Formulation of new biodegradable lubricating greases using ethylated cellulose pulp as thickener agent

J.E. Martin-Alfonso,M.J. Diaz,N. Nunez,C. Valencia,J.M. Franco 한국공업화학회 2011 Journal of Industrial and Engineering Chemistry Vol.17 No.6

The influence of cellulose pulp ethylation processing conditions has been evaluated to design suitable renewable and biodegradable lubricating greases from cellulose pulp-based gel-like dispersions. Ethyl/glucose molar ratio (E/G) has a positive effect on the ethyl groups degree of substitution (DS). Gel-like biodegradable dispersions of cellulose pulp in castor oil have been prepared by adding ethylated cellulose samples differing in the substitution degree to modify the rheological properties of castor oil. The rheology of ethyl cellulose/castor oil binary systems is highly influenced by DS. The linear viscoelastic functions and consistency are very similar to those found in traditional lithium lubricating greases.

Grafting improves salinity tolerance of bell pepper plants during greenhouse production

Blanca E. Orosco-Alcalá,Héctor G. Núñez-Palenius,Fidel Díaz-Serrano,Luis Pérez-Moreno,Mauricio Valencia-Posadas,Libia I. Trejo-Tellez,Nicacio Cruz-Huerta,Juan I. Valiente-Banuet 한국원예학회 2021 Horticulture, Environment, and Biotechnology Vol.62 No.6

Biotic and abiotic stresses aff ect plant growth and productivity. High-salinity stress aff ects crop yield, causing fi nancialloss to growers. The use of salt-tolerant rootstocks is a strategy that has been used to reduce salt damage in crops. A studywas conducted to evaluate the eff ect of salinity-resistant rootstocks on the physiological and morphological characteristicsof bell pepper plants grown under greenhouse conditions. A factorial experiment was conducted using a completely randomizeddesign with two factors. The bell pepper ‘Viper’ cultivar was grafted on two reported salinity-tolerant rootstocks(E21R10144 and E21R10197), and non-grafted (NG) plants were used as the control. Four salinity levels were applied tothe plants (electrical conductivity treatments using NaCl of 2, 4, 6, and 8 dS m −1 ) in Steiner nutritive solution (100%). Theresponse to salinity was determined using morphological and physiological plant parameters, including fruit yield. Increasedtolerance to salinity conditions (NaCl) was observed in the ‘Viper’ bell pepper grafted on E21R10144, which allowed greaterplant height, stem diameter, leaf size, as well as fresh and dry biomass of both the roots and canopy. The impacts on plantphysiological response, including photosynthesis, stomatal conductance, transpiration, water content, stomatal density, andfoliar area, were also determined. Our results indicate that the use of the salinity-tolerant bell pepper rootstock E21R10144maintained plant homeostasis and minimized the damage caused by salts to the morphology and physiology, as well as eff ectson fruit yield; thus, it is a promising tool for the management of salt stress.

Simultaneous pulsatile flow and oscillating wall of a non-Newtonian liquid

E.E. Herrera-Valencia,M.L. Sánchez-Villavicencio,F. Calderas,M. Pérez-Camacho,L. Medina-Torres 한국유변학회 2016 Korea-Australia rheology journal Vol.28 No.4

In this work, analytical predictions of the rectilinear flow of a non-Newtonian liquid are given. The fluid is subjected to a combined flow: A pulsatile time-dependent pressure gradient and a random longitudinal vibration at the wall acting simultaneously. The fluctuating component of the combined pressure gradient and oscillating flow is assumed to be of small amplitude and can be adequately represented by a weakly stochastic process, for which a quasi-static perturbation solution scheme is suggested, in terms of a small parameter. This flow is analyzed with the Tanner constitutive equation model with the viscosity function represented by the Ellis model. According to the coupled Tanner-Ellis model, the flow enhancement can be separated in two contributions (pulsatile and oscillating mechanisms) and the power requirement is always positive and can be interpreted as the sum of a pulsatile, oscillating, and the coupled systems respectively. Both expressions depend on the amplitude of the oscillations, the perturbation parameter, the exponent of the Ellis model (associated to the shear thinning or thickening mechanisms), and the Reynolds and Deborah numbers. At small wall stress values, the flow enhancement is dominated by the axial wall oscillations whereas at high wall stress values, the system is governed by the pulsating noise perturbation. The flow transition is obtained for a critical shear stress which is a function of the Reynolds number, dimensionless frequency and the ratio of the two amplitudes associated with the pulsating and oscillating perturbations. In addition, the flow enhancement is compared with analytical and numerical predictions of the Reiner-Phillipoff and Carreau models. Finally, the flow enhancement and power requirement are predicted using biological rheometric data of blood with low cholesterol content.

Kinetics of the water absorption in GGBS-concretes: A capillary-diffusive model

E. Villar-Cocina,E. Valencia-Morales,J. Vega-Leyva,J. Antiquera Munoz 한국계산역학회 2005 Computers and Concrete, An International Journal Vol.2 No.1

We study the kinetics of absorption of water in Portland cement concretes added with 60, 70 and 80% of granulated blast furnace slag (GGBS) cured in water and at open air and preheated at 50 and 100oC. A mathematical model is presented that allows describing the process not only in early ages where the capillary sorption is predominant but also for later and long times where the diffusive processes through the finer and gel pores are considered. The fitting of the model by computerized methods enables us to determine the parameters that characterize the process: i.e., the sorptivity coefficient (S) and diffusion coefficient (D). This allows the description of the process for all times and offers the possibility to know the contributions of both, the diffusive and capillary processes. The results show the influence of the curing regime and the preheating temperature on the behavior of GGBS mortars.

Thermo-rheological and tribological properties of novel bio-lubricating greases thickened with epoxidized lignocellulosic materials

E. Cortés-Triviño,C. Valencia,M.A. Delgado,J.M. Franco 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.80 No.-

We examined the rheological and tribological behavior of novel formulations based on castor oil andepoxidized cellulose pulp intended for use as biodegradable lubricating greases. Epoxidized cellulosepulp was found to thicken castor oil to a variable extent depending on its modification degree andthe epoxide compound. Greases were subjected to small-amplitude oscillatory shear tests, evaluating thetemperature-dependence of the plateau modulus. In addition, friction coefficient and wear weredetermined in a steel–steel ball-on-three-plates tribological configuration, at two different temperatures(25 and 95 C), generally obtaining smaller values of both parameters when using aromatic diepoxidesinstead of aliphatic to modify the cellulose pulp.

Genome-wide analysis of long, exact DNA repeats in rhizobia

Julie E. Herna´ndez-Salmero´n,Eduardo Valencia-Cantero,Gustavo Santoyo 한국유전학회 2013 Genes & Genomics Vol.35 No.4

The rhizobia are a group of bacteria widely studied for their capacity to form intimate symbiotic relationships with leguminous plants. However, they are also interesting for containing a remarkable abundance of repetitive genetic elements, such as long DNA repeats. In this study we deeply analyzed long, exact DNA repeats in five representative rhizobial genomes; Rhizobium etli,Rhizobium leguminosarum, Bradyrhizobium japonicum,Sinorhizobium meliloti and Mesorhizobium loti. The results suggest that a huge proportion of repeats can be located in either plasmid or chromosome replicons, except in B. japonicum, which lacks plasmids, but contains the largest number, and longest repeat elements of the genomes analyzed here. Interestingly, we detected a slight correlation between the density of repeats (either number or length) and genome size. As expected, the highest percentage of DNA repeats code for mobile genetic elements,including insertion sequences, recombinases, and transposases. Some repeats corresponded to non-coding or intergenic regions, while in genomes like that of R. etli, a significant percentage of large repeats, mainly located in plasmids, were strongly associated with symbiotic and nitrogen fixation activities. In conclusion, our analysis shows that rhizobial genomes contain a high density of long DNA repeats, which might facilitate recombination events and genome rearrangements, functioning in adaption and persistence during saprophytic or symbiotic life.

Formulation and processing of virgin and recycled polyolefin/oil blends for the development of lubricating greases

J.E. Martın-Alfonso,A. Romero,C. Valencia,J.M. Franco 한국공업화학회 2013 Journal of Industrial and Engineering Chemistry Vol.19 No.2

This work has been focused on the development of polyolefins/oil blends potentially suitable as lubricating greases by studying the effect that some thermo-mechanical processing variables exert on their rheological properties and microstructure. Polyolefin/oil blends have been prepared by dispersing recycled and virgin polyolefins such as high-density polyethylenes (HDPEs) and polypropylenes (PPs) in mineral lubricating oil. Linear viscoelasticity functions have been significantly influenced by processing conditions. The nature of polymers used, specially the content of HDPE, has been found to modify the microstructure of blends yielding lower mechanical stability but, on the other hand, higher values of linear viscoelastic functions.

Influence of soap/polymer concentration ratio on the rheological properties of lithium lubricating greases modified with virgin LDPE

J.E. Martin-Alfonso,G. Moreno,C. Valencia,M.C. Sanchez,C. Gallegos,J.M. Franco 한국공업화학회 2009 Journal of Industrial and Engineering Chemistry Vol.15 No.5

The main goal of this work was to study the feasibility of using a low-density polyethylene (LDPE) as additive to improve the rheological properties of lithium lubricating greases. The combined effect that both soap and LDPE concentrations exerts on the rheology of lithium lubricating greases and its relationship with grease microstructure were studied according to an experimental design based on the response surface methodology (RSM). Different lubricating grease formulations were manufactured by modifying lithium 12-hydroxystereate and LDPE concentrations. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as mechanical stability tests, were performed. In addition to these, environmental scanning electronic microscopy (ESEM) was used to determine grease microstructure. LDPE was found to be a useful additive to modify grease rheology, acting as filler in the entangled soap network. The values of both apparent viscosity and linear viscoelasticity functions increase with soap and LDPE concentration. However, the addition of LDPE distorts soapmicrostructural network, yielding greases with lower relative elastic characteristics.

On the yield stress of complex materials

F. Calderas,E. E. Herrera-Valencia,A. Sanchez-Solis,O. Manero,L. Medina-Torres,A. Renteria,G. Sanchez-Olivares 한국유변학회 2013 Korea-Australia rheology journal Vol.25 No.4

In the present work, the yield stress of complex materials is analyzed and modeled using the Bautista-Manero-Puig (BMP) constitutive equation, consisting of the upper-convected Maxwell equation coupled to a kinetic equation to account for the breakdown and reformation of the fluid structure. BMP model predictions for a complex fluid in different flow situations are analyzed and compared with yield stress predictions of other rheological models, and with experiments on fluids that exhibit yield stresses. It is shown that one of the main features of the BMP model is that it predicts a real yield stress (elastic solid or Hookean behavior) as one of the material parameters, the zero shear-rate fluidity, is zero. In addition, the transition to fluid-like behavior is continuous, as opposed to predictions of more empirical models.

Improved Mg–Al–Zn Magnesium Alloys Produced by High Energy Milling and Hot Sintering

Y. Galindez,E. Correa,A. A. Zuleta,A. Valencia‑Escobar,D. Calderon,L. Toro,P. Chacón,F. Echeverría E. 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5

Powders of commercially pure magnesium (c.p. Mg), AZ91 magnesium alloy and zinc were milled using a high-energy mill.The effect of high energy milling (HEM) on powders morphology, chemical composition, crystallite size and compactionof different powders mixtures were studied. After compaction, samples were thermally treated at 450 °C and both densityand hardness were evaluated. It was found that as milling speed and time increases, the AZ91 alloy and c.p. Mg particleswere deformed and fractured up to sizes below 10 μm. X-ray diffraction patterns for both the c.p. Mg and the AZ91 powdersrevealed that the milling process induced changes in both the α-Mg and the β-Mg17Al12 phases. By increasing the millingspeed, the crystallite size decreases by up to 70% for AZ91 powders and by 80% for magnesium powders. The relativedensities of the compacted AZ samples were greater than 85% and this parameter increased for all samples after thermaltreatment at 450 °C, obtaining densities higher than 88%. Hardness measurements disclosed values as high as 84.3 HR15T.Theoretical calculations of mechanical strength were obtained for all samples based on the hardness values measured, findingvery encouraging results for the three Mg alloys.