There are two kinds of fire protection systems in buildings, active and passive fire protection systems, which are an integral part of any modern-day building to protect lives and assets by enhancing the fire prevention and protection techniques [1
]. The active fire protection system includes a fire or smoke alarm, sprinkler, and fire extinguishers. However, this system has required some actions to work efficiently in the event of a fire and this might fail due to lack of maintenance or other possible problems such as frozen pipes and inadequate water pressure. Whereas passive fire protection (PFP) system includes fire or smoke dampers, fire doors, and firewalls. This PFP system plays an essential role to provide fire safety protection by using flame-retardant materials. Therefore, with regards to this research, a new and innovative fire-resistant timber door is incorporated with the intumescent flame-retardant coating (IFRC) that acts as an effective PFP system and its potential application for lightweight fire-rated timber door. The intumescent coating reacts under the influence of fire and swells in a controlled manner to many times its original thickness, and thus produces an insulation carbonaceous char or foam that protects the substrate from the effects of the fire [2
]. By such effectiveness, intumescent coating plays a critical role in protecting the building, and it may also gain extra time for building occupants to escape safely during the outbreak of fire by trapping the fire and smoke as well as insulating the heat.
IFRCs can either be coated as a thin film or act as a binder of PFPs to enhance the fire-resistance performance. Boards are rigid prefabricated materials that usually come along with hydraulic binders [3
]. Common fire doors are made of magnesium oxide boards, gypsum boards and even heavy timber wood [4
]. However, there is one common problem in all the existing commercial fire doors which is their high density [7
]. According to Fire Industry Association, due to the sheer weight and force produced when the heavy fire doors are opened and closed (density > 1200 kg/m3
], it may cause human injury especially in places such as residential care or nursing homes.
In this research study, intumescent coatings and lightweight flame-retardant materials such as vermiculite and perlite are used to construct the lightweight fire-resistant timber door prototypes (density is about 600 ± 50 kg/m3
) for 2-h fire rating. Intumescent paint is the recent trend in fire retarding products in construction building materials because of its many beneficial properties such as providing low-odor, lightweight, and is environmentally friendly. Exhaustive investigations have revealed that the intumescent flame retardant coating has achieved good flammability and physical and chemical performances though many linger widely on steel structure applications [9
]. Up to today, the performance of fire-resistant boards has yet to be tested and investigated with the addition of intumescent fire protective coating for the development of a fire-resistant timber door. Furthermore, this research project has also highlighted huge potential for incorporating the intumescent coating composites, which consists of three main flame-retardant additives, namely ammonium polyphosphate (APP), an acid source; pentaerythritol (PER), a carbon source; and melamine (MEL), blowing agents, into the fire door. These are mixed in a weight ratio of 2:1:1 and are bonded together with flame retardant fillers and vinyl acetate (VA) copolymer as well as vermiculite and perlite which react together to form a protective thermal barrier at high temperature in fire doors [13
]. It is important to note that flame-retardant additives are useful chemical compounds for fire retardant to provide varying degrees of flammability protection. A research study conducted by Xia and his co-workers has stated that adding too much APP into the intumescent formulation may reduce the mechanical properties of the intumescent coating. Hence, an appropriate ratio of APP/PER/MEL should be set prior to the development of intumescent coating [14
]. One of the ingredients, titanium dioxide (TiO2
), is important to formulate an intumescent coating in which it does not only provide the usual properties of colour and opacity, but it also likely takes place in the intumescence process which stabilizes the insulating foam at high temperatures when most of the carbon oxidizes and burn off [15
]. Besides that, polymer binder is also one of the final key materials to produce a uniform cellular structure to provide good thermal insulation. In a research study conducted by Wang and Yang, the influence of the binder, vinyl acetate (VA), copolymer emulsion in the water-based coating is used to minimize the smoke and toxic fume emission without compromising the quality and effectiveness of the intumescent coating in fire protection [16
In addition to that, vermiculite and perlite act as flame-retardant materials promoting a very low density, high porosity, good thermal insulation properties, chemical inertness, and good fire-retardant materials. This makes them attractive to be used widely as pore-forming additives for heat insulation applications [17
]. Moreover, the uniqueness of the materials can insulate the heat from the fire by expanding with small particles under high temperatures. Besides that, a highly porous aggregate that can absorb moisture in varying degrees, the presence of moisture in the aggregate would turn into steam and evaporate from the materials during a fire test, and this will extend the fire duration [18
]. As mentioned, the performance of the IFRC is based on the appropriate materials combination and the compatibility of the flame-retardant fillers with a polymer binder. Therefore, it is essential that the flame-retardant fillers provide good fire protective performance and fire retarding efficiency properties [19
]. The grouping of aluminium hydroxide, Al(OH)3
; calcium silicate, CaSiO3
; magnesium hydroxide, Mg(OH)2
; chicken eggshell (CES) powder (bio-filler derived from CES waste); and calcium carbonate, CaCO3
is used in this research project [20
]. This project aims to formulate an appropriate combination of intumescent flame-retardant coating for the development of fire-resistant timber door prototype. The performances of fire protection, mechanical, chemical and physical properties of intumescent flame-retardant coatings are evaluated and investigated. This research work is intended to design, fabricate, and examine the fire-resistant timber door prototype by incorporating intumescent fire-protective coating in order to fulfil the 2-h fire rating.
From the series of experimental tests, the following conclusions can be deduced. The selection of suitable combinations of flame-retardant materials can directly affect the fire-protective performance and the mechanical properties of the intumescent flame-retardant coating as well as the fire door prototype. Amongst all the coating samples used/manufactured in this research project, the coating J2 with the addition of 3 wt.% of aluminum hydroxide and 3 wt.% of renewable CES bio filler is concluded to have the best fire-protective performance, thermal, mechanical, physical, and chemical properties. On top of that, the P2 prototype with the addition of J2 intumescent coating reveals to a better fire protective result (temperature reduction by up to 54.9 °C), as compared to the existing commercial fire-resistant timber door prototype.
To summarize the conclusions based on the experimental results, an innovative intumescent flame-retardant paint incorporated into the lightweight fire-resistant timber door prototype (P2) has indeed demonstrated to be more efficient in reducing the heat transmission by maintaining its integrity without showing a significant leakage against the 2-h fire test.