1. An induction method of a polypropylene/bamboo fiber interface transverse crystal structure is characterized by comprising the step of modifying bamboo fibers by nano titanium dioxide.

2. The method for inducing the interface transverse crystalline structure of the polypropylene/bamboo fiber as claimed in claim 1, wherein the modification of the nano titanium dioxide is performed by soaking the bamboo fiber with a nano titanium dioxide suspension, wherein the nano titanium dioxide suspension comprises nano titanium dioxide, a KH-570 silane coupling agent, absolute ethyl alcohol and deionized water, and the molar ratio of the nano titanium dioxide to the KH-570 silane coupling agent is 1: 1.

3. The method for inducing the transverse crystal structure of the polypropylene/bamboo fiber interface according to claim 1 or 2, wherein the bamboo fiber obtaining method comprises the following steps: pretreating bamboo into bamboo slices with required size, and cutting off parenchyma cells along the boundary of bamboo fiber and parenchyma cells;

preferably, the bamboo material is moso bamboo.

4. The method for inducing the crosswise crystal structure of the polypropylene/bamboo fiber interface according to any one of claims 1 to 3, wherein the length of the bamboo fiber is 0.5 to 1.5cm, the width is 40 to 300 μm, and the thickness is 25 to 120 μm.

5. The method for inducing the polypropylene/bamboo fiber interface transverse crystal structure as claimed in any one of claims 1 to 4, wherein the nano titanium dioxide is anatase nano titanium dioxide with a particle size of 20 to 40 nm.

6. The method for inducing the polypropylene/bamboo fiber interface transverse crystal structure as claimed in any one of claims 2 to 5, wherein the preparation method of the nano titanium dioxide suspension comprises the following steps: dispersing the nano titanium dioxide in absolute ethyl alcohol through high-frequency ultrasonic, dispersing a KH-570 silane coupling agent in deionized water, mixing the two, heating in a water bath at 75-85 ℃, stirring for 1-2 h, cooling, and then performing high-frequency ultrasonic treatment.

7. The method for inducing the transverse crystal structure of the polypropylene/bamboo fiber interface according to claim 6, wherein the ultrasonic power of the high-frequency ultrasonic is 250-300W, and the ultrasonic working mode is 2 s-4 s intermittent working;

and/or, the high-frequency ultrasound is carried out under the ice-water bath condition.

8. The method for inducing the polypropylene/bamboo fiber interface transverse crystal structure as claimed in any one of claims 2 to 7, wherein the concentration of the nano titanium dioxide in the nano titanium dioxide suspension is 0.035 to 0.063 mol/L.

9. The method for inducing the transverse crystal structure of the polypropylene/bamboo fiber interface as claimed in claim 8, wherein the bamboo fiber accounting for 3-5% of the nano titanium dioxide suspension is added into the nano titanium dioxide suspension, stirred for 1-2 h, taken out and dried at 60 ℃ to obtain the nano titanium dioxide modified bamboo fiber.

10. The application of the polypropylene/bamboo fiber interface transverse crystal structure induction method of any one of claims 1 to 9 in the preparation of a polypropylene/bamboo fiber interface transverse crystal structure is characterized by comprising the step of compounding bamboo fibers modified by nano titanium dioxide with polypropylene;

preferably, the bamboo fiber modified by the nano titanium dioxide is compounded with the molten polypropylene at the temperature of 190-200 ℃, then the temperature is reduced to 135-145 ℃ at the speed of 10-15 ℃/min, isothermal crystallization is carried out for 15min, and a polypropylene/bamboo fiber interface transverse crystal structure is formed.

Background

The plant fiber reinforced thermoplastic polymer composite material has the advantages of easy molding, low processing energy consumption, recyclability, relative environmental friendliness and the like, and is a long-term research hotspot in the field of composite materials. The product prepared by the material can be widely used for garden buildings, automobile interior decoration, packaging materials, indoor decoration materials and the like. Bamboo fiber has the reputation of plant glass fiber, is a bearing structural unit of bamboo, has extremely excellent mechanical strength, and has great potential for preparing high-performance fiber reinforced composite materials. Over the past 20 years, research on bamboo fiber reinforced thermoplastic polymer composites (abbreviated as bamboo-plastic composites) has been widely conducted internationally. However, deep analysis shows that the bamboo-plastic composite material prepared by the prior art has no obvious bending resistance advantage compared with the wood-plastic composite material. This is mainly because the interface compatibility between hydrophilic bamboo fibers and hydrophobic thermoplastic polymers is poor, resulting in low stress transfer efficiency, and the strength advantage of bamboo fibers cannot be fully exerted, thereby hindering the engineering application thereof.

At present, researchers have proposed the following method to enhance the interfacial compatibility of bamboo fiber and polypropylene. Firstly, the bamboo fiber is subjected to surface treatment to enable the surface treatment to be matched with the surface performance of a plastic matrix, so that interface enhancement is realized. Chinese patent CN108677521A proposes a method for alkali treatment of bamboo fiber to improve the interface compatibility between bamboo fiber and polypropylene; chinese patent CN103866570A proposes a surface modifier compounded by a melamine formaldehyde resin surface treating agent and ammonium polyphosphate, which is attached to the surface of bamboo fiber by a spraying method and can improve the interface compatibility of the bamboo fiber and polypropylene. Secondly, the interfacial bonding performance of the bamboo-plastic composite material is improved by carrying out chemical treatment on a plastic matrix (Abdul Khalila H P S, Bhata I U H, Jawaidb M, Zaidonc A, Hermawan D, Hadi Y. Bamboo fiber reinforced biocomposites: A review. materials & Design 2012,42: 353-. Thirdly, adding a coupling agent or a compatilizer to improve the interface compatibility of the bamboo-plastic composite material. Chinese patent CN110105781A proposes that the interfacial bonding strength of the composite material can be improved by adding polyacryl dopamine into a bamboo powder and polyethylene composite system.

However, the above methods have more or less the following problems: the process is complex; the production cost is increased; presenting potential environmental problems. Therefore, there is a constant effort in academia and industry to find a new cost-effective, more environmentally friendly interface enhancement method.

Disclosure of Invention

The invention provides an induction method of a polypropylene/bamboo fiber interface transverse crystal structure, which is an environment-friendly interface enhancement technology and effectively solves the problems that the bamboo fiber and a thermoplastic polymer have poor interface compatibility, the stress transfer efficiency is low, the strength advantage of the bamboo fiber cannot be fully exerted, and the like.

The invention adopts the following technical scheme:

the invention provides an induction method of a polypropylene/bamboo fiber interface transverse crystal structure, which comprises the step of modifying bamboo fibers by nano titanium dioxide.

The transverse crystal layer is a special crystal thin layer formed by heterogeneous nucleation growth on the surface of the fiber when a semi-crystalline thermoplastic polymer such as polypropylene and the like and the fiber form a composite material, and the thickness of the transverse crystal layer is generally dozens of microns to hundreds of microns. The research of the invention finds that compared with the traditional method of carrying out alkali modification and surface modifier modification on bamboo fibers or carrying out chemical treatment on a plastic matrix and the like, the method improves the interface bonding performance of the composite material by inducing semi-crystalline thermoplastic macromolecules to form a transverse crystal layer on the surface of natural fibers, and is more environment-friendly.

The growth of the transverse crystal layer is related to the isothermal crystallization process and the forming mode, is also closely related to the type, surface physical and chemical characteristics of fibers and semi-crystalline thermoplastic macromolecules, and the formation of the transverse crystal layer is not easy and usually needs certain induction. However, the current induction methods have problems such as low efficiency of inducing the growth of the transverse crystal layer, high production cost and potential environmental pollution.

According to the research of the invention, the nano titanium dioxide is adopted to modify the bamboo fiber, wherein the bamboo fiber mainly comprises cellulose, hemicellulose and lignin, the crystallinity is 40-50%, the surface morphology is complex, the lattice matching degree of nano titanium dioxide particles, the bamboo fiber and polypropylene spherulites can be realized, and the efficient growth of an interface transverse crystal layer of the bamboo-plastic composite material can be facilitated, wherein the nano titanium dioxide particles can construct the interface transverse crystal layer with a compact structure in a short time by utilizing a lattice geometric size matching mechanism of the epiphytic effect theory, and meanwhile, the nano titanium dioxide has a good light shielding effect, can endow the composite material with high ageing resistance, and thus the added value of the composite material is improved.

Preferably, the nanometer titanium dioxide is modified by soaking bamboo fibers with a nanometer titanium dioxide suspension, wherein the nanometer titanium dioxide suspension comprises nanometer titanium dioxide, a KH-570 silane coupling agent, absolute ethyl alcohol and deionized water, and the molar ratio of the nanometer titanium dioxide to the KH-570 silane coupling agent is 1: 1.

The preparation of the nano titanium dioxide suspension is very critical, and the nano titanium dioxide suspension directly influences the modification effect of the bamboo fiber and further relates to the growth of a transverse crystal structure. According to a large number of experiments, the invention is found that the nano titanium dioxide, the KH-570 silane coupling agent, the absolute ethyl alcohol and the deionized water are adopted for preparation, and the molar ratio of the nano titanium dioxide to the KH-570 silane coupling agent is controlled to be 1:1, so that the nano titanium dioxide suspension which is stable and does not delaminate for a long time can be formed.

Preferably, the bamboo fiber obtaining method comprises: after bamboo is preprocessed into bamboo slices with required sizes, the parenchyma cells are cut off along the boundary of bamboo fibers and the parenchyma cells. More preferably, the bamboo fiber obtained by separation needs to be further stripped of the parenchyma cells remained on the surface under a microscope.

Preferably, the bamboo material is moso bamboo.

Preferably, the length of the bamboo fiber is 0.5-1.5 cm, the width is 40-300 μm, and the thickness is 25-120 μm. The thickness of the bamboo fiber needs to be strictly controlled, and the thickness of the bamboo fiber is too large, so that a transverse crystal structure is not formed easily; if the thickness of the bamboo fiber is too small, the bamboo fiber has no obvious effect on enhancing the mechanical property of the composite material. In this case, the bamboo fibers may also be referred to as bamboo fiber bundles.

Preferably, the nano titanium dioxide is anatase nano titanium dioxide with the particle size of 20-40 nm, and the surface energy of the anatase nano titanium dioxide is high, and a large number of hydroxyl groups are easy to agglomerate in an organic medium, so that the nano titanium dioxide is difficult to obtain effective dispersion, and therefore, a KH-570 silane coupling agent is required to modify the nano titanium dioxide, so that the dispersibility of the nano titanium dioxide is improved.

Preferably, the preparation method of the nano titanium dioxide suspension comprises the following steps: dispersing the nano titanium dioxide in absolute ethyl alcohol through high-frequency ultrasound, dispersing a KH-570 silane coupling agent in deionized water, mixing the two dispersion systems, heating in a water bath at 75-85 ℃, stirring for 1-2 hours, cooling, and then performing high-frequency ultrasound treatment.

The preparation method of the nano titanium dioxide suspension is also more critical, and if the components are directly mixed and stirred or ultrasonically dispersed, the obtained suspension is not uniformly dispersed and is unstable, and the phenomenon of layering rapidly occurs in a short time, so that the bamboo fiber modification effect is influenced.

The high-frequency ultrasound can be realized by a cell disruption instrument, the ultrasound time is 20min, the ultrasound power is 250-300W, the ultrasound working mode is 2 s-4 s intermittent, and the ultrasound working mode is preferably carried out under the ice-water bath condition, so that the ultrasound heating temperature rise is prevented.

Preferably, the concentration of the nano titanium dioxide in the nano titanium dioxide suspension is 0.035-0.063 mol/L.

In the technical scheme, when the concentration of the nano titanium dioxide is too low, the surface adhesion amount of the bamboo fiber is too small, and polypropylene cannot be induced to form a transverse crystal layer structure on the surface of the bamboo fiber; when the concentration is too high, the nano titanium dioxide suspension is unstable, and even if the nano titanium dioxide suspension is modified by using a silane coupling agent, the nano titanium dioxide suspension can be agglomerated in a short time, and meanwhile, the nano titanium dioxide attached to the surface of the bamboo fiber can be peeled off. The large-particle nano titanium dioxide can not induce polypropylene to form a transverse crystal layer structure on the surface of the bamboo fiber.

In a preferred embodiment of the present invention, the mass ratio of solute to solvent in the nano titania suspension is nano titania: anhydrous ethanol: deionized water 0.5:100:50 or 0.7:100:50 or 0.9:100: 50.

In a preferred embodiment of the invention, the bamboo fibers accounting for 3-5% of the mass fraction of the nano titanium dioxide suspension are added into the nano titanium dioxide suspension, stirred for 1-2 hours, taken out and dried at 60 ℃ to obtain the nano titanium dioxide modified bamboo fibers.

In a preferred embodiment of the present invention, the method for inducing the transverse crystal structure of the polypropylene/bamboo fiber interface comprises the following steps:

step (1), bamboo fiber bundle separation: preprocessing bamboo into bamboo blocks with the length of 1cm, preparing longitudinal sections by using a paraffin slicer, and cutting off parenchyma cells along the boundary of bamboo fibers and the parenchyma cells under a microscope to obtain required fiber bundles;

preparing a nano titanium dioxide suspension liquid: dispersing nano titanium dioxide in absolute ethyl alcohol through high-frequency ultrasonic, dispersing a KH-570 silane coupling agent in deionized water, mixing the two, heating in a water bath at 80 ℃, stirring for 1h, cooling, and then performing high-frequency ultrasonic treatment; wherein the molar ratio of the nano titanium dioxide to the KH-570 silane coupling agent is 1:1, and the concentration of the nano titanium dioxide in the nano titanium dioxide suspension is 0.035-0.063 mol/L;

step (3), bamboo fiber modification: and (3) putting the fiber bundles obtained in the step (1) into the nano titanium dioxide suspension obtained in the step (2), wherein the fiber bundles account for 4% of the nano titanium dioxide suspension, stirring at normal temperature for 1h, taking out, and drying at 60 ℃.

The invention also provides application of the induction method in preparation of a polypropylene/bamboo fiber interface transverse crystal structure, and the method comprises the step of compounding the bamboo fiber modified by the nano titanium dioxide with the polypropylene.

Preferably, the bamboo fiber modified by the nano titanium dioxide is compounded with the molten polypropylene at the temperature of 190-200 ℃, then the temperature is reduced to 135-145 ℃ at the speed of 10-15 ℃/min, isothermal crystallization is carried out for 15min, and a polypropylene/bamboo fiber interface transverse crystal structure is formed.

According to the invention, the bamboo fiber is modified by the efficiently dispersed nano titanium dioxide, the heterogeneous nucleation efficiency of the polypropylene molecular chain on the surface of the fiber bundle is improved, and the interface transverse crystal structure can be induced to form, so that the interface compatibility between the hydrophilic bamboo fiber and the hydrophobic polypropylene is improved, and the method has an important significance for the utilization of the bamboo fiber reinforced thermoplastic polymer composite material.

Drawings

FIG. 1 is an electron micrograph of a bundle of 0.035mol/L nano-titania modified bamboo fibers obtained in example 1;

FIG. 2 is a 15min interface transverse crystal structure polarized light microscope photograph of isothermal crystallization of PP/0.035 mol/L nano-titania modified bamboo fiber in example 1;

FIG. 3 is an electron micrograph of 0.049mol/L nano-titania modified bamboo fiber bundles in example 2;

FIG. 4 is a polarizing microscope photograph of 15min interface transverse crystal structure of isothermal crystallization of PP/0.049 mol/L nano-titania modified bamboo fiber in example 2;

FIG. 5 is an electron micrograph of 0.063mol/L nano titanium dioxide modified bamboo fiber bundle of example 3;

FIG. 6 is a polarizing microscope photograph of 15min interface transverse crystal structure of isothermal crystallization of PP/0.063 mol/L nano-TiO modified bamboo fiber in example 3;

FIG. 7 is an electron micrograph of 0.077mol/L nano-titania-modified bamboo fiber bundles in comparative example 1;

FIG. 8 is a polarizing microscope photograph of 15min interface crystal structure of polypropylene/0.077 mol/L nano titanium dioxide modified bamboo fiber isothermal crystallization in comparative example 1;

FIG. 9 is an electron micrograph of an unmodified bamboo fiber bundle in comparative example 2;

FIG. 10 is a polarizing microscope photograph of 15min interface crystal structure of polypropylene/unmodified bamboo fiber isothermal crystallization in comparative example 2;

FIG. 11 is an electron micrograph of a bundle of 0.035mol/L nano-zinc oxide modified bamboo fibers of comparative example 3;

FIG. 12 is a 15min interface crystal structure polarized light microscope photograph of isothermal crystallization of PP/0.035 mol/L nano-ZnO modified bamboo fiber in comparative example 3.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Bamboo is pretreated into bamboo blocks with length of 1cm, longitudinal sections with thickness of about 25 μm are prepared by a paraffin slicer, and fiber bundles with width of about 50 + -10 μm are cut under a microscope.

Preparing nano titanium dioxide suspension liquid, wherein the concentration of the suspension liquid is 0.035 mol/L. The nanometer titanium dioxide is dried for 12 hours at the temperature of 110 +/-2 ℃, 0.5g of dried nanometer titanium dioxide is dispersed in 100g of absolute ethyl alcohol through high-frequency ultrasound, 1.5ml of LKH-570 silane coupling agent is dispersed in 50g of deionized water and stirred for 2 minutes, the nanometer titanium dioxide and the deionized water are mixed and then heated in a water bath at the temperature of 80 ℃ and stirred for 1 hour, and high-frequency ultrasound treatment is carried out after cooling. The high-frequency ultrasound is realized by a cell disruption instrument, the ultrasound time is 20min, the ultrasound power is 270W, the ultrasound working mode is 2 s-4 s intermittent, and the ultrasound is carried out under the ice-water bath condition, so that the ultrasound is prevented from heating and increasing the temperature.

And (3) putting 6g of the fiber bundle into 152.1g of nano titanium dioxide suspension with the concentration of 0.035mol/L, stirring for 1h at normal temperature, taking out, and drying at 60 ℃ to obtain the 0.035mol/L nano titanium dioxide modified bamboo fiber bundle.

Placing polypropylene film with thickness of 1mm on a glass slide of a heating table, heating at 190 deg.C for 5min to eliminate thermal history, placing modified bamboo fiber bundle in polypropylene melt, covering a layer of polypropylene film on the surface of the modified bamboo fiber bundle until the modified bamboo fiber bundle is completely melted, and sealing with glass slide to obtain the final product. Cooling to 135 ℃ at a cooling speed of 10 ℃/min, and carrying out isothermal crystallization for 15min to form a polypropylene/bamboo fiber interface transverse crystal structure. And (3) rapidly freezing the polypropylene/bamboo fiber composite material after isothermal crystallization in ice water to fix the interface transverse crystal structure. The crystallization process was photographed by observation through a polarizing microscope.

FIG. 1 is an electron micrograph of 0.035mol/L nano titanium dioxide modified bamboo fiber bundles (molar ratio of nano titanium dioxide to KH-570 silane coupling agent is 1: 1).

FIG. 2 is a polarizing microscope photograph of 15min interface transverse crystal structure of polypropylene/0.035 mol/L nano titanium dioxide modified bamboo fiber isothermal crystallization (molar ratio of nano titanium dioxide to KH-570 silane coupling agent is 1: 1).

Example 2

Bamboo is pretreated into bamboo blocks with length of 1cm, longitudinal sections with thickness of about 25 μm are prepared by a paraffin slicer, and fiber bundles with width of about 50 + -10 μm are cut under a microscope.

Preparing a nano titanium dioxide suspension with the concentration of 0.049 mol/L. The nanometer titanium dioxide is dried for 12 hours at the temperature of 110 +/-2 ℃, 0.7g of dried nanometer titanium dioxide is dispersed in 100g of absolute ethyl alcohol through high-frequency ultrasonic, 2.1mLKH-570 silane coupling agent is dispersed in 50g of deionized water and stirred for 2min, the nanometer titanium dioxide and the anhydrous ethyl alcohol are mixed, and then heated and stirred for 1 hour in water bath at the temperature of 80 ℃, and then high-frequency ultrasonic treatment is carried out after cooling. The high-frequency ultrasound is realized by a cell disruption instrument, the ultrasound time is 20min, the ultrasound power is 270W, the ultrasound working mode is 2 s-4 s intermittent, and the ultrasound is carried out under the ice-water bath condition, so that the ultrasound is prevented from heating and increasing the temperature.

And putting 6g of the fiber bundle into 152.9g of nano titanium dioxide suspension with the concentration of 0.049mol/L, stirring for 1h at normal temperature, taking out, and drying at 60 ℃ to obtain the 0.049mol/L nano titanium dioxide modified bamboo fiber bundle.

Placing polypropylene film with thickness of 1mm on a glass slide of a heating table, heating at 190 deg.C for 5min to eliminate thermal history, placing modified bamboo fiber bundle in polypropylene melt, covering a layer of polypropylene film on the surface of the modified bamboo fiber bundle until the modified bamboo fiber bundle is completely melted, and sealing with glass slide to obtain the final product. Cooling to 135 ℃ at a cooling speed of 10 ℃/min, and carrying out isothermal crystallization for 15min to form a polypropylene/bamboo fiber interface transverse crystal structure. And (3) rapidly freezing the polypropylene/bamboo fiber composite material after isothermal crystallization in ice water to fix the interface transverse crystal structure. The crystallization process was photographed by observation through a polarizing microscope.

FIG. 3 is an electron micrograph of 0.049mol/L nano-titanium dioxide modified bamboo fiber bundle.

FIG. 4 is a polarizing microscope photograph of 15min interface transverse crystal structure of polypropylene/0.049 mol/L nano titanium dioxide modified bamboo fiber isothermal crystallization.

Example 3

Bamboo is pretreated into bamboo blocks with length of 1cm, longitudinal sections with thickness of about 25 μm are prepared by a paraffin slicer, and fiber bundles with width of about 50 + -10 μm are cut under a microscope.

Preparing nano titanium dioxide suspension liquid, wherein the concentration of the suspension liquid is 0.063 mol/L. The nanometer titanium dioxide is dried for 12 hours at the temperature of 110 +/-2 ℃, 0.9g of dried nanometer titanium dioxide is dispersed in 100g of absolute ethyl alcohol through high-frequency ultrasound, 2.7ml of LKH-570 silane coupling agent is dispersed in 50g of deionized water and stirred for 2 minutes, the nanometer titanium dioxide and the deionized water are mixed and then heated in a water bath at the temperature of 80 ℃ and stirred for 1 hour, and high-frequency ultrasound treatment is carried out after cooling. The high-frequency ultrasound is realized by a cell disruption instrument, the ultrasound time is 20min, the ultrasound power is 270W, the ultrasound working mode is 2 s-4 s intermittent, and the ultrasound is carried out under the ice-water bath condition, so that the ultrasound is prevented from heating and increasing the temperature.

Putting 6g of fiber bundles into 153.7g of nano titanium dioxide suspension with the concentration of 0.063mol/L, stirring for 1h at normal temperature, taking out and drying at 60 ℃ to obtain 0.063mol/L nano titanium dioxide modified bamboo fiber bundles.

Placing polypropylene film with thickness of 1mm on a glass slide of a heating table, heating at 190 deg.C for 5min to eliminate thermal history, placing modified bamboo fiber bundle in polypropylene melt, covering a layer of polypropylene film on the surface of the modified bamboo fiber bundle until the modified bamboo fiber bundle is completely melted, and sealing with glass slide to obtain the final product. Cooling to 135 ℃ at a cooling speed of 10 ℃/min, and carrying out isothermal crystallization for 15min to form a polypropylene/bamboo fiber interface transverse crystal structure. And (3) rapidly freezing the polypropylene/bamboo fiber composite material after isothermal crystallization in ice water to fix the interface transverse crystal structure. The crystallization process was photographed by observation through a polarizing microscope.

FIG. 5 is an electron micrograph of 0.063mol/L nano titanium dioxide modified bamboo fiber bundle.

FIG. 6 is a 15min interface transverse crystal structure polarized light microscope photograph of polypropylene/0.063 mol/L nano titanium dioxide modified bamboo fiber crystallization.

Comparative example 1

Bamboo is pretreated into bamboo blocks with length of 1cm, longitudinal sections with thickness of about 25 μm are prepared by a paraffin slicer, and fiber bundles with width of about 50 + -10 μm are cut under a microscope.

Preparing a nano titanium dioxide suspension, wherein the concentration of the suspension is 0.077 mol/L. The nanometer titanium dioxide is dried for 12 hours at the temperature of 110 +/-2 ℃, 1.1g of dried nanometer titanium dioxide is dispersed in 100g of absolute ethyl alcohol through high-frequency ultrasound, 3.3mLKH-570 silane coupling agent is dispersed in 50g of deionized water and stirred for 2min, the nanometer titanium dioxide and the anhydrous ethyl alcohol are mixed, heated and stirred for 1 hour in water bath at the temperature of 80 ℃, cooled and then subjected to high-frequency ultrasound treatment. The high-frequency ultrasound is realized by a cell disruption instrument, the ultrasound time is 20min, the ultrasound power is 270W, the ultrasound working mode is 2 s-4 s intermittent, and the ultrasound is carried out under the ice-water bath condition, so that the ultrasound is prevented from heating and increasing the temperature.

Putting 6g of the fiber bundle into 154.4g of nano titanium dioxide suspension with the concentration of 0.077mol/L, stirring for 1h at normal temperature, taking out, and drying at 60 ℃ to obtain the 0.077mol/L nano titanium dioxide modified bamboo fiber bundle.

Placing polypropylene film with thickness of 1mm on a glass slide of a heating table, heating at 190 deg.C for 5min to eliminate thermal history, placing modified bamboo fiber bundle in polypropylene melt, covering a layer of polypropylene film on the surface of the modified bamboo fiber bundle until the modified bamboo fiber bundle is completely melted, and sealing with glass slide to obtain the final product. Cooling to 135 deg.C at a cooling rate of 10 deg.C/min, and performing isothermal crystallization for 15 min. And (3) rapidly freezing the polypropylene/bamboo fiber composite material after isothermal crystallization in ice water to fix the interface crystal structure. The crystallization process was photographed by observation through a polarizing microscope.

FIG. 7 is an electron micrograph of 0.077mol/L nano titanium dioxide modified bamboo fiber bundles.

FIG. 8 is a polarizing microscope photograph of 15min interface crystal structure of polypropylene/0.077 mol/L nano titanium dioxide modified bamboo fiber crystallization.

The average dispersed particle size of the nano titanium dioxide suspension in examples 1 to 3 and comparative example 1 in 1 hour is shown in table 1.

TABLE 1 average dispersed particle size of nano-titania suspension over 1h

As shown in Table 1, the methods of examples 1 to 3 all gave stable suspensions of nano-sized titanium dioxide with almost no change in particle size within 1 hour. In comparative example 1, when the concentration of the nano titanium dioxide reached 0.077mol/L, the suspension was unstable and the particle size rapidly increased within 1 hour.

Comparative example 2

Bamboo is pretreated into bamboo blocks with length of 1cm, longitudinal sections with thickness of about 25 μm are prepared by a paraffin slicer, and fiber bundles with width of about 50 + -10 μm are cut under a microscope.

Placing polypropylene film with thickness of 1mm on glass slide of heating table, heating at 190 deg.C for 5min to eliminate thermal history, placing unmodified bamboo fiber bundle in polypropylene melt, covering a layer of polypropylene film on its surface until it is completely molten, and sealing with cover glass. Cooling to 135 deg.C at a cooling rate of 10 deg.C/min, and performing isothermal crystallization for 15 min. And (3) observing and photographing through a polarizing microscope in the crystallization process, and quickly freezing the polypropylene/unmodified bamboo fiber composite material subjected to isothermal crystallization in ice water to fix the crystal structure.

Fig. 9 is an electron micrograph of an unmodified bamboo fiber bundle.

FIG. 10 is a polarizing microscope photograph of 15min interface crystal structure of polypropylene/unmodified bamboo fiber isothermal crystallization.

Comparative example 3

Bamboo is pretreated into bamboo blocks with length of 1cm, longitudinal sections with thickness of about 25 μm are prepared by a paraffin slicer, and fiber bundles with width of about 50 + -10 μm are cut under a microscope.

And preparing a nano zinc oxide suspension with the concentration of 0.035 mol/L. The nanometer titanium dioxide is dried for 12 hours at the temperature of 110 +/-2 ℃, 0.35g of dried nanometer zinc oxide is dispersed in 100g of absolute ethyl alcohol through high-frequency ultrasound, the high-frequency ultrasound is realized through a cell disruption instrument, the ultrasound time is 20min, the ultrasound power is 270W, the ultrasound working mode is 2 s-4 s of pause, and the drying is carried out under the ice-water bath condition, so that the temperature rise caused by ultrasound heating is prevented.

And (3) putting 6g of the fiber bundle into 100.35g of nano zinc oxide suspension with the concentration of 0.035mol/L, stirring for 1h at normal temperature, taking out, and drying at 60 ℃ to obtain the 0.035mol/L nano zinc oxide modified bamboo fiber bundle.

Placing polypropylene film with thickness of 1mm on a glass slide of a heating table, heating at 190 deg.C for 5min to eliminate thermal history, placing modified bamboo fiber bundle in polypropylene melt, covering a layer of polypropylene film on the surface of the modified bamboo fiber bundle until the modified bamboo fiber bundle is completely melted, and sealing with glass slide to obtain the final product. Cooling to 135 deg.C at a cooling rate of 10 deg.C/min, and performing isothermal crystallization for 15 min. And (3) rapidly freezing the polypropylene/bamboo fiber composite material after isothermal crystallization in ice water to fix the interface crystal structure. The crystallization process was photographed by observation through a polarizing microscope.

FIG. 11 is an electron micrograph of the 0.035mol/L nano-zinc oxide modified bamboo fiber bundle.

FIG. 12 is a polarizing microscope photograph of 15min interface crystal structure of polypropylene/0.035 mol/L nano-zinc oxide modified bamboo fiber isothermal crystallization.

The polarization microscope photographs of the interface transverse crystal structure in examples 1 to 3 and comparative examples 1 to 3 were taken and recorded under the isothermal crystallization process, and the widths of the transverse crystal layers for 15min of isothermal crystallization are shown in table 2.

TABLE 2 width of transverse layer in isothermal crystallization for 15min in each of examples and comparative examples

As shown in Table 2, the interfacial transverse crystal structure was produced by the methods of examples 1 to 3, whereas the transverse crystal structure was not produced in comparative examples 1 to 3, which shows that the production of the interfacial transverse crystal structure can be induced by the method of the present invention.

Example 4

Bamboo is pretreated into bamboo blocks with the length of 1cm, longitudinal sections with the thickness of about 120 mu m are prepared by a sliding-away slicing machine, and fiber bundles with the width of about 300 mu m are cut under a microscope.

Preparing nano titanium dioxide suspension liquid, wherein the concentration of the suspension liquid is 0.035 mol/L. The nanometer titanium dioxide is dried for 12 hours at the temperature of 110 +/-2 ℃, 0.5g of dried nanometer titanium dioxide is dispersed in 100g of absolute ethyl alcohol through high-frequency ultrasound, 1.5ml of LKH-570 silane coupling agent is dispersed in 50g of deionized water and stirred for 2 minutes, the nanometer titanium dioxide and the deionized water are mixed and then heated in a water bath at the temperature of 80 ℃ and stirred for 1 hour, and high-frequency ultrasound treatment is carried out after cooling. The high-frequency ultrasonic dispersion is realized by a cell disruption instrument, the ultrasonic time is 20min, the ultrasonic power is 270W, the ultrasonic working mode is 2 s-4 s intermittent working, and the ultrasonic dispersion is carried out under the ice-water bath condition, so that the ultrasonic heating temperature rise is prevented.

And (3) putting 6g of the fiber bundle into 152.1g of nano titanium dioxide suspension with the concentration of 0.035mol/L, stirring for 1h at normal temperature, taking out, and drying at 60 ℃ to obtain the 0.035mol/L nano titanium dioxide modified bamboo fiber bundle.

Placing a 2mm thick polypropylene film on a glass slide of a heating table, heating at 190 deg.C for 5min to eliminate thermal history, placing one end of the modified bamboo fiber bundle with a thickness of about 600 μm in a polypropylene melt, covering a layer of polypropylene film on the surface of the modified bamboo fiber bundle until the modified bamboo fiber bundle is completely melted, and sealing with a glass cover. Cooling to 135 ℃ at a cooling speed of 10 ℃/min, carrying out isothermal crystallization for 19-20min to form a polypropylene/bamboo fiber interface transverse crystal structure, rapidly freezing the polypropylene/bamboo fiber composite material subjected to isothermal crystallization in ice water, and fixing the interface transverse crystal structure. The other end of the modified fiber bundle is arranged between the two polypropylene film melts by about 0.5cm, and the modified fiber bundle is fixed after natural cooling.

And (3) carrying out a fiber pulling-out experiment on the sample by utilizing a fiber stretching mode of a dynamic thermomechanical analyzer, wherein the pulling-out speed is 50 mu m/min, and calculating to obtain the interface shear strength.

Comparative example 4

Bamboo is pretreated into bamboo blocks with the length of 1cm, longitudinal sections with the thickness of about 120 mu m are prepared by a sliding-away slicing machine, and fiber bundles with the width of about 300 mu m are cut under a microscope.

Placing a 2mm thick polypropylene film on a glass slide of a heating table, heating at 190 deg.C for 5min to eliminate thermal history, placing one end of unmodified bamboo fiber bundle with a thickness of about 600 μm in polypropylene melt, covering a layer of polypropylene film on the surface of the unmodified bamboo fiber bundle until the unmodified bamboo fiber bundle is completely melted, and sealing with a glass slide. Cooling to 135 ℃ at a cooling rate of 10 ℃/min, carrying out isothermal crystallization for 19-20min, rapidly freezing the polypropylene/bamboo fiber composite material subjected to isothermal crystallization in ice water, and fixing the crystal structure. The other end of the unmodified bamboo fiber bundle is arranged between two polypropylene film melts by about 0.5cm, and the unmodified bamboo fiber bundle is fixed after being naturally cooled.

And (3) carrying out a fiber pulling-out experiment on the sample by utilizing a fiber stretching mode of a dynamic thermomechanical analyzer, wherein the pulling-out speed is 50 mu m/min, and calculating to obtain the interface shear strength.

The interfacial shear strength data described in example 4 and comparative example 4 are listed in table 3.

TABLE 3 interfacial shear Strength in example 4 and comparative example 4

	Example 4	Comparative example 4
			Transverse crystal layer width (mum)	60.64±6.91	-
Interfacial shear strength (MPa)	9.34	6.53

As shown in table 3, the interfacial shear strength of example 4 is improved by about 43.0% compared with that of comparative example 4, which indicates that the interfacial transverse crystal structure is induced by modifying bamboo fiber through high-efficiency dispersion of nano titanium dioxide, so that the mechanical strength of the bamboo fiber and polypropylene interface can be effectively improved.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.