Studies on Degumming Eri Silk Cocoons Cultivated in Ethiopia

Abstract

Background: Eri silk (Samia ricini) is a valuable non-mulberry silk with growing potential for sustainable textile production. Effective degumming is essential for removing sericin and other non-fibrous constituents while maintaining the desirable properties of the silk fibre. However, information on suitable degumming conditions for Eri silk cultivated in Ethiopia remains limited.

Objective: This study investigated the effects of sodium carbonate (Na₂CO₃) concentration, neutral soap concentration, and boiling duration on the degumming loss of Ethiopian Eri silk, focusing on Borduar white and Kokrajhar brick-red cocoon types.

Methods: A three-factor, three-level response surface design based on the Box–Behnken approach was employed. Na₂CO₃ concentration, neutral soap concentration, and boiling duration were varied within the ranges of 10–20%, 10–20%, and 0.5–1.5 h, respectively. Degumming loss was determined from the mass loss following treatment. The experimental data were analyzed using Design-Expert 13 through analysis of variance (ANOVA), regression modeling, response surface analysis, and residual diagnostics.

Results: The linear models were statistically significant for both Borduar white (p=0.0033) and Kokrajhar brick-red (p=0.0034). Na₂CO₃ concentration was the most influential factor, followed by boiling duration, whereas neutral soap concentration had no significant linear effect. The models explained approximately 64.0% and 63.7% of the variation in degumming loss for Borduar white and Kokrajhar brick-red, respectively. The predicted responses showed close agreement with the experimental results, with mean absolute errors of approximately 0.28 percentage points for both cocoon types. Kokrajhar brick-red exhibited consistently higher degumming loss than Borduar white, with predicted center-point values of 13.72% and 10.71%, respectively.

Conclusion: Na₂CO₃ concentration and boiling duration are the principal processing variables governing degumming loss of the investigated Ethiopian Eri silk cocoons. The findings provide a quantitative basis for optimizing Eri silk degumming, while further studies incorporating residual sericin and fibre-quality properties are recommended.