Search

Si3N4 saw-tooth nanoribbons (SNSNs) have been synthesized via a novel approach involving a by-product pyrolysis–nitridation process during carbon foam manufacturing at 1450 °C. The SNSNs formed are ribbon shaped, 80–750 nm wide, 70–80 nm thick and several micrometres in length. The process simply involved thermal pyrolysis of a powdered mixture containing carbon foam precursors and silicon powder under flowing high-purity nitrogen. Pyrolysis gases rich in silicon, silicon oxide and active nitrogen vapours promoted the subsequent synthesis of the SNSNs over the outer surface of the carbon foams via a vapour–solid mechanism. The crystal structure, morphology, chemical composition, growth mechanism and photoluminescence (PL) properties have been studied. The infrared adsorption of SNSNs exhibited two absorption bands with all the peaks related to the Si–N bonds of the α-Si3N4 crystalline structure. X-ray photoelectron spectroscopy measurements further confirmed the chemical composition, with minor impurities such as oxygen and carbon. A single nanoribbon has the same width-to-thickness ratio, suggesting a stable morphology resulting from the reduction of the overall surface energy. Intense PL was observed centred at 2.03, 2.48, 2.62, and 3.01 eV, which resulted from the recombination between the intrinsic conduction band edges and silicon dangling bonds with deep-level or trap-level states. [ABSTRACT FROM AUTHOR]

A thermosetting resin system, bismaleimide (BMI) modified allyl novolac (BAN), was developed via reactive blending of formaldehyde and catalyst drop wise to improve the extent of reaction between BMI and phenol-carbenium ions. For improving the curing behavior and mechanical properties, dicumyl peroxide (DCP) was selected as a novel curing initiator to compare with hexamethylenetetramine (HTMA) which is the most common curing initiator used in the manufacture of phenolic resins. BAN was characterized by 1H nuclear magnetic resonance and Fourier transfer infrared spectroscopy. Curing behavior with initiators was analyzed by differential scanning calorimetry and glass transition temperature of the cured resins was examined by dynamic mechanical analysis. For evaluating efficiency of the modified system, composite samples using polyvinyl acetyl fiber were molded and tested for flexural properties before and after ageing at 150°C for 1,000 h. The morphology of composite samples was examined by scanning electron microscope, and the effects of the incorporated initiators on the mechanical and thermal properties of composite were investigated. The results indicated that the initiators reduced the curing temperature effectively and improved the curing process. DCP proved to be more effective in crosslinking and heat resistance than HTMA. Meanwhile, the molded composite with DCP showed higher mechanical properties before and after ageing when compared with HTMA curing initiator. Therefore, DCP/BAN resin system with good heat resistance, higher mechanical properties, and better process ability can be applied as matrix resin for the manufacturing of advanced fiber reinforced composites. POLYM. COMPOS., 37:2260-2271, 2016. © 2015 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

ABSTRACT For reducing the cure temperature and improving the thermal stability and mechanical properties, a thermosetting resin system composed of novolak and bismaleimide (BMI) was developed by reactive blending and using dicumyl peroxide (DCP) as a novel curing agent. Novolak was allylated and reacted with BMI to produce bismaleimide allylated novolak (BAN), and the effect of DCP on flexural, impact and heat distortion temperature of cured resin were investigated. On the basis of improved mechanical and thermal properties at 0.5% DCP contents, the curing behavior of DCP/BAN resin system was evaluated by DSC analysis. Ene, Diels-Alder, homo-polymerization and alternating copolymerization which occurred in DCP/BAN resin system were further verified using FTIR at sequential cure conditions from 140 to 200°C. Kissinger and Ozawa-Flynn-wall methods were used to optimize the process and curing reactions of DCP/BAN resin system. The results showed that the addition of 0.5% DCP in BAN reduced the curing temperature and time of the modified resin. For evaluating process ability of the modified system, composite samples using polyvinyl acetyl fiber were molded and tested for flexural properties. The resulting samples showed better flexural properties when compared with the composite made with neat BAN. The modified 0.5% DCP/BAN resin system with good mechanical properties and manufacturability can be used for making bulk molding compounds and fiber reinforced composites required in various commercial and aerospace applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41829. [ABSTRACT FROM AUTHOR]

There has been growing interest in the use of waste materials as an alternative source for the conventional wood-plastic composites (WPC) in the global market. This paper evaluates the feasibility of two different kinds of wastepaper fibre as reinforcing materials used for WPC. For this purpose, the fibre morphology of old newspaper fibre (ONPF) and old magazine paper fibre (OMGF) was investigated by fibre morphology analyzer, respectively. Wastepaper fibres, recycled polypropylene (rPP), and 2%MAPP were compounded by double-roller mixer and test specimens were prepared by hot press moulding. The tensile, flexural, and water absorption properties of ONPF and OMGF reinforced rPP composites as a function of fibre content were studied. The results showed that the highest mechanical properties of ONP and OMG fibre reinforced composites could be reached with 30 wt. % fibre contents. The mechanical properties of the composites made from ONP fibres were better than those made from OMG fibres. However the addition of wastepaper fibres resulted in a decrease in elongation at break. Both the fibre loading and the fibre morphological characteristics had an effect on the water uptake behaviour. But the effect of fibre size on the water uptake was minimal compared to that of the fibre content. The water uptake of wastepaper fibre/rPP composites may actually be slowed down rather than delayed. Scanning electron microscopy (SEM) of the fracture surface of a tensile specimen with 30 wt.% wastepaper fibre loading showed good fibre dispersion in the matrix and a good compatibility between wastepaper fibre and rPP matrix. The results suggested that both the ONP fibres and the OMG fibres could be used as potential sources and reinforcing agent for composites, but the reinforcement effect of ONPF was better than that of OMGF. [ABSTRACT FROM AUTHOR]

A diblock copolymer, poly(methyl methacrylate)-b-polystyrene (PMMA-b-PS), was grafted onto the surface of nano-titania (nano-TiO2) successfully via reversible addition-fragmentation chain transfer (RAFT) polymerization. The surface of TiO2 nanoparticles was modified initially by attaching dithioester groups to the surface using silane coupling agent 3-(chloropropyl)triethoxy silane and sodium ethyl xanthate. The polymerization of methyl methacrylate and styrene were then initiated and propagated on the TiO2 surface by RAFT polymerization. The resulting composite nanoparticles were characterized by means of XPS, FT-IR, 1H NMR and TGA. The results confirmed the successful grafting of poly(methyl methacrylate) (PMMA) and diblock copolymer chains onto the surface of TiO2. The amount of PMMA grafted onto the TiO2 surface increased with the polymerization time. Moreover, the kinetic studies revealed that the ln([M]0/[M]), where [M]0 is the initial and [M] is the time dependent monomer concentrations, increased linearly with the polymerization time, indicating the living characteristics of the RAFT polymerization. [ABSTRACT FROM AUTHOR]

Manganese dioxide is often used as a curing agent for polysulfide polymers because of its excellent properties. Here, we synthesize a freshly ordered macroporous MnO2 with crystalline framework walls using a handy method called one-pot operation. It is worth noting that this synthesis approach of the ordered macroporous MnO2 is facile and simple. It can obviously improve the mechanical properties of polysulfide polymers and accelerate the rate of vulcanization. [ABSTRACT FROM AUTHOR]

This article presents information on a study related to the mixed system of liquid crystalline epoxy/epoxy resin (EP). The route of toughening EP, at present, is mainly focused on rubber, thermoplastic, chain extending and thermotropic crystalline polymers modification. These methods, however, have disadvantages to various extents. In order to overcome these problems, liquid crystalline epoxy is used to self-reinforce in situ to improve the toughness of cured resin. At the same time, as liquid crystalline epoxy is compatible with EP, it links EP with strong chemical bond by chain-extending of ammoniac cure agent. Moreover, the addition of liquid crystalline epoxy with low molecular weight could not lead to the problem of poor processability.