Search

Crack initiation and propagation in a peroxide-cured polybutadiene rubber reinforced with silanised silica nanofiller were studied under a cyclic loading condition. The fatigue properties of the semi-transparent rubber samples were tested at a constant strain amplitude, test frequency and temperature. Initiation and subsequent growth of cracks in the rubber samples were observed using an optical microscope as a function of the number of cycles until the rubber samples failed, indicating that there are two distinct stages in the fatigue failure of the rubber vulcanisate. The cracks were initiated after the rubber was flexed for about 2817 cycles and then the cracks grew from 500 μm and reached to a critical length of 4.6 mm and followed a further 897 cycles, leading to a catastrophic failure of the rubber samples. Correlation between the rate of crack growth, dc/dn, and the strain energy release rate, T, was investigated using the power law index, and a new expression for the measurement of the cyclic fatigue life of the rubber vulcanisate was proposed.

Star copolymers with good film-forming and mechanical properties were in situ synthesized for fabricating proton exchange membranes. The monomers of 3,4-diaminobenzoic acid were first grafted onto glycidyl-polyhedral oligomeric silsesquioxane (G-POSS) cores and then propagated to the poly(2,5-benzimidazole) (ABPBI) chains. The introduction of the star copolymer improves the movement of the ABPBI polymer chains, resulting in a lower internal viscosity and larger free volume that favor increased membrane flatness and absorbilities of water and phosphoric acid molecules, respectively. It was found that the star copolymers with 1.0 wt% of incorporated POSS (ABPBI-1.0POSS) had the best balance of the acid retentivity and film-forming property as well as mechanical properties that are desirable for proton exchange membranes without PA loss operating at high temperatures. The enhanced cell performance characteristics obtained using the ABPBI-1.0POSS-based membranes indicate that star copolymers are promising materials for use in high-temperature proton exchange membrane fuel cells.

There are very few studies that have investigated directly the effect of an oxide film on tin whisker growth, since the ‘cracked oxide theory’ was proposed by Tu in 1994. The current study has inve...

To broaden the operating temperature range of phosphoric acid (PA) doped polybenzimidazole membrane-based proton exchange membrane fuel cells (PEMFCs) toward low temperatures, a novel series of poly(2,5-benzimidazole) (ABPBI)/sulfonated sepiolite (S-Sep) composite membranes (ABPBI/S-Sep) with low PA doping levels (DLs) were prepared via in-situ synthesis. The desirably enhanced mechanical, thermal, and oxidative stabilities of ABPBI/S-Sep composite membranes were achieved by constructing ABPBI chains arranged along the sepiolite (Sep) fibers and acid-base crosslinks formed between S-Sep fibrous particles and ABPBI chains. Benefiting from the richness of high temperature stable bound water and the excellent water absorbability of Sep particles that enable the formation of additive proton conducting paths, the composite membranes retained bounded PA and achieved much higher proton conductivities under both anhydrous and hydrous conditions compared to PA-doped ABPBI membranes. Proton conductivity values above 0.01 S/cm at 40–90 °C/20–98% RH conditions and 90–180 °C/anhydrous conditions as well as peak power density of 0.13 and 0.23 W/cm2 at 80 and 180 °C with 0% RH, respectively from the ABPBI/2S-Sep composite membrane are more holistic compared to Nafion at low temperatures and polybenzimidazole-based membranes at high temperatures, respectively. The excellent properties of ABPBI/S-Sep composite membranes suggest them as prospective candidates for PEMFCs applications in a wide temperature range.

For the application of proton exchange membrane fuel cells (PEMFCs) in a wide temperature range, an ionogel incorporated into poly(2,5-benzimidazole) (ABPBI) membranes with low phosphoric acid doping levels was designed. The natural sepiolite was first acid-treated to obtain one-dimensional silicon nanorods (SNRs) with a large specific surface area and a hierarchical porous structure. The SNRs were then filled with imidazolium ionic liquid (IL) to prepare IL@SNR ionogels. Analysis of related spectra and thermal behavior verified that the IL molecules were confined in the inner channels of SNRs. The as-prepared IL@SNRs were embedded in the ABPBI to form composite membranes (ABPBI/IL@SNRs) via in situ synthesis. By immobilizing proton conductors, the ABPBI/IL@SNR composite membranes markedly improved proton conductivity with low phosphoric acid doping levels in a wide temperature range. A single-cell based on 5 wt% IL@SNRs embedded in a composite membrane achieved a maximum power density of 0.15 and 0.28 W cm−2 at 80 °C and 180 °C, respectively, with 0% RH. The proton conductivities were comparable to those of Nafion-based PEMFCs under the same temperature and humidity conditions and competed with those of reported polybenzimidazole–inorganic composite membrane-based PEMFCs at high temperatures. By using a facile method to prepare nanostructured fillers, the strategy of avoiding proton carrier wastage can be potentially used in the production of high-performance membranes for PEMFCs.

Novel organic-inorganic composites were in-situ synthesized by using TriSilanolPhenyl polyhedral oligomeric silsesquioxane (SO-POSS) as fillers and poly(2,5-benzimidazole) (ABPBI) as polymer matrix. The uniformly dispersed 3% SO-POSS particles in ABPBI matrix increased the thermal stability of the composite membranes. It was found that both the water and H3PO4 uptakes were increased significantly with the addition of SO-POSS due to the formation of hydrogen bonds between the POSS and H2O/H3PO4, which played a critical role in the improvement of the conductivity of the composite membranes at temperature over 100 °C. Proton conductivities of H3PO4 doped with 3wt% SO-POSS contained ABPBI membranes increased with the increase of H3PO4 absorbance, reaching the maximum proton conductivity of 2.55 × 10-3 S·cm-1 at 160 °C, indicating that the ABPBI/SO-POSS composite membrane could be a promising candidate for mid-temperature PEMFCs.

In this study，nanocomposites of LaCePr-oxide (LCP) and Ni 0.8 Co 0.15 Al 0.05 LiO 2-δ (NCAL) with different contents of polyvinylidene fluoride (PVDF) were prepared and applied to solid oxide fuel cells. The composite materials were characterized by X-ray diffraction analysis (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and electrochemical impedance spectrum (EIS). The effect of PVDF concentration on the conductivity and performance of the fuel cells was investigated. It was found that PVDF plays a template role of pore forming in the nanocomposites, and the changed microstructure by as-formed pores greatly influences the electrochemical property of the nanocomposites. The cell with 3 wt% PVDF heat-treated at 210 °C achieved the highest power density of 982 mW cm −2 at 520 °C, which enhanced performance by more than 57% than when no heat-treatment was implemented. It is 66% higher than the cell with no PVDF and no heat-treatment. Pores formed by PVDF after heat-treatment enlarged the triple phase boundary (TPB), which results in improved fuel cell performance.

Phosphoric acid doped polybenzimidazoles are among the most interesting proton exchange membrane materials for high temperature proton exchange membrane fuel cell applications. As a major challenge the proton conducting decline due to free phosphoric acid leaching during the long term fuel cell operation is addressed by fixing overmuch phosphoric acid in the polymer matrix. Novel organic-inorganic composite membranes are prepared via in situ synthesis of poly(2,5-benzimidazole) (ABPBI) and OctaAmmonium POSS (AM-POSS) hybrid composites (ABPBI/AM-POSS) following phosphoric acid doping and membrane casting procedures. Compared with the pristine ABPBI membrane, the introduction of AM-POSS into ABPBI polymer membrane caused water and phosphoric acid absorbilities increasing dramatically, resulting in the significant increase of proton conductivities at whether hydrous or anhydrous condition. ABPBI/3AM composite membranes with phosphoric acid uptake above 250% showed best proton conductivities from room temperature to 160 °C, indicating these composite membranes could be excellent candidates as a polymer electrolyte membrane for low and intermediate temperature applications.

Although the investigation of thermal damage in composite materials has increased, the short-term thermal degradation and decomposition mechanisms in a non-oxidative environment have not been well established, as the reported thermal damage results were heavily influenced by the analyses of delicately collected volatiles and the presence of oxygen. The aim of this study, using scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetry, along with kinetics, was to develop a post-mortem solid residual-based microscopic characterising methodology for thermal damage in carbon/epoxy composites induced by simulated lightning strikes. Fibre tufting, resin sublimation and discolouration were found to represent the severity of damage in three damage zones. Whilst fibre tufting was caused not by thermal sublimation but by returning shock waves, resin sublimation and discolouration were dominated by Joule heating. The carbon concentration in the damaged zones was found to radially decrease outwards and vice versa with oxygen. Decomposition started from epoxy dehydration, accompanied by discolouration and formation of water and carbonyl, and released chemical compounds like 2-propenal, acetylene and carbonyl-containing aromatic ether. The successful identification of these unique heating-formed functional groups provided the confirmation of the proposed methodology.

The effect of nanoclay cloisite Na + on the mechanical and conductive properties of ionic liquids (ILs) doped sulfonated ABPBI (SABPBI) composite membranes for high temperature proton electrolyte membrane (PEM) applications were investigated in this report. The composite SABPBI membranes with well-dispersed cloisite Na + showed great improvement in mechanical properties with the increase of over 90% in ultimate tensile strength and 40% in Young's modulus, respectively, compared with those of pristine ABPBI membrane. The ILs absorption was also increased due to the incorporation of well-dispersed cloisite Na + , resulting in significant increase in the ionic conductivities of SABPBI membranes at the temperatures above 100 °C. The highest conductivities were 4.0 × 10 −2 S/cm at 220 °C for [HMIM]Cl doped 3 wt% SABPBI composite membranes (doping level 1.32), and 9.6 × 10 −3 S/cm × 10 −3 S/cm at 220 °C for [TMG][BF 4 ] doped SABPBI composite membranes (doping level 1.37), respectively.

Two different synthesis methods, viz. precipitation and hydrothermal treatment, were used to synthesise ultra-fine α-alumina powders from aluminium chloride, ammonia solution and TEAH (tetraethyl ammonium hydroxide). XRD, BET surface area analysis, TEM and FEG-SEM were used to characterise the powders produced. The presence of industrial α-alumina powder as seed particles did not affect the transformation to α-alumina phase during the hydrothermal treatment at 220 °C, either in basic or acidic environments. The results obtained from the precipitation route, however, showed that the combined effect of adding α-alumina seeds and surfactants to the precursor solution could lower the transformation temperature of α-alumina from about 1200 °C for unseeded samples to about 800 °C, as well as reducing the level of agglomeration in the alumina powders. The difference in transformation temperature mainly results from the nucleation process caused by the α-alumina seeds, which enhanced the θ→ α transformation kinetics. The lower level of agglomeration present in the final powders could be due to a surface modifying role of the surfactants, preventing the particles from coalescing during the synthesis process.

Novel organic-inorganic composite membranes involving poly(2,5-benzimidazole) (ABPBI) and polyhedral oligomeric silsesquioxane (POSS) were prepared via in-situ synthesis followed by phosphoric acid doping. The formation of composites was characterized by SEM, XRD and FTIR. The results of water uptake showed that POSS cores emerged extraordinary water absorbability. When doping in phosphoric acid solution, phosphoric acid absorption in composites was dominated by functional groups linked to POSS cores. The excellent proton conductivities i.e. above 0.1S/cm at 100~160oC achieved from anhydrous ABPBI/OA-POSS composite membranes with 241wt.% of phosphoric acid absorption, make them very good candidates as the membranes for high temperature polymer electrolyte membrane fuel cell (PEMFC) applications.

Sodium-montmorillonite (MMT) was modified with two types of AP-POSS and OA-POSS and dual-surfactants (POSS with a ditallow-based second surfactant: 04AP-POSS/08DTDMA and 04OA-POSS/08DTDMA), respectively, via ion-exchange reaction. The interlayer space, interlamellar structure, thermal and surface properties of these organo-montmorillonites were investigated by X-ray diffraction, thermogravimetric analysis, and contact angle measurement. The interlayer space of POSS modified clay was strongly dependent on the arrangement of POSS surfactants, but less on the POSS concentration. The POSS modified montmorillonites have partially exchanged silicate surfaces and good thermal stabilities due to steric hindering and thermal stability of the POSS molecules. Dual-surfactant modified montmorillonites showed higher exchange ratio and possessed better compatibility with PA12 due to the lower interfacial free energy. Polyamide 12-montmorillonite nanocomposites were prepared by conventional melt compounding with the four POSS based organo-montmorillonites. The best dispersion of modified montmorillonite was observed for 3 mass% 04AP-POSS/08DTDMA/MMT filled PA12 nanocomposites, which resulted in the best mechanical performance with an increase of 60% in tensile modulus and 10% in yield strength, respectively, compared to that of pure PA12. Compatibility between montmorillonites and polymer was not the only key factor affecting dispersion, thermal stability and interlayer space were also crucial for good dispersion of montmorillonites in polymer matrix.

Sodium montmorillonite (Na-MMT) was modified with various amounts of aminopropylisooctyl polyhedral oligomeric silsequioxane (POSS) and a second surfactant (alkyl ammonium based) via ion-exchange reactions. Interlayer spacing, interlamellar structure, and thermal and surface properties of these organoclays were characterized by wide angle X-ray diffraction, thermogravimetric analysis, and contact angle measurement. The interlayer space of POSS-modified clay (POSS-MMT) was strongly dependent on the arrangement of POSS surfactant but less dependent on the POSS concentration. The sodium ions in Na-MMT were only partially exchanged by protonized POSS due to the steric hindrance effect. In addition, the dual-surfactant-modified clays exhibited increased exchange ratios by controlling the amount of the second surfactant, resulting in a good balance in hydrophobicity and polarity of the modified clays. The resultant organoclays were mixed with polypropylene (PP) via a melt-compounding method. It was found that the dual-surfactant-modified clays with low polarity and similar hydrophobicity to PP were well dispersed in the PP matrix.

Polyamide 12/Trisilanolphenyl-POSS (PA 12/POSS) composites were prepared via melt-compounding. The effect of polyhedral oligomeric silsesquioxane (POSS) on crystalline structure and crystalline transition of PA 12 was investigated by wide-angle X-ray diffraction (WAXD) and real time fourier transform infrared spectroscopy (FTIR). WAXD results indicated that PA 12 crystallized into γ-form as slowly cooling from melt and the presence of POSS did not influence the crystalline structure of PA 12. Both PA 12 and PA 12/POSS composites underwent Brill transitions when they were heated from room temperature to melt point. Real time FTIR patterns showed that an absorption band at 697 cm−1 ascribed to Amide V (α) mode was emerged along with the disappearance of Amide VI (γ) band at 628 cm−1 with the increase of the temperature for PA 12 and PA 12/POSS composites, which suggested that the γ-form crystalline has transformed into α form. The Brill bands were identified and the transformed mechanism was discussed based on the real FTIR results. The addition of POSS enhanced the tensile strength and thermal stability of PA 12.

Commercially available organoclay (Closite 30B) was modified by using 3-aminopropyltriethoxysilane (APS) via a silylation reaction. Sodium clay (Closite Na) was treated by APS directly as a control. Such modified clays were further melt-compounded with polybutylene terephthalate (PBT). The morphology and properties of the modified organoclays were characterized with X-ray diffraction (XRD), transmission electrical microscopy (TEM), Infra-red spectroscopy, contact angle measurement, and thermogravimetric analysis (TGA). The effects of modified clays on the crystallization behavior of PBT were characterized by differential scanning calorimetry. The basal spacing of Closite Na was enlarged from 1.01 to 1.41 nm after APS treatment, indicating that the APS was intercalated into the clay intergalleries as a monolayer. The basal spacing of Closite 30B increased slightly after APS treatment, partially resulted from the reactions between the APS and hydroxyl groups on the intercalant of Closite 30B. Closite 30B was found to be exfoliated disorderly after melt-compounded with PBT. The APS-modified Closite 30B only dispersed as swollen elliptical clay aggregates, in which the silicate layers were orderly intercalated. TGA results showed that the decomposition temperature at 5% weight loss of Closite 30B was increased from 250 to 270°C after APS treatment. A significant increase in the degree of crystallinity of PBT was observed in the exfoliated PBT/30B composite.

© 2014 Society of Plastics Engineers. The influence of untreated and stearic acid surface pretreated calcium carbonate (CaCO3) nanofiller (U1 - untreated CaCO3 and U1S2 - stearic acid treated CaCO3) on the properties of polyurethane/poly(vinyl acetate) (PUR/PVAC) polymer blends was investigated. Adhesion between fillers and polymers in the polymer blend composite, and filler position in regard to the polymer phases, are predicted on the basis of calculated adhesion parameters and wetting factor ωa of PUR, PVAC, U1, and U1S2. U1 is located in the PUR matrix phase and U1S2 is located at the interface between matrix PUR domain and dispersed PVAC domain. Polymer blend composites with predominant U1S2 showed lower tensile strength and elongation compared to these of polymer blend composites with predominant U1 mainly due to the fillers' different surface properties, which confirmed that the mechanical properties of polymer blend composites were dependent on overall system morphology rather than the filler location.

A water-in-oil microemulsion, water-in-cyclohexane stabilized by poly(ethylene glycol) tert-octylphenyl, was developed to prepare poly(methacrylic acid) (PMAA) particles. Up to 100% conversion of the amphiphilic monomer, methacrylic acid (MAA), which could not be converted to the polymer efficiently in a dioctylsulfosuccinate sodium salt/toluene microemulsion, was achieved. The viscosity-average molecular weight of the PMAA prepared was 1.45 105 g/mol. The effects of some polymerization parameters, including the reaction temperature and the concentrations of the initiator and the monomer, on the polymerization of MAA were investigated. The results showed that the polymerization rate of MAA was slower than that of acrylamide in the microemulsions reported in the literature. The degree of conversion increased with the initiator concentration, reaction temperature, and monomer concentration. However, the stable microemulsions became turbid during the polymerization when the reaction temperature was at 70°C or at a high monomer concentration (40 wt %) The synthesized PMAA particles were spherical and had diameters in the range of 50 nm.

Sol–gel processing is an advantageous route to produce PZT thin film materials with high quality. PZT powders and thin films with good properties were fabricated by sol–gel processing, using acetylacetone as modifier, in the study. The morphologies of PZT powders and thin films were observed by field emission microscopy, and the dielectric and properties of the PZT thin films were measured. Thermal analysis, XRD and FTIR were used to investigate the influence of ligands on the phase transformation in PZT materials, and it is found that the difficulty of decomposing acetylacetone ligands completely resulted in a higher pyrolysis temperature to form PZT with pure phase.

A solution of a polymeric precursor for silicon carbide (SiC) was subjected to electrostatic atomization in the cone-jet mode to spray droplets on a zirconia substrate. The resulting deposit was heated to 1300 °C to obtain SiC relics. Precursor and ceramic relics were characterized by microscopy. The size distribution of the droplet relics was studied at several flow rates of the solution to the electrostatic atomization chamber. The results show that by controlling the flow rate SiC relics approximately 5 μm in diameter can be produced.

Silicon carbide (SiC) coatings and films have been prepared for the first time by electrostatic atomization of a solution of a polymeric precursor and deposition on to alumina and zirconia substrates. The deposits were heated to 1300 degreesC prior to their examination by X-ray energy-dispersive spectra and selected-area diffraction in scanning and transmission electron microscopes. The results show that these coatings and films are crystalline and probably consist of co-existing alpha -SiC and beta -SiC phases.

A polysilane solution used as a silicon carbide (SiC) precursor was mixed with different amounts of titanium carbide (TiC) powder and open cell polyurethane (PU) foams were dipped in these suspensions. The resulting pre-foams were pyrolyzed at 900°C in nitrogen and then heated further at various temperature between 1100 and 1600°C in the same atmosphere to produce SiC–TiC composite foams. The evolution of the composite foams has been studied using thermogravimetry and X-ray diffraction. The PU foam, pre-foams and the SiC–TiC composite foams were characterized by optical and scanning electron microscopy. These studies show that the pre-foams retained their shape well during pyrolysis and the composite foams produced consist of an open cell structure and hole-free solid struts. Prevention of cracking in the foams were dependent on the TiC content. The shrinkage observed during the conversion of the pre-foams to the composite ceramic foams can be controlled by varying the TiC content and the sintering temperature.

A polysilane was used as the precursor for silicon carbide (SiC) and different amounts of it was dissolved in dichloromethane. Subsequently, between 10 to 80 %wt of alumina (Al2O3) powder was added into the solutions to make SiC-Al2O3 suspensions. Cubes of polyurethane (PU) foams with open cells in the size range 500-1200μm were soaked in these suspensions and pyrolysed in flowing nitrogen to produce SiC-Al2O3 composite foams. Some foams were heated further in nitrogen to 1300°C. The foams produced consist of an open cell structure and hole-free solid struts which were also cracks free in the polysilane-Al2O3 80:2Owt% formulation. The retention of shape during processing was excellent. Shrinkage observed after pyrolysis and further heating the foams was measured and can be controlled by varying the Al2O3 content. The foams produced have porosities in the range 87 to 95%. The maximum compressive strength of the pyrolysed foams prepared using the polysilane-Al2O3 80:20 wt% formulation was 2.3MPa.

A new method of forming silicon carbide–silicon nitride composite foams is presented. These are prepared by immersing a polyurethane foam in a polysilane precursor solution mixed with Si3N4 powder to form a pre-foam followed by heating it in nitrogen at >900°C. X-ray diffraction patterns indicate that a SiC–Si3N4 composite was formed after sintering the ceramic foam at >1500°C. Micrographs show that most of these foams have well-defined open-cell structures and macro-defect free struts. The shrinkage is reduced considerably due to the addition of Si3N4 particles.

A simple method was developed to produce silicon carbide foams using polysilane polymeric precursors. Polyurethane foams were immersed in polysilane precursor solutions to prepare pre-foams. Subsequently, these were heated in nitrogen at different temperatures in the range of 900°C to 1300°C. The silicon carbide foams produced in this manner showed well-defined open-cell structures and the struts in the foams were free of voids. The shrinkage which accompanies pyrolysis of the pre-foams was reduced with increasing the concentration of the polymeric precursor solutions.

Several new polycyclodisilazanes with different molecular structures were synthesized and characterized using gel permeation chromatography and Fourier-transform infrared spectroscopy. All the polymers synthesized were tractable. The pyrolysis of these polymers at 900°C in nitrogen in a thermal balance indicated that the ceramic yields were very dependent on the compositions of the precursors. The polycyclodisilazanes with reactable groups (Si–H, N–H) showed higher ceramic yields due to the cross-linked structures formed during pyrolysis. The pyrolyzed residues were crystallized by heating to >1500°C. X-Ray diffraction of the crystallized residues showed that they were mixtures containing silicon nitride and silicon carbide. Chemical analysis of one crystallized residue which gave the highest ceramic yield showed that it contained 70 wt% Si3N4 and 25 wt% SiC after heat treatment at 1600°C. The compositions of the ceramic residues produced depended on the compositions of the polymeric precursors. More silicon carbide was formed in the residues derived from the polymers with phenyl group substituents.

A series of 4′-[(carbonyloxy-1,1,2,2 Tetrahydrofluorodecyl)]-4 -(ω-bromo-alkenyloxy) azobenzenes, 4′-[(carbonyloxy-1,1,2,2-Tetrahydrofluorodecyl)]-4-(alk-1-enyloxy) azobenzenes have been synthesized. Also, a polyacrylate has been formed by phase transfer catalyzed reaction between one of the ω-bromo-alkenyloxy compounds and sodium polyacrylate as well as two polysiloxanes formed by hydrosilylation of the alkenyloxy compounds and a polyhydrosilane. All of the low molar mass compounds show the S A phase on heating and an increase in perfluoroalkyl chain length results in an increase in clearing temperature whilst an increase in the hydrocarbon chain length shows a decrease in clearing temperature. Upon grafting these low molar mass units to a polymer backbone, the resulting materials also show smectic mesophases despite having quite low clearing entropies (ΔS/R to approximately 0.2-0.6). The precursor polymers are of low molar mass (Mw 1200-1800 g mol -1) and this may be the reason why the polymers do not show glass transition temperatures.

A new method that can be used for the synthesis of SiC-Si3N4 composites using a single polymeric precursor is described. A co-polysilane-cyclodisilazane precursor was prepared and characterized. Subsequently, it was heated to 1650oC to form SiC and Si3N4 simultaneously. The ceramic products have been characterized using X-ray diffraction and secondary-ion mass spectrometry.

Three strategies for the synthesis of silicon carbide–silicon nitride composites from organosilicon preceramic polymers were investigated. Firstly, polymeric precursors with reactive groups for silicon carbide and silicon nitride were synthesized, blended and pyrolyzed. Secondly, a polymeric precursor for silicon carbide was mixed with silicon powder which acts as a reactive filler and the resulting mixtures were pyrolyzed. Thirdly, a co-polycyclodisilazane–silane single polymeric precursor was synthesized and pyrolyzed. The precursors and the various stages of processing were studied using gel permeation chromatography, Fourier transform-infrared spectroscopy, thermo-mechanical analysis, thermogravimetry and X-ray diffraction. In each instance silicon carbide–silicon nitride composites were prepared successfully.

Several polysilanes with different overall functionalities have been synthesized and pyrolyzed to produce porous silicon carbide. The polysilanes and their ceramic products have been characterized using gel permeation chromatography, Fourier transform-infrared spectroscopy, thermogravimetry, X-ray diffractometry and microscopy. Some products were foams while others were micro-porous ceramics. The effect of the final pyrolytic yield on the Type of ceramic produced, its pore structure and shape retention are discussed. Two polysilanes were blended in various ratios to control the pyrolysis process more precisely. This allowed the Type, shape and pore-structure of the silicon carbide produced to be controlled more efficiently. There exists a relationship between the composition and structure of the precursors and their final pyrolytic yield and this determines the Type, shape retainability and pore structure of the ceramics produced. In this work, precursors or their blends which gave a final pyrolytic yield of 50–60 wt % produced the best silicon carbide foams.

Several polysilanes, including two groups of copolymers and a group of ter-polymers, with overall functionalities ranging between 2 and 3 were prepared using the alkali metal dechlorination reaction. The yields of the soluble solid fractions of these polymers (the potential ceramic precursor) were in the range 40–70% wt and decreased with increasing overall functionalities in both cases of co- and terpolymers. The molecular weights and FT-IR spectra of the precursors have been determined and the ceramic in the residue after pyrolysis has been identified as silicon carbide. The pyrolytic yield can be increased by using a polymeric precursor of higher overall functionality. The reasons for this are discussed with reference to pyrolysis mechanisms. In particular, some of the ter-polymeric precursors synthesised with a high yield also give a high yield on pyrolysis due to the presence of branched structures and potential cross-linking sites.

Polyacrylates with a 3-nitro-4-(1,1,2,2- tetrahydroperfluroalkyl) benzoate unit as a side chain substituent have been synthesised. These materials form rare examples of side chain thermotropic polymers containing a single aromatic unit. These polymers form smectic phases only. The phase behaviour has been investigated by optical microscopy and d.s.c.

On studying the thermal behaviour of a series of 1,1,2,2-tetrahydro-perfluoroalkyl 4-nitrobenzoates it was found that the decyl and dodecyl compounds showed smectic mesophases. This illustrates that a polar substituent in the 3-position of the aromatic ring for 1,1,2,2-tetrahydroperfluoroalkylbenzoates is not a requirement for thermotropic behaviour.

This paper reports the application of dual-surfactant, thermally stable organoclays (OC) to the production of poly(butylene terephthalate) (PBT) nanocomposites by the masterbatch method. A common failing of single surfactant organoclays is their thermal instability at high polymer processing temperatures, such as that used for PBT (235 °C). This can be overcome by first modifying the clay mineral with a thermally stable surfactant such as aminopropyl-POSS (AP-POSS). In this study, sodium montmorillonite (Na+Mt) was sequentially modified with AP-POSS and ditallowdimethylammonium chloride by ion-exchange reaction to give dual-surfactant organoclay (OC). This dual surfactant clay mineral was then used to prepare masterbatches comprising 40% clay mineral intercalated with CBT polymerized by ring-opening polymerization. The masterbatches were then processed with PBT by melt compounding to give PBT-clay nanocomposites whose morphology was studied by XRD and TEM and mechanical properties were assessed by tensile testing. Spectral examination showed that the dual surfactant clay mineral was readily intercalated by PBT, while electron microscopy revealed that an intercalated/exfoliated micromorphology was achieved. The elastic modulus and tensile strength of PBT were increased by inclusion of dual-surfactant clay, while the reduction in elongation typically associated with nanoclay inclusion was mitigated by the dual surfactant clay. The possible antagonism of the catalyst used in the ring-opening polymerization and the reinforcing effect of the dual surfactant clay is also discussed.

The use of polymeric precursors to produce ceramics is generating considerable interest . Owing to distinct advantages in processability, polymeric precursors have found applications in many areas such as ceramic fibers, foams and coatings. Ceramic coatings, in particular, are of immediate value in industry as a means of providing wear and corrosion resistance for articles used in adverse environments. The coating of engineering parts with ceramics using polymeric precursors is a relatively easy, quick and low-cost process compared with other processing methods such as chemical vapor deposition and plasma-coating.

During the last decade porous ceramic materials have been finding increasing applications due to their favorable properties such as high temperature stability, high permeability, low mass, low specific heat capacity and low thermal conductivity. These characteristics are essential for many technological applications such as catalyst supports, filters for molten metals and hot gases, refractory linings, thermal and fire insulators and porous implants [1, 2]. Ceramic foams can be produced by different methods, principally impregnation of polymer foams with slurries containing appropriate binders and ceramic particles followed by pressureless sintering at elevated temperatures [2–5]. This involves coating an open-cell polymeric sponge with a ceramic slurry several times, pyrolysis of the polymer to form a ceramic skeleton followed by sintering. Ceramic foams produced by this method are generally of low strength as their struts are thin and can contain a hole in the center [2, 6–8]. Recently, a new method to produce silicon carbide (SiC) foams using polymeric precursor solutions was developed by Bao et al. [9] where a polyurethane foam was immersed in a polymeric precursor solution to form a pre-foam which was pyrolyzed in nitrogen. The main advantages of this new approach are the simplicity and ease of control of structure of the final product. This new process was exploited further to prepare silicon carbide-silicon nitride (SiC-Si3N4) composite foams [10]. In this letter we provide microstructural evidence of the improvements in structure of the ceramic foams produced by our method. The polysilane precursor discussed in this study was synthesized by the alkali dechlorination of a combination of chlorinated silane monomers in refluxing toluene/tetrahydrofuran with molten sodium as described previously [11, 12]. The structure of the SiC polysilane precursor synthesized is given below. Ph indicates a phenyl group.

Novel porous aminopropyllsooctyl polyhedral oligomeric silsesquioxane (POSS) modified montmorillonite clay complexes (POSS-Mts) with large interlayer distance and specific surface area have been successfully prepared via ion-exchange reaction and followed by freeze-drying treatment. The morphology of the POSS-Mts is highly influenced by the POSS concentration, pH of the suspension and drying procedure, but the interlayer distance of the POSS-Mts does not change much when the POSS concentration is above 0.4 CEC. The POSS-Mts were used as Sn-catalyst supporters to initiate the ring-opening polymerization of cyclic butylene terephthalate oligomers (CBT) for the first time. No diffraction peak was detected by wide-angle X-ray diffraction for the polymerized composites (pCBT/POSS-Mt), even at 10 wt % loading of POSS-Mt. A clay network rather than exfoliation structure was observed unexpectedly in the composites by transmission electron microscopy. The pCBT/POSS-Mt composite with 10 wt % POSS-Mt was further melt-compounded with commercial PBT resin as a master batch. The tensile properties of the resultant PBT/POSS-Mt composites were highly improved as compared to the pristine PBT due to the homogeneous dispersion of POSS-Mt in the PBT matrix.

The use of polymeric precursors for the preparation of ceramic materials is generating a great deal of interest, and silicon carbide (SiC) has been produced by the pyrolysis of several polymers. However, it is desirable to develop precursors that can be prepared with a high polymer yield, are melt-processable, and give a high SiC yield on pyrolysis close to the theoretical maximum that can be obtained (with a low amount of impurities).