Using poly(3-hydroxybutyrate) (PHB) of two molecular weights and various other polymeric or blend systems, this study has shed a critical clue that cracks are inclined to be guided by interior lamellae via interior inter-lamellae discontinuity and interfaces that exist between the successive ring bands or radial/tangential lamellae. Advanced interior dissection analysis on the aggregated spherulites of several polymers further proves that the cracks occur at the interface between the valley and ridge bands of the ringed spherulites, where interfaces with discontinuous lamellae exist with either impingement or intersection. Propagation of the cracks follows the spiral or circular lamellae assembly into similarly spiral or circular concentric patterns, Such updated views via interior lamellae dissection and analysis on PHB's or other polymers’ banded spherulites provide avenues for cracks to develop upon cooling contraction. The mechanism of spiral/circular cracks’ formation is well proven in this work, which is related to the inner arrangement/assembly of the periodic spiral lamellae into banded types; by contrast, without such lamellae periodicity, cracks tends to be randomly irregular.
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