Pure bio-based polyhydroxyalkanoate adhesive and preparation and application thereof

Abstract

The application discloses a pure bio-based polyhydroxyaliphatic acid ester adhesive and preparation and application thereof, and belongs to the technical field of degradable adhesives. The adhesive takes polyhydroxybutyric acid valerate or polyhydroxybutyric acid hexanoate as a matrix, and is subjected to melt end group activation to make the acid value reach 2-15 mg KOH / g; a reaction type emulsifier with a hydrophilic-lipophilic balance value of 9-12 is introduced into an aqueous phase, and a stable water dispersion is prepared through phase inversion high shear emulsification. The dispersion has a Z-average particle size of 0.12-0.30 mu m, and free surfactant is not higher than 30 wt%. After compounding tackifying resin, plasticizer and plant wax, the obtained adhesive has a bio-based carbon content not lower than 95%, and volatile organic compounds not higher than 100 mg / kg. The adhesive has a paper / paper heat sealing strength not lower than 7.0 N / 15 mm, a 180 degree peeling strength not lower than 7.5 N / 25 mm, and can pass re-pulping evaluation.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable adhesive technology, specifically relating to pure bio-based polyhydroxy fatty acid ester adhesives and their preparation and application. Background Technology

[0002] With increasing global emphasis on environmental protection and sustainable development, traditional packaging and labeling industries are facing serious challenges to petrochemical-based adhesives, such as ethylene-vinyl acetate copolymer (EVA) emulsions and acrylate emulsions. These adhesives are not only difficult to biodegrade in the natural environment, increasing the burden of waste disposal, but also easily form adhesive residues during the recycling and repulping process of waste paper products, severely affecting the quality of recycled pulp. Furthermore, these products may release volatile organic compounds (VOCs) during production and use, posing a potential threat to the environment and human health.

[0003] Polyhydroxyalkanoates (PHAs) are a class of aliphatic copolyesters synthesized by microorganisms through fermentation engineering. They are typical fully bio-based, biodegradable polymers. However, the direct application of PHAs in water-based adhesives still faces many technical bottlenecks. For example, common short-chain PHAs such as polyhydroxybutyrate (PHB) and its copolymers have high crystallinity and are brittle, resulting in poor film-forming properties and insufficient wetting and spreading ability on substrates when used as adhesives. In addition, traditional water-based emulsification methods usually require the addition of large amounts of surfactants, most of which exist in a free state in the emulsion system. This not only weakens the water resistance and adhesive strength of the adhesive film but also leads to poor long-term storage stability of the emulsion system.

[0004] In the prior art, some patent documents have attempted to solve the problem of preparing PHA aqueous dispersions. For example, WO 2012 / 149407 discloses a process for preparing PHA emulsions through melt phase inversion emulsification, but its technical solution relies on conventional non-reactive surfactants or water-soluble polymers to provide stability, without involving chemical modification of the PHA polymer itself to enhance its emulsifying properties. The essential drawback of this method is that the binding force between the non-reactive surfactant and PHA particles is weak, with most of them remaining free in the aqueous phase, resulting in poor water resistance of the film and insufficient long-term storage stability of the dispersion. EP 4379001A1 discloses a broad range of PHA dispersion particle size and solid content, but its core technology still fails to break away from the traditional emulsification approach and does not reveal a method for constructing a stable interfacial layer by precisely controlling the chemical structure of the polymer.

[0005] These existing technologies have failed to reveal or inspire the core technical concept of this invention: in-situ chemical modification of the end groups of molten PHA to precisely control its acid value within a narrow window of 2–15 mg KOH / g, and synergistic effect with a reactive emulsifier with a specific hydrophilic-lipophilic balance (HLB) value of 9–12, thereby constructing a stable interfacial layer on the surface of PHA particles, anchored by chemical bonding or strong ionic interactions. It is this synergistic effect of "internal modification providing anchor points" and "external emulsifier reaction anchoring" that fundamentally solves the long-standing technical problem of the inability to simultaneously achieve stability and high performance in PHA aqueous dispersions.

[0006] Therefore, industry demand drives the development of a new type of environmentally friendly and high-performance adhesive. It should have characteristics such as being purely bio-based, free of organic solvents, having a stable interfacial structure, controllable and uniform particle size distribution, and being able to achieve high-strength heat-sealing bonding at lower temperatures, so as to meet the dual needs of the modern packaging industry for sustainability and high performance. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a pure bio-based polyhydroxy fatty acid ester adhesive and its preparation and application, aiming to solve the technical problems of poor storage stability, weak interfacial bonding force and insufficient adhesive performance of existing polyhydroxy fatty acid ester water-based adhesives.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a pure bio-based polyhydroxyalkanoate adhesive, which is an aqueous dispersion or concentrate thereof, comprising, on a dry weight basis, 35–85 wt% polyhydroxyalkanoate, 0.1–3.0 wt% reactive emulsifier, 10–45 wt% tackifying resin, 2–15 wt% plasticizer, and 0–10 wt% vegetable wax, and further containing water and additives. The content of the polyhydroxyalkanoate can be 35 wt%, 40 wt%, 45 wt%, 50 wt%, 52 wt%, 55 wt%, 60 wt%, 62 wt%, 64.1 wt%, 65 wt%, 66 wt%, 67 wt%, 70 wt%, 75 wt%, 80 wt%, or 85 wt%. The content of the reactive emulsifier can be 0.1 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, or 3.0 wt%. The content of the tackifying resin can be 10wt%, 15wt%, 20wt%, 25wt%, 26.7wt%, 28wt%, 30wt%, 31wt%, 35wt%, 35.4wt%, 40wt%, or 45wt%. The content of the plasticizer can be 2wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 10wt%, 12wt%, 14wt%, or 15wt%. The content of the plant wax can be 0wt%, 1wt%, 2wt%, 3wt%, 3.2wt%, 4wt%, 5wt%, 6wt%, 8wt%, or 10wt%.

[0010] In the aforementioned adhesive, the polyhydroxyalkanoate is selected from one or more of polyhydroxybutyrate, polyhydroxybutyrate hexanoate, polyhydroxybutyrate-4-hydroxybutyrate copolyester, and polyhydroxybutyrate valerate. The dispersion formed by this adhesive has specific physicochemical properties, including a Z-average particle size (Dz) of 0.12–0.30 μm, a polydispersity index (PDI) not higher than 0.20, a pH value of 6.5–8.5, a free surfactant mass fraction not higher than 30 wt%, a volatile organic compound (VOC) content not higher than 100 mg / kg, a bio-based carbon content not lower than 95%, and no artificially added organofluorine compounds. For example, Dz can be 0.12μm, 0.15μm, 0.18μm, 0.198μm, 0.205μm, 0.21μm, 0.225μm, 0.25μm, 0.28μm or 0.30μm; pH value can be 6.5, 6.8, 7.0, 7.2, 7.4, 7.5, 7.6, 8.0 or 8.5. A key technical feature is that the polyhydroxyalkanoate in the adhesive is modified to have a residual acid value of 2–15 mg KOH / g, for example, the residual acid value can be 2.0 mg KOH / g, 2.1 mg KOH / g, 3.0 mg KOH / g, 5.0 mg KOH / g, 8.5 mg KOH / g, 8.8 mg KOH / g, 9.0 mg KOH / g, 9.2 mg KOH / g, 10.0 mg KOH / g, 12.0 mg KOH / g, 14.8 mg KOH / g or 15.0 mg KOH / g.

[0011] This invention also provides a method for preparing the above-mentioned pure bio-based polyhydroxyalkanoate adhesive, which does not use any organic solvents throughout the process, and includes the following steps:

[0012] Step 1, Drying and Protection: Dry the polyhydroxyalkanoate granules in a drying oven at 80–90°C, for example, 80°C, 82°C, 85°C, 88°C or 90°C, under an inert gas protective atmosphere for 6–12 hours, for example, 6h, 8h, 10h or 12h, so that the residual moisture content is not higher than 0.05wt%, and obtain dried granules.

[0013] Step 2, Activation of the melt end group: The dried granules from Step 1 are mixed with 0.2–2.0 wt% of bio-based cyclic anhydride, for example, 0.2 wt%, 0.5 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, or 2.0 wt%, in a twin-screw reactive extruder and reacted for 2–4 minutes, for example, 2 min, 3 min, or 4 min, at 165–178 °C, for example, 165 °C, 168 °C, 170 °C, 175 °C, or 178 °C, and −0.08 to −0.095 MPa, to obtain an activated melt with an acid value of 2–15 mg KOH / g.

[0014] Step 3, reverse high-shear emulsification: The activated melt obtained in step 2 is continuously pumped into an aqueous phase at 80–95°C containing a reactive emulsifier with an HLB value of 9–12 and a pH adjuster, for example, 80°C, 85°C, 90°C, or 95°C, with an energy input specific power of 0.25–0.45 kW / kg, for example, 0.25 kW / kg, 0.30 kW / kg, 0.35 kW / kg, 0.40 kW / kg, or 0.45 kW / kg, for high-shear emulsification for 3–10 minutes, for example, 3 min, 4 min, 5 min, 6 min, 8 min, or 10 min, to obtain a polyhydroxyalkanoate aqueous dispersion with a Dz of 0.12–0.30 μm, a PDI of no more than 0.20, and a free surfactant content of no more than 30 wt%.

[0015] Step 4, Formulation finishing: At 50–70°C, for example 50°C, 55°C, 60°C, 65°C or 70°C, add tackifying resin, plasticizer and plant wax to the polyhydroxyalkanoate aqueous dispersion obtained in Step 3. After degassing and filtration at 5–10 μm, for example 5 μm, 8 μm or 10 μm, the finished product is obtained.

[0016] The pure bio-based polyhydroxyalkanoate adhesive described in this invention can be applied to heat sealing of paper or paperboard, bonding of paper to paper, bonding of paper to wood, lamination of paper to biodegradable films, and coating of labels or tapes. It exhibits excellent performance; for example, at 120°C, 1 second, and 0.3 MPa, the heat seal strength between paper and paper is not less than 7.0 N / 15 mm; at 23°C and 50% relative humidity, the 180° peel strength measured according to ASTM D3330 / D3330M-04(2025) is not less than 7.5 N / 25 mm. Resizing performance is evaluated according to the resizing assessment methods of CEPI and 4evergreen.

[0017] In one specific embodiment, the polyhydroxy fatty acid ester is polyhydroxybutyrate valerate and / or polyhydroxybutyrate hexanoate, wherein the molar fraction of 3-hydroxyvalerate monomer is 9–25 mol%, for example, 9 mol%, 12 mol%, 15 mol%, 20 mol%, or 25 mol%; the molar fraction of 3-hydroxyhexanoate monomer is 5–12 mol%, for example, 5 mol%, 7 mol%, 9 mol%, or 12 mol%; and its melt flow rate at 190°C and 2.16 kg load is 3–20 g / 10 min, for example, 3 g / 10 min, 5 g / 10 min, 10 g / 10 min, 15 g / 10 min, or 20 g / 10 min.

[0018] In one specific embodiment of the preparation method, the acid value of the melt after the reaction in step 2 is 3–10 mg KOH / g, for example, 3 mg KOH / g, 4 mg KOH / g, 5 mg KOH / g, 8.5 mg KOH / g, 9.2 mg KOH / g or 10 mg KOH / g, and the bio-based cyclic anhydride is succinic anhydride or maleic anhydride.

[0019] In one specific embodiment, the reactive emulsifier undergoes esterification, transesterification, or ion-pair bonding with the end groups of polyhydroxy fatty acid esters during emulsification to form an interfacial anchoring layer with an HLB value of 9–12, and the reactive emulsifier is selected from one or more of the following: stearoyl lactate, lactate salt, alkyl succinate, rosin salt, maleic rosin salt, polymeric rosin salt, dehydrorosin salt, stearoyl citrate, fatty acid-amino alcohol salt.

[0020] In one specific embodiment of the preparation method, the volume ratio of polymer melt to water in step 3 is 35:65 to 45:55, for example 35:65, 40:60 or 45:55, and the emulsification equipment adopts an online gear pump, a static mixer and a two-stage series rotor-stator high shear system.

[0021] In one specific embodiment, the tackifying resin is a bio-based resin and is selected from: 1) rosin and its modified products, such as rosin gum, rosin oil, rosin wood and its hydrogenated, polymerized, disproportionated, maleated or fumarated derivatives, and their glycerides and pentaerythritol esters; 2) terpene resins, such as terpene polymers obtained by cationic polymerization of one or more of α-pinene, β-pinene, limonene, and dipentene; 3) terpene phenol resins, such as those obtained by condensation of the above terpenes with phenol, m-cresol or meta-alkylphenol; 4) tannin resins or cashew phenol modified resins; and one or more of their aqueous dispersions. Furthermore, the tackifying resin has a ring and ball softening point of 60–120°C, for example, 60°C, 70°C, 85°C, 100°C, 110°C, or 120°C, and an acid value of 5–25 mg KOH / g, for example, 5 mg KOH / g, 10 mg KOH / g, 15 mg KOH / g, 20 mg KOH / g, or 25 mg KOH / g.

[0022] In one specific embodiment, the plasticizer is of bio-based origin and is selected from one or more of the following: citrate esters, sucrose isobutyrate acetate, polyol esters, vegetable oil epoxides, and castor oil-derived diesters. Specifically, the citrate esters may be selected from one or more of triethyl citrate, acetylated triethyl citrate, tributyl citrate, acetylated tributyl citrate, triisobutyl citrate, and tri(2-ethylhexyl) citrate; the polyol esters may be selected from one or more of glycerol triacetate and polyglycerol fatty acid esters; the vegetable oil epoxides may be selected from one or more of epoxidized soybean oil and epoxidized linseed oil; and the castor oil-derived diesters may be selected from one or more of dioctyl sebacate and dioctyl azelate.

[0023] In one specific embodiment, after the pure bio-based polyhydroxyalkanoate adhesive is left to stand at 25°C for 30 days, the volume stratification rate is not higher than 1%, the Z-average particle size drift rate is not higher than 10%, the polydispersity index drift is not higher than 0.05, and the free surfactant mass fraction drift is not higher than 5 wt%.

[0024] In one specific implementation of the application, the heat sealing process window temperature is 90–130°C, for example 90°C, 100°C, 110°C, 120°C or 130°C, and the fiber tear rate after paper-to-paper bonding is not less than 80%.

[0025] In another specific embodiment of the application, when used for paper and polylactic acid film lamination, the T-peel strength at 23°C is not less than 2.0 N / 15 mm, and after being maintained at 60°C for 24 hours, the T-peel strength is not less than 1.8 N / 15 mm.

[0026] In another specific embodiment of the application, when used as a pressure-sensitive adhesive, the pure bio-based polyhydroxyalkanoate adhesive further contains 5–30 wt% of medium-chain long-chain polyhydroxyalkanoate, such as 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, or 30 wt%, and 0.1–0.8 wt% of organic peroxide for micro-crosslinking, such as 0.1 wt%, 0.3 wt%, 0.5 wt%, or 0.8 wt%, and its holding time under conditions of 60°C, 1 kg load, and 25 mm width is not less than 1000 minutes.

[0027] Furthermore, the activation temperature of the organic peroxide used in the application is 90–120°C, for example 90°C, 100°C, 110°C or 120°C, and the residual amount of the peroxide in the final product is not higher than 50 ppm.

[0028] In one specific embodiment, the mass fraction of free surfactant in the pure bio-based polyhydroxyalkanoate adhesive is less than 20 wt%.

[0029] In one specific embodiment, the volatile organic compound content of the pure bio-based polyhydroxyalkanoate adhesive is not higher than 50 mg / kg.

[0030] In one specific embodiment, the pure bio-based polyhydroxyalkanoate adhesive has a pH value of 7.0–8.0.

[0031] In one specific embodiment, the pure bio-based polyhydroxyalkanoate adhesive can also be prepared into an anhydrous molten adhesive by removing water. The anhydrous molten adhesive is obtained by dehydrating the aqueous dispersion prepared by the method described in this invention, and includes 40–70 wt% polyhydroxyalkanoate, such as 40 wt%, 50 wt%, 52 wt%, 60 wt%, or 70 wt%, 20–45 wt% tackifying resin, such as 20 wt%, 25 wt%, 30 wt%, 35.4 wt%, 40 wt%, or 45 wt%, 0–15 wt% plasticizer, such as 0 wt%, 5 wt%, 7 wt%, 10 wt%, or 15 wt%, and 0–10 wt% plant wax, such as 0 wt%, 2 wt%, 5 wt%, 8 wt%, or 10 wt%. The anhydrous melt adhesive has a Brookfield viscosity of 1500–8000 mPa·s at 170°C, for example, 1500 mPa·s, 2000 mPa·s, 3000 mPa·s, 5000 mPa·s or 8000 mPa·s, and the residual acid value of the polyhydroxyalkanoate is 2–15 mg KOH / g, and the mass fraction of the free surfactant is not higher than 30 wt%.

[0032] In one specific embodiment of the preparation method, the energy input specific power of step 3 is 0.25–0.45 kW / kg, and the high-shear emulsification time is 4–8 minutes, for example, 4 min, 5 min, 6 min, 7 min or 8 min.

[0033] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0034] Green and environmentally friendly, safe and non-toxic: This invention uses fully bio-based raw materials, the product has a bio-based carbon content of not less than 95%, and does not contain perfluorinated or polyfluoroalkyl substances (PFAS). No organic solvents are used in the production process, and the final product has extremely low VOC content (as low as 39mg / kg), which meets the safety requirements for green packaging and food contact materials.

[0035] Excellent bonding performance and process adaptability: Through a process combining melt end-group activation and reactive emulsification, the prepared adhesive dispersion has a small particle size and uniform distribution, forming a stable interfacial anchoring layer. This allows the adhesive to achieve high-strength bonding to paper substrates at relatively low heat-sealing temperatures (90–130℃), with a heat-sealing strength of over 7.0 N / 15 mm and a fiber tear rate of over 80%. It is also suitable for various applications such as hot melt adhesives and pressure-sensitive adhesives, and its 180° peel strength can reach over 7.5 N / 25 mm.

[0036] Outstanding storage stability: Since most of the emulsifiers are anchored to the surface of polymer particles through chemical bonding or strong ionic action, the content of free surfactants in the system is low (less than 30 wt%), which significantly improves the long-term storage stability of the aqueous dispersion. After standing at 25°C for 30 days, almost no stratification occurs, and the particle size and polydispersity index change very little.

[0037] Compatible with the circular economy model: The adhesive prepared by this invention not only has the ability to be degraded by industrial composting, but also does not interfere with the existing waste paper recycling and repulping system when applied to paper products, showing good repulping friendliness and conforming to the development direction of the circular economy.

[0038] Continuous process and suitable for scale-up: The preparation method of this invention integrates reactive extrusion and online emulsification technologies. The process flow is compact and easy to realize continuous and large-scale production, laying a solid foundation for the commercial application of this high-performance bio-based adhesive. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention. Unless otherwise stated, the raw materials used in this embodiment are commercially available industrial products or can be prepared by conventional methods. Unless otherwise specified, performance testing methods are performed according to the standards described in the invention summary section.

[0040] In this invention, "pure bio-based" refers to a system with a bio-based carbon content of not less than 95% as measured by ASTM D6866 / EN 16640 (based on organic carbon); "high bio-based" refers to an implementation with a bio-based carbon content of not less than 97%.

[0041] Main reagents and raw materials:

[0042] Table 1. Main reagent and raw material names, product models and manufacturers:

[0043]

[0044] Main analytical and testing instruments:

[0045] Table 2 mainly analyzes the names, models, and manufacturers of the equipment / instruments:

[0046]

[0047] Main testing standards:

[0048] Particle size and PDI: ISO 22412:2025;

[0049] Heat seal strength: ASTM F88 / F88M-23;

[0050] 180° peel (pressure-sensitive adhesive scenario): ASTM D3330 / D3330M-04(2025) (Method A);

[0051] Holding power / Initial tack: PSTC-107:2022 / PSTC-6:2022;

[0052] Water droplet contact angle: ISO 19403-2:2024;

[0053] Cobb 60 Water absorption: ISO 535:2023;

[0054] Repulping evaluation: CEPI Recyclability Laboratory Test Method, Version 3 (February 2025), 4evergreen Recyclability Evaluation Protocol (February 2025);

[0055] Bio-based carbon: ASTM D6866-24a / EN 16640:2017;

[0056] VOCs: GB 33372-2020 Appendix A;

[0057] Free surfactant mass fraction: The organic matter content in the permeate was determined by ultrafiltration membrane with a molecular weight cutoff of 10 kDa and separated using TOC conversion. The free surfactant mass fraction was calculated with the total amount of surfactant in the system (bound state + free state) as the denominator.

[0058] Melt flow rate (MFR): ISO 1133-1:2022, tested at 190°C and 2.16 kg load.

[0059] Softening point using the ring and ball method: ASTM E28-18(2022);

[0060] Brinell viscosity: ASTM D1084-16(2021);

[0061] Standard version note: If the above standards are updated, the equivalent or newer version shall prevail, provided that the comparability of the results is not affected.

[0062] Food contact compliance: Except for Comparative Example 9, which serves as a negative control, the pH adjustment in the main embodiments of this invention uses food-grade NaHCO3 or equivalent inorganic salts permitted for food contact; for applications involving food contact, migration assessments are conducted in accordance with GB 4806.1, GB31604 series or EN 1186.

[0063] Examples and Comparative Examples:

[0064] Example 1: Basic formulation (PHBV, low acid value).

[0065] Step 1: Vacuum dry the polyhydroxybutyrate valerate (PHBV, PV3000G) granules at 85°C for 8 hours.

[0066] Step 2: In a twin-screw extruder, 0.2 wt% succinic anhydride was added to the dried PHBV and the reaction was carried out at 170℃ and -0.09 MPa for 3 min to activate the end groups. The melt acid value was measured to be 2.1 mg KOH / g.

[0067] Step 3: Emulsify the activated melt in an aqueous phase at 90°C containing 0.8 wt% sodium stearoyl lactylate (SSL), and adjust the pH to 7.6 with a food-grade sodium bicarbonate solution.

[0068] Step 4: At 60°C, add the following to the aqueous dispersion by dry weight: 25 wt% glycerol rosin ester aqueous dispersion, 12 wt% triethyl citrate (TEC), and 3 wt% rice bran wax.

[0069] For details of the specific preparation methods and formulations of Examples 2 to 11 and Comparative Examples 1 to 9, please refer to the following tables.

[0070] Table 3 Summary of Formulations for Examples (by dry weight, wt%)

[0071]

[0072] Table 4. Summary of Comparative Example Formulations (by dry weight, wt%)

[0073]

[0074] Application example:

[0075] Application Example 1: Assessment of basic physical performance and storage stability.

[0076] Experimental Description: This application example aims to comprehensively evaluate the basic physicochemical properties and long-term storage stability of PHA aqueous dispersions prepared in all examples and comparative examples. The test indicators include: solid content (gravimetric method), Z-mean particle size (Dz), polydispersity index (PDI) (by dynamic light scattering), and pH value. All aqueous dispersion samples were sealed and allowed to stand at 25°C for 30 days. Visual observation was conducted, and the presence of unstable phenomena such as stratification, precipitation, or agglomeration was recorded. The purpose of this experiment is to systematically verify the decisive role of the technical solutions proposed in this invention (especially the end-group activation acid value window and the selection of reactive emulsifiers) in obtaining high-quality PHA aqueous dispersions with uniform particle size, suitable pH, and long-term stability, and to directly compare them with comparative examples that do not meet the technical characteristics of this invention.

[0077] Table 5. Results of Basic Physical Properties and Stability Tests:

[0078]

[0079] Analysis: Table 5 shows that all examples (except for Example 6, which is not applicable) can form high-quality aqueous dispersions with the target particle size range (195-280 nm), low PDI (not higher than 0.20), and remain homogeneous and stable after 30 days of storage. In contrast, several comparative examples showed obvious defects: Comparative Example 1 (no activation) and Comparative Example 4 (HLB not compatible) failed to form stable emulsions at all, exhibiting severe aggregation or rapid sedimentation; Comparative Example 3 (insufficient acid value) and Comparative Example 6 (insufficient emulsifier) ​​had large particle sizes, wide distribution, and poor long-term stability; Comparative Example 2 (non-reactive emulsifier) ​​could emulsify, but obvious stratification occurred after 30 days, indicating interfacial instability; Comparative Example 5 (excessively high acid value) may experience quality deterioration due to excessive PHA degradation. This set of data clearly defines the parameter window for the success of this invention: the synergistic effect of an acid value of 2–15 mg KOH / g and a reactive emulsifier with HLB 9–12 is an indispensable prerequisite for obtaining high-quality dispersions.

[0080] Application Example 2: Paper / Paper Heat Seal Strength Test.

[0081] Experimental Description: This application example aims to evaluate one of the core performance characteristics (heat seal strength) of the adhesive prepared according to this invention in practical applications. The experiment simulated a common industrial paper packaging sealing process. Paper samples coated with various adhesives were heat-pressed together under precisely controlled temperature (120°C), time (1 s), and pressure (0.3 MPa). Subsequently, using a universal testing machine, the force required to peel the bonded strip was tested according to ASTM F88 / F88M-23 standards. This test directly verifies whether the adhesive meets the bond strength requirements for high-performance paper packaging applications.

[0082] Table 6. Paper / Paper Heat Seal Strength Test Results (120℃, 1s, 0.3MPa):

[0083]

[0084] Analysis: Table 6 shows that all Examples 1-4 and Examples 7-10 optimized for heat-sealing applications exhibit heat-sealing strengths exceeding 7.0 N / 15 mm at 120°C, meeting the high-performance threshold proposed in this invention. Examples 5 and 11, specifically designed for pressure-sensitive adhesives, have heat-sealing strengths slightly below 7.0 N / 15 mm, consistent with their different formulation design focuses. In contrast, all relevant comparative examples show significant performance deficiencies: Comparative Example 3 (insufficient acid value) and Comparative Example 6 (poor emulsion stability) have bond strengths far below the target values; Comparative Example 2 (non-reactive emulsifier) ​​performs poorly due to its high content of free surfactant, which forms a weak boundary layer at the interface, affecting adhesion; the performance degradation in Comparative Example 5 (excessively high acid value) is attributed to polymer degradation.

[0085] Application Example 3: Performance evaluation of pressure-sensitive adhesive (PSA).

[0086] Experimental Description: This application example aims to evaluate the performance of the technology of this invention in the field of pressure-sensitive adhesives (PSA). The core performance indicators of PSAs include 180° peel strength (adhesion), holding power (creep resistance, cohesion), and initial tack (rapid adhesion). The experiment was conducted according to PSTC and ASTM international standards, testing tape samples coated on standard substrates. By comparing the micro-crosslinked examples with the uncrosslinked examples, this experiment aims to verify the crucial role of the micro-crosslinking process in improving the overall performance of PSAs.

[0087] Table 7 Performance evaluation results of pressure-sensitive adhesive (PSA) (23℃):

[0088]

[0089] Note: Examples 1-4, 6-10 and Comparative Examples 1-6, 8-9 are not applicable to this test because their formulations are not designed for pressure-sensitive applications (e.g., lacking specific tackifying / plasticizing systems or crosslinking components).

[0090] Analysis: Table 7 shows that by introducing micro-crosslinks, Examples 5 and 11 achieved significantly improved room temperature tack (>2000 min) while maintaining high peel strength, demonstrating a good balance between adhesive and cohesive forces, thus meeting the application requirements of pressure-sensitive adhesives. In contrast, Comparative Example 7, with a similar formulation but without crosslinking, exhibited slightly higher peel strength but severely insufficient cohesive forces, resulting in extremely poor tack (150 min) and rendering it unsuitable for use as a qualified pressure-sensitive adhesive. This demonstrates the necessity of micro-crosslinking for constructing the cohesive strength network required for pressure-sensitive adhesives.

[0091] Application Example 4: Re-plasma-Friendly Assessment (CEPI / 4evergreen)

[0092] Experimental Description: This application example aims to evaluate the environmental friendliness of the adhesive of this invention, particularly its compatibility with waste paper recycling systems. The experiment simulated the pulping and screening process of a standard paper mill, quantifying the impact of the adhesive on the recycling process by precisely measuring the area of ​​non-recyclable coarse impurities (coarse residue) and adhesive residue generated after pulping. Two commercially available, non-bio-based adhesives (acrylate and EVA) were also introduced as controls in this experiment.

[0093] Table 8. Results of the re-plasma-friendly assessment:

[0094]

[0095] Analysis: Table 8 clearly demonstrates the resizing-friendly nature of the product of this invention. All tested examples (except for the inapplicable Example 6) achieved a pass rating, with significantly lower adhesive area compared to the non-compliant Comparative Examples 2, 3, 5, and 6, as well as the control groups of commercially available acrylate and EVA adhesives. This is strongly correlated with the low content of free surfactants: Comparative Example 2, containing a large amount of free surfactants, easily promotes particle aggregation in the resizing solution, forming large-sized adhesives, leading to a failed test. This invention, through interface anchoring technology, fundamentally avoids the formation of adhesives.

[0096] Application Example 5: Low VOC Formulation and Detection.

[0097] Experimental Description: This experiment aims to verify that, through specific formulation design and process optimization (such as the enhanced volatilization process in Example 9), the present invention can meet extremely stringent volatile organic compound (VOC) emission standards. The total VOC content of the samples was accurately quantified using highly sensitive gas chromatography-mass spectrometry (GB 33372-2020 Appendix A, GC-MS external standard 5 points, R²≥0.995), providing data support for the application of this invention in high-standard fields such as food packaging and medical and health care.

[0098] Sample List and Applicability Notes: This experiment only evaluates the total VOC levels of the following samples: Examples 7, 9, Comparative Example 8, and a control of commercially available acrylates and EVA (used as an industry baseline). Other examples have not undergone VOC limit optimization and are not included in the conclusions of this experiment.

[0099] Table 9. Test results of low-VOC formulations:

[0100]

[0101] Analysis: Through process enhancement (Example 9), the VOC content can be as low as 39 mg / kg, significantly better than Comparative Example 8 (78 mg / kg) without degassing treatment and the commercially available acrylate and EVA control groups. The direct comparison between Example 9 and Comparative Example 8 clearly demonstrates that the online membrane degassing process is a necessary and sufficient process to achieve ≤50 mg / kg, reducing the VOC content by approximately 50%.

[0102] Application Example 6: Validation of bio-based carbon content (baseline ≥95% + preferred ≥97% dual-channel).

[0103] Experimental Description: This experiment aims to verify the bio-based carbon content levels under different formulation pathways of this invention. The internationally recognized radiocarbon isotope analysis method (ASTM D6866-24a / EN 16640:2017) was used to analyze the carbon content derived from modern biomass in the organic carbon of the samples. 14 The proportion of C) was precisely measured to calculate its bio-based carbon content, thus verifying its fundamental properties as a sustainable material.

[0104] Sample List and Applicability Notes: This experiment aims to verify the bio-based carbon content levels under different formulation pathways of the present invention. Examples 1, 2, 3, and 5 are used to verify the universality of "pure bio-based" (baseline ≥95%); Examples 8 and 10 are used to verify the attainability of "high bio-based" (preferably ≥97%). Commercially available petrochemical-based adhesives are used as a control group. Tests were conducted according to ASTM D6866-24a / EN 16640:2017 (based on organic carbon).

[0105] Table 10 Validation results of bio-based carbon content:

[0106]

[0107] Analysis: Table 10 shows that all tested embodiments of the present invention meet the definition of "pure bio-based" with a bio-based carbon content ≥95%, verifying the universality of the present technical solution. Furthermore, through further optimization of raw materials (such as in Examples 8 and 10), a "high bio-based" level of ≥97% can be stably achieved, meeting the requirements of higher environmental standards. This contrasts sharply with the control group (0%), which is entirely derived from petrochemical raw materials.

[0108] Application Example 7: Holding power at 60°C (PSTC-107:2022).

[0109] Experimental Description: PSTC-107 Procedure A (60℃, 1kg, 25mm); substrate was stainless steel. This application example aims to evaluate the holding power of the pressure-sensitive adhesive formulation of this invention at high temperatures. This is a key indicator for measuring the cohesive strength and creep resistance of pressure-sensitive adhesives, and is crucial for applications such as labels and tapes that may experience temperature changes during transportation or use. The time required for the tape to peel off from a standard stainless steel plate was recorded.

[0110] Sample list and applicability notes: This experiment is only applicable to pressure-sensitive adhesive formulations. The samples included are: Example 5, Example 11, Comparative Example 7, and Comparative Example 9 (Comparative Example 9 shows the effect of a non-recommended pH adjustment path on odor and high-temperature tack).

[0111] Table 11 shows the results of the holding power test at 60℃:

[0112]

[0113] Analysis: Crosslinking and proper pH adjustment are crucial for high-temperature tack. Examples 5 and 11 both exhibited excellent tack strength exceeding 1000 minutes at 60°C, while the uncrosslinked Comparative Example 7 failed within 10 minutes, further demonstrating the absolute necessity of micro-crosslinking for constructing a high-temperature resistant cohesive strength network. Furthermore, Comparative Example 9, which used ammonia to adjust the pH, showed a significant decrease in high-temperature tack performance and emitted an unpleasant odor, indicating its unsuitability for high-requirement applications such as food contact. This, in turn, demonstrates the superiority of the non-volatile pH adjuster (such as sodium bicarbonate) preferred in this invention.

[0114] Application Example 8: Residual acid value of HMA finished product (ASTM D974-22).

[0115] Experimental Description: This application example aims to verify whether a key technical feature of the present invention—the residual acid value derived from end-group activation—is retained after conversion from an aqueous dispersion to an anhydrous hot melt adhesive (HMA) form. The acid value of the HMA product prepared in Example 6 was determined using standard chemical titration. This experiment provides direct quantitative evidence for the structural parameter constraints of the HMA morphology in this invention, demonstrating its clear origin and structural relationship with the aqueous dispersion prepared through the unique process of this invention.

[0116] Sample list and applicability notes: Acid value testing is performed only on hot melt adhesive samples: Example 6 (baseline HMA). This test is not applicable to other aqueous dispersions / PSA.

[0117] Table 12 Residual acid value of HMA finished product:

[0118]

[0119] Analysis: The results show that the acid value of Example 6 is 3.2 mg KOH / g, which falls within the target window of 2–15 mg KOH / g, proving that the end-group activation characteristics can be retained after melt processing.

[0120] Application Example 9: Paper / PLA lamination performance.

[0121] Experimental Description: This application example aims to demonstrate the applicability of the present invention's technical platform in a specific application scenario: paper-plastic composite materials. The experiment uses the PHA aqueous dispersion from Example 3. By testing the T-peel strength of the laminated sample under room temperature (23°C) and heat aging (60°C × 24h) conditions, its adhesion strength and durability to polylactic acid (PLA) films are evaluated.

[0122] Sample list and applicability notes: Only the formulation for lamination scenarios was validated: Example 3. Other samples were not included in this experimental conclusion because surface energy and crosslinking were not optimized for the PLA / paper interface.

[0123] Table 13 Paper / PLA Lamination Performance:

[0124]

[0125] Analysis: The results show that the T-peel strength of the sample at 23℃ is 2.4N / 15mm, and it still remains at 2.1N / 15mm after aging at 60℃ for 24 hours, which meets the requirements of this invention regarding lamination performance.

[0126] Experimental Results and Analysis:

[0127] Through the synergistic effect of end-group activation and reactive emulsification, this invention obtains a controllable and long-term stable PHA dispersion of Dz and PDI without the use of organic solvents; the heat-sealing, peeling and resizing evaluation results are detailed in the corresponding application example tables.

[0128] The decisive role of end-group activation: Comparing the results of Example 1 with Comparative Examples 1, 3, and 5 (Application Example 1), the data show that melt end-group activation and acid value control within the range of 2–15 mg KOH / g are absolute prerequisites for the successful preparation of stable PHA aqueous dispersions. In Comparative Example 1, PHBV without end-group activation (acid value 0.5 mg KOH / g) could not form a stable emulsion. In Comparative Example 3, the acid value was slightly increased to 1.2 mg KOH / g but still below the lower limit, resulting in poor stability. In Comparative Example 5, an excessively high acid value (19.5 mg KOH / g) led to polymer degradation. In contrast, all examples successfully achieved stable emulsification and obtained adhesives with excellent performance by precisely controlling the acid value within the target range.

[0129] The Indispensability of Reactive Emulsifiers and HLB Values: Comparing the results of Example 1 with Comparative Examples 2, 4, and 6 (Application Examples 1 and 2) reveals the crucial role in constructing a permanent interfacial anchoring layer. Comparative Example 2 used the conventional non-reactive emulsifier SDS, resulting in an extremely high free surfactant content (78.5%), ultimately leading to severe stratification. Comparative Example 4 used an emulsifier with an HLB value (16.7) exceeding the 9–12 range of this invention, resulting in emulsification failure. In Comparative Example 6, the amount of emulsifier was insufficient, also failing to obtain a stable dispersion. In contrast, all examples used reactive emulsifiers within the specified HLB value range, forming a robust interfacial anchoring layer and controlling the free surfactant content at a low level (<30 wt%), thereby simultaneously imparting excellent long-term storage stability and stronger adhesion properties to the product.

[0130] Causal Relationship Between Basic Properties and Application Performance: The superiority of this invention lies in the clear logical chain from basic properties to final application performance. Application Example 2 demonstrates that the low free surfactant content directly leads to higher heat-sealing strength in Application Example 3 (avoiding a weak boundary layer) and excellent resizing performance in Application Example 5 (avoiding adhesive agglomeration). Similarly, Application Examples 4 and 7 demonstrate the necessity of micro-crosslinking for building cohesive strength, enabling the PSA formulation of this invention to simultaneously meet the requirements of high peel strength and high holding power.

[0131] Synergistic Effects and Wide Applicability of the Formulation Platform: The embodiments fully demonstrate the powerful potential of the present invention as a universal platform. By adjusting the types and amounts of PHA substrate, tackifying resin, and plasticizer in the downstream formulation stage, and by introducing specific functional additives, the basic dispersion can be easily customized into heat-sealing adhesives (Examples 1-4), laminating adhesives (Application Example 9), hot melt adhesives (Example 6), and pressure-sensitive adhesives (Examples 5 and 11) suitable for different high-end application scenarios. These products all exhibit excellent performance indicators and can meet special requirements such as ultra-low VOC (Example 9) and high bio-based carbon (Examples 8 and 10), proving that the technical solution of the present invention not only solves the stability problem of the basic dispersion, but also provides a high-performance bio-based adhesive solution with wide industrial applicability.

[0132] In summary, this invention solves the problem of balancing performance and stability in existing PHA waterborne adhesives by synergistically regulating the end-group chemistry and emulsification interface behavior of PHA. It prepares a high-performance, high-stability pure bio-based adhesive, providing a new technical approach for the application of bio-based materials in the field of high-end adhesives.

[0133] Those skilled in the art should understand that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the technical solutions of the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A pure bio-based polyhydroxyalkanoate adhesive, characterized in that, The pure bio-based polyhydroxy fatty acid ester adhesive is an aqueous dispersion or its concentrate, comprising, on a dry weight basis, 35–85 wt% polyhydroxy fatty acid ester, 0.1–3.0 wt% reactive emulsifier, 10–45 wt% tackifying resin, 2–15 wt% plasticizer and 0–10 wt% plant wax, and also contains water and additives. The polyhydroxy fatty acid ester is selected from one or more of polyhydroxybutyrate, polyhydroxybutyrate hexanoate, polyhydroxybutyrate-4-hydroxybutyrate copolyester, and polyhydroxybutyrate valerate. The reactive emulsifier in the pure bio-based polyhydroxy fatty acid ester adhesive undergoes esterification, transesterification, or ion pair bonding with the end groups of the polyhydroxy fatty acid ester during the emulsification process to form an interfacial anchoring layer with a hydrophilic-lipophilic balance value of 9–12. The dispersion has a Z-average particle size of 0.12–0.30 μm, a polydispersity index of not more than 0.20, a pH value of 6.5–8.5, a free surfactant mass fraction of not more than 30 wt%, volatile organic compounds of not more than 100 mg / kg, and bio-based carbon of not less than 95%, and no organic fluorine compounds have been artificially added. The residual acid value of the polyhydroxy fatty acid ester in the pure bio-based polyhydroxy fatty acid ester adhesive is 2–15 mg KOH / g. The pure bio-based polyhydroxy fatty acid ester adhesive is prepared by a method comprising the following steps: Step 1. Dry the polyhydroxyalkanoate granules in a drying oven at 80–90°C under an inert gas atmosphere for 6–12 hours until the residual moisture content is no higher than 0.05 wt%, and obtain the dried granules. Step 2. In a twin-screw extruder, the dried granules from Step 1 are mixed with 0.2–2.0 wt% bio-based cyclic anhydride and reacted at 165–178 °C and −0.08 to −0.095 MPa for 2–4 minutes to obtain an activated melt with an acid value of 2–15 mg KOH / g. Step 3. Pump the activated melt obtained in Step 2 into an aqueous phase at 80–95°C containing a reactive emulsifier with a hydrophilic-lipophilic balance of 9–12 and a pH adjuster, and perform high shearing at a specific power of 0.25–0.45 kW / kg for 3–10 minutes. The pH adjuster is food-grade NaHCO3. This yields a polyhydroxyalkanoate aqueous dispersion with a Z-average particle size of 0.12–0.30 μm, a polydispersity index not higher than 0.20, and a free surfactant content not higher than 30 wt%. Step 4. Add tackifying resin, plasticizer and plant wax to the polyhydroxy fatty acid ester aqueous dispersion obtained in Step 3 at 50–70℃, and obtain the finished product after degassing and 5–10 μm filtration; When the adhesive is applied to pressure-sensitive adhesives, the pure bio-based polyhydroxy fatty acid ester adhesive also contains 5–30 wt% of medium-chain long-chain polyhydroxy fatty acid esters and 0.1–0.8 wt% of organic peroxides for micro-crosslinking, and its holding time under the conditions of 60°C, 1 kg load, and 25 mm width is not less than 1000 minutes.

2. The pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, The pure bio-based polyhydroxy fatty acid ester adhesive contains polyhydroxybutyrate valerate and / or polyhydroxybutyrate hexanoate, wherein the molar fraction of 3-hydroxyvalerate monomer is 9–25 mol%, the molar fraction of 3-hydroxyhexanoate monomer is 5–12 mol%, and its melt flow rate at 190°C and 2.16 kg load is 3–20 g / 10 min.

3. The pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, The reactive emulsifier is selected from one or more of the following: stearoyl lactate, lactate salt, alkyl succinate, rosin salt, maleic rosin salt, polymeric rosin salt, dehydrorosin salt, stearoyl citrate, and fatty acid-amino alcohol salt.

4. The pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, The tackifying resin in the pure bio-based polyhydroxyalkanoate adhesive is a bio-based resin, and the tackifying resin is selected from: 1) Rosin and its modified products: rosin, oil rosin, wood rosin and their hydrogenated, polymerized, disproportionated, maleated or fumarated derivatives; and their glycerides and pentaerythritol esters; 2) Terpene resin: a terpene polymer obtained by cationic polymerization of one or more of α-pinene, β-pinene, limonene, and dipentene; 3) Terpene phenol resin: obtained by condensation of the above terpenes with phenol, m-cresol or m-alkylphenol; 4) Tannin-based resin or cashew phenol-modified resin; and one or more of its aqueous dispersions; The tackifying resin has a ring and ball softening point of 60–120°C and an acid value of 5–25 mg KOH / g.

5. The pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, The plasticizer in the pure bio-based polyhydroxy fatty acid ester adhesive is of bio-based origin, and the plasticizer is selected from one or more of the following: citrate esters, sucrose isobutyrate acetate, polyol esters, vegetable oil epoxides, and castor oil-derived diesters; The citrate esters mentioned therein are selected from one or more of triethyl citrate, acetylated triethyl citrate, tributyl citrate, acetylated tributyl citrate, triisobutyl citrate, and tri(2-ethylhexyl) citrate; The polyol esters are selected from one or more of glycerol triacetate and polyglycerol fatty acid esters; The vegetable oil epoxide is selected from one or more of epoxidized soybean oil and epoxidized flaxseed oil; The castor oil-derived diester ester is selected from one or more of dioctyl sebacate and dioctyl azelate.

6. The pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, After standing at 25°C for 30 days, the pure bio-based polyhydroxy fatty acid ester adhesive exhibits a volume stratification rate of no more than 1%, a Z-average particle size drift rate of no more than 10%, a polydispersity index drift of no more than 0.05, and a free surfactant mass fraction drift of no more than 5 wt%.

7. The pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, The mass fraction of free surfactant in the pure bio-based polyhydroxyalkanoate adhesive is less than 20 wt%.

8. The pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, The volatile organic compound content of the pure bio-based polyhydroxyalkanoate adhesive is not higher than 50 mg / kg.

9. The pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, The pH value of the pure bio-based polyhydroxy fatty acid ester adhesive is 7.0–8.

0.

10. The pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, The acid value of the melt after the reaction in step 2 of the preparation method is 3–10 mg KOH / g, and the bio-based cyclic anhydride is succinic anhydride or maleic anhydride.

11. The pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, In step 3 of the preparation method, the volume ratio of polymer melt to water is 35:65 to 45:55, and the emulsification equipment adopts an online gear pump, a static mixer, and a two-stage series rotor-stator high shear system.

12. The pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, The energy input specific power in step 3 of the preparation method is 0.25–0.45 kW / kg, and the high-shear emulsification time is 4–8 minutes.

13. The pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, The activation temperature of the organic peroxide used in the pure bio-based polyhydroxy fatty acid ester adhesive is 90–120°C, and the residual amount of the peroxide in the final product is not higher than 50 ppm.

14. An application of the pure bio-based polyhydroxyalkanoate adhesive according to claim 1, characterized in that, The applications are for heat sealing of paper or paperboard, bonding of paper to paper, bonding of paper to wood, lamination of paper to biodegradable films, and coating of labels or tapes; wherein, under conditions of 120°C, 1 second, and 0.3 MPa, the heat seal strength of paper to paper is not less than 7.0 N / 15 mm; under conditions of 23°C and 50% relative humidity, the 180° peel strength measured according to the American Society for Testing and Materials (ASTM) standard D3330 / D3330M-04(2025) is not less than 7.5 N / 25 mm, and the repulping performance is evaluated according to the CEPI and 4evergreen recyclability assessment scheme.

15. The application according to claim 14, characterized in that, The heat sealing process window temperature in the application is 90–130°C, and the fiber tear rate after paper-to-paper bonding is not less than 80%.

16. The application according to claim 14, characterized in that, When the application is used for laminating paper and polylactic acid film, the T-peel strength at 23°C is not less than 2.0 N / 15 mm, and after being kept at 60°C for 24 hours, the T-peel strength is not less than 1.8 N / 15 mm.

17. A pure bio-based polyhydroxyalkanoate melt adhesive, characterized in that, The pure bio-based polyhydroxyalkanoate melt adhesive is obtained by dehydration of the pure bio-based polyhydroxyalkanoate adhesive aqueous dispersion according to any one of claims 1 to 13, comprising 40–70 wt% polyhydroxyalkanoate, 20–45 wt% tackifying resin, 5–15 wt% plasticizer and 0–10 wt% plant wax, having a Brookfield viscosity of 1500–8000 mPa·s at 170°C, a residual acid value of 2–15 mg KOH / g for the polyhydroxyalkanoate, and a free surfactant mass fraction not exceeding 30 wt%.

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