Wood is the primary component of Philippine households today. Currently, it takes five minutes for the wood to burn, what if we can prolong it to 30 minutes?

For years, man has searched for ways to enhance the resistance of wood to burning and flame spread. The chemical structure of wood, made up mainly of carbon and hydrogen, makes it highly combustible or easy to burn. There are three elements involved in a combustion reaction: fuel, an oxidizer, and a source of heat. When these three elements are combined in the appropriate environment, combustion or burning will occur.

Flame retardants are substances added or a treatment applied to a material in order to suppress, significantly reduce or delay the combustion of a material. Many fire-retarding techniques have already been established, namely: surface treatment with fire-retardant chemicals such as fire resisting coatings, pressure impregnations or input of chemical solutions into wood and even cutting-edge technologies of adding nanocomposites during product manufacturing processes. Nonetheless, these methods need a large capital and the processes are complicated.

Plasma treatment of wood provides a sterile procedural environment in that hazardous chemical components are ionized and decomposed into simple compounds. Thus, the technique is more friendly to the ecosystem compared with direct chemical treatment of wood. The method is advantageous in that it is straightforward, relatively inexpensive, and does not involve heating and high vacuum requirements.

The main purpose of this research was to obtain an improved fire endurance of wood products. Known flame retardants were impregnated in the samples and compared with direct application and vacuum/pressure application of flame retardants.

Plywood samples served as test samples. The surface of the plywood was cleaned with sand paper to ensure uniform surface and freedom from residues. After this, samples were placed inside the Plasma Enhanced Chemical Vapor Deposition (PECVD) facility for vacuum treatment. The device is powered by ordinary electricity which operates under reduced or low-pressure conditions.

Vacuum treatment of wood reduced the moisture content in the pores of the wood and can physically remove organic materials. It has no effect on the chemical structure of the sample.

Boric acid, phosphoric acid and a commercial flame retardant solution were compared. Boric acid and phosphoric acid are both non-flammable and have been known for their insecticidal properties.

For the first chemical treatment, the acid was directly painted over the surface of the untreated wood sample. For the vacuum impregnation and plasma treatment by PECVD, the solutions were placed in a stainless steel cylinder which is connected to the main chamber.

To determine the effects of the solutions on the wood surface, two methods were performed.

The wood samples were exposed to known flame retardants such as boric acid, phosphoric acid and commercially available flame retardant solution and/or reactive gases, such as high purity hydrogen and high purity nitrogen for 30 minutes with varying discharge currents.

Hydrogen was also tested since it was said to inhibit flammability. Nitrogen was also investigated since it is said to increase the effectiveness to flame retardants, especially when combined with other chemicals such as boron and phosphorous compounds.

To ensure that the test samples were not subjected to heating, the temperature was monitored throughout the process. The samples were exposed to flame continuously and then removed upon ignition.

Flame endurance of wood samples was increased using chemical and plasma treatment. The chemical treatment involved the conventional method of spraying the solution over the wood surface at atmospheric condition and chemical vapor deposition in a vacuum chamber. In the plasma treatment, wood samples were immersed in reactive plasmas composed of various ratios of flame retardant solutions and/or reactive gas.

Based on results, chemical treatment by exposure to vapor was found to be more effective compared with the direct application. However, comparing the chemical treatment and plasma treatment, the higher current phosphoric acid plasma treatment was found to yield superior thermal stability and flame retardant properties in terms of the highest onset temperature and temperature of maximum pyrolysis (decomposition of organic material at elevated temperatures in the absence of oxygen). Plasma treatment can reduce flammability of wood by retarding the penetration and spread of flame from an incipient fire. Adding nitrogen to flame retardant agents such as phosphoric acid and boric acid increases the effectiveness of the flame retardant used. Increasing the discharge current upon plasma impregnation of flame retardant does not necessarily reduce the inflammability of the sample further.

The plasma treatment retards the flammability for about seven times compared with the untreatable sample.


Written by: 
Henry J. Ramos, Karel G. Pabelina, Carmencita O. Lumban, Camille Faith P. Romero, Jhoelle Roche Guhit and Joanna A. Dasco
University of the Philippines Diliman

Published by:
The Department of Science and Technology-Science and Technology Information Institute (DOST-STII)