• Looijmans, S.F.S.P.; Spanjaards, M.M.A.; Puskar, L.; Cavallo, D.; Anderson, P.D.; van Breemen, L.C.A.: Synergy of Fiber Surface Chemistry and Flow: Multi-PhaseTranscrystallization in Fiber-Reinforced Thermoplastics. Polymers 14 (2022), p. 4850/1-16

Open Access Version

Fiber-reinforced polymer composites are largely employed for their improved strengthwith respect to unfilled matrices. Considering semi-crystalline materials under relevant processingconditions, the applied pressure and flow induce shear stresses at the fiber–polymer interface.These stresses may strongly enhance the nucleation ability of the fiber surface with respect to thequiescent case. It is thus possible to assume that the fiber features are no longer of importance andthat crystallization is dominated by the effect of flow. However, by making use of an advancedexperimental technique, i.e., polarization-modulated synchrotron infrared microspectroscopy (PM-SIRMS), we are able to show that the opposite is true for the industrially relevant case of isotacticpolypropylene (iPP). With PM-SIRMS, the local chain orientation is measured with micron-size spatialresolution. This orientation can be related to the polymer nucleation density along the fiber surface.For various combinations of an iPP matrix and fiber, the degree of orientation in the cylindricallayer that develops during flow correlates well with the differences in nucleation density found inquiescent conditions. This result shows that the morphological development during processing ofpolymer composites is not solely determined by the flow field, nor by the nucleating ability of the fibersurface alone, but rather by a synergistic combination of the two. In addition, using finite elementmodeling, it is demonstrated that, under the experimentally applied flow conditions, the interphasestructure formation is mostly dominated by the rheological characteristics of the material rather thanperturbations in experimental conditions, such as shear rate, layer thickness, and temperature. Thisonce again highlights the importance of matrix–filler interplay during flow and, thus, of materialselection in the design of hybrid and lightweight composite technologies