Quantifying residual orientation and thermal stress contributions to birefringence in the material extrusion of polylactide.

Material extrusion is a common additive manufacturing process that subjects polymers to non-steady deformation and thermal processing to build a customized part. The mechanical properties of these parts are often worse than those of injection-molded specimens due to failures at or near the weld zone between extrudate layers. Chain orientation is often cited as a contribution to mechanical weaknesss at the weld, and it is therefore of critical importance to develop strategies to quantify the magnitude and location of residual chain orientation as a function of printing conditions.

Cardiovascular sequelae in symptomatic SARS-CoV-2 infection survivors.

Background: SARS-CoV-2 infection may lead to myocardial and endothelial damage. The present study sought to characterize the cardiovascular sequel in a large group of consecutive patients admitted for out-patient cardiovascular follow-up after a symptomatic COVID-19 infection.

Methods: The aims of this study were as follows: to evaluate the presence of post-covid cardiovascular symptoms in an unselected population of outpatients referred to a post-COVID outpatient cardiology clinic and to characterize the long-term abnormalities associated with a more severe COVID-19 infection clinical course.

Composition Dependence of Flow-Induced Crystallization in High-Density Polyethylene/Isotactic Polypropylene Blends.

Polyolefins, including high-density polyethylene (HDPE) and isotactic polypropylene (iPP), account for over half of the worldwide plastics market and have wide-ranging applications. Recycling of these materials is hindered due to separation difficulties as co-mingled blends of HDPE and iPP often exhibit brittle mechanical behavior because phase separated domains detach under stress due to low interfacial adhesion. Motivated to improve mechanical properties of mixed recyclates during processing, this work examines the effect of shear on the crystallization kinetics and rheological properties of HDPE-iPP blends utilizing a combination of differential scanning calorimetry (DSC), rheo-Raman spectroscopy, polarized optical microscopy, and scanning electron microscopy (SEM).

Evaluating models that predict epoxy conversion using rheological properties.

Simultaneous rheology and conversion measurements of neat and composite epoxy resins reveal that conventional models neither accurately nor fully describe the relationship between rheology and conversion. We find that models predicting thermoset conversion based on mixing rules of rheological properties are quantitatively inaccurate and do not account for chemical gelation. Models based on percolation theory and the divergence of the viscosity at the gel point are more accurate but only valid before the gel point.

Accessing pluripotent materials through tempering of dynamic covalent polymer networks.

Pluripotency, which is defined as a system not fixed as to its developmental potentialities, is typically associated with biology and stem cells. Inspired by this concept, we report synthetic polymers that act as a single "pluripotent" feedstock and can be differentiated into a range of materials that exhibit different mechanical properties, from hard and brittle to soft and extensible. To achieve this, we have exploited dynamic covalent networks that contain labile, dynamic thia-Michael bonds, whose extent of bonding can be thermally modulated and retained through tempering, akin to the process used in metallurgy.