Oxidized areas in polyolefin (PE, PP, EPDM) solids can be located by immersion in a warm isopropanolic solution of Sudan 111 and methylene blue, followed by observation of the solid discoloration pattern. Oxidized sites are stained blue, nonoxidized sites are stained pink. UV/Vis transmission and photoacoustic spectra can be obtained from the stained samples.
ZUSAMMENFASSUNG:Oxidierte Bereiche in Polyolefinen (PE, PP, EPDM) konnen durch Eintauchen fester Proben in eine warme Liisung von Sudan I11 und Methylenblau in Isopropanol an der Veranderung der Oberflachenfarbe bestimmt werden. Oxidierte Bereiche werden blau, nicht oxidierte dagegen rosa gefarbt. Die so angefarbten Proben wurden mit Hilfe der UV/Vis-und Photoakustik-Spektroskopie untersucht.
Previous study with nanocomposites of acrylonitrile-butadiene-styrene copolymer (ABS) and organophylized montmorillonite clays (OMMT) investigated the effect of clay modifiers polarities on their performance. Nevertheless, the literature has shown that the use of compatibilizers plays a key role in the dispersion of OMMT in polymeric matrices. Therefore, in the present work, ABS/OMMT nanocomposites compatibilized with styrenic block copolymers prepared by melt intercalation in a twin-screw extruder was studied. Nanocomposites formulations followed a 22 factorial design having different kinds of Cloisite OMMT (30B and 20A + 30B) and of compatibilizers (SBS and SEBS- g-MA) as independent variables. Structural (X-ray diffraction) and morphological (transmission electron microscopy) analyses of the nanocomposites showed a better clay dispersion, partially exfoliated, for ABS/30B/SBS than the intercalated morphology for ABS/20A30B/SEBS- g-MA. Rheological dynamic shear tests indicated a tendency to the formation of a percolating network structure for the ABS/OMMT/SBS nanocomposites, independently of nanoclay kind. Besides, these materials presented non-dripping effect on flammability tests. ABS/OMMT/SBS nanocomposites show also the best performance in both uniaxial tensile and dynamic shear storage moduli. These results are probably due to improved affinity between components. In conclusion, among the styrene block copolymers, SBS compatibilizer is more effective than SEBS- g-MA to improve the properties of ABS/OMMT-based nanocomposites.
In the present investigation, an experimental dental arch model fabricated in epoxy was assayed in Kratos universal testing machine to study the mechanical behavior of ethylene and vinyl acetate copolymer (EVA) in the form of mouthguard for sports and flat plate. The following variables were considered: thickness (3 and 4-mm plates), temperature (room and mouth temperature) and presence/absence of artificial saliva. Mechanical properties of EVA were tested under compressive strength: apparent absorbed energy (J.mm-1), maximum tension (N.mm-1), maximum dislocation (mm) and maximum strength (N). Data were recorded and modeled mathematically. Regarding the absorbed energy, maximum tension and maximum force, it was verified that the higher the thickness of the mouthguards, the better the results of force dissipation and redirection to the system and to several regions of the dental arch. In the presence of saliva and close to mouth temperature, the material responded positively to these alterations, resenting increased ductibility as well as improved mechanical responses. Regarding maximum dislocation, it was observed a better accommodation of the occlusion under conditions that simulate those observed in the oral environment. In conclusion, EVA proved to be an adequate material for fabrication of mouthguards and interocclusal splints. In addition, EVA showed good results in force dissipation and demonstrated a shockabsorbing capacity and a great protection potential.
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