Crystallization and mechanical properties of carbon nanotube/continuous carbon fiber/metallocene polypropylene composites

In this work, a high fluidity polypropylene prepared with the metallocene catalyst (mPP) was used as matrix, carbon nanotube (CNT) and continuous carbon fiber (CCF) were added to prepare composites, and their mechanical properties, melting and crystallization behavior were investigated. In the mechanical properties, the effects of tension force in the preparation process and compatibilizer maleic anhydride grafted polypropylene (MAPP) on the tensile strength of the composites were researched. The results show that the tensile strength of the composites increases first and then decreases with the increase of tractive force. In addition, the melting and crystallization behaviors and dynamic mechanical behaviors of mPP, CNT/mPP and CNT/CCF/mPP composites were characterized and studied by a differential scanning calorimetry (DSC) and dynamic mechanical analyzer (DMA). The results show that the melting point (Tm ), crystallization temperature (Tc ) and storage modulus (E') of CNT/mPP are all increased by adding 1wt% CNT, especially the Tc is increased by 8.8 ºC. It shows that after CNT was added to mPP as inorganic carbon material, it plays a prominent role in heterogeneous nucleation. After CCF was composited with CNT/mPP, the composites with CCF content of 30 and 42wt% were prepared, and their Tm , Tc , crystallinity (Xc ) and E' were all improved, especially E' was greatly improved, such as the initial E' was increased by 5.64 and 11.74 times. Even at the end of the curve, the E' of the composites with CF is still significantly higher than that of mPP and CNT/mPP. It indicates that adding CCF will greatly improved the deformation resistance and load deformation temperature of mPP.

Comparative study of Metallocene catalyst propylene polymerization with different iteration rates

This paper proposed a mathematical model corresponding to metallocene catalyzed propylene polymerization that uses the Me2Si [Ind]2ZrCL2 and Et [Ind]2ZrCL2. Comprehensive kinetic models consisting of mass and population balance equations, are developed based on elementary reactions proposed in the reaction mechanism. The result from the above indicates that metallocene catalysts in the presence of ethylene zirconium dichloride and methylene zirconium dichloride shows modularity and new peaks are obtained. The temperature variation from 25 to 75 also increase the rate and reason for the same could be chain shuttling polymerization. The model is presented through simulative study. Initially genetic approach is used but convergence rate is poor. To achieve best possible result, particle swarm optimization is used. The optimization approach with particle swarm optimization is implemented. The local and global solutions are comparable entities and replace each other in case value of local variable is not optimized. From the simulative study it is discovered that Et [Ind]2ZrCL2 produce best possible polymers both at 25 and 750C.

Crystallization of Random Metallocene-Catalyzed Propylene-Based Copolymers with Ethylene and 1-Hexene on Rapid Cooling

Propylene-based random copolymers with either ethylene or 1-hexene as comonomer, produced using a metallocene catalyst, were studied regarding their crystallization behaviors, with a focus on rapid cooling. To get an impression of processing effects, fast scanning chip calorimetry (FSC) was used in addition to the characterization of the mechanical performance. When comparing the comonomer type and the relation to commercial grades based on Ziegler–Natta-type catalysts, both an interaction with the catalyst-related regio-defects and a significant difference between ethylene and 1-hexene was observed. A soluble-type nucleating agent was found to modify the behavior, but to an increasingly lesser degree at high cooling rates.

Reverse Regioselectivity in Reductive Ring Opening of Epoxide Enabled by Zirconocene and Photoredox Catalysis

A ring opening of epoxide with zirconocene and photoredox catalysis has been developed. Compared to the ring opening methods with titanocene, the present protocol exhibited reverse regioselectivity to afford more-substituted alcohols via putative less-stable radicals. DFT calculations indicated that the observed regioselectivity could be explained by shifting the transition states to more reactant-like structures by changing the metal center of the metallocene catalyst.

Reverse Regioselectivity in Reductive Ring Opening of Epoxide Enabled by Zirconocene and Photoredox Catalysis

A ring opening of epoxide with zirconocene and photoredox catalysis has been developed. Compared to the ring opening methods with titanocene, the present protocol exhibited reverse regioselectivity to afford more-substituted alcohols via putative less-stable radicals. DFT calculations indicated that the observed regioselectivity could be explained by shifting the transition states to more reactant-like structures by changing the metal center of the metallocene catalyst.

SYNTHESIS AND STUDY OF COPOLYMERS OF ETHYLENE WITH HEXENE-1, MODIFIED WITH FINISHED NANOFIBERS-Al2O3 (NAFEN) WITH INCREASED RESISTANCE TO THERMAL OXIDATIVE DEGRADATION

Here we report the study on synthesis and characterization of nanocomposites obtained by in situ catalytic polymerization of ethylene and hexene-1 on metallocene catalyst in the presence of dispersed surface-functionalized -Al2O3 nanofibers (Nafen). It has been determined that surface treatment of Nafen nanofibers with organosilanes allows to obtain stable nanoscale dispersions under ultrasonication. It has been shown that nanocomposites based on copolymers of ethylene with hexene-1 demonstrate improved resistance to thermal oxidative degradation in comparison with nanocomposites based on copolymers of ethylene with propylene, while the influence of the silane chemistry on the mechanical characteristics in these nanocomposites is less pronounced. The best mechanical characteristics were achieved for nanocomposite with Nafen treated with trimethoxyvinylsilane. The melt flow index drop is observed after moderate heat treatment or combined temperature/humidity.