Strontium titanate nanotube reinforced polypropylene film and preparation method thereof

Abstract

The invention relates to a strontium titanate nanotube reinforced polypropylene film and a preparation method thereof, and particularly provides a BOPP (Biaxially-oriented Polypropylene) composite film master batch which comprises a modified strontium titanate nanotube, and the modified strontium titanate nanotube is a strontium titanate nanotube of which the surface is covered with a surfactant. The BOPP composite film prepared from the master batch is a bidirectional reinforced polypropylene film, the glossiness of the BOPP composite film is almost kept unchanged, the transparency and scratch resistance of the BOPP composite film are obviously improved, meanwhile, the heat sealing temperature of the BOPP composite film is reduced, and the BOPP composite film has important application prospects in the packaging field.

Description

Technical Field

[0001] The invention belongs to the technical field of nano materials and plastic processing, and particularly relates to a strontium titanate nanotube reinforced polypropylene film and a preparation method thereof. Background Art

[0002] Reinforcing plastics with high-strength fillers, such as inorganic or metallic ones, is a highly successful strategy in the plastics processing industry. For example, powdered carbon black reinforced rubber is well known. On the other hand, unsaturated polyesters reinforced with glass fibers and carbon fibers of a certain length are widely used in various engineering plastics. The dominant arrangement direction of the fiber filler in the plastic, i.e., its orientation, most significantly enhances the mechanical properties of the composite material. However, while reinforcing plastics with these micron, millimeter, or even larger fillers can significantly improve the strength, modulus, and other mechanical properties of the final composite material, it severely impacts its transparency, gloss, and softness. Therefore, this strategy is unsuitable for film materials, especially packaging films that have high requirements for optical properties and flatness.

[0003] Biaxially oriented polypropylene (BOPP) film has high mechanical properties such as tensile strength, impact strength, rigidity and toughness. It is also non-toxic, odorless and has good transparency. It is the "packaging queen" of flexible packaging materials and is widely used in the packaging of food, medicine, daily light industry, cigarettes and other products. At present, the research on BOPP packaging film mainly focuses on the monomer design of raw material polypropylene, polymerization process improvement and compound modification to further enhance its mechanical properties, improve optical properties and reduce heat sealing temperature (China Food Industry, 2023, (24): 37; China Packaging, 2023, 43 (11): 27). In addition, as a packaging material, BOPP film can also improve its mechanical properties by adding nanomaterials, thereby expanding its application range. Among them, the dispersion of nanomaterials in the BOPP film matrix has a crucial impact on its various properties. However, as a packaging material, BOPP film also requires excellent transparency and glossiness, and therefore has high requirements for the color of the added nanomaterials themselves. The inherent dark color of one-dimensional linear nanomaterials such as carbon nanotubes limits the application of the resulting enhanced BOPP in the field of packaging films.

[0004] Therefore, further research is needed to develop BOPP films with more balanced mechanical and optical properties. Summary of the Invention

[0005] The present invention aims to provide a polypropylene film with more balanced mechanical and optical properties, so as to simultaneously improve the longitudinal and transverse mechanical properties, transparency and scratch resistance of the BOPP film without affecting its glossiness.

[0006] Our company's previous patent application (CN103359778A) disclosed a novel white or light-colored one-dimensional linear nanomaterial: strontium titanate nanotubes. The inventors of this application surprisingly discovered that surfactant-modified strontium titanate nanotubes can improve their dispersion in a matrix. Furthermore, in a masterbatch prepared by mixing the surfactant-modified strontium titanate nanotubes with a carrier material, the strontium titanate nanotubes are uniformly dispersed. Furthermore, a BOPP composite film prepared by mixing this masterbatch with a main material and additives produces a biaxially reinforced polypropylene film with nearly unchanged gloss, significantly improved transparency and scratch resistance, and a significantly lower heat-sealing temperature, suggesting broad application prospects.

[0007] To this end, in a first aspect of the present invention, the present invention provides a BOPP composite film masterbatch, which comprises modified strontium titanate nanotubes, wherein the modified strontium titanate nanotubes are strontium titanate nanotubes whose surfaces are covered with a surfactant.

[0008] In some embodiments, the strontium titanate nanotubes are prepared by the following method: preparing 50 mL of a 2 mol / L solution of sodium hydroxide dissolved in 90% ethanol, adding 50 mL of n-butyl titanate, stirring evenly, placing the mixture into a hydrothermal reactor and reacting at 200°C for 48 hours; adjusting the pH value of the resulting product to neutral with 2 mol / L hydrochloric acid, filtering and washing the precipitate with water, taking 50 grams and adding it to 500 mL of a 0.5 mol / L strontium titanate aqueous solution (solid-liquid mass / volume ratio of 1:10), stirring and mixing, placing the mixture into a hydrothermal reactor and reacting at 150°C for 24 hours, and washing, filtering, and drying the resulting precipitate product to obtain strontium titanate nanotubes.

[0009] In some embodiments, in the BOPP composite film masterbatch, the mass fraction of the modified strontium titanate nanotubes is 1%-25% (e.g., 1%, 3%, 5%, 10%, 15%, 20% or 25%), preferably 1%-20%, more preferably 5%-20%, and most preferably 5-10%.

[0010] In some embodiments, the modified strontium titanate nanotubes are obtained by mixing strontium titanate nanotubes with a surfactant.

[0011] In some embodiments, the modified strontium titanate nanotubes are prepared by the following method:

[0012] (1) Mixing strontium titanate nanotubes with a surfactant aqueous solution;

[0013] (2) The mixture obtained by mixing is filtered, washed with water, and dried to obtain modified strontium titanate nanotubes.

[0014] In some embodiments, the mixing is performed under ultrasonic conditions.

[0015] In some embodiments, the ultrasound duration is 5-60 minutes (eg, 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 60 minutes), preferably 10-40 minutes, and more preferably 30 minutes.

[0016] In some embodiments, the power of the ultrasound is 50W-2000W (e.g., 50W, 100W, 300W, 500W, 800W, 1000W, 1300W, 1500W, 1800W, or 2000W), preferably 50W-1000W, more preferably 100W-800W, and most preferably 300W.

[0017] In some embodiments, the surfactant is selected from sodium stearate, calcium stearate, sodium lauryl sulfate, sodium tetradecyl sulfonate, sodium hexadecyl sulfonate, sodium dodecylbenzene sulfonate, sodium polystyrene sulfonate, or any combination thereof.

[0018] In some embodiments, the surfactant is selected from sodium stearate, sodium lauryl sulfate, sodium tetradecyl sulfonate, sodium hexadecyl sulfonate, sodium dodecylbenzene sulfonate, sodium polystyrene sulfonate, or any combination thereof.

[0019] In some embodiments, the surfactant is selected from sodium stearate, sodium lauryl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, or any combination thereof.

[0020] In some embodiments, the mass volume concentration of the surfactant in the surfactant aqueous solution is 0.1%-10% (w / v), preferably 0.2%-5% (w / v), for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10% (w / v).

[0021] In some embodiments, the ratio of the mass of the strontium titanate nanotubes to the volume of the surfactant aqueous solution is 1:80 to 1:120 (g / mL), preferably 1:100 (g / mL).

[0022] In some embodiments, the BOPP composite film masterbatch further comprises a carrier material.

[0023] In some embodiments, the support material is polypropylene.

[0024] In some embodiments, the support material is maleic anhydride grafted polypropylene.

[0025] In some embodiments, the masterbatch is obtained by mixing the modified strontium titanate nanotubes and the support material in a mixer and then extruding and granulating the mixture in an internal mixer.

[0026] In a second aspect of the present invention, the present invention provides a BOPP composite film, the raw materials of which include: the masterbatch described in any technical solution of the first aspect.

[0027] In some embodiments, the mass fraction of the modified strontium titanate nanotubes in the BOPP composite film is 0.05%-7.5% (e.g., 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0% or 7.5%), preferably 0.1%-6.0%, more preferably 0.5%-4.5%, further preferably 0.5%-3%, and most preferably 3%.

[0028] In some embodiments, the raw materials of the BOPP composite film further include a main material and an auxiliary agent.

[0029] In some embodiments, the body material is polypropylene.

[0030] In some embodiments, the main body material is terpolymer polypropylene or heat-sealable polypropylene.

[0031] In some embodiments, the auxiliary agent comprises a slip agent, an anti-sticking agent, an antioxidant, or any combination thereof.

[0032] In some embodiments, the mass fraction of the auxiliary agent in the BOPP composite film is 1%-5%, preferably 2%.

[0033] In some embodiments, the BOPP composite film is prepared by the following method:

[0034] (1) mixing the masterbatch, the main material and the auxiliary agent, and then extruding and granulating the mixture using a twin-screw extruder to obtain plastic rice;

[0035] (2) The plastic rice is subjected to extrusion casting and planar biaxial stretching processes to obtain the BOPP composite film.

[0036] In some embodiments, the conditions and process of the planar biaxial stretching process are as follows: the temperature of the quenching roller is controlled at 30°C; the longitudinal stretching preheating roller temperature is 80-150°C; the longitudinal stretching roller temperature is 70-150°C; the longitudinal stretching shaping roller temperature is 20-80°C; the longitudinal stretching multiple is 5; the transverse stretching preheating temperature is 120-175°C; the transverse stretching area temperature is 150-170°C; the transverse stretching shaping area temperature is 100-150°C; cooling; pulling at a speed of 200 m / s; winding with a tension of 150 N / m.

[0037] Beneficial effects

[0038] 1. One-dimensional strontium titanate nanotubes have a large aspect ratio, so the biaxial stretching process in the manufacture of BOPP film will also simultaneously orient in the length and width directions of the film plane, thereby achieving biaxial reinforcement of the BOPP film.

[0039] 2. Modified strontium titanate nanotubes and maleic anhydride grafted polypropylene are mixed to obtain a masterbatch to achieve initial uniform dispersion of the strontium titanate nanotubes; the masterbatch is mixed with ternary copolymer polypropylene and then granulated to further improve the good dispersion of the strontium titanate nanotubes and avoid their agglomeration.

[0040] 3. Well-dispersed strontium titanate nanotubes act as nucleating agents to induce polypropylene to crystallize more easily, resulting in a lower crystallization temperature, smaller crystal size, and higher crystallinity in the prepared nanotube-reinforced polypropylene film. As a result, the glossiness remains almost unchanged, but its transparency and scratch resistance are significantly improved, and its heat sealing temperature is significantly reduced when used as a heat-sealing film. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Scanning electron microscope and transmission electron microscope images of the original strontium titanate nanotubes in Example 2 and the sample prepared after 300W ultrasound for 30 minutes.

[0042] Figure 2 Thermogravimetric curves of the original strontium titanate nanotubes and the strontium titanate nanotubes treated with ultrasound for 10 minutes, 20 minutes and 30 minutes involved in Example 2.

[0043] Figure 3 Photos of the seven films prepared in Example 3.

[0044] Figure 4 Polarizing microscope photographs of the BOPP film without additives and the BOPP films with 0.1%, 0.5% and 3.0% addition of modified strontium titanate nanotubes in Example 4.

[0045] Figure 5Wide-angle XRD curves of the BOPP film without additives and the BOPP films with modified strontium titanate nanotubes added in amounts of 0.1%, 0.5%, and 3.0% in Example 4.

[0046] Figure 6 The DSC curves of the heating and cooling of the BOPP film without additives and the BOPP film with 0.1%, 0.5% and 3.0% addition of modified strontium titanate nanotubes in Example 4.

[0047] Figure 7 Transmission electron micrograph of the nanotube-reinforced polypropylene film prepared in Example 5.

[0048] Figure 8 Small-angle XRD curve of the nanotube-reinforced polypropylene film prepared in Example 6. DETAILED DESCRIPTION

[0049] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples, but it will be understood by those skilled in the art that the following drawings and examples are intended only to illustrate the present invention and are not intended to limit the scope of the invention. Various objects and advantages of the present invention will become apparent to those skilled in the art based on the following detailed description of the accompanying drawings and preferred embodiments.

[0050] The present invention relates to a nanotube-reinforced polypropylene film and its preparation method. First, modified strontium titanate nanotubes are mixed with maleic anhydride-grafted polypropylene to produce a masterbatch. Second, the masterbatch is mixed with ternary copolymerized polypropylene and extruded to form granules. Finally, the granulated plastic is subjected to extrusion, film blowing, and biaxial stretching to produce a reinforced polypropylene film. This biaxially reinforced polypropylene film maintains nearly unchanged gloss while significantly improving transparency and scratch resistance. Simultaneously, its heat-sealing temperature is reduced, resulting in significant application prospects in the packaging field.

[0051] The technical solution of the present invention is further illustrated and described below through specific embodiments in combination with the accompanying drawings.

[0052] Example 1 (Preparation of Modified Strontium Titanate Nanotubes)

[0053] First, strontium titanate nanotubes were prepared according to the method of CN103359778A: 50 mL of a 2 mol / L solution of sodium hydroxide dissolved in 90% ethanol was prepared, and then 50 mL of n-butyl titanate was added. After stirring, the mixture was placed in a hydrothermal reactor and reacted at 200°C for 48 hours. The pH value of the obtained product was adjusted to neutral with 2 mol / L hydrochloric acid, the precipitate was filtered and washed with water, and 50 grams was added to 500 mL of a 0.5 mol / L strontium titanate aqueous solution (solid-liquid mass / volume ratio of 1:10). After stirring and mixing, the mixture was placed in a hydrothermal reactor and reacted at 150°C for 24 hours. The obtained precipitate product was washed with water, filtered, and dried to obtain approximately 59.7 grams of strontium titanate nanotubes.

[0054] Based on the solubility of various surfactant modifiers in water at room temperature, 100 mL of homogenous aqueous solutions of sodium stearate (5% w / v concentration), calcium stearate (0.2% w / v concentration), sodium lauryl sulfate (5% w / v concentration), sodium tetradecyl sulfonate (3% w / v concentration), sodium hexadecyl sulfonate (0.8% w / v concentration), sodium dodecylbenzenesulfonate (1% w / v concentration), and sodium polystyrenesulfonate (1% w / v concentration) were prepared. Approximately 1 gram of each of the strontium titanate nanotubes prepared above (weighed on a precision balance) was added to the solutions, shaken evenly, and then ultrasonically vibrated at 300 W for 30 minutes. The product was filtered, washed three times with water, dried, and weighed on a precision balance.

[0055] According to the weighing results, the strontium titanate nanotubes treated with surfactant modifiers all increased in weight. 后 -M 前 ) / M 前 x100%, where M 后 represents the mass of modified strontium titanate nanotubes, M 前 The weight of strontium titanate nanotubes before modification was 4.7% higher after treatment with sodium stearate, 0.3% higher after treatment with calcium stearate, 5.4% higher after treatment with sodium lauryl sulfate, 3.9% higher after treatment with sodium tetradecyl sulfonate, 2.1% higher after treatment with sodium hexadecyl sulfonate, 1.6% higher after treatment with sodium dodecylbenzene sulfonate, and 1.2% higher after treatment with sodium polystyrene sulfonate. These results demonstrate that the surfactant modifiers described above can successfully modify strontium titanate nanotubes; among these, sodium stearate, sodium lauryl sulfate, sodium tetradecyl sulfonate, and sodium hexadecyl sulfonate produced the most significant weight increases.

[0056] Example 2 (ultrasonic power and ultrasonic time)

[0057] Prepare several 10 mL portions of a 5% mass / volume sodium stearate aqueous solution. Accurately weigh approximately 0.1 g of the strontium titanate nanotubes obtained in Example 1 and add them to the sodium stearate aqueous solution. Shake evenly and place in an ultrasonic device. After ultrasonic vibration at 300 W for 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, and 60 minutes, each group of products was filtered, washed with water three times, dried, and weighed using a precision balance. The product weight gain percentages were calculated to be 1.3% (5 minutes), 3.5% (10 minutes), 4.7% (20 minutes), 5.2% (30 minutes), 3.2% (40 minutes), 1.6% (50 minutes), and 0.4% (60 minutes). During the experiment, it was observed that the temperature of the reaction solution increased significantly after 50 minutes and 60 minutes of ultrasound, and the filtrate appeared light blue; this may be because some strontium titanate nanotubes were broken into extremely fine nano-fragments due to high shear during the ultrasound process, and could not remain on the filter paper and entered the filtrate. The above results show that ultrasound for 10-40 minutes is more appropriate. The original strontium titanate nanotubes and the samples prepared after 30 minutes of 300W ultrasound were taken for scanning electron microscopy and transmission electron microscopy observations. The results are as follows Figure 1 As shown in the figure, it shows that after ultrasonic modification, the surface of strontium titanate nanotubes is covered with a layer of amorphous material, which means that the modification is successful. After the unmodified strontium titanate nanotubes and the samples treated with ultrasonic waves for 10 minutes, 20 minutes, and 30 minutes were dried in a vacuum at 60°C for 48 hours, the degree of modification was detected using a Netzsch 449 F3 Jupiter thermogravimetric analyzer. Figure 2 The results shown are consistent with the gravimetric method, again indicating that the modification was successful.

[0058] According to the above method, ultrasonication was performed for a fixed 10-minute duration and with adjustable ultrasonic power levels of 50W, 100W, 300W, 500W, 800W, 1000W, 1500W, and 2000W. The product was filtered, washed three times, dried, and weighed using a precision balance. The calculated weight gains were 1.4% (50W), 2.8% (100W), 3.5% (300W), 3.9% (500W), 3.2% (800W), 2.1% (1000W), 0.1% (1500W), and -20.7% (2000W). During the experiment, it was observed that at an ultrasonic power of 2000W, some strontium titanate nanotubes were broken down into nanofragments due to high shear during sonication and subsequently entered the filtrate. The above results show that ultrasonic power below 1000W can effectively promote the modification of strontium titanate nanotubes; if the ultrasonic power is too high, the strontium titanate nanotubes will be destroyed.

[0059] Example 3 (Modified Strontium Titanate Nanotube Masterbatch and Its Content)

[0060] The method of Example 1 was adopted, sodium stearate was used as a surfactant modifier, and about 600 g of modified strontium titanate nanotubes were prepared in a 10 L reactor; the preparation and mixing of the products were repeated; and finally about 5 kg of modified strontium titanate nanotubes were obtained.

[0061] 500 grams of the modified strontium titanate nanotubes were mixed with maleic anhydride-grafted polypropylene (CMG9801, 1.0% grafting ratio, Shanghai Rizhisheng New Technology Development Co., Ltd.) in a mixer and then extruded and pelletized in an internal mixer to produce a masterbatch. The amount of maleic anhydride-grafted polypropylene added was adjusted to produce masterbatches with modified strontium titanate nanotube contents of 5%, 10%, 15%, 20%, and 25%, respectively.

[0062] As the content of modified strontium titanate nanotubes increases, the resulting masterbatch particles gradually change from uniform, rounded particles to particles with reduced gloss and a whitish appearance. At a modified strontium titanate nanotube content of 25% by weight, the masterbatch particles exhibit fine cracks. This result suggests that a masterbatch content of modified strontium titanate nanotubes of no more than 20% by weight is optimal. Excessive concentrations of modified strontium titanate nanotubes in the masterbatch result in cracks within the particles caused by macroscopic phase separation, i.e., agglomeration of unevenly dispersed modified strontium titanate nanotubes.

[0063] The mass content of modified strontium titanate nanotubes in the final film was set at 1.0%. The masterbatch prepared above with mass contents of modified strontium titanate nanotubes of 5%, 10%, 15%, and 20% were mixed with ternary copolymer polypropylene (brand FS5612, TPC Company, Singapore), respectively. Then, corresponding composite additives used in conventional BOPP film production, such as a lubricant, an anti-sticking agent (in this example, erucamide was used as a lubricant and anti-sticking agent), and an antioxidant (in this example, BASF composite antioxidant XT500 was used as an example), were added (2% of the total mass of the final film). The plastic was granulated using a twin-screw extruder. The obtained plastic rice was added to the biaxial stretching extrusion equipment for BOPP heat-sealing film production for melting and extrusion casting. The conditions and process are as follows: the temperature of the quenching roller is controlled at 30°C; the longitudinal stretching preheating roller temperature is 80-150°C; the longitudinal stretching roller temperature is 70-150°C; the longitudinal stretching shaping roller temperature is 20-80°C; the longitudinal stretching multiple is 5; the transverse stretching preheating temperature is 120-175°C; the transverse stretching area temperature is 150-170°C; the transverse stretching shaping area temperature is 100-150°C; cooling; pulling, the speed is 200 m / s; winding, the tension is 150 N / m. In addition, the control experiments carried out include: no strontium titanate nanotubes, unmodified strontium titanate nanotubes, and directly adding modified strontium titanate nanotubes without using masterbatch to make films through the same extrusion casting and planar biaxial stretching process mentioned above. The photo of the obtained film is shown in the figure. Figure 3As shown: the BOPP films prepared by adding unmodified strontium titanate nanotubes and directly adding modified strontium titanate nanotubes without using masterbatch are partially opaque; the rest of the BOPP films are transparent and uniform film materials.

[0064] Furthermore, the tensile strength, elongation at break, coefficient of friction, gloss, and haze of the prepared BOPP films were tested using the national standard GB / T12026-2000 method. The results are shown in Table 1. The results show that the BOPP films prepared by adding unmodified strontium titanate nanotubes and directly adding modified strontium titanate nanotubes without a masterbatch exhibited lower mechanical properties such as strength and a lower coefficient of friction than the unmodified BOPP films, while exhibiting lower gloss and higher haze. In comparison, the BOPP films prepared by adding modified strontium titanate nanotubes via a masterbatch exhibited improved longitudinal and transverse tensile strength and elongation at break, a lower coefficient of friction, and virtually unchanged gloss, while exhibiting reduced haze.

[0065] The above results show that: (1) the modified strontium titanate nanotubes and maleic anhydride grafted polypropylene are mixed to obtain a masterbatch, which achieves the initial uniform dispersion of the strontium titanate nanotubes; the masterbatch is mixed with ternary copolymer polypropylene and then granulated to further improve the good dispersion of the strontium titanate nanotubes and avoid their agglomeration; (2) the one-dimensional strontium titanate nanotubes with a large aspect ratio will also be oriented in the length and width directions of the film plane during the biaxial stretching process in the manufacture of BOPP film, thereby achieving biaxial reinforcement of the BOPP film in the longitudinal and transverse directions; (3) the oriented modified strontium titanate nanotubes reduce its friction coefficient, thereby improving its scratch resistance; (4) the oriented modified strontium titanate nanotubes are evenly dispersed, which has little effect on the gloss reduction, but reduces its haze, that is, improves its transparency.

[0066] Table 1: Test results of different BOPP films

[0067]

[0068] Example 4 (Content of Modified Strontium Titanate Nanotubes)

[0069] The method of Example 1 was used, sodium lauryl sulfate was used as a surfactant modifier, and about 610 g of modified strontium titanate nanotubes were prepared in a 10 L reactor. The preparation and mixing of the products were repeated to finally obtain more than 5 kg of modified strontium titanate nanotubes.

[0070] The modified strontium titanate nanotubes were mixed with maleic anhydride grafted polypropylene (CMG9801, grafting rate 1.0%, Shanghai Rizhisheng New Technology Development Co., Ltd.), mixed in a mixer, and then extruded and granulated in an internal mixer to produce 5 kg of a masterbatch, in which the modified strontium titanate nanotubes had a mass content of 10%.

[0071] Using the method of Example 3, the masterbatch prepared above was mixed with terpolymer polypropylene (FS5612, TPC, Singapore). Furthermore, corresponding additives used in conventional BOPP film production, such as lubricants, anti-sticking agents, and antioxidants, were added (accounting for 2% of the total weight of the final film). The mixture was extruded and granulated using a twin-screw extruder to produce plastic rice with modified strontium titanate nanotube contents of 0.05%, 0.1%, 0.2%, 0.5%, 1.0%, 2.0%, 3.0%, 4.5%, 6.0%, and 7.5%, respectively. The resulting plastic rice was then formed into films using the same process as in Example 3 and tested. The results are shown in Table 2.

[0072] The results show that: (1) the mechanical properties of BOPP film first increase and then decrease with the increase of modified strontium titanate nanotube content; (2) when the modified strontium titanate nanotube content exceeds 0.5%, the improvement effect is significant; (3) when the modified strontium titanate nanotube content reaches 7.5%, the mechanical properties of BOPP film actually decrease, while the friction coefficient increases, the gloss decreases, and the haze increases. Taking all factors into consideration, the addition amount of modified strontium titanate nanotubes in BOPP film can be selected to be 0.1%-6.0%; preferably 0.5%-4.5%; and more preferably 0.5%-3.0%.

[0073] Table 2: Test results of BOPP films containing different contents of modified strontium titanate nanotubes

[0074]

[0075] The Japanese Olympus BX53 polarizing microscope was used to observe the BOPP film without additives (upper left) and the BOPP film with modified strontium titanate nanotubes added at 0.1% (upper right), 0.5% (lower left) and 3.0% (lower right). The results are as follows Figure 4 As shown, the unmodified BOPP film exhibits a typical spherulite black cross extinction phenomenon with larger crystal sizes. However, after adding modified strontium titanate nanotubes, the spherulites gradually disappear and develop into dendrites. The crystal size decreases with increasing addition of modified strontium titanate nanotubes, while the number increases. This suggests that the modified strontium titanate nanotubes induce the crystallization of polypropylene, forming more and smaller crystals, which may be the main reason for the improved mechanical properties and gloss of the BOPP film, as well as the reduced haze and improved transparency.

[0076] Furthermore, the crystallinity of the above samples was detected using an American Bruker-Axs D8-A25 X-ray diffractometer. The results are as follows: Figure 5 As shown in the figure, the increase in the intensity of the polypropylene diffraction peak indicates that the crystallinity of the obtained BOPP film increases with the increase in the addition amount of modified strontium titanate nanotubes.

[0077] In addition, the above samples were subjected to programmed heating and cooling under nitrogen atmosphere using a Netzsch DSC 204 F1 differential scanning calorimeter to characterize their melting points and crystallization temperatures. Figure 6 As shown, during the heating process, the unmodified BOPP film exhibited a melting point close to 169°C, but this gradually decreased with increasing addition of modified strontium titanate nanotubes, exhibiting multiple melting peaks. During the cooling process, the unmodified BOPP film exhibited a crystallization temperature of approximately 140°C, which gradually decreased with increasing addition of modified strontium titanate nanotubes, also exhibiting multiple crystallization peaks. These results indicate that the introduction of modified strontium titanate nanotubes lowered both the melting and crystallization temperatures of the BOPP film. It is worth noting that BOPP film, when used as a heat-sealing film, is heat-sealed by first heating it to near its melting point to entangle the polypropylene molecular chains on the two contacting film surfaces, and then cooling it to solidify this entangled molecular chain. The lower melting and crystallization temperatures of the reinforced polypropylene film measured by DSC indicate that this modified strontium titanate nanotube-reinforced BOPP film can achieve both thermal melting and molecular chain entanglement at lower temperatures, effectively achieving heat sealing at lower temperatures. Therefore, this nanomaterial-reinforced polypropylene film holds significant promise in the field of packaging films, particularly heat-sealing films.

[0078] Example 5 (Dispersion of Modified Strontium Titanate Nanotubes)

[0079] The masterbatch prepared in Example 4 was mixed with a heat-sealable polypropylene raw material of grade RP129K, and BOPP film was prepared under the same conditions. The results showed that nano-reinforced polypropylene film could be successfully prepared. The dispersion of modified strontium titanate nanotubes was observed by transmission electron microscopy. The results are as follows: Figure 7 , indicating that the modified strontium titanate nanotubes are well dispersed and almost not agglomerated.

[0080] Example 6 (Effect of Modified Strontium Titanate Nanotubes on Crystallization)

[0081] Modified strontium titanate nanotubes were prepared using the method of Example 4. The modified strontium titanate nanotubes were then mixed with ST868M maleic anhydride-grafted polypropylene using the method of Example 4 to prepare a masterbatch. BOPP films containing 0.1%, 1.0%, and 3.0% of the modified strontium titanate nanotubes in the final film material were then prepared using the method of Example 4. Testing showed that the resulting BOPP films achieved both longitudinal and transverse reinforcement, a reduced coefficient of friction, minimal gloss reduction, and reduced haze. The XRD spectra of the modified strontium titanate nanotubes and the BOPP films prepared above were then examined at low angles using a PANalytical X'PertPRO X-ray diffraction spectrometer. Figure 8As shown, the results show that: the diffraction peak intensity of modified strontium titanate nanotubes is greatly reduced and the peak position (2θ=4.2-5.1°) is improved, which means that the degree of dispersion in the BOPP film is increased; the intensity of the polypropylene crystallization peak (2θ=2.2-2.7°) increases with the increase of the content of modified strontium titanate nanotubes, indicating that the modified strontium titanate nanotubes induce polypropylene crystallization and thus improve the crystallinity.

[0082] Example 7 (Modified Strontium Titanate Nanotube Type)

[0083] Using the method of Example 1, calcium stearate was used as a surfactant modifier. Approximately 600 grams of modified strontium titanate nanotubes were produced in a 10-liter reactor. The preparation and mixing of the products were repeated, ultimately yielding approximately 1.2 kg of modified strontium titanate nanotubes. The modified strontium titanate nanotubes were mixed with maleic anhydride-grafted polypropylene (CMG9801, 1.0% grafting ratio, Shanghai Rizhisheng New Technology Development Co., Ltd.), mixed in a mixer, and then extruded and granulated in an internal mixer to produce a masterbatch. The amount of maleic anhydride-grafted polypropylene added was adjusted to produce masterbatches with modified strontium titanate nanotube contents of 1%, 3%, and 5% by weight, respectively. The resulting masterbatch particles were uniform, round, and glossy.

[0084] The method of Example 4 was used to granulate the masterbatch containing 3% by weight of calcium stearate-modified strontium titanate nanotubes, ternary copolymer polypropylene, and composite additives, and then film was formed. The results showed that the mechanical properties of the resulting BOPP films with 0.1%, 0.2%, and 0.5% by weight of modified strontium titanate nanotubes were bidirectionally enhanced.

[0085] The above description is merely a preferred embodiment of the present invention and therefore cannot be used to limit the scope of the present invention. In other words, equivalent changes and modifications made within the scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A BOPP composite film masterbatch comprising modified strontium titanate nanotubes, wherein: The modified strontium titanate nanotubes are strontium titanate nanotubes whose surfaces are covered with a surfactant.

2. The BOPP composite film masterbatch according to claim 1, wherein In the BOPP composite film masterbatch, the mass fraction of the modified strontium titanate nanotubes is 1%-25%, preferably 1%-20%, more preferably 5%-20%, and most preferably 5-10%.

3. The BOPP composite film masterbatch according to claim 1 or 2, wherein: The modified strontium titanate nanotubes are obtained by mixing strontium titanate nanotubes with a surfactant; Preferably, the modified strontium titanate nanotubes are prepared by the following method: (1) Mixing strontium titanate nanotubes with a surfactant aqueous solution; (2) The mixture obtained by mixing is filtered, washed with water, and dried to obtain modified strontium titanate nanotubes.

4. The BOPP composite film masterbatch according to claim 3, wherein The mixing is carried out under ultrasonic conditions; Preferably, the ultrasonic treatment time is 5-60 minutes, preferably 10-40 minutes, more preferably 30 minutes; Preferably, the power of the ultrasound is 50W-2000W, preferably 50W-1000W, more preferably 100W-800W, and most preferably 300W.

5. The BOPP composite film masterbatch according to any one of claims 1 to 4, wherein: The surfactant is selected from sodium stearate, calcium stearate, sodium lauryl sulfate, sodium tetradecyl sulfonate, sodium hexadecyl sulfonate, sodium dodecylbenzene sulfonate, sodium polystyrene sulfonate, or any combination thereof; Preferably, the surfactant is selected from sodium stearate, sodium lauryl sulfate, sodium tetradecyl sulfonate, sodium hexadecyl sulfonate, sodium dodecylbenzene sulfonate, sodium polystyrene sulfonate, or any combination thereof; More preferably, the surfactant is selected from sodium stearate, sodium lauryl sulfate, sodium tetradecyl sulfonate, sodium hexadecyl sulfonate, or any combination thereof.

6. The BOPP composite film masterbatch according to any one of claims 3 to 5, wherein: The method for preparing the modified strontium titanate nanotubes further has one or more technical features selected from the following (i)-(ii): (i) in the surfactant aqueous solution, the mass volume concentration of the surfactant is 0.1%-10% (w / v), preferably 0.2%-5% (w / v), for example 0.2%, 0.8%, 1%, 3% or 5% (w / v); (ii) The ratio of the mass of the strontium titanate nanotubes to the volume of the surfactant aqueous solution is 1:80 to 1:120 (g / mL), preferably 1:100 (g / mL).

7. The BOPP composite film masterbatch according to any one of claims 1 to 6, wherein: The BOPP composite film masterbatch further comprises a carrier material; Preferably, the carrier material is polypropylene; Preferably, the carrier material is maleic anhydride grafted polypropylene; Preferably, the masterbatch is obtained by mixing the modified strontium titanate nanotubes and the carrier material in a mixer and then extruding and granulating the mixture in an internal mixer.

8. A BOPP composite film, the raw materials of which comprise: the masterbatch according to any one of claims 1 to 7.

9. The BOPP composite film according to claim 8, wherein The mass fraction of the modified strontium titanate nanotubes in the BOPP composite film is 0.05%-7.5%, preferably 0.1%-6.0%, more preferably 0.5%-4.5%, further preferably 0.5%-3%, and most preferably 3%.

10. The BOPP composite film according to claim 8 or 9, wherein: The raw materials of the BOPP composite film also include main materials and additives; Preferably, the main body material is polypropylene; Preferably, the main material is terpolymer polypropylene or heat-sealable polypropylene; Preferably, the auxiliary agent comprises a slip agent, an anti-sticking agent, an antioxidant, or any combination thereof; Preferably, the mass fraction of the additive in the BOPP composite film is 1%-5%, preferably 2%; Preferably, the BOPP composite film is prepared by the following method: (1) mixing the masterbatch, the main material and the auxiliary agent, and then extruding and granulating the mixture using a twin-screw extruder to obtain plastic rice; (2) The plastic rice is subjected to extrusion casting and planar biaxial stretching processes to obtain the BOPP composite film.

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