Morphology Control in Waterborne Polyurethane Dispersion Nanocomposites through Tailored Structure, Formulation, and Processing

Waterborne polyurethane dispersions (PUDs) have garnered increasing interest in recent years due to the growing demand for environmentally friendly materials. The unique phase-separated morphologies exhibited in PUD films and coatings provide opportunities for directing the distribution of functional additives and controlling properties. Although there has been extensive research on polyurethanes for several decades, the mechanisms underlying the PUD morphology formation are poorly understood. The morphologies are driven by interactions between hard segments (HS), and the process is further complicated by the presence of colloidal particles and the intricate interaction between the urethane/urea linkages and water. In this work, structure-property-processing relationships between HS content and structure, relative humidity, particle size, and the resulting dry film morphology of PUDs were determined in two diisocyanate systems: hexamethylene diisocyanate (HDI), a symmetric, flexible diisocyanate; and isophorone diisocyanate (IPDI), an asymmetric, sterically hindered cyclic diisocyanate. HDI-based films exhibited semicrystalline morphologies with HS superstructures that are sensitive to relative humidity. IPDI-based films displayed spherical coalescence-suppressed morphologies influenced by particle size and zeta potential. PUD compositions and processing conditions were controlled to produce nanocomposite films with an enhanced dispersion of nanoadditives.

Crystallinity and Liquid Crystallinity of Polyurethanes: How Tailoring of Order Contributes to Customized Properties and Applications

Studies on polyurethane (PU) materials offer advantageous properties utilized in various applications. The complex nature of the PUs structure and morphology gives them unique properties, but at the same time poses a considerable challenge for the characterization and design of structure-property relationships. Polyurethanes with tailored crystallinity can exhibit peculiar resistance to mechanical and chemical factors, allowing a widening range of application. Liquid crystalline polyurethanes have gained renewed interest thanks to the development of research methodologies and new possibilities for modifying diol and isocyanate monomers. The study shows that liquid crystal phenomena in polyurethanes can be effectively used for polymer compatibilization, in the fiber and nanofibers applications, as well as in 'smart' multi-stimuli materials.

Quantification Characterization of Hierarchical Structure of Polyurethane by Advanced AFM and X-ray Techniques

Polyurethane (PU) with microphase separation has garnered significant attention due to its highly designable molecular structure and a wide range of adjustable properties. However, there is currently a lack of systematic approaches for quantifying PU's microphase separation. To address this research gap, we utilized an atomic force microscopy (AFM) nanomechanical mapping technique along with Gaussian fitting to recolor and quantitatively analyze the evolution of PU's microphase separation. By varying the ratios of the chain extender to cross-linking agent, we observed the changes in the hydrogen bonding between the soft and hard segments. As the ratio of the chain extender to cross-linking agent decreases, the strength of the hydrogen bonding weakens, resulting in a reduction in the quantity and phase percentage of hard segment (HS) domains. Consequently, the degree of microphase separation between the soft and hard segments decreases, leading to specific alterations in the material's mechanical properties and dynamic viscoelasticity. To further investigate the hierarchical structure of PU, we employed various techniques, such as X-ray analysis, transmission electron microscopy (TEM), and AFM-based infrared spectroscopy (AFM-IR). Our findings reveal a spherulite pattern composed of lamellae within the HS domains, with the cross-linking density gradually increasing from the center to the periphery. Overall, our comprehensive characterization of PU provides valuable insights into its hierarchical structure and establishes a quantitative framework to explore the intricate relationship between the structure and properties.

Solvent-Free Design of Biobased Non-isocyanate Polyurethanes with Ferroelectric Properties

Increasing energy autonomy and lowering dependence on lithium-based batteries are more and more appealing to meet our current and future needs of energy-demanding applications such as data acquisition, storage, and communication. In this respect, energy harvesting solutions from ambient sources represent a relevant solution by unravelling these challenges and giving access to an unlimited source of portable/renewable energy. Despite more than five decades of intensive study, most of these energy harvesting solutions are exclusively designed from ferroelectric ceramics such as Pb(Zr,Ti)O3 and/or ferroelectric polymers such as polyvinylidene fluoride and its related copolymers, but the large implementation of these piezoelectric materials into these technologies is environmentally problematic, related with elevated toxicity and poor recyclability. In this work, we reveal that fully biobased non-isocyanate polyurethane-based materials could afford a sustainable platform to produce piezoelectric materials of high interest. Interestingly, these non-isocyanate polyurethanes (NIPUs) with ferroelectric properties could be successfully synthesized using a solvent-free reactive extrusion process on the basis of an aminolysis reaction between resorcinol bis-carbonate and different diamine extension agents. Structure-property relationships were established, indicating that the ferroelectric behavior of these NIPUs depends on the nanophase separation inside these materials. These promising results indicate a significant potential for fulfilling the requirements of basic connected sensors equipped with low-power communication technologies.

PEG-POSS Star Molecules Blended in Polyurethane with Flexible Hard Segments: Morphology and Dynamics

A star polymer with a polyhedral oligomeric silsesquioxanne (POSS) core and poly(ethylene glycol) (PEG) vertex groups is incorporated in a polyurethane with flexible hard segments in-situ during the polymerization process. The blends are studied in terms of morphology, molecular dynamics, and charge mobility. The methods utilized for this purpose are scanning electron and atomic force microscopies (SEM, AFM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and to a larger extent dielectric relaxation spectroscopy (DRS). It is found that POSS reduces the degree of crystallinity of the hard segments. Contrary to what was observed in a similar system with POSS pendent along the main chain, soft phase calorimetric glass transition temperature drops as a result of plasticization, and homogenization of the soft phase by the star molecules. The dynamic glass transition though, remains practically unaffected, and a hypothesis is formed to resolve the discrepancy, based on the assumption of different thermal and dielectric responses of slow and fast modes of the system. A relaxation α′, slower than the bulky segmental α and common in polyurethanes, appears here too. A detailed analysis of dielectric spectra provides some evidence that this relaxation has cooperative character. An additional relaxation g, which is not commonly observed, accompanies the Maxwell Wagner Sillars interfacial polarization process, and has dynamics similar to it. POSS is found to introduce conductivity and possibly alter its mechanism. The study points out that different architectures of incorporation of POSS in polyurethane affect its physical properties by different mechanisms.

Preparation and characterization of soybean oil-based waterborne polyurethane/acrylate hybrid emulsions for self-matting coatings

This work aims to explore the feasibility of self-matting coatings based on soybean oil.

The Abrasive Wear Resistance of the Segmented Linear Polyurethane Elastomers Based on a Variety of Polyols as Soft Segments

The presented results make an original contribution to the development of knowledge on the prediction and/or modeling of the abrasive wear properties of polyurethanes. A series of segmented linear polyurethane elastomers (PUR)—In which the hard segments consist of 4,4′-methylene bis(phenylisocyanate) and 1,4-butanodiol, whilst polyether, polycarbonate, or polyester polyols constitute the soft segments—Were synthesized and characterized. The hardness and wear performance as functions of the variable chemical composition of polyurethane elastomers were evaluated in order to define the relationship between studied factors. The microstructure was characterized in detail, including analysis of the hydrogen bonding by Fourier transformed infrared (FT-IR) spectroscopy and the phase structure by X-ray scattering (WAXS) and differential scanning calorimetry (DSC) methods. The presented studies provide the key features of the polymer composition affecting the abrasive resistance as well as attempts to explain the origin of the differences in the polyurethane elastomers’ performance.

Synergistic Effects in Thermoplastic Polyurethanes Incorporating Hybrid Carbon Nanofillers

In this study thermoplastic polyurethane (TPUs) nanocomposites incorporating carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) were prepared via melt blending and compression molding and CNT dispersion was optimized by using non-covalent surface modification (surfactant). Filler dispersion was further improved by combining two fillers with different geometric shape and aspect ratio in hybrid filler nanocomposites. Synergistic effects were observed in the TPU-GNP-CNT hybrid composites, especially when combining GNP and CNT at a ratio of 6 : 4, showing higher tensile modulus and strength with respect to the systems incorporating individual CNTs and GNPs at the same overall filler concentration. This improvement was attributed to the interaction between CNTs and GNPs limiting GNP aggregation and bridging adjacent graphene platelets thus forming a more efficient network. Hybrid systems also exhibited improved creep resistance and recovery ability. Morphological analysis carried out by scanning electron microscopy (SEM) indicated that the hybrid nanocomposite presented slightly smaller and more homogeneous filler aggregates. The well-dispersed nanofillers also favored higher phase separation in TPU, as indicated by atomic force microscopy (AFM), resulting in a better microstructure able to enhance the load transfer and maximize the mechanical and viscoelastic properties.