Polyacetals morphology

A commercial grade of high-impact (notched Izod > 900 J/m) POM resin (Delrin 100 ST, DuPont) is believed to be a blend of POM with >30 wt% of a thermoplastic poly(ester-urethane) elastomer derived from poly(l, 4-butane adipate) diol and methylene-bis-(4,4 -diphenyl diisocyanate) (MDl) (Hexman 1989). This blend is reported to have a cocontinuous or semi-interpenetrating network of the elastomer in a matrix of the polyacetal (Flexman et al. 1990). The toughening effect in such a blend of IPN-type morphology was interpreted to occur partly through a rubber band mechanism by which the fracture energy is absorbed. The bands of rubbery domains were believed to span the crack and participate in the deformation process. 

Fig. 5.50 SEM images of liquid nitrogen fractured polyacetal-pol)mrethane blend show a complex, network morphology (A) made more complicated by chemical etching (B). SEM of the etched fracture surface (B) suggests that the etchant has affected both the dispersed phase and the matrix.

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