MANUFACTURING TECHNIQUES OF NONWOVEN COMPOSITES”- AN OVERVIEW

1. INTRODUCTION:

A composite can be defined as any combination of two or more resources, in any form, and for any use. Composite is a select combination of two or more dissimilar materials formed with a specific internal structure and with a specific external shape or form. Composites are designed to produce unique mechanical properties and superior performance characteristics not possible with any of the component material alone. Whatever scenario is used, the objective of composite development is to produce a product whose performance characteristics combine the beneficial aspects of each constituent component. There are two important steps in nonwoven manufacturing that will influence the characteristics of the final product: the first is the forming of the fiber web, and the second is the web bonding method. In the web forming procedure it is customary to blend two or more fibers in order to improve the characteristics of the final product. The nonwoven composites can be produced from the combination of any of the webs of spunbond, meltblown, wet-laid, dry-laid and other webs produced from nonwoven manufacturing processes. The laminate may contain two or three or more layers of nonwoven webs resulting in a laminated web, which combines the properties of the layers, used in the manufacture of the composite. Combining processes, nonwoven composites can be made whose single layers all contribute with their individual properties to meet the requirement.

 

2. MANUFACTURING TECHNIQUES OF NONWOVEN COMPOSITES:

2.1 Nonwoven composites with two or more fibres:      

 

2.1.1. Nonwoven composites Hemp-Polypropylene:

Natural fibres, such as flax, hemp, jute, and kenaf have received considerable attention as an environmentally friendly alternative for the use of glass fibres in engineering composites. These plant fibres have a number of techno-ecological advantages over traditional glass fibres since they are renewable, can be incinerated with energy recovery, show less concern with safety and health (e.g. skin irritation) and give less abrasive wear to processing equipment such as extruders and moulds. In addition, they exhibit excellent mechanical properties, especially when their low density (1.4 g/cm³ versus 2.5 g/cm³ of glass) and price are taken into account .Although natural fibres have a number of ecological advantages over glass fibres they also possess a number of disadvantages, such as lower impact strength, higher moisture absorption which brings about dimensional changes thus leading to micro-cracking, as well as poor thermal stability, which may also lead to thermal degradation during processing.

Nonwoven fleeces of polypropylene fibre (75 mm long, 11 dtex) and hemp fibres of different blending ratios were prepared. The fibres were blended manually in desired ratios of 30, 40, 50 and 70 % hemp by weight, after carding the thin layers were bonded by needle punching machine. Blended mats containing 40% hemp by weight were also produced by double carding the reinforced polypropylene before needle punching. Composite sheets were then prepared by hot pressing of mats at a temperature of 190ºC. The test specimens were cut in machine and cross-machine directions of the carding machine used for making the mat.

 

2.2. From fibers and particulates:

                                                                                                                         

2.2.1. Melt-blow composite nonwovens Composites with absorbent particles:

Melt-blow composite nonwovens can contain in their structure powder-sorbent particles such as active carbon, alumini­um oxide, chitosan, etc. Composite nonwovens produced according to this method do not require the application of any additional binding agents. Hence, the initial melt-blow nonwoven forms a matrix in which the introduced powder material can be found. Compressed air is the medium which transports the powder material. Sorbent particles have contact points with nonwoven microfibres. Very small fibre diameters (0.5-10 µm) en­able many contact points to be made with sorbent particles, as their sizes are considerably larger in comparison to fi­bre diameter. The flexibility of microfibres also allows for such contact point bonding.

The exact mechanism for retaining sorb­ent particles within a melt-blown nonwo­ven structure is not known in details . It is assumed that the large size of sorbent particles allows them to be set in the non­woven’s porous structure. Sorbent parti­cles are well caught by microfibres thanks to the pores formed by these fibres. The particles are introduced into the nonwo­ven’s structure during its formation. On their mutual way, i.e. from the moment the sorbent particles are introduced into the stream of microfibres coming from a die/nozzle up to the moment they reach the take-up drum, the sorbent particles and microfibres form a compact structure, and are then set to form a nonwoven web on a take-up drum.For manufacturing this composite,first a batch of melt-blown nonwovens made of polypropylene was prepared in different variants of area weight and thickness. These initial nonwovens formed the base material for composite nonwovens. The specified parameters of the base material (the initial nonwoven) allowed the active carbon contents in composite nonwovens to be defined.

 

2.2.2. Knitted Nonwoven composites:

The application of knitted nonwoven composites fabrics which is described here are:-

• As abrasive composite products which can be helpful in finishing activities in the building industry, and
• In the manufacturing of nonwoven composites destined for filtration products and in upholstery constructions.

 

2.2.2.1 Abrasive composites:

The composites developed have been used as abrasive means for sanding smooth surfaces, such as internal and external building walls (indoors and outdoors). The double-sided granulated composites were obtained by spreading the second component (silicon carbide) on the surface of the knitted fabric. The thermal method used for silicon carbide deposition allowed us to achieve a stable fastening of the carbide to the knitting structure.

The selection of the optimum technological parameters connected with the selected structural solutions for the knitting stitches allowed us to achieve a homogeneous distribution of free spaces of the preliminary assumed space-shape and dimensions. A suitable selection of silicon carbide granulation and time-thermal parameters of the spreading process allowed us to obtain the expected abrasive features of the composite, and to protect it against any brittleness and chipping of the abrasive medium.

The knitted samples were manufactured with open-work {double-needle, and three-needle stitches} with the use of flat warp-knitting machines and 16E and 28E needle gauges. Polyester yarns with linear densities of 84 dtex f36 and 110 dtex f24 were applied.

The knitted samples were produced with different partial stitches and systems, with the aim of achieving knitted fabrics of appropriate net structure and with limited (as much as possible) deformation ability in both directions.

The following stitch systems were applied:

• Tricot joined with velvet of increasing link length in the individual variants, and
• Pillar stitches together with weft of irregular laps.

An optimal knitting tightness was selected for all sample variants aimed at achieving the demanded dimension stability of the composites. To achieve a regular structure of the open-work knitted fabrics, the optimum relation between the run-in of the individual warp was selected.

 

2.2.2.2 Abrasive composite materials with nonwoven textile matrix:

NTM (nonwoven textile matrics) as technical textile find its place in different products either as solely textile material or as part of composite. These materials are composites with NTM being the matrix holding dispersed particles of abrasive. These materials are usually made of polyamide, polyester and polypropylene fibers with fineness of 1.5–20 tex1, with phenol–formaldehyde resins as most common adhesives, while polyacrylate, urea and melamine resins are used occasionally. Abrasives are fine- or coarse-milled minerals of different hardness like chalk, quartz, corundum and silicon carbide. These substances are embedded in the synthetic resin-bonding agent, and enable variations to be made within the extensive range of abrasive intensity in conjunction with variations in the elasticity of the fabrics as a whole from a mild polishing effect to a coarse roughening of the surface.

 

2.3. From two or more layers of nonwoven with at least one being a nonwoven:

The superior properties of the nonwoven composites are finding rapid acceptance

and integration in a variety of products. Recently developed applications for SMS (Sponbond-meltblown-spunbond) and SMMS (Spunbond-meltblown melt blown spunbond) technologies products are applicable for baby diapers include standing leg gathers, soft outer cover, stretchable fastening tapes and stretchable outer covers and panels. At least 40 to 50 % of diaper is made of synthetic fiber and advanced composite structure. In the present scenario various techniques are used to produce the composite nonwovens.

 

2.3.1. AquaJet Spun lace Technique:

Fleissner has optimized its AquaJet spunlace technology to produce at lower cost and higher efficiency.

 

2.3.1.1. Layer Nonwoven Composite By Aquajet technology:

3-layer composites of carded staple fibers and wood pulp or spun bond and wood pulp are especially suitable for the wipes market because of the advantages offered by a pulp layer in the middle and fiber layers at the. Instead of wood pulp, cotton linters naturally can also be used. 2-layer and 3-layer composites are used for wipes, wet wipes, medical products, surgical gowns and drapes etc. These nonwovens allow their properties such as strength, bulk, softness, absorbency etc. to be influenced in an optimum manner. Product with cellulose fibres in the form of pulp or tissue can be obtained by highly cost-efficient processes due to the considerably lower cost of these fibres.

 

 

 

 

 

2.3.1.2. Production of 2-layer and 3-layer nonwoven composite:

 It is also possible, of course, to produce 2-layer composites with one fiber layer and one cellulose layer on a 3-layer production line. It is not possible, however, to produce 3-layer structures on a production line designed for 2 layer nonwovens without infringing the patent, even when making the respective modifications. The webs in all processing lines for 2-layer and 3-layer composites are bonded with the AquaJet Spunlace process.

Generally, the middle layer can be formed either from tissue rolls or from loose fluff pulp coming from one or more airlaid forming heads. The advantage of using tissue rolls consists in lower investment cost for the processing line. On the other hand, when using fluff pulp the cellulose fibers can be obtained at much lower cost which can more than compensate the higher investment cost. Naturally production lines can also be designed for both cellulose products (fluff pulp and tissue). A 3-layer composite line usually consists of the following machinery:

 

 

 

 

 

 

 

 

 

Advantaged of 3-layer Nonwoven Composite:

Webs offer high absorbency (pulp serves as absorbing pad).

• •Advantages compared with 2-layer webs: no pulp on the outside, i.e. no risk of
• “Dusting” during converting and no deposit of pulp particles when wiping.
•  Improved appearance compared with 100% fiber webs because pulp compensates the irregularities of the carding web.[8]
• Strength practically identical with that of 100% fiber webs although consisting of 50% short fibers.
•  Softness when wet identical with that of 100% carding webs.
• Thickness of product with identical weight higher than for 100% fiber webs.
• Considerably reduced production cost due to the use of pulp.

 

2.3.1.4. Aqua Jet Spun Bond Technology:

The Aqua Jet System in particular allows economical production of nonwovens, because it uses only 20 to 25 % of the energy necessary with conventional technique. With 100 % air laid nonwovens for wet wipes (from fluff pulp), chemical bonding with binders or thermal bonding with bonding fibers or combinations of these two bonding methods are mostly used today. However, the importance of chemical bonding has decreased in recent years because spun lacing allows to produce more user-friendly (i.e. hygiene and cosmetic products without addition of chemicals, hence offering good skin tolerance) and softer products of identical or higher strength. At the same time thermal bonding can be run at high speed, whereas the speed of chemical bonding is limited by the drying and curing stage. Thermal bonding takes up little space compared with drying and curing ovens. Also thermal bonding requires less heat compared with the heat required to evaporate water from the binder, so it is more energy efficient. Reduced energy consumption per kg of raw material used, reduction of material loss, reduction of consumed water quantities due to optimized filter systems and reliability and minimum maintenance requirements of the processing lines are decisive factors for using the spunlacing process for airlaid composite products. It is therefore ideal that spunlacing allows combining various raw materials for the production of so called composites. In the process, the individual layers are assigned certain properties such as moisture absorbency, moisture barrier, strength or softness. Baby wipes can be named as one example of many products.

Web weights: 10-1000 g/m²

• Pressures: up to 600 bar (8800 psi)
• Speeds: up to 500 m/min

Web widths: up to 6000 mm (240 inches)

 

2.3.1.5. Nonwovens-Production Lines with Aqua Jet Spunlace Systems:

 

 

 

 

 

 

 

• Aqua Jet – Entangling of light weight nonwovens up to 150 g/m² and heavy weight nonwovens up to 600 g/m², for natural fibers up to 3000g/m²
• Aqua Spun – Entangling of spunbonded webs
• Aqua Split – Entangling and splitting of microfiber webs
• Aqua Pulp – Entangling and bonding of nonwovens with a pulp layer
• Aqua Tex – Enhancement of woven fabrics with the PGI Inter Spun (TM) technology
• Aqua Tuft – Latex-free carpet backing for tufted carpets by hydro entanglement.

 

2.3.2. Spunbond-Spunlace (Hydroknit Process)

Hydroknit material is comprised of soft absorbent paper fibres and extra strong polypropylene non-woven fabric. The paper component allows wiping cloths to absorb water quickly and effectively, while the tear-resistant polypropylene fabric soaks up more than it’s own weight in oil and grease. The result is a durable and fast absorbing wiper – strong enough to handle tough cleaning tasks and absorbent enough to make soaking up liquids a breeze.

 

 

 

 

 

 

 

Joining SB and MB webs together for the final laminated web to attain the optimum properties of high strength of SB and barrier and filtration properties of MB webs produce SM and SMS laminates. The composite structure of the SB/MB/SB (SMS) and SB/MB (SM) are the most popular examples of the composite structures. These composite structures have been tremendously successful as they can be engineered to high strength products. SB and MB spinning beams are placed on the same machine in a configuration to facilitate the production of SM and SMS laminates. A multi-station line consisting of at least one spunbond die assembly and at least one meltblown die assembly produces SM and SMS laminates. Each station includes–

• A melt spinning die which can be selectively equipped with a spunbond die insert or a die insert and meltblown.
• A moveable support structure for adjusting the proper die-to-collector (DCD) distance, depending on spunbond or meltblown mode of operation. The multi-station line permits the selective manufacture of a variety of SM or SMS laminates, including SMMS laminates. The layers may be bonded together by compaction or by calendering and exhibit outstanding strength properties, energy absorption, tensile strength and tear resistance, and yet possess a soft, flexible hand. The SMS structure is typically made inline wherein-

• Spunbond filaments are laid on a moveable collector forming a first layer.
• MB filaments are deposited on the first layer.

 

A second layer of SB filaments is deposited on the top of the MB layer. The three-layered structure then can be bonded together. The inline operation is restricted to manufacturing only one SM and SMS laminates. However, the use of bicomponent and blend fibers requires more complex equipment than required for monofilaments, and can also require additional processing steps. The SM and SMS composites made from side-by side bicomponent fiber PP/PE MB webs. Preliminary work has shown that SM and SMS had a softer hand and lower flexural rigidity than did laminates made from 100% PP MB.

 

 

 

 

 

 

 

 

Composite webs are finding rapid acceptance and integration in a variety of products. Recently developed applications for SMS (spunbond-meltblown spunbond) and SMMS (spunbond-meltblown-meltblown-spunbond) technologies on baby diapers include standing leg gathers, soft outer cover, stretchable fastening tapes, and stretchable outer covers and panels. At least 40 to 50 percent of a diaper is made of synthetic fibers and advanced composite structures. Like nanofibers, meltblown fibers typically need a supporting structure and are generally employed in a composite structure.[10]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2.3.3. Woven and Nonwoven Composite Structure

In the case the woven and nonwoven fabric layers are bounded together either mechanically (heat, needle punching, stitching) or chemically. The figure below shows the illustration of a bi-axial reinforced nonwoven with elements warp, weft, interlacing yarns and nonwoven.

 

 

 

 

 

 

 

 

2.3.4. Multi Axial Nonwoven composites:

In the case fibers or filaments are arranged in different directions in a regular manner to produce a nonwoven fabric.

 

 

 

 

 

 

 

Advantages of multi-axial multi-ply structures:

• Dimensionally stable in any direction.
• Isotropic distribution of stress forces, uniform strain behavior.
• Optimal utilization of tensile yarn strength in any directions of strain unlike    woven fabrics.
• Directly oriented, parallel yarn layers straightly placed each on top of the other without yarn crimp, providing the following advantages.
  • Enhanced interlaminar shearing strength
  • Quick curing of resin
  • Reduced resin quantities
  • Increased impact resistance
  • Excellent draping characteristics
  • Lowest weight per unit area at maximum total strength possible
  • Cost effective production and economical ready made
• For this type of fabric construction generally Fiberglass, aramid, carbon, high tenacity PES, PA, PE, PP etc. fibers are used. While for Matrix Thermosetting or duroplastic materials as polyvinyl chloride PVC, ethylene vinyl, acetate EVA, synthetic rubber are used.

 

2.3.5. Layer nonwoven composites by melt blown technology:

In the case the nonwoven composite structure has at least two melt extruded nonwoven layers in which the fibers of at least one layer are prepared by the melt extrusion of a mixture of an additive and a thermoplastic polymer. The first nonwoven web is comprised of continuous and randomly deposited filaments having the fiber diameter in excess of 7 micrometer. The second layer is also made of continues randomly oriented filaments with diameter 0.1 to 10 micrometer. The third layer is similar to first one. All three layers are bonded together by placation of heat or pressure. The study of three-layered non-woven laminate with two exterior layers of SB PP and an internal layer of mixture of MB PE and PP was found useful in producing strong laminates with.

 

3. CONCLUSION

“Nonwovens provide a wealth of functional benefits ranging from thermal and acoustic insulation and high tensile strength, to puncture resistance and excellent shape stability. Nonwoven textile composite is the gain an importance in future due to their superior properties and numerous advantages of production technologies over conventional products. Some of the most important advantages of these technologies are higher production rate (in comparison to traditional processes), smaller average use of raw materials, smaller average mass of the product, flexibility that is possible to produce the variety of different products utilized in various application fields in the same factory. The cheapest composite product, we can say, that is 3-layer composites which also another proof for the excellent possibility of bonding nonwovens composite structures Aquajet spunlacing technology by Fleissner group.