Abstract: • PDEF-b-PCL polyurethanes were synthesized with three types of diisocyanates. • The copolymers consisted of crystalline PCL, and amorphous PCL and PDEF phases. • Mechanical properties of PDEF was governed by the stiffness of the isocyanate. • In PCL-based samples crystallinity was promoted by isocyanate segment mobility. • PDEF-b-PCL copolymers had outstanding toughness and increased thermal stability. Thermoplastic polyurethane elastomers combine the durability and toughness of thermoplastics with the elasticity of rubber. Since most conventional polyurethanes are fossil-based, the development of sustainable alternatives is essential. While the composition and phase separation have been explored extensively, only a few reports have systematically examined the effect of isocyanate type on polyurethanes. In this work, bio-based poly(diethylene furanoate)-b-poly(caprolactone) (PDEF-b-PCL) copolymers were synthesized, where diisocyanates with three different structures were used as a chain-extender: methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), and dicyclohexylmethane 4,4′-diisocyanate (H12MDI) to systematically evaluate how their structure affects the structure–property relationships of the resulting copolymers. DSC and DMA confirmed that the copolymers exhibited dual-phase transitions, indicating that they consisted of a crystalline phase formed by PCL and an amorphous phase comprising PCL and PDEF. Structural analysis revealed that crystallinity was governed by PCL content and was highest in HDI-based samples, which was the most mobile among the isocyanates. For PDEF, due to its amorphous structure, the tensile properties were mainly influenced by the structure of the isocyanate. The copolymers exhibited enhanced elongation at break compared to the homopolymers, reaching up to 2372 ± 340%, attributed to strain hardening of the PCL crystalline domains and the amorphous PDEF segments acting as physical crosslinks that distributed stress. Some of the copolymers achieved superior toughness up to 233 MJ/m 3 , compared to both PCL and PDEF homopolymers. The incorporation of PDEF significantly improved thermal stability with higher T d,max values, and all copolymers showed higher T d,5% compared to their homopolymer counterparts.

Abstract: • TPT exhibits high flame-retardant efficiency towards polyamide 6. • TPT effectively retards the initial degradation of polyamide 6. • TPT significantly improves the mechanical properties of polyamide 6. • TPT exerts radical capturing effect during combustion of polyamide 6. The rapid advancement of modern industries has placed higher demands on the comprehensive performance of nylon 6 (PA6) and addressing its flammability issue has also received significant attention. Therefore, developing flame-retardant PA6 with superior overall performance has become a key research objective. In this work, a novel and highly efficient triazine-based flame retardant, phthalimidoxy-1,3,5-triazine (TPT), was successfully synthesized, and it was found to have a radical quenching mechanism analogous to that of hindered amine light stabilizers (HALS). Incorporating only 1.5 wt% TPT significantly improved the limiting oxygen index (LOI) of PA6/1.5TPT to 28% and increased both tensile strength and flexural strength to 80.49 and 93.25 MPa, respectively. Compared to pure PA6, the time to ignition (TTI) of PA6/1.5TPT was extended by 46.7%, and the total smoke production (TSP) was reduced by 42%. The hygrothermal aging results demonstrated that the PA6 composites maintained outstanding flame-retardant performance and mechanical integrity even after aging. Moreover, density functional theory (DFT) calculations and gas-phase mechanism analysis indicated that TPT generated stable radicals during thermal decomposition, which effectively captured hydrogen (H·) and carbon (C·) radicals produced in the initial degradation stage of PA6, thereby suppressing the combustion. This work presents a promising strategy for creating high-efficiency, multifunctional flame retardants for PA6, thus broadening its application potential.

Abstract: • PEKK shows <1% mass loss below 450°C after 5 h, confirming high thermal stability during repeated MEX processing. • Tensile and flexural strengths remain stable after three recycling cycles, indicating preserved mechanical integrity. • Cyclic DSC demonstrates unchanged melting and crystallization behavior under repeated thermal exposure. • FTIR, XRF, and SEM analyses reveal minimal chemical modification and limited contamination (<0.5 wt%). • PEKK exhibits superior recyclability compared with conventional AM polymers, supporting circular high-performance manufacturing. The recyclability of high-performance poly(ether ketone ketone) (PEKK) is critical for sustainable additive manufacturing and future in-space resource utilization. This study systematically evaluates the thermal, mechanical, and chemical stability of PEKK subjected to multiple recycling loops to elucidate potential degradation mechanisms. Thermogravimetric analysis revealed negligible (<1%) mass loss after 5 h of isothermal exposure below 450°C, confirming the polymer’s excellent thermal resistance under extrusion and printing conditions. Cyclic differential scanning calorimetry (DSC) demonstrated stable melting and cold-crystallization behavior across six thermal cycles, indicating preserved crystallization kinetics. Tensile testing showed that the amorphous strength remained within 83–91 MPa across all cycles, while annealed samples maintained strengths of 102–116 MPa. Flexural strength similarly remained consistent, ranging from 112–127 MPa (amorphous) and 147–160 MPa (annealed), and dynamic mechanical analysis (DMA) results indicated minimal changes in viscoelastic properties. Together, these mechanical and thermomechanical analyses confirm that PEKK retains its structural integrity after three complete recycling sequences involving shredding, pulverization, extrusion, and reprinting. Fourier transform infrared spectroscopy detected no new carbonyl or hydroxyl bands, excluding oxidative chain scission, while X-ray fluorescence (XRF) revealed only trace (<0.5 wt%) metallic contamination. Scanning electron microscopy (SEM) of fracture surfaces further confirmed well-fused interlayer morphology and minimal porosity evolution. Collectively, these results demonstrate that PEKK maintains its molecular and microstructural integrity during repeated thermal–mechanical cycles, highlighting its exceptional thermal-oxidative stability and its suitability for circular, high-performance, and extended-lifetime polymer applications.