Polyethylene is a type of polymer, primarily composed of long chains of ethylene (C2H4) units. These units consist of carbon (C) and hydrogen (H) atoms. In the polymerization process, ethylene monomers join together through a reaction that forms single bonds between the carbon atoms, resulting in a saturated hydrocarbon. The basic structure of polyethylene can be represented as (-CH2-CH2-)n, where "n" indicates the number of repeating units. The properties of polyethylene, such as density and strength, vary depending on the length of the chain and the degree of branching. This plastic is widely used due to its versatility, chemical resistance, and electrical insulation properties.

Polymers derived from petroleum, also known as petrochemicals, make up a large majority of the synthetic polymer market. Roughly 80-90% of polymers are produced from fossil fuels, a category in which petroleum is a primary source. This high percentage is attributed to the cost-effectiveness and abundance of petroleum compared to alternative raw materials. Petrochemical polymers include plastics like polyethylene, polypropylene, and polystyrene, which are integral to numerous industries including packaging, automotive, and construction. However, the environmental impact of these petroleum-based polymers has spurred research into bio-based and sustainable alternatives. Efforts to reduce reliance on petroleum-derived polymers are increasing, aiming to decrease pollution and carbon footprint.

At neutral pH, not all amino acids are negatively charged; their charge depends on the specific amino acid and its functional groups. Amino acids are the building blocks of proteins, each containing an amino group (–NH2) and a carboxyl group (–COOH). These groups can ionize, gaining or losing protons. At neutral pH (approximately 7), some amino acids have no net charge and exist as zwitterions, where the amino group is positively charged (+1) and the carboxyl group is negatively charged (-1). However, acidic amino acids, such as aspartic acid and glutamic acid, have additional carboxyl groups that can also ionize, making these molecules predominantly negatively charged at neutral pH. Conversely, basic amino acids like lysine and arginine have extra amino groups that remain protonated, giving them a net positive charge. Therefore, whether an amino acid is negative at neutral pH depends on its specific structure and the balance between its ionizable groups.