To address the limited solution processability and insufficient thermo-oxidative char stability of conventional polyarylates, a molecular structure regulation strategy was proposed in this work. A series of DOPO-HQ-containing copolyarylates were synthesized by incorporating 10 - (2,5 - dihydroxyphenyl) - 10H - 9- oxa-10-phosphaphenanthrene-10-oxide (DOPO-HQ) into the polyarylate backbone through solution copolycondensation. The chemical structures and copolymer compositions were confirmed by 1H NMR, HSQC NMR, quantitative 1H NMR, and FT-IR analyses, while GPC and XRD were used to characterize the molar-mass parameters and amorphous structures, respectively. Thermal analysis showed that DOBA-20, prepared with 20 mol% DOPO-HQ in the total bisphenol feed, exhibited a glass transition temperature of 194.9°C and a char yield of 38.3% at 800°C under nitrogen. More importantly, DOBA-20 retained a char yield of 32.7% at 800°C under air atmosphere, far exceeding that of the DOPO-HQ-free polyarylate, DOBA-0 (0.04%), indicating significantly enhanced char stability under oxidative conditions. TG-FTIR and Py-GC/MS analyses, together with XPS and SEM analyses of char residues, demonstrated that DOPO-HQ mainly promoted the retention of phosphorus species in the condensed phase, facilitating the formation of a continuous and compact phosphorus-rich char layer containing phosphate/pyrophosphate structures. This stable char layer could suppress heat transfer and oxygen diffusion, possibly accompanied by limited gas-phase inhibition. This work provides a molecular design strategy for regulating the thermal degradation pathway of polyarylates and improving their solution processability and thermo-oxidative stability.
Achieving a balance among flame retardancy, mechanical strength, and optical transparency remains a longstanding challenge for polycarbonate (PC) in advanced engineering applications. Herein, a cage-phosphorus cinnamate ester (CA-PEPA) is synthesized as a multifunctional molecular additive and incorporated into PC via melt blending to simultaneously address these competing requirements. The incorporation of CA-PEPA significantly enhances the mechanical performance of PC, with a 39.8% increase in tensile strength at 10 wt% loading while maintaining high ductility. Meanwhile, excellent optical transparency is retained, with negligible variation in visible-light transmittance. In addition, the limiting oxygen index (LOI) increases from 25.5% to 31.0%, and a UL-94 V-0 rating is achieved at optimal loadings. These results demonstrate that CA-PEPA enables a favorable balance among mechanical reinforcement, transparency retention, and flame retardancy in PC. Mechanistic investigations reveal that CA-PEPA induces a heterogeneous interaction environment within the PC matrix through π–π interactions and dipolar associations, leading to restricted local segmental mobility while preserving global chain deformability. During combustion, CA-PEPA undergoes preferential decomposition to release phosphorus-containing species that act in the gas phase by radical scavenging, while in the condensed phase, phosphoric acid derivatives promote catalytic charring of PC to form a compact, phosphorus-enriched barrier layer. This synergistic action results in optimized flame retardancy at intermediate loadings (5–7 wt%). This work provides a simple molecular design strategy for developing multifunctional additives that simultaneously enhance mechanical reinforcement, flame retardancy, and optical transparency in engineering thermoplastics.
The conditions under which phosphorus-containing radicals can already form during low-temperature degradation of flame-retardant-treated textiles remain insufficiently understood. Here, we investigate the degradation and flame-retardant action of phosphonate-functionalized silanes featuring distinct P–C linkage motifs: a classical phosphonate (TRI/DPTS(1:3)), a triazine-linked derivative (2DTA), and a carbamoylphosphonate (ID). The compounds were studied both as neat materials and as cotton finishes using a multimethod approach combining standardized flame testing and thermal analysis with steady-state in situ molecular beam mass spectrometry employing mild electron-impact ionization under pyrolytic and oxidative conditions, complemented by transient in situ MS as well as spectroscopic and elemental characterization of evolved gases and residues.Cotton treated with 2DTA showed the best flame retardancy, consistent with a comparatively stronger condensed-phase contribution. In neat decomposition experiments, no detectable volatilization of phosphorus-containing species was observed for 2DTA, whereas TRI/DPTS(1:3) showed minor and ID pronounced volatilization, mirroring the trend in condensed-phase action on cotton. Notably, PO radical formation on cotton under pyrolytic conditions was detected only for 2DTA. Under oxidative conditions 2DTA also exhibited the highest PO emission, indicating competing oxidative and pyrolytic formation pathways. Overall, PO formation correlates inversely with phosphorus volatilization, supporting the hypothesis that low-temperature radical activity (<500°C) may be strongly influenced by condensed-phase collision and transfer reactions.These findings provide a new perspective on the flame-poisoning mechanism of organophosphorus flame retardants.
Biodegradable polymer blends are increasingly used to balance material performance and end-of-life degradability, yet their degradation behaviour cannot be predicted from the properties of the individual polymers alone. This is particularly relevant for immiscible blends where the predominant polymer in the blend may encapsulate and restrict access of enzymes and microorganisms to the minor component. The blend of poly(butylene adipate-co-terephthalate) (PBAT) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is of particular interest because it is increasingly used in flexible films and compostable products and PBAT is sparingly biodegradable, particularly in anaerobic environments. Here, we systematically investigated the anaerobic degradation behaviour of PBAT, PHBV, and three PBAT/PHBV blends (75/25, 50/50, and 25/75, w/w) in bench scale batch tests under mesophilic conditions (37°C). PBAT formed a continuous phase that encapsulated PHBV when present as the dominant fraction while PHBV did the same when it was the dominant fraction. As expected, PHBV was the only fraction that biodegraded. The effect of PBAT restricting access to PHBV was demonstrated with the maximum degradation rate of PHBV (mL CH4/gVS/d) in the 75% PBAT blend less than 1/3 the rate in the 25% PBAT blend. The residual PBAT was recoverable as an intact porous sheet when it was the predominant phase. PBAT disintegrated to unrecoverable particles when it was the minor fraction. Microbial community analysis further showed that PHBV-containing blends developed distinct attached biofilms compared with PBAT, supporting the role of polymer surface accessibility in blend degradation. These findings show that the anaerobic degradation of PBAT/PHBV blends is governed by selective PHBV removal and PBAT phase persistence, demonstrating that blend morphology controls not only degradation kinetics but also the physical fate of residual biodegradable polymer blends under anaerobic environmental conditions.
Laser ablation of quartz fiber reinforced phenolic resin composites is governed by coupled irradiation parameters and high-speed airflow, but the underlying interactions remain unclear. We combined the controlled laser ablation experiments with an experimentally validated thermo-chemical-fluid model that accounts for resin pyrolysis, carbon oxidation and sublimation, quartz fiber softening and melting, SiO₂ evaporation, surface recession, and airflow induced mechanical erosion. The model reproduced peak temperature and maximum ablation depth with errors of 0.8-4.6% and 2.0-13.8%, respectively. Laser power and spot size jointly regulated local power density and produced a nonlinear transition in the dominant removal mechanism: high-power, small-spot irradiation promoted SiO₂ evaporation and carbon sublimation, whereas larger spots suppressed high-temperature phase changes and favored oxidation dominated degradation. Supersonic airflow lowered the surface temperature through aerodynamic cooling but intensified material removal by stripping molten and carbonaceous products, destabilizing the protective layer, and repeatedly exposing fresh material. At 1000 W with a 10 mm spot, Mach 3 airflow increased the maximum ablation depth from 0.877 to 1.863 mm while producing narrower and asymmetric damage. These findings establish a predictive framework for laser damage assessment and thermal protection design.
