Elsevier

Energy and Buildings

Volume 43, Issue 7, July 2011, Pages 1732-1739
Energy and Buildings

New thermal insulation boards made from coconut husk and bagasse

https://doi.org/10.1016/j.enbuild.2011.03.015Get rights and content

Abstract

This study describes the production of low density thermal insulation boards made from coconut husk and bagasse without the use of chemical binding additives. Dwelling in Thailand use thermal insulation to reduce air conditioning loads; the aim of this study was to develop a thermal insulation with lower environmental footprint than conventional materials. The hot pressing method was used and this article reports on the effect of board density and pressing conditions on the properties of the insulation boards. Mechanical properties of the coconut husk and bagasse insulation boards were measured for comparison with the standard employed in Thailand: JIS A 5905: 2003 Insulation Fibreboards. It was found that the bagasse insulation board with a density of 350 kg/m3, using a 13 min pressing time at a temperature of 200 °C, met all of the requirements except for swelling thickness. Thermal conductivity of the coconut husk and bagasse insulation boards was measured according to ISO 8301 and this suggested that both insulation boards have thermal conductivity values ranging from 0.046 to 0.068 W/mK which were close to those of conventional insulation materials such as cellulose fibres and mineral wool.

Highlights

► We produced low density thermal insulation boards from coconut husk and bagasse without binders. ► Thermal conductivities of both thermal insulation boards are close to conventional insulations. ► We evaluate the effects of board density, pressing conditions on board physical properties. ► Board physical properties are improved with increasing density, pressing time and temperature. ► Physical properties of bagasse boards are superior to those of coconut husk boards.

Introduction

The design of residential buildings in Thailand has tended to move away from traditional, climate responsive architecture, towards a design influenced by western architecture. This trend means that dwellings are less able to control the internal environment to comfortable conditions and mechanical air conditioning systems are needed. Energy consumption in the residential sector accounts for approximately 20–25% of annual energy use in Thailand [1] and 65% of this is consumed by mechanical space cooling [2]. Thermal insulation of the building envelope is one of techniques that have been adopted to reduce energy consumed by air conditioning.

Thermal insulation products available in Thailand tend to be manufactured from fibreglass, mineral wool or polyurethane foams. Although these materials have good physical properties, e.g. low thermal conductivity, good moisture protection and fire resistance, they can be hazardous to human health and to the environment [3], [4], [5]. For example, exposure to the small particles from fibreglass and glass wool insulation can cause respiratory or skin irritation [3]. In addition, these materials cannot be found locally; they need to be imported from overseas, primarily the United States [6], which makes them expensive to use in Thailand.

Thailand is an agricultural country: 41% of the total area is used for agriculture [7] and the waste and disposal produced by agricultural industry can be a major problem [8], [9]. One solution to the problem of waste management is reuse rather than disposal or combustion. This article discusses the manufacture of thermal insulation from agricultural waste, thus creating a useful building material [10], [11]. Coconut husk and bagasse were considered to be the raw materials offering greatest potential for manufacture of thermal insulation [12], particularly in the context of Thailand [13]. This is because these raw materials are available within Thailand, and reducing the transportation component of embodied energy gives the potential for an improved environmental profile compared with those that are imported from overseas. In addition the production of insulation materials tends to require use of chemical binders such as formaldehyde or phenolic resins which are toxic to humans; coconut husk and bagasse can be used to manufacture thermal insulation without a binder, a benefit in terms of environmental and health impacts [14], [15], [16], [17], [18].

Coconuts are abundant in coastal areas of tropical countries. The coconut husk is available in large quantities as residue from coconut-fibre mattress production in many areas, which yields the coarse coir fibre. The husk consists of 30% fibre and 70% pith. Both fibre and pith are extremely high in lignin and phenolic content and it has been found that the coconut husk lignin can be used as intrinsic resin in board production [15]. Bagasse, the by-product of sugar production, is now considered to be one of the most promising non-wood lignocellulosic raw materials [19]. Large quantities of this waste are still left unused or burnt in developing countries. Bagasse is rich in celluloses which may act as a binder when making a board [16], [18] and thus bagasse has good potential for the manufacture of binderless thermal insulation boards.Synthetic binders1 (e.g. formaldehyde resins) are normally used for the production of boards such as particleboard and fibreboard. These raw materials are expensive particularly for developing countries like Thailand where the supply of chemical products are limited. It is therefore considered that in the context of Thailand with a surplus of agricultural waste materials, the production of binderless board is the preferred option [17]. While efforts have been made to develop binderless boards by using a high-temperature hot pressing process, it appears that the process can only produce binderless board with high densities [14], [15], [16], [17], [18] whereas thermal insulation requires a low density.

The objective of this study is to develop low density, binderless boards using coconut husk and bagasse as the raw material. Low density boards tend to have lower thermal conductivity than boards with higher density, which makes them more suitable for use as thermal insulation boards. Binderless boards were made using the hot pressing method to investigate the effects of board density, hot pressing conditions (temperatures and times), proportion and size of the raw materials on the properties of the insulation board. The target board densities were relatively low, ranging from 250 to 450 kg/m3.

Section snippets

Raw materials

Both coconut husk and bagasse are rich in cellulose and lignin, which are two major compositions for producing binderless boards [14], [15], [16], [17], [18]. The chemical components of coconut husk (fibre and pith) and bagasse using for the production of binderless boards in this study are shown in Table 1 and these were measured according to the procedures in TAPPI standard2

Board appearance

All the binderless boards were dark brown and had a peculiar smell, especially those boards made from bagasse at high temperature. The dark colour and smell indicate a modification of the chemical components during hot pressing. The binderless bagasse insulation boards had smooth surfaces similar to those of typical MDF board, as a result of the fineness of particles and the strong bonding generated by chemical reaction of the particles.

The actual densities of the test boards were in the range

Conclusions

Binderless insulation boards with a low density of 250–450 kg/m3 were made from coconut husk and bagasse using the hot pressing method. The effects of board density and pressing conditions on the physical properties of the board were evaluated. The results show that the mechanical properties (MOR, MOE and IB strength) of the boards increased with increasing board density, pressing time and temperature. The binderless insulation boards made from bagasse at density of 350 kg/m3 treated at a hot

Acknowledgments

The authors thank the laboratory at the Royal Department of Forestry, Bangkok, Thailand for providing equipment for this study, and Victory Industrial Co. Ltd. and Baan Pong sugar factory for supplying the raw materials.

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