This work explores the use of mechanical (MP), thermomechanical (TMP), and chemi-thermomechanical (CTMP) pulps from orange tree pruning fibers (OPF) as reinforcing elements of polypropylene (PP) composites. Due to the nature of the natural fibers, the use of a coupling agent is needed to attain a good interface and to prevent fiber slippage from the matrix. The main objective of the present work was to investigate the orientation factor, the interfacial shear strength, and the intrinsic strength of the OPF. Coupled and non-coupled composites were formulated and tested, optimizing the coupling agent content with the objective of maximizing the tensile strength of the composites. Hirsch and Kelly-Tyson models and the Bowyer-Bader methodology were used to compute the micromechanic properties. The contribution of subcritical, supercritical fibers, and matrix were also calculated.
Peer-assessment provides students with multiple benefits during their learning process.The aim of our study is to examine students' perception of peer-assessment.Questionnaires were administered before and after the peer-assessment process to 416 students studying eleven different subjects in four different fields taught at the University of Girona. Results suggest that students have a positive predisposition towards this methodology, both before and after its implementation. Students perceive it as both a motivating and recommended methodology that facilitates the acquisition of learning at different levels. As for its limitations, students highlight the responsibility that comes with it and a certain amount of distrust in fellow students' abilities to peerassess.
Please, cite this article as: Puig-Bargués, J.; Arbat, G.; Elbana, M.; Duran-Ros, M.; Barragán, J.; Ramírez de Cartagena, F.; Lamm, F.R.
AbstractFlushing is an important maintenance task that removes accumulated particles in microirrigation laterals that can help to reduce clogging problems. The effect of three dripline flushing frequency treatments (no flushing, one flushing at the end of each irrigation period, and a monthly flushing during the irrigation period) was studied in surface and subsurface drip irrigation systems that operated using a wastewater treatment plant effluent for three irrigation periods of 540 h each. The irrigation systems had two different emitters, one pressure compensating and the other not, both molded and welded onto the interior dripline wall, placed in laterals 87 meters long. Dripline flow of the pressure compensating emitter increased 8% over time, while in the nonpressure compensating emitter, dripline flow increased 25% in the surface driplines and decreased 3% in the subsurface driplines by the emitter clogging. Emitter clogging was affected primarily by the interactions between emitter location, emitter type, and flushing frequency treatment. The number of completely clogged emitters was affected by the interaction between irrigation system and emitter type. There was an average of 3.7% less totally clogged emitters in flushed surface driplines with the pressurecompensating emitter as compared to flushed subsurface laterals with the nonpressure compensating emitter.
This paper explores the evolution in the tensile strength of orange pruning fiber-reinforced polypropylene composites. The exploitation of these pruning's can effectively avoid incineration, with the consequence of CO2 emissions and fire risk, while extending the value chain of the agricultural industry. This biomass was subjected to three different treatments yielding mechanical, thermomechanical, and chemi-thermomechanical pulps. It was found that 20 to 50% of these pulps, together with a coupling agent, were used as polypropylene reinforcement. The evolution in the tensile strength and morphological properties of the fibers, and the effect of treatments on these properties were analyzed. A modified rule of mixtures (mROM) was used to analyze the micromechanical properties of the interface. In addition, the mechanical properties were weighted against the fiber treatment yields. Finally, factors to compute the net contribution of the fibers to the final strength of the composite materials were proposed.
The feasibility of incorporating purified kraft lignin, at different concentrations ranging from 5 to 29%, into fiberboards made from corn residues was studied. The lignin was obtained from black liquor, which is a residue of the paper industry. Corn stalk raw material and its thermomechanically produced fiber were characterized in terms of their chemical composition. The physical and mechanical properties of the resulting fiberboards were evaluated. The fiberboards produced following a wet process had good mechanical and water resistance properties that satisfied the requirements of the relevant standards. In addition, a Life Cycle Thinking (LCT) approach suggested that lignin-based fiberboards are environmentally preferable than those based on thermosetting resins.
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