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ESD protective garments made with core conductive fibres knitted in double layer

Acronym: Garm ESD

Programe: PN II - PARTNERSHIPS IN PRIORITY DOMAINS

Project type: PCCA Type 2

Period: 02.07.2012 – 30.06.2015

Contracting authority: UEFISCDI

Contractor: I.N.C.D.T.P -Bucuresti

Partners:
- Tehnical University “Gh. Asachi” - Iasi
- ICPE-CA Bucuresti
- S.C.TANEX S.R.L.-Bucuresti

Objective: Developing of the functional model for ESD garments made with core conductive fibres knitted in double layer

Phase list

Phase I:                      ESD/EMC behavioural simulation of active layered composite fibres for a predefined double layer knitted topology.
Phase II:         Research upon double layer knitting topology regarding ESD/EMC            features.
Phase III:       Realization of double layered composite fibres garments via integral           knitting with tailored ESD/EMC properties.
Phase IV:       Technology transfer plan development. Disemination of the results.

Stage I Summary

                Multidisciplinary research of nanotechnology-based solutions, new functionalization techniques, and knowledge –based processes that include bioprocesses, innovative products based on new fibres and composites, biomedical sensors, microelectronics, mobile communication and telemedicine have led to the development of textile products and markets that have an added value.
                The existing ESD garments do not solve integrally the problem of accidental electrostatic discharge. In order to make an ESD garment with superior features the present project proposes the development of a two-layer structure with an external layer and an internal layer. The two layers with different electrostatic behaviour allow to solve problems that cannot be solved by using a single layer.
                The external layer is given by the surface of the material that comes into contact with the human operator working environment and the internal layer is given by the surface that is in contact with the operator. Under these circumstances, the two-layer approach allows to delimit the accidental discharge path from the controlled discharge of the material.
                The external layer has a higher surface resistivity and thus does not permit a path with high circulation of static energy. This is achieved by using insulating/dissipative materials. Moreover, the structure of the external layer is a composite one, the constituent yarns have a conductive core. The conductive part of the external layer has no contact with the environment.
                The internal layer was introduced to ensure a larger drainage area for the electrical charges – larger than the area ensured by the conductive part of the external layer. This layer can be made of conductive core composite yarns but also of conductive core composite yarns that are in contact with the environment.
                The external layer is predominantly dissipative and ensures protection to short circuit and limits the electrostatic energy that can be dissipated to the working environment and the internal layer is predominantly conductive, ensuring controlled drainage of the accumulated electric charges. An additional requirement for the internal layer is ensuring the user’s comfort.  
                In this context, the activities of stage I were:
-  Comparative study of composite fibres suited for two-layer knitting and available on the market.
- Electrical and micromechanical simulations
- Two-layer test panels knitting
- Determination of electrical impedance of the test panels at various frequencies
- Thermally Stimulated Discharge Currents (TSDC) measurements
- Evaluation of the electrical insulation efficiency of the two-layer test panels
- Analysis of the discharge time of the electrically charged two-layer panels
- Investigation of the shielding efficiency of the two-layer panels
- Results analysis and interpretation

Given that two-layer knitting involves the use of textile yarns with a high capacity of being processed through knitting, consideration has been given to the execution of a comparative study of composite fibres/yarns available on the market, with a focus on conductive-carbon or conductive-exotic yarns.
Conductive yarns can be obtained by the following methods:
- Adding carbon or metal: silver, copper, stainless steel, brass, Monel (nickel alloy) to the structure either as a wire, fibre and micro- or nano-particles;
- Use of conductive polymers;
- Conductive substances coverage.
Conductivity of yarns depends on three major factors: conductivity of materials used; percentage of conductive fibres; longitudinal and transversal configuration.
There are various possibilities to develop conductive yarns, depending on the conductive element (as conductive surface or conductive core) or the nature of the conductive element.

For preliminary knitting experiments the following assortments of yarns were purchased:
- yarns covered with conductive substances;
- yarns with carbon trilobate core.

Characterization of the test panels from a textile point of view:
- two-layer structures: plated flat knitting, flat knitting in two layers, sandwich;
- weight: 255-275 g/m2;
- thickness: 1.07-1.37 mm;
- density: Do: 26-37,5 rows/5cm; Dv: 34 -61,5 rows/5cm.

Characterization of the test panels from an electrical point of view:

  • Determination of electrical impedance of the test panels at various frequencies
  • TSDC measurements
  • Evaluation of the electrical insulation efficiency of the two-layer test panels
  • Analysis of the discharge time of the electrically charged two-layer panels
  • Investigation of the shielding efficiency of the two-layer panels

Based on the results obtained in the evaluation of the electrical insulation efficiency of the two-layer test panels, the following destinations were set for the yarns that are part of the conductive textile layer.


No.

Internal Code

Resistivity of the conductive textile layer [Ω]

Destination

1.

Copper monofilament with cotton yarns

< 2 × 105

Internal layer

2.

Cotton fibres (75%) + Epitropic fibres (25% - polyester covered with Carbon)

< 2 × 105

Internal layer

3.

Polyester filament with trilobate Carbon core

2.8 × 108

External layer

4.

Polyester filament with internal trilobate Carbon core

7.82 × 1011

External layer

5.

Nylon filaments superficially saturated with Carbon particles

5.11 × 1011

External layer

6.

Polyester (65%) and cotton (35%) yarns + nylon filaments with trilobate Carbon core

3.1 × 109

External layer

7.

Polyester filaments + nylon filaments covered with Carbon

8.1 × 1011

External layer

8.

Polyester (64.4%) + cotton (35%) + nylon fibres with Carbon core (0.6%)

4.7 × 1011

External layer

9.

Polyester covered with bamboo charcoal

9.5× 1011

External layer

10.

Polyester covered with Nickel

< 2 × 105

Internal layer

                According to the objective of Stage I (Determination of the type/structure of the yarn/fibre based on the analysis and ESD/EMC investigations that ensures higher ESD properties to the double layer knitted structure), the following configuration was set for the double layer structure:

  • Internal layer: variant no. 2 (the best electrostatic discharge properties);
  • External layer: variants 3, 5 and 6 (good electrostatic discharge properties and high superficial resistivity).