Complex formation and stability of colloidal wood resin pitch suspensions with hemicellulose polymers

Abstract

This paper explores the impact of the wood polymers released by Pinus radiata on the stability of wood resin colloids under varying ionic strength conditions with the addition of calcium chloride. A photometric dispersion analyser was used to study the kinetics of aggregation under shear conditions. Addition of the wood polymers to an aqueous dispersion of wood resins was found to cause destabilisation of the wood extractive colloids in two stages, separated by an apparent stabilisation region. The behaviour observed is typical of aggregation due to polymer bridging at low polymer addition, followed by steric stabilisation of the colloids at medium polymer concentration and depletion flocculation at higher polymer additions and then finally depletion stabilisation. At 10mM calcium ion concentration, destabilisation of the colloids occurred at low wood polymer addition, while at wood polymer concentrations above 50mg/L restabilisation of the colloids occurred at this level of calcium. The wood polymers were found to be unable to stabilise the colloids at high calcium levels of 50mM. At high calcium levels the wood polymers themselves were found to undergo aggregation. The stabilisation of the colloids was found to be affected by the way in which the colloids and wood polymer complexes are formed and allowed to reorganise with time.Adsorption isotherms for the adsorption of the wood polymers onto wood resin coated surfaces were determined. A low affinity Langmuir isotherm was obtained in the absence of electrolyte indicating that interaction between the wood polymers and the wood resin arises due to hydrogen bonding between the carboxylic acid groups despite the negative charge on both. The higher than expected loading capacity showed that the wood polymers adsorb as aggregates which extend from the surface and act to screen the negative charge of the wood resin colloids. In the presence of 10mM CaCl2 the isotherm was found to be modelled by a Freundlich isotherm with a greater amount of wood polymer being adsorbed due to folding of the wood polymer and reduction in its volume.