NISTIR 7592

Study of Acid Generation from

Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-

benzimidazole

Amanda L. Forster, Guillaume H. R. Messin, Kirk D. Rice,

Michael A. Riley, and Stephanie S. Watson

NISTIR 7592

Study of Acid Generation from

Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-

benzimidazole

Amanda L. Forster, Guillaume H. R. Messin,

Kirk D. Rice, Michael A. Riley

Office of Law Enforcement Standards

Electronics and Electrical Engineering Laboratory

Stephanie S. Watson

Materials and Construction Research Division

Building and Fire Research Laboratory

September 1, 2009

U.S. Department of Commerce

Gary Locke, Secretary

National Institute of Standards and Technology

Patrick D. Gallagher, Deputy Director

Abstract

In a communication to the ballistic vest community released in January

2006, there was an allegation by a competing fiber manufacturer that copolymer fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole can release

hydrochloric acid, which could potentially be detrimental to other fibers

that might come in contact with these materials. Despite the fact that

these allegations came from a competing manufacturer, this issue was investigated to determine if it was an officer safety issue. This study investigates

the evolution of acid in aqueous environments from these fibers, reviews the

available literature on the fibers, and provides an analysis of the chemical

structure of these fibers to serve as the basis for future studies. It was determined that there is some evidence to support the allegations; two of the

fiber samples studied released a sufficient amount of acid to drop the pH of

an aqueous solution from approximately pH 6.0 to approximately pH 3.0 in

less than ten days. Further ion-selective electrode (ISE) studies of chloride

ion released from these fibers indicated that hydrochloric acid may not be

the species responsible for this pH reduction. Future studies are planned to

better elucidate the species responsible for this pH reduction and examine

the effect of moisture on the pH reduction of the fibers, as well as the effect

of water vapor on the chemical and physical properties of these fibers.

v
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

This page intentionally left blank.

vi
Acknowledgments

Financial support for this research effort was provided by the National

Institute of Justice under Interagency Agreement Number 2003-IJ-R-029.

Their support is gratefully acknowledged.

vii
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

This page intentionally left blank.

viii
Disclaimer

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.

ix
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

This page intentionally left blank.

x
Contents

1 Introduction 1

2 Background 5

2.1 Fiber Manufacture . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2 Structure and Physical Properties . . . . . . . . . . . . . . . . 5

2.3 Moisture Sorption and Other Properties . . . . . . . . . . . . 7

2.4 Suitability for Ballistic Applications . . . . . . . . . . . . . . 8

2.5 Acid Generation . . . . . . . . . . . . . . . . . . . . . . . . . 8

3 Experimental 11

3.1 Fiber Exposure to Aqueous Environments . . . . . . . . . . . 11

3.2 Infrared Spectroscopy Measurements . . . . . . . . . . . . . . 11

4 Results and Discussion 13

4.1 Chloride Ion Concentration and

pH Measurements . . . . . . . . . . . . . . . . . . . . . . . . 13

4.2 Analysis of Chemical Structure . . . . . . . . . . . . . . . . . 17

5 Conclusions and Future Work 19

6 References 29

xi
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

This page intentionally left blank.

xii
List of Tables

5.1 Infrared peak assignments for all fibers studied. . . . . . . . . 22

xiii
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

This page intentionally left blank.

xiv
List of Figures

1.1 Basic chemical structure of the copolymer fibers (Armos, Rusar,

and Artec). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Basic chemical structure of PPTA fibers. . . . . . . . . . . . . 3

1.3 Basic chemical structure of SVM fibers. . . . . . . . . . . . . 3

2.1 Schematic of spinning process for the copolymer fibers. . . . . 6

2.2 Characteristic moisture sorption isotherms for PPTA and the

copolymer fibers . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.1 Change in pH following immersion in deionized water. . . . . 14

4.2 Chloride ion generation following immersion in deionized (DI)

water for all fibers. . . . . . . . . . . . . . . . . . . . . . . . . 15

4.3 Chloride ion generation following immersion in deionized (DI)

water for all fibers except SVM. . . . . . . . . . . . . . . . . . 16

5.1 ATR FT-IR spectrum of virgin Armos fiber. . . . . . . . . . . 23

5.2 ATR FT-IR spectrum of virgin Artec fiber. . . . . . . . . . . 24

5.3 ATR FT-IR spectrum of virgin Rusar fiber. . . . . . . . . . . 25

5.4 ATR FT-IR spectrum of virgin SVM fiber. . . . . . . . . . . 26

5.5 ATR FT-IR spectrum of virgin PPTA fiber. . . . . . . . . . . 27

xv
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

This page intentionally left blank.

xvi
1. Introduction

Modern body armor utilizes a wide range of polymers to provide the

level of performance required for these applications. The materials most

commonly utilized in body armor are poly(p-phenylene terephthalamide)

(PPTA) and the ultra-high molecular weight polyethylenes (UHMWPE);

however, in an effort to provide additional consumer choices, several additional fibers have been recently introduced into the United States body

armor marketplace. These fibers were developed in the former USSR in the

late 1970s, and are based on several starting monomers [1]. Several of these

fibers were investigated in this study, including Artec, Rusar, SVM, and Armos. PPTA fiber was used as a comparison fiber. Artec, Rusar, and Armos

all have the same basic chemical composition, as depicted in Figure 1.1, and

are formed by polycondensation reaction of two diamines, p-phenylene diamine and 5-amino-2-(p-aminophenyl)-benzimidazole with terephthalic acid

(or anhydrides or acid chloride derivatives of these monomers). PPTA

fibers, sold under trade names Kevlar and Twaron, are manufacturered

by polycondensation of p-phenylenediamine with terephthalic acid. The

structure of PPTA fibers is shown in Figure 1.2. For the purposes of this

work, linkages between terephthalic acid and 5-amino-2-(p-aminophenyl)-

benzimidazole will be referred to as benzimidazole linkages and linkages

between p-phenylene diamine and terephthalic acid will be referred to as

PPTA linkages.

The main difference between these fibers is the ratio of benzimidazole

linkages to PPTA linkages [2]. While specific information on these ratios is

difficult to obtain, one weaver of these fibers supplied information indicating

that in the case of Artec, the ratio of PPTA to benzimidazole linkages was

2:1, and in the case of Rusar, the ratio of diamine to benzimidazole linkages was 1:1. Additionally, Rusar is made with raw materials sourced from

Eastern Europe, and Artec is made with raw materials sourced from the

United States [3]. Another fiber that was investigated in this study is sold

under the trade name SVM. This homopolymer fiber is manufacturered by

direct polycondensation of 5-amino-2-(p-aminophenyl)-benzimidazole with

terephthalic acid [4]. The structure of SVM fiber is shown in Figure 1.3.

In a communication to the body armor community released in January

2006, there was an allegation by a competing fiber manufacturer that copolymer fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole can release

1
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

hydrochloric acid, which could potentially be detrimental to other fibers

that might come in contact with these materials [5]. Despite the fact that

these allegations came from a competing manufacturer, due to recent issues

with degradation of another fiber in field use, it was determined that this

allegation should be investigated to determine if it was an officer safety issue.

2
1. Introduction

N

H

N

NHC

O

C

O

HN

HN NHC

O

C

O

m n

Figure 1.1: Basic chemical structure of the copolymer fibers (Armos, Rusar,

and Artec).

HN NHC

O

C

O

n

Figure 1.2: Basic chemical structure of PPTA fibers.

N

H

N

NHC

O

C

O

HN

m

Figure 1.3: Basic chemical structure of SVM fibers.

3
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

This page intentionally left blank.

4
2. Background

2.1 Fiber Manufacture

While details of the specific processes by which these fibers are made is

difficult to find in the literature, a general idea of the fabrication of Armos

fiber can be determined from a paper published by Machalaba et al., in 2000.

One can readily assume that the general processing steps would apply to the

other fibers as well. The homopolymer (SVM) or copolymer (Armos, Rusar,

Artec) is manufactured by polycondensation of terephthalic acid chloride

and some combination of para-aromatic diamines (p-phenylene diamine or

5-amino-2-(p-aminophenyl)-benzimidazole) in an amide-salt solvent system

(specified as dimethylacetamide and lithium chloride in the Machalaba paper). The polymer formed from this reaction is then filtered and degassed

prior to being spun into a filament yarn. This yarn is then drawn and heat

treated to form the final finished product. Dyeing and twisting can also be

performed, if necessary, after the spinning step. A schematic of this process

is shown in Figure 2.1 [6].

2.2 Structure and Physical Properties

Slugin et al., published two papers in 2006 related to the use of Rusar

fibers for composites and ballistic protection applications. In one of these papers, they disclose the information discussed in Section 1 regarding the structure and monomers of this fiber [4, 7]. Additional information is given regarding the rationale for use of the co-monomer 5-amino-2-(p-aminophenyl)-

benzimidazole. The authors state that the incorporation of this second

diamine in the Rusar fibers significantly alters the rigidity of the polymer

chain (as is evident from an analysis of the slight nonlinearity in the polymer

backbone), as compared to PPTA fibers. This decreases the ability of the

polymer to form a lyotropic liquid crystalline spinning solution because the

molecule is not capable of forming a highly organized structure, leading to a

reduced overall crystallinity. However, this reduced crystallinity allows for

additional organization of the amorphous portions of the Rusar fiber during

post-spinning drawing and heat treatment [4]. This work is supported by

a paper from Zavadskii et al., in which the structure of Armos and SVM

were investigated using X-ray diffraction, and evidence was found to indi5
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

Monomers

Polycondensation

Filtration

Degassing

Spinning,

Finishing,

Dyeing,

Twisting

Heat treatment,

Thermal drawing

Regeneration of solvent from 

spinning bath and washing 

solutions

Twisting Armos twist

Armos fibers of 

various linear 

densities

Oiling

Figure 2.1: Schematic of spinning process for the copolymer fibers.

cate the absence of rigorous order in the position of the molecular chains in

the direction perpendicular to the axis of the fiber [8]. A paper published by

Perepelkin in 2001 compares the properties of Armos and SVM with commercial polyamide yarns. The primary difference between these fibers is in

their structural properties. Polyamide fibers have a fibrillar structure with

stretched chains and three-dimensional order. SVM fibers also have a fibrillar structure with stretched chains, but only one-dimensional crystalline

order. The Armos fiber, one of the copolymer fibers, has a fibrillar structure

with stretched chains, but no crystalline order. The strength at break of the

Armos fiber is reported at 4.5 GPa to 5.5 GPa as compared to 2.7 GPa

to 3.5 GPa for the polyamide fibers, leading the authors to conclude that

crystallinity is not a prerequisite for preparing fibers with good mechanical properties [9]. It appears that the Armos fiber has been investigated

for use in composite applications due to its unique transverse mechanical

properties. A paper by Leal et al., from 2007 attributes the lack of threedimensional organization in Armos fiber to the ability to achieve greater

draw ratios, better molecular orientation, and improved mechanical properties. Additionally, Armos develops intermolecular hydrogen bonds that

allow for stress transfer between adjacent chains. This improves the compressive properties of the fiber and makes it attractive for use in composite

applications [2, 10].

6
2. Background

10

9

8

7

6

5

4

3

2

1

0

0.0 0.2 0.4 0.6 0.8 1.0 P/P0 0.0

a

à, %

1

Figure 2.2: Characteristic moisture sorption isotherms for PPTA (triangles)

and the copolymer (diamonds) fibers [12].

2.3 Moisture Sorption and Other Properties

Studies on the moisture sorption properties of several fibers as compared to PPTA have shown that Rusar has very similar sorption isotherms

to PPTA, as shown in Figure 2.2. Differences in the sorption properties of

these materials are attributed to the lower crystallinity of SVM and Rusar

as compared with PPTA. As previously discussed, the benzimidazole linkages in these polymers do not crystallize as readily as do the more linear

polyamide linkages [11, 12].

Much work [13, 14, 15, 16] has been performed to investigate the thermal

stability of these fibers for use in high-temperature environments and fire

applications. These materials are chemically similar to other fibers used in

fire-resistant applications, such as para and meta-aramid fibers, so interest

in their thermal properties is not surprising. The decomposition tempera7
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

tures in air for Armos showed that it was stable to oxidation and onset of

degradation to approximately 400 ◦C [15]. A separate study on the thermal stability of PPTA, SVM, Rusar, and Armos fibers in which the fibers

were exposed to 250 ◦C for periods of time between 0 h and 100 h showed

that the mechanical properties of the SVM fibers decreased the most rapidly,

and that there was little difference in the thermal stability of the other fibers

examined [13].

2.4 Suitability for Ballistic Applications

The authors present V50 data on ballistic packages manufactured from

two different linear densities of Rusar yarn to demonstrate the appropriateness of this material for ballistic applications. The authors report a V50

of 640 m/s and 550 m/s for packages made from microfilament yarn fibers

with linear densities of 29.4 tex (264.6 denier) and 58.8 tex (529.2 denier),

respectively [7]. It is important to note several omissions in the presentation

of this data. No details were provided as to the areal density of the ballistic

packages created, no details were provided as to the characteristics of the

ballistic fabrics used, and no mention was made of the number of layers

of fabric used to make the ballistic packages, making it difficult to draw

meaningful conclusions from these results.

2.5 Acid Generation

A paper published by Shchetinin et al., in 2006 attempted to address the

allegations raised by the competitive fiber manufacturer about the evolution

of acid from these fibers. In this paper, it is revealed that hydrochloric acid

is a by-product in the synthesis of the polymer, but most of the acid is

removed when the fiber is washed after spinning and heat treatment [17].

The acidity of the finished fiber is also discussed in a paper from 1995 by

Kotomin et al., which indicated that the pH of the fiber varied with heat

treatment conditions to between 3.5 and 6.5, as determined by titration of an

aqueous extract of the fiber [10]. There is a residual amount of acid (0.1 %

to 2.5 % of the fiber’s mass) chemically bound to the amide and imidazole

groups in the fibers. This amount of bound acid is greatest for the SVM

fibers, indicating that it is a by-product of synthesis with the 5-amino-2-

(p-aminophenyl)-benzimidazole and the terphthalic acid or anhydrate. The

authors used SVM yarns for their study, and in the paper indicate that

the amount of bound HCl in the Armos and Rusar copolymer fibers is less

than 0.2 %. SVM fiber samples with an initial hydrochloric acid content of

1.5 % were stored in sealed flasks with deionized water at a ratio of 1 part

fiber to 10 parts water, and the pH of the water in solution was periodically

evaluated after storage at 15 ◦C to 25 ◦C. The pH of the extract decreased

from 6.4 initially to 4.8 after 360 d of storage under these conditions. The

authors conclude that this is an insignificant change in the pH of the water

over this period of time. They also indicate that since the acid content of the

Rusar/Artek (in this paper they use Rusar and Artec/Artek interchangeably,

8
2. Background

leading to the conclusion that these fibers are chemically very similar) and

Armos is so low, that this is not an issue for these fibers; however no data

is offered to support this conclusion [17].

9
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

This page intentionally left blank.

10
3. Experimental

The principal objective of this study is to evaluate the amount of chloride

released from Rusar, Armos, Artec, SVM, and PPTA fibers while exposed to

water in a liquid or gas state. Fibers were immersed in deionized water for

a specified period of time, and the pH and chloride ion content of the water

were measured over time using ion-selective electrodes. Infrared analysis was

performed on the unexposed fibers to assist in verification of their structure

and will form a basis for future studies of the effect of exposure to water on

their chemical structure.

3.1 Fiber Exposure to Aqueous Environments

As mentioned previously, during the first part of this study, chlorine

emission and pH were monitored by ion-selective electrodes as a function

of time under controlled conditions on fibers submerged in deionized water.

Fiber samples of the Armos, Artec (removed from a fabric sample), Rusar,

SVM, and PPTA (removed from a fabric sample) weighing 5 g, were immersed in 500 mL of deionized water for 10 d and measured at specified

intervals. Previous studies in our laboratory had shown that, after 10 d, no

further changes in pH or chlorine emission were observed. The beakers were

kept tightly sealed with paraffin wax film except when measurements were

being made. The total volume of water was kept constant in the beakers

by addition of deionized water, if necessary, over the course of the experiment. The generation of chloride ions into solution and solution pH were

monitored using a Fisher Scientific Accumet Excel XL50 multichannel meter

with a chloride combination ion-selective electrode (ISE) and a pH electrode.

The standard uncertainty for the pH electrode is ± 0.1 pH units, and the

standard uncertainty is ± 0.2 % for the ion-selective elctrode [18].

3.2 Infrared Spectroscopy Measurements

Infrared analysis was carried out using a Bruker Vertex 80 Fourier Transform Infrared Spectrascope (FTIR), equipped with a Smiths Detection Durascope Attenuated Total Reflectance (ATR) accessory. Dry air was used as

the purge gas. Constant pressure on the yarns was applied using the force

monitor on the Durascope. FTIR spectra were recorded at a resolution of 4

11
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

cm−1 between 4000 cm−1 and 600 cm−1 and averaged over 128 scans. Three

different locations on each yarn were analyzed. Standard uncertainties associated with this measurement are typically ± 4 cm−1

in wavenumber and

1 % in peak intensity [19].

12
4. Results and Discussion

4.1 Chloride Ion Concentration and

pH Measurements

Representative pH and chloride ion concentration measurements as a

function of time are shown in Figure 4.1 through Figure 4.3. The most

rapid changes in both pH and chloride ion concentration occur in the first

five days of liquid water exposure. The change was greatest for the SVM

yarn, which is expected due to the high chlorine content of this yarn [17].

The change in pH as a function of immersion time is shown in Figure 4.1.

The SVM and Rusar fibers showed a pH decrease from approximately pH

6.0 to approximately pH 3.0. Artec showed the smallest change in pH as a

function of time, with a reduction to approximately pH 5.5 in 10 d. Armos

and PPTA showed a decrease in pH from approximately pH 6.0 to pH 4.5.

As would be expected from the pH results, SVM showed the greatest

increase in overall chloride ion concentration, as shown in Figure 4.2. The

overall increase was from almost zero mg/L chlorine in solution up to 158

mg/L chlorine in solution for the SVM yarn. Interestingly, this trend is

not mimicked by the Rusar fiber, indicating that another species may be

responsible for its drop in pH. In an effort to better separate the scale, the

chloride ion results obtained for the Artec, PPTA, Armos, and Rusar fibers

are replotted in a separate graph, Figure 4.3. None of the other fibers investigated exhibited a significant change in the chloride ion concentration.

One may note that the pH of the deionized water control is approximately

6.0. We attribute this lower-than-expected pH to the well-known formation

of weak carbonic acid in deionized water after exposure to carbon dioxide

in the air [20]. The water deionizer source used for these experiments stores

the deionized water in a large reservior as it is made, so the water is exposed

to air, and carbon dioxide, for a long time before use, allowing for ample

formation of carbonic acid. We believe that the presence of the carbonic

acid in solution may contribute to the removal of chloride ions from some

of the fibers in solution. Though further chemical analysis will be necessary

to confirm this hypothesis, one can surmise that the source of the chloride

ion is residual ammonium chloride formed from the reaction of terephthalic

acid chloride and the primary or secondary amines to form the polymers

studied herein. The polycondensation reaction of the amine and the acid

13
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

Immersion (d)

0 2 4 6 8 10

pH

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

DI Water 

PPTA

Artec 

Armos 

SVM 

Rusar 

Figure 4.1: Change in pH following immersion in deionized (DI) water. The

low pH value observed for deionized water is probably due to the formation

of carbonic acid in deionized water after exposure to carbon dioxide in the

air.

14
4. Results and Discussion

Immersion time (d)

0 2 4 6 8 10

Chloride ion concentration (mg/L)

0

20

40

60

80

100

120

140

160

180

DI Water 

PPTA

Artec

Armos 

SVM

Rusar 

Figure 4.2: Chloride ion generation following immersion in deionized (DI)

water for all fibers.

15
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

Immersion time (d)

0 2 4 6 8 10

Chloride ion concentration (mg/L)

0

1

2

3

4

5

DI Water 

PPTA

Artec

Armos 

Rusar 

Figure 4.3: Chloride ion generation following immersion in deionized (DI)

water for all fibers except SVM.

16
4. Results and Discussion

chloride to form the amide bond will result in the small molecule byproduct

HCl. The nitrogen in the amide bond has a lone pair of electrons that can

react with the HCl to form the ammonium chloride ion pair. Traces of this

salt may remain after thorough washing of the fibers, and when the polymer

is immersed in water for these studies, small amounts of chloride ion may

be gradually released from the polymer. The carbonate ion could displace

some of the chloride ion associated with the ammonium salt, thereby increasing the chloride ion concentration in the solution and contributing to

the increasing levels of chloride ion detected in this study, and also potentially forming HCl in solution. Future studies are planned to examine this

phenomenon.

4.2 Analysis of Chemical Structure

Due to the apparent lack of available literature regarding the infrared

analysis of the chemical structure of the copolymer fibers utilized in this

study, a separate effort was undertaken to investigate their spectra. This

will form the basis of work to examine the effect of moisture exposure on the

chemical structure of these fibers, which will be the subject of a forthcoming

report. Peak assignments were generated through the review of several references on PPTA fibers [21, 22], general infrared spectroscopy [23, 24, 25],

and benzimidazole spectroscopy [26, 27]. The results of this analysis are presented in Table 1. Representative ATR FT-IR spectra for all fibers studied

are presented in the Appendix. As expected, the spectra of the copolymer

fibers show characteristics found in the spectra of the two homopolymers.

No information related to relative copolymer ratios for the different fibers

could be determined from this analysis, but this may be a subject of future

work.

17
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

This page intentionally left blank.

18
5. Conclusions and Future Work

All fibers studied herein, even PPTA, emit some quantity of acid when

immersed in liquid water. However, the pH drop for the fibers SVM and

Rusar was greater than that observed for the other fibers. The theory that

hydrochloric acid is responsible for this reduction in pH may only be true for

the SVM fibers, as these fibers were the only ones that exhibited an increase

in chloride ion concentration to correspond to the reduction in pH. This leads

us to the conclusion that another type of acid must be responsible for the pH

reduction in the Rusar sample. Elemental analysis via X-ray fluorescence

(XRF) of all the fibers in this study will be performed in a future study to

estimate the concentration of chlorine in the samples, and possibly further

elucidate the species responsible for the pH reduction, especially in the Rusar

sample. Additionally, studies to examine whether exposure to water vapor

has the same effect on pH as liquid water are currently underway, as these

studies better represent the use environment for body armor. These results

will be the subject of a future publication. Finally, a study to examine the

effect of exposure to water in both its liquid and vapor form on the chemical

and physical properties of these fibers will be performed to determine if

these fibers have any of the vulnerabilities to hydrolysis that have become

apparent in other commercial fibers used in body armor.

19
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

This page intentionally left blank.

20
Appendix

21
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

Wavenumber (cm−1)

Artec Armos Rusar SVM PPTA Note General Assignment

3309 Broad NH Stretch [22]

3271 3271 3271 Broad Imidazole NH proton hydrogen

bonding to water molecules or

nearby imine [26]

2917 2917 2916 2925 2916 Weak Aromatic CH stretch [24]

2849 2849 2855 2848 2848 Weak Aromatic CH stretch [24]

1638 1639 1638 1632 1638 Strong Amide I band carbonyl [21]

1596 1596 1596 1593 Shoulder Benzimidazole NH in plane

bend [27]

1537 Sharp

Shoulder

Amide II band carbonyl [21]

1525 Sharp

Shoulder

Aromatic CH stretch [24]

1513 1512 1513 1510 Sharp

Shoulder

Amide II band carbonyl [21]

1487 1486 1488 1488 Shoulder Benzimidazole ring stretch [27]

1467 1464 Shoulder Benzimidazole ring stretch [27]

1443 1443 1443 1443 Shoulder Benzimidazole [27]

1417 Shoulder Benzimidazole ring stretch [27]

1406 1406 1406 1394 Shoulder Primary amine salts [24]

1305 1304 1304 1300 1303 Shoulder CN stretch; Amide III group motion [22]

1244 1245 1247 1244 Shoulder Benzimidazole ring stretch [27]

1187 1186 1186 1186 Medium Benzimidazole in-plane CH

bend [27]

1108 1107 1108 1106 1107 Medium Benzimidazole in-plane CH

bend [26]

1016 1016 1016 1015 1017 Medium CH out of plane bend [22]

957 957 955 957 Weak Imidazole in plane bend [27]

890 889 890 889 893 Weak CH out of plane [21]

862 862 862 861 862 Shoulder Unassigned

820 Strong CH out of plane [22]

808 808 808 806 Broad,

Medium

Unassigned

820 Strong CH out of plane [22]

712 712 712 712 Broad,

Shoulder

Unassigned

689 689 689 689 Shoulder Unassigned

608 609 608 609 Shoulder Unassigned

Table 5.1: Infrared peak assignments for all fibers studied.

22
5. Conclusions and Future Work

Armos

Wavenumber (cm-1)

3600 3000 2400 1800 1200 600

Absorbance

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

Imidazole N-H proton

hydrogen bonding

to water molecules

or nearby imine

3271 cm-1

Benzimidazole

ring stretch

1487 cm-1

Amide I band 

carbonyl, 1639 cm-1

Benzimidazole

ring stretch

1244 cm-1

Figure 5.1: ATR FT-IR spectrum of virgin Armos fiber.

23
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

Artec

Wavenumber (cm-1)

3600 3000 2400 1800 1200 600

Absorbance

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

Imidazole N-H proton

hydrogen bonding

to water molecules

or nearby imine

3271 cm-1

Benzimidazole

ring stretch

1486 cm-1

Amide I band 

carbonyl, 1638 cm-1

Benzimidazole

ring stretch

1245 cm-1

Amide II band 

carbonyl, 1513 cm-1

Figure 5.2: ATR FT-IR spectrum of virgin Artec fiber.

24
5. Conclusions and Future Work

Rusar

Wavenumber (cm-1)

3600 3000 2400 1800 1200 600

Absorbance

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

Imidazole N-H proton

hydrogen bonding

to water molecules

or nearby imine

3271 cm-1

Benzimidazole

ring stretch

1488 cm-1

Amide II band 

carbonyl, 1513 cm-1

Benzimidazole

ring stretch

1247 cm-1

Amide I band 

carbonyl, 1638 cm-1

Figure 5.3: ATR FT-IR spectrum of virgin Rusar fiber.

25
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

SVM

wavenumber (cm-1)

3600 3000 2400 1800 1200 600

Absorbance

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

Benzimidazole

ring stretch

1488 cm-1

Benzimidazole

ring stretch

1244 cm-1

Amide I band 

carbonyl, 1638 cm-1

Aromatic 

CH stretch, 

1525 cm-1

Figure 5.4: ATR FT-IR spectrum of virgin SVM fiber.

26
5. Conclusions and Future Work

PPTA

Wavenumber (cm-1)

3600 3000 2400 1800 1200 600

Absorbance

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

NH stretch,

3309 cm-1

Amide I 

carbonyl,

1638 cm-1

Amide II band carbonyl,

1537 cm-1

Primary amine

salts,

1394 cm-1

CN Stretch

Amide III

group motion,

1303 cm-1

Figure 5.5: ATR FT-IR spectrum of virgin PPTA fiber.

27
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

This page intentionally left blank.

28
6. References

[1] J. W. S. Hearle. High Performance Fibers. Woodhead Publishing,

Cambridge, 2001.

[2] A. A. Leal, J. M. Deitzel, and J. W. Gillespie. Assessment of compressive properties of high performance organic fibers. Composites Science

and Technology, 67(13):2786–2794, 2007.

[3] Artec fiber vs rusar fiber technical differences (as per yarn manufacturer

communication), 2006.

[4] I. V. Slugin, G. B. Sklyarova, A. I. Kashirin, and L. V. Tkacheva.

Rusar para-aramid fibres for composite materials for construction applications. Fibre Chemistry, 38(1):25–26, 2006.

[5] David Hand. Hybrid vests made from twaron fibers and co-polymer

aramid yarns containing 5-amino-2-(p-aminophenyl)-benzimidazole or

related monomers, January 2006.

[6] N. N. Machalaba, N. N. Kuryleva, L. V. Okhlobystina, P. A. Matytsyn,

and I. A. Andriyuk. Tver’ fibres of the armos type: Manufacture and

properties. Fibre Chemistry, 32(5):319–324, 2000.

[7] I. V. Slugin, G. B. Sklyarova, A. I. Kashirin, L. V. Tkacheva, and S. V.

Komissarov. Rusar microfilament yarn for ballistic protection. Fibre

Chemistry, 38(1):22–24, 2006.

[8] A. E. Zavadskii, I. M. Zakharova, and Z. N. Zhukova. Features of the

fine structure of aramid fibres. Fibre Chemistry, 30(1):6–10, 1998.

[9] K. E. Perepelkin, N. N. Machalaba, and V. A. Kvaratskheliya. Properties of armos para-aramid fibres in conditions of use. comparison with

other para-aramids. Fibre Chemistry, 33(2):105–114, 2001.

[10] S. V. Kotomin, A. A. Basharov, V. G. Bova, and E. M. Sapozhnikov.

Realization of the strength of armos fibres with different acidity in epoxy

plastics. Fibre Chemistry, 28(1):48–49, 1996.

[11] S. F. Grebennikov, T. V. Smotrina, N. P. Lebedeva, and K. E. Perepelkin. Molecular mobility in the superstrong para-aramid fibre-water

system. Fibre Chemistry, 40(3):206–207, 2008.

29
Study of Acid Generation from Copolymer Fibers based on

5-amino-2-(p-aminophenyl)-benzimidazole

[12] K. E. Perepelkin, S. F. Grebennikov, and N. P. Lebedeva. Sorption

of water vapors by high-strength para-aramid fibres. Fibre Chemistry,

39(5):420–423, 2007.

[13] K. E. Perepelkin, I. V. Andreeva, G. P. Meshchervakova, and I. Y.

Morgoeva. Change in the mechanical properties of para-aramid fibres

in thermal aging. Fibre Chemistry, 38(5):400–405, 2006.

[14] K. E. Perepelkin, I. V. Andreeva, E. A. Pakshver, and I. Y. Morgoeva. Thermal characteristics of para-aramid fibres. Fibre Chemistry,

35(4):265–269, 2003.

[15] K. E. Perepelkin, O. B. Malan’ina, E. A. Pakshver, and R. A. Makarova.

Comparative evaluation of the thermal properties of aromatic fibres

(polyoxazole, polyimide, and polyaramid). Fibre Chemistry, 36(5):365–

369, 2004.

[16] V. A. Platonov, G. G. Frenkel, and A. M. Shchetinin. X-ray study of

the effect of heat on the structural parameters of armos fibres. Fibre

Chemistry, 35(4):283–286, 2003.

[17] V. M. Shchetinin, I. V. Tikhonov, and A. V. Tokarev. The pseudoeffect

of the hydrogen chloride contained in the aramid fibres svm, armos,

and rusar on their properties during prolonged storage and use. Fibre

Chemistry, 38(6):450–452, 2006.

[18] Accumet Excel XL Series Meters User Manual. Fisher Scientific, 1st

edition, 2006.

[19] Vertex 80 User Manual. Bruker Optics, Ettlingen, Germany, 1st edition, 2006.

[20] L. M. Nollet. Handbook of Water Analysis. CRC Press, New York, 1st

edition, 2000.

[21] L. Penn and F. Larsen. Physicochemical properties of kevlar 49 fiber.

Journal of Applied Polymer Science, 23:59–73, 1979.

[22] A.M. Tiefenthaler and M.W. Urban. Surface studies of polymer films

and fibers cy circle atr ft-ir. Applied Spectroscopy, 42(1):163–166, 1988.

[23] R. R. Gupta. Physical Methods in Heterocyclic Chemistry. General

Heterocyclic Chemistry Series. John Wiley, New York, 1984.

[24] R.M. Silverstein, G.C. Bassler, and T.C. Morrill. Spectrometric Identification of Organic Compounds. John Wiley and Sons, New York, 5th

edition, 1991.

[25] G. Socrates. Infrared Characteristic Group Frequencies. John Wiley,

Chichester, 1980.

[26] C. Cameron. Enhanced Rates of Electron Transport in ConjugatedRedox Polymer Hybrids. PhD thesis, Memorial University of Newfoundland, 2000.

30
REFERENCES

[27] A. Suwaiyan, R. Zwarich, and N. Baig. Infrared and raman spectra of

benzimidazole. Journal of Raman Spectroscopy, 21:243–249, 1990.

31