Client Citation Analysis
Water contact angle on electrospun lignin/PLA fiber mats, measured with deionized water by sessile drop under ambient conditions, with average values reported in Table 3 and representative images shown in Figure 9.
The paper states that water contact angle was measured using the “Droplet Lab smartphone-based tensiometer (Toronto, ON, Canada)” with the Sessile drop method, and contact angle was calculated using Young–Laplace fitting.
The contact-angle data were used to compare hydrophobicity across lignin biomass origins, isolation methods, and fractions, and to interpret those trends together with thermal behavior, hydroxyl-group content, and mechanical stiffness. The authors use these combined results to differentiate formulations suited to flexible, hydrophobic, or antioxidant-focused end uses.
Triplicate measurements were taken within 10 s by applying the water droplet in three different areas of each sample, and the average contact angle was calculated for each sample.
The primary surface measurement reported is water contact angle of electrospun 1:1 lignin/PLA fiber mats. Average water contact angle values are listed for KL/PLA, AIKL/PLA, ASKL/PLA, EIKL/PLA, ESKL/PLA, ALE40/PLA, ALE60/PLA, ALE100/PLA, ALE100INS/PLA, SGL/PLA, and neat PLA in Table 3.
The paper pairs contact-angle data with suspension conductivity, fiber diameter, and SEM-observed morphology, as well as FTIR-based lignin structural analysis, DSC thermal behavior, DMA mechanical properties, and DPPH antioxidant activity. These measurements are used to interpret hydrophobicity differences across lignin source, extraction route, and fractionation condition.
Droplet Lab smartphone-based tensiometer (Toronto, ON, Canada)
Carl Zeiss AG LEO 1550 Field Emission Scanning Electron Microscope (FE-SEM) with InLens and SE2 detectors
SEM Keck (FEI Company, Hillsboro, OR, USA) and ImageJ.JS software (version 1.54p)
FTIR-ATR Perkin Elmer Spectrum spectrometer
Differential Scanning Calorimetry (DSC) Q2000, V24.9, Build 121 instrument from TA Instruments
TA Instruments Dynamic Mechanical Analysis (DMA) Model Q800DMA
Mitutoyo Digimatic Indicator Type IDF-112E
BioTek Synergy Neo2 multimode microplate reader
Water contact angle measurement was carried out using the Droplet Lab smartphone-based tensiometer with the Sessile drop method under ambient conditions. A droplet of deionized water was generated on each sample surface using a Hamilton Gastight #1750 syringe fitted with an 18-gauge needle, and the resulting contact angle was calculated using Young–Laplace fitting; analysis was performed automatically by Droplet Lab software at the time of measurement collection.
In the study workflow, these Dropometer-derived contact-angle results were used to compare hydrophobic performance across lignin formulations and to interpret those differences together with FTIR, DSC, and DMA trends.
Across nearly all formulations, adding lignin to PLA increased the hydrophobicity of the fiber mats relative to neat PLA. This is visible in Table 3, where most lignin/PLA samples have average water contact angles above the PLA control value of 110.75 ± 2.98°.
Table 3 reports the highest average water contact angles for ALE60/PLA at 138.67 ± 4.37° and ALE100INS/PLA at 136.16 ± 5.10°, with KL/PLA and SGL/PLA also high at 131.37 ± 4.56° and 130.26 ± 2.63°, respectively. In the discussion, the authors group KL-, SGL-, and ALE60-containing mats among the strongest hydrophobic performers.
The paper shows that solvent fractionation did not shift contact angle in one uniform direction. In the Kraft series, ASKL/PLA was higher than AIKL/PLA, while EIKL/PLA was higher than ESKL/PLA, and the discussion links these differences to solvent hydrogen-bonding capacity and hydroxyl-group content.
The authors report that higher-performing hydrophobic samples tended to correlate with higher Tg values (r = 0.45), while contact angle showed a moderate inverse correlation with relative total hydroxyl-group content (r = −0.43). Earlier in the paper, they also note a negative correlation between the ~3400 cm⁻¹ FTIR peak area and contact angle measurements.
The paper links hydrophobicity to the mechanical character of the mats, reporting a strong correlation between hydrophobicity and Young’s modulus (r = 0.79). This is especially relevant for Alcell-based mats, which combined high contact angles with stiff, brittle mechanical behavior, while SGL/PLA paired high contact angle with stronger and more flexible performance.
Figure 9 shows representative water contact angle images for ESKL/PLA, neat PLA, and ALE60/PLA, making the wettability contrast visible at a glance.
Figure 6 provides SEM views of AIKL/PLA, ALE60/PLA, ASKL/PLA, and SGL/PLA, which the authors use alongside contact-angle results when discussing surface roughness, rigidity, and hydrophobic behavior.
Figure 4 supports the paper’s interpretation that lignin hydrogen bonding / total OH content and crosslinking relationships connect to thermal behavior and contact-angle trends.
Figure 5 shows photographs of KL/PLA, ALE60/PLA, and SGL/PLA mats, the same classes of materials highlighted in the paper’s wettability and application discussion.
In this paper, contact angle is one of the core functional readouts used to distinguish how lignin source, extraction method, and fractionation reshape electrospun lignin/PLA mat performance. The Dropometer-derived wettability data are not treated in isolation; they are interpreted together with FTIR, DSC, DMA, SEM, conductivity, and antioxidant results to separate formulations that behave as more flexible, more rigid, more hydrophobic, or more antioxidant-active materials.
That matters because the authors use those combined property maps to recommend different lignin/PLA systems for different end-use directions. In their conclusions, SGL/PLA is associated with air filtration, KL/PLA with wound dressings or cosmetic care, and Alcell/PLA with packaging and water-filtration-type barrier applications; the contact-angle data help define the hydrophobic side of those distinctions.
The paper uses average water contact angle to separate performance across lignin origin, extraction route, and fraction, with ALE60/PLA and ALE100INS/PLA sitting at the top of the Table 3 wettability range.
The authors tie contact-angle behavior to hydroxyl-group content, hydrogen bonding, crosslinking, and thermal response, which makes the Dropometer output more informative when paired with FTIR and DSC.
The acetone- and ethanol-fractionated Kraft samples do not move in one uniform direction, so the wettability gain depends on the specific fraction and solvent history rather than fractionation by itself.
In the paper’s interpretation, Alcell-based mats combine high contact angle with higher stiffness, while SGL/PLA and KL/PLA combine high contact angle with more favorable strength–flexibility balances for their proposed application contexts.
The reported contact-angle workflow is practical and direct: deionized-water sessile drops, Young–Laplace fitting, triplicate measurements, and three locations per sample.