Following the successful sulfonation of waste expanded polystyrene packaging from our teaching laboratories to produce polystyrene sulfonic acid (PSSA), we have now extended this protocol to other polystyrene (PS) laboratory consumables, including serological pipettes, spectroscopy cuvettes, and Petri dishes. The resulting PSSA can be used as a solid acid catalyst in organic synthesis.

In the YouTube video included in this post, the complete process, from PS purification and precipitation to sulfonation and PSSA production, is demonstrated using waste serological pipettes. However, the same procedure can be applied to a wide range of PS-based laboratory waste.

The process begins with the purification of the waste PS to remove potential impurities and additives. For approximately 6 g of polystyrene pipettes, 75 mL of ethyl acetate was used to dissolve the material in a warm water bath. Any insoluble impurities, such as printing ink from the pipette graduations, can then be easily removed by filtration. Subsequently, around 50 mL of ethanol was added to precipitate the dissolved polymer. The recovered PS was isolated by vacuum filtration and dried overnight in an oven.

The following day, the purified PS was ground using a pestle and mortar to obtain a fine powder suitable for sulfonation. One gram of the purified PS was then sulfonated to produce PSSA. The reaction was carried out using 10 mL of concentrated sulfuric acid at 100 °C for 1 hour. After completion, the reaction mixture was quenched with ice-cold water, and the resulting solid was isolated by vacuum filtration. The material was washed repeatedly with water until the filtrate reached a neutral pH. The PSSA was then dried overnight in an oven at 80 °C.

The degree of sulfonation of the PSSA samples was determined by acid–base titration using phenolphthalein as an indicator. Depending on the starting PS waste material and reaction conditions, sulfonation degrees ranging from 19% to 27% were obtained. The resulting PSSA was slightly off-white in colour compared with the purified PS precursor.

FTIR analysis of the PSSA samples reveals the appearance of a broad absorption band ~3400 cm⁻¹, corresponding to O–H stretching vibrations associated with sulfonic acid (–SO₃H) groups. In addition, characteristic bands in the 1000–1200 cm⁻¹ region are observed, corresponding to sulfonate stretching vibrations that are absent in the original waste PS sample. These spectral changes provide clear evidence of successful sulfonation.

Watch our titration video to learn how to determine the number of acidic sites in your PSSA using a simple titration with NaOH and phenolphthalein. Once you have quantified the number of acidic sites per gram of resin, you are ready to use your upcycled PSSA as a solid acid catalyst in organic synthesis.