Polymer plastics have become ubiquitous worldwide and include some of the most important and useful materials available. The plastics industry is one of the largest manufacturing segments in the U.S. and in 2011 accounted for almost $4 billion in shipments and employed almost 1 million people. Common synthetic polymers include polypropylene, polyethylene, polyvinyl chloride, polyamide and polyester.
However, in addition to their advancing use and value, increasing awareness has been given to their environmental impact, both in regard to manufacture as well as post-use.
Significant attention is being directed to recycling these plastics in order to minimize their environmental impact and to reduce the need for petrochemical raw materials used in their manufacture.
Polyethylene – An Important Polymer
The most important of these polymers both in volume of material produced as well as environmental impact may be polyethylene. Polyethylene is a thermoplastic made through the polymerization of ethene and is used in packaging films, toys, barrels, plumbing pipes, molded housewares, and trash and grocery bags. A variety of different polyethylene types has been developed based mostly on density of the material and branching of the intrinsic molecular chains.
The unequivocal identification of the feedstock is of key importance in manufacturing items as well as proper recycling of these materials. Properly identifying and separating different recyclable plastics from each other so that they are processed correctly requires a great deal of effort. In addition to separating polyethylene items from other plastics, different types (densities) of polyethylene need to be separated as do items co-polymerized with other types of plastics. Unfortunately, this is often difficult to do without complex chemical analysis.
Fourier transform near-infrared spectroscopy (FT-NIR) provides a means to identify and analyze various polyethylenes. Certain FT-NIR analyzers have proven to be useful for identifying and measuring a wide range of materials quickly and easily with no sample preparation. In-depth analyses of different densities of polyethylene as well as the amount of ethylene present in polypropylene samples have been conducted, and the feasibility of this technique has been demonstrated.
In our next article, we will outline an experiment where two separate studies on different polyethylene materials were performed: qualitative classification of different polyethylene materials as well as a quantitative analysis.