CN114133588A - Method for regulating and controlling alpha-olefin homopolymer crystallization through processing conditions - Google Patents
Method for regulating and controlling alpha-olefin homopolymer crystallization through processing conditions Download PDFInfo
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Abstract
The invention discloses a method for regulating and controlling crystallization of an alpha-olefin homopolymer through processing conditions, and belongs to the technical field of polymer crystallization. Heating a long-chain alpha-olefin homopolymer with 12-20 carbon atoms to 160 ℃, preserving heat for 10min, and cooling to crystallize the long-chain alpha-olefin homopolymer to obtain an initial sample; heating to 45-160 ℃ for melting, preserving heat for 1-3600s, and then cooling to 10-75 ℃ at a speed of 10 ℃/min; applying shear strain at a rate of 0-5s‑1A flow field with a shear time of 0-5s and crystallization at an isothermal crystallization temperature. In the invention, the crystallization time of the long-chain alpha-olefin homopolymer has obvious difference under different processing conditions, which shows that the processing conditions have great influence on the crystallization time of the long-chain alpha-olefin homopolymer, and provides a feasible scheme for improving the processing and forming efficiency.
Description
Technical Field
The invention belongs to the technical field of polymer crystallization, and particularly relates to a method for regulating and controlling crystallization of an alpha-olefin homopolymer through processing conditions.
Background
Long chain alpha-olefin homopolymers are unique comb polymers that can crystallize in both the main chain and the side chains, depending on the length of the side chains. The crystal formed by main chain crystallization is Type I crystal form. Type i crystal form is obtained by melt quenching and then heating to a temperature range of 5-30 ℃ below the melting temperature. The Type II crystal form formed by orderly arranging side chains can be directly obtained by cooling and crystallizing from a melt. The ability of the long chain alpha-olefin homopolymer to crystallize increases with increasing side chain length. The crystallization behavior of long chain alpha-olefins is reported in more detail in the prior art, but the long chain alpha-olefin homopolymer is not easy to process and form due to the low crystallization temperature. And there are few reports on methods for regulating the crystallization time of long chain alpha-olefins by processing conditions. It is therefore of great importance to develop a method for controlling the crystallization time of long chain alpha-olefin homopolymers by means of processing conditions.
Disclosure of Invention
Aiming at the technical problems, the invention provides a method for regulating and controlling the crystallization of the alpha-olefin homopolymer through processing conditions, and provides a feasible method for the existing long-chain alpha-olefin homopolymer which is not beneficial to processing and forming and has low processing and forming efficiency.
In order to achieve the purpose, the invention provides the following technical scheme:
a method for regulating crystallization of an alpha-olefin homopolymer via processing conditions, comprising the steps of:
(1) heating the long-chain alpha-olefin homopolymer to 160 ℃, preserving heat for 10min, and then cooling to obtain an initial sample;
(2) the initial sample of the long-chain alpha-olefin homopolymer crystal is heated to the melting temperature, then is subjected to heat preservation treatment, and then is cooled to the isothermal crystallization temperature.
Further, the step (2) further comprises applying a flow field when the temperature is raised and then just lowered to the isothermal crystallization temperature.
Further, the number of carbon atoms of the long-chain alpha-olefin homopolymer in the step (1) is 12-20, the molecular weight is 100000-350000, and the molecular weight distribution is 1.8-2.3. The proportion of mmmm isotactic pentads of the long-chain alpha-olefin homopolymer is more than 99 percent.
Further, the temperature reduction treatment in the step (1) comprises two methods:
(a) cooling to-30 ℃ at a speed of 10 ℃/min, and crystallizing to obtain a Type II crystal form;
(b) quenching with liquid nitrogen for 30s and returning to room temperature, and crystallizing to obtain Type I crystal form (quenching to form local ordered structure in liquid nitrogen and converting into Type I crystal form at room temperature).
Further, the heating rate in the step (2) is 5 ℃/min, the melting temperature is 45-160 ℃, and the heat preservation time is 1-3600 s.
Further, the isothermal crystallization temperature in the step (2) is 10-75 ℃.
Further, the shear strain rate of the rheological field is 0-5s-1The shearing time is 0-5 s.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a method for regulating and controlling the crystallization of a long-chain alpha-olefin homopolymer through processing conditions, which overcomes the defect that the existing long-chain alpha-olefin homopolymer is low in crystallization rate and not beneficial to processing and forming, and simultaneously improves the processing and forming efficiency. In the invention, partial ordered structure is kept in the polymer melt at lower melting temperature, and simultaneously, the flow field action is applied to orient molecular chains and induce the crystal to be rapidly formed, thereby achieving the purpose of shortening the crystallization time.
The technical method provided by the invention is suitable for the long-chain alpha-olefin homopolymer with the carbon atom number of 12-20, two crystal forms can be obtained by adopting different cooling methods, and the crystallization time of the long-chain alpha-olefin homopolymer can be changed through different melting temperatures and flow field conditions. The invention provides an effective way for regulating and controlling the crystallization time of long-chain alpha-olefin through processing conditions.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a WAXD graph of Type II crystal form obtained from different long chain alpha-olefin homopolymers in example 1 of the present invention;
FIG. 2 is a WAXD chart of Type I crystal form obtained from poly-1-tetradecene according to example 1 of the present invention;
FIG. 3 shows the relative crystallinity X of poly-1-hexadecene in the isothermal crystallization process at 44 ℃ after melting at 90 ℃ and 160 ℃ in example 2 of the present inventioncA graph of changes over time;
FIG. 4 shows relative crystallinity X of poly-1-octadecene in 52 deg.C isothermal crystallization process after melting at 110 deg.C and 160 deg.C in example 3 of the present inventioncA graph of changes over time;
FIG. 5 shows the relative crystallinity X of poly-1-eicosene in accordance with example 4 of the present invention after melting at 100 ℃ and 160 ℃ in the course of isothermal crystallization at 72 ℃cA graph of changes over time;
FIG. 6 shows relative crystallinity X in isothermal crystallization at 34 ℃ after melting poly-1-tetradecene at 52 ℃ and 160 ℃ in example 5 of the present inventioncA graph of changes over time;
FIG. 7 is a graph of the storage modulus versus time for poly-1-eicosene of example 6 of the present invention under different processing conditions;
FIG. 8 is a graph of semi-crystallization half-time as a function of melting time for isothermal crystallization at 52 ℃ after melting at 90 ℃ and 160 ℃ for comparative examples 1-2 of the present invention;
FIG. 9 is a graph of the storage modulus as a function of time for comparative examples 3-4 poly 1-twenty of the present invention at different flow fields over time after melting at 90 ℃.
Detailed Description
Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The specification and examples are exemplary only.
As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.
The long-chain alpha-olefin homopolymer used in the invention has the carbon atom number of 12-20, the molecular weight of 100000-350000 and the molecular weight distribution of 1.8-2.3. The proportion of mmmm isotactic pentads of the long-chain alpha-olefin homopolymer is more than 99 percent.
Example 1 a method for preparing α -olefin homopolymers of different crystal forms by modulation of processing conditions, comprising the steps of:
the long chain alpha-olefin homopolymer was heat treated using a Linkam heat station. Heating to 160 ℃ at a speed of 10 ℃/min, preserving heat for 10min, then cooling to-30 ℃ at a speed of 10 ℃/min, and crystallizing to obtain the Type II crystal form. The samples obtained from the temperature-reduced crystallization were characterized by WAXD, as shown in fig. 1. The sample has obvious diffraction signals at 2 theta of 21 degrees and 23.7 degrees, which shows that the Type II crystal form is formed by cooling at 10 ℃/min.
The poly-1-tetradecene sample is subjected to heat treatment by a Linkam heat station, heated to 160 ℃ at a temperature of 10 ℃/min and kept for 10min, and then quenched by liquid nitrogen for 30s and returned to room temperature. The samples obtained from the temperature-reduced crystallization were characterized by WAXD, as shown in fig. 2. The samples had significant diffraction signals at 19.1 ° and 21 ° 2 θ, indicating that Type i form was formed using liquid nitrogen quenching for 30s and returning to room temperature.
Example 2
The test was performed using DSC Q2000 (TAInstructor). Weighing 5mg of poly-1-hexadecene sample, putting the sample into a crucible, heating to 160 ℃ at a speed of 10 ℃/min, preserving heat for 10min, then cooling to-30 ℃ at a speed of 10 ℃/min, and preserving heat for 2min to obtain a Type II crystal form sample; then heating to 90 ℃ and 160 ℃ at the speed of 5 ℃/min, preserving heat for 10min, cooling to 44 ℃ at the speed of 10 ℃/min, and carrying out isothermal crystallization until complete crystallization. Relative crystallinity X of samples melted at 90 ℃ and 160 ℃ in isothermal crystallization at 44 ℃cThe time course is shown in FIG. 3.
Relative degree of crystallinity XcThe calculation is made by the following formula:
wherein, Δ Hm(t) is the enthalpy of the sample at isothermal time t, Δ H∞Is the enthalpy value after completion of isothermal crystallization. The crystallization times under different conditions can be compared based on the change in relative crystallinity over time. As can be seen from FIG. 3, under the same isothermal crystallization temperature conditions, the crystallization was complete at a melting temperature of 90 ℃ (X)c1) is shorter than the time taken when the melting temperature is 160 ℃, which indicates that the crystallization time can be effectively shortened by lowering the melting temperature. It is noted here that lowering the melting temperature accelerates the crystallization of the polymer, since a partially ordered structure, such as a helical conformation, etc., can still remain in the melt. As the melting temperature decreases, the crystallization rate increases. However, if the melting temperature is too low, i.e., does not exceed the melting region of the polymer, crystals that are not completely melted exist in the polymer at that temperature, which affects subsequent processing. Here, the melting temperature of the poly-1-hexadecene is chosen to be above 90 ℃ but low enough that the ordered structure remains in the meltThe crystallization was fast and compared with the result that the crystal was in a homogeneous melt state at 160 ℃. Similar considerations apply to examples 3-6.
Example 3
The test was performed using DSC Q2000(TA Instrument). Weighing 5mg of poly-1-octadecene sample, putting the sample into a crucible, heating to 160 ℃ at a speed of 10 ℃/min, preserving heat for 10min, then cooling to-30 ℃ at a speed of 10 ℃/min, preserving heat for 2min to obtain a Type II crystal form sample, heating to 110 ℃ and 160 ℃ at a speed of 5 ℃/min, preserving heat for 180min, cooling to 52 ℃ at a speed of 10 ℃/min, and carrying out isothermal crystallization until complete crystallization. Relative crystallinity X of the samples after melting at 110 ℃ and 160 ℃ in the isothermal crystallization process at 52 DEG CcThe time course is shown in fig. 4. As can be seen from FIG. 4, under the same isothermal crystallization temperature conditions, the time for complete crystallization at a melting temperature of 110 ℃ is shorter than the time for crystallization at a melting temperature of 160 ℃, which indicates that the crystallization time can be effectively shortened by lowering the melting temperature.
Example 4
The test was performed using DSC Q2000(TA Instrument). Weighing 5mg of poly-1-eicosene sample, putting the sample into a crucible, heating to 160 ℃ at a speed of 10 ℃/min, preserving heat for 10min, then cooling to-30 ℃ at a speed of 10 ℃/min, preserving heat for 2min to obtain a Type II crystal form sample, heating to 100 ℃ and 160 ℃ at a speed of 5 ℃/min, preserving heat for 10min, cooling to 72 ℃ at a speed of 10 ℃/min, and carrying out isothermal crystallization until complete crystallization. In the method, the relative crystallinity X of the sample after melting at 100 ℃ and 160 ℃ in the isothermal crystallization process at 72 DEG CcThe time course is shown in fig. 5. As can be seen from FIG. 5, under the same isothermal crystallization temperature conditions, the time for complete crystallization at a melting temperature of 100 ℃ is shorter than the time for crystallization at a melting temperature of 160 ℃, which indicates that the crystallization time can be effectively shortened by lowering the melting temperature.
Example 5
And (3) carrying out heat treatment on the poly-1-tetradecene sample by adopting a Linkam heat station, heating to 160 ℃ at the speed of 10 ℃/min, keeping the temperature for 10min, and then quenching for 30s by using liquid nitrogen to obtain the Type I crystal form sample. Performing subsequent test by DSC Q2000(TA Instrument), heating to 52 deg.C and 160 deg.C at 5 deg.C/min respectively, maintaining the temperature for 10min,and then respectively cooling to 34 ℃ at the speed of 10 ℃/min and carrying out isothermal crystallization until complete crystallization. In the method, the relative crystallinity X of the samples melted at 52 ℃ and 160 ℃ in the isothermal crystallization process at 34 DEG CcShown in graph 6 as a function of time. As can be seen from FIG. 6, under the same isothermal crystallization temperature conditions, the time for complete crystallization at a melting temperature of 52 ℃ is shorter than the time for crystallization at a melting temperature of 160 ℃, which indicates that the crystallization time can be effectively shortened by lowering the melting temperature.
Example 6
Carrying out heat treatment on a poly-1-eicosene sample by adopting a Linkam heat station, heating to 160 ℃ at a speed of 10 ℃/min, preserving heat for 10min, then cooling to-30 ℃ at a speed of 10 ℃/min, preserving heat for 2min, and cooling and crystallizing to form a Type II crystal form.
1. And (3) placing the pretreated poly-1-eicosene sample with the Type II crystal form in a 8mm flat plate clamp, heating to 160 ℃, preserving heat for 10min, cooling to 72 ℃ at the speed of 10 ℃/min respectively, and carrying out isothermal crystallization.
2. Placing the pretreated poly-1-eicosene sample with Type II crystal form in a flat plate clamp with the thickness of 8mm, respectively heating to 90 and 160 ℃, preserving heat for 10min, cooling to 72 ℃, and simultaneously applying shear strain at the rate of 5s-1A flow field with a shear strain time of 5s, isothermal crystallization.
The change in storage modulus with time in this method versus storage modulus under static conditions is shown in FIG. 7. And judging the crystallization process of the polymer according to the change of the storage modulus with time. It can be observed from fig. 7 that melting at 160 ℃ and without application of a flow field, the storage modulus goes upward only for 400s and gradually plateaus after 2000s, completely crystallizing. However, melting at 160 ℃ and applying a shear strain rate of 5s-1When the shear time is 5s of the flow field, the time for raising the storage modulus is shortened to 200s, and the storage modulus gradually reaches the platform after 1000s and is completely crystallized. This demonstrates that the application of a flow field can significantly shorten the crystallization time. Melting at 90 ℃ and applying a shear strain at a rate of 5s-1When the shear time is 5s of the flow field, the time for raising the storage modulus is shortened to 60s, and the storage modulus gradually reaches the level after 800sAnd finally, completely crystallizing. This further illustrates that applying a flow field while lowering the melting temperature can significantly shorten the crystallization time.
Comparative example 1
The difference from example 2 is that the temperature was raised to 90 ℃ and 160 ℃ at 5 ℃/min and the temperature was maintained for 1 s. FIG. 8 shows different melting times (t) at 90 ℃ and 160 ℃a) Semi-crystallization time (t) followed by isothermal crystallization at 52 DEG C1/2). As a result, it was found that the crystallization time was still significantly less after melting at 90 ℃ than after melting at 160 ℃. But the semicrystallization time does not vary significantly for polymers of the same melting temperature.
Comparative example 2
The difference from example 2 is that the temperature was raised to 90 ℃ and 160 ℃ at a rate of 5 ℃/min, and the temperature was maintained at 3600. FIG. 8 shows the semi-crystallization half time for isothermal crystallization at 52 ℃ after melting at 90 ℃ and 160 ℃ for different times. As a result, it was found that the crystallization time was still significantly faster after melting at 90 ℃ than after melting at 160 ℃. But the semicrystallization time does not vary significantly for polymers of the same melting temperature.
As can be seen from the results of comparative examples 1 to 2, the present invention can maintain the crystallization accelerating effect for a long annealing time by lowering the melting temperature.
Comparative example 3
The same rheological field portion as in example 6 was applied except that the shear strain time was 0.5 s.
Comparative example 4
The same rheological field portion as in example 6 was applied except that the shear strain time was 10 s. The results of comparative examples 3-4 are shown in fig. 8, and it can be seen from fig. 8 that the crystallization time is shorter and shorter as the application time of the rheological field is prolonged under the same shear stress, but increasing from 0.5s to 5s causes the magnitude of the decrease in crystallization time to be significantly greater than increasing from 5s to 10 s. That is, further increasing the shear time does not continue to increase the crystallization rate, but has a plateau value, so that the shear time is set to be optimal for 5 s. This also demonstrates that varying the shear time can significantly control the crystallization of the alpha-olefin homopolymer.
In the above examples, the crystallization times of the long-chain α -olefin homopolymers under different processing conditions are significantly different, which indicates that the processing conditions have a large influence on the crystallization time of the long-chain α -olefin homopolymers, and provides a feasible scheme for improving the processing molding efficiency.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included therein.
Claims (7)
1. A method for regulating crystallization of an alpha-olefin homopolymer via processing conditions, comprising the steps of:
(1) heating the long-chain alpha-olefin homopolymer to 160 ℃, preserving heat for 10min, and then cooling to obtain an initial sample;
(2) the obtained long-chain alpha-olefin homopolymer initial sample is heated to the melting temperature, then is subjected to heat preservation treatment, and is cooled to the isothermal crystallization temperature.
2. The method of claim 1, wherein step (2) further comprises applying a flow field prior to increasing the temperature and immediately after decreasing the temperature to the isothermal temperature.
3. The method as claimed in claim 1 or 2, wherein the number of carbon atoms of the long-chain α -olefin homopolymer in step (1) is 12-20, the molecular weight is 100000-350000, and the molecular weight distribution is 1.8-2.3.
4. The method according to claim 1 or 2, wherein the temperature reduction treatment of step (1) comprises two methods:
(a) cooling to-30 ℃ at a speed of 10 ℃/min, and crystallizing to obtain a Type II crystal form;
(b) quenching for 30s by liquid nitrogen, recovering to room temperature, and crystallizing to obtain Type I crystal form.
5. The method according to claim 1 or 2, wherein the temperature rise rate in step (2) is 5 ℃/min, the melting temperature is 45-160 ℃, and the holding time is 1-3600 s.
6. The method according to claim 1 or 2, wherein the isothermal crystallization temperature of step (2) is 10-75 ℃.
7. The method of claim 2, wherein the flow field has a shear strain rate of 0-5s-1The shearing time is 0-5 s.
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| CN117777484A (en) * | 2023-12-26 | 2024-03-29 | 天津大学 | Method for synergistically regulating and controlling crystallization capacity and crystal form of 1-butene/ethylene random copolymer through multiple physical fields |
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| CN104610551A (en) * | 2013-11-01 | 2015-05-13 | 天津大学 | Method for improving crystallization degree of isotactic poly 1-butylene by shear flow |
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| CN117777484A (en) * | 2023-12-26 | 2024-03-29 | 天津大学 | Method for synergistically regulating and controlling crystallization capacity and crystal form of 1-butene/ethylene random copolymer through multiple physical fields |
| CN117777484B (en) * | 2023-12-26 | 2024-06-11 | 天津大学 | Method for synergistically regulating and controlling crystallization capacity and crystal form of 1-butene/ethylene random copolymer through multiple physical fields |
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