Isotactic Polypropylene-Exfoliated Graphene Nanoplatelet (iPP-xGnP TM ) nanocomposites were prepared through an in-situ polymerization technique and compared to analogous composites prepared by melt compounding. In-situ preparation of iPP-xGnP nanocomposites was accomplished via single site metallocene polymerization of propylene within a toluene dispersion of xGnP nanoparticles. The in-situ prepared nanocomposites were compared to analogous nanocomposites prepared by melt compounding of commercial Ziegler-Natta iPP with xGnP. Optical microscopy showed the in-situ prepared nanocomposites demonstrated poorer xGnP dispersion compared to composites prepared by melt compounding. All xGnP-reinforced nanocomposites demonstrated increased crystallization temperature, as well as increases in mechanical strength and modulus, relative to neat iPP. However, the non-linear mechanical properties were found to be influenced by the both the preparation method and nanoparticle loading. Nanocomposites prepared by in-situ polymerization generally demonstrated superior ductility and fracture toughness compared to composites prepared by melt compounding. The results are discussed with regard to the preparation technique and xGnP loading. IntroductionPolyolefin nanocomposites offer opportunities to improve the properties of polyolefins with relatively small amounts of reinforcement. Compared to traditional fiber-reinforced composites, nanocomposites only require small reinforcement concentrations (< 2 vol %) to create property improvements. Polyolefin nanocomposites have shown property improvements such as M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 3 mechanical reinforcement, controlled gas permeability, and increased electrical conductivity when compared to the neat polyolefin resins [1].Many researchers strive to improve the mechanical properties of polyolefins using nanoscale reinforcement in order to create new and economical materials. For example, interest in the automotive industry has been directed toward developing reinforced polyolefins to replace engineering thermoplastic and metallic automotive materials, enabling cost and weight savings [2]. Polyolefin nanocomposites are ideal materials for this application due to the availability of low cost nanoscale reinforcements and polyolefin resins.Recently, graphene nanoplatelets (GNPs) have been investigated as nanoreinforcements for polyolefins [3,4]. The production of GNPs can be achieved by the thermal exfoliation of mineral graphite. Most notably, Drzal et al. developed an efficient method to produce Exfoliated Graphene Nanoplatelets (xGnP TM ) using acid intercalation followed by microwave assisted exfoliation [5,6]. These nanoplatelets are ideal nanoscale reinforcements due to their high aspect ratio, surface area, stiffness, thermal conductivity, and nucleation efficiency for crystallization of polyolefins [3,4,7,8]. Typically, polyolefin-GNP nanocomposites demonstrate improved modulus, strength, and higher crystallization temperature, along with decreased st...
Composites of linear low-density polyethylene were obtained in toluene slurry by in situ copolymerization of ethylene and 1-octene in the presence of untreated magnesium oxide-hydroxide nanoparticles (MgO@Mg(OH) 2 ) of ±50 nm and such treated with dibutylmagnesium (DBM) as support for a bis(n-butylcyclopentadienyl)zirconium dichloride-methylaluminoxane (MAO) catalyst system. Treatment of the nanoparticles with DBM (0.5-6 mmol g −1 MgO@Mg(OH) 2 ) allows one to decrease the amount of MAO by 1.2 mmol Al g −1 MgO@Mg(OH) 2 , while reaching the same average catalyst activity and a finer distribution of the particles. Energy-dispersive X-ray mapping shows that the MAO is mainly associated with the filler. The crystallinity of the matrix polymer decreases with filler content.
SF6 is used as an insulation and interruption medium in medium-voltage (MV) gas-insulated switchgear (GIS), but has a very high global warming potential. In recent years, several environmentally-friendly (eco-efficient) alternatives have been explored, focusing on dielectric and thermal properties. The interruption of low currents in MV application is emerging as an important topic for equipment manufacturers and users. The reduced arcquenching properties of the most prominent eco-efficient alternatives may require the use of vacuum interrupters for simple load current interruptions. However, this may not be a cost-effective solution and simpler interruption principles are desirable. In this paper, we explore low-current interruption in AirPlus TM , a m i x t u r e o f d r y a i r a n d t h e C 5 F 10O fluoroketone (C5-FK) as well as mixtures of CO2 and C5-FK. We find that it is possible to achieve the E3 electrical endurance class (100 c/o) with a switch based on the puffer principle in AirPlus with a condensation temperature of-25˚C, suitable for secondary distribution MV GIS. The chemical analysis of gas samples taken from the switchgear after 100 successful interruptions indicate only trace amounts of fluoroketone decomposition products.
Nanocomposites of isotactic polypropylene (iPP) with 0.5 wt% filler of MgO@Mg(OH)2 (35 nm) or silicon dioxide (20–60 nm) or barium titanate (50 nm) nanoparticles were obtained from melt compounding of filler masterbatches with commercial iPP. The masterbatches with 5 wt% nanofiller were prepared in an in situ polymerization procedure using a metallocene/methylaluminoxane (MAO) catalyst system that was supported on the respective oxides. The original agglomerates of the nanoparticles were broken up by treatment with dibutylmagnesium for MgO@Mg(OH)2, and with ultrasound in the presence of MAO for SiO2 and BaTiO3. The tacticity (98% mmmm) of the in situ formed PP was not influenced by the presence of the nanofillers. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy mapping show a fine dispersion of single particles and small clouds or clusters. The primary nanoparticles appear to be surrounded by polymer. The elongation at break was decreased to 50, 17 and 9% for MgO@Mg(OH)2), SiO2 and BaTiO3, respectively. After melt compounding with iPP, a homogeneous single‐particle distribution of the oxidic nanoparticles was found in the resulting composites with 0.5 wt% filler content. © 2019 Society of Chemical Industry
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