Study of flammability and thermal properties of high-impact polystyrene nanocomposites

To increase thermal stability and flammability of high-impact polystyrene (HIPS) nanocomposites with silica nanoparticles and two types of polyphosphate flame retardants were prepared by extrusion. Nanocomposites were characterized by thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, limiting oxygen index (LOI) analysis and the evaluation of mechanical properties. It was found that organic polyphosphate in combination with silica increased thermal stability and fire retardancy by 50% in LOI test. Morphology characterization revealed existence of crystalline order which affected mechanical properties; tensile strength was approximately the same as virgin HIPS while elasticity was sharply decreased. Ammonium polyphosphate did not affect mechanical properties as much as the organic material but was not equally efficient in flame retardancy which was just marginally increased.     

Use of inorganic materials to enhance thermal stability and flammability behavior of a polyimide

While a great variety of high temperature polyimide materials exist, these materials are being subjected to higher and higher use temperatures in oxidative and environmentally aggressive environments. There is a limit to the extent one can take a polyimide before it will oxidize and subsequently suffer property degradation, thermal decomposition, and structural failure. Therefore, we instead sought to use materials which do not oxidize (inorganic materials) to enhance the polyimide composition and perhaps move the properties of the organic polymer more into the realm of ceramics while maintaining polyimide composite weights and processing advantages. In this paper we present results of the combination of inorganic micron sized particles with and without carbon nanofibers to produce a variety of highly inorganic particle filled polyimides. These polyimides were tested for thermal stability and flammability in resin pellet form and as a protective coating for a carbon-fiber composite structure. Our results demonstrate that the resin with inorganic particles exhibited significant reductions in flammability by themselves, but minimal flammability reduction when used as a thin coating to protect a carbon-fiber composite. Further, the gains in thermal stability are limited by the thermal stability of the polyimide matrix, suggesting that more work is needed in measuring the limits of inorganic fillers to improve thermal stability. Still, the results are promising and may yield polyimide systems useful for providing resistance to damage from high heat flux exposures/fire risk scenarios.     

Effects of thermal-oxidative aging on the flammability and thermal-oxidative degradation kinetics of tris(tribromophenyl) cyanurate flame retardant PA6/LGF composites

The influence of thermal-oxidative aging on the flame retardancy of the flame retardant long-glass-fiber reinforced polyamide 6 composites (FR/PA6/LGF) with different thermal-oxidative exposure times at 160 °C were studied in this work. The flammability and flame-retardant properties of FR/PA6/LGF were investigated by means of the limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimeter test (CONE), and scanning electronic microscopy (SEM), before and after thermal-oxidative aging. The thermal-oxidative stability and degradation kinetics of the unaged and aged composites were studied by thermogravimetric analysis (TGA) with the methods of Kissinger and Ozawa in dynamic measurements (10 °C/min–40 °C/min). The results indicated that the flammability properties mirrored the degradation behaviors of these FR/PA6/LGF composites whatever their forms (aged or not). The Ozawa method showed that the causes of the first peak in the heat release rate change by CONE measurement corresponded to the apparent activation energies of the first stage degradation of aged FR/PA6/LGF composites, and the same conclusion with respect to the other heat release rate peak. Moreover, this aging slightly enhanced the solid phase flame-retardant mechanism by a char-promotion function, but had no effect on the gaseous flame-retardant mechanism and the decrease of harmful gas release rates. The existence of a surface migration effect on the flame retardant would endow FR/PA6/LGF composites with better LOI values, a more protective char layer structure, and excellent UL-94 ratings.     

Studies of ABS-graft-maleic anhydride/clay nanocomposites: Morphologies, thermal stability and flammability properties

ABS-g-MAH (maleic anhydride) with different grafting degree, ABS/OMT (organo montmorillonite) and ABS-g-MAH/OMT nanocomposites were prepared via melt blending. The grafting reaction, phase morphology, clay dispersion, thermal properties, dynamic mechanical properties and flammability properties were investigated. FTIR spectra results indicate that maleic anhydride was successfully grafted onto butadiene chains of the ABS backbone in the molten state using dicumyl peroxide as the initiator and styrene as the comonomer and the relative grafting degree increased with increasing loading of MAH. TEM images show the size of the dispersed rubber domains of ABS-g-MAH increased and the dispersion is more uniform than that of neat ABS resin. XRD and TEM results show that intercalated/exfoliated structure formed in ABS-g-MAH/OMT nanocomposites and the rubber phase intercalated into clay layers distributed in both SAN phase and rubber phase. TGA results reveal the intercalated/exfoliated structure of ABS-g-MAH/OMT nanocomposites has better barrier properties and thermal stability than intercalated ones of ABS/OMT nanocomposites. The T_g of ABS-g-MAH/OMT nanocomposites was also higher than that of neat ABS/OMT nanocomposites. The results of cone measurements show that ABS-g-MAH/OMT nanocomposites exhibit significantly reduced flammability when compared to ABS/OMT nanocomposites even at the same clay content. The chars of ABS-g-MAH/OMT nanocomposites were tighter, denser, more integrated and fewer surface microcracks than ABS/OMT residues.     

Calcium and aluminium-based fillers as flame-retardant additives in silicone matrices. I. Blend preparation and thermal properties

This series investigates silicone composites with enhanced thermal behaviour for cable applications. Calcium and aluminium-based fillers introduced into silicone formulations were classified according to three categories: non-hydrated fillers such as CaCO₃ (precipitated calcium carbonate and natural calcite) and wollastonite, water-releasing fillers such as calcium hydroxide, ATH, boehmite, and hydroxyl-functionalized fillers including alumina and mica. The fillers were first characterized in detail, and the thermal stability of their blends with silicone was recorded by thermogravimetric analyses. A discussion on various aspects of the filler morphology (size, microstructure, release profile with temperature) on the silicone stability is finally given.     

Thermal stability and flame retardancy of PET/magnesium salt composites

Nano-Mg(OH)₂ (nanometre magnesium hydroxide, nano-MH) was successfully introduced into the esterification and polycondensation system by in situ polymerization to obtain PET/magnesium salt composites (PETMS). The thermal properties and flame retardancy of PETMS were investigated by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), UL-94 vertical burning and limited oxygen index (LOI) test. The DSC and TGA results show that magnesium salts in the PET matrix have little effect on the thermal properties of PET, but a significant effect on the thermal stabilities of the composites. The results of LOI and UL-94 test show PETMS have higher LOI values (≥25%) and V-0 rating without melt dripping in the UL-94 test, indicating that PETMS have good flame retardancy and anti-dripping property. Moreover, the residues of magnesium salts and composites after TGA test were also studied by Fourier transform infrared spectroscopy (FTIR) to better understand the mechanism of flame retardancy, which reveals that magnesium salts accelerate the degradation of PET and catalyze the formation of char. The SEM results show the morphological structures of the char effectively protect the composites’ internal structures and inhibit the heat, smoke transmission and reduce the fuel gases when the fire contacts them.     

Investigation of the thermal decomposition and flammability of PEEK and its carbon and glass-fibre composites

Conventional thermally durable materials such as metals are being replaced with heat resistant engineering polymers and their composites in applications where burn-through resistance and structural integrity after exposure to fire are required. Poly aryl ether ether ketone (PEEK) is one such engineering polymer. Little work has been published with regards to the flammability of PEEK and its filled composites. The current study aims to assess the flammability and fire behaviour of PEEK and its composites using thermogravimetric analysis, pyrolysis combustion flow calorimetry, limiting oxygen index, a vertical flame resistance test, and fire (cone) calorimetry.     

Thermal stability and flammability performance of polypropylene composites with silica pillared montmorillonites

In present work, silica pillared montmorillonite material (C‐SiO₂‐OMT) was prepared via the sol–gel method, and the influence of the powder on thermal stability and flammability performance of polypropylene (PP) composites was investigated. Characterization of C‐SiO₂‐OMT, elucidated with X‐ray diffraction, transmission electron microscopy, and N₂ adsorption–desorption, suggested that the powder had a mesoporous lamellar structure with high specific surface area and mesoporous volume. The formation of porous structure of C‐SiO₂‐OMT was more conducive than organically modified montmorillonite (OMT) to slowing the volatilization of pyrolytic products generated during thermal degradation process, which led to PP/C‐SiO₂‐OMT microcomposite show better thermal stability than PP/OMT nanocomposite at high temperature range. Flammability properties of these polymer materials evaluated by microscale combustion calorimetry, and cone calorimetry showed a contrary tendency, but C‐SiO₂‐OMT holds high promise to reduce the smoke yield. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of silphenylene units on the thermal stability of silicone resins

A series of silicone resins containing silphenylene units were synthesized by a hydrolysis-polycondensation method, with methyltriethoxysilane, dimethyldiethoxysilane and 1,4-bis(ethoxydimethylsilyl)benzene. Their thermal degradation behaviours were studied by thermogravimetric analysis (TGA), differential thermogravimetry (DTG) and Fourier-transform infrared (FTIR) spectroscopy, and the effect of silphenylene units on the thermal stability of silicone resins was also investigated. Results showed that the thermal stability of silicone resins was improved by the introduction of silphenylene units into the backbone. Under nitrogen atmosphere, the temperature for maximum degradation rate of silicone resins with silphenylene units was lower compared to the pure methylsilicone resin. With the increase of silphenylene units, the amount of degradation residues increased under nitrogen atmosphere while it decreased under air atmosphere. Additionally, the short-term and long-term stability of silicone resins were also improved by the introduction of silphenylene units.     

Crystallization properties and thermal stability of polypropylene composites filled with wollastonite

The influence of wollastonite (CaSiO₃) content on the crystallization properties and thermal stability of polypropylene (PP) composites was investigated. The results showed that the crystallization temperature, crystallization end temperature and crystallization temperature interval, as well as the degree of crystallinity of the composites, were higher than those of the unfilled PP resin, while the crystallization onset temperature was little changed from that of the unfilled PP resin. The increase of degree of crystallinity for the composites could be attributed to the heterogeneous nucleation of the CaSiO₃ in the PP matrix. The thermal stability increased with increasing filler weight fraction (ϕ_f); the thermal decomposition rate decreased nonlinearly with increasingϕ_f. Finally, the dispersion of the filler particles in the matrix was observed, and the mechanisms of thermal stability and crystallizing behavior were discussed.     

Thermal degradation of ethanolamine treated poly(vinyl chloride)/wood flour composites

The influence of ethanolamine treatment of wood flour on the thermal degradation behaviour of PVC/wood flour composites was investigated. The decomposition of untreated and treated wood flour and PVC/wood flour composites was measured using thermogravimetric analysis (TGA). The TGA indicated an accelerated degradation of the composite after treatment in a temperature range between 240 and 350 °C. This was caused by a synergistic decomposition of treated wood flour and polymer. Additionally, the colour of the material was measured in order to analyse the effect of the treatment. The lightness of the composite was reduced with increasing ethanolamine concentration.     

Combination effect of nanoparticles with flame retardants on the flammability of nanocomposites

Polystyrene based nanocomposites (PNCs) with and without flame retardant additives were successfully prepared through a single-screw extrusion technique. The combination effect of nanoparticles and flame retardants was investigated with nanosilica and attapulgite clay as nanofillers, and with a NASA formulated SINK flame retardant. A comprehensive study was done by Cone Calorimetry, UL94 and TGA.The addition of nanoparticles to polystyrene generally improved the OI of polystyrene. The horizontal burning tests suggested that nanofiller types have different impacts on the flammability of nanocomposites. According to the vertical burning tests and oxygen indices, it was found that polystyrene/silica and polystyrene/attapulgite clay PNCs alone are not flame retardant. In fact, the materials burned faster. However, the combination of nanocomposites with the SINK flame retardant significantly altered the thermal stability, and flammability of the materials. A remarkable reduction in heat release rates of polystyrene was achieved for both silica and attapulgite with flame retardant nanocomposites. For instance, the introduction of 20% SINK into PS reduced the PHRR of PS from 1212 to 838 (−31%); 10% silica reduced it from 1212 to 1060 (−13%), while the combination of silica and SINK reduced it to 530 (−56%), which clearly shows interaction between nanosilica and SINK.     

Thermal stability and degradation products analysis of benzocyclobutene-terminated imide polymers

Benzocyclobutene-terminated imides were prepared and fully characterized with ¹H NMR, MS, and FT-IR. The thermal degradation of polymers was investigated by using thermogravimetric analyzer (TGA) and high-resolution pyrolysis-gas chromatography–mass spectrometry (HR-Py-GC–MS). TGA showed that thermal degradation of the polymer was a single-stage process in N₂, whereas a three-stage degradation in air atmosphere. The major involved products were found to be CO₂, naphthalene and naphthalene derivatives. Degradation mechanism of the polymer was suggested and the relationship between structures of the polymer and degradation products was also discussed.     

Thermal and volumetric property analysis of polymer networks and composites using elevated temperature digital image correlation

Digital Image Correlation (DIC), which exploits non-contact advantages and full-field analysis, provides more data in-situ that are not possible with traditional techniques. In this work, elevated temperature digital image correlation techniques were applied to a glassy polymer network via thermal expansion and contraction experiments to study volumetric behavior during the curing process. A glassy epoxy network was tested in both cured and under-cured states and heated to the ultimate cure temperature. Matrix volume changes due to both thermal expansion and cure shrinkage were quantified. Concurrently, the thermal expansion of aerospace-grade composite laminates was also observed in matrix and fiber-dominant directions. Additionally, the strain-free temperature of a non-symmetric composite laminate was identified through thermal compensation of process-induced curvatures. Finally, laminate dimension changes were related to the strain-free temperature as means to probe process-induced strains within composite laminates. Thermal properties of the neat matrix and composite laminates were compared to traditional techniques, validating the benefit of elevated temperature digital image correlation for composite matrix qualification.     

Thermal and microbial degradation of alginate-based superabsorbent polymer

In this study, an alginate-based superabsorbent polymer (SAP), alginate-graft-poly[acrylamide-co-(itaconic acid)-g-(acrylic acid)] or Alg-g-P(AM-co-IA-g-AA), was prepared to examine its thermal and microbial degradation properties through Thermogravimetric Analysis (TGA), and soil supernatant test (with and without added nutrient) and soil burial test, respectively. The TGA thermogram of the SAP showed three degradation steps. The first degradation step was due to the thermal degradation of alginate and decomposition of the functional groups of PAM, PIA and PAA; whereas the second degradation step occurred as a result of the decomposition of PAM, PAA and PIA chains. Further decomposition of PIA contributed to the third degradation step. Among all the soil samples [tropical forest soil (TF), former tin mine lake soil (TM), peanut farm soil (PF), indigenous microorganism soil from an organic vegetable farm (OF), and oil palm plantation soil (OP)] tested, OF soil degraded the polymer sample most effectively, with the highest weight loss of 82.6% (with added nutrient) and 82.8% (without added nutrient) in soil supernatant tests, and 63.5% in soil burial test. Morphological observation under an Illuminated Stereo Microscope showed some holes and weak topographical spots on the surface of the polymer material after it had been incubated in OF solution for 40 days. Meanwhile, the intrinsic viscosities, [η], of NaAlg and the Alg-based SAP solutions were 2.62 and 2.75 respectively.     

Thermal and thermo-oxidative degradation of high density polyethylene/fullerene composites

Fullerene (C₆₀)/high density polyethylene (HDPE) composites were studied in order to understand for their behaviors on thermal and thermo-oxidative degradation. Under different atmosphere, the influences of C₆₀ on the thermal stability of HDPE are different. Thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) demonstrate that in N₂ the addition of C₆₀ increases the onset decomposition temperature by about 10 °C with more heavy compounds (more than 34 carbon). Also the thermal stability of HDPE in air is remarkably improved with the addition of C₆₀. When the content of C₆₀ is 2.5 wt% the onset decomposition temperature increases by about 91 °C. The results of viscoelastic behavior and gel content reveal that C₆₀ can trap the alkyl radicals and alkyl peroxide radicals to inhibit hydrogen abstraction to suppress the chain scission and preserve the long chain structure. However, in the absence of C₆₀ or with low C₆₀ concentration, hydrogen abstraction occurs, resulting in the formation of a series of alkyl radicals and alkyl peroxide radicals, which accelerates the chain scission and plays a leading role in the thermal oxidative degradation.     

Thermal stability of plasma deposited polysilanes

A new method for studying thermal stability and concomitant chemical composition changes on thermal treatment of thin polymeric films is presented. It is applied to the study of thermal properties and modification of properties of polysilane-like materials with variable dimensionality prepared by radio frequency plasma enhanced chemical vapour deposition (CVD). Structure and microphysical properties of these materials, modified by progressive annealing, are examined by fluorimetry, FTIR absorption spectroscopy and XPS. In addition, the role, bonding conditions and structural environments of organic moieties as well as their influence on thermal degradation processes are examined. It is found that plasma polysilanes undergo three consecutive thermal degradation processes: Si-Si bond cleavage, elimination of side groups and final carbide formation. Presence of disorder and crosslinking stabilises the plasmatic material in comparison to classically prepared polysilanes. Nanostructural units in low dimensional polysilanes enable the peak of the luminescence to be adjusted in the spectral range from near UV (360 nm) to red (600 nm).     

Morphology,thermal stability,and flammability of polymer matrix composites coated with hybrid nanopapers

In this study, a hybrid nanopaper consisting of carbon nanofiber (CNF) and polyhedral oligomeric silsequioxane (POSS) or cloisite Na⁺ clay, has been fabricated through the papermaking process. The hybrid nanopaper was then coated on the surface of glass fiber (GF) reinforced polymer matrix composites through resin transfer molding (RTM) process. The morphologies of the hybrid nanopaper and resulting nanocomposites were characterized with scanning electron microscopy (SEM). It can be seen that the nanopaper had a porous structure with highly entangled carbon nanofibers and the polyester resin completely penetrated the nanopaper throughout the thickness. The thermal decomposition behavior of the hybrid nanopapers and nanocomposites was studied with the real‐time thermogravimetric analysis/ flourier transform infrared spectrometry (TGA/FTIR). The test results indicate that the addition of pristine nanoclay increased the thermal stability of the nanopaper, whereas the POSS particles decreased the thermal stability of the nanopaper. The fire retardant performance of composite laminates coated with the hybrid nanopaper was evaluated with cone calorimeter tests using a radiated heat flux of 50 kW/m². The cone calorimeter test results indicate that the peak heat release rate (PHRR) decreased dramatically in composite laminates coated with the CNF‐clay nanopaper. However, the PHRRs of the CNF‐POSS nanopaper coated composite laminates increased. The formation of compact char materials was observed on the surface of the residues of the CNF‐clay nanopaper after cone calorimeter test. The flame retardant mechanisms of the hybrid nanopaper in the composite laminates are discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Polymer matrix influence on stability of wood polymer composites

The aim of the presented work is to show the influence of the various polymer matrices and the different amounts of the cellulose filler on the composites properties. Samples based on polypropylene, polystyrene, polyoxymethylene, acrylonitrile butadiene styrene, polyester resin, and polylactic acid with different contents of cellulose fibers were prepared by injection molding process. The mechanical and dielectric properties of these composites were studied in order to check whether investigated wood polymer composites fulfill requirements for their application in electrical devices. For all tested composites, a linear increase of modulus with cellulose content was observed. Addition of cellulose to the tested polymers significantly reduces strain at break. In the case of polypropylene and polyoxymethylene composites, the tensile strength increases with the content of the filler. For other materials, there is an inverse relationship, namely the addition of cellulose decreases the tensile strength. The electrical strength decrease was observed with increased cellulose content for the majority of the investigated composites. Polar groups incorporated by cellulose fibers have led to dielectric constant increase. Furthermore, aging of composites in mineral oil and evaluation of water uptake for wood–plastic samples were performed. Wood polymer composites have changed significantly after aging. The water diffusion coefficients were determined, and the significant influence of the amount of cellulose on the water absorption was shown. Copyright © 2015 John Wiley & Sons, Ltd.     

Thermal properties stability of UV irradiated PVA nanohybrid composites

Zn‐Al‐salicylic nanohybrid layers have been prepared and used as fillers for polyvinyl alcohol (PVA). Nanohybrid layers of a broad absorption area in UV region were completely and uniformly dispersed in a continuous polymer matrix. PVA and PVA nanohybrid composite (NHC) films were exposed to UV irradiation. Thermal properties (diffusivity, effusivity, and conductivity) of both have been measured through photoacoustic technique before and after UV irradiation. Thermal parameters of PVA suffered from a quick deterioration with UV exposure due to reduction of the phonon mean free path as a result of molecular chain scissions. However, significant stability in such parameters of NHC has been obtained under the influence of UV irradiation. This thermal properties stability may be an important step on the way of obtaining photostable polymer NHC. Copyright © 2012 John Wiley & Sons, Ltd.