The complex crystalline behavior and tribological performance of polyhydroxyalkanoates

Structural, thermal, mechanical and tribological characterization of two polyhydroxyalkanoates were studied. The chemical composition of Poly[3-hydroxybutyrate-co-3-hydroxyhexanoate] (PHBHHx) and Poly[3-hydroxybutyrate-co-4-hydroxybutyrate] (P3HB4HB) was evaluated by means of NMR finding that the content of 3-hydroxyhexanoate in PHBHHx was 9.74 % and the content of 4-hydroxybutyrate in P3HB4HB was 29.65 %. XRD data showed that PHBHHx presented much higher crystallinity than P3HB4HB. However, the viscoelastic and mechanical tests conducted showed a complex and time-dependent crystalline behavior. Progressive-load and multi-scratch tests were carried out on these bioplastics with subsequent profilometry and SEM studies. The load resistance of PHBHHx was higher and the performance and wear mechanisms were found to be similar to thermoplastic materials. On the other hand, P3HB4HB presented a lower resistance to load and a wear mechanism similar to elastomeric materials. • The chemical composition of PHBHHx and P3HB4HB was determined by NMR and FT-IR. • PHBHHx showed higher crystallinity than P3HB4HB, as confirmed by XRD and FT-IR. • Viscoelastic and mechanical tests revealed time-dependent crystalline behavior. • Tribological tests indicated thermoplastic-like wear in PHBHHx and elastomeric-like wear in P3HB4HB. • PHBHHx exhibited greater load resistance compared to P3HB4HB under progressive and multi-scratch testing.