Hydrogen Bond Association to Prepare Flame Retardant Polyvinyl Alcohol Film with High Performance

It has always been the goal of flame retardant research to improve the flame retardancy of a polymer efficiently without compromising comprehensive properties such as mechanical properties. For polyvinyl alcohol (PVA), inspired by the multiple hydrogen bonding in spider silk, we design a new type of compound containing phosphorus and nitrogen with multiple hydrogen-bonding reaction sites (N,N',N''-tris(2-aminoethyl)phosphoric triamide (TE)) as it is flame retardant. The dynamic cross-linking structure is constructed, and the hyperdispersion of flame retardancy is achieved by the hydrogen bond self-assembly between TE and PVA, thus the high-performance flame retardant PVA is obtained. With only a 10 wt % addition of TE, the PVA film with a thickness of 0.15 mm can reach the UL94 VTM-0 level, and its tensile strength, ductility, and initial decomposition temperature can be increased by 33, 15, and 12 °C, respectively. In addition, the hydrogen-bonding effect and flame retardant mechanism are characterized and studied. This work overcomes the shortcomings of traditional flame retarding approaches and provides an effective strategy for the preparation of flame retardant polymers with an excellent performance.

Kinetic Model under Light-Limited Condition for Photoinitiated Thiol-Ene Coupling Reactions

Thiol-ene click chemistry has become a powerful paradigm in synthesis, materials science, and surface modification in the past decade. In the photoinitiated thiol-ene reaction, an induction period is often observed before the major change in its kinetic curve, for which a possible mechanism is proposed in this report. Briefly, light soaking generates radicals following the zeroth-order reaction kinetics. The radical is the reactant that initializes the chain reaction of thiol-ene coupling, which is a first-order reaction. Combining both and under the light-limited conditions, a surprising kinetics represented by a Gaussian-like model evolves that is different from the exponential model used to describe the first-order reaction of the final product. The experimental data are fitted well with the new model, and the reaction kinetic constants can be pulled out from the fitting.

Flame-retardant polyvinyl alcohol membrane with high transparency based on a reactive phosphorus-containing compound

Flame-retardant polyvinyl alcohol (PVA) membranes with high transparency and flexibility were prepared by mixing an aqueous solution of a phosphorus-containing acrylic acid (AOPA) with PVA. The reaction between AOPA and PVA, the transparency, the crystallinity and the flexibility of the membrane were investigated with Fourier transform infrared spectrometry (FTIR), UV-vis light transmittance, X-ray diffraction and tensile tests, respectively. The limited oxygen index (LOI) and vertical flame (UL 94 VTM), microscale combustion calorimetry, thermogravimetric analysis (TGA) and TGA-FTIR were employed to evaluate the flame retardancy as well as to reveal the corresponding mechanisms. Results showed that PVA containing 30 wt% of AOPA can reach the UL 94 VTM V0 rating with an LOI of 27.3% and retain 95% of the original transparency of pure PVA. Adding AOPA reduces crystallinity of PVA, while the flexibility is increased. AOPA depresses the thermal degradation of PVA and promotes char formation during combustion. The proposed decomposition mechanism indicates that AOPA acts mainly in the condensed phase.