Polyethylene composite material as well as preparation method and application thereof

Abstract

The invention discloses a polyethylene composite material as well as a preparation method and application thereof, and belongs to the technical field of high polymer materials. The polyethylene composite material is prepared from the following components in parts by weight: 60 to 80 parts of bimodal high-density polyethylene, 2 to 5 parts of modified nano silicon dioxide, 6 to 15 parts of a modified ethylene-octene copolymer, 0.15 to 0.45 part of a composite antioxidant, 0.2 to 0.5 part of a light stabilizer, 0.5 to 1.5 parts of a composite lubricant and 0.05 to 0.1 part of a beta crystal form nucleating agent. The polyethylene composite material which is high in pressure resistance, long in service life and high in sag resistance is provided, so that the polyethylene composite material can be well suitable for high-pressure application scenes such as municipal water supply and drainage, fuel gas conveying and industrial pipelines when being used as a pipe.

Description

Technical Field

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

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] High-density polyethylene (HDPE) is a highly crystalline, non-polar thermoplastic resin. Polyethylene pipes are increasingly being used in gas transmission, water supply, sewage disposal, heating, agricultural irrigation, and transportation of fine-grained solids in mines. However, polyethylene pipes still have the following problems: (1) Insufficient long-term hydrostatic strength: The long-term hydrostatic strength (LTHS) of conventional HDPE pipes at a design life of 50 years is less than 8.0 MPa, which cannot meet the requirements of ultra-high-pressure gas transmission; (2) Poor slow crack growth (SCG) resistance: The SCG life of conventional materials in the notch test is less than 500 h (ISO 13479 standard), which makes the pipes prone to brittle failure under soil stress; (3) Defective anti-sag performance: Low melt strength during extrusion molding and uneven pipe wall thickness affect the pressure bearing capacity; (4) Inconsistency between processing performance and mechanical properties: Although the processability is good, the impact strength is reduced.

[0004] Therefore, how to provide a high-density polyethylene (HDPE) pipe with high pressure resistance, long life and high anti-sag performance is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] In order to address the shortcomings of the prior art, the purpose of the present invention is to provide a polyethylene composite material, a preparation method and application thereof. The present invention provides a polyethylene composite material with high pressure resistance, long life and high anti-sag performance through multi-scale structural design and synergistic enhancement mechanism, coupled with the optimization of processing performance, so that it can be used in high-pressure application scenarios such as municipal water supply and drainage, gas transportation, and industrial pipelines.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] In a first aspect, the present invention provides a polyethylene composite material comprising the following parts by weight: 60-80 parts of bimodal high-density polyethylene, 2-5 parts of modified nano-silica, 6-15 parts of modified ethylene-octene copolymer, 0.15-0.45 parts of composite antioxidant, 0.2-0.5 parts of light stabilizer, 0.5-1.5 parts of composite lubricant, and 0.05-0.1 parts of β-crystal nucleating agent.

[0008] Preferably, the composition comprises 65-75 parts of bimodal high density polyethylene, 3-4 parts of modified nano-silica, 8-12 parts of modified ethylene-octene copolymer, 0.35-0.45 parts of composite antioxidant, 0.25-0.35 parts of light stabilizer, 0.8-1.2 parts of composite lubricant and 0.07-0.09 parts of β-crystal nucleating agent.

[0009] In one or more embodiments, due to the high surface activity, polarity, and easy agglomeration of nano-silica, surface modification (e.g., using a silane coupling agent) is required to improve compatibility with the non-polar ethylene-octene copolymer (POE). Therefore, the modified nano-silica is modified with a titanate coupling agent. The titanate coupling agent-modified layer (thickness 3-5 nm) is provided.

[0010] The structure of modified nano-silica consists of unmodified original nano-silica (SiO2) as the core, and a coating formed on the surface of the nano-SiO2 by a titanate coupling agent through a chemical reaction (such as hydrolysis and condensation) as the shell. The modified nano-silica is referred to as "modified nano-silica," or "core-shell structured particles" (SiO2@titanate).

[0011] The mass ratio of nano-silica to titanate coupling agent is 1:0.5-1:2.

[0012] The particle size of the nano-silicon dioxide is 10-200 nm, preferably 10-50 nm.

[0013] In one or more embodiments, the bimodal high-density polyethylene (HDPE) comprises low molecular weight HDPE and high molecular weight HDPE. The low molecular weight HDPE has an Mw of 50,000-80,000, and the high molecular weight HDPE has an Mw of 300,000-500,000. The low molecular weight HDPE accounts for 40-60% of the mass of the bimodal high-density polyethylene. The molecular weight distribution index (PDI) of the bimodal high-density polyethylene is controlled within a range of 15-25.

[0014] The bimodal high-density polyethylene molecular weight distribution achieves "hardness and flexibility", in which the low molecular weight chain segments promote processing fluidity and the ultra-high molecular weight chains form a physical cross-linked network.

[0015] In one or more embodiments, the modified ethylene-octene copolymer is grafted with maleic anhydride to enhance the interfacial bonding between the modified nano-SiO2 and the POE segments and promote stress transfer, wherein the maleic anhydride grafting rate is controlled at 0.8-1.2 wt%.

[0016] In one or more embodiments, the composite antioxidant includes 0.1-0.3 parts of a main antioxidant and 0.05-0.15 parts of an auxiliary antioxidant. Wherein, the main antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and the auxiliary antioxidant is tris(2,4-di-tert-butylphenyl) phosphite. The composite antioxidant significantly improves the processing stability and long-term durability of polyethylene pipes through a main-auxiliary synergistic mechanism, and is a core additive to ensure its 50-year service life. Under a reasonable ratio, cost and performance can be balanced to avoid mechanical failure or appearance defects caused by oxidation. It is recommended to select an appropriate antioxidant system according to the pipe application scenario (such as underground, open air, water / gas transmission), and optimize the addition amount through experiments.

[0017] In one or more embodiments, the light stabilizer is a hindered amine light stabilizer (HALS-622).

[0018] In one or more embodiments, the composite lubricant is a calcium stearate / oxidized polyethylene wax composite lubricant. The oxidized polyethylene wax serves as the primary lubricant, while the calcium stearate serves as the secondary lubricant. The combined use of the two exhibits a significant synergistic effect. The composite lubricant comprises 0.3-0.6 parts of the oxidized polyethylene wax and 0.2-0.6 parts of the calcium stearate.

[0019] The composite lubricant is prepared by melt blending in a twin-screw extruder. The melt temperature is 160-180°C, the shear rate is 200-500 rpm to ensure uniform dispersion, and the mixing time is 5-10 minutes. The specific steps are: heating oxidized polyethylene wax to a molten state, gradually adding calcium stearate, and mixing at high shear speed, followed by cooling and granulation to obtain composite lubricant particles.

[0020] The addition of the composite lubricant can reduce the extrusion pressure by 20-30% during processing, control the sag rate within 3%, and achieve a melt strength of 330-350.

[0021] In one or more embodiments, the β-crystal nucleating agent is a sodium benzoate / pimelic acid composite system, wherein the mass ratio of sodium benzoate / pimelic acid is 1-2: 1. The β-crystal nucleating agent is obtained by dry mixing.

[0022] The β-crystal nucleating agent of the sodium benzoate / pimelic acid composite system can make the crystallinity of the material reach more than 75% and increase the chip thickness to 20-25nm.

[0023] In a second aspect, the present invention provides a method for preparing the above-mentioned polyethylene composite material, comprising the following steps:

[0024] Modified nano-silica and modified ethylene-octene copolymer are subjected to banburying and blending to obtain a compound system, which is dried and then mixed with bimodal high-density polyethylene, a composite antioxidant, a light stabilizer, and a β-crystal nucleating agent, melt-mixed, and an ultrasonic field is introduced into the mixing section, followed by post-treatment to obtain the polyethylene composite material.

[0025] In one or more embodiments, during the banburying blending, the blending temperature is 150-160° C., the rotation speed is 50-100 rpm, and the blending time is 5-10 min.

[0026] In one or more embodiments, the melt mixing is performed using a twin-screw extruder, the aspect ratio of the screw in the twin-screw extruder is 30-40, the temperature of zone 1 is 160-170°C, zone 2 is 175-180°C, zone 3 is 190-200°C, and the rotation speed is 200-500rpm.

[0027] In one or more embodiments, the ultrasonic field has a frequency of 20-40 kHz and a power of 150-300 W. Introducing the ultrasonic field in the mixing stage can make the dispersion more uniform and can also induce the formation of an oriented crystal structure, greatly improving the hoop tensile strength.

[0028] In one or more embodiments, the post-treatment is as follows: after the melt is pelletized by water ring, it is crystallized and annealed under nitrogen protection, the annealing temperature is 90-100° C., and the annealing time is 2-4 hours.

[0029] In a third aspect, the present invention provides the use of the above-mentioned polyethylene composite material in the preparation of drainage, gas transmission and industrial pipelines.

[0030] In a fourth aspect, the present invention provides a pipe comprising the above-mentioned polyethylene composite material.

[0031] One or more of the above technical solutions have the following advantages or beneficial effects:

[0032] (1) The present invention uses bimodal high-density polyethylene as a base resin system, modified nano-silica as a nano-reinforcement phase, and modified ethylene-octene copolymer as a nano-toughening phase. The modified nano-silica and modified ethylene-octene copolymer form a "core-shell structure" that is uniformly distributed in the bimodal high-density polyethylene matrix, thereby achieving a synergistic strengthening and toughening effect; and then adds a processing aid system such as a composite antioxidant, a light stabilizer, a composite lubricant, and a β-crystal nucleating agent to form a polyethylene composite material with high pressure resistance, long life, and high anti-sag performance.

[0033] (2) In the present invention, the surface hydroxylated SiO2 is modified by using a titanate coupling agent to form a "core-shell" structure distributed in a bimodal high-density polyethylene matrix; the modified SiO2 surface and the POE molecular chain form a strong interface through physical entanglement or chemical bonding, thereby enhancing the stress transfer efficiency; when the SiO2 addition reaches a critical concentration (percolation threshold), the distance between the particles is reduced, and a continuous "bridge" network is formed through van der Waals forces or mechanical interlocking, significantly improving the mechanical properties of the material (such as strength and toughness); and the shear force or post-treatment (such as annealing) during processing further strengthens the bridge connection, thereby forming an "island-bridge" structure in the SiO2 / POE system.

[0034] (3) The “core-shell” structure achieves nanoparticle functionalization through chemical bonding, while the “island-bridge” structure synergistically optimizes the mechanical transmission path through the multiphase interface. The combination of the two not only solves the problem of nanofiller dispersion, but also gives the polyethylene composite material excellent comprehensive performance through a multi-level design of rigid-flexible-toughness, which has significant technological advancement and commercial potential. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0036] Example 1

[0037] 1. Raw material ratio:

[0038] 72 parts of bimodal high-density polyethylene (40% of low molecular weight HDPE with Mw = 60,000 and 60% of high molecular weight HDPE with Mw = 400,000), 4 parts of modified nano-silica, 10 parts of modified ethylene-octene copolymer, composite antioxidant including 0.3 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and 0.1 parts of tris(2,4-di-tert-butylphenyl) phosphite, 0.3 parts of light stabilizer, composite lubricant including 0.4 parts of calcium stearate and 0.6 parts of oxidized polyethylene wax, 0.08 parts of β-crystal nucleating agent (the mass ratio of sodium benzoate / pimelic acid is 2:1).

[0039] 2. Preparation process:

[0040] (1) The modified nano-silica and the modified ethylene-octene copolymer were mixed by kneading to obtain a compound system at a mixing temperature of 160°C, a rotation speed of 50 rpm, and a mixing time of 8 min.

[0041] (2) The obtained composite system was dried at 60°C and mixed with bimodal high-density polyethylene, composite antioxidant, light stabilizer, and β-crystal nucleating agent in a high-speed mixer, and then fed into a twin-screw extruder with L / D = 40, zone 1 temperature of 160°C, zone 2 of 175°C, zone 3 of 190°C, and a rotation speed of 200 rpm. An ultrasonic field (frequency 28 kHz, power 200 W) was introduced into the mixing section.

[0042] (3) After melt extrusion, the product was pelletized by water ring cutting and then crystallized and annealed under nitrogen protection (90°C, 4h). The extrusion speed was 2.5m / min.

[0043] When the composite material of Example 1 is used to prepare a pipe, the ovality of the pipe is ≤2% (good processing performance); the hoop stress creep resistance is improved by 50%, the burst pressure at 80°C for 10,000 hours reaches 6.5 MPa, and the low-temperature (-40°C) impact strength retention rate is >85% (good mechanical properties); the tensile strength retention rate after 3,000 hours of xenon lamp testing is 92%, and the 50-year failure probability calculated based on the Palmgren-Miner theory is <0.1% (long life).

[0044] Example 2

[0045] The difference from Example 1 is that 2 parts of modified nano-silica are used.

[0046] Comparative Example 1:

[0047] Different from Example 1, no ultrasonic field is introduced in step (2).

[0048] Comparative Example 2:

[0049] The difference from Example 1 is that the bimodal high-density polyethylene is replaced by ordinary unimodal high-density polyethylene (high molecular weight HDPE, Mw=400,000).

[0050] Comparative Example 3

[0051] The difference from Example 1 is that 0.5 parts of modified nano-silica is used.

[0052] Comparative Example 4

[0053] The difference from Example 1 is that 10 parts of modified nano-silicon dioxide are used.

[0054] The materials obtained in Examples 1-2 and Comparative Examples 1-4 were tested according to ISO 1133 for melt flow rate, ISO 527-2 for tensile strength, ISO 179 for notched impact strength, ISO 1167 for hydrostatic strength, ISO 13479 for SCG life, and ISO 16790 for melt strength. The specific test results are shown in Table 1.

[0055] Table 1

[0056]

[0057] From Examples 1-2 and Comparative Examples 3-4, it can be seen that only when the content of modified nano-silica is controlled within a certain range can the "island-bridge" structure be formed, thereby improving the various properties of the polyethylene material. If the amount of modified nano-silica added is too low, only an "island" structure will be formed, while if too much, the structure will easily agglomerate, which will affect the performance of the polyethylene material.

[0058] In the processing technology, the introduction of ultrasound can avoid the agglomeration of various components, make them more evenly distributed in the matrix, and improve the mechanical properties of polyethylene composites.

[0059] Therefore, the present invention forms a polyethylene composite material with high pressure resistance, long life and high anti-sag performance through the synergy of various components, with a melt flow rate of 0.2-0.3g / 10min, a tensile strength of 30-33MPa, and a notched impact strength of 45-50kJ / m 2 , hydrostatic strength is 11-13MPa, SCG life is greater than 1500h, melt strength is 330-350, and sag rate is 2-3%.

[0060] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A polyethylene composite material, characterized in that The invention comprises the following parts by weight: 60-80 parts of bimodal high-density polyethylene, 2-5 parts of modified nano-silicon dioxide, 6-15 parts of modified ethylene-octene copolymer, 0.15-0.45 parts of composite antioxidant, 0.2-0.5 parts of light stabilizer, 0.5-1.5 parts of composite lubricant and 0.05-0.1 parts of beta crystal nucleating agent.

2. The polyethylene composite material according to claim 1, characterized in that 65-75 parts of bimodal high-density polyethylene, 3-4 parts of modified nano-silica, 8-12 parts of modified ethylene-octene copolymer, 0.35-0.45 parts of composite antioxidant, 0.25-0.35 parts of light stabilizer, 0.8-1.2 parts of composite lubricant, and 0.07-0.09 parts of β-crystal nucleating agent.

3. The polyethylene composite material according to claim 1, characterized in that The modified nano-silica is modified by a titanate coupling agent, and the mass ratio of the nano-silica to the titanate coupling agent is 1:0.5-1:2; Preferably, the particle size of the nano-silicon dioxide is 10-200 nm, preferably 10-50 nm; Preferably, the bimodal high-density polyethylene comprises low molecular weight high-density polyethylene and high molecular weight high-density polyethylene; Preferably, the low molecular weight high density polyethylene has a Mw of 50,000-80,000; Preferably, the high molecular weight high density polyethylene has a Mw of 300,000-500,000; Preferably, the low molecular weight high density polyethylene is 40-60% by mass of the bimodal high density polyethylene.

4. The polyethylene composite material according to claim 1, characterized in that The modified ethylene-octene copolymer is obtained by grafting ethylene-octene copolymer with maleic anhydride, wherein the grafting rate of maleic anhydride is controlled at 0.8-1.2 wt%.

5. The polyethylene composite material according to claim 1, characterized in that The composite antioxidant comprises 0.1-0.3 parts of a primary antioxidant and 0.05-0.15 parts of an auxiliary antioxidant; wherein the primary antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], and the auxiliary antioxidant is tris(2,4-di-tert-butylphenyl) phosphite; Or, the light stabilizer is a hindered amine light stabilizer; Alternatively, the composite lubricant is a calcium stearate / oxidized polyethylene wax composite lubricant; in the composite lubricant, the oxidized polyethylene wax is 0.3-0.6 parts, and the calcium stearate is 0.2-0.6 parts; Alternatively, the β-crystal nucleating agent is a sodium benzoate / pimelic acid composite system, wherein the mass ratio of sodium benzoate / pimelic acid is 1-2:

1.

6. A method for preparing the polyethylene composite material according to any one of claims 1 to 5, characterized in that: The following steps are involved: Modified nano-silica and modified ethylene-octene copolymer are subjected to banburying and blending to obtain a compound system, which is dried and then mixed with bimodal high-density polyethylene, a composite antioxidant, a light stabilizer, and a β-crystal nucleating agent, melt-mixed, and an ultrasonic field is introduced into the mixing section, followed by post-treatment to obtain the polyethylene composite material.

7. The preparation method according to claim 6, characterized in that During the banbury blending, the blending temperature is 150-160° C., the rotation speed is 50-100 rpm, and the blending time is 5-10 min; Alternatively, the melt mixing is performed using a twin-screw extruder, wherein the aspect ratio of the screw in the twin-screw extruder is 30-40, the temperature of zone 1 is 160-170° C., zone 2 is 175-180° C., zone 3 is 190-200° C., and the rotation speed is 200-500 rpm; Alternatively, the ultrasonic field has a frequency of 20-40 kHz and a power of 150-300 W.

8. The preparation method according to claim 6, characterized in that The post-treatment is as follows: after the melt is pelletized by water ring, it is crystallized and annealed under nitrogen protection, the annealing temperature is 90-100° C., and the annealing time is 2-4 hours.

9. Use of the polyethylene composite material according to any one of claims 1 to 5 or the polyethylene composite material obtained by the preparation method according to any one of claims 6 to 8 in the preparation of drainage, gas transportation and industrial pipelines.

10. A pipeline, characterized in that: The invention comprises the polyethylene composite material according to any one of claims 1 to 5 or the polyethylene composite material obtained by the preparation method according to any one of claims 6 to 8.

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