Use of recycled plastic in concrete: A review

Antioxidant activity in different fractions of tomatoes

The current global plastics economy is highly linear, with the exceptional performance and low carbon footprint of polymeric materials at odds with dramatic increases in plastic waste. Transitioning to a circular economy that retains plastic in its highest value condition is essential to reduce environmental impacts, promoting reduction, reuse, and recycling. Mechanical recycling is an essential tool in an environmentally and economically sustainable economy of plastics, but current mechanical recycling processes are limited by cost, degradation of mechanical properties, and inconsistent quality products. This review covers the current methods and challenges for the mechanical recycling of the five main packaging plastics: poly(ethylene terephthalate), polyethylene, polypropylene, polystyrene, and poly(vinyl chloride) through the lens of a circular economy. Their reprocessing induced degradation mechanisms are introduced and strategies to improve their recycling are discussed. Additionally, this review briefly examines approaches to improve polymer blending in mixed plastic waste streams and applications of lower quality recyclate.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/marc.202000415

Mechanical Recycling of Packaging Plastics: A Review.

A review on bio-based lubricants and their applications

Extraction of lithium with functionalized lithium ion-sieves

The effects that both soap concentration and base oil viscosity exert on the rheology of lubricating greases and its relationship with grease microstructure are discussed in this work. With this aim, different lubricating grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and the viscosity of the base oil, according to an RSM statistical design. These lubricating greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, scanning electronic microscopy (SEM) observations and mechanical stability tests were also carried out. It has been found that the structural skeleton (size and shape of the disperse phase particles) was highly influenced by the base oil viscosity. In this sense, the values of the viscoelastic functions in the linear viscoelastic region and the mechanical stability of the lubricating greases increase as the viscosity of the base oil decreases. An opposite ten...

Influence of Soap Concentration and Oil Viscosity on the Rheology and Microstructure of Lubricating Greases

Thermal-induced changes in the viscous and viscoelastic responses of lubricating greases have been investigated through different rheological techniques in a temperature range of 0–175 °C. Small-amplitude oscillatory shear and viscous flow measurements were carried out on a model conventional lithium lubricating grease prepared by inducing the in situ saponification reaction between 12-hydroxystearic acid and hydrated lithium hydroxide. The linear viscoelasticity functions dramatically decrease above 110 °C, but not below this critical temperature, which determines the maximum recommended operating temperature in relation to its durability and resistance under working conditions. Two different regions, below and above this critical temperature, in the plateau modulus versus temperature plot have been detected. From this thermal dependence, a much larger thermal susceptibility of the lubricating grease at temperatures above 110 °C is apparent. The thermo-mechanical reversibility of this material has been studied by applying different combined stress–temperature protocols. Regarding the viscous flow, a minimum in the shear stress versus shear rate plots appeared at temperatures above 60 °C, more pronounced as temperature increases, resulting from material instabilities. The experimental results obtained have been explained on the basis of the thermo-mechanical degradation of the lubricating grease microstructure.

Thermorheological behaviour of a lithium lubricating grease

The overall objective of this work was to evaluate the evolution of the microstructure and rheology of a lubricating grease during its manufacturing process. With this aim, lithium lubricating greases were prepared by inducing the saponification reaction between 12-hydroxystearic acid and hydrated lithium hydroxide within a naphtenic lubricating oil medium, applying a controlled-temperature programme. The manufacturing process was followed through the mixing rheometry technique by measuring the evolution of torque with processing time. Samples of incipient and finished grease were taken from the stirred tank at different processing times. Rheological (linear viscoelasticity and viscous flow) and mechanical stability tests, as well as morphological studies, were carried out on each sample. The changes found in the microstructure and rheology of a lubricating grease during its processing have been related to the soap concentration in the reacting mixture, the waxy soap transition at high temperatures and the further cooling steps. From the experimental results obtained, we may conclude that a suitable lithium lubricating grease is a highly structured system, based on the development of a three-dimensional network due to the presence of metallic soap crystallites.

Relationship among microstructure, rheology and processing of a lithium lubricating grease

In this work, non-perturbed microstructures of several commercial and model lubricating greases, differing in nature and concentration of the thickener agent, were examined using the atomic force microscopy (AFM) technique. Grease microstructure mainly depends on the nature of the thickener employed and, also, on thickener concentration and viscosity of the base oil. Thermal-induced changes in the viscoelastic response of lubricating greases have been investigated by using different rheological techniques in a temperature range of 0–175 °C. Small-amplitude oscillatory shear (SAOS) measurements were carried out to determine the mechanical spectra of the different samples studied. Lubricating grease rheological thermal susceptibility was analysed by following the evolution of the plateau modulus with temperature. SAOS functions dramatically decrease, in most cases, above a characteristic temperature, which depends on nature and/or concentration of the thickener used and therefore on grease microstructure. The thermo-mechanical reversibility of grease microstructure has been studied by carrying out triple-step-shear stress tests (shear stresses inside and outside of the linear viscoelasticity range), at different temperatures. The degree of lubricating grease non-reversible structural breakdown, which increases with temperature, depends on the shear stress applied above the linear viscoelasticity limits.

M.C. Sánchez

Papers

Influence of Soap Concentration and Oil Viscosity on the Rheology and Microstructure of Lubricating Greases

Thermorheological behaviour of a lithium lubricating grease

Relationship among microstructure, rheology and processing of a lithium lubricating grease

Atomic Force Microscopy and Thermo-Rheological Characterisation of Lubricating Greases

Mixing rheometry for studying the manufacture of lubricating greases