PBAT degradable composite material for preparing film and preparation method and application of PBAT degradable composite material

Abstract

The invention relates to the technical field of thin film materials, in particular to a PBAT degradable composite material for preparing a thin film and a preparation method and application thereof. The PBAT degradation composite material is prepared from poly (butylene adipate-co-terephthalate), modified nanocellulose and a photosensitizer through melt blending, the photosensitizer is specifically added into the preparation raw materials for preparing the PBAT degradation composite material, the photosensitizer generates active oxygen under ultraviolet light by utilizing a photo-biological synergistic degradation mechanism, ester bonds in PBAT molecular chains are preferentially attacked, and the modified nanocellulose provides microorganism attachment sites to accelerate the enzymolysis process during biological composting; compared with a film without adding the photosensitizer, the tensile strength and the elongation at break of the film prepared by the invention are improved, and the tensile strength and the elongation at break after ultraviolet aging are obviously reduced, so that the degradation of the film is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thin film materials, in particular to a PBAT degradable composite material for preparing a thin film, a preparation method and application thereof. BACKGROUND

[0002] PBAT (polybutylene adipate terephthalate) is a biodegradable polyester material obtained by copolymerization of adipic acid butylene glycol and terephthalic acid butylene glycol. The flexible aliphatic chain in the molecular structure endows it with good flexibility and film-forming property. The rigid aromatic structure endows it with excellent mechanical properties. However, the degradation rate is limited by crystallinity, molecular weight and degradation environment conditions, which is difficult to match the actual application requirements. In the prior art, starch or inorganic fillers (such as calcium carbonate) are often added to regulate the degradation performance, but the following problems exist: 1. Poor compatibility between starch and PBAT, resulting in a decrease in mechanical properties. For example, CN112625304A discloses a new high-starch filled PBAT and a preparation method thereof. The new high-starch filled PBAT comprises the following raw materials: PBAT, starch gel, silane coupling agent KH550, crosslinking agent, compatibilizer, starch modifier, antioxidant, erucic acid amide, PE wax, polytetrafluoroethylene powder, nucleating agent, and nano barium sulfate. The new high-starch filled PBAT is prepared by preparing the main material, preparing the modified material, then mixing the main material, the modified material, the compatibilizer and the nano barium sulfate, heating, plasticizing, extruding, and drawing. However, the high-starch filled PBAT material has a high starch content and a strong tensile strength. However, due to the high starch content, the un-plasticized or poorly plasticized starch will agglomerate during film blowing, resulting in a large number of crystal points on the film surface. In addition, the added compatibilizers, plasticizers and other additives may precipitate during film blowing, which may also cause crystal points or roughness on the film surface.

[0003] 2. Traditional fillers (such as calcium carbonate) can only physically accelerate disintegration and cannot achieve enzymatic degradation of molecular chains. For example, CN120665405A discloses an environmentally friendly degradable modified composite material, a preparation method and application thereof. The mass percentage of each raw material is as follows: polybutylene adipate terephthalate: 18%-28%; polybutylene succinate: 10%-16%; polylactic acid: 28%-55%; natural plant fiber: 2%-5%; PBAT-PTMO block copolymer: 2%-8%; inorganic mineral filler: 5%-18%, the filler being any one or a combination of more than one of talc, calcium sulfate, calcium silicate and calcium carbonate.

[0004] However, the prior art still has the technical problems that the degradation rate and the mechanical strength are difficult to balance, and most of the PBAT composite materials can only be biodegraded by using biological composting. The dynamic randomness of the biological composting system, the heterogeneity of the material properties, the nonlinear coupling of multiple factors, and the mutual interference of the above factors make the degradation process difficult to proceed along the preset path, and finally lead to unstable degradation rate and other technical problems. SUMMARY

[0005] To solve the above technical problems, the present application provides a PBAT degradation composite material for preparing a film, which is prepared by melt blending of poly(butylene adipate-co-terephthalate) (PBAT), modified nanocellulose and photosensitizer. In terms of weight parts, the components and contents in the PBAT degradation composite material are as follows: Poly(butylene adipate-co-terephthalate) (PBAT): 88-98.9 parts by weight; Modified nanocellulose: 1-10 parts by weight; Photosensitizer: 0.1-2 parts by weight; The modified nanocellulose is obtained by modifying nanocellulose with a coupling agent; When the thickness of the film is 10 μm, the water vapor transmission rate is 351.2-364.5 g / (m 2 ·24h); wherein the water vapor transmission rate test adopts the weighing method, the temperature is 38℃, and the humidity is 90RH%; The film is subjected to a tensile test at a tensile rate of 500 mm / min, and the transverse tensile strength is 36.1-38.9 Mpa, the longitudinal tensile strength is 40.3-43.6 Mpa, the transverse elongation at break is 425.3-430.2%, and the longitudinal elongation at break is 309.0-314.2%; After ultraviolet aging, the transverse tensile strength is 18.7-21.4 Mpa, the longitudinal tensile strength is 16.2-19.5 Mpa, the transverse elongation at break is 200.6-204.3%, and the longitudinal elongation at break is 153.7-156.1%; Wherein, the ultraviolet aging condition is: ultraviolet QUV accelerated test, UVA-340 lamp tube, 0.51 W / m²@340nm, irradiation for 100h.

[0006] Further, the weight ratio of the modified nanocellulose to the photosensitizer is preferably (5-10):1.

[0007] Further, the polybutylene adipate-co-terephthalate (PBAT) has a melt index of 3-5 g / 10 min at 190℃ under a pressure of 2.16 kg.

[0008] Further, the polybutylene adipate-co-terephthalate (PBAT) has a weight average molecular weight of 80000-90000 Da.

[0009] Further, the polybutylene adipate-co-terephthalate (PBAT) has a weight average molecular weight of 80000-90000 Da.

[0010] Further, the photosensitizer is a benzophenone compound.

[0011] Further, the photosensitizer includes but is not limited to 2-hydroxy-4-methoxybenzophenone.

[0012] Further, the nanocellulose has a diameter of 10-50 nm.

[0013] Further, the coupling agent contains amino groups (-NH2), ethoxy groups (-OC2H5) and silicon-oxygen bonds.

[0014] Further, the coupling agent is a silane coupling agent.

[0015] Further, the silane coupling agent is preferably γ-aminopropyl triethoxysilane, model number KH550.

[0016] The present application provides a preparation method of the above-mentioned PBAT degradation composite material, comprising the following steps: Step 1, preparing modified nanocellulose: dispersing nanocellulose (CNF) in an organic solvent, adding a coupling agent, and obtaining modified nanocellulose after ultrasonic treatment and drying treatment; Further, the organic solvent is an alcohol solvent.

[0017] Further, the organic solvent is preferably ethanol.

[0018] Further, the mass content of the nanocellulose in the organic solvent is 3-7%.

[0019] Further, the mass content of the nanocellulose in the organic solvent is preferably 5%.

[0020] Further, the mass of the coupling agent is 1-6% of the mass of the nanocellulose.

[0021] Further, the mass of the coupling agent is preferably 3% of the mass of the nanocellulose.

[0022] Further, the temperature of the ultrasonic is 60-70℃, the time is 1-1.5h, and the power is 300-400W.

[0023] Further, the temperature of the drying is 60-70℃, and the time is 6-8h.

[0024] Step 2, preparing the premix: the modified nanocellulose and photosensitizer are premixed in a high-speed mixer to obtain a premix.

[0025] Further, the rotation speed during the premixing is 300-400r / min, the temperature is 20-30℃, and the time is 3-5min.

[0026] Step 3, preparing the PBAT degradation composite material: the polybutylene adipate terephthalate (PBAT) is fed into the twin-screw extruder through the main feeder connected to the first zone of the twin-screw extruder, and the premix prepared in step 2 is fed into the twin-screw extruder through the side feeder connected to the fourth zone of the twin-screw extruder. After extrusion by the twin-screw extruder, the PBAT degradation composite material is obtained by pelletizing and drying. Among them, the PBAT and the premix are fed into the twin-screw extruder separately to ensure uniform dispersion of the premix in the entire system.

[0027] Further, the screw rotation speed of the twin-screw extruder is 200-300 r / min, and the length-diameter ratio is 48:1.

[0028] Further, the feeding speed of the twin-screw extruder is 10-40Hz.

[0029] Further, the screw diameter of the twin-screw extruder is 30-45mm.

[0030] Further, the screw diameter of the twin-screw extruder is preferably 35mm.

[0031] Further, the screw combination of the twin-screw extruder includes a starting section, a melting section, a high-shear dispersion section, and a homogenization and exhaust section in sequence from the main feeding port to the head.

[0032] Further, the starting section is configured with six large-pitch forward conveying elements, and the nominal diameter / pitch of the large-pitch forward conveying elements is 48 / 48, i.e., the nominal diameter is 48mm and the pitch is 48mm, to realize stable conveying of the polybutylene adipate terephthalate (PBAT).

[0033] Further, the melting section includes three groups of 30° kneading blocks, three groups of medium-pitch forward elements, and two groups of 60° kneading blocks in sequence, to ensure that the material is fully melted and preliminarily mixed; wherein the nominal diameter / pitch of the medium-pitch forward elements is 32 / 32, i.e., the nominal diameter is 32mm and the pitch is 32mm.

[0034] Further, at the end of the melting section, a reverse conveying element and two first small lead positive elements are sequentially arranged to form a sealing area, and the premix is injected through a side feeder at this position; wherein the nominal diameter / lead of the reverse conveying element is 90 / 90, i.e. the nominal diameter is 90 mm and the lead is 90 mm; the nominal diameter / lead of the first small lead positive element is 24 / 24, i.e. the nominal diameter is 24 mm and the lead is 24 mm.

[0035] Further, the high-shear dispersion section sequentially includes three second small lead positive elements, four groups of 45° kneading blocks, two groups of tooth-shaped elements, and two groups of 30° kneading blocks, to provide longer residence time and stronger shearing effect, as the core dispersion zone, which can break the agglomeration of modified nanocellulose and achieve uniform distribution; the nominal diameter / lead of the second small lead positive element is 20 / 20, i.e. the nominal diameter is 20 mm and the lead is 20 mm.

[0036] Further, the homogenization and degassing section sequentially includes four large lead positive elements, one reverse conveying element, six medium lead positive elements, three groups of 90° kneading blocks, two groups of tooth-shaped elements, three first small lead positive elements, and three second small lead positive elements. The nominal diameter / lead of the large lead positive element is 48 / 48, i.e. the nominal diameter is 48 mm and the lead is 48 mm, to expand the screw channel for facilitating volatilization. The reverse conveying element is arranged behind the vacuum degassing port, and the nominal diameter / lead of the reverse conveying element is 90 / 90, i.e. the nominal diameter is 90 mm and the lead is 90 mm, to maintain sealing. The nominal diameter / lead of the medium lead positive element is 32 / 32, i.e. the nominal diameter is 32 mm and the lead is 32 mm. The nominal diameter / lead of the first small lead positive element is 24 / 24, i.e. the nominal diameter is 24 mm and the lead is 24 mm. The nominal diameter / lead of the second small lead positive element is 20 / 20, i.e. the nominal diameter is 20 mm and the lead is 20 mm, to build pressure and ensure smooth extrusion of the melt to the die head. The three groups of 90° kneading blocks, two groups of tooth-shaped elements, and three small lead positive elements are used for final homogenization and temperature equalization.

[0037] Further, the tooth-shaped element is one or more of straight-tooth elements and bevel-tooth elements.

[0038] Further, the twin-screw extruder has ten temperature zones, and the temperature of each zone is as follows: 110-120 DEG C for the first zone, 120-130 DEG C for the second zone, 130-140 DEG C for the third zone, 140-150 DEG C for the fourth zone, 150-160 DEG C for the fifth zone, 150-160 DEG C for the sixth zone, 160-170 DEG C for the seventh zone, 160-170 DEG C for the eighth zone, 160-170 DEG C for the ninth zone, and 160-170 DEG C for the tenth zone.

[0039] Further, the pelletizing is obtained by water-cooling pelletizing of the extruded melt.

[0040] Further, the drying is performed at a temperature of 60-70 DEG C for 4-5 hours.

[0041] The application further provides a film, which is prepared by stretching the PBAT degradable composite material for preparing a film.

[0042] The application further provides a degradable agricultural mulching film, which is prepared from the film or the PBAT degradable composite material for preparing a film.

[0043] The application has the following beneficial effects: 1. The PBAT degradable composite material for preparing a film is prepared by melt blending of polybutylene adipate terephthalate, modified nanocellulose and photosensitizer; when the thickness of the film is 10 microns, the water vapor transmission rate is 351.2-364.5 g / (m 2 ·24h); the tensile test of the degradable agricultural mulching film is performed at a stretching rate of 500 mm / min, the transverse tensile strength is 36.1-38.9 MPa, the longitudinal tensile strength is 40.3-43.6 MPa, the transverse elongation at break is 425.3-430.2%, and the longitudinal elongation at break is 309.0-314.2%; after ultraviolet aging, the transverse tensile strength is 18.7-21.4 MPa, the longitudinal tensile strength is 16.2-19.5 MPa, the transverse elongation at break is 200.6-204.3%, and the longitudinal elongation at break is 153.7-156.1%; 2. The nanocellulose modification technology of the application is to modify the hydroxyl group on the surface of nanocellulose by using a silane coupling agent (such as KH550) to improve the interfacial compatibility of nanocellulose with PBAT and avoid loss of mechanical properties; The core mechanism of the coupling agent modification is to build a stable "molecular bridge" between the surface of nanocellulose and PBAT; one end of the bridge is connected to the hydrophilic surface of nanocellulose through chemical reaction or strong physical action, and the other end is compatible or reacts with the hydrophobic organic system, thereby greatly improving the dispersibility and interfacial bonding force of nanocellulose in the organic phase; Meanwhile, the good interfacial bonding reduces the tiny gaps and pores between nanocellulose and PBAT, and the uniformly dispersed nanocellulose sheets / fibers set up more and more effective barriers for water vapor molecules. These factors increase the difficulty for water vapor molecules to penetrate the film, thereby reducing the water vapor permeability and improving the moisture barrier performance of the film. Furthermore, as a reinforcing phase and degradation promoter in PBAT degradation composites, nanocellulose forms hydrogen bonds with PBAT molecular chains through its surface hydroxyl groups, thereby improving mechanical properties. 3. In this invention, a photosensitizer is specifically added to the raw materials for preparing PBAT degradable composite materials. By utilizing the photo-biological synergistic degradation mechanism, the photosensitizer generates reactive oxygen species under ultraviolet light, which preferentially attack the ester bonds in the PBAT molecular chain. Meanwhile, the modified nanocellulose provides microbial attachment sites, accelerating the enzymatic hydrolysis process during biocomposting. The tensile strength and elongation at break of the film prepared by this invention are improved compared with the film without photosensitizer, and the tensile strength and elongation at break after ultraviolet aging are significantly reduced, which is more conducive to the degradation of the film. 4. The biodegradable agricultural mulch film prepared by this invention, when combined with ultraviolet irradiation during the biodegradation process, can accelerate the degradation of the mulch film, reduce the impact on subsequent crop planting, and is more likely to be widely promoted. 5. The nanocellulose used in this invention has a wide range of sources (wood, straw, etc.), has a high cost advantage, and can be rapidly degraded during the biodegradation process, reducing the impact on the environment; 6. The preparation process of the PBAT degradable composite material of the present invention is simple and has high industrialization feasibility, that is, it is compatible with existing plastic processing equipment (such as twin-screw extruders). Attached Figure Description

[0044] Figure 1 PBAT degradable composite material particles were prepared for Example 1 of the present invention; Figure 2 The thin film prepared in Example 1 of this invention. Detailed Implementation

[0045] Example 1 This embodiment provides a PBAT degradable composite material, which is prepared by melt blending poly(ethylene PBAT), modified nanocellulose, and a photosensitizer. The components and contents of the PBAT degradable composite material are as follows, by weight: Polybutylene adipate / terephthalate (PBAT): 92 parts by weight; Modified nanocellulose: 7 parts by weight; Photosensitizer: 1 part by weight.

[0046] The polybutylene adipate / terephthalate (PBAT) has a weight-average molecular weight of 86,000 Da and a melt index of 3.6 g / 10 min at 190 °C and 2.16 kg pressure. The diameter of the nanocellulose ranges from 10 to 30 nm; The coupling agent is a silane coupling agent, specifically γ-aminopropyltriethoxysilane, model KH550; The photosensitizer is 2-hydroxy-4-methoxybenzophenone; This embodiment also provides a method for preparing the above-mentioned PBAT degradable composite material, including the following steps: Step 1: Preparation of modified nanocellulose: Nanocellulose (CNF) is dispersed in anhydrous ethanol, wherein the mass content of the nanocellulose in anhydrous ethanol is 5%; A coupling agent, γ-aminopropyltriethoxysilane (model KH550), was added, and the mass of the coupling agent was 3% of the mass of the nanocellulose. Modified nanocellulose was obtained by sonication at 400W power and 60℃ for 1 hour, followed by drying at 65℃ for 6 hours. Step 2: Preparation of premix: Modified nanocellulose and photosensitizer 2-hydroxy-4-methoxybenzophenone are premixed in a high-speed mixer according to the above mass ratio. The speed of premixing is 300 r / min, the temperature is 30℃, and the time is 3 min to obtain the premix. Step 3: Preparation of PBAT degradable composite material: Polybutylene adipate (PBAT) is fed into the twin-screw extruder through the main feeder connected to Zone 1 of the twin-screw extruder. The premix prepared in Step 2 is fed into the twin-screw extruder through the side feeder connected to Zone 4 of the twin-screw extruder. After extrusion by the twin-screw extruder, the material is pelletized and dried to obtain the PBAT degradable composite material. The twin-screw extruder's screw assembly, from the main feed port to the die head, includes, in sequence, a starting section, a melting section, a high-shear dispersion section, and a homogenization and venting section. The starting section is equipped with six large-lead forward conveying elements. The nominal diameter / lead of the large-lead forward conveying elements is 48 / 48, that is, the nominal diameter is 48mm and the lead is 48mm, in order to achieve stable conveying of polybutylene adipate / terephthalate (PBAT). The melting section includes three sets of 30° kneading blocks, three sections of medium-lead positive elements, and two sets of 60° kneading blocks to ensure that the material is fully melted and initially mixed; wherein the nominal diameter / lead of the medium-lead positive element is 32 / 32, that is, the nominal diameter is 32mm and the lead is 32mm. At the end of the melting section, a reverse conveying element and two first small-lead forward elements are sequentially arranged to form a sealed area, and the premix is ​​injected here through a side feeder; wherein the nominal diameter / lead of the reverse conveying element is 90 / 90, that is, the nominal diameter is 90mm and the lead is 90mm; the nominal diameter / lead of the first small-lead forward elements is 24 / 24, that is, the nominal diameter is 24mm and the lead is 24mm. The high-shear dispersion section comprises three sections of second small-lead positive elements, four sets of 45° kneading blocks, two sets of toothed elements, and two sets of 30° kneading blocks, which provide a longer residence time and stronger shearing action. It forms the core dispersion zone, which can break up the agglomeration of modified nanocellulose and achieve uniform distribution. The nominal diameter / lead of the second small-lead positive element is 20 / 20, that is, the nominal diameter is 20 mm and the lead is 20 mm. The homogenization exhaust section includes, in sequence, four large-lead forward elements, one reverse conveying element, six medium-lead forward elements, three sets of 90° kneading blocks, two sets of toothed elements, three first small-lead forward elements, and three second small-lead forward elements; The nominal diameter / lead of the large lead positive element is 48 / 48, that is, the nominal diameter is 48mm and the lead is 48mm, which is used to expand the screw groove to facilitate volatilization. The reverse conveying element is located after the vacuum exhaust port. The nominal diameter / lead of the reverse conveying element is 90 / 90, that is, the nominal diameter is 90mm and the lead is 90mm, in order to maintain a seal. The nominal diameter / lead of the medium-lead positive element is 32 / 32, that is, the nominal diameter is 32mm and the lead is 32mm. The nominal diameter / lead of the first small-lead positive element is 24 / 24, that is, the nominal diameter is 24mm and the lead is 24mm. The nominal diameter / lead of the second small-lead positive element is 20 / 20, that is, the nominal diameter is 20mm and the lead is 20mm, which is used to build up pressure and ensure that the melt is smoothly extruded to the die head; The three sets of 90° kneading blocks, two sets of toothed elements, and three sections of small-lead positive elements are used for final homogenization and temperature equalization. The toothed element is a straight toothed element; The twin-screw extruder has ten temperature zones, with the following temperatures: Zone 1 110℃, Zone 2 120℃, Zone 3 130℃, Zone 4 150℃, Zone 5 160℃, Zone 6 160℃, Zone 7 170℃, Zone 8 170℃, Zone 9 170℃, and Zone 10 160℃. The twin-screw extruder has a screw speed of 200 r / min, a length-to-diameter ratio of 48:1, and a feeding speed of 20 Hz; the screw diameter of the twin-screw extruder is preferably 35 mm.

[0047] The pellets are obtained by water-cooling and pelletizing the extruded melt.

[0048] The drying temperature was 60℃, and the time was 5 hours, ultimately yielding the following result: Figure 1 The granular PBAT degradation composite material shown.

[0049] Example 2 This embodiment provides a PBAT degradable composite material, which is prepared by melt blending poly(ethylene PBAT), modified nanocellulose, and a photosensitizer. The components and contents of the PBAT degradable composite material are as follows, by weight: Polybutylene adipate / terephthalate (PBAT): 88 parts by weight; Modified nanocellulose: 10 parts by weight; Photosensitizer: 2 parts by weight.

[0050] The polybutylene adipate / terephthalate (PBAT) has a weight-average molecular weight of 80,000 Da and a melt index of 3 g / 10 min at 190 °C and 2.16 kg pressure. The diameter of the nanocellulose ranges from 20 to 40 nm; The coupling agent is a silane coupling agent, specifically γ-aminopropyltriethoxysilane, model KH550; The photosensitizer is 2-hydroxy-4-methoxybenzophenone; This embodiment also provides a method for preparing the above-mentioned PBAT degradable composite material for preparing thin films, comprising the following steps: Step 1: Preparation of modified nanocellulose: Nanocellulose (CNF) is dispersed in anhydrous ethanol, wherein the mass content of the nanocellulose in anhydrous ethanol is 3%; A coupling agent, γ-aminopropyltriethoxysilane (model KH550), was added, and the mass of the coupling agent was 6% of the mass of the nanocellulose. Modified nanocellulose was obtained by sonication at 300W power and 65℃ for 1.5h, followed by drying at 60℃ for 8h. Step 2: Preparation of premix: Modified nanocellulose and photosensitizer 2-hydroxy-4-methoxybenzophenone are premixed in a high-speed mixer according to the above mass ratio. The speed of premixing is 350 r / min, the temperature is 25℃, and the time is 4 min to obtain the premix. Step 3: Preparation of PBAT degradable composite material: Polybutylene adipate (PBAT) is fed into the twin-screw extruder through the main feeder connected to Zone 1 of the twin-screw extruder. The premix prepared in Step 2 is fed into the twin-screw extruder through the side feeder connected to Zone 4 of the twin-screw extruder. After extrusion by the twin-screw extruder, the material is pelletized and dried to obtain the PBAT degradable composite material. The twin-screw extruder's screw assembly, from the main feed port to the die head, includes, in sequence, a starting section, a melting section, a high-shear dispersion section, and a homogenization and venting section. The starting section is equipped with six large-lead forward conveying elements. The nominal diameter / lead of the large-lead forward conveying elements is 48 / 48, that is, the nominal diameter is 48mm and the lead is 48mm, in order to achieve stable conveying of polybutylene adipate / terephthalate (PBAT). The melting section includes three sets of 30° kneading blocks, three sections of medium-lead positive elements, and two sets of 60° kneading blocks to ensure that the material is fully melted and initially mixed; wherein the nominal diameter / lead of the medium-lead positive element is 32 / 32, that is, the nominal diameter is 32mm and the lead is 32mm. At the end of the melting section, a reverse conveying element and two first small-lead forward elements are sequentially arranged to form a sealed area, and the premix is ​​injected here through a side feeder; wherein the nominal diameter / lead of the reverse conveying element is 90 / 90, that is, the nominal diameter is 90mm and the lead is 90mm; the nominal diameter / lead of the first small-lead forward elements is 24 / 24, that is, the nominal diameter is 24mm and the lead is 24mm. The high-shear dispersion section comprises three sections of second small-lead positive elements, four sets of 45° kneading blocks, two sets of toothed elements, and two sets of 30° kneading blocks, which provide a longer residence time and stronger shearing action. It forms the core dispersion zone, which can break up the agglomeration of modified nanocellulose and achieve uniform distribution. The nominal diameter / lead of the second small-lead positive element is 20 / 20, that is, the nominal diameter is 20 mm and the lead is 20 mm. The homogenization exhaust section includes, in sequence, four large-lead forward elements, one reverse conveying element, six medium-lead forward elements, three sets of 90° kneading blocks, two sets of toothed elements, three first small-lead forward elements, and three second small-lead forward elements; The nominal diameter / lead of the large lead positive element is 48 / 48, that is, the nominal diameter is 48mm and the lead is 48mm, which is used to expand the screw groove to facilitate volatilization. The reverse conveying element is located after the vacuum exhaust port. The nominal diameter / lead of the reverse conveying element is 90 / 90, that is, the nominal diameter is 90mm and the lead is 90mm, in order to maintain a seal. The nominal diameter / lead of the medium-lead positive element is 32 / 32, that is, the nominal diameter is 32mm and the lead is 32mm. The nominal diameter / lead of the first small-lead positive element is 24 / 24, that is, the nominal diameter is 24mm and the lead is 24mm. The nominal diameter / lead of the second small-lead positive element is 20 / 20, that is, the nominal diameter is 20mm and the lead is 20mm, which is used to build up pressure and ensure that the melt is smoothly extruded to the die head; The three sets of 90° kneading blocks, two sets of toothed elements, and three sections of small-lead positive elements are used for final homogenization and temperature equalization. The toothed element is a straight toothed element; The twin-screw extruder has ten temperature zones, with the following temperatures: Zone 1 120℃, Zone 2 130℃, Zone 3 140℃, Zone 4 140℃, Zone 5 150℃, Zone 6 150℃, Zone 7 160℃, Zone 8 160℃, Zone 9 160℃, and Zone 10 160℃. The twin-screw extruder has a screw speed of 250 r / min, a length-to-diameter ratio of 48:1, and a feeding speed of 40 Hz; the screw diameter of the twin-screw extruder is preferably 30 mm.

[0051] The pellets are obtained by water-cooling and pelletizing the extruded melt.

[0052] The drying temperature was 70°C and the time was 4 hours, finally obtaining the PBAT degradable composite material.

[0053] Example 3 This embodiment provides a PBAT degradable composite material, which is prepared by melt blending poly(ethylene PBAT), modified nanocellulose, and a photosensitizer. The components and contents of the PBAT degradable composite material are as follows, by weight: Polybutylene adipate / terephthalate (PBAT): 98.9 parts by weight; Modified nanocellulose: 1 part by weight; Photosensitizer: 0.1 parts by weight.

[0054] The polybutylene adipate / terephthalate (PBAT) has a weight-average molecular weight of 90,000 Da and a melt index of 5 g / 10 min at 190 °C and 2.16 kg pressure. The diameter of the nanocellulose is in the range of 30-50 nm; The coupling agent is a silane coupling agent, specifically γ-aminopropyltriethoxysilane, model KH550; The photosensitizer is 2-hydroxy-4-methoxybenzophenone; This embodiment also provides a method for preparing the above-mentioned PBAT degradable composite material, including the following steps: Step 1: Preparation of modified nanocellulose: Nanocellulose (CNF) is dispersed in anhydrous ethanol, wherein the mass content of the nanocellulose in anhydrous ethanol is 7%; A coupling agent, γ-aminopropyltriethoxysilane (model KH550), was added, and the mass of the coupling agent was 1% of the mass of the nanocellulose. Modified nanocellulose was obtained by sonication at 350W power and 70℃ for 1 hour, followed by drying at 70℃ for 7 hours. Step 2: Preparation of premix: Modified nanocellulose and photosensitizer 2-hydroxy-4-methoxybenzophenone are premixed in a high-speed mixer according to the above mass ratio. The speed of premixing is 400 r / min, the temperature is 20℃, and the time is 5 min to obtain the premix. Step 3: Preparation of PBAT degradable composite material: Polybutylene adipate (PBAT) is fed into the twin-screw extruder through the main feeder connected to Zone 1 of the twin-screw extruder. The premix prepared in Step 2 is fed into the twin-screw extruder through the side feeder connected to Zone 4 of the twin-screw extruder. After extrusion by the twin-screw extruder, the material is pelletized and dried to obtain the PBAT degradable composite material. The twin-screw extruder's screw assembly, from the main feed port to the die head, includes, in sequence, a starting section, a melting section, a high-shear dispersion section, and a homogenization and venting section. The starting section is equipped with six large-lead forward conveying elements. The nominal diameter / lead of the large-lead forward conveying elements is 48 / 48, that is, the nominal diameter is 48mm and the lead is 48mm, in order to achieve stable conveying of polybutylene adipate / terephthalate (PBAT). The melting section includes three sets of 30° kneading blocks, three sections of medium-lead positive elements, and two sets of 60° kneading blocks to ensure that the material is fully melted and initially mixed; wherein the nominal diameter / lead of the medium-lead positive element is 32 / 32, that is, the nominal diameter is 32mm and the lead is 32mm. At the end of the melting section, a reverse conveying element and two first small-lead forward elements are sequentially arranged to form a sealed area, and the premix is ​​injected here through a side feeder; wherein the nominal diameter / lead of the reverse conveying element is 90 / 90, that is, the nominal diameter is 90mm and the lead is 90mm; the nominal diameter / lead of the first small-lead forward elements is 24 / 24, that is, the nominal diameter is 24mm and the lead is 24mm. The high-shear dispersion section comprises three sections of second small-lead positive elements, four sets of 45° kneading blocks, two sets of toothed elements, and two sets of 30° kneading blocks, which provide a longer residence time and stronger shearing action. It forms the core dispersion zone, which can break up the agglomeration of modified nanocellulose and achieve uniform distribution. The nominal diameter / lead of the second small-lead positive element is 20 / 20, that is, the nominal diameter is 20 mm and the lead is 20 mm. The homogenization exhaust section includes, in sequence, four large-lead forward elements, one reverse conveying element, six medium-lead forward elements, three sets of 90° kneading blocks, two sets of toothed elements, three first small-lead forward elements, and three second small-lead forward elements; The nominal diameter / lead of the large lead positive element is 48 / 48, that is, the nominal diameter is 48mm and the lead is 48mm, which is used to expand the screw groove to facilitate volatilization. The reverse conveying element is located after the vacuum exhaust port. The nominal diameter / lead of the reverse conveying element is 90 / 90, that is, the nominal diameter is 90mm and the lead is 90mm, in order to maintain a seal. The nominal diameter / lead of the medium-lead positive element is 32 / 32, that is, the nominal diameter is 32mm and the lead is 32mm. The nominal diameter / lead of the first small-lead positive element is 24 / 24, that is, the nominal diameter is 24mm and the lead is 24mm. The nominal diameter / lead of the second small-lead positive element is 20 / 20, that is, the nominal diameter is 20mm and the lead is 20mm, which is used to build up pressure and ensure that the melt is smoothly extruded to the die head; The three sets of 90° kneading blocks, two sets of toothed elements, and three sections of small-lead positive elements are used for final homogenization and temperature equalization. The toothed element is a straight toothed element; The twin-screw extruder has ten temperature zones, with the following temperatures: Zone 1 110℃, Zone 2 130℃, Zone 3 140℃, Zone 4 150℃, Zone 5 150℃, Zone 6 160℃, Zone 7 160℃, Zone 8 160℃, Zone 9 170℃, and Zone 10 170℃. The twin-screw extruder has a screw speed of 300 r / min, a length-to-diameter ratio of 48:1, and a feeding speed of 10 Hz; the screw diameter of the twin-screw extruder is preferably 45 mm.

[0055] The pellets are obtained by water-cooling and pelletizing the extruded melt.

[0056] The drying temperature was 65°C and the time was 4 hours, finally obtaining the PBAT degradable composite material.

[0057] Comparative Example 1 This comparative example did not modify the nanocellulose compared to Example 1, but otherwise remained the same as Example 1.

[0058] Comparative Example 2 This comparative example did not contain a photosensitizer, unlike Example 1, but otherwise remained the same as Example 1.

[0059] Comparative Example 3 The comparative formulation is the same as in Example 1, except that in step 2, polybutylene adipate / terephthalate (PBAT) is prepared into a blend with modified nanocellulose and photosensitizer, and then in step 3, it is fed into the twin-screw extruder through the main feeding system connected to zone 1 of the twin-screw extruder. The rest is the same as in Example 1.

[0060] Comparative Example 4 Replace the modified nanocellulose with talc, and otherwise follow the same procedure as in Example 1.

[0061] Test case The materials prepared in the above embodiments and comparative examples were blown into films with a thickness of 10 micrometers. Tensile testing was then performed at a stretching rate of 500 mm / min. Accelerated UV (QUV) testing was conducted using a UVA-340 lamp at 0.51 W / m²@340 nm for 100 h. Water vapor transmission was measured using a gravimetric method at 38°C and 90% RH. The test results are listed in Table 1. Figure 2 As shown, this is the thin film prepared in Example 1.

[0062] Table 1 Test data for the examples and comparative examples

[0063] As can be seen from the data in Table 1, compared with Example 1, Comparative Example 1, which did not undergo modification treatment, had poor dispersibility, resulting in lower tensile strength and elongation at break, and higher water vapor transmission rate, significantly reducing the moisture barrier performance of the film; Comparative Example 2, which did not add photosensitizer, had higher tensile strength and elongation at break after UV aging; Comparative Example 3 had lower tensile strength, elongation at break, and water vapor transmission rate, which was also related to the uneven dispersion of the modified nanocellulose; Comparative Example 4, which replaced the modified nanocellulose with talc, had tensile strength and elongation at break that were not much different from Example 1, and was superior to Example 1 after UV aging, but its water vapor transmission rate was much higher than that of Example 1.

[0064] It should be understood that the present invention is not limited to what has been described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A PBAT degradable composite material for preparing thin films, characterized in that, The PBAT degradable composite material is prepared by melt blending poly(butylene adipate / terephthalate), modified nanocellulose, and photosensitizer. The components and contents of the PBAT degradable composite material, by weight, are as follows: Polybutylene adipate / terephthalate: 88-98.9 parts by weight; Modified nanocellulose: 1-10 parts by weight; Photosensitizer: 0.1-2 parts by weight; The modified nanocellulose is obtained by modifying nanocellulose with a coupling agent; When the thickness of the film is 10 μm, the water vapor permeability is 351.2-364.5 g / (m²). 2 •24h); The film was subjected to a tensile test at a stretching rate of 500 mm / min. Its transverse tensile strength was 36.1-38.9 MPa, its longitudinal tensile strength was 40.3-43.6 MPa, its transverse elongation at break was 425.3-430.2%, and its longitudinal elongation at break was 309.0-314.2%. After UV aging, its transverse tensile strength is 18.7-21.4 MPa, its longitudinal tensile strength is 16.2-19.5 MPa, its transverse elongation at break is 200.6-204.3%, and its longitudinal elongation at break is 153.7-156.1%.

2. The PBAT degradable composite material for preparing thin films according to claim 1, characterized in that, The poly(butylene adipate) / terephthalate has a melt index of 3-5 g / 10 min at 190 °C and 2.16 kg pressure.

3. The PBAT degradable composite material for preparing thin films according to claim 2, characterized in that, The photosensitizer is a benzophenone compound.

4. The PBAT degradable composite material for preparing thin films according to claim 1, characterized in that, The diameter of the nanocellulose is 10-50 nm.

5. A method for preparing a PBAT degradable composite material for preparing a thin film according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Preparation of modified nanocellulose: Nanocellulose is dispersed in an organic solvent, a coupling agent is added, and modified nanocellulose is obtained after ultrasonic and drying treatment. Step 2: Preparation of premix: Modified nanocellulose and photosensitizer are premixed in a high-speed mixer to obtain a premix; Step 3: Preparation of PBAT degradable composite material: Poly(butylene adipate) terephthalate (PBAT) is fed into the twin-screw extruder through the main feeder connected to zone one of the twin-screw extruder. The premix prepared in step 2 is fed into the twin-screw extruder through the side feeder connected to zone four of the twin-screw extruder. After extrusion by the twin-screw extruder, the mixture is pelletized and dried to obtain the PBAT degradable composite material.

6. The method for preparing the PBAT degradable composite material for preparing thin films according to claim 5, characterized in that, The nanocellulose has a mass content of 3-7% in the organic solvent.

7. The method for preparing the PBAT degradable composite material for preparing thin films according to claim 5, characterized in that, The premixing speed is 300-400 r / min, the temperature is 20-30℃, and the time is 3-5 min.

8. The method for preparing the PBAT degradable composite material for preparing thin films according to claim 5, characterized in that, The screw assembly of the twin-screw extruder, from the main feed port to the die head, includes the starting section, melting section, high-shear dispersion section, and homogenization and venting section in sequence.

9. A thin film, characterized in that, The film is prepared by stretching using the PBAT degradable composite material for preparing the film as described in any one of claims 1-4.

10. A biodegradable agricultural mulch film, characterized in that, The biodegradable agricultural mulch film is prepared from the film of claim 9 or the PBAT biodegradable composite material used to prepare the film as described in any one of claims 1-4.

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