A novel strategy for enhancing the flame resistance, dynamic mechanical and the thermal degradation properties of epoxy nanocomposites

In this study, aiming at improving the flame resistance of bisphenol-A epoxy resin (EP), a novel self-assembled montmorillonite-multiwalled carbon nanotube (MMT-MWCNT) was designed and prepared by using triethylenetetramine (TETA) as grafting agent. The chemical component, structure and morphology of the MMT-MWCNT and its corresponding EP nanocomposites were well characterized. It was disclosed that the MMT was intercalated or exfoliated by the grafted MWCNT, and the MWCNT could be better distributed with the presence of MMT as well. The flame resistance analysis revealed that as compared with the pure EP, the peaks of heat release rate (HRR), smoke production rate (SPR) and carbon monoxide release rate (CORR) of EP/MMT-MWCNT decreased by 7.4%, 26.3% and 13.9%, respectively. The time to ignition (TTI) of EP nanocomposites showed increase compared to pure EP, especially for EP/MMT-MWCNT with an increase by 65.9%. The activation energy (Ea) and the integral procedural decomposition temperature (IPDT) of the EP/MMT-MWCNT based on TGA were found to be 9.7% and 14.1% higher than those of EP, respectively. Furthermore, the EP/MMT-MWCNT exhibited superior mechanical performance against the EP, that is the storage modulus and loss factor of EP/MMT-MWCNT were increased by 21.5% and decreased by 34.2%, respectively. This novel self-assembled MMT-MWCNT performed advantage over simply mixing MMT and MWCNT in enhancing the flame resistance, dynamic mechanical and the thermal degradation properties of EP

Polyphosphoramide-intercalated MXene for simultaneously enhancing the thermal stability, flame retardancy and mechanical properties of polylactide

The creation of thermostable, flame-retardant, mechanically robust bioplastics is highly desirable in the industry as one sustainable alternative to traditional petroleum-based plastics. Unfortunately, to date there lacks an effective strategy to endow commercial bioplastics, such as polylactide (PLA) with such desired integrated performances. Herein, we have demonstrated the fabrication of a novel MXene-phenyl phosphonic diaminohexane (MXene-PPDA) nanohybrid via the intercalation of PPDA into the MXene interlayer. The interlayer spacing of MXene nanosheets is enlarged and as-prepared MXene-PPDA is homogeneously dispersed in the PLA matrix. Incorporating 1.0 wt% MXene-PPDA enables PLA to achieve a UL-94 V-0 rating, with a ~22.2% reduction in peak heat release rate, indicating a significantly improved flame retardancy. Meanwhile, the 1.0 wt% MXene-PPDA also increases the initial decomposition temperature of PLA composite, giving rise to a ~25-fold enhancement in char yield relative to pure PLA. Additionally, the MXene-PPDA enhances the toughness while retains the mechanical strength for PLA. This work offers an innovative strategy for the design of multifunctional additives and the creation of high-performance polymers with high thermal stability, mechanical robustness and low flammability, expecting to find many practical applications in the industry

Highly Stretchable, Ultratough, and Strong Polyesters with Improved Postcrystallization Optical Property Enabled by Dynamic Multiple Hydrogen Bonds

It has been highly desirable to develop high-performance thermoplastic polyesters that are strong, tough, and highly stretchable, in addition to high glass transition and excellent optical properties. The performance portfolio is essential for the practical applications of polyesters in high-end areas of aerospace, energy, medical sterilization, and optics. However, current material design strategies have failed to endow polyesters with such integrated performances. Herein, we report the facile synthesis of modified copolyesters with multiple hydrogen bonds (H-bonds) on the main chains via condensed polymerization. The resultant copolyester records a break strain as high as 438% and a large toughness of 106.7 MJ/m3, representing the most stretchable and toughest thermoplastic polyesters so far, while exhibiting a high tensile strength of 59.6 MPa because of intermolecular multiple H-bonding. In addition to achieving an enhanced glass transition temperature (∼85.9 °C), the copolyester films exhibit improved postcrystallization optical transparence and good flexibility due to the grain refinement effect. This work provides an innovative design concept to prepare a new class of advanced polyesters with outstanding mechanical, thermal, and optical properties, thus holding great promise for many potential industrial applications

One-pot scalable fabrication of an oligomeric phosphoramide towards high-performance flame retardant polylactic acid with a submicron-grained structure

Last years have witnessed great advances in minimizing the flammability of the polylactic acid (PLA) bioplastic. Unfortunately, to date there remains an urgent lack of a facile strategy to develop highly effective flame retardants for PLA. Herein, we report one-pot scalable fabrication of an oligomeric phosphoramide, phenyl phosphonic piperazine (PPP), via a one-step condensation polymerization. PPP can finely disperse within the PLA matrix showing a submicron-grained structure with a domain size of 100–300 nm. The addition of 3 wt% PPP increases the limiting oxygen index (LOI) of PLA to 32.5 vol%, and a V-0 rating is achieved. Such high flame retardancy is mainly attributed to the free radical quenching, gas dilution and the thermal barrier action of the char layer. Moreover, the PLA/3%PPP composite retains a tensile strength of 55.4 MPa. This work provides a facile and scalable approach to preparing high-performance flame retardant PLA materials

Mechanically robust and flame-retardant polylactide composites based on molecularly-engineered polyphosphoramides

Intrinsic flammability significantly impedes practical applications of polylactide (PLA), despite many merits. Phosphoramides have shown exceptional flame retardancy efficiency in PLA, but to date it remains a grand challenge to create strong, tough and flame-retardant PLA based on phosphoramides due to lack of fundamental understanding of structure-property correlation. Herein, we design a series of polyphosphoramides (PPDA-x) with tunable structures and compositions. With 1.0 wt% of PPDA-8, tensile strength and toughness of PLA are increased by 11% and 44%, respectively, because of balanced hydrogen-bonding and interfacial tension. Meanwhile, the final PLA achieves a desirable UL-94V-0 rating and a high limited oxygen index (LOI) of ~26.8% because phosphorus contents and interfacial tension govern flame retardancy. This work offers a general methodology for creating robust and flame-retardant polymers by molecularly tailoring flame retardants and shedding light on their structure-property relationship

Multifunctional graphene-based nano-additives toward high-performance polymer nanocomposites with enhanced mechanical, thermal, flame retardancy and smoke suppressive properties

Despite many important industrial applications, the acrylonitrile–butadienestyrene copolymer (ABS) suffers from an inherent flammability, extremely hampering its practical use. Current flame retardants can effectively reduce the flammability issue but give rise to degraded mechanical and thermal properties of ABS. To address this intractable challenge, a graphene-derived flame retardant (Mo5/PN-rGO) was designed by introducing the functional elements (phosphorus, nitrogen and molybdate) onto the graphene oxides nanosheets. The resultant ABS nanocomposite containing 1.0 wt% of Mo5/PN-rGO exhibits a 28% increase in the tensile strength and a 58% enhancement in the Young’s modulus as compared to the ABS host. Furthermore, the glass transition temperature (Tg) increases by ca. 12 °C while the onset thermal decomposition temperature is significantly delayed by ca. 21 °C. In addition, the final ABS nanomaterial shows a 20% reduction in the total heat release and a 45% decrease in the total smoke production in comparison to the ABS bulk. This work paves a new way for the creation of high-performance flame retardants towards advanced flame-retardant polymer nanocomposites with expandable industrial applications

Advances and challenges in eco-benign fire-retardant polylactide

Polylactide (PLA) derived from renewable resources has drawn great interests in packaging, electronics, and automotive fields because of its biodegradability, high mechanical strength, high transparency, and ease of processing. However, inherent flammability and heavy melt dripping exceedingly impede its real-world applications in the forgoing fields. The last decade has witnessed the development of a variety of eco-benign fire retardants for PLA, but to date there has been an urgent lack of a comprehensive yet critical review on this topic. Herein, three major categories of fire retardants, organic, inorganic, and inorganic/organic FRs are reviewed, and fire retardant and mechanical properties of their PLA materials are discussed. This review highlights some representative fire retardants and their modes of actions in PLA followed by performance comparisons. Some important practical applications of fire-retardant PLA also are reviewed. Finally, key challenges with current fire-retardant PLA materials are discussed and some design principles are proposed for creating fire-retardant and mechanically robust PLA materials

Molecularly Engineered Lignin-Derived Additives Enable Fire-Retardant, UV-Shielding, and Mechanically Strong Polylactide Biocomposites

From a perspective of sustainable development and practical applications, there has been a great need for the design of advanced polylactide (PLA) biocomposites that are flame-retardant, ultraviolet (UV)-resistant, and mechanically strong by using biomass-derived additives. Unfortunately, the achievement of a desirable performance portfolio remains unsatisfactory because of improper design strategies. Herein, we report the design of lignin-derived multifunctional bioadditives (TP-g-lignin) with tunable chemical compositions through graft polymerization of a phosphorus-/nitrogen-containing vinyl monomer (TP). Our results show that the incorporation of 5.0 wt % of TP-g-lignin (at a lignin-to-TP ratio of 1:4 by mass) enables PLA to achieve a desirable flame retardancy rating meeting the UL-94 V-0 industrial standard requirements. Meanwhile, the final PLA composite exhibits an exceptional UV-shielding capability. Moreover, with 5.0 wt % of the bio-derived additive, the elastic modulus of PLA is increased by ∼26%, while mechanical strength is fully retained due to engineered favorable interfaces. This work offers an innovative and sustainable strategy for creating bio-based multifunctional additives by using industrial lignin waste and further the application of PLA in the areas of packaging, fabrics, electronics, automobiles, etc

Stretchable, Ultratough, and Intrinsically Self-Extinguishing Elastomers with Desirable Recyclability

Advanced elastomers are increasingly used in emerging areas, for example, flexible electronics and devices, and these real-world applications often require elastomers to be stretchable, tough and fire safe. However, to date there are few successes in achieving such a performance portfolio due to their different governing mechanisms. Herein, a stretchable, supertough, and self-extinguishing polyurethane elastomers by introducing dynamic π–π stacking motifs and phosphorus-containing moieties are reported. The resultant elastomer shows a large break strain of ≈2260% and a record-high toughness (ca. 460 MJ m−3), which arises from its dynamic microphase-separated microstructure resulting in increased entropic elasticity, and strain-hardening at large strains. The elastomer also exhibits a self-extinguishing ability thanks to the presence of both phosphorus-containing units and π–π stacking interactions. Its promising applications as a reliable yet recyclable substrate for strain sensors are demonstrated. The work will help to expedite next-generation sustainable advanced elastomers for flexible electronics and devices applications.</p