PVC (polyvinyl chloride) composite pipeline wound by in-situ impregnated modified wood veneer

Abstract

The invention discloses a PVC (polyvinyl chloride) composite pipeline wound by an in-situ impregnated modified wood veneer, and belongs to the technical field of wood modification treatment. According to the invention, the wood veneer is subjected to in-situ dipping modification treatment, and the PVC pipe is coated with the wood veneer through a winding forming method, so that the PVC composite pipeline is prepared; the PVC composite pipeline disclosed by the invention not only retains the excellent characteristics of a PVC material, but also overcomes the defects of the PVC material in the aspects of pressure bearing capacity, low-temperature brittleness and flame retardance, and expands the application fields of PVC and wood at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of wood modification and treatment, in particular to an in-situ impregnated modified wood veneer wound PVC composite pipe. Background Art

[0002] Traditional polyvinyl chloride (PVC) pipes are widely used in construction, drainage systems, power protection and other fields, with good corrosion resistance, chemical resistance and easy processing. However, PVC pipes have some disadvantages, such as low mechanical strength, high low-temperature brittleness, poor flame retardancy, and prominent environmental protection issues, which limit the application of PVC pipes in a wider range of fields.

[0003] In order to improve the performance of PVC pipes, external coating materials (such as foam plastics, glass fiber, aluminum foil composite materials) are usually used to enhance a specific property among mechanical strength, toughness or flame retardancy. However, it is difficult for the composite modified materials to have multiple properties required above, that is, it is impossible to achieve the integration of strength, toughness and flame retardancy. In addition, the introduction of secondary processing and other industrial materials increases costs and environmental pressures. Therefore, it is necessary to find low-cost green alternative materials to realize the multifunctionality of PVC pipes.

[0004] At present, green alternative materials mainly include wood-wrapped pipes and bamboo-wrapped pipes. The thick veneer used in traditional wood-wrapped pipes needs to be softened and balanced before winding; bamboo-wrapped pipes are formed by bamboo strips, which are hard, have many gaps, and are easy to delaminate. Therefore, the processes of both are complex and the processing costs are high. Summary of the invention

[0005] In view of the above-mentioned prior art, the purpose of the present invention is to provide an in-situ impregnated modified wood veneer wrapped PVC composite pipe. The present invention prepares a PVC composite pipe by in-situ impregnation modification of the wood veneer and coating it on a PVC pipe by a winding molding method. The PVC composite pipe of the present invention not only retains the excellent properties of PVC materials, but also overcomes its deficiencies in pressure bearing capacity, low temperature brittleness and flame retardancy, and at the same time expands the application field of PVC and wood.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] An in-situ impregnated modified wood veneer wrapped PVC composite pipe is prepared by the following method:

[0008] (1) immersing the wood veneer in a pretreatment agent consisting of glycerol triglycidyl ether, benzyltrimethylammonium chloride and lactic acid, treating at 100-140° C. for 2-8 hours to obtain a pretreated wood veneer;

[0009] (2) impregnating the pretreated wood veneer with a modifier, wherein the modifier consists of sodium alginate and phenolic resin to obtain a modified wood veneer;

[0010] (3) The modified wood veneer is subjected to hot pressing treatment and resin coating treatment in sequence, and then the resin-coated wood veneer is wrapped around a PVC pipe and cured to form, thereby preparing an in-situ impregnated modified wood veneer wrapped PVC composite pipe.

[0011] Preferably, in step (1), in the pretreatment reagent, the concentration of glycerol triglycidyl ether is 0.1-1M, the concentration of benzyltrimethylammonium chloride is 0.5-2M, and the concentration of lactic acid is 1-2M.

[0012] The present invention selects a pretreatment agent composed of a specific concentration of glycerol triglycidyl ether, benzyl trimethyl ammonium chloride and lactic acid to modify the wood veneer, which can effectively remove lignin in the wood veneer and increase porosity. Wherein, the addition of glycerol triglycidyl ether can cross-link the cellulose component, which enhances the tissue adhesion of vascular bundles and thin-walled cells, and enhances resistance to disintegration, so that the delignified wood will not crack during the pretreatment process, and a wood cellulose scaffold with high structural integrity and rich porous structure is prepared; benzyl trimethyl ammonium chloride and lactic acid solution are subsequently used to remove lignin. In this process, benzyl trimethyl ammonium chloride, as a hydrogen bond acceptor, forms hydrogen bonds with the phenolic hydroxyl groups in the lignin molecule, effectively destroys the hydrogen bonds between lignin and carbohydrates, and promotes the dissolution and separation of lignin. At the same time, lactic acid, as a hydrogen bond donor, forms hydrogen bonds with the hydroxyl groups in the lignin molecule, enhancing the solubility of lignin in a deep eutectic solvent. The synergistic effect of these two organic molecules weakens the forces between and within lignin molecules, allowing lignin to be efficiently separated and removed from wood while retaining the intact cellulose skeleton.

[0013] The method of the present invention is applicable to various wood veneers, such as poplar veneer, eucalyptus veneer, fir veneer, pine veneer and the like.

[0014] Preferably, in step (2), in the modifier, the concentration of sodium alginate is 0.5-2M, and the content of phenolic resin is 10-30wt%.

[0015] Preferably, in step (2), the conditions for the modifier impregnation treatment are: vacuum degree -0.08MPa to -0.1MPa, temperature 25°C to 80°C.

[0016] The present invention impregnates the pretreated wood veneer with a modifier, and the modifier enters the pretreated wood veneer, fills the wood pores, and increases the density, thereby increasing the strength of the modified wood. At the same time, the carboxyl group of sodium alginate itself forms a strong dynamic hydrogen bond with the hydroxyl group on the wood, which improves the toughness of the modified wood. The phenolic resin itself contains a large number of benzene rings and a unique conjugated π electron system, which enables the benzene rings to maintain the stability of their structure when heated; further, when sodium alginate burns, a carbon layer is formed on the outside of the wood to isolate oxygen, that is, the double cross-linked network organic molecular structure generated by the two organisms increases the flame retardancy of the wood veneer.

[0017] Preferably, in step (3), the temperature of the hot pressing treatment is 80°C-120°C, the hot pressing pressure is 10MPa-20MPa, and the time is 1-3h.

[0018] The moisture content and compression rate of the modified wood veneer are regulated through hot pressing treatment, thereby further reducing the wood pores, increasing the density, forming densified wood with shrunken cell cavities, and simultaneously improving the strength and toughness of the modified wood.

[0019] Preferably, in step (3), a thermosetting resin is used for resin impregnation treatment; the thermosetting resin can be selected from one or more of epoxy resin, polyester resin, and phenolic resin.

[0020] Preferably, in step (3), the winding parameter conditions are: 0° winding angle, 5N winding tension, and 100mm / min winding speed.

[0021] Preferably, in step (3), the curing temperature is 40-120°C.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention first uses a pretreatment reagent to remove lignin in the wood veneer to further increase the porosity, and then uses a modifier to perform an impregnation treatment to generate a double cross-linked network organic molecular structure inside the wood veneer, and synergistically performs a hot pressing treatment to improve the strength, toughness and flame retardancy of the wood, thereby obtaining a green, strong, and flame-retardant modified wood veneer. Then, after the surface of the modified wood veneer is coated with a thermosetting resin, it is coated on a PVC pipe through a winding process, and finally cured and formed to obtain an in-situ impregnated modified wood veneer wrapped PVC composite pipe. The present invention improves the mechanical properties and environmental adaptability of PVC pipes, solves the problems of low mechanical properties, high brittleness and non-flammability of traditional PVC pipes, and extends the service life of the pipes; the winding process is simple and the inner diameter is controllable, which provides a new technical route for the application of wood veneers in composite materials and has broad market prospects.

[0024] (2) The in-situ impregnated modified wood veneer wrapped PVC composite pipe prepared by the present invention has a wide range of application prospects in multiple fields, and is particularly suitable for occasions with high requirements for pipe pressure bearing performance, toughness and flame retardancy, such as high-pressure water pipelines, outdoor drainage systems and power protection pipelines. In addition, the method has low cost, simple process, easy to realize industrial production, and has good economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 : The preparation flow chart of the wood veneer wrapped PVC composite pipe of the present invention.

[0026] Figure 2 : Photograph of the in-situ impregnated modified wood veneer wrapped around the PVC composite pipe prepared in Example 1

[0027] Figure 3 : Photograph of PVC composite pipe A prepared in Comparative Example 1.

[0028] Figure 4 : Photograph of PVC composite pipe B prepared in Comparative Example 2.

[0029] Figure 5 : Photograph of PVC composite pipe C prepared in Comparative Example 3.

[0030] Figure 6 : Vertical combustion test experimental photos; in the figure, A is a PVC pipe, B is a PVC composite pipe prepared in Comparative Example 1, and C is an in-situ impregnated modified wood veneer wrapped PVC composite pipe prepared in Example 1. DETAILED DESCRIPTION

[0031] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0032] As mentioned above, existing PVC pipes have problems such as low mechanical strength, high low-temperature brittleness, and poor flame retardancy, which limit their application. Wood is a green and renewable raw material. Using wood as the outer covering material of PVC pipes is a green and environmentally friendly way to transform PVC pipes. However, due to the large cell cavity, loose material, low density, low strength, and easy burning of wood, it is difficult to meet practical requirements by directly covering PVC pipes with wood veneers.

[0033] In view of this, the present invention proposes a novel in-situ impregnated modified wood veneer wrapped PVC composite pipe and a preparation method thereof. The preparation process diagram of the in-situ impregnated modified wood veneer wrapped PVC composite pipe of the present invention is as follows: Figure 1As shown. The present invention firstly uses glycerol triglycidyl ether, benzyltrimethylammonium chloride and lactic acid to form a pretreatment reagent to pretreat the wood veneer to remove lignin in the wood and further increase the porosity; then uses a modifier composed of sodium alginate and phenolic resin to perform in-situ impregnation treatment to form an organic molecular structure of a double cross-linked network inside the wood veneer; then the moisture and compression rate of the impregnated wood veneer are regulated by regulating the hot pressing temperature, time and hot pressing pressure to avoid the formation of pores due to the volatilization of moisture during the pipeline preparation process; by regulating the type, viscosity, time and other aspects of the resin, the wood veneer is evenly coated so that the wood veneer coated with the resin has a thermal curing molding characteristic; by regulating the winding angle, speed, tension, PVC pipe diameter and other aspects, the composite pipe is formed and prepared; by regulating the temperature and rotation speed, good pipe curing is achieved, and finally a wood veneer wrapped with PVC composite pipe is prepared.

[0034] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in conjunction with specific embodiments.

[0035] The test materials used in the examples and comparative examples of the present invention are all conventional test materials in the art and can be purchased through commercial channels. The experimental methods without detailed conditions are carried out in accordance with conventional test methods or the operating instructions recommended by the supplier. Among them:

[0036] The CAS registration number of glycerol triglycidyl ether is 13236-02-7; the CAS registration number of benzyltrimethylammonium chloride is 56-93-9; and the CAS registration number of sodium alginate is 9005-38-3.

[0037] The size of the PVC pipe used in the present invention is 100×3 mm.

[0038] Phenolic resin was purchased from Beijing Taier Chemical Co., Ltd.; E54 epoxy resin was purchased from Guangzhou Yuebao Chemical Technology Co., Ltd.

[0039] Example 1: Preparation of in-situ impregnated modified wood veneer wrapped PVC composite pipe

[0040] (1) immersing a poplar veneer with a thickness of 0.5 mm and a width of 40 mm in a pretreatment reagent, wherein the pretreatment reagent is composed of glycerol triglycidyl ether, benzyltrimethylammonium chloride and lactic acid, wherein the concentration of glycerol triglycidyl ether is 0.5 M, the concentration of benzyltrimethylammonium chloride is 1 M, and the concentration of lactic acid is 1.5 M; treating at 120° C. for 4 h to obtain a pretreated wood veneer;

[0041] (2) in situ impregnation of the pretreated wood veneer with a modifier under the conditions of a vacuum degree of -0.08 MPa and a temperature of 25° C. to obtain a modified wood veneer; the modifier is composed of sodium alginate and a phenolic resin, wherein the concentration of the sodium alginate in the modifier is 1 M and the solid content of the phenolic resin is 20 wt %;

[0042] (3) The modified wood veneer was hot-pressed at 15 MPa and 120 °C for 2 h and then coated with E54 epoxy resin (coating amount was 20 g / m 2 ); the resin-coated wood veneer is wrapped around the PVC pipe, and the winding parameters are: 0° winding angle, 5N winding tension, and 100mm / min winding speed; after one circle of winding, it is cured at 80°C to prepare an in-situ impregnated modified wood veneer wrapped PVC composite pipe.

[0043] Comparative Example 1:

[0044] Directly coat the poplar veneer with a thickness of 0.5 mm and a width of 40 mm with E54 epoxy resin (coating amount of 20 g / m 2 ), the resin-coated wood veneer is wrapped around the PVC pipe, and the winding parameters are: 0° winding angle, 5N winding tension, and 100mm / min winding speed; after one circle of winding, it is cured at 80°C to prepare PVC composite pipe A.

[0045] Comparative Example 2:

[0046] A poplar veneer with a thickness of 0.5 mm and a width of 40 mm is immersed in a pretreatment reagent, wherein the pretreatment reagent consists of glycerol triglycidyl ether, benzyltrimethylammonium chloride and lactic acid, wherein the concentration of glycerol triglycidyl ether is 0.5 M, the concentration of benzyltrimethylammonium chloride is 1 M, and the concentration of lactic acid is 1.5 M; the pretreatment is carried out at 120° C. for 4 hours to obtain a pretreated wood veneer;

[0047] The pretreated wood veneer was hot-pressed at 15 MPa and 120 °C for 2 h, and then coated with E54 epoxy resin (coating amount was 20 g / m 2 ); the resin-coated wood veneer was wrapped around the PVC pipe, and the winding parameters were: 0° winding angle, 5N winding tension, and 100mm / min winding speed; after one circle of winding, it was cured at 80°C to prepare a PVC composite pipe B.

[0048] Comparative Example 3:

[0049] A poplar veneer with a thickness of 0.5 mm and a width of 40 mm is in-situ impregnated with a modifier under the conditions of a vacuum degree of -0.08 MPa and a temperature of 25° C. to obtain a modified wood veneer; the modifier is composed of sodium alginate and a phenolic resin, wherein the concentration of the sodium alginate is 1 M and the solid content of the phenolic resin is 20 wt %;

[0050] The modified wood veneer was hot-pressed at 15 MPa and 120 °C for 2 h, and then coated with E54 epoxy resin (coating amount was 20 g / m 2 ); the resin-coated wood veneer was wrapped around the PVC pipe, and the winding parameters were: 0° winding angle, 5N winding tension, and 100mm / min winding speed; after one circle of winding, it was cured at 80°C to prepare a PVC composite pipe C.

[0051] Test example: Performance test of PVC composite pipe

[0052] The performance tests of the PVC composite pipes prepared in the embodiments of the present invention and the comparative examples are as follows:

[0053] 1. Flame retardant performance test:

[0054] The pipe samples prepared in Example 1 and Comparative Example 1 were cut and polished, and the limiting oxygen index of the pipes was tested according to GB / T2406.1-2008. A 10 mm long burning distance mark was made, and the sample was fixed vertically in the combustion tube using the HC-2 oxygen index tester. Oxygen and nitrogen were mixed, and the burning end of the sample was ignited from bottom to top, and the time was recorded and the burning length of the sample was observed; the oxygen concentration was changed so that the oxygen concentration was the minimum when the sample reached a continuous and stable state of combustion, and the limiting oxygen index was calculated. The results are shown in Table 1.

[0055] Table 1: Limiting oxygen index test results

[0056]

[0057] The limiting oxygen index is an index that characterizes the combustion behavior of a material. A higher limiting oxygen index indicates that the material is not easy to burn, and a lower limiting oxygen index indicates that the material is easy to burn. It is generally believed that materials with a limiting oxygen index of less than 22% are flammable materials, and materials with a limiting oxygen index of more than 27% are flame-retardant materials. As can be seen from Table 1, the limiting oxygen index of the in-situ impregnated modified wood-wrapped pipe prepared by the present invention is greater than 27%. Therefore, the material prepared by the present invention has good flame retardant properties, while the limiting oxygen index of the material prepared in Comparative Example 1 is only 18.2%.

[0058] In addition, according to the ASTM D2863-2017 standard, a vertical burning test machine (czf-5 burning test machine, Beijing AVIC Times Instruments, Beijing, China) was used to test the vertical burning behavior of the material. Twelve specimens were tested in parallel in each group, and the results were averaged. The sample size was 130 × 13 × 3 mm (L × R × T).

[0059] In order to comprehensively investigate whether the in-situ impregnated modified wood veneer wrapped pipe has flame retardancy, its fire protection effect was evaluated and a vertical burning test was carried out.

[0060] Figure 6 The alcohol lamp vertical combustion test of each sample presented shows that the PVC pipe and the PVC composite pipe prepared in comparative example 1 are easily ignited and burn violently until they are completely burned out. However, the PVC composite pipe prepared in example 1 is still not ignited after 10 seconds, showing anti-flammability. It can be seen that the double network structure formed by in-situ impregnation has a significant contribution to the flame retardancy of the wood veneer wound pipe.

[0061] 2. Compression resistance test:

[0062] The pipe samples prepared in Comparative Examples 1 to 3 and Example 1 and the PVC pipe samples were cut, and the ring stiffness when the pipe deformation was 3% and the ring stiffness at low temperature for 24 hours were tested according to GB / T9647-2015 / ISO 9969:2007. The length and area of ​​the pipe material were 75 cm. The pipe material was placed on a mechanical testing machine for compression, and the maximum force when the pipe material was deformed by 3% was determined according to the force-displacement curve, and then the ring stiffness (KPa) of the pipe material was obtained.

[0063] Table 2: Compressive strength test results

[0064]

[0065] Ring stiffness is used to evaluate the deformation resistance of pipelines and pipe structures under external loads. It can be seen from Table 2 that the ring stiffness of the wood veneer wrapped PVC composite pipeline prepared by the present invention reaches 592.09 kPa, which is significantly higher than that of the PVC pipe; and after being placed at a low temperature of -60°C for 24 hours, it still has a ring stiffness of 555.54 kPa; compared with comparative examples 1-3, it can be seen that the combination of the pretreatment agent and the modifier has a synergistic effect in improving the technical effect of the ring stiffness of the prepared pipeline compared with the treatment with the pretreatment agent alone and the treatment with the modifier alone, and the effect of 1+1>2 is achieved.

[0066] 3. Bending strength test:

[0067] The pipe samples prepared in Comparative Examples 1 to 3 and Example 1 and the PVC pipe samples were cut and the bending strength of the pipes was tested according to GB / T17657-2013. The size of the pipe material was 100 mm×20 mm×2.5 mm. The pipe material was placed on a mechanical testing machine for bending and compression, and the bending strength (MPa) and bending modulus (GPa) of the pipe material were determined according to the stress-strain curve.

[0068] Table 3: Flexural strength and flexural modulus test results

[0069]

[0070] Bending strength refers to the maximum stress that a material can withstand when it breaks under a bending load or reaches a specified bending moment. This stress is the maximum normal stress during bending and is measured in MPa (megapascals). It reflects the material's ability to resist bending and is used to measure the material's bending performance. As shown in Table 3, wood veneer wrapped around PVC composite pipes has a significant effect on enhancing the mechanical properties of PVC pipes.

[0071] 4. Impact strength test:

[0072] The pipe samples prepared in Comparative Examples 1 to 3 and Example 1 and the PVC pipe samples were cut and the impact strength of the pipes was tested according to GB / T18743.1-2022. The size of the pipe material was 120 mm × 10 mm × 2.5 mm. The pipe material was placed on an impact tester for impact, and the impact strength (KJ / cm 2 ).

[0073] Table 4: Impact strength test results

[0074]

[0075] Impact strength is an indicator to measure the toughness of a material, and is usually defined as the energy absorbed per unit cross-sectional area when a sample breaks or cracks under an impact load. As shown in Table 4, the wood veneer wrapped PVC composite pipe prepared in the present invention has a significant effect of enhancing the impact strength of the PVC pipe.

[0076] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the technical combination of the present application may be subject to various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An in-situ impregnated modified wood veneer wrapped PVC composite pipe, characterized in that: Prepared by the following method: (1) immersing the wood veneer in a pretreatment agent consisting of glycerol triglycidyl ether, benzyltrimethylammonium chloride and lactic acid, treating at 100-140° C. for 2-8 hours to obtain a pretreated wood veneer; (2) impregnating the pretreated wood veneer with a modifier, wherein the modifier consists of sodium alginate and phenolic resin to obtain a modified wood veneer; (3) The modified wood veneer is subjected to hot pressing treatment and resin coating treatment in sequence, and then the resin-coated wood veneer is wrapped around a PVC pipe and cured to form, thereby preparing an in-situ impregnated modified wood veneer wrapped PVC composite pipe.

2. The in-situ impregnated modified wood veneer wrapped PVC composite pipe according to claim 1, characterized in that: In step (1), in the pretreatment reagent, the concentration of glycerol triglycidyl ether is 0.1-1M, the concentration of benzyltrimethylammonium chloride is 0.5-2M, and the concentration of lactic acid is 1-2M.

3. The in-situ impregnated modified wood veneer wrapped PVC composite pipe according to claim 1, characterized in that: In step (2), in the modifier, the concentration of sodium alginate is 0.5-2M, and the content of phenolic resin is 10-30wt%.

4. The in-situ impregnated modified wood veneer wrapped PVC composite pipe according to claim 1 or 3, characterized in that: In step (2), the conditions for the modifier impregnation treatment are: vacuum degree -0.08MPa to -0.1MPa, temperature 25°C to 80°C.

5. The in-situ impregnated modified wood veneer wrapped PVC composite pipe according to claim 1, characterized in that: In step (3), the temperature of the hot pressing treatment is 80°C-120°C, the hot pressing pressure is 10MPa-20MPa, and the time is 1-3h.

6. The in-situ impregnated modified wood veneer wrapped PVC composite pipe according to claim 1, characterized in that: In step (3), a thermosetting resin is used for resin coating treatment; the thermosetting resin is selected from one or more of epoxy resin, polyester resin, and phenolic resin.

7. The in-situ impregnated modified wood veneer wrapped PVC composite pipe according to claim 1, characterized in that: In step (3), the winding parameter conditions are: 0° winding angle, 5N winding tension, and 100mm / min winding speed.

8. The in-situ impregnated modified wood veneer wrapped PVC composite pipe according to claim 1, characterized in that: In step (3), the curing temperature is 40-120°C.

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