Photochemistry of polymeric systems. III. Photocrosslinking of polymers and copolymers including cyanocinnamylydene–pyridinium groups

Photocrosslinkable polymers were obtained by reacting esters of cinnamic acid or cyanocinnamylideneacetic acid onto pyridine units of a homopolymer or onto a suitable copolymer. These photosensitive polymers were characterized by conventional analysis and spectrometry. The photocrosslinking was studied on thin films measuring the threshold of insolubilization together with UV and IR spectrometry.     

Application of Near and Mid-Infrared Spectroscopy to Determine Cheese Quality and Authenticity

This paper reviews the current state of development of both near-infrared (NIR) and mid-infrared (MIR) spectroscopic techniques for process monitoring, quality control, and authenticity determination in cheese processing. Infrared spectroscopy has been identified as an ideal process analytical technology tool, and recent publications have demonstrated the potential of both NIR and MIR spectroscopy, coupled with chemometric techniques, for monitoring coagulation, syneresis, and ripening as well as determination of authenticity, composition, sensory, and rheological parameters. Recent research is reviewed and compared on the basis of experimental design, spectroscopic and chemometric methods employed to assess the potential of infrared spectroscopy as a technology for improving process control and quality in cheese manufacture. Emerging research areas for these technologies, such as cheese authenticity and food chain traceability, are also discussed.     

Visible-near infrared spectroscopy sensor for predicting curd and whey composition during cheese processing

The potential of visible-near infrared spectra, obtained using a light backscatter sensor, in conjunction with chemometrics, to predict curd moisture and whey fat content in a cheese vat was examined. A three-factor (renneting temperature, calcium chloride, cutting time), central composite design was carried out in triplicate. Spectra (300–1,100 nm) of the product in the cheese vat were captured during syneresis using a prototype light backscatter sensor. Stirring followed upon cutting the gel, and samples of curd and whey were removed at 10 min intervals and analyzed for curd moisture and whey fat content. Spectral data were used to develop models for predicting curd moisture and whey fat contents using partial least squares regression. Subjecting the spectral data set to Jack-knifing improved the accuracy of the models. The whey fat models (R = 0.91, 0.95) and curd moisture model (R = 0.86, 0.89) provided good and approximate predictions, respectively. Visible-near infrared spectroscopy was found to have potential for the prediction of important syneresis indices in stirred cheese vats.     

Changes in the volatile profile of skim milk powder prepared under different processing conditions and the effect on the volatile flavor profile of model white chocolate

The objective of this work is to determine the extent to which changes in the skim milk powder (SMP) manufacturing process alter the volatile profile of SMP, and whether these changes are carried through to a final product when the SMP is used as an ingredient and subjected to further processing. The manufacture of SMP is a multistage process involving a preliminary concentration step, heat treatment, and a drying stage. However, the methods and conditions used by the industry are not standardized, and the inherent variability in the production of SMP has consequences for the end-users, such as the confectionery industry, where the SMP is used as an ingredient during the production of milk chocolate, white chocolate, and caramel. This study investigates the effect of each stage of the manufacturing process on the concentration of reducing sugars and available amino groups (as precursors of the Maillard reaction) as well as on the volatile products of the Maillard reaction and lipid degradation. Eight types of SMP were produced using combinations of different processing conditions: concentration (by evaporation or reverse osmosis), heat treatment (low heat or high heat), and drying (spray-drying or freeze-drying). Maillard precursors were quantified after each processing stage and volatile compounds were extracted using solid-phase microextraction, and analyzed by gas chromatography-mass spectrometry. The resulting SMP were incorporated into a model white chocolate system, produced under varying conching conditions. We demonstrate not only that changes in the SMP manufacturing conditions affect the volatile profile of SMP, but also that these differences can be carried through to a final product when the SMP is used to prepare a model white chocolate. Understanding these differences is important to the industry for controlling the flavor of the end product.     

Study of the miscibility gap in H2SO4/HI/I2/H2O mixtures produced by the Bunsen reaction – Part I: Preliminary results at 308 K

In the framework of the optimization of the sulfur–iodine thermochemical cycle for massive hydrogen production, investigations were performed in order to characterize the liquid phase (HIx and H₂SO_4(aq) phases) separation of solutions resulting from Bunsen reaction. Quaternary H₂SO₄/HI/I₂/H₂O mixtures were prepared at 308 K with different relative proportions of reactants and the chemical composition of each of the two phases formed was analyzed. An increase in iodine concentration and a decrease in water concentration appeared to improve the liquid–liquid equilibrium phase separation. However, a too low concentration of water also promoted the formation of byproducts. An increase in the [H₂SO₄]/[HI] ratio tended to favor the separation and seemed to lead to a dehydration of the HIx phase.     

Les enseignants et les conduites sociales de leurs élèves.

Compared the viewpoints of 45 teachers and 744 students concerning social behaviors in secondary school. Questionnaire data indicate that girls were evaluated by teachers or evaluated themselves more postively than boys and that behaviors found more appropriate for the academic environment were more often observed among Ss with above-average scholastic attainments. (English abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Workplace aggression in teenage part-time employees.

Among adult employees, interpersonal injustice and abusive supervision predict aggression toward supervisors at work. The aim of this study was to assess whether similar relationships exist among teenage employees and, further, whether teenagers' reasons for working moderate these relationships. Multiple regression analyses on data from 119 teenage employees showed that financial and personal fulfillment reasons for working moderate the impact of interpersonal injustice and abusive supervision on aggression directed at workplace supervisors. These findings contribute to the understanding of workplace aggression by demonstrating that (a) teenagers engage in this workplace behavior, (b) the predictors are similar to those of adult aggression, and (c) reasons for working play a moderating role among this particular cohort. The possible long-term consequences of teenagers' use of aggression at work are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conductive sizing for improving electrical conductivity of carbon fiber/polyaryl ether ketone/AgNWs composites

The aim of this work is to enhance the electrical conductivity of PAEK/continuous carbon fiber (CF) composites while maintaining their mechanical properties. A conductive sizing was elaborated by mixing polyetherimide (PEI) with silver nanoplates (AgNpts) in suspension in dichloromethane. An aqueous PEI formulation was used as insulating sizing reference. The presence of AgNpts into the sizing enhances electrical conductivity up to 0.2 S.m⁻¹ for a silver content ∼ 0.2 vol % without any modification of mechanical properties. The influence of conductive sizing on PAEK–AgNWs/CF was observed. For low AgNWs content lower (<1 vol %); the conductive sizing increases the electrical conductivity of the composite by one decade. This result shows that both types of Ag particles participate to the conductive path. For higher AgNWs content, electrical conductivity (200 S.m⁻¹) is independent from the AgNpts content: the conductive path is only constituted by AgNWs. Mechanical properties of such composites show that the value of the conservative modulus is almost the same, while the dissipative modulus slightly increases. The global mechanical properties of the composite are preserved despite the addition of the CF, AgNWs, and AgNpts. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47872.     

Effect of PEKK oligomers sizing on the dynamic mechanical behavior of poly(ether ketone ketone)/carbon fiber composites

Poly(ether ketone ketone) (PEKK)/unidirectional carbon fiber (CF) composites have a poor interface. Accordingly, PEKK oligomer (PEKKo) sizing with a chemical compatibility with PEKK is proposed for promoting interfacial interactions in order to enhance mechanical performances. The thermal stability until 500 °C has been shown by thermogravimetric analysis (TGA). In order to compare static and dynamic sizing methods, “lab sizing” and “pilot sizing” were carried out. Scanning electron microscopy images of freeze fractures of PEKK/unsized CF, PEKK/PEKKo lab-sized CF and PEKK/PEKKo pilot-sized CF show that the PEKKo sizing causes an improvement of fiber/PEKK interactions, regardless of the sizing method. Indeed, in both cases, there is a continuity of matter at the interface while we observe a poor wetting of CF by matrix in PEKK/unsized CF. Dynamic mechanical relaxations in shear were analyzed as a function of temperature. The increase of storage modulus upon sizing is observed for both methods but it is more important for PEKKo pilot sizing. In the same way, the mechanical energy loss increases, it reflects the optimization of stress transfer between matrix and fibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48818.     

Evolution of dispersion of carbon nanotubes in Polyamide 11 matrix composites as determined by DC conductivity

Double-walled Carbon NanoTubes (DWCNTs) have been dispersed in a Polyamide 11 (PA11) matrix by two routes: in the solvent way, Polyamide 11 was first dissolved in its solvent to ensure a liquid state dispersion of carbon nanotubes by ultrasonic way; in the melt mixing way, an optimization of the extrusion parameters, such as mixing time, mixing speed, mixing temperature and screw rotation direction allow to reach satisfactory dispersion. Dispersion and percolation threshold have been compared thanks to the evolution of DC conductivity with carbon nanotubes weight fraction in Polyamide 11.