1,721,072 research outputs found
Mechanical and dielectric relaxations during post-cure of thermosetting composite matrices
No full textRheological Characterization of concentrated nanoclay dispersions in an organic solvent
No full textNanoclay dispersions in organic solvents are widely used in cosmetics for a variety of gels and creams, whose properties depend on the powder content and the processing method. The control of the shear applied during processing is therefore essential for achieving the required properties.This study demonstrates the utility of applying rheological measurements for characterizing cosmetic products based on nanoclays and relating their viscoelastic properties to end-use performances. In particular, a rheological characterization of bentonite dispersions in isododecane at different clay content and shear history is presented. For each inorganic content, both mixed samples and samples subjected to several calendering runs were studied. The effect of shear and clay content on the viscoelastic properties was investigated by a combination of oscillatory shear experiments under small-deformation conditions and by X-Ray diffraction. The tested samples showed a gel-like behaviour with a final structure depending on the applied shear stress. By increasing the inorganic content in the dispersion, a reduction in the gel stability to a further shear application was observed. Two models, developed for colloidal gels,were used to fit the rheological results enabling to evaluate the microstructure and the degree of dispersion of the tested samples and to relate the colloidal structure to the elastic propertie
Mechanical and Natural Durability Properties of Wood Treated with a Novel Organic Preservative/Consolidant Product
No full textAn organic preservative/consolidant of new formulation was selected in order to evaluate its effect on the mechanical properties of worm-eaten walnut wood. Walnut wood is widely used for the realization of artistic handworks (e.g. statues, altars, etc.) furniture and flooring. The flexural strength and modulus of elasticity, the toughness and the hardness were determined on both treated and untreated samples.
The experimental results showed that the product increased significantly the flexural strength while the other mechanical properties were not appreciably affected by the chemical treatment. The microstructure of the samples tested was observed using scanning electron microscopy.
The preserving character against insects of the investigated product was assessed by both visual inspection and measurements of weight loss on the treated specimens after their exposure to living insects. The samples on which the product was applied, exposed to Oligomerus ptilinoides for one year, were more resistant to decay than the corresponding untreated samples
Caratterizzazione del comportamento acustico di vernici tramite analisi agli elementi finiti
No full text
Relaxations during post-cure of unsaturated polyester networks by ultrasonic wave propagation, dynamic mechanical analysis and dielectric analysis
No full textUltrasonic wave propagation, dynamic mechanical analysis, and dielectric
analysis were used to monitor relaxation phenomena during the nonisothermal postcure
of unsaturated polyester networks. The measurements covered 6 decades of
frequency. As a result, the residual reactive groups, immobilized in the glassy state by
vitrification during an isothermal cure step, gained molecular mobility, which promoted
the formation of additional crosslinks. After the postcure, the reaction was complete,
and the maximum achievable glass-transition temperature was reached. Moreover, the
frequency and temperature dependence of the two relaxations, one related to the
glass-transition temperature of the partially cured sample and the other to the glass
transition of the fully cured sample, was evaluated. The Williams–Landel–Ferry equation
was used to model the frequency dependence of the main -relaxation data
obtained with the different techniques
Ultrasonic cure monitoring of composite matrices/Monitoraggio ultrasonoro del processo di “cura” di matrici di materiali compositi
No full textAn experimental set-up for ultrasonic cure monitoring has been developed at the Laboratory of Composite Materials (University of Salento). The obtained results demonstrate that ultrasonic wave propagation is able to detect and monitor the physical changes taking place during curing of thermosetting matrices. Moreover, the set-up has the potential for online monitoring during composite processin
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