WO2024194712A1

WO2024194712A1 - A method for manufacturing a dispersion coated fiber-based substrate

Info

Publication number: WO2024194712A1
Application number: PCT/IB2024/052115
Authority: WO
Inventors: Kaj Backfolk; Åsa NYFLÖTT; Gisela CUNHA; Mari HILTUNEN
Original assignee: Stora Enso Oyj
Priority date: 2023-03-20
Filing date: 2024-03-05
Publication date: 2024-09-26
Also published as: SE2330130A1

Abstract

The present invention relates to a method for manufacturing a dispersion coated fiber-based substrate, said method comprising the steps of: a) forming a fibrous web from one or more fiber suspensions, at least one of said fiber suspensions being a broke suspension, and dewatering, and optionally drying, the fibrous web to obtain a fiber-based substrate having a first main surface and a second main surface; b) forming a dispersion coating layer on the first main surface by applying a dispersion coating composition and drying the applied dispersion coating composition to obtain a dispersion coated fiber-based substrate; wherein the broke suspension in a) comprises 0.1-20 wt% of PHA based on the total solid content of the broke suspension.

Description

3089PC A METHOD FOR MANUFACTURING A DISPERSION COATED FIBER-BASED SUBSTRATE 5 Technical field The present disclosure relates to methods for preparing coated fiber-based substrates, specifically polyhydroxyalkanoate (PHA) coated paper or paperboard, for use as packaging materials. 10 Background 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 15 properties needed to make the paper or paperboard suitable for many demanding applications, for example as liquid or food packaging board. 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 20 products must typically also be provided with a condensation layer on the outside of the package. This condensation layer prevents condensated liquid 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. 25 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. 30 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 5 emulsions such as styrene/acrylate or styrene/butadiene emulsions are, however, not biodegradable or compostable. Dispersion coating barriers based on polyhydroxyalkanoates (PHA), on the other hand, are both compostable and biodegradable. The challenge with PHA 10 dispersions is to find a suitable composition, which enables good coater runnability, good coating coverage (hold-out), and good barrier performance. Coating coverage, and subsequent good barrier performance, is very dependent on substrate roughness and coat weight, whereas higher coat weights have a negative impact on recyclability, drying efficiency, and cost. PHA dispersions are 15 usually stabilized with surfactants and/or surface active polymers, which may cause uneven barrier quality due to migration of dispersants, or to higher foaming tendency. The foaming tendency may further create problems when recycling and repulping or disintegrating the coated web. 20 Many of the aforementioned problems can be avoided by applying the PHA using melt extrusion coating. However, extrusion coating of PHA is unfortunately not implementable on-line on full scale paper or paperboard machines. Also, extrusion coating usually requires relatively high coat weights and leads to inferior adhesion as compared to dispersion coated grades, and extrusion coated grades are more 25 difficult to re-pulp than dispersion coated grades. Thus, there remains a need for improved PHA coating solutions to replace conventional plastic coatings, especially polyolefin coatings, in paper and paperboard based packaging materials, while maintaining acceptable liquid barrier 30 properties. At the same time, there is a need for improved methods for manufacturing PHA coated paper and paperboard, that facilitate repulping and recycling of the coated paper or board in the mill, as well as at the pre-consumer and post-consumer stage. Description of the invention It is an object of the present disclosure to provide polyhydroxyalkanoate (PHA) 5 coatings as alternatives 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. It is a further object of the present disclosure to provide an improved method for 10 manufacturing a PHA dispersion coated fiber-based substrate. It is a further object of the present disclosure to provide an improved method for manufacturing a PHA dispersion coated fiber-based substrate, which overcomes or ameliorates at least some of the problems associated with previous PHA 15 coating methods. It is a further object of the present disclosure to provide an improved method for manufacturing a PHA dispersion coated fiber-based substrate, which allows for efficient recycling of PHA coated broke. Particularly, it is an object of the present20 disclosure to provide a method for manufacturing a PHA dispersion coated fiber- based substrate, which allows for efficient recycling of PHA coated broke without causing undue foaming or uneven barrier properties in the coated substrate. The above-mentioned objects, as well as other objects as will be realized by the 25 skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure. The present invention is based on the understanding that many problems associated with PHA dispersion coating of fiber-based substrates, and particularly 30 associated with the recycling of PHA coated broke, can be overcome or ameliorated by using a relatively high amount of a low molecular weight polyol as a dispersant for the PHA particles. Problems that can be overcome or ameliorated include excessive foaming and formation of large PHA flakes during repulping, which may in turn lead to poor yield in the recycling process. A surprising observation is that the high amounts of a low molecular weight polyol does not negatively affect the barrier properties of the PHA coating. Typically, dispersants are used in amounts less than 1 wt% based on dry weight of the dispersion coating composition, as it would be expected that the dispersant would deteriorate 5 the barrier properties of the PHA coating. Another surprising observation is that the amounts of low molecular weight polyol remaining in the recycled pulp after repulping do not negatively affect the mechanical properties of the new paper or paperboard formed using the recycled pulp. 10 According to a first aspect illustrated herein, there is provided a method for manufacturing a dispersion coated fiber-based substrate, said method comprising the steps of: a) forming a fibrous web from one or more fiber suspensions, at least one of said fiber suspensions being a broke suspension, and dewatering, and optionally 15 drying, the fibrous web to obtain a fiber-based substrate having a first main surface and a second main surface; b) forming a dispersion coating layer on the first main surface by applying a dispersion coating composition comprising, in a liquid medium: 20 50-99 wt% of dispersed PHA (polyhydroxyalkanoate) particles, based on the total solid content of the dispersion coating composition, and 1-50 wt% of dissolved low molecular weight polyol dispersant, based on the total solid content of the dispersion coating composition, 25 wherein the dispersion coating composition has a total solid content in the range of 20-80 wt%, and drying the applied dispersion coating composition to obtain a dispersion coated fiber-based substrate; 30 wherein the broke suspension in a) comprises 0.1-20 wt% of PHA based on the total solid content of the broke suspension. The fibrous web and fiber-based substrate (also referred to herein as “the substrate”) formed in step a) is preferably mainly formed from pulp of wood or other fibrous substances. In some embodiments, the fiber-based substrate is paper or paperboard, preferably paperboard. Paper generally refers to a material manufactured in sheets or rolls from the pulp 5 of wood or other fibrous substances comprising cellulose fibers, used for e.g. writing, drawing, or printing on, or as packaging material. Paper can either be bleached or unbleached and produced in a variety of thicknesses, depending on the end-use requirements. 10 Paperboard generally refers to strong, thick paper or cardboard comprising cellulose fibers used for example as flat substrates, trays, boxes and/or other types of packaging. Paperboard can either be bleached or unbleached and produced in a variety of thicknesses, depending on the end-use requirements. 15 Although different arrangements for performing the steps of the inventive method could be contemplated by the skilled person, the inventive method may advantageously be performed in a paper making machine, more preferably in a Fourdrinier paper machine. A paper making machine (or paper machine) is an industrial machine which is used in the pulp and paper industry to create paper or 20 paperboard in large quantities at high speed. Modern paper making machines are typically based on the principles of the Fourdrinier machine, which uses a moving woven mesh, a so-called “wire”, to create a continuously moving fibrous web by filtering out and dewatering fibrous material held in one or more fiber suspensions. The fiber suspension or fiber suspensions is applied to the wire using one or more 25 headboxes. The function of the headbox is to dose and distribute the fiber suspension uniformly across the width of the wire. The fibrous web can be formed as a single ply or multiply structure using the same or different fiber suspensions in the different plies. Dewatering of the fibrous web on the wire may be performed using methods and equipment known in the art, examples include but are not30 limited to table roll and foils, suction boxes, friction less dewatering and ultra- sound assisted dewatering. This dewatered fibrous web is then typically dried in the machine to produce a fiber-based substrate. The drying may for example include drying the fibrous web by passing the fibrous web around a series of heated drying cylinders. In the inventive method, a fibrous web is formed from one or more fiber suspensions, at least one of said fiber suspensions being a broke suspension comprising 0.1-20 wt% of PHA based on the total solid content of the broke 5 suspension. The term “broke“, as used herein, refers to partly or fully manufactured paper or board that is discarded from paper or board making, converting, or finishing processes. The broke may be uncoated broke, i.e. broke formed before coating of 10 the paper or board, or coated broke, i.e. broke formed after coating of the paper or board, or a mixture of uncoated broke and coated broke. The broke is typically collected, fed to a repulper, pulped in aqueous media, and optionally blended with other fiber sources in order to obtain a broke suspension useful for paper manufacturing. 15 The term “broke suspension”, as used herein, refers generally to a fiber suspension wherein at least a part of the fiber content is derived from broke. In some embodiments, the fiber content of the broke suspension is entirely derived from broke. In some embodiments, at least 1 wt%, preferably at least 5 wt%, of the 20 fiber content of the broke suspension is derived from broke. In some embodiments, at least 10 wt%, preferably at least 20 wt%, at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, or at least 90 wt%, of the fiber content of the broke suspension is derived from broke. In some embodiments 1-50 wt%, preferably 1-40 wt%, and more preferably 1-30 25 wt%, of the fiber content of the broke suspension is derived from broke. In some embodiments 5-50 wt%, preferably 5-40 wt%, and more preferably 5-30 wt%, of the fiber content of the broke suspension is derived from broke. In some embodiments 10-50 wt%, preferably 10-40 wt%, and more preferably 10-30 wt%, of the fiber content of the broke suspension is derived from broke. The remaining 30 part of the fiber content of the broke suspension may consist of any other type of pulp fibers, such as fibers from bleached and/or unbleached Kraft pulp, sulfite pulp, dissolving pulp, thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), high-temperature CTMP (HT-CTMP), pressure groundwood (PGW), recycled pulp such as pre or post consumer waste, and/or mixtures thereof. In some embodiments, the fibrous web formed in a) is a single ply fibrous web formed entirely from the broke suspension. 5 In some embodiments, the fibrous web formed in a) is a multiply fibrous web formed entirely from the broke suspension. In some embodiments, the fibrous web formed in a) is a single ply fibrous web formed from a mixture of the broke suspension and at least one more fiber 10 suspension. In some embodiments, the fibrous web formed in a) is a multiply fibrous web formed from the broke suspension and at least one more fiber suspension. 15 In some embodiments, the fibrous web formed in a) is a multiply fibrous web wherein at least one ply is formed from the broke suspension and at least one ply is formed from another fiber suspension. In some embodiments, the fibrous web formed in a) is a multiply fibrous web 20 comprising a top-ply a mid-ply and a bottom-ply, wherein the mid-ply is formed from the broke suspension and the top-ply and bottom-ply are formed from one or more other fiber suspensions. The fiber content of the other fiber suspensions, besides the broke suspension, 25 may consist of any other type of pulp fibers, such as fibers from bleached and/or unbleached Kraft pulp, sulfite pulp, dissolving pulp, thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), high-temperature CTMP (HT-CTMP), pressure groundwood (PGW), broke, recycled pulp such as pre or post consumer waste, and/or mixtures thereof. 30 In some embodiments, the basis weight of the fiber-based substrate is in the range of 20-800 g/m². In some embodiments, the fiber-based substrate has a grammage of at least 100 g/m². In some embodiments, the fiber-based substrate has a grammage of at least 150 g/m², 200 g/m², 250 g/m², 300 g/m², 350 g/m², or 400 g/m². The grammage of the fiber-based substrate is preferably below 1000 g/m², 800 g/m², or 600 g/m². Unless otherwise stated, the grammage is determined according to the standard ISO 536. The fiber-based substrate formed in step a) may also be surface sized or impregnated. In some embodiments, the fiber-based substrate is subjected to surface sizing or impregnation on one or both sides with a surface sizing composition, preferably comprising a starch derivative, a cellulose derivative, or polyvinyl alcohol (PVOH) or a combination of thereof. The starch derivative may for example be a slightly modified, such as oxidized or cationized starch. The cellulose derivative may for example be a sodium carboxymethyl cellulose with a degree of substitution higher than 0.4 such as in the range of 0.5-1.5. The PVOH may be fully or partly hydrolyzed. The surface sizing composition may also comprise a hydrophobic sizing agent, such as alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), or a rosin sizing agent. The fiber-based substrate is preferably subjected to surface sizing or impregnation on the first main surface to be subjected to the dispersion coating. The surface sizing or impregnation may provide a more even, and less water absorbent surface for the dispersion coating composition. The surface sizing or impregnation may also facilitate the release of the PHA coating structure from the fiber-based substrate during repulping. In some embodiments, the grammage of the surface sizing composition is 0.2-10 g/m², preferably 0.4-8 g/m², and more preferably 0.8-5 g/m² per side, based on dry weight. The fiber-based substrate itself, before PHA coating, may have a relatively high permeability for liquids, such as water, oil and grease, water vapor and gases, such as oxygen, air and carbon dioxide. In some embodiments, the fiber-based substrate has a water vapor transmission rate (WVTR), measured according to the standard ASTM F1249 - 20 at 50% relative humidity and 23 °C, of at least 200 g/m²/24h. In some embodiments, the fiber-based substrate has a COBB60 value as measured according to the standard ISO 535 of less than 100 g/m², preferably less than 80 g/m², less than 60 g/m², or less than 40 g/m². The fiber-based substrate itself, before PHA coating, preferably has a L&W (15°) bending resistance of at least 145 mN (MD) as determined according to ISO 2493- 1. 5 The broke suspension in step a) is preferably formed at least in part from fibers obtained from recycled PHA dispersion coated broke. In some embodiments, 1-100 wt% of the fibers of the broke suspension in a) comes from recycled PHA dispersion coated broke from the method for 10 manufacturing the dispersion coated fiber-based substrate. In some embodiments, 5-100 wt%, and more preferably 5-50 wt% or 10-20 wt%, of the fibers of the broke suspension in a) comes from recycled PHA dispersion coated broke from the method for manufacturing the dispersion coated fiber-based substrate. 15 The broke suspension in step a) is preferably formed at least in part from fibers obtained from recycled PHA dispersion coated broke. As a result, the broke suspension in a) comprises 0.1-20 wt% of PHA based on the total solid content of the broke suspension. In some embodiments, the broke suspension in a) comprises 0.1-15 wt%, preferably 0.1-10 wt%, and more preferably 0.1-5 wt%, of 20 PHA based on the total solid content of the broke suspension. In some embodiments, the PHA in the broke suspension in a) comes from recycled PHA dispersion coated broke from the method for manufacturing the dispersion coated fiber-based substrate. 25 As the broke suspension in a) comprises PHA, the fiber-based substrate obtained in a) will also comprise PHA. In some embodiments, the fiber-based substrate obtained in a) comprises 0.1-20 wt% of PHA based on the total solid content of the fiber-based substrate. In some embodiments, the fiber-based substrate obtained in a) comprises 0.1-15 wt%, preferably 0.1-10 wt%, and more preferably 0.1-5 wt%, 30 of PHA based on the total solid content of the fiber-based substrate. Since the broke suspension is often used in combination with other fiber suspensions, the fiber-based substrate obtained in a) may also comprise significantly less PHA. Thus, in some embodiments, the fiber-based substrate obtained in a) comprises 0.1-5 wt% of PHA based on the total solid content of the fiber fiber-based substrate. In some embodiments, the fiber-based substrate obtained in a) comprises 0.1-5 wt%, preferably 0.1-2.5 wt%, and more preferably 0.1-2 wt%, of PHA based on the total solid content of the fiber-based substrate. 5 When the fiber-based substrate obtained in a) is a multiply fiber-based substrate, at least one of the plies may comprise a higher content of PHA, whereas the other plies may comprise a lower content of PHA, or no PHA. Thus, in some embodiments, wherein the fiber-based substrate obtained in a) is a multiply fiber- 10 based substrate, at least one of the plies comprises 0.1-20 wt%, such as 0.1-15 wt%, 0.1-10 wt%, or 0.1-5 wt%, of PHA based on the total solid content of the ply. In some embodiments, the method comprises recycling fibers from PHA dispersion coated broke in the broke suspension in a). PHA dispersion coated 15 broke refers to partly or fully manufactured PHA dispersion coated fiber-based substrate. In some embodiments, the method comprises recycling fibers from PHA dispersion coated broke formed in the inventive method for manufacturing the 20 dispersion coated fiber-based substrate in the broke suspension in a). The recycling of fibers from PHA dispersion coated broke differs from recycling of conventional mineral coated paper and paperboard in that the PHA coating often comes off as large flakes when the PHA dispersion coated broke is treated in a 25 pulper. The use in the present invention of a relatively high amount of a low molecular weight polyol as a dispersant for the PHA particles reduces the amount of flakes formed during the pulping. Since some PHA flakes and PHA agglomerates may still form during the pulping, the recycling of the PHA dispersion coated broke preferably also comprises at least one deflaking and/or screening 30 step to remove PHA flakes and PHA agglomerates. In some embodiments, the recycling comprises: i) pulping the PHA dispersion coated broke in an aqueous medium; ii) subjecting the pulped PHA dispersion coated broke to deflaking and/or screening to remove PHA flakes and PHA agglomerates. The temperature during the pulping is preferably in the range of 30-95 °C, and 5 more preferably in the range of 50-80 °C. Sodium hydroxide is preferably added to adjust the pH to above 7.5, preferably above 8, and more preferably in the range of 8.5-11. The consistency during the pulping may be low consistency (1-6 wt%) medium consistency (8-20 wt%) or high consistency (>20%). Medium or high consistency is preferred since it provides both for better pulping, and for better 10 energy efficiency. After the broke pulping, the pulped PHA dispersion coated broke is subjected to deflaking and/or screening to remove PHA flakes and PHA agglomerates. The deflaking may for example be done in a disc or conical deflaking unit. The screening may for example be performed using at least one first broke screening unit using slots (slot width <0.3 mm, preferably 0.1-0.3 mm) 15 or holes (hole diameter <4 mm, preferably 1-3 mm), and at least one second broke screening unit using slots (slot width <0.2 mm, preferably 0.1-0.2) or holes (hole diameter <1 mm, preferably 0.1-1 mm). Reject from the deflaking and/or screening units can be fed back to the screening or deflaking units. This recycling method ensures good quality of the recycled fibers and prevents large agglomerates from 20 being reused. There is always a risk that the drying-pulping-deflaking-screening operations of recycling will affect the fiber profile and composition of the fiber suspension so that it starts to impact on runnability in wet end including drainage behavior, as well as 25 sheet properties such as bulk, roughness, stiffness and strength properties of the formed fiber-based substrates. The aim of the recycling is to obtain a high amount of recycled fiber accept with good quality. The use of a high amount of low molecular weight polyol as a dispersant helps to ensure this. The high content of dispersant could have a negative impact on pulping and sheet properties. 30 However, stock quality degree (SQD) measurements comparing sheets prepared with only fresh CTMP to sheets prepared with only recycled PHA dispersion coated broke, and sheets prepared with mixtures of fresh CTMP and recycled PHA dispersion coated broke show that this is not the case. SQD is calculated according to the following formula, wherein the process sample sheet is a sheet prepared with only recycled PHA dispersion coated broke or a mixture of recycled PHA dispersion coated broke and fresh CTMP, and the laboratory sample sheet is a sheet prepared with only fresh CTMP. 5

In some embodiments, the SQD is at least 60% preferably at least 70%, and more preferably at least 80%, such as in the range of 85-150%. 10 The fiber-based substrate obtained in a) is coated with a dispersion coating layer comprising PHA (polyhydroxyalkanoate) particles on the first main surface. The dispersion coating layer is formed by applying a dispersion coating composition comprising, in a liquid medium: 15 50-99 wt% of dispersed PHA (polyhydroxyalkanoate) particles, based on the total solid content of the dispersion coating composition, and 1-50 wt% of dissolved low molecular weight polyol dispersant, based on the total solid content of the dispersion coating composition, 20 wherein the dispersion coating composition has a total solid content in the range of 20-80 wt%, on the first main surface, and drying the applied dispersion coating composition to obtain a dispersion coated fiber-based substrate. 25 The PHA particles are preferably the main component of the dispersion coating composition based on dry weight of the composition. In some embodiments, the dispersion coating composition comprises at least 50 wt%, at least 65 wt%, at least 70 wt%, or at least 90 wt% of PHA particles based on the total solid content of the dispersion coating composition. In some embodiments, the dispersion 30 coating composition comprises 70-99 wt%, preferably 90-99 wt%, of PHA particles based on the total solid content of the dispersion coating composition. In some embodiments, the dispersion coating composition comprises 50-97 wt%, 50-95 wt%, 50-92.5 wt%, 50-90 wt%, 50-87.5 wt%, or 50-85 wt%, of PHA particles based on the total solid content of the dispersion coating composition. In some embodiments, the dispersion coating composition comprises 65-97 wt%, 65-95 wt%, 65-92.5 wt%, 65-90 wt%, 65-87.5 wt%, or 65-85 wt%, of PHA particles based 5 on the total solid content of the dispersion coating composition. In some embodiments, the dispersion coating composition comprises 70-97 wt%, 70-95 wt%, 70-92.5 wt%, 70-90 wt%, 70-87.5 wt%, or 70-85 wt%, of PHA particles based on the total solid content of the dispersion coating composition. In some embodiments, the dispersion coating composition comprises 90-97 wt%, 90-95 10 wt%, 90-92.5 wt%, of PHA particles based on the total solid content of the dispersion coating composition. 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 15 distribution. In some embodiments, the PHA particles have a unimodal particle size distribution. In some embodiments, the PHA particles have a median particle size (D50) below 15 µm, preferably below 12 µm, and more preferably in the range of 0.5-11 µm, or 20 in the range of 0.8-8 µm. In some embodiments, the dispersion coating composition is free from, or substantially free from particles or particle agglomerates having a particle size above 50 µm, above 20 µm, or above 15 µm. 25 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. 30 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. In some embodiments, the PHA is selected from the group consisting of poly(3- hydroxyoctanoate) (PHO), poly(3-hydroxydecanoate) (PHD), poly(3- hydroxyhexanoate) (PHH), and poly(3-hydroxyvalerate) (PHV), poly(3- hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3- 5 hydroxyhexanoate) (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’s suitable for use in the 10 dispersion coating composition are not limited to those listed here. In some embodiments, the PHA is a PHA co-polymer. In some embodiments, the PHA is selected from the group consisting of poly(3-15 hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3- hydroxyhexanoate) (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 20 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. In some embodiments, the PHA is a medium chain length PHA, preferably a PHA having 6-14 carbon atoms per monomer unit. 25 The type of PHA suitable for use in the dispersion coating composition may 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 30 differential scanning calorimetry according to standard ASTM D3418. The inventive dispersion coating composition comprises 1-50 wt% of low molecular weight polyol dispersant, based on the total solid content of the dispersion coating composition. Dispersants are usually low molecular polymers which are used for improving the colloidal stability of a dispersion, and reducing viscosity (due to less floc formation, etc.). Dispersants are not normally used for improving barrier properties of a coating. In fact, many dispersants, especially at higher concentrations, are expected to migrate and deteriorate the barrier 5 properties of a barrier coating. In some embodiments, the dispersion coating composition comprises 3-35 wt%, and more preferably 5-30 wt%, of the low molecular weight polyol dispersant, based on the total solid content of the dispersion coating composition. In some 10 embodiments, the dispersion coating composition comprises 7.5-35 wt%, preferably 10-35 wt%, more preferably 12.5-35 wt%, and more preferably 15-35 wt% of the low molecular weight polyol dispersant, based on the total solid content of the dispersion coating composition. In some embodiments, the dispersion coating composition comprises 7.5-30 wt%, preferably 10-30 wt%, more preferably 15 12.5-30 wt%, and more preferably 15-30 wt% of the low molecular weight polyol dispersant, based on the total solid content of the dispersion coating composition. In some embodiments, the dispersion coating composition comprises 7.5-25 wt%, preferably 10-25 wt%, more preferably 12.5-25 wt%, and more preferably 15-25 wt% of the low molecular weight polyol dispersant, based on the total solid content 20 of the dispersion coating composition. In some embodiments, the dispersion coating composition comprises 3-35 wt% of the low molecular weight polyol dispersant and 65-97 wt% of PHA particles, or 5- 30 wt% of the low molecular weight polyol dispersant and 70-95 wt% of PHA 25 particles, based on the total solid content of the dispersion coating composition. In some embodiments, the dispersion coating composition comprises 7.5-30 wt% of the low molecular weight polyol dispersant and 70-92.5 wt% of PHA particles, or 10-30 wt% of the low molecular weight polyol dispersant and 70-90 wt% of PHA particles, or 12.5-30 wt% of the low molecular weight polyol dispersant and 70- 30 87.5 wt% of PHA particles, or 15-30 wt% of the low molecular weight polyol dispersant and 70-85 wt% of PHA particles, based on the total solid content of the dispersion coating composition. 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. 5 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. In some embodiments, the low molecular weight polyol dispersant is selected from 10 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 15 polysaccharides may be charged, uncharged, amphoteric, or combination thereof. The low molecular weight polysaccharides may be linear or branched. In some embodiments, the low molecular weight polyol dispersant is a sugar alcohol, preferably a sugar alcohol selected from the group consisting of sorbitol, 20 maltitol, xylitol, mannitol, and glycerol, and combinations thereof. In some embodiments, the low molecular weight polyol dispersant is selected from the group consisting of sorbitol, maltitol, xylitol, mannitol, and combinations thereof. In some embodiments, the low molecular weight polyol dispersant is sorbitol. 25 In some embodiments, the dispersion coating composition further comprises 0.01- 15 wt%, preferably in the range of 0.01-10 wt%, and more preferably in the range of 0.1-5 wt%, of a rheology modifier, based on the total solid content of the dispersion coating composition. The rheology modifier is used for adjusting the viscosity and water retention of the dispersion coating composition such that it is 30 suitable for application by the preferred application method. In some embodiments, the rheology modifier comprises a polymer selected from the group consisting of polysaccharides, polysaccharide derivatives, polypeptides, polypeptide derivatives, or a combination thereof. In some embodiments, the dispersion coating composition further comprises 1-30 wt% of filler particles, based on the total solid content of the dispersion coating composition. Too much filler particles can lead to cracking and deterioration of 5 barrier properties. The amount of filler particles is preferably 5-25 wt%, and more preferably 5-15 wt%, based on the total solid content of the dispersion coating composition. In some embodiments, the filler particles are selected from the group consisting of 10 clay (such as kaolin or calcined kaolin), talcum, CaCO3 (such as PCC or GCC), TiO2, Al2O3, SiO2, bentonite, fibers, phyllosilicates, or a combination thereof. The filler particles are preferably high aspect ratio filler particles, e.g. flaky particles having median particle size (D90) below 2 µm. 15 In some embodiments, the dispersion coating composition comprises at least 50 wt% of PHA (polyhydroxyalkanoate) particles, the low molecular weight polyol dispersant in the amounts disclosed herein, optionally a rheology modifier in the amounts disclosed herein, and optionally filler particles in the amounts disclosed herein, based on the total solid content of the dispersion coating composition. In 20 some embodiments, the dispersion coating composition comprises at least 70 wt% of PHA (polyhydroxyalkanoate) particles, 7.5-30 wt% of the low molecular weight polyol dispersant, 0.1-5 wt% of the rheology modifier, and optionally 5-25 wt% of the filler particles, based on the total solid content of the dispersion coating composition. 25 In some embodiments, the dispersion coating composition may also comprise further additives such as lubricants, humectants or softeners, sizing agents, dewatering accelerators, slimicides, wet-strength agents, pH regulation agents, defoamers, crosslinkers, biocides, preservatives, and/or colorants. 30 In some embodiments, the dispersion coating composition is free from added foaming agents, such as non-polymeric or polymeric surfactants. In some embodiments, the dispersion coating composition comprises less than 0.5 wt%, preferably less than 0.1 wt%, more preferably less than 0.01 wt%, of added foaming agents, such as non-polymeric or polymeric surfactants. In some embodiments, the dispersion coating composition is de-aerated. The low 5 molecular weight polyol dispersant is advantageous in this respect since a molecular weight polyol dispersant is less prone to entrapping gas bubbles that a high molecular weight dispersant. Thus, in some embodiments, the dispersion coating composition is preferably free from, or substantially free from bubbles of air and other gases. 10 In some embodiments, the dispersion coating composition has a total solid content in the range of 30-70 wt%, preferably in the range of 40-60 wt%. In some embodiments, the dispersion coating composition has a viscosity in the 15 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. In some embodiments, the dispersion coating composition has a ÅAGWR water 20 retention value (Åbo 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. The liquid medium may comprise water, organic solvent, or a mixture of water and 25 organic solvent. In some embodiments, the liquid medium is water. The dispersion coating composition used in step b) herein allows for an improved manufacture of PHA coated fiber-based substrates. 30 The dispersion coating layer is preferably formed by means of a liquid film coating process, whereby the dispersion coating composition is applied on the substrate, spread out to a thin, uniform layer, and thereafter dried. In some embodiments, the dispersion coating composition is applied at a grammage in the range of 5-40 g/m², preferably in the range of 5-30 g/m², and more preferably in the range of 5-20 g/m², based on dry weight. The thickness of the wet dispersion coating composition when applied on the substrate is typically 5 in the range of 20-100 µm, preferably in the range of 20-50 µm. Accordingly, it is preferred that the dispersion coating composition is free from particles or particle agglomerates that are larger than 20-50 µm. Thus, in some embodiments, the dispersion coating composition is free from, or substantially free from particles or particle agglomerates having a particle size above 50 µm, above 20 µm, or above 10 15 µm. In some embodiments, a tie-layer may be applied between the fiber-based substrate and the dispersion coating layer, in order to improve adhesion between the substrate and the dispersion coating layer. The tie layer preferably comprises 15 and adhesive polymer that can further improve the adhesion between the substrate and the dispersion coating layer. The tie layer may for example comprise a PHA with a lower melting point than the PHA of the dispersion coating layer, such as in the range of 60-120 °C, a polyvinyl alcohol (PVOH) or any other bio- based and/or biodegradable and compostable polymer that can further improve 20 the adhesion between the substrate and the dispersion coating layer. In some embodiments, the dispersion coating composition is applied by a non- contact application method. In some embodiments, the dispersion coating composition is applied by an application method selected from the group 25 consisting of roller coating, spray coating, curtain, blade coating, slot coating, immersion coating, gravure roll coating, reverse direct gravure coating, rod coating, soft-tip blade coating, short dwell, and soft-tip rod coating, and combinations thereof. In some embodiments, the dispersion coating composition is applied by blade coating or rod coating. The dispersion coating composition may 30 be applied directly onto the fiber-based substrate or indirectly, for example via a transfer roll or belt. To minimize the risk of pinholes in the dispersion coating layer, the dispersion coating layer may be formed by applying the dispersion coating composition in two or more steps with interim drying between the steps. In such embodiments, the dispersion coating composition in each step may be applied at a grammage in the range of 5-10 g/m², based on dry weight. In some embodiments, the dispersion coating composition applied in the first step may be different from the dispersion 5 coating composition applied in the second step. In some embodiments, the PHA particles in the dispersion coating composition applied in the second step have a median particle size which is smaller than the median particle size of the particles in the dispersion coating composition applied in the first step. In some embodiments, the median PHA particle size in the second step is at least 10% 10 smaller, preferably at least 20% smaller and more preferably at least 30% smaller, than the median PHA particle size in the second step. In some embodiments, the drying comprises subjecting the dispersion coating composition to heating. In some embodiments, the drying comprises subjecting 15 the dispersion coating composition to at least one non-contact drying step, such as infrared radiation, electron beam radiation, ultraviolet radiation, microwave radiation, hot air, such as impingement, or a combination thereof. Optionally, the dispersion coating composition is then subjected to at least one additional drying step, which can be a hot air drying step or a contact drying step, such as heat 20 conduction drying, e.g. using a heated belt or heated cylinders. In some embodiments, the dry dispersion coating layer has a grammage in the range of 5-40 g/m², preferably in the range of 5-30 g/m², and more preferably in the range of 5-20 g/m². In some embodiments, the dry dispersion coating layer has 25 a thickness in the range of 8-20 µm. In some embodiments the method further comprises: c) forming a heat sealable liquid barrier layer on the second main surface. 30 In some embodiments, the method further comprises: c) forming a dispersion coating layer comprising 50-99 wt% of PHA (polyhydroxyalkanoate) particles, based on the total solid content of the dispersion coating layer, and 1-50 wt% of low molecular weight polyol dispersant, based on the total solid content of the dispersion coating layer, on the second main surface. The dispersion coating layer on the second main surface may be further defined as the dispersion coating layer on the first main surface. The dispersion coating layer on the second main surface may be identical to, or different from, the dispersion coating layer on the first main surface. Some non-limiting examples of possible embodiments of the dispersion coated fiber-based substrate are shown below: - PHA dispersion coating/paperboard/PHA dispersion coating - PHA dispersion coating/paperboard/tie layer/PHA dispersion coating - PHA dispersion coating/paperboard/tie layer/barrier paper or barrier film/PHA dispersion coating In some embodiments, the dispersion coated fiber-based substrate has a water vapor transmission rate (WVTR), measured according to the standard ASTM F1249 - 20 at 50% relative humidity and 23 °C, of less than 25 g/m²/24h, preferably less than 20 g/m²/24h, and more preferably less than 17 g/m²/24h. In some embodiments, the dispersion coated first main surface of the dispersion coated fiber-based substrate has a COBB600 value, measured according to the standard SCAN-P 12:64, of less than 25 g/m², preferably less than 20 g/m², and more preferably less than 15 g/m². In some embodiments, the dispersion coated first main surface of the dispersion coated fiber-based substrate has a KIT value of at least 5, preferably at least 10. In some embodiments, the dispersion coated first main surface of the dispersion coated fiber-based substrate is pinhole free. The number of pinholes may for example be determined according to standard EN13676:2001. The substrate film preferably comprises less than 10 pinholes/m², preferably less than 8 pinholes/m², 5 and more preferably less than 2 pinholes/m². The number of pinholes per m² may for example be measured by optical inspection, for example according to standard EN13676:2001. The dispersion coated fiber-based substrate may be recycled into other paper 10 products using common repulping technology. In the repulping, the cellulose fibers of the fiber-based substrate are separated from a non-repulpable fraction referred to as rejects. Rejects may for example comprise agglomerated fibers and solid foreign materials, that have to be removed for disposal or burning. In some embodiments, the dispersion coated fiber-based substrate has a repulpability 15 characterized by a reject rate, as determined according to the PTS RH 021/97 test method for Category II products, below 20%, preferably below 10%, more preferably below 5%. Thanks to the use of a relatively high amount of a low molecular weight polyol as a dispersant for the PHA particles, the dispersion coated fiber-based substrate provides very good repulpability. The dispersion 20 coated fiber-based substrate may thus be referred to as a repulpable material. Generally, while the products, polymers, materials, layers and processes are described in terms of “comprising” various components or steps, the products, polymers, materials, layers and processes can also “consist essentially of” or 25 “consist of” the various components and steps. 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 30 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 not be 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. 5 Examples Starting material – PHA dispersion coated paperboard The following examples demonstrate the repulping and recycling of a PHA dispersion coated fiber-based paperboard. 10 As the starting material a 3-ply base board having top-ply and bottom-ply formed of kraft pulp, and a mid-ply formed of a mixture of CTMP and kraft pulp was used. The 3-ply base board was coated on one side with a PHA dispersion coating selected from PHA 1 and PHA 2. 15 PHA 1 was a poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) dispersion used as received, which contained high content of surfactant and/or stabilizing, wetting agents which provided a stabilized dispersion. The high content of additives gave, on the other hand, higher tendency to foaming. The foaming was 20 reduced by using a defoamer. The barrier properties of the PHA 1 coated paperboard were good, with COBB600 <20 g/m² and KIT of at least 7. PHA 2 was a poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) dispersion stabilized with sorbitol, a polysaccharide-based rheology modifier and a defoamer. 25 No foaming occurred during coating, although the content of sorbitol was relatively high (17.5 wt%). The barrier properties of the PHA 2 coated paperboard were good, with COBB600 <40 g/m², KIT 12, and WVTR 17 g/m²/day. The PHA dispersion coating was made with PHA 1 to a total coat weight of 20 gsm 30 and then dried at temperature below 150 °C or with PHA 2 to a total coat weight of 20 gsm and then dried at temperature of 110 °C. Base sheets for physical testing were prepared according to ISO 5269-1. Repulping method Repulping was made according to PTS RH 021/97 test method for Category II products, pH 7-8, consistency 3%, temperature 40 °C and 150 gsm. 5 Example 1 (comparative) – Disintegration of 100 wt% PHA 1 dispersion coated board 100 wt% PHA 1 dispersion coated board (DCB) was disintegrated according to the repulping method described above. The disintegrated pulp gave high content of 10 foam despite the use of defoaming agent in the dispersion. Also, the disintegration failed due to high content of large PHA flakes. Example 2 – Disintegration of 10 wt% PHA 2 dispersion coated board A mixture of 10 wt% PHA 2 dispersion coated board (DCB) and 90 wt% CTMP 15 pulp was disintegrated according to the repulping method described above. The disintegrated pulp was homogenous and contained no reject, as determined according to the PTS RH 021/97 test method for Category II products. No problems with foaming or high air content were observed. 20 Example 3 – Disintegration of 100 wt% PHA 2 dispersion coated board 100 wt% PHA 2 dispersion coated board (DCB) was disintegrated according to the repulping method described above. The disintegrated pulp was homogenous and contained no reject, as determined according to the PTS RH 021/97 test method for Category II products. No problems with foaming or high air content were 25 observed. Example 4 (comparative) – Base sheet with 100 wt% fresh CTMP A base sheet was prepared with 100 wt% fresh CTMP according to the base sheet preparation method. The pulp and the prepared sheets were characterized and the 30 results are presented in Table 1. Example 5 (comparative) – Base sheet with 10 wt% recycled uncoated broke A base sheet was prepared with 90 wt% fresh CTMP and 10 wt% recycled uncoated broke (UCB, 3-ply base board as used above) according to the base sheet preparation method. The pulp and the prepared sheets were characterized and the results are presented in Table 1. Example 6 (comparative) – Base sheet with 20 wt% recycled uncoated broke 5 A base sheet was prepared with 80 wt% fresh CTMP and 20 wt% recycled uncoated broke (UCB, 3-ply base board as used above) according to the base sheet preparation method. The pulp and the prepared sheets were characterized and the results are presented in Table 1. 10 Example 7 (comparative) – Base sheet with 100 wt% recycled uncoated broke A base sheet was prepared with 100 wt% recycled uncoated broke (UCB, 3-ply base board as used above) according to the base sheet preparation method. The pulp and the prepared sheets were characterized and the results are presented in Table 1. 15 Example 8 – Base sheet with 10 wt% recycled coated broke A base sheet was prepared with 10 wt% PHA 2 coated broke (CB, Example 3) and 90 wt% CTMP according to the base sheet preparation method. The pulp and the prepared sheets were characterized and the results are presented in Table 1. 20 Stiffness index, z-strength and tensile index are basically on same level as the reference sample, whereas bulk was even slightly improved. Example 9 – Base sheet with 20 wt% recycled coated broke A base sheet was prepared with 20 wt% PHA 2 coated broke (CB, Example 3) and 25 80 wt% CTMP according to the base sheet preparation method. The pulp and the prepared sheets were characterized and the results are presented in Table 1. Stiffness index, z-strength and tensile index are basically on same level as the reference sample, whereas bulk was even slightly improved. 30 Example 10 – Base sheet with 100 wt% recycled coated broke A base sheet was prepared with 100 wt% coated broke (CB, Example 3) according to the base sheet preparation method. The pulp and the prepared sheets were characterized and the results are presented in Table 1. The high content of broke gave a reduction in strength properties, but the effects were surprisingly small, especially regarding tensile index. The drainage resistance, however, was even lower than the comparative reference. The good drainage behavior and the low or no tendency for foaming, as well as 5 maintained strength properties of the formed sheets, demonstrate the PHA 2 coating dispersion is suitable for on-line/off-line dispersion coating of paperboard and that the coated board can be disintegrated and reused as coated broke. 10

Table 1. Ex.4 Ex.5 Ex.6 Ex.7 Ex.8 Ex.9 Ex.10 (comp) (comp) (comp) (comp) PHA 0 0 0 0 0.9 1.9 9.4 content (wt%) Pulp CTMP CTMP+ CTMP+ 100% CTMP+ CTMP+ 100% 10% 20% UCB 10% CB 20% CB CB UCB UCB Drainage 19.3 17.5 16.8 20.5 18.9 17.9 17.6 resistance (°SR) Bulk 3.56 3.36 3.09 1.61 3.55 3.3 1.91 (dm³/kg) Density 281 297 324 622 282 303 524 (kg/m³) Grammage 148 147.1 148.3 151.7 153.8 156.1 152.6 (g/m²) Tensile 18.66 18.76 21.72 41.84 18.65 20.24 35.87 Index (Nm/g) Stiffness 2.61 2.64 2.98 5.82 2.56 2.67 4.32 index (kNm/g) z-strength 77 77 97 422 72 82 261 (kPa) Tensile 2.76 2.76 3.22 6.35 2.87 3.16 5.48 strength (kN/m) SQD (%) - 100 117 230 103 114 198 5 Analysis methods The pulps and sheets were characterized using the following analysis methods: 5 Drainage resistance was determined according to SCAN C19:65. Bulk was determined according to ISO 534:2011. Density was determined according to ISO 534:2011. Grammage was determined according to the standard ISO 536:2019. Tensile Index was determined according to ISO 1924-3:2005. 10 Stiffness index was determined according to ISO 1924-3:2005. Tensile strength (kN/m) was determined according to ISO 1924-3:2005. z-strength was determined according to ISO 15754:2009. SQD is calculated according to the following formula, wherein the process sample sheet is a sheet prepared with only recycled PHA dispersion coated broke or a 15 mixture of recycled PHA dispersion coated broke and fresh CTMP, and the laboratory sample sheet is a sheet prepared with only fresh CTMP.

Claims

CLAIMS 1. A method for manufacturing a dispersion coated fiber-based substrate, said method comprising the steps of: 5 a) forming a fibrous web from one or more fiber suspensions, at least one of said fiber suspensions being a broke suspension, and dewatering, and optionally drying, the fibrous web to obtain a fiber-based substrate having a first main surface and a second main surface; b) forming a dispersion coating layer on the first main surface by applying a 10 dispersion coating composition comprising, in a liquid medium: 50-99 wt% of dispersed PHA (polyhydroxyalkanoate) particles, based on the total solid content of the dispersion coating composition, and 15 1-50 wt% of dissolved low molecular weight polyol dispersant, based on the total solid content of the dispersion coating composition, wherein the dispersion coating composition has a total solid content in the range of 20-80 wt%, and drying the applied dispersion coating composition to obtain a 20 dispersion coated fiber-based substrate; wherein the broke suspension in a) comprises 0.1-20 wt% of PHA based on the total solid content of the broke suspension. 25 2. The method according to claim 1, wherein the broke suspension in a) comprises 0.1-15 wt%, preferably 0.1-10 wt%, and more preferably 0.1-5 wt%, of PHA based on the total solid content of the broke suspension.

3. The method according to any one of the preceding claims, wherein the fiber- 30 based substrate obtained in a) comprises 0.1-5 wt%, preferably 0.1-2.5 wt%, and more preferably 0.1-2 wt%, of PHA based on the total solid content of the fiber- based substrate.

4. The method according to any one of the preceding claims, wherein the method comprises recycling fibers from PHA dispersion coated broke formed in the inventive method for manufacturing the dispersion coated fiber-based substrate in the broke suspension in a). 5 5. The method according to any one of the preceding claims, wherein 1-100 wt% of the fibers of the broke suspension in a) comes from recycled PHA dispersion coated broke from the method for manufacturing the dispersion coated fiber-based substrate. 10 6. The method according to any one of the preceding claims, wherein the PHA in the broke suspension in a) comes from recycled PHA dispersion coated broke from the method for manufacturing the dispersion coated fiber-based substrate. 15 7. The method according to any one of the preceding claims, wherein the fibrous web formed in a) is a multiply fibrous web comprising a top-ply a mid-ply and a bottom-ply, wherein the mid-ply is formed from the broke suspension. 8. The method according to any one of the preceding claims, wherein the PHA 20 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. 9. The method according to any one of the preceding claims, wherein the PHA is selected from the group consisting of poly(3-hydroxyoctanoate) (PHO), poly(3-25 hydroxydecanoate) (PHD), poly(3-hydroxyhexanoate) (PHH), and poly(3- hydroxyvalerate) (PHV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate- co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxyoctanoate-co-3- hydroxyhexanoate) (PHOHH), poly(3-hydroxyoctanoate-co-3-hydroxydecanoate) 30 (PHOHD), and poly(3-hydroxyoctanoate-co-3-hydroxydodecanoate) (PHDHDD), or a combination thereof. 10. The method according to any one of the preceding claims, wherein the PHA is a PHA co-polymer. 11. The method according to any one of the preceding claims, wherein the PHA is selected from the group consisting of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) 5 (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. 10 12. The method according to 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. 13. The method according to any one of the preceding claims, wherein the 15 dispersion coating composition comprises 3-35 wt%, and more preferably 5-30 wt%, of the low molecular weight polyol dispersant, based on the total solid content of the dispersion coating composition. 14. The method according to any one of the preceding claims, wherein the low 20 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. 15. The method according to any one of the preceding claims, wherein the low 25 molecular weight polyol dispersant is selected from the group consisting of low molecular weight polysaccharides and sugar alcohols, and combinations thereof.