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A-3 Content in Polyethylene Compounds by the Muffle-Furnace ing cooling of the plastic from the melt. One would normally Technique. About 1 g of sample was placed in an aluminum integrate the PP curve from 100C to 175C to determine the dish and heated in a small muffle furnace for 3 minutes. Upon heat of fusion. However, in a sample containing both HDPE cooling, the final weight was obtained and the percentage and PP, the end of the HDPE curve will cut off a portion of the black/color + ash was calculated. PP curve. So, a method was devised to account for the miss- ing portion of the PP curve. The first step was to obtain a bag full of PP chips from a A.2.5 Percentage Ash (ASTM D5630) recycler who separates out PP caps. Then, 15 different colored This was generally done in accordance with Procedure B of chips were analyzed by DSC to determine the Heat of Fusion, ASTM D5630, Ash Content of Plastics. The sample mass was the Melting Onset Temperature and the Melting Peak Tem- 1 g and the ashing temperature was 800C. After heating for perature. The results are shown in Table A-1. at least 10 minutes, the sample was cooled, reweighed, and the Next, a master curve was prepared by determining the heat % Ash determined. of fusion of the PP starting at different initial temperatures. This is demonstrated in Figure A-2. The four sets of onset temperatures and heats of fusion A.2.6 Percentage Polypropylene represent the area under the curve starting at temperatures of (TRI Method) 130, 135, 140, and 145C. This represents what would happen The percentage polypropylene was determined with a at different HDPE overlap temperatures in a blend of HDPE differential scanning calorimeter (DSC) and by a procedure and PP. developed for this project. This was done for all 15 cap samples and a master curve A combination DSC curve with both high-density poly- was generated by plotting the average heat of fusion as a func- ethylene (HDPE) and PP melting profiles is shown in Fig- tion of overlap temperature. This is shown in Figure A-3. ure A-1. When a blend of PE and PP is analyzed, the temperature at Notice that there is an overlap between the two peaks near the end of the HDPE peak is noted along with the area under 136C. The area under each of these two curves is the heat of the PP curve. This is shown in Figure A-4. fusion, which relates to the percentage crystallinity of the The inset graph is the portion of the curve from 135C to two polymers. The tail of the HDPE curve will vary, depend- 180C. Notice the overlap temperature is 139.1C and the ing upon the size and quality of the crystallites formed dur- heat of fusion for the PP curve is 3.18 J/g. Figure A-1. DSC melting profiles for HDPE and PP.

OCR for page 57
A-4 Table A-1. Average melting properties for 15 different colored PP bottle closures. Heat of Fusion (J/g) Onset Temperature (C) Peak Temperature (C) 100.0 4.9 156.9 3.4 167.2 2.2 Figure A-2. DSC curve for PP showing integration from four starting temperatures. 86 84 82 Heat of Fusion 80 78 76 y = -0.035x2 + 8.851x - 475.57 R2 = 0.9995 74 72 70 128 130 132 134 136 138 140 142 144 146 Initial Temp (C) Figure A-3. PP heat of fusion as a function of overlap temperature (average of 15 PP caps).