Civil Engineering Reference
In-Depth Information
structures. Due to the evolution and adaptation to changeable conditions in nature,
their structures are hierarchically organized and optimized with multifunctions
which make them outperform man-made synthetic insulation in strength, dura-
bility, and thermal and moisture performances. Most natural fibres are hygroscopic
in nature and they absorb and release moisture depending on environments which
can reduce the condensation and mould risks through careful design process. They
also have the unique ability to absorb volatile organic compound gases and lock
them up permanently which reduces health risks. These unique features as
''breathable'' materials are especially important in achieving NZEB/ZEB goal as
the use of thick and very airtight insulation, or even super insulation, is an essential
solution in zero energy buildings. Very thick insulation tends to increase the
moisture levels of the constructions and the risks of condensation, mould, mildew
and structural damages if it is not designed or installed properly. Therefore, these
good features, such as breathable and moisture-absorbable, plus low processing
costs make vegetable fibres by far the most common materials used in insulation
market (Crosson
2012
).
However, the strong ability to absorb water means that vegetable fibres are
prone to becoming saturated or swelling to mould growth and the structures may
gradually deteriorates. Their hydrogen bonds account for fibres' strong ability to
absorb water. Due to hydrogen bonding of water molecules to the hydroxyl groups
within the fibre cell wall and fibre-matrix interface (Rowell
1997
), natural fibres
can contain high moistures which support mould growth. Some moulds are known
human pathogens and found in natural vegetable fibres and fibre-processing plants
(Forgacs et al.
1972
). Generally, borates are added to the vegetable fibres acting as
a fungicide, insecticide and fire retardant in the insulation manufacturing process.
Note that processing of natural fibres must be also designed to be green and
chemical free simultaneously to ensure a sustainable manufacturing process for
green insulating products, which entails challenges. Therefore, an understanding of
the performance of vegetable-based fibres from growing the plants to the manu-
facture of insulating products by researchers is of growing importance. Such
knowledge is critical to the design and control of energy-efficient and sustainable
buildings because insulation in buildings is not independent unit, but part of the
building system.
This chapter presents an update of literature reviews on vegetable-based fibres,
composites and their physical, mechanical and chemical characteristics incorpo-
rating building thermal insulating properties with recommendations and sugges-
tions. Subsequently, relevant issues of the raw materials and the manufacturing
processes that lead to certain common characteristics are highlighted. The greatest
challenge in working with vegetable fibres is their large variations in thermal
properties and characteristics dependent on their complex architectures of geo-
metrical structures. Mathematical models critical to understanding and predicting
the thermal performances of the fibres and their global responses in the building
system as insulation systems are an important part of building systems. Therefore,
heat and mass transfer through fibrous insulations in buildings is briefly presented
since the basic theories and models associated with fibrous insulations do not differ
