PLYWOODS AND PLASTIC ADHESIVE

Dunstan Times, 13 November 1944, Page 3

PLYWOODS AND PLASTIC ADHESIVE

Not least in importance among the discoveries war has sent tumbling out of the laboratories of research workers, arc the latest adhesivcs for building plywoods. Gradually the chemists are making new synthetic glues, free from the serious weakness of the older types. Until* comparatively recently, plywoods were useful only up to the point when the glue failed, throng]] heat, cold, humidity, rain, or some similar cause. Now glues can be obtained in forms which are practically unaffected by any of these things. This means that plywoods can be used in almost any position, and for an infinite variety of purposes. , The strength and rigidity of plywood is, of course, enormous, compared with ordinary timber, and by modern techniques boarding of practically any size and thickness can be made. Built-up girders for small or large spans, composed of multiple plys, are now just ordinary practice. Designed with a camber to counteract the unavoidable sag which occurs, and reduced in height from the centre towards the point of support, a plywood girder is attractive but not costly. It is specially economical because the different members can be made up of short lengths, too small to be otherwise useful, and— where the stresses lessen— of inferior classes of timber. With the laps properly distributed and sufficient laminations, the design of plywood structures is perfectly feasible and presents only commonplace problems.' There is no intricate framing involved, such as would be necessary in the equivalent truss, composed of smaller pieces. When treated with fireproof and termite resisting solutions and attractively painted there is not much wrong with a plywood girder, or in fact any structure made of this material. As can be readily understood, the whole success or otherwise of plywood depends upon the quality of the adhesive which binds the laminations together. As long ago as 1721, that celebrated scientist Isaac Newton, observed that there was "agents in Nature able to make the particles of bodies stick together by very strong attraction", and he concluded it was "the business of experimental philosophy to find them out." It was not until about 200 years later, however, that any comprehensive study was made of the subject. We are still far from the perfect adhesive, though great advances have certainly been made. The exigencies of the war have naturally forced the pace, especially in the making of aeroplanes, where plywoods and plastics have been extensively used. There are many first-class adhesives now, gelatine glue being one of the strongest. A joint made with this is actually stronger* than the wood itself, so it has not been necessary for modern research to find a stronger glue, so much as a more stable one. What is necessary is a glue which can be easily applied land has a greater resistance to the effects of Humidity and the normal processed of decay. Glueing does for timber what welding does for steel—it enables joints to be made without weakening the structure by cutting material out of the i members joined. jThe perfect glue that will be discovered some day will be one that will not lose its strength when wet, will not be subject to decay, will maintain Its efficiency over a wide range of temperatures and will be as permanent as the wood that it binds. This will revolutionise timber construction and give almost unlimited scope and freedom of achi.tectural expression.