Showing papers on "Thermomechanical analysis published in 2012"

Characterization of Nanocomposites by Thermal Analysis

Abstract: In materials research, the development of polymer nanocomposites (PN) is rapidly emerging as a multidisciplinary research field with results that could broaden the applications of polymers to many different industries. PN are polymer matrices (thermoplastics, thermosets or elastomers) that have been reinforced with small quantities of nano-sized particles, preferably characterized by high aspect ratios, such as layered silicates and carbon nanotubes. Thermal analysis (TA) is a useful tool to investigate a wide variety of properties of polymers and it can be also applied to PN in order to gain further insight into their structure. This review illustrates the versatile applications of TA methods in the emerging field of polymer nanomaterial research, presenting some examples of applications of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA) and thermal mechanical analysis (TMA) for the characterization of nanocomposite materials.

Effects of surface treatment of ramie fibers in a ramie/poly(lactic acid) composite

Abstract: The chemical and morphological properties of ramie fibers treated by chemical surface modification were examined with Fourier transform infrared (FT-IR) spectroscopy. The mechanical and thermal decomposition properties were evaluated with respect to tensile strength, tensile modulus and thermogravimetric analysis (TGA). Surface morphological changes were investigated with scanning electron microscopy (SEM). Finally, the capabilities of composites reinforced with various chemically treated fibers were analyzed by investigating tensile and impact strengths. Additionally, the thermal mechanical properties of the composites were investigated with thermal mechanical analysis (TMA). Based on the results of these analyses, we concluded that pectin, lignin and hemicellulose were removed and thermal stability was increased with chemical treatments. The composites reinforced with ramie fiber showed better properties compared with pure PLA matrix with respect to tensile and impact strengths. The peroxide-treated fiber composite had the smallest thermal expansion.

Network structure and thermomechanical properties of hybrid DGEBA networks cured with 1-methylimidazole and hyperbranched poly(ethyleneimine)s

Abstract: he use of commercially available hyperbranched poly(ethyleneimine)s (Lupasol TM , BASF) as polymeric modifiers in diglycidyl ether of bisphenol A thermosetting formulations using 1-methylimidazole (MI) as anionic initiator has been studied. Poly(ethyleneimine)s can get incorporated into the network structure by condensation of amine and epoxy groups. The excess, over-stoichiometric epoxy groups can undergo ani- onic homopolymerization initiated by MI. The thermal, dyna- momechanical, and mechanical properties of the resulting materials have been determined using DSC, thermomechanical analysis (TMA), dynamomechanical analysis (DMA), and me- chanical testing. The effect of the different amine modifiers on the MI networks, determined by their structure, is complex. Low initiator content and high molecular weight modifiers cre- ate significant mobility restrictions, which have a strong effect on the glass transition temperature and the apparent crosslink- ing density of the cured materials.

Effect of the epoxy/amine stoichiometry on the properties of carbon nanotube/epoxy composites

Abstract: The effect of different amine/epoxy ratios on different properties of an epoxy resin was evaluated. Also, different amounts of carbon nanotubes (CNT) were added in order to analyse which of these two factors is more relevant. Dynamic thermomechanical analysis and flexural tests were carried out. The results obtained for the epoxy resin are in agreement with that reported by several researchers. The glass transition temperature of the resin and composites is maximal for the amine/epoxy stoichi- ometric ratio, while the highest glassy storage and flexural modulus correspond to the epoxy-rich systems, showing that the most crosslinked network is not the stiffest one. The effect of changing the stoichiometry is more relevant than adding CNT to the epoxy resin used in this work. However, the addition of CNT causes more remarkable changes in the epoxy-rich resin, promoting an increase of the glass transition temperature and the elastic modulus.

Stiff lattices with zero thermal expansion

Abstract: Lattice microstructures are presented with zero coefficient of thermal expansion. These are made of positive expansion materials. The behavior is primarily stretch dominated, resulting in favorable stiffness. The behavior of these lattices is compared with that of triangular and hexagonal honeycombs in a modulus–density map. These lattices do not undergo thermal buckling, in contrast to designs based on sublattices.

Thermal and Mechanical Properties of Epoxy/Carbon Fiber Composites Reinforced with Multi-walled Carbon Nanotubes

Abstract: Multi-scale hybrid composite laminates of epoxy/carbon fiber (CF) reinforced with multi-walled carbon nanotubes (MWCNTs) were fabricated in an autoclave. For laminate fabrication, 0.5 wt% of pristine MWCNTs or silane-functionalized MWNCTs (f-MWCNTs) were dispersed into a diglycidyl ether of bisphenol-A epoxy system and applied on the woven carbon fabric. The neat epoxy/CF composite and the MWCNTs-reinforced epoxy/CF hybrid composites were characterized by thermogravimetric analysis (TGA), thermomechanical analysis (TMA), tensile testing, and field emission scanning electron microscopy (FE-SEM). A significant improvement in initial decomposition temperature and glass transition temperature of epoxy/CF composite was observed when reinforced with 0.5 wt% of f-MWCNTs. The coefficient of thermal expansion (CTE), measured by TMA, diminished by 22% compared to the epoxy/CF composite, indicating an improvement in dimensional stability of the hybrid composite. No significant improvement in tensile properties of ei...

Thermomechanical behaviors and dielectric properties of polyaniline-doped para-toluene sulfonic acid/epoxy resin composites

Abstract: Composites based on conductive organic/inorganic fillers dispersed in insulating matrix have been widely investigated because of their widespread applications such as electromagnetic shielding, electrostatic discharge, and sensors In this context, novel composite materials based on epoxy resin matrix charged with polyaniline (PANI)-doped para-toluene sulfonic acid were elaborated Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy were used to check the structure and the morphology of the samples Viscoelastic behavior and thermal stability of the composites were explored by dynamic mechanical thermal analysis and thermogravimetric analysis It was shown that the PANI particles exhibited a partial crystalline structure and were homogeneously dispersed in epoxy matrix Consequently, this structure affected the thermal stability and viscoelastic properties of the composites Furthermore, the dielectric and electrical properties were investigated up to 1 MHz Measurements of dielectric properties revealed that with loading fillers in matrix, the dielectric parameters increased to high values at low frequency then decreased at values around 40 and 32 of real and imaginary parts, respectively, at 1 MHz with 15% of PANI content Copyright © 2011 John Wiley & Sons, Ltd

High thermal conductivity/low coefficient of thermal expansion composites

Abstract: A high thermal conductivity/low coefficient of thermal expansion thermally conductive composite material for heat sinks and an electronic apparatus comprising a heat sink formed from such composites. The thermally conductive composite comprises a high thermal conductivity layer disposed between two substrates having a low coefficient of thermal expansion. The substrates have a low coefficient of thermal expansion and a relatively high modulus of elasticity, and the composite exhibits high thermal conductivity and low coefficient of thermal expansion even for composites with high loadings of the thermally conductive material.

Rotational Molding of Polyamide-6 Nanocomposites with Improved Flame Retardancy

Abstract: The aim of this work was to develop polyamide-6/ organic-modified montmorillonite (omMMT) nanocomposites for the production of hollow parts by rotational molding. Particular emphasis was placed on the mechanical and flame retardancy properties needed for the fabrication of vessels for flammable liquids. The morphology of the melt compounded nanocomposites, produced by melt compounding, was investigated by X-ray diffraction measurements (WAXD), and Transmission Electron Microscopy (TEM) showed an exfoliated structure. Rheological measurements were used in order to verify whether the viscosity of materials was adequate for rotational molding. While thermomechanical analysis has revealed that neat PA6 and its nanocomposites were not suitable for rotational molding, due to the very low thermal stability of the polymer, the addition of a thermal stabilizer, shifted the onset of degradation to higher temperatures, thus widening the processing window of both PA6 and PA6 nanocomposites. Large-scale vesse...

Thermal properties of thermosets

Abstract: This chapter discusses the thermal properties of thermoset resins. Unlike thermoplastics, whose thermal properties depend only upon molecular weight, the thermal properties of a thermoset depend on various factors. The chapter covers the thermal conductivity, thermal expansion coefficient, thermal stability, heat distortion temperature, flammability, thermal cure characteristics and transition behavior (especially glass transition temperature) of thermoset resins.

Cyclic tetravinylsiloxanetetraols as hybrid inorganic-organic thiol-ene networks

Abstract: In this work, organic-inorganic hybrid materials containing stable silanol functionalities were designed by incorporating cyclic tetravinylsiloxanetetraols into photopolymerized polymer networks via the thiol-ene reaction, with the intent of tailoring the thermal and mechanical properties of the resulting materials The effects of the cyclic tetravinylsiloxanetetraols concentration on the thermomechanical properties and thermal stability of pentaerythritol triallyl ether/pentaerythritol tetra(3-mercaptopropionate) (APE-PETMP) and allyl isocyanurate/pentaerythritol tetra(3-mercaptopropionate) (TTT-PETMP) ternary networks were evaluated using dynamic thermomechanical analysis and thermogravimetric analysis, respectively Photopolymerization kinetics were monitored using real-time FTIR Interestingly, an increase in glass transition temperature was observed with the APE-PETMP networks while a decrease in glass transition temperature was observed for the TTT-PETMP networks with increasing concentration of [Vi(OH)SiO]4 These observations are discussed in terms of cross-link density and monomer rigidity

Integrated fire dynamic and thermomechanical modeling of a bridge under fire

Abstract: 【This paper proposes a nonlinear computational modeling approach for the behaviors of structural systems subjected to fire. The proposed modeling approach consists of fire dynamics analysis, nonlinear transient-heat transfer analysis for predicting thermal distributions, and thermomechanical analysis for structural behaviors. For concretes, transient heat formulations are written considering temperature dependent heat conduction and specific heat capacity and included within the thermomechanical analyses. Also, temperature dependent stress-strain behaviors including compression hardening and tension softening effects are implemented within the analyses. The proposed modeling technique for transient heat and thermomechanical analyses is first validated with experimental data of reinforced concrete (RC) beams subjected to high temperatures, and then applied to a bridge model. The bridge model is generated to simulate the fire incident occurred by a gas truck on April 29, 2007 in Oakland California, USA. From the simulation, not only temperature distributions and deformations of the bridge can be found, but critical locations and time frame where collapse occurs can be predicted. The analytical results from the simulation are qualitatively compared with the real incident and show good agreements.】

Thermal–mechanical property and fracture behaviour of plasticised PLA–CaCO3 nanocomposite

Abstract: This study investigates the influence of two plasticisers, polyethylene glycol (PEG) and tributyl citrate (TbC), on the thermomechanical properties and fracture behaviour of nanosized calcium carbonate blended poly(lactic acid). Various compositions of nanocomposites were compounded and processed using co-rotating twin screw extrusion and compression moulding. DMA analysis shows that adding nano-CaCO3 reduced the storage modulus (E′) of the nanocomposite while the glass transition temperature (Tg) of the samples was not affected. Furthermore, plasticised poly(lactic acid) (PLA) showed an improvement in elongation at break in all samples, and the impact resistance of the nanocomposites was also improved by 1·6 times with the addition of 20 phr PEG plasticiser and by 1·4 times with the addition of 20 phr TbC plasticiser. Morphological study reveals that the fracture behaviour of PLA-CaCO3 nanocomposites changed from brittle to ductile after plasticisers were incorporated.

Single/few-layer boron nitride-based nanocomposites for high thermal conductivity underfills

Abstract: Thermal management in 3D packaging plays an important role in the device performance and reliability. The development of thermally conductive underfills is highly crucial, but still challenging. In this work, single/few-layer boron nitride (BN) was exfoliated from bulk h-BN flakes and was incorporated into epoxy resin via a solvent transfer method.[1] The structure of exfoliated BN was characterized by varieties of techniques, including scanning electron microscopy, transmission electron microscopy, electron diffraction, Raman microscopy, and UV-vis microscopy. The single/few layer boron nitride/epoxy composite was characterized by thermomechanical analysis and thermogravimetric analysis. The thermal conductivity of exfoliated BN was measured by an infrared thermal imaging method. A significant enhancement of thermal conductivity (220 %) is observed at a low filler loading of 5 wt%, indicating that the single/few-layer BN is a promising filler for the development of novel underfill for 3D packaging.

Applications of some thermo-analytical techniques to glasses and polymers

Abstract: Thermal characterization of materials provides conclusions regarding the identification of materials as well as their purity and composition, polymorphism, and structural changes. Analytical experimental techniques for thermal characterization comprise of a group of techniques, in which physical properties of materials are ascertained through controlled temperature program. Among these techniques, traditional differential scanning calorimetry (DSC) is a well-accepted technique for analyzing thermal transitions in condensed systems. Modulated DSC (MDSC) is used to study the same material properties as conventional DSC including: transition temperatures, melting and crystallization, and heat capacity. Further, MDSC also provides unique feature of increased resolution and increased sensitivity in the same measurement. “Hot disk thermal constant analyzer”, based on Transient Plane Source (TPS) technique, offers simultaneous measurement of thermal transport properties of specimen, which are directly related to heat conduction such as thermal conductivity (λ) and thermal diffusivity (χ). This method enables the thermal analysis on large number of materials from building materials to materials with high thermal conductivity like iron. The temperature range covered so far extends from the liquid nitrogen point to 1000 K and should be possible to extend further. This review also presents some interesting results of phase transition temperature of miscible (CPI/TPI) and immiscible (PS/PMMA) polymeric systems carried out through dynamic mechanical analyzer along with the thermal transport properties obtained for cis-polyisoprene (CPI), trans-polyisoprene (TPI), and their blends determined by TPS technique.

Thermomechanical finite element analysis of hot water boiler structure

Abstract: The paper presents an application of the finite elements method for stress and strain analysis of the hot water boiler structure. The aim of the research was to investigate the influence of the boiler scale on the thermal stresses and strains of the structure of hot water boilers. Results show that maximum thermal stresses appear in the zone of the pipe carrying wall of the first reversing chamber. This indicates that the most critical part of the boiler are weld spots of the smoke pipes and pipe carrying plate, which in the case of significant scale deposits can lead to cracks in the welds and water leakage from the boiler. The non-linear effects were taken into account by defining the bilinear isotropic hardening model for all boiler elements. Temperature dependency was defined for all relevant material properties, i. e. isotropic coefficient of thermal expansion, Young’s modulus, and isotropic thermal conductivity. The verification of the FEA model was performed by comparing the measured deformations of the hot water boiler with the simulation results. As a reference object, a Viessmann-Vitomax 200 HW boiler was used, with the installed power of 18.2 MW. CAD modeling was done within the Autodesk Inventor, and stress and strain analysis was performed in the ANSYS software.

Effect of the aggregation structure on the thermal shrinkage of polyacrylonitrile fibers during the heat-treatment process

Abstract: Secondary thermal shrinkage or chemical shrinkage involved in the thermal shrinkage of polyacrylonitrile (PAN) fibers was not only associated with the cyclization degree but also the thermal mobility of molecular chains in the aggregation structures during crosslinking. In this study, the cyclization process was monitored with differential scanning calorimetry and IR spectroscopy. The evolution of aggregation structures throughout cyclization and variations in the secondary shrinkage for the PAN fibers were characterized with wide-angle X-ray diffraction and thermal mechanical analysis, respectively. The results show that with increasing temperature, the cyclization degree increased; the cyclization occurred first in amorphous regions and then extended to the crystalline regions. Correspondingly, the secondary shrinkage also increased and could be separated into two stages: those of the amorphous and crystalline phases. The shrinkage of the crystalline regions was much bigger than that of the amorphous regions. For fibers with different aggregation structures, the crystallinity affected the cyclization degree in the amorphous and crystalline regions and resulted in the difference in total shrinkage. Furthermore, because the unoriented molecular chains in both the amorphous and crystalline regions shrank more after cyclization, the shrinkage of both regions was primarily decided by the level of orientated molecular chains participating in the cyclization. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Glass-Transition Temperature Profile Measured in a Wood Cell Wall Using Scanning Thermal Expansion Microscope (SThEM)

Abstract: This study aims to assess the in situ spatial distribution of glass-transition temperatures (Tg) of the main lignocellulosic biopolymers of plant cell walls. Studies are conducted using scanning thermal expansion microscopy to analyze the cross-section of the cell wall of poplar. The surface topography is mapped over a range of probe-tip temperatures to capture the change of thermal expansion on the sample surface versus temperature. For different temperature values chosen between 20 °C and 250 °C, several quantitative mappings were made to show the spatial variation of the thermal expansion. As the glass transition affects the thermal expansion coefficient and elastic modulus considerably, the same data line of each topography image was extracted to identify specific thermal events in their topographic evolution as a function of temperature. In particular, it is shown that the thermal expansion of the contact surface is not uniform across the cell wall and a profile of the glass-transition temperature could thus be evidenced and quantified corresponding to the mobility of lignocellulosic polymers having a role in the organization of the cell wall structures.

Potential of AFM-nanothermal analysis to study the microscale thermal characteristics in soils and natural organic matter (NOM)

Abstract: This exploratory study evaluates the potential of nanothermal analysis (nTA) coupled with atomic force microscopy (AFM) of soil samples for understanding physicochemical processes in soil and for linking the nanospatial and microspatial distribution of thermal characteristics with the macroscopic properties of soil samples. Soil and reference samples were investigated by differential scanning calorimetry and AFM-nTA. nTA was conducted on 16 points of each AFM image in two subsequent heating cycles (55–120°C and 55–300°C, respectively). Thermograms were subdivided into characteristic types and their spatial distribution was compared between sample replicates and materials. Thermogram types consisted of partly structured expansion and compression phases, suggesting material-specific thermal profiles. The distribution of thermogram types reflected sample-dependent nanoscale and microscale heterogeneity. Indications for water molecule bridge transitions were found by nTA in peat and soil. Organic materials generally revealed strong expansion and irreversible compression phases, latter probably due to the collapse of pore and aggregate structures. In contrast to charcoal and manure, peat shows strong expansion below 120°C and compression only above 120°C. All investigated samples are heterogeneous on the nanoscale and microscale with respect to thermal behaviour. AFM-nTA allows distinguishing numerous different materials on nanometre and micrometre scales in soil samples. The material-dependent characteristics will help in understanding and learning more about the nanoscale distribution of different materials and properties. Related to the macroscopic thermal behaviour, this will allow studying links between the properties of biogeochemical interfaces and the processes governed by them.

Thermomechanical model of cutter self-oscillation in perpendicular free cutting

Abstract: On the basis of thermomechanical analysis, cutter self-excitation in perpendicular free cutting of metals may be attributed to the nonlinear temperature dependence of the blank’s mechanical characteristics. By simulation, the conditions favorable to self-oscillation may be identified for different materials.