Process Parameters for Fiber Formation in Spunbond Technology

Transcription

1 Tekstil Teknolojileri Elektronik Dergisi Cilt: 5, No: 3, 2011 (33-45) Electronic Journal of Textile Technologies Vol: 5, No: 3, 2011 (33-45) TEKNOLOJİK ARAŞTIRMALAR e-issn: Review (Derleme) Process Parameters for Fiber Formation in Spunbond Technology M. Fatih CANBOLAT, Murat KODALOĞLU Süleyman Demirel Üniversitesi, Mühendislik Mimarlık Fakültesi, Tekstil Mühendisliği, Çünür-ISPARTA Abstract Fiber formation with melt spinning is a well known, old method. On the other hand, nonwovens production with some amendments in melt spinning setup is a relatively new production method. There are two types of nonwovens production seen based on this method, first one is spunbounding, and the other is melt-blowing. Basically, nonwoven web structure is produced by the collection of continuous filaments on a moving conveyor band. Polymer structure and process parameters are affected on the quality of the end product, and it is vital to understand and optimize the parameters effectively. In this study, general production methods will be mentioned and the relationship between structural properties and process parameters which were given in the literature will be discussed. Keywords: Melt spinning, spunbounding, nonwovens Sonsuz Uzunlukta Filament Çekimi ile Yüzey Eldesinde Lif Oluşumu Üzerine Etkiyen Proses Parametreleri Özet Eriyikten çekim sonucu lif eldesi çok eskilere dayanan, bilinen bir metoddur. Bunun yanında söz konusu metod üzerinde bazı değişiklikler yapılması sonrası dokusuz kumaş eldesi nispeten yeni bir üretim metodudur. İki tip üretim söz konusu olup, birincisi sonsuz uzunlukta filament çekimi ile yüzey oluşturma, diğeri ise eriyikten üfleyerek çekim sonucu yüzey oluşturma. Her iki metod içinde temel olarak üretilen liflerin hareket halinde bir bandın üzerine dökülmesi sonucu dokusuz yüzey eldesi söz konusudur. Elde edilecek son ürünün kalitesi üzerinde kullanılan polimer yapısı ve proses parametreleri etkimekte olup, bu parametrelerin iyi anlaşılıp, optimizasyonu hayati önem taşımaktadır. Bu çalışmada genel üretim metodlarından bahsedilip, literatürde yer alan yüzey yapısı-proses parametreleri ilişkisi açıklanacaktır. Anahtar Kelimeler: Eriyikten çekim, sonsuz uzunlukta filament çekimi, dokusuz yüzeyler Bu makaleye atıf yapmak için Canbolat, M., F., Kodaloglu, M., Sonsuz Uzunlukta Filament Çekimi ile Yüzey Eldesinde Lif Oluşumu Üzerine Etkiyen Proses Parametreleri, Tekstil Teknolojileri Elektronik Dergisi 2011, 5(3)33-45 How to cite this article Canbolat, M., F., Kodaloglu, M., Process Parameters for Fiber Formation in Spunbound Technology, Electronic Journal of Textile Technologies, 2011, 5 (3) 33-45

2 Teknolojik Araştırmalar: TTED 2011 (3) Process Parameters for Fiber Formation in. INTRODUCTION Web formation techniques in nonwovens technology are classified under three main categories such as dry laid, web laid and polymer laid systems. Among these techniques polymer-laid systems are mainly the derivation of melt spinning fiber formation technology that may or may not eliminate drawing and winding steps and gives opportunity to direct deposition of fiber bundles onto a moving screen. Because of intermediate steps elimination, this technology gives opportunity to have increase in production rates and thus cost reduction in fabric formation. Spunbond and meltblown are the two commonly used polymer-laid techniques which use thermoplastic polymers as a raw material. There is a distinction between polymers according to their molecular weights and distributions that are suitable for each technique. Generally high molecular weight polymers are preferred for spunbond technology whereas low molecular weight polymers for meltblown technology. While polyolefins, polyester, nylon, and rayon are the primary polymers in spunbond technology, polypropylene has the biggest market share among them. [1] The main reasons for polypropylene to be leader in the spunbond market are cost effectiveness, easy processability, low density, and high bulk production depends on low density. Other polymers also have their additional better properties comparing with polypropylene but they do not meet all the criteria required for the ideal spunbond production. For instance, polyester has better tensile properties and heat stability than polypropylene but it is more expensive and generates low production volume; polyamide has better cover and strength properties with hydrophilic structure but it is much more expensive than both polyester and polypropylene [2]. Spunbond technology which dates back 1950s is a single step process that produces continuous filaments and fabric structures from the polymer melts at the same time as partially mentioned in above parts. During the process, the molten polymer is extruded through a series of holes known as spinnerets and then drawn and cooled by means of quenched air, drawing rolls and suction blowers. After then, attenuated filaments are laid down on a moving belt, web bonding is occurred and the spunbond fabric is transferred to the winding unit to roll up onto winders [4]. The fabrics produced by spunbond technology can be usually between 3.0 m 5.2 m wide to facilitate productivity. While fiber size ranges between 0.8 to 50 dtex, most common fiber size is seen between 1.5 to 20 dtex. Fabric basis weight for spunbond fabrics ranges from 10 to 800 gsm while the standard values are between 17 to 180 gsm [2]. The final properties of the spunbond fabrics are the combination of the properties of filaments, arrangements of the filaments in the web, and the bonding conditions. It is essential to understand the relationship between process conditions and the properties of the fabrics to produce reproducible, same quality, uniform products with this technology [5]. 34

3 Canbolat, M., F., Kodaloglu, M. Teknolojik Araştırmalar: TTED 2011 (3) Following the first appearance of spunbond technology in the market, it took sometimes to be recognized the application potential of the spunbond fabrics. During early 1970s numerous studies and patent applications on spunbond technology were committed. During those years and later some key products and production lines were introduced by the pioneer and leader companies in the market which provide developments for the spunbond technology. Du Pont, Amoco Fibers and Fabrics, and Nordson from USA; Freudenberg, Neumag, and Reifenhauser from Germany; Kobelco from Japan; Meccaniche Moderne S.p.A from Italy; and Sodoca from France have been the giant players in spunbond market from the beginning till now. Reemay, Typar, and Tyvek brand named products developed by Du Pont. Additionally, Freudenberg introduced Viledon brand named product and Lutravil, and Docan brand named processing systems. More recently, Reicofil processing system developed by Reifenhauser, RFX system developed by Amoco Fibers and Fabrics, and S-Tex system developed by Sodoca, France [1]. PROPERTIES, APPLICATION FIELDS & MARKET FOR SPUNBOND NONWOVENS Nonwovens which are produced from web of fibrous materials by fusing or tangling by means of mechanical, chemical or thermal methods differ from conventional fabrication methods [10]. The characterization of the nonwovens also shows disparity because of its totally different structural formation. In this regard, some structural analysis methods were developed special to nonwovens. Among them maybe the most important one is orientation distribution function, ODF. Orientation of fibers in the web structure was considered as an important parameter because of possible effects on the mechanical strength of the fabric. Based on the characteristic of the spunbond technology itself, it is expected from the structure to show isotropy. However, by means of some auxiliary apparatus in the spinning line and the speed of the moving belt, it is possible to produce spunbond webs with anisotropy in a preferred orientation direction. It is difficult to generalize the properties of the final spunbond fabric, because of the fact that they are dependent on all the process parameters from filament formation to bonding procedure. However, in order to have some ideas about spunbond structures, general specifications of spunbond nonwovens can be classified as following; they possess high tear strength (especially in CD), good fray and crease resistance, high liquid retention capacity, low drape, high in-plane shear resistance, high strength to weight ratios and some others [1]. Application fields of spunbond products can be categorized under four main groups such as automotive textiles, textiles for civil engineering applications, textiles for hygiene and medical industry, and textiles for packaging industry. More specifically, spunbond fabrics are used as coverstock for baby diapers, sanitary napkins, adult incontinence products, dust covers, upholstery reinforcement, spring insulators, 35

4 Teknolojik Araştırmalar: TTED 2011 (3) Process Parameters for Fiber Formation in. mattress toppers, surgical apparel, surgical drapes and gowns, trunk liners, door trim, backing for tufted floor coverings, geotextiles, floppy disk liners and so on and so forth [1, 11]. In today spunbond market, two major application fields are calendared spunbonds for the hygiene sector and needled spunbonds for geotextiles and roofing applications. However, future expectations for the market show disparities than today with the integration of fairly new bonding technology, spunlace to the spunbond market. Spunlace technology provides many contributions to spunbond structures such as softness in the structure and increase in production speed [12]. According to 2007 spunbond market report prepared by Wuagneux, anticipations of INDA and the addition of new capacities to the spunbond lines indicate the spunbond market will grow in further years. Forecast for the growth of spunbond market is about more than 8.5% per year between 2009 and 2012 [13]. Results of an old data about spunbond market shares by region between 1988 and 2000 were given in Figure 1. According to data, around 2000s there were three major economies that lead to spunbond market, North America, Europe and Japan. However, about a decade ago it was also anticipated that for the year 2010 some emerging markets will share the 35% of the spunbond market around the globe which include China, Mexico, South America, Southern Africa, India and other Pacific Rim. The main reason behind the high demand for spunbond nonwovens are the cost effectiveness because of elimination of separate yarn formation and the high strength to mass ratio [11]. Moreover spunbond technology presents promising results for various applications with the endless combination opportunities with other nonwoven technologies. Most well known is sandwich structure which is formed by using spunbond and melt-blown nonwovens together like SSM, SMS and several others [14]. FIG. 1 Spunbond Nonwoven Production by Region Between 1988 and

5 Canbolat, M., F., Kodaloglu, M. Teknolojik Araştırmalar: TTED 2011 (3) SPUNBOND MECHANISM Melt spinning of synthetic filaments is the technology that constitutes the main framework of the spunbond technology today. By means of some modifications on the spinning line, filaments were collected on a moving belt directly after spinning of filaments and with different bonding techniques fabric structure was obtained in an easy and unusual way. In a spunbond mechanism main functional elements for fiber formation can be listed as, extrusion part, spinneret, and cooling and drawing part. First, granules or pellets are fed to the extruder for grinding and melting and polymer melt is transferred into a metering pump to adjust consistent flow. Polymer flow is pumped to the polymer feed distribution section for filtration and distribution purposes. In the next section spinneret part is present which includes numerous nozzles on each separate spinneret block. When tiny polymer melts expose into an air from nozzles they start cooling and solidification is occurred. Cooling can be occurred by means of air in a room temperature or with using an extra cooling air. In later stage, in the presence of drawing rollers or air suction units drawing (attenuation of the filaments) is generated and filaments are deposited on a moving belt [1]. In the course of a time, with some amendments in the spinning line several different types of configurations emerged in the spunbond market. Amendments heavily were seen in the cooling and drawing zone by addition of new blowing duct units, lay-down apparatus, or entangler units. The schematic view of four different types spinning line systems which are commonly used in the market can be seen in Figure 2. In the Figure numbers stand for the different zones under specific effects of process conditions. Number 1 is used as drawing or cooling air also known as primary air, while number 2 is stand for secondary air. Number 3 is used as drawing chamber or jets, where pressurized air is used. Number 4 is the last zone before deposition and is stand for air suction unit. As seen in route 4 (Figure 1, d), it is possible to use drawing rollers in drawing zones [1]. 37

6 Teknolojik Araştırmalar: TTED 2011 (3) Process Parameters for Fiber Formation in. FIG. 2 Different Configurations of Spinning Lines in Spunbonding Process, [1] In the market commonly used spunbond spinning lines are produced by Lurgi Kohle & Mineraloltechnik, Reifenhaiser and Freudenberg companies based on aforementioned configurations. Docan system which is patented by Lurgi Kohle & Mineraloltechnik uses draw-off jet and laid down system and the force required for filament drawing is generated by aerodynamic system. In Reicofil system which is most commonly used system in the market today developed by Reifenhauser, there are extra blowing units and entangler units available in the spinning line. In Lutravil system which is based on Freudenberg company, extra air drawing jets and continuous cooling zones were used in the spinning line. Air drawing jets provide high pressure tertiary air to draw and orient the filaments [1, 6]. Relevant schematic view of the systems was given in Figure 3. 38

7 Canbolat, M., F., Kodaloglu, M. Teknolojik Araştırmalar: TTED 2011 (3) FIG. 3 Common Spinning Line Systems for Spunbonding Process, [6] 39

8 Teknolojik Araştırmalar: TTED 2011 (3) Process Parameters for Fiber Formation in. EFFECTS OF SPINNING PROCESS PARAMETERS ON FIBER PROPERTIES IN SPUNBOND TECHNOLOGY The importance of spinning conditions on the properties of melt-spun fibers first realized by Carothers and Hill in 1932 and in further years, researches on determining the behavior of melt-spinning were performed. In the early times, experimental studies were executed with measuring surface temperature, birefringence, and diameter of the melt-spun filaments [3]. Afterwards, spinning system parts from feeder to deposition area for spunbond were examined in depth. It is found that different pressure and temperature zones must be exist in extruder in order to have better mixed polymer melt with easy flowing characteristic. Similarly, it is realized that the design of the polymer distribution section is fairly important to provide standard flow and can be consistent with different types of polymers in use [1]. These and similar kinds of observations and assessments were obtained for various parts in the system, but most remarkable and impressive results were found out for throughput and primary air temperature and around spinline region. In Figure 4, development of fiber structure around spinline, while polymer melt leaves from nozzle is seen. It is understood that depends on the process parameters, particularly throughput and primary air temperature, fiber diameter, orientation of molecules and other fiber properties undergo a change [3]. FIG. 4 Schematic View of Development of Fiber Structure in Spinline, [7] It is reported in several references about effects of throughput and primary air temperature that decrease in these process parameters induced decrease in diameter whereas induced increase in crystallinity, birefringence, tensile strength, initial modulus, thermal stability, and density [3, 5, 8, 9]. It is also reported that lower throughput rate, higher extrusion temperature, higher air suction speed, higher quench air pressure, and higher venture gap are resulted in finer fiber production [4]. One another inference is about 40

9 Canbolat, M., F., Kodaloglu, M. Teknolojik Araştırmalar: TTED 2011 (3) crystallinity and it is understood that molecular orientation resulting from elongational flow and drawdown forces greatly increase crystallization rate at where high crystallization temperature and rapid cooling is applied. It is also understood that crystallization begins at a point near the exit of nozzle and around 60% is completed in spinline section [8]. On the other hand increase in tensile stress, modulus, and molecular orientation was associated with spinline stress which is produced by low throughput and extrusion temperature [8]. It is true to say that, increase in diameter with increase in primary air temperature as stated before is not realistic and logical. Since theoretically increase in temperature induce decrease in viscosity, increase in drawability and decrease in fiber diameter. However, decrease in crystallinity of the structure is observed as a result of decrease in stress on the threadline and it obstructs the efficiency of draw-down. As a result of insufficient drawing, the diameter of the filaments increases [3]. In the following parts of the study some experimental results from various studies which show relationship between throughput, primary air temperature, diameter and other fiber properties will be explained. The first study that was assessed is about polyethylene melt-spun fibers. In Figure 5a, relationship between fiber diameter and distance from spinneret was given for 3 different take-up velocities. It is seen that fiber diameter reduces from the beginning of the spinneret exit till to a point where the fiber velocity reaches take-up velocity. In Figure 5b, it is seen that temperature decrease is more quick and higher with high take-up velocities [8]. 5a 5b FIG. 5 Relationship between fiber diameter distance & temperature-distance (distance from spinneret for PE melt-spun fiber), [8] 41

10 Teknolojik Araştırmalar: TTED 2011 (3) Process Parameters for Fiber Formation in. In another study performed by Zhang et al., effects of throughput and primary air temperature on PP homopolymers and PP/PE copolymers were examined. As it can be seen in the Table I, both with increase in throughput and cooling air temperature induce increase in the diameter of the filaments. It is also seen that reversely birefringence increase with the increase of throughput and primary air temperature. The birefringence also related with the orientation of the molecules and higher the birefringence means higher the orientation [3]. Generally with decrease in fiber diameter increase in birefringence is observed. Increase in birefringence means increase in molecular orientation and higher crystallinity. Thus, the tensile strength increases while elongation at break values decreases [2]. In the same experimental study of Zhang et. al [3], the relationship of the throughput and primary air temperature with tensile properties and crystallinity of filaments were investigated. The results can be seen in Table II and Table III, respectively. According to results, tenacity and initial modulus values decrease with increase in cooling air temperature whereas elongation at break and crystallinity values increase with increase of both throughput and cooling air temperature. These results confirm that the orientation of the molecules in filaments is higher for low primary air temperature. 42

11 Canbolat, M., F., Kodaloglu, M. Teknolojik Araştırmalar: TTED 2011 (3) Furthermore Zhang et. al compared the tensile strength of filament and nonwoven samples under various primary air temperature and throughput values. They found that as can be seen also in Figure 6, even though nonwoven samples are not affected from the changes as much as filaments they tend to decrease in strength with increase in throughput and cooling air temperature [3]. 43

12 Teknolojik Araştırmalar: TTED 2011 (3) Process Parameters for Fiber Formation in. FIG. 6 Tensile Strength of Filament and Nonwoven Samples, [3] Bhat et. al studied the effects of spinning parameters of spunbond technology on fiber properties. In one of the remarkable results as can be seen in Figure 7, they showed the relationship between diameter and suction speed. Similar with drawing rollers, increase in suction speed induces decrease in fiber diameter [2]. FIG. 7 Effect of Suction Speed on Final Fiber Diameter, [2] Resembling results on fiber diameter-throughput relationship, fiber diameter-air suction speed relationship, and fiber diameter-extruder temperature relationship were shown in the study of Bo, as well [5]. However, extraordinary result was obtained about primary air temperature effect on the fiber diameter. In opposition to many other results of experimental studies [3, 5, 8, 9] as given in the previous parts of the study, he found that primary air temperature increase induce decrease in fiber diameter. It might be evaluated as an exceptional result or pretty serious mistake which may cause real problems for many industrial applications of which take this reference as a guide. 44

13 Canbolat, M., F., Kodaloglu, M. Teknolojik Araştırmalar: TTED 2011 (3) REFERENCES [1] Russell, S., Handbook of Nonwovens, Woodhead Publishing Ltd, 2007 [2] Bhat, G., S., Malkan, S., R., Extruded Continuous Filament Nonwovens: Advances in Scientific Aspects, J App. Pol. Sci., Vol. 83, 2002 [3] Zhang, D., Bhat, G., Sanjiv, M., Wadsworth, L., Evolution of Structure and Properties in a Spunbonding Process, Textile Research J, Vol. 68, 1998 [4] Bo, Z., Effects of Processing Parameters on the Filament Fiber Diameter of Spunbonded Nonwoven Fabrics, Polymer Eng. Sci., 2007 [5] Nanjundappa, R., Bhat, G., S., Effect of Processing Conditions on the Structure and Properties of Polypropylene Spunbond Fabrics, J App. Pol. Sci., Vol. 98, 2005 [6] Retrieved on [7] Retrieved on [8] Dees, J., R., Spruiell, J., E., Structure Development During Melt Spinning of Linear Polyethylene Fibers, J App. Pol. Sci., Vol. 18, 1974 [9] Bhat, G., S., Nanjundappa, R., Kotra, R., Development of structure and properties during spunbonding of propylene polymers, Thermochimica Acta, 2002 [10] Batra, S., K., et. al., The Nonwoven Fabrics Handbook, 1992 [11] Vaughn, E., Wadsworth, L., Spunbonded and Melt Blown Technology Handbook, INDA, 1999 [12] Retrieved on [13] Retrieved on [14] Retrieved on