Process for the continuous suspension grafting of polar monomers onto polypropylene

Abstract

The present application relates to the technical field of polymer grafting, and discloses a method for continuously grafting polar monomers on polypropylene in suspension. The method comprises the following steps: continuously adding a premix containing polar monomers, an initiator and polypropylene powder into water to carry out a grafting reaction; continuously leading out the product of the grafting reaction and adding water to maintain the water content in the grafting reaction system, so as to realize the continuous grafting of the polar monomers. The method of the present application can realize the continuous grafting of polar monomers on polypropylene in suspension, and high-quality grafted products can be obtained.

Description

Technical Field

[0001] This invention relates to the field of polymer grafting technology, and more specifically to a method for continuous suspension grafting of polar monomers onto polypropylene. Background Technology

[0002] Grafting is a common technique for modifying polypropylene. As an important general-purpose plastic, polypropylene can have its mechanical and thermal properties improved, and its compatibility with other materials enhanced, by introducing polar or non-polar functional groups through grafting monomers. This has significant practical value. Current grafting modification methods include melt grafting, solution grafting, solid-phase grafting, and suspension grafting. Solution grafting is gradually being phased out due to its complex post-processing and significant environmental pollution, while melt grafting easily leads to polymer degradation. Currently, solid-phase grafting and suspension grafting are hot topics in the field. Suspension grafting, based on solid-phase grafting, introduces water as a dispersant, offering advantages such as high product purity and easy temperature control, and has attracted considerable attention. US5585435 discloses a continuous solid-phase grafting method that fluidizes polypropylene powder using steam / alcohol vapor and adds a vaporized monomer initiator. CN1704436A discloses an improved reactor with internal and external double spiral ribbons, enabling continuous solid-phase grafting of powder. There are currently no reports on continuous suspension grafting production processes for polypropylene. Summary of the Invention

[0003] The purpose of this invention is to overcome the limitations of existing technologies where polypropylene suspension grafting only involves intermittent reactions, which are complex to operate and lead to unstable product quality. This invention provides a method for continuous suspension grafting of polar monomers onto polypropylene.

[0004] The inventors of this invention have discovered that, based on the principle of aqueous transport, by continuously introducing the material to be reacted into the water and carrying out the grafting reaction in an overflow manner, continuous and stable suspension grafting production can be achieved. Therefore, in order to achieve the above objective, this invention provides a method for continuous suspension grafting of polar monomers onto polypropylene. The method includes: continuously adding a premix containing polar monomers, an initiator, and polypropylene powder underwater to carry out a grafting reaction; continuously extracting the grafting reaction product and adding water to maintain the water content in the grafting reaction system, thereby achieving continuous grafting of polar monomers.

[0005] The method of this invention enables continuous suspension grafting of polar monomers onto polypropylene, yielding high-quality grafted products. Using this method, the yield of grafted products is high, with a grafting rate of 0.9-4.9%. Attached Figure Description

[0006] Figure 1 This is a schematic diagram of the production process of polypropylene continuous suspension grafting polar monomer according to one embodiment of the present invention.

[0007] Figure 2 This is an infrared comparison analysis diagram of the grafted product and polypropylene in Embodiment 1 of the present invention.

[0008] Explanation of reference numerals in the attached figures

[0009] 2-Continuous conveyor mixer 3-Demineralized water tank

[0010] 4-Grafting reactor 5-Particle dryer

[0011] 6-Devolve unit 7-Heat exchanger

[0012] 8-Circulating fan 9-Heater

[0013] 10-Circulating water pump 12-Exhaust fan Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] This invention provides a method for continuous suspension grafting of polar monomers onto polypropylene. The method includes: continuously adding a premix containing polar monomers, an initiator, and polypropylene powder underwater to carry out a grafting reaction; continuously extracting the grafting reaction products and adding water to maintain the water content in the grafting reaction system, thereby achieving continuous grafting of polar monomers.

[0016] According to the present invention, preferably, the method further includes solid-liquid separation of the product of the induced grafting reaction to obtain a solid product and a liquid medium. The solid product is subjected to devolatilization treatment, and optionally, the liquid medium is filtered and reused. The liquid medium mainly contains soluble initiator residues, which have little impact on the reaction. Therefore, reuse is beneficial for cost savings.

[0017] According to the present invention, preferably, a portion of the liquid medium is used as recycled water after filtration, and the remaining portion is discharged as wastewater. More preferably, the weight flow ratio of the recycled water to the wastewater is 1:5-10, and even more preferably 1:7-8.

[0018] According to the present invention, preferably, the devolatilization treatment is carried out at a temperature of 100-120°C for a time of 0.5-1 h. During the devolatilization treatment, not only moisture and volatiles can be removed from the grafted product, but the residual initiator in the grafted product can also be further decomposed and deactivated, thereby improving the performance of the grafted product.

[0019] According to the present invention, the polar monomer is selected from monomers that are slightly soluble or sparingly soluble in water. In order to improve the grafting rate, preferably, the polar monomer is at least one of acrylic acid, vinyl silane monomers and acrylate monomers containing unsaturated double bonds; more preferably, the polar monomer is at least one of glycidyl methacrylate, methyl acrylate, acrylic acid, n-butyl acrylate and vinyltriethoxysilane.

[0020] According to the present invention, preferably, the initiator is a peroxide-based free radical initiator with a half-life of less than 90 min at 90°C; more preferably, the initiator is at least one selected from benzoyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, tert-butyl peroxide, diisopropyl peroxide, tert-butyl peroxide (2-ethylhexanoate), and dicyclohexyl peroxide.

[0021] According to the present invention, the polypropylene powder can be a powder obtained by reactor particle technology using a Ziegler-Natta catalyst, without any melt granulation or addition of antioxidants. Preferably, the polypropylene powder is homopolymer polypropylene and / or random copolymer polypropylene; or, the polypropylene powder is impact-resistant polypropylene. More preferably, the particle size distribution of the polypropylene powder is between 0.2-3 mm, preferably 0.5-3 mm. The random copolymer polypropylene uses ethylene and / or α-olefin as comonomers, wherein the α-olefin is one of butene, hexene, or octene. For example, the random copolymer polypropylene can be ethylene-propylene copolymer impact-resistant polypropylene powder. The xylene-soluble content in the polypropylene powder is 1-70 wt%, preferably 1.5-65 wt%. The xylene-soluble content in the polypropylene powder is tested according to the method of GB / T24282-2009 (Determination of xylene-soluble content in polypropylene plastics).

[0022] According to the present invention, preferably, the amount of the polar monomer is 1-10 parts by weight, more preferably 2-8 parts by weight, relative to 100 parts by weight of polypropylene powder, and the amount of the initiator is 0.01-0.5 parts by weight.

[0023] According to the present invention, preferably, the weight flow ratio of the polypropylene powder to water is 1:2-8. Limiting the weight flow ratio of polypropylene powder to water within the above range allows the premix to be uniformly dispersed in water, thereby improving the quality of the grafted product.

[0024] According to the present invention, preferably, the method further includes adding an organic solvent to a premix containing a polar monomer, an initiator, and polypropylene powder, and then continuously adding it underwater to carry out a grafting reaction. Adding an organic solvent to the premix can cause the polypropylene powder to swell, facilitating material transport.

[0025] According to the present invention, the organic solvent can be any common reagent that causes polypropylene powder to expand in volume. Preferably, the organic solvent is at least one selected from toluene, xylene, chlorobenzene, tetrahydrofuran, hexane, cyclohexane, decahydronaphthalene, and heptane. In the present invention, the organic solvent is also referred to as a swelling agent.

[0026] According to the present invention, preferably, the amount of the organic solvent is 4-15 parts by weight relative to 100 parts by weight of polypropylene powder.

[0027] According to the present invention, preferably, the grafting reaction temperature is 80-95°C, more preferably 85-92°C, and the time is 0.5-6 hours, more preferably 1-4 hours. Limiting the temperature and time of the grafting reaction within the above range can avoid the increased degree of water vaporization caused by excessively high operating temperature, which would lead to some monomers being carried away from the reaction system by water vapor and thus reducing the grafting rate.

[0028] The present invention also provides a system for continuous suspension grafting of polar monomers onto polypropylene, the system comprising a continuous conveying mixer, a grafting reactor, a particle dryer and a devolatilizer connected sequentially along the material direction;

[0029] The continuous conveying mixer is used to premix the initiator, graft monomer and polypropylene powder;

[0030] The grafting reactor is used to carry out the grafting reaction;

[0031] The particle dryer is used to perform solid-liquid separation to obtain solid products and liquid media.

[0032] The devolatilizer is used to perform devolatilization treatment on the solid phase product obtained by solid-liquid separation.

[0033] The grafting reactor is equipped with a submersible pipe and an overflow port at the top. The submersible pipe is used to continuously transport the material from the continuous conveyor mixer into the underwater portion of the grafting reactor, and the overflow port is used to continuously extract the products of the grafting reaction.

[0034] In this invention, the reaction raw materials are accurately measured, and corresponding metering devices should be provided, including but not limited to metering pumps, metering tanks, and loss-in-weight balances. Specific setup methods are well known to those skilled in the art and will not be described in detail here.

[0035] According to the present invention, preferably, the continuous conveying mixer should be supplied with a small flow of nitrogen to maintain a slight positive pressure inside and ensure the pressure at the outlet. More preferably, the pressure is not less than 0.2 bar, and more preferably 0.3-0.5 bar.

[0036] According to the present invention, preferably, the grafting reactor is equipped with a stirrer suitable for solid-liquid mixing systems, including but not limited to three- or four-bladed turbine impellers, ribbon stirrers, and single- or multi-layer three- or four-bladed inclined impellers. The grafting reactor may also be equipped with two or more baffles to enhance the uniform dispersion of solid particles in water. The grafting reactor should have at least two inlets, respectively connected to a submerged pipe for the premix and a demineralized water tank. The premix enters the lower part of the grafting reactor under pressure through the submerged pipe, ensuring the mixing of the newly added material with the existing material in the reactor. An overflow port is provided on the upper side of the grafting reactor body, connected to a particle dryer, allowing the grafting reaction product to enter the particle dryer through the overflow port.

[0037] According to the present invention, preferably, the premix containing polar monomers, initiators and polypropylene powder is added to water through a submersible tube, and the distance between the end of the submersible tube immersed in water and the water surface is not less than 5 cm, preferably 8-15 cm.

[0038] According to the present invention, preferably, the particle dryer is equipped with an induced draft fan, which provides an air source for the particle dryer. The induced draft fan and the particle dryer work together to perform solid-liquid separation to obtain a solid product and a liquid medium.

[0039] According to the present invention, preferably, the system further includes a heat exchanger, a circulating fan, and a heater connected in sequence, wherein the heat exchanger and the heater are respectively connected to the top and bottom of the devolatilizer. The heat exchanger, circulating fan, and heater are auxiliary equipment of the devolatilizer, and the devolatilizer, together with the heat exchanger, circulating fan, heater, and devolatilizer, complete the devolatilization treatment of solid products.

[0040] According to the present invention, preferably, the demineralized water tank is connected to the particle dryer, and the liquid medium separated by the particle dryer is filtered and then flows into the demineralized water tank for reuse.

[0041] According to the present invention, preferably, the demineralized water tank is equipped with a stirrer and a jacket. The stirrer is used to mix the original water in the demineralized water tank, the newly added water, and the recycled water separated by the particle dryer. The jacket is used to regulate the feed water temperature by introducing low-pressure steam or circulating water according to process requirements. More preferably, the temperature of the water in the demineralized water tank is the same as the temperature of the grafting reaction.

[0042] Combination Figure 1The method for continuous suspension grafting of polar monomers onto polypropylene according to the present invention is described. Polar monomers, initiators, and polypropylene powder are metered and added to a continuous conveying mixer 2 in proportion. After being mixed evenly in the continuous conveying mixer 2, the mixture enters the lower part of the grafting reactor 4 through a submersible pipe under the action of nitrogen (pressure not less than 0.2 bar), i.e., the outlet of the submersible pipe is located below the water level. At the same time, the demineralized water tank 3 continuously feeds water into the grafting reactor 4, so that the polar monomers, initiators, and polypropylene powder undergo a grafting reaction in the water. The product of the grafting reaction enters the particle dryer 5 through the overflow port at the top of the grafting reactor 4 for solid-liquid separation to obtain a solid product and a liquid medium. The solid product enters the devolatilizer 6. Under the combined action of the heat exchanger 7, the circulating fan 8, the heater 9, and the devolatilizer 6, the devolatilization treatment of the solid product is completed to obtain the grafted product. After filtration, part of the liquid medium is returned to the demineralized water tank 3 as recycled water, and the remainder is discharged as wastewater.

[0043] The present invention will be described in detail below through embodiments. In the following embodiments,

[0044] Grafting rate test method: Place 2-4g of grafted product into a Soxhlet extractor and extract with acetone for 24 hours to remove unreacted monomers and their homopolymers, and obtain pure grafted product. Dry and weigh the product, and calculate the grafting rate (Gp%) = (W1-W0) / W0×100%; where W1 is the weight of grafted polypropylene and W0 is the weight of ungrafted polypropylene.

[0045] Infrared characterization of grafted groups: 2-4g of grafted product was placed in a Soxhlet extractor and extracted with acetone for 24 hours to remove unreacted monomers and their homopolymers, resulting in pure grafted product. The product was then hot-pressed into thin sheets, and the characteristic peaks of functional groups on the grafted modified polypropylene could be observed by quantitative Fourier transform infrared (FTIR) spectroscopy.

[0046] Polypropylene A: Granular homopolymer polypropylene powder with a particle size distribution between 0.5-2 mm. The content of xylene-soluble substances in the polypropylene powder is 2.3 wt%.

[0047] Polypropylene B: Granular ethylene-propylene copolymer impact-resistant polypropylene powder with a particle size distribution between 1-3 mm. The content of xylene-soluble substances in the polypropylene powder is 47.8 wt%.

[0048] Example

[0049] Polar monomers, initiators, polypropylene powder, and optional swelling agents are metered and added to continuous conveying mixer 2 in proportion. After being mixed evenly in continuous conveying mixer 2, the mixture is continuously introduced into the lower part of grafting reactor 4, which has been pre-stored with deionized water, through a submerged pipe (located 10 cm below the liquid surface) under the action of nitrogen (pressure 0.3 bar). Simultaneously, demineralized water tank 3 continuously feeds water into grafting reactor 4, allowing the polar monomers, initiators, and polypropylene powder to undergo a grafting reaction in water. The grafting reaction product enters particle dryer 5 through the overflow port at the top of grafting reactor 4 for solid-liquid separation, obtaining a solid product and a liquid medium. The solid product enters devolatilizer 6 for devolatilization treatment to obtain the grafted product. After filtration, a portion of the liquid medium is recycled back to demineralized water tank 3 via circulating water pump 10, and the remainder is discharged as wastewater. Specific reaction conditions and product properties for Examples 1-4 are shown in Table 1.

[0050] Figure 2 This is an infrared comparison analysis image of the grafted product and polypropylene powder from Example 1. The image shows that the grafted product has a lower infrared signature at 1731 cm⁻¹. -1 The presence of a bimodal characteristic peak indicates that glycidyl methacrylate has been grafted onto the polypropylene powder.

[0051] Table 1

[0052]

[0053] Example 5

[0054] The grafting reaction was carried out according to the method of Example 1, except that the distance between the end of the submerged tube immersed in water and the water surface was 6 cm. The yield was 58.8 kg / h, and the grafting rate was 4.2%.

[0055] Comparative Example 1

[0056] The grafting reaction was carried out according to the method of Example 1, except that the mixed material was not fed into the grafting reactor directly through the feed inlet, without passing through the submersible tube. The yield was 58.5 kg / h, and the grafting rate was 3.3%.

[0057] The method of this invention not only enables continuous suspension grafting of polar monomers onto polypropylene, but also yields grafted products with a high grafting rate. As shown in Examples 1-5, using the method of this invention, the yield of grafted products is 29-70 kg / h, and the grafting rate is 0.9-4.9%. Comparing Example 1 with the comparative example, it is evident that the grafting rate of the grafted products decreases significantly when a submersible feed tube is not used.

[0058] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for continuous suspension grafting of polar monomers onto polypropylene, characterized in that, The method includes: continuously adding a premix containing polar monomers, initiators and polypropylene powder underwater to carry out a grafting reaction; continuously extracting the grafting reaction products and adding water to maintain the water content in the grafting reaction system, thereby achieving continuous grafting of polar monomers. The premix containing polar monomers, initiators and polypropylene powder is added to water through a submersible tube, and the distance between the end of the submersible tube immersed in water and the water surface is 8-15 cm. The polar monomer is at least one selected from glycidyl methacrylate, methyl acrylate, acrylic acid, n-butyl acrylate, and vinyltriethoxysilane; the amount of the polar monomer relative to 100 parts by weight of polypropylene powder is 1-10 parts by weight, and the amount of the initiator is 0.01-0.5 parts by weight; the weight flow ratio of the polypropylene powder to water is 1:2-8; the grafting reaction temperature is 80-95℃, and the time is 0.5-6h; the particle size distribution of the polypropylene powder is between 0.2-3mm. The method is carried out in a system for continuous suspension grafting of polar monomers onto polypropylene, wherein the system includes a continuous conveying mixer, a grafting reactor, a particle dryer, and a devolatilizer connected sequentially along the material flow direction; The continuous conveying mixer is used to premix the initiator, graft monomer and polypropylene powder; The grafting reactor is used to carry out the grafting reaction; The particle dryer is used to perform solid-liquid separation to obtain solid products and liquid media. The devolatilizer is used to perform devolatilization treatment on the solid product obtained from solid-liquid separation; the devolatilization treatment temperature is 100-120℃ and the time is 0.5-1h. The grafting reactor is equipped with a submersible pipe and an overflow port at the top. The submersible pipe is used to continuously feed the material from the continuous conveying mixer into the underwater portion of the grafting reactor, and the overflow port is used to continuously draw out the products of the grafting reaction. The continuous conveying mixer is supplied with a small flow of nitrogen to maintain a slight positive pressure inside and to ensure the pressure at the outlet, which is not less than 0.2 bar.

2. The method according to claim 1, wherein, The method further includes solid-liquid separation of the product of the induced grafting reaction to obtain a solid product and a liquid medium. The solid product is subjected to devolatilization treatment, and optionally, the liquid medium is filtered and reused.

3. The method according to claim 1, wherein, The polypropylene powder is homopolymer polypropylene and / or random copolymer polypropylene; The amount of the polar monomer is 2-8 parts by weight relative to 100 parts by weight of polypropylene powder, and the amount of the initiator is 0.01-0.5 parts by weight.

4. The method according to claim 3, wherein, The initiator is at least one selected from benzoyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, tert-butyl peroxide, diisopropyl peroxide, tert-butyl peroxide (2-ethylhexanoate), and dicyclohexyl peroxide. And / or, the polypropylene powder is impact-resistant polypropylene.

5. The method according to claim 1, wherein, The method further includes adding an organic solvent to a premix containing polar monomers, initiators, and polypropylene powder, and then continuously adding it underwater to carry out a grafting reaction.

6. The method according to claim 5, wherein, The organic solvent is at least one selected from toluene, xylene, chlorobenzene, tetrahydrofuran, hexane, cyclohexane, decahydronaphthalene, and heptane; And / or, relative to 100 parts by weight of polypropylene powder, the amount of said organic solvent is 4-15 parts by weight.

7. The method according to claim 1, wherein, The grafting reaction was carried out at a temperature of 85-92 °C for 1-4 h.

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