Researchers developed biobased interpenetrating polymer network (IPN) membranes using natural compounds with opposing polarity in water, without toxic cross-linking agents. Agarose and natural rubber latex were self-assembled and self-cross-linked to form nanodomains. The membranes exhibited excellent solvent resistance and tunable molecular sieving, with separation performance ranging from 227–623 g mol⁻¹. A carcinogenic impurity at 5 ppm was successfully removed with minimal pharmaceutical loss. The membranes are biodegradable, enabling an environmentally friendly end-of-life phase. The IPN membranes showed improved thermal and mechanical stability, with a swelling degree of ~158% and long-term stability in nanofiltration. The membranes demonstrated high rejection rates for solutes like oleuropein (99.5%) and Methyl Orange (88.1%), with an average acetone flux of 53 L m⁻² h⁻¹. The membranes were used for API purification, removing carcinogenic impurities below toxicological concern thresholds. The IPN membranes offer a sustainable alternative to conventional membranes, with biodegradability confirmed over 14 days of enzymatic treatment. The study highlights the potential of biobased IPN membranes for sustainable molecular sieving in various applications.Researchers developed biobased interpenetrating polymer network (IPN) membranes using natural compounds with opposing polarity in water, without toxic cross-linking agents. Agarose and natural rubber latex were self-assembled and self-cross-linked to form nanodomains. The membranes exhibited excellent solvent resistance and tunable molecular sieving, with separation performance ranging from 227–623 g mol⁻¹. A carcinogenic impurity at 5 ppm was successfully removed with minimal pharmaceutical loss. The membranes are biodegradable, enabling an environmentally friendly end-of-life phase. The IPN membranes showed improved thermal and mechanical stability, with a swelling degree of ~158% and long-term stability in nanofiltration. The membranes demonstrated high rejection rates for solutes like oleuropein (99.5%) and Methyl Orange (88.1%), with an average acetone flux of 53 L m⁻² h⁻¹. The membranes were used for API purification, removing carcinogenic impurities below toxicological concern thresholds. The IPN membranes offer a sustainable alternative to conventional membranes, with biodegradability confirmed over 14 days of enzymatic treatment. The study highlights the potential of biobased IPN membranes for sustainable molecular sieving in various applications.