Changes In Thermomechanical Properties Research Articles

Effect of Irradiation Temperature and Atmosphere on Aging of Epoxy Resins for Superconducting Magnets.

The superconducting magnets of future particle accelerators will be exposed to high irradiation doses at cryogenic temperatures. To investigate the effect of irradiation temperature and atmosphere on the aging behavior, we have characterized the changes in thermomechanical properties of six epoxy resins for potential use in superconducting magnets after irradiation up to 20 MGy in ambient air, inert gas, and liquid helium. Based on the results obtained by Dynamic Mechanical Analysis (DMA), we discuss the effect of irradiation temperature and the presence of oxygen. The irradiation temperature can have a strong influence on the rates at which cross-linking and chain scission occur.

Structuring step dependent characteristics in joining using pin-like structures in the vibration welding process

Abstract With this study, correlations in the structuring step of pin-like joining were derived. Increased friction energy due to higher amplitude or force leads to a reduction in structuring time. Changes in thermo-mechanical properties for humid specimens result in increased process times. The theoretical geometry of the pin-like structures is well reproduced in the lower pin area, regardless of the process control. In the upper pin area, increased force and amplitude results in increased defects and air inclusions as a result of an accelerate and more inhomogeneous pin formation. Humidity does not affect the general pin geometry, but should be avoided due to increased air inclusions that can weaken the structure. For the multi-material joints, high bond strengths of up to 30 % of the base material (max. 50 % possible with the geometry used) can be achieved. Therefore, a minimum undercut is required. Once this is reached, the pin defects and the corresponding pin-foot ratio are decisive for the resulting bond quality.

Analysis of the Impact of Changes in Thermomechanical Properties of Annealed Semi-Crystalline Plastics on the Surface Condition after the Machining Process.

In this paper, the authors present a comparative analysis of the thermomechanical properties of plastics intended for machining before and after the annealing process. The research included the dynamic properties, thermal analysis and a study of the surface after machining. The dynamic properties were tested using the DMTA method. The characteristics of changes in the value of the storage modulus E' and the tangent of the mechanical loss angle tgδ depending on the temperature and vibration frequency were determined. The thermal properties were tested using the DSC method, and a comparative analysis of the roughness parameters of the tested materials obtained from the profilometer was carried out. The presented studies indicate the extent of the impact of the annealing process on the machinability of structural polymer materials, taking into account the analysis of changes in the thermomechanical properties of the tested materials.

Emulsion templated poly(thiol-enes): Selective oxidation improves mechanical properties

Porous thiol-ene polymer networks were prepared with different sulfur contents from high internal phase emulsions (HIPEs). A rigid thiol, tris [2-(3-mercaptopropionyloxy) ethyl] isocyanurate (TEMPIC), together with 1,6-hexanediol diacrylate (HDDA), was employed for this study. A modification of the polymer network was performed via the oxidation of the thioethers present in the polymer backbone to sulfoxides and sulfones. Infrared spectroscopy measurements confirmed that the selective oxidation of thioether groups was possible. Furthermore, the changes in thermomechanical properties were determined by dynamic mechanical analysis and thermogravimetric analysis. A significant increase in glass transition temperature from 4.9 to 41.5 °C for the resulting sulfone could be observed for networks with the highest sulfur content. Changes in mechanical properties were determined via tensile and compression testing and showed considerable improvement of tensile and compressive strength after the oxidation. The behavior of the materials upon hydrolytic stress was investigated and led to the highest mass loss for sulfone materials.

Experimental investigation of the effect of thermal cycling on the thermomechanical properties of three rock varieties for high temperature thermal energy storage

During the past years “rock batteries” have become increasingly relevant for the storage of renewable energy sources, such as wind and solar energy, because of their economic and ecological advantages with respect to previously more common materials for thermal energy storage (TES) such as salt. In rock-based TES systems, thermal energy is stored in packed-bed rock using air as heat transfer fluid. We investigated three different rock types with respect to changes in thermomechanical properties after different numbers of thermal cycles, Ruhr sandstone (Oberste quarry in Dortmund - Germany), basalt (commercial MTV basalt) and Calanca gneiss. Cylindrical samples were heated to 800°C within 11,5 h before temperature was kept constant for another 30 min and then decreased within 11,5 h. Samples were thermomechanically investigated before thermal treatment, and again after 1, 3, 7 and 15 cycles. Additionally, two samples of each rock type were subjected to a thermal cycle with a maximum temperature of 450°C and to 1000°C, respectively, at a heating/cooling rate corresponding to that of the samples heated to 800°C. Samples were characterised with respect to ultrasound wave velocity, bulk density, thermal conductivity, thermal diffusivity, uniaxial compressive strength, splitting tensile strength, mineral content (X-ray powder diffraction) and microstructure (thin section analysis). Samples of basalt could not withstand the standard heating rate. The samples crushed into small pieces also when heating rates were reduced and at a maximum heating temperature of 800°C. For sandstone and gneiss, the ultrasound wave velocity, bulk density, thermal conductivity, thermal diffusivity, uniaxial compressive strength and splitting tensile strength decreased systematically with increasing number of cycles, while the maximum reduction occurred after the first cycle and the relative reduction was similar between both rocks. Microstructural analysis indicated an increase in crack density and minor mineralogical changes upon heating. Both rocks, Ruhr sandstone and Calanca gneiss, appear suitable for TES, but Calanca gneiss is less suitable for temperatures above 800°C due to a significant reduction in bulk density and uniaxial compressive strength when heated to 1000°C. Also, its anisotropy and anisotropic response to heating can lead to preferred flow paths of the heat transfer fluid. Ruhr sandstone maintains a high uniaxial compressive strength of about 100 MPa even after 15 cycles while thermal capacity was only slightly reduced or even increased, and can be recommended for use in high temperature TES. This study is the outcome of a research-oriented teaching program at Ruhr-University Bochum within the Geoscience curriculum for students with focus on Engineering Geology. Student authors (Fränzer to Thomas) are listed in alphabetical order.

THERMOMECHANICAL PROPERTIES OF COMPOSITE MATERIALS BASED ON MIXTURES OF HIGH AND LOW DENSITY POLYETHYLENES

The results of the research into the influence of polymer components ratio - high density polyethylene and low density polyethylene, into the regularity of changes in thermomechanical properties are presented. The deformation was measured at varying temperatures and at a constant load of 0.5 kg/cm2 . The concentration of low density polyethylene varied from 10 to 100 wt%. Depending upon the test temperature, two physical states were recorded: solid and viscous-flow. It found that as the concentration of low-density polyethylene in the composition of the polymer mixture rose, the transition temperature in the softened state and the transition temperature in the viscous-flow state dropped. The differential thermal analysis curves showed that at low concentrations of high density polyethylene, two-phase systems were formed in the polymer system. The study of composites based on aluminum hydroxide and a mixture of high and low density polyethylene revealed a wave-like change in softening and viscous-flow temperatures.

Changes in thermomechanical properties of feed in relation to composition and their effect on pellet manufacturing

Due to the growing demand for food, the availability of starch-rich ingredients (e.g. feed grade cereals), whose areal can be used for producing food, is expect to decline. In turn, the use of co-products, from food- and biofuel industry, is expected to increase in livestock feed. However, these co-products are fibre-rich and can negatively affect pellet manufacturing, by reducing pellet quality and increasing energy costs. The thermomechanical properties of feed mashes are considered to be important for agglomeration processes, but its relation to feed composition and its role in pellet manufacturing is poorly understood. The aim of this study was to investigate the effect of fibrous co-product inclusion in feed mashes on their thermomechanical properties and subsequent effects on pellet manufacturing. Treatment mashes were formulated to contain 700 g/kg basic mash, consisting of soybean meal, maize, and soy oil, to which 0–300 g/kg palm kernel expeller, sugar beet pulp, wheat straw and isolated native maize starch were added, according to a four-component mixture design. Treatments were prepared in duplicate, conditioned using a single-shaft conditioner and compacted using a ring-die pelletizer (die hole diameter 6 mm, L/D ratio 12). Pellet quality, production capacity and gross specific mechanical energy consumption per megagram (Mg) were documented. Mash deformability was evaluated by increasing the moisture content of a mash sample to 150 g/kg, followed by compression at 10 MPa and increasing temperature by 4 °C/minute using the Phase Transition Analyzer (PTA; Wenger Manufacturing, Sabetha, KS, US). Inclusion of wheat straw significantly increased mash deformability. Inclusion of isolated native maize starch and fibrous co-products was observed to increase pellet quality in comparison to the basic mash. Mash deformability at compactor temperature was correlated with bulk density (r = −0,83; P < 0.001). Pellet compressive strength was associated with mash deformability (r = 0.78; P < 0.001), but this association was observed to be influenced by wheat straw. Material deformability was correlated with production capacity (r = −0.85; P < 0.001) and energy consumption (r = 0.80; P < 0.001). In conclusion, inclusion of fibrous co-products affects pellet quality in a non-linear relation and increases pellet quality similar to inclusion of isolated native maize starch. Mash deformability could provide an indicator for pellet quality, but the underlying mechanism requires further study. Pelleting of feed mashes with a higher deformability increases energy costs of pellet manufacturing, due to the behaviour during compaction. The thermomechanical properties of feed mashes play a significant role in the pellet manufacturing process.

Determination of Thermo-Mechanical Properties of Recycled Polyurethane From Glycolysis Polyol

This study aimed to determine the possible changes in thermo-mechanical properties between recycled polyurethane with benchmark polyurethane. The glycolysis polyol was used as a raw material for recycled polyurethane production. The glass transition temperature of the recycled polyurethane was determined using DSC. Tensile strength, elastic modulus, toughness, and hardness test of the recycled polyurethane were conducted at 24°C, 40°C, and 60°C. The glass transition temperatures for the recycled and the benchmark polyurethane occurred at 43°C and 50.4°C, respectively. Tensile strength for recycled polyurethane was lower than that of benchmark polyurethane by 29-43%. Recycled polyurethane recorded lower toughness than petroleum-based pure polyurethane by 13-16%. However, recycled polyurethane recorded high shored D values than the benchmark polyurethane by 9-29%. This study reveals that recycled polyol could be used as feedstock for polyurethane production with applications tailored to its mechanical properties.

Determination of thermo-mechanical properties of recycled polyurethane from glycolysis polyol

Polyurethane foam is one of the most versatile polymers widely used in the automotive industry. However, due to the rising amount of polyurethane foam waste in the environment, there is growing research attention focusing on circular economy solutions to closing the material loop. This study aimed to determine the possible changes in thermo-mechanical properties between rigid polyurethane prepared using polyols derived from depolymerization of commercial polyurethane foam with benchmark rigid polyurethane (Ben PU). Polyurethane foams containing dispersion polyol were reacted with dipropylene glycol (DPG) and diethylene glycol (DEG) with a ratio of DPG: DEG of 1:1 in the presence of a consumable catalyst (Di-n-butyl amine). The recovered polyol was used as a raw material replacing 100% benchmark rigid polyurethane petroleum-based polyester polyol to produce the recycled polyurethane (Rec PU). Thermal analysis was conducted to measure the recycled polyurethane's glass transition temperatures (Tg) using differential scanning calorimetry (DSC). Tensile strength, elastic modulus, toughness, and hardness test of the recycled polyurethane were conducted under three different temperatures; 24°C, 40°C, and 60°C. From the DSC results, the glass transition temperatures for the recycled and the benchmark rigid polyurethane occurred at 43°C and 50.4°C, respectively. Both polymers showed the brittle-ductile transition from 24°C to 40°C. Tensile strength for recycled polyurethane was lower than that of benchmark rigid polyurethane by 29-43% and a corresponding 24-50% decrease in elastic modulus. Recycled polyurethane recorded lower toughness than petroleum-based pure polyurethane by 13-16%. However, the recycled polymer recorded high shored D values than the benchmark rigid polyurethane by 9-29%. This study reveals that recycled polyol could be used as feedstock for polyurethane production with applications tailored to its mechanical properties.

Recycling of waste PP and crumb rubber together by use of self-healing ionomer as process compatibilizer

Recycling of mixed waste, including plastic and rubber, by the blending process is one of the promising sustainable routes. In this paper, the processing of crumb rubber with waste thermoplastic polypropylene is reported. The poly(ethylene-co-methacrylic acid) copolymer sodium ion was introduced as a compatibilizer. The waste materials were processed by injection molding to a property improved value-added plastic–rubber recyclate. There was an improvement of tensile strength and modulus of about 60 and 85%, respectively, by addition of 7 wt.% of ionomer as compatibilizer. Enhanced thermal stability was also observed as compared to that of neat blend. The change in morphological characteristics that influence the end properties was analyzed by field emission scanning electron microscope and atomic force microscope. Evaluation of dispersion of different phases and their stress transfer tendency was studied for both tensile fractured and molded samples. The changes in thermo-mechanical properties are correlated to morphological characteristics, and the efficacy of the compatibilization process was estimated.

Changes in thermomechanical properties due to air and water cooling of hot dry granite rocks under unconfined compression

Water has been used as a working fluid injected into the hot reservoirs during the exploitation of deep geothermal energy, therefore, understanding the thermomechanical properties of reservoir rocks after water cooling is essential. For that reason, we have conducted a series of laboratory tests on air and water cooled granites from normal temperature to 600 °C, to reveal the changes in their thermomechanical properties. At 600 °C, the average values of uniaxial compressive strength, elastic modulus and P-wave velocity of water cooled granite decrease by 84.9%, 73.1% and 66.2%, which are 11.0%, 17.0% and 17.7% larger than those of air cooled granite. Through optical microscopic analysis, the microcrack density and average width of water cooled granite increase with thermal temperature and are 4.18 mm/mm2 and 54.62 μm at 600 °C, while the values of air cooled granite are only 1.97 mm/mm2 and 25.16 μm. We thus combined the deterioration of the macroscopic mechanical characteristics of air and water cooled granites with the propagation and development of microcracks. Supported by data from international literature, the changes in the thermomechanical characteristics of granite has been systematically compared to international literature, which is hoped to provide technical support for the geothermal energy exploitation.

Analysis of the Impact of Changes in Thermomechanical Properties of Polymer Materials on the Machining Process of Gears.

This paper presents an analysis of the impact of modification of thermomechanical properties of polymer materials on the process of gear wheel machining on a CNC machine tool. Polymer materials Tecaflon (PVDA) and polyethylene (PE) were used for processing. The materials underwent thermal modification i.e., annealing. Prepared samples (gear wheel dimensions Ø76.5 × 20 mm) were machined under the same conditions, only changing the feed rate parameter. A CNC milling machine of its own construction was used for machining with a horizontal numerical dividing attachment. The obtained gear wheels were tested using ZEISS GEAR PRO gear analyzes software. Deviations of the involute outline and the tooth line allowed classification of wheels in the 9th grade of accuracy. Machined teeth surfaces were examined for changes in the properties of surface layer, taking into account the influence of polymer material thermal modification on the surface condition. The samples were tested for mechanical properties (tensile strength) and thermomechanical properties (DSC and DMTA). The tests showed positive changes in material strength and significant improvements in PVDA Tecaflon after heat treatment.

In-situ changes of thermo-mechanical properties of poly(lactic acid) film immersed in alcohol solutions

Poly (lactic acid) (PLA) has properties suitable for many applications. However, PLA's properties are affected by environmental conditions. In this study, the glass-rubber transition temperatures (Tg) of PLA films were measured during immersion (i.e., in-situ) in pure alcohols and alcohol aqueous solutions using a dynamic mechanical analysis technique. The Tg of PLA decreased when immersed in alcohols. For pure aliphatic alcohols, the Tg reduction became smaller as the number of carbons (C1–C10) in the alcohol main chains increased. The Fox equation and the Hansen solubility parameters (HSP)/Flory-Huggins (FH) model were used to explain the Tg reduction. The relationships explained the interactions between PLA and pure alcohols with small molecules (C1–C8), but bigger pure alcohols (C9–C10) did not fit the prediction. The chemical isomerism in pure propanol (i.e., propan-1-ol and propan-2-ol) did not affect the Tg reduction. The Tg reduction in propan-2-ol aqueous solutions was concentration dependent although the partition coefficients based on the HSP and the FH parameters did not fit this relationship. The in-situ immersion of PLA in alcohol solutions could be used to evaluate the change in Tg from the Tg of dry PLA.

Coupling of nonlinear shape memory polymer cantilever dynamics with focused ultrasound field

Research has found significant potential for ultrasound actuation of shape memory polymers (SMPs) in several fields such as biomedical and electronic devices among others. Example applications range from controlled drug delivery containers to soft robotics and flexible electronics located in otherwise inaccessible places or hazardous environments, where direct external heating is not possible. SMPs can be manipulated into any temporary shape and later recover to their stress-free permanent shape when triggered with external stimuli such as heat. Focused ultrasound (FU) has the ability to induce localized heating and activate multiple intermediate shapes and achieve complete shape recovery in the polymer, non-invasively and remotely. In addition, FU has a superior capability for temporal and spatial control of shape recovery by adjusting sample size, ultrasound frequency, exposure time and intensity as well as the position of ultrasound focusing. In this paper, indirect actuation of the thermally-induced shape-memory effect of SMPs by FU is studied theoretically and experimentally with a focus on the acoustic field, medium, geometric and material properties. The changes in thermomechanical properties, during FU actuation, are studied through dynamic mechanical analyzer tests. Using these properties, an analytical acoustic-thermo-elastic dynamic model is developed to predict the shape memory response of a SMP cantilever beam, considering acoustic and geometric nonlinearities. The governing equations of motion are derived using reduced order modeling and solved by perturbation techniques. Having obtained an analytical expression for the shape recovery of the beam as a function of acoustic parameters, experimental validations for a cantilever SMP beam exposed to FU are performed. The model has the ability to successfully estimate the variation in the amount of shape recovery due to the change in source frequency of the transducer and peak acoustic pressure field inside SMP domain without the need of analyzing any intermediary acoustic/thermal/elastic behavior.

From the promotion of biodiversity to the Recovery of organic waste

This article presents an empirical research to classify a new renewable resource material, as opposed to eco-composites, it has been neglected by the materials specialist. This classification is based on the typology of elastic behavior demonstrated by tensile tests. In addition, some identifying criterions of the usefulness of this material were examined. To justify the relevance of this classification, curves from the extension of tests focusing on the virgin material, illustrate significant results of the review. Obtained from waste, having a significant recycling possibilities and potential from renewable resources, bio-mechanically characterized loads will be injected into polymeric materials of different categories. All in the perspective of promoting changes in thermomechanical properties, whether static or dynamic; such as resistance to corrosion, heat, wear… They result in functional changes such as security, relief, coatings and stability…

Electrical, Thermal and Mechanical Properties of Epoxy/CNT/Calcium Carbonate Nanocomposites

Epoxy/CNT and epoxy/CNT/calcium carbonate nanocomposites were produced via in situ polymerization assisted by ultrasonication without solvent and electrical, mechanical, thermal and thermomechanical properties of nanocomposites were evaluated. Epoxy/CNT presented very low percolation threshold, near 0.05 wt % and nanocomposites with higher contents of CNT presented further increase in electrical conductivity. The addition of calcium carbonate in epoxy/CNT nanocomposites increased the electrical conductivity, due to volume exclusion phenomena. Regarding thermal properties, due to the low content of the CNT and calcium carbonate no changes in glass transition (Tg) were observed. DMA results showed no significant changes in thermomechanical properties, once the contents of CNT and calcium carbonate are below stiffness threshold, however an increase of flexural modulus by adding CNT and calcium carbonate was observed.

Evaluation of epoxy crosslinking using ultrasonic Lamb waves

The use of epoxy adhesives in structural bonding provides lightweight materials, however the assessment of the integrity and quality of the joint is of critical concern. Thus it is essential to know if the adhesive is well crosslinked. This work deals with the nondestructive acoustic characterization of epoxy networks, representative of the adhesive family, of different crosslinking density; i.e. conversion. Different curing cycles were applied and differential scanning calorimetry measurements allowed the determination of their glass transition temperature and epoxy conversion. The acoustic study was performed on epoxy plane plates, all in the glassy state and well beyond the gel point. The methods were based on the propagation of bulk longitudinal and shear waves, as well as on guided Lamb waves. Depending on the conversion of the epoxy, it was shown that the changes in thermo-mechanical properties, resulting from different degrees of cure, greatly influence the acoustic behavior of some Lamb modes if a selection of the sensitive modes has been performed upstream.

Analysis of Changes in Thermomechanical Properties and Structure of Polyamide Modified with Fly Ash from Biomass Combustion

Study of performance of polyamide with fly ash addition with different contents of filler was carried out. In this article studies were performed: dynamical mechanical properties, thermal properties and structure research. The profiles of changes in the value of storage modulus E′ and tangent of mechanical loss angle tgδ depend on the temperature and frequency of vibrations. The crystallinity degree was examined using DSC methodology whereas the structure was analysed by means of the optical microscope. The increase in the value of storage modulus versus temperature and vibration frequency for the samples with addition of filler and the increase in the crystallinity degree and polymer matrix with reduced addition of fly ash were observed. A reduction in size of the structural components was also found, particularly for the composites with filler content.Graphical

Chemical modifications of graphene and their influence on properties of polyurethane composites: a review

Polyurethane composites are materials of great interest nowadays due to their wide range of available forms and applications in industry. Controlling and achieving unique properties via matrix modifications and addition of various specific nanofillers seems be one of the key elements to success. The purpose of this work is to briefly present some examples of graphene nanoderivatives, their syntheses, properties and influence on polyurethane matrix after application. Structural, mechanical and electrical properties of graphene nanofillers were analyzed before and after implementation into polymer matrices. Additionally properties of obtained composites were considered in the context of shape memory. The first chapter presents methods of synthesizing carbon nanofillers and some structure investigations via x-ray Diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy. The second part discusses influence of graphene modifications on polymer structure and changes in thermomechanical properties via stress-strain tests and Thermogravimetry (TG).

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.