ARTICLE IN PRESS
JID: JOBAB
[m3GeSsc;February 6, 2026;11:5]
Z. Wei, J. Liu, Y. Wang et al.
Journal of Bioresources and Bioproducts xxx (xxxx) xxx
Fig. 5. Water- and oil-proof properties of P-PLS. (a) The water contact angle (WCA) of uncoated paper, P-PLS, and paper coated with non-emulsified PLS 2 coating (P-PLS 2 − M). (b) Cobb 60 value of uncoated paper, P-PLS, and P-PLS 2 − M. (c) Contact angle of common beverages on the surface of P-PLS 2 . (d) Kit rating of uncoated paper, P-PLS, and P-PLS 2 − M. (e) Photographs showing the barrier properties of uncoated paper and P-PLS 2 against different liquids after 24 h of direct contact. (f) Photographs showing uncoated paper and P-PLS 2 in direct contact with jelly, fried chicken, and soybean oil (dyed with oil red) at various temperatures for 10 min. the paper by the PLS emulsion coating. P-PLS 2 − M demonstrated a lower Cobb 60 value compared to the uncoated paper, which can be attributed to the abundant SA particles on its surface ( Fig. 5 b). However, its Cobb 60 value remained higher than that of P-PLS 2 , likely due to the uneven dispersion of SA particles that exposed the hydrophilic PVA. Despite the improvement in water-proof properties achieved by the PLS emulsion coated paper, a significant gap remains compared to conventional LDPE coated paper commonly used in daily applications (Table S2). Additionally, the PLS 2 emulsion-coated paper exhibited good barrier performance against common beverages such as coffee, cola, tea, and milk, with contact angles exceeding 105° ( Fig. 5 c). The barrier properties against oil are equally important for paper-based packaging materials, especially for food packaging papers. The Kit rating of coated paper was measured to evaluate its oil-proof performance, with a higher Kit rating indicating better oil-proof performance. Uncoated paper, due to its porous structure, allows easy penetration of oil, resulting in a Kit rating of 0/12. In contrast, the oil-proof performance of coated paper was significantly improved by the PLS emulsion coating. The P-PLS 0 exhibited the best oil-proof properties, with a Kit rating of (11.4 ± 0.55)/12, primarily due to the strong oil-proof performance of PVA. However, the introduction of SA in the coating slightly decreased the oil-proof performance because of the lipophilic nature of SA and the reduced proportion of PVA. Nonetheless, all coated papers maintained a Kit rating exceeding 9/12, which is sufficient for daily applications and comparable to the oil-proof properties of LDPE coated paper ( Figs. 5 d and S13, Table S2).
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