The prediction of adhesion in filled polymeric composites.

摘要

The notion that separate surface characterizations of the component materials in a composite can lead to the prediction of the bond strength between them is a recurring theme in the adhesion literature. In this work, the group contribution method of UNIFAC is used to investigate the influence of thermodynamic compatibility on the practical adhesion between mineral particulate fillers and matrix polymers in composites. Compatibility is enhanced between polymers and mineral surfaces through the use of silane coupling agents of varying chemistry. Adhesion strength measurements are obtained using the "single-particle composite" (SPC) method and then correlated with thermodynamic mixing quantities calculated from the UNIFAC method. The results indicate that enhanced adhesion strength corresponds to systems with more favorable thermodynamic mixing for three different thermoplastic amorphous polymers. Adhesion studies performed on a fourth amorphous polymer, polystyrene, indicated that the polymer was not wetting the glass beads. A similar study is conducted using a crystalline polymer that requires a nonoptical method for adhesion testing, viz., beam deflection tests of highly filled composites, since the polymer is not transparent. Results from these measurements indicate that higher flexural yield strengths also correlate with the UNIFAC-computed mixing parameter, providing another type of mechanical test whose measured adhesion parameter can be predicted using thermodynamics.;One of the limitations of the UNIFAC method to predict the adhesion performance between polymers and silane-treated surfaces is that it cannot fully account for the importance of the structure of the silane layer on the glass surface, and it does not address the significance of lateral crosslinking to an adhesive bond. Thus, a study was also conducted to explore the effect of silane adsorbate structure on adhesion performance. Finally, another mechanical test, an acoustic emission method for investigating adhesion failure in low volume fraction filled polymeric composites is described and used to study the influence of Lewis acid-base interactions on adhesion. The results indicate that the acoustic emission method can also be effectively used to study the adhesion between polymers and silane-treated surfaces.