Evaluation of short term–high intensity thermal degradation of graphite fiber reinforced laminates via ultrasonic spectroscopy

In certain fire situations, a structural or load‐bearing polymer matrix composite (PMC) may be exposed to excessive thermal loads that degrade the matrix. In this paper, we report the results of a study to assess the utility of ultrasonic spectroscopy as a means of assessing the residual physical and mechanical characteristics of PMCs exposed to excessive thermal loads. We show that the measured power spectra of ultrasonic energy correlates with performance of graphite fiber epoxy matrix composites exposed to thermal degradation. Unidirectional composites were exposed to short term–high intensity thermal loads at one end of the specimen. Thus, inducing a thermal gradient along the length of the specimen. Simultaneous thermogravimetric analysis–differential scanning calorimetry (TGA/DSC) and Fourier transform infrared spectroscopy (FTIR) analysis of the aged specimens revealed a gradient in thermal degradation. The thermal loads induced substantial degradation of the composite. However, the amplitude of the power spectra is observed to increase gradually then sharply prior to its complete attenuation due to delaminations. Mode I fracture toughness tests correlate with the observed changes in the ultrasonic spectra. FTIR, TGA/DSC, fracture toughness, and ultrasonic spectral analysis all indicate the same critical temperature at which thermally induced damage sharply increased. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2601–2610, 1999     

Surface modification of nanoclays by catalytically active transition metal ions

A unique class of nanoclays was prepared by modification of pristine clays or organoclays (Cloisite C20A) with transition metal ions (TMIs). The composition, structure, morphology and thermal properties of TMI-modified nanoclays were investigated by atomic absorption spectroscopy (AAS), elemental analysis (EA), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray absorption near-edge structure (XANES) spectroscopy. The content of TMIs in modified clays was found to be close to the limiting value of ion exchange capacity. SEM and X-ray results confirmed that TMIs were located between the mineral layers instead of being adsorbed on the surface of clay particles. TGA results indicated that the TMI treatment of organoclays could significantly increase the thermal stability, which was more pronounced in air than in nitrogen. Temperature-resolved SAXS measurements revealed that the presence of TMIs increased the onset temperature of structural degradation. The higher thermal stability of TMI-modified organoclays can be attributed to the change in the thermal degradation mechanism, resulting in a decrease in the yield of volatile products and the formation of char facilitated by the presence of catalytically active TMIs.     

Optical and electromagnetic characteristics of clay�Ciron oxide nanocomposites

Fe-pillared bentonite clay-based nanoadsorbent was synthesized by the thermal aging technique. The characteristics of the nanocomposite were detected by X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), thermal gravimetric analysis (TGA), scanning electron microscope (SEM), electron dispersive X-ray spectrometer (EDX), reflectance spectrophotometer (RS), and electromagnetic transition instrument (ETI). The TGA result demonstrated that the Fe particles generated on the clay surface can significantly improve the thermal stability of clay particles. The SEM and EDX results showed the presence of chemical elements of Fe, Al, and Si on the surface of clay. In this research, the successful synthesis of Fe-pillared clay nanocomposite can be concluded from the FTIR spectra.     

Thermal degradation and isothermal crystalline behavior of poly（trimethylene terephthalate）

Poly(trimethylene terephthalate)(PTT) is an excellent fiber material.Its thermal degradation and isothermal crystalline behaviors were in this study investigated using thermogravimetric analysis(TGA),thermogravimetric analysis-Fourier transform infrared spectroscopy(TGA-FTIR) analysis,differential scanning calorimetry(DSC) and X-ray diffraction(XRD).The thermal degradation mechanism of PTT follows Mclafferty rearrangement principle.The PTTwithintrinsicviscosity(Ⅳ) of 0.74 dL/g has a maximum crystallinity...     

Modification of wool fiber using steam explosion

Wool fiber was modified by steam explosion in this study. SEM results show that some scales on the fiber surface were cleaved and tiny grooves generated during the explosion. FTIR results suggest no evident changes in the chemical composition of the fiber after the explosion treatment. However, the crystallinity of the fiber decreased slightly as the steam pressure increased based on the X-ray results. In the thermal analysis, DSC results show that the temperature corresponding to vaporization of absorbed water and cleavage of disulfide bonds respectively decreased as the steam pressure increased. The reduction in thermal decomposition energy of the treated fiber indicates that steam explosion might have destroyed some crystals and crosslinks of macromolecular chains in the fiber. The treatment also led to some alterations of the fiber properties, including reduction in strength, moisture regain and solubility in caustic solution.     

Effects of trichloroethylene and tetrachloroethylene on fine structure of wool

Studies have been made on the structure of wool fibres treated with trichloroethylene (TRI) and tetrachloroethylene (PER) by means of differential thermal analysis (DTA), differential scanning calorimetry (DSC) and X-ray diffractometry. The samples were treated with TRI at temperatures ranging from 40? to 87?, and with PER at temperatures from 40? to 121?. TRI and PER treatment caused changes in the wool samples which were detected on the DTA curves. Changes in the degree of order brought about by TRI and PER, calculated from the DSC scans, were in accord with those determined from the X-ray data. The wool samples treated with TRI showed an increase, and those treated with PER a decrease, in the content of the ordered phase as the treatment time was increased.     

Synthesis of Oil Spill Sorbents Based on Cellulose Derivatives

In this work, hydroxypropyl cellulose (HPC) was used to synthesize hydroxypropylcellulose acrylate (HPCA) macromonomer by esterification of HPC with acryloyl chloride in homogenous solution of DMF. Then the produced HPCA monomer was copolymerized with ethylhexyl acrylate (EHA) in presence of two types of crosslinkers to produce oil gel. Several parameters were considered, namely, monomers feed ratio, type and concentration of the applied crosslinkers. The chemical structures of both HPC and HPCA were confirmed by using FTIR and ¹H NMR spectroscopic analyses. Also, the thermal properties of the crosslinked oil absorbents were investigated by using TGA. Furthermore, morphological propoeries of these crosslinked sorbers were studied through SEM and their swelling efficiency was thoroughly investigated in heavy and light oil.     

Investigation of structural,rheological and thermal properties of PMMA/ONi-Al LDH nanocomposites synthesized <Emphasis Type="Italic">via</Emphasis> solvent blending method: Effect of LDH loading

This article addresses the synthesis of organically tailored Ni-Al layered double hydroxide (ONi-Al LDH) and its use in the fabrication of exfoliated poly(methyl methacrylate) (PMMA) nanocomposites. The pristine Ni-Al LDH was initially synthesized by co-precipitation method and subsequently modified using sodium dodecyl sulfate to obtain ONi-Al LDH. Nanocomposites of PMMA containing various amounts of modified Ni-Al LDH (3 wt%-7 wt%) were synthesized via solvent blending method to investigate the influence of LDH content on the properties of PMMA matrix. Several characterization methods such as X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), rheological analysis, differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA), were employed to examine the structural, viscoelastic and thermal properties of PMMA/OLDH nanocomposites. The results of XRD and TEM examination confirm the formation of partially exfoliated PMMA/OLDH nanocomposites. The FTIR results elucidate that the characteristic bands for both pure PMMA and modified LDH are present in the spectra of PMMA/OLDH nanocomposites. Rheological analyses were carried out to examine the adhesion between polymer matrix and fillers present in the nanocomposite sample. The TGA data indicate that the PMMA nanocomposites exhibit higher thermal stability when compared to pure PMMA. The thermal decomposition temperature of PMMA/OLDH nanocomposites increases by 28 K compared to that of pure PMMA at 15% weight loss as a point of reference. In comparison with pure PMMA, the PMMA nanocomposite containing 7 wt% LDH demonstrates improved glass transition temperature (T _g) of around 3 K. The activation energy (E _a), reaction orders (n) and reaction mechanism of thermal degradation of PMMA/OLDH nanocomposites were evaluated using different kinetic models. Water uptake capacity of the PMMA/OLDH nanocomposites is less than that of the pure PMMA.     

Effects of synthetic and natural zeolites on morphology and thermal degradation of poly(lactic acid) composites

Poly(lactic acid) (PLA) composites containing 5 wt% synthetic (type 4A) and natural (chabazite) zeolites were prepared using extrusion/injection molding. Morphological, structural, and thermal properties of composites were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). DSC results revealed that the glass transition and melting temperatures were not significantly changed; however, the incorporation of both type 4A and chabazite zeolites enhanced the nucleation of PLA crystallites as well as increased the percent crystallinity. Thermal degradation properties of PLA and PLA/zeolite composites were studied by non-isothermal thermogravimetric analysis (TGA) in nitrogen atmosphere. TGA results showed that at temperatures above 300 °C, PLA/type 4A synthetic zeolite composites were thermally decomposed more easily than the PLA and PLA/chabazite natural zeolite composites. The apparent activation energies of thermal degradation of PLA and PLA/zeolites composites estimated using both the Flynn-Wall-Ozawa and Kissinger methods followed the same order: PLA/type 4A < PLA/chabazite < PLA.     

Thermal Behavior of Dodecylpyridinium-Based Surfactant Salts with Varied Anionic Constituent

Three novel dodecylpyridinium-based catanionic compounds were synthesized. A combination of techniques was used to examine their thermal properties: differential scanning calorimetry, powder x-ray diffraction, and polarizing microscopy. Briefly, the absence of mesomorphic properties and the formation of zig-zag blade textures were obtained in dodecylpyridinium picrate, thermotropic mesomorphism, and polymorphism in dodecylpyridinium dodecylbenzenesulfonate, and melting accompanied with degradation in combination with cholate. The anionic part of the molecule promotes behavior of novel compounds, resulting in different packing and thermal properties of catanionics in their solid state.      

Improvement in Uranium Adsorption Properties of Amidoxime-Based Adsorbent Through Cografting of Amine Group

Amidoxime (AO)/amine co-functionalized polypropylene fiber adsorbents were prepared. The all-polymeric structures were characterized by using Fourier transform infrared spectroscopy (FTIR), optical microscope, contact angle meter and electron spin resonance (ESR) analysis methods, confirming the grafting, modification, and amidoximation stages gravimetrically, spectroscopically, and visually. The properties for the removal of uranyl(VI) from aqueous solutions were investigated. For amidoxime (AO) fiber, high adsorption rate was observed within the first 30 minutes and the plateau value of 40.6% uranium loading (0.0812 mg/g) was reached at around 30 minutes. The adsorption equilibrium for AO/amine fiber was attained within 20 minutes, resulting in the adsorption of 92.6% uranium loading (0.185 mg/g). The percentage of adsorption increases with increasing pH value (2–6), reaches a maximum at pH 6.0 and then remains almost constant for AO/amine fiber, whereas reduces slightly for AO fiber.     

HMSPP nanocomposite and Brazilian bentonite properties after gamma radiation exposure

This work concerns the study of the mechanical and thermal behavior of the nanocomposite high melt strength polypropylene (HMSPP) (obtained at a dose of 12.5 kGy) and a bentonite clay Brazilian Paraiba (PB), which is known as “chocolate” and is used in concentrations of 5% and 10% by weight, in comparison to the American Cloisite 20A clay nanocomposites. An agent compatibilizer polypropylene-graft (PP-g-AM) was added at a 3% concentration, and the clay was dispersed using the melt intercalation technique using a twin-screw extruder. The specimens were prepared by the injection process. The mechanical behavior was evaluated by strength, flexural strength and impact tests. The thermal behavior was evaluated by the techniques of differential scanning calorimetry (DSC) and thermogravimetry (TGA). The morphology of the nanocomposites was studied with scanning electron microscopy (SEM), while the organophilic bentonite and nanocomposites were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR).     

Silkworm silk/poly(lactic acid) biocomposites: Dynamic mechanical, thermal and biodegradable properties

Silkworm silk/Poly(lactic acid) (silk/PLA) biocomposites with potential for environmental engineering applications were prepared by using melting compound methods. By means of Dynamic mechanical analysis (DMA), Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), Coefficient of thermal expansion test, Enzymatic degradation test and Scanning electron microscopy (SEM), the effect of silk fiber on the structural, thermal and dynamic mechanical properties and enzymatic degradation behavior of the PLA matrix was investigated. As silk fiber was incorporated into PLA matrix, the stiffness of the PLA matrix at higher temperature (70-160 °C) was remarkably enhanced and the dimension stability also was improved, but its thermal stability became poorer. Moreover, the presence of silk fibers also significantly enhanced the enzymatic degradation ability of the PLA matrix. The higher the silk fiber content, the more the weight loss.     

Influence of core materials on thermal properties of melamine-formaldehyde microcapsules

A series of melamine-formaldehyde microcapsules as an intrinsic intumescent system was prepared by an in situ polymerization. The structural and thermal properties of the resultant microcapsules were studied. The surface morphology and chemical structure of microcapsules were investigated using scanning electron microscope (SEM), and Fourier-transform infrared spectroscope (FT-IR), respectively. The thermal properties of samples were investigated by thermogravimetric analysis (TGA) and by differential scanning calorimetry (DSC). The results showed that the thermo-physical properties are strongly dependant on the nature core content and the synthesis conditions. From the thermal analysis, it was concluded that microcapsules containing di-ammonium hydrogen phosphate exhibits characteristics of an intumescent system during their thermal degradation and could be interpreted due to the interaction between phosphate and melamine.     

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.     

Molecular composites by incorporation of a rod-like polymer into a functionalized high-performance polymer,and their conversion into microcellular foams

Molecular composites were prepared from sulfonated modifications of polysulfone and polyphenylsulfone by incorporating relatively stiff polybenzimidazole (PBI) chains into them. The composites were characterized by Fourier-transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The FT-IR results demonstrated strong specific interactions between the sulfonated polymers and the PBI, which was presumed to be the reason for the enhanced miscibility observed. Miscibility was also indicated in the DSC and TMA results, by the presence of a single glass transition temperature (which was composition dependent), although there did appear to be a small degree of phase separation. TGA results showed improvements in the thermal stability of the polymer matrix because of the incorporation of PBI. Results from SEM were also consistent with considerable miscibility. Microcellular foams processed from these molecular composites had partial open-cell cell structures, with average cell sizes ranging from 0.2 to 5 m, in unusual bimodal cell-size distributions.     

The use of low-temperature plasmas in wool finishing

Processes that occur in wool fiber under the action of a glow-discharge plasma were considered. The kinetics of plasma etching, the amino acid compositions of whole fiber and separated cuticle elements, the surface of fiber (using scanning electron microscopy and attenuated total multiple internal reflection IR spectroscopy), as well as the electrosurface, friction, and other properties, were studied. These studies demonstrated that undergoing degradation and modification were primarily the fiber cuticle and its proteins and, particularly, lipids. Important reaction paths were processes involving the transformations of free radicals. Cystine, peptide, alanine, and glycine radicals were identified on the basis of EPR spectra. Plasma treatment enhanced the wettability of wool and the diffusion of dyes into fibers upon dyeing and printing and decreased the felting ability. This treatment did not impair the physicomechanical, heat-insulation, and thermal properties of wool. However, the resulting changes somewhat decreased the hydrophilicity of wool after plasma treatment.     

聚碳酸1,2-丙二酯/聚琥珀酸丁二酯/邻苯二甲酸二烯丙酯共混体系的研究

采用熔融共混的方法制备了聚碳酸1,2-丙二酯(PPC)/聚琥珀酸丁二酯(PBS)共混物和PPC/PBS/DAOP(邻苯二甲酸二烯丙酯)增塑共混物,对共混物的相容性、热性能、结晶性和物理机械性能进行了初步研究.研究结果表明PPC/PBS共混物为不相容体系,PPC对PBS的结晶度影响很小;PBS的加入提高了共混物的起始热分解温度(Td-5%),当共混物中PBS含量从10%增加到90%时,共混物的Td-5%可分别增加15℃到59℃.DAOP对PPC/PBS共混物有增塑作用,当PPC/PBS/DAOP的比例从30/70/0变化到30/70/30时,共混物玻璃化转变温度(Tg)下降了36.9℃.与PPC/PBS共混物相比,组成优化的DAOP增塑共混物PPC/PBS/DAOP(PPC/PBS/DAOP=30/70/5)的断裂伸长率和断裂能最大可提高31倍和34倍,分别达到655.1%和3.4 J/mm2,因此引入DAOP尽管使共混材料的热稳定性有所下降,但拓宽了PPC/PBS共混材料的使用温度窗口.