Thermal and mechanical properties of UV irradiated collagen/chitosan thin films

The thermal and mechanical properties of collagen/chitosan blends before and after UV irradiation have been investigated using thermal analysis and mechanical (Instron) techniques. Comparisons were made with the thermal and mechanical properties of both collagen and chitosan films. Air-dried collagen, chitosan and collagen/chitosan films were exposed to UV irradiation (wavelength 254 nm) for different time intervals. Thermal properties of collagen/chitosan blends depend on the composition of the blend and are not significantly altered by UV irradiation.Mechanical properties such as ultimate tensile strength and ultimate percentage of elongation were much better for collagen films than for collagen/chitosan films. The results have shown that the mechanical properties of the blends were greatly affected by the duration of UV irradiation. Ultimate tensile strength and ultimate percentage elongation decreased after UV irradiation of the blend. Increasing UV irradiation leads to an increase in Young's modulus of the collagen/chitosan blend.     

Mechanical and thermal properties of green polylactide composites with natural fillers

Green composites of PLA with micropowders derived from agricultural by-products such as oat husks, cocoa shells, and apple solids that remain after pressing have been prepared by melt mixing. The thermal and mechanical properties of the composites, including the effect of matrix crystallization and plasticization with poly(propylene glycol), have been studied. All fillers nucleated PLA crystallization and decreased the cold-crystallization temperature. They also affected the mechanical properties of the compositions, increasing the modulus of elasticity but decreasing the elongation at break and tensile impact strength although with few exceptions. Plasticization of the PLA matrix improved the ductility of the composites.     

Thermal properties and stability of lithium titanophosphate glasses

DTA was used to study thermal properties and thermal stability of (50-x)Li₂O-xTiO₂-50P₂O₅ (x=0–10 mol%) and 45Li₂Ot-yTiO₂-(55-y)P₂O₅ (y=5–20 mol%) glasses. The addition of TiO₂ to lithium phosphate glasses results in a non-linear increase of glass transition temperature. All prepared glasses crystallize under heating within the temperature range of 400–540°C. The lowest tendency towards crystallization have the glasses with x=7.5 and y=10 mol% TiO₂. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were LiPO₃, Li₄ P₂O₇, TiP₂O₇ and NASICON-type LiTi₂(PO₄)₃. DTA results also indicated that the maximum of nucleation rate for 45Li₂O-5TiO₂-50P₂O₅ glass is close to the glass transition temperature.     

Thermal stability and glass transition behavior of PANI/MWNT composites

Polyaniline/multi-walled carbon nanotube (PANI/MWNT) composites were prepared by in situ polymerization. Transmission electron microscope (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) were used to characterize the PANI/MWNT composites. Thermal stability and glass transition temperature (T _g) were measured by thermogravimetry (TG) and temperature modulated differential scanning calorimetry (TMDSC), respectively. The TG and derivative thermogravimetry (DTG) curves indicated that with augment of MWNTs content, the thermal stability of PANI/MWNT composites increased continuously. While, T _g increased and then decreased with the MWNTs content increasing from 0 to 20 mass%.     

Preparation and properties of polycarbonate/polyhedral oligomeric silsesquioxanes (POSS) hybrid composites

Octaphenylsilsesquioxane (PH‐POSS) and octa(γ‐methacryloxypropyl)silsesquioxane (MA‐POSS) were successfully synthesized by hydrolytic condensation of phenyltrichlorosilane and γ‐methacryloxypropyltrimethoxysilane, and characterized by Fourier transform infrared (FT‐IR), ¹H and ²⁹Si nuclear magnetic resonance (NMR), and matrix‐assisted laser desorption/ionization‐time of flight (MALDI‐TOF) mass spectrum. Morphology, degradation behavior, thermal, and mechanical properties of hybrid composites were studied by transmission electron microscopy (TEM), polarized optical microscopy (POM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), surface contact angle (SCA), tensile, and impact testing. Domains of PH‐POSS and MA‐POSS dispersed in the matrix with a wide size distribution in a range of 0.1–0.5 µm, while PH‐POSS exhibited a preferential dispersion. Because of the possible homopolymerization of MA‐POSS during the melt blending, the glass transition temperature of polycarbonate (PC)/MA‐POSS composites remained nearly unchanged with respect to PC/PH‐POSS composites that showed a depression of T_g due to the plasticization effect. It is interesting to note that the incorporation of POSS retarded the degradation rates of PC composites and thus significantly improved the thermal stabilities. Si? O fractions left during POSS degradations were a key factor governing the formation of a gel network layer on the exterior surface. This layer possessed more compact structures, higher thermal stabilities, and some thermal insulation. In addition, percentage residues at 700°C (C₇₀₀) significantly increased from 10.8% to 15.8–22.1% in air. Fracture stress of two composites showed a slight improvement, and the impact strength of them decreased monotonically with the increase of POSS loading. Copyright © 2011 John Wiley & Sons, Ltd.     

Influence of heat treatment on electromagnetic properties of polyimide/carbon black composites

A kind of absorbing materials was prepared by hot pressing method using polyimide as matrix and carbon black (CB) as filler. The mechanical properties, the electromagnetic properties, and the thermal stability of polyimide/CB composites were studied. The results showed that the complex permittivity increased from 6.82 + 1.38i to 18.69 + 9.47i, whereas the flexural strength decreased from 108 MPa to 77 MPa, respectively, when the CB content increased from 2 wt% to 8 wt%. The reflection loss curves shifted to low frequency with increase of the thickness at the same content. The reflection loss below ?10 dB could be obtained in the X band with 6 wt% CB content and did not display significant difference before and after the heat treatment at 400°C for 5 h. When the content of CB was 8 wt%, the decomposition temperature (at 5% weight loss) increased approximately 42°C compared with pure polyimide matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermophysical properties of polypropylene/aluminum composites

This article is dedicated to the study of the thermal parameters of composite materials. A nonlinear least‐squares criterion is used on experimental transfer functions to identify the thermal conductivity and the diffusivity of aluminum‐polymer composite materials. The density measurements were achieved to deduce the specific heat and thereafter they were compared to values given by differential scanning calorimetry measurement. The thermal parameters of the composite material polypropylene/aluminum were investigated for the two different types of aluminum filler sizes. The experimental data were compared with several theoretical thermal conductivity prediction models. It was found that both the Agari and Bruggeman models provide a good estimation for thermal conductivity. The experimental values of both thermal conductivity and diffusivity have shown a better heat transport for the composite filled with large particles. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 722–732, 2004     

The mobility of PEG chains versus micellar stability towards the formation of PE‐b‐PEG nanohybrid shish‐kebab on carbon nanotubes

A comparative study of the effect of copolymer composition on nanohybrid shish‐kebab (NHSK) architecture on carbon nanotubes (CNTs) is presented. A semi‐crystalline amphiphilic di‐block copolymer, polyethylene‐b‐polyethylene glycol (PE‐b‐PEG) was used in this study. Copolymer composition was varied on the basis of the molecular weight of individual copolymers and the ratio between PE and PEG. NHSK structure was characterized using a combination of scanning and transmission electron microscopy. The mobility of PEG, which is determined by its chain length was found to have a significant impact on the periodic decoration of the copolymer on CNTs. With higher chain length or molecular weight, PEG chains provided better stability to micelles formed by the copolymer. Further, PEG assisted micellar stability to create a foundation for PE chains to interact and orient along the tube axis of CNTs as a function of the copolymer composition. It was found that the stability of NHSK architecture can also be changed over time at the same crystallization temperature. This work offers novel and fundamental insights towards the mobility of PEG in the copolymer and its disk‐shaped crystal's formation and micellar stability during crystallization with CNTs. This study provides a better understanding of a mechanically tunable NHSK where the architecture of copolymer crystals can be modified by adjusting the molecular weight of PEG.     

Thermal stability and flammability of silicone polymer composites

Silicone polymer composites filled with mica, glass frit, ferric oxide and/or a combination of these were developed as part of a ceramifiable polymer range for electrical power cables and other high temperature applications. This paper reports on the thermal stability of polymer composites as determined by thermogravimetric techniques, thermal conductivity and heat release rate as measured by cone calorimetry. The effects of fillers on thermal stability and flammability of silicone polymer are investigated. Of the fillers studied, mica and ferric oxide were found to have a stabilising effect on the thermal stability of silicone polymer. Additionally, mica and ferric oxide were found to lower heat release rates during combustion, but only mica was found to increase time to ignition.     

Thermal properties of pure and doped (polyvinyl-alcohol) PVA

Films ≈350 μm of poly(vinyl-alcohol) composites, containing copper (Cu), aluminium (Al) and iron (Fe), metallic powder very fine, were prepared by a casting method. Thermal conductivity, phonon velocity, mean free path and specific heat were studied. The pure sample of PVA has a lower values of thermal conductivity than that which are doped with metals. For all samples the thermal conductivityK increases up to a certain temperatureT _gg (120–160°C) and then decreases with temperature. The specific heat increase with temperature up to ≈120°C and above 120°C is nearly independent on temperature. The pure sample of PVA has small values of mean free path (L)≈0.2 Å at room temperature, but for PVA⁺ metalsL≈2.0 Å. The phonon velocity of pure PVA is larger than that of PVA containing metals.     

Fabrication,characterization and X-band microwave absorption properties of PAni/Fe3O4/PVA nanofiber composites materials

This work presents a study of microwave absorption properties of PAni/Fe₃O₄/PVA nanofiber composites with different ratio of Fe₃O₄ nanoparticles. The morphology of the composites nanofibers study by Field Emission Scanning Electron Microscopes (FESEM) and Transmission Electron Microscope (TEM) showed that the low content of Fe₃O₄ nanoparticles presence in the composites nanofibers indicates very much uniform surface, in the composites nanofiber without many bends, but some bends develop at higher content of Fe₃O₄ nanoparticles as indicated in the TEM image. Image-J software was used to further investigate the diameter of the composites nanofiber and found to be in the range of 152 to 195 nm. The nanofiber composites show excellent electric and magnetic properties and therefore vary with the addition of Fe₃O₄ nanoparticles in the composites nanofiber. In addition the PAni/Fe₃O₄/PVA composites nanofibers were further characterized by X-ray diffraction spectra (XRD) and Four Transformation infrared spectra (FTIR). The XRD pattern shows the presence of PAni nanotubes containing Fe₃O₄ nanoparticles by indicating peaks at 23.4⁰ and 35.43⁰ which was further supported by FTIR analysis. Microwave vector network analyzers (MVNA) were used to estimate the microwave absorption properties of the composites nanofibers. The absorption parameters was found to be −6.4 dB at 12.9 GHz within the range of X-band microwave absorption frequency, this reflection loss is attributed to the multiple absorption mechanisms as a result of the improved of impedance matching between dielectric and magnetic loss of the absorbent materials demonstrating that these materials can be used as protective material for electromagnetic radiation.     

Synthesis and characterization of fluorine functionalized graphene oxide dispersed quinoline-based polyimide composites having low-k and UV shielding properties

Polyimide nanocomposites having low-k and UV shielding properties have been developed using fluorine functionalized graphene oxide and bis(quinoline amine) based polyimide. The polyimide was synthesized using bis(quinoline amine) and pyromellitic dianhydride at appropriate experimental conditions, and its molecular structure was confirmed through various spectral analysis such as FTIR and NMR. The polyimide (PI) composites were prepared using bis(quinoline amine), pyromellitic dianhydride, and separately filled with 1, 5, 10 wt% of fluorinated graphene oxide (FGO) through in situ polymerization. The polymer composites were characterized using thermo gravimetric analysis (TGA), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). In addition, the water contact angle, dielectric behavior, and UV–Vis shielding behavior of FGO/PI composites were evaluated. The value of the water contact angle of the polyimide was increased with increment of FGO in the polyimide matrix. The highest water contact angle of polyimide composites observed 108° was obtained for 15 wt% FGO reinforced polyimide composite. The value of the dielectric constant for neat, 1, 5, and 15 wt% FGO reinforced polyimide composites was obtained as 4.5, 3.7, 2.6, and 2.0, respectively. It is also observed from by UV–Vis spectroscopy analysis that the FGO reinforced polyimide composites have good UV shielding behavior.     

Thermal stability and electrochemical performance of Polyaniline/Pr6O11 composites

In order to describe the influence of Pr₆O₁₁ on thermal and electrochemical performance of polyaniline (PANI), PANI/Pr₆O₁₁ composites were synthesized by in situ polymerization in the presence of sulfosalicylic acid (as dopant). The composites obtained was characterized by scanning electron microscope, Fourier transform infrared spectra, and X‐ray diffraction. The thermal stability of the composites was investigated by thermogravimetry and derivative thermogravimetry. Finally, the comparative analysis on the electrochemical properties of PANI/Pr₆O₁₁ composites electrodes, such as cyclic voltammetry, electrochemical impedance spectroscopy, and constant current charge–discharge test, was conducted under similar conditions. Scanning electron microscope, infrared, and X‐ray diffraction results show that interaction exists between PANI and Pr₆O₁₁, and the composites are more crystalline than pure PANI. Thermogravimetry and derivative thermogravimetry analyses indicate that PANI/Pr₆O₁₁ composites and pure PANI have similar thermal stability. Moreover, the studies regarded to capacitive properties show that the electrochemical performance of the composites is improved greatly when Pr₆O₁₁ is added in small amount. However, with increasing the amount of Pr₆O₁₁, the electrochemical performance of the composites become worse, which indicates a large amount of Pr₆O₁₁ has a negative effect on the capacitance. These results suggest that PANI is still in the conductive form after inserting the Pr₆O₁₁, and the capacitance performance of PANI can be improved only by a low percentage of Pr₆O₁₁. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of alkali and ultraviolet aging on physical,thermal, and mechanical properties of fibers for potential use as reinforcing elements in glass/silicate composites

This work reports the effect of an alkaline environment and ultraviolet (UV) radiation on the physical, thermal, and tensile properties of different fibers selected as potential reinforcing elements to enhance the impact properties of brittle glass/silicate composites. The fibers, which included regenerated cellulosic (viscose and rayon), synthetic (ultrahigh molecular weight polyethylene, polypropylene, polyamide, acrylic), glass, ceramic, and steel, were aged in different alkaline solutions with pH ranging from 11.1 to 13.6 at 70°C for different periods of time and exposed to UV radiation for 330 h. The physical and thermal properties of aged fibers were studied using tensile testing, scanning electron microscopy, and simultaneous differential and thermogravimetric analysis. Results showed that the regenerated cellulosic fibers, acrylic, E‐glass, and A‐glass fibers could not withstand the highly alkaline environment. Overall, ultrahigh molecular weight polyethylene, UV‐stable polypropylene, polyamide 6.6, AR‐glass, ceramic (alumino borosilicate), and steel fibers performed very well under all conditions, indicating that they have the potential to be used as reinforcing elements in glass/silicate composites. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermal conductive PS/graphite composites

Polystyrene (PS) was compounded with graphite that possesses high thermal conductivity and layer structures, and the PS/graphite thermal conductive nano‐composites were prepared. Thermal conductivity of PS improved remarkably in the presence of the graphite, and a much higher thermal conductivity of 1.95 W/m K can be achieved for the composite with 34 vol% of colloidal graphite. The Maxwell‐Eucken model and the Agari model were used to evaluate the thermal conductivity of the composites. For the purpose of improving the interfacial compatibility of PS/graphite, realizing the exfoliation and nano‐dispersion of graphite in the PS matrix, three intercalation methods, including rolling intercalation, solvent intercalation, and pan milling intercalation, were applied to prepare the composites, and the morphologies, thermal conductivities, and mechanical properties of the composites were investigated. It should be noted that the one prepared by pan milling intercalation not only had excellent thermal conductivity but also much higher mechanical properties, resulting from a high degree of layer exfoliation of the graphite, the formation of the chain structure agglomerates of the graphite, and the creation of more conductive paths under the strong shear stress of pan milling. Copyright © 2008 John Wiley & Sons, Ltd.     

Biocompatible agar/xanthan gum composite films: Thermal,mechanical, UV,and water barrier properties

Binary composite films were prepared from agar (A) and xanthan gum (X) with different weight percentages. The composite films were transparent, lightweight, eco‐friendly, and biodegradable. The structure and morphology of the prepared agar and AX composite films were confirmed by Fourier transform infrared spectroscopy (FT‐IR), X‐ray powder diffraction (XRD), and scanning electron microscopy (SEM) technique. The glass transition temperature (T_g) and melting temperature (T_m) of the AX composite films was slightly improved, when compared with the neat agar. Thermogravimetric analysis (TGA) analysis showed a considerable increment in the char yield and an improved thermal stability. The tensile strength was in the range of 25 to 40 MPa, and elongation at break was in the range of 28.9 to 39.4%. Though, the water vapor permeability (WVP) value reduced in the composite films the difference was not significant. From the mechanical studies, we can deduce that agar and xanthan gum are compatible and miscible with one another leading to prospects of their composite films being considered for different biomedical and packaging applications.     

Dielectric,thermal, and mechanical properties of CeO2‐filled HDPE composites for microwave substrate applications

Cerium oxide‐filled high density polyethylene (HDPE) composites for microwave substrate applications were prepared by sigma‐blend technique. The HDPE was used as the matrix and the dispersion of CeO₂ in the composite was varied up to 0.5 by volume fraction, and the dielectric properties were studied at 1 MHz and microwave frequencies. The variations of thermal conductivity (k_eff), coefficient of thermal expansion (α_c) and Vicker's microhardness with the volume fraction of the filler were also measured. The relative permittivity (ε_eff) and dielectric loss (tan δ) were found to increase with increase in CeO₂ content. For 0.4 volume fraction loading of the ceramic, the composite had ε_eff = 5.7, tan δ = 0.0068 (at 7 GHz), k_eff = 2.6 W/m °C, α_c = 98.5 ppm/°C, Vicker's microhardness of 18 kg/mm² and tensile strength of 14.6 MPa. Different theoretical approaches have been used to predict the effective permittivity, thermal conductivity, and coefficient of thermal expansion of composite systems and the results were compared with the experimental data. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 998–1008, 2010     

Photoacoustic infrared spectroscopy and thermophysical properties of syncrude cokes

This paper presents and interprets photoacoustic (PA) infrared spectra and four different thermophysical properties (thermal conductivity, thermal diffusivity, volumetric specific heat and thermal effusivity) for four sets of hydrocarbon cokes. A total of 12 samples, with varying histories, were analyzed. These cokes are a by-product of the upgrading of bitumen to Syncrude Sweet Blend (a blend of hydrotreated components), and were obtained from several locations in the thermal cokers operated by Syncrude Canada Ltd. in Fort McMurray, Alberta, Canada. PA infrared spectroscopy provides detailed information on the amount and type of residual aromatic hydrocarbons in cokes; aliphatic hydrocarbons are sometimes detected in smaller quantities. Three of the thermophysical properties (thermal conductivity, diffusivity and effusivity) display systematic differences among the cokes. On the other hand, volumetric specific heat hardly varies, a phenomenon that accounts for the observed proportionality between thermal diffusivity and conductivity. Analogous relationships exist between thermal effusivity and both thermal conductivity and thermal diffusivity for these cokes. The magnitudes of these three thermophysical properties tend to increase as aromatics contents, determined by PA spectroscopy, decrease.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermal,structural and electrical properties

The chloro compound of 3-hydroxy-2-quinoxalinecarboxylic acid with nickel(II) has been prepared in ethanolic solution from which a solid compound was isolated. Spectral and magnetic measurements show that the nickel ions are in an octahedral environment. Thermogravimetry, differential thermal analysis and electrical conductivity data are reported for 3-hydroxy-2-quinoxalinecarboxylic acid and its nickel complex. The conductivity measurements indicate that electron/hole traps are emptied during heating of the complex but repopulation occurs in about 24 h at room temperature.     

Non-steady effective thermal properties of semi-infinite unidirectional fiber-reinforced composites using thermal wave method

Photothermal techniques and effective medium method combining with image method are applied to investigate the non-steady effective thermal properties of semi-infinite unidirectional fiber-reinforced composites, and the effect of the semi-infinite surface on the non-steady effective thermal properties is considered. The dispersion relation for the effective wave number in the semi-infinite random composites is derived. The image method is used to satisfy the adiabatic boundary condition at the semi-infinite surface. The numerical solutions of the non-steady effective thermal properties are obtained by using an iterative scheme. Analyses show that the variation of the non-steady effective thermal properties near the semi-infinite surface is significantly different from those of the infinite composite structure. The effects of the circular frequency of thermal waves, the volume fraction of fibers, and the properties contrast ratio on the maximum non-steady effective properties near the surface are examined. Comparison with the steady case is also given.