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A-2 A.1 Procedures mold temperature was recorded and the cooling process begun. The mold temperature was lowered by slowly open- A.1.1 Melt Blending by Extrusion ing a needle valve with cooling water. The temperature was All blending and extruding was performed on a laboratory recorded every 30 seconds and the cooling was done at a rate line consisting of a Welding Engineers Model HT8-222-2251 of 15C 2C. Once the temperature was below 50C, the Twin Screw Extruder, a custom-built cooling bath equipped mold was removed. with a chiller and circulator and a Berlyn Corporation Model HV1 Pelletizer. The extruder has counter-rotating screws at an A.2 Index Test Methods L:D ratio of 24:1. The extruder temperatures were set at 115C (240F) for the feed zone, and 177C (350F) for the mixing and A.2.1 Density (ASTM D1505) metering zones. The die temperature was also 177C (350F). The density of the samples was determined by ASTM D1505, The die was a single 6.35-mm (0.25-in.) diameter rod and the Standard Test Method for Density of Plastics by the Density- die was fitted with two, 1-in. diameter melt filter screen holders. Gradient Technique. The test is performed with the use of a All samples for extrusion were dry blended then gravity glass column filled in a specified procedure with isopropanol fed. The batch size was typically 2.2 lb (1 kg). The screw speed and water that creates a gradient of densities from around was set at 220 rpm, which produced an output rate of about 0.910 to 0.970 g/cm3. Standard glass density beads are placed 6.8 kg/hr (15 lb/hr). The residence time in the extruder was less in the column for calibration. Samples are cut into small pieces than 45 seconds. (1/16-in. diameter), degassed under vacuum in isopropanol, Samples of recycled regrind chips were melt blended twice and placed in the column. Once settled, the position is recorded and recycled reprocessed pellets were melt blended once. from a graduated scale on the glass column and the density All the experimental blends were melt blended three times calculated from the position of the standard beads. to ensure optimum blending. Virgin resins were also blended in the same manner to duplicate the heat history of the blends. It is worth mentioning that the processing conditions used A.2.2 Melt Flow Index and Flow Rate during this study are different than what is actually going on (ASTM D1238) in the recycled suppliers' plants or in the pipe manufacturers' The melt index was determined in accordance to ASTM plants. First of all, the twin screw mixes much better than a D1238, Standard Test Method for Flow Rates of Thermoplastics single screw, or even a high-length/diameter single screw. So, by Extrusion Plastometer. A sample of plastic was heated inside the blends studied herein were optimally blended. Secondly, the a standard-sized cylinder for a controlled amount of time. study on the effects of polypropylene (PP) might not translate Then, a weight was applied, forcing the molten plastic through well to the plants because the PP may not be as well blended a standard die. The mass of plastic that is extruded through the as in the study. And thirdly, the twin screw processing is very die in a specific period of time was reported. Two conditions gentle compared to a large single screw. So, even though there were used for the polyethylene samples in this study. The first were no signs of oxidation in the study on the twin screw, oxi- were a temperature of 190C and a load of 2.16 kg (Melt dation may still be an important consideration in the plants. Index) and the second were a temperature of 190C and a load of 21.6 kg (Flow Rate). The results are reported as grams per A.1.2 Plaque Preparation (ASTM D4703) 10 minutes. The melt flow tests were performed on pellets after melt Sample plaques were prepared according to ASTM D4703, blending. Practice for Compression Molding Thermoplastic Materials into Test Specimens, Plaques, or Sheets on a Pasadena Hydraulic Industries Model P215H Platen Press. Two sizes of plaques A.2.3 Percentage Volatiles (TRI Method) were prepared. The plaque used for the BAM test specimens Duplicate 2.000 g 0.100 g samples were placed in an alu- was 15.24 cm 15.24 cm 1.27 mm (6 in. 6 in. 0.05 in.). minum weighing boat and heated at 175C for 1 hour in a The plaque used for all other tests was 17.78 cm 17.78 cm forced air oven. Upon cooling, the final weight was obtained 1.9 mm (7 in. 7 in. 0.075 in.). The smaller mold used 50g and the percentage volatiles were calculated. This test was of pellets while the larger one used 75g. performed on the as-received pellets, before melt blending. The open cavity mold was charged with pipe pieces about 5 cm 5 cm in between two Mylar release sheets and placed A.2.4 Percentage Black/Color Ash in the press, which was preheated to 190C. Once the mold (ASTM D4218) reached 160C, the set-point temperature was reduced to 177C and the mold quickly pressed to 20.68 MPa (3000 psi). This was done by the muffle furnace method described in After the plastic was allowed to relax for at least 5 minutes, the ASTM D4218, Test Method for Determination of Carbon Black