Date of Graduation


Document Type


Degree Type



Statler College of Engineering and Mineral Resources


Chemical and Biomedical Engineering

Committee Chair

Rakesh K. Gupta.


The main barrier to recycling of post-consumer plastics is the commingled nature of these materials with consequent poor and variable mechanical, thermal and flow properties; separating the polymers by chemical type is prohibitively expensive and does not completely solve the problem of batch-to-batch variability in properties that results from variations in the nature and amount of impurities and variation in polymer molecular weight and molecular weight distribution. In the present work, it is proposed that the addition of up to 20 wt% short glass fibers to the mixed plastic makes the mechanical and flow properties of the composite depend more on the glass reinforcement than on the polymeric matrix. The truth of this hypothesis is demonstrated by providing data on polymers obtained from end-of-life electronics, typically polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS). It is shown that impact strength and elongation-to-break in a tensile test are the two mechanical properties that are most sensitive to the presence of impurities in PC. On adding short glass fibers, these two properties become almost insensitive to changes in matrix composition provided that the matrix contains at least 75% virgin PC. Thus, a sample containing 15 wt% glass fibers has an impact strength of 1.4 ft-lb/in when the matrix contains recycled PC, and this impact strength goes up to only 1.8 ft-lb/in when the matrix is entirely virgin PC; the increase in strain-at-fracture is from 5% to 6.7%. Similarly, the viscosity difference between PC melts with added glass fibers is acceptably small if the matrix contains at least 75% virgin PC. This says that, for purposes of recycling, separation of commingled plastics is not necessary, and one can formulate a "green" product having 25% recycled polymer (based on resin content) by the addition of an appropriate amount of short glass fibers.