non woven hydrophilic

Journal of Fiber Bioengineering & Informatics 4:4 (2011) 403–411http://www.jfbi.org | doi:10.3993/jfbi12201110

Hydrophilic Properties of PP/CHA Nonwoven Fabrics

Lingling Fan, Deshan Cheng, Xiangyu Jin∗Engineering Research Center of Technical Textiles, Ministry of Education

Donghua University, Shanghai 201620, China

Abstract

This paper presents the preparation of PP/CHA melt-blown nonwoven fabric and the studies on itshydrophilic property. The property of polymer materials was investigated at the first place by differentialthermal analysis (DSC) and rheology analysis. SEM was used to study the web structure affectedby the hot air temperature. Wide-angle X-ray Diffraction (WAXD) was used to study the degree ofcrystallization of PP/CHA melt-blown nonwovens produced at different hot air temperatures. Thehydrophilic property of PP/CHA melt-blown nonwoven fabrics was studied by testing the static watercontact angle, the liquid wicking rate and the multiple liquid strikethrough time. The static contact angletest proves that hydrophilic properties were obtained by means of using the Commercial HydrophilicAdditive (CHA), while the addition of the Traditional Hydrophilic Additive (THA) did not. The liquidwicking rate test shows that PP/CHA nonwoven fabric has the highest liquid wicking rate due toits hydrophilic groups transferred to the surface and forming a hydrophilic film. The multiple liquidstrikethrough time indicates that the nonwoven fabric treated by THA loses its wettability after 3insults, while nonwovens containing 5.5% CHA remained hydrophilic even after 12 insults. It can beconcluded that PP/CHA melt-blown nonwoven fabrics have durable hydrophilic property.

Keywords: PP/CHA Melt-blown Nonwoven; Preparation; Additive; Hydrophilicity; Static ContactAngle

1 Introduction

Nonwovens have become one of the fast growing industries in the textile world. Nonwoven fabricsare processed by web forming and web consolidation, which are different from the processes ofconventional textile fabrics. Melt-blown nonwovens possess a 3-dimentional network structurefabricated by ultrafine fibers, which gives them small pore size, high porosity, good filtration andabsorption properties [1].

With nonwoven products moving into more technical end-uses, Polypropylene (PP) fibres havegrown to be one of the dominant materials in the nonwovens industry. It is estimated that over90% of all Melt-blown (MB) nonwovens are made from Polypropylene (PP), because of its low

∗Corresponding author.Email address: [email protected] (Xiangyu Jin).

1940–8676 / Copyright © 2011 Binary Information Press & Textile Bioengineering and Informatics SocietyDecember 2011

404 L. Fan et al. / Journal of Fiber Bioengineering & Informatics 4:4 (2011) 403–411

cost, ease of processing, favorable chemical and physical properties, such as lack of heat shrinkage,impact strength, tensile strength, and its ability to be drawn into very fine fibers [2].

However, PP is a typical hydrophobic polymer, so its melt-blown nonwovens have poor hy-drophilicity, which limits their use in some areas. To improve wettability and increase the surfaceenergy of PP nonwoven fabrics, many techniques have been studied to introduce polar groupsto the surface and enrich surface functionality. Chemical treatments have been used to createhydroxyl and carboxylic acid groups on PP nonwoven fabrics [3-7]. Surface coatings with a solu-tion containing hydrophilic substances have also been used to improve the hydrophilic properties[8, 9].

Besides these modification techniques, the use of migratory additives, i.e., materials added tothe melt that exhibit controlled migration to the surface of the PP nonwoven fabrics, have beenrecognized as low cost materials and reliable method to generate desirable surface propertieswithout altering the bulk properties [10]. Migratory additives have been of great interest forseveral reasons. They are efficient, as only a small quantity of additive is needed to significantlychange the polymer surface property [11]. Furthermore, compared with other techniques such asplasma treatment [12-14], surface grafting [15-18], and solution coating [8, 9], migratory additivesdo not require post processing and solvent handling.

Many nonionic surfactants have been used as migratory additives to render PP nonwovens’surface hydrophilic. Examples include lauric acid diethanol amide [11], and polyethylene glycol(PEG) lauryl ether [19]. An ionic surfactant, sodium alkenesulfonate with 15 carbons, was usedto hydrophilize PP fabric as well [20]. Although a lot of surfactants are reported to be able tochange the surface properties of PP films, there has been a little work reported to systematicallystudy the effects of hydrophilic additives on the surface hydrophilicity of PP melt-blown nonwovenfabrics.

In this article, we investigate the properties of PP melt-blown nonwoven fabrics modified byblending with a Novel Hydrophilic Additive (CHA) in different melt-blown process conditions.

2 Experiments

2.1 Materials

Polypropylene was obtained from Shanghai Expert Company as the base polymer for this study.The Novel Hydrophilic Additive (CHA) was a pre blended mixture of 40% PP and 60% activeingredients, which structure as CH3CH2(CH2CH2)aCH2CH2(OCH2CH2)bOH, in which a=9-25and b=1-10. A Traditional Hydrophilic Additive (THA), which probably contains a substancestructured as HO (CH2CH2O)nH.

2.2 Polymer Characterization

2.2.1 Thermal Analysis

Thermal analysis was carried out using the Differential Scanning Calorimeter (DSC). Polymermaterials were heated from room temperature to 200℃ at a heating rate of 10℃/min in the N2

L. Fan et al. / Journal of Fiber Bioengineering & Informatics 4:4 (2011) 403–411 405

atmosphere, held at that temperature for 10 mins to ensure complete melting of all the crystals,and then cooled to room temperature at the rate of 65℃/min.

2.2.2 Rheological Property

The rheological behavior of polymer materials was performed by an ARES-RFS rheometer. Thesamples were cylinders of 8 mm in diameter and 2mm thick and were placed on the rheometerplates. The measurements were done at 180℃ - 220℃. The rheometer was interfaced with acomputer so that the viscosity and stress signals could be directly recorded and analyzed.

2.3 Preparation of Melt-blown Nonwoven Fabrics

The experiments were carried out using the melt-blowing nonwoven equipment at Donghua Uni-versity. PP was extruded through the extruder with CHA and THA respectively. The concen-tration of CHA and THA in the melt-blown nonwoven fabrics was formulated at from 2.5wt% to6.5wt%. The dual-slot-die parameters were as follows: slot width=0.2 mm, die length=200 mm,head extended width=0.5 mm, and the spinneret diameter=0.18 mm. The polymer throughputwas 0.28g/hole/min, the die temperature was 240℃, hot air temperature was 275℃-295 ℃,the hot air pressure was 0.10 Mpa - 0.40 Mpa, and the Die-to-collector Distance (DCD) was8 cm-14 cm.

2.4 Nonwoven Fabric Characterization

2.4.1 Scanning Electron Microscopy (SEM) Analysis

The morphologies of PP/CHA melt-blown nonwoven fabrics produced in different hot air tem-perature were examined using a JSM-5600 scanning electron microscopy. The specimens werecoated with gold using a sputter coater and their morphology was observed under the SEM at anacceleration voltage of 10 kV.

2.4.2 Wide-angle x-ray Diffraction

Wide-angle x-ray diffraction (WAXD) of the nonwoven samples was carried out using a D/max-2550 PC X-ray diffractometer in continuous scan mode to evaluate the degree of crystallization.Equatorial scans were obtained from 2θ=2◦ to 30◦ in steps of 0.02◦ and a dwell time of 0.12 s,whilst operating at 40 kV and 200 mA.

2.4.3 Hydrophilic Properties Analysis

2.4.3.1 Static Water Contact Angle

The static contact angle of the original and the modified nonwovens were measured to quantifythe change in hydrophilicity, using a contact angle goniometer (OCA15EC, dataphysics, Ger-many). A Sessile Drop method, which was preferred for explanate surfaces, was chosen. Anultra-pure water drop (3µl) was added to a dry sample in ambient atmosphere, and the sam-ple was observed through a traveling microscope fitted with a goniometer eyepiece. The data


shown represented an average over five measurements performed on five different areas of thesame specimen.

2.4.3.2 The Liquid Wicking Rate

The capillarity method measures the rate of vertical capillary rise in a specimen strip suspendedin the test liquid. The liquid wicking rate was investigated according to ISO 9073-6 TextilesTesting standard.

2.4.3.3 Multiple Liquid Strikethrough Time

This test measures the strikethrough time, i.e. the time taken for a known volume of liquid(simulated urine) applied to the surface of the test piece of nonwoven cover stock, which is incontact with an underlying standard absorbent pad, to pass through the nonwoven. In this test,the liquid strikethrough time of the fabrics has been examined for 12 times. Liquid strikethroughtime was investigated according to ISO 9073-8 Textiles Testing standard.

3 Results and Discussion

3.1 Raw Materials Analysis

3.1.1 DSC Analysis

Since the web structure can be significantly affected by the heating during melt-blown process, itis very important to investigate the thermal properties of the three raw materials. Fig. 1 showsthe DSC curves for the raw materials, where the melt temperature of PP is 160℃, while THAand CHA show more complicated on DSC curve which have multi-melting points performance,indicating that they are both intermixture, therefore, the condition of the melt blowing processof the mixture may be different from pure PP.

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Fig. 1: DSC curves of raw materials

3.1.2 Rheological Property Analysis

As shown in Fig. 2, the rheological behaviour of the materials was obtained by shear stress-shearrate and shear viscosity -shear rate measurements within a range of shear rates (0.1-100 s−1).Via rheological analysis, the fluid viscosity decreases and the sheer stress increases of the polymer


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Fig. 2: Rheology curves of raw materials

materials with the rise of hot air temperature, so they are typical non-Newtonian fluids. Combinedwith the thermal result, the die temperature was set at 240℃ in this experiment.

3.2 Nonwoven Fabric Analysis

3.2.1 SEM Observation

The representative SEM images of the samples processed at different temperature are shown inFig. 3. Comparing the three samples, we can see that the morphology is apparently different. Inaddition, the fiber diameters were measured from the SEM image using Image-Pro Plus software.Both the diameters and the pore space decreases with the hot air temperature rising, whichindicates that the web structure is significantly affected by the heating during melt-blown process.Since the thermal and fluid properties of the polymer materials are infected by hot air temperature,it is not surprising that the heat notably affects the web structure of the nonwoven fabrics.

3.2.2 Crystallization Property Analysis

The WAXD scans of different melt-blown web samples are shown in Fig. 4. Results of crystallinitymeasured by WAXD are as follows: 33.98% (Fig. 4 (a)), 42.52% (Fig. 4 (b)) and 37.53% (Fig. 4(c)), respectively. The results illustrate that the degree of crystallization increases at first and thendecreases with hot air temperature rising. This is probably because when the temperature is lower,

(a) 275°C (b) 285°C (c) 295°C

Fig. 3: SEM images of PP/CHA nonwoven fabrics


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Fig. 4: Wide-angle x-ray diffraction of PP/CHA nonwoven ((a) 275 ℃, (b) 285 ℃, (c) 295 ℃)

the crystal nucleus in the system will lead to heteropical nucleation, resulting in a higher speedof crystallization, therefore, a higher degree of crystallization. However, when the temperatureis come up to 285℃, the crystal nucleus is mainly generated by homogeneous nucleation, andbecause nucleation takes time (induction period), the speed of crystallization is lower, resultingin a lower crystallization. The increase of the hot air temperature is beneficial to the activity ofmacromolecules and renders it easier to enter into the crystal lattice. Besides, it is also conduciveto the elimination of internal stress, leading to a more sufficient crystallization.

3.2.3 Hydrophilic Properties Analysis

3.2.3.1 Static Water Contact Angle

Fig. 5 indicates that unmodified PP nonwoven (a) is hydrophobic, PP nonwoven fabric con-taining 5.5%THA (b) has little hydrophilic property, and while PP nonwoven fabric containing5.5%CHA (c) exhibits excellent hydrophilic property. Furthermore, the water contact angleswere measured and the results were as follows: the static water contact angle value of pristinepolypropylene nonwoven fabrics is 136.4◦, while the contact angle value of PP nonwoven fabricscontaining 5.5% CHA is 38.3◦. The value for the modified nonwoven fabrics was much smallerthan the PP nonwoven fabrics containing 5.5% THA (129.2◦) indicating that the PP nonwovenfabrics containing CHA have much better hydrophilic property. For THA, because the C-O hasweak dissociation in water, it can only contribute limitative hydrophilic effect to PP melt-blownfabrics. However, for CHA, due to its special structure, the hydrophilic groups can transfer to

(a) (b) (c)

Fig. 5: Contact angle of nonwoven fabrics: pristine sample (a), the modified sample with 5.5% THA (b)and 5.5% CHA (c)


the surface and in the meantime, the hydrophobic groups can prevent molecules breaking fromthe surface, therefore endows PP nonwovens with durable hydrophilicity.

3.2.3.2 Liquid Wicking Rate (Capillarity)

The liquid conveying property of melt-blown nonwoven fabric is mainly in connection withthe liquid infiltration into the fibres, the structures and surface characteristics of the fibres andnonwovens.

From Fig. 6, we can see that PP nonwoven fabric containing CHA have the highest liquidwicking rate due to its hydrophilic groups transferred to the surface and forming a hydrophilicfilm, which is beneficial to the liquid transferring.

3.2.3.4 Multiple Liquid Strikethrough Time

It can be seen from Fig. 7 that PP/CHA melt-blown nonwoven samples are repeatedly subjectedto saline solution for multiple strike-through time measurements show values below 3s. Thenonwoven fabric treated by THA lost its wettability after 3 insults, while nonwovens containing4.5% and 5.5% CHA remain hydrophilic even after 12 insults. We can conclude that CHA providesa durable hydrophilic surface effect to PP melt-blown nonwoven fabrics.

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Fig. 7: The multiple liquid strikethrough time of nonwoven fabrics


4 Conclusion

PP melt-blown nonwovens containing hydrophilic additives were prepared and their hydrophilic-ity was investigated. The THA didn’t give necessary hydrophilic properties to PP melt-blownnonwoven fabrics, while CHA was effective in rendering PP melt-blown nonwoven fabric surfaceshydrophilic. CHA is a hydrophilic internal additive for PP melt-blown nonwovens and allowsPP melt-blown nonwoven fabrics to absorb liquid quickly. PP/CHA melt-blown nonwoven fab-ric represents a breakthrough for wipes and similar applications since it continues to be highlyabsorbent after repeated use. What’s more, it has a short strikethrough time, even after dozensof insults, which is an innovative feature for hygiene products. Due to its specific advantages,PP/CHA melt-blown nonwoven fabric will be used more and more widely in many applications.

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