Fire-Retardant, Self-Extinguishing Inorganic/Polymer Composite Memory Foams

Polymeric foams used in furniture and automotive and aircraft seating applications rely on the incorporation of environmentally hazardous fire-retardant additives to meet fire safety norms. This has occasioned significant interest in novel approaches to the elimination of fire-retardant additives. Foams based on polymer nanocomposites or based on fire-retardant coatings show compromised mechanical performance and require additional processing steps. Here, we demonstrate a one-step preparation of a fire-retardant ice-templated inorganic/polymer hybrid that does not incorporate fire-retardant additives. The hybrid foams exhibit excellent mechanical properties. They are elastic to large compressional strain, despite the high inorganic content. They also exhibit tunable mechanical recovery, including viscoelastic “memory”. These hybrid foams are prepared using ice-templating that relies on a green solvent, water, as a porogen. Because these foams are predominantly comprised of inorganic components, they exhibit exceptional fire retardance in torch burn tests and are self-extinguishing. After being subjected to a flame, the foam retains its porous structure and does not drip or collapse. In micro-combustion calorimetry, the hybrid foams show a peak heat release rate that is only 25% that of a commercial fire-retardant polyurethanes. Finally, we demonstrate that we can use ice-templating to prepare hybrid foams with different inorganic colloids, including cheap commercial materials. We also demonstrate that ice-templating is amenable to scale up, without loss of mechanical performance or fire-retardant properties

Fire-Retardant, Self-Extinguishing Inorganic/Polymer Composite Memory Foams

Polymeric foams used in furniture and automotive and aircraft seating applications rely on the incorporation of environmentally hazardous fire-retardant additives to meet fire safety norms. This has occasioned significant interest in novel approaches to the elimination of fire-retardant additives. Foams based on polymer nanocomposites or based on fire-retardant coatings show compromised mechanical performance and require additional processing steps. Here, we demonstrate a one-step preparation of a fire-retardant ice-templated inorganic/polymer hybrid that does not incorporate fire-retardant additives. The hybrid foams exhibit excellent mechanical properties. They are elastic to large compressional strain, despite the high inorganic content. They also exhibit tunable mechanical recovery, including viscoelastic “memory”. These hybrid foams are prepared using ice-templating that relies on a green solvent, water, as a porogen. Because these foams are predominantly comprised of inorganic components, they exhibit exceptional fire retardance in torch burn tests and are self-extinguishing. After being subjected to a flame, the foam retains its porous structure and does not drip or collapse. In micro-combustion calorimetry, the hybrid foams show a peak heat release rate that is only 25% that of a commercial fire-retardant polyurethanes. Finally, we demonstrate that we can use ice-templating to prepare hybrid foams with different inorganic colloids, including cheap commercial materials. We also demonstrate that ice-templating is amenable to scale up, without loss of mechanical performance or fire-retardant properties

Mechanically Stable Thermally Crosslinked Poly(acrylic acid)/Reduced Graphene Oxide Aerogels

Graphene oxide (GO) aerogels, high porosity (>99%) low density (∼3–10 mg cm^–3) porous materials with GO pore walls, are particularly attractive due to their lightweight, high surface area, and potential use in environmental remediation, superhydrophobic and superoleophilic materials, energy storage, etc. However, pure GO aerogels are generally weak and delicate which complicates their handling and potentially limits their commercial implementation. The focus of this work was to synthesize highly elastic, mechanically stable aerogels that are robust and easy to handle without substantially sacrificing their high porosity or low density. To overcome this challenge, a small amount of readily available and thermally cross-linkable poly­(acrylic acid) (PAA) was intermixed with GO to enhance the mechanical integrity of the aerogel without disrupting other desirable characteristic properties. This method is a simple straightforward procedure that does not include multistep or complicated chemical reactions, and it produces aerogels with mass densities of about 4–6 mg cm^–3 and >99.6% porosity that can reversibly support up to 10 000 times their weight with full recovery of their original volume. Finally, pressure sensing capabilities were demonstrated and their oil absorption capacities were measured to be around 120 g oil per g aerogel^–1 which highlights their potential use in practical applications

Bioinspired Catecholic Copolymers for Antifouling Surface Coatings

We report here a synthetic approach to prepare poly­(methyl methacrylate)-polydopamine diblock (PMMA-PDA) and triblock (PDA-PMMA-PDA) copolymers combining mussel-inspired catecholic oxidative chemistry and atom transfer radical polymerization (ATRP). These copolymers display very good solubility in a range of organic solvents and also a broad band photo absorbance that increases with increasing PDA content in the copolymer. Spin-cast thin films of the copolymer were stable in water and showed a sharp reduction (by up to 50%) in protein adsorption compared to those of neat PMMA. Also the peak decomposition temperature of the copolymers was up to 43°C higher than neat PMMA. The enhanced solvent processability, thermal stability and low protein adsorption characteristics of this copolymer makes it attractive for variety of applications including antifouling coatings on large surfaces such as ship hulls, buoys, and wave energy converters

Polyhedral Oligomeric Silsesquioxane-Containing Thiol–ene Fibers with Tunable Thermal and Mechanical Properties

Polyhedral oligomeric silsesquioxanes (POSS) are versatile inorganic–organic hybrid building blocks that have potential applications as reinforcement nanofillers, thermal stabilizers, and catalyst supports for metal nanoparticles. However, fabrication of fibrous materials with high POSS content has been a challenge because of the aggregation and solubility limits of POSS units. In this paper, we describe a robust and environmentally friendly fabrication approach of inorganic–organic hybrid POSS fibers by integrating UV initiated thiol–ene polymerization and centrifugal fiber spinning. The use of monomeric liquids in this approach not only reduces the consumption of heat energy and solvent, but it also promotes homogeneous mixing of organic and inorganic components that allows integration of large amount of POSS (up to 80 wt %) into the polymer network. The POSS containing thiol–ene fibers exhibited enhanced thermomechanical properties compared to purely organic analogs as revealed by substantial increases in residual weight and a factor of 4 increase in modulus after thermal treatment at 1000 °C. This simple fabrication approach combined with the tunability in fiber properties afforded by tailoring monomer composition make POSS containing thiol–ene fibers attractive candidates for catalyst supports and filtration media, particularly in high-temperature and harsh environments

Thiol–Ene Chemistry: A Greener Approach to Making Chemically and Thermally Stable Fibers

Fibers of micrometer and submicrometer diameters have been of significant interest in recent years owing to their advanced applications in diverse fields such as optoelectronics, regenerative medicine, piezoelectrics, ceramic materials, etc. There are a number of processes to make thin fibers including electrospinning, melt blowing, and recently developed Forcespinning. However, use of solvents or heat to lower viscosity for processing is common to all existing polymer fiber manufacturing methods, and a greener approach to making fibers remains a challenge. Interestingly, nature has engineered spiders and silkworms with a benign way of making mechanically strong and tough fibers through an intricate self-assembly of protein constituents during the fiber formation process. Comprehending the biosynthetic process and precisely replicating it has been a challenging task. However, we find that extruding small functional segments into solid fibrillar structures, through mediation of chemical interactions between the subunits, is a design approach that can be broadly adapted from nature to realize a greener fiber manufacturing process. Using the robust chemistry of thiol–ene photopolymerization, we demonstrate here that a photocurable mixture of a multifunctional acrylate, a tetrafunctional thiol, and a photoinitiator can be processed into continuous fibers by <i>in situ</i> photopolymerization during electrospinning under ambient conditions. The fibers are mechanically robust and have excellent chemical and thermal stability. While electrospinning has been used to demonstrate this concept, the chemistry could be broadly adapted into other fiber manufacturing methods to produce fibers without using solvents or heat

Water-Triggered Modulus Changes of Cellulose Nanofiber Nanocomposites with Hydrophobic Polymer Matrices

Biomimetic, stimuli-responsive nanocomposites were made using either poly­(styrene-<i>co</i>-butadiene) (SBR) or polybutadiene (PBD) as the hydrophobic, low-modulus matrix and hydrophilic cellulose whiskers isolated from tunicates (TW) as the high-modulus filler. These materials were prepared using a template approach, which involves the formation of a percolating TW network and filling this template with either of the matrix polymers. Dynamic mechanical analysis (DMA) studies of the dry nanocomposite films reveal that the incorporation of TWs into the rubbery polymers increases the tensile storage modulus <i>E</i>′ significantly. The reinforcement is attributed to the formation of a three-dimensional TW network within the SBR and PBD matrices. The incorporation of the TWs did not affect the main relaxation temperature of the matrix SBR polymer, suggesting weak nanofiller–polymer interactions. Thus, the reinforcement is primarily on account of the nanofiller–nanofiller interactions, which involve hydrogen bonding. Interestingly, submersion of these hydrophobic matrix nanocomposites in water results in dramatic softening, consistent with disengagement of the TW network as a consequence of competitive hydrogen bonding with water. The kinetics of the modulus change and the amount of water uptake were shown to depend on the TW content. Given the hydrophobic nature of the matrices, it is proposed that the TWs create a percolating network of hydrophilic channels within the hydrophobic SBR and PBD matrices

Soybean Oil Based Fibers Made Without Solvent or Heat

Thiol–ene chemistry was harnessed to enable production of thermochemically stable thermoset fibers containing 50–87 wt % acrylated epoxidized soybean oil and 49–72% biobased carbon without using solvent or heat. In this demonstration, the fibers were made by simultaneous electrospinning and photocuring of a liquid monomer mixture, which could be translated to other fiber manufacturing processes such as melt blowing or Forcespinning. Scanning electron micrographs illustrate the fiber quality and an average diameter of about 30 μm. Photochemical conversion kinetics of functional groups during light exposure were measured by real-time Fourier transform infrared spectroscopy, providing insight into the advantages of using high-functionality monomers and thiol–ene chemistry in this application

pH-Responsive Cellulose Nanocrystal Gels and Nanocomposites

We show that functionalization of the surface of cellulose nanocrystals (CNCs) with either carboxylic acid (CNC–CO₂H) or amine (CNC–NH₂) moieties renders the CNCs pH-responsive. At low pH, where the amine groups are protonated, CNC–NH₂ forms aqueous dispersions in water on account of electrostatic repulsions of the ammonium moieties inhibiting aggregation. However, a transition to hydrogels is observed at higher pH where the CNC–NH₂ are neutral and the attractive forces based on hydrogen bonding dominate. The opposite behavior is observed for CNC–CO₂H, which are dispersible at high pH and form gels in an acidic environment. We further show that these pH-responsive CNCs can be incorporated into a poly­(vinyl acetate) matrix to yield mechanically adaptive pH-responsive nanocomposite films

Synthesis of Amphiphilic Naturally-Derived Oligosaccharide-<i>block</i>-Wax Oligomers and Their Self-Assembly

Self-assembly characteristics of amphiphilic macromolecules into micelles, nanoparticles and vesicles has been of fundamental interest for many applications including designed nanoscale therapeutic delivery systems and enzymatic reactors. In this work, a class of amphiphilic block oligomers was synthesized from naturally occurring oligosaccharides and aliphatic alcohol precursors, which are all currently prominent in the pharmaceutical, food, and supplement industries. These block oligomer materials were synthesized by functionalization of the precursor materials followed by subsequent coupling by azide–alkyne cycloaddition and their bulk self-assembly was investigated after solvent vapor annealing. Self-assembly of the amphiphilic materials into liposomes in aqueous solution was also investigated after preparing solutions using a nanoprecipitation method. Encapsulation of hydrophobic components was demonstrated and verified using dynamic light scattering, transmission electron microscopy, and fluorescence spectroscopy experiments