It has always been critical to develop high‐performance polymeric materials with exceptional mechanical strength and toughness, thermal stability, and even healable properties for meeting performance ...requirements in industry. Conventional chemical cross‐linking leads to enhanced mechanical strength and thermostability at the expense of extensibility due to mutually exclusive mechanisms. Such major challenges have recently been addressed by using noncovalent cross‐linking of reversible multiple hydrogen‐bonds (H‐bonds) that widely exist in biological materials, such as silk and muscle. Recent decades have witnessed the development of many tailor‐made high‐performance H‐bond cross‐linked polymeric materials. Here, recent advances in H‐bond cross‐linking strategies are reviewed for creating high‐performance polymeric materials. H‐bond cross‐linking of polymers can be realized via i) self‐association of interchain multiple H‐bonding interactions or specific H‐bond cross‐linking motifs, such as 2‐ureido‐4‐pyrimidone units with self‐complementary quadruple H‐bonds and ii) addition of external cross‐linkers, including small molecules, nanoparticles, and polymer aggregates. The resultant cross‐linked polymers normally exhibit tunable high strength, large extensibility, improved thermostability, and healable capability. Such performance portfolios enable these advanced polymers to find many significant cutting‐edge applications. Major challenges facing existing H‐bond cross‐linking strategies are discussed, and some promising approaches for designing H‐bond cross‐linked polymeric materials in the future are also proposed.
Hydrogen‐bond cross‐linking has recently emerged as a promising strategy for creating high‐performance polymeric materials via self‐association of multiple hydrogen bonds or the addition of external cross‐linkers. These polymers exhibit a unique combination of high strength, large extensibility, thermostability, and even healable capability. Such a performance portfolio enables these polymeric materials to find many potential applications in the electronics and gas‐separation fields.
Their pervasive use in industrial applications renders the development of environmentally benign flame-retardant epoxy (EP) thermosets a timely and important goal. The last two decades have witnessed ...the rise of phosphorus (P)-containing flame retardants for EP due to their high flame retardancy efficiency, low toxicity, multiple modes of action, molecular diversity and other favorable properties. P-containing flame retardants are classified into two types: reactive and additive, according to whether they participate in the curing process. Recent advances in both of these classes of P-containing flame retardants motivate this comprehensive review on the design and synthesis of P-containing flame retardants and their impact on the material properties of EP thermosets. This review focuses on the state-of-the-art knowledge of P-containing flame retardants and their effects on flame retardancy, thermal stability and mechanical properties of the resultant EP. First, representative flame-retardant mechanisms are reviewed. Subsequently, practical applications of P-containing flame-retardant EP thermosets are presented. Finally, the key challenges associated with P-containing flame retardants for EP thermosets are highlighted, and opportunities for future research in the field are proposed.
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Dynamic vulcanization has been demonstrated to be a versatile and efficient way of improving impact toughness of PLA. However, the existing vulcanization routes usually suffer from complicated ...presynthetic procedures and use of nonrenewable modifiers as well as markedly enhanced melt-viscosity. Herein, using both biomass-derived hydrogenated dimer acid (HDA) and an excess molar amount of l-lysine ethyl ester diisocyanate (LDI) as toughening monomers, we have developed a facile yet highly effective diisocyanate method for the design of fully bio-based PLA blends with excellent impact toughness and melt-flowability. The in situ formation and self-cross-linking of flexible biopolyamide (HDAPA) toughener, as well as its reactive compatibilization with PLA, were accomplished in a single melt-blending step. When incorporating the amount of HDAPA from 15 to 20 wt % or higher, the resulting blends evolved from the network-like morphology to the bi-continuous one with the cross-linked HDAPA network. At HDAPA content higher than 10 wt %, a sharp and persistent brittle–ductile transition occurred with an equilibrium impact strength of over 1200 J/m, and elongation-at-break was over 400%. Moreover, such a tremendous toughening effect was accompanied by low melt-viscosity and enhanced PLA crystallization. The matrix yielding triggered by internal cavitation of percolated HDAPA domains, together with the pull-out of many in situ formed block copolymers located at the interfaces, was found to be the major impact-toughening mechanism. This work offers a novel and facile strategy for fabricating high-performance and fully bio-based polymeric materials.
The combination of high strength, great toughness, and high heat resistance for polymeric materials is a vital factor for their practical applications. Unfortunately, until now it has remained a ...major challenge to achieve this performance portfolio because the mechanisms of strength and toughness are mutually exclusive. In the natural world, spider silk features the combination of high strength, great toughness, and excellent thermal stability, which are governed by the nanoconfinement of hydrogen-bonded β-sheets. Here, we report a facile bioinspired methodology for fabricating advanced polymer composite films with a high tensile strength of 152.8 MPa, a high stiffness of 4.35 GPa, and a tensile toughness of 30.3 MJ/m3 in addition to high thermal stability (69 °C higher than that of the polymer matrix) only by adding 2.0 wt % of artificial β-sheets. The mechanical and thermostable performance portfolio is superior to that of its counterparts developed to date because of the nanoconfinement and hydrogen-bond cross-linking effects of artificial β-sheets. Our study offers a facile biomimetic strategy for the design of integrated mechanically robust and thermostable polymer materials, which hold promise for many applications in electrical devices and tissue engineering fields.
Conventional three-dimensional (3D) thermal conductors or heat sinks are normally bulky solids with high density, which is cumbersome and not portable to satisfy current demands for soft and flexible ...electronic devices. To address this issue, here, a lightweight, superelastic yet thermally conductive boron nitride (BN) nanocomposite aerogel is designed by a facile freeze-drying method. The attained aerogel constituting of tailored interconnected binary inorganic–organic network structure exhibits low bulk density (6.5 mg cm–3) and outstanding mechanical performances for compression, clotting, and stretching. Meanwhile, the aerogel has promising thermal stability and high thermal conductivity over wide temperature ranges (30–300 °C), validating the application even in extremely hot environments. Moreover, the aerogel can serve as a lightweight and elastic heat conductor for the enhancement of thermal energy harvest. Interestingly, during alternate strain loading/unloading under heating, the superelasticity and the anisotropy of thermal conductive transduction make the aerogel enable the elastic thermal energy capture and dynamic regulation. Therefore, our findings provide a potential use for the thermally conductive aerogel in future green energy applications.
The inherent flammability of biodegradable polybutylene succinate (PBS) extremely restricts the growing applications as packaging and construction materials; meanwhile, only a minority of industrial ...alkali lignin has been effectively utilized until now. To address these two challenges, herein we have converted alkali lignin into one biobased additive for PBS by chemically modified lignin with phosphorus, nitrogen, and the zinc(II) ions. Cone calorimetry results show that addition of 10 wt % modified lignin (PNZn-lignin) reduces the peak heat release rate and total heat release of PBS strikingly by 50 and 67%, respectively. Moreover, the total smoke production is decreased noticeably by 50%. Observations of char residues indicate that adding PNZn-lignin leads to a compact, intact, and thick char layer that is responsible for such enhanced properties. This work offers a new strategy for reducing the flammability and smoke release of PBS, promoting high-value-added utilization of industrial lignin, and designing biobased advanced polymeric materials.
Two natural biomass derivatives i.e., tannic acid (TA) and phosphorylated-cellulose nanofibrils (P-CNFs) were employed to decorate graphene oxide network and the as-prepared flame-retardant GTP paper ...with ultrasensitive fire alarm response can be applied as desirable smart fire alarm sensor material.
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•Biomass-derivatives decorated graphene oxide networks were fabricated via a facile strategy.•The synergistic reinforcing effect was formed in the hybrid networks based on bionic design.•The bio-based hybrid networks showed excellent flame resistance and structural stability.•Ultrasensitive fire alarm time of < 1 s and desirable fire early warning responses were achieved.•Such hybrid networks can be used as sustainable fireproof and fire alarm sensor materials.
Effective utilization of natural biomass-derivatives for developing sustainable, mechanically robust, and fireproof materials remains a huge challenge in fire safety and prevention field. Herein, based on bionic design, the hybrid interconnected networks composed of two-dimensional (2D) graphene oxide (GO) nanosheets, renewable one-dimensional (1D) phosphorylated-cellulose nanofibrils (P-CNFs) and tannic acid molecules (TA) were prepared via a green and facile evaporation-induced self-assembly strategy. Through construction of the multiple synergistic interactions among the TA, P-CNFs and GO, the optimized 1D/2D interconnected networks with hierarchical nacre-like structure were achieved and exhibited improved mechanical properties (tensile strength and Young’s modulus up to ∼ 132 MPa and ∼ 7 GPa, i.e. ∼ 3.6 and ∼ 14 times higher than that of the pure GO paper), good structural stability in various environments (aqueous solutions with different pH values), excellent flame retardancy (keeping structural integrity after flame attack), and ultrasensitive fire alarm functions (e.g., ultrafast flame alarm time of < 1 s and sensitive fire warning responses). Further, such 1D/2D interconnected networks can act as effective flame-retardant nanocoatings to significantly improve the flame retardancy of combustible PU foam materials (e.g., ∼48% decrease in peak heat release rate at only 10 wt% content). Based on the structure observation and analysis, the related synergistic reinforcing and flame-retardant mechanisms were proposed and clarified. Clearly, this work provides a new route for design and development of environmentally friendly fireproof and fire alarm materials based on utilization of natural biomass-derivatives.
Highlights
Graphene oxide-based hybrid networks were fabricated via introducing multi-amino molecule with triple roles (i.e., cross-linker, fire retardant and reducing agent).
The optimized hybrid ...network with mechanically robust, exceptional intumescent effect and ultra-sensitive fire alarm response (~ 0.6 s) can be used as desirable smart fire alarm sensor materials.
Exceptional fire shielding performances, e.g., ~ 60% reduction in peak heat release rate and limiting oxygen index of ~ 36.5%, are achieved, when coated such hybrid network onto combustible polymer foam.
Smart fire alarm sensor (FAS) materials with mechanically robust, excellent flame retardancy as well as ultra-sensitive temperature-responsive capability are highly attractive platforms for fire safety application. However, most reported FAS materials can hardly provide sensitive, continuous and reliable alarm signal output due to their undesirable temperature-responsive, flame-resistant and mechanical performances. To overcome these hurdles, herein, we utilize the multi-amino molecule, named HCPA, that can serve as triple-roles including cross-linker, fire retardant and reducing agent for decorating graphene oxide (GO) sheets and obtaining the GO/HCPA hybrid networks. Benefiting from the formation of multi-interactions in hybrid network, the optimized GO/HCPA network exhibits significant increment in mechanical strength, e.g., tensile strength and toughness increase of ~ 2.3 and ~ 5.7 times, respectively, compared to the control one. More importantly, based on P and N doping and promoting thermal reduction effect on GO network, the excellent flame retardancy (withstanding ~ 1200 °C flame attack), ultra-fast fire alarm response time (~ 0.6 s) and ultra-long alarming period (> 600 s) are obtained, representing the best comprehensive performance of GO-based FAS counterparts. Furthermore, based on GO/HCPA network, the fireproof coating is constructed and applied in polymer foam and exhibited exceptional fire shielding performance. This work provides a new idea for designing and fabricating desirable FAS materials and fireproof coatings.
Despite extraordinary mechanical properties and excellent biodegradability, poly(lactic acid) (PLA) still suffers from a highly inherent flammability, restricting its wide applications in the ...electric and automobile fields. Although a wide range of flame retardants have been developed to reduce the flammability, so far, they normally compromise the mechanical strength of PLA. Herein, we have demonstrated the fabrication of a novel core–shell nanofibrous flame-retardant system, PN-FR@CNF, through in situ chemically grafting the phosphorus–nitrogen-based polymer onto the cellulose nanofiber (CNF) surface. The results show that adding 10 wt % PN-FR@CNF enables PLA to achieve a V-0 flame resistance rating during vertical burning tests and to exhibit a dramatically reduced peak heat release rate in cone calorimetry measurements, indicating a significantly reduced flammability. In addition, the tensile strength of PLA also increases by around 24% (about 72 MPa). This work offers an innovative methodology for the design of the unique integration of extraordinary flame retardancy and mechanical reinforcement into one hierarchical nanostructured additive system for creating advanced green polymeric materials.
Polymeric materials are ubiquitously utilized in modern society and continuously improve quality of life. Unfortunately, most of them suffer from intrinsic flammability, significantly limiting their ...practical applications. Fundamentally, free‐radical reaction is a critical “trigger” for their thermal pyrolysis and following combustion process regardless of the anaerobic thermal pyrolysis in the condensed phase or aerobic combustion of polymers in the gaseous phase. The addition of free radical scavengers represents a promising and effective means to enhance the fire safety of polymeric materials. This review aims to offer a state‐of‐the‐art overview on the creation of fire‐retardant polymeric nanocomposites by adding fire retardants with an ability to trap free radicals. Their specific modes of action (condensed‐phase action, gaseous‐phase action, and dual‐phases action) and performances in some typical polymers are reviewed and discussed in detail. Following this, some key challenges associated with these free‐radical capturers are discussed, and design strategies are also proposed. This review provides some insights into the modes of action of free radical capturing agents and paves the avenue for the design of advanced fire‐retardant polymeric nanocomposites for expanded real‐world applications in industries.
This work provides a state‐of‐the‐art overview on the creation of fire‐retardant polymeric nanocomposites by adding free radical fighters. The action of modes and performances of these free radical fighters in some of typical polymer matrices are reviewed. The key challenges associated with these free radical scavengers are discussed, followed by some proposed strategies. This review is expected to pave a new avenue for the design of advanced fire‐retardant polymeric nanocomposites which help to create a sustainable and fireresilient world.
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