Meltblown & Spunbond Technology I

The research investigates meltblowing thermoplastic elastomers mainly ether and ester thermoplastic polyurethane (TPU) and polyether-block-amide (PEBA) systems to understand the relationship between polymer type, melt blown process and web properties. A series of melt blown webs from the three Shore hardness of ester and ether TPU, and PEBA elastomers were produced at three different die-to-collector distance: (DCD) 5.5, 8 and 12 inches. Crystallization kinetics of produced webs was studied through DSC and the data was analyzed by the Avrami model. For all studied polymer systems, it was observed that crystallization rates increase with increasing polymer hardness and supercooling (temperature difference between melt and crystallization temperature). It was also found that crystallization onset and peak temperatures fall within the DCD region of rapid velocity and temperature drop i.e. between the die and 4-5 inches below it. This suggests that studied polymer systems have already started to crystallize, the extent of which depends on their crystallization kinetics, before reaching the collector, thereby significantly influencing the degree of fiber solidification and resultant web tensile properties. Increasing polymer Shore hardness resulted in increased tensile strength at a given DCD for TPU series, while PEBA displayed an opposite trend. The strong influence of the crystallization kinetics on web tensile strength was clearly demonstrated in PEBA series, in particular with the hardest grade, which produced the lowest web tensile strength mainly due to its significantly higher crystallization rate and lower degree of supercooling required than others. It is therefore concluded that, tensile behavior of web structure is strongly dependent on degree of fiber solidification achieved within the web, which is determined by its crystallization kinetics and distances traveled between the die and collector.

This paper will outline common data gathering techniques and the various ways in which to present the information. The paper will also give several examples of performance data, some of which can be misleading without detailed explanation. Further, the paper will discuss a new method of describing distribution performance which is easier to follow than conventional methods.

The majority of commodity thermoplastic products marketed today include some mineral additives in their formulation. These additives have financial advantages and often times enhance some physical properties. For example, almost all trash bags contain these additives which have been found to reduce the overall raw material cost and also significantly increase the toughness of the bag. Even though nonwoven products such as spunbond polypropylene are in a similar cost sensitive market, they have not followed this trend. Imerys, a mining company, recently conducted trials at TANDEC to establish the best inorganic mineral additives for use in nonwoven fibrous products such as spunbonds. The results of these trials demonstrate the impact of the fillers on both the process parameters and the physical properties of the end products. There were also some novel effects associated with suspending high density, inorganic particles within a low density polyolefin matrix. Obviously, the overall density of the fibers will be a function of the ratio of ingredients with minerals generally having densities around 2.5 g/cc, whereas polyolefin polymers are somewhere around 1. One of the end properties dependent on the density is water buoyancy, which did vary throughout the trial. These and other physical properties like tensile and elongation are described in the full paper to justify the recommended additives and loading levels.

The specialty polyolefin elastomers (Vistamaxx^TM specialty elastomers) are a new generation of polyolefin that can be processed in conventional spunmelt equipment to produce elastic nonwoven fabrics.  However, a great variety of elastic fabrics can be produced by combining different layer structures to take advantage of the special attributes of each of the individual layers.  Most of the modern spunmelt production lines have multi-beam capability and can be used to produce elastic fabrics of tailored elasticity, barrier, aesthetic and surface feel to meet the needs of the end use applications.

A laminated structure of spunbond/spunbond (SS), spunbond/melt blown/spunbond (SMS), or spunbond/spunbond/meltblown (SSM) can be produced.  The composite fabric attributes can be tailored by the properties of individual layers.  A light basis weight layer of PP or PP/SPE blend spunbond on the outside while having a highly elastic middle layer can make an elastic nonwoven with PP touch.  A melt blown layer can be used to enhance the opacity of the fabric, modify barrier or increase the SPE content of the fabric to improve the elasticity.

This paper discusses the utilization of modern multi-beam spunmelt equipment to produce multi-layer composite structure.  The elastic properties of some composite fabric are discussed.  By manipulating the layer composition of each layer using SPE, PP, or their blends as well as the additives, a processor can produce unique fabrics that are currently not available in the market.

For the production of spunbonded nonwovens from splittable filaments experimental investigations were accomplished on laboratory spunbond line and spunbond pilot line, which both work according to combined suction air/compressed air procedure. Mechanical treatment and bonding of nonwovens was carried out by spunlacing (laboratory and industrial plants) and needle-punching (laboratory needle loom). In addition, orientation trials were accomplished on stitch-bonding machines.

Polypropylene and Polyethylene (PP/PE), partly with additives, as well as Polyester/Polyamide (PET/PA) were chosen at different ratios between 50/50 and 75/25 as bi-component polymer combinations during these trials. Throughput per nozzle and air speed were varied to determine spinning reliability. Filament fineness was between 1.15 - 5.55 den. Mass per unit area of the nonwoven base lay between 30 - 200 gsm. Best mechanical characteristics and splitting effects were achieved with hydroentangled nonwovens made from PPa/PET, PP/PET, PET/PE and PET/PA. Remaining combinations did not show sufficient splitting effects. The needle-punched products partially showed good mechanical characteristics, however, the splitting effect was rather minimal. Same applies to the splitting effect of the stitch-bonded products. Further investigations regarding process stability and product quality will be necessary.

Bi-component spunbonded nonwovens have the potential for developing customer designed products. Especially splitted filaments made by spunlacing offer different properties like high specific surface, voluminous structure, high absorbency and very good softness. Therefore, important technical applications will be acoustic absorption, insulation layers, gas- and liquid filtration and inside protective clothing.