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
Table 1 The coding and formulation of emulsion coatings.
Sample
LNPs (2%) (g)
PVA (12%) (g)
SA (g)
PLS 0
5 5 5 5 5 5
5 5 5 5 5 5
0
PLS 0.25 PLS 0.5
0.15
0.3 0.6 0.9 1.2
PLS 1
PLS 1.5
PLS 2
LNPs, lignin nanoparticles; PVA, polyvinyl alcohol; SA, stearic acid; PLS, PVA/LNPs/SA.
2.3. Preparation of Pickering emulsion coatings
Firstly, PVA was dissolved in deionized water under constant stirring at 90°C to prepare a 12% ( w/w ) aqueous solution. Subse- quently, 5 g of this PVA solution was mixed with 5 g of a 2% ( w/w ) LNPs suspension and a specified amount of SA. The mixture was heated to 80°C in a water bath to completely melt the SA, and then homogenized using a high-shear emulsifier (D-500, Wiggens, Germany) at 15 000 r/min for 5 min to form a stable emulsion. After homogenization, the emulsion was rapidly cooled in an ice-water bath to induce SA recrystallization. The resulting emulsion coatings were labeled as PLS x emulsion coatings, where x represents the mass ratio of SA to PVA ( Table 1 ).
2.4. Preparation of PLS emulsion coated paper
The PLS emulsion was uniformly applied on both sides of the bleached paper using a coating machine (ZY-TB-X3, Zhongyi, China) equipped with a 100 μm coating bar, operating at a constant speed of 5 mm/s. The coated paper was initially dried at room temperature, followed by complete drying in a vacuum oven at 50°C until a constant weight was achieved. The obtained paper was named P-PLS x , while the paper treated with the coating without SA was designated as P-PLS 0 . The paper coated with non-emulsified PLS 2 coating was named P-PLS 2 − M.
2.5. Characterization
The particle size and zeta potential of LNPs were determined using a particle nano sizer and zeta-potential tester (Zetasizer Nano ZS90, Malvern Instruments, UK). Morphological analysis of the LNPs was performed by transmission electron microscopy (TEM, JEM 2100, JEOL, Japan) at an accelerating voltage of 200 kV. The average droplet diameter and size distribution of PLS emulsions were measured with a laser particle size analyzer (Mastersizer 3000, Malvern Instruments, UK). The morphology of emulsions was characterized by confocal laser scanning microscopy (CLSM, LSM 900, ZEISS, Germany). The PVA and LNPs were stained with fluorescein sodium, while the SA was stained with Lumogen F Red 305. The excitation/emission spectra were 488/515 nm for fluorescein sodium and 561/616 nm for Lumogen F Red 305. The morphology of dried emulsions and coated paper was examined by using scanning electron microscopy (SEM, Adpreo S HiVac, Thermo Scientific, USA). The dynamic rheological properties of PLS emulsions were evaluated with a rotational rheometer (AR2000ex, TA Instruments, USA) at 25°C. The chemical properties of the coated paper surface were measured by using an X-ray photoelectron spectrometer (XPS, SCALAB 250Xi, Thermo Scientific, USA). According to the Chinese standard GB/T 453 —1989 (Paper and board —Determination of tensile strength —Constant rate of elongation method ), the tensile strength of the coated paper was assessed using an electronic universal testing machine (UTM 2503, Suns, China). To determine the wet tensile strength, the paper was first immersed in deionized water for 20 min. Surface wettability was characterized using a contact angle meter (Attension Theta, Biolin Scientific, Sweden). Paper absorbency was quantified with a Cobb sizing instrument (ZZ-100, Changchun Paper Machinery Co., Ltd., China) according to the Chinese standard GB/T 1540 —2002 (Paper and Board-Determination of Water Absorption-Cobb Method, China). Oil resistance was evaluated following TAPPI T 559 cm- 12 (Grease Resistance Test for Paper and Paperboard), with test solvents prepared by blending castor oil, n -heptane, and toluene in specified ratios. The water vapor transmission rate (WVTR) of paper was determined in accordance with the Chinese standard GB/T 1037 —2021 (Test Method for Water Vapor Transmission of Plastic Film and Sheet-Desiccant Method and Water Method, China) using a water vapor permeability tester (C360M, Languang, China) under conditions of (23 ± 2)°C and (50 ± 2)% relative humidity. The oxygen transmission rate (OTR) of the paper was determined using a gas permeability tester (VAC-V2, Languang, China) in accordance with Chinese standard GB/T1038.1 —2022 (Plastics-Film and Sheeting-Determination of Gas-Transmission Rate-Part 1: Differential-Pressure Methods, China) under conditions of (23 ± 2)°C and (50 ± 2)% relative humidity.
2.6. Fruit preservation test
To evaluate the effect of paper packaging on fruit preservation, bayberries, grapes, and cherry tomatoes were wrapped in bags made of uncoated paper and P-PLS 2 , with the openings sealed using adhesive tape. These packaged fruits were then compared with unpackaged control samples exposed to ambient conditions. The experiment was conducted under natural environmental conditions,
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