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.     

Synthesis, characterization, flame retardance and thermal properties of halogen-free expandable graphite/PMMA composites prepared from sol-gel method

In this work, silane was grafted on expandable graphite via a free-radical reaction. The modified expandable graphite has an -OEt functional group which reacts with TEOS and PMMA that was modified via a sol-gel reaction using a coupling agent that contains silicon. Synergism between silicon flame retardant and expandable graphite increased the flame retardance of the materials. Expandable graphite was functionalized using a coupling agent to increase the interactive force between the organic and inorganic phases. It enhanced the thermal stability of the composites. SEM was adopted to observe the morphology of the composites, and the behavior associated with expansion after the materials had been burned is elucidated. LOI, TGA and IPDT were employed to calculate the flame retardance and thermal stability. The results indicate that the composites are halogen-free flame retardant organic/inorganic composites. Two methods for elucidating the kinetics of thermal degradation were utilized to measure the activation energy when the composites degraded in the high-temperature atmosphere.     

Thermal stability and toughening of epoxy resin with polysulfone resin

The cure behavior, thermal stability, and mechanical properties of diglycidylether of bisphenol A (DGEBA)/polysulfone (PSF) blends initiated by 1 wt % N‐benzylpyrazinium hexafluoroantimonate as a cationic latent catalyst were investigated. The DGEBA/PSF content was varied within 100/0–100/40 wt %. Latent properties were studied through the measurement of the conversion as a function of the curing temperature, and the cure activation energy (E_a) was studied by the Kissinger method with a dynamic differential scanning calorimetry analysis. The thermal stabilities, largely based on the integral procedural decomposition temperature (IPDT) and decomposed activation energy (E_t), were investigated by the measurement of thermogravimetric analysis. For the mechanical properties of the casting specimens, the critical stress intensity factor (K_IC) test was performed, and their fractured surfaces were examined with scanning electron microscopy. E_a, IPDT, E_t, and K_IC increased with PSF increasing in the neat epoxy resin up to 30 wt %. However, there was a marginal decrease in the blend system in both the thermal and mechanical properties due to the phase separation between DGEBA and PSF. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 121–128, 2001     

Effect of organically modified montmorillonite filler on the dynamic cure kinetics, thermal stability, and mechanical properties of brominated epoxy/aniline formaldehyde condensates system

Nanocomposites, based on tetrabromo-bisphenol-A epoxy and aniline formaldehyde condensates, containing 5 and 10 % organically modified montmorillonite (O-MMT), were prepared. The morphologies of these nanocomposites were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of O-MMT on the dynamic cure kinetics, thermal stability, and mechanical properties were investigated by differential scanning calorimetry, thermogravimetric analysis, and non-destructive ultrasonic testing techniques. The XRD and SEM results indicated a good dispersion of O-MMT within the epoxy matrix. The relation between the activation energy, E _a, and the degree of cure, α, for the examined systems was obtained by applying model-free isoconversional Kissinger–Akahira–Sunose method. As α increases, E _a increases gradually, almost independent of the amount of O-MMT. The dynamic cure kinetics of the neat epoxy system as well as its nanocomposites were described by ?estàk–Berggren, [SB (m, n)], autocatalytic model. The O-MMT enhances the thermal stability of the examined epoxy system. The results of the mechanical properties indicated that the addition of O-MMT enhances the Young’s and shear elastic modulus and microhardness. The values of these parameters increase with increasing O-MMT loading.     

Thermo-oxidative degradation of novel epoxy containing silicon and phosphorous nanocomposites

Modified epoxy nanocomposites containing silicon and phosphorous was prepared and compared with pure epoxy. The study of thermo-oxidative degradation of modified epoxy nanocomposites and pure epoxy has been utilized by thermal analysis. The thermal stability of modified epoxy nanocomposites is not superior to that of the pure epoxy at low temperature, however, the char yield of modified epoxy nanocomposites is higher than that of the pure epoxy at 800 °C in air atmosphere. The modified epoxy nanocomposites possess better thermal stability at high temperature range. The values of the limiting oxygen index of pure epoxy and modified epoxy nanocomposites are 24 and 32, respectively. This indicates that modified epoxy nanocomposites possesses better flame retardance.By the Kissinger’s method, the activation energies of thermo-oxidative degradation for epoxy nanocomposites are less than those of thermo-oxidative degradation for pure epoxy in first stage of thermo-oxidative degradation. However, the activation energies of thermo-oxidative degradation for epoxy nanocomposites are more than those of thermo-oxidative degradation for pure epoxy in second stage of thermo-oxidative degradation.     

Study on the PMMA/GO nanocomposites with good thermal stability prepared by in situ Pickering emulsion polymerization

Graphene oxide (GO) is used as a stabilizer in the Pickering emulsion polymerization of methyl methacrylate (MMA) to prepare PMMA/GO nanocomposites. Transmission electron microscope studies of the emulsion polymerization products showed that the average diameter of nanocomposite particles was about 150 nm, the transparent GO flakes covered the surface of the particles, and were well dispersed in polymer matrix. The influence of GO on the thermal stability of PMMA was investigated by thermogravimetry analysis and differential scanning calorimetry. The results showed that the thermal stability and the glass transition temperature (T _g) of PMMA/GO nanocomposites were improved obviously compared with PMMA. The apparent activation energy (E _a) for the degradation process of PMMA/GO nanocomposites was evaluated by Kissinger method, which indicated that their E _a s were much higher than those of PMMA both in nitrogen and air atmosphere.     

Sol–gel synthesis and enhanced properties of a novel transparent PMMA based organic–inorganic hybrid containing phosphorus,nitrogen and silicon

A novel flame-retardant silane containing phosphorus and nitrogen, tetramethyl(3-(triethoxysilyl)propylazanediyl) bis(methylene) diphosphonate (TMSAP), is firstly synthesized and then incorporated into poly(methyl methacrylate) (PMMA) matrix through sol–gel method to produce organic–inorganic hybrids. The chemical structure of TMSAP was confirmed by Fourier transform infrared spectra, ¹H nuclear magnetic resonance (NMR) and ³¹P NMR spectra. The hybrids obtained maintain relatively high transparency, and exhibit a significant improvement in thermal properties, mechanical performance and flame retardancy when compared to pure PMMA, including increased glass transition temperature (T _g ) by 11.4 °C, increased onset thermal degradation temperature (T_0.1) by 82.6 °C, increased half thermal degradation temperature (T_0.5) by 42.0 °C, increased hardness, increased limited oxygen index and decreased heat release rate. Morphological studies of hybrids by scanning electron microscopy (SEM) and ²⁹Si MAS NMR suggest that cross-linked silica network is formed in the hybrids and the inorganic silica particles are distributed well in the polymer matrix. Thermal degradation behaviors investigated by thermogravimetric analysis and char structure analysis studied by SEM and X-ray photoelectron spectroscopy demonstrate the catalytic charring function of TMSAP, and synergistic effect between phosphorus, nitrogen and silicon element. The formation of network structure, homogeneous distribution of silica and the char formation during degradation play key roles in these property enhancements. Detailed mechanisms for these enhancements are proposed.     

Flexible inorganic–organic hybrids with dual inorganic components

Combining multiple inorganic components is an effective approach to improve the mechanical properties of inorganic–organic hybrid materials. The inorganic components can form interactions with the organic polymer matrix, and there is thus a need to understand the reinforcement mechanism under the optimal combination of organic polymer and inorganic particles. In this work, we prepared a series of dual inorganic particle–based titania/silica–poly(tetrahydrofuran)–poly(ε-caprolactone) (TiO₂/SiO₂–PTHF–PCL) hybrids by means of simultaneous cationic ring-opening polymerization and sol–gel reaction. In addition to constructing hybrid networks, the SiO₂ and TiO₂ components play important roles in multiple toughening mechanisms. The prepared dual inorganic hybrids feature enhanced thermal stability and mechanical properties when compared with the ones with a single inorganic component. The optimized mixing of such two inorganic components is identified through mechanical tests, revealing that the hybrid polymer₇₀/(Si_0.6Ti_0.4)₃₀ (70/18/12 mass ratio) has the highest compressive failure strain (80%) and compressive ultimate strength (1.3 MPa) as well as storage modulus (120 kPa), enabling elongation of up to 37% when compared with its original length. We thus find that the dual inorganic component approach is an effective strategy to enhance the mechanical properties of hybrid materials, suggesting potential applications as scaffolds for tissue engineering and soft robotics.     

Enhanced thermal and combustion resistance of cotton linked to natural inorganic salt components

A comparison of the thermal decomposition and combustion characteristics of raw and scoured cottons has demonstrated a mechanistic link caused by the presence of inorganic salts in raw cotton, which enhances resistance to heat and flame. Thermogravimetry, differential thermogravimetry, and microscale combustion calorimetry were used to examine the thermal decomposition kinetics and thermal stability of cotton. During pyrolysis, both raw cotton nonwoven and woven fabrics exhibited a slower decomposition with a larger initial weight loss and produced a greater char yield, as compared to the fabrics after scouring, which removes most inorganic components from cotton. The activation energy (E _a ) values, calculated using the Kissinger method, the Flynn–Wall–Ozawa method, and the modified Coats–Redfern method, were consistently determined to be smaller for raw cotton than for scoured cotton. The analyses of cotton fabrics heated at elevated temperatures by ¹³C CP/MAS NMR and ATR-FTIR showed that trace quantities of inorganic components promoted the formations of oxygenated moieties at low temperatures and aliphatic intermediate char. In the combustion, raw cotton exhibited a much smaller heat release capacity and a smaller total heat release than scoured cotton, indicating enhanced thermal stability when the inorganic components are intact.     

Bismaleimide/rice husk silica reinforced composites

Silica derived from the renewable resource rice husk is modified using stearic acid and N-[4-(chlorocarbonyl)phenyl]maleimide. These materials are used as fillers in the bismaleimide, 4,4′-bismaleimidodiphenylmethane (BMIM), and thermally cured. The thermogravimetric (TG) curves for polyBMIM/silica composites showed no pronounced changes compared to the TG curve for the pure polyBMIM. Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, and Friedman methods are used to compute the activation energy (E _a) for degradation. Silica and surface-modified silica using stearic acid dispersed by ultrasonication increase the activation energy for degradation and show considerable influence on the thermal stability of cured BMIM. The long alkyl chain present in the stearic acid modified silica and the bulky spacer present in the chemically modified silica definitely alter the degradation process of cured BMIM. The SEM studies indicated uniform dispersion of the silica particles in the polyBMIM.     

Effect of nanosilica on thermal oxidative degradation of SBR

The effect of silica content on thermal oxidative stability of styrene–butadiene rubber (SBR)/silica composites has been studied. Morphologies of silica in SBR with different contents are investigated by scanning electron microscopy, which indicates that silica can well disperse in SBR matrix below the content of 40 %, otherwise aggregates or agglomerates will generate. Composites with around 40 % silica content show excellent mechanical properties and retention ratios after aging at 85 °C for 6 days. The values of activation energy (E _a) of pure SBR and its composites are calculated by Kissinger and Flynn–Wall–Ozawa methods based on thermogravimetric (TG) results, which suggests that composite with about 20 % silica has minimum E _a, and composite with 30–40 % silica has maximum E _a. According to TG curves, it is found that silica can suppress the formation of char leading to decline in stability to some extent. On the other side, silica also has positive effect on improving thermal stability of the matrix as filler. Thus, the SBR/silica composites with silica content of 30–40 % can possess both excellent resistance to thermal oxidative degradation and superior mechanical properties.     

Effect of compatibilization on thermal degradation kinetics of HDPE-based composites containing cellulose reinforcements

Dynamic thermogravimetric analysis under nitrogen flow was used to investigate the thermal decomposition process of high-density poly(ethylene) (HDPE)-based composites reinforced with cellulose fibers obtained from the recycling of multilayer carton scraps, as a function of the cellulose content and the compatibilization. The Friedman, Flynn–Wall–Ozawa, and Coats–Redfern methods were used to determine the apparent activation energy (E _a) of the thermal degradation of the cellulose component into the composites. E _a has been found dependent on the cellulose amount and on the cellulose/polymer matrix interfacial adhesion. In particular, it has been evidenced an increase of the cellulose thermal stability as a consequence of the improved interfacial adhesion between the components in NFR composites.     

Optical,thermal and microstructural studies of epoxy-CoSO4.7H2O hybrid material

Organic–inorganic polymer hybrid films of epoxy polymer were prepared, using Cobaltous sulfate heptahydrate (CoSO₄.7H₂O) as a filler component, by physical blending method. UV–Vis optical absorption spectra were analyzed to determine optical band gaps (E_g) of the hybrid material. FTIR studies revealed the interaction of inorganic component with molecules of the polymer matrix. Glass transition temperature (T_g) and degradation temperature were determined by DSC. TG analysis showed the improvement in thermal stability of prepared hybrid films. XRD patterns revealed the amorphous nature of the pure epoxy polymer. Additional sharp peaks were seen for higher filler levels (FLs), indicating self formed nanostructures in the material, which was also evident from SEM analysis.     

Synthesis and properties of conducting organic/inorganic polyurethane hybrids

A series of polyurethane/polyaniline/silica organic/inorganic hybrids were synthesized via the conventional polyurethane (PU) prepolymer technique. Amine-endcapped polyaniline (PANI) with low molecular weight and higher solubility was firstly synthesized. This PANI oligomer was then used together with nano-silica bearing silanol groups as chain extenders to prepare the conducting polyurethane hybrids. The polyurethane hybrids were designated as PU-xPANI-ySiO₂ (x + y = 1). For comparison, the urethane-aniline block copolymer and the PU/silica hybrid were designated as PU-PANI and PU-SiO₂, respectively.The structures of PU-PANI, PU-SiO₂ and conducting polyurethane hybrids were confirmed by FT-IR, solid-state ¹³C, and ²⁹Si NMR spectra. In nano-silica containing organic/inorganic conducting polyurethane hybrids, UV-vis spectra revealed the maximum absorption bands similar to that of PU-PANI. X-ray diffraction patterns indicated that these samples are typical of semicrystalline/amorphous materials. SEM image of PU-0.5PANI-0.5SiO₂ showed that PANI was dispersed homogeneously and interconnected continuously in the insulating PU-silica matrix. TGA results of the polymer hybrids exhibited higher thermal stabilities and lower decomposition rates than that of PU-PANI both in nitrogen and air. Differential scanning calorimetry (DSC) studies indicated that the polyurethane hybrids had higher glass-transition temperatures (T_g) with the increase of PANI, but lower than that of PU-PANI. Stress-strain curves for all of the polyurethane hybrids showed the elastomeric behavior of typical polyurethanes. The surface resistivity values of all hybrids were about 10⁸ ∼ 10¹⁰ Ω/sq. and might meet the requirement of the anti-electrostatic materials.     

The investigation of methyl phenyl silicone resin/epoxy resin using epoxy-polysiloxane as compatibilizer

Styrene–butadiene rubber was subjected to long-term thermal aging treatment at 80 °C with aging period up to 180 days. The degradation kinetics of the aged sample was analyzed by thermogravimetric analysis. Multiple heating rate experiments were carried out in nonisothermal conditions and three isoconversional model-free methods (Friedman; Kissinger–Akahira–Sunose; Li and Tang methods) were employed. The results showed that the temperature for 5 % mass loss increased, whereas the maximum mass loss temperature decreased after aging. Activation energies (E _a) derived from the three methods were found to be dependent on conversion degree (α). E _a increased with increasing α in the whole range of conversion for samples aged for 0, 60, and 120 days, while the aged samples displayed higher E _a values. However, samples aged for 180 days showed declining E _a versus α. The changes on the degradation kinetics were associated with the modification on the chemical structure after thermal aging.     

Kinetic study of the thermal and thermo-oxidative degradations of polylactide-modified films for food packaging

In this study, the thermal degradations of some commercial polylactide (PLA) films, pure and subjected to various superficial treatments, were investigated in both inert (flowing nitrogen) and oxidative (static air) atmospheres. Degradations were carried out in a thermobalance, in the scanning mode, at various heating rates, and the obtained thermogravimetric curves were discussed and interpreted. Experiments, performed in the temperature range of 35–700 °C, showed similar behavior in both the atmospheres used. The initial decomposition temperature (T _i) and the apparent activation energy (E _a) of degradation of the differently treated PLA films were determined and compared with each other and with those of untreated PLA. The E _a of degradation was obtained by Kissinger’s method, and the values were found increased linearly as a function of crystallinity percentage (%c) as well as the T _i values. The glass transition temperature (T _g) was also determined by differential scanning calorimetry. All the investigated parameters showed dependence on different treatments made to the films. The results obtained for the degradations of PLA films were compared with each other, and a classification of thermal stability in the studied environments were made.     

Investigations and molecular modeling of some thermophysical properties of polysulfones

Degradation of commercial polysulfones (PSF) was investigated in air and in inert atmosphere (nitrogen) using thermogravimetric (TG) method. It has been found that the degradation of Udel P-1800 PSF is initiated about 400°C, both in air and in nitrogen. The activation energy of degradation of PSF, (E _a), has been calculated by the Kissinger and Ozawa methods. The value ofE _a about 200 kJ·mol^?1 has been found for both air and nitrogen atmosphere. Experimental results concerning thermal properties of PSF (T _g andT _d,1/2) were compared with those obtained by the computer modeling technique, and a good agreement has been found.     

A kinetic study of the thermal and thermal oxidative degradations of new bridged POSS/PS nanocomposites

The thermal degradation of a series of three novel bridged polyhedral oligomeric silsesquioxanes (POSS)/polystyrene (PS) nanocomposites, at different POSS content (3%, 5% and 10%), was studied in both inert (flowing nitrogen) and oxidative (static air) atmospheres, in order to investigate the effects of this new dumbbell-shaped structure on the filler–polymer interaction and then on the thermal stability of the obtained materials. Nanocomposites were synthesized by in situ polymerization of styrene in the presence of POSS which has not polymerizable groups, aiming to obtain well dispersed POSS/PS systems. The actual filler concentration in the obtained nanocomposites was checked by ¹H NMR spectroscopy. Scanning electron microscopy (SEM) and FTIR spectroscopy evidenced the presence of filler–polymer interactions. Degradations were carried out into a thermobalance, in the scanning mode, at various heating rates, and the characteristic parameters of thermal stability, namely temperature at 5% mass loss (T₅%) and the activation energy (E_a) of degradation, of the various nanocomposites were determined. The results were discussed and interpreted.     

Thermal decomposition reactions of metal carboxylato complexes in the solid state: II. Thermographic and differential thermal studies of metal oxalato,malonato and succinato complexes

The thermal investigations of metal carboxylato complexes of the first transition metals, Mn(II), Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) and non transition metals like Zn(II) and Cd(II) in solid state were carried out under non-isothermal condition in nitrogen atmopshere by thermogravimetric (TG) and differential thermal analyses (DTA) methods. The results of DTA curves inferred that the thermal stability of the complex decreased approximately with the increase of standard potential of the central metal ion. The thermal parameters like activation energy (E_a¹), enthalpy change (ΔH) and entropy change (ΔS) corresponding to deaquation, deammoniation and decomposition processes occurred simultaneously or separately were determined from TG and DTA curves by the standard methods. A linear correlation has been found in the plots of ΔH vs. ΔS and E_a¹ vs. ΔS in deaquation, deammoniation and decomposition processes. An irreversible phase transition was noticed for H₂[Mn(suc)₂] and H₂[Co(suc)₂] complexes in DTA curves. The residual pyrolysed products were metal carbonates.     

A two-dimensional infrared correlation spectroscopic study on the thermal degradation of poly(2-hydroxyethyl acrylate)-co-methyl methacrylate/SiO2 nanohybrids

Two-dimensional infrared (2D IR) correlation spectroscopy was applied to study the structural changes occurring in the decomposition of PHEA-co-MMA/SiO₂. Complicated absorption spectral changes were observed in the heating process. 2D IR analysis indicates that during heating, covalent bonds, (Si-O-C), between the polymer and the inorganic moiety were formed, which was the main factor in the improvement in thermal properties of the hybrids such as the decomposition temperatures (T_d). The thermal stability of the hybrids was also studied by solid-state ²⁹Si MAS NMR spectroscopy and TGA tests. Their results complemented each other well.