Structure-property relationship, rheological behavior, and thermal degradability of poly(lactic acid)/fulvic acid amide composites

Humic acid amide (HA-amide) was prepared by amidation of HA and dodecylamine (DDA) with carbonyl diimidazole (CDI) as coupling reagent. Furthermore, HA-amide was added to poly (lactic acid) (PLA) a...

Structure, Performance and Crystallization Behavior of Poly (Lactic Acid)/Humic Acid Amide Composites

Modified layered double hydroxides (E-LDHs) were successfully prepared by the intercalation of ethylenediamine tetraacetic acid disodium salt (EDTA). Then, amide EDTA intercalation layered double hydroxides (AE-LDHs) were synthesized using aniline. The structure characterization of AE-LDHs demonstrated that AE-LDHs was successfully amidified. To enhance the properties of poly (lactic acid) (PLA), PLA/AE-LDHs nanocomposites were prepared by using AE-LDHs as the nucleating agent. Mechanical properties, thermal stabilities and crystallization properties of PLA/AE-LDHs nanocomposites were investigated by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), polarized optical microscopy (POM), and rheological behavior analysis. Results of mechanical properties and TG analysis showed that mechanical properties, thermal stabilities of PLA/AE-LDHs nanocomposites were improved significantly compared to pure PLA. Differential scanning calorimetry (DSC) demonstrated that AE-LDHs restricted the cold crystallization of PLA matrix and improved the crystallinity of PLA by 30.15%. POM analysis showed that AE-LDHs acted as an excellent nucleating agent, which greatly increased the crystallization rate of PLA. Compared with pure PLA, the maximum torque and apparent viscosity of PLA/AE-LDHs nanocomposites were improved by 46.21% and 85.86%, respectively, which proved that the AE-LDHs increased the rigidity of network structure of PLA matrix. In this work, an efficient and feasible nucleating agent for improving the crystallinity of PLA was presented through the amidation of LDHs.

Structure and performance of poly (lactic acid)/amide ethylenediamine tetraacetic acid disodium salt intercalation layered double hydroxides nanocomposites

An improved Hummers method was used to prepare graphene oxide (GO). Then, the orthogonal experiment design methods were used to select the optimum conditions of the preparation for amidated graphene oxide (AGO) via amidation. The optimum scheme was followed by: reaction temperature 70 °C, reaction time 5 h and GO: benzohydrazide of 1:3 (g:g). The structure of AGO was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscope (TEM) techniques, which demonstrated that the amidation of GO was successful. Furthermore, poly(lactic acid) (PLA)/AGO nanocomposites were prepared by melt blending to improve the comprehensive performance of PLA. Mechanical properties, thermal stabilities, crystallization properties, and rheological behavior of PLA/AGO nanocomposites were investigated, which showed that the addition of 0.3 wt % of AGO increased the tensile strength, elongation-at-break, and impact strength of PLA/AGO nanocomposites by 7.68, 47.32 and 41.27%, respectively, compared with neat PLA. Scanning electron microscopy analysis showed ductile fracture of the PLA/AGO nanocomposites. TEM analysis showed that nano-AGO single layers were evenly dispersed in the PLA matrix, confirming the formation of an exfoliated nanocomposite structure. Differential scanning calorimetry demonstrated that AGO eliminated the cold crystallization of PLA matrix and improved the crystallinity of PLA by 34.1%. In all, this study provided an effective and feasible method for improving the comprehensive performance of PLA.

Preparation and characterization of amidated graphene oxide and its effect on the performance of poly(lactic acid)

Amidated humic acid (AHA) was prepared by amidation of humic acid (HA) and its structure was verified by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Then poly(lactic acid)/amidated humic acid composites (PLA/AHA) were prepared using AHA as the nucleating agent. The mechanical properties, thermal stability, and crystallization behavior of the PLA/AHA composites were investigated by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), polarized optical microscopy (POM), and rheological analysis. The mechanical properties and thermogravimetric analysis showed that the tensile properties, impact resistance, and thermal stability of the PLA/AHA composites were improved. The cross-sectional morphology of the fractured surface showed that the addition of the nucleating agent significantly changed the crystallinity of PLA. The DSC results showed that the crystallinity of PLA/AHA composites increased from 4.19 to 35.36% after introduction of the nucleating agent. The POM of PLA/AHA composites demonstrated that AHA increased the crystallization rate of PLA. The maximum torque of PLA/AHA composites was 75.0% higher than that of PLA and the apparent viscosity was increased by 172.5%. This proved that the AHA changed the crystalline lattice structure and stiffness of PLA matrix. Non-isothermal crystallization kinetics showed that HA provided a large number of heterogeneous nucleation sites and improved the crystallization rate of PLA.

Preparation, performance and non-isothermal crystallization kinetics of poly(lactic acid)/amidated humic acid composites

Sodium humate was 
oxidized with nitric acid to obtain fulvic acid (FA), which was further quaternized to obtain quaternary fulvic acid (QFA). QFA-intercalated saponite (QFA-saponite) was prepared ultrasonically. Thermoplastic poly(lactic acid) (PLA)/quaternary fulvic acid-intercalated saponite nanocomposites were prepared by melt intercalation technique. The morphology and dispersion of QFA-saponite were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Mechanical properties, thermal stability and crystallization behavior of PLA/QFA-saponite nanocomposites were also tested. Results showed a predominantly flocculated structure and partially intercalated morphology for QFA-saponite. Mechanical testing and thermogravimetric analysis showed that the tensile strength, impact properties, and thermostability of PLA/QFA-saponite nanocomposites improved significantly compared to pure PLA. Differential scanning calorimetry results showed that crystallinity of PLA increased from 22.5 to 68.3 % on addition of QFA-saponite. Polarized optical microscopy showed QFA-saponite as a nucleating agent for PLA that enhanced its crystallization rate. Rotational rheological behaviors of PLA/QFA-saponite nanocomposites demonstrated that incorporation of QFA-saponite increased rigidity of the network structure in PLA matrix.

Structure, properties and rheological behavior of thermoplastic poly(lactic acid)/quaternary fulvic acid-intercalated saponite nanocomposites

In order to graft poly(isoprene) on the surface of fulvic acid (FA), fulvic acid-g-poly(isoprene) grafting polymer (FA-g-PI) was synthesized by reversible addition–fragmentation chain transfer polymerization. Because FA-g-PI became more hydrophobic, the static contact angle of FA-g-PI was 67°, which was increased by 37° compared with FA. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis showed that PI was grafted onto the FA. Furthermore, FA-g-PI was used as a modifier to melt blend with PLA to prepare poly(lactic acid)/fulvic acid-g-poly(isoprene) grafting copolymer composites (PLA/FA-g-PI). The mechanical performance results presented that the impact strength, tensile strength and elongation at break of PLA/FA-g-PI (0.3 wt%) reached 18.8 kJ/m2, 81.5 MPa and 18.47%, respectively, which were increased by 97.8%, 3.6% and 5.0% compared with PLA. The scanning electron microscopy analysis of impact fracture for PLA/FA-g-PI (0.3 wt%) also clearly showed that PLA/FA-g-PI (0.3 wt%) had the typical toughness fracture morphology feature. The results of differential scanning calorimetry and polarized optical microscope analysis indicated that the addition of FA-g-PI reduced the crystallite size during PLA crystallization. The kinetics of thermo-oxygen degradation by Kissinger method showed that the apparent activation energy of PLA/FA-g-PI (0.3 wt%) composites was increased from 153.73 kJ/mol to 179.17 kJ/mol, which was shown that FA-g-PI improved the thermal stability of PLA. Moreover, the reaction order showed that FA-g-PI had little effect on the PLA thermo-oxygen degradation reaction kinetic order under the air atmosphere.

Preparation, crystallization and thermo-oxygen degradation kinetics of poly(lactic acid)/fulvic acid-g-poly(isoprene) grafting polymer composites

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Preparation, performance and non-isothermal crystallization kinetics of poly(lactic acid)/amidated humic acid composites

Structure, properties and rheological behavior of thermoplastic poly(lactic acid)/quaternary fulvic acid-intercalated saponite nanocomposites

Preparation, crystallization and thermo-oxygen degradation kinetics of poly(lactic acid)/fulvic acid-g-poly(isoprene) grafting polymer composites