## 4 Conclusions  
It was found that chlorosulfonation in solution is an efficient method to prepare R-HIPS sulfonated material for membrane preparation. Sulfonated recycled HIPS asymmetric membranes were prepared using a phase inversion method, with a coagulation bath of commercial vinegar/isopropanol (15/85% \(v/v\)) and 0.12% NaHCO\({}_{3}\). This process resulted  
Figure 5: Salts and dye rejection performances of R-HIPS, R-HIPS-3, R-HIPS-5 membranes.  
in the formation of asymmetric membranes, with pore sizes ranging from 4.0 to 3.3 nm and porosities between 75.0% and 63.9%, attributed to a delayed demixing process, particularly for R-HIPS sulfonated membranes. The degree of sulfonation significantly impacted the membrane's morphology, hydrophilicity, antifouling properties, and particle rejection capabilities for substances such as MgSO\({}_{4}\), Na\({}_{2}\)SO\({}_{4}\), and Black 5 dye. As the sulfonation degree increased, R-HIPS, R-HIPS-3, and R-HIPS-5 membranes exhibited a decrease in pore size and porosity, with a slight reduction in water permeation flux, dropping from 6.0 L/m\({}^{2}\)h in the R-HIPS membrane to 3.1 L/m\({}^{2}\)h in the R-HIPS-5. Notably, higher sulfonation levels enhanced hydrophilicity, leading to improved antifouling properties and separation performance. In particular, R-HIPS-5 membrane demonstrated promising results, achieving a separation efficiency of 94% for Black 5, 72% for MgSO\({}_{4}\), and 67% for Na\({}_{2}\)SO\({}_{4}\), with a high flux recovery ratio of 58%. These results are attributed to a smaller pore size and increased sulfonic acid group concentration in R-HIPS-3 and particularly R-HIPS-5 membranes, which enhanced their rejection efficiency.  
Given the feasibility of producing flat membranes and their separation properties, these membranes could be useful for the production of spiral-wound modules. Scaling up could enhance their separation efficiency in large-scale wastewater treatment processes for the removal of dyes from water industrial stream and for industrial product purification applications. Recycling materials such as HIPS waste offers an alternative way to reduce plastic waste and reintroduce it into the circular economy using membranes for water purification, increasing its value.  
Conceptualization, M.O.G.-D. and M.A.-V.; Methodology, M.A.-Y.-C., R.S.-S.D. and E.U.-F.; Validation, M.H.-I., D.P.-C. and E.U.-F.; Formal analysis, M.A.Y.-C. and R.S.-S.; Investigation, M.A.Y.-C., R.S.-S., S.D. and M.H.-I.; Resources, M.O.G.-D. and M.A.-V.; Writing--original draft preparation, M.A.Y.-C.; Writing--review and editing, M.O.G.-D., D.P.-C. and M.A.-V.; Supervision, M.O.G.-D.; Funding acquisition, M.O.G.-D. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Ciencia de Frontera CONAHCYT, grant number CF-2023-I-670.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
[PERSON] acknowledges the CONAHCYT postdoctoral scholarship 96869. Moreover, the authors thank [PERSON] for the contact angle measurements and [PERSON] for the SEM technical assistance.  
The authors declare no conflicts of interest.