Reaction gelling

Gellan m [71010-52-1] Gelling agent Gelling agents Gelling reaction... 

Catalysis of the flexible polyurethane foaming operation is accompHshed through the use of tertiary amine compounds, often using two different amines to balance the blowing and gelling reactions. OrganometalHc compounds, usually staimous salts, are also used to faciHtate gelling and promote final cure. 

Acid-induced gelling reactions of PF resins can cause severe deterioration of the wood substrate and therefore have lost any importance in the wood adhesives field. Pizzi et al. [85] describe a procedure for the neutralization of acid-hardened PF glue lines by partly using as hardener a mix of p-toluene sulfonic acid with a... 

Branching leads in many cases to gelation and network formation. Sometimes only precursors, i.e. synthetic resins, are wanted where gelation has to be prevented. Here, of course, a theory is most efficient which contains explicitly the chemical parameters responsible for the branching reactions, which can be altered in a similar manner as in real gelling reactions. This again is warranted by the close relation of the link probability to the extent of reaction (branching). 

It is known that many microorganisms found in soil and natural waters assimilate ungelled acrylamide so that hazards of the unreacted material persist only a relatively short period of time. These organisms do not affect the gel itself. However, an application near a water supply which may be used for drinking or recreational purposes should be undertaken only when conditions indicate that no appreciable quantity of acrylamide will find its way into water. Under most usual circumstances, significant contamination will be unlikely. In this connection, it is important that excessive dilution of catalyzed solutions be prevented until the gelling reaction has had sufficient time to proceed to completion. 

An add- rather than alkali-induced gelling reaction of PF adhesive resins can cause severe deterioration of the wood substrate at the interface and, therefore, its use has lost its significance in the application of PF resins to bond wood. Pizzi et al. [156] describe. 

Very often mixtures of the two types are used, because the tertiary amine-based catalysts tend to catalyze the blowing reaction preferentially, and the metal salts—like dibutyltin dilaurate or stannous octoate—promote the gelling reaction more. Moreover it has been found that these two types of catalysts have a synergistic effect when used together. 

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