As a product of the polymerization of ethylene, any type of polyethylene (PE) is represented by the chemical formula C2H4. But, if primary polyethylene is the result of polymerization of ethylene, then the secondary granule of polyethylene is the result of the processing of waste primary polyethylene.
We will analyze the main differences between the structure and properties of polyethylene obtained by these two technologies.
Primary PE has a branched structure of the polymer chain, and the larger it is, the softer the polyethylene is, it has a lower density and a greater degree of elongation. For LDPE, the branching can be about 15-25 branches per 1,000 carbon atoms of the chain, while for PND this indicator is only 3-6 branches.
The secondary granule of polyethylene due to the difficulty in determining the initial characteristics of the feedstock (polymer waste) has not strictly defined indicators for the number of branches. Typically, such an indicator for the secondary granule of LDPE is 10-20, and for HDPE 5-8.
The main properties of PE obtained by primary polymerization of ethylene are dielectricity, impact resistance, resistance to breakage, low absorption of water (only 0.03% per month), air and chemicals, chemical neutrality. Primary PE can be dissolved only in a 50 percent solution of nitric acid. It can be used for contact with food and medicine, as well as for the production of prostheses.
The secondary is used mainly for the manufacture of technical products, where properties such as absorbability and chemical neutrality are not critical. The rest of the secondary PE has the same properties as the primary. It does not conduct electricity, is strong enough and moderately plastic. The parameters of the secondary granule are not standardized and only a part of enterprises produce them according to internal standards or specifications. Despite this, the LDPE and PND granule obtained after the secondary processing of PE is used in many areas. These are construction materials, containers, technical packaging, seals, pipes, etc. A wide range of products where a secondary granule of polyethylene is used is explained not only by its properties, but also by a significantly lower price in comparison with the primary one.
As a result, we can conclude that there is a small difference in the structure and properties of primary and secondary polyethylene, with the obvious economic benefits of using secondary granules.