Method for manufacturing a stable PHA dispersion

Abstract

The present invention relates to a method for manufacturing a stable polyhydroxyalkanoate (PHA) dispersion, said method comprising: a) providing an aqueous dispersant comprising a water-soluble dispersing agent in water, b) adding PHA particles in solid powder form to the aqueous dispersant and mixing the PHA particles with the aqueous dispersant to obtain a PHA dispersion, and c) adding a gel-forming polymeric stabilizer to the PHA dispersion to obtain a stable PHA dispersion. The present invention further relates to a stable polyhydroxyalkanoate (PHA) dispersion in water, wherein the stable PHA dispersion is stable for at least 2 weeks at 25 °C.

Description

[0001] METHOD FOR MANUFACTURING A STABLE PHA DISPERSION

[0002] Technical field

[0003] The present disclosure relates to methods for manufacturing stable polyhydroxyalkanoate (PHA) dispersions useful for coating of fiber-based substrates, such as paper and paperboard.

[0004] Background

[0005] Coating of fiber-based substrates, such as paper and paperboard, with plastics is often used to combine the mechanical properties of the fiber-based substrate with the barrier and sealing properties of a plastic film. Paper or paperboard provided with even a relatively small amount of a suitable plastic material can provide the properties needed to make the paper or paperboard suitable for many demanding applications, for example as liquid or food packaging board.

[0006] In addition to a liquid barrier on the inside of the package, fiber-based packaging products such as cups or trays that are intended especially for packaging cold products must typically also be provided with a condensation layer on the outside of the package. This condensation layer prevents condensate from softening the bulky fiber-based substrate. The packaging product is further typically provided with at least one heat sealable liquid barrier on the inside.

[0007] In liquid or food packaging board, extrusion coated polyolefin coatings are frequently used as liquid barrier layers, heat sealing layers and adhesives. However, the recycling of such polymer coated board is difficult since it is difficult to separate the polymers from the fibers.

[0008] In the prior art, attempts have been made to replace extrusion coated polyolefin coatings with more environmentally friendly and / or easier to recycle solutions, but so far with no real success. In many cases some, but not all, of the properties of the extrusion coated polyolefin coatings are achieved by the alternative solutions. Dispersion barrier coatings for paper and paperboard is an interesting alternative to extrusion coating for improving repulpability and recyclability of barrier coated fiber-based substrates. Dispersion coating is especially useful as it can be implemented on-line in paper or paperboard machines. Many dispersions or emulsions such as styrene / acrylate or styrene / butadiene emulsions are, however, not biodegradable or compostable.

[0009] Dispersion coating barriers based on water insoluble polyhydroxyalkanoates (PHA), on the other hand, are both compostable and biodegradable. The challenge with PHA dispersions is to find a suitable coating composition, which enables good coater runnability, good coating coverage (hold-out), and good barrier performance. PHA particles are difficult to disperse stably in water and cluster or agglomerate formation of water insoluble components in the dispersions may cause problems in the coating process, and lead to streaks, patchiness and pinholes on the coated surfaces.

[0010] PHA dispersions are usually stabilized with surfactants and / or surface- active polymers, which may cause uneven barrier quality due to migration of dispersants, formation of air bubbles, or coating defects due to higher foaming tendency. The foaming tendency may further create problems when recycling and repulping or disintegrating the coated web.

[0011] Thus, there remains a need for improved solutions to replace conventional plastic coatings, especially polyolefin coatings, in paper and paperboard-based packaging materials, while maintaining acceptable liquid barrier properties. At the same time, there is a need for liquid barrier layers for fiber-based substrates, such as paper or paperboard substrates that facilitate repulping and recycling of the used packaging materials as compared to packaging laminates using conventional plastic films. of the invention

[0012] It is an object of the present disclosure to provide a compostable or biodegradable alternative to the plastic films commonly used as barrier layers for providing liquid barrier properties in paper or paperboard-based packaging materials, such as liquid or food packaging board.

[0013] It is a further object of the present disclosure to provide improved methods for manufacturing stable polyhydroxyalkanoate (PHA) dispersions, which overcome or ameliorate at least some of the problems associated with prior art methods.

[0014] The above-mentioned objects, as well as other objects as will be realized by the skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure.

[0015] Polymer dispersions are usually prepared by mixing dried powder with water or different solvents, and then adding different dispersing agents, stabilizers and additives when the polymer is already in the aqueous media. The present disclosure is based on the understanding that the problems associated with manufacturing stable polyhydroxyalkanoate (PHA) dispersions can be reduced by combining the components in a specific order.

[0016] According to a first aspect illustrated herein, there is provided a method for manufacturing a stable polyhydroxyalkanoate (PHA) dispersion, said method comprising: a) providing an aqueous dispersant comprising a water-soluble dispersing agent in water, b) adding PHA particles in solid powder form to the aqueous dispersant and mixing the PHA particles with the aqueous dispersant to obtain a PHA dispersion, and c) adding a gel-forming polymeric stabilizer to the PHA dispersion to obtain a stable PHA dispersion.

[0017] The inventive method comprises providing an aqueous dispersant comprising a water-soluble dispersing agent in water. Dispersing agents are compounds which are used for improving the colloidal stability of a dispersion and reducing viscosity. A dispersing agent helps to prevent the settling or agglomeration of particles in liquid dispersion by promoting their uniform distribution throughout the liquid medium. Dispersing agents typically act by reducing the attractive forces between particles, such as van der Waals forces or electrostatic forces, that may cause the particles to agglomerate or settle. By doing so, dispersing agents improve the flow properties, stability, and overall performance of the dispersed system. The dispersing agent may further act as a wetting agent and facilitate wetting of the solid powder form PHA particles when they are added to the aqueous dispersant. The term water-soluble as used herein with reference to the dispersing agent generally means that the dispersing agent is at least partially soluble, and preferably fully soluble, in the aqueous dispersant. The aqueous dispersant is an aqueous solution comprising a water-soluble dispersing agent at least partially dissolved in water.

[0018] The inventive method further comprises adding PHA particles in solid powder form to the aqueous dispersant and mixing the PHA particles with the aqueous dispersant to obtain a PHA dispersion. The PHA particles are preferably the main component of the dispersion coating composition based on dry weight of the composition.

[0019] The PHA particles are preferably added slowly to the aqueous dispersant under vigorous mixing. The PHA particles are mixed or homogenized with the aqueous dispersant to obtain a PHA dispersion. The mixing or homogenization may be done using a suitable mixer or homogenizer, for example a propeller mixer, a high shear mixer, or a homogenizer, preferably a rotor-stator homogenizer, such as an Ultra Turrax® homogenizer. The mixing or homogenization may for example comprise mixing at a speed of 4000-12000 rpm, preferably 8000-12000 rpm, for 10-20 min. The mixing or homogenization is preferably performed at room temperature.

[0020] The obtained PHA dispersion is preferably a homogeneous dispersion. The term homogenous dispersion means that the PHA particles are uniformly distributed, or at least substantially uniformly distributed, in the aqueous dispersant. This means that the PHA particles are evenly mixed with the dispersing agent in the aqueous dispersant, resulting in a single-phase system.

[0021] The inventive method further comprises adding a gel-forming polymeric stabilizer to the PHA dispersion to obtain a stable PHA dispersion. The gel-forming polymeric stabilizer stabilizes the dispersion and helps to prevent settling or agglomeration of the dispersed PHA particles. The PHA dispersion is preferably mixed with the gel-forming polymeric stabilizer such that the polymeric stabilizer is uniformly distributed throughout the PHA dispersion. The polymeric stabilizer comprises a polymer capable of forming a gel or a gel-like structure in the dispersion. The gel-forming polymeric stabilizer may further adjust the viscosity and water retention of the PHA dispersion such that it is suitable for further use.

[0022] The term "stable PHA dispersion" as used herein refers to a dispersion in which the PHA particles and other components are evenly and uniformly distributed, and the dispersion remains resistant to settling or agglomeration over an extended period of time. A stable PHA dispersion is characterized by its ability to maintain a consistent and homogeneous distribution of the dispersed PHA particles and other components, even when subjected to various environmental conditions or physical stresses. In the present disclosure, the term stable PHA dispersion typically means that the PHA dispersion is stable for at least 2 weeks, preferably at least 4 weeks, and more preferably at least 8 weeks, at 25 °C.

[0023] In some embodiments, inorganic filler particles are added to the PHA dispersion. The inorganic filler particles may be added during mixing of the PHA particles with the aqueous dispersant to obtain a PHA dispersion or to the obtained PHA dispersion in step b). The inorganic filler particles are preferably added to the obtained PHA dispersion in b). In other words, the inorganic filler particles are preferably added to the PHA dispersion before the gel-forming polymeric stabilizer is added.

[0024] One or more further additives may also be added to the PHA dispersion. The further additives may for example be selected from the group consisting of antifoaming agents, antioxidants, antibacterial agents, preservatives, pH adjusting agents, crosslinkers and biocides. The further additives may be added during mixing of the PHA particles with the aqueous dispersant to obtain a PHA dispersion or to the obtained PHA dispersion in step b), or to the obtained stable PHA dispersion in step c).

[0025] The term “PHA dispersion” herein refers to the dispersion, with optional inorganic filler particles and / or further additives, obtained in step b).

[0026] The term “stable PHA dispersion” herein refers to the stable dispersion, with optional inorganic filler particles and / or further additives, obtained in step c).

[0027] In some embodiments, the total solid content of the stable PHA dispersion is in the range of 20-70 wt%, preferably in the range of 30-60 wt%, and more preferably in the range of 40-50 wt%. The total solid content of a dispersion refers to the total amount of solid material present in a dispersion, expressed as a percentage of the total weight of the dispersion.

[0028] In some embodiments, the stable PHA dispersion has a viscosity in the range of 50-4000 mPas, preferably in the range of 250-3500 mPas, determined according to SCAN-P50:84 using a Brookfield viscosimeter with an LV-4 spindle at a rotational speed of 100 rpm.

[0029] In some embodiments, the stable PHA dispersion has a AAGWR water retention value (Abo Akademi Water retention value) of less than 250 g / m2, preferably less than 200 g / m2, and more preferably in the range of 50-150 g / m2, determined according to TAPPI T701pm-0.

[0030] The water-soluble dispersing agent is preferably present in the aqueous dispersant provided in a) in an amount such that the obtained stable PHA dispersion comprises 1-30 wt%, preferably 2-15 wt%, of the water-soluble dispersing agent based on the total solid content of the stable PHA dispersion. Thus, in some embodiments, the stable PHA dispersion comprises 1-30 wt%, preferably 2-15 wt%, of the water-soluble dispersing agent based on the total solid content of the stable PHA dispersion. A suitable amount of a specific dispersing agent may be readily selected by the skilled person depending on the type of dispersing agent. For example, a polymeric dispersing agent may typically be used in a lower amount than a non-polymeric dispersing agent.

[0031] In some embodiments, the dispersing agent is selected from the group consisting of water-soluble polymers, starch, low molecular weight polyols, urea, and combinations thereof.

[0032] In some embodiments, the dispersing agent is a water-soluble polymer, preferably selected from the group consisting of water-soluble polysaccharides and polyethylene glycol.

[0033] In some embodiments, the dispersing agent is starch.

[0034] In some embodiments, the dispersing agent is a low molecular weight polyol.

[0035] In some embodiments, the low molecular weight polyol dispersant has a molecular weight in the range of 50-2000 g / mol, preferably in the range of 50-1500 g / mol, and more preferably in the range of 50-1000 g / mol or in the range of 50-500 g / mol.

[0036] In some embodiments, the low molecular weight polyol dispersant is selected from the group consisting of low molecular weight polysaccharides and sugar alcohols, and combinations thereof.

[0037] In some embodiments, the low molecular weight polyol dispersant is selected from the group consisting of low molecular weight polysaccharides having a degree of polymerization (DP) in the range of 2-100, preferably in the range of 2-50. In some embodiments, the low molecular weight polyol dispersant is selected from the group consisting of low molecular weight polysaccharides having a degree of polymerization (DP) in the range of 2-12. The low molecular weight polysaccharides may be charged, uncharged, amphoteric, or combination thereof. The low molecular weight polysaccharides may be linear or branched. In some embodiments, the dispersing agent is a low molecular weight polyol, selected from the group consisting of sorbitol, maltitol, xylitol, mannitol, and glycerol. In some embodiments, the low molecular weight polyol dispersant is sorbitol.

[0038] In some embodiments, the dispersing agent is urea.

[0039] The dispersing agent is preferably biodegradable and compostable. The dispersing agent is preferably biodegradable according to ISO 14855-2:2018, ASTM D5511-18, or ASTM D5988-18. The dispersing agent is preferably compostable according to ASTM D5338-15.

[0040] PHA particles are added in solid powder form to the aqueous dispersant and mixed with the aqueous dispersant to obtain a PHA dispersion.

[0041] The PHA particles are preferably the main component of the dispersion coating composition based on dry weight of the composition. The PHA particles are preferably added to the aqueous dispersant in an amount such that the obtained stable PHA dispersion comprises 70-98.9 wt%, preferably 90-98.9 wt%, of the PHA particles based on the total solid content of the stable PHA dispersion. Thus, in some embodiments, the stable PHA dispersion comprises 70-98.9 wt%, preferably 90-98.9 wt%, of the PHA particles based on the total solid content of the stable PHA dispersion.

[0042] The PHA particles are preferably added in dry, or substantially dry, solid powder form. The PHA particles preferably have a moisture content of less than 5 wt%, preferably less than 2 wt%, and more preferably less than 0.5 wt% before being added to the aqueous dispersant.

[0043] The particle size distribution of the PHA particles can be multimodal or unimodal. In some embodiments, the PHA particles have a unimodal or bimodal particle size distribution. In some embodiments, the PHA particles have a unimodal particle size distribution. The inventive method has been found useful for manufacturing stable dispersions of larger PHA particles having median particle sizes (D50) up to below 100 pm as well as smaller PHA particles having median particle sizes (D50) below 20 pm. In some embodiments, the PHA particles have a median particle size (D50) below 100 pm, preferably below 50 pm.

[0044] To avoid clustering of PHA particles having a median particle size (D50) below 20 pm are preferred. In some embodiments, the PHA particles have a median particle size (D50) below 20 pm, preferably below 15 pm, and more preferably in the range of 0.5-10 pm or in the range of 0.5-5 pm.

[0045] In some embodiments, the dispersion coating composition is free from, or substantially free from particles or particle agglomerates having a particle size above 50 pm, above 20 pm, or above 15 pm.

[0046] Unless stated otherwise, all particle sizes and particle size distributions herein are determined by a laser diffraction method using a Mastersizer 3000 according to ISO 13320:2009.

[0047] In some embodiments, the PHA particles comprise PHA in an amount of 70-99.9 wt%, preferably in an amount of 90-99.9 wt%, based on the dry weight of the PHA particles.

[0048] In some embodiments, the PHA is selected from the group consisting of poly(3- hydroxyoctanoate) (PHO), poly(3-hydroxydecanoate) (PHD), poly(3- hydroxy hexanoate) (PHH), and poly(3-hydroxyvalerate) (PHV), poly(3- hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3- hydroxy hexanoate) (PHBH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxyoctanoate-co-3-hydroxyhexanoate) (PHOHH), poly(3- hydroxyoctanoate-co-3-hydroxydecanoate) (PHOHD), and poly(3- hydroxyoctanoate-co-3-hydroxydodecanoate) (PHDHDD), or a combination thereof. The skilled person understands that the PHA suitable for use in the dispersion coating composition is not limited to those listed here. In some embodiments, the PHA is a PHA co-polymer.

[0049] In some embodiments, the PHA is selected from the group consisting of poly(3- hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3- hydroxy hexanoate) (PHBH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxyoctanoate-co-3-hydroxyhexanoate) (PHOHH), poly(3- hydroxyoctanoate-co-3-hydroxydecanoate) (PHOHD), and poly(3- hydroxyoctanoate-co-3-hydroxydodecanoate) (PHDHDD), or a combination thereof. The skilled person understands that the PHA co-polymers suitable for use in the dispersion coating composition are not limited to those listed here.

[0050] In some embodiments, the PHA is a medium chain length PHA, preferably a PHA having 6-14 carbon atoms per monomer unit.

[0051] In some embodiments, the PHA particles comprise a blend of PHA and one or more additional polymers, preferably selected from the group consisting of polylactic acid (PLA), polybutylene succinate (PBS), polybutylene succinate-co- adipate (PBSA), polyethylene (PE), and polyethylene terephthalate (PET). In some embodiments, the PHA particles comprise a blend of PHA and one or more additional biodegradable polymers. In some embodiments, the PHA particles comprise a blend of PHA and one or more additional polymers selected from the group consisting of polylactic acid (PLA), polybutylene succinate (PBS), and polybutylene succinate-co-adipate (PBSA).

[0052] In some embodiments, the PHA has a melting point in the range of 100-170 °C preferably in the range of 120-160 °C.

[0053] The PHA may further be characterized by its melting point. In some embodiments, the PHA has a melting point in the range of 100-170 °C preferably in the range of 120-160 °C. Unless stated otherwise, the melting points mentioned herein are determined by differential scanning calorimetry according to standard ASTM D3418. The PHA particles are preferably biodegradable according to ISO 14855-2:2018, ASTM D5511-18, or ASTM D5988-18. The PHA particles are preferably compostable according to ASTM D5338-15.

[0054] The inventive method further comprises adding a gel-forming polymeric stabilizer to the PHA dispersion to obtain a stable PHA dispersion. The gel-forming polymeric stabilizer stabilizes the dispersion and prevents settling or agglomeration of the dispersed PHA particles. The term “gel-forming polymeric stabilizer” as used herein refers to a polymer, or a combination of polymers, capable of forming a gel or a gel-like structure in the PHA dispersion. This gelforming process can occur through various mechanisms, such as physical interactions, chemical reactions, or a combination thereof.

[0055] The gel-forming polymeric stabilizer is preferably added to the PHA dispersion in an amount such that the obtained stable PHA dispersion comprises 0.1-10 wt%, preferably 0.1-5 wt%, and more preferably 0.1-2 wt%, of the gel-forming polymeric stabilizer based on the total solid content of the stable PHA dispersion. Thus, in some embodiments, the stable PHA dispersion comprises 0.1-10 wt%, preferably 0.1-5 wt%, and more preferably 0.1-2 wt%, of the gel-forming polymeric stabilizer based on the total solid content of the stable PHA dispersion.

[0056] In some embodiments, the gel-forming polymeric stabilizer comprises a polymer selected from the group consisting of polysaccharides, polysaccharide derivatives, polypeptides, and polypeptide derivatives, or a combination thereof, capable of forming a gel or a gel-like structure.

[0057] In some embodiments, the gel-forming polymeric stabilizer comprises a polysaccharide or polysaccharide derivative capable of forming a gel or a gel-like structure. This gel-forming process can occur through various mechanisms, such as physical interactions, chemical reactions, or a combination thereof.

[0058] In some embodiments, the gel-forming polymeric stabilizer comprises cellulose, methyl cellulose, carboxymethyl cellulose, hydroxypropylmethyl cellulose, microfibri Hated cellulose (MFC), cellulose nanocrystals (CNC), cellulose nanofibers (CNF), starch, modified starch, xanthan gum, guar gum, alginate, pectin carrageenan, gellan, agar, cassava flour, or gelatin.

[0059] In some embodiments, the gel-forming polymeric stabilizer comprises a polysaccharide gum, preferably a gum selected from xanthan gum, guar gum, alginate, pectin carrageenan, gellan, and agar, or a combination thereof.

[0060] The gel-forming polymeric stabilizer is preferably biodegradable and compostable. The gel-forming polymeric stabilizer is preferably biodegradable according to ISO 14855-2:2018, ASTM D5511-18, or ASTM D5988-18. The gel-forming polymeric stabilizer is preferably compostable according to ASTM D5338-15.

[0061] In some embodiments, the method further comprises adding inorganic filler particles to the obtained PHA dispersion in b).

[0062] In some embodiments, the stable PHA dispersion comprises 1-30 wt%, preferably 3-15 wt%, of the inorganic filler particles based on the total solid content of the stable PHA dispersion. Too much inorganic filler particles can lead to cracking and deterioration of barrier properties when the stable PHA dispersion is used as a coating composition.

[0063] In some embodiments, the inorganic filler particles are selected from the group consisting of clay, talc, CaCOs, TiC>2, AI2O3, SiC>2, kaolin, bentonite, and phyllosilicates, or a combination thereof. The inorganic filler particles are preferably high aspect ratio filler particles, e.g. flaky particles having median particle size (D90) below 2 pm.

[0064] The stable PHA dispersion obtained by the method is a dispersion in which the PHA particles and other components are evenly and uniformly distributed, and the dispersion remains resistant to settling or agglomeration over an extended period of time. In some embodiments, the PHA dispersion is stable for at least 2 weeks at 25 °C. In some embodiments, the stable PHA dispersion is stable for at least 4 weeks at 25 °C. In some embodiments, the stable PHA dispersion is stable for at least 8 weeks at 25 °C. The term “stable” or “stability” as used herein with reference to the dispersions generally refers to the resistance of the dispersion to settling or agglomeration over an extended period of time. In some embodiments, the stable PHA dispersion is resistant to settling or agglomeration for at least 2 weeks at 25 °C based on visual inspection. In some embodiments, the stable PHA dispersion is resistant to settling or agglomeration for at least 4 weeks at 25 °C based on visual inspection. In some embodiments, the stable PHA dispersion is resistant to settling or agglomeration for at least 8 weeks at 25 °C based on visual inspection.

[0065] Settling or agglomeration can be monitored by a range of analytical methods.

[0066] Visual Inspection:

[0067] The dispersion is observed over time and look for signs of settling or agglomeration. Examples include, but are not limited to turbidity measurement, zeta potential measurement, dynamic light scattering, and rheological measurements.

[0068] Dynamic Light Scattering (DLS):

[0069] DLS measures the Brownian motion of particles in a dispersion. It provides information about the particle size distribution and can be used to monitor changes over time. Settling or agglomeration of particles may lead to changes in the DLS profile.

[0070] Rheological Measurements:

[0071] Rheology studies the flow and deformation of materials. Changes in the rheological properties of a dispersion may indicate instability. For example, an increase in viscosity may suggest particle agglomeration.

[0072] According to a second aspect illustrated herein, there is provided a stable polyhydroxyalkanoate (PHA) dispersion in water comprising:

[0073] 1-30 wt% water-soluble dispersing agent, 70-98.9 wt% PHA particles having a median particle size (D50) below 20 pm, and

[0074] 0.1-10 wt% gel-forming polymeric stabilizer, based on the total solid content of the stable PHA dispersion, wherein the total solid content of the stable PHA dispersion is in the range of 20- 70 wt%, and wherein the stable PHA dispersion is stable for at least 2 weeks at 25 °C.

[0075] The stable PHA dispersion of the second aspect may be obtained by the method described herein with reference to the first aspect.

[0076] The stable PHA dispersion of the second aspect may be further defined or characterized by any of the features described herein with reference to the first aspect.

[0077] Generally, while the products and processes are described in terms of “comprising” various components or steps, the products and processes can also “consist essentially of” or “consist of” the various components and steps.

[0078] While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes can be made, and equivalents may be substituted for elements thereof, without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention is not limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Specific embodiments invention will now be described more in detail with reference to the following non-limiting examples. added to PHA particles in water

[0079] In Examples prepared according to Preparatory method 1 PHA particles were slowly added to water under mixing over a period of 2 minutes. A dispersing agent was added to the PHA / water mixture and the mixture was then subjected to high intensity mixing at room temperature at a mixing speed of 8000-12000 rpm for 10 min using a T18 digital Ultra-Turrax® homogenizer (I KA, Germany) to obtain a homogenous dispersion of the PHA particles in the aqueous dispersant.

[0080] Preparatory method 2 - PHA particles added to dispersing agent in water

[0081] In Examples prepared according to Preparatory method 2 an aqueous dispersant was first prepared by dissolving the dispersing agent in water. PHA particles were then slowly added to the dispersant solution under mixing over a period of 2 minutes. The PHA / dispersant mixture was then subjected to high intensity mixing at room temperature at a mixing speed of 8000-12000 rpm for 10 min using a T18 digital Ultra-Turrax® homogenizer (I KA, Germany) to obtain a homogenous dispersion of the PHA particles in the aqueous dispersant.

[0082] Where filler particles were used the filler particles were added to the homogenous dispersion and the high intensity mixing was continued for 10 minutes to obtain a homogenous dispersion of the PHA and filler particles in the aqueous dispersant.

[0083] Where a gel-forming polymeric stabilizer was used, the polymeric stabilizer was then added to the homogenous dispersion, optionally including filler particles, and the dispersion was subjected to further mixing to homogenously distribute the polymeric stabilizer in the dispersion. Example 1-5 (Reference) - Dispersing agent added to PHA particles in water Examples 1-5 were carried out according to Preparatory method 1 with parameters as set out in Table 1. Various dispersing agents were used.

[0084] PHA particle type 1 was poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) particles having a unimodal particle distribution with a particle size below about 6 pm.

[0085] PHA particle type 2 was poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) particles having a bimodal particle distribution with particle sizes below about 10 pm as well as up to about 100 pm.

[0086] None of Examples 1-5 resulted in a stable dispersion. The obtained dispersions began to phase separate immediately and complete phase separation occurred overnight at 25 °C as observed by visual inspection.

[0087] Example 6-14 (Invention) - PHA particles added to dispersing agent in water followed by addition of a gel-forming polymeric stabilizer

[0088] Examples 6-14 were carried out according to Preparatory method 2 with parameters as set out in Table 1. Various dispersing agents were used. In some Examples a filler was added.

[0089] PHA particle type 1 was poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) particles having a unimodal particle distribution with a particle size below about 6 pm.

[0090] PHA particle type 2 was poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) particles having a bimodal particle distribution with particle sizes below about 10 pm as well as up to about 100 pm.

[0091] The gel-forming polymeric stabilizer used was xanthan gum.

[0092] The filler, where used, was talc (Fintalc C15B), CaCOs, or kaolin.

[0093] The obtained dispersions were stable for a period of at least 4 weeks at 25 °C as no settling or agglomeration was observed by visual inspection. This shows that the combination of the order of addition when preparing the dispersion, corresponding to Preparatory method 2 and the addition of a gel-forming polymeric stabilizer, can be used to provide stable PHA dispersions.

[0094] Example 15 - Coating of paperboard with stable PHA dispersions

[0095] Coating formulations comprising stable PHA dispersions prepared according to Example 8 (without filler) and 10 (with filler) were prepared by adding a small amount of defoamer (0.05 wt% BIM CF 7640) to remove the air bubbles and get a smooth coating formulation.

[0096] Coating of paperboard with the coating formulations in a pilot scale coater produced even PHA coatings with homogeneous distribution of the PHA particles and no pinholes or streaking on the coated board. The results were similar for the formulations with and without filler particles. The formulation without filler particles gave a water vapor transmission rate (WVTR) for the coated paperboard of 26 g / m2 / day (measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C). With filler particles the WVTR was 19 g / m2 / day.

[0097] Table 1.

[0098] Example Preparatory PHA PHA Dispersing agent Dispersing Filler Filler Polymeric Polymeric Solid Dispersion method type amount type agent type amount stabilizer type stabilizer content stability amount amount

[0099] 1 (Reference) 1 1 100g Polyglycerol 10g . . . - 42wt% No

[0100] 2 (Reference) 1 1 100g Polyethylene 10g . . . - 42wt% No glycol

[0101] 3 (Reference) 1 1 100g Glycerol 10g . . . - 42wt% No

[0102] 4(Reference) 1 1 100g Sorbitol 10g . . . - 42wt% No

[0103] 5 (Reference) 1 1 100g Dissolved starch 10g . . . - 42wt% No

[0104] 6(lnvention) 2 1 100g Glycerol 10g - - Xanthangum 0.5g 42wt% Stable

[0105] 7 (Invention) 2 1 100g Sorbitol 10g - - Xanthangum 0.5g 42wt% Stable

[0106] 8(lnvention) 2 1 100g Dissolved starch 10g - - Xanthangum 0.5g 42wt% Stable

[0107] 9 (Invention) 2 2 100g Dissolved starch 10g - - Xanthangum 0.5g 42wt% Stable

[0108] 10 (Invention) 2 1 100g Dissolved starch 10g Talc 20g Xanthangum 0.5g 47wt% Stable

[0109] 11 (Invention) 2 2 100g Dissolved starch 10g Talc 20g Xanthangum 0.5g 47wt% Stable

[0110] 12 (Invention) 2 2 100g Dissolved starch 10g CaCO320g Xanthangum 0.5g 47wt% Stable

[0111] 13 (Invention) 2 2 100g Dissolved starch 10g Kaolin 20g Xanthangum 0.5g 47wt% Stable

[0112] 14 (Invention) 2 2 75gPHA+ Dissolved starch 10g - - Xanthangum 0.5g 42wt% Stable

[0113] 25 g PLA

Claims

CLAIMS1. A method for manufacturing a stable polyhydroxyalkanoate (PHA) dispersion, said method comprising: a) providing an aqueous dispersant comprising a water-soluble dispersing agent in water, b) adding PHA particles in solid powder form to the aqueous dispersant and mixing the PHA particles with the aqueous dispersant to obtain a PHA dispersion, and c) adding a gel-forming polymeric stabilizer to the PHA dispersion to obtain a stable PHA dispersion.

2. The method of claim 1, further comprising: adding inorganic filler particles to the PHA dispersion obtained in b).

3. The method of any one of the preceding claims, wherein the total solid content of the stable PHA dispersion is in the range of 20-70 wt%, preferably in the range of 30-60 wt%, and more preferably in the range of 40-50 wt%.

4. The method of any one of the preceding claims, wherein the dispersing agent is selected from the group consisting of water-soluble polymers, starch, low molecular weight polyols, urea, and combinations thereof.

5. The method of any one of the preceding claims, wherein the stable PHA dispersion comprises 1-30 wt%, preferably 2-15 wt%, of the water-soluble dispersing agent based on the total solid content of the stable PHA dispersion.

6. The method of any one of the preceding claims, wherein the dispersing agent is a water-soluble polymer, preferably selected from the group consisting of water- soluble polysaccharides and polyethylene glycol.

7. The method of any one of the preceding claims, wherein the dispersing agent is starch.

8. The method of any one of the preceding claims, wherein the dispersing agent is a low molecular weight polyol, preferably selected from the group consisting of sorbitol, maltitol, xylitol, mannitol, and glycerol.

9. The method of any one of the preceding claims, wherein the dispersing agent is urea.

10. The method of any one of the preceding claims, wherein the stable PHA dispersion comprises 70-98.9 wt%, preferably 90-98.9 wt%, of the PHA particles based on the total solid content of the stable PHA dispersion.

11. The method of any one of the preceding claims, wherein the PHA particles have a median particle size (D50) below 100 pm, preferably below 50 pm.

12. The method of any one of the preceding claims, wherein the PHA particles have a median particle size (D50) below 20 pm, preferably below 15 pm, and more preferably in the range of 0.5-10 pm or in the range of 0.5-5 pm.

13. The method of any one of the preceding claims, wherein the dispersion coating composition is free from, or substantially free from particles or particle agglomerates having a particle size above 50 pm, above 20 pm, or above 15 pm.

14. The method of any one of the preceding claims, wherein the PHA particles comprise PHA in an amount of 70-99.9 wt%, preferably in an amount of 90-99.9 wt%, based on the dry weight of the PHA particles.

15. The method of any one of the preceding claims, wherein the PHA is a PHA co-polymer.

16. The method of any one of the preceding claims, wherein the PHA is a medium chain length PHA, preferably a PHA having 6-14 carbon atoms per monomer unit.

17. The method of any one of the preceding claims, wherein the PHA particles comprise a blend of PHA and one or more additional polymers, preferably selected from the group consisting of polylactic acid (PLA), polybutylene succinate (PBS), polybutylene succinate-co-adipate (PBSA), polyethylene (PE), and polyethylene terephthalate (PET), and more preferably selected from the group consisting of polylactic acid (PLA), polybutylene succinate (PBS), and polybutylene succinate- co-adipate (PBSA).

18. The method of any one of the preceding claims, wherein the PHA has a melting point in the range of 100-170 °C preferably in the range of 120-160 °C.

19. The method of any one of the preceding claims, wherein the stable PHA dispersion comprises 0.1-10 wt%, preferably 0.1-5 wt%, and more preferably 0.1-2 wt%, of the gel-forming polymeric stabilizer based on the total solid content of the stable PHA dispersion.

20. The method of any one of the preceding claims, wherein the gel-forming polymeric stabilizer comprises a polymer selected from the group consisting of polysaccharides, polysaccharide derivatives, polypeptides, and polypeptide derivatives, or a combination thereof, capable of forming a gel or a gel-like structure.

21. The method of any one of the preceding claims, wherein the gel-forming polymeric stabilizer comprises cellulose, methyl cellulose, hydroxypropylmethyl cellulose, microfibrillated cellulose (MFC), cellulose nanocrystals (CNC), cellulose nanofibers (CNF), starch, modified starch, xanthan gum, guar gum, alginate, pectin carrageenan, gellan, agar, cassava flour, or gelatin.

22. The method of any one of the preceding claims, wherein the gel-forming polymeric stabilizer comprises a polysaccharide gum, preferably a gum selectedfrom xanthan gum, guar gum, alginate, pectin carrageenan, gellan, and agar, or a combination thereof.

23. The method of claim 5, wherein the stable PHA dispersion comprises 1-30 wt%, preferably 3-15 wt%, of the inorganic filler particles based on the total solid content of the stable PHA dispersion.

24. The method of any one of claims 2-23, wherein the inorganic filler particles are selected from the group consisting of clay, talc, CaCOs, TiC>2, AI2O3, SiC>2, kaolin, bentonite, and phyllosilicates, or a combination thereof.

25. A stable polyhydroxyalkanoate (PHA) dispersion in water comprising:1-30 wt% water-soluble dispersing agent,70-98.9 wt% PHA particles having a median particle size (D50) below 20 pm, and0.1-10 wt% gel-forming polymeric stabilizer, based on the total solid content of the stable PHA dispersion, wherein the total solid content of the stable PHA dispersion is in the range of 20- 70 wt%, and wherein the stable PHA dispersion is stable for at least 2 weeks at 25 °C.

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