The durable application of polylactide (PLA) under atmospheric conditions is restricted by its poor ultraviolet (UV) stability. To improve the UV stability of polymers, titanium dioxide (TiO 2 ) is often used as a UV light capture agent. However, TiO 2 is also a photocatalytic agent, with detrimental effects on the polymer properties. To overcome these two conflicting issues, we used the following approach. TiO 2 nanoparticles were first coated with silicon dioxide (SiO 2 ) (with a SiO 2 shell content of 5.3 wt %). Subsequently, poly(D-lactide) (PDLA) was grafted onto TiO 2 @SiO 2 nanoparticles, approximately 20 wt %, via a ring-opening polymerization of D-lactide to obtain well-designed double-shell TiO 2 @SiO 2 -g-PDLA nanohybrids. These double-shell nanoparticles could be well dispersed in a poly(L-lactide) (PLLA) matrix making use of the stereocomplexation between the two enantiomers. In our concept, the inner SiO 2 shell on the TiO 2 nanoparticles prevents the direct contact between TiO 2 and the PLLA matrix and hence considerably restricts the detrimental photocatalytic effect of TiO 2 on PLLA degradation. Additionally, the outer PDLA shell facilitates an improved dispersion of these nanohybrid particles by interfacial stereocomplexation with its enantiomer PLLA. As a consequence, the PLLA/TiO 2 @SiO 2 -g-PDLA nanocomposites simultaneously possess excellent UV-shielding property, high(er) tensile strength (>60 MPa), and superior UV resistance, for example, the mechanical properties remain at a level of >90% after 72 h of UV irradiation. In our view, this work provides a novel strategy to make advanced PLA nanocomposites with improved mechanical properties and excellent UV resistance, which enables potential application of PLA in more critical areas such as in durable packaging and fiber/textile applications.

COMMUNICATIONThis journal is Stereocomplexation of poly(lactide) was significantly promoted by seeding with nanocrystal cellulose (NCC). A NCCaccelerated and a time-dependent stereocomplex crystal (SC) growth are discovered. Moreover, SC-crystallization regime transitions (Ⅱ Ⅱ Ⅱ Ⅱ-Ⅲ Ⅲ Ⅲ Ⅲ) were identified and both of the nucleation constant (K g ) and transition temperature (T tr ) was strongly increased in the presence of the NCC.

Sustainable antibacterial poly­(lactide) (PLA) nanocomposites have attracted plenty of attention due to their potential application in biomedical and packaging fields. However, the preparation of nonleaching antibacterial PLA nanocomposites with high crystallinity is still a challenge due to their poor compatibility and the low crystallization rate of PLA. An effective and facile way by compounding poly­(d-lactide) (PDLA) with poly­(l-lactide) (PLLA)-grafted ZnO that was synthesized via in situ aminolysis reaction at the surface of ZnO was designed to simultaneously overcome these limitations. During solution mixing, the PDLA matrix and the grafted PLLA chains tend to orient side by side at the PDLA/ZnO interface and finally cocrystallize into stereocomplex (sc) crystallites. The interfacial stereocomplexation not only serves as a nucleator to increase the crystallization rate of the matrix but also effectively prevents ZnO from leaching out of the polymer matrix. Meanwhile, the nanocomposites have excellent biocompatibility. Therefore, it may provide an effective route to prepare advanced PLA-based materials with a fast crystallization rate, excellent biocompatibility, and nonleaching antibacterial property in this work, thus broadening the application range of PLA in biomedical applications.

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