Synergistic effects in the simultaneous supercritical CO2 impregnation of two compounds into poly(L- lactic acid) and polyethylene

•Aspirin, carvone and ketoprofen loading were compared with their simultaneous loading.•Synergy in {ketoprofen + aspirin/carvone} impregnation in PLLA increases the loading.•Ketoprofen or carvone plasticizes PLLA and helps aspirin or ketoprofen diffusion.•PLLA chain mobility and interaction with the compounds collaborate in the synergy.•Ketoprofen and aspirin releases from PLLA are faster in double impregnated samples.