China
Africa
Explore chapters and articles related to this topic
Polymers
Published in Yip-Wah Chung, Monica Kapoor, Introduction to Materials Science and Engineering, 2022
Polyethylene in different forms is used in household containers, electrical insulation, chemical containers, tubings, housewares, packaging, prosthetic implants, etc. The chemical formula is – CH2 – CH2 – CH2 – CH2 –…, or (–C2H4–)n, where n is the number of repeating C2H4 units and is known as the degree of polymerization. Polyethylene can be synthesized via the reaction between hydrogen peroxide (H2O2) and ethylene (C2H4), in the presence of a catalyst such as palladium, as follows:
Extractables and Leachables in Drug Products
Published in James Agalloco, Phil DeSantis, Anthony Grilli, Anthony Pavell, Handbook of Validation in Pharmaceutical Processes, 2021
Secondary packaging should not be ignored. At minimum, it should be addressed as either being a risk or not. That determination is mainly dependent upon the materials of construction of the primary packaging system. Leaching from secondary packaging may not be considered a risk in many scenarios. Nonpermeable primary packaging containers such as glass vials, glass syringes, or aluminum canisters pose low risk for migration from secondary packaging. Many ODPs are packaged in semipermeable polymer primary packaging systems. Common polymers include polypropylene (PP), high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE). There are others, but in ODPs these are common primary packaging materials that are also used to deliver the drug to the eye. These primary packaging materials also account for the largest surface area through which migration may occur. Their material of construction is the primary factor in determining whether the drug product’s secondary packaging should be examined as a source of leachables over the shelf life of the drug product.
Fibres
Published in Ashok R. Khare, Principles of Spinning, 2021
The ethylene molecule is very stable, and it is polymerized using catalyst titanium chloride. The polyethylene is not bio-degradable except when exposed to ultra-violet light. This leads to many environmental problems. Recently, it has been discovered that some types of bacteria can degrade polyethylene up to 40% of its weight, and that too after a really long time. The polyethylene with ultra high molecular weight has a very tough structure and hence it is used in making bottle handling machine parts, moving parts on weaving machine, bearings, gears and butcher’s chopping boards.
Green synthesized Pd-Ni nanohybrids for controlled degradation of low-density polyethylene films
Published in Chemical Engineering Communications, 2023
Aminat Aderonke Mohammed, Ojeyemi Matthew Olabemiwo, Abass Abiola Olajire
Polyethylene is a polymeric material that is utilized, among other things, in the production of food packaging, shampoo bottles, grocery bags, containers for laboratories, and so forth. Polyethylene is a major contributor to environmental pollution because of its usage (Alka et al. 2015). The burning or incineration of polyethylene waste has resulted in the release of toxic pollutants like dioxins, furans, and phthalates, which eventually return to the environment and pose serious threats (Singh and Sharma 2008). However, scientists have been able to develop a scientific approach for the degradation of polyethylene wastes, such as the thermal or catalytic conversion of polymer wastes into fossil fuels. Thus, these methods required a high temperature and appropriate cost-effective catalysts for the conversion of the end products to useful hydrocarbons (Dong et al. 2001; Uddin et al. 1998). Biodegradation of polymer is a new scientific method for the degradation of polymer wastes, but they have major drawbacks such as difficulties for the microbes to penetrate hydrophobic and high molecular weight polymers. Mechano-chemical, ozone-induced, and photo-oxidative degradation are among other additional methods of polymer degradation (Singh and Sharma 2008).
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).
Effect of γ-irradiation on thermally stimulated depolarization current spectra of polyethylene-grafted-poly(Acrylic acid)
Published in Radiation Effects and Defects in Solids, 2022
W. B. Elsharkawy, M. T. Ahmed, E. O. Abdelmuttlib, Z. M. Elqahtani, M. A. Azzam, T. Fahmy
Polymer materials are often used in power transformers, capacitors, etc., due to their good dielectric properties and outstanding mechanical properties. Polyethylene has excellent dielectric and mechanical properties and, therefore, has various industrial applications, as well as electrical applications. Due to its good heat resistance and low dielectric loss, it has been widely used as electrical insulation. Polyethylene (PE) is a common polymer studied for numerous applications, including microwave in pure form and combined with other materials (1). Depending on the molecular structure of hydrocarbon polymers, such as polyethylene (PE), the dipole moments of the (C–H apolar) groups are very low, in the order of 0.1 D, and are barely detectable by usual dielectric techniques (2). In general, measurable dielectric relaxation is generally attributed to impurities, and these hydrocarbon polymers undergo oxidation and thus contain polar groups (3, 4).