Efficient Flame Retardant Thin Films Synthesized by Atmospheric Pressure PECVD through the High Co-deposition Rate of Hexamethyldisiloxane and Triethylphosphate on Polycarbonate and Polyamide-6 Substrates

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.

A cross-linked charring strategy for mitigating the hazards of smoke and heat of aluminum diethylphosphonate/polyamide 6 by caged octaphenyl polyhedral oligomeric silsesquioxanes

Aluminum diethylphosphonate (ADP) is a highly efficient phosphorus-based flame retardant, widely used in polyamide 6 (PA6). However, ADP/PA6 releases large amounts of heat and smoke under high heat flux, which commonly means serious hazards to life and property. Octaphenyl polyhedral oligomeric silsesquioxanes (OPS) is an organic-inorganic hybrid silicon compound, playing flame retardant role in condensed phase. In this work, combustion behaviors of OPS/ADP/PA6 were investigated by limited oxygen index (LOI), UL94 and cone calorimeter (CONE) tests. The LOI and UL94 rating results did not change obviously, while the CONE data and smoke density data showed the synergistic effect of OPS and ADP in PA6. For 2.5%OPS/7.5%ADP/PA6, the peak values of heat, smoke and CO release rate (pk-HRR, pk-RSR, D_s, max with/without pilot flame and pk-COP) decreased by 60.2%, 82.1%, 45.9%/38.3% and 80.4% respectively, compared with 10%ADP/PA6. Moreover, 2.5%OPS/7.5%ADP/PA6 produced 337.5% more residue than 10%ADP/PA6. TGA, TG-IR, SEM-EDS, XPS and py-GC/MS were used to further explore the synergistic mechanism of OPS and ADP. It was verified that the cross-linked charring strategy apparently has weakened the hazards of smoke and heat of PA6. This work proposed a possible technical approach to solve both fire risk and heat/smoke hazards of PA6.

Multi-scale investigation in the frequency domain of Ar/HMDSO dusty plasma with pulsed injection of HMDSO

A combination of time-resolved optical emission spectroscopy measurements and collisional-radiative modeling is used to investigate the phenomena occurring over multiple time scales in the frequency domain of a low-pressure, axially-asymmetric capacitively-coupled RF argon plasma with pulsed injection of hexamethyldisiloxane (HMDSO, Si₂O(CH₃)₆). The collisional-radiative model developed here considers the population of argon 1s and all ten 2p levels (in Paschen's notation). The presence of HMDSO in the plasma is accounted for in the model by quenching of the argon 1s states by species generated by plasma processing of HMDSO, including HMDSO-15 (Si₂O(CH₃)₅), acetylene (C₂H₂) and methane (CH₄). Detailed analysis of the relative populations of Ar 2p states reveals cyclic evolutions of the electron temperature, electron density and quenching frequency that are shown to be linked to the kinetics of dust formation in Ar/HMDSO plasmas. Penning ionization of HMDSO and its fragments is found to be an important source of electrons for the plasma maintenance. It is at the origin of the cyclic formation/disappearance of the dust cloud, without attenuation of the phenomenon, as long as the pulsed injection of HMDSO is sustained. The multi-scale approach used in this study further reveals the straightforward relation of the frequency of HMDSO pulsed injection, in particular the HMDSO duty cycle, with the frequency of dust formation/disappearance cycle.

Atmospheric Aerosol Assisted Pulsed Plasma Polymerization: An Environmentally Friendly Technique for Tunable Catechol-Bearing Thin Films

In this work, an atmospheric aerosol assisted pulsed plasma process is reported as an environmentally friendly technique for the preparation of tunable catechol-bearing thin films under solvent and catalyst free conditions. The approach relies on the direct injection of dopamine acrylamide dissolved in 2-hydroxyethylmethacrylate as comonomer into the plasma zone. By adjusting the pulsing of the electrical discharge, the reactive plasma process can be alternatively switch ON (tON) and OFF (tOFF) during different periods of time, thus allowing a facile and fine tuning of the catechol density, morphology and deposition rate of the coating. An optimal tON/tOFF ratio is established, that permits maximizing the catechol content in the deposited film. Finally, a diagram, based on the average energy input into the process, is proposed allowing for easy custom synthesis of layers with specific chemical and physical properties, thus highlighting the utility of the developed dry plasma route.

UV-Protective TiO2 Thin Films with High Transparency in Visible Light Region Fabricated via Atmospheric-Pressure Plasma-Enhanced Chemical Vapor Deposition

This article focuses on control of film thickness and roughness to improve the ultraviolet (UV)-protective performance of TiO₂ films prepared by atmospheric-pressure plasma-enhanced chemical vapor deposition using titanium(IV) isopropoxide (TTIP) as the precursor and argon as the plasma working gas. The relationship between the film morphology and UV-protective performance suggested that a decrease in roughness is the key factor to achieve performance improvement. The effects of substrate temperature and precursor concentration were investigated, and the results showed that an increase in both substrate temperature and precursor concentration reduced the roughness and improved the transparency to visible light without reducing the ability to block UV light. Finally, a TiO₂ film with greater than 99% UV light blockage and greater than 95% transmittance of visible light was obtained.