3.2. Effect of temperature on composites
Fig. 13 displays the mean weekly variation of temperature
in the composite material. It can be observed
that it does not exceed 50 C. Normally, the temperature
will affect the property of natural fiber based construction
material when a temperature of about 75 C or
above is reached. Durian fiber based lightweight construction
material was composed of fibers from durian
peel. Cellulose content in the durian peel is quite high, as
shown in Table 1. The decomposition of cellulose in an
alkaline environment can take place in accordance with
different mechanisms (Shafiq et al., 1988). One is the
peeling-off mechanism which occurs at the end of the
molecular chain. Since the degree of polymerization of
cellulose of many natural fibers is high, about 25,000,
the peeling-off mechanism is fairly harmless in itself.
Peeling-off is said to occur within a wide temperature
interval but the rate does not become markedly high
until a temperature of about 75 C or above is reached.
The other form of cellulose decomposition consists of
alkaline hydrolysis. This is caused by the molecular
chain to divide and the degree of polymerization is decreased.
Since the division of the molecular chain entails
the exposure of new end groups, the peeling-off mechanism
can be started. Alkaline hydrolysis does not take
place at a high rate until the temperature is in excess of
100 C is present. Thus the primary causes of the change in the characteristics of the natural fibers in the composite
material are due to the chemical decomposition of
lignin and hemicelluloses. The alkaline pore water in the
composite dissolves lignin and hemicelluloses and thus
breaks the link between the individual fiber cells. On the
other hand, temperature in the durian fiber based construction
material is not high; therefore, the long term
durability of the composite is possible.
The mean weekly variation of temperature at different
positions in the mortar is shown in Fig. 14. When
compared to the common construction material mortar,
mean weekly variation relative humidity of durian fiber
based lightweight construction material is not much
different to mortar.
The mean weekly variation of temperature at different
positions in the materials coated with resin finishing
is shown in Figs. 15 and 16. Here too, they are not much
different compared to material without coating.