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Rubberwood: From waste product to furniture.

Rubberwood: From waste product to furniture.

Rubberwood is the name given to lumber from the rubber tree (Hevea brasiliensis), which is a tree producing latex to produce natural rubber. (Other names today include parawood and Malaysian oak.) 

Although Christopher Columbus was shown rubber on his journeys to the New World, it was not until 1839 that the vulcanization process was invented that made the elastic properties of rubber permanent. 

Prior to WW II, a vast forest area of rubber tree plantations, especially in the Amazon region, were envisioned and planted to satisfy the world’s growing demand for natural rubber. But then synthetic rubber was developed, making the rubber forests essentially obsolete. Today, with natural rubber being in more demand, Malaysia, Thailand and Indonesia grow most of the trees (covering 9 million acres), produce most of the natural rubber, and have the largest supplies of lumber.

The reason that rubberwood is an important lumber species is that the latex production from the trees drops after about 25 years. Further, newer genotypes have been developed in recent years resulting in higher production of latex, compared to older trees. So, the 25-year-old trees are being cut to renew the rubber forest. 

In the past, these old trees were burned. However, today, most of these older trees are being sawn into lumber. This lumber production from plantation grown trees is indeed quite environmentally friendly. Products made from this wood include furniture and cabinets, household woodenware, and parquet flooring, and this species is fairly popular in furniture that is being imported into the U.S.

Processing suggestions and characteristics

Density. Most plantation grown stock will run about 35 to 37 pounds per cubic foot at 7 percent MC. For a piece of wood at 7 percent MC that is ¾ inch thick by 6 inches wide and 24 inches long, the weight is 2.3 pounds. Kiln-dried, rough lumber will weigh about 3000 pounds per 1,000 BF.

Drying. Rubberwood dries rapidly with a medium to high risk of warp development. Splitting can also occur on the ends of the lumber pieces. Radially (thickness of a flatsawn piece) the shrinkage in drying is under 2 percent. Tangentially (the width in flatsawn lumber), shrinkage is 4 percent. 

Gluing and machining. Gluing is reported to be excellent. The wood machines well with few defects or problems.

Stability. It takes a 12 percent moisture content change for a 1 percent size change radially. It takes a 6 percent MC change tangentially. Kiln drying to the correct final MC (usualy about 7.0 percent MC) is required.

Strength. The strength (MOR) of dried rubberwood is 9,500 psi. The stiffness is 1.3 million psi. The hardness is 500 pounds.

Color and grain. The color of rubberwood is initially creamy when sawn, but after kiln drying and exposure to light, the wood turns darker with brownish and pinkish tints. The sapwood and heartwood appear similar and cannot be easily separated. The vertically running vessels give the grain a coarse appearance. These vessels also give the wood a bit of character.

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