Water dispersions reaction sequence

The in situ process is simpler because it requires less material handling (35) however, this process has been used only for resole resins. When phenol is used, the reaction system is initially one-phase alkylated phenols and bisphenol A present special problems. As the reaction with formaldehyde progresses at 80—100°C, the resin becomes water-insoluble and phase separation takes place. Catalysts such as hexa produce an early phase separation, whereas NaOH-based resins retain water solubiUty to a higher molecular weight. If the reaction medium contains a protective coUoid at phase separation, a resin-in-water dispersion forms. Alternatively, the protective coUoid can be added later in the reaction sequence, in which case the reaction mass may temporarily be a water-in-resin dispersion. The protective coUoid serves to assist particle formation and stabUizes the final particles against coalescence. Some examples of protective coUoids are poly(vinyl alcohol), gum arabic, and hydroxyethjlceUulose. 

Colloidal suspension of cellulose whiskers in water prepared as described elsewhere (Azizi Samir et al., 2004). Acid hydrolysis was done at 45°C with 65 wt% H SO (pre-heated), for 40 min, under mechanical stirring. The suspension was diluted with ice cubes to stop the reaction and washed with water until nentrality before successive centrifugation at 10,000 rpm at 10°C for 10 min each step and dialyzed against distilled water in the sequence. The dispersion of whiskers was completed by an nl-trasonic treatment. The resulting suspension was subsequently stored in a refrigerator after adding several drops of chloroform in order to avoid bacterial growth. 

An evaluation of numerous clays, including kaolins and bentonites of comparable particle size and distribution, revealed a wide variation in the properties of LDEE-clay composites prepared under identical conditions with similar loadings. This may be attributed to the interference with the radical reactions involved in the coupling sequence. This is confirmed, in part, by the finding that the most effective clays were those which were reported to have been treated with sodium polyphosphate to improve their dispersibility in water during papermaking processes. Solomon reported (1) that treatment of the clays which inhibited radical reactions with sodium polyphosphate reduced the inhibition. 

A major disadvantage of an undivided cell is the fire and explosion hazard caused by electrical sparking in the case of mixing finely dispersed H2 and 02 formed during the electrolysis of water. Weintraub et al. [159] utilized porous Fe anodes that are oxidized while air or oxygen is bubbled through the solution to separate oil-water emulsions. The overall process can be explained by the following sequence of reactions [160,161] ... 

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