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    Evaluation of the thermal comfort performance ofdifferent knitted fabrics and fibre blends suitable for skin

    layer of firefighters protective clothing

    Nazia Nawaz, OlgaTroynikov

    Royal Melbourne Institute of Technology, Australia

    1Corresponding author: [email protected]

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    Introduction

    Protective clothing is required to shield the wearers from a variety of

    hazardous environments or extreme conditions encountered by humans in

    some industries, military or firefighting.

    Firefighters protective clothing Firefighters protective clothing plays a vital role for their protection against

    heat, hot liquids, chemicals and mechanical impacts.

    The protective clothing facilitates the firefighter to approach the fire to

    rescue people from fire and to fight the fire.

    Modern firefighters clothing is a multi-layered garment assembly which isusually worn over an undergarment (skin layer).

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    Firefighting and thermal comfort

    To provide thermal comfort to the human body the garment next to skin must

    have three important attributes: to absorb

    Heat

    Vapour

    Liquid perspiration from skin and

    then transfer these to the outside of the garment

    Thermal comfort and fabric propertiesThermal comfort properties of textile fabrics are actually influenced by

    the type of fibre

    spinning method of yarns

    yarn count

    yarn twist yarn hairiness

    fabric thickness,

    fabric cover factor

    fabric porosity and finish

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    Background

    Milenkovic et al. (2009) demonstrated that fabric thickness, enclosed still air

    and external air movement are the major factors that affect the heat transfer

    through fabric.Ozdil (2007) experimentally verified that yarn properties such as yarn count,

    yarn twist and spinning process influence thermal comfort properties of 11 rib

    knitted fabrics. He verified that,

    The 1 1 rib fabrics produced from finer yarns showed lower thermal

    conductivity and higher water vapour permeability values than coarser

    yarns counts.

    Combed yarn showed the higher water vapour permeability

    By increasing yarn twist used for 1 1 rib fabrics , thermal and water

    vapour permeability of the fabrics was also increased.

    Thermal resistance values decreased as the twist coefficient of yarn

    increased. Thermal resistance values of fabrics knitted with combed

    cotton yarns were lower than the fabrics knitted with carded cotton yarns.Milenkovic, L., Skundric, P., Sokolovic, R., Nikolic, T., (1999). "comfort Properties of Defence Protective clothing." The scientific Journal FactaUniversities 1(4): 101-106.zdil, N., A. MarmaralI, et al. (2007). "Effect of yarn properties on thermal comfort of knitted fabrics." International Journal of Thermal Sciences

    46(12): 1318-1322.

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    Background

    Arzu Marmarali (2009) studied thermal comfort properties of blended yarns

    and knitted fabrics of Cotton /Soybean fibres and Cotton/Seacell fibres in

    different blend ratios and found that,

    The thermal resistance value of 100% cotton fabric was significantly

    higher than whole blended materials.

    50/50% blend ratio of both fabrics (Co/Seacell, Co/Soybean) had the

    lowest thermal resistance values than the other blend ratios and that was

    due to lower fabric thickness value of 50/50% Co/SeaCell and

    Co/Soybean fabrics. Therefore with the decreasing of fabric thickness,

    thermal resistance decreases.

    Troynikov et.al (2011) studied moisture management properties of wool/

    polyester and wool/bamboo knitted in single jersey fabrics for the

    sportswear base layers and concluded that,

    Blending wool fibre with polyester fibre and, in particular, wool fibre with

    regenerated bamboo fibre, improved moisture management properties

    than fabrics in wool fibre or regenerated bamboo fibre without blending.

    Troynikov, O., et all, Wiah, W., (2011). "Moisture management properties of wool/polyester and wool/bamboo knitted fabrics for sportswear baselayer." Textile Research Journal 0: 1-11.Arzu Marmarali, M. B., Tuba Bedez Ute, Gozde Damci (2009). Thermal comfort Properties of Blended Yarns Knitted Fabrics. ITMC. Casablanca,

    Morocco.

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    Objective of the study

    The Objective of present study is:

    To evaluate thermal and moisture management properties of six commercially

    available knitted fabrics of different fibre blends and knitted structures for

    skin layer garments of firefighters protective clothing The assessment and ranking of their thermal and moisture management

    performance.

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    Materials and methods

    Following are six commercially available knitted fabrics having different

    fibre content and knit structure that were evaluated

    100% Merino wool

    60% Merino Wool/ 40% Bamboo

    100%Cotton

    94% Merino wool/ 6% spandex

    100%Polyester

    52% Merino wool / 48% Biophyl

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    Fabric physical properties

    Fabric mass per unit area (gram / meter square)

    Fabric thickness (mm)

    Fabric density (No. of wales/cm and No. of courses/cm)

    Fabric Moisture management properties

    For evaluation of fabrics moisture management properties Moisture

    Management Tester (MMT) was used according to American Association

    of Textile Chemists and Colourists (AATCC) Test Method 1952009.

    Figure 1. Moisture management tester Figure 2. Schematic view of tester sensors

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    Moisture management tester indices

    A series of indexes are defined and calculated to characterize liquid

    moisture management performance of the test sample by using moisture

    management tester, which are as follow;

    Top wetting time WTt and bottom wetting time WTb Top absorption rate (ARt) and bottom absorption rate (ARb)

    Top max wetted radius (MWRt) and bottom max wetted radius (MWRb)

    Top spreading speed (SSt) and bottom spreading speed (SSb)

    Accumulative one-way transport index (AOTI) and overall moisture

    management capacity (OMMC)

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    The OMMC is an index indicating the overall capacity of the fabric to manage

    the transport of liquid moisture, which includes three aspects1. Average moisture absorption rate at the bottom surface

    2. One-way liquid transport capacity

    3. Maximum moisture spreading speed on the bottom surface

    The larger the OMMC is the higher the overall moisture management ability of

    the fabric is.According to AATCC Test Method 1952009, the indices are graded and

    converted from value to grade based on a five grade scale (15). The five

    grades of indices represent:

    1 Poor

    2 Fair3 Good

    4 Very good

    5 Excellent

    Moisture management tester indices

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    Table 1. Grading of MMT indices

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    Fabric thermal properties (Thermal and water vapour resistance)

    Thermal resistance and water vapour resistance of fabrics were

    evaluated using sweating guarded hot plate according to ISO 11092.

    Sweating guarded hot plate is able to simulate both heat and moisture

    transfer from the body surface through the clothing layers to the

    environment. It measures both the thermal resistance (insulation

    value) and water vapour resistance of fabrics.

    Figure 3. Sweating Guarded Hot Plate Figure 4. Schematic diagram of sweating guarded hot plate

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    Fabrics thermal resistance

    For the determination of thermal resistance of the sample, the air

    temperature is set to 20 rC and the relative humidity is controlled at 65%.

    Air speed generated by the air flow hood is 1 m/s. After the system

    reaches steady state, total thermal resistance of the fabric is governed by:

    HTaTsARct /)( ! (1)

    Where,

    Rctis the total thermal resistance plus the boundary air layer measured

    in m K/W,

    A, the area of the test section in m

    Ts, the surface temperature of the plate in K

    Ta, the temperature of ambient air in K

    H, the electrical power in Watts

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    Fabrics water vapour resistance

    To measure the water vapour resistance of the fabric air temperature is set

    at 35 rC and relative humidity is controlled at 40%.After a steady state isreached, the total evaporative resistance of the fabric is calculated by:

    HPaPst /)(Re !

    Where,Ret, is total vapour resistance provided by liquid barrier, fabric and

    boundary air layer measured in m2KPa/W)

    A, the area of test section in m2

    Ps, the water vapour pressure at plate surface in Pa

    Pa, the water vapour pressure of the air on PaH, the electrical power in Watts

    (2)

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    Fabriccode

    Fibrecomposition

    Construction Fabricweight(g/m2)

    Fabricthickness

    (mm)

    No. ofwales/c

    m

    No. ofcourses

    /cm

    SJ1 100% Merinowool

    Single Jersey 139 0.35 18 18

    SJ2 60% Merino

    Wool/ 40%Bamboo

    Single Jersey 156 0.34 16 16

    SJ3 100%Cotton Single Jersey 149 0.47 19 15

    SJ4 94% Merinowool/ 6%spandex

    Single Jersey 185 0.55 20 20

    IM1 100%Polyest

    er

    Interlock based mock mesh 168 0.61 16 16

    IM2 52% Merinowool / 48%

    Biophyl

    Interlock based mock mesh 216 0.97 16 12

    Results and discussion

    Table 2. Physical and structural properties of sample fabrics

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    MoistureManagement Properties of sample fabrics

    Table 3. MMT results in value

    Fabric code WTt(sec)

    WTb(sec)

    ARt(%/sec)

    ARb(%/sec)

    MWRt(mm)

    MWRb(mm)

    SSt(mm/sec)

    SSb(mm/sec)

    AOTI(%)

    OMMC

    SJ1CV

    63.3121.265

    50.5151.343

    3.6711.414

    5.1170.290

    2.51.414

    51.414

    0.3651.414

    0.9591.414

    319.1820.011

    0.4480.112

    SJ2CV

    7.8830.071

    5.0000.137

    8.1520.236

    5.9250.114

    12.50.282

    12.50.282

    1.2860.097

    3.1020.098

    133.3960.251

    0.3790.030

    SJ3CV

    41.2550.249

    5.4160.979

    8.0610.194

    14.2860.276

    13.333

    0.216

    13.3330.216

    0.3490.419

    1.6000.614

    102.1180.394

    0.2440.383

    SJ4

    CV

    3.281

    1.084

    29.274

    1.064

    7.153

    0.046

    6.853

    0.181

    5

    0

    10

    0

    3.131

    1.035

    1.154

    0.043

    500.714

    0.033

    0.521

    0.057

    IM1CV

    30.6171.165

    47.0631.242

    39.8940.953

    5.2000.548

    7.50.471

    7.50.471

    0.9471.280

    0.9411.329

    102.3990.283

    0.2030.397

    IM2CV

    119.9530

    3.8350.250

    00

    5.0690.561

    00

    7.50.471

    00

    0.8980.091

    434.1050.184

    0.4870.036

    Results and discussion

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    0

    1

    2

    3

    4

    5

    Gra

    e

    Top

    Tt rade 2 3 2 4 2 1 5

    ottom

    Tb rade 2 3 5 3 5 2 2 4

    S 1 S 2 S 3 S 4 IM1 IM2

    Figure 5 Tt and Tb grades of sample fabrics

    0

    0 51

    15

    2

    25

    3

    35

    Gra

    e

    Top

    Rt grade 1 1 1 1 3 1

    ottom

    Rb grade 1 1 2 1 1 1

    S

    1 S

    2 S

    3 S

    4 IM1 IM2

    Figure 6 Rt and Rb (%/sec) grades of sample fabrics

    Results an iscussion

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    0

    2Grade

    A TI

    MM 2 2 2

    S S 2 S S IM IM2

    Figure 9. A TI and MM grades for sample fabrics

    These results show that S , S and IM2 have better moisture managementproperties as compared to the other sample fabrics of the study. These threefabrics are composed of 00 wool, wool/spandex and wool/biophyl and

    having single jersey structures

    Results and discussion

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    Thermal properties (Thermal and vapour resistance)

    Results and discussion

    0.00 0.008 0.00

    0.0110.01

    0.02

    0

    0.00

    0.01

    0.010.02

    0.02

    0.0

    0.0

    S 1 S 2 S S IM1 IM2

    Fabric code

    MeanR

    ct

    Mean Rct (m / )

    Figure 10. Thermal resistance (Rct) of sample fabrics

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    2.0 . 2. 22.

    2.8

    .

    0

    2

    SJ SJ2 SJ SJ IM IM2

    Fab i e

    MeanRet

    Mean Ret m a/

    Results an is ussi n

    Figure . ater vapour resistance Ret of sample fabrics

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    Conclusion

    The results and discussions demonstrate that

    wool and wool blends are the most suitable fabric to be used next to

    skin to achieve thermal comfort

    The fibre content, fabric construction and fabric thickness influence

    thermal comfort significantly.

    Therefore it can be concluded that 100% wool and wool blends with

    spandex and bamboo (SJ1, SJ2 and SJ4) in single jersey structure are more

    suitable to use next to skin than SJ4, IM1 and IM2.

    100% cotton in single jersey structure can also be a good choice because it

    has lower thermal and water vapour resistance like SJ1, SJ2, and SJ3 but

    not in extremely hot environments like firefighting where body perspiresheavily in liquid form and cotton is unable to provide better liquid moisture

    transfer properties like wool and wool blends to keep skin dry.

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