**1. Introduction**

242 Thermoplastic Elastomers

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Nonwovens are a unique class of textile materials, formed by bonding the fibers by various techniques. The demand through the nonwovens is increasing on the world day by day and nonwovens are getting integrated to more application areas rapidly. Today, nonwovens have achieved an excellent position among the products of daily use like hygiene, medicine, household and more. (Ebeling et al., 2006)

Meltblown nonwovens are a relatively new class of thermoplastic based nonwoven materials which integrate to new application areas to replace conventional textile materials. Due to their unique micro structure, low porosity, absorbency, light weight and high surface area, microfiber meltblown nonwovens are promising materials of the future. Meltblowing is a one step process which enables to produce microfiber nonwovens directly from thermoplastic polymers with the aid of high velocity air to attenuate the melt filaments. In this process high velocity air blows a molten thermoplastic resin from an extruder die tip onto a conveyor or take up screen to form a fine fiberous and selfbonding web. (Bang One Lee et al., 2010) It has become an important industrial technique in nonwovens because of its ability to produce fabrics of microfiber structure suitable for filtration media, thermal insulators, battery seperators, oil absorbents, wipes, apparel, medical applications and many lamination applications. (Zhang et al., 2002 , Duran&Perincek, 2010; Dutton, 2008)

Meltblowing is a unique process since it is used almost exclusively to produce microfibers rather than fibers the size of conventional textile fibers. Meltblown microfibers generally have diameters in the range of 2 to 4 µm, although they may be as small as 0.1 µm and as large as 10 to 15 µm. Differences between meltblown nonwoven fabrics and other nonwoven fabrics, such as degree of softness, cover or opacity, and porosity can generally be traced to differences in filament size. (Bang One Lee et al., 2010)

Meltblowing technology is used for producing light fiber webs directly from polymers. This process process allows the production of ultrafine filament nonwovens under very economical conditions. In the basic melt blowing process, a thermoplastic fibre forming polymer is melted in an extruder, pumped through die holes and then the melt enters high-

Investigation of the Production Parameters and

fibers occurs. (Dahiya et al., 2004)

form fine fibers.

Physical Characteristics of Polypropylene Meltblown Nonwovens 245

from these holes to form filament strands which are subsequently attenuated by hot air to

As soon as the molten polymer is extruded from the die holes, high velocity hot air streams blown from the top and bottom sides of the die nosepiece, attenuate the polymer streams to form microfibers. As the hot air stream containing the microfibers progresses toward the collector screen, it draws in a large amount of surrounding air that cools and solidifies the fibers. The solidified fibers subsequently get laid randomly onto the collecting screen, forming a self-bonded nonwoven web. (Duran&Perincek,2010; Dutton, 2008; Dahiya et al., 2004) Usually, a vacuum is applied to the inside of the collector screen to withdraw the hot air and enhance the fiber laying process. The combination of fiber entanglement and fiberto-fiber bonding generally produce enough web cohesion so that the web can be readily used without further bonding. However, additional bonding and finishing processes may

The properties of the meltblown webs are affected by various production parameters including air temperature, polymer/die temperature, die to collector distance (DCD), collector speed, polymer throughput, air throughput, die hole size and air angle. All of these affect the final properties of the nonwoven web. Both polymer throughput and air flow rate control the final fiber diameter, fiber entanglement, basis weight and the attenuating zone. Polymer/die and air temperatures combined with air flow rate affect the uniformity, shot formation which can be described as large globules of nonfibrous polymer larger in diameter than fibers in webs, rope and fly formation, fabric appearance and touch. (Dahiya et al., 2004) Because meltblowing uses an attenuating air stream to draw and orient the fibres, the distance between the polymer orifice and the collection surface includes the fiber characteristics and resulting fabric properties. This distance is commonly referred to as the die-to-collector distance (DCD). The period of time that fibres spend in flight before being collected influences fiber orientation, strength and surface properties. A varying DCD permits the production of structures with varying properties from stiff and brittle at close distance to soft and bulky at large distance. (Farer et al., 2003) Die hole size along with die set back affects the fiber size. Air angle controls the nature of air flow, i.e. as the air angle approaches 90 it results in a high degree of fiber separation or turbulence that leads to random fiber distribution. At an angle of 30, roped or parallel fibers deposited as loosely coiled bundles of fibers are generated. This structure is undesirable. At angles greater than 30, attenuation as well as breakage of

The melt blowing process is amenable to a wide range of polymers in terms of viscosities and blends. The type of polymer or resin used defines the elasticity, softness, wetability, dyeability, chemical resistance and other related properties of formed webs. Some polymers, which can be used for the formation of melt-blown webs are listed as polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA) and polylacticacid (PLA). Polypropylene (PP) is the most widely used polymer for meltblowing process, because it has a low viscosity, a low melting point and is easy to draw into fibers. A lot of efforts have been made in the last 30 years on the process study, new resin and product

development and process improvements. (Zhang et al., 2002; Dahiya et al., 2004)

further be applied to these melt-blown webs. (Dahiya et al., 2004)

speed, hot air streams. Streams of hot air exiting from the left and right sides of the die nosepiece rapidly attenuate the extruded polymer streams to form extremely fine filaments. The filaments then are blown by high-velocity air onto a collector screen, thus forming a fine-filtered, self-bonded nonwoven web. After that, they are bonded and wound to form roll goods for further processing. Web structure begins to develop when fiber entanglement first occurs, but network structure becomes fixed only when fibers contact the collector and their motion ceases. (Duran&Perincek, 2010; Randall et al, 2004; Rupp, 2008)

Because the meltblowing process employs high velocity air to impinge upon the polymer as it exits the orifices, it elongates the polymer strands from 500 m diameter to diameters as small as 0.1 m. Extreme entanglemet of fibres, characterizing meltblown fibrous webs, produces coherent fiber webs. Unique micrometer characteristics of meltblown structures produce a high surface area per unit weight and fine porosity. Therefore meltblown technology can be used to produce efficient filter materials that are able to filter particles as small as 0.5 m. (Farer et al., 2003)

The melt blown process generally consists of five major components, which are the extruder, metering pump, die assembly, web formation, and winding. The extruder, which consists of a heated barrel with a rotating screw inside is one of the important elements in all polymer processing. In the extruder, the polymer pellets or granules are heated and melted until appropriate temperature and viscosity are reached. The extruder is divided in to three different zones. (Dahiya et al., 2004) The feed zone, is the zone where the polymer pellets are preheated and pushed to the next zone. The transition zone has a decreasing depth channel in order to compress and homogenize the melted polymer. The melting of the pellets in the extruder is due to the heat and friction of the viscous flow and the mechanical action between the screw and the walls of the barrel. The molten polymer is then fed to the metering pump to ensure uniform polymer feed to the die assembly. (Duran&Perincek,2010; Dutton, 2008; Dahiya et al., 2004) The metering zone is the last zone in the extruder whose main purpose is to generate maximum pressure in order to pump the molten polymer in the forward direction. (Dahiya et al., 2004) The metering pump is a device for uniform melt delivery to the die assembly. It ensures consistent flow of clean polymer mix under process variations in viscosity, pressure, and temperature. The metering pump also provides polymer metering and the required process pressure. At this point the breaker plate controls the pressure generated with a screen pack placed near to the screw discharge. The breaker plate also filters out any impurities such as dirt, foreign particle metal particles and melted polymer lumps. (Dahiya et al., 2004)

The die assembly is the most important element of the melt blown process. It has three distinct components: polymer-feed distribution, die nosepiece, and air manifolds. The feed distribution is usually designed in such a way that the polymer distribution is less dependent on the shear properties of the polymer. This feature allows the melt blowing of widely different polymeric materials with one distribution system. The feed distribution balances both the flow and the residence time across the width of the die. From the feed distribution channel the polymer melt goes directly to the die nosepiece. The web uniformity hinges largely on the design and fabrication of the nosepiece. Therefore, the die nosepiece in the melt blowing process requires very tight tolerances, which have made their fabrication very costly. The die nosepiece is a wide, hollow, and tapered piece of metal having several hundred orifices or holes across the width. The polymer melt is extruded

speed, hot air streams. Streams of hot air exiting from the left and right sides of the die nosepiece rapidly attenuate the extruded polymer streams to form extremely fine filaments. The filaments then are blown by high-velocity air onto a collector screen, thus forming a fine-filtered, self-bonded nonwoven web. After that, they are bonded and wound to form roll goods for further processing. Web structure begins to develop when fiber entanglement first occurs, but network structure becomes fixed only when fibers contact the collector and

Because the meltblowing process employs high velocity air to impinge upon the polymer as it exits the orifices, it elongates the polymer strands from 500 m diameter to diameters as small as 0.1 m. Extreme entanglemet of fibres, characterizing meltblown fibrous webs, produces coherent fiber webs. Unique micrometer characteristics of meltblown structures produce a high surface area per unit weight and fine porosity. Therefore meltblown technology can be used to produce efficient filter materials that are able to filter particles as

The melt blown process generally consists of five major components, which are the extruder, metering pump, die assembly, web formation, and winding. The extruder, which consists of a heated barrel with a rotating screw inside is one of the important elements in all polymer processing. In the extruder, the polymer pellets or granules are heated and melted until appropriate temperature and viscosity are reached. The extruder is divided in to three different zones. (Dahiya et al., 2004) The feed zone, is the zone where the polymer pellets are preheated and pushed to the next zone. The transition zone has a decreasing depth channel in order to compress and homogenize the melted polymer. The melting of the pellets in the extruder is due to the heat and friction of the viscous flow and the mechanical action between the screw and the walls of the barrel. The molten polymer is then fed to the metering pump to ensure uniform polymer feed to the die assembly. (Duran&Perincek,2010; Dutton, 2008; Dahiya et al., 2004) The metering zone is the last zone in the extruder whose main purpose is to generate maximum pressure in order to pump the molten polymer in the forward direction. (Dahiya et al., 2004) The metering pump is a device for uniform melt delivery to the die assembly. It ensures consistent flow of clean polymer mix under process variations in viscosity, pressure, and temperature. The metering pump also provides polymer metering and the required process pressure. At this point the breaker plate controls the pressure generated with a screen pack placed near to the screw discharge. The breaker plate also filters out any impurities such as dirt, foreign particle metal particles and melted

The die assembly is the most important element of the melt blown process. It has three distinct components: polymer-feed distribution, die nosepiece, and air manifolds. The feed distribution is usually designed in such a way that the polymer distribution is less dependent on the shear properties of the polymer. This feature allows the melt blowing of widely different polymeric materials with one distribution system. The feed distribution balances both the flow and the residence time across the width of the die. From the feed distribution channel the polymer melt goes directly to the die nosepiece. The web uniformity hinges largely on the design and fabrication of the nosepiece. Therefore, the die nosepiece in the melt blowing process requires very tight tolerances, which have made their fabrication very costly. The die nosepiece is a wide, hollow, and tapered piece of metal having several hundred orifices or holes across the width. The polymer melt is extruded

their motion ceases. (Duran&Perincek, 2010; Randall et al, 2004; Rupp, 2008)

small as 0.5 m. (Farer et al., 2003)

polymer lumps. (Dahiya et al., 2004)

from these holes to form filament strands which are subsequently attenuated by hot air to form fine fibers.

As soon as the molten polymer is extruded from the die holes, high velocity hot air streams blown from the top and bottom sides of the die nosepiece, attenuate the polymer streams to form microfibers. As the hot air stream containing the microfibers progresses toward the collector screen, it draws in a large amount of surrounding air that cools and solidifies the fibers. The solidified fibers subsequently get laid randomly onto the collecting screen, forming a self-bonded nonwoven web. (Duran&Perincek,2010; Dutton, 2008; Dahiya et al., 2004) Usually, a vacuum is applied to the inside of the collector screen to withdraw the hot air and enhance the fiber laying process. The combination of fiber entanglement and fiberto-fiber bonding generally produce enough web cohesion so that the web can be readily used without further bonding. However, additional bonding and finishing processes may further be applied to these melt-blown webs. (Dahiya et al., 2004)

The properties of the meltblown webs are affected by various production parameters including air temperature, polymer/die temperature, die to collector distance (DCD), collector speed, polymer throughput, air throughput, die hole size and air angle. All of these affect the final properties of the nonwoven web. Both polymer throughput and air flow rate control the final fiber diameter, fiber entanglement, basis weight and the attenuating zone. Polymer/die and air temperatures combined with air flow rate affect the uniformity, shot formation which can be described as large globules of nonfibrous polymer larger in diameter than fibers in webs, rope and fly formation, fabric appearance and touch. (Dahiya et al., 2004) Because meltblowing uses an attenuating air stream to draw and orient the fibres, the distance between the polymer orifice and the collection surface includes the fiber characteristics and resulting fabric properties. This distance is commonly referred to as the die-to-collector distance (DCD). The period of time that fibres spend in flight before being collected influences fiber orientation, strength and surface properties. A varying DCD permits the production of structures with varying properties from stiff and brittle at close distance to soft and bulky at large distance. (Farer et al., 2003) Die hole size along with die set back affects the fiber size. Air angle controls the nature of air flow, i.e. as the air angle approaches 90 it results in a high degree of fiber separation or turbulence that leads to random fiber distribution. At an angle of 30, roped or parallel fibers deposited as loosely coiled bundles of fibers are generated. This structure is undesirable. At angles greater than 30, attenuation as well as breakage of fibers occurs. (Dahiya et al., 2004)

The melt blowing process is amenable to a wide range of polymers in terms of viscosities and blends. The type of polymer or resin used defines the elasticity, softness, wetability, dyeability, chemical resistance and other related properties of formed webs. Some polymers, which can be used for the formation of melt-blown webs are listed as polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA) and polylacticacid (PLA). Polypropylene (PP) is the most widely used polymer for meltblowing process, because it has a low viscosity, a low melting point and is easy to draw into fibers. A lot of efforts have been made in the last 30 years on the process study, new resin and product development and process improvements. (Zhang et al., 2002; Dahiya et al., 2004)

Investigation of the Production Parameters and

**2. Material and method** 

in this study can be seen in Table 2.

diameter and tensile properties.

Physical Characteristics of Polypropylene Meltblown Nonwovens 247

Beside many advantages they provide, meltblowns have limited strength characteristics and poor abrasion resistance. (Farer et al., 2003) Therefore, they often are combined with other nonwovens. Spunbonds and other types of nonwovens also can be covered and refined with meltblowns. Today it is possible to implement production lines not only with spunbonds, but also with a meltblown component, to produce different types of nonwovens with an even more of a textile feeling. Approximately 40 percent of meltblowns are manufactured using a stand-alone process. The remaining meltblowns are combined with spunbonds or laminated to form other materials. Combinations with spunbonded fabrics are primarily used to make nonwoven materials with barrier properties. Another variation is the combination of meltblown with cellulose or an absorbent powder to produce a soft, strong, but still absorbent material that can retain absorbed liquid while still keeping its strength. The outcome is a combination of spunbonds (S) and meltblowns (M), resulting in SMS, or even SSMMMSS or other combinations, depending on the final product. So many different products can be manufactured and implemented from SMS to SSMMMSS. Some examples of their applications are hygiene, baby and adult diapers, medical products, protective masks for medical use, general use as a barrier layers, paper composites, work safety, protective clothing, breathing masks and combination with other nonwovens. (Rupp, 2008)

In this chapter, the results of a study about polypropylene microfibre meltblown nonwovens were covered. Aspects related to the production phase, properties of the materials produced and application areas were discussed. In the content of this study, effect of some production parameters namely die air pressure, collector drum speed, collector vacuum and extruder pressure on the physical properties of the web structure such as thickness, basis weight, air permeability, tensile properties, surface friction and fiber diameter were investigated.

As raw material, PP with 1100 melt flow rate (MFR), 0.75 g/cm3 density and 335 F melting point was used. The main production settings namely; extruder temperatures, die temperature, air temperature (the air fed to the spinerette to spin the fibers), die hole

> **Production Setting Value**  Extruder zone 1 temperature (°F) 270 Extruder zone 2 temperature (°F) 320 Extruder zone 3 temperature (°F) 370 Die temperature (°F) 336 Air temperature (°F) 350 Die hole diameter (inches) 0.09 Die-to collector distance (cm) 50

The sample codes and production parameters of the PP melt blown nonwovens investigated

The produced samples were characterized for thickness, basis weight, air permeability, fiber

diameter and die-to-collector distance were given in Table 1.

Table 1. Main production settings and their values used in experiments

The main characteristics and properties of melt-blown nonwovens can be summarised as follows:


Meltblowing is a unique system since the process generates a fine fiber not available to the other nonwoven processes. Because the micro-denier fiber (less than 0.1 denier per filament) is not really available as a nonwoven fibrous raw material, the meltblown process, which can produce such a fiber, opens new vistas of products and applications. (Dahiya et al., 2004) Microfiber nonwovens produced via meltblowing technique are suitable to be used as thermal insulators, filtration media, oil absorbents, battery separators, medical area, wipes, apparel, laminates and many other applications. (Duran&Perincek, 2010, Dutton, 2008) Meltblown nonwovens find extensive use especially in absorbent cloths and wipes; oil absorption; and filtration for liquids, gas and air. Also, very important end uses of meltblowns include sanitary applications such as hygiene and incontinence products for babies, adults and feminine hygiene. The application areas of meltblown nonwovens can be summarised as follows: (Dahiya et al., 2004)


Beside many advantages they provide, meltblowns have limited strength characteristics and poor abrasion resistance. (Farer et al., 2003) Therefore, they often are combined with other nonwovens. Spunbonds and other types of nonwovens also can be covered and refined with meltblowns. Today it is possible to implement production lines not only with spunbonds, but also with a meltblown component, to produce different types of nonwovens with an even more of a textile feeling. Approximately 40 percent of meltblowns are manufactured using a stand-alone process. The remaining meltblowns are combined with spunbonds or laminated to form other materials. Combinations with spunbonded fabrics are primarily used to make nonwoven materials with barrier properties. Another variation is the combination of meltblown with cellulose or an absorbent powder to produce a soft, strong, but still absorbent material that can retain absorbed liquid while still keeping its strength. The outcome is a combination of spunbonds (S) and meltblowns (M), resulting in SMS, or even SSMMMSS or other combinations, depending on the final product. So many different products can be manufactured and implemented from SMS to SSMMMSS. Some examples of their applications are hygiene, baby and adult diapers, medical products, protective masks for medical use, general use as a barrier layers, paper composites, work safety, protective clothing, breathing masks and combination with other nonwovens. (Rupp, 2008)
