Polylactide stereocomplex crystallization prompted by multiwall carbon nanotubes

Abstract

Nanocomposites of equimolar enantiomeric polylactide blends with multiwall carbon nanotubes (MWCNTs) were prepared by a solvent casting/sonication procedure. The first objective of the study was to investigate the effect of MWCNTs as nucleating agents for the selective crystallization of the polylactide (PLA) stereocomplex to obtain PLA‐based nanocomposites. Transmission Electron Microscopy (TEM) studies revealed large agglomerates and poor distribution of the non‐functionalized MWCNTs within the matrix. To enhance the compatibility between PLA and MWCNTs, pyrene‐end‐functionalized PLLA (py‐end‐PLLA) nanocomposites were prepared because of the ability of the pyrene moieties to interact with the MWCNTs via π−π stacking, and were subsequently blended with poly(d‐lactide) (PDLA) to investigate the possibility of achieving nanocomposites in which the enantiomeric blend crystallizes as stereocomplex. The resulting nanocomposites were characterized by Differential Scanning Calorimetry (DSC), X‐ray Diffraction (XRD), TEM, and Nuclear Magnetic Resonance Spectroscopy (NMR), revealing that MWCNTs were efficient nucleating agents for the overall crystallization of the blends. Interestingly, full stereocomplexation could be achieved with the aid of soft specific thermal treatments. According to these results, the addition of small amounts of MWCNTs combined with a mild thermal treatment might extend the processing window for the preparation of polylactides exclusively crystallized in the stereocomplex form. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4327–4337, 2013

Investigation on the environmental‐friendly poly(lactic acid) composites based on precipitated barium sulfate: Mechanical, thermal properties, and kinetic study of thermal degradation

“…The composites of PLA with inorganic fillers have been proved very useful to enhance the impact toughness and thermal properties without significant deteriorated strength and stiffness, [6][7][8][9][10] of which barium sulfate (BaSO 4 ) must be the most promising candidate. 11,12 BaSO 4 is a well-known bioinert filler and usually considered as the gold standard in clinical applications for the x-ray photography and gamma-ray absorber, because it is nonharmful to humans and possessed of characteristic radiopacity and biocompatibility. [13][14][15] So, it is very suitable for such inorganic filler to design and fabricate the PLA composites with high biosafety.…”

“…[13][14][15] So, it is very suitable for such inorganic filler to design and fabricate the PLA composites with high biosafety. de Arenaza and his co-workers 11 investigated the positive influence of BaSO 4 on the strength, stiffness, and elongation of PLA carefully, while Cai 12 claimed BaSO 4 showing an accelerating effect on the thermal properties of PLA, presenting the significantly increased crystallization temperature and enthalpy, as well as the slightly higher decomposition temperature when compared to pure polymer. Our previous study also stated that, with the appropriate amount of precipitated BaSO 4 , the impact toughness of PLA (previously filled with 10% calcium carbonate) was increased significantly.…”

Melt compounding and characterization of poly(lactide) stereocomplex/natural rubber composites

“…T g was determined from the second scan. Degree of crystallinity ( χ st ) was calculated : where is the melting enthalpy, is the melting enthalpy for 100% crystalline material (142 J/g for stereocomplex crystallites ), is the cold crystallization enthalpy, and is the fraction of NR in the St‐PLA/NR blends.…”

Dynamic Monte Carlo simulations of competition in crystallization of mixed polymers grafted on a substrate

“…Thus, nowadays, many researchers focus on the formation mechanism of the stereocomplexation between enantiomeric PLAs, and different methods to improve the content of SCs have been proposed. For instance, the formation of SCs can be promoted by applying a shearing field, adding specific nucleating agents, or one‐dimensional fillers, such as carbon nanotubes, synthesizing polymers with new topology, and changing crystallization temperatures …”