Transport properties of carboxylated nitrile butadiene rubber (XNBR)-nanoclay composites; a promising material for protective gloves in occupational exposures
© Mirzaei Aliabadi et al.; licensee BioMed Central Ltd. 2014
Received: 14 June 2013
Accepted: 19 February 2014
Published: 28 February 2014
This study was conducted in response to one of the research needs of National Institute for Occupational Safety and Health (NIOSH), i.e. the application of nanomaterials and nanotechnology in the field of occupational safety and health. In order to fill this important knowledge gap, the equilibrium solubility and diffusion of carbon tetrachloride and ethyl acetate through carboxylated nitrile butadiene rubber (XNBR)-clay nanocomposite, as a promising new material for chemical protective gloves (or barrier against the transport of organic solvent contaminant), were examined by swelling procedure. Near Fickian diffusion was observed for XNBR based nanocomposites containing different amounts of nanoclay. Decontamination potential is a key factor in development of a new material for reusable chemical protective gloves applications, specifically for routine or highly toxic exposures. A thermal decontamination regime for nanocomposite was developed for the first time. Then, successive cycles of exposure/decontamination for nanocomposite were performed to the maximum 10 cycles for the first time. This result confirms that the two selected solvents cannot deteriorate the rubber-nanoclay interaction and, therefore, such gloves can be reusable after decontamination.
KeywordsNanocomposite Chemical protective barrier Swelling Solvent transport properties
Chemical protective gloves are extensively used as solvent barriers to prevent or lower the exposure to hazardous chemicals . In such applications, permeability of gloves against solvents is of great practical concern. This process is commonly described by a three-step mechanism: (i) dissolving of the penetrant molecules in the polymer, (ii) diffusion of the penetrant molecules through the polymer; and finally (iii) desorption of the penetrant molecules on the inner surface of the gloves [2–5]. There are many factors influencing the intensity of solvent permeability including; the affinity of polymer molecule to penetrant molecule, size, shape, and the nature of the penetrant molecules [6, 7], presence of fillers, and solvent-induced structural changes duo to the successive cycles of exposure/decontamination .
Nowadays, polymer-clay nanocomposites are widely used due to their outstanding properties such as chemical resistance, thermal stability, mechanical strength, and inflammability [9, 10]. The enhancement of solvent barrierity in these nanocomposites is attributed to the implanted impermeable platelet structure of nanoclay, which forces the penetrant molecules to wiggle around them and thus creating a tortuous route for passing of penetrant [11–13]. Therefore, wherever good barrierity is needed such as chemical protective gloves, commercial applications of these material products seem to be promising. In addition, this study is a response to one of the research needs of National Institute for Occupational Safety and Health (NIOSH), i.e. the application of nanomaterials and nanotechnology in the field of occupational safety and health [14–17].
The present paper focuses on the transport properties of a nanocomposite based on carboxylated nitrile butadiene rubber (XNBR)-nanoclay. Liquid immersion measurements were conducted for different nanocomposites using two neat organic solvents (i.e. carbon tetrachloride (CCl4) and ethyl acetate). Diffusion and solubility coefficients of these solvents were estimated in the nanocomposite samples. In addition, a thermal decontamination regime for the nanocomposite was developed for the first time. Then, the successive cycles of exposure/decontamination of nanocomposite were conducted to a maximum 10 cycles for the first time. The results were used to predict the extent of rubber–nanoclay interaction after increasing the number of use/decontamination of gloves in the presence of nanoclay.
XNBR latex used in this research was SYNTHOMER 6617 which was kindly supplied by SYNTHOMER company (SYNTHOMER, Malaysia). Ingredients of vulcanizations and selected solvents (Carbon tetrachloride [solubility parameter, 17.6 MPa1/2] and Ethyl acetate [solubility parameter, 18.6 MPa1/2]) were provided by the standard suppliers. Listed purities were at least 99 percent for the Carbon tetrachloride and Ethyl acetate. Pristine sodium montmorillonite (Na+ MMT), with a cationic exchange capacity (CEC) of 92.6 mequiv/100 g, was obtained from Southern Clay Products, Texas, USA.
Based on the protocol designed for preparation of the nanocomposite, firstly, a 5% aqueous suspension of clay was prepared by a mechanical stirrer. The pH of this dispersion was adjusted to the pH of XNBR latex by adding KOH (potassium hydroxide) solution. In order to counteract the sensitizing effect of layered silicates, sufficient amounts of Emulvin WA was added to the aqueous dispersion of clay and then, it was vigorously stirred for a given time. Subsequently, the as-prepared clay aqueous dispersion was added into the XNBR latex, and the mixture was stirred using a magnetic stirrer at room temperature for a period of 24 hours. The procedure was similarly repeated to prepare samples containing different amounts of clay; i.e. 3, 6, 9 phr (parts per hundred of rubber). Thereafter, curative ingredients, which were prepared in the colloidal form, were added to the XNBR nanocomposite and the mixture was further stirred for 24 hours. A glove former was then used to produce films of nanocomposites by coagulating dipping. In practice, glove former was dipped in a 40% calcium nitrate solution (as coagulant) for 15 seconds and dried at 100°C for 3 minutes. It was then cooled until temperature reached below 65°C. This coagulant coated former was dipped into the latex nanocomposite and was dwelled for one minute. The sample was kept at room temperature for 3 minutes to form a gel and it was then leached with the water at 45°C. Finally, the dipped samples were cured in the hot air oven at 130°C.
Designation and formulation details of XNBR-clay nanocomposite
XNBR rubber (dry parts/phr)
Zinc oxide (phr)
5% clay dispersion
In each experiment the circular samples of 2 cm diameter of were punched out using a sharp edged steel die. The average thickness of nanocoposite samples was 0.35 ± 0.02 mm and difference in samples thicknesses was not significant. In order to mimic the worst-case conditions for protective gloves during usage, the punched samples were weighted and placed in a screw tight glass bottle containing liquid. At specified time intervals, samples were picked up from the test bottle and blotted to remove excess solvent, and then were weighed. The weighting procedure was carried out fast enough within 30-40 seconds to minimize the errors raised from the solvent evaporation. The samples were placed back into the test bottle after each weighting. The results of swelling measurements were expressed as the mass of solvent uptake. The reported values for mass uptake are the average of three swelling experiments. It has been practically observed that the temperature at the inside of a glove can approach to the body temperature (37°C), therefore, the aforementioned procedure was performed at 37°C [18–20].
Evaluation of decontamination efficiency
Swelling procedure was used to contaminate (exposure) XNBR-clay nanocomposites by the selected solvent. Once the required time for maximum mass uptake was elapsed, which was determined previously by swelling procedure, the sample was removed from the test bottle and was placed into a hot-air oven for decontamination at 100°C for 16 hours. Decontamination conditions were selected based on the work of Vahdat and Delaney , which were the same as Gao study .
In the equation (1), the weight gain is the difference of weight before and after of the decontamination process. Similarly, the weight lost was considered as the difference between the weight of the contaminated sample prior- and post–decontamination.
Examination of polymer–nanoclay interactions
A unique approach based on the repeated cycles of contamination and decontamination was used to examine the extent of the polymer–nanoclay interactions. To this end, an ascending number of exposure/decontamination cycles up to maximum 10 cycles was imposed on the samples. Hence, the change in permeability coefficient of the nanocomposite film was demonstrated. Subsequently, it was determined whether these gloves would be reusable. To do this, swelling procedure was conducted until maximum mass solvent uptake accomplished. Then, sample was removed from the test bottle and the liquid on the surface of the samples was rubbed off and the decontamination procedure was started.
Results and discussion
The dynamic swelling characteristics of a nanocomposite film includes; the solvent sorption rate, the transport mechanism that regulates solvent sorption, the rate of reaching to the equilibrium swelling, and the sorption of solvent or equilibrium solubility.
The value of n and k at different nanoclay loading in selected solvents
n ± 0.01
k ± 0.007
n ± 0.01
k ± 0.007
Where h is the thickness of nanocomposite film.
Solubility [S], Diffusion [D], and Permeability [P] coefficient values of XNBR- nanocomposites
D × 107(cm2/ s)
P × 107( g/cm2- s)
D × 107(cm2/ s)
P × 107( g/cm2- s)
It can be seen from the data in Table 3 that the values of S and D for ethyl acetate are higher than those of CCl4 in all nanocomposites.
The higher value of S could be attributed to this fact that the molecular weight of ethyl acetate is lower than CCl4 in each experiment.
The higher value of D could be related to the existence of difference in the solubility parameter (thermodynamic affinity) of the solvent and the polymer. The solubility parameter of CCl4, ethyl acetate, and the polymer are 17.6, 18.6, and 20.5 MPa1/2 respectively. The difference in the solubility parameter of CCl4 and polymer (2.9 MPa1/2) is lower than for ethyl acetate and polymer (1.9 MPa1/2). Therefore, the thermodynamic affinity of ethyl acetate is higher for XNBR polymer. Also, moderate hydrogen-bonding tendency of ethyl acetate along with the hydrophilic features of the surface of nanoclay increase the interaction between ethyl acetate and nanocomposite.
Where the D and S have already been defined. The permeability results are given in Table 3. It is evident that the permeability coefficient value decreases as the filler loading in the composite is increased. The dispersed nanoclay hinders the mobility of the permeant molecules across the polymer strands. Accordingly, as the filler loading in the composite was increased a lower value of D was obtained. The value of S also illustrates the same direction. Since P is the net product of D and S, the P value exhibits a decrement as the filler loading in the composite increases.
Evaluation of decontamination efficiency
The feasibility for decontamination is an important issue in the development of a new material for reusable chemical protective gloves applications specifically for routine or highly toxic exposures. Therefore, materials are essentially expensive to be regarded as disposable.
Since XNBR3 containing the minimum amount of nanoclay shows the efficient decrease in permeability coefficient of ethyl acetate compared to the neat polymer, the XNBR3-ethyl acetate pair was selected for decontamination procedure. Also, for comparison with XNBR3, the same exposure/decontamination procedure was carried out on the neat polymer (XNBR0).
Thermal decontamination of ethyl acetate from XNBR composite at 100°C for different time periods
Examination of polymer–nanoclay interactions
Because the XNBR3 containing the minimum amount of nanoclay showed the maximum decrease in permeability coefficient of ethyl acetate compared with neat polymer, the XNBR3-ethyl acetate pair was selected for the examination of polymer–nanoclay interaction.
Change in the transport properties (Solubility [S], Diffusion [D], and Permeability [P] coefficient values of) of XNBR 3 –ethyl acetate pair after exposure/decontamination cycles
S (g/cm3) g/cm3
D × 107(cm2/ s)
P × 107( g/ cm- s)
D × 107(cm2/ s)
P × 107( g/ cm- s)
The ratio of both diffusion and permeability coefficients of the XNBR 3 to the neat rubber after exposure/decontamination cycles
In this study, the equilibrium solubility and diffusion of selected solvents in carboxylated nitrile butadiene rubber (XNBR)-clay nanocomposite, as a promising new material for chemical protective gloves or barrier against the transport of organic solvent contaminant, were examined by swelling procedure. By virtue of the favoring affinity between the rubber and the nanoclay, nanocomposites eventually lower the permeability coefficients of solvents. This occurs due to some events such as the creation of a zigzag path, the reduction in the availability of free volume, and the restriction on the mobility of rubber chain segments. Ethyl acetate permeability coefficients decreased significantly at 3 phr loading of nanoclay (5.44 × 10- 7g/cm ‒ s) in comparison with the neat polymer (9.03 × 10‒ 7g/cm ‒ s). For the same reason that permeability decreased due to the dispersed nanoclay, a longer time is required for the effective decontamination of absorbed chemicals from the nanocomposite compared to conventional nitrile gloves. Successive cycles of exposure/decontamination confirm that solvent are not able to demolish the rubber-nanoclay interaction, promising gloves could be reusable after decontamination.
This research has been supported by Tehran University of Medical Sciences and Health Services grant (project no. 19570-27-03-91). Also, the supports received by Iran Polymer and Petrochemical Institutes are highly appreciated. Also, the authors would like to express appreciation to Siau Woon Wang from Synthomer Company for effective assistant.
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