Preparation method of polypropylene with high melt strength

Abstract

The invention discloses a preparation method of high-melt-strength polypropylene, which comprises the following steps: hydrating an inorganic silicon source, mixing the obtained hydrated silica gel with a coupling agent for modification, mixing the obtained modified silica gel with a free radical initiator, a free radical stabilizer, a grafting monomer and the like, preparing a modifier dispersion liquid by using a dispersion solvent, and preparing the high-melt-strength polypropylene by using the modifier dispersion liquid. And mixing the obtained modifier dispersion liquid with polypropylene, and extruding to obtain the modified polypropylene composite material. According to the invention, the problem that silicon dioxide is easy to agglomerate is solved by using a new free radical initiator, so that the crosslinking degree of polypropylene is greatly improved, the melt strength of polypropylene is improved, and the application prospect of polypropylene is further expanded.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of plastic materials, and particularly relates to a preparation method of high-melt-strength polypropylene. BACKGROUND

[0002] Polypropylene has become the core polymer material in the fields of mechanical manufacturing, textile industry, electronic packaging, building materials and food packaging due to its excellent comprehensive performance. However, the traditional linear polypropylene has obvious structural limitations: firstly, the narrow molecular weight distribution leads to insufficient melt rheological performance; and secondly, the proximity of the processing softening point and the crystal phase melting point causes a very narrow processing window. These inherent defects are specifically manifested in the bubble structure instability in the extrusion foaming process and the uneven wall thickness distribution in the thermoforming process, which seriously restricts the engineering application of the material. Molecular modification research shows that the enhancement mechanism of the melt strength of polypropylene mainly depends on three key factors: (1) molecular weight improvement; (2) molecular weight distribution regulation; and (3) introduction of long-chain branched (LCB) structure. Among them, the long-chain branched structure contributes most significantly to the enhancement of the melt strength due to its unique topological entanglement effect. This structure-property relationship provides clear theoretical guidance for the engineering modification of polypropylene.

[0003] At present, a large number of researches are carried out by adding organic grafting monomers, inorganic materials such as nano-silica, and the like in the process of solution preparation or melt extrusion, and reacting at high temperature to improve the crosslinking degree between polypropylene molecular chains, so as to modify the traditional linear structure of polypropylene to improve the melt strength. Silane-modified silica can enhance the interfacial compatibility, improve the mechanical properties and expand the functions of polypropylene materials, and therefore is particularly favored in recent years. However, due to its extremely high specific surface area, the silica is more likely to agglomerate under silane modification, and cannot be well dispersed in the PP powder, and the agglomeration phenomenon will greatly affect the modification effect. Therefore, it is of great significance to develop a simple, convenient and efficient method for modifying polypropylene by dispersing silica. SUMMARY

[0004] The application provides a preparation method of high-melt-strength polypropylene, which uses a mixture of peroxide, zinc oxide (ZnO) and guanidine compound as a free radical initiator, and pre-treats silane-modified silica by using a dispersing medium, so as to solve the problem of easy agglomeration of the silica in the PP powder. The benzene ring of DPG is compatible with the non-polar chain of PP, and Zn 2+ is combined with the surface hydroxyl group of the filler, so that the agglomeration phenomenon of the modified silica generated during the melting of the PP is improved, and the dispersion state of the modified silica in the PP powder is enhanced. Meanwhile, Zn(DPG)2 can decompose to generate free radicals in the presence of peroxide, further intensify the crosslinking of PP molecular chains, and faster form a three-dimensional network structure, so that the crosslinking degree is improved.

[0005] To achieve the above object, the application adopts the following technical solutions: A preparation method of high melt strength polypropylene, the preparation comprising the following steps: (1) Activating an inorganic silicon source by acid pickling with an inorganic acid, and then hydrating the inorganic silicon source in a sealed device to obtain hydrated silica gel with an adsorbed water content of 5wt%-20wt%, and then degassing the obtained hydrated silica gel in an organic solvent; (2) Mixing the hydrated silica gel treated in step (1) with a coupling agent solution, and stirring the mixture at room temperature for 16-24 hours, and then washing the obtained solid product to neutral with desalted water and an organic solvent in sequence, and drying to obtain modified silica gel; (3) Fully mixing a free radical initiator, a free radical stabilizer, a grafting monomer, a primary antioxidant, a secondary antioxidant, and a lubricant according to a proportion, and then ultrasonically dispersing the mixture and the modified silica gel in a dispersion medium to obtain a modifier dispersion liquid; (4) Fully mixing the obtained modifier dispersion liquid and polypropylene powder in a high-speed mixer to uniformly disperse the modifier in the polypropylene powder, and then melt blending and extruding in a twin-screw extruder to obtain a modified polypropylene composite material.

[0006] Further, the inorganic silicon source in step (1) is at least one of silica nanoparticles or 40-mesh-400-mesh silica gel particles, with a purity of ≥99.5wt%, and a single impurity content requirement of chloride ≤0.02%, iron ≤0.02%, pH (10% water suspension) in the range of 6.0-7.0, and heating weight loss ≤2.0%.

[0007] Further, the inorganic acid in step (1) is one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, with a concentration of 1-5mol / L.

[0008] Further, the volume ratio of the inorganic silicon source to the inorganic acid used in step (1) is 1:2-1:10.

[0009] Further, the acid pickling time in step (1) is 2-4 hours.

[0010] Further, the hydration in step (1) is carried out under a nitrogen atmosphere at 120°C for 2-4 hours.

[0011] Further, the organic solvent in step (1) is one or more of n-hexane, anhydrous methanol, and anhydrous ethanol.

[0012] Further, the coupling agent solution in step (2) is prepared by dissolving one or more of aminopropyltriethoxysilane, aminopropyltrimethoxysilane, diethylenetriaminepropyltrimethoxysilane, N-aminoethyl-3-aminopropylmethyldimethoxysilane, and ureidopropyltriethoxysilane in an organic solvent.

[0013] Further, the organic solvent is one or more of n-hexane, anhydrous methanol, and anhydrous ethanol.

[0014] Further, the mass ratio of the hydrated silica gel to the coupling agent used in step (2) is 2:1 to 10:1.

[0015] Further, the free radical initiator in step (3) is prepared by mixing zinc oxide and a guanidino compound at a molar ratio of 1:2 to 4:5, grinding for 15 to 30 minutes to form a complex, and then mixing the peroxide with the complex at a mass ratio of 1:1 to 5:6; the peroxide is one or more of benzoyl peroxide (BPO), dicumyl peroxide (DCP), dilauryl peroxide (LPO), di-tert-butyl peroxide (DTBP), and peroxide carbonates such as diisopropyl peroxydicarbonate (IPP), dicyclohexyl peroxydicarbonate (DCPD), and dihexadecyl peroxydicarbonate (Rx24L); and the guanidino compound is any one of 1,3-diphenyl guanidine (DPG), di-o-tolyl guanidine, and triphenyl guanidine.

[0016] Further, the free radical stabilizer in step (3) is one or more of metal oxides such as neodymium oxide, lanthanum oxide, cerium oxide, yttrium oxide, and titanium dioxide, or one or more of natural free radical stabilizers such as vitamin E and tea polyphenol.

[0017] Further, the grafting monomer in step (3) is one or more of divinylbenzene (DVB), trivinylbenzene (TVB), vinyltrimethoxysilane (VTMS), and tetra-vinylsilane (TVS).

[0018] Further, the primary antioxidant in step (3) is any one of antioxidant 1010, antioxidant 1076, antioxidant 3114, and antioxidant 1330.

[0019] Further, the secondary antioxidant in step (3) is any one of antioxidant 168 and antioxidant 626.

[0020] Specifically, the primary and secondary antioxidants can be combined as primary antioxidant 1010 + secondary antioxidant 168, primary antioxidant 1076 + secondary antioxidant 626, primary antioxidant 3114 + secondary antioxidant 168, or primary antioxidant 1330 + secondary antioxidant 626.

[0021] Further, the lubricant in step (3) is one or more of calcium stearate (Cast. Ca), zinc stearate (Cast. Zn), etc.

[0022] Further, the mass ratio of the radical initiator, the radical stabilizer, the grafting monomer, the modified silica gel, the primary antioxidant, the secondary antioxidant, and the lubricant used in step (3) is (4-10):(1-3):(3.5-10):(4-10):(1-250):(0.5-5):(0.2-1).

[0023] Further, the mass ratio of the mixture and the dispersion solvent used in step (3) is (0.5-1.5):4.

[0024] Further, the dispersion medium is one or more of safflower seed oil, grape seed oil, soybean oil, turpentine oil, and sunflower oil, or one or more of benzene, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, tetrahydrofuran, and 1,4-dioxane.

[0025] Further, the temperature of the ultrasonic in step (3) is 25-40℃, the frequency is 40-200Hz, and the time is 15-45min.

[0026] Further, the particle size of the polypropylene powder in step (4) is 100-600 mesh.

[0027] Further, the mass ratio of the modifier dispersion liquid and the polypropylene powder used in step (4) is (0.5-1.5):100.

[0028] Further, the temperature of the high-speed mixer in step (4) is 80-100℃, the rotation speed is 200-500rpm / min, and the mixing time is 10-15min.

[0029] Further, the temperature of the twin-screw extruder in step (4) is set as follows: 80-100℃ for zone 1, 140-160℃ for zones 2-4, 160-220℃ for zone 5, 200-220℃ for zone 6, 180-200℃ for zone 7, and 160-180℃ for the die head, the screw rotation speed is 150-220rpm / min, the extrusion rate is 10-20kg / h, and the rotation speed of the granulator is 200-300r / min.

[0030] Compared with the prior art, the present application has the following beneficial effects: 1) Compared with traditional silica-modified polypropylene, the silica surface modified by silane in this invention has more active groups. After hydrolysis, the silane coupling agent condenses with the hydroxyl groups on the SiO2 surface to form an organic long-chain coating layer (-Si-O-Si-). At the same time, its organic ends (such as amino and vinyl groups) are physically entangled or chemically grafted with the PP molecular chain, which can be more efficiently and conveniently dispersed in the polypropylene molecular chain. 2) In this invention, zinc oxide (ZnO) and 1,3-diphenylguanidine (DPG) are used as free radical initiators in the additive formulation stage before the polypropylene melt extrusion process, combined with a dispersion medium to pretreat silane-modified silica. During this process, ZnO and DPG can generate Zn(DPG)₂ during the preheating stage of the extruder. 2+ By combining with the hydroxyl groups on the surface of silica filler, modified silica can effectively improve the agglomeration phenomenon that occurs when PP melts, further enhancing the dispersion of modified silica in PP powder. Simultaneously, the benzene rings of DPG are compatible with the nonpolar chains of PP, further enhancing the bonding between modified silica and PP chains, thereby strengthening the dispersion of silica in PP and weakening agglomeration. Furthermore, Zn(DPG)2 can decompose to generate free radicals in the presence of peroxides, further intensifying the cross-linking of PP molecular chains and accelerating the formation of a three-dimensional network structure. In addition, Zn... 2+ Not only can it act as a nucleating agent, that is, coordinate with PP segments to act as a heterogeneous nucleating agent, thereby increasing the crystallinity by 5-8% and thus improving the rigidity and transparency of PP materials, but zinc oxide can also partially replace the function of free radical stabilizers such as neodymium oxide and lanthanum oxide, prolonging the activity of free radicals in the reaction process and enhancing the degree of cross-linking reaction. Attached Figure Description

[0031] Figure 1 The FTIR spectrum of APTES(Si)-PP prepared in Example 2 without the addition of zinc oxide and DPG is shown.

[0032] Figure 2 GPC spectra of APTES(Si)-Zn(DPG)2-PP and s17475(Si)-Zn(DPG)2-PP with PP powder. Detailed Implementation

[0033] A method for preparing high melt strength polypropylene, comprising the following steps: (1) After the inorganic silicon source is activated by washing with inorganic acid for 2-4 hours, it is activated with water vapor at 120°C for 2-4 hours in a sealed device under nitrogen atmosphere to obtain hydrated silica gel with an adsorption water content of 5wt%-20wt%. Then, the obtained hydrated silica gel is degassed in an organic solvent. (2) The coupling agent and the organic solvent are mixed rapidly under dry gas protection at a volume ratio of 1:2-1:20 to obtain a coupling agent solution; then the hydrated silica gel after the treatment in step (1) is mixed with the coupling agent solution at a mass ratio of the hydrated silica gel used to the coupling agent used of 2:1-10:1, and stirred at room temperature for 16-24 hours; the obtained solid product after filtration is washed with desalted water and an organic solvent in sequence until neutral, dried, and modified silica gel is obtained; (3) The free radical initiator, the free radical stabilizer, the grafting monomer, the modified silica gel, the main antioxidant, the auxiliary antioxidant, and the lubricant are weighed at a mass ratio of (4-10):(1-3):(3.5-10):(4-10):(1-250):(0.5-5):(0.2-1), and then mixed fully using a high-speed mixer; then the mixture is mixed with a dispersion medium at a mass ratio of (0.5-1.5):4, and the modified silica gel weighed is fully mixed and ultrasonically dispersed at 25-40℃ and 40-200Hz for 15-45min to obtain a modified agent dispersion liquid; (4) The modified agent dispersion liquid and the polypropylene powder are added into a high-speed mixer at a mass ratio of (0.5-1.5):100, the temperature of the high-speed mixer is set to 80-100℃, the rotating speed is set to 200-500rpm / min, and mixed for 10-15min; then the temperature of a double-screw extruder is set to 80-100℃ in zone 1, 140-160℃ in zones 2-4, 160-220℃ in zone 5, 200-220℃ in zone 6, and 180-200℃ in zone 7, the rotating speed of the screw is set to 150-220rpm / min, the extrusion rate is set to 10-20kg / h, and the rotating speed of the granulator is set to 200-300r / min to obtain a modified polypropylene composite material.

[0034] In step (1), the inorganic silicon source is at least one of silica nanoparticles or 40-400 mesh silica gel particles. The inorganic acid is one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

[0035] In step (2), the coupling agent is one or more of aminopropyltriethoxysilane, aminopropyltrimethoxysilane, diethylenetriaminepropyltrimethoxysilane, N-aminoethyl-3-aminopropylmethyldimethoxysilane, and ureidopropyltriethoxysilane.

[0036] In the operation, the organic solvent is one or more of n-hexane, anhydrous methanol, and anhydrous ethanol.

[0037] The free radical initiator in step (3) is prepared by mixing zinc oxide and guanidino compound at a molar ratio of 1:2-4:5 and grinding for 15-30 min to form a complex, and then mixing the peroxide with the complex at a mass ratio of 1:1-5:6; the peroxide is one or more of benzoyl peroxide (BPO), dicumyl peroxide (DCP), dilauryl peroxide (LPO), di-tert-butyl peroxide (DTBP), and peroxide carbonates such as diisopropyl peroxide carbonate (IPP), dicyclohexyl peroxide carbonate (DCPD), and dihexadecyl peroxide carbonate (Rx24L); the guanidino compound is any one of 1,3-diphenyl guanidine (DPG), di-o-tolyl guanidine, and triphenyl guanidine. The free radical stabilizer is one or more of metal oxides such as neodymium oxide, lanthanum oxide, cerium oxide, yttrium oxide, titanium dioxide, and cerium oxide, or one or more of natural free radical stabilizers such as vitamin E and tea polyphenol. The grafting monomer is one or more of divinylbenzene (DVB), trivinylbenzene (TVB), vinyltrimethoxysilane (VTMS), and tetravinylsilane (TVS). The primary antioxidant is any one of antioxidants 1010, 1076, 3114, and 1330. The secondary antioxidant is any one of antioxidants 168 and 626. The lubricant is one or more of calcium stearate (Cast. Ca), zinc stearate (Cast. Zn), and the like. The dispersion medium is one or more of plant-based oil agents such as safflower seed oil, grape seed oil, soybean oil, turpentine oil, and sunflower oil, or one or more of polar organic solvents such as benzene, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, tetrahydrofuran, and 1,4-dioxane.

[0038] The particle size of the polypropylene powder in step (4) is 100-600 mesh.

[0039] Silicon dioxide, as an inorganic additive material with extremely excellent performance, plays an extremely important role in material modification. As a rigid support point, silicon dioxide nanoparticles can effectively transmit stress, and the high modulus of silicon dioxide can enhance the rigidity of the composite material. After the modification of silicon dioxide using a silane coupling agent, the hydroxyl groups on the surface of silicon dioxide can be fully activated, and more functional groups can be introduced, so that the modified material has more properties that do not belong to its own structure. However, both silicon dioxide and silane-modified silicon dioxide will cause strong agglomeration due to the active groups on the surface, which seriously affects the dispersion state of silicon dioxide particles in the modified material, thereby affecting the modification effect and even reducing the strength of the material itself.

[0040] This invention discloses a method for modifying silica, which solves the agglomeration problem of silica by adding Zn(DPG)2. On one hand, Zn... 2+ By combining with the hydroxyl groups on the surface of silica filler, the agglomeration tendency of SiO2 during PP melt processing can be effectively suppressed, further enhancing the dispersion of silica in PP powder. On the other hand, the benzene ring structure in DPG molecules can interact with the nonpolar segments of PP through van der Waals forces, while its polar ends interact through Zn. 2+ By bonding with SiO2, a gradient interface layer of "PP-DPG-Zn-SiO2" can be formed, further enhancing the dispersion of silica in PP and weakening agglomeration. Secondly, Zn(DPG)2 can decompose in the presence of peroxides to generate free radicals, further intensifying the cross-linking of PP molecular chains and accelerating the formation of a three-dimensional network structure. Finally, Zn... 2+ Not only can it act as a nucleating agent, coordinating with PP segments, Zn 2+ Coordination with tertiary carbon atoms in PP segments can increase crystallinity by 5-8%, thereby improving the rigidity and transparency of PP materials. Finally, zinc oxide can also partially replace the function of free radical stabilizers such as neodymium oxide and lanthanum oxide through valence state changes (Zn... 2+ ↔Zn + It extends the free radical lifetime, shortens the cross-linking reaction time by 30%, and enhances the degree of cross-linking reaction.

[0041] The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Modifications and substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are all within the scope of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0042] Example 1 This embodiment provides a high melt strength polypropylene prepared by improving silica agglomeration, and the preparation steps are as follows: 1) Silica gel activation: Place 40-60 mesh reagent-grade silica gel in a 500 ml three-necked volumetric flask, add 5 wt% nitric acid solution, and heat at 120°C for 4 hours. Immediately after heating, pass the reaction solution through a sintered glass funnel and wash successively with pure water and methanol until the pH value reaches 7. Then, dry it in an oven at 100°C to constant weight. Place the obtained activated silica gel in a hydration apparatus container, seal the container, and then activate the silica gel with water vapor at 120°C under a nitrogen atmosphere. After 4 hours, the silica gel will adsorb water to reach adsorption equilibrium, yielding hydrated silica gel with an adsorbed water content of 10 wt%.

[0043] 2) Preparation of modified silica: ① Add anhydrous sodium sulfate to n-hexane, let it stand for 6 hours to dehydrate, and then filter to obtain dehydrated n-hexane; ② Add 250 mL of dehydrated n-hexane to 200 g of hydrated silica gel prepared in step 1), stir, degas under vacuum for 10 minutes, and maintain a nitrogen atmosphere in the reactor after degassing. ③ Accurately measure 90 mL of aminopropyltriethoxysilane (APTES) silane coupling agent and add it to 250 mL of dehydrated n-hexane. Mix rapidly under dry nitrogen protection to prepare the coupling agent solution. ④ Nitrogen gas is continuously introduced into the reactor containing hydrated silica gel, and the coupling agent solution prepared in the previous step is quickly poured into the reactor. The reaction is carried out at a speed of 1000 r and a normal temperature for 16 hours. The reaction product is immediately filtered using a sand core funnel and washed sequentially with deionized water, n-hexane and methanol to obtain alkylated silica gel with aminosiloxane groups bonded to the surface. ⑤ Place the above alkylated silica gel in a vacuum drying oven or baking oven and dry it at 100°C to constant weight to obtain modified silica gel.

[0044] 3) Preparation of additives: 3.1) Preparation of auxiliary agent formula 1-1: Accurately weigh 20g of zinc oxide and grind it thoroughly in a mortar for 20 minutes. Then add 16g of benzoyl peroxide (BPO), mix thoroughly, and store in an explosion-proof refrigerator (0~7℃) to obtain the free radical initiator auxiliary.

[0045] Accurately weigh 4g of neodymium oxide, 12g of divinylbenzene, 4g of primary antioxidant 1010, 2g of secondary antioxidant 168, 200g of modified silica, and 0.8g of calcium stearate, and mix them thoroughly with the prepared free radical initiator to obtain a polypropylene modification agent.

[0046] The prepared polypropylene modified additive was poured into a beaker containing 228g of sunflower oil. The beaker was then placed in an ultrasonic oscillator with the temperature set at 30℃, the frequency at 300Hz, and the oscillation time at 30min. The additive was observed to be uniformly dispersed in the oil. After that, it was poured into 5kg of polypropylene powder.

[0047] 3.2) Preparation of auxiliary agent formulations 1-2: Accurately weigh 20g of DPG and grind it thoroughly in a mortar for 20 minutes. Then add 16g of BPO, mix thoroughly, and store in an explosion-proof refrigerator (0~7℃) to obtain the free radical initiator auxiliary.

[0048] Accurately weigh 4g of neodymium oxide, 12g of divinylbenzene, 4g of primary antioxidant 1010, 2g of secondary antioxidant 168, 200g of modified silica, and 0.8g of calcium stearate, and mix them thoroughly with the prepared free radical initiator to obtain a polypropylene modification agent.

[0049] The prepared polypropylene modified additive was poured into a beaker containing 228g of sunflower oil. The beaker was then placed in an ultrasonic oscillator with the temperature set at 30℃, the frequency at 300Hz, and the oscillation time at 30min. The additive was observed to be uniformly dispersed in the oil. After that, it was poured into 5kg of polypropylene powder.

[0050] 3.3) Preparation of additive formulations 1-3: Accurately weigh 5.5g (0.068mol) zinc oxide and 14.5g (0.068mol) DPG, grind them thoroughly in a mortar for 20min, then add 16g BPO, mix thoroughly and store in an explosion-proof refrigerator (0~7℃) to obtain the free radical initiator auxiliary.

[0051] Accurately weigh 4g of neodymium oxide, 12g of divinylbenzene, 4g of primary antioxidant 1010, 2g of secondary antioxidant 168, 200g of modified silica, and 0.8g of calcium stearate, and mix them thoroughly with the prepared free radical initiator to obtain a polypropylene modification agent.

[0052] The prepared polypropylene modified additive was poured into a beaker containing 228g of sunflower oil. The beaker was then placed in an ultrasonic oscillator with the temperature set at 30℃, the frequency at 300Hz, and the oscillation time at 30min. The additive was observed to be uniformly dispersed in the oil. After that, it was poured into 5kg of polypropylene powder.

[0053] 3.4) Preparation of additive formulations 1-4: Accurately weigh 4.1g (0.050mol) zinc oxide and 16g (0.075mol) DPG, grind them thoroughly in a mortar for 20min, then add 16g BPO, mix thoroughly and store in an explosion-proof refrigerator (0~7℃) to obtain the free radical initiator auxiliary.

[0054] Accurately weigh 4g of neodymium oxide, 12g of divinylbenzene, 4g of primary antioxidant 1010, 2g of secondary antioxidant 168, 200g of modified silica, and 0.8g of calcium stearate, and mix them thoroughly with the prepared free radical initiator to obtain a polypropylene modification agent.

[0055] The prepared polypropylene modified additive was poured into a beaker containing 228g of sunflower oil. The beaker was then placed in an ultrasonic oscillator with the temperature set at 30℃, the frequency at 300Hz, and the oscillation time at 30min. The additive was observed to be uniformly dispersed in the oil. After that, it was poured into 5kg of polypropylene powder.

[0056] 3.5) Preparation of additive formulations 1-5: Accurately weigh 3.2g (0.039mol) zinc oxide and 16.8g (0.079mol) DPG, grind them thoroughly in a mortar for 20min, then add 16g BPO, mix thoroughly and store in an explosion-proof refrigerator (0~7℃) to obtain the free radical initiator auxiliary.

[0057] Accurately weigh 4g of neodymium oxide, 12g of divinylbenzene, 4g of primary antioxidant 1010, 2g of secondary antioxidant 168, 200g of modified silica, and 0.8g of calcium stearate, and mix them thoroughly with the prepared free radical initiator to obtain a polypropylene modification agent.

[0058] The prepared polypropylene modified additive was poured into a beaker containing 228g of sunflower oil. The beaker was then placed in an ultrasonic oscillator with the temperature set at 30℃, the frequency at 300Hz, and the oscillation time at 30min. The additive was observed to be uniformly dispersed in the oil. After that, it was poured into 5kg of polypropylene powder.

[0059] 4) Twin-screw extrusion The high-speed mixer temperature was set to 90℃ and the speed to 500 r / min. Polypropylene powder with different additives was poured into the high-speed mixer and stirred for 15 min to ensure thorough mixing of the additives and powder. The mixed powder was then fed into a twin-screw extruder. The twin-screw extruder temperature was set as follows: Zone 1 80℃, Zones 2-3 150℃, Zone 4 160℃, Zone 5 200℃, Zone 6 220℃, Zone 7 200℃, and Die 160℃. The screw speed was 200 rpm / min, the extrusion rate was 15 kg / h, and the pelletizer speed was 240 r / min. The extruded polypropylene pellets were designated as Sample 1-1, Sample 1-2, Sample 1-3, Sample 1-4, and Sample 1-5, depending on the additives used.

[0060] Example 2 This embodiment provides a high melt strength polypropylene prepared by improving silica agglomeration, and the preparation steps are as follows: 1) Silica gel activation: Place 40-60 mesh reagent-grade silica gel in a 500 ml three-necked volumetric flask, add 5 wt% nitric acid solution, and heat at 120°C for 4 hours. Immediately after heating, pass the reaction solution through a sintered glass funnel and wash successively with pure water and methanol until the pH reaches 7. Then, dry in an oven at 100°C to constant weight. Place the obtained activated silica gel in a hydration apparatus container, seal the container, and then activate the silica gel with steam at 120°C under a nitrogen atmosphere. After 4 hours, allow the silica gel to reach adsorption equilibrium, obtaining hydrated silica gel with an adsorbed water content of 10 wt%.

[0061] 2) Preparation of modified silica: ① Add anhydrous sodium sulfate to n-hexane, let it stand for 6 hours to dehydrate, and then filter to obtain dehydrated n-hexane; ② Add 250 mL of dehydrated n-hexane to 200 g of hydrated silica gel prepared in step 1), stir, degas under vacuum for 10 minutes, and maintain a nitrogen atmosphere in the reactor after degassing. ③ Accurately measure 90 mL of aminopropyltriethoxysilane (APTES) silane coupling agent and add it to 250 mL of dehydrated n-hexane. Mix rapidly under dry nitrogen protection to prepare the coupling agent solution. ④ Nitrogen gas is continuously introduced into the reactor containing hydrated silica gel, and the coupling agent solution prepared in the previous step is quickly poured into the reactor. The reaction is carried out at a speed of 1000 r and a normal temperature for 16 hours. The reaction product is immediately filtered using a sand core funnel and washed with deionized water, n-hexane and methanol in sequence to obtain alkylated silica gel with aminosiloxane groups bonded to the surface. ⑤ Place the above alkylated silica gel in a vacuum drying oven or baking oven and dry it at 100°C to constant weight to obtain modified silica gel.

[0062] 3) Preparation of additives: Accurately weigh 6.7g (0.08mol) zinc oxide and 33.8g (0.16mol) DPG, grind them thoroughly in a mortar for 20min, then add 16g BPO, mix thoroughly and store in an explosion-proof refrigerator (0~7℃) to obtain the free radical initiator auxiliary.

[0063] Accurately weigh 4g of neodymium oxide, 12g of divinylbenzene, 4g of primary antioxidant 1010, 2g of secondary antioxidant 168, 200g of modified silica, and 0.8g of calcium stearate, and mix them thoroughly with the prepared free radical initiator to obtain a polypropylene modification agent.

[0064] The prepared polypropylene modified additive was poured into a beaker containing 228g of sunflower oil. The beaker was then placed in an ultrasonic oscillator with the temperature set at 30℃, the frequency at 300Hz, and the oscillation time at 30min. The additive was observed to be uniformly dispersed in the oil. After that, it was poured into 5kg of polypropylene powder.

[0065] 4) Twin-screw extrusion The high-speed mixer temperature was set to 90℃ and the rotation speed to 500 r / min. Polypropylene powder with added additives was poured into the high-speed mixer and stirred for 15 min to ensure thorough mixing. The mixed powder was then fed into a twin-screw extruder. The twin-screw extruder temperature was set as follows: Zone 1 80℃, Zones 2-3 150℃, Zone 4 160℃, Zone 5 200℃, Zone 6 220℃, Zone 7 200℃, and Die 160℃. The screw speed was 200 rpm / min, the extrusion rate was 15 kg / h, and the pelletizer speed was 240 r / min. The extruded polypropylene granules were denoted as APTES(Si)-Zn(DPG)2-PP. Simultaneously, polypropylene granules without added zinc oxide and DPG (i.e., without Zn(DPG)2) were prepared and denoted as APTES(Si)-PP, and pure polypropylene granules without any additives were denoted as PP.

[0066] Example 3 This embodiment provides a high melt strength polypropylene prepared by improving silica agglomeration, and the preparation steps are as follows: 1) Silica gel activation: Place 40-60 mesh reagent-grade silica gel in a 500 ml three-necked volumetric flask, add 5 wt% nitric acid solution, and heat at 120°C for 4 hours. Immediately after heating, pass the reaction solution through a sintered glass funnel and wash successively with pure water and methanol until the pH reaches 7. Then, dry in an oven at 100°C to constant weight. Place the obtained activated silica gel in a hydration apparatus container, seal the container, and then activate the silica gel with steam at 120°C under a nitrogen atmosphere. After 4 hours, allow the silica gel to reach adsorption equilibrium, obtaining hydrated silica gel with an adsorbed water content of 10 wt%.

[0067] 2) Preparation of modified silica: ① Add anhydrous sodium sulfate to n-hexane, let it stand for 6 hours to dehydrate, and then filter to obtain dehydrated n-hexane; ② Add 250 mL of dehydrated n-hexane to 200 g of hydrated silica gel prepared in step 1), stir, degas under vacuum for 10 minutes, and maintain a nitrogen atmosphere in the reactor after degassing. ③ Accurately measure 45 mL of ureapropyltrimethoxysilane (s17475) silane coupling agent and add it to 250 mL of dehydrated n-hexane. Mix rapidly under dry nitrogen protection to prepare the coupling agent solution. ④ Nitrogen gas is continuously introduced into the reactor containing hydrated silica gel, and the coupling agent solution prepared in the previous step is quickly poured into the reactor. The reaction is carried out at a speed of 1000 r and a normal temperature for 16 hours. The reaction product is immediately filtered using a sand core funnel and washed with deionized water, n-hexane and methanol in sequence to obtain alkylated silica gel with aminosiloxane groups bonded to the surface. ⑤ Place the above alkylated silica gel in a vacuum drying oven or baking oven and dry it at 100°C to constant weight to obtain modified silica gel.

[0068] 3) Preparation of additives: Accurately weigh 6g (0.073mol) of zinc oxide and 30.8g (0.146mol) of DPG, grind them thoroughly in a mortar for 20min, then add 16g of BPO, mix thoroughly and store in an explosion-proof refrigerator (0~7℃) to obtain the free radical initiator auxiliary.

[0069] Accurately weigh 4g of neodymium oxide, 12g of divinylbenzene, 4g of primary antioxidant 1010, 2g of secondary antioxidant 168, 200g of modified silica, and 0.8g of calcium stearate, and mix them thoroughly with the prepared free radical initiator to obtain a polypropylene modification agent.

[0070] The prepared polypropylene modified additive was poured into a beaker containing 228g of sunflower oil. The beaker was then placed in an ultrasonic oscillator with the temperature set at 30℃, the frequency at 300Hz, and the oscillation time at 30min. The additive was observed to be uniformly dispersed in the oil. After that, it was poured into 5kg of polypropylene powder.

[0071] 4) Twin-screw extrusion The high-speed mixer temperature was set to 90℃ and the speed to 500 r / min. Polypropylene powder with added additives was poured into the high-speed mixer and stirred for 15 minutes to ensure thorough mixing. The mixed powder was then fed into a twin-screw extruder. The twin-screw extruder temperature was set as follows: Zone 1 80℃, Zones 2-3 150℃, Zone 4 160℃, Zone 5 200℃, Zone 6 220℃, Zone 7 200℃, and Die 160℃. The screw speed was 200 rpm / min, the extrusion rate was 15 kg / h, and the pelletizer speed was 240 r / min. The extruded polypropylene pellets were denoted as s17475(Si)-Zn(DPG)2-PP.

[0072] Characterization experiment 1) Infrared characterization of grafting experiment: Accurately weigh 3g of polypropylene granules APTES(Si)-PP and place them in a hot press film forming apparatus. Set the heating temperature to 180℃, apply a pressure of 2.5 tons, and hold for 1 minute to obtain a film sample of polypropylene granules. Test the polypropylene film using infrared spectroscopy.

[0073] like Figure 1 As shown, APTES(Si)-PP at 2900-2800 cm⁻¹ -1 Nearby (APTES: 2926.40cm) -1 and 2871.30cm -1Two characteristic peaks appear, representing the antisymmetric and symmetric stretching vibrations of the primary amine group, at 1625–1365 cm⁻¹. -1 Nearby (DVB: 1376.89cm) -1 The characteristic peak representing the bending vibration of the aromatic ring skeleton appears at 1500 cm⁻¹. -1 Nearby (APTES: 1452.74cm) -1 The characteristic peak representing the in-plane bending vibration of NH appears, in the range of 870~740 cm⁻¹. -1 Nearby (APTES: 752.04cm) -1 The characteristic peak representing the out-of-plane bending vibration of Si-C appears. Furthermore, at 1300 cm⁻¹... -1 (APTES: 1376.89cm) -1 Characteristic peaks representing CN stretching vibrations were also observed nearby. Elemental analysis revealed that the modified polypropylene film contained 4.72% nitrogen. These results directly confirm the successful grafting.

[0074] 2) Melt Index and Melt Strength Determination: Method B for testing PP was selected for the melt index test (die height 8.00 mm, die diameter 2.0950 mm, set temperature 230℃, allowable temperature deviation 1.0℃, allowable temperature deviation at test start 10℃, test force 2.16 kg); Compaction and Preheating: Compaction force 10 kg, compaction time 5 s, preheating time 300 s, preheating position 60 mm, preheating stage load 2.16 kg, loading started after 80 s; Measurement: Piston position during cutting / measurement time - piston position 55 mm, number of cuts 8, measurement displacement / time Δs / Δt - piston path 3 mm. Samples tested by the melt indexer were retained for melt strength calculation. Preliminary calculations were performed using the empirical formula in GB / T 3682.1 to obtain the melt strength of each sample, as shown in Table 1.

[0075] Table 1. Comparison of melt index and melt strength of different samples prepared in the examples.

[0076] As shown in Table 1, the melt strength of PP powder was not significantly improved when ZnO or DPG was used alone. However, the effect of adding ZnO to DPG at a mass ratio of 1:2 was better than that of 1:1 or 2:3. This is because ZnO needs to coordinate with DPG in a 1:2 ratio to form Zn(DPG)2, so as to form a gradient interface layer of "PP-DPG-Zn-SiO2", thereby further enhancing the dispersion of silica in PP and weakening the agglomeration phenomenon.

[0077] Meanwhile, compared with PP, the melt strength of APTES(Si)-PP and APTES(Si)-Zn(DPG)2-PP increased by 64.48% and 65.23% respectively, while the melt strength of APTES(Si)-Zn(DPG)2-PP increased by 2.18% compared with APTES(Si)-PP; compared with APTES, the modification effect of using s17475 is better, which can further improve the melt strength.

[0078] 3) Mechanical property testing: The mechanical properties of each sample were tested according to GB / T 1040.1~1040.2.

[0079] Table 2 Comparison of mechanical properties of the examples and PP powder

[0080] As shown in Table 2, APTES(Si)-Zn(DPG)2-PP has an impact strength of 5.17 kJ / m², a tensile strength of 33.6 MPa, and a flexural strength of 29.2 MPa; while s17475(Si)-Zn(DPG)2-PP has an impact strength of 5.41 kJ / m², a tensile strength of 35.7 MPa, and a flexural strength of 31.8 MPa, both of which are superior to APTES(Si)-PP.

[0081] 4) GPC test: Each sample was tested according to GB / T 27843-2011.

[0082] Table 3 Comparison of molecular weight distribution data between the examples and PP powder

[0083] Table 4 Comparison of molecular weight data between the examples and PP powder

[0084] From Tables 3 and 4 and Figure 2 As can be seen, the change in molecular weight distribution and the increase in macromolecular chains indicate increased PP entanglement and improved cross-linking. The significant increase in PDI suggests that the modified PP exhibits higher heat resistance and impact resistance.

[0085] 5) Haze test: The haze of each sample shall be tested in accordance with GB / T 2410.

[0086] Table 5 Comparison of haze data between the examples and PP powder

[0087] The data in Table 5 show that the addition of Zn(DPG)2 can effectively improve the agglomeration phenomenon caused by SiO2, while ZnO, as a nucleating agent, can also play a synergistic role in further improving the transparency of PP.

[0088] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing high melt strength polypropylene, characterized in that, Includes the following steps: (1) The inorganic silicon source was activated by washing with inorganic acid and then hydrated to obtain hydrated silica gel with an adsorption water content of 5wt%~20wt%. The hydrated silica gel was then degassed in an organic solvent. (2) Mix the hydrated silica gel treated in step (1) with the coupling agent solution, stir and react at room temperature for 16-24 hours, filter and wash the solid product obtained by washing with deionized water and organic solvent until neutral, dry and obtain modified silica gel. (3) Mix the free radical initiator, free radical stabilizer, graft monomer, main antioxidant, secondary antioxidant and lubricant in proportion, and then ultrasonically disperse the mixture and modified silica gel in a dispersion medium to obtain the modifier dispersion. (4) The obtained modifier dispersion and polypropylene powder are thoroughly mixed in a high-speed mixer, and then melt-blended and extruded in a twin-screw extruder to obtain the modified polypropylene composite material.

2. The preparation method according to claim 1, characterized in that: The inorganic silicon source in step (1) is at least one of silica nanoparticles or 40-400 mesh silica gel particles; the inorganic acid is one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; the acid washing time is 2-4 hours; the hydration is carried out in a nitrogen atmosphere and activated with water vapor at 120°C for 2-4 hours.

3. The preparation method according to claim 1, characterized in that: The coupling agent solution mentioned in step (2) is prepared by dissolving one or more of aminopropyltriethoxysilane, aminopropyltrimethoxysilane, diethylenetriaminopropyltrimethoxysilane, N-aminoethyl-3-aminopropylmethyldimethoxysilane, and ureopropyltriethoxysilane in an organic solvent; the organic solvent used is one or more of n-hexane, anhydrous methanol, and anhydrous ethanol; the mass ratio of hydrated silica gel to coupling agent used is 2:1 to 10:

1.

4. The preparation method according to claim 1, characterized in that: The mass ratio of free radical initiator, free radical stabilizer, graft monomer, modified silica gel, primary antioxidant, secondary antioxidant and lubricant used in step (3) is (4~10):(1~3):(3.5~10):(4~10):(1~250):(0.5~5):(0.2~1).

5. The preparation method according to claim 1 or 4, characterized in that: The free radical initiator is composed of a peroxide, zinc oxide, and a guanidine compound, wherein the zinc oxide and the guanidine compound form a complex in a molar ratio of 1:2 to 4:5, and the mass ratio of the peroxide to the complex is 1:1 to 5:6; the peroxide is one or more of benzoyl peroxide, dicumyl peroxide, dilauroyl peroxide, di-tert-butyl peroxide, diisopropyl peroxide, dicyclohexyl peroxide, and di(hexadecyl)dicarbonate peroxide; the guanidine compound is any one of 1,3-diphenylguanidine, di-o-tolueneguanidine, and triphenylguanidine. The free radical stabilizer is one or more of neodymium oxide, lanthanum oxide, cerium oxide, yttrium oxide, titanium dioxide, and cerium oxide, or one or more of vitamin E and tea polyphenols; The grafting monomer is one or more of divinylbenzene, trivinylbenzene, vinyltrimethoxysilane, and tetravinylsilane; The main antioxidant is any one of the following: antioxidant 1010, antioxidant 1076, antioxidant 3114, and antioxidant 1330. The secondary antioxidant is either antioxidant 168 or antioxidant 626. The lubricant is one or more of calcium stearate and zinc stearate.

6. The preparation method according to claim 1, characterized in that: The mass ratio of the mixture to the dispersing solvent used in step (3) is (0.5~1.5):4; the dispersing medium is a plant-based oil or a polar organic solvent.

7. The preparation method according to claim 1, characterized in that: The mass ratio of the modifier dispersion to the polypropylene powder used in step (4) is (0.5~1.5):100; the particle size of the polypropylene powder is 100~600 mesh.

8. The preparation method according to claim 1, characterized in that: The temperature of the high-speed mixer in step (4) is set to 80℃~100℃, the speed is 200~500rpm / min, and the mixing time is 10~15min.

9. The preparation method according to claim 1, characterized in that: The temperature settings of the twin-screw extruder in step (4) are as follows: Zone 1 80~100℃, Zones 2~4 140~160℃, Zone 5 160~220℃, Zone 6 200~220℃, Zone 7 180~200℃, Die head 160~180℃, Screw speed 150~220rpm / min, Extrusion rate 10~20kg / h, Pelletizer speed 200~300r / min.

10. A high melt strength polypropylene prepared by the method of claim 1.

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