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This study examined the durability of extruded HDPE/wood-flour composites exposed to 15 accelerated cycles of water submersion, freezing, and thawing, according to ASTM standard D6662. The durability of both maple and pine composites was assessed by testing the flexural properties and density. Mercury intrusion porosimetry and scanning electron microscopy were also used to evaluate the interfacial adhesion between the matrix and wood flour before and after exposure to accelerated freezethaw cycling. Freeze-thaw actions had no apparent effect on the density of the composites after exposure, regardless of the wood species. However, these actions led to moisture uptake, which decreased the interfacial adhesion and increased the pore size and quantity in the composites, which resulted in a significant loss in flexural properties.

Error sources associated with the spectrophotometric determination of low levels (e.g. <21J.g g-1 ) of nitrate in sediments have been examined and problems identified included incomplete nitrate recovery (attributable in part to anion resorption) and light scattering by colloidal (<0.451J.m) matter in extract solutions (minimised by using uncoloured extract in the reference beam). Optimum retrieval (>90%) of nitrate from the marine lake sediments studied was achieved with 15 min mixing with 0.1 M NH4CI, using a sediment to extractant ratio of 1 :30. The nitrate in the extracts was determined by reducing it to nitrite (using Cd powder), with subsequent colour development based on the addition of sulfanilic acid and N-1-naphthyl-ethylenediamine dihydrochloride. The reduction step was sensitive to the experimental conditions used, but was near quantitative using 0.1 M NH4CI extracts. (Much lower transformation levels were observed when the nitrate solutions contained KCI or CaS04, or when Zn powder was used as the reductant). All the sediments tested sorbed nitrate ion from solution (some very avidly) and this sorbed ion was not readily retrieved by back extraction into NH4CI solutions.

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