Paper Number
PF9
Session
Applied Rheology for Pharmaceuticals, Food and Consumer Products
Title
Frictional shear stress dissipation in slip-induced solid lubricant using tribo-rheometry
Presentation Date and Time
October 13, 2022 (Thursday) 9:25
Track / Room
Track 2 / Mayfair
Authors
- Jani, Pallav K. (North Carolina State University, Chemical and Biomolecular Engineering)
- Khan, Saad A. (North Carolina State University, Chemical and Biomolecular Engineering)
- Hsiao, Lilian (North Carolina State University, Chemical and Biomolecular Engineering)
Author and Affiliation Lines
Pallav K. Jani, Saad A. Khan and Lilian Hsiao
Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27606
Speaker / Presenter
Jani, Pallav K.
Keywords
experimental methods; consumer products; microscopy; rheometry techniques
Text of Abstract
Organic slip-induced solid lubricants are amphiphiles added as additives during polymer processing which migrate to the surface over time to form a boundary film that reduces friction. One such widely used solid lubricant is erucamide (ER), a C22 chain fatty amide, extensively used in packaging films, bottle caps, nonwovens in hygiene products as well as anti-biofouling elastomeric coatings to impart a slippery surface. While ER migration in polymeric matrices is well understood, a comprehensive understanding of the slip properties under different tribological operating conditions and materials encountered in the various applications is lacking. We examine the dry kinetic frictional properties of ER boundary films on a range of polymer-polymer contacts using a tribology accessory on a stress-controlled rheometer. Specifically, we investigate how the changes in contact pressure and substrate modulus affect the frictional shear stress dissipation in five solid-solid contacts: Si wafer/ER-polypropylene (PP), PP/ER-PP, low density polyethylene/ER-PP, polydimethylsiloxane (PDMS)/ER-PP and PDMS/ER-PDMS. ER boundary films are obtained by drop-casting ER solution in 2-propanol to achieve a complete surface coverage. Utilizing Bowden and Tabor’s adhesive theory of friction to calculate the pressure dependence of the shear stress, we find two different regimes of frictional dissipation of ER boundary films–below a threshold pressure, the interfacial shear stress is independent of pressure, indicative of the adhesion-dominant frictional regime. This constant shear stress represents the energy barrier required to continuously shear the ER layer and maintain sliding. Above the threshold, ER demonstrates a linear increment in shear stress with pressure, suggestive of the macroscopic load-dominant regime, wherein the ER layers are squeezed as a function of the pressure. Our results show how applied pressure impacts the stress dissipation mechanism which can affect the frictional benefit offered by ER films in consumer products.