Variables that determine the fiber-matrix bond strength in ethylene-type ionomer composites

The effects of some variables, namely, ion concentration, matrix tensile st rength, matrix yield strength and the matrix tensile modulus on the fiber-m atrix bonding strength were determined for six-ionomers (coded PEA-1 to PEA -6) bonded to surface-modified poly (p-phenylene terephthalamide) (PPTA) fi bers. The results obtained show that the mean bonding shear strength of the ionomers correlates well with both their ultimate tensile strengths and th eir tensile yield stresses. However, correlation of the bonding shear stren gths with the matrix yield stresses reveals that the bonding shear strength was about 11 times that of the matrix tensile stress. Failure criteria for all the materials predict maximum shear stress to be either 0.5 or 0.577 o f the tensile yield stress, hence a value greater than unity cannot be inte rpreted nor theoretically justified. It was found that the bonding shear st rength of the ethylene-type ionomer PEA-6 compared to carboxymethyl surface -modified PPTA is about 20% lower than the bonding shear strength of this r esin against sized PPTA fibers. The reduction of entanglements and/or ionic crosslinking across the bound polymer/bulk polymer interface leads to a we ak interface with a subsequent decrease in the measured shear strength.