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The effect of a self-assembly nucleating agent, N , N ′, N ″-tricyclohexyl-1,3,5-benzenetricarboxylamide (BTCA), on the crystallization behavior of poly(lactic acid) (PLA) was probed by time-resolved Fourier transform infrared spectroscopy (FTIR) and wide angle X-ray diffraction (WAXD). The vibrational changes associated with inter- and intra-chain interactions during crystallization were monitored. In the initial period of crystallization, the order of intensity changes is as follows: 1458 cm −1 > 1210 cm −1 » 921 cm −1 , 1458 cm −1 ∼ 1210 cm −1 > 921 cm −1 , and 1458 cm −1 ∼ 1210 cm −1 ∼ 921 cm −1 for neat PLA, PLAs containing 0.1 wt% and 0.3 wt% BTCA, respectively. This indicates that BTCA can accelerate both the formation of skeletal conformational-ordered structure and, especially, the 10 3 helix one. The incorporation of BTCA changes the crystallization mechanism but has no impact on the crystal form of PLA. [ABSTRACT FROM AUTHOR]

Uniaxial deformation of amorphous poly(lactic acid) (PLA) film was performed at 60 °C (around the glass transition temperature). The deformed samples revealed a strain-induced mesophase, and its fraction and thermal stability increased with draw strain. Further annealing was performed in situ at constant length, at the drawing temperature for the films drawn to strains of 100% and 230%. Interestingly, the orientation of amorphous phase relaxed more rapidly for the 100% sample compared with the 230% one. This could be ascribed to the constraint effect of mesophase on the amorphous chains. In addition, the chains of mesophase relaxed slightly for the 100% sample while it retained high orientation for the 230% sample. Meanwhile, the mesophase fraction decreased, and the trend was more significant for the sample drawn to 100%. These effects can be ascribed to the melting of mesophase and the different thermal stabilities of the mesophases. [ABSTRACT FROM AUTHOR]

The effects of drawing temperature ( T d ) and draw strain on the orientation and structure of semicrystalline poly(lactic acid) (PLA) films were investigated by wide angle X-ray diffraction and polarized Fourier transform infrared spectroscopy. Semicrystalline PLA samples with two initial levels of crystallinity, X c = 1% and 11%, were prepared by cold crystallization at 80 ° C. Whatever X c and T d , the total amount of the ordered phases ( i.e. crystalline + mesophase) increased with draw strain, which could be ascribed to the formation of strain-induced mesophase at T d = 60 or 70 ° C but crystalline at 80 ° C. Also, the molecular orientation of both the amorphous and ordered phases increased with draw strain. Whatever X c , the orientation of the ordered phases was insensitive to T d , whereas higher orientation in the amorphous phase was achieved at lower T d , and the trend was more significant for X c = 1% compared with 11%. [ABSTRACT FROM AUTHOR]

Abstract: The effect of one of the 1,3,5-benzenetrisamide derivatives, N,N',N''-tricyclohexyl-1,3,5- benzenetricarboxylamide (defined here as TMC), on the crystallization behavior of isotactic polypropylene (iPP) was investigated by differential scanning calorimetry. TMC shows excellent nucleating effect on iPP. The nucleation efficiency of the blends reaches 30% even at a very low loading of 0.05 wt% TMC. For 0.1 wt% TMC, the crystallization half-time of the blend decreases from 39.41 to 3.97 min at 136 °C, compared with pure iPP. The isothermal crystallization data were further analyzed by the Avrami model. The values of the Avrami exponent of the blends are comparable to that of pure iPP, indicating that the presence of TMC does not change the crystallization mechanism of the matrix. The presence of TMC increases significantly the nuclei density of iPP but has no discernible effect on its crystalline structure, evidenced by polarized optical microscopy and wide angle X-ray diffraction measurements. [Copyright &y& Elsevier]

Polyethylene oxide (PEO) was introduced to improve the dispersion of graphene nanoplatelets (GNPs) in poly (lactic acid) (PLA) matrix. GNPs were dispersed into PEO aqueous solution and freeze-dried to form PEO/GNPs masterbatch, followed by melt-mixed with PLA to prepare the nanocomposites. Three grades of PEO with different molecular weights were evaluated. It is found that adding very low loading of PEO (1 wt%) enhances the dispersion of GNPs in PLA matrix, resulting in remarkable improvement in elongation at break of PLA/GNPs without obviously sacrificing its modulus and tensile strength. Meanwhile, PEO reveals a synergistic effect with GNPs in promoting PLA crystallization. Moreover, GNPs enhances significantly the thermal stability of PLA, while further addition of PEO does not apparent compromise this effect. In addition, PEO with low molecular weight presents the best effect in improving the properties of PLA/GNPs nanocomposites. • Freeze-dried PEO/GNPs masterbatch was melt-mixed with PLA. • PEO effectively promotes the dispersion of GNPs in PLA matrix. • PEO enhances the toughness of PLA/GNPs. • PEO enhances the crystallization ability of PLA/GNPs. • Effect of the molecular weights of PEO was addressed. [ABSTRACT FROM AUTHOR]