![steam way to the woods steam way to the woods](http://blog.reedfurnituredesign.com/wp-content/uploads/2013/11/IMG_5866_opt.jpg)
Wood heated for long enough comes out of the steam chamber around 20-25% moisture content, so for green wood you are starting to season it as well as getting it ready for bending (which is magic coup in the world of woodwork). Proportionally tighter bends are possible with steam/wet bending than dry heat bending. Water in the porous cell walls (from steam or may already be present in unseasoned wood) makes the material softer and more flexible so helps with the bending process too. When it cools the Lignin bonds re-establish and the bend become permanent (unless we re-heat the wood and bend it again!) When the wood is heated a profound change occurs to the Lignin at a very tiny scale weakening or breaking bonds which enable the cellulose bundles to slide past each other when we bend the wood. Lignin (a natural thermo-plastic) is composed of molecules that have many arms that bond onto themselves and the adjacent Cellulose bundles. The thin Cellulose molecules tend to group together as bundles to make flexible fibres which are very strong in tension. When the wood is heated the lignin softens to allow the material to be bent/squashed/stretched/twisted into new forms.Ĭellulose (what paper is made from), is a polymer a chain of ring-like Glucose molecules which the plant miraculously makes from nothing but water, CO2 and sunlight during photosynthesis. The hollow, porous straw-like plant cell walls that wood is made from are composed of about 50% Cellulose and 30% Lignin.