Influence of temperature and shear rate on the rheology and processability of reprocessed ABS in injection molding process

The effects of reprocessing on the processability of two Acrylonitrile–Butadiene–Styrene (ABS) grade thermoplastic polymers have been investigated. Reprocessing in an injection molding process of a low and a high viscosity ABS grade has been done changing operating temperatures and shear rates, design of experiments (DOE) techniques were applied to plan experiments and later analysis. The flow properties of virgin and reprocessed materials have been evaluated by capillary rheology.Experimental results clearly indicate a qualitatively different behavior of the two polymers upon reprocessing. Low viscosity grade shows a reduction of viscosity upon increasing the number of processing cycles, thus confirming the degradation of this polymer. High viscosity grade, conversely, shows an increase of melt viscosity as the number of injection molding cycles is increased. It has been confirmed that applied shear rates in injection molding process affect material behavior as well as applied temperatures.     

Surface modification of polypropylene substrates by UV photografting of methyl methacrylate (MMA) for improved surface wettability

Despite polypropylene is one of the most used commodity plastics, its adhesion properties are remarkably restricted by its non-polar nature which leads to low wetting properties and, consequently, poor adhesion behavior. We report the use of ultraviolet photografting process of methyl methacrylate (MMA) monomer as an efficient chemical treatment for surface activation of polypropylene. Contact angle measurements are used for evaluating changes in polypropylene wetting properties together with surface free energy calculations. Chemical changes are showed in terms of the exposure time to UV radiation. Scanning electron microscopy has been used to evaluate topography changes in a qualitative way; atomic force microscopy has been used for a quantitative evaluation of surface changes in terms of roughness. The use of Fourier transformed infrared spectroscopy has revealed the nature of the chemical changes induced by the photografting process of MMA.     

Variational calculation of the binding energy of one3He impurity in liquid4He

We present a variational microscopic study of the liquid⁴He with one³He impurity at zero temperature, within the framework of the average correlation approximation. In this approach all calculations can be referred to quantities of liquid⁴He. The chemical potentials of liquid⁴He and of a³He impurity are studied in the liquid range of densities and the results show an overall good agreement with the experimental data. Detailed comparisons with previous calculations are also presented. Due to the presence of the pressure term, the calculation of chemical potentials is a severe test to the capability of the wave function and the interaction to obtain a good saturation density. The calculation of the chemical potential of the impurity using the Lennard-Jones and the Aziz potentials, points out the different balance of kinetic and potential energies obtained in the variational minimization of these two potentials.Supported by a Fulbright Fellowship.     

Study of the effects of multi‐walled carbon nanotubes on mechanical performance and thermal stability of polypropylene

Carbon nanotubes (CNTs) have been added to polypropylene (PP) matrix to improve the overall performance of composites. The mixing process has been carried out by melt compounding using a twin screw co‐rotating extruder with different CNTs amounts in the 0.5–10 wt% from a concentrated PP‐CNTs masterbatch (20 wt% CNTs). Results show a remarkable increase in tensile strength and elastic modulus while a decrease in elongation at break is detected. With regard to thermal behavior, a remarkable increase in thermal stability at high temperatures (decomposition process studied by thermogravimetric analysis) is obtained as the CNTs amount increases. In addition to this improvement, a noticeable increase in thermal stability at medium temperatures (degradation onset determined by differential scanning calorimetry, DSC) is also observed. In a similar way, other property related to thermal and mechanical performance, such as Vicat softening temperature (VST) is improved with CNTs content. The optimum balance between cost and properties seems to be in the 1–3 wt% range. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Differential splicing of the growth hormone-releasing hormone gene in rat placenta generates a novel pre-proGHRH mRNA that encodes a different C-terminal flanking peptide

We have isolated and characterized a novel rat placental pre-proGHRH mRNA (pre-proGHRH-2 mRNA). This mRNA is generated by an alternative splicing process which results in the presence of an additional exon of 156 bp (designated exon 4.5) located between exons 4 and 5 of the previously reported hypothalamic and placental pre-proGHRH mRNA (pre-proGHRH-1 mRNA). Since the sequences encoding mature GHRH are included within exons 3 and 4, the processing of pre-proGHRH-2 would not affect the synthesis of mature GHRH but would generate a C-terminal peptide (designated GCTP-2) different from that previously reported in the hypothalamus and placenta (GCTP-1). The putative GCTP-2 has 64 amino acids, and the first 18 N-terminal residues are identical to those present in GCTP-1 (30 amino acids long). Pre-proGHRH-2 mRNA has not been detected in the hypothalamus.     

Thermal and Mechanical Characterization of Epoxy Resins (ELO and ESO) Cured with Anhydrides

In this work we have developed polymeric materials from epoxidized vegetable oils in order to obtain materials with excellent mechanical properties for use as green matrix composites. Epoxidized soybean oil (ESO), epoxidized linseed oil (ELO) and different mixtures of the two oils were used to produce the polymers. Phthalic anhydride (17 mol%) and maleic anhydride (83 mol%) which has a eutectic reaction temperature of 48 °C were used as crosslinking agents while benzyl dimethyl amine (BDMA) and ethylene glycol were used as the catalyst and initiator, respectively. The results showed that samples 100ELO and 80ELO20ESO could be used as a matrix in green composites because they demonstrated good mechanical properties.     

Use of eco‐friendly epoxy resins from renewable resources as potential substitutes of petrochemical epoxy resins for ambient cured composites with flax reinforcements

In the last years, some high renewable content epoxy resins, derived from vegetable oils, have been developed at industrial level and are now commercially available; these can compete with petroleum‐based resins as thermoset matrices for composite materials. Nevertheless, due to the relatively high cost in comparison to petroleum‐based resins, their use is still restricted to applications with relatively low volume consumption such as model making, tuning components, nautical parts, special effects, outdoor sculptures, etc. in which, the use of composite laminates with carbon, aramid and, mainly, glass fibers is generalized by using hand layup and vacuum assisted resin transfer molding (VARTM) techniques due to low manufacturing costs and easy implementation. In this work, we study the behavior of two high renewable content epoxy resins derived from vegetable oils as potential substitutes of petroleum‐based epoxies in composite laminates with flax reinforcements by using the VARTM technique. The curing behavior of the different epoxy resins is compared in terms of the gel point and exothermicity profile by differential scanning calorimetry (DSC). In addition, overall performance of flax‐epoxy composites is compared with standardized mechanical (tensile, flexural and impact) and thermal (Vicat softening temperature, heat deflection temperature, thermo‐mechanical analysis) tests. The curing DSC profiles of the two eco‐friendly epoxy resins are similar to a conventional epoxy resin. They can be easily handled and processed by conventional VARTM process thus leading to composite laminates with flax with balanced mechanical and thermal properties, similar or even higher to a multipurpose epoxy resin. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Antioxidant and antibacterial effects of natural phenolic compounds on green composite materials

The aim of this study is to establish the thermal performance of a biocomposite (Arbofill kokos®), stabilized with different natural phenolic additives, to check the antioxidant capacity of the resulting compounds. Different phenolic compounds (thymol, carvacrol, α‐tocopherol, and tannic acid) were used as biobased additives and the concentrations ranged between 0.5 wt% and 2 wt%. The results obtained were compared with formulations containing a typical industrial petroleum‐based antioxidant agent (octadecyl‐3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl) propionate). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterize the antioxidant performance of the selected natural additives. The antimicrobial effect of these natural phenolic compounds was also studied by analyzing the growth of bacterial colonies. The comparison between the natural phenolic compounds and the petroleum‐based antioxidant compound showed good antioxidant action for natural phenolic compounds; in all the mixtures of biocomposite and antioxidant agent the oxidation onset temperature (OOT) increased in a remarkable way, but the highest stabilization effect was achieved with α‐tocopherol with provides a % increase on OOT of about 45%. With regard to antibacterial activity of the different natural phenolic compounds, thymol, and carvacrol showed interesting antibacterial properties against Staphylococcus aureus. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Subclinical Cushing's syndrome due to adrenal myelolipoma

We describe a patient with an incidental adrenal myelolipoma associated with biochemical evidence of Cushing's syndrome who lacked the physical stigmata of cortisol excess (subclinical Cushing's syndrome). Pathologic examination revealed the presence of adrenocortical cells mixed with myelolipomatous tissue. Although cases of clinically evident Cushing's syndrome due to adrenal myelolipomas have been reported previously, to our knowledge this is the first report associating adrenal myelolipoma and subclinical Cushing's syndrome.     

Quantum Monte Carlo Study of Two-Dimensional H2 on a Rb Substrate

A quantum Monte Carlo study at zero temperature of twodimensional H₂ on top of a solid Rb surface is presented. The lattice constituted by the alkali atoms frustrates the formation of solid H₂, which is the natural phase of pure two-dimensional H₂. Therefore, H₂ with the Rb atoms acting like fixed impurities remains in a liquid phase even at zero temperature. We present resugts for the H₂ equation of state, structural properties, superfluid density and condensate fraction for a fixed Rb lattice.