The modification of magnesium hydroxide (MH) with triethoxy vinyl silane (TVS) was carried out via three different methods and the results are discussed with respect to their effect on the flame retardant and the tensile properties of high density polyethylene (HDPE) nanocomposites. Via a xylene suspension of MH and TVS, via a water suspension of MH and TVS, and via powder mixing of MH and TVS. It was found that in all three cases, SiAOAMg bonds formed on the MH particles surface. Also, this silane modification induced a certain level of particle agglomeration, but without modifying their morphology or particle size. It was also found that the flame retardant properties of the HDPE nanocomposites did not improve because of the use of silane modified MH. During the flame retardant tests, all nanocomposites passed the UL-94-HB, but it was observed that the flame permanence time was longer when using modified MH. The tensile properties were negatively affected by the addition of unmodified MH; the nanocomposites became hard and brittle, with reduced flexibility. This negative effect was diminished when using silane modified MH.
High impact polystyrene(HIPS) was repeatedly coextruded at 220°C, maintaining a constant composition of 70 wt% of virgin HIPS and 30 wt% of recycled HIPS. The gel content (GC), grafting degree (GD), swell index (SI), morphology of the rubber phase, and average molecular weight of the polystyrene (PS) matrix (M w ) were characterized after each processing cycle. The effect of these parameters on the melt flow index (MFI), the shear viscosity (), the power law index (n), the Izod impact, and the stress at break were evaluated. The results demonstrated that the rheological properties changed with the number of processing cycles, e.g. the MFI decreased in the first cycle from 2.8 to 1.7 g/10 min, while from the second to the sixth cycle increased to 3.4 ؎ 0.2 g/10 min. The power law index increased from n ؍ 0.29, after the first processing cycle, to n ؍ 0.34 in the sixth cycle. The changes in MFI and n were attributed to changes in the physical structure of the rubber phase and to chain scissions in the PS matrix, caused by the recycling. Finally, the impact strength decreased with the increasing number of processing cycles, while the tensile stress at break remained constant. POLYM. ENG. SCI., 46:1698 -1705,
2006.
Starlike block copolymers of Nylon-6 and polyurethane were synthesized using -caprolactam as a monomer, caprolactam magnesium bromide as a catalyst, and a star prepolymer of polyurethane. These copolymers were compared with the linear block copolymers of Nylon-6 and polyurethane. Such copolymers were obtained using the reaction injection-molding process (RIM) of -caprolactam at different contents of polyurethane (5-30 wt %). In increasing the content of the soft phase, in FTIR, a displacement was observed in the band at 1637 cm Ϫ1 , assigned to the amide I of the Nylon 6, to a higher wavenumber. This suggests a bigger interaction between the urethane group of the polyurethane and the amide group of the Nylon 6. Star block copolymers showed better mechanical properties compared with the linear ones. This behavior is attributed to the higher crystallinity and ramifications present in the materials. The structure and the thermal properties of the copolymers were studied using different techniques such as DSC, WAXS, DMA, and SEM. A decrease in the crystallinity when increasing the soft phase was also observed. Finally, physical tensile, impact, and hardness tests of the copolymers were carried out.
The interest in the Coordinative Chain Transfer Polymerization (CCTP) of a family of naturally occurring hydrocarbon monomers, namely terpenes, for the production of high-performance rubbers is increasing year by year. In this work, the synthesis of poly(β-myrcene) via CCTP is introduced, using neodymium versatate (NdV3), diisobutylaluminum hydrade (DIBAH) as the catalytic system and dimethyldichlorosilane (Me2SiCl2) as the activator. A bimodal distribution in the GPC signal reveals the presence of two populations at low conversions, attributable to dormants (arising from reversible chain transfer reactions) and dead chains (arising from termination and irreversible chain transfer reactions); a unimodal distribution is generated at medium and high conversions, corresponding to the dominant species, the dormant chains. Additionally, a mathematical kinetic model was developed based on the Method of Moments to study a set of selected experiments: ([β-myrcene]0:[NdV3]0:[DIBAH]0:[Me2SiCl2]0 = 660:1:2:1, 885:1:2:1, and 533:1:2:1). In order to estimate the kinetic rate constant of the systems, a minimization of the sum of squared errors (SSE) between the model predicted values and the experimental measurements was carried out, resulting in an excellent fit. A set of the Arrhenius parameters were estimated for the ratio [β-myrcene]0:[NdV3]0:[DIBAH]0:[Me2SiCl2]0 = 660:1:2:1 in a temperature range between 50 to 70 °C. While the end-group functionality (EGF) was predominantly preserved as the ratio [β-myrcene]0:[NdV3]0 was decreased, higher catalytic activity was obtained with a high ratio.
Bionanocomposites (BNCs) of waxy corn starch, glycerol, and graphene oxide (GO) or graphite oxide (GrO) were prepared by melt mixing. First, the GrO was pre-exfoliated in a water solution using ultrasound at 1 wt %. Small-angle X-ray scattering was used to determinate the interlaminar separation of GrO and transmission electron microscopy, Fourier infrared spectroscopy, and thermogravimetric analysis were used to characterized the GrO. Next, BNCs were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and mechanical property measurements. A complete exfoliation of GrO was obtained in the waxy corn matrix. Amorphous X-ray patterns of the BNCs were observed, indicating that the exfoliated GO avoid the retrogradation of starch. According to scanning electron microscopy results, the BNCs showed an irregular texture and a good dispersion of GO, while thermoplastic starch showed a smooth morphology with a fragile structure. The BNCs exhibited higher thermal stability than thermoplastic starch. The tensile strength and the Young's modulus increased by 140% and 230% at a GO loading levels of 0.5% due to good interfacial interactions of GO and the waxy corn starch matrix.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.