Effects of molecular weight,stereo configuration of PLA,and processing on the dispersion of multiwalled carbon nanotubes and properties of corresponding nanocomposites

Multiwalled carbon nanotubes (MWCNTs) were dispersed and distributed via a co-rotating twin-screw extruder (TSE) in high (h)- and low (l)-molecular-weight amorphous and semicrystalline polylactides (PLAs) (aPLA and scPLA, respectively). Effects of PLA molecular weight and D-lactic acid equivalents content (D-content), as well as processing parameters, were examined on the MWCNT dispersion quality in PLA. The effectiveness of the MWCNT dispersion in various PLA matrices was investigated using scanning electron microscopy (SEM) and small-amplitude oscillatory and transient shear flow rheometry in the molten state. The results showed a better dispersion of MWCNTs in the low-molecular-weight PLA grades (aPLAl and scPLAl). In addition, better MWCNT dispersion was observed in aPLA grades when processed at a higher temperature of 190°C than at 150°C. At 150°C, while MWCNT bundles in aPLAl could be broken down, a good dispersion could not be achieved in aPLAh due to the lower molecular mobility at such a temperature. The electrical conductivity of the samples was also shown to increase as the MWCNT dispersion was improved. The existence of crystallites in scPLA-based nanocomposites, however, disrupted the connectivity of the MWCNTs and decreased the final electrical conductivity. The lower molecular weight aPLAl prepared at 190°C showed the highest electrical conductivity (~10⁻⁵ S/m) at a low loading of 0.5 wt.% MWCNTs.     

Phenol biodegradation in a bioreactor considering different geometries and process parameters

In this study, a three-dimensional coupled lattice Boltzmann model and cellular automata platform was developed to simulate biofilm growth and phenol biodegradation as an effective and sustainable way to remove phenolic contaminants in aquatic systems. Two three-dimensional bioreactors with cubic or spherical obstacles at varying inlet phenol concentrations and flow velocities were examined. The results showed that the cubic-bioreactor had higher phenol reduction than the spheric-bioreactor due to the greater effects of cubic obstacles on flow patterns. The biofilm concentration in bioreactors decreased up to 36.4% as inlet velocity increased and in the spheric-bioreactor at the same inlet phenol concentration. The cubic-bioreactor had the highest normalized reduction rate of 1.194 at the lowest inlet phenol concentration, while the spheric-bioreactor had the lowest one of 0.871 at the highest inlet phenol concentration. The results proved the accuracy of the model to assess the performance of wastewater treatment bioreactors under different conditions.