Development of an Agar–Lignin Composite as a Sustainable Shoe Insole Material with Improved Moisture Control and Antibacterial Activity
Yejin Kim
The American School in Japan, Tokyo, Japan
Publication date: July 10, 2026
The American School in Japan, Tokyo, Japan
Publication date: July 10, 2026
DOI: http://doi.org/10.34614/JIYRC2026I24
ABSTRACT
The growing demand for sustainable footwear materials has increased interest in biodegradable alternatives to petroleum-based shoe insoles. This study developed and evaluated agar–lignin composite films as eco-friendly insole materials with a focus on moisture behavior and antibacterial performance. Agar was selected for its flexibility and moisture-absorbing properties, while lignin was incorporated for its structural strength and natural antibacterial activity. Composite samples containing varying lignin concentrations were prepared, cast into thin films, and tested for drying behavior, surface moisture performance, and antibacterial activity against Escherichia coli (DH5α). Increasing lignin concentration reduced drying time, decreased retained surface moisture, and enhanced antibacterial activity. Moisture absorption improved at low-to-moderate lignin levels before stabilizing, while higher lignin levels promoted faster surface drying. Although higher lignin concentrations produced faster drying and stronger antibacterial effects, excessive lignin incorporation caused increased brittleness and visible structural cracking during film casting and handling. Therefore, the 5–10% lignin range was identified as the most balanced formulation because it improved moisture control and antibacterial activity while maintaining better physical integrity for potential insole applications. These findings suggest that agar–lignin composites are promising sustainable candidates for hygienic and moisture-managing shoe insole applications.
The growing demand for sustainable footwear materials has increased interest in biodegradable alternatives to petroleum-based shoe insoles. This study developed and evaluated agar–lignin composite films as eco-friendly insole materials with a focus on moisture behavior and antibacterial performance. Agar was selected for its flexibility and moisture-absorbing properties, while lignin was incorporated for its structural strength and natural antibacterial activity. Composite samples containing varying lignin concentrations were prepared, cast into thin films, and tested for drying behavior, surface moisture performance, and antibacterial activity against Escherichia coli (DH5α). Increasing lignin concentration reduced drying time, decreased retained surface moisture, and enhanced antibacterial activity. Moisture absorption improved at low-to-moderate lignin levels before stabilizing, while higher lignin levels promoted faster surface drying. Although higher lignin concentrations produced faster drying and stronger antibacterial effects, excessive lignin incorporation caused increased brittleness and visible structural cracking during film casting and handling. Therefore, the 5–10% lignin range was identified as the most balanced formulation because it improved moisture control and antibacterial activity while maintaining better physical integrity for potential insole applications. These findings suggest that agar–lignin composites are promising sustainable candidates for hygienic and moisture-managing shoe insole applications.
