Crystalline structure and phase structure of mLLDPE/LDPE blends

Thermally activated dynamic bonding network for enhancing high-temperature energy storage performance of PEI-based dielectrics

To address the paradox of mutually exclusive confusions between the breakdown strength and polarization of the polymer-based composites at high-temperature, a dynamic multisite bonding network is constructed by connecting the -NH2 groups of polyetherimide (PEI) and Zn2+ in metal-organic frameworks (MOFs). Owing to the multisite bonding network being dynamically stable at high-temperature, the composites possess a high breakdown strength of 588.1 MV m-1 at 150 °C, which is 85.2% higher than that of PEI. Importantly, the multisite bonding network could be thermally activated at high-temperature to generate extra polarization, which is because the Zn-N coordination bonds are evenly stretched. At similar electric fields, the composites show higher energy storage density at high-temperature compared with that at room temperature, and present excellent cycling stability even with increased electrode size. Finally, the reversible stretching of the multisite bonding network against temperature variation is confirmed by the in situ X-ray absorption fine structure (XAFS) and theoretical calculations. This work presents a pioneering example of the construction of self-adaptive polymer dielectrics in extreme environments, which might be a potential method for designing recyclable polymer-based capacitive dielectrics.

Effect of Blending Protocol on the Rheological Properties and Morphology of HDPE/LLDPE Blend-based Nanocomposites

Nanocomposites based on high density polyethylene (HDPE)/linear low density polyethylene (LLDPE) blend were prepared by melt compounding in a torque rheometer using an organoclay (montmorillonite) as nano-filler and maleic anhydride-grafted linear low density polyethylene (LLDPE-g-MA) as compatibilizer. The effects of five blending protocols on microstructure, crystallinity and rheological properties of the prepared samples were examined. The steady state rheological properties showed that the addition of nanoclay to the HDPE/LLDPE blend increased its shear viscosity at low shear rates changing the behavior of the HDPE/LLDPE matrix to a more pronounced shear thinning behavior. The blending sequence (LLDPE/LLDPE-g-MA/20A)/HDPE (where LLDPE and LLDPE-g-MA were first mixed with organoclay and then this system was later blended with HDPE) showed a lower slope of the log versus log curve and these results can be an indicative that the interactions between the matrix and the organoclay are stronger. The organoclay interlayer spacing and the crystallinity of the polymer domains were also influenced by the blending sequence. The crystallinity was calculated through the mathematical deconvolution of the peaks observed in the WAXD profiles. Overall, the crystallization of HDPE in the blends was hardly influenced by the presence of LLDPE. The blending sequence (LLDPE/LLDPE-g-MA/20A)/HDPE showed lower cristallinity when compared to others blending sequences. On the other hand, it was observed an increase in the organoclay interlayer spacing of this nanocomposite because the intercalation and/or exfoliation process occurs preferentially in the amorphous phase.