New Ways Of Preserving Wood Described

Press, Volume CIII, Issue 30390, 14 March 1964, Page 15

New Ways Of Preserving Wood Described

New processes in wood preservation were described to the Canterbury branch of the New Zealand Institution of Engineers by Dr. M. S. Hudson, an American consulting chemist, who has decided to spend a good deal of his time in New Zealand. Dr. Hudson described a vapour-drying method by which sleepers and poles could be prepared for impregnation with preservatives as they came from the mill, without the customary 12month outdoor seasoning period. He also explained means of recovering solvents used in impregnation, and experiments aimed to discover ways of preventing wood from shrinking or swelling. The processes could be carried out in the cylinders traditionally used to hold wood being impregnated at woodprocessing plants, said Dr. Mason. All that had to be added were heating coils in the bottom of tfib cylinder and an oil-water condenser and separator, with instruments to indicate the progress of the treatment. Waipa Plant The vapour-drying process was being carried out at a pilot plant built by the New Zealand Forest Service at Waipa to plans he had provided, and the Railways Department and other organisations were interested, said

Dr. Mason. Species such as red and silver beech which could not be -prepared for use for sleepers by air-drying methods could be impregnated satisfactorily with creosote as the result of this process, he said. The basis of the process was that water was driven out of the. wood by the vapour of a hydrocarbon, the one used being a kerosenelike petroleum fraction. The mixed water and hydrocarbon vapour was condensed and the two separated, the hydrocarbon being returned to the cylinder while the water was used as an index of the extent of drying. Because creosote tended to ooze out of treated wood and was thus messy and prevented the wood being painted, dry preservatives such as copper napthanate and pentachlorophenol were often used instead with the help of oily solvents. Usually the wood was then subjected to air-drying; but this wasted the solvent, took up a good deal of time, and created a fire hazard. The solvent c uld be removed in the cylinder, however, by vap-our-drying. Large Savings

The vapour-drying process had saved several American railway system and other ma. jor timber-users amounts ranging into millions of dollars, because they no longer needed to keep huge quantities of timber drying in yards. The savings had paid for new drying plants.

The experiments Dr. Hudson was carrying out in the prevention of swelling or shrinking (dimensional stabilisation) were also based on the use of the cylinder. Asked what advantages vapour-drying had over kilndrying, Dr. Hudson said many species could not be kilndried because they split too badly under that process. Dr. Hudson described a recently-patented process for detecting those poles or sleepers which would be victims of “early failure” through not having absorbed enough preservative. He had discovered, he said, that because of individual variation from tree to tree, some pieces of timber took up creosote much more rapidly than others; the slow ones became the “early failures.” The new detection method relied on chemical examination of borings from the treated sleepers or poles; those which had not taken up enough preservative were simply put beck in the cylinder for a little while longer. Dr. Hudson’s main office and laboratory are in Spartanburg, South Carolina, but he intends for the future to spend between a quarter and a third of his time in New Zealand, where he has an [office in .Wellington.