Effects of Amphiphilic Chitosan on Stereocomplexation and Properties of Poly(lactic acid) Nano-biocomposite

Abstract

This article demonstrates an elegant approach for the fabrication of high heat-stable PLA using an industrially viable technique i.e. melt extrusion, which is quite challenging due to the higher viscosity of poly(lactic acid) melt. scPLA has been fabricated by melt extrusion of PLLA/PDLA using nano-amphiphilic chitosan (modified chitosan, MCH) which has been synthesized by grafting chitosan with oligomeric PLA via insitu polycondensation of L-lactic acid that possibly increases the molecular surface area and transforms it into nano-amphiphilic morphology and in turn lead to the formation of stereocomplex crystallites. The effect of MCH loading on the structural, morphological, mechanical and thermal properties of PLLA/PDLA have been investigated. The modification of chitosan and formation of stereocomplexation in PLA has been confirmed by FTIR and XRD techniques, respectively. Heat treatment has also laid a significant effect on the stereocomplexation and the degree of crystallinity of stereocomplex crystallites has been increased to ~70% for 1.5 wt % MCH content with the absence of homocrystals. The heat deflection temperature is found to be more than 140 °C for the biocomposite with 1.5% MCH in comparison to ~70 °C for pristine scPLA. The biocomposites display significant improvement in UTS and Young’s modulus.

Nano‐Crystalline Sandwich Formed in Polylactic Acid Fibers

“…As shown in Figure a, a significantly higher strength is observed at peak 1037 cm −1 indicating not only molecular stereo‐complexation between PLLA and PDLA, but also the formation of stereo‐complex crystalline structures in the bicomponent fibers. As compared to the FTIR spectra of homo‐PLLA, PDLA fibers, the new peak at 908 cm −1 (Figure b) is the characteristic band for the stereo‐complex crystallites with 3 1 molecular helical conformation . Frequency up‐shift in the band for CCOO from 868 to 872 cm −1 (Figure b), further confirms the formation of the stereo‐complex molecules due to carbonyl group interaction with the methyl group of the neighboring enantiomeric PLA chain .…”

Effect of molecular weight of polyethylene glycol on crystallization behaviors, thermal properties and tensile performance of polylactic acid stereocomplexes

“…This is a very important feature of the formation of stereocomplex. 27 In addition, a weak absorption peak appears at 2881 cm À1 in the spectra of the blends, which is attributed to the stretching vibration peak of CH 2 in PEG, as shown in the curve of PEG spectrum. But this absorption peak is not found in the pure PLLA spectrum, which also proves that the stereocomplex is successfully fabricated.…”

Preparation and Properties of Stereocomplex of Poly(lactic acid) and Its Amphiphilic Copolymers Containing Glucose Groups

“…Figure 4 shows the infrared spectra of PLLA, PDLAG-5%, and sc-PLGA samples in the carbonyl bond and hydrogen bond regions and crystalline regions. In Figure 4, the FT-IR spectrum of PLLA presented a relatively wide peak at 3483 cm −1 due to the stretch vibration of both free and hydrogen-bonded -OH groups and the strongest peak at 1750 cm −1 due to the stretch vibration of ester carbonyl C=O [6,38,39]. The FT-IR spectrum of PDLAG-5% resembled that of PLLA, while the wider peak of -OH groups moved to 3510 cm −1 , and the C=O peak slightly redshifted with increasing peak intensity, which could result from the existence of glucose groups and its interaction with lactic units.…”