A method for judging the degree of cross-linking of polysiloxane based on sieving rate

Abstract

The present invention relates to a method for determining the degree of crosslinking of polysiloxane based on sieving rate, and relates to the field of organosilicon polymer technology. The method addresses the problems of difficulty in determining the degree of crosslinking of existing polysiloxane crosslinked solids, which often suffer from complex testing procedures, high experimental environment requirements, and difficulty in popularization in actual production. The method comprises the following steps: 1. mixing polysiloxane with a crosslinking catalyst, subjecting the polysiloxane and catalyst mixture to static crosslinking at 40-60°C for 2 days or more to obtain a crosslinked polysiloxane solid, and thoroughly grinding the obtained crosslinked polysiloxane solid to obtain a crosslinked polysiloxane solid powder; 2. thoroughly passing the crosslinked polysiloxane solid powder through a 200-250 mesh sieve, and calculating the sieving rate. If the sieving rate exceeds 80%, it indicates that the crosslinking degree of the crosslinked polysiloxane solid is high; if the sieving rate is 60-80%, it indicates that the crosslinking degree of the crosslinked polysiloxane solid is good; and if the sieving rate is less than 60%, it indicates that the crosslinking degree of the crosslinked polysiloxane solid is poor.

Description

Technical Field

[0001] The present invention relates to the technical field of organosilicon polymers, and in particular to a method for determining the crosslinking degree of polysiloxane based on screening rate. Background Art

[0002] Ceramic particle-reinforced metal matrix composites (CMMCs) not only possess the advantages of ceramic materials, such as high hardness, good wear resistance, and high temperature resistance, but also possess the toughness and high ductility of metal materials. Therefore, these materials are ideal for the normal operation of certain key core components under extreme environments such as high loads and high temperature differences. High-temperature ceramicization of organic-metal powder crosslinked mixtures and high-pressure rolling techniques are ideal methods for preparing CMMCs. The resulting metal composites exhibit excellent uniformity of ceramic particle dispersion and can significantly improve their strength and wear resistance. The specific implementation process of this method is as follows: After mixing an organic liquid (such as polysiloxane) with metal powder in a certain proportion, a crosslinking catalyst is added to induce a crosslinking reaction between the organic molecules encapsulating the metal particles, gradually transforming the organic material from a liquid state to a solid state, forming a solid CMMC crosslinked organic-metal powder mixture. This CMMC crosslinked organic-metal powder mixture is then pyrolyzed at a certain temperature to convert the crosslinked organic material into inorganic ceramic particles. The pyrolysis products are then subjected to a large plastic deformation process to achieve uniform dispersion of the ceramic particles in the metal, thereby achieving ceramic reinforcement of the metal matrix. In summary, the core of this method is the cross-linking reaction of the organic liquid under the action of a catalyst. Only cross-linked organic molecules can be converted into ceramic particles during the pyrolysis process, while free organic molecules that are not fully cross-linked are evaporated and removed during the pyrolysis process. Therefore, the degree of cross-linking in the organic liquid is a key factor affecting the performance of metal matrix composites.

[0003] For polysiloxane liquid, after adding the crosslinking catalyst, the viscosity of free-flowing liquid polysiloxane increases rapidly in a short period of time and eventually turns into a solid with dense pores, such as Figure 1 As shown. However, even if the polysiloxane has been cross-linked and formed into a macroscopic solid, there are still large differences in the degree of cross-linking of the polysiloxane under different environmental conditions such as temperature, humidity, and storage time. The greater the degree of cross-linking of the polysiloxane, the more conducive it is to link more free polysiloxane molecules together, which is beneficial to reduce the loss of free polysiloxane molecules during the subsequent high-temperature pyrolysis of the cross-linked solid powder, thereby increasing the yield of the high-temperature pyrolysis product, ensuring that the metal-based composite material has good performance, and is beneficial to the subsequent calculation of the content and composition control of the pyrolysis product. Therefore, in actual production and application, it is hoped that the cross-linked solid can achieve a higher degree of cross-linking before high-temperature pyrolysis.

[0004] However, there is currently no clear method for determining the degree of crosslinking in such solids. Since the crosslinked solid formed by crosslinking polysiloxane is a typically soft and brittle material that easily breaks when subjected to external forces, it is impossible to measure the degree of crosslinking in the crosslinked solid using the dynamic torsional vibration method used in resin curing determination. Consequently, during the high-temperature sintering of the ceramicized polysiloxane crosslinked solid, the yield of the sintered product is difficult to control and optimize, resulting in low yields and high costs in actual production applications. Summary of the Invention

[0005] The technical problems to be solved by the present invention are:

[0006] The degree of cross-linking of existing polysiloxane cross-linked solids is difficult to determine, and there are often problems such as complex testing processes, high experimental environment requirements, and difficulty in popularization in actual production.

[0007] The present invention is to solve the above technical problems using the following technical solutions:

[0008] The present invention provides a method for determining the crosslinking degree of polysiloxane based on screening rate, which is characterized by comprising the following steps:

[0009] Step 1: mechanically mixing polysiloxane and a cross-linking catalyst according to a cross-linking process to obtain a polysiloxane and catalyst mixture, allowing the polysiloxane and catalyst mixture to stand for cross-linking at 40-60° C. for 2 days or more to obtain a polysiloxane cross-linked solid, and fully grinding the obtained polysiloxane cross-linked solid to obtain a polysiloxane cross-linked solid powder;

[0010] Step 2: The cross-linked polysiloxane solid powder is thoroughly passed through a 200-250 mesh sieve, and the sieving rate is calculated. If the sieving rate exceeds 80%, it indicates that the cross-linking degree of the cross-linked polysiloxane solid is high; if the sieving rate is 60%-80%, it indicates that the cross-linking degree of the cross-linked polysiloxane solid is good; if the sieving rate is less than 60%, it indicates that the cross-linking degree of the cross-linked polysiloxane solid is poor.

[0011] Furthermore, in step 1, a cross-linking catalyst is added at a mass fraction of 5 to 8%.

[0012] Furthermore, the cross-linked polysiloxane solid obtained in step 1 is fully ground, specifically, the cross-linked polysiloxane solid is ground until the number of particles with a particle size of less than 70 μm accounts for no less than 80%.

[0013] Furthermore, in step 1, the obtained polysiloxane solid is fully ground using a ball mill, the ball milling speed is 200-600 r / min, and the ball milling time is not less than 5 min.

[0014] Furthermore, the viscosity of the polysiloxane at 20° C. is 15 to 40 mPa·s.

[0015] Furthermore, the polysiloxane in step 1 is one of polymethylhydrogensiloxane, polyvinylsiloxane, polycarbosiloxane, polymethylsilsesquioxane or polyvinylsiloxane.

[0016] Furthermore, the catalyst in step 1 is one of triethylenediamine, platinum-based complex or vinyl polymer.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention provides a method for determining the crosslinking degree of polysiloxane based on screening rate, which can conveniently and quickly determine the crosslinking degree of polysiloxane and has the following advantages:

[0019] a) The method of the present invention fills a gap in the field of rapid estimation and judgment of the cross-linking degree of polysiloxanes, can be used for extensive exploration and optimization of cross-linking processes, and provides technical support for stably achieving a high degree of cross-linking of polysiloxanes.

[0020] b) The method of the present invention requires less cross-linked solids during the testing process, which can reduce testing costs. It is easy to perform and can quickly determine the degree of cross-linking in a short period of time, thereby improving testing efficiency.

[0021] c) The method of the present invention utilizes the differences in the sieving properties of cross-linked solid powders at different cross-linking levels to determine the degree of cross-linking. The determination results are accurate, reliable, and have high precision. The method of the present invention can be used to prepare SiOC microceramics, laying the foundation for the further preparation of metal-based composite materials with high strength, high wear resistance, and high toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a morphology diagram of a cross-linked polysiloxane solid in the background technology of the present invention;

[0023] Figure 2 This is a scanning electron microscope image of a highly cross-linked polysiloxane solid after grinding according to an embodiment of the present invention;

[0024] Figure 3 This is a scanning electron microscope image of a ground polysiloxane solid with a low cross-linking degree in an embodiment of the present invention;

[0025] Figure 4 is a relationship diagram between the degree of cross-linking and the screening rate in an embodiment of the present invention;

[0026] Figure 5 This is a scanning electron microscope image of a polysiloxane solid powder with a high degree of cross-linking in an embodiment of the present invention;

[0027] Figure 6This is a scanning electron microscope image of a polysiloxane solid powder with a low degree of cross-linking in an embodiment of the present invention;

[0028] Figure 7 The particle size statistics of the powder particles in the embodiment of the present invention are Figure 1 ;

[0029] Figure 8 The particle size statistics of the powder particles in the embodiment of the present invention are Figure 2 ;

[0030] Figure 9 The particle size statistics of the powder particles in the embodiment of the present invention are Figure 3 ;

[0031] Figure 10 The particle size statistics of the powder particles in the embodiment of the present invention are Figure 4 ;

[0032] Figure 11 The particle size statistics of the powder particles in the embodiment of the present invention are Figure 5 . DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the present invention, exemplary embodiments or examples of the present invention will be described below with reference to the accompanying drawings. Obviously, the described embodiments or examples are only some of the embodiments or examples of the present invention, and not all of them. Based on the embodiments or examples of the present invention, all other embodiments or examples obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0035] Example 1

[0036] Step 1-1: Weigh 19 g of polymethylhydrogensiloxane and 1 g of catalyst triethylenediamine respectively;

[0037] Step 1-2: 19 g of polymethylhydrogensiloxane was weighed and placed in a beaker, which was then placed in a heat-collecting constant temperature heating magnetic stirrer preheated to 50° C. for heating;

[0038] Step 1-3: Add 1 g of the catalyst to a beaker containing polysiloxane, turn on the magnetic stirring function of a heat-collecting constant temperature heating magnetic stirrer, set the speed to 20 r / s, and mechanically mix the polysiloxane and the catalyst until the catalyst is fully dissolved to obtain a mixture of polysiloxane and the catalyst;

[0039] Step 1-4: placing the polysiloxane and catalyst mixture in a constant temperature and humidity test chamber preheated to 50° C. and 40% RH, and allowing it to crosslink for 5 days to obtain a polysiloxane crosslinked solid;

[0040] Step 1-5: Take a solid sample of the polysiloxane cross-linked product and put it into a small ball mill. Set the speed to 500 r / min and the ball milling time to 5 minutes. Then start the ball mill to grind the cross-linked sample.

[0041] Step 1-6: Take out a small amount of ground solid powder and place it under an ultra-depth-of-field optical microscope for observation. At a magnification of 500 times, observe the microscopic morphology of individual powder particles and measure and count the particle size of individual powder particles in the current observation area.

[0042] Step 1-7: Move the observation area position, and measure and count the particle size of individual powder particles in the current observation area again. The number of areas used for observation is not less than three and they do not overlap with each other.

[0043] Step 1-8: Calculate and analyze the statistical particle size data to obtain the particle size distribution curve, such as Figure 7 shown.

[0044] Step 1-9: From the particle size distribution curve, it can be seen that the proportion of powder particles with a particle size of less than or equal to 70 μm reaches about 89.13%. If it is greater than 80%, proceed to the next step. Otherwise, continue grinding until the proportion of powder particles with a particle size of less than or equal to 70 μm is not less than 80%.

[0045] Step 1-10: The mass of the ground polysiloxane solid powder is weighed using an electronic balance with an accuracy of not less than 0.1 mg to obtain a mass of 11.309 g, which is recorded as m1.

[0046] Step 2-1: Pour all the weighed polysiloxane solid powder into a small vibrating sieve machine, select the sieve aperture size as 200 mesh, set the vibrating time to 3 minutes, the vibrating frequency to 1400 times / minute, the amplitude to 2 mm, and then start the vibrating sieve machine.

[0047] Step 2-2: The solid powder passing through the sieve is collected and retained.

[0048] Step 2-3: Collect the larger solid powder that does not pass through the sieve and pour it into a ball mill or mortar for further grinding and refinement.

[0049] Step 2-4: Pour the re-ground solid powder into the cleaned small vibrating sieve machine and sieve it again using the parameters in step 2-1.

[0050] Step 2-5: Repeat grinding and sieving until the amount of powder passing through the sieve no longer increases, and mix the polysiloxane solid powders sieved each time.

[0051] Step 2-6: Use an electronic balance to weigh the mass of the solid powder that passes through the sieve to find 10.430 g, and record it as m2.

[0052] Step 2-7: Calculate the sieving rate:

[0053] η=(m2 / m1)*100% (1)

[0054] Step 2-8: Calculate the screening rate to be 92.24%.

[0055] Step 2-9: Weigh 5 g of the sieved polysiloxane cross-linked product using an electronic balance with an accuracy of 0.1 mg, and record it as m3.

[0056] Step 2-10: Place the weighed cross-linked product into a corundum crucible, and place the crucible containing the cross-linked product into a tube furnace.

[0057] Step 2-11: introduce argon into the tubular furnace, set the heating rate to 5°C / min, set the maximum heating temperature to 1000°C, heat to 1000°C, keep warm for 2 hours, and cool with the furnace.

[0058] Step 2-12: After the tube furnace is cooled to room temperature, the cross-linked product after pyrolysis is taken out.

[0059] Step 2-13: Use an electronic balance with an accuracy of 0.1 mg to weigh the mass of the product obtained by pyrolysis to be 4.356 g and record it as m4.

[0060] Step 2-14: Calculate the mass ratio θ of the polysiloxane cross-linked solid powder before and after pyrolysis using formula (2):

[0061] The obtained θ is 87.12%.

[0062] The cross-linking reaction of polysiloxane forms a solid three-dimensional network structure, which easily entraps liquid uncross-linked polysiloxane linear molecules. Polysiloxane cross-linked products with a high degree of cross-linking have fewer residual uncross-linked polysiloxane linear molecules, so fewer liquid uncross-linked polysiloxane linear molecules are entrapped in their network structure, resulting in a completely hard and brittle solid appearance from a macroscopic perspective. The polysiloxane cross-linked product of this example has a high degree of dispersion after grinding, as shown in FIG. Figure 2 As shown in Figure 2, the fracture of the polysiloxane cross-linked solid is sharp, and cracks can be observed on its surface. Such cracks are usually found on the surface of hard and brittle phases. The solid powder is drier and easier to disperse, as shown in Figure 2. Figure 5As shown in the figure, it can pass through the screen smoothly during the screening operation. On the contrary, the cross-linked polysiloxane with a low degree of cross-linking has a large number of liquid uncross-linked polysiloxane linear molecules wrapped in its network structure. Macroscopically, some of them appear to be in an intermediate state during the liquid-solid transition process, making them exhibit soft elastic properties. After grinding, the dispersion of the cross-linked polysiloxane is low, as shown in the figure. Figure 3 As shown in the figure, the fracture of the cross-linked polysiloxane solid is smooth, and the linear molecules of the liquid uncross-linked polysiloxane are sticky, which makes the surface of the polysiloxane particles also sticky, and the dispersed polysiloxane solid particles are bonded together, which makes them easy to agglomerate and difficult to disperse. The solid powder is softer and more elastic and easy to agglomerate into large-sized flocculent particles, such as Figure 6 As shown, it is difficult to pass through the screen during the screening operation.

[0063] The solid cross-linked polysiloxane can be fully pyrolyzed at 1000 ° C. The uncross-linked polysiloxane molecules will volatilize during the pyrolysis process. The higher the degree of cross-linking, the fewer the number of uncross-linked polysiloxane molecules and the less mass loss. At the same time, there are also main bond breakage, side chain decomposition and the release of small molecular gases. The polysiloxane cross-linked product is converted into the final product SiOC, resulting in a loss of mass of the product after pyrolysis, but the loss amount is less than that of the uncross-linked polysiloxane. Therefore, the degree of cross-linking is characterized by the mass ratio of the solid powder of the polysiloxane cross-linked product before and after pyrolysis. Therefore, in this embodiment, a high degree of cross-linking is defined as a θ value greater than or equal to 80%, a good degree of cross-linking is defined as a θ value in the range of 60% to 80%, and a poor degree of cross-linking is defined as a θ value less than or equal to 60%.

[0064] Example 2

[0065] Step 1-1: Weigh 19 g of polymethylhydrogensiloxane and 1 g of catalyst triethylenediamine respectively;

[0066] Step 1-2: 19 g of polymethylhydrogensiloxane was weighed and placed in a beaker, which was then placed in a heat-collecting constant temperature heating magnetic stirrer preheated to 50° C. for heating;

[0067] Step 1-3: Add 1 g of the catalyst to a beaker containing polysiloxane, turn on the magnetic stirring function of a heat-collecting constant temperature heating magnetic stirrer, set the speed to 20 r / s, and mechanically mix the polysiloxane and the catalyst until the catalyst is fully dissolved to obtain a mixture of polysiloxane and the catalyst.

[0068] Step 1-4: placing the polysiloxane and catalyst mixture in a constant temperature and humidity test chamber preheated to 50° C. and 40% RH, and allowing to crosslink for 2 days to obtain a polysiloxane crosslinked solid;

[0069] Step 1-5: Place the polysiloxane cross-linked solid sample into a small ball mill, set the speed to 500 r / min, and the ball milling time to 5 min. Then start the ball mill to grind the cross-linked sample. Figure 2 shown.

[0070] Step 1-6: Take out a small amount of solid powder after grinding and place it under an ultra-depth of field optical microscope for observation, such as Figure 5 As shown, at a magnification of 500 times, the microscopic morphology of a single powder particle is observed, and the particle size of a single powder particle in the current observation area is measured and counted.

[0071] Step 1-7: Move the observation area position, and measure and count the particle size of individual powder particles in the current observation area again. The number of areas used for observation is not less than three and they do not overlap with each other.

[0072] Step 1-8: Calculate and analyze the statistical particle size data to obtain the particle size distribution curve, such as Figure 8 shown.

[0073] Step 1-9: From the particle size distribution curve, it can be seen that the number of powder particles with a particle size of less than or equal to 70 μm accounts for about 91.30%. If it is greater than 80%, proceed to the next step.

[0074] Step 1-10: The mass of the ground polysiloxane solid powder is weighed using an electronic balance with an accuracy of not less than 0.1 mg to obtain 11.186 g, which is recorded as m1.

[0075] Step 2-1: Pour all the weighed polysiloxane solid powder into a small vibrating sieve machine, select the sieve aperture size to be 200 mesh, set the vibrating time to 3 minutes, the vibrating frequency to be 1400 times / minute, the amplitude to be 2 mm, and then start the vibrating sieve machine.

[0076] Step 2-2: The solid powder passing through the sieve is collected and retained.

[0077] Step 2-3: Collect the larger solid powder that does not pass through the sieve and pour it into a ball mill or mortar for further grinding and refinement.

[0078] Step 2-4: Pour the re-ground solid powder into the cleaned small vibrating sieve machine and sieve it again using the parameters in step 2-1.

[0079] Step 2-5: Repeat the grinding and sieving until the amount of powder passing through the sieve no longer increases, and mix the polysiloxane solid powders sieved each time.

[0080] Step 2-6: Use an electronic balance to weigh the mass of the solid powder that passes through the sieve to find 9.497 g, and record it as m2.

[0081] Step 2-7: Calculate the sieving rate:

[0082] η=(m2 / m1)*100% (1)

[0083] Step 2-8: Calculate the screening rate to 84.94%.

[0084] Step 2-9: Weigh 5 g of the sieved polysiloxane cross-linked product using an electronic balance with an accuracy of 0.1 mg, and record it as m3.

[0085] Step 2-10: Place the weighed cross-linked product into a corundum crucible, and place the crucible containing the cross-linked product into a tube furnace.

[0086] Step 2-11: introduce argon into the tubular furnace, set the heating rate to 5°C / min, set the maximum heating temperature to 1000°C, heat to 1000°C, keep warm for 2 hours, and cool with the furnace.

[0087] Step 2-12: After the tube furnace is cooled to room temperature, the cross-linked product after pyrolysis is taken out.

[0088] Step 2-13: Use an electronic balance with an accuracy of 0.1 mg to weigh the mass of the product obtained by pyrolysis to be 4.019 g and record it as m4.

[0089] Step 2-14: Calculate the mass ratio θ of the polysiloxane cross-linked solid powder after pyrolysis to that before pyrolysis using formula (2):

[0090] θ=(m4 / m3)*100% (2)

[0091] The calculated θ value is 80.38%. It can be seen that the polysiloxane cross-linked solid with a screening rate of 84.94% has a high degree of cross-linking and can be used for subsequent high-temperature pyrolysis to obtain a higher pyrolysis yield.

[0092] Example 3

[0093] Step 1-1: Weigh 19 g of polymethylhydrogensiloxane and 1 g of catalyst triethylenediamine respectively;

[0094] Step 1-2: 19 g of polymethylhydrogensiloxane was weighed and placed in a beaker, which was then placed in a heat-collecting constant temperature heating magnetic stirrer preheated to 50° C. for heating;

[0095] Step 1-3: Add 1 g of catalyst to a beaker containing polysiloxane, turn on the magnetic stirring function of a heat-collecting constant temperature heating magnetic stirrer, set the speed to 20 r / s, and mechanically mix the polysiloxane and the catalyst until the catalyst is fully dissolved to obtain a mixture of polysiloxane and catalyst.

[0096] Step 1-4: placing the polysiloxane and catalyst mixture in a constant temperature and humidity test chamber preheated to 50° C. and 40% RH, and allowing it to stand for crosslinking for 1 day to obtain a solid polysiloxane crosslinked product;

[0097] Step 1-5: Place the polysiloxane cross-linked solid sample into a small ball mill, set the rotation speed to 500 r / min, and the ball milling time to 5 minutes, then start the ball mill to grind the cross-linked sample.

[0098] Step 1-6: Take out a small amount of ground solid powder and place it under an ultra-depth-of-field optical microscope for observation. At a magnification of 500 times, observe the microscopic morphology of individual powder particles and measure and count the particle size of individual powder particles in the current observation area.

[0099] Step 1-7: Move the observation area position, and measure and count the particle size of individual powder particles in the current observation area again. The number of areas used for observation is not less than three and they do not overlap with each other.

[0100] Step 1-8: Calculate and analyze the statistical particle size data to obtain the particle size distribution curve, such as Figure 9 shown.

[0101] Step 1-9: From the particle size distribution curve, it can be seen that the number of powder particles with a particle size of less than or equal to 70 μm accounts for about 84.78%. If it is greater than 80%, proceed to the next step.

[0102] Step 1-10: The mass of the ground polysiloxane solid powder is weighed using an electronic balance with an accuracy of not less than 0.1 mg to obtain 11.439 g, which is recorded as m1.

[0103] Step 2-1: Pour all the weighed polysiloxane solid powder into a small vibrating sieve machine, select the sieve aperture size as 200 mesh, set the vibrating time to 3 minutes, the vibrating frequency to 1400 times / minute, the amplitude to 2 mm, and then start the vibrating sieve machine.

[0104] Step 2-2: The solid powder passing through the sieve is collected and retained.

[0105] Step 2-3: Collect the larger solid powder that does not pass through the sieve and pour it into a ball mill or mortar for further grinding and refinement.

[0106] Step 2-4: Pour the re-ground solid powder into the cleaned small vibrating sieve machine and sieve it again using the parameters in step 2-1.

[0107] Step 2-5: Repeat the grinding and sieving until the amount of powder passing through the sieve no longer increases, and mix the polysiloxane solid powders sieved each time.

[0108] Step 2-6: Use an electronic balance to weigh the mass of the solid powder that passes through the sieve to find it is 7.594 g and record it as m2.

[0109] Step 2-7: Calculate the sieving rate:

[0110] η=(m2 / m1)*100% (1)

[0111] Step 2-8: Calculate the screening rate to 66.39%.

[0112] Step 2-9: Weigh 5 g of the sieved polysiloxane cross-linked product using an electronic balance with an accuracy of 0.1 mg, and record it as m3.

[0113] Step 2-10: Place the weighed cross-linked product into a corundum crucible, and place the crucible containing the cross-linked product into a tube furnace.

[0114] Step 2-11: introduce argon into the tubular furnace, set the heating rate to 5°C / min, set the maximum heating temperature to 1000°C, heat to 1000°C, keep warm for 2 hours, and cool with the furnace.

[0115] Step 2-12: After the tube furnace is cooled to room temperature, the cross-linked product after pyrolysis is taken out.

[0116] Step 2-13: Use an electronic balance with an accuracy of 0.1 mg to weigh the mass of the product obtained by pyrolysis to be 3.576 g and record it as m4.

[0117] Step 2-14: Calculate the mass ratio of the polysiloxane cross-linked solid powder before and after pyrolysis using formula (2) to characterize the degree of cross-linking of the polysiloxane θ:

[0118] θ=(m4 / m3)*100% (2)

[0119] The calculated θ value is 71.52%, indicating that the polysiloxane cross-linked solid with a sieving rate of 66.39% has a lower degree of cross-linking.

[0120] Example 4

[0121] Step 1-1: Weigh 19 g of polymethylhydrogensiloxane and 1 g of catalyst triethylenediamine respectively;

[0122] Step 1-2: 19 g of polymethylhydrogensiloxane was weighed and placed in a beaker, which was then placed in a heat-collecting constant temperature heating magnetic stirrer preheated to 50° C. for heating;

[0123] Step 1-3: Add 1 g of the catalyst to a beaker containing polysiloxane, turn on the magnetic stirring function of a heat-collecting constant temperature heating magnetic stirrer, set the speed to 20 r / s, and mechanically mix the polysiloxane and the catalyst until the catalyst is fully dissolved to obtain a mixture of polysiloxane and the catalyst.

[0124] Step 1-4: placing the polysiloxane and catalyst mixture into a constant temperature and humidity test chamber preheated to 50° C. and 40% RH, and allowing to crosslink for 12 hours to obtain a polysiloxane crosslinked solid;

[0125] Step 1-5: Place the polysiloxane cross-linked solid sample into a small ball mill, set the speed to 500 r / min, and the ball milling time to 5 min. Then start the ball mill to grind the cross-linked sample. Figure 3 shown.

[0126] Step 1-6: Take out a small amount of solid powder after grinding and place it under an ultra-depth of field optical microscope for observation. At a magnification of 500 times, observe the microscopic morphology of individual powder particles, such as Figure 6 As shown, the particle size of each powder particle in the current observation area is measured and counted.

[0127] Step 1-7: Move the observation area position, and measure and count the particle size of individual powder particles in the current observation area again. The number of areas used for observation is not less than three and they do not overlap with each other.

[0128] Step 1-8: Calculate and analyze the statistical particle size data to obtain the particle size distribution curve, such as Figure 10 shown.

[0129] Step 1-9: From the particle size distribution curve, it can be seen that the number of powder particles with a particle size of less than or equal to 70 μm accounts for about 80.44%. If it is greater than 80%, proceed to the next step.

[0130] Step 1-10: The mass of the ground polysiloxane solid powder is weighed using an electronic balance with an accuracy of not less than 0.1 mg to obtain a mass of 10.996 g, which is recorded as m1.

[0131] Step 2-1: Pour all the weighed polysiloxane solid powder into a small vibrating sieve machine, select the sieve aperture size as 200 mesh, set the vibrating time to 3 minutes, the vibrating frequency to 1400 times / minute, the amplitude to 2 mm, and then start the vibrating sieve machine.

[0132] Step 2-2: The solid powder passing through the sieve is collected and retained.

[0133] Step 2-3: Collect the larger solid powder that does not pass through the sieve and pour it into a ball mill or mortar for further grinding and refinement.

[0134] Step 2-4: Pour the re-ground solid powder into the cleaned small vibrating sieve machine and sieve it again using the parameters in step 2-1.

[0135] Step 2-5: Repeat grinding and sieving until the amount of powder passing through the sieve no longer increases, and mix the polysiloxane solid powders sieved each time.

[0136] Step 2-6: Use an electronic balance to weigh the mass of the solid powder that passes through the sieve to find 4.421 g, and record it as m2.

[0137] Step 2-7: Calculate the sieving rate:

[0138] η=(m2 / m1)*100% (1)

[0139] Step 2-8: Calculate the screening rate to be 40.21%.

[0140] Step 2-9: Weigh 5 g of the sieved polysiloxane cross-linked product using an electronic balance with an accuracy of 0.1 mg, and record it as m3.

[0141] Step 2-10: Place the weighed cross-linked product into a corundum crucible, and place the crucible containing the cross-linked product into a tube furnace.

[0142] Step 2-11: introduce argon into the tubular furnace, set the heating rate to 5°C / min, set the maximum heating temperature to 1000°C, heat to 1000°C, keep warm for 2 hours, and cool with the furnace.

[0143] Step 2-12: After the tube furnace is cooled to room temperature, the cross-linked product after pyrolysis is taken out.

[0144] Step 2-13: Use an electronic balance with an accuracy of 0.1 mg to weigh the mass of the product obtained by pyrolysis to be 3.262 g and record it as m4.

[0145] Step 2-14: Calculate the mass ratio of the polysiloxane cross-linked solid powder before and after pyrolysis using formula (2) to characterize the degree of cross-linking of the polysiloxane θ:

[0146] θ=(m4 / m3)*100% (2)

[0147] The calculated θ value is 65.23%, indicating that the polysiloxane cross-linked solid with a sieving rate of 40.21% has a lower degree of cross-linking.

[0148] Example 5

[0149] In steps 1-4 of this embodiment, the static crosslinking time is 8 hours, and the rest is the same as in Example 2. The calculated sieving rate η is 6.42%, and the value θ is 40.12%, indicating that the crosslinked polysiloxane solid has a low degree of crosslinking.

[0150] Example 6

[0151] In steps 1-4 of this embodiment, the static crosslinking time is 7 days, and the rest is the same as in Example 2. The calculated sieving rate η is 94.98%, and the value θ is 90.16%, indicating that the polysiloxane crosslinked solid has a high degree of crosslinking.

[0152] Example 7

[0153] Step 1-1: Weigh 19 g of polymethylhydrogensiloxane and 1 g of catalyst triethylenediamine respectively;

[0154] Step 1-2: 19 g of polymethylhydrogensiloxane was weighed and placed in a beaker, which was then placed in a heat-collecting constant temperature heating magnetic stirrer preheated to 40° C. for heating;

[0155] Step 1-3: Add 1 g of the catalyst to a beaker containing polysiloxane, turn on the magnetic stirring function of a heat-collecting constant temperature heating magnetic stirrer, set the speed to 20 r / s, and mechanically mix the polysiloxane and the catalyst until the catalyst is fully dissolved to obtain a mixture of polysiloxane and the catalyst.

[0156] Step 1-4: placing the polysiloxane and catalyst mixture into a constant temperature and humidity test chamber preheated to 40° C. and 40% RH, and allowing to crosslink for 2 days to obtain a polysiloxane crosslinked solid;

[0157] Step 1-5: Place the polysiloxane cross-linked solid sample into a small ball mill, set the rotation speed to 500 r / min, and the ball milling time to 5 minutes, then start the ball mill to grind the cross-linked sample.

[0158] Step 1-6: Take out a small amount of ground solid powder and place it under an ultra-depth-of-field optical microscope for observation. At a magnification of 500 times, observe the microscopic morphology of individual powder particles and measure and count the particle size of individual powder particles in the current observation area.

[0159] Step 1-7: Move the observation area position, and measure and count the particle size of individual powder particles in the current observation area again. The number of areas used for observation is not less than three and they do not overlap with each other.

[0160] Step 1-8: Calculate and analyze the statistical particle size data to obtain the particle size distribution curve, such as Figure 11 shown.

[0161] Step 1-9: According to the particle size distribution curve, the proportion of powder particles with a particle size of less than or equal to 70 μm is calculated to be approximately 86.96%. If it is greater than 80%, proceed to the next step.

[0162] Step 1-10: The mass of the ground polysiloxane solid powder is weighed using an electronic balance with an accuracy of not less than 0.1 mg to obtain 11.238 g, which is recorded as m1.

[0163] Step 2-1: Pour all the weighed polysiloxane solid powder into a small vibrating sieve machine, select the sieve aperture size to be 200 mesh, set the vibrating time to 3 minutes, the vibrating frequency to be 1400 times / minute, the amplitude to be 2 mm, and then start the vibrating sieve machine.

[0164] Step 2-2: The solid powder passing through the sieve is collected and retained.

[0165] Step 2-3: Collect the larger solid powder that does not pass through the sieve and pour it into a ball mill or mortar for further grinding and refinement.

[0166] Step 2-4: Pour the re-ground solid powder into the cleaned small vibrating sieve machine and sieve it again using the parameters in step 2-1.

[0167] Step 2-5: Mix the polysiloxane solid powders that have been sieved twice.

[0168] Step 2-6: Use an electronic balance to weigh the mass of the solid powder that passes through the sieve to find it is 9.476 g and record it as m2.

[0169] Step 2-7: Calculate the sieving rate:

[0170] η=(m2 / m1)*100% (1)

[0171] Step 2-8: Calculate the screening rate to 84.32%.

[0172] Step 2-9: Weigh 5 g of the sieved polysiloxane cross-linked product using an electronic balance with an accuracy of 0.1 mg, and record it as m3.

[0173] Step 2-10: Place the weighed cross-linked product into a corundum crucible, and place the crucible containing the cross-linked product into a tube furnace.

[0174] Step 2-11: introduce argon into the tubular furnace, set the heating rate to 5°C / min, set the maximum heating temperature to 1000°C, heat to 1000°C, keep warm for 2 hours, and cool with the furnace.

[0175] Step 2-12: After the tube furnace is cooled to room temperature, the cross-linked product after pyrolysis is taken out.

[0176] Step 2-13: Use an electronic balance with an accuracy of 0.1 mg to weigh the mass of the product obtained by pyrolysis to be 4.001 g and record it as m4.

[0177] Step 2-14: Calculate the mass ratio θ of the polysiloxane cross-linked solid powder before and after pyrolysis using formula (2):

[0178] θ=(m4 / m3)*100% (2)

[0179] The calculated θ value is 80.02%, indicating that the polysiloxane cross-linked solid with a sieving rate η of 84.32% has a high degree of cross-linking.

[0180] Example 8

[0181] In steps 1-2 and 1-4 of this embodiment, the temperature was set to 20° C., and the rest was the same as in Example 2. The calculated sieving rate η was 19.47%, and the value θ was 58.32%, indicating that the cross-linked polysiloxane solid had a low degree of cross-linking.

[0182] Example 9

[0183] In steps 1-2 and 1-4 of this embodiment, the temperature was set at 30° C., and the rest was the same as in embodiment 2. The calculated sieving rate η was 22.18%, and the value θ was 61.37%, indicating that the cross-linked polysiloxane solid had a low degree of cross-linking.

[0184] Example 10

[0185] In steps 1-2 and 1-4 of this embodiment, the temperature is set to 60° C., and the rest is the same as in embodiment 2. The calculated sieving rate η is 86.15%, and the value θ is 85.28%, indicating that the polysiloxane cross-linked solid has a high degree of cross-linking.

[0186] Example 11

[0187] In this example, the temperature in steps 1-2 and 1-4 was set at 80°C, and all other conditions were the same as in Example 2. During the experiment, a clear white solid precipitate was observed at the bottom of the container. This is because the higher temperature during crosslinking accelerates the reaction between the polysiloxane and the catalyst, which in turn accelerates the liquid curing process. However, due to the rapid curing process, some of the catalyst did not dissolve in the polysiloxane and instead precipitated at the bottom of the container, resulting in an uneven polysiloxane solid.

[0188] Example 12

[0189] In step 2-1 of this embodiment, the sieve aperture size is selected to be 250 mesh, and the rest is the same as in embodiment 2. The calculated screening rate η is 83.64%, and the value θ is 80.38%, indicating that the polysiloxane cross-linked solid has a high degree of cross-linking.

[0190] Example 13

[0191] In step 2-1 of this embodiment, the sieve aperture size is selected to be 150 mesh, and the rest is the same as in Example 2. Since the aperture of the 100 mesh sieve is 100 μm, the polysiloxane solid powder passes through the sieve all at once, with a screening rate of 100%, and this result is invalid.

[0192] Example 14

[0193] In step 2-1 of this embodiment, the sieve aperture size was selected to be 350 mesh, and all other aspects were the same as in Example 2. Due to the small mesh diameter of the 350-mesh sieve, steps 2-3, 2-4, and 2-5 had to be repeated multiple times. During these repeated steps, the polysiloxane powder could partially adhere to the sieve or be repeatedly dumped, resulting in mass loss, leading to inaccurate calculation of the sieving rate.

[0194] Example 15

[0195] In this example, steps 1-5 were set at a rotational speed of 500 rpm and a ball milling time of 3 minutes, with all other parameters being the same as in Example 2. The calculated sieving rate η was 53.69%, and the value θ was 80.38%. Due to the short milling time, the polysiloxane solid particles were large, and the proportion of powder particles with a particle size of less than or equal to 70 μm exceeded 80%. The subsequent sieving process required repeated ball milling and sieving, which was prone to mass loss and resulted in inaccurate calculations of the sieving rate.

[0196] Example 16

[0197] In this example, steps 1-5 were set at a rotational speed of 500 rpm and a ball milling time of 4 minutes, with all other parameters being the same as in Example 2. The calculated sieving rate η was 74.87%, and the value θ was 80.38%. At a ball milling time of 3 minutes, the proportion of powder particles with a particle size of 70 μm or less exceeded 80%. After two additional milling cycles, a small amount of unscreened polysiloxane particles remained, requiring the ball milling and screening process to be repeated three or more times. This process can lead to significant mass loss of the polysiloxane powder, resulting in inaccurate sieving rate calculations.

[0198] Example 17

[0199] In steps 1-5 of this embodiment, the rotation speed was set to 500 r / min and the ball milling time was set to 7 min, and the rest was the same as in embodiment 2. The calculated screening rate η was 85.12% and the value θ was 80.38%, which were similar to those in embodiment 2.

[0200] Example 18

[0201] In step 1-1 of this example, 19.8 g of polymethylhydrogensiloxane and 0.2 g of triethylenediamine catalyst (catalyst mass fraction 1%) were weighed, and all other conditions were the same as in Example 2. The calculated sieving rate η was 16.01%, and the value θ was 48.83%, indicating that the crosslinked polysiloxane solid had a low degree of crosslinking.

[0202] Example 19

[0203] In step 1-1 of this example, 19.6 g of polymethylhydrogensiloxane and 0.4 g of triethylenediamine catalyst (catalyst mass fraction 2%) were weighed, with all other ingredients being the same as in Example 2. The calculated sieving rate η was 18.33%, and the value θ was 57.41%, indicating that the crosslinked polysiloxane solid had a low degree of crosslinking.

[0204] Example 20

[0205] In step 1-1 of this example, 18.4 g of polymethylhydrogensiloxane and 1.6 g of triethylenediamine catalyst (8% by mass) were weighed, with all other ingredients being the same as in Example 2. The calculated sieving rate η was 85.46%, and the value θ was 81.13%, indicating that the polysiloxane cross-linked solid had a high degree of crosslinking.

[0206] Example 21

[0207] In step 1-1 of this example, 18 g of polymethylhydrogensiloxane and 2 g of triethylenediamine catalyst (catalyst mass fraction 10%) were weighed, with all other preparations being the same as in Example 2. The calculated sieving rate η was 86.23%, and the value θ was 82.16%. This indicates that the cross-linked polysiloxane solid had a high degree of crosslinking. However, excess catalyst was observed, forming a white precipitate at the bottom of the container.

[0208] The pyrolysis yield-screening rate results of the polysiloxane cross-linked solids obtained in Examples 1 to 11 and Examples 19 to 21 are as follows: Figure 4 As shown, when the pyrolysis yield reaches more than 70%, the screening rate increases significantly; when the screening rate is 80%, it can be considered that the polysiloxane has reached a high degree of crosslinking.

[0209] In the embodiment of the present invention, the polysiloxane may also be polyethylene siloxane, polycarbosiloxane, polymethylsilsesquioxane or polyethylene siloxane. The viscosity of the polysiloxane at 20° C. is 15 to 40 mPa·s. The catalyst may also be a platinum-based complex or a vinyl polymer.

[0210] Although the present invention is disclosed as above, the scope of protection disclosed by the present invention is not limited thereto. Those skilled in the art of the present invention may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for determining the degree of crosslinking of polysiloxane based on sieving rate, characterized in that: The steps include: Step 1: mechanically mixing polysiloxane and a cross-linking catalyst according to a cross-linking process to obtain a polysiloxane and catalyst mixture, statically cross-linking the polysiloxane and catalyst mixture at 40-60° C. for 2 days or more to obtain a polysiloxane cross-linked solid, and fully grinding the obtained polysiloxane cross-linked solid to obtain a polysiloxane cross-linked solid powder, and weighing the powder mass as m1; Step 2: The polysiloxane cross-linked solid powder is fully passed through a 200-250 mesh sieve, the solid powder that passes through the sieve is collected and retained, the solid powder that does not pass through the sieve is collected and ground again, the re-ground solid powder is sieved again, and the grinding and sieving are repeated until the amount of powder passing through the sieve no longer increases. The polysiloxane solid powders sieved each time are mixed, and the mass of the mixed powder is weighed as m2. The sieving rate is calculated as follows: η=(m2 / m1)*100% (1) If the screening rate exceeds 80%, it indicates that the cross-linking degree of the polysiloxane cross-linked solid is high; if the screening rate is 60% to 80%, it indicates that the cross-linking degree of the polysiloxane cross-linked solid is good; if the screening rate is less than 60%, it indicates that the cross-linking degree of the polysiloxane cross-linked solid is poor; In step 1, a cross-linking catalyst is added at a mass fraction of 5 to 8%; The polysiloxane cross-linked solid obtained in step 1 is fully ground, specifically: the polysiloxane cross-linked solid is ground until the number of particles with a particle size of less than 70 μm accounts for no less than 80%; In step 1, the obtained polysiloxane solid is fully ground using a ball mill, the ball milling speed is 200-600 r / min, and the ball milling time is not less than 5 minutes.

2. The method for determining the degree of crosslinking of polysiloxane based on screening rate according to claim 1, wherein: The viscosity of the polysiloxane at 20° C. is 15 to 40 mPa·s.

3. The method for determining the degree of crosslinking of polysiloxane based on screening rate according to claim 1, wherein: The polysiloxane in step 1 is one of polymethylhydrogensiloxane, polyvinylsiloxane, polycarbosiloxane, polymethylsilsesquioxane or polyvinylsiloxane.

4. The method for determining the degree of crosslinking of polysiloxane based on screening rate according to claim 1, wherein: The catalyst in step 1 is one of triethylenediamine, platinum-based complex or vinyl polymer.

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