CN109521054B - Characterization method of entanglement degree of high molecular weight polyethylene - Google Patents
Characterization method of entanglement degree of high molecular weight polyethylene Download PDFInfo
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Abstract
The invention relates to a method for characterizing the entanglement degree of high molecular weight polyethylene, which comprises the following steps: (1) placing high molecular weight polyethylene to be detected and an antioxidant into a solvent, and dissolving at high temperature to obtain a mixed solution; (2) adding the mixed solution into a low-temperature medium which does not react with polyethylene for rapid cooling, and then drying the precipitated high polymer to obtain a low-entanglement standard sample; (3) respectively placing the standard sample and the high molecular weight polyethylene to be measured in a differential scanning calorimeter for the same measurement to obtain the melting enthalpy value H of the standard sample1And the fusion enthalpy value H of the sample to be measured2(ii) a (4) Will (H)1‑H2)/H1The entanglement level of the high molecular weight polyethylene to be measured. Compared with the prior art, the invention mainly adopts a differential scanning calorimeter for experiment, solves the problem that the molecular chain entanglement degree of the high molecular weight polyethylene raw material and product, especially the ultra-high molecular weight polyethylene raw material and product is difficult to represent at present, and the surface evidence method has convenient and simple operation and representative data.
Description
Technical Field
The invention relates to the technical field of high molecular material characterization, in particular to a method for characterizing the entanglement degree of high molecular weight polyethylene.
Background
With the rapid development of science and technology, the application range of polyethylene raw materials is wider and wider, the yield is increased year by year, and the performance of polyethylene is also continuously improved. In many high-performance material fields, the proportion of polyethylene products is also increasing, such as body armor, high-speed rail bridge supports, wear-resistant pipes, aerospace materials, elevator sliding blocks and the like. The relationship between the performance of these polyethylene products and the molecular chain entanglement of polyethylene is inseparable, especially for high molecular weight polyethylene products, and the degree of molecular chain entanglement is often the key to the performance difference. The difference of the entanglement degrees directly influences the processability and mechanical properties of the polyethylene product, the higher the entanglement degree is, the poorer the processability of the polyethylene is, but the corresponding mechanical properties such as tensile strength, impact strength, wear resistance and the like are greatly improved.
However, the current characterization means for the entanglement degree of polyethylene products and raw materials mainly comprises the steps of deducing the entanglement condition of molecular chains in a molten polyethylene melt through a viscoelasticity test of high-temperature rheology on the molecular chains in the polyethylene melt; the high-temperature gel chromatography infers the entanglement degree according to the characterization data of the molecular weight and the distribution of the polyethylene; the degree of entanglement between the articles without short chain branches was compared by the article density test. The data obtained by high-temperature rheology is the entanglement condition of molecular chains when polyethylene is molten, and the data is effective in representing the entanglement of the molecular chains in the material processing process, but is difficult to test for the entanglement degree of the product. The data obtained by the high-temperature gel chromatography is only the size and the distribution of molecular weight, and for high-molecular weight polyethylene, especially ultra-high molecular weight polyethylene, the influence of the molecular structure on the entanglement degree of molecular chains of raw materials and products is only one aspect, the thermal history of a sample can also greatly influence the entanglement degree, and after the influence of different thermal histories and the influence of the molecular structure are superposed, the judgment of the entanglement degree of the molecular chains of the polyethylene is extremely difficult. The method for judging the entanglement degree of molecular chains of the polyethylene by a polyethylene density test is only suitable for products of polyethylene homopolymerization, and cannot judge raw materials and products containing short-chain branches.
At present, most of mechanical property analyses do not leave the entanglement degree of polyethylene products, and a characterization method of the entanglement degree of the polyethylene raw material and the products is found, so that the relationship between the molecular structure of polyethylene and the product performance is particularly important.
Disclosure of Invention
The object of the present invention is to overcome the above-mentioned drawbacks of the prior art by providing a method for characterizing the degree of entanglement of high molecular weight polyethylene, which is simple to operate and reliable in result.
The purpose of the invention can be realized by the following technical scheme: a method of characterizing the degree of entanglement of a high molecular weight polyethylene, the method comprising the steps of:
(1) placing high molecular weight polyethylene to be detected and an antioxidant into a solvent, and dissolving at high temperature to obtain a mixed solution;
(2) adding the mixed solution into a low-temperature medium which does not react with polyethylene for rapid cooling, and then drying the precipitated high polymer to obtain a low-entanglement standard sample;
(3) placing the standard sample in a differential scanning calorimeter forMeasuring to obtain the melting enthalpy value H of the standard sample1；
(4) Measuring the high molecular weight polyethylene to be measured by adopting the same test conditions as the step (3) to obtain the melting enthalpy value H of the high molecular weight polyethylene to be measured2；
(5) Will (H)1-H2)/H1The entanglement level of the high molecular weight polyethylene to be measured.
The invention dissolves high molecular weight polyethylene powder in solvent to prepare solution with extremely low concentration, and makes polyethylene molecular chains in extremely low entanglement state under the action of solvent molecules. After the solution is moved into the cooling liquid at a high temperature, molecular chains in the solution are instantly frozen and the original low entanglement state is maintained. After removal of the solvent by the drying process, the low entanglement sample is preserved. In the experiment, a Differential Scanning Calorimeter (DSC) can be used for representing the current state of a polyethylene product or a raw material, the obtained data directly reflects the crystallization condition of the polyethylene, and the crystallization condition after annealing has better correspondence with the entanglement condition of the polyethylene, so that the reliability of representing the entanglement degree of the polyethylene by using the DSC is high.
The solution concentration test for the preparation of the low entanglement samples can be performed as follows. Three kinds of polyethylene with different molecular weights, namely polyethylene with 8 ten thousand weight average molecular weight, polyethylene with 40 ten thousand weight average molecular weight and polyethylene with 900 ten thousand viscosity average molecular weight, are prepared into polyethylene solutions with different solid contents, and the corresponding samples are obtained after the steps of quenching, extracting, drying and the like are carried out on the solutions. The obtained sample was compared with the enthalpy of fusion obtained by re-heating after DSC high temperature annealing, and the results are shown in Table 1.
TABLE 1. melting enthalpy of different molecular weight polyethylenes at different concentrations
From the above table it can be seen that at sufficiently low solids content, the enthalpy of fusion of the treated sample of the same high molecular weight polyethylene will be at a relatively high enthalpy of fusion and will not decrease as the solids content increases until after a certain concentration of solids is exceeded, the enthalpy of fusion begins to decrease, the cause of the decrease in enthalpy of fusion being an increase in the degree of entanglement. For polyethylene with different molecular weights, the concentration range selected for preparing the standard sample is different, the concentration in the step 1 is selected to ensure that the melting enthalpy value of the polyethylene is in a higher concentration range, for example, the solid content range of the standard sample is 0.2-1 percent of the ultrahigh molecular weight polyethylene with the molecular weight of 900 ten thousand, the solid content range of the polyethylene with the weight-average molecular weight of 40 ten thousand is 1-5 percent of the solution, and the concentration of the polyethylene with the weight-average molecular weight of 7 ten thousand can be very high, so that a low-entanglement sample can be obtained.
The invention sets the melting enthalpy value of the polyethylene sample with 100 percent of entanglement as 0J/g, and the lowest entanglement degree which can be achieved by processing the raw materials is the melting enthalpy value H obtained in the step 41. Melting enthalpy value H of high molecular weight polyethylene raw material or product2And H1The difference in (b) can be used as the influence of crystallinity caused by introduction of molecular chain entanglement factors, so that the resin entanglement degree can be quantified through the following formula by virtue of the difference of melting enthalpies.
In the formula H1Can be obtained by step 4, H2Can be obtained by step 5, H100％The enthalpy of fusion at 100% entanglement was set at 0J/g. The lower the value calculated by the formula, the lower the degree of entanglement of the article, and conversely, the higher the degree of entanglement.
The technology establishes a corresponding relation between the molecular chain entanglement of the high molecular weight polyethylene and the fusion enthalpy by using a differential scanning calorimeter, provides a characterization means for the molecular chain entanglement degree of the high molecular weight polyethylene, can aim at the entanglement degree difference among different polyethylene products, the entanglement degree difference of the same polyethylene product caused by different processing processes, the entanglement degree difference of polyethylene raw materials caused by different polymerization processes and the like, and is particularly suitable for representing the entanglement degrees of ultra-high molecular weight polyethylene products and raw materials.
The antioxidant comprises one or more of 2, 6-di-tert-butyl-p-cresol, octadecyl 3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate (1076) and pentaerythritol tetrakis [ beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ] (1010), and the mass ratio of the high molecular weight polyethylene to be detected to the antioxidant is 100: (0.1 to 1), preferably 100: (0.2-0.6). The invention discovers that the addition of the antioxidant can effectively prevent the influence of long-time high temperature on the degradation of a polyethylene molecular chain in the preparation process of the solution, thereby causing the change of the molecular structure of the polyethylene molecular chain.
Preferably, the solvent is one selected from decalin, trichlorobenzene, white oil or paraffin oil, and more preferably, decalin.
Preferably, the dissolution temperature of the high molecular weight polyethylene to be detected and the antioxidant in the solvent is 135-160 ℃, and the dissolution time is 2-4 h. More preferably, the dissolution temperature is 150 ℃.
Preferably, the mass fraction of the high molecular weight polyethylene to be measured in the mixed solution is 0.05-5%, and the preferred mass fraction is 0.5-2%.
Preferably, the low-temperature medium is one of water, high-boiling alkane, white oil or kerosene. By adopting the mode to carry out rapid cooling, the cooling contact surface can be enlarged, and the cooling speed is maximized.
Preferably, the temperature of the low-temperature medium is less than or equal to 50 ℃, more preferably less than 20 ℃, and still more preferably less than 5 ℃.
Preferably, the drying is carried out at normal temperature under reduced pressure and in vacuum or after washing by using a low-boiling-point solvent, the drying temperature is 0-50 ℃, and the drying time is more than or equal to 1 hour until the constant weight of the precipitated high polymer is obtained.
Wherein the low boiling point solvent comprises one of ethanol, diethyl ether, acetone, cyclohexanone, 2-methyl pentanone, n-hexane, methyl acetate, ethyl acetate, trichlorotrifluoroethane, diethyl ether or dioxane.
Preferably, the test conditions of the standard sample or the high molecular weight polyethylene to be tested in the differential scanning calorimeter are as follows: firstly heating to 60-120 ℃, staying at the temperature for more than 5min, and then cooling to 30 ℃ at the speed of 1-10 ℃/min.
Compared with the prior art, the beneficial effects of the invention are embodied in the following aspects:
(1) the experiment is carried out by adopting a differential scanning calorimeter, so that the problem that the molecular chain entanglement degree of the high molecular weight polyethylene raw material and product, especially the ultra-high molecular weight polyethylene raw material and product is difficult to represent at present is solved;
(2) the method for demonstrating the exterior syndrome is convenient and simple to operate, and has representative data.
Detailed Description
The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.
Example 1
Taking an ultra-high molecular weight polyethylene raw material with the viscosity average molecular weight of 300 ten thousand, and polymerizing the raw material in a kettle type reactor at 80 ℃ by using 120# gasoline as a diluent. The raw material and a decalin solvent are dissolved for 3 hours at 150 ℃ with the solid content of 1 percent, and the content of the antioxidant is 2 per mill. The resulting solution was cooled in 5 ℃ cooling water at high temperature for 10 minutes. And (3) extracting the obtained solid in n-hexane for 5 minutes, taking out the solid, and drying the solid in a drying oven at normal temperature.
The dried polyethylene sample was weighed 5.0mg and tested in DSC. Heating to 110 deg.C at a speed of 10 deg.C/min, standing for 10min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 211J/g.
The powdery raw material polymerized in this process was weighed out in an amount of 5.0mg and subjected to DSC measurement. Heating to 110 deg.C at a speed of 10 deg.C/min, standing for 10min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 183J/g.
The degree of entanglement of the powder was 13% as obtained by data processing.
Example 2
Taking an ultra-high molecular weight polyethylene raw material with the viscosity average molecular weight of 300 ten thousand, and polymerizing the raw material in a tubular reactor at the temperature of 20 ℃ by using n-hexane as a diluent. The raw material and a decalin solvent are dissolved for 3 hours at 150 ℃ with the solid content of 1 percent, and the content of the antioxidant is 2 per mill. The resulting solution was cooled in 35 ℃ cooling water at high temperature for 10 minutes. And (3) extracting the obtained solid in n-hexane for 5 minutes, taking out the solid, and drying the solid in a drying oven at normal temperature.
The dried polyethylene sample was weighed 5.0mg and tested in DSC. Heating to 110 deg.C at a speed of 10 deg.C/min, standing for 10min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 208J/g.
The powdery raw material polymerized in this process was weighed out in an amount of 5.0mg and subjected to DSC measurement. Heating to 110 deg.C at a speed of 10 deg.C/min, standing for 10min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 205J/g.
The degree of entanglement of the powder was found to be 2% by data processing.
Example 3
Taking an ultra-high molecular weight polyethylene raw material with the viscosity average molecular weight of 200 ten thousand, putting the raw material on a hot-pressing forming machine for hot-pressing forming, wherein the hot-pressing temperature is 220 ℃, the hot-pressing time is 4 hours, and the hot-pressing pressure is 10 MPa. The ultra-high molecular weight polyethylene raw material and trichlorobenzene solvent are dissolved for 4 hours at 150 ℃ with the solid content of 2 percent, and the content of the antioxidant is 4 per mill. The resulting solution was transferred to 5 ℃ cooling water at high temperature for 10 minutes. And (3) extracting the obtained solid in n-hexane for 5 minutes, taking out the solid, and drying the solid in a drying oven at normal temperature.
The dried polyethylene sample was weighed 5.0mg and tested in DSC. Heating to 110 deg.C at a speed of 10 deg.C/min, standing for 10min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 200J/g.
The raw material molded plate product was sampled by cutting, and 5.2mg was weighed and tested in DSC. Heating to 110 deg.C at a speed of 10 deg.C/min, standing for 10min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 112J/g.
The degree of entanglement of the panel was 44% obtained by data processing.
Example 4
Taking an ultra-high molecular weight polyethylene raw material with the viscosity average molecular weight of 200 ten thousand, putting the raw material on a hot-pressing forming machine for hot-pressing forming, wherein the hot-pressing temperature is 220 ℃, the hot-pressing time is 4 hours, and the hot-pressing pressure is 10 MPa. The ultra-high molecular weight polyethylene raw material and trichlorobenzene solvent are dissolved for 4 hours at 150 ℃ with the solid content of 2 percent, and the content of the antioxidant is 4 per mill. The resulting solution was transferred to 5 ℃ cooling water at high temperature for 10 minutes. And (3) extracting the obtained solid in n-hexane for 5 minutes, taking out the solid, and drying the solid in a drying oven at normal temperature.
The dried polyethylene sample was weighed 5.0mg and tested in DSC. Heating to 100 deg.C at a speed of 10 deg.C/min, standing for 120min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 210J/g.
The molded sheet product was sampled by cutting, and 3.9mg was weighed out and tested in DSC. Heating to 100 deg.C at a speed of 10 deg.C/min, standing for 120min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 120J/g.
The degree of entanglement of the panel was found to be 43% by data processing.
Example 5
The method comprises the steps of taking a pipe mixture of the ultrahigh molecular weight polyethylene with the viscosity average molecular weight of 200 ten thousand, and carrying out extrusion molding on the raw material through a screw extruder, wherein the extrusion temperature is 220 ℃, the extrusion speed is 0.3m/min, and the extrusion pressure is 3 MPa. The pipe mix was dissolved with decalin solvent at 1.5% solids for 3 hours at 150 ℃. The resulting solution was transferred to 5 ℃ cooling water at high temperature for 10 minutes. And putting the obtained solid into a low-pressure vacuum box, and vacuumizing and drying at normal temperature.
The dried polyethylene sample was weighed 5.0mg and tested in DSC. Heating to 110 deg.C at a speed of 10 deg.C/min, standing for 30min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 192J/g.
The molded sheet product was sampled by cutting, and 5.2mg was weighed and tested in DSC. Heating to 110 deg.C at a speed of 10 deg.C/min, standing for 30min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 143J/g.
The degree of entanglement of the tube was found to be 26% by data processing.
Example 6
Taking a raw material of single-active-center polyethylene with the weight-average molecular weight of 40 ten thousand, putting the raw material on a hot-press forming machine for hot-press forming, wherein the hot-press temperature is 220 ℃, the hot-press time is 20min, and the hot-press pressure is 10 MPa. The starting material was dissolved with decalin solvent at 5% solids for 3 hours at 150 ℃. The resulting solution was transferred to 5 ℃ cooling water at high temperature for 10 minutes. And putting the obtained solid into a low-pressure vacuum box, and vacuumizing and drying at normal temperature.
The dried polyethylene sample was weighed 5.0mg and tested in DSC. Heating to 90 deg.C at a speed of 10 deg.C/min, standing for 10min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 194J/g.
The raw material molded plate product was sampled by cutting, and 5.1mg was weighed and tested in DSC. Heating to 90 deg.C at a speed of 10 deg.C/min, standing for 10min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 161J/g.
The degree of entanglement of the panel was found to be 17% by data processing.
Example 7
Taking a polyethylene raw material obtained by polymerizing a Ziegler Natta catalyst with the weight-average molecular weight of 24 ten thousand, and carrying out injection molding on the raw material by using an injection molding grade to obtain a special-shaped piece, wherein the injection molding temperature is 200 ℃. The starting material was dissolved with decalin solvent at 5% solids for 2 hours at 150 ℃. The resulting solution was transferred to 5 ℃ cooling water at high temperature for 10 minutes. And putting the obtained solid into a low-pressure vacuum box, and vacuumizing and drying at normal temperature.
The dried polyethylene sample was weighed to 4.8mg and tested in DSC. Heating to 100 deg.C at a speed of 10 deg.C/min, standing for 10min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 188J/g.
The injection-molded parts of this raw material were sampled by cutting, and 5.1mg were weighed out and tested in DSC. Heating to 100 deg.C at a speed of 10 deg.C/min, standing for 10min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after the temperature rise was integrated to obtain a melting enthalpy of 171J/g.
By data processing, the degree of entanglement of the injection-molded part was found to be 9%.
Example 8
Taking a polyethylene raw material obtained by polymerization of a Ziegler Natta catalyst with the weight-average molecular weight of 7 ten thousand, and carrying out injection molding on the raw material by using an injection molding grade to obtain a special-shaped piece, wherein the injection molding temperature is 200 ℃. The starting material was dissolved with decalin solvent at 5% solids for 2 hours at 150 ℃. The resulting solution was transferred to 5 ℃ cooling water at high temperature for 10 minutes. And putting the obtained solid into a low-pressure vacuum box, and vacuumizing and drying at normal temperature.
The dried polyethylene sample was weighed 4.9mg and tested in DSC. Heating to 100 deg.C at a speed of 10 deg.C/min, standing for 10min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 181J/g.
The injection-molded parts of this raw material were sampled by cutting, and 5.1mg were weighed out and tested in DSC. Heating to 100 deg.C at a speed of 10 deg.C/min, standing for 10min, cooling to 30 deg.C at a speed of 10 deg.C/min, and heating to 160 deg.C at a speed of 10 deg.C/min. The melting peak after temperature rise was integrated to obtain a melting enthalpy of 180J/g.
By data processing, the degree of entanglement of the injection-molded part was found to be 1%.
TABLE 2 data of examples of the invention
As can be seen from the above table, the invention can characterize the entanglement degree of the raw materials produced by different processes and the products produced by different raw materials by using a differential scanning calorimeter, and obtain the quantified entanglement degree value, and the operation process is simple and controllable.
The raw material of the ultra-high molecular weight polyethylene suitable for the die pressing process has no requirement on the fluidity, but has higher mechanical property, so the entanglement degree of the product is generally higher; the modified pipe needs certain fluidity and can be extruded by a screw at a certain speed, but the mechanical property is slightly lower than that of a molded product, so the entanglement degree of the product is generally moderate, and the polyethylene injection molding part has the fastest injection molding speed, so that the requirement on the entanglement degree of a molecular structure is very high for achieving the purpose of rapid extrusion, and a polyethylene raw material with lower entanglement degree is needed. This relationship is consistent with the conclusions drawn from the data in the above table, demonstrating the effectiveness of the characterization instrument.
Meanwhile, the density of the polyethylene product without short chain branches in the table is tested, the obtained density and the obtained entanglement degree have corresponding relation, and the feasibility of the method is further proved through the relation between the density and the entanglement degree.
From the above data, it can be seen that the degree of entanglement of the polyethylene resin raw material is also sensitive to different polymerization processes. However, the present invention is only suitable for high molecular weight polyethylene, and for polyethylene with a lower molecular weight, like example 8, the sensitivity is poor, and it is difficult to process polyethylene products with a molecular weight of less than 10 ten thousand.
Claims (10)
1. A method for characterizing the degree of entanglement of a high molecular weight polyethylene, the method comprising the steps of:
(1) placing high molecular weight polyethylene to be detected and an antioxidant into a solvent, and dissolving at high temperature to obtain a mixed solution;
(2) adding the mixed solution into a low-temperature medium which does not react with polyethylene for rapid cooling, and then drying the precipitated high-molecular-weight polyethylene to obtain a low-entanglement standard sample;
(3) the standard sample is placed in a differential scanning calorimeter for measurement to obtain the melting enthalpy value H of the standard sample1；
(4) Measuring the high molecular weight polyethylene to be measured by adopting the same test conditions as the step (3) to obtain the melting enthalpy value H of the high molecular weight polyethylene to be measured2；
(5) Will (H)1-H2)/H1The entanglement level of the high molecular weight polyethylene to be measured.
2. The method as claimed in claim 1, wherein the antioxidant comprises one or more of 2, 6-di-tert-butyl-p-cresol, octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate (1076), and pentaerythritol tetrakis [ β - (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate (1010), and the mass ratio of the high molecular weight polyethylene to be measured to the antioxidant is 100: (0.1 to 1).
3. The method as claimed in claim 1, wherein the solvent is one selected from decalin, trichlorobenzene, white oil and paraffin oil.
4. The method as claimed in claim 1 or 3, wherein the dissolution temperature of the high molecular weight polyethylene to be measured and the antioxidant in the solvent is 135-160 ℃ and the dissolution time is 2-4 h.
5. The method as claimed in claim 1, wherein the mass fraction of the high molecular weight polyethylene to be measured in the mixed solution is 0.05-5%.
6. The method of claim 1, wherein the low temperature medium is one of water, high boiling point alkane, white oil or kerosene.
7. The method according to claim 1 or 6, wherein the low temperature medium has a temperature of 50 ℃ or less.
8. The method as claimed in claim 1, wherein the drying is carried out at room temperature under reduced pressure and under vacuum or after washing with a low-boiling solvent, the drying temperature is 0-50 ℃, and the drying time is not less than 1h until the precipitated high molecular weight polyethylene has constant weight.
9. The method of claim 8, wherein the low boiling solvent comprises one of ethanol, diethyl ether, acetone, cyclohexanone, 2-methyl pentanone, n-hexane, methyl acetate, ethyl acetate, trichlorotrifluoroethane, diethyl ether, or dioxane.
10. The method of claim 1, wherein the standard sample or the high molecular weight polyethylene to be tested is tested under the following conditions in a differential scanning calorimeter: firstly heating to 60-120 ℃, staying at the temperature for more than 5min, and then cooling to 30 ℃ at the speed of 1-10 ℃/min.
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