Patent Application
20250215648
The present invention relates to a method for coating a paper substrate to provide said paper substrate with improved barrier properties.
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.
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.
In this context, compounds extracted from plant matter and their derivatives may represent an attracting alternative.
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.
From a chemical point of view, cutin is a polymeric network of polyhydroxylated C16 and C18 fatty acids cross-linked by ester bonds. However, when extracted from plant matter (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.
G. Tedeschi et al., ACS 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 sodium alginate, unsaturated and polyhydroxylated fatty acids derived from the agro-waste of tomato peeling industrial process, beeswax in water and ethanol, and subsequent thermal treatment.
However, in the prior art there is no reference to the use of a modified cutin extract in the preparation of aqueous barrier coating compositions for a paper substrate.
It is therefore an object of the present invention a method for coating a paper substrate comprising:
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 formation of a polyester derived from the hydroxyl fatty acids that are the main components of the raw cutin extract.
The method for coating a paper substrate may comprise:
Preferably, the method for coating a paper substrate comprises:
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.
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.
According to the invention, plant matter can include agricultural waste 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.
The raw cutin extract of the present invention is obtained preferably from tomato, more preferably from waste tomato peels.
According to the invention, the raw cutin extract obtained from waste tomato peels is a complex mixture of long-chain w-hydroxy acids with typically a 16- or 18-carbon skeleton and their oligomers, whose main component is 10,16-dihydroxyhexadecanoic acid.
According to the invention, the raw cutin extract is water-based and typically has a dry content ranging from 30 to 95 wt %, preferably from 50 to 80 wt %. In addition, the raw cutin extract typically has a pH ranging from 3 to 6. The raw cutin extract 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 process for preparing the modified cutin extract of the present invention comprises a thermal treatment at a temperature comprised between 4° and 120° C., preferably between 80° C. and 100° C.
Advantageously, the process for preparing the modified cutin extract of the present invention comprises a thermal treatment at a temperature comprised between 60° C. which is the approximate melting temperature of dry raw cutin extract, and 100° C.
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), and/or by radiation (for example, heat transfer using electromagnetic waves).
Solvents selected among water, organic solvents or mixtures thereof can be added in the process for preparing the modified cutin extract of the present invention. Preferably the solvent which can be added is water.
The solvent used in the process may be removed by distillation under reduced pressure.
The thermal treatment for preparing the modified cutin extract of the present invention is conducted at atmospheric pressure or under reduced pressure (typically between 0.001 to 0.6 bar). Preferably, the thermal treatment is conducted at atmospheric pressure.
The thermal treatment for preparing the 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 (II) n-octanoate, tin (II) 2-ethylhexanoate, tin (II) laurate, dibutyltin dichloride, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin dimaleate, dioctyltin diacetate, antimony triethoxide or boronic acid derivatives, such as pyridineboronic acid. Preferably, the catalyst is zirconium acetylacetonate.
The thermal treatment for preparing the modified cutin extract of the present invention can 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.
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.
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.
The process for preparing the modified cutin extract of the present invention comprises a thermal treatment that may last from 2 to 72 hours.
The process for preparing the modified cutin extract of the present invention comprises a thermal treatment that preferably lasts from 2 to 24 hours, more preferably from 3 to 15 hours.
The modified cutin extract of the present invention is water-based and typically has a dry content ranging from 10 to 60 wt %, preferably from 20 and 40 wt %, and pH comprised between 6 and 11, preferably between 7 and 10. The modified cutin extract has a Brookfield® viscosity (measured on a 31 wt % aqueous solution, at 25° C. and at pH 9) comprised between 100 and 3000 mPa*s, preferably between 300 and 1500 mPa*s.
The aqueous barrier coating composition of the invention can further contain customary additives in the field of paper coating, such as pigments, binders, waxes, thickeners, antiblocking agents, dyes, flow control agents or defoamers.
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.
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. Suitable starch includes natural starches, such as potato, wheat, maize, rice or tapioca starch. Suitable starch derivatives include, but are not limited to, chemically modified starches, such as for example hydroxyethyl starch, hydroxypropyl starch or phosphate starch.
Preferred starch and starch derivatives include degraded starch and degraded starch derivatives having a molecular weight Mn of 500 to 30,000 Da, more preferably from 500 to 20,000 Da. Said degraded starches are obtained from the degradation of natural starch or chemically modified starch.
Suitable waxes include, but are not limited to, polyethylene, polypropylene, paraffins, amides, waxes of vegetable of origin, carnauba waxes, or mixtures thereof.
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.
The present invention is further illustrated by the following examples.
The raw cutin extracts used in the examples are obtained from waste tomato peels and have a Brookfield® viscosity (measured on a 31 wt % aqueous solution, at 25° C. and at pH 9) of 100 mPa*s.
Raw cutin extract (50-80 wt % dry content, pH 3-6) polymerization reaction was carried out under vacuum evaporation (100-300 mbar) in a four-necked round-bottom reactor equipped with a mechanical IKA stirrer, thermometer and fitted with a Dean Stark adapter and a condenser for reflux. The reaction was carried out at 90° C. until a very high viscosity product (>50,000 mPas) was achieved with a dry content up to 99.9%. The polymerization reaction was stopped when the product started climbing the impeller (6 h after whole water evaporation). The obtained modified cutin extract was cooled down and an ammonia solution was added until an aqueous solution of modified cutin extract having a 25-35 wt % dry content and pH 7-9 was obtained. Filtration was performed using a 100 μm filter cloth. Brookfield® viscosity (31 wt % aqueous solution, at 25° C. and pH 9) of the modified cutin extract: 700 mPa*s.
Raw cutin extract (50-80 wt % dry content, pH 3-6) polymerization reaction was carried out under atmospheric pressure in a four-necked round-bottom reactor equipped with a mechanical IKA stirrer, thermometer and a condenser for reflux. The reaction was carried out at 90° C. for 10 h. The modified cutin extract was cooled down and an ammonia solution was added until an aqueous solution of modified cutin extract having a 25-35 wt % dry content and pH 7-9 was obtained. Filtration was performed using a 100 μm filter cloth. Brookfield® viscosity (31 wt % aqueous solution, at 25° C. and pH 9) of the modified cutin extract: 850 mPa*s.
Raw cutin extract (50-80 wt % dry content, pH 3-6) polymerization reaction was carried out under atmospheric pressure in a four-necked round-bottom reactor equipped with a mechanical IKA stirrer, thermometer and a condenser for reflux. Before starting the heating, raw cutin extract was treated with ammonia to reach a pH of 9.5. The reaction was carried out at 90° C. for 15 h. The modified cutin extract was cooled down and an aqueous solution of modified cutin extract having a 25-35 wt % dry content and pH 7-9 was obtained. Filtration was performed using a 100 μm filter cloth. Brookfield® viscosity (31 wt % aqueous solution, at 25° C. and pH 9) of the modified cutin extract: 450 mPa*s.
Raw cutin extract (50-80 wt % dry content, pH 3-6) polymerization reaction was carried out under atmospheric pressure in a four-necked round-bottom reactor equipped with a mechanical IKA stirrer, thermometer and a condenser for reflux. The reaction was carried out at 70° C. for 15 h. The modified cutin extract was cooled down and an ammonia solution was added until an aqueous solution of modified cutin extract having a 25-35 wt % dry content and pH 7-9 was obtained. Filtration was performed using a 100 μm filter cloth. Brookfield® viscosity (31 wt % aqueous solution, at 25° C. and pH 9) of the modified cutin extract: 800 mPa*s.
Acrylic emulsion copolymer derived from ethylhexyl acrylate, methyl methacrylate and methacrylic acid, a synthetic polymer commonly used to improved water resistance of paper substrates.
Avedex® 125 HI 12, dextrin derived from potato starch, commercially available from Avebe, commonly used to improve oil resistance of paper substrates.
Raw cutin extract (50-80 wt % dry content, pH 3-6) obtained from waste tomato peels.
The modified cutin extracts prepared in the previous examples were used to prepare aqueous barrier coating compositions.
The obtained aqueous barrier coating compositions were applied at a coat weight of 5.5 g/m2 on a paper substrate having a grammage of 80 g/m2.
Water resistance and oil resistance of the coated paper substrates were evaluated.
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.
Oil absorption capacity was tested using the KIT method, according to TAPPI Test Method UM 557. In this test numbered (from 1 to 16) solutions of increasing hydrophobicity are applied onto the paper substrate. The highest numbered solution that does not stain the surface is reported as result of the KIT test.
Heat sealability of the coated paper substrates was also evaluated.
Heat sealability was evaluated using a Gandus DD 100-200 ATR 121-141, an automatic sealing machine in compliance with DIN 58953 p-7, with a maximum heat sealing area of 196 mm×13 mm and a heat sealing temperature range within 50-150±1° C. The testing was conducted contacting two coated paper samples (50 mm×50 mm) at a given temperature for 1 second. Then the heat sealing strengths were visually verified peeling off the two layers of the seal after cooling down at room temperature. The minimum temperature at which heat sealing occurs is reported.
Table 1 reports the results of the Cobb test and KIT test for aqueous barrier coating compositions containing the modified cutin extract of the invention, compared with aqueous barrier coating compositions containing an acrylic emulsion copolymer (Comparative Example 1), a dextrin derived from potato starch (Comparative Example 2), or a raw cutin extract (Comparative Example 3).
Table 2 reports the results of the heat sealability test for aqueous barrier coating compositions containing the modified cutin extract of inventive Examples 2 and 3, compared with aqueous barrier coating compositions containing an acrylic emulsion copolymer (Comparative Example 1), a dextrin derived from potato starch (Comparative Example 2), or a raw cutin extract (Comparative Example 3).
The results reported in Table 1 show that, while raw cutin extract (Comparative Example 3) has no significant effect on water and oil resistance properties, the modified cutin extracts of the present invention (Examples 1-4) provide the treated paper substrate with excellent water and oil resistance.
When compared with a synthetic polymer commonly used as waterproofing agent (Comparative Example 1), the modified cutin extracts of the present invention (Examples 1-4) allow to obtain a paper substrate that has a similar water resistance, but a significantly improved oil resistance.
When compared with a dextrin derived from potato starch (Comparative Example 2), the modified cutin extracts of the present invention (Examples 1-4) allow to obtain a paper substrate with improved oil resistance and significantly improved water resistance. This result is particularly remarkable, as paper substrates coated with natural polymers (such as starch) are typically affected by poor water resistance.
The results reported in Table 2 show that the modified cutin extracts of the present invention (Examples 2-3) allow to obtain a heat sealable paper substrate, just as it can be obtained by using a synthetic polymer (Comparative Example 1).
Instead, aqueous barrier coating compositions based on a dextrin derived from potato starch (Comparative Example 2) or a raw cutin extract (Comparative Example 3) did not allow to obtain a heat sealable paper substrate.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102022000006464 | Apr 2022 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/058459 | 3/31/2023 | WO |
