A rotomolded polyethylene composite powder for vehicle compressed natural gas wrapping bottles and its preparation method

Abstract

The present invention relates to the field of polymer composite materials. In order to solve the problem of poor rotational molding of high-density polyethylene gas cylinders, a rotational molding polyethylene composite powder for a compressed natural gas wrapped bottle for a vehicle and a preparation method thereof are provided. The composition of the composite powder is as follows: HDPE 70-82%, high-branched polyolefin 15-35%, antioxidant 0.1-0.5%, light stabilizer 0.05-0.2%, and processing aid 0.1-0.4%. The present invention adds high-branched polyolefin and regulates the content of each component, so that the polyethylene composite powder has the advantages of high yield rate, low-temperature toughness and small shrinkage when used for rotational molding of gas cylinders. The present invention also provides a method for preparing the composite powder, wherein the components are weighed according to a ratio and then mixed uniformly to obtain a mixture; then the mixture is added to a twin-screw extruder for melt extrusion, material making, and powder grinding to obtain the rotational molding polyethylene composite powder.

Description

Technical Field

[0001] The present invention relates to the field of polymer composite materials, in particular to a roto-molded polyethylene composite powder for a vehicle compressed natural gas wrapping bottle and a preparation method thereof. Background Art

[0002] The use of natural gas as a clean fuel in automobiles can significantly improve the emission performance of automobiles. Under the active promotion of relevant national policies, taxis and buses in large and medium-sized cities in China have basically achieved the full use of compressed natural gas as fuel. Seamless steel gas cylinders as gas fuel containers have perfect manufacturing processes and performance, but are relatively heavy, which limits their development in automobiles. In order to improve the volume-to-weight ratio of gas cylinders and reduce the weight of gas cylinders of the same volume, research on composite gas cylinders with different liners has been conducted at home and abroad. At present, large-scale commercial natural gas containers for vehicles at home and abroad (50-400L) generally use plastic liners and full fiber winding reinforced composite materials. Among them, the preparation of plastic liners (inner liner) generally adopts rotational molding process.

[0003] Rotomolding, also known as rotational molding or rotational molding, is a method for hollow molding thermoplastics. This method involves first adding plastic powder into a mold, which is then continuously rotated along two perpendicular axes and heated, gradually and evenly coated, melted, and adhered to the entire surface of the mold cavity, forming it into the desired shape, and then cooled and shaped to form the product. Currently, the inner liner of a fully plastic vehicle compressed natural gas cylinder is mainly rotomolded from high-density polyethylene (HDPE) powder. For example, patent CN106893175A discloses a masterbatch containing high-density polyethylene for rotomolded products. Although HDPE material has high density, high modulus, and good impermeability, it has the following main problems in the application of cylinder liners: poor rotomolding of cylinders, the bottle body will show obvious deformation or even collapse, and the yield rate is low; the material has poor low-temperature toughness; the cylinder shrinkage rate is large, and the HDPE cylinder liner will warp and deform. Therefore, an ideal solution is needed. Summary of the Invention

[0004] In order to overcome the above technical problems, the present invention provides a roto-molded polyethylene composite powder for wrapped compressed natural gas cylinders for vehicles, which has the advantages of high yield of roto-molding of cylinders, low low-temperature toughness and low shrinkage.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A rotomolded polyethylene composite powder for a compressed natural gas wrap bottle for a vehicle, the composition and weight percentage of the composite powder are as follows: HDPE 70-82%

[0007] Highly branched polyolefins 15-35%

[0008] Antioxidant 0.1-0.5%

[0009] Light stabilizer 0.05-0.2%

[0010] Processing aids 0.1-0.4%;

[0011] The sum of the weight percentages of each component is 100%.

[0012] The present invention adds high-branched polyolefin, antioxidant, light stabilizer and processing aid to HDPE, and regulates the content of each component, so that the polyethylene composite powder has the advantages of high yield of gas cylinder rotational molding, low temperature toughness and small shrinkage when used for rotational molding.

[0013] Preferably, the density of the HDPE is 0.950-0.970 g / cm 3 .

[0014] Preferably, the HDPE has a melt index of 5-10 g / 10 min, measured under test conditions of 190° C. and 2.16 kg.

[0015] Preferably, the highly branched polyolefin is one or more of low-density polyethylene (LDPE), ultra-low-density polyethylene (ULDPE), polyolefin elastomer (POE) and metallocene low-density polyolefin; further preferably, it is ethylene-butene copolymer ultra-low-density polyethylene, ethylene-octene copolymer elastomer, ethylene-hexene copolymer elastomer, ethylene-butene copolymer elastomer or ethylene-octene block copolymer elastomer.

[0016] The highly branched polyolefin has a branching degree greater than 15N / 1000C and a melt index less than 6g / 10min; more preferably, the branching degree is 30N / 1000C-45N / 1000C and the melt index is 0.5-5.5g / 10min.

[0017] Preferably, the modulus ratio of the highly branched polyolefin to HDPE is less than 0.06, more preferably 0.005-0.05.

[0018] The present invention uses a blend of highly branched polyolefins and HDPE to achieve the toughening of HDPE while solving the problem of warping and deformation of HDPE rollers. The principle is analyzed as follows: After the HDPE powder is heated and melted in a rotational molding machine, it is removed from the heating furnace and cooled by air or natural cooling. The temperature of the metal mold drops rapidly from 200-280°C, causing the mold surface material where the roller contacts the mold to drop sharply in temperature, resulting in insufficient crystallization. However, the air surface where the roller contacts the air can be completely crystallized due to the slower cooling. Generally, the temperature at which the roller leaves the mold is 80-110°C. After the roller leaves the mold, the insufficiently crystallized mold surface in the roller will continue to crystallize, causing the roller mold surface to shrink, ultimately causing the entire roller to warp. On the other hand, HDPE has good compatibility with polyolefins, but as the degree of branching of the polyolefin increases, its compatibility with highly branched polyolefins decreases, resulting in a blend with a viscosity greater than that of the pure polymer. The present invention has discovered that utilizing this phenomenon can effectively increase the viscosity of HDPE blends, reduce the crystallization rate of HDPE, and minimize the difference in crystallization rates between the roller mold surface and the air surface. Simultaneously, the interfacial tension generated by the low compatibility can, to a certain extent, synergistically regulate the stress generated during crystallization, thereby reducing the degree of warping deformation, or even eliminating the occurrence of warping deformation. Of course, achieving the above objectives requires defining key properties such as the melt index ratio and degree of branching of HDPE and highly branched polyolefins.

[0019] Preferably, the antioxidant is a compound of a hindered phenol antioxidant and a phosphite antioxidant; further preferably, it is tetrakis[β-(3.5-di-tert-butyl, 4-hydroxyphenyl) propionate] pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, dioctadecyl pentaerythritol bisphosphite, and tris(2.4-di-tert-butylphenyl) phosphite.

[0020] Preferably, the light stabilizer is a benzotriazole, benzophenone or triazine ultraviolet light absorber; more preferably, it is 2'-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2H-benzotriazole-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol, and 2-hydroxy-4-n-octyloxybenzophenone.

[0021] Preferably, the processing aid is one or more of low molecular polyethylene wax, fatty acid esters, fatty acid amides and organosilicon compounds; more preferably, it is one or more of low molecular polyethylene wax, zinc stearate, calcium stearate, erucamide and silicone powder.

[0022] The present invention also provides a method for preparing the rotomolded polyethylene composite powder, comprising weighing the components according to a ratio and uniformly mixing them to obtain a mixture; then adding the mixture into a twin-screw extruder for melt extrusion, material preparation, and powder grinding to obtain the rotomolded polyethylene composite powder.

[0023] Preferably, the aspect ratio of the twin-screw extruder is 30-40:1, the extrusion temperature is 150-220°C, and the screw speed is 300-500 rpm; and / or the particle size of the powder after grinding is less than 30 mesh, and the proportion of particles less than 100 mesh is less than 20%.

[0024] Therefore, the beneficial effects of the present invention are as follows: by rationally selecting additives and regulating the dosage of the additives, the degree of warping deformation of the rotationally molded polyethylene composite powder of the present invention is significantly reduced when used for wrapped compressed natural gas bottles for vehicles, the yield rate of the rotationally molded gas cylinders is greater than 85%, the low-temperature tensile elongation at -55°C is greater than 20%, and the shrinkage rate of the gas cylinders is less than 3%, meeting the requirements of high rotationally molded gas cylinder yield, low-temperature toughness and low shrinkage. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below through specific embodiments.

[0026] In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the embodiments, unless otherwise specified, are all conventional methods in the art.

[0027] Overall embodiment

[0028] A rotomolded polyethylene compound powder for wrapping compressed natural gas bottles for vehicles, the composition and weight percentage of each component are as follows: HDPE 70-82%

[0029] Highly branched polyolefins 15-35%

[0030] Antioxidant 0.1-0.5%

[0031] Light stabilizer 0.05-0.2%

[0032] Processing aids 0.1-0.4%;

[0033] The sum of the weight percentages of each component is 100%.

[0034] The density of the HDPE is 0.950-0.970 g / cm 3 , the melt index is 5-10g / 10min.

[0035] The highly branched polyolefin is one or more of low-density polyethylene, ultra-low-density polyethylene, polyolefin elastomer or metallocene low-density polyolefin; the branching degree of the highly branched polyolefin is greater than 15N / 1000C and the melt index is less than 6g / 10min.

[0036] The modulus ratio of the highly branched polyolefin to HDPE is less than 0.06.

[0037] The antioxidant is a compound of a hindered phenol antioxidant and a phosphite antioxidant; the light stabilizer is a benzotriazole, benzophenone or triazine ultraviolet light absorber; and the processing aid is one or more of low molecular polyethylene wax, fatty acid esters, fatty acid amides or organosilicon compounds.

[0038] The present invention also provides a method for preparing the rotomolded polyethylene composite powder, comprising weighing the components according to a proportion and uniformly mixing them to obtain a mixture; then adding the mixture to a twin-screw extruder with a length-to-diameter ratio of 30-40:1 and a screw speed of 300-500 rpm, performing melt extrusion at 150-220° C., preparing materials, and grinding powder to obtain the rotomolded polyethylene composite powder, wherein the particle size of the powder is less than 30 mesh, and the content less than 100 mesh is less than 20%.

[0039] Example 1

[0040] A rotomolded polyethylene composite powder for wrap-around compressed natural gas bottles for vehicles has the following composition and weight percentage of each component: 72.5% HDPE, 27.0% highly branched polyolefin, 0.3% antioxidant, 0.1% light stabilizer, and 0.1% processing aid.

[0041] The HDPE is KT10000 high-density polyethylene (density 0.964 g / cm 3 The highly branched polyolefin is Sinopec Tianjin Petrochemical 0505 (ethylene-butene copolymer ultra-low density polyethylene, with a branching degree of 19 N / 1000C and a melt index of 0.7 g / 10 min). The modulus ratio of the highly branched polyolefin to HDPE is 0.03. The antioxidant is a mixture of SI Group AT-10 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl, 4-hydroxyphenyl) propionate) and AT-168 (tris(2,4-di-tert-butylphenyl) phosphite) in a mass ratio of 1:2. The light stabilizer is BASF Tinuvin 326 (2'-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole). The processing aid is zinc stearate.

[0042] The preparation method of the rotomolded polyethylene composite powder comprises the following steps: weighing the components according to a proportion and uniformly mixing them to obtain a mixture; then adding the mixture to a twin-screw extruder with a length-to-diameter ratio of 35:1 and a screw speed of 350 rpm, performing melt extrusion at 200° C., preparing the material, and grinding the powder to obtain the rotomolded polyethylene composite powder, wherein the particle size of the powder is less than 30 mesh, and the proportion of the powder less than 100 mesh is less than 20%.

[0043] Example 2

[0044] A rotomolded polyethylene composite powder for wrap-around compressed natural gas bottles for vehicles has the following composition and weight percentage of each component: 72.5% HDPE, 27.0% highly branched polyolefin, 0.3% antioxidant, 0.1% light stabilizer, and 0.1% processing aid.

[0045] The HDPE is KT10000 high-density polyethylene (density 0.964 g / cm 3 , melt index 8g / 10min). The highly branched polyolefin is Dow Chemical's ENGAGE 8200 (ethylene-octene copolymer elastomer, branching degree 41N / 1000C, melt index 5g / 10min). The modulus ratio of the highly branched polyolefin to HDPE is 0.007. The antioxidant is a mixture of SI Group AT-10 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl, 4-hydroxyphenyl) propionate) and AT-168 (tris(2,4-di-tert-butylphenyl) phosphite) in a mass ratio of 1:2. The light stabilizer is BASF's Tinuvin 326 (2'-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole). The processing aid is zinc stearate.

[0046] The preparation method of the rotomolded polyethylene composite powder comprises the following steps: weighing the components according to a proportion and uniformly mixing them to obtain a mixture; then adding the mixture to a twin-screw extruder with a length-to-diameter ratio of 35:1 and a screw speed of 350 rpm, performing melt extrusion at 200° C., preparing the material, and grinding the powder to obtain the rotomolded polyethylene composite powder, wherein the particle size of the powder is less than 30 mesh, and the proportion of the powder less than 100 mesh is less than 20%.

[0047] Example 3

[0048] The difference from Example 1 is that the HDPE is 7260 high-density polyethylene (density 0.960 g / cm 3 , melt index 7.5g / 10min); the modulus ratio of highly branched polyolefin to HDPE is 0.04.

[0049] Example 4

[0050] A rotomolded polyethylene composite powder for wrap-around compressed natural gas bottles for vehicles has the following composition and weight percentage of each component: 82% HDPE, 17% highly branched polyolefin, 0.4% antioxidant, 0.2% light stabilizer, and 0.4% processing aid.

[0051] The HDPE density is 0.950 g / cm 3 , melt index of 10 g / 10 min. The highly branched polyolefin is a metallocene low-density polyolefin (branching degree 45 N / 1000C, melt index 0.2 g / 10 min). The modulus ratio of the highly branched polyolefin to HDPE is 0.06. The antioxidant is 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione. The light stabilizer is 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol. The processing aid is erucamide.

[0052] The preparation method of the rotomolded polyethylene composite powder is the same as that in Example 1.

[0053] Comparative Example 1

[0054] The difference from Example 2 is that the branching degree of the highly branched polyolefin is 38N / 1000C and the melt index is 8g / 10min.

[0055] Comparative Example 2

[0056] The difference from Example 2 is that the density of HDPE is 0.965 g / cm 3 , the melt index is 4g / 10min; the modulus ratio of high-branched polyolefin to HDPE is 0.006.

[0057] Comparative Example 3

[0058] The difference from Example 2 is that the density of HDPE is 0.963 g / cm 3 , the melt index is 15g / 10min; the modulus ratio of high-branched polyolefin to HDPE is 0.008.

[0059] Comparative Example 4

[0060] The difference from Example 2 is that the highly branched polyolefin is Exxon EXCEED3812 (ethylene-hexene copolymer, branching degree 13N / 1000C, melt index 3.8g / 10min) from the United States; and the modulus ratio of the highly branched polyolefin to HDPE is 0.08.

[0061] Performance Characterization

[0062] Performance tests were conducted on the rotomolded polyethylene composite powders from each example and comparative example. The processing conditions for a 220L rotomolded gas cylinder were as follows: 20kg feed, 290°C furnace temperature, 10 rpm main spindle speed, 1.5 rpm secondary spindle speed, 205°C maximum mold temperature, 150 seconds of natural cooling, and 1500 seconds of air cooling. Cylinder shrinkage refers to the percentage reduction in the straight-cut length of the cylinder compared to the corresponding mold length; head runout refers to the maximum deviation between the cylinder head and the mold.

[0063] Table 1.

[0064]

[0065] The rotational molding yield of the gas cylinder of the present invention is greater than 85%. As can be seen from Table 1, the low-temperature tensile elongation at -55°C is greater than 20%, and the shrinkage of the gas cylinder is less than 3%.

[0066] Table 2.

[0067]

[0068] The anti-warping deformation performance of the rotational molding polyethylene composite powder was further studied, and the results are shown in Table 2. Compared with Example 2: ① In Comparative Examples 1 and 3, the melt index of the highly branched polyolefin or HDPE increased, which reduced the viscosity of the polymer blend, and the crystallization rate of HDPE could not be effectively suppressed, resulting in a decrease in the effect of reducing warping deformation. ② In Comparative Example 2, the melt index of HDPE decreased, which made the viscosity of the polymer blend too high, making it difficult for the material to level during rotational molding and making the warping deformation more difficult to control. ③ In Comparative Example 4, the branching degree of the highly branched polyolefin was low, and the compatibility with HDPE decreased only slightly, resulting in a small interfacial tension, so the anti-warping deformation performance was not as good as that of Example 2.

[0069] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A rotomolded polyethylene composite powder for wrap-around compressed natural gas bottles for vehicles, characterized in that: The composition of the composite powder and the weight percentage of each component are as follows: HDPE 70-82% Highly branched polyolefins 15-35% Antioxidant 0.1-0.5% Light stabilizer 0.05-0.2% Processing aids 0.1-0.4%; The sum of the weight percentages of each component is 100%; the density of the HDPE is 0.950-0.964 g / cm 3 , a melt index of 7.5-10 g / 10 min, measured under test conditions of 190°C and 2.16 kg; the degree of branching of the highly branched polyolefin is 19N / 1000C-45N / 1000C, and the melt index is 0.2 g / 10min-5 g / 10min; the highly branched polyolefin is one or more of low-density polyethylene, ultra-low-density polyethylene, polyolefin elastomer and metallocene low-density polyolefin.

2. The rotomolded polyethylene compound powder according to claim 1, characterized in that The density of the HDPE is 0.960-0.964 g / cm 3 .

3. The rotomolded polyethylene compound powder according to claim 1 or 2, characterized in that The melt index of the HDPE is 8-10 g / 10 min.

4. The rotomolded polyethylene compound powder according to claim 1, characterized in that The highly branched polyolefin is ethylene-butene copolymer ultra-low density polyethylene, ethylene-octene copolymer elastomer, ethylene-hexene copolymer elastomer, ethylene-butene copolymer elastomer or ethylene-octene block copolymer elastomer.

5. The rotomolded polyethylene compound powder according to claim 1 or 4, characterized in that The highly branched polyolefin has a branching degree of 30N / 1000C-45N / 1000C and a melt index of 0.7-5g / 10min.

6. The rotomolded polyethylene compound powder according to claim 1, characterized in that The antioxidant is a compound of a hindered phenol antioxidant and a phosphite antioxidant.

7. The rotomolded polyethylene compound powder according to claim 1, characterized in that The light stabilizer is a benzotriazole, benzophenone or triazine ultraviolet light absorber.

8. The rotomolded polyethylene compound powder according to claim 1 or 7, characterized in that The processing aid is one or more of low molecular weight polyethylene wax, fatty acid esters, fatty acid amides and organosilicon compounds.

9. A method for preparing rotomolded polyethylene composite powder, characterized in that: The preparation of the rotomolded polyethylene composite powder according to any one of claims 1 to 8 comprises the following steps: weighing the components according to a ratio and mixing them evenly to obtain a mixture; then adding the mixture into a twin-screw extruder for melt extrusion, material preparation, and powder grinding to obtain the rotomolded polyethylene composite powder.

10. The preparation method according to claim 9, wherein The length-to-diameter ratio of the twin-screw extruder is 30-40:1, the extrusion temperature is 150-220°C, and the screw speed is 300-500 rpm.

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