Polyethylene composition and preparation method and application thereof

Abstract

The invention discloses a polyethylene composition, belonging to the technical field of polymer material modification. The polyethylene composition provided by the invention comprises the following raw materials in parts by weight: 60-90 parts of high-density polyethylene resin, 5-35 parts of toughening agent, 2-8 parts of compatibilizer, 0.1-0.5 parts of nucleating agent, 0.1-0.5 parts of nano silicon carbide whisker, and 0.2-0.8 parts of antioxidant; the aspect ratio of the nano silicon carbide whisker is 50-250; the obtained product has excellent environmental stress cracking resistance and mechanical properties; meanwhile, the preparation method of the polyethylene composition provided by the invention is simple, which is conducive to actual production.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material modification, and in particular relates to a polyethylene composition and a preparation method and application thereof. Background Art

[0002] High-density polyethylene (HDPE) is a crystalline thermoplastic resin with excellent physical and mechanical properties, as well as good heat resistance, cold resistance and chemical stability. It is widely used in fluid transportation pipes, automobile manufacturing, electronic appliances, cable sheaths and other fields. HDPE pipes have low manufacturing costs, low energy consumption, easy installation and maintenance, and corrosion resistance. However, HDPE has poor environmental stress cracking resistance (ESCR). After contact with low surface energy solvents or surfactants, the speed of stress cracking will be greatly accelerated, reducing the service life of the product.

[0003] HDPE is a crystalline polymer, and its crystals are composed of many folded polymer chains. In the actual processing process, it is difficult for HDPE to develop into single crystals. Small crystals are often centered on certain crystal nuclei and stacked on all four sides to form spherulites. The sensitivity of HDPE itself to environmental stress cracking is related to the heterogeneity of its structure and properties, such as molecular weight and its distribution, molecular chain branching, crystal state, crystal defects, micro-voids in amorphous regions, interlamellar spacing, and inter-spherulite regions. Micro-voids and structural defects can absorb environmental reagents, induce silver streaks and cracks; the amorphous regions between lamellae include condensates at the ends of molecules, loose entangled root molecular chains, and connecting molecules, and only the connecting molecules have the ability to resist environmental stress cracking. Stress cracking mainly occurs at the spherulite interface and its radial part. When large spherulites are generated, the stress cracking resistance is poor. Too high crystallinity reduces flexibility and also deteriorates the stress cracking performance.

[0004] Therefore, a high-density polyethylene composite material with high toughness and resistance to environmental stress cracking is prepared, which has excellent industrial application prospects. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and to provide a polyethylene composition having excellent environmental stress cracking resistance and excellent mechanical properties, and a preparation method and application thereof.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a polyethylene composition, which includes the following raw materials in parts by weight: 60-90 parts of high-density polyethylene resin, 5-35 parts of toughening agent, 2-8 parts of compatibilizer, 0.1-0.5 parts of nucleating agent, 0.1-0.5 parts of nano-silicon carbide whiskers, and 0.2-0.8 parts of antioxidant; the average aspect ratio of the nano-silicon carbide whiskers is 50-250.

[0007] The polyethylene composition provided by the present invention has excellent synergistic effects between the components by adding the above-mentioned specific mass parts, so that the product can achieve excellent environmental stress cracking resistance and mechanical properties; specifically, the present invention selects nano silicon carbide whiskers with a specific aspect ratio and a nucleating agent for use in combination, so that a string of crystals can be formed, inserted into the end of the crystal region, and connected to the amorphous region, which can effectively prevent the crystal region from slipping and resist cracking due to external impact, thereby further enhancing the environmental stress cracking resistance of the product on the basis of ensuring the mechanical properties.

[0008] The test method for the average aspect ratio of the nano silicon carbide whiskers is: using a static needle-shaped powder image taken by hand or by software intelligent recognition technology to obtain the long diameter and short diameter data, and then calculating the aspect ratio.

[0009] Preferably, the average aspect ratio of the nano-silicon carbide whiskers is 150.

[0010] Nano-SiC whiskers with appropriate average aspect ratio can help achieve stronger skewers, especially when the average aspect ratio is 150, the overall effect of the obtained product is the best. If the average aspect ratio of the nano-SiC whiskers is too short, the length of the skewers will be insufficient, making it difficult to penetrate into the farther crystal end of the high-density polyethylene resin, thus making it difficult to achieve good impact strength and environmental stress cracking resistance. If the average aspect ratio of the nano-SiC whiskers is too long, it will be difficult to process.

[0011] As a preferred embodiment of the polyethylene composition of the present invention, the nucleating agent is at least one of an α-crystalline nucleating agent and a β-crystalline nucleating agent.

[0012] Preferably, the α-crystal nucleating agent is at least one of an organic carboxylate nucleating agent and a sorbitol nucleating agent.

[0013] Preferably, the β-crystal nucleating agent is at least one of an aromatic amide nucleating agent, a metal oxide, and a hydroxide.

[0014] As a preferred embodiment of the polyethylene composition of the present invention, the nucleating agent is a β-crystalline nucleating agent.

[0015] Preferably, the β-crystal nucleating agent is an aromatic amide nucleating agent.

[0016] The inventors have found that when the preferred nucleating agent is at least one of the above-mentioned α-crystal nucleating agent and β-crystal nucleating agent, the high-density polyethylene resin spherulites can be refined and the crystallization can be more uniform and regular, so that it can be well compounded with nano-silicon carbide whiskers to form string crystals in the later stage; when the preferred nucleating agent is further preferably an aromatic amide nucleating agent among the β-crystal nucleating agents, it can be better compounded with nano-silicon carbide whiskers to form stronger string crystals, thereby achieving a more excellent environmental stress cracking resistance effect.

[0017] As a preferred embodiment of the polyethylene composition of the present invention, the mass ratio of the nucleating agent to the nano-silicon carbide whisker is nucleating agent: nano-silicon carbide whisker=1:(0.2-5).

[0018] Preferably, the mass ratio of the nucleating agent to the nano-silicon carbide whisker is nucleating agent: nano-silicon carbide whisker=1:(1-5).

[0019] Further preferably, the mass ratio of the nucleating agent to the nano-silicon carbide whisker is nucleating agent: nano-silicon carbide whisker=1:1.

[0020] When the mass ratio of the nucleating agent to the nano-silicon carbide whisker is preferably 1:(0.2-5), the composite effect of the two is excellent, especially when the mass ratio of the nucleating agent to the nano-silicon carbide whisker is further preferably 1:(1-5), that is, the mass ratio of the nano-silicon carbide whisker to the nucleating agent is the same as or greater than the nucleating agent, thereby enabling the nano-silicon carbide whisker to play a leading role in the crystal stringing process and form a stronger crystal string; especially when the mass ratio of the two is further preferably 1:1, the composite effect of the two can be optimized.

[0021] As a preferred embodiment of the polyethylene composition of the present invention, the density of the high-density polyethylene resin is 0.94-0.96 g / cm 3 ; The test method for the density of the high-density polyethylene resin refers to the ISO 1183-1-2012 standard.

[0022] As a preferred embodiment of the polyethylene composition of the present invention, at least one of (a) to (c):

[0023] (a) the toughening agent is at least one of styrene-butadiene-styrene block copolymer, low-density polyethylene, and polyolefin elastomer;

[0024] (b) the compatibilizer is an ethylene-propylene block copolymer and / or a polypropylene-based olefin block copolymer;

[0025] (c) The antioxidant is a mixture of hindered phenol and phosphite antioxidants.

[0026] The density of the low-density polyethylene resin is 0.91-0.93 g / cm3 ; The test method for the density of the low-density polyethylene resin refers to the ISO 1183-1-2012 standard.

[0027] Preferably, the toughening agent is styrene-butadiene-styrene block copolymer (SBS).

[0028] The notched impact strength of high-density polyethylene resin itself is relatively low, and the addition of the above-mentioned toughening agent can improve the low-temperature impact resistance of the product; especially when the toughening agent is further preferred to be SBS, the added SBS exists in the HDPE body in the form of dispersed small balls, and HDPE as a continuous phase plays a role in maintaining sufficient strength and rigidity of the blend, while the SBS small balls in the dispersed phase can absorb and disperse external impact energy, hinder the extension of silver streaks, and thus greatly improve the toughness of the material.

[0029] The addition of compatibilizer can increase the branching degree of HDPE, and then cooperate with other components to strengthen the connection between crystals, improve impact resistance, prevent cracks from occurring or further expanding, and enhance the product's resistance to environmental stress cracking.

[0030] Preferably, the antioxidant is a mixture of antioxidant 1010 and antioxidant 168, and the mass ratio of antioxidant 1010 to antioxidant 168 is 1:1.

[0031] In addition, the present invention also provides a method for preparing the polyethylene composition, which comprises the following steps: mixing the raw materials and then melt-extruding them to obtain the polyethylene composition.

[0032] As a preferred embodiment of the preparation method of the present invention, the extrusion parameters are: aspect ratio is (30-50): 1, temperature is 100-190°C, rotation speed is 350-450r / min, and vacuum degree is (-0.04)-(-0.08)MPa.

[0033] In addition, the present invention also provides an application of the polyethylene composition in preparing automobile pipes.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The polyethylene composition provided by the present invention has excellent synergistic effect between the components by adding specific mass parts, so that the product can achieve excellent environmental stress cracking resistance and mechanical properties; specifically, the obtained reaction environmental stress cracking resistance F50 value is above 501h, the tensile strength is above 21.6MPa, and the Izod notched impact strength is above 31KJ / m 2 At the same time, the preparation method of the polyethylene composition provided by the present invention is simple and is conducive to actual production. DETAILED DESCRIPTION

[0036] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0037] The reagents, methods and equipment used in the present invention, unless otherwise specified, are all conventional reagents, methods and equipment in the art; and the components used in the parallel embodiments and comparative examples are consistent unless otherwise specified.

[0038] High-density polyethylene resin (HDPE): HDPE DMD A8008, density 0.95g / cm 3 , Dushanzi Petrochemical;

[0039] Toughener 1: SBS 1401, Yanshan Petrochemical;

[0040] Toughener 2: POE, 7467, Dow Chemical;

[0041] Compatibilizer 1: polypropylene-based olefin block copolymer, D5545, Dow Chemical;

[0042] Compatibilizer 2: ethylene propylene block copolymer, Hifax X1956A, LyondellBasell;

[0043] Compatibilizer 3: maleic anhydride grafted ethylene copolymer, N493, DuPont;

[0044] Nucleating agent 1: aromatic amide β-crystalline nucleating agent, TMB-5, Shanxi Chemical Industry;

[0045] Nucleating agent 2: inorganic salt β nucleating, calcium carbonate AC-05N, Shandong Sanfeng;

[0046] Nucleating agent 3: Organic carboxylate α-crystalline nucleating agent, HPN-68L, Milliken

[0047] Nano silicon carbide whisker 1: SiC-150, average aspect ratio of 150, Yamei Nano;

[0048] Nano silicon carbide whisker 2: SiC-250, average aspect ratio of 250, Yamei Nano;

[0049] Nano silicon carbide whisker 3: SiC-50, average aspect ratio of 50, Yamei nanometer;

[0050] Nano silicon carbide whisker 4: SiC-20, average aspect ratio of 20, Yamei Nano;

[0051] Nano titanium dioxide whiskers: TiO 2 -NW-15, aspect ratio 150, Stellite metal;

[0052] Antioxidant: a mixture of antioxidant 1010 and antioxidant 168 (mass ratio 1:1), commercially available.

[0053] Examples 1-14 and Comparative Examples 1-8

[0054] Examples 1-14 of the present invention and comparative examples 1-8 provide a polyethylene composition, and the component contents of the polyethylene composition are shown in Table 1-2;

[0055] Table 1

[0056]

[0057]

[0058] Table 2

[0059]

[0060] The preparation method of the polyethylene composition in Example 1 is as follows: after mixing the raw materials in a high-speed mixer for 4 minutes, adding them into a twin-screw extruder with a length-to-diameter ratio of 40:1 for melt extrusion, the processing temperatures (from the feed port to the die head) are: 100°C, 150°C, 160°C, 180°C, 180°C, 180°C, 180°C, 180°C, 190°C, 190°C, the main engine speed is 400rpm, the vacuum degree is -0.06MPa, and finally extrusion and pelletization are performed to obtain the polyethylene composition;

[0061] The preparation methods of Examples 2-14 and Comparative Examples 1-8 are consistent with the preparation method in Example 1. If there are no related components, they may not be added.

[0062] Effect example

[0063] This effect example verifies the performance of the polyethylene composition prepared in Examples 1-14 and Comparative Examples 1-8. The specific test performance is:

[0064] (1) Tensile strength: tested in accordance with ISO 527-2-2012, 50 mm / min;

[0065] (2) Izod notched impact strength: according to ISO 180-2000, 4 mm, pendulum impact force 4 J, 23 °C;

[0066] (3) ESCR test: The sample was injection molded into a 200*50*2 mm specimen, and then cut into 150*50*2 mm specimens. The test was performed according to the standard method GB1842-2008. The time F50 (h) for half of the specimens to crack was observed and recorded.

[0067] The test results are shown in Table 3;

[0068] Table 3

[0069]

[0070] It can be seen from Table 3 that the product obtained by adopting the technical solution of the present invention has excellent environmental stress cracking resistance and mechanical properties. Among them, the tensile strength of the obtained product is above 21.6MPa and the Izod beam notched impact strength is above 31KJ / m 2 Above, F50 value is above 501h;

[0071] It can be seen from Examples 1 and 4-5 that the mass ratio of the nucleating agent to the nano-silicon carbide whisker will affect the comprehensive performance of the product. When the mass ratio of the nucleating agent to the nano-silicon carbide whisker is further preferably 1:(1-5), the comprehensive performance of the obtained product is more excellent. Specifically, the tensile strength of the product is above 23.8MPa, and the notched cantilever beam impact strength is above 45KJ / m 2 Above, F50 value is above 580h;

[0072] It can be seen from Example 1 and Example 8, Example 1 and Examples 9-10, and Example 1 and Examples 11-12 that the selection of the types of toughening agent, compatibilizer and nucleating agent will also affect the performance of the product. When the toughening agent is preferably SBS, the compatibilizer is preferably a polypropylene-based olefin block copolymer, and the nucleating agent is preferably an aromatic amide β-crystalline nucleating agent, the comprehensive performance of the obtained product is better;

[0073] It can be seen from Example 1, Examples 13-14 and Comparative Example 6 that the aspect ratio of the nano-silicon carbide whisker will also have a significant impact on the performance of the product. Only when the aspect ratio is 50-250, the comprehensive performance of the obtained product is better. Specifically, the tensile strength of the product is above 21.6MPa and the notched impact strength of the cantilever beam is above 32KJ / m 2 Above, when the F50 value is above 538h, especially when the aspect ratio is further preferably 150, the comprehensive performance is the best;

[0074] It can be seen from Example 1, Examples 6-7 and Comparative Examples 7-8 that the amount of nano-silicon carbide whiskers added will also have a significant impact on the performance of the product. Only when the amount of nano-silicon carbide whiskers added is within the scope of the present invention can an excellent comprehensive effect be guaranteed;

[0075] It can be seen from Example 1 and Comparative Example 1 that when no nano-silicon carbide whiskers are added, the environmental stress cracking resistance of the obtained product decreases significantly. Compared with Example 1, the F50 value decreases by 26.23%, and the mechanical properties also show a significant downward trend; it can be seen from Example 1 and Comparative Example 2 that when no nucleating agent is added, the environmental stress cracking resistance and mechanical properties of the obtained product also show a significant downward trend. Compared with Example 1, the F50 value decreases by 21.31%, the tensile strength decreases by 13.22%, and the Izod notched impact strength decreases by 32.65%; it can be seen from Example 1 and Comparative Example 3 that when no compatibilizer is added, the environmental stress cracking resistance and mechanical properties of the obtained product also show a significant downward trend. Compared with Example 1, the F50 value decreases by 32.79%, the tensile strength decreases by 6.61%, and the Izod notched impact strength decreases by 51.02%; from Example 1 and Comparative Example 4 It can be seen that when no compatibilizer, nucleating agent and nano-silicon carbide whisker are added, the environmental stress cracking resistance and mechanical properties of the obtained product also show a sharp downward trend. Compared with Example 1, the F50 value decreases by 65.57%, the tensile strength decreases by 12.40%, and the Izod notched impact strength decreases by 63.27%; it can be seen from Example 1 and Comparative Example 5 that when nano-calcium hydroxide whiskers are used instead of nano-silicon carbide whiskers, the Izod notched impact strength and environmental stress cracking resistance of the obtained product are significantly reduced, especially the environmental stress cracking resistance, which decreases by 47.54% and the Izod notched impact strength decreases by 48.98% compared with Example 1; it can be seen from Example 1 and Comparative Example 6 that when the aspect ratio of the nano-silicon carbide whiskers used is too short, the characteristics of improving the environmental stress cracking resistance and mechanical properties of the product cannot be achieved, and the F50 value of the obtained product is less than 500h, which is 37.70% lower than that of Example 1.

[0076] Finally, it should be noted that the above embodiments are intended to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A polyethylene composition, It is characterized in that The polyethylene composition comprises the following raw materials in parts by weight: 60-90 parts of high-density polyethylene resin, 5-35 parts of toughening agent, 2-8 parts of compatibilizer, 0.1-0.5 parts of nucleating agent, 0.1-0.3 parts of nano silicon carbide whisker, and 0.2-0.8 parts of antioxidant; The average aspect ratio of the nano silicon carbide whiskers is 50-250.

2. The polyethylene composition according to claim 1, It is characterized in that The nucleating agent is at least one of an α-crystal nucleating agent and a β-crystal nucleating agent.

3. The polyethylene composition according to claim 1, It is characterized in that The nucleating agent is a β-crystal nucleating agent.

4. The polyethylene composition according to claim 1, It is characterized in that The mass ratio of the nucleating agent to the nano-silicon carbide whisker is nucleating agent: nano-silicon carbide whisker=1:(0.2-5).

5. The polyethylene composition according to claim 1, It is characterized in that The density of the high-density polyethylene resin is 0.94-0.96 g / cm 3 .

6. The polyethylene composition according to claim 1, It is characterized in that At least one of (a)-(c): (a) The toughening agent is at least one of styrene-butadiene-styrene block copolymer, low-density polyethylene, and polyolefin elastomer (b) the compatibilizer is a propylene-based olefin block copolymer; (c) The antioxidant is a mixture of hindered phenol and phosphite antioxidants.

7. The polyethylene composition according to claim 6, It is characterized in that The density of the low-density polyethylene resin is 0.91-0.93 g / cm 3 .

8. A method for preparing a polyethylene composition according to any one of claims 1 to 7, It is characterized in that The preparation method comprises the following steps: mixing raw materials and then melt-extruding them to obtain a polyethylene composition.

9. The preparation method according to claim 8, It is characterized in that The extrusion parameters are: aspect ratio (30-50): 1, temperature (100-190°C), rotation speed (350-450r / min), and vacuum degree (-0.04)-(-0.08)MPa.

10. Use of the polyethylene composition according to any one of claims 1 to 7 in the preparation of automobile pipes.

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