A PHA, PBAT and PVOH blended water-based emulsion and its application in paper-based barrier coatings

Abstract

The present invention discloses a water-based emulsion of PHA, PBAT and PVOH and its application in paper-based barrier coatings. This emulsion is prepared by first melt-blending PHA and PBAT at 150-170 °C and then dispersing them into an aqueous PVOH solution at 80-95 °C. Plasticizers, cross-linking agents and surfactants can be added to improve the performance. After coating on paper and drying at 80-150 °C, a barrier film with a Cobb value of 10-15 g / m² and a Kit ≥ 10 grade is formed. Compared with traditional PE film laminating or fluorine-containing coatings, this system is more environmentally friendly and recyclable; PVOH dissolves in pulping water, PHA and PBAT are easily separated, and fibers can be efficiently recovered; in composting, soil and marine environments, PHA and PBAT have extensive biodegradability and are superior to PLA which is difficult to recycle and requires industrial composting. It is applicable to food, industrial, special packaging and agricultural paper products.

Description

Technical Field

[0001] The present invention belongs to the cross - field of degradable polymer materials and paper - based packaging technologies, and specifically relates to a PHA, PBAT and PVOH blended aqueous emulsion and its application in paper - based barrier coatings. This technology can significantly improve the water - proof, oil - proof and barrier properties on the paper surface, and also has the characteristics of recyclability and extensive biodegradability, being suitable for fields such as food, industrial and special packaging. Background Art

[0002] Paper and paperboard are commonly used packaging materials. However, unmodified paper fibers lack sufficient barrier properties against water, oil and other permeates. Although traditional PE film laminating or PFAS coatings can improve the barrier, they are limited in terms of recycling and environmental safety. Although polylactic acid (PLA) coated paper has certain bio - based characteristics, it is difficult to separate during normal - temperature pulping, forms "sticky impurities" when bonded to fibers, and mainly degrades under industrial composting conditions above 55°C.

[0003] Polyhydroxyalkanoates (PHA) are a class of polymers with biodegradation potential under various environmental conditions, including soil and ocean; poly(butylene adipate - co - terephthalate) (PBAT) is commonly used for flexibility improvement and industrial composting scenarios; poly(vinyl alcohol) (PVOH) has water - solubility and dry - state barrier properties. If the three can be combined into an aqueous coating system, it is expected to provide excellent barrier on paper surfaces and be easy to recycle and widely degrade. However, there are problems such as differences in melt viscosity, hydrolysis risk and particle - size stability during the aqueous - phase dispersion of PHA / PBAT. The present invention designs a solution and conducts experimental verification for this technical problem. Summary of the Invention

[0004] The purpose of the present invention is to disclose a PHA, PBAT and PVOH blended aqueous emulsion and its application in paper - based barrier coatings to solve the deficiencies of traditional PE film laminating, PFAS coatings and PLA coating in terms of barrier performance, recycling difficulty and environmental degradability. The specific objectives include:

[0005] Provide an environmentally friendly and safe aqueous coating system, avoiding organic solvents and fluorinated chemicals to ensure food - contact safety;

[0006] Improve the water - proof, oil - proof and barrier properties of paper - based materials, achieve excellent Cobb60 values and Kit grades, and also have heat - sealing ability;

[0007] Achieve efficient recovery of the coating during pulping, with high fiber recovery rate and easy separation;

[0008] Endow paper - based materials with biodegradation ability in a wide range of environments such as soil, ocean and household composting, exceeding the limitations of PLA;

[0009] Simplify the preparation process, suitable for industrial production, and promote the development of sustainable packaging materials.

[0010] The technical solution of the present invention mainly includes the following parts:

[0011] (1) Main components of the formulation

[0012] PHA 10 - 60 parts by mass, PBAT 10 - 60 parts by mass, PVOH 5 - 30 parts by mass;

[0013] Plasticizer (1 - 10 parts by mass) improves flexibility; cross - linker (0.5 - 5 parts by mass) enhances the water resistance of PVOH; surfactant (0.1 - 5 parts by mass) stabilizes emulsification;

[0014] The balance is water, keeping the solid content of the emulsion at 20 - 50 wt%.

[0015] (2) Preparation by melt - aqueous phase emulsification

[0016] Step 1. Dissolve PVOH in deionized water at 80 - 95 °C to obtain a 5 - 15 wt% PVOH aqueous solution;

[0017] Step 2. Melt - blend PHA and PBAT at 150 - 170 °C to obtain a homogeneous melt;

[0018] Step 3. At 80 - 95 °C, slowly add the melt obtained in Step 2 to the PVOH aqueous solution described in Step 1 through high - speed stirring or high - pressure homogenization and emulsify and disperse for 5 - 30 minutes;

[0019] Step 4. Cool the emulsion obtained in Step 3 to no higher than 50 °C, add plasticizer, cross - linker, and surfactant as needed, stir evenly and filter to obtain the final stable ternary blended aqueous emulsion.

[0020] During the emulsification process in Step 3, control the feeding rate and shear time, and adjust the pH to neutral 6.5 - 7.5 to avoid high - temperature hydrolysis, so that PHA / PBAT and PVOH form a stable O / W type emulsion.

[0021] (3) Paper - based coating

[0022] Apply the emulsion (dry basis 5 - 15 g / m²) to the paper surface by means of a doctor blade, wire bar or spraying;

[0023] Dry at 80 - 150 °C, so that Cobb60 ≤ 15 g / m², Kit ≥ 10 grades, and the heat - seal strength ≥ 5 N / 15 mm.

[0024] (4) Recycling and degradation

[0025] Under the conditions of recycled pulping, PVOH can be dissolved in the aqueous phase, and PHA and PBAT are removed in the form of fragments or particles by screening or flotation, and the fiber recovery rate can reach 90-95%; and in the household composting, soil or marine environment, PHA and PBAT can be degraded by microorganisms, and PVOH is removed by hydrolysis or enzymatic hydrolysis, finally realizing the recyclable and biodegradable treatment of paper-based materials.

[0026] The polyhydroxyalkanoate PHA is selected from short-chain or medium-chain types, including one or more of poly(3-hydroxybutyrate) PHB, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) PHBHHx, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) P34HB, and the crystallinity, thermal stability and toughness are regulated by combining different comonomer contents.

[0027] The PBAT is an aliphatic-aromatic compostable polyester with a melting point of 110-130 °C; the degree of hydrolysis of the PVOH is in the range of 85-98%, and the viscosity of the 4 wt% aqueous solution is 2-30 mPa·s.

[0028] The plasticizer is selected from one or more of glycerol, glycerin, triethyl citrate, tributyl acetylcitrate; the cross-linking agent is selected from one or more of boric acid, borax, citric acid, glyoxal or glutaraldehyde; the surfactant is selected from food contact permitted auxiliaries such as Tween, Span, lecithin or sodium stearoyl lactate.

[0029] The melting temperature of the PHA and PBAT is controlled in the range of 150-170 °C, and then the molten stream is dispersed into the PVOH aqueous solution by high-speed stirring or high-pressure homogenization at 80-95 °C at 1000-5000 rpm, so that the average particle size of the final dispersed phase is maintained in the range of 0.5-5 μm.

[0030] Under the conditions of recycled pulping, PVOH can be dissolved in the aqueous phase, and PHA and PBAT are removed in the form of fragments or particles by screening or flotation, and the fiber recovery rate reaches 90-95%; in the household composting, soil, marine environment, PHA and PBAT can be degraded by microorganisms, and PVOH is removed by hydrolysis or enzymatic hydrolysis, having recyclable and biodegradable characteristics.

[0031] The aqueous emulsion is applicable to the fields of food packaging, industrial packaging, special packaging and agricultural paper products, and has excellent waterproof and oil-proof properties, convenient recycling and wide environmental biodegradability.

[0032] Using the present invention can obtain the following beneficial effects:

[0033] Green Safety: Compared with PE or PFAS coatings, waterborne emulsions are used, without organic solvents and fluorine-containing chemicals, with no VOC emissions. Safe auxiliaries such as glycerol and Tween are selected, with no toxic residues, ensuring food contact safety, environmentally friendly and reliable.

[0034] Excellent Barrier Performance: The coating makes the Cobb60 value of the paper surface as low as 10 - 15 g / m², the Kit grade ≥ 10, the heat seal strength ≥ 5 N / 15 mm, and the waterproof and oil-proof effects are comparable to or even better than PLA lamination, meeting the high requirements of food packaging, etc.

[0035] More Efficient Recycling: When pulping, PVOH is water-soluble, PHA and PBAT are easy to screen or float and separate, and the fiber recovery rate reaches 90 - 95%. It is easier to peel off than PE coatings and PLA lamination, avoiding the problem of fiber adhesion, and having obvious recycling advantages.

[0036] Wide Degradation Range: PHA can be degraded in soil and the ocean, PBAT is suitable for industrial composting, and PVOH is removed by hydrolysis. Compared with PLA which is only suitable for high-temperature composting, it degrades more thoroughly in home composting and natural environments, with stronger environmental protection.

[0037] Simple and Stable Process: Only an extruder for melting and a high-speed stirring device are needed for batch production. Combining pH regulation and particle size control, the emulsion is stable, the coating is flexible and water-resistant, suitable for industrial applications, and the operation is simple and practical.

[0038] Widely Used: Suitable for food, industrial, special packaging and agricultural paper products, with excellent performance and environmental protection characteristics, great market potential, and significant economic and social benefits. Detailed Implementation Modes

[0039] The following examples and comparative examples are used to illustrate the feasibility and technical effects of the present invention, but not to limit the scope of the present invention. Those skilled in the art can make appropriate adjustments based on this.

[0040] Raw Materials

[0041] PHA (PHBV): HV content is 3 - 5 mol%, the melt index MFI is 5 - 10 g / 10 min, and the melting point is 160 - 175 °C. PHBHHx, P34HB, etc. can also be used;

[0042] PBAT: Commercially available compostable grades, such as Ecoflex®, etc., MFI is 30 g / 10 min, and the melting point is 120 °C;

[0043] PVOH: Degree of hydrolysis is 88%, and the viscosity of 4 wt% aqueous solution is ≈ 20 mPa·s;

[0044] Plasticizers: Glycerol, triethyl citrate, etc.;

[0045] Crosslinking Agents: Borax, citric acid or glyoxal;

[0046] Surfactants: Tween 80, Span 60, etc.;

[0047] Others: deionized water, equipment such as twin-screw extruder, high-speed disperser (2000 - 3000 rpm), or high-pressure homogenizer, etc.

[0048] Preparation process example

[0049] Step 1. PVOH solution: Take PVOH with 88% hydrolysis degree, stir in deionized water at 90 °C for 30 min to obtain a 10 wt% aqueous solution;

[0050] Step 2. Melting of PHA / PBAT: Continuously extrude in the 150 - 160 °C section of the twin-screw extruder to obtain a uniform melt;

[0051] Step 3. Aqueous phase emulsification: Place the PVOH solution at 80 - 90 °C in a high-shear stirrer with a rotation speed of 2000 rpm, slowly inject the molten PHA / PBAT stream at an injection rate of about 10 g / min, and continue stirring for 5 - 10 min to initially form an O / W emulsion;

[0052] Step 4. Addition of additives: Cool to about 50 °C, add glycerol, borax, and Tween 80, and stir for 15 min; Filter to obtain a ternary blend aqueous emulsion with a solid content of 30 wt%.

[0053] Particle size characterization (optional): Measure D50 to be 1.5 - 3 μm, PDI < 0.4, and no obvious stratification by dynamic light scattering;

[0054] Examples and comparative examples

[0055] Example 1

[0056] PHA: 30 parts by mass, PBAT: 30 parts by mass, PVOH: 10 parts by mass, glycerol: 5 parts by mass, borax: 1 part by mass, Tween 80: 1 part by mass; The total solid components are 77 parts by mass, add water to a solid content of 30 wt%, about 179.67 parts by mass of water, and a total of 256.67 parts by mass.

[0057] Coating amount 10 g / m² (dry basis), hot air drying at 80 - 100 °C.

[0058] Testing:

[0059] Cobb60 = 9.2 g / m² (according to ISO 535 / TAPPI T441),

[0060] Kit = 12 levels (TAPPI T559),

[0061] The dry film is uniform and free of cracks.

[0062] Example 2

[0063] PHA: 25 parts by mass, PBAT: 35 parts by mass, PVOH: 8 parts by mass, triethyl citrate: 3 parts by mass, citric acid: 1 part by mass, Span 60: 0.5 part by mass; the total solid components are 72.5 parts by mass, water is added to a solid content of 30 wt%, about 169.17 parts by mass of water, and the total is 241.67 parts by mass.

[0064] Cobb60 = 8.7 g / m², Kit = 11, with high flexibility.

[0065] Example 3

[0066] PHA: 50 parts by mass, PBAT: 10 parts by mass, PVOH: 10 parts by mass, glycerol: 4 parts by mass, borax: 1.5 parts by mass, Tween 80: 1 part by mass; the total solid components are 76.5 parts by mass, water is added to a solid content of 30 wt%, about 178.5 parts by mass of water, and the total is 255 parts by mass.

[0067] Coating Cobb60 = 9.8 g / m², Kit = 11, with a tight surface; it is proved that a film can also be formed when the PHA content is high.

[0068] Comparative Example A

[0069] The same main formulation as in Example 1 but without surfactant;

[0070] The emulsion is prone to stratification, the coating is uneven, Cobb60 > 18 g / m², Kit = 7.

[0071] Comparative Example B

[0072] The same main formulation as in Example 1 but without crosslinking agent;

[0073] The wet water resistance is poor, Cobb60 = 25 g / m², Kit = 9.

[0074] It can be seen by comparing with the comparative examples that the surfactant and crosslinking agent significantly affect the coating barrier performance and film-forming stability in this technical solution, so they are preferably added.

[0075] Verification of the recycling and repulping of the present invention

[0076] Purpose: To verify the easy recyclability of the coating of the present invention compared with PLA film lamination. The PLA film laminated paper used in the comparative example is a commercially available product, and its base paper is the same as that in Example 1. This laminated paper uses REVODE ® PLA resin of grade 190 for film lamination, and the film lamination weight is 25 g / m².

[0077] Method: Referring to TAPPI UM 213, pulping was carried out in the laboratory at 45 °C, pH = 7, with stirring for 30 min; non-recyclable materials were separated with a sieve aperture of 0.15 mm.

[0078] Control: Coated paper of Example 1 vs. PLA laminated paper (same base paper and grammage), see Table 1 below.

[0079]

[0080] Results: The PVOH coating of the present invention dissolved into the aqueous phase, and PHA / PBAT was in the form of debris and easy to screen; the fiber recovery rate was about 95% and the pulp was clean; while for PLA lamination, large films were formed and adhered to the fibers, resulting in a low recovery rate.

[0081] Biodegradability test of the present invention

[0082] 1. Home composting (30 ± 5 °C): The coated paper of Example 1 and PLA laminated paper were placed in a home composting simulation device and weighed every 2 weeks; the weight loss rates at 8 weeks / 12 weeks are shown in the following Table 2:

[0083]

[0084] The degradation rate of Example 1 was significantly higher than that of PLA, indicating that the PHA / PBAT system also has better degradability in a low-temperature composting environment. If in industrial composting (>55 °C) or other environments (such as soil, ocean), the potential degradation rate of PHA / PBAT is higher.

[0085] If further characterization of soil or ocean degradation is required, ASTM D5988 (soil) or ASTM D6691 (ocean) standards can be referred to; the comprehensive degradation rate and toughness of the system of the present invention can be adjusted through HV monomers and PBAT components.

[0086] Barrier and heat-sealing property test of the present invention

[0087] Barrier performance: Cobb60 was measured according to ISO 535 (or GB / T 1540) for the water absorption in 60 seconds; the Kit value was measured according to TAPPIT559 for the oil resistance grade; multiple examples of the present invention were all within the range of Cobb60 ≤ 10 - 10.5 g / m² and Kit ≥ 10 grades.

[0088] Heat-sealing strength: The coated paper of Ex1 was selected, and the 15-mm-wide seam was measured under the conditions of a heat-sealing machine (temperature 160 °C, pressure 0.2 MPa, 2 s), and a value of ≥ 5 N / 15 mm was obtained, indicating its suitability for heat-sealing applications (such as paper cups or packaging bags).

[0089] Comparison of the present invention with the prior art

[0090] Compared with PE film or PFAS coating: The present invention is water-based, fluorine-free, free of VOC and fluorine residue problems, and is easier to remove during the pulping process;

[0091] Compared with PLA film laminating: Barrier index (equal or better Cobb60 / Kit), high recovery rate (>95% vs. 87%), and faster home composting degradation rate (58% vs. 14%);

[0092] Compared with other bio-based coatings (such as binary PHA / PVOH or PBAT / PVOH): Through the high melt blending and aqueous phase emulsification of the ternary combination of the present invention, the best balance can be achieved in barrier, recycling and multi-environment degradation, and it has better industrial adaptability.

[0093] The ternary blend aqueous emulsion and its paper-based coating of the present invention are mainly applied to:

[0094] Food packaging: Paper cups, takeout boxes, baking liners, cold drink cups, etc.;

[0095] Industrial packaging: Moisture-proof paper bags, carton liners for wet or oily materials;

[0096] Special packaging: Medical and chemical outer packages that require water and moisture resistance and meet the requirements of recyclability or degradability;

[0097] Agricultural paper products: Seedling trays, nursery containers, degradable mulch papers, etc.

[0098] By melt-aqueous phase emulsification blending of PHA, PBAT and PVOH, the present invention constructs a coating system on paper-based materials with excellent waterproof and oil-proof barrier, recyclability for repulping and multi-environment biodegradability. Compared with traditional PE or PFAS solutions, the present invention is more environmentally friendly; compared with PLA film laminating, its recyclability and degradation adaptability are more prominent, and it can be applied to home composting, soil and even marine environments. The emulsion process is simple and can be applied to existing papermaking coating production lines. Any replacement, change and secondary modification of the proportions of PHA, PBAT, PVOH or the types of additives within the framework of the present invention's concept shall be regarded as falling within the protection scope of the present invention.

Claims

1. A water-based emulsion of PHA, PBAT and PVOH, characterized in that, Comprising by mass parts: Polyhydroxyalkanoate PHA is 10 - 50 parts; Polybutylene adipate-co-terephthalate PBAT is 10 - 35 parts; Polyvinyl alcohol PVOH is 8 - 30 parts; Plasticizer is 1 - 10 parts; Crosslinking agent is 0.5 - 1.5 parts; Surfactant is 0.1 - 5 parts; The balance is water, keeping the solid content of the emulsion at 20 - 50 wt%; And, the average particle size D50 of the dispersed phase in the emulsion is 1.5 - 3 μm; when the aqueous emulsion is coated on the surface of paper or cardboard and dried at 80 - 150 °C to form a barrier coating, the Cobb60 value of the paper-based material does not exceed 15 g / m², and the Kit grade is not lower than grade 10.

2. The aqueous emulsion according to claim 1, wherein: The polyhydroxyalkanoate PHA is selected from short-chain or medium-chain types, including one or more of poly(3-hydroxybutyrate) PHB, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) PHBHHx, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) P34HB.

3. The aqueous emulsion according to claim 1, wherein: The PBAT is an aliphatic-aromatic compostable polyester with a melting point of 110 - 130 °C; the degree of hydrolysis of the PVOH is in the range of 85 - 98%, and the viscosity of a 4 wt% aqueous solution is 2 - 30 mPa·s.

4. The aqueous emulsion according to claim 1, wherein The plasticizer is selected from one or more of glycerol, glycerin, triethyl citrate, tributyl acetylcitrate; the crosslinking agent is selected from one or more of boric acid, borax, citric acid, glyoxal or glutaraldehyde; the surfactant is selected from food-contact approved auxiliaries such as Tween, Span, lecithin or sodium stearoyl lactate.

5. The aqueous emulsion according to claim 1, characterized in that, The melting temperature of the PHA and PBAT is controlled in the range of 150 - 170 °C, and then the molten stream is dispersed into the PVOH aqueous solution by high-speed stirring at 80 - 95 °C at 1000 - 5000 rpm or by high-pressure homogenization.

6. A method for preparing the aqueous emulsion according to claim 1, characterized in that, Including the following steps: Step 1. Dissolve PVOH in deionized water at 80 - 95 °C to prepare a 5 - 15 wt% PVOH aqueous solution; Step 2. Melt-blend PHA and PBAT at 150 - 170 °C for 3 - 10 minutes to obtain a uniform melt; Step 3. At 80 - 95 °C, slowly add the melt obtained in Step 2 to the PVOH aqueous solution described in Step 1 by high-speed stirring at 1000 - 5000 rpm or by high-pressure homogenization and emulsify and disperse for 5 - 30 minutes, adjusting the pH to 6.5 - 7.5 during the emulsification process; Step 4. Cool the emulsion obtained in Step 3 to no higher than 50 °C, add a plasticizer, a crosslinking agent, and a surfactant, stir evenly and filter to obtain a ternary blend aqueous emulsion with a final average particle size D50 of the dispersed phase of 1.5 - 3 μm and a solid content of 20 - 50 wt%.

7. The method according to claim 6, wherein: During the emulsification process in Step 3, control the feeding rate and shear time to make PHA / PBAT and PVOH form a stable O / W type emulsion.

8. A paper-based material, characterized in that, Coating on the surface of paper or cardboard The water-based emulsion according to claim 1, and after drying at 80 to 150 °C, a barrier coating is formed, so that the Cobb60 value of the paper-based material does not exceed 15 g / m², the Kit grade is ≥ 10, and the heat seal strength of the coating is ≥ 5 N / 15 mm, and the fiber recovery rate is not less than 90% under the laboratory pulping conditions with reference to the TAPPI UM 213 standard.

9. The paper-based material according to claim 8, characterized in that, Under the conditions of recycled pulping, PVOH can be dissolved in the aqueous phase, and PHA and PBAT can be removed by screening or flotation in the form of fragments or particles; in home composting, soil, and marine environments, PHA and PBAT can be degraded by microorganisms, and PVOH can be removed by hydrolysis or enzymatic hydrolysis, having the characteristics of recyclability and degradability.

10. Use of the aqueous emulsion according to any one of claims 1 to 5 in a paper-based barrier coating, characterized in that The water-based emulsion is applicable to the fields of food packaging, industrial packaging, special packaging, and agricultural paper products.

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