Studi pengaruh penambahan fraksi volum penguat Multi Wall Carbon Nano Tubes (MWCNT) terhadap konduktivitas listrik dan sifat mekanis material pelat bipolar berbasis nanokomposit MWCNT/PP = Study of influences of addition volume fraction of Multi Wall Carbon Nano Tubes (MWCNT) reinforcement to the electrical conductivity and mechanical properties of bipolar plate material based on nanocomposite MWCNT/PP