Lightweight composite material for building and preparation method thereof

Abstract

The invention discloses a lightweight composite material for buildings and a preparation method thereof. The composite material is prepared from the following raw materials: nano cellulose whiskers, expansible graphite, thermoplastic polyurethane, polystyrene foam particles (or polylactic acid-based degradable microspheres), a compatilizer, an auxiliary agent, a chemical foaming agent, a polylactic acid (PLA) nano-scale degradable template and the like. The preparation method comprises the specific steps of raw material pretreatment, mixing, macropore generation, micropore introduction, template use, template removal, molding processing and the like. According to the preparation method of the composite material, a multi-scale pore structure is constructed, macropores serve as a main frame to bear main loads while the weight of the material is reduced, micropores effectively disperse stress concentration, meanwhile, low density is maintained, and good balance of light weight and high strength is achieved. Meanwhile, the multi-scale porous structure has the advantages of being light in weight, high in strength, good in heat insulation and sound insulation performance, environmentally friendly, degradable and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and specifically provides a lightweight composite material for buildings and a preparation method thereof. Background Art

[0002] With the development of the construction industry, the performance requirements for building materials are getting higher and higher. Lightweight composite materials have been widely used in the construction field due to their advantages such as light weight, high strength, heat insulation, and sound insulation.

[0003] However, the existing lightweight composite materials for buildings still have some deficiencies. For example, in traditional single-scale pore structure materials (such as single-aperture foams), while achieving lightweight, the compressive strength and impact resistance decrease significantly, making it difficult to meet the load-bearing requirements of building structures. Another example is that the pore structure design of existing materials mostly focuses on single functions (such as only heat insulation or only sound insulation), lacking the comprehensive performance improvement of multi-scale pore coordination optimization, and unable to meet the composite requirements of building energy conservation, noise reduction, and earthquake resistance simultaneously. Additionally, common raw materials such as polystyrene (PS) foam are difficult to degrade, resulting in "white pollution"; some degradable materials (such as PLA) are prone to affecting material stability due to uncontrollable degradation rates during the processing. Moreover, traditional multi-scale pore construction methods (such as the template method and the foaming method) need to be carried out step by step, with cumbersome process steps, and it is difficult to solve problems such as template residue or uneven foaming, which limits large-scale application.

[0004] Therefore, it is necessary to provide a lightweight composite material for buildings and a preparation method thereof to prepare a building composite material with the characteristics of lightweight, high strength, multi-function (heat insulation / sound insulation / vibration reduction), and environmental protection and degradability, and to achieve efficient preparation through process optimization. Summary of the Invention

[0005] The purpose of the present invention is to provide a lightweight composite material for buildings and a preparation method thereof to solve the problems raised in the above background art, as well as the technical problems of insufficient strength, single function, poor environmental protection, and complex preparation process in the lightweight process of existing building materials, and to achieve the coordinated optimization of lightweight, high strength, multi-function (heat insulation / sound insulation / vibration reduction), and environmental protection and degradability.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] In the first aspect of the present invention, a lightweight composite material for construction is provided, which is composed of the following raw materials in parts by weight: 5-15 parts of nanocrystalline cellulose whiskers, 10-20 parts of expandable graphite, 20-40 parts of thermoplastic polyurethane (TPU), 15-30 parts of polystyrene foam particles, 5-10 parts of compatibilizer, 3-8 parts of auxiliary agent, 2-5 parts of chemical foaming agent, and 8-15 parts of polylactic acid (PLA) nanoscale degradable template; the polystyrene foam particles have a particle size of 100-300 μm and are treated with a silane coupling agent on the surface.

[0008] In the second aspect of the present invention, a preparation method of a lightweight composite material for construction is provided, which includes the following steps:

[0009] Step 1: Pretreatment of raw materials

[0010] 5-15 parts of nanocrystalline cellulose whiskers are dried at a vacuum degree ≤ -0.09 MPa and 60-80 °C for 4-6 h to remove moisture to ensure its dispersibility; 10-20 parts of expandable graphite are pulverized to a particle size of 50-100 μm by a jet mill, and nitrogen is introduced for protection during the pulverization process.

[0011] Step 2: Mixing and kneading

[0012] Weigh 20-40 parts of thermoplastic polyurethane, 15-30 parts of polystyrene foam particles, 5-15 parts of dried nanocrystalline cellulose whiskers, 10-20 parts of expandable graphite, 5-10 parts of compatibilizer, and 3-8 parts of auxiliary agent according to parts by weight, and add them to a twin-screw extruder; set the temperature range of the extruder to 180-220 °C, and the screw speed to 150-250 r / min. Under this condition, co-extrusion is carried out to make each raw material fully mixed and uniform, forming a uniform composite material.

[0013] Step 3: Macropore formation

[0014] 3-4 parts of chemical foaming agent and an additional 5-10 parts of thermoplastic polyurethane (TPU) are mixed in a kneader at 150-160 °C for 8 min to make a masterbatch; the masterbatch is added to the twin-screw extruder, and after being preliminarily mixed with the composite material obtained in Step 2, it is extruded in the twin-screw extruder at 140-160 °C to form millimeter-sized macropores, with a screw speed of 150-250 r / min, obtaining a preliminarily formed material containing macropores.

[0015] Step 4: Introduction of micropores and use of templates

[0016] Polylactic acid is made into nanoscale template particles, which are mixed with the preliminarily formed material containing macropores obtained in Step 3 again, and secondary injection molding is carried out at 160-180 °C; during this process, the matrix material around the template solidifies, forming nanoscale micropores surrounding the template.

[0017] Step Five: Template Removal

[0018] The degradation solution is a phosphate buffer solution containing 0.2% lipase, with a pH value of 5, and the volume ratio of the solution to the material is 5:1 - 10:1; after the material is formed in Step Four, it is placed in the above-mentioned phosphate buffer solution, and in an environment of 37 ± 1°C, the polylactic acid (PLA) nano-scale degradable template will start to gradually degrade within 5 - 10 days; after 14 - 21 days, most of the templates can be degraded into small molecule lactic acid, and by soaking in the phosphate buffer solution, the degradation products (lactic acid) dissolve in the solution and are naturally removed, with a degradation rate ≥ 95%;

[0019] Step Six: Molding Process

[0020] Molding is carried out by compression molding, with a molding temperature of 190 - 210°C, a molding pressure of 5 - 10 MPa, and a holding pressure time of 5 - 10 min, and the material processed in Step Five is formed into the required shape.

[0021] Preferably, in Step Two, the compatibilizer is maleic anhydride grafted SEBS, with a dosage of 7 - 8 parts; the auxiliaries include antioxidant 1010 (1 - 3 parts) and calcium stearate (2 - 5 parts).

[0022] Preferably, the chemical foaming agent is sodium bicarbonate.

[0023] Preferably, in Step Four, the polylactic acid (PLA) nano-scale degradable template (particle size 50 - 200 nm) and the macroporous material-containing are dispersed in a high-speed mixer at a volume ratio of 1:5 - 1:10, and 0.3% - 0.8% dispersant is added.

[0024] Preferably, in Step Four, the molecular weight of the polylactic acid (PLA) nano-scale degradable template is 50,000 - 100,000, and its degradation rate is controlled by adding stannous octoate as an additive, and the addition amount of stannous octoate is 0.1% - 0.5% of the weight of polylactic acid.

[0025] Preferably, the polystyrene foam particles are replaced by polylactic acid-based degradable microspheres, and the particle sizes of the microspheres show a gradient distribution, and the ratio of the gradient distribution is: 100 nm:500 nm:1 μm = 3:2:1, and uniform dispersion is achieved by adding 0.5% Span80 dispersant and using ultrasonic-assisted mixing technology, with an ultrasonic power of 200 W and an ultrasonic time of 5 min.

[0026] Preferably, in Step Four, dynamic pressure holding technology is used for secondary injection molding, with an injection pressure of 80 - 100 MPa, a holding pressure of 60 - 80 MPa, and a holding pressure time of 60 - 90 s.

[0027] Preferably, in the fifth step, when the formed material is placed in the phosphate buffer solution, the volume ratio of the solution to the material is 8:1.

[0028] Preferably, in the sixth step, the molding is carried out by gradient heating: preheating at 190°C for 3 min → pressurizing at 200°C with 7 MPa and holding for 7 min → cooling and shaping at 180°C for 5 min; the density of the final product is controlled at 0.3 - 0.5 g / cm³, and the porosity is ≥60%.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. The preparation method of the lightweight composite material for buildings provided by the present invention constructs a multi-scale pore structure. The macropores reduce the weight of the material and act as the main framework to bear the main load, while the micropores effectively disperse the stress concentration, so that the compressive strength of the material is greatly increased by 25% - 35% compared with the single-scale pore structure, and at the same time, a lower density is maintained, achieving a good balance between light weight and high strength.

[0031] 2. The lightweight composite material for buildings provided by the present invention forms an air barrier layer through millimeter-sized macropores, and the nanometer-sized micropores further inhibit air convection and heat conduction. The thermal conductivity of the material is successfully reduced to 0.05 - 0.07 W / (m・K), which is better than that of conventional porous materials (such as the thermal conductivity of cement-based porous materials is 0.08 - 0.12 W / (m・K)), significantly enhancing the heat insulation effect and helping to reduce building energy consumption.

[0032] 3. The lightweight composite material for buildings provided by the present invention has excellent sound barrier and absorption effects on sound through the multi-scale pore structure. The millimeter-sized macropores initially buffer low-frequency sounds and change the propagation path, and the nanometer-sized micropores, relying on their huge specific surface area, convert sound energy into heat energy through friction and viscous effects to absorb high-frequency sounds. Under the synergistic effect, the average sound absorption coefficient of the material is increased by 30% - 40%, which can effectively reduce external noise interference and is suitable for building spaces with strict requirements for the acoustic environment.

[0033] 4. The lightweight composite material for buildings provided by the present invention uses macropores as a flexible support structure, which can undergo large deformations when subjected to impacts and absorb part of the impact energy; the nanometer-sized micropores are distributed on the pore walls, further refining the energy dissipation path. When the material is subjected to dynamic load impacts, the shock absorption coefficient is increased by 20% - 30% compared with the single-scale pore structure material, which can effectively protect the building structure and internal facilities from vibration effects, especially suitable for buildings in earthquake-prone areas or areas where precision instrument equipment is placed.

[0034] 5. The preparation method of the lightweight composite material for construction provided by the present invention uses a polylactic acid (PLA) nanoscale degradable template, which can be degraded by a specific degradation solution and conditions after the material is formed, and the degradation rate is ≥95%, avoiding environmental pollution caused by template residues. Detailed implementation manners

[0035] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0036] Example 1:

[0037] This example provides a preparation method of a lightweight composite material for construction, including the following steps:

[0038] Step 1: Pretreatment of raw materials

[0039] 5 - 15 parts of nanocellulose whiskers are dried at a vacuum degree ≤ -0.09 MPa and a temperature of 60 - 80 °C for 4 - 6 h to remove moisture to ensure its dispersibility; 10 - 20 parts of expandable graphite are pulverized by a jet mill to a particle size of 50 - 100 μm, and nitrogen is introduced for protection during the pulverization process.

[0040] In this step, nanocellulose whiskers are hydrophilic, and the presence of moisture will cause them to agglomerate, affecting the dispersion uniformity in the composite material. After drying treatment, it can be better dispersed uniformly in the subsequent mixing process, enhancing the interaction with other raw materials, thereby effectively improving the properties such as the strength of the composite material. Pulverization reduces the particle size of expandable graphite and increases its specific surface area, enabling it to better contact with other raw materials and play a reinforcing role. Introducing nitrogen for protection can prevent expandable graphite from being oxidized during the pulverization process, ensuring the stability of its structure and properties, and laying a foundation for playing excellent mechanical reinforcement and thermal conductivity regulation and other functions in the composite material subsequently.

[0041] Step 2: Mixing and kneading

[0042] Weigh 20 - 40 parts of thermoplastic polyurethane, 15 - 30 parts of polystyrene foam particles, 5 - 15 parts of dried nanocellulose whiskers, 10 - 20 parts of expandable graphite, 5 - 10 parts of compatibilizer, and 3 - 8 parts of auxiliary agent by weight, and add them to a twin-screw extruder; set the temperature range of the extruder to 180 - 220 °C and the screw speed to 150 - 250 r / min, and carry out co-extrusion under these conditions to make all raw materials fully mixed and uniform, forming a uniform composite material.

[0043] In this step, the set temperature range can keep thermoplastic materials such as thermoplastic polyurethane (TPU) in a good molten state, which is conducive to mixing with other raw materials. The set screw speed ensures that all raw materials are fully stirred and evenly mixed in the extruder to form a uniform composite material. Uniform mixing can give full play to the synergistic effect among raw materials. For example, nanocellulose whiskers and expandable graphite are evenly dispersed in the matrix, effectively enhancing the mechanical properties of the material; the compatibilizer can improve the compatibility between different raw materials, make the internal structure of the composite material more stable, and enhance the overall performance.

[0044] The separate extrusion in Step 2 allows all basic raw materials to be fully mixed without the interference of chemical blowing agents. Since chemical blowing agents decompose and generate gas at high temperatures, if they are extruded together with other raw materials in Step 2, it may affect the full mixing of raw materials because the generation of gas will disrupt the flow state and mixing uniformity of the material. Extruding twice in Step 2 and Step 3 respectively can enable the basic raw materials to reach a good mixing state first, laying a foundation for the subsequent formation of a uniform composite material structure.

[0045] Step 3: Macropore formation

[0046] Mix 3 - 4 parts of chemical blowing agent with 5 - 10 parts of additional thermoplastic polyurethane (TPU) in a mixer at 150 - 160 °C for 8 minutes to make masterbatch; add the masterbatch to a twin-screw extruder. After it is preliminarily mixed with the composite material obtained in Step 2, extrude it in the twin-screw extruder at 140 - 160 °C to form millimeter-sized macropores. The screw speed is 150 - 250 r / min to obtain a preliminarily formed macroporous material.

[0047] In this step, the chemical blowing agent decomposes to generate gas at the set temperature, forming a macroporous structure in the TPU matrix. On the one hand, this macroporous structure can reduce the material density and achieve lightweight; on the other hand, the existence of macropores can change the stress distribution inside the material, improve the toughness of the material to a certain extent, and also have a positive impact on heat insulation and sound insulation performance. Macropores can block heat transfer and sound wave propagation.

[0048] The extrusion in Step 3 is specifically for the mixing and foaming process of the masterbatch containing blowing agent and the composite material in Step 2. This can more precisely control the decomposition of the blowing agent and the formation of macropores, avoid the premature decomposition or uneven decomposition of the blowing agent during the mixing process, and thus obtain a macroporous material with a more uniform macropore distribution and a more stable structure.

[0049] Step 4: Microvoid introduction and template use

[0050] Prepare polylactic acid into nano-sized template particles, mix them with the preliminarily formed macroporous material in Step 3 again, and perform secondary injection molding at 160 - 180 °C; during this process, the matrix material around the template solidifies to form nano-sized micropores surrounding the template.

[0051] In this step, prepare polylactic acid into nano-sized template particles, mix them with the macroporous material again and perform secondary injection molding. During this process, the matrix material around the template solidifies to form nano-sized micropores. The polylactic acid nano-sized template particles serve as pore-forming templates, and their nano-sized dimensions enable the formed micropores to also be at the nano level. These nano-sized micropores further optimize the internal structure of the material, increase the specific surface area of the material, and improve the heat insulation performance of the material because the nano-sized micropores have a stronger hindering effect on heat conduction; at the same time, the microporous structure also helps to enhance the sound insulation performance of the material, playing a role in multiple scattering and absorption of sound.

[0052] Step Five: Template Removal

[0053] The degradation solution uses a phosphate buffer solution containing 0.2% lipase, with a pH value of 5, and the volume ratio of the solution to the material is 5:1 - 10:1; after the material is formed in Step 4, place it in the above-mentioned phosphate buffer solution. In an environment of 37 ± 1 °C, the polylactic acid (PLA) nano-sized degradable template will start to gradually degrade within 5 - 10 days; after 14 - 21 days, most of the template can be degraded into small molecule lactic acid, and by soaking in the phosphate buffer solution, the degradation products (lactic acid) dissolve in the solution and are naturally removed, with a degradation rate ≥ 95%.

[0054] In this step, the set degradation solution and conditions can efficiently and gently degrade the polylactic acid template, avoiding damage to other components of the composite material. After removing the template, the remaining nano-sized microporous structure is retained, achieving the expected microporous structure design, and at the same time avoiding the negative impact of template residue on the material properties, ensuring the purity and performance stability of the material.

[0055] Step Six: Forming and Processing

[0056] Use compression molding, with a molding temperature of 190 - 210 °C, a molding pressure of 5 - 10 MPa, and a holding pressure time of 5 - 10 min to process the material treated in Step Five into the required shape.

[0057] In this step, the set molding temperature and pressure can further compact the material, improve the density and structural stability of the material, and at the same time ensure that the pore structure inside the material is not damaged.

[0058] More specifically, in Step Two, the compatibilizer is maleic anhydride grafted SEBS, with a dosage of 7 - 8 parts; the additives include antioxidant 1010 (1 - 3 parts) and calcium stearate (2 - 5 parts).

[0059] In this step, further, maleic anhydride grafted SEBS as a compatibilizer can form chemical bonds or strong physical forces between inorganic materials such as nanocellulose whiskers and expandable graphite and organic matrices such as thermoplastic polyurethane, greatly enhancing the interfacial bonding force. The set dosage (7 - 8 parts) can ensure that no excessive impurities are introduced during the improvement of compatibility, thus not affecting the material properties. Antioxidant 1010 can capture free radicals generated during the processing and use of the composite material, effectively inhibiting the oxidative degradation of the material and prolonging the service life of the material. Calcium stearate as a lubricant can reduce the friction between the material and the screw and barrel, making the mixing process smoother, reducing energy consumption, and at the same time ensuring the surface quality of the material, preventing the performance deterioration caused by local overheating of the material due to friction during processing.

[0060] More specifically, the chemical blowing agent is sodium bicarbonate.

[0061] In this step, further, sodium bicarbonate decomposes to produce gas at a relatively low temperature. Compared with azodicarbonamide, it avoids thermal damage to the PLA template at high temperature and at the same time ensures sufficient generation of macropores. The decomposition temperature is adapted to the mixing temperature of the internal mixer, with a large and stable gas production, which can accurately form uniform and appropriately sized millimeter-scale macropores in the TPU matrix, ensuring the realization of effects such as lightweighting of the material, adjustment of stress distribution, and improvement of heat insulation and sound insulation performance.

[0062] More specifically, in step four, a polylactic acid (PLA) nanoscale degradable template (particle size 50 - 200 nm) and the macroporous-containing material are dispersed in a high-speed mixer at a volume ratio of 1:5 - 1:10, and 0.3% - 0.8% of a dispersant is added.

[0063] In this step, further, it ensures the uniform dispersion of the template particles in the macroporous-containing material, so that the formed micropores are evenly distributed in the material, avoiding the influence of micropore aggregation or uneven distribution on the material properties. The set volume ratio (1:5 - 1:10) ensures that after the template particles are mixed with the macroporous-containing material, the number and density of the subsequent formed nanoscale micropores are moderate, and it will not cause the micropores to be too dense and affect the material strength due to too much template, nor will it cause insufficient micropore quantity and inability to fully exert performance advantages such as heat insulation and sound insulation due to too little template. The high-speed mixer combined with the dispersant (0.3% - 0.8%) can highly disperse the template particles in the macroporous-containing material, ensuring the uniform distribution of the finally formed micropores in the material, avoiding anisotropy of the material properties caused by local aggregation or absence of micropores, and ensuring the uniformity of the overall material properties.

[0064] More specifically, in the fourth step, the molecular weight of the polylactic acid (PLA) nano-scale degradable template is 50,000 to 100,000, and the degradation rate is controlled by adding stannous octoate as an additive. The addition amount of stannous octoate is 0.1% to 0.5% of the weight of polylactic acid.

[0065] In this step, further, it can ensure that the template degrades according to a predetermined time and degree during subsequent degradation, providing a guarantee for the subsequent template removal step. The polylactic acid template with a molecular weight of 50,000 - 100,000 has appropriate mechanical strength and thermal stability, and can maintain its own structural stability during the secondary injection molding process, ensuring the formation of micropores. By controlling the degradation rate with stannous octoate, the template can degrade according to a predetermined time and degree in the subsequent steps. In the template removal step, it can not only ensure that the template is fully degraded into small molecule lactic acid for washing removal, but also prevent the degradation from being too fast, resulting in the collapse of the microporous structure when the material is not fully cured and stabilized, ensuring the integrity of the microporous structure inside the material and maintaining the material properties.

[0066] More specifically, the polystyrene foam particles are replaced with polylactic acid-based degradable microspheres, and the particle size of the microspheres shows a gradient distribution. The gradient distribution ratio is: 100nm:500nm:1μm = 3:2:1. By adding 0.5% Span80 dispersant and adopting ultrasonic-assisted mixing technology to achieve uniform dispersion, with an ultrasonic power of 200W and an ultrasonic time of 5min, it avoids the problem that micron-sized and nano-sized particles are prone to sedimentation and separation during the mixing process and it is difficult to achieve uniform dispersion.

[0067] In this step, further, the polystyrene foam particles are replaced with polylactic acid-based degradable microspheres with a gradient particle size distribution, and a gradient construction of the pore structure can be carried out:

[0068] 100nm microspheres: As a secondary reinforcing phase, they are filled in the macropore gaps to form a secondary pore network, improving pore connectivity.

[0069] 500nm microspheres: Construct a middle layer support structure to balance the mechanical properties of macropores and micropores.

[0070] 1μm microspheres: Form a millimeter-level main pore framework to provide initial structural support.

[0071] Example: Among 60 microspheres, 30 100nm microspheres are filled between 20 500nm microspheres and 10 1μm microspheres to form a three-level nested structure of "macropore - mesopore - micropore".

[0072] PLA nano-template (50 - 200nm): Forms nano-scale micropores in the microsphere gaps, forming a four-level pore system (main pore → mesopore → secondary pore → nano-pore) with the gradient microspheres, and the porosity is increased to more than 65%.

[0073] Furthermore, polylactic acid-based degradable microspheres of different particle sizes (100 nm:500 nm:1 μm = 3:2:1) and PLA nano-templates (50 - 200 nm) construct a four-level pore network (main pores → mesopores → secondary pores → nano-pores) to achieve the synergistic optimization of mechanical, thermal, acoustic, and degradation properties: the gradient microspheres form a multi-level support structure, combined with the stress relaxation effect induced by the nano-template, increasing the compressive strength by 35% and having an impact toughness of 8.5 kJ / m²; the multi-level pores synergistically reduce the thermal conductivity to 0.04 W / (m·K) through the stationary air layer, convection suppression, and Knudsen effect, while achieving an absorption coefficient of 0.85 across the entire frequency band; the gradient degradation period (3 - 28 days) accelerates the material disintegration and maintains a weight loss rate of 92%, and the degradation products are completely harmless; the grading design also increases the melt flowability by 30% and reduces the cost by 22%, achieving a balance between the lightweight and high performance of building materials.

[0074] More specifically, in the fourth step, dynamic pressure holding technology is used for the secondary injection molding, with an injection pressure of 80 - 100 MPa, a pressure holding pressure of 60 - 80 MPa, and a pressure holding time of 60 - 90 s.

[0075] In this step, further, the use of dynamic pressure holding technology in the secondary injection molding can make the material more dense during the molding process, ensure the stability of the microporous structure, avoid problems such as micropore collapse, and thus ensure the consistency and stability of the material properties.

[0076] More specifically, in the fifth step, when the molded material is placed in a phosphate buffer solution, the volume ratio of the solution to the material is 8:1.

[0077] More specifically, in the sixth step, gradient heating is used for the compression molding: preheat at 190 °C for 3 min → pressurize at 200 °C with 7 MPa and hold the pressure for 7 min → cool and shape at 180 °C for 5 min; the density of the final product is controlled at 0.3 - 0.5 g / cm³, and the porosity is ≥60%.

[0078] In this step, further, the method of gradient heating helps the material to solidify and adjust its structure orderly at different stages, making the molecular arrangement inside the material more regular, thereby improving the mechanical properties such as the strength of the material. Preheating at 190°C for 3 minutes can make the material heat up slowly, and each component is heated evenly, avoiding defects caused by uneven internal thermal stress due to rapid heating. Pressurize at 200°C with 7 MPa and hold the pressure for 7 minutes. At this temperature and pressure, the material is further compacted, the intermolecular distance decreases, enhancing the material density and structural stability. At the same time, the macropore and micropore structures are further optimized under the action of pressure, improving the mechanical properties such as the strength of the material. Cool and shape at 180°C for 5 minutes, making the material cool slowly at a suitable temperature, and the internal molecules are arranged orderly, avoiding internal stress caused by rapid cooling and ensuring the dimensional stability of the material. Through this gradient heating and molding process, the goals of product density and porosity are accurately achieved, endowing the material with comprehensive properties such as light weight, high strength, good heat insulation and sound insulation, meeting the requirements of building applications.

[0079] In summary, in this embodiment, in terms of improving mechanical properties: in the multi-scale pore structure, macropores reduce weight, and micropores enhance the strength of the pore walls. Macropores act as the main framework to bear the main load, and micropores disperse stress concentration, increasing the compressive strength of the material by 25%-35% compared with the single-scale pore structure, while maintaining a relatively low density. Optimization of thermal insulation performance: millimeter-scale macropores form an air barrier layer, and nanometer-scale micropores further prevent air convection and heat conduction. The thermal conductivity of the material is reduced to 0.05-0.07 W / (m・K), which is better than that of conventional porous materials (such as the thermal conductivity of cement-based porous materials is 0.08-0.12 W / (m・K)), significantly improving the thermal insulation effect. Enhancement of sound insulation performance: The multi-scale pore structure has good blocking and absorption effects on sound. Millimeter-scale macropores can initially buffer low-frequency sounds and change the sound propagation path; nanometer-scale micropores, with their extremely large specific surface area, convert sound energy into heat energy through friction and viscous effects, absorbing high-frequency sounds. This synergistic effect significantly improves the sound insulation performance of the material, increasing the average sound absorption coefficient of the material by 30%-40%, effectively reducing external noise interference, and is suitable for building spaces with high acoustic environment requirements, such as conference rooms, recording studios, etc. Improvement of shock absorption and buffering performance: Macropores act as a flexible support structure and can undergo large deformations when subjected to impacts, absorbing part of the impact energy; nanometer-scale micropores are distributed on the pore walls, further refining the energy dissipation path. When the material is subjected to dynamic load impacts, its shock absorption coefficient is increased by 20%-30% compared with the single-scale pore structure material, effectively protecting the building structure and internal facilities from vibration effects, and can be applied to buildings in earthquake-prone areas or building areas where precision instrument equipment is placed.

[0080] Comparative Example 1:

[0081] The difference between Comparative Example 1 and Example 1 is only that: Steps Four and Five are missing. Due to the absence of Steps Four and Five, no nano-scale microporous structure is introduced into the material, and there is no degradation process of the polylactic acid template.

[0082] Comparative Example 2:

[0083] The difference between Comparative Example 2 and Example 1 is only that: in Step Four, a non-degradable template is used instead of the nano-scale degradable polylactic acid (PLA) template. Using a non-degradable template can form a microporous structure, but the template cannot be degraded and will remain inside the material, affecting the purity and performance of the material.

[0084] Comparative Example 3:

[0085] The difference between Comparative Example 3 and Example 1 is only that: in Steps Two and Three, extrusion is carried out only once. Combining Steps Two and Three into one extrusion, the chemical foaming agent may not be fully mixed with other raw materials, and the formation process of macropores is difficult to precisely control, resulting in an uneven material structure.

[0086] Comparative Example 4:

[0087] The difference between Comparative Example 4 and Example 1 is only that: in Step Two, the polystyrene foam particles are replaced with polylactic acid-based degradable microspheres with a uniform particle size distribution. The uniform particle size distribution of the polylactic acid-based degradable microspheres cannot form a multi-scale synergistic effect compared with the gradient distribution in Example 1.

[0088] Comparative Example 5:

[0089] The difference between Comparative Example 5 and Example 1 is only that: in Step Four, dynamic pressure holding technology is not used for the secondary injection molding. Without using dynamic pressure holding technology, the material may not be fully compacted during the molding process, and the stability of the microporous structure is difficult to guarantee.

[0090] Comparative Example 6:

[0091] The difference between Comparative Example 6 and Example 1 is only that: in Step Six, the gradient heating molding method is not used, but the molding is carried out under the conditions of 190 °C, a molding pressure of 5 MPa, and a pressure holding time of 5 min throughout the process. Without using gradient heating, the material may not be able to fully adjust its internal structure during the molding process, resulting in a decrease in performance.

[0092] The comparative experimental data of the above various comparative examples and examples are as follows:

[0093] Comparison items Density (g / cm³) Compressive strength (MPa) Thermal conductivity (W / (m・K)) Increase amplitude of average sound absorption coefficient Increase amplitude of shock absorption coefficient Example 1 0.3-0.5 20 (25%-35% higher than the single-scale pore structure) 0.05 - 0.07 (superior to conventional porous materials) 30%-40% 20%-30% Comparative example 1 0.55 16 (about 20% lower than Example 1) 0.075 Around 10% Within 10% Comparative example 2 0.45 18 (about 10% lower than Example 1) 0.068 Around 20% Around 15% Comparative example 3 0.52 15 (about 25% lower than Example 1) 0.07 Within 5% Almost no improvement Comparative example 4 0.45 17 (about 15% lower than Example 1) 0.062 Around 15% Around 12% Comparative example 5 0.48 17.5 (about 12% lower than Example 1) 0.063 Around 22% Around 13% Comparative example 6 0.52 16.5 (about 17.5% lower than Example 1) 0.065 Around 12% Around 8%

[0094] By analyzing the experimental data of Example 1 and each comparative example, it is possible to clearly understand the influence of different preparation conditions and raw material characteristics on the properties of lightweight composite materials for construction. The following is a detailed summary and analysis of these experimental data:

[0095] 1. In terms of density: The density of Example 1 is controlled within 0.3 - 0.5 g / cm³, achieving the goal of lightweighting. In Comparative Example 1, due to the lack of steps for introducing micropores and removing templates, a nano-scale microporous structure cannot be formed to optimize the porosity, resulting in a higher density of 0.55 g / cm³; in Comparative Example 3, only one extrusion is carried out, and the formation of macropores is uneven, unable to effectively reduce the density, reaching 0.52 g / cm³; in Comparative Example 4, the particle sizes of the polylactic acid-based degradable microspheres are evenly distributed, failing to form a multi-scale synergistic effect to optimize the pore structure, and the density is 0.45 g / cm³; in Comparative Example 5, the dynamic pressure holding technology is not adopted, and the material density is insufficient, with the density slightly increasing to 0.48 g / cm³; in Comparative Example 6, non-gradient temperature rise leads to a loose structure, the porosity increases but is not fully closed, and the density is 0.52 g / cm³; in Comparative Example 2, a non-degradable template is used, although micropores can be formed, but the template residue causes a slight increase in density to 0.45 g / cm³. It can be seen that the preparation method and raw material selection of Example 1 of the present invention are more conducive to achieving the lightweighting of the material.

[0096] 2. In terms of compressive strength: The compressive strength of Example 1 is 20 MPa, and it is increased by 25% - 35% compared with the single-scale pore structure, and the multi-scale pore structure plays a good strengthening role. In Comparative Example 1, the key steps are lacking, and the compressive strength drops to 16 MPa, a decrease of about 20%; in Comparative Example 2, a non-degradable template is used, and the template residue forms defects, and the compressive strength is 18 MPa, a decrease of about 10%; in Comparative Example 3, a single extrusion results in an uneven macropore structure, and the compressive strength is only 15 MPa, a decrease of about 25%; in Comparative Example 4, the microsphere particle sizes are evenly distributed, and the compressive strength is 17 MPa, a decrease of about 15%; in Comparative Example 5, the dynamic pressure holding technology is not adopted, and the micropore structure is unstable, and the compressive strength is 17.5 MPa, a decrease of about 12%; in Comparative Example 6, non-gradient temperature rise and molding by pressing are not adopted, and the internal molecular arrangement is irregular, and the compressive strength is 16.5 MPa, a decrease of about 17.5%. This shows that the preparation process and raw material combination of the present invention are crucial for improving the compressive strength of the material.

[0097] 3. In terms of thermal conductivity: The thermal conductivity of Example 1 is as low as 0.05 - 0.07 W / (m·K), with excellent heat insulation performance, superior to conventional porous materials (0.08 - 0.12 W / (m·K)). Comparative Example 1 has no further heat insulation effect of nanoscale micropores, and its thermal conductivity is 0.065 W / (m·K); in Comparative Example 2, the non-degradable template affects the heat conduction path, and the template residue increases the solid-phase heat conduction, with a thermal conductivity of 0.065 W / (m·K); in Comparative Example 3, the macroporous structure is uneven and cannot effectively block heat, with a thermal conductivity of 0.07 W / (m·K); in Comparative Example 4, the uniform pore structure formed by uniformly distributed microspheres lacks a nanoscale thermal resistance layer, and the heat insulation effect is slightly poor, with a thermal conductivity of 0.062 W / (m·K); in Comparative Example 5, the collapse of micropores increases gas convection heat conduction, with a thermal conductivity of 0.063 W / (m·K); in Comparative Example 6, the non-dense structure leads to an increase in gas convection, with a thermal conductivity of 0.065 W / (m·K). It shows that the structural design of Example 1 of the present invention has obvious advantages in heat insulation.

[0098] 4. In terms of the average sound absorption coefficient: The average sound absorption coefficient of Example 1 can be increased by 30% - 40%, and the multi-scale pore structure has a significant effect on blocking and absorbing sound. In Comparative Example 1, the lack of nanoscale micropores for absorbing high-frequency sound results in an increase in the average sound absorption coefficient of only about 10%; in Comparative Example 2, the non-degradable template interferes with sound propagation and absorption, and the increase is about 20%; in Comparative Example 3, the macroporous structure is chaotic, and the sound absorption effect is poor, with an increase within 5%; in Comparative Example 4, the single-scale microspheres have limited ability to process sounds of different frequencies, and the increase is about 15%; in Comparative Example 5, the defects in the microporous structure affect sound absorption, and the increase is about 22%; in Comparative Example 6, the internal structure of the material is imperfect, and the sound blocking and absorption effects are poor, with an increase of about 18%. It reflects the superiority of the structure of Example 1 of the present invention in sound insulation.

[0099] 5. In terms of the shock absorption coefficient: The shock absorption coefficient of Example 1 is increased by 20% - 30% compared with the single-scale pore structure material, and the multi-scale pore structure can effectively dissipate impact energy. In Comparative Example 1, the energy dissipation path is single, and the increase in the shock absorption coefficient is within 10%; in Comparative Example 2, the non-degradable template affects the structural uniformity, and the increase is about 15%; in Comparative Example 3, the macroporous structure is uneven, with almost no increase; in Comparative Example 4, the single-scale microspheres have weak ability to absorb and disperse impact energy, and the increase is about 12%; in Comparative Example 5, the unstable microporous structure has limited energy dissipation ability, and the increase is about 13%; in Comparative Example 6, the non-dense structure leads to pore collapse, weakening the energy dissipation ability, and the increase is about 8%. It shows that the structure of Example 1 of the present invention has obvious advantages in shock absorption and buffering.

[0100] In summary, the preparation method and raw material formula of Embodiment 1 of the present invention can prepare a lightweight composite material for construction with excellent performance, which is superior to each comparative example in terms of light weight, high strength, heat insulation, sound insulation, shock absorption and buffering. The synergistic effect of each step and raw material plays a key role in improving the material performance.

[0101] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. A lightweight composite material for construction, characterized in that: It is composed of the following raw materials in parts by weight: 5-15 parts of nanocellulose whiskers, 10-20 parts of expandable graphite, 20-40 parts of thermoplastic polyurethane (TPU), 15-30 parts of polystyrene foam particles, 5-10 parts of compatibilizer, 3-8 parts of auxiliary agent, 2-5 parts of chemical foaming agent, 8-15 parts of polylactic acid (PLA) nano-scale degradable template; The particle size of the polystyrene foam particles is 100-300 μm, and the surface is treated with a silane coupling agent.

2. A method for preparing a lightweight composite material for construction according to claim 1, characterized in that: The following steps are involved: Step 1: Raw material pretreatment Dry 5 to 15 parts of nanocellulose whiskers at a vacuum degree of ≤-0.09 MPa and 60 to 80°C for 4 to 6 hours to remove moisture to ensure its dispersibility; 10 to 20 parts of expandable graphite are crushed into a particle size of 50 to 100 μm by a jet mill, and nitrogen is introduced during the crushing process; Step 2: Mixing and kneading Weigh 20-40 parts of thermoplastic polyurethane, 15-30 parts of polystyrene foam particles, 5-15 parts of dried nanocellulose whiskers, 10-20 parts of expandable graphite, 5-10 parts of compatibilizer and 3-8 parts of auxiliary agent according to weight, and add them into a twin-screw extruder; The temperature range of the extruder is set to 180-220°C, and the screw speed is set to 150-250r / min. Under this condition, the blending extrusion is carried out to make the raw materials fully mixed and uniform to form a uniform composite material; Step 3: Macropore Generation Mix 3-4 parts of chemical foaming agent and 5-10 parts of additional thermoplastic polyurethane (TPU) in an internal mixer at 150-160°C for 8 minutes to prepare a masterbatch; The masterbatch is added to a twin-screw extruder, and after being preliminarily mixed with the composite material obtained in step 2, it is extruded in the twin-screw extruder at 140-160° C. to form millimeter-level macropores, and the screw speed is 150-250 r / min to obtain a preliminarily formed macroporous material; Step 4: Micropore introduction and template use The polylactic acid is made into nano-scale template particles, which are mixed again with the macroporous material initially formed in step 3, and secondary injection molding is performed at 160-180° C. During this process, the matrix material around the template is solidified to form nano-scale micropores around the template; Step 5: Template Removal The degradation solution uses a phosphate buffer solution containing 0.2% lipase, with a pH value of 5 and a ratio of solution volume to material volume of 5:1 to 10:1; After the material in step 4 is formed, it is placed in the above-mentioned phosphate buffer solution. At 37±1°C, the polylactic acid (PLA) nano-scale degradable template will gradually degrade within 5 to 10 days; After 14 to 21 days, most of the templates can be degraded into small molecule lactic acid. By soaking in phosphate buffer solution, the degradation product (lactic acid) is dissolved in the solution and removed naturally, and the degradation rate is ≥95%; Step 6: Molding The material processed in step 5 is processed into a desired shape by compression molding at a compression temperature of 190 to 210° C., a compression pressure of 5 to 10 MPa, and a holding time of 5 to 10 minutes.

3. The method for preparing a lightweight composite material for construction according to claim 2, characterized in that: In the step 2, the compatibilizer is maleic anhydride grafted SEBS, and the dosage is 7-8 parts; the auxiliary agents include antioxidant 1010 (1-3 parts) and calcium stearate (2-5 parts).

4. The method for preparing a lightweight composite material for construction according to claim 2, characterized in that: The chemical foaming agent is sodium bicarbonate.

5. The method for preparing a lightweight composite material for construction according to claim 2, characterized in that: In the step 4, a polylactic acid (PLA) nano-scale degradable template (particle size 50-200 nm) and a macroporous material are dispersed in a high-speed mixer at a volume ratio of 1:5-1:10, and 0.3%-0.8% of a dispersant is added.

6. The method for preparing a lightweight composite material for construction according to claim 2, characterized in that: In the step 4, the molecular weight of the polylactic acid (PLA) nano-scale degradable template is 50,000 to 100,000, and its degradation rate is controlled by adding stannous octoate as an additive, and the amount of stannous octoate added is 0.1% to 0.5% of the weight of the polylactic acid.

7. The method for preparing a lightweight composite material for construction according to claim 2, characterized in that: The polystyrene foam particles are replaced with polylactic acid-based degradable microspheres, and the particle sizes of the microspheres are gradient distributed in a ratio of 100nm:500nm:1μm=3:2:

1. Uniform dispersion is achieved by adding 0.5% Span80 dispersant and using ultrasound-assisted mixing technology, with an ultrasound power of 200W and an ultrasound time of 5min.

8. The method for preparing a lightweight composite material for construction according to claim 2, characterized in that: In the step 4, the secondary injection molding adopts a dynamic pressure holding technology, with an injection pressure of 80 to 100 MPa, a holding pressure of 60 to 80 MPa, and a holding time of 60 to 90 s.

9. The method for preparing a lightweight composite material for construction according to claim 2, characterized in that: In the step 5, when the molded material is placed in a phosphate buffer solution, the volume ratio of the solution to the volume of the material is 8:

1.

10. The method for preparing a lightweight composite material for construction according to claim 2, characterized in that: In the step six, the compression molding adopts a gradient temperature increase: preheating at 190°C for 3 minutes → pressurizing at 200°C at 7MPa for 7 minutes → cooling and shaping at 180°C for 5 minutes; the density of the final product is controlled at 0.3-0.5g / cm³, and the porosity is ≥60%.