A method for assessing the extent of glass fiber breakage in a matrix

Abstract

The application belongs to the field of polymer materials, and discloses a method for evaluating the breaking degree of glass fibers in a matrix. According to the characteristics of the matrix resin to be evaluated, the matrix resin is removed by high-temperature combustion, melting or solvent dissolution, etc. to obtain a glass fiber bundle. The obtained glass fiber bundle is soaked in a certain amount of solvent, and ultrasonic untangling is performed for a certain time to obtain a glass fiber suspension. The obtained glass fiber suspension is poured into a filter structure with multiple stacked screens, and then an external vibration is applied to the filter structure. The glass fibers retained in each screen and at the bottom are separated and weighed to obtain w1, w2, w3, w4, w5, and so on. n wherein n = the number of screens + 1. According to the above weighing results, the breaking degree of the glass fibers is obtained according to the actual combination of the screens. According to the breaking degree of the glass fibers, the breaking of the glass fibers is evaluated, and the iteration of the raw material formula and the process parameters is performed.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of high polymer materials, and particularly relates to a method for evaluating the breaking degree of glass fibers in a matrix. BACKGROUND

[0002] Glass fiber materials have been widely used in the preparation of fiber reinforced resin matrix composites for a long time, and the performance of the composites is directly related to the retained length of the glass fibers in the matrix. In order to improve the filling efficiency of the glass fibers, microtechniques and manual measurement methods are generally used to evaluate the breaking degree of the glass fibers. However, such methods are too cumbersome and do not meet the needs of industrial production which requires repeated iterations. Therefore, it is necessary to study a feasible and simple method for evaluating the breaking degree of the glass fibers in the matrix of the composite material. SUMMARY

[0003] In view of the limitations of the traditional evaluation method of the glass fibers in the matrix, the primary purpose of the application is to provide a method for evaluating the breaking degree of the glass fibers in the matrix.

[0004] The purpose of the application is achieved by the following technical solutions.

[0005] A method for evaluating the breaking degree of glass fibers in a matrix, comprising the following preparation steps:

[0006] (1) According to the characteristics of the matrix resin to be evaluated, the glass fiber matrix resin is removed by high-temperature combustion, melting or solvent dissolution to obtain a glass fiber bundle;

[0007] (2) The obtained glass fiber bundle is poured into a filtering structure in which a plurality of screen meshes are stacked, and then an external vibration is applied to the filtering structure;

[0008] (3) The glass fibers retained in each screen mesh and at the bottom are separated and weighed to obtain W1, W2, W3, W4, W5, and so on, in sequence; n wherein n = the number of screen meshes + 1. At the same time, the mass fractions w1, w2, w3, w4, w5, and so on are calculated. n .

[0009] (4) According to the weighing results above, the breaking degree of the glass fibers is obtained as follows:

[0010]

[0011] In the formula, σ < n, and is an integer, σ can be any integer between 1 and n, and is usually taken as 1, 2 or 3, and can also be adjusted according to the actual combination of the screen meshes;

[0012] Meanwhile, according to the results, the mass of each part obtained is fitted using a Weibull distribution model to obtain the proportion parameter k and the shape parameter λ of the Weibull distribution, and the number average length of the glass fiber bundle to be measured is further obtained according to the following formula and the weight average length

[0013]

[0014]

[0015]

[0016] (5) According to the glass fiber breaking degree and the dispersion coefficient, the glass fiber breaking situation is evaluated, and the raw material formula and the process parameter are iterated.

[0017] Preferably, the glass fiber in step (1) refers to the glass fiber entering the resin matrix by impregnation coating, melt blending, solution blending and the like;

[0018] Preferably, the high-temperature combustion in step (1) refers to combustion for more than 15 minutes above the ignition point of the resin matrix in an atmospheric environment;

[0019] Preferably, the matrix characteristics in step (1) refer to the physicochemical properties of the resin matrix, such as melting point, ignition point, and easily soluble solvent, and a suitable method for removing the resin matrix of the glass fiber is selected; removing the resin matrix refers to detaching the resin matrix from the surface of the glass fiber without damaging the structure of the glass fiber to obtain bare glass fiber bundles.

[0020] Preferably, the stacked filter structure of multiple screens in step (2) refers to a tower structure formed by vertically arranging multiple screens, with large-pore screens at the top layer, and the mesh size of the screens between the top layer and the bottom layer decreasing with the layer, and a filter paper or other powder collection device (such as shown in Figure 1 ) is provided at the bottom.

[0021] The difference in mesh size between the top layer and the bottom layer should be as large as possible, and the number of screens should be as large as possible. Preferably, the screen used in step (3) has 10-4000 meshes, and the number of screens is 3-20.

[0022] Preferably, the additional vibration in step (2) refers to vibration in the form of simple tapping, shaking, mechanical vibration and the like, so that the glass fibers smaller than the pore size can pass through the screen as much as possible.

[0023] Preferably, the separation in step (3) refers to detaching and collecting the glass fibers remaining on the screen by mechanical force, air blowing and the like.

[0024] Preferably, the sigma in step (4) can be any integer between 1 and n, the value of which is related to the distribution state of the glass fiber in actual production, and the glass fiber fracture mode that needs to be concerned.

[0025] Preferably, in step (5), the evaluation of the glass fiber fracture condition refers to the use of the index to judge the fracture condition of the glass fiber, such as glass fiber fracture degree = 1, which means that the glass fiber is in a nearly completely crushed state; glass fiber fracture degree = 0, which means that all glass fibers are in an unbroken state. The process iteration refers to a method of closed-loop control for optimizing the matrix formulation, optimizing the process parameters, and optimizing the mechanical conditions.

[0026] The principle of the present application is that the glass fiber is sheared in the melt, and its size distribution is usually close to the Weibull distribution. The present application is inspired by the basic principle of gel permeation chromatography (GPC), and uses gravity as the driving force, and uses the resistance and retention of the pore size to reduce the probability of long glass fibers appearing in the next layer.

[0027] Of course, before introducing the present method, the possible errors brought by the test method must be evaluated. For glass fibers with high aspect ratio, the radial length is necessarily much smaller than the screen aperture, so it cannot be simply described by the aperture of the screen, because high aspect ratio fillers may directly pass through the screen due to different falling angles. However, this does not mean that there is no mathematical relationship between the retention quality of the glass fiber and the actual distribution. For the sake of illustration, a certain glass fiber with a length of L falls at an angle of θ with the filter screen to a filter screen with a certain aperture D. In this process, the glass fiber mainly goes through two processes: 1. Falling at an angle to the filter screen plane, the glass fiber falls to the next layer or is in a retention state parallel to the filter screen plane; 2. Under mechanical vibration, the glass fiber changes its orientation at an angle close to parallel and displaces. Process 2 must occur before the event of "process 1 retention".

[0028]

[0029] For process 2, the glass fiber in a single-point support state is in an unstable state and is easily passed through the aperture in oscillation, so there is

[0030]

[0031]

[0032] Obviously, when , the probability of being retained in the screen also monotonically increases with the increase of L. It is proved that there is a one-to-one correspondence between L / D and P (retention in this layer). According to the above formula, when The mass of the retained can be used to approximate the definite integral of the glass fiber distribution function over two intervals.

[0033] where F(x) is the indefinite integral of f(x). In most cases, the glass fiber distribution is a Weibull distribution, whose probability density function is as follows:

[0034]

[0035] where k is the shape parameter and λ is the scale parameter. After integration, the cumulative density function is as follows:

[0036]

[0037] Obviously, any glass fiber can be regarded as a coaxial cylinder with equal cross-sectional area, so there is

[0038] w x = l x

[0039] (Formula 7)

[0040] Then, according to the method of the present patent, the mass of each screen is measured, and the corresponding F(x n )

[0041] F(x1) = 1 - w1

[0042]

[0043] Rewrite formula 6 as

[0044]

[0045] g(x) = ln(1 - F(x)) (Formula 9)

[0046] Using the computer, take lnx as the independent variable and g(x) as the dependent variable, then k and λ can be obtained by linear programming.

[0047] In addition, there is

[0048]

[0049]

[0050]

[0051] In addition, since the number average length gives higher weight to the broken fibers and the chopped fibers, in actual production, the glass fibers with longer length play a more important role in the performance of the glass fiber composite material, therefore, new indicators of weight average length and dispersion coefficient need to be introduced for evaluation.

[0052]

[0053]

[0054] It must be pointed out that the present application uses four indicators: glass fiber fracture degree, number average length, weight average length and dispersion coefficient, in order to describe the glass fiber fracture degree from different angles. The glass fiber fracture degree is a method for evaluating the glass fiber fracture degree without being affected by any mathematical model, which represents "how much mass of glass fiber has been fractured". The remaining three indicators are derived indicators under the Weibull distribution model, the number average length gives higher weight to the single glass fiber, and the mass is used to evaluate the remaining length of the glass fiber, and the disadvantage is that it cannot more specifically describe the specific fracture of the glass fiber. For example, two 10mm glass fibers are fractured into five, one group is fractured into 6, 1, 1, 1, 1mm, and the other group is fractured into 2, 2, 2, 2, 2mm, and the number average length of the two groups of glass fibers is the same, which is 2mm, and the weight average length of the two groups of glass fibers is 4mm and 2mm respectively. Obviously, by reasonably describing the weight average length and the number average length, that is, introducing the quotient of the two, the dispersion coefficient, that is, the different fracture modes of the glass fiber can be described, the higher the dispersion coefficient, the more the glass fiber retains the main structure, and the generation of broken fibers is mainly; the lower the dispersion coefficient, the more the overall structure of the glass fiber is destroyed, and the broken fibers are generated.

[0055] The method of the present application has the following advantages and beneficial effects:

[0056] (1) The present application has very high operability and simplicity, and does not require complex instruments and equipment, so that the glass fiber particle size distribution analysis is free from the dependence on microscopic methods and multi-layer imaging technology.

[0057] (2) The present application reflects the macroscopic characteristics of the overall fracture of the glass fiber, and is representative, and can be used to guide related research and industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is a schematic diagram of the filter structure of the plurality of screens stacked in the present application.

[0059] Figure 2 is a schematic diagram of the pore size, wherein is the diagonal length of the filter screen. DETAILED DESCRIPTION

[0060] The present application will be further described in detail below in conjunction with the embodiments and the drawings, but the embodiments of the present application are not limited thereto.

[0061] Example 1

[0062] Glass fiber composite analysis

[0063] The evaluation method of the present invention can analyze the breaking degree of long glass fiber composite. The specific operation steps are as follows:

[0064] (1) Prepare long glass fiber impregnated masterbatch with a length of 12 mm. Add the glass fiber impregnated masterbatch to the hopper of the extruder, stay at 230℃ for 5 min, and then pass through a single screw extruder at 240℃, 250℃, 260℃, 270℃, 280℃, 270℃, and then through the head to injection molding into a long strip sample.

[0065] (2) Take 20g of sample, burn in air at 800℃, and obtain the ash.

[0066] (3) The ash is sequentially passed through a combination of 8, 40, 250, and 1800 mesh screens, and its weight is measured. w1=0.05, w2=0.41, w3=0.20, w4=0.39, w5=0, and σ value represents the glass fiber retained from σ to the last screen as broken glass fiber. For long glass fiber system, the glass fiber that can pass through the 40 mesh screen is 0.95 mm long. Broken to ~1mm from 12mm, it can be considered as broken fiber. Therefore, σ=3, and the calculation result is that the glass fiber breaking degree is 56.19%, the number average length of glass fiber is 2.00mm, the weight average length is 2.23mm, and the distribution width is 1.11.

[0067] (4) According to the calculation result, it is found that the glass fiber is strongly sheared during processing, which cannot play its due performance according to the material design.

[0068] Example 2

[0069] Glass fiber distribution in complex flow channel

[0070] The evaluation method of the present invention can be used to analyze the glass fiber distribution state of complex parts. The specific operation steps are as follows:

[0071] (1) Take 20g of sample from the complex shape of long glass fiber impregnated masterbatch injection molding part with a length of 12mm, burn in air at 800℃, and obtain the ash.

[0072] (2) The ash is sequentially passed through the 8, 40, 250, 1800 mesh screen combination, and weighed. w1=0.002g, w2=0.001g, w3=0.618g, w4=0g, w5=0, take σ=3, the calculation obtains its glass fiber breaking degree is 99.52%, the number average length is 0.25mm, the weight average length is 0.06mm, the distribution width is 0.26. Obviously, compared with example 1, the melt flow at the complex shape makes the glass fiber be concentrated shear strongly, causes the glass fiber to be unable to play its reinforcing role.

[0073] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, which are all included in the protection scope of the present application.

Claims

1. A method for assessing the extent of glass fiber breakage in a matrix, characterized by The method comprises the following steps: (1) removing the glass fiber matrix resin by high-temperature combustion, melting or solvent dissolution according to the characteristics of the matrix resin to be evaluated to obtain a glass fiber bundle; (2) pouring the obtained glass fiber bundle into a filter structure of multiple stacked screens, and then applying an external vibration to the filter structure; (3) separate and weigh the glass fibers retained in each level of screen and at the bottom to obtain W1, W2, W3, W4, W5, and so on, in turn n wherein n = the number of screens + 1, and the mass fractions are calculated to be w1, w2, w3, w4, w5, and so on, in turn n ; (4) according to the above weighing results, the glass fiber breaking degree is calculated according to formula 1: wherein σ < n and is an integer, usually σ = 1, 2 or 3, and can also be adjusted according to the actual combination of screens; Meanwhile, according to the obtained results, the mass of each part weighed is fitted using a Weibull distribution model to obtain the proportional parameter k and the shape parameter λ of the Weibull distribution, and the number average length of the measured glass fiber bundle is further obtained according to the following formula and the weight average length (5) according to the glass fiber breaking degree and the dispersion coefficient, the glass fiber breaking condition is evaluated, and the raw material formula and process parameters are iterated.

2. The method for evaluating the degree of breakage of glass fibers in a matrix according to claim 1, characterized in that: The glass fiber in step (1) refers to the glass fiber entering the resin matrix by impregnation coating, melt blending or solution blending.

3. The method of evaluating the degree of breakage of glass fibers in a matrix according to claim 1, characterized in that: The high-temperature combustion in step (1) refers to combustion above the ignition point of the resin matrix for more than 15 minutes in an atmospheric environment.

4. The method of claim 1, wherein the step of determining the degree of breakage of the glass fibers in the matrix comprises: The removal of the resin matrix in step (1) refers to the detachment of the resin matrix from the surface of the glass fiber without damaging the structure of the glass fiber, to obtain a bare glass fiber bundle. ​ 5. The method of evaluating the degree of glass fiber breakage in a matrix according to claim 1, characterized in that: The multiple stacked screen filter structure in step (2) refers to a tower structure formed by vertically arranging multiple screens, with large-pore screens at the top layer, and the mesh size decreasing from the top layer to the bottom layer, and a filter paper or powder collection device at the bottom.

6. The method of evaluating the degree of glass fiber breakage in a matrix according to claim 1, characterized in that: The screens used in step (3) are 10-4000 mesh, and the number of screens is 3-20.

7. The method of evaluating the degree of glass fiber breakage in a matrix according to claim 1, characterized in that: The external vibration in step (2) refers to vibration in the form of simple patting, shaking or mechanical vibration, so that the glass fibers smaller than the pore size can pass through the screen.

8. The method of claim 1, wherein the step of determining the degree of breakage of the glass fibers in the matrix comprises: The separation in step (3) refers to the use of mechanical force or air blowing to detach and collect the glass fibers retained on the screen. ​ 9. The method of claim 1, wherein the step of determining the degree of breakage of the glass fibers in the matrix comprises: In step (4), σ can be any integer between 1 and n, and its value is related to the distribution state of the glass fiber in actual production and the glass fiber breaking mode to be concerned. ​ 10. The method for evaluating the degree of glass fiber fracture in a matrix according to claim 1, characterized in that: In step (5), the evaluation of the glass fiber breaking condition refers to the use of the glass fiber breaking degree to judge the breaking condition of the glass fiber, wherein a glass fiber breaking degree of 1 indicates that the glass fiber is in a nearly completely crushed state, and a glass fiber breaking degree of 0 indicates that all glass fibers are in an unbroken state.

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