Corrosion-resistant polypropylene modified thermoplastic plastic and preparation method thereof

Abstract

The invention relates to a corrosion-resistant polypropylene modified thermoplastic plastic and a preparation method thereof, and belongs to the technical field of polypropylene plastic modification. The modified plastic is prepared from isotactic polypropylene, exfoliated montmorillonite, polyvinylidene fluoride powder, anhydride grafted polypropylene, a beta-crystal nucleating agent, diethyl aluminum chloride, peroxide, hindered phenol, phosphite ester and N, N-distearoyl hydroxylamine. The preparation method comprises the steps of low-shear melting and blending, high-shear supercritical COviscosity reduction, vacuum exhaust, bidirectional orientation, infrared local crosslinking, co-extrusion cooling and the like. The obtained material is excellent in tensile strength, elongation at break, low-temperature impact strength, strong acid corrosion resistance and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polypropylene plastics, and particularly to a corrosion-resistant polypropylene modified thermoplastic and a preparation method thereof. BACKGROUND

[0002] Polypropylene is a thermoplastic with excellent performance and low cost, and is widely used in packaging, pipe materials, automobile parts and other fields. With the complication of application environment, the stability and durability of polypropylene materials under high temperature, low temperature, acid and alkali corrosion and other working conditions gradually appear, which limits its further application in some fields.

[0003] At present, in order to improve the heat resistance, mechanical properties and corrosion resistance of polypropylene, blending modification, filler reinforcement or crystallization induction are often used. However, the existing modification technology generally has the following problems: first, the material is prone to performance degradation in high temperature or strong corrosion environment; second, the mechanical properties and processing properties are difficult to balance, especially when high strength is required while still having good forming fluidity; third, the material is prone to aging, deformation, cracking and other problems during long-term use, which is difficult to meet the demand of high reliability scene.

[0004] Therefore, it is still necessary to develop a polypropylene modified material with excellent thermoplasticity, corrosion resistance and mechanical stability to improve its comprehensive performance and service life in complex service environment. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a corrosion-resistant polypropylene modified thermoplastic and a preparation method thereof.

[0006] A corrosion-resistant polypropylene modified thermoplastic, comprising the following components by weight: Isotactic polypropylene 100-130 parts; Exfoliated montmorillonite 3-5 parts; Polyvinylidene fluoride powder with an average particle size of 3 µm 5-7 parts; Anhydride grafted polypropylene 3-5 parts; Beta-crystal nucleating agent 0.1-0.14 parts; Diethylaluminum chloride 0.02-0.04 parts; 2,5-Dimethyl-2,5-di-tert-butylperoxyhexane 0.02-0.04 parts; Hindered phenol 0.1-0.2 parts Phosphite 0.05-0.15 parts; N,N-Distearylhydroxylamine 0.02-0.05 parts.

[0007] The isotactic polypropylene provides a main resin phase, the high crystallinity of which endows the material with excellent heat distortion temperature; the montmorillonite is uniformly dispersed in a low shear to form a labyrinth barrier structure, which can significantly improve the penetration resistance of acid-base medium and ions; the polyvinylidene fluoride (PVDF) powder with an average particle size of about 3 µm is finely distributed in a phase-fibrous manner with the polypropylene during melt blending, and the β crystal is induced by the polar-nonpolar interface to improve the impact toughness and stress cracking resistance; the anhydride grafted polypropylene acts as a polar phase compatibilizer to build a covalent or polar hydrogen bond bridge between the PP matrix and the PVDF / montmorillonite, so that the interfacial bonding strength of the two phases is increased by more than 30%; the β-crystal nucleating agent precisely induces the β crystal content to be more than 80%, so that the low temperature impact strength at -30 ℃ is improved while maintaining high thermal plasticity; the diethyl aluminum chloride and peroxide synergistically trigger moderate chain elongation and micro-crosslinking to improve the melt strength; the three agents of hindered phenol, phosphite and N,N-distearylhydroxylamine are used together to significantly inhibit thermal oxidative degradation in the processing and service stages.

[0008] Preferably, 0.20-0.40 parts by mass of sodium benzoate and 0.40-0.80 parts by mass of Mg4Al2(OH) 12 CO3·3H2O are further included.

[0009] The sodium benzoate rapidly induces α-crystal nucleation during the cooling process of the polypropylene melt, and cooperates with the β-crystal nucleating agent to form fine and interlaced α / β bimorph layers, so that the heat distortion temperature is improved, and the notched impact toughness at -30 ℃ is also improved; the sodium benzoate slowly releases benzoic acid under the condition of 140 ℃, which can inhibit the growth of bacteria and mold for a long time, and the mold rating is reduced from level 5 to level 0 in 30 days. The OH 12 groups on the surface of the hydrotalcite (Mg4Al2(OH) - CO3·3H2O) lamellar structure reversibly esterify with the anhydride grafted PP, so that the interfacial shear strength is improved, and the CO3 2- / OH - groups between the layers can capture the degradation acidic by-products and the HCl / HF that may be released by the PVDF, so that the pH of the system is more stable; at the same time, the hydrotalcite and the montmorillonite together construct a multi-stage labyrinth barrier channel, which can increase the diffusion path and improve the corrosion resistance barrier effect.

[0010] A preparation method of a corrosion-resistant polypropylene modified thermoplastic plastic, comprising the following steps: S1 low shear melt mixing: melt mixing the raw materials in the low shear zone of a parallel co-rotating twin screw extruder; the shear rate of the low shear zone is 150 s -1 , and the barrel temperature is 190-200 °C; S2 High-Shear Supercritical Viscosity Reduction: In the high-shear zone of the extruder, supercritical carbon dioxide at a pressure of 9–11 MPa is injected into the melt for a contact time of 30–120 s, reducing the melt viscosity by 25–35%; the shear rate in the high-shear zone is 600 s⁻¹. -1 The cylinder temperature is 160°C; S3 vacuum exhaust for carbon dioxide removal: A vacuum is drawn to -80kPa to -90kPa in the negative pressure zone to remove carbon dioxide and volatile components, with the residual carbon dioxide mass fraction not exceeding 0.02%; S4 Bidirectional Orientation Setting: The extruded sheet is stretched longitudinally by 1.9 to 2.1 times at 115 to 125°C and held for 5 to 10 seconds, then stretched transversely by 1.45 to 1.55 times at 100 to 110°C, and then set at 105°C. S5 Infrared Local Crosslinking and Prepolymerization: Applying a wavelength of 3–5 µm and a power density of 10–14 kWm to the oriented sheet. -2 Infrared radiation, radiating for 3-4 seconds; S6 Co-extrusion Molding Cooling: The infrared-treated melt is extruded through a co-extrusion die at -60 kPa and then cooled and shaped.

[0011] In 150s -1 The combination of a low shear rate and a cylinder temperature of 190–200°C effectively prevents the agglomeration of exfoliated montmorillonite lamellae caused by high shear; simultaneously, PVDF micropowder can melt and stretch at the phase interface to form microfibers, thereby increasing the tensile yield strength. Supercritical CO2 at 9–11 MPa is applied for 600 s⁻¹. -1 In the shear field, it instantly dissolves in the PP-PVDF blend melt. The swelling effect increases the distance between molecular chains, resulting in an immediate decrease in viscosity and further exfoliation of the nanosheets. The viscosity reduction window avoids thermo-oxidative degradation caused by high temperature, ensuring the "low viscosity-high molecular weight" dual characteristics required for the next efficient orientation process. A negative pressure of -80 to -90 kPa rapidly removes CO2 and volatiles, ensuring a residual gas mass fraction ≤0.02%, preventing bubbles or silver streaks in the formed sheets, and reducing the retention of electrochemical corrosion media by interfacial voids, thus improving corrosion resistance.

[0012] A high longitudinal-to-medium transverse ratio of 1.9–2.1 times and a transverse ratio of 1.45–1.55 times allows β-crystal-like crystals to preferentially align along the MD direction, forming a "β-crystal-α-crystal interleaved layer." This layered structure can increase the heat distortion temperature and simultaneously improve the elongation at break. The infrared wavelengths in the 3–5 µm band are selectively absorbed by the PVDF and montmorillonite interface, and the wavelengths in the 10–14 kWm band are also affected. -2 Power density 3-4s radiation induces peroxide-aluminane coupling crosslinking on the surface of the sheet, forming a highly crosslinked barrier layer and improving corrosion resistance.

[0013] -60kPa negative pressure assisted by 0.3% cross-sectional area suction channel, which can remove residual volatile and force the melt to adhere to the mold wall, suppress warping; co-extrusion block 200 ℃ holding to ensure the secondary perfection of the core layer crystal, the final sheet warping degree is reduced.

[0014] Preferably, the supercritical carbon dioxide injection mass flow rate of step S2 is 0.06-0.08 kg per kg of polypropylene.

[0015] The flow rate interval can ensure that the viscosity drop is stable within an appropriate range, and avoid excessive CO2 causing too many bubble nuclei and causing melt rupture.

[0016] Preferably, the sheet is sent into the co-extrusion die of step S6 within ten seconds after step S5 is completed, and the core temperature of the sheet is controlled at 180-190°C.

[0017] The thermal shrinkage stress after orientation-crosslinking is balanced at this temperature, which can prevent interface wrinkling caused by cooling delay; the order of completion within 10s can increase the orientation degree retention rate.

[0018] Preferably, the longitudinal stretching of step S4 is completed at a tension of 1.0-1.5 N·cm -1 and the duration is not more than 0.5s, and the transverse stretching is completed at a tension of 0.5-1.0 N·cm -1 and the duration is 0.5-1.5s.

[0019] Preferably, the infrared radiation of step S5 forms a radiation intensity ratio of 1.5-2.0 between the outer surface and the inner surface of the sheet, and the radiation duration is 2-3s.

[0020] The radiation gradient of the outer layer being higher than the inner layer can cause the crosslinking degree of the outer layer to be greater than the inside, forming a "hard shell-tough core" gradient, which can significantly improve the fatigue life.

[0021] Preferably, the co-extrusion die of step S6 is provided with a negative pressure channel with a cross-sectional area of 0.3% of the cross-sectional area of the sheet, and the co-extrusion block temperature is maintained at 200°C.

[0022] Preferably, the distance between the carbon dioxide injection port of step S2 and the vacuum exhaust port of step S3 on the extruder barrel is 8-10 screw diameters, and the exhaust start time is set within 0.2s after the carbon dioxide injection stops.

[0023] This spatial and temporal design ensures uniform and timely exhaust of CO2, avoiding gas retention to form cavities.

[0024] Preferably, the distance between the second set of stretching rollers of step S4 and the infrared radiation device of step S5 is 30-60 cm, and the sheet linear speed is maintained at 3 m / min.

[0025] The distance makes the sheet surface temperature decay to 95-100℃, i.e. slightly higher than the beta-crystal transition temperature interval, to quickly freeze the orientation and provide the best heat-sensitive window for infrared absorption; the orientation degree retention rate is further improved.

[0026] Compared with the prior art, the application has the following beneficial effects: The application synchronously improves the heat distortion temperature and the notched impact strength at -30℃ by the interlaced arrangement of alpha / beta lamellae under the bidirectional induction of sodium benzoate and beta-crystal nucleating agent; the interface shear strength is improved by firmly coupling the PVDF fine phase and exfoliated montmorillonite layers by anhydride grafted PP, avoiding stress concentration; the beta crystal preferentially grows along the longitudinal direction by the 9-11 MPa supercritical CO2 instant viscosity reduction and bidirectional orientation, giving high modulus-high elongation synergy; the dense micro-crosslinking barrier layer is formed on the surface by triggering the coupling reaction of peroxide and diethylaluminum chloride by 3-5 µm infrared pulse selective heating, improving the barrier performance; the ion diffusion path is greatly extended by the superposition of the reversible acid capture of hydrotalcite (Mg4Al2(OH) 12 CO3·3H2O) and the montmorillonite maze effect, and the mass retention rate of the system in acid / alkali medium is significantly improved; the thermal-oxidative aging resistance is improved by the synergistic inhibition of hindered phenol, phosphite and N,N-distearylhydroxylamine on free radicals, acidic by-products and metal chelation. DETAILED DESCRIPTION

[0027] The application will be described in detail below in conjunction with examples.

[0028] The information of the raw materials used in all the examples and comparative examples below is as follows: Isotactic polypropylene: Sinopec T30S of SINOPEC was selected; melt index (MFR): 3.0 g / 10min (230℃, 2.16 kg); melting point: about 165℃; Exfoliated montmorillonite: BYK Cloisite 30B of BYK was selected, which is a quaternary ammonium salt modified montmorillonite; Polyvinylidene fluoride powder: Arkema Kynar 720 of Arkema was selected; crystallinity: about 55%; density: 1.78 g / cm³; Anhydride grafted polypropylene: G-3003 (MAH-g-PP) was selected; anhydride content: 1.0 wt%; MFR: 7.0 g / 10min (230℃, 2.16 kg); Beta-crystal nucleating agent: N,N'-dicyclohexyl-2,6-naphthalene dicarboxamide was used; Hindered phenol (Irganox 1010): tetra[β-(3,5-di-tert-butyl-4-hydroxyphenylpropionic acid)]pentaerythritol ester; Phosphite: Tris(2,4-di-tert-butylphenyl) phosphite.

[0029] Example 1 The present example discloses a method for preparing a corrosion-resistant polypropylene modified thermoplastic, comprising the following steps: S1 Low-shear melt compounding: the raw materials were metered into the low-shear zone of a parallel co-rotating twin-screw extruder with a diameter of Φ 35 mm and L / D = 40; the shear rate was 150 s -1 , the barrel temperature was 195℃, and the screw rotation speed was 80 rpm. A uniform primary melt was obtained within an average residence time of about 35 s.

[0030] The raw materials included the following components by weight: Isotactic polypropylene 120 parts; exfoliated montmorillonite clay 4 parts; polyvinylidene fluoride powder with an average particle size of 3 µm 6 parts; anhydride-grafted polypropylene (anhydride content 1.0%; MFR 7.0 g·10 min -1 ) 4 parts; β-crystal nucleating agent 0.12 parts; diethylaluminum chloride 0.03 parts; 2,5-dimethyl-2,5-di-tert-butylperoxyhexane 0.03 parts; hindered phenol (Irganox 1010) 0.15 parts; phosphite 0.1 parts; N,N-distearylhydroxylamine 0.03 parts; sodium benzoate 0.3 parts; Mg4Al2(OH) 12 CO3·3H2O (specific surface area 98 m²·g -1 ) 0.6 parts.

[0031] S2 High-shear supercritical viscosity reduction: supercritical CO2 at a temperature of 160℃ and a pressure of 10 MPa was injected through a Ø 0.8 mm annular nozzle in the high-shear zone (shear rate 600 s -1 , barrel temperature 160℃).

[0032] Mass flow rate of supercritical CO2: 0.07 kg CO2 / kg polypropylene.

[0033] Contact time: 60 s; melt viscosity reduction 26%.

[0034] 0.15 s after injection was stopped, the next step was performed.

[0035] S3 Vacuum venting to remove carbon dioxide: the vent was set 9 times the screw diameter downstream of the CO2 nozzle, and the negative pressure was −85 kPa. After 4 s of vacuum, the residual CO2 mass fraction was < method limit of quantification (0.02 wt%).

[0036] S4 Biaxial orientation and shaping: the melt was extruded into a 1.0 mm thick sheet, which was immediately stretched 2.0 times in the longitudinal direction at 118℃.

[0037] Longitudinal tension: 1.3 N·cm⁻¹ for 0.4 s.

[0038] Subsequently stretched 1.5 times in the transverse direction at 105℃, tension 0.8 N·cm⁻¹, duration 1.0 s.

[0039] Setting temperature 105℃, holding time 6 s.

[0040] Distance from the second set of stretching rollers to the infrared radiation device 45 cm, linear velocity stable at 3 m·min -1 .

[0041] S5 Infrared local crosslinking and prepolymerization: The sheet enters a medium infrared box with a wavelength of 3-5 µm, power density 12 kW·m -2 (outer surface) and 7 kW·m -2 (inside surface), intensity ratio 1.7, radiation time 3 s. Within 8 s after radiation, it is sent into the co-extrusion die, at which time the core temperature of the sheet is 180-190℃.

[0042] S6 Co-extrusion molding and cooling: The melt after infrared treatment is extruded through a co-extrusion die at 200℃ under a negative pressure of -60 kPa, the negative pressure channel cross-sectional area accounting for 0.3% of the cross-sectional area of the sheet, and then the sheet is cooled in a 20-10℃ staged water tank and wound up, with a final thickness of 300±5 µm.

[0043] Example 2 This example discloses a method for preparing a corrosion-resistant polypropylene modified thermoplastic, comprising the following steps: S1 Low-shear melt mixing: The raw materials are metered into a Φ35 mm, L / D=40 parallel co-rotating twin-screw extruder low-shear zone; shear rate 150 s -1 , barrel temperature 200℃, screw rotation speed 80 rpm. A uniform primary melt is obtained within an average residence time of about 30 s.

[0044] The raw materials include the following components in parts by weight: Isotactic polypropylene 130 parts; exfoliated montmorillonite 5 parts; polyvinylidene fluoride powder with an average particle size of 3 µm 7 parts; anhydride grafted polypropylene (anhydride content 1.0%; MFR 7.0 g·10 min -1 ) 5 parts; β-crystal nucleating agent 0.14 parts; diethylaluminum chloride 0.04 parts; 2,5-dimethyl-2,5-di-tert-butylperoxyhexane 0.04 parts; hindered phenol (Irganox 1010) 0.2 parts; phosphite 0.15 parts; N,N-distearylhydroxylamine 0.05 parts; sodium benzoate 0.4 parts; Mg4Al2(OH) 12 CO3·3H2O (specific surface area 98 m²·g -1 ) 0.8 parts.

[0045] S2 High-shear supercritical viscosity reduction: In the high-shear zone (shear rate 600 s-1 , the barrel 160 °C) through a 0.8 mm annular nozzle injection temperature 160 °C, 11 MPa pressure of supercritical CO2.

[0046] The mass flow rate of supercritical CO2: 0.08 kg CO2 / kg polypropylene.

[0047] Contact time: 30 s; the melt viscosity is reduced by 30%.

[0048] 0.15 s after injection stops, the next step is performed.

[0049] S3 vacuum exhaust to remove carbon dioxide: the exhaust port is set 10 times the screw diameter downstream of the CO2 nozzle, and the negative pressure is -90 kPa. After vacuumizing for 4 s, the residual CO2 mass fraction is < the method limit of quantity (0.02 wt%).

[0050] S4 biaxial orientation setting: the melt is extruded into a 1.0 mm thick sheet, which is immediately stretched longitudinally by 2.1 times at 125 °C.

[0051] Longitudinal tension: 1.5 N·cm⁻¹, for 0.2 s.

[0052] Subsequently, it is stretched transversely by 1.55 times at 110 °C, with a tension of 1 N·cm⁻¹ for 0.9 s.

[0053] Setting temperature 105 °C, holding for 6 s.

[0054] The distance from the second set of stretching rollers to the infrared radiation device is 30 cm, and the linear speed is stabilized at 3 m·min -1 .

[0055] S5 infrared local crosslinking and pre-polymerization: the sheet enters a medium infrared box with a wavelength of 3-5 µm, a power density of 12 kW·m -2 (outside surface) and 7 kW·m -2 (interior surface), an intensity ratio of 1.7, and is radiated for 3 s. Within 8 s after radiation, it is sent into a co-extrusion die, at which time the core temperature of the sheet is 180-190 °C.

[0056] S6 co-extrusion molding and cooling: the infrared-treated melt is extruded through a co-extrusion die at 200 °C under a negative pressure of -60 kPa, and the negative pressure channel cross-sectional area accounts for 0.3% of the sheet cross-sectional area. Subsequently, the sheet is cooled through a 20-10 °C staged water tank and is wound up, with a final thickness of 300±5 µm.

[0057] Example 3 The present example discloses a preparation method of a corrosion-resistant polypropylene modified thermoplastic plastic, comprising the following steps: S1 low shear melt mixing: the raw materials are metered into a Φ35 mm, L / D=40 parallel co-rotating twin-screw extruder low shear zone; the shear rate is 150 s-1 , barrel temperature 190 °C, screw rotation speed 80 rpm. A homogeneous primary melt was obtained in an average residence time of about 40 s.

[0058] The raw material included the following components in parts by weight: Isotactic polypropylene 100 parts; exfoliated montmorillonite 3 parts; polyvinylidene fluoride powder with an average particle size of 3 pm 5 parts; anhydride-grafted polypropylene (anhydride content 1.0%; MFR 7.0 g-10 min -1 ) 3 parts; beta-crystal nucleating agent 0.1 parts; diethylaluminum chloride 0.02 parts; 2,5-dimethyl-2,5-di-tert-butylperoxyhexane 0.02 parts; hindered phenol (Irganox 1010) 0.1 parts; phosphite 0.05 parts; N,N-distearylhydroxylamine 0.02 parts; sodium benzoate 0.2 parts; Mg4Al2(OH) 12 CO3-3H2O (specific surface area 98 m2-g -1 ) 0.4 parts.

[0059] S2 High-shear supercritical viscosity reduction: injection of supercritical CO2 at a temperature of 160 °C and a pressure of 9 MPa through a Ø 0.8 mm annular nozzle in a high-shear zone (shear rate 600 s -1 , barrel 160 °C).

[0060] Mass flow rate of supercritical CO2: 0.06 kg CO2 / kg polypropylene.

[0061] Contact time: 120 s; reduction in melt viscosity by 23%.

[0062] 0.15 s after injection was stopped, the next step was carried out.

[0063] S3 Removal of carbon dioxide by vacuum venting: the vent was positioned 8 times the screw diameter downstream of the CO2 nozzle, and the negative pressure was -80 kPa. After 4 s of vacuum, the residual CO2 mass fraction was < method limit of quantification (0.02 wt%).

[0064] S4 Biaxial orientation and setting: the melt was extruded into a 1.0 mm thick sheet, which was immediately stretched 1.9 times in the longitudinal direction at 115 °C.

[0065] Longitudinal tension: 1 N-cm-1for 0.4 s.

[0066] Subsequently, the sheet was stretched 1.45 times in the transverse direction at 100 °C, with a tension of 0.5 N-cm-1for 1.3 s.

[0067] Setting temperature 105 °C, holding time 6 s.

[0068] Distance from the second set of stretching rollers to the infrared radiation device 30 cm, linear speed stable at 3 m-min -1 .

[0069] S5 Infrared local crosslinking and pre-polymerization: The sheet enters a mid-infrared oven with wavelength 3-5 pm, power density 12 kW·m -2 (outer surface) and 7 kW·m -2 (inside surface), intensity ratio 1.7, radiation 3 s. The sheet is fed into the co-extrusion die within 8 s after radiation, at which time the core temperature of the sheet is 180-190 °C.

[0070] S6 Co-extrusion and cooling: The infrared treated melt is extruded through a co-extrusion die at 200 °C under -60 kPa, with the negative pressure channel cross-sectional area accounting for 0.3% of the cross-sectional area of the sheet, and then the sheet is cooled in a 20-10 °C staged water tank and wound up, with the final thickness being 300 ± 5 pm.

[0071] Example 4 The present example discloses a method for preparing a corrosion-resistant polypropylene modified thermoplastic, comprising the following steps: S1 Low-shear melt mixing: The raw materials are fed into the low-shear zone of a Φ 35 mm, L / D = 40 parallel co-rotating twin-screw extruder after metering; the shear rate is 150 s -1 , the barrel temperature is 195 °C, and the screw rotation speed is 80 rpm. A uniform primary melt is obtained within an average residence time of about 35 s.

[0072] The raw materials include the following components in parts by weight: Isotactic polypropylene 120 parts; exfoliated montmorillonite clay 4 parts; polyvinylidene fluoride powder with an average particle size of 3 pm 6 parts; anhydride-grafted polypropylene (anhydride content 1.0%; MFR 7.0 g·10 min -1 ) 4 parts; β-crystal nucleating agent 0.12 parts; diethylaluminum chloride 0.03 parts; 2,5-dimethyl-2,5-di-tert-butylperoxyhexane 0.03 parts; hindered phenol (Irganox 1010) 0.15 parts; phosphite 0.1 parts; N,N-distearylhydroxylamine 0.03 parts.

[0073] S2 High-shear supercritical viscosity reduction: Supercritical CO2 at a temperature of 160 °C and a pressure of 10 MPa is injected through a Ø 0.8 mm annular nozzle in the high-shear zone (shear rate 600 s -1 , barrel 160 °C).

[0074] Mass flow rate of supercritical CO2: 0.07 kg CO2 / kg polypropylene.

[0075] Contact time: 60 s; melt viscosity reduction 26%.

[0076] 0.15 s after injection is stopped, the next step is performed.

[0077] S3 vacuum venting to remove carbon dioxide: venting port was set at 9 times screw diameter downstream of CO2 nozzle, negative pressure -85 kPa. After 4 s vacuuming, residual CO2 mass fraction < method limit of quantification (0.02 wt%).

[0078] S4 biaxial orientation: melt was extruded into 1.0 mm thick sheet, immediately stretched 2.0 times in machine direction at 118 °C.

[0079] Machine direction tension: 1.3 N-cm-1 for 0.4 s.

[0080] Subsequently stretched 1.5 times in transverse direction at 105 °C for 1.0 s with a tension of 0.8 N-cm-1.

[0081] Setting temperature 105 °C, holding for 6 s.

[0082] Distance from second set of stretching rollers to infrared radiation device 45 cm, linear velocity stabilized at 3 m-min -1 .

[0083] S5 infrared local crosslinking and pre-polymerization: sheet entered a mid-infrared box with wavelength 3-5 pm, power density 12 kW-m -2 (outer surface) and 7 kW-m -2 (inside surface), intensity ratio 1.7, radiation for 3 s. Within 8 s after radiation, the sheet was fed into the co-extrusion die, at which time the core temperature of the sheet was 180-190 °C.

[0084] S6 co-extrusion and cooling: the infrared treated melt was extruded through a co-extrusion die at 200 °C under -60 kPa, the negative pressure channel cross-sectional area accounted for 0.3% of the cross-sectional area of the sheet, then the sheet was cooled through a 20-10 °C staged water tank and wound up, the final thickness was 300±5 pm.

[0085] Example 5 The present example discloses a method for preparing a corrosion-resistant polypropylene modified thermoplastic, comprising the following steps: S1 low shear melt mixing: the raw materials were fed into a Φ35 mm, L / D=40 parallel co-rotating twin-screw extruder low shear zone after metering; shear rate 150 s -1 , barrel temperature 195 °C, screw rotation speed 80 rpm. A uniform primary melt was obtained within an average residence time of about 35 s.

[0086] The raw materials included the following components in parts by weight: Isotactic polypropylene 120 parts; exfoliated montmorillonite clay 4 parts; polyvinylidene fluoride powder with average particle size 3 pm 6 parts; anhydride grafted polypropylene (anhydride content 1.0%; MFR 7.0 g-10 min -1) 4 parts; beta-nucleating agent 0.12 parts; diethylaluminum chloride 0.03 parts; 2,5-dimethyl-2,5-di-tert-butylperoxyhexane 0.03 parts; hindered phenol (Irganox 1010) 0.15 parts; phosphite 0.1 parts; N,N-distearylhydroxylamine 0.03 parts.

[0087] S2 High shear supercritical viscosity reduction: Inject supercritical CO2 at temperature 160 °C and pressure 10 MPa through a 0.8 mm annular nozzle in a high shear zone (shear rate 600 s -1 , barrel temperature 160 °C).

[0088] Mass flow rate of supercritical CO2: 0.09 kg CO2 / kg polypropylene.

[0089] Contact time: 60 s; reduction in melt viscosity 26%.

[0090] 0.15 s after injection is stopped, the next step is performed.

[0091] S3 Removal of carbon dioxide by vacuum venting: The vent is located 9 times the screw diameter downstream of the CO2 nozzle, and the negative pressure is -85 kPa. After 4 s of vacuum, the residual CO2 mass fraction is < method limit of quantification (0.02 wt%).

[0092] S4 Biaxial orientation and setting: The melt is extruded into a 1.0 mm thick sheet, which is immediately stretched 2.0 times in the machine direction at 118 °C.

[0093] Machine direction tension: 1.3 N-cm-1 for 0.4 s.

[0094] Subsequently stretched 1.5 times in the transverse direction at 105 °C for 1.0 s with a tension of 0.8 N-cm-1.

[0095] Setting temperature 105 °C for 6 s.

[0096] The distance from the second set of stretching rolls to the infrared radiation device is 45 cm, and the linear velocity is stabilized at 3 m-min -1 .

[0097] S5 Localized infrared crosslinking and pre-polymerization: The sheet enters a mid-infrared oven with a wavelength of 3-5 pm, a power density of 12 kW-m -2 (-outer surface) and 7 kW-m -2 (-inner surface), a strength ratio of 1.7, and is radiated for 3 s. It is fed into the co-extrusion die within 8 s after radiation, at which time the core temperature of the sheet is 180-190 °C.

[0098] S6 Co-extrusion cooling: The infrared treated melt was extruded through a 200 °C co-extrusion die at -60 kPa, the negative pressure channel cross-sectional area was 0.3% of the cross-sectional area of the sheet, then the sheet was cooled through a 20-10 °C staged water tank and wound up, the final thickness was 300 ± 5 µm.

[0099] Example 6 The present example discloses a method for preparing a corrosion-resistant polypropylene modified thermoplastic, comprising the following steps: S1 Low shear melt compounding: The raw materials were metered into a Φ35 mm, L / D = 40 parallel co-rotating twin-screw extruder low shear zone; shear rate 150 s -1 , barrel temperature 195 °C, screw speed 80 rpm. A uniform primary melt was obtained in an average residence time of about 35 s.

[0100] The raw materials include the following components by weight: Isotactic polypropylene 120 parts; exfoliated montmorillonite clay 4 parts; polyvinylidene fluoride powder with an average particle size of 3 µm 6 parts; anhydride grafted polypropylene (anhydride content 1.0%; MFR 7.0 g·10 min -1 ) 4 parts; β-crystal nucleating agent 0.12 parts; diethylaluminum chloride 0.03 parts; 2,5-dimethyl-2,5-di-tert-butylperoxyhexane 0.03 parts; hindered phenol (Irganox 1010) 0.15 parts; phosphite 0.1 parts; N,N-distearylhydroxylamine 0.03 parts.

[0101] S2 High shear supercritical viscosity reduction: Supercritical CO2 at a temperature of 160 °C and a pressure of 10 MPa was injected through a Ø0.8 mm annular nozzle in the high shear zone (shear rate 600 s -1 , barrel 160 °C).

[0102] Mass flow rate of supercritical CO2: 0.07 kg CO2 / kg polypropylene.

[0103] Contact time: 60 s; melt viscosity reduction 26%.

[0104] 0.15 s after injection stopped, the next step was performed.

[0105] S3 Vacuum venting to remove carbon dioxide: The vent was set 9 times the screw diameter downstream of the CO2 nozzle, negative pressure -85 kPa. After vacuuming for 4 s, the residual CO2 mass fraction was < method limit of quantification (0.02 wt%).

[0106] S4 Biaxial orientation setting: The melt was extruded into a 1.0 mm thick sheet, which was immediately stretched 2.0 times in the longitudinal direction at 118 °C.

[0107] Longitudinal tension: 1.3 N·cm⁻¹, lasting 0.4 s.

[0108] Subsequently stretched 1.5 times in the transverse direction at 105℃, tension 0.8 N-cm-1, duration 1.0 s.

[0109] Setting temperature 105℃, holding for 6 s.

[0110] Distance from the second set of stretching rollers to the infrared radiation device 45 cm, linear velocity stable at 3 m-min -1 .

[0111] S5 Infrared local crosslinking and pre-polymerization: the sheet enters a mid-infrared box with a wavelength of 3-5 pm, power density 12 kW-m -2 (outer surface) and 7 kW-m -2 (inside surface), intensity ratio 1.7, radiation for 3 s. After 11 s of radiation, it is sent into the co-extrusion die head, at which time the core temperature of the sheet is 180-190℃.

[0112] S6 Co-extrusion molding and cooling: the melt after infrared treatment is extruded through a co-extrusion die head at 200℃ under a negative pressure of -60 kPa, the negative pressure channel cross-sectional area accounting for 0.3% of the cross-sectional area of the sheet, then the sheet is cooled through a 20-10℃ staged water tank and wound up, the final thickness being 300±5 pm.

[0113] Example 7 The present example discloses a method for preparing a corrosion-resistant polypropylene modified thermoplastic, comprising the following steps: S1 Low-shear melt mixing: the raw materials are metered into a Φ35 mm, L / D=40 parallel co-rotating twin-screw extruder low-shear zone; shear rate 150 s -1 , barrel temperature 195℃, screw rotation speed 80 rpm. A uniform primary melt is obtained in an average residence time of about 35 s.

[0114] The raw materials include the following components in parts by weight: Isotactic polypropylene 120 parts; exfoliated montmorillonite clay 4 parts; polyvinylidene fluoride powder with an average particle size of 3 pm 6 parts; anhydride grafted polypropylene (anhydride content 1.0%; MFR 7.0 g-10 min -1 ) 4 parts; β-crystal nucleating agent 0.12 parts; diethylaluminum chloride 0.03 parts; 2,5-dimethyl-2,5-di-tert-butylperoxyhexane 0.03 parts; hindered phenol (Irganox 1010) 0.15 parts; phosphite 0.1 parts; N,N-distearylhydroxylamine 0.03 parts.

[0115] S2 High-shear supercritical viscosity reduction: supercritical CO2 at a temperature of 160℃ and a pressure of 10 MPa is injected through a Ø0.8 mm annular nozzle in the high-shear zone (shear rate 600 s -1 , barrel 160℃).

[0116] Mass flow rate of supercritical CO2: 0.07 kg CO2 / kg polypropylene.

[0117] Contact time: 60 s; 26% reduction in melt viscosity.

[0118] 0.15 s after injection stopped, next step was performed.

[0119] S3 vacuum venting to remove CO2: vent was set 9 times screw diameter downstream of CO2 nozzle, negative pressure -85 kPa. After 4 s vacuum, residual CO2 mass fraction < method limit of quantification (0.02 wt%).

[0120] S4 biaxial orientation and setting: melt was extruded into 1.0 mm thick sheet, immediately stretched 2.0 times in machine direction at 118 °C.

[0121] Machine direction tension: 1.3 N-cm-1 for 0.4 s.

[0122] Subsequently, 1.5 times in transverse direction at 105 °C for 1.0 s with 0.8 N-cm-1 tension.

[0123] Setting temperature 105 °C for 6 s.

[0124] Distance from second set of stretching rolls to infrared radiation device 45 cm, linear velocity stabilized at 3 m-min -1 .

[0125] S5 infrared local crosslinking and pre-polymerization: sheet entered mid-infrared oven with wavelength 3-5 pm, power density 12 kW-m -2 (outer surface) and 9 kW-m -2 (inner surface), intensity ratio 1.3, radiation 3 s. Within 8 s after radiation, sheet was fed into co-extrusion die, at this time sheet core temperature 180-190 °C.

[0126] S6 co-extrusion and cooling: infrared treated melt was extruded through 200 °C co-extrusion die at -60 kPa, negative pressure channel cross-sectional area was 0.3% of sheet cross-sectional area, then sheet was cooled through 20-10 °C staged water tank and wound up, final thickness 300 ± 5 pm.

[0127] Example 8 The embodiment discloses a preparation method of a corrosion-resistant polypropylene modified thermoplastic plastic, and comprises the following steps: S1 low shear melt mixing: raw materials were fed into a Φ35 mm, L / D=40 parallel co-rotating twin-screw extruder low shear zone after metering; shear rate 150 s -1 , barrel temperature 195 °C, screw rotation speed 80 rpm. Uniform primary melt was obtained within an average residence time of about 35 s.

[0128] The raw material includes the following components in parts by weight: Isotactic polypropylene 120 parts; exfoliated montmorillonite 4 parts; polyvinylidene fluoride powder with an average particle size of 3 pm 6 parts; anhydride grafted polypropylene (anhydride content 1.0%; MFR 7.0 g·10 min -1 ) 4 parts; beta-crystal nucleating agent 0.12 parts; diethylaluminum chloride 0.03 parts; 2,5-dimethyl-2,5-di-tert-butylperoxyhexane 0.03 parts; hindered phenol (Irganox 1010) 0.15 parts; phosphite 0.1 parts; N,N-distearylhydroxylamine 0.03 parts.

[0129] S2 High-shear supercritical viscosity reduction: Inject supercritical CO2 at a temperature of 160 °C and a pressure of 10 MPa through a Ø 0.8 mm annular nozzle in a high-shear zone (shear rate 600 s -1 , barrel 160 °C).

[0130] Mass flow rate of supercritical CO2: 0.07 kg CO2 / kg polypropylene.

[0131] Contact time: 60 s; reduction in melt viscosity by 26%.

[0132] 0.15 s after injection has stopped, the next step is carried out.

[0133] S3 Removal of carbon dioxide by vacuum venting: The vent is located 6 times the screw diameter downstream of the CO2 nozzle, and the negative pressure is -85 kPa. After 4 s of vacuum, the residual CO2 mass fraction is < method limit of quantification (0.02 wt%).

[0134] S4 Biaxial orientation and setting: The melt is extruded into a 1.0 mm thick sheet, which is immediately stretched 2.0 times in the longitudinal direction at 118 °C.

[0135] Longitudinal tension: 1.3 N·cm⁻¹ for 0.4 s.

[0136] Subsequently, the sheet is stretched 1.5 times in the transverse direction at 105 °C with a tension of 0.8 N·cm⁻¹ for 1.0 s.

[0137] Setting temperature 105 °C for 6 s.

[0138] The distance from the second set of stretching rollers to the infrared radiation device is 45 cm, and the linear speed is stabilized at 3 m·min -1 .

[0139] S5 Local crosslinking and pre-polymerization by infrared radiation: The sheet enters a medium infrared cabinet with a wavelength of 3-5 pm, with a power density of 12 kW·m -2 (outer surface) and 7 kW·m -2(inside surface), strength ratio 1.7, radiation 3 s. Within 8 s after radiation, the sheet core temperature was 180-190 °C.

[0140] S6 co-extrusion cooling: the infrared treated melt was extruded through a co-extrusion die at 200 °C under a negative pressure of -60 kPa, the negative pressure channel cross-sectional area was 0.3% of the sheet cross-sectional area, then the sheet was cooled through a 20-10 °C staged water tank and wound up, the final thickness was 300 ± 5 pm.

[0141] Example 9 The present example discloses a method for preparing a corrosion-resistant polypropylene modified thermoplastic, comprising the following steps: S1 low shear melt compounding: the raw materials were fed into a Φ 35 mm, L / D = 40 parallel co-rotating twin-screw extruder low shear zone; shear rate 150 s -1 , barrel temperature 195 °C, screw speed 80 rpm. A uniform primary melt was obtained within an average residence time of about 35 s.

[0142] The raw materials include the following components by weight: Isotactic polypropylene 120 parts; exfoliated montmorillonite clay 4 parts; polyvinylidene fluoride powder with an average particle size of 3 pm 6 parts; anhydride grafted polypropylene (anhydride content 1.0%; MFR 7.0 g·10 min -1 ) 4 parts; beta-crystal nucleating agent 0.12 parts; diethylaluminum chloride 0.03 parts; 2,5-dimethyl-2,5-di-tert-butylperoxyhexane 0.03 parts; hindered phenol (Irganox 1010) 0.15 parts; phosphite 0.1 parts; N,N-distearylhydroxylamine 0.03 parts.

[0143] S2 high shear supercritical viscosity reduction: supercritical CO2 at a temperature of 160 °C and a pressure of 10 MPa was injected through a Ø 0.8 mm annular nozzle in the high shear zone (shear rate 600 s -1 , barrel 160 °C).

[0144] Mass flow rate of supercritical CO2: 0.07 kg CO2 / kg polypropylene.

[0145] Contact time: 60 s; melt viscosity reduction 26%.

[0146] 0.15 s after injection stopped, the next step was performed.

[0147] S3 vacuum venting to remove carbon dioxide: the vent was set 9 times the screw diameter downstream of the CO2 nozzle, negative pressure -85 kPa. After vacuuming for 4 s, the residual CO2 mass fraction was < method limit of quantification (0.02 wt%).

[0148] S4 Bi-axial orientation setting: The melt was extruded into 1.0 mm thick sheet, immediately stretched 2.0 times in machine direction at 118 °C.

[0149] Machine direction tension: 1.3 N-cm-1 for 0.4 s.

[0150] Subsequently stretched 1.5 times in transverse direction at 105 °C with tension 0.8 N-cm-1 for 1.0 s.

[0151] Setting temperature 105 °C, holding for 6 s.

[0152] Distance from the second set of stretching rollers to the infrared radiation device 65 cm, linear velocity stable at 4 m-min -1 .

[0153] S5 Infrared local cross-linking and pre-polymerization: The sheet entered a medium infrared box with wavelength 3-5 pm, power density 12 kW-m -2 (outside surface) and 7 kW-m -2 (inside surface), intensity ratio 1.7, radiation 3 s. Within 8 s after radiation, it was sent into the co-extrusion die, at which time the core temperature of the sheet was 180-190 °C.

[0154] S6 Co-extrusion molding and cooling: The infrared treated melt was extruded through a co-extrusion die at 200 °C under -60 kPa, the negative pressure channel cross-sectional area accounting for 0.3% of the cross-sectional area of the sheet, then the sheet was cooled through a 20-10 °C staged water tank and wound up, the final thickness being 300 ± 5 pm.

[0155] Comparative Example 1 This comparative example discloses a method for preparing a polypropylene modified plastic, comprising the following steps: S1 Low shear melt mixing: The raw materials were metered into a Φ 35 mm, L / D = 40 parallel co-rotating twin-screw extruder low shear zone; shear rate 150 s -1 , barrel temperature 195 °C, screw rotation speed 80 rpm. A uniform primary melt was obtained within an average residence time of about 35 s.

[0156] The raw materials included the following components in parts by weight: Isotactic polypropylene 100 parts; β-crystal nucleating agent 0.12 parts; hindered phenol (Irganox 1010) 0.15 parts; phosphite 0.1 part.

[0157] S2 Unidirectional orientation setting: The melt was extruded into 1.0 mm thick sheet, immediately stretched 2.0 times in machine direction at 118 °C.

[0158] Machine direction tension: 1.3 N-cm-1 for 0.4 s.

[0159] Setting temperature 105 °C, holding for 6 s.

[0160] The distance from the second set of stretching rollers to the infrared radiation device was 45 cm, and the linear speed was stabilized at 3 m·min -1 .

[0161] S3 Co-extrusion cooling: the whole co-extrusion die was at 200℃. The sheet was cooled by a water tank at 20℃ and wound up, with a final thickness of 300±5 µm.

[0162] Performance test The polypropylene modified plastics obtained from Examples 1-9 and Comparative Example 1 were subjected to the following tests, and the test results are shown in Table 1.

[0163] 1. Tensile strength (MPa) Test method: According to the test method for polypropylene extruded sheet in ISO527-3:2018. An electronic universal testing machine was used, the sample was ISO standard 1B type (long rectangular), the thickness was about 300 µm, the tensile rate was 50 mm / min, the maximum load was recorded during testing, and the tensile strength was calculated according to the cross-sectional area.

[0164] 2. Elongation at break (%) Test method: Same as the tensile test procedure, the deformation at break was recorded. Elongation at break = (gauge length at break - initial gauge length) / initial gauge length x 100%.

[0165] 3. Notched impact strength (kJ / m², -30℃) Test method: Tested according to ISO179-1:2010 (charpy method). Rectangular samples (80x10x4mm) with standard V-shaped notches were selected according to the standard requirements. The sample was tested after being cooled at -30℃ for 30 minutes, and the absorbed energy was recorded and converted into impact strength (energy per unit area).

[0166] 4. Mass retention rate (%) after H2SO4 / HNO3 corrosion Test method: The corrosion solution was prepared: a mixed solution of 50wt% H2SO4 and 20wt% HNO3 (volume ratio 1:1) was prepared and used immediately.

[0167] Test steps: (1) Take a sheet sample with a size of 30mm x 10mm x 0.3mm, and pre-dry to constant weight (record the mass m0); (2) Completely immerse the sample in the mixed acid and soak in a constant temperature water bath at 70℃ for 72h; (3) After taking out, rinse repeatedly with deionized water, and dry at 60℃ to constant weight (record m1); Calculate according to the following formula: Mass retention rate (%) = (m1 / m0) x 100%.

[0168] Table 1 The polypropylene modified plastic prepared by the embodiments of the present application has excellent overall performance in tensile strength, elongation at break, low-temperature impact strength and acid and alkali corrosion resistance, and is significantly better than the comparative example material without adding the modified component. Among them, examples 1-3 exhibit higher comprehensive performance, indicating that the designed compound system has good compatibility and synergistic effect. In contrast, the performance of examples 4-9 has decreased to varying degrees, indicating that sodium benzoate, hydrotalcite, supercritical CO2 flow rate, infrared treatment timing and exhaust position and other parameters have important influence on the performance of the final material. The mechanical and corrosion resistance of comparative example 1 are significantly lower than those of each example, further verifying the effectiveness and necessity of the modification design of the present application.

[0169] In summary, the polypropylene modification scheme proposed by the present application has significant advantages in improving mechanical properties, toughness and corrosion resistance.

[0170] The above is only the preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical solution falling within the scope of the present application is within the protection scope of the present application. It should be noted that for ordinary skilled persons in the art, some improvements and refinements without departing from the principles of the present application are also considered to be within the protection scope of the present application.

Claims

1. A corrosion-resistant polypropylene modified thermoplastic, characterized in that, The components include the following parts by weight: 100-130 parts of isotactic polypropylene; 3-5 parts of stripped montmorillonite; 5-7 parts of polyvinylidene fluoride powder with an average particle size of 3µm; 3-5 parts of anhydride-grafted polypropylene; 0.1–0.14 parts of β-crystal nucleating agent; Diethylaluminum chloride 0.02–0.04 parts; 0.02 to 0.04 parts of 2,5-dimethyl-2,5-di-tert-butylperoxyhexane; Hindered phenol 0.1–0.2 parts Phosphite 0.05–0.15 parts; 0.02 to 0.05 parts of N,N-distearate hydroxylamine.

2. The corrosion-resistant polypropylene modified thermoplastic according to claim 1, characterized in that, It also includes 0.20–0.40 parts by weight of sodium benzoate and 0.40–0.80 parts by weight of Mg4Al2(OH). 12 CO3·3H2O.

3. A method for preparing a corrosion-resistant polypropylene modified thermoplastic according to any one of claims 1 to 2, characterized in that, Includes the following steps: S1 Low-shear melt mixing: The raw materials are melt-mixed in the low-shear zone of a parallel co-rotating twin-screw extruder; the shear rate in the low-shear zone is 150 s. -1 The cylinder temperature is 190–200°C; S2 High-Shear Supercritical Viscosity Reduction: In the high-shear zone of the extruder, supercritical carbon dioxide at a pressure of 9–11 MPa is injected into the melt for a contact time of 30–120 s, reducing the melt viscosity by 25–35%; the shear rate in the high-shear zone is 600 s⁻¹. -1 The cylinder temperature is 160°C; S3 vacuum exhaust for carbon dioxide removal: A vacuum is drawn to -80kPa to -90kPa in the negative pressure zone to remove carbon dioxide and volatile components, with the residual carbon dioxide mass fraction not exceeding 0.02%; S4 Bidirectional Orientation Setting: The extruded sheet is stretched longitudinally by 1.9 to 2.1 times at 115 to 125°C and held for 5 to 10 seconds, then stretched transversely by 1.45 to 1.55 times at 100 to 110°C, and then set at 105°C. S5 Infrared Local Crosslinking and Prepolymerization: Applying a wavelength of 3–5 µm and a power density of 10–14 kWm to the oriented sheet. -2 Infrared radiation, radiating for 3-4 seconds; S6 Co-extrusion Molding Cooling: The infrared-treated melt is extruded through a co-extrusion die at -60 kPa and then cooled and shaped.

4. The method for preparing the corrosion-resistant polypropylene modified thermoplastic according to claim 3, characterized in that, In step S2, the supercritical carbon dioxide injection mass flow rate is 0.06–0.08 kg per kg of polypropylene.

5. The method for preparing the corrosion-resistant polypropylene modified thermoplastic according to claim 3, characterized in that, Within ten seconds of completing step S5, the sheet is fed into the co-extrusion die of step S6, and the core temperature of the sheet is controlled at 180-190°C.

6. The method for preparing the corrosion-resistant polypropylene modified thermoplastic according to claim 3, characterized in that, The longitudinal stretching in step S4 is performed under a tension of 1.0–1.5 N·cm. -1 The process is completed within 0.5 seconds, with the transverse tension between 0.5 and 1.0 N·cm. -1 The process is completed and lasts for 0.5 to 1.5 seconds.

7. The method for preparing the corrosion-resistant polypropylene modified thermoplastic according to claim 3, characterized in that, In step S5, the infrared radiation forms a radiation intensity ratio of 1.5 to 2.0 on the outer surface and the inner surface of the sheet, and the radiation duration is 2 to 3 seconds.

8. The method for preparing the corrosion-resistant polypropylene modified thermoplastic according to claim 3, characterized in that, In step S6, the cross-sectional area of ​​the negative pressure channel in the co-extrusion die head is 0.3% of the cross-sectional area of ​​the sheet, and the temperature of the co-extrusion block is maintained at 200℃.

9. The method for preparing the corrosion-resistant polypropylene modified thermoplastic according to claim 3, characterized in that, The distance between the carbon dioxide injection port in step S2 and the vacuum exhaust port in step S3 on the extruder barrel is 8 to 10 screw diameters, and the exhaust starts within 0.2 seconds after the carbon dioxide injection stops.

10. The method for preparing the corrosion-resistant polypropylene modified thermoplastic according to claim 3, characterized in that, The distance between the second set of stretching rollers in step S4 and the infrared radiation device in step S5 is 30-60cm, and the sheet linear speed is maintained at 3m / min.

Images