Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 18


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 17
17 blends labeled "mixed color plus" by project personnel. Two of The high yield stress is due to the higher density. Yield stress these are MCR with added high molecular-weight (HMW)- and density are linearly related. HDPE to assist with processing, and to improve properties such The percentage strain-at-break was low compared to virgin as impact strength and stress-crack resistance. The third is a materials (>500%). This property can be considered a flaw blend of mixed-color PCR HDPE with PIR HDPE. detector, since every break in a tensile test occurs at a flaw. These resins were made into plaques and characterized by a These results indicate that the small amount of particles pres- variety of tests. The full test reports for these materials are ent in the recycled result in early breaks. In turn, the flaws can found in Appendix B, Section B.5. The results were originally also be initiators of stress cracks in the resultant pipe. generated on plaques made from the "as-received" pellets. Test The 15% NCTL times are low, which is a result of the high results indicated that further blending was necessary to obtain density and the fact that milk bottle resin is a homopolymer. homogeneous material for characterization. This is reasonable The OIT values are indicative of stabilizer concentration, because single screw production lines are not as well suited for but how much is there cannot be determined without blending as a twin screw. If the recyclers were to improve the knowing the specific additive package and what the rela- mixing on their extruders, the changes could cause more tionship between OIT and concentration is for that specific thermal-oxidative degradation to the material. Therefore, the package. However, the data do indicate that there is some MCRGs and reprocessed materials were further blended and antioxidant protection remaining in the recycled HDPE. recharacterized. In general, the regrind samples received were melt-blended at least twice and the reprocessed samples were The advantage of this recycled resin is that it is clean and further blended at least one additional time. strong; the disadvantages include the cost and the poor crack- ing resistance. PCR Natural Resin PCR Mixed-Color Resin The average resin properties for post-consumer natural Most of the samples obtained fell into the category of recycled HDPE have been summarized in Table 4. TRI-repro PCR mixed-color resin. There were 15 different samples from was a blend of the others made in-house as an "average" sam- eight different suppliers. There were five regrind resins and ple. A milk bottle was also tested for comparison. 10 reprocessed resins. And, of the 10 reprocessed resins, three Observations from the summary table include the following: had something else added. Suppliers 2 and 3 sent samples with added HMW PE to improve processing and stress-crack resist- The density and melt flow values are higher than typically ance. Supplier 5 sent a product with additional PIRHDPE found for AASHTO pipe resin. AASHTO pipe resins are added to improve its properties. Suppliers 1 and 3 sent samples typically around 0.950 g/cm3 and 0.15 g/10 min. The ash of regrind resins at different times, so the consistency of their content is low. This demonstrates that recycled natural resin products could be examined. is very clean. The average properties of all the mixed-color resins received are found in Table 5. This table provides a snapshot of the PCR Table 4. Post-consumer natural recycled resins available in the first half of 2007. The sample called TRI PE properties. Repro 1 was a batch prepared in house on the twin screw extruder. All the available mixed-color reprocessed samples Resin Type were combined to prepare 20 lbs of resin that was basically Property TRI Milk Repro Bottle Average Range an average of the samples received. Density There are a number of important observations from these (g/cm3) 0.960 0.958 0.957 0.002 0.9550.960 results: Melt Index (g/10 min) 0.79 0.74 0.67 0.1 0.570.81 MFR The density, melt index, and yield stress vary with the (21.6/2.16kg) 71 75 87 8 7696 amount of milk bottles present in the mixed-color waste % Ash 0.06 0.04 0.11 0.05 0.050.14 stream. The values are probably more consistent in 2010 Yield than in 2007 because more processors are separating the Strength 4523 4316 4402 79 43044489 milk bottles due to their increased value over colored bottles. (psi) Break These resins typically have little color. In this case, all the Strain (%) 365 114 157 73 75229 values were less than 0.4%, except one sample where the 15% NCTL manufacturer added 1.3%. (h) 2.0 5.4 3.7 1.6 1.85.7 The percentage ash in the products can be reduced by melt OIT (min) -- 23 16.5 7.5 927 filtration through a larger mesh size (smaller openings). Note: "--" = no data available. This, in turn, will improve the percentage break strain.