Exploring the Impact of the Synthesis Variables Involved in the Polyurethane Aerogels-like Materials Design

This research presents a novel approach to synthesising polyurethane (PUR)-based aerogels at the pilot scale, optimizing synthesis variables such as the gelation solvent, solids content, chain extender/isocyanate ratio, and dispersion mode. The solids content (2-11 wt.%) is the parameter with the most influence on the density of the aerogels, with a clear decrease in this property as the solids content decreases. On the other hand, it was demonstrated that minimizing the excess of ethylenediamine (used as chain extender) in relation to the isocyanate is a valuable consideration to improve the thermal conductivity of the aerogel. Related to the chain extender/isocyanate ratio, a compromise situation where the initial isocyanate reacts almost completely is crucial. Fourier-transform infrared spectroscopy was used to conduct such monitoring during the reaction. Once the conditions were optimised, the aerogel showing improved properties was synthesised using ethyl acetate as the gelling solvent, a 3.7 wt.% solids content, an ethylenediamine/isocyanate ratio of 0.20, and sonication as the dispersion mode, attaining a thermal conductivity of 0.030 W m-1 K-1 and a density of 0.046 g cm-3. Therefore, the synthesized aerogel emerges as a promising candidate for use in the construction and automotive industries.

Design of Acrylate-Terminated Polyurethane for Nylon Seamless Bonding Fabric Part I: Design of the End-Capping Thermoplastic Polyurethane Adhesive with Acrylate Copolymer

This series of studies aims to design acrylate-terminated polyurethanes for use in nylon seamless bonded fabrics. The first part used N,N-dimethylacrylamide (DMAA) and methyl methacrylate (MMA) to replace the chain extender in polyurethane synthesis as end-capping agent to synthesize thermoplastic polyurethane (TPU) adhesive. The molecular weight of the TPU is controlled to further influence the mechanical and processing properties of the polyurethane. Here, polytetramethylene ether glycol (PTMG) and 4,4-methylene diphenyl diisocyanate (MDI) were polymerized, and then a blocking agent was added thereto. The results show that the characteristic peaks of benzene ring and carbamate of TPU adhesive are at 1596 cm−1 and 1413 cm−1, respectively, while the characteristic peaks of DMAA are at 1644 cm−1 and 1642 cm−1 in the FT-IR spectrum. There is an absorption peak –N=C=O– which is not shown near 2268 cm−1, which proves that the structure of TPU contains the molecular structure of capping agent, PTMG and MDI. When the DMAA concentration in the capping agent was increased from 3.0 wt% to 10 wt%, the –C=O (H-bond) area percentage of hydrogen bonds formed at 1711 cm−1 increased from 41.7% to 57.6%, while the –NH (H bond) produced at 3330 cm−1 increased from 70% to 81%. These phenomena suggest that increasing the concentration of DMAA capping agent can effectively promote the formation of complex supramolecular network structures by hydrogen bonding in TPU. The content and concentration of the capping agent affects the molecular weight of the TPU. Chain growth is terminated when molecular weight growth can be effectively controlled and reduced. It was observed in thermal analysis that with increasing DMAA concentration in the molecular structure, the concentration of capping agent in TPU, hydrogen bonding force between hard segments, melting point (Tmh) and melting enthalpy (ΔH) all increased the capping agent. The pyrolysis temperature of TPU is increased by 10–20 °C.

Blocking and Deblocking of Diisocyanate to Synthesize Polyurethanes

Diisocyanates, particularly toluene diisocyanate (TDI), are useful for the preparation of various polyurethanes with specific applications as leather-like materials, adhesives and insoles, etc. Blocking agents can be used for the operational simplicity and to reduce the hazards of TDI. In this paper, we reported the use of 3-(4-bromo-phenyl)-1H-pyrazole to block toluene diisocyanate (TDI). FTIR, NMR, thermogravimetric analysis, contact angle analysis and differential scanning calorimetry (DSC) were used for the characterization. The effectiveness of the blocking was confirmed by spectroscopic techniques. The DSC thermogram showed that blocked adducts deblock at 240 °C, causing the regeneration of TDI, and causing the diisocyanates to react with polyols of different molecular weights, forming polyurethanes. The characterization of the polyurethanes was performed by infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry and a contact angle study.

Stereochemical effects on the mechanical and viscoelastic properties of renewable polyurethanes derived from isohexides and hydroxymethylfurfural

Biomass-derived polyurethanes were synthesized using 2,5-bishydroxymethylfuran (BHMF) and diisocyanate functionalized isohexides, isosorbide bis(3-isocyanatopropanoate) (ISBIP) and isomannide bis(3-isocyanatopropanoate) (IMBIP), at varying feed ratios.

Enhancement of the physicochemical properties of polyurethane–perovskite nanocomposites via addition of nickel titanate nanoparticles

Perovskite is integrated by in situ addition with polyurethane (PU) to form unprecedented nanocomposite films (~1.5 mm). Trace amount of NiTiO₃ NPs (0.5 wt%) has been added to enhance the physicochemical, electrical, optical and magnetic properties.

Augmentation of properties on sparingly loaded nanocomposites via functionalized single-walled carbon nanotubes using a covalent approach

Polymer nanocomposites are developed, for the first time, as transparent film by covalent addition of [OH]n–SWCNTs with PU via an efficient route. PU nanocomposites, which were augmented, show enhanced mechanical, thermal and conductivity properties.

The influence of applied silica nanoparticles on a bio-renewable castor oil based polyurethane nanocomposite and its physicochemical properties

Bio-renewable castor oil polyurethane–silica nanocomposite films with improved thermal, surface and mechanical properties were prepared. These films find application in biomaterials development.