Non-Isocyanate Polyurethane Bio-Foam with Inherent Heat and Fire Resistance.

Polyurethanes (PUs) are versatile and widespread, particularly as flexible and rigid foams. To avoid isocyanates and other toxic reagents required for synthesis, such as phosgene, alternative synthetic routes have been utilized to produce non-isocyanate polyurethanes (NIPUs). A thermally and flame-resistant rigid NIPU was produced from environmentally benign and bio-sourced ingredients, requiring no catalyst or solvents. A foamed structure was obtained by the addition of glutaraldehyde and four different carboxylic acids: malic acid, maleic acid, citric acid, and aconitic acid. The resulting morphology, thermal degradation, and flame resistance of each foam were compared. The properties vary with each carboxylic acid used, but in each case, peak thermal degradation and peak heat release are postponed by >100 °C compared to commercial rigid PU foam. Furthermore, in a butane torch test, NIPU foams exhibit an 80% higher remaining mass and a 75% reduction in afterburn time, compared to commercial polyurethane. This bio-based polyurethane eliminates the hazards of traditional PUs, while imparting inherent thermal stability and flame resistance uncharacteristic of conventional foams.

Biorenewable Polyelectrolyte Nanocoating for Flame-Retardant Cotton-Based Paper.

Cotton-based raw paper, made of 100% cellulose, is used to make humidity-sensing, cottonid for bio-architecture applications. Despite its renewability and excellent mechanical properties, it is inherently flammable. In an effort to reduce its flammability, thin films of fully renewable and environmentally benign polyelectrolytes, chitosan (CH) and phytic acid (PA), were deposited on raw paper via layer-by-layer (LbL) assembly. Only four bilayers (BL) of the CH/PA coating are required to achieve self-extinguishing behavior, with a 69% reduction in peak heat release rate measured by microscale combustion calorimetry. These results demonstrate that this renewable intumescent LbL-assembled film provides an effective flame-retardant treatment for these environmentally friendly, climate-adaptive construction materials and could potentially be used to protect many cellulosic materials.

Immobilization of Phosphatidylinositides Revealed by Bilayer Leaflet Decoupling.

Phosphatidylinositol 4,5-bisphosphate (PIP2) has a significantly lower mobile fraction than most other lipids in supported lipid bilayers (SLBs). Moreover, the fraction of mobile PIP2 continuously decreases with time. To explore this, a bilayer unzipping technique was designed to uncouple the two leaflets of the SLB. The results demonstrate that PIP2 molecules in the top leaflet are fully mobile, while the PIP2 molecules in the lower leaflet are immobilized on the oxide support. Over time, mobile PIP2 species flip from the top leaflet to the bottom leaflet and become trapped. It was found that PIP2 flipped between the leaflets through a defect-mediated process. The flipping could be completely inhibited when holes in the bilayer were backfilled with bovine serum albumin (BSA). Moreover, by switching from H2O to D2O, it was shown that the primary interaction between PIP2 and the underlying substrate was due to hydrogen bond formation, which outcompeted electrostatic repulsion. Using substrates with fewer surface silanol groups, like oxidized polydimethylsiloxane, led to a large increase in the mobile fraction of PIP2. Moreover, PIP2 immobilization also occurred when the bilayer was supported on a protein surface rather than glass. These results may help to explain the behavior of PIP2 on the inner leaflet of the plasma membrane, where it is involved in attaching the membrane to the underlying cytoskeleton.