CN101025413A - Method for rapid detecting ISO 9080 grade of PVC pipe material - Google Patents

Abstract

The invention discloses a method to quickly detect polyethylene pipe material rank of ISO9080, it includes (1) detect polyethylene pipe material structure distribution in condensation state, the structure distribution in condensation state includes mass per centum content distribution of crystal phase, interface phase and amorphism phase;(2)compute the mass per centum content distribution of crystal phase, interface phase and amorphism phase;(3) bases the result of the (2)step, process the ISO9080 ratings of the polyethylene pipe material: the mass per centum content of crystal phase is 50-90%for polyethylene pipe material with PE80 rank and more than it, the mass per centum content of interface phase is 5-45%, the mass per centum content of amorphism phase is 0-15%. Compared to pipe certification authority hydrostatic test rating, This method has advantages of convenient, fast, and saving money, accelerate the new pipe material products into research development process, and with high accuracy, wide adaptation.

Description

A method for quickly detecting the ISO9080 grade of polyethylene pipe material

technical field

The invention relates to a method for evaluating and grading the performance of polyethylene pipe materials, in particular to a method for quickly detecting the ISO9080 grade of polyethylene pipe materials.

technical background

Since 1980, polyethylene pipes have been widely used in water and gas transportation, especially after the Kobe earthquake in Japan in 1995, the superiority of PE pipes has been widely recognized by the world. Today, in the gas field, whether it is for the repair and renewal of new laying or old pipelines, polyethylene pipes are one of the main choices. The polyethylene buried gas pipeline is reliable in quality, safe in operation, easy to maintain and economical in cost.

The grading of PE pipe materials is the basis for the application of PE pipes. When grading PE pipes, it is necessary to perform hydrostatic tests for at least 9,000 hours under the three temperature conditions of 20°C, 60°C and 80°C in accordance with the requirements of ISO9080 [1], and then conduct complex Multiple linear regression analysis, extrapolated to 97.5% lower confidence limit σ _LCL for predicted hydrostatic strength at 20 °C and 50 years. The polyethylene material with σ _LCL of 8.00~9.99MPa is PE80 grade pipe material. The pipe material can only be used to produce gas pipes on the premise of completing the above tests and obtaining the corresponding grade certification. The minimum requirement for the material grade of the gas pipe is PE80 grade. Today, with the continuous development of polyethylene production technology, the third-generation polyethylene pipe PE100 has been developed and quickly occupied the high-end polyethylene pipe market. Compared with the first-generation PE63 grade and the second-generation PE80 grade pipe material, PE100 resin mostly adopts bimodal distribution and hexene copolymerization technology (some manufacturers also use butene copolymerization), which not only improves the long-term hydrostatic strength, but also improves It is resistant to slow crack growth and has good processability, creating conditions for increasing the delivery pressure of the pipeline network, increasing the diameter of the pipeline, and expanding the application range of the pipeline. At present, the usage of PE100 pipes, especially the usage of large-diameter pipes, is rising rapidly.

As mentioned earlier, PE piping is rated for long-term hydrostatic testing at an internationally recognized certification body such as Bodycote, Sweden. The grade of PE pipe determined by this evaluation method has high reliability, but its disadvantage is that the test cycle is long and the manufacturer has a long waiting time, which is especially unfavorable for the research and development of higher grade pipe materials. Therefore, it is of great practical significance to propose a quick test method for evaluating the performance of pipe materials, optimize PE pipes for certification, and speed up the pace of research and development. Achieving this goal will greatly reduce the risk of manufacturers' pipe resin passing the certification and reduce unnecessary expenditures for enterprises.

At present, the research on performance evaluation and quality control of pipe materials mainly focuses on two aspects. The first is based on the testing and regulation of resin molecular structure parameters, such as molecular weight, molecular weight distribution, branching degree and other parameters. The advantage of this method is that it has a deep understanding of the nature of the matrix resin of the tube material and is easy to adjust at the reaction end. The disadvantage is that it is far away from the application end of the pipe material, and it is impossible to evaluate the changes of the pipe material in various processing processes. The second is various short-term mechanical performance tests on pipes, such as low temperature creep performance tests. Such test results have large deviations when used for long-term performance prediction of pipes.

More and more experiments and molecular simulations support the theoretically predicted existence of crystalline and amorphous interface phases, such as the article "Evidence for a PartiallyOrdered Component in Polyethylene from Wide-angle X-ray Diffraction" by A.M.E.Baker and A.H.Windle (Polymer 2002, 42, 667), L. Mandelkem's article "The Sructure of Crystalline Polymers" (Acc.Chem.Res.1990, 23, 380), R.R.Eckman, P.M.Henrichs, A.T.Peacock's article "Study of Polyethylene by Solid State NMR Relaxation and Spin Diffusion" (Macromolecules 1997, 30, 2474), but this theory has not been practically applied so far.

Contents of the invention

The invention provides a method for detecting polyethylene pipe material, through the test and analysis of resin crystal phase, interface phase and amorphous phase, convenient and quick performance evaluation and quality control for PE pipe material.

A method for quickly detecting the ISO9080 grade of polyethylene pipe material, comprising the steps:

(1) Detect polyethylene pipe material condensed state structure distribution, described condensed state structure distribution comprises the distribution of the mass percentage content of crystalline phase, interfacial phase and amorphous phase;

(2) Calculate the mass percentage content of crystalline phase, interface phase and amorphous phase;

(3) According to the result of step (2), carry out the ISO9080 grading of the polyethylene pipe material: the mass percentage content of the crystalline phase of the polyethylene pipe material of PE80 and above grade is 50～90%, the mass percentage content of the interface phase is 5 ~45%, and the content of amorphous phase mass percentage is 0~15%.

In the method, when the polyethylene pipe material has a crystalline phase mass percentage content of 60-80%, an interface phase mass percentage content of 10-30%, and an amorphous phase mass percentage content of 1-5%, its performance is even better. Excellent, or it can be more accurately stated that the polyethylene pipe material has reached the grade of PE80 and above.

The polyethylene used in the polyethylene pipe material is an ethylene homopolymer and/or a copolymer of ethylene and C3-C12 olefin comonomers. The C3-C12 olefin comonomer is one or more of butene, hexene or octene.

The polyethylene pipe material includes polyethylene powder, uncolored pellets, carbon black mixed pellets, tableted materials, extruded materials or finished pipe materials.

The detection of the condensed state structure distribution of polyethylene pipe materials adopts solid nuclear magnetic technology, Raman spectroscopy technology, X-ray diffraction and differential calorimetry combined technology, small angle neutron scattering technology or infrared spectroscopy technology, preferably solid nuclear magnetic technology , to get more accurate results.

The present invention evaluates the performance of the pipe based on the condensed state composition and property analysis of the PE pipe material resin, and its characteristics are:

(a) Compared with the polymer molecular structure, the condensed state structure, that is, the solid powder, granulated material, sheet material and even the pipe molding material structure of the pipe resin, is not only closer to the actual use process of the pipe, but also covers its processing. various stages. Therefore, it is more effective to test and analyze the structure of this level to evaluate and control the performance of the pipe.

(b) Compared with the short-term mechanical performance test, the analysis of the condensed matter structure goes deep into the level of molecular packing and movement in the solid material, and the understanding of the microstructure of the material is more profound, so the evaluation of the performance is more accurate.

(c) The analysis of the condensed matter structure can be achieved by a variety of testing methods, and even the online analysis of the production process can be implemented, so the application range is wider.

Therefore, the key of the present invention is to develop a method for evaluating and even grading the performance of PE pipe materials from the testing and analysis of solid polyethylene condensed state structure.

The feature of the invention is to quantitatively characterize the condensed state structure of the tube material and evaluate the performance of the tube material accordingly. The condensed matter structure of polymer refers to the arrangement and stacking structure between polymer chains, also known as supramolecular structure. For semi-crystalline polyethylene, it includes crystalline phase, amorphous phase and the content of interface phase between crystalline phase and amorphous phase, the size of each phase region and the molecular mobility in the phase region. The chain structure (molecular structure) of polymers is the main factor determining the basic properties of polymers, and the condensed state structure of polymers is the main factor determining the properties of polymers. The performance of polyethylene pipe materials is directly determined by the aggregated structure formed during the molding process. In this sense, it can be considered that the chain structure, that is, the molecular structure, only indirectly affects the performance of polyethylene pipe materials, while the condensed structure is the factor that directly affects its performance. For the traditional crystalline and amorphous two-phase model of polyethylene condensed state structure, it is believed that the mechanical properties of polyethylene pipe materials are closely related to the properties of the crystalline region, such as the mass fraction of the crystalline region (crystallinity) and the number of defects in the crystalline region. Recent studies have found that the properties of polyethylene amorphous phase have a great relationship with its pipe material resistance to slow crack growth (SCG). It is also worth noting that more and more experiments and molecular simulations support the existence of crystalline and amorphous interface phases that have been theoretically predicted, and the properties of the interface phases are closely related to the molecular weight of the tie between the grains of polyethylene materials. It has an important impact on the long-term mechanical properties of the tube material. All these indicate that the analysis of polyethylene condensed matter structure can provide important information on the performance of pipe materials.

The phase content and phase morphology analysis of tube material resin can be achieved by solid-state hydrogen nuclear magnetic spectrum and carbon spectrum technology, Raman spectroscopy technology, small angle x-ray diffraction technology, small angle neutron scattering technology and wide angle x-ray diffraction combined with DSC technology. Each technology subdivides the condensed state structure of solid polyethylene according to its own test principle, and distinguishes the crystalline phase in which the molecular chains of polyethylene are highly ordered, the completely amorphous phase in which the molecular chains are randomly oriented similar to the solution state, and the interfacial phase between the two. Among them, solid-state nuclear magnetic carbon spectrum and hydrogen spectrum analysis technology can give complete information on phase content and phase structure, while other analysis methods can only give information on phase content and phase domain size, so solid-state nuclear magnetic technology is preferred as Standard method for grading pipe materials and evaluating properties of advanced pipe materials. Due to the development of nuclear magnetic on-line analysis technology and optical fiber transmission technology, both solid-state nuclear magnetic and Raman spectroscopy technologies are likely to realize on-line analysis of polyethylene pipes at different stages and states in the production process, so these two technologies are preferred as pipe material production and On-line technology for process quality evaluation and control.

The standards adopted for grading pipe materials according to the present invention are based on the summary of analysis and test results of a large number of different grades of PE pipe materials. The samples used include PE63, PE80, and PE100 pipe material resins produced by Ziegler-Natta catalysts and Cr-based catalysts. These resins also come in a wide variety of forms from reactor fines, natural colored pellets, carbon black compounds and the resulting pellets, melt extrudates and even finished tubing. The condensed state structure analysis results of PE80 and above pipe material resins show that this type of material contains a large number of interfacial phases (mass percentage 10% to 30%), while the content of completely amorphous phase is very low (mass percentage less than 8%) or extremely low (less than 4% by mass). However, pipe materials below PE80 generally lack this feature, and the pipe materials can be graded accordingly. Furthermore, since PE80 and above grade pipe materials, especially PE100 pipe materials, have excellent environmental stress crack resistance (ESCR), the content of interfacial phase can be related to the long-term mechanical properties of pipe materials, that is, high The interfacial phase content corresponds to better resistance to slow stress cracking, which can be used to predict the long-term mechanical properties of pipe materials. When evaluating the performance of PE80 and above grade pipe materials, in addition to comparing the content of the three phases, especially the content of the interface phase, it is necessary to consider the morphology of each phase region, including the morphology and size of the phase region and the PE molecular chain in the phase region of sportiness. Solid-state NMR experiments can give complete information on the morphology of these phase regions, such as: the linewidth of the hydrogen spectrum in the three-phase region corresponds to the lateral delay time of the PE molecular chain; the determination of the spin-lattice delay time in the three-phase region ; Determination of the phase domain size of the three-phase domain by spin/diffusion experiments. Based on the analysis results of phase content and phase morphology of polyethylene pipe materials, the long-term and short-term mechanical properties and some processing properties of PE80 and above grade polyethylene pipe materials can be evaluated. The specific contents include:

(a) The higher the interface phase content, the more hindered the molecular movement in the interface phase, and the better the slow cracking resistance (SCG) of the pipe.

(b) Different polyethylene pipe materials with similar interface phase content (the difference in interface phase mass content is less than 2%), the higher the crystal phase (or solid phase) content, the higher the mechanical strength, and the poorer the processability.

(c) For different polyethylene pipe materials with similar phase composition, the more hindered the molecular motion in the three-phase region, the better the long-term and short-term mechanical properties of the material, corresponding to higher-grade pipe materials.

(d) The molecular mobility in the interface phase and the amorphous phase can also be used as a criterion for the anti-sagging performance of the tube material during processing. That is, in the case of similar two-phase content in different pipe resins, the longer spin/lattice relaxation time of the phase region corresponds to better anti-sag performance.

Description of drawings

Fig. 1 Broad-line H NMR spectra of PE1 and PE2 polyethylene pipe material resins;

Figure 2 Schematic diagram of decomposition of PE1 sample broad-line NMR spectrum;

Fig. 3 Schematic diagram of decomposition of Raman spectrum C-H bond vibration region of PE2 sample;

Figure 4 Schematic diagram of Raman spectrum decomposition in the C-H bond vibration region of PE1 sample;

Figure 5 Comparison of complex viscosity curves of PE1 and PE4 carbon black blends with shear frequency;

Detailed ways

Example 1 The grade judgment of different PE pipe materials by solid-state nuclear magnetic proton spectrum analysis technology

The powders of the two kinds of pipe material resins, the NMR broad-line hydrogen spectrum and the three-phase analysis of the hydrogen spectrum are shown in Figure 1 and Figure 2, respectively. The mass fractions of the three phases are given by the integral area fractions corresponding to the model curves, and the results are shown in Table 1.

Table 1 The phase content analysis results of two samples of PE1 and PE2 by solid-state NMR broad-line proton spectrum

sample Phase content   Crystal phase interface phase Amorphous phase PE1PE2 0.840.97 0.140 0.020.03

^* The error of the result is not more than 3%.

According to the results in Table 1, it can be judged that the pipe material corresponding to the PE1 sample is PE80 and above, while the pipe material corresponding to the PE2 sample is PE63 or lower. This conclusion is consistent with the sample information provided by the manufacturer.

Example 2 Raman Spectroscopy Analysis Technology for Grade Judgment of Different Tube Materials

When using Raman spectroscopy to analyze the phase structure of solid polyethylene pipes, it is based on the spectral peak analysis of the CH bond torsional vibration and bending vibration regions in the region from 1200 cm ^-1 to 1600 cm ^-1 [13]. The contents of crystalline phase, amorphous phase and interface phase are calculated by the following formulas respectively:

Crystal phase content X _C ＝I ₁₄₁₆ /[0.46(I ₁₂₉₅ +I ₁₃₀₃ )]

Amorphous phase content X _a =I1303/(I ₁₂₉₅ +I ₁₃₀₃ )

Interfacial phase content _Xi = 1-X _c -X _a

Where I refers to the integral area of the spectrum peak, which is given by the computer peak division result.

The results of the analysis of the two polyethylene phase structures are shown in Table 2:

Table 2 Raman spectroscopy phase content analysis results of PE1 and PE2 samples

sample Phase content   Crystal phase interface phase Amorphous phase PE1PE2 0.610.80 0.370.06 0.020.14

^* The error of the result is not more than 10%.

The results given in Table 2 also show that the pipe material corresponding to the PE1 sample reaches the grade of PE80 or above, while the pipe material grade corresponding to the PE2 sample is lower.

Example 3 The combination of wide-angle X-ray and DSC analysis technology for grade determination of different grades of pipe materials

The wide-angle X-ray (WAXD) method can analyze the phase structure of solid polymers, and the obtained crystalline phase content includes the contribution of the interface phase, and the crystallinity given by DSC technology is approximately equivalent to the highly ordered molecular chain content of the crystalline phase. The difference in crystallinity given by the two test methods reflects the content of the interfacial phase in the solid material, from which the three-phase composition in the polyethylene pipe resin can be distinguished. The analysis and test results of the two samples of PE1 and PE2 are shown in the table 3 shows:

Table 3 Phase composition analysis of PE pipe materials by WAXD and DSC combined technology

sample Phase content   Crystal phase interface phase Amorphous phase PE1PE2 0.650.81 0.260.03 0.090.16

Comparing the results of Examples 1, 2, and 3, it can be found that the subdivision results of the condensed matter structure of the tube material by different analysis and test methods are different, which can be explained by the different test principles on which the various methods are based. The solid-state nuclear magnetic technology is based on the different mobility of molecular chains in different phase regions; the Raman spectroscopy technology is based on the different vibration characteristics of the C-H bond in different phase regions, and the DSC method is based on the enthalpy of different phase regions effect, the WAXD method relies on the different electron densities in different phase regions. But no matter which type of method is used, the characteristics of the three-phase composition given by different grades of PE pipe materials after the same treatment are the same, that is, pipe resins of PE80 and above grades contain more abundant interface phases, and there is no interface phase at all. The shaped phase content is low, as demonstrated in the three examples above. Based on this, a preliminary judgment can be made on the grade of the pipe material.

Example 4 Evaluation of Condensed Matter Structure Analysis on the Properties of Different PE100 Pipe Materials

Two kinds of PE100 pipe materials are produced by Cr-based catalyst gas phase fluidized bed process, ethylene hexene copolymerization and Ziggler-Natta catalyst series reactor process, ethylene butene copolymerization. The resin characteristics of the tube material are shown in Table 4:

Table 4 Resin properties of PE1 and PE3 pipe materials

sample M _w M _w /M _n T _m (°C) _Xc (%DSC)

PE1, bimodal PE100 pipe material PE3, unimodal PE100 pipe material 282162241756 36.727.1 131128 67% 59%

The powder of these two kinds of high-end pipe materials and the natural color pellet are carried out the analysis of nuclear magnetic condensed state structure, and analysis process is the same as embodiment 1, and its result is as shown in table 5:

Table 5 Solid NMR phase structure analysis of PE1 and PE3 pipe materials

sample Phase composition (%) Line width of hydrogen spectrum (Hz)   Crystal phase interface phase Amorphous phase   Crystal phase interface phase Amorphous phase PE1 natural color pellets PE3 natural color pellets PE1 powder PE3 powder 78.1473.4684.1682.21 17.7821.4214.0815.94 4.085.121.761.85 50879479314922747974   10646110611182312858 3383321023592328

The spectral linewidth here refers to the half-maximum width at half maximum of the fitting curve corresponding to each phase region. The larger the linewidth value, the more restricted the molecular mobility in the corresponding phase region[14]. The performance comparison of the two pipe materials has the following characteristics: (1) both have passed the certification to reach the PE100 grade; (2) the high-temperature hydrostatic failure time of the bimodal PE100 pipe material is longer than that of the unimodal PE100 pipe material; (3) the unimodal ethylene The process operating range of hexene copolymerization pipe material is narrower. Through the three-phase structure analysis result of solid nuclear magnetic, can have following explanation respectively: (1) all contain rich interface phase content in two kinds of tube materials, and amorphous phase content is very low relatively, according to the judging standard of the present invention, can all Reach PE80 grade or above. (2) PE1 pipe material has a higher crystallinity, and the reduced crystallinity of PE3 relative to PE1 is mostly transformed into the interface phase. Because the interfacial phase is more prone to stress failure caused by disentanglement of molecular chains at higher temperatures, the hydrostatic failure of PE3 occurs earlier at higher temperatures. (3) The reactor series process can separately control the crystal phase and interface phase properties of the tube material, while the single reactor ethylene hexene polymerization process requires the content of hexene monomer to be controlled in an appropriate range. A high hexene content will reduce the crystallinity of the material and lead to poor mechanical properties of the material, while a low hexene content cannot produce enough interfacial phases to meet the requirements. In contrast, the latter has a narrower process adjustable range.

The results of this example also show that the introduction of the condensed matter structure evaluation method proposed by the present invention avoids the confusion that both unimodal and bimodal polyethylenes can be used to prepare PE100 pipe materials, and reveals the inherent factors that determine the short-term and long-term mechanical properties of PE pipe materials. structural nature. The reason why the ethylene-hexene unimodal copolymer can also reach the level of PE100 is that it contains more abundant interfacial phases, and the mutual entanglement of molecular chains in the interfacial phase is enhanced, and the movement of molecular chains is more restricted, as shown in Table 5 shown.

Example 5 Analysis of the anti-sag performance of two kinds of polyethylene materials with grades above PE80

The carbon black blends of PE1 and PE4, two kinds of polyethylene pipe materials above PE80, are used in the production of small-diameter and large-diameter pipes because of their different anti-sag properties. The molecular weight distributions of both are bimodal, and the carbon black content and dispersion grades are the same.

Table 6 Phase structure analysis of PE1 and PE4 pipe materials

sample Phase composition (%) Line width of hydrogen spectrum (Hz)   Crystal phase interface phase Amorphous phase   Crystal phase interface phase Amorphous phase PE1 carbon black compounding PE4 carbon black compounding 75.9877.20 19.2617.44 4.775.37 4989051143   1070610348 29042912

Table 7 The hydrogen spectrum spin/lattice delay times of PE1 and PE4 tube materials

sample T1 (one-component fit) T1 (two-component fitting) PE1 Carbon Black Mixing PE4 Carbon Black Mixing 758ms794ms 781ms854ms 160ms306ms

The anti-sagging performance of PE pipe materials is of great significance for the production of large-diameter PE pipe materials. Its meaning is that the PE pipe resists deformation and collapse caused by its own weight when it is extruded. Figure 5 shows the comparison of rheological curves of PE1 and PE4 pipe materials. It can be seen that PE4 pipe material has significantly higher complex viscosity in the low frequency region, so it has better melt strength and sag resistance. Correspondingly, Table 6 and Table 7 respectively give the results of solid NMR phase structure analysis of the two tube materials. In Table 6, the phase composition and hydrogen spectrum line width of the two materials are not significantly different, which may be due to the fact that the two materials are prepared by the same polymerization process, and both belong to PE pipe materials above PE80, so the broad-line hydrogen spectrum analysis results are similar. However, when the spin/lattice relaxation time of the two materials is further tested, it is observed that PE4 has a significantly higher spin/lattice relaxation time. From this, it can be preliminarily inferred that the anti-sag performance of the tube material is closely related to its spin/lattice delay time, and a higher spin-lattice delay time corresponds to a better anti-sag performance.

Claims (7)

1. A method for quickly detecting the ISO9080 grade of polyethylene pipe material, characterized in that it comprises the steps: (1) Detect polyethylene pipe material condensed state structure distribution, described condensed state structure distribution comprises the distribution of the mass percentage content of crystalline phase, interfacial phase and amorphous phase; (2) Calculate the mass percentage content of crystalline phase, interface phase and amorphous phase; (3) According to the result of step (2), carry out the ISO9080 grading of the polyethylene pipe material: the mass percentage content of the crystalline phase of the polyethylene pipe material of PE80 and above grade is 50～90%, the mass percentage content of the interface phase is 5 ~45%, and the content of amorphous phase mass percentage is 0~15%. 2. The method according to claim 1, characterized in that: in the ISO9080 grade, the polyethylene pipe material of PE80 and above grade has a crystalline phase content of 60-80% by mass and an interface phase content of 10% by mass. ～30%, and the content of amorphous phase mass percentage is 1～5%. 3. The method according to claim 1, characterized in that: said polyethylene pipe material includes polyethylene powder, uncolored pellets, carbon black mixed pellets, tablet material, extruded material or finished pipe material . 4. The method according to claim 1, characterized in that: the polyethylene used in the polyethylene pipe material is ethylene homopolymer and/or a copolymer of ethylene and C3-C12 olefin comonomers. 5. The method according to claim 1, characterized in that the C3-C12 olefin comonomer is one or more of butene, hexene or octene. 6. The method according to claim 1, characterized in that: the detection of the distribution of the condensed state structure of the polyethylene pipe material adopts solid-state nuclear magnetic technology, Raman spectroscopy technology, X-ray diffraction and differential calorimetry combined technology or Small Angle Neutron Scattering Technique. 7. The method according to claim 6, characterized in that the detection of the condensed state structure distribution of the polyethylene pipe material adopts solid nuclear magnetic technology.

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