Civil Engineering Reference
In-Depth Information
have provided a basis of study for the sustainable properties of vegetable fibrous
insulations that are used and examined today. Based on these requirements, veg-
etable fibrous materials sustainable properties are presented below.
4.2 Insulating Properties
As described previously, porous fibres have the void structures which make them
very good at reducing heat, sound, electrical and chemical transfer. They are at low
thermal conductivity due to the trapped air or gases in the void pores and hollow
lumens. Therefore, they are naturally resistant to heat losses through both con-
duction and convection. Their cellulose contains many polar hydroxyl groups
which make fibres structurally strong and resistant to chemicals.
The thermal conductivity range of all vegetable fibres is 0.29-0.32 W/m.K
(Wallenberger
2004
) with large specific heat capacity of the order of 1900 J/kg. K
(Mussig
2010
). Therefore, they make a good thermal insulation. Furthermore,
approximately constant conductivity is observed for most vegetable fibrous insu-
lators over a large range of temperatures. This thermal property plays an important
role in extreme temperatures. Thus, under extreme cold and hot conditions, they
outperform many other types of insulators, for example, fibreglass and mineral
fibres, with more consistent R-value (ASHRAE ''Handbook of Fundamentals'',
BNL 50862).
The densities of vegetable fibres lie roughly in the 1.25-1.51 g/cm3 (Beckwith
2003
) which are of the same order as those of plastics and only half of those of
glass fibres (Natural-fibre-reinforced polyurethane microfoams, Andrzej K. Bled-
zki). They are light weighted, flexible and easily to shape which possess the
greatest potential for lightweight construction. Lightweight construction is a trend
that is present in building construction industry. Furthermore, when vegetable
fibres are used as natural fibre insulations, such as hemp, woodfibre and cellulose,
high densities can be achieved (Crosson
2012
). These features can be combined
effectively to provide good indoor temperature control through reducing temper-
ature fluctuations in order to prevent overheating or cooling.
Overall, vegetable fibres generally give good thermal protection. However, they
suffer low thermal stability in terms of the possibility at moderate temperature
230-250 C thereby have the drawback of low thermal processing temperatures,
which in turns affect the qualities of the reinforced composites due to inadequate
bond strength between fibre and matrix (Cristaldi et al.
2010
).
4.3 Combustion Properties
Most natural cellulosic fibres absorb oxygen readily and burn rapidly owing to
their cellulosic structures. Cotton and flax, for example, can smoulder for weeks
inside their bales without discovering it. They have poor fire resistance. Therefore,
