Influence of Viscosity Modifying Agents on Pinus radiata Extract

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A number of different Pinus radiata extracts have been studied to examine their suitability as additives in the preparation of adhesives. Results have demonstrated that, under the conditions used in the extraction, the addition of NH 3 and Na 2 SO 3 contributed to a significant reduction in the apparent viscosity and the degree of shear thinning, giving near Newtonian behaviour. The size variation of molecular clusters observed by photon correlation spectroscopy in these extracts could explain this variation of the viscosity. The reactivity of these extracts with paraformaldehyde was compared by observing the variation of dynamic elastic and viscous moduli over time at 40°C, 60°C and 80°C. The most extreme reactivity was observed with the sodium hydroxide extract at all temperatures examined at its extraction pH of 8.8. For extracts at their extraction pH, increasing the temperature from 40°C to 60°C produced the greatest increase in reactivity with the hot water extract and Na 2 SO 3 extracts. However, increasing the pH of the extracts to 8.8 increased the overall reactivity, with the hot water extract showing the greatest increase. The sulphited extract reacted in a similar mode to the hot water and NaOH extracts but with a gelling rate intermediate between these extracts. The NH 3 extract showed an initial rapid gelation stage in the reaction followed by a slow stage at every temperature examined which differed significantly from the other extracts at the same pH.