Polyolefin blends
Mahsa Mobini-Dehkordi; Gholam-Reza Nejabat; Mohammad-Mahdi Mortazavi
Abstract
Varying amounts of a high molecular weight poly(1-hexene) (PH, Mv=1.7×106 Da) are substituted for EPDM in an iPP/iPP-g-MA/EPDM blend (weight ratio: 76:4:20) and mechanical properties as well as phase morphology of the blends are studied and compared. The results show that by substituting the entire ...
Read More
Varying amounts of a high molecular weight poly(1-hexene) (PH, Mv=1.7×106 Da) are substituted for EPDM in an iPP/iPP-g-MA/EPDM blend (weight ratio: 76:4:20) and mechanical properties as well as phase morphology of the blends are studied and compared. The results show that by substituting the entire EPDM with PH, the tensile strength-at-break increases from 18.7 to 21.1 MPa, elongation-at-break increases from 15.5% to 370.8%, and impact strength increases from 6.4 to 50.1 kJ.m-2. Dynamic mechanical thermal analysis (DMTA) of the blends proved their immiscibility and SEM analysis confirmed these findings by showing droplet-matrix morphologies. Studying the creep behavior of the samples shows that the blends containing PH have more creep so that by substituting all EPDM in the blends with PH, the permanent deformation increases from 0.425% to 0.505%. According to the results, PH is introduced as a candidate for improving the impact properties of iPP/iPP-g-MA/EPDM blend.
Polyolefin degradation
Sara Zarei; Gholam-Reza Nejabat; Mohammad-Mahdi Mortazavi; Soheyl KhajehPour-Tadavani
Abstract
Varying amounts of an amorphous poly(1-hexene) (PH, Mv 1.7×106 Da) were added to an LLDPE matrix containing 3% w/w Addiflex oxo-biodegradable additive (HES-W) and extruded and converted into films. Then the effect of presence of PH was investigated on microstructure, thermal and tensile behavior ...
Read More
Varying amounts of an amorphous poly(1-hexene) (PH, Mv 1.7×106 Da) were added to an LLDPE matrix containing 3% w/w Addiflex oxo-biodegradable additive (HES-W) and extruded and converted into films. Then the effect of presence of PH was investigated on microstructure, thermal and tensile behavior of polymer films before and after 6 weeks of ultra violet irradiation (UVR). Due to UVR, viscosity average molecular weight (Mv) of the sample without PH decreased from 9.6×104 to 4.6×103 Da and for the sample containing 3% w/w PH from 11.3×104 to 3.0×104 Da, also carbonyl index (CI) of the sample without PH increased from 0 to 28.7 while for the sample containing 3% w/w PH increased from 1.8 to 30.4. Moreover, differential scanning calorimetry (DSC) showed that crystallinity of the sample without PH increased from 34.4% to 36.9% and from 28.7% to 32.1% for the sample containing 3% w/w PH. Thermal gravimetric analysis (TGA) showed lower decomposition temperature for the samples containing PH. The elongation-at-break decreased from 723.0% to 88% for the sample without PH and from 410% to 10% for the sample containing PH. Atomic force microscopy (AFM) indicated smoother surfaces for samples containing 3% w/w PH before and after UVR. Although, the aforementioned results showed that the presence of limited amounts of PH in the LLDPE matrix deteriorated thermal and mechanical properties of the matrix, it hindered the oxo-biodegradablity of the matrix by opposing assimilation process perhaps due to high Mv and/or gelation.
Polyolefin degradation
Soheyl Khajehpour-Tadavani; Gholam-Reza Nejabat; Mohammad-Mahdi Mortazavi
Abstract
Crystallinities of high-density polyethylene (HDPE) films containing various amounts of an oxo-biodegradable additive (HES-W) were investigated immediately after preparation and 6 weeks after ultraviolet (UV) irradiation (λ=254 nm). HDPE granules were mixed with oxo-biodegradable masterbatch in ...
Read More
Crystallinities of high-density polyethylene (HDPE) films containing various amounts of an oxo-biodegradable additive (HES-W) were investigated immediately after preparation and 6 weeks after ultraviolet (UV) irradiation (λ=254 nm). HDPE granules were mixed with oxo-biodegradable masterbatch in a twin-screw extruder and the extrudates were converted into films with thicknesses of 35±5 micrometers. The films were exposed to UV light for 6 weeks. Crystallinities of the films are investigated by X-ray diffraction spectroscopy (XRD) and differential scanning calorimetry (DSC). The XRD results show that upon UV exposure, the crystallinities of the films enhance. The DSC thermograms have confirmed the XRD results and also show a decrease in melting points of the samples after UV exposure. Further investigations on viscosity average molecular weights (Mv) of the samples show that their Mv decrease sharply after UV exposure. Scanning electron microscopy (SEM) shows clear cracks on the samples surfaces after 6 weeks exposure to UV irradiation. Investigating the functionalities of the polymers through Fourier transform infrared spectroscopy (FTIR) show the emergence of carbonyl peaks after UV irradiation so that the carbonyl index of the samples increases. It is concluded that maximum oxo-biodegradation enhancement of the HDPE film samples can be achieved by using a specific amount of the oxo-compound (3 wt%); furthermore the crystallinities of the samples show considerable enhancement after UV exposure which can be due to better packing ability of low molecular weight chains along with probable dipole-dipole attractions between the carbonyl groups on different newly formed short polar chains.
Catalysis
Gholam-Reza Nejabat
Abstract
Since 1999, when Takuzo Aida proposed the preparation of high density polyethylene (HDPE) crystalline nanofibers through polymerization of ethylene by a Cp2 TiCl2 /MCM-41 catalyst, many researchers have published various papers on different aspects of the idea. The published researches show that the ...
Read More
Since 1999, when Takuzo Aida proposed the preparation of high density polyethylene (HDPE) crystalline nanofibers through polymerization of ethylene by a Cp2 TiCl2 /MCM-41 catalyst, many researchers have published various papers on different aspects of the idea. The published researches show that the endeavors to polymerize other types of alpha olefins, especially propylene, to obtain polyolefins with crystalline nanofiberous morphology have not been successful and no one has reported such morphology for them. In the present article, a possible reason behind these observations is proposed. Comparing the direction of the growth of HDPE chains and isotactic polypropylene (iPP) helices to become appropriate for making polymer crystals shows that HDPE chains are able to form crystal unit cells without concerning upward or downward chain growth direction, while the growth direction of adjacent iPP chains might be responsible for unsuccessful synthesis of crystalline iPP nanofibers in confined channels of the mesoporous catalysts. iPP helices can crystallize beside each other only in the form of anticline isochiral helices.
Catalysis
Gholam-Reza Nejabat; Mehdi Nekoomanesh; Hassan Arabi; Hamid Salehi-Mobarakeh; Gholam-Hossein Zohuri; Mohammad-Mahdi Mortazavi; Saeid Ahmadjo; Stephen A. Miller
Abstract
Several types of hybrid catalysts are made through mixing of 4th generation Ziegler-Natta (ZN) and (2-PhInd)2ZrCl2 metallocene catalysts using triethylaluminum (TEA) as coupling agent. Response surface methodology (RSM) is used to evaluate the interactive effects of different parameters including ...
Read More
Several types of hybrid catalysts are made through mixing of 4th generation Ziegler-Natta (ZN) and (2-PhInd)2ZrCl2 metallocene catalysts using triethylaluminum (TEA) as coupling agent. Response surface methodology (RSM) is used to evaluate the interactive effects of different parameters including amounts of metallocene and TEA and temperature on metallocene loading. Analyzing the amounts of Al and Zr elements in the hybrid catalysts through ICP-OES and EDXA reveals that temperature plays a crucial role on anchoring of the metallocene catalyst on ZN while TEA has the least determining effect. The ICP analysis shows that as the concentration of Al goes up in the hybrid catalyst the concentration of Zr passes a maximum, while EDXA shows a direct relationship between the Al and Zr contents. Using triisobutylaluminum (TIBA) and methylaluminoxane (MAO) as the coupling agents, almost similar metallocene loadings are observed. Finally, the performance of hybrid catalysts is investigated in propylene polymerization and the obtained polymers are characterized using DSC and DMTA through which the presence of two types of polymers in the final product are confirmed.
