Rapid Stereocomplexation between Enantiomeric Comb-Shaped Cellulose-g-poly(L-lactide) Nanohybrids and Poly(D-lactide) from the Melt.

In this work we report the in situ preparation of fully biobased stereocomplex poly(lactide) (SC-PLA) nanocomposites grafted onto nanocrystalline cellulose (NCC). The stereocomplexation rate by compounding high-molar-mass poly(D-lactide) (PDLA) with comb-like NCC grafted poly(L-lactide) is rather high in comparison with mixtures of PDLA and PLLA. The rapid stereocomplexation was evidenced by a high stereocomplexation temperature (Tc-sc = 145 °C) and a high SC crystallinity (Xc-sc = 38%) upon fast cooling (50 °C/min) from the melt (250 °C for 2 min), which are higher than currently reported values. Moreover, the half-life crystallization time (175-190 °C) of the SC-PLA was shortened by 84-92% in comparison with the PDLA/PLLA blends. The high(er) stereocomplexation rate and the melt stability of the SC in the nanocomposites were ascribed to the nucleation effect of the chemically bonded NCC and the "memory effect" of molecular pairs in the stereocomplex melt because of the confined freedom of the grafted PLLA chains.

Segmental Mobility in the Non-crystalline Regions of Semicrystalline Polymers and its Implications on Melting.

Detailed knowledge on chain mobility in polymers is of fundamental interest in order to understand their mechanical properties. As a specific example, the melting behavior of semicrystalline polyethylene can be studied by thermal analysis and NMR spectroscopy. In ultra high molecular weight polyethylene (UHMW-PE) crystallised via different routes, i.e., directly during polymerisation, from solution, or from the melt, and melted under different protocols, different melting processes involving detachment of stems from the crystals and cluster melting can be distinguished. Melting by the consecutive detachment of chain stems from the crystal substrate ultimately results in a melt state where chain dynamics for entanglement formation are much more restricted.