A method for determining the low temperature plasticization capability of polyethylene

Abstract

The application relates to a method for judging the low-temperature plasticizing capacity of polyethylene, which detects the peak temperature, lamella thickness, methylene sequence length and peak area of each fraction of a polyethylene sample by testing the resin chain structure branching degree and the performance of the aggregate structure through SSA, establishes the correlation with the plasticizing condition of the polyethylene, and realizes the rapid evaluation of the plasticizing condition of the polyethylene in the low-temperature extrusion.

Description

Technical Field

[0001] This invention belongs to the technical field of polyethylene material performance evaluation, specifically relating to a method for determining the low-temperature plasticizing ability of polyethylene. Background Technology

[0002] High-voltage power transmission boasts advantages such as long distance, large capacity, and low loss, representing the highest level and development trend of current power transmission technology, and is increasingly attracting global attention. Internationally, high-voltage power transmission technology has evolved from high voltage and ultra-high voltage to extra-high voltage. Wires and cables are key components of power transmission, and their insulation material is one of the key factors determining the cable's voltage resistance. Cross-linked polyethylene (XLPE) has become the main insulation material for high-voltage cables in recent years due to its excellent dielectric properties, good heat resistance, and processing performance. Currently, XLPE insulation is widely used in 110-220kV cables internationally, and some 500kV XLPE insulated cable lines have also begun operation. Currently, my country has fully domestically produced cross-linkable polyethylene cable materials for 35kV and below, with product quality comparable to that of advanced countries worldwide. However, cross-linkable polyethylene insulation materials for 35kV and above, especially the base material for 110kV, 220kV, and above grades of cross-linkable polyethylene cable materials, cannot be produced domestically and are entirely dependent on imports.

[0003] Cross-linked polyethylene (PE) is made by cross-linking polyethylene, making cross-linking technology a crucial means of improving its material properties. In branched polymers, there are no chemical bonds between the branches. Theoretically, their structure still approximates linear polymers: they can dissolve and melt. However, when chemical bonds form between the side chains of the same or different polymers, the polymer forms a network-like structure. The size of the network depends on the number of chemical bonds between the polymer branches. Polymers can form independent supramolecular networks through cross-linking. Two independent interpenetrating networks are called interpenetrating networks, and the interpenetration between a non-cross-linked polymer and a cross-linked network is called a semi-interpenetrating network. After cross-linking, the rotation and movement of molecules are greatly restricted, thereby increasing the macroscopic strength and stiffness of the polymer. Crosslinked modification of PE can significantly improve its properties, not only significantly enhancing its comprehensive properties such as mechanical properties, resistance to environmental stress cracking, resistance to chemical corrosion, creep resistance, and electrical properties, but also significantly improving its temperature resistance, raising the heat resistance temperature of PE from 70℃ to over 100℃, thereby greatly expanding the application fields of PE.

[0004] Before cross-linking, antioxidants and peroxides are added to cable materials. To prevent premature cross-linking of the peroxides, extrusion tests need to be conducted at a relatively low temperature, around 120°C, slightly above the melting point of polyethylene. Polyethylene is a semi-crystalline polymer; its melting process does not occur within a narrow range of about 0.2°C like low-molecular-weight polyethylene, but rather has a wider melting temperature range. Within this range, melting and heating occur simultaneously until all crystalline phases melt. Polyethylene contains crystals of varying degrees of perfection; less perfect crystals melt at lower temperatures, while more perfect crystals require higher temperatures to melt. Since the processing temperature of cable materials is slightly higher than the melting temperature of high-density polyethylene, the more perfectly crystalline polyethylene portions may not fully melt within the limited processing time before flowing out of the extruder, forming incompletely plasticized protrusions on the surface, commonly known as bulges. These bulges can easily cause cable material breakdown, resulting in significant economic losses.

[0005] To evaluate the plasticizing ability of cable materials, an impurity detector is typically used. A certain amount of material is weighed and extruded into sheets using a single-screw extruder. The sample strip is then exposed to a light beam. Impurity particles, which are light-blocking, are detected by an electronic camera using a constant, continuous, and adjustable light source. The transmitted and blocked light beams are then captured by the impurity particle detector, which identifies the particle size and quantity. However, this instrument is expensive, complex to operate, and requires a large amount of raw material.

[0006] The development of thermal classification technology based on differential scanning calorimetry (DSC) began in the 1870s. Thermal classification is a new technology that rapidly assesses the degree of chain heterogeneity in thermoplastic semi-crystalline materials through carefully designed thermal cycling test procedures. Among them, continuous self-nucleation annealing (SSA) thermal classification, which began in the 1890s, is a more timely and promising new thermal classification technology. SSA technology is a thermal classification method based on differential scanning calorimetry, applying a series of self-nucleation and annealing steps to polymer samples. In recent decades, due to the advantages of DSC equipment such as ease of operation, small sample volume, and short processing time, DSC-based thermal classification technology has developed rapidly and gradually matured. After performing certain specific DSC thermal classification treatments on polyethylene samples, a series of chain structure information similar to that obtained by temperature-wash classification (TREF) can also be obtained. The multiple melting peaks obtained after thermal classification correspond to chain segments with different crystallizable sequence lengths, and the chain segments with different crystallizable sequence lengths, branching degrees, and different wafer thicknesses are also correlated. The content of corresponding chain segments can be quantified by the size of the integral area of ​​the multiple melt peak curves obtained after thermal classification. Thermal classification technology has been widely used to examine the degree and distribution of short-chain branching in linear low-density polyethylene. Thermal classification technology is very suitable as a rapid and effective means for quality testing of ethylene / α-olefin copolymers in petrochemical enterprises or other research institutions.

[0007] CN102954980 B discloses a method for rapid detection of the grade of polyethylene pipe special material, including: (1) obtaining differential scanning calorimetry curves of test samples; (2) dividing the various melting peaks on the curve into four groups according to temperature greater than or equal to 127℃; 127-120℃; 110-120℃; less than or equal to 110℃, and calculating the corresponding integral area; calculating the weight percentage and corresponding crystallizable sequence length: long sequence is ≥260 methylene; relatively long sequence is 260-160 methylene; short sequence is 160-90 methylene and short sequence is ≤90 methylene; according to the crystallizable sequence length, the polyethylene pipe material is graded according to the mass content: long sequence is 30-86%; relatively long sequence is 3-25%; short sequence is 3-30%; short sequence is 0-50%; this method has the advantages of being convenient, fast, and cost-saving, and can accelerate the research and development process of new pipe materials. It can be used for online detection, but it is not suitable for evaluating the plasticizing performance of polyethylene materials.

[0008] CN104483235 A discloses a method for detecting the chain structure of crosslinkable ethylene polymers for ultra-high voltage cables. This method includes characterization of short-branched structures and long-branched structures. The characterization of short-branched structures includes: (1) standard deviation calorimetric analysis; (2) determination of the initial self-nucleation temperature; and (3) continuous self-nucleation annealing thermal classification analysis. The characterization of long-branched structures includes: (i) determination of the linear viscoelastic region range; and (ii) rheological property parameters. This invention's method for detecting the chain structure of crosslinkable ethylene polymers for ultra-high voltage cables can achieve comprehensive characterization of both short-branched and long-branched structures, thus providing guidance for the development of cable insulation materials with different withstand voltage ratings. This method proposes a systematic approach to testing the chain structure of crosslinkable ethylene polymers for ultra-high voltage cables, but it is not suitable for evaluating the plasticizing properties of polyethylene materials.

[0009] CN102183539 A discloses a method for rapidly detecting the structure of cross-linked polyethylene (XLPE) cable insulation material. Its key feature is the use of a thermal grading method to detect the crystallinity, crystal thickness, and distribution of the XLPE cable material, and a dynamic mechanical method to detect the elastic modulus and entanglement density of the XLPE cable material under high-temperature conditions. This method combines these two approaches to provide a simple and effective method for detecting the structure of XLPE cable insulation material. This invention provides a theoretical basis for improving the polymerization process of polyethylene crystals and adjusting the formulation of polyethylene cable insulation materials. The experimental process of this invention is simple, the results are sensitive, accurate, and have good repeatability. However, this method cannot rapidly evaluate the plasticizing properties of cable materials.

[0010] The paper “Research on Thermal Grading of Linear Low-Density Polyethylene” (Jiang Huijing, Modern Plastics Processing and Application, 2019, 31(6)44-47) discloses a thermal grading method for linear low-density polyethylene, as well as a method for calculating wafer thickness, thickness distribution and estimating methylene sequence length through heat treatment results. The paper points out that the longer the methylene sequence length, the higher the crystallization ability, but does not disclose how to use these indicators to quickly evaluate plasticizing performance.

[0011] The paper "Thermal Classification Study of High-Density Polyethylene for Pipes" (Liu Xiaozhou, Synthetic Resins and Plastics, 2012, 29(5): 62-65) discloses a method for studying the crystallization and melting behavior of PE100 grade high-density polyethylene (HDPE) resin for pipes using differential scanning calorimetry and continuous self-nucleation annealing classification (SSA). It reveals the degree of short-chain branching and crystal sequence length of HDPE and their relationship with mechanical properties. This paper involves the length of the methylene crystal sequence and the degree of short-chain branching, indicating that the higher the degree of short-chain branching, the shorter the crystal sequence, the weaker the crystallization ability, and the thinner the resulting lamellar crystals. However, it does not disclose how to use these indicators to quickly evaluate plasticizing properties. Summary of the Invention

[0012] The purpose of this invention is to provide a method for determining the low-temperature plasticizing ability of polyethylene. This method uses a differential scanning calorimeter to conveniently and quickly determine the plasticizing ability of a sample, and requires less sample material.

[0013] To achieve the above objectives, the present invention provides a method for determining the low-temperature plasticizing ability of polyethylene, comprising the following steps:

[0014] (1) The melting curves of polyethylene samples were recorded using the continuous self-nucleating annealing (SSA) technique on a differential scanning calorimeter. The melting curves were then subjected to peak fitting, and the melting point T of each melting peak was calculated. m and peak area A;

[0015] (2) The thickness L of the corresponding lamellar crystals of each melting peak is calculated according to formula (1).

[0016]

[0017] Among them, the equilibrium melting point T m 0 =414.5K, surface free energy σ = 5.0kJ / mol, enthalpy of fusion Δh = 8.2kJ / mol, Δz is the length of a repeating unit C2H4 in the polyethylene crystal, Δz = 0.254nm;

[0018] (3) Calculate the methylene sequence length (MSL) value of each melting peak according to formulas (2) and (3).

[0019] ln x = 0.3451 - 142.2 / T m Formula (2)

[0020]

[0021] Where x is the number of moles of methylene;

[0022] (4) If one of the conditions (a) and (b) is met, the plasticizing ability of the sample is qualified; if (c) is met, it is unqualified: (a) the melting point Tm of all melting peaks is less than 111℃; (b) there is at least one melting peak with a melting point Tm ≥ 111℃, but the sum of the peak areas of melting peaks with a melting point greater than 111℃ is less than 0.2J / g; (c) there is at least one melting peak with a melting point Tm greater than 111℃, and the sum of the peak areas of melting peaks with a melting point greater than 111℃ is ≥ 0.2J / g.

[0023] The method for determining the low-temperature plasticizing ability of polyethylene according to the present invention includes the following: (a) the melting point Tm of all melting peaks is less than 111°C, the crystal thickness of each melting peak of the sample is less than 7.2 nm, and the length of the methylene sequence is less than 78.5 nm.

[0024] The method for determining the low-temperature plasticizing ability of polyethylene according to the present invention includes (c) having at least one melting peak with a melting point Tm greater than 111℃ and the sum of the peak areas of melting peaks greater than 111℃ being 0.2J / g; the crystal thickness of each melting peak in the sample with a melting point greater than 111℃ being ≥7.2nm and the length of each methylene sequence being ≥78.5nm.

[0025] The method for determining the low-temperature plasticizing ability of polyethylene according to the present invention includes the following specific steps for measuring the melt curve:

[0026] a. Under inert gas protection, the polyethylene sample is heated to the point of melting, and then kept at a constant temperature to eliminate thermal history;

[0027] b. Cool the sample to a temperature at which it can crystallize, and hold it at that temperature to establish a standard thermal history of the sample;

[0028] c. Heat the sample to the initial self-nucleation temperature and maintain it at that temperature;

[0029] d. Cool the sample again from the initial nucleation temperature to the temperature at which it can crystallize and maintain this temperature at a constant temperature;

[0030] e. Heat the sample to the next self-nucleation temperature, which is lower than the initial self-nucleation temperature, and maintain it at that temperature.

[0031] f. Repeat steps b to e until the sample is held at the last self-nucleation temperature. After holding at the last self-nucleation temperature and cooling down to the crystallization temperature, heat the sample until it melts.

[0032] The initial self-nucleation temperature is 110–120℃, and the temperature of each self-nucleation decreases sequentially, with the last self-nucleation temperature being 80–60℃.

[0033] The method for determining the low-temperature plasticizing ability of polyethylene described in this invention has a temperature change rate of 5-20 K / min during the heating and cooling processes.

[0034] In the method for determining the low-temperature plasticizing ability of polyethylene described in this invention, the melting temperature of the sample in steps a and f is 160-230℃, and the temperature is held for 2-10 minutes.

[0035] In the method for determining the low-temperature plasticizing ability of polyethylene described in this invention, the crystallization temperature in steps b and d is 20-60℃, and the temperature is held for 2-10 minutes.

[0036] In the method for determining the low-temperature plasticizing ability of polyethylene described in this invention, the isothermal time in steps c and e is 1-30 min.

[0037] The beneficial effects of this invention are:

[0038] Polyethylene resin is a semi-crystalline polymer composed of molecular chains with varying degrees of perfection. Under normal heating rates, less perfect segments melt at lower temperatures, while more perfect segments melt at higher temperatures, resulting in a wider melting range. The processing temperature of cable material resin is slightly higher than the melting point of ordinary polyethylene. During processing, the speed and temperature remain constant, and the amount of heat absorbed is essentially constant. Molecular chain segments with large lamellar thickness and long methylene sequences cannot absorb enough heat to completely melt, resulting in partial non-plasticization.

[0039] This technical solution uses SSA testing to measure the branching degree and aggregated structure of the resin chain, and detects the peak temperature, lamellar thickness, methylene sequence length and peak area of ​​each fraction of polyethylene sample. It establishes a correlation with the plasticization of polyethylene, which can quickly evaluate the plasticization of polyethylene during low-temperature extrusion with a small sample amount. Moreover, the method is simple and quick to operate. Attached Figure Description

[0040] Figure 1 The results of peak temperature testing after SSA grading in Example 1;

[0041] Figure 2 The results of peak temperature testing after SSA grading in Example 2;

[0042] Figure 3 The results of peak temperature testing after SSA grading in Example 3;

[0043] Figure 4 The results of peak temperature testing after SSA grading in Example 4;

[0044] Figure 5 The results of peak temperature testing after SSA grading in Example 5;

[0045] Figure 6 The results of peak temperature testing after SSA grading in Example 6;

[0046] Figure 7 The results are the peak temperature test results after SSA grading in Example 7. Detailed Implementation

[0047] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0048] Raw material or equipment sources: Lanzhou Petrochemical Company LDPE 2240H, 2426H, Iranian Petrochemical LDPE LF2119, Yangba 2220H.

[0049] Evaluation and analysis method: The sample surface was tested using a Harp company impurity detector at a temperature of 110℃ and a rotation speed of 40rpm.

[0050] Example 1

[0051] Taking Lanzhou Petrochemical Company's 2240H (batch number 201904055510E) as an example, the SSA thermal classification test steps are as follows: (a) Elimination of thermal history: Under nitrogen protection, the sample is first heated from room temperature to 220℃ at a heating rate of 5K / min and held for 2min to eliminate thermal history; (b) The sample is cooled to 20℃ at a cooling rate of 5K / min and held for 2min; (c) The sample is heated to the initial self-nucleation temperature of 120℃ at a heating rate of 5K / min and held for 2min; (d) From the initial self-nucleation temperature... The nucleation temperature is cooled to 20°C at a cooling rate of 5 K / min, and the corresponding heat treatment will be reflected in the crystallization of the sample; (e) The sample is heated to the next self-nucleation temperature of 115°C and held at that temperature for 2 min; (f) Steps (b) to (e) are repeated, with each self-nucleation temperature decreasing by 5°C until the self-nucleation temperature reaches 70°C. After holding at 70°C for 2 min, the temperature is cooled to 20°C at a cooling rate of 5 K / min; (g) Finally, the sample is heated from 20°C to 220°C at a heating rate of 5 K / min, and the melting curve is recorded.

[0052] (1) Calculation of the relative content of each melting peak

[0053] The final melt curve was processed using professional peak fitting software (NETZSCH Proteus Thermal Analysis software from Germany) to separate the curve into independent melt peaks, and the melting point T of each melt peak was calculated. m The peak area A is shown in Table 1, and the melting point T of each melting peak is also shown in Table 1. m Test results are as follows Figure 1 As shown.

[0054] (2) Estimating the plasticization status of polyethylene products

[0055] The thickness L of the corresponding lamellar crystals for each melting peak is calculated according to formula (1).

[0056]

[0057] Among them, the equilibrium melting point T m 0 =414.5K, surface free energy σ = 5.0kJ / mol, enthalpy of fusion Δh = 8.2kJ / mol, Δz is the length of a repeating unit C2H4 in the polyethylene crystal, Δz = 0.254nm;

[0058] The methylene sequence length (MSL) of each melting peak was calculated using formulas (2) and (3).

[0059] ln x = 0.3451 - 142.2 / T m Formula (2)

[0060]

[0061] Where x is the number of moles of methylene.

[0062] Table 1

[0063]

[0064] The highest temperature of this sample is T. m1 The peak area A at temperatures greater than 111℃ is greater than 0.2 J / g, the crystal thickness is greater than 7.2 nm, and the methylene sequence length is greater than 78.5 nm, suggesting that the polyethylene cable material has a problem with poor plasticization.

[0065] The samples were tested using a Harp company impurity detector at a temperature of 110℃ and a rotation speed of 40rpm. The plasticization of the samples was observed, and the surface showed protrusions that were difficult to plasticize, indicating poor plasticization performance, which was consistent with the inferred results.

[0066] Example 2

[0067] Taking Lanzhou Petrochemical Company's 2240H (batch number 202105145510E) as an example, the SSA thermal classification test steps are as follows: (a) Eliminating thermal history: The sample is first heated from room temperature to 200℃ at a heating rate of 10K / min and held for 5min to eliminate thermal history; (b) The sample is cooled to 60℃ at a cooling rate of 10K / min and held for 5min; (c) The sample is heated to the initial self-nucleation temperature of 115℃ at a heating rate of 10K / min and held for 5min; (d) From the initial self-nucleation temperature... The nucleation temperature is cooled to 60°C at a cooling rate of 10 K / min, and the corresponding heat treatment will be reflected in the crystallization of the sample; (e) The sample is heated to the next self-nucleation temperature of 110°C and held at that temperature for 5 min; (f) Steps (b) to (e) are repeated, with each self-nucleation temperature decreasing by 5°C until the self-nucleation temperature reaches 80°C. After holding at 80°C for 5 min, the temperature is cooled to 60°C at a cooling rate of 10 K / min; (g) Finally, the sample is heated from 60°C to 200°C at a heating rate of 10 K / min, and the melting curve is recorded.

[0068] (1) Calculation of the relative content of each melting peak

[0069] The final melt curve was processed using professional peak fitting software (NETZSCH Proteus Thermal Analysis software from Germany) to separate the curve into independent melt peaks, and the melting point T of each melt peak was calculated. m The peak area A is shown in Table 2, and the melting point T of each melting peak is also shown in Table 2. m Test results are as follows Figure 2 As shown.

[0070] (2) Estimating the plasticization status of polyethylene products

[0071] The thickness L of the corresponding lamellar crystals for each melting peak is calculated according to formula (1).

[0072]

[0073] Among them, the equilibrium melting point T m 0 =414.5K, surface free energy σ = 5.0kJ / mol, enthalpy of fusion Δh = 8.2kJ / mol, Δz is the length of a repeating unit C2H4 in the polyethylene crystal, Δz = 0.254nm;

[0074] The methylene sequence length (MSL) of each melting peak was calculated using formulas (2) and (3).

[0075] ln x = 0.3451 - 142.2 / T m Formula (2)

[0076]

[0077] Where x is the number of moles of methylene.

[0078] Table 2

[0079]

[0080] The highest temperature of this sample is T. m1 At temperatures below 111℃, the wafer thickness is less than 7.2nm and the methylene sequence length is less than 78.5nm, indicating that the polyethylene cable material has good plasticization properties and there is no problem with poor plasticization.

[0081] The samples were tested using a Harp company impurity detector at a temperature of 110℃ and a rotation speed of 40rpm. The plasticization of the samples was observed, and no protrusions that were difficult to plasticize appeared on the surface, which was consistent with the inferred results.

[0082] Example 3

[0083] Taking Lanzhou Petrochemical Company's 2240H (batch number 202007015510D) as an example, the SSA thermal classification test steps are as follows: (a) Eliminating thermal history: The sample is first heated from room temperature to 180℃ at a heating rate of 20K / min and held for 10min to eliminate thermal history; (b) The sample is cooled to 20℃ at a cooling rate of 20K / min and held for 10min; (c) The sample is heated to the initial self-nucleation temperature of 110℃ at a cooling rate of 20K / min and held for 5min; (d) From the initial self-nucleation temperature... (e) The sample is cooled to 40°C at a cooling rate of 20 K / min, and the corresponding heat treatment will be reflected in the crystallization of the sample; (f) The sample is heated to the next self-nucleation temperature of 105°C and held at that temperature for 10 min; (g) Steps (b) to (e) are repeated, with each self-nucleation temperature decreasing by 5°C until the self-nucleation temperature reaches 60°C. After holding at 60°C for 2 min, the sample is cooled to 40°C at a cooling rate of 20 K / min; (g) Finally, the sample is heated from 40°C to 180°C at a heating rate of 20 K / min, and the melting curve is recorded.

[0084] (1) Calculation of the relative content of each melting peak

[0085] The final melt curve was processed using professional peak fitting software (NETZSCH Proteus Thermal Analysis software from Germany) to separate the curve into independent melt peaks, and the melting point T of each melt peak was calculated. m The peak area A is shown in Table 3, and the melting point T of each melting peak is also shown in Table 3. m Test results are as follows Figure 3 As shown.

[0086] (2) Estimating the plasticization status of polyethylene products

[0087] The thickness L of the corresponding lamellar crystals for each melting peak is calculated according to formula (1).

[0088]

[0089] Among them, the equilibrium melting point T m 0 =414.5K, surface free energy σ = 5.0kJ / mol, enthalpy of fusion Δh = 8.2kJ / mol, Δz is the length of a repeating unit C2H4 in the polyethylene crystal, Δz = 0.254nm;

[0090] The methylene sequence length (MSL) of each melting peak was calculated using formulas (2) and (3).

[0091] ln x = 0.3451 - 142.2 / T m Formula (2)

[0092]

[0093] Where x is the number of moles of methylene.

[0094] Table 3

[0095]

[0096] The highest temperature of this sample is T. m1 With a temperature below 111℃, a crystal thickness of less than 7.2nm, and a methylene sequence length of less than 78.5nm, it can be inferred that the polyethylene cable material has good plasticizing properties and there is no problem with poor plasticizing.

[0097] The samples were tested using a Harp company impurity detector at a temperature of 110℃ and a rotation speed of 50rpm. The plasticization of the samples was observed, and no protrusions that were difficult to plasticize appeared on the surface, which was consistent with the inferred results.

[0098] Example 4

[0099] Taking Lanzhou Petrochemical Company's 2426H (batch number 20200312) as an example, the SSA thermal classification test steps are as follows: (a) Eliminating thermal history: The sample is first heated from room temperature to 160℃ at a heating rate of 10K / min and held for 5min to eliminate thermal history; (b) The sample is cooled to 20℃ at a cooling rate of 10K / min and held for 5min; (c) The sample is heated to the initial self-nucleation temperature of 115℃ at a heating rate of 10K / min and held for 5min; (d) From the initial self-nucleation temperature... (e) The sample is cooled to 20°C at a rate of 10 K / min, and the corresponding heat treatment will be reflected in the crystallization of the sample; (f) The sample is heated to the next self-nucleation temperature of 110°C and held at that temperature for 5 min; (g) Steps (b) to (e) are repeated, with each self-nucleation temperature decreasing by 5°C until the self-nucleation temperature reaches 75°C. After holding at 75°C for 5 min, the sample is cooled to 20°C at a rate of 10 K / min; (g) Finally, the sample is heated from 20°C to 160°C at a rate of 10 K / min, and the melting curve is recorded.

[0100] (1) Calculation of the relative content of each melting peak

[0101] The final melt curve was processed using professional peak fitting software (NETZSCH Proteus Thermal Analysis software from Germany) to separate the curve into independent melt peaks, and the melting point T of each melt peak was calculated. m The peak area A is shown in Table 4, and the melting point T of each melting peak is also shown in Table 4. m Test results are as follows Figure 4 As shown.

[0102] (2) Estimating the plasticization status of polyethylene products

[0103] The thickness L of the corresponding lamellar crystals for each melting peak is calculated according to formula (1).

[0104]

[0105] Among them, the equilibrium melting point T m 0 =414.5K, surface free energy σ = 5.0kJ / mol, enthalpy of fusion Δh = 8.2kJ / mol, Δz is the length of a repeating unit C2H4 in the polyethylene crystal, Δz = 0.254nm;

[0106] The methylene sequence length (MSL) of each melting peak was calculated using formulas (2) and (3).

[0107] ln x = 0.3451 - 142.2 / T m Formula (2)

[0108]

[0109] Where x is the number of moles of methylene.

[0110] Table 4

[0111]

[0112] The highest temperature of this sample is T. m1 The peak area A at temperatures greater than 111℃ is much greater than 0.2 J / g, the crystal thickness is greater than 7.2 nm, and the methylene sequence length is greater than 78.5 nm, suggesting that the polyethylene cable material has a problem with poor plasticization.

[0113] The samples were tested using a Harp company impurity detector at a temperature of 110℃ and a rotation speed of 40rpm. The plasticization of the samples was observed. There were many protrusions on the surface that were difficult to plasticize, indicating poor plasticization performance, which was consistent with the inferred results.

[0114] Example 5

[0115] Taking LF2119 from the Iranian Petrochemical Company as an example, the SSA thermal grading experimental steps are as follows: (a) Eliminating thermal history: The sample is first heated from room temperature to 230°C at a heating rate of 15 K / min and held for 5 min to eliminate thermal history; (b) The sample is cooled to 30°C at a cooling rate of 15 K / min and held for 5 min; (c) The sample is heated to the initial self-nucleation temperature of 115°C at a cooling rate of 15 K / min and held for 5 min; (d) The sample is heated from the initial self-nucleation temperature at a cooling rate of 15 K / min to the initial self-nucleation temperature of 115°C and held for 5 min. (e) The sample is heated to the next self-nucleation temperature of 110°C and held at that temperature for 5 min. (f) Steps (b) to (e) are repeated, with each self-nucleation temperature decreasing by 5°C until the self-nucleation temperature reaches 65°C. After holding at 65°C for 5 min, the sample is cooled to 30°C at a cooling rate of 15 K / min. (g) Finally, the sample is heated from 30°C to 230°C at a heating rate of 15 K / min, and the melting curve is recorded.

[0116] (1) Calculation of the relative content of each melting peak

[0117] The final melt curve was processed using professional peak fitting software (NETZSCH Proteus Thermal Analysis software from Germany) to separate the curve into independent melt peaks, and the melting point T of each melt peak was calculated. m The peak area A is shown in Table 5, and the melting point T of each melting peak is also shown in Table 5. m Test results are as follows Figure 5 As shown.

[0118] (2) Estimating the plasticization status of polyethylene products

[0119] The thickness L of the corresponding lamellar crystals for each melting peak is calculated according to formula (1).

[0120]

[0121] Among them, the equilibrium melting point T m 0 =414.5K, surface free energy σ = 5.0kJ / mol, enthalpy of fusion Δh = 8.2kJ / mol, Δz is the length of a repeating unit C2H4 in the polyethylene crystal, Δz = 0.254nm;

[0122] The methylene sequence length (MSL) of each melting peak was calculated using formulas (2) and (3).

[0123] ln x = 0.3451 - 142.2 / T m Formula (2)

[0124]

[0125] Where x is the number of moles of methylene.

[0126] Table 5

[0127]

[0128] The highest temperature of this sample is T. m1 With a temperature below 111℃, a crystal thickness of less than 7.2nm, and a methylene sequence length of less than 78.5nm, it can be inferred that the polyethylene cable material has good plasticizing properties and there is no problem with poor plasticizing.

[0129] The samples were tested using a Harp company impurity detector at a temperature of 110℃ and a rotation speed of 40rpm. The plasticization of the samples was observed, and no protrusions that were difficult to plasticize appeared on the surface, which was consistent with the inferred results.

[0130] Example 6

[0131] Taking Yangba Petrochemical Company's 2220H sample as an example, the SSA thermal classification test steps are as follows: (a) Eliminating thermal history: The sample is first heated from room temperature to 160℃ at a heating rate of 20K / min and held for 7min to eliminate thermal history; (b) The sample is cooled to 40℃ at a cooling rate of 20K / min and held for 7min; (c) The sample is heated to the initial self-nucleation temperature of 110℃ at a cooling rate of 20K / min and held for 7min; (d) The sample is heated from the initial self-nucleation temperature at a cooling rate of 20K / min to the initial self-nucleation temperature of 110℃ and held for 7min. (e) The sample is heated to the next self-nucleation temperature of 105°C and held at that temperature for 7 min. (f) Steps (b) to (e) are repeated, with each self-nucleation temperature decreasing by 5°C until the self-nucleation temperature reaches 60°C. After holding at 60°C for 7 min, the sample is cooled to 40°C at a cooling rate of 20 K / min. (g) Finally, the sample is heated from 40°C to 160°C at a heating rate of 20 K / min, and the melting curve is recorded.

[0132] (1) Calculation of the relative content of each melting peak

[0133] The final melt curve was processed using professional peak fitting software (NETZSCH Proteus Thermal Analysis software from Germany) to separate the curve into independent melt peaks, and the melting point T of each melt peak was calculated. m The peak area A is shown in Table 6, and the melting point T of each melting peak is also shown in Table 6. m Test results are as follows Figure 6 As shown.

[0134] (2) Estimating the plasticization status of polyethylene products

[0135] The thickness L of the corresponding lamellar crystals for each melting peak is calculated according to formula (1).

[0136]

[0137] Among them, the equilibrium melting point T m 0 =414.5K, surface free energy σ = 5.0kJ / mol, enthalpy of fusion Δh = 8.2kJ / mol, Δz is the length of a repeating unit C2H4 in the polyethylene crystal, Δz = 0.254nm;

[0138] The methylene sequence length (MSL) of each melting peak was calculated using formulas (2) and (3).

[0139] ln x = 0.3451 - 142.2 / T m Formula (2)

[0140]

[0141] Where x is the number of moles of methylene.

[0142] Table 6

[0143]

[0144] The highest temperature of this sample is T. m1 With a temperature below 111℃, a crystal thickness of less than 7.2nm, and a methylene sequence length of less than 78.5nm, it can be inferred that the polyethylene cable material has good plasticizing properties and there is no problem with poor plasticizing.

[0145] The samples were tested using a Harp company impurity detector at a temperature of 110℃ and a rotation speed of 40rpm. The plasticization of the samples was observed, and no protrusions that were difficult to plasticize appeared on the surface, which was consistent with the inferred results.

[0146] Example 7

[0147] Taking Lanzhou Petrochemical Company's 2240H (batch number 202104095510D) as an example, the SSA thermal classification test steps are as follows: (a) Eliminating thermal history: The sample is first heated from room temperature to 170℃ at a heating rate of 20K / min and held for 10min to eliminate thermal history; (b) The sample is cooled to 20℃ at a cooling rate of 10K / min and held for 10min; (c) The sample is heated to the initial self-nucleation temperature of 115℃ at a cooling rate of 10K / min and held for 5min; (d) From the initial self-nucleation... The temperature is cooled to 30°C at a cooling rate of 10 K / min, and the corresponding heat treatment will be reflected in the crystallization of the sample; (e) The sample is heated to the next self-nucleation temperature of 110°C and held at that temperature for 5 min; (f) Steps (b) to (e) are repeated, with each self-nucleation temperature decreasing by 5°C until the self-nucleation temperature reaches 70°C. After holding at 70°C for 2 min, the temperature is cooled to 30°C at a cooling rate of 10 K / min; (g) Finally, the sample is heated from 30°C to 170°C at a heating rate of 10 K / min, and the melting curve is recorded.

[0148] (1) Calculation of the relative content of each melting peak

[0149] The final melt curve was processed using professional peak fitting software (NETZSCH Proteus Thermal Analysis software from Germany) to separate the curve into independent melt peaks, and the melting point T of each melt peak was calculated. m The peak area A is shown in Table 7, and the melting point T of each melting peak is also shown in Table 7. m Test results are as follows Figure 7 As shown.

[0150] (2) Estimating the plasticization status of polyethylene products

[0151] The thickness L of the corresponding lamellar crystals for each melting peak is calculated according to formula (1).

[0152]

[0153] Among them, the equilibrium melting point T m 0 =414.5K, surface free energy σ = 5.0kJ / mol, enthalpy of fusion Δh = 8.2kJ / mol, Δz is the length of a repeating unit C2H4 in the polyethylene crystal, Δz = 0.254nm;

[0154] The methylene sequence length (MSL) of each melting peak was calculated using formulas (2) and (3).

[0155] ln x = 0.3451 - 142.2 / T m Formula (2)

[0156]

[0157] Where x is the number of moles of methylene.

[0158] Table 7

[0159]

[0160] The highest temperature of this sample is T. m1 The peak area A above 111℃ is less than 0.2 J / g, indicating that the polyethylene cable material has good plasticizing properties and there is no problem with poor plasticizing.

[0161] The samples were tested using a Harp company impurity detector at a temperature of 110℃ and a rotation speed of 40rpm. The plasticization of the samples was observed, and no protrusions that were difficult to plasticize appeared on the surface, which was consistent with the inferred results.

[0162] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for determining the low-temperature plasticizing ability of polyethylene, characterized in that, Includes the following steps: (1) Using the continuous self-nucleating annealing thermal classification technique on a differential scanning calorimeter, the melting curve of the polyethylene sample was recorded. The melting curve was then subjected to peak fitting, and the melting point T of each melting peak was calculated. m and peak area A; (2) The thickness L of the corresponding lamellar crystals for each melting peak is calculated according to formula (1). Official (1) Among them, the equilibrium melting point T m 0 =414.5 K, surface free energy σ=5.0 kJ / mol, enthalpy of fusion Δh=8.2 kJ / mol, Δz is the length of a repeating unit C2H4 in the polyethylene crystal, Δz=0.254 nm; (3) Calculate the methylene sequence length (MSL) value of each melting peak according to formulas (2) and (3). Official (2) Official (3) Where x is the number of moles of methylene; (4) If one of the conditions (a) and (b) is met, the plasticizing ability of the sample is qualified; if (c) is met, it is unqualified: (a) the melting point Tm of all melting peaks is less than 111℃, the crystal thickness of each melting peak of the sample is less than 7.2nm, and the length of each methylene sequence is less than 78.5nm; (b) there is at least one melting peak with a melting point Tm ≥ 111℃, but the sum of the peak areas of the melting peaks greater than 111℃ is less than 0.2J / g; (c) there is at least one melting peak with a melting point Tm greater than 111℃, and the sum of the peak areas of the melting peaks greater than 111℃ is ≥ 0.2J / g, the crystal thickness of each melting peak in the melting peaks greater than 111℃ in the sample is ≥ 7.2nm, and the length of each methylene sequence is ≥ 78.5nm.

2. The method for determining the low-temperature plasticizing ability of polyethylene according to claim 1, characterized in that, The specific steps for determining the melt profile are as follows: a. Under inert gas protection, the polyethylene sample is heated to the point of melting, and then held at the same temperature to eliminate thermal history; b. Cool the sample to a temperature at which it can crystallize, and hold it at that temperature to establish a standard thermal history of the sample; c. Heat the sample to the initial self-nucleation temperature and maintain it at that temperature; d. Cool the sample again from the initial nucleation temperature to the temperature at which it can crystallize and maintain this temperature at a constant temperature; e. Heat the sample to the next self-nucleation temperature, which is lower than the initial self-nucleation temperature, and maintain it at that temperature. f. Repeat steps b to e until the sample is held at the last self-nucleation temperature. After holding at the last self-nucleation temperature and cooling down to the crystallization temperature, heat the sample until it melts. The initial self-nucleation temperature is 110~120℃, and the temperature of each self-nucleation decreases sequentially, with the last self-nucleation temperature being 80~60℃.

3. The method for determining the low-temperature plasticizing ability of polyethylene according to claim 2, characterized in that, The rate of temperature change during the heating and cooling process is 5-20 K / min.

4. The method for determining the low-temperature plasticizing ability of polyethylene according to claim 2, characterized in that, The melting temperature of the sample in steps a and f is 160-230℃, and the temperature is held for 2-10 min.

5. The method for determining the low-temperature plasticizing ability of polyethylene according to claim 2, characterized in that, In steps b and d, the crystallization temperature is 20-60℃, and the temperature is held constant for 2-10 minutes.

6. The method for determining the low-temperature plasticizing ability of polyethylene according to claim 2, characterized in that, The isothermal time in steps c and e is 1-30 min.

Images