A series of in situ synchrotron X-ray diffraction experiments are performed during the stretching of weakly and highly vulcanized carbon black (CB), silica and grafted silica filled natural rubber sample (NR). Conversely to literature, Mullins effect observed after one stretching cycle modifies the strain induced crystallization (SIC) behaviour of the sample. The onset of crystallization is ruled by the strain amplification induced by the filler presence. Moreover, fillers (CB and silica) behave as additional crosslinks into NR network, through fillererubber interactions that either accelerate or slow down the crystallization rate depending on NR matrix chemical crosslink density. This is consistent with the assumption that effective network density, which is due to chemical crosslinks, entanglements, and fillererubber interactions, controls the crystallization rate.
The -crystalline form of isotactic poly(propylene) (PP) has been long recognized to have a greater mechanical absorption capacity than the ␣-crystalline form. This is of major importance for improving impact properties and crack resistance of injection-molding parts. Unfilled PP samples together with calcium carbonate-filled PP samples having various /␣-phase ratios, with nearly constant morphological parameters, have been investigated from the standpoint of ductile crack propagation and impact behavior. The presence of the -crystalline phase turned out to improve both properties. The  spherulites are notably more prone to craze initiation than ␣ spherulites that display a propensity for cracking. Subsequent crack propagation appears to be faster in the latter ones. The plastic zone ahead from the crack tip broadens, and the specific plastic energy increases with increasing -phase content. The lower elastic limit of the  phase is likely to promote the early crazing. However, the suspected higher density of tie molecules in  spherulites provides more numerous and stiffer microfibrils. The impact strength of PP is also improved by the presence of  crystals as a result of greater energy-absorption capabilities. However, filled samples turned out insensitive to the  phase. A discussion is made about the origins of the -phaseinduced improvement of the mechanical properties. The possible role of the  3 ␣ transition is also explained.
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