Chemical Recycling of Fully Recyclable Bio-Epoxy Matrices and Reuse Strategies: A Cradle-to-Cradle Approach.

Currently, the epoxy resin market is expressing concerns about epoxy resins' non-recyclability, which can hinder their widespread use. Moreover, epoxy monomers are synthesized via petroleum-based raw materials, which also limits their use. So, it is crucial to find more environmentally friendly alternative solution for their formulation. Within this context, the aim of this paper is to exploit a Cradle-to-Cradle approach, which consists of remodeling and reshaping the productive cycle of consumer products to make sure that they can be infinitely reused rather than just being recycled with a downgrading of their properties or uses, according to the principle of the complete circular economy. Indeed, after starting with a fully-recyclable bio-based epoxy formulation and assessing its recyclability as having a process yield of 99%, we obtained a recycled polymer that could be reused, mixing with the same bio-based epoxy formulation with percentages varying from 15 wt% to 27 wt%. The formulation obtained was thoroughly characterized by a dynamic-mechanical analysis, differential scanning calorimetry, and flexural tests. This approach had two advantages: (1) it represented a sustainable disposal route for the epoxy resin, with nearly all the epoxy resin recovered, and (2) the obtained recycled polymer could be used as a green component of the primary bio-based epoxy matrix. In the end, by using replicated general factorial designs (as statistical tools) combined with a proper optimization process, after carrying out a complete thermo-mechanical characterization of the developed epoxy formulations, the right percentage of recycled polymer content was selected with the aim of identifying the most performing epoxy matrix formulation in terms of its thermo-mechanical properties.

Polymer Blends Based on 1-Hexadecyl-3-methyl Imidazolium 1,3-Dimethyl 5-Sulfoisophthalate Ionic Liquid: Thermo-Mechanical, Surface Morphology and Antibacterial Properties.

In this study, antibacterial polymer blends based on Polyvinyl Chloride (PVC) and Polystyrene-Ethylene-Butylene-Styrene (SEBS), loaded with the ionic liquid (IL) 1-hexadecyl-3-methyl imidazolium 1,3-dimethyl 5-sulfoisophthalate (HdmimDMSIP) at three different concentrations (1%, 5%, and 10%), were produced. The IL/blends were characterized by their thermo-mechanical properties, surface morphology, and wettability. IL release from the blends was also evaluated. The agar diffusion method was used to test the antibacterial activity of the blends against Staphylococcus epidermidis and Escherichia coli. Results from thermal analyses showed compatibility between the IL and the PVC matrix, while phase separation in the SEBS/IL blends was observed. These results were confirmed using PY-GC MS data. SEM analyses highlighted abundant IL deposition on PVC blend film surfaces containing the IL at 5-10% concentrations, whereas the SEBS blend film surfaces showed irregular structures similar to islands of different sizes. Data on water contact angle proved that the loading of the IL into both polymer matrices induced higher wettability of the blends' surfaces, mostly in the SEBS films. The mechanical analyses evidenced a lowering of Young's Modulus, Tensile Stress, and Strain at Break in the SEBS blends, according to IL concentration. The PVC/IL blends showed a similar trend, but with an increase in the Strain at Break as IL concentration in the blends increased. Both PVC/IL and SEBS/IL blends displayed the best performance against Staphylococcus epidermidis, being active at low concentration (1%), whereas the antimicrobial activity against Escherichia coli was lower than that of S. epidermidis. Release data highlighted an IL dose-dependent release. These results are promising for a versatile use of these antimicrobial polymers in a variety of fields.

Fused Filament Fabrication of Alumina/Polymer Filaments for Obtaining Ceramic Parts after Debinding and Sintering Processes.

In this paper, a hybrid commercially available alumina/polymer filament was 3D printed and thermally treated (debinding and sintering) to obtain ceramic parts. Microscopic and spectroscopic analysis was used to thoroughly characterize the green and sintered parts in terms of their mesostructured, as well as their flexural properties. The sintered samples show an α alumina crystalline phase with a mean density of 3.80 g/cm3, a tensile strength of 232.6 ± 12.3 MPa, and a Vickers hardness of 21 ± 0.7 GPa. The mean thermal conductivity value at room temperature was equal to 21.52 ± 0.02 W/(mK). The values obtained through FFF production are lower than those obtained by conventional processes as the 3D-printed samples exhibited imperfect interlayer bonding and voids similar to those found in the structures of polymeric FFFs. Nonetheless, the highly filled ceramic filament is suitable for use in affordable and easy-to-operate FFF machines, as shown by the cost analysis of a real printed and sintered FFF part.

Specific Heat Capacity and Thermal Conductivity Measurements of PLA-Based 3D-Printed Parts with Milled Carbon Fiber Reinforcement.

This research focuses on the thermal characterization of 3D-printed parts obtained via fused filament fabrication (FFF) technology, which uses a poly(lactic acid) (PLA)-based filament filled with milled carbon fibers (MCF) from pyrolysis at different percentages by weight (10, 20, 30 wt%). Differential scanning calorimetry (DSC) and thermal conductivity measurements were used to evaluate the thermal characteristics, morphological features, and heat transport behavior of the printed specimens. The experimental results showed that the addition of MCF to the PLA matrix improved the conductive properties. Scanning electron microscopy (SEM) micrographs were used to obtain further information about the porosity of the systems.

Mechanical, Wear and Thermal Behavior of Polyethylene Blended with Graphite Treated in Ball Milling.

Additive manufacturing, civil, and biomechanical applications are among the most important sectors, where the filler's presence can significantly improve the quality of polymeric products blends. The high market demand of new low-cost material to be used as shock absorbers and mechanical joints arouses our curiosity to study a relatively common commercial polymer and filler. The possible improvement by blending high-density polyethylene (HDPE) and graphite was investigated for these sectors. To achieve this objective, we have prepared HDPE/graphite nanocomposites following mechanical treatment to understand which parameter provides the researched properties. As widely reported in the literature, milling treatment leads to the decrease of the particle size and the exfoliation of graphitic layers. Therefore, graphite has been previously treated with a ball mill for different times (1-16 h) to enhance its lubricating action. We checked an improvement in stiffness, yielding strength, thermal stability, and, in particularly, wear resistance that increased by 65% with respect to that of polyethylene (PE). A treatment time of eight hours in ball milling could be enough to give an appreciable improvement. The wear behavior of HDPE with treated graphite has not been deeply investigated so far, and it could be important because HDPE is considered a "carrier polymer" for different low-friction applications.

Thermo-mechanical, antimicrobial and biocompatible properties of PVC blends based on imidazolium ionic liquids.

The aim of this study was the development of antimicrobial polyvinylchloride (PVC) blends loaded with 0.1-10% (w/w) of the ILs 1-hexadecyl-3-methylimidazolium 1,3-dimethyl 5-sulfoisophthalate (HdmimDMSIP) and 1-octyloximethyl-3-methylimidazolium hexafluorophosphate (OOMmimPF6). The synthetized ILs were characterized by 1HNMR, MALDI-TOF, DSC and TGA. PVC/ILs films were obtained by solvent casting.Thermal and mechanical properties (tensile stress TS and elongation at break EB), morphology by SEM, surface wettability, antimicrobial activity, cytotoxicity and ILs release in sterile water from PVC/ILs film blends were determined. Results demonstrated that the presence of both ILs in PVC formulation slightly affected thermal and mechanical properties of blends. The loading of both ILs into PVC matrix made PVC/ILs films hydrophilic, especially at the highest concentration of HdmimDMSIP. The PVC/ILs blends displayed antibacterial activity up to ILs lowest concentrations (0.1-0.5%). The inhibition of Escherichia coli growth was lower than that showed toward Staphylococcus epidermidis. The addition of 10% ILs concentration resulted excessive as demonstrated by accumulation of ILs on film surfaces (SEM) and ILs high release from PVC/ILs blends during the first day of water immersion. Biocompatibility studies highlighted that the addition of low amounts of both ILs into PVC matrix is not cytotoxic for mouse fibroblast cells (L929), supporting their potential use for biomedical porposes.

Influence of the Processing Conditions on the Mechanical Performance of Sustainable Bio-Based PLA Compounds.

Cellulose/PLA-based blends (up to 77 vol./vol.% of the added fibers) for applications in extrusion-based technology were realized in an internal mixer by setting different operating conditions. In particular, both the mixing time and temperature were increased in order to simulate a recycling operation (10 or 25 min, 170 or 190 °C) and gain information on the potential reuse of the developed systems. The torque measurements during the compound's preparation, and the compound's mechanical tensile features, both in the static and dynamic mode, were evaluated for each investigated composition. The final results confirmed a reduction of the torque trend over time for the PLA matrix, which was attributed to a possible degradation mechanism, and confirmed by infrared spectroscopy. The mechanical behaviour of the pristine polymer changed from elastoplastic to brittle, with a significant loss in ductility going from the lower mixing temperatures up to the higher ones for the longest time. Through the addition of cellulose fibers into the composite systems, a higher stabilization of the torque in the time and an improvement in the mechanical performance were always verified compared to the neat PLA, with a maximum increase in the Young modulus (+100%) and the tensile strength (+57%), and a partial recovery of the ductility.

Synthesis and Characterization of Copoly(Ether Sulfone)s with Different Percentages of Diphenolic Acid Units.

New functionalized Poly(ether sulfone)s having different molar ratio (10, 20, 30, 50, 70, 100 mol%) of 4,4-bis phenoxy pentanoic acid unit (diphenolic acid; DPA) units were synthesized and characterized by (1H and 13C)-NMR, MALDI-TOF MS, FT-IR, DSC and DMA analyses. The microstructural analysis of the copolymers, obtained by 13C-NMR using an appropriate statistical model, shows a random distribution of copolymer sequences, as expected. The presence of different amount of DPA units along the polymer chains affects the chemical and physical properties of the copolymers. The Tg and the contact angle values decrease as the molar fraction of DPA units increases, whereas the hydrophilicity increases. NMR and MALDI-TOF MS analyses show that all polymer chains are almost terminated with hydroxyl and chlorine as end groups. The presence of cyclic oligomers was also observed by MALDI-TOF MS analysis.

3D-Printed micro-optofluidic device for chemical fluids and cells detection.

In this work, it is presented a micro-optofluidic flow detector used for on-chip biological and chemical samples investigation. It is made in Poly-dimethyl-siloxane using a master-slave approach based on the 3D-Printing techniques. The micro-optofluidic device is made by assembling a microfluidic T-junction with a micro-optical section that consists of two optical fiber insertions and a PDMS gold-spattered micro-waveguide. The working principle in the detection is based on a different light transmission correlated to the fluid interfering with the laser beam in a micro-channel section. The proposed solution allows to realize a PDMS micro-device taking the advantage of 3D- Printing and goes beyond the restriction in the material selection. The device's performances were tested in the fluids detection and in the evaluation of the cell concentrations. Additionally, the micro-device was used as a real-time two-phase fluids flow detector. The two-phases flows were successfully monitored in different experimental conditions, varying both hydrodynamic and optical external stimuli.

Interlaminar Toughening of Epoxy Carbon Fiber Reinforced Laminates: Soluble Versus Non-Soluble Veils.

This work describes the evaluation of different interlaminar veils to improve the toughening of epoxy/carbon fiber composites manufactured by resin infusion. Three commercial veils have been used in the study: two electro spun thermoplastic nanofiber (Xantulayr® from Revolution Fibres) with different areal weight, and one micro carbon fibers veil (Optiveil® from TFP). Two laboratory made veils were also manufactured by electrospinning commercial polyethersulfone (PES) tougheners (Virantage by Solvay). The veils were selected to be either soluble or non-soluble in the epoxy resin matrix during curing. The solubility was analyzed by scanning electron microscopy and dynamic mechanical analysis testing on the cured laminates. The fracture energy was evaluated by double cantilever bending (DCB) testing under Mode I loading. The insoluble thermoplastic nanofibers showed the highest toughening efficiency, followed by the soluble nanofiber veils. The carbon fiber based veil showed no toughness improvement.

Comparison of Ultem 9085 Used in Fused Deposition Modelling (FDM) with Polytherimide Blends.

Polyetherimide (PEI) blends modified by either polycarbonate (PC) or polyethylene terephthalate glycol-modified (PETG) were prepared. The latter modifier (PETG) was an industrial grade widely used for fused deposition modelling (FDM) printing. PEI blends were compared to Ultem 9085, which is the standard PEI grade for FDM printing in advanced applications. All the blends were thoroughly characterized in terms of their rheological, morphological, thermomechanical and tensile properties. Ultem 9085 showed improved rheology for processing over standard PEI. PEI/PC blends with 10 wt % of modifier developed here closely matched the viscosity behavior of Ultem 9085. On the other hand, the blends with low PC content (i.e., less than 20 wt %) outperformed Ultem 9085 in terms of thermal and tensile properties. When PETG was added, similar tensile properties to Ultem 9085 were found. The immiscibility for PC contents higher than 20 wt % deteriorated the tensile properties, making it less attractive for applications, although melt viscosity decreased further for increasing PC contents.

Engineering Thermoplastics for Additive Manufacturing: A Critical Perspective with Experimental Evidence to Support Functional Applications.

BACKGROUND: Among additive manufacturing techniques, the filament-based technique involves what is referred to as fused deposition modeling (FDM). FDM materials are currently limited to a selected number of polymers. The present study focused on investigating the potential of using high-end engineering polymers in FDM. In addition, a critical review of the materials available on the market compared with those studied here was completed. METHODS: Different engineering thermoplastics, ranging from industrial grade polycarbonates to novel polyetheretherketones (PEEKs), were processed by FDM. Prior to this, for innovative filaments based on PEEK, extrusion processing was carried out. Mechanical properties (i.e., tensile and flexural) were investigated for each extruded material. An industrial-type FDM machine (Stratasys Fortus® 400 mc) was used to fully characterize the effect of printing parameters on the mechanical properties of polycarbonate. The obtained properties were compared with samples obtained by injection molding. Finally, FDM samples made of PEEK were also characterized and compared with those obtained by injection molding. RESULTS: The effect of raster to raster air gap and raster angle on tensile and flexural properties of printed PC was evidenced; the potential of PEEK filaments, as novel FDM material, was highlighted in comparison to state of the art materials. CONCLUSIONS: Comparison with injection molded parts allowed to better understand FDM potential for functional applications. The study discussed pros and cons of the different materials. Finally, the development of novel PEEK filaments achieved important results offering a novel solution to the market when high mechanical and thermal properties are required.

Poly-paper: a sustainable material for packaging, based on recycled paper and recyclable with paper.

BACKGROUND: Until now, environmental sustainability issues are almost entirely unsolved for packaging materials. With the final aim of finding materials with a single recycling channel, cellulose fiber/poly(vinyl)alcohol composites were investigated. METHODS: After extrusion and injection molding, samples of composite with different cellulose fiber content (30%, 50% and 70% w/w) were tested. RESULTS: Tensile mechanical tests exhibited an improvement in composite stiffness when the reinforcement content was increased together with a decrease in composite elongation. Solubility tests performed at room temperature and 45°C showed different behavior depending on the water-resistant film applied on the composite (50% cellulose fiber content). In particular, the uncoated composite showed complete solubility after 2 hours, whereas at the same time point, no solubility occurred when a non-water-soluble varnish was used. CONCLUSIONS: The proposed composites, named Poly-paper, appear to warrant further investigation as highly sustainable packaging.