Guan-Qi Zheng,Jia-Ning Wu,Lin Zhang,Qin Zhang,Lin Chen,Xiu-Li Wang,Hai-Bo Zhao,Bo-Wen Liu,Yu-Zhong Wang
Constructing thermally cross-linkable structures into thermoplastic polymers has emerged as a compelling strategy to enhance flame retardancy. However, the cross-linking reactions are hard to control, leading unexpected deterioration of processability and mechanical properties. Here, we report a novel strategy to modulate cross-linking reactions utilizing intramolecular hydrogen bonding and steric hindrance effects. Taking aromatic Schiff base (SA) as an example, novel monomers SAP and SAPN were designed and synthesized by incorporating phenolic and naphthalene units. As expected, the resultant copolymer PET- co -SAPN n exhibited a 120 °C higher cross-linking temperature compared with that of PET- co -SA n , powering them with great processability. Robust mechanical properties were obtained owing to the enhanced polymerization stability and intramolecular hydrogen bonding of SAPN, as evidenced by the tensile strength of 86.0 MPa for PET- co -SAPN 15 , 1.6 times to that of pure PET. Additionally, PET- co -SAPN n exhibits the highest fire safety, whose peak heat release rate (pHRR) and maximum smoke density ( D m ) decreased by 49% and 53%, attributing to enhanced char-forming ability from the cross-linking and the phenolic and naphthalene units in SAPN. Considering these adequate improvements, this study provides a novel strategy for designing “self-cross-linking” flame-retardant polymers with improved processability and fire-safety.
Yuan Chen,Jinchao Qin,Tong Tong,Haoli Zhou,Xingzhong Cao,Wanqin Jin
Membrane performance is a vital factor for the membrane-based waste VOCs treatment, which is not only affected by the properties of monomers or polymers, but also by crosslinking temperature during the membrane-forming procedure. However, little attention has been paid to the latter. In this work, the effect of the crosslinking temperature on membrane structure and separation performance was studied. The properties of polymers and membranes were first characterized by X-ray photoelectron spectroscopy, positron annihilation lifetime spectra, and so on. Apparent differences in physicochemical properties between polymers and membranes can be observed. Different crosslinking temperatures were thus chosen to investigate their effects on the membrane structure, and the separation performances of membranes obtained under different crosslinking temperatures for the molecular sieving of nitrogen over cyclohexane were also evaluated. Results showed that higher temperature leads to higher crosslink and smaller pore size so that 99% rejection can be obtained when the crosslinking temperature over 80 °C was used. While the permeability of nitrogen slightly decreases with increasing temperature from 50 to 120 °C.
Xinxing Zhang,Qingyin Wang,Shaoying Liu,Lilei Zhang,Gongying Wang
To get better processability and preparing process of Poly (ethylene terephthalate) polymer, -NO 2 was used to modify Schiff Base to synthesize a novel flame retardant monomer of 5-([3-nitrobenzylidene] amino) isophthalic acid (BNA) to prepare flame retardant and anti-dripping PET copolyester (BNA n PETs), where the electron effect of -NO 2 passivate the cross-linking reactivity of BNA in BNA n PETs to enhance its cross-linking temperature to improve its processing zone with better processability. The results demonstrated that the cross-linking temperature of BNA n PETs was improved from the range of (250–348°C) to (355–385°C), and BNA accelerated the reaction of the polycondensation of PET for saving time of 42%. -NO 2 enhanced the residue char of BNA n PETs in high temperature and further improved its flame retardancy. BNA 10 PET with 7.2 mol% of BNA had LOI of 31.8% and V-0 of UL-94 without drip, and the introduction of –NO 2 did not change the flame retardant mechanism in BNA n PETs.
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