PHA (polyhydroxyalkanoate), PBAT (poly (butylene adipate-co-terephthalate)) and PVOH (polyvinyl alcohol) blended aqueous emulsion and application thereof in paper-based barrier coating

Abstract

The invention discloses a PHA (polyhydroxyalkanoate), PBAT (poly (butyleneadipate-co-terephthalate)) and PVOH (polyvinyl alcohol) blended water-based emulsion and application thereof in a paper-based barrier coating. The emulsion is prepared by performing melt blending on PHA and PBAT at 150-170 DEG C and then dispersing the mixture into a PVOH aqueous solution at 80-95 DEG C, and a plasticizer, a cross-linking agent and a surfactant can be added to improve the performance. And after coating paper, drying at the temperature of 80-150 DEG C to form the barrier film with the Cobb value of 10-15g / m and the Kit greater than or equal to grade 10. Compared with a traditional PE film or fluorine-containing coating, the system is more environmentally friendly and recyclable; pVOH is dissolved in pulping water, PHA and PBAT are easy to separate, and fibers are efficiently recycled; in compost, soil and marine environments, PHA and PBAT have wide biodegradability and are superior to PLA which is difficult to recycle and re-slurry and needs industrial compost. The method is suitable for food, industrial, special packaging and agricultural paper products.

Description

Technical Field

[0001] The present invention belongs to the intersection of biodegradable polymer materials and paper-based packaging technology, 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 waterproof, oil-proof and barrier properties on the surface of the paper base, and has both recyclable repulping and extensive biodegradability, and is suitable for food, industrial and special packaging and other fields. Background Art

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

[0003] Polyhydroxyalkanoates (PHA) are a type of polymer that has the potential to biodegrade under a variety of environmental conditions, including soil and ocean; polybutylene adipate-terephthalate (PBAT) is often used to improve flexibility and industrial composting scenarios; polyvinyl alcohol (PVOH) has water solubility and dry barrier properties. If the three can be combined into a water-based coating system, it is expected to provide excellent barrier properties on the paper surface and be easy to recycle and widely degrade. However, PHA / PBAT has problems with melt viscosity differences, hydrolysis risks, and particle size stability during the aqueous phase dispersion process. The present invention designs solutions and conducts experimental verification to address 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 coating to solve the deficiencies of traditional PE coating, PFAS coating and PLA coating in terms of barrier performance, recycling difficulty and environmental degradation. Specific objectives include:

[0005] Provide an environmentally friendly and safe water-based coating system that avoids organic solvents and fluorinated chemicals to ensure food contact safety;

[0006] Improve the waterproof, oil-proof and barrier properties of paper-based materials, achieve excellent Cobb60 value and Kit grade, and have heat-sealing ability;

[0007] Achieve efficient recycling of coating in pulping, high fiber recovery rate and easy separation;

[0008] Endow paper-based materials with biodegradability in a wide range of environments, including soil, ocean and home compost, surpassing the limitations of PLA;

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

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

[0011] (1) Main ingredients of the formula

[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; crosslinker (0.5-5 parts by mass) enhances PVOH water resistance; surfactant (0.1-5 parts by mass) stabilizes emulsification;

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

[0015] (2) Preparation by melt-water emulsification

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

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

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

[0019] Step 4. Cool the emulsion obtained in step 3 to no more than 50° C., add plasticizer, crosslinking agent 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, the feed rate and shear time are controlled, and the pH can be adjusted to a neutral range of 6.5 to 7.5 to avoid high-temperature hydrolysis, so that PHA / PBAT and PVOH form a stable O / W emulsion.

[0021] (3) Paper base coating

[0022] Apply the emulsion (5-15 g / m² on a dry basis) to the paper surface using a scraper, wire rod or spray;

[0023] Dry at 80~150℃ to make Cobb60≤15g / m², Kit≥10 grade, and heat seal strength≥5N / 15mm.

[0024] (4) Recycling and degradation

[0025] Under recycling pulping conditions, PVOH can be dissolved in the aqueous phase, and PHA and PBAT can be removed in the form of fragments or particles through screening or flotation, and the fiber recovery rate can reach 90-95%; and in household compost, soil or marine environment, PHA and PBAT can be degraded by microorganisms, and PVOH is removed by hydrolysis or enzymolysis, ultimately realizing the recyclable and degradable 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, and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) P34HB, combined with different comonomer contents to regulate crystallinity, thermal stability and toughness.

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

[0028] The plasticizer is selected from one or more of glycerol, propylene glycol, triethyl citrate, acetyl tributyl citrate; the cross-linking agent is selected from one or more of boric acid, borax, citric acid, glyoxal or glutaraldehyde; the surfactant is selected from Tween, Span, lecithin or sodium stearoyl lactylate and other food contact permitted additives.

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

[0030] Under the recycling pulping conditions, the barrier coating can dissolve PVOH in the water phase, and PHA and PBAT are removed in the form of fragments or particles through screening or flotation, with a fiber recovery rate of 90-95%. In household compost, soil, and marine environments, PHA and PBAT can be degraded by microorganisms, and PVOH is removed by hydrolysis or enzymolysis, and has the characteristics of being recyclable and degradable.

[0031] The aqueous emulsion is suitable for food packaging, industrial packaging, special packaging and agricultural paper products, and has excellent water and oil resistance, convenient recycling and wide environmental biodegradability.

[0032] The following beneficial effects can be obtained by using the present invention:

[0033] Green and safe: Compared with PE or PFAS coatings, it uses water-based emulsion, no organic solvents and fluorinated chemicals, and has no VOC emissions. It uses safe additives such as glycerol and Tween, and has no toxic residues, ensuring food contact safety. It is environmentally friendly and reliable.

[0034] Excellent barrier properties: The coating can reduce the Cobb60 value of the paper surface to 10-15g / m², Kit grade ≥10, heat sealing strength ≥5N / 15mm, and the waterproof and oil-proof effect is comparable to or even better than PLA coating, meeting the high requirements of food packaging.

[0035] More efficient recycling: PVOH is water-soluble during pulping, 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 coating and PLA film, avoiding the problem of fiber adhesion, and has obvious recycling advantages.

[0036] Wide degradation range: PHA can be degraded in soil and ocean, PBAT is suitable for industrial composting, and PVOH is removed by hydrolysis. Compared with PLA, which is only limited to high-temperature composting, it can be degraded more thoroughly in home composting and natural environment, and is more environmentally friendly.

[0037] The process is simple and stable: only extruder melting and high-speed stirring equipment are required for mass production. Combined with 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] Wide range of uses: Suitable for food, industry, special packaging and agricultural paper products, with excellent performance and environmental protection characteristics, great market potential, and significant economic and social benefits. DETAILED DESCRIPTION

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

[0040] raw materials

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

[0042] PBAT: Commercial compostable grades, such as Ecoflex®, MFI is 30g / 10min, melting point is 120℃;

[0043] PVOH: hydrolysis degree 88%, 4wt% aqueous solution viscosity ≈20mPa·s;

[0044] Plasticizer: glycerol, triethyl citrate, etc.;

[0045] Cross-linking agent: 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 (2000-3000rpm) or high-pressure homogenizer, etc.

[0048] Preparation process example

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

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

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

[0052] Step 4. Adding additives: cooling to about 50°C, adding glycerol, borax, and Tween 80, and stirring for 15 minutes; filtering to obtain a ternary blended aqueous emulsion with a solid content of 30 wt%;

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

[0054] Examples and Comparative Examples

[0055] Example 1

[0056] PHA: 30 parts by mass, PBAT: 30 parts by mass, PVOH: 10 parts by mass, glycerin: 5 parts by mass, borax: 1 part by mass, Tween 80: 1 part by mass; the solid components total 77 parts by mass, water is added to the solid content of 30wt%, about 179.67 parts by mass of water, a total of 256.67 parts by mass.

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

[0058] test:

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

[0060] Kit = Level 12 (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 parts by mass; the solid components total 72.5 parts by mass, water is added to the solid content of 30wt%, about 169.17 parts by mass of water, a total of 241.67 parts by mass.

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

[0065] Example 3

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

[0067] The coating Cobb60=9.8 g / m², Kit=11, the surface is firm; it proves that film can be formed even at high PHA content.

[0068] Comparative Example A

[0069] Same main formula as Example 1 but without surfactant;

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

[0071] Comparative Example B

[0072] Same main formula as Example 1 but without cross-linking agent;

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

[0074] By comparing with the comparative example, it can be seen that the surfactant and the cross-linking agent significantly affect the barrier properties and film-forming stability of the coating in the present technical solution, so they are preferably added.

[0075] Recycling and repulping verification of the present invention

[0076] Purpose: To verify the recyclability of the coating of the present invention compared with that of PLA coating. The PLA coating paper used in the comparative example is a commercially available product, and its base paper is the same as that in Example 1. The coating paper is made of REVODE produced by Zhejiang Hisun Biomaterials Co., Ltd. ® 190 brand PLA resin is used for lamination, and the weight of the lamination is 25g / m².

[0077] Method: Refer to TAPPI UM 213, slurry was crushed in the laboratory at 45℃, pH=7, and stirring for 30 minutes; the sieve hole was 0.15mm to separate non-recyclables.

[0078] Comparison: Example 1 coated paper vs. PLA coated paper (same base paper and grammage) See Table 1 below.

[0079]

[0080] Results: The PVOH coating of the present invention dissolved into the water phase, and PHA / PBAT was in the form of debris that was easy to screen out; the fiber recovery rate was about 95% and the pulp was clean; while PLA coating formed large pieces of film-bonded fibers, and the recovery rate was low.

[0081] Biodegradability test of the present invention

[0082] 1. Home composting (30±5°C): Example 1 and PLA coated paper were placed in a home composting simulation device and weighed every 2 weeks; the following table shows the 8-week / 12-week weight loss rate, see Table 2 below:

[0083]

[0084] The degradation rate of Example 1 is 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 even higher.

[0085] To further characterize soil or ocean degradation, reference may be made to ASTM D5988 (soil) or ASTM D6691 (ocean) standards; the system of the present invention can adjust the comprehensive degradation rate and toughness through HV monomers and PBAT components.

[0086] Barrier and heat seal test of the present invention

[0087] Barrier performance: Cobb60 refers to the water absorption in 60 seconds measured by ISO 535 (or GB / T 1540); Kit value refers to TAPPIT559 to measure the oil resistance level; multiple groups of embodiments of the present invention are all within the range of Cobb60≤10~10.5g / m² and Kit≥10.

[0088] Heat seal strength: Ex1 coated paper was selected and a 15mm wide seam was measured under the conditions of a heat sealer (temperature 160°C, pressure 0.2MPa, 2s), and the result was ≥5N / 15mm, indicating that it is suitable for heat sealing applications (such as paper cups or packaging bags).

[0089] Comparison between the present invention and the prior art

[0090] With PE coating or PFAS coating: the present invention is water-based, fluorine-free, has no VOC and fluorine residue problems, and is easier to remove in the pulping process;

[0091] Compared with PLA coating: barrier performance (same or better Cobb60 / Kit), high recovery rate (>95% vs. 87%), and faster degradation rate in home composting (58% vs. 14%);

[0092] With other bio-based coatings (such as binary PHA / PVOH or PBAT / PVOH): through high melt mixing and water phase emulsification of the ternary combination of the present invention, the best balance can be achieved in barrier, recycling and multi-environmental degradation, and it is more industrially adaptable.

[0093] The ternary blended aqueous emulsion and the paper-based coating thereof of the present invention are mainly used in:

[0094] Food packaging: paper cups, takeaway boxes, baking lining paper, cold drink cups, etc.

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

[0096] Special packaging: pharmaceutical and chemical packaging that needs to be waterproof and anti-seepage and recyclable or degradable;

[0097] Agricultural paper products: seedling trays, nursery containers, biodegradable mulch paper, etc.

[0098] By emulsifying and blending PHA, PBAT and PVOH in a melt-water phase, the present invention constructs a coating system on paper-based materials that has excellent waterproof and oil-proof barrier properties, is recyclable and repulpable, and is biodegradable in multiple environments. Compared with traditional PE or PFAS solutions, the present invention is more environmentally friendly; compared with PLA coating, the recyclability and degradation adaptability are more prominent, and it can be used in household compost, soil, and even marine environments. The emulsion process is simple and can be applied to existing paper coating production lines. Any replacement, change, and secondary modification of the proportion of PHA, PBAT, PVOH, or the type of additives within the framework of the present invention should be deemed to fall within the scope of protection of the present invention.

Claims

1. A PHA, PBAT and PVOH blended aqueous emulsion, characterized in that: Included by mass: Polyhydroxyalkanoate PHA is 10 to 60 parts; Polybutylene adipate-terephthalate PBAT is 10 to 60 parts; Polyvinyl alcohol PVOH is 5 to 30 parts; Plasticizer: 1 to 10 parts; The cross-linking agent is 0.5 to 5 parts; The surfactant is 0.1 to 5 parts; The balance is water, so that the solid content of the emulsion is maintained at 20-50wt%.

2. The aqueous emulsion according to claim 1, characterized in that: 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, and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) P34HB, combined with different comonomer contents to regulate crystallinity, thermal stability and toughness.

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

4. The aqueous emulsion according to claim 1, characterized in that The plasticizer is selected from one or more of glycerol, propylene glycol, triethyl citrate, and acetyl tributyl citrate; the crosslinking agent is selected from one or more of boric acid, borax, citric acid, glyoxal, or glutaraldehyde; the surfactant is selected from one or more of food contact permitted additives, such as Tween, Span, lecithin, or sodium stearoyl lactylate.

5. The aqueous emulsion according to claim 1, characterized in that The melting temperature of the PHA and PBAT is controlled within the range of 150-170°C, and then the molten stream is dispersed into the PVOH aqueous solution at 80-95°C by high-speed stirring at 1000-5000 rpm or high-pressure homogenization, so that the average particle size of the final dispersed phase is maintained within the range of 0.5-5 μm.

6. A method for preparing the aqueous emulsion according to claim 1, characterized in that: The following steps are involved: Step 1. dissolving PVOH in deionized water at 80-95° C. to prepare a 5-15 wt % PVOH aqueous solution; Step 2. Melt-blending PHA and PBAT at 150-170° C. to obtain a uniform melt; Step 3. Slowly add the melt obtained in step 2 to the PVOH aqueous solution in step 1 at 80-95° C. by high-speed stirring or high-pressure homogenization and emulsify and disperse for 5-30 minutes; Step 4. Cool the emulsion obtained in step 3 to no more than 50° C., add plasticizer, crosslinking agent and surfactant as needed, stir evenly and filter to obtain the final stable ternary blended aqueous emulsion.

7. The method according to claim 6, characterized in that: During the emulsification process in step 3, the feed rate and shear time are controlled, and the pH can be adjusted to a neutral range of 6.5 to 7.5 to avoid high-temperature hydrolysis, so that PHA / PBAT and PVOH form a stable O / W emulsion.

8. A paper-based material, characterized in that: The aqueous emulsion according to any one of claims 1 to 5 is coated on the surface of paper or paperboard, and a barrier coating is formed after drying at 80 to 150° C., so that the Cobb 60 value of the paper-based material does not exceed 15 g / m², the Kit grade is ≥10, and the heat sealing strength of the coating is ≥5 N / 15 mm.

9. The paper-based material according to claim 8, characterized in that: Under the recycling pulping conditions, the barrier coating can dissolve PVOH in the water phase, and PHA and PBAT are removed in the form of fragments or particles through screening or flotation, with a fiber recovery rate of 90-95%. In household compost, soil, and marine environments, PHA and PBAT can be degraded by microorganisms, and PVOH is removed by hydrolysis or enzymolysis, and has the characteristics of being recyclable and degradable.

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 aqueous emulsion is suitable for food packaging, industrial packaging, special packaging and agricultural paper products, and has excellent water and oil resistance, convenient recycling and wide environmental biodegradability.

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