Changes In Thermomechanical Properties Research Articles

Bio‐based hydrophobic epoxy‐amine networks derived from renewable terpenoids

ABSTRACTCarvacrol and p‐cymene are sustainable and versatile starting materials for the preparation of hydrophobic monomers. These molecules can be readily derived from pine resin or produced from other sustainable feedstocks via a biosynthetic approach. A hydrophobic epoxy monomer [bis(2‐isopropyl‐5‐methyl‐4‐(oxiran‐2‐ylmethoxy)phenyl)methane, 3] with methyl and isopropyl substituents on the aromatic rings was synthesized from carvacrol. A bisaniline [4,4′‐methylenebis(5‐isopropyl‐2‐methylaniline, 4] was then synthesized from p‐cymene. Using a cured epoxy‐amine network prepared from the diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐methylenedianiline (MDA) as a baseline system, three additional networks were prepared from DGEBA:4, 3:MDA, and 3:4. The cured epoxy‐amine networks were tested for moisture uptake as well as changes in thermomechanical properties after exposure to boiling water for several days. Incorporation of the bio‐based monomers resulted in up to 53% lower water uptake compared to the baseline system. The bio‐based resins also showed greater resistance to degradation under hot‐wet conditions, with wet‐TG knockdowns as low as 8% as compared to a 19% decrease for the baseline system. These results show that the unique functionality of the renewable bisphenol and aniline used in this study can result in materials with improved hot/wet performance as compared to conventional thermosetting resins. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43621.

Thermo-Mechanical Properties and Tensile Behaviour of Modified HDPE by Beta Rays after Temperature Load at 220 °C

Radiation processing of polymers is a well-established and economical commercial method of precisely modifying the properties of polymers, especially thermo-mechanical properties. The tensile behaviour of modified HDPE samples by radiation cross-linking was measured at the ambient temperature and after temperature load at 220 °C. The tested samples showed significant changes of thermo-mechanical properties and tensile behaviour after 220 °C. From this point of view, new applications could also be seen in areas with service temperatures higher than their former melting point.

Physical state of the amorphous phase of polypropylene-influence on thermo-mechanical properties

Stable polypropylene, PP – low molecular weight modifier systems were prepared in order to analyze the influence of the physical state of the amorphous phase on thermo-mechanical properties. The modifier was introduced into solidified material by diffusion to the amorphous phase regions. The change of state of stress of the transmitters connecting adjacent crystals caused by substantial increase of interlamellar distance was observed. The new state of stress of the molecular network of the amorphous phase induced respective change of the stress state of the crystalline component. As the effect the tensile yield stress value was substantially reduced, also the stress caused a decrease of melting temperature of PP crystals. The above proposed mechanism served to explain the changes of thermo-mechanical properties of the blends with identical composition prepared by blending in a molten state. During the solidification of the blend, the modifier molecules were exuded out of the growing crystals. The physical state of the molecular network of the amorphous phase was changed in a similar way as for the systems with infused modifier into previously solidified polymer matrix. The changes of mechanical properties were additionally correlated with the observed change of the melting temperature of the crystals.

Application of dilatometry with modulated temperature for thermomechanical analysis of anti-wear coating/substrate systems

Modern vacuum-plasma surface modification technologies of tools for metal and wood machining are based inter alia on the deposition of thin gradient and multilayer protection coatings with a thickness of several micrometers. Exploitation of tools are frequently carried out in complex tribological nodes, where next to mechanical loads, there are significant changes in temperature at the interface of the tool/workpiece material; hence, the knowledge of the thermomechanical stability of the coatings operating under these conditions is an important criterion used in the processes of designing of wear-resistant coating technology. In this paper, the objects of research were three types of gradient PVD coating/molybdenum substrate systems, for which time courses of amplitudes of elongation and equivalent thermal expansion coefficients of the systems were measured. Experimental measurements were made using a temperature-modulated dilatometry using concepts of dynamic load thermomechanical analysis. It was demonstrated that the developed method allows a quantitative determination of the influence of the gradient layer type on the total elongation of the substrate of the system. It was also shown that the changes of thermomechanical properties of the systems during annealing process are correlated with the time evolution of the equivalent thermal expansion coefficient. In addition, using the concepts of transition function describing the continuous change of physical and chemical parameters as a function of the spatial variables and finite element method for each of the systems, the distributions of internal thermal stresses were determined.

Effect of thermal treatment on structure and properties of polyester tire cords

AbstractPolyester and nylon are the mostly used reinforcing textile fibers in many industrial rubber applications. Now‐a‐days body ply of a passenger car radial is mostly made up of polyester fiber. Because of its thermoplastic nature, it undergoes some kind of thermal shrinkage during processing and vulcanization, which lead to many problems related to shape, dimension, and dimensional stability. To avoid this, polyester is subjected to thermal treatment at higher temperature. Hence, thermomechanical properties of polyester tire cords become very important. During the thermal treatment, there is not only change in shrinkage, shrinkage force, and mechanical properties but also it affects structural and morphological properties. In this work, the changes in thermomechanical properties due to heat setting have been correlated to structural and morphological changes like crystallinity, crystal size, orientation, crystal perfection, etc. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Molecular modeling of crosslinked epoxy polymers: The effect of crosslink density on thermomechanical properties

Molecular dynamics and molecular mechanics simulations are used to establish well-equilibrated, validated molecular models of the EPON 862-DETDA epoxy system with a range of crosslink densities using a united atom force field. Molecular dynamics simulations are subsequently used to predict the glass transition temperature, thermal expansion coefficients, and elastic properties of each of the crosslinked systems. The results indicate that glass transition temperature and elastic properties increase with increasing levels of crosslink density and the thermal expansion coefficient decreases with crosslink density, both above and below the glass transition temperature. The results demonstrate reasonable agreement with thermomechanical properties in the literature. The results also indicate that there may be a range of crosslink densities in epoxy systems beyond which there are limited changes in thermomechanical properties.

경년열화가 증용량 저이도 송전선의 기계적특성에 미치는 영향 (II)

Today, restricted energy sources, environmental considerations and the high cost of transporting fuel have limited the number and location of available power plant sites. The pressures resulting from these conditions have tended to require the construction of long, high-capacity, high-voltage power lines. it's used to adapt to STACIR/AW(Super Thermal-resistant Aluminum alloy Conductors, aluminum-clad Invar-Reinforced) conductor for coping with these situations. STACIR/AW conductor was formed by the combination of INVAR/AW as the core for low sag and super thermal-resistant aluminum alloy conductor for current capacity increase. increase of temperature by current capacity and long span lines make the susceptible to the deterioration of thermo-mechanical properties(conductivity, tensile strength, E-modulus and twist property et al). In the present work, changes of thermo-mechanical properties with aging have been studied in STACIR/AW <TEX>$410 mm^2$</TEX> conductor with forms of single wire and strand wire.

Variability between chitosan membrane surface characteristics as function of its composition and environmental conditions

The object of the present work is investigate the morphological modifications of several composition chitosan films, due to components concentration changes, under temperature and relative humidity controlled conditions. For the surface analysis study results obtained by conventional optical and polarization microscopies so as UV–vis spectroscopy are used. Different capacity adsorption of different chitosan membranes introduce changes in thermo-mechanical properties.

Experimental determination of the effects of industrial oil immersion on polymer-based composites

This paper presents a unique set of experimental data on the long-term oil immersion effects on various carbon fiber-reinforced thermoplastic composites. Five materials—unidirectional AS4/PEEK, unidirectional AS4/PPS, unidirectional AS4/PEI, woven AS4/PEI, and short random AS4/PFA—were immersed in oil and water for several months at four temperatures between room temperature and 80 °C. The weights of the four samples were monitored. The samples exposed to oil were tested via Dynamic Mechanical Analysis (DMA). The results show that the four AS4/PEEK, AS4/PPS, AS4/PEI and woven AS4/PEI composites did not exhibit any changes in thermo-mechanical properties. However, the Teflon-based composite showed significantly altered behavior despite no changes in weight. The glass transition temperature was lowered by 30 °C after a 2-month immersion in oil (independently of the temperature). No change in the glass transition temperature but a stiffness degradation was observed after immersion in water. A dramatic decrease in the glass transition temperature of reinforced PFA can be attributed solely to prolonged industrial oil contact including that at room temperature.

Prediction of thermoelastic properties of composite laminates with matrix cracks

A theory is presented for the determination of changes in the elastic compliance tensor and the thermal expansion coefficients due to matrix cracking. Effects of residual stresses are taken into account. The theory is valid for two- or three-dimensional laminates of arbitrary lay-ups and is asymptotically exact for dilute micro-crack densities. For large micro-crack densities an alternative model is described which is asymptotically exact for large crack densities. Combined, the two models cover to a good approximation the whole range of micro-crack densities. The theory is applied to a micro-cracking cross-ply GFRP laminate for which the stress/strain curve is calculated. Data are also presented for changes in thermomechanical properties of angle ply laminates as functions of the lay-up angle.