to reinforce polyurea materials to improve the mechanical properties of polyurea materials. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a polyurea material modified by coconut shell fiber and a preparation method thereof. The present invention modifies the polyurea matrix by using modified coconut shell fiber, thereby effectively reducing the surface energy of the polyurea material, improving the hydrophobic characteristics of the polyurea material, and at the same time significantly enhancing the tensile strength and elongation at break.

[0006] The present invention is implemented by adopting the following technical solutions:

[0007] A preparation method of a polyurea material modified by coconut shell fiber, comprising the following steps:

[0008] (1) Prepare modified coconut shell fiber

[0009] Soak the coconut shell fibers in an alkali solution for modification, and filter to obtain alkali-modified coconut shell fibers; place the alkali-modified coconut shell fibers in an oxalic acid solution for cleaning, and then rinse with deionized water until the pH value of the rinsing solution is neutral; dry the rinsed alkali-modified coconut shell fibers to obtain modified coconut shell fibers; preferably, the coconut shell fibers of the present invention are made after being processed by processes such as mechanical loosening. The diameter range of the coconut shell fibers is 350-400 μm, and the bulk density is 1.25 g·cm -3 .

[0010] (2) Prepare the polyurea matrix

[0011] Mix 3,3-dimethyl-4,4-diaminodicyclohexylmethane and polyetheramine and dissolve them in dimethylacetamide to obtain a first solution;

[0012] Dissolve isophorone diisocyanate and diphenylmethane diisocyanate in dimethylacetamide to obtain a second solution;

[0013] Drop the second solution into the first solution under stirring, and heat and react under an inert atmosphere to obtain a polyurea matrix;

[0014] The present invention selects 3,3-dimethyl-4,4-diaminodicyclohexylmethane as the chain extender, and polyetheramine PEA, polyethyleneimine PEI, and polyvinyl alcohol as the crosslinking agents to increase the crosslinking density and form a three-dimensional network structure.

[0015] (3) Prepare the coconut shell fiber-modified polyurea material

[0016] Soak the modified coconut shell fibers in dimethylacetamide, then add them to the polyurea matrix, add a catalyst and stir and react for 3-4 h;

[0017] After the reaction, remove the solvent by rotary evaporation to obtain a viscous liquid; place the viscous liquid in a mold and vacuum dry to obtain the coconut shell fiber-modified polyurea material.

[0018] Preferably, the alkali solution in step (1) is an aqueous sodium hydroxide solution with a mass concentration of 10-30%; the mass concentration of the oxalic acid solution is 3-5%.

[0019] Preferably, in step (2), the mass ratio of 3,3-dimethyl-4,4-diaminodicyclohexylmethane, polyetheramine, isophorone diisocyanate, and diphenylmethane diisocyanate is 25:15:3.75:5.

[0020] Preferably, the heating reaction temperature in step (2) is 50-60 °C.

[0021] Preferably, the mass ratio of the modified coconut shell fiber to the polyurea matrix in step (3) is 1:8 to 10.

[0022] Preferably, the catalyst in step (3) is dibutyltin dilaurate.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] In the present invention, the coconut shell fiber is modified by using an alkali, and the prepared modified coconut shell fiber is reacted with the polyurea matrix, so that the prepared coconut shell fiber modified polyurea material has excellent mechanical properties and hydrophobic properties. Description of the Drawings

[0025] Figure 1 It is a dynamic contact angle test diagram of the polyurea matrix prepared in Example 1;

[0026] Figure 2 It is a dynamic contact angle test diagram of the coconut shell fiber modified polyurea material prepared in Example 1;

[0027] Figure 3 It is an SEM diagram of the polyurea matrix prepared in Example 1;

[0028] Figure 4 It is an SEM diagram of the coconut shell fiber modified polyurea material prepared in Example 1. Detailed Embodiments

[0029] To make the objectives, technical solutions and advantages of the present invention clearer, the preferred embodiments of the present invention will be further described in detail below with reference to the examples. Based on the examples in the present invention, all other examples obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0030] Example 1

[0031] Put 2.3 g of coconut shell fiber into a NaOH solution with a mass fraction of 10%, and carry out an immersion treatment for 6 hours. After the immersion treatment, remove the soaked coconut shell fiber, and transfer the coconut shell fiber to an oxalic acid solution with a mass fraction of 3.5%, and perform repeated cleaning operations on it. After cleaning, rinse the coconut shell fiber repeatedly with deionized water until the rinsing liquid shows a neutral state. Then, put the treated coconut shell fiber into an oven at a temperature of 50 °C, dry it for 4 hours and then take it out to obtain modified coconut shell fiber for standby.

[0032] Dissolve 25 g of 3,3-dimethyl-4,4-diaminodicyclohexylmethane and 15 g of polyetheramine PEA in 120 mL of dimethylacetamide, put it into a three-necked flask for preheating treatment, the preheating temperature is about 45 °C, and then cool it to room temperature for standby;

[0033] Then it was placed in a three-necked flask equipped with a vacuum pump, a condensation device, a mechanical stirrer and a thermometer. Isophorone diisocyanate (IPDI) and diphenylmethane diisocyanate (MDI) were weighed with a mass fraction of 3.75 g: 5 g and dissolved in 100 mL of dimethylacetamide. The isocyanate was added dropwise to the amine solution while stirring continuously. After reacting for 24 h at 55 °C under a nitrogen atmosphere, a polyurea matrix was obtained and reserved for use.

[0034] 2.3 g of alkali-modified coconut shell fiber was weighed and soaked in 20 ml of dimethylacetamide, then added to 23 g of the polyurea matrix and placed in a three-necked flask and stirred continuously for 4 h. 2 drops of dibutyltin dilaurate as a catalyst were added to accelerate the reaction. After the reaction, most of the solvent was removed by rotary evaporation to obtain a viscous liquid, which was then inverted on a polytetrafluoroethylene mold with an inner groove of 5 mm×100 mm×100 mm and dried in a vacuum drying oven at 50 °C for 12 h to obtain the coconut shell fiber-modified polyurea material.

[0035] The polyurea matrix prepared in Example 1 and the coconut shell fiber-modified polyurea material were subjected to dynamic contact angle measurement, microscopic morphology characterization, tensile strength and elongation at break detection.

[0036] From Figure 1 and Figure 2 it can be seen that before and after the modification of the polyurea matrix with modified coconut shell fiber, the contact angle on the material surface shows a significant increasing trend. This phenomenon clearly indicates that the introduction of modified coconut shell fiber has a very significant promoting effect on the hydrophobic performance of the polyurea matrix. A good combination is achieved between the modified coconut shell fiber and the polyurea matrix. The modified coconut shell fiber itself has hydrophobic characteristics. When it is evenly distributed in the polyurea material, it can effectively reduce the surface energy of the polyurea material. The reduction of surface energy makes it more difficult for water molecules to adhere to the material surface, thereby promoting the increase of the water contact angle.

[0037] From Figure 3 and Figure 4It can be seen that after the modification treatment, the internal structural characteristics of the polyurea material have changed significantly, and the number of internal defects has been greatly reduced. Before the modification treatment, there were many obvious cavities inside the polyurea matrix, and these cavities were unevenly distributed. However, when the polyurea material was modified, the situation was greatly improved. The modified coconut shell fibers introduced into the polyurea matrix played a key filling role. With their unique fiber structure and good physical properties, the modified coconut shell fibers were evenly filled into the cavities inside the polyurea matrix material. As the modified coconut shell fibers continued to be filled, the originally scattered cavities were gradually filled, and the internal defects of the polyurea material were significantly reduced. This optimization of the internal structure enables the material to transfer stress more evenly when stressed, effectively avoiding the occurrence of stress concentration phenomena.

[0038] Dumbbell-shaped molds were prepared to detect the tensile strength, elongation at break, and breakdown strength of the polyurea matrix before and after modification, as shown in Table 1.

[0039] Table 1

[0040] Elongation at break % Tensile strength MPa Breakdown strength MPa Polyurea matrix 378 14.8 14.7 Coconut shell fiber modified polyurea material 512 20.5 21.4

[0041] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

Claims

1. A method for preparing a coconut shell fiber modified polyurea material, characterized in that: The following steps are involved: (1) Preparation of modified coconut shell fiber The coconut shell fiber is placed in an alkali solution for modification, and then filtered to obtain alkali-modified coconut shell fiber; the alkali-modified coconut shell fiber is placed in an oxalic acid solution for cleaning, and then rinsed with deionized water until the pH value of the rinsed washing solution is neutral; the rinsed alkali-modified coconut shell fiber is dried to obtain modified coconut shell fiber; (2) Preparation of polyurea matrix Mixing 3,3-dimethyl-4,4-diaminodicyclohexylmethane and polyetheramine and dissolving them in dimethylacetamide to obtain a first solution; dissolving isophorone diisocyanate and diphenylmethane diisocyanate in dimethylacetamide to obtain a second solution; The second solution is added dropwise to the first solution under stirring, and heated to react under an inert atmosphere to obtain a polyurea matrix; (3) Preparation of polyurea materials modified with coconut shell fiber The modified coconut shell fiber is soaked in dimethylacetamide, and then added into the polyurea matrix, and the catalyst is added and stirred for reaction for 3-4 hours; After the reaction is completed, the solvent is removed by rotary evaporation to obtain a viscous liquid; the viscous liquid is placed in a mold and vacuum dried to obtain a coconut shell fiber modified polyurea material.

2. The method for preparing the coconut shell fiber modified polyurea material according to claim 1, characterized in that: The alkali solution in step (1) is a sodium hydroxide aqueous solution with a mass concentration of 10-30%; the mass concentration of the oxalic acid solution is 3-5%.

3. The method for preparing the coconut shell fiber modified polyurea material according to claim 1, characterized in that: In step (2), the mass ratio of 3,3-dimethyl-4,4-diaminodicyclohexylmethane, polyetheramine, isophorone diisocyanate and diphenylmethane diisocyanate is 25:15:3.75:

5.

4. The method for preparing the coconut shell fiber modified polyurea material according to claim 1, characterized in that: The heating reaction temperature of step (2) is 50-60°C.

5. The method for preparing the coconut shell fiber modified polyurea material according to claim 1, characterized in that: The mass ratio of the modified coconut shell fiber to the polyurea matrix in step (3) is 1:8-10.

6. The method for preparing the coconut shell fiber modified polyurea material according to claim 1, characterized in that: The catalyst in step (3) is dibutyltin dilaurate.

7. A coconut shell fiber modified polyurea material, characterized in that: Prepared by any one of the methods of claims 1 to 6.

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