Molecularly imprinted polymer nanoparticle-carbon nanotube composite electrochemical gas sensor for highly selective and sensitive detection of methanol vapour.

An electrochemical gas sensor has been fabricated using molecularly imprinted polymer nanoparticles (nanoMIPs) and multiwalled carbon nanotubes on screen-printed electrodes. Methanol vapour was chosen as the target due to its toxicity as its suitability as a model for more harmful pollutant gases. The sensor functions under ambient conditions and in the required concentration range, in contrast to all previous MIP-based gas sensors for methanol. The sensitivity of the sensor was greatly improved by the addition of multiwall carbon nanotubes, resulting in a limit of detection of approximately 10 ppm. The nanoMIPs provide an inherent selectivity for the target inherent in its design. Selectivity studies were performed with structurally analogous alcohols at various concentrations, demonstrating selectivity for methanol 12.1 times that for ethanol at 2 mmol dm-3 and 4.2 times that for ethanol at 1 mmol dm-3. Interactions with isopropanol and n-propanol were found to be non-specific, and the response to water was negligible. This demonstrates an improvement over previous methanol gas sensors based on molecularly imprinted polymers. No response was observed with carbon nanotubes alone, and no selectivity was observed with non-imprinted equivalents of the nanoMIP sensor. The resulting device is by far the most practical MIP-based instrument for methanol gas sensing thus far described in the literature, being the only example capable of functioning at the necessary methanol vapour concentrations and at the required temperature and humidity. With the selectivity and sensitivity described and the simple design, the developed device provides a substantial advance in the field of molecularly imprinted gas sensors.

On the Response to Hygrothermal Ageing of Fully Recyclable Flax and Glass Fibre Reinforced Polymer Composites.

The present work studies the response to hygrothermal ageing of natural fibre composites (NFCs) against synthetic fibre composites when using three different types of polymers as matrices. For ageing, coupons were fully immersed in distilled water at 23, 40, and 60 °C for a total ageing period of 56 days. Flax fibre-reinforced composites, using two recyclable polymer systems: (i) a bio-based recyclable epoxy and (ii) an acrylic-based liquid thermoplastic resin, were tested against conventional glass fibre-reinforced composites employing a synthetic (petroleum-based) epoxy. Different fibre/polymer matrix material combinations were tested to evaluate the effects of hygrothermal ageing degradation on the reinforcement, matrix, and fibre/matrix interface. The hygrothermal ageing response of unaged and aged composite coupons was assessed in terms of flexural and viscoelastic performance, physicochemical properties, and microscopy (SEM-Scanning Electron Microscopy).

Theoretical and Experimental Determination of Thermomechanical Properties of Epoxy-SiO2 Nanocomposites.

Improvements in the thermomechanical properties of epoxy upon inclusion of well-dispersed SiO2 nanoparticles have been demonstrated both experimentally and through molecular dynamics simulations. The SiO2 was represented by two different dispersion models: dispersed individual molecules and as spherical nanoparticles. The calculated thermodynamic and thermomechanical properties were consistent with experimental results. Radial distribution functions highlight the interactions of different parts of the polymer chains with the SiO2 between 3 and 5 nm into the epoxy, depending on the particle size. The findings from both models were verified against experimental results, such as the glass transition temperature and tensile elastic mechanical properties, and proved suitable for predicting thermomechanical and physicochemical properties of epoxy-SiO2 nanocomposites.

Silicon Carbide Nanoparticles as a Mechanical Boosting Agent in Material Extrusion 3D-Printed Polycarbonate.

In this work, the effect of silicon carbide (carborundum, SiC), as a boosting agent of the mechanical response of the polycarbonate (PC) polymer, was investigated. The work aimed to fabricate nanocomposites with an improved mechanical performance and to further expand the utilization of 3D printing in fields requiring an enhanced material response. The nanocomposites were produced by a thermomechanical process in various SiC concentrations in order to evaluate the filler loading in the mechanical enhancement. The samples were 3D printed with the material extrusion (MEX) method. Their mechanical performance was characterized, following international standards, by using dynamic mechanical analysis (DMA) and tensile, flexural, and Charpy's impact tests. The microhardness of the samples was also measured. The morphological characteristics were examined, and Raman spectra revealed their structure. It was found that SiC can improve the mechanical performance of the PC thermoplastic. A 19.5% increase in the tensile strength was found for the 2 wt.% loading nanocomposite, while the 3 wt.% nanocomposite showed a 16% increase in the flexural strength and a 35.9% higher impact strength when compared to the unfilled PC. No processability issues were faced for the filler loadings that have been studied here.

High-performance medical-grade resin radically reinforced with cellulose nanofibers for 3D printing.

The effect of Cellulose NanoFiber (CNF) addition to a medical-grade resin in Stereolithography (SLA) Additive Manufacturing (AM) technology is reported, aiming to elaborate an easily processable, highly stiff bio-compound. CNFs were shear stir blended at various weight ratios with liquid resin. The fabricated nanocomposite materials were introduced in an SLA 3D printer for specimens manufacturing. The mechanical performance was studied according to international standards. Charpy Toughness and Vickers microhardness were calculated for all tested materials. A microscopic and surface analysis was conducted on fractured tensile specimens by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), respectively. The thermal and thermomechanical properties were investigated by Thermogravimetric Analysis (TGA), Differential Calorimetry (DSC), and Dynamic Mechanical Analysis (DMA). Significant reinforcement of the medical-grade nanocomposites is reported, with the highest values calculated to be at 1.0 wt% concentration (more than 100% at the tensile strength), while brittleness and rigidity were increased.

High Performance Polycarbonate Nanocomposites Mechanically Boosted with Titanium Carbide in Material Extrusion Additive Manufacturing.

Herein, a polycarbonate (PC) polymer is melt extruded together with titanium carbide (TiC) nano powder for the development of advanced nanocomposite materials in material extrusion (MEX) 3D printing. Raw material for the 3D printing process was prepared in filament form with a thermomechanical extrusion process and specimens were built to be tested according to international standards. A thorough mechanical characterization testing course (tensile, flexural, impact, microhardness, and dynamic mechanical analysis-DMA) was conducted on the 3D printed specimens. The effect of the ceramic filler loading was also investigated. The nanocomposites' thermal and stoichiometric properties were investigated with thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), energy-dispersive X-ray spectroscopy (EDS), and Raman respectively. The specimens' 3D printing morphology, quality, and fracture mechanism were investigated with atomic force microscopy (AFM) and scanning electron microscopy (SEM) respectively. The results depicted that the addition of the filler decidedly enhances the mechanical response of the virgin polymer, without compromising properties such as its processability or its thermal stability. The highest improvement of 41.9% was reported for the 2 wt.% filler loading, making the nanocomposite suitable for applications requiring a high mechanical response in 3D printing, in which the matrix material cannot meet the design requirements.

Recent developments in microbial degradation of polypropylene: Integrated approaches towards a sustainable environment.

Fossil-fuel-based plastics have many enticing properties, but their production has resulted in significant environmental issues that require immediate attention. Despite the fact that these polymers are manmade, some bacteria can degrade and metabolise them, suggesting that biotechnologies based on the principle of plastic biodegradation could be beneficial. Among different types of plastics, polypropylene (PP), either having low or high density, is one of the most consumed plastics (18.85%). Their debasement under natural conditions is somewhat tricky. Still, their debasement under natural conditions is rather difficult slightly. However, different scientists have still made efforts by employing other microbes such as bacteria, fungi, and guts bacteria of larvae of insects to bio-deteriorate the PP plastic. Pre-irradiation techniques (ultraviolet and gamma irradiations), compatibilizers, and bio-additives (natural fibers, starch, and polylactic acid) have been found to impact percent bio-deterioration of different PP derivatives stronglythe various. The fungal and bacterial study showed that PP macro/microplastic might serve as an energy source and sole carbon during bio-degradation. Generally, gravimetric method or physical characterization techniques such as FTIR, XRD, SEM, etc., are utilized to affirm the bio-degradation of PP plastics-based materials. However, these techniques are not enough to warrant the bio-deterioration of PP. In this regard, a new technique approach that measures the amount of carbon dioxide emitted during bacterial or fungus degradation has also been discussed. In addition, further exploration is needed on novel isolates from plastisphere environments, sub-atomic strategies to describe plastic-debasing microorganisms and improve enzymatic action strategies, and omics-based innovations to speed up plastic waste bio-deterioration.

Development and Optimization of Medical-Grade Multi-Functional Polyamide 12-Cuprous Oxide Nanocomposites with Superior Mechanical and Antibacterial Properties for Cost-Effective 3D Printing.

In the current study, nanocomposites of medical-grade polyamide 12 (PA12) with incorporated copper (I) oxide (cuprous oxide-Cu2O) were prepared and fully characterized for their mechanical, thermal, and antibacterial properties. The investigation was performed on specimens manufactured by fused filament fabrication (FFF) and aimed to produce multi-purpose geometrically complex nanocomposite materials that could be employed in medical, food, and other sectors. Tensile, flexural, impact and Vickers microhardness measurements were conducted on the 3D-printed specimens. The fractographic inspection was conducted utilizing scanning electron microscopy (SEM), to determine the fracture mechanism and qualitatively evaluate the process. Moreover, the thermal properties were determined by thermogravimetric analysis (D/TGA). Finally, their antibacterial performance was assessed through a screening method of well agar diffusion. The results demonstrate that the overall optimum performance was achieved for the nanocomposites with 2.0 wt.% loading, while 0.5 wt.% to 4.0 wt.% loading was concluded to have discrete improvements of either the mechanical, the thermal, or the antibacterial performance.

Synthesis of Bio-based monomers and polymers using microbes for a sustainable bioeconomy.

As a result of environmental concerns and the depletion of biomass assets, eco-friendly, renewable biomass-based chemical extraction has recently received significant attention. Bio-based chemicals can be prepared using different renewable feedstockbio-resources through microbial fermentation. Chemicals produced from renewable feedstockscan reduce ecological consequences from improper disposal and repurpose them into valuable products. Biodegradability, biocompatibility and non-toxicity, particularly in biomedical applications, have inspired researchers towards developing novel technologies that have social benefit. Among semi-synthetic and synthetic polymeric materials, utilization of natural bio-based monomeric materials can provide opportunities for sustainable development of novel non-toxic, biodegradable and biocompatible products. The purpose of this work is to give a summary of research into the generation of natural bio-based succinic acid (SA) monomer, the development of poly(butylene succinate) (PBS) as biodegradable polymer, PBS-based nanocomposites and their innovative uses.

On the Mechanical Response of Silicon Dioxide Nanofiller Concentration on Fused Filament Fabrication 3D Printed Isotactic Polypropylene Nanocomposites.

Utilization of advanced engineering thermoplastic materials in fused filament fabrication (FFF) 3D printing process is critical in expanding additive manufacturing (AM) applications. Polypropylene (PP) is a widely used thermoplastic material, while silicon dioxide (SiO2) nanoparticles (NPs), which can be found in many living organisms, are commonly employed as fillers in polymers to improve their mechanical properties and processability. In this work, PP/SiO2 nanocomposite filaments at various concentrations were developed following a melt mixing extrusion process, and used for FFF 3D printing of specimens' characterization according to international standards. Tensile, flexural, impact, microhardness, and dynamic mechanical analysis (DMA) tests were conducted to determine the effect of the nanofiller loading on the mechanical and viscoelastic properties of the polymer matrix. Scanning electron microscopy (SEM), Raman spectroscopy and atomic force microscopy (AFM) were performed for microstructural analysis, and finally melt flow index (MFI) tests were conducted to assess the melt rheological properties. An improvement in the mechanical performance was observed for silica loading up to 2.0 wt.%, while 4.0 wt.% was a potential threshold revealing processability challenges. Overall, PP/SiO2 nanocomposites could be ideal candidates for advanced 3D printing engineering applications towards structural plastic components with enhanced mechanical performance.

Optimization of the Filler Concentration on Fused Filament Fabrication 3D Printed Polypropylene with Titanium Dioxide Nanocomposites.

Polypropylene (PP) is an engineered thermoplastic polymer widely used in various applications. This work aims to enhance the properties of PP with the introduction of titanium dioxide (TiO2) nanoparticles (NPs) as nanofillers. Novel nanocomposite filaments were produced at 0.5, 1, 2, and 4 wt.% filler concentrations, following a melt mixing extrusion process. These filaments were then fed to a commercially available fused filament fabrication (FFF) 3D printer for the preparation of specimens, to be assessed for their mechanical, viscoelastic, physicochemical, and fractographic properties, according to international standards. Tensile, flexural, impact, and microhardness tests, as well as dynamic mechanical analysis (DMA), Raman, scanning electron microscopy (SEM), melt flow volume index (MVR), and atomic force microscopy (AFM), were conducted, to fully characterize the filler concentration effect on the 3D printed nanocomposite material properties. The results revealed an improvement in the nanocomposites properties, with the increase of the filler amount, while the microstructural effect and processability of the material was not significantly affected, which is important for the possible industrialization of the reported protocol. This work showed that PP/TiO2 can be a novel nanocomposite system in AM applications that the polymer industry can benefit from.

Sustainable Additive Manufacturing: Mechanical Response of Polyethylene Terephthalate Glycol over Multiple Recycling Processes.

The continuous demand for thermoplastic polymers in a great variety of applications, combined with an urgent need to minimize the quantity of waste for a balanced energy-from-waste strategy, has led to increasing scientific interest in developing new recycling processes for plastic products. Glycol-modified polyethylene terephthalate (PETG) is known to have some enhanced properties as compared to polyethylene terephthalate (PET) homopolymer; this has recently attracted the interest from the fused filament fabrication (FFF) three-dimensional (3D) printing community. PET has shown a reduced ability for repeated recycling through traditional processes. Herein, we demonstrate the potential for using recycled PETG in consecutive 3D printing manufacturing processes. Distributed recycling additive manufacturing (DRAM)-oriented equipment was chosen in order to test the mechanical and thermal response of PETG material in continuous recycling processes. Tensile, flexure, impact strength, and Vickers micro-hardness tests were carried out for six (6) cycles of recycling. Finally, Raman spectroscopy as well as thermal and morphological analyses via scanning electron microscopy (SEM) fractography were carried out. In general, the results revealed a minor knockdown effect on the mechanical properties as well as the thermal properties of PETG following the process proposed herein, even after six rounds of recycling.

Enhanced Mechanical, Thermal and Antimicrobial Properties of Additively Manufactured Polylactic Acid with Optimized Nano Silica Content.

The scope of this work was to create, with melt mixing compounding process, novel nanocomposite filaments with enhanced properties that industry can benefit from, using commercially available materials, to enhance the performance of three-dimensional (3D) printed structures fabricated via fused filament fabrication (FFF) process. Silicon Dioxide (SiO2) nanoparticles (NPs) were selected as fillers for a polylactic acid (PLA) thermoplastic matrix at various weight % (wt.%) concentrations, namely, 0.5, 1.0, 2.0 and 4.0 wt.%. Tensile, flexural and impact test specimens were 3D printed and tested according to international standards and their Vickers microhardness was also examined. It was proven that SiO2 filler enhanced the overall strength at concentrations up to 1 wt.%, compared to pure PLA. Atomic force microscopy (AFM) was employed to investigate the produced nanocomposite extruded filaments roughness. Raman spectroscopy was performed for the 3D printed nanocomposites to verify the polymer nanocomposite structure, while thermogravimetric analysis (TGA) revealed the 3D printed samples' thermal stability. Scanning electron microscopy (SEM) was carried out for the interlayer fusion and fractography morphological characterization of the specimens. Finally, the antibacterial properties of the produced nanocomposites were investigated with a screening process, to evaluate their performance against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus).

3D Printed Thermoelectric Polyurethane/Multiwalled Carbon Nanotube Nanocomposites: A Novel Approach towards the Fabrication of Flexible and Stretchable Organic Thermoelectrics.

Three-dimensional (3D) printing of thermoelectric polymer nanocomposites is reported for the first time employing flexible, stretchable and electrically conductive 3D printable thermoplastic polyurethane (TPU)/multiwalled carbon nanotube (MWCNT) filaments. TPU/MWCNT conductive polymer composites (CPC) have been initially developed employing melt-mixing and extrusion processes. TPU pellets and two different types of MWCNTs, namely the NC-7000 MWCNTs (NC-MWCNT) and Long MWCNTs (L-MWCNT) were used to manufacture TPU/MWCNT nanocomposite filaments with 1.0, 2.5 and 5.0 wt.%. 3D printed thermoelectric TPU/MWCNT nanocomposites were fabricated through a fused deposition modelling (FDM) process. Raman and scanning electron microscopy (SEM) revealed the graphitic nature and morphological characteristics of CNTs. SEM and transmission electron microscopy (TEM) exhibited an excellent CNT nanodispersion in the TPU matrix. Tensile tests showed no significant deterioration of the moduli and strengths for the 3D printed samples compared to the nanocomposites prepared by compression moulding, indicating an excellent interlayer adhesion and mechanical performance of the 3D printed nanocomposites. Electrical and thermoelectric investigations showed that L-MWCNT exhibits 19.8 ± 0.2 µV/K Seebeck coefficient (S) and 8.4 × 103 S/m electrical conductivity (σ), while TPU/L-MWCNT CPCs at 5.0 wt.% exhibited the highest thermoelectric performance (σ = 133.1 S/m, S = 19.8 ± 0.2 µV/K and PF = 0.04 µW/mK2) among TPU/CNT CPCs in the literature. All 3D printed samples exhibited an anisotropic electrical conductivity and the same Seebeck coefficient in the through- and cross-layer printing directions. TPU/MWCNT could act as excellent organic thermoelectric material towards 3D printed thermoelectric generators (TEGs) for potential large-scale energy harvesting applications.

Three-Dimensional (3D) Conductive Network of CNT-Modified Short Jute Fiber-Reinforced Natural Rubber: Hierarchical CNT-Enabled Thermoelectric and Electrically Conductive Composite Interfaces.

Jute fibers (JFs) coated with multiwall carbon nanotubes (MWCNTs) have been introduced in a natural rubber (NR) matrix creating a three-dimensional (3D) electrically conductive percolated network. The JF-CNT endowed electrical conductivity and thermoelectric properties to the final composites. CNT networks fully covered the fiber surfaces as shown by the corresponding scanning electron microscopy (SEM) analysis. NR/JF-CNT composites, at 10, 20 and 30 phr (parts per hundred gram of rubber) have been manufactured using a two-roll mixing process. The highest value of electrical conductivity (σ) was 81 S/m for the 30 phr composite. Thermoelectric measurements revealed slight differences in the Seebeck coefficient (S), while the highest power factor (PF) was 1.80 × 10-2 µW/m K-2 for the 30 phr loading. The micromechanical properties and electrical response of the composite's conductive interface have been studied in peak force tapping quantitative nanomechanical (PFT QNM) and conductive atomic force microscopy (c-AFM) mode. The JF-CNT create an electrically percolated network at all fiber loadings endowing electrical and thermoelectric properties to the NR matrix, considered thus as promising thermoelectric stretchable materials.

Permeable Nanomontmorillonite and Fibre Reinforced Cementitious Binders.

Clinker reduction in cementitious binders is of paramount importance today, and nanotechnology has extended permissible limits. In the present study, a reference binder consisting of 60% Portland cement, 20% limestone, 20% fly ash, 3% polyvinyl alcohol (PVA) fibres and 2% superplasticizer is optimized with three different types of nano-montmorillonite (nMt) dispersions; two organomodified ones and an inorganic one at different proportions (0.5% to 4%). Flexural strength, measured on day 7, 28, 56 and 90, was improved after day 28 with the addition of inorganic nMt. Thermal gravimetric analyses carried out on day 7, 28, 56 and 90 coupled with x-ray diffraction (at day 28) showed a distinctively enhanced pozzolanic reaction. Backscattered electron imaging confirmed changes in the microstructure. Late age relative density measurements of the nMt cementitious nanocomposites showed higher values than these of the reference paste, which can be attributed to better particle packing. Mercury intrusion porosimetry measurements give support to the optimal nMt dosage, being 1% by total mass of binder and water impermeability tests (modified with BS EN 492:2012) suggest that inorganic nMt can be a viable option material where permeability constitutes a prerequisite. Suggestions for further activation of the nMt-fibre reinforced cementitious nanocomposites were also made.