Method for preparing a modified cutin extract at reduced pressure

Abstract

The present invention relates to a method for preparing an odorless modified cutin extract comprising: i) feeding a raw cutin extract having a dry content ranging from 30 to 95 wt% (% by weight) into an apparatus; ii) carrying out a thermal treatment inside the apparatus, wherein said thermal treatment is carried out at a pressure higher than Pa and lower than the atmospheric pressure, and at a temperature higher than 120 °C and equal to or lower than 150 °C.

Description

[0001] METHOD FOR PREPARING A MODIFIED CUTIN EXTRACT AT REDUCED PRESSURE TECHNICAL FIELD

[0002] The present invention relates to a method for preparing an odorless modified cutin extract and its use for coating a paper substrate to provide said paper substrate with improved barrier properties.

[0003] STATE OF THE ART

[0004] In the paper and packaging industry, barrier coating compositions are used for improving barrier properties (such as water and / or oil resistance) of paper substrates. Traditionally, barrier coating compositions are based on film-forming polymers derived from fossil resources.

[0005] In the recent years there is a growing interest in replacing the synthetic polymers traditionally employed in the barrier coating compositions without adversely affecting the barrier properties of the coated paper substrate. This may be achieved by introducing compounds derived from renewable resources.

[0006] In this context, compounds extracted from plant matter and their derivatives may represent an attracting alternative.

[0007] Cutin is a support biopolyester involved in waterproofing the leaves and fruits of higher plants. Cutin is the main component (between 40% and 85 wt%) of the plant cuticle, the continuous and lipidic extracellular membrane that covers the aerial parts of leaves, fruits and non-lignified stems of plant.

[0008] From a chemical point of view, cutin is a polymeric network of polyhydroxylated Ci6 and Cis fatty acids cross-linked by ester bonds. However, when extracted from plantmatter (for example through the methods described in WO2015 / 028299 or WO2016 / 187581), cutin undergoes depolymerization. Therefore, a raw cutin extract is mainly composed of hydroxy fatty acids and fatty esters, as well as their oligomers. It is known that raw cutin extract can be at least partially re-polymerized by thermal treatments, mainly through reaction of the hydroxy fatty acids and fatty esters contained therein, to obtain what is herein referred to as "modified cutin extract". G. Tedeschi et al., / CS Sustainable Chem. Eng., 2018, 6, 11, 14955-14966 describe a procedure for the fabrication of composite free-standing films inspired by plant cuticles, consisting of the blending of unsaturated and polyhydroxylated fatty acids derived from the agro-waste of tomato peeling industrial process (raw cutin extract), sodium alginate, beeswax in water and ethanol, and subsequent thermal treatment, which is preferably conducted at 150 °C for 8 hours.

[0009] WO2023 / 187159 describes a method for coating a paper substrate by using a modified cutin extract, wherein said modified cutin extract is obtained by thermal treatment of a raw cutin extract comprising at least 5% by weight of water at a temperature comprised between 40 and 120 °C.

[0010] WO2024 / 023795 relates a to method for hot-melt coating a product by a layer having anti-microbial and / or hydrophobic properties, the layer being obtained by extruding formulations comprising a biobased polymer and up to 10% by weight of active biomolecules, among which "cutin" (described as "non-water-soluble crosslinked polyester") in a vented extruder, preferably under vacuum, at a temperature ranging from 50 to 110°C (see Example 4 and Table 2, at page 21), followed by cooling, chopping into pellets and hot-melting the obtained strand.WO2024 / 161155 describes a method of manufacturing a film-coated substrate by extruding a mixture comprising cutin (a raw cutin extract) and from 1 to 50 wt% of water (5% in Example 1), through a die to obtain a "suitably dried" film, wherein the extrusion is conducted at a temperature comprised between 50 and 150 °C. WO2024 / 161155 reports that the method is not restricted to any particular extruder and may be performed by any extruding machine, but does not mention the use of a venting system or a vacuum suction system.

[0011] Despite the recent advances in the preparation of barrier coatings essentially based on cutin, the removal of the odors generated by such barrier coatings still represents a major challenge in the field. This is particularly relevant in the packaging of food or beverage, as the presence of odors generated by the packaging can alter their organoleptic properties.

[0012] In addition, a need still exists in the art to further improve the barrier properties, particularly water resistance, of modified cutin extracts used to coat paper substrates. It has now been found that a thermal treatment of a raw cutin extract at temperature T in the range 120 °C <T< 150 °C in an apparatus operating at reduced ambient pressure, provides an odorless modified cutin extract with barrier properties that are improved respect to a raw cutin extract treated at the same temperature in a closed vessel or non-vented extruder.

[0013] SUMMARYOFTHE INVENTION

[0014] It is therefore an object of the present invention a method for preparing an odorless modified cutin extract comprising:i) feeding a raw cutin extract having a dry content ranging from 30 to 95 wt% (% by weight) into an apparatus;

[0015] ii) carrying out a thermal treatment inside the apparatus, wherein said thermal treatment is carried out at a pressure higher than 10 Pa and lower than the atmospheric pressure, and at a temperature higher than 120 °C and equal to or lower than 150 °C.

[0016] It is another object of the present invention a method for coating a paper substrate comprising:

[0017] i) providing a paper substrate;

[0018] ii) applying to the paper substrate an aqueous barrier coating composition comprising from 10 to 50 wt% (% by weight) of said odorless modified cutin extract (as dry matter).

[0019] It is still another object of the present invention a method for coating a paper substrate comprising:

[0020] i) providing a paper substrate;

[0021] ii) applying to the paper substrate said odorless modified cutin extract by extrusion coating or lamination.

[0022] With the expression "modified cutin extract", we refer to the modification of a raw cutin extract through a thermal treatment. Without wishing to be bound by any theory, it is believed that the thermal treatment allows the regeneration of the cutin biopolyester polymeric network starting from the hydroxyl fatty acids that are the main components of the raw cutin extract.

[0023] DETAILED DESCRIPTION OFTHE INVENTIONPreferably, the method for preparing an odorless modified cutin extract comprises: i) feeding a raw cutin extract having a dry content ranging from 30 to 95 wt% (% by weight) into an apparatus;

[0024] ii) carrying out a thermal treatment inside the apparatus, wherein said thermal treatment is carried out at a pressure higher than 100 Pa and lower than the atmospheric pressure, and at a temperature higher than 120 °C and equal to or lower than 150 °C.

[0025] The raw cutin extract suitable for preparing the modified cutin extract of the present invention can be obtained by any extraction method known in the art for extracting cutin from plant matter.

[0026] As used herein, "plant matter" refers to any portion of a plant that contains cutin including, for example, fruits (in the botanical sense, fruit peels and juice sacs), leaves, stems, barks, seeds, flowers, or any other portion of the plant.

[0027] According to the invention, plant matter can include agricultural by-products such as, for example, tomato peels, grape skins, apple peels, pepper peels, lemon peels, lemon leaves, lime peels, lime leaves, orange peels, orange leaves, orange fruit, clementine leaves, clementine fruit, mandarin leaves, mandarin fruit, pea seeds, grapefruit peels, grapefruit leaves, grapefruit seeds, papaya peels, cherry fruits, cranberry skins, grass clippings.

[0028] The raw cutin extract of the present invention is obtained preferably from tomato, more preferably from waste tomato peels.

[0029] According to the invention, the raw cutin extract obtained from waste tomato peels is a complex mixture of long-chain co-hydroxy acids with typically a 16- or 18-carbonskeleton and their oligomers, whose main component is 10,16-dihydroxyhexadecanoic acid.

[0030] According to the invention, the raw cutin extract is water-based and typically has a dry content ranging from 30to95wt%, preferably from 50to80wt%. In addition, the raw cutin extract typically has a pH ranging from 3 to 6. The raw cutin extract typically has a Brookfield® viscosity (measured on a 31 wt% aqueous solution, at 25 °C and at pH 9) comprised between 10 and 500 mPa*s, preferably between 50 and 200 mPa*s. The method for preparing the odorless modified cutin extract of the present invention comprises a thermal treatment which takes places in an apparatus, wherein said apparatus is a vented extruder or thin-film evaporator.

[0031] The thermal treatment is carried out at a temperature higher than 120 °C and equal to or lower than 150 °C, preferably higher than 120 °C and lower than 140 °C, and at a pressure higher than 10 Pa and lower than the atmospheric pressure, preferably higher than 100 Pa and lower than the atmospheric pressure, more preferably higher than 1,000 Pa, even more preferably higher than 10,000 Pa, and lower than the atmospheric pressure.

[0032] The thermal treatment may be carried out under air atmosphere or under inert atmosphere by introduction of an inert gas into the apparatus.

[0033] With the expression "atmospheric pressure", we refer to the average pressure at mean sea level, which is 101,325 Pa.

[0034] It has been surprisingly found that, when the thermal treatment is conducted at relatively low temperature, if a vacuum suction system is applied, despite shortresidence time inside the apparatus, the obtained modified cutin extract is odorless and provides excellent barrier properties when applied to paper substrates.

[0035] As used herein, "thermal treatment" refers to the application of heat to a raw cutin extract. Heat may be applied by conduction (for example, a heating coil), by convection (for example, heat transfer through a fluid, such as water or air), by induction, and / or by radiation (for example, heat transfer using electromagnetic waves).

[0036] According to one embodiment, the thermal treatment is carried out in a vented extruder.

[0037] Suitable extruders include any device that applies sufficient pressure to push the raw cutin extract through the device. For example, a pump-type extruder, such as a positive displacement piston or a gear pump, can be used. Another example of suitable extrusion equipment is a screw-type extruder which advances the mixture by means of a screw rotating inside a cylinder. A twin-screw extruder in co-rotating or counter-rotating mode, intermeshing or non-intermeshing may be utilized in the method of the invention, but equally a single screw extruder or a multi screw extruder may also be suitable. Preferably the extruder is a twin-screw extruder or a single screw extruder.

[0038] The temperature at which the thermal treatment is carried out may vary depending on the zone of extruder, but also a uniform temperature profile may be used.

[0039] The mixture may be extruded without a die or through a die, preferably a multi-hole die. In general, if a die is present, the shape and size of the orifices of the die fix the cross-sectional shape and size of the extrudate. Although any shape of orifice may beused, i.e. circle, triangle, square, rectangle and star, it is preferred that the extrusion of the mixture is through equiaxial orifices. Equiaxial orifices are orifices that have approximately equal dimensions in all directions. Generally, the orifices are of dimensions ranging from 1.0 to 6.0 mm, preferably from 2.0 to 3.5 mm.

[0040] The vented extruder of the invention comprises at least one vent, preferably from one to seven vents. Said at least one vent operates at reduced pressure (i.e., at a pressure higher than 100 Pa and lower than the atmospheric pressure, preferably higher than 1,000 Pa and lower than the atmospheric pressure), which is generated through a vacuum suction system comprising a vacuum pump.

[0041] According to another embodiment, the thermal treatment is carried out in a thin-film evaporator.

[0042] Suitable thin-film evaporators, also known as thin-layer evaporators, include falling film evaporators, rising film evaporators, wiped film evaporators, short-path evaporators, flash evaporators, agitated thin film evaporators, or wiped-film short path (WFSP) evaporators.

[0043] Ina thin-film evaporator, a thin film of a product to be distilled is formed on a hot inner surface of the evaporator by continuously applying the product to be distilled on its inner surface. The thin-film evaporator is usually equipped with a cylindrical heated body and a rotor which helps to evenly distribute the product as a thin film to be distilled over the evaporator's inner surface. As the product spirals down the wall, the high rotor tip speed generates highly turbulent flow resulting in the formation of waves and creating optimal heat flux and mass transfer conditions. Subsequently, volatile components are quickly evaporated via conductive heat transfer and thevapors are directed to a condenser, while non-volatile components are discharged at an outlet.The thin-film evaporator of the invention operates at reduced pressure (i.e., at a pressure higher than 10 Pa and lower than the atmospheric pressure, preferably higher than 100 Pa and lower than the atmospheric pressure, more preferably higher than 1,000 Pa and lower than the atmospheric pressure).

[0044] Typically, the odorless modified cutin extract obtained according to the method of the invention has a residual moisture content ranging from 0 to 10 % by weight, preferably from 0.5 to 5 % by weight.

[0045] Typically, the odorless modified cutin extract obtained according to the method of the invention has a dry content ranging from 70 to 100 wt%, preferably from 80 to 95 wt%.

[0046] Typically, the odorless modified cutin extract obtained according to the method of the invention is in the form of a liquid paste or a solid and can be comminuted in order to reduce / optimize its dimensions.

[0047] Comminuting can be accomplished by using standard equipment known in the art. Typical comminuting devices are air-swept impact mills, ball mills, hammer mills, and disk mills. This is preferably done in an air-swept impact mill because the other mills, i.e. ball mills, tend to overmill the product into fine particles that are dusty. In addition, an air-swept impact mill will dry the extruded material, if necessary, by blowing hot air across the mill.

[0048] Another method for comminuting the odorless modified cutin extract is to cut it with a die-faced cutter used in combination with the vented extruder. A die-face cutter operates by moving a blade across a stationary die or by moving a die across thestationary blade. Thus, the odorless modified cutin extract obtained after the extrusion is cut as it comes out through the plurality of orifices in the die.

[0049] The size of the orifice fixes two of the dimensions of the product. Therefore, it is only necessary to cut the filaments to shorten the length. Typically, the extruded product is cut to a length / dia meter ratio of from 0.2 to 3, preferably to a length / diameter ratio of from 1 to 2.

[0050] It may be advantageous to dry the odorless modified cutin extract obtained from the described process. The drying can be accomplished with standard drying equipment and methods known in the art. Typical driers include those commonly used in the art, for example belt driers and fluid bed driers.

[0051] Before being feeded into the extruder, the raw cutin extract may be mixed with additives that are customary in the field of extrusion, such as plasticizers, waxes, rosins, colourants, anti-blocking agents, processing aids, or hygroscopic salts.

[0052] Solvents selected among water, organic solvents or mixtures thereof may be added to the raw cutin extract before feeding it into the extruder. Preferably the solvent which can be added is water.

[0053] The thermal treatment for preparing the odorless modified cutin extract of the present invention may be carried out in the presence of a catalyst. Non-limiting examples of the catalysts that may be used include, for example, titanium tetraisopropoxide, dibutyltin oxide, tin octanoate, aluminum isopropoxide, zirconium acetylacetonate, zirconium tetrabutoxide, tin(ll) n-octanoate, tin(ll) 2-ethylhexanoate, tin(ll) laurate, dibutyltin dichloride, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin dimaleate, dioctyltin diacetate, antimony triethoxide or boronicacid derivatives, such as pyridineboronic acid. Preferably, the catalyst is zirconium acetylacetonate.

[0054] The thermal treatment for preparing the odorless modified cutin extract of the present invention may be carried out under acidic (i.e., at a pH ranging from 2 to 7, preferably from 3 to 7) or alkaline conditions (i.e., at a pH ranging from 7 to 12, preferably from 7 to 11). Preferably, the thermal treatment is carried out under acidic conditions.

[0055] When the thermal treatment is carried out under acidic conditions, the thermal treatment is started immediately, as the raw cutin extract typically already has an acidic pH, ranging from 3 to 6. After the end of the thermal treatment, the obtained modified cutin extract is treated with a base until a pH ranging between 7 and 11 is reached. The base is preferably ammonia, an inorganic base or an amine. More preferably, the base is ammonia.

[0056] When the thermal treatment is carried out under alkaline conditions, before starting the thermal treatment the raw cutin extract is treated with a base until a pH ranging between 7 and 11 is reached. The base is preferably ammonia, an inorganic base or an amine. More preferably, the base is ammonia.

[0057] According to one embodiment, the odorless modified cutin extract obtained after the thermal treatment is dispersed in water to obtain an aqueous barrier coating composition which is suitable for being applied to a paper substrate.

[0058] The aqueous barrier coating composition of the invention comprises from 10 to 50 wt%, preferably from 20 to 40 wt% of an odorless modified cutin extract (as dry matter).The aqueous barrier coating composition of the invention has a solids content from 10 to 60 wt%.

[0059] The aqueous barrier coating composition of the invention can further contain customary additives in the field of paper coating, such as pigments, binders, waxes, fatty acid metal salts, thickeners, antiblocking agents, dyes, flow control agents or defoamers.

[0060] Suitable pigments include, for example, metal salt pigments such as, for example, calcium sulfate, calcium aluminate sulfate, barium sulfate, magnesium carbonate and calcium carbonate. Calcium carbonate may be natural ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), lime or chalk. Further suitable pigments include, for example, silica, alumina, aluminum hydrate, silicates, titanium dioxide, zinc oxide, kaolin, argillaceous earths, talc or silicon dioxide.

[0061] Suitable binders include both synthetic and natural binders. Suitable synthetic binders include, but are not limited to, (meth)acrylic (co)polymers, ethylene-(meth)acrylic copolymers, styrene-(meth)acrylic copolymers and polyvinyl alcohol. Suitable natural binders include, but are not limited to, carboxymethyl cellulose, starch and starch derivatives.

[0062] Suitable starch includes natural starch, such as potato, wheat, maize, rice or tapioca starch.

[0063] Suitable starch derivatives include, but are not limited to, chemically modified starch, such as for example hydroxyethyl starch, hydroxypropyl starch or phosphate starch. Preferred starch and starch derivatives include degraded starch or degraded starch derivatives having a molecular weight Mn of 500 to 30,000 Da, more preferably from500 to 20,000 Da. Said degraded starch and starch derivatives are obtained from the degradation of natural starch or chemically modified starch. Said degradation may be oxidative, thermal, acidic or enzymatic degradation.

[0064] Suitable waxes include, but are not limited to, polyethylene, polypropylene, paraffins, amides, waxes of vegetable of origin, carnauba waxes, or mixtures thereof.

[0065] Suitable fatty acid metal salts include divalent or trivalent fatty acid metal salts. In the fatty acid metal salts, the metal is selected from, calcium, zinc, magnesium, beryllium, barium, strontium, aluminum, iron, gallium, or indium. Preferably the metal is selected from calcium, magnesium, or zinc.

[0066] In the fatty acid metal salts, the fatty acid is a linear or branched, saturated or unsaturated monocarboxylic acid having from 4 to 40 carbon atoms, preferably from 10 to 28 carbon atoms, more preferably from 14 to 20 carbon atoms. Suitable fatty acids include, but are not limited to, stearic acid, oleic acid, palmitic acid, linoleic acid, linolenic acid, arachidonic acid, icosapentaenoic acid, docosahexaenoic acid, montanic acid, myristic acid, or lauric acid. Preferably the fatty acid is stearic acid. The divalent or trivalent fatty acid metal salt is preferably a divalent fatty acid metal salt.

[0067] The divalent or trivalent fatty acid metal salt is preferably selected from calcium stearate, magnesium stearate, or zinc stearate. More preferably, the divalent or trivalent fatty acid metal salt is calcium stearate.

[0068] The aqueous barrier coating composition of the invention is usually applied to the paper substrate at a coat weight from 0.5 to 40 g / m2, preferably from 1 to 25 g / m2.Suitable paper substrates typically have a grammage from 25 to 800 g / m2, preferably from 30 to 700 g / m2, more preferably from 40 to 500 g / m2.

[0069] The application of the aqueous barrier coating composition of the invention to the paper substrate can be carried out for example by roller coating, spray coating, curtain coating, blade coating, immersion coating, gravure roll coating, reverse direct gravure coating, rod coating, soft-tip blade coating, jet coating and / or combinations thereof.

[0070] According to another embodiment, the odorless modified cutin extract is applied to a paper substrate by extrusion coating or lamination. Extrusion coating refers to the process in which an extruder forces the odorless modified cutin extract through a die onto a moving paper substrate. Lamination refers to application of the odorless modified cutin extract to a paper substrate using heat pressing.

[0071] The present invention is further illustrated by the following examples.

[0072] EXAMPLES

[0073] Comparative Example A

[0074] A raw cutin extract (dry content: 65 wt%) was fed into an ICMA MCM 25 HT extruder (commercially available from ICMA San Giorgio) equipped with two counter rotating screws, not bearing a die nor a die-faced cutter. The extruder was equipped with 3 vents, two operating at atmospheric pressure and one operating under vacuum pressure in the range 80 kPa. The speed of the screws was at 150 rpm.

[0075] The internal maximum temperature (reached in at least one zone of the extruder) is 110°C.

[0076] Example 1A raw cutin extract (dry content: 65 wt%) was fed into an ICMA MCM 25 HT extruder (commercially available from ICMA San Giorgio) equipped with two counter rotating screws, not bearing a die nor a die-faced cutter. The extruder was equipped with 3 vents, two operating at atmospheric pressure and one operating under vacuum pressure in the range 70-90 kPa. The speed of the screws was at 150 rpm.

[0077] The internal maximum temperature (reached in at least one zone of the extruder) is 140°C.

[0078] Applicative tests

[0079] The modified cutin extracts obtained after the extrusion were dispersed in water to obtain aqueous barrier coating compositions. Each composition has a solids content of 32 wt%.

[0080] The obtained aqueous barrier coating compositions were applied at a coat weight of 7.0 g / m2on a paper substrate having a grammage of 80 g / m2.

[0081] Water resistance of the coated paper substrates was evaluated.

[0082] Liquid water resistance was tested using the Cobb method, as described by TAPPI Method T 441-om. The test time was 600 s. This method determines the amount of liquid water absorbed by paper or paperboard in a specific time under standardized conditions.

[0083] Odor assessment test was conducted on the coated paper, sealed in a polypropylene plastic bag for 24 hours at room temperature.

[0084] Table 1 reports the results of the Cobb test and odor assessment test for aqueous barrier coating compositions previously prepared and applied at a coat weight of 7.0 g / m2.Table 1

[0085]

[0086] *Comparative

[0087] nd = coating film was completely removed, when the coated paper substrate was contacted with water

[0088] The results reported in Table 1 show that conducting the thermal treatment at a temperature of 140°C is more effective for removing the odor. The aqueous barrier coating composition of the invention provided also improved water resistance properties of the paper substrate, when compared with a modified cutin extract obtained after thermal treatment at 110 °C (Comparative Example A).

Claims

CLAIMS1. A method for preparing an odorless modified cutin extract comprising:i) feeding a raw cutin extract having a dry content ranging from 30 to 95 wt% (% by weight) into an apparatus;ii) carrying out a thermal treatment inside the apparatus, wherein said thermal treatment is carried out at a pressure higher than 10 Pa and lower than the atmospheric pressure, and at a temperature higher than 120 °C and equal to or lowerthan 150 °C.

2. The method for preparing an odorless modified cutin extract according to claim 1, wherein the apparatus is a vented extruder or a thin-film evaporator.

3. The method for preparing an odorless modified cutin extract according to claim 1, wherein the thermal treatment is carried out at a pressure higher than 100 Pa and lower than the atmospheric pressure.

4. The method for preparing an odorless modified cutin extract according to claim 1, wherein the thermal treatment is carried out at a temperature higherthan 120 °C and lower than 140 °C.

5. The method for preparing an odorless modified cutin extract according to claim 1, wherein the raw cutin extract has a dry content ranging from 50 to 80 wt%.

6. A method for coating a paper substrate comprising:i) providing a paper substrate;ii) applying to the paper substrate an aqueous barrier coating composition comprising from 10 to 50 wt% (% by weight) of an odorless modified cutin extract (as dry matter) prepared according to the method of claim 1.

7. The method for coating a paper substrate according to Claim 6, wherein the aqueous barrier coating composition further comprises pigments, binders, waxes, fatty acid metal salts, thickeners, antiblocking agents, dyes, flow control agents or defoamers.

8. The method for coating a paper substrate according to Claim 6, wherein the aqueous barrier coating composition comprises from 20 to 40 wt% of odorless modified cutin extract (as dry matter).

9. The method for coating a paper substrate according to claim 6, wherein the aqueous barrier coating composition has a solids content from 10 to 60 wt%.

10. A method for coating a paper substrate comprising:i) providing a paper substrate;ii) applying to the paper substrate an odorless modified cutin extract prepared according to the method of claim 1 by extrusion coating or lamination.

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