Pembuatan pelumas bio berbasis minyak kelapa sawit melalui reaksi pembukaan cincin efame (Epoxidized Fatty Acid Methyl Esther) menggunakan resin penukar kation amberlyst-15 = synthesis of palm oil based biolubricant through ring opening reaction of efame (Epoxidized Fatty Acid methyl Esther) using cation exchange resin amberlyst-15