About 10 g of a 30% (w/w) of lyophilized tannins solution, 5%
of powdered paraformaldehyde on a dry and solid tannins matter
content basis were added to a test tube and placed in a water bath,
which was maintained at boiling temperature (just below 100 ◦C)
at normal atmospheric pressure. The time taken to reach the gel
point was recorded during constant stirring with the aid of a wire
spring and a stopwatch. The test was duplicated and the average
value was reported. The pH of the mixture was measured using a
microprocessor pH meter (Hanna pH 211). 33% of sodium hydroxide
solution (NaOH) and hydrochloric acid solution (HCl 4M) were
used to adjust different pH of the mixture.