The influence of particle size and polyester content on rheological properties and enzymatic hydrolysis of knife-milled polycotton textile waste

While textile production increases annually, <1 % enter closed-loop recycling. Current recycling technologies require pure input streams, necessitating separation of blended fabrics. Enzymatic hydrolysis of cotton from polyester-cotton blends yields a solid polyester fraction (allowing closed-loop mechanical recycling) and glucose solution. To convert clothing into processable feedstock, a disintegration step is essential.
The aim of the work was to assess how cutting mill disintegration affects key material parameters (rheological behaviour and specific surface area (SSA)). The milling process efficiency and correlation between material parameters and hydrolysis yield were studied for textile waste with 10, 50, and 100 % cotton, using a cutting mill with sieve hole sizes of 2, 4, and 8 mm. Average milling efficiency exceeded 90 % for 8 and 4 mm, with a composition-dependent decrease of up to 30 % at 2 mm.
The suspension flow factor indicates the formation of a homogenous network for substrate concentrations ≥ 30g L-1. Viscosity of the suspension increases by an order of magnitude with substrate concentration and cotton content but decreases with sieve hole size.
SSA does not correlate to sieve hole size but correlates linearly with enzymatic hydrolysis yield. The material fraction with the largest SSA showed an average 15 % increase in cotton degradation. SSA also weakly correlates to the suspension flow factor but is independent of viscosity.
When requiring high milling efficiency, SSA and hydrolysis yield and low suspension viscosity, 8 mm are the ideal sieve hole size for blended textiles, while 4 mm are preferable for pure cotton.