Polyethylene is chemically the simplest polymer resulting from the polymerization of ethylene monomer and consists of a long carbon chain in which each carbon atom is bonded to two hydrogen atoms. Certain molecules or chains may be very long, containing hundreds to tens of thousands of carbon atoms. Polyethylene chains may be linear or branched, depending on how the polymer is synthesized. There are many methods for synthesizing polyethylene. The methods of blowing film processing vary in part depending on the type of polyethylene. These differences will be discussed in the following sections. In general, an important similarity is that all types of polyethylene have a high specific heat, specific heat is the amount of energy required to raise the temperature per unit mass of the material per degree of temperature. If a polymer has a high heat capacity, it means that heat transfer from the melt is relatively slow. The heat capacity is approximately 2 kg while the heat capacity of most other polymers is approximately 1 kg. This is one of the reasons why cooling towers are so high in the polyethylene blowing film production process. It takes a long time to cool the two layers of film passing through the nip rolls to prevent sticking, which sometimes leads to blocking.
