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2 Review of Literature: Motorcycle helmet
this, they can be pumped in a closed loop that can transport more heat than water
alone. Subsequent work by them led to the development of the first non-toxic PCM
coolant, which produced a tenfold increase in the system’s effective fluid capacitance
and a twofold increase in the heat transfer coefficient under isothermal conditions
[223].
Aqueous-based non-toxic micro-PCM coolant was used for the cooling of spacesuits used by NASA [224]. The thermal stability of microencapsulated n-octadecane
was improved by using different mole ratios of urea-melamine-formaldehyde copolymers as shells [225]. It has been shown that 163 °C is the highest thermal stable
temperature of microcapsules with a diameter range of 0.4–5.6 µm and with a ureamelamine-formaldehyde mole ratio of 0.2:0.8:3. The core material diffuses out of the
shell due to the expansion of n-octadecane as the temperature continuously increases.
To obtain microcapsules, which are thermally stable up to 200 °C, the microencapsulated n-octadecane is added with cyclohexane in the oil phase and heated at 160 °C
for 30 min.
According to the performance properties and end-use of the finished product, the
proper treatment process for incorporating PCM microcapsules into textiles should
be selected. Hittle and Andre [226] used a loading of 60-wt % for coated fabrics
and observed that the properties of fabrics such as drape, breathability, softness and
tensile strength are adversely affected as the loading increases.
2.14.1 Classification of Microencapsulation
The encapsulation method for PCM to be applied to textiles should be easy, cheap
and robust. Microcapsules of PCM can be encased in one or several shells arranged in
strata of varying thicknesses around the core. Up to now, the main methods employed
for microencapsulation are polymerisation; emulsification; phase separation; spray
drying and grinding, which are discussed in the following sections.
2.14.1.1 Polymerisation
The polymerisation method or chemical method can be classified into interfacial
polymerisation, in situ polymerisation and matrix polymerisation. In the interfacial polymerisation process, the two reactants react rapidly in a polycondensation.
This is based on the classical Schotten–Baumann reaction between an acid chloride and an active hydrogen containing compound such as polyurea or polyester. If
the conditions are suitable, condensed polymer walls are formed at the interface of
the emulsion droplets. Interfacial polymerisation was used to prepare the microcapsules of polyurea for finishing applications, which was stable at curing temperatures
higher than 80 °C [177]. In situ polymerisation consists of the direct polymerisation of a single monomer on the particle surface. One example of this process is the
encapsulation of cellulose fibres in polyethylene. In matrix polymerisation, a core
2 Review of Literature: Motorcycle helmet
this, they can be pumped in a closed loop that can transport more heat than water
alone. Subsequent work by them led to the development of the first non-toxic PCM
coolant, which produced a tenfold increase in the system’s effective fluid capacitance
and a twofold increase in the heat transfer coefficient under isothermal conditions
[223].
Aqueous-based non-toxic micro-PCM coolant was used for the cooling of spacesuits used by NASA [224]. The thermal stability of microencapsulated n-octadecane
was improved by using different mole ratios of urea-melamine-formaldehyde copolymers as shells [225]. It has been shown that 163 °C is the highest thermal stable
temperature of microcapsules with a diameter range of 0.4–5.6 µm and with a ureamelamine-formaldehyde mole ratio of 0.2:0.8:3. The core material diffuses out of the
shell due to the expansion of n-octadecane as the temperature continuously increases.
To obtain microcapsules, which are thermally stable up to 200 °C, the microencapsulated n-octadecane is added with cyclohexane in the oil phase and heated at 160 °C
for 30 min.
According to the performance properties and end-use of the finished product, the
proper treatment process for incorporating PCM microcapsules into textiles should
be selected. Hittle and Andre [226] used a loading of 60-wt % for coated fabrics
and observed that the properties of fabrics such as drape, breathability, softness and
tensile strength are adversely affected as the loading increases.
2.14.1 Classification of Microencapsulation
The encapsulation method for PCM to be applied to textiles should be easy, cheap
and robust. Microcapsules of PCM can be encased in one or several shells arranged in
strata of varying thicknesses around the core. Up to now, the main methods employed
for microencapsulation are polymerisation; emulsification; phase separation; spray
drying and grinding, which are discussed in the following sections.
2.14.1.1 Polymerisation
The polymerisation method or chemical method can be classified into interfacial
polymerisation, in situ polymerisation and matrix polymerisation. In the interfacial polymerisation process, the two reactants react rapidly in a polycondensation.
This is based on the classical Schotten–Baumann reaction between an acid chloride and an active hydrogen containing compound such as polyurea or polyester. If
the conditions are suitable, condensed polymer walls are formed at the interface of
the emulsion droplets. Interfacial polymerisation was used to prepare the microcapsules of polyurea for finishing applications, which was stable at curing temperatures
higher than 80 °C [177]. In situ polymerisation consists of the direct polymerisation of a single monomer on the particle surface. One example of this process is the
encapsulation of cellulose fibres in polyethylene. In matrix polymerisation, a core