Evaluation of the thermal comfort performance of different knitted fabrics and fibre blends suitable...

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

skin layer of firefighters’ protective clothing

Nazia Nawaz, OlgaTroynikovRoyal Melbourne Institute of Technology, Australia

1Corresponding author: [email protected]

RMIT University©2008 Information Technology Services 2

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 is

usually worn over an undergarment (skin layer).


Firefighting and thermal comfort

• Firefighting is an exhaustive physical task which generates body heat, also in

addition extremely hot working environment results in substantial elevation of

body core temperature.

• To reduce that temperature to normal, the body perspires in liquid and vapour

form. For better control of body temperature in keeping it a normal level the

evaporation of perspiration is necessary.

• Thermal comfort of human body is maintained by perspiring both in vapour and

liquid form and moisture transmission through clothing has a great influence on

its thermal comfort


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 properties

Thermal 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


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 1×1 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 Facta Universities 1(4): 101-106.Özdil, 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.


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 base layer." 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.


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 firefighter’s protective clothing

• The assessment and ranking of their thermal and moisture management

performance.


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


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 195–2009.

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

http://www.sdlatlas.com/media/uploads/highres/M290-1.jpg


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)


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

the transport of liquid moisture, which includes three aspects

1. 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 195–2009, the indices are graded and

converted from value to grade based on a five grade scale (1–5). The five

grades of indices represent:

1 – Poor

2 – Fair

3 – Good

4 – Very good

5 – Excellent

Moisture management tester indices


Table 1. Grading of MMT indices


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


Fabrics’ thermal resistance

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

temperature is set to 20 C 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,

Rct is the total thermal resistance plus the boundary air layer measured

in m² K/W,

A, the area of the test section in m²

Ts, the surface temperature of the plate in K

Ta, the temperature of ambient air in K

H, the electrical power in Watts


Fabrics’ water vapour resistance

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

at 35 C and relative humidity is controlled at 40%.After a steady state is

reached, the total evaporative resistance of the fabric is calculated by:

HPaPsAt /)(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 Pa

H, the electrical power in Watts

(2)


Fabric code

Fibre composition

Construction Fabric weight(g/m2)

Fabric thickness

(mm)

No. of wales/c

m

No. of courses /

cm

SJ1 100% Merino wool

Single Jersey 139 0.35 18 18

SJ2 60% Merino Wool/ 40%

Bamboo


SJ3 100%Cotton Single Jersey 149 0.47 19 15

SJ4 94% Merino wool/ 6% spandex


IM1 100%Polyester

Interlock based mock mesh

168 0.61 16 16

IM2 52% Merino wool / 48%

Biophyl

Interlock based mock mesh

216 0.97 16 12

Results and discussion

Table 2. Physical and structural properties of sample fabrics


Moisture Management 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

SJ4CV

3.2811.084

29.2741.064

7.1530.046

6.8530.181

50

100

3.1311.035

1.1540.043

500.7140.033

0.5210.057

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



0

1

2

3

4

5

Gra

de

Top WTt Grade 2 3 2 4 2 1.5

Bottom WTb Grade 2 3.5 3.5 2 2 4

SJ1 SJ2 SJ3 SJ4 IM1 IM2

Figure 5. WTt and WTb grades of sample fabrics

0

0.5

1

1.5

2

2.5

3

3.5

Gra

de

Top ARt grade 1 1 1 1 3 1

Bottom ARb grade 1 1 2 1 1 1


Figure 6. ARt and ARb (%/sec) grades of sample fabrics



0

0.5

1

1.5

2

2.5

3

3.5

Gra

de

Top MWRt grade 1 2.5 3 1 1.5 1

Bottom MWRb grade 1 2.5 3 2 1.5 1.5


Figure 7. MWRt and MWRb (mm) grades of sample fabrics

0

0.5

1

1.5

2

2.5

3

3.5

4

Gra

de

Top SSt mm/sec grade 1 1.5 1 3.5 1 1

Bottom SSb mm/sec grade 1 3.5 2 2 1 1


Figure 8. SSt and SSb (mm/sec) grades of sample fabrics



0

1

2

3

4

5

6

Gra

de

AOTI % 4 3 3 5 3 5

OMMC 3 2 2 4 2 3


Figure 9. AOTI % and OMMC grades for sample fabrics

These results show that SJ1, SJ4 and IM2 have better moisture management properties as compared to the other sample fabrics of the study. These three fabrics are composed of 100% wool, wool/spandex and wool/biophyl and having single jersey structures



Thermal properties (Thermal and vapour resistance)


0.009 0.008 0.007

0.0110.013

0.029

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035


Fabric code

Mea

n R

ct

Mean Rct (m²K/W)

Figure 10. Thermal resistance (Rct) of sample fabrics


2.093 1.994 2.1232.44

2.861

4.955

0

1

2

3

4

5

6


Fabric code

Mea

n R

et

Mean Ret (m² Pa/W)


Figure 11. Water vapour resistance (Ret) of sample fabrics


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 perspires

heavily 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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Evaluation of the thermal comfort performance of different knitted fabrics and fibre blends suitable...

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