Interfacial stereocomplexation in heterogeneous polymer powder formulations for reinforcing (laser) sintered welds

To understand the relation of molecular design of powder formulations in the realization of effective stress transfer at sintered polymer – polymer interfaces by the concept of interfacial stereocomplex crystallization in a broad temperature range, the effect of temperature and molar mass ratio are studied in heterogeneous poly(lactide) melt-states. Whereas the stereocomplex crystallization rate is dictated by supercooling and relative viscosities, the length-scales depend on the formation of crystalline stereocomplex domains connected via amorphous regions resulting in network formation, gelation. Upon gelation, further diffusion is impeded, which is supported by rheometry, DSC and FTIR imaging. When the initial relative viscosity between the PLA fractions is low, the time to reach critical network density is high. On the contrary, the length-scales of stereocomplex crystallization and ultimate mechanical stiffening are strongly influenced by the chosen temperature and molar mass ratio of the PLA fractions. Occurrence of interfacial stereocomplex crystallization under the non-isothermal conditions of selective laser sintering is validated. This fundamental understanding on the time- and length-scales of interfacial diffusion, successive stereocomplex crystallization, and nucleation of homocrystals upon further cooling, assists in the technical assurance of mechanically reinforced polymer-polymer interfaces – not only in sintered but in additively manufactured polymeric constructs in general.