Adenine heat stabilizer and its application in PVC composite material

Abstract

This invention discloses an adenine-based heat stabilizer and its application in PVC composites, belonging to the field of heat stabilizer technology. The heat stabilizer is an adenine-based substance or a compound of an adenine-based substance and an auxiliary stabilizer. The adenine-based substance is adenine or adenine nucleoside, and the auxiliary stabilizer is at least one of calcium salt stabilizers, zinc salt stabilizers, and polyol stabilizers. This adenine-based heat stabilizer can improve the initial whiteness of PVC and impart better long-term stability to PVC. Its application in PVC composites can effectively improve the thermal stability and mechanical properties of PVC composites, possessing practical application value.

Description

Technical Field

[0001] This invention relates to the field of heat stabilizer technology, and more specifically, to an adenine-based heat stabilizer and its application in PVC composite materials. Background Technology

[0002] PVC, as a thermoplastic synthetic resin with excellent comprehensive performance, possesses good mechanical properties, flame retardancy, and corrosion resistance when used alone. In the field of composite materials, it can be used as a matrix material, reinforcement material, or adhesive. However, structural defects of PVC inevitably lead to thermal decomposition during hot processing, requiring the addition of heat stabilizers to improve processability.

[0003] Extensive research has been conducted on PVC heat stabilizers, and the principles by which various heat stabilizers improve PVC performance are well-founded theoretically. For example, polyol structures can effectively suppress the "zinc burning" effect caused by cadmium and zinc stabilizers, while organic nitrogen structures can effectively improve the stability of PVC and are relatively environmentally friendly. However, most current research is limited to single specific functional groups, and studies on the effects of multiple functional groups are still relatively limited, especially on organic nitrogen heat stabilizers with purine structures. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide an adenine-based heat stabilizer and its application in PVC composite materials.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A heat stabilizer based on adenine, wherein the heat stabilizer is an adenine substance or a compound of an adenine substance and an auxiliary stabilizer; wherein the adenine substance is adenine or adenine nucleoside.

[0007] Furthermore, the auxiliary stabilizer is at least one of calcium salt stabilizers, zinc salt stabilizers, and polyol stabilizers.

[0008] Furthermore, the heat stabilizer is a compound of adenine and zinc salt stabilizers, and the mass ratio of adenine to zinc salt stabilizers is greater than 1.

[0009] Furthermore, the heat stabilizer is a compound of adenine and zinc salt stabilizers, and the mass ratio of adenine to zinc salt stabilizers is (1.5-4):1.

[0010] Furthermore, the heat stabilizer is a compound of adenine, zinc salt, and polyol stabilizers, and the mass ratio of adenine to zinc salt and polyol stabilizers is (0.5-3):1:(0.5-3).

[0011] Furthermore, the calcium salt stabilizer is calcium stearate. The zinc salt stabilizer is zinc stearate.

[0012] Furthermore, the polyol stabilizer is a sugar alcohol. Specifically, the polyol stabilizer is at least one of galactitol and mannitol.

[0013] The application of an adenine-based heat stabilizer as described above in PVC composite materials.

[0014] In summary, the present invention has the following beneficial effects:

[0015] (1) The present invention uses adenine-like substances (adenine or adenine nucleoside) or a compound of adenine-like substances and auxiliary stabilizers as heat stabilizers. Adenine-like substances can give PVC good long-term stability and can form a good synergistic effect with zinc salt stabilizers (such as zinc stearate). While improving the initial whiteness of PVC, it can also prolong the stabilization time. It can also be compounded with zinc salt stabilizers (such as zinc stearate) and polyol stabilizers (such as galactitol or mannitol) to effectively suppress the "zinc burning" problem caused by zinc salt stabilizers and further improve the effect of improving the heat stability of PVC.

[0016] (2) The adenine-based heat stabilizer of the present invention can be used in the preparation of PVC composite materials (such as PVC / rice husk composite materials) to effectively improve the thermal stability and mechanical properties of PVC composite materials and has practical application value. Attached Figure Description

[0017] 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.

[0018] Figure 2 The 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).

[0019] Figure 3 The image shows a comparison of the infrared and visible spectra of adenine before and after the heating reaction.

[0020] Figure 4 A schematic diagram illustrating the principle by which adenine improves the thermal stability of PVC;

[0021] 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.

[0022] Figure 6The Congo red test results are shown in the figure for PVC samples with added stabilizers from Examples 1-1 to 1-5 and Comparative Example 1.

[0023] Figure 7 The graph shows the oven aging test results of PVC samples with stabilizers added in Examples 1-6 to 1-11;

[0024] Figure 8 The graph shows the oven aging test results of PVC samples with stabilizers from Examples 1-12 to 1-17 added.

[0025] Figure 9 The graph shows the Congo red test results for PVC with stabilizers added in Examples 1-6 to 1-17;

[0026] Figure 10 UV absorption curves of PVC samples from Examples 1-2, 1-8, and 1-14 added at 0 min and 60 min of heating;

[0027] Figure 11 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 12 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 13 Figure 1 shows the oven aging test results of PVC samples with added stabilizers from Examples 1-19, 1-8, and 1-14.

[0030] Figure 14 Linear fitting curves of Ozawa thermal decomposition kinetics for PVC samples with stabilizers added in Examples 1-1, 1-18, and 1-19, and for pure PVC samples;

[0031] Figure 15 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 16 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 17 Cross-sectional micrographs of PVC composite materials with different rice husk fiber additions (10%) Figure 17 Part A to Figure 17Part C corresponds sequentially to the PVC composite materials prepared in Examples 3-3, 2-3, and 2-9.

[0034] Figure 18 The image shows the oven aging test results of the PVC sample with added stabilizer (Comparative Example 4).

[0035] In the above diagram, X0 represents adenine, X represents adenine nucleoside, ZnSt2 represents zinc stearate, CaSt2 represents calcium stearate, B represents galactitol, and G represents mannitol. Detailed Implementation

[0036] 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.

[0037] The adenine-based heat stabilizer applicable to PVC composite materials is an adenine substance or a compound of an adenine substance and an auxiliary stabilizer; the adenine substance is adenine or adenine nucleoside; 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 at least one of galactitol and mannitol).

[0038] When the heat stabilizer is a compound of adenine and zinc salt stabilizer, the mass ratio of adenine to zinc salt stabilizer is greater than 1, preferably (1.5-4):1. When the heat stabilizer is a compound of adenine, zinc salt stabilizer, and polyol stabilizer, the mass ratio of adenine to zinc salt stabilizer and polyol stabilizer is (0.5-3):1:(0.5-3).

[0039] Example 1: Adenine-based heat stabilizers

[0040] The heat stabilizer components and formulations of Examples 1-1 to 1-22 are shown in Table 1:

[0041] Table 1

[0042]

[0043] Comparative Examples 1 to 2

[0044] The heat stabilizer for Comparative Example 1 was zinc stearate; the heat stabilizer for Comparative Example 2 was calcium stearate.

[0045] The performance of the heat stabilizers in the above embodiments and comparative examples was tested respectively. The test methods were as follows:

[0046] (1) Oven color change method

[0047] 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.

[0048] 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.

[0049] (2) Static Congo Red Method

[0050] 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.

[0051] (3) Infrared spectroscopy analysis

[0052] Take two equal masses of adenine solid powder. One portion of adenine solid powder is left untreated and used as a control group; the other portion of adenine solid powder is added to a three-necked flask, and the loaded three-necked flask is placed in an oil bath at 180°C for heating. At the same time, HCl gas is introduced into the three-necked flask, and a magnetic particle is placed at the bottom of the flask to ensure that the adenine 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 unreacted HCl gas.

[0053] The adenine 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 adenine 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.

[0054] 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 .

[0055] (4) Ultraviolet-visible spectroscopy analysis

[0056] The PVC film sample was cut into square sheets with a size of 15.0×15.0mm. The PVC sheets were scanned in an air atmosphere under heating conditions of 0℃ and 180℃ to observe the change in the number of conjugated double bonds on the PVC molecular chain. The test wavelength range of the UV-Vis spectrophotometer was set to 200-800nm, the test interval was set to 2nm, and the scan speed was set to slow.

[0057] (5) Thermal decomposition kinetic analysis

[0058] 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).

[0059] (3-1)

[0060] (3-2)

[0061] 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.

[0062] Test Result Analysis:

[0063] (1) Effects of adenine and adenine nucleoside on the thermal stability of PVC

[0064] 1.1 Oven aging test results:

[0065] The oven aging test results of adenine, adenine nucleoside and other common heat stabilizers acting alone on PVC are as follows: Figure 1 As shown in the figure, the PVC samples in the zinc stearate group exhibited the best initial stability and whiteness. However, due to the "zinc burning" phenomenon caused by zinc-based heat stabilizers, the PVC samples aged and turned black after 20 minutes of heating. Calcium stearate showed the best stabilizing effect, resulting in a lighter final color and good long-term thermal stability. Adenine was the next best, while adenine nucleoside showed a slightly inferior stabilizing effect. This is because the nucleoside structure did not significantly improve the thermal stability of PVC, and the content of the purine structure with the improving effect decreased, leading to a decline in the overall improvement effect on the thermal stability of PVC. However, the stabilizing effects of both adenine nucleoside and adenine were better than those of pure PVC.

[0066] 1.2 Congo Red Test Results:

[0067] Test results for Congo red in PVC with added adenine, adenine nucleoside, and other common heat stabilizers are as follows: Figure 2 As shown in the figure, the stability time of the PVC group with added adenine is 1097 s, and that of the PVC group with added adenine nucleoside is 1090 s, both slightly lower than that of the PVC group with added calcium stearate, but significantly higher than that of pure PVC. This further demonstrates that adenine and adenine nucleoside have the ability to substitute unstable chlorine atoms on the PVC chain. The PVC with added zinc stearate, due to the effect of "zinc burning," has a shorter stability time, which is consistent with the results of the oven aging test.

[0068] (2) Mechanism by which adenine improves the thermal stability of PVC

[0069] When silver nitrate solution was added to the rinsing solutions of two adenine samples, no obvious phenomenon was observed in the rinsing solution of the adenine sample that had not undergone the heating reaction, while a small amount of white precipitate appeared in the rinsing solution that had undergone the heating reaction, indicating that adenine can absorb a certain amount of HCl in a hot environment.

[0070] To further verify the thermal stability mechanism of adenine, adenine samples before and after the heating reaction were subjected to infrared and visible spectroscopy tests. The results are as follows: Figure 3 As shown in the figure, it can be observed that the characteristic peaks at positions 1, 2, and 3 show significant changes before and after the reaction, ranging from 750 to 1250 cm⁻¹. -1 The characteristic peaks in the region also show a slight shifting trend. (Point 1: 1930 cm⁻¹)-1 The characteristic peak of adenine at this location, which is a C=N stretching vibration, shows signs of disappearance after the introduction of HCl; 2 at 1685 cm⁻¹ -1 and 1610 cm -1 The characteristic peak at 1410 cm⁻¹ is a C=C stretching vibration, and changes in the chiral atomic structure result in certain variations in this vibration; 3 locations at 1410 cm⁻¹ -1 The characteristic peak at this point, representing the deformation vibration of the NH bond, indicates an increase in nitrogen-hydrogen bonds and a convergence in structural uniformity. Based on the mechanism of HCl absorption by organic nitrogen structures described in the literature, it is speculated that the carbon-nitrogen double bond in the adenine structure undergoes an addition reaction with the HCl released from PVC, thereby improving the thermal stability of PVC.

[0071] Based on data summarized from infrared spectroscopy analysis and literature, the inferred equation for how adenine improves the thermal stability of PVC is as follows: Figure 4 As shown, PVC thermal decomposition produces HCl. When adenine comes into contact with HCl, the nitrogen-carbon bonds in its molecular structure absorb it in one of three ways or a combination of three ways as shown in the figure, thus slowing down the catalytic effect of HCl on the thermal degradation of PVC and improving the long-term stability of PVC.

[0072] (3) Effect of adenine and zinc stearate combination on the thermal stability of PVC

[0073] 3.1 Oven aging test results:

[0074] The results of oven aging tests on PVC films stabilized by adding different proportions of adenine and zinc stearate are shown in the figure. Figure 5 As shown in the figure, the combination of adenine and zinc stearate can effectively improve the initial whiteness of PVC and achieve better initial thermal stability. The combination of adenine with an appropriate ratio of zinc stearate can improve the long-term thermal stability of PVC, indicating that adenine can form a good synergistic effect with zinc stearate and improve the thermal stability of PVC. However, due to the "zinc burning" effect of zinc stearate, when the content of zinc stearate is higher than that of adenine, the PVC sample will turn black due to thermal aging in a short period of time.

[0075] 3.2 Congo Red Test Results:

[0076] The test results for adding Congo red to PVC stabilized by a binary compound of adenine and zinc stearate in different proportions are shown in the figure. Figure 6The graph shows that the thermal stability time gradually decreases with increasing zinc stearate content, further indicating that the "zinc burning" effect of zinc stearate suppresses the long-term stabilizing effect of adenine on PVC. This is consistent with the oven aging test results of PVC with adenine / zinc stearate dual compound. Introducing an auxiliary heat stabilizer with an inhibitory effect of "zinc burning" might further enhance the improving effect of adenine on the thermal stability of PVC.

[0077] (4) Effect of the triple combination of adenine and zinc stearate on the thermal stability of PVC

[0078] 4.1 Oven aging test results:

[0079] Based on different ratios of adenine 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 adenine better inhibit the "zinc burning" effect caused by zinc stearate and improves the initial stability of PVC film. The figure also shows that the optimal compound ratio of adenine / zinc stearate / galactitol is 1.2 / 1.2 / 0.6. 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 segment; galactitol complexes zinc with chlorine atoms to form zinc chloride, inhibiting the catalytic effect of zinc chloride on the thermal degradation of PVC; and the HCl released by the thermal decomposition of PVC is absorbed by adenine. The three stabilizers work synergistically to significantly improve the thermal stability of PVC.

[0080] The oven aging test results of PVC samples with added adenine / zinc stearate / mannitol (G) triple stabilizer are as follows: Figure 8 As shown in the figure, mannitol can effectively inhibit the negative effects of zinc chloride, but its effect on improving PVC stability is relatively weak. Furthermore, the optimal ratio of adenine / zinc stearate / mannitol is 1.2 / 1.2 / 0.6. Compared to galactitol, mannitol has a better inhibitory effect on zinc chloride, resulting in better initial stabilization.

[0081] 4.2 Congo Red Test Results:

[0082] The PVC Congo Red test results obtained by adding galactitol and mannitol to the adenine / zinc stearate compound are as follows: Figure 9As shown in the figure, the heat stabilizer blend ratios with the longest stabilization times are adenine / zinc stearate / galactitol (1.2 / 1.2 / 0.6) and adenine / zinc stearate / mannitol (1.2 / 1.2 / 0.6), with corresponding Congo Red times of 959 s and 996 s, respectively. This is consistent with the oven aging test results of the adenine three-component blend. The figure also shows that galactitol and mannitol, as auxiliary heat stabilizers, do not significantly improve the stabilization effect of PVC, but they can inhibit "zinc burning" and improve the effect when combined with zinc-based heat stabilizers, with mannitol showing a more significant effect.

[0083] 4.3 Ultraviolet-Vis Spectroscopic Analysis

[0084] Literature review revealed that PVC undergoes chain dechlorination during thermal degradation, leading to a continuous increase in the number of conjugated olefins. This increase in conjugated olefins results in aging and color deepening of PVC products. Furthermore, the length of the conjugated polyene chain follows a specific pattern with the ultraviolet absorption wavelength; the maximum absorption value corresponds to a higher number of conjugated olefins (2–13), and this peak value appears at specific positions within the ultraviolet absorption wavelength. In conclusion, the larger the peak in the ultraviolet band of the ultraviolet-visible absorption curve, the higher the concentration of conjugated olefins in the PVC, and the greater the degree of aging.

[0085] In this experiment, three groups of PVC samples with the best thermal stability—adenine / zinc stearate (2.4 / 0.6), adenine / zinc stearate / galactitol (1.2 / 1.2 / 0.6), and adenine / zinc stearate / mannitol (1.2 / 1.2 / 0.6)—were heated in an oven at 180℃ for 60 min. The corresponding samples were then subjected to UV-Vis spectroscopy analysis to compare the concentrations of conjugated olefins in the corresponding PVC films. The experimental results are as follows: Figure 10 As shown.

[0086] As shown in the figure, the PVC samples require heating to 140℃ during preparation, inevitably generating a small amount of conjugated double bonds. When PVC begins thermal degradation, the absorption of ultraviolet light increases with the formation of these double bonds. The figure reveals that all three groups of PVC samples with different heat stabilizers showed a significant increase in ultraviolet light absorption after heating for 60 minutes. The group with adenine and zinc stearate showed the most significant increase, indicating the highest degree of aging in this group. The group with adenine / zinc stearate / galactitol (mannitol) showed similar increases, indicating that the addition of galactitol and mannitol effectively inhibited the "zinc burning" effect of zinc stearate, alleviating the thermal aging of PVC. This also demonstrates the good improvement effect of adenine / zinc stearate / mannitol (galactitol) on the thermal stability of PVC.

[0087] (5) Effect of adenine nucleoside and zinc stearate double pairing on the thermal stability of PVC

[0088] 5.1 Oven aging test results:

[0089] Figure 11 Oven aging test results for PVC with different adenine / zinc stearate ratios. Results are compared with those of PVC samples with added adenine / zinc stearate (2.4 / 0.6) stabilizers (see [link to oven aging test results]). Figure 5 In comparison, it can be clearly observed that the aging and discoloration time of PVC after the combination of adenine nucleoside and zinc stearate (2.4 / 0.6) is significantly longer than that of the adenine / zinc stearate combination group. This indicates that adenine nucleoside can form a better synergistic effect with zinc stearate, and also shows that the nucleoside structure of adenine nucleoside also has the function of complexing zinc chloride and inhibiting "zinc burning".

[0090] 5.2 Congo Red Test Results:

[0091] Figure 12 The results of Congo Red tests on PVC samples with different X0 / ZnSt2 stabilizer ratios and different X / ZnSt2 stabilizer ratios are shown. It is clearly observed that the optimal ratio of adenine nucleoside to zinc stearate is 2.4 / 0.6, with an optimal static Congo Red time of 1288 s, significantly higher than the 955 s when the optimal ratio of adenine to zinc stearate is 2.4 / 0.6. Furthermore, under the same ratio after being combined with zinc stearate, the static Congo Red time of PVC samples with the adenine nucleoside / zinc stearate stabilizer combination was longer than that of PVC samples with the adenine / zinc stearate stabilizer combination, indicating that adenine nucleoside can better form a synergistic effect with zinc stearate, and that the combination of adenine nucleoside and zinc stearate can better delay the thermal aging of PVC.

[0092] To better investigate the effect of the combination of adenine nucleoside and zinc stearate on the thermal stability of PVC Figure 13 The results of oven aging tests are shown for PVC samples with added adenine nucleoside / zinc stearate (2.4 / 0.6) stabilizer, compared to those with added adenine / zinc stearate / galactitol (1.2 / 1.2 / 0.6) stabilizer and adenine / zinc stearate / mannitol (1.2 / 1.2 / 0.6) stabilizer. In comparison, the effect of the combination of adenine nucleoside and zinc stearate falls between that of adenine / zinc stearate / galactitol and adenine / zinc stearate / mannitol. In terms of practicality, the two-component combination of adenine nucleoside / zinc stearate is superior to the three-component combination of adenine, and the difference in their effects on PVC heat stability is not significant, demonstrating the value of adenine nucleoside in the development of PVC heat stabilizers.

[0093] 5.3 Thermal Decomposition Kinetic Analysis

[0094] The stabilization effect was evaluated using the Ozawa thermal decomposition kinetics method. PVC samples with added adenine (i.e., Example 1-1), adenine nucleoside (i.e., Example 1-18), and the optimal ratio of adenine nucleoside / zinc stearate 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 14 The figure shown is a linear fitting curve of the thermal decomposition kinetics of four samples.

[0095] 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. Combining the data in the table, it can be concluded that both adenine and adenine nucleoside can improve the thermal stability of PVC, with adenine having a stronger effect than adenine nucleoside, which is consistent with the comprehensive test analysis results above. Adding zinc stearate to adenine nucleoside resulted in the PVC sample with the highest thermal decomposition activation energy after compounding with the two-component stabilizer, further demonstrating that this compound can effectively improve the thermal stability of PVC.

[0096] Table 2

[0097]

[0098] Example 2: Application of adenine-based heat stabilizers in PVC composites

[0099] Using the heat stabilizers from Examples 1-19 (adenine nucleoside / zinc stearate = 2.4 / 0.6) and Examples 1-14 (adenine / zinc stearate / mannitol = 1.2 / 1.2 / 0.6) as PVC stabilizers, PVC composite materials with different amounts of rice husk fiber were prepared. The preparation methods are as follows:

[0100] (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.

[0101] (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.

[0102] The amount of heat stabilizer and rice husk fiber added to the composite materials used in each embodiment is shown in Table 3:

[0103] Table 3

[0104]

[0105] Comparative Example 3

[0106] 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.

[0107] The performance of the composite materials of Example 2 and Comparative Example 3 were tested respectively. The test methods were as follows:

[0108] (1) Mechanical property testing

[0109] 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.

[0110] (2) Microscopic morphology analysis

[0111] 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.

[0112] Test Result Analysis:

[0113] (1) Results of mechanical property tests

[0114] Figure 15The 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.

[0115] Figure 16 The graphs show the elongation at break of PVC composites with different amounts of rice husk fiber added in Examples 2 and 3. 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 after adding rice husk fiber shows a decreasing trend.

[0116] (3) Results of microscopic morphology analysis

[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] Comparative Example 4

[0119] Adenine zinc heat stabilizer was prepared according to the method described in Example 1 of the patent "A method for preparing a bio-based adenine zinc salt environmentally friendly PVC heat stabilizer and its application" (CN120398924A).

[0120] Using zinc adenine as a heat stabilizer, PVC samples were prepared according to the above method and subjected to oven aging tests. The test results are shown in [Figure number missing]. Figure 18 Compared with the oven aging test results of PVC samples with added zinc adenine and adenine / zinc stearate / mannitol (G) triple stabilizer (1.2 / 1.2 / 0.6), it can be seen that the heat stabilization effect of the adenine / zinc stearate / mannitol (G) triple stabilizer (1.2 / 1.2 / 0.6) is better than that of zinc adenine.

[0121] 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. An adenine-based thermostabilizer, characterized by, The heat stabilizer is an adenine substance or a compound of an adenine substance and an auxiliary stabilizer; the adenine substance is adenine or adenine nucleoside; The auxiliary stabilizer is at least one of calcium salt stabilizers, zinc salt stabilizers, and polyol stabilizers.

2. The adenine-based thermostabilizer of claim 1, wherein The heat stabilizer is a compound of adenine and zinc salt stabilizers, and the mass ratio of adenine to zinc salt stabilizers is (0.25-4):

1.

3. The adenine-based heat stabilizer according to claim 1, characterized in that, The heat stabilizer is a compound of adenine and zinc salt stabilizers, and the mass ratio of adenine to zinc salt stabilizer is (1.5-4):

1.

4. The adenine-based heat stabilizer according to claim 1, characterized in that, The heat stabilizer is a compound of adenine, zinc salt, and polyol stabilizers, with a mass ratio of adenine to zinc salt and polyol stabilizers of (0.34-2):1:(0.34-2).

5. The thermostable adenine analog of claim 1, wherein, The calcium salt stabilizer is calcium stearate.

6. The adenine-based heat stabilizer according to claim 1, characterized in that, The zinc salt stabilizer is zinc stearate.

7. The thermostable adenine class of the claim 1, wherein, The polyol stabilizer is a sugar alcohol.

8. The thermostable adenine class of the claim 1, wherein, The polyol stabilizer is at least one of galactitol and mannitol.

9. The application of an adenine-based heat stabilizer as described in any one of claims 1-8 in PVC composite materials.

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