A biodegradable polymer nanocomposite film with high transparency, high barrier and high toughness and a preparation method thereof

Abstract

The application discloses a kind of high-transparency high-barrier high-toughness biodegradable polymer nanocomposite films and preparation method thereof, including 40-90wt% of hydrophilic biodegradable polymer and 10-60wt% of organic modified layered nanoparticles;The hydrophilic biodegradable polymer is polyester containing hydrophilic group, and the preparation method comprises, after ultrasonic dispersion in water and water-organic mixed solvent respectively, then mixing, pouring, spraying or spreading on the surface of substrate, drying into film, to obtain the biodegradable polymer nanocomposite film.The biodegradable polymer nanocomposite film of the application can increase the addition amount of nanoparticles, and the obtained nanocomposite film has high gas barrier property, and also has high transparency, high toughness and significantly improved rigidity, and the mechanical properties are more balanced, and the comprehensive performance is excellent in all aspects, and has obvious advantages for biodegradable packaging materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-molecular film, in particular to a kind of high-transparency high-barrier high-toughness biodegradable polymer nanocomposite film and preparation method thereof. BACKGROUND

[0002] Due to the difficulty in degrading into harmless products in the natural environment, the large-scale application and abandonment of traditional plastic products, especially disposable plastic products, have led to increasingly serious environmental problems, such as water / soil deterioration, marine pollution, and microplastic pollution. Replacing traditional non-degradable polymers with biodegradable polymers such as aliphatic polyesters and aliphatic-aromatic copolyesters is an important measure to solve plastic pollution from the source. Currently, aliphatic polyesters such as polylactic acid (PLA) and polybutylene succinate (PBS), as well as aliphatic-aromatic copolyesters such as poly(butylene adipate-co-terephthalate) (PBAT) and poly(butylene succinate-co-terephthalate) (PBST), have achieved industrial production and are gradually being applied in areas such as shopping bags, disposable tableware, mulch, sanitary materials, textiles, and medical materials.

[0003] Packaging materials are a typical and important application field of biodegradable polymers. High-end packaging materials for beverages, food, pharmaceuticals, and electronic products require high oxygen and / or carbon dioxide barrier properties to make them more stable during production, transportation, and storage, in order to achieve the purpose of preservation, shelf life extension, and quality assurance. However, the gas barrier properties of commonly used biodegradable polymers are generally low, for example, the oxygen and CO2 barrier properties of PBAT and PLA are much lower than those of common packaging material PET polyester, and even lower than most high-barrier packaging materials. Preparing polymer nanocomposites by melt intercalation, in-situ polymerization, and other nanocomposite methods is a common means to improve the gas barrier properties of polymers, but it is difficult to effectively achieve the full exfoliation and orientation of nanofillers, and even more difficult to achieve exfoliation and orientation at high nanofiller content. Therefore, the improvement of gas barrier properties is often limited, and the barrier improvement factor is generally not more than 5, i.e., the gas barrier properties of nanocomposites are generally not more than 5 times that of the base resin.

[0004] CN 111848937A discloses biodegradable polymers with hydrophilic groups and their gas barrier properties, the presence of hydrophilic groups improves their oxygen barrier properties. CN 113813796A and document 1 (Ind. Eng. Chem. Res. 2022, 61, 13283-13293) disclose the use of biodegradable polymers with hydrophilic groups and inorganic layered nanoparticles without organic modification, which are dispersed in water to prepare a nanocomposite dispersion, and dried into a film to prepare a biodegradable polymer layered nanocomposite film (referred to as NCF film). This method achieves full exfoliation and orientation at high nanofiller content, which can significantly improve the oxygen and carbon dioxide barrier properties, and the oxygen barrier modification factor is more than 100. However, the nanocomposite film has poor toughness, high rigidity and extremely unbalanced mechanical properties. The nanocomposite dispersion is coated on a biodegradable base film, and after drying, a nanocomposite coating film (referred to as NCCF film) is prepared, which significantly improves the toughness and oxygen barrier properties (document 2: Polymer Degradation and Stability 216, 110489, 2023).

[0005] In addition to high barrier property and high toughness, transparency is also an important technical index as a packaging material. However, it is extremely challenging to balance high gas barrier property and transparency for nanocomposite films with sufficiently high nanoparticle content. For PBAT nanocomposite films, there are some reports in the literature that the transparency can be maintained at a high level when the nanoparticle content is <8wt%, and there are also many reports that the transparency decreases significantly even when the nanoparticle content is <8wt%, but there are no reports that the transparency can be maintained at a high level at high nanoparticle content (such as >8wt%). For example, document 3 (Journal of Applied Polymer Science 2020, 137(46), 49522.) reported that the transmittance of PBAT / nSiO2 0.7 (meaning containing 0.7wt% nSiO2, the same below) composite film decreased significantly compared with PBAT, but the transmittance of PBAT / OMMT 4.5 and PBAT / sepiolite 2.5 was basically unchanged; document 4 (Applied Clay Science 2016, 126:72-80) reported that the PBAT / ODLH 0.5-8 nanocomposite film prepared by solution intercalation method had high transparency, and the transmittance increased and the haze decreased with the increase of ODLH content; but document 5 (ACS Omega 2018, 3, 1187-1196) reported that the transmittance of PBAT / ODLH 0.5-4 nanocomposite film prepared by melt intercalation method first increased and then decreased, and the highest transmittance was about 86.9% when the ODLH content was 1wt%;

[0006] Document 6 (LWT Food Science and Technology 2020, 132: 109874) reports that the light transmittance of PBAT / SiO2-Ag nanocomposite film decreases significantly with the increase of nanoparticle content (1-10 wt%).

[0007] In summary, how to obtain a biodegradable polymer nanocomposite film with a significant improvement of gas barrier by an order of magnitude while maintaining high toughness and high transparency under the condition of a large amount of nanoparticle addition and its preparation method are still technical problems to be solved. SUMMARY

[0008] To solve the problem of the prior art biodegradable polymer nanocomposite film that the gas barrier is significantly improved by an order of magnitude while maintaining high toughness and high transparency, the present application provides a biodegradable polymer nanocomposite film with high transparency, high barrier and high toughness and a preparation method thereof. The nanocomposite film has high gas barrier, high toughness and high transparency.

[0009] To achieve the above-mentioned object, the technical scheme adopted by the present application is:

[0010] A biodegradable polymer nanocomposite film with high transparency, high barrier and high toughness, according to mass percentage, comprising 40-90 wt% of hydrophilic biodegradable polymer and 10-60 wt% of organic modified layered nanoparticles;

[0011] The hydrophilic biodegradable polymer is prepared by polycondensation reaction of dihydric alcohol, dibasic acid or its diester and sulfonated dibasic acid or its diester; the sulfonated dibasic acid or its diester is dibasic acid or its diester containing sulfonate side groups;

[0012] The sulfonated dibasic acid or its diester is selected from one or more of 5-sulfonated sodium isophthalic acid or its diester, 2-sulfonated sodium succinic acid or its diester, and 2-methylene sulfonated sodium succinic acid or its diester, and the amount is 5-15 mol% of the total amount of dibasic acid or its diester and sulfonated dibasic acid or its diester;

[0013] The preparation method of the biodegradable polymer nanocomposite film comprises the following steps:

[0014] Step 1: stirring and / or ultrasonic dispersion of the hydrophilic biodegradable polymer in water to obtain a dispersion PD; stirring and / or ultrasonic dispersion of the organic modified layered nanoparticles in a mixed solvent to obtain a dispersion OND;

[0015] Step 2: mixing PD and OND, and obtaining a composite dispersion ONCD by ultrasonic stirring;

[0016] Step 3: pouring, spraying or spreading the ONCD on the surface of the substrate, drying into a film to obtain the biodegradable polymer nanocomposite film.

[0017] In the present application, the hydrophilic biodegradable polymer is dispersed in water, the organic modified layered nanoparticles are dispersed in the mixed solvent containing the hydrophilic organic solvent, and the polymer and the nanoparticles are each fully dispersed in the dispersion medium before ultrasonic mixing. In the presence of a large amount of nanoparticles, a high-transparency composite film with excellent dispersion effect can be obtained, and the toughness of the composite film is also excellent, realizing the improvement of comprehensive performance in many aspects.

[0018] The diol is selected from one or more of C2-C6 aliphatic diols, C6-C 10 The diol is selected from one or more of C2-C6 aliphatic diols, C6-C

[0019] The diol is selected from one or more of C2-C6 aliphatic diols, C6-C 16 linear aliphatic diacid or diester thereof, C6-C8 aromatic diacid or diester thereof, C8-C 10 linear aliphatic diacid or diester thereof, C6-C8 aromatic diacid or diester thereof, C8-C

[0020] The hydrophilic biodegradable polymer has an intrinsic viscosity of 0.3-1.0 dL / g, the hydrophilic group is a sulfonic acid group, and the content of the hydrophilic group in the polymer is 0.3-1.0 mmol / g.

[0021] The biodegradable polymer nanocomposite film has a light transmittance of more than 70%, an oxygen barrier improvement factor of more than 5, a ductile tensile behavior, and an elongation at break of more than 35%. The light transmittance refers to the data at 550 nm.

[0022] Preferably, the biodegradable polymer nanocomposite film has a light transmittance of more than 75%, and more preferably, the biodegradable polymer nanocomposite film has a light transmittance of more than 80%. When used as a packaging material, the higher the light transmittance, the more convenient it is to clearly observe the contents of the package.

[0023] Preferably, the biodegradable polymer nanocomposite film has an oxygen barrier improvement factor of 10 or more, preferably, an oxygen barrier improvement factor of 20 or more; more preferably, an oxygen barrier improvement factor of 25 or more. The higher the oxygen barrier factor, the higher the oxygen barrier of the nanocomposite film compared to the biodegradable polymer substrate, which is more conducive to preventing the penetration of oxygen when used as a packaging film, and is more conducive to preventing the oxidation and corruption of the contents of the package, and is conducive to improving the shelf life and shelf life.

[0024] Preferably, the biodegradable polymer nanocomposite film has an elongation at break of 100% or more; preferably, an elongation at break of 200% or more; more preferably, an elongation at break of 300% or more. The higher the elongation at break, the better the flexibility of the material.

[0025] The mass fraction of the organic modified layered nanoparticles is 20-60 wt%; preferably, the mass fraction of the organic modified layered nanoparticles is 30-60 wt%, the higher the content, the better the oxygen barrier of the product, but the toughness will decrease, but the overall still maintains excellent.

[0026] The organic modified layered nanoparticles are organic modified layered silicates or organic modified layered dihydroxides, including quaternary ammonium salts, quaternary phosphonium salts, long-chain alkyl amines or omega-amino long-chain fatty acid modified layered montmorillonite.

[0027] The application also provides a preparation method of the biodegradable polymer nanocomposite film with high transparency, high barrier and high toughness, comprising the following steps:

[0028] Step 1: stirring and / or ultrasonic dispersion of the hydrophilic biodegradable polymer in water to obtain a dispersion PD; stirring and / or ultrasonic dispersion of the organic modified layered nanoparticles in a mixed solvent to obtain a dispersion OND;

[0029] Step 2: mixing PD and OND, and ultrasonic stirring to obtain a composite dispersion ONCD;

[0030] Step 3: pouring, spraying or spreading ONCD on the surface of the substrate, and drying to form a film to obtain the biodegradable polymer nanocomposite film.

[0031] The mixed solvent in step 1 is a mixed solvent of any one or more of methanol, ethanol, tetrahydrofuran, acetone, butanone and water, wherein the volume ratio of the hydrophilic organic solvent to water is 5:95-95:5. The addition of the hydrophilic organic solvent greatly improves the dispersion of the organic nanoparticles, and a suitable volume ratio is conducive to the dispersion and exfoliation of the organic modified nanoparticles, and is conducive to obtaining exfoliated nanosheets with high aspect ratio.

[0032] In step 1, the mass ratio of the hydrophilic biodegradable polymer to water is 5:95-30:70, and the dispersion time is 0.5-6 hours. The stirring and / or ultrasonic temperature is room temperature-95℃.

[0033] In step 1, the mass ratio of the organic modified layered nanoparticles to the mixed solvent is 0.5:99.5-15:85, and the dispersion time is 0.5-6 hours. The stirring and / or ultrasonic temperature is room temperature.

[0034] In step 2, the stirring and / or ultrasonic temperature is room temperature, and the time is 0.5-2 hours.

[0035] In the present application, the organic modification of the layered nanoparticles enables them to be effectively dispersed in the organic solvent-water mixed medium under the action of stirring and ultrasonic, and to be fully exfoliated to form a nanoscale dispersion liquid OND. After the nanocomposite dispersion liquid ONCD obtained by mixing the OND and the PD is dried into a film, the organic modified nanosheets, although having a certain hydrophobicity, still have a certain affinity and interfacial interaction with the moderately hydrophilically modified biodegradable polymer, forming a well-dispersed nanocomposite film.

[0036] The biodegradable polymer nanocomposite film has a thickness of 10-200 microns.

[0037] The nanocomposite film obtained in the present application not only has excellent oxygen barrier property, but also unexpectedly has excellent flexibility, showing the tensile behavior of a tough plastic. When the OMMT content is ≤30wt% (or 22vol%), the elongation at break is >300%; when the OMMT content is ≤37wt% (or 28vol%), the elongation at break is >100%; and when the OMMT content is ≤42wt% (or 33vol%), the elongation at break is >35%. At the same time, compared with the biodegradable polymer substrate, the tensile modulus is significantly improved, avoiding the drawbacks of excessive softness and insufficient rigidity of the existing biodegradable copolyester.

[0038] The nanocomposite film obtained in the present application not only has excellent oxygen barrier property, but also unexpectedly has excellent transparency. When the OMMT content is 23wt% (or 16vol%), the light transmittance is as high as 85.1%; when the OMMT content is 42wt% (or 32vol%), the light transmittance is as high as 77.5%; and when the organic modified MMT (OMMT) content is 59wt% (or 49vol%), the light transmittance is still as high as 73.0%.

[0039] Compared with the prior art, the present application has the following beneficial effects:

[0040] The hydrophilic degradable polymer and modified nanoparticles are mixed by ultrasonic dispersion in the application, the addition amount of the nanoparticles can be improved, the obtained nanocomposite film has high gas barrier property, meanwhile, the nanocomposite film has high transparency, high toughness and significantly improved rigidity, the mechanical properties are more balanced, the defects of the prior biodegradable copolyester, such as too soft, too poor rigidity and unbalanced mechanical properties, are overcome, the comprehensive performance is excellent, and the biodegradable packaging material has obvious advantages. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 AFM images (a) and size (b) of the commercial organic montmorillonite I.34TCN after dispersion and exfoliation (3 vol%) in a 50:50 ethanol / water mixture.

[0042] Figure 2 WAXD patterns (a) of Na-MMT, OMMT (I.34TCN) and ONCF nanocomposite films of Examples 1-6 and TEM image (b) of ONCF22 of Example 3.

[0043] Figure 3 Transparency of PBAT film, sPBAT film and ONCF nanocomposite films of Examples 1-6.

[0044] Figure 4 Light transmittance in the visible region of OMD, PD and ONCD dispersions and PBAT film, sPBAT film and ONCF nanocomposite films of Examples 1-6.

[0045] Figure 5 Comparison of light transmittance in the visible region of ONCF nanocomposite films of Examples 1, 3-5 and NCF nanocomposite films of Comparative Examples 1-4 and comparison of transparency of ONCF32 film of Example 5 and NCF32 film of Comparative Example 4.

[0046] Figure 6 Tensile curves of sPBAT film and ONCF nanocomposite films of Examples 1-6. DETAILED DESCRIPTION

[0047] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to examples. It should be understood that the specific examples described herein are only used to explain the present application and not used to limit the present application. Any modification or equivalent replacement made by those skilled in the art based on the technical solutions of the present application without departing from the spirit and scope of the present application should be covered in the protection scope of the present application.

[0048] The raw materials used in the following specific embodiments are all purchased from the market, and the organic modified layered nanoparticles used are shown in Table 1.

[0049] Table 1 Unmodified and organically modified layered nanoparticles used in the present application

[0050] Layered nanoparticle Class Cation exchange capacity Source Na-MMT Sodium montmorillonite 145 meq / 100 g Nanocor I.28E Organically modified montmorillonite / Nanocor I.34TCN Organically modified montmorillonite / Nanocor CMMT Organically modified montmorillonite / Home-made OLDH Organically modified layered double hydroxide / Home-made

[0051] Preparation of CMMT: Take 3 grams of sodium-based montmorillonite (Na-MMT) and add it to 500 mL of pure water, stir at 500 rpm and apply 40 KHz ultrasound for 2 hours; then, add a slow 50 mL aqueous solution of cetyltrimethylammonium bromide (CTAB), the amount of CTAB being equivalent to the cation exchange capacity of Na-MMT, warm to 80°C and continue stirring and sonication for 3 hours; finally, filter, wash with ethanol and dry to obtain CTAB-modified montmorillonite, denoted as CMMT.

[0052] Preparation of OLDH: prepared according to reference 4 (Applied Clay Science 2016, 126: 72-80).

[0053] The biodegradable polymers and hydrophilic biodegradable polymers used in the embodiments of the present application are shown in Table 2.

[0054] Table 2 Properties of the hydrophilic biodegradable polyester substrates used in the present application

[0055]

[0056] IV: intrinsic viscosity, solvent chloroform, temperature 25°C; Tr: transmittance (@550 nm); Haze: haze; BIF: oxygen barrier improvement factor; E: tensile modulus; σ b : tensile breaking strength; ε b : elongation at break.

[0057] PBAT refers to poly(butylene adipate-co-terephthalate), PBST refers to poly(butylene succinate-co-terephthalate), and PBS refers to poly(butylene succinate); sPBAT, sPBST and sPBS refer to the corresponding polyesters containing a sodium sulfonate hydrophilic group.

[0058] Wherein, the synthesis of sPBAT is as follows: (1) add 28.94 g (0.198 mol) adipic acid, 26.91 g (0.162 mol) terephthalic acid and 64.89 g (0.72 mol) 1,4-butanediol to a 250 mL four-necked flask, wherein the acid / alcohol ratio is 1:2, under the protection of nitrogen atmosphere and mechanical stirring, when the esterification temperature reaches 180°C, add 0.12 g of catalyst tetra-n-butyl titanate, react at 180°C for about 2 h, warm up to 215°C, react until the distillate water no longer increases and the system is clear and transparent, to obtain a prepolymer 1.

[0059] Into a 25 mL three-necked flask, 12.80 g (0.142 mol) 1,4-butanediol and 9.73 g (0.0328 mol) dimethyl isophthalate-5-sodium sulfonate (dimethyl isophthalate-5-sodium sulfonate accounts for 8.4 mol% of the total mole number of all diacid and diester of diacid, acid / alcohol ratio is 1:4.3), under the protection of nitrogen atmosphere and mechanical stirring, when the ester exchange temperature reaches 180℃, 0.02 g catalyst tetrabutyl titanate is added, and the reaction is carried out for about 1 h until the clear transparent state is reached, at which time the distillate mass no longer changes, and the prepolymer 2 is obtained.

[0060] (2) The prepolymer 1 and the prepolymer 2 are uniformly mixed, and under the condition of vacuum degree less than 50 Pa and 230℃-250℃, the reaction is carried out for about 3 h, after the climbing rod effect appears, the stirring speed is reduced, and the reaction is continued until the climbing rod effect still appears under very slow speed, and the sulfonated poly(butanediol terephthalate adipate) -sPBAT is prepared, the intrinsic viscosity of which is 0.91 dL / g, and the sodium sulfonate group content is 0.43 mmol / g.

[0061] The adipic acid is replaced by succinic acid, and other steps are the same as the above steps, and the sPBST is synthesized, the intrinsic viscosity of which is 0.85 dL / g, and the sodium sulfonate group content is 0.42 mmol / g.

[0062] The adipic acid and the terephthalic acid are both replaced by succinic acid, and other steps are the same as the above steps, and the sPBS is synthesized, the intrinsic viscosity of which is 0.87 dL / g, and the sodium sulfonate group content is 0.43 mmol / g.

[0063] In the present application, the transparency of the film is expressed by the light transmittance and the haze, which is measured by a CS-821N table spectrophotometer of Hangzhou Caipu Science and Technology Company in the range of 400-800 nm, the light transmittance at 550 nm is taken as the value for comparison, and is recorded as the light transmittance (@550 nm).

[0064] In the present application, the oxygen barrier property of the film is expressed by an oxygen permeation coefficient P O2 , the unit of which is barrer, 1 barrer = 10 -10 cm 3 (STP).cm.cm -2 .s -1 .cmHg -1 . P O2 is lower, the better the oxygen barrier property is. For the nanocomposite film, in addition to the P O2 value (absolute value), the oxygen barrier improvement factor BIF (relative value) is also used to express the multiple of the oxygen barrier property of the polymer matrix. The definition of BIF is: BIF = P O2,基材 / P O2,复合膜 , wherein, PO2,基材 and P O2,复合膜 represent the oxygen permeability coefficients of the polymer base and the nanocomposite film, respectively.

[0065] Preparation of nanocomposite film ONCF10

[0066] 1) Preparation of nanocomposite dispersion ONCD

[0067] (A) sPBAT was pulverized, 2 grams of which was added to hot water at 90°C, and stirred at 500 rpm for 2 hours to obtain a semi-transparent sPBAT nanodispersion with blue light, which was recorded as PD, wherein the volume fraction of sPBAT was 10 vol%;

[0068] (B) Organic modified montmorillonite I.34TCN was added to a 50:50 water / ethanol mixed medium, and stirred at 500 rpm and subjected to 40 KHz ultrasonic action for 2 hours, so that the organic montmorillonite was uniformly dispersed and fully exfoliated into nanosheets of one to several layers, to obtain an organic modified montmorillonite sheet nanodispersion, which was recorded as OND, wherein the content of I.34TCN was 3 vol%. The AFM photo of the exfoliated organic montmorillonite and its size are shown in Figure 1 .

[0069] (C) 20 mL of PD and 7.5 mL of OND were mixed together, and stirring and ultrasonic action were continued for half an hour to obtain a nanocomposite dispersion containing both sPBAT nanoparticles and organic modified montmorillonite I.34TCN sheet nanosheets, which was recorded as ONCD.

[0070] 2) ONCD was cast into a PTFE mold, and dried into a film to obtain nanocomposite film ONCF10, wherein the meaning of the number "10" is that the volume content of I.34TCN in the nanocomposite film is 10 vol%, and the corresponding mass content is 14.5 wt%.

[0071] Preparation of nanocomposite films ONCF16-49

[0072] In Reference Example 1, 20 mL of PD and 13.0 mL, 19.0 mL, 26.0 mL, 31.0 mL or 64 mL of OND were mixed together in step 1C, respectively, and other operations were the same as in Example 5, to obtain nanocomposite films ONCF16, ONCF22, ONCF28, ONCF32 and ONCF49, respectively, wherein the meaning of the numbers "16, 22, 28, 32, 49" is that the volume content of OMMT in the nanocomposite films is 16 vol%, 22 vol%, 28 vol%, 32 vol% and 49 vol%, respectively, and the corresponding mass content is 23 wt%, 30 wt%, 37 wt%, 42 wt% and 59 wt%, respectively.

[0073] Example 7: Preparation of ONCF32 with sPBST and I.34TCN

[0074] 1) Preparation of nanocomposite dispersion ONCD

[0075] (A) sPBST was pulverized, 2 grams of which was added to hot water at 90°C, and stirred at 500 rpm for 2 hours to obtain a semi-transparent sPBST nanodispersion with blue light, which was recorded as PD, wherein the volume fraction of sPBST was 10 vol%;

[0076] (B) Organic modified montmorillonite I.34TCN was added to a 50:50 water / ethanol mixed medium, stirred at 500 rpm and subjected to 40 KHz ultrasonic action for 2 hours, and the organic montmorillonite was uniformly dispersed and fully exfoliated into nanosheets of one to several layers to obtain an organic modified montmorillonite I.34TCN sheet nanodispersion, which was recorded as OND, wherein the content of I.34TCN was 3 vol%;

[0077] (C) 20 mL of PD and 31.0 mL of OND were mixed together, and stirring and ultrasonic action were continued for half an hour to obtain a nanocomposite dispersion containing both sPBST nanoparticles and organic modified montmorillonite sheet nanoparticles, which was recorded as ONCD.

[0078] 2) ONCD was cast into a PTFE mold and dried into a film to obtain a nanocomposite film ONCF32, wherein the volume content of I.34TCN was 32 vol%, and the corresponding mass content was 42 wt%.

[0079] Example 8: Preparation of ONCF32 with sPBS and I.34TCN

[0080] 1) Preparation of nanocomposite dispersion ONCD

[0081] (A) sPBS was pulverized, 2 grams of which was added to hot water at 90°C, and stirred at 500 rpm for 2 hours to obtain a semi-transparent sPBS nanodispersion with blue light, which was recorded as PD, wherein the volume fraction of sPBS was 10 vol%;

[0082] (B) Organic modified montmorillonite I.34TCN was added to a 50:50 water / ethanol mixed medium, stirred at 500 rpm and subjected to 40 KHz ultrasonic action for 2 hours, and the organic montmorillonite was uniformly dispersed and fully exfoliated into nanosheets of one to several layers to obtain an organic modified montmorillonite I.34TCN sheet nanodispersion, which was recorded as OND, wherein the content of I.34TCN was 3 vol%;

[0083] (C) Mix 20 mL of PD and 31.0 mL of OND together, continue stirring and ultrasonicating for half an hour to obtain a nanocomposite dispersion liquid containing both sPBS nanoparticles and organic modified montmorillonite sheet nanoparticles, denoted as ONCD.

[0084] 2) Pour ONCD into a PTFE mold, dry into a film to obtain nanocomposite film ONCF32, wherein the volume content of I.34TCN is 32 vol%, and the corresponding mass content is 42 wt%.

[0085] Example 9: Preparation of ONCF32 using sPBAT and I.28E

[0086] 1) Preparation of nanocomposite dispersion liquid ONCD

[0087] (A) Grind sPBAT, take 2 grams and add to hot water at 90°C, high speed stirring at 500 rpm for 2 hours to obtain a semi-transparent sPBAT nanodispersion liquid with blue light, denoted as PD, wherein the volume fraction of sPBAT is 10 vol%;

[0088] (B) Add organic modified montmorillonite I.28E to a 30:70 water / ethanol mixed medium, stir at 500 rpm and ultrasonicate at 40 KHz for 2 hours, and the organic montmorillonite is uniformly dispersed and fully exfoliated into one or several sheet layers of nanosheets to obtain an organic modified montmorillonite sheet nanoparticle dispersion liquid, denoted as OND, wherein the content of I.28E is 3 vol%;

[0089] (C) Mix 20 mL of PD and 31.0 mL of OND together, continue stirring and ultrasonicating for half an hour to obtain a nanocomposite dispersion liquid containing both sPBAT nanoparticles and organic modified montmorillonite I.28E sheet nanoparticles, denoted as ONCD.

[0090] 2) Pour ONCD into a PTFE mold, dry into a film to obtain nanocomposite film ONCF32, wherein the volume content of I.28E is 32 vol%, and the corresponding mass content is 42 wt%.

[0091] Example 10: Preparation of ONCF32 using sPBAT and CMMT

[0092] 1) Preparation of nanocomposite dispersion liquid ONCD

[0093] (A) Grind sPBAT, take 2 grams and add to hot water at 90°C, high speed stirring at 500 rpm for 2 hours to obtain a semi-transparent sPBAT nanodispersion liquid with blue light, denoted as PD, wherein the volume fraction of sPBAT is 10 vol%;

[0094] (B) The organic modified montmorillonite CMMT was added into 50:50 water / ethanol mixed medium, stirred at 500 rpm and subjected to 40 KHz ultrasonic for 2 hours. The organic montmorillonite was uniformly dispersed and fully exfoliated into nanosheets of one to several layers, obtaining a dispersion of organic modified montmorillonite nanosheet particles, denoted as OND, wherein the content of CMMT was 3 vol%;

[0095] (C) 20 mL of PD and 31.0 mL of OND were mixed together, and stirring and ultrasonic were continued for half an hour, obtaining a nanocomposite dispersion containing both sPBAT nanoparticles and organic modified montmorillonite CMMT nanosheet particles, denoted as ONCD.

[0096] 2) The ONCD was cast into a PTFE mold and dried into a film, obtaining a nanocomposite film ONCF32, wherein the volume content of I.28E was 32 vol%, and the corresponding mass content was 42 wt%.

[0097] Example 11: Preparation of ONCF32 from sPBAT and ODLH

[0098] 1) Preparation of nanocomposite dispersion ONCD

[0099] (A) sPBAT was pulverized, and 2 grams were added into hot water at 90°C, stirred at 500 rpm for 2 hours, obtaining a semi-transparent sPBAT nanodispersion with blue light, denoted as PD, wherein the volume fraction of sPBAT was 10 vol%;

[0100] (B) The OLDH was added into 60:40 water / ethanol mixed medium, stirred at 500 rpm and subjected to 40 KHz ultrasonic for 2 hours. The OLDH was uniformly dispersed and fully exfoliated, obtaining a dispersion of OLDH nanosheet particles, denoted as OND, wherein the content of OLDH was 3 vol%;

[0101] (C) 20 mL of PD and 31.0 mL of OND were mixed together, and stirring and ultrasonic were continued for half an hour, obtaining a nanocomposite dispersion containing both sPBAT nanoparticles and OLDH nanosheet particles, denoted as ONCD.

[0102] 2) The ONCD was cast into a PTFE mold and dried into a film, obtaining a nanocomposite film ONCF32, wherein the volume content of I.28E was 32 vol%, and the corresponding mass content was 42 wt%.

[0103] Comparative Example 1: Preparation of NCF10 from sPBAT and Na-MMT

[0104] 1) Preparation of nanocomposite dispersion NCD

[0105] (A) sPBAT was crushed, 2 g was added into hot water at 90 °C, and stirred at 500 rpm for 2 hours to obtain a semi-transparent sPBAT nano-dispersion with blue light, noted as PD, wherein the volume fraction of sPBAT was 10 vol%;

[0106] (B) Na-MMT was added into pure water, stirred at 500 rpm and subjected to ultrasonic treatment at 40 KHz for 2 hours, and Na-MMT was uniformly dispersed and fully exfoliated to obtain a Na-MMT sheet nano-particle dispersion, noted as ND, wherein the content of Na-MMT was 3 vol%;

[0107] (C) 20 mL of PD and 7.5 mL of ND were mixed together, and stirring and ultrasonic treatment were continued for half an hour to obtain a nano-composite dispersion containing both sPBAT nano-particles and Na-MMT sheet nano-particles, noted as NCD.

[0108] 2) NCD was cast into a PTFE mold, and dried into a film to obtain a nano-composite film NCF10, wherein the volume content of Na-MMT was 10 vol%, and the corresponding mass content was 19 wt%.

[0109] Comparative Examples 2-4: Preparation of NCF22, NCF28, NCF32 using sPBAT and Na-MMT

[0110] Referring to Comparative Example 1, in step 1C, 20 mL of PD and 19.0 mL, 26.0 mL or 31.0 mL of ND were mixed together respectively, and other operations were the same as in Comparative Example 1 to obtain nano-composite films NCF22, NCF28, NCF32 respectively, wherein the numerical values “22, 28, 32” mean that the volume content of Na-MMT in the nano-composite films was 22 vol%, 28 vol%, 32 vol% respectively, and the corresponding mass content was 38 wt%, 45 wt%, 50 wt% respectively.

[0111] The results of the composite films prepared in the examples and comparative examples are summarized in Table 3.

[0112] Table 3 Properties of the composite films prepared in the examples and comparative examples

[0113]

[0114] Tr: transmittance (@550 nm); Haze: haze; BIF: oxygen barrier improvement factor; E: tensile modulus; σ b : tensile breaking strength; ε b : elongation at break.

[0115] Figure 1The results show that the commercial organic modified montmorillonite I.34TCN can be dispersed and exfoliated in 50:50 ethanol / water mixed medium, and the obtained nanosheet contains one to several layers of single-layer nanosheet. The lateral size of the exfoliated I.34TCN nanosheet is 0.2-2 um, the thickness is 1.0-7.0 nm, and the diameter-thickness ratio is 100-500 (average value 280). Other layered nanofillers in the present application, including commercial or self-made, can also be dispersed and exfoliated in mixed medium by adjusting the type and proportion of hydrophilic organic solvent in the mixed medium according to the structure and amount of the modifier.

[0116] Figure 2 The results show that the interlayer distance of the commercial organic montmorillonite I.34TCN is larger than that of Na-MMT, and the interlayer distance further increases after the I.34TCN is combined with sPBAT to form an ONCF nanocomposite film, and even reaches full exfoliation, and basically no diffraction peak is observed. Similar effects can also be achieved by using other organic modified layered nanofillers in the present application, including commercial or self-made. Figure 2 The results show that the organic montmorillonite in the ONCF22 nanocomposite film formed by the combination of I.34TCN and sPBAT is fully exfoliated and oriented. Other ONCF nanocomposite films prepared from other organic modified layered nanoparticles and hydrophilic biodegradable polymers also have similar high exfoliation and orientation effects.

[0117] Figures 3-4 The results in Table 3 show that the transparency of PBAT is poor, and the transparency of sPBAT is significantly higher than that of PBAT. The nanocomposite films ONCF10-49 prepared from sPBAT and commercial organic modified montmorillonite I.34TCN all exhibit high transparency, and the light transmittance is 81.6-73.0%, and the haze is 24.3-75.0%. Although the light transmittance decreases and the haze increases with the increase of the content of I.34TCN, even when the content of I.34TCN is as high as 49 vol% (59 wt%), the light transmittance still reaches 73.0%, which shows good transparency. Figure 3 At the same time, these ONCF films all exhibit excellent oxygen barrier property, which is 11-26 times that of the substrate sPBAT (Table 3); the oxygen permeation coefficient is as low as 0.065-0.027 barrer, and the oxygen barrier property is comparable to that of the commonly used packaging material PET. Moreover, these ONCF films also exhibit the characteristics of ductile plastics, and yield phenomenon occurs during the tensile test. Figure 6), the elongation at break of which is 35-474%, which decreases with the increase of the content of I.34TCN; the tensile modulus (i.e. Young's modulus) of which is 79-524 MPa, which is obviously higher than 56 MPa of the substrate sPBAT, and also higher than 50-100 MPa of PBAT, while maintaining a relatively high tensile strength. It is to be noted that the advantage of PBAT lies in its excellent flexibility, but it has the disadvantages of poor transparency, low Young's modulus and poor gas barrier property. Compared with PBAT, the above ONCF film better maintains the advantage of excellent flexibility, while significantly improves the transparency, Young's modulus and gas barrier property.

[0118] The results in Table 3 also show that the NCF nanocomposite films (Comparative Examples 1-4) prepared using sPBAT and Na-MMT as raw materials and water as dispersion medium have excellent oxygen barrier property, which is better than that of the corresponding ONCF film. However, compared with NCF10, the ONCF10 nanocomposite film prepared in Example 1 has a slightly lower light transmittance (81.6% vs. 86.1%) but much lower haze (24.3% vs. 65.6%), thus better transparency; compared with the NCF22, NCF28 and NCF32 nanocomposite films prepared in Comparative Examples 2-4, the ONCF22, ONCF28 and ONCF32 nanocomposite films prepared in Examples 3-5 have higher light transmittance (80.0-77.5 vs. 75.6-49.2) and much lower haze (36.7-48.4% vs. 69.6-94.7%), thus better transparency, as shown in Table 3. Figure 5 The NCF films have poor tensile ductility, showing brittle fracture, with very low elongation at break and extremely unbalanced mechanical properties; in contrast, the ONCF films show ductile tensile behavior and balanced mechanical properties, with higher tensile modulus than the commonly used biodegradable copolyester PBAT. These advantages of the ONCF films in transparency and mechanical properties are more conducive to meet the application requirements of packaging materials.

[0119] The results of Examples 7-8 show that the ONCF nanocomposite films prepared using other hydrophilic biodegradable polymers and organically modified nanoparticles as raw materials also have the characteristics of high transparency, high barrier, high toughness, balanced mechanical properties and biodegradability. The results of Examples 9-11 show that the biodegradable polymer nanocomposite films with high transparency, high barrier, high toughness and balanced mechanical properties can also be prepared using other commercial layered nanoparticles or self-made layered nanoparticles and hydrophilic biodegradable polymers as raw materials. Therefore, the high-transparency high-barrier high-toughness biodegradable polymer nanocomposite film and the preparation method thereof proposed by the present application have good universality.

Claims

1. A biodegradable polymer nanocomposite film with high transparency, high barrier and high toughness, characterized in that, According to the mass percentage, the biodegradable polymer nanocomposite film comprises 40-90wt% of the hydrophilic biodegradable polymer and 10-60wt% of the organic modified layered nanoparticles; The hydrophilic biodegradable polymer is prepared by polycondensation reaction of dihydric alcohol, diacid or its diester and sulfonated diacid or its diester; the sulfonated diacid or its diester is diacid or its diester containing sulfonate side groups; The sulfonated diacid or its diester is selected from one or more of 5-sodium sulfonate isophthalic acid or its diester, 2-sodium sulfonate succinic acid or its diester and 2-sodium sulfonate methylene succinic acid or its diester, and the amount of the sulfonated diacid or its diester is 5-15mol% of the total amount of diacid or its diester and sulfonated diacid or its diester; The preparation method of the biodegradable polymer nanocomposite film comprises the following steps: Step 1: stirring and / or ultrasonic dispersion of the hydrophilic biodegradable polymer in water to obtain a dispersion PD; stirring and / or ultrasonic dispersion of the organic modified layered nanoparticles in a mixed solvent to obtain a dispersion OND; Step 2: mixing of the PD and OND and ultrasonic stirring to obtain a composite dispersion ONCD; Step 3: pouring, spraying or spreading of the ONCD on the surface of a substrate and drying to form a film to obtain the biodegradable polymer nanocomposite film; The organic modified layered nanoparticles are organic modified layered silicates or organic modified layered double hydroxides, including quaternary ammonium salt, quaternary phosphonium salt, long-chain alkyl amine or omega-amino long-chain fatty acid modified layered montmorillonite.

2. The biodegradable polymer nanocomposite film of claim 1, wherein, said diol is selected from the group consisting of C2-C6aliphatic diols, C6-C 10 one or more of the group consisting of aliphatic diols, cycloaliphatic diols, said dibasic acid or diester thereof is selected from the group consisting of C4-C 16 linear aliphatic dibasic acid or diester thereof, C6-C8aromatic dibasic acid or diester thereof, C8-C 10 cycloaliphatic dibasic acid or diester thereof.

3. The biodegradable polymer nanocomposite film of high transparency, high barrier and high toughness according to claim 1, characterized in that, The intrinsic viscosity of the hydrophilic biodegradable polymer is 0.3-1.0dL / g, the hydrophilic group is sulfonic acid group, and the content of the hydrophilic group in the polymer is 0.3-1.0mmol / g.

4. The biodegradable polymer nanocomposite film of claim 1, wherein the film has a high transparency, a high barrier property, and a high toughness. The biodegradable polymer nanocomposite film has a light transmittance of more than 70%, an oxygen barrier improvement factor of more than 5, and a ductile tensile behavior with an elongation at break of more than 35%.

5. The biodegradable polymer nanocomposite film of high transparency, high barrier and high toughness according to claim 1, characterized in that, The mass fraction of the organic modified layered nanoparticles is 20-60wt%.

6. The biodegradable polymer nanocomposite film of high transparency, high barrier and high toughness according to claim 1, characterized in that, The mass fraction of the organic modified layered nanoparticles is 30-60wt%.

7. The process for the preparation of high transparent high barrier high ductility biodegradable polymer nanocomposite film as claimed in any one of claims 1 to 6, wherein the process is characterized by, The preparation method comprises the following steps: Step 1: stirring and / or ultrasonic dispersion of the hydrophilic biodegradable polymer in water to obtain a dispersion PD; stirring and / or ultrasonic dispersion of the organic modified layered nanoparticles in a mixed solvent to obtain a dispersion OND; Step 2: mixing of the PD and OND and ultrasonic stirring to obtain a composite dispersion ONCD; Step 3: pouring, spraying or spreading of the ONCD on the surface of a substrate and drying to form a film to obtain the biodegradable polymer nanocomposite film.

8. The process for the preparation of high transparent high barrier high ductility biodegradable polymer nanocomposite film as claimed in claim 7, wherein, The mixed solvent in step 1 is a mixed solvent of any one or more of hydrophilic organic solvents of methanol, ethanol, tetrahydrofuran, acetone and butanone and water, wherein the volume ratio of the hydrophilic organic solvent to water is 5:95-95:

5.

9. The process for the preparation of high transparent high barrier high ductility biodegradable polymer nanocomposite film as claimed in claim 7, wherein, In step 1, the mass ratio of the hydrophilic biodegradable polymer to water is 5:95-30:70, and the dispersion time is 0.5-6 hours.

10. The process for the preparation of high transparent high barrier high ductility biodegradable polymer nanocomposite film as claimed in claim 7, wherein, In step 1, the mass ratio of the organic modified layered nanoparticles to the mixed solvent is 0.5:99.5-15:85, and the dispersion time is 0.5-6 hours.

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