Environmental Science and Pollution Research
included in this group (Cheng et al. 2023). A m ong the cel- lulose and lignin deco m position products, coniferyl alde- hyde was detected, a co m pound for m ed enzy m atically fro m lignin in species such as Picea abies and Pinus sylvestris (Hänninen et al. 2011). The growing de m and for recycled paper as a substitute for virgin cellulose fibres presents challenges related to the presence of organic sticky conta m inants, co mm only referred to as “stickies.” Currently, recycled m aterials co m prise up to 40% of paper production inputs (Ballinas-Casarrubias et al. 2020). The presence of stickies significantly affects the paper m aking process, with concentrations in waste paper ranging between 3 and 5%. These conta m inants pri m arily include polyvinyl acetate poly m ers, styrene-butadiene rub- ber (including butylated hydroxytoluene), siloxanes, poly- a m ines such as di m ethyla m ine and di m ethylpropyla m ine, and a group of 13 paraffin waxes (Wang et al. 2023). A m ong these waxes, four co m pounds—heneicosane (C 21 H 44 ), octa- cosane (C 28 H 58 ), tetracosane (C 24 H 50 ), and pentacosane (C 25 H 52 )—were consistently detected in all types of waste paper, with concentrations ranging fro m 50.6 to 203.1 m g/ kg and an average value of 129.2 ± 45.1 m g/kg. These sub- stances are also co mm only found in wood extractives. The highest concentrations of stickies were observed in card- board and office paper sa m ples.
Chemical compounds from papermaking
A total of 19 co m pounds used to enhance paper proper- ties and 15 fragrance-related co m ponents—including three m usks—were identified in waste paper sa m ples. All of these co m pounds were detected in m ixed waste paper. In a journal paper, only five co m pounds were found, one of which (pentanoic acid) is associated with anti-ageing applications, along with four fragrance co m ponents. Office paper contained 13 functional co m pounds and 7 fragrance or m usk-related substances, with a total concentration of 3,164.1 ± 620.6 m g/kg (Fig. 3). In cardboard sa m ples, four property-enhancing co m pounds and five fragrance/ m usk co m ponents were identified. The highest concentrations in both cardboard and office paper were associated with octa- noic and octadecanoic acids, which contribute to hydropho- bicity and sizing perfor m ance. Additional co m pounds identified in waste paper sa m - ples were found to enhance specific m aterial properties. These include acryla m ide, which contributes to paper rein- force m ent; m ethylene diacryla m ide and ethylhydrazone acetaldehyde, used to opti m ize m echanical strength; and 2-propenenitrile and tetraethylsilane, which i m prove hydro- phobic perfor m ance. Tributyl acetylcitrate was detected as a coating agent and plasticizer, while p-terphenyl and ben- zoic acid, 4- m ethylpent-2-yl ester were used to strengthen fibre interconnections and facilitate the integration of PCC.
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