Degradable heat-resistant composite material and preparation method thereof

Abstract

The application discloses a degradable heat-resistant composite material and a preparation method thereof, and relates to the technical field of degradable heat-resistant composite materials, and is composed of the following raw materials in proportion by weight: 70-80 parts of polylactic acid, 20-30 parts of polybutylene adipate terephthalate, 5-20 parts of modified titanium diboride filler, 0.5-3 parts of a compatilizer, 0.1-0.5 parts of an antioxidant, and 0.2-1 parts of a lubricant; wherein the modified titanium diboride filler is obtained by grafting polycaprolactone with a side chain containing a biphenyl group onto the surface of titanium diboride through diisocyanate. The polycaprolactone with the side chain containing the biphenyl group is chemically grafted onto the surface of titanium diboride, titanium diboride is used as a rigid physical crosslinking point to limit the thermal motion of molecular chains, and the heat resistance is improved; the biphenyl group constructs a low-thermal-resistance heat conduction channel through pi-pi stacking, and cooperates with titanium diboride to improve the heat conductivity of the composite material.

Description

Technical Field

[0001] This invention relates to the field of biodegradable heat-resistant composite materials, and particularly to biodegradable heat-resistant composite materials and their preparation methods. Background Technology

[0002] Polylactic acid (PLA), as a bio-based biodegradable material, possesses good biocompatibility and high tensile strength. However, its slow crystallization rate and low crystallinity result in poor heat resistance, severely limiting its application in high-temperature environments. Furthermore, PLA's hard and brittle texture and low elongation at break further restrict its engineering applications.

[0003] The common method to improve the brittleness of polylactic acid (PLA) is to toughen it by blending it with flexible biodegradable polymers. Polybutylene adipate terephthalate (PBDT) is one of the most widely used biodegradable polyesters for PLA toughening modification due to its excellent toughness and biodegradability. Blending PBDT with PLA can significantly improve PLA's brittleness; however, PBDT itself has poor heat resistance and cannot promote PLA's crystallization behavior. This results in a decrease in the heat resistance of PLA / PBDT composites compared to pure PLA, with a lower crystallization rate and degree, further weakening the material's heat resistance. To improve the heat resistance of PLA or PLA / PBDT composites, existing technologies typically employ methods such as adding nucleating agents, blending with high heat-resistant polymers, forming stereocomposite crystals, or adding inorganic fillers. However, the above methods have the following shortcomings: Although nucleating agents or high heat-resistant polymers can improve the crystallinity of polylactic acid and thus improve its heat resistance, the resulting material has poor thermal conductivity. When applied to electronic and electrical housings, automotive interior parts, or peripheral components of heat-generating devices, heat easily accumulates inside the material, leading to local overheating, accelerating thermal deformation, or even degradation and failure. Adding conventional inorganic fillers can improve heat resistance to some extent, but the filler has weak interfacial bonding with the matrix and is prone to agglomeration, resulting in a decrease in mechanical properties and failing to improve thermal conductivity simultaneously. Adding high thermal conductivity fillers can improve the thermal conductivity of composite materials, but these fillers have poor compatibility with the polylactic acid / polybutylene adipate terephthalate composite matrix, and severe agglomeration occurs at high addition levels, which in turn reduces heat resistance and mechanical properties. Summary of the Invention

[0004] The purpose of this invention is to provide a biodegradable heat-resistant composite material and its preparation method, so as to solve the technical problem that polylactic acid / polybutylene adipate terephthalate composite materials in the prior art are difficult to achieve a synergistic improvement in heat resistance and thermal conductivity at the same time.

[0005] The technical problem to be solved by this invention can be achieved through the following technical solution: The biodegradable heat-resistant composite material, by weight, is composed of the following raw materials: 70-80 parts polylactic acid, 20-30 parts polybutylene adipate terephthalate, 5-20 parts modified titanium diboride filler, 0.5-3 parts compatibilizer, 0.1-0.5 parts antioxidant, and 0.2-1 parts lubricant; The modified titanium diboride filler has polycaprolactone containing biphenyl groups grafted onto its surface.

[0006] Preferably, the antioxidant includes at least one of antioxidant 1010, antioxidant 1076, and antioxidant 168.

[0007] Preferably, the lubricant includes at least one of stearic acid, calcium stearate, zinc stearate, ethylene bis-stearamide, polyethylene wax, and pentaerythritol stearate.

[0008] Preferably, the compatibilizer includes at least one of polyethylene glycol, polylactic acid-polycaprolactone block copolymer, polylactic acid-polyethylene glycol block copolymer, and ethylene-methyl acrylate-glycidyl methacrylate copolymer.

[0009] By employing the above technical solution, this invention generates active hydroxyl groups on the surface of titanium diboride through high-temperature heat treatment, and then uses diisocyanate as a bridging agent to chemically graft polycaprolactone containing biphenyl groups on the surface of titanium diboride. Titanium diboride itself has extremely high hardness and excellent intrinsic thermal conductivity, and can act as a rigid physical crosslinking point in the polymer matrix, restricting the thermal movement of molecular chains, thereby increasing the heat distortion temperature and Vicat softening temperature of the material. Polycaprolactone is a semi-crystalline aliphatic polyester with good compatibility with both polylactic acid and polybutylene adipate terephthalate. During melt blending, the grafted polycaprolactone segments entangle with the matrix molecular chains, forming a strong interfacial bond, effectively preventing filler agglomeration. At the same time, the flexible segments can absorb impact energy and improve the toughness of the composite material. The biphenyl group possesses a large π-conjugated structure, and the biphenyl groups on adjacent polycaprolactone segments can form an ordered arrangement through π-π stacking, significantly reducing the interfacial thermal resistance between the filler and the matrix. This, combined with the high intrinsic thermal conductivity of titanium diboride, greatly improves the overall thermal conductivity of the composite material. Furthermore, the rigid structure of the biphenyl group can provide additional nucleation sites, promoting the crystallization of polylactic acid and further enhancing its heat resistance.

[0010] By employing the above technical solution, this invention further reduces interfacial tension and promotes filler dispersion through compatibilizers, and synergistically enhances interfacial bonding with polycaprolactone grafted segments. Antioxidants and lubricants ensure processing stability and molding efficiency without affecting the core's heat resistance, thermal conductivity, and mechanical properties.

[0011] Preferably, the modified titanium diboride filler comprises the following raw materials in parts by weight: 80-100 parts of titanium diboride, 15-30 parts of diisocyanate, 50-70 parts of polycaprolactone with biphenyl groups in the side chain, and 0.5-2 parts of catalyst.

[0012] Preferably, the diisocyanate includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, and lysine diisocyanate.

[0013] Preferably, the catalyst includes at least one of dibutyltin dilaurate, stannous octoate, and triethylamine.

[0014] Preferably, the polycaprolactone containing biphenyl groups in the side chain is prepared by esterification reaction of 4-hydroxybiphenyl with polycaprolactone containing carboxyl groups in the side chain.

[0015] By adopting the above technical solution, the present invention dissolves polycaprolactone with carboxyl groups in anhydrous dichloromethane, adds 4-hydroxybiphenyl, dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and stirs the mixture at room temperature under an inert atmosphere for 12-24 hours. After the reaction is completed, the mixture is filtered, and the filtrate is washed successively with dilute hydrochloric acid, saturated sodium bicarbonate solution and deionized water. The organic phase is dried and concentrated, precipitated with cold methanol, filtered, and dried under vacuum to obtain polycaprolactone with biphenyl groups in the side chain.

[0016] Preferably, the preparation method of modified titanium diboride filler includes the following steps: S1. Titanium diboride is dispersed in a 20%–30% H2O2 aqueous solution and stirred at 60–70°C for 3–4 hours. After filtration, washing, and drying, activated titanium diboride is obtained. S2. Activated titanium diboride is dispersed in an anhydrous organic solvent, diisocyanate and catalyst are added, and the reaction is carried out at 40-80℃ for 1-4 hours. Pretreated titanium diboride is then separated. S3. Disperse titanium diboride with isocyanate groups on its surface in an anhydrous organic solvent, add polycaprolactone with biphenyl groups on its side chain and a catalyst, react at 60-100℃ for 2-6 hours, separate, wash and dry to obtain modified titanium diboride filler.

[0017] Preferably, the anhydrous organic solvent includes at least one of anhydrous toluene, anhydrous dichloromethane, anhydrous tetrahydrofuran, and anhydrous acetone.

[0018] By adopting the above technical solution, this invention introduces flexible polycaprolactone segments and rigid biphenyl groups on the surface of titanium diboride. When subsequently melt-blended with polylactic acid / polybutylene adipate terephthalate matrix, the polycaprolactone segments can entangle with the matrix molecular chains, improving filler dispersibility and interfacial bonding. The biphenyl groups construct low thermal resistance thermally conductive channels through π-π stacking. The rigid core of titanium diboride serves as a physical crosslinking point, restricting the thermal movement of molecular chains, thereby improving the heat resistance, thermal conductivity, and mechanical properties of the composite material.

[0019] A method for preparing biodegradable heat-resistant composite materials includes the following steps: S11. Dry polylactic acid and polybutylene adipate-terephthalate at 60-90°C for 4-8 hours respectively; S12. Add the dried polylactic acid, polybutylene adipate terephthalate, modified titanium diboride filler, compatibilizer, antioxidant, and lubricant to a high-speed mixer and mix for 3-10 minutes to obtain a premix. S13. Add the premixed material to a twin-screw extruder, melt-blend at a temperature of 170-200℃, and extrude and granulate at a screw speed of 50-150 rpm to obtain granules.

[0020] The beneficial effects of this invention are: 1. This invention generates active hydroxyl groups on the surface of titanium diboride through high-temperature heat treatment, and then uses diisocyanate as a bridging agent to chemically graft polycaprolactone with biphenyl groups in its side chains onto the surface of titanium diboride. Titanium diboride acts as a rigid physical crosslinking point to restrict the thermal motion of molecular chains and improve heat resistance; the flexible chains of polycaprolactone improve interfacial compatibility and absorb impact energy, enhancing toughness; the biphenyl groups construct low thermal resistance thermal conduction channels through π-π stacking, which, in conjunction with the intrinsic high thermal conductivity of titanium diboride, significantly improves the thermal conductivity. At the same time, the biphenyl groups can also act as nucleating agents to promote polylactic acid crystallization, further improving heat resistance.

[0021] 2. The flexible polycaprolactone segments grafted in this invention have good interfacial compatibility with the polylactic acid / polybutylene adipate terephthalate matrix, which not only ensures the reinforcing effect of the rigid titanium diboride skeleton, but also absorbs impact energy through the flexible interface layer, thus solving the defect of material brittleness after filling with traditional inorganic fillers.

[0022] 3. The matrix polylactic acid and polybutylene adipate terephthalate used in this invention are both bio-based biodegradable polyesters, and the grafted polycaprolactone is also biodegradable. The overall composite material still has excellent biodegradability, which meets the requirements of green environmental protection and sustainable development. Detailed Implementation

[0023] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0024] Preparation Example Preparation Example 1: A method for preparing a modified titanium diboride filler, comprising the following steps: S1. Disperse 100g of titanium diboride powder in a 30% H2O2 aqueous solution, stir and react at 70℃ for 4h, filter, wash and dry to obtain activated titanium diboride.

[0025] S2. Under nitrogen protection, the activated titanium diboride was dispersed in 500 mL of anhydrous toluene, and 25 g of diisocyanate and 1.2 g of dibutyltin dilaurate were added. The mixture was stirred and reacted for 2.5 hours. After the reaction was completed, the mixture was centrifuged and washed three times with anhydrous toluene to obtain pretreated titanium diboride.

[0026] S3. Dissolve 10.0 g of carboxylated polycaprolactone (molecular weight 5000) in 50 mL of anhydrous dichloromethane, add 0.67 g of 4-hydroxybiphenyl, 0.82 g of dicyclohexylcarbodiimide, and 0.04 g of 4-dimethylaminopyridine, and stir at room temperature for 24 hours under nitrogen protection. Filter, wash the filtrate successively with dilute hydrochloric acid, saturated sodium bicarbonate solution, and deionized water, dry, concentrate, precipitate with cold methanol, filter, and vacuum dry to obtain polycaprolactone with biphenyl groups in the side chain.

[0027] S4. Titanium diboride with isocyanate groups on its surface was redispersed in 500 mL of anhydrous toluene. 60 g of polycaprolactone with biphenyl side chains and 1.2 g of dibutyltin dilaurate were added. The mixture was heated to 80 °C and stirred for 4 hours. After the reaction, the mixture was centrifuged, washed three times each with anhydrous toluene and anhydrous ethanol, and dried under vacuum at 50 °C for 12 hours to obtain the modified titanium diboride filler.

[0028] Preparation Example 2 S1. Disperse 100g of titanium diboride powder in a 30% H2O2 aqueous solution, stir and react at 70℃ for 4h, filter, wash and dry to obtain activated titanium diboride.

[0029] S2. Under nitrogen protection, the activated titanium diboride was dispersed in 500 mL of anhydrous toluene, and 25 g of diisocyanate and 1.2 g of dibutyltin dilaurate were added. The mixture was stirred and reacted for 2.5 hours. After the reaction was completed, the mixture was centrifuged and washed three times with anhydrous toluene to obtain pretreated titanium diboride.

[0030] Titanium diboride with isocyanate groups on its surface was dispersed in 500 mL of anhydrous toluene, and 60 g of hydroxyl-terminated polycaprolactone (number average molecular weight approximately 3000 Da) and 1.2 g of dibutyltin dilaurate were added. The mixture was heated to 80 °C and stirred for 4 hours to obtain modified titanium diboride filler grafted with polycaprolactone.

[0031] Preparation Example 3: A method for preparing a modified talc filler The only difference between this preparation example and Preparation Example 1 is that titanium diboride is replaced with an equal amount of talc powder.

[0032] Preparation Example 4: A method for preparing a modified titanium diboride filler, comprising the following steps: S1. Disperse 100g of titanium diboride powder in a 30% H2O2 aqueous solution, stir and react at 70℃ for 4h, filter, wash and dry to obtain activated titanium diboride.

[0033] S2. Under nitrogen protection, the activated titanium diboride was dispersed in 500 mL of anhydrous toluene, and 30 g of diisocyanate and 2 g of dibutyltin dilaurate were added. The mixture was stirred and reacted for 5 hours. After the reaction was completed, the mixture was centrifuged and washed three times with anhydrous toluene to obtain pretreated titanium diboride.

[0034] S3. Dissolve 10.0 g of carboxylated polycaprolactone (molecular weight 5000) in 50 mL of anhydrous dichloromethane, add 0.67 g of 4-hydroxybiphenyl, 0.82 g of dicyclohexylcarbodiimide, and 0.04 g of 4-dimethylaminopyridine, and stir at room temperature for 24 hours under nitrogen protection. Filter, wash the filtrate successively with dilute hydrochloric acid, saturated sodium bicarbonate solution, and deionized water, dry, concentrate, precipitate with cold methanol, filter, and vacuum dry to obtain polycaprolactone with biphenyl groups in the side chain.

[0035] S4. Titanium diboride with isocyanate groups on its surface was redispersed in 500 mL of anhydrous toluene. 70 g of polycaprolactone with biphenyl side chains and 2 g of dibutyltin dilaurate were added. The mixture was heated to 90 °C and stirred for 8 hours. After the reaction was completed, the mixture was centrifuged and washed three times each with anhydrous toluene and anhydrous ethanol. It was then dried under vacuum at 50 °C for 12 hours to obtain the modified titanium diboride filler.

[0036] Preparation Example 5: A method for preparing a modified titanium diboride filler, comprising the following steps: S1. Disperse 100g of titanium diboride powder in a 30% H2O2 aqueous solution, stir and react at 70℃ for 4h, filter, wash and dry to obtain activated titanium diboride.

[0037] S2. Under nitrogen protection, the activated titanium diboride was dispersed in 500 mL of anhydrous toluene, and 15 g of diisocyanate and 0.5 g of dibutyltin dilaurate were added. The mixture was stirred and reacted for 1.5 hours. After the reaction was completed, the mixture was centrifuged and washed three times with anhydrous toluene to obtain pretreated titanium diboride.

[0038] S3. Dissolve 10.0 g of carboxylated polycaprolactone (molecular weight 5000) in 50 mL of anhydrous dichloromethane, add 0.67 g of 4-hydroxybiphenyl, 0.82 g of dicyclohexylcarbodiimide, and 0.04 g of 4-dimethylaminopyridine, and stir at room temperature for 24 hours under nitrogen protection. Filter, wash the filtrate successively with dilute hydrochloric acid, saturated sodium bicarbonate solution, and deionized water, dry, concentrate, precipitate with cold methanol, filter, and vacuum dry to obtain polycaprolactone with biphenyl groups in the side chain.

[0039] S4. Titanium diboride with isocyanate groups on its surface was redispersed in 500 mL of anhydrous toluene. 50 g of polycaprolactone with biphenyl side chains and 0.5 g of dibutyltin dilaurate were added. The mixture was heated to 70 °C and stirred for 2 hours. After the reaction was complete, the mixture was centrifuged and washed three times each with anhydrous toluene and anhydrous ethanol. The mixture was then vacuum dried at 50 °C for 12 hours to obtain the modified titanium diboride filler.

[0040] Example Example 1, a method for preparing a biodegradable heat-resistant composite material, includes the following steps: S11. Dry polylactic acid and polybutylene adipate at 80°C for 6 hours respectively. S12. Add 75 parts of dried polylactic acid, 25 parts of polybutylene adipate terephthalate, 12 parts of modified titanium diboride filler prepared in Preparation Example 1, 2 parts of compatibilizer, 0.3 parts of antioxidant, and 0.5 parts of lubricant to a high-speed mixer and mix for 5 minutes to obtain a premix. S13. Add the premixed material to a twin-screw extruder, melt-blend at 190°C, and extrude and granulate at a screw speed of 100 rpm to obtain granules.

[0041] Examples 2 to 7 describe the preparation methods of biodegradable heat-resistant composite materials. The only difference between these examples and Example 1 is the different component ratios in each example, as shown in Table 1.

[0042] Table 1. Group allocation ratio for each embodiment

[0043] Comparative Example Comparative Example 1 differs from Example 1 only in that an equal amount of unmodified titanium diboride is used to replace the modified titanium diboride filler prepared in Preparation Example 1.

[0044] Comparative Example 2 differs from Example 1 only in that, in step S12, 75 parts of dried polylactic acid, 25 parts of polybutylene adipate terephthalate, 12 parts of modified titanium diboride filler prepared in Preparation Example 2, 2 parts of compatibilizer, 0.3 parts of antioxidant, and 0.5 parts of lubricant are added to a high-speed mixer and mixed for 5 minutes to obtain a premix.

[0045] Comparative Example 3 differs from Example 1 only in that, in step S12, 75 parts of dried polylactic acid, 25 parts of polybutylene adipate terephthalate, 12 parts of modified talc filler prepared in Preparation Example 3, 2 parts of compatibilizer, 0.3 parts of antioxidant, and 0.5 parts of lubricant are added to a high-speed mixer and mixed for 5 minutes to obtain a premix.

[0046] Performance testing 1. Mechanical properties: (1) Tensile strength and elongation at break: tested according to GB / T 1040.1-2018. The film obtained by casting was cut into dumbbell-shaped specimens, tested with a universal testing machine, and the tensile strength and elongation at break were calculated. Each example and comparative example were tested 5 times using the same method, and the average value was taken.

[0047] (2) Bending strength: Tested according to GB / T 9341-2008. Each embodiment and comparative example was tested 5 times using the same method, and the average value was taken.

[0048] 2. Heat resistance: (1) Vicat softening temperature: Tested according to GB / T 1633-2000. Each example and comparative example were tested 5 times using the same method, and the average value was taken.

[0049] (2) Heat distortion temperature: Tested according to GB / T 1634.2-2019. Each embodiment and comparative example was tested 5 times using the same method, and the average value was taken.

[0050] 3. Thermophysical properties: Thermal conductivity: tested according to GB / T 10295-2008. Each embodiment and comparative example was tested 5 times using the same method, and the average value was taken.

[0051] The results of the above experiments are shown in Table 2: Table 2. Performance test results of the examples and comparative examples.

[0052] Combining Example 1 and Comparative Example 1, it can be seen that the Vicat softening temperature of Example 1 is 40°C higher than that of Comparative Example 1, the heat distortion temperature is 35°C higher, the thermal conductivity is 2.36 times that of Comparative Example 1, the tensile strength is increased by 41.3%, the flexural strength is increased by 40.4%, and the elongation at break is increased by 77.1%. The data results indicate that when titanium diboride is directly filled without any surface modification, all properties are at their lowest levels. This may be because the surface polarity of unmodified titanium diboride does not match the polarity of the polylactic acid / polybutylene adipate terephthalate matrix, resulting in poor dispersibility, forming numerous stress concentration points and thermally resistive interfaces. This prevents the rigid skeleton of titanium diboride from forming an effective connection with the matrix, causing the molecular chains to easily slip at high temperatures and resulting in poor heat resistance. Example 1 introduced polycaprolactone segments containing biphenyl groups through chemical grafting, which not only improved the compatibility between the filler and the matrix, but also constructed a rigid skeleton and a π-π thermally conductive network, thereby achieving a comprehensive improvement in heat resistance, thermal conductivity and mechanical properties.

[0053] Combining Example 1 and Comparative Example 2, it can be seen that the Vicat softening temperature of Example 1 is 23°C higher than that of Comparative Example 2, the heat distortion temperature is 22°C higher, the thermal conductivity is 1.36 times that of Comparative Example 2, the tensile strength is increased by 15.3%, the flexural strength is increased by 15.1%, and the elongation at break is increased by 34.8%. The data results indicate that when only polycaprolactone is grafted without biphenyl groups, the improvement in heat resistance and thermal conductivity is limited, and the strength improvement is small. This may be because grafting polycaprolactone segments can improve the interfacial compatibility between titanium diboride and the matrix, reduce agglomeration, and improve mechanical properties to some extent. However, due to the lack of a large π-conjugated structure with biphenyl groups, it is impossible to form intermolecular π-π stacking, and the thermal conductivity only increases from 0.22 to 0.32. At the same time, the flexible polycaprolactone layer without biphenyl cannot provide additional rigid support, has a weak inducing effect on matrix crystallization, and the improvement in heat resistance is limited. In Example 1, after the introduction of biphenyl groups, the π-π stacking of benzene rings forms a low thermal resistance network, and the rigid blocks of biphenyl can act as heterogeneous nucleating agents to improve the crystallinity of polylactic acid, thereby synergistically improving thermal conductivity and heat resistance.

[0054] Combining Example 1 and Comparative Example 3, it can be seen that the Vicat softening temperature of Example 1 is 29°C higher than that of Comparative Example 3, the heat distortion temperature is 26°C higher, the thermal conductivity is 1.86 times that of Comparative Example 3, the tensile strength is increased by 21.5%, the flexural strength is increased by 24.2%, and the elongation at break is increased by 19.2%. The data results indicate that even using the same modification process as Example 1, the performance improvement of the talc-filled system is still far less than that of the modified titanium diboride system. This may be because talc has a low intrinsic thermal conductivity, while titanium diboride has a high intrinsic thermal conductivity, making it impossible to change the upper limit of the filler's own thermal conductivity. Therefore, the difference in thermal conductivity cannot be bridged by surface modification. Talc has a layered silicate structure with limited surface active sites and low chemical grafting density, resulting in a thin and discontinuous interface layer, leading to low interface heat transfer and stress transfer efficiency. Furthermore, talc has a plate-like structure and tends to be arranged in parallel orientation in the matrix, making it difficult to form continuous three-dimensional thermal conduction pathways. The π-π stacking effect of the phenyl groups can form a through-thermal conductive pathway between titanium diboride particles. This mechanism depends on the surface chemical properties of titanium diboride. A similar π-π stacking effect cannot be achieved on the surface of talc.

[0055] Based on Examples 1-3, Example 2 exhibits the highest Vicat softening temperature and heat distortion temperature, as well as the highest tensile strength and flexural strength, but its elongation at break is moderate. Example 3 has the highest elongation at break, but its Vicat softening temperature, heat distortion temperature, tensile strength, and flexural strength are all the lowest. Example 1 falls between the two in terms of properties, with a Vicat softening temperature of 105℃, a heat distortion temperature of 90℃, a thermal conductivity of 0.52 W / (m·K), a tensile strength of 56.5 MPa, a flexural strength of 70.2 MPa, and an elongation at break of 62%, demonstrating the best overall balance. The data results indicate that as the proportion of polylactic acid in the matrix increases, the heat resistance and strength of the composite material gradually increase, but the toughness first increases and then decreases. The reason for this may be that polylactic acid (PLA) itself has high crystallinity and rigidity, which can synergistically form a denser physical cross-linking network with the rigid skeleton of modified titanium diboride, restricting the thermal motion of molecular chains and thus improving heat resistance and strength. Meanwhile, the flexible segments of polybutylene adipate terephthalate (PEG) impart better plastic deformation ability to the material, increasing elongation at break. When the proportion of PLA is too high, rigidity dominates in the continuous phase, making molecular chain slippage difficult and slightly reducing toughness. When the proportion of PLA is too low, there is too much flexible phase, diluting the reinforcing effect of the rigid skeleton and reducing heat resistance and strength.

[0056] Based on Examples 1, 4, and 5, Example 4 exhibits the highest Vicat softening temperature, heat distortion temperature, thermal conductivity, tensile strength, and flexural strength, but the lowest elongation at break. Example 5 shows the highest elongation at break, but the lowest heat resistance and strength. The properties of the other examples fall between these two, with an elongation at break close to that of Example 5, while its heat resistance and strength are significantly higher, and it also demonstrates better toughness than Example 4. The data results indicate that with increasing amounts of modified titanium diboride filler, the heat resistance, thermal conductivity, and strength of the composite material gradually increase, but the elongation at break gradually decreases. This may be because the polycaprolactone segments on the surface of the modified titanium diboride filler form a good interfacial bond with the matrix, and the π-π stacking of the biphenyl groups constructs thermally conductive channels. Simultaneously, the rigid core of titanium diboride forms a three-dimensional physical network within the matrix. When the filler content is low, the rigid network is discontinuous, resulting in limited reinforcement, but the movement of the matrix molecular chains is less restricted, and the toughness remains high. When the filler content is increased to a moderate level, the heat resistance and strength are significantly improved, while the flexible polycaprolactone layer can still provide a certain plastic deformation capacity, and the decrease in toughness is not obvious. When the filler content continues to increase to a high level, the rigid network becomes too dense, the distance between titanium diboride particles decreases, and the matrix molecular chains are excessively bound. Although the heat resistance and strength reach their peak, the plastic deformation capacity is significantly reduced, and the elongation at break decreases.

[0057] Combining Examples 1 and 6, it can be seen that the Vicat softening temperature of Example 1 is 11°C higher than that of Example 6, the heat distortion temperature is 8°C higher, the thermal conductivity is slightly higher than that of Example 6, the tensile strength is increased by 4.6%, the flexural strength is increased by 4.8%, and the elongation at break is increased by 40.9% compared with Example 6. The data results show that when grafting is excessive, although the thermal conductivity and heat resistance are still better than the unmodified and biphenyl-free samples, the overall performance is not as good as that of Example 1, especially the elongation at break is significantly reduced. The reason may be that excessive grafting results in an excessively thick polycaprolactone layer coating on the surface of titanium diboride. Although the biphenyl groups are still present, the excessively thick polymer layer itself has a large thermal resistance, which partially blocks the heat transfer to the rigid core of titanium diboride, causing the thermal conductivity to drop from 0.52 to 0.48. At the same time, the excessively thick flexible layer dilutes the rigid skeleton effect of titanium diboride. When heated, the polymer layer softens first, and the rigid support effect is weakened, resulting in a decrease in Vicat and heat distortion temperatures. Mechanically, the excessively thick coating layer is prone to plastic flow during stretching, which actually reduces the elongation at break.

[0058] Combining Examples 1 and 7, it can be seen that the Vicat softening temperature and heat distortion temperature of Example 1 are 25°C higher than those of Example 7, the thermal conductivity is 1.44 times that of Example 7, the tensile strength is increased by 18.9%, the flexural strength by 21.0%, and the elongation at break is increased by 63.2%. The data results indicate that when grafting is insufficient, although the performance is improved, it is far inferior to that of Example 1. This may be because when the grafting rate is too low, the surface of titanium diboride only has sparse polycaprolactone segments, which cannot form a complete and dense coating layer. Some filler surfaces remain exposed, and the exposed areas are in direct contact with the matrix, interface defects still exist, and filler agglomeration is not completely eliminated. At this time, although chemical grafting has occurred, the grafting density is insufficient to construct a continuous π-π stacking network, the thermal conduction channels are incomplete, and the synergistic effect of the biphenyl groups cannot be fully utilized. Simultaneously, the incomplete coating layer has limited improvement on stress transfer, and the mechanical properties are only slightly improved compared to the unmodified version.

[0059] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A biodegradable heat-resistant composite material, characterized in that, By weight, it is composed of the following raw materials: 70-80 parts polylactic acid, 20-30 parts polybutylene adipate terephthalate, 5-20 parts modified titanium diboride filler, 0.5-3 parts compatibilizer, 0.1-0.5 parts antioxidant, and 0.2-1 parts lubricant; The modified titanium diboride filler has polycaprolactone containing biphenyl groups grafted onto its surface.

2. The biodegradable heat-resistant composite material according to claim 1, characterized in that, The modified titanium diboride filler comprises the following raw materials in parts by weight: 80-100 parts titanium diboride, 15-30 parts diisocyanate, 50-70 parts polycaprolactone with biphenyl groups in the side chain, and 0.5-2 parts catalyst.

3. The biodegradable heat-resistant composite material according to claim 2, characterized in that, The polycaprolactone containing biphenyl groups in its side chain is prepared by esterification of 4-hydroxybiphenyl with polycaprolactone containing carboxyl groups in its side chain.

4. The biodegradable heat-resistant composite material according to claim 2, characterized in that, The diisocyanate includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, and lysine diisocyanate.

5. The biodegradable heat-resistant composite material according to claim 2, characterized in that, The catalyst includes at least one of dibutyltin dilaurate, stannous octoate, and triethylamine.

6. The biodegradable heat-resistant composite material according to claim 2, characterized in that, The preparation method of the modified titanium diboride filler includes the following steps: S1. Disperse titanium diboride powder in a 20%–30% H2O2 aqueous solution, stir and react at 60–70°C for 3–4 hours, filter, wash and dry to obtain activated titanium diboride; S2. Activated titanium diboride is dispersed in an anhydrous organic solvent, diisocyanate and catalyst are added, and the reaction is carried out at 40-80℃ for 1-4 hours. Pretreated titanium diboride is then separated. S3. Disperse the pretreated titanium diboride in an anhydrous organic solvent, add polycaprolactone with biphenyl side chains and a catalyst, react at 60-100℃ for 2-6 hours, separate, wash and dry to obtain the modified titanium diboride filler.

7. The biodegradable heat-resistant composite material according to claim 6, characterized in that, The anhydrous organic solvent includes at least one of anhydrous toluene, anhydrous dichloromethane, anhydrous tetrahydrofuran, and anhydrous acetone.

8. The biodegradable heat-resistant composite material according to claim 1, characterized in that, The lubricant includes at least one of stearic acid, calcium stearate, zinc stearate, ethylene bis-stearamide, polyethylene wax, and pentaerythritol stearate.

9. The biodegradable heat-resistant composite material according to claim 1, characterized in that, The compatibilizer includes at least one of polyethylene glycol, polylactic acid-polycaprolactone block copolymer, polylactic acid-polyethylene glycol block copolymer, and ethylene-methyl acrylate-glycidyl methacrylate copolymer.

10. A method for preparing a biodegradable heat-resistant composite material, used to prepare the biodegradable heat-resistant composite material according to any one of claims 1-9, characterized in that, Includes the following steps: S11. Dry polylactic acid and polybutylene adipate-terephthalate at 60-90°C for 4-8 hours respectively; S12. Add the dried polylactic acid, polybutylene adipate terephthalate, modified titanium diboride filler, compatibilizer, antioxidant, and lubricant to a high-speed mixer and mix for 3-10 minutes to obtain a premix. S13. Add the premixed material to a twin-screw extruder, melt-blend at a temperature of 170-200℃, and extrude and granulate at a screw speed of 50-150 rpm to obtain granules.

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