On the Application of Vickers Micro Hardness Testing to Isotactic Polypropylene.

Area of Science:

• Materials Science
• Polymer Science
• Mechanical Engineering

Background:

• Hardness is a key material property, but viscoelastic polymers present challenges due to test parameter dependency.
• Vickers microhardness testing offers a method for evaluating polymer indentation resistance.
• Standardized protocols are needed for reliable polymer microhardness testing.

Purpose of the Study:

• To establish a detailed protocol for Vickers microhardness testing of isotactic polypropylene (iPP).
• To investigate the influence of test parameters (load, dwell time) on iPP hardness measurements.
• To demonstrate the application of the calibrated method for assessing polymer composites.

Main Methods:

• Sample preparation involved epoxy mounting, grinding with SiC paper, and polishing with alumina suspensions (down to 0.05 µm).
• Vickers microhardness testing was performed on isotactic polypropylene, varying load and dwell times.
• Data analysis included fitting hardness equations to a power law model and comparing results with literature values.

Main Results:

• Hardness measurements showed significant dependence on dwell time, more so than load.
• Strain recovery was complete after a dwell time period, with indent measurement recommended within 24 hours.
• Calibrated hardness data for carbon black-filled iPP were at least double those reported in the literature, highlighting the importance of specified testing parameters.

Conclusions:

• A robust methodology for Vickers microhardness testing of polymers, specifically iPP, has been developed.
• Accurate polymer hardness assessment requires careful consideration and calibration of test parameters, particularly dwell time.
• This work serves as a critical guide for polymer microhardness testing, addressing inconsistencies in existing literature data.