Reinforcement of the aromatic polyamide poly(trimethylhexamethylene terephthalamide): Comparisons among blended ex situ silica with and without a bonding agent and in situ generated silica

Samples of poly(trimethylhexamethylene terephthalamide) were first blended with separately prepared fumed silica in the absence of a coupling agent, a nd their mechanical properties were measured in continuous extension. The r einforcement obtained in this ex situ approach was qualitatively similar to that obtained by the in situ generation of silica in the sol-gel hydrolysi s and condensation of tetraethoxysilane. The increase of ultimate (tensile) strength, however, was only 10%, compared to the 25% obtained in the in si tu approach. Adding 20 or 40 mol% of an epoxysilane coupling agent to the e x situ samples gave increases in tensile strength up to 50%. Scanning elect ron microscopy showed interesting differences in the structures of these va rious fillers. For example, the fumed silica particles without the coupling agent showed a tendency to form heterogeneous aggregates in a spherical te xture. The particles coated with the coupling agent showed little aggregati on and evidence of good adhesion to the polyamide matrix. Concentrations up to a 20 mol% coupling agent also yielded spherical textures, but 40 mol% g ave an unusual fibrous structure.