Synergistic Effect of Mesoporous SBA‐15 Particles and Processing Strategy for Improving PLA Crystallization Capability in their Composites

Several composites based on an L-rich poly(lactic acid) (PLA) and mesoporous Santa Barbara Amorphous-15 (SBA-15) are prepared by their addition through two methods: solution-mixed (solvent casting) or melt-mixed (extrusion). Subsequently, films of all the materials are processed by compression molding. The nucleating capacity of silica on PLA crystallization is found to be strongly dependent on protocol used for SBA-15 incorporation. Thus, mesoporous particles induce some PLA ordering in composites when extrusion is used but nucleating ability is much more remarkable when PLA-SBA composites are prepared by SBA-15 addition through casting, PLA crystallization being observed on cooling even at 40 degrees C min(-1). Crystallinity, crystallization temperature, and polymorphs developed are also dependent on preparation method and cooling rate. Mechanical properties are tested on the just compressed-molded films. At a given SBA-15 content, the melt-mixed composite is less stiff than the solution-mixed material despite both are completely amorphous. Accordingly, microhardness shows a smaller value in the former. For the solution-mixed approach, a partial coating (either external or internal) of the silica particles by PLA chains is suggested to occur during the first preparation stage, enabling a better transfer of reinforcement exerted by SBA-15 silica into the PLA matrix.