Quasi Yarn Stabilized ROTIS Structures with Improved Thermal Insulation

Militky J; Hanus J; Mohanapriya Venkataraman

Review Article

Adv Res Text Eng. 2022; 7(2): 1074.

Quasi Yarn Stabilized ROTIS Structures with Improved Thermal Insulation

Militký J*, Hanuš J and Mohanapriya Venkataraman

Department of Material Engineering, Textile Faculty, Technical University of Liberec, Studentská 2, 46117 Liberec, Czech Republic

*Corresponding author: Jiri Militky, Department of Material Engineering, Textile Faculty, Technical University of Liberec, Studentská 2 , 46117 Liberec, Czech Republic

Received: August 09, 2022; Accepted: August 22, 2022; Published: August 29, 2022

Abstract

The fast and relatively inexpensive new technique of stabilization of the 3D structure based on mechanical twisting of fibre ends protruding from the fabric surface to quasi-yarns is proposed and tested. The principles and conditions of building of quasi-yarns, their cohesion dependence on technological parameters and application of this technique on the 3D nonwoven structures are shown. A suitable machinery ROTIS using new bonding technique with quasi yarns is briefly described. There are also demonstrated 3D textile structures. Second part is devoted to description of factor responsible for of high thermal insulation fibrous structures.

Introduction

Form stabilization is one of the basic nonwoven production technology steps. Textile structure made by different process, for instance, by stratification of fibers, fiber bunches, carded web, nonwovens, has to be form stabilized (shape fixed). The structure can be fixed by bonding in every fiber contact (impregnation) or in the local places of the structure (by print). Thick (3D) textile structure is therefore possible to bond in all their cross-section, or in the chosen locations as e.g. surfaces. The fibrous structures fixed on the surface have specific properties, which are interested for many of targeted applications including thermal insulation. Some of technologies allow also attachment and bonding surface reinforcing net to the surface of fibrous structures. These nets ensure properties like strength, toughness and rest of the textile structure ensures other functions, like acoustic or thermal or acoustic insulation, filtration etc. A specific task of the production technology of nonwovens is mechanical fixation of thick textile structures. In practice the mechanical bonding of such structures has been realized at special machines (Multiknit of Mayer Company) where the surface layers of the 3D textile fabric are stitch bonded only. The fiber bundles being drawn from the surface of the bonded textile fabrics are here used as the stitching material. Using this technology textile fabric bonded on both sides are necessary to be produced on two machines. The surface stitch bonding gives to the textile fabric specific properties, especially softness and shape adaptability.

The simpler method described here is to use fibers ends protruded from surface of fibrous structures for form fixing by quasi yarns. 3D textile fabrics created by special technology ROTIS are here used for enhancing of thermal insulation.

3D Nonwovens

In thick 3D textile structures the number of practically-important dimensions is three in contrast to 2D textiles (thin structures like textile fabrics) and 1D textile (yarns, ropes). Thickness of 3D nonwoven structures is made by stratification of semi-products i.e. fibres, carded webs or 2D nonwovens. Directions of this stratification can be different, predominate directions are horizontal and vertical (Figure 1).

Direction of stratification determinates an orientation of structural elements in the structure of product and significantly influences the choice of fixation principle. 3D products with horizontal orientation of structural elements, for example, cannot be fixed on the surfaces of product only. Delamination of the product in this case is evident.

The creation of a web waves (corrugates) as the basic construction element of 3D nonwoven fabric is described in work of Hanus and Jirsak [1]. For the 3D textiles manufactured through vertical folding of a web into waves the main characteristic is, that the folded structures (fibrous assemblies, nonwoven) goes through from one side to the other side (Figure 2).

The basic relations between the 3D textiles parameters and producing technology parameters are known and were already described [3]. Development of corrugated 3D textile fabrics by technology STRUTO (shape fixation by thermal bonding) and ROTIS (shape fixation by qusi-yarns) and their main applications are described in works of authors [3,10].

Today, there are two main methods of mechanical surface shape fixation of nonwoven structures that can be applied for 3D structures.

First is splicing by means of fibre bundles which is used by the MULTIKNIT machine supplied by the German company Mayer [5].

Second one developed at TUL Liberec is based on twisting of fibers ends protruding from the web surface into so-called quasi-yarns [2]. The machine for implementation of this method includes no parts performing oscillatory motion. The appearance and properties of the products of course conform to the different fixation principles. Advantage of this method is posibility to attach and fix surface reinforcing nets to the surface of fixed structures.

This method is less energy demanding than e.g. fixation by the thermal bonding and the structure or shape of the product will be not changed “(Figure 3).

Quasi-Yarn Formation

Both classic and quasi-yarns are made by fibre twisting. In contradiction to classic yarns, quasi-yarns are formed by twisting of protruding ends or of loose segments of fibres situated on surface of a fibrous structure.

A model of a quasi-yarn structure is illustrated in the (Figure 3). Major part represented by twisted fibres lies on the s surface, but some fibres reach the sub surface layers.

We have found that if a rotating cylinder- or cone-shaped body moves on the corrugated 3D textile fabrics surface by its base (Figure 4), it leaves behind a �track� in form of twisted fibres. The shape of this track is similar to the classical yarn and therefore is called quasiyarn. Quasi-yarns can be laid on the corrugated 3D textile fabrics surface in optional spacing. The basic technological parameter of the quasi-yarn is apparent number of the twists per meter T [1/m] as function of number of revolutions of twisting device n per minute [1/ min] and shift rate of fibrous mass movementv₁ [m/min].

T = n/v₁ (1)

Precise experimental evaluation of the quasi-yarn apparent twist is very difficult.

By suitable mutual arrangement of the rotating body and the corrugated 3D textile fabrics surface, e.g. according to (Figure 5), it is also possible to bond textile fabrics together by �surface lamination�. By repeated lamination it is possible to produce textile fabrics of requested thickness (e.g. 10 to 50 mm).

By analysis of the system for quasi-yarn production (Figure 4) it is possible to specify most important technological parameters, as:

� Diameter of the twisting device d;

� Revolutions of the twisting device n;

� Rate of the fibrous mass shift motion v₁;

� Inclination angle a between the twisting device and the surface;

� Contact pressure between the surface of the twisting device and the structure surface.

It is evident that the effect of the twisting device depends on its geometric shape and the roughness of its friction area.

The contact pressure value is influenced by corrugated 3D textile fabrics surface structure (orientation of structure elements against loading) and used fibre material characteristics (flexural rigidity, fibre fineness etc.).

Quasi-yarns technology may be used both for structure fixation and for lamination of specific products. Products suitable for quasiyarn technology application can be characterized as follows:

Characteristics of nonwoven structures: The basic requirement is that fibres have to go through the nonwoven from one side to the other one. This important condition fulfils all structures based on perpendicularly corrugated thin layer (carded web, nonwoven web), or pneumatic manufactured structures. Quasi-yarn technology has been developed especially for corrugated 3D fabrics structures manufactured through vertical folding of a web e.g. according to (Figure 3).

Characteristic of reinforcing nets: Considering that during the quasi-yarn formation a rotating device has to grip loose segments of fibres going through the opening of the reinforcing net and to twist them into quasi-yarn, these openings must be sufficiently large. It is suitable to use reinforcing textiles with openings larger than 2x2 mm.

Characteristic of textiles for lamination: The surface of the both laminated textile fabrics, between which the quasi-yarn is to be formed, has to contain loose fibre segments or fibre ends that can be gripped and twisted by the rotating device into quasi-yarn.

Testing of Quasi-Yarns Cohesion

For testing of quasi-yarn strength, it is not possible to use standard methods as for classic yarn testing. This is because it is difficult to separate quasi-yarns from the product surface as well as because a quasi-yarn separation interferes with cohesion [4].

For studying of technological parameters influence on the quasiyarn cohesion we proposed a method according to the scheme in (Figure 6).

As a parameter characterizing the quasi-yarn “cohesion� we consider the bond strength of two reinforcing nets strips.

The dependence of cohesion S [N] on the shift velocity v of the corrugated 3D textile fabrics by using cylinder body rotating with constant revolutions n = 815 per minute is shown in (Figure 7).

The dependence of cohesion S [N] on the revolutions n of rotating cylinder body when the shift velocity v = 0.33 m/min and thickness of fabric is 3 mm is shown in (Figure 8).

It is visible than cohesion force dependent on the shift rate of the corrugated 3D fabrics mainly. By proper selection of these parameters is possible to obtain cohesion force about 30 N for quasi-yarn with twist about 6006.6 1/m.

ROTIS Principle

The main characteristics of conventional nonwoven products are their constant thickness and density. Non-conventional products are characterized by locally different density mainly. One possibility how to create 3D product based on conventional 2D nonwoven web is shown in (Figure 2).

For forming of 3D textile structures with prescribed thickness in the range 4 till 60 mm based on conventional planar web with thickness 0, 2 till 2 mm the ROTIS device was invented and designed. Principle is preparation of perpendicularly laid structures by deformation between toothed gears. Combination of ROTIS principle with quasi yarns formation is shown in (Figure 9).

ROTIS type 3D structures can be prepared in huge variation of porosities due to changing density of “waves�. Provided that a wave is the basic building unit of the product, we can easily deduce the basic relations between the parameters of technology and the geometric dimensions of the product [3]. If we substitute wave simply by triangle with height equals the height of the product, the product thickness H [m] is expressed as

https://www.HostMath.com/Show.aspx?Code=H%3D%5Cfrac%7BAV_%7B1%7D%7D%7B2V_%7B3%7D%7D

Quasi Yarn Stabilized ROTIS Structures with Improved Thermal Insulation

Abstract

Introduction

3D Nonwovens

Quasi-Yarn Formation

Testing of Quasi-Yarns Cohesion

ROTIS Principle

Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

References