of modified lignin phenolic resins was also investigated.
In uncastable region, high temperature changes the gel time
to a very short time and casting cannot take place.
Of course, one technique which is widely used is the measurement of gel time
In the production process of cast of RIM PUs, it would be necessary to use some extent of chain extender in the PU formulation that together with induction of desired mechanical properties in the final product, maintains the gel time
of suitable length in a processing temperature window sufficient to complete filling of a mold while permitting a short demold time (20).
Clay in Mixing Gel time
Rise time Foam type foam (% wt) time (s) (s) (s) PU Nil 7 49 64 3 pphp VMT 1.
Table 2 compares gel time
and properties at gel and 1000 s after gel.
Flow properties Spiral flow length 165 cm Gel time
41 s [T.
First, the slurries, which were prepared for the novolac cured epoxy resin/clay nanocomposites, were characterized by their solution gel time
by the gel tester (CECO, TA650).
The peak exotherm temperature and gel time
values of the modified epoxy resins are as shown in Table 3.
The gel point data can be used to build up a model, which is useful to predict the gel time
at temperatures different from those of the test.
Assuming that the gel time
is a characteristic time of the crosslinking reaction, these data show that the crosslinking process does not depend on the octene concentration of the copolymer at the same molecular weight.
This criterion was chosen for determining the gel time
Organometallic promoters for polyesters include Cobalt/potassium complex, which can extend more costly cobalt promoters and reduce color; Nuxtra cobalt-12%, a standard cobalt promoter; which helps control speed of gel promotion and prevents gel time
The composition, porosity, particle sizes, gel time
, surface areas, and density can be tailored and controlled by the solution chemistry.
Rheological experiments give the trend of the changes in gel time
especially in the critical point of gelation temperature.