Fiber reinforced polylactic acid composite material, and preparation method and application thereof

Abstract

The application discloses a kind of fiber reinforced polylactic acid composite material and its preparation method and application, it is related to fiber material technical field.The composite material is made of polylactic acid matrix 50-90 parts, polymer fiber 5-40 parts, plasticizer 1-10 parts, coupling agent 0.5-5 parts, stabilizer 0.5-5 parts are composed, wherein stabilizer is realized molecular level anti-aging protection by deuterium group and heterocyclic structure, and polymer fiber is treated by alkali solution and enhanced interface bonding.The material has excellent toughness and weather resistance, and can be widely used in biodegradable medical implant devices, high weather resistance packaging materials and environmental protection daily necessities field.

Description

Technical Field

[0001] This invention relates to the field of fiber materials technology, specifically to a fiber-reinforced polylactic acid composite material, its preparation method, and its application. Background Technology

[0002] Polylactic acid (PLA), as a novel biodegradable material, has attracted much attention and its applications are gradually increasing in many fields such as packaging, fiber, and biomedicine due to its good biocompatibility, mechanical properties, and renewability. However, in practical applications, PLA materials still face some bottlenecks that need to be addressed, particularly in terms of aging and toughness.

[0003] On the one hand, polylactic acid (PLA) materials suffer from aging issues. Under conditions such as sunlight, high temperatures, or prolonged use, the ester bonds in the PLA molecular chain are prone to hydrolysis or oxidation, leading to a decrease in molecular weight and consequently a significant decline in mechanical properties and transparency. For example, in outdoor packaging materials, PLA products, due to prolonged exposure to sunlight and air, exhibit aging phenomena such as brittleness and discoloration, shortening the material's lifespan and limiting its promotion in some long-term application areas.

[0004] On the other hand, insufficient toughness is also a major drawback of polylactic acid (PLA) materials. Pure PLA is relatively brittle and hard, with relatively high tensile strength and elastic modulus, but low elongation at break. It is prone to brittle fracture when subjected to impact or significant external forces. This limits the use of PLA in applications requiring high impact resistance, such as automotive parts and medical devices, and prevents it from meeting practical needs.

[0005] To address these issues, the industry has undertaken numerous attempts. For instance, some studies have improved the aging performance of polylactic acid (PLA) by adding antioxidants and light stabilizers, which to some extent slows down the degradation rate. However, these additives often exhibit migration problems and may have potential impacts on environmental and biosafety. In terms of improving toughness, methods such as adding plasticizers and blending with other polymers have been employed. While these methods can increase elongation at break to some extent, they may lead to a decrease in the material's mechanical strength and thermal stability, making it difficult to achieve a comprehensive performance balance and fundamentally meet the diverse needs of practical applications. Therefore, developing a new material and preparation method that can effectively solve the problems of PLA aging and insufficient toughness has become an urgent technical challenge. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the prior art by providing a fiber-reinforced polylactic acid composite material with excellent aging performance and toughness, as well as its preparation method and application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a fiber-reinforced polylactic acid composite material, comprising the following components and mass ratios: 50-90 parts of polylactic acid matrix, 5-40 parts of polymer fiber, 1-10 parts of plasticizer, 0.5-5 parts of coupling agent, and 0.5-5 parts of stabilizer;

[0008] The polymer fiber is selected from any one of polybutylene terephthalate, polyethylene terephthalate, and polybutylene succinate, and has a length of 0.1-5 mm.

[0009] The stabilizer has the structure shown in Formula 1:

[0010]

[0011] Z1 is selected from: O, S, N(R1), C(CH3)2;

[0012] The D represents deuterium;

[0013] The R1 is selected from: H, methyl, phenyl, deuterated methyl, deuterated phenyl, deuterated tert-butyl.

[0014] Furthermore, the stabilizer is selected from any one of the compounds shown in the following structures:

[0015]

[0016] Furthermore, the method for synthesizing the stabilizer is as follows:

[0017]

[0018] Step 1: Raw material 1 and raw material 2 are synthesized into intermediate 1 via the Suzuki reaction;

[0019] Step 2: Intermediate 1 and raw material 3 are synthesized through a substitution reaction to obtain intermediate 2;

[0020] Step 3: Intermediate 2 is synthesized by hydroxylation reaction to obtain intermediate 3;

[0021] Step 4: The stabilizer is synthesized by reacting intermediate 3 and raw material 4 with Williamson synthesis.

[0022] Furthermore, the plasticizer is one or more of glycerol, citrate, or polyethylene glycol.

[0023] Furthermore, the coupling agent is a silane coupling agent.

[0024] Furthermore, the silane coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and methacryloyloxypropyltrimethoxysilane.

[0025] Furthermore, the polylactic acid matrix is ​​a blend of polylactic acid and polycaprolactone, wherein the mass ratio of polylactic acid to polycaprolactone is 5 parts: 1 part.

[0026] A method for preparing a fiber-reinforced polylactic acid composite material includes the following steps:

[0027] S1. The polymer fiber is immersed in an alkaline solution with a concentration of 2-10% for 10-60 minutes, washed and dried to obtain the treated polymer fiber;

[0028] S2. The treated polymer fiber is melt-blended with the polylactic acid matrix, plasticizer, coupling agent and stabilizer at 160-200°C for 5-30 minutes to obtain a blend.

[0029] S3. The blend is cooled to room temperature by air cooling to obtain a fiber-reinforced polylactic acid composite material.

[0030] Furthermore, the alkaline solution is an aqueous solution of sodium hydroxide or potassium hydroxide, and the treatment temperature is 40-80℃.

[0031] Furthermore, the melt blending process is carried out in a twin-screw extruder with a screw speed of 50-200 rpm.

[0032] Furthermore, the air velocity of the air cooling system is 5 m / s, and the air cooling temperature is 5 °C.

[0033] An application of a fiber-reinforced polylactic acid composite material for the preparation of biodegradable medical implant materials, packaging materials, or daily necessities; said medical implant materials include bone fixation devices or absorbable sutures.

[0034] The stabilizer described in this invention functions as a hindered amine light stabilizer, blocking free radical chain reactions and delaying material aging by capturing free radicals generated during polylactic acid (PLA) degradation. Sulfur (S) or oxygen (O) heteroatoms may chelate metal ions through coordination, inhibiting metal-catalyzed oxidation reactions. The deuterated groups (D-substituted H) in the molecule utilize the stronger bond energy of the CD bond compared to the CH bond (isotope effect) to significantly slow down the hydrolysis rate of PLA under humid and hot conditions, while simultaneously inhibiting light / heat-induced dehydrogenation reactions, thereby improving the material's thermal stability and weather resistance. Branched structures such as C(CH3)2 provide steric hindrance, preventing small molecules such as oxygen and moisture from penetrating into the PLA matrix, reducing the surface erosion rate.

[0035] The polylactic acid (PLA) and polycaprolactone (PCL) blend described in this invention improve the brittleness of PLA, while the flexibility of PCL complements the rigidity of the fibers. The polymer fibers (0.1-5 mm) undergo alkali treatment (step S1) to enhance surface roughness. Combined with the chemical bonding effect of silane coupling agents (such as KH550), this strengthens the interfacial bonding between the fibers and the matrix, preventing crack propagation caused by stress concentration. Plasticizers such as glycerol / citric acid esters lower the glass transition temperature (Tg) by intercalating between PLA molecular chains, improving material toughness, but may accelerate chain segment movement, leading to decreased thermal stability. Stabilizers counteract the negative impact of plasticizers on stability by inhibiting thermo-oxidative degradation and deuteration protection, achieving a balance between toughness and aging resistance. The high shear force (50-200 rpm) of the twin-screw extruder promotes uniform fiber dispersion in the matrix, while the stabilizer effectively migrates to the interfacial region at the melt blending temperature (160-200℃), forming a protective layer.

[0036] The superior aging performance relies on a multi-level synergistic protection system from the molecular to the macroscopic level. At the molecular level, the deuterated groups of the stabilizer significantly slow down the hydrolysis rate of polylactic acid (PLA) under humid and hot conditions through the isotope effect (CD bond energy is higher than CH bond energy). Its nitrogen-containing / sulfur heterocyclic structure can efficiently capture free radicals generated during photothermal oxidation, blocking the chain degradation reaction. At the same time, the silane coupling agent forms a dense hydrophobic layer at the fiber-matrix interface, effectively blocking the penetration of water molecules. In terms of thermal stability, the stabilizer inhibits the breakage of PLA molecular chains during high-temperature processing through steric hindrance, maintaining the initial molecular weight of the material and avoiding the degradation of mechanical properties caused by thermal degradation.

[0037] The high toughness is achieved through a cross-scale synergistic mechanism of plasticization and reinforcement. Plasticizers such as glycerol are inserted into the interstices of polylactic acid molecular chains, lowering the glass transition temperature and giving the matrix higher chain mobility. The island structure formed by polycaprolactone (PCL) and PLA induces a craze-shear band energy dissipation mechanism under stress, thereby increasing the elongation at break. Nanoscale pits are formed on the surface of 0.1-5 mm short-cut fibers after alkali etching, and the chemical bonding with the silane coupling agent improves the interfacial bonding strength.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] 1. Significant synergistic enhancement effect: Through the synergistic effect of stabilizers, polymer fibers and plasticizing system, the material maintains high toughness while simultaneously improving anti-aging performance, breaking through the bottleneck of traditional technology where toughness and weather resistance are difficult to balance.

[0040] 2. Outstanding long-term stability: Based on the design of stabilizers with deuterated groups and polycyclic heterocyclic structures, a molecular-level protective network is formed, which effectively inhibits hydrolysis and photothermal oxidation under humid and hot environments, and significantly delays the trend of material performance degradation.

[0041] 3. Process adaptability optimization: The combination of alkali-treated fibers and controllable melt blending process strengthens the fiber-matrix interface bonding force, avoids the uneven dispersion or interface debonding problems that are easy to occur in traditional fiber reinforcement, and improves the homogeneity and processing stability of materials. Attached Figure Description

[0042] Figure 1 This is the synthetic route for the stabilizer described in this invention. Detailed Implementation

[0043] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Synthesis example 1

[0045] Synthesis of Stabilizer 1:

[0046]

[0047] Step 1: Under a nitrogen atmosphere, 20 g of starting material 1, 58.75 g of starting material 2, 25.24 g of potassium carbonate, and 3.17 g of tetra(triphenylphosphine)palladium were added sequentially to the reaction system, dissolved in a mixed solution of toluene, ethanol, and water (volume ratio 2:1:1). The mixture was heated to 75°C and refluxed for 10 hours. Heating was then turned off, and the mixture was cooled to room temperature and allowed to stand before separation. The aqueous phase was extracted twice with ethyl acetate, the organic phases were combined, washed three times with water, evaporated to dryness, and subjected to column chromatography using a mixture of petroleum ether and dichloromethane as eluent. The final product was 47.72 g of intermediate 1. MS [MS+H + ]:675.

[0048] Step 2: Under a nitrogen atmosphere, 47.72 g of intermediate 1, 400 g of dichloromethane, and 18.85 g of AlCl3 were added sequentially to the phase system. After stirring until homogeneous, 100 ml of a dichloromethane solution containing 18.62 g of raw material 3 was slowly added dropwise (starting from -20°C, with the temperature not exceeding 0°C during the addition). The reaction proceeded to completion at room temperature. Subsequently, the reaction system temperature was lowered to 0°C, and the pH was adjusted to neutral with 0.1 mol / L HCl. After stirring for 30 min, the mixture was allowed to stand and separated, retaining the organic phase. The aqueous phase was washed 2-3 times with 50 ml of dichloromethane. The organic phases were combined, dried over anhydrous magnesium sulfate, filtered, and rotary evaporated to obtain the solid. Purification was performed using a silica gel column chromatography with a petroleum ether / ethyl acetate mixture as the eluent. The solid was concentrated and dried to obtain 49.92 g of intermediate 2. MS [MS+1]: 856.

[0049] Step 3: Under a nitrogen atmosphere, 49.92 g of intermediate 2, 4.25 g of hydroxylamine hydrochloride, and 9.56 g of sodium acetate were added sequentially to the phase system, followed by 500 g of tetrahydrofuran. The reaction mixture was reacted at 70 °C for 12 h. The reaction solution was poured into 1500 ml of water and incubated overnight at 0 °C. After filtration, a powdery solid was obtained. Purification was performed by silica gel column chromatography using petroleum ether and ethyl acetate as eluents, ultimately yielding 42.76 g of intermediate 3. MS [MS+1]: 871.

[0050] Step 4: Under a nitrogen atmosphere, 42.76 g of intermediate 3, 7.89 g of starting material 4, 26.12 g of potassium phosphate trihydrate, 0.06 g of pyridine-2-carboxylic acid, 0.5 g of CuI, and 450 g of DMSO were added sequentially to the reaction system. The mixture was heated to 85 °C and maintained for 16 h. After cooling, the reaction mixture was extracted with ammonia solution and methyl tert-butyl ether. The organic phase was washed five times with water and then twice with saturated NaCl solution. Finally, the combined organic phases were dried over anhydrous Na2SO4, evaporated to dryness, and purified by silica gel column chromatography using a petroleum ether / ethyl acetate mixture as the eluent. The purified phase was concentrated and dried to obtain 32.74 g of stabilizer 1. MS [MS+1]: 925.

[0051] Stabilizer 1 1 ¹H NMR (deuterated chloroform) δ 7.66–7.59 (m, 1H), 7.48–7.29 (m, 5H), 7.06–6.98 (m, 2H), 6.56 (d, 1H), 4.17 (p, 2H), 3.49 (t, 4H), 1.94 (dd, 4H), 1.74–1.56 (m, 10H), 1.43–1.29 (m, 4H), 1.24 (s, 12H), 1.12 (s, 12H), 0.95 (t, 6H).

[0052] Synthesis Example 2-Synthesis Example 6

[0053] The synthesis methods of the stabilizers prepared in Synthesis Examples 2-6 are the same as those in Synthesis Example 1, except that raw material 4 is replaced. The specific structures of raw material 4, stabilizer structures and MS[MS+1] are shown in the table below.

[0054]

[0055]

[0056] Example 1

[0057] Preparation of a fiber-reinforced polylactic acid composite material:

[0058] S1. The polymer fiber (polybutylene terephthalate, 5 mm in length, 40 parts) is immersed in a 10% alkaline solution (potassium hydroxide aqueous solution, alkaline solution of 10 times the mass of polybutylene terephthalate) and treated at 80°C for 60 minutes, washed and dried to obtain the treated polymer fiber.

[0059] S2. The treated polymer fiber is melt-blended with the polylactic acid matrix (a blend of lactic acid and polycaprolactone in a mass ratio of 5 parts: 1 part, 90 parts), plasticizer (citric acid ester, 10 parts), coupling agent (γ-aminopropyltriethoxysilane, 5 parts), and stabilizer (prepared in Synthesis Example 1, 5 parts) at 200°C (in a twin-screw extruder at a screw speed of 100 rpm) for 30 minutes to obtain a blend.

[0060] S3. The blend is cooled to room temperature by air cooling (air speed of 5 m / s, air cooling temperature of 5℃) to obtain a fiber-reinforced polylactic acid composite material.

[0061] Examples 2-6

[0062] The fiber-reinforced polylactic acid composite materials prepared in Examples 2-6 were prepared by referring to the preparation method of Example 1, except that the stabilizers were replaced with the stabilizers prepared in Synthesis Examples 2-6, and the rest remained the same as in Example 1.

[0063] Comparative Example 1

[0064] A fiber-reinforced polylactic acid composite material was prepared according to the method of Example 1, except that the stabilizer was replaced with comparative compound 1, and the rest remained the same as in Example 1.

[0065] Comparative compound 1:

[0066] Comparative Example 2

[0067] A fiber-reinforced polylactic acid composite material was prepared according to the method of Example 1, except that the stabilizer was replaced with comparative compound 2, and the rest remained the same as in Example 1.

[0068] Comparative compound 2:

[0069] Comparative Example 3

[0070] A fiber-reinforced polylactic acid composite material is prepared according to the method of Example 1, but without the addition of the stabilizer, and otherwise remains the same as in Example 1.

[0071] Performance testing:

[0072] (1) Tensile strength test: The tensile strength of the fiber-reinforced polylactic acid composite material prepared in each example and comparative example was tested according to the method in GB / T 1040-2006.

[0073] (2) Bending performance after aging: 3D printing filaments were prepared from a fiber-reinforced polylactic acid composite material used in the examples and comparative examples under the following conditions: a single-screw extruder with a diameter of 55 mm and a die diameter of 4 mm was used; the temperature was set at 180℃, the extrusion frequency at 20 Hz, and the traction frequency at 25 Hz. The 3D printing filaments were placed in a constant temperature and humidity aging chamber at 40℃ and 60% humidity for 5 days. After aging, the 3D printing filaments were removed, and two experimenters manually performed bending tests until the filaments broke. The bending data before breakage was recorded, and the average value of the bending test data from the two experimenters was taken. Considering testing error, the difference between the bending test data from the two experimenters should be less than or equal to 5.

[0074] Tensile strength (MPa) Bending resistance (number of times) Example 1 86.2 138 Example 2 84.5 124 Example 3 87.9 145 Example 4 85.1 131 Example 5 88.6 152 Example 6 89.4 165 Comparative Example 1 72.3 89 Comparative Example 2 78.8 101 Comparative Example 3 61.5 77

[0075] Examples incorporating the stabilizer described in this invention significantly outperformed comparative examples without the stabilizer or using alternative structures in terms of tensile strength and flexural strength, indicating that the introduction of the stabilizer effectively improved the mechanical properties and anti-aging ability of the material. Performance differences among the examples show a gradient effect of different stabilizer structures on the reinforcing effect, with stabilizers containing specific deuterated groups and heterocyclic structures (such as in Example 6) exhibiting the best overall performance. In the comparative examples, the sample without any stabilizer showed the weakest performance, confirming the crucial role of this component in the material's aging and toughness; while samples using non-comparative compounds of this invention, although superior to the blank control, were still significantly inferior to the examples, further highlighting the unique advantages of the designed stabilizer structure.

[0076] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A fiber-reinforced polylactic acid composite material, characterized in that, It contains the following components and their mass ratios: 50-90 parts polylactic acid matrix, 5-40 parts polymer fiber, 1-10 parts plasticizer, 0.5-5 parts coupling agent, and 0.5-5 parts stabilizer; The polymer fiber is selected from any one of polybutylene terephthalate, polyethylene terephthalate, and polybutylene succinate, and has a length of 0.1-5 mm. The stabilizer has the structure shown in Formula 1: Formula 1; Z1 is selected from: O, S, N(R1), C(CH3)2; The D represents deuterium; The R1 is selected from: H, methyl, phenyl, deuterated methyl, deuterated phenyl, deuterated tert-butyl; The polylactic acid matrix is ​​a blend of polylactic acid and polycaprolactone, wherein the mass ratio of polylactic acid to polycaprolactone is 5 parts: 1 part.

2. The fiber-reinforced polylactic acid composite material according to claim 1, characterized in that, The plasticizer is one or more of glycerol, citrate, or polyethylene glycol.

3. The fiber-reinforced polylactic acid composite material according to claim 1, characterized in that, The coupling agent is a silane coupling agent.

4. The fiber-reinforced polylactic acid composite material according to claim 3, characterized in that, The silane coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and methacryloyloxypropyltrimethoxysilane.

5. A method for preparing a fiber-reinforced polylactic acid composite material according to any one of claims 1-4, characterized in that, Includes the following steps: S1. The polymer fiber is immersed in an alkaline solution with a concentration of 2-10% for 10-60 minutes, washed and dried to obtain the treated polymer fiber; S2. The treated polymer fiber is melt-blended with the polylactic acid matrix, plasticizer, coupling agent and stabilizer at 160-200°C for 5-30 minutes to obtain a blend. S3. The blend is cooled to room temperature by air cooling to obtain a fiber-reinforced polylactic acid composite material.

6. The method for preparing a fiber-reinforced polylactic acid composite material according to claim 5, characterized in that, The alkaline solution is an aqueous solution of sodium hydroxide or potassium hydroxide, and the treatment temperature is 40-80℃.

7. The method for preparing a fiber-reinforced polylactic acid composite material according to claim 5, characterized in that, The melt blending process is carried out in a twin-screw extruder with a screw speed of 50-200 rpm.

8. The application of a fiber-reinforced polylactic acid composite material according to any one of claims 1-4, characterized in that, Used to prepare biodegradable medical implant materials, packaging materials or daily necessities; The medical implant materials include bone fixation devices or absorbable sutures.

Images