Chemical Preservative Treatment For Bamboo
Bamboo, in spite of its numerous advantages as a substitute for timber and other material suffers from a major drawback viz. that it is prone to biodeterioration. Bamboo is attacked by a number of pests and moulds that both disfigure the products as well as cause more severe damage often rendering it unutilizable for a number of uses
Fortunately several measures can be taken to overcome the problem. The solutions depend on the uses to which bamboo is put to and whether it is exposed to the weather and water.
In this section since only handicrafts are considered, the chemical treatment methods discussed is limited to those that are suitable for products that are used indoors and for decorative/ornamental uses alone.
Traditional treatments against biodeterioration
Submergence in water
The most common treatment against attack by pests is to keep the newly cut culms underwater a few weeks. The starch content in the culm is thus brought down due the activity of enzymes within the cells.
When placed in constant contact with smoke from burning wood the penetration of chemicals results in improving the resistance of bamboo to moulds and pests.
A 10 % Borax –boric acid in 3:2 ratio in water is used for treating bamboo when required in situation where it is not in contact with water or moisture constantly viz. Building, furniture, handicrafts etc. The treatment can be carried out in different ways depending on the scale of operation and the costs
Freshly cut bamboo culms are kept erect for about a week or more in a container containing the chemical solution with the bottom immersed upto 20 cms.
ii. Dip treatment:
For small quantities and especially for items that are small in size a treatment by dipping the product the solution in a small tank or container will be sufficient. A treatment time of several days will be required. Whole culms, split culms and finished products can be treated. Whole culms will require the diaphragm at the nodes to be punctured with a iron rod to permit ingress of the preservative. The solution can be reused several times.
iii. Boucherie method
The method involves replacing the sap in freshly cut culms with the preservative solution by applying pressure using a compressor or a simple hand air pump connected to a reservoir with the preservatives solution or if no such facilities are available with gravity. A rubber tube of sufficient diameter is fixed in the bottom cut end of the culms by means of a wire hose clamp or worm clip so as to form a watertight seal. When pressure ( 20-25 psi) is applied the solution enters the culm and pushes out the sap. In the gravity methods the culms are kept slanting with the tank at the higher end. The sap starts flowing out in a few minutes. The chemical solution emerges from the other end usually within half an hour but treatment is done for about an hour to ensure complete penetration. The culms are then dried and stored protected from rain.
iv. Evapotranspiration method
Freshly cut culms with the branches and leaves intact is left standing with the cut end in a tank of the chemical preservative solution. Due to the transpiration taking place in the leaves the solution is sucked into the culms.
v. Vacuum pressure treatment
For a large scale operations, effective treatment of culms both fresh and dried, a vaccum- pressure treatment plant is ideal. The treatment plant consists of a vaccum-pressure chamber of appropriate size into which the culms are stacked tightly, a vaccum pump to remove the air from the chamber and a tank from which the preservative solution is pumped into the above chamber.
Method for testing the penetration of Boron in bamboo treated with Boric acid – Borax preservatives
It is possible through the following simple test to ascertain if proper penetration of the chemical into all parts of the bamboo tissues has taken place.
Solution 1. 10 grams turmeric is extracted with 90 ml of ethyl alcohol. A clear solution is obtained by decanting or filtration.
Solution 2. 20 ml. of concentrated hydrochloric acid is diluted to 100 ml. with ethyl alcohol and then saturated with salicylic acid (by addition of about 13 grams).
Procedure: The surface of the bamboo must be dry and smooth to get satisfactory results. Solution 1 is applied to the treated bamboo surface with a dropper and allowed to dry for a few minutes . Solution 2 is then applied to the same area which will now be coloured yellow. The yellow color of the turmeric solution is turned red only in treated bamboo, indicating presence of boron.