CHAPTER 9 PCABS, PP and PPS Composites Characterization - Results and Discussion: Part II Thermal Analysis: Thermal Conductivity, Thermogravimetric

Transcription

1 CHAPTER 9 PCABS, PP and PPS Composites Characterization - Results and Discussion: Part II Thermal Analysis: Thermal Conductivity, Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) 199

2 9.1 Through Plane Thermal Conductivity Results Through-plane thermal conductivity test was performed on all the formulation screated. The through-plane conductivity was tested using the HotDisk TPS 2500S instrument. The basic principle is Transient Plane Source (TPS) technique. The through-plane conductivity was tested using the procedure described in chapter 3, section The sensor is normally placed between the surfaces of two pieces of the sample to be measured. During measurement, a current pass through the nickel and creates an increase in temperature. The heat generated dissipates through the sample on either side at a rate dependent on the thermal transport characteristics of the material. By recording the temperature versus time response in the sensor, these characteristics can accurately be calculated. Each formulation had different concentrations of expanded graphite and Ni coated expanded graphite in single filler system and with varying different concentration of CF in two filler system in PCABS, PP and PPS resin. As discussed in the chapter 7, section 7.4 experimental designs, each formulation has 12 different concentrations of loadings shown in table 7.1, 7.2 and 7.3. Same nomenclature has been used in this chapter. 9.2 Single and Two filler system: Through plane thermal conductivity data Single filler system: PCABS based composites Sample code Sensor (mm) Power (W) Time (sec) Thermal diffusivity mm 2 /s Specific Heat MJ/m 3 K Thermal Conductivity (W/m-K) SR SR SR

3 SR SR SR Table 9.1 PCABS based composite: Single filler system thermal conductivity data Two filler system: PCABS based composites Sample code SR-7 Sensor (mm) Power (W) Time (sec) Thermal diffusivity mm 2 /s Specific Heat MJ/m 3 K Thermal Conductivity (W/m-K) SR SR SR SR SR Note: SR-12 same as SR-9 composition Table 9.2 PCABS based composite: Two filler system thermal conductivity data Single filler system: PP based composites Sample code SR-13 Sensor (mm) Power (W) Time (sec) Thermal diffusivity mm 2 /s Specific Heat MJ/m 3 K Thermal Conductivity (W/m-K) SR SR SR SR SR Table 9.3 PP based composite: Single filler system thermal conductivity data 201

4 9.2.4 Two filler system: PP based composites Sample code SR-19 Sensor (mm) Power (W) Time (sec) Thermal diffusivity mm 2 /s Specific Heat MJ/m 3 K Thermal Conductivity (W/m-K) SR SR SR SR SR Note: SR-24 same as SR-21 composition Table 9.4 PP based composite: Two filler system thermal conductivity data Single filler system: PPS based composites Sample code SR-25 Sensor (mm) Power (W) Time (sec) Thermal diffusivity mm 2 /s Specific Heat MJ/m 3 K Thermal Conductivity (W/m-K) SR SR SR SR SR Table 9.5 PPS based composite: Single filler system thermal conductivity data Two filler system: PPS based composites Sample code SR-31 Sensor (mm) Power (W) Time (sec) 202 Thermal diffusivity mm 2 /s Specific Heat MJ/m 3 K Thermal Conductivity (W/m-K) SR SR

5 SR SR SR Note: SR-36 same as SR-33 composition Table 9.6 PPS based composite: Two filler system thermal conductivity data Tables 9.1, 9.3 and 9.5 shows the average (3 readings) through plane thermal conductivity results for single filler system and table 9.2, 9.4 and 9.6 show the average (3 readings) through plane thermal conductivity results for two filler system using HotDisk method for all the formulations. Sensor, time and power kept constant for all the measurements Comparison Studies Figure 9.1 (a & b) shows that the single filler system both expanded graphite and Ni coated expanded graphite filler does increase the through-plane thermal conductivity. It causes the thermal conductivity to increase from 0.20 W/m-K, W/m-K and W/m-K for pure PCABS, PP and PPS to 7 W/m-K to 13 W/m-K for all the formulation at single filler. However, there was not much change in Ni coated expanded graphite thermal conductivity values as compare to neat expanded graphite compositions. (a) (b) Figure 9.1 comparison plots of single filler (a) EG system (b) Ni-EG system for all the composites 203

6 (a) (b) Figure 9.2 comparison plots of two filler (a) Effect of Ni-EG system (b) Effect of CF system for all composites Thermal conductivity of Ni is about 91 W/m-K which is very lesser than the thermal conductivity of expanded graphite which is W/m-K. Expanded graphite composites had the highest through plane thermal conductivity values with the composite containing 60 wt % expanded graphite in PCABS, PP and PPS having the highest value of W/m-K, W/m-K and W/m-K respectively, shown in figure 9.1a also illustrates the similarity loading of Ni EG composites have shown less through plane thermal conductivity and composite having highest value of W/m-K, W/m- K and W/m-K respectively, shown in figure 9.1b at 60 wt%. One possible reason why expanded graphite had the highest through-plane thermal conductivity compared to Ni coated expanded graphite is, because of the high thermal conductivity of expanded graphite is about W/m-K. Another reason could be Ni coating ratio on expanded graphite is 0.5:1. So that 50% lesser addition of expanded graphite compare to original composition. However, two filler system determines what effect individual filler will have on the thermal conductivity and the possible interactions between the fillers in resin. The loading levels were chosen so that the composite would be conductive as well as have a low enough viscosity so thatit could be compounded and compression molded into samples for testing. Thermal conductivity test was performed on varying Ni-EG from 10 wt% to 30wt% with fixed 30 wt% loading of CF and another compositions varying CF 204

7 from 10 wt% to 30 wt% with fixed 30 wt% loading of Ni-EG in all the formulations. (Table 7.1, 7.2 and 7.3) Figure 9.2 (a & b) shows that the two filler system both Ni coated expanded graphite and CF filler does increase the through-plane thermal conductivity. However, Single filler Ni expanded graphite composites having 60 wt% loading has shown very high thermal conductivity in all formulation compare to two filler system composites having 30 wt% Ni expanded graphite and 30 wt% PAN CF has shown very less thermal conductivity at similarly loading. The possible reason is PAN based CF having thermal conductivity of 20 W/m-K for standard modulus and W/m-K for high modulus and also its transverse to the direction of measurements. Compositions having fixed 30 wt% loading of Ni EG and increasing CF from 10 wt% to 30wt% are shown higher thermal conductivity compare to fixed loading of CF compositions. 9.3 Thermogravimetric analysis (TGA) During the lab station brabender batch mixing operations, inconsistencies with the material rate would occur. Therefore, actual filler contents in each composite were validated by Thermogravimetric analysis (TGA). TGA measures changes in weight in relation to change in temperature, and TGA was also used to determine thermal stability of composite. In addition, the precision of fillerloading values implies the effectiveness of filler dispersion in polymer matrix. Thermogravimetric analysis was determined in a TA Instrument Q500. Small amounts approximately mg of each composite were placed in platinum crucibles, which were then loaded into the TGA chamber. The sample was heated at 10 C/min to 700 C, 600 C and 850 C for PCABS, PP and PPS composites in N 2 atmosphere with purging gas at 50 ml/min. Once experiment was completed equipment was then air cooled to ambient before beginning the next set of experiments. The detail procedure has been discussed in the chapter 3, section As discussed in the chapter 7, section 7.4 experimental designs, each formulation has 12 different concentrations of loadings shown in table 7.1, 7.2 and 7.3. Same nomenclature 205

8 has been used in this chapter. Four single filler composition and one two filler composition were studied to find out actual filler contents in each composite. Table 9.7 shows the designed TGA experimental compositions. Sample code Matrix (wt %) Filler -1 Filler-2 Neat EG (wt %) Ni EG (wt %) PAN CF (wt %) PCABS, PP and PPS SR-2, SR-14, SR SR-3, SR-15, SR SR-5, SR-17, SR SR-6, SR-18, SR SR SR-21, SR Table 9.7 Designed TGA experimental compositions 9.4 Single and Two filler system: TGA data PCABS based composites Figure 9.3 shows the thermal stability and degradation of virgin PCABS. PCABS has decomposed in two steps. While neat ABS and neat PC decomposes in a single decomposition step. According to neat PCABS, the first step mainly corresponds to the decomposition of ABS with a weight loss of approximately 32% at maximum decomposed temperature at The second degradation process relates to PC. Naturally PC is a charring material [1], with a weight loss of approximately 53% at maximum decomposed temperature at Generally neat ABS almost decomposes completely at 600. As to PCABS blend, the residue is higher than neat ABS and lower than neat PC. The entire phenomenon indicates that during the decomposition there is an interaction between PC and ABS which influences both the release of ABS and PC decomposition. Similar with the studies has been discussed in Perret B and his coworkers. PCABS decomposition temperature is 375 and remains 14.55% char at

9 Figure 9.3 Thermal behavior of neat PCABS resin Sample code Decomposition Nitrogen charred Actual filler temperature ( C) residue (wt%) content (wt%) Neat PCABS SR SR SR SR SR Table 9.8 Filler content data PCABS composites TGA was also performed to observe the thermal stability of composites as a function of temperature. The stability improves as EG loading increases due the synergistic influence EG, which has a higher decomposition temperature than the PCABS matrix, which is 405 C. However, for Ni-EG composites have not shown much higher thermal stability than EG composite, which is similar to PCABS resin about 375 C. In two filler system we could observe as addition of 30 wt% of CF along with 30 wt% of Ni-EG filler system improves the thermal stability about 403 C which is 28 C increase in 207

10 temperature. Table 9.8 shown summary of the TGA results of PCABS composites. Neat PCABS has around 14.55% char left out at 650 C under N 2 atmosphere. Addition of fillers such as; EG, Ni-EG and combination of Ni-EG/CF composites have shown higher charring content at 650 C than of actual filler content. The possible reason could be degradation of PC in N 2 atmosphere left out some percentage of residues within it due to this; composite of TGA residues have shown higher filler content. Further, left out PC residues are subtracted with composites to arrive the actual experimental filler content. All composite weight percentages are well aligned with theatrical weight percentages PP based composites Figure 9.4 Thermal behaviour of neat PP resin Figure 9.4 shows the thermal stability and degradation of virgin PP. PP has one step. The step mainly corresponds to the decomposition of PP with complete weight loss of approximately 99.9% at maximum decomposed temperature at under N 2 atmosphere. PP decomposition temperature is 386 and remains 0.092% char at

11 Sample code Decomposition temperature ( C) Nitrogen charred residue (wt%) Neat PP SR SR SR SR SR Table 9.9 Filler content data PP composites EG, Ni-EG and combination of Ni-EG/CF composites improves thermal stability significantly higher than the neat PP. Higher the decomposition temperature in composites was observed the reason due to synergistic influence of all the fillers, which leads to increase in 30 C to 40 C temperature in 50 wt% and 60 wt% compositions. Table 9.9 shown summaries of the TGA results of PP composites. Neat PP almost nil char left out at 550 C under N 2 atmosphere. Addition of fillers such as; EG, Ni-EG and combination of Ni-EG/CF composites have shown left out residue content at 550 C which is well aligned with theatrical weight percentages PPS based composites Polyphenylene sulfide (PPS) is a semi-crystalline plastic with high thermal durability. The degradation behavior of PPS has been studied by numerous researchers. The thermal degradation of PPS polymers is usually illustrated as one-stage shown in figure 9.5. The major pyrolystates of PPS were benzenethiol and H 2 S. The major mechanisms included depolymerization, main chain random dividing, and carbonization. The initial cutting of PPS was depolymerization and main chain random dividing to evolve benzenethiol and hydrogen sulfide, respectively, as major products; while depolymerization dominated in lower temperature carbonization and main chain random scission dominated in higher temperature. The chain transfers of carbonization also produced in initial carbonization and gradually dominated at higher carbonization temperatures to form the high char yield of solid residue. Maximum decomposed temperature at under N 2 atmosphere. PPS decomposition temperature is 423 and remains 44.18% char at

12 Figure 9.5 Thermal behavior of neat PPS resin Sample code Decomposition temperature ( C) Nitrogen charred residue (wt%) Neat PPS SR SR SR SR SR Table 9.10 Filler content data PPS composites PPS is a semicrystalline polymer composed of phenyl rings and sulfur atoms that possesses outstanding mechanical and thermal properties. Thermal stability of EG, Ni-EG and combination of Ni-EG/CF filler composites improves significantly higher than the neat PPS. Higher the decomposition temperature in composites was observed due to attributed to both the high thermal conductivity of the expanded graphite and Nickel as compared to PPS, which allows rapid heat transport and enables excessive radial heat radiation, hence slowing down the decomposition process. Which lead to increase in 25 C to 40 C temperature in EG composites having 50 wt% and 60 wt%. However, 210

13 there is a steep increase in temperature about 60 C in Ni-EG composites. Table 9.10 shown summaries of the TGA results of PPS composites. 9.5 Differential Scanning Calorimetry (DSC) The effect of Ni-EG and carbon fiber fillers on the crystallization parameters of neat PP, PPS and PP/PPS Ni-EG/carbon fiber filler composites was observed by differential scanning calorimetry. DSC is a useful tool for characterizing the glass transition region of amorphous thermoplastics (PCABS). Effect of Ni-EG and carbon fiber filler on glass transition temperature (Tg) was studied using DSC. Differential scanning calorimetry was carried out in a TA instruments Q2000, provides capability for glass transition analysis of amorphous thermoplastic alloys and for semicrystalline, crystalline thermoplastic provides melting, cooling behaviors and their ΔHm (enthalpy of melting). The detail procedure of DSC method and crystallinity calculations has been discussed in the chapter 3, section As discussed in the chapter 7, section 7.4 experimental designs, each formulation has 12 different concentrations of loadings shown in table 7.1, 7.2 and 7.3. Same nomenclature has been used in this chapter. This chapter is mainly focused on two aspects namely; Effect of Ni-EG on PCABS glass transition temperature (Tg) Effect of Ni-EG on PP/PPS crystallinity Effect of Ni-EG on PCABS composites glass transition temperature (Tg) PCABS containing a blend of polycarbonate and ABS copolymer with other additives added improves the interface between the two. If there were no miscibility between the phases then the blend would look like a simple addition of the two DSC curves. If there were complete miscibility there would be one Tg roughly midway between the ABS and PC glass transitions. If there were partial miscibility then the glass transitions of the mixed amorphous phases would e etween the two Tg s of the components, exactly what we have observed in this study. 211

14 Figure 9.6 DSC curves of neat PCABS It is observed that the Tg of neat PCABS has two Tg's, one is about C which is Tg of ABS and another is about C which is Tg of PC. PC Tg gradually increases to C as the EG content increases from 40 to 60 wt%. The increase in Tg of the composites can be attributed to strong interaction between the EG and the PCABS matrix. Composites filled with Ni-EG and Ni-EG/CF drop in Tg has been attributed to possible by improving the miscibility of the amorphous phases the formulation increases the bonding across the phase boundaries. Sample Code Tg ( C) ABS PC Neat PCABS SR SR SR SR SR SR SR SR

15 SR SR SR SR Note: SR-12 same as SR-9 composition Table 9.11 Summary of the DSC Tg results of PCABS composites Effect of Ni-EGon PP compositescrystallinity The effect of Ni-EG and combination of both Ni-EG/CF on the crystallization parameters of neat PP and PP/Ni-EG, CF filler composites was observed by DSC. Figure 9.7 DSC curves of neat PP Composite degree of crystallinity can be calculated from the melting heat fusion (enthalpy). Crystallization regrinding a process represented in equation 3.5.b. The melting heat of fusion of 100% crystalline polypropylene used for the calculation is J/g [2] as per many references in literature. Previous literature [3-5] reports neat PP crystallinity (X c ) 40.4 % to 46 %. 213

16 DSC cooling scans and the second heating scans of neat PP, PP/EG, PP/Ni-EG and PP/Ni-EG/CF composites at a cooling or heating rate of 10 K/min. Heating enthalpy shown in all figure is unnormalized and same has been used in the calculations. Table 9.11 shows the summarised of DSC results ofneat PP and its single and two filler composites. Sample Code Filler wf T m ( C) T c ( C) ΔH m J/g (1-wf) Crystallinity (X c ) % Neat PP SR SR SR SR SR SR SR SR SR SR SR SR Note: SR-24 same as SR-21 composition Table 9.12 Single and two filler system PP composites crystallinity data T m : Melting temperature recorded during the second scan. H m : Heating enthalpy (unnormalized) ΔH 0 : J/g Heat of fusion of 100% crystalline polypropylene T c : Crystallization peak temperature. Wf: Weight fraction of filler. Neat PP has T m at C and T c at C and second heating normalized enthalpy of J/g and crystallinity (X c ) 45.36% (figure 9.16a and table 9.11). For the composites (figure 9.16b to 9.16l), Trend confirms the EG, Ni-EG and Ni-EG/CFs are acts as a good nucleating agent for crystallization of PP. The observed 214

17 crystallization temperature (117 C to 125 C) is consistent with crystallization temperature for the nucleation of the β crystalline form. The increase in crystallization temperature of PP in the presence EG/NiEG/CF has technological importance because it results in a shorter processing cycle, thery by increase the production rate. Higher crystallinity content and higher crystallization temperature in cooling reveal a possible nucleating role of EG, Ni-EG and Ni-EG/CF. For composites based on semicrystalline matrix polymers, the crystallinity depends on processing parameters; e.g., crystallization temperature, cooling rate, nucleation density [6]. It can be seen from Table 9.12 that addition of EG, Ni-EG and Ni-EG/CF has different effects on T c and T m. While there is not significantly change in Tm and there is a relatively more pronounced increase in T c with the addition of EG, Ni-EG and Ni-EG/CF to the PP matrix. T c increases with increase in EG, Ni-EG and Ni-EG/CF loading with 40 to 60 wt% composite. The addition of EG, Ni-EG and Ni-EG/CF results in a decrease in the heat of reaction associated with melting process. This could be primarily attributed to the dilution effect of PP by the Ni-EG and Ni-EG/CF fillers. It can be seen from the Table 9.11 that the values increase significantly with the addition of EG, Ni-EG and Ni-EG/CF to PP matrix. Compare to all the fillers, Ni-EG play a clear role in the nucleation and crystallization process and combination of Ni-EG (30 wt %) and CF (10 wt % to 30 wt %) Effect of Ni-EG on PPS composites crystallinity The effect of Ni-EG and combination of Ni-EG and carbon fiber on the crystallization parameters of neat PPS and PPS/Ni-EG, CF filler composites was observed by DSC. Values of ΔH 0 establish in the literature for polyphenylene sulphide range from about 50 J/g to J/g. These dissimilarities are much too huge to be due to dissimilarities in the nature of the polymers were studied. Thedifficulty of obtaining an accurate value of ΔH 0 is caused by the impossibility of obtaining a100% crystalline sample. Many investigators have used a value of ΔH 0 80J/g, based on the early work of Brady [7]. More recently, Huo and Cebe [8] measured heat of fusionas a function of measured sample specific 215

18 volume. This resulted in a higher value of ΔH J/g. Present study for calculating crystallinity of PPS, ΔH 0 = 80 J/g and ΔH 0 = 112 J/g proposed by Brady, Huo and Cebe was used. Figure 9.8 DSC curves of neat PPS Sample Code Filler wf Tm ( C) Tc ( C) ΔHm J/g (1-wf) Crystallinity (Xc)* % Crystallinity (Xc)** % Neat PPS SR SR SR SR SR SR SR SR SR SR

19 SR SR Note: SR-36 same as SR-33 composition Table 9.13 Single and two filler system PPS composites crystallinity data T m : Melting temperature recorded during the second scan. H m : Heating enthalpy (unnormalized) ΔH 0* : 80 J/g Heat of fusion of 100% crystalline PPS ΔH 0** : 112 J/g Heat of fusion of 100% crystalline PPS T c : Crystallization peak temperature. Wf: Weight fraction of filler. A typical example of DSC curve for a PPS resin was shown in Figure 9.17 and table 9.12 shows the cooling and second heating cycle for the resin. T m at C and T c at C and second heating normalized enthalpy of J/g were found. If the value of 80 J/g crystallinity (X c ) = 64.55% and if the value of 112 J/g crystallinity (X c ) = 46.11%. The measured Xc values were matched with literature values which was sited about 65%. Generally, polymers crystallize slowly at temperature above glass transition temperature due to low mobility of the molecules at this temperature. Likewise, polymers crystallize slowly at temperatures slightly below their equilibrium melting point due to low driving force for crystal nucleation at these temperatures. The maximum crystallization rate occurs at a temperature where the combination of nucleation and crystal growth rates is optimized. For PPS it s mainly depending on the molecular architecture and crystallinity, the glass transition and the equilibrium melting temperature. DSC cooling scans and the second heating scans of PPS/EG, PPS/Ni-EG and PPS/Ni-EG/CF composites at a cooling or heating rate of 10 K/min. Heating enthalpy shown in all figure is unnormalized and same has been used in the calculations. Table 9.12 shows the summarised of DSC results ofneat PPS and its single and two filler composites. 217

20 In general, the influence of inorganic phase on polymer crystallization can be embodied in two aspects. Firstly, the addition of inorganic phase results in heterogeneous nucleation crystallization of polymer, and improves the crystallinity of polymer, and secondly, the addition of inorganic phase increases the viscosity of the blend system, hinders the polymer segmental motion and inhibits crystallization. It can be seen from Table The addition of EG, Ni-EG and Ni-EG/CF results in a decrease in the heat of reaction associated with melting process. There was not much significant change in T m and T C composites and we could see the decrease in crystallinity of composites. The reason could be phases were not making heterogeneous nucleation among the single filler system. Compare to all the fillers, Ni-EG and combination with CF (10 wt% to 30 wt%) dispersed in PPS matrix which increases the crystallization rate and promote polymer crystallization Comparison studies: DSC Figure 9.18, 9.19 and 9.20 shows the comparison DSC plots of PCABS, PP and PPS both single filler and two filler system respectively. Comparison plots will give an clear vision over change in Tg, Tm, Tc over different loading system (40 wt% to 60 wt%). In PP and PPS compositions, we could see clear changes in Tc and enthalpy with respect to filler loading. Detailed DSC analyses were captured in previous section. 218

21 PCABS Composites (a) (b) 219

22 Figure 9.9 Comparison DSC plot (a & b) single filler system (c) two filler system of PCABS composites PP Composites (c) 220

23 (a) (b) (c) 221

24 (d) Figure 9.10 Comparison DSC plot (a & b) single filler system (c & d) two filler system of PP composites PPS Composites (a) 222

25 (b) (c) 223

26 (d) Figure 9.11 Comparison DSC plot (a & b) single filler system (c & d) two filler system of PP composites 9.6 Conclusion This chapter describes the results and discussions of thermal analysis such as thermal conductivity, filler content by TGA and crystallization studies by DSC of developed electrically conductive composites both single and two filler systems. In through plane thermal conductivity expanded graphite, Ni coated expanded graphite and carbon fibers are mainly oriented transverse to the direction of thermal conductivity measurement. Considering only the through plane conductivity of composites containing a varying amount of single filler which is neat expanded graphite and Ni coated expanded graphite. Among the two fillers, expanded graphite caused the largest increase in composite through plane thermal conductivity compare to Ni coated expanded graphite composites. PCABS formulations have shown higher through plane thermal conductivity in both single and two filler systems. By addition of carbon fiber in two filler system decreased 224

27 through plane thermal conductivity due to its transverse to the direction of measurements. From TGA curves we can conclude that derived from experimental composite weight percentages are well aligned with theoretical weight percentage. Effect of Ni EG on crystallinity was studied in PP and PPS composites. Addition of Ni coated expanded graphite was influenced in heterogeneous nucleation crystallization in composites. Resulting higher crystallinity was found in PP composites. In PPS composites, there was not much change in crystallization temperature and observed slight decrease in crystallinity of composites due to not making heterogeneous nucleation among the fillers. The above properties are well supported with electrical, EMI properties and together can make next generation material for electronic applications. 225

28 9.7 References 1. Daniel L. P. and Sovinski M.F., NASA/TM Wunderlich, B. (1990). Thermal Analysis, New York, Academic 3. Suzhou Yin., Wood and fiber science, 39(1), 2007, pp Ha-da Bao, Zhao-xia Guo and Jian Yu., Chinese journal of polymer science vol. 27, no. 3, (2009), Ch.Pandis. E. Logakis., NSTI Nanotech 2007 ISBN Vol.2, E. Schulz, G. kalinka and W. Auersch. J. Macromole. Sci.Phys.B 35, 527, Brady, D. G. Journal of Applied Polymer Science 1976, 20, Huo, P.; Cebe, P. Colloid Polymer Science 1992, 270,