A melt-processable PVC resin and its plasticizing method

Abstract

This solution provides a melt-processable PVC resin and its plasticizing method. The PVC resin powder undergoes multiple freeze-heat treatments. The freeze-heat treated PVC resin powder is then subjected to vacuum dehydration. The vacuum-dehydrated PVC resin powder is then subjected to ultrasonic vibration to obtain pretreated PVC resin. The pretreated PVC resin powder is placed in a vacuum filtration device, and formamide is sprayed onto its surface. The vacuum filtration device is then sealed, and the mixture is drawn off. The mixture is transferred to a mixer and kneaded to obtain externally plasticized PVC resin powder. Methyl methacrylate, butyl acrylate, and an initiator are added to ethanol and mixed evenly to obtain an internal plasticizing solution. This internal plasticizing solution is sprayed onto the externally plasticized PVC resin powder and wrapped with plastic wrap. The plastic-wrapped externally plasticized PVC resin powder is placed in a high-temperature heating chamber for a period of time, cooled to room temperature, and then removed. It is then further treated at a high temperature to obtain melt-processable PVC resin.

Description

Technical Field

[0001] This invention relates to the field of PVC, and particularly to a melt-processable PVC resin and its plasticizing method. Background Technology

[0002] Polyvinyl chloride (PVC) is a general-purpose plastic with a consistently high global production volume. It has properties such as strong acid and alkali resistance, good wear resistance, and flame retardancy, and is also inexpensive. Related products are widely used in industries such as medical, chemical, construction, and textile.

[0003] However, the inherent challenges faced by PVC during melt processing severely restrict the further expansion of its application range. From a molecular structure perspective, PVC molecules contain a large number of chlorine atoms. The high electronegativity of chlorine atoms leads to strong van der Waals forces between molecules. This force results in a significantly higher melt viscosity than other general-purpose plastics when PVC is heated to a molten state. This directly leads to extremely poor flowability, making it difficult to fully fill mold cavities in injection molding and extrusion processes. This easily results in defects such as rough surfaces, material shortages, and bubbles, affecting product quality and production efficiency. More importantly, the decomposition temperature of PVC is extremely close to its thermoplastic processing temperature. Its decomposition temperature is typically between 160 and 180°C, and even prolonged processing above 140°C will show signs of decomposition. The effective thermoplastic processing temperature is also roughly in the range of 160 to 200°C. This overlap makes PVC highly susceptible to thermal degradation during processing. High temperatures can even cause PVC to thermally degrade, releasing toxic HCl gas.

[0004] To address the aforementioned issues, modifying PVC resin to broaden its melt processing window has become a key research focus in the industry. Plasticization is one of the most widely used and relatively mature modification methods. Plasticizers can insert into the PVC molecular chains, weakening intermolecular van der Waals forces, reducing melt viscosity, and improving melt flowability. Simultaneously, it can lower the glass transition temperature and melting temperature of PVC, expanding the processing temperature range and allowing PVC to be melt-processed at lower temperatures, reducing thermal degradation reactions. Currently, plasticization of PVC mainly involves internal or external plasticization. However, while simple external plasticization achieves the desired plasticizing effect, plasticizers are prone to migration; simple internal plasticization, while preventing plasticizer migration, does not achieve a significant plasticizing effect, and both methods suffer from low processing efficiency.

[0005] In summary, current plasticizing solutions for PVC cannot simultaneously achieve high plasticizing efficiency and prevent plasticizer migration, and their low processing efficiency means that PVC cannot adequately meet the requirements of melt processing. Summary of the Invention

[0006] The purpose of this invention is to provide a melt-processable PVC resin and its plasticizing method. By employing a strategy of synergistic internal and external plasticizing, PVC is plasticized to obtain a melt-processable PVC resin, which solves the problems of easy migration of plasticizers and poor plasticizing efficiency, while improving processing efficiency.

[0007] To achieve the above objectives, this technical solution provides a plasticizing method for melt-processable PVC resin, comprising:

[0008] S1: Take PVC resin powder and perform multiple freeze-heat treatments. Take the freeze-heat treated PVC resin powder and perform vacuum dehydration treatment. Take the vacuum dehydration treated PVC resin powder and perform ultrasonic vibration treatment to obtain pretreated PVC resin. The freeze-heat treatment is to place the PVC resin powder in a low-temperature environment for freeze treatment and then place it in a high-temperature environment for heat treatment.

[0009] S2: Take the pretreated PVC resin powder and place it in a vacuum filtration device and spray formamide on the surface of the pretreated PVC resin powder. Seal the vacuum filtration device to draw a vacuum and suck up the mixture. Then transfer the mixture into a mixing machine to mix and obtain externally plasticized PVC resin powder.

[0010] S3: Add methyl methacrylate, butyl acrylate and initiator to ethanol and mix evenly to obtain an internal plasticizing solution. Spray the internal plasticizing solution onto the external plasticized PVC resin powder and wrap it with plastic wrap. Place the external plasticized PVC resin powder wrapped with plastic wrap in a high-temperature heating barrel for a period of time, cool it to room temperature and take it out. Continue to process it at a high temperature. After taking it out, you can obtain melt-processable PVC resin.

[0011] In step S1, since PVC resin will generate continuous internal stress due to thermal expansion and contraction, this solution performs multiple freeze-heat treatments on the PVC resin. Under the repeated freeze-heat treatment "destructive" process, the PVC resin becomes brittle and the surface cracks, so as to facilitate the subsequent penetration of small molecule plasticizers into the interior of the PVC resin. In addition, ultrasonic vibration treatment is used to generate microcracks on the surface of PVC resin particles, thereby increasing the contact area between PVC resin and subsequent plasticizers, accelerating the absorption and penetration of plasticizers, and preventing plasticizer migration.

[0012] Specifically, the freeze-heat treatment in step S1 involves freezing the PVC resin powder at -15℃ to 0℃ for 3 to 5 hours, followed by heat treatment at 80 to 100℃ for 2 to 3 hours. At low temperatures, the molecular chain mobility of PVC resin decreases significantly, the intermolecular distance shrinks, and the resin particles shrink overall. Because different regions within the resin particles shrink at different rates (the surface shrinks faster than the core), tensile stress is generated within the particles. When this stress exceeds the resin's tensile strength, microcracks appear first on the surface and near-surface layers, providing a channel for the subsequent entry of plasticizers. Upon heating, the resin molecular chain mobility recovers, and the particles expand from a contracted state. At this point, the microcracks generated during the freezing stage further expand due to the expansion, extending from the surface to the core layer, forming penetrating microporous channels.

[0013] In some embodiments, the PVC resin powder is frozen at -15℃ to 0℃ for 3 to 5 hours and then transferred to an oven at 80 to 100℃ for heat treatment for 2 to 3 hours.

[0014] In some embodiments, PVC resin powder is subjected to 2 to 4 freeze-heat treatments, preferably 3 freeze-heat treatments.

[0015] In some embodiments, vacuum dehydration involves placing the PVC resin powder under a vacuum of 0.05~0.07 MPa and a temperature of 85~90℃ for 20~25 minutes. During the freeze-heat treatment process, moisture in the air can easily penetrate into the interior of the PVC resin powder through microcracks on the particle surface. If not removed in time, this can cause multiple adverse effects on subsequent processing. This solution uses vacuum dehydration to quickly remove moisture from the PVC resin powder in a short time. Moreover, during the vacuum dehydration process of the PVC resin powder, the vaporization of moisture inside the PVC resin particles generates a certain thrust, which expands the micropores formed by the freeze-heat treatment.

[0016] In some embodiments, ultrasonic vibration treatment involves placing PVC resin powder in an ultrasonic vibrator, setting the ultrasonic frequency to 120 kHz, and vibrating for 10-15 minutes. The energy of the ultrasound can create microcracks on the surface of the PVC resin particles, increasing the contact area with the plasticizer, accelerating the absorption and penetration of the plasticizer, and preventing the migration of the plasticizer.

[0017] In some embodiments, the degree of polymerization of the PVC resin powder is greater than 1000. This solution selects PVC resin powder with a degree of polymerization greater than 1000, as its molecular chains are longer, the intermolecular entanglement is tighter, the structural strength of the resin particles is relatively higher, and its heat resistance is superior to that of low-polymerization-degree resins. This ensures that under heat treatment temperatures of 85~90℃, the PVC resin will not undergo thermal softening or thermal degradation due to excessively high temperatures, and can also accelerate moisture vaporization in a medium-to-high vacuum environment due to the moderate mobility of its molecular chains.

[0018] In step S2, a small-molecule plasticizer is used to externally plasticize the pretreated PVC resin powder. The small-molecule plasticizer can insert into the PVC molecular chains, weakening the intermolecular forces and lowering its glass transition temperature (from 80~85℃ to 60~70℃). Simultaneously, it lowers the melting point of PVC, making the originally rigid PVC easier to melt and process (such as extrusion and injection molding), and improving the flexibility and ductility of the product. Furthermore, under negative pressure, the small-molecule plasticizer formamide is "deeply penetrated" into the PVC resin through vacuum suction. Compared to adsorption relying solely on intermolecular forces, gravity, and capillary forces, vacuum suction is more efficient and can achieve a deep bond between formamide and PVC resin.

[0019] In some embodiments, formamide has a molecular weight of 192.96 and is classified as a small molecule plasticizer.

[0020] In some embodiments, 100 parts of pretreated PVC resin powder are placed in a vacuum filtration device and 15-20 parts of formamide are sprayed onto the surface of the pretreated PVC resin powder.

[0021] In some embodiments, the closed vacuum filtration device maintains a vacuum of 0.1 MPa and continuously suctions the mixture for 15-20 minutes. This condition utilizes the pressure difference generated by the high vacuum to drive formamide to quickly and uniformly penetrate into the micropores of the pretreated resin, ensuring full binding and guaranteeing the plasticizing effect. At the same time, the 15-20 minute duration allows for efficient suction, avoids excessive formamide residue (reducing the risk of migration), and matches the compatibility of the resin and formamide ratio, helping to achieve the goal of easy resin processing and high-performance modification.

[0022] In some embodiments, the mixture is transferred into a mixer, and the temperature is set to 130~140℃ and held for 20~30 minutes to obtain externally plasticized PVC resin powder. This temperature is lower than the decomposition temperature of PVC and is suitable for the plasticizing requirements of formamide, which can promote the full integration of formamide and resin. The 20~30 minute duration can ensure the external plasticizing effect, and finally obtain an easily processed externally plasticized PVC resin powder, which works synergistically with the previous vacuum filtration and proportion setting.

[0023] In step S3, in-situ modification of PVC resin is achieved by copolymerizing methyl methacrylate and butyl acrylate. The poly(methyl methacrylate-butyl acrylate) obtained by copolymerizing methyl methacrylate and butyl acrylate has plasticizing, lubricating and protective effects. After exceeding the glass transition temperature (85~95℃) of poly(methyl methacrylate-butyl acrylate), the softened poly(methyl methacrylate-butyl acrylate) will anchor on the surface of PVC resin. As the processing temperature increases, it will gradually penetrate into the cracks on the surface of PVC resin, forming intercalation in PVC resin, weakening its intermolecular forces, and reducing the regularity of the molecular structure, thus achieving plasticization.

[0024] In some embodiments, the initiator is either benzoyl peroxide or azobisisobutyronitrile, and methyl methacrylate, butyl acrylate and the initiator are added to ethanol to react and obtain poly(methyl methacrylate-butyl acrylate).

[0025] In some embodiments, 25-30 parts of methyl methacrylate, 10-15 parts of butyl acrylate and 4-5 parts of initiator are sequentially added to 50 parts of ethanol and mixed evenly to obtain an external plasticizing solution.

[0026] In some embodiments, the internal plasticizer solution is sprayed onto 100 parts of external plasticizer PVC resin powder and wrapped with plastic wrap.

[0027] In some embodiments, plasticized PVC resin powder wrapped in cling film is placed in a heating barrel at 80°C to 95°C and kept at a constant temperature for 3 to 5 hours. After cooling to room temperature, it is taken out and further processed at 100°C to 105°C. After taking it out, melt-processable PVC resin can be obtained.

[0028] It should be noted that this solution employs a synergistic, stepwise internal plasticizing strategy using both small-molecule and large-molecule plasticizers to ensure the stability of the plasticizing effect. Small-molecule plasticizers penetrate more easily into the interior of the PVC resin, while large-molecule plasticizers are embedded on the surface of the PVC resin. This not only prevents the outward migration of small-molecule plasticizers but also "repairs" cracks that appear on the surface of the PVC resin. The melt-processable PVC resin after internal and external plasticizing treatment contains grafted acrylate polymers and has a glass transition temperature of 40~50 ℃.

[0029] As mentioned above, this solution provides a melt-processable PVC resin, obtained by plasticizing according to the aforementioned plasticizing method. The melt-processable PVC resin contains grafted acrylate polymers and has a glass transition temperature of 40-50 °C. The melt-processable PVC resin of this solution can be used in melt-processing applications.

[0030] Compared with existing technologies, this technical solution has the following characteristics and beneficial effects:

[0031] 1. This solution addresses the problem of plasticizer migration in traditional external plasticizing methods: This approach treats PVC resin powder with cooling-heat treatment combined with ultrasonic vibration, creating penetrating micropores within the powder. Vacuum dehydration further optimizes the micropore structure. During the external plasticizing stage, small-molecule plasticizer formamide is used in conjunction with vacuum suction, allowing for deep penetration and full integration with the resin, reducing free plasticizer. Subsequent internal plasticizing produces poly(methyl methacrylate-butyl acrylate), which anchors on the resin surface and within cracks, forming a physical barrier. The synergistic effect of these three methods keeps plasticizer migration at a low level, avoiding the defects of traditional plasticizers that easily migrate outwards.

[0032] 2. This solution addresses the low plasticizing efficiency of traditional internal plasticizing methods: Pretreatment makes PVC resin powder brittle, creating microcracks and micropores, significantly increasing the plasticizer's contact area and accelerating absorption and penetration. Simultaneously, formamide is used in the external plasticizing stage to effectively weaken intermolecular forces, and vacuum suction promotes rapid and uniform penetration of formamide, while mixing ensures a fusion effect. In the internal plasticizing stage, copolymers flow into the cracks and intercalate, further weakening intermolecular forces. This step-by-step plasticizing approach, with its process compatibility, allows the plasticizer to function more effectively, solving the problems of uneven plasticizing effects and low efficiency associated with traditional methods.

[0033] 3. This solution solves the problem of low processing efficiency in traditional plasticizing methods: The internal and external plasticizing processes in this solution are closely integrated. Through reasonable parameter settings, the overall efficiency from resin pretreatment to final processing is significantly improved compared to traditional methods. Attached Figure Description

[0034] Figure 1 This is a scanning electron microscope image of the PVC resin powder that underwent the destructive treatment in Example 1.

[0035] Figure 2 This is a scanning electron microscope image of the untreated PVC resin powder from Comparative Example 1.

[0036] Figure 3 This is a scanning electron microscope image of the PVC resin powder from Example 2.

[0037] Figure 4 This is a scanning electron microscope image of the PVC resin powder in Comparative Example 2.

[0038] Figure 5 This is a scanning electron microscope image of the melt-processable PVC resin powder of Example 3.

[0039] Figure 6 This is a scanning electron microscope image of the PVC resin powder in Comparative Example 3.

[0040] Figure 7This is a scanning electron microscope image of the PVC resin powder in Comparative Example 4. Detailed Implementation

[0041] 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. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0042] Example 1:

[0043] PVC resin powder with a degree of polymerization of 1200 was frozen at -10 ℃ for 4 hours, then placed in an oven at 90 ℃ for 3 hours. This freeze-heat treatment process was repeated 3 times. The PVC resin powder after freeze-heat treatment was vacuum dehydrated at a vacuum degree of 0.06 MPa and a temperature of 90 ℃ for 25 minutes. Then the resin was taken out and placed in an ultrasonic oscillator. The ultrasonic frequency was set to 120 kHz and the oscillation was performed for 12 minutes. The PVC resin powder was then taken out.

[0044] Comparative Example 1:

[0045] Take PVC resin powder with a degree of polymerization of 1200 and do not perform any treatment.

[0046] Example 2:

[0047] Take 100 parts of the PVC resin powder obtained in Example 1 and place it in a vacuum filtration flask. Then, spray 15 parts of formamide evenly onto the PVC resin. After sealing the filtration flask, turn on the vacuum pump and maintain the vacuum degree at 0.1 MPa. Continue evacuation for 20 minutes and then pour out the mixture. Transfer the mixture into a mixer, set the temperature to 140 ℃, keep it at that temperature for 30 minutes, and then take out the PVC resin.

[0048] Comparative Example 2:

[0049] Take 100 parts of the PVC resin powder obtained in Comparative Example 1 and place it in a vacuum filtration flask. Then, spray 15 parts of formamide evenly onto the PVC resin. After sealing the filtration flask, turn on the vacuum pump and maintain the vacuum degree at 0.1 MPa. Continue evacuation for 20 minutes and then pour out the mixture. Transfer the mixture into a mixer, set the temperature to 140 ℃, and keep it at that temperature for 30 minutes. Remove the resin and set it aside for later use.

[0050] Example 3:

[0051] Take 25 parts of methyl methacrylate, 12 parts of butyl acrylate and 5 parts of benzoyl peroxide and add them to 50 parts of ethanol in sequence. After mixing evenly, spray the mixture onto 100 parts of PVC resin obtained in Example 2 using a spray gun. Then wrap the resin with plastic wrap and place it in a heating barrel at 80 °C. After maintaining the temperature for 4 hours, cool it to room temperature and take out the powder material to obtain PVC resin containing acrylate polymer grafted onto it.

[0052] Comparative Example 3:

[0053] Take 25 parts of methyl methacrylate, 12 parts of butyl acrylate and 5 parts of benzoyl peroxide and add them to 50 parts of ethanol. After mixing evenly, spray the mixture onto 100 parts of PVC resin obtained in Comparative Example 2 using a spray gun. Then wrap the resin with plastic wrap and place it in a heating barrel at 80 ℃. After maintaining the constant temperature for 4 hours, cool it to room temperature and remove the powder material to obtain PVC resin.

[0054] Comparative Example 4:

[0055] Take 25 parts of methyl methacrylate, 12 parts of butyl acrylate and 5 parts of benzoyl peroxide and add them to 50 parts of ethanol. After mixing evenly, spray the mixture onto 100 parts of PVC resin obtained in Comparative Example 1 using a spray gun. Then wrap the resin with plastic wrap and place it in a heating barrel at 80 ℃. After maintaining the constant temperature for 4 hours, cool it to room temperature and remove the powder material to obtain PVC resin.

[0056] Performance testing:

[0057] The PVC resins obtained in each embodiment and comparative example were observed, and scanning electron micrographs of the PVC resin powders in each embodiment and comparative example were obtained as follows: Figure 1-7 As shown in the figure, the original PVC resin surface is rough and contains a small number of micropores. After destructive treatment, the sample shows obvious cracks and spherical particles distributed on the surface. Destructive treatment can promote the penetration of formamide into the resin cracks and enhance the external plasticizing process. Compared with Comparative Example 2 without destructive treatment, the surface cracks in Example 2 are lighter, and the surface protruding particles are reduced. The surface grooves and spherical particles of Example 2 after destructive process combined with internal plasticizing are basically eliminated. Compared with Comparative Examples 3 and 4, it can be seen that the destructive process + external plasticizing + internal plasticizing of this scheme have a synergistic effect, taking into account both high plasticizing efficiency and high plasticizing stability, and meeting the needs of subsequent melt processing.

[0058] The glass transition temperature of the PVC resin powder obtained in each embodiment and comparative example was tested, and the melting point test results are shown in Table 1:

[0059] Table 1

[0060] .

[0061] It is evident that destructive pretreatment has little effect on the glass transition temperature of PVC resin, while external plasticizing and internal plasticizing simultaneously reduce the glass transition temperature of PVC resin. In comparison, the internal plasticizing process can more effectively reduce the softening temperature and improve its processability. After combining the three treatment methods, the glass transition temperature of the sample is as low as 42.8℃, which effectively reduces the subsequent processing temperature, improves the fluidity of PVC, and thus improves the efficiency of molding processes such as calendering and extrusion.

[0062] The PVC resin powders obtained in each embodiment and comparative example were subjected to 10 heat-cooling cycles, with the heat treatment temperature exceeding the glass transition temperature, to determine the stability of the plasticized PVC resin. It was found that the PVC resin that underwent destructive treatment followed by external and internal plasticizing had a stable glass transition temperature, with an error of 1.5℃ over 10 tests. The PVC resin that underwent external and internal plasticizing without destructive treatment had a glass transition temperature error of 10.9℃ over 10 tests, indicating poor stability.

[0063] Those skilled in the art should understand that the technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method of plasticizing a melt processable PVC resin characterized in that, The method comprises the following steps: S1: taking PVC resin powder for multiple freeze-heat treatment, taking the freeze-heat treated PVC resin powder for vacuum dehydration treatment, and taking the vacuum dehydration treated PVC resin powder for ultrasonic oscillation treatment to obtain pretreated PVC resin powder, wherein the freeze-heat treatment is that the PVC resin powder is placed in a low-temperature environment for freezing treatment and then placed in a high-temperature environment for heat treatment, the freeze-heat treatment is that the PVC resin powder is placed in a low-temperature environment at-15-0 DEG C for freezing treatment for 3-5 hours and then placed in a high-temperature environment at 80-100 DEG C for heat treatment for 2-3 hours, the vacuum dehydration treatment is that the PVC resin powder is placed in a vacuum environment with a vacuum degree of 0.05-0.07 MPa and a temperature of 85-90 DEG C for vacuum dehydration treatment for 20-25 minutes, and the ultrasonic oscillation treatment is that the PVC resin powder is placed in an ultrasonic oscillator, the ultrasonic frequency is set to 120 kHz, and the PVC resin powder is vibrated for 10-15 minutes; S2: taking the pretreated PVC resin powder into a vacuum filtration device, spraying formamide on the surface of the pretreated PVC resin powder, and vacuumizing and sucking the mixture in the vacuum filtration device, and then moving the mixture into a mixing machine to obtain externally plasticized PVC resin powder, wherein the vacuum filtration device is kept at a vacuum degree of 0.1 MPa and continuously sucks the mixture for 15-20 minutes; S3: mixing methyl methacrylate, butyl acrylate and an initiator in ethanol to obtain an internal plasticizing solution, spraying the internal plasticizing solution on the externally plasticized PVC resin powder, wrapping the externally plasticized PVC resin powder with plastic wrap, placing the externally plasticized PVC resin powder wrapped with plastic wrap in a high-temperature heating barrel for a period of time, taking out the externally plasticized PVC resin powder after cooling to room temperature, and continuously treating the externally plasticized PVC resin powder at high temperature to obtain a melt-processable PVC resin, wherein the externally plasticized PVC resin powder wrapped with plastic wrap is placed in a heating barrel at 80 DEG C-95 DEG C and kept at a constant temperature for 3-5 hours, and then taken out after cooling to room temperature, and continuously treated at 100 DEG C-105 DEG C to obtain the melt-processable PVC resin.

2. The method of plasticizing a melt processable PVC resin according to claim 1, characterized in that, The mixture is moved into a mixing machine, the temperature is set to 130-140 DEG C, and the mixture is mixed and kept for 20-30 minutes to obtain externally plasticized PVC resin powder.

3. The method of plasticizing a melt processable PVC resin according to claim 1, characterized in that, The initiator is one of dibenzoyl peroxide and azobisisobutyronitrile.

4. The method of plasticizing a melt processable PVC resin according to claim 1, characterized in that, The PVC resin powder has a polymerization degree greater than 1000.

5. A melt processable PVC resin characterized in that, The melt-processable PVC resin is grafted with an acrylate polymer and has a glass transition temperature of 40-50 DEG C.

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