Zi-Xun Chen,Ze-Yong Zhao,Peng Lu,Xiang-Xin Xiao,Shuang He,Cong Deng,Yu-Zhong Wang
Macromolecular flame retardants possess unique advantages in endowing compatible polymers with simultaneous high performance and functionalization because they may greatly reduce incompatibility-caused damage to overall properties of polymer substrates. To address the contraction between fire safety and high performance of polycarbonate (PC), a novel sulfonated naphthalene monomer-containing copolymer polycarbonate, that is named NSD, was synthesized by melt copolymerization and used as flame retardant of PC. Thermal analysis confirmed that the initial decomposition temperature of NSD was 387 °C under nitrogen atmosphere and met the processing of PC. Burning tests results indicated that incorporation of 2 wt.% NSD enabled PC to achieve UL-94 V-0 rating and the LOI value increased to 28.0%; the peak heat release (PHRR) and smoke release of the PC/NSD showed a decreasing trend. Moreover, flame-retarded PC with 2 wt.% NSD maintained comparable tensile strength and elongation at break to neat PC. The flame-retardant and anti-dripping mechanisms were also investigated. Sulfur-containing substances and sulfate in the condensed phase concentrated in the residue and thus strengthened the char layer, and the sulfur dioxide in the gas phase diluted the combustible gas, thus leading to excellent fire retardance of PC/NSDs. Reasons for excellent tensile property of PC/NSDs were also studied in detail. This work demonstrates that macromolecular flame retardants NSD may enable PC to achieve simultaneous high performance and flame retardation.
Nan Liu,Qi Chen,Xianwu Jiang,Jie Chen,Lidong Zhang,Jiaying Pan,Haiqiao Wei,Xingqian Mao
This work presents a three-stage hybrid nanosecond discharge (NSD) and direct current (DC) discharge assisted n -C 5 H 12 /O 2 /N 2 ignition with lower discharge energy and higher energy efficiency. The reaction rate coefficients between O 2 (a 1 Δ g ) and n -C 5 H 12 are updated by mass/Master equation simulation. The promotive ignition enhancement via reaction channel O 2 (a 1 Δ g ) + n -C 5 H 12 → C 5 H 10 + H 2 O 2 in the hybrid NSD/DC discharge is demonstrated. The results show that the ignition delay time of the three-stage hybrid plasma assisted ignition is 1–2 orders of magnitude shorter than that of the two-stage hybrid discharge when the reduced electric field strength in the DC discharge stage is over 10 Td. Meanwhile, the plasma-enhanced energy efficiency of three-stage hybrid discharge increases. This improved efficiency on ignition enhancement is due to the kinetic enhancement by the electronically excited species and radicals (O 2 (a 1 Δ g ), O( 1 D), N 2 (B) and O). The kinetic and thermal effects by plasma are effectively intergated to enhance ignition. However, more discharge energy deposited in the vibrationally excited states N 2 ( v ) in the two-stage hybrid discharge is less efficient on ignition enhancement due to the thermal contribution via vibrational-translational relaxation. In the aspect of NO x /N 2 O emissions, reduction efficiency of the three-stage hybrid discharge is two times higher than that of the two-stage hybrid discharge. By controlling the N/N( 2 D) production pathway e + N 2 → e + N + N( 2 D), the three-stage hybrid discharge reduces NO x and N 2 O production by 61.1 % and 90 %, respectively. The results show that the ignition delay time is non-monotonically dependent on the discharge pulse number. There exist optimal pulse number, reduced electric field and effective threshold power density of DC discharge to achieve maximum ignition enhancement and low NO x /N 2 O emissions. This study provides valuable insights into the use of NSD/DC hybrid discharge technology in advanced engines to achieve energy-efficient ignition enhancement and reduce NO x /N 2 O emissions.
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