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Monomers, Polymers, and Plastics
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
Reaction conditions are generally mild, but they differ from one process to another. For example, in the Unipol process, which is used to produce both high-density polyethyleneand linear low-density polyethylene (LLDPE), the reaction occurs in the gas phase. Ethylene and the comonomers (propene, 1-butene, etc.) are fed to the reactor containing a fluidized bed of growing ymer particles. Operation temperature and pressure are approximately 100°C (212°F) and 300 psi. A single-stage centrifugal compressor circulates unreacted ethylene. The circulated gas fluidizes the bed and removes some of the exothermic reaction heat. The product from the reactor is mixed with additives and then pelletized. The polymerization of ethylene can also occur in a liquid-phase system where a hydrocarbon diluent is added. This requires a hydrocarbon recovery system.
Thermoplastics Foams
Published in Omar Faruk , Jimi Tjong , Mohini Sain, Lightweight and Sustainable Materials for Automotive Applications, 2017
Sai Aditya Pradeep, Srishti Shukla, Nathaniel Brown, Srikanth Pilla
Melt strength is defined as the maximum tension force that can be applied to a polymer resin in its molten state, and is essentially a measure of extensional or elongation viscosity of a polymer. Thermoplastic polymer resins constitute long polymer chains entangled with each other even in the molten state. On application of strain to the melt, these chains become disentangled and slide. At the molecular scale, melt strength can be understood as the resistance offered by polymer chains to being disentangled and sliding over each other. Important polymeric properties that affect such entanglement or disentanglement of polymeric chains, and thereby its melt strength, are molecular weight, molecular weight distribution, and molecular branching of the polymer. With regard to all three properties, increase in any of these properties leads to augmentation of melt strength. For this reason, linear polymers like polypropylene and high density polyethylene (HDPE), and polymers with short branches like linear low density polyethylene (LLDPE) have low melt strength, while heavily branched polymers like low density polyethylene (LDPE) have high melt strength. This intrinsically affects foaming as polymers that possess low melt strength have cell walls separating the cells do not have enough strength to bear extensional force resulting in rupture and decreased foaming.
A review on reaction mechanisms and catalysts of methanol to olefins process
Published in Chemical Engineering Communications, 2022
Currently, light olefins including ethylene and propylene are identified as the most strategic feedstock for polymeric industries (Mei et al. 2008). Different types of polymers such as low density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) are derived from ethylene monomer. On the other hand, numerous kinds of products such as polypropylene (PP), poly-acrylonitrile, acrolein, acrylic acid, poly-urethanes, propylene glycol, etc. are produced from propylene monomer (Liu et al. 2009). Products originated from ethylene and propylene, are extensively employed in automobile industry, construction, architecture, textile industry and household appliances. Because of cost-effectiveness, beauty and strength of the novel polymeric fabrications, they are quickly developed as substitutes for similar products which have been conventionally manufactured by iron, aluminum, wood, etc. Hence, the demand for derivatives of ethylene and propylene is progressively growing over the recent years. Ethylene and propylene have conventionally been produced as side-products via steam cracking and catalytic cracking of different petroleum cuts such as naphtha (Keil 1999). Product analysis verifies that approximately 20 mol% of ethylene and only 5 mol% of propylene are produced by these conventional processes (Fournier et al. 2019). Therefore, the conventional processes cannot afford the soaring world-wide request for ethylene and principally propylene (Baliban et al. 2012).
Comparison of rheological properties and compatibility of asphalt modified with various polyethylene
Published in International Journal of Pavement Engineering, 2021
Ming Liang, Xue Xin, Weiyu Fan, Jizhe Zhang, Hongguang Jiang, Zhanyong Yao
Other important issue is the compatibility. Mixing PE with asphalt is not an easy task due to their large difference in viscosities, polarity and molecular weight (Ouyang et al. 2006). This can be accomplished by means of high shear homogenisers where polymer is disintegrated by mechanical shear force. Consequently, a dispersion system is formed where swollen polymer is dispersed in asphalt (low polymer content). In microscopy, the compatibility is determined by swelling degree of polymer, interaction and migration among polymer and asphalt component. PE structural parameters significantly influence the microscopic process (Yousefi 2003, Wekumbura et al. 2007, Fang et al. 2014) and thus affect compatibility. Based on this, the compatibility of constituents can be enhanced by optimising the structure of PE. The common types of polyethylene include high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE), et al. For different polyethylene, the structural parameters, including density, crystallinity, melt-flow index (MFI), portray the architecture of the polyethylene molecular structure. Schematic illustrations of molecule structure for different polyethylene are presented in Figure 1.
An approach toward augmenting materials, additives, processability and parameterization in rotational molding: a review
Published in Materials and Manufacturing Processes, 2020
Nikita Gupta, PL. Ramkumar, Vrushang Sangani
Usually, linear low-density polyethylene is used for rotational molding process. But in some applications where strength is major criteria, like battleships, armor tanks, LLDPE lacks in providing the needed properties and are prone to initialize cracks on the vessel. In order to meet the required criteria for delivering the optimum mechanical properties in roto-molded product, additives and fillers have proved to enhance the properties when added in base resin for rotational molding process.[69,70] And hence recent advancements are coagulating and concluding toward the enhancement of properties of roto-molded product. Additives can be added by simply dry blending or by melting or by means of chemical agents.[71] Several additives that can be blended with the base resin can be bifurcated into various segments based on the type of material inculcated for the purpose of additive.[72,73]