An anti-stress whitening transparent polyethylene pipe and its preparation method and application

Abstract

The present invention discloses an anti-stress whitening transparent polyethylene pipe and its preparation method and application. Through a simple and efficient melt blending and rolling process, UHMWPE with an extremely high molecular entanglement density is introduced into the PE matrix to achieve good miscibility between the two, enhance the entanglement degree between the two-phase molecules, construct a highly molecularly entangled network structure in the blend system and enhance viscoelasticity, endow the PE pipe material with excellent stretchability, inhibit and impede the non-uniform plastic deformation of the pipe during the unidirectional large-strain stretching molding process at room temperature and the chain scission and debonding of the PE and UHMWPE components, significantly reduce the generation of nano-scale cracks and cavities, and further effectively weaken the scattering effect on visible light, eliminate the stress whitening defect of PE, improve the visible light transmittance and optical transparency of the pipe, and have good application prospects in a stress environment.

Description

Technical Field

[0001] The present invention belongs to the field of polymer processing, and particularly relates to an anti-stress whitening transparent polyethylene pipe, a preparation method thereof and an application thereof. Background Art

[0002] Polyethylene (PE) pipes have excellent comprehensive properties and are widely used in fields such as building water supply and drainage, gas transmission, electrical and telecommunications protection, and agricultural irrigation. However, when PE pipes are subjected to stress such as tension, compression, bending, and folding, microcracks and cavities are easily generated inside, which changes the refractive index and causes obvious stress whitening phenomenon, greatly affecting the product appearance and mechanical properties (such as the decrease of mechanical strength and stress cracking resistance), and seriously shortening the long-term service life of PE pipes.

[0003] At present, there are few studies on anti-stress whitening transparent polyethylene pipes. Shen Kaizhi et al., Engineering Plastics Application, 2000, (01): 15-18, prepared high-density polyethylene (HDPE) pipes by melt deformation method under special process conditions, and the product changed from conventional white opaque to colorless transparent. Wu Shijian et al., Engineering Plastics Application, 2002, (08): 23-26, prepared HDPE pipes by optimizing the design of the die of industrial twin-screw extrusion equipment and specially controlling the processing parameters, and nanocrystals with grain size smaller than the visible light wavelength were formed inside the pipes under the action of unidirectional tensile flow field, making them transparent. Although the above common modification methods can improve the optical transparency of PE pipes to a certain extent, their processing and molding rely on high temperature. At this time, the molecular chain mobility of PE is extremely strong, which is conducive to the formation of fine crystals, and at the same time can effectively avoid the generation of defects such as molecular chain fracture under the action of tensile flow field, endowing PE pipes with good transparency. However, at room temperature, the molecular chain mobility of PE is weak, and under the action of external force, its molecular chains are severely broken, easily generating microcracks and cavities, and do not have anti-stress whitening performance. Furthermore, it is impossible to obtain PE pipes with excellent optical transparency through methods such as tensile orientation, which limits the application of PE pipes in stress environments. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides an anti-stress whitening transparent polyethylene pipe, a preparation method thereof and an application thereof. Ultra-high molecular weight polyethylene (UHMWPE) with extremely high molecular entanglement density is introduced into the polyethylene (PE) matrix by a simple melt blending and rolling process to construct a highly chain-entangled structure and high viscoelasticity in the system, endowing it with excellent stretchability, inhibiting and hindering the non-uniform plastic deformation and the generation of micro-nano scale cracks and cavities of PE pipes during the unidirectional large-strain tensile molding process at room temperature, effectively eliminating the stress whitening defect, improving the optical transparency of PE pipes, and broadening their application in stress environments.

[0005] A preparation method of an anti-stress whitening transparent polyethylene pipe, comprising the following steps:

[0006] Step 1, adding 100 parts by weight of PE, 3-70 parts by weight of UHMWPE, and 0.01-10 parts by weight of an antioxidant into a mixer and melting and blending at 160-230 °C for 5-60 min at a rotation speed of 20-80 rpm to obtain a PE / UHMWPE blend;

[0007] Step 2, preparing a PE / UHMWPE strip material through an extruder, with the barrel temperature being 170-240 °C and the screw rotation speed being 70-210 rpm, then performing a rolling treatment on the PE / UHMWPE strip material and cooling it to 25 °C, further crushing the strip material into fine particles, and transferring it to a twin-screw extruder to extrude a PE / UHMWPE blend pipe;

[0008] Step 3, axially large-strain solid-phase stretching and forming of the PE / UHMWPE blend pipe;

[0009] Fix the PE / UHMWPE blend pipe on a universal material testing machine, and perform solid-phase stretching and forming at 25 °C at a stretching rate of 10-500 mm / min. After the stretching ratio reaches 200%-1500%, stop stretching, unload, and sample to obtain an anti-stress whitening transparent polyethylene pipe.

[0010] Preferably, the molecular weight of the PE in Step 1 is 2-50×10 4 g / mol.

[0011] More preferably, the PE is high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), or linear low-density polyethylene (LLDPE).

[0012] Preferably, the molecular weight of the UHMWPE in Step 1 is 80-750×10 4 g / mol.

[0013] Preferably, the antioxidant in Step 1 is any one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-bis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hexanediamine, octadecyl β-(4-hydroxy-3,5-di-tert-butylphenyl)propionate, 2,6-di-tert-butyl-4-methylphenol, and triethylene glycol bis-3-(3-tert-butyl-4-hydroxy-5-methylbenzyl)propionate.

[0014] Preferably, the pressure during the rolling treatment in Step 2 is 20-200 kPa.

[0015] Preferably, in step 2, the particle size of the fine particles is 4 to 32 mesh.

[0016] Preferably, in step 2, the extrusion temperature is 180 to 230 °C, and the screw speed is 150 to 200 rpm.

[0017] The anti-stress whitening transparent polyethylene pipe prepared by the above preparation method has a visible light transmittance exceeding 60%, an axial tensile strength of up to 191.79 MPa, and an axial fracture toughness of up to 102.34 MJ / m 3 .

[0018] The anti-stress whitening transparent polyethylene pipe prepared by the above preparation method is used in a stress environment.

[0019] Beneficial effects:

[0020] Compared with the prior art, the anti-stress whitening transparent polyethylene pipe and its preparation method and application of the present invention have the following characteristics:

[0021] 1. In the present invention, through a simple and efficient melt blending and rolling process, UHMWPE with an extremely high molecular entanglement density is introduced into the PE matrix, achieving good miscibility between the two, enhancing the entanglement degree between the two-phase molecules, constructing a highly molecularly entangled network structure of the blend system and enhancing viscoelasticity, endowing the PE pipe with excellent stretchability, inhibiting and hindering the non-uniform plastic deformation of the pipe and the chain breaking and debonding of the PE and UHMWPE components during the unidirectional large-strain stretching molding process at room temperature, significantly reducing the generation of nano-scale cracks and cavities, and further effectively weakening the scattering effect on visible light, eliminating the stress whitening defect of PE, and improving its visible light transmittance and optical transparency;

[0022] 2. During the unidirectional large-strain stretching molding process, the UHMWPE molecular chains are fully stretched and extended, forming a shish crystal structure with a straight-chain conformation, and inducing a large number of PE molecular chains to be arranged orderly, forming a kebab crystal structure. The lamellar stacking is more compact, making its grain size smaller than the visible light size, and further improving the optical transparency of the pipe. <^ Description of the drawings

[0023] Figure 1 (a) is a physical diagram of the stretched and unstretched molded PE pipe;

[0024] Figure 1 (b) is a physical diagram of the stretched and unstretched molded PE / UHMWPE pipe;

[0025] Figure 2 (a) is the visible light transmittance of the PE pipe and the PE / UHMWPE pipe;

[0026] Figure 2(b) Axial tensile strength and fracture toughness of PE pipes and PE / UHMWPE pipes. Detailed implementation mode

[0027] The present invention will be specifically described below through embodiments. It is necessary to point out here that these embodiments are only used to further illustrate the present invention and cannot be understood as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0028] Example 1

[0029] 1 kg of HDPE (molecular weight 2 - 10×10 4 g / mol), 300 g of UHMWPE (molecular weight 50 - 150×10 4 g / mol), and 10 g of N,N'-bis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl] hexanediamine were added to a mixer for melt blending. The processing temperature was 190 °C, the rotor speed was 40 rpm, and the processing time was 15 min to obtain a PE / UHMWPE blend. Subsequently, a PE / UHMWPE strip material was prepared by an extruder. The barrel temperature was 185 °C, the screw speed was 150 rpm. After rolling and cooling to room temperature (the pressure applied by the roller to the strip material was 50 kPa), the strip material was crushed into fine particles using a high-speed crusher. Further, the blend particles were added to a twin-screw extruder to extrude PE / UHMWPE pipes, and the extrusion temperature was 190 °C, and the screw speed was 160 rpm.

[0030] The PE / UHMWPE blend pipes were fixed on a universal material testing machine and subjected to solid-phase tensile forming at room temperature (25 °C) at a tensile rate of 10 mm / min. After the tensile ratio reached 300%, the tensile was stopped, unloaded, and samples were taken to obtain stress-whitening resistant transparent polyethylene pipes.

[0031] The anti-stress whitening transparent PE / UHMWPE pipes prepared in Example 1 and PE pipes were tested. The preparation process of the PE pipes is as follows: 100 parts by weight of PE and 0.5 parts of N,N'-bis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl] hexanediamine were added to a kneader and melt-blended at 200 °C for 30 min at a rotation speed of 50 rpm to obtain a PE / UHMWPE blend. On this basis, the PE / UHMWPE blend was used to prepare a PE / UHMWPE strip material through an extruder, with the barrel temperature at 220 °C and the screw rotation speed at 130 rpm. Then, the PE / UHMWPE strip material was roll-pressed and cooled to 25 °C. Next, the strip material was crushed into small particles and transferred to a twin-screw extruder to extrude the PE / UHMWPE blend pipes. Further, the PE / UHMWPE blend pipes were fixed on a universal material testing machine and subjected to solid-phase tensile forming at 25 °C at a tensile rate of 50 mm / min. After the tensile ratio reached 500%, the tensile was stopped, the load was unloaded, and samples were taken to obtain the PE pipes. The testing methods are as follows:

[0032] Visible light transmittance test:

[0033] The transmittance of PE and PE / UHMWPE pipes was tested using an ultraviolet-visible-near infrared spectrophotometer (UV-3600, Shimazu) from Shimadzu Corporation, Japan. The PE and PE / UHMWPE pipes were cut into sheets with a thickness of 2 mm, and their transmittance was measured within the wavelength range of 200 - 900 nm.

[0034] Axial tensile strength and fracture toughness test:

[0035] The tensile strength of PE and PE / UHMWPE pipes was tested using an Instron 5567 universal material testing machine from the United States at a tensile rate of 40 mm / min. The fracture toughness (W) of the pipe samples can be calculated by the following formula:

[0036]

[0037] where ε0 and ε max are the strain at the beginning and end of the test respectively, and σ is the stress.

[0038] The test results are as Figure 2 shown. After tensile forming, the visible light transmittance of the PE pipes approaches 0, showing stress whitening, while the visible light transmittance of the PE / UHMWPE pipes exceeds 60%, achieving a significant improvement in its optical transparency and eliminating the stress whitening effect. In addition, compared with the PE pipes, the axial tensile strength and fracture toughness of the PE / UHMWPE pipes are significantly increased, reaching 191.79 MPa and 102.34 MJ / m respectively3 。

[0039] Example 2

[0040] 1 kg of LDPE (molecular weight 15 - 30×10 4 g / mol), 400 g of UHMWPE (molecular weight 160 - 300×10 4 g / mol), and 15 g of pentaerythritol tetrakis [β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] were added to a kneader for melt blending. The processing temperature was 210 °C, the rotor speed was 60 rpm, and the processing time was 30 min to obtain a PE / UHMWPE blend. Subsequently, a PE / UHMWPE strip material was prepared by an extruder. The barrel temperature was 205 °C, the screw speed was 170 rpm. After being subjected to a rolling process and cooled to room temperature (the pressure applied by the roller to the strip material was 80 kPa), the strip material was crushed into fine particles using a high-speed grinder. Further, the blend particles were added to a twin-screw extruder to extrude PE / UHMWPE pipes. The extrusion temperature was 210 °C, and the screw speed was 180 rpm.

[0041] The PE / UHMWPE blend pipes were fixed on a universal material testing machine and subjected to solid-phase tensile forming at room temperature (25 °C). The tensile rate was 100 mm / min. After the tensile ratio reached 800%, the tensile was stopped, the load was unloaded, and samples were taken to obtain stress-whitening-resistant transparent polyethylene pipes.

[0042] Example 3

[0043] 1 kg of LLDPE (molecular weight 40 - 50×10 4 g / mol), 600 g of UHMWPE (molecular weight 350 - 450×10 4 g / mol), and 20 g of octadecyl β-(4-hydroxy-3,5-di-tert-butylphenyl) propionate were added to a kneader for melt blending. The processing temperature was 230 °C, the rotor speed was 80 rpm, and the processing time was 40 min to obtain a PE / UHMWPE blend. Subsequently, a PE / UHMWPE strip material was prepared by an extruder. The barrel temperature was 225 °C, the screw speed was 190 rpm. After being subjected to a rolling process and cooled to room temperature (the pressure applied by the roller to the strip material was 100 kPa), the strip material was crushed into fine particles using a high-speed grinder. Further, the blend particles were added to a twin-screw extruder to extrude PE / UHMWPE pipes. The extrusion temperature was 230 °C, and the screw speed was 200 rpm.

[0044] Fix the PE / UHMWPE blend pipe on a universal material testing machine and perform solid-phase stretching molding at room temperature (25 °C) with a stretching rate of 300 mm / min. Stop stretching, unload, and sample after the stretching ratio reaches 1500%, and obtain a stress-whitening-resistant transparent polyethylene pipe.

[0045] In summary, through the simple and efficient melt blending and rolling processes, the present invention introduces UHMWPE with an extremely high molecular entanglement density into the PE matrix, achieving good miscibility between the two, enhancing the entanglement degree between the two-phase molecules, constructing a highly molecularly entangled network structure and enhancing viscoelasticity in the blend system, endowing the PE pipe with excellent stretchability, inhibiting and hindering the non-uniform plastic deformation of the pipe and the chain breakage and debonding of the PE and UHMWPE components during the unidirectional large-strain stretching molding process at room temperature, significantly reducing the generation of nano-scale cracks and cavities, and thus effectively weakening the scattering effect on visible light, eliminating the stress-whitening defect of PE, and improving its visible light transmittance and optical transparency.

Claims

1. A method for preparing a stress-whitening-resistant transparent polyethylene pipe, characterized in that: The following steps are involved: Step 1: adding 100 parts by weight of PE, 3 to 70 parts by weight of UHMWPE, and 0.01 to 10 parts by weight of an antioxidant into an internal mixer, and melt-blending them at 160 to 230° C. for 5 to 60 minutes at a rotation speed of 20 to 80 rpm to obtain a PE / UHMWPE blend; Step 2: The PE / UHMWPE blend is extruded through an extruder at an extrusion temperature of 180-230° C. and a screw speed of 150-200 rpm to prepare a PE / UHMWPE strip material, the barrel temperature is 170-240° C., and the screw speed is 70-210 rpm. The PE / UHMWPE strip material is then roller-pressed at 50-100 kPa and cooled to 25° C. The strip material is further crushed into fine particles, and then transferred to a twin-screw extruder to extrude a PE / UHMWPE blend pipe. Step 3: Axial large strain solid phase stretching of PE / UHMWPE blend pipes The PE / UHMWPE blend pipe is fixed on a universal material testing machine and solid-phase stretching is performed at 25°C at a stretching rate of 10 to 500 mm / min. After the stretching ratio reaches 200% to 1500%, the stretching is stopped, the pipe is unloaded, and sampling is performed to obtain a stress-resistant, whitening, transparent polyethylene pipe.

2. The method for preparing a stress-whitening-resistant transparent polyethylene pipe according to claim 1, characterized in that: The molecular weight of PE in step 1 is 2 to 50×10 4 g / mol.

3. The method for preparing a stress-whitening-resistant transparent polyethylene pipe according to claim 2, characterized in that: The PE is high-density polyethylene, medium-density polyethylene, low-density polyethylene or linear low-density polyethylene.

4. The method for preparing a stress-whitening-resistant transparent polyethylene pipe according to claim 1, characterized in that: The molecular weight of the UHMWPE in step 1 is 80 to 750×10 4 g / mol.

5. The method for preparing a stress-whitening-resistant transparent polyethylene pipe according to claim 1, characterized in that: The antioxidant in step 1 is any one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, N,N'-bis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hexanediamine, β-(4-hydroxy-3,5-di-tert-butylphenyl)propionate, 2,6-di-tert-butyl-4-methylphenol and triethylene glycol bis-3-(3-tert-butyl-4-hydroxy-5-methylbenzyl)propionate.

6. The method for preparing a stress-whitening-resistant transparent polyethylene pipe according to claim 1, characterized in that: The particle size of the fine particles in step 2 is 4 to 32 meshes.

7. The stress-whitening transparent polyethylene pipe prepared by the preparation method according to any one of claims 1 to 6 has a visible light transmittance exceeding 60%, an axial tensile strength of up to 191.79 MPa, and an axial fracture toughness of up to 102.34 MJ / m 3 .

8. Application of the stress-whitening transparent polyethylene pipe prepared by the preparation method according to any one of claims 1 to 6 in a stress environment.

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