Density-reducing composition containing ultrafine plant powder, mulching film containing ultrafine plant powder and preparation methods of density-reducing composition and mulching film

Abstract

The invention discloses a density-reducing composition containing ultrafine plant powder, a mulching film and a preparation method of the mulching film. According to the density-reducing composition, ultrafine plant powder is used as a core component, plant raw materials are processed through an air jet pulverization technology, the powder fineness reaches the micron level, and active terminal hydroxyl groups are reserved. After the powder is blended with biodegradable resin, a reticular cross-linked structure is formed through esterification or etherification reaction, so that the density of the material is remarkably reduced, and the mechanical property is improved. The mulching film is prepared from the composition through twin-screw extrusion granulation and a film blowing process, the density of the mulching film is greatly reduced compared with that of a traditional biodegradable material, the tensile strength and the elongation at break meet agricultural application requirements, and the biological decomposition rate meets the international environmental protection standard. The problems of high density and high cost of the full-biodegradable mulching film are solved, environmental protection and economical efficiency are achieved, and a new way is provided for efficient utilization of plant resources and popularization of degradable materials.

Description

Technical Field

[0001] The invention relates to a density-reducing composition containing ultrafine plant powder, a ground film prepared by using the density-reducing composition, and a preparation method of the density-reducing composition, belonging to the technical field of biodegradable materials. Background Art

[0002] With growing environmental awareness, environmentally friendly materials are being evaluated not only during the material's use phase but also throughout its entire lifecycle. Degradable plastics, such as those that undergo photo-oxidative degradation, ultimately form microplastics, which not only directly pollute the natural environment but also threaten the survival of wildlife and fish through ingestion. Therefore, the current focus is on the development of fully biodegradable plastics.

[0003] Therefore, in December 2023, the National Development and Reform Commission, together with the Ministry of Industry and Information Technology, the Ministry of Finance, the National Forestry and Grassland Administration and other departments, formulated the "Three-Year Action Plan for Accelerating the Development of Bamboo Instead of Plastic", encouraging the use of bamboo to replace plastic in the production of shopping bags, stationery, tableware, furniture, etc.; and encouraging the use of bamboo packaging materials and other materials in industrial production to replace corresponding plastic products.

[0004] In the Chinese patent application with application number 202310288705.7, it is disclosed that the coarser plant fiber used in injection molding is 20-100 mesh, and the plant fiber used in blown film and extruded thin-walled products is 400-800 mesh, and the plant fiber content is 25%-40%. In the Chinese patent application with application number 201710097637.0, it is disclosed that natural plant fiber powder is any one or two of rice husk powder, straw powder, peanut shell powder and cotton husk powder, and vinyl chloride (PVC) resin or a mixed resin composed of three resins of polyethylene (LDPE), linear low-density polyethylene (LLDPE) and metallocene polyethylene (mPE) to prepare ground film. The particle size of the natural plant fiber powder is greater than 800 mesh and the moisture content is ≤3%. It can be seen from both patents that in such mixed film products, the role played by plant fibers with a particle size of 800 mesh or coarser in film products is similar to that of calcium carbonate in film products, which is to enable film products to disintegrate without chemical reactions. Because the main component of plant fibers is cellulose, which contains a large number of hydroxyl groups, these hydroxyl groups form intermolecular hydrogen bonds or intramolecular hydrogen bonds, making it water-absorbent, with a moisture absorption rate of 8% to 12%, and very strong polarity; therefore, its compatibility with the resin is poor, and the interfacial adhesion is small. This results in poor dispersion in molten thermoplastics, poor fluidity, and difficulty in extrusion molding. Moreover, in addition to cellulose, plant fibers also contain substances such as hemicellulose and lignin. Lignin is a thermoplastic substance. Lignin acts as a binder in the fiber raw material, making it difficult to disperse the plant fiber raw material. On the other hand, the decomposition temperature of lignin is low, which increases the difficulty of its direct use. Moreover, if Figure 1A and Figure 1B As shown, the microstructure of plants is heterogeneous. For example, bamboo fibers and parenchyma cells differ in their anatomical structure and chemical composition. Bamboo fibers are elongated cells, approximately 3 mm in length and 20 microns in diameter (aspect ratio greater than 100), with a small or invisible lumen. In contrast, parenchyma cells are granular, less than 100 microns in length (aspect ratio close to 1), with a large lumen.

[0005] Furthermore, since the density of fully biodegradable plastics (PLA polylactic acid, PBAT, PBS polyhydroxyalkanoate, PPC carbon dioxide copolymer, PCL polycaprolactone, PHA, PHB, PHBV polyhydroxyalkanoate, etc.) is 1.23-1.26 g / cm 3 , higher than the density of ordinary PE plastic (about 0.94g / cm 3 ) or the density of PP plastic (about 0.90g / cm 3), resulting in the number and area of ​​products (such as agricultural mulch) that can be produced from the same weight of raw materials being less than that of ordinary plastics. This increases the cost of products made from fully biodegradable materials by approximately 25-35%, thereby reducing the competitive advantage of fully biodegradable plastics. Therefore, high cost is a major factor hindering the promotion of fully biodegradable plastics. Summary of the Invention

[0006] The primary technical problem to be solved by the present invention is to provide a density-reducing composition comprising ultrafine plant powder.

[0007] Another technical problem to be solved by the present invention is to provide a ground film prepared using a density-reducing composition containing ultrafine plant powder.

[0008] Another technical problem to be solved by the present invention is to provide a method for preparing a density-reducing composition containing ultrafine plant powder.

[0009] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0010] According to a first aspect of an embodiment of the present invention, there is provided a density-reducing composition comprising ultrafine plant powder, the composition comprising the following components in percentage by weight:

[0011] PBAT 65% to 85%;

[0012] 4.5% to 25% of ultrafine plant powder, wherein the ultrafine plant powder has a D50 fineness value of ≤8 microns and a moisture content of ≤6%;

[0013] Surfactant / dispersant 0.2% to 2%;

[0014] Cross-linking agent / coupling agent 0.2% to 2%;

[0015] Plant fiber plasticizer 0.5% to 2%;

[0016] PBAT / PLA plasticizer 0.2% to 1%;

[0017] Other additives 0.5%~3.5%.

[0018] According to a second aspect of an embodiment of the present invention, a ground film is provided, which is made from the above-mentioned density-reducing composition through a film blowing process, and the density of the ground film is 0.3-0.9 g / cm 3 , longitudinal tensile strength ≥14MPa, transverse tensile strength ≥14MPa, and biodegradability ≥90%.

[0019] According to a third aspect of an embodiment of the present invention, there is provided a method for preparing a density-reducing composition, comprising the following steps:

[0020] (1) After the plant raw material is roughly processed to 200-400 mesh, it is crushed by a jet mill to a D50 fineness of ≤8 microns and dried to a moisture content of ≤6% to obtain ultrafine plant powder;

[0021] (2) mixing the ultrafine plant powder with a silane coupling agent, silicon dioxide, and ethanol in a ratio of 0.5-2:0.5-3:100, and treating at 90-105° C. for 15-35 minutes to form active ultrafine plant powder;

[0022] (3) mixing the active ultrafine plant powder with PBAT, surfactant / dispersant, crosslinking agent / coupling agent, plant fiber plasticizer, PBAT / PLA plasticizer and other additives;

[0023] (4) The mixture is extruded into pellets through a twin-screw extruder at an extrusion temperature of 110°C to 165°C, a screw aspect ratio of 52 / 1 to 68 / 1, and a screw speed of 10 to 900 rpm, and pelletized to form masterbatches.

[0024] Compared with the existing technology, the ultrafine plant powder used in the present invention is active plant powder, which enables various types of ultrafine plant powders to be used in the manufacture of mulch film products, providing a new way for the industrial application of various types of ultrafine plant powders; and can reduce the density of fully biodegradable agricultural mulch films, improve product competitiveness, and is conducive to the widespread popularization and promotion of fully biodegradable products. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1A This is a high-magnification image of the thin-walled cell structure of natural bamboo powder;

[0026] Figure 1B This is a high-magnification image of the bamboo fiber structure of natural bamboo powder;

[0027] Figure 2 This is an example of a fineness distribution table of ultrafine plant powder according to the first embodiment of the present invention;

[0028] Figure 3 for Figure 2 Particle size distribution curve of ultrafine plant powder;

[0029] Figure 4 This is a schematic diagram of a density-reducing composition comprising ultrafine plant powder according to a second embodiment of the present invention;

[0030] Figure 5A and Figure 5B High-magnification images of the film product of the third embodiment of the present invention at different magnifications;

[0031] Figure 6 This is a table showing the mechanical properties test data of the ground film of Example 1 in the third embodiment of the present invention;

[0032] Figure 7 This is a test diagram of the mechanical properties of the ground film of Example 2 in the third embodiment of the present invention;

[0033] Figure 8 This is a test diagram of the mechanical properties of the ground film of Example 1 in the third embodiment of the present invention;

[0034] Figure 9 This is a graph showing the mechanical properties of the ground film of Example 4 in the third embodiment of the present invention;

[0035] Figure 10 Schematic diagram of the film blowing process according to the fourth embodiment of the present invention. DETAILED DESCRIPTION

[0036] The technical content of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Before introducing the density reducing composition comprising ultrafine plant powder of the present invention, the ultrafine plant powder will be first introduced.

[0038] First embodiment

[0039] like Figures 2 to 4 As shown, the first embodiment of the present invention provides an ultrafine plant powder, which is tested using a laser diffraction particle size analyzer (for example, the particle size analyzer model winner 3003 of Jinan Micro-Nano) in accordance with the GB / T 19077-2016 "Particle Size Analysis Laser Diffraction Method" standard with water as a dispersant, and its fineness reaches D50 of less than or equal to 8 microns, preferably D50 of less than or equal to 7 microns, and more preferably D50 of less than or equal to 6 microns or D50 of less than or equal to 5 microns. Here, D50 represents the median diameter or median particle size of the powder in the test using water as the dispersion medium, and D50 refers to the particle size value corresponding to the cumulative distribution percentage reaching 50%. In other words, D50 means that in the powder sample, 50% of the particles have a particle size exceeding this value, and another 50% of the particles have a particle size below this value. Figure 2 and Figure 3 An example of the ultrafine plant powder of the present invention is provided, wherein the D50 fineness thereof is 7.758 μm (with water as the dispersion medium).

[0040] Ultrafine plant powder is a mixture of one or more of sawdust powder, fruit shell powder, bamboo powder, straw powder, husk powder, other crops or plant stem and leaf powder. In the present embodiment, the ultrafine plant powder is obtained by rough-processing any one of bamboo chips, corn stalks, coconut shreds, coffee grounds, flax, and wheat straw to 200-400 mesh, and then processing it through a jet mill. Because these plant powders are tough and flammable, the plant powders currently obtained by ball milling in the fields of traditional Chinese medicine are generally 200-400 mesh, and can reach 800 mesh / D50 standard (approximately 15 to 18 microns) at most. Therefore, the ultrafine plant powder of the first embodiment of the present invention is processed using a jet mill. The working principle of a jet mill is as follows: After being filtered and dried, compressed air is injected at high speed into the grinding chamber through a Laval nozzle. At the intersection of multiple high-pressure airflows, the material is repeatedly collided, rubbed, and sheared, causing it to be crushed. The crushed material, driven by the fan's suction, moves with the rising airflow to the classification zone. The powerful centrifugal force generated by the high-speed rotating classification turbine separates the coarse and fine materials. Fine particles that meet the particle size requirements pass through the classification wheel and are collected in the cyclone separator and dust collector, while coarse particles descend to the grinding zone for further crushing. Therefore, jet mills avoid the combustion of plant powders and are more suitable for processing plant powders than ball mills and impact mills.

[0041] According to research, only when the fineness of the plant powder reaches 8 microns or finer, the terminal hydroxyl groups of the plant fiber will have sufficient activity to participate in the esterification or etherification chemical reaction, so that it has thermoplastic properties and can be used for the manufacture of blown film, injection molding or blister products. The finer the plant fiber, the more terminal hydroxyl groups there are, which improves accessibility. Therefore, the plant powder in the first embodiment of the present invention is a plant powder with active terminal hydroxyl groups (i.e., active plant powder), which is used to participate in the esterification or etherification chemical reaction, so that the plant powder has thermoplastic properties ( Figure 1A and Figure 1B This is a high-magnification image of the cell structure of natural bamboo powder. Figure 5A and Figure 5B (High-magnification images of thermoplastic film products processed from natural bamboo powder at different magnifications) Furthermore, this ultrafine plant powder is physically processed from natural plants and is not chemically modified or modified. This plant powder meets the environmental requirements of the "Guidelines for Single-Use Plastic Products" issued by the European Union on May 31, 2021. This ultrafine plant powder can be further processed into granules for easy transportation and storage.

[0042] The moisture content of the ultrafine plant powder in this embodiment is less than or equal to 6%, preferably less than or equal to 5%, and more preferably less than or equal to 4%. The fineness of the drying process is such that the ultrafine plant powder with a D50 of 7 microns or finer improves the accessibility and reactivity of cellulose, and also improves the dispersibility and compatibility of the ultrafine plant powder. Ultrafine plant powder of sufficient fineness causes more cellulose chain ends to be exposed, thereby relatively increasing the number of terminal hydroxyl groups and also changing the structure of the fiber surface. In this way, the accessibility of hydroxyl groups is improved, and the hydroxyl groups are more likely to undergo esterification or etherification reactions, which is conducive to the formation of a network structure (reference Figure 5A and Figure 5B ), improving the intermolecular binding force.

[0043] Second embodiment

[0044] The second embodiment of the present invention provides a density-reducing composition containing ultrafine plant powder (hereinafter referred to as density-reducing composition) prepared using the ultrafine plant powder provided by the first embodiment of the present invention.

[0045] The ultrafine plant powder (for example, bamboo fiber powder) in the first embodiment is continuously extruded and chemically reacted to become an industrial thermoplastic natural polymer material. The active groups (terminal hydroxyl groups OH) of the plant fiber (element) are used to cause an esterification / etherification reaction, thereby giving it thermoplastic properties; in combination with biodegradable oligomers, biodegradable core additives (activators, compatibilizers, plasticizers, reactants), etc., chain extension technology, cross-linking technology, grafting technology, etc. are used to form new chemical bonds between molecules to form a network structure. Therefore, the network structure increases the mechanical properties or processing properties such as tensile properties and heat sealing properties of the blown film product, meeting the performance requirements of the group standard T / GDPIA 60-2023 "Specialized materials for bamboo powder-based fully biodegradable films" issued by the Guangdong Plastics Industry Association. Similarly, the performance of injection-molded products and blister products also meet the requirements of relevant technical standards for biodegradable products, such as the group standards T / GDPIA 63-2023 "Bamboo powder-based fully biodegradable injection molding materials", T / GDPIA 62-2023 "Bamboo powder-based fully biodegradable blister molding materials", and T / GDPIA61-2023 "Bamboo powder-based fully biodegradable straw materials" issued by the Guangdong Plastics Industry Association.

[0046] The density of the density-reducing composition prepared by using active ultrafine plant powder is 0.3-0.9 g / cm 3 The best is 0.5~0.86g / cm 3 , the better one is 0.4~0.8g / cm 3The density-reducing composition is used as a raw material to produce fully biodegradable agricultural mulch film products, reducing the density of the products to a level lower than that of PE mulch films, thereby reducing costs. The melt flow rate (MI) of the density-reducing composition used for mulch films is 8-20 g / min.

[0047] 1. Example without PPC

[0048] The density-reducing composition of this embodiment is used to prepare a ground film and is prepared from raw materials comprising the following components in percentage by weight:

[0049] PBAT 65-85%

[0050] Ultrafine plant powder 4.5% to 25%

[0051] Surfactant / dispersant 0.2~2%

[0052] Crosslinking agent / coupling agent 0.2~2%

[0053] Plant fiber plasticizer 0.5-2%

[0054] PBAT\PLA plasticizer 0.2~1%

[0055] Other additives 0.5~3.5%.

[0056] In this embodiment, the PBAT is Blue Mountain Tunhe TH801T PBAT. PLA is Blue Mountain Tunhe THJS-8801-1 PLA. The ultrafine plant powder is one or a mixture of sawdust powder, fruit shell powder, bamboo powder, husk powder, corn stalk powder, coconut shreds powder, coffee grounds, flax powder, wheat straw powder, crop waste powder, or plant stem and leaf powder. The surfactant / dispersant is any one of polyglycerol ester and sodium dodecylbenzenesulfonate. The crosslinker / coupling agent is one of PEG-4000 polyethylene glycol, bis-25, and maleic anhydride (MAH). The plant fiber plasticizer is epoxidized soybean oil. Other additives include light stabilizers, antioxidants, etc. The plant fiber plasticizer mentioned in the present invention is a plant oil polyol, which is used to improve the dispersion of each dispersed phase and enhance toughness. Preferably, the vegetable oil polyol is one or more of castor oil polyol, soybean oil polyol, peanut oil polyol, coconut oil polyol, palm oil polyol, linseed oil polyol, cottonseed oil polyol, corn oil polyol, sunflower seed oil polyol, pine nut oil polyol, and tung oil polyol. Commercially available vegetable oil polyols can be used. Further preferably, the vegetable oil polyol is castor oil polyol or epoxidized soybean oil, which can significantly improve the toughness of the PLA / PBAT biodegradable composite material of the present invention.

[0057] The proportions of auxiliary agents such as cross-linking agents, dispersants, and surfactants can be adjusted appropriately.

[0058] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0059] Example 11 (Example 1)

[0060] PBAT 83%

[0061] Ultrafine plant powder (bamboo powder with a D50 fineness of 8 microns) 11%

[0062] Surfactant / dispersant 1%

[0063] Crosslinker / coupling agent 0.5%

[0064] Plant fiber plasticizer 1.5%

[0065] PBAT / PLA plasticizer 0.5%

[0066] Other additives 3.5%

[0067] Example 12

[0068] PBAT: 72%

[0069] Ultrafine plant powder (corn straw powder with a D50 fineness of 7 microns): 20%

[0070] Surfactant / dispersant: 2%

[0071] Cross-linking agent / coupling agent: 2%

[0072] Plant fiber plasticizer: 2%

[0073] PBAT / PLA plasticizer: 0.8%

[0074] Other additives: 1.2%

[0075] Example 13

[0076] PBAT 65%

[0077] Ultrafine plant powder (sawdust powder with a D50 fineness of 6 microns) 25%

[0078] Surfactant 2%

[0079] Crosslinker / coupling agent 2%

[0080] Plant plasticizer 2%

[0081] PBAT / PLA plasticizer 1%

[0082] Other additives 3%

[0083] Example 14 (Example 2)

[0084] PBAT 85%

[0085] Ultrafine plant powder (nut shell powder with a D50 fineness of 5 microns) 4.5%

[0086] Surfactant 2%

[0087] Crosslinker 2%

[0088] Plant plasticizer 2%

[0089] PBAT plasticizer 1%

[0090] Other additives 3.5%

[0091] 2. Example containing PPC:

[0092] The density-reducing composition of this embodiment is used to prepare a ground film and is prepared from raw materials comprising the following components in percentage by weight:

[0093] PBAT 5-20%

[0094] PPC 50-80%

[0095] Ultrafine plant powder 5% to 20%

[0096] Surfactant / dispersant 0.2~2%

[0097] Crosslinking agent / coupling agent 0.2~2%

[0098] Plant fiber plasticizer 0.5-2%

[0099] PBAT\PLA plasticizer 0.2~1%

[0100] Other additives 0.5-3%.

[0101] The PBAT mentioned above is Blue Mountain Tunhe TH801T. The PLA is Blue Mountain Tunhe THJS-8801-1. The ultrafine plant powder is one or a mixture of sawdust powder, fruit shell powder, bamboo powder, husk powder, corn stalk powder, coconut shreds powder, coffee grounds, flax powder, wheat straw powder, crop waste powder, or plant stem and leaf powder. The surfactant / dispersant is either polyglycerol ester or sodium dodecylbenzenesulfonate. The crosslinker / coupling agent is one of PEG-4000 polyethylene glycol, bis-25, or maleic anhydride (MAH). The plant fiber plasticizer is a citrate ester. The PBAT / PLA plasticizer is epoxidized soybean oil. Other additives include light stabilizers and antioxidants.

[0102] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples.

[0103] Example 21

[0104]

[0105] Example 22 (Example 3)

[0106]

[0107] Example 23

[0108]

[0109] Example 24

[0110]

[0111] 3. Embodiments containing foaming agent

[0112]

[0113] The above foaming agents are conventional foaming agents, such as inorganic foaming agents such as sodium bicarbonate. Organic foaming agents such as disulfonylhydrazide diphenyl ether (OBSH) can also be used.

[0114] Example 31 (Example 4)

[0115]

[0116] Comparative Example 1:

[0117] PBAT 79%

[0118] PPC 20

[0119] Additive 1%

[0120] The above density-reducing composition (masterbatch) was made into a completely biodegradable mulch film with a thickness of 0.012 mm using a conventional film blowing process. The density of the mulch film was tested according to GB / T1033.1-2008, and the mechanical properties were tested according to GB / T1040.3-2006. The density was used to test the performance of the mulch films of various embodiments. The results are shown in Table 1:

[0121] Table 1

[0122]

[0123]

[0124] In Example 5, the mechanism of "density reduction" of Example 1 is added as follows:

[0125] Through a large number of experiments on blending, reactive extrusion, and film blowing of ultrafine plant powders of different fineness and activity with the aforementioned biodegradable materials such as PBAT, as well as density test data of the film, it was unexpectedly discovered that:

[0126] (1) The density of the composition and film formed by blending ultrafine active plant powder with biodegradable materials such as PBAT and reacting and extruding it is reduced from the original density of 1.23g / cm3 of PBAT and other materials to 0.9g / cm3 or even lower, and the film density reduction rate is about 28%;

[0127] (2) The density of the composition and film formed by blending and reactively extruding ultrafine active plant powders with insufficient fineness with biodegradable materials such as PBAT increased from the original density of 1.23 g / cm3 of PBAT and other materials to 1.26-1.3 g / cm3 or even higher, with an increase rate of about 5% in film density;

[0128] (3) The density of the composition and its film formed by blending and reactive extrusion of 8-5 micron ultrafine active plant powder with biodegradable materials such as PBAT is increased from the original density of PBAT and other materials of 1.23-1.26 g / cm 3 , but will increase to 1.3-1.4g / cm 3 Even higher, the film density increase rate is about 5-15%;

[0129] At the same time, the surfactant in this scheme provides interfacial compatibility of the ultrafine active plant powder in the molten state of biodegradable materials such as PBAT; the dispersant provides uniform dispersion of the ultrafine active plant powder in the molten state of biodegradable materials such as PBAT; the cross-linking agent and coupling agent provide a network-like, interwoven three-dimensional cross-linked structure formed between the ultrafine active plant powder and biodegradable materials such as PBAT in the molten state, providing pore space for reducing the density of the composition.

[0130] (4) In the embodiment in which a foaming agent is added, the foaming agent is a foaming agent that has been ultra-finely ground and has a fineness of 5000 mesh or more, which can be evenly dispersed in the resin composition system and cooperate with biodegradable materials such as PBAT to produce micro-foaming; at the same time, under the action of cross-linking agents and coupling agents, the biodegradable materials such as PBAT can provide their melt strength in the molten state and maintain a continuous closed-cell foam, thereby significantly reducing the density of the resin composition and film.

[0131] The reasons for this phenomenon are:

[0132] (1) The density of the composition and film formed by blending and reactive extrusion of 8-5 micron ultrafine active plant powder with biodegradable materials such as PBAT is greatly reduced because the microscopic pore structure of the ultrafine plant powder within this fineness range is not destroyed, resulting in a significant effect of reducing the density of the composition and film.

[0133] At the same time, by regulating the interfacial compatibility differences between plant fiber powder (polar or non-polar) and PBAT (medium polarity), the polar repulsion between the two is utilized to prevent the molten PBAT from completely infiltrating the pores and network structure of the plant powder. This forms a continuous and stable pore between ultra-fine plant fibers, and a microscopic morphology wrapped by PBAT resin.

[0134] (2) The density of the composition and film formed by blending and reactive extrusion of ultrafine active plant powder with insufficient fineness with biodegradable materials such as PBAT did not change significantly or increased slightly. This is because the microstructure of the ultrafine plant powder within this fineness range has a relatively rough surface and large fiber diameter voids, which causes the resin such as PBAT to enter the pores or loose structure in the molten state, and the density of the reduced density composition and film thereby changes significantly or increases slightly.

[0135] (3) When ultrafine active plant powder is blended with biodegradable materials such as PBAT and reacted and extruded to form the reduced density composition and its film, the density will increase to 1.3-1.4 g / cm3 or even higher. This is because the finer plant powder destroys its pore structure, loose structure and cell wall density; the relative density of plant powder is the bulk density including the pore structure and loose fiber structure; and the absolute density of plant powder is the cell wall density after removing the pore structure and loose fiber structure, and the cell wall density of plants is 1.4-1.6 g / cm3, resulting in the higher the fineness of the plant powder filled into the PBAT resin, the higher the density of the composition and film.

[0136] Third embodiment

[0137] The low-density ground film prepared based on the density-reducing raw material of the second embodiment has a density of 0.3-1.1 g / cm 3 , the better one is 0.3~1.0g / cm 3 , the better one is 0.3~0.9g / cm 3 The best is 0.5~0.8g / cm 3 Furthermore, the tensile strength can meet the mechanical performance requirements of GB / T35795-2017. In other words, the mechanical properties are not affected by the reduction in density. This is because the network structure formed between the cellulose fibers enhances the mechanical properties. Figures 6 to 10Provided are the ground film detection data and tensile curve graphs of Example 1 to Example 2.

[0138] As shown in the figure, the fully biodegradable ground films of various embodiments meet the mechanical performance requirements of GB / T35795-2017, "Fully Biodegradable Agricultural Ground Covering Film." The fully biodegradable film products of the present invention achieve a biodegradability rate of 90% or higher, meeting the biodegradability requirements of the Chinese standard GB / T38082-2019, as well as the European standard EN13432 and the US standard ASTM D6400.

[0139] Fourth embodiment

[0140] This embodiment provides a method for preparing a density-reducing composition containing ultrafine plant powder.

[0141] Step 1: Dry the ultrafine plant powder and control the moisture content below 1%.

[0142] Use a jet mill to grind plant coarse powder (such as bamboo coarse powder) of 200-400 mesh into ultrafine plant powder with D50 of 8 microns (the fineness of wet method detection using water as a dispersant) or finer for standby use.

[0143] The silane coupling agent and silicon dioxide were mixed uniformly in the following proportions (parts by weight) to prepare a treatment solution:

[0144] Silane coupling agent: 0.5-2 parts

[0145] Silicon dioxide: 0.5-3 parts

[0146] Ethanol: 100 parts

[0147] Active ultrafine plant powder is obtained by uniformly mixing 5-8 micron ultrafine plant powder and treatment liquid in a high-speed mixer for 15-35 minutes, with the material temperature controlled at 90-105°C. The principle is to form a chemically bonded film layer on the surface of plant fibers, improving the interfacial bonding strength between the plant fibers and the matrix, while also introducing hydrophilic or hydrophobic groups to enhance the surface activity of the plant fibers.

[0148] Then, add a variety of additives to dry the moisture, rotate at high speed in a high-speed mixer, and achieve the drying effect when the mixer reaches 100-105°C. After the moisture content is tested and meets the use requirements, the material is discharged and sealed.

[0149] Step 2: Add all ingredients to the dried ultrafine plant powder in a high-speed mixer and mix thoroughly.

[0150] First, the dried ultrafine plant powder is treated with a dispersant in a high-speed mixer, and then the other components in the formula shown in Table 1 are added and mixed uniformly to obtain a mixture. For example, the high-speed mixer is rotated at a speed of 150 rpm or higher and the temperature is above 130 degrees Celsius, and the mixture is stirred for more than 30 minutes to ensure uniform mixing.

[0151] After being fully stirred from low speed to low-medium speed, it is fed into the feeder of the twin-screw extruder.

[0152] It should be noted that the foaming agent in Example 31 needs to be mixed with the ultrafine plant powder in advance, then left to stand for 20 minutes, and then other components are added and then fully mixed to obtain a mixture.

[0153] Step 3: Add the mixture into a twin-screw extruder for extrusion granulation, wherein the temperature of each zone of the extruder is between 110 degrees and 165 degrees.

[0154] When the mixture is added to the twin-screw extruder for extrusion and granulation, the temperature setting of zones 1-5 of the twin-screw extruder is particularly important. The best state is the molten state. The temperature of the next 10 zones decreases slowly, which allows the material to have a good chemical reaction in the screw without losing its original physical properties.

[0155] Reactive extrusion process conditions:

[0156] Zone 1: 110C°; Zone 2: 155C°; Zone 3: 165C°; Zone 4: 165C°; Zone 5: 160C°; Zone 6: 150C°; Zone 7: 145C°; Zone 8: 135C°; Zone 9: 125C°; Zone 10: 115C°; Zone 11: 115C°; Zone 12: 115C°; Zone 13: 115C°; Zone 14: 115C°; Zone 15: 115C°.

[0157] Such a temperature setting can cause the hydroxyl groups of cellulose in the ultrafine plant powder to undergo esterification or etherification to form a network structure, while also reducing the density.

[0158] Here, the twin-screw extruder used is a large length-to-diameter ratio, co-rotating twin-screw extruder with an L / D ratio ranging from 52 / 1 to 68 / 1, to provide a sufficient reaction zone for the density-reduced composition (resin). The screw speed is 10 to 900 rpm, providing the digital composition with a sufficient shear rate at a high speed, so that the material is crushed and reacted more fully.

[0159] Step 4: pelletizing to form particles, which are used as a density-reducing composition for preparing film products.

[0160] After being extruded from the twin-screw extruder, the pellets are cooled by a high-pressure circulating water pipe, then enter a centrifugal dehydrator to remove moisture, and are then pelletized and packaged.

[0161] The density-reduced composition obtained in the previous steps is extruded using conventional twin-screw extruders to produce a mulch film masterbatch. This mulch film masterbatch is then blown in a film blowing machine to produce a mulch film. This mulch film meets the density and performance parameters described in the second or third embodiment.

[0162] Table 2 Parameters of film blowing machine for preparing mulch film from mulch film masterbatch

[0163]

[0164]

[0165] The pressure inside the die is required to ensure that the tube film opens quickly after coming out of the die. Figure 10 As shown, the left image is correct, while the right image is incorrect. This is because the blow-up ratio in the right image is insufficient, which seriously affects density and physical properties. The low-density ground film masterbatch (model PFM-LDAF) produced in the same batch of the present invention has a density of 0.43 g / cm³ when blown using the method shown in the left image, while using the method shown in the right image, the density is 0.61-0.7 g / cm³, or even higher.

[0166] Because the density of PBAT is 1.2-1.3g / cm 3 , bamboo fiber density is about 1.4g / cm 3 , the density of inorganic filler is as high as 2.2-2.8g / cm 3 The density of conventional biodegradable film products obtained from these components is 1.24 g / cm 3 However, based on the low-density biodegradable film products obtained by the present invention, the density of conventional biodegradable film products is increased from 1.24 g / cm 3 and above to 0.3~0.9g / cm 3 , resulting in a material cost reduction of 73% for the membrane products of the present invention, with a minimum reduction of 24%, representing significant economic benefits. It should be noted that when density measurements are performed according to the GB / T 1033 technical standard, a non-polar liquid that is insoluble in water and does not interact with plant fibers (no physical or chemical adsorption) is used instead of water to ensure accurate data, as plant fibers absorb water.

[0167] It should be noted that the above-mentioned multiple embodiments are only examples, and the technical solutions of the various embodiments can be combined, and the order of the steps can be changed, all within the scope of protection of this patent.

[0168] The density-reducing composition and ground film containing ultrafine plant powders and their preparation methods provided herein are described in detail above. For those skilled in the art, any obvious modification thereof without departing from the essence of the present invention would constitute an infringement of the patent rights of the present invention and would incur corresponding legal liability.

Claims

1. A density-reducing composition comprising ultrafine plant powder, characterized in that It is composed of the following components in percentage by weight: PBAT 65% to 85%; 4.5% to 25% of ultrafine plant powder, wherein the ultrafine plant powder has a D50 fineness value of ≤8 microns and a moisture content of ≤6%; Surfactant / dispersant 0.2% to 2%; Cross-linking agent / coupling agent 0.2% to 2%; Plant fiber plasticizer 0.5% to 2%; PBAT / PLA plasticizer 0.2% to 1%; Other additives 0.5%~3.5%.

2. The density reducing composition according to claim 1, wherein The ultrafine plant powder is selected from one or more mixtures of bamboo powder, sawdust powder, fruit shell powder, straw powder, chaff shell powder, coconut shreds powder, coffee grounds, flax powder, and wheat straw powder, and the plant powder is not chemically modified.

3. The density reducing composition according to claim 1, wherein The density of the density-reducing composition is 0.3 to 0.9 g / cm 3 , the melt flow rate (MI) is 8 to 20 g / min, and the crosslinking agent / coupling agent is one of polyethylene glycol, bis-25 or maleic anhydride.

4. The density reducing composition according to claim 1, wherein The plant fiber plasticizer is castor oil polyol or epoxidized soybean oil, and the surfactant / dispersant is polyglycerol ester or sodium dodecylbenzene sulfonate.

5. A ground film, characterized in that The density-reducing composition according to any one of claims 1 to 4 is prepared by a film blowing process, wherein the density of the film is 0.3 to 0.9 g / cm 3 , longitudinal tensile strength ≥14MPa, transverse tensile strength ≥14MPa, and biodegradability ≥90%.

6. The ground film according to claim 5, characterized in that The longitudinal elongation at break of the ground film is ≥110%, and the transverse elongation is ≥105%.

7. A method for preparing the density-reducing composition according to any one of claims 1 to 4, characterized in that The following steps are involved: (1) After the plant raw material is roughly processed to 200-400 mesh, it is crushed by a jet mill to a D50 fineness of ≤8 microns and dried to a moisture content of ≤6% to obtain ultrafine plant powder; (2) mixing the ultrafine plant powder with a silane coupling agent, silicon dioxide, and ethanol in a ratio of 0.5-2:0.5-3:100, and treating at 90-105° C. for 15-35 minutes to form active ultrafine plant powder; (3) mixing the active ultrafine plant powder with PBAT, surfactant / dispersant, crosslinking agent / coupling agent, plant fiber plasticizer, PBAT / PLA plasticizer and other additives; (4) The mixture is extruded into pellets through a twin-screw extruder at an extrusion temperature of 110°C to 165°C, a screw aspect ratio of 52 / 1 to 68 / 1, and a screw speed of 10 to 900 rpm, and pelletized to form masterbatches.

8. The preparation method according to claim 7, wherein In step (4), the zone temperatures of the twin-screw extruder are set to: 110°C for zone 1, 155°C for zone 2, 165°C for zone 3, 165°C for zone 4, and 160°C for zone 5, and the temperatures of the subsequent zones are gradually reduced to 115°C.

9. The preparation method according to claim 7, wherein The film blowing process parameters include: die gap ≤1.2mm, blow-up ratio 1:(4.5-6.5), pellet moisture content ≤0.21%, and the pressure inside the die must ensure that the tubular film opens quickly after the die.

10. The preparation method according to claim 7, wherein The twin-screw extruder is a co-rotating twin-screw extruder, and the ultrafine plant powder is processed by a jet mill in step (2) to avoid burning.

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