PLA composite material for 3D printing and preparation method thereof

Abstract

The application relates to the field of composite materials and specifically discloses a PLA composite material for 3D printing and a preparation method thereof. The PLA composite material for 3D printing is prepared from the following components: 100 parts of PLA, 4-6 parts of nano-silicon dioxide, 4-6 parts of micro-nano mixed fibers, 4-6.5 parts of a DOPO type flame retardant, 0.5-1.5 parts of a polyphosphate type ultraviolet light absorption agent, wherein the micro-nano mixed fibers are composed of micron cellulose and nano cellulose at a weight ratio of (1-3):2; and the preparation method comprises the following steps: S1, PLA pretreatment; and S2, melt extrusion: blending the PLA, the nano-silicon dioxide, the micro-nano mixed fibers, the DOPO type flame retardant and the polyphosphate type ultraviolet light absorption agent, and extruding to form a PLA composite material, which has good tensile strength, toughness, flame retardancy, ultraviolet light resistance and degradability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite materials, and in particular to a PLA composite material for 3D printing and a preparation method thereof. BACKGROUND

[0002] 3D printing technology, as a disruptive manufacturing technology, has made great progress in recent years and has shown great application potential in many fields. It breaks the limitations of traditional manufacturing processes, especially in personalized customization, complex structure manufacturing and small batch production, and brings more possibilities to product design and manufacturing. In the consumer electronics field, 3D printing can quickly manufacture various personalized shells and parts; in the medical device field, it can customize implants and rehabilitation devices that meet patient needs; in the field of art design, it can achieve complex modeling creation. As a common biobased degradable polymer material, polylactic acid (PLA) has become one of the widely used materials in the field of 3D printing due to its good biocompatibility, processability and relatively low cost. It is made from renewable resources such as corn starch through fermentation and polymerization processes, and can gradually degrade in the natural environment, meeting the current social requirements for environmental protection and sustainable development. With the continuous expansion of 3D printing technology in various fields, higher requirements are placed on the performance of PLA composite materials used for 3D printing, and the development of high-performance PLA composite materials has become a current research hotspot.

[0003] Currently, for PLA composite materials used for 3D printing, existing technologies mainly improve their performance through the following ways. One common method is to add inorganic fillers such as calcium carbonate, talc powder, glass fibers, etc. These inorganic fillers can increase the strength and stiffness of PLA composite materials, improve their heat distortion temperature, and make them better maintain their shape during printing. The addition of glass fibers can significantly improve the tensile strength and bending strength of PLA composite materials. In addition, some other physical or chemical modification methods may be used, but the addition of inorganic fillers is a common means. By adding different types and proportions of inorganic fillers to PLA composite materials, researchers try to find a balance to meet the requirements of different application scenarios for material performance.

[0004] There are still some obvious defects in existing technologies. In terms of adding inorganic fillers, although the strength and stiffness of PLA composite materials can be improved, the toughness is often reduced, leading to brittle fracture of the material when subjected to external force impact. Moreover, the compatibility between inorganic fillers and the PLA matrix is poor, and agglomeration phenomenon easily occurs, affecting the performance uniformity of the material and the printing quality. This makes the printed products have unstable performance problems during use, limiting the application of PLA composite materials in some fields with higher performance requirements. SUMMARY

[0005] To solve the above technical problems, the application provides a PLA composite material for 3D printing and a preparation method thereof.

[0006] In a first aspect, the application provides a PLA composite material for 3D printing, wherein the raw materials used include the following components by weight: 100 parts of PLA; 4-6 parts of nano-silicon dioxide; 4-6 parts of micro-nano mixed fibers; 4-6.5 parts of DOPO type flame retardant; 0.5-1.5 parts of polyphosphate type ultraviolet light absorbing agent; the micro-nano mixed fibers include microcellulose and nanocellulose in a weight ratio of (1-3):2; when preparing the DOPO type flame retardant, the raw materials used include 4-hydroxybenzaldehyde, p-toluenesulfonamide and DOPO; when preparing the polyphosphate type ultraviolet light absorbing agent, the raw materials used include phenylphosphoryl dichloride, 4,4'-dihydroxydiphenyl and hydroxyl-terminated dimethylsiloxane.

[0007] Optionally, the microcellulose is prepared by the following method: waste paper residue is dissolved in deionized water, and sodium silicate, sodium dodecylbenzenesulfonate, an emulsifier, hydrogen peroxide and sodium hydroxide are added, and the solution is left to stand to remove the ink on the waste paper residue, then the solution is beaten, sieved and washed to completely remove the ink, then the ink-washed deinking pulp is dried to constant weight, crushed to obtain microcellulose.

[0008] Optionally, the nanocellulose is prepared by the following method: the microcellulose is blended with sulfuric acid solution, heated and stirred, cooled, left to stand, filtered to obtain filter residue, the filter residue is dispersed in boiling water and dialyzed, then ultrasonic treatment is performed, and dried to obtain nanocellulose.

[0009] By adopting the technical scheme, the micro-nano mixed fiber composed of micron cellulose and nanocellulose in a weight ratio of (1-3):2 is added to the blending system of PLA and nanosilica, the waste paper is used as raw material, deinking treatment is carried out, and the micron cellulose is extracted from the high-purity deinking pulp through a mechanical process, which can produce good interfacial bonding effect with PLA, thereby improving the tensile strength of the PLA composite material, and can also play a good heat conduction role in the blending system, thereby improving the heat resistance of the PLA composite material; the nanocellulose is extracted from the micron cellulose by an acid hydrolysis method, as a nanoscale filler, can fill the micro defects in the PLA matrix and effectively inhibit the crack propagation, which can improve the toughness of the PLA composite material, a small amount of nanocellulose as a filler added to the PLA matrix can form a good interfacial bond with the PLA matrix, and the enhanced interfacial bond can also effectively prevent the crack propagation, in addition, the addition of nanocellulose can also improve the crystallization behavior of the PLA matrix, making the crystallization more uniform and dense, and the uniform crystalline structure can increase the strength and toughness of the material, thereby improving the tensile strength and elongation at break. Overall, the micron cellulose and nanocellulose of the application are compounded according to a certain proportion, used as micro-nano mixed fiber and added to the blending system of PLA and nanosilica, which can significantly improve the toughness of the PLA composite material, and also can help to improve the tensile strength of the PLA composite material, the micro-nano mixed fiber and the nanosilica have a good coordination effect, which can improve the tensile strength of the PLA composite material without affecting its toughness, so that it can adapt to more diverse working conditions and scenes in 3D printing applications, and has better performance. It is worth mentioning that the micron cellulose and nanocellulose of the application are both waste paper residue recycling, which has certain environmental protection significance. In terms of degradation of the PLA composite material, the micro-nano mixed fiber can provide more degradation reaction sites, thereby promoting the degradation process, has good water absorption, can absorb moisture in the surrounding environment and promote the hydrolysis reaction of the PLA composite material, the addition of the micro-nano mixed fiber also increases the pore structure of the PLA composite material, which is also beneficial to the penetration of moisture and the diffusion of reactants, accelerates the degradation process, and greatly improves the natural degradation rate in soil.

[0010] To improve the overall performance of PLA composites, this application also incorporates a DOPO-type flame retardant prepared from 4-hydroxybenzaldehyde, p-toluenesulfonamide, and DOPO. This flame retardant exhibits a good P / N / S synergistic effect, quenching oxygen-containing active free radicals in the gas phase and promoting the formation of a char layer in the condensed phase. This significantly optimizes the flame retardancy of PLA composites. Furthermore, experimental data shows that the DOPO-type flame retardant can also compensate for the brittleness of the PLA matrix to a certain extent, improving the toughness of the PLA composites without negatively impacting their tensile strength. This application also prepared a polyphosphate-type UV absorber using phenylphosphodichloro, 4,4'-dihydroxybiphenyl, and hydroxyl-terminated dimethylsiloxane as raw materials. The π electrons in the polyphosphate-type UV absorber have a conjugated effect and can absorb radiation in the ultraviolet region. Furthermore, the Si-O-Si bonds in the polyphosphate-type UV absorber have a certain degree of chemical inertness to ultraviolet radiation. Therefore, this substance can significantly improve the UV resistance of PLA composite materials. According to experimental data, the polyphosphate-type UV absorber can also partially improve the flame retardancy and toughness of PLA composite materials, but it will have a certain negative impact on tensile strength. Therefore, this application strictly controls the amount of polyphosphate-type UV absorber added. Overall, this application incorporates DOPO-type flame retardant and polyphosphate-type UV absorber, controlling the amount of both, and successfully optimizes the comprehensive performance of PLA composite materials. Experimental data shows a significant improvement in limiting oxygen index and tensile strength retention after UV irradiation, while tensile strength and toughness are also slightly optimized. This successfully enhances the flame retardancy and UV resistance of PLA composite materials while balancing their mechanical properties, further broadening the application range of PLA composite materials and enabling them to adapt well to outdoor environments.

[0011] In summary, the nano-silica, micro-nano hybrid fibers, DOPO-type flame retardant, and polyphosphate-type UV absorber in the PLA composite material of this application achieve a sufficient synergistic effect, optimizing the tensile strength, toughness, flame retardancy, UV resistance, and biodegradability of the PLA composite material. This broadens the application range of PLA composite materials, enabling them to adapt to more diverse working conditions and scenarios in 3D printing applications, possessing superior performance, and well-suited to outdoor environments.

[0012] Preferably, the amount of the micro-nano hybrid fiber is 5 parts by weight.

[0013] Preferably, the micro / nano hybrid fiber comprises micron-cellulose and nano-cellulose in a weight ratio of 2:2.

[0014] By adopting the above technical solution, this application has strictly controlled the amount of micro-nano hybrid fibers added and the ratio of micron cellulose to nano cellulose, which can maximize the toughness of PLA composite material without affecting its tensile strength, while maintaining a high degradation rate.

[0015] Preferably, the amount of the DOPO-type flame retardant is 6 parts by weight, and the amount of the polyphosphate-type UV absorber is 1 part.

[0016] By adopting the above technical solution, this application strictly controls the amount of DOPO-type flame retardant and polyphosphate-type UV absorber, further optimizing the overall performance of PLA composite materials.

[0017] Preferably, the nano-silica is further modified with polydopamine. The specific steps are as follows: the nano-silica is placed in Tris-HCl buffer and ultrasonically dispersed, then dopamine hydrochloride is added, stirred and centrifuged to obtain a solid, the obtained solid is washed and dried to obtain polydopamine-modified silica.

[0018] By adopting the above technical solution, this application uses polydopamine-modified silica to replace ordinary nano silica, which can exhibit better dispersion performance, stronger bonding force with PLA matrix, and a certain rigid particle reinforcement effect when the material fractures. During fracture, the particles act as stress concentrates, causing deformation of the matrix around the particles and absorbing a large amount of external force. The bonding force between the particles and the matrix enables the particles to prevent the propagation of matrix cracks. The peeling of the particles from the fracture surface can also play a role in absorbing impact energy. Ultimately, the tensile strength of PLA composite material is greatly improved while minimizing toughness loss.

[0019] Preferably, the preparation method of the DOPO type flame retardant includes the following steps: 4-hydroxybenzaldehyde and p-toluenesulfonamide are mixed and dispersed in an organic solvent under inert gas protection, reacted at a temperature of 70-80°C for 7-8 hours, then DOPO is added, and the reaction continues for 12-13 hours. The solvent and unreacted substances are removed, and the mixture is dried to obtain the DOPO type flame retardant.

[0020] Preferably, the preparation method of the polyphosphate type UV absorber includes the following steps: under inert gas protection, phenylphosphodichloro and 4,4'-dihydroxybiphenyl are mixed and reacted for 2-3 hours, then the temperature is raised to 70-75°C and the reaction is continued for 3-5 hours. Subsequently, hydroxyl-terminated dimethylsiloxane is added, the reaction conditions are kept unchanged and the reaction is continued for 10-12 hours, the oily product is extracted, washed, and dried to obtain the polyphosphate type UV absorber.

[0021] Secondly, this application provides a method for preparing PLA composite material for 3D printing, including the following steps: S1, PLA pretreatment: drying PLA to constant weight under vacuum conditions; S2, melt extrusion: blending dried PLA, nano silica, micro-nano mixed fibers, DOPO flame retardant and polyphosphate ester UV absorber, and extruding to obtain PLA composite material.

[0022] Preferably, in step S1, the drying temperature is 80-90℃.

[0023] Preferably, in step S2, the extrusion molding temperature is 180-210℃.

[0024] By adopting the above technical solution, this application first dries PLA to constant weight under vacuum conditions, achieving more thorough moisture removal, preventing hydrolysis and bubble formation during processing, reducing thermal degradation and oxidation, and improving melt flowability and processing stability, thereby improving the mechanical properties and appearance quality of the final product. Subsequently, this application blends the dried PLA, nano-silica, micro-nano hybrid fibers, DOPO-type flame retardant, and polyphosphate-type UV absorber, and extrudes them to obtain a PLA composite material with good comprehensive properties. The method is simple, the steps are clear, and it has good practical value.

[0025] In summary, this application has the following beneficial technical effects:

[0026] 1. The nano-silica, micro-nano hybrid fibers, DOPO flame retardant and polyphosphate UV absorber in the PLA composite material of this application can achieve a sufficient synergistic effect, which optimizes the tensile strength, toughness, flame retardancy, UV resistance and degradability of the PLA composite material, broadens the application range of PLA composite material, and enables it to adapt to more diverse working conditions and scenarios in 3D printing applications, with better performance and good adaptability to outdoor environment;

[0027] 2. This application first dries PLA to constant weight under vacuum conditions, achieving more thorough moisture removal, preventing hydrolysis and bubble formation during processing, reducing thermal degradation and oxidation, and improving melt flowability and processing stability, thereby improving the mechanical properties and appearance quality of the final product. Subsequently, this application blends the dried PLA, nano-silica, micro-nano hybrid fibers, DOPO-type flame retardant, and polyphosphate-type UV absorber, and extrudes them to obtain a PLA composite material with good comprehensive properties. The method is simple, the steps are clear, and it has good practical value. Detailed Implementation

[0028] Material source

[0029] Unless otherwise specified, all raw materials used in this application are commercially available products, specifically:

[0030] OP emulsifier, purchased from Tianjin Dongli District Tianda Chemical Reagent Factory;

[0031] 4-Hydroxybenzaldehyde, CAS number 123-08-0;

[0032] p-Toluenesulfonamide, CAS number 70-55-3;

[0033] DOPO, CAS number 35948-25-5;

[0034] Phenylphosphoryl dichloro, CAS number 824-72-6;

[0035] 4,4'-Dihydroxybiphenyl, CAS number 92-88-6;

[0036] Hydroxyl-terminated dimethylsiloxane, Mn = 4200;

[0037] Nano-silica, purchased from Aladdin Reagent, with a particle size of 15 nm and a purity of 99.5 wt%;

[0038] Dopamine hydrochloride, purchased from Aladdin Reagent, purity 98 wt%;

[0039] PLA, purchased from Nature Works, brand name 4032D;

[0040] 2-Hydroxy-4-n-octyloxybenzophenone, CAS number 1843-05-6.

[0041] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0042] Preparation Example 1

[0043] The method for preparing micron-sized cellulose includes the following steps:

[0044] 900g of waste paper residue was poured into 24L of deionized water, and 45g of sodium silicate, 13.5g of sodium dodecylbenzenesulfonate, 13.5g of OP-emulsifier, 90g of hydrogen peroxide, and 13.5g of sodium hydroxide were added sequentially as deinking agents. The mixture was then stirred continuously to ensure uniform dispersion of the deinking agents. The mixture was allowed to stand at room temperature for 0.5h, and then poured into a pulper for 30min to obtain waste paper pulp. The pulp was poured into a standard test sieve with a 0.045mm aperture and rinsed repeatedly with water until no obvious ink traces were visible. The deinked pulp, after being rinsed clean of ink, was placed in an oven and dried at 80℃ to constant weight. The pulp was then pulverized in a pulverizer for 30min to obtain micronized cellulose.

[0045] Preparation Example 2

[0046] The preparation method of nanocellulose includes the following steps:

[0047] 200g of micronized cellulose obtained in Preparation Example 1 was immersed in a 59wt% sulfuric acid aqueous solution and reacted for 1h at 45℃ and 270r / min. Then, it was immediately poured into ice water and allowed to stand for 1h. The excess sulfuric acid aqueous solution was removed by vacuum filtration using a vacuum pump and a 0.22μm filter membrane. The filter residue (crude nanocellulose) was obtained by filtration. The filter residue was dispersed in boiling water and dialyzed using a dialysis bag with a molecular weight of 3000. The deionized water was continuously replaced until the suspension was dialyzed to neutral. After sonication for 30min, it was freeze-dried for 48h to obtain nanocellulose.

[0048] Preparation Example 3.1

[0049] The preparation method of DOPO type flame retardant includes the following steps:

[0050] 24.4 g of 4-hydroxybenzaldehyde and 34.2 g of p-toluenesulfonamide were mixed and placed in a closed system. The system was then repeatedly evacuated and purged with nitrogen. 3 mL of glacial acetic acid and 200 mL of ethanol were added, and the mixture was reacted at 80 °C for 7 h. 43.2 g of DOPO was completely dispersed in 200 mL of ethanol and then added to the above system. The reaction conditions were kept constant and the reaction was continued for 12 h. After the ethanol evaporated, the product was dissolved in petroleum ether solution to remove unreacted substances. The product was then dried in a vacuum drying oven at 70 °C for 24 h to obtain the DOPO flame retardant.

[0051] Preparation Example 3.2

[0052] The preparation method of DOPO type flame retardant includes the following steps:

[0053] 24.4 g of 4-hydroxybenzaldehyde and 34.2 g of p-toluenesulfonamide were mixed and placed in a closed system. The system was then repeatedly evacuated and purged with nitrogen. 3 mL of glacial acetic acid and 200 mL of ethanol were added, and the mixture was reacted at 70 °C for 8 h. 43.2 g of DOPO was completely dispersed in 200 mL of ethanol and then added to the above system. The reaction conditions were kept constant and the reaction was continued for 10 h. After the ethanol evaporated, the product was dissolved in petroleum ether solution to remove unreacted substances. The product was then dried in a vacuum drying oven at 70 °C for 24 h to obtain the DOPO flame retardant.

[0054] Preparation Example 4.1

[0055] A method for preparing a polyphosphate-based UV absorber includes the following steps:

[0056] Under nitrogen protection, 37.4 g of phenylphosphine dichloride, 22.2 g of triethylamine, and 200 mL of tetrahydrofuran were mixed and stirred evenly in an ice-water bath. Then, 200 mL of a 1 mol / L solution of 4,4'-dihydroxybiphenyl tetrahydrofuran was added, and the reaction was carried out for 3 h. The temperature was then raised to 70 °C, and the reaction was continued for 5 h. Then, 100 mL of a 0.1 mol / L solution of hydroxyl-terminated dimethylsiloxane tetrahydrofuran was added, and the reaction was continued for 10 h while maintaining the same reaction conditions. The triethylamine salt and tetrahydrofuran were removed by vacuum filtration and rotary evaporation, respectively, and the oily product was extracted. It was dissolved in a small amount of CH2Cl2, repeatedly washed and purified with deionized water, and finally dried under vacuum at 60 °C for 24 h to obtain a polyphosphate-type UV absorber.

[0057] Preparation Example 4.2

[0058] A method for preparing a polyphosphate-based UV absorber includes the following steps:

[0059] Under nitrogen protection, 37.4 g of phenylphosphine dichloride, 22.2 g of triethylamine, and 200 mL of tetrahydrofuran were mixed and stirred evenly in an ice-water bath. Then, 200 mL of a 1 mol / L solution of 4,4'-dihydroxybiphenyl tetrahydrofuran was added, and the reaction was carried out for 2 h. The temperature was then raised to 75 °C, and the reaction was continued for 3 h. Then, 100 mL of a 0.1 mol / L solution of hydroxyl-terminated dimethylsiloxane tetrahydrofuran was added, and the reaction was continued for 12 h while maintaining the same reaction conditions. The triethylamine salt and tetrahydrofuran were removed by vacuum filtration and rotary evaporation, respectively, and the oily product was extracted. It was dissolved in a small amount of CH2Cl2, repeatedly washed and purified with deionized water, and finally dried under vacuum at 60 °C for 24 h to obtain a polyphosphate-type UV absorber.

[0060] Preparation Example 5

[0061] The preparation method of polydopamine-modified silica includes the following steps:

[0062] Prepare 1 L of Tris buffer with a content of 0.1 mol, and adjust the pH to 8.5 by adding 5% hydrochloric acid. Then add 10 g of nano-silica to the Tris-HCl buffer and sonicate for 1 h. Then add 2 g of dopamine hydrochloride to the solution and stir magnetically for 24 h at room temperature. Centrifuge the mixture for 20 min, wash three times with ethanol to remove unreacted monomers, and place the obtained solid in an oven to dry at 170 °C for 12 h to obtain polydopamine modified silica.

[0063] Example 1.1

[0064] A method for preparing PLA composite material for 3D printing includes the following steps:

[0065] S1. PLA pretreatment: PLA is dried to constant weight in a vacuum system at a temperature of 90℃.

[0066] S2. The dried PLA, nano-silica, micro-nano mixed fibers (micronized cellulose obtained in Preparation Example 1 and nano-cellulose obtained in Preparation Example 2 with a weight ratio of 1:2), the DOPO-type flame retardant obtained in Preparation Example 3.1 and the polyphosphate-type UV absorber obtained in Preparation Example 4.2 are blended and extruded at a temperature of 180-210°C, with zone 1 temperature of 180-190°C, zone 2 temperature of 195-205°C, zone 3 temperature of 185-195°C, and zone 4 temperature of 200-210°C, to finally obtain the PLA composite material.

[0067] Example 1.2

[0068] A method for preparing PLA composite material for 3D printing includes the following steps:

[0069] S1. PLA pretreatment: PLA is dried to constant weight in a vacuum system at a temperature of 80℃.

[0070] S2. The dried PLA, nano-silica, micro-nano mixed fibers (micronized cellulose obtained in Preparation Example 1 and nano-cellulose obtained in Preparation Example 2 with a weight ratio of 3:2), the DOPO-type flame retardant obtained in Preparation Example 3.2 and the polyphosphate-type UV absorber obtained in Preparation Example 4.1 are blended and extruded at a temperature of 180-210°C, with zone 1 temperature of 180-190°C, zone 2 temperature of 195-205°C, zone 3 temperature of 185-195°C, and zone 4 temperature of 200-210°C, to finally obtain the PLA composite material.

[0071] Table of substance usage (g) for Examples 1.1-1.2

[0072] Example 1.1 Example 1.2 Dried PLA 1000 1000 Nano-silica 40 60 Micro-nano hybrid fiber 40 60 DOPO type flame retardant 65 40 Polyphosphate type ultraviolet absorbing agent 5 15

[0073] Example 2.1

[0074] A method for preparing PLA composite material for 3D printing differs from Example 1.1 in that the amount of micro-nano hybrid fibers used is 45g, while the rest is the same as in Example 1.1.

[0075] Example 2.2

[0076] A method for preparing PLA composite material for 3D printing differs from Example 1.1 in that the amount of micro-nano hybrid fibers used is 50g, while the rest is the same as in Example 1.1.

[0077] Example 2.3

[0078] A method for preparing PLA composite material for 3D printing differs from Example 1.1 in that the amount of micro-nano hybrid fibers used is 55g, while the rest is the same as in Example 1.1.

[0079] Example 3.1

[0080] A method for preparing PLA composite material for 3D printing differs from Example 2.2 in that the weight ratio of micronized cellulose obtained in Preparation Example 1 to nanocellulose obtained in Preparation Example 2 is 1.5:2, while the rest is the same as in Example 2.2.

[0081] Example 3.2

[0082] A method for preparing PLA composite material for 3D printing differs from Example 2.2 in that the weight ratio of micronized cellulose obtained in Preparation Example 1 to nanocellulose obtained in Preparation Example 2 is 2:2, while the rest is the same as in Example 2.2.

[0083] Example 3.3

[0084] A method for preparing PLA composite material for 3D printing differs from Example 2.2 in that the weight ratio of micronized cellulose obtained in Preparation Example 1 to nanocellulose obtained in Preparation Example 2 is 2.5:2, while the rest is the same as in Example 2.2.

[0085] Example 4.1

[0086] A method for preparing PLA composite material for 3D printing differs from Example 1.1 in that: the amount of DOPO-type flame retardant obtained in Preparation Example 3.1 is 60g, and the amount of polyphosphate-type UV absorber obtained in Preparation Example 4.2 is 10g; the rest are the same as in Example 1.1.

[0087] Example 4.2

[0088] A method for preparing PLA composite material for 3D printing differs from Example 1.1 in that: the amount of DOPO-type flame retardant prepared in Preparation Example 3.1 is 57.5g, the amount of polyphosphate-type UV absorber prepared in Preparation Example 4.2 is 12.5g, and the rest is the same as in Example 1.1.

[0089] Example 5

[0090] A method for preparing PLA composite material for 3D printing differs from Example 1.1 in that nano-silica is replaced with polydopamine-modified silica prepared in Preparation Example 5, while the rest is the same as in Example 1.1.

[0091] Comparative Example 1

[0092] The difference from Example 1.1 is that the micro-nano hybrid fibers are removed, while the rest are the same as in Example 1.1.

[0093] Comparative Example 2.1

[0094] The difference from Example 1.1 is that the weight ratio of the micronized cellulose obtained in Preparation Example 1 to the nanocellulose obtained in Preparation Example 2 is 0.5:2, and all other aspects are the same as in Example 1.1.

[0095] Comparative Example 2.2

[0096] The difference from Example 1.1 is that the weight ratio of the micronized cellulose obtained in Preparation Example 1 to the nanocellulose obtained in Preparation Example 2 is 4:2, and all other aspects are the same as in Example 1.1.

[0097] Comparative Example 3

[0098] The difference from Example 1.1 is that the DOPO-type flame retardant prepared in Preparation Example 3.1 is replaced with DOPO, and all other aspects are the same as in Example 1.1.

[0099] Comparative Example 4

[0100] The difference from Example 1.1 is that the polyphosphate-type UV absorber prepared in Preparation Example 4.2 is replaced with 2-hydroxy-4-n-octyloxybenzophenone, and all other aspects are the same as in Example 1.1.

[0101] Comparative Example 5

[0102] The difference from Example 1.1 is that the amount of DOPO flame retardant prepared in Preparation Example 3.1 is 35g, and the amount of polyphosphate ester UV absorber prepared in Preparation Example 4.2 is 35g. All other aspects are the same as in Example 1.1.

[0103] Performance testing

[0104] The PLA composite materials obtained in the examples and comparative examples were tested for tensile strength, elongation at break, limiting oxygen index, UV aging, and degradation rate, specifically as follows:

[0105] 1. Tensile strength and elongation at break: determined according to GB / T 1040.2, with a tensile rate of 10 mm / min;

[0106] 2. Limiting Oxygen Index: The LOI (Limiting Oxygen Index) (%) was determined according to ISO 4589-2.

[0107] 3. Ultraviolet aging: Sample preparation was carried out in accordance with ASTM D3039 / D3039M-17 and GB / T 21196.2. The prepared samples were exposed to ultraviolet light in the 320nm band at 50℃ and 85% relative humidity for 30 days. The tensile strength was tested and compared with that before the ultraviolet aging test. The tensile strength retention rate (%) was recorded.

[0108] 4. Degradation Rate: Soil samples from the city were selected as the simulated soil environment. The soil pH was determined to be 8.29 according to standards. Based on the actual application scenario, the temperature of the simulated soil environment was set between 20-30℃, and the humidity was maintained at a suitable moisture content. PLA composite material samples were buried in the selected soil at a certain depth below the soil surface. After placing the samples, soil was covered, ensuring full contact between the samples and the soil. The samples were buried for 120 days, during which time appropriate moisture was sprayed periodically according to air humidity. Afterward, the samples were removed, cleaned, dried in a forced-air drying oven, and weighed. Changes before and after burial were compared through macroscopic observation, mass measurement, and SEM characterization to evaluate the degradation performance of the composite material in the soil environment, and the degradation rate (%) was recorded.

[0109] Table 2 Performance Test Table

[0110]

[0111] Data Analysis:

[0112] As shown in Table 2, the tensile strength of Examples 1.1-1.2 is 86.2-86.5 MPa, the elongation at break is 27.4-27.5%, the LOI is 28.6-29.2%, the tensile strength retention rate is 99.23-99.34%, and the degradation rate is 2.12-2.41%. This demonstrates that the nano-silica, micro-nano hybrid fibers, DOPO flame retardant, and polyphosphate UV absorber in the PLA composite material of this application can achieve a sufficient synergistic effect, optimizing the tensile strength, toughness, flame retardancy, UV resistance, and degradability of the PLA composite material. This broadens the application range of the PLA composite material, enabling it to adapt to more diverse working conditions and scenarios in 3D printing applications, possessing better performance, and well adapting to outdoor environments.

[0113] In Examples 2.1-2.3, the amount of micro-nano hybrid fibers added was changed. The results showed that the tensile strength and elongation at break of Example 2.2 were both high, and the rigidity and toughness were well balanced. It can be seen that by controlling the amount of micro-nano hybrid fibers added, the toughness of PLA composite material can be maximized without affecting the tensile strength of PLA composite material.

[0114] In Examples 3.1-3.3, the ratio of micron-cellulose and nano-cellulose was changed. The results showed that Example 3.2 had high tensile strength and elongation at break, as well as a high degradation rate. It can be seen that by controlling the ratio of micron-cellulose and nano-cellulose, the present application can maximize the toughness of PLA composite material without affecting its tensile strength, while maintaining a high degradation capacity.

[0115] In Examples 4.1-4.2, the dosage of DOPO-type flame retardant and polyphosphate-type UV absorber was changed. The results showed that the combined tensile strength and elongation at break data of Example 4.1 were better, and the rigidity and toughness were well balanced. It can be seen that the comprehensive performance of PLA composite material was successfully optimized by strictly controlling the dosage of DOPO-type flame retardant and polyphosphate-type UV absorber.

[0116] In Example 5, this application replaced nano-silica with polydopamine-modified silica. The results showed that the overall data of Example 5 was significantly improved. It can be seen that polydopamine-modified silica can indeed exhibit better dispersion performance, stronger bonding force with PLA matrix, and a certain rigid particle reinforcement effect when the material fractures. During fracture, the particles act as stress concentrates, causing deformation of the matrix around the particles and absorbing a large amount of external force. The bonding force between the particles and the matrix allows the particles to prevent the propagation of matrix cracks. The peeling of the particles from the fracture surface can also play a role in absorbing impact energy. Ultimately, the tensile strength of PLA composite material is greatly improved while minimizing toughness loss.

[0117] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A PLA composite material for 3D printing, characterized in that, By weight, the raw materials used include the following components: 100 parts PLA; 4-6 parts nano silica; 4-6 parts micro-nano mixed fibers; 4-6.5 parts of DOPO type flame retardant; 0.5-1.5 parts of polyphosphate-type UV absorber; the micro-nano hybrid fiber includes micron cellulose and nano cellulose in a weight ratio of (1-3):2; the raw materials used in preparing the DOPO-type flame retardant include 4-hydroxybenzaldehyde, p-toluenesulfonamide and DOPO; the raw materials used in preparing the polyphosphate-type UV absorber include phenylphosphodichloro, 4,4'-dihydroxybiphenyl and hydroxyl-terminated dimethylsiloxane. The preparation method of the DOPO-type flame retardant includes the following steps: 4-hydroxybenzaldehyde and p-toluenesulfonamide were blended and dispersed in an organic solvent under inert gas protection. The mixture was reacted at 70-80°C for 7-8 hours. Then DOPO was added and the reaction was continued for 12-13 hours. The solvent and unreacted substances were removed and the mixture was dried to obtain a DOPO-type flame retardant. The preparation method of the polyphosphate-type UV absorber includes the following steps: Under inert gas protection, phenylphosphodichloro and 4,4'-dihydroxybiphenyl were mixed and reacted for 2-3 hours. The temperature was then raised to 70-75°C and the reaction was continued for 3-5 hours. Subsequently, hydroxyl-terminated dimethylsiloxane was added, and the reaction was continued for 10-12 hours while maintaining the reaction conditions. The oily product was extracted, washed, and dried to obtain a polyphosphate-type UV absorber.

2. The PLA composite material for 3D printing according to claim 1, characterized in that, The amount of the micro-nano hybrid fiber is 5 parts by weight.

3. The PLA composite material for 3D printing according to claim 2, characterized in that, The micro-nano hybrid fiber comprises micron-cellulose and nano-cellulose in a weight ratio of 2:

2.

4. The PLA composite material for 3D printing according to claim 1, characterized in that, The amount of the DOPO-type flame retardant is 6 parts by weight, and the amount of the polyphosphate-type UV absorber is 1 part.

5. The PLA composite material for 3D printing according to claim 1, characterized in that, The nano-silica is also modified with polydopamine, and the specific steps are as follows: Nano-silica was placed in Tris-HCl buffer and ultrasonically dispersed. Then, dopamine hydrochloride was added, stirred, and centrifuged to obtain a solid. The obtained solid was washed and dried to obtain polydopamine-modified silica.

6. A method for preparing PLA composite material for 3D printing according to any one of claims 1-5, characterized in that, Includes the following steps: S1. PLA pretreatment: Dry PLA to constant weight under vacuum conditions; S2. Melt extrusion: The dried PLA, nano silica, micro-nano mixed fibers, DOPO flame retardant and polyphosphate UV absorber are blended and extruded to obtain PLA composite material.

7. A method for preparing PLA composite material for 3D printing according to claim 6, characterized in that, In step S1, the drying temperature is 80-90℃.

8. A method for preparing PLA composite material for 3D printing according to claim 6, characterized in that, In step S2, the extrusion molding temperature is 180-210℃.

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