A flame-retardant wood-plastic composite material and its preparation method

Abstract

This application relates to the field of natural materials technology, specifically to a flame-retardant wood-plastic composite material and its preparation method. The method includes: S1: drying natural wood fiber materials; S2: mixing the dried natural wood fiber materials with various raw materials to obtain a raw material mixture; S3: melt-extruding the raw material mixture in a twin-screw extruder to obtain flame-retardant wood-plastic composite material particles, wherein the proportional coefficient of the temperature control process for each barrel heating section is adjusted based on the temperature changes in each barrel heating section during the melt extrusion process; S4: cooling the flame-retardant wood-plastic composite material particles to obtain the flame-retardant wood-plastic composite material. This application solves the temperature lag and fluctuation problems by dynamically adjusting the proportional coefficient of each heating section of the extruder, thereby improving the mechanical properties and appearance quality of the flame-retardant wood-plastic composite material.

Description

Technical Field

[0001] This application relates to the field of natural materials technology, specifically to a flame-retardant wood-plastic composite material and its preparation method. Background Technology

[0002] Because natural wood materials typically have disadvantages such as being easily perishable, easily deformed, and flammable, existing methods usually utilize natural wood fiber materials such as wood flour and bamboo flour to modify and fill plastic plastics, and add flame retardants to prepare flame-retardant wood-plastic composite materials. This composite material has an appearance similar to natural wood materials, but has advantages such as good corrosion resistance, deformation resistance, and flame retardancy, and is widely used in furniture building materials, landscaping, interior and exterior decoration, and other fields.

[0003] Extrusion is the mainstream process for producing flame-retardant wood-plastic composites, with the twin-screw extruder being the core equipment. In actual production, to ensure uniform extrudate temperature, strict segmented temperature control of the barrel is usually required to improve the quality of the final product. However, significant temperature coupling effects exist between the heating sections of the twin-screw extruder barrel, especially between adjacent sections, causing materials in different heating sections to affect each other due to temperature differences. Furthermore, external disturbances such as screw speed variations and heating voltage fluctuations can exacerbate temperature fluctuations, making it difficult to stabilize the material temperature during extrusion and thus reducing the mechanical properties and appearance quality of the flame-retardant wood-plastic composite. Summary of the Invention

[0004] In a first aspect, one embodiment of this application provides a method for preparing a flame-retardant wood-plastic composite material, the method comprising the following steps:

[0005] S1: Drying process for natural wood fiber materials;

[0006] S2: The dried natural wood fiber material is mixed with various raw materials to obtain a raw material mixture.

[0007] S3: The raw material mixture is melt-extruded in a twin-screw extruder to obtain flame-retardant wood-plastic composite particles. Specifically, based on the temperature changes in each barrel heating section during melt extrusion, the proportional coefficient of the temperature control process for each barrel heating section is adjusted.

[0008] The temperature and pressure of all heating sections on the twin-screw extruder and the screw speed of the twin-screw extruder are collected in real time. All heating sections include the barrel heating section and the non-barrel heating section.

[0009] By analyzing the temperature difference trends between each barrel heating section and its adjacent heating sections in space at all times within a preset time period before each time, the temperature difference trend value of each barrel heating section at each time is determined.

[0010] By analyzing the pressure fluctuations of each barrel heating section and the screw speed fluctuations of the twin-screw extruder at all times within a preset time period before each time, the fluctuation characteristic values ​​of each barrel heating section at each time are determined.

[0011] Based on the temperature difference characteristic value and the fluctuation characteristic value, the proportional coefficient adjustment factor of each barrel heating section at each time point is determined so as to regulate the proportional coefficient in the PID controller used for each barrel heating section within a preset time period after each time point;

[0012] S4: Flame-retardant wood-plastic composite material particles are cooled to obtain flame-retardant wood-plastic composite material.

[0013] Preferably, the mesh size of the natural wood fiber material is 60-120.

[0014] Preferably, the natural wood fiber material is either wood powder or bamboo powder.

[0015] Preferably, the content of plastic particles in each raw material mixture is 15-30 parts by weight, the content of flame retardant is 20-35 parts by weight, the content of compatibilizer is 1-3 parts by weight, the content of foaming agent is 1-3 parts by weight, the content of antioxidant is 0.2-1 parts by weight, and the content of stabilizer is 0.2-1 parts by weight; the content of dried natural wood fiber material in the raw material mixture is 15-30 parts by weight.

[0016] Preferably, the plastic particles in the various raw materials are one or more mixtures of polyethylene plastic particles and polyvinyl chloride plastic particles; the flame retardant is one or more mixtures of ammonium polyphosphate, aluminum hydroxide, and magnesium hydroxide; the compatibilizer is one or more mixtures of maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, and maleic anhydride-grafted EVA; the foaming agent is one or more mixtures of melamine, dicyandiamide, and polyamide; the antioxidant is one or more mixtures of antioxidants 1010, 1076, and BHT; and the stabilizer is one or more mixtures of light stabilizers 994, 744, and AM-101.

[0017] Preferably, the method for determining the temperature difference trend value of each barrel heating section at each time point is as follows:

[0018] The time series decomposition algorithm is used to obtain the trend sequence of temperature difference between each barrel heating segment and its spatially adjacent previous heating segment at all times within a preset time period before each time, as well as the trend sequence of temperature difference between each barrel stage and its adjacent subsequent heating segment. The correlation coefficient between the two trend sequence sequences is used as the temperature difference trend value of each barrel heating segment at each time.

[0019] Preferably, the method for determining the fluctuation characteristic value of each barrel heating section at each time point is as follows:

[0020] The moving standard deviation algorithm is used to obtain the moving standard deviation sequence of the pressure of each barrel heating section and the moving standard deviation sequence of the screw speed of the twin-screw extruder at all times within a preset time period before each time.

[0021] The mean of all elements in the moving standard deviation sequence of pressure and the mean of all elements in the moving standard deviation sequence of screw speed are calculated separately and denoted as the mean of pressure standard deviation and the mean of screw speed standard deviation, respectively. The result of positively fusing the mean of pressure standard deviation and the mean of screw speed standard deviation is used as the fluctuation characteristic value of each barrel heating section.

[0022] Preferably, the proportional coefficient adjustment factor for each barrel heating section at each time point is the ratio of the normalized value of the fluctuation characteristic value to the normalized value of the temperature difference trend value for each barrel heating section at each time point.

[0023] Preferably, the adjustment of the proportional coefficient in the PID controller used for each barrel heating section within a preset time period after each time point includes:

[0024] The proportional coefficient in the PID controller used for the j-th barrel heating section within a preset time period after time i. The expression is: In the formula, This represents the proportional coefficient adjustment factor for the j-th barrel heating section at time i; , These represent the preset additive factor and the preset multiplicative factor, respectively. This represents the rounding function.

[0025] Secondly, this application also provides a flame-retardant wood-plastic composite material, which is prepared by the aforementioned method for preparing a flame-retardant wood-plastic composite material.

[0026] This application has at least the following beneficial effects:

[0027] The application evaluates the temperature lag risk and optimizes the temperature control response by analyzing the consistency of the temperature difference change trend between the barrel heating section and its adjacent heating sections before and after it, constructing a temperature difference trend value, thereby reducing material defects caused by local overheating or uneven cooling, and improving the mechanical properties and appearance quality of the flame-retardant plastic-wood composite material; further, the application evaluates the influence of external interference on temperature control by analyzing the fluctuation of the pressure of the barrel heating section and the screw speed, constructing a fluctuation characteristic value, thereby improving the response speed of the system to the temperature lag phenomenon and reducing the local overheating or uneven problem caused by temperature fluctuation, which helps to improve the mechanical properties and appearance quality of the flame-retardant plastic-wood composite material; finally, the application constructs a proportional coefficient tuning factor by combining the temperature difference trend value and the fluctuation characteristic value, dynamically adjusts the proportional coefficient of the PID controller, improves the response speed and stability of the temperature control system, effectively suppresses the temperature lag and fluctuation, ensures that the temperature of the flame-retardant plastic-wood composite material is uniform and controllable during the extrusion process, and improves the mechanical properties and appearance quality of the flame-retardant plastic-wood composite material. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0029] Figure 1 A step flow chart of a flame-retardant plastic-wood composite material preparation method provided by an embodiment of the present application is shown in the figure.

[0030] Figure 2 A proportional coefficient regulation step flow chart provided by an embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0031] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the specific implementation, structure, features and effects of the flame-retardant plastic-wood composite material and its preparation method according to the present application are described in detail as follows by combining the drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures or characteristics in one or more embodiments can be combined in any suitable form.

[0032] Unless otherwise defined, terms such as "comprising", "including", or any other variant thereof, are intended to cover non-exclusive inclusions, such that the circuit structure, item or apparatus including a list of elements does not only include those elements, but also includes other elements not explicitly listed, or other elements inherent to such item or apparatus. Without more limitations, the element defined by the phrase "including a" does not exclude the presence of additional identical elements in the item or apparatus including the element. In addition, the term "and / or" used herein includes any one and all combinations of the associated listed items. All technical and scientific terms used herein have the same meaning as understood by those skilled in the art to which the present application belongs. The specific schemes of the flame-retardant plastic-wood composite material and the preparation method thereof provided by the present application are specifically described below with reference to the accompanying drawings.

[0033] The specific schemes of the preparation method of the flame-retardant plastic-wood composite material provided by the present application are specifically described below with reference to the accompanying drawings.

[0034] Example 1

[0035] The preparation method of the flame-retardant plastic-wood composite material provided by Example 1 is specifically described below with reference to Figure 1 The process method comprises the following steps:

[0036] S1: drying treatment is performed on the natural wood fiber material.

[0037] In this embodiment, the wood powder with a mesh number of 60 and an ash content of 4% is placed in an oven at 110°C for 24h of drying treatment, so that the water content is less than 3%, and the dried natural wood fiber material is obtained, wherein the ash content is generally less than 5%, and in this embodiment, the value is 4%. In actual application, as another embodiment, the implementer can also set it by himself according to the specific situation, and this embodiment does not have special limitations.

[0038] S2: mixing the dried natural wood fiber material with various raw materials to obtain a raw material mixture.

[0039] The plastic particles in the various raw materials are one or more mixtures of polyethylene plastic particles and polyvinyl chloride plastic particles, the flame retardant is one or more mixtures of ammonium polyphosphate, aluminum hydroxide and magnesium hydroxide, the compatibilizer is one or more mixtures of maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene and maleic anhydride grafted EVA, the foaming agent is one or more mixtures of melamine, dicyandiamide and polyamide, the antioxidant is one or more mixtures of antioxidants 1010, 1076 and BHT, and the stabilizer is one or more mixtures of light stabilizers 994, 744 and AM-101.

[0040] In the embodiment, 15 parts of polyethylene plastic particles and 20 parts of ammonium polyphosphate are added into a mixer for stirring and mixing, then 15 parts of dried natural wood fiber material, 1 part of maleic anhydride grafted polyethylene, 1 part of melamine, 0.2 parts of antioxidant 1010 and 0.2 parts of light stabilizer 994 are added into the mixer for stirring and mixing to obtain a raw material mixture. In the embodiment, the rotating speed of the mixer is set to 300 r / min, and the stirring and mixing time is 2 min. In actual application, the rotating speed of the mixer and the stirring and mixing time can be set by the implementer according to the specific conditions, which are not specially limited in the embodiment.

[0041] The raw material mixture obtained in step S2 is added into a double screw extruder for melt blending, and the flame-retardant plastic-wood composite material particles are extruded. The double screw extruder is a conical double screw extruder. In the conical double screw extruder, the extrusion process of the material generally goes through a feeding section, a conveying section, a melting section, a plasticizing section, a converging core heating section and a die heating section in sequence. The feeding section, the conveying section, the melting section and the plasticizing section are collectively referred to as the barrel heating section, and the converging core heating section and the die heating section are collectively referred to as the non-barrel heating section. The four barrel heating sections have temperature ranges of 180-225°C, 180-210°C, 130-180°C and 130-170°C in sequence, the temperature range of the converging core heating section is generally 120-160°C, and the temperature range of the die heating section is generally 140-170°C. The feeding rotating speed of the double screw extruder is 10 r / min. In actual application, the feeding rotating speed can be set by the implementer according to the specific conditions, which is not specially limited in the embodiment.

[0042] It should be noted that the four barrel heating sections and all the non-barrel heating sections are not time periods, but physical regions responsible for heating the material, but they have a certain sequence in time, i.e., the material extrusion process goes through the feeding section, the conveying section, the melting section, the plasticizing section, the converging core heating section and the die heating section in sequence, and they are arranged in the direction of the feeding position along the base extrusion position in space, which is exactly the same as the above-mentioned time sequence, for example, the feeding section is the adjacent previous heating section of the conveying section in space and time, and the melting section is the adjacent next heating section of the conveying section in space and time, i.e., the adjacent previous heating section and the adjacent next heating section of the conveying section are the feeding section and the melting section, respectively.

[0043] However, in the actual extrusion process, due to the serious thermal coupling effect between the heating sections of the barrel, especially between adjacent heating sections, combined with the interference of external factors such as the change of screw speed of the double screw and the voltage fluctuation of the heating device used by the barrel, it is easy to cause the temperature of each heating section of the barrel to fluctuate and lag, thereby affecting the uniformity of the melting blending and the quality of the final flame-retardant plastic-wood composite material. In order to solve this problem, the embodiment quantitatively evaluates the change trend of the temperature difference between adjacent heating sections and the interference degree of external factors, and dynamically adjusts the proportional coefficient of the PID controller used by each heating section of the barrel, thereby improving the response speed to temperature lag and fluctuation, ensuring the stability of the melting process, and laying a foundation for the subsequent high-quality extrusion of the flame-retardant plastic-wood composite material. The proportional coefficient control step flow chart provided by the embodiment is shown in Figure 2 The specific control process of the proportional coefficient is as follows:

[0044] S3.1 Real-time acquisition of the temperature and pressure of all heating sections of the double screw extruder and the screw speed of the double screw extruder, wherein all the heating sections include barrel heating sections and non-barrel heating sections.

[0045] The temperature of the surface of all the heating sections in the double screw extruder is collected in real time by using temperature sensors, and the voltage of the heating device used by each heating section is collected in real time by using voltage sensors, and the screw speed of the double screw extruder is collected in real time by using a screw speed sensor, wherein all the heating sections include barrel heating sections and non-barrel heating sections, and the collection frequency of the above data is f. In the embodiment, the value of f is artificially set, and in the embodiment, the value of f is 10 Hz. In actual application, as other implementation manners, the implementer can also set it according to the specific situation, and the embodiment does not make special limitations.

[0046] The collected temperature, pressure and screw speed are normalized respectively to eliminate the influence of different data dimensions. There are many commonly used normalization methods, and in the embodiment, the maximum and minimum value normalization method is used to normalize the data. In actual application, as other implementation manners, the implementer can also use other normalization methods such as z-score standardization method according to the specific situation. The selection of the normalization method is not limited in the embodiment.

[0047] S3.2 Determine the temperature difference trend value of each barrel heating section at each time by analyzing the change trend of the temperature difference between each barrel heating section and its left and right adjacent heating sections at all times within a preset time length before each time.

[0048] In the process of heating and melting the raw material mixture of the flame-retardant plastic-wood composite material by using the barrels of the twin-screw extruder, the material in the barrel is continuously pushed towards the die direction with the rotation of the screw of the twin-screw extruder, so that the materials in each barrel heating section of the twin-screw extruder are interconnected, and the temperature difference between different parts of the same object will cause heat transfer phenomenon, and the heat will be transferred from the high temperature part to the low temperature part. Therefore, for any barrel heating section of the twin-screw extruder, when the temperature difference between the barrel heating section and its time-sequentially adjacent heating sections has inconsistent change trend, the heat input or heat output on the front and rear sides of the barrel heating section will usually change, thereby destroying the original temperature balance state between the barrel heating section and its spatially adjacent heating sections in front and behind, causing the temperature in the barrel heating section to fluctuate, and the temperature change of the object usually has certain thermal inertia, which will cause the temperature of the barrel heating section to be unable to be adjusted rapidly, resulting in temperature lag phenomenon, further intensifying the instability of the temperature in the barrel heating section.

[0049] Therefore, in order to improve the response speed of the temperature control module to the inconsistent temperature difference change trend and avoid subsequent temperature fluctuation, the embodiment determines the temperature difference trend value of each barrel heating section at each moment by analyzing the temperature difference change trend between each barrel heating section and its spatially adjacent heating sections in front and behind at all moments within a preset time length before each moment, and the specific process is as follows:

[0050] In the embodiment, the time series decomposition algorithm is used to obtain the trend item sequence of the temperature difference between each barrel heating section and its spatially adjacent previous heating section at all moments within a preset time length before each moment, and the trend item sequence of the temperature difference between each barrel heating section and its adjacent next heating section. The correlation coefficient between the two trend item sequences is used as the temperature difference trend value of each barrel heating section at each moment. In order to more clearly and specifically describe the obtaining process of the temperature difference trend value, the following description process is given, which is specifically as follows:

[0051] Firstly, the temperature difference between each barrel heating section and its spatially adjacent previous heating section and adjacent next heating section at each moment is calculated, which is respectively recorded as the front adjacent temperature difference and the rear adjacent temperature difference of each barrel heating section at each moment.

[0052] It should be noted that there are many methods for measuring the difference between data, for example: in the embodiment, the absolute value of the temperature difference between each heating section of the cylinder at each time and its spatially adjacent previous heating section is taken as the temperature difference between each heating section of the cylinder at each time and its spatially adjacent previous heating section, and similarly, the calculation of the rear adjacent temperature difference also adopts the method of taking the absolute value of the difference, in the actual application process, as other implementation manners, the implementer can also combine the specific circumstances to adopt the square or ratio of the difference and other methods for measuring the difference between data, regarding the selection of the method for measuring the difference between data, the embodiment does not make special limitation.

[0053] Further, the front adjacent temperature difference and the rear adjacent temperature difference of each cylinder heating at all times within a preset time length before each time are taken as the input of the time series decomposition algorithm, and the trend item sequence of the front adjacent temperature difference and the trend item sequence of the rear adjacent temperature difference are respectively output.

[0054] It should be noted that there are many commonly used time series decomposition algorithms, in the embodiment, the STL time series decomposition algorithm is adopted to obtain the trend item sequence of the front adjacent temperature difference and the rear adjacent temperature difference, in the actual application process, as other implementation manners, the implementer can also combine the specific circumstances to adopt other time series decomposition algorithms such as time series X-12-ARIMA seasonal adjustment algorithm, the embodiment does not make special limitation.

[0055] Among them, the STL time series decomposition algorithm is a known technology, and the specific process of obtaining the trend item sequence will not be repeated.

[0056] It should be noted that the value of the preset time length is set by human, in the embodiment, the value of the preset time length is 5s, in the actual application process, the implementer can also set it by himself according to the specific circumstances, the embodiment does not make special limitation.

[0057] Further, the embodiment takes the correlation coefficient between the trend item sequences of the front adjacent temperature difference and the rear adjacent temperature difference as the temperature difference trend value of each heating section of the cylinder at each time.

[0058] It should be noted that there are many commonly used correlation coefficient calculation methods, in the embodiment, the Pearson correlation coefficient between the trend item sequences of the front adjacent temperature difference and the rear adjacent temperature difference is taken as the correlation coefficient between the trend item sequences of the front adjacent temperature difference and the rear adjacent temperature difference, in the actual application process, as other implementation manners, the implementer can also combine the specific circumstances to adopt other methods for measuring the correlation between sequences such as Spearman correlation coefficient or Kendall rank correlation coefficient, regarding the selection of the correlation coefficient, the embodiment does not make special limitation.

[0059] Among them, the calculation method of the Pearson correlation coefficient is a known technology, and the specific calculation process will not be repeated.

[0060] Specifically, if there is no heating section before the barrel heating section, the temperature difference trend value of the barrel heating section is assigned to 1.

[0061] Based on the temperature difference trend value of each barrel heating section at each time point, it can be understood that the temperature difference trend value is used to evaluate whether the temperature difference change trend between the barrel heating section and its spatially adjacent heating sections is consistent. The closer the correlation coefficient of the trend term sequence between the preceding and following temperature differences of the barrel heating section at the current time point is to 1, the larger the corresponding temperature difference trend value is. This indicates that the temperature difference change trend of the heating sections on both sides of the barrel heating section is highly consistent, the barrel heating section is relatively balanced by the temperature influence of both sides, and the possibility of temperature lag between different heating sections is smaller. This indicates that the temperature change between adjacent heating sections can be synchronized. This means that the flame-retardant wood-plastic composite material can reach and stabilize at the target temperature in each heating section in the barrel within a predetermined time. This helps to reduce defects such as bubbles and cracks caused by local overheating or uneven cooling, and improves the mechanical properties and appearance quality of the flame-retardant wood-plastic composite material.

[0062] Conversely, the closer the correlation coefficient of the trend term sequence between the preceding and following temperature differences of the barrel heating section at the current moment is to 0 or -1, the smaller the corresponding temperature difference trend value. This indicates that the temperature difference change trends of the heating sections on both sides of the barrel heating section are highly inconsistent, the barrel heating section is unbalanced due to the temperature influence of both sides, and the possibility of temperature lag between different heating sections is greater. This indicates that the temperature changes between adjacent heating sections cannot be synchronized. This means that the flame-retardant wood-plastic composite material is difficult to reach and stabilize at the target temperature in each heating section of the barrel within the predetermined time. It is prone to defects such as bubbles and cracks due to local overheating or uneven cooling, which reduces the mechanical properties and appearance quality of the flame-retardant wood-plastic composite material.

[0063] Thus, this embodiment analyzes the consistency of the temperature difference change trend between the barrel heating section and its adjacent heating sections before and after it, constructs a temperature difference trend value, assesses the risk of temperature lag, and optimizes the temperature control response, thereby reducing material defects caused by local overheating or uneven cooling, and improving the mechanical properties and appearance quality of flame-retardant wood-plastic composite materials.

[0064] S3.3 By analyzing the pressure fluctuation of each barrel heating section and the screw speed fluctuation of the twin-screw extruder at all times within the preset time period before each time, the fluctuation characteristic value of each barrel heating section at each time is determined.

[0065] During the heating and melting of the raw material mixture of flame-retardant wood-plastic composite material in the barrel of a twin-screw extruder, the temperature of the material inside the barrel is affected not only by the heating voltage of the barrel heating device but also by the internal friction generated by the shearing action of the screw rotation. Under normal circumstances, temperature is positively correlated with voltage and internal friction, respectively. Therefore, when the voltage of the heating device used in any barrel heating section of the twin-screw extruder or the screw speed of the twin-screw extruder fluctuates, the temperature in that barrel heating section will also fluctuate, and the temperature change in that barrel heating section has a certain lag.

[0066] Therefore, based on the above analysis, in order to improve the response speed to temperature hysteresis caused by external disturbances such as screw speed and voltage fluctuations, and to avoid subsequent temperature fluctuations, this embodiment analyzes the pressure fluctuation of each barrel heating section at all times within a preset time period before each time, as well as the screw speed fluctuation of the twin-screw extruder, to determine the fluctuation characteristic value of each barrel heating section at each time. The specific process is as follows:

[0067] In this embodiment, the moving standard deviation algorithm is used to obtain the moving standard deviation sequence of the pressure of each barrel heating section and the moving standard deviation sequence of the screw speed of the twin-screw extruder at all times within a preset time period before each time. In this embodiment, the moving window size and the moving step size in the moving standard deviation algorithm are set to 1 second. In actual application, the implementer can also set the moving window size and moving step size according to the specific situation. This embodiment does not impose any special restrictions.

[0068] Furthermore, the mean of all elements in the moving standard deviation sequence of pressure and the mean of all elements in the moving standard deviation sequence of screw speed are calculated separately and denoted as the mean of pressure standard deviation and the mean of screw speed standard deviation, respectively. The result of positively fusing the mean of pressure standard deviation and the mean of screw speed standard deviation is used as the fluctuation characteristic value of each barrel heating section.

[0069] The moving standard deviation algorithm is a well-known technique, and the specific process of obtaining the moving standard deviation sequence using it will not be described in detail.

[0070] It should be understood that positive fusion refers to combining two or more indicators through addition or multiplication to obtain a comprehensive indicator, thereby more comprehensively and accurately assessing a phenomenon or problem. This fusion method is not limited to simple arithmetic operations, but can also include more complex statistical models and analytical methods. Implementers can choose according to specific circumstances, and this embodiment does not impose any special restrictions.

[0071] Preferably, as one implementation method, in this embodiment, the average of the pressure standard deviation and the screw speed standard deviation is used as the fluctuation characteristic value of each barrel heating section. In actual application, as another implementation method, the implementer may also use other positive fusion methods such as product or sum, depending on the specific situation. This embodiment does not impose any special restrictions on the selection of positive fusion methods.

[0072] Based on the fluctuation characteristic values ​​of each barrel heating section at each time point, it can be understood that the fluctuation characteristic values ​​are used to characterize the overall fluctuation degree of voltage and screw speed. If the mean of all elements in the standard deviation sequence of voltage movement is larger at the current time, and the mean of all elements in the standard deviation sequence of screw speed movement is larger, it indicates that the heating power of the heating device has increased, the temperature of the barrel heating section has changed suddenly, and the PID controller needs more time to catch up with the set temperature, which leads to an aggravation of temperature lag. At the same time, when the screw speed suddenly increases, the shear heat will also increase, but the PID controller fails to respond in time, resulting in local overheating or uneven temperature. Correspondingly, the fluctuation characteristic value is larger, which leads to a decrease in the mechanical properties and quality of flame-retardant wood-plastic composite material.

[0073] Conversely, if the mean of all elements in the moving standard deviation sequence of voltage at the current moment is smaller, and the mean of all elements in the moving standard deviation sequence of screw speed is smaller, it indicates that the heating power of the heating device changes steadily, the temperature change of the barrel heating section is relatively gentle, and the PID controller can respond quickly and stabilize at the set temperature, thereby effectively alleviating the temperature lag phenomenon. At the same time, when the screw speed remains stable, the shear heat is generated uniformly, and the PID controller can adjust the temperature control strategy in a timely manner to avoid local overheating or temperature unevenness. Correspondingly, the fluctuation characteristic value is smaller, which helps to improve the mechanical properties and appearance quality of flame-retardant wood-plastic composite materials.

[0074] Thus, this embodiment analyzes the fluctuations in pressure and screw speed in the barrel heating section and constructs fluctuation characteristic values ​​to comprehensively evaluate the impact of external disturbances on temperature control. This improves the system's response speed to temperature lag and reduces local overheating or unevenness caused by temperature fluctuations, thereby helping to improve the mechanical properties and appearance quality of flame-retardant wood-plastic composite materials.

[0075] S3.4 Based on the temperature difference characteristic value and the fluctuation characteristic value, determine the proportional coefficient adjustment factor of each barrel heating section at each time point, so as to regulate the proportional coefficient in the PID controller used for each barrel heating section within a preset time period after each time point.

[0076] Furthermore, based on the temperature difference trend value and fluctuation characteristic value obtained in steps S3.2 and S3.3, this embodiment determines the proportional coefficient adjustment factor to regulate the proportional coefficient in the PID controller used in each barrel heating section within a preset time period after each time point. This improves the response capability of the barrel heating section to the inconsistency of temperature difference change trends and suppresses the temperature lag problem caused by external factors such as screw speed changes and voltage fluctuations. Specifically:

[0077] In this embodiment, the ratio of the normalized value of the fluctuation characteristic value of each barrel heating section at each time point to the normalized value of the temperature difference trend value is used as the proportional coefficient adjustment factor for each barrel heating section at each time point.

[0078] Based on the proportional coefficient adjustment factor, it can be understood that it is used to comprehensively evaluate the degree of influence of inconsistent temperature change trends and external fluctuations on control requirements. If the fluctuation characteristic value of the barrel heating section is larger and the temperature difference trend value is smaller at the current moment, it indicates that the flame-retardant wood-plastic composite material preparation process faces a more serious temperature lag problem and requires a rapid response. Therefore, the corresponding proportional coefficient adjustment factor should be larger. Conversely, if the fluctuation characteristic value of the barrel heating section is smaller and the temperature difference trend value is larger at the current moment, it indicates that the temperature change trend is more consistent during the preparation of the flame-retardant wood-plastic composite material, the impact of external fluctuations is smaller, the temperature lag problem is milder, and the control is relatively stable. Therefore, the corresponding proportional coefficient adjustment factor should be smaller to avoid system oscillations or unnecessary control interventions caused by over-adjustment, thereby maintaining the stability and reliability of temperature control, which is conducive to improving the production stability and product quality of flame-retardant wood-plastic composite materials.

[0079] Furthermore, based on the aforementioned proportional coefficient adjustment factor, the proportional coefficient in the PID controller used for each barrel heating section is adjusted within a preset time period after each time point. Specifically:

[0080] The proportional coefficient in the PID controller used for the j-th barrel heating section within a preset time period after time i. The expression is: In the formula, This represents the proportional coefficient adjustment factor for the j-th barrel heating section at time i; , These represent the preset additive factor and the preset multiplicative factor, respectively. This represents the rounding function.

[0081] It should be noted that the values ​​of the preset additive factor and the preset multiplicative factor are both manually set. In this embodiment, the preset additive factor... The preset multiplicative factor is 0.1. The value is 10, which is used to control the proportional coefficient to be within the range of 0.1 to 1. In actual application, the implementer can also set it according to the specific situation. This embodiment does not impose any special restrictions.

[0082] The proportional coefficients of each barrel heating section in the twin-screw extruder at each time point calculated above are used as the proportional coefficients of the PID controllers used for the corresponding barrel heating sections within a preset time period after each time point. The PID controllers are then used to control the temperature of the corresponding barrel heating sections in real time within the preset time period, thereby avoiding temperature fluctuations in the material within each barrel heating section of the twin-screw extruder when extruding and granulating the raw material mixture of flame-retardant wood-plastic composite material.

[0083] Thus, this embodiment constructs a proportional coefficient adjustment factor by combining temperature difference trend value and fluctuation characteristic value, dynamically adjusts the proportional coefficient of the PID controller, improves the response speed and stability of the temperature control system, effectively suppresses temperature lag and fluctuation, ensures uniform and controllable temperature of flame-retardant wood-plastic composite material during extrusion, and improves the mechanical properties and appearance quality of flame-retardant wood-plastic composite material.

[0084] S4: Flame-retardant wood-plastic composite material particles are cooled to obtain flame-retardant wood-plastic composite material.

[0085] The flame-retardant wood-plastic composite material particles extruded by the twin-screw extruder in step S3 are sprayed and cooled using a circulating cooling water tank to complete the preparation of the flame-retardant wood-plastic composite material.

[0086] Example 2

[0087] Example 2 provides a method for preparing a flame-retardant wood-plastic composite material. For details, please refer to [link / reference]. Figure 1 The method includes the following steps:

[0088] S1: Drying process for natural wood fiber materials.

[0089] In this embodiment, the mesh size of the natural wood fiber material is 80, and the rest of the operation is the same as in Embodiment 1.

[0090] S2: The dried natural wood fiber material is mixed with various raw materials to obtain a raw material mixture.

[0091] In this embodiment, 20 parts by weight of polyvinyl chloride plastic granules and 30 parts by weight of aluminum hydroxide were added to a mixer and stirred. Then, 20 parts of dried natural wood fiber material, 2 parts of maleic anhydride grafted polypropylene, 2 parts of dicyandiamide, 0.6 parts of antioxidant 1076 and 0.6 parts of light stabilizer 744 were added to the mixer and stirred to obtain a raw material mixture. The remaining operations were the same as in Example 1.

[0092] S3: The raw material mixture is melt-extruded in a twin-screw extruder to obtain flame-retardant wood-plastic composite material particles. The proportional coefficient of the temperature control process of each barrel heating section is adjusted based on the temperature change of each barrel heating section during the melt extrusion process.

[0093] S4: Flame-retardant wood-plastic composite material particles are cooled to obtain flame-retardant wood-plastic composite material.

[0094] Example 3

[0095] Example 3 provides a method for preparing a flame-retardant wood-plastic composite material. For details, please refer to [link / reference]. Figure 1 The method includes the following steps:

[0096] S1: Drying process for natural wood fiber materials.

[0097] In this embodiment, the mesh size of the natural wood fiber material is 80, the natural fiber material is bamboo powder, and the rest of the operation is the same as in Example 1.

[0098] S2: The dried natural wood fiber material is mixed with various raw materials to obtain a raw material mixture.

[0099] In this embodiment, 30 parts by weight of polyvinyl chloride plastic granules and 35 parts by weight of aluminum hydroxide are added to a mixer for stirring and mixing. Then, 20 parts of dried natural wood fiber material, 3 parts of maleic anhydride grafted polypropylene, 3 parts of dicyandiamide, 1 part of antioxidant 1076 and 1 part of light stabilizer 744 are added to the mixer for stirring and mixing to obtain a raw material mixture. The remaining operations are the same as in Example 1.

[0100] S3: The raw material mixture is melt-extruded in a twin-screw extruder to obtain flame-retardant wood-plastic composite material particles. The proportional coefficient of the temperature control process of each barrel heating section is adjusted based on the temperature change of each barrel heating section during the melt extrusion process.

[0101] S4: Flame-retardant wood-plastic composite material particles are cooled to obtain flame-retardant wood-plastic composite material.

[0102] Based on the same inventive concept as the above method, this application also provides a flame-retardant wood-plastic composite material, which is prepared by the aforementioned method for preparing a flame-retardant wood-plastic composite material.

[0103] It should be noted that the order of the embodiments described above is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. Furthermore, specific embodiments of this specification have been described above. Additionally, the processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired results. In some implementations, multitasking and parallel processing are possible or may be advantageous.

[0104] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0105] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them; modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions of some of the technical features, do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preparing a flame-retardant plastic-wood composite material, characterized in that, The method comprises the following steps: S1: drying treatment is performed on the natural wood fiber material; S2: the natural wood fiber material after drying treatment is mixed with various raw materials to obtain a raw material mixture; S3: the raw material mixture is subjected to melt extrusion treatment in a double screw extruder to obtain flame-retardant plastic-wood composite material particles, wherein, based on the temperature variation of each barrel heating section during melt extrusion, the proportional coefficient of the temperature control process of each barrel heating section is regulated, specifically as follows: Real-time acquisition of the temperature and pressure of all heating sections of the double screw extruder and the screw rotation speed of the double screw extruder, wherein all heating sections include barrel heating sections and non-barrel heating sections; By analyzing the temperature difference variation trend between each barrel heating section and its spatially adjacent front and rear heating sections at all times within a preset time period before each time, the temperature difference trend value of each barrel heating section at each time is determined; By analyzing the pressure fluctuation of each barrel heating section at all times within a preset time period before each time and the fluctuation of the screw rotation speed of the double screw extruder, the fluctuation characteristic value of each barrel heating section at each time is determined; Based on the temperature difference characteristic value and the fluctuation characteristic value, the proportional coefficient regulation factor of each barrel heating section at each time is determined to regulate the proportional coefficient of the PID controller used in each barrel heating section within a preset time period after each time; S4: cooling treatment is performed on the flame-retardant plastic-wood composite material particles to obtain flame-retardant plastic-wood composite material; The regulation of the proportional coefficient of the PID controller used in each barrel heating section within a preset time period after each time comprises: a proportionality coefficient in a PID controller used by the jth barrel heating section within a preset time length after time i is expressed as: ; in the formula, denotes a proportionality coefficient tuning factor of the jth barrel heating section at time i; , denote a preset additive factor and a preset multiplicative factor, respectively; denotes a rounding function.

2. The method for preparing a flame-retardant wood-plastic composite material as described in claim 1, characterized in that, The natural wood fiber material has a mesh number of 60-120.

3. The method of claim 1, wherein the flame-retardant plastic-wood composite is prepared by adding 0.1 to 1 wt% of the flame-retardant agent to the plastic-wood composite. The natural wood fiber material is one of wood powder or bamboo powder.

4. The method of claim 1, wherein the flame-retardant plastic-wood composite is prepared by adding 0.1 to 1 wt% of the flame-retardant agent to the plastic-wood composite. The content of plastic particles in the various raw materials in the raw material mixture is 15-30 parts by weight, the content of flame retardant is 20-35 parts by weight, the content of compatibilizer is 1-3 parts by weight, the content of foaming agent is 1-3 parts by weight, the content of antioxidant is 0.2-1 part by weight, and the content of stabilizer is 0.2-1 part by weight; the content of dried natural wood fiber material in the raw material mixture is 15-30 parts by weight.

5. The method of claim 1, wherein the flame-retardant plastic-wood composite is prepared by adding 0.1 to 1 wt% of the flame-retardant agent to the plastic-wood composite. The plastic particles in the various raw materials are one or a mixture of more than one of polyethylene plastic particles and polyvinyl chloride plastic particles, the flame retardant is one or a mixture of more than one of ammonium polyphosphate, aluminum hydroxide and magnesium hydroxide, the compatibilizer is one or a mixture of more than one of maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene and maleic anhydride grafted EVA, the foaming agent is one or a mixture of more than one of melamine, dicyandiamide and polyamide, the antioxidant is one or a mixture of more than one of antioxidants 1010, 1076 and BHT, and the stabilizer is one or a mixture of more than one of light stabilizers 994, 744 and AM-101.

6. The method for preparing a flame-retardant wood-plastic composite material as described in claim 1, characterized in that, The determination method of the temperature difference trend value of each barrel heating section at each time is as follows: The time series decomposition algorithm is used to obtain a trend item sequence of temperature difference between each heating section of the cylinder and its spatially adjacent previous heating section at all time points within a preset time length before each time point, and a trend item sequence of temperature difference between each heating section of the cylinder and its spatially adjacent next heating section, and a correlation coefficient between the two trend item sequences is taken as a temperature difference trend value of each heating section of the cylinder at each time point.

7. The method for preparing a flame-retardant wood-plastic composite material as described in claim 1, characterized in that, The determination method of the fluctuation characteristic value of each heating section of the cylinder at each time point is as follows: The moving standard deviation algorithm is used to obtain a moving standard deviation sequence of pressure of each heating section of the cylinder at all time points within a preset time length before each time point, and a moving standard deviation sequence of screw rotation speed of the twin-screw extruder; The mean value of all elements in the moving standard deviation sequence of pressure and the mean value of all elements in the moving standard deviation sequence of screw rotation speed are calculated respectively, and are denoted as a pressure standard deviation mean value and a screw rotation speed standard deviation mean value respectively, and a result of positive fusion of the pressure standard deviation mean value and the screw rotation speed standard deviation mean value is taken as the fluctuation characteristic value of each heating section of the cylinder.

8. The method for preparing a flame-retardant wood-plastic composite material as described in claim 1, characterized in that, The proportional coefficient tuning factor of each heating section of the cylinder at each time point is a ratio of a normalized value of the fluctuation characteristic value of each heating section of the cylinder at each time point to a normalized value of the temperature difference trend value.

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