Patent GB-497477-A (GB)
Title: Improvements relating to the manufacture of moulded products from raw ligno-cellulose
IPC: C08H8/00
Filed: 1937-03-16
Abstract: A moulding material for manufacture by hot pressure moulding of dense, water-resistant, amorphous products is obtained by subjecting ligno-cellulose, e.g. wood-chips, sawdust, cornstalks, cane bagasse, or straw to the action of heat and moisture for a longer period of time and/or at a higher temperature and pressure than employed in known methods of reducing ligno-cellulose to a coarse fibrous state (as described for instance in U.S.A. Specifications 1,578,609 and 1,824,221) until it is converted to a predominantly plastic state, i.e. it has useful flow properties when moulded in the manner usual for synthetic resins.  In a modification, the moulding material is obtained by separating from the product of the above-mentioned known methods the predominantly plaster bye-products which are produced, e.g. by screening.  In a further modification, the moulding material may be obtained by subjecting the ligno-cellulose to the action of heat and moisture for a considerably longer period of time and at lower temperature than is employed in the above-mentioned known methods until it is converted to a predominantly plastic state and reducing the material to the degree of fineness necessary for moulding.  The moulded products obtained from material made according to this modification are not quite so water-resistant as the others. Incompletely converted material in the mass acts as filler.  The treatment with heat and moisture is preferably terminated by explosive discharge of the material through a narrow aperture and/or the material may be ground, e.g. in a rod mill after the treatment. In an example, pine wood chips are treated for 30 minutes with steam at 300 pounds per sq. inch pressure (216 DEG  C.) and explosively discharged into a region of atmospheric pressure. With steam at 600 pounds (255 DEG  C.), 1 minute suffices, and 1000 pounds (285 DEG C.) 12 seconds.  Gum wood chips require rather less time, and cereal straws still less.  For a slightly less water-resistant material southern pine for example may be treated for 6 hours with steam or water at 120 pounds per sq. inch and 176 DEG  C.  The product is washed, ground and screened.  The moulding material of this invention may contain some water soluble material which may be removed by leaching before use.  It is dried before use either incompletely to retain 1-11 per cent of water or completely, in which case it is re-moistened to this extent with water, or alcohol as a plasticizer. Resins, fillers, lubricants, or pigments may be added to the material.  Suitable moulding conditions are 120-200 DEG  C. and 1000-3000 pounds per sq. inch pressure.  If the material is dried completely, pressures as high as 5000 pounds may be needed.  The moulded products when no pigment is added are dark-brown or black. The material may be felted into mats, dried to a low moisture content, e.g. 5 per cent, and pressed or moulded between platens, or it may be felted to paper-like sheets which are dried as before, piled one on another and pressed between platens.  A vitreous-like sheet product is obtained suitable for bathroom tiles.  The top and bottom sheets of the pile may contain synthetic resin material, e.g. phenolformaldehyde resin, or resins may be sprayed or dusted on to the surface.