Young's modulus of the different crystalline phases of poly (l-lactic acid)

Sustainable Electrospun Poly(l-lactic acid) Fibers for Controlled Release of the Mosquito-Repellent Ethyl Butylacetylaminopropionate (IR3535)

“…Thermal and structural analyses revealed that IR3535 results in a decrease in the glass transition temperature of the polymer component, confirming thermodynamic solubility, as suggested in earlier works, , and causing plasticization of the amorphous PLLA phase. In addition, the presence of IR3535 enhances crystallization of PLLA, with the crystals presumably contributing to the mechanical properties of the fibers, as proven for bulk PLLA . Important from the point of view of functionality, evaporation/release of IR3535 is delayed in the electrospun fibers, allowing a continuous controlled release of the insect repellent for periods of the order of magnitude of many days/few weeks.…”

“…In addition, the presence of IR3535 enhances crystallization of PLLA, with the crystals presumably contributing to the mechanical properties of the fibers, as proven for bulk PLLA. 65 Important from the point of view of functionality, evaporation/release of IR3535 is delayed in the electrospun fibers, allowing a continuous controlled release of the insect repellent for periods of the order of magnitude of many days/few weeks. As such, electrospun PLLA fibers containing IR3535 have potential to be used for controlled release of IR3535, suggesting, for example, possible use for the production of fabrics and textiles with long-lasting and active insect protection.…”

Lamellar Morphology of Disorder α′-Crystals of Poly(L-Lactic Acid)

“…In both cases, after hot-and cold-crystallization at 90 °C in the DSC and FSC, respectively, connected with the growth of α′crystals, a long-period peak cannot be detected in the SAXS patterns (see blue curves), though AFM images provide evidence of the presence of lamellar crystals and their stacking in the direction of the fold surface (Figure 6). Note that also long-term annealing of PLLA at the crystallization temperature of 90 °C, involving secondary crystallization, 23,25 does not lead to a change of the SAXS curve.…”

“…As a function of the conditions of solidification, different supermolecular structures can be obtained. These include the fully amorphous state when cooling the melt faster than about 1 K/s to below T g , − disorder α′-crystals when crystallizing the melt at temperatures lower than about 100–120 °C, and α-crystals when crystallizing at higher temperatures. − While α-crystals are consistently described as exhibiting an orthorhombic symmetry, − the unit cell of α′-crystals is either orthorhombic , or pseudohexagonal. , In the latter crystal polymorph, the distances between neighbored molecular stems are slightly larger than in the α-phase, and the helical chains contain conformational defects/distortions. − These defects then also cause a decrease in the thermal stability/melting temperature and enthalpy of melting, affecting all material properties. − Crystallization of both crystal forms occurs spherulitically; however, information about the morphology and organization/spatial arrangement of α′-crystals beyond conclusions, which may be derived from the spherulitic growth, is not available yet.…”

Crystallinity-Independent Toughness in Renewable Poly(l-lactide) Triblock Plastics

“…This decrease of modulus with crystallinity contrasts with the intuition that crystallization increases modulus in semicrystalline polymers, including PLLA. 104 The intercalation of rubbery domains between crystal lamellae may have positioned PγMCL interfaces to reduce the local T g of PLLA chains that would otherwise comprise the rigid amorphous fraction at the lamellar fold surfaces. 93 Because the rigid amorphous fraction has a stiffness contribution similar to that of crystalline domains, global rubbery-crystalline impingement as occurs in the low-f PLLA materials could reduce the effective rigid amorphous fraction even as crystallinity increases, decreasing modulus.…”