(2018) in an analysis of published results related to the effects of the shapes of filler particles on barrier properties of polymer composite films. J. Coat. Care must be taken to use the correct form of the governing equation (Milne and Amirfazli 2012). Two of the most viable and still economically relevant alternatives, parchmentized paper and glassine paper, actually pre-date the introduction of fluorochemicals. It is reasonable to expect similar effects with cationic acrylamide copolymer retention aids, which are more commonly employed in the industry. Wood from the oldest trees yielded the highest resistance to grease. The process is illustrated schematically in Fig. 2194498. Faraday Soc. 1998; Parket al. Schematic illustration of the kit test (TAPPI Method T559) for determination of the extent of resistance to grease penetration. Before the emergence of plastic films, the paper industry addressed these objectives in two ways, by parchmentizing and by high levels of refining of the fibers. Bio-nanocomposites for food packaging applications,Prog. Such application processes have been employed to evaluate the effects of MNFC applied to paper surfaces (Aulin and Strm 2013; Lavoineet al. Envir. 2015; Mudumbiet al. 154(45), 54-55. Nanocellulose in thin films, coatings, and plies for packaging applications: A review,BioResources12(1), 2143-2233. Sachsenroeder, G. H. (1902). Schematic illustration of a two-layer system by which nanocellulose-rich layers are used to achieve grease resistance (due to an MNFC layer) and protection of that layer using a water-resistant layer (with CNC, montmorillonite, protein, and reacted alkylketene dimer). 7. (2013) likewise showed that algal biomass can be used. Goswami, T., Kalita, D., and Rao, P. G. (2008). 2. 2015), have provided motivations for innovations in greaseproof paper products. 2022 NC State University. 131(8), article no. (2). (2008) mention some alternative monomeric fluorochemicals that also could be used, such as perfluoro-octadecanoic acid or the reactive agent pentadecafluoro-octanoyl chloride. Mater. The market size of greaseproof paper has been projected to reach about $1.1 billion by 2025 (Acumen 2019). (2013). 2008; Rajput 2009). Vaswani, S., Koskinen, J., and Hess, D. W. (2005). DOI: 10.1021/la991440a. (2010) showed that a variety of reaction paths can lead to breakdown of certain perfluorocarbons that they studied. Garbassi, F., Morra, M., and Occhiello, E. (1994). 
DOI: 10.1111/j.1365-2621.1994.tb08156.x. Earlier work by the same group showed that alkylketene dimer (AKD) also can be used in such formulations with CNC to increase resistance to water (Tyagiet al. Nanocellulose-based multilayer barrier coatings for gas, oil, and grease resistance,Carbohyd. Thus, the degree of refining needs to be optimized in each case. Surface modification of paper and cellulose by plasma-assisted deposition of fluorocarbon films,Surf. To lay the groundwork for a discussion of this class of greaseproof products (as well as some of the other greaseproofing technologies to be described later), the testing procedures are considered first. Coated greaseproof paper as barrier material,Paperi Puu83(2), 138-141. 3. On the other hand, there is a continuing need to advance the technologies to achieve greater cost-effectiveness and better meet customer needs. Water vapour and grease resistance properties of paper coating based starch-bentonite clay,Journal of Physics: Conference Series1153(1), February 26, 2019, 9thInternational Conference on Physics and Its Applications, ICOPIA 2018; Article number: 012090. Repellency of paper and board to grease, oil, and waxes (Kit Test), TAPPI Useful Method UM 557, pp. Given the fact that glassine papers owe their barrier performance to their density, it makes logical sense to consider calendering. The strong acid causes the fibers to swell, forming a homogeneous sheet (Meinander 2000). Glassine papers having grease resistance also can be produced from some less-considered fiber sources. (2018). 15(4), 209-224. Montmorillonite for starch-based barrier dispersion coating Part 2: Pilot trials and PE-lamination,Appl. It is worth considering again the 1922 patent by Wright that was cited at the very start of this article. Promising results also have been obtained with plasma etching of paper followed by perfluorochemical treatment (Liet al. Because diverse types of nanocellulose and related materials are available, it is important to consider what type to select when the aim is to achieve greaseproof performance. Further enhancement was obtained with the incorporation of plate-like mineral particles. Health Perspectives123(5), A107-A111. To better understand these systems, some key concepts related to diffusion are reviewed, followed by a discussion of relevant research results relating to factors affecting diffusion of grease through nanocellulose films. Greaseproof paper fromPopulus deltoidesG-3,IPPTA7(2), 39-42. 6. 2011a,b; Hagiopol and Johnston 2012; Zabaletaet al. (1998). Grease resistance of corn zein coated paper,J. Schematic illustration of how hydrogen bonds can be expected to form between adjacent cellulose-containing solids that are dried in contact with each other. Hidayat, T., Sasuki, T., and Adhi, V. (1996). 2018), could provide future options for glassine paper production. Mater. Super-oleophobic systems work in a manner that is analogous to that employed by lotus leaves, which can remain mostly dry even when directly exposed to a heavy rainstorm while floating on water. 69, 46-58. Proposed nano-scale coalescence of cellulose in chemical pulp fibers during technical treatments,BioResources7(4), 6077-6108. 21, 2293. It is notable that the casein, glycerol, and sugar cited in that patent are all relatively hydrophilic, hydrogen-bondable substances. The performance of glassine-type based-sheets can be improved by applying various water-loving polymers to the surface. 
2014; Javedet al. DOI: 10.1021/am900394y, Beneventi, D., Chaussy, D., Curtil, D., Zolin, L., Gerbaldi, C., and Penazzi, N. (2014). Once a surface film on the paper has been dried, the hydrogen bonds can be expected to hold the polymeric chains together firmly, decreasing the probability that a molecule of a gas or grease can diffuse through the material. DOI: 10.1021/acsapm.8b00106, Liu, A. D., Walther, A., Ikkala, O., Belova, L., and Berglund, L. A. (2012). In any case, the field of grease-resistant products based on paper seems to be a promising field for further research in the coming years. Health and regulatory issues deserve to be discussed early, since, to a greater extent than other issues, changes in future regulations and industry practices have the potential to bring about abrupt changes in the greaseproof paper market. 170, 48-55. Because the phosphate-type perfluorinated monomers commonly used in such applications bear a negative ionic charge, it is generally recommended to pretreat the fiber furnish with a suitable cationic additive (Giatti 1996, 1997; Perng and Wang 2004). At the same time, the dependency of such films on hydrogen bonding can explain a strong drop-off in barrier properties when the relative humidity increases above about 65% (sterberget al. In the latter case, monomeric agents are typically applied. (1995). 1997). B Biol. Fluorinated Surfactants and Repellents, Revised and Expanded, Marcel Dekker, New York, NY. Regulations, and the uncertainty regarding future regulations have led to interest in perfluorocarbon-free systems for greaseproofing of paper (Anon 2017). As illustrated, a super-phobic situation arises in cases in which the fluid is essentially being held out on the points of fine-scale roughness. 2013; Rice 2015; Schaideret al. Applying a layer of platy minerals to papers surface is another option to enhance holdout. (2008). These results were interpreted by assuming that the glassine paper is inherently an extremely effective barrier, but at the same time it contains isolated defects, consisting of pores allowing free access for the passage of molecules. Protein and surface surface sizings for oil and grease resistant paper, US Patent 6,790,270 B1. Fig. Schematic illustration of parchmentizing process. The collected data from a very large number of studies showed extremely diverse results. The other thing that glassine product manufacturing is known for is very long Fourdrinier dewatering zones, associated with the relatively slow rates of drainage. As illustrated in Fig. Such wicking, combined with the fact that only a thin layer might be required in order to achieve the needed barrier properties, has the potential of speeding up the immobilization of the surface layer, making it possible to achieve commercially viable rates of production. DOI: 10.1016/j.talanta.2016.02.022, 2820 Faucette Dr., Campus Box 8001Raleigh, NC 27695. DOI: 10.1016/j.fct.2018.01.012. Use of fluorocarbon compounds for the manufacture of greaseproof paper,Papir a Celuloza30(9), 205-206. Mater. Influence of paper structure on barrier properties of starch-coated greaseproof paper,Nordic Pulp Paper Res. The main distinction between a super-oleophilic surface and an ordinary super-hydrophobic surface is that the low-energy substance is a fluorinated compound. (2002), Koivulaet al. Eng. It is important to keep in mind that the success of any surface treatment of paper is invariably linked to attributes of the base sheet. GREASEPROOF SYSTEMS INVOLVING NANOCELLULOSE. Sci. Studies of the Effects of Hydrophilic Polymer Surface Films to Enhance the Grease Resistance of Paper, Notes: PVOH = poly-(vinyl alcohol); PAMA = poly-alkylmethacrylate; CMC = carboxymethyl cellulose. DOI: 10.1007/s11356-010-0439-3, Trier, X., Nielsen, N. J., and Christensen, J. H. (2011b). Sci. Aulinet al. Technol. The Cassie equation: How it is meant to be used,Advan. The high electronegativity of fluorine causes it to hold tightly to its electrons. 364(1526), 2047-2062. DOI: 10.1021/bk-2001-0787. By identification of breakdown products, they were able to conclude that several mechanisms of degradation must have been involved, including a beta-oxidation pathway. Almgren, T. (1980). These two features working together are illustrated together in Fig. DOI: 10.1021/bm300465d. (1970). Table 1. 40, 546-551. 13(6), 1927-1932. 2010; Lavoineet al. (2008) reported a strong correlation between contact angles and the concentration of fluorine at paper surfaces. Greaseproof Quo vadis,Svensk Papperstiding83(7), 186. Sci. A distinguishing feature of parchmentized paper is that it does not have a non-stick surface, so that in its default form it is not recommended for baking (MetaTissue 2019). Colloid Interface Sci. 2011a; Zabaletaet al. FRC: Pulp and Paper Fundamental Research Symposia Proceedings, Distance Education: Online Masters Degree & Individual Courses. DOI: 10.1007/s10570-019-02504-y, Sirvi, J. 2010). For conventional perfluorocarbon treatment of paper, the oil-repellent agent can be added either to the surface of the paper or to a suspension of fibers before the formation of the sheet (Giatti 1996, 1997). (2001). Possibilities for energy savings in the production of greaseproof papers,Przeglad Papeiriniczy51(3), 114-118. 2012). On the other hand, it should be borne in mind that MNFC can be regarded as just a more extreme example of the high levels of refining already being used for the production of glassine paper (Kjellgren and Engstrm 2005). A fast method to produce strong NFC films as a platform for barrier and functional materials,ACS Appl. 61(3), 259-265. The resistance to grease penetration varied in a wide range, as indicated by passing the penetration test between oil #3 to #6 of the test kit. However, the long-chain products, though not made in the US, continue to be made and used elsewhere in the world (Schaideret al. Cold plasmas, in which only a small fraction of the molecules are in a high energy state, have been employed for food packaging (Ekezieet al. 1994; Castner and Grainger 2001). Tsurko, E. S., Feicht, P., Habel, C., Schilling, T., Daab, M., Rosenfeldt, S, and Breu, J. The reason that highly refined chemical pulp fibers can resist grease can be attributed not only to the high density of such paper layers but also to the extensive and well-organized hydrogen bonding that occurs between cellulosic surfaces dried while remaining in contact. DOI: 10.1021/ie301785a, Aulin, C., Yun, S. H., Wgberg, L., and Lindstrm, T. (2009). Greaseproof paper, U.S. Patent No. The mechanism of super-oleophobicity has been reviewed (Song and Rojas 2013; Hubbeet al. Polym. Grease resistance test for paper and paperboard, TAPPI Press, Atlanta. Claude, P. (1997). Polym. DOI: 10.1021/es9028183. It has been shown that the refining requirement can be reduced by at least 10% by pretreating the pulp with a cellulase enzyme mixture (Yamaguchi and Yaguchi 1996). Chem. The health effects of fluorinated materials are a concern, especially in cases where the paper products come into contact with food (Birnbaum and Grandjean 2015; Blumet al. Perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and their salts: Scientific opinion of the panel on contaminants in the food chain,EFSA J. DOI: 10.3390/coatings5040887, Rhim, J. W., Park, H. M., and Ha, C. S. (2013). Barrier and surface properties of chitosan-coated greaseproof paper,Carbohyd. Billmers, R. L., Mackewicz, V. L., and Trksak, R. M. (2003). Rapid preparation of smooth nanocellulose films using spray coating,Cellulose24(7), 2669-2676. Anal. A common feature of the listed polymers is that all of them have a strong hydrogen bonding ability. The next logical step to consider, beyond the use of glassine paper with its highly refined fibers, is to refine the fibers much more extensively, until they become microfibrillated or nanofibrillated. In view of the earlier discussion of tortuosity, it should not be surprising that promising results for resistance to grease and various gases have been achieved in systems in which highly platy minerals were used as an ingredient in film in barrier layers that were mainly comprised of MNFC or CNC (Sanchez-Garciaet al. 2010). Peiet al. Mater. Dense specialty papers Alive and very well,Paper Film Foil Converter51(12), 43-46. DOI: 10.1039/c2nr31726e, Aulin, C., Shchukarev, A, Lindqvist, J., Malmstrm, E., Wgberg, L., and Lindstrm, T. (2008). DOI: 10.3183/NPPRJ-2013-28-02-p216-238, Song, Z. P., Xiao, H. N., and Li, Y. For instance, di-butylphthalate, a widely used plasticizer, has been shows to disrupt the endocrine systems of mammals. 2016). The use of calendering in the production of greaseproof paper has been widely reported (Giatti 1996; Girard and Trillat 1996; Meinander 2000; Kjellgren and Engstrm 2005). Res. 402. The observed effects were likely due to coalescence among the polymer segments at the cellulose surfaces, with the formation of a denser and more organized system of hydrogen bonding (Pnniet al. Hupfield, P. C., Masutani, T., Minami, S., and Yamamoto, I. Fluorinated Surfaces, Coatings, and Filmsi, Amer. Crosslinking agents are also used, presumably with the intention of keeping the barrier layer intact even when the material is in the proximity of aqueous solution (Hagiopol and Johnston 2012). Barrier properties and heat sealability/failure mechanisms of dispersion-coated paperboard,Packaging Technol. Polym. DOI: 10.1002/adma.200400760, Ham-Pichavant, F., Sebe, G., Pardon, P., and Coma, V. (2005). Stolpe, E. (1996). These include banana pseudostem (Saikiaet al. 2017a). Kissa (2001) has provided a listing of the extensive patent literature covering such products. This sheet is passed between hard pressure rollers (supercalendered) to further increase the density, creating a paper called glassine. It is suggested that related research focused on resistance to grease and oils could be considered in future research. Fiber beating with enzyme pretreatment,50thAppita Annual General Conference, 1996: Proceedings, Vol. Next to be discussed is the topic of superoleophobicity, which uses nanostructures as a means of amplifying effects of fluorochemicals. They also have been found in the sludge of wastewater treatment plants (Leeet al. Birnbaum, L. S., and Grandjean, P. (2015). Saikia, D. C., Goswami, T., and Saikia, C. N. (1997). 2015). Health Perspectives123(5), A104-A105. This point was brought out most clearly by Wolfet al. For instance, some products such as three-dimensionally formed paper plates do not include size-press treatment option. Recently Tokranovet al. Mater. 23(3), 272-276. All rights reserved. 2009). 12(3), 633-641. Paper wrapping or baking material, Britain Patent No. Grease resistance and mechanical properties of isolated soy protein-coated paper,J. Amer Oil Chem. That is because, as noted earlier, the high surface area per unit mass of mineral particles implies that a higher dosage may be needed to form a monolayer on the available solid surfaces. 2019). Examples of polymeric products added to the paper surface to achieve greaseproof performance are listed in Table 1. Let. This printmaking-related article is a stub. An important prediction of the so-called Lucas-Washburn concept is that resistance to passage of liquids through porous solids is strongly favored by small pore diameters. Baking and steaming papers for industrial users, viewed November 2019, https://www.ahlstrom-munksjo.com/products/food-packaging-baking-and-cooking-solutions/cooking-baking-papers-and-molding-materials/baking-and-steaming-papers-for-industrial-users/. Fig. (2015). 2011; Aulinet al. Lechiffre, V. (1992). The glassine is treated with starches, alginates or carboxymethyl cellulose (CMC) in a size press to fill pores or treat the paper chemically to make it fat repellent. Pollut. Table 2. Tayeb and Tajvidi (2019) showed that polyamidoamine-epichlorohydrin, a reactive wet-strength resin, can be used for greaseproof coatings. Packaging of fats: Properties required of packaging papers. The latter authors were able to distinguish fourteen different perfluorocarbon compounds and ten related compounds in a variety of fast-food packages, such as popcorn bags. 1,420,173. Figure 6 illustrates the concept of dense layers that can be prepared from cellulose nanofibrils, which combine a high level of nanocrystal content (which are completely impervious to diffusing molecules) and the high flexibility contributed by the non-crystalline cellulose. (2017), it is essential for a coating comprised of starch and PVOH to be protected on both sides from the effects of moisture.
DOI: 10.1021/es900100d, Ekezie, F. G. C., Sun, D. W., and Cheng, J. H. (2017). Also, logic would suggest that a smooth sheet with relatively small pore openings would be helpful in reducing the required amount of greaseproof formulation that would need to be applied to the surface of the sheet. The relationship can be unpredictable, however, because the effective surface area of refined kraft fibers decreases drastically during the process of drying, and the hydrophobic agent generally becomes spread out on the external surfaces only after the paper has become at least partly dried (Hubbe 2014). Analogs having eight-carbon chains have been shown to accumulate in animal tissues (Kabadiet al. 72, 200-205. The necessary roughness can be advantageously achieved by depositing a layer of nanoparticles onto the surface. 90, 735-764. The subsequent topics to be discussed include defects in nanocellulose films and their susceptibility to and protection against moisture. nanoclay), or related highly platy mineral products that have been used in other approaches to achieving grease resistance (Girard and Trillat 1996; Perng and Wang 2012; Olssonet al. DOI: 10.1007/978-981-13-3768-0_3, Sanchez-Garcia, M. D., Lopez-Rubio, A., and Lagaron, J. M. (2010). The acrylate emulsion tested by Rosenet al. 2017), it is important to keep in mind the known alternative approaches. 8(2), 33-38. Knudson, M. I. Using agar extraction waste ofGracilaria lemaneiformisin the papermaking industry,J. Appl. Besides, spray application has been used to form MNFC layers onto paper (Beneventiet al. The very high flexibility of the fibrils is expected due to their content of amorphous cellulose, while at the same time the high content of crystalline cellulose provides about 70% of the materials that allow no permeation at all (Hubbeet al. nanoclay). Montmorillonite (MMT), which is sometimes known as bentonite or nanoclay, can be prepared so that extremely thin platelets (< 10 nm) separate from each other (Knudson 1995). DOI: 10.1007/s10570-015-0833-6, Lucas, R. (1918). DOI: 10.15376/biores.12.1.2143-2233. Contact angle tests can be carried out in a way to distinguish between the contributions of dispersion forces (relevant for all surfaces, but reduced in magnitude on perfluorinated surfaces) and polar and hydrogen bonding forces to the free energy of the surface. 
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