Search

Despite the excellent overall performance, the application of polyesters is severely restricted by their inherently high flammability. Although many gratifying results have been achieved through different fire-safety methods, customization is still needed for every specific polymer, thus a generally applicable method is highly desired. Herein, we developed an eco-friendly and general fire-safety method for semi-aromatic polyesters based on the “end-group-capturing” concept. The functional monomer was chemically incorporated into the main chains of a series of semi-aromatic polyesters with similar structures (i.e., polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT) and polybutylene terephthalate (PBT)), and the specific contribution of the fire-safety method was investigated comprehensively. The results showed that the fire safety of all the copolyesters were efficiently improved, while interestingly, the fire safety gradually declined with the increase of the methylene group numbers in their molecular chains. The reason behind this phenomenon was comprehensively studied by both theoretical calculation and experiments. The increasing cyclization tendency of the copolyesters derived from the increase of the methylene group numbers was proved to be responsible for the decrease of the fire safety. The successful application and in-depth mechanism revealed here provide theoretical supports for the development of novel fire-safety polymeric materials.

The flame-retardant waterborne polyurethane (WPU) has attracted more and more attentions from academia and industry. However, the addition of conventional flame retardants into WPU will damage the emulsion stability and introduce the potential further risk to demulsification and preparation failure. In this work, a novel flame-retardant approach is proposed, demonstrating outstanding efficiency, excellent compatibility and minimized side effect. A water-soluble ionic liquid 1-methyl-3-((6-oxidodibenzo[c,e] (Akindoyo et al., 2016; Chattopadhyay and Raju, 2007) [1,2]oxaphosphinin-6-yl)methyl)-1-H-imidazol-3-ium-4-methylbenzenesulfonate ([Dmim]Tos) is applied as the additive flame retardant for the WPU dispersions. The resulting WPUs (WPU/[Dmim]Toses) display excellent flame retardancy via a low loading content (max 6.0 wt%) and potential adhesion applicable to industries, while maintaining the major comprehensive performance, including storage stability, mechanical property, thermal stability, transparency, hydrophobicity, etc. Effort from this work, besides of overcoming the explicit drawback, also serves as reference of novel methodologies to solve the compatibility issue between additive agents and WPU.

In order to avoid the serious melt-dripping problems caused by conventional phosphorus flame retardants, a new arylene-ether containing monomer named 2,2′-(4,4′-(1,4-phenylenebis(oxy))bis(4,1-phenylene))bis(oxy) diethanol (PBPBD) was synthesized and introduced into the PET main-chain via condensation polymerization. With the incorporation of arylene-ether units, the thermal stability and the char residue from combustion of flame-retardant-element-free copolyesters containing PBPBD (BDxPETs) increased dramatically. However, the crystallinity and melting temperature of these copolymers were lower than the same quantities for PET. Thermal degradation kinetic was investigated using the Ozawa-Flynn-Wall method, which illustrated that the apparent activation energy for decomposition of the copolyesters was enhanced with increasing the conversion and the content of PBPBD. Py-GC/MS results showed that the PBBPD structural units undergo rearrangement reactions at high temperature, and ultimately form conjugated heteroaromatic structures, which lead to the formation of stable char residues with unique “stick-shaped” micro-morphology. Due to these rearrangement reactions, BDxPETs showed an expected flame retardant performance and a reduction in smoke generation during combustion. For example, the LOI value for BD10PET was 28.4, and the total smoke production (TSP) was 10.4 m2, much smaller than that for PET, 18.8 m2. Moreover, melt-dripping was restricted.