Guanine class PVC heat stabilizer and its application

Abstract

The application discloses a guanine type PVC heat stabilizer and application thereof, and belongs to the technical field of heat stabilizers. The heat stabilizer is guanine or guanine nucleoside, or is a compound of a main stabilizer and an auxiliary stabilizer, wherein the main stabilizer is guanine or guanine nucleoside, and the auxiliary stabilizer is at least one of calcium salt type stabilizers, zinc salt type stabilizers and polyhydric alcohol type stabilizers. The guanine type heat stabilizer can improve the initial whiteness of PVC, endows PVC with good long-term stability, can be used for preparing PVC composite materials, improves the heat stabilization performance and mechanical properties of the PVC composite materials, and meets the use requirements of PVC composite materials in most scenes.

Description

Technical Field

[0001] This invention relates to the field of heat stabilizer technology, and more specifically, to a guanine-based PVC heat stabilizer and its application. Background Technology

[0002] PVC, or polyvinyl chloride, is a synthetic resin with excellent overall performance. It is polymerized from vinyl chloride monomer under specific conditions through a free radical polymerization mechanism. PVC has poor light and heat stability; it decomposes when the temperature reaches above 120°C or after prolonged exposure to sunlight. Chlorine atoms on the macromolecular chain combine with adjacent hydrogen atoms to form hydrogen chloride (HCl) and create carbon-carbon double bonds. The released HCl catalyzes the decomposition of PVC, leading to a vicious cycle. As chlorine atoms are continuously released and conjugated double bonds are continuously formed, the color of the PVC material gradually darkens, and its mechanical properties decline rapidly. During production and processing, PVC often needs to be heated to relatively high temperatures; therefore, in practical applications, appropriate heat stabilizers need to be added to improve the processability and usability of PVC.

[0003] With the advancement of technology and the continuous development of PVC heat stabilization technology, heat stabilizers that were previously harmful to the environment have gradually been phased out. Organic nitrogen heat stabilizers, due to their outstanding environmental protection characteristics, have seen rapid development in recent years. Current research on organic nitrogen heat stabilizers mainly focuses on thiourea and pyrimidine heat stabilizers; research on the application of guanine and its derivatives in PVC heat stabilizers is still in its infancy.

[0004] Therefore, developing a new type of high-efficiency heat stabilizer that has good synergy with zinc salts and can be applied to PVC composite materials has become an urgent need in the industry. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a guanine-based PVC heat stabilizer and its application.

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

[0007] A guanine-based PVC heat stabilizer, wherein the heat stabilizer is a compound of a main stabilizer and an auxiliary stabilizer or is only a main stabilizer, wherein the main stabilizer is guanine or guanine nucleoside, and the auxiliary stabilizer is at least one of calcium salt stabilizers, zinc salt stabilizers, and polyol stabilizers.

[0008] The present invention is further configured such that when the heat stabilizer is a compound of the main stabilizer and the zinc salt stabilizer, the mass ratio of the main stabilizer to the zinc salt stabilizer is >1.

[0009] The present invention is further configured such that the mass ratio of the main stabilizer to the zinc salt stabilizer is (1.5-4):1.

[0010] The present invention is further configured such that the calcium salt stabilizer is calcium stearate; the zinc salt stabilizer is zinc stearate; and the polyol stabilizer is galactitol or mannitol.

[0011] The present invention is further configured such that the heat stabilizer is a compound of the main stabilizer, zinc stearate, and galactitol, and the mass ratio of the main stabilizer to zinc stearate and galactitol is (1-3):1:(0.5-2).

[0012] The present invention is further configured such that the heat stabilizer is a compound of the main stabilizer, zinc stearate, and mannitol, and the mass ratio of the main stabilizer to zinc stearate and mannitol is (0.5-3):1:(0.5-3).

[0013] An application of a guanine-based PVC heat stabilizer as described above, wherein the heat stabilizer is used to prepare PVC composite materials.

[0014] The present invention is further configured such that the heat stabilizer is used to prepare PVC / rice husk composite material.

[0015] The present invention is further configured such that PVC resin, plasticizer, heat stabilizer, and silane coupling agent are mixed with modified rice husk fiber and then molded to obtain PVC / rice husk composite material.

[0016] In summary, the present invention has the following beneficial effects:

[0017] This invention uses guanine or guanine nucleoside as the key component. It can be used alone as a PVC heat stabilizer or compounded with auxiliary stabilizers to form a heat stabilizer. Its significant advantages are: guanine-like substances themselves can provide good long-term thermal stability for PVC and can synergistically interact with zinc salts such as zinc stearate, improving both the initial whiteness and long-term stability of PVC; at the same time, adding polyols such as galactitol and mannitol to the guanine or guanine nucleoside compound with zinc salts can effectively prevent the "zinc burning" problem, further enhancing the thermal stability of PVC. The heat stabilizer of this invention can be extended to fields such as PVC / rice husk composites, enhancing the mechanical properties and thermal stability of composite materials without affecting the microscopic aggregation state of PVC resin, meeting the application requirements of PVC composite materials in most scenarios. Attached Figure Description

[0018] Figure 1 Figure 1 shows the oven aging test results of PVC samples with added stabilizers (Comparative Example 1, Comparative Example 2, Example 1-1, Example 1-18) and pure PVC samples.

[0019] Figure 2The Congo red test results are shown for PVC and pure PVC with added stabilizers (Comparative Example 1, Comparative Example 2, Example 1-1, Example 1-18).

[0020] Figure 3 The image shows a comparison of the infrared and visible spectra of guanine before and after the heating reaction.

[0021] Figure 4 A schematic diagram illustrating the principle by which guanine improves the thermal stability of PVC;

[0022] Figure 5 The image shows the oven aging test results of PVC samples with stabilizers from Examples 1-1 to 1-5 and Comparative Example 1 added.

[0023] Figure 6 The Congo Red test results are shown for PVC containing stabilizers from Examples 1-1 to 1-5 and Comparative Example 1.

[0024] Figure 7 The graph shows the oven aging test results of PVC samples with stabilizers added in Examples 1-6 to 1-11;

[0025] Figure 8 The graph shows the oven aging test results of PVC samples with stabilizers from Examples 1-12 to 1-17 added.

[0026] Figure 9 The graph shows the Congo red test results for PVC with stabilizers added in Examples 1-6 to 1-17;

[0027] Figure 10 The image shows the oven aging test results of PVC samples with stabilizers from Examples 1-18 to 1-22 and Comparative Example 1 added.

[0028] Figure 11 The Congo Red test results of PVC with added stabilizers from Examples 1-1 to 1-5, Examples 1-18 to 1-22, and Comparative Example 1 are shown in the figure.

[0029] Figure 12 Figure 1 shows the oven aging test results of PVC samples with added stabilizers from Examples 1-19, 1-7, and 1-13.

[0030] Figure 13 Linear fitting plots of Ozawa thermal decomposition kinetics for PVC samples with stabilizers added according to Examples 1-1, 1-18, and 1-19, and for pure PVC samples;

[0031] Figure 14 The graph shows the trend of tensile strength of the PVC composite materials prepared in Example 2 and Comparative Example 3 as a function of rice husk content.

[0032] Figure 15 The graph shows the trend of elongation at break of the PVC composite materials prepared in Example 2 and Comparative Example 3 as a function of rice husk content.

[0033] Figure 16 Microscopic cross-sectional views of the PVC composite materials prepared in Examples 2-1 to 2-5 ( Figure 16 part a to Figure 16 The e part corresponds sequentially to Examples 2-1 to 2-5).

[0034] Figure 17 Cross-sectional micrographs of PVC composite materials with different rice husk fiber additions (10%) Figure 17 Part A to Figure 17 Part C corresponds sequentially to Example 3-3, Example 2-3, and Example 2-9.

[0035] Figure 18 The graph shows the water absorption test results of the PVC composite materials prepared in Examples 2-1 to 2-6.

[0036] In the above diagram, N0 represents guanine, N represents guanine nucleoside, ZnSt2 represents zinc stearate, CaSt2 represents calcium stearate, B represents galactitol, and G represents mannitol. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The present invention relates to a compound of guanine-based PVC heat stabilizers as the main stabilizer and auxiliary stabilizers, or as the main stabilizer alone. The main stabilizer is guanine or guanine nucleoside, and the auxiliary stabilizer is at least one of calcium salt stabilizers (preferably calcium stearate), zinc salt stabilizers (preferably zinc stearate), and polyol stabilizers (preferably sugar alcohols, more preferably galactitol or mannitol).

[0039] When the heat stabilizer is a compound of the main stabilizer and the zinc salt stabilizer, the mass ratio of the main stabilizer to the zinc salt stabilizer is >1. Preferably, the mass ratio of the main stabilizer to the zinc salt stabilizer is (1.5-4):1.

[0040] When the heat stabilizer is a compound of the main stabilizer, zinc stearate, and galactitol, the preferred mass ratio of the main stabilizer to zinc stearate and galactitol is (1-3):1:(0.5-2); when the heat stabilizer is a compound of the main stabilizer, zinc stearate, and mannitol, the preferred mass ratio of the main stabilizer to zinc stearate and mannitol is (0.5-3):1:(0.5-3).

[0041] The guanine-based PVC heat stabilizer of this invention can be used to prepare PVC composite materials, especially PVC / rice husk composite materials (by mixing PVC resin, plasticizer, heat stabilizer, and silane coupling agent with modified rice husk fiber and then molding it).

[0042] Example 1: Guanine-based heat stabilizers

[0043] The components and formulations of the heat stabilizers in Examples 1-1 to 1-22 are shown in Table 1.

[0044] Table 1

[0045]

[0046] Comparative Examples 1 to 2

[0047] The heat stabilizer for Comparative Example 1 was zinc stearate; the heat stabilizer for Comparative Example 2 was calcium stearate.

[0048] The performance of the heat stabilizers in the above embodiments and comparative examples was tested respectively. The test methods were as follows:

[0049] (1) Oven color change method

[0050] 12g of PVC powdered resin (purchased from Xinjiang Tianye Group Co., Ltd., brand name SG-5), 12g of PVC paste resin (P-450, purchased from Ordos Junzheng Energy Chemical Co., Ltd.), 3.6g of CaCO3 (light calcium carbonate, purchased from Zhejiang Haipton New Material Co., Ltd.), and 0.72g of heat stabilizer were poured into a mortar and ground in a fixed direction using a pestle. The mixed materials were then transferred to a disposable grinding cup, and 12g of dioctyl phthalate plasticizer was added and further stirred until the mixture could flow uniformly. The mixture was then transferred to a double-layered glass mold, clamped, and placed in a 140℃ forced-air oven for 30 minutes to plasticize. After the mold cooled, it was demolded to obtain PVC samples. A film prepared using only PVC resin without heating the stabilizer (i.e., a 1:1 mass ratio of PVC powdered resin and PVC paste resin) was used as a control group, referred to as a pure PVC sample.

[0051] Reference standard: GB / T 9349-2002. Prepared PVC samples were cut into square sheets measuring 15.0 × 15.0 mm, laid flat on a smooth tray, and stably transferred to a 180℃ forced-air oven. The heating time was set, and one heated sample was removed every 10 minutes. The heated samples were then sorted according to their heating time until the remaining samples in the oven had all turned black or showed no further darkening. Heating was then stopped. The sorted samples were scanned, and the colors were extracted to create a table for observing the aging and discoloration trends of the PVC samples.

[0052] (2) Static Congo Red Method

[0053] Reference standard: GB / T 2917.1-2002. Weigh 5g of PVC powdered resin and 0.15g of heat stabilizer and grind and mix thoroughly. Place the mixed experimental material into a test tube and heat in a 180℃ oil bath, ensuring the upper surface of the mixture inside the test tube is flush with the oil bath surface at the outer end of the test tube. Fix Congo red test paper to the mouth of the test tube, ensuring the bottom of the test paper is parallel to the surface of the mixture inside the test tube and 20mm away. Record the time required for the Congo red test paper to completely turn from red to blue from the start of heating. Each group should be tested three times, and the average value should be taken as the static Congo red time. A control group consisting of PVC resin without heating the stabilizer (referred to as pure PVC) should be used.

[0054] (3) Infrared spectroscopy analysis

[0055] Take two equal masses of guanine solid powder. One portion of guanine solid powder is left untreated and serves as a control group. The other portion of guanine solid powder is added to a three-necked flask. The loaded three-necked flask is placed in an oil bath at 180°C and heated while HCl gas is introduced into the flask. A magnetic particle is placed at the bottom of the flask to ensure that the guanine powder inside the flask is in full contact with the HCl gas. After heating for 1 hour, the supply of HCl gas is stopped, and the three-necked flask is placed in air and heated for another hour to fully remove any unreacted HCl gas.

[0056] The guanine samples before and after heating were rinsed and dried with a small amount of deionized water. Two rinse solutions were then added dropwise to silver nitrate solution, and the appearance of a white precipitate was observed. The two dried guanine samples were analyzed by infrared spectroscopy. The changes in characteristic peaks at different wavelengths were compared, and the changes in functional groups before and after the reaction were analyzed to summarize the reaction principle.

[0057] The instrument used in the experiment was an IR Prestige 21 infrared spectrometer, and the experimental wavelength range was set to 400-4000 cm⁻¹. -1 .

[0058] (4) Thermal decomposition kinetic analysis

[0059] The thermal decomposition kinetics were studied using a TGA-6300 thermogravimetric analyzer. The sample heating range was set from room temperature to 400℃, with heating rates of 10, 15, 20, 25, and 30℃ / min. Kinetic parameters such as activation energy (Ea, kJ / mol) were calculated using the Ozawa equations (Equations 3-1 and 3-2).

[0060] (3-1)

[0061] (3-2)

[0062] In the above formula: β is the heating rate, R is the gas constant (8.314 J / (mol·K)), and Ta is the peak temperature of the DTG curve.

[0063] Test Result Analysis:

[0064] (1) Effects of guanine and guanine nucleoside on the thermal stability of PVC

[0065] 1.1 Oven aging test results:

[0066] PVC samples were prepared using zinc stearate, calcium stearate, guanine, and guanine nucleoside as heat stabilizers, respectively, and the oven aging results were measured as follows: Figure 1 As shown in the figure, while zinc stearate provides good initial stability and optimal whiteness to PVC, the resulting "zinc burning" effect causes the PVC to completely turn black due to thermal degradation and aging after only 20 minutes of heating. Guanine exhibits the best stabilizing effect, good long-term thermal stability, and a light final color. While the stabilizing effect of guanine nucleoside is not as good as guanine, it is similar to that of calcium stearate, a commonly used long-term heat stabilizer. Guanine and guanine nucleoside, as heat stabilizers for PVC, provide excellent long-term thermal stability.

[0067] 1.2 Congo Red Test Results:

[0068] Test results for Congo red in PVC with added guanine, guanine nucleoside, and other common heat stabilizers are as follows: Figure 2 As shown in the figure, it can be concluded that the static Congo red time of guanine nucleoside (1130s) is slightly lower than that of guanine (1179s) and slightly higher than that of calcium stearate. This is consistent with the oven aging test results of guanine nucleoside and guanine, further illustrating the good improvement effect of guanine and guanine nucleoside on the thermal stability of PVC.

[0069] (2) Mechanism of guanine in improving the thermal stability of PVC

[0070] Based on the oven aging test results and the Congo red test results, guanine can impart a longer stability time and better initial whiteness to PVC, suggesting that guanine may have the ability to absorb HCl generated during the thermal degradation of PVC. The silver nitrate experiment showed that after adding silver nitrate solution, a white precipitate formed in the filtrate of the guanine sample after heating, indicating the presence of chloride ions in the filtrate. However, no obvious phenomenon was observed in the filtrate of the guanine sample that did not undergo the heating reaction, suggesting that guanine has a certain absorption capacity for HCl.

[0071] To further verify the thermal stability mechanism of guanine, infrared and visible spectroscopy results are as follows: Figure 3 The image shows a height of 1560 cm. -1 and 1730 cm -1 The two characteristic peaks showed significant changes. After consulting the literature, the former is the deformation vibration of the NH bond in the amide structure, and the latter is the stretching vibration of the C=O bond in the secondary amide structure. Combining the previous text and literature on the mechanism of the effect of organic nitrogen compounds on the thermal stability of PVC, it is speculated that the C=O bond in the guanine structure undergoes an addition reaction, absorbing the HCl produced by the thermal degradation of PVC, thereby improving the thermal stability of PVC.

[0072] Figure 4 The mechanism by which guanine improves the thermal stability of PVC is inferred from infrared spectroscopy analysis. When PVC is thermally degraded, it produces HCl. When guanine comes into contact with HCl, it is absorbed and locked in the molecular chain through an addition reaction, thereby slowing down its further catalytic degradation of PVC.

[0073] (3) Effect of guanine and zinc stearate double complex on the thermal stability of PVC

[0074] 3.1 Oven aging test results:

[0075] The oven aging test results of PVC with different proportions of guanine and zinc stearate compound stabilizers are shown in the figure. Figure 5 As can be seen from the figure, the combination of guanine and zinc stearate can effectively improve the initial whiteness of PVC and achieve better initial thermal stability. However, the "zinc burning" effect caused by zinc stearate will still cause the PVC sample to age and turn black rapidly in a short period of time. Even when the ratio of guanine to zinc stearate is 2.4 / 0.6, the initial stability time of the sample only reaches 30 minutes before it begins to age and turn black.

[0076] 3.2 Congo Red Test Results:

[0077] The test results of Congo red in PVC with different proportions of guanine and zinc stearate compound stabilizers are shown in the figure. Figure 6As can be seen from the figure, the static Congo red time gradually decreases with the increase of zinc stearate ratio, indicating that the "zinc burning" effect of zinc stearate will suppress the long-term stabilizing effect of guanine on PVC. This is consistent with the oven aging test results of PVC after guanine / zinc stearate double compounding. It is necessary to introduce polyol auxiliary heat stabilizers to suppress the negative impact of "zinc burning".

[0078] (4) Effect of the triple combination of guanine and zinc stearate on the thermal stability of PVC

[0079] 4.1 Oven aging test results:

[0080] Based on different ratios of guanine and zinc stearate compounded together, galactitol (B) was added to the compounded system, and the oven aging test results of the obtained PVC samples are as follows: Figure 7 As shown in the figure, the addition of galactitol helps guanine effectively inhibit the "zinc burning" effect caused by zinc stearate, thus prolonging the initial stability time of PVC film. The table also shows that the optimal combination of guanine / zinc stearate / galactitol is 1.2 / 0.6 / 1.2. Based on the mechanism of action of adenine and zinc stearate, it can be inferred that the stearic acid in zinc stearate replaces the unstable chlorine atoms on the PVC chain segments, while the zinc chloride formed by the combination of zinc and chlorine atoms is complexed by galactitol, thereby inhibiting the catalytic effect of zinc chloride on the thermal degradation of PVC. The HCl released from the thermal degradation of PVC is absorbed by guanine. The three stabilizers work synergistically to effectively improve the thermal stability of PVC.

[0081] The oven aging test results of PVC samples with different proportions of guanine / zinc stearate / mannitol (G) as a three-component stabilizer are as follows: Figure 8 As shown in the figure, mannitol can effectively suppress the negative effects of zinc chloride. However, mannitol itself has a weak effect on improving PVC stability. When the proportion of mannitol is too high, the effect of the composite heat stabilizer on PVC is actually worse. The optimal ratio of guanine / zinc stearate / mannitol is 1.2 / 0.6 / 1.2. Compared with galactitol, mannitol has a better inhibitory effect on zinc chloride and can achieve better initial stabilization.

[0082] 4.2 Congo Red Test Results:

[0083] The test results of PVC Congo Red obtained by adding galactitol and mannitol to guanine / zinc stearate bis-compounds at different ratios are as follows: Figure 9As shown in the figure, the compound groups with the longest stability times are guanine / zinc stearate / galactitol (1.2 / 0.6 / 1.2) and guanine / zinc stearate / mannitol (1.2 / 0.6 / 1.2), with corresponding Congo red times of 968s and 1040s, respectively. This is consistent with the oven aging test results of the guanine triad compound. The figure also shows that galactitol and mannitol, as auxiliary heat stabilizers, do not significantly contribute to the stabilization of PVC themselves, but they can improve the effect of zinc-based heat stabilizers on PVC by inhibiting the "zinc burning" effect, with mannitol showing a more significant effect.

[0084] (5) Effect of guanine nucleoside and zinc stearate double pairing on the thermal stability of PVC

[0085] 5.1 Oven aging test results:

[0086] Figure 10 The results of oven aging tests on PVC with different ratios of guanine nucleoside / zinc stearate stabilizers are presented. A comparison clearly shows that the aging and discoloration time of PVC with the combination of guanine nucleoside and zinc stearate is significantly longer than that of the guanine-zinc stearate combination. This indicates that guanine nucleoside can better form a synergistic effect with zinc stearate, and also shows that the polyol structure of the nucleoside moiety also has the function of complexing zinc chloride and inhibiting "zinc burning". Therefore, it is inferred that combining guanine nucleoside with zinc-based heat stabilizers such as zinc stearate can better improve the thermal stability of PVC and enhance its processability.

[0087] 5.2 Congo Red Test Results:

[0088] Figure 11 The figure shows the Congo red test results for PVC samples with different X0 / ZnSt2 stabilizer ratios and different X / ZnSt2 stabilizer ratios. As can be seen from the figure, the optimal ratio of guanine nucleoside to zinc stearate is 2.4 / 0.6, with an optimal static Congo red time of 1411 s, significantly higher than the 886 s of the optimal ratio of guanine to zinc stearate. It can also be clearly observed that, at the same ratio as with zinc stearate, the static Congo red time of PVC with the guanine nucleoside and zinc stearate combination is longer than that with the guanine and zinc stearate combination. This indicates that guanine nucleoside can better form a synergistic effect with zinc stearate, significantly prolonging the static Congo red time of PVC.

[0089] Figure 12The results of oven aging tests are shown for PVC samples with added guanine nucleoside / zinc stearate (2.4 / 0.6) stabilizer, compared to those with added guanine / zinc stearate / galactitol (1.2 / 0.6 / 1.2) stabilizer and guanine / zinc stearate / mannitol (1.2 / 0.6 / 1.2) stabilizer. In comparison, the guanine triad heat stabilizer group showed better initial stabilization and longer whiteness retention time. However, the guanine nucleoside / zinc stearate duoad heat stabilizer group provided better long-term stability for PVC, indicating that the combination of guanine nucleoside and zinc stearate produces a synergistic effect, resulting in better improvement of PVC thermal stability and demonstrating good practicality.

[0090] 5.3 Thermal Decomposition Kinetic Analysis

[0091] The stabilization effect was evaluated using the Ozawa thermal decomposition kinetics method. PVC samples with added guanine (i.e., Example 1-1), guanine nucleoside (i.e., Example 1-18), and guanine nucleoside / zinc stearate optimal ratio stabilizer (i.e., Example 1-19) were subjected to thermogravimetric analysis at heating rates of 10, 15, 20, 25, and 30 K / min, respectively, and the activation energy of thermal decomposition was calculated by comparing with that of pure PVC samples. Figure 13 The figure shown is a linear fitting curve of the thermal decomposition kinetics of four samples.

[0092] The results of the thermal decomposition activation energy calculation are shown in Table 2. According to the table, the activation energies of the three groups of PVC with added heat stabilizers were all higher than those of pure PVC. The activation energy reflects the speed and difficulty of the reaction; the higher the activation energy, the more energy is required for the reaction, the more difficult the reaction, and thus the better the stability. Therefore, it can be concluded that both guanine and guanine nucleoside can improve the thermal stability of PVC, and guanine has a better effect than guanine nucleoside, consistent with the analysis results of the comprehensive tests above. The PVC sample prepared with the guanine nucleoside / zinc stearate two-component stabilizer had the highest thermal decomposition activation energy, further indicating that this compound group can better improve the thermal stability of PVC and significantly improve its processability.

[0093] Table 2

[0094]

[0095] Example 2: Application of guanine-based heat stabilizers in PVC composites

[0096] Using the heat stabilizers from Examples 1-19 (guanine nucleoside / zinc stearate = 2.4 / 0.6) and Examples 1-13 (guanine / zinc stearate / mannitol = 1.2 / 0.6 / 1.2) as PVC stabilizers, PVC composite materials with different amounts of rice husk fiber were prepared. The preparation methods are as follows:

[0097] (a) Untreated rice husk fiber (purchased from Yufengyuan Straw Processing Plant in Donghai County) was screened through a 100-mesh sieve. The sieved rice husk fiber was then dried in an oven at 80°C for 8 hours. A fiber modifier was prepared by mixing anhydrous ethanol and KH550 in a mass ratio of 95:5. Five times the mass of the fiber modifier was then weighed and added to the rice husk fiber. The mixture was subjected to a magnetic reaction for 2 hours, then filtered and dried in an 80°C oven for 6 hours to obtain modified rice husk fiber.

[0098] (b) Mix PVC resin, plasticizer dioctyl phthalate, and heat stabilizer at a mass ratio of PVC resin:plasticizer:heat stabilizer = 100:50:18, add modified rice husk fiber, mix well, and then mold (set hot pressing temperature 140℃) to obtain PVC composite material.

[0099] The amount of heat stabilizer and rice husk fiber added to the composite materials used in each embodiment is shown in Table 3:

[0100] Table 3

[0101]

[0102] Comparative Example 3

[0103] Using a heat stabilizer made of zinc stearate and calcium stearate in a mass ratio of 1:1 as a PVC stabilizer, PVC composite materials with rice husk fiber additions of 0, 5, 10, 15, 20, and 25% were prepared according to the method in Example 2, and were successively referred to as Comparative Examples 3-1 to 3-6.

[0104] The performance of the composite materials of Example 2 and Comparative Example 3 were tested respectively. The test methods were as follows:

[0105] (1) Mechanical property testing

[0106] This experiment was conducted according to GB / T 1040.3-2006 using a universal testing machine. The sample dimensions were 170 mm in length and 20 mm in width, with a clamp spacing of 150 mm and a testing speed of 150 mm / min. Each sample was tested at least 5 times, and the average value was taken.

[0107] (2) Microscopic morphology analysis

[0108] This experiment used a Hitachi SU3800 scanning electron microscope to perform microscopic scanning imaging of the tensile fracture surface of composite materials. Composite material specimens that fractured under tension after mechanical property testing were used as scanning samples to observe the microstructure of the material on the tensile fracture surface, and to deduce and analyze the stress state of each phase and the fracture mechanism during tensile fracture.

[0109] (3) Water absorption rate test

[0110] The water absorption performance test was conducted according to GB / T1034-2008. A representative lightweight sample was taken, and any surface impurities and contaminants were removed. The sample was then air-dried at room temperature. The dried sample was placed in a sealed container, and the container was then placed in water to completely submerge the sample. The soaking time was 24 hours. Afterward, any excess moisture on the sample surface was wiped dry, and the wet weight of the sample was immediately determined.

[0111] Test Result Analysis:

[0112] (1) Results of mechanical property tests

[0113] Figure 14 The figures show the tensile strength test results of PVC composites with different amounts of rice husk fiber (referring to the proportion of rice husk fiber in the composite material) in Examples 2 and 3, and Comparative Example 3. As can be seen from the figures, the tensile strength of the composites decreases with increasing rice husk fiber content, and the rate of decrease gradually increases. This may be due to differences in the molecular structure of rice husk fiber and PVC, resulting in insufficient interfacial bonding. Furthermore, the rice husk fiber modification method has limited effect on improving compatibility. Alternatively, the rice husk fiber itself may have low strength, leading to a decrease in material strength. When the rice husk fiber content is below 15%, the composite material still has good practical value, and the strength of the PVC / rice husk composite material can be enhanced through further optimization of the modification scheme.

[0114] Figure 15 The graphs show the elongation at break of PVC composites with different amounts of rice husk fiber added in Examples 2 and 3, respectively. The graphs show that as the rice husk fiber content increases, the elongation at break of the composite initially increases slightly, then decreases, and the rate of decrease gradually increases. Based on the tensile strength test results, it is inferred that rice husk fiber and PVC have a certain bonding force, which can improve the elongation at break of the composite to some extent during tensile testing. However, because the strength of rice husk fiber itself is not high, the strength of the PVC composite with added rice husk fiber shows a decreasing trend. Furthermore, among the different groups of PVC / rice husk composites with the same amount of rice husk added, the PVC material in the guanine nucleoside group has the highest elongation at break, further indicating that the guanine heat stabilizer can effectively improve the thermal stability of PVC.

[0115] (3) Results of microscopic morphology analysis

[0116] Figure 16 The image shows microscopic images of the tensile fracture surfaces of PVC composites with different rice husk fiber contents and guanine nucleoside groups (i.e., Examples 2-1 to 2-5). Figure 16 part a to Figure 16The 'e' portion corresponds to rice husk fiber content of 0%, 5%, 10%, 15%, and 20%, respectively. (Comparison) Figure 16 part a and Figure 16 In part b, the composite material with added rice husks showed a small amount of exposed fibers and also some pores that appeared to be formed by fiber detachment. As the rice husk fiber content increased, the distribution of fibers and pores on the tensile cross-section of the composite material gradually increased.

[0117] Figure 17 The images show cross-sectional micrographs of the PVC / rice husk composite materials with 10% rice husk fiber added in Examples 2 and 3. As can be observed from the images, the resin agglomeration in the cross-sections of the PVC / rice husk composite materials with different heat stabilizers is not significantly different; there is no obvious agglomeration or excessive dispersion. This indicates that the two selected heat stabilizers do not have a significant impact on the performance of the PVC / rice husk composite material system at the microscopic level.

[0118] (4) Water absorption rate test results

[0119] Figure 18 The results show the water absorption rate of PVC composite materials prepared using the guanine nucleoside group (i.e., Examples 2-1 to 2-6) at different rice husk addition amounts. The water absorption rate of PVC resin itself is below 0.5%. When the rice husk fiber content is low, the PVC resin can effectively encapsulate the rice husk fibers, resulting in a low water absorption rate for the composite material. As the rice husk fiber content increases, the water absorption rate gradually rises. When the rice husk content reaches 15%, the water absorption rate of the PVC / rice husk composite material reaches 1.74%, meeting the requirements for commonly used materials. With further increases in rice husk content, reaching 25%, the water absorption rate of the PVC / rice husk composite material reaches 3.28%, still at a low level. The woody parts of the material are less prone to moisture absorption and mold growth, resulting in a longer service life. Furthermore, the increased water absorption rate allows the material to absorb water vapor from the air, which can mitigate the potential for static electricity generation in PVC materials and help broaden their application areas.

[0120] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A guanine-based PVC heat stabilizer, characterized in that, The heat stabilizer is a compound of the main stabilizer, zinc stearate, and galactitol, with a mass ratio of (1-3):1:(0.5-2) for the main stabilizer; or the heat stabilizer is a compound of the main stabilizer, zinc stearate, and mannitol, with a mass ratio of (0.5-3):1:(0.5-3) for the main stabilizer. The primary stabilizer is guanine or guanine nucleoside.

2. The application of a guanine-based PVC heat stabilizer as described in claim 1, characterized in that, The heat stabilizer is used to prepare PVC composite materials.

3. The application of the guanine-based PVC heat stabilizer according to claim 2, characterized in that, The heat stabilizer is used to prepare PVC / rice husk composite materials.

4. The application of the guanine-based PVC heat stabilizer according to claim 3, characterized in that, PVC resin, plasticizer, heat stabilizer, and silane coupling agent are mixed with modified rice husk fiber and then molded to obtain PVC / rice husk composite material.

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