Nanoclay Reinforced Fibers and Nonwovens

In this research, polypropylene fibers and nonwoven samples were produced with the commercial samples of nanoclay additives in semi-commercial processing machinery. Influence of two different types of nanoclay additives, at different add on levels on processing, structure and morphology of nonwovens is studied. The WAXD and DSC data showed some change in crystallinity and melting behavior indicating changes in the fiber morphology towards improved mechanical properties. Presence and extent of exfoliation of nanoclay in the polymer was verified using transmission electron microscopy (TEM). TEM image reveals intercalated and exfoliated morphology of nanocomposites. About 10 to 20 % increase in tensile strength and modulus in both machine and cross directions is observed. This increase in strength is not accompanied by a decrease in breaking elongation as is the case for most of the fibers. Similarly 10 to 25 % increase in web stiffness and 20 to 80 % increase in web burst strength was observed. Furthermore there is improvement in other performance properties of the spunbond nonwovens. SEM images showed improved thermal bonding in the presence of nanoclay additives. The main advantage of this process is that these fabrics can be produced without any need for change in the processing equipment. This study has shown that by using a suitable compounding method, nanoparticle reinforced fibers and fibrous products with improved performance properties can be produced using conventional production machinery. INTRODUCTION The history and growth in synthesis, characterization, and understanding of microscopic structures has given rise to a new chapter, the nanoscience and nanotechnology [1]. There is a continuing effort to take advantage of recent advances in nanotechnology, in the polymer and fiber industry. In its most basic form, nanotechnology refers to the manipulation of materials at the atomic or molecular level. The name derives from the nanometer, a scientific measurement unit representing one billionth of a meter. With various manufacturing techniques such as vapor deposition, sputtering, scanning tunneling microscopy, and supersonic molecular beams, it is now possible to produce materials of nanometer size. Nanotechnology gives scientists the ability to create new materials containing fine layered atomic clusters, quantum dots, etc. that exhibit mechanical, electrical and optical properties different from the same materials in the bulk form. This difference is attributed to the observed increase in reactivity level due to the large surface to volume ratio that depends on size, shape, and lattice structure etc. studied extensively by X-ray diffraction methods [2]. Advances in microscopy: scanning tunneling microscopy, scanning electron microscopy and transmission electron microscopy has further facilitated the studies. With these powerful tools, scientists are able to better comprehend and account surface topology, structure and morphology up to atomic scale [3]. Nanoclay is one of the most affordable materials that have shown promising results in polymers. Nanoclay is made from montmorillonite mineral deposits known to have “platelet” structure with average dimension of 1 nm thick and 70 to 150nm wide. Nanoclays are known to enhance properties of many polymers such as nylon 6, EVA, epoxy, PET, PE and PP leading to better clarity, stiffness, thermal stability, barrier properties to moisture, solvents, vapors, gases and flavors; reduced static cling and UV transmission in film and bottles; improved chemical, flame, scratch resistance, and dimensional stability in injection molded products [4]. Plastic molded parts exhibit higher heat distortion temperatures, and better appearance when painted. Nanomer® and Cloisite® are the popular nanoclays available in the market. Nanomer® is a nanoclay [5] product developed by Nanocor/AMCOL International Corporation, and Cloisite® nanoclays are produced by Southern Clay Products, Inc., of Texas, USA. Journal of Engineered Fibers and Fabrics 22 http://www.jeffjournal.org Volume 3, Issue 3 2008 Cloisite additives have been used in injection-molded parts, films, bottles, trays, blister packs, and wire and cable coatings. Cloisite® Na+ is a natural montmorillonite well known additive used to improve various plastic physical properties, such as reinforcement, heat deflection temperature (HDT), coefficient of linear thermal expansion (CLTE) and barrier properties. Cloisite15A is a natural montmorillonite modified with quaternary ammonium salt containing organic modifier, dimethyl dehydrogenated tallow [2M2HT], where HT is hydrogenated tallow with approximate composition 65% C18, 30% C16, 5% C14 [6]. Specific gravity of Cloisite 15A is 1.66 and bulk density 172.84 kg/m. Particle size distribution is such that 90 % are less than 13 micron and 50 % are less than 6 micron and 10% less than 2 micron. Average particle diameter as determined by x-ray diffraction is 31.5Å [7]. According to a US Patent [8] by Nanocor, the knowhow of uniform dispersion of nanoclay (0.5 to 10% level) in polyolefins to produce concentrates that can be used in nanocomposites is claimed. The nanoclay dispersion is used to improve modulus and tensile strength, barrier properties, flame resistance, and thermal and structural properties of many plastics to extend their reach into areas dominated by metal, glass and wood. Three different types of morphology in case of polymer-nanoclay composites are shown in Figure 1. When there is partial intercalation of extended chain in between the sheets intercalated (Figure 1, A) structure is obtained. When clay layers are completely dispersed in the polymer matrix gives exfoliated (Figure 1, B) morphology and when polymer is unable to intercalate between the clay sheets, phase separated nanocomposites (Figure 1, C) is obtained. Exfoliated structure has proved to incur better properties for the final product compared to intercalated structure [9]. Recent studies are focused towards modification of clay, altering processing conditions to achieve better exfoliation [10], change in rheological behavior with percentage and clay exfoliation etc [11-15]. Polykemi [16] claims that the nanoclay-reinforced polypropylene can be made scratch resistant, low density, higher stiffness compared to alternative to the mineral reinforced and virgin polypropylene. Nanocor claims that the nanocomposite with 6% nanoclays by weight that also contains 10%-12% glass fibers will deliver a property equivalent to 30 % straight glass-filled composite material with added advantage of lower specific gravity and lower part weight [17]. Influence of clay loading on properties of polypropylene-clay nanocomposites has been studied by X. Liu et al, where they observed increase in tensile strength and modulus with increase in clay content from 0 to 5 wt %, considerable increase in storage modulus and decrease in tan (δ) and Tg were seen [18]. Structure and properties of polypropylene/montmorillonite hybrid composite and melt spun fibers have also been studied and found that good intercalation of clay in PP matrix improves the spinnability. At same draw ratio, fiber with clay had higher crystallinity and lower orientation. Improved moisture absorption and dye affinity was observed for fibers with clay [19]. In our previous studies influence of nanoclay on crystallization kinetics of nylon 6, polypropylene and PET fibers were investigated [20]. Though extensive research has been done to study the influence of nanoclay additive on the processing, structure and morphology of polymer products [21-25], influence of nanoclay additive on the spunbond processing, web properties and thermal bonding has not been studied. This research was conducted to investigate the development of structure and properties during spunbonding with nanoclay. Spunbond web reinforced with natural and organo modified nanoclay additive has been produced successfully. Influences of two different type of nanoclay additive at two different add on levels on structure, morphology and mechanical properties of resultant spunbond web has studied. Influence of nanoclay additive on processing and intricacies necessary for successful processing of nanoclay incorporated spunbond products has been revealed.