I, Crystallization and morphological studies of ICI's intermediate temperature semicrystalline (ITX) polymer and, II, The influence of deformation (shear strain) during bond formation on adhesive bond strength

Abstract

Results for two unrelated studies are included in this dissertation. The primary investigation focused on evaluation of the crystallization conditions utilized in commercial consolidation of ICI's semicrystalline "ITX" polymer. Manipulating the initial polymer melting temperature and time was seen to influence the crystallization behavior and final morphology of the material. Variations in the crystallization kinetics, nucleation density, and crystalline texture of ITX were observed as a function of melt history. Experimental evidence suggests that ITX, like several other rigid-chain high-performance semicrystalline materials, is melt sensitive in that its nucleation density greatly decreases as a function of time and temperature in the melt. Melt degradation does not appear to strongly influence the crystallization behavior of ITX under normal processing conditions; however, spherulitic growth rates were seen to decrease after melting under the most severe conditions indicating that some degradation may be present. Unlike polyetheretherketone, ITX which was previously melted at the processing window high temperature limit can regenerate crystalline nuclei within the material via thermal treatments. Cooling and reheating the material to a lesser temperature increases the level of crystallinity generated such that it is equivalent to that found in material treated to less harsh conditions. Wide angle x-ray diffraction and the method of Hermans and Weidinger were utilized to calculate a theoretical heat of fusion of 180 J/g for ITX, and show that absolute crystallinity decreases by ~5% within the ICI recommended processing range.

The second dissertation topic discusses the effect of adhesive deformation during bond preparation on the mechanical performance of two commercial hot-melt adhesives, Dow DAF® 821 and Du Pont Surlyn® 1601. Lap shear bonds were sheared (// or ⟂ to load) during preparation to induce molecular orientation within the adhesive, before the mechanical properties were evaluated. The measured DAF 821 tensile strengths were similar, however, the Surlyn bond strengths varied in that sheared bonds were weaker than control bonds. Linear dichroism was used to quantify the level of orientation present within similarly prepared adhesive films. The technique indicated that there was no measurable preferential orientation in either adhesive.