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The production of biomass and biopolyesters (polyhydroxyalkanoates) by the marine bacterium Saccharophagus degradans from: glucose, starch, glucosamine, and xylose were studied. The effect of yeast extract, trace elements, vitamins, and initial concentration of each carbon source on biomass production was evaluated. The addition of yeast extract, together with trace elements, increased the biomass production by 5- fold, obtaining the maximum values when using an initial substrate concentration of 20 g/L for: starch, 8.61; glucosamine, 7.06; and xylose, 4.47 (g dry cell weight/ L). From glucose at 40 g/L the maximum biomass production was 9.07 g/L. Next, the biopolymer production under nutrient-limiting conditions (by N, P, S and Mg) was investigated, as well as the ability of S. degradans to produce copolymers from precursors. The biopolyester produced in all cases was poly(3-hydroxybutyrate) (PHB). Different accumulation percentages (g PHB/100 g biomass) were achieved depending on the carbon source used: glucose, 27.72; starch, 18.11; glucosamine 3.33; there was not biopolymer accumulated from xylose. Finally, the PHB produced from each carbohydrate was characterized, presenting molecular weights between 53 and 58 KDa, and fusion temperatures between 164 and 174°C. [ABSTRACT FROM AUTHOR]

The linearization of adsorption equations is controversial. The estimation of fitting parameters strongly depends on the linearization method, magnitude of experimental error, and data range. Although many studies contrast linear versions of these equations with their non-linear counterparts, linearization is preferred due to its simplicity since a line could be represented with fewer experimental points than a curve. An in-depth analysis was carried out to compare the accuracy of linear and non-linear models. Although different transformations linearize Langmuir isotherms, only one form yields reliable fitting parameters. Linear transformations could also lead to a statistical bias, favoring a model that does not represent the experimental behavior. Similar observations are discussed regarding the pseudo-second-order kinetic model. Linearization of Freundlich isotherms, pseudo-first-order kinetic models, and fixed-bed adsorption models through logarithms implies that attention must be taken on the logarithm limits by properly selecting the data range. Linearization also promotes the incorrect interpretation of models due to oversimplification. The linearized van't Hoff equation would yield a reasonable fit with fewer experimental points than the non-linear regression, which requires more data to assure convergence. In this sense, there is convincing evidence that non-linear regression is a more robust and reliable tool for adsorption modeling. [ABSTRACT FROM AUTHOR]

Combining polylactic acid (PLA) with waste fibers to produce reinforced biocomposites is of top interest to replace conventional polymers for environmentally friendlier materials. Natural fibers have a remarkable effect on the mechanical and thermal properties of the biocomposites. This reinforcing effect strongly depends on the chemical compositions of fibers, which will also influence the susceptibility of the biocomposites to abiotic and biotic degradation processes. This study evaluated the effect of agave and coir waste fibers over the abiotic and composting degradation of PLA-based biocomposites. Compression-molded PLA/agave and PLA/coir biocomposites using GMA-g-PLA as compatibilizer were subjected to accelerated weathering. Weathered and unweathered samples were further submitted to water absorption to analyze their hydrolytic degradation and composting for biotic degradation. Both fibers showed significant influence on biocomposites degradation. The role of the fibers in UV and hydrolytic degradation was positive for impact properties since the biocomposites were less affected than PLA. Water uptake was increased with fiber addition, while hydrolytic degradation was decreased. The weathering (abiotic degradation) accelerated the PLA biodegradation rate. In general, the results showed that adding both fibers to PLA could help its outdoor performance, maintaining the biodegradable characteristics of these materials. [ABSTRACT FROM AUTHOR]

In this study, the internal air temperature (IAT) profile was measured to analyze the thermal behavior of a polymer for a complete rotational molding cycle. Foamed and unfoamed linear low density polyethylene parts were produced by biaxial rotational molding using a chemical blowing agent based on azodicarbonamide at different concentrations (0, 0.15, 0.25, 0.50, 0.75, and 1.0% wt) with different oven temperatures (270, 280, and 285°C). The analysis proposed is based on the temperature profiles and their derivatives to better determine the different transitions occurring in a complete molding cycle. The analysis is completed with differential scanning calorimetry (DSC) to get more information related to the dynamics of the different processing stages like polymer melting, exothermic decomposition of the chemical blowing agent, and polymer crystallization. The results obtained show a good agreement between the melting and crystallization temperatures from IAT derivatives and DSC. POLYM. ENG. SCI., 58:E235–E241, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

In this study, natural fibers (agave, coir, and pine) were surface treated with maleated polyethylene (MAPE) with two main objectives: (1) to improve the mechanical properties of natural fiber composites produced by rotational molding and (2) to increase the fiber content in the composite. The rotomolded composites were produced at 0, 10, 20, 30, and 40% wt. of fiber contents (treated or untreated) and characterized in terms of morphology and mechanical properties (hardness, impact, tension, and flexion). The results showed that MAPE surface treatment was more successful for agave and coir than for pine fibers due to their respective chemical composition. In general, surface treatment led to better fiber distribution and a more uniform composite morphology allowing the possibility to use higher fiber contents in rotational molding. At low fiber contents (10 and 20% wt.), the mechanical properties were improved using treated fiber composites (TFC) compared to the neat polymer and untreated fiber composites (UFC). Although the mechanical properties of TFC decreased at high fiber contents (30 and 40% wt.), they were substantially higher (about 160, 400, and 100% for impact, tensile, and flexural properties, respectively) than for UFC. [ABSTRACT FROM AUTHOR]

Foamed linear medium density polyethylene parts were prepared by rotational molding in biaxial mode, using different amounts of chemical-blowing agent (azodicarbonamide). Morphological and mechanical properties are presented and discussed in terms of foam density, cell density, average cell diameter, and open cell content. Internal air temperature of the mold was measured as a function of time. Significant differences were observed between unfoamed and foamed parts. The use of an exothermic chemical-blowing agent increased the peak internal air temperature and part cooling was slower due to the presence of gas bubbles acting as insulating material. The most important changes were observed for foam density: adding 1 phr of azodicarbonamide the density decreased from 0.931 g/cm3 (0 phr azodicarbonamide) to 0.295 g/cm3. Finally, the mechanical properties were highly influenced by azodicarbonamide content. Tensile and impact properties were correlated with part density using a simple power–law equation. [ABSTRACT FROM AUTHOR]