liquid sorption behavior of superabsorbent fiber based nonwoven media

Fibers and Polymers 2013, Vol.14, No.7, 1165-1171

1165

Liquid Sorption Behavior of Superabsorbent Fiber Based Nonwoven Media

Dipayan Das*, R. S. Rengasamy, and Mritunjay Kumar

Department of Textile Technology, Indian Institute of Technology Delhi, New Delhi-110016, India

(Received July 4, 2012; Revised October 2, 2012; Accepted December 23, 2012)

Abstract: Nonwovens are widely used as liquid absorbent media. Currently, superabsorbent fibers are used in nonwovens formaking them less bulky yet very effective in absorbing liquids. In this work, a series of nonwovens were prepared by randommixing and layer-wise combining of superabsorbent fibers with fibers of different cross-sectional geometries. Thesenonwovens were studied for their liquid absorption behavior by using gravimetric testing absorption system. It was observedthat in case of random mixing, the increase in weight fraction of superabsorbent fibers led to a tremendous increase in liquidsorption capacity and liquid sorption rate. When mixed randomly with superabsorbent fibers, the finer fibers exhibited bettersorption characteristics than the coarser fibers, but the non-circular fibers displayed poorer sorption characteristics than thecircular ones. In case of layer-wise combining, better sorption characteristics were obtained when the liquid was firstchallenged by the polypropylene fiber side as compared to that by superabsorbent fiber side. The superabsorbent fibers andthe circular polypropylene fibers, when combined layer-wise, resulted in higher sorption capacity but lower sorption rate thanthose when mixed randomly.

Keywords: Superabsorbent fiber, Deep-grooved fiber, Trilobal fiber, Nonwovens, Sorption capacity, Sorption rate

Introduction

Nonwovens are widely used as liquid absorbent media.

Baby diapers, sanitary napkins, and adult incontinence pads

are the excellent examples of the usage of nonwovens as

liquid absorbent media. The performance of nonwoven

absorbent media is determined by their liquid sorption

behavior, which is characterized by the capacity of liquid

sorption and the rate of liquid sorption. The liquid sorption

behavior of nonwoven absorbent media has been reported by

many researchers [1-19]. Earlier, cellulosic fiber based

nonwovens were used as liquid absorbent media, however,

their liquid sorption characteristics were found to be limited.

The synthetic fibers such as polyester and polypropylene,

either mixed with cellulosic fibers or finished with hydrophilic

chemicals, were also widely used. To improve the liquid

sorption characteristics, the synthetic fibers of different

cross-sectional sizes and shapes were tried. However, the

role of fiber cross-sectional size on the liquid sorption

behavior of nonwovens was found to be contradictory. In

one research work [13], it was observed that the coarser

fibers resulted in higher sorption capacity and higher rate of

sorption. But, in another research work [14], it was found

that the finer fibers resulted in higher sorption capacity and

higher rate of sorption. The effect of fiber cross-sectional

shape on the liquid sorption characteristics of nonwovens

was also examined. The deeply-grooved fiber cross-sections

were found to enhance the sorption capacity and sorption

rate to a remarkable extent [13-15]. Apart from fiber

characteristics, the properties of the test liquids such as

density, viscosity, and surface tension were found to play a

decisive role in determining the liquid sorption behavior of

nonwovens. The structure of the nonwovens was also found

to play a very important role in determining their liquid

sorption behavior. The important structural characteristics

include volumetric porosity and cross-sectional size and

shape of the capillaries. The latter, in turn, depends on the

cross sectional size, shape, and aggregate pattern of the

fibers used to prepare nonwovens [7-9,17,18].

Currently, superabsorbent fibers are used in nonwovens

for making the liquid absorbent products less bulky yet

effective in absorbing liquids. In this case, the liquid transports

to the interfiber pore space by capillary action and to the

superabsorbent fiber by diffusion. As a result, the liquid

sorption capacity of the nonwovens increases tremendously.

However, diffusion of the liquid into the superabsorbent

fibers reduces the pore space on account of extensive

swelling of the fibers and hence decreases the rate of liquid

absorption [20]. Gel blocking occurs when extensive swelling

of the superabsorbent causes closure of the wicking channels

such that further liquid transport is prevented. Hence, a

higher amount of superabsorbent fibers does not necessarily

result in better liquid sorption behavior, especially in term of

liquid sorption rate. Today’s research has revealed that there

is a need to invent novel composite nonwoven structures by

useful combination of “normal plus “super absorbent materials

so as to achieve enhanced liquid sorption behavior. It is thus

often said that the design of absorbent products must be

carefully considered for maximum performance.

In this work, a series of nonwoven absorbent media was

developed by combining superabsorbent fibers with fibers of

different cross-sections by means of random mixing and

layer-wise combining. The cross-section of the fibers was

differed with respect to their size and shape. The liquid

sorption behavior of the nonwovens was evaluated by means

of gravimetric absorption testing system (GATS). The*Corresponding author: [email protected]

DOI 10.1007/s12221-013-1165-5

1166 Fibers and Polymers 2013, Vol.14, No.7 Dipayan Das et al.

random mixing of fibers was compared to the layer-wise

combining of fibers with respect to the liquid sorption

characteristics of the nonwovens.

Materials and Methods

Fiber Materials

In this work, superabsorbent fibers (SAF) of 51 mm length

and 10 den fineness were used. The superabsorbent fibers

were procured from Technical Absorbents, UK through

Business Coordinating House, India. The fibers were prepared

by using three different monomers namely, acrylic acid,

methylacrylate, and a small quantity of special acrylate/

methylacrylate monomer and employing a patented process.

In this process, acrylic acid was partially neutralized to the

sodium salt of acrylic acid and the cross-links between

polymer chains were formed as ester groups by reaction

between the acid groups in acrylic acid and the special

acrylate/methylacrylate monomer. The density of the super-

absorbent fibers, as reported by the manufacturer, was taken

as 1.4 g/cm3. Besides superabsorbent fibers, polypropylene

fibers of two different finenesses (2.5 den and 6 den) but of

same length (51 mm) and same cross-sectional shape (circular)

were used. The density of the polypropylene fibers was

taken as 0.91 g/cm3. Further, polyester fibers of two different

cross-sectional shapes (trilobal and deep-grooved) but of

Table 1. Physical characteristics of fibers

Fiber Length (mm) Fineness (den) Density (g/cm3) Diameter (µm) Shape

Polypropylene 512.5

0.9119.72

Circular6 30.55

Polyester 51 6 1.38 24.81Trilobal

Deep-grooved

Superabsorbent 51 10 1.40 31.80 Circular

Table 2. Details of nonwovens prepared by random mixing of fibers

Percentage of fibers in the blend Structural characteristics Sorption characteristics

Polypropylene Polyester SAF Basis weight

(g/m2)

Thickness

(mm)

Density

(g/cm3)

Sorption

capacity (g/g)

Sorption rate

(g/g·s)2.5 den 6 den Trilobal Deep-grooved 10 den

100 0 0 0 0 127.22 2.47 0.0515 18.56 0.1764

90 0 0 0 10 108.93 2.29 0.0476 24.38 0.2082

80 0 0 0 20 120.46 2.38 0.0506 27.58 0.2792

70 0 0 0 30 125.59 2.39 0.0525 29.59 0.3370

60 0 0 0 40 109.56 2.12 0.0517 36.79 0.3728

50 0 0 0 50 103.64 1.89 0.0548 44.61 0.4761

0 100 0 0 0 147.30 3.13 0.0471 15.89 0.0852

0 90 0 0 10 144.80 3.02 0.0479 20.83 0.1699

0 80 0 0 20 125.40 2.76 0.0454 27.49 0.2541

0 70 0 0 30 133.90 2.76 0.0485 31.62 0.3249

0 60 0 0 40 163.40 3.05 0.0536 34.08 0.3629

0 50 0 0 50 163.70 3.16 0.0518 39.39 0.4342

0 0 100 0 0 191.56 3.37 0.0568 9.79 0.0472

0 0 90 0 10 193.29 3.25 0.0595 18.73 0.0701

0 0 80 0 20 190.72 3.36 0.0568 22.45 0.0891

0 0 70 0 30 192.14 3.24 0.0593 24.60 0.1038

0 0 60 0 40 235.37 3.81 0.0618 27.20 0.1056

0 0 50 0 50 221.64 3.65 0.0607 31.94 0.1248

0 0 0 100 0 163.40 3.16 0.0517 10.41 0.0510

0 0 0 90 10 166.75 3.41 0.0489 19.47 0.1315

0 0 0 80 20 180.96 3.36 0.0539 22.90 0.2356

0 0 0 70 30 182.70 3.42 0.0534 24.45 0.2515

0 0 0 60 40 187.07 3.30 0.0567 27.33 0.2877

0 0 0 50 50 150.40 2.43 0.0619 30.63 0.3976

Superabsorbent Fiber Nonwoven Fibers and Polymers 2013, Vol.14, No.7 1167

same length (51 mm) and same fineness (6 den) were used.

The density of the polyester fibers was taken as 1.38 g/cm3.

The physical characteristics of the fibers including their

equivalent diameters are reported in Table 1. The equivalent

diameter (d) of the fibers was calculated from the following

formula, , where t denotes fiber fineness and ρ

indicates fiber density.

Development of Nonwovens

A laboratory-based needle-punching line was used for

preparation of nonwoven materials. The line was comprised

of opening and mixing machine, roller carding machine,

cross-lapping machine, and needle-punching machine. The

superabsorbent fibers were randomly mixed with polypropylene

fibers of different finenesses or polyester fibers of different

cross-sectional shapes, each at six different blend ratios (0/

100, 10/90, 20/80, 30/70, 40/60, 50/50). The details of these

mixings are mentioned in Table 2. While preparing the

aforesaid nonwoven materials, the machine and process

parameters were kept constant. The punch density during

needle-punching was kept at 120 punches per cm2 and the

advancement per stroke was maintained at 7.5 mm. Another

set of nonwoven materials were prepared by layer-wise

combining of superabsorbent fibers and polypropylene fibers of

different finenesses at a blend ratio of 50/50. The details of

these materials are mentioned in Table 3.

Testing of Nonwovens

The randomly-mixed fiber nonwovens and layer-wise-

combined fiber nonwovens were tested for their basis weight

by using a standard weighing balance and thickness by using

a digital thickness tester. Each of the nonwoven materials

was tested ten times and the average of ten readings is

mentioned in Table 2 and Table 3. The density of the

nonwovens was calculated by dividing their basis weight by

their thickness. The density of the nonwovens was found to

be practically same. The nonwovens were further tested for

their liquid absorption behavior by employing gravimetric

absorption testing system (GATS) and distilled water as a

test liquid. This test was replicated three times on each

material. The liquid sorption capacity of the nonwovens was

determined by the ratio of amount of liquid absorbed at the

end of the test to the dry weight of the nonwoven. The test

was ended when the liquid was found to come out of the

nonwoven, indicating that it was unable to absorb liquid any

more. The higher value of liquid sorption capacity was

indicative of higher amount of liquid absorbed by the

nonwoven material. The liquid sorption rate was determined

by the slope in the initial phase of the test. The higher value

of liquid sorption rate was an indication of faster absorption

of the liquid by the nonwoven material.

Results and Discussion

Liquid Sorption Capacity of Randomly-Mixed Fiber

Nonwovens

The liquid sorption capacity of the nonwovens prepared

by random mixing of superabsorbent fibers and polypropylene


shapes are reported in Table 2. Figure 1 displays the effect of

addition of superabsorbent fibers on the liquid sorption

capacity of the nonwovens for different fiber finenesses. It

can be observed that the liquid sorption capacity of all the

nonwoven materials was increased with an increase in the

amount of superabsorbent fibers. This can be understood as

a natural consequence of extraordinarily high liquid sorption

d 4t/πρ=

Table 3. Details of nonwovens prepared by layer-wise combining of fibers and their comparison with randomly-mixed fiber nonwovens

MaterialBasis weight

(g/m2)

Thickness

(mm)

Density

(g/cm3)

Sorption

capacity (g/g)

Sorption rate

(g/g·s)

Nonwoven prepared by layer-wise combining of superabsorbent

fibers and polypropylene fibers of 2.5 den fineness at 50/50 blend

ratio (PP side)

115.98 2.21 0.0525 65.41 0.3347


fibers and polypropylene fibers of 2.5 den fineness at 50/50 blend

ratio (SAF side)

115.98 2.21 0.0525 58.22 0.1800


fibers and polypropylene fibers of 6 den fineness at 50/50 blend ratio

(PP side)

148.00 2.73 0.0542 50.29 0.2575


fibers and polypropylene fibers of 6 den fineness at 50/50 blend ratio

(SAF side)

148.00 2.73 0.0542 49.23 0.1386

Nonwoven prepared by random mixing of superabsorbent fibers and

polypropylene fibers of 2.5 den fineness at 50/50 blend ratio

103.64 1.89 0.0548 44.61 0.4761

Nonwoven prepared by random mixing of superabsorbent fibers and

polypropylene fibers of 6 den fineness at 50/50 blend ratio

163.70 3.16 0.0518 39.39 0.4342


by the superabsorbent fibers. The addition of finer fibers in

the blend was found to generally result in higher liquid

sorption capacity as compared to that of coarser fibers. This

can be ascribed due to the fact that the finer fibers resulted in

creation of smaller pores, which would develop higher

capillary pressure, leading to higher amount of liquid wicked

through the porous structure. Further, the liquid sorption

capacity of the nonwovens prepared from the blends of

superabsorbent and trilobal polyester fibers was found

practically the same as that of the nonwovens prepared from

the blends of superabsorbent and deep-grooved polyester

fibers. Evidently, the random mixing of circular fibers with

superabsorbent fibers resulted in higher liquid sorption

capacity as compared to the random mixing of trilobal or

deep-grooved fibers with superabsorbent fibers.

In order to examine the effect of fiber fineness and the

amount of superabsorbent fibers on the liquid sorption capacity

of nonwovens, a two-way analysis of variance (ANOVA) of

the experimental data was performed. The experimental data

included liquid sorption capacity of twelve nonwoven

Figure 1. Plot of liquid sorption capacity of nonwovens prepared

by random mixing of superabsorbent fibers and polypropylene


shapes.

Table 4a. ANOVA for sorption capacity of nonwovens prepared by random mixing of superabsorbent fibers and polypropylene fibers of

different finenesses

Source Sum of squares Degree of freedom Mean sum of squares F-value Probability>F-value

Fiber fineness 41.18 1 41.18 9.45 0.0052

Amount of superabsorbent fibers 1900.36 5 380.071 87.25 0

Fiber fineness×

Amount of superabsorbent fibers

73.71 5 14.742 3.38 0.0187

Error 104.54 24 4.356

Total 2119.78 35

Table 4b. ANOVA for sorption capacity of nonwovens prepared by random mixing of superabsorbent fibers and polyester fibers of different

shapes


Fiber shape 0.72 1 0.724 0.2 0.6549


Fiber shape×


23.91 5 4.783 1.35 0.2770

Error 84.9 24 3.538

Total 1731.5 35

Table 4c. ANOVA for sorption rate of nonwovens prepared by random mixing of superabsorbent fibers and polypropylene fibers of different

finenesses


Fiber fineness 0.01195 1 0.01195 10.24 0.0038


Fiber fineness×

Superabsorbent fibers

0.01882 5 0.00376 3.23 0.0228

Error 0.02801 24 0.00117

Total 0.47341 35


materials, each with three replicates, prepared by blending of

superabsorbent fibers and polypropylene fibers of two

different finenesses (2.5 den and 6 den) at six different blend

ratios. The results are displayed in Table 4(a). The fineness

of fibers, amount of superabsorbent fibers in the blend, and

their interaction were found to be statistically significant at a

significance level of 0.05. In this case, the amount of

superabsorbent fibers in the blend contributed maximum to

the total variability in the data (89.65 %), followed by the

interaction between the fineness of fibers and the amount of

superabsorbent fibers (3.48 %) and the fineness of fibers

(1.94 %). In a similar way, a two-way analysis of variance

was carried out to examine the effect of fiber cross-sectional

shape and percentage of superabsorbent fibers on the capacity

of liquid sorption. Here, the experimental data included

liquid sorption capacity of twelve nonwoven materials, each

with three replicates, prepared by blending of superabsorbent

fibers and polyester fibers of two different shapes (trilobal

and deep-grooved) at six different blend ratios. The results

are reported in Table 4(b). It can be observed that the amount

of superabsorbent fibers in the blend was found to be

statistically significant at a significance level of 0.05, but the

shape of fiber cross-section and its interaction with the

amount of superabsorbent fibers in the blend were not found

to be significant. In this case, the amount of superabsorbent

fibers in the blend contributed maximum to the total

variability in the data (93.67 %), followed by the interaction

between the shape of fiber cross-section and the amount of

superabsorbent fibers in the blend (1.38 %) and the shape of

fiber cross-section (0.04 %).

Liquid Sorption Rate of Randomly-Mixed Fiber Non-

wovens

The liquid sorption rate of the nonwovens prepared by

random mixing of superabsorbent fibers and polypropylene


shapes are reported in Table 2. Figure 2 displays the effect of

addition of superabsorbent fibers in the nonwovens on the

liquid sorption rate for different fiber shapes. It can be seen

that the rate of liquid sorption of all the nonwoven materials

was increased with the increase in the amount of superabsorbent

fibers. This observation was however not in agreement to

that reported by Gupta and Hong [20]. They prepared a set

of air-laid and needle-bonded nonwoven materials by

randomly mixing superabsorbent and polyester fibers at

different blend ratios and tested their liquid sorption

behavior. They observed that the liquid sorption rate of the

nonwovens was decreased with an increase in the amount of

superabsorbent fibers. Further, it can be observed from

Figure 2 that the nonwovens made up of blends of finer

polypropylene fibers and superabsorbent fibers showed

higher liquid sorption rate as compared to the nonwovens

prepared from mixing of coarser polypropylene fibers and

superabsorbent fibers. Furthermore, the addition of trilobal

fibers showed a slight increase in the liquid sorption rate, but

a remarkable increase in the liquid sorption rate was

obtained with the addition of deep-grooved fibers. Clearly,

the random mixing of circular fibers with superabsorbent

fibers resulted in higher liquid sorption rate as compared to

the random mixing of deep-grooved or trilobal fibers with

superabsorbent fibers.

In order to further analyze the effect of fiber fineness and

percentage of superabsorbent fibers on the liquid sorption

rate, a two-way analysis of variance of the experimental data

was carried out. The experimental data included liquid

Table 4d. ANOVA for sorption rate of nonwovens prepared by random mixing of superabsorbent fibers and polyester fibers of different shapes


Fiber shape 0.72469 1 0.72469 644.15 0


Fiber shape×


0.82105 5 0.16421 145.96 0

Error 0.027 24 0.00113

Total 2.24482 35

Figure 2. Plot of liquid sorption rate of nonwovens prepared by

random mixing of superabsorbent fibers and polypropylene fibers

of different finenesses or polyester fibers of different shapes.


sorption rate of twelve nonwoven materials, each with three

replicates, prepared by blending of superabsorbent fibers

and polypropylene fibers of two different finenesses (2.5 den

and 6 den) at six different blend ratios. The results are shown

in Table 4(c). It can be observed that the fineness of fibers,

amount of superabsorbent fibers in the blend, and their

interaction were found to be statistically significant at a level

of significance of 0.05. In this case, the amount of

superabsorbent fibers in the blend contributed maximum to

the total variability in the data (87.58 %), followed by the

interaction between fineness of fibers and amount of

superabsorbent fibers in the blend (3.98 %) and the fineness

of fibers (2.52 %). Similarly, a two-way analysis of variance

was performed to examine the effects of fiber cross-sectional

shape and percentage of superabsorbent fibers on the rate of

liquid sorption. Here, the experimental data included liquid

sorption rate of twelve nonwoven materials, each with three

replicates, prepared by blending of superabsorbent fibers

and polyester fibers of two different shapes (trilobal and

deep-grooved) at six different blend ratios. The results are

displayed in Table 4(d). It can be observed that the shape of

fiber cross-section, amount of superabsorbent fibers in the

blend, and their interaction were statistically significant at

0.05 level of significance. In this case, the interaction between

shape of fiber cross-section and amount of superabsorbent

fibers in the blend contributed maximum to the total variability in

the data (36.58 %), followed by the shape of fiber cross-

sections (32.28 %) and the amount of superabsorbent fibers

in the blend (29.94 %).

Liquid Sorption Characteristics of Layer-Wise-Combined

Fiber Nonwovens

The liquid sorption characteristics of the nonwoven materials

prepared by layer-wise combining of superabsorbent fibers

and polypropylene fibers of 2.5 den or 6 den fineness at a

blend ratio of 50/50 are reported in Table 3. These characteristics

were compared to those of the nonwovens prepared by


fibers of 2.5 den or 6 den fineness at a blend ratio of 50/50.

They are also reported in Table 3. It can be observed that the

nonwoven prepared by layer-wise combining of superabsorbent

fibers and polypropylene fibers of 2.5 den fineness at 50/50

blend ratio exhibited higher liquid sorption capacity and

higher liquid sorption rate than the nonwoven prepared by

layer-wise combining of superabsorbent fibers and poly-

propylene fibers of 6 den fineness at 50/50 blend ratio,

regardless of whether the liquid was first challenged by the

polypropylene side or the superabsorbent fiber side. This can

be explained by the effect of fiber fineness on the liquid

sorption characteristics. Further, better sorption characteristics

were obtained when the liquid was challenged by the

polypropylene fiber side as compared to when the liquid was

challenged by the superabsorbent fiber side. In the case of

the former, the liquid first got absorbed by the inter-fiber

pores and then diffused into the superabsorbent fibers. But,

in the case of the latter, the liquid first diffused into the

superabsorbent fibers, which resulted in tremendous swelling

of the fibers, offering high resistance to the liquid to be reach

to the inter-fiber pores. Furthermore, the layer-wise combining

of superabsorbent fibers and polypropylene fibers resulted in

higher sorption capacity but lower sorption rate than the


fibers at same blend ratio, irrespective of the fineness of

polypropylene fibers.

Conclusion

The nonwovens prepared by layer-wise combining of

superabsorbent and polypropylene fibers were found to

absorb higher amount of liquid and at a faster rate as

compared to the nonwovens prepared by random mixing of

superabsorbent and polypropylene fibers. In case of layer-

wise combining of superabsorbent and polypropylene fibers,

better sorption characteristics were obtained when the liquid

was first challenged by the polypropylene fiber side as

compared to when the liquid was first challenged by the

superabsorbent fiber side. Better sorption characteristics were

obtained when the polypropylene fibers were finer. In the

case of random mixing of superabsorbent and polypropylene

or polyester fibers, an increase in weight fraction of

superabsorbent fibers led to tremendous increase in their

liquid sorption capacity as well as liquid sorption rate. When

mixed randomly with superabsorbent fibers, the finer fibers

exhibited higher sorption capacity and higher sorption rate

than the coarser fibers, but the non-circular fibers displayed

poorer sorption characteristics than the circular fibers. The

nonwovens prepared by random mixing of equal proportion

of superabsorbent fibers and circular polypropylene fibers of

2.5 den fineness resulted in highest sorption capacity and

highest sorption rate among all the nonwovens prepared by

random mixing of fibers.

Acknowledgements

The authors are very much thankful to Business Coordination

House, India and The Nonwovens Institute of the North

Carolina State University, USA for supplying superabsorbent

fibers and deep-grooved fibers, respectively for this research

work.

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liquid sorption behavior of superabsorbent fiber based nonwoven media

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