An analytic solution to the transient diffusion-reaction problem in particles dispersed in a slurry reactor

In this work, we present the solution of the equations that govern the reactant transport in a well mixed system that contains particles where diffusion and first-order reaction occur. The transport equations are coupled by an interfacial boundary condition that includes mass transfer resistance. The statement of the problem allows arbitrary time depending feed functions. The evaluation of the solution obtained by the Laplace method requires the solution of an eigenvalue problem. We discuss the evaluation of the solution, and typical results for three different feed functions: step, pulse and oscillatory functions are presented. The resulting equations are able to show the effect of internal and external mass transfer limitations on the particle and fluid concentrations and on kinetic experimental results.     

Sulfuric acid treatment of ground tire rubber and its effect on the mechanical and thermal properties of polypropylene composites

Ground tire rubber (GTR) was modified by sulfuric acid in order to improve its compatibility with and reinforcement of a polypropylene (PP) matrix. Polymer composites PP/GTR were prepared by melt mixing at different concentrations, with a maximum of 50 wt % of GTR. Studies by Fourier transform infrared spectroscopy (FTIR), surface specific area by BET (Brunauer, Emmett, and Teller), and scanning electron microscopy were used to characterize the untreated GTR and treated GTR, while the mechanical and thermal properties of the PP/GTR composites were assessed to understand how the surface treatment of GTR affected the mechanical and thermal properties of the composite PP/GTR. FTIR revealed the presence of sulfonic groups on the surface of sulfuric acid–treated GTR, and BET analyses showed an increase of about 625% in the specific surface area as a result of the high porosity produced by the treatment. In all composites containing treated GTR, a higher Young's modulus was obtained than for composites containing untreated GTR. Particularly, an increase of about 275% in the Young's modulus was obtained in composites with treated GTR (40 wt %) against that containing untreated GTR. However, a more significant reduction of the elongation at break was observed in composites containing treated GTR than in those containing untreated GTR. Also, an increase of the crystallization temperature of PP as a function of GTR was observed by differential scanning calorimetry, but the crystallinity of the composites was reduced by the addition of both untreated and treated GTR. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44858.     

The traditional Mestizo view: Implications for modern psychotherapeutic interventions.

Provides mental health professionals with an overview of basic Mestizo tenets. Fundamental issues such as the Mestizo perception of health, the mind–body relationship, metaphysics, and family and community factors are discussed to increase therapeutic sensitivity when working with Mestizos. Suggestions for dealing with these factors are outlined. A holographic model is suggested as a Western-based means of understanding the Mestizo perspective. A holographic paradigm is also recommended as a unifying conceptual model between the 2 divergent world views. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Graphite effect on the mechanical and fire-retardant performance of low-density polyethylene and ethylene-vinyl-acetate foam composites

In this study, the graphite effect on the mechanical and fire-retardant performance of low-density polyethylene (LDPE) and ethylene-vinyl-acetate (EVA) foam composites was investigated. Polymer composites were prepared by melt mixing process and foamed by hot press molding at different graphite content (0, 3, 6, and 12 phr). Cone calorimetric tests through heat release rate (HRR) curves obtained, revealed a decreasing of 45% on peak heat release rate (pHRR) of foam composites LDPE-EVA with 12 phr of untreated graphite content compared than those LDPE-EVA foamed composites without graphite, which was attributed to the good distribution of graphite in the composite and more residual generates as thermogravimetric analysis suggested. Mechanical properties of polymer foamed composites with high graphite content do not show significant detrimental as a result to the formation of more uniform cells with smaller size incorporating a material with high modulus like graphite. The results suggest that polymer foam composites with graphite are suitable for the building and construction industry, in sealing and thermal insulation applications with good fire-retardant performance.     

Starch‐graphene oxide bionanocomposites prepared through melt mixing

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. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46037.     

Performance of nylon 6 composites reinforced with modified agave fiber: Structural,morphological, and mechanical features

Nylon 6 (Ny6) composites reinforced with treated agave fiber (AF) at different concentrations (5–20 wt%) were achieved by melt mixing process at 250°C, without the addition of any compatibilizing or coupling agents, and characterized in terms of their structural, morphological, and mechanical properties. The alkaline-ultrasound (NaOH-U) treatment in AF resulted in the removal of the low thermal stability components (pectin and hemicellulose), concentrating the cellulose fraction, and favoring the crystallinity percentages (X_c) of the Ny/AF composites. Moreover, the interfacial interactions between functional groups of agave fiber and Ny6 resulted in the increase Young's modulus (18.8%), flexural strength (11.3%), and density (3.7%). These findings could be useful when looking for potential applications in the mobility industry.     

Training of Inspectors and Engineers in Horizontal Directional Drilling (HDD): The California Experience

This paper presents an overview of training academies on horizontal directional drilling (HDD) conducted for the education and training of 125 resident engineers and permit inspectors for the California Dept. of Transportation, 54 utility inspectors, 16 consultants, and 26 city/county Inspectors. Each of the four academies took place over a 3-day period during which the first and third days involved intense classroom preparation. The second day provided field experience through demonstrations of various equipment and construction methods used in HDD. A pretest was administered on the first day, prior to any instruction, followed by a final test administered at the end of the last day. A grade of 70% or better was required to pass the course. The overall average of all 221 participants was 75.27% with a standard deviation of 8.10%. Further analysis of the test results concluded that level of formal education did not have any significant effect on the final grade obtained in the course. In addition, the average grade of each academy increased slightly with each subsequent academy. The improved scores could be a function of the quality of the class as well as the quality of instruction with each academy.     

Productivity and cytogenetic characteristics of guayule. Screening of plants from the mapimi region

Guayule plants were screened in the region of Mapimi (Durango, Mexico) to evaluate physicochemical parameters for selection of increased productivity. The objective was to characterize rubber, and resin content, stem diameter, rubber molecular weight and cytology of these plants to identify and select high productivity sites. Samples were collected from nine locations within the Mapimi Region. Inflorescences containing young floral buds of the same plants were selected to determine ploidy level. Cytogenetic results showed the presence of di-, tri- and tetraploids. Samples for rubber and resin analysis were cut from the branches. Genetic variation in molecular weight and molecular weight distributions for rubber was measured. Significant differences were found in resin content and stem diameter between the sampling sites, but differences were not significant for the rubber content between sites. A productivity parameter was defined and used to identify two locations where guayule genotypes exhibited the best characteristics for commercialization. This information may increase the industrial development and understanding of the polymerization bioprocess.