Economics of plastics processing

The economics of plastics processing is determined by the type of process. Plastics can be processed with the following methods: machining, compression molding, transfer molding, injection molding, extrusion, rotational molding, blow molding, thermoforming, casting, forging, and foam molding. Processing methods are selected based on equipment cost, production rate, tooling cost, and build volume. High equipment and tooling cost methods are typically used for large production volumes whereas low - medium equipment cost and tooling cost methods are used for low production volumes. Compression molding, transfer molding, injection molding, forging, and foam molding have high equipment and tooling cost. Lower cost processes are machining, extruding, rotational molding, blow molding, thermoforming, and casting. A summary of each process and its cost is displayed in figure 1. Oxo-degradable plastics: these are petroleum-based plastics with additives such as transition metals and metals salts that promote the process of fragmentation of the plastic when exposed to a particular environment, such as high temperature or oxygen rich one, for a prolonged period of time. Fragmentation exposes a larger surface area of the plastic to colonies of bacteria that eventually decompose the polymer into its lower energy state components: carbon dioxide and water. Some aspects to take into account regarding this method to dispose of end-of-life plastics are: The type of polymer: experiments conducted by Chiellini et al. confirmed that bacteria are only able to decompose low molecular weight polymers (at least at a rate that can be appreciated). Environmental conditions: the time for fragmentation/degradation varies according to conditions which aren’t always controllable. Material’s potential to be recycled: this characteristic will be compromised, since the polymer’s durability or strength will be affected by the additives that accelerate fragmentation. Classifying a polymer as bio-degradable requires specifications regarding these aspects.