Method for manufacturing cement foam board by using waste polyester fiber board

Abstract

The present application relates to the technical field of building insulation material preparation, and relates to a method for manufacturing cement foam board from waste polyester fiber board, which comprises eleven core steps of crushing pretreatment, soaking softening, freezing modification, thawing and drying, grading screening, surface modification, dry mixing, water adding and slurry making, foaming and stirring, and pouring and curing in sequence; the waste polyester fiber board is divided into fine particles and coarse particles after crushing and screening, and is respectively subjected to alkali treatment modification and silane coupling agent modification, and then is mixed with cement and fly ash to prepare fiber reinforced cement foam board by foaming. The present application combines the physical modification of freezing and thawing with the chemical modification of alkali treatment and coupling agent treatment, and grades and controls the surface morphology and interfacial activity of the fibers, so that the fine particle fibers fill the pores of the cement matrix and improve the material density, and the coarse particle fibers play a role of skeleton toughening in the matrix, and the cement foam board has a compression strength improved by 40% to 80% and a water absorption rate reduced by 30% to 50% through the cooperation of the two.

Description

Technical Field

[0001] This invention relates to the field of building insulation material preparation technology, and in particular to a method for producing cement foamed board from waste polyester fiberboard. Background Technology

[0002] Foamed cement board is an inorganic thermal insulation material made primarily of cement through foaming and curing. It features fire resistance, flame retardancy, and good durability, and is widely used in building exterior wall insulation, roof insulation, and other fields. However, ordinary foamed cement board suffers from drawbacks such as high brittleness, low flexural and compressive strength, and susceptibility to cracking, limiting its application scenarios and service life.

[0003] Polyester fiberboard is a type of board made from polyester fibers through hot pressing or bonding. It is commonly used in building decoration, automotive interiors, thermal insulation, and soundproofing. With the development of the industry, a large amount of scrap and waste boards have been generated. These waste polyester fiberboards are difficult to degrade, and conventional landfill and incineration treatments easily cause environmental pollution and resource waste. Although there are attempts to incorporate waste fibers into cement-based materials in existing technologies, these often suffer from weak interfacial bonding between fibers and cement matrix, poor fiber dispersion, and limited effect on improving board strength. Furthermore, there is a lack of systematic pretreatment and modification processes for waste polyester fiberboards, making it impossible to achieve high-value-added resource utilization. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing the following technical solution: a method for producing cement foamed board from waste polyester fiberboard, comprising the following steps: Step 1: The waste polyester fiberboard is fed into the crusher for crushing. After primary screening to remove oversized particles and re-crushing, polyester fiber fragments with a particle size of 5mm to 30mm are obtained. Step 2: Soak the polyester fiber fragments obtained in Step 1 in water for 2 to 6 hours to soften them. After soaking, drain the water to obtain softened polyester fiber fragments. Step 3: Place the softened polyester fiber fragments obtained in Step 2 into a freezing device and freeze them at -10°C to -25°C for 4 to 12 hours to allow the water in the gaps and pores of the softened polyester fiber fragments to freeze and expand, thus obtaining frozen polyester fiber fragments. Step 4: Take out the frozen polyester fiber fragments obtained in Step 3, thaw them naturally at room temperature, and then put them into a drying device to dry them at a temperature of 50°C to 80°C for 2 to 5 hours to obtain pretreated polyester fiber fragments. Step 5: Screen the pretreated polyester fiber fragments obtained in Step 4 to obtain fine polyester fiber and coarse polyester fiber respectively. The particle size of the fine polyester fiber is 0.5 mm to 3 mm, and the particle size of the coarse polyester fiber is greater than 3 mm and less than or equal to 10 mm. The material with a particle size greater than 10 mm is returned to Step 1 for re-crushing. Step 6: Immerse the fine polyester fibers obtained in Step 5 in a sodium hydroxide solution with a mass percentage concentration of 3% to 10% for 30 to 90 minutes at a temperature of 30°C to 50°C. After rinsing with water until near neutral, and then drying, alkali-treated fine polyester fibers are obtained. Step 7: Immerse the coarse polyester fibers obtained in Step 5 in a sodium hydroxide solution with a mass percentage concentration of 1%~2% at room temperature for 10 to 20 minutes for alkaline washing and activation. After rinsing until nearly neutral, drain the solution and then mix it with a silane coupling agent ethanol solution with a mass percentage concentration of 5%~15% at a mass ratio of 100:2 to 100:6. Stir and react at a temperature of 50℃ to 70℃ for 20 to 50 minutes. After drying, the coupling agent treated coarse polyester fibers are obtained. Step 8: By weight, add 100 parts of silicate cement, 15 to 35 parts of fly ash, 8 to 25 parts of the alkali-treated fine-particle polyester fiber obtained in Step 6, and 5 to 15 parts of the coupling agent-treated coarse-particle polyester fiber obtained in Step 7 to a mixer and dry mix for 5 to 10 minutes to obtain a dry mixture. Step 9: Add water to the dry mixture obtained in Step 8. The amount of water added is 25% to 45% of the weight of the silicate cement. Continue stirring for 2 to 5 minutes to obtain cement slurry. Step 10: Add a foaming agent to the cement slurry obtained in Step 9. The amount of foaming agent added is 0.5% to 2% of the weight of the silicate cement. Stir at high speed for 3 to 8 minutes and the stirring speed is 200 to 400 rpm to obtain foamed cement slurry. Step 11: Pour the foamed cement slurry obtained in Step 10 into the mold and cure it at a temperature of 20°C to 35°C for 24 to 48 hours. After demolding, continue to cure it at the same temperature for 7 to 14 days to obtain the finished foamed cement board.

[0005] In step two, sodium bicarbonate of 0.5% to 2% by weight is added to the water in which the polyester fiber fragments are soaked, and an ultrasonic generator is turned on to assist the soaking. The ultrasonic frequency is 25kHz to 40kHz, and the ultrasonic treatment time is 10 minutes to 30 minutes.

[0006] In step three, after the softened polyester fiber fragments are placed in the freezing equipment, they are first cooled to -5°C at a cooling rate of 3°C to 8°C per hour, maintained at -5°C for 1 to 2 hours, and then cooled to -10°C to -25°C at a cooling rate of 8°C to 15°C per hour.

[0007] In step four, during the natural thawing process, a sodium chloride solution with a mass percentage concentration of 0.5% to 2% is sprayed onto the surface of the frozen polyester fiber fragments, and the amount sprayed is 3% to 8% of the weight of the frozen polyester fiber fragments.

[0008] In step five, the screening is carried out on a vibrating screen with a screen surface tilt angle of 10 to 20 degrees and a vibration frequency of 800 to 1200 times per minute. During the screening process, bouncing balls and negative pressure ventilation are used to assist in preventing blockage.

[0009] In step six, after immersing the fine polyester fibers in the sodium hydroxide solution, stirring is started every 5 to 10 minutes, each stirring lasting 2 to 3 minutes and then stopped, and this process is repeated until the soaking time is over.

[0010] In step seven, the coarse polyester fiber particles are mixed with the silane coupling agent ethanol solution, and then irradiated with an ultraviolet lamp while stirring. The ultraviolet wavelength is 250 nm to 380 nm, and the irradiation time is 10 minutes to 20 minutes.

[0011] In step eight, the dry mixing is carried out in a horizontal plow mixer. During the mixing process, hot air is introduced into the mixer, and the temperature of the hot air is 40°C to 60°C.

[0012] In step ten, while adding the foaming agent to the cement slurry, calcium stearate (0.1% to 0.5% of the weight of the silicate cement) and polyacrylamide (0.05% to 0.2% of the weight of the silicate cement) are added. The high-speed stirring foaming process involves first stirring at 200 to 250 rpm for 1 to 2 minutes, and then increasing the speed to 350 to 400 rpm for 2 to 6 minutes.

[0013] In step eleven, before the foamed cement slurry is poured into the mold, the mold is preheated to 25°C to 30°C; after the foamed cement slurry is poured into the mold, a layer of breathable thermal insulation felt is covered on top of the mold, the thickness of the breathable thermal insulation felt being 5mm to 15mm. As an improvement to the above technical solution, sodium bicarbonate is added and ultrasonic cavitation treatment is used in the soaking and softening stage; a stepped gradient cooling process is adopted in the freezing stage; sodium chloride solution is sprayed in the thawing stage to help loosen the fibers; calcium stearate and polyacrylamide are compounded in the foaming stage to improve the slurry performance; and mold preheating and breathable heat insulation felt covering process are adopted in the curing stage to further improve the product performance stability and production adaptability.

[0014] The beneficial effects of this invention are: it achieves high-value recycling of waste polyester fiberboard, with an overall resource utilization rate of over 90%, reducing the pressure of solid waste disposal and lowering the raw material cost of cement foam board. By combining physical modification through freezing and thawing with chemical modification through alkali treatment and coupling agent treatment, the surface morphology and interfacial activity of the fibers are controlled in stages. Fine-particle fibers fill the pores of the cement matrix and improve the density of the material; coarse-particle fibers play a skeletal toughening role in the matrix. The two work synergistically to increase the compressive strength of cement foam board by 40% to 80%, reduce water absorption by 30% to 50%, and maintain excellent thermal insulation performance. Detailed Implementation

[0015] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. Example

[0016] A method for producing cement foam board from waste polyester fiberboard includes the following steps: Step 1: Crushing Process Waste polyester fiberboard is fed into a crusher for crushing to obtain polyester fiber fragments. The waste polyester fiberboard refers to waste boards made of polyester fiber as the main raw material through hot pressing or bonding. Its sources include, but are not limited to, waste scraps from building decoration, waste insulation boards, and waste automotive interior boards. During the crushing process, either a hammer crusher or a shear crusher can be used. After crushing, the material is first screened, and the material with a particle size greater than 30mm is returned to the crusher for further crushing. Finally, polyester fiber fragments with a particle size of 5mm to 30mm are obtained to facilitate subsequent soaking and softening treatment. The dust removal device of the crusher can be turned on during the crushing process to reduce dust pollution.

[0017] Step 2: Soaking and softening treatment The polyester fiber fragments obtained in step one are immersed in water for softening treatment. The water used for immersion can be industrial water or tap water. The water temperature is preferably room temperature (20°C to 30°C). The immersion time is 2 to 6 hours, preferably 3 to 5 hours. During the immersion process, the polyester fiber fragments should be completely submerged below the water surface. The water level is preferably 10 to 20 centimeters above the material to ensure uniform immersion.

[0018] After soaking, remove the polyester fiber fragments and drain the water until there is no obvious dripping. This will give you softened polyester fiber fragments. The draining can be done by natural drainage or by centrifugal dehydration. The preferred speed for centrifugal dehydration is 500 to 1000 rpm, and the preferred dehydration time is 2 to 5 minutes.

[0019] As a preferred embodiment, during the soaking process in step two, sodium bicarbonate (0.5% to 2% by weight of the water) can be added to the water used to soak the polyester fiber fragments. Simultaneously, an ultrasonic generator is activated to assist the soaking. The addition of sodium bicarbonate adjusts the pH value of the soaking solution, which helps remove impurities from the fiber surface and loosen the fiber structure. The ultrasonic frequency is 25 kHz to 40 kHz, and the ultrasonic treatment time is 10 to 30 minutes. The introduction of ultrasound can promote the penetration of water into the interior of the polyester fiber through cavitation, shortening the soaking softening time and improving the softening effect.

[0020] Step 3: Freezing The softened polyester fiber fragments obtained in step two are placed in a freezing device and frozen at -10°C to -25°C for a total freezing time of 4 to 12 hours (including cooling and heat preservation stages). During the freezing process, the residual moisture in the gaps between the fiber bundles and the internal pores of the softened polyester fiber fragments gradually freezes and expands in volume. The growth of ice crystals has a physical expansion effect on the fiber bundle structure, causing microcracks and a loose structure to form inside the fiber bundle, thereby increasing the specific surface area and roughness of the fiber, which is beneficial for subsequent bonding with cement-based materials.

[0021] As a preferred embodiment, the freezing process employs a stepped cooling method: after the softened polyester fiber fragments are placed in the freezing equipment, they are first cooled to -5°C at a cooling rate of 3°C to 8°C per hour, and then kept at -5°C for 1 to 2 hours to allow the moisture inside the fiber to initially form ice crystal nuclei; then, the temperature is further reduced to the target temperature (i.e., -10°C to -25°C) at a cooling rate of 8°C to 15°C per hour, and kept warm until the end of the total freezing time. This stepped cooling method can avoid excessive damage to the fiber structure due to excessively rapid cooling, while ensuring uniform nucleation and growth of ice crystals, resulting in a more uniform distribution of microcracks inside the fiber.

[0022] The refrigeration equipment can be any of the following: industrial cold storage, low-temperature freezer, or liquid nitrogen refrigeration device. When using a liquid nitrogen refrigeration device, the required cooling rate and target temperature can be achieved by controlling the liquid nitrogen supply rate.

[0023] Step 4: Thawing and Drying The frozen polyester fiber fragments obtained in step three are removed from the freezing equipment and allowed to thaw naturally at room temperature. The natural thawing time is preferably 2 to 6 hours, and the specific time can be adjusted according to the ambient temperature and the amount of material, until the frozen polyester fiber fragments are completely thawed and no ice crystals remain.

[0024] As a preferred embodiment, during the natural thawing process, a sodium chloride solution with a mass percentage concentration of 0.5% to 2% is sprayed onto the surface of the frozen polyester fiber fragments, with the spraying amount being 3% to 8% of the weight of the frozen polyester fiber fragments. The spraying of sodium chloride solution can lower the melting point of ice crystals, accelerate the thawing process, and the penetrating effect of the salt solution can further loosen the inter-fiber bundle structure, helping to improve the roughness of the fiber surface.

[0025] After thawing, the thawed polyester fiber fragments are fed into a drying device and dried at a temperature of 50°C to 80°C for 2 to 5 hours until the moisture content drops below 5%, yielding pretreated polyester fiber fragments. The drying device can be any one of a hot air circulating oven, a fluidized bed dryer, or a rotary drum dryer. The preferred drying temperature is 60°C to 70°C, and the preferred drying time is 3 to 4 hours.

[0026] Step 5: Screening The pretreated polyester fiber fragments obtained in step four are screened to obtain fine-particle polyester fibers and coarse-particle polyester fibers. The particle size of the fine-particle polyester fibers is 0.5 mm to 3 mm, and the particle size of the coarse-particle polyester fibers is greater than 3 mm and less than or equal to 10 mm. The material with a particle size greater than 10 mm after screening is returned to step one for re-crushing to form a closed-loop material system.

[0027] Screening can be carried out on a vibrating screen with a screen surface inclination angle of 10 to 20 degrees and a vibration frequency of 800 to 1200 times per minute. By adjusting the screen mesh size and screen surface inclination angle, fibers of different particle sizes can be effectively separated. During the screening process, screen surface bouncing balls and negative pressure ventilation can be used to assist screening, preventing fiber agglomeration and adhesion to the screen and improving screening efficiency.

[0028] Step Six: Alkali Treatment The fine polyester fibers obtained in step five are immersed in a sodium hydroxide solution with a mass percentage concentration of 3% to 10% for 30 to 90 minutes at a temperature of 30°C to 50°C. After being taken out, they are rinsed with water until the pH value of the rinsing solution is 7 to 8, and then dried to obtain alkali-treated fine polyester fibers.

[0029] The purpose of alkali treatment is to modify the surface of fine-particle polyester fibers through hydrolysis. The ester bonds in the polyester fiber molecular chain can undergo hydrolysis under alkaline conditions, generating active functional groups such as carboxyl and hydroxyl groups on the fiber surface. These functional groups can enhance the chemical bonding between the fiber and cement-based materials. The preferred mass percentage concentration of sodium hydroxide solution is 5% to 8%, the preferred treatment temperature is 35°C to 45°C, and the preferred treatment time is 40 minutes to 60 minutes. If the alkali treatment temperature is too low, the reaction rate will be slow and the treatment effect will be poor; if the temperature is too high, it may lead to excessive hydrolysis of the fiber and a decrease in mechanical properties.

[0030] Deionized water or tap water can be used for rinsing, and rinsing should continue until the pH of the rinsing solution is 7 to 8. The rinsed fibers can then be dried at 50°C to 70°C for 2 to 4 hours.

[0031] As a preferred embodiment, during the alkali treatment in step six, after immersing the fine polyester fibers in the sodium hydroxide solution, stirring is initiated every 5 to 10 minutes, with each stirring lasting 2 to 3 minutes and then stopped, repeating this process until the immersion time is over. This intermittent stirring method ensures sufficient contact between the fibers and the alkali solution while avoiding fiber entanglement and damage that may result from continuous stirring.

[0032] Step 7: Coupling agent treatment First, immerse the coarse polyester fiber obtained in step five in a sodium hydroxide solution with a mass percentage concentration of 1% to 2% at room temperature for 10 to 20 minutes. After rinsing until nearly neutral, drain the solution and then mix it with a silane coupling agent ethanol solution at a mass ratio of 100:2 to 100:6. Stir and react the mixture at a temperature of 50°C to 70°C for 20 to 50 minutes. After drying, the coarse polyester fiber treated with the coupling agent is obtained.

[0033] The silane coupling agent ethanol solution is prepared by dissolving the silane coupling agent in anhydrous ethanol. The preferred mass percentage concentration of the silane coupling agent in the ethanol solution is 5% to 15%. The silane coupling agent can be selected from any one or a mixture of γ-aminopropyltriethoxysilane (KH-550), γ-glycidoxypropyltrimethoxysilane (KH-560), and γ-methacryloyloxypropyltrimethoxysilane (KH-570). The preferred mass ratio of the coarse-particle polyester fiber to the silane coupling agent ethanol solution is 100:3 to 100:5. The preferred reaction temperature is 55°C to 65°C, and the preferred reaction time is 30 to 40 minutes. After the reaction is complete, the fiber can be dried at 50°C to 70°C for 2 to 4 hours.

[0034] The role of silane coupling agents is to form an organic-inorganic transition layer on the surface of coarse-particle polyester fibers. One end of the layer bonds to the active groups on the polyester fiber surface, while the other end bonds to the silanol groups in cement hydration products, thereby forming chemical bonds between the fibers and the cement matrix and improving the interfacial bonding strength. Coarse-particle polyester fibers mainly serve as a skeletal support in cement foamed boards; after treatment with coupling agents, the interfacial bonding strength between them and the cement matrix is ​​significantly improved.

[0035] In a preferred embodiment, during the coupling agent treatment in step seven, the coarse-particle polyester fibers are mixed with the silane coupling agent ethanol solution, and then irradiated with an ultraviolet lamp while stirring. The ultraviolet wavelength is 250 nm to 380 nm, and the irradiation time is 10 to 20 minutes. Ultraviolet irradiation can activate the active groups in the silane coupling agent, accelerate the coupling reaction rate, and improve the grafting rate and reaction uniformity of the coupling agent on the fiber surface.

[0036] Step 8: Dry Mixing By weight, 100 parts of silicate cement, 15 to 35 parts of fly ash, 8 to 25 parts of the alkali-treated fine-particle polyester fiber obtained in step six, and 5 to 15 parts of the coupling agent-treated coarse-particle polyester fiber obtained in step seven are added to a mixer and dry-mixed for 5 to 10 minutes to obtain a dry mixture.

[0037] The silicate cement can be ordinary silicate cement, the amount of fly ash added is preferably 20 to 30 parts, the amount of alkali-treated fine-particle polyester fiber added is preferably 12 to 20 parts, the amount of coupling agent-treated coarse-particle polyester fiber added is preferably 8 to 12 parts, and the dry mixing time is preferably 6 to 8 minutes.

[0038] Dry mixing is carried out in a horizontal plow mixer. The horizontal plow mixer has high-speed rotating plow-type mixing blades, which can efficiently shear and mix fibers and powders, avoiding fiber agglomeration. During the mixing process, hot air can be introduced into the mixer. The temperature of the hot air is 40°C to 60°C. The introduction of hot air can reduce the moisture content of the material, improve the uniformity of powder adhesion on the fiber surface, and preheat the material, which is beneficial to the subsequent hydration reaction.

[0039] Step 9: Add water and stir Add water to the dry mixture obtained in step eight, the amount of water being 25% to 45% of the weight of the silicate cement, and continue stirring for 2 to 5 minutes to obtain cement slurry.

[0040] The amount of water added is preferably 30% to 40% of the weight of the silicate cement. Adding water and mixing can be done in the same mixer as in step eight, or it can be transferred to a dedicated mixer. The mixing time is preferably 3 to 4 minutes, until the materials are evenly mixed and there are no dry powder lumps. During the mixing process, the accumulated material on the inner wall and bottom of the mixer can be scraped off as needed to ensure uniform mixing.

[0041] Step 10: Foaming Treatment Add a foaming agent to the cement slurry obtained in step nine. The amount of foaming agent added is 0.5% to 2% of the weight of the silicate cement. Perform high-speed stirring and foaming for 3 to 8 minutes at a stirring speed of 200 to 400 rpm to obtain foamed cement slurry.

[0042] The foaming agent can be selected from any one or a mixture of plant protein foaming agents, animal protein foaming agents, and surfactant foaming agents (such as sodium dodecyl sulfate and sodium fatty alcohol polyoxyethylene ether sulfate). The amount of foaming agent added is preferably 0.8% to 1.5% of the weight of silicate cement. The foaming time of high-speed stirring is preferably 4 to 6 minutes.

[0043] In a preferred embodiment, in step ten, while adding the foaming agent to the cement slurry, calcium stearate (0.1% to 0.5% by weight of the silicate cement) and polyacrylamide (0.05% to 0.2% by weight of the silicate cement) are also added. Calcium stearate, as a foam stabilizer and water repellent, can improve the stability of the foam and the waterproof performance of the foamed board; polyacrylamide, as a thickener and dispersant, can improve the rheological properties of the slurry, prevent fiber sedimentation, and improve the uniformity of foam distribution.

[0044] For high-speed foaming, the preferred mixing speed is variable speed mixing: first, mix at 200 to 250 rpm for 1 to 2 minutes to allow the foaming agent to initially mix with the cement slurry and begin foaming; then increase the speed to 350 to 400 rpm for 2 to 6 minutes to allow the bubbles to be fully refined and evenly distributed in the cement slurry. This variable speed mixing method is beneficial for forming a fine, uniform, and stable foam structure.

[0045] Step 11: Pouring and Curing The foamed cement slurry obtained in step 10 is poured into a mold and cured statically for 24 to 48 hours at a temperature of 20°C to 35°C. After demolding, it is cured for another 7 to 14 days at the same temperature to obtain the finished foamed cement board.

[0046] Before pouring, a release agent can be applied to the inner wall of the mold to facilitate subsequent demolding. During pouring, the foamed cement slurry should be poured slowly and evenly from one end of the mold to the other to avoid air bubble aggregation and slurry segregation. After pouring, the upper surface of the mold can be smoothed with a scraper.

[0047] As a preferred embodiment, the mold is preheated to 25°C to 30°C before the foamed cement slurry is poured into it. Preheating the mold can prevent the hydration reaction from being slow due to the low temperature of the mold after the foamed cement slurry is poured, and ensure that the hydration reaction of each part of the foamed board proceeds synchronously.

[0048] After the foamed cement slurry is poured into the mold, a layer of breathable thermal insulation felt is covered on top of the mold. The thickness of the breathable thermal insulation felt is 5mm to 15mm. The breathable thermal insulation felt can maintain the stability of temperature and humidity inside the mold, prevent the surface from cracking due to excessive evaporation of moisture, and allow excess gas to escape, avoiding surface blistering defects caused by gas accumulation.

[0049] The optimal temperature for static curing is 25℃ to 30℃, and the optimal time is 30 to 36 hours. The optimal temperature for post-demolding curing is also 25℃ to 30℃, and the optimal time is 10 to 12 days. During curing, the ambient humidity should be maintained above 60%, and the surface of the foamed board can be sprayed with water periodically to prevent surface cracking. Example

[0050] The difference between this embodiment and Embodiment 1 lies in the specific parameters of the soaking and softening treatment in step two.

[0051] In this embodiment, the soaking time in step two is 2 hours, the water temperature is 25°C, sodium bicarbonate (0.5% by weight) is added to the soaking water, and an ultrasonic generator is turned on to assist the soaking at a frequency of 25 kHz for 30 minutes. The remaining steps are the same as in embodiment one. Example

[0052] The difference between this embodiment and Embodiment 1 lies in the specific parameters of the soaking and softening treatment in step two.

[0053] In this embodiment, the soaking time in step two is 6 hours, and the water temperature is 30°C. Sodium bicarbonate (2% by weight of the water) is added to the soaking water, and an ultrasonic generator is simultaneously turned on to assist the soaking. The ultrasonic frequency is 40kHz, and the ultrasonic treatment time is 10 minutes. The remaining steps are the same as in embodiment one. Example

[0054] The difference between this embodiment and Embodiment 1 lies in the specific parameters of the freezing process in step three.

[0055] In this embodiment, the freezing process in step three adopts a stepped cooling method: after the softened polyester fiber fragments are placed in the freezing equipment, they are first cooled to -5°C at a cooling rate of 3°C per hour, maintained at -5°C for 2 hours, and then cooled to -25°C at a cooling rate of 8°C per hour. The total freezing time is approximately 5 hours. The remaining steps are the same as in embodiment one. Example

[0056] The difference between Example 5 and Example 1 lies in the specific parameters of the freezing process in step 3.

[0057] In this embodiment, the freezing process in step three adopts a stepped cooling method: after the softened polyester fiber fragments are placed in the freezing equipment, they are first cooled to -5°C at a cooling rate of 8°C per hour, maintained at -5°C for 1 hour, and then cooled to -10°C at a cooling rate of 15°C per hour. The total freezing time is approximately 4.5 hours. The remaining steps are the same as in embodiment one. Example

[0058] The difference between this embodiment and Embodiment 1 is that sodium chloride solution is sprayed during natural thawing in step four.

[0059] In this embodiment, during the natural thawing process in step four, a sodium chloride solution with a mass percentage concentration of 0.5% is sprayed onto the surface of the frozen polyester fiber fragments, and the spraying amount is 3% of the weight of the frozen polyester fiber fragments. The remaining steps are the same as in embodiment one. Example

[0060] The difference between this embodiment and Embodiment 1 is that sodium chloride solution is sprayed during natural thawing in step four.

[0061] In this embodiment, during the natural thawing process in step four, a 2% sodium chloride solution is sprayed onto the surface of the frozen polyester fiber fragments, with the spraying amount being 8% of the weight of the frozen polyester fiber fragments. The remaining steps are the same as in embodiment one. Example

[0062] The difference between this embodiment and Embodiment 1 lies in the specific parameters of the alkali treatment in step six.

[0063] In this embodiment, the alkaline treatment conditions in step six are as follows: sodium hydroxide solution concentration of 3% by mass, treatment temperature of 30°C, and treatment time of 90 minutes. During the alkaline treatment, stirring is started every 5 minutes, with each stirring lasting 3 minutes and then stopped, repeating this process until the soaking time is completed. The remaining steps are the same as in Example 1. Example

[0064] The difference between this embodiment and Embodiment 1 lies in the specific parameters of the alkali treatment in step six.

[0065] In this embodiment, the alkaline treatment conditions in step six are as follows: sodium hydroxide solution concentration of 10% by mass, treatment temperature of 50°C, and treatment time of 30 minutes. During the alkaline treatment, stirring is started every 10 minutes, with each stirring lasting 2 minutes and then stopped, repeating this process until the soaking time is completed. The remaining steps are the same as in embodiment one. Example

[0066] The difference between this embodiment and Embodiment 1 lies in the specific parameters of the coupling agent treatment in step seven.

[0067] In this embodiment, the coupling agent treatment conditions in step seven are as follows: coarse polyester fibers are first pretreated by soaking in a 1% sodium hydroxide solution at room temperature for 20 minutes, then the mass ratio of the coarse polyester fibers to the silane coupling agent ethanol solution is 100:2, the reaction temperature is 50°C, and the reaction time is 50 minutes. The silane coupling agent is γ-aminopropyltriethoxysilane (KH-550). The remaining steps are the same as in Example 1. Example

[0068] The difference between this embodiment and Embodiment 1 lies in the specific parameters of the coupling agent treatment in step seven.

[0069] In this embodiment, the coupling agent treatment conditions in step seven are as follows: coarse polyester fibers are first pretreated by soaking in a 2% sodium hydroxide solution at room temperature for 10 minutes, then the mass ratio of the coarse polyester fibers to the silane coupling agent ethanol solution is 100:6, the reaction temperature is 70°C, and the reaction time is 20 minutes. The silane coupling agent is a mixture of γ-glycidoxypropyltrimethoxysilane (KH-560) and γ-methacryloyloxypropyltrimethoxysilane (KH-570) in a mass ratio of 1:1. The remaining steps are the same as in Example 1. Example

[0070] The difference between this embodiment and Embodiment 1 lies in the different proportions of the raw materials in step eight.

[0071] In this embodiment, the raw material ratio for step eight is: 100 parts silicate cement, 15 parts fly ash, 8 parts alkali-treated fine-particle polyester fiber, and 5 parts coupling agent-treated coarse-particle polyester fiber. The dry mixing time is 5 minutes. The temperature of the hot air is 40°C. The remaining steps are the same as in embodiment one. Example

[0072] The difference between this embodiment and Embodiment 1 lies in the different proportions of the raw materials in step eight.

[0073] In this embodiment, the raw material ratio for step eight is: 100 parts silicate cement, 35 parts fly ash, 25 parts alkali-treated fine-particle polyester fiber, and 15 parts coupling agent-treated coarse-particle polyester fiber. The dry mixing time is 10 minutes. The temperature of the hot air is 60°C. The remaining steps are the same as in embodiment one. Example

[0074] The difference between this embodiment and Embodiment 1 is the amount of water added in step nine.

[0075] In this embodiment, the amount of water added in step nine is 25% of the weight of the silicate cement. The stirring time after adding water is 5 minutes. The remaining steps are the same as in embodiment one. Example

[0076] The difference between this embodiment and Embodiment 1 is the amount of water added in step nine.

[0077] In this embodiment, the amount of water added in step nine is 45% of the weight of the silicate cement. The stirring time after adding water is 2 minutes. The remaining steps are the same as in embodiment one. Example

[0078] The difference between this embodiment and Embodiment 1 lies in the different specific parameters of the foaming process in step ten.

[0079] In this embodiment, the amount of foaming agent added in step ten is 0.5% of the weight of silicate cement. Simultaneously, calcium stearate (0.1% of the weight of silicate cement) and polyacrylamide (0.05% of the weight of silicate cement) are added. High-speed foaming is achieved using variable-speed stirring: first stirring at 200 rpm for 2 minutes, then increasing the speed to 350 rpm for 6 minutes. The foaming agent is a plant-based protein foaming agent. The remaining steps are the same as in Example 1. Example

[0080] The difference between this embodiment and Embodiment 1 lies in the different specific parameters of the foaming process in step ten.

[0081] In this embodiment, the amount of foaming agent added in step ten is 2% of the weight of the silicate cement. Simultaneously, calcium stearate (0.5% of the weight of the silicate cement) and polyacrylamide (0.2% of the weight of the silicate cement) are added. High-speed foaming is achieved using variable-speed stirring: first stirring at 250 rpm for 1 minute, then increasing the speed to 400 rpm for 2 minutes. The foaming agent is a mixture of sodium dodecyl sulfate and sodium fatty alcohol polyoxyethylene ether sulfate in a 1:1 mass ratio. The remaining steps are the same as in Example 1. Example

[0082] The difference between this embodiment and Embodiment 1 lies in the different specific parameters for maintenance in step eleven.

[0083] In this embodiment, the static curing temperature in step eleven is 20°C, and the curing time is 48 hours; after demolding, curing continues at 20°C for 14 days. Before pouring, the mold is preheated to 25°C, and after pouring, it is covered with a 5mm thick breathable insulating felt. The remaining steps are the same as in embodiment one. Example

[0084] The difference between this embodiment and Embodiment 1 lies in the different specific parameters for maintenance in step eleven.

[0085] In this embodiment, the static curing temperature in step eleven is 35°C, and the curing time is 24 hours; after demolding, curing continues at 35°C for 7 days. Before pouring, the mold is preheated to 30°C, and after pouring, it is covered with a 15mm thick breathable insulating felt. The remaining steps are the same as in embodiment one.

[0086] The finished cement foamed boards obtained in Examples 1 to 19 were subjected to performance tests. The test items included apparent density, compressive strength, thermal conductivity, and water absorption. The test methods were in accordance with GB / T5486-2023 "Test Methods for Inorganic Rigid Thermal Insulation Products" and GB / T10294-2023 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method". At the same time, a blank control example (ordinary cement foamed board without added polyester fiber, with other raw materials and processes the same as in Example 1) was set up for performance comparison. The measured performance of the blank control example was: apparent density of about 215 kg / m³, compressive strength of about 1.0 MPa, thermal conductivity of about 0.051 W / (m·K), and water absorption of about 13%.

[0087] Test results show that the foamed cement board prepared by the method of this invention has the following performance characteristics: apparent density of 150 kg / m³ to 350 kg / m³, compressive strength of 0.5 MPa to 2.5 MPa, thermal conductivity of 0.0451 W / (m·K) to 0.0701 W / (m·K), and water absorption rate of 5% to 15%. Among them, Example 1 has the best overall performance: apparent density of about 220 kg / m³, compressive strength of about 1.8 MPa, thermal conductivity of about 0.0521 W / (m·K), and water absorption rate of about 8%.

[0088] Compared with ordinary cement foam boards without fiber reinforcement, the cement foam boards made by the method of this invention have 40% to 80% higher compressive strength, 30% to 50% lower water absorption, and maintain a low thermal conductivity and apparent density. The resource utilization rate of waste polyester fiber boards reaches more than 90%, realizing high-value recycling of waste polyester fiber boards.

[0089] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Anyone skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for producing cement foamed board from waste polyester fiberboard, characterized in that, Includes the following steps: Step 1: Waste polyester fiberboard is crushed and primary screened, and oversized particles are recycled to obtain polyester fiber fragments with a particle size of 5~30mm. Step 2: Soak the fragments in water to soften for 2-6 hours, then remove and drain to obtain softened fiber fragments; Step 3: Soften the fragments and freeze them at -10℃ to -25℃ for 4 to 12 hours. The freezing and expansion of water in the fiber gaps and pores will modify the fibers and produce frozen fiber fragments. Step 4: After the frozen fragments thaw naturally at room temperature, they are dried at 50~80℃ for 2~5 hours to obtain pretreated fiber fragments; Step 5: Screen the pre-treated fragments to obtain fine fiber particles with a particle size of 0.5~3mm and coarse fiber particles with a particle size >3mm and ≤10mm. The material with a particle size >10mm is returned to Step 1 for re-crushing. Step 6: Immerse the fine granular fibers in a sodium hydroxide solution with a mass percentage concentration of 3%~10% at 30~50℃ for 30~90 minutes, remove and rinse until near neutral, then dry to obtain alkali-treated fine granular fibers; Step 7: The coarse granular fiber is first soaked in a sodium hydroxide solution with a mass percentage concentration of 1%~2% at room temperature for 10~20 minutes for alkaline washing and activation. After rinsing and draining, it is mixed with a silane coupling agent ethanol solution with a mass percentage concentration of 5%~15% at a mass ratio of 100:2~100:

6. The mixture is stirred and reacted at 50~70℃ for 20~50 minutes. After drying, the coupling agent-treated coarse granular fiber is obtained. Step 8: By weight, mix 100 parts silicate cement, 15-35 parts fly ash, 8-25 parts alkali-treated fine fiber, and 5-15 parts coupling agent-treated coarse fiber for 5-10 minutes to obtain a dry mixture. Step 9: Add water (25% to 45% of the weight of silicate cement) to the dry mixture and continue stirring for 2 to 5 minutes to obtain cement slurry; Step 10: Add 0.5% to 2% of the foaming agent by weight of silicate cement to the cement slurry, and stir at 200 to 400 r / min for 3 to 8 minutes to foam the cement slurry. Step 11: Inject the foamed cement slurry into the mold, let it stand at 20~35℃ for 24~48 hours, and continue to cure at the same temperature for 7~14 days after demolding to obtain the finished foamed cement board.

2. The method for producing cement foam board from waste polyester fiberboard according to claim 1, characterized in that: In step two, sodium bicarbonate of 0.5% to 2% by weight is added to the water in which the polyester fiber fragments are soaked, and an ultrasonic generator is turned on to assist the soaking. The ultrasonic frequency is 25kHz to 40kHz, and the ultrasonic treatment time is 10 minutes to 30 minutes.

3. The method for producing cement foam board from waste polyester fiberboard according to claim 1, characterized in that: In step three, after the softened polyester fiber fragments are placed in the freezing equipment, they are first cooled to -5°C at a cooling rate of 3°C to 8°C per hour, maintained at -5°C for 1 to 2 hours, and then cooled to -10°C to -25°C at a cooling rate of 8°C to 15°C per hour.

4. The method for producing cement foam board from waste polyester fiberboard according to claim 1, characterized in that: In step four, during the natural thawing process, a sodium chloride solution with a mass percentage concentration of 0.5% to 2% is sprayed onto the surface of the frozen polyester fiber fragments, and the amount sprayed is 3% to 8% of the weight of the frozen polyester fiber fragments.

5. The method for producing cement foam board from waste polyester fiberboard according to claim 1, characterized in that: In step five, the screening is carried out on a vibrating screen with a screen surface tilt angle of 10 to 20 degrees and a vibration frequency of 800 to 1200 times per minute. During the screening process, bouncing balls and negative pressure ventilation are used to assist in preventing blockage.

6. The method for producing cement foam board from waste polyester fiberboard according to claim 1, characterized in that: In step six, after immersing the fine polyester fibers in the sodium hydroxide solution, stirring is started every 5 to 10 minutes, each stirring lasting 2 to 3 minutes and then stopped, and this process is repeated until the soaking time is over.

7. The method for producing cement foam board from waste polyester fiberboard according to claim 1, characterized in that: In step seven, the coarse polyester fiber particles are mixed with the silane coupling agent ethanol solution, and then irradiated with an ultraviolet lamp while stirring. The ultraviolet wavelength is 250 nm to 380 nm, and the irradiation time is 10 minutes to 20 minutes.

8. The method for producing cement foam board from waste polyester fiberboard according to claim 1, characterized in that: In step eight, the dry mixing is carried out in a horizontal plow mixer. During the mixing process, hot air is introduced into the mixer, and the temperature of the hot air is 40°C to 60°C.

9. The method for producing cement foam board from waste polyester fiberboard according to claim 1, characterized in that: In step ten, while adding the foaming agent to the cement slurry, calcium stearate (0.1% to 0.5% of the weight of the silicate cement) and polyacrylamide (0.05% to 0.2% of the weight of the silicate cement) are added. The high-speed stirring foaming process involves first stirring at 200 to 250 rpm for 1 to 2 minutes, and then increasing the speed to 350 to 400 rpm for 2 to 6 minutes.

10. The method for producing cement foam board from waste polyester fiberboard according to claim 1, characterized in that: In step eleven, before the foamed cement slurry is poured into the mold, the mold is preheated to 25°C to 30°C; after the foamed cement slurry is poured into the mold, a layer of breathable thermal insulation felt is covered on top of the mold, and the thickness of the breathable thermal insulation felt is 5mm to 15mm.