Synergistic effect of modified anhydrous magnesium carbonate and hexaphenoxycyclotriphosphazene on flame retardancy of ethylene-vinyl acetate copolymer.

Ethylene-vinyl acetate copolymer (EVA) is widely used in various applications; however, its flammability limits its application in wire and cable industries. In this study, 3-methacryloxypropyltrimethoxysilane (KH570) was successfully grafted onto the surface of anhydrous magnesium carbonate (AMC) by alkali activation treatment. The KH570 modified AMC (AMC@KH570) was then introduced into the EVA matrix along with hexaphenoxycyclotriphosphazene (HPCTP) to assess their effects on the flame retardancy and mechanical properties of EVA composites. The results illustrate a significant synergistic effect in enhancing the flame retardancy of EVA composites by using AMC@KH570 and HPCTP, and the limiting oxygen index (LOI) and vertical burning test (UL-94) of EVA filled with 5 wt% HPCTP and 45 wt% AMC@KH570 (mAMC/H-45-5) reached 27.6% and V-0, respectively. The flame retardant mechanism was investigated by thermogravimetric/infrared (TG-IR) spectroscopy and residual carbon composition analysis. The results show that the thermal decomposition of AMC@KH570 and HPCTP consists of gas dilution, free radical quenching, and catalytic carbonization. Furthermore, KH570 works as a bridge to improve the compatibility of AMC and EVA matrix, which offsets the mechanical loss of EVA to some extent. The present research provides a new path to modify AMC and fabricate EVA composites with excellent flame retardant properties.

Preparation and characterization of polydopamine and n-butyl methacrylate copolymer coatings on titanium-nickel alloy stents.

Cardiovascular diseases pose a significant global health threat, and stents play a crucial role in managing these diseases. However, challenges exist with respect to the poor adhesion of stent coatings. Cardiac stents are often composed of titanium-nickel (TiNi) alloys as the metallic component and poly(n-butyl methacrylate) (PBMA) as the coating. The poor adhesion of PBMA to TiNi alloy surface may cause detachment and subsequent thrombosis post-implantation. This study utilizes Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization to synthesize a novel block copolymer, PBMA-b-PVP, composed of PBMA and poly(N-vinylpyrrolidone) (PVP). TiNi alloy surfaces are functionalized with polydopamine (PDA) to enhance polymer coating adhesion. PBMA-b-PVP exhibits a remarkable improvement in adhesion from class 5 to class 0 and high coating stability after a 15 days immersion in a phosphate buffer solution. The corrosion current density is reduced by 44% with the incorporation of PDA into PBMA-b-PVP coatings, suggesting high corrosion resistance. PDA-functionalized coatings promote cell viability without cytotoxicity, suggesting high biocompatibility. This study provides a robust strategy for preparing stent coatings with high adhesion, corrosion resistance, and biocompatibility.

Effect of Different Compatibilizers on the Mechanical, Flame Retardant, and Rheological Properties of Highly Filled Linear Low-Density Polyethylene/Magnesium Hydroxide Composites.

Maleic anhydride-modified homopolymerized polypropylene (PP-g-MAH) and maleic anhydride-modified polyolefin elastomer (POE-g-MAH) were used as bulking agents to improve the poor processing and mechanical properties of highly filled composites due to high filler content. In this study, a series of linear low-density polyethylene (LLDPE)/magnesium hydroxide (MH) composites were prepared by the melt blending method, and the effects of the compatibilizer on the mechanical properties, flame retardancy, and rheological behavior of the composites were investigated. The addition of the compatibilizer decreased the limiting oxygen index (LOI) values of the composites, but they were all greater than 30.00%, which belonged to the flame retardant grade. Mechanical property tests showed that the addition of the compatibilizer significantly increased the tensile and impact strengths of the LLDPE/60MH (MH addition of 60 wt%) composites. Specifically, the addition of 5 wt% POE-g-MAH increased 154.07% and 415.47% compared to the LLDPE/60MH composites, respectively. The rotational rheology test showed that the addition of the compatibilizer could effectively improve the processing flow properties of the composites. However, due to the hydrocarbon structure of the compatibilizer, its flame retardant properties were adversely affected. This study provides a strategy that can improve the processing and mechanical properties of highly filled composites.

Preparation of Flame-Retardant Rigid Polyurethane Foams by Combining Modified Melamine-Formaldehyde Resin and Phosphorus Flame Retardants.

In this work, ethylene glycol-modified melamine-formaldehyde resin (EMF) was synthesized from ethylene glycol, paraformaldehyde, and melamine, and then rigid polyurethane foams (RPUFs) were prepared using EMF, polyols and polyisocyanate. The effects of ammonium polyphosphate (APP) and dimethyl methylphosphonate (DMMP) on the flame retardancy, mechanical properties, thermal stability, and morphology of the prepared RPUFs were studied. It is shown that the flame-retardant performance of EMF-filled RPUFs can be enhanced by the addition of APP and DMMP. Thus, APP and DMMP can synergistically improve the flame retardancy of RPUFs. APP has good smoke suppression, while DMMP can increase the total smoke production and CO/CO2 weight ratio during the combustion of RPUFs.

Effects of α-zirconium phosphate and zirconium organophosphonate on the thermal, mechanical and flame retardant properties of intumescent flame retardant high density polyethylene composites.

The combination of synergistic agents with intumescent flame retardants (IFRs) is an excellent strategy for the development of high-performance flame retardant composites. Zirconium-based compounds are multifunctional materials with applications in various fields. In this study, zirconium-based compounds were synthesized and then combined with an IFR composed of ammonium polyphosphate (APP) and tris (2-hydroxyethyl) isocyanurate (THEIC) to prepare flame retardant high density polyethylene (HDPE) composites. α-Zirconium phosphate (α-ZrP) and two organic-inorganic hybrids (zirconium organophosphonate), Zr-ATMP and Zr-PA, were prepared using amino tri (methylene phosphonic acid) (ATMP) and phytic acid (PA), respectively, and their thermal, mechanical and flame retardant properties were characterized by thermogravimetric analysis, tensile test, limiting oxygen index (LOI) measurement and cone calorimetry test. The results showed that the LOI value of HD/IFR/Zr-ATMP composite reached a maximum of 26.2% using 25 wt% of flame retardant containing 3 wt% of Zr-ATMP. Of the three zirconium-based compounds, Zr-ATMP and α-ZrP can reduce the peak heat release rate compared with the composite containing only IFR. However, zirconium-based compounds showed no significant improvement of tensile strength.

Preparation and fire behavior of rigid polyurethane foams synthesized from modified urea-melamine-formaldehyde resins.

In this study, a series of ethylene glycol modified urea-melamine-formaldehyde resins (EUMFs) were synthesized from urea, melamine, paraformaldehyde and ethylene glycol, and then incorporated into rigid polyurethane foams (RPUFs) as a reactive-type liquid flame retardant. The structure of EUMFs was characterized by Fourier transform infrared spectrometry; the morphology of the foams was characterized by scanning electron microscopy; and the thermal degradation and fire behavior of RPUFs were characterized by limiting oxygen index (LOI), cone calorimetry test and thermogravimetry analysis. The results show that the incorporation of EUMFs results in an increase in thermal stability, smoke suppression and LOI of RPUFs. As the melamine loading in EUMFs increases, the peak heat release rate and the total heat release of RPUFs decrease significantly, but the LOI increases slightly. Compared with the original foam, the cells of RPUFs become less regular with nonuniform diameters. In general, EUMFs show excellent flame retardancy and smoke suppression for RPUFs.

Multiple gold nanorods@hierarchically porous silica nanospheres for efficient multi-drug delivery and photothermal therapy.

Gold-based nanocomposites have attracted intensive attention due to their unique optical properties and great potential in biomedical applications. Herein, we report a simple route for the synthesis of multiple gold nanorods encapsulated, hierarchically porous silica nanospheres (MGNRs@HPSNs) based on the cooperative self-assembly of amphiphilic block copolymer polystyrene-b-poly (acrylic acid) (PS-b-PAA), cetyl trimethyl ammonium bromide (CTAB), gold nanorods and the organosilane of tetraethyl orthosilicate (TEOS) in an oil/water system. Multiple gold nanorods have been loaded successfully into the interior of the hierarchically porous silica nanospheres, which consist of large, interconnected pores of 13.2 nm throughout the whole sphere and small pores of 2.7 nm in the silica framework. Moreover, the loading amount (or number) of gold nanorods in the silica matrix can be tuned by simply changing the initial concentration of preformed gold nanorods. Due to the presence of the hierarchically porous structure, the PEGylated MGNRs@HPSNs display high loading capability for both small anti-tumor drugs (i.e., doxorubicin hydrochloride, 69.2 ± 7.2 mg g-1) and bio-macromolecules (i.e., bovine serum albumin, 248.1 ± 12.3 mg g-1). More importantly, MGNRs@HPSNs present better photothermal effect than that of hierarchically porous silica nanoparticles containing less (one or two) gold nanorods at the same Au concentration. It is thus demonstrated that MGNRs@HPSNs can not only act as promising drug/protein nanocarriers, but also can be used as photoabsorbers for photothermal tumor therapy under NIR laser irradiation.

Mechanical Properties and Morphologies of Carboxyl-Terminated Butadiene Acrylonitrile Liquid Rubber/Epoxy Blends Compatibilized by Pre-Crosslinking.

In order to enhance the compatibilization and interfacial adhesion between epoxy and liquid carboxyl-terminated butadiene acrylonitrile (CTBN) rubber, an initiator was introduced into the mixture and heated to initiate the cross-linking reaction of CTBN. After the addition of curing agents, the CTBN/epoxy blends with a localized interpenetrating network structure were prepared. The mechanical properties and morphologies of pre-crosslinked and non-crosslinked CTBN/epoxy blends were investigated. The results show that the tensile strength, elongation at break and impact strength of pre-crosslinked CTBN/epoxy blends are significantly higher than those of non-crosslinked CTBN/epoxy blends, which is primarily due to the enhanced interfacial strength caused by the chemical bond between the two phases and the localized interpenetrating network structure. Both pre-crosslinked and non-crosslinked CTBN/epoxy blends show a bimodal distribution of micron- and nano-sized rubber particles. However, pre-crosslinked CTBN/epoxy blends have smaller micron-sized rubber particles and larger nano-sized rubber particles than non-crosslinked CTBN/epoxy blends. The dynamic mechanical analysis shows that the storage modulus of pre-crosslinked CTBN/epoxy blends is higher than that of non-crosslinked CTBN/epoxy blends. The glass transition temperature of the CTBN phase in pre-crosslinked CTBN/epoxy blends increases slightly compared with the CTBN/epoxy system. The pre-crosslinking of rubber is a promising method for compatibilization and controlling the morphology of rubber-modified epoxy materials.

Sonochemical preparation of carbon nanosheet from carbon black.

Preparation of carbon nanosheet via ultrasound irradiation of carbon black under ambient conditions was reported for the first time. The structure of resulting carbon nanosheet was characterized by TEM, HRTEM, EDX and AFM. The experimental results showed that the carbon nanosheet is composed of ordered graphite carbon layers with a thickness of several nanometers.