Molecular interaction study of dimethyl sulfoxide solvent on cellulose and polyester dissolution from textile waste

Blended textile waste, such as polycotton (polyester and cotton), presents significant challenges to conventional textile recycling due to different physicochemical properties. Chemical recycling, particularly dissolution, is a method that highly promising strategy for selective fibre separation. However, most reported studies show that it highly depends on hazardous solvents and requires high energy input, which limits their environmental and economic feasibility. Since there are limited studies on the application of pure dimethyl sulfoxide (DMSO) as an alternative solvent for the selective dissolution of cotton from polycotton blends, marking this as a novel research area. Therefore, this study used an integrated computational and experimental framework to investigate the potential of using DMSO as a single solvent for fibre separation. Firstly, BIOVIA Material Studio 2023 were used to run molecular dynamics (MD) simulation to predict the intermolecular interactions between pure DMSO with cotton (cellulose) and polyester from textile waste. COMPASS force field was applied under NPT-NVT ensembles and paired with Andrensen-Berendsen thermostat to enable a reliable representation of molecular interaction. Next, the prediction was validated experimentally using a Taguchi L9 orthogonal array design for a precise result. Three main factors have been evaluated, which are temperature (50, 100, 150℃), concentration (4.5, 6.0, 7.5 mg/ml) and dissolution time (4, 6, 8 hours). The dissolution efficiency was evaluated using signal-to-noise (S/N) ratio analysis under the “larger the better” criterion and further assessed by analysis of variance (ANOVA). Lastly, the dissolved cotton was regenerated using water as an anti-solvent with a 1:10 ratio of cotton/DMSO to water method. Then, the quality of regenerated cotton and polyester fibre were analysed in terms of structural, thermal and morphological properties and compared to their respective pure fibres. Based on the results, MD simulation had predicted that cotton has stronger interactions with DMSO at 150℃ and 4.5mg/ml compared to polyester. These predictions were proven by the experimental process through dissolution. Based on the measured dissolution efficiency, cotton shows higher solubility in DMSO (~80%) compared to polyester (<20%). The final condition of Experiment E7 (150℃, 4.5 mg/ml, 8 hours) was the optimal combination in maximising dissolution performance of both cotton and polyester. In the meantime, S/N ratio and ANOVA analysis had confirmed that temperature is the most influential parameter affecting the dissolution process, as indicated by a p-value (<0.05) for both cotton (p=0.007) and polyester (p=0.043). These results show that solvent–polymer interactions and the dissolution performance of textile fibres in DMSO are significantly influenced by temperature. Finally, the characterisation shows result confirmed that both regenerated cotton and polyester fibres properties were similar to their respective pure fibres. For example, the FTIR spectrum exhibited a characteristic absorption band at 1427 cm⁻¹ and 898 cm⁻¹. This peak is assigned to the crystalline regions of cellulose I and β-glycosidic linkages, typically related to the amorphous structure of cellulose, respectively. The calculated lateral order index (LOI) of the absorbance ratio A1427/A898 was 3.25. This value suggests a predominance of the cellulose II crystalline structure in the analysed sample. Overall, this study has proven the effectiveness of DMSO as a selective solvent for cotton separation from polycotton blends.