Preparation of New Polyols Based on Cis-1,4-Polyisoprene by Using 1,3-Dipolar Cycloaddition

This research focuses on synthesis and modification of polyol precursors derived from cis-1,4-polyisoprene (PI). These new polyol precursors can be converted to high value-added polyurethane (PU). The epoxidized hydroxytelechelic PI (EHTPI) prepared by chemical modification from PI was used as starting material for polyol synthesis. 1,3-Dipolar cycloaddition between a terminal alkyne and an azide has rapidly become the most popular click reaction. We applied this reaction to couple azide-functionalized PI and alkyne-functionalized sugar for preparing polyols. For azide functionalization, 1-methyl epoxidized cyclohexane was used as a model molecule, and various conditions for epoxide ring opening of 1-methyl epoxidized cyclohexane and EHTPI were investigated. The cycloaddition of alkyne and azide was carried out in the presence of sodium ascorbate and copper sulfate. The polyol precursors obtained might be used to prepare biodegradable polyol PU

Influence of Matrix Polarity on the Properties of Ethylene Vinyl Acetate–Carbon Nanofiller Nanocomposites

A series of ethylene vinyl acetate (EVA) nanocomposites using four kinds of EVA with 40, 50, 60, and 70 wt% vinyl acetate (VA) contents and three different carbon-based nanofillers—expanded graphite (EG), multi-walled carbon nanotube (MWCNT), and carbon nanofiber (CNF) have been prepared via solution blending. The influence of the matrix polarity and the nature of nanofillers on the morphology and properties of EVA nanocomposites have been investigated. It is observed that the sample with lowest vinyl acetate content exhibits highest mechanical properties. However, the enhancement in mechanical properties with the incorporation of various nanofillers is the highest for EVA with high VA content. This trend has been followed in both dynamic mechanical properties and thermal conductivity of the nanocomposites. EVA copolymer undergoes a transition from partial to complete amorphousness between 40 and 50 wt% VA content, and this changes the dispersion of the nanofillers. The high VA-containing polymers show more affinity toward fillers due to the large free volume available and allow easy dispersion of nanofillers in the amorphous rubbery phase, as confirmed from the morphological studies. The thermal stability of the nanocomposites is also influenced by the type of nanofiller

TRIBOLOGICAL STUDY OF VARIOUS GRAPHITE POWDERS SLIDING AGAINST STEEL

ABSTRACT With its high resistance, good hardness and electrical conductibility in the basal plans, graphite is used for many years in various tribological fields such as seals, bearings or electrical motor brushes, and also for applications needing excellent lubrication and wear-reducing properties. But thanks to its low density, graphite is at the moment destined for technologies for which the combination of the possibility of reducing the weight of the components, and the ability of enhancing their efficiency is a fundamental asset. This is especially the case in the aeronautical industry where composites containing carbon, and more particularly graphite, are more and more widespread. In this context, the friction and wear of industrially produced graphite powders were evaluated in order to identify promising tribomaterials for braking use. Six different powders (natural and synthetic) having various grains sizes, were tested when sliding against steel, under various applied normal loads. The morphological and structural modifications of the graphites were observed by Scanning Electron Microscopy and AFM, and analysed by Raman spectroscopy. A classification of the various graphite powders could thus be realised ; the determining of the friction and wear mechanisms for the different materials, according to their own characteristics, as well as to the applied normal load, was also achieved

Nanotribological Characterization of Carbonaceous Materials: Study of Diamond Coatings and Graphite

International audienc

Nanofriction of diamond coatings obtained by flame process

International audienc

Tribological behaviour of graphite powders at nano- and macroscopic scales

International audienc

Surface modifications induced by the friction of graphites against steel

International audienc