No abstract

A new phosphorus-based organic additive (PDA) was designed and successfully synthesized using a three-component reaction for improvement of the thermal and combustion resistance of polylactic acid (PLA). For compensate for mechanical properties of PLA, hydroxyapatite nanoparticles was modified via in situ surface modification with PDA and was used for preparation of PLA nanocomposites. The structure and morphology as well as thermal, combustion, and mechanical properties of the all PLA systems were investigated. The X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) results indicated that the presence of PDA as surface modifier has been necessary for a desirable dispersion of hydroxyapatite (HA) nanoparticles in the PLA matrix. The thermal, combustion, and mechanical properties of the PLA system films were investigated using thermogravimetric analysis (TGA), microscale combustion calorimeter (MCC), and tensile test, respectively. The initial decomposition temperature and char residue of PLA containing 6 mass% of PDA along with 2 mass% HA nanoparticles were increased 20°C and 12% respectively, compared with that of the neat PLA. The peak of heat release rate was decreased from 566 W/g for the neat PLA to 412 W/g for PLA containing 2 mass% of PDA along with 6 mass% HA nanoparticles. By incorporation of only 2 mass% HA nanoparticles and 6 mass% of PDA, the tensile strength was obtained 51 MPa higher than that of the neat PLA.

A new dicarboxylic acid modified Mg‐Al LDH (DLDH) containing imide groups was prepared and its effects on the thermal and mechanical properties of the new synthesized aliphatic‐aromatic poly (amide‐imide) (PAI) were investigated via preparation of PAI/nanocomposite films by solution casting method. The results of X‐ray diffraction (XRD), field emission‐scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM) showed a uniform dispersion for LDH layers into the PAI matrix. For comparison, the effects of polyacrylic acid‐co‐poly‐2‐acrylamido‐ 2‐methylpropanesulfonic acid (PAMPS‐co‐PAA) modified Mg‐Al LDH (ALDH) on the PAI properties were also studied. The thermogravimetric analysis (TGA) results exhibited that the temperature at 5 mass% loss (T5) increased from 277 °C to 310 °C for nanocomposite containing 2 mass% of DLDH, while T5 for nanocomposite containing 2 mass% of ALDH increased to 320 °C, along with the more enhancement of char residue compared to the neat PAI. According to the tensile test results, with 5 mass% DLDH loading in the PAI matrix, the tensile strength increased from 51.6 to 70.8 MPa along with an increase in Young's modulus. Also the Young's modulus of PAI nanocomposite containing 5 mass% ALDH reduced from 1.95 to 0.81 GPa.

Kinetic modeling and degradation study of liquid polysulfide (LPS)/clay nanocomposite is possible through Ozawa–Flynn–Wall (OFW) and Kissinger methods. Comparing the results of these models with experimental data leads to provide an accurate degradation kinetic evaluation of these materials. To this aim, the morphology and distribution of clay nanoparticles (CNPs) within the LPS matrix were investigated using Field Emission Scanning Electron Microscopy (FESEM) and X-ray diffraction (XRD). To evaluate the interaction between the LPS and the CNPs, the Fourier transform infrared (FTIR) identification was utilized. Furthermore, to investigate the kinetics of degradation, the thermal gravimetric analysis (TGA) and derivative thermogravimetry (DTG) of the samples were used in the nitrogen atmosphere with the help of Kissinger and Ozawa–Flynn–Wall (OFW) models. The characterization results confirmed the homogenous dispersion of the CNPs into the LPS matrix. In addition, the presence of CNPs increased the thermal stability and activation energy (Ea) of the samples at different conversion rates. Moreover, the OFW method was highly consistent with the experimental data and provided an appropriate fit for the degradation kinetics.