Thermal behaviour and mechanical properties of novel RTV silicone rubbers using divinyl-hexa[(trimethoxysilyl)ethyl]-POSS as cross-linker

Divinyl-hexa[(trimethoxysilyl)ethyl]-POSS (DVPS) as an octavinyl-POSS derivative was first prepared. A series of novel polydimethylsiloxane (PDMS)/DVPS hybrid materials as room temperature vulcanized (RTV) silicone rubber were prepared. The chemical incorporation of novel POSS into hydroxyl-terminated PDMS system by hydrolytic condensation reaction was verified by attenuated total reflection (ATR) infrared spectroscopy. Thermal degradation, thermo-oxidative stability and mechanical properties of these novel RTV silicone rubbers were studied by means of thermogravimetric analysis and tensile testing. The results exhibited significantly enhanced effects on the thermal stabilities and mechanical properties as compared to the PDMS polymer prepared with tetraethoxysilane (TEOS). The observed improvements in thermal properties could be attributed to the effective three-dimensional network structures resulting from the structure of DVPS. The thermal decomposition of the RTV silicone rubbers in nitrogen was also monitored by TGA coupled with real-time FTIR, and the degradation residues were also characterized by FTIR. It was found that the POSS cross-linker facilitated the formation of cross-links in the degradation residues. The striking improvement in mechanical properties could be attributed to the synergistic action of the structure of three-dimensional multi-arm cross-linker (vinyl-POSS derivative), the plasticization of self-cross-linking Vinyl-POSS derivative and perfect distribution of vinyl-POSS derivative.     

Influence of polyhedral oligomeric silsesquioxanes (POSS) on blue light-emitting materials for OLED

By using Heck polycondensation, we have synthesized carbazole-based alt-copolymers tethered with polyhedral oligomeric silsesquioxanes (POSS), which had well-defined architectures, similar polymerization degrees and the different contents of POSS. The effect of POSS content and the length of the side chain containing POSS on the electroluminescence properties of these polymers were investigated. POSS particles in these alt-copolymers showed excellent dispersity and prevented the interchain aggregation of polymers in film state well. Besides, POSS benefited charge balance by increasing the electron current density, which led to a higher luminance and current efficiency, as well as purer blue light-emitting.     

Effect of silica content on thermal stability of fumed silica/epoxy composites

Composites of a fumed silica industrial residue and an epoxy resin were prepared and their thermal stability and thermal degradation behaviour were studied by TGA in air. Classical thermal stability parameters, based on the initial decomposition temperature (IDT), temperature of maximum rate of mass loss (T_max) and integral procedure decomposition temperature (IPDT) were calculated before and after subtraction of the filler mass from the TGA curves. Without filler mass subtraction, the thermal stability of the epoxy resin seems to be improved and the mass loss rate was reduced by the addition of fumed silica. Nevertheless, after subtraction of the filler mass, the thermal degradation behaviour of the resin was only slightly affected by the silica content. A possible negative effect of the silica content on the cure was also found.     

Phenolic resin/polyhedral oligomeric silsesquioxane (POSS) composites: Mechanical,ablative, thermal,and flame retardant properties

Three different polyhedral oligomeric silsesquioxanes (POSS), trisilanolphenyl polyhedral oligomeric silsesquioxane (T‐POSS), octaaminophenyl polyhedral oligomeric silsesquioxanes (OAPS), and octaphenyl polyhedral oligomeric silsesquioxanes (OPS) were incorporated into phenolic resin (PR), respectively; PR/POSS composites were successfully prepared, and the properties of PR/POSS composites were studied. The limiting oxygen index (LOI), cone calorimeter, and thermal gravimetric analysis (TGA) were used for the estimation of flame retardancy and thermal stability. Oxyacetylene flame test and flexural strength test were used to study the ablative and mechanical properties of the PR/POSS composites. The results indicated that T‐POSS was more effective in improving the flame retardancy of PR than OAPS or OPS. Meanwhile, compared with pure PR, the second line ablation rates of PR/4% T‐POSS, PR/4% OAPS, and PR/4% OPS were significantly reduced by 53.3%, 61.9%, and 40.0%, respectively. In addition, the thermal stability and flexural strength of PR/4% T‐POSS were significantly higher than that of all other PR composites.     

POSS‐based poly(aryl ether sulfone)s random terpolymer linked POSS to the main chain: effect of chemical structure and POSS content on properties

In order to investigate the effect of polyhedral oligomeric silsesquioxane content and the structure‐function related on the dielectric property and hydrophobicity, three kinds of poly(aryl ether sulfone)s (PAESs) random terpolymer with different chemistry structure at variable polyhedral oligomeric silsesquioxane content in the main chain are prepared. The structures of PAESs are characterized by infrared (IR), nuclear magnetic resonance (NMR), and wide‐angle X‐ray diffraction (WXRD) spectra. The results show that the dielectric constant initially increases then decrease to 2.68 at 100%‐double‐decker silsesquioxane (DDSQ)‐PAES(molar content of DDSQ = 100%) at 1 MHz. The contact angle increased to 97.5° at 100%‐DDSQ‐PAES. While the chemical structure of organic chains also plays an important role on thermostability, dielectric, and hydrophobic properties. The results are discussed and interpreted in detail. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of the modification of silica on thermal properties and flammability of cross-linked butadiene-acrylonitrile rubbers

The paper presents the results of testing the thermal stability and flammability of butadiene-acrylonitrile rubber vulcanizates with different contents of combined acrylonitrile: Perbunan NT 1845 and Perbunan NT 3945 from Bayer, containing unmodified and bromine- or iodine-modified silica. The test results were obtained with the use of a derivatograph, measurements of flammability by the method of oxygen index, in air and also with the use of a cone calorimeter. The effect of the modification on the zeta potential was also examined. A considerable reduction in the flammability of nitrile rubber vulcanizates filled with silica can be obtained by the modification of filler with bromine or iodine. All the vulcanizates containing modified silica are self-extinguishing. An appropriate filling of NBR 39 vulcanizates with bromine-modified silica makes it possible to obtain non-flammable polymeric materials. They neither ignite nor glow under the action of a flame source for 30 s. The findings can be a rational basis for the synthesis of modified silica that can act as active filler and effective flame-retardant agent at the same time.     

Investigation of photo‐oxidative effect on morphology and degradation of mechanical and physical properties of nano CaCO3 silicone rubber composites

Photo‐oxidative degradation of treated and untreated nano CaCO₃: silicone rubber composite was studied under accelerated UV irradiation (≥290 nm) at different time intervals. Prolonged exposure to UV leads to a progressive decrease in mechanical and physical properties along with the change in behavior of filler‐matrix interaction. This was due to decrease in cross‐linking density with increase in mobility of rubber chains. Meanwhile, synthesized nano CaCO₃ was modified with stearic acid for uniform dispersion in rubber matrix. The increase in carbonyl (>CO), hydroxyl (? OH), CO₂, and alkene functional groups on the UV exposed surface of treated and untreated nano CaCO₃: silicone rubber composites at different time intervals was studied using Fourier transform infrared (FTIR) spectroscopy. The change in morphological behavior of filler‐matrix interaction after UV exposure was studied using SEM. Overall, the study showed that the treated nano CaCO₃: silicone composites were affected more by UV exposure than untreated nano CaCO₃: silicone composites and pristine composite after UV exposure. This effect was due to peeling of stearic acid from the surface of CaCO₃, which makes the rubber chains slippery and thus separation of filler and rubber chains takes place with initiation of fast‐degradation. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of surface modification of fumed silica on interfacial structures and mechanical properties of poly(vinyl chloride) composites

Poly(vinyl chloride) (PVC)-based composites were prepared by blending PVC with nano-SiO₂ particles, which were treated with dimethyl dichlorosilane (DMCS), γ-methylacryloxypropyl trimethoxy silane (KH570). The dispersion and interfacial compatibility of nano-SiO₂ particles in PVC matrix was characterized by SEM, which indicated that DDS had a better dispersion and compatibility than UTS but worse than KHS. The mechanical properties, processability and effective interfacial interaction of nano-SiO₂/PVC composites were studied. The nano-SiO₂ particles treated with KH570 or DMCS significantly reinforced and toughened the PVC composites. The maximum impact strength of PVC composites was achieved at a weight ratio of nano-SiO₂/PVC:4/100. The tensile yield stress increased with increasing the content of treated inorganic particles. The incorporation of untreated nano-SiO₂ particles adversely affected the tensile strength of the composite. Although the equilibrium torques of all nano-SiO₂/PVC composites were higher than that of pure PVC, the surface treatments did reduce the equilibrium torque. The interfacial interaction parameter, B, and interfacial immobility parameter, b, calculated respectively from tensile yield stress and loss module of nano-SiO₂/PVC composites, were employed to quantitatively characterize the effective interfacial interaction between the nano-SiO₂ particles and PVC matrix. It was demonstrated that the nano-SiO₂ particles treated with KH570 had stronger effective interface interaction with PVC matrix than those treated with DMCS, which also had stronger effective interface interaction than the untreated nano-SiO₂ particles.     

Synergistic effect of ammonium polyphosphate and layered double hydroxide on flame retardant properties of poly(vinyl alcohol)

A novel flame retardant system of poly(vinyl alcohol) (PVA) is prepared via using ammonium polyphosphate (APP) and layered double hydroxide (LDH). The flammability of PVA composites containing APP-based LDH at a 15 wt.% global percentage showed that the flame retardancy of all PVA/APP/LDH samples increase with the increase of LDH concentration in the range of 0.1-1.0 wt.%, and reach a LOI value of up to 33 and UL-94 V-0 rating for most composites. Thermo-gravimetric analysis reveals that PVA/APP/LDH samples show higher initial decomposition temperature in comparison with PVA/APP composite. The morphology and structures of residues generated during LOI test were investigated by scanning electronic microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the composition of the residue formed after thermo-oxidation to support a fundamental analysis for the mechanism of char formation. The test of mechanical properties demonstrated that LDH can enhance tensile strength, Young's modulus and elongation at break of PVA/APP composites.     

Synergistic effect between hydrophobic oxide nanoparticles and ammonium polyphosphate on fire properties of poly(methyl methacrylate) and polystyrene

Synergism on fire properties has been investigated between nano-sized hydrophobic oxides (alumina and silica) and ammonium polyphosphate (AP) flame-retardant additive. Thermal degradation of mixed additives (50% w/w) showed the impact of oxides on AP degradation. The effect of modified nanoparticles was compared with corresponding hydrophilic oxide as regards thermal and fire behaviour. The nanocomposites prepared by melt-blending were evaluated by thermogravimetric analysis and cone calorimetry measurements. Residues were characterized by ATR-FTIR spectroscopy, X-ray diffraction and SEM-EDX experiments. A noteworthy decrease of peak of heat release rate and smoke opacity as well as an increase of LOI were noticed with hydrophobic silica combined with AP both in PMMA and PS. This flame-retardant behaviour was ascribed mainly to the formation of a specific silicon metaphosphate (SiP₂O₇) crystalline phase which contributes to promote charring and an efficient insulating layer.     

Study on ablative properties and mechanisms of hydrogenated nitrile butadiene rubber (HNBR) composites containing different fillers

The ablative properties of hydrogenated nitrile butadiene rubber (HNBR) composites filled with fumed silica, organically modified montmorillonite (OMMT), or expanded graphite (EG) were examined. The HNBR/OMMT composite has the lowest linear ablation rate and the highest mass ablation rate and does not tend to be carbonized. On the other hand, the HNBR/EG composite has the highest linear ablation rate and the lowest mass ablation rate, and is prone to carbonization. The ablative properties of the HNBR/silica composite are between those of HNBR/OMMT and HNBR/EG. From the viewpoint of thermal shielding capability, the HNBR/OMMT has the best ablation resistance. Thermogravimetric analysis (TGA) on different HNBR composites indicated that the filler type has no significant effect on the thermal stability of the composites. To understand the ablation mechanisms, the char layers of different HNBR composites after ablation experiments were characterized by scanning electron microscopy (SEM), energy disperse X-ray spectroscopy (EDS), and wide-angle X-ray diffraction (WAXD). The results showed that the porosity in the char layers of the HNBR/OMMT composite was the highest and the corresponding structure was the loosest of the three composites. The montmorillonite (MMT) dispersed in HNBR experienced phase transition, melting and vaporization when exposed to the flame with the temperature over 2000 °C. Fumed silica only melted at such situation. On the other hand, the EG kept their original crystalline structures after the ablation test. Based on these results, the effect of the filler type on the ablation mechanisms of the HNBR composites was discussed.     

Effects of incorporation of modified silica nanoparticles on the mechanical and thermal properties of PMMA

Silica nanoparticles of various sizes have been incorporated by melt compounding in a poly(methyl methacrylate) (PMMA) matrix to enhance its thermal and mechanical properties. In order to improve nanoparticles dispersion, PMMA grafted particles have been prepared by atom transfer radical polymerization (ATRP) from well-defined silica nanoparticles. This strategy was expected to ensure compatibility between both components of the PMMA nanocomposites. TEM analysis have been performed to evaluate the nanosilica dispersion whereas modified and non-modified silica/PMMA nanocomposites thermal stability and mechanical properties have been investigated by both thermogravimetric and dynamical mechanical analysis.     

Effect of nano-filler dispersion on the thermal, mechanical and water sorption properties of green environmental polymer

Partially exfoliated nanocomposite（2） has been synthesized by intercalation of poly（propylene carbonate）（PPC） into commercial clay,Cloisite 20B（PPC/C-20B）.Nanocomposite 2 was characterized phiso-chemically and exhibited high thermal,mechanical and anti-water sorption properties as compared to PPC and intercalated nanocomposite（1） of PPC/C-20B having same amount of clay.TGA results revealed that the thermal decomposition temperature(T_d,50%) of 2 increased significantly,being 40 K and 17 K higher than that of pure PPC and 1,respectively,while DSC measurements indicated that the nano-filler dispersion of 2 increased the glass transition temperature from 21℃to 31℃.Accordingly,2 showed high elastic modulus,hardness and anti-water absorption capacity.These thermal,mechanical and anti-water absorption improvements are of great importance for the application of PPC as packaging and biomaterials.     

Effect of thermal cycling and open-hole size on mechanical properties of polymer matrix composites

This paper investigates the effects of thermal cycling on mechanical degradation of polymer matrix composites (PMCs). Un-notched and open-hole specimens are tested using developed thermal cycling apparatus and tensile test machine. In addition, the hole-size effect of open-hole tension glass/epoxy composite laminates is investigated. The tensile strength, mass loss and surface degradation of the specimens were obtained during 250 cycles. Experimental results showed that the holes diameter is the main parameter to control the thermal cycling effects on open hole structure. Also, it is found that laminates with smaller holes have higher tensile strength variation than those with larger holes. The results showed that increment of the hole diameter and number of cycles decreases the tensile strength.     

The effect of preparation temperature on the mechanical and antibacterial properties of poly(vinyl alcohol)/silver nitrate films

There has been a growing interest in developing antibacterial polymeric materials. The logical consequence following development of a new material is optimisation of its processing conditions and investigation of the influence of processing parameters on functionality of a given material. The present work deals with investigation of the effect of preparation temperature on the mechanical and antibacterial properties of polymer films based on poly(vinyl alcohol) (PVA) and silver nitrate (0, 1, 3, 5, 7, 9 wt.% silver content). The mechanical properties of the films prepared at various temperatures (25, 35, 50, 60, 75 °C) were characterized by using stress-strain analysis. Antibacterial properties were determined by using an agar diffusion test and a dilution and spread plate technique against both Gram positive (Staphylococcus aureus) and Gram negative (Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae). The results show significant effect of the elevated temperature on the samples properties.     

Effects of Surface Properties on Rheological and Interfacial Properties of Pickering Emulsions Prepared by Fumed Silica Suspensions Pre-Adsorbed Poly(N-Isopropylacrylamide)

The hydrophobic fumed silica suspensions physically pre-adsorbed poly(N-isopropylacrylamide) (PNIPAM) in water could prepare oil dispersed in water (O/W) Pickering emulsion by mixing of silicone oil. The resulting Pickering emulsions were characterized by the measurements of volume factions of emulsified silicone oil, adsorbed amounts of the silica suspensions, oil droplet size, and some rheological responses, such as stress-strain sweep curve and dynamic viscoelastic moduli as a function of the added amount of PNIPAM. Moreover, their characteristics were compared with those of the O/W Pickering emulsions prepared by the hydrophilic fumed silica suspensions pre-adsorbed PNIPAM. For the emulsions prepared by the hydrophobic silica suspensions, an increase in the added amount of PNIPAM led to (1) a decrease in the volume fraction of the emulsified oil in the emulsified phase, (2) both the size of oil droplets and the adsorbed amount of the corresponding silica suspensions being almost constant, except for the higher added amounts, and (3) both the storage modulus (G′) and the yield shear strain being constant. The term of 1 is the same for the emulsions prepared by the hydrophilic silica suspensions, whereas both the adsorbed amount of the corresponding silica suspension and the G′ value increase and both the droplet size and the yield shear strain decrease with an increase in the added amount of PNIPAM. The differences between the rheological properties of the emulsions prepared by the hydrophilic silica suspensions and those by the hydrophobic ones are attributed to the hydrophobic interactions of the flocculated silica particles in the Pickering emulsions.     

Preparation and properties of poly(urethane-imide)s derived from amine-blocked-polyurethane prepolymer and pyromellitic dianhydride

Poly(urethane-imide)s were prepared using amine-blocked-polyurethane (PU) prepolymer and pyromellitic dianhydride. The PU prepolymers were prepared by the reaction of different diols (polypropyleneoxy glycol, polytetramethyleneoxy glycol, polycaprolactonediol and hydroxyl terminated polybutadiene) and different diisocyanates (2,4-tolylene diisocyanate, 1,4-phenelene diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate and 4,4^′-methylenebis(cyclohexyl)isocyanate) and end capped with N-methylaniline. The polymerization was faster with aromatic isocyanates than with aliphatic isocyanates. The effect of imide content on the thermal and mechanical properties was studied. The poly(urethane-imide)s were characterized by FTIR, GPC, TGA and for dynamic and static mechanical properties. Weight average molecular weight (M_w) of the polymers did not vary significantly with change in -NCO/-OH ratio where as number average molecular weight (M_n) increased with increasing -NCO/-OH ratio, correspondingly, the dispersity (PD) decreased. Polymers with higher hard segment content exhibited higher glass transition temperature. The thermal stability of the PU was found to increase significantly by the introduction of imide component.     

Fully biodegradable blends of poly(butylene succinate) and poly(butylene carbonate): Miscibility, thermal properties, crystallization behavior and mechanical properties

Fully biodegradable poly(butylene succinate) (PBS) and poly(butylene carbonate) (PBC) blends were prepared by melt blending. Miscibility, thermal properties, crystallization behavior and mechanical properties of PBS/PBC blends were investigated by scanning electron microscopy (SEM), phase contrast optical microscopy (PCOM), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and mechanical properties tests. The SEM and PCOM results indicated that PBS was immiscible with PBC. The WAXD results showed that the crystal structures of both PBS and PBC were not changed by blending and the two components crystallized separately in the blends. The isothermal crystallization data showed that the crystallization rate of PBS increased with the increase of PBC content in the blends. The impact strength of PBS was improved significantly by blending with PBC. When the PBC content was 40%, the impact strength of PBS was increased by nearly 9 times.     

Synergistic effects of functionalized graphene and functionalized multi-walled carbon nanotubes on the electrical and mechanical properties of poly(ether sulfone) composites

Mixed fillers composed of functionalized graphene (f-G) and functionalized multi-walled carbon nanotubes (f-CNTs) (f-G-f-CNTs) were prepared and their synergistic effects in terms of enhancing the electrical conductivity and tensile modulus of poly(ether sulfone) (PES) composites were investigated. The results indicate that the electrical conductivity of the 5 wt% f-G-f-CNTs(W_f-G/W_f-CNTs = 1:1)/PES composite was 2.2 times higher than that of the 5 wt% f-G/PES composite and 8.9 times higher than that of the 5 wt% f-CNTs/PES composite. Moreover, the tensile modulus of the 5 wt% f-G-f-CNTs(W_f-G/W_f-CNTs = 1:1)/PES composite relative to that of the 5 wt% f-G/PES composite and 5 wt% f-CNTs/PES composite increased by 16.5% and 50.6%, respectively. Additionally, enhancements in the electrical conductivity and tensile modulus of the PES composite depended on the weight ratio of f-G and f-CNTs in the mixed fillers. The electrical conductivity and tensile modulus exhibited maximum values when the weight ratios of f-G and f-CNTs were 1:3 and 1:1, respectively. When the weight ratio of f-G and f-CNTs was fixed at 1:1, the f-G-f-CNTs(W_f-G/W_f-CNTs = 1:1)/PES composite showed a percolation threshold of 0.22 vol%, much lower than that of the f-G/PES composite.     

Thermal and mechanical properties of cationic guar gum/poly(acrylic acid) hydrogel membranes

Novel hydrogel membranes (coded as GA) based on cationic guar gum (CGG) and poly(acrylic acid) (PAA) were synthesized with various feed compositions. Their structure and properties were studied by Fourier transform infrared spectra, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analyses and tensile tests. The structure analyses indicated that there existed strong electrostatic interaction between CGG and PAA, which resulted in uniform structure and complete miscibility between the two components. On the basis of thermogravimetric analyses, the activation energies (E_a) of the first degradation of the membranes increased from 34.5 to 77.1 kJ/mol with an increase of CGG content, while the residual ratios of the membranes increased from 7.6 to 36.1 wt% at 600 °C. This indicated an elevated thermal stability of PAA-based materials through an introduction of CGG. The tensile tests exhibited the mechanical properties of the membranes were improved with an increase of CGG content, and the maximum value of 41.1 MPa was reached.