Polycaprolactone-based composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of polymer composite materials, in particular to a polycaprolactone-based composite material as well as a preparation method and application thereof. The preparation method comprises the following steps: carrying out surface grafting treatment on nano cellulose to obtain modified nano cellulose; mixing the modified nanocellulose, polycaprolactone and a solvent to obtain slurry; carrying out melt blending and granulation on the slurry to obtain composite granules; and carrying out melt blending and granulation on the composite granules, a metal soap stabilizer and a natural resin derivative to obtain the polycaprolactone-based composite material. The polycaprolactone-based composite material prepared by a novel composite process of nano cellulose graft modification-solvent replacement synergetic melt co-extrusion has the core advantages of high mechanical strength, excellent light transmittance, long-acting weather resistance and the like, is good in processing adaptability and simple and convenient to operate, can realize continuous large-scale production, and remarkably reduces energy consumption and raw material cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer composite materials, in particular to a polycaprolactone-based composite material and a preparation method and application thereof. BACKGROUND

[0002] Polycaprolactone (PCL) has become an important modified material for improving the comprehensive performance of automobile paint protection film (car film) due to its excellent biocompatibility, outstanding low-temperature flexibility and unique self-repairing properties. Car film needs to meet good light transmittance, high mechanical strength and stable processing performance at the same time. Therefore, in the prior art, the comprehensive performance of PCL-based materials is often improved by introducing reinforcing phases. However, in practical applications, PCL-based car films face the challenge of significant performance synergy imbalance: when traditional inorganic fillers are used for reinforcement, the light transmittance of the material is often severely degraded; while when nanocellulose is selected, agglomeration defects are easily caused due to poor interfacial compatibility, thereby causing the simultaneous decline of material toughness and optical performance. In addition, the weak interfacial bonding of the physical blending system further aggravates the risk of phase separation under high addition amount. At the same time, the existing processing technology cannot avoid the damage of high-temperature shear force to the nano structure or the product defects caused by solvent residues. These problems are intertwined and jointly restrict the performance improvement and application expansion of polycaprolactone-based car films. SUMMARY

[0003] The present application aims to solve the problem that PCL-based car films cannot balance light transmittance, mechanical strength and processing performance in the prior art, and provides a polycaprolactone-based composite material and a preparation method and application thereof. The polycaprolactone-based composite material prepared by the new composite process of "nanocellulose grafting modification-solvent replacement synergistic melt co-extrusion" has core advantages such as high mechanical strength, excellent light transmittance, long-term weather resistance, good processing adaptability and simple operation, and can realize continuous large-scale production, thereby significantly reducing energy consumption and raw material cost.

[0004] To achieve the above-mentioned purpose, the present application provides a preparation method of a polycaprolactone-based composite material, comprising the following steps: S1. Surface grafting treatment is performed on nanocellulose to obtain modified nanocellulose; S2. The modified nanocellulose, polycaprolactone and solvent are mixed to obtain a slurry; S3. The slurry is melt blended and granulated to obtain a composite granule; S4. The composite granule, metal soap stabilizer and natural resin derivative are melt blended and granulated to obtain a polycaprolactone-based composite material.

[0005] Preferably, in S1, the surface grafting treatment on nanocellulose comprises: (1) mixing the nanocellulose suspension, oxidizing agent, alkali metal bromide and hypochlorite salt, and performing reaction to obtain an intermediate product; (2) mixing the intermediate product, polycaprolactone oligomer and catalyst, and performing esterification reaction to obtain modified nanocellulose.

[0006] Preferably, in step (1), the mass fraction of nanocellulose in the nanocellulose suspension is 0.5%-1.5%; the oxidizing agent includes at least one of 2,2,6,6-tetramethylpiperidine-1-oxyl radical and 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl radical; the alkali metal bromide includes at least one of sodium bromide and potassium bromide; the hypochlorite salt includes sodium hypochlorite; In step (1), the mass ratio of nanocellulose in the nanocellulose suspension to the amount of substance of the oxidizing agent is 0.5g-1.5g:0.05mol-0.15mol; the molar ratio of the oxidizing agent, the alkali metal bromide and the hypochlorite salt is 0.05-0.15:0.5-1.5:4-6.

[0007] Preferably, in step (2), the molecular weight of the polycaprolactone oligomer is 1800-2200; the catalyst includes at least one of 4-dimethylaminopyridine and triethylamine; The mass ratio of the polycaprolactone oligomer to nanocellulose in the nanocellulose suspension is 25-35:100; the molar ratio of the polycaprolactone oligomer to the catalyst is 100:0.05-0.2.

[0008] Preferably, in step (1), the pH value of the reaction is 6.5-7.5, the temperature is 20℃-30℃, and the time is 5h-7h; In step (2), the temperature of the esterification reaction is 75℃-85℃, and the time is 3h-5h.

[0009] Preferably, in S2, the solvent includes at least one of tetrahydrofuran and 2-methyltetrahydrofuran; the molecular weight of the polycaprolactone is 78000-82000; In S2, the mass ratio of the modified nanocellulose to the polycaprolactone is 1-3:97-99; the mass ratio of the polycaprolactone to the solvent is 1:13-17.

[0010] Preferably, in S3, the feeding section temperature of the melt blending is 125℃-135℃, the mixing section temperature is 135℃-145℃, the die section temperature is 150℃-160℃, and the screw rotation speed is 110r / min-130r / min; In S3, the diameter of the composite granules is 2.5mm-3.5mm.

[0011] Preferably, in S4, the metal soap stabilizer comprises at least one of zinc stearate and calcium stearate; and the natural resin derivative comprises at least one of abietic acid and hydrogenated rosin glyceride. The mass ratio of the composite granules, the metal soap stabilizer and the natural resin derivative is 100:0.3-0.5:0.1-0.2. In S4, the temperature for melt blending is 135-145℃.

[0012] The application also provides a polycaprolactone-based composite material prepared according to the preparation method of the polycaprolactone-based composite material.

[0013] The application also provides application of the polycaprolactone-based composite material in automobile paint protection film.

[0014] The application has the following beneficial effects: 1. The application provides a preparation method of a polycaprolactone-based composite material, comprising the following steps: performing surface grafting treatment on nanocellulose to obtain modified nanocellulose; mixing the modified nanocellulose, polycaprolactone and a solvent to obtain slurry; performing melt blending and granulation on the slurry to obtain composite granules; and performing melt blending and granulation on the composite granules, a metal soap stabilizer and a natural resin derivative to obtain the polycaprolactone-based composite material. The polycaprolactone-based composite material prepared by the new composite process of “nanocellulose grafting modification-solvent replacement synergistic melt co-extrusion” has the core advantages of high mechanical strength, excellent light transmittance and long-term weather resistance, and has good processing adaptability and simple operation, and can realize continuous large-scale production, thereby significantly reducing energy consumption and raw material cost.

[0015] 2. The application significantly improves the interfacial compatibility of nanocellulose and the polycaprolactone matrix by performing surface grafting modification on nanocellulose, effectively avoids the agglomeration defect of the nanoreinforcing phase, and improves the mechanical properties of the material while maintaining excellent light transmittance.

[0016] 3. The application combines ultrasonic assisted extrusion through the synergistic action of solvent pre-dispersion (mixing the modified nanocellulose, polycaprolactone and a solvent) and melt blending process with a specific temperature gradient (in S3, the temperature of the feeding section is 125-135℃, the temperature of the mixing section is 135-145℃, and the temperature of the die section is 150-160℃), not only reduces the damage of high-temperature shearing to the structure of nanocellulose, but also ensures the stability of the melt flow rate, ensures the feasibility of continuous large-scale production, and improves the processing efficiency.

[0017] 4. The added natural resin derivative effectively improves the ultraviolet shielding rate and enhances the long-term weather resistance of the car film; meanwhile, no harmful plasticizer needs to be added in the process, no imported aliphatic polyurethane base material needs to be relied on, the raw material cost and environmental load are reduced, and the green manufacturing trend is met.

[0018] 5. The application effectively solves the risk of phase separation under a high filling system by adjusting the melt viscosity and optimizing the compatibility through graft modification of the metal soap stabilizer, so that the master batch has high uniformity and film forming mechanical stability, avoids the cracking problem of the coating during installation and stretching, and meets the demand for high performance of the automobile paint protection film. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a preparation process schematic diagram of the polycaprolactone-based composite material in Embodiment 1 of the application. DETAILED DESCRIPTION

[0020] The application provides a preparation method of a polycaprolactone-based composite material, including the following steps: S1. Surface grafting treatment is performed on nanocellulose to obtain modified nanocellulose; S2. The modified nanocellulose, polycaprolactone and a solvent are mixed to obtain slurry; S3. The slurry is subjected to melt blending and granulation to obtain composite granules; S4. The composite granules, a metal soap stabilizer and a natural resin derivative are subjected to melt blending and granulation to obtain the polycaprolactone-based composite material.

[0021] In the application, in S1, the surface grafting treatment on the nanocellulose includes: (1) The nanocellulose suspension, an oxidizing agent, an alkali metal bromide and a hypochlorite are mixed to perform a reaction to obtain an intermediate product; (2) The intermediate product, a polycaprolactone oligomer and a catalyst are mixed to perform an esterification reaction to obtain the modified nanocellulose.

[0022] In the application, in step (1), the obtaining of the nanocellulose suspension includes: crushing banana stem into a filament, extracting after removing lignin to obtain nanocellulose, and mixing the nanocellulose and water to obtain the nanocellulose suspension. The crushing, lignin removal and extraction are completed by using conventional technical means in the field.

[0023] In the present application, in step (1), the mass fraction of nanocellulose in the nanocellulose suspension is 0.5%-1.5%; the oxidizing agent includes at least one of 2,2,6,6-tetramethylpiperidine-1-oxyl radical and 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl radical; the alkali metal bromide includes at least one of sodium bromide and potassium bromide; and the hypochlorite includes sodium hypochlorite.

[0024] In the present application, in step (1), the mass and the amount of substance ratio of the oxidizing agent in the nanocellulose suspension is 0.5g-1.5g:0.05mol-0.15mol; and the molar ratio of the oxidizing agent, the alkali metal bromide and the hypochlorite is 0.05-0.15:0.5-1.5:4-6.

[0025] In the present application, in step (2), the molecular weight of the polycaprolactone oligomer is 1800-2200; and the catalyst includes at least one of 4-dimethylaminopyridine and triethylamine.

[0026] In the present application, the mass ratio of the polycaprolactone oligomer and the nanocellulose in the nanocellulose suspension is 25-35:100; and the molar ratio of the polycaprolactone oligomer and the catalyst is 100:0.05-0.2.

[0027] In the present application, in step (1), the pH value of the reaction is 6.5-7.5, the temperature is 20℃-30℃, and the time is 5h-7h.

[0028] In the present application, in step (1), after the mixing is completed, the aqueous solution of triethanolamine with a mass fraction of 8-12% is added, and the pH value of the system is adjusted to 6.5-7.5.

[0029] In the present application, in step (1), after the reaction is completed, centrifugation and washing are sequentially performed to obtain an intermediate product; the centrifugation is performed at a speed of 4000-5000rpm for 15-20min; and the washing is performed by water washing until the intermediate product is obtained.

[0030] In the present application, in step (2), the temperature of the esterification reaction is 75℃-85℃, and the time is 3h-5h.

[0031] In the present application, in S2, the solvent includes at least one of tetrahydrofuran and 2-methyltetrahydrofuran; and the molecular weight of the polycaprolactone is 78000-82000.

[0032] In the present application, in S2, the mass ratio of the modified nanocellulose and the polycaprolactone is 1-3:97-99; and the mass ratio of the polycaprolactone and the solvent is 1:13-17.

[0033] In the present application, in S2, the mixing is carried out under ultrasonic conditions, the temperature of the ultrasonic is 75-85℃, and the time is 3.5-4.5h.

[0034] In the present application, in S2, after the modified nanocellulose, polycaprolactone and solvent are mixed, drying is carried out to obtain a slurry; the temperature of the drying is 50℃-55℃, and the time is 22h-26h.

[0035] In the present application, in S3, the feeding section temperature of the melt blending is 125℃-135℃, the mixing section temperature is 135℃-145℃, the die section temperature is 150℃-160℃, and the screw rotation speed is 110r / min-130r / min.

[0036] In the present application, in S3, after the melt blending is completed, extrusion is carried out, and after the extrusion, underwater pelletization is carried out to obtain a composite pellet; the extrusion is carried out under ultrasonic assistance, the ultrasonic adopts an 'intermittent' mode: working for 2 seconds and pausing for 1 second (2s ON / 1s OFF), the frequency of the ultrasonic is 20-25kHz, the power density is 8-10W / mL (calculated based on the melt volume), and the ultrasonic head temperature is 145-155℃; the water temperature for the underwater pelletization is 15-20℃.

[0037] In the present application, in S3, the diameter of the composite pellet is 2.5mm-3.5mm.

[0038] In the present application, in S4, the metal soap stabilizer includes at least one of zinc stearate and calcium stearate; the natural resin derivative includes at least one of abietic acid and hydrogenated rosin glyceride; and the mass ratio of the composite pellet, the metal soap stabilizer and the natural resin derivative is 100:0.3-0.5:0.1-0.2.

[0039] The metal soap stabilizer functions to reduce the viscosity of the system; and the natural resin derivative functions to improve the ultraviolet shielding rate.

[0040] In the present application, in S4, the temperature of the melt blending is 135℃-145℃.

[0041] The present application also provides a polycaprolactone-based composite material prepared according to the preparation method of the polycaprolactone-based composite material.

[0042] The present application also provides an application of the polycaprolactone-based composite material in an automobile paint surface protection film.

[0043] The application will be further described below in conjunction with the accompanying drawings and examples. Unless otherwise defined, the technical terms or scientific terms used in the present application shall be understood as the usual meanings understood by those with ordinary skills in the art to which the present application pertains. The features mentioned above or the features mentioned in the specific examples can be combined in any manner, and these specific examples are only used to illustrate the present application and not to limit the scope of the present application.

[0044] In the following examples and comparative examples of the present application, the polycaprolactone oligomer (molecular weight 2000) was purchased from Dongguan Jixin Polymer Technology Co., Ltd., model PCL-2000; the polycaprolactone (molecular weight 80000) was purchased from Dongguan Jixin Polymer Technology Co., Ltd., model PCL-80000.

[0045] Example 1 The present example provides a preparation method of a polycaprolactone-based composite material, comprising the following steps: The banana stem was crushed into a filamentous shape, and after removing lignin, nanocellulose was obtained by extraction. The nanocellulose was mixed with water to obtain a nanocellulose suspension, and the mass fraction of nanocellulose in the nanocellulose suspension was 1%.

[0046] The nanocellulose suspension, 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO), sodium bromide (NaBr), and sodium hypochlorite (NaClO) were mixed, wherein the mass ratio of nanocellulose in the nanocellulose suspension to the amount of substance of TEMPO was 1 g:0.1 mol; the molar ratio of TEMPO, NaBr, and NaClO was 0.1:1:5; the reaction was carried out at 25°C for 6h at pH=7 (after mixing, a 10% triethanolamine aqueous solution was added to adjust the pH value of the system to 7); after the reaction was completed, centrifugation (the speed was 4500 rpm, and the time was 18 min) and washing (water washing until neutral) were sequentially performed to obtain an intermediate product.

[0047] The intermediate product, polycaprolactone oligomer with a molecular weight of 2000, and 4-dimethylaminopyridine (DMAP) were mixed, wherein the mass ratio of polycaprolactone oligomer to nanocellulose in the nanocellulose suspension was 30:100, and the molar ratio of polycaprolactone oligomer to DMAP was 100:0.1; esterification was carried out at 80°C for 4h to obtain modified nanocellulose.

[0048] The modified nanocellulose, polycaprolactone with a molecular weight of 80000, and tetrahydrofuran (THF) were mixed, wherein the mass ratio of modified nanocellulose to polycaprolactone was 1:99; the mass ratio of polycaprolactone to THF was 1:15; the mixing was carried out under ultrasonic conditions, the ultrasonic temperature was 80°C, and the time was 4h; after mixing, drying was carried out at 52°C for 24h to obtain a slurry.

[0049] The slurry was injected into a twin-screw extruder for melt blending, the feeding section temperature for melt blending was set to 130℃, the mixing section temperature was 140℃, the die section temperature was 155℃, the screw rotation speed was 120r / min, after melt blending, extrusion was carried out, the extrusion was carried out under ultrasonic assistance, the ultrasonic was in "intermittent" mode: working for 2 seconds, pausing for 1 second (2s ON / 1s OFF), the frequency of ultrasonic was 23kHz, the power density was 9W / mL (based on the volume of melt), the temperature of ultrasonic head was 150℃, after extrusion, underwater pelletizing was carried out (water temperature was 18℃), and the composite granules with a diameter of 3mm were prepared.

[0050] The composite granules, zinc stearate and rosin acid (the mass ratio of composite granules, zinc stearate and rosin acid was 100:0.3:0.1) were mixed and fed into the extruder for melt blending at 140℃, and then pelletizing was carried out after extrusion to obtain a polycaprolactone-based composite material.

[0051] The preparation process of the polycaprolactone-based composite material in Example 1 is shown in the schematic diagram as shown in Figure 1 .

[0052] Example 2 The preparation method of the polycaprolactone-based composite material provided in this example is basically the same as that in Example 1, except that the mass ratio of modified nanocellulose and polycaprolactone was modified to 3:97, and the mass ratio of composite granules, zinc stearate and rosin acid was 100:0.5:0.2.

[0053] Comparative Example 1 In this comparative example, commercially available polycaprolactone (molecular weight of 80000) was used; purchased from Dongguan Jixin Polymer Technology Co., Ltd., model PCL-80000.

[0054] Experimental Example 1 The polycaprolactone-based composite materials in Examples 1-2 and the polycaprolactone in Comparative Example 1 were respectively tested for light transmittance, haze, tensile strength, elongation and peel strength, wherein the light transmittance test was carried out according to ASTM D1003, the haze test was carried out according to ASTM D1003, the tensile strength test was carried out according to ASTM D882, the elongation test was carried out according to ASTM D882, and the peel strength test was carried out according to GB / T 2792, and the performance test results of different materials were obtained, as shown in Table 1.

[0055] Table 1 Performance test results of different materials

[0056] Experimental Example 2 The polycaprolactone-based composite material in Example 1 and the polycaprolactone in Comparative Example 1 were respectively subjected to color, TPU thickness, density, hardness, ultraviolet resistance grade and melting point tests, wherein the TPU thickness test was performed according to GB / T 6672-2001, the density test was performed according to ASTM D792, the hardness test was performed according to ASTM D-2240, the ultraviolet resistance grade test was performed according to ASTM D1148, and the physical property test results of different materials were obtained, as shown in Table 2.

[0057] Table 2 Physical property test results of different materials

[0058] Experimental Example 3 The polycaprolactone-based composite material prepared in Example 1 was subjected to melt flow rate (MFR) test according to ISO 1133 and ASTM D1238 standards. The test was performed at 190℃ under the condition of applying a standard load of 2.16kg, and the melt flow rate of the material was measured to be 6.5±0.5g / 10min. The specific test procedure was as follows: the polycaprolactone-based composite material was added to the melt indexer cylinder, heated and kept at 190℃ constant temperature; then a 2.16kg weight was applied on the top of the piston to make the melt extrude from the standard die (diameter 2.095mm); finally, the mass of the melt extruded in 10min was measured, and the obtained result was the MFR value.

[0059] Therefore, by using the above-mentioned preparation method of the polycaprolactone-based composite material, the polycaprolactone-based composite material prepared by the new composite process of “nanocellulose graft modification-solvent replacement synergistic melt co-extrusion” has the core advantages of high mechanical strength, excellent light transmittance, long-term weather resistance, etc., and has good processing adaptability, simple operation, can realize continuous large-scale production, and significantly reduces energy consumption and raw material cost.

[0060] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit it, although the present application 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 application can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for producing a polycaprolactone-based composite material, characterized by, The method comprises the following steps: S1. Surface grafting treatment is performed on the nanocellulose to obtain modified nanocellulose; S2. The modified nanocellulose, polycaprolactone and a solvent are mixed to obtain a slurry; S3. The slurry is subjected to melt blending and granulation to obtain composite granules; S4. The composite granules, a metal soap stabilizer and a natural resin derivative are subjected to melt blending and granulation to obtain a polycaprolactone-based composite material.

2. The method for preparing the polycaprolactone-based composite material according to claim 1, characterized in that, In S1, the surface grafting treatment performed on the nanocellulose comprises: (1) mixing a nanocellulose suspension, an oxidizing agent, an alkali metal bromide and a hypochlorite salt to perform a reaction to obtain an intermediate product; (2) mixing the intermediate product, a polycaprolactone oligomer and a catalyst to perform an esterification reaction to obtain modified nanocellulose.

3. The method for preparing the polycaprolactone-based composite material according to claim 2, characterized in that, In step (1), the mass fraction of nanocellulose in the nanocellulose suspension is 0.5%-1.5%; the oxidizing agent comprises at least one of 2,2,6,6-tetramethylpiperidine-1-oxyl and 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl; the alkali metal bromide comprises at least one of sodium bromide and potassium bromide; the hypochlorite salt comprises sodium hypochlorite; In step (1), the mass of nanocellulose in the nanocellulose suspension to the amount of substance of the oxidizing agent is 0.5g-1.5g:0.05mol-0.15mol; the molar ratio of the oxidizing agent, the alkali metal bromide and the hypochlorite salt is 0.05-0.15:0.5-1.5:4-6.

4. The method for preparing the polycaprolactone-based composite material according to claim 2 or 3, characterized in that, In step (2), the molecular weight of the polycaprolactone oligomer is 1800-2200; the catalyst comprises at least one of 4-dimethylaminopyridine and triethylamine; The mass ratio of the polycaprolactone oligomer to nanocellulose in the nanocellulose suspension is 25-35:100; the molar ratio of the polycaprolactone oligomer to the catalyst is 100:0.05-0.

2.

5. The method for preparing the polycaprolactone-based composite material according to claim 2, characterized in that, In step (1), the pH value of the reaction is 6.5-7.5, the temperature is 20℃-30℃, and the time is 5h-7h; In step (2), the temperature of the esterification reaction is 75℃-85℃, and the time is 3h-5h.

6. The method for preparing the polycaprolactone-based composite material according to claim 1, characterized in that, In S2, the solvent comprises at least one of tetrahydrofuran and 2-methyltetrahydrofuran; the molecular weight of the polycaprolactone is 78000-82000; In S2, the mass ratio of the modified nanocellulose to the polycaprolactone is 1-3:97-99; the mass ratio of the polycaprolactone to the solvent is 1:13-17.

7. The method for preparing the polycaprolactone-based composite material according to claim 1, characterized in that, In S3, the temperature of the feeding section of the melt blending is 125℃-135℃, the temperature of the mixing section is 135℃-145℃, the temperature of the die section is 150℃-160℃, and the screw rotation speed is 110r / min-130r / min; In S3, the diameter of the composite granules is 2.5mm-3.5mm.

8. The method for preparing the polycaprolactone-based composite material according to claim 1, characterized in that, In S4, the metal soap stabilizer comprises at least one of zinc stearate and calcium stearate; the natural resin derivative comprises at least one of abietic acid and hydrogenated rosin glyceride; The mass ratio of the composite granules, the metal soap stabilizer and the natural resin derivative is 100:0.3-0.6:0.1-0.2; In S4, the temperature of the melt blending is 135℃-145℃.

9. A polycaprolactone-based composite material, characterized by, The poly-caprolactone-based composite material is prepared by the preparation method according to any one of claims 1-8.

10. Use of the poly-caprolactone-based composite material according to claim 9 in automobile paint protection film.

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