Preparation of ultra-fine polyimide fibers containing silver nanoparticles via in situ technique

Ultra-fine polyimide fibers containing silver nanoparticles were prepared by electrospinning from poly(amic acid)/(trifluoroacetylacetonoto)silver(I) (PAA/AgTFA) solution. Thermal curing of the silver(I)-containing fibers led to cycloimidization of the poly(amic acid) into polyimide with concomitant silver(I) reduction. The polyimide–silver fibers were characterized by FT-IR, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The average diameters of silver nanoparticles and ultra-fine PI fibers electrospun from solutions with different amounts of AgTFA were studied, and the crystal structure of silver nanoparticles was also presented.     

Enhancing flame retardant and antistatic properties of polyamide 6 by a grafted multiwall carbon nanotubes

In order to improve the flame retardancy and antistatic properties of polyamide 6 (PA6) at as low amount of additives as possible, an integrated-functional additive was synthesized by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and multiwalled carbon nanotubes (MWCNTs). The results showed 2 wt% of DOPO-MWCNTs distributed in PA6 formed an electric network and decreased volume resistivity sharply to 3.1 × 10⁸ Ω cm. In other words, it helped PA6 to get to the percolation threshold of semiconductor. By using of 3 wt% DOPO-MWCNTs, the severe dripping in burning of PA6 was almost controlled. The possible reason was also ascribed to the network formed by evenly dispersed DOPO-MWCNTs, which strengthened the char structure and held severe dripping of PA6. As a result, the heat and smoke release were also suppressed obviously. The most important is that CO release was about half cut in CONE test.     

Engineering all-aromatic polyamide surface from hydrophilic to superhydrophobic and the accelerated strategy

Being a new kind of nanomaterials, aromatic polyamide nanofibers (ANF) have been much highlighted in recent studies. We here demonstrate an isopropyl alcohol (IPA) accelerated chemical cleavage on poly (p-phenylene terephthalamide) chopped fibers, which provides an efficient preparation method of ANF. The comprehensive study on the processes accelerated by different alcohols revealed that the preparation time of ANF in the mixed medium of dimethyl sulfoxide (DMSO)-alcohol (20:1 in volume) was shorten to 45 min and 75 min for methanol (ethanol) and isopropanol, respectively. However, the nanofibers prepared in DMSO-IPA exhibited the minimum in axial and radial dimensions, providing the finest and most uniform diameter of 16 nm. The corresponding ANF films through vacuum assisted filtration also showed the highest tensile strength of 150 MPa, in comparison with those of the ANF films prepared using other alcohols, which were about 110 MPa. Furthermore, ANF/silicon hybrid films were prepared by the ionic ring-opening reaction followed by the alkoxysilane condensation and nanoparticle fabrication. By changing the organo functional groups in the alkoxysilane, the surface of the films were adjustable in a wide contact angle range from 56° (hydrophilic) to 150° (superhydrophobic), suggesting the amendable interfacial properties potential applicable to composite fabrication with most of the resin matrix.     

Fabrication of phytic acid embellished kaolinite and its effect on the flame retardancy and thermal stability of ethylene vinyl acetate composites

A modified kaolinite by grafting with phytic acid (PA-g-Kaol) is fabricated, and it was introduced into ethylene vinyl acetate (EVA) with intumescent flame retardancy (IFR) together to improve the flame retardancy of EVA composites. The results show the limiting oxygen index value of EVA/ (18.0 wt% IFR)/ (2.0 wt% PA-g-Kaol) is 30.8%. Meanwhile, there is only one dripping produced in the vertical burning test. What's more, the flame-retardant mechanism is demonstrated by TG-IR, real-time-IR and GC–MS analysis. The results indicate that some pyrolytic products of IFR and PA-g-Kaol, like ammonia and phosphoric acid, catalyze the crosslinking of EVA and flame retardant, the resultant compact char protects the substrate from further burning.     

Flexible Cationic Nanoparticles with Photosensitizer Cores for Multifunctional Biomedical Applications

One challenge for multimodal therapy is to develop appropriate multifunctional agents to meet the requirements of potential applications. Photodynamic therapy (PDT) is proven to be an effective way to treat cancers. Diverse polycations, such as ethylenediamine‐functionalized poly(glycidyl methacrylate) (PGED) with plentiful primary amines, secondary amines, and hydroxyl groups, demonstrate good gene transfection performances. Herein, a series of multifunctional cationic nanoparticles (PRP) consisting of photosensitizer cores and PGED shells are readily developed through simple dopamine‐involving processes for versatile bioapplications. A series of experiments demonstrates that PRP nanoparticles are able to effectively mediate gene delivery in different cell lines. PRP nanoparticles are further validated to possess remarkable capability of combined PDT and gene therapy for complementary tumor treatment. In addition, because of their high dispersities in biological matrix, the PRP nanoparticles can also be used for in vitro and in vivo imaging with minimal aggregation‐caused quenching. Therefore, such flexible nanoplatforms with photosensitizer cores and polycationic shells are very promising for multimodal tumor therapy with high efficacy.     

The effect of γ-radiation on the mechanical properties of structural adhesive

The modular satellite concept iBOSS (intelligent Building Blocks for On-Orbit Satellite Servicing and Assembly) enables on-orbit servicing and reconfiguration of satellite systems and has the potential to be a game changer in the space industry. Such building blocks have to withstand all environmental loads in space, e.g.: radiation, vacuum and thermal cycling.The present paper investigates the mechanical properties of the two component epoxy adhesive 3M SW9323 under the environmental effect of radiation. This adhesive is part of the building block's primary structure. Furthermore, adhesive bonding is the sole joining technique used in the whole structure. It is therefore critical to know the influence of ionizing radiation on its load-carrying capacity. For this purpose bulk specimens were manufactured and exposed to γ-radiation, generated by a ⁶⁰Co source. Four different doses were achieved by varying the distance to the source and irradiation time. Afterwards the specimen were tested under tensile loading. Using the digital image correlation technique properties like elastic modulus, shear modulus, tensile strength and elongation at break were determined.The results show that the mechanical properties of the bulk specimen of 3M SW9323 are not influenced by γ-radiation up to a dose of 17.6 kGy. This is explained by the phenomena of crosslinking and chain scission which occur simultaneously and cancel each other out. In addition, Fourier-transform infrared spectroscopy (FTIR) was carried out to investigate if one mechanism is predominant. A slight shift in the spectra indicates the supremacy of chain scission.     

Study on the dual-curing mechanism of epoxy/allyl compound/sulfur system

Allyl-based epoxy resin/Sulfur (S) system is a facile and novel dual-curing system which conducts a unique curing mechanism. In this paper, Bisphenol-A diglycidyl ether (BADGE) and 2-Allylphenol (OAP) cured by S were comparatively investigated to clarify the dual-curing mechanism of Epoxy (EP)/Allyl Compound (AC)/S system. When the temperature was above 170 °C, DSC and FTIR data showed that S could cleave to form thiyl radicals, and FTIR, NIR, and ¹H NMR measurements proved the disappearance of allyl groups and the generation of thiol groups by the thiyl radicals abstracting α-H atoms of allyl groups in the OAP/S reaction system. Real-time infrared spectroscopy (RT-FTIR) results showed that the reaction of the generation of thiol groups is the dominant reaction in the two possible pathways of the OAP/S system; allyl groups and epoxy groups disappeared sequentially in the OAP/S/BADGE system. DSC curve also revealed the one-stage reaction for OAP/S system and two-stage reaction for OAP/S/BADGE system. These data were used to develop a detailed, experimentally validated pathway for the dual-curing of EP/AC/S system, in which thiol groups are important intermediate, and the dual-curing process included the crosslinking of double bonds that initiated by thiyl radicals and the ring-opening reaction of epoxy groups with thiol groups. Besides, the dual-curing mechanism of EP/AC/S system shares a close resemblance to the classical rubber vulcanization mechanism and the recent thiol-ene radical addition mechanism.     

Synergistic catalysis effects of lanthanum oxide in polypropylene/magnesium hydroxide flame retarded system

Lanthanum oxide (La₂O₃) was incorporated as a catalytic synergist to enhance the flame retardancy of the environmental friendly halogen free inorganic compound magnesium hydroxide (MH), the main flame retardant, filled in the flammable polymer polypropylene (PP) matrix. It was found that the addition of an appropriate loading of La₂O₃ could remarkably improve the flame retardancy of MH filled PP FR composite. The significant enhancement in the flame retardancy was attributed to the greatly improved quality of the condensed phase charred layers deposited on the surface of the formed magnesium oxide (MgO) particles through participation of PP macromolecular chains themselves in the char formation reaction under the catalytic action of La₂O₃. It was believed that the char formation reaction involved with the PP macromolecular chains is composed of two processes related to the catalytic role of La₂O₃, i.e. catalytic oxidation hydrogenation and catalytic partial oxidation.     

Hydrolysis-resistant polyurethane elastomers synthesized from hydrophobic bio-based polyfarnesene diol

Hydrolytic stability is an essential requirement for polyurethanes (PUs) that are used in highly humid and aqueous environments. In this study, hydrolysis-resistant PU elastomers (PUEs) are synthesized based on hydrophobic bio-based polyfarnesene diol (PFD), which contains unique “bottle brushes” structure (with long branched hydrocarbon side chains). The effect of hard segment (HS) content, ranging from 30 to 50%, on the morphology and properties of PUEs is investigated by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, tensile, water absorption, and contact angle measurements. The results show that there are prominent phase separations in the synthesized PUEs. The PUEs show a three-stage degradation process and two T_g, one is at about −66 °C and the other 61 °C, which are related to the soft segment and HS, respectively. Water contact angles of PUEs increase from 98.6 to 105.2° with the increasing of PFD structural unit fraction. After being immersed in deionized water for 30 days, PUEs show no significant degradation of both tensile strength and elongation at break, and mass changes of all samples are less than 0.5%. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47673.