Multi-layer packaging material with high barrier property and application thereof

Abstract

The invention relates to a multilayer packaging material with high barrier property and application thereof. The multi-layer packaging material at least comprises three layers, namely a layer A, a layer B and a layer C, wherein the layer B is located between the layer A and the layer C; the layer A is prepared from the following raw materials: first biodegradable polyurethane and a cellulose nanocrystal graft which is obtained by performing grafting treatment on cellulose nanocrystal after hydrophobic modification, and the content of the cellulose nanocrystal graft is 1wt%-10wt% of that of the first biodegradable polyurethane; the raw material of the layer B comprises biodegradable polyester containing a glycollic acid structural unit, and the content of the glycollic acid structural unit is not less than 60% mol; the raw material of the layer C comprises second biodegradable polyurethane. The hydrophobic modified cellulose nanocrystals are uniformly dispersed in the layer A, so that the adsorption of water vapor on the layer A is reduced, the permeation of the water vapor is hindered, and the barrier property of the whole material is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of packaging materials, and particularly relates to a multi-layer packaging material with high barrier property and application thereof. BACKGROUND

[0002] In daily life application scenarios, packaging materials have high requirements for gas barrier property and water resistance. For example, without the barrier of oxygen and / or moisture, the food or other products contained in the packaging may lose freshness, taste, color, or may otherwise expire more quickly and become inedible or unusable.

[0003] With the continuous development of economy, the requirements for the environment are getting higher and higher. The most common polymers used in the original packaging industry, such as polyethylene (PE), polypropylene (PP), polyethylene-vinyl alcohol (EVOH), polyamide (nylon, PA), ionomer (EAA, EMAA), and ethylene vinyl acetate (EVA), are gradually replaced by biodegradable polymers due to their difficulty in recycling or degradation.

[0004] However, the biodegradable polymers in the prior art have many deficiencies in the synergy of gas barrier and water resistance. For example, biodegradable materials containing glycolic acid units have good gas barrier and water resistance as barrier layers, but are prone to hydrolysis after encountering water, resulting in a decrease or failure of barrier properties. The gas barrier and water resistance of biodegradable materials such as polybutylene succinate (PBS), polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polycaprolactone (PCL), polybutylene succinate adipate (PBSA), and polyhydroxyalkanoate (PHA) are relatively weak.

[0005] Patent CN115515788A discloses a multi-layer structure and an article thereof, which includes an A layer base layer, a B layer adhesive layer, and a C layer barrier layer. The A layer contains a polylactide polymer, the B layer contains a poly(lactide-co-glycolide) polymer with more than 30 mol% lactide, and the C layer contains a poly(lactide-co-glycolide) polymer with 2-30 mol% lactide. Water molecules from the outside easily penetrate into the adhesive layer and the barrier layer inside the material. Since the adhesive layer and the barrier layer are made of materials containing glycolic acid units, they are prone to structural damage, a shorter barrier period, or functional failure when encountering water molecules, making it difficult to effectively block the penetration of moisture and gases such as oxygen and carbon dioxide. SUMMARY

[0006] The purpose of the present application is to provide a multi-layer packaging material with high barrier property and application thereof, which can reduce the adsorption of water vapor on the outer surface layer and hinder the penetration of water vapor, thereby improving the overall barrier property of the material.

[0007] In a first aspect, the present invention provides a multilayer packaging material with high barrier properties, comprising at least three layers: layer A, layer B, and layer C, wherein layer B is located between layer A and layer C;

[0008] The raw materials of the A layer include a first biodegradable polyurethane and a cellulose nanocrystal graft obtained by hydrophobic modification of cellulose nanocrystals and then grafting treatment. The content of the cellulose nanocrystal graft is 1 wt% to 10 wt% of the first biodegradable polyurethane.

[0009] The raw material of the B layer includes a biodegradable polyester containing glycolic acid structural units, and the content of glycolic acid structural units is not less than 60% mol.

[0010] The raw material for the C layer includes a second biodegradable polyurethane.

[0011] In one embodiment, the cellulose nanocrystal graft is obtained through the following steps:

[0012] (a) The cellulose nanocrystals are hydrophobically modified using a silanizing agent, wherein the silanizing agent is selected from aminosilane coupling agents or epoxysilane coupling agents;

[0013] (b) The cellulose nanocrystal graft is obtained by grafting hydrophobically modified cellulose nanocrystals with carboxyl-terminated polyester prepolymer.

[0014] In one embodiment, the carboxyl-terminated polyester prepolymer is obtained by ring-opening copolymerization of lactide, caprolactone, and maleic anhydride, wherein the molar ratio of maleic anhydride to the sum of the molar amounts of lactide and caprolactone is (0.1-0.5):1.

[0015] In one embodiment, step (a) specifically includes:

[0016] (a1) Dissolve cellulose nanocrystals in an ethanol solution with a volume concentration of not less than 75% to form a dispersion A with a mass concentration of 1 to 5 wt%, and adjust the pH of dispersion A to 3 to 4; and dissolve a silanizing agent in an ethanol solution with a volume concentration of not less than 90% to form a dispersion B with a mass concentration of 1 to 5 wt%.

[0017] (a2) Under stirring conditions, dispersion B is slowly added to dispersion A, and the amount of silanizing agent added is 20wt% to 50wt% of the cellulose nanocrystals;

[0018] (a3) React at 40-60℃ for 30-60 min, centrifuge to separate, wash the obtained solid with anhydrous ethanol and deionized water until the washing solution is close to neutral, and then vacuum dry to obtain hydrophobically modified cellulose nanocrystals.

[0019] In one embodiment, step (b) specifically includes:

[0020] (b1) Under a nitrogen atmosphere, lactide, caprolactone, maleic anhydride and catalyst are added to the reaction vessel in proportion, heated and mixed evenly, the reaction system is heated to 120-160℃ and reacted for 4-8 hours to obtain carboxyl-terminated polylactide caprolactone prepolymer.

[0021] (b2) Add hydrophobically modified cellulose nanocrystals, raise the temperature and lower the pressure, control the temperature at 170-210℃ and the absolute pressure at 50Pa-50kPa, and continue the reaction for 2-10 hours. The amount of hydrophobically modified cellulose nanocrystals added is 5%-20% of the total mass of lactide and caprolactone.

[0022] (b3) After the reaction is complete, the temperature is lowered to below 60°C, dichloromethane is added to dissolve the product, then excess methanol or ethanol is added, the product is precipitated, filtered, and dried to obtain the cellulose nanocrystal graft.

[0023] In some embodiments, layer A comprises the following components in parts by weight: 100 parts of first biodegradable polyurethane, 1 to 10 parts of cellulose nanocrystal graft, 0 to 30 parts of first biodegradable polyester, 0 to 10 parts of inorganic filler, and 0.2 to 2 parts of processing aid.

[0024] The C layer comprises the following components in parts by weight: 100 parts of second biodegradable polyurethane, 0-40 parts of second biodegradable polyester, and 0.2-2 parts of processing aids;

[0025] The first biodegradable polyurethane comprises polyester segments and isocyanate segments formed from cyclic ester monomers, wherein the cyclic ester monomers are lactide and / or caprolactone.

[0026] The second biodegradable polyurethane comprises polyester segments and isocyanate segments formed from cyclic ester monomers, wherein the cyclic ester monomers are selected from one or more of glycolide, lactide, and caprolactone, and include at least glycolide.

[0027] In some embodiments, layer A comprises the following components in parts by weight: 100 parts of first biodegradable polyurethane, 1 to 10 parts of cellulose nanocrystal graft, 0 to 30 parts of first biodegradable polyester, 0 to 10 parts of inorganic filler, and 0.2 to 2 parts of processing aid.

[0028] The C layer comprises the following components in parts by weight: 100 parts of second biodegradable polyurethane, 1-10 parts of cellulose nanocrystal graft, 0-40 parts of second biodegradable polyester, and 0.2-2 parts of processing aids.

[0029] Both the first biodegradable polyurethane and the second biodegradable polyurethane include polyester segments and isocyanate segments formed from cyclic ester monomers, wherein the cyclic ester monomers are lactide and / or caprolactone.

[0030] In some embodiments, the first biodegradable polyurethane or the second biodegradable polyurethane is obtained through the following steps:

[0031] (1) The cyclic ester monomers for synthesizing the first biodegradable polyurethane or the second biodegradable polyurethane and the polyol are added to a reaction vessel in proportion, and a ring-opening copolymerization reaction is carried out under the action of a catalyst to obtain a polyester polyol, wherein the hydroxyl value of the polyester polyol is between 30-300 mg KOH / g.

[0032] (2) Using the polyester polyol obtained in step (1) as raw material, it is polymerized with isocyanate and 1,4-butanediol to obtain the corresponding biodegradable polyurethane.

[0033] Optionally, in step (1), the molar ratio of the cyclic ester monomer to the polyol is (2-30):1, and the polyol is selected from at least one of polyethylene glycol, 1,4-butanediol, glycerol, pentaerythritol, polycaprolactone polyol, and polycarbonate diol.

[0034] Optionally, in step (2), the molar ratio of the -OH group of 1,4-butanediol to the -OH group of polyester polyol is (0.1~1):1, and the molar ratio of the total content of the -NCO group of isocyanate to the total content of the -OH group of polyester polyol to the -OH group of 1,4-butanediol is (1.0~1.2):1.

[0035] A second aspect of the present invention provides an application of the multilayer packaging material as described above for manufacturing multilayer film products, multilayer hollow blow-molded products, or multilayer injection-molded products.

[0036] The multilayer packaging material with high barrier properties provided in this embodiment of the invention comprises at least three layers: layer A, layer B, and layer C, with layer B located between layer A and layer C. Layer A contains cellulose nanocrystal grafts obtained by hydrophobic modification and grafting of cellulose nanocrystals. The hydrophobic modified cellulose nanocrystals are uniformly dispersed in layer A, reducing the adsorption of water vapor on layer A. Furthermore, the structure of layer A is more compact, further hindering the penetration of water vapor and improving the overall barrier performance of the material. Detailed Implementation

[0037] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0038] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0039] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0040] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0041] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the claims.

[0042] This invention provides a multi-layer packaging material with high barrier properties, comprising at least three layers: layer A, layer B, and layer C, with layer B located between layers A and C. Layer A is the outermost layer, used to prevent external moisture from entering layer B, which would cause layer B to degrade upon contact with water, resulting in a decrease or failure of its barrier properties. Layer A also has a preliminary gas barrier function. Layer B is a gas barrier layer, which serves two purposes: firstly, to prevent external oxygen from entering the packaging, and secondly, to prevent the loss of pre-filled preservative gases such as nitrogen, which would lead to a deterioration in the quality of the product inside the packaging. Layer C is the innermost layer, used to prevent the loss of pre-filled preservative gases. When the product inside the packaging contains a certain amount of moisture, it also prevents moisture from entering layer B, which would lead to moisture loss, deterioration in product quality, and degradation of layer B upon contact with water, resulting in a decrease or failure of its barrier properties. Layer C also has a preliminary gas barrier function.

[0043] The specific layer structure of packaging materials can be set according to their specific application and / or product form. For example, packaging materials can be set as a three-layer structure of layer A-layer-B-layer-C, or a four-layer structure of layer A-layer-A-layer-B-layer-C, or a five-layer structure of layer A-layer-B-layer-C, or a five-layer structure of layer A-layer-A-layer-B-layer-C.

[0044] The raw materials for layer A include a first biodegradable polyurethane and a cellulose nanocrystal graft obtained by hydrophobic modification and grafting of cellulose nanocrystals. By hydrophobically modifying the cellulose nanocrystals and performing grafting, the hydrophobically modified cellulose nanocrystals can be uniformly dispersed in the polyurethane, reducing the adsorption of water vapor on the polyurethane, i.e., layer A, and improving the waterproofness of the material. Furthermore, the uniformly dispersed cellulose nanocrystals can make the structure of layer A more compact, further hindering the penetration of water vapor and improving the overall barrier performance of the material.

[0045] The amount of cellulose nanocrystal graft is 0.1wt% to 10wt% of the first biodegradable polyurethane, so as to avoid compatibility problems between the cellulose nanocrystal graft and the first biodegradable polyurethane, and between the cellulose nanocrystal graft and the B layer, if the amount of cellulose nanocrystal graft is too large.

[0046] Preferably, the cellulose nanocrystals have a diameter of 5–30 nm and a length of less than 500 nm.

[0047] Furthermore, the cellulose nanocrystal graft is obtained through the following steps:

[0048] (a) The cellulose nanocrystals were hydrophobically modified by using a silanizing agent, which was selected from an aminosilane coupling agent or an epoxysilane coupling agent.

[0049] (b) The cellulose nanocrystal graft is obtained by grafting hydrophobically modified cellulose nanocrystals with carboxyl-terminated polyester prepolymer.

[0050] The surface of CNCs is rich in hydroxyl groups. By modifying them with silanizing agents, hydrophobic groups can be grafted onto the surface of CNCs to reduce their hydrophilicity. By selecting aminosilane coupling agents (KH-550, KH-792, etc.) or epoxysilane coupling agents (KH-560, KH-561, etc.), the hydrophobically modified CNCs can have amino or epoxy active groups, which are easy to graft with carboxyl-terminated polyester prepolymers to obtain cellulose nanocrystal grafts.

[0051] Furthermore, the carboxyl-terminated polyester prepolymer is obtained by ring-opening copolymerization of lactide (LA), caprolactone (CL), and maleic anhydride. The proportions of lactide and caprolactone can be arbitrary, and the molar ratio of maleic anhydride to the sum of the molar amounts of lactide and caprolactone is (0.1–0.5):1. As a preferred embodiment, the molar ratio of caprolactone to lactide is (1–5):1. Increasing the molar proportion of caprolactone increases the proportion of flexible segments, thereby enhancing the interfacial bonding between the obtained cellulose nanocrystal graft and the polyurethane.

[0052] In a more specific implementation, step (a) includes:

[0053] (a1) Dissolve cellulose nanocrystals in an ethanol solution with a volume concentration of not less than 75% to form a dispersion A with a mass concentration of 1 to 5 wt%, and adjust the pH of dispersion A to 3 to 4; and dissolve a silanizing agent in an ethanol solution with a volume concentration of not less than 90% to form a dispersion B with a mass concentration of 1 to 5 wt%.

[0054] (a2) Under stirring conditions, dispersion B is slowly added to dispersion A, and the amount of silanizing agent added is 20wt% to 50wt% of cellulose nanocrystals.

[0055] (a3) React at 40-60℃ for 30-60 min, centrifuge to separate, wash the obtained solid with anhydrous ethanol and deionized water until the washing solution is close to neutral, and then vacuum dry to obtain hydrophobically modified cellulose nanocrystals.

[0056] Specifically, in step (a1) above, dispersion A and dispersion B can be obtained by ultrasound assistance. For example, cellulose nanocrystals are dissolved in an ethanol-water mixed solvent (the volume ratio of ethanol to water is 7:1 to 9:1), and after ultrasonic dispersion for 1 hour, dispersion A with a mass concentration of 1 to 5 wt% is formed; silanizing reagent is dissolved in a 95 vol% ethanol solution, and after ultrasonic dispersion for 30 minutes, dispersion B with a mass concentration of 1 to 5 wt% is formed.

[0057] In a more specific implementation, step (b) includes:

[0058] (b1) Under a nitrogen atmosphere, lactide, caprolactone, maleic anhydride and catalyst are added to the reaction vessel in proportion, heated and mixed evenly, the reaction system is heated to 120-160℃ and reacted for 4-8 hours to obtain carboxyl-terminated polylactide caprolactone prepolymer.

[0059] (b2) Add hydrophobically modified cellulose nanocrystals, raise the temperature and lower the pressure, control the temperature at 170-210℃ and the absolute pressure at 50Pa-50kPa, and continue the reaction for 2-10 hours. The amount of hydrophobically modified cellulose nanocrystals added is 5%-20% of the sum of the mass of lactide and caprolactone.

[0060] (b3) After the reaction is complete, cool the temperature to below 60°C, add dichloromethane to dissolve the product, then add excess methanol or ethanol, precipitate, filter and dry the product to obtain cellulose nanocrystal grafts.

[0061] The catalyst is preferably tin-based, including but not limited to one or more of stannous chloride, stannous octanoate, and dibutyltin diacetate, and the amount of catalyst added is 0.1% to 1% of the total mass of lactide and caprolactone.

[0062] Further, step (b1) above can be performed using a gradient temperature increase for the prepolymerization reaction. For example, after the raw material monomer and catalyst are mixed uniformly at 60–90°C, the reaction system is heated to 120–130°C and reacted for 2–3 hours, then heated to 140–160°C and reacted for another 2–5 hours. Step (b2) above can be performed using a gradient temperature increase and / or pressure decrease for the polymerization reaction. For example, the reaction system is evacuated at a rate of 0.1–10 kPa / min until the absolute pressure reaches 20–50 kPa, while simultaneously heating to 170–180°C and reacting for a period of time; then, the reaction system is evacuated again at a rate of 0.1–10 kPa / min until the absolute pressure is below 10 kPa, while simultaneously heating to 190–210°C and reacting for a period of time.

[0063] In some embodiments, layer A comprises the following components in parts by weight: 100 parts of a first biodegradable polyurethane, 1 to 10 parts of cellulose nanocrystal graft, 0 to 30 parts of a first biodegradable polyester, 0 to 10 parts of an inorganic filler, and 0.2 to 2 parts of a processing aid.

[0064] The first biodegradable polyurethane comprises polyester segments and isocyanate segments formed from cyclic ester monomers, and has certain flexibility and mechanical properties. Preferably, the cyclic ester monomers are lactide and / or caprolactone.

[0065] The first biodegradable polyester is selected from the group consisting of: polybutylene succinate (PBS), polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polycaprolactone (PCL), polylactide-caprolactone copolymer (PLCL), polybutylene adipate succinate (PBSA), and polyhydroxyalkanoate (PHA).

[0066] Inorganic fillers include, but are not limited to: talc, calcium carbonate, calcium sulfate, magnesium sulfate, titanium dioxide, silicon dioxide, zinc oxide, calcium oxide, aluminum oxide, magnesium oxide, etc.

[0067] Processing aids include, but are not limited to, antioxidants, chain extenders, anti-hydrolysis agents, light stabilizers, opening agents, lubricants, plasticizers, etc., and the total amount of processing aids added is 0.2 to 2 parts.

[0068] In some embodiments, the raw material for layer B comprises a biodegradable polyester containing glycolic acid structural units, and the content of glycolic acid structural units is not less than 60% mol. Further, the weight-average molecular weight of the biodegradable polyester is above 150,000.

[0069] Preferably, the biodegradable polyester is synthesized by polymerization of glycolide, or glycolide with at least one copolymerizable monomer, wherein the monomer may be selected from lactide, caprolactone or propylene carbonate.

[0070] Layer B may also include processing aids, including but not limited to antioxidants, anti-hydrolysis agents, opening agents, lubricants, plasticizers, etc., with the total amount of processing aids not exceeding 2 wt% of the biodegradable polyester.

[0071] In some embodiments, when the packaging material is used for packaging products that are free of moisture or have low moisture content, layer C comprises the following components in parts by weight: 100 parts of second biodegradable polyurethane, 0 to 40 parts of second biodegradable polyester, and 0.2 to 2 parts of processing aids.

[0072] The second biodegradable polyurethane comprises polyester segments and isocyanate segments formed from cyclic ester monomers, wherein the cyclic ester monomers are selected from one or more of glycolide, lactide, and caprolactone, and include at least glycolide to enhance the barrier properties of the C layer.

[0073] The second biodegradable polyester is selected from the group consisting of: polybutylene succinate (PBS), polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polyglycolic acid copolymer (PLGA), polycaprolactone (PCL), polyglycolic acid copolymer (PGCL), polyglycolic acid copolymer (PLCL), polybutylene adipate succinate (PBSA), polyhydroxyalkanoate (PHA), and polyglycolic acid (PGA).

[0074] Processing aids include, but are not limited to, antioxidants, chain extenders, anti-hydrolysis agents, opening agents, lubricants, plasticizers, etc., and the total amount of processing aids added is 0.2 to 2 parts.

[0075] In some embodiments, when the packaging material is used to package products containing moisture, to prevent moisture from entering the B layer, leading to moisture loss, deterioration of product quality, and degradation of the B layer upon contact with water, resulting in decreased or failed barrier performance, the C layer comprises the following components in parts by weight: 100 parts of a second biodegradable polyurethane, 1-10 parts of cellulose nanocrystal grafted material, 0-40 parts of a second biodegradable polyester, and 0.2-2 parts of processing aids. By adding cellulose nanocrystal grafted material to the C layer, the adsorption of moisture on the C layer is reduced, improving the material's water resistance; furthermore, the uniformly dispersed cellulose nanocrystals make the C layer structure denser, further hindering the penetration of moisture from the product into the B layer, thus improving the overall barrier performance of the material.

[0076] The second biodegradable polyurethane comprises polyester segments and isocyanate segments formed from cyclic ester monomers, wherein the cyclic ester monomers are lactide and / or caprolactone.

[0077] The second biodegradable polyester is selected from the group consisting of: polybutylene succinate (PBS), polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polycaprolactone (PCL), polylactide-caprolactone copolymer (PLCL), polybutylene adipate succinate (PBSA), and polyhydroxyalkanoate (PHA).

[0078] Processing aids include, but are not limited to, antioxidants, chain extenders, anti-hydrolysis agents, opening agents, lubricants, plasticizers, etc., and the total amount of processing aids added is 0.2 to 2 parts.

[0079] Furthermore, the first biodegradable polyurethane and the second biodegradable polyurethane described above can be obtained through the following steps:

[0080] (1) The cyclic ester monomers for synthesizing the first biodegradable polyurethane or the second biodegradable polyurethane and the polyol are added to the reaction vessel in proportion, and the ring-opening copolymerization reaction is carried out under the action of a catalyst to obtain polyester polyol. The hydroxyl value of the polyester polyol is between 30-300 mg KOH / g.

[0081] (2) Using the polyester polyol obtained in step (1) as raw material, it is polymerized with isocyanate and 1,4-butanediol to obtain the corresponding biodegradable polyurethane.

[0082] Further, in step (1), the mass ratio of the cyclic ester monomer to the polyol is (2-30):1, preferably (5-20):1, and the polyol is selected from at least one of polyethylene glycol, 1,4-butanediol, glycerol, pentaerythritol, polycaprolactone polyol, and polycarbonate diol; the molecular weight of polyethylene glycol, polycaprolactone polyol, and polycarbonate diol is 500-10000.

[0083] The catalyst is preferably tin-based, including but not limited to one or more of stannous chloride, stannous octanoate, and dibutyltin diacetate, and the amount of catalyst added is 0.01% to 0.5% of the total mass of the cyclic ester monomer.

[0084] In a more specific embodiment, step (1) includes: adding cyclic ester monomer and polyol in proportion under a nitrogen atmosphere, mechanically stirring, heating and reacting at 100-130°C for 30-60 minutes, adding catalyst after the reaction system becomes transparent, purging with nitrogen three times, and finally reducing the pressure to below 10 kPa absolute pressure, reacting at 100-180°C for 4-24 hours to obtain polyester polyol.

[0085] Further, in step (2), the molar ratio of the -OH group of 1,4-butanediol to the -OH group of polyester polyol is (0.1~1):1, and the molar ratio of the total content of the -NCO group of isocyanate to the total content of the -OH group of polyester polyol to the -OH group of 1,4-butanediol is (1.0~1.2):1. That is, the isocyanate is reacted with polyester polyol in a slightly excessive manner. The isocyanate is preferably an aliphatic diisocyanate, including but not limited to hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI) and dicyclohexylmethane diisocyanate (HMDI).

[0086] In a more specific implementation, step (2) includes:

[0087] Under a nitrogen atmosphere, isocyanate and catalyst are added to a reaction vessel. Under stirring, the solution of polyester polyol synthesized in step (1) dissolved in dioxane is added dropwise to the reaction vessel. The reaction is carried out at 60-120°C for 2-8 hours to obtain a double-terminated isocyanate prepolymer. The catalyst used is the same as that used in the preparation of the carboxyl-terminated polyester prepolymer and polyester polyol. The catalyst is preferably tin-based, including but not limited to one or more of dibutyltin dilaurate, stannous octoate, and dibutyltin diacetate. The amount of catalyst added is 0.01% to 0.1% of the total mass of the cyclic ester monomer.

[0088] A solution of 1,4-butanediol dissolved in dioxane was added dropwise to a reaction vessel. After the addition was complete, the reaction was carried out at 60–110 °C for 6–10 hours under nitrogen protection. The product was repeatedly precipitated with water and icy ethanol, and then vacuum dried at room temperature to obtain biodegradable polyurethane.

[0089] This invention also provides an application of the above-mentioned multilayer packaging material for manufacturing multilayer film products, multilayer hollow blow-molded products, or multilayer injection-molded products.

[0090] Specifically, the aforementioned multi-layer packaging materials can be formed into multi-layer film products, multi-layer hollow blow-molded products, or multi-layer injection-molded products through existing extrusion molding, blow molding, or injection molding processes, including but not limited to multi-layer blown film products, multi-layer cast film products, multi-layer uniaxial stretch film products, multi-layer biaxial stretch film products, multi-layer hollow blow-molded products, multi-layer sheet products, multi-layer board products, and multi-layer thermoformed products.

[0091] Taking multilayer blown film products as an example, multilayer packaging films are prepared using extrusion molding process:

[0092] 1) Add the components of layer A into a twin-screw extruder in proportion and granulate by twin-screw extrusion to obtain layer A granules. The temperature of the twin-screw extruder is 60℃~200℃.

[0093] 2) Add the components of layer C to a twin-screw extruder in proportion and granulate by twin-screw extrusion to obtain layer C granules. The temperature of the twin-screw extruder is 60℃~230℃.

[0094] 3) Add the A-layer, B-layer, and C-layer granules to be processed into the three-layer co-extrusion blown film mill through the corresponding feeding ports for multi-layer blown film production. The temperature of each section of the A-layer screw is 150-200℃; the temperature of each section of the B-layer screw is 150-230℃; the temperature of each section of the C-layer screw is 150-230℃; the temperature of the extrusion blown film die is 190-230℃; and the blow-up ratio is controlled at (2.5-5):1 to obtain a multi-layer packaging film.

[0095] The embodiments of the present invention have the following beneficial effects:

[0096] 1. By hydrophobically modifying the cellulose nanocrystals in layer A, the adsorption of water vapor on layer A is reduced, which makes the polyurethane layer of layer A have good water-blocking properties and prevents the biodegradable polyester in layer B, which is mainly composed of glycolic acid structural units, from degrading after encountering water, resulting in a decrease or failure of barrier performance.

[0097] 2. Cellulose nanocrystals are hydrophobically modified and then grafted, so that the hydrophobically modified cellulose nanocrystals can be uniformly dispersed in the polyurethane layer A. The structure of the polyurethane layer A is more compact, which further hinders the penetration of water vapor and improves the overall barrier performance of the material.

[0098] 3. By adding cellulose nanocrystal grafts to layer C, the packaging material can be applied to the packaging of products containing moisture, which can prevent moisture from entering layer B, thus preventing product moisture loss and deterioration in product quality.

[0099] 4. By grafting cellulose nanocrystals onto polylactide polymer, the cellulose nanocrystal grafts have better interfacial compatibility with the first biodegradable polyurethane and with the second biodegradable polyurethane, improving the adhesion between layer A and layer B, and between layer B and layer C, thereby improving the overall toughness of the material.

[0100] Testing method:

[0101] 1. Hydroxyl value of polyester polyol: determined by titration. A certain amount of sample is weighed into an acylation bottle, 25 mL of acylation agent is added for amidation reaction, and then cooled to room temperature. Phenolphthalein is used as an indicator, and titration is performed with 1 mol / L NaOH standard solution until the endpoint is pink. A blank test is performed at the same time.

[0102] 2. Tensile strength and elongation at break test: The test was conducted according to the test standard GB / T1040.3-2022. The tensile speed was 50 mm / min. The transverse (MD) and longitudinal (TD) properties of the membrane were tested, and the average value of the three samples was taken.

[0103] 3. Barrier performance test:

[0104] According to GB / T1037, a water vapor transmission rate tester is used for testing. Under specified temperature and relative humidity conditions, a certain water vapor pressure difference is maintained on both sides of the sample, the amount of water vapor passing through the sample is measured, and the water vapor transmission coefficient is calculated.

[0105] According to GB / T1038, the gas permeability coefficient of plastic films and sheets is measured using the differential pressure method. Under constant temperature and unit pressure difference, during stable permeation, it is the volume of oxygen permeating through a unit thickness and unit area of ​​the sample per unit time.

[0106] 4. Moisture absorption rate test: Place a membrane sample with dimensions of 20mm×20mm×0.1mm in a vacuum drying oven at 50℃ and dry for 24 hours. Weigh the mass of the membrane sample (recorded as M0). Then, place the dried membrane sample in a sealed container with a relative humidity of 57% and a temperature of 25℃ and leave it for 48 hours. Weigh the mass of the membrane sample (recorded as M1). The moisture absorption rate (%) of the membrane sample = 100*(M1-M0) / M0.

[0107] Example 1

[0108] Preparation of hydrophobically modified cellulose nanocrystals:

[0109] 1) Cellulose nanocrystals (diameter ~10nm, length ~200nm) were dissolved in an ethanol-water mixed solvent (ethanol to water volume ratio of 9:1) and ultrasonically dispersed for 1h to form a dispersion A with a mass concentration of 2wt%. Dilute HCl was slowly added dropwise to adjust the pH of the dispersion to 4. Silanizing reagents were dissolved in an ethanol-water mixed solvent (ethanol to water volume ratio of 20:1) and ultrasonically dispersed for 0.5h to form a dispersion B with a mass concentration of 2wt%. The silanizing reagents were KH-550 and KH-560, respectively.

[0110] 2) Under stirring conditions, dispersion B is slowly added to dispersion A, and the amount of silanizing agent added is 40 wt% of cellulose nanocrystals.

[0111] 3) Continue the reaction at 50℃ for 40 min, centrifuge to separate the solids, wash the solids several times with anhydrous ethanol and deionized water until the washing solution is close to neutral, and vacuum dry to obtain hydrophobically modified cellulose nanocrystals, which are labeled as CNC-KH550 and CNC-KH560, respectively.

[0112] Example 2

[0113] Preparation of cellulose nanocrystal grafts:

[0114] 1) Under a nitrogen atmosphere, lactide, caprolactone, maleic anhydride, and stannous octoate were added to a reaction vessel in a certain proportion. The molar ratio of caprolactone to lactide was 2:1, the sum of the molar amounts of maleic anhydride and lactide and caprolactone was 0.2:1, and the amount of stannous octoate added was 0.5% of the total mass of lactide and caprolactone. The mixture was stirred evenly at 80°C, the reaction system was heated to 120°C and reacted for 2 hours, and then the temperature was raised to 150°C and the reaction was continued for 4 hours to obtain carboxyl-terminated polylactide-caprolactone prepolymer.

[0115] 2) Add hydrophobically modified cellulose nanocrystals, then evacuate to 50 kPa at a rate of 5 kPa / min while simultaneously heating to 170 °C and react for 2 h; continue evacuating to 100 Pa at a rate of 5 kPa / min while simultaneously heating to 190 °C and react for 6 h.

[0116] 3) After the reaction is complete, the temperature is lowered to below 60°C, dichloromethane is added to dissolve the product, excess methanol is poured in, precipitation is carried out, and the product is dried after filtration to obtain cellulose nanocrystal grafts, which are labeled as 5% CNC-KH550 / PLCL, 10% CNC-KH550 / PLCL, 10% CNC-KH570 / PLCL, and 20% CNC-KH570 / PLCL, respectively. The type and content of hydrophobically modified cellulose nanocrystals in each product are shown in Table 1.

[0117] Table 1

[0118] Product Type Addition amount 5% CNC-KH550 / PLCL CNC-KH550 5％ 10% CNC-KH550 / PLCL CNC-KH550 10％ 10% CNC-KH560 / PLCL CNC-KH560 10％ 20% CNC-KH560 / PLCL CNC-KH560 20％

[0119] Example 3

[0120] Preparation of biodegradable polyurethane:

[0121] (1) The reactor was dried at 120°C for 12 hours before the reaction. Before the reaction, the reactor was evacuated and purged with nitrogen three times. Under the nitrogen atmosphere, the cyclic ester monomer and polyol were added in proportion. The reactor was mechanically stirred and heated at 130°C for 40 minutes. After the system became transparent, stannous octoate (0.1% of the total mass of the cyclic ester monomer) was added. The reactor was then evacuated and purged with nitrogen three times. Finally, the reactor was evacuated to 20 Pa. The reaction temperature was 150°C and the reaction was carried out for 10 hours to obtain polyester polyol.

[0122] (2) The reactor was dried at 120°C for 12 hours before the reaction. Before the reaction, the reactor was evacuated and purged with nitrogen three times. Under the nitrogen atmosphere, hexamethylene diisocyanate (HDI) and diisobutyltin dilaurate (0.1% of the total mass of the cyclic ester monomers) were added to the reactor. The polyester polyol synthesized in step 1 dissolved in dioxane (0.6 kg of polyester polyol dissolved in 1 L of dioxane) was added dropwise to the reactor. The reactor was mechanically stirred and the reaction temperature was 100°C. The reaction was carried out for 5 hours to obtain the double-terminated isocyanate prepolymer.

[0123] A solution of 1,4-butanediol as a chain extender (1 g of chain extender dissolved in 5 mL of 1,4-butanediol) was added dropwise. After the addition was complete, the reaction was continued at a constant temperature of 60°C for 8 hours under nitrogen protection. The products were precipitated three times with water and ice-cold ethanol, respectively, and dried under vacuum at room temperature to obtain biodegradable polyurethanes, which were labeled as PLA-PU, PLCL-PU, and PLGA-PU, respectively. The types of cyclic ester monomers and their molar ratios, as well as the amounts of each component, are shown in Table 2.

[0124] Table 2

[0125]

[0126] Example 4

[0127] Multilayer packaging films are prepared using an extrusion molding process:

[0128] (1) The components of layer A are added to a twin-screw extruder in proportion and granulated by twin-screw extrusion to obtain layer A granules. The temperature of the twin-screw extruder is 60℃~200℃, the speed is 200 rpm, and L / D=42.

[0129] (2) The components of layer C are added to a twin-screw extruder in proportion and granulated by twin-screw extrusion to obtain layer C granules. The temperature of the twin-screw extruder is 60℃~230℃, the speed is 200 rpm, and L / D=42.

[0130] (3) Add the A-layer granules, B-layer granules, and C-layer granules into the three-layer co-extrusion blown film mill through the corresponding feeding ports for multi-layer blown film production. The temperature of each section of the A-layer screw is 150-200℃, the diameter of the A-layer screw is 45mm, L / D=30, and the speed of the A-layer screw is 25 rpm. The temperature of each section of the B-layer screw is 150-230℃, the diameter of the B-layer screw is 30mm, L / D=28, and the speed of the B-layer screw is 20 rpm. The temperature of each section of the C-layer screw is 150-230℃, the diameter of the C-layer screw is 45mm, L / D=30, and the speed of the C-layer screw is 25 rpm. The temperature of the extrusion blown film die is 220℃, and the blow-up ratio is controlled at 3:1 to obtain a multi-layer packaging film with a total thickness of 0.012mm.

[0131] The main raw materials of layers A and C are shown in Table 3. The raw materials of layer A also include: 20 parts of biodegradable polyester (PBAT, molecular weight 10W), 5 parts of inorganic filler (calcium carbonate), 0.2 parts of lubricant (calcium stearate), 0.5 parts of antioxidant (BASF Irganox 1010), 0.5 parts of anti-hydrolysis agent (polycarbodiimide, molecular weight 4000), and 0.5 parts of chain extender (Joncryl ADR-4368).

[0132] The raw materials for layer B include: 100 parts PLGA copolyester, 0.2 parts lubricant (calcium stearate), and 0.5 parts antioxidant (BASFIrganox 1010); wherein, the PLGA copolyester is a PLGA copolyester with a molecular weight of 180,000 (GA:LA = 8:2).

[0133] The raw materials for layer C also include: 20 parts of biodegradable polyester (PLA, molecular weight 150,000), 0.2 parts of lubricant (calcium stearate), 0.2 parts of opening agent (calcium carbonate), 0.5 parts of antioxidant (BASF Irganox 1010), and 0.5 parts of chain extender (Joncryl ADR-4368).

[0134] Table 3. Main raw materials of layers A and C in each sample and comparative example.

[0135]

[0136]

[0137] Comparative Example 1

[0138] Similar to packaging film 1, except that no cellulose nanocrystal grafts are added to layer A.

[0139] Comparative Example 2

[0140] Similar to packaging film 1, except that 20 parts of cellulose nanocrystal grafts are added to layer A.

[0141] Comparative Example 3

[0142] Similar to packaging film 5, the difference is that the cellulose nanocrystals in the cellulose nanocrystal graft in layer A were not hydrophobically modified, and the resulting cellulose nanocrystal graft was labeled as 10% CNC / PLCL.

[0143] Comparative Example 4

[0144] Similar to packaging film 5, except that the cellulose nanocrystal graft in layer A is replaced with 1 part of hydrophobically modified cellulose nanocrystal CNC-KH560.

[0145] Table 4. Test results for each sample and comparative example.

[0146]

[0147]

[0148] As can be seen from the packaging film 1 and comparative examples 1 and 2 in the table above, adding hydrophobically modified cellulose nanocrystal grafts to layer A can significantly reduce the water vapor transmission coefficient, oxygen transmission coefficient, and moisture absorption rate. However, when the amount of cellulose nanocrystal grafts added is too large, it has a significant impact on the mechanical properties of the packaging film, especially the elongation at break. The water vapor transmission coefficient and oxygen transmission coefficient both increase. It is speculated that the addition of too many cellulose nanocrystal grafts leads to poor compatibility with the polyurethane in layer A, which not only affects the structure of the polyurethane layer in layer A, but also further affects the adhesion between film layers, resulting in a decrease in strength and elongation at break, as well as an increase in water vapor transmission coefficient and oxygen transmission coefficient.

[0149] As can be seen from the table above, for packaging film 5 and comparative examples 3 and 4, after adding unmodified hydrophobic cellulose nanocrystal grafts to layer A, the water vapor transmission coefficient and moisture absorption rate of the packaging film are both high due to the hydroxyl structure of the cellulose nanocrystals. Although the cellulose nanocrystals in comparative example 4 were hydrophobically modified, they were not grafted. During the melt blending process with polyurethane, the hydrophobic modified cellulose nanocrystals had poor dispersibility and were prone to agglomeration. As a result, the water vapor transmission coefficient, oxygen transmission coefficient, and moisture absorption rate of comparative example 4 were all higher than those of packaging film 5, and the elongation at break was reduced. This indicates that by grafting hydrophobic modified cellulose nanocrystals and blending them with polyurethane, not only is the water vapor adsorption capacity of the polyurethane layer in layer A reduced, giving the polyurethane layer in layer A good water-blocking performance, but the structure of the polyurethane layer in layer A is also made denser, further hindering the permeation of water vapor and oxygen. At the same time, it can improve the adhesion between film layers and improve the overall toughness of the material.

[0150] While the present invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those skilled in the art. Furthermore, it should be understood that the aspects described in the invention, the parts of different embodiments, and the various features listed can be combined or interchanged in whole or in part. In the various embodiments described above, those embodiments referencing another embodiment can be appropriately combined with other embodiments, as will be understood by those skilled in the art. Moreover, those skilled in the art will understand that the foregoing description is merely illustrative and not intended to limit the invention.

Claims

1. A multi-layer packaging material with high barrier properties, characterized in that, It includes at least three layers: layer A, layer B, and layer C, with layer B located between layer A and layer C; The raw materials of the A layer include a first biodegradable polyurethane and a cellulose nanocrystal graft obtained by hydrophobic modification of cellulose nanocrystals and then grafting treatment. The content of the cellulose nanocrystal graft is 1 wt% to 10 wt% of the first biodegradable polyurethane. The raw material of the B layer includes a biodegradable polyester containing glycolic acid structural units, and the content of glycolic acid structural units is not less than 60% mol. The raw material for the C layer includes a second biodegradable polyurethane.

2. The multi-layer packaging material according to claim 1, characterized in that, The cellulose nanocrystal graft was obtained through the following steps: (a) The cellulose nanocrystals are hydrophobically modified using a silanizing agent, wherein the silanizing agent is selected from aminosilane coupling agents or epoxysilane coupling agents; (b) The cellulose nanocrystal graft is obtained by grafting hydrophobically modified cellulose nanocrystals with carboxyl-terminated polyester prepolymer.

3. The multi-layer packaging material according to claim 2, characterized in that, The carboxyl-terminated polyester prepolymer is obtained by ring-opening copolymerization of lactide, caprolactone, and maleic anhydride, with the molar ratio of maleic anhydride to the sum of the molar amounts of lactide and caprolactone being (0.1–0.5):

1.

4. The multi-layer packaging material according to claim 3, characterized in that, Step (a) specifically includes: (a1) Dissolve cellulose nanocrystals in an ethanol solution with a volume concentration of not less than 75% to form a dispersion A with a mass concentration of 1 to 5 wt%, and adjust the pH of dispersion A to 3 to 4; and dissolve a silanizing agent in an ethanol solution with a volume concentration of not less than 90% to form a dispersion B with a mass concentration of 1 to 5 wt%. (a2) Under stirring conditions, dispersion B is slowly added to dispersion A, and the amount of silanizing agent added is 20wt% to 50wt% of the cellulose nanocrystals; (a3) React at 40-60℃ for 30-60 min, centrifuge to separate, wash the obtained solid with anhydrous ethanol and deionized water until the washing solution is close to neutral, and then vacuum dry to obtain hydrophobically modified cellulose nanocrystals.

5. The multi-layer packaging material according to claim 3, characterized in that, Step (b) specifically includes: (b1) Under a nitrogen atmosphere, lactide, caprolactone, maleic anhydride and catalyst are added to the reaction vessel in proportion, heated and mixed evenly, the reaction system is heated to 120-160℃ and reacted for 4-8 hours to obtain carboxyl-terminated polylactide caprolactone prepolymer. (b2) Add hydrophobically modified cellulose nanocrystals, raise the temperature and lower the pressure, control the temperature at 170-210℃ and the absolute pressure at 50Pa-50kPa, and continue the reaction for 2-10 hours. The amount of hydrophobically modified cellulose nanocrystals added is 5%-20% of the total mass of lactide and caprolactone. (b3) After the reaction is complete, the temperature is lowered to below 60°C, dichloromethane is added to dissolve the product, then excess methanol or ethanol is added, the product is precipitated, filtered, and dried to obtain the cellulose nanocrystal graft.

6. The multi-layer packaging material according to any one of claims 1 to 5, characterized in that, The A layer comprises the following components in parts by weight: 100 parts of the first biodegradable polyurethane, 1-10 parts of cellulose nanocrystal graft, 0-30 parts of the first biodegradable polyester, 0-10 parts of inorganic filler, and 0.2-2 parts of processing aid. The C layer comprises the following components in parts by weight: 100 parts of second biodegradable polyurethane, 0-40 parts of second biodegradable polyester, and 0.2-2 parts of processing aids; The first biodegradable polyurethane comprises polyester segments and isocyanate segments formed from cyclic ester monomers, wherein the cyclic ester monomers are lactide and / or caprolactone. The second biodegradable polyurethane comprises polyester segments and isocyanate segments formed from cyclic ester monomers, wherein the cyclic ester monomers are selected from one or more of glycolide, lactide, and caprolactone, and include at least glycolide.

7. The multi-layer packaging material according to any one of claims 1 to 5, characterized in that, The A layer comprises the following components in parts by weight: 100 parts of the first biodegradable polyurethane, 1-10 parts of cellulose nanocrystal graft, 0-30 parts of the first biodegradable polyester, 0-10 parts of inorganic filler, and 0.2-2 parts of processing aid. The C layer comprises the following components in parts by weight: 100 parts of second biodegradable polyurethane, 1-10 parts of cellulose nanocrystal graft, 0-40 parts of second biodegradable polyester, and 0.2-2 parts of processing aids. Both the first biodegradable polyurethane and the second biodegradable polyurethane include polyester segments and isocyanate segments formed from cyclic ester monomers, wherein the cyclic ester monomers are lactide and / or caprolactone.

8. The multi-layer packaging material according to claim 6 or 7, characterized in that, The first biodegradable polyurethane or the second biodegradable polyurethane is obtained through the following steps: (1) The cyclic ester monomers for synthesizing the first biodegradable polyurethane or the second biodegradable polyurethane and the polyol are added to a reaction vessel in proportion, and a ring-opening copolymerization reaction is carried out under the action of a catalyst to obtain a polyester polyol, wherein the hydroxyl value of the polyester polyol is between 30-300 mg KOH / g. (2) Using the polyester polyol obtained in step (1) as raw material, it is polymerized with isocyanate and 1,4-butanediol to obtain the corresponding biodegradable polyurethane.

9. The multi-layer packaging material according to claim 8, characterized in that, In step (1), the molar ratio of the cyclic ester monomer to the polyol is (2-30):1, and the polyol is selected from at least one of polyethylene glycol, 1,4-butanediol, glycerol, pentaerythritol, polycaprolactone polyol, and polycarbonate diol. In step (2), the molar ratio of the -OH group of 1,4-butanediol to the -OH group of polyester polyol is (0.1~1):1, and the molar ratio of the total content of the -NCO group of isocyanate to the total content of the -OH group of polyester polyol to the total content of the -OH group of 1,4-butanediol is (1.0~1.2):

1.

10. An application of a multilayer packaging material as described in any one of claims 1 to 9, characterized in that, It is used to manufacture multi-layer film products, multi-layer hollow blow molded products, or multi-layer injection molded products.

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