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Wood Substitutes Emerging

Alternative wood substitutes fall into three main categories — ferrocement substitutes, fibre-reinforced composites and polymers.

by T V Padma
FACED with shrinking forest reserves and spiralling demand for wood In some core sectors, scientists have launched a massive hunt for wood substitutes that can cut down the use of timber in construction. -
The Central Building Research Institute at Roorkee has taken a lead with the development of several alternatives for wood in buildings, which were discussed at a two-day national symposium at Roorkee in December.
While the cost of these alternatives is comparable to that of timber, they serve the main purpose of saving timber, Dr S K Mishra CBRI director, told PT1. If found to be commercially viable they can save up lo 30 per cent timber, he said.
"We arc not working on substitutes for decorative uses of wood, but concentrating only on alternatives for semi-slructural and building components," he said, adding that some of these technologies would be ready by next year.
Timber is used in buildings for a horde of structures: piles posts, lintel, doors, windows, frames, trusses and shutters. It is also used in flooring, ceiling, panelling and partition walls and ends up contributing to almost 15 per cent of the total cost of the buildings.
The draft housing policy for the Eighth Five Year Plan envisages nearly 21.8 million dwelling units by 1995. which would require almost 4.84
million cubic metres of wood. With the current availability estimated at 2.32 million cubic metres, the need for substitutes is becoming imperative.
Alternative wood substitutes tall into three main categories — ferrocement substitutes, fibre-reinforced composites and polymers.
Ferrocement is a versatile material that can replace Um- ' ber, steel concrete and even baked clay products. A composite made of wire mesh, sand arid cement ferrocement possess unique qualities of strength and serviceability and can be used to directly replace not only limber components but also concrete walls, columns, and in roofing and flooring.
dustries. Wood based composites presently manufactured in India are plywood, block boards, particle and fibre boards.
Ce'ment bonded particle boards consist essentially of a mixture of fibrous wood particles (typically chips and shavings) and portland cement or other cement with equivalent properties, to which fillers and pigments may be added.
Cement bonded particle boards and wood fibres reinforced cement sheets are commercially available abroad and have been found lo be cheaper than good quality timber. They arc being used for various applications such as panelling, partitioning, cladding, false ceilings and wall
A second and recent trend is to develop composites using industrial wood wastes and residues and natural fibres in inorganic matrices like gypsum, portland cement and other cements.
Wood composites are being promoted the world over to reduce consumption of industrial wood. These composites can be manufactured using small girth wood, fast growing species wood, low-grade wood and wood residues available from saw mills and other in-
lining.
There has been a growing interest in incorporating natural vegetable fibres like sisal, coir, bamboo, bagasse and jute in the cement matrix. Sisal and other natural fibres reinforced concrete corrugated roofing sheets are used In Australia and some African countries while sheets reinforced with Jute and bamboos fibre are being used in Bangladesh, and with coconut in the Philippines Thailand and Indonesia.
The Indian Jute Research Inslilute has developed Jute reinforced composites as a wood substitute. A prototype model of these panels fixed with steel sections Is giving promising results in a six-year outdoor exposure study, although the cost Is proving to be slightly more than that of timber.
Also on the anvil are particle boards from Jute sticks, a waste product obtained during jute cultivation to the tune of 4 million tonnes. The boards, prepared from dry Jute sticks, flakes or powder coal with resin binders and casted into shape in heated metal plates under high temperature and pressure, are fire resistant, termite and water resistant, scientists report.
Considerable work has been done al the Regional Research Laboratory, Trivandrum, on lignocellulosic fibre polymer composites, with a recent coir polymer system emerging as a potential substitute.
Bambooply boards, formed by pressing bamboo mats at high temperature and pressure, are an elegant and strong panelling material. Resistant to boiling water and termites, these boards can also be used tn furniture, panelling, false ceilings and partitioning. The strength of bambooply can be Improved by putting veneer between the bamboo mats.
Rice husk boards developed by the Indian Plywood Industries Research Institute. Bangalore, have 18 per cent silica and. therefore, not at tacked by termites, wood bor Ing Insects, wood decaying or
ganisms or rodent*. An added advantage I* that they do not catch fire immediately but only smoulder slowly when Ignited
Another viable alternative is gypsum boards, consisting of a gypsum piaster core with or without fibre, encased in and firmly bonded to strong durable paper liners. India has 1249 million tonnes of natural gypsum and 4 million tonnes of phospho gypsum obtained as a byproduct from the phosphate fertiliser industry.
Particle boards and glass reinforced gypsum composites can be used as an alternative to wood because of their inherent wood-like properties such as ease cutting, nailing screwing, chisseling and sawing.
In the field of polymer substitutes showing considerable promise is an interpenetrating polymer network by blending a high-performance polyurethane (PU) polymer with a low-cost phenolic rigid foam. i
Developed scientists at the Indian Institute of Chemical Technology (1ICT), Hyderabad, have developed. The researchers developed the substitute using cashew nut shell liquid and castor oil a* raw materials.
The Institute is trying to cut down costs in the area of door and frames. It first developed frames from magnesium oxy-choloride cement and sawdust, which although economical, suffered from a major drawback: they were not water-resistant.
The scientists then turned to frames made from saw dust, using organic resins as binders. which were found lo have the same density, and flexural and compressive strength as normal wood, and reasonably good nail, screw-and paint-holding properties.
The quality of these frames was markedly improved after lamination with plywood or sunmica. The lamination, which docs not require any extra bindir also protects the core material from water and weather changes, according to a report by CBRJ -scientist Dr Y Singh, which was presented at the symposium.
CBRJ is now working on an even more wood-saving concept — use no frames at all. For low-cost housing. Its scientists have developed substitute panels which can be fixed directly into the walls with the aid of bolts and screws.
The institute ha* also Identified about 400 secondary species of wood, such as mango and eucalyptus, which can be used for building construction without affecting the quality in any way, Dr H C Mital. assistant director at CBRI. told PTI.
Scientists of the Regional Research Laboratory, Bhopal, advocate the use of red mud. and Industrial waste available in large quantities 1n India as a filler In polyester resin. Flat sheets prepared from compos Ites of red mud in polyester resin could be used as switch board and as strips for electrical fitting*.
— PTI Science Service