Pure Chitosan Biomedical Textile Fibers from Mixtures of Low- and High-Molecular Weight Bidisperse Polymer Solutions: Processing and Understanding of Microstructure–Mechanical Properties’ Relationship

Natural polymers, as extracted from biomass, may exhibit large macromolecular polydispersity. We investigated the impact of low molar mass chitosan (LMW, DP_w~115) on the properties of chitosan fibers obtained by wet spinning of chitosan solutions with bimodal distributions of molar masses. The fiber crystallinity index (CrI) was assessed by synchrotron X-ray diffraction and the mechanical properties were obtained by uniaxial tensile tests. The LMW chitosan showed to slightly increase the crystallinity index in films which were initially processed from the bimodal molar mass chitosan solutions, as a result of increased molecular mobility and possible crystal nucleating effects. Nevertheless, the CrI remained almost constant or slightly decreased in stretched fibers at increasing content of LMW chitosan in the bidisperse chitosan collodion. The ultimate mechanical properties of fibers were altered by the addition of LMW chitosan as a result of a decrease of entanglement density and chain orientation in the solid state. An increase of crystallinity might not be expected from LMW chitosan with a still relatively high degree of polymerization (DPw ≥ 115). Instead, different nucleation agents—either smaller molecules or nanoparticles—should be used to improve the mechanical properties of chitosan fibers for textile applications.     

Addressing Learner Satisfaction Outcomes in Electronic Instrumentation and Measurement Laboratory Course Organization

This paper proposes and details a course organization methodology based on learner satisfaction achievement. The approach follows the prevailing tendency in modern university reforms which are primarily concerned about "how people learn." As a consequence, the learner has been placed as the main actor of the teaching-learning process. Nevertheless, the current learning literature has not addressed the measurement of learner satisfaction within laboratory and practical subjects. This study develops a general and comprehensive methodology for learner satisfaction measurement in practical subjects. As a case example, the proposed methodology has been applied to an electronic instrumentation and measurement course, confirming the variables with a significant influence on learner satisfaction and becoming the starting point for curriculum redesign based on the learner satisfaction approach. To assess the improvement of the proposed course organization methodology, a comparison with previous academic years has been performed showing the students' rated score evolution. Results fully confirm the validity of the technique and the novel course organization     

Monitoring the Formation of Thin Films by Photothermal Technique

Evaporation is a widely used technique for developing thin films. In this study the formation of a film on top of a substrate is investigated using a photothermal technique. The configuration implies the illumination of an opaque substrate by modulated laser radiation and the detection of the heat at the illuminated zone. The system is considered as a two-layer system in which the non-illuminated layer presents a dynamic response, the thickness and thermophysical properties, which change as a function of time. Results of modeling such a system, which depend on the evaporation rate and concentration changes are presented. It was found that for the process in which evaporation constitutes a dominant contribution, one observes a stable long time process, and at a certain instant, the amplitude of the photothermal signal suddenly grows. On the other hand, additional contributions (such as the increase of concentration) involve processes that cause the amplitude of the photothermal signal to grow smoothly with time. The contributions of different mechanisms involved during the film formation are discussed.     

Effect of thermal sterilization on ferulic, coumaric and cinnamic acids: dimerization and antioxidant activity

BACKGROUND: Some phenolic compounds, such as ferulic acid and p‐coumaric acid, exist in the form of free acids, in fruits, rice, corn and other grains. Thermal treatment (121 °C at 15–17 psi) for different times on ferulic, p‐coumaric and cinnamic acids as well as equimolar mixtures of these acids was investigated. RESULTS: Ferulic and p‐coumaric acids underwent decarboxylation, yielding dimeric products formed through their corresponding radical intermediates, while cinnamic acid was recovered unreacted. High‐performance liquid chromatography analysis showed no cross‐dimerization when equimolar mixtures of pairs of hydroxycinnamic acids were treated under the same conditions. Dimers were characterized as (E)‐4′,4″‐(but‐1‐ene‐1,3‐diyl)bis(2′‐methoxyphenol)) (dimer of 4‐vinylguaiacol) and (E)‐4,4′‐(but‐1‐ene‐1,3‐diyl)diphenol) (dimer of 4‐vinylphenol) by nuclear magnetic resonance and mass spectrometry. CONCLUSION: Sterilization by thermal processing produced dimers of ferulic and coumaric acid. The antioxidant activity of these dimers was greater than that of the respective hydroxycinnamic acids. These results may be relevant for fruits and grains that contain hydroxycinnamic acids and undergo sterilization processes such as canning. Copyright © 2012 Society of Chemical Industry