CN109470601B - Method for evaluating ultrahigh molecular weight polyethylene resin by using online rheometer - Google Patents
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Abstract
The invention relates to a method for evaluating ultra-high molecular weight polyethylene resin by using an online rheometer, which is characterized in that the online viscosity of the ultra-high molecular weight polyethylene resin is analyzed, then a lithium battery diaphragm is prepared by thermally induced phase separation and biaxial stretching technologies or fibers are prepared by extraction drying and multistage stretching, and the performance of the lithium battery diaphragm is analyzed to obtain the corresponding relation between the online viscosity of the resin, the film forming performance of the diaphragm and the spinnability of the fibers. Therefore, the film forming property, spinnability, etc. of the ultra-high molecular weight polyethylene can be judged by the on-line viscosity of the resin. Compared with the prior art, the method has the advantages of simplicity, good effect and the like.
Description
Technical Field
The invention relates to the field of high polymer material forming processing, in particular to a method for evaluating and preparing ultrahigh molecular weight polyethylene resin for lithium battery diaphragms or fibers by using an online rheometer.
Background
Due to the long molecular chain and high molecular weight of the ultra-high molecular weight polyethylene (UHMWPE), the ultra-high molecular weight polyethylene (UHMWPE) has excellent mechanical, wear-resisting and chemical corrosion-resisting performances which are incomparable with other materials. The UHMWPE membrane is used as a high-end product in a lithium battery membrane, has excellent comprehensive performance, particularly has gel-like melt at high temperature, is not melted and collapsed, has excellent safety protection on short circuit and explosion which can occur when overcharging or the temperature is overhigh, and is a preferred raw material of a power lithium battery membrane material.
The rheological property is the viscosity and elastic deformation behavior generated by the flow of the high polymer material under the action of temperature and stress, the relationship between the rheological property and various factors is the most basic process parameter in the molding processing of the high polymer material, and the rheological property plays an important role in guiding the use of raw materials, the selection of additives, the determination of processing process parameters and the design of molding equipment and molds. Through testing the rheological property of the polymer, the processing technology of the polymer can be guided and optimized, and the product quality is improved, so that the rheological testing technology has important significance in actual processing and production. Due to the limitation of the non-online rheometer, the test result of the non-online rheometer is not completely consistent with the actual production state, the rheological property of the polymer melt in the processing process cannot be truly reflected, and the requirements of actual processing cannot be met, so the online rheometer is more and more widely applied.
At present, the corresponding relation of the system between the processing performance and the film forming property or the spinnability of the special resin for the ultra-high molecular weight polyethylene lithium battery diaphragm or fiber is not established, and enterprises often adjust process parameters through experience. The processing performance of the UHMWPE resin can be evaluated on line through the on-line capillary rheometer, the processing performance of the UHMWPE resin can be fed back on line, and the processing technology of the UHMWPE resin can be accurately adjusted on line to prepare the diaphragm or fiber with excellent and stable performance. Different from the method for evaluating the film forming property of a plurality of ultra-high molecular weight polyethylene resins by testing the apparent physical property parameters, which is referred to in the patent [ CN105259019A ], the method is an off-line evaluation, while the patent focuses on the on-line evaluation of the actual processability of the UHMWPE resin, which is beneficial to establishing the relationship between the processability and the film forming property or spinnability, thereby being beneficial to enterprises to improve the production efficiency of diaphragms or fibers and the stability of the properties of the diaphragms or the fibers.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a simple and efficient method for evaluating an ultrahigh molecular weight polyethylene resin by using an online rheometer. According to the requirement of the product on the fluidity of the resin, the method has good guiding effect on the determination of the actual processing technology.
The purpose of the invention can be realized by the following technical scheme: a method for evaluating an ultra-high molecular weight polyethylene resin by using an online rheometer, an online capillary rheometer is led out from a side path of an extruder and is used for evaluating the online viscosity of the ultra-high molecular weight polyethylene resin in a processing process, and the method is characterized by comprising the following steps of:
(1) connecting a capillary rheometer on a side route leading-out line of the double-screw extruder, feeding ultrahigh molecular weight polyethylene and a solvent into the double-screw extruder, feeding the obtained melt into the capillary rheometer at a constant pressure, and measuring the pressure difference at an inlet and an outlet of a neck ring die of the capillary rheometer in the extrusion process to obtain the shear viscosity of the melt at different shear rates;
(2) changing the processing temperature of the ultra-high molecular weight polyethylene in a double-screw extruder to obtain a curve of the viscosity of the ultra-high molecular weight polyethylene changing along with the shear rate at different processing temperatures;
(3) changing the concentration of the ultrahigh molecular weight polyethylene in the solution to obtain a curve of the viscosity of the ultrahigh molecular weight polyethylene changing along with the shear rate under different concentrations;
(4) combining the processing parameters of the steps (2) and (3), preparing the ultra-high molecular weight polyethylene into a lithium battery diaphragm or fiber to obtain the film forming property of the diaphragm and the spinnability of the fiber, and analyzing the mechanical property, porosity and air permeability of the diaphragm and the mechanical property of the fiber;
(5) respectively establishing corresponding relations between the viscosities obtained in the steps (2), (3) and (4) and the membrane forming performance or the fiber spinnability of the membrane, determining the relations between the viscosities of different ultrahigh molecular weight polyethylenes and parameters of temperature, shearing and concentration, adjusting the processing technology according to the corresponding relations, and determining the membrane forming performance or the fiber spinnability of the membrane by measuring the viscosities or the concentrations of the ultrahigh molecular weight polyethylenes.
The characteristic evaluated is the on-line viscosity of the UHMWPE resin at the time of processing.
The ultra-high molecular weight polyethylene in the step (1) is polyethylene resin with viscosity average molecular weight of 30-400 ten thousand;
the solvent comprises decalin, paraffin oil, toluene or xylene;
the concentration of the ultra-high molecular weight polyethylene fed into the twin-screw extruder is 2-40 wt.%.
The ultra-high molecular weight polyethylene is a mixture of one or more polyethylene resins with different properties in any proportion.
The shear viscosity of the melt under different shear rates in the step (1) is that the pressure of the melt entering a capillary rheometer is kept the same, and the capillary neck molds with different length-diameter ratios are replaced at intervals of 1-10 min to obtain different melt shear speeds; the shear viscosity is obtained by measuring the pressure difference at the inlet and the outlet of the capillary tube neck ring mold and then combining the known melt shear speed parameters, neck ring mold and charging basket parameters and a rheological model for calculation.
The diaphragm for the ultra-high molecular weight polyethylene lithium battery in the step (4) is prepared by a thermally induced phase separation and biaxial stretching technology and an extraction drying technology, and the film-forming performance is judged; the ultra-high molecular weight polyethylene fiber is prepared by thermally induced phase separation, extraction and multi-stage hot stretching, and the spinnability of the ultra-high molecular weight polyethylene fiber is judged.
The diaphragm or the fiber for the ultra-high molecular weight polyethylene lithium battery is prepared by the following method:
a. dissolving ultra-high molecular weight polyethylene resin in an organic solvent to prepare a semi-dilute solution, wherein the concentration of the formed semi-dilute solution is 2-40 wt.%;
b. adding an antioxidant into the semi-dilute solution formed in the step a, wherein the mass concentration of the antioxidant is 0-2 wt.%;
c. b, extruding the solution obtained in the step b through an oral die, and then carrying out tape casting or calendering to form a primary film; spraying the solution obtained in the step (2) through a spinneret orifice, and forming gel strands after entering a coagulating bath;
d. c, longitudinally and transversely stretching the primary film obtained in the step c in a bidirectional way, extracting and drying to prepare a finished film; and c, extracting and performing multistage hot drawing on the gel threads obtained in the step c to prepare fibers.
The concentration range of the semi-dilute solution in the step a is 2-40 wt.%, and the preferable range is 2-25 wt.%; the concentration of the antioxidant in the step b is 0-2 wt.%, and the preferable range is 0.05 wt.% to 0.5 wt.%.
The organic solvent in the step a comprises decalin, paraffin oil, toluene or xylene;
the antioxidant in the step b comprises one or more of antioxidant 1010, antioxidant 1076, antioxidant 168, antioxidant 164, antioxidant 264 and antioxidant BHT;
c, extracting and drying the primary membrane before or after the biaxial stretching; the gel strands were made into fibers by extraction and multistage hot drawing using dichloromethane as the extractant.
The film forming performance of the diaphragm and the spinnability of the fiber in the step (4) are obtained by evaluating the melt viscosity of the ultra-high molecular weight polyethylene obtained by an online capillary rheometer; the mechanical properties, porosity and air permeability of the membrane and the mechanical properties of the fibers are measured by international or national standard test methods.
The melt viscosity is within the range of 90-115 Pa.s when the shear rate is 400-500 rad/s, and preferably, the melt viscosity is within the range of 45-65 Pa.s when the shear rate is 400-500 rad/s.
The ultrahigh molecular weight polyethylene obtained by the method has better film-forming property or spinnability when having the following characteristics:
when the shearing rate is within the range of 400-500 rad/s, the melt viscosity is 95-110 Pa.s, and the film forming performance is good, wherein the processing temperature of the ultrahigh molecular weight polyethylene is preferably 200-240 ℃, and the concentration is 15-25 wt.%.
When the shearing rate is within the range of 400-500 rad/s, the melt viscosity is within the range of 50-60 Pa.s, the spinning performance is good, wherein the processing temperature of the ultrahigh molecular weight polyethylene is preferably 200-240 ℃, and the concentration is 8-15 wt.%.
Compared with the prior art, the invention establishes the corresponding relation of the ultrahigh molecular weight polyethylene processing technology to the film formation, the spinnability and the performance thereof through a large number of experiments, and realizes the online regulation and control of the processing technology, thereby obtaining the diaphragm and the fiber with excellent performance. The viscosity of the polymer can be determined according to an on-line capillary viscometer, so that whether the polymer has film-forming property or spinnability or whether the polymer has film-forming property or spinnability can be regulated. The online adjustment of the processing technology of the ultra-high molecular weight polyethylene wet diaphragm and the fiber can be realized, the effect is better and accurate, and the efficiency is high.
Drawings
FIG. 1 is a graph of viscosity versus shear rate for samples # 1 and # 2 at different temperatures;
FIG. 2 is a plot of viscosity as a function of shear rate at 200 ℃ for samples # 3, # 4, and # 5;
FIG. 3 is a graph of viscosity versus shear rate for sample # 6 at various temperatures;
FIG. 4 is a graph of viscosity versus shear rate for sample # 7 at various concentrations;
FIG. 5 is a plot of viscosity as a function of shear rate for samples of the A & B blends at different temperatures;
FIG. 6 is a plot of viscosity as a function of shear rate for sample # 8 at various temperatures.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Example 1
Taking two ultra-high molecular weight polyethylene resins with different performance characteristics, number 1# and number 2# which are respectively dissolved in paraffin oil, adding an antioxidant 168, wherein the mass concentration is 0.1 wt.%, forming a semi-dilute solution (the concentration of the ultra-high molecular weight polyethylene is 20 wt.%), feeding the obtained semi-dilute solution into a double-screw extruder, then starting a pressure closed-loop control system to provide stable extrusion pressure, opening a valve positioned between a melt pump and a die of the extruder on a side path, feeding the melt into a capillary rheometer at constant pressure, extruding the melt through the die of the capillary rheometer, regulating and controlling the processing technology through obtained online rheological parameters (the test result is shown in figure 1, the k value represents the slope of a straight line), then carrying out tape casting or calendering to form a primary film, and finally judging the film forming performance through a thermally induced phase separation and a bidirectional stretching technology.
The result shows that the viscosity of the 1# sample is sensitive to temperature within the processing temperature range (200-240 ℃), and the sensitivity change of the viscosity to shear is not obvious along with the increase of the temperature under the same shear rate, so that the viscosity of the 1# sample can be effectively reduced by increasing the processing temperature, and the film forming property of the 1# sample is improved (the shear rate is regulated and controlled to be 400-500 rad/s, the processing temperature is 220 ℃, the 1# sample has good film forming property, and when the processing temperature is 240 ℃, the melt fluidity is large, and a primary film is easy to break or has large defects). The results shown in FIG. 1 and Table 1 show that when the processing temperature is 220 ℃, the shear rate is in the range of 400 to 500rad/s, and the melt viscosity of the sample No. 1 is in the range stated in the invention, the prepared lithium battery diaphragm has the best performance.
The viscosity sensitivity to shear of the sample No. 2 is close (the slope is close) at different processing temperatures (200-240 ℃), but the viscosity sensitivity to temperature is different at the same shear rate. The concrete expression is as follows: when the temperature is lower (less than or equal to 220 ℃), the influence of the temperature rise on the viscosity is not obvious, and when the temperature is higher (more than or equal to 220 ℃), the viscosity is obviously reduced along with the temperature rise. Therefore, the viscosity of the 2# sample can be obviously reduced by increasing the temperature rise amplitude, so that the film forming property of the 2# sample is improved (the shearing rate is 400-500 rad/s, the processing temperature is 200 ℃ and 220 ℃, the flowability of the 2# sample is poor, the viscosity change is not obvious, the diaphragm subjected to biaxial stretching can be obviously wrinkled and defected by naked eyes, the processing temperature is increased to 240 ℃, and the primary film has good uniformity and good film forming property). The results in FIG. 1 and Table 1 show that the lithium battery separator prepared by the method has the best performance when the processing temperature is 240 ℃, the shear rate is within the range of 400-500 rad/s, and the melt viscosity of the No. 2 sample is within the range stated by the invention.
TABLE 1 comparison of Performance parameters of lithium battery separators made at different processing temperatures for sample # 1 and sample # 2
Example 2
The method comprises the steps of dissolving ultra-high molecular weight polyethylene resins with different performance characteristics, number 3#, number 4#, and number 5 in paraffin oil respectively, adding an antioxidant 1076, wherein the concentration is 0.1 wt.%, forming a semi-dilute solution (the concentration of the ultra-high molecular weight polyethylene is 20 wt.%), feeding the obtained semi-dilute solution into a twin-screw extruder, starting a pressure closed-loop control system to provide stable extrusion pressure, opening a valve positioned between a melt pump and a die of the extruder on a side path, feeding a melt into a capillary rheometer at a constant pressure, extruding the melt through the die of the capillary rheometer, regulating and controlling the processing technology of the melt through obtained online rheological parameters (a test result is shown in figure 2, a k value represents the slope of a straight line), then carrying out tape casting or calendering to form a primary film, and finally judging the film forming performance through a thermal phase separation and bidirectional stretching technology.
The results show that the viscosity of the sample # 3 is more sensitive to shear (the absolute value of the slope of the line is the greatest) than the sample # 4, # 5 at the same processing temperature. As can be seen by naked eye observation, the film forming property of the No. 3 sample is good, no obvious holes and defects exist on the film surface after biaxial stretching, a few holes exist on the primary film of the No. 4 and No. 5 samples, and large holes and defects appear on the film surface after biaxial stretching. The results in table 2 show that the lithium battery separator prepared from the sample # 3 has better performance than the lithium battery separator prepared from the sample # 4 and the sample # 5. In conclusion, compared with the samples No. 4 and 5, the 3 sample has better film forming performance when the shear rate is 400-500 rad/s at 200 ℃ and the melt viscosity is in the range stated by the invention.
TABLE 2.3 #, 4#, and 5# samples comparison of performance parameters of lithium battery separators made at 200 deg.C
Example 3
Taking ultra-high molecular weight polyethylene resin No. 6, respectively dissolving in paraffin oil, adding an antioxidant 1076 with the concentration of 0.1 wt.% to form a semi-dilute solution (the concentration of the ultra-high molecular weight polyethylene is 20 wt.%), feeding the obtained semi-dilute solution into a double-screw extruder at different processing temperatures, starting a pressure closed-loop control system to provide stable extrusion pressure, opening a valve positioned between a melt pump and a neck ring of the extruder on a side path, feeding the melt into a capillary rheometer at constant pressure, extruding the melt through the neck ring of the capillary rheometer, regulating and controlling the processing technology of the melt through obtained online rheological parameters (a test result is shown in figure 3, a k value represents the slope of a straight line), then carrying out tape casting or calendering to form a primary film, and finally judging the film forming performance through a thermally induced phase separation and a bidirectional stretching technology.
The result shows that the viscosity of the sample No. 6 has no obvious sensitivity difference to temperature under different processing temperatures (the viscosity is almost overlapped with the shearing curve under different temperatures), and the melt viscosity is in the range stated by the invention when the shearing rate is 400-500 rad/s, so the sample No. 6 has better film forming performance under three processing temperatures.
The comparison of the performance of the 6# sample at different temperatures in table 3 shows that the 6# sample can prepare the membrane with better comprehensive performance at a relatively lower processing temperature (200 ℃).
TABLE 3.6 comparison of diaphragm Performance parameters prepared for sample # s at different temperatures
Example 4
Respectively dissolving ultra-high molecular weight polyethylene resin No. 7 in paraffin oil, adding antioxidant 1076 at concentration of 0.1 wt.% to form semi-dilute solution (the concentration of ultra-high molecular weight polyethylene is 20 wt.%, 25 wt.%, and 30 wt.%), feeding the obtained semi-dilute solution with different concentrations into a twin-screw extruder at the same processing temperature, opening a pressure closed-loop control system to provide stable extrusion pressure, opening a valve positioned between a melt pump and a neck ring of the extruder on a side path, allowing the melt to enter a capillary rheometer at a constant pressure, extruding the melt through the neck ring of the capillary rheometer, and regulating and controlling the processing technology through obtained online rheological parameters (the test result is shown in figure 4, and the k value represents the slope of a straight line), then, casting or calendering is carried out to form a primary film, and finally, the film forming performance is judged by a thermally induced phase separation and biaxial stretching technology.
The results show that the viscosity of the 7# sample at different concentrations has a significant difference in sensitivity to temperature, and the viscosity decreases significantly with increasing temperature. Therefore, when the sample 7 is at 200 ℃ and the ultrahigh molecular weight polyethylene concentration is 25 wt.%, the film-forming property is best visible to the naked eye, and when the sample 7 is at 200 ℃ and the ultrahigh molecular weight polyethylene concentration is 20 wt.% or 30 wt.%, the film has obvious holes or wrinkles, as can be seen from the comparison of the performance parameters of the lithium battery separator prepared at different concentrations in table 4, the lithium battery separator prepared at 200 ℃ and the ultrahigh molecular weight polyethylene concentration is 25 wt.%, the performance of the lithium battery separator is best.
TABLE 4.7 comparison of Performance parameters of lithium Battery separators made with sample # s at various concentrations
Example 5
Respectively taking the ultra-high molecular weight polyethylene resin, numbering A and B, and mixing the ultra-high molecular weight polyethylene resin A and the ultra-high molecular weight polyethylene resin B according to the weight ratio of 3: 1, then dissolving in paraffin oil solvent, forming a semi-dilute solution with the mass concentration of 20 wt.%, adding an antioxidant 1010 in the semi-dilute solution, wherein the mass concentration is 0.2 wt.%, after feeding the obtained solution into a double-screw extruder, starting a pressure closed-loop control system to provide stable extrusion pressure, opening a valve with a side path between an extruder melt pump and a die, feeding the melt into a capillary rheometer at constant pressure, extruding through the die of the capillary rheometer, then performing tape casting or calendering to form a primary film, and preparing a lithium battery diaphragm by thermally induced phase separation and bidirectional stretching technology.
The change curve of the viscosity of the ultra-high molecular weight polyethylene A & B blend sample along with the shear rate at different temperatures is shown in FIG. 5, and the result shows that the viscosity of the resin A and resin B blend is in the range stated in the invention within the range of the shear rate of 400-500 rad/s, so that the ultra-high molecular weight polyethylene resin blend can be judged to be used for preparing a lithium battery diaphragm. The performance of the lithium battery separator made of the ultra-high molecular weight polyethylene resin blend was evaluated, and the results are shown in table 5.
TABLE 5 lithium battery diaphragm performance parameter test results obtained from ultra-high molecular weight polyethylene A & B
| Detecting items | Performance parameter |
| Thickness μm | 19 |
| Air permeability s/100cc | 354 |
| Porosity% | 50.3 |
| Puncture strength g/20 μm | 426 |
| Longitudinal tensile strength MPa | 178 |
| MD shrinkage (%) of 90 ℃ for 2h | 1.4 |
| TD shrinkage (%) of 90 ℃ for 2h | 0.5 |
The results in table 5 show that the lithium battery separator made of the ultra-high molecular weight polyethylene resin mixture is excellent in various properties, indicating that the previous judgment is correct.
Example 6
The preparation method comprises the steps of adding a proper amount of main antioxidant and auxiliary antioxidant into 8# ultrahigh molecular weight polyethylene by using decalin, paraffin oil or kerosene as a solvent to prepare a semi-dilute solution, extruding the semi-dilute solution through a spinneret orifice, quenching the extruded solution into gel precursor, extracting and drying the gel precursor, and then carrying out ultra-drawing to prepare the UHMWPE fibers.
The change curve of the viscosity of the 8# sample with the shear rate at different temperatures is shown in fig. 6, and the result shows that the viscosity of the 8# sample at 220 ℃ is within the range stated in the invention within the range of the shear rate of 400-500 rad/s, so that the ultrahigh molecular weight polyethylene resin can be judged to have good spinnability. The performance of the fiber made of the ultra-high molecular weight polyethylene resin was evaluated, and the fiber strength was 35cN/dtex, the elongation at break was 3.0%, and the initial modulus was 1400 cN/dtex.
Example 7
(1) Dissolving ultra-high molecular weight polyethylene resin in an organic solvent to prepare a semi-dilute solution, wherein the concentration of the formed semi-dilute solution is 2 wt.%;
(2) adding an antioxidant into the semi-dilute solution formed in the step (1), wherein the mass concentration of the antioxidant is 0 wt.%;
(3) feeding the solution obtained in the step (2) into a double-screw extruder, starting a pressure closed-loop control system to provide stable extrusion pressure, opening a valve positioned between a melt pump and a port die of the extruder in a side path, feeding the melt into a capillary rheometer at constant pressure, extruding the melt through the port die of the capillary rheometer, and then carrying out tape casting or calendaring to form a primary film;
(4) and (4) carrying out longitudinal and transverse biaxial stretching and extraction drying on the primary film obtained in the step (3) to prepare a finished film.
(5) And (3) according to the curve that the viscosity of the ultra-high molecular weight polyethylene changes along with the shear rate at different processing temperatures and the curve that the viscosity of the ultra-high molecular weight polyethylene changes along with the shear rate at different concentrations, obtaining the corresponding relation between the performance and the viscosity of the finished product obtained in the step (4), and adjusting the processing technology (the temperature-sensitive polymer can realize on-line feedback by regulating and controlling the processing temperature and the shear-sensitive polymer can realize on-line feedback by regulating and controlling the rotating speed), so as to obtain the diaphragm product with good film forming property.
Example 8
(1) Dissolving ultra-high molecular weight polyethylene resin in an organic solvent to prepare a semi-dilute solution, wherein the concentration of the formed semi-dilute solution is 40 wt.%;
(2) adding an antioxidant into the semi-dilute solution formed in the step (1), wherein the mass concentration of the antioxidant is 2 wt.%;
(3) feeding the solution obtained in the step (2) into a double-screw extruder, starting a pressure closed-loop control system to provide stable extrusion pressure, opening a valve positioned between a melt pump and a port die of the extruder in a side path, feeding the melt into a capillary rheometer at constant pressure, extruding the melt through the port die of the capillary rheometer, and then carrying out tape casting or calendaring to form a primary film;
(4) and (4) carrying out longitudinal and transverse biaxial stretching and extraction drying on the primary film obtained in the step (3) to prepare a finished film.
(5) And (3) according to the curve that the viscosity of the ultra-high molecular weight polyethylene changes along with the shear rate at different processing temperatures and the curve that the viscosity of the ultra-high molecular weight polyethylene changes along with the shear rate at different concentrations, obtaining the corresponding relation between the performance and the viscosity of the finished product obtained in the step (4), and adjusting the processing technology (the temperature-sensitive polymer can realize on-line feedback by regulating and controlling the processing temperature and the shear-sensitive polymer can realize on-line feedback by regulating and controlling the rotating speed), so as to obtain the diaphragm product with good film forming property.
Claims (11)
1. A method for evaluating an ultra-high molecular weight polyethylene resin with an on-line rheometer, the method comprising the steps of:
(1) connecting a capillary rheometer on a side route leading-out line of the double-screw extruder, feeding ultrahigh molecular weight polyethylene and a solvent into the double-screw extruder, feeding the obtained melt into the capillary rheometer at a constant pressure, and measuring the pressure difference at an inlet and an outlet of a neck ring die of the capillary rheometer in the extrusion process to obtain the shear viscosity of the melt at different shear rates;
(2) changing the processing temperature of the ultra-high molecular weight polyethylene in a double-screw extruder to obtain a curve of the viscosity of the ultra-high molecular weight polyethylene changing along with the shear rate at different processing temperatures;
(3) changing the concentration of the ultrahigh molecular weight polyethylene in the solution to obtain a curve of the viscosity of the ultrahigh molecular weight polyethylene changing along with the shear rate under different concentrations;
(4) combining the processing parameters of the steps (2) and (3), preparing the ultra-high molecular weight polyethylene into a lithium battery diaphragm to obtain the film forming performance of the diaphragm, and analyzing the mechanical property, porosity and air permeability of the diaphragm, or preparing the ultra-high molecular weight polyethylene into fibers to obtain the spinnability of the fibers and analyzing the mechanical property of the fibers;
(5) respectively establishing corresponding relations between the viscosities obtained in the steps (2), (3) and (4) and the membrane forming performance or the fiber spinnability of the membrane, determining the relations between the viscosities of different ultrahigh molecular weight polyethylenes and parameters of temperature, shearing and concentration, adjusting the processing technology according to the corresponding relations, and determining the membrane forming performance or the fiber spinnability of the membrane by measuring the viscosities or the concentrations of the ultrahigh molecular weight polyethylenes.
2. The method for evaluating an ultrahigh-molecular-weight polyethylene resin by an on-line rheometer as claimed in claim 1, wherein the ultrahigh-molecular-weight polyethylene of step (1) is a polyethylene resin having a viscosity-average molecular weight of from 30 to 400 million;
the solvent comprises decalin, paraffin oil, toluene or xylene;
the mass concentration of the ultrahigh molecular weight polyethylene fed into the double-screw extruder is 2-40 wt.%.
3. The method for evaluating an ultra-high-molecular-weight polyethylene resin by an on-line rheometer as claimed in claim 1 or 2, wherein the ultra-high-molecular-weight polyethylene is a mixture of two or more polyethylene resins of different properties at any ratio.
4. The method for evaluating the ultra-high molecular weight polyethylene resin by using the online rheometer according to claim 1, wherein the shear viscosity of the melt at different shear rates in the step (1) is that the pressure of the melt entering the capillary rheometer is kept the same, and the capillary dies with different length-diameter ratios are replaced at intervals of 1-10 min to obtain different melt shear rates; the shear viscosity is obtained by measuring the pressure difference at the inlet and the outlet of the capillary tube neck ring mold and then combining the known melt shear speed parameters, neck ring mold and charging basket parameters and a rheological model for calculation.
5. The method for evaluating the ultra-high molecular weight polyethylene resin by the on-line rheometer as claimed in claim 1, wherein the ultra-high molecular weight polyethylene in the step (4) is prepared into the lithium battery separator by a thermally induced phase separation and biaxial stretching technique, an extraction drying process, and the film forming property is judged; the fiber made of ultra-high molecular weight polyethylene is prepared by thermally induced phase separation, extraction and multi-stage hot drawing, and the spinnability of the fiber is judged.
6. The method for evaluating the ultra-high molecular weight polyethylene resin by the on-line rheometer as claimed in claim 5, wherein the ultra-high molecular weight polyethylene is made into the lithium battery separator or the fiber by the following method:
a. dissolving ultra-high molecular weight polyethylene resin in an organic solvent to prepare a semi-dilute solution, wherein the concentration of the formed semi-dilute solution is 2-40 wt.%;
b. adding an antioxidant into the semi-dilute solution formed in the step a, wherein the mass concentration of the antioxidant is 0-2 wt.%;
c. b, extruding the solution obtained in the step b through an oral die, and then carrying out tape casting or calendering to form a primary film; or the solution obtained in the step b is sprayed out through a spinneret orifice and enters a coagulating bath to form gel strands;
d. c, longitudinally and transversely stretching the primary film obtained in the step c in a bidirectional way, extracting and drying to prepare a finished film; or the gel threads obtained in the step c are extracted and subjected to multi-stage hot drawing to prepare fibers.
7. The method for evaluating an ultra-high molecular weight polyethylene resin with an on-line rheometer according to claim 6,
the concentration range of the semi-dilute solution in the step a is 2-25 wt.%; the concentration of the antioxidant in the step b is 0.05 wt.% to 0.5 wt.%.
8. The method for evaluating ultrahigh molecular weight polyethylene resin by an on-line rheometer according to claim 6, wherein the organic solvent of step a comprises decalin, paraffin oil, toluene or xylene;
the antioxidant in the step b comprises one or more of antioxidant 1010, antioxidant 1076, antioxidant 168, antioxidant 164, antioxidant 264 and antioxidant BHT;
c, extracting and drying the primary membrane before or after the biaxial stretching; the gel strands were made into fibers by extraction and multistage hot drawing using dichloromethane as the extractant.
9. The method for evaluating an ultra-high molecular weight polyethylene resin by an online rheometer according to claim 1, wherein the film forming property of the separator and the spinnability of the fiber in step (4) are evaluated by obtaining the melt viscosity of the ultra-high molecular weight polyethylene by an online capillary rheometer; the mechanical properties, porosity and air permeability of the membrane and the mechanical properties of the fibers are measured by international or national standard test methods.
10. The method for evaluating an ultrahigh molecular weight polyethylene resin by an on-line rheometer according to claim 9, wherein the melt viscosity is in the range of 90 to 115 Pa-s at a shear rate of 400 to 500rad/s, and the separator has a good film forming property.
11. The method for evaluating an ultra-high molecular weight polyethylene resin by an on-line rheometer according to claim 9, wherein the melt viscosity is 50 to 60 Pa-s at a shear rate of 400 to 500rad/s, and the spinnability is good.
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