P34HB / PLA full-bio-based high-barrier film cooperatively regulated and controlled by biaxial stretching and reactive compatilizer and preparation method of P34HB / PLA full-bio-based high-barrier film

Abstract

The invention discloses a P34HB / PLA full-bio-based high-barrier film cooperatively regulated and controlled by biaxial stretching and a reactive compatilizer and a preparation method of the P34HB / PLA full-bio-based high-barrier film, and relates to the technical field of bio-based degradable high polymer materials and processing of the bio-based degradable high polymer materials. The preparation method comprises the following steps: carrying out melt blending on P34HB, PLA and a citric acid-triglycidyl ether compatilizer, so as to obtain a reaction type compatible blending system; preparing the reaction type compatible blending system into an initial thin film in a hot pressing manner; and performing synchronous biaxial stretching on the initial film to obtain a biaxially stretched film, namely the P34HB / PLA full bio-based high-barrier film. The P34HB / PLA full-bio-based high-barrier film provided by the invention not only overcomes the defect that P34HB is easy to tear, but also obtains excellent mechanical strength, high transparency and good water and oxygen barrier performance, and has wide application prospects in the fields of high-barrier food packaging and medical plastic packaging.

Description

Technical Field

[0001] This invention relates to the field of bio-based biodegradable polymer materials and their processing technology, and in particular to a P34HB / PLA fully bio-based high-barrier film synergistically regulated by biaxial stretching and reactive compatibilizers, and its preparation method. Background Technology

[0002] Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) offers advantages such as renewable sources, complete biodegradability, and good biocompatibility. Furthermore, due to its regular molecular chain and high crystallinity, P34HB exhibits significant advantages in gas barrier properties. However, its rapid crystallization rate and high crystallinity easily lead to the formation of coarse spherulites, resulting in insufficient material toughness. Additionally, its narrow processing window makes it prone to brittle fracture during film forming and subsequent orientation processes, hindering its industrial application.

[0003] Polylactic acid (PLA) is a preferred blending component for modifying P34HB due to its bio-based origin, high mechanical strength, good transparency, and mature processing performance. By introducing PLA as a dispersed phase into the P34HB matrix, the overall crystallization rate of the system can be reduced to a certain extent, inhibiting the formation of coarse spherulites in P34HB, thereby improving the toughness and processing stability of the material.

[0004] However, due to differences in molecular structure and crystallization behavior, P34HB and PLA are prone to phase separation during melt blending, resulting in insufficient interfacial bonding and limited mechanical properties and structural stability of the blended film. This is particularly evident during stretching and orientation, where interfacial debonding and stress concentration are likely to occur. Existing research often employs compatibilizers to improve the interfacial interaction between P34HB and PLA. However, commonly used compatibilizers are mostly petroleum-based, and their compatibility and structural stability still fall short of the requirements for high-performance films.

[0005] On the other hand, stretching and orientation is an effective means to improve film performance. However, in the P34HB / PLA system with insufficient compatibility, stretching and orientation processing stability is poor, making it difficult to achieve high-ratio stretching. Moreover, existing technologies mostly use uniaxial stretching, which easily introduces significant anisotropy, resulting in uneven in-plane properties of the obtained film. Therefore, how to maintain the fully bio-based properties while synergistically solving the problems of insufficient compatibility, poor processing stability, and uneven in-plane properties of the P34HB / PLA system to obtain high-performance fully bio-based barrier films is the current research focus of those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a P34HB / PLA fully bio-based high-barrier film and its preparation method, which are synergistically regulated by biaxial stretching and reactive compatibilizers, to solve the problems existing in the prior art. This invention uses P34HB as the main component, and through PLA blending modification and reactive compatibilizer modification combined with simultaneous biaxial stretching, it synergistically solves the problems of insufficient compatibility, poor processing stability, and uneven in-plane properties of the P34HB system while maintaining its fully bio-based properties.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] One of the technical solutions of the present invention is a method for preparing a P34HB / PLA fully bio-based high-barrier film synergistically regulated by biaxial stretching and reactive compatibilizer, comprising the following steps:

[0009] P34HB, PLA, and a citric acid-triglycidyl ether compatibilizer (a bio-based epoxy compatibilizer, abbreviated as TE3) were melt-blended to obtain a reactive compatibilized blend system. The reactive compatibilized blend system was prepared into an initial film by hot pressing. The initial film was subjected to simultaneous biaxial stretching (i.e., simultaneous bidirectional stretching, applying tensile strain simultaneously in the machine direction and transverse direction, so that the film is simultaneously oriented in the machine direction (longitudinal) and transverse direction) to obtain a biaxially stretched film, which is the P34HB / PLA fully bio-based high-barrier film.

[0010] During melt blending, the epoxy functional groups in TE3 react chemically with the end groups of the P34HB / PLA molecular chains to construct an interfacial covalent bond structure, resulting in a reactive compatibility blend system. TE3 enhances the interfacial bonding between the P34HB and PLA phases through reactive compatibility, reducing interfacial defects and micropores caused by phase separation, thus limiting the effective diffusion paths of oxygen and water vapor within the membrane. Subsequent simultaneous biaxial stretching further induces the coordinated orientation of chain segments within the film plane, promoting structural densification and increasing the tortuosity of the transport paths. Biaxial stretching also facilitates the acquisition of a film structure with balanced in-plane performance. These combined effects significantly suppress oxygen and water vapor transport, thereby improving the membrane's barrier properties.

[0011] Moreover, TE3 has a certain chain extension effect, which can improve the efficiency of interface load transfer and suppress interface debonding and stress concentration during the stretching process, which is conducive to the smooth progress of subsequent synchronous biaxial stretching (in the P34HB / PLA system with insufficient compatibility, the biaxial stretching process has poor stability and it is difficult to achieve high-ratio stretching).

[0012] Furthermore, the preparation steps of the citric acid-triglycidyl ether compatibilizer include: mixing citric acid, polyethylene glycol diglycidyl ether and an acidic catalyst, and heating to react (specifically, an acid-catalyzed ring-opening reaction) to obtain the citric acid-triglycidyl ether compatibilizer.

[0013] Citric acid-triglycidyl ether compatibilizer is a triepoxide-functionalized citrate ester derivative. Its molecule contains three epoxy functional groups that can undergo ring-opening reactions with polyester end groups, classifying it as a reactive compatibilizer. Its high number of epoxy functional groups gives it advantages such as good compatibility and excellent structural stability, meeting the requirements of high-performance thin films.

[0014] Furthermore, the molar ratio of the citric acid to the polyethylene glycol diglycidyl ether is 1:3.

[0015] Furthermore, the acidic catalyst comprises an aqueous solution of hydrochloric acid.

[0016] Furthermore, the heating reaction is carried out at a temperature of 110–140 °C for a duration of 0.5–1 h.

[0017] Furthermore, the concentration of the hydrochloric acid aqueous solution is 36–38 wt%.

[0018] Furthermore, the ratio of citric acid to acidic catalyst is 1 g: 0.01 to 0.10 mL.

[0019] Furthermore, the mass ratio of P34HB to PLA is 1:1.

[0020] Furthermore, the amount of the citric acid-triglycidyl ether compatibilizer is 2-3% of the total mass of the P34HB and the PLA.

[0021] Preferably, the amount of the citric acid-triglycidyl ether compatibilizer is 2% of the total mass of the P34HB and the PLA.

[0022] Furthermore, the number-average molecular weight (M) of P34HB n The value is 4.0 × 10 4 ~9.0×10 4 g / mol, the M of the PLA n 3.0×10 4 ~11×10 4 g / mol.

[0023] Furthermore, the melt blending temperature is 170–185 °C, and the time is 3–5 min.

[0024] Furthermore, the parameters of the hot pressing include: platen temperature of 175–190 °C, pressure of 80–100 MPa, and pressing time of 3–5 min.

[0025] Furthermore, the thickness of the initial film is 0.1 to 0.3 mm.

[0026] Furthermore, the parameters for the synchronous biaxial stretching include: a stretching temperature of 60–70 °C (this temperature range is higher than the glass transition temperature of the reactive compatibility blend system and lower than the melting point of the reactive compatibility blend system), a stretching speed of 10–30 mm / s, and a stretching ratio of 2×2–3×3.

[0027] Furthermore, after the hot pressing is completed, the process also includes a step of quenching and cooling the initial film obtained by hot pressing in ice water at 0°C.

[0028] The second technical solution of the present invention: A P34HB / PLA fully bio-based high-barrier film prepared by the above-described method of preparing a P34HB / PLA fully bio-based high-barrier film synergistically regulated by biaxial stretching and reactive compatibilizer.

[0029] The third technical solution of the present invention: the application of the above-mentioned P34HB / PLA fully bio-based high-barrier film in the preparation of high-barrier biodegradable packaging materials.

[0030] The packaging materials include, but are not limited to, food packaging films, medical packaging films, and biodegradable packaging products that have comprehensive requirements for gas barrier properties, mechanical properties, and optical properties.

[0031] This invention significantly improves the compatibility of the P34HB / PLA system by using TE3 as a compatibilizer. The effectiveness of a compatibilizer in polymer blends in terms of compatibility and chain extension depends not only on the presence of reactive functional groups but also on its molecular structure and its interaction with the polymer. The inventors discovered that for polyester blends, compatibilizers containing epoxy functional groups can undergo ring-opening reactions with the hydroxyl or carboxyl groups at the ends of the polymer molecular chains during melt processing, thereby enhancing the interfacial bonding between different polymer phases. However, when the compatibilizer molecular chain is too long, the epoxy functional groups are located in the middle of the molecular chain, or the number of functional groups is small, its reaction efficiency and interfacial interaction ability are limited, making it difficult to form a stable and effective interfacial structure. The bio-based compatibilizer used in this invention is a triepoxy-functionalized citrate derivative. Its molecule contains multiple highly reactive epoxy functional groups, which can react with the end groups of the molecular chains of the two-phase blend materials in the P34HB / PLA blend system at the same time, and construct a stable covalent connection structure at the interface, thereby significantly improving the system compatibility and improving the processing stability.

[0032] Based on this, combined with the synchronous biaxial stretching process, the interfacial covalent connection structure induces the coordinated orientation of molecular chains under the action of an external field, promoting the formation of a more uniform and dense orientation structure, thereby improving the mechanical properties, optical properties and gas barrier properties of the film.

[0033] The present invention discloses the following technical effects:

[0034] (1) This invention introduces a tricyclic oxygen-functionalized bio-based compatibilizer TE3, which undergoes a ring-opening reaction with the end groups of the P34HB / PLA molecular chain during melt blending to construct an interfacial covalent connection structure, significantly enhancing the interfacial bonding force between the two phases, inhibiting phase separation, and improving the compatibility and structural stability of the blend system.

[0035] (2) The present invention adopts an immediate ice-water quenching process after the film hot pressing, which can effectively suppress the excessively rapid crystallization of P34HB and the formation of coarse spherulites, fix a more uniform initial morphology, and provide a wider processing window and a more stable deformation basis for subsequent orientation processing.

[0036] (3) The present invention combines reactive compatibility with synchronous biaxial stretching to induce molecular chains to coordinate orientation and crystal rearrangement in the thin film plane under stretching conditions of 60-70 °C and 10-30 mm / s, so that the thin film obtains a more uniform in-plane texture structure, thereby improving the anisotropy problem caused by traditional uniaxial orientation.

[0037] (4) Through experiments, the present invention found that among the ratios of 8 / 2, 7 / 3, 6 / 4, and 5 / 5, the system has the best overall processing stability when P34HB / PLA = 5 / 5 (i.e., 1:1) and the amount of TE3 added is 2 phr. It can stably achieve 3×3 biaxial stretching and significantly reduce the risk of interface debonding, stress concentration and tensile instability during the stretching process.

[0038] (5) The biaxially stretched film obtained by the present invention can achieve synergistic improvement of mechanical properties, optical transparency and gas / water vapor barrier properties while maintaining the properties of a fully bio-based film. It is suitable for the preparation and application of high-barrier biodegradable packaging materials and related film products (such as high-barrier food packaging and medical plastic packaging materials).

[0039] (6) The raw materials used in this invention are low in cost, renewable in source, and meet the requirements of green environmental protection. Moreover, the process is simple and does not pollute the environment. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a schematic diagram of the structure of the compounds present in TE3 prepared in Example 1.

[0042] Figure 2 A photograph of the TE3 prepared in Example 1.

[0043] Figure 3 The above are the 1H NMR spectra of the raw material PEGDE used in Example 1 and the product TE3 obtained.

[0044] Figure 4 The stress-strain curves of the initial films after ice water cooling are shown in Comparative Example 6, obtained in the 8 / 2-P34HB / PLA system with different types and proportions of compatibilizers added.

[0045] Figure 5 The stress-strain curves of the initial films after ice water cooling are obtained in Example 2 and Comparative Examples 1-5 with different P34HB / PLA blend ratios under conditions of no addition or addition of 2 phrTE3.

[0046] Figure 6 The stress-strain curves are those of the biaxially stretched films obtained in Example 2 under the 5 / 5-P34HB / PLA system with different stretching ratios.

[0047] Figure 7 The images show a visual comparison of the biaxially stretched films obtained under different stretching ratios in the 5 / 5-P34HB / PLA system in Example 2 before (i.e. before stretching) and after fracture.

[0048] Figure 8 The UV-Vis transmittance curves of films in different states of the 5 / 5-P34HB / PLA system are shown.

[0049] Figure 9 These are photographs of films in different states of the 5 / 5-P34HB / PLA system.

[0050] Figure 10 The image shows surface SEM images of biaxially stretched films obtained in Example 2 under different stretching ratios in the 5 / 5-P34HB / PLA system.

[0051] Figure 11The image shows cross-sectional SEM images of biaxially stretched films obtained under different stretching ratios in the 5 / 5-P34HB / PLA system in Example 2. Detailed Implementation

[0052] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0053] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0054] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0055] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0056] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0057] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0058] In the following embodiments, comparative examples and test examples of the present invention, if room temperature is involved, it specifically refers to 20-30 ℃.

[0059] All raw materials used in the following examples, comparative examples, and test examples of this invention are commercially available products. Citric acid was purchased from Beijing Mairuida Technology Co., Ltd.; polyethylene glycol diglycidyl ether (PEGDE, M...) was also used. n=500 g / mol) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; hydrochloric acid aqueous solution (concentration 37 wt%) was purchased from Beijing Chemical Reagent Research Institute Co., Ltd.; poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid) (P34HB, M n =9.0×10 4 g / mol), purchased from Beijing Microstructure Factory Biotechnology Co., Ltd.; Polylactic acid (PLA, M n =10.8×10 4 g / mol), purchased from Natureworks 4032D (Minnesota); compatibilizer Joncryl® ADR-4468 purchased from BASF (Joncryl® series).

[0060] In the test examples of this invention, the tables distinguish different raw material systems in the form of "mass ratio of P34HB to PLA - amount of P34HB / PLA / TE3 added TE3", and distinguish biaxially stretched film products obtained under different stretching ratios in different raw material systems in the form of "mass ratio of P34HB to PLA - amount of P34HB / PLA / TE3 added TE3 - stretching ratio". In the figures, for the sake of simplicity, the prefix about the mass ratio is omitted where it will not make the mass ratio of P34HB to PLA unclear.

[0061] Example 1

[0062] A method for preparing a bio-based epoxy compatibilizer (citric acid-triglycidyl ether compatibilizer, abbreviated as TE3) includes the following steps:

[0063] 10 g (0.05 mol) of citric acid and 68.48 mL (0.15 mol) of polyethylene glycol diglycidyl ether (PEGDE) were added to a reaction vessel and mixed. 0.5 mL of hydrochloric acid aqueous solution was added dropwise as a catalyst under stirring. After mixing thoroughly, the mixture was heated to 120 °C and maintained at this temperature for 1 h. After the reaction was complete, the reaction solution was cooled to room temperature and poured into hexane to precipitate the product. The precipitate was collected by filtration and dried under vacuum at 60 °C to obtain the bio-based epoxy compatibilizer TE3 (i.e., citric acid-triglycidyl ether compatibilizer).

[0064] The structural diagram of the compounds present in the TE3 prepared in this embodiment is shown below. Figure 1 As shown; a photograph of the prepared TE3 is shown. Figure 2 As shown.

[0065] Example 2

[0066] A method for preparing a P34HB / PLA fully bio-based high-barrier film synergistically regulated by biaxial stretching and reactive compatibilizers, comprising the following steps:

[0067] (1) Weigh P34HB, PLA and bio-based epoxy compatibilizer TE3 in the following proportions: the mass ratio of P34HB to PLA is 5:5 (i.e. 1:1), and the amount of TE3 added is 2% (i.e. 2 phr) of the total mass of P34HB and PLA.

[0068] (2) Add the above raw materials into a mixer (Haake rheometer) and mix at 175 °C at 60 rpm for 5 min (i.e., melt mixing in a mixer) to obtain a homogeneous mixture (i.e., a reactive compatibility blend system).

[0069] (3) The mixture was hot-pressed into a film using a hydraulic hot press (Carver Corporation, USA). The pressing conditions were: platen temperature 180 ℃, pressure 80 MPa, and pressing time 3 min. A blend film with a thickness of about 0.2 mm (i.e., the initial film) was obtained. The initial film obtained by hot pressing was immediately placed in ice water (0 ℃) for rapid quenching until the film turned white.

[0070] (4) The initial film cooled by ice water was subjected to simultaneous biaxial stretching (i.e., simultaneous bidirectional stretching) at 70 ℃ (i.e., heating the initial film to 70 ℃). The stretching speed was selected as 10 mm / s, 20 mm / s or 30 mm / s (the stretching speed in the transverse and longitudinal directions was the same), and the stretching ratio was selected as 2×2 (meaning that the film was stretched to twice the original length in both the longitudinal and transverse directions) or 3×3, to obtain multiple sets of biaxially stretched films (i.e., P34HB / PLA all-bio-based high-barrier films). Among them, when the stretching ratio was 2×2, a biaxially stretched film with a thickness of about 0.08 mm was obtained; when the stretching ratio was 3×3, a biaxially stretched film with a thickness of about 0.03 mm was obtained.

[0071] Example 3

[0072] Similar to Example 2, the only difference is that the amount of bio-based epoxy compatibilizer TE3 added is 3% (i.e., 3 phr) of the total mass of P34HB and PLA. Otherwise, the melt blending, hot pressing, ice-water cooling, and simultaneous biaxial stretching conditions are the same as in Example 2. In this example, the film can achieve a stretch ratio of 2×2 and 3×3 at all three stretching speeds during simultaneous biaxial stretching.

[0073] Comparative Example 1

[0074] Similar to Example 2, the only difference is that the addition of the bio-based epoxy compatibilizer TE3 is omitted. Otherwise, the melt blending, hot pressing, ice-water cooling, and simultaneous biaxial stretching conditions are the same as in Example 2. In this comparative example, the film can achieve a stretching ratio of 2×2 at all three stretching speeds during simultaneous biaxial stretching, but it is difficult to consistently reach a stretching ratio of 3×3.

[0075] Comparative Example 2

[0076] Similar to Example 2, the only difference is that the mass ratio of P34HB to PLA is 6:4, and the addition of the bio-based epoxy compatibilizer TE3 is omitted. Otherwise, the melt blending, hot pressing, ice-water cooling, and simultaneous biaxial stretching conditions are the same as in Example 2. In this comparative example, the film can achieve a stretching ratio of 2×2 at all three stretching speeds during simultaneous biaxial stretching, but it is difficult to consistently reach a stretching ratio of 3×3.

[0077] Comparative Example 3

[0078] Similar to Example 2, the only difference is that the mass ratio of P34HB to PLA is 7:3, and the addition of the bio-based epoxy compatibilizer TE3 is omitted. Otherwise, the melt blending, hot pressing, ice-water cooling, and simultaneous biaxial stretching conditions are the same as in Example 2. In this comparative example, the film can achieve a stretching ratio of 2×2 at all three stretching speeds during simultaneous biaxial stretching, but it is difficult to consistently achieve a stretching ratio of 3×3.

[0079] Comparative Example 4

[0080] Similar to Example 2, the only difference is that the mass ratio of P34HB to PLA is 6:4, and the amount of TE3 added is still 2% of the total mass of P34HB and PLA. Otherwise, the melt blending, hot pressing, ice-water cooling, and simultaneous biaxial stretching conditions are the same as in Example 2. In this comparative example, the film can achieve a stretch ratio of 2×2 at all three stretching speeds during simultaneous biaxial stretching, but it is difficult to consistently reach a stretch ratio of 3×3.

[0081] Comparative Example 5

[0082] Same as Example 2, except that the mass ratio of P34HB to PLA is 7:3, and the amount of TE3 added is still 2% of the total mass of P34HB and PLA. Otherwise, the melt blending, hot pressing, ice water cooling, and simultaneous biaxial stretching conditions are the same as in Example 2. In this comparative example, the film could not be uniformly stretched at any of the three stretching speeds during simultaneous biaxial stretching.

[0083] Comparative Example 6

[0084] The P34HB:PLA mixture was prepared at a mass ratio of 8:2. Different amounts (0, 1, 2, or 3 phr of the total mass of P34HB and PLA) of TE3 or compatibilizer Joncryl® ADR-4468 (hereinafter referred to as ADR) were added. The remaining processes (melt blending, hot pressing, ice water cooling, and simultaneous biaxial stretching) were the same as in Example 2. This was used to compare the compatibilization effects of different compatibilizers. In this comparative example, the film could not be uniformly stretched at any of the three stretching speeds during simultaneous biaxial stretching.

[0085] Test Example 1

[0086] (1) Nuclear magnetic resonance hydrogen spectrum ( 1 H NMR test

[0087] Test method: 1 H NMR spectra were acquired on a Bruker Avance 400 NMR spectrometer (operating frequency 400 MHz) in Germany, using deuterated chloroform (CDCl3) as solvent.

[0088] Figure 3 The 1H NMR spectra of the raw material PEGDE used in Example 1 and the resulting product TE3 show that the methylene protons on the citric acid backbone exhibit a characteristic signal at 4.0–4.2 ppm; simultaneously, characteristic proton signals related to the epoxy structure are observed in the range of 2.3–2.8 ppm. Furthermore, the integral area ratio of the methylene protons in citric acid to the protons related to the epoxy structure is close to 1:2, consistent with the expected stoichiometry. These results indicate that the target product TE3 has been successfully synthesized.

[0089] (2) Mechanical property testing

[0090] Test Method: The mechanical properties of the initial film after ice water cooling were evaluated according to standard GB / T 1040.1-2006, and the elongation at break (%) and tensile strength (MPa) were determined. The tests were conducted on a computer-controlled Instron 5967 electronic universal testing machine (USA) equipped with a 500 N range sensor. The clamp spacing was 30 mm, and the tensile speed was 10 mm / min. Each sample was tested five times, and the results are expressed as mean ± standard deviation.

[0091] The mechanical properties of the initial films (i.e. blend films) obtained after ice water cooling in Comparative Example 6 under the conditions of 8 / 2-P34HB / PLA system with different types and proportions of compatibilizers are as follows: Figure 4 (Stress-strain curves) and Table 1 are shown.

[0092] Table 1 Mechanical properties of initial films with different types and proportions of compatibilizers added to the 8 / 2-P34HB / PLA system

[0093]

[0094] Table 1 shows that compared with the 8 / 2-P34HB / PLA blend film without compatibilizer, the addition of bio-based epoxy compatibilizer TE3 improved the elongation at break and tensile strength of the material, proving that the addition of TE3 can effectively enhance the interfacial bonding force between the two phases and improve mechanical properties. Specifically, when the TE3 addition amount increased from 1 phr to 2 phr, the elongation at break increased significantly from 19.4% to 332.7%, while the tensile strength remained at 24.3 MPa, exhibiting the best toughening effect. Comparing with the ADR system, it can be seen that ADR has limited improvement on elongation at break in the 1-3 phr range, indicating that the compatibility effect of TE3 is better than that of ADR in this blend system. The above results also indicate that there is an optimal addition window for the compatibilizer TE3, with 2-3 phr being a relatively optimal addition amount and 2 phr being the optimal addition amount.

[0095] The mechanical properties of the initial films (i.e. blend films) obtained after ice water cooling in Examples 2-3 and Comparative Examples 1-5 with different P34HB / PLA blend ratios, under conditions of no addition or addition of 2 or 3 phrTE3, are as follows: Figure 5 (Stress-strain curves) and Table 2 are shown.

[0096] Table 2 Mechanical properties of initial films with different blending ratios under conditions of no addition, addition of 2 or 3 phr TE3.

[0097]

[0098] As shown in Table 2, without the addition of TE3, the tensile strength increases with the increase of PLA ratio (7 / 3 → 5 / 5), but the elongation at break decreases sharply (only 8.4% in 5 / 5), demonstrating a typical contradiction between strength and toughness. After adding 2 or 3 phr TE3, the elongation at break of all ratios significantly increases, and the strength of the 5 / 5 system increases to 39.6 MPa, indicating that TE3 can significantly improve toughness while maintaining or increasing strength. Combined with the process performance, 5 / 5-P34HB / PLA / 2TE3 provides the most stable mechanical basis and processing window for subsequent high-ratio biaxial tensile testing.

[0099] The mechanical properties of the biaxially stretched films obtained in Example 2 under the 5 / 5-P34HB / PLA system at different stretching ratios (all stretching rates were 20 mm / s) are as follows: Figure 6-7 , Figure 10-11 (in Figure 6 The stress-strain curve is shown. Figure 7 Visual comparison images of the film before and after fracture. Figure 10 Here is a surface SEM image of the thin film. Figure 11The cross-sectional SEM images of the film are shown in Table 3 (where a stretching ratio of 1×1 represents the cross-sectional SEM image of the film before simultaneous biaxial stretching).

[0100] Table 3 Mechanical properties of biaxially stretched films obtained at different stretching ratios (stretching rate 20 mm / s) in the 5 / 5-P34HB / PLA system.

[0101]

[0102] As shown in Table 3, the film strength is significantly improved after introducing biaxial stretching based on the 5 / 5 blend ratio. Especially with the addition of 2 phr TE3, the film can stably achieve higher biaxial stretching ratios and obtain better mechanical properties: the elongation at break of 5 / 5-P34HB / PLA / 2TE3-1×1 reaches 190.1%, while after biaxial stretching, the tensile strength of the 2x and 3x stretched films increases to 70.7 MPa and 75.3 MPa, respectively, and the elongation at break remains at a relatively high level of 87.4% and 77.7%. Comparing with the 5 / 5 system without TE3, although the strength can be improved by 2×2 stretching (45.5 ± 2.2 MPa), it is difficult to stably achieve 3×3 high-ratio stretching in processing. This indicates that the interfacial compatibility structure constructed by TE3 is the key to achieving high-ratio bidirectional orientation and the synergistic effect of strength and toughness.

[0103] In addition, from Figure 10-11As can be seen, the introduction of TE3 significantly altered the two-phase morphology and interfacial characteristics of PLA / P34HB: On the one hand, the characteristic size of the PLA dispersed phase decreased significantly, and the previously clearly distinguishable phase interface boundaries became blurred or even indistinguishable, exhibiting a morphological characteristic of "interface disappearance / interfacial transition layer thickening." This indicates that TE3 effectively reacted and compatible at the two-phase interface, reducing interfacial tension and enhancing interfacial adhesion and segment interpenetration, thereby suppressing phase coarsening and interfacial debonding during melt processing and subsequent stretching. On the other hand, after 3×3 biaxial stretching, the PLA phase further evolved from the initial elliptical / island-like dispersion into a thin-layered structure spreading along the film surface. This morphological transformation indicates that under a biaxial stress field, the dispersed phase undergoes a continuous evolution path of "deformation-elongation-spreading / layering": when interfacial adhesion is insufficient, the dispersed phase is more prone to interfacial peeling and fracture shrinkage, making it difficult to form a stable high aspect ratio structure; however, under the action of TE3, after the interface is strengthened, the PLA phase can be continuously "pulled" in biaxial stretching and spread in the film surface direction, ultimately forming a thin-layer structure with higher orientation and higher morphological anisotropy. This thinning process has two important structural implications: first, the thin-layer scale significantly reduces the effective size of visible light scattering (especially in the thickness direction), which is beneficial for maintaining high transparency; second, the formation of the layered phase can significantly increase the tortuosity of the gas permeation path and improve the barrier performance through the interlayer "densification-continuous barrier phase" effect, while providing more effective energy dissipation units (interlayer shear, interface synergistic deformation) for toughness improvement.

[0104] The excellent performance of the material demonstrates that TE3 contains multiple epoxy functional groups. On the one hand, it can improve the adhesion between the two phases through hydrogen bonding interactions. On the other hand, it can undergo ring-opening reactions with the carboxyl or hydroxyl groups at the ends of PLA and P34HB molecular chains, forming chemical fixation at the interface of the two phases, accompanied by a certain chain extension effect. This improves the interface load transfer efficiency and inhibits interface debonding and stress concentration during stretching. On this basis, biaxial stretching induces the molecular chains to synergistically align within the film surface and promotes structural compactness, thereby increasing the orientation degree of the load-bearing chain segments and forming a more uniform orientation structure. This significantly improves the strength and stiffness of the film while maintaining high ductility, achieving a balance between high strength and high ductility.

[0105] (3) Optical performance testing

[0106] Test Method: The optical properties of the initial film after ice-water cooling (i.e., before biaxial stretching) or the biaxially stretched film after synchronous biaxial stretching were measured using a UV-Vis-NIR spectrophotometer (UV3600, Japan). Transmittance (%) curves at wavelengths of 400-700 nm were obtained, and the transmittance at 650 nm was used as the characterization index for film transparency. Each sample was tested three times, and the results are expressed as mean ± standard deviation. The transparency of films in different states of the 5 / 5-P34HB / PLA system is shown in the figure. Figure 8-9 (in Figure 8 The UV-Vis transmittance curve of the thin film is shown. Figure 9 (See the actual image of the thin film) and Table 4.

[0107] Table 4. Comparison of transparency of films in different states of the 5 / 5-P34HB / PLA system (all stretched at a rate of 20 mm / s).

[0108]

[0109] As shown in Table 4, the transmittance of the 5 / 5-P34HB / PLA film without TE3 was only 29.2%; after adding 2 phr of TE3, the transmittance of the 5 / 5-P34HB / PLA / 2TE3 increased to 44.7%. Further biaxial stretching increased the transmittance of the 2x stretched film without TE3 to 51.5%, while the transmittance of the 3x stretched film with TE3 reached 80.1%.

[0110] The results show that the reactive compatibility of TE3 reduces light scattering caused by phase separation and interface defects, and induces in-plane co-orientation and dense structure of the film under the action of biaxial tensile external field, thereby significantly improving transparency and finally obtaining a highly transparent 5 / 5-P34HB / PLA / 2TE3 biaxially stretched film.

[0111] (4) Oxygen barrier performance test

[0112] Test Method: Following ASTM D 3985, under conditions of 23 ℃ and 30% relative humidity, the oxygen transmissibility (OTR), oxygen permeability (OP), oxygen diffusion coefficient, and oxygen solubility coefficient of the initial film after ice-water cooling (i.e., before biaxial stretching) or after synchronous biaxial stretching (stretching rate 20 mm / s) were determined using a VAC-V2 differential pressure gas permeation apparatus. Each test was repeated three times, and the average value was taken. The oxygen barrier properties of the films in different states of the 5 / 5-P34HB / PLA system are shown in Table 5.

[0113] Table 5. Oxygen barrier properties of films in different states of the 5 / 5-P34HB / PLA system

[0114]

[0115] As shown in Table 5, the oxygen permeability coefficient of the film without compatibilizer decreased after 2×2 biaxial stretching, while the diffusion coefficient also decreased significantly. The oxygen permeability coefficient decreased further after adding the bio-based epoxy compatibilizer TE3, with a more pronounced decrease in the diffusion coefficient. This indicates that TE3 enhances interfacial bonding and reduces interfacial defects and micropores through reactive compatibilization, thereby further restricting oxygen diffusion. Based on this, the permeability coefficient decreased further after 3×3 simultaneous biaxial stretching, demonstrating an even better oxygen barrier effect.

[0116] (5) Water vapor barrier performance test

[0117] Test Method: The water vapor transmission rate (WVTR) and water vapor permeability coefficient of the initial film after ice water cooling (i.e., before biaxial stretching) or the biaxially stretched film after simultaneous biaxial stretching were determined according to GB / T 1037-2021 using a thin water vapor transmission rate tester (Labthink, C360M). Samples were cut into circular pieces (area 33.18 cm²). 2 The tests were conducted at 38 ℃ and 90% relative humidity. Each test was repeated three times and the average value was taken. The water vapor barrier properties of the films in different states of the 5 / 5-P34HB / PLA system are shown in Table 6.

[0118] Table 6. Water vapor barrier properties of films in different states of the 5 / 5-P34HB / PLA system

[0119]

[0120] As shown in Table 6, the 5 / 5-P34HB / PLA film without compatibilizer exhibits certain water vapor barrier properties. After 2×2 biaxial stretching, the water vapor permeability increases due to the significant reduction in film thickness, but the water vapor permeability coefficient normalized to thickness decreases. In contrast, the water vapor permeability coefficient of the film with added TE3 is lower than that of the sample without compatibilizer, indicating that the introduction of TE3 can improve the water vapor barrier capacity of the film. Further 3×3 biaxial stretching further reduces the water vapor permeability coefficient to its lowest value, indicating that the reactive compatibilization of TE3 and the bidirectional orientation structure regulation have a synergistic effect, significantly improving the water vapor barrier performance of the film.

[0121] TE3 enhances the interfacial bonding between P34HB and PLA through reactive compatibility, reducing interfacial defects and micropores caused by phase separation, thus limiting the effective diffusion paths of oxygen and water vapor within the membrane. Simultaneous biaxial stretching further induces the coordinated orientation of segments within the film plane, promoting structural densification and increasing the tortuosity of the transport paths. These combined effects significantly suppress oxygen and water vapor transport, thereby improving the membrane's barrier properties.

[0122] The embodiments described are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a biaxially stretched P34HB / PLA fully bio-based high-barrier film synergistically regulated by a reactive compatibilizer, characterized in that, The method comprises the following steps: melting blending P34HB, PLA and citric acid-triglycidyl ether compatibilizer to obtain a reactive compatibilized blending system; and preparing an initial film by hot pressing the reactive compatibilized blending system; synchronously biaxially stretching the initial film to obtain a biaxially stretched film, which is the P34HB / PLA full-bio-based high-barrier film.

2. The preparation method of P34HB / PLA fully-bio-based high-barrier film synergistically regulated by biaxial stretching and reactive compatibilizer according to claim 1, characterized in that, The preparation steps of the citric acid-triglycidyl ether compatibilizer include: mixing citric acid, polyethylene glycol diglycidyl ether and an acidic catalyst, and heating and reacting to obtain the citric acid-triglycidyl ether compatibilizer.

3. The preparation method of P34HB / PLA fully-bio-based high-barrier film synergistically regulated by biaxial stretching and reactive compatibilizer according to claim 2, characterized in that, The molar ratio of the citric acid to the polyethylene glycol diglycidyl ether is 1:3; and / or, the acidic catalyst comprises an aqueous hydrochloric acid solution; and / or, the heating reaction is performed at a temperature of 110-140 ℃ for 0.5-1 h.

4. The preparation method of P34HB / PLA fully-bio-based high-barrier film synergistically regulated by biaxial stretching and reactive compatibilizer according to claim 3, characterized in that, The concentration of the aqueous hydrochloric acid solution is 36-38 wt%; and / or, the use amount ratio of the citric acid to the acidic catalyst is 1 g:0.01-0.10 mL.

5. The preparation method of P34HB / PLA fully-bio-based high-barrier film synergistically regulated by biaxial stretching and reactive compatibilizer according to claim 1, characterized in that, The mass ratio of the P34HB to the PLA is 1:

1.

6. The preparation method of P34HB / PLA fully-bio-based high-barrier film synergistically regulated by biaxial stretching and reactive compatibilizer according to claim 1, characterized in that, The use amount of the citric acid-triglycidyl ether compatibilizer is 2-3 % of the total mass of the P34HB and the PLA.

7. The preparation method of P34HB / PLA fully-bio-based high-barrier film synergistically regulated by biaxial stretching and reactive compatibilizer according to claim 1, characterized in that, The melting blending is performed at a temperature of 170-185 ℃ for 3-5 min; and / or, the parameters of the hot pressing include: a platen temperature of 175-190 ℃, a pressure of 80-100 MPa, and a pressing time of 3-5 min; and / or, the parameters of the synchronous biaxial stretching include: a stretching temperature of 60-70 ℃, a stretching speed of 10-30 mm / s, and a stretching ratio of 2×2-3×3.

8. The preparation method of P34HB / PLA fully-bio-based high-barrier film synergistically regulated by biaxial stretching and reactive compatibilizer according to claim 1, characterized in that, After the hot pressing, the method further comprises the step of quenching and cooling the initial film obtained by the hot pressing in ice water at 0 ℃. 9.A P34HB / PLA full-bio-based high-barrier film prepared by the method of any one of claims 1-8. 10.Use of the P34HB / PLA full-bio-based high-barrier film of claim 9 in preparing a high-barrier degradable packaging material.

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