Evaluation of Cellulase Reusability for Efficient Separation of Cotton and Polyester Blends

Abstract

Textile waste, mainly composed of cotton-polyester blended fabrics, poses a major challenge for achieving circularity in textile industry. Enzymatic recycling technologies offer promising solutions by enabling separation of PET from blends by cellulose hydrolysis using specific enzymes, cellulases. However, industrial application of this technology is currently affected by relative high costs due to slow hydrolysis rates.
This master's thesis investigated the recyclability of cellulases for the treatment of cotton-polyester blended textile waste. Specifically, a particular enzyme formulation was used for several consecutive cotton degradation cycles on cotton-polyester substrate in a 50:50 ratio and its recyclability was evaluated by measuring total protein concentration via Bradford assay, protein composition by SDS-PAGE and cellulase activity using filter paper assay. Cotton degradation products were monitored by measuring the soluble reducing sugar content in the solution via the neocuproine method. The quantitative change in substrate was determined by the total fabric weight loss and related cellulose hydrolysis. FT-IR analysis was performed to detect compositional changes in the treated textile. The starting solution was reused for all further sequential degradation cycles, with fresh substrate introduced after each cylce. The experimental setup was continuously optimised and evaluated for its suitability. Using this adapted setup, the enzyme formulation ‘Cellic CTec 3 EU HS’ was analysed for trends in hydrolysis rate, cotton degradation efficiency, and the feasibility of reusing cellulases was assessed on the basis of these results.
The adapted experimental setup was considered suitable for investigating the recyclability of cellulases, using a 6-hour test duration, 2-hour sampling frequency, 1.5 cm² substrate size and 0.5 ml enzyme formulation (φ = 1%). The Neocuproine method showed partially deviating results, suggesting it may only be suitable for gaining an initial insight. The determination of cotton weight loss in combination with FT-IR analysis of the remaining substrate proved to be a more reliable method to investigate the efficiency of enzymatic cotton degradation. Bradford assay for monitoring total protein concentration was a useful tool and SDS-PAGE analysis provided additional insight, albeit only partially with consistent results that should be interpreted carefully. In the first two reuse cycles with recycled cellulases, the enzyme formulation ‘Cellic CTec 3 HS’ still achieved a cotton degradation of over 85% of the weight loss observed in the initial degradation cycle, dropping to 82% in the third cycle and 75% in the fourth. FT-IR analysis indicated the highest cotton degradation in the initial hydrolysis cycle, with decreasing levels in subsequent cycles. Bradford assay and filter paper assay showed the strongest decrease during the initial application cycle and slower decreases in subsequent cycles. Cellulase activity decreased from 135 FPU/ml after the initial cycle to 102 FPU/ml after the fourth cellulase recycling cycle. These findings demonstrate the feasibility of cellulase recycling and provide a basis for further research, potentially supporting industrial application by minimising process costs and improving cotton-polyester blended textiles recyclability.

Date of Award	2024
Original language	English
Supervisor	Christian B. Schimper (Supervisor) & Susanne Gangl (Supervisor)