Development of a test equipment for pesticide protective fabric evaluation and studies on simple cotton woven fabrics

Abstract

In this study, efforts were taken to identify the most suitable cotton fabric with commonly used structure to be used as protective fabric by the pesticide applicators in the tropical regions, specifically at the time of spraying in the field. As the situation demanded the generation and use of pesticide-borne air for the evaluation of cotton fabrics considered in the study, a test equipment with appropriate features was developed and used. The study revealed that twill fabrics of medium weight construction provide better protection than plain fabrics, especially when they are produced with coarser yarns to achieve the required fabric weight. They are found to give enhanced protection when they are subjected to raising operation. Fabric raised on both the sides performs better than the face side raised fabric. On the contrary, these fabrics in raised or unraised state are found to slightly go down in their performance when they are wet and their performance decreases with increase in wetness. Hence, it is suggested that use of raised fabrics may be avoided for the preparation of pesticide protective clothing as the pesticide applicators are bound to sweat at the time of spraying. As the unraised fabrics give comparatively lower performance reduction on wetting, it can be recommended for the pesticide applicators with the instruction to change the clothing when it become wet to ensure protection.

Keywords

Test equipment fabric structure weight/unit area absorption penetration raising decontamination wetting

Background

India is one of the largest producers [1] and consumers of pesticides, especially insecticides [2]. As per the recent statistical data, India consumes considerable quantity of moderately and slightly hazardous organophosphate insecticides like Chloropyrivos, Malathion, Quinalphos, Dimethoate, Fenthion, etc. [3,4]. Human exposure to pesticides at the application sites through dermal contact [5 –7], which leads to a number of skin diseases [8], can occur as a result of a splash, spill or drift while mixing loading or spraying of them [9]. To prevent such dermal exposure, use of personal protective equipment by the applicators becomes pertinent [10 –12]. One such means is pesticide protective clothing (PPC). Different types of PPCs like woven fabrics coated with fluorocarbon finishes [13,14], nonwoven fabrics laminated to a microporous membrane and fabrics coated with a plastic or rubber films are used [15 –18]. Often these chemical-resistant materials do not allow permeation/penetration and sufficient respiration at the same time and generate undesirable effects on applicators in tropical regions [19]. A survey on usage of pesticide protective clothing among the farmers in south India states that 88% of the pesticide applicators took no precaution while handling and spraying pesticides and the main reasons stated for such situation was the physical discomfort experienced by them due to hot and humid weather conditions [3]. Hence, there is a need for recommending a right type of cotton fabrics from commonly manufactured apparel fabrics in India to prepare PPCs either directly or suitably modifying the nature of such fabrics without compromising on its original comfort values.

Further, consideration of standard methods developed for performance evaluation of PPCs reveal that they are all based on making the liquid pesticide to come in direct contact with the fabric either in the form of drops, stream or minute droplets. The relevant test methods in the order of mode of contact of pesticide with the fabric mentioned above are pipette test, gutter test and atomizer test, respectively [20 –22]. These methods do not reflect the conditions prevailing at the time of pesticide attack on the applicators during their spraying activity. Ensuring the presence of the best meteorological conditions [23 –25] namely, temperature (20–30℃), relative humidity (>45%) and wind velocity (3–7 km/h) and, the best practice of spraying of starting near the downwind edge of the field and proceeding in the upwind direction [26] are to be followed by the applicators during spraying of pesticides. When these recommendations are followed, there would be only a minimum attack of pesticide on the applicators, by way of pesticide dissolved in the moisture carried by the air. There is a lack of availability of reported literature in this area. Hence, there is a need for designing and fabricating a test equipment to expose fabric sample to pesticide borne air, using which absorption and penetration of pesticide by/through it can be estimated.

One another point which is recommended to the applicators to follow is to wash the PPCs to decontaminate them before reuse [27]. Further, it is reported that wetting of PPCs due to sweating by the applicators lead to higher pesticide absorption and penetration [28]. From the above, it is clear that fabrics to be used for PPCs should be invariably evaluated for decontamination from pesticide during washing and its performance behavior when wet. Also, from the available literature it is understood that no effort has been taken so far by subjecting the fabrics used for PPCs to a mechanical finish, namely raising, which leads to increase in surface area.

With the due consideration of the background explained above, the present study was conducted keeping the following as objectives:

Designing and fabrication of a test equipment to generate pesticide borne air of known qualities and to make it to come in contact with fabric sample,

Identification of two most commonly used fabric structures in cotton textiles in India and the production of these fabrics,

Effect of specifications of the given fabric with the specific structure on pesticide absorption and penetration,

Effect of different types of washing on pesticide decontamination,

Effect of raising on face and both sides of the fabric towards pesticide absorption and penetration and

Assessment of performance of normal and raised fabrics towards their absorption and penetration of pesticide on wetting.

Test equipment

The following principle was adopted in the fabrication of the test equipment. Continuous flow of air at a particular temperature carrying specific quantity of pesticide dissolved in known amount of moisture was generated by passing air at a predetermined velocity through a water column and a container filled with pesticide vapor. The pesticide borne air in turn was made to come in contact with fabric sample backed by impervious absorbent paper. This type of fabric-absorbent paper presentation was used to replicate the exposure of applicators to pesticide during spraying. The amount of pesticide absorbed by the fabric and paper would directly give the protective efficiency of the clothing worn by the applicator and pesticide contact with the skin respectively.

The construction features of the equipment are given in Figure 1. A 0.5 hp air compressor was connected to a ‘J’-shaped glass tube carrying water to generate moist air. ‘J’ shape for the tube was so selected to prevent the water from entering into the subsequent unit when compressed air is forced through it. The tube in turn was connected to the pesticide container mounted on a heating mantle to generate cloud of pesticide vapor inside the container by mild heating. The output from the pesticide container, which is a moist pesticide borne air, was passed through a homogenizer to ensure uniform distribution of pesticide in the moist air. Provision was made to keep a hygrometer inside the homogenizer to measure the temperature and relative humidity of the air. Pesticide borne air from the homogenizer was transferred through a 8 mm diameter tube to the sample holding device. It comprised of necessary components to hold the fabric sample with a circular (8 mm diameter) exposure area of 0.5 cm² suitably backed by absorbent paper.

Figure 1.

Test equipment.

Materials and methods

As per the information gathered from the fabric manufacturers and merchants in India, it was found that cotton fabrics with plain and twill structures were produced and sold in the country to a maximum extent. Hence cotton fabrics with these structures were considered in the present study.

A number of 100% cotton light weight plain and warp faced medium weight right hand (2 × 1) twill fabrics were woven (Niranjana Weaving Mills, India) using standard manufacturing practices. The plain and twill fabrics were produced using combed × combed and carded × carded yarns, respectively. All these fabrics were thoroughly desized and well scoured using standard procedures taking necessary precautions to avoid fibre damage and presence of residual chemicals. Specifications of such prepared fabrics are given in Table 1. Twist per centimeter (tpcm) was determined following ASTM 1422 method using a single yarn twist tester.

Table 1.

Fabrics produced and their pesticide protective performance.

Fabric code	Count (Ne)		tpcm		Yarns/cm		Weight (g/m²)	% Pesticide absorption per hour		% Pesticide penetration per hour
	Warp	Weft	Warp	Weft	Warp	Weft		% Pesticide absorption per hour		% Pesticide penetration per hour
	Warp	Weft	Warp	Weft	Warp	Weft		Mean	SD	Mean	SD
P1	80	50	15	12	43	22	70	2.13	0.06	10	0.4
P2	80	50	15	12	43	35	90	3.2	0.14	9.52	0.49
P3	80	60	15	13	43	26	70	2.03	0.06	10.6	0.39
P4	80	60	15	13	43	35	80	2.7	0.12	10.2	0.43
P5	80	80	15	15	43	35	70	2	0.06	11	0.58
P6	40	40	10	10	49	26	125	4.3	0.13	8.32	0.34
P7	50	50	12	12	52	40	125	3.7	0.13	9.15	0.38
T1	30	20	9	7	49	18	170	6.13	0.28	6.3	0.30
T2	30	20	9	7	49	26	195	6.4	0.28	5.09	0.19
T3	30	30	9	9	49	26	170	6	0.29	6.66	0.21
T4	30	40	9	10	49	26	170	5.9	0.31	6.91	0.24

P: plain fabric; T: twill fabric; tpcm: twist per centimeter.

Sample preparation and estimation of pesticide

As per the recommendations of Food and Agriculture Organization of the United Nations, Rome²⁵ spraying of pesticides has to be carried out when the air velocity in the field is between 3 and 7 km/h. It was decided to achieve an air velocity of 6.5 km/h in the test equipment. The above velocity was attained by suitably adjusting the compressor output and length of water column in the j tube. The amount of moisture carried by the air was decided by the length of the water column and will be always constant for the given velocity. The length of the water level inside the j tube was maintained by adding sufficient quantity of water through the inlet provided in the short arm of the tube during the experiment. Determination of air velocity was carried out using beehive shelf set up by connecting it at the place of sample holding device in the test equipment. Among the widely used organophosphate insecticides in India, Dimethoate 30% (Emulsifiable Concentrate, Rallis India Ltd) was chosen and used as procured in the study. For the conduct of experiments, a constant quantity of 100 mL of pesticide was taken in the pesticide container every time. The temperature of the pesticide was raised to 35℃, taking care in fixation of the temperature to prevent its degradation [29,30], to get required concentration in the air. The concentration of pesticide in the air was determined by dissolving it in the acetone taken in a set of impingers connected in series and positioned at the place of sample holding device of the test equipment. The acetone collected from the impingers was reduced to a volume of 5 mL using a rotary evaporator (Buchirotavapor R–215, Switzerland) and its concentration was found out using gas chromatography (GC) (Shimadzu GC 2010) having flame photometric detector. The concentration was found to be 0.996 mg/m³. The experiment was repeated for number of times to check the reproducibility of the concentration of pesticide in the air and was found to be almost same in all the tests. Concentration beyond this was not used to avoid the possibility of pesticide degradation due to heating.

The hygrometer kept inside the homogenizer was continuously monitored and the temperature and RH was found to be maintained at 29℃ ± 1℃ and 65% ± 2%, respectively and these conditions satisfy the recommended conditions to be present at the time of spraying in the field [23,24]. For the above temperature and RH, the moisture content in the air was calculated and found to be 0.34 kg/kg [31]. For every experiment, 5 cm × 5 cm each of the bone dry fabric and Benchkote plus absorbent paper (Whatmann 2301-6150) were cut and mounted in the sample holding device and connected to the test equipment and exposed to pesticide borne air with above qualities for an hour. After the conduct of the experiments the exposed fabrics and absorbent papers were trimmed to 2 cm × 2 cm with the exposed area at the centre and taken for further analysis. Pesticide in them was extracted following ASTM 2130-01 method using HPLC grade acetone (Merck Specialities Pvt. Ltd, India). The extracted solutions were evaluated for pesticide concentration using GC following the procedure described earlier. From the concentration, the quantity of pesticide present in the entire extract volume, which in turn represents the quantity of pesticide present either in the fabrics or absorbent paper were found out. Absorption and penetration of pesticide was calculated from the average of the amount of Dimethoate absorbed by the fabric and paper respectively from two specimens for each sample and the results are expressed in terms of % absorption per hour and % penetration per hour, respectively. From the results obtained, the fabric sample, which has given least penetration was chosen, henceforth called as control sample, and taken for further studies.

Decontamination

For decontamination of the control sample both manual and mechanical means of washings were employed. In manual washing, two types of samples were produced by varying the rinsing method, i.e. involving only cold rinsings – thrice (A) and with intermediate hot rinsing between cold rinsings – (C), keeping the soaping method constant. In mechanical washing, either launderometer or washing machine could not be used because of the very small size (2 cm × 2 cm) of the samples. Hence, an orbital shaker (Orbitek, Scigenics Biotech Pvt Ltd, India) set at 120 r/min was used. The recipe and conditions of soaping method followed was same as that used in manual washing. It was followed by cold rinsing thrice (B) in the shaker itself. Soaping was carried out with 0.5% w/v nonionic detergent – Labolene (Qualigens fine chemicals Pvt. Ltd. India) using L:M of 500:1 at room temperature (RT) for 30 min. Cold (RT) and hot (80℃) rinsings were carried out using L:M of 500:1 for 5 min. After drying, all the washed samples were taken for estimation of residual pesticide concentration in them following the procedure described earlier. Two specimens were considered for every sample and finally % decontamination of the washed samples was calculated taking intial pesticide concentration into account.

Treatment of raised fabrics

Raising of the control fabric was carried out using a Single acting raising machine (Kirpal Textile Engineering Work, India) on face side (RFS) as well as on both the sides (RBS) of the fabric. In order to check the quality suffered by the raised fabrics, tensile strength was found out using the test method ASTM 5035. Bone dry raised fabrics were then exposed to pesticide borne air using the test equipment and their pesticide absorption and penetration were determined following the methods described earlier. Two specimens were considered for every sample. Using the average of these values, % improvement in absorption and % reduction in penetration over the control sample were calculated.

Treatment of wet fabrics

Studies on the effect of wetting on the performance behavior of control and raised (RFS and RBS) fabrics were carried out by adjusting the moisture content in them to 25%, 50% and 75% odwm (on the bone dry weight of the material) using padding mangle. After exposing them to pesticide borne air in the test equipment, they were dried at ambient conditions and taken for determination of pesticide absorption and penetration following the procedures described earlier. Two specimens were considered for every sample. Using the average of these values, % decrease in absorption and % increase in penetration over the bone dry fabrics were calculated.

Results and discussions

Performance behavior of the fabrics

The pesticide absorption and penetration values obtained for the various fabrics are given in Table 1 and the standard deviation determined was found to fall between 0.06% and 0.58%. The performance behavior of the fabric was analyzed from the angle of penetration of pesticide, since lower the penetration better is the protection rendered by the fabrics. In order to understand this behavior of the fabrics, they were divided into six groups. Group I, II and III consists of fabrics having same yarn and fabric construction parameters but varying pick density. Groups I and II consist of plain fabrics and Group III consists of twill fabrics. Figure 2 shows the effect of increase in pick density on pesticide penetration. Increase in pick density, which in turn increases the fabric weight per unit area results in decrease in pesticide penetration due to increase in surface area and closing up of the interstices. Hence, when the weight of the fabric is raised by increasing the pick density, keeping all other yarn and fabric construction parameters same, the pesticide penetration through it can be brought down.

Figure 2.

Effect of pick density on pesticide penetration.

Group IV, V and VI consists of fabrics having same weight per unit area within the group but achieved by varying either weft count and its density (Group IV and VI) or count and density of warp and weft yarns (Group V). Groups IV and V consist of plain fabrics and Group VI consists of twill fabrics. Figure 3 shows the effect of these groups of fabrics on pesticide penetration. In general, it can be inferred from the figure that higher the fabric weight lower is the pesticide penetration. Further, considering various groups, it can be said that as the count becomes finer, which increases the twist level in the yarn, the penetration behavior of the fabrics increases due to poor absorption. The increase in penetration with respect to increase in twist level can be explained as follows. Woven fabrics being porous in nature, the capillaries present in them can be intrafibre, interfibre and interyarn [32]. When the twist level in the yarn increases, the intrafibre capillary volume will remain the same. With respect to interfibre scenario, as the twist level increases the capillary volume would decrease due to closer packing of the fibers with the associated increase in tortuosity in the capillary path. It would have direct effect on bringing down the penetration behavior of the fabric when the twist level in the yarn is increased keeping all the other fabric parameters same. In the case of interyarn capillaries, the increase in twist level would result in increase in capillary volume or in other words make the fabric more porous in nature resulting in higher penetration. In the present case, the pesticide borne air that comes in contact with the fabric, prefer to pass through interyarn capillaries, being easy to move through, as the twist level in the yarn increases and hence showing an increase in the penetration behavior. From the above findings, it can be said that when pesticide protective fabric is required with certain weight per unit area, it should be produced using coarser yarns rather than by varying the yarn density in warp or weft direction or both.

Figure 3.

Effect of fabric weight on pesticide penetration.

Taking into account the performance behavior of all the fabrics, it is suggested that the fabric P6 can be considered for the production of pesticide protective shirting preferably with an advise to use it along with an inner garment and T2 for protective suiting or overall. The other aspects of the present study were carried out with fabric T2, henceforth called as control fabric, chosen due to its lowest pesticide penetration behavior.

Effect of type of washing on decontamination

Findings by various researchers indicate that the removal of pesticide during washing (involves soaping followed by rinsing) through mechanical means depends on the active ingredient and type of formulation of the pesticides and not on their chemical class [33,42]. Further, it is reported that among the formulations, emulsifiable concentrate is more difficult to remove compared to others [34,35]. Jaw et al. [36] stated that the nature of detergents either anionic or nonionic or combination of these did not have effect on the removal of pesticides. Higher the concentration of the detergent [37,38], and temperature [39 –42] of soaping and rinsing better is the efficiency of removal of pesticides. The washing experiments in the present study were designed keeping the above findings as well as the poor economic status of the pesticide applicators in India into consideration. The results obtained from these experiments are given in Figure 4. The extent of removal of pesticide varies from 93% to nearly 98%, depending on the method of washing used.

Figure 4.

Effect of washing type on decontamination.

Manual washing carried out involving cold conditions throughout (A) gives roughly 5% lesser pesticide removal compared to that of mechanical washing (B). However, in the rinsing stage of manual method, when hot water is used (C), the efficiency of removal achieved becomes almost comparable with mechanical (B) wash. Hence, pesticide applicators, who cannot afford a washing machine, can decontaminate their clothes to a larger extent through manual washing with the use of intermediate hot water rinsing during washing.

Effect of raising

The following observations were made when the control fabric (T2) was subjected to raising. The extent of raising that could be achieved on the face side was minimum inspite of better exposure of warp yarns due to 2/1 twill structure since the twist levels used in the warp and weft yarns were higher than the yarns generally used in the fabric meant for raising. This fabric was found to undergo a strength loss of 3% and 2% in the warp and weft direction respectively. When the fabric was subjected to raising on the back side, it had undergone still a reduced level of raising compared to the face side due to lack of presence of yarn floats. Raising on both sides of the fabric was found to give 5% and 4% strength loss in the warp and weft direction respectively. The strength loss occurred in either case of raising is not appreciable. Raising of the fabric leads to increase in absorption and decrease in penetration and the change is more for both sides raised fabric than face side raised fabric. It can be seen from Figure 5 that the face side raised fabric gives improved absorption of pesticide of 8.75% and reduced penetration of 14.7% over the control fabric. This could be due to raising leading to increase in surface area and increase in deflection of pesticide borne air from the surface of the fabric. Further, it is clear from the figure that though raising on both sides of the fabric results in improved absorption of pesticide (4.55%) and reduced penetration (9%), it does not give proportionate change when compared with face side raised fabric. It could be due to reduced amount of raising at the back of the fabric. It may also be due to transfer of the absorbed pesticide from such raised fibers to the absorbent paper due to increase in surface contact with it resulting in decreasing the improvement in absorption and reduction in penetration.

Figure 5.

Effect of raising on pesticide absorption and penetration.

Influence of wetting

Wetting of all types of fabrics results in decrease in absorption and increase in penetration of pesticide. Figure 6 gives the % decrease in absorption and % increase in penetration over the bone dry fabric for different wet pick up levels. It can further be observed from the figure that as the wet pick-up increases, decrease in absorption and increase in penetration also increases. Wetting of raised fabrics results in higher decrease in absorption and increase in penetration of pesticide compared to control fabric and raising on both sides of the fabric has higher effect than the fabric raised only on face side.

Figure 6.

Effect of wetting on pesticide absorption and penetration.

The effect of water is highest at 25% odwm wet pick-up level and further increase in the level increases these effects gradually. The water present in the wet cotton fabrics can be looked upon in the following ways. Moisture content upto 19% odwm is called as bound water [43], wherein the water molecules are directly attached to –OH group present in the fiber. Between 19% and 40% odwm, it is called as free water [44] and in this case water molecules are present between the polymer chains. Above 40% odwm is known as bulk water [45] and such water molecules are present on the surface of the fiber. The above distribution becomes (a) 19%/6%/0%, (b) 19%/21%/10% and (c) 19%/21%/35% for 25%, 50% and 75% odwm wet pick-up levels respectively. From the above, it can be said that the hydroxyl groups in the fiber is fully occupied by the water molecules at all wet pick up levels and with the increase in wet pick-up level, free and bulk water contents increase. It reveals that maximum decrease in absorption and increase in penetration occurs when bound water is present in the fabric and these effects are changed to a lesser extent by free and bulk water contents.

Conclusions

It is believed that with the test equipment developed in the present study one would able to make realistic evaluation of the protective fabrics to be used by the applicators at the time of spraying as it has capability to generate field conditions. As the use of pesticide protective fabrics made up of cotton is unavoidable in the tropical regions, fabric with appropriate structure would be chosen and used. It is found that medium weight cotton fabrics with twill structure perform better than plain structure fabrics as they render lower penetration of pesticide. The performance of the fabrics depends on its weight/unit area and to arrive at the required weight, use of coarser yarn for the fabric production would be beneficial. It is found that such fabrics exposed to pesticide environment can be effectively decontaminated using manual washing with the inclusion of use of hot water atleast once in the rinsing stage. Though it is found that raising of cotton fabrics further reduces the penetration, as wetting of the fabrics results in increasing the penetration, it is suggested that such fabrics should be avoided for production of pesticide protective clothing. Further, when unraised cotton fabrics are used for the purpose, pesticide applicators may be instructed to change the clothing when it becomes wet since even in this case pesticide penetration increases with increase in wetness. It is opined that pesticide protective clothing made using cotton fabric with appropriate specifications can be recommended for the pesticide applicators for using them at the time of spraying in the field. In addition to rendering protection from pesticide, such clothing would be comfortable to wear and economical.

Footnotes

Funding

The authors are thankful to All India Council for Technical Education (AICTE), India for providing fellowship and contingency grant (AICTE F. No. 1-10/RID/NDF- PG/(50) 2007-2008) to carry out this research study.

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