Our latest work entitled: "Structure-Properties relationships in renewable composites based on polylactide filled with Tannin and Kraft Lignin - Crystallization and molecular mobility", has been recently published in Thermochimica Acta 703:178998. (https://doi.org/10.1016/j.tca.2021.178998)
This work was also supported by the postdoctoral research core founding of Ministry of education, science and sport, No. OP20.04343 and funding through the Research Program P2–0118 Textile Chemistry (Slovenian Research Agency).
Abstract
Calorimetry and dielectric spectroscopy supplemented by polarized light microscopy, X-ray, infrared spectroscopy and scanning electron microscopy are employed here to assess the crystallization, interactions and molecular mobility in polylactide (PLA) filled with Tannin and kraft-Lignin prepared by melt extrusion. The direct and indirect effects of the fillers are investigated within two states of the polymer, namely, amorphous and semicrystalline (melt-crystallization annealed). The extremely slow and weak crystallization of PLA is enhanced by the fillers, mainly in the rate, via the combined effects of providing sites for crystallization and moderately enhancing polymer mobility (chains diffusion). Interestingly, the crystal structure and semicrystalline morphology were found altered in the composites as compared to the unfilled PLA. The effect on crystallization was found slightly stronger in PLA/Tannin, whereas the overall results were found in accordance to previously proposed models on the role of weak or absent interfacial interactions on promoting nucleation, such as in our case. Dielectric spectroscopy enabled the recording of the overall molecular dynamics mapping. Local dynamics was found to consist mainly of two individual processes. Regarding segmental mobility of PLA, the presence of tannin and lignin was found to impose moderate changes, namely, slight acceleration, narrowing of relaxation times range and suppression in fragility, however, not systematic changes in the calorimetric or dielectric strengths. The overall data could be rationalized exploiting known models involving as an indirect filler effect the increase in free volume. Despite the weak effects, Tannin was found again more effective and this seems to correlate with their smaller size and moderately better distribution as compared to lignin. The involvement of crystallization resulted in an expected blocking of ions transport, which, along the recorded potential for tuning semicrystalline morphology, make these materials interesting and worth to be further studied with regard to their permeation, mechanical and antioxidation performance.
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