Abstract
Despite the extensive studies of poly(L-lactic acid)(PLLA), the crystallization of PLLA-based materials is still not completely understood. This chapter presents recent developments of crystallization of PLLA-based blends, block copolymers and nanocomposites. The first section of the chapter discusses the acceleration of PLLA crystallization by the inclusion of biobased (solid and liquid state) additives. It was found that the solid state additives work as a nucleating agent while the liquid-state additive works as a plasticizer. Both type of the additives can significantly enhance the crystallization of PLLA, as indicated by crystallization half-time (t0.5) values. Such composites are of great interest as they are 100% based on renewable resources. The second section talks about the enhanced formation of stereocomplex (SC) crystals in the PLLA/PDLA (50/50) blends by adding 1% SFN. It was found that the loading of SFN enhances the formation of SC crystals and it suppresses the formation of HC (homocrystal). The third section deals with confined crystallization of poly(ethylene glycol) (PEG) in a PLLA/PEG blend. The PLLA/PEG (50/50) blend specimen was heated up to 180.0°C and kept at this temperature for 5 min. Then, a two-step temperature-jump was conducted as 180.0°C → 127.0°C → 45.0°C. For this particular condition, it was found that PEG can crystallize only in the preformed spherulites of PLLA, as no crystallization of PEG was found in the matrix of the mixed PLLA/PEG amorphous phase. The last section describes the confined crystallization of PCL in the diblock and triblock copolymers of PLA-PCL. Furthermore, enantiomeric blends of PLLA-PCL and PDLA-PCL or PLLA-PCL-PLLA and PDLA-PCL-PDLA have been examined for the purpose of the improvement of the poor mechanical property of PLLA to which the SC formation of PLLA with PDLA components are relevant.
Highlights
IntroductionBiobased polymers are gaining great popularity recently due to the increasing environmental concerns associated with conventional polymers
We review the recent developments [7–15] of crystallization of PLLAbased blends, block copolymers and nanocomposites
For the case of liquid-state additive i.e. organic acid monoglyceride (OMG), nucleation and spherulite growth rate both were found to be increased which improves the crystallizability of poly(L-lactic acid) (PLLA)
Summary
Biobased polymers are gaining great popularity recently due to the increasing environmental concerns associated with conventional polymers. It is an emerging trend to utilize renewable resources for the improvement of crystallizability of PLLA In this regard, we used solidstate biobased additives like silk fibroin nanodisc (SFN) and cellulose nanocrystal (CNC) with the aim of improving the crystallization of PLLA. The SC is known to improve the thermal stability of PLA [22, 23] This is due to the approximately 50°C higher melting temperature of the SC crystals compared to the PLLA or PDLA homopolymer crystal (HC). The crystalline structure of PLA stereocomplex is triclinic with dimension of a = b = 0.916 nm, c (chain axis) = 0.87 nm, α = β = 109.2°, and γ = 109.8°, in Recent Developments in the Crystallization of PLLA-Based Blends, Block Copolymers. The final section of this chapter deals with the block copolymers of PLA (PLLA or PDLA) and poly (ε-caprolactone), PCL. The details of the experimental set-up are reported elsewhere [7]
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