Stereocomplex mesophase and its phase transition in enantiomeric polylactides

A Versatile Disorder-to-Order Technology to Upgrade Polymers into High-Performance Bioinspired Materials

Biodegradable polymer as traditional material has been widely used in the medical and tissue engineering fields, but there is a great limitation as to its inferior mechanical performance for repairing load-bearing tissues. Thus, it is highly desirable to develop a novel technology to fabricate high-performance biodegradable polymers. Herein, inspired by the bone's superstructure, a versatile disorder-to-order technology (VDOT) is proposed to manufacture a high-strength and high-elastic modulus stereo-composite self-reinforced polymer fiber. The mean tensile strength (336.1 MPa) and elastic modulus (4.1 GPa) of the self-reinforced polylactic acid (PLA) fiber are 5.2 and 2.1 times their counterparts of the traditional PLA fiber prepared by the existing spinning method. Moreover, the polymer fibers have the best ability of strength retention during degradation. Interestingly, the fiber tensile strength is even higher than those of bone (200 MPa) and some medical metals (e.g., Al and Mg). Based on all-polymeric raw materials, the VDOT endows bioinspired polymers with improved strength, elastic modulus, and degradation-controlled mechanical maintenance, making it a versatile update technology for the massive industrial production of high-performance biomedical polymers.

Controlling stereocomplex crystal morphology in poly(lactide) through chain alignment

The incorporation of poly(d-lactide) (PDLA) to form stereocomplex crystallites (SCs) within a poly(l-lactide) (PLLA) matrix is among the most effective strategies in overcoming PLLA's numerous drawbacks. However, high concentrations of PDLA (>3 wt%) are required to improve PLLA's crystallization kinetics and melt strength, which is undesirable owing to PDLA's high cost. In this study, we use chain alignment as a levier to tune stereocomplex superstructure morphology to overcome these limitations. Herein, PLLA/PDLA blends were manufactured using an environmentally friendly and low-cost single step spunbond fibrillation process, yielding microfibers stretched to diameters of 5-20 μm. During this stretching process, PLLA and PDLA chains are aligned along the flow direction. SCs subsequently formed in situ upon heating, dramatically improving crystallization kinetics, melt elasticity, and tensile performance compared with neat PLLA and non-stretched blend analogues, even with low PDLA content (<3 wt%). These improvements were attributed to topological variations in SC superstructures caused by alignment of PLLA and PDLA chains. The application of chain alignment in tuning SC superstructure morphology is ubiquitous in fibrillation processes.

Crystalline titanium-dioxide nanofinish impregnated on electrospun stereocomplex poly (lactic acid) as non-woven nanotextile with superhydrophilic, anti-shrinkage, dark dyeing and waste dye removal ability for sustainable application

An environmentally friendly non-woven nanotextile has been prepared using enantiomeric pairs of poly (lactic acid) PLA by electrospinning technique. Solution blending of synthesized high molecular weight (⁓10⁵ Da) poly (L-lactic acid) PLLA and poly (D-lactic acid), PDLA for prolonged time stirring produce solely stereocrystallites (sc). The high crosslinking effect of sc-PLA has played an important role, with multifunctional behaviour on the addition of anatase-TiO₂ (a-TiO₂) in three different ways (Case-I-III). The high crystallinity of a-TiO₂ (~7.14 nm), has been confirmed from XRD and TEM studies as 98 %. The nanofinish as studied in (Case -III) by dipping and drying has decreased the water contact angle for the electrospun sc-PLA nanotextile from highly hydrophobic (132°) to superhydrophilicity after 8 min. An easy demonstration of high temperature treated nanofabric (at 100 °C) has proven to obtain an anti-shrinkage sc-PLA nanofabric. Even, the presence of a-TiO₂ has improved the colour strength ability of sc-PLA as a dark dyed nanofabric. The loading of as-synthesized a-TiO₂ nanoparticle has enhanced adsorbent dosages for 5T_dipscPLA up to 1.44 mg/g of MB dosage, at contact time (8 h), and 68 % methylene blue (MB) removal efficiency under UV irradiation. Thereby, this a-TiO₂ impregnated sc-PLA nanofabric tends to dye removal.

Stereocomplexation of enantiomeric star-shaped poly(lactide)s with a chromophore core

Herein, we aim to investigate the influence of the cooling rate from the melt on stereocomplex formation of equimolar blends of enantiomeric star-shaped poly(lactide)s with a dipyridamole core.