Effect of Blend Composition on Scratch Behavior of Polystyrene/Poly(2,6-dimethyl-1,4-phenyleneoxide) Blends

The relationship between the scratch behavior and molecular aggregation states of polystyrene (PS), poly(2,6-dimethyl-1,4-phenyleneoxide) (PPO), and their blends, is investigated based on differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), polarized optical microscopy (POM), and indentation and scratch tests. DSC reveals that all the PS/PPO blends show the single glass transition temperature (T_g) and the T_g monotonically increase and T_g breadth exhibits a maximum, with an increase in PPO content. Furthermore, density and intermolecular chain distance obtained by WAXD exhibits maximum and minimum values at near 50 wt% of PPO, respectively. It is evident that densification occurs by blending PS and PPO. The scratch coefficient of friction (SCOF) value of PS is the largest and PS exhibits a fish-scale pattern after scratch testing, while the SCOF value of PPO is much smaller than PS and PPO exhibits smooth groove formation. The PS50/PPO50 and PS20/PPO80 blends exhibit superior scratch and indentation resistance than PS and PPO. Damage morphology observation by POM and indentation tests reveals that molecular orientation is more restricted, and resistance against indentation increases for blends. This is due mainly to densification of the blend system.