Philip Harding

The role of adhesion in the mechanical properties of filled polymer composites

Filled polymer composites have been prepared in which the energetics of the filler surfaces was systematically varied in order to investigate the dependence of the mechanical properties of the composite on the interfacial strength as predicted by the thermodynamic work of adhesion at the filler-matrix interface. A high-purity silica filler was used, treated with three different organofunctional silane coupling agents (two alkylsilanes and an aminosilane) to varying degrees from zero to complete coverage. The surface energetics of the modified fillers was characterized using both inverse gas chromatography (IGC) and dynamic contact angle analysis (DCA). While the surface energy assessments from IGC were higher than those obtained with wetting measurements, as expected, the trends with fractional coverage of silane were the same for each method, and were used to evaluate the thermodynamic work of adhesion. Highly filled polymer composites were prepared by dispersing the variously treated silica fillers into...

The adhesion promotion mechanism of organofunctional silanes

The adhesion promotion mechanism of organofunctional silanes has historically been attributed to the formation of an “interpenetrating polymer network” between a polymerized silane film and the polymer. This notion was investigated by formulating and testing two hypotheses. First, if the adhesion promotion is due to the formation of an interpenetrating polymer network, variation in the time-temperature profile of the bonding conditions should alter the extent of interdiffusion and thus interfacial strength. Second, if the adhesion promotion is due to compatibility and penetration of the silane organofunctional group, not the bulk silane film, variation in the structure of that group should change interfacial strength. Direct interfacial strength measurements using single-particle composites show that variation in the time-temperature profile of bond formation does not significantly affect interfacial strength. However, use of a series of aminofunctional silanes (with constant C : N ratio and identical surface energetics) revealed a relationship between length of the aminofunctional group and interfacial strength. These results suggest that the adhesion promotion for the system studied is controlled by compatibility and penetration of the silane organofunctional group. Whereas all of the interfaces studied here featured poly(vinyl butyral), the conclusions should apply to all amorphous polymeric materials.

The characterization of interfacial strength using single-particle composites

The adhesion between two dissimilar materials is best characterized by measurement of its mechanical strength. By determining adhesion, or interfacial strength, in the most direct way possible, one can identify more readily the relevant adhesion mechanisms that might be at play at the interface. A technique is presented here whereby a single spherical particle is introduced into a polymeric matrix and particle-matrix adhesion is directly measured. The interfacial strength is determined by submitting the single-particle composite (SPC) to a uni-axial tensile field, recording the macroscopic stress at which interfacial failure occurs and relating this stress to the actual stress experienced at the interface using elasticity theory. Experiments using glass spheres embedded in a poly(vinyl butyral) matrix showed interfacial failure at stress levels that varied significantly with the surface treatment of the glass sphere. Results from the SPC measurements compared well with those of a modified 180° peel test. ...

Influence of the fiber surface properties on the mechanical strength of unidirectional fiber composites

The influence of the thermodynamic adhesion between fibers and matrix on the mechanical properties of a continuous fiber reinforced composite is studied for two systems: carbon fiber reinforced poly(ether ether ketone) and glass fiber reinforced poly(ether imide). The fibers are modified chemically and characterized by measuring the contact angle formed by molten resin on the fibers. Various fiber treatments yield a wide range of contact angles, which are determined optically. Unidirectional fiber reinforced laminates are manufactured and transverse flexural strength is measured with the values reported as a function of the specific work of adhesion. It is shown that adhesion at the fiber-resin interface correlates with both the composite strength and the void morphology within the laminate after consolidation.

Measurement of residual stress effects by means of single-particle composite tests

Keywords: adhesion ; interfacial strength ; residual stress ; adhesion meaurement Reference LTC-ARTICLE-1998-010View record in Web of Science URL: http://www.ingentaconnect.com/content/01694243 Record created on 2006-06-26, modified on 2016-08-08