Polymers 2023 , 15 , x FOR PEER REVIEW
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Polymers 2023 , 15 , 2876
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Figure3. Scheme of ASA sizing process.
Figure 3. Scheme of ASA sizing process. The commercial papermaking process is more complex than laboratory hand-sheet making, and the chance of covalent bond formation is even lower than the already low laboratory results due to the following reasons: • Laboratory water quality is superior to that in the mill (deionized water vs. white water) [35,38,39]. • Laboratory ASA dosage is usually higher than that used in the mill, [23,30,31,33–35]. • In some studies, ASA is applied in organic solvents (DMVPB, DMSO, acetone, toluene, chloroform, ethanol, xylene, ethyl acetate . . . ) that are not found on paper machines to create idealized systems [23,30,31,33–35]. • One additive (ASA) is usually studied in the laboratory to prevent the influence of other variables while in real papermaking processes many organics, inorganics, additives and even bacteria compete with ASA to dwell with the fiber. In short, there are more uncontrolled variables in field experiments than in lab ones [39,40]. • In commercial paper mills, common ASA application consists of preparing the ASA emulsion, which is later added to the pulp at a point close to the fan pump. The mixture is moved to the headbox where the average consistency of the pulp is about 1%, and the predominant component is water, not organic solvent. Although other materials such as alum, PAE (Polyamide Epichlorohydrin), GCC (Ground Calcium Carbonate), CPAM (cat- ionic polyacrylamide), etc., are added to the furnish depending on the paper grade and the papermaker, the predominant component remains water, and the chance of the for- mation of hydrolyzed ASA is high. The slurry is dewatered then dried in the dryer section of the machine to develop sizing, i.e., the resistance to liquid penetration of the sheet (Fig- ure 3). The commercial papermaking process is more complex than laboratory hand-sheet making, and the chance of covalent bond formation is even lower than the already low laboratory results due to the following reasons: • Laboratory water quality is superior to that in the mill (deionized water vs. white water) [35,38,39]. • Laboratory ASA dosage is usually higher than that used in the mill, [23,30,31,33–35]. • In some studies, ASA is applied in organic solvents (DMVPB, DMSO, acetone, tolu- ene, chloroform, ethanol, xylene, ethyl acetate…) that are not found on paper ma- chines to create idealized systems [23,30,31,33–35]. • One additive (ASA) is usually studied in the laboratory to prevent the in fl uence of other variables while in real papermaking processes many organics, inorganics, ad- ditives and even bacteria compete with ASA to dwell with the fi ber. In short, there are more uncontrolled variables in fi eld experiments than in lab ones [39,40]. • Lastly, in laboratory studies, sometimes the pulp or the substrate has a special treat- ment not found in the mill. Such treatment can be ethanol or methanol wash of the pulp or the substrate, although it is well known that these solvents esterify with ASA, and their leftovers in the pulp can mislead the interpretation of FTIR results [23,26,33,41,42]. The covalent bond theory was not believed or developed or affirmed by the inventors Wurzburg and Mazzarella in the available patent document [1]. It is assumed that if a strong catalyst, a special condition, or an aid that promotes covalent bonding between the ASA and the cellulose is added to the process in the paper mill, it might be possible to form covalent bonds between ASA and cellulose. Some of these catalysts are triethylamine, methanesulfonic, sulfuric acid, and 4-dimethylaminopyridine [23,26,29,43]. As of now, such aids are missing in paper mills and the amount of covalent bond between ASA and cellulose is very low. Covalent bonding is not a prerequisite and does not play a major role in the sizing. In addition, the contact between ASA and starch in a real papermaking process is far more intimate and extensive than the contact with cellulose [26,34,44]. The “nebule” of starch that vehiculates ASA on the paper machine will eventually break and release the additive. Assuming starch does not evaporate after the burst, which is realistic, another selectivity mechanism will be needed to explain the reason why ASA chooses to bond with cellulose instead of starch, which is in closer contact for the assumed esterification reaction. Furthermore, even if paper mills start using strong catalysts or solvents or a special condition for ASA cellulose esterification, careful choice of these materials needs to be made with respect to the reaction selectivity, so ASA “droplets” enveloped in starch (emulsion) do not react with the starch itself or lignin (coniferyl alcohol and sinapyl alcohol) Lastly, in laboratory studies, sometimes the pulp or the substrate has a special treat- ment not found in the mill. Such treatment can be ethanol or methanol wash of the pulp or the substrate, although it is well known that these solvents esterify with ASA, and their leftovers in the pulp can mislead the interpretation of FTIR results [23,26,33,41,42]. The covalent bond theory was not believed or developed or a ffi rmed by the inventors Wurzburg and Mazzarella in the available patent document [1]. It is assumed that if a strong catalyst, a special condition, or an aid that promotes covalent bonding between the ASA and the cellulose is added to the process in the paper mill, it might be possible to
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