Development of a Zr-Based Metal-Organic Framework (UiO-66) for a Cooperative Flame Retardant in the PC/ABS.

Polycarbonate/acrylonitrile butadiene styrene (PC/ABS) blends are widely used as engineering plastic alloys; however, they have a low fire safety level. To improve the flame-retardant property of PC/ABS, a zirconium-based metal-organic framework material (UiO-66) was synthesized with zirconium chloride and terephthalic acid and used as a flame-retardant cooperative agent. Its flame-retardant performance and mode of action in the PC/ABS blends were carefully investigated. The results showed that UiO-66 had good thermal stability and delayed the pyrolysis of the materials, thus significantly enhancing the efficiency of intumescent flame retardants. By compounding 7.0 wt% hexaphenyloxy-cyclotri-phosphazene (HPCTP) with 3.0 wt% UiO-66, the PC/ABS blends reached a limiting oxygen index value of 27.0% and V0 rating in the UL-94 test, showing significantly improved resistance to combustion dripping. In addition, UiO-66 enhanced the smoke and heat suppression characteristics of the intumescent flame-retardant materials. Finally, the flame-retardant mode of action in the blends was indicative of UiO-66 having a cooperative effect on the flame-retardant performance of PC/ABS/HPCTP materials. This work provides good ideas for further development of the flame-retardant ABS/PC.

Development of a UiO-66 Based Waterborne Flame-Retardant Coating for PC/ABS Material.

The flame-retardancy of polymeric materials has garnered great interest. Most of the flame retardants used in copolymers are functionalized additives, which can deteriorate the intrinsic properties of these materials. As a new type of flame retardant, functionalized metal-organic frameworks (MOFs) can be used in surface coatings of polymers. To reduce the flammability, a mixture of phytic acid, multi-wall carbon nanotubes, zirconium-based MOFs, and UiO-66 was coated on a PC/ABS substrate. The structure of the UiO-66-based flame retardant was established by FT-IR, XRD, XPS, and SEM. The flammable properties of coated PC/ABS materials were assessed by LOI, a vertical combustion test, TGA, CCT, and Raman spectroscopy. The presence of a UiO-66-based coating on the PC/ABS surface resulted in a good flame-retardant performance. Heat release and smoke generation were significantly reduced. Importantly, the structure and mechanical properties of PC/ABS were less impacted by the presence of the flame-retardant coating. Hence, this work presents a new strategy for the development of high-performance PC/ABC materials with both excellent flame-retardancy and good mechanical properties.

Bulk Polymerization of Thermoplastic Shape Memory Epoxy Polymer for Recycling Applications.

Conventional epoxy polymers are thermo-set and difficult to recycle and reuse. In this study, a series of linear thermoplastic epoxy polymers (EPx) with shape memory properties were prepared by using a bifunctional monoamine diglycolamine (DGA) as a curing agent and an equivalent amount of bifunctional rigid epoxy resin (E-51) and bifunctional flexible epoxy resin (polypropylenglycol diglycidyl ether, PPGDGE) in a bulk polymerization reaction. The results showed that these samples can fully react under the curing process of, 60 °C/2 h, followed by 80 °C/2 h, followed by 120 °C/2 h. The introduction of different contents of PPGDGE can adjust the Tg of the material to adapt to different environmental requirements, and can significantly increase the fracture strain of the material and improve its micro-phase separation structure. Thus, Rf of the material is close to 100%, and Rr is increased from 87.98% to 97.76%. Importantly, this linear chain structure allows the material to be easily recycled and reprocessed by dissolving or melting, and also means the material shows potential for 3D printing or other thermoplastic remolding.

Ionic Liquid-Acrylic Acid Copolymer Derived Nitrogen-Boron Codoped Carbon-Covered Na3V2(PO4)2F3 as Cathode Material of High-Performance Sodium-Ion Batteries.

In this study, a nitrogen-boron codoped carbon layer, Na3V2(PO4)2F3 sample, obtained by using an ionic liquid-acrylic acid copolymer as the nitrogen-boron source was used as the cathode material for sodium-ion batteries. The optimized and modified nitrogen and boron codoped carbon layer, Na3V2(PO4)2F3 (denoted as NVPF-PCNB-20), illustrated better rate capability and cycling performance. The discharge capacities of NVPF-PCNB-20 at 0.5C and 10C were 109 and 90 mAh g-1, respectively, and the capacity retention rate was 93.2% after 100 cycles at 0.5C and 92.8% after 750 cycles at 10C. Through in situ X-ray diffraction analysis of NVPF-PCNB-20, the results show that the modified Na3V2(PO4)2F3 has excellent cycle reversibility. The scanning electron microscopy and transmission electron microscopy images reveal that NVPF-PCNB-20 particles were finer and covered by a uniform coating. The results show that the ionic liquid-acrylic acid copolymer not only make the material dispersion more uniform but also enhance the electronic conductivity and sodium storage performance of Na3V2(PO4)3F3 effectively. This study may provide an effective way to synthesize nitrogen and boron codoped carbon-coated Na3V2(PO4)2F3 with excellent electrochemical performance.

Realizing outstanding electrochemical performance with Na3V2(PO4)2F3 modified with an ionic liquid for sodium-ion batteries.

Na3V2(PO4)2F3 is a typical NASICON structure with a high voltage plateau and capacity. Nevertheless, its applications are limited due to its low conductivity and poor rate performance. In this study, nitrogen-boron co-doped carbon-coated Na3V2(PO4)2F3 (NVPF-CNB) was prepared by a simple sol-gel method using an ionic liquid (1-vinyl-3-methyl imidazole tetrafluoroborate) as a source of nitrogen and boron for the first time. The morphology and electrochemical properties of NVPF-CNB composites were investigated. The results show that a nitrogen-boron co-doped carbon layer could increase the electron and ion diffusion rate, reduce internal resistance, and help alleviate particle agglomeration. NVPF-CNB-30 exhibited better rate performance under 5C and 10C charge/discharge with initial reversible capacities of 99 and 90 mA h g-1, respectively. Furthermore, NVPF-CNB-30 illustrates excellent cyclic performance with the capacity retention rate reaching 91.9% after 500 cycles at 5C, as well as a capacity retention rate of about 95.5% after 730 cycles at 10C. The evolution of the material's structure during charge/discharge processes studied by in situ X-ray diffraction confirms the stable structure of nitrogen-boron co-doped carbon-coated Na3V2(PO4)2F3. Co-doping of nitrogen and boron also provides more active sites on the surface of Na3V2(PO4)2F3, revealing a new strategy for the modification of sodium-ion batteries.

Rational Design of Effective Binders for LiFePO4 Cathodes.

Polymer binders are critical auxiliary additives to Li-ion batteries that provide adhesion and cohesion for electrodes to maintain conductive networks upon charge/discharge processes. Therefore, polymer binders become interconnected electrode structures affecting electrochemical performances, especially in LiFePO4 cathodes with one-dimensional Li+ channels. In this paper, recent improvements in the polymer binders used in the LiFePO4 cathodes of Li-ion batteries are reviewed in terms of structural design, synthetic methods, and working mechanisms. The polymer binders were classified into three types depending on their effects on the performances of LiFePO4 cathodes. The first consisted of PVDF and related composites, and the second relied on waterborne and conductive binders. Profound insights into the ability of binder structures to enhance cathode performance were discovered. Overcoming the bottleneck shortage originating from olivine structure LiFePO4 using efficient polymer structures is discussed. We forecast design principles for the polymer binders used in the high-performance LiFePO4 cathodes of Li-ion batteries. Finally, perspectives on the application of future binder designs for electrodes with poor conductivity are presented to provide possible design directions for chemical structures.

Crystalline iceplant-like nano-NaVPO4F@graphene as an intercalation-type anode material for sodium-ion batteries.

A crystalline iceplant-like nano-NaVPO4F@graphene composite is successfully synthesized by a freeze-drying process. Graphene forms a lamellar structure wherein NaVPO4F nanoparticles are uniformly adhered to the surface of graphene. The composite displays an intercalation-type reaction mechanism and excellent cycling and rate performance.

Shape Memory Polyurethanes Based on Zwitterionic Hard Segments.

This work aimed at elucidating the influence of zwitterionic hard segments on the structures and properties of shape memory polyurethanes (SMPUs). A series of zwitterionic SMPUs was successfully prepared with N-methyldiethanolamine (MDEA), 1,3-propanesultone (1,3-PS), 1,6-hexamethylene diisocyanate (HDI) and polyethylene glycol (PEG6000). The influence of MDEA-PS-based zwitterionic hard segment on structure, morphology, thermal property, shape memory property and cytocompatibility were systematically investigated. The results demonstrated that the PEG-based zwitterionic SMPUs (PEG-ZSMPUs) formed phase separation structure consisting of crystalline soft phase and amorphous hard phase. The MDEA-PS zwitterionic segments showed a tendency to form ionic clusters in hard segments, which served as reinforced net points. Shape memory analysis showed that zwitterionic PEG-ZSMPUs containing a high content of zwitterionic segments had thermal-induced shape memory effects. Finally, cytotoxic assays demonstrated that MDEA-PS zwitterionic segment improved the biocompatibility of PEG-ZSMPUs. The zwitterionic PEG-ZSMPUs could thus have a promising application in smart biomedical fields.

A New Type of Photo-Thermo Staged-Responsive Shape-Memory Polyurethanes Network.

In this paper, we developed a photo-thermo staged-responsive shape-memory polymer network which has a unique ability of being spontaneously photo-responsive deformable and thermo-responsive shape recovery. This new type of shape-memory polyurethane network (A-SMPUs) was successfully synthesized with 4,4-azodibenzoic acid (Azoa), hexamethylenediisocyanate (HDI) and polycaprolactone (PCL), followed by chemical cross-linking with glycerol (Gl). The structures, morphology, and shape-memory properties of A-SMPUs have been carefully investigated. The results demonstrate that the A-SMPUs form micro-phase separation structures consisting of a semi-crystallized PCL soft phase and an Azoa amorphous hard phase that could influence the crystallinity of PCL soft phases. The chemical cross-linking provided a stable network and good thermal stability to the A-SMPUs. All A-SMPUs exhibited good triple-shape-memory properties with higher than 97% shape fixity ratio and 95% shape recovery ratio. Additionally, the A-SMPUs with higher Azoa content exhibited interesting photo-thermo two-staged responsiveness. A pre-processed film with orientated Azoa structure exhibited spontaneous curling deformation upon exposing to ultraviolet (UV) light, and curling deformation is constant even under Vis light. Finally, the curling deformation can spontaneously recover to the original shape by applying a thermal stimulus. This work demonstrates new synergistically multi-responsive SMPUs that will have many applications in smart science and technology.

Exploring the Biocompatibility of Zwitterionic Copolymers for Controlling Macrophage Phagocytosis of Bacteria.

This paper provides a biomaterial derived from zwitterionic polymer for controlling macrophage phagocytosis of bacteria. A series of zwitterionic copolymers, named DMAPS-co-AA, are synthesized with 3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate (DMAPS) and acrylic acid (AA). The biocompatibility of DMAPS-co-AA copolymers can be adjusted by adjusting the DMAPS-content or pH value. As the DMAPS-content increases, the biocompatibility of zwitterionic copolymer increases. The zwitterionic copolymers with DMAPS content above 30 wt% have higher biocompatibility. Moreover, the biocompatibility also increases significantly as the pH increases from 3.4 to 7.2. By adjusting the pH above 5.8, the zwitterionic copolymer with lower DMAPS-content also shows higher biocompatibility. Importantly, after incubation with the DMAPS-co-AA copolymer solutions at different pH values, phagocytosis behavior of macrophage RAW264.7 cells can also be adjusted. The phagocytosis of bacteria is enhanced at pH = 7.2. Thus, it is proposed that zwitterionic copolymers can be used for controlling phagocytosis of bacteria.

Development of zwitterionic copolymers with multi-shape memory effects and moisture-sensitive shape memory effects.

Shape memory polymers (SMP) and zwitterionic polymers both have great applications in biomedical fields. This works successfully combines functionalities of zwitterionic polymers and SMP, developing new kind of zwitterionic copolymers having a multi-shape memory effect (SME) and a moisture-sensitive SME. The results demonstrate that a series of zwitterionic multi-SMPs, coded as p(DMAPS-co-AA), were synthesized from DMAPS and acrylic acid (AA). A micro-phase separated structure is formed in the resulting p(DMAPS-co-AA). The strong hydrogen bonding between AA segments serves as a reversible switch, while the strong electrostatic forces among DMAPS segments serve as physical crosslinkers. Therefore, shape memory testing demonstrates that p(DMAPS-co-AA) shows not only dual-SME, but also triple-SME and quadruple-sSME. Moreover, in addition to the thermally-induced SME, p(DMAPS-co-AA) also shows moisture-sensitive SME. It is thus proposed that this zwitterionic multi-SMP could find great potential applications in smart biomedical fields.