Film based on multilayer biodegradable polymer nanocomposites

Abstract

The invention provides a method for preparing a biodegradable polymer nano composite film. The film has excellent gas barrier property, tensile property and dimensional stability at the distillation temperature. The methods involve employing a one-step reactive mixing process to improve the interaction between biodegradable polymers and nanoparticles, including phyllosilicate nanoclays and metal organic frameworks (MOFs). The obtained nano composite film shows excellent gas barrier property, and has improved tensile strength and dimensional stability at distillation temperature. Various biodegradable polymers such as PBAT, PLA, PHA, PBS, PCL and PHBV can be used as a supporting outer layer of the nano-composite film, so that the nano-composite film has multiple purposes in application. The one-step reaction mixing method provides an economical and environment-friendly way for preparing the advanced biodegradable polymer nano composite film.

Description

Technical Field

[0001] The present invention relates to the development of biodegradable polymer nanocomposite films having excellent gas barrier properties and dimensional stability, and discloses a method for preparing the same. Background Art

[0002] With the rise of modern ready-to-eat meals, the demand for sustainable food packaging has been increasing continuously. The light weight and high gas barrier properties of polymers have made them highly favored in the food packaging field. Traditional polymers such as polyethylene terephthalate (PET), ethylene-vinyl alcohol copolymer (EVOH), polyamide (PA), polyethylene (PE), and polypropylene (PP) are widely used in food packaging due to their gas barrier and aroma barrier properties, as well as mechanical properties and processability. However, a large amount of such plastic packaging ultimately either ends up in landfills (40%) or leaks into the ecosystem (32%). [1] Only 14% of such packaging is collected for recycling, and another 14% is incinerated. The development of biodegradable (including compostable and hydrolytically degradable) packaging materials can provide a way to solve the landfill problem because these materials can be degraded or composted after use. However, compared with traditional polymers, the poor gas barrier properties, poor dimensional stability, and high cost (e.g., about four times more expensive than polyethylene) of biodegradable polymers limit their application in food packaging. The oxygen and water vapor permeation through plastic packaging depends on the type of food itself. The oxygen and water vapor barrier properties of common biodegradable polymers such as polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), and polybutylene succinate (PBS) are about ten times higher than those of polyethylene terephthalate (PET) and polycaprolactam (PA6) widely used in packaging. Improving the oxygen and water vapor barrier properties, in other words, reducing the permeation rate of target molecules in biodegradable polymers, in this case, PBAT is at a comparable level to traditional plastics, which enables the industry to design sustainable packaging with high barrier properties for future market demands.

[0003] Between 2021 and 2028, the market for high-barrier films for food packaging is expected to grow at a compound annual growth rate (CAGR) of 5.9% and reach $30.8 billion by 2028. This growth trend is attributed to the preference for ready-to-eat (MRE) packaged products, the increasing demand for longer shelf life, the growing consumer concern about reducing food waste, and the continuous growth in demand from the meat industry. [2] It is expected that the global sales of ready-to-eat (MRE) packaging in 2027 will increase by about 2.0 times compared to 2019, which was estimated to be over $1.9 billion. [3] In addition, the growing demand for high-barrier biodegradable packaging films is expected to create profitable opportunities for barrier film manufacturers. [2] Various strategies for enhancing the gas barrier properties of polymeric materials include reducing absorption, dissolution, diffusion, and desorption of permeants as they pass through the material. Common methods for improving gas barrier properties include customizing the polymer structure, controlling crystallization and orientation, blending different polymers, multilayer coextrusion, coating using different techniques (such as layer-by-layer deposition, chemical vapor deposition, etc.), and adding fillers (such as nanoclays, graphene oxide, nanocellulose crystals, zinc oxide, zeolites, combinations of magnesium oxide and silver nanoparticles, nanosilica, titanium dioxide, silver oxide, etc.). [4-14] WO2021 / 226722 A1 discloses that incorporating 15% of micron-sized Miscanthus fiber biochar into polybutylene succinate (PBS) by melt blending can reduce the oxygen permeability by approximately 99.8% in compression-molded specimens with a thickness of 0.8 mm compared to pure PBS.

[15] US 7619025 B2 relates to a composition that includes polylactic acid (PLA) or polyhydroxybutyrate (PHB), polybutylene adipate / terephthalate (PBAT), and nanoclay modified with fatty acid triglyceride quaternary ammonium salts for developing a high-barrier, biodegradable material for packaging. The extruded pellets of the blend and composite are made into films for testing gas barrier properties by compression molding. The authors claim that the oxygen barrier properties of the molded PLLA / PBAT / Cloisite 25A (57 / 38 / 5) film can be comparable to those of an oriented polypropylene film. The results show that the oxygen permeability of the PLLA / PBAT / Cloisite 25A (57 / 38 / 5) film can be reduced by approximately 78% relative to the PBAT film, while for the PHB / PBAT / Cloisite 30B (66.5 / 28.5 / 5) film, the oxygen permeability can be reduced by approximately 62.5%.

[0004] US 2012 / 0183779 A1 aims to provide a multilayer film with excellent adhesion strength between the interfaces of two resins by co-extruding an aliphatic polycarbonate and a copolyester polymer, and no separate adhesive or bonding layer is required anymore.

[17] Compared with PBAT films, in the PBAT / PPC (poly(propylene carbonate)) / PBAT three-layer film with a layer thickness of 75 / 45 / 75, the oxygen permeability can be reduced by about 87.6%. Similarly, compared with only PBAT films, in the PBAT / PPC / PBAT three-layer film with a layer thickness of 60 / 50 / 60 µm, the oxygen permeability can be reduced by nearly 91%. In the three-layer structure of the film or sheet, the surface layer is made of PBAT laminated / co-extruded on both surfaces of PPC. However, PPC also has its own challenges: its relatively low Vicat softening temperature and poor mechanical properties due to its ester molecular structure limit its applications. The material will shrink rapidly when approaching the Vicat softening temperature.

[0005] CN 111234279B discloses a method for improving the water vapor barrier performance of PBAT-based films, which contain 0.5 to 10 wt% of cross-linking agents such as triallyl isocyanurate, trimethylopropane trimethacrylate, and trimethylopropane triacrylate. Biaxial stretching and electron beam irradiation are used to improve the water vapor barrier performance of the corresponding films.

[18] Metal-organic frameworks (MOFs) are widely known for their highly porous structures required in absorption and separation applications. For example, CN110064311B discloses a method for preparing a multilayer composite film using ionic liquids and MOFs by the layer-by-layer deposition method, and the corresponding film can separate hydrogen and carbon dioxide.

[19] The adsorption characteristics of MOFs help to improve the gas barrier performance of polymer nanocomposite-based products or films.

[0006] When nanoparticles are introduced into a polymer matrix, the key functions that need to be constructed include improving the interaction between the matrix and the filler, controlling fluidity, crystallization, and dispersibility. Although adding compatibilizers / grafted polymers can improve the interaction between the matrix and the filler, chain extenders and crosslinkers limit the flow behavior. Nakayama et al. reported that Joncryl improved the interaction between PLA and PBAT, but weakened the hydrogen bonds between the filaments caused by the reaction between the epoxy groups of Joncryl.

[20] In our previous research work, we proposed grafting maleic anhydride (MA) onto polypropylene simultaneously and then reacting it with amino silane, which can improve the thermomechanical properties of polypropylene.

[21] Niemoeller demonstrated a preparation process for MA-grafted PBAT.

[22] The authors employed supercritical graft copolymerization, which is a viable alternative to grafting polymers using azo-type or peroxide radical initiators in the melt or solution phase. Othman et al. have demonstrated the compatibilization of PP and bentonite in the presence of PP-g-MA.

[23] Generally, peroxides are used in the process of grafting MA onto polymers. For example, Saraphat et al. used LuperoX as an initiator to graft maleic anhydride onto PBAT.

[24] In another case, US 8541109 B2 relates to a biodegradable polyester suitable for extrusion coating, which contains units derived from at least one dicarboxylic acid and at least one diol, has long-chain branches (equidistant from the main chain of the polyester), and α,α′-bis(tert-butylperoxy) diisopropylbenzene (LuperoXF).

[25] It has similar viscosity, higher melt strength, higher elongation at break ratio, lower drawdown, optimal adhesion to paper, excellent sealing properties, and processability in an extrusion coating system. LuperoX is an organic peroxide, and the mixing process is called reactive extrusion. The samples of reactive extrusion exhibit lower melt viscosity, which can be attributed to the breakage of polymer chains and the reduction of the average molecular weight of the product due to high-temperature and high-shear melt processing in the presence of free radicals.

[0007] Another challenge of biodegradable polymers is their dependence of biodegradability on the thickness of the sample. In fact, the literature shows that compared with pure resins, adding nanoscale fillers can endow various polymers with multifunctional properties.

[26] Multiple studies have reported on the preparation of PBAT / organoclay nanocomposites. Santosh et al. studied the effects of different types of organically modified nanoclays (C10A, C20A, and C30B) on the dispersibility of PBAT and thus on its thermomechanical properties.

[27] In the presence of these nanoclays, the dispersibility and properties were not substantially improved. Falcão et al. observed that for PBAT / C20A films (containing 5 wt% of C20A) blended by a Haake Rheomixer and then processed into films by a single-screw extruder, the oxygen permeability decreased by more than 50%.

[28] The authors also reported that while PBAT degraded only 1% after being buried in soil for 14 weeks, it degraded significantly after being exposed to ultraviolet radiation for one week (degrading 49% and 62% after 5 days and 30 days of exposure to ultraviolet light, respectively).

[0008] Therefore, an object of the present invention is to provide a biodegradable packaging material with excellent gas barrier properties and dimensional stability, which can meet the requirements of the future market for high-barrier sustainable packaging. Summary of the Invention

[0009] According to the present invention, there is provided a method for preparing a biodegradable polymer nanocomposite film, which has excellent gas barrier properties, tensile properties, and dimensional stability at the distillation temperature. The method includes: Providing a biodegradable polymer; Providing nanoparticles, the particles including layered silicate-type nanoclays; Providing nanoparticles, the particles including metal-organic frameworks (MOFs); Among them, the improvement of the interaction between the polymer and the nanoparticles and thus the enhancement of the dispersion and distribution of the nanoparticles are attributed to the one-step reaction mixing method.

[0010] The selection of the biodegradable polymer may include aliphatic-aromatic copolyesters based on the monomers 1,4-butanediol, adipic acid, terephthalic acid, succinic acid, and lactic acid in the polymer chain.

[0011] In one formulation, the biodegradable polymer used to prepare the nanocomposites disclosed herein is preferably a biodegradable polyester, such as PBAT.

[0012] PBAT is an aliphatic-aromatic copolyester based on the monomers 1,4-butanediol, adipic acid, and terephthalic acid in the polymer chain, and its trade name is ecoflexF Blend C1200.

[0013] The nanoparticles may comprise natural or synthetic nanoclays, and may be surface-treated or ion-exchanged modified or not, and are preferably selected from the group of layered silicates and metal-organic frameworks (MOFs) with high adsorption capacity.

[0014] In one formulation, the nanoparticles comprise layered silicate-type nanoclays, preferably in the pristine form.

[0015] In one formulation, the MOF comprises aluminum sulfate octadecahydrate (Al 2 (SO4) 3 .18H 2 O, 99%), with fumaric acid (C 4 H 4 O 4 , 99%) as the organic linker.

[0016] In the method as described above, the concentration of the nanoparticles can be between 1 and 10 wt%; preferably below 5 wt%.

[0017] In one formulation, the concentrations of nanoclay and MOF in the nanocomposite can be varied; but preferably below 5 wt%.

[0018] In one embodiment of the present invention, the reactive mixing process may involve an extrusion technique, preferably co-rotating twin-screw extrusion of a biodegradable polymer and nanoscale fillers in the presence of a free-radical initiator (such as dicumyl peroxide, DCP), a functional organic moiety for enhancing the wettability of the nanoclay in the polymer matrix (such as maleic anhydride, MA), and a chain extender Joncryl ADR 4368 (a customized styrene-acrylic oligomer with epoxy functionality) to minimize the reduction of molecular weight during processing. Preferably, the reactive extrusion can be carried out in the presence of an antioxidant (such as Irganox B225, which is a mixture of two different antioxidants, namely an organic phosphite called Irgafos® 168 and a hindered phenolic antioxidant called Irganox® 1010).

[0019] In one formulation, the free-radical initiator can be provided in the form of a peroxide, such as dicumyl peroxide at a content of 0.2 to 0.5 wt%, preferably 0.1 wt%.

[0020] In one formulation, the functional organic moiety can be 1 to 6 wt%, preferably 1.9 wt% of maleic anhydride.

[0021] In a formulation, the typical concentrations of the initiator, MA, chain extender, and antioxidant are maintained at 0.1 wt%, 1.9 wt%, 0.5 wt%, and 0.4 wt%, respectively.

[0022] In one method, the nanocomposite can be processed using a temperature profile of 120|130|140|145|130|120|110|110|110|110 °C, a screw speed of 80 to 200 rpm, preferably 116 rpm, and a feed rate of 1 to 15 kg / h, preferably 6.6 kg / h.

[0023] In a formulation, the extrudate can be collected by a water bath or air, preferably by air before pelletization. The pellets are then dried at 70 °C for 16 hours and used to prepare multilayer nanocomposite films.

[0024] The uniform distribution of the nanofillers can be achieved by simultaneously grafting MA onto PBAT and subsequent reaction of MA with nanoclay and MOF during a one-step reactive extrusion process.

[0025] The one-step method is a more economically viable and environmentally friendly method. During the grafting process, the CO-O-CO bond of the anhydride will open and form hydrogen bonds with the hydroxyl groups (OH) present in the nanoclay, thus compatibilizing between the nanoclay and PBAT. Compared with the nanocomposite composed of the original nanoclay, this limits the stretching vibration of the hydroxyl groups (OH) in the nanocomposite after reactive processing.

[0026] The compatibilization between the polymer and the nanoclay improves the dispersion and distribution of the nanoclay in the nanocomposite; when this nanocomposite is integrated into a multilayer film, it forms an impermeable barrier to oxygen molecules and hinders the penetration of oxygen by forming a tortuous path. However, unless a high aspect ratio of the nanoclay is maintained in the nanocomposite, this film cannot provide sufficient water vapor barrier performance; moreover, the volume of water molecules, which is smaller than that of oxygen molecules, also affects the permeation performance.

[0027] Compared with the control film made of pure polymer, depending on the film structure, the oxygen permeability of the reactive processed nanocomposite film is reduced by about 20 to 89%.

[0028] The nanocomposite film of the nanocomposite prepared by reactive extrusion not only has improved oxygen barrier performance, but also has improved tensile properties and dimensional stability at the distillation temperature.

[0029] In the reactive processed MOF nanocomposites, the CO-O-CO bonds of the anhydride are opened in a similar manner, and the C=O of the conjugated anhydride reacts with the bridging coordinated OH bond of Al 4 (OH) 2 in the MOF, thus enhancing the compatibilization between PBAT and MOF. Due to this matrix-filler interaction, the uniform distribution of MOF in the PBAT nanocomposites is achieved.

[0030] The films composed of the reactive processed MOF nanocomposites provide barriers to oxygen and water vapor by forming tortuous paths and their inherent absorption properties. The MOF has a high specific surface area (744.9 m 2 / g, determined by BET) and a total pore volume of single-point adsorption (0.47 cm 3 / g). Compared to the control films containing pure polymers, the films composed of the reactive processed MOF nanocomposites also have better tensile properties and higher dimensional stability at the distillation temperature.

[0031] The films can be processed by the above method, and the films contain reactive processed polymer nanocomposites, such as using PBAT nanocomposites as the intermediate layer and selecting specific biodegradable polymers as the supporting outer layer.

[0032] In another aspect of the present invention, a biodegradable polymer nanocomposite film obtained according to the above method is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 - shows the development of a biodegradable polymer nanocomposite film with excellent barrier properties related to the present invention and discloses its preparation method; Figure 2- shows the cross-sections of different multilayer films; film structures 100, 200, and 400 are used as comparative examples; film structures 300, 320, and 330 contain nanocomposites prepared by reactive processing with different concentrations of nanoclay; structure 500 contains a nanocomposite film of a 2:1 type layered silicate prepared by reactive processing, namely Eccafeed sodium-based bentonite nanoclay (EFD) [nanocomposite abbreviated as EFD rxn]; film structure 600 contains a nanocomposite prepared by reactive processing, which includes a 1:1 type layered silicate (i.e., kaolin, [nanocomposite abbreviated as kaolin rxn]) as the intermediate layer, EFD rxn supporting the intermediate layer, and a PBAT layer on the outer surface; film structure 700 contains a nanocomposite based on EFD but not prepared by reactive processing [nanocomposite abbreviated as EFD w / o rxn], and uses kaolin rxn as the intermediate layer; film structure 800 includes a nanocomposite prepared by reactive processing with MOF [nanocomposite abbreviated as MOF rxn] as the intermediate layer; film structure 900 contains kaolin rxn as the intermediate layer, which is supported by MOF rxn, and uses pure PBAT as the outer layer. The sample identifications corresponding to structures 400, 500, 600, 700, 800, and 900 are abbreviated as MV570, MV573, MV574, MV572, MV575, and MV576, respectively; Figure 3 - shows the thermal stability of the nanocomposites: (a) the effect of nanoclay concentration on the nanocomposites prepared by reactive processing, and (b) the effect of different types of nanoparticles; Figure 4 - shows scanning electron microscope (SEM) images showing the distribution of EFD nanoclay in the nanocomposites with different EFD nanoclay concentrations; Figure 5 - shows Fourier transform infrared spectroscopy (FTIR) spectra showing the characteristic molecular vibrations in the nanocomposites with different EFD nanoclay loadings; Figure 6 - shows FTIR spectra showing the matrix-filler compatibilization in the nanocomposites with different EFD nanoclay concentrations; Figure 7 - shows FTIR spectra showing the characteristic molecular vibrations in the nanocomposites composed of EFD, kaolin nanoclay, and MOF; Figure 8 - shows FTIR spectra showing the matrix-filler compatibilization in the nanocomposites composed of different nanoparticles; Figure 9- Shows a schematic diagram of the matrix-filler interaction due to reactive processing; Figure 10 - Shows a transmission electron microscope (TEM) image showing the distribution of different nanoparticles in the nanocomposite; Figure 11 - Shows the water vapor transmission rate of selected films over time: the intermediate layers of MV570, MV573, and MV575 are PBAT, EFD rxn, and MOF rxn, respectively. Pure PBAT is used as the outer layer; Figure 12 - Shows the biodegradation characteristics of microcrystalline cellulose and multilayer films MV570, MV573, MV574, MV572, MV575, and MV576 measured by respirometer analysis under controlled composting conditions during an 180-day incubation period; Figure 13 - Shows a photograph of the degraded film; Figure 14 - Shows SEM images of the surface of degraded film fragments at different time intervals; Figure 15 - Shows the FTIR spectrum of the degraded film fragment of film MV570; Figure 16 - Shows the FTIR spectrum of the degraded film fragment of film MV573; Figure 17 - Shows the FTIR spectrum of the degraded film fragment of film MV574; Figure 18 - Shows the FTIR spectrum of the degraded film fragment of film MV572; Figure 19 - Shows the FTIR spectrum of the degraded film fragment of film MV575; Figure 20 - Shows the FTIR spectrum of the degraded film fragment of film MV576; Figure 21 - Shows the scattering curves of the experiment (.ift) and approximation (.app) before and after 90-day composting; Figure 22 - Shows the pair-distance distribution functions in different films before and after 90-day composting; Figure 23 - Shows the electron density functions in different films before and after 90-day composting obtained by small-angle X-ray scattering (SAXS) analysis; Figure 24 - Shows the experimental scattering curves of MV575 and MV576 before and after 90-day composting; Figure 25 - shows the wide-angle X-ray scattering patterns of different films before and after 90-day composting; and Figure 26 - shows the biodegradation of multilayer films: (a) compost-soil mixture, (b) seed planting, (c, c') seed germination and representative plant growth in soil, (d, d') in soil for composting cellulose, in soil for composting the following films: (e, e') MV570, (f, f') MV573, (g, g') MV574, (h, h') MV572, (i, i') MV575, and (j, j') MV576. Detailed Description

[0034] The present invention describes a method for preparing a biodegradable polymer nanocomposite film having excellent gas barrier properties, tensile properties, and dimensional stability. This requires a one-step reactive mixing, preferably a twin-screw extrusion process related to the preparation of a biodegradable polymer-based nanocomposite and the integration of the nanocomposite in a multilayer film structure. The biodegradable polymers selected may include aliphatic-aromatic copolyesters based on monomers 1,4-butanediol, adipic acid, terephthalic acid, succinic acid, and lactic acid in the polymer chain. Preferred nanoparticles are layered silicate-type nanoclays with a high aspect ratio and metal-organic frameworks (MOFs) with a high aspect ratio, which can form tortuous paths, and / or have a relatively high specific surface area and pore volume available for adsorbing gas molecules.

[0035] Figure 1 Illustrates the strategy adopted for developing a biodegradable polymer nanocomposite film with excellent barrier properties. As described herein, reactive processing is disclosed, which is a method of simultaneously grafting functional moieties and nanoparticles, and this method improves the dispersion and distribution of the nanoparticles in the biodegradable polymer matrix. Subsequently, in the exemplary films, the nanocomposite constitutes the intermediate barrier layer of the multilayer biodegradable polymer film, and the pure polymer is used as the support layer / outer layer. The comparative films are composed of pure polymers, such as poly(butylene adipate terephthalate) (PBAT), poly(butylene succinate) (PBS), or a combination of a pure polymer and PBAT grafted with MA (PBAT-g-MA).

[0036] Figure 2 Shows the cross-sections of different multilayer films. Figure 2 a shows Comparative Example 1 100, which has pure PBS110 as the outer layer and pure PBAT 120 as the intermediate layer.

[0037] Figure 2b shows Comparative Example 2 200, with pure PBS 110 as the outer layer and PBAT-g-MA 210 as the intermediate layer.

[0038] Figure 2 c shows Example 1 300, with pure PBS 110 as the outer layer and a reactive processed nanocomposite 310 containing 2.1 wt% nanoclay as the intermediate layer.

[0039] Figure 2 d shows Example 2 320, with pure PBS 110 as the outer layer and a reactive processed nanocomposite 312 containing 3.5 wt% nanoclay as the intermediate layer.

[0040] Figure 2 e shows Example 3 330, with pure PBS 110 as the outer layer and a reactive processed nanocomposite 314 containing 4.9 wt% nanoclay as the intermediate layer.

[0041] Figure 2 f shows Comparative Example 3 400, consisting only of pure PBAT 410.

[0042] Figure 2 g shows Example 4 500, with PBAT 410 as the outer layer and a nanocomposite 510 containing EFD nanoclay prepared by reactive extrusion as the intermediate layer.

[0043] Figure 2 h shows Example 5 600, with pure PBAT 410 as the outer layer, a nanocomposite 610 containing kaolin nanoclay prepared by reactive processing as the core material, and a nanocomposite 510 containing EFD nanoclay prepared by reactive processing sandwiched between the core material and the outer layer.

[0044] Figure 2 i shows Example 6 700, with pure PBAT 410 as the outer layer, a nanocomposite 610 containing kaolin nanoclay prepared by reactive processing as the core material, and an unreacted nanocomposite 710 containing EFD nanoclay sandwiched between the core material and the outer layer.

[0045] Figure 2 j shows Example 7 800, with pure PBAT 410 as the outer layer and a nanocomposite 810 containing MOF prepared by reactive processing as the intermediate layer.

[0046] Figure 2k shows Example 8900, with pure PBAT (410) as the outer layer, a reactive processed nanocomposite containing kaolin nanoclay (610) as the core material, and a reactive processed MOF-containing nanocomposite 810 sandwiched between the core material and the outer layer.

[0047] The inorganic content in the nanocomposites was determined by thermogravimetric analysis (TGA), and the results are as Figure 3 shown. The thermal stability of the nanocomposites shows the same trend as that of pure PBAT. The thermal stability of PBAT slightly decreases in PBAT-g-MA and also slightly decreases in the nanocomposites. During the reactive processing, the free radical initiator used under heating and shear conditions may cause polymer chain scission, thus reducing the thermal stability of PBAT-g-MA and the nanocomposites. The inorganic contents in the reactive processed nanocomposites 310, 312, 314, 510, 610 and 810 are approximately 2.1 wt%, 3.5 wt%, 4.9 wt%, 5.4 wt%, 5.0 wt% and 2.5 wt% respectively, while the inorganic content in the non-reactive processed nanocomposite 710 is 3.4 wt%.

[0048] The dispersion characteristics of nanoclay in the reactive processed nanocomposites 310, 312, 314 with different nanoclay concentrations were studied by scanning electron microscopy (SEM, Zeiss Auriga CrossBeam FIB workstation with GEMINI FESEM column), and the results are as Figure 4 shown. Figure 4 The white parts in represent the nanoclay dispersed in different nanocomposites. It can be clearly seen from the figure that compared with the nanocomposite 310 containing 2.1 wt% nanoclay, the distribution of nanoclay in the nanocomposite 312 containing 3.5 wt% nanoclay is improved. In the nanocomposite 314 containing 4.9 wt% nanoclay, only a small amount of nanoclay stacking is visible, which may be due to the formation of an aggregated structure of nanoclay at a higher loading.

[0049] Table 1 summarizes the typical properties of the reactive processed nanocomposites 310, 312 and 314 with different nanoclay concentrations. The crystallization peak temperature (T c ), crystallization enthalpy (ΔH c ), glass transition temperature (T g ), melting peak temperature (T m ), and melting enthalpy (ΔH f)Measurements were carried out by differential scanning calorimetry (DSC, model Q2000, from TA Instruments, USA). The samples were heated from -70 °C to 190 °C at a rate of 10 °C / min, cooled to -70 °C at the same rate, and reheated. As is evident from Table 1, the T c of pure PBAT shifts to higher temperatures; and after grafting the MA functional moiety onto PBAT, ΔH c decreases slightly. The formation of free radicals and subsequent grafting of MA promote the nucleation process but hinder the crystal growth mechanism. This also makes the T g of PBAT-g-MA 210 higher than that of pure PBAT. At lower concentrations, the nanoclay retards the nucleation process and crystal growth behavior of nanocomposites 310, 312, but at higher nanoclay loadings, nanocomposite 314 exhibits properties similar to those of pure PBAT. Compared with pure PBAT, the T m of PBAT-g-MA increases; and then decreases slightly in the presence of nanoclay. The increase in nanoclay concentration has no significant effect on T m . The higher T m in PBAT-g-MA 210 indicates that the grafting of MA and the polymer chains are extended to some extent. The ΔH f of all samples is roughly in a similar range. The properties of PBAT vary depending on batch 410 and are accordingly reported in Table 2. Regardless of the processing method, T c significantly increases in nanocomposites 510, 710 containing EFD nanoclay. Nanocomposite 610 containing kaolin nanoclay also shows a similar trend. The reactive processed MOF nanocomposite 810 exhibits the highest nucleation effect and thus has the highest T c . The ΔH c of non-reactive processed nanocomposite 710 and reactive processed nanocomposite 510 decreases slightly; they contain EFD nanoclay, kaolin nanocomposite 610, and reactive processed MOF nanocomposite 810. The T g of the pure polymer remains unchanged in nanocomposites 510, 610, and 710 containing nanoclay. The T g of the reactive processed MOF nanocomposite 810 shifts to lower temperatures, indicating an increase in chain segment mobility in the presence of nanofillers. The T m and ΔH f of the nanocomposites are in a similar range.

[0050] The grafting degree of MA was determined by titration. As is evident from Table 1, in the nanocomposites, it decreases with the increase in the concentration of nanoclay. The melt flow rate (MFR) represents the change in the flow behavior after MA was grafted onto PBAT 210 and in the nanocomposites 310, 312, and 314 with different nanoclay loadings. The MFR of PBAT-g-MA210 decreased by approximately 10.5%, which also indicates that MA was grafted and the polymer chains were extended to a certain extent. The relatively high MFRs in the nanocomposites 310, 312, and 314 can be attributed to the polymer chain scission during the reactive processing, which is supported by the TGA results. As is evident from Table 2, regardless of the processing method and the type of nanoparticles, the MFRs of the nanocomposites 510, 610, 710, and 810 increased compared to the matrix.

[0051] The reaction mechanism and the changes in the molecular bonds were studied by Fourier transform infrared spectroscopy (FTIR, model Spectrum 100, Perkin Elmer), and the results are as Figures 5 - 8 shown. Figure 5 The characteristic asymmetric C-H stretching vibration peak of pure PBAT, the C=O stretching vibration peak of the ester group, and the C-O asymmetric stretching vibration peak appear at 2955 cm -1 , 1715 cm -1 and 1268 cm -1 respectively. In contrast, the in-plane peaks of trans-CH 2 appear at 1410 cm -1 and 1390 cm -1 respectively. The stretching vibration peaks of CO-O-CO and C=O in maleic acid in MA appear at 1046 cm -1 and 1707 cm -1 respectively. The C=O stretching vibration peak of the conjugated anhydride appears at 1720 cm -1 , 1778 cm -1 and 1853 cm -1 respectively. The OH bond vibration of PBAT is clearly shown in Figure 6 and Figure 8 . The characteristic vibration bands of PBAT remain unchanged in PBAT-g-MA. The CO-O-CO stretching vibration peak of MA does not exist in PBAT-g-MA 210. However, the presence of the C=O stretching vibration peak of the conjugated anhydride (1778 cm -1 ) confirms that functional groups have been added to the PBAT chain. After the grafting reaction, the vibration intensity of the OH bond at 3439 cm -1 decreases, which may be due to the hydrogen bond between the MA counterpart and the OH in the polymer chain.

[0052] The characteristic bond vibrations of EFD nanoclay around 3600 cm -1 and 3439 cm -1 represent OH, while the characteristic bond vibration at 1632 cm -1 is due to the presence of water in the interlayer space (see Figure 7 ). The asymmetric metal - O vibration occurs at 690 cm -1 . It can be clearly seen from Figures 5 - 8 that during reactive processing, the CO - O - CO bond of the anhydride opens and forms hydrogen bonds with the OH present in the nanoclay, thus compatibilizing the nanoclay with PBAT. Compared with the nanocomposite 710 composed of the original nanoclay, this limits the stretching vibration of OH in the reactive - processed nanocomposite 510. Therefore, it can be observed from Figure 8 that in the nanocomposites prepared by reactive processing, the OH vibration is slightly weakened.

[0053] Figure 7 shows that the characteristic peaks of the OH bond vibration of kaolin nanoclay appear around 3694 cm -1 and 3619 cm -1 . The bands of Si - O - Al, Mg / Al - OH, Si - O, and Al - OH appear at 789 cm -1 , 696 cm -1 , 1115 cm -1 and 912 cm -1 respectively. However, the reactive - processed nanocomposite 610 composed of kaolin exhibits similar bond vibrations to those observed in the reactive - processed nanocomposite 510 composed of EFD nanoclay.

[0054] Figure 7 shows that the vibration of the OH bond bridging coordination between the organic ligand and Al 4 (OH) 2 in the MOF appears at 3690 cm -1 and 3442 cm -1 . The COO - of the organic ligand appears at 1600 cm -1 and 1457 cm -1 . The presence of the vibration related to COO - and the absence of the vibration at 3442 cm -1 indicate that in the reactive - processed MOF nanocomposite 810, the CO - O - CO bond of the anhydride opens in a similar way, and the C = O of the conjugated anhydride forms hydrogen bonds with the organic ligand and Al 4 (OH) 2The bridging coordination OH bond reaction enhances the compatibilization between PBAT and MOF.

[0055] Based on the above discussion, as Figure 9 shown, the structures of PBAT-g-MA, the nanocomposites containing nanoclay, and the MOF nanocomposites are proposed. The formation of functional moieties and the extension of polymer chains may have occurred in PBAT-g-MA 210 and the nanocomposites, but more obvious effects were observed in PBAT-g-MA 210. The one-step method simultaneously achieved grafting and nanoparticle dispersion, enhancing the compatibilization between PBAT and the nanoparticles, thus enabling the uniform dispersion and distribution of the nanoparticles in the polymer matrix.

[0056] Figure 10 Transmission electron microscopy (TEM) images of the nanoclay-based nanocomposites and the MOF nanocomposites prepared by non-reactive processing and reactive processing are shown. Before preparing the TEM samples, the samples were exposed to osmium tetroxide vapor overnight. Each sample was cryo-sectioned at -100 °C using a Leica UFC7 microtome. For TEM, the sections were collected on copper grids and imaged using a JEOL 1010 transmission electron microscope at room temperature. The black parts represent the nanoparticles dispersed in the PBAT matrix. It can be seen from the figure that the dispersion and distribution of the nanoclay were improved in the reactive processed nanocomposite 510 containing EFD nanoclay compared to the non-reactive processed nanocomposite 710. Kaolin and MOF were also well-distributed in their respective nanocomposites 710 and 810.

[0057] In subsequent processes, the multilayer biodegradable polymer films were prepared using the pure polymers of the comparative examples or a combination of the pure polymers and the nanocomposite layers in the disclosed example films. The multilayer films can be prepared using any advanced film processing technology. The films mentioned in this article were produced using a five-layer coextrusion blown film machine (Thailand Laboratory Technology Engineering Co., Ltd.). The typical film processing temperature was 150 °C and the screw speed was 50 rpm. Table 3 lists the reference film numbers of the multilayer films and the typical layer structures.

[0058] Oxtran measured the oxygen transmission rate of the films at 23 °C and 0% relative humidity. The surface area of the tested films was 50 cm 2 . The results are summarized in Table 3.

[0059] The dimensional stability of the films was tested according to ASTM D1204 standard under distillation conditions (15 minutes at 120 °C), and the results are summarized in Table 3.

[0060] The tensile properties of the films were tested longitudinally and transversely using an Instron tensile testing machine (model Instron 5966) equipped with a 10 kN load cell. The test speed and gauge length used were 20 mm / min and 25 mm, respectively. The test results are summarized in Table 4. The size of the films tested was 20 mm × 100 mm.

[0061] The water vapor transmission rate was studied using a self-made (assembled in-house) water vapor permeability tester in accordance with ASTM E 96 standard. The instrument was filled with calcium chloride (CaCl 2 ), covered with the test film, and placed in a humidity chamber at a temperature of 23°C and a humidity condition of 50% RH. After a certain time interval, the sample holder was removed from the chamber and weighed to determine the water vapor transmission rate. The variation of the water vapor transmission rate of different films with time is as Figure 11 shown.

[0062] The CO 2 / CH 4 / O 2 emissions of the test samples and microcrystalline cellulose (positive reference) were measured in triplicate under controlled composting conditions at 58 - 60°C using an Echo automated respirometer system (equipped with CO 2 sensors). (Disintegration tests and respirometric CO 2 emission tests (mineralization) were carried out in accordance with ASTM D6400 and ASTM D5338 standards). This compost biodegradation study used well-aerated compost rich in organic matter for 3 months (from Garden Master Compost, Pretoria, South Africa). The compost was sieved (sieve aperture less than 0.8 cm) to obtain a uniform particle size for biodegradation studies. A known volume of compost was taken and dried at about 105°C for 10 hours, and the total dry solid content obtained was 48%. After incineration at about 550°C for 30 minutes, the residue amount of the known volume of compost was subtracted, and the volatile solid content obtained was 33%. The pH value of the compost solution was 7.5. The total organic carbon content, total nitrogen content, and carbon-nitrogen ratio determined by elemental analysis were 15.15%, 0.5%, and 30.3%, respectively.

[0063] The ultimate biodegradability of the test sample films together with microcrystalline cellulose as a positive control was tested in triplicate under composting conditions in accordance with ASTM D5338 method (CO 2Release). This biodegradation study used 2-L glass bioreactors. Each reactor was filled with compost and the test sample at a ratio of 6:1 (weight / weight on a dry weight basis). To simulate aerobic biodegradation conditions, air was bubbled into the reactors at a rate of 500 ml / min. A respirometer measured the released CO 2 emissions, and then the biodegradation rate of each sample was calculated based on the incubation period. Under the test conditions, the total amount of carbon dioxide emitted from each reactor was considered the total degradation of the test sample. The biodegradation rate of the test sample was calculated based on the total organic carbon present in the test sample determined by elemental analysis. The theoretical amount of carbon dioxide (CO 2 (t)) in the total dry weight of the plastic material was calculated using Equation (1) below.

[0064]

[0065] M t and C t represent the total dry weight of the plastic material added to the compost and the relative weight of the total organic carbon in the dry plastic material, respectively. The biodegradation percentage of the organic carbon mineralized to carbon dioxide in the test sample was calculated using Equation (2), where (CO 2 ) s is the carbon dioxide from the test sample (compost + sample), (CO 2 ) c is the carbon dioxide generated from the blank compost, and (CO 2 ) t is the theoretical total amount of carbon dioxide in the test material. The biodegradation curve was obtained by plotting the biodegradation percentage against the incubation time.

[0066] Biodegradability (%) = (2) Under industrial composting conditions, the average cumulative carbon dioxide emissions from the compost inoculum on days 1, 3, 5, 8, and 10 were 404.8 ± 0.9 mg, 686.4 ± 1.1 mg, 783.2 ± 2.0 mg, 1724.8 ± 1.0 mg, and 2050.4 ± 2.1 mg, respectively. After 10 days, the average cumulative carbon dioxide emissions were calculated based on the volatile solids per gram of compost. The experimental results of the industrial compost inoculum showed a volatile solids content of 62.1 mg / g. According to ASTM D5338 standards, the compost inoculum should produce 50 - 150 mg of carbon dioxide per gram of volatile solids within the first ten days of testing. Therefore, the compost inoculum in this study met the standard requirements.

[0067] The degradation test is a major degradation step for monitoring whether the material decomposes into small pieces. According to ASTM D6400, EN13432, and ISO 17088 standards, if after 12 weeks of controlled composting test, the remaining dry weight of the plastic product does not exceed 10% of its original dry weight after sieving through a 2.0 mm sieve, it can be considered that the plastic product has shown satisfactory degradation ability. The degradation study of the test samples was carried out under controlled composting conditions at 58 - 60 °C. The samples (2 cm × 2 cm films) were placed on the surface of the compost and tested regularly to study their degradation mechanism.

[0068] After the biodegradation respiration experiment, 5 grams of compost in each reactor was mixed with 5 grams of fresh farmland soil, and five tomato seeds were planted. The pH value of the compost - soil mixture was measured, and the results were between 7.2 - 7.4. Water was added to keep the relative humidity of the compost - soil mixture between 50 - 55%. This experiment was repeated 3 times.

[0069] The dispersion and distribution characteristics of the nanofillers in the multilayer films, as well as the changes in crystallinity before and after biodegradation, were studied by small - angle and wide - angle X - ray scattering (SWAXS). The SWAXS experiment was carried out using an Anton Paar SAXSess instrument (Anton Paar GmbH, Austria) at 40 kV and 50 mA. The instrument used CuKα radiation (PANalytical X - ray source) with a wavelength of 0.1542 nm. The intensity distribution was obtained using a line - collimated SAXSess instrument and recorded by a two - dimensional imaging plate. The distance from the sample to the detector was 261.2 mm, covering the scattering vector (q) length from 0.09 to 28 nm -1 According to the pixel size, the read - out angle was calculated, and the obtained q range was cross - checked by measuring silver behenate (the equidistant peak positions are known). SWAXS data were collected at room temperature (20.6 °C) and with all samples exposed to X - rays for 15 minutes.

[0070] The film 100 described in Comparative Example 1 includes pure PBS 110 as the outer layer and pure PBAT 120 as the intermediate layer. The oxygen transmission rate of this film is 850.1 cc / m 2 / day (see Table 3). The dimensional stabilities measured in the longitudinal and transverse directions are 2.7% and 0.3% respectively; the negative sign indicates the shrinkage of the film. The tensile modulus, yield load, ultimate tensile stress (UTS), and elongation at break in the longitudinal direction of the film (see Table 4) are 320.0 ± 15.1 MPa, 53.2 ± 3.1 N, 23.3 ± 1.2 MPa, and 408.2 ± 68.4% respectively; the corresponding values in the transverse direction are 363.5 ± 6.5 MPa, 53.1 ± 1.7 N, 21.3 ± 0.6 MPa, and 123.0 ± 58.0% respectively.

[0071] The film 200 described in Comparative Example 2 includes pure PBS 110 as the outer layer and PBAT-g-MA 210 as the intermediate layer. The oxygen transmission rate of this film is 1145.6 cc / m 2 / day (see Table 3). The increase in the oxygen transmission rate is mainly attributed to the change in the polymer chain conformation in the intermediate layer. The dimensional stabilities measured in the longitudinal and transverse directions are 8% and 0%, respectively; the negative sign indicates shrinkage of the film. The tensile modulus, yield load, ultimate tensile stress (UTS), and elongation at break of this film in the longitudinal direction (see Table 4) are 265.6 ± 28.8 MPa, 44.0 ± 5.2 N, 24.7 ± 2.5 MPa, and 515.9 ± 84.3%, respectively; the corresponding values in the transverse direction are 330.8 ± 16.9 MPa, 47.5 ± 4.6 N, 21.3 ± 1.0 MPa, and 465.4 ± 177.1%, respectively. The decrease in the tensile modulus indicates a decrease in stiffness, which may be due to the overall decrease in crystallinity observed from the trend of ΔHc. However, compared with Comparative Example 1, PBAT-g-MA 210 improves the flexibility of the film in both directions due to the significant increase in the elongation at break.

[0072] The film 300 described in Example 1 includes pure PBS 110 as the outer layer and a reactive processed nanocomposite 310 containing 2.1 wt% nanoclay as the intermediate layer. The oxygen transmission rate of this film is 93.8 cc / m 2 / day (see Table 3). Compared with Comparative Example 1, the oxygen transmission rate in Example 1 is reduced by approximately 89%. The decrease in the oxygen transmission rate is attributed to the matrix-filler interaction achieved through the reactive processing of the nanocomposite 310, which ultimately enables the uniform dispersion and distribution of the nanoclay in the nanocomposite. Similar to the case of Comparative Example 1, the dimensional stabilities measured in the longitudinal and transverse directions are 3% and 0%, respectively. The negative sign indicates shrinkage of the film. The tensile modulus, yield load, ultimate tensile stress (UTS), and elongation at break of this film in the longitudinal direction (see Table 4) are 251.3 ± 17.6 MPa, 46.4 ± 1.6 N, 19.7 ± 1 MPa, and 390.2 ± 81.2%, respectively; the corresponding values in the transverse direction are 267.6 ± 14.6 MPa, 41.0 ± 4.2 N, 18.5 ± 2.0 MPa, and 466.3 ± 132.2%, respectively. The decrease in the tensile modulus indicates a decrease in stiffness, which may be due to the overall decrease in crystallinity observed from the trend of ΔHc. However, compared with Comparative Example 1, the nanocomposite 310 improves the flexibility of the film in the transverse direction due to the significant increase in the elongation at break.

[0073] The film 320 described in Example 2 includes pure PBS 110 as the outer layer and a reactive processed nanocomposite 312 containing 3.5 wt% nanoclay as the intermediate layer. The oxygen transmission rate of this film is 92.4 cc / m 2 / day (see Table 3). Compared with Comparative Example 1, the oxygen transmission rate in Example 2 is reduced by approximately 89%. The reduction in the oxygen transmission rate is attributed to the matrix-filler interaction achieved through the reactive processing of the nanocomposite 312, which ultimately enables the uniform dispersion and distribution of the nanoclay in the nanocomposite. The dimensional stabilities measured in the longitudinal and transverse directions are 1.3% and 0%, respectively. Therefore, the stability of the film in this example under distillation conditions is improved by approximately 50% compared to the film in Comparative Example 1. The negative sign indicates the shrinkage of the film. The tensile modulus, yield load, ultimate tensile stress (UTS), and elongation at break (see Table 4) of this film in the longitudinal direction are 245.8 ± 42.6 MPa, 44.0 ± 7.4 N, 18.5 ± 3.6 MPa, and 425.1 ± 63.2%, respectively; the corresponding values in the transverse direction are 263.1 ± 3.3 MPa, 35.7 ± 1.1 N, 15.8 ± 1.4 MPa, and 331.6 ± 109.0%, respectively. With the increase in the nanoclay concentration in the nanoclay-based nanocomposite 320 used as the intermediate layer, the tensile properties of the film decrease.

[0074] The film 330 described in Example 3 includes pure PBS 110 as the outer layer and a reactive processed nanocomposite 314 containing 4.9 wt% nanoclay as the intermediate layer. In addition, the increase in the nanoclay concentration in the nanoclay-based nanocomposite 314 results in the deterioration of all properties of the film 330 disclosed in Example 3.

[0075] The film 400 described in Comparative Example 3 includes only pure PBAT (sample number MV570) 410. The oxygen transmission rate of this film is 449.5 cc / m 2 / day (see Table 3). The dimensional stabilities measured longitudinally and transversely were 6% and 2%, respectively; the negative sign indicates shrinkage of the film (see Table 3). The tensile modulus, yield load, ultimate tensile stress (UTS), and elongation at break of the film longitudinally (see Table 4) were 91.1 ± 12.3 MPa, 33.5 ± 2.4 N, 13.9 ± 1.0 MPa, and 489.8 ± 94.1%, respectively; the corresponding values transversely were 73.3 ± 14.9 MPa, 26.4 ± 3.8 N, 11.1 ± 1.6 MPa, and 467.8 ± 117.6%, respectively. The amount of carbon dioxide released from the mass of the test sample was obtained by theoretical estimation and used to determine the degree of biodegradation (inorganic physicochemical), and the results are shown in Table 5. The mass of the tested film was approximately 25 g, and the mass of microcrystalline cellulose was 25 g. Figure 12Shows the biodegradation characteristics of cellulose and multilayer films measured by respirometer analysis under controlled composting conditions over a 180-day incubation period. Although cellulose degraded by 18% within the first 15 days, no significant biodegradation was observed for the multilayer film. During this period, microorganisms multiplied where they adapted to the composting conditions. Microcrystalline cellulose exhibited more than 70% biodegradation within 45 days. This indicates that the biodegradation device employed meets the effectiveness requirements of the ASTM D5338 test method. Cellulose showed a degradation rate of 90% after 80 days and thereafter showed a plateau as expected; while the MV570 film degraded by 4% within the first 70 days and reached 53% at the end of 180 days. PBAT is commercially available in a fully biodegradable form. However, the biodegradation performance of PBAT depends to a large extent on the form (powder, sheet or film) and thickness of the test sample. For example, under the industrial composting conditions used in this study, PBAT fine-ground particles with an average particle size ≥100 μm can exhibit a degradation rate of 88%.

[29] In contrast, under industrial composting conditions, a PBAT film with a thickness of 100 μm had a degradation rate of approximately 50% at the end of 120 days.

[30] The degradation rate of compression-molded PBAT sheets (with a thickness of 1 mm) was less than 5%.

[31] Not only depending on the sample size, the biodegradation of PBAT also depends on the type of compost. Kijchavengkul et al. reported that within 45 days, the total biodegradation rates of PBAT films (with a thickness of 38.1 ± 5.1 μm) in manure compost, food compost and yard compost were 67.3%, 44.9% and 33.9% respectively.

[32] A PBAT blown film with a thickness of approximately 70 μm can reach a biodegradation rate of 80% within 180 days.

[33] Therefore, the MV570 film (with a thickness of approximately 120 μm) follows a similar trend as observed by Šerá et al. In addition, the aged PBAT film degraded by approximately 18% after 182 days.

[34] Mohanty and Nayak found that incorporating 3 wt% of Cloisite 30B nanoclay did not hinder the biodegradation of pure PBAT. Falcão et al. studied the effect of ultraviolet irradiation on the biodegradability of PBAT composites containing 1 wt% and 5 wt% Cloisite 20A nanoclay.

[28] The authors found that a longer aging time (30 days) led to a significant mass loss within a shorter biodegradation test period. In addition, a higher concentration of Cloisite 20A nanoclay slowed down the biodegradation. The ester bonds in PBAT are prone to hydrolysis, resulting in random scission of the main chain and a rapid decrease in molecular weight.

[35] Figure 12It shows that primary degradation occurs within the first 70 days, during which long-chain polymer molecules break into shorter chains by surface erosion. During surface erosion, microorganisms start to consume the polymer through enzymatic action, resulting in a slow early decrease in molecular weight.

[29] Subsequently, during bulk erosion, the polymer begins to degrade throughout its cross-section by hydrolysis, and low-molecular-weight fragments are digested to produce CO 2 . The crystalline and amorphous regions and conformational flexibility (i.e., the ease of bond rotation and the ease of atoms approaching or moving away from other atoms) play important roles in controlling hydrolysis. Factors affecting conformational flexibility include bulky side groups and certain linkages on the polymer backbone. Bulky side groups restrict the movement of polymer chains and reduce their flexibility. In contrast, certain linkages on the polymer backbone (such as carbon-carbon double bonds) increase flexibility by making adjacent bonds easy to rotate. In semi-crystalline polymers such as PBAT, the amorphous regions of polymer chains degrade much faster than the crystalline regions. It is well known that amorphous materials absorb liquids more easily and degrade faster (requiring less energy). The thermal parameters related to melting and crystallization of the film samples collected during the degradation study are summarized in Table 6. During the studied time period, the T g of the MV570 film shifted to lower temperatures. Short polymer chains that melted at around 59.6 °C disappeared on and after the 30th day. The apparent melting peak temperature (T m ) of the MV570 film started to shift to higher temperatures on the 30th day, decreased significantly on the 90th day, and remained unchanged on the 125th day. The corresponding ΔH f showed a trend similar to that of T m . These results indicate that during biodegradation, microorganisms secrete extracellular enzymes that break down the crystalline regions of the polymer, forming amorphous groups of low molecular weight that are easily digested by microorganisms. After the microorganisms digest the amorphous groups, the remaining material becomes more crystalline.

[36] Therefore, during subsequent cooling and second heating, T c , ΔH c , T m and ΔH fIncreased on the 30th day and remained almost unchanged during the study. Conformational flexibility plays an important role in the biodegradation of polymers. The stronger the flexibility and divisibility of the polymer, the easier it is for microorganisms and water to approach, and thus it is more easily biodegradable. As described in the patent, the one-step reactive extrusion process can simultaneously graft functional moieties (such as MA) onto biodegradable polymers, which further interact with the selected nanoparticles to enhance the interaction between the two, and partial cross-linking occurs between the polymer chains in the presence of a chain extender. MA and the chain extender may also react with the nanoclay. The presence of functional groups can provide hydrolysis sites and increase the flexibility of the polymer chains, making the polymer easily biodegradable. Mohanty et al. also reported that under industrial composting conditions, the degradation rate of PBAT-g-MA / Cloisite 30B nanocomposites is faster than that of PBAT / Cloisite 30B nanocomposites.

[33] Figure 13 and Figure 14 respectively show the photographs of the degraded films and the corresponding SEM images of the surface of the degraded film fragments at different time intervals. In the degradation study device, the films were kept on the compost surface for easy sampling for further testing. However, no traces of the polymer films were found in the compost collected from the reactor used for studying biodegradation (the films were buried in the compost). The FTIR spectra of the degraded film fragments are as shown in Figures 15 - 20 . The characteristic molecular vibrations of PBAT before biodegradation are as follows ( Figure 15 ): 2955 cm -1 represents the asymmetric stretching vibration of CH 2 , and 1715 cm -1 represents the stretching vibration of C–O. The trans-CH in-plane bending vibration is represented by 1409 cm -1 and 1395 cm -1 ; in this comparative example, it appears at 1390 cm -1 . In addition, the symmetric stretching vibration of C-O, the left-right symmetric stretching vibration absorption and bending vibration absorption of C-O on the surface of adjacent hydrogen atoms on the benzene ring appear at 1268 cm -1 , 1104 cm -1 and 1019 cm -1 . In addition to these vibrations, the intermolecular stretching vibration of the OH of the alcohol (near 3200 - 3500 cm -1 ) seems to have a composting cycle of 31 days. The OH vibration becomes obvious with the increase of the composting time; thus, significant changes in the spectral vibrations at 1104 cm -1 and 1019 cm -1 were observed. The C=C stretching vibration of the olefin appears at 1530 cm -1。The biodegradation mechanism of PBAT includes hydrolysis degradation, main chain scission degradation, and β-C-H hydrogen transfer mainly occurring on the ester bonds between terephthalate and adipate groups.

[37] Chemical degradation of the polymer chain usually triggers main chain scission and causes the material to become brittle.

[38] Olefins are one of the end products of β-C-H hydrogen transfer of PBAT. There may be N-O stretching vibrations (1500 - 1550 cm -1 ) of nitro compounds in the compost used for biodegradation testing. The germination percentage of tomato seeds within 15 days is listed in Table 5, and representative photos of germinated seeds and seedlings are as Figure 26 shown. According to the OECD 208 standard test method, compared with the blank compost-soil mixture, at least 50% of the seeds should germinate. Table 5 and Figure 26 show that at the end of the biodegradation test, 90% of the seeds germinated in the compost-soil mixture in the reactor. Similar degrees of seed germination were also observed in the blank compost and microcrystalline cellulose compost soil.

[0076] The film 500 described in Example 4 includes PBAT 410 as the outer layer and a reactive processed nanocomposite 510 containing EFD nanoclay as the intermediate layer. The oxygen transmission rate of this film is 307.8 cc / m 2 / day (see Table 3). Compared with Comparative Example 3, the oxygen transmission rate in Example 4 decreased by approximately 31.5%. The decrease in the oxygen transmission rate is attributed to the formation of tortuous paths by the dispersed nanoclay in the reactive processed nanocomposite 510. Reactive processing improved the compatibilization between PBAT and the nanoclay, resulting in a highly layered structure of the nanocomposite 510. The dimensional stabilities measured longitudinally and transversely are 2.3% and 0.3% respectively (see Table 3). The negative sign indicates film shrinkage. Therefore, compared with Comparative Example 3, the dimensional stabilities of the nanocomposite film disclosed in this example in the longitudinal and transverse directions increased by 61.6% and 85% respectively. The amorphous chain segments in the polymer have a natural random chain orientation, so their expected relaxation is lower than that of the crystalline chain segments. In addition, during film blowing, the polymer is subjected to flow-induced stress orientation and mechanical stretching, which will relax at high temperatures and cause shrinkage. The nanoclay platelets in the composite-based film can inhibit this relaxation of the polymer. Similarly, as shown by the lower ΔH in Table 2 fAs shown by the values, the overall crystallinity of the nanoclay-containing composite material is lower than that of pure PBAT. The composite film exhibits dimensional stability, possibly due to the lower crystallinity of the composite material and the fewer polymer chain relaxation phenomena. The tensile modulus, yield load, ultimate tensile stress (UTS), and elongation at break of the film in the longitudinal direction are 90.0 ± 7.3 MPa, 54.1 ± 3.7 N, 20.8 ± 1.4 MPa, and 620.9 ± 47.2%, respectively; the corresponding values in the transverse direction are 102.7 ± 14.3 MPa, 22.6 ± 2.7 N, 17.4 ± 4.8 MPa, and 660.5 ± 165.1% (see Table 4). Therefore, compared with Comparative Example 3, the film disclosed in this Example has a significant improvement in tensile properties. The significant improvements in oxygen permeability, dimensional stability, and tensile properties can be attributed to the effective compatibilization, dispersion, and distribution of the nanoclay achieved through the reactive processing of the nanocomposite 510. Figure 11 Shows the trend of water vapor transmission rate changing with time. Compared with Comparative Example 3, the film described in Example 4 shows a higher transmission rate. The compatibilization between the polymer and the nanoclay improves the dispersion and distribution of the nanoclay in the nanocomposite, which forms a difficult-to-penetrate barrier for oxygen molecules, and when the nanocomposite is incorporated into a multilayer film, it hinders the penetration of oxygen by forming a tortuous path. However, unless a high aspect ratio of the nanoclay is maintained in the nanocomposite, such a film cannot provide sufficient water vapor barrier performance; the volume of water molecules is smaller than that of oxygen molecules, which also affects its permeation performance. Figure 12 Shows the evolution of caCO 2 during the industrial compostability test. The MV573 film degraded by 19.4% and 58% at 70 days and 180 days, respectively. In the MV573 film, the core nanocomposite layer is protected by pure PBAT. The change of thermal parameters with time can be attributed to the biodegradation of different layers in the multilayer film. The biodegradation of the composite material depends on the hydrolysis process of PBAT provided by the type of nanofiller present in the composite material. For example, the water absorption characteristic mechanism of EFD (montmorillonite) depends on its structure and exchangeable cations. According to Table 5 and Figure 12 , the biodegradability of different films follows the trend of MV574 > MV573 > MV570 ≥ MV572. The cation exchange capacity (CEC) of EFD is ≥ 50 meq / 100 g, while the CEC of montmorillonite is 92.6 meq / 100 g. The lower CEC of the EFD nanoclay results in a decrease in the biodegradability of MV573. Figure 13 and Figure 14Photographs of the degraded films and the corresponding scanning electron microscopy (SEM) images of the surface of the degraded film fragments at different time intervals are shown. The larger voids and structural decomposition in MV573 are obvious. The FTIR spectra of the degraded film fragments are as Figure 16 shown. Clearly, biodegradation by main chain scission in MV573 is evident. The absence of olefin vibrations indicates that biodegradation by β-C-H hydrogen transfer in the composite film is inhibited. Thus, the composite film degrades mainly by hydrolysis degradation and main chain scission; while the biodegradation of pure PBAT may involve all three mechanisms discussed herein. After subtracting the background (PBAT), the scattering patterns in the small angle region are as Figure 21 shown. In all the films tested, long-range periodic ordering of the PBAT chains appears near 0.6 nm, and this feature becomes more prominent after 90 days of composting. The characteristic diffractions of EFD and kaolin appear at 8.7° and 9°, corresponding to scattering vectors (q) of -1 6.18 nm -1 and -1 6.32 nm (3) where L p is the long period in nm, and q max = 0.6 nm -1 . Then, the crystalline layer thickness (l c ) and the amorphous layer thickness (l a ) can be determined according to equations (4) and (5) respectively. X c is the crystallinity of the film determined by equation (6).

[0077] (4) (5) where ρ a and ρ c are the amorphous density and the crystalline density, respectively, and are 1.23 g.cm -3 and 1.36 g.cm -3 .

[39] (6) where ∆H f is the melting enthalpy measured during the first heating, and ∆H f 0is the melting enthalpy of 100% crystalline PBAT (equal to 114 J / g).

[40] X at 0 days and 90 days c 、L p 、l c and l a are listed in Table 7. Although X in MV570 shows an upward trend after 90 days, X of the MV573 film c remains unchanged. For all the films tested, L c is constant. With the decrease of l p in the MV570 film after 90 days of biodegradation (decomposition), l a increases, which can be interpreted as the thickening of the lamella. The decrease of l c is due to the chemical crystallization process during the hydrolysis of PBAT. No obvious changes in l a and l c and l a are observed in the composite film. Therefore, compared with the MV570 film, the hydrolysis delay of PBAT in the composite film is minimal. According to Figure 12 , the trend of biodegradation after 90 days follows MV574 > MV573 > MV570 ≥ MV572. As observed from FTIR, the biodegradation through β-C-H hydrogen transfer is inhibited in the composite film. Therefore, in the initial stage, the main chain scission is the driving factor for the biodegradation of the composite film. As shown in Figure 22 and Figure 23 respectively, the pair distance distribution function (p(r)) and the corresponding electron density distribution (ρ(r)) are determined from the scattering pattern by using the generalized interpolation Fourier transform (GIFT). The experimental scattering curve is represented by the extension *.ift, and the approximate scattering curve theoretically determined by the GIFT method is represented by the extension *.app. Since the two patterns overlap, the p(r) estimated by the GIFT method should represent the p(r) of the experimental scattering curve. In addition, the deconvolution of the approximate electron density distribution by DECON provides information about p(r). Since the nature of p(r) determined by GIFT and DECON is similar, it is obvious that the electron density distribution (ρ(r)) determined by DECON should represent the experimental scattering curve. The probabilities of finding adjacent nanoclays in MV573, MV574 and MV572 are 15.6 nm, 18 nm and 12.5 nm respectively. This indicates that the distribution of nanoclays improves in the following order: MV574 > MV573 > MV572. Figure 22 shows three main correlation peaks in MV573 that appear near 1.5 nm, 2 nm and 2.8 nm. These correlation maxima indicate the probability of finding the presence of adjacent nanoclay particles; and as shown in Figure 22 , after 90 days of biodegradation, the probability of finding adjacent EFD lamellae in the range of 4 to 14 nm increases.Figure 23 The electron density distribution shown indicates a small amount of EFD single layers with a thickness of approximately 1 nm, as well as a stack of approximately 4 to 5 layers (shown between 1.4 and 5.6 nm). This trend remains unchanged after 90 days of biodegradation. Figure 25 The changes in the crystal structure before and after 90 days of biodegradation / decomposition are clearly shown. The diffraction peaks of PBAT crystals appear at 16.2°, 17.3°, 20.4°, 23.2°, and 24.8°. Before biodegradation, except for one peak at 17.3° (which appears at 18.5°), the peaks of PBAT appear at the same positions. However, after biodegradation, a new peak appears at 17.6°. The increase in peak intensity after biodegradation supports the increase in hydrolytic degradation and crystallinity. Table 5 and Figure 26 show that at the end of the biodegradation test, 90% of the seeds germinated in the compost - soil mixture in the reactor.

[0078] The film 600 described in Example 5 includes pure PBAT 410 as the outer layer and, as the intermediate layers, a reactive - processed nanocomposite 510 containing EFD nanoclay and a nanocomposite 610 containing kaolin nanoclay. The oxygen transmission rate of this film is 312.3 cc / m 2 / day (see Table 3). Compared with Comparative Example 3, the oxygen transmission rate in Example 5 is reduced by approximately 30.5%. The reduction in the oxygen transmission rate is attributed to the tortuous paths formed by the dispersed nanoclays in the reactive - processed nanocomposite. Reactive processing improves the compatibilization between PBAT and the nanoclay, resulting in a highly stratified structure of the nanocomposite 510. The dimensional stabilities measured in the longitudinal and transverse directions are 3.5% and 0% respectively (see Table 3). The negative sign indicates film shrinkage. Therefore, compared with Comparative Example 3, the dimensional stabilities of the nanocomposite film disclosed in this example in the longitudinal and transverse directions are increased by 41.7% and 100% respectively. The tensile modulus, yield load, ultimate tensile stress (UTS), and elongation at break 068 of this film in the longitudinal direction are 80.7 ± 14.9 MPa, 49.0 ± 3.9 N, 18.9 ± 1.5 MPa, and 702.3 ± 27.3% respectively; the corresponding values in the transverse direction are 100.3 ± 13.6 MPa, 20.9 ± 0.5 N, 20.9 ± 3.0 MPa, and 896.9 ± 103.0% respectively (see Table 4). Therefore, compared with Comparative Example 3, the film disclosed in this example shows a significant improvement in tensile properties. The significant improvements in oxygen transmission rate, dimensional stability, and tensile properties can be attributed to the effective compatibilization, dispersion, and distribution of the nanoclays achieved through the reactive processing of the nanocomposite 510 and the nanocomposite 610. Figure 12Shows the evolution of carbon dioxide during industrial compostability testing. The MV574 film degraded by 22.6% and 82% at 70 days and 180 days, respectively. In the MV574 film, the core nanocomposite layer is protected by pure PBAT. The variation of thermal parameters over time can be attributed to the biodegradation of different layers in the multilayer film. No significant changes in lc and la were observed in the composite film. Therefore, compared with the MV570 film, the hydrolysis delay of PBAT in the composite film is minimal. The biodegradation of the composite depends on the PBAT hydrolysis process affected by the type of nanofiller present in the composite. For example, the absorption process after initial adsorption may be the splitting of kaolin aggregates or the splitting of lamellar structures weakly bound by stretched hydrogen bonds or van der Waals forces. The water absorption characteristic mechanism of EFD (montmorillonite) is related to its structure and exchangeable cations. According to Table 5 and Figure 12 , the biodegradability of different films follows the trend of MV574 > MV573 > MV570 ≥ MV572. The cation exchange capacity (CEC) of EFD is ≥ 50 meq / 100 g, while the CEC of montmorillonite is 92.6 meq / 100 g. The lower CEC of EFD nanoclay results in a decrease in the biodegradability of MV573. Therefore, the presence of kaolin in the composite plays an important role in the biodegradability of PBAT films with a thickness of about 120 μm. Girdthep et al. studied the compostability of a hybrid composite of polylactic acid, PBAT, and silver-loaded kaolin (Ag-KT) in powder form. They reported that Ag-KT in the hybrid composite hindered the biodegradation of the PLA-PBAT mixture; the composite degraded by 69.9% within 90 days.

[41] Due to the silver loading of kaolin and the form of the samples used to test biodegradability, these results cannot be compared with the results disclosed in this article. Figure 13 and Figure 14 Show the photographs of the degraded films and the corresponding scanning electron microscope (SEM) images of the surface of the degraded film fragments at different time intervals, respectively. Similar to MV573, larger voids and structural decomposition were also observed in the MV574 film. After 90 days, the growth of separated bacteria may occur in MV574. Therefore, MV574 achieved 82% biodegradation, while MV570 only achieved 53% biodegradation. The FTIR spectra of the degraded film fragments are as shown in Figure 17 ; it is obvious that in the presence of kaolin nanoclay in the MV574 film, the main chain breakage is slightly reduced. The absence of olefin vibration indicates that the biodegradation through β-C-H hydrogen transfer in the composite film is inhibited. Therefore, the composite film degrades mainly through hydrolysis degradation and main chain breakage, while the biodegradation of pure PBAT involves all three mechanisms discussed in this article. After subtracting the background (PBAT), the scattering patterns in the small-angle region are as shown in Figure 21 ; According toFigure 12 After 90 days, biodegradation follows the trend of MV574 > MV573 > MV570 ≥ MV572. As observed from FTIR, biodegradation via β-C-H hydrogen transfer in the composite film is inhibited. Therefore, main-chain scission is the driving factor for the biodegradation of the composite film in the initial stage. The probabilities of finding adjacent nanoclays in MV573, MV574, and MV572 are 15.6 nm, 18 nm, and 12.5 nm, respectively. This indicates that the distribution of nanoclays improves in the following order: MV574 > MV573 > MV572. According to Figure 22 , the MV574 film shows a similar trend to the MV573 film. Figure 23 The electron density distribution shown in Figure 25 shows the change in crystal structure before and after 90-day biodegradation / decomposition. The MV574 film shows a similar trend to the MV573 film. Table 5 and Figure 26 show that at the end of the biodegradation test, 100% of the seeds germinated in the compost-soil mixture in the reactor.

[0079] The film 700 described in Example 6 includes pure PBAT 410 as the outer layer and non-reactively processed nanocomposites 710 containing EFD nanoclay and nanocomposites 610 containing kaolin nanoclay as the intermediate layer. The oxygen transmission rate of this film is 339.2 cc / m 2 / day (see Table 3). Compared with Comparative Example 3, the oxygen transmission rate in Example 6 is reduced by about 24.5%. There are aggregated EFD nanoclays in EFD w / o rxn 710 (see Figure 10 ), which creates a less tortuous path for diffusing oxygen molecules. Therefore, the reduction in OTR of the MV572 film is the smallest. The dimensional stabilities measured in the longitudinal and transverse directions are 3.8% and 0%, respectively (see Table 3). The negative sign indicates film shrinkage. Therefore, compared with Comparative Example 3, the dimensional stabilities of the nanocomposite film disclosed in this example in the longitudinal and transverse directions are increased by 36.7% and 100%, respectively. The tensile modulus, yield load, ultimate tensile stress (UTS), and elongation at break of this film in the longitudinal direction are 84.5 ± 15.2 MPa, 17.8 ± 1.8 N, 15.2 ± 2.4 MPa, and 537.6 ± 84.9%, respectively; the corresponding values in the transverse direction are 91.6 ± 18.1 MPa, 21.8 ± 1.9 N, 13.4 ± 1.0 MPa, and 455.7 ± 90.4% (see Table 4). Therefore, the film disclosed in this example has similar tensile properties to Comparative Example 3. Figure 12Shows the evolution of carbon dioxide during industrial compostability testing. The MV572 film degraded by 4% and 51% at 70 days and 180 days, respectively. In the MV572 film, the core nanocomposite layer is protected by pure PBAT. The variation of thermal parameters over time can be attributed to the biodegradation of different layers in the multilayer film. No significant changes were observed in l c and l a There were significant changes. Therefore, compared with the MV570 film, the hydrolysis of PBAT in the composite film was delayed minimally. The biodegradation of the composite depends on the PBAT hydrolysis process affected by the type and dispersion of the nanofillers present in the composite. Tables 5 and Figure 12 Show that the biodegradability of the MV572 film is similar to that of the MV570 film. Figure 13 and Figure 14 Show photographs of the degraded films and corresponding scanning electron microscopy (SEM) images of the surfaces of the degraded film fragments at different time intervals, respectively. After 90 days, small voids were clearly formed in MV572. The FTIR spectra of the degraded film fragments are as shown in Figure 18 . Obviously, biodegradation mainly proceeds through the scission of the main chain in the MV572 film. After subtracting the background (PBAT), the scattering patterns in the small-angle region are as shown in Figure 21 . There were significant changes in p(r) in MV572 before and after 90 days of biodegradation. Apparently, the aggregated nanoclay present in the film separated after 90 days, which may be triggered when adsorption occurs in the central composite layer (including kaolin). Figure 23 The electron density distribution presented in shows that the MV572 film exhibits a similar trend to the MV573 film. Figure 25 Shows the changes in the crystal structure before and after 90 days of biodegradation / decomposition. The MV572 film exhibits a similar trend to the MV573 film. Tables 5 and Figure 26 Show that at the end of the biodegradation test, 100% of the seeds germinated in the compost-soil mixture in the reactor.

[0080] The film 800 described in Example 7 includes pure PBAT 410 as the outer layer and a reactive-processed nanocomposite 810 containing MOF nanoclay as the intermediate layer. The oxygen transmission rate of the film is 328.2 cc / m 2 / day (see Table 3). Compared with Comparative Example 3, the oxygen transmission rate in Example 7 decreased by approximately 27%. The decrease in the oxygen transmission rate is attributed to the high specific surface area (BET specific surface area is 744.9 m 2 / g), and the tortuous paths formed by MOF nanoparticles in the reactive processed nanocomposites. The dimensional stabilities measured longitudinally and transversely were 2.5% and 1% respectively (see Table 3). The negative sign indicates the shrinkage of the film. Therefore, compared with Comparative Example 3, the dimensional stabilities of the nanocomposite films disclosed herein in the longitudinal and transverse directions were increased by 58.3% and 83.3% respectively. The tensile modulus, yield load, ultimate tensile stress (UTS), and elongation at break of the film in the longitudinal direction were 96.2 ± 15.0 MPa, 43.2 ± 3.1 N, 18.0 ± 1.3 MPa, and 624.2 ± 37.2% respectively. The corresponding values in the transverse direction were 74.1 ± 19.8 MPa, 30.7 ± 5.3 N, 12.8 ± 2.2 MPa, and 445.6 ± 50.9% respectively (see Table 4). Therefore, the films disclosed in this example have significantly similar tensile properties to those of Comparative Example 3. Figure 11 shows the trend of water vapor transmission rate over time; compared with Comparative Example 3, the transmission rate of the film described in Example 7 was significantly reduced, which may be due to its high specific surface area and high total pore volume of single-point adsorption (0.47 cm 3 / g). Figure 12 shows the evolution of carbon dioxide during the industrial compostability test. The MV575 film degraded by approximately 10% and 79.3% at 70 days and 180 days respectively. Therefore, the presence of MOF in the composite plays an important role in the biodegradation of PBAT films (with a thickness of approximately 120 μm). Figure 13 and Figure 14 show the photographs of the degraded films and the corresponding scanning electron microscope (SEM) images of the surface of the degraded film fragments at different time intervals respectively. Void formation and structural decomposition were observed in the MV575 film. The FTIR spectra of the degraded film fragments are as Figure 19 shown. The MV575 film showed bond vibrations similar to those of nanocomposite films containing nanoclay. Therefore, the MV575 film disclosed in this example is expected to degrade mainly by hydrolysis degradation and main chain scission degradation. In contrast, the biodegradation of pure PBAT may involve all three mechanisms discussed herein. No significant changes were observed in l c and l a . Therefore, compared with the MV570 film, the hydrolysis of PBAT in the composite film was delayed to the least extent. The scattering pattern of the MV575 film is as Figure 24 shown. The characteristic X-ray diffraction of MOF appeared at 10.6°, corresponding to a scattering vector of 7.5 nm -1 . Therefore, the peak position shifted to 6.8 nm -1 , which illustrates the dispersion of nanoparticles in the PBAT matrix. Although most MOF nanoparticles were well dispersed, at 7.5 nm -1The small peaks that appear nearby indicate the existence of some agglomeration phenomena. Figure 25 The changes in the crystal structure before and after 90 days of biodegradation / decomposition are shown in. The MV575 film shows a similar trend to the MV573 film. Table 5 and Figure 26 show that at the end of the biodegradation test, 100% of the seeds germinated in the compost-soil mixture in the reactor.

[0081] The film 900 described in Example 8 includes pure PBAT 410 as the outer layer and reactive processed nanocomposites 810 containing MOF nanoclay and nanocomposites 610 containing kaolin nanoclay as the intermediate layer. The oxygen transmission rate of this film is 366.4 cc / m 2 / day (see Table 3). Compared with Comparative Example 3, the oxygen transmission rate in Example 8 is reduced by about 18.5%. Compared with other nanocomposite films, the less reduction in the oxygen transmission rate indicates a poorer interface between the layers of the MV576 film. The dimensional stability measured in the longitudinal and transverse directions is 2.6% and 1% respectively (see Table 3). The negative sign indicates the shrinkage of the film. Therefore, compared with Comparative Example 3, the nanocomposite film disclosed in this example achieves similar improvements to the MV575 film. The tensile modulus, yield load, ultimate tensile stress (UTS), and elongation at break of this film in the longitudinal direction are 107.0±7.0 MPa, 35.0±8.8 N, 15.0±3.2 MPa, and 604.1±149.4% respectively. The corresponding values in the transverse direction are 103.9±15.8 MPa, 31.5±3.6 N, 13.2±1.6 MPa, and 574.2±157.9% respectively (see Table 4). Therefore, the film disclosed in this example exhibits better tensile properties than Comparative Example 3. Figure 12 Shows the evolution of carbon dioxide during the industrial compostability test. The MV576 film degraded by about 22% and 86.9% at 70 days and 180 days respectively. Therefore, MOF and kaolin nanoclay play important roles in the biodegradation of PBAT films (with a thickness of about 120 μm). Figure 13 and Figure 14 Show the photos of the degraded films and the corresponding scanning electron microscope (SEM) images of the surfaces of the degraded film fragments at different time intervals respectively. Void formation and structural decomposition were observed in the MV576 film. The FTIR spectra of the degraded film fragments are as Figure 20 shown. The MV576 film shows similar bond vibrations to the nanocomposite films containing nanoclay. Therefore, the MV576 film disclosed in this example is expected to degrade by hydrolysis degradation and main chain scission degradation. In contrast, the biodegradation of pure PBAT may involve all three mechanisms discussed herein. No l c and l aThere are significant changes. Therefore, compared with the MV570 film, the PBAT hydrolysis in the composite film has the lowest delay. The scattering pattern of the MV576 film is as Figure 24 shown. The dispersion of MOF nanoparticles in MV576 is similar to that in the MV575 film. Figure 25 shows the changes in the crystal structure before and after 90 days of biodegradation / decomposition. The MV576 film shows a similar trend to the MV573 film. Table 5 and Figure 26 show that at the end of the biodegradation test, 100% of the seeds germinated in the compost-soil mixture in the reactor.

[0082] Table Table 1. Characteristics of nanocomposites containing different loadings of nanoclay

[0083] Table 2. Characteristics of nanocomposites including different nanofillers.

[0084]

[0085] Table 3. Oxygen permeability and dimensional stability of multilayer films

[0086] Table 4. Tensile properties of multilayer films

[0087] a MV570: PBAT | PBAT | PBAT | PBAT | PBAT; b MV573: PBAT | EFD rxn | EFD rxn | EFD rxn | PBAT; c MV574: PBAT | EFD rxn | kaolin rxn | EFD rxn | PBAT; d MV572: PBAT | EFD w / o rxn | kaolin rxn | EFD w / o rxn | PBAT; e MV575: PBAT | MOF rxn | MOF rxn | MOF rxn | PBAT; PBAT | MOF rxn | MOFrxn | MOF rxn | PBAT; fMV576: PBAT | MOF reaction | Kaolin reaction | MOF reaction | PBAT Table 5. Biodegradability of different films and percentage of seed germination in compost at the end of biodegradation study

[0088] a MV570: PBAT | PBAT | PBAT | PBAT | PBAT; b MV573: PBAT | EFD reaction | EFD reaction | EFD reaction | PBAT; c MV574: PBAT | EFD reaction | Kaolin reaction | EFD reaction | PBAT; d MV572: PBAT | EFD without reaction | Kaolin reaction | EFD without reaction | PBAT; e MV575: PBAT | MOF reaction | MOF reaction | MOF reaction | PBAT; PBAT | MOF reaction | MOF reaction | MOF reaction | PBAT; f MV576: PBAT | MOF reaction | Kaolin reaction | MOF reaction | PBAT Table 6. Parameters related to melting and crystallization of samples collected at specific intervals during decomposition study

[0089] a MV570: PBAT | PBAT | PBAT | PBAT | PBAT; b MV573: PBAT | EFD reaction | EFD reaction | EFD reaction | PBAT; c MV574: PBAT | EFD reaction | Kaolin reaction | EFD reaction | PBAT; d MV572: PBAT | EFD without reaction | Kaolin reaction | EFD without reaction | PBAT; e MV575: PBAT | MOF reaction | MOF reaction | MOF reaction | PBAT; PBAT | MOF reaction | MOF reaction | MOF reaction | PBAT; f MV576: PBAT | MOF reaction | kaolin reaction | MOF reaction | PBAT; An obvious transformation is reported here.

[0090] Table 7. Relationship between crystallinity, long-range periodic order, crystalline layer thickness, and amorphous layer thickness and biodegradation

[0091] a MV570: PBAT | PBAT | PBAT | PBAT | PBAT; b MV573: PBAT | EFD reaction | EFD reaction | EFD reaction | PBAT; c MV574: PBAT | EFD reaction | kaolin reaction | EFD reaction | PBAT; and d MV572: PBAT | EFD without reaction | kaolin reaction | EFD without reaction | PBAT.

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Claims

1. A method for preparing a polymer nanocomposite film, the polymer nanocomposite film being biodegradable with excellent gas barrier properties, tensile properties, and dimensional stability at the distillation temperature, the method comprises: providing a biodegradable polymer, wherein the biodegradable polymer is an aliphatic-aromatic copolyester based on monomers 1,4-butanediol, adipic acid, terephthalic acid, succinic acid, and lactic acid in the polymer chain; providing nanoparticles, the particles comprising layered silicate-type nanoclay; providing nanoparticles, the particles comprising a metal-organic framework (MOF); providing an organic linker, wherein the organic linker comprises fumaric acid; and, using a one-step reactive mixing method to achieve enhanced interaction between the biodegradable polymer and the nanoparticles, thereby enhancing the dispersion and distribution of the nanoparticles in the nanocomposite film.

2. The method for preparing a biodegradable polymer nanocomposite film according to claim 1, wherein, the content of the nanoparticles is 1 to 10% by weight.

3. The method for preparing a biodegradable polymer nanocomposite film according to claim 2, wherein, the content of the nanoparticles is less than 5% by weight.

4. The method for preparing a biodegradable polymer nanocomposite film according to claim 1, wherein, the one-step reactive mixing method involves reactive extrusion technology.

5. The method for preparing a biodegradable polymer nanocomposite film according to claim 4, wherein, the extrusion technology comprises co-rotating twin-screw extrusion of the biodegradable polymer and the nano-filler in the presence of a free radical initiator.

6. The method for preparing a biodegradable polymer nanocomposite film according to claim 5, wherein, the extrusion process further comprises adding a functional organic moiety to enhance the wettability of the nanoclay in the polymer matrix.

7. The method for preparing a biodegradable polymer nanocomposite film according to claim 5, wherein, the extrusion process further comprises adding a chain extender to minimize the reduction in molecular weight during processing.

8. The method for preparing a biodegradable polymer nanocomposite film according to claim 5, wherein, the extrusion process further comprises adding an antioxidant to improve processing stability.

9. The method for preparing a biodegradable polymer nanocomposite film according to claim 8, wherein, the free radical initiator comprises dicumyl peroxide, and the content of the free radical initiator is 0.2 to 0.5% by weight.

10. The method for preparing a biodegradable polymer nanocomposite film according to claim 1, wherein, the functional organic moiety comprises maleic anhydride, and the content of the functional organic moiety is 1 to 6% by weight.

11. The method for preparing a biodegradable polymer nanocomposite film according to claim 1, wherein, the functional organic moiety comprises maleic anhydride, and the content of the functional organic moiety is 1.9% by weight.

12. The method for preparing a biodegradable polymer nanocomposite film according to claim 1, wherein, the nanocomposite is processed using the following conditions: Temperature curves of 120|130|140|145|130|120|110|110|110|110 °C, screw speed of 80 to 200 rpm, and feed rate of 1 to 15 kg / h.

13. The method for preparing a biodegradable polymer nanocomposite film according to claim 12, wherein, the screw speed is preferably 116 rpm.

14. The method for preparing a biodegradable polymer nanocomposite film according to claim 12, wherein, the feed rate is preferably 6.6 kg / h.

15. The method for preparing a biodegradable polymer nanocomposite film according to claim 1, wherein, the extrudate can be collected by a water bath or air; preferably collected by air before granulation; subsequently, the granules are dried at 70 °C for 16 hours and used to prepare a multilayer nanocomposite film.

16. The biodegradable polymer nanocomposite film obtained by the preparation method according to claim 1, wherein, the nanocomposite film comprises a poly(butylene adipate-co-terephthalate) (PBAT) nanocomposite as the intermediate layer and a specifically selected biodegradable polymer as the supporting outer layer.

17. The biodegradable polymer nanocomposite film according to claim 16, wherein, the specifically selected biodegradable polymer for the supporting outer layer comprises poly(butylene succinate) (PBS).

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