Technology of Polymer Recycling and Reuse

Recovery of Polystyrene in Lost Foam Casting Technology:  This research program was initiated to assist the metal casting industry in prevention of polymer waste disposal, and to promote engineering solutions leading to reuse of the polymer. Our strategy adapts the principles of modern mineral processing technology to polymer recovery. The program includes particulate characterization, examination of surface-interfacial properties of the pattern components, development of an analytical technique for contaminant concentration measurements, shredding and size reduction, and selective separation testing based on component density. Our results indicate that as high as 98% of the polystyrene can be recovered, while the level of coating contaminants did not exceed 5 wt% in the final product, after using our new technology. 

Purification of PET from PVC: A technology involving treatment of PET and PVC particles with alkaline solutions followed by froth flotation of PVC with noinonc surfactants has been developed. It was demonstrated that using this technology 95-100% recovery of PET and PVC can be achieved in separate products from a variety of PVC/PET mixtures. 

Surface Chemistry Aspects of Flotation Deinking

Flocculation: We reported the improvement of flotation deinking through flocculation of fine ink particles using synthetic copolymers 

Solution Chemistry: The results of our fundamental work confirmed that polyalkylene oxide/fatty acid mixture, common surfactant blend in flotation deinking systems, has a dual role in separation of ink particles. Polyalkylene oxide serves as a frother, building stable froth layer that allows the floated ink particles to be skimmed from the top of the flotation cell.  The fatty acids activated by calcium ions serve as collector and promote attachment of ink particles to gas bubbles. 

Atomic force microscopy (AFM) has been applied to recovered paper deinking systems for measuring the interfacial forces acting between pulp particulates.  This new analytical technique mimics the conditions of recovered paper pulping and deinking separation at a micro scale.  A new procedure for the preparation of spherical toner has been developed in collaboration with the University of Utah.  Next, systematic measurements of interfacial forces in flotation deinking systems have been undertaken.  For example, it was found that attractive hydrophobic forces are the dominant forces in flotation deinking systems.  The repulsive forces are only significant in low ionic strength solutions.  This observation has important practical implications indicating that the process water used in the paper recycling mill should carry enough dissolved ions to eliminate the negative effect of an energetic barrier associated with negative surface potentials on water-air and ink-water interfaces, on the attachment of ink particles to gas bubbles.  It was further shown that the range of hydrophobic forces increases and the energy barrier decreases in the presence of calcium carboxylate.

Publications