Flame-retardant smoke-suppressing PVC (polyvinyl chloride) pipe and preparation method thereof

Abstract

The invention belongs to the technical field of plastic processing, and particularly relates to a flame-retardant smoke-suppressing PVC pipe and a preparation method thereof. According to the invention, the seaweed mud is innovatively used as a filler of the PVC pipe and is ingeniously blended into a composite system of dialkyl phosphate and polyol, and the flame-retardant and smoke-suppressing effects, mechanical properties and whiteness value of the PVC pipe are remarkably improved by utilizing a synergistic effect. Wherein a unique porous microstructure of the seaweed mud and dialkyl phosphate serving as an intumescent flame-retardant auxiliary agent generate a strong synergistic enhancement effect through a pore effect, so that not only is the use amount of a flame retardant reduced, but also the mechanical property of the PVC pipe is improved; the polyhydric alcohol is used as a plasticizing and cross-linking auxiliary agent, is subjected to esterification reaction with the dialkyl phosphate to strengthen the overall flame-retardant and smoke-suppression effect, and is cooperated with the seaweed mud to enhance the whiteness of the PVC pipe. The PVC pipe which is flame-retardant, smoke-suppressing, excellent in mechanical property, high in whiteness value and low in cost is successfully prepared, and the application field of the PVC pipe is widened.

Description

Technical Field

[0001] The present invention belongs to the technical field of plastic processing, and more specifically, relates to a flame-retardant and smoke-suppressing PVC pipe and a preparation method thereof. Background Art

[0002] With the rapid development of social economy and the continuous deepening of technological innovation, high-rise buildings, as landmark buildings in modern cities, have increasingly prominent fire safety issues, especially the rapid spread of fire, difficulty in evacuating personnel, and limited external rescue. In recent years, many high-rise building fire incidents have highlighted the urgency of improving building fire safety performance. In this context, high-rise building materials, especially those that require high strength and high flame retardancy, have become a research focus.

[0003] In traditional high-rise buildings, key components such as PVC drainage pipes often use halogen (such as organic chlorides, bromides) and phosphorus (such as red phosphorus, phosphates, halogenated phosphates) flame retardants to enhance flame retardancy. However, these materials are expensive and complex to process, and their addition often leads to decreased mechanical properties and increased smoke. Among them, the smoke and corrosive gases released when halogen flame retardants burn pose a threat to personnel safety and the environment.

[0004] Therefore, developing a new type of PVC pipe that combines high flame retardancy, high strength, low cost, easy processing and environmental protection with the help of halogen-free flame retardants has become the key to improving the fire safety performance of high-rise buildings. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of PVC pipes, such as high cost, great processing difficulty, poor flame retardant and smoke suppression effect and mechanical properties, and to provide a flame retardant and smoke suppression PVC pipe.

[0006] Another object of the present invention is to provide a method for preparing the flame-retardant and smoke-suppressing PVC pipe.

[0007] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0008] The present invention protects a flame retardant and smoke suppressing PVC pipe material, which comprises the following components by weight:

[0009] 100-120 parts of PVC resin;

[0010] 10-20 parts of calcium carbonate;

[0011] 1-10 parts seaweed mud;

[0012] 1 to 10 parts of dialkyl phosphate;

[0013] 1-8 parts of calcium zinc stabilizer;

[0014] 1-5 parts of polyol;

[0015] 1-2 parts lubricant;

[0016] 1-5 parts of titanium dioxide;

[0017] 0.5-1 part of impact modifier;

[0018] 0.5-1 part of other processing aids;

[0019] Wherein, the number of carbon atoms in a single alkyl chain of the dialkyl phosphate is ≥ 10;

[0020] Polyols are alcohol compounds containing two or three hydroxyl groups.

[0021] The present invention uses seaweed mud as the filler of PVC pipes, and utilizes its porous surface characteristics and the synergistic strengthening effect of the intumescent flame retardant additive, which can not only reduce the amount of flame retardant used, but also improve the mechanical properties of the PVC pipes, thereby achieving cost reduction and efficiency improvement while promoting environmental protection; dialkyl phosphate is selected as the acid source and carbon source of the intumescent flame retardant, and the dialkyl phosphate releases inorganic acid during combustion, esterifies with polyols, and then dehydrates and carbonizes. The viscous carbonization product expands under the action of volatile substances such as the inert gas released by the gas source, the water vapor generated by the reaction, and the small molecular compounds generated by the degradation of the polymer, forming a carbon layer with a microporous structure, and a uniform intumescent carbon layer is formed on the surface, which plays the role of heat insulation, oxygen isolation, smoke suppression, and preventing dripping; polyols are used as plasticizers and cross-linking additives, and the esterification reaction with dialkyl phosphate strengthens the overall flame retardant and smoke suppression effect, and synergistically enhances the whiteness of the PVC pipe with seaweed mud.

[0022] Furthermore, the mesh size of the seaweed mud is 1500-2000, and the seaweed mud within this range can be better dispersed in the PVC matrix.

[0023] Furthermore, the seaweed mud replaces calcium carbonate as a filler for PVC drainage pipes because the surface of the seaweed mud particles has countless tiny holes with high porosity. This prominent molecular sieve structure is conducive to the dispersion of the filler and the enhancement of the mechanical properties.

[0024] Furthermore, the dialkyl phosphate includes one or more of di(dodecyl) phosphate, didodecyl) phosphate, and didetradecyl) phosphate.

[0025] Furthermore, the carbon chain of a single alkyl chain in the dialkyl phosphate with a carbon number of ≥10 is longer, and the arrangement of the molecules in the solid state is more compact, and more heat needs to be absorbed when melting, thereby increasing energy consumption; on the contrary, the carbon chain of a single alkyl chain in the dialkyl phosphate with a carbon number of <10 is shorter, the interaction between the molecules is weaker, the molecular arrangement is looser in the solid state, and relatively less heat is required when melting, so it will decompose and become ineffective after high-temperature treatment.

[0026] Furthermore, the polyol includes one or more of 2-propylene glycol, methyl propylene glycol, and glycerol. If the polyol is a simple monohydroxy alcohol compound, the stability is poor; if an alcohol compound with two or three hydroxy groups is used, it has good lubricity, moisture retention and stability due to the presence of the hydroxy groups; if an alcohol compound with more than three hydroxy groups is used, it is too active and is easy to combine with free hydrogen ions and become ineffective before being processed with seaweed mud and other materials for mixed granules.

[0027] Furthermore, the calcium carbonate is light calcium carbonate and / or heavy calcium carbonate. Light calcium carbonate is a calcium carbonate product obtained by calcining limestone raw materials to generate lime and carbon dioxide, adding water to digest the lime to generate lime milk, introducing carbon dioxide to carbonize the lime milk to generate calcium carbonate precipitation, and finally dehydrating, drying and crushing. Heavy calcium carbonate is an inorganic salt product obtained by directly crushing natural carbonate minerals using a mechanical method. Among them, light calcium carbonate has better effects on whitening, adjusting color and enhancing mechanical properties, but heavy calcium carbonate has a lower cost, so heavy calcium carbonate is preferred.

[0028] Furthermore, the average polymerization degree of the PVC resin is 741 to 1135. All PVC resins with the above polymerization degrees can be used in the present invention.

[0029] Preferably, the average degree of polymerization of the PVC resin is 846-1135.

[0030] More preferably, the average degree of polymerization of the PVC resin is 981 to 1135. The PVC resin in this range is selected because of its high average degree of polymerization and large viscosity, and the corresponding PVC pipe has better strength, rigidity, toughness, heat resistance and low temperature resistance.

[0031] Furthermore, the calcium zinc stabilizer has good thermal stability, light stability, transparency and tinting power.

[0032] Furthermore, the lubricant includes at least two of paraffin wax, polyethylene wax (PE wax), and stearic acid.

[0033] Furthermore, the lubricant is preferably paraffin, PE wax and stearic acid.

[0034] Furthermore, the amount of the paraffin wax is preferably 1 to 2 parts.

[0035] Furthermore, the amount of the PE wax is preferably 1 to 2 parts.

[0036] Furthermore, the amount of stearic acid is preferably 0 to 1 part.

[0037] Specifically, the lubricant includes 1 to 2 parts of paraffin wax, 1 to 2 parts of PE wax and 0 to 1 part of stearic acid.

[0038] Furthermore, the lubricant can reduce the friction between molecules and between molecules and processing equipment during the processing of PVC pipes, thereby improving the fluidity of the resin and enhancing the transparency and smoothness of the products.

[0039] Furthermore, the titanium dioxide is rutile titanium dioxide and / or anatase titanium dioxide. The above titanium dioxide has the characteristics of dense structure, stability, low optical activity, high hiding power and color-reducing power, and can improve the whiteness and weather resistance of the pipe.

[0040] Furthermore, the impact modifier includes one or more of acrylic copolymers (ACR), methyl methacrylate-butadiene-styrene copolymers (MBS), and chlorinated polyethylene (CPE). Such impact modifiers can improve the notched impact resistance, weather resistance and thermal stability of PVC pipes, thereby achieving high performance and functionalization of general resins.

[0041] Furthermore, the other processing aids include one or more of LPA-40, PA-20, and K-400P. Such substances can assist the impact modifier to improve the impact resistance and plasticizing properties of the PVC pipe.

[0042] The method for preparing the flame-retardant and smoke-suppressing PVC pipe of the present invention comprises the following steps:

[0043] S1. The polyol, dialkyl phosphate, seaweed mud and water are fully mixed at pH 6 to 7, and dried to obtain mixed granules.

[0044] S2. The mixed pellets obtained in step S1 are mixed with other raw materials, melt-granulated, and extruded to prepare the flame-retardant and smoke-suppressing PVC pipe.

[0045] The present invention innovatively uses seaweed mud as a filler for PVC pipes, skillfully integrates it into a composite system of dialkyl phosphate and polyol to form a flame retardant and smoke suppression composite agent, and then cooperates with other raw materials to prepare high-strength flame retardant and smoke suppression PVC pipes. Small tests, pilot tests and final debugging are carried out in suitable process schemes and equipment to produce PVC pipes with excellent flame retardancy, smoke suppression and mechanical properties and a white and beautiful appearance.

[0046] Furthermore, the present invention uses a step-by-step method to manufacture PVC pipes, which can maximize the use of the molecular sieve structure of seaweed mud, improve the dispersion of fillers, and improve the performance of flame-retardant and smoke-suppressing PVC pipes.

[0047] Furthermore, the weakly acidic environment of pH 6 to 7 is conducive to improving the porosity of the seaweed mud, further removing a small amount of Al2O3 and Fe2O3 in the seaweed mud, and can promote the blending effect of dialkyl phosphate, seaweed mud and polyol.

[0048] Furthermore, the mixing is stirring mixing.

[0049] Furthermore, the melt granulation includes hot mixing, cold mixing and granulation.

[0050] Furthermore, the hot mixing is to heat mix the raw materials to 140-160°C.

[0051] Furthermore, the cold mixing is to cold mix the raw materials to 45-55°C.

[0052] Furthermore, the granulation is to granulate the cold mixed material.

[0053] Specifically, the melt granulation is to heat-mix the raw materials to 140-160° C., and then cold-mix to 45-55° C. before discharging and granulating.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] The present invention innovatively uses seaweed mud as a filler for PVC pipes, cleverly integrating it into the composite system of dialkyl phosphate and polyols, and utilizing synergistic effects to significantly improve the flame retardant and smoke suppression effects, mechanical properties and whiteness value of PVC pipes. Among them, the unique porous microstructure of seaweed mud produces a strong synergistic enhancement effect with dialkyl phosphate as an expansion flame retardant additive through the pore effect, which not only reduces the amount of flame retardant, but also improves the mechanical properties of PVC pipes; polyols act as plasticizers and cross-linking additives, and undergo esterification reactions with dialkyl phosphate to enhance the overall flame retardant and smoke suppression effects, and synergistically enhance the whiteness of PVC pipes with seaweed mud. The present invention successfully prepares a PVC pipe with excellent flame retardant, smoke suppression and mechanical properties, high whiteness value and low cost, broadening the application field of PVC pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 The present invention is a flow chart for preparing the flame retardant and smoke suppressing PVC pipe. DETAILED DESCRIPTION

[0057] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0058] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0059] The average degree of polymerization of PVC resin was 981-1135 and was purchased from Xinjiang Zhongtai Chemical Co., Ltd.;

[0060] Seaweed mud 1500-2000 mesh, purchased from Jiangmen Tuba Building Materials Industry Co., Ltd.;

[0061] Heavy calcium carbonate was purchased from Guilin Jinshan New Materials Co., Ltd.;

[0062] Rutile titanium dioxide was purchased from Longbai Group Co., Ltd.;

[0063] LPA-40 was purchased from Shandong Ruifeng Polymer Materials Co., Ltd.;

[0064] PA-20 was purchased from Foshan Ruishan Group Co., Ltd.;

[0065] K-400P was purchased from Dow Chemical (Shanghai) Co., Ltd.

[0066] Example 1 Preparation of a flame retardant and smoke suppressing PVC pipe

[0067] A flame retardant and smoke suppression PVC pipe comprises the following components by weight: 100 parts of PVC resin, 20 parts of heavy calcium carbonate, 5 parts of seaweed mud, 10 parts of didodecyl phosphate, 2 parts of 2-propylene glycol, 1 part of paraffin, 1 part of PE wax, 1 part of stearic acid, 5 parts of rutile titanium dioxide, 5 parts of calcium zinc stabilizer, 0.5 parts of processing aid LPA-40, and 0.5 parts of impact modifier CPE.

[0068] Preparation process such as Figure 1 As shown, specifically, 5 parts of seaweed mud, 10 parts of didodecyl phosphate, and 2 parts of 2-propylene glycol are added to a weakly acidic aqueous solution of pH 6 to 7, mixed, stirred at room temperature for 2 hours, and dried to obtain small-particle mixed pellets. Then 100 parts of PVC resin, 20 parts of heavy calcium carbonate, 1 part of paraffin, 1 part of PE wax, 1 part of stearic acid, 5 parts of rutile titanium dioxide, 5 parts of calcium zinc stabilizer, 0.5 parts of processing aid LPA-40 and 0.5 parts of impact modifier CPE are added to mix in a high-speed mixer, hot mixed to 150°C, then discharged into a low-speed mixer for cooling, cold mixed to 50°C for discharge, and finally granulated in an extruder, and the obtained pellets are extruded to obtain flame-retardant and smoke-suppressing PVC pipes.

[0069] Example 2 Preparation of a flame retardant and smoke suppressing PVC pipe

[0070] The difference from Example 1 is that the amount of seaweed mud is changed from 5 parts to 8 parts, the amount of processing aid LPA-40 is changed from 0.5 parts to 1 parts, and the amount of impact modifier CPE is changed from 0.5 parts to 1 parts.

[0071] The other steps and conditions are the same as those in Example 1.

[0072] Example 3 Preparation of a flame retardant and smoke suppressing PVC pipe

[0073] The difference from Example 1 is that the number of seaweed mud is changed from 5 parts to 10 parts, the number of 2-propylene glycol is changed from 2 parts to 5 parts, the number of calcium zinc stabilizer is changed from 5 parts to 8 parts, the number of processing aid LPA-40 is changed from 0.5 parts to 1 parts, and the number of impact modifier CPE is changed from 0.5 parts to 1 parts.

[0074] The other steps and conditions are the same as those in Example 1.

[0075] Example 4 Preparation of a flame retardant and smoke suppressing PVC pipe

[0076] The difference from Example 1 is that the number of seaweed mud is changed from 5 parts to 2 parts, the number of 2-propylene glycol is changed from 2 parts to 5 parts, and the number of calcium zinc stabilizer is changed from 5 parts to 8 parts.

[0077] The other steps and conditions are the same as those in Example 1.

[0078] Comparative Example 1 Preparation of a flame retardant and smoke suppressing PVC pipe

[0079] The difference from Example 1 is that the number of portions of seaweed mud is changed from 5 portions to 0 portions.

[0080] The other steps and conditions are the same as those in Example 1.

[0081] Comparative Example 2 Preparation of a flame retardant and smoke suppressing PVC pipe

[0082] The difference from Example 1 is that the number of parts of 2-propylene glycol is changed from 2 parts to 0 parts.

[0083] The other steps and conditions are the same as those in Example 1.

[0084] Comparative Example 3 Preparation of a flame retardant and smoke suppressing PVC pipe

[0085] The difference from Example 1 is that the number of didodecyl phosphate is changed from 10 parts to 0 parts.

[0086] The other steps and conditions are the same as those in Example 1.

[0087] Comparative Example 4 Preparation of a flame retardant and smoke suppressing PVC pipe

[0088] The difference from Example 1 is that didodecyl phosphate is replaced by dibutyl phosphate.

[0089] The other steps and conditions are the same as those in Example 1.

[0090] Comparative Example 5 Preparation of a flame retardant and smoke suppressing PVC pipe

[0091] The difference from Example 1 is that 2-propylene glycol is replaced by n-propanol.

[0092] The other steps and conditions are the same as those in Example 1.

[0093] Comparative Example 6 Preparation of a flame retardant and smoke suppressing PVC pipe

[0094] The difference from Example 1 is that the amount of seaweed mud is changed from 5 parts to 0 parts, and the amount of 2-propylene glycol is changed from 2 parts to 0 parts.

[0095] The other steps and conditions are the same as those in Example 1.

[0096] Comparative Example 7 Preparation of a flame retardant and smoke suppressing PVC pipe

[0097] The difference from Example 1 is that the number of didodecyl phosphate is changed from 10 parts to 0 parts, and the number of 2-propylene glycol is changed from 2 parts to 0 parts.

[0098] The other steps and conditions are the same as those in Example 1.

[0099] Experimental example: Mechanical properties, combustion performance and optical properties test of PVC pipe

[0100] 1. Experimental methods

[0101] (1) The test method for the drop weight impact test is the National Standard of the People's Republic of China GB / T 5836.1-2018. (2) The test method for the tensile yield strength is the National Standard of the People's Republic of China GB / T 5836.1-2018. (3) The test method for the longitudinal shrinkage rate is the National Standard of the People's Republic of China GB / T 5836.1-2018.

[0102] (4) The test method for oxygen index (OI) is the National Standard of the People's Republic of China GB / T 2406.2-2009, Determination of combustion behavior of plastics by oxygen index method Part 2: Room temperature test.

[0103] (5) The test method for smoke density is the National Standard of the People’s Republic of China GB / T 8627-2007.

[0104] (6) The CIE test method for whiteness is the National Standard of the People’s Republic of China GB / T 5950-2008.

[0105] 2. Experimental results

[0106] Table 1 Mechanical properties, combustion performance and appearance performance tests of flame retardant and smoke suppression PVC pipes

[0107]

[0108] As can be seen from Table 1, the results of Example 1 and Comparative Example 1 show that when seaweed mud is not added, the PVC pipe lacks seaweed mud as a filler, resulting in a sharp deterioration in oxygen index and smoke density indicators, a decrease in flame retardant and smoke suppression performance, and limiting the mechanical properties of the pipe.

[0109] The results of Example 1 and Comparative Example 2 show that when 2-propylene glycol is not added, the PVC pipe lacks plasticizers and cross-linking aids, that is, lacks the abundant hydroxyl functional groups in the polyol to participate in the cross-linking blending reaction, resulting in a significant decrease in whiteness value and flame retardant and smoke suppression properties, and also limits the mechanical properties of the pipe.

[0110] The results of Example 1 and Comparative Example 3 show that when didodecyl phosphate is not added, the pipe lacks the acid source and carbon source of the intumescent flame retardant when burning, resulting in reduced oxygen index and smoke density performance, and reduced flame retardant and smoke suppression capabilities.

[0111] The results of Example 1 and Comparative Example 4 show that when only short-chain dibutyl phosphate is added, the dibutyl phosphate decomposes and loses some of its activity due to high-temperature processing and extrusion during pipe combustion, resulting in reduced oxygen index and smoke density performance, and reduced flame retardant and smoke suppression capabilities.

[0112] The results of Example 1 and Comparative Example 5 show that when 2-propylene glycol is changed to monohydroxyl n-propanol, its stability under high temperature conditions is not as good as that of polyhydroxyl 2-propylene glycol, and it is easy to volatilize or lose activity during processing, resulting in deterioration of oxygen index and smoke density, and decreased flame retardant and smoke suppression capabilities.

[0113] The results of Example 1 and Example 6 show that when seaweed mud and 2-propylene glycol are not added, that is, the pipe lacks both filler and heat stabilizer when burning, the smoke density increases, the oxygen index and longitudinal shrinkage performance decrease, resulting in weakened flame retardancy, smoke suppression and mechanical properties.

[0114] The results of Example 1 and Comparative Example 7 show that when didodecyl phosphate and polyol are not added, the seaweed mud is not adequately processed during processing due to the lack of acid and carbon sources of the intumescent flame retardant and plasticizers and cross-linking aids, which directly leads to a significant decrease in its dispersion performance, manifested as the accumulation and agglomeration of particles. This not only affects the appearance quality of the material, making it prone to yellowing and blackening, and significantly deteriorating the color whiteness, but also limits the mechanical properties of the material.

[0115] In summary, in the flame retardant and smoke suppressing PVC pipe of the present invention, seaweed mud, polyol and dialkyl phosphate play a synergistic role, which not only significantly enhances the flame retardant and smoke suppressing ability, reaches a more superior safety standard, and greatly improves the mechanical properties of the pipe, making it excellent in impact resistance, bending resistance and other aspects, but also ensures that the PVC pipe has a high whiteness value, and successfully prepares a PVC pipe with excellent flame retardant, smoke suppression and mechanical properties and a white and beautiful appearance.

[0116] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A flame retardant and smoke suppressing PVC pipe, characterized in that: By weight, it contains the following components: 100-120 parts of PVC resin; 10-20 parts of calcium carbonate; 1-10 parts seaweed mud; 1 to 10 parts of dialkyl phosphate; 1-8 parts of calcium zinc stabilizer; 1-5 parts of polyol; 1-2 parts lubricant; 1-5 parts of titanium dioxide; 0.5-1 part of impact modifier; 0.5-1 part of other processing aids; Wherein, the number of carbon atoms of a single alkyl chain in the dialkyl phosphate is ≥10; The polyol is an alcohol compound containing two or three hydroxyl groups.

2. The flame-retardant and smoke-suppressing PVC pipe according to claim 1, characterized in that: The mesh number of the seaweed mud is 1500-2000.

3. The flame retardant and smoke suppressing PVC pipe according to claim 1, characterized in that: The dialkyl phosphate includes one or more of di(dodecyl)phosphate, didodecyl)phosphate, and didetradecyl)phosphate.

4. The flame retardant and smoke suppressing PVC pipe according to claim 1, characterized in that: The polyol includes one or more of 2-propylene glycol, methylpropylene glycol, and glycerol.

5. The flame retardant and smoke suppressing PVC pipe according to claim 1, characterized in that: The lubricant includes at least two of paraffin wax, polyethylene wax and stearic acid.

6. The flame-retardant and smoke-suppressing PVC pipe according to claim 1, characterized in that: The titanium dioxide is rutile titanium dioxide and / or anatase titanium dioxide.

7. The flame retardant and smoke suppressing PVC pipe according to claim 1, characterized in that: The impact modifier includes one or more of acrylate copolymer, methacrylate-butylene-styrene copolymer, and chlorinated polyethylene.

8. The flame-retardant and smoke-suppressing PVC pipe according to claim 1, characterized in that: The other processing aids include one or more of LPA-40, PA-20, and K-400P.

9. The flame-retardant and smoke-suppressing PVC pipe according to claim 1, characterized in that: The calcium carbonate is light calcium carbonate and / or heavy calcium carbonate.

10. The method for preparing the flame-retardant and smoke-suppressing PVC pipe according to any one of claims 1 to 9, characterized in that: The steps include: S1. The polyol, dialkyl phosphate, seaweed mud and water are fully mixed at pH 6 to 7, and dried to obtain mixed granules. S2. The mixed pellets obtained in step S1 are mixed with other raw materials, melt-granulated, and extruded to prepare the flame-retardant and smoke-suppressing PVC pipe.

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