Anti-aging PPR pipe and preparation method thereof

Abstract

The invention belongs to the technical field of high polymer material synthesis, and discloses an anti-aging PPR pipe and a preparation method thereof.The PPR base material is chemically modified through a melt grafting method, polar groups with the free radical capturing capacity are introduced to a PPR main chain, a stable three-dimensional Si-O-Si cross-linked network is formed through silane hydrolytic condensation, and the anti-aging PPR pipe is prepared. Therefore, a physical and chemical dual anti-aging mechanism is constructed, molecular chain breakage and structural deterioration in ultraviolet and thermo-oxidative aging processes are effectively inhibited, and efficient melt grafting is realized on the premise of not using a solvent.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer material synthesis, and particularly relates to an anti-aging PPR pipe and a preparation method thereof. BACKGROUND

[0002] PPR pipe is widely used in building water supply and drainage, industrial fluid transportation and other fields due to its excellent heat resistance, pressure resistance and chemical stability. However, the molecular chain structure of PPR material also has significant defects: the non-polar segment has weak ability to capture free radicals, which leads to chain oxidation reaction under ultraviolet irradiation or high temperature environment; although high crystallinity improves pressure resistance, the grain boundaries are easy to become stress concentration points, and micro-cracks are easily initiated under the action of heat and oxygen or ultraviolet light, accelerating material failure; in addition, transition metal ions (such as Fe 2+ , Cu 2+ ) commonly seen in industrial environments can catalyze the decomposition of hydrogen peroxide to generate highly active hydroxyl radicals (·OH), which further initiate PPR molecular chain scission and crosslinking reaction. However, PPR material is easily affected by factors such as ultraviolet light, heat and oxygen aging, and metal ion catalysis during long-term use, leading to a decrease in mechanical properties, surface yellowing and even failure, which limits its application life in outdoor or high temperature environments.

[0003] The aging problem of PPR material is mainly due to the weak ability of its non-polar molecular chain structure to capture free radicals, and the limited impact resistance due to high crystallinity. In the prior art, the improvement of PPR anti-aging performance mainly depends on the addition of anti-aging agents, however, such additives are prone to precipitation and performance degradation in long-term use due to poor migration or insufficient compatibility with the base material. SUMMARY

[0004] In order to solve the technical problems in the prior art that the improvement of PPR anti-aging performance mainly depends on the addition of anti-aging agents, and such additives are prone to precipitation and performance degradation in long-term use due to poor migration or insufficient compatibility with the base material, the application provides an anti-aging PPR pipe, which uses a melt grafting method to chemically modify the PPR base material, effectively inhibits molecular chain scission and structural degradation during ultraviolet and heat and oxygen aging, and realizes efficient melt grafting without using solvents.

[0005] The specific technical scheme of the application is as follows: an anti-aging PPR pipe and a preparation method thereof, comprising the following steps: 1) premix PPR base material, maleic anhydride (MAH), hydroxyethyl acrylate (HEA), vinyl triethoxysilane (VTEOS), dicumyl peroxide, to obtain a premix, and then perform gradient melt grafting after heating, add ammonia after the grafting is completed, and perform hydrolysis crosslinking reaction to obtain a grafted PPR base material; 2) after water cooling, granulation and drying of the grafted PPR base material in step 1), modified PPR particles are obtained; 3) after melt blending of the modified PPR particles obtained in step 2) and a composite anti-aging agent, cooling and setting, and gradient annealing, an anti-aging PPR pipe is obtained.

[0006] The method of melt grafting is used to chemically modify the PPR base material in the application, not only the polar groups with free radical capturing ability are introduced on the PPR main chain, but also a stable three-dimensional Si-O-Si crosslinking network is formed through silane hydrolysis and condensation, thereby a physical and chemical double anti-aging mechanism is constructed to effectively inhibit the molecular chain rupture and structure deterioration in the process of ultraviolet and thermal oxidative aging, and high-efficiency melt grafting is realized without using solvent.

[0007] Further, in step 1), 80-95wt% of PPR base material, 2-4wt% of maleic anhydride, 1-3wt% of hydroxyethyl acrylate, 1-2wt% of vinyl triethoxysilane and 0.5-1wt% of dicumyl peroxide are premixed.

[0008] Further, in step 1), the concentration of ammonia is 0.1-0.5%.

[0009] Further, in step 1), the gradient melt grafting step is as follows: the premix is heated, heated to 188-192℃, reacted for 2-3min, then continuously heated to 198-202℃, reacted for 2-3min, and heated to 208-212℃, reacted for 2-3min.

[0010] Further, in step 3), the addition amount of the composite anti-aging agent is 2-4wt%.

[0011] Further, the composite anti-aging agent comprises: amine antioxidant (HALS), phosphorus antioxidant and ethylenediaminetetraacetic acid (EDTA).

[0012] The application adopts a composite anti-aging system composed of hindered amine light stabilizer, phosphorus antioxidant and metal ion chelating agent, and a good interface synergistic effect is formed between the components and the grafted polar groups, wherein the hindered amine light stabilizer can efficiently capture free radicals generated in the process of ultraviolet aging, the phosphorus antioxidant can inhibit the chain reaction in the process of thermal oxidative aging, and the metal ion chelating agent can effectively complex Fe 2+ , Cu 2+The three synergistically prolong the service life of the material, and the material still maintains good stability under high-temperature processing conditions, avoiding the attenuation of the efficiency of the traditional single anti-aging agent due to migration or precipitation, and low-concentration ammonia is added after the melting to promote the rapid hydrolysis of VTEOS to generate Si-OH, and further condensation to form a dense siloxane crosslinked structure. The process does not require an additional crosslinking post-processing step, realizes the integration of grafting and crosslinking, greatly improves the production efficiency and material structure stability, avoids the common "secondary crosslinking" problem in the traditional silane crosslinking process, ensures that the crosslinked structure is uniformly distributed in the entire substrate, and enhances the long-term service performance.

[0013] Further, the composite anti-aging agent is 45-47.5wt% amine antioxidant, 45-47.5wt% phosphorus antioxidant and 5-7.5wt% ethylenediaminetetraacetic acid.

[0014] Further, in step 3), the gradient annealing step is: after the pipe is shaped, it is reacted at 198-202℃ for 1-2min, then heated to 218-222℃ for 1-2min, and then heated to 228-232℃ for 1-2min.

[0015] Compared with the prior art, the beneficial effects of the present application are: 1) The present application uses a melt grafting method to chemically modify the PPR substrate, not only introducing polar groups with free radical capturing ability on the PPR main chain, but also forming a stable three-dimensional Si-O-Si crosslinked network through silane hydrolysis and condensation, thereby constructing a physical and chemical double anti-aging mechanism to effectively inhibit molecular chain rupture and structural degradation during ultraviolet and thermal oxidative aging, and realizing efficient melt grafting without using solvents.

[0016] 2) The present application uses a composite anti-aging system composed of hindered amine light stabilizer, phosphorus antioxidant and metal ion chelating agent, and each component forms a good interfacial synergistic effect with the grafted polar groups through hydrogen bonding, wherein the hindered amine light stabilizer can efficiently capture free radicals generated during ultraviolet aging, the phosphorus antioxidant inhibits thermal oxidative chain reaction, and the metal ion chelating agent effectively complexes Fe 2+ , Cu 2+ and other catalytic metal ions, and the three synergistically prolong the service life of the material, and the material still maintains good stability under high-temperature processing conditions, avoiding the attenuation of the efficiency of the traditional single anti-aging agent due to migration or precipitation.

[0017] 3) The present application adds low-concentration ammonia water after melting to promote the rapid hydrolysis of VTEOS to generate Si-OH and further condensation to form a dense siloxane cross-linked structure. This process does not require additional cross-linking post-processing steps, realizes the integration of grafting and cross-linking, greatly improves production efficiency and material structure stability, avoids the common "secondary cross-linking" problem in traditional silane cross-linking process, ensures uniform distribution of cross-linked structure in the entire substrate, and enhances long-term service performance.

[0018] 4) The present application does not use organic solvents required by traditional solution grafting process, avoiding environmental pollution and solvent residue problems, and meeting the requirements of relevant environmental protection regulations. DETAILED DESCRIPTION

[0019] All features disclosed in this specification, and all methods or processes disclosed in this specification, can be combined in any combination, except combinations where at least some of the features and / or steps are mutually exclusive.

[0020] The present application will be further described below with reference to examples.

[0021] Example 1 An anti-aging PPR pipe 1) PPR chemical grafting High-speed mix 94.2wt% PPR substrate, 2.5wt% maleic anhydride, 1.5wt% hydroxyethyl acrylate, 1.0wt% vinyl triethoxysilane, and 0.8wt% dicumyl peroxide to obtain a premix, and then feed the premix into a double-screw extruder with a preset temperature of 200℃. In the double-screw extruder, three temperature gradients are set: 190℃ (Zone 1), 200℃ (Zone 2), and 210℃ (Zone 3). The premix is sequentially passed through Zone 1, Zone 2, and Zone 3 in the double-screw extruder, with a residence time of 2min in each zone to ensure sufficient grafting. A spraying device is added at the end of the double-screw extruder to spray 0.2% ammonia water on the grafted material to trigger VTEOS hydrolysis and cross-linking, and then perform hydrolysis and cross-linking reaction to form a Si-O-Si network, thereby obtaining a grafted PPR substrate.

[0022] 2) Pelletizing Cool the grafted PPR substrate obtained in step 1) in a water cooling tank at 15℃, and then quickly pelletize the structure-stabilized material with a particle length controlled at 2mm. To prevent performance changes or microbial growth due to water residue during long-term storage, the surface of the pelletized material is attached with a small amount of cooling water, and then vacuum dried at 60℃ for 40min to obtain modified PPR particles.

[0023] 3) Pipe forming The modified PPR particles obtained in step 2) are added with 2wt% of a composite anti-aging agent, and then added into a single-screw extruder, melt-extruded at 220°C, and then cooled and shaped in water at 25°C. The shaped pipe is reacted at 200°C for 1 min, then the temperature is increased to 220°C for 1 min, and then the temperature is increased to 230°C for 1 min, to perform gradient annealing treatment, promote crystal curvature ordering, and improve creep resistance. The anti-aging PPR pipe obtained after gradient annealing comprises 47.5wt% of an amine antioxidant, 47.5wt% of a phosphorus antioxidant, and 5wt% of ethylenediaminetetraacetic acid.

[0024] 4) Performance detection The anti-aging PPR pipe obtained in step 3) is subjected to performance detection, to detect the grafting rate of the PPR pipe, the yellowing index and tensile strength retention rate after 500h of ultraviolet aging test, the crystallinity and elongation at break of the PPR pipe detected by DSC test.

[0025] Comparative Example 1 The difference between the present comparative example and Example 1 is that, in the present comparative example, the pre-mixture in step 1) is not subjected to temperature gradient grafting, i.e., only chemical grafting is performed at 200°C for 6min, and the rest of the process is the same as that of Example 1. The specific steps are as follows: 1) PPR chemical grafting The pre-mixture obtained by high-speed mixing 94.2wt% of PPR base material, 2.5wt% of maleic anhydride, 1.5wt% of hydroxyethyl acrylate, 1.0wt% of vinyl triethoxysilane, and 0.8wt% of dicumyl peroxide is fed into a double-screw extruder with a preset temperature of 200°C, and subjected to chemical grafting at 200°C for 6min to ensure sufficient grafting. A spraying device is added at the end of the double-screw extruder to spray 0.2% of ammonia water on the grafted material to trigger the hydrolysis crosslinking of VTEOS, perform hydrolysis crosslinking reaction, and form a Si-O-Si network to obtain grafted PPR base material.

[0026] 2) Pelletizing The grafted PPR base material in step 1) is rapidly cooled in a water cooling tank at 15°C, and then rapidly cut into particles with a length of 2mm. A small amount of cooling water is attached to the surface of the cut particles. To prevent performance changes or microbial growth due to water residue during long-term storage, the particles are vacuum dried at 60°C for 40min to obtain modified PPR particles.

[0027] 3) Pipe forming The modified PPR particles obtained in step 2) are added with 2wt% of a composite anti-aging agent, and then added into a single-screw extruder, and then melt-extruded at 220°C, and then cooled and shaped in water at 25°C, and then the shaped pipe is reacted at 200°C for 1min, and then the temperature is increased to 220°C for 1min, and then the temperature is increased to 230°C for 1min, and then gradient annealing treatment is performed, so as to promote crystal curving ordering and improve creep resistance, and then an anti-aging PPR pipe is obtained after the gradient annealing, wherein the composite anti-aging agent comprises 47.5wt% of an amine antioxidant, 47.5wt% of a phosphorus antioxidant, and 5wt% of ethylenediaminetetraacetic acid.

[0028] 4) Performance detection The anti-aging PPR pipe obtained in step 3) is subjected to performance detection.

[0029] Table 1 Influence of temperature gradient grafting on the performance of PPR pipe Grafting method Grafting rate Yellowing index (YI) Tensile strength retention rate Example 1 Temperature gradient grafting 5.2 1.5 90% Comparative example 1 Constant temperature grafting 3.8 2.2 85% According to the data in Table 1, it can be seen that temperature gradient grafting can reduce the grafting rate of the material, and the yellowing index after 500 hours of ultraviolet aging test increases obviously, and the tensile strength decreases.

[0030] Comparative Example 2 The difference between this comparative example and Example 2 is that, in this comparative example, the shaped pipe is not subjected to gradient annealing in step 3), that is, only reacted at 220°C for 3min, and the rest of the process is the same as Example 1. The specific steps are as follows: 1) PPR chemical grafting 94.2wt% PPR base material, 2.5wt% maleic anhydride, 1.5wt% hydroxyethyl acrylate, 1.0wt% vinyl triethoxysilane, and 0.8wt% dicumyl peroxide are subjected to high-speed mixing to obtain a premix, and the premix is fed into a double-screw extruder with a preset temperature of 200°C, wherein three temperature gradients are set in the double-screw extruder: 190°C (first zone), 200°C (second zone), and 210°C (third zone), and the premix is sequentially subjected to the first zone, the second zone, and the third zone in the double-screw extruder, and the residence time in each zone is 2min to ensure sufficient grafting, and a spraying device is added at the end of the double-screw extruder to spray 0.2% ammonia water on the grafted material to trigger VTEOS hydrolysis crosslinking, and then hydrolysis crosslinking reaction is performed to form a Si-O-Si network, and then a grafted PPR base material is obtained.

[0031] 2) Pelletizing The grafted PPR substrate in step 1) is rapidly cooled in a water cooling tank at 15℃, and after the structure is stabilized, it is rapidly cut into particles with a length of 2mm. A small amount of cooling water is attached to the surface of the particles after cutting. To prevent changes in performance or the growth of microorganisms due to residual moisture during long-term storage, the material is vacuum dried at 60℃ for 40min. The modified PPR particles are obtained after drying.

[0032] 3) Pipe forming The modified PPR particles obtained in step 2) are added with 2wt% of a composite anti-aging agent, and then blended again. The blended material is then added to a single screw extruder, melted and extruded at 220℃, and then cooled and shaped in water at 25℃. The shaped pipe is annealed by reacting at 220℃ for 3min. The anti-aging PPR pipe is obtained after annealing, wherein the composite anti-aging agent comprises 47.5wt% of an amine antioxidant, 47.5wt% of a phosphorus antioxidant, and 5wt% of ethylenediaminetetraacetic acid.

[0033] 4) Performance detection The anti-aging PPR pipe obtained in step 3) is subjected to performance detection.

[0034] Table 2 Influence of temperature gradient annealing on the performance of PPR pipe Annealing method Crystallinity Creep strain Elongation at break Example 1 Temperature gradient annealing 58 ＜2 620 Comparative example 2 Constant temperature annealing 52 2.5 580 According to the data in Table 2, it can be concluded that temperature gradient annealing increases the crystallinity of the pipe, so that the PPR pipe produced under the same conditions has lower creep strain and larger elongation at break. It is speculated that the reason is that the crystallization growth of PPR is promoted and the order of the crystal region is improved, thereby improving the creep resistance and dimensional stability of the material, reducing the risk of deformation caused by thermal expansion and cold contraction during later use, and further improving the long-term mechanical reliability of the product.

[0035] The raw materials and equipment used in the present application are conventional raw materials and equipment in the art unless otherwise specified; the methods used in the present application are conventional methods in the art unless otherwise specified.

[0036] The above-described embodiments only express the specific implementation of the present application, and the description is more specific and detailed, but it should not be construed as limiting the scope of protection of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the technical concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application.

Claims

1. A process for the preparation of an anti-aging PPR pipe, characterized by, The method comprises the following steps: 1) premixing PPR base material, maleic anhydride, hydroxyethyl acrylate, vinyl triethoxysilane and dicumyl peroxide to obtain a premix, heating for gradient melt grafting, adding ammonia after the grafting is completed, and performing hydrolysis crosslinking reaction to obtain a grafted PPR base material; 2) obtaining modified PPR particles after water cooling, granulation and drying of the grafted PPR base material in step 1); 3) blending the modified PPR particles obtained in step 2) with a composite anti-aging agent, melt blending, cooling and setting, and gradient annealing to obtain an anti-aging PPR pipe.

2. A process for the preparation of an anti-aging PPR pipe as claimed in claim 1, wherein, In step 1), 80-95wt% of PPR base material, 2-4wt% of maleic anhydride, 1-3wt% of hydroxyethyl acrylate, 1-2wt% of vinyl triethoxysilane and 0.5-1wt% of dicumyl peroxide are premixed.

3. A process for the preparation of an anti-ageing PPR pipe as claimed in claim 1 or 2, wherein, The concentration of ammonia in step 1) is 0.1-0.5%.

4. A process for the preparation of an anti-aging PPR pipe as claimed in claim 1, wherein, In step 1), the gradient melt grafting step is: heating the premix, heating to 188-192℃, reacting for 2-3min, continuing to heat to 198-202℃, reacting for 2-3min, heating to 208-212℃, and reacting for 2-3min.

5. A process for the preparation of an anti-aging PPR pipe as claimed in claim 1, wherein, In step 3), the addition amount of the composite anti-aging agent is 2-4wt%.

6. A process for the preparation of an anti-aging PPR pipe as claimed in claim 5, wherein, The composite anti-aging agent comprises: amine antioxidant, phosphorus antioxidant and ethylenediaminetetraacetic acid.

7. A process for the preparation of an anti-aging PPR pipe as claimed in claim 6, wherein, The composite anti-aging agent comprises: 45-47.5wt% of amine antioxidant, 45-47.5wt% of phosphorus antioxidant and 5-7.5wt% of ethylenediaminetetraacetic acid.

8. A process for the preparation of an anti-aging PPR pipe as claimed in claim 1, wherein, In step 3), the gradient annealing step is: reacting the set pipe at 198-202℃ for 1-2min, then heating to 218-222℃ for 1-2min, and heating to 228-232℃ for 1-2min.

9. An anti-aging PPR pipe prepared by the method for preparing the anti-aging PPR pipe according to any one of claims 1-8.