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Electron Beam Processes
Published in Jiri George Drobny, Radiation Technology for Polymers, 2020
Under normal conditions, polytetrafluorothylene (PTFE) undergoes chain scission. In fact, this behavior is exploited commercially by converting PTFE scrap into a low-molecular-weight product that is then used in the form of very fine powders as additive to inks and lubricants. However, there is evidence that irradiation of PTFE at temperatures above its melting point (e.g., at 603–613 K, or 626–644°F) in vacuum results in a significant improvement in tensile strength and elongation at 473 K (392°F) and in the tensile modulus at room temperature.98–100 These findings strongly contrast with the greatly reduced properties after irradiation at lower temperatures than that. This clearly indicates cross-linking in the molten state, similar to effects of irradiation on polyethylene. At temperatures above 623 K (662°F), thermal depolymerization is increasingly accelerated by irradiation and predominated over cross-linking at yet higher temperatures.101
Polymers
Published in Ghenadii Korotcenkov, Handbook of Humidity Measurement, 2020
It should be noted that thermal oxidation of polymers can also be accompanied by combustion. Although some polymers, such as PVC, do not easily ignite, most organic polymers, such as hydrocarbons, will burn. Some will support combustion, such as polyolefins, styrene-butadiene rubber (SBR), wood, and paper, when lit with a match or some other source of flame. Thermally, simple combustion of polymeric materials gives a complex of compounds that vary according to the particular reaction conditions. In particular, for vinyl polymers thermal degradation in the air (combustion) produces the expected products of water, carbon dioxide (or carbon monoxide if insufficient oxygen is present), and char along with numerous hydrocarbon products (Carraher 2008). Application of heat under controlled conditions can result in true depolymerization, usually occurring via an unzipping. Such depolymerization can be related to the ceiling temperature of the particular polymer. Polymers such as poly(methylmethacrylate) (PMMA) and poly(alpha-methylstyrene) depolymerize to give large amounts of monomer when heated under the appropriate conditions. Thermal depolymerization usually leads to some charring and the formation of smaller molecules, including water, methanol, and carbon dioxide.
Bioenergy From Activated Sludge and Wastewater
Published in Veera Gnaneswar Gude, Green chemistry for Sustainable Biofuel Production, 2018
Andro Mondala, Rafael Hernandez, Todd French, Emmanuel Revellame, Dhan Lord Fortela, Marta Amirsadeghi
Renewable diesel or green diesel can be produced by hydrotreating or hydroprocessing, thermal depolymerization, or the biomass-to-liquid (BTL) with Fischer-Tropsch process [222]. In the hydrotreating process, the lipid feedstock is reacted with hydrogen in the presence of a catalyst to convert TAGs into paraffinic hydrocarbons with similar properties to petrodiesel. Thermal depolymerization processes involves subjecting carbon-containing substrates to high-temperature and -pressure conditions to convert them into “bio-oil,” which is then refined into petrodiesel-like fuel. The BTL process involves high temperature gasification of biomass substrates into syngas, which is then condensed into liquid fuels via the Fischer-Tropsch process. As mentioned earlier, one of the major sustainability challenges in the use of these bio-based petrodiesel compounds is the cost and source of the feedstock. Current trends for achieving sustainability indicate the diversion from crop oils or animal fats that are also used in food production towards nonfood or waste derived sources of lipidic raw materials. The use of sewage sludge and biosolids and microbial oils generated by oleaginous microbes grown in wastewater as an oil feedstock source for biodiesel or renewable diesel production offers advantages of having low to zero costs, year-round availability, and renewability of sources.
Analysis of fracture structure evolution of bituminous coal subjected to in situ steam pyrolysis combined with in situ micro-computed tomography technology
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Jianhang Shi, Zengchao Feng, Dong Zhou, Xuecheng Li, Qiaorong Meng
When the temperature is >400°C and <600°C, the fracture structural parameters of coal samples tend to increase sharply. This is because in this temperature range, the coal sample undergoes an intense pyrolysis reaction, resulting in a large amount of volatile matter production and an increase in gas production (Figure 11 (a)). Additionally, during coal sample pyrolysis, thermal depolymerization of oxygen-containing functional groups and aliphatic hydrocarbons occurs, breaking C – H, C – O, and O – H bonds between and within molecules (Liu et al. 2021; Lu et al. 2021). Consequently, the loss of organic matter directly produces many new fractures in the coal body. Furthermore, for pillar coal under external stress, the output of pyrolysis products must accumulate a certain pressure, generating new fractures when the resulting expansive force gradually increases to greater than the fracture strength of the coal sample. Figure 10 shows that the axial strain of coal samples at this stage presents a rapid growth trend and the linear thermal expansion coefficient is also at a high value. Moreover, gas production at this stage accounts for 94.21% of the total gas production (Figure 11 (b)), indicating that coal samples at this stage are in the stage of intense pyrolysis. Further, severe pyrolytic deformation and plastic damage occurred in coal samples. The fracture formation, propagation, and communication areas are much larger than the areas of fracture closure, causing an increase in fracture structure parameters and permeability of the samples.
The reversible modification of acrylate adhesive system by introducing anthracene groups
Published in The Journal of Adhesion, 2023
Yingmin Feng, Xu Han, Yumei Ji, Shaolong Li, Kongyu Dong, Shuo Liang, Yao Ma, Yike Yang, Feng Liu
The debonding performance of the adhesive system containing a 4 wt% photo-initiator was investigated by testing the shear strength at a debonding temperature of 100°C, as shown in Figure 14a. Unlike the bonding properties, the shear strength after thermal depolymerization decayed first and then enhanced with increasing molar feeding ratio of the trifunctional acrylate monomers. This anomaly should be explained by the fact that the long chains are prone to entanglement for reinforcing mechanical properties in the system without trifunctional monomers, while the doping of trifunctional monomers will promote the formation of a strong and complex chemical crosslinking network, which may lead to difficulties in the depolymerization of anthracene dimers due to entanglement or confinement. The results showed that the samples prepared from formulation #7 (i.e. #3) achieved the easiest debonding with a minimum shear strength of 0.15 ± 0.07 MPa. To further compare their comprehensive performance, all debonding rates were also calculated by correlating them with Figure 9 and visualized in Figure 14b. The highest debonding rate (up to 91%) was achieved based on formulation #3 with a 9:1 molar feeding ratio of difunctional to trifunctional monomers, and the corresponding sample was able to provide both the strongest bonding effect and the best debonding ability, revealing the most comprehensive performance.
New channel flow control agent for high-temperature and high-salinity fractured-vuggy carbonate reservoirs
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Jichao Fang, Guang Zhao, Mingwei Zhao, Caili Dai
The temperature resistance of the CFC agent is notably important for controlling the channel flow at high temperatures. In particular, fractured-vuggy carbonate reservoirs, which are at temperatures up to 180 °C, have been found in western China. To evaluate the temperature resistance of the CFC agent, a TG-DSC experiment was performed. The thermal decomposition of the CFC agent occurs in a programmed temperature range of 25–800 °C. The results (Figure 6) show that the CFC agent has very good temperature resistance. The decomposition of the CFC agent begins at approximately 392 °C and is complete at 431°C because of the thermal depolymerization of the main organic chain. The maximal thermal decomposition temperature is 392 °C. The DSC curve shows that the chemical bonds of the CFC agent are sufficiently strong to resist high temperatures up to 392 °C. With further temperature increase (> 392°C), the DSC profile of the CFC agent shows an obvious and large endothermic peak at ~ 426°C, which may be attributed to the primary pyrolysis reaction of the CFC agent. Excessively high temperatures will break the chemical bonds in the CFC agent and destroy the network structure. Consequently, the stability of the CFC agent is guaranteed at the reservoir temperature.