11of 15 known to form a bridge between cellulose and the sizing agent depending on the pH a the species of the aluminum ions available. As shown in Figure 4, alum generally will ex in one of three dominant species: Al 3+ (pH less than 4.3), Al 8 (OH) 20 4+ (pH 4.3–5.0), Al(OH) 3 (pH 5.0–8.0). The adsorption of the aluminum ions Al 3+ to the fi ber occurs at lo pH and understanding the pH regions of alum is paramount for ASA addition and rete tion [8,57,74,75].
Polymers 2023 , 15 , 2876
Figure 4. Distribution of Hydrolyzed Aluminum (III) as a Function of pH. Al (III) = 1.0 × 10 − 3 M, h (Adopted from Rubin and Hayden [76]). ASA salt, mainly aluminum-ASA salt, is one of the predominant forms of ASA fou in the sheet beside the hydrolyzed ASA. The use of alum enables the formation of the no tacky aluminum salt which is preferred over the sticky calcium- or magnesium-ASA sa In addition, the use of alum controls the deposit of hydrolyzed ASA, and the aluminu salt of the hydrolyzed ASA may interact with the anionic charges on cellulose to impro sizing. Furthermore, the application of alum can anchor free hydrolyzed ASA to the fi b as a metal salt to reduce, to delay, or to reverse size reversion due to migration, reorien tion or fugitivity [26,52,67,75]. The dosage of alum or PAC is critical as it can improve or impair the papermaki process and paper properties. It is reported that 0.5% alum based on dry pulp is genera su ffi cient [75]. However, a preliminary alum or PAC application optimization study w be ideal for each paper mill to determine the dosage, injection location, and the sizi e ffi ciency. An excessive use of alum can lead to deposits on the paper machine, loss sizing, and loss of sheet strength. Alum, PAC, or sodium aluminate deposits requ downtime for cleanup; analysis has shown that these deposits are mainly aluminum h droxide [Al(OH) 3 ] and complex aluminum hydroxides [Al x (OH) y (SO 4 )nH 2 Al x (OH) y Cl 2 nH 2 O], which can be found on the primary screens, machine chest, headbo blades, and vacuum box [73]. In addition, excessive use of alum has li tt le e ff ect on sizi at low concentrations but decreased sizing at higher concentrations. The overuse of alu has a degradative e ff ect on paper as it becomes more acidic and undergoes acid hydroly that causes cellulose chain scission resulting in the loss of paper strength [8,52,68,70]. Finally, excessive use of defoamer and certain biocides has an adverse e ff ect on sizi performance. It is known the excessive application of defoamer, especially at the wet en ASA salt, mainly aluminum-ASA salt, is one of the predominant forms of ASA found in the sheet beside the hydrolyzed ASA. The use of alum enables the formation of the non- tacky aluminum salt which is preferred over the sticky calcium- or magnesium-ASA salt. In addition, the use of alum controls the deposit of hydrolyzed ASA, and the aluminum salt of the hydrolyzed ASA may interact with the anionic charges on cellulose to improve sizing. Furthermore, the application of alum can anchor free hydrolyzed ASA to the fiber as a metal salt to reduce, to delay, or to reverse size reversion due to migration, reorientation or fugitivity [26,52,67,75]. The dosage of alum or PAC is critical as it can improve or impair the papermaking process and paper properties. It is reported that 0.5% alum based on dry pulp is generally sufficient [75]. However, a preliminary alum or PAC application optimization study will be ideal for each paper mill to determine the dosage, injection location, and the sizing efficiency. An excessive use of alum can lead to deposits on the paper machine, loss of sizing, and loss of sheet strength. Alum, PAC, or sodium aluminate deposits require downtime for cleanup; analysis has shown that these deposits are mainly aluminum hydroxide [Al(OH) 3 ] and complex aluminum hydroxides [Al x (OH) y (SO 4 )nH 2 O,Al x (OH) y Cl 2 nH 2 O], which can be found on the primary screens, machine chest, headbox, blades, and vacuum box [73]. In addition, excessive use of alum has little effect on sizing at low concentrations but decreased sizing at higher concentrations. The overuse of alum has a degradative effect on paper as it becomes more acidic and undergoes acid hydrolysis that causes cellulose chain scission resulting in the loss of paper strength [8,52,68,70]. Finally, excessive use of defoamer and certain biocides has an adverse effect on sizing performance. It is known the excessive application of defoamer, especially at the wet end, destroys sizing [58,77,78], but it is not well understood if the defoamer or the biocide prevents ASA from anchoring to cellulose or if these chemicals just attack and ruin the sizing agent. Quaternary ammonium salt biocide is known to cause adverse effects on sizing Figure 4. Distribution of Hydrolyzed Aluminum (III) as a Function of pH. Al (III) = 1.0 × 10 − 3 M, 24 h (Adopted from Rubin and Hayden [76]).
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