Composite mixture based on hemicellulose esters, process for obtaining it, and testing the specific properties of packaging for AGRI-food products

Abstract

The invention refers to a composite mixture based on xylan hemicelulose esters, with improved thermal stability and hydrophobic properties and a method for obtaining it. The composite mixture, according to the invention, is used for surface treatment of paper for agri-food products packaging. The preparation process of the composite mixture involves, in the first stage, obtaining hemicellulose esters of the xylan type through an acetylation reaction between native xylan, ionic liquids based on imidazolium salts, and acetic anhydride. These are then mixed with other natural polymers (chitosan) and / or metal oxide nanoparticles (ZnO and CuO). The mixture is homogenized at a temperature of 20°C for 12...24 hours using magnetic stirring, and the specific properties of the food packaging are tested by applying the mixture as a layer / film with a mass of 2.5 - 5 g / m2 on each side of the paper / cardboard support, followed by drying for 10 minutes. The paper / cardboard treated with this composite mixture ensures protection of agri-food products against bacterial action and provides resistance to moisture, water vapor, oxygen, oils, and fats

Description

[0001] 1. DESCRIPTION OF INVENTION

[0002] TITLE: COMPOSITE MIXTURE BASED ON HEMICELLULOSE ESTERS, PROCESS FOR OBTAINING IT, AND TESTING THE SPECIFIC PROPERTIES OF PACKAGING FOR AGRI-FOOD PRODUCTS

[0003] The present invention relates to a composite mixture based on natural polymers obtained through special processes, which, after being applied as a film / layer on the surface of paper or cardboard, provides these materials with suitable properties for use in contact with food.

[0004] Considering their advantages (biodegradability, biocompatibility, etc.), natural polymers have attracted significant interest for use as films or coating layers for packaging intended for food products. Generally, films made from natural polymers exhibit barrier properties against air, water, water vapor, oils, and fats, contributing to maintaining the quality and extending the shelf life of food products. Compared to synthetic polymers, packaging materials based on polymers from renewable resources offer important environmental benefits, such as a high degree of biodegradability, recyclability, and reusability [1,2]. Additionally, natural polymers serve as an effective matrix for incorporating additives to improve other specific functional properties (such as resistance to certain bacterial attacks, antioxidant properties, etc.). Most applications of natural polymers in the field of food packaging are known for their use as individual films / coatings to protect agri-food products such as vegetables or fruits, while their applications for treating paper intended for food packaging have been relatively little studied and reported [1].

[0005] The currently known technological solutions in the field of food packaging papers are based on laminating paper with plastic or aluminum films, or coating with synthetic polymer dispersions. These methods have the following disadvantages:

[0006] • Complex and high-cost technologies;

[0007] • The resulting papers have a low degree of recyclability and reusability in the paper and cardboard manufacturing process;

[0008] • Negative environmental impact due to the low degree of biodegradability and compostability.

[0009] The problem addressed by the proposed invention lies in the use of polysaccharides of the hemicellulose type to obtain mixtures with suitable properties for the surface treatment of paper for packaging agri-food products. Polysaccharides represent a broad class of natural polymers with the potential to replace synthetic polymers, being non-toxic, biodegradable, with good film-forming capacity and protection against oxygen Or liquids. Hemicelluloses are the second largest group of polysaccharides after cellulose, found in plant resources and with significant potential for valorization in obtaining high-value-added materials [3-6]. Among hemicelluloses, xylan holds the largest share, being widely available in hardwood (approx. 30%) and softwood (10%), as well as in agricultural residues or as a by-product of the dissolving pulp manufacturing [7-9],

[0010] The main disadvantages of the widespread use of hemicelluloses, in general, are related to their highly hydrophilic nature, caused by the presence of a large number of free hydroxyl groups distributed along the polymer chain of the structural unit

[0010] , Therefore, in their native state, xylan- type hemicellulose exhibits low resistance to water, water vapor, oxygen, or microbial attack [11- 14]. However, the presence of hydroxyl groups in the chemical structure of xylan facilitates its chemical modification through various reactions that can introduce hydrophobic functional groups, thus transforming xylan-type hemicellulose into a compound with new functionalities and extending its range of applications, including in the field of food packaging (in the form of edible films or for surface treatment of food packaging paper).

[0011] There are known and reported results for a variety of chemical reactions applied for the functionalization / modification of hemicelluloses, such as: oxidation, reduction, esterification (acetylation, propionylation, benzylation, or cross-linking), or etherification (cationization, carboxymethylation, or alkoxylation) [15-21]. These studies have demonstrated that hemicelluloses can be esterified under homogeneous conditions, achieving a high degree of substitution. However, these reactions often use organic solvents based on dimethylformamide or pyridine, which have high toxicity, thus limiting the widespread application of these methods. Therefore, there is a need to identify and use methods that can achieve similar results with a reduced environmental impact [22, 23].

[0012] Ionic liquids are compounds composed exclusively of ions and their combinations, which, unlike salts, exist in liquid form at room temperature even without the presence of a molecular solvent. Ionic liquids (ILs) are considered environmentally friendly alternatives (“green approach”) for modifying polysaccharides, as they exhibit low vapor pressure, non-flammable properties, and high recycling potential. The use of ionic liquids gained significant interest among researchers around the 1960s. Very few data are known regarding the complete esterification of hemicellulose using ionic liquids, with most results reported concerning their use in dissolving and chemically modifying cellulose.

[0013] The composite mixture, according to the invention, aims to eliminate the aforementioned disadvantages by incorporating xylan hemicellulose esters obtained through the esterification reaction between xylan and l-Ethyl-3-methylimidazolium acetate, which provides improved barrier properties against water, water vapor, oxygen, oils, fats, thermal stability, and protection against microbial attack.

[0014] The advantages of the present invention are as follows:

[0015] • The production of natural polymer derivatives (xylan hemicellulose esters) through esterification reactions with ionic liquids, in accordance with environmental protection restrictions, capable of replacing synthetic polymers in formulations for producing food packaging films or surface treatment mixtures for paper used in agri-food product packaging.

[0016] • A high degree of recyclability and biodegradability upon contact with soil.

[0017] • The composite mixture applied to the surface of the paper in quantities of 2.5 - 5 g / m2provides protection for packaged food products against water and water vapor, oxygen, oils, fats, and microbial attacks.

[0018] The process of obtaining and testing the composite mixture, according to the invention, involves the following steps:

[0019] 1. Obtaining xylan hemicellulose esters.

[0020] 2. Dispersing the xylan hemicellulose esters and obtaining the composite mixture.

[0021] 3. Applying the dispersion and composite mixture to the surface of the paper / cardboard.

[0022] 1. Obtaining xylan hemicellulose esters - Acetylation of xylan hemicellulose with l-Ethyl-3- methylimidazolium acetate [EmimOAc]

[0023] For chemical modification, xylan hemicellulose from beech wood is used, following this procedure: a solution of xylan and l-Ethyl-3-methylimidazolium acetate at a concentration of 4.5% to 5% is stirred for 30 to 40 minutes at a temperature of 80°C. Then, acetic anhydride is added in a molar ratio of 1 :20 relative to xylan. Stirring continues at the same temperature for an additional 25 to 30 minutes. The resulting mixture is precipitated in 100 to 250 ml of 96% ethyl alcohol and then washed with distilled water to remove residual reaction products. The xylan acetate ester is dried in an oven at 40 to 50°C for 20 to 24 hours.

[0024] Structural analysis of the FTIR and 1H NMR spectra of xylan acetate reveals the presence of intense absorption bands at 1742 and 1738 cm1attributed to ester groups (C=C and C=O), as well as a strong signal at 2.0 ppm specific to protons from acetyl groups (-CH3-CO-), indicating the acetylation of xylan hemicellulose (Fig. 1 and 2). Thermogravimetric analysis shows improved thermal stability of xylan acetate compared to native xylan due to the decrease in the number of free OH groups remaining after acetylation, which are oxidized during heating (Fig. 3).

[0025] 2. Dispersion of Xylan Hemicellulose Esters and the Obtaining of the Composite Mixture

[0026] The xylan hemicellulose acetate is introduced into distilled water in a proportion of 2.5% to 3% by mixing and maintaining under magnetic stirring at 1000 1500 rpm for 12 to 24 hours until a uniform dispersion is obtained. The resulting dispersion can be used as is by applying it in the form of a film / layer to the surface of the paper or cardboard (option 0), or it can be used as a polymer matrix for obtaining the composite mixture in the following options:

[0027] Variant 1: Mixture of Xylan Acetate and Chitosan (1:1)

[0028] (a) The xylan acetate dispersion is obtained according to the description in point 2. (b) The chitosan dispersion is prepared in a 1% acetic acid solution by magnetic stirring at 1500 rpm for 24 hours.

[0029] (c) Appropriate volumes of xylan acetate dispersion are dosed into the chitosan dispersion under continuous stirring (the pH value must be 5 for both dispersions before mixing) until a 1 : 1 ratio between the two components is achieved, and stirring continues for 24 hours at 1500 rpm.

[0030] Variant 2: Mixture of Xylan Acetate and ZnO nanoparticles

[0031] (a) The xylan acetate dispersion is obtained according to the description in point 2 (variant 0)

[0032] (b) Appropriate volumes of zinc oxide nanoparticle dispersion are dosed into the xylan acetate dispersion under continuous stirring, ensuring that concentrations of 10% to 20% ZnO relative to xylan acetate are achieved. The stirring of the mixture continues for 8 to 12 hours at 1500 rpm

[0033] Variant 3: Mixture of Xylan Acetate and CuO nanoparticles

[0034] (a) The xylan acetate dispersion is obtained according to the description in point 2

[0035] (b) A dispersion of 10% CuO nanoparticles in water is prepared under continuous stirring for 1 to 2 hours at 1000 rpm.

[0036] (c) Appropriate volumes of the CuO nanoparticle dispersion are dosed into the xylan acetate dispersion under continuous stirring, ensuring that concentrations of 10% to 20% CuO relative to xylan acetate are achieved. The stirring of the mixture continues for 8 to 12 hours at 1500 rpm.

[0037] 3. Application of the Dispersion and Composite Mixture to the Surface of the Paper / C ardboard

[0038] The composite mixtures obtained according to the above options are applied to the surface of the paper or cardboard in a uniform layer with a mass of 2.5 to 5 g / m2on each side of the paper / cardboard. This is done through manual dosing and leveling on the paper surface using an automatic system with a Meyer rod with a diameter of 6 mm and a drawn down speed of 120 to 150 mm / s (Figure 4).

[0039] After application, the coated paper is air-dried for 10 minutes and then placed in an oven at 50 to 60°C. After drying, the treated paper is maintained in a conditioned atmosphere at 23 °C and 50% relative humidity. The performance of the composite mixture, as the subject of this invention, in terms of its use for treating paper for food packaging, can be determined by conducting the following analyses:

[0040] Determination of water barrier properties: water contact angle measurement.

[0041] Determination of oil and grease barrier properties: KIT test.

[0042] Determination of air permeability.

[0043] Testing of antimicrobial and antifungal activity.

[0044] Global migration testing of components in isooctane.

[0045] The quality characteristics of papers coated with composite mixtures based on xylan hemicellulose esters, obtained according to the previous description, are presented in the following table:

[0046] References Johansson, C.; Brass, J.; Mondragon, L; Nechita, P.; Plackett, D.; Simon, P.; Gregor Svetec, D.; Virtanen, S.; Baschetti, M.G.; Breen, C.; et al. Renewable fibers and bio-based materials for packaging applications — A review of recent developments. BioResources 2012, 7, 2506 2552. Rastogi, K.V.; Samyn, P. Bio-Based Coatings for Paper Applications. Coatings 2015, 5, 887-930. doi: 10.3390 / coatings5040887. Ramosa, A.; Sousaa, S.; Evtuguinb, D.; Gamelasd, J. Functionalized xylans in the production of xylan-coated paper laminates. React. Funct. Polym. 2017, 117, 89-96. Gao, Y.; Guo, M.; Wang, D.; Zhao, D.; Wang, M. Advances in extraction, purification, structural characteristics and biological activities of hemicelluloses: A review. Int. J. Biol. Macromol. 2023, 225, 467-483. Liu, G.S.; Shi, K.; Sun, H. Research Progress in Hemicellulose-Based Nanocomposite Film as Food Packaging. Polymers 2023, 15, 4. Zhang, X.Q.; Luo, W.H.; Xiao, N.Y.; Chen, M.J.; Liu, C.F. Construction of functional composite films originating from hemicellulose reinforced with poly(vinyl alcohol) and nano-ZnO. Cellulose 2020, 27, 1341-1355. Ebringerova, A.; Heinze, T. Xylan and xylan derivatives — Biopolymers with valuable properties, 1. Naturally occurring xylans structures, isolation procedures and properties. Macromol. Rapid Commun. 2000, 21, 542-556. Girio, F.M.; Fonseca, C.; Carvalheiro, F.; Duarte, L.C.; Marques, S.; Bogel-Lukasik, R. Hemicelluloses for fuel ethanol: A review. Bioresour. Technol. 2010, 101, 4775 4800. Mikkonen, K.S.; Tenkanen, M. Sustainable food-packaging materials based on future biorefinery products: Xylans and mannans. Trends Food Sci. Technol. 2012, 28, 90. Cheng, H.N.; Biswas, A.; Sanghoon, K.; Carlucio, R.; Furtado, A.R. Synthesis and Characterization of Hydrophobically Modified Xylans. Polymers 2021, 13, 291. Nechita, P.; Roman, M.; Ciolacu, F. Xylan Hemicellulose: A Renewable Material with Potential Properties for Food Packaging Applications. Sustainability 2021, 13, 13504. https: / / doi.org / 10.3390 / sul32413504. Bello, F., Chimpango, A. Tailor-Made Conversion of Mango Seed Husks to Obtain Hemicellulose Suitable for the Production of Thermally Stable Films. Waste and Biomass Valorization 2022, 13(1), 719-737 Yang, Y.C.; Mei, X.W.; Hu, Y.J.; Su, L.Y.; Bian, J.; Li, M.F.; Peng, F.; Sun, R.C. Fabrication of antimicrobial composite films based on xylan frompulping process for food packaging. Int. J. Biol. Macromol. 2019, 134, 122-130. Lobo, F.C.M.; Franco, A.R.; Fernandes, E.M.; Reis, R.L. An Overview of the Antimicrobial

[0047] Properties of Lignocellulosic Materials. Molecules 2021, 26, 1749. https: / / doi.org / 10.3390 / molecules 26061749. Laine, C.; Harlin, A.; Hartman, J.; Hyvarinen, S.; Kammiovirta, K.; Krogerus, B.; Pajari, H.; Rautkoski, H.; Setala, H.; Sievanen, J.; et al. Hydroxyalkylated xylans — Their synthesis and application in coatings for packaging and paper. Ind. Crops Prod. 2013, 44, 692-704. Ren, J.L.; Peng, X.W.; Zhong, L.X.; Peng, F.; Sun, R.C. Novel hydrophobic hemicelluloses: Synthesis and characteristic. Carbohydr. Polym. 2012, 89, 152-157. Sun, R.; Fang, J.M.; Tomkinson, J.; Hill, C.A.S. Esterification of hemicelluloses from poplar chips in homogeneous solution of N,N-dimethylformamide / lithium chloride. J. Wood Chem. Technol. 1999, 19, 287-306. Alekhina, M., Mikkonen, K.S., Ale'n, R., Tenkanen, M., Sixta, fl. Carboxymefhylation of alkali extracted xylan for preparation of bio-based packaging films. Carbohydr Polym 2014, 100, 89-96. https:z7doi.org / 10.1016 / i.carbpol.2013. 03.048 Deralia, P.K., du Poset, A.M., Westman, G. Hydrophobization of arabinoxylan with n-butyl glycidyl ether yields stretchable thermoplastic materials. Int. J. Biol. Macromol. 2021, 188, 491-500. Miki, K.j Kamitakahara, H.. _ Takano, T. _ Methylation-triggered fractionation of lignocellulosic biomass to afford cellulose-, hemicellulose-, and lignin-based functional polymers via click chemi stiy . Green Chem. 2020, 22. 2909-2928. Geng, W.; Venditti, R.A.; Pawlak, J. J.; Hou-Ming, C.; Lokendra, P.; Ericka, F. Carboxymethylation of hemicellulose isolated from poplar (Populus grandidentata) and its potential in water-soluble. Cellulose 2020, 27, 3359-3377. Fukaya, Y.; Hayashi, K.; Wada, M.; Ohno, H. Cellulose dissolution with polar ionic liquids under mild conditions: Required factors for anions. Green Chem. 2008, 10, 44-46. Gericke, M.; Fardim, P.; Heinze, T. Ionic Liquids — Promising but Challenging Solvents for Homogeneous Derivatization of Cellulose. Molecules 2012, 17, 7458-7502.

Claims

2. CLAIMS1. Xylan hemicellulose ester characterized by being obtained through the acetylation reaction between native xylan, l-Ethyl-3-methylimidazolium acetate, and acetic anhydride in a molar ratio of 1 :20 at a temperature of 80°C for a total duration of 55 to 70 minutes, followed by precipitation in 96% ethanol, washing with distilled water, and drying at 40 to 50°C for 20 to 24 hours.

2. Composite mixture based on xylan hemicellulose esters according to Claim 1 , in combination with chitosan in a ratio of 1 : 1 and nanoparticles of ZnO and CuO in a proportion of 10-20%, obtained through mixing and homogenization at 1500 rpm for 12 to 24 hours, characterized by being applied to the surface of paper or cardboard in the form of a film / layer with a mass of 2.5 to 5 g / m2, ensuring protection of agri-food products against bacterial action, moisture, oils, and fats.

Images