Chemicals from Wood 



639 



realized, although even yet the resins 

 do not promise that their bond with 

 wood will be spontaneous, for the pro- 

 duction of a good joint generally re- 

 quires high pressure, with or without 

 added heat. 



Phenol-formaldehyde and urea-for- 

 maldehyde are the most widely used 

 synthetic-resin glues. Melamine and 

 resorcinol glues, among the discoveries 

 during the Second World War, promise 

 good performance, the resorcinols par- 

 ticularly so because highly durable 

 bonds can be obtained without hot 

 pressing. The resins are available as 

 powders, solutions, or prepared films. 

 Their special advantage is that they re- 

 duce surface swelling and the other 

 changes caused by the water in the less 

 concentrated adhesives, particularly in 

 furniture and other fine veneer work 

 in which they are being adopted. 



THE GLUING OF WOOD is not a sim- 

 ple, infallible procedure, because wood 

 species vary chemically and physically, 

 and glues vary in source, methods of 

 preparation, and use. 



Findings at the Forest Products 

 Laboratory after years of research lead 

 to five general recommendations for 

 applying glue. 



It is usually unnecessary, and often 

 detrimental, to roughen the wood sur- 

 face; in fact, the mating surfaces 

 should be machined to a smooth, true 

 fit. 



Animal glue must not be overheat- 

 ed. Heating the wood is generally un- 

 necessary or detrimental. 



Glue should be thick, rather than 

 thin, in consistency when it is pressed. 



A relatively heavy pressure should 

 be applied to bring the surfaces to be 

 joined into firm contact until at least 

 partial setting has occurred. 



Minor details of procedure can be 

 varied in any way that will assure a 

 proper jellylike consistency of the glue 

 at time of pressing. 



DON BROUSE, a native of Indiana, 

 joined the Forest Products Laboratory 

 in 1923 and was assigned to work on 

 the problems connected with the ap- 

 plication of wood-working adhesives. 

 He is assistant to the chief of the Divi- 

 sion of Wood Preservation at the Labo- 

 ratory and has general supervision over 

 investigations on adhesives, veneer and 

 plywood production, and sandwich 

 panel fabrication. Dr. Brouse has de- 

 grees from Purdue University and the 

 University of Wisconsin. 



CHEMICALS FROM WOOD 



ALFRED J. STAMM 



Chemical processing of wood, up 

 to the present time, has been limited 

 to ( 1 ) destructive distillation, whereby 

 charcoal, wood alcohol, acetic acid, 

 turpentine, and tars are produced, and 

 (2) extraction processes with water or 

 petroleum solvents that remove the ex- 

 traneous materials, such as tannins, 

 turpentine, rosin, and essential oils. 



The destructive-distillation process 

 in recent years has not proved to be 

 very profitable, because many of the 

 products formerly produced exclu- 

 sively by the process are now made 

 more cheaply by synthetic methods. 



The extraction process, although 

 highly profitable when applied to a few 

 species, is not suitable for all woods 

 and actually utilizes only from 1 to 20 

 percent of the weight of the wood. 



Two rather new processing methods, 

 hydrolysis and hydrogenation, show 

 promise of broader application. Hy- 

 drolysis changes the cellulose and other 

 carbohydrate material into sugars. 

 Hydrogenation causes hydrogen gas to 

 react with the wood components at 

 high temperatures and pressure to 

 form liquid products. 



The new procedures, together with 



