Case Study 606 Polyolefin Adhesion Study
This case study, authored by Daniel Burnett of Surface Measurement Systems Ltd., investigates how the surface energies of six thermoplastic polyolefin (TPO) formulations influence paint adhesion. Using Inverse Gas Chromatography (IGC SEA) on a SMS‑IGC SEA 2000 system, the dispersive component of surface energy was measured for TPO samples containing three different elastomers (Exxact 3125, 4033, 4049) at two loadings (12 wt% and 25 wt%). The study correlated these thermodynamic measurements with practical adhesion performance obtained from SLIDO compressive‑shear (traction force) tests on painted specimens, and with microhardness testing as a proxy for crystallinity. Key findings include: (1) dispersive surface energy rises with increasing elastomer content and follows the trend 3125 < 4033 < 4049; (2) higher dispersive energy yields higher traction force, indicating better paint adhesion; (3) higher crystallinity (higher microhardness) corresponds to lower dispersive energy and poorer adhesion. The polar probe measurements were inconclusive, confirming that TPO surfaces are dominated by dispersive interactions. The authors conclude that IGC SEA can serve as a predictive tool for TPO‑paint adhesion and substrate performance.
Topics
IGC SEA Methodology for Quantifying Dispersive Surface Energy of TPOs
Details the inverse gas chromatography experimental setup, probe molecules, column preparation, temperature, flow rates, and calculation of dispersive surface energy from n‑alkane retention times.
Elastomer Type and Loading Effects on Surface Energy and Adhesion
Analyzes how three elastomers (3125, 4033, 4049) and two weight‑percent loadings (12 % vs 25 %) modify the dispersive surface energy and consequently the paint adhesion performance.
Correlation Between Dispersive Surface Energy and SLIDO Traction Force
Presents the empirical relationship linking measured dispersive surface energies to the peak compressive‑shear load required for shear delamination of painted TPO samples.
Crystallinity (Microhardness) Versus Surface Energy: Inverse Relationship
Shows that higher microhardness (indicating greater crystallinity) corresponds to lower dispersive surface energy and reduced paint adhesion, establishing crystallinity as a secondary factor.
Practical Implications: IGC SEA as a Predictive Tool for TPO‑Paint Performance
Summarizes the study’s conclusion that IGC SEA measurements can forecast paint adhesion outcomes, offering a rapid, non‑destructive alternative to extensive mechanical testing.
Experimental Protocols: Sample Preparation, Coating System, and SLIDO Testing
Outlines the preparation of TPO pellets, the wet‑on‑wet‑on‑wet spray‑applied adhesion promoter/basecoat/clearcoat system, bake schedule, and the SLIDO compressive‑shear testing parameters.