TY - JOUR
T1 - Carbon-dioxide-based microsortation of postconsumer polyolefins and its effect on polyolefin properties
AU - Karmana, Eddy
AU - Simon, Sindee
AU - Enick, Robert
PY - 1999
Y1 - 1999
N2 - Postconsumer polyolefin flake has been sorted using liquid carbon dioxide as a float-sink medium. This separation of PP and LDPE from HDPE was conducted at ambient temperature and a pressure that yielded a CO2 specific gravity of 0.955, causing the HDPE to sink and the LDPE and PP to float. Although this process provided a high-purity (99+%) HDPE product stream, the effect of immersing the plastics in liquid carbon dioxide at these conditions was not previously measured. Therefore, six HDPE samples, two LDPE samples, and five PP samples were exposed to high-pressure carbon dioxide for 20 min. After this exposure, the polyolefins did not foam when the carbon dioxide was rapidly vented from the vessel. The weight reduction averaged 0.17%, which was attributed to the dissolution of low-molecular-weight additives or contaminants present on the surface of the plastics. No significant change in the melting point or latent heat of melting was observed, indicating that the degree of crystallinity was not affected by the exposure to carbon dioxide. No reduction was observed in the temperature at which the onset of thermal degradation occurred, because of the low solubility and degree of extraction of thermal stabilizers during the immersion in carbon dioxide. These results indicated that no deleterious effects on the polyolefin properties were associated with this separation technique.
AB - Postconsumer polyolefin flake has been sorted using liquid carbon dioxide as a float-sink medium. This separation of PP and LDPE from HDPE was conducted at ambient temperature and a pressure that yielded a CO2 specific gravity of 0.955, causing the HDPE to sink and the LDPE and PP to float. Although this process provided a high-purity (99+%) HDPE product stream, the effect of immersing the plastics in liquid carbon dioxide at these conditions was not previously measured. Therefore, six HDPE samples, two LDPE samples, and five PP samples were exposed to high-pressure carbon dioxide for 20 min. After this exposure, the polyolefins did not foam when the carbon dioxide was rapidly vented from the vessel. The weight reduction averaged 0.17%, which was attributed to the dissolution of low-molecular-weight additives or contaminants present on the surface of the plastics. No significant change in the melting point or latent heat of melting was observed, indicating that the degree of crystallinity was not affected by the exposure to carbon dioxide. No reduction was observed in the temperature at which the onset of thermal degradation occurred, because of the low solubility and degree of extraction of thermal stabilizers during the immersion in carbon dioxide. These results indicated that no deleterious effects on the polyolefin properties were associated with this separation technique.
KW - Carbon dioxide
KW - Density
KW - Latent heat of melting
KW - Microsortation
KW - Polyolefins
KW - Recycling
KW - Thermal stability
UR - http://www.scopus.com/inward/record.url?scp=0032860242&partnerID=8YFLogxK
U2 - 10.1080/03602559909351591
DO - 10.1080/03602559909351591
M3 - Article
AN - SCOPUS:0032860242
VL - 38
SP - 433
EP - 444
JO - Polymer-Plastics Technology and Engineering
JF - Polymer-Plastics Technology and Engineering
SN - 0360-2559
IS - 3
ER -