*3.2. Structure*

Examples of 2D-WAXS and 2D-SAXS patterns of sheared PLLA specimens are collected in Figures 7 and 8. Generally, the intensities of the reflections from the crystalline phase correlated with χc determined from DSC thermograms and plotted in Figure 2, and increased with increasing χc. (200)/(110) and (203) reflections (indicated by arrows in Figure S2 in SI) typical of both alpha and alpha' modifications were well visible on all

patterns. Also, (210) reflection near 2θ of 22◦ characteristic of the alpha form was present in all the patterns, evidencing that the alpha phase was formed in all sheared specimens.

**Figure 7.** 2D-WAXS patterns of PLLAs: L339 sheared at 170 ◦C at 5/s for 20 s (**a**) and at 20/s for 5 s (**b**) and cooled at 10 ◦C/min, 4S123 sheared at 150 ◦C at 10/s for 10 s (**c**) and at 20/s for5s(**d**) cooled at 30 ◦C/min, L240 sheared at 150 ◦C at 10/s for 10 s (**e**) and at 20/s for 5 s (**f**) cooled at 30 ◦C/min, 6S245 sheared at 150 ◦C at 10/s for 10 s (**g**) and at 20/s for 5 s (**h**) cooled at 30 ◦C/min. Shearing direction -vertical.

**Figure 8.** 2D-SAXS patterns of PLLAs: L339 sheared at 170 ◦C at 5/s for 20 s (**a**) and at 20/s for 5 s (**b**) and cooled at 10 ◦C/min, 4S123 sheared at 150 ◦C at 10/s for 10 s (**c**) and at 20/s for5s(**d**) cooled at 30 ◦C/min, L240 sheared at 150 ◦C at 10/s for 10 s (**e**) and at 20/s for 5 s (**f**) cooled at 30 ◦C/min, 6S245 sheared at 150 ◦C at 10/s for 10 s (**g**) and at 20/s for 5 s (**h**) cooled at 30 ◦C/min. Shearing direction-vertical.

This is in accordance with the Tc values shown in Figure 4, which indicate that the crystallization of most of the specimens occurred fully or partially above 110 ◦C; the higher the Tc the more intense was the (210) reflection. Only very weak (210) reflections were discernible in the patterns of PLLAs (not shown), which Tc was close to 100 ◦C, for instance, L121 and 6S120 sheared at 150 ◦C at 5/s and cooled at 30 ◦C/min, which indicated small alpha content.

In some of the 2D-WAXS patterns, intensities of (200)/(110) and (210) reflections were enhanced in equatorial regions, indicating the orientation of the respective crystallographic planes parallel to the shearing direction, and thus evidencing the orientation of polymer chain axes in the flow direction. This was corroborated by the strong polar reflections in the corresponding 2D-SAXS patterns reflecting the orientation of lamellae stacks perpendicular to the flow direction.

Among the specimens sheared at 170 ◦C and next cooled at 10 ◦C/min, L339 clearly exhibited such orientation, as shown in Figure 7a,b, and in Figure 8a,b. Weaker orientation was also detected in 6S245 and L240 sheared at 20/s (not shown). Shearing at 150 ◦C followed by cooling at 30 ◦C/min resulted in the crystal orientation in L240, 6S245, and 4S123 evidenced in Figures 7c–g and 8c–g. The orientation, although weaker, was also reflected in the patterns of L121 sheared at 20/s, 6S120 sheared at 10/s and 20/s (not shown). 2D-WAXS and 2D-SAXS patterns of PLLAs sheared at 150 ◦C and next cooled at 10 ◦C/min evidenced the same features of the morphology. It is well visible in 2D-SAXS patterns collected in Figure 9a–e, in which scattering from the crystalline phase was enhanced due to the higher χc developed during slower cooling.

**Figure 9.** 2D-SAXS patterns of PLLAs: sheared at 150 ◦C at 20/s for 5 s and cooled at 10 ◦C/min: L121 (**a**), 4S123 (**b**), 6S120 (**c**), L240 (**d**), 6S245 (**e**). Shearing direction–vertical.

The reason for the orientation of crystals was the shear-induced formation of fibrillar nuclei aligned in the shearing direction on which grew lamella stacks perpendicular to the shearing direction. This is well seen in SEM micrographs of cross-section surfaces of sheared PLLAs, presented in Figure 10. The micrograph of L339 sheared at 170 ◦C at 20/s and next cooled at 10 ◦C/min, in Figure 9a, evidences the presence of lamellar stacks perpendicular or nearly perpendicular to the shearing direction, and lamella fans developed from the stacks. The stacks form cylindrical structures suggestive of nucleation on fibrillar nuclei. Similar morphology was found in L240 sheared at 150 ◦C at 20/s, and next cooled at 30 ◦C/min, as shown in Figure 10b, although spherulites between cylindrical structures were also discernible. Figure 10c presents 6S245 sheared at the same conditions and cooled at the same rate. In the micrograph, cylindrical structures are seen accompanied by spherulites, with radii of several micrometers. Amorphous areas are visible in few places between the spherulites, where crystallization was not accomplished. In L121, 6S120 and 4S123 sheared at 150 ◦C at 20/s crystallization during cooling at 30 ◦C/min was even less advanced, as shown in Figure 10d–f. The cylindrical structures and spherulites between them are well distinguishable, the latter more numerous than in PLLAs with higher M w. The effect of slower cooling on PLLAs sheared at 150 ◦C at 20/s is illustrated in Figure 11. The morphology of L240 and 6S245 cooled at 10 ◦C/min was similar to that observed after faster cooing, as exemplified in Figure 11a showing L240. In PLLAs with M w close to 120 kg/mol amorphous areas were not visible any longer because of high χc reached in these polymers during slower cooling. The specimens were completely filled with cylindrical structures and spherulites between them, as seen in Figure 11b showing L121.

**Figure 10.** SEM micrographs of etched cross-section surfaces of PLLAs: L339 sheared at 170 ◦C at 5/s for 20 s, and next cooled at 10 ◦C/min (**a**), and L240 (**b**) 6S245 (**c**), L121 (**d**), 4S123 (**e**), 6S120 (**f**) sheared at 150 ◦C at 20/s for 5 s, and next cooled at 30 ◦C/min. Shearing direction–vertical.

**Figure 11.** SEM micrographs of etched cross-section surfaces of L240 (**a**) and L121(**b**) sheared at 150 ◦C at 20/s for 5 s, and next cooled at 10 ◦C/min. Shearing direction—vertical.

2D-WAXS results evidenced orientation of the orthorhombic crystals of PLLAs with (200)/(110) and (210) crystallographic planes parallel to the shearing direction; hence, the orientation of polymer chain axes in the flow direction. It was accompanied by strong polar reflections in the corresponding 2D-SAXS patterns reflecting the orientation of lamellae stacks perpendicular to the flow direction. The orientation of crystals was stronger in PLLAs with Mw above 200 kg/mol than in those with Mw close to 120 kg/mol. However, among the latter, 4S123 exhibited the strongest orientation, whereas that of L121 was the weakest.

SEM analysis demonstrated the presence of lamellae stacks perpendicular to the shearing direction forming cylindrical structures, nucleated on fibrillar nuclei. These structures were accompanied by spherulites, especially in PLLAs with Mw close to 120 kg/mol. Obviously, the shear-induced fibrillar nucleation, although occurred, was less intense in these polymers than in PLLAs with higher Mw, which corroborated the conclusions drawn based on the results of X-ray scattering experiments.

In general, the strongest orientation of crystals was observed for the specimens, which crystallized at the highest temperatures and reached the highest χc. The crystal orientation resulted from the crystal growth on the shear-induced fibrillar nuclei; the more intense the nucleation, the higher Tc and χc. On the contrary, the weak or absent crystal orientation indicated the predominant point-like nucleation.
