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
In addition, further demonstrations illustrated the good water- and oil-proof properties of P-PLS 2 . First, the long-term barrier performance of P-PLS 2 against water, milk, and cola was evaluated. When 100 mL of these liquids were poured into a filtration device containing uncoated paper and P-PLS 2 , the uncoated paper allowed liquid penetration after 24 h. In contrast, P-PLS 2 effectively prevented liquid passage due to its enhanced water-proof properties ( Figs. 5 e and S14). Furthermore, jelly, fried chicken, and soybean oil at different temperatures were placed on the paper surface. Due to the poor water- and oil-proof performance of uncoated paper, after 10 min, water from the jelly, oil from the fried chicken, and soybean oil had penetrated and spread into the paper. In comparison, P-PLS 2 exhibited an effective barrier that inhibited the penetration and diffusion of both water and oil ( Fig. 5 f). These demonstrations fully confirm the good water- oil-proof properties of P-PLS 2 . To verify the universality of the PLS emulsion coating, it was applied to the surface of corrugating medium paper, producing PLS emulsion-coated corrugating medium paper (CP-PLS). The uncoated corrugating medium paper exhibited hydrophobicity due to the high lignin content in its fibers. After treatment with the PLS emulsion coating, CP-PLS with lower SA content showed a reduced WCA and an increased Cobb 60 value, primarily due to the dominant surface hydrophilicity imparted by the PVA in the coating. As the SA content in the PLS emulsion coating increased, the water-proof properties of CP-PLS gradually improved, as indicated by an increase in WCA and a decrease in Cobb 60 value. Notably, the water-proof performance of CP-PLS 2 (WCA of (120.1 ± 4.5)°, Cobb 60 value of (19.65 ± 1.50) g/m 2 ) surpassed that of the uncoated corrugating medium paper (Figs. S15A and S15B). Regarding oil-proof performance, CP-PLS exhibited a trend similar to P-PLS, with both demonstrating significantly better oil-proof performance than uncoated paper. Although the Kit rating slightly decreased with increasing SA content, all CP-PLS maintained a Kit rating exceeding 8/12 (Figs. S15C and S15D). These results demonstrate the broad applicability of the PLS emulsion coating. The PLS emulsion coating endowed the coated paper with good water- and oil-proof properties, which can be attributed to the synergistic interaction among PVA, SA, and LNPs, collectively forming a dense and hydrophobic functional surface. In terms of water- proofing, the dense structure of the coating effectively compensates for the deficiencies of the inherently porous fiber network of the paper, significantly suppressing water penetration caused by capillary action. Additionally, the incorporation of hydrophobic SA microparticles, effectively emulsified by LNPs, further enhances the hydrophobic performance of the coating, thereby significantly improving the overall water-proof properties of the coated paper ( Zhang et al., 2023 ). Regarding oil-proof properties, the good oil- proof performance primarily arises from the physical barrier formed by the tight interconnection of PVA macromolecular chains. Although the SA component exhibits oleophilicity, PVA, as the continuous phase, plays a dominant role in oil-proofing. Its molecular chains construct a dense structure that effectively obstructs the penetration and migration of oily substances ( Li et al., 2024 ; Peng et al., 2024 ). Consequently, even with the incorporation of SA into the system, the composite coating can still rely on the continuous protective barrier provided by PVA to maintain a high Kit rating.
3.5. Gas barrier performance of PLS emulsion coated paper
The water vapor barrier performance plays a crucial role in many packaging applications as high water vapor barrier performance ensures the extended shelf life of moisture-sensitive or water-losing foods. Due to the extensive porous structure of uncoated paper, it exhibited a high WVTR. In contrast, the WVTR of P-PLS 0 and P-PLS 2 was reduced to 599.72 and 557.30 g/(m 2 ·d), respectively, demonstrating an enhancement in water vapor barrier performance ( Fig. 6 a). This enhancement can primarily be attributed to two factors. First, the dense coating uniformly covers the paper surface, effectively sealing its porous structure, thereby inhibiting the rapid transmission of water vapor ( Chen et al., 2024 ). Second, the hydrophobic SA particles embedded in the PLS emulsion coating obstruct the passage of water vapor molecules and increase their diffusion path, resulting in a lower WVTR for P-PLS 2 compared to P-PLS 0 ( Zhong et al., 2015 ; Zhang et al., 2024 ). Similar to the WVTR, the OTR of P-PLS 2 was significantly lower than that of both the uncoated paper and P-PLS 0 ( Fig. 6 b). Although the gas barrier properties of P-PLS 2 were improved, they remain inferior to those of LDPE coated paper and PLA coated paper, indicating a need for further optimization in future work (Table S3). The improved water vapor barrier performance of PLS emulsion coated paper offers significant potential for food preservation. To demonstrate its effectiveness in fruit preservation, an assessment was conducted using P-PLS 2 on three types of fruits (bayberry, grape, and cherry tomato). The preservation effectiveness of these fruits was compared with those exposed to the natural environment and those wrapped in uncoated paper. Compared to bare fruits and those wrapped in uncoated paper, fruits wrapped in P-PLS 2 effectively inhibited moisture loss due to its enhanced water vapor barrier properties. Across all fruits, quality gradually declined during the testing period, and their appearance underwent varying degrees of shrinkage ( Figs. 6c–6f and S16). However, the weight loss of all fruits wrapped in P-PLS 2 was lower than that of bare fruits and those wrapped in uncoated paper ( Figs. 6c–6e ). Notably, the effect was most pronounced in bayberries, where the weight loss of bare and uncoated paper-wrapped fruits exceeded 70% by the 9th day, resulting in surface cracking due to excessive dehydration. In contrast, the weight loss of bayberries wrapped in P-PLS 2 was < 40% on the 9th day, with no significant surface cracking observed ( Fig. 6 f). These results underscore the good fruit preservation capability of P-PLS 2 , attributed to its PLS 2 emulsion coating, which effectively retains moisture.
3.6. Recyclability and biodegradability of PLS emulsion coated paper
The recyclability of packaging paper is essential to the circular economy, as recyclable paper can significantly reduce costs and improve environmental sustainability. Currently, common coated papers (such as LDPE coated paper) face considerable challenges during recycling ( Aayanifard et al., 2024 ). These plastic coatings are difficult to separate from paper fibers, which adversely affects the mechanical properties and uniformity of recycled paper products. Therefore, the recyclability of P-PLS 2 was evaluated. When the coated paper was immersed in water at 100°C, the PVA in the PLS emulsion coating completely dissolved due to the disruption of its
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