Bamboo fiber grain and preparation method thereof

Abstract

The invention belongs to the technical field of fiber composite materials, and particularly relates to bamboo fiber grains and a preparation method thereof. The bamboo fibers containing aldehyde groups are chemically modified through oligomeric glutamic acid, then epoxy group modified talcum powder with different particle sizes reacts with carboxyl in the bamboo fiber grafted polyglutamic acid to obtain first modified bamboo fibers and second modified bamboo fibers, organic molecular chains are grafted on the surfaces of the first modified bamboo fibers, and the second modified bamboo fibers are grafted on the surfaces of the second modified bamboo fibers. A large amount of small-particle-size talcum powder is bonded on the organic molecular chain, an organic molecular chain is grafted on the surface of the second modified bamboo fiber, and a large amount of large-particle-size talcum powder is bonded on the organic molecular chain; in the melt extrusion process of the polylactic acid, the first modified bamboo fiber and the second modified bamboo fiber, the small-particle-size talcum powder on the surface of the first modified bamboo fiber, the large-particle-size talcum powder on the surface of the second modified bamboo fiber and the bamboo fiber body can be firmly combined, and therefore the mechanical performance of the composite material is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber composite materials, and particularly relates to a bamboo fiber pellet and a preparation method thereof. Background Art

[0002] Bamboo fiber is a cellulose fiber extracted from naturally growing bamboo. Its main component is cellulose, and it is a natural, environmentally friendly green fiber. In daily life, it is mainly used for clothing fabrics, cooling mats, bed sheets, curtains, scarves, etc. It can be spun pure or blended with cotton, wool, linen and chemical fibers to produce various specifications of woven fabrics and knitted fabrics. The products made of bamboo fiber can be naturally degraded in the soil and have no pollution to the environment after decomposition. It is a natural, green and environmentally friendly raw material with broad application prospects.

[0003] Polylactic acid is a polymer obtained by polymerizing lactic acid as the main raw material. The raw material source is sufficient and can be recycled. The production process of polylactic acid is pollution-free, and the product can be biodegradable, realizing the cycle in nature. Therefore, it is an ideal green polymer material. Polylactic acid has good thermal stability, and the processing temperature is 170 - 230 °C. It has good solvent resistance and can be processed in various ways, such as extrusion, spinning, biaxial stretching, injection blow molding. The products made of polylactic acid have good biocompatibility, gloss, transparency, hand feeling and heat resistance in addition to being biodegradable. Polylactic acid also has certain antibacterial, flame retardant and ultraviolet resistance properties, so it has a wide range of uses and can be used as packaging materials, fibers and non-woven fabrics, etc. Currently, it is mainly used in the fields of clothing (underwear, outerwear), industry (construction, agriculture, forestry, papermaking) and medical and health care, etc.

[0004] Polylactic acid, bamboo fiber and auxiliary materials can be mixed to produce environmentally friendly materials, which are applied to various food fields such as tableware. However, after physical mixing of bamboo fiber and polylactic acid, the interfacial bonding between the two is poor, resulting in poor mechanical properties of the composite material made of polylactic acid and bamboo fiber. Summary of the Invention

[0005] In view of the above problems, the present invention provides a bamboo fiber pellet and a preparation method thereof, which are used to solve the problem that the interfacial bonding between polylactic acid and bamboo fiber is poor, resulting in poor mechanical properties of the composite material made of the two.

[0006] To achieve the above object, the technical solution adopted by the present invention is: A preparation method of a bamboo fiber pellet, comprising the following steps: (1) Performing a Schiff base reaction on aldehyde group-modified bamboo fiber and oligoglutamic acid in water to obtain polyglutamic acid-modified bamboo fiber; the molar ratio of the aldehyde group in the aldehyde group-modified bamboo fiber to oligoglutamic acid is 1:(1.5 - 2); the average molecular weight of oligoglutamic acid is 5000 - 10000 daltons; (2) Small-sized talc powder and large-sized talc powder were respectively modified with γ-(2,3-epoxypropoxy)propyltrimethoxysilane to obtain epoxy group-modified small-sized talc powder and epoxy group-modified large-sized talc powder; the average particle size of the small-sized talc powder was 10 - 20 nm, and the average particle size of the large-sized talc powder was 0.1 - 0.5 μm; (3) The epoxy group-modified small-sized talc powder and the polyglutamic acid-modified bamboo fiber were reacted at 95 - 100 °C for 4 - 6 h under the catalysis of tetrabutylammonium bromide to obtain the first modified bamboo fiber; The epoxy group-modified large-sized talc powder and the polyglutamic acid-modified bamboo fiber were reacted at 95 - 100 °C for 4 - 6 h under the catalysis of tetrabutylammonium bromide to obtain the second modified bamboo fiber; (4) Polylactic acid, the first modified bamboo fiber and the second modified bamboo fiber were melt-extruded and pelletized to obtain bamboo fiber pellets; the mass ratio of polylactic acid, the first modified bamboo fiber and the second modified bamboo fiber was 100:(5 - 8):(2 - 3).

[0007] Preferably, the preparation method of the aldehyde group-modified bamboo fiber is as follows: The reaction material mainly composed of bamboo fiber, sodium periodate and water was mixed and reacted at 35 - 45 °C in the dark for 20 - 24 h, and the aldehyde group-modified bamboo fiber was obtained after impurity removal; the pH of the reaction material was 4 - 5.

[0008] Preferably, the diameter of the bamboo fiber was 5 - 10 μm, and the length was 0.05 - 0.1 mm.

[0009] Preferably, the mass ratio of bamboo fiber, sodium periodate and water was 1:1 - 1.2:100 - 200.

[0010] Preferably, the temperature of the Schiff base reaction was room temperature, and the time was 24 - 30 h.

[0011] Preferably, the method for modifying small-sized talc powder with γ-(2,3-epoxypropoxy)propyltrimethoxysilane is as follows: γ-(2,3-epoxypropoxy)propyltrimethoxysilane, ethanol and water were mixed and the pH was adjusted to 3 - 4 with hydrochloric acid, then small-sized talc powder was added, and the mixture was reacted at 60 - 75 °C for 2 - 4 h; the mass ratio of γ-(2,3-epoxypropoxy)propyltrimethoxysilane to small-sized talc powder was (30 - 35):30.

[0012] Preferably, the method for modifying large-particle-size talcum powder with γ-(2,3-epoxypropoxy)propyltrimethoxysilane is as follows: Mix γ-(2,3-epoxypropoxy)propyltrimethoxysilane, ethanol and water, and adjust the pH to 3-4 with hydrochloric acid, then add large-particle-size talcum powder, and mix and react at 60-75 °C for 2-4 h; the mass ratio of γ-(2,3-epoxypropoxy)propyltrimethoxysilane to large-particle-size talcum powder is (20-25):30.

[0013] Preferably, in step (3), the mass ratio of polyglutamic acid-modified bamboo fiber to epoxy group-modified small-particle-size talcum powder is 1:(0.2-0.4), and the mass of tetrabutylammonium bromide is 1-2% of the mass of polyglutamic acid-modified bamboo fiber.

[0014] Preferably, in step (3), the mass ratio of polyglutamic acid-modified bamboo fiber to epoxy group-modified large-particle-size talcum powder is 1:(0.1-0.3), and the mass of tetrabutylammonium bromide is 1-2% of the mass of polyglutamic acid-modified bamboo fiber.

[0015] A bamboo fiber pellet prepared by the method for preparing bamboo fiber pellets as described above.

[0016] Compared with the prior art, the beneficial effects of the method for preparing bamboo fiber pellets of the present invention are as follows: (1) In the present invention, the amino group in oligoglutamic acid is used to chemically modify bamboo fiber containing aldehyde groups, and then different particle-size talcum powders modified with epoxy groups are reacted with the carboxyl groups in the polyglutamic acid grafted on the bamboo fiber to obtain the first modified bamboo fiber and the second modified bamboo fiber. The surface of the first modified bamboo fiber is grafted with an organic molecular chain, and a large number of small-particle-size talcum powders are bonded to the organic molecular chain. The surface of the second modified bamboo fiber is grafted with an organic molecular chain, and a large number of large-particle-size talcum powders are bonded to the organic molecular chain. During the melting, mixing and extrusion of polylactic acid, the first modified bamboo fiber, and the second modified bamboo fiber, the small-particle-size talcum powder on the surface of the first modified bamboo fiber, the large-particle-size talcum powder on the surface of the second modified bamboo fiber, and the bamboo fiber body can form a physical snap structure, thereby realizing the firm combination between the first modified bamboo fiber and the second modified bamboo fiber, and improving the mechanical properties of the composite material. The experimental results show that if the molecular weight of polyglutamic acid is too large or too small, it will affect the bonding strength between the first modified bamboo fiber and the second modified bamboo fiber, resulting in a decrease in the mechanical properties of the composite material. This may be because the molecular weight affects the formation of the snap structure.

[0017] (2) In the present invention, oligoglutamic acid and talcum powder are used to modify bamboo fiber, which can ensure that the final composite material has good degradation performance. The polyglutamic acid chain segments, talcum powder particles, and bamboo fibers in the composite material prepared in the present invention can play a synergistic role and endow the composite material with good antibacterial properties. Description of the Drawings

[0018] Figure 1 Schematic diagram of comparison of tensile strength and flexural strength of bamboo fiber pellets prepared in each example and comparative example; Figure 2 Schematic diagram of comparison of degradation performance of bamboo fiber pellets prepared in each example and comparative example; Figure 3 Schematic diagram of comparison of antibacterial performance of bamboo fiber pellets prepared in each example and comparative example. Detailed implementation manners

[0019] In order to enable those skilled in the art to better understand the technical solution, the present invention will be described in detail below in conjunction with embodiments. The description of this part is only exemplary and explanatory, and should not have any restrictive effect on the protection scope of the present invention.

[0020] Example 1:

[0021] The bamboo fiber pellets of this example are prepared by a method including the following steps: (1) Add bamboo fibers (with a diameter of 5 - 10 μm and a length of 0.05 - 0.1 mm) and sodium periodate into a reactor, then add water, stir until the sodium periodate is completely dissolved, then add hydrochloric acid into the reactor to adjust the pH of the liquid in the reactor to 4, then heat the materials in the reactor to 35°C, stir and react for 20 h in the dark, filter, wash the filter cake with water to remove the unreacted sodium periodate, and dry to obtain aldehyde group - modified bamboo fibers. The aldehyde group content in the aldehyde group - modified bamboo fibers is determined by the hydrochloric acid hydroxylamine titration method. The mass ratio of bamboo fibers, sodium periodate and water is 1:1:150.

[0022] (2) Add the aldehyde group - modified bamboo fibers and oligoglutamic acid (with an average molecular weight of 5000 daltons) into a stirring reaction kettle, then add water, stir until the oligoglutamic acid is dispersed and dissolved completely, stir and react for 30 h at room temperature, filter, wash the filter cake with water to remove the unreacted oligoglutamic acid, and dry to obtain polyglutamic acid - modified bamboo fibers; the molar ratio of the aldehyde group in the aldehyde group - modified bamboo fibers to oligoglutamic acid is 1:1.5, and the mass ratio of the aldehyde group - modified bamboo fibers to water is 1:80.

[0023] (3) Add 30 g of γ - (2,3 - epoxypropoxy) propyltrimethoxysilane, 500 mL of absolute ethanol and 30 mL of deionized water into a reaction kettle, then add hydrochloric acid into the reaction kettle to adjust the pH of the materials in the reaction kettle to 3, then add 30 g of small - particle - size talc (with an average particle size of 10 nm) into the reaction kettle, then heat the materials in the reaction kettle to 60°C, stir and react for 2 h, after the reaction is completed, filter, wash the filter cake with ethanol, and dry to obtain epoxy - group - modified small - particle - size talc.

[0024] (4) Add 20 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 500 mL of absolute ethanol, and 30 mL of deionized water into a reaction kettle. Then add hydrochloric acid into the reaction kettle to adjust the pH of the materials in the reaction kettle to 3. Next, add 30 g of large-particle-size talcum powder (average particle size is 0.1 μm) into the reaction kettle. Then heat the materials in the reaction kettle to 60 °C and stir for 2 h. After the reaction is completed, filter, wash the filter cake with ethanol, and dry to obtain epoxy-group-modified large-particle-size talcum powder.

[0025] (5) Add polyglutamic acid-modified bamboo fiber, ethanol, and epoxy-group-modified small-particle-size talcum powder into a reaction kettle, stir evenly. Then add tetrabutylammonium bromide into the reaction kettle and stir evenly. Then heat the materials in the reaction kettle to 95 °C and stir for reflux reaction for 4 h. After the reaction is completed, filter, wash the filter cake with ethanol, and dry to obtain the first modified bamboo fiber; the mass ratio of polyglutamic acid-modified bamboo fiber, ethanol, and epoxy-group-modified small-particle-size talcum powder is 1:30:0.2, and the mass of tetrabutylammonium bromide is 1% of the mass of polyglutamic acid-modified bamboo fiber.

[0026] (6) Add polyglutamic acid-modified bamboo fiber, ethanol, and epoxy-group-modified large-particle-size talcum powder into a reaction kettle, stir evenly. Then add tetrabutylammonium bromide into the reaction kettle and stir evenly. Then heat the materials in the reaction kettle to 95 °C and stir for reflux reaction for 4 h. After the reaction is completed, filter, wash the filter cake with ethanol, and dry to obtain the second modified bamboo fiber; the mass ratio of polyglutamic acid-modified bamboo fiber, ethanol, and epoxy-group-modified large-particle-size talcum powder is 1:30:0.1, and the mass of tetrabutylammonium bromide is 1% of the mass of polyglutamic acid-modified bamboo fiber.

[0027] (7) Add polylactic acid, the first modified bamboo fiber, and the second modified bamboo fiber into a melt extrusion granulator for mixing and melt extrusion granulation to obtain bamboo fiber pellets; the mass ratio of polylactic acid, the first modified bamboo fiber, and the second modified bamboo fiber is 100:5:3, and the melt extrusion temperature is 175 °C.

[0028] Example 2:

[0029] The bamboo fiber pellets of this example are prepared by a method including the following steps: (1) Add bamboo fiber (diameter is 5 - 10 μm, length is 0.05 - 0.1 mm) and sodium periodate into a reactor. Then add water and stir until sodium periodate is completely dissolved. Next, add hydrochloric acid into the reactor to adjust the pH of the liquid in the reactor to 5. Then heat the materials in the reactor to 45 °C and stir for reaction for 24 h in the dark. Filter, wash the filter cake with water to remove unreacted sodium periodate, and dry to obtain aldehyde-group-modified bamboo fiber. Use the hydrochloric acid hydroxylamine titration method to determine the aldehyde group content in the aldehyde-group-modified bamboo fiber. The mass ratio of bamboo fiber, sodium periodate, and water is 1:1.2:200.

[0030] (2) Add the aldehyde group - modified bamboo fiber and oligoglutamic acid (average molecular weight of 10,000 Daltons) into a stirring reaction kettle, then add water, stir until the oligoglutamic acid is completely dispersed and dissolved, stir and react at room temperature for 24 h, filter, wash the filter cake with water to remove the unreacted oligoglutamic acid, and obtain polyglutamic acid - modified bamboo fiber after drying; the molar ratio of the aldehyde group in the aldehyde group - modified bamboo fiber to oligoglutamic acid is 1:2, and the mass ratio of the aldehyde group - modified bamboo fiber to water is 1:100.

[0031] (3) Add 35 g of γ - (2,3 - epoxypropoxy) propyltrimethoxysilane, 500 mL of absolute ethanol and 30 mL of deionized water into the reaction kettle, then add hydrochloric acid into the reaction kettle to adjust the pH of the materials in the reaction kettle to 4, then add 30 g of small - particle - size talc powder (average particle size of 20 nm) into the reaction kettle, and then heat the materials in the reaction kettle to 75 °C, stir and react for 4 h. After the reaction ends, filter, wash the filter cake with ethanol, and obtain epoxy - group - modified small - particle - size talc powder after drying.

[0032] (4) Add 25 g of γ - (2,3 - epoxypropoxy) propyltrimethoxysilane, 500 mL of absolute ethanol and 30 mL of deionized water into the reaction kettle, then add hydrochloric acid into the reaction kettle to adjust the pH of the materials in the reaction kettle to 4, then add 30 g of large - particle - size talc powder (average particle size of 0.5 μm) into the reaction kettle, and then heat the materials in the reaction kettle to 75 °C, stir and react for 4 h. After the reaction ends, filter, wash the filter cake with ethanol, and obtain epoxy - group - modified large - particle - size talc powder after drying.

[0033] (5) Add the polyglutamic acid - modified bamboo fiber, ethanol and epoxy - group - modified small - particle - size talc powder into the reaction kettle, stir evenly, then add tetrabutylammonium bromide into the reaction kettle, stir evenly, and then heat the materials in the reaction kettle to 100 °C, stir and reflux for 6 h. After the reaction ends, filter, wash the filter cake with ethanol, and obtain the first - modified bamboo fiber after drying; the mass ratio of the polyglutamic acid - modified bamboo fiber, ethanol and epoxy - group - modified small - particle - size talc powder is 1:50:0.4, and the mass of tetrabutylammonium bromide is 2% of the mass of the polyglutamic acid - modified bamboo fiber.

[0034] (6) Add the polyglutamic acid - modified bamboo fiber, ethanol and epoxy - group - modified large - particle - size talc powder into the reaction kettle, stir evenly, then add tetrabutylammonium bromide into the reaction kettle, stir evenly, and then heat the materials in the reaction kettle to 100 °C, stir and reflux for 6 h. After the reaction ends, filter, wash the filter cake with ethanol, and obtain the second - modified bamboo fiber after drying; the mass ratio of the polyglutamic acid - modified bamboo fiber, ethanol and epoxy - group - modified large - particle - size talc powder is 1:50:0.3, and the mass of tetrabutylammonium bromide is 2% of the mass of the polyglutamic acid - modified bamboo fiber.

[0035] (7) Add polylactic acid, the first modified bamboo fiber, and the second modified bamboo fiber into a melt extrusion granulator for mixing, melt extrusion, and granulation to obtain bamboo fiber pellets; the mass ratio of polylactic acid, the first modified bamboo fiber, and the second modified bamboo fiber is 100:8:2, and the melt extrusion temperature is 180 °C.

[0036] Example 3:

[0037] The bamboo fiber pellets of this example are prepared by a method comprising the following steps: (1) Add bamboo fiber (with a diameter of 5 - 10 μm and a length of 0.05 - 0.1 mm) and sodium periodate into a reactor, then add water, stir until sodium periodate is completely dissolved, then add hydrochloric acid into the reactor, adjust the pH of the liquid in the reactor to 4.5, then heat the materials in the reactor to 40 °C, stir and react for 22 h in the dark, filter, wash the filter cake with water to remove unreacted sodium periodate, and dry to obtain aldehyde group - modified bamboo fiber. The aldehyde group content in the aldehyde group - modified bamboo fiber is determined by the hydroxylamine hydrochloride titration method. The mass ratio of bamboo fiber, sodium periodate, and water is 1:1:100.

[0038] (2) Add the aldehyde group - modified bamboo fiber and oligoglutamic acid (with an average molecular weight of 8000 daltons) into a stirring reaction kettle, then add water, stir until oligoglutamic acid is dispersed and dissolved completely, stir and react for 27 h at room temperature, filter, wash the filter cake with water to remove unreacted oligoglutamic acid, and dry to obtain polyglutamic acid - modified bamboo fiber; the molar ratio of the aldehyde group in the aldehyde group - modified bamboo fiber to oligoglutamic acid is 1:1.8, and the mass ratio of the aldehyde group - modified bamboo fiber to water is 1:90.

[0039] (3) Add 32 g of γ - (2,3 - epoxypropoxy) propyltrimethoxysilane, 500 mL of absolute ethanol, and 30 mL of deionized water into a reaction kettle, then add hydrochloric acid into the reaction kettle to adjust the pH of the materials in the reaction kettle to 3.5, then add 30 g of small - particle - size talc powder (with an average particle size of 15 nm) into the reaction kettle, then heat the materials in the reaction kettle to 70 °C, stir and react for 3 h, after the reaction is completed, filter, wash the filter cake with ethanol, and dry to obtain epoxy - group - modified small - particle - size talc powder.

[0040] (4) Add 22 g of γ - (2,3 - epoxypropoxy) propyltrimethoxysilane, 500 mL of absolute ethanol, and 30 mL of deionized water into a reaction kettle, then add hydrochloric acid into the reaction kettle to adjust the pH of the materials in the reaction kettle to 3.5, then add 30 g of large - particle - size talc powder (with an average particle size of 0.3 μm) into the reaction kettle, then heat the materials in the reaction kettle to 70 °C, stir and react for 3 h, after the reaction is completed, filter, wash the filter cake with ethanol, and dry to obtain epoxy - group - modified large - particle - size talc powder.

[0041] (5) Add polyglutamic acid-modified bamboo fiber, ethanol, and epoxy group-modified small particle size talc powder into a reaction kettle, stir evenly, then add tetrabutylammonium bromide into the reaction kettle, stir evenly, and then heat the materials in the reaction kettle to 98 °C, stir and reflux for 5 h. After the reaction is completed, filter, wash the filter cake with ethanol, and dry to obtain the first modified bamboo fiber; the mass ratio of polyglutamic acid-modified bamboo fiber, ethanol, and epoxy group-modified small particle size talc powder is 1:40:0.3, and the mass of tetrabutylammonium bromide is 1.5% of the mass of polyglutamic acid-modified bamboo fiber.

[0042] (6) Add polyglutamic acid-modified bamboo fiber, ethanol, and epoxy group-modified large particle size talc powder into a reaction kettle, stir evenly, then add tetrabutylammonium bromide into the reaction kettle, stir evenly, and then heat the materials in the reaction kettle to 98 °C, stir and reflux for 5 h. After the reaction is completed, filter, wash the filter cake with ethanol, and dry to obtain the second modified bamboo fiber; the mass ratio of polyglutamic acid-modified bamboo fiber, ethanol, and epoxy group-modified large particle size talc powder is 1:40:0.2, and the mass of tetrabutylammonium bromide is 1.5% of the mass of polyglutamic acid-modified bamboo fiber.

[0043] (7) Add polylactic acid, the first modified bamboo fiber, and the second modified bamboo fiber into a melt extrusion granulator for mixing, melt extrusion granulation to obtain bamboo fiber pellets; the mass ratio of polylactic acid, the first modified bamboo fiber, and the second modified bamboo fiber is 100:7:2.5, and the melt extrusion temperature is 178 °C.

[0044] Comparative Example 1 The difference between the bamboo fiber pellets of this comparative example and those of Example 1 is only that in step (7) of the preparation method of the bamboo fiber pellets of this comparative example, the mass of the first modified bamboo fiber is adjusted to 0, and the mass ratio of polylactic acid and the second modified bamboo fiber is 100:8.

[0045] Comparative Example 2 The difference between the bamboo fiber pellets of this comparative example and those of Example 1 is only that in step (7) of the preparation method of the bamboo fiber pellets of this comparative example, the mass of the second modified bamboo fiber is adjusted to 0, and the mass ratio of polylactic acid and the first modified bamboo fiber is 100:8.

[0046] Comparative Example 3 The difference between the bamboo fiber pellets of this comparative example and those of Example 1 is only that in step (7) of the preparation method of the bamboo fiber pellets of this comparative example, polylactic acid, polyglutamic acid-modified bamboo fiber, small particle size talc powder, and large particle size talc powder are added into a melt extrusion granulator for mixing, melt extrusion granulation to obtain bamboo fiber pellets; the mass ratio of polylactic acid, polyglutamic acid-modified bamboo fiber, small particle size talc powder, and large particle size talc powder is 100:6.9:0.8:0.3, and the melt extrusion temperature is 175 °C.

[0047] Comparative Example 4 The difference between the bamboo fiber pellets of this comparative example and those of Example 1 lies only in that in step (2) of the preparation method of the bamboo fiber pellets of this comparative example, oligoglutamic acid is replaced by hexaglutamic acid.

[0048] Comparative Example 5 The difference between the bamboo fiber pellets of this comparative example and those of Example 1 lies only in that in step (2) of the preparation method of the bamboo fiber pellets of this comparative example, oligoglutamic acid is replaced by polyglutamic acid with an average molecular weight of 50,000 daltons.

[0049] Comparative Example 6 The difference between the bamboo fiber pellets of this comparative example and those of Example 1 lies only in that in step (3) of the preparation method of the bamboo fiber pellets of this comparative example, the average particle size of the small particle size talc powder is 2 nm.

[0050] Comparative Example 7 The difference between the bamboo fiber pellets of this comparative example and those of Example 1 lies only in that in step (3) of the preparation method of the bamboo fiber pellets of this comparative example, the average particle size of the small particle size talc powder is 40 nm.

[0051] Comparative Example 8 The difference between the bamboo fiber pellets of this comparative example and those of Example 1 lies only in that in step (4) of the preparation method of the bamboo fiber pellets of this comparative example, the average particle size of the large particle size talc powder is 5 μm.

[0052] Comparative Example 9 The difference between the bamboo fiber pellets of this comparative example and those of Example 1 lies only in that in step (4) of the preparation method of the bamboo fiber pellets of this comparative example, the average particle size of the large particle size talc powder is 0.01 μm.

[0053] Effect Example To evaluate the comprehensive properties of the bamboo fiber pellets prepared in each example and comparative example, the pure polylactic acid resin or the bamboo fiber pellets were respectively injection molded to obtain test samples, and then the tensile strength and elongation at break were tested according to the method in Standard GB / T 1040.1-2006, the flexural strength was tested according to the method in Standard GB / T 9341-2008, the notched impact strength was tested according to the method in Standard GB / T 1843-2008, and the degradation performance was tested under the same conditions according to the method in Standard GB / T 18006.2-1999. The percentage A of the mold coverage on the surface of the specimen and the percentage B of the damage or crack area in the external surface area were recorded at the same time. The antibacterial rate was tested according to the method in Standard QB / T 2591-2003, and the bacterial strains used for the test were Escherichia coli and Staphylococcus aureus. The test results of the tensile strength, elongation at break, flexural strength, notched impact strength, degradation performance and antibacterial performance of the bamboo fiber pellets prepared in each example and comparative example are shown in Table 1 and Figures 1-3 as follows.

[0054] Table 1 Comprehensive properties of the bamboo fiber pellets prepared in each example and comparative example

[0055] As can be seen from Table 1, compared with adding talcum powder by physical blending or using only one particle size of talcum powder, the composite material of the present invention has better mechanical strength, probably because: the small particle size talcum powder on the surface of the first modified bamboo fiber, the large particle size talcum powder on the surface of the second modified bamboo fiber and the bamboo fiber body can form a physical snap structure, thereby realizing the firm combination between the first modified bamboo fiber and the second modified bamboo fiber, and thus improving the mechanical properties of the composite material. In addition, the bamboo fiber pellets of the examples of the present invention can significantly increase the elongation at break of polylactic acid, while the elongation at break of the bamboo fiber pellets of Comparative Examples 1-2 is decreased, which may be because the bamboo fibers modified with only one particle size of talcum powder in Comparative Examples 1-2 cannot form a physical snap structure, resulting in a significant decrease in elastic shrinkage. Finally, the use of low molecular weight polyglutamic acid and talcum powder to modify bamboo fibers in the present invention can ensure that the final composite material has good degradation performance; the polyglutamic acid segments, talcum powder particles and bamboo fibers in the composite material can play a synergistic role, endowing the composite material with good antibacterial performance, and the antibacterial property of the bamboo fiber pellets of Examples 1-3 of the present invention is significantly higher than that of the comparative examples, because a firm combination structure can be formed between the first modified bamboo fiber and the second modified bamboo fiber in the examples, enabling the polyglutamic acid segments, talcum powder particles and bamboo fibers to be arranged orderly, improving the distribution uniformity, and thus improving the degradation performance of the composite material and significantly enhancing the antibacterial synergistic effect.

[0056] As can be seen from Example 1 and Comparative Examples 4-5, if the molecular weight of polyglutamic acid is too large or too small, it will affect the bonding strength between the first modified bamboo fiber and the second modified bamboo fiber, resulting in a decrease in the mechanical properties of the composite material. This may be because the molecular weight affects the formation of the snap structure. When the molecular chain is too long, the polymer chain entanglement is obvious, leading to disorder of the molecular chain. When the molecular chain is too short, misalignment cannot be formed between talcum powders, affecting the formation of the snap structure.

[0057] As can be seen from Example 1 and Comparative Examples 6-9, when experiments are carried out by using talcum powders with different particle sizes, only when the average particle size of the small-particle-size talcum powder and the average particle size of the large-particle-size talcum powder are both within a suitable range can an effective physical snap bond be formed between the first modified bamboo fiber and the second modified bamboo fiber, improving the comprehensive properties of the composite material. If the matching of the average particle size of the small-particle-size talcum powder and the average particle size of the large-particle-size talcum powder is inappropriate, the compounding and bonding effect of the two will be affected.

[0058] It should be noted that in this article, the terms: including, containing and any other variants are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to this process, method, article or device. Specific examples are used in this article to elaborate on the principle and implementation mode of the technical solution of the present invention. The description of the above examples is only used to help understand the method of the present invention and its core idea. The above is only the preferred implementation mode of the present invention. It should be pointed out that due to the limited nature of written expression and the objectively infinite specific structures, for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements, refinements or changes can be made, or the above technical features can be combined in an appropriate manner; these improvements, refinements, changes or combinations, or directly applying the concept and technical solution of the present invention to other occasions without improvement, should all be regarded as the protection scope of the present invention.

Claims

1. A preparation method of bamboo fiber pellets, characterized in that, It includes the following steps: (1) Perform Schiff base reaction on aldehyde group-modified bamboo fiber and oligoglutamic acid in water to obtain polyglutamic acid-modified bamboo fiber; The molar ratio of the aldehyde group in the aldehyde group-modified bamboo fiber to oligoglutamic acid is 1:(1.5 - 2); the average molecular weight of oligoglutamic acid is 5000 - 10000 Daltons; (2) Modify small particle size talc powder and large particle size talc powder respectively with γ-(2,3-epoxypropoxy)propyltrimethoxysilane to obtain epoxy group-modified small particle size talc powder and epoxy group-modified large particle size talc powder; the average particle size of the small particle size talc powder is 10 - 20 nm, and the average particle size of the large particle size talc powder is 0.1 - 0.5 μm; (3) React the epoxy group-modified small particle size talc powder and polyglutamic acid-modified bamboo fiber under the catalysis of tetrabutylammonium bromide at 95 - 100 °C for 4 - 6 h to obtain the first modified bamboo fiber; React the epoxy group-modified large particle size talc powder and polyglutamic acid-modified bamboo fiber under the catalysis of tetrabutylammonium bromide at 95 - 100 °C for 4 - 6 h to obtain the second modified bamboo fiber; (4) Melt-extrude and granulate polylactic acid, the first modified bamboo fiber and the second modified bamboo fiber to obtain bamboo fiber pellets; the mass ratio of polylactic acid, the first modified bamboo fiber and the second modified bamboo fiber is 100:(5 - 8):(2 - 3).

2. The preparation method of bamboo fiber pellet according to claim 1, characterized in that, The preparation method of the aldehyde group-modified bamboo fiber is as follows: Mix the reaction materials mainly composed of bamboo fiber, sodium periodate and water at 35 - 45 °C and in the dark for 20 - 24 h, and obtain the aldehyde group-modified bamboo fiber after impurity removal; the pH of the reaction materials is 4 - 5.

3. The preparation method of bamboo fiber pellets according to claim 2, characterized in that, The diameter of the bamboo fiber is 5 - 10 μm, and the length is 0.05 - 0.1 mm.

4. The preparation method of bamboo fiber pellets according to claim 2, characterized in that, The mass ratio of bamboo fiber, sodium periodate and water is 1:1 - 1.2:100 - 200.

5. The preparation method of bamboo fiber pellet according to claim 1, characterized in that, The temperature of the Schiff base reaction is room temperature, and the time is 24 - 30 h.

6. The preparation method of bamboo fiber pellets according to claim 1, characterized in that, The method for modifying small particle size talc powder with γ-(2,3-epoxypropoxy)propyltrimethoxysilane is as follows: Mix γ-(2,3-epoxypropoxy)propyltrimethoxysilane, ethanol and water, adjust the pH to 3 - 4 with hydrochloric acid, then add small particle size talc powder, and mix and react at 60 - 75 °C for 2 - 4 h; the mass ratio of γ-(2,3-epoxypropoxy)propyltrimethoxysilane to small particle size talc powder is (30 - 35):

30.

7. The preparation method of bamboo fiber pellets according to claim 1, characterized in that, The method for modifying large particle size talc powder with γ-(2,3-epoxypropoxy)propyltrimethoxysilane is as follows: Mix γ-(2,3-epoxypropoxy)propyltrimethoxysilane, ethanol and water, adjust the pH to 3 - 4 with hydrochloric acid, then add large particle size talc powder, and mix and react at 60 - 75 °C for 2 - 4 h; the mass ratio of γ-(2,3-epoxypropoxy)propyltrimethoxysilane to large particle size talc powder is (20 - 25):

30.

8. The preparation method of bamboo fiber pellets according to claim 1, characterized in that, In step (3), the mass ratio of polyglutamic acid-modified bamboo fiber to epoxy group-modified small particle size talc powder is 1:(0.2 - 0.4), and the mass of tetrabutylammonium bromide is 1 - 2% of the mass of polyglutamic acid-modified bamboo fiber.

9. The preparation method of bamboo fiber pellets according to claim 1, characterized in that, In step (3), the mass ratio of the polyglutamic acid-modified bamboo fiber to the epoxy group-modified large-particle talc powder is 1:(0.1~0.3), and the mass of tetrabutylammonium bromide is 1~2% of the mass of the polyglutamic acid-modified bamboo fiber.

10. A bamboo fiber pellet prepared by the method for preparing bamboo fiber pellets according to any one of claims 1-9.

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