Transport Properties of N-Methylolated Nylon-6: 

Chitosan Blend Membranes 

by Eugene Napadensky and Yossef A. Elabd 

ARL-TR-3917 September 2006 

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Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-3917 September 2006 

Transport Properties of N-Methylolated Nylon-6: 

Chitosan Blend Membranes 

Eugene Napadensky 

Weapons and Materials Research Directorate, ARL 

Yossef A. Elabd 

Department of Chemical and Biological Engineering, Drexel University 

Approved for public release; distribution is unlimited.
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 Transport Properties of N-Methylolated Nylon-6: Chitosan Blend 

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14. ABSTRACT 

A series of N-Methylolated Nylon-6−chitosan blend membranes was evaluated for their potential use as breathable (high water 

transport) barriers (low chemical agent transport) for military and civilian protective clothing apparel. Nylon-6 was methylolated and subsequently blended with chitosan at different compositions and processing conditions (room temperature, 100 oC, 

and 200 oC). Vapor transport rates of water (breathability) and dimethyl methylphosphonate (protection) (a simulant of the 

nerve agent Sarin) were measured as a function of these blend parameters with the use of a modified ASTM (American Society 

for Testing Materials) method E-96-95 and were compared to Nafion1

 117. Water transport rate was found to be between 1,000 

and 2,000 g/m2

day, depending on specific composition of the membranes and thermal treatment. The effective dimethylmethylphosphonate permeability (a thickness independent value) of the blend membranes was two orders of magnitude lower than 

Nafion 117. The selectivity of N-Methylolated Nylon-6−chitosan blend was 15.3, seven times higher than Nafion 117. It was 

shown that these membranes, manufactured when hydrophilic and hydrophobic polymers were conjoined, have resulted in a 

material that is both breathable and protective. These semi-permeable membranes will be economically attractive for military 

and civilian applications in the area of personal protection since the polymer components are inexpensive and the membrane 

fabrication is simple. 

1

Nafion is a registered trademark of DuPont.

15. SUBJECT TERMS

 breathable barrier; chemical warfare; chitosan; nylon-6; polymer; protective clothing; vapor permeation 

16. SECURITY CLASSIFICATION OF:

19a. NAME OF RESPONSIBLE PERSON

 Eugene Napadensky 

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 Standard Form 298 (Rev. 8/98) 

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iii

Contents 

List of Figures iv

List of Tables iv

Acknowledgments v

1. Introduction 1

2. Experimental 2

2.1 Materials..........................................................................................................................2 

2.2 Methylolation Procedure .................................................................................................2 

2.3 Membrane Preparation ....................................................................................................3 

2.4 Sorption Experiments......................................................................................................4

2.5 Vapor Permeation Procedure...........................................................................................4 

3. Results and Discussion 6

3.1 Elemental Analysis..........................................................................................................6 

3.2 Visual Evaluation of Membranes....................................................................................7 

3.3 Sorption Experiments......................................................................................................7

3.4 Vapor Permeation and Selectivity...................................................................................8 

3.5 Effect of Composition and Thermal Treatment ............................................................11 

4. Conclusion 12

5. References 13

Distribution List 14 
iv

List of Figures 

Figure 1. Methylolation of Nylon-6 with formaldehyde. .............................................................. 2 

Figure 2. Thermal crosslinking reaction illustrating cross linking of Nylon-6 with methylol 

group to form a -CH2- bridge.................................................................................................. 3 

Figure 3. Schematic representing a cutaway of the cap-membrane assembly showing an opentop cap, membrane, and cored septa. ...................................................................................... 5 

Figure 4. Comparison of optical clarity of selected MNC membranes ......................................... 7 

Figure 5. MNC-41-(T200) showing phase segregation regions. ................................................... 8 

Figure 6. Water vapor transmission rate........................................................................................ 9 

Figure 7. DMMP vapor transmission rate...................................................................................... 9 

Figure 8. Selectivity of materials................................................................................................. 10 

Figure 9. Water and DMMP transport rates as a function of blend composition. ....................... 11 

Figure 10. Effects of thermal treatment on transport of water and DMMP vapor....................... 12 

List of Tables 

Table 1. N-methylol Nylon-6: chitosan blend membranes: blend compositions and 

processing conditions.............................................................................................................. 4 

Table 2. Water and DMMP sorption of blended membranes. ....................................................... 8 

Table 3. Vapor permeability and selectivity results..................................................................... 10 
v

Acknowledgments 

This work was a collaborative project between Drexel University and the U.S. Army Research 

Laboratory. The authors gratefully acknowledge the financial support of the U.S. Army Research 

Office through grants W911NF-05-1-0036 and W911NF-04-1-0258. 
vi

INTENTIONALLY LEFT BLANK
1

1. Introduction 

Chemical-biological protective clothing technology remains a high priority among people responsible for the safety of U.S. military personnel, not just from the obvious point of exposure to 

chemical or biological agents abroad and at home but also from another, less often considered but 

still important safety factor: breathability. Until recently, the main goal in the development of 

chemical-biological protective clothing was to maximize protection. In the past, one of the more 

commonly used materials for this application was butyl rubber, which worked on the principle of 

total blockage. Butyl rubber is an effective barrier to most harmful agents at certain thicknesses, 

but it has certain disadvantages. Wearing garments manufactured from this material in combat or 

in other situations that involve physical activity is not practical since the lack of breathability of 

this material causes heat fatigue and exhaustion (1). A different approach for protection against 

chemical-biological threats is sorption materials. Protective suits such as MOPP (mission-oriented 

protective posture) and JSLIST (Joint Service Lightweight Integrated Suit Technology) work on 

the principle of capturing toxic materials with fillers such as activated carbon. JSLIST is more 

breathable, but it does not provide as much protection as butyl rubber and is still heavy and bulky, 

and working in this suit is limited to about 45 min/hr (2). In addition, the absorbent materials last 

no longer than 3 to 6 months after initial unpacking of the garment. The time starts the moment 

when the garment is removed from its hermetically sealed packing for the first time, regardless 

whether it was actually worn. After that time period, activated carbon loses a significant amount 

of its sorption ability and no longer provides the required levels of protection. 

A completely different approach to the problem of chemical-biological protection is the concept of 

semi-permeable membranes, namely, materials that allow passage of moisture (perspiration) but 

block harmful molecules and organisms. These materials will offer protection in a hostile environment without causing significant heat fatigue and exhaustion. A number of such semi-permeable 

membranes are being developed in industry and at the U.S. Army Research Laboratory. 

The scope of this work was to examine membranes manufactured when hydrophilic and hydrophobic polymers are conjoined, which results in a material that is both breathable and protective. 

In this study, the transport properties of polymer blend membranes of chitosan and N-methylol 

Nylon-6 were examined and evaluated for their use as chemical and biological protective clothing. 

Shieh and Huang (3) recently investigated N-methylol Nylon-6: chitosan blend membranes as they 

apply to the separation of ethanol-water mixtures via a pervaporation process. In this work, 

Nylon-6 was methylolated and subsequently blended with chitosan at different compositions and 

processing conditions. Vapor transport rates of water (breathability) and dimethyl-methylphosphonate (DMMP1

) (protection) were measured as a function of these blend parameters. 

 1a simulant of the nerve agent Sarin
2

2. Experimental 

2.1 Materials 

Experimental membranes were manufactured from Nylon-6 (Collomer Associates, Inc., molecular 

weight approximately 150,000) and chitosan (Aldrich, 75% to 85% deacetylation, molecular 

weight 190,000 to 310,000). Other materials in this study included BDU (battle dress uniform) 

fabric, (50/50 Nylon/cotton, obtained from the U.S. Army Natick Soldier Center), and Nafion2

-117 

purchased from Aldrich. In addition, other chemicals used in these experiments were dry nitrogen 

gas, water (J.T. Baker, HPLC [high performance liquid chromatography] grade), DMMP 

(Lancaster Synthesis, 97%), Drierite3 (anhydrous calcium sulfate, 97%), 37% formaldehyde 

solution (J.T Baker, reagent grade), formic acid (EM4

 Science, 98% assay), acetone (WarnerGraham Co., reagent grade), and glacial acetic acid (J.T. Baker). 

2.2 Methylolation Procedure 

Nylon-6 was modified through a reaction with formaldehyde in formic acid (see figure 1), 

described in detail by Cairns et al. (4). Specifically, we dissolved Nylon-6 in 88% formic acid 

by stirring for 12 hours at room temperature in a covered beaker, which yielded a 6.5% (weight 

per volume) solution. To this solution, five molar equivalents of 37% formaldehyde were added 

and allowed to react for 4 hours at 60 °C. According to Shieh and Huang (5), this molar ratio of 

formaldehyde to Nylon-6 should result in 33% methylolation of amide functional groups in the 

“backbone” of the polymer. The modified polymer was precipitated from solution by the addition 

of water and was washed repeatedly with alternating water and acetone to remove residual formic 

acid. The purified polymer was dried in a convection oven at 40 °C. 

+ CH2

O

R

O

NH C R

CH2OH

R

O

N C R

O

H OH C

Figure 1. Methylolation of Nylon-6 with formaldehyde. 

This reaction incorporates methylol groups in Nylon-6, which may improve miscibility with 

chitosan. More importantly, these added methylol groups provide an avenue for thermal 

crosslinking. When the material is exposed to heat, methylol groups react with secondary 

 2

Nafion is a registered trademark of DuPont.

3

Drierite is a registered trademark of W. A. Hammond Drierite Co.

4EM is not an acronym.
3

ammines, expelling water and creating a -CH2- crosslink (see figure 2). This reaction could also 

lead to improved strength in the polymer blend. 

By varying the initial methylolation content, we can selectively control the crosslink density and 

subsequently, the physical properties. In addition to reactions with amines in the Nylon-6 backbone, methylol groups should react with chitosan when the polymer blends are exposed to 

thermal treatment. Since deacetylation of chitosan is listed as 75% to 85%, 15% to 25% 

of secondary amines remain completely available for participation in this reaction. This new 

covalent bond between chitosan and Nylon-6 should prevent chitosan dissolution during acidic 

conditions, allowing for the use of the membranes in a wider range of applications. 

R

NH

O C

R

+

R

N

O C

R

CH2 OH

R

N

C O

R

CH2

R

N

C O

R

Figure 2. Thermal crosslinking reaction illustrating cross linking of Nylon-6 with methylol group 

to form a -CH2- bridge. 

2.3 Membrane Preparation 

Before blending, solid debris present in the chitosan solution (1% weight per volume [w/v] 

chitosan in a 5% acetic acid) was removed by vacuum filtration. After filtration, the solvent was 

evaporated and the chitosan film was dried in convection oven at 40 °C for 2 days. We prepared 

membranes of N-methylol Nylon-6: chitosan by dissolving the two polymers together in 88% 

formic acid and then solution casting onto a Teflon5 surface. Methylolated Nylon-6 dissolves 

quickly; however, chitosan dissolution above 2% w/v was difficult because of gelation. Because 

of this, different blend compositions were cast at different polymer concentrations (see table 1) 

to facilitate chitosan dissolution. After the cast films were dried (~24 to 48 hours), portions of 

each film were retained for evaluation and are referred to as “as cast” (labeled “Nox” in table 1), 

while other portions were thermally crosslinked by heat pressing at 20,000 lb/in2

 for approximately 30 to 60 minutes at 100 °C. In addition, selected samples were annealed (thermally 

crosslinked) at 200 °C and 20,000 lb/in2

 for 30 minutes to further investigate the effects of 

thermal treatment. 

Table 1 lists the information on each blend investigated. MNC-ab (c) is used for sample names, 

in which ab refers to the weight ratio of N-methylol Nylon to chitosan and c refers to the thermal 

 5Teflon is a registered trademark of E. I. DuPont de Nemours and Co., Inc.
4

treatment (Nox represents no thermal treatment, T100 represents heat pressed at 100 °C, and 

T200 represents heat pressed at 200 °C). 

Table 1. N-methylol Nylon-6: chitosan blend membranes: blend compositions and processing conditions. 

Blend Membrane Polymer Concentration 

(percent; w/v) 

Blend Composition Nmethylol Nylon-6: chitosanTemperature and Heat 

Pressing (20 Klb/in2

) Time 

MNC-12 (Nox) 3.3 1:2 NA 

MNC-12 (T100) 3.3 1:2 100 °C (1 hr) 

MNC-11 (Nox) 3.3 1:1 NA 

MNC-11 (T100) 3.3 1:1 100 °C (1 hr) 

MNC-21 (Nox) 2.8 2:1 NA 

MNC-21 (T100) 2.8 2:1 100 °C (30 min) 

MNC-21 (T200) 2.8 2:1 200 °C (30 min) 

MNC-41 (Nox) 4.2 4:1 NA 

MNC-41 (T100) 4.2 4:1 100 °C (30 min) 

MNC-41 (T200) 4.2 4:1 200 °C (30 min) 

NA = not applicable 

2.4 Sorption Experiments 

Sorption of the cast films was evaluated by exposure to water and DMMP (separately). Samples 

were dried, weighed (dry weight), and submerged in the corresponding liquid. After a specified 

period of time, samples were removed, excess moisture was dabbed from the surface, the weight 

of swollen samples was recorded (wet weight), and samples were returned to the solvent. This 

operation was performed at intervals of 24 hours until no weight change was observed. Even 

though this procedure is unsophisticated and simple to perform, it generally yields good, reproducible results. Difficulties start to arise when material becomes tacky or slimy and starts to 

break apart during the dabbing process. Of course, with any analytical method, a certain scatter 

is associated with the measurements and if the weight change is small overall, it becomes 

undistinguishable from zero. Sorption is defined here as 

100

dry polymer wt

(wet polymer wt- dry polymer wt) wt% = ∗ (1) 

A balance with 0.01 mg accuracy was used. Three experiments were conducted on each sample. 

The weights and errors reported are the averages and standard deviations of these experiments, 

respectively. 

2.5 Vapor Permeation Procedure 

Vapor permeation experimental procedure was based on a modified ASTM (American Society 

for Testing and Materials) E 96-95 (Standard Test Methods for Vapor Transmission of 

Materials) method and is described in more detail elsewhere (6). Equipment for this experiment 

consisted of a temperature-controlled (35 °C) oven with a nitrogen gas sweep, which maintained 

a low relative humidity (10%). Equipment consisted of 20-ml vials with open-top caps and 
5

Teflon-lined septa with a 14-mm hole cut in the center of the septa to match the hole in the cap. 

Sample membranes were cut into circles with a 22-mm diameter (the size of the original septa) 

and placed inside the cap with the cored septa placed behind to provide an air-tight seal (see 

figure 3). 

Figure 3. Schematic representing a cutaway of the cap-membrane 

assembly showing an open-top cap, membrane, and cored 

septa. 

Vials were filled with 10 to 15 ml of liquid (water or DMMP), capped with the previously 

described caps, and placed in the oven. Liquid inside the vials creates a 100% saturated 

environment on the internal side of the membrane; this provides a concentration gradient across 

the membrane. Vial weights were recorded every 24 hours as more vapor penetrated through the 

membrane, until a sufficient amount of data was collected to determine constant (steady state) 

rate of weight loss for each vial. From these data, vapor transfer rates for water and DMMP, 

effective permeability, and selectivity were calculated. 

The vapor transport rates (VTRs) of water and DMMP through the membranes were calculated 

on the basis of weight loss from permeant-containing vials described in the previous section. 

VTR is defined as steady state transport rate per unit area and can be expressed as follows: 

(t A)

G VTR

∗ = (2) 

in which A is exposed area of the membrane that covered the vial (for this experiment, the diameter 

of the opening in the cap is constant at 14 mm, and that corresponds to area of 0.000154 m2

), and 

G/t can be regressed from weight loss data, as explained before. However, VTR does not account 

for the thickness of the membrane effectively; its value is different for the same material of different thicknesses. To accurately compare properties of evaluated materials independently of the 

thickness, an effective permeability must be calculated. Effective permeability (Peff) can be 

expressed as 

Cored septa

Open-top cap

Membrane
6

S*(P P )

L VTR P

1 2

eff

−

∗ = (3) 

in which S is the saturation vapor pressure at the test temperature (millimeters mercury [Hg]), P1 is 

the partial pressure or relative humidity on the challenge side, P2 is partial pressure on the exit side, 

and L is the sample thickness (m). Saturation vapor pressure for water at 35 °C is 41.175 mm Hg 

(7) and for DMMP at 35 °C is 6.77 mm Hg. We determined the DMMP vapor pressure by interpolating from known values at 25 °C and 65 °C (8). 

Another important parameter for perm-selective membranes is selectivity (α), which is defined 

as a ratio of effective permeabilities (equation 3): 

Peff (water)

Peff (DMMP)

α = (4) 

It provides numerical assessment of preferential transport of the desired permeant compared to 

the undesired permeant. In this case, water vapor transport (desired permeant) is compared to 

DMMP vapor transport (undesired permeant). 

A high value for selectivity indicates high affinity to transport water vapor (thus providing 

breathability to reduce heat fatigue), while having low affinity to transport of DMMP vapor 

(providing protection from chemical agents). Thus, a material with high selectivity is desirable 

for breathable chemical and biological protective garments. High water permeability will help to 

remove perspiration and thus reduce possibility of heat fatigue, while low DMMP permeability 

indicates that harmful chemical agents (e.g., nerve agent gas) will have difficulty penetrating the 

garment and affecting the Soldier. 

3. Results and Discussion 

3.1 Elemental Analysis 

Elemental analysis was performed by Atlantic Microlabs, Inc., on Nylon-6 and methylolated 

Nylon-6 samples to quantify the level of methylolation. The theoretical molar ratio of nitrogen: 

oxygen:carbon for Nylon-6 is 1:1:6 and the analytical result for Nylon-6 was 1:1.07:6. For 33% 

methylololated Nylon-6, it was expected to be 1:1.3:6.3, but actual results were 1:1.22:6.08. 

Based on these data and taking into account that oxygen is present in amounts slightly elevated 

over the theoretical level, it is estimated that the actual level of methololation is approximately 

15%. 
7

3.2 Visual Evaluation of Membranes 

Visual observations of blend membranes show some differences that are attributed to individual 

composition ratios and thermal treatments of the examined membranes. All films possess a 

yellowish tint, which is not really surprising if we consider the presence of chitosan. Also, it was 

noted that the yellow color darkens with thermal treatment. 

Samples appear to be semi-transparent and show differences in optical clarity. Optical clarity, 

unlike color, does not seem to be significantly affected by thermal treatment. For example, 

MNC-41 films do not become more opaque with thermal treatment; only a color change from 

white to yellow is observed. The transparency of the material ranges from almost completely 

transparent (MNC-21) to borderline opaque (MNC-41). Figure 4 shows photographs of several 

of the membranes in this study. 

Figure 4. Comparison of optical clarity of selected MNC membranes. (Membranes are weighed 

down with glass slides.) 

These different levels of transparency may be an indication of relative levels of phase separation. 

Increase in opacity may be a sign of gross (large scale) phase separation. For the case of MNC-41 

membranes (80 wt% N-methylol Nylon-6), a close visual examination clearly reveals significant 

phase separation. A multitude of roughly circular regions ~1 to 3 mm diameter, evenly spaced 

throughout the film, is easily discerned even without any special optical equipment, as shown in 

figure 5. 

3.3 Sorption Experiments 

As shown in table 2, weight uptake in DMMP is, for all intents and purposes, zero. This 

suggests that blend membranes at all compositions will be good barriers (resistant) to harmful 

chemical nerve agents. Water sorption increases with increasing chitosan content in the blend. 

This is not surprising since chitosan is hydrophilic. The only exception is MNC-11 (Nox), and it 

is not really clear what is the cause of such low values associated with that particular sample. 

Another observation can be made about the effects of thermal processing. Again, as would be 

expected, water sorption levels decrease for membranes that were exposed to higher temperatures. This indicates that higher temperatures result in a higher crosslinking density. 
8

Figure 5. MNC-41-(T200) showing phase segregation regions. 

Table 2. Water and DMMP sorption of blended membranes. 

Blend Membrane Blend Composition Nmethylol Nylon-6: ChitosanSorption (wt%) 

Water DMMP 

MNC-12 (Nox) 1:2 134 ±4 -8 ±1 

MNC-12 (T100) 1:2 90 ±9 3 ±3 

MNC-11 (Nox) 1:1 68 ±2 -4 ±1 

MNC-11 (T100) 1:1 99 ±13 3 ±17 

MNC-21 (Nox) 2:1 112 ±10 10 ±10 

MNC-21 (T100) 2:1 89 ±13 0 ±2 

MNC-21 (T200) 2:1 36 ±9 -2 ±1 

MNC-41 (Nox) 4:1 77 ±8 12 ±6 

MNC-41 (T100) 4:1 66 ±5 1 ±1 

MNC-41 (T200) 4:1 28 ±10 2 ±1 

In addition to measuring water and DMMP uptake, we checked selected samples of N-methylolated 

Nylon-6 for solubility in 88% formic acid. The rationale for this experiment was to verify crosslinking. Although this material dissolves in formic acid initially, after going through thermal 

processing, it becomes insoluble. This confirms the ability to modify Nylon-6 to create a crosslinked network. 

3.4 Vapor Permeation and Selectivity 

Figures 6 and 7 and show VTR results for water and DMMP, respectively, of the chitosanmethylololated Nylon-6 blend membranes. Table 3 shows numerical values for the data in 
9

figures 6 and 7. Data for Nafion 117 were collected and included as a standard frame of 

reference. 

WATER VTR 

MNC-12 (Nox)MNC-12 (T100)

MNC-11 (Nox)

MNC-11 (T100)MNC-21 Nox

MNC-21 (T100)

MNC-21 (T200)

MNC-41 (Nox)

MNC-41 (T100)

MNC-41 (T200)

Nafion® 117

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

g/m2 day

Figure 6. Water vapor transmission rate. 

DMMP VTR 

MNC-41 (Nox

MNC-41 (T100)

MNC-41 (T200)

Nafion® 117

)

MNC-21 No

MNC-21 (T100)

MNC-21 (T200)

x

MNC-11 (NoxMNC-11 (T100)

)

MNC-12 (NoxMNC-12 (T100)

)

0

50

100

150

200

250

300

350

400

450

g/m2 day

Figure 7. DMMP vapor transmission rate. 

As mentioned before, VTR corresponds to amount of permeant diffusing through a given 

membrane during given conditions. A value above 1000 g/m2

•day is generally considered 

“breathable” and should provide comfort. Water VTR for a standard BDU fabric was measured 

at approximately 5,600 g/m2

•day (9). Since this is an open, air-permeable structure and most 

likely will be integrated into final garment produced for actual use, it is an upper limit of what 

can be achieved. MNC membranes show water VTR values between 1000 and 2000 g/m2

•day 

and can be classified as a breathable material. The more impressive results were found when we 
10

examined VTR data for DMMP (a simulant for Sarin nerve agent). The values are truly 

spectacular: 20 to 50 g/m2

•day at steady state, an order of magnitude lower than Nafion 117. 

The effective DMMP permeability (a thickness-independent value) is two orders of magnitude 

lower than Nafion 117. When a delay for the initial break-through time is incorporated, these 

values are certainly within reach of U.S. Army target requirements for nerve agent permeation 

levels of less than 13 g/m2•day. 

Table 3. Vapor permeability and selectivity results. 

Blend Membrane 

Water VTR 

(g/m2

•day) 

P effective (water) 

(g/mm Hg•m•day)

Average 

DMMP VTR

(g/m2

•day) 

P effective (DMMP) 

(g/mm Hg•m•day)

Average 

Selectivity 

MNC-12 (Nox) 1,457 2.26E-03 38 3.21E-04 7 

MNC-12 (T100) 1,494 1.86E-03 27 1.82E-04 10.2 

MNC-11 (Nox) 1,903 1.71E-03 52 2.61E-04 6.6 

MNC-11 (T100) 1,589 1.58E-03 39 2.10E-04 7.5 

MNC-21 (Nox) 1,642 1.52E-03 23 1.14E-04 13.3 

MNC-21 (T100) 1,543 1.92E-03 19 1.26E-04 15.3 

MNC-21 (T200) 1,221 1.67E-03 20 1.48E-04 11.3 

MNC-41 (Nox) 1,247 2.90E-03 46 6.03E-04 4.8 

MNC-41 (T100) 1,068 2.13E-03 31 3.45E-04 6.2 

MNC-41 (T200) 1,122 2.03E-03 35 3.03E-04 6.7 

Nafion 117 4,921 2.45E-02 421 1.13E-02 2.2 

The selectivity for MNC materials, shown in figure 8, is an order of magnitude higher than 

Nafion 117. It indicates a substantial preferential transport of water vapor to DMMP and serves 

as a great indicator for potentially a new membrane for chemical and biological protective 

clothing. 

Selectivity

MNC-12 (Nox)

MNC-12 (T100)

MNC-11 (Nox)

MNC-11 (T100)

MNC-21 (Nox)

MNC-21 (T100)

MNC-21 (T200)

MNC-41 (Nox)

MNC-41 (T100)

MNC-41 (T200)

Nafion® 117 

0

5

10

15

20

25

Figure 8. Selectivity of materials. 
11

3.5 Effect of Composition and Thermal Treatment 

Figure 9 demonstrates the effect of membrane composition on transport rates of water and 

DMMP vapor. As can be observed from this plot, the most promising composition is MNC-21. 

It provides balanced values for both Army requirements: high water permeation and low DMMP 

permeation. This observation is also confirmed by high values from selectivity measurements. 

MNC-21 films have a selectivity of ~11 to 15, depending on the thermal treatment. That is five 

to seven times higher (more selective) than Nafion 117. 

The effect of thermal treatment of N-Methylolated Nylon-6−chitosan blends on the permeation 

of water and DMMP vapor can be observed in figure 10. It is clear that for most of the samples, 

water VTR across the membrane decreases by ~10% to 20% after thermal processing at 100 °C. 

The additional effect from processing membranes at 200 °C is less clear. The water VTR for 

MNC-21 membrane decreases significantly, while the transport rate for MNC-41 membrane 

remains relatively constant. 

1,000

1,100

1,200

1,300

1,400

1,500

1,600

1,700

1,800

1,900

2,000

Nylon / Chitosan composition

Water VTR (g/m2day)

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90

Wt % Nylon

DMMP VTR (g/m2day)

Water (NOX)

DMMP (NOX)

1 :2 2 :1 1 :1 4 :1

Figure 9. Water and DMMP transport rates as a function of blend composition. 

A similar trend is observed for DMMP vapor transport. Although thermal treatment at 100 °C 

shows improvements in resistance against DMMP vapor transport, annealing at 200 °C does not 

produce any significant additional improvement. In general, the temperature treatment of the 

membranes at 100 °C seems to provide a better ensemble of properties for chemical protection. 

It is also interesting to note that for some compositions, the thermal treatment effect is significantly larger than for the others. 
12

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

0 25 50 75 100 125 150 175 200 225

Annealing Temperature (°C) 

Water VTR (g/m2day)

0

10

20

30

40

50

60

70

DMMP VTR (g/m2day)

MNC-21 / Water

MNC-41 / Water

MNC-21 / DMMP

MNC-41 / DMMP

Figure 10. Effects of thermal treatment on transport of water and DMMP vapor. 

4. Conclusion 

In this study, the water vapor transmission rate, effective permeability, and selectivity of water 

vapor and DMMP vapor were measured for blends of N-methylol Nylon-6 and chitosan. It was 

found that these membranes have unusually high selectivity, especially in the case of the 

membrane with the blend composition of a 2:1 weight ratio of N-methylol Nylon-6: chitosan 

annealed at 100 °C. For that particular membrane, selectivity was measured to be 15.3, seven 

times higher than Nafion 117. It was also determined that methylolated Nylon-6: chitosan blends 

can be thermally crosslinked, but it does result in a slight decrease in both water and DMMP 

transport rates. Water transport rates were found to be between 1,000 and 2,000 g/m2

•day, 

depending on specific composition of the membrane and thermal treatment. This value is 

promising, especially when such a high level of selectivity is taken into account. Low 

permeation of DMMP is critical for Army application. Overall, these blends are good candidates 

for breathable chemical and biological protective garments for Army and civilian applications. 

In addition, these membranes are economically attractive for personal protection since the 

polymer components are inexpensive and the membrane fabrication is simple. 
13

5. References 

1. Lee. B. T.; Yang, T. W.; Wilusz, E. Moisture Effects on Isobutylene-Isoprene CopolymerBased Composite Barrier. 1. Moisture Diffusion and Detection. Polymer Engineering & 

Science 1996, 36 (9), 1217. 

2. Siegrist, D. Chemical-Biological Warfare: Protective Measures. Jane’s Defence Weekly. 

April 17, 2002. 

3. Shieh, J.-J.; Huang R. Y. M. Chitosan/N-methylol Nylon 6 blend Membranes for the 

Pervaporation Separation of Ethanol–Water Mixtures. Journal of Membrane Science 30 

September 1998, 148, Issue 2, 243–255. 

4. Clairns, T.L.; Foster, H.D.; Larchar, A.W.; Schneider, A.K.; Schreiber, R.S. Preparation and 

Properties of N-Methylol, N-Alkoxymethyl and N-Alkylthiomethyl Polyamides. Journal of 

American Chemical Society 1949 71, 665. 

5. Shieh, J.-J.; Huang, R. Y. M. Huang. Preparation of N-Methylol Nylon-6 Membranes for 

Pervaporation of Ethanol–Water Mixtures. Journal of Applied Polymer Science 1997, 64

855–863. 

6. Napadensky, E.; Elabd, Y.A. Breathability and Selectivity of Selected Materials for 

Protective Clothing; ARL-TR-3235; U.S. Army Research Laboratory: Aberdeen Proving 

Ground, MD, July 2004. 

7. Handbook of Chemistry and Physics; 66th edition, CRC Press Inc. FL, 1985. 

8. The Merck Index. An Encyclopedia of Chemicals, Drugs, and Biologicals; 13th edition, 

Merck & Co., Inc, Whitehouse Station, NJ, 2001. 

9. Napadensky, E.; Elabd, Y.A. unpublished data; U.S. Army Research Laboratory: Aberdeen 

Proving Ground, MD, no date. 
14

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