Polyurethane nanocomposite coatings: state of the art and perspectives

High-Value and Environmentally Friendly Recycling Method for Coal-Based Solid Waste Based on Polyurethane Composite Materials

This study aims to provide a high-value and environmentally friendly method for the application of coal-based solid waste. Modified fly ash/polyurethane (MFA/PU) and modified coal gangue powder/polyurethane (MCG/PU) composites were prepared by adding different contents of MFA and MCG (10%, 20%, 30%, 40%). At the filler content of 30%, the compressive strengths of MFA/PU and MCG/PU are 84.1 MPa and 46.3 MPa, respectively, likely due to an improvement in interface compatibility, as indicated by scanning electron microscopy (SEM). The MFA/PU and MCG/PU composites present their highest limiting oxygen index (LOI) values of 29% and 23.5%, respectively, when their filler content is 30%. MFA has advantages in improving the LOIs of composites. Cone calorimetry (CCT) and SEM demonstrate that the two composites exhibit similar condensed-phase flame-retardant behaviors during combustion, which releases CO2 in advance and accelerates the formation of a dense barrier layer. Compared with the MFA/PU composites, the MCG/PU composites could produce a more stable and dense barrier structure. Water quality tests show that heavy metals do not leak from FA and CG embedded in PU. This work provided a new strategy for the safe and high-value recycling of coal-based solid waste.

Fabrication of Polycaprolactone-Based Polyurethanes with Enhanced Thermal Stability

The benefit of being acquainted with thermal properties, especially the thermal stability of polyurethanes (PU), and simplified methods for their improvement is manifold. Considering this, the effect of embedding different amounts of unmodified and surface-modified TiO2 nanoparticles (NPs) within PU, based on polycaprolactone (PCL) and Boltorn® aliphatic hyperbranched polyester, on PU properties was investigated. Results obtained via scanning electron microscopy, swelling measurements, mechanical tests and thermogravimetric analysis revealed that TiO2 NPs can be primarily applied to improve the thermal performance of PU. Through surface modification of TiO2 NPs with an amphiphilic gallic acid ester containing a C12 long alkyl chain (lauryl gallate), the impact on thermal stability of PU was greater due to the better dispersion of modified TiO2 NPs in the PU matrix compared to the unmodified ones. Also, the distinct shape of DTG peaks of the composite prepared using modified TiO2 NPs indicates that applied nano-filler is mostly embedded in soft segments of PU, leading to the delay in thermal degradation of PCL, simultaneously improving the overall thermal stability of PU. In order to further explore the thermal degradation process of the prepared composites and prove the dominant role of incorporated TiO2 NPs in the course of thermal stability of PU, various iso-conversional model-free methods were applied. The evaluated apparent activation energy of the thermal degradation reaction at different conversions clearly confirmed the positive impact of TiO2 NPs on the thermal stability and aging resistance of PU.

Numerical Simulation of Flow Characteristics for Supercritical CO2-Sprayed Polyurethane Resin

Conventional paint spraying processes often use small molecule organic solvents and emit a large amount of volatile organic compounds (VOCs) that are highly toxic, flammable, and explosive. Alternatively, the spraying technology using supercritical CO2 (scCO2) as a solvent has attracted attention because of its ability to reduce VOC emissions, but the flow characteristics of coatings have not been thoroughly studied. Therefore, we numerically simulate the spraying process based on the actual process of scCO2 spraying polyurethane coatings by computational fluid dynamics (CFD). The effects of inlet pressure and volume fraction of scCO2 on the fluid motion parameters inside the nozzle as well as the atomization effect of droplets outside the nozzle are investigated. The simulated results show that a fluid with a large volume fraction of scCO2 will obtain a smaller density, resulting in a larger velocity and a larger distance for the spray to effectively spray. Higher coating content and bigger inlet pressures will result in higher discrete phase model (DPM) concentrations, and thus a bigger inlet pressure should be used to make the droplets more uniform across the 30° spray range. This study can provide theoretical guidance for the process of scCO2-sprayed polyurethane resin.

Polyurea-Graphene Nanocomposites-The Influence of Hard-Segment Content and Nanoparticle Loading on Mechanical Properties

Polyurethane and polyurea-based adhesives are widely used in various applications, from automotive to electronics and medical applications. The adhesive performance depends strongly on its composition, and developing the formulation-structure-property relationship is crucial to making better products. Here, we investigate the dependence of the linear viscoelastic properties of polyurea nanocomposites, with an IPDI-based polyurea (PUa) matrix and exfoliated graphene nanoplatelet (xGnP) fillers, on the hard-segment weight fraction (HSWF) and the xGnP loading. We characterize the material using scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). It is found that changing the HSWF leads to a significant variation in the stiffness of the material, from about 10 MPa for 20% HSWF to about 100 MPa for 30% HSWF and about 250 MPa for the 40% HSWF polymer (as measured by the tensile storage modulus at room temperature). The effect of the xGNP loading was significantly more limited and was generally within experimental error, except for the 20% HSWF material, where the xGNP addition led to about an 80% increase in stiffness. To correctly interpret the DMA results, we developed a new physics-based rheological model for the description of the storage and loss moduli. The model is based on the fractional calculus approach and successfully describes the material rheology in a broad range of temperatures (-70 °C-+70 °C) and frequencies (0.1-100 s-1), using only six physically meaningful fitting parameters for each material. The results provide guidance for the development of nanocomposite PUa-based materials.

An effective purification of double-effect distillation for bio-based pentamethylene diisocyanate

Bio-based pentamethylene diisocyanate (PDI) is a new type of sustainable isocyanate, which has important applications in coatings, foams, and adhesives. Technical-economic analysis of the PDI distillation process can promote the industrialization of PDI. The thermal analysis of PDI facilitates the smooth running of the simulation process. A new PDI heat capacity prediction method was established. The distillation processes of a crude PDI solution by conventional distillation and double-effect distillation were studied. Countercurrent double-effect distillation showed the best energy-saving effects in all double-effect distillation. However, combined with total annual charge (TAC), parallel double-effect distillation was the optimal method for PDI purification. Parallel double-effect distillation can significantly reduce the TAC of production PDI, which is 33.39% lower than that of the conventional distillation. The study demonstrates a clear economic incentive for reducing the cost of PDI purification by parallel double-effect distillation.

Hydrophobic, Mechanical, and Physical Properties of Polyurethane Nanocomposite: Synergistic Impact of Mg(OH)2 and SiO2

Polyurethane (PU) is one of the most well-known polymer coatings because of its favorable characteristics, which include its low density, nontoxicity, nonflammability, longevity, adhesion, simple manufacture, flexibility, and hardness. However, PU does come with several major drawbacks, among which are poor mechanical properties as well as low thermal and chemical stability, particularly in the high-temperature mode, where becomes gets flammable and loses adhesion ability. The limitations have inspired researchers to develop a PU composite to improve the weaknesses by adding different reinforcements. Magnesium hydroxide, having the ability to be produced with exceptional properties such as flammability, has consistently attracted the interest of researchers. Additionally, silica nanoparticles with high strength and hardness are one of the excellent reinforcements of polymers these days. The hydrophobic, physical, and mechanical properties of pure polyurethane and the composite type (nano, micro, and hybrid) fabricated with the drop casting method were examined in this study. 3-Aminopropyl triethoxysilane was applied as a functionalized agent. To confirm that hydrophilic particles turned into hydrophobic, FTIR analysis was carried out. The impact of size, percentage, and kind of fillers on different properties of PU/Mg(OH)2-SiO2 was then investigated using different analyses including spectroscopy and mechanical and hydrophobicity tests. The resultant observations demonstrated that different surface topographies can be obtained from the presence of particles of different sizes and percentages on the hybrid composite's surface. Surface roughness allowed for exceptionally high water contact angles, which confirmed the hybrid polymer coatings' superhydrophobic properties. According to the particle size and content, the distribution of fillers in the matrix also improved the mechanical properties.

Polymeric Coatings and Antimicrobial Peptides as Efficient Systems for Treating Implantable Medical Devices Associated-Infections

Many infections are associated with the use of implantable medical devices. The excessive utilization of antibiotic treatment has resulted in the development of antimicrobial resistance. Consequently, scientists have recently focused on conceiving new ways for treating infections with a longer duration of action and minimum environmental toxicity. One approach in infection control is based on the development of antimicrobial coatings based on polymers and antimicrobial peptides, also termed as “natural antibiotics”.

Microwave-promoted continuous flow synthesis of thermoplastic polyurethane–silver nanocomposites and their antimicrobial performance

The present study reports a reducing agent-free continuous manufacturing of ∼5 nm silver nanoparticles in a thermoplastic polyurethane matrix using a microwave-promoted fluidic system.

Conjugated Polymer/Graphene Oxide Nanocomposites—State-of-the-Art

Graphene oxide is an imperative modified form of graphene. Similar to graphene, graphene oxide has gained vast interest for the myriad of industrial applications. Conjugated polymers or conducting polymers are well known organic materials having conducting backbone. These polymers have semiconducting nature due to π-conjugation along the main chain. Doping and modification have been used to enhance the electrical conductivity of the conjugated polymers. The nanocomposites of the conjugated polymers have been reported with the nanocarbon nanofillers including graphene oxide. This review essentially presents the structure, properties, and advancements in the field of conducting polymer/graphene oxide nanocomposites. The facile synthesis, processability, and physical properties of the polymer/graphene oxide nanocomposites have been discussed. The conjugated polymer/graphene oxide nanocomposites have essential significance for the supercapacitors, solar cells, and anti-corrosion materials. Nevertheless, the further advanced properties and technical applications of the conjugated polymer/graphene oxide nanocomposites need to be explored to overcome the challenges related to the high performance.

Edge-Localized Biodeterioration and Secondary Microplastic Formation by Papiliotrema laurentii Unsaturated Biofilm Cells on Polyurethane Films

Painted environmental surfaces are prone to microbiological colonization with potential coating deterioration induced by the microorganisms. Accurate mechanistic models of these interactions require an understanding of the heterogeneity in which the deterioration processes proceed. Here, unsaturated biofilms (i.e., at air/solid interfaces) of the yeast Papiliotrema laurentii were prepared on polyether polyurethane (PEUR) and polyester-polyether polyurethane (PEST-PEUR) coatings and incubated for up to 33 days at controlled temperature and humidity with no additional nutrients. Transmission micro-Fourier transform infrared microscopy (μFTIR) confirmed preferential hydrolysis of the ester component by the biofilm. Atomic force microscopy combined with infrared nanospectroscopy (AFM-IR) was used to analyze initial PEST-PEUR coating deterioration processes at the single-cell level, including underlying surfaces that became exposed following cell translocation. The results revealed distinct deterioration features that remained localized within ∼10 μm or less of the edges of individual cells and cell clusters. These features comprised depressions of up to ∼300 nm with locally reduced ester/urethane ratios. They are consistent with a formation process initiated by enzymatic ester hydrolysis followed by erosion from water condensation cycles. Further observations included particle accumulation in the broader biofilm vicinity. AFM-IR spectroscopy indicated these to be secondary microplastics consisting of urethane-rich oligomeric aggregates. Overall, multiple contributing factors have been identified that can facilitate differential deterioration rates across the PEST-PEUR surface. Effects of the imposed nutrient conditions on Papiliotrema laurentii physiology were also apparent, with cells developing the characteristics of starvation response, despite the availability of polyester metabolites as a carbon source. The combined results provide new laboratory insights into field-relevant microbiological polymer deterioration mechanisms and biofilm physiology at polymer coating interfaces.