Environmental Science and Pollution Research
widely used as a filler, available both in its natural for m and as synthetic precipitated calciu m carbonate (PCC). Fillers are incorporated into cellulose fibres at the early stage of the paper m aking process. The quantity of filler used depends on the intended application of the paper. For office paper, filler content typically ranges between 5 and 30%. For PCC specifically, the reco mm ended m axi m u m concentration is 20–25%, depending on the paper grade (Dölle 2021). Nota- bly, certain products, such as Kleenex, contain no fillers at all. When fillers are used as substitutes for cellulose fibres, several advantages are co mm only cited: reduced consu m p- tion of natural fibres, lower drying energy costs, and m odi- fied paper properties. Incorporating fillers enhances bright- ness and opacity due to their particle size characteristics. Depending on the poly m orphous phase contained in PCC, fillers can affect friction and pore size (Hubbe And Gill 2016), as well as surface s m oothness and ink absorption in paper m aking (Ji m oh et al. 2018). Beyond their role as fill- ers, PCC is also utilized as a coating m aterial. For effective perfor m ance in paper production, calcite should exhibit a highly unifor m particle size distribution. At least 75 wt.% of particles should have a dia m eter below 1 μ m for coat- ings, or below 5 μ m when used as fillers (Dhar et al. 2020). The particle size of PCC can be reduced through the addi- tion of organic co m pounds, such as ethylene glycols, which also pro m ote the for m ation of highly aggregated crystals (Konopacka-Łyskawa et al. 2017). PCC m odification is car- ried out using che m ical agents like chitosan, acetic acid, car- boxy m ethyl cellulose (CMC), and alu m (Al 2 (SO 4 ) 3 ·nH 2 O), i m proving physical characteristics (Ji m oh et al. 2018; Ghosh
et al. 2020). Alterations in crystal m orphology have also been achieved using a mm oniu m carba m ate and urea (Liendo et al. 2022). The use of CMC and polyalu m iniu m chloride (PAC) for encapsulating PCC fillers has been shown to enhance paper properties, particularly brightness and opac- ity (Mousavipazhouh et al. 2018). Differences in m ineralogical co m position and filler con- tent are presented in Table 1, with filler proportions cor- responding to the m easured ash content (Fig. 1). All three for m s of calciu m carbonate are e m ployed in office paper production. In journal-grade papers, synthetic dicalciu m silicate derived fro m fly ash has e m erged as a significant filler co m ponent, recently introduced to the paper industry, particularly for high-quality applications (Song et al. 2018; Qiu et al. 2020).
Printing inks
Modern printing inks typically consist of pig m ents (5–30%); binders (15–50%), which m ay include oils, resins, or vari- ous types of varnishes; solvents (15–65%); and excipients (< 10%) such as drying agents, chelating co m pounds, and other additives that influence ink properties. Co mm on che m - icals found in printing inks include 1-octane, 2-butanone, butyl acetate, citric acid, cyclohexanone, dichloro m eth- ane, ethyl acetate, ethylene glycol, gu m arabic, isopro- panol, m ethyl isobutyl ketone (used as dilution solvents), n-heptane, organic pig m ents, phthalate esters, polybutyl- ene terephthalate resin, soybean oil, toluene, xylene, and polyvinyl acetate (used as adhesives and glues) (Tsai et al.
Fig. 1 Ash (dicalciu m silicate) after co m bustion of journals at 815 °C ( a ); ash ( m icro-calcite) after co m bustion of office paper ( b )
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