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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 15°C ± 2°C. Once the temperature was below 50°C, 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 115°C
(240°F) for the feed zone, and 177°C (350°F) for the mixing and A.2.1 Density (ASTM D1505)
metering zones. The die temperature was also 177°C (350°F). 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 190°C 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 190°C 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 175°C 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 190°C. Once the mold
(ASTM D4218)
reached 160°C, the set-point temperature was reduced to
177°C 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
