A facile approach to prepare cage-ladder-structure phosphorus-containing amino-functionalized POSS for enhancing flame retardancy of epoxy resins

The cage-ladder-structure phosphorus-containing amino-functionalized polyhedral oligomeric silsesquinoxanes (CLNH₂-POSS) have been synthesized through a facile catalyst-free hydrolytic condensation of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-vinyltrimethoxysilane (DOPO-VTMS) with 3-aminopropyl trimethoxysilane (KH540). The successful preparation of CLNH₂-POSS has been proven by the characterization of Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy (¹H-NMR, ²⁹Si-NMR), matrix-assisted laser desorption ionization time of flight (MALDI-TOF), and X-ray diffraction (XRD). Then flame retardant (FR) epoxy resins (EPs) were prepared by the addition of different content of CLNH₂-POSS into EPs with thermal curing technology. The CLNH₂-POSS showed good solubility in EP matrix. The well-dispersed CLNH₂-POSS contributed to thermal, mechanical, and FR properties of EP. Dynamic scanning calorimetry nonisothermal curing scans showed that CLNH₂-POSS had accelerating effect on the curing of EP. With the addition of only 3 wt% CLNH₂-POSS (0.30% phosphorus loading), the limiting oxygen index value of the EP composite increased from 25.5 of pure EP to 31.8, and vertical burning (UL-94) V-0 ratings was achieved. In addition, the EP composites showed improved thermal and mechanical properties. The investigations on char residue and pyrolysis volatiles of cured EP further revealed that CLNH₂-POSS exerted FR effects in condensed and gas phase simultaneously.     

Patterning of worm-like soft polydimethylsiloxane structures using a TiO2 nanotubular array

Patterned polydimethylsiloxane (PDMS) is an important structure for soft lithography. Various materials have been deployed as mold for patterning PDMS. Anodized nanotubular array has been sought after as cost-effective alternative for textured silicon. An array of TiO₂ nanotubes with characteristic diameter ≈140 nm and the length of ≈1.5 microns, created by anodic oxidation of a titanium substrate, was used here as a template for soft PDMS molding. The optimal molding process was developed by a combination of silanization, use of solvent, application of a vacuum, and hydraulic pressing. The silanization was confirmed by Fourier transform infrared spectroscopy and contact angle measurements while the PDMS structure was examined by scanning electron microscope and energy dispersive X-ray spectroscopy. Hydraulic pressing significantly improved the infiltration of PDMS into the pores of nanotubular array resulting in formation of PDMS nanobumps after separation of the polymer from the template. Complete infiltration of PDMS precursor into the cavity of nanotubes was observed on the hydraulic-pressed sample without toluene impurities. The hydraulic-pressed samples exhibited higher adhesion strength than nonpressed ones. The adhesive strength was measured by a simple experimental arrangement, in which the PDMS layer was stuck on a vertical glass surface followed by pulling it downwards.     

Flame retardancy and thermal properties of organoclay and phosphorous compound synergistically modified epoxy resin

Phosphorous flame retardants (PFRs) are common halogen‐free flame retardants. However, the flame retardancy of PFRs has not been fully exploited. Herein, the synergistic flame retardant effect of a typical phosphorous compound, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), and organoclay on epoxy is studied. Results show that the peak of heat release rate (pHRR) and smoke production rate of modified epoxy resin (EP) with both 2.0 wt % phosphorus and 4.0 wt % organoclay are only 40% and 46% of that of neat EP resin, respectively, while the sole use of 2.0 wt % phosphorus only decrease the pHRR to 59% of that of neat EP resin. The structure and thermal decomposition behavior of as‐prepared nanocomposites are analyzed, and a synergistic flame retardant mechanism is proposed. This investigation opens a new approach to obtain halogen‐free EPs with higher flame retardancy and better overall properties than the EPs loaded with DOPO only. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43367.     

Mechanical properties of epoxy resins reinforced with synthetic boehmite (AlOOH) nanosheets

In this article, sheet boehmite (AlOOH), which was synthesized via a facile and environmental friendly method, was used as reinforcing agent to toughen Bisphenol A epoxy resin. The result of X–ray Diffraction (XRD) and IR spectrum indicated that the as–synthesized product was pure crystalline and high purity AlOOH. The effects of sheet AlOOH on the mechanical properties of AlOOH/epoxy nanocomposites were investigated. The results indicated that the introduction of AlOOH significantly improved the mechanical properties of epoxy resin. Compared with neat epoxy resin, the tensile strength and the fracture toughness (K_IC) of the AlOOH/epoxy nanocomposites filled with 4 wt % AlOOH increased by 24.2% and 28.7%, respectively, while the flexural strength increased from 40.92 to 50.00 MPa. From Scanning Electron Microscope (SEM), a phase‐separated morphology and plenty of cervices and river branches were observed in the fractured surfaces of composites. With the increase of sheet AlOOH content, river‐shaped cracks became more and more intensive. Overall, the addition of sheet AlOOH is shown as a promising method for mechanical properties enhancement of epoxy matrix. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41409.     

Plasticizing effect of biodegradable dipropylene glycol bibenzoate and epoxidized linseed oil on diglycidyl ether of bisphenol A based epoxy resin

Major limitation for use of epoxy thermosets in engineering applications is its sudden brittle failure. In the present study dipropylene glycol dibenzoate (DPGDB) based plasticizer is used to modify diglycidyl ether of bisphenol A (DEGEBA) based epoxy resin system via simple blending technique. Bio-based epoxidized linseed oil was also used to modify epoxy resin system and compared with DPGDB modified resin. For DPGDB modified resin storage modulus and loss modulus of the epoxy system modified with 10% plasticizer increased by 7.54% and 12.24%, respectively. The primary mechanism responsible for such behavior is improved crosslinking density. With 5% plasticizer loading, flexural strength increased by 21%. There was an improvement of 312.74% in strain at failure for 10% plasticizer loading, while preserving its mechanical strength. It was found that DPGDB based modification was better than epoxidized linseed oil modification.     

A statistical approach to evaluate the oxidative process of electrospun polyacrylonitrile ultrathin fibers

A systematic study using design of experiments was applied in order to map out the thermal stabilization of electrospun polyacrylonitrile mats and to investigate how oxidation and cyclization reactions are affected by rate, temperature, and time in an oxidative environment. Cyclization indexes were estimated by a simple methodology based on differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy data. Values of enthalpy and relative intensities of bands assigned to C?N and C?N bonds were used on calculation. The statistical planning applied in this study was important to show that not always longest treatment is effective to stabilize polyacrylonitrile, but also samples obtained in less than 3 h presented low values of exothermic peak on DSC, values of cyclization indexes near to 90%, both from DSC and Fourier transform infrared spectroscopy techniques, reduced weight loss in thermogravimetric analysis and O/C ratio higher than 10% by X‐ray photoelectron spectroscopy, that are appreciated characteristics to a precursor of high‐performance carbon materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45458.     

Furfuryl alcohol functionalized graphene nanosheets for synthesis of high carbon yield novolak composites

Graphene oxide and furfuryl alcohol modified graphene nanosheets (G‐FA) were used to prepare graphene/novolak composites. Effect of graphene compatibilization on the properties of the composites especially carbon yield value is evaluated. Both types of graphene nanosheets were dispersed uniquely in the novolak matrix as proved by X‐ray diffraction analysis. However, modification of graphene sheets by furfuryl alcohol results in more improved dispersions. Thermogravimetric analysis confirms the elevated thermal stability of the nanocomposites in comparison with the neat novolak. In addition, G‐FA containing composites have higher carbon yield values. A shift in the wave number of characteristic bonds of graphene after oxidation and modification with furfuryl alcohol, O? H, C?O, and C? O bonds, are seen in the Fourier transform infrared spectroscopy spectra. Raman results and scanning electron microscopy images show that graphene nanosheets reduced in size and wrinkled by oxidation and functionalization. Transmission electron microscopy image of the composite with 0.2 wt % of G‐FA reveals the presence of nanosheets with curvature. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40273.     

Novel strategy for molybdenum disulfide nanosheets grown on titanate nanotubes for enhancing the flame retardancy and smoke suppression of epoxy resin

A novel hybrid consisting of a molybdenum disulfide (MoS₂) coating on a titanium dioxide nanotube (TNT) surface (MoS₂–TNT) was synthesized by a hydrothermal method. The MoS₂, TNTs, and MoS₂–TNT hybrid were incorporated into epoxy resin (EP) to study their effects on its thermal performance and flame retardancy. Thermogravimetric analysis results show that the char yield at 700 °C of EP–MoS₂–TNTs was obviously increased compared with that of the EP–MoS₂ or EP–TNTs; this indicated that MoS₂–TNTs had a good carbonization effect. The limiting oxygen index, cone calorimetry, and smoke density tests showed that MoS₂–TNTs effectively improved the flame retardancy and smoke suppression of EP. This was attributed to the physical barrier effect of MoS₂ and the adsorption of TNTs. Moreover, the flame retardancy and smoke suppression of the EP–MoS₂–TNTs were better than those of the EP–MoS₂ or EP–TNTs alone with the same amount of addition; this indicated that there was a synergistic effect between MoS₂ and TNTs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46064.     

Effect of functionalized graphene oxide with phosphaphenanthrene and isocyanurate on flammability,mechanical properties,and thermal stability of epoxy composites

Maleic anhydride, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and 1, 3, 5-triglycidyl isocyanurate functionalized graphene oxide (GO) was prepared in this paper. The resultant phosphorus-nitrogen functionalized GO called GOMT was homogeneously dispersed and incorporated into diglycidyl ether of bisphenol A to prepare composites. The char residue of GOMT/EP composites increased and its LOI value increased to 28.1% with UL-94 V-1 rating. T _g of composite containing 1 phr GOMT increases to 165.6 °C, and the storage modulus of the sample with 3 phr GOMT was increased by 19% compared with pure EP. Furthermore, the elastic modulus and flexural strength of epoxy composite with 5 phr GOMT were increased by 17.9 and 26.7% at room temperature, respectively. Besides, the incorporation of GOMT into EP significantly reduces the PHRR and THR of the matrix. Therefore, the as-designed GOMT not just obviously enhances the flame retardancy with low loading but raises the mechanical behavior and thermal stability of epoxy resins. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48761.     

Effect of particle size on flame retardancy and mechanical properties of hydroxyethyl diphosphate modified aluminum hydroxide intrinsic polyethylene terephthalate

Organic–inorganic hybrid flame retardant was obtained by modifying aluminum hydroxide with different particle size with 1-hydroxyethylidene-1,1-diphosphonic acid. The structure of the organic–inorganic hybrid flame retardant is characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, while ¹H-NMR spectroscopy only characterizes specific samples. The thermal stability and flame retardancy of the samples were analyzed by thermogravimetric analysis, limiting oxygen index (LOI), vertical combustion of UL-94 and cone calorimeter. The results show that the modified 10 μm aluminum hydroxide has a better effect than the 25 μm aluminum hydroxide and 100 nm aluminum hydroxide. Compared with pure polyethylene terephthalate (PET), the LOI value of the best sample is increased by 24.4%, and UL-94 V reaches V-0 level. Heat release rate, total heat release rate, and carbon monoxide production rate decreased by 45.8%, 33.2%, and 41.5%, respectively, compared to pure PET. The results showed that the aluminum hydroxide with a particle size of 10 μm exhibited the best flame retardant effect, which could be attributed to the decomposition of organic phosphoric acid and the dehydration of aluminum hydroxide, yielding a higher amount of residual carbon.     

Preparation of alginate flame retardant containing P and Si and its flame retardancy in epoxy resin

In the present paper, a novel biomass flame retardant based on alginic acid was synthesized through chemical combination with a reactive P–Si compound. Compared with alginates, the modified alginate showed obviously increased thermal stability and water resisting property, as well as better compatibility with epoxy resin, which can satisfy the requirements of a flame‐retardant additive in the polymer. The flame‐retardant properties were evaluated by vertical burning tests, limiting oxygen index, and microscale combustion calorimetry. Due to the self‐charring capacity of alginate combined with the charring catalyst from P and the charring reinforcer from Si, the modified alginate exhibited much better flame retardancy, taking advantage of the formation of a more continuous, denser, and strengthened char layer than either individual alginate or P–Si flame retardant. The corresponding flame‐retardant mechanisms were investigated and discussed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45552.     

Synthesis of curing agent for epoxy resin based on halogenophosphazene

Epoxy resins are, due to their excellent properties (such as chemical resistance, dimensional stability, and heat resistence), widely used in practice. The basic principle of curing epoxy resins with a hardener containing multiple amino groups is the crosslinking reaction between active hydrogen atoms in the hardener and the oxirane groups in the epoxy resin. This study deals with the synthesis and characterization of hexachloro‐cyclo‐triphosphazene derivative and its subsequent use for curing epoxy resins. The new hardener was prepared from hexachloro‐cyclo‐triphosphazene by nucleophilic substitution with isophorone diamine and its curing capability was compared with original isophorone diamine. The prepared derivative hexaisophorone diamino‐cyclo‐triphosphazene (HICTP) provided advantages over conventional curing system, as it improved mechanical properties as well as the flame resistance. Testing of the cured epoxy resin during burning was carried out using dual cone calorimeter, which enables more extensive monitoring of parameters in comparison with testing using oxygen index that has been used in many publications. The epoxy resin cured with the prepared phosphorus containing HICTP exhibits lower values for total heat release, amount of smoke released and oxygen consumed, which may cause a slower flame spread. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42917.     

Influence of phenyl group number on enantioseparation performance of chitosan-based materials

In order to investigate the influence of phenyl group number on enantioseparation capability of a chitosan-based chiral selector (CS), in this study, two series of chitosan derivative and their enantioseparation were presented. According to the functional group at 2-position of glucosamine, the derivatives were classified as amido-type and ureido-type. In the amido-type CSs, the CS with two phenyl groups showed the best enantioseparation capability; the CS with one phenyl group exhibited the poorest enantioseparation; and the enantioseparation performance of the CS with three phenyl groups intermediated between those of the CSs with one and two phenyl groups. In the ureido-type, the CS bearing three phenyl groups was in the middle of two CSs with two phenyl groups in enantioseparation capability. Based on the results obtained in the present study, one phenyl group in a chitosan derivative is not enough for enantioseparation, and two or three phenyl groups are necessary. On the other hand, introducing three phenyl groups onto one glucosamine unit of chitosan, can not definitely result in a better enantioseparation capability, comparing with introducing two phenyl groups.     

Thermal degradation behaviors and flame retardancy of epoxy resins with novel silicon‐containing flame retardant

A novel macromolecular silicon‐containing intumescent flame retardants (Si‐IFR) was synthesized, and its structure was a caged bicyclic macromolecule containing phosphorus‐silicon characterized by IR. Epoxy resins (EP) were modified with Si‐IFR to get the flame retardant EP, whose flammability and burning behavior were characterized by UL 94 and limiting oxygen index (LOI). Twenty percentage of weight of Si‐IFR was doped into EP to get 27.5% of LOI and UL 94 V‐0. The degradation behavior of the flame retardant EP was studied by thermogravimetry, differential thermogravimetry, scanning electron microscopy, and X‐ray photoelectron spectroscopy analysis. The experimental results exhibited that when EP/Si‐IFR was heated, the phosphorus‐containing groups firstly decompose to hydrate the char source‐containing groups to form a continuous and protective carbonaceous char, which changed into heat‐resistant swollen char by gaseous products from the nitrogen‐containing groups. Meanwhile, SiO₂ reacts with phosphate to yield silicophosphate, which stabilizes the swollen char. The barrier properties and thermal stability of the swollen char are most effective in resisting the transport of heat and mass to improve the flame retardancy and thermal stability of EP. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Phase distribution changes of neat unsaturated polyester resin and their effects on both thermal stability and dynamic-mechanical properties

A relationship between phase distribution of a commercial unsaturated polyester resin (UPR) and both thermal stability and dynamical mechanical properties, measured by thermogravimetric analysis and dynamic-mechanical analysis respectively, is observed. Changes in phase distributions are achieved varying UPR components miscibility by means of temperature. Morphologies of the internal surfaces are analyzed by atomic force microscopy showing that more homogeneous nanostructures with smaller nodules result in the increase of the storage modulus and glass transition temperature of the thermosetting UPR. Tan δ peaks show that the phase rich in UP and the phase rich in polystyrene tend to decrease their differences at higher curing temperatures. Changes in the curing mechanism and kinetics with curing temperature are verified by differential scanning calorimetry. A theoretical explanation of archived morphology is proposed using interaction parameter between UP and styrene showing that higher temperatures increased their miscibility.     

Boosting flame retardancy of thermoplastic polyurethane: Synergistic effect of nickel phosphide nanoparticles and molybdenum disulfide nanosheets

For the first time, a novel nanohybrid based on nickel phosphide (Ni₂P) nanoparticles and molybdenum disulfide (MoS₂) nanosheets was facilely synthesized for enhancing flame retardancy and smoke suppression of thermoplastic polyurethane (TPU). The synergistic effect on flame retardancy is proposed. TPU composite with 2 wt% Ni₂P/MoS₂ hybrid exhibits the best overall flame retardancy, while TPU composites with the same amount of individual Ni₂P nanoparticles and MoS₂ nanosheets are average in performance. Specifically, the 41.2% reduction of peak heat release rate (PHRR) is achieved for TPU/Ni₂P/MoS₂ composite, which is only 16.8% and 26.4% for TPU/Ni₂P and TPU/MoS₂ composites, respectively. In addition, a more intact protective char layer of TPU/Ni₂P/MoS₂ composite can be observed. These results clearly suggest the synergistic effect between Ni₂P nanoparticles and MoS₂ nanosheets. It is hypothesized that physical barrier effect and chemical catalytic ability of Ni₂P/MoS₂ hybrid contribute to the dramatic reduction of heat release and smoke production. The strategy proposed here is a simple yet efficient approach to fabricate high-performance MoS₂-based flame retardants.     

Preparation of polyurethane foam fine polishing wheel for stainless steel surface

Comparing with dry polishing, the wet-polishing of the stainless steel surface can significantly reduce dust, noise and other pollution, and improve the polished quality. Thus, it is important to develop new polishing tools. In this work, the effects of the foaming agent and diluents on the mechanical properties of the polyurethane foam (PUF) system were investigated, and then the effect of the filler of graphite on the structure and mechanical properties of PUF was studied. Furthermore, the PUF fine polishing wheel with aluminum oxide was prepared. Results show that the bi-component diluents combined cyclohexane and dimethylformamide significantly affects the porosity and hardness of the PUF matrix. The filler of graphite can decrease the mechanical properties of the polyurethane matrix and increase the porosity of PUF, consequently, improve the self-sharpening of the PUF polishing wheel. The PUF fine polishing wheel with aluminum oxide shows fine polishing performance.     

Toughening of epoxy thermosets with nano-sized or micron-sized domains of poly(ethylene oxide)-b-poly(butadiene-co-acrylonitrile)-b-poly(ethylene oxide) triblock copolymers synthesized using room temperature ester coupling reaction

Poly(ethylene oxide)-b-poly(butadiene-co-acrylonitrile)-b-poly(ethylene oxide) (PEO-b-PBN-b–PEO) triblock copolymers with three different compositions were synthesized from poly(ethylene glycol) methyl ethers and carboxylic acid-terminated poly(butadiene-co-acrylonitrile) (CTBN) by ester coupling reaction at room temperature. The PEO-b-PBN-b-PEO was incorporated into anhydride cured epoxy thermosets to improve the fracture toughness by the formation of either nano-sized spherical micelles or micron-sized vesicles. The polymer chemical structure was confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and gel permeation chromatography. The morphology of PEO-b-PBN-b–PEO within the epoxy thermosets was investigated using a transmission electron microscope, an atomic force microscope, and a scanning electron microscope. Also, we conducted impact testing and plane-strain fracture toughness testing to evaluate the fracture toughness in terms of the impact strength and the critical stress intensity factors (K_IC) for the modified epoxy thermosets. The results revealed that all the PEO-b-PBN-b-PEO triblock copolymers are more effective in the toughening of epoxy thermoset compare to CTBN. We found that the 5 wt% PEO-b-PBN-b-PEO modified epoxy thermoset containing micron-sized vesicles exhibited the highest K_IC, which was 3.23 times as high as the K_IC of pristine epoxy thermoset. Besides, the glass transition temperature remained and the tensile modulus did not reduce remarkably when the amount of PEO-b-PBN-b-PEO added into epoxy was 5 wt%.     

Development of a completely recyclable glass fiber-reinforced epoxy thermoset composite

Stimulated by the growing demand for more sustainable polymer systems, experiments were performed to develop completely recyclable epoxy-based thermoset composite materials involving the separation, recovery, and complete reuse of both components of the composite, the resin and the fibers. In this study, a possibility to design such composites by incorporation of reversible chemistry for dedicated repair and recycling is demonstrated. Relying on Diels–Alder (DA) adducts located on the cross-links between the polymeric chains, uncross-linking the thermoset via the reverse DA reactions becomes possible. The network breaks up at elevated temperatures in shorter segments, which can be solubilized in solvents like acetic acid, butan-1-ol, or toluene. Specific processes for each of these solvents were developed to recover the resin and fibers with virtually unchanged properties. Both components were used in a second manufacturing step to produce recycled composites which display properties comparable with the original composites.     

Synthesis and performance of a novel nitrogen‐containing cyclic phosphate for intumescent flame retardant and its application in epoxy resin

A novel nitrogen‐containing cyclic phosphate (NDP) was synthesized and well characterized by ¹H, ¹³C, ³¹P NMR, mass spectra and elemental analysis. NDP was used as an additive intumescent flame retardant (AIFR) to impart flame retardancy and dripping resistance for diglycidyl ether of bisphenol‐A epoxy resin (DGEBA) curied by 4,4′‐diaminodiphenylsulfone (DDS) with different phosphorus content. The flammability, thermal stability, and mechanical properties of NDP modified DGEBA/DDS thermosets were investigated by UL‐94 vertical burning test, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Izod impact strength and flexural property tests. The results showed that NDP modified DGEBA/DDS thermosets exhibited excellent flame retardancy, moderate changes in glass transition temperature and thermal stability. When the phosphorus content reached only 1.5 wt %, the NDP modified DGEBA/DDS thermoset could result in satisfied flame retardancy (UL‐94, V‐0). The TGA curves under nitrogen and air atmosphere suggested that NDP had good ability of char formation, and there existed a distinct synergistic effect between phosphorus and nitrogen. The flame retardant mechanism was further realized by studying the structure and morphology of char residues using FT‐IR and scanning electron microscopy (SEM). It indicated that NDP as phosphorus‐nitrogen containing flame retardant worked by both of the condensed phase action and the vapor phase action. Additionally, the addition of NDP decreased slightly the flexural strength of the flame retarded DGEBA epoxy resins, and increased the Izod impact strength of these thermosets. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41859.