Thermal Analysis & Rheology THERMAL SOLUTIONS DETERMINATION OF POLYMER BLEND COMPOSITION PROBLEM SOLUTION The blending of two or more polymers is becoming a Conventional DSC is a technique which measures the total common method for developing new materials for demand- heat flow into and out of a material as a function of ing applications such as impact-resistant parts and temperature and/or time. Hence, conventional DSC packaging films. Since the ultimate properties of blends can measures the sum of all thermal events occurring in the TM be significantly affected by what polymers are present, as material. Modulated DSC , on the other hand, is a new well as by small changes in the blend composition, technique which subjects a material to a linear heating suppliers of these materials are interested in rapid tests method which has a superimposed sinusoidal temperature which provide verification that the correct polymers and oscillation (modulation) resulting in a cyclic heating profile. amount of each polymer are present in the blend. Differen- tial scanning calorimetry (DSC) has proven to be an Deconvolution of the resultant heat flow profile during this effective technique for characterizing blends such as cyclic heating provides not only the "total" heat flow polyethylene/polypropylene where the crystalline melting obtained from conventional DSC, but also separates that endotherms or other transitions (e.g., glass transition) "total" heat flow into its heat capacity-related (reversing) associated with the polymer components are sufficiently and kinetic (nonreversing) components. It is this separa- TM separated to allow identification and/or quantitation. tion aspect which allows MDSC to more completely However, many blends do not exhibit this convenient evaluate polymer blend compositions. separation and thus are difficult to accurately evaluate by Figure 1, for example, shows the conventional DSC (total conventional DSC. Figure 1. PET/ABS BLEND (AS RECEIVED) CONVENTIONAL DSC -0.2 120.92°C 67.38°C -0.4 + 70.26°C (H) 235.36°C 22.63 J/g 111.82°C 9.016 J/g Heat(W/g) Flow -0.6 249.76°C -0.8 50 100 150 200 250 Temperature (o C) TS-22 heat flow) result for an as received polymer blend reversing under MDSC, while cold crystallization is containing polyethylene terephthalate (PET) and acryloni- nonreversing. Hence, separation of the total heat flow into trile-butadiene-styrene (ABS). Three transitions indicative its reversing and nonreversing components separates of the glass transition, cold crystallization, and crystalline overlapping thermal events with different behavior. The melting of the PET are seen at 67oC, 112oC, and 235oC nonreversing curve in this case shows only the exotherm respectively. However, no apparent ABS transitions are associated with the PET cold crystallization . The reversing observed. Upon reheating, after cooling at a controlled rate curve shows three transitions - the glass transition (69oC) (10oC/minute), the conventional DSC result changes and crystalline melting associated with PET [this melting is (Figure 2). Now only two transitions are observed - a glass not shown in Figure 3 since it's outside the temperature transition at 106oC and a crystalline melt at 238oC. Explana- range chosen], as well as a second glass transition (at tion of these changes on reheating, particularly the 105oC) associated with the ABS. In conventional DSC, this apparent shift in the glass transition temperature, isdifficult latter glass transition is hidden under the PET cold based on only these results. crystallization peak and only becomes visible on reheating after a less amorphous PET phase is produced. The MDSCTM results for the "as received" material shown Figures 4 and 5 show another example of the improved in Figure 3 resolve these interpretation issues. Phenomena interpretation provided by MDSCTM. The total heat flow such as glass transitions and melting are predominately (Figure 4) is the conventional DSC result for a blend believed to contain PET, polycarbonate (PC) and polyeth- Figure 2. PET/ABS BLEND (REHEAT) CONVENTIONAL DSC -0.2 106.31°C -0.4 108.95°C (H) + 237.84°C 20.64 J/g Heat Flow (W/g) Flow Heat -0.6 249.95°C -0.8 50 100 150 200 250 Temperature (o C) ylene (PE). Obviously, interpretation of this curve is not CURVE TRANSITION ASSIGNMENT straightforward. The MDSC results (reversing and Reversing Glass Transition (73oC) PET nonreversing heat flow in Figures 4 & 5), on the other Melt (116oC) PE hand, again facilitate interpretation. The total heat flow Glass Transition (140oC) PC curve shows a glass transition, an overlapping group of Melt (224oC) PET o transitions at 110 - 140oC, and a crystalline melt. Separa- Nonreversing Relaxation (75 C) PET Cold Crystallization (120oC) PET tion of the total heat flow into its reversing and nonreversing components allows the following transitions to be resolved and assigned. Figure 3. PET/ABS BLEND (AS RECEIVED) MODULATED DSCTM -0.10 -0.02 -0.04 Nonreversing -0.11 -0.03 -0.05 -0.12 -0.04 -0.06 Total Reversing 69.00°C 72.69°C (H) -0.13 PET Tg -0.05 -0.07 Heat (W/g) Flow 104.48°C 107.25°C (H) -0.14 ABS Tg -0.06 -0.08 [ ] Rev Heat Flow (W/g) [ - - - - - - -] Nonrev Heat Flow (W/g) Flow Heat Nonrev - -] - - [ - -0.15 -0.09 20 40 60 80 100 120 140 160 180 200 Temperature ( o C) Figure 4. PE/PC/PET BLEND) MODULATED DSCTM -0.70 0.00 -0.80 -0.03 NONREVERSING -0.90 -0.20 -1.00 TOTAL -0.05 -1.10 -0.40 Heat Flow (mW) Heat Flow REVERSING Nonrev Heat Flow (mW) Flow Heat Nonrev -1.20 (mW) Flow Heat Rev -0.07 -1.30 -0.60 -1.40 0 50 100 150 200 250 300 Temperature ( o C) Figure 5. PE/PC/PET BLEND) MDSC TM REVERSING HEAT FLOW -0.3 PET Tg -0.4 72.59°C POLYCARBONATE Tg 75.28°C (H) 139.90°C 115.90°C 143.55°C (H)72.59°C -0.5 6.358 Jg 223.61°C Heat Flow (mW) Flow Heat 21.55 Jg -0.6 123.29°C HDPE MELTING 249.08°C -0.7 PET MELTING 50 100 150 200 250 Temperature (°C) Modulated DSC and MDSC are TA Instruments trademarks used to describe technology invented by Dr. Mike Reading of ICI (Slough, UK) and patented by TA Instmments (US Patent No. B1 5,224,775; 5,248,199; 5,335,993; 5,346,306). 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