Melt-crystallization Of PLLA Research Articles

Non-isothermal Crystallization, Melting Behavior, Thermal Decomposition, Fluidity and Mechanical Properties of Melt Processed Poly(L-lactic acid) Nucleated by N,N'-Adipic Bis(piperonylic acid) Dihydrazide

Enhancing on the crystallization ability of poly(L-lactic acid) (PLLA) during practical processing is one of the most effective way to overcome the poor heat resistance. In this work, N,N '-adipic bis(piperonylic acid)dihydrazide (PAAH) was synthesized to be firstly used as a heterogeneous nucleating agent to evaluate its influence on the performances, including the crystallization, melting behavior, thermal stability, fluidity and mechanical property, of PLLA. The nucleation effect of PAAH was determined via the melt-crystallization of PLLA with various PAAH concentrations from 0.5 to 3 wt % at different cooling rates, as well as the different final melting temperature Tf . The results revealed that the PAAH could significantly accelerate the crystallization of PLLA in cooling, and the melt-crystallization peak shifted toward the higher temperature with increasing of PAAH concentration, resulting from an increase of nucleation density in PLLA matrix. Additionally, both the cooling rate and Tf were two critical factors to crystallization, a higher cooling rate could weaken the crystallization ability of PLLA/PAAH, and the 200°C was the optimum melting process temperature. For cold-crystallization, PAAH had an inhibition for the cold-crystallization of PLLA, but the cold-crystallization peak moved toward the higher temperature with increasing of heating rate because of thermal inertia. There existed only a single melting peak after melt-crystallization at cooling of 1°C, which further confirmed the advanced nucleation effect of PAAH, but the double-melting peaks appeared after isothermal crystallization at 110°C, which was attributed to the melt-recrystallization. The other measurements showed that, compared to the neat PLLA, the addition of PAAH decreased the thermal stability and tensile modulus of PLLA, but PLLA/PAAH samples had the better fluidity, the higher tensile strength and the longer elongation at break.

Physical properties of Poly(L-lactic acid) fabricated using salicylic hydrazide derivative with tetraamide structure

ABSTRACTWith the aim of overcoming the slow crystallization rate of Poly(L-lactic acid) (PLLA), a heterogeneous nucleating agent, N, N, N, N’-salicylic tetra(1, 2, 4, 5-benzenetetracarboxylic acid) hydrazide (BAS), was synthesized to accelerate the crystallization of PLLA in this work. The effects of BAS on the non-isothermal crystallization, melting behavior, thermal stability, the fluidity and optical property of PLLA were evaluated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), melt index instrument and light transmittance meter. DSC results from the non-isothermal crystallization behavior revealed that BAS acted as an excellent crystallization promoter for promoting the nuclear of PLLA. Upon the cooling of 1°C/min from the melt of 190°C, 3 wt% exhibited the best accelerating effect on the melt-crystallization of PLLA. Even the BAS as a high-efficient nucleating agent could significantly promote the crystallization of PLLA upon fast cooling at 20°C/min. Additionally, the final melting temperature was another important factor for the crystallization process, and the 200°C is the best melting temperature for melt-crystallization of PLLA. The studies on the cold-crystallization process and melting behavior of PLLA/BAS samples under different conditions further confirmed the heterogeneous nucleating effect of BAS. And for the melting behavior of PLLA/BAS, both the crystallization temperatures and heating rates affected the melting behavior, and the double-melting peaks were assigned to melting-recrystallization. Overall, the addition of BAS could effectively improve the thermal stability and fluidity comparing with the primary PLLA, but decrease the light transmittance of PLLA.

The effect of N,N’-bis(benzoyl)dodecanedihydrazide on enhancing the crystallizationrate of poly(L-lactic acid)

The effect of N,N’-bis(benzoyl)dodecanedihydrazide (BADH) as a newly-developed organic nucleating agent on the crystallization process of poly(L-lactic acid) (PLLA) was examined in this study. Non-isothermal crystallization results indicated that BADH had excellent acceleration effects on the melt-crystallization of PLLA, and a larger proportion of BADH promoted more powerful crystallization. However, BADH inhibited the crystal growth of PLLA during the cold-crystallization process, and an increase of BADH concentration caused the non-isothermal crystallization peak to shift towards a higher temperature and become much wider. Although increased cooling rates might decrease nuclei density, it was surprising to see that BADH contents of 2 wt % to 3 wt % were able to accelerate the crystallization of PLLA upon fast cooling at 20 °C/min or even higher cooling rates. Besides, the effect of the final melting temperature on the melt-crystallization process of PLLA was not negligible, the relevant results implied that 190 °C was the optimal blending temperature of PLLA and BADH. Isothermal crystallization showed that, in the best case of the PLLA/3% BADH sample, the half-time of crystallization has a minimum value of 22.9 s at 115 °C. The calculation of frontier molecular orbital energies confirmed that the interaction between PLLA and BADH could form more easily during the melting blend than PLLA itself, indicating that the probable nucleating mechanism was chemical nucleation.

Magnesium phenylphosphonate: a additive for poly(L-lactic acid)

Developing a advanced additive to promote the crystallization of poly(L-lactic acid) (PLLA) is still one of the main challenges for application. Here, magnesium phenylphosphonate (MgP), as a heterogeneous nucleating agent, was prepared to investigate directly its influence on the crystallization behavior and thermal stability of PLLA via a combination of differential scanning calorimetry (DSC), x-ray diffraction (XRD), and thermogravimetric analysis (TGA). The relevant results, from measurements of non-isothermal crystallization, the glass transition temperature, and XRD after melt crystallization, revealed that the MgP had excellent acceleration effectiveness in the melt crystallization of PLLA, and PLLA–0.7% MgP exhibited the sharpest non-isothermal crystallization peak and the highest non-isothermal crystallization enthalpy, suggesting that 0.7 wt% MgP is the optimal concentration in the PLLA matrix. In addition, these measurements also indicated that the incorporation of MgP could not change the crystal form of PLLA, and the non-isothermal crystallization behavior of PLLA–0.7% MgP did not have a significant relationship with the set final melting temperature. The melting behavior after non-isothermal crystallization further confirmed the crystallization-promoting effect of MgP for PLLA, and the second heating rate significantly affected the melting behavior of PLLA–MgP samples, resulting from the effect of heating rate on formation of crystallites. Thermal stability measurement showed that the addition of MgP could not change the thermal decomposition behavior of the primary PLLA, though MgP exhibited completely different thermal decomposition behavior. Furthermore, the influence of MgP concentration on the thermal decomposition temperatures of PLLA–MgP samples is negligible.

Preparation and Properties of Biodegradable Poly(l-lactide)/Octamethyl-Polyhedral Oligomeric Silsesquioxanes Nanocomposites with Enhanced Crystallization Rate via Simple Melt Compounding

Biodegradable poly(l-lactide) (PLLA)/octamethyl-polyhedral oligomeric silsesquioxanes (ome-POSS) nanocomposites were prepared via simple melt compounding at various ome-POSS loadings in this work. Scanning and transmission electron microscopy observations indicate that ome-POSS were homogeneously dispersed in the PLLA matrix. Effect of ome-POSS on the nonisothermal crystallization behavior, isothermal melt crystallization kinetics, spherulitic morphology, crystal structure, dynamic mechanical properties, and thermal stability of PLLA in the nanocomposites was investigated in detail. It is found that the presence of ome-POSS enhances both nonisothermal cold and melt crystallization of PLLA in the nanocomposites relative to neat PLLA. The overall isothermal melt crystallization rates are faster in the PLLA/ome-POSS nanocomposites than in neat PLLA and increase with increasing the ome-POSS loading; however, the crystallization mechanism of PLLA remains unchanged. The nucleation density of PLLA spherulites is enhanced, while the crystal structure of PLLA is not modified in the PLLA/ome-POSS nanocomposites. The storage modulus has been apparently improved in the PLLA/ome-POSS nanocomposites with respect to neat PLLA, whereas the glass-transition temperatures vary slightly between neat PLLA and the PLLA/ome-POSS nanocomposites. The thermal stability of PLLA matrix is reduced slightly in the PLLA/ome-POSS nanocomposites.