Microcalorimetry and Infrared Spectroscopy
Thermal processes related to solid waste, ageing rubber, phase change materials, and biomass gasification
Time: Fri 2022-10-21 10.00
Location: Kollegiesalen, Brinellvägen 8, Stockholm
Video link: https://kth-se.zoom.us/j/62413970769
Subject area: Fibre and Polymer Science
Doctoral student: Mohit Pushp , Fiber- och polymerteknologi, RISE, Borås
Opponent: Professor Lars Wadsö, Lunds universitet
Supervisor: Professor Mikael S. Hedenqvist, Polymera material; Teknologie doktor Anders Lönnermark, RISE
Microcalorimetry (MC) is a unique technique for an online measurement of heat production. It can be applied to solids, liquids, or gases. MC can be used to measure the heat involved in either exothermic or endothermic processes. The heat signal obtained from MC is a lumped parameter so chemical, biological, and physical changes involving heat are measured simultaneously. In this study MC has been used to study the thermal processes in municipal solid waste, phase change materials and polymeric materials. A self-heating phenomenon, which may lead to significant heat production in piles of stored municipal solid waste, was studied with MC. This enabled us to understand the propensity of self-heating in municipal solid waste in storage conditions closer to real-life. The results showed that the self-heating in the solid waste was due to the aerobic metabolism of microorganisms.
With the development of a third generation MC and better temperature control mechanisms, MC can be operated in non-isothermal mode as a differential scanning calorimeter (DSC). However, MC is capable of measuring heat flow using significantly larger sample masses than DSC. The larger sample mass is more representative of complex/heterogeneous materials, like cementitious blocks. Hence, MC was applied here to determine if it could be a useful tool in characterizing the thermal properties (latent heat and specific heat) of cementitious grout containing phase change materials (PCMs). It was observed that the phase changes (melting and crystallization) due to the PCM could be accurately characterized with MC. Performance of PCM can be investigated using thermal cycling tests that mimic real-life temperature scans.
The high sensitivity of MC (μW/10000 mg) means that chemical changes can be measured at least 100 K lower than DSC (μW/~30 mg). The increased sensitivity opens up the possibility of measuring the ageing/degradation of polymers at closer to real-life temperatures and conditions. This is advantageous, since the normally used accelerated testing at significantly higher temperatures leads to degradation conditions that do not resemble service conditions. It is shown here, with the MC technique on a highly filled ethylene propylene diene monomer (EPDM) material, that the ageing processes, as well as the activation energy of the ageing processes, at close to real-life temperature are different from those at high temperature. With the high sensitivity of the MC, local thermal processes on a small scale could be readily observed, such as the melting of the antioxidant and further reactions in the peroxide cross-linking system. Hence, the results indicate that MC is a promising technique for measuring chemical changes and reaction parameters closer to the real-life temperatures in complex systems like highly filled EPDM rubber. To relate heat flow data to chemical mechanisms, post analysis of polymeric materials should be carried out with alternate techniques, for example, infrared spectroscopy (FTIR), gas chromatography and scanning electron microscopy coupled to energy dispersive X-ray.
In principle, the signature of hydrocarbons can be detected using FTIR. However, subjecting the instrument to the raw gas from biomass gasification runs the risk of condensation of tars on optical components and subsequent malfunction. As a solution, an external cell that can be heated to at least 400 °C was designed to ensure that tars remain in the gas phase. The on-line measurements for permanent gases, water and tars were made using a lab-scale downdraft gasifier. Concentrations of permanent gases are in good agreement with Micro-GC and spectral signatures of tars are comparable with measurements using the solid phase adsorption (SPA) technique.