Method for detecting the distribution of branches of a pe100 resin by cooling crystallization assisted thermal fractionation

Abstract

The application relates to a method for detecting the branch chain distribution of PE100 resin by cooling crystallization and auxiliary thermal grading, which comprises the following steps: firstly, mixing and heating PE100 resin, an organic solvent and an antioxidant to dissolve, then adding a polar solvent, slowly precipitating an easy crystallization component by gradually cooling, and obtaining the precipitate through filtering, washing and drying. The remaining PE resin solution is concentrated to precipitate a PE component with weak crystallization ability. The two obtained PE components are respectively subjected to SSA thermal grading test, and the distribution result of short branch chains in the PE is obtained. The advantage of the application is that: by combining the solution grading with the cooling crystallization, part of the PE molecules with low branch degree and strong crystallization ability are limitedly precipitated, so that the effect of enriching the PE component containing part of the multi-branch chains to a certain extent is achieved, and the sensitivity and accuracy of the SSA detection of the branch chain distribution of the resin can be better improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of PE100 resin structure research, and particularly relates to a method for detecting the branch chain distribution of PE100 resin by cooling crystallization assisted thermal fractionation. BACKGROUND

[0002] Polyethylene (PE) pipe special resin has the advantages of corrosion resistance, easy processing, low friction resistance, excellent mechanical properties, etc., and has been widely used in the fields of gas pipes, water supply and drainage pipes, irrigation water pipes, etc. According to the long-term hydrostatic strength of PE pipe special resin, the pipe material and its raw material can be divided into different grades such as PE63, PE80 and PE100. The grading of PE100 pipe special resin needs to be evaluated according to GB / T 18252-2020 "Determination of long-term hydrostatic strength of thermoplastic materials in the form of pipe material by extrapolation for plastic pipe systems", which is continuously tested for about 10000h under the conditions of 20℃, 60℃ and 80℃, and then analyzed by multiple linear regression to extrapolate the pipe long-term hydrostatic strength σ LPL of 20℃, 97.5% confidence lower limit to 50 years.

[0003] Generally, PE100 resin is obtained by copolymerization of ethylene and comonomers such as butene and hexene, and the molecular weight of the product generally presents a bimodal distribution. The content and distribution of comonomers in PE resin directly affect the aggregation structure of PE resin, and then affect the mechanical properties and processing properties of the resin, and ultimately affect the appearance and mechanical properties of PE100 pipe material. The slow crack growth (SCG) resistance of PE pipe material is a key performance indicator for measuring the quality of the pipe material. The SCG resistance of the pipe material mainly depends on the PE lamella, tie molecules and their interaction (Seguela R et al., J. Polym. Sci. B: Polym. Phys. 2005, 43: 1729-1748). The SCG performance of the pipe material is mainly determined by the content of the tie molecules between the PE lamella, and the higher the content of the tie molecules, the stronger the ability to hinder crack propagation during use. The number of tie molecules is closely related to the content and distribution of comonomers in the PE molecular chain, so it is of great significance to study the distribution of short branch chains or comonomers in PE pipe material.

[0004] The average branching degree of PE resin can be detected using nuclear magnetic resonance (NMR) or Fourier transform infrared spectroscopy (FTIR). While techniques such as temperature-programmed wash classification (TREF) can analyze detailed short-chain branch distributions, they suffer from drawbacks such as expensive equipment, cumbersome experimental procedures, and long testing cycles. In recent years, thermal classification techniques based on differential scanning calorimetry (DSC) have gradually developed and attracted increasing attention from researchers. Among them, the continuous self-nucleation and annealing (SSA) method can analyze information such as crystals with different chain structures and their corresponding melting temperatures in PE resin. Chinese patent CN102954980 discloses a method for rapidly detecting the grade of PE pipe material using thermal classification. Based on the melting peaks at different positions in the DSC curve, the lengths of different crystal sequences can be calculated according to temperature ranges. However, it should be noted that for PE100 resin, the production process involves multiple reactors to construct PE molecules with different molecular weights and aggregate structures. The molecular structure is a complex bimodal or multimodal resin. When using DSC for thermal classification, small amounts of multi-branched components are easily masked by the peak shapes of other structural components, ultimately leading to significant deviations in the calculation of different component contents.

[0005] Solution fractionation is a method of fractionating components based on molecular weight. It utilizes the dependence of the solubility of different molecular weight fractions of the same polymer on solvent properties to sequentially separate components with similar or identical molecular weights. For solutions of polydisperse polymers, according to the quasi-lattice model theory, the partial molar mixing free energy of the solvent is derived from equation (1):

[0006]

[0007] Where V1 is the solvent volume fraction; V2 is the polymer volume fraction; χ1 is the polymer-solvent interaction parameter; and x is the number of polymer segments, which is proportional to the molecular weight. When phase separation occurs, the system satisfies formulas (2) and (3).

[0008]

[0009]

[0010] The critical polymer-solvent interaction parameters can be obtained from (2) and (3).

[0011]

[0012] (4) In the formula, This is the critical interaction parameter, which decreases with increasing molecular weight. By gradually adding a precipitant to the polymer solvent, the χ1 value of the system gradually increases, and the polymers in the solution will gradually separate in order of decreasing molecular weight.

[0013] To further improve the accuracy of SSA analysis, Wu Tong et al. (Polymer Materials Science and Engineering, 2014, 30: 77-82) first used different solvents to fractionate PE100 resin into high molecular weight and low molecular weight components at 130℃, and then performed thermal fractionation tests to obtain the distribution of branches in each component. The experiment involved filtration at 130℃. On the one hand, high-temperature filtration is relatively difficult; on the other hand, both the high and low molecular weight PE main chains obtained by fractionation based on molecular weight contain a certain number of branches, thus the problem of peak overlap during thermal fractionation makes it difficult to accurately integrate and calculate the content of each melting point component.

[0014] Therefore, in view of the above-mentioned problems in the existing PE100 resin branch distribution test, it is very necessary to develop a method for accurately detecting the branch distribution of PE100 resin using thermal grading technology. Summary of the Invention

[0015] To address the shortcomings of existing technologies, the present invention aims to provide a method for detecting the branch distribution of PE100 resin using a cooling crystallization-assisted thermal classification method. To achieve this objective, the present invention first dissolves PE100 resin in an organic solvent A at a certain temperature (T1), then adds a certain amount of a strongly polar solvent B to the solvent, and subsequently slowly cools the solution to a lower temperature (T2) to allow the dissolved resin to precipitate in order of decreasing crystallinity. The resin is then filtered, washed, and dried at temperature T2 to obtain the component P with the strongest crystallinity. T2 Concentrating and crystallizing the PE component dissolved in solvent A yields component S, which has poor crystallization ability. T2 Subsequently, component P was separately... T2 With S T2 SSA thermal grading tests were performed, and the branches were mainly distributed in S T2 In this process, the branch distribution can be obtained more accurately through integral calculation.

[0016] To achieve the above objectives, the present invention adopts the following technical solution: a method for detecting the branch distribution of PE100 resin using cooling crystallization-assisted thermal grading, mainly comprising the following steps:

[0017] (1) Add m parts of PE100 resin to a round-bottom flask, add n parts of solvent A to the flask, then add k parts of antioxidant, and reflux at 120-160℃ for 5-30 minutes until the resin is completely dissolved.

[0018] (2) A certain amount of polar solvent B is slowly added to the above flask. At this time, no PE precipitate is formed. Then, the temperature is gradually and slowly lowered to 70-100℃ (preferably 87-100℃). After filtration, washing, and vacuum drying, precipitate P can be obtained. T2 ;

[0019] (3) The PE resin solution in the flask is concentrated at 60-70°C under nitrogen blowing, the PE component (S) dissolved in solvent A is gradually precipitated, and the component S with poor crystallization ability can be obtained by vacuum drying T2 .

[0020] (4) The components P T2 and S T2 are respectively subjected to SSA thermal fractionation test, and the process is as follows:

[0021] 1) Eliminate thermal history to obtain standard state, heat from 40°C to above Tm (200°C) at a rate of 10°C / min and keep for 5 min to eliminate all self-nucleation points, and then decrease to Tc1 (40°C) far below the crystallization temperature at a rate of 10°C / min;

[0022] 2) Continuous self-nucleation, heat from 40°C to the first self-nucleation temperature Ts0 (135°C) at a rate of 10°C / min, keep for 5 min, then decrease to 40°C, and then increase to the second nucleation temperature Ts1 (lower than Ts0) at a rate of 10°C / min, keep for 5 min, and then decrease to Tc1 at a certain rate, the interval between the two nucleation temperatures is set to 5°C, and the above steps are repeated to continuously perform nucleation and crystallization;

[0023] 3) Melt record SSA curve, after the last nucleation and crystallization is completed, heat to 200°C at a rate of 10°C / min, and record the melting peak of the crystals formed in each nucleation and crystallization stage.

[0024] The PE100 dissolution amount m in step (1) is 0.1-2.0 parts by weight, and preferably 0.1-1.0 parts by weight; and the amount of solvent A is 30-150 parts by weight to ensure that the PE resin is better dispersed in the solvent A.

[0025] The antioxidant in step (1) can be one or a mixture of two of hindered phenolic antioxidants or phosphorus antioxidants. Among them, the hindered phenolic antioxidant is preferably one or several of antioxidant 1010 (tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester), antioxidant 1076 (β-(3,5-di-tert-butyl-4-hydroxyphenyl) octadecyl propionate) and the like; and the phosphorus antioxidant is preferably antioxidant 168.

[0026] The amount of antioxidant in step (1) is 0.001-0.015 parts by weight, and when two antioxidants are used in combination, the mass ratio of the hindered phenolic antioxidant to the phosphorus antioxidant is 1:2 to 2:1.

[0027] The solvent A is one or several of mixed xylene, o-xylene, p-xylene, and is preferably one of o-xylene, m-xylene or p-xylene.

[0028] The slow addition of solvent B in step (2) means that solvent B is added drop by drop into the PE resin solution while the PE resin solution is under stirring, so as to avoid local excess of solvent B and thus cause the PE resin to be unable to uniformly precipitate.

[0029] The cooling rate in step (2) is controlled at 0.1-3.0℃ / min, preferably 0.3-1.0℃ / min, so as to prevent the PE from crystallizing too fast and thus causing the PE to be inlaid with the components that are not easy to crystallize.

[0030] By adding the alcohol substance with strong polarity and a boiling point greater than 100℃ into the solution of PE100, the interaction between the solvent and the PE resin is adjusted, and then part of the PE molecules with low branching degree and strong crystallization ability are precipitated in a limited manner by combining with the cooling crystallization, so as to achieve the effect of enriching the part of the PE containing multi-branch components to a certain extent, and the sensitivity and accuracy of the SSA in detecting the branching distribution of the resin can be better improved.

[0031] The solvent B is an alcohol substance with strong polarity and a boiling point greater than 100℃, which can be one or a mixture of several of 1-octanol, 2-octanol, 3-octanol, 1-heptanol, 1-hexanol, 1-nonanol, etc.

[0032] The addition amount of the solvent B is 1-50 parts by weight, preferably 3-10 parts by weight.

[0033] The cooling crystallization is a method of grading according to the crystallization ability of the molecular chain, and the relationship between the crystallization temperature of the crystal formed in the cooling process and the wafer thickness is given by the Gibbs-Thomson equation (5):

[0034]

[0035] Wherein, T c is the crystallization temperature of the crystal formed; T s 0 is the crystallization temperature of the crystal with infinite wafer thickness; ζ is the wafer thickness of the crystal formed; α is a constant, which is inversely proportional to the melting enthalpy; β is the supercooling degree, which can be considered as a constant in the cooling process. As can be seen from equation (5), the crystallization temperature of the crystal with a larger wafer thickness is the highest, and the crystal with a larger wafer thickness is precipitated first in the cooling process.

[0036] By adding the solvent B with strong polarity into the solution of PE100 resin, the interaction parameter χ1 between the PE and the solvent A can be adjusted, and then the PE molecules with low branching degree, relatively large molecular weight and strong crystallization ability are precipitated under the condition of cooling, so as to achieve the effect of enriching the multi-branch components in the PE to a certain extent, and the sensitivity and accuracy of the SSA in detecting the branching distribution of the resin can be better improved.

[0037] The present application has the following advantages:

[0038] In view of the deficiencies of the prior art, the present application aims to provide a method for detecting the branch chain distribution of PE100 resin by dual-solvent cooling crystallization assisted thermal fractionation. By optimizing the high-boiling-point solvent with strong polarity and the appropriate amount of addition, the interaction between the PE resin and the solvent is adjusted, and then the solution fractionation and cooling crystallization are combined to make the PE macromolecular chains with low branching degree and strong crystallization ability in the complex-structure PE100 resin preferentially precipitate and separate out, thereby realizing the effective enrichment of the multi-branch chain components in the PE100 resin to a certain extent. Compared with the methods reported in the previous patents or documents, the superposition degree of the peaks of each component in the SSA melting curve obtained in the present application is lower, and it is more convenient to calculate the content of different components by integration, thereby further improving the sensitivity and accuracy of the SSA in detecting the branch chain distribution of PE100 resin. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 SSA test temperature control program

[0040] Figure 2 Molecular weight distribution of the PE100 original sample used in the examples and comparative examples

[0041] Figure 3 Molecular weight distribution of the precipitated samples in Examples 1-3 and Comparative Example 2

[0042] Figure 4 Molecular weight distribution of the soluble samples in Examples 1-3 and Comparative Example 2

[0043] Figure 5 SSA curve of the precipitated samples in Examples 1-3 and Comparative Example 2

[0044] Figure 6 SSA curve of the soluble samples in Examples 1-3 and Comparative Example 2

[0045] Figure 7 SSA curve of the sample (PE100 original sample) in Comparative Example 1

[0046] Figure 8 SSA curve of the precipitated sample in Comparative Example 3 DETAILED DESCRIPTION

[0047] The method for detecting the branch chain distribution of PE100 resin by cooling crystallization assisted thermal fractionation provided by the present application is further illustrated by the following examples. The examples are implemented on the premise of the technical solutions of the present application, and the detailed implementation manners, specific operation steps, technical parameters, etc. are given in the examples and comparative examples, but the protection scope of the present application is not limited to the examples. Unless otherwise specified, the experimental methods in the examples are the conventional operations in the field, and the experimental materials or reagents used in the examples can be obtained from the market.

[0048] The molecular weight and molecular weight distribution of the PE sample were determined by using a Polymer Char high-temperature gel permeation chromatograph (GPC-IR type). Specifically, about 6 mg of the sample was weighed and dissolved in 15 ml of trichlorobenzene at 160°C, and then about 2 ml of the solution was taken into a sample bottle for testing at a temperature of 160°C. The test was performed according to the provisions of “SH / T 1759 Determination of Molecular Weight Distribution of Solution Polymers by Gel Permeation Chromatography”.

[0049] The multiple melting peaks in the SSA detection results, in which the peaks of different melting points correspond to the molecular chains of different short branch chain (SCB) contents, have the following relationship between Tm (°C) and SCB (%) for 1-hexene and ethylene copolymer:

[0050] Tm = -1.2 × SCB + 130.2 (6)

[0051] The SSA melting curve was subjected to peak fitting, the peak areas were counted, the contents of different Tm crystals were obtained, the SCB corresponding to different Tm crystals was calculated by using formula (6), and thus the short branch chain distribution of each fraction was obtained. According to the different SCB contents, the SSA curve was divided into five peaks, in which F1 is the peak with SCB content of 0; F2 is the peak with SCB content of 0-4.3; F3 is the peak with SCB content of 4.3-8.5; F4 is the peak with SCB content of 8.5-12.7; and F5 is the peak with SCB content greater than 12.7. The percentage of the peak area of each peak in the total melting peak area was calculated as the content of the short branch chain.

[0052] Example 1

[0053] A method for detecting the branch chain distribution of PE100 resin by cooling crystallization assisted thermal fractionation, comprising the following steps:

[0054] (1) 0.53 parts by weight of PE100 resin (MFR 0.28 g / 10 min, density 0.948 g / cm 3 ) was added to a round-bottom flask, 100 parts by weight of solvent o-xylene and 0.005 parts by weight of antioxidant 1010 were added to the flask, and the mixture was refluxed at 140°C for 30 min until the resin was completely dissolved;

[0055] (2) Slowly add 5 parts by weight of 1-octanol to the flask, at this time no PE precipitates. Then cool to 93°C at a rate of 1°C / min, filter, wash, and vacuum dry at 40°C to obtain precipitate P 93 ;

[0056] (3) Concentrate the PE resin solution in the flask at 60°C under nitrogen blowing, the PE component dissolved in solvent A gradually precipitates, vacuum dry at 40°C to obtain component S with poor crystallization ability 93 .

[0057] (4) Perform SSA thermal fractionation tests on components P 93 and S 93 respectively, as follows:

[0058] 1) Eliminate thermal history, obtain standard state, from 40°C to 200°C at a rate of 10°C / min and maintain for 5 min to eliminate all self-nucleation points, then cool to Tc1(25°C) which is much lower than the crystallization temperature at a rate of 10°C / min;

[0059] 2) Continuous self-nucleation, from 25°C to the first self-nucleation temperature Ts0(135°C) at a rate of 10°C / min, maintain for 5 min, then cool to 25°C, then increase to the second nucleation temperature Ts1 which is lower than Ts0 at a rate of 10°C / min, maintain for 5 min, then cool to Tc1 at a certain rate, the interval between the two nucleation temperatures is set to 3-5°C, repeat the above steps, continuously nucleate and crystallize;

[0060] 3) Record the SSA curve by melting, after the last nucleation and crystallization, increase to 200°C at a rate of 10°C / min, record the melting peak of the crystals formed in each nucleation and crystallization stage. The temperature control program of the SSA test is shown in Figure 1 , the molecular weight and its distribution of PE100 initial sample, P 93 and S 93 are shown in Figure 2 , Figure 3 and Figure 4 . The SSA test results of P 93 and S 93 are shown in Figure 5 and Figure 6 . The calculation results of the distribution of short and medium chain branches in P 93 and S 93 are shown in Table 1.

[0061] Example 2

[0062] A method for detecting the branch chain distribution of PE100 resin by cooling crystallization assisted thermal fractionation, comprising the following steps: changing the amount of 1-octanol in step (2) in Example 1 to 12 parts by weight, and keeping the rest of the experimental operations consistent with Example 1 (cooling temperature 96℃).P 96 The molecular weight and its distribution of S 96 are shown in Table 1. Figure 2 , Figure 3 The SSA test results of S Figure 4 are shown in Table 2.P 96 The molecular weight and its distribution of S 96 are shown in Table 1. Figure 5 The SSA test results of S Figure 6 are shown in Table 2.P 96 The molecular weight and its distribution of S 96 are shown in Table 1.

[0063] Example 3

[0064] A method for detecting the branch chain distribution of PE100 resin by cooling crystallization assisted thermal fractionation, comprising the following steps:

[0065] (1) 0.56 parts by weight of PE100 resin (MFR 0.28 g / 10 min, density 0.948 g / cm 3 ) was added to a round-bottom flask, 100 parts by weight of solvent m-xylene and 0.008 parts by weight of antioxidant 1010 were added to the flask, and the resin was completely dissolved by refluxing at 150℃ for 30 min;

[0066] (2) 10 parts by weight of 1-heptanol was slowly added to the above flask, and no PE precipitate was generated at this time. Then, the temperature was lowered to 87℃ at a rate of 1℃ / min, and the precipitate P T2 was obtained by filtration, washing, and vacuum drying at 40℃.

[0067] (3) The PE resin solution in the flask was concentrated by nitrogen blowing at 50℃, and the PE component dissolved in solvent A was gradually precipitated, and component S T2 with poor crystallization ability was obtained by vacuum drying at 40℃.

[0068] The rest of the experimental operations were kept consistent with Example 1.P 87 The molecular weight and its distribution of S 87 are shown in Table 1. Figure 2 , Figure 3 The SSA test results of S Figure 4 are shown in Table 2.P 87 The molecular weight and its distribution of S 87 are shown in Table 1. Figure 5 The SSA test results of S Figure 6 are shown in Table 2.P 87 The molecular weight and its distribution of S 87 are shown in Table 1.

[0069] Comparative Example 1

[0070] The untreated PE100 resin was directly subjected to SSA thermal fractionation test, and the SSA test procedure was consistent with Example 1. The SSA test results are shown in Table 1. Figure 7 The short chain branch distribution is shown in Table 1.

[0071] Comparative Example 2

[0072] A method for detecting the branch distribution of PE100 resin by cooling crystallization assisted thermal fractionation, comprising the following steps:

[0073] (1) 0.53 parts by weight of PE100 resin (MFR 0.28 g / 10 min, density 0.948 g / cm 3 ) was added to a round-bottom flask, 100 parts by weight of solvent o-xylene and 0.005 parts by weight of antioxidant 1010 were added to the flask, and the mixture was refluxed at 140°C for 30 min until the resin was completely dissolved;

[0074] (2) Without adding solvent B, the temperature was decreased from 140°C to 89°C at a rate of 1°C / min, and the precipitate P 89 was obtained by filtration, washing and vacuum drying at 40°C;

[0075] (3) The PE resin solution in the flask was concentrated at 60°C under nitrogen blowing, and the PE component dissolved in solvent A was gradually precipitated, and component S 89 with poor crystallization ability was obtained by vacuum drying at 40°C.

[0076] The other experimental operations were consistent with Example 1. The SSA test results of P 89 and S 89 are shown in Table 1. Figure 5 Figure 6 The calculation results of the short chain branch distribution in P 89 and S 89 are shown in Table 1.

[0077] Comparative Example 3

[0078] A method for detecting the branch distribution of PE100 resin by cooling crystallization assisted thermal fractionation, comprising the following steps:

[0079] (1) 0.65 parts by weight of PE100 resin (MFR 0.28 g / 10 min, density 0.948 g / cm 3 ) was added to a round-bottom flask, 100 parts by weight of solvent m-xylene and 0.010 parts by weight of a composite antioxidant of antioxidant 1010 and 168 were added to the flask, wherein the ratio of antioxidant 1010 to 168 was 1:1. The mixture was refluxed at 150°C for 30 min until the resin was completely dissolved; ​

[0080] (2) Slowly add 18 parts by weight of 1-nonanol to the above flask, at this time no PE precipitates. Then cool to 84°C at a rate of 1°C / min, and obtain precipitate P by filtration, washing, and vacuum drying at 40°C T2 ;

[0081] (3) Concentrate the PE resin solution in the flask at 50°C under nitrogen blowing, and gradually precipitate the PE component dissolved in solvent A, and obtain component S with poor crystallization ability by vacuum drying at 40°C T2 .

[0082] The remaining experimental operations are consistent with Example 1. P 84 The SSA test results of P Figure 8 .

[0083] Table 1 shows the content and short-chain branch distribution of each component calculated by integrating the SSA curve

[0084]

[0085]

[0086] In Comparative Example 1, when the PE100 resin is directly subjected to SSA detection without using temperature-reducing crystallization, the peaks of each component in the SSA curve are severely overlapped, and the peak shape corresponding to the small amount of branched-chain component is not obvious Figure 7 . When the peaks are integrated for calculation, the fitting error is large, which seriously affects the accuracy of the test results of the short-chain branch distribution of the sample.

[0087] In Comparative Example 2, the P 89 sample is pre-precipitated by using only a single solvent for temperature-reducing fractionation, and the corresponding soluble S 89 component is obtained. As can be seen from Figure 4 and Figure 5 , the peak shape of each component in the SSA curve of P 89 and S 89 is still not obvious, indicating that the effect of using a single solvent for temperature-reducing fractionation to enrich the component with a high content of short-chain branches is limited.

[0088] As can be seen from Comparative Example 3, when a higher amount of polar solvent and a lower crystallization temperature are used during temperature-reducing crystallization, more PE is precipitated from the solution, and a relatively obvious peak shape appears near 125°C in the SSA graph of the precipitate, indicating that the PE with a certain amount of branched chains is also precipitated. The effect of temperature-reducing crystallization under this condition on the enrichment of the short-chain PE component in the PE100 resin decreases.

[0089] From the examples 1-3, it can be seen that by adding precipitants in the fractional crystallization, the macromolecules and the solvent are adjusted to interact with each other, and the P 93 , P 96 , P 87 components are precipitated at different precipitant contents and temperatures, and the overlapping problem of the peak shapes of the components in the corresponding SSA curves is improved to different degrees. The content of the F1 component is 81.7%, 79.8%, and 74.4% in turn, which is higher than that of the original PE100 sample, indicating that the low-branched fraction with strong crystallization ability can be separated from the PE100 sample under the action of temperature reduction and precipitants. The content of the F1 component of the soluble samples S 93 , S 96 , S 87 of the examples 1-3 is 60.8%, 57.9%, and 47.3% in turn, which is lower than that of the original PE100 sample, indicating that the fractional crystallization and the precipitants can make the component with high short-chain content enriched in the soluble sample. With the decrease of the content of the F1 component, the overlapping of the peak shapes in the SSA curves of the soluble fractions of the examples 1-3 is improved, and the sensitivity and accuracy of the SSA method for detecting the short-chain distribution of the PE100 resin are improved.

[0090] The above only describes the preferred embodiments of the present application, and any changes and modifications made within the scope of the present application should be included in the scope of the present application.

Claims

1. A method for detecting the branch distribution of a PE 100 resin by means of a cooling crystallization assisted thermal fractionation, characterized in that: Firstly, the PE100 resin, organic solvent A and antioxidant are mixed in a container, and then refluxed under heating until the resin is completely dissolved. Then a certain amount of polar solvent B is slowly added to the solution, and the easily crystallizable PE component is slowly precipitated by gradually slow cooling. The precipitate is obtained by filtration, washing and vacuum drying. The remaining PE resin solution is concentrated to precipitate the PE component with weak crystallization ability. The two obtained PE components are respectively subjected to SSA thermal fractionation test to obtain the distribution of short chain branches in PE. The organic solvent A is one or more of mixed xylene, o-xylene and p-xylene. The solvent B is an alcohol with strong polarity and a boiling point greater than 100℃, specifically one or a mixture of several of 1-octanol, 2-octanol, 3-octanol, 1-heptanol, 1-hexanol and 1-nonanol.

2. The method of claim 1, wherein, The amount of PE100 resin is 0.1-2.0 parts by weight.

3. The method of claim 1, wherein, The antioxidant is one or a mixture of two of hindered phenolic antioxidant or phosphorus antioxidant; the hindered phenolic antioxidant is one or several of antioxidant 1010 and antioxidant 1076; the phosphorus antioxidant is antioxidant 168.

4. The method of claim 1, wherein, The slow addition of solvent B is a dropwise addition of solvent B to the PE resin solution under stirring to avoid local excess of solvent B, which causes uneven precipitation of PE resin.

5. The method of claim 1, wherein, The addition amount of solvent B is 1-50 parts by weight.

6. The method of claim 1, wherein, The slow cooling rate is controlled at 0.1-3.0℃ / min to prevent the PE from crystallizing too fast and causing the inclusion of the less crystallizable component.

7. The method of claim 1, wherein, The SSA test procedure is as follows: 1) The test sample is heated from 40℃ to 200℃ at a rate of 10℃ / min and kept for 5 min, and then cooled to 40℃ at a rate of 10℃ / min; 2) heated from 40℃ to the first self-nucleation temperature 135℃ at a rate of 10℃ / min and kept for 5 min, then cooled to 40℃, and then heated to the second nucleation temperature Ts1 at a rate of 10℃ / min and kept for 5 min, and then cooled to Tc1 at a certain rate, the interval between the two nucleation temperatures is set to 5℃, and the above steps are repeated to continuously perform nucleation and crystallization; 3) record the SSA curve by melting, and then heated to 200℃ at a rate of 10℃ / min after the last nucleation and crystallization, and record the melting peak of the crystal formed in each nucleation and crystallization stage.

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