Nano titanium dioxide and polylactic acid composite material and preparation method thereof

Abstract

The invention relates to the field of biodegradable materials, and discloses a nano titanium dioxide and polylactic acid composite material and a preparation method thereof, the nano titanium dioxide and polylactic acid composite material comprises the following components by mass: 90-99% of polylactic acid; 1%-10% of modified nano titanium dioxide; wherein the nano titanium dioxide is modified by a silane coupling agent, the silane coupling agent is gamma-aminopropyltriethoxysilane, and the addition amount of the silane coupling agent is 0.5%-2.0% of the mass of the nano titanium dioxide; the average particle size of the modified nano titanium dioxide is 10-50 nanometers; the weight-average molecular weight of the polylactic acid is 50000 to 100000 g / mo l; the modified nano titanium dioxide and the polylactic acid are blended in a molten state. According to the invention, through surface modification of nano TiO2 and structural adaptive design of nano TiO2 and polylactic acid, a composite material system with a stable interface and uniform dispersion is constructed, and the thermal stability, mechanical properties and processing consistency of the material are effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of biodegradable materials, in particular to a nano titanium dioxide and polylactic acid composite material and a preparation method thereof. Background Art

[0002] Polylactic acid (PLA), as a new type of biodegradable material, is derived from natural organic matter or artificial synthesis. In nature, polylactic acid is widely present in plants, animals and microorganisms. For example, crops such as corn, sugar beets, and cassava contain small amounts of polylactic acid. In addition, certain bacteria can also produce polylactic acid through fermentation. In industrial production, commonly used polylactic acid raw materials include natural organic matter such as starch, glucose, and cellulose, as well as synthetic compounds such as acrylic acid. In recent years, it has attracted widespread attention in fields such as industry and scientific research. PLA is polymerized with lactic acid as the main raw material, has unique biocompatibility and biodegradability, and provides an ideal alternative to solving the environmental problems caused by traditional petrochemical-based materials.

[0003] Existing modification methods often rely on polymer compatibilizers or chemical crosslinkers. While these methods can improve interfacial compatibility to a certain extent, in practice, they still face problems such as uneven filler dispersion, a narrow processing window, and limited improvement in mechanical properties. In particular, the use of nanoparticles such as titanium dioxide, while capable of enhancing the mechanical properties and thermal stability of polylactic acid, suffers from poor dispersion within the polylactic acid matrix and prone to agglomeration, leading to unstable performance and increased processing difficulty. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a nano-titanium dioxide and polylactic acid composite material and a preparation method thereof, which solves the problems of interface incompatibility and processing instability in the existing technology.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: a nano-titanium dioxide and polylactic acid composite material and a preparation method thereof, comprising the following components in percentage by mass:

[0006] Polylactic acid 90% to 99%;

[0007] Modified nano titanium dioxide 1% to 10%;

[0008] The nano titanium dioxide is modified by a silane coupling agent, and the silane coupling agent is gamma-aminopropyltriethoxysilane, and the addition amount thereof is 0.5% to 2.0% of the mass of the nano titanium dioxide.

[0009] Preferably, the average particle size of the modified nano-titanium dioxide is 10 to 50 nanometers.

[0010] Preferably, the weight average molecular weight of the polylactic acid is 50,000 to 100,000 g / mol.

[0011] Preferably, the modified nano-titanium dioxide is blended with polylactic acid in a molten state, using a twin-screw extruder with an extrusion temperature of 160-210° C. and a screw speed of 30-80 rpm.

[0012] A method for preparing a composite material of nano-titanium dioxide and polylactic acid comprises the following steps:

[0013] S1: dispersing nano-titanium dioxide in an ethanol-water mixture, adding a silane coupling agent, reacting at a temperature of 50-80°C for 1-3 hours to obtain modified nano-titanium dioxide;

[0014] S2: drying the polylactic acid at 60-80° C. for 6-12 hours;

[0015] S3: dry-mixing the modified nano-titanium dioxide and the dried polylactic acid in a mass ratio of 1% to 10%: 90% to 99%, and stirring for 5 to 15 minutes;

[0016] S4: melt-blending the mixture through a twin-screw extruder at a temperature of 160 to 210° C. and a screw speed of 30 to 80 rpm, extruding, cooling, and then pelletizing to obtain a composite material.

[0017] Preferably, the volume ratio of ethanol to water is 95:5.

[0018] Preferably, the modified nano-titanium dioxide is dried in vacuum at 60-80° C. for 12-24 hours before use.

[0019] Preferably, the blended composite material is further processed into a molded product by injection molding, with the injection molding temperature being 180-200° C. and the injection pressure being 40-80 MPa.

[0020] Preferably, the average particle size of the nano-titanium dioxide is 10 to 50 nanometers, and the molecular weight of the polylactic acid is 50,000 to 100,000 g / mol.

[0021] Preferably, the dry mixing step is carried out using a high-speed mixer at a stirring speed of 500 to 1500 rpm.

[0022] The present invention provides a nano-titanium dioxide and polylactic acid composite material and a preparation method thereof. It has the following beneficial effects:

[0023] 1. The present invention constructs a stable interface system by introducing surface-modified nano-TiO2, effectively improving the dispersion uniformity of the inorganic phase in the polylactic acid matrix, thereby enhancing the synergistic consistency of the internal structure of the composite material and significantly improving the interface incompatibility and aggregation problems that are prone to occur in traditional composite systems.

[0024] 2. The present invention directionally modifies nano-TiO2 to form an interface structure with physical entanglement or weak bond adsorption in polylactic acid, fundamentally improving the mechanical response ability of the composite material and reflecting the synergistic reinforcement effect of the inorganic reinforcing phase and the polymer matrix at the microscopic level.

[0025] 3. The present invention adopts a multi-stage temperature control processing technology to achieve dynamic thermal field optimization of the composite material during the melting process, so that the disaggregation of particles and the melting behavior of the matrix proceed synchronously, thereby ensuring the flow stability and structural continuity of the system in the processing path.

[0026] 4. Through the overall coordinated design of component composition and process path, the present invention significantly improves the molding adaptability and operational stability of the material, demonstrates better production consistency in large-scale injection molding applications, and embodies the application advantages of the synergistic integration of structural design and engineering technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A diagram showing the steps of the method of the present invention;

[0028] Figure 2 This is a sample diagram of TiO2 surface modification sedimentation analysis in the present invention;

[0029] Figure 3 Schematic diagram of melt blending in infrared spectra of pure PLA and TiO2 / PLA with different contents in infrared analysis;

[0030] Figure 4 Schematic diagram of solution blending in infrared spectra of pure PLA and TiO2 / PLA with different contents in infrared analysis;

[0031] Figure 5 Schematic diagram of melt blending in XRD spectra of pure PLA and TiO2 / PLA with different contents;

[0032] Figure 6 Schematic diagram of solution blending in XRD spectra of pure PLA and TiO2 / PLA with different contents;

[0033] Figure 7 SEM images of TiO2 / PLA with different contents. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the present specification. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] Please see the attached Figure 1 -Attached Figure 7 The embodiment of the present invention provides a nano-titanium dioxide and polylactic acid composite material and a preparation method thereof, comprising the following components in percentage by mass:

[0036] Polylactic acid 90% to 99%;

[0037] Modified nano titanium dioxide 1% to 10%;

[0038] The nano-titanium dioxide is modified by a silane coupling agent, wherein the silane coupling agent is γ-aminopropyltriethoxysilane, and the addition amount thereof is 0.5% to 2.0% of the mass of the nano-titanium dioxide;

[0039] This composite material uses polylactic acid (PLA) as the polymer matrix and nano-sized titanium dioxide as the functional filler. A silane coupling agent is introduced to modify the TiO2 surface, enhancing its compatibility within the PLA matrix. By manipulating the surface and interfacial chemical environment of the nanoparticles, their tendency to aggregate is effectively suppressed, creating a more stable dispersed structure. Furthermore, the two phases are uniformly compounded through a melt blending process, forming a multiphase composite system with excellent structural continuity.

[0040] The core structural basis of the composite material lies in the re-matching of the interface energy level between modified nano-TiO2 and PLA. Because the surface of unmodified nano-TiO2 is rich in hydroxyl groups and has strong hydrophilicity, the interface compatibility is poor when directly acting on hydrophobic PLA, and phase boundary aggregation phenomenon is easily formed. To solve this problem, the present invention introduces a silane coupling agent for pretreatment in the material structure design stage. By the coupling agent, an organic-inorganic bridging layer is formed on the TiO2 surface, which changes the TiO2 surface polarity, makes it have certain organophilicity, and strengthens the interaction interface affinity with the polylactic acid molecular chain. This treatment not only helps the steric hindrance of nano-TiO2 to stably disperse, but also builds the interface association network between TiO2 and PLA to a certain extent, supporting the stability of the overall composite material system from a structural level.

[0041] Regarding matrix processing, polylactic acid (PLA), due to the numerous ester bonds in its molecular structure, is sensitive to moisture during processing. Without pre-drying, it is prone to degradation at high temperatures, affecting its melt viscoelasticity and the final composite quality. Therefore, the present invention incorporates a vacuum drying pretreatment step for the PLA into the preparation process to ensure molecular stability during processing. This measure plays a fundamental role in the entire process and is a key prerequisite for subsequent uniform blending and molding.

[0042] During the material mixing stage, dry mixing is used for pre-dispersion, combined with high-speed shear stirring to achieve initial homogenization on a macroscopic scale. Although this step does not achieve complete fusion of particles and the matrix at the molecular level, it significantly reduces the tendency of localized aggregation of nanoparticles caused by density differences or packing effects during feeding, providing a uniformly distributed feed foundation for subsequent melt blending.

[0043] Melt blending is the core process of the present invention. Its mechanism is based on the deagglomeration and redispersion of nanofillers under high temperature and high shear, resulting in physical nesting or a certain degree of interfacial entanglement with PLA molecular chains in the rheological field. Through segmented temperature control and screw structure design, the material undergoes a thorough melting, conveying, mixing, and compaction process in a thermoplastic state, ultimately forming a composite system with nano-TiO2 particles embedded in the continuous phase. This structure exhibits typical "particle reinforcement" characteristics, but its reinforcement behavior is not solely dependent on rigid fillers, but rather the synergistic effect of particle interface regulation, distribution uniformity, and molecular chain motion.

[0044] The entire material system is constructed without relying on special additives or complex chemical modification processes. Instead, the target functionality is achieved solely through physical interface design and controlled thermal processing paths, demonstrating strong universal applicability in biodegradable material modification. Compared to traditional methods, this method prioritizes interfacial layer structure construction and dispersed state control, without relying on bulk material changes or high-energy processing equipment. This method offers a clear preparation path, strong replicability, and engineering potential.

[0045] In summary, the present invention achieves efficient dispersion and structural integration of TiO2 in PLA through the path of interface modification-drying pretreatment-macro pre-dispersion-melt blending molding. The obtained composite material has the characteristics of high structural integrity, good processing stability, and excellent synergy of mechanical and thermal properties, providing a technical basis and process support for the subsequent preparation of green and degradable functional materials.

[0046] Example 1 Raw material ratio:

[0047] Polylactic acid (PLA): 95wt%;

[0048] Modified nano-TiO2: 5wt%;

[0049] Silane coupling agent (KH-550): 1% of the mass of TiO2.

[0050] Preparation steps:

[0051] TiO2 modification treatment:

[0052] 10 g of nano-TiO2 was added to 200 mL of ethanol-water mixed solution (volume ratio 95:5) and ultrasonically dispersed for 20 minutes;

[0053] Add 0.1 g KH-550 and stir the mixture at 60°C for 2 hours;

[0054] After the reaction, the product was filtered, washed three times with ethanol and deionized water in sequence, and dried in vacuum at 70° C. for 16 hours to obtain modified TiO2.

[0055] PLA pre-drying:

[0056] 95 g of PLA particles were vacuum dried at 70° C. for 10 hours and set aside.

[0057] Dry mix premix:

[0058] Dry PLA and modified TiO2 were mixed in a mass ratio of 95:5 and stirred in a high-speed mixer for 10 minutes.

[0059] Melt blending and granulation:

[0060] The mixture was fed into a twin-screw extruder and the temperature range was set as follows:

[0061] Feeding section: 170℃;

[0062] Compression section: 180°C;

[0063] Metering section: 190℃;

[0064] Die section: 200℃;

[0065] The screw speed was set at 60 rpm, the blending time was about 8 minutes, and the mixture was cooled with water before pelletizing.

[0066] Injection molding (optional):

[0067] The obtained particles were injection molded at an injection temperature of 190°C, a mold temperature of 40°C, and an injection pressure of 60 MPa.

[0068] Example 2

[0069] Raw material ratio:

[0070] PLA: 99wt%;

[0071] Modified TiO2: 1wt%;

[0072] KH-550: 0.5% of TiO2 mass.

[0073] Preparation steps:

[0074] TiO2 modification treatment:

[0075] Take 1g TiO2 and add it to 50mL ethanol-water (volume ratio 95:5) and ultrasonicate for 10 minutes;

[0076] Add 0.005 g of KH-550 and stir the mixture at 50°C for 1 hour;

[0077] The product was filtered and washed twice with ethanol and deionized water, and dried under vacuum at 60°C for 24 hours to obtain modified TiO2.

[0078] PLA pre-drying:

[0079] 99 g of PLA was taken and vacuum dried at 60°C for 6 hours.

[0080] Dry mix premix:

[0081] PLA and modified TiO2 were mixed at a ratio of 99:1 and stirred in a high-speed blender for 5 minutes.

[0082] Melt blending and granulation:

[0083] The extruder temperature settings are as follows:

[0084] Feeding section: 160℃;

[0085] Compression section: 170°C;

[0086] Metering section: 180°C;

[0087] Die section: 180°C;

[0088] The screw speed was set to 30 rpm, the extrusion time was controlled at 5 minutes, and pelletized after cooling.

[0089] Injection molding (optional):

[0090] The injection temperature was set at 180°C, the mold temperature at 25°C, and the injection pressure at 40 MPa.

[0091] Example 3

[0092] Raw material ratio: PLA: 90wt%;

[0093] Modified TiO2: 10wt%;

[0094] KH-550: 2% of TiO2 by mass.

[0095] Preparation steps:

[0096] TiO2 modification treatment:

[0097] 20 g TiO2 was added to 400 mL of ethanol-water mixture (volume ratio 95:5) and ultrasonically dispersed for 30 min;

[0098] Add 0.4 g KH-550 and stir the mixture at 80 °C for 3 hours;

[0099] The modified TiO2 was obtained by washing with ethanol and deionized water three times in sequence and drying in vacuo at 80°C for 12 hours.

[0100] PLA pre-drying:

[0101] 90 g of PLA was placed in a vacuum drying oven at 80° C. and dried for 12 hours, and then cooled for later use.

[0102] Dry mix premix:

[0103] PLA and modified TiO2 were mixed in a mass ratio of 90:10 and stirred at high speed for 15 minutes.

[0104] Melt blending and granulation:

[0105] The temperature settings are as follows:

[0106] Feeding section: 180℃;

[0107] Compression section: 190°C;

[0108] Metering section: 200℃;

[0109] Die section: 210℃;

[0110] The screw speed was set to 80 rpm, the extrusion time was controlled at 10 minutes, and pelletized after cooling.

[0111] Injection molding (optional):

[0112] The injection temperature was set at 200°C, the mold temperature at 50°C, and the injection pressure at 80 MPa.

[0113] Comparative Example 1:

[0114] Compared with Example 1, the difference is that the nano-TiO2 is not modified with a silane coupling agent, and the untreated nano-TiO2 is directly used to blend with PLA. The remaining steps and parameters are the same.

[0115] Comparative Example 2:

[0116] Compared with Example 1, the difference is that the addition amount of modified nano-TiO2 is set to 12wt%, which exceeds the mass percentage upper limit of 1-10wt% specified in the present invention, and the other component ratios and step parameters are the same.

[0117] Comparative Example 3:

[0118] Compared with Example 1, the difference is that the pre-drying step of polylactic acid is omitted, and PLA is directly used for blending processing at room temperature, and the proportions of other components and melting process parameters remain consistent.

[0119] Comparative Example 4:

[0120] Compared with Example 1, the difference is that no multi-stage temperature control zone is set in the blending process, the temperature of each section of the twin-screw extruder is uniformly set to 180°C, and the zoned temperature control design in the process of the present invention is omitted. The remaining component ratios and other operating steps are consistent.

[0121] Test Example 1: Composite Material Processing Stability Test

[0122] 1. Experimental Purpose

[0123] The thermal stability of PLA matrix and nano-TiO2 composites under different pretreatment conditions during processing and the flow consistency during the molding process were evaluated, with special attention paid to the effect of PLA drying treatment on the extrusion and injection molding stages.

[0124] 2. Experimental Materials and Samples

[0125] Sample A (control sample): composite material particles of Example 1;

[0126] Sample B (comparative sample): composite material particles of Comparative Example 3 (PLA was not dried, and the rest was the same);

[0127] equipment:

[0128] Experimental twin-screw extruder;

[0129] Injection molding machines;

[0130] Electronic balance, stopwatch, and spline demoulding detection tools.

[0131] 3. Experimental steps

[0132] Extrusion stage operation

[0133] Take 500g of sample A and sample B respectively;

[0134] Feed the materials into the preheated twin-screw extruder respectively;

[0135] Set the unified temperature parameters (the four temperature zones are set to: 170℃ / 180℃ / 190℃ / 200℃), and the screw speed is fixed at 60rpm;

[0136] Observe and record:

[0137] Check whether there are any processing abnormalities such as bubbles, paste, discontinuous discharge, etc.

[0138] Time the time required to extrude the first 50g of material;

[0139] Whether the discharge is stable and smooth.

[0140] Injection molding operation

[0141] The pellets obtained by the above extrusion were respectively injection molded into standard tensile test strips;

[0142] The injection molding machine temperature was set to 190°C, the mold temperature to 40°C, and the injection pressure to 60 MPa;

[0143] Record whether there is any:

[0144] The feeding is not smooth and the nozzle is clogged;

[0145] Incomplete molding and difficult demoulding;

[0146] Abnormal fluctuations in molding cycle;

[0147] Record the number of rejects in the 50-piece sample.

[0148] Data collation and judgment basis

[0149] Abnormal machining behavior during machining will serve as an important indication of unstable performance;

[0150] Molding cycle fluctuation and scrap rate will serve as indirect indicators of processing adaptability.

[0151] Table 1 Comparison of processing stability test data:

[0152]

[0153]

[0154] The present invention achieves the unification of fluidity control and interface structure stability during melt processing by introducing a drying pretreatment step of polylactic acid in the preparation process of the composite material, combined with the interface regulation mechanism of modified nano-titanium dioxide. From the processing stability test results shown in Test Example 1, it can be seen that the drying treatment significantly reduces the degradation tendency of polylactic acid at high temperatures, reduces the melt viscosity fluctuation caused by hydrolysis during processing, and effectively avoids the occurrence of unstable phenomena such as paste and bubbles. This basic treatment measure ensures the thermophysical stability of the entire melt blending system and is a prerequisite for achieving a macroscopically homogeneous structure of the composite material.

[0155] Surface modification of nano-TiO2 not only enhances its dispersion within the PLA matrix but also forms an organic interface layer on the surface of the inorganic particles via the coupling agent, promoting physical entanglement or hydrogen bonding between the particles and the polymer. This interfacial synergy stabilizes the particle distribution during melt processing, inhibiting localized aggregation or migration, thereby further improving process continuity and discharging consistency. The discharging process stability observed in the test is the result of the composite system maintaining uniform flow in a high-temperature shear field. Its essence is the ability of the interfacial modification measures to maintain structural shape under processing conditions.

[0156] Furthermore, during the actual injection molding process, the presence of modified TiO2 regulates the thermal stability and structural viscoelasticity of the polylactic acid melt. On the one hand, it acts as a heat-conducting particle to improve the thermal balance of the melt, and on the other hand, it provides physical limiting points for the movement of the molecular chains, thereby widening the processing window and making the molding process more stable. Combined with the test results, it can be seen that this integrated structural and process design effectively supports the processing consistency and operational controllability of the composite material from the melting stage to the final molding stage, and is a key breakthrough in the material engineering path of this invention.

[0157] Test Example 2: Tensile Properties Test

[0158] 1. Experimental Purpose

[0159] The difference in the reinforcing effect of modified and unmodified TiO2 in polylactic acid (PLA) composites was evaluated. The effect of surface modification on the mechanical properties of the material was analyzed by comparing the tensile strength and elongation at break of the composites under different interface treatments (see Appendix Figure 2 ).

[0160] 2. Experimental Samples

[0161] Sample A (Example 1): using TiO2 modified with KH-550 silane;

[0162] Sample B (Comparative Example 1): Unmodified original TiO2 was used, and the other proportions and processing parameters were the same;

[0163] Specimen type: ASTM D638 standard tensile specimen, prepared by injection molding;

[0164] Number of samples: no less than 5 for each group, and the average value of valid samples is taken.

[0165] 3. Experimental equipment and parameter settings

[0166] Testing machine: electronic universal material testing machine;

[0167] Clamp spacing: 50mm;

[0168] Tensile rate: 5 mm / min;

[0169] Environmental conditions: room temperature (23±2°C), relative humidity approximately 50%.

[0170] IV. Experimental Procedure

[0171] Use a vernier caliper to measure the initial width and thickness of each specimen strip and record the effective cross-sectional area;

[0172] Clamp the specimen at both ends of the tensile testing machine and adjust the initial load to zero;

[0173] Start the equipment, stretch at a constant speed, and record the maximum load before fracture;

[0174] Simultaneously record the elongation at break for calculating the elongation at break;

[0175] The five groups of data were summarized, averaged, and archived for analysis.

[0176] Table 2 Comparison of tensile properties test results:

[0177]

[0178]

[0179] From the tensile performance comparison results of Test Example 2, it can be seen that the composite system constructed by modified nano-titanium dioxide and polylactic acid shows higher stability and load-bearing capacity in mechanical properties, which is closely related to the interface control mechanism established by the present invention. By introducing a silane coupling agent on the surface of the nanoparticles, the surface polarity of the inorganic phase is effectively adjusted, so that it has a certain organic affinity, thereby being easier to form a synergistic interface with the matrix molecular chain in the molten state of polylactic acid. The formation of this interface not only reduces particle agglomeration, but also promotes the load to be more evenly distributed to the composite system during the macroscopic tensile process, slowing down the occurrence of stress concentration.

[0180] The modified nano-TiO2 surface has active groups, which can generate physical entanglement and weak interaction forces with the ester chains of polylactic acid, making the "embedded" state of the particles in the polymer matrix more stable. During the stretching process, the particles will not easily detach or migrate. This stable interface state still has a strong load transfer capacity under the action of external forces and is a key factor in improving the overall mechanical response of the composite material. In contrast, the unmodified nano-TiO2 is incompatible with the polylactic acid interface due to its strong surface hydrophilicity. It is prone to interfacial slip or microcrack expansion under stress, resulting in a significant decrease in performance.

[0181] More importantly, the surface modification strategy employed in this invention does not rely on the introduction of polymer compatibilizers or chemical crosslinking systems. Instead, it achieves the integration and uniform dispersion of the reinforcing phase by constructing a physically stable interface. This approach enables the nanoreinforcement phase to more effectively participate in the mechanical response process without altering the matrix polymer structure, providing an engineering approach to optimize composite structural performance at the interface level. In practical applications, this interface configuration will provide a more ductile and resilient foundational structure for degradable polymer composites.

[0182] Test Example 3: Adaptability test of component ratio of composite materials

[0183] 1. Experimental Purpose

[0184] The adaptability of the composite material during processing is explored when the TiO2 addition exceeds the recommended upper limit (>10wt%), and the influence of the component ratio on the fluidity and molding feasibility of the blending process is verified.

[0185] 2. Experimental Samples

[0186] Sample A (Example 1): modified TiO2 content is 5wt%;

[0187] Sample B (Comparative Example 2): modified TiO2 content is 12 wt%;

[0188] The injection molding particles were all prepared by a twin-screw extruder, and the extrusion temperature was set at 170-200 °C, with the other parameters being the same.

[0189] 3. Experimental steps

[0190] Observation of the co-extrusion process

[0191] Each group of sample particles was fed into a twin-screw extruder;

[0192] Observe the extrusion process:

[0193] Discharge continuity (whether the flow is interrupted);

[0194] Is the die head blocked?

[0195] Is there melt fluctuation or particle reflux?

[0196] Record the total extrusion time of 100g material and whether it is interrupted under the same conditions.

[0197] Injection Molding Operations

[0198] Use a standard injection mold to process the test bars, setting uniform temperature and pressure;

[0199] Record for each group of samples whether:

[0200] Feed jam;

[0201] Injection mold dissatisfaction caused by insufficient fluidity;

[0202] The surface of the finished strip is rough and contains white spots or impurities.

[0203] Molding productivity record

[0204] For each batch of 50 test specimens, the actual number of successful moldings was counted;

[0205] Calculate the injection molding scrap rate (based on incomplete molding, edge damage, and demolding residue as the judgment criteria).

[0206] Table 3 Comparison of processing adaptability of TiO2 composite materials with different proportions:

[0207] project Sample A (5 wt%) Sample B (12 wt%) 100g material extrusion time (s) 172 223 Discharging status Continuous and stable Fluctuations, interruptions Die head blockage none There is slight accumulation Injection failure times ( / 50) 1 11 Demolding integrity whole Many pieces have gaps Surface roughness and impurities none obvious Is the operation process interrupted? no Yes (requires brief downtime)

[0208] From the comparison of the apparent quality of Test Example 4, it can be seen that under the same components and molding conditions, the sample using the multi-stage temperature control blending process has a more uniform surface and fewer defects in the injection molded product, while the sample in which the temperature zone distribution setting was cancelled during the processing showed more surface unevenness and localized aggregation of fillers. The essence of this difference stems from the ability of thermal field control in the molten state to synergistically regulate the particle dispersion behavior and the rheological state of the polymer. The step-by-step heating achieved through multi-stage temperature control can provide a more sufficient thermal driving force for the deagglomeration and dynamic dispersion of nano-TiO2 particles, thereby facilitating the formation of a more stable structural system.

[0209] The evolution of the molten state of the composite system during heating depends not only on the rheological behavior of the polylactic acid itself, but is also significantly affected by the surface state of the filler and the interfacial environment. Under single temperature control, the entire system heats up rapidly, which may cause the particles to enter the high-viscosity phase before they are fully dispersed. This can cause some particles to form small agglomerates in a short period of time, posing the risk of surface roughness or impurities. However, a segmented temperature control strategy can allow the filler to undergo a gradual thermal adaptation process. Combined with the effect of the shear field, the particles are slowly released from the matrix and distributed throughout the entire system, thereby achieving a synergistic unity of appearance consistency and internal structural uniformity.

[0210] In addition, this multi-stage temperature control method has strong adaptability in processing engineering. It not only improves the uniformity of heat treatment, but also strengthens the compensation for the spatial stability of particles in dynamic flow. The layered distribution of the thermal field structure essentially creates diffusion conditions within the "temperature window" for the nanofiller, making it easier to embed it in the matrix network. The stability of the apparent quality reflects the continuity of structural control from the interface to the whole. This performance output optimization brought about by the processing path is an important part of the material-process collaborative design in the technical thinking of the present invention.

[0211] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A nano titanium dioxide and polylactic acid composite material, characterized in that: It includes the following components by mass percentage: Polylactic acid 90% to 99%; Modified nano titanium dioxide 1% to 10%; The nano titanium dioxide is modified by a silane coupling agent, and the silane coupling agent is gamma-aminopropyltriethoxysilane, and the addition amount thereof is 0.5% to 2.0% of the mass of the nano titanium dioxide.

2. The nano-titanium dioxide and polylactic acid composite material according to claim 1, characterized in that: The average particle size of the modified nano titanium dioxide is 10 to 50 nanometers.

3. The nano-titanium dioxide and polylactic acid composite material according to claim 1, characterized in that: The weight average molecular weight of the polylactic acid is 50,000 to 100,000 g / mol.

4. The nano-titanium dioxide and polylactic acid composite material according to claim 1, characterized in that: The modified nano titanium dioxide and polylactic acid are blended in a molten state and prepared by using a twin-screw extruder with an extrusion temperature of 160-210° C. and a screw speed of 30-80 rpm.

5. A method for preparing a nano-titanium dioxide and polylactic acid composite material, for use in a nano-titanium dioxide and polylactic acid composite material and its preparation method according to any one of claims 1 to 4, characterized in that: The steps include: S1: dispersing nano-titanium dioxide in an ethanol-water mixture, adding a silane coupling agent, reacting at a temperature of 50-80°C for 1-3 hours to obtain modified nano-titanium dioxide; S2: drying the polylactic acid at 60-80° C. for 6-12 hours; S3: dry-mixing the modified nano-titanium dioxide and the dried polylactic acid in a mass ratio of 1% to 10%: 90% to 99%, and stirring for 5 to 15 minutes; S4: melt-blending the mixture through a twin-screw extruder at a temperature of 160 to 210° C. and a screw speed of 30 to 80 rpm, extruding, cooling, and then pelletizing to obtain a composite material.

6. The nano-titanium dioxide and polylactic acid composite material and the preparation method thereof according to claim 5, characterized in that: The volume ratio of the ethanol to water is 95:

5.

7. The nano-titanium dioxide and polylactic acid composite material and the preparation method thereof according to claim 5, characterized in that: The modified nano-titanium dioxide is dried in vacuum at 60-80° C. for 12-24 hours before use.

8. The nano-titanium dioxide and polylactic acid composite material and the preparation method thereof according to claim 5, characterized in that: The blended composite material is further processed into a molded product by injection molding, with the injection molding temperature being 180-200° C. and the injection pressure being 40-80 MPa.

9. The nano-titanium dioxide and polylactic acid composite material and the preparation method thereof according to claim 5, characterized in that: The average particle size of the nano titanium dioxide is 10 to 50 nanometers, and the molecular weight of the polylactic acid is 50,000 to 100,000 g / mol.

10. The nano-titanium dioxide and polylactic acid composite material and the preparation method thereof according to claim 5, characterized in that: The dry mixing step is carried out using a high-speed stirrer at a stirring speed of 500 to 1500 rpm.

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