Primary surface measurement reported
Water contact angle of electrospun lignin/PLA fiber mats and a neat PLA control, measured by the sessile drop method under ambient conditions.
Client Citation Analysis
Multifunctional, Flexible, Electrospun Lignin/PLA Micro/Nanofiber Mats from Softwood Kraft, Hardwood Alcell, and Switchgrass CELF Lignin
This study compares electrospun 1:1 lignin/PLA micro/nanofiber mats from multiple lignin origins and fractions, with water contact angle used as a functional readout for hydrophobicity alongside morphology, thermal, mechanical, and antioxidant measurements.
At-a-Glance Summary
Dropometer attribution in the paper
The methods state that water contact angle measurement was carried out using the “Droplet Lab smartphone-based tensiometer (Toronto, ON, Canada)” with the sessile drop method, and the resulting contact angle was calculated using Young–Laplace fitting with automatic Droplet Lab software analysis.
How the surface-tension / contact-angle data were used in the study
The contact-angle data were used to compare hydrophobicity across lignin biomass origins, isolation methods, and fractions within a common 50:50 lignin/PLA electrospinning platform. The authors then interpreted those wettability trends together with hydroxyl-group content, crosslinking behavior, thermal transitions, modulus, and morphology to discuss application-relevant differences among the mats.
Replication / reliability statement
Triplicate measurements were taken within 10 s in three different areas of each sample, and the average contact angle was calculated for each sample.
Paper Details
Title
Multifunctional, Flexible, Electrospun Lignin/PLA Micro/Nanofiber Mats from Softwood Kraft, Hardwood Alcell, and Switchgrass CELF Lignin
Authors
Dorota B. Szlek; Emily L. Fan; Margaret W. Frey
Journal
Fibers
Year
2025
Volume
13
Pages / Article
129
License
CC BY 4.0
Journal context
What it is
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How to read it
Compare metrics within category; updates are annual and lag current-year publications.
Scopus metrics (Elsevier / Scopus rating 2024)
CiteScore 2024
7.4
CiteScore subject ranks (CiteScore 2024)
- Q1 - Civil and Structural Engineering (66/407)
- Q1 - Ceramics and Composites (32/130)
- Q1 - Mechanics of Materials (76/403)
- Q2 - Biomaterials
Journal Impact Factor (Clarivate JCR)
Journal Impact Factor (JCR 2024)
3.9
5-Year Impact Factor
4.1
JCR category rank
Q2 - Materials Science, Multidisciplinary
What Was Measured
Primary surface / interfacial measurement
The paper reports water contact angle as the surface measurement used to assess hydrophobicity of electrospun 1:1 lignin/PLA mats and a neat PLA control. Average contact-angle values are summarized in Table 3, with representative sessile-drop images shown in Figure 9.
Supporting measurements
The authors also measured suspension conductivity, fiber diameter, fiber morphology by SEM, chemical structure by FTIR, thermal behavior by DSC, mechanical properties by DMA, and antioxidant activity by DPPH reduction/UV-Vis. These measurements were used together with contact angle to interpret how lignin origin, isolation route, and fraction changed fiber performance.
Role of the Dropometer
Water contact angle measurement was carried out under ambient conditions using the Droplet Lab smartphone-based tensiometer and the sessile drop method. 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; the paper also states that Droplet Lab software performed the analysis automatically at the time of measurement collection.
In the study workflow, these Dropometer outputs served as the direct hydrophobicity readout used to compare lignin source, pretreatment method, and fraction within the electrospun 1:1 lignin/PLA system.
Key Findings
Lignin generally increased hydrophobicity
Nearly every lignin/PLA mat showed a higher average water contact angle than neat PLA, which was reported at 110.75 ± 2.98°. The highest tabled values were 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.
Fraction effects depended on the fractionation route
Within Kraft lignin fractions, ASKL/PLA reached 126.72 ± 1.14° while AIKL/PLA was 114.47 ± 1.86°, and EIKL/PLA reached 125.66 ± 7.06° while ESKL/PLA was 110.62 ± 2.30°. The authors connected these differences to solvent hydrogen-bonding capacity and differences in hydroxyl-group content across the fractions.
Contact-angle trends were interpreted with chemistry and mechanics
The paper reports a moderate inverse correlation between relative total hydroxyl-group content and contact angle (r = −0.43), along with positive relationships between contact angle and higher glass transition temperature (r = 0.45) and Young’s modulus (r = 0.79). In the authors’ interpretation, wettability was therefore tied to OH content, rigidity, and surface roughness of the fiber mats.
Alcell-based mats paired high contact angle with rigidity
ALE60/PLA combined the highest average water contact angle with the highest Young’s modulus and the lowest elongation at break among the mechanically tested mats. The paper also notes that SEM micrographs of Alcell-based fibers showed cracked lignin fiber cores encased in a more flexible PLA skin, reinforcing the distinct structural profile of this group.
Dropometer data fed directly into end-use differentiation
In the conclusions, hydrophobicity was part of the evidence used to distinguish mat families for different applications: SGL/PLA for air filtration, KL/PLA for biomedical and cosmetic-care contexts, and Alcell/PLA for water-filtration and packaging systems. Contact-angle data were one of the functional signals supporting those assignments.
Figures & Visuals
Figure 9 — Representative Dropometer outputs
What it shows
Figure 9 shows example sessile-drop contact-angle images for ESKL/PLA, neat PLA, and ALE60/PLA, giving a visual comparison of lower, baseline, and higher hydrophobic responses within the study.
Figure 6 — Surface morphology context for wettability
What it shows
Figure 6 provides SEM views of selected fiber mats, including ALE60/PLA and SGL/PLA, which the authors discuss alongside rigidity, roughness, and hydrophobic behavior.
Figure 3 — FTIR evidence tied to contact-angle interpretation
What it shows
Figure 3 maps OH-related and monolignol-related FTIR features that the authors later use to interpret differences in thermal behavior and contact angle across the lignin series.
Figure 4 — Crosslinking versus OH-content relationship
What it shows
Figure 4 visualizes the inverse relationship between degree of crosslinking and hydrogen bonding / total OH content, which supports the paper’s chemistry-based reading of wettability trends.
Why It Matters
In this paper, contact angle is one of the functional measurements that separates otherwise similarly processed 1:1 lignin/PLA electrospun mats. Because the electrospinning framework was held constant while lignin source and fraction changed, the Dropometer data gave the authors a direct way to compare how lignin selection shifted surface hydrophobicity across the series.
Those wettability results were then read together with FTIR, DSC, DMA, SEM, conductivity, and antioxidant data to build a fuller property map for the mats. In practical terms, the Dropometer output helped the authors sort which lignin/PLA combinations aligned better with flexible, rigid, barrier-oriented, or multifunctional fiber applications.
Practical Takeaways
Same blend ratio, different wetting outcome
With a fixed 50:50 lignin/PLA formulation and common electrospinning settings, average water contact angle still varied substantially across lignin families and fractions, showing that lignin selection materially changed surface behavior.
Fractionation can tune hydrophobicity
The separation between AIKL/PLA and ASKL/PLA, and between ESKL/PLA and EIKL/PLA, shows that solvent-based fraction choice changed the contact-angle result even within the same Kraft-lignin family.
Alcell fractions delivered the highest tabled contact angles
ALE60/PLA and ALE100INS/PLA provided the top average water contact angles in Table 3, and the paper discusses these materials together with rigidity and barrier-oriented application directions.
Neat KL and SGL already performed strongly
The conclusions emphasize that KL/PLA and SGL/PLA combined strong hydrophobicity with broader functional performance without requiring an extra fractionation step for fiber formation.