Thermoplastic Electromagnetic Shielding Materials from the Integral Recycling of Waste from Electronic Equipment

The European Green Deal's goals are anticipated to be fulfilled in large part thanks to the New Circular Economy Action Plan. It is believed that recycling materials will have a significant positive impact on the environment, particularly in terms of reducing greenhouse gas emissions and the impacts this will have on preventing climate change. Due to the complexity of the issue and its significant practical ramifications, the activity of Waste Electrical and Electronic Equipment (WEEE) collection networks is a subject of interest for researchers and managers, in accordance with the principles that recent laws have addressed in a large number of industrialized countries. The goal of this paper is to characterize and obtain composite materials using an injection process with a matrix of LDPE, PP, and HDPE, with up to a 10% addition of nonmetallic powders from PCBs and electronic parts from an integrated process of WEEE recycling. The composites present relevant thermal, electrical, and mechanical properties. Such composite materials, due to their relevant dielectric properties, may be further tested for applications in electromagnetic shielding at frequencies above 1 kHz, or for electromagnetic interference/electromagnetic compatibility (EMI/EMC and ESD) applications at lower frequencies due to their superior dielectric loss factor values, associated with relevant behaviors around exploitation temperatures, mainly for the electric, electronic, or automotive industries.

Research on the Quality of Partially Removable Skeletal Prostheses Made Using Classical Versus Modern Sintering Techniques

Conventional partially removable skeletal dentures are one of the most common therapeutic solutions offered to edentulous patients worldwide. The present study aims to compare the skeleton of removable dentures realized via classical techniques to that realized via modern techniques, represented by the laser sintering technique, with the comparative aspects being realized through the evaluation of atomic force microscopy (AFM). A total of 20 metal frameworks made of Co-Cr were sectioned, representing the infrastructure of partially removable skeletal dentures, developed using the classical technique versus the laser sintering technique. The infrastructures of partially removable skeletal dentures were designed for both the maxilla and the mandible, with the design of each type of denture being identical, and were developed using both techniques. The roughness values are different depending on the technological method used; for the conventional casting technique, we have higher roughness for the component elements of the partially removable skeletal denture that have more stretch, e.g., the major connector, and for the 3D laser sintering technique, lower roughness is obtained for the component elements that have a lower stretch, e.g., the clasp arms, the minor connector, or the junction between the saddles and the major connector. The clinical implications of the presence of roughness at the level of the active arms or at the level of the connector saddle junction are represented by the risk of fracture, which confers real discomfort to the patient.

Special Packaging Materials from Recycled PET and Metallic Nano-Powders

The European methodology for plastics, as a feature of the EU's circular economy activity plan, ought to support the decrease in plastic waste. The improvement of recycled plastics' economics and quality is one important part of this action plan. Additionally, achieving the requirement that all plastic packaging sold in the EU by 2030 be recyclable or reusable is an important objective. This means that food packaging materials should be recycled in a closed loop at the end. One of the most significant engineering polymers is polyethylene terephthalate (PET), which is widely used. Due to its numerous crucial qualities, it has a wide variety of applications, from packaging to fibers. The thermoplastic polyolefin, primarily polyethylene and polypropylene (PP), is a popular choice utilized globally in a wide range of applications. In the first phase of the current experiment, the materials were obtained by hot pressing with the press machine. The reinforcer is made of Al nanopowder 800 nm and Fe nanopowder 790 nm and the quality of the recycled polymer was examined using Fourier transform infrared spectroscopy (FTIR), a scanning electron microscope (SEM), and differential scanning calorimetry (DSC). From DSC variation curves as a function of temperature, the values from the transformation processes (glass transition, crystallization, and melting) are obtained. SEM measurements revealed that the polymer composites with Al have smooth spherical particles while the ones with Fe have bigger rough spherical particles.

Atomic Force Microscopy Probing and Analysis of Polyimide Supramolecular Systems for Sensor Devices

A series of polyimide supramolecular systems containing different amounts of azochromophore were tested as flexible supports that can be used in the fabrication of certain devices, such as sensors for monitoring the temperature changes, by coating them with conductive metals. That is why it is required to have good interfacial compatibility between the flexible substrate and the inorganic layer. The interface of the sensor elements must be designed in such a way as to improve the sensitivity, accuracy, and response time of the device. Laser irradiation is one of the commonly employed techniques used for surface adaptation by patterning polyimides to increase contact and enhance device reliability and signal transmission. In this context, this work highlights unreported aspects arising from the azo-polyimide morphology, local nanomechanical properties and wettability, which are impacting the compatibility with silver. The texture parameters indicate an improvement of the modulations' quality arising after laser irradiation through the phase mask, increasing the bearing capacity, fluid retention, and surface anisotropy when the amount of the azochromophore increases. The force curve spectroscopy and wettability studies indicated that the modification of the polymer morphology and surface chemistry lead to a better interfacial interaction with the metal lines when the azo component and the polyamidic acid are in equimolar quantities.

Effect of scanning speed on AFM height images and 3D surface texture parameters explored on smooth and rough polymer surfaces

Atomic force microscopy (AFM) is a powerfull technique developed in the last decades that is widely used for surface morphology investigation at micro and nanometric scale. Along with the environment in which the scan is performed and the type of sample, the scanning conditions play an important role in obtaining the best results in imaging, without any artifacts that may be occure. In the present study, in order to establish the proper scanning conditions, smooth and rough polymer surfaces were used to investigate the influence of the scanning speed on height images and amplitude, hybrid, spatial, and functional 3D surface texture parameters in atomic force microscopy.

Lactoferrin-Immobilized Surfaces onto Functionalized PLA Assisted by the Gamma-Rays and Nitrogen Plasma to Create Materials with Multifunctional Properties

Both cold nitrogen radiofrequency plasma and gamma irradiation have been applied to activate and functionalize the polylactic acid (PLA) surface and the subsequent lactoferrin immobilization. Modified films were comparatively characterized with respect to the procedure of activation and also with unmodified sample by water contact angle measurements, mass loss, X-ray photoelectron spectroscopy (XPS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM), and chemiluminescence measurements. All modified samples exhibit enhanced surface properties mainly those concerning biocompatibility, antimicrobial, and antioxidant properties, and furthermore, they are biodegradable and environmentally friendly. Lactoferrin deposited layer by covalent coupling using carbodiimide chemistry showed a good stability. It was found that the lactoferrin-modified PLA materials present significantly increased oxidative stability. Gamma-irradiated samples and lactoferrin-functionalized samples show higher antioxidant, antimicrobial, and cell proliferation activity than plasma-activated and lactoferrin-functionalized ones. The multifunctional materials thus obtained could find application as biomaterials or as bioactive packaging films.

New Heterocyclic Polyurethane-ureas Based on 4,4'-dibenzyl diisocyanate. 2. Influence of Pyridine Units on the Mechanical Properties

Heterocyclic polyurethane-ureas containing pyridine units on the main chain have been prepared by a two-step polyadition reaction. First, an urethane prepolymer was prepared in bulk starting from a macrodiol, which was a polyester-diol such as poly(ethylene adipate) (PEA) or a polyether-diol such as poly(tetramethylene glycol) (PTMG), and a diisocyanate such as 4,4'-dibenzyl diisocyanate (DBDI) or 4,4'-methylene-bis(phenyl-isocyanate) (MDI). The resulting urethane prepolymer containing NCO end groups was polymerized afterwards in DMF solution by using 2,6-diamino pyridine (DAPy) as chain extender, leading to polyurethane-ureas containing pyridine units The hard segments contents varied between 1.458–1.967 mol NHCOO/1000 g polymer. The resulting polymers were characterized by IR spectra, elemental and thermogravimetric analyses, differential scanning calorimetry, gel permeation chromatography, inherent viscosity, water retention measurements and mechanical properties. The study of the relationship between structure and properties reveals the influence of the nature of starting materials, macrodiols, the heterocyclic diamine and diisocyanates on the mechanical properties of the polymers. The large number of hydrogen bondings that formed between urea and urethane groups and the presence of pyridine rings in the polymer chain induced an improved thermal stability and good mechanical properties. The influence of the hard segment length was also studied. A greater length of the hard segments led to higher values of some mechanical tests such as: 100 and 300% moduli, strength stress and elongation at break. The mechanical behavior of these polymers is discussed and compared with that of earlier reported linear polyurethane-ureas based on MDI or with that of related polyurethanes chain-extended with diols.

Establishing proper scanning conditions in atomic force microscopy on polyimide and polyurethane samples and their effect on 3D surface texture parameters

Several atomic force microscopy (AFM) tests have been carried out on both smooth (polyimide) and rough (polyurethane) surfaces so that to obtain the best results; subsequently, the optimization of experiments performed is presented. A special emphasis has been put on the effect of tip geometry, image pre-processing procedure, scanning area, resolution, pixel size, and cantilever oscillation amplitude in tapping mode, as well as on the quality of the topographical images and 3D surface texture parameters. After viewing the scanning tip and finding out its sharpness, degradation, and contamination, a simultaneous calibration in X, Y, and Z directions, lateral calibration of SPM scanners and detection of lateral non-linearity, hysteresis, creep, and cross-coupling effects has been made. We have established the following experimental parameters: proper scanning resolution (512 × 512 pixels), adequate pixel size (between 2.9 and 19.5 nm) and suitable intermittent contact region (moderate tapping) for which the AFM images present good contrast and resolution. Using these parameters, the values of 3D texture parameters remain constant. These kinds of measurements are extremely important to conduct further AFM experiments on polyimide and polyurethane surfaces under optimal conditions, thus avoiding unwanted artifacts on the morphological images or unrealistic values for the 3D surface texture parameters that might occur.