Degradable plastic packaging pipe and preparation method thereof

Abstract

The invention discloses a degradable plastic packaging pipe and a preparation method thereof, and relates to the technical field of packaging materials. The degradable plastic packaging pipe is at least prepared from the following raw materials in parts by weight: 50 to 60 parts of polylactic acid, 20 to 30 parts of ethylene-methyl acrylate, 10 to 15 parts of polyolefin elastomer, 3 to 5 parts of maleic anhydride grafted polylactic acid, 5 to 10 parts of dual-modified chitin nanofiber, 1 to 2 parts of nano titanium dioxide, 0.5 to 1 part of calcium stearate and 1 to 3 parts of auxiliaries. The polylactic acid, the ethylene-methyl acrylate, the polyolefin elastomer and the esterified and deacetylated dual-modified chitin nanofibers are blended, the ethylene-methyl acrylate provides flexibility, the polyolefin provides elasticity, the chitin nanofibers provide rigidity, a'rigid-tough-elastic 'triple network is achieved, and the manufactured packaging pipe has the advantages that the packaging pipe is good in mechanical property and good in mechanical property, and the service life of the packaging pipe is prolonged. The composite material has balanced rigidity and impact resistance, excellent anti-aging performance and long service life.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging materials, and particularly relates to a degradable plastic packaging tube and a preparation method thereof. Background Art

[0002] Plastics are widely used in various fields due to their advantages such as low cost and good plasticity. However, the extensive use of plastics will inevitably generate a large amount of waste, which will cause serious environmental pollution if not properly treated. In the face of "white pollution", countries around the world are trying to solve this environmental problem. At the same time, most plastic polymer materials are refined from petroleum. Therefore, the shortage of petroleum resources is another serious problem faced. If not controlled, the OECD predicts that: by 2025, the weight of plastics in the ocean will reach one-third of the weight of fish; by 2050, the weight of plastics will exceed the weight of fish. And microplastics have now been found in the snow in Antarctica. Thus, it is of great significance to develop new polymer materials that can not only meet performance requirements but also have good degradability.

[0003] The packaging industry is an important part of the national economy. The greening of packaging materials is of great significance for improving the green development level of the packaging industry and achieving sustainable development. As an environmentally friendly material, degradable packaging materials can not only reduce the dependence on fossil energy, but also have certain mechanical properties and excellent degradability, becoming an important representative of green packaging materials. The main raw materials of degradable packaging materials include polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), and polycaprolactone (PCL), etc. Among them, PLA-based degradable packaging materials made from starch-based materials through complex processes are currently the most produced and industrially mature degradable packaging materials, and have been widely used in various packaging forms such as films, packaging bags, packaging tubes, and packaging boxes. However, it has defects such as slow crystallization rate, high brittleness, and poor heat resistance, which limit the engineering applications of polylactic acid. Therefore, the existing PLA-based degradable plastic packaging tubes have defects such as high brittleness, poor heat resistance, and short service life during use, making the technology very limited in use. Summary of the Invention

[0004] The purpose of the present invention is to provide a degradable plastic packaging tube and a preparation method thereof, and solve the following technical problems: The existing PLA-based degradable plastic packaging tubes have problems of high brittleness, poor heat resistance, and short service life during use.

[0005] The purpose of the present invention can be achieved by the following technical solutions: A degradable plastic packaging tube, comprising at least the following raw materials in parts by weight: 50 - 60 parts of polylactic acid, 20 - 30 parts of ethylene - methyl acrylate, 10 - 15 parts of polyolefin elastomer, 3 - 5 parts of maleic anhydride grafted polylactic acid, 5 - 10 parts of double - modified chitin nanofibers, 1 - 2 parts of nano - titanium dioxide, 0.5 - 1 part of calcium stearate, 1 - 3 parts of additives.

[0006] As a further aspect of the present invention, the preparation method of the double - modified chitin nanofibers comprises the following steps: Mix maleic anhydride with chitin, carry out an esterification reaction at 120 °C, after washing, add it to a sodium hydroxide solution for a deacetylation reaction, after the reaction and washing, dropwise add glacial acetic acid, and perform ultrasonic fragmentation to obtain double - modified chitin nanofibers.

[0007] As a further aspect of the present invention, the particle size of the double - modified chitin nanofibers is 100 - 150 nm.

[0008] As a further aspect of the present invention, the mass ratio of chitin to maleic anhydride is 1:4 - 6.

[0009] As a further aspect of the present invention, the mass fraction of the sodium hydroxide solution is 30 - 40%, and the time of the deacetylation reaction is 6 - 10 h.

[0010] As a further aspect of the present invention, the polylactic acid is composed of L - lactic acid and D - lactic acid, and the mass ratio of L - lactic acid to D - lactic acid is 95:5 - 98:2.

[0011] As a further aspect of the present invention, the content of methyl acrylate in the ethylene - methyl acrylate copolymer is 18 - 25%.

[0012] As a further aspect of the present invention, the additives at least include one or several mixtures of heat stabilizers, flow modifiers, dispersants, light stabilizers or colorants.

[0013] A preparation method of a degradable plastic packaging tube at least comprises the following preparation steps: Ball - mill and mix the double - modified chitin nanofibers and maleic anhydride grafted polylactic acid to obtain a premix; Add the premix, polylactic acid, ethylene - methyl acrylate, polyolefin elastomer, nano - titanium dioxide, calcium stearate and additives into a twin - screw extruder, melt - blend, extrude and pelletize to obtain pellets; Inject the pellets into a hollow blow - molding machine to form a tubular blank, and blow - mold and cool - set it with compressed air to obtain a degradable plastic packaging tube.

[0014] The beneficial effects of the present invention: The present invention utilizes the blending of polylactic acid, ethylene-methyl acrylate, and polyolefin elastomer, and adds auxiliaries such as esterified and deacetylated double-modified chitin nanofibers and nano-titanium dioxide. Ethylene-methyl acrylate provides flexibility, polyolefin elastomer provides elasticity, and chitin nanofibers provide rigidity, realizing a "rigid-tough-elastic" triple network. The prepared polylactic acid composition has good physical properties and extrusion processability. The packaging pipe manufactured by continuously extruding this polylactic acid composition has balanced rigidity and impact resistance, excellent anti-aging performance, and a long service life. In the present invention, the polylactic acid is selected as a mixture of L-lactic acid and D-lactic acid. The molecular chain regularity of L-lactic acid is high, and the crystallinity is relatively high. A high L-lactic acid content endows the material with good rigidity, tensile strength, and heat resistance. A small amount of D-lactic acid disrupts the molecular chain regularity, appropriately reduces the crystallinity, improves the toughness and processing performance, and avoids excessive brittleness of polylactic acid. The degradable plastic packaging pipe provided by the present invention has the advantages of being odorless, non-toxic, and degradable, and can be widely applied in the fields of food, cosmetics, medicine, chemical industry, etc.

[0015] In the present invention, ethylene-methyl acrylate and polyolefin elastomer are added to synergistically toughen polylactic acid. Ethylene-methyl acrylate can act as a toughening agent and a compatibilizer. When the prepared degradable plastic packaging pipe is subjected to an external force, while the elastomer polyolefin elastomer serves as a stress concentrator, the compatibilizing effect of ethylene-methyl acrylate can make the polyolefin elastomer disperse more uniformly, forming a smaller "island" structure. And a larger number and more uniform polyolefin elastomers are more conducive to inducing plastic deformation of the matrix, indicating that ethylene-methyl acrylate and polyolefin elastomer can produce a synergistic effect on the toughening of polylactic acid. The dispersed phase particles of the polyolefin elastomer induce matrix yielding through deformation. Because ethylene-methyl acrylate has better compatibility with polylactic acid, on the one hand, it can more effectively plasticize the polylactic acid matrix, and on the other hand, it can improve the interfacial compatibility of polylactic acid / polyolefin elastomer, enabling the material to better disperse stress when subjected to an external force. Therefore, more energy can be absorbed when the material is damaged, thereby improving the comprehensive mechanical properties of the material.

[0016] In the present invention, chitin nanofibers are added and interpenetrated in the polylactic acid matrix, entangling with each other, enhancing the interfacial compatibility between composite components, and being beneficial to improving the mechanical properties of the material. Through the esterification modification of chitin with maleic anhydride, the ring-opening maleic anhydride forms an ester bond with the hydroxyl group on chitin, reducing the hydroxyl group, decreasing water absorption, improving the compatibility with ethylene-methyl acrylate and polyolefin elastomers, and the flexible chain segment delays brittle fracture and increases the elongation at break. Then, deacetylation reaction is carried out with sodium hydroxide solution to expose more amino groups on the chitin molecule. The amino group forms a hydrogen bond with the ester group of polylactic acid, improving the interfacial bonding strength, reducing crack propagation caused by stress concentration, inhibiting the thermal movement of molecular chains in the amorphous region, and simultaneously improving the heat resistance of polylactic acid. By the double modification of esterification and deacetylation, the present invention significantly reduces the equivalent particle size of nanofibers and promotes the improvement of fiber particle size uniformity, effectively improving the bonding strength of chitin nanofibers with polylactic acid, ethylene-methyl acrylate, and polyolefin elastomers, enhancing the dispersion stability, and the nanofibers as heterogeneous nucleating agents promote the regular arrangement of polylactic acid molecular chains and improve the crystallinity. Detailed implementation mode

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] Example 1 The preparation method of double-modified chitin nanofibers includes the following steps: 1.5 g of chitin and 7.5 g of maleic anhydride are ground in a mortar to mix them evenly. The mixture is slowly poured into a conical flask for sealing, and then placed in an oven for esterification reaction at 120 °C for 3 h. After the reaction, it is washed with anhydrous ethanol 3 - 4 times until the supernatant color is colorless after centrifugation. Then, the reaction product is washed with pure water until the pH of the supernatant is 7. The product is transferred to 150 mL of 30 wt% sodium hydroxide solution, and the reaction system is placed in a water bath at 90 °C for 6 h for deacetylation reaction. After the reaction, it is washed with pure water until the pH of the supernatant is 7. Then, glacial acetic acid is added dropwise until the pH of the system is reduced to 3. After removing the supernatant, it is diluted with pure water to a concentration of 0.5 wt% and the pH of the system is adjusted to 3 with acetic acid. Then, it is placed in an ultrasonic cell disruptor, the ultrasonic disruption power is set to 500 W, the pulse is 1 s / 1 s on / off, and ultrasonic disruption is carried out for 45 min. After freeze-drying, double-modified chitin nanofibers are obtained.

[0019] Example 2 The preparation method of double-modified chitin nanofibers includes the following steps: 1.5 g of chitin and 7.5 g of maleic anhydride were ground in a mortar to mix them evenly. The mixture was slowly poured into a conical flask and sealed. Then it was placed in an oven and subjected to an esterification reaction at 120 °C for 3 h. After the reaction, it was washed 3 - 4 times with absolute ethanol until the supernatant was colorless after centrifugation. Then the reaction product was washed with pure water until the pH of the supernatant was 7. The product was transferred to 150 mL of 35 wt% sodium hydroxide solution, and the reaction system was placed in a water bath at 90 °C for 8 h for deacetylation reaction. After the reaction, it was washed with pure water until the pH of the supernatant was 7. Then glacial acetic acid was added dropwise until the pH of the system decreased to 3. After removing the supernatant, it was diluted with pure water to a concentration of 0.5 wt% and the pH of the system was adjusted to 3 with acetic acid. Then it was placed in an ultrasonic cell disruptor, with the ultrasonic disruption power set at 500 W, the pulse at 1 s / 1 s on / off, and ultrasonic disruption was carried out for 45 min. After freeze-drying, double-modified chitin nanofibers were obtained.

[0020] Example 3 A degradable plastic packaging tube was made by the following method: 6 parts by weight of the double-modified chitin nanofibers prepared in Example 1 and 3 parts by weight of maleic anhydride-grafted polylactic acid were ball-milled and mixed to obtain a premix; The above premix, 53 parts by weight of L-lactic acid, 2 parts by weight of D-lactic acid, 25 parts by weight of ethylene-methyl acrylate 1125AC, 10 parts by mass of polyolefin elastomer Engage 8100, 2 parts by weight of nano-titanium dioxide, 0.6 part by weight of calcium stearate, and 0.4 part by weight of antioxidant 1010 were added to a twin-screw extruder, melt-blended, and extruded into pellets to obtain pellets; The above pellets were injected into a hollow blow molding machine to form a tubular blank, and after blow molding with compressed air and cooling and shaping, a degradable plastic packaging tube was obtained.

[0021] Example 4 A degradable plastic packaging tube was made by the following method: 6 parts by weight of the double-modified chitin nanofibers prepared in Example 2 and 3 parts by weight of maleic anhydride-grafted polylactic acid were ball-milled and mixed to obtain a premix; The above premix, 53 parts by weight of L-lactic acid, 2 parts by weight of D-lactic acid, 25 parts by weight of ethylene-methyl acrylate 1125AC, 10 parts by mass of polyolefin elastomer Engage 8100, 2 parts by weight of nano-titanium dioxide, 0.6 part by weight of calcium stearate, and 0.4 part by weight of antioxidant 1010 were added to a twin-screw extruder, melt-blended, and extruded into pellets to obtain pellets; The above pellets were injected into a hollow blow molding machine to form a tubular blank, and after blow molding with compressed air and cooling and shaping, a degradable plastic packaging tube was obtained.

[0022] Example 5 A degradable plastic packaging tube was made by the following method: 8 parts by weight of the double-modified chitin nanofibers prepared in Example 1 and 4 parts by weight of maleic anhydride-grafted polylactic acid were ball-milled and mixed to obtain a premix; The above premix, 55 parts by weight of L-lactic acid, 3 parts by weight of D-lactic acid, 22 parts by weight of ethylene-methyl acrylate 1125AC, 13 parts by mass of polyolefin elastomer Engage 8100, 2 parts by weight of nano-titanium dioxide, 0.6 part by weight of calcium stearate, and 0.4 part by weight of antioxidant 1010 were added to a twin-screw extruder, melt-blended, and pelletized by extrusion to obtain pellets; The above pellets were injected into a hollow blow molding machine to form a tubular blank, and then blow molded with compressed air and cooled and shaped to obtain a degradable plastic packaging tube.

[0023] Example 6 A degradable plastic packaging tube was made by the following method: 8 parts by weight of the double-modified chitin nanofibers prepared in Example 2 and 4 parts by weight of maleic anhydride-grafted polylactic acid were ball-milled and mixed to obtain a premix; The above premix, 55 parts by weight of L-lactic acid, 3 parts by weight of D-lactic acid, 22 parts by weight of ethylene-methyl acrylate 1125AC, 13 parts by mass of polyolefin elastomer Engage 8100, 2 parts by weight of nano-titanium dioxide, 0.6 part by weight of calcium stearate, and 0.4 part by weight of antioxidant 1010 were added to a twin-screw extruder, melt-blended, and pelletized by extrusion to obtain pellets; The above pellets were injected into a hollow blow molding machine to form a tubular blank, and then blow molded with compressed air and cooled and shaped to obtain a degradable plastic packaging tube.

[0024] Comparative Example 1 The preparation method of esterified chitin nanofibers includes the following steps: 1.5 g of chitin and 7.5 g of maleic anhydride were ground in a mortar to mix them evenly. The mixture was slowly poured into a conical flask and sealed, and then placed in an oven and reacted at 120 °C for 3 h. After the reaction, the esterification reaction product was immediately washed 3-4 times with absolute ethanol by centrifugation until the supernatant color after centrifugation was colorless, and then the reaction product was washed with pure water until the pH of the supernatant was 7. 1 mol / L sodium hydroxide solution was slowly added dropwise to the dispersion until the pH of the system was 11, and then the excess NaOH was washed away with pure water. The pH of the dispersion was adjusted to 7.8. Finally, the chitin dispersion was diluted with pure water to adjust the dispersion concentration to 0.5 wt%. It was placed in an ultrasonic cell disruptor, the ultrasonic disruption power was set to 500 W, the pulse was 1 s / 1 s on / off, and the esterified chitin was ultrasonically disrupted for 45 min. After freeze-drying, esterified chitin nanofibers were obtained.

[0025] Comparative Example 2 The preparation method of deacetylated chitin nanofibers includes the following steps: Weigh 2.0 g of chitin and slowly pour it into 200 mL of 35 wt% sodium hydroxide solution. Place the reaction system in a water bath at 90 °C for 6 h. After the reaction, wash the product several times with pure water by centrifugation until the pH of the supernatant is 7.0. Then, slowly add glacial acetic acid to the dispersion until the pH of the system drops to 3.0. After removing the supernatant, dilute it with pure water to a concentration of 0.5 wt% and adjust the pH of the system to 3 with acetic acid. Place it in an ultrasonic cell disruptor, set the ultrasonic disruption power to 500 W, and the pulse to 1 s / 1 s on / off. Ultrasonically disrupt the partially deacetylated chitin nanofibers for 45 min, and after freeze-drying, obtain deacetylated chitin nanofibers.

[0026] Comparative Example 3: Compared with Example 3, in Comparative Example 3, the double-modified chitin nanofibers prepared in Example 1 added in Example 3 were simply replaced with the esterified chitin nanofibers prepared in Comparative Example 1 in equal mass, and the remaining components and preparation methods were exactly the same as those in Example 3.

[0027] Comparative Example 4: Compared with Example 3, in Comparative Example 4, the double-modified chitin nanofibers prepared in Example 3 added in Example 3 were simply replaced with the deacetylated chitin nanofibers prepared in Comparative Example 2 in equal mass, and the remaining components and preparation methods were exactly the same as those in Example 3.

[0028] Comparative Example 5: Compared with Example 3, in Comparative Example 5, the polyolefin elastomer prepared in Example 1 was replaced with ethylene-methyl acrylate in equal mass, and the remaining components and preparation methods were exactly the same as those in Example 3.

[0029] Comparative Example 6: Compared with Example 3, in Comparative Example 6, the ethylene-methyl acrylate prepared in Example 1 was replaced with a polyolefin elastomer in equal mass, and the remaining components and preparation methods were exactly the same as those in Example 3.

[0030] Performance Testing Tensile Property Testing: Mold the blends obtained in Examples 3 - 6 and Comparative Examples 3 - 6 into dumbbell-shaped tensile specimens. According to the standard of GB / T 1040.1 - 2006, test them on a universal material testing machine with a gauge length of 25 mm and a tensile rate of 5 mm / min, record the tensile modulus, tensile strength, and elongation at break of each group of specimens, and take the arithmetic mean after testing at least 5 samples; the test results are shown in Table 1. Impact Property Testing: Mold the blends obtained in Examples 3 - 6 and Comparative Examples 3 - 6 into Type A notched impact specimens. According to the standard of GB / T 1043.1 - 2008, test them on a cantilever beam impact testing machine. The specimen size of the impact specimen is 80 mm (length) × 10 mm (width) × 4 mm (height), the notch depth is 2 mm, and take the arithmetic mean after testing at least 5 samples for the notched impact strength; the test results are shown in Table 1. Heat distortion temperature test: According to the standard of GB / T 1633-2000, a heat distortion and Vicat softening point temperature tester was used to measure the heat distortion temperature of the degradable plastic packaging tubes obtained in Examples 3-6 and Comparative Examples 3-6. The size of the test sample was 10.0 mm × 10.0 mm × 4.0 mm. The heat transfer medium was silicone oil, the heating rate was set at 120 °C / h, the applied load was 10 N, and the maximum deformation of the sample was 1 mm; the test results are shown in Table 1; Table 1: Statistical table of performance test data of degradable plastic packaging tubes in Examples 3-6 and Comparative Examples 3-6

[0031] As can be seen from Table 1, the degradable plastic packaging tubes prepared in Examples 3-6 of the present invention have excellent mechanical strength, and the heat resistance performance is also improved, which is suitable for degradable packaging scenarios that require high temperature resistance and high strength. In Comparative Example 3, the chitin nanofibers added were only esterified, and in Comparative Example 4, the chitin nanofibers added were only deacetylated. The heat distortion temperature of the obtained degradable plastic packaging tubes decreased, and the mechanical properties also decreased. In Comparative Example 5, polyolefin elastomer was not added, and in Comparative Example 6, ethylene-methyl acrylate was not added. The mechanical properties of the obtained degradable plastic packaging tubes decreased significantly.

[0032] In the description of this specification, the descriptions of reference terms "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0033] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A degradable plastic packaging tube, characterized in that, Comprising at least the following raw materials in parts by weight: 50 - 60 parts of polylactic acid, 20 - 30 parts of ethylene-methyl acrylate, 10 - 15 parts of polyolefin elastomer, 3 - 5 parts of maleic anhydride grafted polylactic acid, 5 - 10 parts of double-modified chitin nanofibers, 1 - 2 parts of nano-titanium dioxide, 0.5 - 1 part of calcium stearate, 1 - 3 parts of additives.

2. The degradable plastic packaging tube according to claim 1, wherein The preparation method of the double-modified chitin nanofibers comprises the following steps: Mix maleic anhydride with chitin, carry out an esterification reaction at 120 °C, after washing, add it to a sodium hydroxide solution for a deacetylation reaction, after the reaction and washing, dropwise add glacial acetic acid, and perform ultrasonic fragmentation to obtain double-modified chitin nanofibers.

3. The biodegradable plastic packaging tube according to claim 2, characterized in that, The particle size of the double-modified chitin nanofibers is 100 - 150 nm.

4. The biodegradable plastic packaging tube according to claim 2, characterized in that, The mass ratio of the chitin to the maleic anhydride is 1:4 - 6.

5. A degradable plastic packaging tube according to claim 2, characterized in that, The mass fraction of the sodium hydroxide solution is 30 - 40%, and the time of the deacetylation reaction is 6 - 10 h.

6. The biodegradable plastic packaging tube according to claim 1, characterized in that, The polylactic acid is composed of L-lactic acid and D-lactic acid, and the mass ratio of the L-lactic acid to the D-lactic acid is 95:5 - 98:

2.

7. The degradable plastic packaging tube according to claim 1, characterized in that, The content of methyl acrylate in the ethylene-methyl acrylate copolymer is 18 - 25%.

8. A degradable plastic packaging tube according to claim 1, characterized in that, The additives at least include one or several mixtures of a heat stabilizer, a flow modifier, a dispersant, a light stabilizer or a colorant.

9. A preparation method of a degradable plastic packaging tube, characterized in that, At least comprising the following preparation steps: Ball-mill and mix the double-modified chitin nanofibers and maleic anhydride grafted polylactic acid to obtain a premix; Add the premix, polylactic acid, ethylene-methyl acrylate, polyolefin elastomer, nano-titanium dioxide, calcium stearate and additives into a twin-screw extruder, melt and blend, and extrude and pelletize to obtain pellets; Inject the pellets into a hollow blow molding machine to form a tubular blank, and blow mold and cool and shape it with compressed air to obtain a degradable plastic packaging tube.

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