Preparation method of straw / high-density polyethylene color composite material

Abstract

The present application provides a kind of straw / high density polyethylene color composite material preparation method, steps are: with straw as raw material, washing, drying, section after microwave treatment;Straw is bleached using ultrasonic assisted bleaching technology;With nano attapulgite as color fixing agent, combine ultrasonic and high pressure homogenization treatment technology to color fixing iron oxide pigment, prepare straw / high density polyethylene color composite material by vacuum hot pressing forming process and vacuum heat fixing technology.The present application solves the problems of poor color stability, color number adjustment is greatly influenced by original color of straw and other problems in the preparation of color composite material by directly adding pigment or colorant in traditional preparation process, gives straw / high density polyethylene composite material stable color, and further expands the application range of straw / high density polyethylene composite material.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a method for preparing straw / high-density polyethylene colored composite material. Background Technology

[0002] Wood-plastic composites are a rapidly developing green and environmentally friendly material in recent years. They are made primarily from plant fibers such as wood flour and straw, combined with thermoplastic plastics, and supplemented with functional additives such as coupling agents and stabilizers. The composites are then processed through molding, extrusion, or injection molding. Straw, the plant stem residue left after crop harvesting, is generally considered waste. However, its rich cellulose and fibrous structure makes it an ideal raw material for preparing composite materials. Furthermore, the effective utilization of straw resources can reduce agricultural waste emissions and improve the comprehensive utilization rate of agricultural waste.

[0003] High-density polyethylene (HDPE) is a plastic material with excellent physical properties, including superior weather resistance, chemical corrosion resistance, and mechanical strength. It is also a recyclable material. Combining straw with HDPE can improve the performance of HDPE and give the composite material more functions.

[0004] However, with the rapid expansion of the application fields of wood-plastic products and the gradual diversification of market requirements for the appearance of wood-plastic products, the limited color range restricts its further promotion and application. Therefore, adding inorganic pigments to composite materials can give straw / high-density polyethylene composite materials rich colors and aesthetics. However, the colored composite materials prepared by directly adding pigments or colorants in the existing preparation process have problems such as poor color stability and color matching being greatly affected by the original color of straw, which in turn affects the outdoor application of colored composite materials.

[0005] Microwave-assisted cleaning technology utilizes the heating properties of microwaves to accelerate the cleaning process. Straw surfaces often have impurities and contaminants, requiring cleaning to improve material quality. Applying microwave-assisted cleaning to straw processing allows microwave energy to rapidly heat the material through frictional heat generated by the solvents and water molecules, achieving fast and uniform cleaning. This quickly and efficiently removes impurities and pigments from the straw surface. The technology also achieves the effect of heat treatment of straw while significantly reducing energy consumption compared to traditional methods.

[0006] Ultrasonic waves can generate tiny bubbles in liquids, which then collapse instantaneously, creating strong localized impacts and eddy currents. Using ultrasound technology for bleaching can promote the diffusion and reaction of bleach on material surfaces, achieving a rapid and uniform bleaching effect. Applying ultrasound-assisted bleaching technology to the preparation of colored wood-plastic composites can reduce the amount of bleach used, saving resources. Compared to traditional bleaching methods, ultrasound-assisted bleaching does not require high temperatures or strong acid / alkali conditions, reducing damage to materials. It also uses harmless bleach, posing no harm to the environment or human health. Furthermore, the frequency, power, and duration of ultrasound waves can be adjusted to achieve the optimal bleaching effect.

[0007] Iron oxide is a non-toxic and harmless inorganic substance that can be used as an inorganic pigment to obtain different colors through various processing methods. It exhibits good lightfastness, is not easily faded by prolonged exposure to sunlight, and can maintain the color stability and durability of composite materials. Using inorganic pigments in the preparation of wood-plastic composites is more environmentally friendly than organic pigments and has no adverse effects on human health. Therefore, using iron oxide inorganic pigments as an effective color regulator for wood-plastic composites not only enables diverse color choices but also provides excellent lightfastness, weather resistance, and environmental friendliness.

[0008] Nano-attapulgite is a natural mineral clay with a microporous structure. Its high specific surface area and adsorption capacity make it an ideal color-fixing agent. In the preparation of colored wood-plastic composites, nano-attapulgite is ball-milled and mixed with iron oxide pigments for pigment fixation. The adsorption capacity of the nano-attapulgite surface can be used to fix the pigment particles, preventing color fading due to external factors such as sunlight and rain. Furthermore, the very small particle size and high surface area of ​​nano-attapulgite enable the pigment particles to be uniformly dispersed in the composite material, improving color uniformity.

[0009] Therefore, developing a method for preparing straw / high-density polyethylene colored composite materials by combining ultrasonic-assisted bleaching of straw with coloring of iron oxide inorganic pigments and nano-attapulgite color fixing process is of great significance for endowing straw / high-density polyethylene composite materials with stable and rich colors and aesthetics, thereby expanding the application range of straw / high-density polyethylene composite materials. Summary of the Invention

[0010] Based on the aforementioned background technology and the problems of poor color stability and significant influence of the original color of straw on color matching in traditional preparation processes for colored composite materials, it is necessary to provide a method for preparing straw / high-density polyethylene colored composite materials. This method modifies and bleaches the straw to improve its mechanical properties and its bonding with high-density polyethylene, reduces the negative impact of the straw's own color on the coloring of the composite material, and uses color-fixed modified inorganic pigments to improve its color stability under outdoor aging conditions.

[0011] To achieve the above objectives, the present invention proposes the following technical solution:

[0012] A method for preparing a straw / high-density polyethylene colored composite material, characterized by comprising the following steps:

[0013] Step 1, Straw Processing: Using straw as raw material, wash, dry, and cut the straw into sections, then place it in distilled water in a certain proportion for microwave-assisted cleaning;

[0014] Step 2, Straw bleaching: After drying the straw washed in Step 1, crush it, place it in hydrogen peroxide solution, bleach it under ultrasonic conditions, and then wash and dry it.

[0015] Step 3, Pigment Fixation: The inorganic pigment and fixing agent are ball-milled and mixed, then dispersed in deionized water. A dispersant is added, and the mixture is subjected to alternating high-pressure homogenization and low-frequency ultrasonic treatment. The fixing agent is a nano-attapulgite.

[0016] Step 4: Filter and separate the suspension treated in Step 3, and dry and pulverize the resulting precipitate;

[0017] Step 5, Material Preparation: The color-fixing pigment powder obtained in Step 4, the straw powder obtained in Step 2, the coupling agent, and high-density polyethylene are blended and then molded using a vacuum molding device;

[0018] Step 6: Secondary color fixation of composite material: After vacuum hot pressing, the composite material is quickly placed in a vacuum drying oven and kept at 80°C for 2.5 hours for secondary color fixation.

[0019] Furthermore, in step one, the ratio of straw to distilled water is 100g:1L to 100g:1.5L; the microwave power is 450W, and the time is 3 to 3.5 minutes.

[0020] Furthermore, in step two, the concentration of hydrogen peroxide solution is 3-5%; the ratio of straw to hydrogen peroxide solution is 100g:0.5L to 100g:1L; the ultrasonic treatment uses a frequency of 25kHz, with a 1-minute pause after every 5 minutes of ultrasonic treatment, and an amplitude of 50-60%; the bleaching time is 1 hour; and the straw powder is dried by spray drying.

[0021] Furthermore, in step three, the inorganic pigment is one or more of iron oxide red, iron oxide yellow, and iron oxide blue mixed in any proportion; the dispersant is sodium hexametaphosphate; the mass ratio of the fixing agent to the inorganic pigment is 1:2; the ratio of the dispersant to the pigment is 1:3; the high-pressure homogenization and low-frequency ultrasonic treatment are alternated, with each high-pressure homogenization lasting 4 minutes and the low-frequency ultrasonic treatment lasting 8 minutes, for a total of two cycles. The pressure of the high-pressure homogenization is 70-80 MPa, and the low-frequency ultrasonic parameters are the same as those in step two.

[0022] Furthermore, in step five, the ratio of the color-fixing pigment powder, straw powder, coupling agent, and high-density polyethylene is 4:50:3:50; the heating temperature of the vacuum hot press is 170-180℃, the hot pressing holding time is 25-30 minutes, and the hot press pressure is 20MPa.

[0023] Working principle of this invention:

[0024] This invention addresses the problems of poor coloring effect, unstable color, and significant influence of pigments carried by straw on straw in straw / high-density polyethylene composite materials. By modifying straw and pigments, and using nano-attapulgite as a fixing agent to fix the pigments, the coloring effect of the pigments becomes more uniform and stable. At the same time, the straw is bleached to reduce the influence of the straw's own color on the coloring effect. Finally, the prepared composite material is subjected to secondary vacuum thermosetting.

[0025] More specifically, in the straw bleaching technology, the straw is first cleaned with microwave assistance. Microwaves quickly and efficiently remove impurities and pigments from the surface of the straw, while simultaneously opening up the internal structure of the straw fibers to facilitate pigment dissolution. During bleaching, ultrasonic treatment is used to promote the diffusion and reaction of the bleaching agent inside the straw, achieving a rapid and uniform bleaching effect. The straw is also pre-treated with ultrasound. The bleached straw powder is then spray-dried to maximize the dispersibility and surface properties of the straw fibers, which is beneficial for the uniform dispersion and efficient bonding with other components during the preparation of composite materials.

[0026] The beneficial effects of this invention are as follows:

[0027] In terms of technological innovation, this invention employs a series of innovative technologies and methods to improve the preparation process of straw / high-density polyethylene composite materials. First, it introduces microwave-assisted cleaning and ultrasonic treatment technologies into the straw bleaching process, which can rapidly remove impurities and pigments from the straw surface in a short time, achieving a fast and uniform bleaching effect. Second, addressing the problems of poor coloring effect and unstable color, this invention successfully achieves uniform and stable pigment coloring by modifying straw and pigments and introducing nano-attapulgite as a color-fixing agent, thus improving the coloring effect. This endows the straw / high-density polyethylene composite material with rich colors and aesthetic appeal, thereby expanding its application range.

[0028] In terms of material utilization, this invention makes full use of waste straw resources and combines them with high-density polyethylene, thereby achieving effective utilization and regeneration of straw resources. This method of resource utilization aligns with current societal requirements for environmental protection and sustainable development. By effectively utilizing waste straw resources, this invention can also create new economic value for farmers and improve the development level of rural areas. Attached Figure Description

[0029] Figure 1 These are the colorimetric test results before and after the aging tests in Examples 1 to 3 and Comparative Examples 1 to 3;

[0030] Figure 2 This is the surface microstructure of the composite material after aging in Example 1;

[0031] Figure 3 This is the surface microstructure of the composite material after aging in Example 2;

[0032] Figure 4 This is the surface microstructure of the composite material after aging in Example 3;

[0033] Figure 5 The surface microstructure of the composite material in Comparative Example 1 after aging is shown.

[0034] Figure 6 The surface microstructure of the composite material in Comparative Example 2 after aging is shown.

[0035] Figure 7 The microstructure of the composite material after aging is shown in Comparative Example 3. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products. Example 1

[0038] A method for preparing a red wheat straw / high-density polyethylene composite material, characterized by comprising the following steps:

[0039] Step 1: Wheat straw processing: Using wheat straw as raw material, wash and dry the wheat straw, cut it into sections, and place it in distilled water in a certain proportion for microwave-assisted cleaning;

[0040] Step 2, Bleaching of wheat straw: After drying the wheat straw washed in Step 2, crush it, place it in hydrogen peroxide solution, bleach it under ultrasonic conditions, and then wash and dry it.

[0041] Step 3: Pigment Fixation: After ball milling and mixing the inorganic pigment and fixing agent, disperse them in deionized water, add a dispersant, and perform alternating high-pressure homogenization and low-frequency ultrasonic treatment.

[0042] Step 4: Filter and separate the suspension treated in Step 3, and dry and pulverize the resulting precipitate;

[0043] Step 5, Material Preparation: The color-fixing pigment powder obtained in Step 4, the wheat straw powder obtained in Step 2, the coupling agent, and high-density polyethylene are blended and then molded using a vacuum molding device;

[0044] Step 6: Secondary color fixation of composite material: After vacuum hot pressing, the composite material is quickly placed in a vacuum drying oven and kept at 80°C for 2.5 hours for secondary color fixation.

[0045] Furthermore, in step one, the ratio of wheat straw to distilled water is 100 g: 1.5 L; the microwave power is 450 W, and the time is 3 min.

[0046] Furthermore, in step two, the concentration of hydrogen peroxide solution is 4%; the ratio of wheat straw to hydrogen peroxide solution is 100 g: 0.8 L; the ultrasonic treatment uses a frequency of 25 kHz, with a 1-minute pause every 5 minutes, and an amplitude of 55%; the bleaching time is 1 hour; and the wheat straw powder is dried by spray drying.

[0047] Furthermore, in step three, the fixing agent is nano-attapulgite; the inorganic pigment is iron oxide red; the dispersant is sodium hexametaphosphate; the mass ratio of the fixing agent to the inorganic pigment is 1:2; the ratio of the dispersant to the pigment is 1:3; the high-pressure homogenization and low-frequency ultrasound treatment are alternated, with each high-pressure homogenization lasting 4 minutes and the low-frequency ultrasound lasting 8 minutes, for a total of two cycles. The pressure of the high-pressure homogenization is 80 MPa, and the low-frequency ultrasound parameters are the same as those in step two.

[0048] Furthermore, in step five, the ratio of the color-fixing pigment powder, wheat straw powder, coupling agent, and high-density polyethylene is 4:50:3:50; the heating temperature of the vacuum hot press is 175 ℃, the hot pressing holding time is 25 min, and the hot press pressure is 20 MPa.

[0049] The color stability test results of the manufactured wheat straw / high-density polyethylene red composite material under ultraviolet accelerated aging conditions are as follows: Figure 1 As shown, the appearance color of the composite material before and after aging is as follows: Figure 2 As shown. Example 2

[0050] A method for preparing a yellow wheat straw / high-density polyethylene composite material, characterized by comprising the following steps:

[0051] Step 1: Wheat straw processing: Using wheat straw as raw material, wash and dry the wheat straw, cut it into sections, and place it in distilled water in a certain proportion for microwave-assisted cleaning;

[0052] Step 2, Bleaching of wheat straw: After drying the wheat straw washed in Step 2, crush it, place it in hydrogen peroxide solution, bleach it under ultrasonic conditions, and then wash and dry it.

[0053] Step 3: Pigment Fixation: After ball milling and mixing the inorganic pigment and fixing agent, disperse them in deionized water, add a dispersant, and perform alternating high-pressure homogenization and low-frequency ultrasonic treatment.

[0054] Step 4: Filter and separate the suspension treated in Step 3, and dry and pulverize the resulting precipitate;

[0055] Step 5, Material Preparation: The color-fixing pigment powder obtained in Step 4, the wheat straw powder obtained in Step 2, the coupling agent, and high-density polyethylene are blended and then molded using a vacuum molding device;

[0056] Step 6: Secondary color fixation of composite material: After vacuum hot pressing, the composite material is quickly placed in a vacuum drying oven and kept at 80°C for 2.5 hours for secondary color fixation.

[0057] Furthermore, in step one, the ratio of wheat straw to distilled water is 100 g: 1.5 L; the microwave power is 450 W, and the time is 3 min.

[0058] Furthermore, in step two, the concentration of hydrogen peroxide solution is 4%; the ratio of wheat straw to hydrogen peroxide solution is 100 g: 0.8 L; the ultrasonic treatment uses a frequency of 25 kHz, with a 1-minute pause every 5 minutes, and an amplitude of 55%; the bleaching time is 1 hour; and the wheat straw powder is dried by spray drying.

[0059] Furthermore, in step three, the fixing agent is nano-attapulgite; the inorganic pigment is iron oxide yellow; the dispersant is sodium hexametaphosphate; the mass ratio of the fixing agent to the inorganic pigment is 1:2; the ratio of the dispersant to the pigment is 1:3; the high-pressure homogenization and low-frequency ultrasound treatment are alternated, with each high-pressure homogenization lasting 4 minutes and the low-frequency ultrasound lasting 8 minutes, for a total of two cycles. The pressure of the high-pressure homogenization is 80 MPa, and the low-frequency ultrasound parameters are the same as those in step two.

[0060] Furthermore, in step five, the ratio of the color-fixing pigment powder, wheat straw powder, coupling agent, and high-density polyethylene is 4:50:3:50; the heating temperature of the vacuum hot press is 175 ℃, the hot pressing holding time is 25 min, and the hot press pressure is 20 MPa.

[0061] The color stability test results of the manufactured wheat straw / high-density polyethylene yellow composite material under ultraviolet accelerated aging conditions are as follows: Figure 1 As shown, the appearance color of the composite material before and after aging is as follows: Figure 3 As shown. Example 3

[0062] A method for preparing a blue wheat straw / high-density polyethylene composite material, characterized by comprising the following steps:

[0063] Step 1: Wheat straw processing: Using wheat straw as raw material, wash and dry the wheat straw, cut it into sections, and place it in distilled water in a certain proportion for microwave-assisted cleaning;

[0064] Step 2, Bleaching of wheat straw: After drying the wheat straw washed in Step 2, crush it, place it in hydrogen peroxide solution, bleach it under ultrasonic conditions, and then wash and dry it.

[0065] Step 3: Pigment Fixation: After ball milling and mixing the inorganic pigment and fixing agent, disperse them in deionized water, add a dispersant, and perform alternating high-pressure homogenization and low-frequency ultrasonic treatment.

[0066] Step 4: Filter and separate the suspension treated in Step 3, and dry and pulverize the resulting precipitate;

[0067] Step 5, Material Preparation: The color-fixing pigment powder obtained in Step 4, the wheat straw powder obtained in Step 2, the coupling agent, and high-density polyethylene are blended and then molded using a vacuum molding device;

[0068] Step 6: Secondary color fixation of composite material: After vacuum hot pressing, the composite material is quickly placed in a vacuum drying oven and kept at 80°C for 2.5 hours for secondary color fixation.

[0069] Furthermore, in step one, the ratio of wheat straw to distilled water is 100 g: 1.5 L; the microwave power is 450 W, and the time is 3 min.

[0070] Furthermore, in step two, the concentration of hydrogen peroxide solution is 4%; the ratio of wheat straw to hydrogen peroxide solution is 100 g: 0.8 L; the ultrasonic treatment uses a frequency of 25 kHz, with a 1-minute pause every 5 minutes, and an amplitude of 55%; the bleaching time is 1 hour; and the wheat straw powder is dried by spray drying.

[0071] Furthermore, in step three, the fixing agent is nano-attapulgite; the inorganic pigment is iron oxide blue; the dispersant is sodium hexametaphosphate; the mass ratio of the fixing agent to the inorganic pigment is 1:2; the ratio of the dispersant to the pigment is 1:3; the high-pressure homogenization and low-frequency ultrasound treatment are alternated, with each high-pressure homogenization lasting 4 minutes and the low-frequency ultrasound lasting 8 minutes, for a total of two cycles. The pressure of the high-pressure homogenization is 80 MPa, and the low-frequency ultrasound parameters are the same as those in step two.

[0072] Furthermore, in step five, the ratio of the color-fixing pigment powder, wheat straw powder, coupling agent, and high-density polyethylene is 4:50:3:50; the heating temperature of the vacuum hot press is 175 ℃, the hot pressing holding time is 25 min, and the hot press pressure is 20 MPa.

[0073] The color stability test results of the manufactured wheat straw / high-density polyethylene yellow composite material under ultraviolet accelerated aging conditions are as follows: Figure 1 As shown, the appearance color of the composite material before and after aging is as follows: Figure 4 As shown. Comparative Example 1

[0074] A method for preparing a red wheat straw / high-density polyethylene composite material, characterized by comprising the following steps:

[0075] Step 1: Wheat straw processing: Using wheat straw as raw material, wash, dry, and then crush the wheat straw;

[0076] Step 2, Material Preparation: Iron oxide red pigment, wheat straw powder obtained in Step 1, coupling agent and high-density polyethylene are blended and then molded using a vacuum molding device;

[0077] Step 3, Secondary color fixation of composite material: After vacuum hot pressing, the composite material is quickly placed in a vacuum drying oven and kept at 80°C for 2.5 hours for secondary color fixation.

[0078] Furthermore, in step two, the ratio of pigment, wheat straw powder, coupling agent, and high-density polyethylene is 4:50:3:50; the heating temperature of the vacuum hot press is 175 ℃, the hot pressing holding time is 25 min, and the hot press pressure is 20 MPa.

[0079] The color stability test results of the manufactured wheat straw / high-density polyethylene red composite material under ultraviolet accelerated aging conditions are as follows: Figure 1 As shown, the appearance color of the composite material before and after aging is as follows: Figure 5 As shown. Comparative Example 2

[0080] A method for preparing a red wheat straw / high-density polyethylene composite material, characterized by comprising the following steps:

[0081] Step 1: Wheat straw processing: Using wheat straw as raw material, wash and dry the wheat straw, cut it into sections, place it in distilled water in a certain proportion, microwave-assisted cleaning, and then dry and pulverize it.

[0082] Step 2, Pigment Fixation: After ball milling and mixing the inorganic pigment and fixing agent, disperse them in deionized water, add dispersant, and perform alternating high-pressure homogenization and low-frequency ultrasonic treatment;

[0083] Step 3: Filter and separate the suspension treated in Step 2, and dry and pulverize the resulting precipitate;

[0084] Step 4, Material Preparation: The color-fixing pigment powder obtained in Step 3, the wheat straw powder obtained in Step 1, the coupling agent, and high-density polyethylene are blended and then molded using a vacuum molding device.

[0085] Step 5, Secondary color fixation of composite material: After vacuum hot pressing, the composite material is quickly placed in a vacuum drying oven and kept at 80°C for 2.5 hours for secondary color fixation.

[0086] Furthermore, in step one, the ratio of wheat straw to distilled water is 100 g: 1.5 L; the microwave power is 450 W, and the time is 3 min.

[0087] Furthermore, in step two, the fixing agent is nano-attapulgite; the inorganic pigment is iron oxide red; the dispersant is sodium hexametaphosphate; the mass ratio of the fixing agent to the inorganic pigment is 1:2; the ratio of the dispersant to the pigment is 1:3; the alternating high-pressure homogenization and low-frequency ultrasonic treatment is performed with 4 minutes of high-pressure homogenization and 8 minutes of low-frequency ultrasonic treatment, for a total of two cycles; the pressure of high-pressure homogenization is 80 MPa; the ultrasonic treatment uses a frequency of 25 kHz and an amplitude of 55%.

[0088] Furthermore, in step four, the ratio of the color-fixing pigment powder, wheat straw powder, coupling agent, and high-density polyethylene is 4:50:3:50; the heating temperature of the vacuum hot press is 175 ℃, the hot pressing holding time is 25 min, and the hot press pressure is 20 MPa.

[0089] The color stability test results of the manufactured wheat straw / high-density polyethylene red composite material under ultraviolet accelerated aging conditions are as follows: Figure 1 As shown, the appearance color of the composite material before and after aging is as follows: Figure 6 As shown. Comparative Example 3

[0090] A method for preparing a red wheat straw / high-density polyethylene composite material, characterized by comprising the following steps:

[0091] Step 1: Wheat straw processing: Using wheat straw as raw material, wash and dry the wheat straw, cut it into sections, and place it in distilled water in a certain proportion for microwave-assisted cleaning;

[0092] Step 2, Bleaching of wheat straw: After drying the wheat straw washed in Step 2, crush it, place it in hydrogen peroxide solution, bleach it under ultrasonic conditions, and then wash and dry it.

[0093] Step 3, Material Preparation: Iron oxide red pigment, wheat straw powder obtained in Step 2, coupling agent and high-density polyethylene are blended and then molded using a vacuum molding device;

[0094] Step 4: Secondary color fixation of composite material: After vacuum hot pressing, the composite material is quickly placed in a vacuum drying oven and kept at 80°C for 2.5 hours for secondary color fixation.

[0095] Furthermore, in step one, the ratio of wheat straw to distilled water is 100 g: 1.5 L; the microwave power is 450 W, and the time is 3 min.

[0096] Furthermore, in step two, the concentration of hydrogen peroxide solution is 4%; the ratio of wheat straw to hydrogen peroxide solution is 100 g: 0.8 L; the ultrasonic treatment uses a frequency of 25 kHz, with a 1-minute pause every 5 minutes, and an amplitude of 55%; the bleaching time is 1 hour; and the wheat straw powder is dried by spray drying.

[0097] Furthermore, in step three, the ratio of pigment, wheat straw powder, coupling agent, and high-density polyethylene is 4:50:3:50; the heating temperature of the vacuum hot press is 175 ℃, the hot pressing time is 25 min, and the hot press pressure is 20 MPa.

[0098] The color stability test results of the prepared wheat straw / high-density polyethylene red composite material under ultraviolet accelerated aging conditions are as follows: Figure 1 As shown, the appearance color of the composite material before and after aging is as follows: Figure 7 As shown.

[0099] To better illustrate the present invention, the wheat straw / high-density polyethylene colored composite materials obtained in Examples 1-3 and Comparative Examples 1-3 were subjected to accelerated ultraviolet aging tests using industry-standard testing methods to verify the color stability of the composite materials prepared by the technical method of the present invention. The instrument used for the aging test was a UV aging chamber, and the test conditions were set as follows: each 12-hour aging cycle consisted of 8 hours of UV exposure at 60°C and 4 hours of condensation at 50°C; the UV wavelength was 340 nm, and the UV irradiance was 0.77 W / m². 2 The process was repeated 40 times, and the color change of the tested material was tested after a cumulative exposure of 480 hours.

[0100] The color change of the composite material was tested according to the CIE 1976 L*a*b* color space, with the color of the composite material before aging as the standard value. The color difference value of the composite material ( ΔE The calculation formula for is shown in equation (1).

[0101] (1)

[0102] In the formula: ΔL Differences in color brightness; Δa The color is red ( Δa >0) / Green ( Δa <0) difference; Δb The color is yellow ( Δb >0) / Blue ( Δb <0) difference.

[0103] The results of the color change test of the composite material are as follows Figure 1 As shown.

[0104] Depend on Figure 1 It can be seen that the composite material prepared by the technical method of the present invention has a more obvious color, the color difference value changes less after aging, and the color stability is significantly improved.

[0105] This invention provides a method for preparing straw / high-density polyethylene (HDPE) colored composite materials by microwave cleaning followed by ultrasonic-assisted bleaching of straw, combined with an inorganic pigment fixing process. By modifying the straw and pigments, and using nano-attapulgite as a fixing agent to fix the pigments, the coloring effect of the pigments becomes more uniform and stable. Simultaneously, bleaching the straw reduces the influence of the straw's own color on the coloring effect. Finally, the prepared composite material undergoes secondary vacuum thermosetting, successfully achieving uniform and stable pigment coloring, improving the coloring effect, endowing the straw / HDPE composite material with rich colors and aesthetics, and expanding the application range of straw / HDPE composite materials.

[0106] The above embodiments of the present invention are merely illustrative examples and are not intended to limit the specific implementation of the invention. Those skilled in the art can make other variations or modifications based on the above examples. It is impossible to provide detailed examples of all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a straw / high-density polyethylene colored composite material, characterized in that: Includes the following steps: Step 1, Straw Processing: Using straw as raw material, wash, dry, and cut the straw into sections, then place it in distilled water in a certain proportion for microwave-assisted cleaning; Step 2, Straw bleaching: After drying the straw washed in Step 1, crush it, place it in hydrogen peroxide solution, bleach it under ultrasonic conditions, and then wash and dry it. Step 3, Pigment Fixation: The inorganic pigment and fixing agent are ball-milled and dispersed in deionized water. A dispersant is added, and the mixture is subjected to alternating high-pressure homogenization and low-frequency ultrasonic treatment. The fixing agent is nano-attapulgite. The inorganic pigment is one or more of iron oxide red, iron oxide yellow, and iron oxide blue in any proportion. The dispersant is sodium hexametaphosphate. The mass ratio of fixing agent to inorganic pigment is 1:

2. The ratio of dispersant to pigment is 1:

3. The alternating high-pressure homogenization and low-frequency ultrasonic treatment consists of 4 minutes of high-pressure homogenization followed by 8 minutes of low-frequency ultrasonic treatment, for a total of two cycles. The pressure of high-pressure homogenization is 70-80 MPa, and the low-frequency ultrasonic parameters are the same as those in Step 2. Step 4: Filter and separate the suspension treated in Step 3, and dry and pulverize the resulting precipitate; Step 5, Material Preparation: The color-fixing pigment powder obtained in Step 4, the straw powder obtained in Step 2, the coupling agent, and high-density polyethylene are blended and then molded using a vacuum molding device; Step 6: Secondary color fixation of composite material: After vacuum hot pressing, the composite material is quickly placed in a vacuum drying oven and kept at 80°C for 2.5 hours for secondary color fixation.

2. The method for preparing a straw / high-density polyethylene colored composite material according to claim 1, characterized in that: In step one, the ratio of straw to distilled water is 100g:1L to 100g:1.5L; the microwave power is 450W, and the time is 3 to 3.5 minutes. In step two, the concentration of hydrogen peroxide solution is 3 to 5%; the ratio of straw to hydrogen peroxide solution is 100g:0.5L to 100g:1L; the ultrasonic treatment uses a frequency of 25kHz, with a 1-minute pause every 5 minutes, and an amplitude of 50 to 60%; the bleaching time is 1 hour; the straw powder is dried by spray drying.

3. The method for preparing a straw / high-density polyethylene colored composite material according to claim 1, characterized in that: In step five, the ratio of color-fixing pigment powder, straw powder, coupling agent and high-density polyethylene is 4:50:3:50; the heating temperature of the vacuum hot press is 170-180℃, the hot pressing time is 25-30 minutes, and the hot press pressure is 20MPa.

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