**4. Conclusions**

PLLA-based nonwovens were obtained by electrospinning. The PLLA nonwovens were modified with 0.1 wt.% of multiwall carbon nanotubes (MWCNT) and 5 and 10 wt.% of linear ladder poly(silsesquioxane) with methoxycarbonyl side groups (LPSQ-COOMe), which were added to the polymer solution before the electrospinning. In addition, nonwovens of PLLA grafted to modified MWCNT were electrospun; the content of MWCNT was 0.1 wt.%. The additives significantly reduced the fiber diameters. An average diameter decreased from 2.5 μm for neat PLLA fibers to about 1 μm for PL-LPSQ5-CNT and PL-LPSQ10-CNT. LPSQ-COOMe decreased Tg of the fibers by up to 7 ◦C and increased their thermal stability. A decrease of cold crystallization temperature of modified fibers

in comparison to those of neat PLLA was observed; the cold crystallization peak shifted from 97 ◦C to 81 ◦C. All modified nonwovens exhibited higher tensile strength than the neat PLLA nonwoven. The addition of 10 wt.% LPSQ-COOMe and 0.1 wt.% of MWCNT to PLLA increased the tensile strength of the nonwovens 2.4 times, improving also the elongation at maximum stress. FTIR analysis suggested the stronger orientation of PLLA chains in the modified fibers, which contributed to the improvement of their tensile strength.

**Supplementary Materials:** Figure S1: 1H NMR spectrum of LPSQ-COOMe, recorded in THF-d8 on a Bruker 200 spectrometer. Figure S2: Preparation scheme of PLLA-based nonwovens. Figure S3: TGA thermograms of PLLA-based nonwovens, in a nitrogen atmosphere at a heating rate of 20 ◦C/min. Table S1: Thermogravimetric data of PLLA-based nonwovens. Figure S4: EDS carbon and silicon mapping of (**a,b**) PL-LPSQ5 and (**c,d**) PL-LPSQ10 nonwovens.

**Author Contributions:** Conceptualization, M.S., T.M.; methodology, M.S., T.M., M.B., A.K.; validation, M.S., T.M., E.P.; formal analysis, M.S., T.M.; investigation, M.S., A.H., M.B.; writing—original draft preparation, M.S., T.M., M.B., A.K.; writing—review and editing, M.S., T.M., E.P.; visualization, M.S.; supervision, T.M.; funding acquisition, T.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by National Science Centre (Narodowe Centrum Nauki), Poland, gran<sup>t</sup> no. 2016/21/D/ST8/02908.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** Grant no. 2016/21/D/ST8/02908 from National Science Centre (Narodowe Centrum Nauki), Poland, and statutory funds of CMMS PAS. The authors are grateful to Total Corbion, The Netherlands, for providing PLLA *Luminy®* L175.

**Conflicts of Interest:** The authors declare no conflict of interest.
