A method for preparing modified PHA composite material using a twin-screw extruder and its application

Abstract

The present invention discloses a method for preparing a modified PHA composite material using a twin-screw extruder and its application. The method is carried out by in-situ melt blending of polyhydroxyalkanoate PHA, polybutylene terephthalate-adipate PBAT, polyvinyl alcohol PVOH and a chain extender in a twin-screw extruder, so that a multifunctional epoxy or isocyanate chain extender reacts with the terminal groups of PHA, PBAT and PVOH molecules to form a partially cross-linked or grafted structure, thereby achieving enhanced compatibility, improved thermal stability and significant improvement in barrier properties. Experiments have shown that the modified PHA composite material obtained by the present invention has high strength, high elongation, excellent water and oxygen barrier properties and biodegradable properties, and meets the stringent requirements for mechanical properties and barrier properties in multiple fields such as food packaging, agricultural mulch and medical consumables. The preparation method of the present invention is simple and efficient, and can be used for large-scale continuous production on existing twin-screw extrusion equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of biodegradable polymer materials, and specifically to a method for preparing a modified PHA composite material using a twin-screw extruder and its application. The method is to prepare a composite material with excellent mechanical properties, barrier properties and biodegradable characteristics by in-situ melt blending of polyhydroxyalkanoate PHA, polybutylene terephthalate-adipate PBAT and polyvinyl alcohol PVOH, and modifying them with a chain extender, and is suitable for the fields of degradable food packaging, agricultural mulch, disposable tableware and consumables, and medical protective products. Background Art

[0002] As biodegradable polymer materials, polyhydroxyalkanoates (PHA), polybutylene terephthalate (PBAT) and polyvinyl alcohol (PVOH) have broad application potential in environmentally friendly packaging, agricultural covering films and medical products. However, the performance defects of these materials limit their effects when used alone, and there are technical difficulties in composite modification.

[0003] PHA is a biodegradable polymer with good biocompatibility and certain gas barrier properties due to its high crystallinity. However, it has a narrow processing window, poor thermal stability, and is prone to degradation or embrittlement at high temperatures, resulting in limited processing performance.

[0004] PBAT is known for its flexibility and good blown film processability, which makes it suitable for industrial production needs. However, its barrier properties to oxygen and water vapor are relatively weak, making it difficult to meet the requirements of high-barrier packaging.

[0005] PVOH has excellent gas barrier capabilities, especially in dry environments, where it has a significant oxygen barrier effect, and is biodegradable; however, its strong hydrophilicity makes it easy to swell or decompose under humid conditions. It is also prone to degradation at high thermal processing temperatures, and has extremely poor compatibility with hydrophobic polyesters.

[0006] In the prior art, the blending of PHA and PBAT has been widely studied in order to improve the material performance through the complementarity of rigidity and toughness. Although this method improves the mechanical properties to a certain extent, the improvement in barrier properties is still limited and it is difficult to meet the needs of practical applications. PVOH is often used as an independent layer in multilayer composite films due to its excellent barrier properties, but because it is easily degraded by moisture or high temperature in the molten state, and has phase separation problems with the polyester system, the technology of directly melt blending it with PHA and PBAT is not yet mature. In order to solve the compatibility and processing stability problems of polyester blending systems, existing studies have attempted to introduce multifunctional chain extenders for modification, and have achieved certain results in two-component systems such as PLA and PBAT or PBS and PBAT. However, there is still a lack of systematic technical solutions for the blending modification of the ternary system of PHA, PBAT, and PVOH, especially in terms of simultaneously improving compatibility, processing stability, and barrier properties.

[0007] Therefore, there is an urgent need for a technology that can overcome the above-mentioned material defects and achieve synergistic modification of the ternary system to meet the needs of biodegradable composite materials in high-performance applications. Summary of the invention

[0008] The purpose of the present invention is to disclose a method for preparing a modified PHA composite material using a twin-screw extruder and its application. The method is to prepare a composite material with high barrier properties, excellent mechanical properties and biodegradable properties by in-situ melt blending of polyhydroxyalkanoate PHA, polybutylene terephthalate-adipate PBAT and polyvinyl alcohol PVOH in a twin-screw extruder, and introduce a chain extender to achieve chemical modification, thereby meeting the demand for high-performance degradable materials in the fields of food packaging, agricultural mulch, disposable tableware and consumables, and medical protective products.

[0009] The technical solution of the present invention is a method for preparing a modified PHA composite material using a twin-screw extruder and its application, which is achieved by the following steps:

[0010] Step 1. Raw material ratio

[0011] Take 40 to 80 parts of polyhydroxyalkanoate PHA, 10 to 50 parts of polybutylene terephthalate-adipate PBAT, 5 to 20 parts of polyvinyl alcohol PVOH, 0.1 to 5 parts of chain extender, and 0 to 5 parts of auxiliary agent by mass, and mix the above components evenly;

[0012] Step 2. Preheat the conveyor

[0013] The mixture is preheated and initially conveyed through the feed port of a twin-screw extruder at 70 to 120°C;

[0014] Step 3. Melt mixing and reaction

[0015] In the melting section of the twin-screw extruder, the mixture is subjected to high-temperature shear mixing at 150-190°C, and the chain extender is injected in the middle and rear sections to allow the chain extender to undergo in-situ chain extension or cross-linking reactions with the molten PHA, PBAT and PVOH to form a partial grafted or cross-linked network, thereby improving the interfacial adhesion and melt viscosity.

[0016] Step 4. Extrusion

[0017] After the water and low molecular weight by-products are removed by setting a vacuum exhaust port, the melt is extruded or cooled and pelletized at a die head at 160-180° C. to obtain a modified PHA composite material.

[0018] In step 1, PVOH is mixed with a plasticizer of 5 to 10% by weight of the PVOH itself, and then vacuum dried at 60 to 80°C for 4 hours before use. The amount of the plasticizer is only used for PVOH modification and is not included in the total amount of 0 to 5 parts by weight of the additives in the overall formula. The PVOH is a partially hydrolyzed PVOH with a hydrolysis degree of 80 to 98%.

[0019] The PHA is selected from poly(3-hydroxybutyrate) PHB, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) PHB4HB, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) PHBH or a combination thereof.

[0020] The chain extender is mainly a multifunctional compound containing epoxy or isocyanate groups. These functional groups can react with active groups such as hydroxyl and carboxyl groups at the ends of the PHA, PBAT, and PVOH molecular chains to achieve chain growth, branching, or mild crosslinking, thereby increasing molecular weight, improving compatibility, and increasing melt strength. In order to achieve a more specific modification effect, the chain extender may contain maleic anhydride or carbodiimide groups as auxiliary reaction groups in addition to the main epoxy or isocyanate multifunctional compounds, in order to have a more complex chemical reaction with the polymer and further regulate the material properties.

[0021] Step 1 also includes adding 0 to 5 parts by weight of an auxiliary agent, wherein the auxiliary agent is selected from one or more of a plasticizer, an antioxidant, an anti-hydrolysis agent, a lubricant or a compatibilizer; wherein the plasticizer is selected from glycerol, propylene glycol or sorbitol, the antioxidant is selected from antioxidant 1010 or antioxidant 168, the anti-hydrolysis agent is polycarbodiimide, the lubricant is selected from calcium stearate or polyethylene wax, and the compatibilizer is maleic anhydride grafted PBAT.

[0022] The screw length-to-diameter ratio L / D of the twin-screw extruder is ≥30, and the screw speed is 100-300 rpm.

[0023] The present invention also provides a modified PHA composite material prepared by the above method, wherein the oxygen transmission rate (OTR) thereof is reduced by 20 to 50% compared with unmodified PHA or a PHA / PBAT blend system alone, and the water vapor transmission rate (WVTR) thereof is reduced by 20 to 50% compared with unmodified PHA or a PHA / PBAT blend system alone.

[0024] The present invention also provides an application of the modified PHA composite material for preparing food packaging, agricultural mulch films, disposable tableware or medical protective equipment.

[0025] The method for preparing a modified PHA composite material using a twin-screw extruder and its application of the present invention can achieve the following beneficial effects:

[0026] Significantly improved barrier properties: By integrating polyvinyl alcohol (PVOH) into the matrix and using chain extenders to improve compatibility, the oxygen permeability (OTR) of the composite material is reduced by 20-50% compared with unmodified PHA or PHA and PBAT blends, and the water vapor permeability (WVTR) is reduced by 20-50% compared with unmodified PHA or only PHA / PBAT blends. It still maintains excellent oxygen and moisture barrier capabilities in high humidity environments, meeting the needs of high barrier applications such as food packaging.

[0027] Excellent balance of mechanical properties: PHA provides rigidity, PBAT enhances toughness, and chain extenders promote uniform dispersion between phases, so that the tensile strength of the composite material reaches 28-34MPa, the elongation at break reaches 190-245%, and the impact strength is increased to 14-16kJ / m², overcoming the brittleness of PHA and the processing limitations of PVOH, and is suitable for scenes requiring mechanical strength such as agricultural mulch.

[0028] Improve thermal stability and processing fluidity: The chain extender blocks the molecular chain ends and inhibits ester exchange and hydrolysis reactions, which increases the initial decomposition temperature of the composite material by 10 to 18°C. The melt has good processing fluidity and stability within the processing window of 150 to 190°C, reduces high-temperature degradation, and ensures process reliability during twin-screw extrusion.

[0029] Excellent biodegradability: The composite material is composed of degradable components such as PHA, PBAT, PVOH, etc. Under industrial composting conditions of 58°C and humidity >90%, the degradation rate is more than 70% within 180 days, which complies with standards such as EN13432 or GB / T 20197. It can be naturally decomposed after use without producing persistent plastic pollution, which meets the green requirements of environmentally friendly packaging and agricultural mulch.

[0030] Efficient industrial production: The method of the present invention is simple and can realize continuous production by using existing twin-screw extruder equipment. The process parameters are controllable and easy to promote on a large scale, thereby reducing production costs and improving economic benefits. DETAILED DESCRIPTION

[0031] The following describes the embodiments of the present invention in detail through specific examples so that those skilled in the art can clearly understand and implement the present invention. These examples are only used for illustration and do not limit the scope of protection of the present invention in any way.

[0032] Example design and experimental methods

[0033] Raw materials and equipment

[0034] Raw materials: polyhydroxyalkanoate PHA: selected from poly(3-hydroxybutyrate) PHB, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) PHB4HB, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) PHBH or a combination thereof, in powder or granular form, wherein PHB is selected from commercial brands such as Tianan ENMAT PHB and Goodfellow PHB; PHB4HB is selected from commercial brands such as Tianjin GreenBio PHB4HB; PHBH is selected from commercial brands such as Kaneka PHBH and Tianan ENMAT PHBH;

[0035] Polybutylene terephthalate-adipate PBAT: select commercially available brands, such as BASF Ecoflex F Blend C1200, granular;

[0036] Polyvinyl alcohol PVOH: hydrolysis degree 88% or 92%, can be pre-plasticized, choose commercial brands such as Japan Kuraray, Poval;

[0037] Chain extender: epoxy group is selected from BASF Joncryl ADR-4368; isocyanate group is selected from Wanhua WANNATE MDI-50, Covestro Desmodur; maleic anhydride group is selected from Shanghai Faber Chemical Fine-Blend MAG-POE; carbodiimide group is selected from Lanxess Stabaxol P, Nisshinbo Carbodilite;

[0038] Additives: one or more selected from plasticizers, antioxidants, anti-hydrolysis agents, lubricants or compatibilizers. Among them, the plasticizer is selected from Sinopec industrial grade glycerin, Dow Chemical PGI propylene glycol or Roquette NEOSORB sorbitol; the antioxidant is selected from BASF Irganox 1010; the anti-hydrolysis agent is selected from Nisshinbo Carbodilite polycarbodiimide; the lubricant is selected from KLK OLEO calcium stearate or Clariant Licowax PE 520 polyethylene wax; the compatibilizer is selected from PolyramBondyram 7103.

[0039] equipment:

[0040] Twin-screw extruder: The screw length-diameter ratio L / D is 40:1, equipped with a main feed port, a side feed port and a vacuum exhaust port, and the screw speed can be adjusted in the range of 100 to 300 rpm;

[0041] Auxiliary equipment: vacuum drying oven, pelletizer, tensile tester, oxygen permeability tester, water vapor permeability tester, thermogravimetric analyzer and biodegradation testing equipment.

[0042] Implementation of process flow

[0043] Raw material pretreatment:

[0044] Mix PVOH with a plasticizer that is 5 to 10% by weight of the PVOH itself, and vacuum dry at 60 to 80° C. for 4 hours to remove moisture. The amount of the plasticizer is only used for PVOH modification and is not included in the total amount of 0 to 5 parts by weight of the additives in the overall formula;

[0045] PHA and PBAT were dried at 50 °C for 6 h respectively to ensure that the moisture content was less than 0.1%.

[0046] Mixing and extrusion:

[0047] The pretreated raw materials are mixed evenly according to the formula ratio and added to the main feed port of the twin-screw extruder;

[0048] Extruder temperature zone setting: feed section 70-120°C, melting section 150-190°C, die section 160-180°C;

[0049] The screw speed was controlled at 150-250 rpm, the chain extender was injected in the middle and rear sections through the side feed port, and the barrel temperature was 170°C;

[0050] Remove moisture and volatile by-products through vacuum exhaust port;

[0051] After the melt is extruded from the die, it is water-cooled, drawn into strands and pelletized. The die temperature is 170°C.

[0052] Performance Test:

[0053] Mechanical properties: tensile strength and elongation at break are tested according to GB / T 1040, and impact strength is tested according to GB / T 1843;

[0054] Barrier properties: Water vapor transmission rate WVTR is tested according to GB / T 1037, and oxygen transmission rate OTR is tested according to ASTM D3985;

[0055] Thermal stability: Decomposition temperature was determined by thermogravimetric analysis (TGA);

[0056] Melt flowability: Test melt flow index MFI according to ASTM D1238-13

[0057] Biodegradability: Degradation rate was tested in a composting environment at 58°C and humidity greater than 90% for 180 days according to ISO 14855.

[0058] Specific Examples and Comparative Examples

[0059] Example 1

[0060] Raw material ratio:

[0061] By mass, take 60 parts of PHB4HB, choose Tianjin GreenBio PHB4HB; 30 parts of poly PBAT, choose BASF Ecoflex F Blend C1200; 8 parts of PVOH, choose Kuraray Poval, with a hydrolysis degree of 88%; 1.2 parts of chain extender, choose BASF Joncryl ADR-4368, containing epoxy group; 0.5 parts of auxiliary agent, choose BASF Irganox 1010, antioxidant.

[0062] Preprocessing:

[0063] 8 parts of PVOH were mixed with 5% of its own weight of glycerol, 0.4 parts of glycerol was Sinopec industrial grade, and vacuum dried at 60°C for 4 hours. PHB4HB and PBAT were dried at 50°C for 6 hours.

[0064] Preparation process:

[0065] Step 1. Mix the pretreated PHB4HB, PBAT, PVOH and 0.5 parts of BASF Irganox 1010 evenly and add them through the main feed port of the twin-screw extruder;

[0066] Step 2. The temperature zones of the extruder are set as follows: 90°C for the feed section, 160°C for the melt section, 170°C for the die section, and 200 rpm for the screw speed;

[0067] Step 3. Inject 1.2 parts of BASF Joncryl ADR-4368 through the side feed port in the middle and rear part of the melting section to carry out in-situ chain extension reaction;

[0068] Step 4: Remove moisture and by-products through the vacuum exhaust port, and water-cool and pelletize the melt after extrusion.

[0069] Performance Results:

[0070] Tensile strength: 32.4 ± 0.5MPa; Elongation at break: 210 ± 15%; Impact strength: 14.2 ± 0.3kJ / m²; Water vapor transmission rate WVTR: 2.5 ± 0.1g·mm / m²·24h; Oxygen transmission rate OTR: 230 ± 10cm³·mm / m²·24h·0.1MPa; Onset decomposition temperature: 285℃; Melt flow index MFI: 10.5g / 10min; Biodegradation rate, 180 days, 72%.

[0071] Example 2

[0072] Raw material ratio:

[0073] By mass, 50 parts of PHBH, Kaneka PHBH is selected; 40 parts of PBAT, BASF Ecoflex FBlend C1200 is selected; 5 parts of PVOH, Kuraray Poval is selected, with a hydrolysis degree of 92%; 1.5 parts of chain extender, Wanhua WANNATEMDI-50 is selected, containing isocyanate group; 1 part of auxiliary agent, KLK OLEO calcium stearate is selected as a lubricant.

[0074] Preprocessing:

[0075] 5 parts of PVOH were vacuum dried at 60°C for 4 hours without adding plasticizer. PHBH and PBAT were dried at 50°C for 6 hours.

[0076] Preparation process:

[0077] Step 1. Mix the pretreated PHBH, PBAT, PVOH and 1 part of KLK OLEO calcium stearate evenly and add them through the main feed port of the twin-screw extruder;

[0078] Step 2. The extruder temperature zones are set as follows: 80°C for the feed section, 155°C for the melt section, 175°C for the die section, and 150 rpm for the screw speed;

[0079] Step 3. Inject 1.5 parts of Wanhua WANNATE MDI-50 through the side feed port in the middle and rear part of the melting section to carry out in-situ chain extension reaction;

[0080] Step 4: Remove moisture and by-products through the vacuum exhaust port, and water-cool and pelletize the melt after extrusion.

[0081] Performance Results:

[0082] Tensile strength: 28.1 ± 0.8MPa; elongation at break: 245 ± 10%; impact strength: 16.3 ± 0.4kJ / m²; water vapor transmission rate WVTR: 3.2 ± 0.2g·mm / m²·24h; oxygen transmission rate OTR: 250 ± 15cm³·mm / m²·24h·0.1MPa; onset decomposition temperature: 290℃; melt flow index MFI: 12.0 g / 10min; biodegradation rate, 180 days, 70%.

[0083] Example 3

[0084] Raw material ratio:

[0085] By mass, 70 parts of PHB, Tianan ENMAT PHB is selected; 20 parts of PBAT, BASF Ecoflex FBlend C1200 is selected; 8 parts of PVOH, Kuraray Poval is selected, with a hydrolysis degree of 88%; 1.0 part of chain extender, Lanxess Stabaxol P, containing carbodiimide group is selected; 0.5 parts of auxiliary agent, Nisshinbo Carbodilite is selected as anti-hydrolysis agent.

[0086] Preprocessing:

[0087] 8 parts of PVOH were mixed with 8% of its own weight of propylene glycol, 0.64 parts of Dow Chemical PGI, and vacuum dried at 80°C for 4 hours. PHB and PBAT were dried at 50°C for 6 hours.

[0088] Preparation process:

[0089] Step 1. Mix the pretreated PHB, PBAT, PVOH and 0.5 parts of Nisshinbo Carbodilite evenly and add them through the main feed port of the twin-screw extruder;

[0090] Step 2. The extruder temperature zones are set as follows: 95°C for the feed section, 165°C for the melt section, 180°C for the die section, and 250 rpm for the screw speed;

[0091] Step 3. Inject 1.0 part of Lanxess Stabaxol P through the side feed port in the middle and rear part of the melting section to carry out in-situ chain extension reaction;

[0092] Step 4: Remove moisture and by-products through the vacuum exhaust port, and water-cool and pelletize the melt after extrusion.

[0093] Performance Results:

[0094] Tensile strength: 34.2 ± 0.7MPa; Elongation at break: 190 ± 10%; Impact strength: 15.1 ± 0.2kJ / m²; Water vapor transmission rate WVTR: 2.3 ± 0.1g·mm / m²·24h; Oxygen transmission rate OTR: 200 ± 10cm³·mm / m²·24h·0.1MPa; Onset decomposition temperature: 288℃; Melt flow index MFI: 9.8g / 10min; Biodegradation rate, 180 days, 73%.

[0095] Comparative Example 1

[0096] Raw material ratio:

[0097] By mass, take 60 parts of PHB4HB, choose Tianjin GreenBio PHB4HB; 40 parts of PBAT, choose BASF Ecoflex F Blend C1200; 0 parts of PVOH; 0 parts of chain extender; 0.3 parts of additives, choose Clariant Licowax PE 520 polyethylene wax, lubricant.

[0098] Preprocessing:

[0099] PHB4HB and PBAT were dried at 50°C for 6 hours.

[0100] Preparation process:

[0101] Step 1. Mix the pretreated PHB4HB, PBAT and 0.3 parts of Clariant Licowax PE 520 evenly and add them through the main feed port of the twin-screw extruder;

[0102] Step 2. The extruder temperature zones are set as follows: feed section 90°C, melting section 160°C, die section 160°C, and screw speed 200 rpm;

[0103] Step 3. No chain extender is injected, and the water is directly removed through the vacuum exhaust port. The melt is extruded and then water-cooled and pelletized.

[0104] Performance Results:

[0105] Tensile strength: 23.5 ± 0.6MPa; Elongation at break: 160 ± 8%; Impact strength: 11.7 ± 0.5kJ / m²; Water vapor transmission rate WVTR: 4.6 ± 0.3g·mm / m²·24h; Oxygen transmission rate OTR: 380 ± 20cm³·mm / m²·24h·0.1MPa; Onset decomposition temperature: 273℃; Melt flow index MFI: 8.2g / 10min; Biodegradation rate, 180 days, 68%.

[0106] Comparative Example 2

[0107] Raw material ratio:

[0108] By mass, take 0 parts of PHA; 60 parts of PBAT, BASF Ecoflex F Blend C1200; 40 parts of PVOH, Kuraray Poval, with a hydrolysis degree of 88%; 0.5 parts of chain extender, Fine-Blend MAG-POE, containing maleic anhydride; 1 part of auxiliary agent, BASF Irganox 1010, antioxidant.

[0109] Preprocessing:

[0110] 40 parts of PVOH were mixed with 5% of its own weight of glycerol, 2 parts of glycerol was Sinopec industrial grade, and vacuum dried at 60°C for 4 hours. PBAT was dried at 50°C for 6 hours.

[0111] Preparation process:

[0112] Step 1. Mix the pretreated PBAT, PVOH and 1 part of BASF Irganox 1010 evenly and add them through the main feed port of the twin-screw extruder;

[0113] Step 2. The temperature zones of the extruder are set as follows: 80°C for the feed section, 160°C for the melt section, 160°C for the die section, and 150 rpm for the screw speed;

[0114] Step 3. Inject 0.5 parts of Fine-Blend MAG-POE through the side feed port in the middle and rear part of the melting section to carry out in-situ chain extension reaction;

[0115] Step 4: Remove moisture and by-products through the vacuum exhaust port, and water-cool and pelletize the melt after extrusion.

[0116] Performance Results:

[0117] Tensile strength: 26.4 ± 0.7MPa; Elongation at break: 280 ± 20%; Impact strength: 10.9 ± 0.4kJ / m²; Water vapor transmission rate WVTR: 2.1 ± 0.1g·mm / m²·24h; Oxygen transmission rate OTR: 210 ± 10cm³·mm / m²·24h·0.1MPa; Onset decomposition temperature: 275℃; Melt flow index MFI: 13.5g / 10min; Biodegradation rate, 180 days, 65%.

[0118] Performance comparison analysis

[0119] Table 1 below summarizes the performance data of Examples 1 to 3 and Comparative Examples 1 to 2:

[0120]

[0121] By analyzing the data in Table 1, we can draw the following conclusions:

[0122] 1. PVOH significantly improves the mechanical properties and barrier properties of PHA and PBAT blends

[0123] Mechanical properties: 5-8 parts of PVOH are used in Examples 1, 2, and 3, and the tensile strength reaches 28.1-34.2 MPa, the elongation at break reaches 190-245%, and the impact strength reaches 14.2-16.3 kJ / m², which are significantly higher than those of Comparative Example 1 in which PVOH is not used, which are 23.5 MPa, 160%, and 11.7 kJ / m², respectively, indicating that PVOH enhances the toughness and strength of the blend.

[0124] Barrier performance: The WVTR of Examples 1, 2, and 3 is 2.3-3.2 g·mm / m²·24h, and the OTR is 200-250 cm³·mm / m²·24h·0.1 MPa. Compared with 4.6 g·mm / m²·24h and 380 cm³·mm / m²·24h·0.1 MPa of Comparative Example 1 without PVOH, the WVTR is reduced by about 30%-50%, and the OTR is reduced by about 34%-47%, which proves that PVOH effectively improves the barrier properties.

[0125] 2. Chain extenders enhance blend performance

[0126] Examples 1, 2, and 3 use 1.0 to 1.5 parts of chain extenders, and their mechanical properties and barrier properties are better than those of Comparative Example 1 without chain extenders, indicating that the chain extender significantly improves the mechanical properties and barrier properties of the blend by increasing the molecular weight and crosslinking density. Example 1 uses 1.2 parts of BASF Joncryl ADR-4368 containing epoxy groups, Example 2 uses 1.5 parts of Wanhua WANNATE MDI-50 containing isocyanate groups, Example 3 uses 1.0 parts of Lanxess Stabaxol P containing carbodiimide groups, and Comparative Example 2 uses 0.5 parts of Fine-Blend MAG-POE containing maleic anhydride groups. The difference in chain extender type has a certain effect on mechanical properties and thermal stability. For example, isocyanate groups are more conducive to elongation at break, and carbodiimide groups improve thermal stability. However, the performance of Examples 1 to 3 is significantly better than that of Comparative Examples 1 and 2, indicating that the synergistic effect of the PHA, PBAT, PVOH ternary system and chain extenders is the key to performance improvement, rather than a single chain extender type determining the result. This diversity design verifies the universality of the method of the present invention to a variety of chain extenders.

[0127] 3. PHA type and PVOH plasticization affect performance differences

[0128] Example 3 uses PHB and PVOH to plasticize 8% propylene glycol, and the tensile strength reaches 34.2 MPa, which is the highest value; Example 2 uses PHBH and unplasticized PVOH, and the elongation at break reaches 245%, which is the highest value, indicating that PHA type and PVOH plasticization have a regulating effect on rigidity and toughness.

[0129] Comparative Example 2 contains only PBAT and PVOH, with excellent barrier properties, WVTR of 2.1g·mm / m²·24h, and OTR of 210cm³·mm / m²·24h·0.1MPa, but the impact strength is only 10.9 kJ / m², which is obviously insufficient in rigidity.

[0130] The present invention successfully prepares a modified PHA composite material with excellent barrier properties, good mechanical properties and high impact strength by introducing PHA, PBAT, PVOH and chain extender during the twin-screw extrusion process. The addition of PVOH and chain extender is the key to improving performance. The formula optimization of the ternary system achieves a balance between toughness and barrier properties, which is significantly better than the traditional PHA and PBAT binary blend or single system.

[0131] 4. Thermal stability, processing fluidity and degradation performance of the present invention

[0132] Thermal stability and processing fluidity: The initial decomposition temperature of Example 1, Example 2 and Example 3 is 12-17°C higher than that of Comparative Example 1, and the weight loss peak is delayed, indicating that the chain extender effectively terminates or crosslinks PHA and PVOH, reducing degradation caused by transesterification and hydrolysis. The melt flow index MFI is 9.8 to 12.0 g / 10 min, indicating that the chain extender improves thermal stability and processing fluidity.

[0133] Degradation performance: Under industrial composting conditions of 58°C and relative humidity>90%, the composite material composed of degradable components such as PHA, PBAT, and PVOH has a degradation rate of more than 70% within 180 days, slightly higher than the 68% of Comparative Example 1 and 65% of Comparative Example 2, which meets the industrial compostable plastic standards such as EN13432 or GB / T 20197. It can be naturally decomposed after use without producing persistent plastic pollution, which is far superior to traditional petrochemical plastics such as PE and PP films, and meets the green requirements of environmentally friendly packaging and agricultural mulch films.

[0134] These properties are due to the modification effect of the chain extender and the optimized ratio of the PHA, PBAT, and PVOH ternary system. In addition to mechanical properties and barrier properties, the present invention further achieves a synergistic improvement in thermal stability and degradation performance, and has significant technical advantages and application prospects.

[0135] Application prospects of the present invention

[0136] The modified polyhydroxyalkanoate (PHA) composite material prepared by the twin-screw extrusion process of the present invention has broad application prospects in multiple fields due to its excellent comprehensive properties.

[0137] Degradable food packaging: provides a good shelf life for sensitive items such as grain, coffee, tea, etc., and can be directly composted or degraded after use. It is suitable for food packaging films or containers such as grain, coffee, tea, meat products, etc. that are sensitive to oxygen and water vapor.

[0138] Agricultural mulch film: It has sufficient mechanical strength and water-blocking ability. The film gradually degrades after the crop growing season ends. It is suitable for crop covering, surface moisture retention and weed suppression, such as mulch film used in vegetable and fruit tree planting.

[0139] Disposable tableware and consumables: They maintain good deformation stability in high temperature or greasy environments, and have both high barrier properties and biodegradability. They are suitable for disposable lunch boxes, straws, cup lids and other catering supplies, as well as scenarios where there is contact with greasy or high-temperature food.

[0140] Medical protective equipment and consumables: Since PHA and PVOH are both biosafe, they are suitable for potential application scenarios such as medical dressings, protective films, and drug sustained-release carriers.

[0141] Other potential applications: Industrial packaging, such as moisture-proof packaging for electronic products, using its water and oxygen barrier properties to protect precision components.

[0142] Therefore, the modified PHA composite material prepared by the present invention has broad application prospects in the fields of degradable food packaging, agricultural mulch, disposable tableware and consumables, and medical protective equipment. Its comprehensive advantages of high barrier properties, mechanical properties, thermal stability, and biodegradability not only make up for the performance defects of a single PHA or PHA / PBAT system, but also provide a green solution for replacing traditional petrochemical plastics. With the increasingly stringent environmental regulations and the growing market demand for sustainable materials, the present invention has significant industrialization potential and social and economic benefits, and can be widely used in many fields in the future.

[0143] In summary, the present invention prepares a modified PHA composite material with high barrier, toughness and degradable properties by in-situ blending PHA, PBAT, PVOH in a twin-screw extruder and combining a chain extender, which is suitable for multiple scenarios such as degradable food packaging, agricultural mulch, disposable tableware and consumables, and medical protective equipment. The technical solution has significant innovations in raw material selection, melt extrusion process and chain extension mechanism; compared with existing binary blending or multi-layer composite technology, the material processing of the present invention is simpler, the comprehensive performance is better, and it is biodegradable, which is in line with the green environmental protection trend. The methods and material properties covered by the present invention have laid a solid foundation for high-performance degradable products in the fields of environmentally friendly packaging, agriculture, and medicine. Any implementation or equivalent variation based on the technical solution of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a modified PHA composite material using a twin-screw extruder, characterized in that: The following steps are involved: Step 1. Mix the following components in proportion by mass: 40-80 parts of polyhydroxyalkanoate PHA; 10 to 50 parts of polybutylene terephthalate-adipate PBAT; 5-20 parts of polyvinyl alcohol PVOH; 0.1 to 5 parts of chain extender; 0-5 parts of additives; Step 2. Preheat the mixture obtained in step 1 and convey it through the feed port of a twin-screw extruder at 70-120° C.; Step 3. The mixture is subjected to high-temperature shearing and kneading in the melting section at 150-190° C., and the chain extender is injected into the middle and rear sections to cause in-situ chain extension or cross-linking reaction with the molten PHA, PBAT, and PVOH; Step 4. After the water and low molecular weight by-products are discharged through the exhaust port, the melt is extruded at a die head at 160-180° C., cooled and pelletized to obtain a modified PHA composite material; The polyvinyl alcohol PVOH is a partially hydrolyzed PVOH with a hydrolysis degree of 80 to 98%. Before extrusion, it can be premixed with 5 to 10 parts by weight of a plasticizer based on the weight of PVOH itself and fully dried to improve the melt processing stability. The plasticizer is selected from glycerol, propylene glycol or sorbitol; the amount of the premixed plasticizer is only used for PVOH modification and is not included in the total amount of 0 to 5 parts by weight of the additives in the overall formula.

2. The method according to claim 1, characterized in that The chain extender is a multifunctional compound containing epoxy groups or isocyanate groups.

3. The method according to claim 1, characterized in that The twin-screw extruder has a screw length-to-diameter ratio L / D≥30, a screw speed of 100-300 rpm, and a vacuum exhaust port is arranged in the middle and rear sections to remove moisture and volatile low-molecular by-products during the melt extrusion process.

4. The method according to claim 1, characterized in that: The PHA is selected from poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), or a combination thereof.

5. The method according to claim 1, characterized in that The auxiliary agent includes one or more of a plasticizer, an antioxidant, an anti-hydrolysis agent, a lubricant or a compatibilizer.

6. An application of a modified PHA composite material prepared by a twin-screw extruder according to any one of claims 1 to 5, characterized in that: The modified PHA composite material is used for preparing degradable food packaging, agricultural mulch film, disposable tableware, and medical protective equipment.

Images