i

NIST Technical Note 1746 

Accelerated Weathering of Firefighter 

Protective Clothing: Delineating the 

Impact of Thermal, Moisture, and 

Ultraviolet Light Exposures 

Shonali Nazaré 

Rick D. Davis 

Jyun-Siang Peng 

Joannie Chin 

http://dx.doi.org/10.6028/NIST.TN.1746
 ii

NIST Technical Note 1746 

Accelerated Weathering of Firefighter 

Protective Clothing: Delineating the 

Impact of Thermal, Moisture, and 

Ultraviolet Light Exposures 

Shonali Nazaré and Rick D. Davis 

Flammability Reduction Group 

Fire Research Division 

Engineering Laboratory 

Jyun-Siang Peng and Joannie Chin 

Polymeric Materials Group 

Materials and Structural Systems Division 

Engineering Laboratory 

http://dx.doi.org/10.6028/NIST.TN.1746 

June 2012 

U.S. Department of Commerce 

Rebecca Blank, Acting Secretary 

National Institute of Standards and Technology 

Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and Director 
 iii

Certain commercial entities, equipment, or materials may be identified in this 

 document in order to describe an experimental procedure or concept adequately. 

Such identification is not intended to imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor is it intended to imply that the 

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1746 

Natl. Inst. Stand. Technol. Tech. Note 1746, NNN pages (June 2012) 

http://dx.doi.org/10.6028/NIST.TN.1746

CODEN: NTNOEF 
 iv

Abstract 

Previously, the chemical and mechanical deterioration of polyaramid and polybenzimidazolebased protective clothing fabrics that resulted from concurrent thermal, moisture, and 

simulated sunlight exposure were quantified. This manuscript discusses the individual impacts 

of ultraviolet (UV) light irradiation at ambient conditions and moisture and elevated 

temperature in the absence of irradiation on the performance properties of outer shell (OS) 

fabrics used in firefighters’ turnout gear. The mechanical properties which most often 

determine the protective performance of firefighters’ turnout gear, including unidirectional 

stretching, tear resistance, and elastic properties, were tested before and after an accelerated 

weathering process. To assess and compare the protective performance of outer shell fabric 

samples against UV irradiation, the UV protection factor (UPF) was calculated. Attenuated 

Total Reflectance-Fourier Transform Infrared Spectroscopy analysis was used to elucidate the 

chemical changes induced by the weathering process. The data suggests that the deterioration 

in the physical properties of polyaramids and polybenzimidazoles are mainly due to photooxidative reactions, which result in chemical and mechanical deterioration of the fabrics. 

However, the UV exposure has a lesser detrimental effect on the UPF value. 

Keywords 

Accelerated weathering, UV irradiation, moisture effects, firefighters turnout gear, polyaramid, 

polybenzimidazole
 v

This page left intentionally blank. 
 vi

Contents 

List of Tables .......................................................................................................................... vii

List of Figures ........................................................................................................................ viii

List of Acronyms ..................................................................................................................... ix

1. Introduction .........................................................................................................................11

2. Experimental .......................................................................................................................12

2.1. Fabrics ......................................................................................................................... 12

2.2. UV aging and Thermal/Moisture aging ........................................................................ 13

2.3. Mechanical testing ....................................................................................................... 14

2.4. Ultraviolet Transmittance ............................................................................................ 15

2.5. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) .... 15

3. Results and Discussion ........................................................................................................16

3.1. Tear Testing ................................................................................................................ 16

3.2. Yarn Tensile Testing ................................................................................................... 20

3.3. UV Protection Factor (UPF) ........................................................................................ 24

3.4. Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) Spectroscopy .. 27

4. Summary and Conclusions ................................................................................................29

5. References ...........................................................................................................................30
 vii

List of Tables 

Table 1. Standard table for equivalance solar spectral irradiance.[10] ..................................... 14

Table 2. Tear strength and loss of tear strength of NKB and KPB fabrics exposed to varying 

environmental conditions. Uncertainties are reported as with experimental standard deviations.

............................................................................................................................................... 17

Table 3. Tensile strength and % elongation at break for NKB and KPB yarns exposed to 

varying environmental conditions. .......................................................................................... 22

Table 4. Ultraviolet protection factor (UPF) and the average UV transmittance of NKB and 

KPB fabrics. ........................................................................................................................... 25

Table 5: UPF classification system for textile materials [23] .................................................. 26

 

 
 viii

List of Figures 

Figure 1. Deterioration in tear strength as a function of exposure conditions for (a) NKB and 

(b) KPB fabrics. Error bars show experimental standard deviations. ....................................... 19

Figure 2. Percent change in tear strength of UV exposed NKB and KPB fabrics w.r.t. 

unexposed samples ................................................................................................................. 20

Figure 3. Deterioration in tensile strength as a function of exposure conditions for (a) NKB and 

(b) KPB fabrics. ..................................................................................................................... 24

Figure 4. UPF rating as a function of UV irradiation for: (a) NKB and (b) KPB fabrics. ......... 27

Figure 5. ATR-FTIR spectra of NKB: (a) 3550 cm -1 to 2950 cm-1 and (b) 1825 cm-1 to 1625 

cm

-1 stacked as a functional of aging time. Dash lines are aging at UV/50 o

C/50 % RH, and 

solid lines at UV/25 oC/0 % RH, and dotted lines at no UV 50 oC/50 % RH. .......................... 28

Figure 6. ATR-FTIR spectra of KPB: (a) 3550 cm-1 to 2950 cm-1 and (b) 1825 cm-1 to 1625 

cm

-1 stacked as a function of aging time. Dashed lines represent samples aged at UV/50 o

C/50 

% RH, solid lines samples aged at UV/25 o

C/0 % RH, and dotted lines samples aged with no 

UV 50 oC/50 % RH ................................................................................................................ 28
 ix

List of Acronyms 

AATCC American Association of Textile Chemists and Colorist 

ASTM ASTM International 

ATR-FTIR Attenuated Total Reflectance – Fourier Transform Infrared 

Spectroscopy 

APP 

CS 

Ageing Performance Profile 

Continuous Sun exposure 

DMTA Dynamic Mechanical-Thermal Analyzer 

KPB 

LOI 

LSCM 

Kevlar Polybenzimidazole Blend 

Limiting oxygen index 

Laser Scanning Confocal Microscopy 

MCT Mercury Cadmium Telluride 

MB Moisture Barrier 

NC Natural Conditions exposure 

NFPA National Fire Protection Association 

NIST National Institute of Standards and Technology 

NKB 

OS 

Nomex Kevlar Blend 

Outer Shell 

RH Relative Humidity 

SPHERE Simulated Photodegradation via High Energy Radiant Exposure 

TGC Turnout Gear Conditions 

TL Thermal Liner 

UPF Ultraviolet Protection Factor 

UV Ultraviolet 

UVR Ultraviolet Radiation Irradiance 
 x

This page left intentionally blank.
11

1. Introduction 

Firefighter protective clothing (FFPC) is constructed of high performance fiber-containing 

fabrics capable of protecting against a wide range of potentially extreme exposure conditions 

(e.g., climate, nature and frequency of fires, firefighter’s physiology, and cleaning frequency). 

Depending on the position of a firefighter in relation to the fire front line and type of activity in 

which the firefighter is involved, the firefighters’ turnout gear is exposed to different 

conditions. The type of activity defines the thermal exposure conditions, exposure to 

ultraviolet (UV) radiation, level of usage, and frequency of cleaning of a turnout gear over its 

lifetime. The useful lifetime of turnout gear for firefighters is therefore difficult to estimate. 

Generally after 10 years, the FFPC is removed from service as it no longer complies with the 

qualitative performance metrics defined in National Fire Protection Association (NFPA) 1851 

Standard on Selection, Care, and Maintenance of Protective Ensembles for Structural Fire 

Fighting and Proximity Fire Fighting [1]. The guidelines for the retirement of turnout gear 

however, are very limited. 

The NFPA 1851 standard on selection, care, and maintenance of protective ensembles 

recommends retirement of the protective ensemble based on simple visual inspection and 

economic analysis. However, some form of degradation might not be visually detectable, for 

example, loss in tear strength or thermal protective performance of the ensemble due to 

prolonged usage and/or storage. Moreover, firefighter turnout gear is very expensive and 

disposal of such garments based solely on qualitative visual judgments could put undue 

financial burden on fire departments. It is therefore important to develop improved guidelines 

for the retirement of firefighters turnout gear that are based on performance metrics. 

Sunlight is generally considered to be the most important element in weathering [2]. The nearUV light reaching the earth’s surface delivers more energy per photon than does visible or 

infrared irradiation. The energies of photons in the near-UV region correspond to or exceed 

the covalent-bond energies of some chemical structures and therefore some bond rupture is 

likely to result from their absorption. Sunlight interacts with virtually all organic polymers to 

cause irreversible chemical changes and the photo-oxidative degradation of polymers usually 

leads to embrittlement, followed by loss of tensile properties. Two conditions are necessary 

for light of a particular wavelength to cause polymer degradation. First, the polymer must 

absorb the light. Second, sufficient energy must be present to break the chemical bonds. The 

chemical aging of the polymers often involves three main reactions: chain scission, crosslinking, and depolymerization of which chain scission largely dominates the aging process [3]. 

The likelihood of a given polymer to undergo chain scission depends on the nature of its 

constitutive chemical bonds and their particular dissociation energy. Chain scission is often 

coupled with oxidation, which leads to a self-sustained process that involves highly reactive 

free radicals produced during oxidation. The decrease in molecular weight associated with 

chain scission is expected to have an effect on the ultimate mechanical properties of the 

polymer, such as breaking strength, ultimate elongation, etc. 

The mechanical properties important to the protective performance of firefighter turnout gear 

include unidirectional stretching, tear resistance, and elastic properties. Loss in 

aforementioned properties of the turnout gear fabric could result in inadequate protection and 
12

thereby unwarranted injuries to the firefighters. Previous research [4,5,6,7,8] has established 

that, due to their complex physics and chemistry, high-performance fibers, in particular, are 

inherent absorbers of UV and undergo degradation via photolytic degradations initiated by 

primary photoreactions that cause main chain bond breakage. Susceptibility to photo-oxidation 

is particularly severe in the case of polyaramids. Photodegradation of fabrics is also related to 

the effects of surface treatment and abrasion damage during the weaving process. The weaving 

process includes application of a surface finish to the yarns and a further poly(vinyl alcohol) 

size application to the warp yarns. Studies [9] have shown that the surface finish may sensitize 

photolytic degradation of warp yarns. 

In an attempt to quantify the relationship between turnout gear performance with 

environmental exposure, environmental stress factors were selected based on routine firefighter 

activities and general storage practices for turnout gear. Environmental stress factors that 

affect the durability of turnout gear include thermal exposure, UV radiation, moisture 

exposure, abrasion, and laundering. In the first phase of this work, accelerated weathering of 

polyaramid and polybenzimidazole outer shell (OS) fabrics was studied and reported [10]. OS 

fabrics were exposed to simulated UV sunlight at 50 °C and 50 % relative humidity (RH). The 

ageing performance profile (APP), which is the deterioration of properties as a function of 

time, suggested that 13 days continuous exposure (equating to 6.6 years of turnout gear 

exposure to UV radiation under natural conditions of usage) to the conditions mentioned above 

caused significant deterioration in the mechanical performance of OS fabrics. OS fabrics 

containing polybenzimidazole fiber blends showed less deterioration in tear resistance and 

tensile strength as compared to fabrics made from polyaramid fiber blends. Microscopic 

studies and infrared spectroscopy indicated that these exposure conditions caused significant 

surface decomposition of polyaramid fibers via photo oxidation while polybenzimidazole 

fibers showed negligible degradation. The impact of increased temperature, moisture, and UV 

irradiation was not singled-out during this phase of the study. 

Reported here is a study of the individual environmental stress factors on the performance 

metrics of OS fabrics used in firefighters turnout gear, i.e. UV exposure under dry conditions 

and elevated moisture and temperature exposure in the absence of UV. The OS fabrics were 

exposed to; i) UV radiation (295 cm-1 to 495 cm-1) at ambient temperature and 0 % relative 

humidity (RH) (UV /25 °C/ 0 % RH) and ii) elevated temperature and relative humidity in a 

‘dark’ chamber with no UV radiation (no UV/50 °C/ 50 % RH). After exposure, the 

mechanical and chemical properties of the OS fabrics were evaluated and their APP values 

were compared. 

2. Experimental 

2.1. Fabrics 

The two OS fabrics and fabric lots previously studied were used again for this study [10]. KPB 

is a rip-stop weave fabric constructed of a (40/60) number fraction % fiber blend of 

polybenzimidazole (PBI) and poly(p-phenylene terephthalamide) (PPA). PBI fibers have 

excellent heat resistance (e.g., Limiting oxygen index (LOI) of 41 %, no melting, and high 
13

temperature strength retention) and good mechanical properties (e.g., tenacity of 2 g/denier to 

3g/denier). The PPA fibers have high tenacity (22 g/denier to 26 g/denier), tensile modulus 

(460 g/denier to 1100 g/denier), and heat resistance (LOI of 25 % to 28 %), and very low 

elongation at break for tensile failure (<5 %). NKB is a plain weave fabric constructed of 

(93/5/2) number fraction % fiber blend of poly(m-phenylene isophthalate) (PPI), poly(pphenylene terephthalamide), and P-140 (antistatic fiber). The P-140 fiber has a conductive 

carbon black core covered in a protective polyamide sheath. PPA and PPI are both 

polyaramids with the only chemical structure difference being the para- versus meta- linkage, 

respectively, in the polymer backbone. However, this difference strongly influences properties 

and processability of these polyaramids. PPI fibers are also inherently fire resistant fibers (LOI 

of 30 %) and have excellent mechanical strength (tenacity of 4 g/denier to 7g/denier and tensile 

elongation at break of 20 % to 30 %). Both fabrics are coated with a water-repellant coating. 

There are several OS manufacturers that produce similar fiber blend ratios as the fabrics used 

in this study, as this particular fiber blend is a very cost-effective approach to produce turnout 

gear complying with NFPA 1971 [11] specifications. 

2.2. UV aging and Thermal/Moisture aging 

In an attempt to delineate the impact of UV irradiation from heat and moisture on deterioration 

rate of OS fabrics, the fabrics were exposed to UV radiation at ambient temperature (25 °C ± 

0.1 °C) and RH of 0 %. The fabrics were also exposed to elevated temperature and moisture 

conditions in the absence of UV radiation (no UV, temperature and RH of 50 °C ± 0.1 °C and 

50 % ± 1 %, respectively). 

 

UV irradiation experiments were conducted as previously described [10]. Fabric specimens 

with approximate dimensions of 10.2 cm  7.5 cm (4 in  3 in), were exposed to high UV 

irradiance in the NIST integrating sphere-based weathering device, referred to as SPHERE 

(Simulated Photodegradation via High Energy Radiant Exposure). Accelerated exposure of the 

fabrics to high UV irradiance was carried out using the mercury arc lamp system that produced 

a collimated and highly uniform UV flux in the environmental chambers of the SPHERE. A 

borosilicate glass window was placed between the lamp system and the integrating sphere to 

eliminate all UV wavelengths < 290 nm. The dichroic reflector in the lamps removed 

wavelengths > 450 nm. Additional details on the construction and properties of the SPHERE 

have been published elsewhere [12]. The fabric samples were exposed to UV irradiance 

dosage of 15.9 kJ/m2 ± 0.02 kJ/m2

 for 24 h of the day. Based on this prescribed amount of UV 

exposure on the SPHERE, various parameters including continuous sun (CS) days (calculated 

number of days where sunlight is assumed for 24 h of the day), natural conditions (NC) day 

calculated assuming 9 h of sunlight in a day and exposure period for turnout gear have been 

calculated and reported elsewhere [10] and reproduced in Table 1. 

 
14

Table 1. Standard table for equivalance solar spectral irradiance.[10] 

SPEHRE 

(d) 

Continuous Sun 

(d) 

Natural Conditions 

(d) 

Turnout Gear Conditions 

 (d) (year) 

S CS = 7.4 x S NC = 19.7 x S TGC = 177.3 x S 

13 96 256 2305 6.3 

28 207 552 4964 13.6 

42 311 827 7447 20.0 

56 414 1103 9929 27.2 

66 488 1300 11702 32.0 

The thermal/moisture aging was conducted in experimental chambers with the same design and 

operational specifications as those on the SPHERE. The only difference is the ‘dark side’ 

chambers are not attached to the SPHERE. 

2.3. Mechanical testing 

NFPA 1971 [11] requires testing tear resistance of OS fabrics using the test procedure 

described in ASTM D 5587 [13]. The standard describes measurement of tear strength by the 

trapezoidal method (an in-the-plane tear propagation). In the textile industry, this method is 

not frequently used as the stress pattern measured by this method is largely determined by 

variables at the disposition of the operator and the tear strength values are high since the fabric 

yarn is pulled, not torn, apart. For these reasons, the fabric tear resistance for this study was 

determined using the static, single tear method described in ASTM D 2261[14]. The single 

tear test (also called the single rip tear test) is an out-of-the-plane tear that propagates at 

relatively low loads and results in tearing of the yarn and, therefore, lower tear strength values. 

The single tear tests were conducted on an Instron universal testing machine (model 5582, 

Instron corp., Northwood, MA1

) equipped with 2 kN load cell and custom grips for fabrics. 

The gauge length between grips was 25 mm, and crosshead speed was 50 mm/sec. A single 25 

mm (1 in) tear was introduced at one end of specimen having approximate dimensions of 68 

mm  25 mm (2.7 in  1.0 in). Four replicates of each fabric were tested per sampling interval. 

Uncertainties in measurement of tear strength are reported as Type A uncertainties [15,16] with 

experimental standard deviations in Table 2. 

Due to specimen size restrictions, the tensile strength of the fabrics were based on yarn tensile 

strength values. Tensile strength or breaking strength of a fabric is generally greater than its 

tear strength. In the single tear test described above, each cross-section of yarn is subjected to 

progressively increasing tension. The cross-yarn fails singly, doubly or even in multiples, 

 

1 Certain commercial equipment, instruments or materials are identified in this paper in order to 

specify the experimental procedure adequately. Such identification is not intended to imply 

recommendation or endorsement by the National Institute of Standards and Technology, nor is 

it intended to imply that the materials or equipment identified are necessarily the best available 

for this purpose.
15

depending on the type of weave, yarn strength and elongation properties. It is important to 

note that in a tear test, the yarn fails individually in tension and for this reason the fabric tear 

strength is much lower than its breaking strength; where all yarns fail at the same time. Thus, 

for a more precise understanding of fabric deterioration, the individual yarns unraveled from 

fabrics exposed to various conditions have been tested for their tensile strength and percentage 

elongation properties. The yarn strength is the stress at which the yarn fails or fractures. 

Elongation at break is the increase in length produced by the breaking force, expressed as a 

percentage of the original nominal length. Since the properties depend on the specimen 

dimensions and testing conditions (e.g., strain rate and gauge length) the values reported here 

are best used for relative comparison and as absolute values to compare with results reported 

elsewhere. 

Yarn tensile testing was measured following ASTM D2256 [17] straight strength method. 

Tensile properties of ply-twisted yarn from fabric specimens were measured using a TA 

Instruments RSA III Dynamic Mechanical-Thermal Analyzer operating in transient mode 

(DMTA, TA Instruments-Waters LLC, New Castle, DE). Gauge length was 10 mm and 

specimen extension rate was 0.005 mm/s. Since the instrument is not equipped with an 

extensometer, the strain was calculated by the change in grip spacing. Therefore, the data 

represent trends and not absolute values. A minimum of five individual ply-twisted yarns was 

analyzed per sampling interval. Uncertainties in measurement of tensile strength are reported 

as Type A uncertainties [15,16] with experimental standard deviations in Table 3. The yarn 

diameter was measured using an optical microscope. 

2.4. Ultraviolet Transmittance 

The amount of UV irradiation passing through the fabric was measured on the SPHERE. The 

NIST SPHERE provided the UV irradiation with an output intensity of 480 W/m2

. UV-visible 

transmittance spectra were measured using a Hewlett Packard 8452A diode array UV-Visible 

spectrophotometer (HP/Agilent, Santa Clara, CA) with a custom integrating sphere collector. 

The distance between the integrating sphere and the fabric specimen was kept constant (20 

mm) for each measurement. The UV spectra were recorded between 290 nm to 690 nm before 

(to record the dark current) and after the fabric specimen was mounted. Three measurements 

were taken per sampling interval. The calculated UV protection factor (UPF) and the average 

UV transmittance may be slightly shifted from the exact values due to drift of dark current. 

The Type B evaluation of standard uncertainty [15, 16] for UPF was ± 5 % of the value (2 σ) 

[18]. 

2.5. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) 

ATR-FTIR analysis was used to elucidate the chemical changes induced by UV irradiation. 

ATR-FTIR is a technique where the infrared beam penetrates only a few microns into the 

specimen and therefore is appropriate for the identification of structural changes on the surface 

of the fabrics. Infrared analysis was carried out using a Nicolet Nexus 670 FTIR (Nicolet 

Instrument Corp. Madison, WI) equipped with a mercury cadmium telluride (MCT) detector 

and a SensIR Durascope (Smiths Detection) attenuated total reflectance (ATR) accessory. 

Uniform pressure was applied on the fabric using the force monitor on the durascope. Dry 
16

breathing quality air was used as the purge gas. FTIR spectra were collected at nine different 

locations from fabric swatch having approximate dimensions of 102 mm  76 mm (4 in  3 in) 

and 128 scans were accumulated. 

 

Spectral analysis, including spectral baseline correction and normalizing, was carried out using 

a custom software program [19] developed in the Polymeric Materials Group at NIST to 

catalogue and analyze multiple spectra. The spectra were baseline corrected and normalized 

using the peak at 781 cm-1 for NKB, and the peak at 820 cm-1 for KPB. Both peaks are 

attributed to out-of-plane aromatic C-H bending. Type B evaluation of standard uncertainties 

[15, 16] associated with this measurement are typically ±1 cm-1 in wave number and ± 1 % in 

peak intensity [18]. 

3. Results and Discussion 

3.1. Tear Testing 

A typical tear test load-extension plot has a saw-tooth shape. The middle part of the loadextension curve represents 50 % of the entire tear distance. For a given sample, determining 

tear strength by static single tear test method (ASTM D2261) relies on determining the median 

of the five largest tear forces from the middle part of the load-extension curve. Tear strength 

of NKB and KPB fabrics for various exposure conditions are provided in Table 2 and 

deterioration in tear strength is plotted as a function of exposure time in Figure 1. 

14 d ± 0.5 d of UV irradiation at 50 o

C and 50 % RH, the tear strength of both fabrics had 

significantly deteriorated (87 % and 70 % decrease for NKB and KPB fabrics respectively). 

Further exposures up to 56 d resulted in continued deterioration of tear strength, but at a 

significantly slower rate. By the end of the 56 d ±0.5 d exposure the deteriorations in percent 

tear strength was comparable for both fabrics (95 % and 88 % for NKB and KPB, 

respectively). Because of the higher initial tear strength value and slower deterioration rate, 

KPB maintained higher tear strength throughout the exposure duration. For example, KPB had 

a tear strength value of 10 N ± 0.2 N at the end of 56 d ±0.5 d exposure, which was 4 times 

longer than the exposure time required for NKB to reach the same value. 

To quantify the contributions of UV irradiation, temperature, and moisture on tear strength 

deterioration, the OS fabrics were exposed either to UV irradiance at ambient conditions 

(UV/25 o

C/0 % RH) or only elevated moisture and temperature (no UV/50 oC/50 % RH). 

There was no statistical change in the tear strength of the fabrics after 56 d exposure at 

50 o

C/50 % RH with no UV irradiation. However, UV irradiation at 25 oC/0 % RH resulted in 

a similar deterioration profile as previously reported for UV irradiation at 50 oC and 50 % RH 

(initial rapid deterioration followed by much slower deterioration rate). However, the 

deterioration was less severe in these UV irradiation only (UV/25 oC/0 %RH) exposures 

suggesting there is a contribution of higher temperature and moisture on the photo degradation 

of fabrics. It appears that the contribution of temperature and moisture was more critical to the 

KPB tear strength deterioration as the tear strength values were 15 % to 20 % lower than the 

full exposure conditions (NKB values were only 5 % to 10 % lower). 
17

Table 2. Tear strength and loss of tear strength of NKB and KPB fabrics exposed to varying 

environmental conditions. Uncertainties are reported as with experimental standard deviations. 

SPHERE 

(d) 

NKB KPB 

Tear strength (N) 

Approximate 

decrease in tear 

strength (%) 

Tear strength (N) 

Approximate 

decrease in 

tear strength 

(%) 

No UV / 50 °C / 50 % RH 

 0.0 75 ± 8.0 - 81 ± 4.3 -

14.0±0.5 76 ± 7.0 0.0 74 ± 3.1 8

28.0±0.5 68 ± 2.6 1.0 74 ± 5.2 8

42.0±0.5 68 ± 4.2 0.9 81 ± 2.6 0

56.0±0.5 72 ± 6.9 0.5 81 ± 2.3 0

UV / 25 °C / 0 % RH 

 0.0 75 ± 8.0 - 81 ± 4.3 -

13.5±0.5 15 ± 0.9 80 35 ± 3.0 56

27.7±0.5 11 ± 0.7 85 26 ± 0.8 68

42.0±0.5 9.8 ± 0.5 87 22 ± 0.7 72

55.8±0.5 8.4 ± 1.3 89 21 ± 1.3 74

UV / 50 °C / 50 % RH 

 0.0 75 ± 8.0 - 81 ± 4.3 -

14.0±0.5 10 ± 0.3 87 24 ± 1.5 70

28.0±0.5 5.9 ± 0.7 92 16 ± 0.7 80

42.0±0.5 4.8 ± 0.6 94 13 ± 0.5 84

56.0±0.5 4.1 ± 0.1 95 10 ± 0.2 88
18

(a) 
19

(b) 

Figure 1. Deterioration in tear strength as a function of exposure conditions for (a) NKB and 

(b) KPB fabrics. Error bars show experimental standard deviations. 

Percentage loss of tear strength with respect to unexposed control specimens for both the 

fabrics is plotted in Figure 2 and it can be seen that the NKB fabrics deteriorates faster than 

KPB fabrics suggesting that KPB has greater UV resistance. Better performance of KPB 

compared to NKB is due to the fact that KPB is a blend of PBI fibers and para-aramid (40/60), 

which both have greater UV resistance than the meta-aramid fibers used in NKB. 

Additionally, the meta-aramid fibers in NKB have lower tenacity (4 g/denier to 7 g/denier) 

than the para-aramid fibers in KPB (22 g/denier to 26 g/denier). Dobbe et al [20] have shown 

that para-aramids have a highly crystalline core with a less ordered skin. Any chemical 

degradation occurs more easily within disordered regions, which in para-aramids is only a 

small fraction of polymer and hence less susceptible to photo degradation. Carlsson et al [21] 

showed that para-aramids are more stable than meta-aramids due to increased conjugation and 

delocalization of absorbed energy through the enol form of the amide group in para-aramids. 
20

Figure 2. Percent change in tear strength of UV exposed NKB and KPB fabrics w.r.t. 

unexposed samples 

3.2. Yarn Tensile Testing 

The tensile strength and % elongation values for NKB and KPB yarns for various exposure 

conditions are given in Table 3 and their APP in terms of tensile strength of yarns from NKB 

and KPB fabrics are shown Figure 3. Stress at break was calculated based on cylindrical 

geometry with circular cross-section of the ply-twisted yarn. Within the uncertainties of 

measurements, tensile strength of unexposed NKB and KPB yarns were similar (55 ± 8 MPa). 

The NKB yarns exhibited ductile failure with % elongation at break of 42 % ± 7 % whereas 

KPB exhibited brittle failure with % elongation at break of 4.0 % ± 0.3 %. Meta-aramid fibers 

constitute the majority of the NKB yarns (93%) and, therefore, the NKB tensile properties 

were dominated by linear chain polymer fibers with inherent strength anisotropy and imperfect 

orientation in the fibers. This unique failure mechanism is generally contributed to the rod-like 

structure of liquid crystals as they are spun into fibers. The tensile failure of meta-aramid 

fibers is unique in that when they fail, the fibers break into small fibrils. Tensile strength 

failure is believed to initiate at the ends of the fibrils and is propagated through the fibers by 

shear. Therefore, meta-aramid fibers fail by series of fibril failures rather than a brittle failure. 

Such ductile failure was also confirmed by confocal microscopy in our previous studies [10]. 

Comparing the APP of NKB and KPB yarns in Figure 3, it can be noted that both the yarns 

rapidly lose tensile strength upon UV exposure. NKB yarns lost more than 80 % of their initial 

tensile strength after 13 d of continuous exposure to UV radiation while KPB lost only 50 % of 
21

initial strength. Similar to loss of tear strength, further exposure up to 56 d resulted in 

continued deterioration of tensile strength at a significantly slower rate. The KPB yarns 

retained 16 % whereas NKB retained only 3 % of its original strength at the end of 56 d 

exposure to UV/50oC/50%RH. The UV exposure also drastically changed tensile behavior of 

NKB from ductile failure (% elongation at break of 41 % ± 4 %) to brittle failure (% 

elongation at break of 5 % ± 1.1 %). KPB yarns showed no change in failure mechanism. 

This is in agreement with our previous studies wherein changes in failure mechanism are 

illustrated by microscopic studies [10]. In absence of UV irradiation, prolonged exposures to 

elevated temperatures and higher moisture (no UV/50 °C /50 %RH) levels did not affect tensile 

properties of NKB and KPB yarns. However, in presence of UV radiation with increased 

temperature and moisture levels (UV/50 °C/50 %RH) there was a slightly higher deterioration 

in tensile strength of both NKB and KPB yarns. 

Conversely, KPB yarns exhibited more brittle failure with very little elongation (4 % ± 0.3 %). 

Para-aramid fibers, which constitute 60 % of fibers in KBP yarns, dominate their tensile 

properties. Para-aramid fibers exhibit more brittle failure as compared to meta-aramid fibers. 

As mentioned earlier, the highly oriented structure of poly(p-phenylene terephthalamide) yields 

higher strength, but the fibers fail with less elongation. 
 22

Table 3. Tensile strength and % elongation at break for NKB and KPB yarns exposed to varying environmental c§ Positive values indicate decrease in tensile strength w.r.t. control sample whereas negative values suggests incrstrength. ^ Positive values indicate increase in % elongation at break w.r.t. control sample whereas negative values suggest elongation at break. 

SPHERE (d) 

NKB KPB Tensile strength (MPa) 

Approximate decrease in tensile strength§

(%) 

%-Elongation 

Approximate change in % elongation^

Tensile strength (MPa) 

Approximate decrease in tensile strength§ (%) 

%-Elongat

No UV / 50 °C / 50 % RH 0 55 ± 8.0 - 41 ± 4 - 55 ± 5.3 - 4 ± 14±0.5 56 ± 2.7 -1 41 ± 6 1 58 ± 5.8 -6 4 ± 28±0.5 55 ± 4.7 0 42 ± 6 -2 58 ± 6.1 -6 4 ± 42±0.5 54 ± 4.5 1 41± 4 -1 62 ± 5.3 -13 4 ± 56±0.5 53 ± 4.6 4 43 ± 2 -6 61 ± 5.4 -11 4 ± UV / 25 °C / 0 % RH  0 54 ± 4.8 - 42 ± 7 - 60 ± 5.7 - 5 ± 13±0.5 10 ± 2.7 81 7 ± 3 83 32 ± 4.3 46 4 ± 28±0.5 7 ± 1.4 88 7 ± 1 84 23 ± 2.7 61 3 ± 42±0.5 5 ± 1.2 92 6 ± 1 86 21 ± 3.6 65 3 ± 56±0.5 4 ± 1.1 93 6 ± 0.8 85 17 ± 3.4 71 3 ± UV /50 °C / 50 % RH 0 55 ± 8.0 - 41 ± 4 - 55 ± 5.3 - 4 ± 14±0.5 6± 1.4 89 5 ± 0.8 88 27 ± 3.2 51 3 ± 28±0.5 3± 0.9 95 5 ± 1.4 88 16 ± 2.2 71 3 ± 42±0.5 - - - - 12 ± 2.4 78 3 ± 55±0.5 2± 0.4 97 5 ± 1.1 88 9 ± 1.5 84 3 ± 
 23

(a) 
 24

 (b) 

Figure 3. Deterioration in tensile strength as a function of exposure conditions for (a) 

NKB and (b) KPB fabrics. 

3.3. UV Protection Factor (UPF) 

The UV transmittance data for NKB and KPB fabrics is given in Table 4. The UV 

transmittance of tested fabrics (NKB and KPB) is very low for UV-A (% of UV light 

transmitted within the wavelength range from 280 nm to 315 nm) or UV-B (% of UV 

light transmitted within the wavelength range from between 315 nm and 400 nm) and 

therefore inconclusive. The ultra violet protection factor (UPF) has therefore been 

calculated, using the methodology described in previous studies [10], to assess and 

compare the protective performance of fabric samples against UV radiation. Three 

important factors that are taken into consideration while calculating UPF include: i) 

spectral transmittance of fabrics, ii) the solar spectral transmittance and iii) the relative 

erythermal effectiveness. Spectral transmittance of fabric is the proportion of radiant 

light that passes through the fabric after reflection and absorption by the fabric. The 

transmittance spectra of fabrics can vary significantly depending on the fibers in fabric 

composition, structural characteristics of fabric, finishing ancillaries such as optical 

brightening agents, dyestuff, UV-absorbers etc., and laundering conditions [22]. The 

higher the transmittance of UV radiation through fabric, the lower the UPF value. 
 25

The UPF values for unexposed NKB and KPB fabric samples are 43 and 25 respectively. 

According to the ASTM D6603 [23] classification system for UV protection of textile 

materials, NKB exhibits “excellent” UV protection whereas KPB provides reasonable 

(“very good”) protection. While both the fabrics provide sufficient protection to avoid 

photolytic degradation of underlying layers via solar UV radiation, the proportion of UV 

radiation passing through KPB fabric is comparatively greater than that passing through 

NKB. Greater spectral transmittance of KPB may be attributed to lower fabric density 

(44 warp/inch and 38 weft/inch) compared to that of NKB (50 warp/inch and 42 

weft/inch) or higher reflection/absorbance of UV radiation by NKB fabric. 

Previous studies on accelerated weathering of NKB and KPB fabrics indicated 

comparable UPF values for both fabrics after 13 d exposure to UV/50 oC/ 50 % RH on 

the NIST SPHERE [10]. However, if we compare the UPF rating (which always has a 

value which is a multiple of 5) based on UPF classification system described in Table 5, 

the UPF rating of 40 for NKB is reduced to 20 which is a noticeable reduction from 

“excellent” protection to “good” protection. The UPF rating for KPB is changed from 25 

to 20, which is a marginal change from “very good” to “good” protection. Compared to 

KPB the UV exposure causes significant change in UV transmittance of NKB. With 

unaltered fabrics density, greater transmittance of UV exposed NKB suggests greater 

reflection/absorption of UV radiation due to chemical changes on the surface of NKB 

fabrics. 

Ageing performance profile (APP) in terms of UPF rating for three different exposure 

conditions have been compared and graphically presented for NKB and KPB fabrics in 

Figure 4 (a) and (b), respectively. In absence of UV radiation, there is no change in UPF 

rating of NKB and KPB fabrics suggesting that elevated temperature and increased 

humidity have no impact on UV transmittance of the fabrics studied. APP profiles for 

both the fabrics in Figures 4(a) and (b) indicate that UV irradiation at elevated 

temperature and humidity (UV/50 o

C/50 % RH) and UV irradiation at ambient conditions 

(UV/25 oC/0 % RH) has similar impact on UPF rating of fabrics. For both tested fabrics, 

the 13 d exposure to UV radiation on the NIST SPHERE (which equates to 6.6 years of 

exposure in natural conditions) has maximum detrimental effect on UV transmittance. 

Further exposures have no impact on UV transmittance of fabrics. 

Table 4. Ultraviolet protection factor (UPF) and the average UV transmittance of NKB 

and KPB fabrics. 

SPHERE (d) UPF T

(280-400)

(%) T(280-315)(%) T(315-400)(%) T(400-500)(%) 

NKB 0.0 43 0.12 0.00 0.17 0.10 

No UV / 50 °C / 50 % RH 

14.0±0.5 41 0.13 0.01 0.09 0.09 

28.0±0.5 43 0.21 0.00 0.15 0.12 

42.0±0.5 44 0.14 0.00 0.10 0.07 

56.0±0.5 42 0.11 0.01 0.09 0.06 

UV / 25 °C / 0 % RH 

13.5±0.5 25 0.13 0.00 0.20 0.34 

27.7±0.5 18 0.06 0.02 0.14 0.28 
 26

42.0±0.5 18 0.04 0.08 0.16 0.32 

55.8±0.5 18 0.06 0.00 0.16 0.32 

KPB 0.0 18 0.06 0.02 0.12 0.22 

No UV / 50 °C / 50 % RH 

14.0±0.5 24 0.10 0.01 0.13 0.24 

28.0±0.5 22 0.04 0.02 0.05 0.10 

42.0±0.5 22 0.08 0.03 0.10 0.19 

56.0±0.5 24 0.06 0.02 0.08 0.19 

UV / 25 °C / 0 % RH 

14.0±0.5 18 0.09 0.02 0.12 0.12 

27.8±0.5 18 0.08 0.02 0.11 0.12 

44.0±0.5 18 0.08 0.02 0.10 0.07 

58.4±0.5 18 0.08 0.02 0.10 0.07 

Table 5: UPF classification system for textile materials [23] 

UPF range UV radiation 

Protection category 

Effective UV 

transmission (%) 

UPF ratings 

15 to 24 Good protection 6.7 to 4.2 15, 20 

25 to 39 Very good protection 4.1 to 2.6 25, 30, 35 

40 to 50, 50+ Excellent protection ≤ 2.5 40, 45, 50, 50+ 

(a) 
 27

(b) 

Figure 4. UPF rating as a function of UV irradiation for: (a) NKB and (b) KPB fabrics. 

3.4. Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) Spectroscopy 

FTIR spectra interpretation is based on the literature peak assignments of poly(mphenylene isophthalate), poly(p-phenylene terephthalamide), and polybenzimidazole [24, 

25, 26, 27, 28, 29, 30]. The spectra for NKB and KPB fabrics for two different regions 

are stacked as a function of aging time (Figure 5 and Figure 6, (a) 3550 cm-1 to 2950 cm-1

and (b) 1825 cmto 1625 cm-1). Dash lines are aging at UV/50 o

C/50 % RH, and solid 

lines at UV/25 o

C/0 % RH, and dotted lines at no UV 50 oC/50 % RH. 

Characteristic peaks of unexposed NKB fabrics can be noted in baseline spectrum shown 

in Figure 5(a) and (b). The characteristic peaks in Figure 5(a) are 3320 cm-1 (N-H 

stretching of amide) and 3050 cm-1 (C-H stretching of aromatic rings), and in Figure 5(b) 

is 1600 cm-1 (stretching of aromatic ring C=C). Other characteristic peaks (not shown 

here) at 1525 cm-1 and 1236 cm-1 are assigned to amide II and III, respectively. 

The baseline spectrum of unexposed KPB fabric is shown in Figure 6(a) and (b). FTIR 

spectra of KPB and NKB fabric are similar due to the similar structure of poly(mphenylene isophthalate) and poly(p-phenylene terephthalamide). The characteristic peaks 

of polybenzimidazole are 3050 cm-1 (aromatic N-H stretching), 1626 cm-1 (C=C/C=N 
 28

stretching), and 1050 cm-1 (benzene ring vibration) have not been identified in Figure 6 

as it was difficult to resolve these peaks from the poly(p-phenylene terephthalamide) 

peaks. Polybenzimidazole is a minor component in the KPB blend and hence also 

difficult to resolve from the other these peaks. Additionally, a strong heterocyclic peak at 

802 cm-1 (C-H out-of-plane bending) has not been included in Figure 6. 

3400 3200 3000

28 d

14 d

56 d

Baseline

Absorbance

Wavenumber (cm-1)

42 d

(a)

1800 1750 1700 1650

Absorbance

Wavenumber (cm-1)

(b)

56 d

42 d

28 d

14 d

Baseline

Figure 5. ATR-FTIR spectra of NKB: (a) 3550 cm -1 to 2950 cm-1 and (b) 1825 cm-1 to 

1625 cm-1 stacked as a functional of aging time. Dash lines are aging at UV/50 oC/50 % 

RH, and solid lines at UV/25 oC/0 % RH, and dotted lines at no UV 50 oC/50 % RH. 

3400 3200 3000

Absorbance

Wavenumber (cm-1)

56 d

42 d

28 d

14 d

Baseline

(a)

1800 1750 1700 1650

Absorbance

Wavenumber (cm-1)

56 d

42 d

28 d

14 d

Baseline

(b)

Figure 6. ATR-FTIR spectra of KPB: (a) 3550 cm-1 to 2950 cm-1 and (b) 1825 cm-1 to 

1625 cm-1 stacked as a function of aging time. Dashed lines represent samples aged at 
 29

UV/50 oC/50 % RH, solid lines samples aged at UV/25 oC/0 % RH, and dotted lines 

samples aged with no UV 50 oC/50 % RH 

There was no change in the FTIR spectra of NKB fabrics exposed to elevated 

temperature and RH with no UV irradiation (no UV/50 oC/50 % RH), relative to the 

unexposed NKB baseline (Figure 5(a)). However, exposure to UV irradiation (regardless 

of temperature and RH) resulted in a change in peak intensity and peak broadening (3320 

cm

-1 ranging from 3500 cm-1 to 3000 cm-1). This suggests polymer degradation likely 

occurred through UV-initiated photolytic oxidation of the amide backbone linkages to 

form hydroxyl groups. Consistent with this observation is the conversion of the amide 

peak at 1720 cm-1 to a peak consistent with carboxylic acid and/or esters as observed at 

1745 cm-1 (Figure 5(b)). Additional evidence of amide cleavage is a reduction in peak 

intensities of Amide I ((1536 cm-1) and Amide II ((1650 cm-1) (not shown here). It should 

also be noted that UV exposure greater than 14 d appears to cause no further degradation 

of the NKB fabrics or that the decomposition is below the detection depth of the FTIR 

analysis. 

FTIR spectra of KPB fabrics in Figure 6(a) and (b) show the same trend as NKB except 

that the magnitude of the peak intensity and peak broadening at 3320 cm-1 ranging from 

3500 cm-1 to 3000 cm-1 , which is assigned to formation of O-H group, is greater for KPB 

fabrics aged at 25 o

C ± 0.1 oC and 0 % ± 1 % RH in the presence of UV irradiation 

compared to 50 o

C ± 0.1 oC and 50 % ± 1 % RH with UV radiation. This can be 

attributed to the fact that NKB and KPB fabrics have different water-repellent coatings 

and that this coating is significantly degraded during first 13 d exposure to UV radiation, 

which in turn affects water absorption properties [10]. 

4. Summary and Conclusions 

The objective of this study was to delineate the individual impacts of UV irradiation, 

elevated temperature, and moisture on the chemical and mechanical attributes of OS 

fabrics used in firefighter turnout gear. Results indicate that physical and chemical 

properties of both the OS fabrics considered in this study remain unaltered when exposed 

to elevated temperature and moisture (50 °C and 50 % ± 1 % RH). However, exposure of 

NKB and KPB fabrics to simulated UV light caused rapid and extremely large loss in tear 

and tensile strength. The aging performance profiles (APP) of both the fabrics were 

similar in that significant deterioration occurred due to 13 d exposure to UV irradiation. 

Exposure in excess of 13 d had minimal changes in properties of NKB and KPB fabrics. 

UV exposure at elevated temperature with higher moisture levels caused slightly greater 

degradation of constituent fibers due to photo oxidation when compared to UV exposures 

at ambient temperature and moisture. This study indicates that the deterioration in the 

physical properties of polyaramids and polybenzimidazole are mainly due to photooxidative reactions, which change the chemical composition of the polymeric system. 

These chemical changes are the result of the breaking of chemical bonds in the polymeric 

chains and thereby formation of lower molecular weight species. The photochemical 

reactions are associated with build-up of oxidation reaction products and new polymer 
 30

end groups. These changes are known to be responsible for the loss in tensile strength as 

well as the color change. 

Exposure of the fabrics at elevated temperature and humidity, however, has less 

detrimental effect on UPF rating of fabrics when compared to UV irradiation at ambient 

conditions, suggesting that if the protective garments are exposed to UV radiation at 

ambient conditions, then the chances of underlying layers being exposed to UV radiation 

is greater. It is therefore critical to the service life of firefighters turnout gear that they be 

stored out of direct sunlight. 

Several UV blockers, including organic and inorganic, have recently been developed to 

improve the UV protective properties of textiles in general. The organic UV blockers 

absorb UV rays whereas inorganic UV blockers, by virtue of their high refractive indices, 

operate primarily by reflecting and/or scattering most of the UV rays. The inorganic UV 

blocking agents are preferred due to their unique features including non-toxicity and 

chemical stability under both high temperature and UV ray exposure. Titanium dioxide 

(TiO2) is a semiconducting, inorganic UV blocking agent and is a very attractive additive 

for films and fabrics. In general, two main methods used to modify textile materials is 

the incorporation of additives in the fibers, and application of a functional coating on the 

fabrics during the finishing process. Currently, we are investigating a novel coating 

method using a layer-by-layer (LbL) deposition to fabricate nanometer- to micrometerthick TiO2 coatings on the high performing fiber fabrics. The LBL coated fabrics will be 

evaluated for thermal and mechanical properties that are critical to the protective 

performance of firefighter turnout gear. The performance of LbL coated fabrics exposed 

to accelerated environmental stressing including UV exposure, laundering , wear and 

abrasion will also be evaluated. 

5. References 

 

[1] NFPA 1851, Standard on Selection, Care and Maintenance of Structural Firefighting and Proximity Fire-Fighting Protective Ensembles, National Fire 

Protection Association, Quincy, Massachusetts, 2008 Edition. 

[2] Wall MJ, Frank GC. A study of the spectral distribution of sun-sky and Xenon-arc 

radiation in relation to the degradation of some textile yarns. Textile Research 

Journal 1971; 41 (1): 32-38. 

[3] Arrieta C, David E, Patricia D and Vu-Khanh T, Thermal aging of a blend of highperformance fibers, Journal of Applied Polymer Science, 115: 3031-3039 (2010) 

[4] Blais P, Carlsson DJ, Parnell RD, Wiles DM. High Performance Fibers. Part II: 

Limitations: Photo-and Thermal Degradation, Canadian Textile Journal 90 (7): 93-

96 (1973) 

[5] Carlsson DJ, Wiles DM. High performance fibers Part I: Types, properties and 

applications, Canadian Textile Journal 90 (6): 107-110(1973) 
 31

 

[6] Carlsson DJ, Gan LH, Paranell RD, Wiles DM. The photodegradation of Poly (1,3-

Phenylene Isophtalamide) films in air, Journal of Polymer science 1973; Part B 11: 

683-688. 

[7] Brown JR, Browne NM, Burchill PJ, Egglestone GT. Photochemical ageing of 

Kevlar 49, Textile Research Journal 1983; 53 (4): 214-219. 

[8] Said MA, Dingwall B, Gupta A, Seyam AM, Mock G, Theyson T. Investigation of 

ultraviolet resistance of high strength fibers 2006; 37: 2052-2058. 

[9] Davis A, Howes BV, Howes EA. unpublished research. 

[10] Davis R, Chin J, Lin C, Petit S. Accelerated weathering of polyaramid and 

polybenzimidazole firefighter protective clothing fabrics, Polymer degradation 

stability 2010; 95: 1642-2654. 

[11] NFPA 1971: Standard on Protective Ensembles for Structural Fire Fighting and

Proximity Fire Fighting. National Fire Protection Association, Quincy, 

Massachusetts , 2007 Edition. 

[12] Chin J, Byrd E, Embree N, Garver J, Dickens B, Finn T, Martin J. Accelerated 

UV weathering device based on integrating sphere technology. Review of 

Scientific Instruments 2004;75: 4951. 

[13] ASTM D 5587-Standard test method for the tearing Strength of Fabrics by 

Trapezoidal method, ASTM, Philadelphia, PA. 2008 Edition. 

[14] ASTM D2261 - Standard test method for tearing strength of fabrics by the tongue 

(single rip) procedure (constant-rate-of-extension tensile testing machine), ASTM, 

Philadelphia, PA. 2002 Edition. Available from: 

http://www.astm.org/DATABASE.CART/HISTORICAL/D2261-96R02.htm. 

[15] Taylor BN and Kuyatt CE, Guidelines for Evaluating and Expressing the 

Uncertainty of NIST Measurement Results, NIST Technical Note 1297 

1994 Edition (Supersedes 1993 Edition), Gaithersburg, MD, 20878. 

[16] Evaluation of measurement data — Guide to the expression of uncertainty in 

measurement. JCGM 100:2008 

http://www.bipm.org/utils/common/documents/jcgm/JCGM_100_2008_E.pdf

[17] ASTM D2256 / D2256M - Standard Test Method for Tensile Properties of Yarns 

by the Single-Strand Method, ASTM,	Philadelphia,	PA.	2009	Edition.

[18] Chin J, Byrd E, Embree E, Martin J. Integrating Sphere Sources for UV Exposure: 

A Novel Approach to the Artificial UV Weathering of Coatings, Plastics and 

Composites. In: Service Life Prediction: Methodologies and Metrologies. 2002. p. 

144-160. Available from: 

http://www.fire.nist.gov/bfrlpubs/build03/PDF/b03045.pdf. 

[19] Dickens B. In: Martin JW, Bauer DR, editors. Service life prediction methodology 

and metrologies. Washington, DC: American Chemical Society;2001. 

[20] Dobb MG, Johnson DJ, and Saville BP. Supramolecular structure of a highmodulus polyaromatic fiber (Kevlar 49), Journal of Polymer Science. Physics, Ed 

15. 1977; 2201-2211. 

[21] Carlsson D J, Gan LH, And Wiles DM, The photolysis of fully aromatic amides, 

Canadian Journal of Chemistry 1975; 53: 2337-2344. 

[22] Algaba I, Riva A. In vitro measurement of the ultraviolet protection factor of 

apparel textiles, Coloration Technology 2002; 118: 52-58. 
 32

 

[23] ASTM D6603 - Standard Guide for Labeling of UV-Protective Textiles,	ASTM,	

Philadelphia,	PA.	2011	Edition.

[24] Chang Z, Pu H, Wan D. Liu L, Yuan J, Yang Z. Chemical oxidative degradation of 

Polybenzimidazole in simulated environment of fuel cells. Polymer Degradation 

and Stability 2009; 94 (8):1206-1212. 

[25] Jang MY, Yamazaki Y. Preparation, characterization and proton conductivity of 

membrane based on zirconium tricarboxybutylphosphonate and polybenzimidazole 

for fuel cells. Solid State Ionics 2004; 167: 107–112. 

[26] Coates J. Interpretation of Infrared Spectra, A Practical Approach. In: 

Encyclopedia of Analytical Chemistry. Chinchester: John Wiley and Sons Ltd, 

2000; pp. 10815-10837. 

[27] Tiefenthaler AM, Urban MW. Surface studies of polymer films and fibers by 

CIRCLE ATR FT-IR. Applied Spectroscopy 1988;42: 163–166. 

[28] Deimede V, Voyiatzis GA, Kallitsis JK, Qingfeng L, Bjerrums NJ. Miscibility 

behavior of polybenzimidazole/sulfonated polysulfone blends for use in fuel cell 

applications Macromolecules 2000; 33: 7609–7617. 

[29] Mosquera ME, Jamond M, Martinez-Alonso A, Tascon JM. Thermal 

transformations of Kevlar aramid fibers during pyrolysis: infrared and thermal 

analysis studies. Chemistry of Materials 1994; 6: 1918–1924. 

[30] Luo J, Sun Y. Acyclic N-Halamine coated Kevlar fabric materials: preparation and 

biocidal Functions. Industrial and Engineering Chemistry Research 2008; 47 (15): 

5291–5297.