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The experimental technique used here establishes the starting point of compression by connecting the displacement transducer directly to the top cylinder as shown in Figure 2. The ram of the press (not shown in Figure 2) is not connected to the top cylinder. Therefore, the origin of the data of each load cell data is precisely set when the displacement transducer records compressive strain as the press ram is lowered.

Temperature of the resin in the sample is monitored during the test, and this has been added since the last report [3]. A thermocouple made of 30 gauge wire was made by twisting the wire pair to approximate the bulk temperature. The thermocouple extended half of the distance (~6 mm) across the diameter (~12 mm) of the cell cavity. The small size of wire minimized the effect of its presence on the compressive strain and had optimized response time. The initial value and maximum values of temperature are recorded. All resins had an initial bulk temperature of about 27

Figures 3-6 show the raw data for lateral stress versus primary stress for the four polymers, PS, ABS, HIPS, and PP. The data are repeated to provide two data sets (1 and 2) for each polymer. As can be seen, the variation in lateral stress versus primary stress is slight for PC, HIPS, and PP, but is noticeable for ABS in Figure 4. This suggests that the variation in lateral stress for ABS may be unique to it.

Regression curves for the data of lateral stress versus primary stress shown in Figures 3-6 are given in Figure 7. The data for each of the two sample runs of each polymer shown in Figures 3-6 are combined and fitted with the regression function (trend line). A (0,0) intercept is assumed (zero primary stress = zero lateral stress). The trend line consistently used is a 6

Figure 7 clearly shows the relationship between the lateral stresses for the four polymers. PP has the greatest value of lateral stress while PC has the lowest lateral stress function. ABS and HIPS appear to be very comparable, which is logical since they are both styrene. However, it is not generally the case that the same general polymer has similar lateral stress as was shown for lateral stress measurement of three polyethylene resins; LLDPE, LDPE, and HDPE [2].

Equations 1-4 are only applicable within the shown specified limits of primary stress. Extrapolation above the upper limit will likely result in large error. Limited extrapolation above the upper limit of primary stress should be done with a linear trend line, if need be.

The resulting equations for stress ratio are the same as Equations 1-4 but with the exponential power of each term reduced by a value of one. Equations 1-4 are 6

The lateral stress ratio as defined cannot be calculated from the raw data at zero primary stress (0/0 has no mathematical result). This is obvious from Figures 8- 11 by the sporadic nature of the curves near zero primary stress. However, the 5

Table 1 Stress Ratio Limit at Zero Primary Stress

Table 2 Temperatures, Maximum Stress, and Plasticity Ratio

Finally, the phenomenon of bulk temperature increase during compression of the resin feed is measured to be up to 3

2. The lateral stress for the PC was the lowest, and the lateral stress ratio was about 0.3 over most of its range. However, it had a lateral stress ratio of up to about 0.5 at initial primary stress levels. This relatively high initial stress ratio was unique among the four resins tested.

3. The lateral stress for ABS and HIPS (both styrene resin) were measured to be very similar and between that of PC and PP.

4. The lateral stress ratio for ABS and HIPS was just above 0.3 over most of the measured range. Low initial values of about 0.23 greatly differentiate these resins from PC and PP with initial stress ratios of about 0.4.

5. Heat is generated during the compression of bulk resin feed stock as measured by an increase in bulk temperature of 1 to 3

6. The energy of plastic deformation for all resins was above 90% of the total energy of compression as calculated by integration of the density versus pressure data.

2. S. J. Derezinski 2010. “Measurements of Biaxial Stresses During the Compression of Bulk Resin Feed,” ANTEC 2010-Proceedings of the 68th Annual Conference & Exhibition, Orlando, Fl, May 16-20, 2010, Society of Plastic Engineers, pp. 617-622.

3. S. J. Derezinski, “Lateral Stress and Bulk Density of PET Resin with Recycle”, ANTEC 2011- Proceedings of the 69th Annual Conference and Exhibition, Boston, Ma, May 1-3, 2011, Society of Plastic Engineers, pp 100-100.

Figure 1. Four Resins Tested

Figure 2. The Test Cell for Measuring the Primary and Lateral Forces During Compression of Bulk Resin Feed as a function of bulk density [1,2]. Diameter of the cylinder is 12.7 mm. The linear displacement transducer records the height of the sample to establish the evolving bulk density value and lateral area of force. A thermocouple is centered in the resin to obtain the starting and maximum temperatures during compression.

Figure 3. Polycarbonate Lateral Stress versus Primary Stress Raw Data

Figure 4 Lateral Stress Raw Data for ABS Resin

Figure 5. Lateral Stress Raw Data for HIPS

Figure 6. Raw Data for Polypropylene Lateral Stress

Figure 7. Lateral Stess Function for Four Polymers. Curves obtained by regression analsysis of two data sets for each of the four polymers (Figures 3-6).

Figure 8. Polycarbonate Stress Ratio Data versus Primary Stress. Curves calculated from data of Figure 3.

Figure 9. Stress Ratio for ABS Resin. Raw data of Figure 4 used to calculate the stress ratios.

Figure 10. Lateral Stress Ratio for HIPS. Curves calculated directly from raw data of Figure 5.

Figure 11. Stress Ratio for Polypropylene Curves calculated directly from raw data of Figure 6.

Figure 12. Lateral Stress Ratio Functions for Four Resins The curves are based on the regression equations, Equations 1-4, represented in Figure 7. The lateral stress ratio functions are obtained from Equations 1-4 by merely lowering the exponent in each term by a value of 1.

Figure 13. Raw Data for Polycarbonate Density versus Primary Stress. Two samples shown. Arrows indicate compression and release.

Figure 14. Raw Data for Density of Two ABS Samples. Arrows indicate compression and release.

Figure 15, Raw Density Data for HIPS Resin Density Arrows indicate compression and release.

Figure 16. Raw Data for Bulk Density of Polypropylene Arrows indicate compression and release.

Figure 17. Regression Curves for Bulk Density of Four Resins Only the density during the compression of each resin is shown See Equations 5 to 8.

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