Hydrophilic polypropylene film and preparation method thereof

Abstract

The invention discloses a preparation method of a hydrophilic polypropylene film, which comprises the following steps: uniformly mixing polypropylene, maleic anhydride grafted polypropylene, span 80 and polyethyleneimine to obtain a mixture; adding the mixture into an extruder, and melting the mixture by heating and stirring to form a molten material; and extruding the molten material through a screw rod and a die head of an extruder to form a strip-shaped or tubular film, and meanwhile, forming the film to the required width and thickness through rolling and traction. The invention also discloses the hydrophilic polypropylene film prepared by the preparation method. Polyethyleneimine, maleic anhydride grafted polypropylene and Span 80 are used as modifiers to be added into polypropylene, the hydrophilicity of the polypropylene film is improved, maleic anhydride grafted polypropylene is used as a compatilizer, the compatibility between polypropylene and polyethyleneimine is enhanced, maleic anhydride grafted polypropylene is utilized, and the hydrophilicity of the polypropylene film is improved. The mechanical strength of the film is improved, and the application range of the polypropylene film is expanded.

Description

Technical Field

[0001] The present invention relates to a hydrophilic polypropylene film and a method for preparing the same. Background Art

[0002] In the field of modern agriculture, greenhouse greenhouses have been widely used in the production of crops. When the temperature difference between the inside and outside of the greenhouse is large, fog droplets will form on the inner surface of the greenhouse film. These fog droplets will affect the transmission of light, cause light scattering, reduce the light utilization rate, and affect the photosynthesis and metabolism of crops, reducing the crop yield to a certain extent and reducing the quality of crops.

[0003] In terms of eliminating fog droplets, generally the following two types of technologies are adopted: (1) changing external environmental factors, including controlling temperature, humidity, air flow, etc.; (2) achieving anti-fog effect by surface coating or changing the microstructure and chemical properties of the greenhouse film surface. This method enhances the hydrophilicity of the material surface, adjusts the affinity between the material surface and water droplets, and enables the water droplets to spread into a water film instantly when contacting the substrate surface, thus not affecting the transmission of light.

[0004] Polypropylene (PP) materials are preferred as film materials because of their series of excellent properties such as low cost, good mechanical strength, easy processing, high temperature resistance and high transparency. However, due to its poor surface polarity, low surface energy and strong hydrophobicity, polypropylene is greatly limited in applications such as anti-fog, anti-fouling and water treatment. At the same time, due to the non-polarity of polypropylene, it is extremely difficult to perform hydrophilic modification on polypropylene, which further hinders the functional modification of polypropylene.

[0005] At present, the hydrophilic modification of polypropylene is physical modification and chemical modification. Among them, physical modification can be specifically divided into methods such as surface coating, blending modification and plasma treatment; chemical modification can be specifically divided into surface grafting and ozone treatment, etc.

[0006] Ojstrsek, A et al. modified polypropylene (PP) films with polydopamine / polyethyleneimine (PDA / PEI) and tetraethyl orthosilicate (TEOS), and obtained a hydrophilic mineral-rich surface using a simple dip-coating procedure, reducing the contact angle from 103° of the pure PP film to 28° of the modified film. Wang et al. used the continuous deposition of tannic acid (TA)-titanium (Ti-IV) complex interconnection network with high adhesion and long-term stability on the surface of polypropylene (PP) film to achieve oil-water separation. The hydrophilic TA-Ti nanostructured coating showed high adhesion and long-term stability on the non-polar surface of the PP film. However, the above-mentioned modification methods all have the problem of complex modification processes, resulting in an increase in the production cost of the film. Summary of the Invention

[0007] To solve the problem that polypropylene films are prone to fogging due to poor hydrophilicity, this application first proposes a method for preparing hydrophilic polypropylene films, and the steps are as follows:

[0008] (1) Mix polypropylene, maleic anhydride grafted polypropylene, span 80 and polyethyleneimine evenly to form a mixture;

[0009] (2) Add the mixture into an extruder, and melt the mixture by heating and stirring to form a molten material;

[0010] (3) Extrude the molten material through the screw and die head of the extruder to extrude it into a strip or tubular film, and at the same time, form the film to the required width and thickness through rolling and traction.

[0011] Specifically, in the mixture, the mass fractions of each component are as follows: polypropylene accounts for 65-75%, maleic anhydride grafted polypropylene accounts for 3-6%, polyethyleneimine accounts for 18-25%, and span 80 accounts for 2-8%.

[0012] Preferably, in the mixture, the mass fractions of each component are as follows: polypropylene accounts for 68-72%, maleic anhydride grafted polypropylene accounts for 3-6%, polyethyleneimine accounts for 19-22%, and span 80 accounts for 3-6%.

[0013] Specifically, in the maleic anhydride grafted polypropylene, the grafting rate of maleic anhydride is 0.9-1.1%.

[0014] Specifically, the extrusion temperature of the molten material is 175-210 °C.

[0015] In this application, polyethyleneimine (PEI), maleic anhydride grafted polypropylene (PP-g-MAH) and span 80 are added to polypropylene as modifiers to improve the hydrophilicity of polypropylene films. Among them, maleic anhydride grafted polypropylene is used as a compatibilizer to enhance the compatibility between non-polar polypropylene and polar polyethyleneimine. Through the combined action of polyethyleneimine (PEI), maleic anhydride grafted polypropylene (PP-g-MAH) and span 80, the hydrophilic performance of polypropylene films is improved, and due to the addition of maleic anhydride grafted polypropylene, unexpectedly, the mechanical strength of the films is also synchronously improved, expanding the scope of use of polypropylene films. In the existing chemical field, span 80 is also known as sorbitan monooleate.

[0016] In the research process, the inventors of this application found that although Span 80 is often used as an anti-fogging agent for non-polar plastics as a surfactant, it does not show the desired effect when used as an anti-fogging agent for polypropylene (PP). When only Span 80 is added as an anti-fogging agent, when 2 wt% of Span 80 is added, the water contact angle of the PP film is 88.2°. When the addition amount of Span 80 reaches 8 wt%, the water contact angle of the PP film can be reduced to 80.5°, and there is still a large gap from the desired hydrophilicity. It is unrealistic to greatly increase the addition amount of Span 80 to improve the hydrophilicity of the PP film. It is analyzed that when Span 80 is used as an anti-fogging agent, since a large amount of Span 80 is wrapped inside the film, the amount of Span 80 on the surface layer of the film is actually very small, and it is unable to effectively increase the polarity of the PP film surface, thus failing to significantly reduce the water contact angle of the PP film.

[0017] In this application, maleic anhydride grafted polypropylene (PP-g-MAH) and polyethyleneimine (PEI) are used to cooperate with Span 80 to form a composite additive, jointly improving the hydrophilic property of the PP film. PEI is rich in amino groups and can react with the anhydride of PP-g-MAH to form a more polar amide bond, and at the same time form a hydrogen bond network with the hydroxyl groups of Span 80. The three polar components (PP-g-MAH, PEI, Span 80) jointly construct a highly polar surface, which can make the water contact angle of the PP film lower than 7°, endowing the PP film with strong hydrophilicity. During the use of the film, the Span 80 wrapped inside the film will gradually migrate outwards to make up for the lost Span 80, keeping the polarity of the film surface in a stable state until the Span 80 migrating from the inside out can no longer make up for the lost Span 80, at which point the hydrophilic property of the film begins to decrease until it fails to meet the corresponding requirements and loses its use value.

[0018] When used as an agricultural film, a good light transmittance is often required. The film prepared by this application has good natural light transmittance, and the transmittance is higher than 80% in the wavelength range of 800 - 500 nm. The light transmittance of the film decreases with the increase in the addition amount of Span 80. When the addition amount of Span 80 is low, Span 80 can act as a compatibilizer, be compatible with the PP matrix through its hydrophobic chain, and interact with the polar groups of PP-g-MAH and PEI through its hydrophilic group, reducing phase separation and maintaining a relatively high light transmittance. However, when the addition amount of Span 80 exceeds 8 wt%, it will exceed the critical micelle concentration (CMC) and form nano-scale micelles or microphase regions. Due to the strong interaction (hydrogen bonding, ion-dipole interaction) between the polar groups of PP-g-MAH and PEI and Span 80, the size of the phase region is limited to a relatively small range, resulting in weak light scattering and a larger decrease in light transmittance. In view of the above factors, the film prepared by this application has good light transmittance performance both in hot fog and frozen fog.

[0019] To achieve the balance between anti-fog performance and light transmittance, in the mixture, polypropylene accounts for 65 - 75%, maleic anhydride grafted polypropylene accounts for 3 - 6%, polyethyleneimine accounts for 18 - 25%, and Span 80 accounts for 2 - 8%. Preferably, maleic anhydride grafted polypropylene accounts for 3 - 6%, polyethyleneimine accounts for 19 - 22%, and Span 80 accounts for 3 - 6%. At the same time, in order to keep the polarity of maleic anhydride grafted polypropylene within a certain range to match with polyethyleneimine and Span 80, the grafting rate of maleic anhydride is limited to 0.9 - 1.1%.

[0020] As an additional effect, since maleic anhydride grafted polypropylene is used in this application to synergistically improve the hydrophilic property of the PP film, the mechanical properties of the film material are also improved simultaneously, and the elongation at break and impact strength are increased by at least 78.8% and 97.7% respectively.

[0021] Span 80 can not only reduce the interfacial tension between non-polar PP and polar group-containing PEI / PP-g-MAH, promoting the uniform dispersion of polar components in the PP matrix, but also the hydroxyl group of Span 80 may form hydrogen bonds with the anhydride group (hydrolyzed to form carboxylic acid) of PP-g-MAH or the amino group of PEI. The anhydride group of maleic anhydride grafted polypropylene can also react with the amino group of polyethyleneimine to form an amide group, enhancing the interfacial bonding and reducing phase separation. However, at the same time, the flexible long-chain alkyl group of Span 80 can endow the system with a certain plasticizing effect, and the enhanced interfacial bonding makes the stress distribution more uniform, delaying crack propagation, so that the tensile strength of the film material remains roughly unchanged, but its elongation at break has a significant increase.

[0022] However, since Span 80 forms a flexible interfacial layer between PP and polar components through hydrogen bonds, energy is dissipated during impact through interfacial debonding, molecular chain slippage, and dynamic fracture of hydrogen bonds. At the same time, the plasticizing effect of Span 80 makes the matrix more likely to form shear bands and crazes under high-speed impact, absorb energy, and improve the impact strength of the film material. However, when the addition amount of Span 80 is too large, it will cause excessive softening of the PP matrix, unable to effectively transfer stress, making it difficult for crazes / shear bands to expand, resulting in a decrease in energy dissipation ability. Moreover, excessive Span 80 hinders the chemical cross-linking of PP-g-MAH and PEI, weakening the interfacial bonding strength, thus leading to a reduction in the impact strength of the film material.

[0023] Secondly, the present application also discloses a hydrophilic polypropylene film prepared by using the preparation method described in any one of the above. Description of the Drawings

[0024] Figure 1 It is a comparison diagram of Fourier infrared spectra of Example 1, Comparative Example 1, and polypropylene grafted maleic anhydride.

[0025] Figure 2 It is a comparison diagram of the water contact angles of the films in Examples 1-3 and Comparative Examples 1-5.

[0026] Figure 3 It is a detection diagram of the migration of Span 80 in the 1# film in Example 1.

[0027] Figure 4 It is a comparison diagram of the tensile strength and elongation at break of the 1#-5# films.

[0028] Figure 5 It is a comparison diagram of the impact strength of the 1#-5# films.

[0029] Figure 6 It is a scanning electron micrograph of the impact fracture surface of the 1#-4# film materials. Detailed Embodiments

[0030] In the following examples and comparative examples, the Mn of polypropylene (PP) is 8500 Da, and the Mw of polyethyleneimine (PEI) is 600 Da. In the following examples and comparative examples, the thickness of the prepared hydrophilic polypropylene films is 0.06 mm.

[0031] Example 1

[0032] Preparation of hydrophilic polypropylene film:

[0033] (1) Mix polypropylene, maleic anhydride grafted polypropylene, polyethyleneimine and Span 80 evenly to form a mixed material; the mass ratio of polypropylene, maleic anhydride grafted polypropylene, polyethyleneimine and Span 80 is 75:3:20:2. Among them, in the maleic anhydride grafted polypropylene, the grafting rate of maleic anhydride is 0.9%.

[0034] (2) Add the mixed material into an extruder, and melt the mixed material through heating and stirring to form a molten material;

[0035] (3) Extrude the molten material through the screw and die head of the extruder, the extrusion temperature is 200 °C, and extrude it into a tubular film. At the same time, roll and draw the film to the required width and thickness. Mark it as Film No. 1.

[0036] Example 2

[0037] Preparation of hydrophilic polypropylene film:

[0038] (1) Mix polypropylene, maleic anhydride grafted polypropylene, polyethyleneimine and Span 80 evenly to form a mixed material; the mass ratio of polypropylene, maleic anhydride grafted polypropylene, polyethyleneimine and Span 80 is 70:5:20:5. Among them, in the maleic anhydride grafted polypropylene, the grafting rate of maleic anhydride is 1%.

[0039] (2) Add the mixed material into an extruder, and melt the mixed material through heating and stirring to form a molten material;

[0040] (3) Extrude the molten material through the screw and die head of the extruder, the extrusion temperature is 190 °C, and extrude it into a tubular film. At the same time, roll and draw the film to the required width and thickness. Mark it as Film No. 2.

[0041] Example 3

[0042] Preparation of hydrophilic polypropylene film:

[0043] (1) Mix polypropylene, maleic anhydride grafted polypropylene, polyethyleneimine and Span 80 evenly to form a mixed material; the mass ratio of polypropylene, maleic anhydride grafted polypropylene, polyethyleneimine and Span 80 is 64:5:23:8. Among them, in the maleic anhydride grafted polypropylene, the grafting rate of maleic anhydride is 1.1%.

[0044] (2) Add the mixed material into an extruder, and melt the mixed material through heating and stirring to form a molten material;

[0045] (3) Extrude the molten material through the screw and die head of the extruder, the extrusion temperature is 180 °C, and extrude it into a tubular film. At the same time, roll and draw the film to the required width and thickness. Mark it as Film No. 3.

[0046] Comparative Example 1

[0047] This comparative example is basically the same as Example 2, except that maleic anhydride grafted polypropylene, polyethyleneimine, and Span 80 are removed. It is marked as Film No. 4#.

[0048] Comparative Example 2

[0049] This comparative example is basically the same as Example 2, except that polyethyleneimine and Span 80 are removed. It is marked as Film No. 5#.

[0050] Comparative Example 3

[0051] This comparative example is basically the same as Example 2, except that maleic anhydride grafted polypropylene and polyethyleneimine are removed. It is marked as Film No. 6#.

[0052] Comparative Example 4

[0053] This comparative example is basically the same as Example 2, except that Span 80 is removed. It is marked as Film No. 7#.

[0054] Comparative Example 5

[0055] This comparative example is basically the same as Example 2, except that polyethyleneimine is removed. It is marked as Film No. 8#.

[0056] Detection:

[0057] Detect Example 2, Comparative Example 1 and polypropylene grafted maleic anhydride. Among them, Comparative Example 1 is actually a polypropylene film, and obtain Figure 1 the Fourier transform infrared spectrum as described above.

[0058] Figure 1 Among them, at 2950 - 2850 cm -1 , it corresponds to the C-H stretching vibration peaks of methyl and methylene in polypropylene, and 1450 cm -1 and 1375 cm -1 correspond to the CH2 bending vibration and the symmetric deformation vibration of CH3 in polypropylene respectively. At 1780 cm -1 and 1715 cm -1 , the C=O characteristic peak of maleic anhydride and the carboxylic acid characteristic peak generated by partial hydrolysis of maleic anhydride appear. Due to partial hydrolysis of maleic anhydride, the double peak of the anhydride becomes a single peak.

[0059] The 1# film in Example 1 is at 3200 - 3500 cm -1A relatively wide peak appears, corresponding to the overlapping of the amino characteristic peak in the unreacted polyethyleneimine and the amide characteristic peak of the reaction between the amino group of polyethyleneimine and the anhydride group, as well as the hydroxyl - OH characteristic peak of Span80. At the same time, the addition of the hydrogen - bond effect leads to the formation of a wide peak. At 1651 cm -1 and 1566 cm -1 , they respectively correspond to the C=O stretching vibration peak of amide Ⅰ band and the coupling peak of amide Ⅱ band that appear in the 1# film. However, the characteristic peak representing the anhydride group disappears, indicating that the amino group of polyethyleneimine has successfully reacted with the anhydride group of polypropylene grafted maleic anhydride to form an acylamino group. At 1742 cm -1 , it corresponds to the C=O stretching vibration peak of the ester group of Span80, indicating that Span80 migrates to the film surface.

[0060] The water contact angle of the film was detected, and the detection instrument was the SDC - 350 integral tilt - type contact angle measuring instrument of Dongguan Shengding Precision Instrument Co., Ltd.

[0061] The water contact angles of the films in Examples 1 - 3 and Comparative Examples 1 - 5 were detected. The water contact angles of the films in Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, Example 1, Example 2, and Example 3 were 101.6°, 90.5°, 85.7°, 61.5°, 80.7°, 9.7°, 8.8°, and 6.9° respectively. Each data forms Figure 2 , Figure 2 , in which, from left to right, they respectively correspond to the water contact angles of the films in Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, Example 1, Example 2, and Example 3. It can be seen from Figure 2 that when using maleic anhydride - grafted polypropylene or Span80 alone as the anti - fog component, the water contact angle of the film can be reduced, but the reduction amplitude is limited; while using a three - component film of polypropylene + maleic anhydride - grafted polypropylene + Span80 or polypropylene + maleic anhydride - grafted polypropylene + polyethyleneimine, its water contact angle further decreases; when using a four - component film of polypropylene + maleic anhydride - grafted polypropylene + polyethyleneimine + Span80, the water contact angle can be reduced to less than 10°.

[0062] The migration performance of Span 80 in the 1# film of Example 1 was detected. The specific detection method was as follows: Prepare Span80 / 10% ethanol - distilled water solutions with different concentrations. Use a UV - Vis spectrophotometer (UV752N) to determine the maximum wavelength corresponding to the absorbance peak of Span80 as the control table. Immerse the 2# film in a 10% ethanol - distilled water solution at 60 °C. Take a fixed - volume solution every hour and supplement the same volume of standard solution to keep the total solution volume constant. Use a UV - Vis spectrophotometer (UV752N) to measure the absorbance of the solution at the determined wavelength to obtainFigure 3 The attached drawings shown

[0063] It can be seen from Figure 3 that as the soaking time increases, the absorbance of the solution at a wavelength of 205 nm gradually increases, indicating that the concentration of Span 80 in the solution gradually increases. It can be seen from the curve slope that the migration rate of Span 80 initially slows down with the change of time. This is because at the initial stage of soaking, Span 80 molecules tend to accumulate on the surface of the blend. Under the synergistic action of high temperature (60 °C) and ethanol-aqueous solution, the hydrophilic group of Span 80 is more likely to interact with water molecules, resulting in its rapid dissolution from the material surface into the solution. The rapid increase in absorbance at the initial stage reflects the rapid release of Span 80. In the middle and late stages, since PP is a hydrophobic polymer, its crystalline regions may hinder the further migration of Span 80. As the Span 80 on the surface is released, the internal Span 80 needs to slowly diffuse to the surface through the amorphous region or the interfacial channel, resulting in a slowdown in the growth rate of absorbance. At the same time, the anhydride groups of PP-g-MAH and the amino groups of PEI may fix some Span 80 molecules through hydrogen bonding or ionic interactions, delaying its release and achieving a stable release.

[0064] The light transmittance of Films 1# - 4# was detected as follows. The light transmittance of Films 1# - 4# was 85.3%, 84.7%, 84.5% and 87.2% respectively. Compared with Film 4# (pure PP film), the light transmittance of the films prepared in this application decreased to a certain extent, but the decrease was limited, and all could meet the light transmittance requirements of agricultural films.

[0065] The anti-fogging performance of Films 1# - 8# was detected. The anti-fogging performance was specifically tested according to GB / T31726—2015 "Test Method for Anti-fogging Property of Plastic Films". The anti-fogging performance levels of Films 1# - 8# were Grade 1, Grade 1, Grade 1, Grade 5, Grade 4, Grade 4, Grade 2 and Grade 4 in sequence.

[0066] In this application, maleic anhydride grafted polypropylene and polyethyleneimine were used to synergistically act with Span80 to reduce the water contact angle of the film, and it also had a great impact on the mechanical strength of the film material. To comprehensively reflect the influence of the added components on the film, the tensile strength, elongation at break and impact strength of the film materials of Films 1# - 5# were detected. The film materials refer to the corresponding test samples prepared from the raw materials of Films 1# - 5# for testing, rather than directly using the films for testing. The test data are as follows:

[0067] The tensile strengths of the film materials of Films 1# - 5# were 37.3 MPa, 36.1 MPa, 35.3 MPa, 35.7 MPa and 35.0 MPa respectively, and a comparison chart of tensile strengths as shown in Figure 4 (a) was made.

[0068] The elongation at break of the 1#-5# thin film materials are 1226%, 1150%, 1091%, 610% and 939% respectively, and they are made into Figure 4 the elongation at break comparison diagram shown in (b).

[0069] The impact strength of the 1#-5# thin film materials are 9.55 KJ / m 2 , 9.90 KJ / m 2 , 9.49 KJ / m 2 , 4.80 KJ / m 2 and 4.54 KJ / m 2 respectively, and they are made into Figure 5 the impact strength comparison diagram shown in.

[0070] It can be seen from Figure 4 that the tensile strength differences of the 1#-5# thin film materials are not significant, but their elongation at break differences are relatively large. Especially for the 1#-3# thin film materials added with maleic anhydride grafted polypropylene, polyethyleneimine and Span80, the elongation at break is at least 15% higher than that of the 5# thin film material added only with maleic anhydride grafted polypropylene. The reasons may be: (1) A small amount of Span 80 can reduce the interfacial tension between non-polar PP and maleic anhydride grafted polypropylene containing polar groups, and promote the uniform dispersion of polar components in the PP matrix; (2) The hydroxyl groups of Span 80 can form hydrogen bonds with the anhydride groups (hydrolyzed to form carboxylic acids) of PP-g-MAH or the amino groups of PEI. The anhydride groups of PP-g-MAH and the amino groups of PEI can also react to form amide groups, enhancing the interfacial bonding and reducing phase separation; (3) The flexible long-chain alkyl groups of Span 80 endow the film with a certain plasticizing effect. At the same time, the enhanced interfacial bonding makes the stress distribution more uniform and delays crack propagation. As the mass ratio of Span80 increases continuously, the tensile strength and elongation at break of the blend gradually decrease. This is because excessive Span 80 may exist in the form of an independent phase and become the crack initiation point, reducing strength and toughness. Secondly, the hydroxyl groups of excessive Span 80 may form hydrogen bonds with the amino groups of PEI or the carboxylic acid groups of PP-g-MAH, resulting in a reduction in the effective interaction between PEI and PP-g-MAH and weakening the interfacial enhancement effect. Therefore, the dosage of Span 80 should not be too high either.

[0071] Combined with the impact strength data of the 1#-5# thin film materials and Figure 5It can be seen that when only PP-g-MAH is added, the impact strength of the thin film material becomes weaker instead. The data shows that the impact strength of the 1#-3# thin film materials first increases and then decreases. This is because Span80 forms a flexible interfacial layer between PP and the polar component through hydrogen bonds, and energy is dissipated through interfacial debonding, molecular chain slip, and dynamic fracture of hydrogen bonds during impact. At the same time, the plasticizing effect of Span80 makes the matrix more likely to form shear bands and crazes under high-speed impact, absorbing energy. When the addition amount of Span80 exceeds 5wt%, the impact strength begins to decline. This is because excessive Span80 causes excessive softening of the PP matrix, unable to effectively transfer stress, making it difficult for crazes / shear bands to expand, resulting in a decrease in energy dissipation ability. Moreover, excessive Span80 hinders the chemical cross-linking between PP-g-MAH and PEI, weakening the interfacial bonding strength.

[0072] Combined with Figure 6 explain the fracture strength of the thin film material, Figure 6 in which, (a), (b), (c), and (d) are the scanning electron microscope images of the impact cross-sections of the 4# thin film material, 1# thin film material, 2# thin film material, and 3# thin film material, respectively. Figure 6 Figure (a) shows an obvious brittle fracture smooth area, and the crack propagation path is straight, belonging to the brittle fracture mode of polypropylene. Figure 6 Figure (b) shows an increase in cross-section roughness and the appearance of a small number of ductile cracks, indicating that with the participation of Span 80, the dispersibility of PP-g-MAH and PEI is improved, and the toughness of the thin film material is enhanced. Figure 6 Figure (c) shows that the overall cross-section of the material is significantly roughened, and the uneven morphology indicates that plastic deformation has occurred during the fracture process. Compared with the smooth brittle cross-section of pure PP, the interface between the PEI dispersed phase and the PP matrix is blurred, without obvious phase separation, indicating that Span 80 and PP-g-MAH effectively enhance the compatibility between PEI and PP. A large number of fine dimples can be seen at the cross-section, showing a uniform distribution, indicating an increase in the fracture toughness of the material. Figure 6 Figure (d) shows that the overall cross-section roughness is still relatively high, but there is unevenness in local areas, and there are shallow dimple structures in some areas, indicating that the material still has a certain plastic deformation ability; micron-sized holes can be seen at the interface between the PP matrix and PEI, which may be due to the enrichment of the compatibilizer caused by excessive Span 80, weakening the interfacial bonding force and resulting in a decrease in the overall mechanical properties. Figure 6 It also shows that the addition of Span 80 should not be excessive.

Claims

1. A method for preparing a hydrophilic polypropylene film, characterized in that, The steps are as follows: (1) Mix polypropylene, maleic anhydride grafted polypropylene, Span 80 and polyethyleneimine evenly to form a mixture; (2) Add the mixture into an extruder, and melt the mixture by heating and stirring to form a molten material; (3) Extrude the molten material through the screw and die head of the extruder to extrude it into a strip-shaped or tubular film, and at the same time, form the film to the required width and thickness through rolling and traction.

2. The preparation method according to claim 1, characterized in that, In the mixture, the mass fractions of each component are as follows: Polypropylene accounts for 65 - 75%, maleic anhydride grafted polypropylene accounts for 3 - 6%, polyethyleneimine accounts for 18 - 25%, and Span 80 accounts for 2 - 8%.

3. The preparation method according to claim 1, characterized in that, In the mixture, the mass fractions of each component are as follows: Polypropylene accounts for 68 - 72%, maleic anhydride grafted polypropylene accounts for 3 - 6%, polyethyleneimine accounts for 19 - 22%, and Span 80 accounts for 3 - 6%.

4. The preparation method according to claim 1, wherein in the maleic anhydride grafted polypropylene, the grafting rate of maleic anhydride is 0.9 - 1.1%.

5. The preparation method according to claim 1, wherein the extrusion temperature of the molten material is 175 - 210 °C.

6. A hydrophilic polypropylene film prepared by the preparation method according to any one of claims 1 - 5.

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