Blends of Linear and Long-Chain
Branched Poly(l‑lactide)s with High Melt Strength
and Fast Crystallization
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Abstract
The long-chain branched polylactides (LCB-PLAs) prepared
by coupling
the hydroxyl-terminated two-arm (linear) and triarm PLA prepolymers
of identical arm length with hexamethylenediacianate (HDI) were used
to improve the melt rheological and crystallization properties of
linear polylactide resin, PLA 4032D from NatureWorks. The blends containing
LCB-PLA displayed higher zero shear viscosities, more significant
shear shinning, more melt elasticity, and much longer relaxation times
together with significant strain hardening in elongational deformation. <i>T</i><sub>g</sub>, <i>T</i><sub>m</sub> and crystallinity
(<i>X</i><sub>c</sub>) of linear PLA remained virtually
unaffected, but the crystallization rate increased obviously, since
the branch points of LCB-PLAs could play a role of nucleating agent.
High melt strength, fast crystallization, and favorable miscibility
improved the foaming ability of the linear/LCB-PLA blends, substantially