Degradable food contact material with heat-resistant antibacterial function and preparation method thereof

Abstract

The application discloses a degradable food contact material with heat-resistant and antibacterial functions and a preparation method thereof, and belongs to the technical field of biodegradable polymer materials. The application is composed of a biobased degradable resin matrix and a functionalized bamboo charcoal dispersed phase to form a composite system, and the composition is as follows in terms of weight percentage: 40-100 parts of biobased degradable resin, 0.1-25 parts of modified bamboo charcoal powder, 0.1-10 parts of biobased plasticizer, 0-2 parts of chain extender, 0-1 part of antioxidant, and 0-0.5 part of lubricant. The application selects a specific proportion of biobased degradable resin, and cooperatively uses surface modified bamboo charcoal powder and a specific biobased plasticizer, so that the heat-resistant performance of the food contact material is significantly improved without damaging the biobased controllable degradation characteristics of the material, the food contact material can resist a high-temperature environment above 80 DEG C, good processing fluidity, flexibility and mechanical strength are ensured, and the application is completely suitable for industrialized continuous production.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable polymer materials technology, specifically relating to a biodegradable food contact material with heat-resistant and antibacterial functions and its preparation method. Background Technology

[0002] Traditional petroleum-based single-use plastic products, especially various food contact materials, are gradually being phased out. Developing environmentally friendly, high-performance biodegradable food contact materials has become a core trend in the industry.

[0003] Currently, the variety of bio-based biodegradable resins is increasingly rich, including polylactic acid (PLA), polybutylene adipate / terephthalate (PAT), polyhydroxyalkanoates (PHA), polybutylene succinate (PBS), and starch-based composites. Among these, PLA, as a representative material derived from renewable resources such as corn and sugarcane, possesses good rigidity and biocompatibility, but suffers from inherent defects such as high brittleness, low heat distortion temperature (typically below 60 °C), and slow crystallization rate. PAT has excellent flexibility and ductility, effectively toughening PLA, but it is thermodynamically incompatible with PLA, resulting in weak interfacial bonding, which easily leads to a decline in the mechanical properties of the material and further reduces the heat resistance of the blend. While PHA and PBS possess good degradation performance and flexibility, they are costly, and their heat resistance and processing stability need optimization. Starch-based composites are widely available and inexpensive, but their poor mechanical properties and insufficient water resistance limit their application range.

[0004] To improve the overall performance of bio-based biodegradable resins, the industry typically employs blending modification or the addition of fillers. Existing technologies have explored adding modified natural fibers or inorganic fillers to enhance material properties. For example, Chinese patent CN113234305A discloses the use of polyol surfactants to modify corn stalk powder as a filler in polylactic acid / polyadipate / butyl terephthalate composites to improve processability and mechanical properties. However, such methods primarily focus on improving room-temperature performance, with limited effect on improving the heat resistance and insulation of the composites. Other technical solutions utilize the addition of conventional inorganic powder fillers such as talc and calcium carbonate to improve rigidity and heat resistance. However, these fillers exhibit poor interfacial compatibility with the bio-based polymer matrix, and excessive addition can severely impair the material's flexibility and biodegradability.

[0005] In the field of plasticizers, plasticizers are needed in formulations to obtain more suitable feel and processing performance for food contact materials. Traditional phthalate plasticizers are being abandoned due to potential health and environmental risks, and the market is shifting towards bio-based plasticizers such as citrate esters. However, existing bio-based plasticizers are relatively limited in variety and their compatibility with different bio-based biodegradable resin systems varies. Some plasticizers also exhibit problems such as high migration and significant negative impacts on the heat resistance of materials. Natural bio-based derivatives such as lignin, cellulose, and chitosan are widely available and environmentally friendly, possessing the potential to serve as plasticizers. However, their application in biodegradable food contact materials has not yet been fully developed. How to achieve good compatibility with bio-based biodegradable resins through structural modification or compound optimization, while synergistically improving the overall performance of the materials, is a technical challenge that urgently needs to be solved in this field.

[0006] In addition, food contact materials need to have certain antibacterial properties to extend the shelf life of food and reduce the risk of microbial contamination. However, most existing biodegradable food contact materials lack targeted antibacterial function design. At the same time, for high-temperature food contact scenarios, the thermal insulation performance of materials is also crucial, which can effectively reduce heat transfer, improve safety and food preservation. However, existing technologies pay little attention to the thermal insulation function of biodegradable food contact materials.

[0007] Therefore, there is an urgent need in this field to develop a novel formulation and process for biodegradable food contact materials, which needs to simultaneously address the following technical issues: significantly improving the heat distortion temperature (target ≥80 ℃) and thermal insulation performance of food contact materials while ensuring complete biodegradability; effectively improving the compatibility between different bio-based biodegradable resins and between resins and fillers to ensure processing stability; achieving a balance between rigidity and toughness of materials through the precise application of diversified bio-based plasticizers; endowing materials with excellent antibacterial properties; and achieving high efficiency and continuity of the entire production process. Summary of the Invention

[0008] The technical problem to be solved by this invention is to provide a biodegradable food contact material with heat resistance and antibacterial function, which has excellent heat resistance, antibacterial and mechanical properties. The second technical problem to be solved by this invention is to provide a method for preparing a biodegradable food contact material with heat resistance and antibacterial function. This method ensures continuous and stable production throughout the entire process from composite masterbatch to final food contact material product by strictly controlling the viscosity matching of multi-component resins, the dispersion morphology of modified bamboo charcoal powder, the compounding ratio of composite plasticizers, and the precise temperature control curve from granulation to molding.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0010] A biodegradable food contact material with heat resistance and antibacterial function is composed of a bio-based biodegradable resin matrix and a functionalized bamboo charcoal dispersion phase. The composition by weight is as follows: 40-100 parts of bio-based biodegradable resin, 0.1-25 parts of modified bamboo charcoal powder, 0.1-10 parts of bio-based plasticizer, 0-2 parts of chain extender, 0-1 part of antioxidant, and 0-0.5 parts of lubricant.

[0011] Furthermore, the bio-based biodegradable resin is selected from one or more composite resins selected from polylactic acid, polybutylene adipate / terephthalate, polyhydroxy fatty acid ester, polybutylene succinate, polyhydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), polybutylene succinate-adipate, polycaprolactone, and thermoplastic starch.

[0012] Furthermore, the modification method of the modified bamboo charcoal powder is: surface modification, plasma treatment, oxidation modification, or composite modification using a bio-based modifier, or a combination of a bio-based modifier and a surface treatment method; the bio-based modifier is selected from at least one of cashew nut shell powder, ricinoleic acid, lactic acid oligomers, or rosin derivatives.

[0013] Furthermore, the modified bamboo charcoal powder has a dispersed particle size of 200-4000 mesh and a specific surface area >1000 m². 2 / g.

[0014] Furthermore, the bio-based plasticizer is selected from at least one of lignin esters, cellulose esters, chitosan esters, succinates, citrates, cashew phenol esters, and acetylated monoglycerides.

[0015] Furthermore, the method for preparing the aforementioned heat-resistant and antibacterial biodegradable food contact material is characterized by comprising the following steps:

[0016] (1) Bamboo charcoal powder is mixed with a bio-based modifier to obtain modified bamboo charcoal powder;

[0017] (2) The bio-based biodegradable resin, the modified bamboo charcoal powder obtained in step (1), the bio-based plasticizer and other additives are mixed and stirred to obtain a premix;

[0018] (3) The premix obtained in step (2) is fed into a co-rotating twin-screw extruder for melt blending, and then cooled, pelletized and dried to obtain a composite masterbatch;

[0019] (4) The composite masterbatch obtained in step (3) is molded and cooled to obtain food contact material.

[0020] Furthermore, in step (1), the mixing temperature is 80~120 ℃.

[0021] Furthermore, in step (3), the screw length-to-diameter ratio of the co-rotating twin-screw extruder is 40:1 to 48:1, the screw speed is 150 to 350 rpm, and the mixing temperature is 150 to 250 ℃.

[0022] Furthermore, in step (4), the mixing temperature is 150~200 ℃, and the cooling and shaping temperature is 10~30 ℃.

[0023] Furthermore, the tensile strength is 32~40 MPa, the elongation at break is 150%~220%, the thermal stability is ≥80 ℃, and the antibacterial rate is ≥89%.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) The present invention uses surface-modified bamboo charcoal powder as a functional filler, which has both high-efficiency heat resistance and natural antibacterial properties; after modification, it can enhance interfacial compatibility, promote heterogeneous nucleation, significantly improve resin crystallinity and heat resistance, and heat distortion temperature ≥80 ℃.

[0026] (2) The present invention innovatively combines natural bio-based derivative plasticizers to improve processing fluidity and reduce migration. It works synergistically with bamboo charcoal powder to achieve plasticization, antibacterial and heat resistance in an integrated manner, breaking through the limitations of single plasticizers.

[0027] (3) The formulation of the present invention is precisely matched with the extrusion, molding / injection molding process. Through fine parameter control, the dispersion of fillers and molding stability are improved, the processing defects and performance fluctuations are solved, and the needs of large-scale production of food contact materials are met. Attached Figure Description

[0028] Figure 1 The infrared spectrum of the heat-resistant and antibacterial biodegradable food contact material prepared in Example 1 of this application is shown. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0030] The following examples contain polylactic acid (NatureWorks (USA)), polybutylene adipate / terephthalate (Sinopec), cashew phenol (Cardolite, USA), bamboo charcoal powder (Institute of Chemical Industry of Forest Products, Chinese Academy of Forestry), tributyl acetylacetic acid (Hefei Tianjian Chemical Co., Ltd.), epoxy functional group chain extender (ADR) (BASF (Germany)), antioxidant 1010 (BASF (Germany)), stearamide (Coconut Palm Group, Malaysia), ricinoleic acid (Adani, India), polyethylene glycol (PEG600) (Dow Chemical Company, USA), antioxidant 168 (BASF (Germany)), lactic acid oligomer (Corbion, Germany), epoxidized soybean oil (Jiangsu Zhengdan Chemical Industry Co., Ltd.), triethyl citrate (Suzhou Qiubai Chemical Co., Ltd.), palm wax (Shanghai Changwei Pharmaceutical Excipients Technology Co., Ltd.), polyethylene glycol (Dow Chemical Company, USA), and acetylated monoglycerides (Dansco (China) Co., Ltd.).

[0031] Preparation method of cashew phenol maleate derivative plasticizer: Cashew phenol and maleic anhydride are added to the reaction vessel at a molar ratio of 1:1.05, and p-toluenesulfonic acid is used as catalyst (2% of the total mass). The reaction is carried out at 100℃ for 4 hours. Unreacted monomers are removed under reduced pressure to obtain a brownish-yellow viscous liquid product.

[0032] Example 1

[0033] A method for preparing a biodegradable food contact material with heat-resistant and antibacterial functions includes the following steps:

[0034] The raw materials are calculated by the following weight: 50 parts polylactic acid (MFR=8 g / 10 min); 40 parts polybutylene adipate / terephthalate (MFR=4 g / 10 min); and bamboo charcoal powder with cashew phenol surface modification (particle size 2000 mesh, specific surface area >1000 m²). 2 8 parts ( / g); 4 parts acetylsicitrin tributyl citrate; 0.8 parts epoxy functional group chain extender (ADR); 0.2 parts antioxidant 1010; 0.3 parts stearamide.

[0035] (1) Bamboo charcoal powder and 3% (relative to the filler mass) of cashew phenol were stirred and modified in a high-speed mixer at 100 °C for 15 min, and then cooled for later use.

[0036] (2) Dry polylactic acid and poly(adipate adipate / butyl terephthalate) at 75 °C for 6 h. Add the dried polylactic acid, poly(adipate adipate / butyl terephthalate), modified bamboo charcoal powder, tributyl acetyl citrate, chain extender, antioxidant, and lubricant to a high-speed mixer and mix at room temperature for 10 min.

[0037] (3) The premixed material was fed into a co-rotating twin-screw extruder with a length-to-diameter ratio of 44:1. The temperatures of each section were set as follows: Zone 1 155℃, Zone 2 165℃, Zone 3 170℃, Zone 4 175℃, Zone 5 170℃, Die head 175℃, and screw speed 280 rpm. The melt was water-cooled, pelletized, and dried to obtain the composite masterbatch.

[0038] (4) The composite masterbatch is fed into the injection molding machine. The barrel temperature is 170 ℃ in zone 1, 180 ℃ in zone 2, and 185 ℃ in zone 3. The mold temperature is 30 ℃, the pressure is 100 MPa, and the holding time is 10 s. After injection molding and cooling, the cooling temperature is 20~40 ℃, and a food contact sheet with a thickness of 2 mm is obtained.

[0039] Depend on Figure 1 It can be seen that the material exhibits characteristic peaks of bio-based resin, modified bamboo charcoal functional groups, and bio-based plasticizer at the corresponding wavenumbers, with no impurity peaks, indicating that the components have good compatibility, no obvious side reactions, and stable interfacial bonding.

[0040] Example 2

[0041] A method for preparing a biodegradable food contact material with heat-resistant and antibacterial functions includes the following steps:

[0042] The raw materials are calculated by the following weight: 45 parts polylactic acid (MFR=12 g / 10 min); 45 parts poly(butylene adipate / terephthalate) (MFR=3 g / 10 min); and bamboo charcoal powder (particle size 1250 mesh, specific surface area >1000 m²) surface-modified with ricinoleic acid. 2 10 parts of ( / g); 5 parts of polyethylene glycol (PEG600); 0.3 parts of antioxidant 168.

[0043] (1) Bamboo charcoal powder and 2% (relative to the filler mass) of ricinoleic acid were stirred and modified in a high-speed mixer at 100 °C for 15 min, and then cooled for later use.

[0044] (2) Dry polylactic acid and poly(adipate adipate / butyl terephthalate) at 75 °C for 6 h. Add the dried polylactic acid, poly(adipate adipate / butyl terephthalate), modified bamboo charcoal powder, polyethylene glycol, and antioxidant 168 to a high-speed mixer and mix at room temperature for 10 min.

[0045] (3) The premixed material was fed into a co-rotating twin-screw extruder with a length-to-diameter ratio of 44:1. The temperatures of each section were set as follows: Zone 1 155℃, Zone 2 165℃, Zone 3 170℃, Zone 4 175℃, Zone 5 170℃, Die head 175℃, and screw speed 250 rpm. The melt was water-cooled, pelletized, and dried to obtain the composite masterbatch.

[0046] (4) The composite masterbatch is fed into the injection molding machine. The barrel temperature is 175 ℃ in zone 1, 185 ℃ in zone 2, and 185 ℃ in zone 3. The mold temperature is 20 ℃ and the pressure is 15 MPa. The temperature and pressure are maintained for 10 min. After injection molding and cooling, the food contact sheet with a thickness of 2 mm is obtained at a cooling and setting temperature of 25 ℃.

[0047] Example 3

[0048] A method for preparing a biodegradable food contact material with heat-resistant and antibacterial functions includes the following steps:

[0049] Raw materials are calculated by the following weight: 55 parts polylactic acid (L-content >99%, MFR = 6 g / 10 min); 35 parts poly(butylene adipate / terephthalate); and lactic acid oligomer-modified bamboo charcoal powder (particle size 2000 mesh, specific surface area >1000 m²). 2 6 parts ( / g); 3.5 parts cashew phenol maleate derivative plasticizer; 1 part epoxidized soybean oil.

[0050] (1) Bamboo charcoal powder and 3% (relative to the filler mass) of lactic acid oligomer were stirred and modified in a high-speed mixer at 110 °C for 15 min, and then cooled for later use.

[0051] (2) Dry polylactic acid and poly(adipate adipate / butyl terephthalate) at 75 °C for 6 h. Add the dried polylactic acid, poly(adipate adipate / butyl terephthalate), modified bamboo charcoal powder, cashew phenol maleate derivative plasticizer, and epoxidized soybean oil to a high-speed mixer and mix at room temperature for 10 min.

[0052] (3) The premixed material is fed into a co-rotating twin-screw extruder with a length-to-diameter ratio of 48:1. The temperatures of each section are set as follows: Zone 1 158℃, Zone 2 165℃, Zone 3 170℃, Zone 4 175℃, Zone 5 170℃, Die head 178℃, and screw speed 300 rpm. The melt is water-cooled, pelletized, and dried to obtain composite masterbatch.

[0053] (4) The composite masterbatch is fed into the injection molding machine. The barrel temperature is 185 ℃ in zone 1, 195 ℃ in zone 2, and 195 ℃ in zone 3. The mold temperature is 25 ℃, the pressure is 100 MPa, and the holding time is 10 s. A slow cooling process is adopted to promote crystallization. The slow cooling process is: the temperature is kept constant at 110 ℃ for 30 min, and then naturally cooled to room temperature to obtain a food contact sheet with a thickness of 2 mm.

[0054] Example 4

[0055] A method for preparing a biodegradable food contact material with heat-resistant and antibacterial functions includes the following steps:

[0056] The raw materials are calculated by the following weight: 60 parts polylactic acid; 30 parts poly(adipate) / butylene terephthalate; 5 parts bamboo charcoal powder (particle size 2000 mesh, specific surface area > 1000 m² / g) modified with cashew phenol; 3 parts triethyl citrate; and 0.4 parts lubricant (palm wax: polyethylene glycol 6000 = 1:1 (mass ratio) composite lubricant).

[0057] (1) Bamboo charcoal powder and 3% (relative to the filler mass) of cashew phenol were stirred and modified in a high-speed mixer at 100 °C for 15 min, and then cooled for later use.

[0058] (2) Dry polylactic acid and poly(adipate adipate / butyl terephthalate) at 75 °C for 6 h. Add the dried polylactic acid, poly(adipate adipate / butyl terephthalate), modified bamboo charcoal powder, triethyl citrate, and lubricant to a high-speed mixer and mix at room temperature for 10 min.

[0059] (3) The premixed material was fed into a co-rotating twin-screw extruder with a length-to-diameter ratio of 44:1. The temperatures of each section were set as follows: Zone 1 160℃, Zone 2 165℃, Zone 3 170℃, Zone 4 175℃, Zone 5 175℃, Die head 180℃, and screw speed 280 rpm. The melt was water-cooled, pelletized, and dried to obtain the composite masterbatch.

[0060] (4) The composite masterbatch is fed into the injection molding machine. The barrel temperature is 170 ℃ in zone 1, 180 ℃ in zone 2, and 180 ℃ in zone 3. The mold temperature is 30 ℃, the pressure is 18 MPa, and the heat and pressure holding time is 10 s. After injection molding and cooling, the cooling and shaping temperature is 15 ℃, and a food contact sheet with a thickness of 2 mm is obtained.

[0061] Example 5

[0062] A method for preparing a biodegradable food contact material with heat-resistant and antibacterial functions includes the following steps:

[0063] The raw materials are calculated by the following weight: 48 parts polylactic acid; 42 parts poly(butylene adipate / terephthalate); and compounded bio-based modified bamboo charcoal powder (particle size 2000 mesh, specific surface area > 1000 m²). 2 12 parts ( / g); 6 parts acetylated monoglycerides.

[0064] (1) Bamboo charcoal powder and 3% (relative to the mass of filler) of compound modifier (cashew phenol: ricinoleic acid mass ratio 1:1) are stirred and modified in a high-speed mixer at 100 °C for 15 min, and then cooled for later use.

[0065] (2) Dry polylactic acid and poly(adipate adipate / butyl terephthalate) at 75 °C for 6 h. Add the dried polylactic acid, poly(adipate adipate / butyl terephthalate), modified bamboo charcoal powder and acetylated monoglyceride to a high-speed mixer and mix at room temperature for 15 min.

[0066] (3) The premixed material was fed into a co-rotating twin-screw extruder with a length-to-diameter ratio of 44:1. The temperatures of each section were set as follows: Zone 1 155℃, Zone 2 165℃, Zone 3 170℃, Zone 4 175℃, Zone 5 170℃, Die head 175℃, and screw speed 280 rpm. The melt was water-cooled, pelletized, and dried to obtain the composite masterbatch.

[0067] (4) The composite masterbatch is fed into the injection molding machine. The injection molding equipment is Haitian MAV / F PRO, high-speed injection molding, injection speed 300mm / s, barrel temperature: zone 1 185 ℃, zone 2 195 ℃, zone 3 195 ℃; mold temperature 25 ℃, pressure 100 MPa, heat and pressure holding time 10 s. After injection molding and cooling and shaping, the cooling and shaping temperature is 20~40 ℃, and a food contact sheet with a thickness of 2 mm is obtained.

[0068] Comparative Example 1

[0069] The raw materials are calculated by the following weight: 100 parts polylactic acid (PLA, NatureWorks 4032D); 2.5 parts tributyl acetylacetonate; 0.3 parts epoxy functional group chain extender (ADR); 0.3 parts antioxidant 1010; and 0.5 parts stearamide lubricant.

[0070] (1) Dry polylactic acid at 75 °C for 6 h. Add the dried polylactic acid, tributyl acetylacetate, chain extender, antioxidant and lubricant to a high-speed mixer and mix at room temperature for 10 min.

[0071] (2) The premixed material was fed into a co-rotating twin-screw extruder with a length-to-diameter ratio of 44:1. The temperatures of each section were set as follows: Zone 1 150℃, Zone 2 165℃, Zone 3 170℃, Zone 4 175℃, Zone 5 170℃, Die head 170℃, and screw speed 250 rpm. The melt was water-cooled, pelletized, and dried to obtain the composite masterbatch.

[0072] (3) The composite masterbatch is fed into the injection molding machine. The barrel temperature is 170 ℃ in zone 1, 180 ℃ in zone 2, and 185 ℃ in zone 3. The mold temperature is 30 ℃, the pressure is 100 MPa, and the holding time is 10 s. After injection molding and cooling, the cooling temperature is 20~40 ℃, and a food contact sheet with a thickness of 2 mm is obtained.

[0073] Comparative Example 2

[0074] The raw materials are calculated by the following weight: 100 parts of polybutylene adipate terephthalate (PBAT, Sinopec PBAT 1002D); 0.3 parts of antioxidant 1010.

[0075] (1) Polybutylene adipate-terephthalate was dried by blowing at 75 °C for 6 h. The dried pure polybutylene adipate-terephthalate and antioxidant were added to a high-speed mixer and mixed at room temperature for 10 min.

[0076] (2) The premixed material was fed into a co-rotating twin-screw extruder with a length-to-diameter ratio of 44:1. The temperatures of each section were set as follows: Zone 1 170℃, Zone 2 175℃, Zone 3 180℃, Zone 4 185℃, Zone 5 190℃, Die head temperature 190℃, and screw speed 250 rpm. The melt was water-cooled, pelletized, and dried to obtain the composite masterbatch.

[0077] (3) The composite masterbatch is fed into the injection molding machine. The barrel temperature is 175 ℃ in zone 1, 185 ℃ in zone 2, and 185 ℃ in zone 3. The mold temperature is 20 ℃, the pressure is 15 MPa, and the temperature and pressure are maintained for 10 min. After injection molding and cooling, the cooling and shaping temperature is 25 ℃, and a food contact sheet with a thickness of 2 mm is obtained.

[0078] The food contact sheets prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to performance tests. The results are shown in Table 1.

[0079] Tensile strength / elongation at break: GB / T 1040.1-2018 Determination of tensile properties of plastics; Thermal stability: GB / T1633-2000 Determination of heat distortion temperature, combined with static heat resistance test.

[0080] Table 1 Performance tests of food contact sheets prepared in Examples 1-5 and Comparative Examples 1-2

[0081]

[0082] As shown in Table 1, Examples 1-5 achieve a balance of rigidity and flexibility compared to Comparative Examples 1 and 2, with tensile strength of 32~40 MPa, elongation at break of 150%~220%, and thermal stability of ≥80 ℃. They overcome the defects of pure PLA being brittle and pure PBAT being soft, making them suitable for contact with high-temperature foods.

[0083] Comparative Example 1, with its melt-extruded straw exhibiting high tensile strength (up to 62 MPa) and excellent initial rigidity, demonstrates superior tensile strength due to the inherent brittleness of PLA. However, the resulting straw exhibits low notched impact strength and elongation at break (typically below 10%). Under lateral bending or localized compression, the straw wall is highly susceptible to cracking and even brittle fracture, especially at low temperatures (below 5°C) or after prolonged storage, where the cracking rate increases significantly. Furthermore, during high-speed traction, the PLA melt strength is temperature-sensitive; insufficient cooling or improper traction ratio settings can easily lead to straw breakage, necessitating extremely high stability of process parameters. The resulting PLA straws possess good gloss, making them suitable for cold beverage applications. However, their heat resistance is significantly insufficient for hot beverage use, and they are prone to softening and twisting upon contact with high-temperature liquids.

[0084] The PBAT used in Comparative Example 2, due to its flexible aliphatic-aromatic copolymer structure, exhibits flexibility similar to low-density polyethylene. The resulting plates showed extremely high elongation at break (over 500%), excellent impact resistance, and were not easily broken by bending. However, its drawbacks include low tensile strength (only 15 MPa), a relatively soft material, and insufficient rigidity. Extrusion-compression molding of plates made from pure PBAT faces certain challenges: due to its high melt flowability (high melt index) and slow cooling and crystallization rate, the plate blank is difficult to quickly solidify after leaving the molding head, easily leading to edge deformation and dents. To maintain the regular shape of the plate, it is often necessary to reduce the traction and molding speed, or to use a dedicated cooling and solidification device.

[0085] The processing temperature of PBAT is slightly higher than that of PLA, controlled between 170 and 190 ℃. However, due to its insufficient melt strength, if the tension and pressure control is slightly off during the forming and molding process of the plate, the blank is very easy to become thin, damaged or even broken, resulting in poor forming stability.

[0086] The antibacterial properties of the food contact sheets prepared in Examples 1-5 and Comparative Example 1 were tested, and the results are shown in Table 2. Antibacterial properties: GB / T 31402-2015 Determination of antibacterial properties of plastics.

[0087] Table 2. Antimicrobial performance tests of food contact boards prepared in Examples 1-5 and Comparative Examples 1-2

[0088]

[0089] As shown in Table 2, Examples 1-5 showed an inhibition rate of ≥89% against the two pathogenic bacteria, which is much higher than that of the pure resin comparison. The modified bamboo charcoal and bio-based plasticizer synergistically endowed the bamboo charcoal with excellent antibacterial properties, meeting the food contact hygiene requirements.

[0090] As can be seen from the above examples and comparative examples, this application clearly demonstrates the performance evolution path from "rigid and fragile" (pure PLA) to "soft and weak" (pure PBAT), and then to "rigid and flexible" with antistatic function achieved by PLA / PBAT / carbon powder composite, through the precise proportioning and synergy of each component, especially the key role of surface-modified bamboo charcoal powder and bio-based plasticizer. With the assistance of optimized twin-screw extruder and molding process, a fully bio-based biodegradable straw that meets the requirements for hot beverage use, has controllable performance, and can be industrially produced has been successfully prepared.

[0091] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A biodegradable food contact material with heat-resistant and antibacterial functions, characterized in that, The composite system is composed of a bio-based biodegradable resin matrix and a functionalized bamboo charcoal dispersion phase, and is composed of the following parts by weight: 40-100 parts of bio-based biodegradable resin, 0.1-25 parts of modified bamboo charcoal powder, 0.1-10 parts of bio-based plasticizer, 0-2 parts of chain extender, 0-1 part of antioxidant, and 0-0.5 parts of lubricant; The modification method of the modified bamboo charcoal powder is as follows: surface modification is performed using a bio-based modifier; the bio-based modifier is selected from at least one of cashew nut shell powder, ricinoleic acid, lactic acid oligomers, or rosin derivatives; the dispersed particle size of the modified bamboo charcoal powder is 200~4000 mesh, and the specific surface area is >1000 m². 2 / g; The bio-based plasticizer is selected from at least one of lignin esters, cellulose esters, chitosan esters, succinates, citrates, cashew phenol esters, and acetylated monoglycerides.

2. The biodegradable food contact material with heat-resistant and antibacterial functions according to claim 1, characterized in that: The bio-based biodegradable resin is selected from one or more composite resins selected from polylactic acid, polybutylene adipate / terephthalate, polyhydroxy fatty acid ester, polybutylene succinate, polyhydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), polybutylene succinate-adipate, polycaprolactone, and thermoplastic starch.

3. The method for preparing the heat-resistant and antibacterial biodegradable food contact material according to any one of claims 1 to 2, characterized in that: Includes the following steps: (1) Bamboo charcoal powder is mixed with a bio-based modifier to obtain modified bamboo charcoal powder; (2) The bio-based biodegradable resin, the modified bamboo charcoal powder obtained in step (1), the bio-based plasticizer and other additives are mixed and stirred to obtain a premix; (3) The premix obtained in step (2) is fed into a co-rotating twin-screw extruder for melt blending, and then cooled, pelletized and dried to obtain a composite masterbatch; (4) The composite masterbatch obtained in step (3) is molded and cooled to obtain food contact material.

4. The method for preparing the heat-resistant and antibacterial biodegradable food contact material according to claim 3, characterized in that: In step (1), the mixing temperature is 80~120 ℃.

5. The method for preparing the heat-resistant and antibacterial biodegradable food contact material according to claim 3, characterized in that: In step (3), the screw length-to-diameter ratio of the co-rotating twin-screw extruder is 40:1 to 48:1, the screw speed is 150 to 350 rpm, and the mixing temperature is 150 to 250 ℃.

6. The method for preparing the heat-resistant and antibacterial biodegradable food contact material according to claim 3, characterized in that: In step (4), the mixing temperature is 150~200 ℃ and the cooling and shaping temperature is 10~30 ℃.

7. The method for preparing the heat-resistant and antibacterial biodegradable food contact material according to claim 3, characterized in that: Tensile strength is 32~40 MPa, elongation at break is 150%~220%, thermal stability is ≥80 ℃, and antibacterial rate is ≥89%.

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