Adhesion of Thermoplastic Matrices with Different Molecular Weights to Fibers

The dependence of the interfacial strength in polymer-fiber systems on the molecular weight (MW) of the matrix is investigated. Adhesive joints of poly(phenylene-sulfide sulfones) and polysulfones with a steel wire 150 μm in diameter and glass fibers 200-300 μm in diameter are examined. The MW of both polymers was controlled during the synthesis process. The shear adhesive strength τ was determined by the pull-out technique. For all the systems investigated, it is shown that the adhesive strength in relation to the duration tf of their isothermal formation is described by curves with a maximum, whose values depend on the formation temperature Tf. For each polymer with a given MW, the greatest possible of these values, called “optimum” and denoted by τopt, are determined. It is found that τopt increases with molecular weight. It is speculated that the effect observed stems from the different packing of polymer chains with distinct lengths in the near-surface layers.