An experimental investigation of the scratch behaviour of polymers – 2: Influence of hard or soft fillers

• Effect of hard and soft fillers on scratch behaviour of two polymers was assessed.
• Bulk mechanical properties were compared with predictions of theoretical models.
• Variations in scratch hardness were discussed in view of particle type and size.
• Hard fillers increase hardness but scratching mode may change from ductile to brittle.
• Scratch behaviour upsets if phase inversion occurs on varying filler content.

Variation in the scratch behaviour of polymers with incorporation of different types and amounts of fillers was investigated both in terms of scratch visibility and scratch hardness. Scratch tests were carried out by a microscratch tester. The effect of fillers on the scratch deformation mode and hence on scratch visibility was evaluated by examining recorded penetration depth and acoustic emission traces together with optical microscope images of the groove left on the surface. Scratch hardness was determined by using a recently proposed scratch model. Adequacy of the model to interpret the local phenomenon induced by addition of fillers was questioned.It was demonstrated that incorporation of hard fillers can enhance the scratch hardness of polymers as well as their basic mechanical properties but leads to an increase in scratch visibility due to a change in scratch deformation mode from ductile ploughing to a brittle failure with crack formation. On the contrary, addition of soft fillers causes a reduction in scratch hardness but it also reduces scratch visibility since it improves the recovery characteristics of the polymer.