A novel phosphorus-nitrogen-based hyperbranched polysiloxane for improving the fire safety of PA6 with suppressed melt droplets and good mechanical properties

The combustible defects of polyamide 6 (PA6), especially the flammable melt-dripping behavior, have greatly limited its application in some particular fields. In this work, a halogen-free hyperbranched polysiloxane (PBDSi) containing DOPO and Schiff base was designed via Michael's addition reaction and dehydration-condensation reaction. Results showed that the char yield (Yc) of PBDSi attained 37.9 wt%, confirming the satisfactory charring behavior of PBDSi for preparing flame-retardant PA6. Just by adding 3 wt% of PBDSi, the serious melt droplets of PA6 were suppressed effectively. The prepared PA6/PBDSi-3 with 5 wt% of PBDSi could achieve the highest value of limited oxygen index (LOI) of 27.2 %, while that of PA6 is 21.0 %. Meanwhile, PA6/PBDSi-3 obtained an apparent reduction in the peak heat release rate (PHRR) value of 31.1 % compared with pure PA6. The cooperated effect of DOPO, Schiff base, and polysiloxane that contributed to generating a silicon-phosphorous-rich char layer and releasing incombustible volatiles that were determined to be the essential factor for the improved fire safety of PA6/PBDSi were explored intensively. Inspiringly, PA6/PBDSi composites exhibited a slight mechanical loss concerning PA6, overcoming the great challenge of developing additive flame-retardant materials to balance mechanical properties and fire safety.

Flame Retardancy of Nylon 6 Fibers: A Review

As synthetic fibers with superior performances, nylon 6 fibers are widely used in many fields. Due to the potential fire hazard caused by flammability, the study of the flame retardancy of nylon 6 fibers has been attracting more and more attention. The review has summarized the present research status of flame-retarded nylon 6 fibers from three aspects: intrinsic flame-retarded nylon 6, nylon 6 composites, and surface strategies of nylon 6 fibers/fabrics. The current main focus is still how to balance the application performances, flame retardancy, and production cost. Moreover, melt dripping during combustion remains a key challenge for nylon 6 fibers, and the further developing trend is to study novel flame retardants and new flame-retardancy technologies for nylon 6 fibers.

Silicon/nitrogen synergistically reinforced flame-retardant PA6 nanocomposites with simultaneously improved anti-dripping and mechanical properties

A facile route of ‘copolymerization/blending’ was proposed to fabricate silicon/nitrogen synergistically reinforced flame-retardant PA6 nanocomposites with simultaneously improved anti-dripping and mechanical properties. Firstly, a persistently inherent flame-retardant PA6 (FR-PA6), with 1,3-bis(3-aminopropyl)tetramethyl disiloxane (MSDS), was synthesized via controllable amidation and a polycondensation reaction. Melamine cyanurate (MCA) nanoparticles as a ‘gas phase’ synergistic agent were then added into FR-PA6 to further improve its flame retardancy. The primarily obtained FR-PA6 could be extinguished after a few melt droplets dropped as ignited, and passed the V-2 rating with enhanced mechanical properties, while PA6 had no rating (NR). The prepared FR-PA6/MCA nanocomposites could attain a limiting oxygen index (LOI) value of 32.7%, and passed the V-0 level with only 1 melting droplet with similar mechanical properties to PA6. Accordingly, the special ‘condensed-gas phase’ synergistic flame-retardant mechanism of FR-PA6/MCA nanocomposites was proposed through studying the residues and pyrolysis volatiles. This work provided a facile route as a model for developing functional PA6 for diverse engineering applications.

A facile route was provided to prepare silicon/nitrogen synergistically reinforced flame-retardant PA6 nanocomposites with simultaneously improved anti-dripping and mechanical properties.

Evans hole and non linear optical activity in Bis(melaminium) sulphate dihydrate: A vibrational spectral study

Bis(melaminium) sulphate dihydrate (BMSD), an interesting melaminium derivative for nonlinear optical activity, has been subjected to vibrational spectral analysis using FT IR and FT Raman spectra. The analysis has been aided by the Potential Energy Distribution (PED) of vibrational spectral bands, derived using density functional theory (DFT) at B3LYP/6-31G(d) level. The geometry is found to correlate well with the XRD structure and the band profiles for certain vibrations in the finger print region have been theoretically explained using Evans hole. The detailed Natural Bond Orbital (NBO) analysis of the hydrogen bonding in BMSD has also been carried out to understand the correlation between the stabilization energy of hyperconjugation of the lone pair of donor with the σ(∗) orbital of hydrogen-acceptor bond and the strength of hydrogen bond. The theoretical calculation shows that BMSD has NLO efficiency, 2.66 times that of urea. The frontier molecular orbital analysis points to a charge transfer, which contributes to NLO activity, through N-H…O intermolecular hydrogen bonding between the melaminium ring and the sulphate. The molecular electrostatic potential (MEP) mapping has also been performed for the detailed analysis of the mutual interactions between melaminium ring and sulphate ion.