Correlation of Microstructure, Rheological and Morphological Characteristics of Synthesized Polypropylene (PP) Reactor Blends Using Homogeneous Binary Metallocene Catalyst
Abstract
:1. Introduction
2. Experimental
2.1. Materials and Methods
2.2. Catalyst Preparation
2.3. Polymerization
2.4. Characterization
2.4.1. Gel Permeation Chromatography (GPC)
2.4.2. Xylene Solubility
2.4.3. Rheological Properties
2.4.4. Scanning Electron Microscopy (SEM)
2.4.5. FTIR Analysis
3. Results and Discussion
3.1. Polymerization
3.2. Molecular Weight and Molecular Weight Distribution
3.3. FTIR Results
3.4. Linear Rheological Behavior
3.4.1. Strain Sweep
3.4.2. Frequency Sweep
3.4.3. Effect of Increasing Molar Ratio of Cat (II)/Cat (I) on the Relaxation Time
3.5. Correlation of Morphological and Rheological Properties
4. Conclusions
- The MWD curves of synthesized products by the individual use of catalysts (I) and (II) and their binary systems show that MWD was broadened and became bimodal for products obtained from the catalysts’ mixtures. In addition, the average MWs were shifted to higher values in PP reactor blends. Actually, the appearance of two peaks in the MWD curves is indicative of the fact that two catalysts are active during the polymerization in the case of binary systems. In these blends, the peak at higher MW leads to a product with remarkable enhancement in mechanical properties, while the peak at lower MW leads to a product with improved processability. In other words, the improved tensile strength of the products is accompanied by their improved processability.
- The complex viscosity of the synthesized blends shows a remarkable 47-fold enhancement as the molar ratio of II/I is increased. It can be concluded that upon the changes in the molar ratio of catalyst (II), the structure of the growing chains is changed such that the amorphous blocks along the polymer chains are formed due to the presence of catalyst (II) and its activeness in the course of polymerization. The formation of those amorphous blocks along the polymer chains increases the chains’ entanglements and thus enhances the complex viscosity of the synthesized PP reactor blends.
- As the molar ratio of II/I changes, the cross-over modulus and frequency are reduced due to the increased elasticity of the polymer melt as a result of the existence of amorphous blocks along the polymer chains.
- With increasing the molar ratio of II/I, all the peaks exhibited an individual relaxation peak which tends towards longer times as the molar ratio of catalyst (II) is increased. As a result, PP-H Cat (40) exhibits the longest relaxation time among the samples.
- The changes in morphological features of obtained products induced by the increased molar ratio of II/I in the synthesized blends was precisely demonstrated via SEM images and also dynamic rheological data. Therefore, it can be concluded that there exists a robust relationship between the obtained results of linear rheology and morphological characteristics such that with increasing the molar ratio of the catalyst (II) within the binary system, the chains’ elasticity was significantly increased. It was also found that the amount of the mentioned enhancement within the low-frequency region is dependent on the formation of amorphous blocks along the PP chains.
Author Contributions
Conflicts of Interest
References
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Run | Sample rode | Zr(II)/Zr(I) (Molar ratio) | Zr(t) × 104 (mmol) | Al/Zr(t) | Polymer wt (g) | Productivity (kg PP/mmol Zr(t)·h) |
---|---|---|---|---|---|---|
1 | PP-Cat I | (I) only | 3.5 | 1100 | 10.0 | 28.8 |
2 | PP-Cat II | (II) only | 75 | 1100 | 6.0 | 0.80 |
3 | PP-H Cat (25) | 25 | 45.6 | 1100 | 54.3 | 11.9 |
4 | PP-H Cat (32) | 32 | 57.8 | 1100 | 66.5 | 11.5 |
5 | PP-H Cat (40) | 40 | 71.8 | 1100 | 30.9 | 4.3 |
Run | Sample code | Zr(II)/Zr(I) | MW (g/mol) | PDI a | Peak max | Xylene solubility (wt %) | |
---|---|---|---|---|---|---|---|
Low MW (g/mol) | High MW (g/mol) | ||||||
1 | PP-Cat I | (I) only | 469,000 | 2.8 | 383,000 b | 2.6 | |
2 | PP-Cat II | (II) only | 115,000 | 4.5 | 43,000 b | 84 | |
3 | PP-H Cat (25) | 25 | 1,340,000 | b.m c | 66,000 | 704,000 | 23 |
4 | PP-H Cat (32) | 32 | 2,850,000 | b.m | 201,000 | 2,410,000 | 28 |
5 | PP-H Cat (40) | 40 | 4,420,000 | b.m | 366,000 | 4,120,000 | 35 |
Sample code | Zr(II)/Zr(I) | A998 (Peak height) | A973 (Peak height) | A998/A973 | Isotacticity 1 | Isotacticity 2 |
---|---|---|---|---|---|---|
PP-Cat I | (I) only | 64.7 | 75.2 | 0.86 | 96.8 | 97.4 |
PP-Cat II | (II) only | 7.8 | 77.9 | 0.10 | 20 | 16 |
PP-H Cat (25) | 25 | 49.1 | 74.4 | 0.66 | 76.2 | 77 |
PP-H Cat (32) | 32 | 43.5 | 76.3 | 0.57 | 70.1 | 72 |
PP-H Cat (40) | 40 | 40.4 | 77.6 | 0.52 | 63.3 | 65 |
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Vaezi, J.; Nekoomanesh, M.; Khonakdar, H.A.; Jafari, S.H.; Mojarrad, A. Correlation of Microstructure, Rheological and Morphological Characteristics of Synthesized Polypropylene (PP) Reactor Blends Using Homogeneous Binary Metallocene Catalyst. Polymers 2017, 9, 75. https://doi.org/10.3390/polym9030075
Vaezi J, Nekoomanesh M, Khonakdar HA, Jafari SH, Mojarrad A. Correlation of Microstructure, Rheological and Morphological Characteristics of Synthesized Polypropylene (PP) Reactor Blends Using Homogeneous Binary Metallocene Catalyst. Polymers. 2017; 9(3):75. https://doi.org/10.3390/polym9030075
Chicago/Turabian StyleVaezi, Javid, Mehdi Nekoomanesh, Hossein Ali Khonakdar, Seyed Hassan Jafari, and Alireza Mojarrad. 2017. "Correlation of Microstructure, Rheological and Morphological Characteristics of Synthesized Polypropylene (PP) Reactor Blends Using Homogeneous Binary Metallocene Catalyst" Polymers 9, no. 3: 75. https://doi.org/10.3390/polym9030075