Rheological and mechanical properties of blends of LDPE with high contents of UHMWPE wastes

Development and Characterization of LLDPE Blends with Different UHMWPE Concentrations Obtained by Hot Pressing

To modify its characteristics, expand its applicability, and, in some cases, its processability, new blends using ultra-high-molecular-weight polyethylene (UHMWPE) have been developed. In this study, three different formulations of linear low-density polyethylene (LLDPE) and UHMWPE blends were prepared with 15, 30, and 45% (% w/w) UHMWPE in the LLDPE matrix. All mixtures were prepared by hot pressing and were immersed in water for one hour afterwards at a controlled temperature of 90 °C to relieve the internal stresses that developed during the forming process. The thermal characterization showed that the blends showed endothermic peaks with different melting temperatures, which may be the result of co-crystallization without mixing between the polymers during the forming process. The mechanical characteristics presented are typical of a ductile material, but with the increase in the percentage of UHMWPE, there was a decrease in the ductility of the blends, as the elongation at rupture of the blends was higher than that of the pure components. The morphologies observed by SEM indicate that there were two phases in the blends. This is the result of the system’s immiscibility due to the mode of preparation of the blends, wherein the two polymers may not have mixed intimately, confirming the results found with the thermal analyses.

The Effect of Dialkyl Peroxide Crosslinking on the Properties of LLDPE and UHMWPE

Peroxide has been considered a chemical agent that can be used to tune the properties of polymeric materials. This research evaluated the influence of different concentrations of dialkyl peroxides on the mechanical, thermal, and morphological properties of linear low-density polyethylene (LLDPE) and ultra-high molecular weight polyethylene (UHMWPE). The neat polymer, as well as those with the addition of 1% and 2% by mass of dialkyl peroxides, were subjected to compression molding and immersion in water for 1 h, under controlled temperatures of 90 °C. The values of the gel content found in the samples indicated that the addition of peroxide to the LLDPE and to the UHMWPE promoted the formation of a reticulated network. The structure obtained by the crosslinking led to less reorganization of the chains during the crystallization process, resulting in the formation of imperfect crystals and, consequently, in the reduction in melting temperatures, crystallization and enthalpy. The mechanical properties were altered with the presence of the crosslinker. The polymers presented had predominant characteristics of a ductile material, with the occurrence of crazing with an increased peroxide content.

Ovalbumin-Loaded Gelation Microneedles Made of Predictive Formulation by Molecular Dynamics Simulation for Enhancement of Skin Immunization

Gelation microneedle (GMNs) based vaccinations with tumor antigens have been considered to be an attractive method for transcutaneous immunization because of their superior ability to deliver vaccines through the stratum corneum (SC) in a minimally invasive manner, which subsequently induces adaptive antitumor immunity. In this study, molecular dynamics (MD) uniaxial tension simulations were conducted to predict the formulation of poly(vinyl alcohol) (PVA; possesses high water solubility) and poly(methyl vinyl ether-altmaleic anhydride) (PMVEMA; possesses high mechanical strength) blend that has the strongest mechanical properties. To validate the accuracy of the Dreiding potential for these two polymers, their densities and Hildebrand solubility parameters were first predicted using MD simulations. These values exhibited good agreement with the corresponding experimental results, indicating the accuracy of the Dreiding potential for the polymers. Regarding the simulation results, the number density of H-bonds between PVA and PMVEMA was the highest at 50% PMVEMA, which can significantly enhance the mechanical strength of pristine PVA for enhanced skin immunization. In terms of further experimental validation, evidence from mechanical strength, solubility, in vitro porcine skin penetration tests, and in vivo immunization were consistent with our simulation predictions. In addition, our results indicated that delivery of ovalbumin (OVA) using GMN patches fabricated using PVA/PMVEMA (50%/50%) provided even stronger immune responses. Using this molecular simulation procedure, the optimal fraction of PVA/PMVEMA composite for the strongest mechanical properties can be rapidly predicted to reduce research time and costs in related experiments.