Reducing electrostatic Charge · 2018. 7. 31. · ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS 54 KGK · 7-8 2018 Electrostatic charge (ESC) polyvinyl chloride (PVC) floor

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Electrostatic charge (ESC) polyvinyl chloride (PVC) floor material friction coefficient grounded stainless steel strips

The aim of this research is to develop a new material for reducing electrostatic charge (ESC) generated from the wal-king of polypropylene shoes against po-lymeric floor in hospitals. Stainless steel strips have been adhered to the back of two proposed polymeric floor materials (A & B). It has been observed that the ESC increased by increasing the number of stainless steel strips. Although the strips were grounded, ESC has increa-sed, due to charging by induction. On other hand the grounded strips decrea-sed the friction coefficient by 4% and 5% in dry sliding and water/chlorine wet sliding respectively.

Reduzierung der an Polymer-fußbodenmaterialien in Kran-kenhäusern hervorgerufenen elektrostatischen Aufladung Elektrostatische Aufladung (ESC) Poly-vinylchlorid (PVC) Fußbodenmaterial Reibungskoeffizient geerdete Stahl-streifen

Das Ziel dieser Forschung ist die Ent-wicklung eines neuen Materials, um die an polymerhaltigen Fußböden in Kran-kenhäusern durch das Gehen mit Poly-propylenschuhen hervorgerufene elekt-rostatischen Aufladung (ESC) zu redu-zieren. Es wurden Edelstahlstreifen an die Rückseite von zwei vorgeschlagenen polymerhaltigen Fußbodenmaterialien (A und B) geklebt. Es konnte beobachtet werden, dass die ESC mit der Anzahl der Edelstahlstreifen zunahm. Obwohl die Streifen geerdet wurden, nahm die ESC in gleichem Maße zu wie die induktive Aufladung. Auf der anderen Seite er-niedrigen die geerdeten Streifen insbe-sondere den Reibungskoeffizient um 4 % und 5 % unter trockenen Reibbedin-gungen bzw. unter Chlorwassernassrei-bungsbedingungen.

Figures and Tables:By a kind approval of the authors.

IntroductionElectrostatic discharge (ESC) results from the separation of static charge, and there are several ways of producing such sepa-ration. Rubbing two kinds of insulating materials together can cause static charge to be transferred from one mate-rial to another, similar to walking across a carpet on a dry day and touching a metallic doorknob. Additionally, dis-charges can occur between metal ob-jects, such as chairs and tables, in the proximity of equipment. As two materi-als are separated, the charge separation creates strong electric fields, and thus voltage differences between the materi-als will occur. [1-5] When a conductor is connected to the Earth by means of con-ducting wire or pipe, it is said to be grounded. The earth can then be consid-ered an infinite “skin” to which electric charges can easily migrate. To under-stand induction, consider a neutral (un-charged) conducting sphere insulated from ground. When a negatively charged rubber rod is brought near the sphere, the region of the sphere nearest the rod obtains an excess of positive charge while the region farthest from the rod obtains an equal excess of negative charge. [6]

Friction coefficient slightly increased with increasing metallic content. Based on the quantification of floor slip-resist-ance, the static friction coefficient of 0.5 was recommended as the slip resistant standard for normal walking conditions. For the test specimens friction coeffi-cient exceeded 1.0 which confirmed that the floor made of the tested composites will be very safe for walking. At brass content where the generated voltage di-minished, friction coefficient value ap-proached 1.4. This observation recom-mends that composites to be used as floor tiles. Besides, addition of copper particles caused significant friction in-crease. [7, 8]

The factors affecting friction coeffi-cient measurement were the material and surface geometry of the footwear and floor, floor contamination conditions and even the slipmeter used. [8-10] In-

vestigators have concentrated on the friction coefficient measurements on liq-uid contaminated floors because most slip/fall incidents occur on the surfaces of such floors. [11]

Slipping and falling are common phe-nomena in both workplaces and daily activities. The materials of floor or foot-wear, wetted condition and geometric design of the sole are related to the dan-gers of slipping and falling. [12-20] Slip resistance of flooring materials is one of the major environmental factors affect-ing walking and materials handling be-havior. Floor slipperiness may be quanti-fied using the static and dynamic friction coefficient. Certain values of friction co-efficient were recommended as the slip-resistant standard for unloaded, normal walking conditions. [21-23] The ESC in-creases by increasing the number of cop-per strips, because the double layer of the ESC generated on the sliding surfaces causes an E-field which generates an ex-tra ESC. The increase of the ESC has a pronounced effect on adhesion force be-tween the contact surfaces leading to an increase in the friction coefficient. The grounding facilitates the leakage of 78 % of the generated ESC and consequently decreases the friction coefficient by 35 %. [8] The triboelectric series can be used to determine the charge polarity of the ma-

Reducing electrostatic Charge generated on Polymeric Floor in Hospitals

AuthorsM. I. Rehab Khashaba, W. Y. Ali Minia, Egypt

Corresponding Author:W. Y. Ali Production Engineering and Mechanical Design Dept., Faculty of Engineering, Minia University EI-Minia, Egypt E-Mail: [email protected]


55KGK · 7-8 2018www.kgk-rubberpoint.de

terials. This series can be used to evalu-ate the relative charging capacity of many polymeric materials. [24, 25] Stain-less steels have a high modulus of elas-ticity (200 MPa, or 30 ksi) that is nearly twice that of copper alloys. Also it has a very high thermal conductivity and the corrosion resistance is frequently the most important characteristic of a stain-less steel. General corrosion resistance to pure chemical solutions is comparatively easy to determine, but actual environ-ments are usually much more complex. [26]

The aim of this study is to reduce elec-trostatic charge and enhances the fric-tion coefficient during walking by poly-propylene shoes against floor material A and B in hospitals. The effect of adhering different numbers of grounded or un-grounded stainless steel strips to the back of the floor materials on ESC and friction coefficient is investigated.

Experimental workThe test specimens (polyvinyl chloride floor PVC) were adhered by stainless steel strips (0, 1, 2, 3, 4, 5 and 6 strips) as illustrated in Fig. 1. They were added in the back of polyvinyl chloride floor mate-rial sheets (A & B) by 300 × 400 mm² area and 5 mm thickness. The mechanical and electrical properties of PVC are shown in table 1.

Ultra Stable Surface DC Voltmeter de-vice was used to measure ESC (electro-static field). It measures down to 1/10 volt on a surface, and up to volts (20 kV). Readings are normally done with the sensor 25 mm apart from the surface be-ing tested, as illustrated in Fig. 2. The friction coefficient was calculated by di-viding the horizontal force (friction force) on the vertical force (normal force) which measured by using a test rig device, as illustrated in Fig. 3.

Results and discussionAfter sliding to 200 mm against floor material (A), it was observed that, ESC slightly increased by increasing the nor-mal load up to 459, 512, 538 volts in floor material fitted by four, five and six un-grounded strips respectively. These val-ues were higher than floor material without strips due to the ability of strips to generate extra amount of ESC as illus-trated in Fig. 4. It was also noted that the voltage increased with increasing ap-plied normal load where the intensity of ESC depends on the pressure and time of sliding as illustrated in Fig. 5.

The floor material as insulator con-tains a distribution of charges which are conserved, when the polypropylene shoe slides against the floor material, the dou-ble layer of ESC is generated and conse-quently the generated electric field in-creases. Presence of stainless steel strips in the back of the floor material gener-ates extra ESC on the sliding surface. Based on that observation, it can be no-ticed that ESC increases by increasing the number of strips, Fig. 5.

Figure 6 illustrates that, friction coef-ficient slightly increased by increasing the number of ungrounded strips. This

Fig. 1: Distribution of the copper strips.

1

1 The properties of the tested floor materials A & BMaterial properties Material (A) Material (B)Electrical resistance 5 × 104 ≤ R ≤ 106 Ohms R ≤ 108 OhmsStatic electrical charge < 2 KV < 2 KVTotal weight/m² 3000 gram 3000 gram

Fig. 2: Electrostatic charge (voltage) measuring device.

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Fig. 3: Arrangement of the experimental test.

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Polypropylene shoe

Test rig

Adhered to the back of the tile

Grounded EndFloor material

Floor material

Test rig

Polypropylene shoe

Grounded EndSliding direction



Fig. 4: Effect of number of ungrounded strips on ESC on material (A) at dry sliding.

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Fig. 5: Schematic illustration of ESC generated on floor material and polypropylene.

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Fig. 6: Effect of number of ungrounded strips on friction coeffici-ent on material (A) at dry sliding.

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Fig. 7: Effect of number of grounded strips on ESC on material (A) at dry sliding.

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Fig. 8: Effect of number of grounded strips on friction coefficient on material (A) at dry sliding.

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Fig. 9: Effect of number of ungrounded strips on ESC on material (B) at dry sliding.

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Floor material

Test rig

Polypropylene shoe

Grounded end

Sliding direction

Stainless Steel Strips

Electric field



Fig. 10 Effect of number of ungrounded strips on friction coeffici-ent on material (B) at dry sliding.

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Fig. 11: Effect of number of grounded strips on ESC on material (B) at dry sliding.

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Fig. 12: Effect of number of grounded strips on friction coefficient on material (B) at dry sliding.

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Fig. 13: Effect of number of ungrounded strips on ESC on material (A) at wet chlorine sliding.

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Fig. 14: Effect of number of ungrounded strips on friction coef-ficient on material (A) at wet chlorine sliding.

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Fig. 15: Effect of number of grounded strips on ESC on material (A) at wet chlorine sliding.

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Fig. 16: Effect of number of grounded strips on friction coefficient on material (A) at wet chlorine sliding.

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Fig. 17: Effect of number of ungrounded strips on ESC on materi-al (B) at wet chlorine sliding.

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Fig. 18: Effect of number of ungrounded strips on friction coeffici-ent on material (B) at wet chlorine sliding.

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Fig. 19: Effect of number of grounded strips on ESC on material (B) at wet chlorine sliding.

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behavior is attributed to due to ESC in-crease, Fig. 4, which consequently in-creases the adhesion force between sur-faces, so that the friction coefficient was 0.81 in floor material fitted by six strips.

Although the strips were grounded the charge has increased, this is due to charging by induction. The most of elec-trons escaped to the earth and leave unbalance positive charge so that the strips have excess positive charge to bal-ance the negative one. This discussion illustrates why ESC increased with in-creasing grounded strips in Fig. 7 up to 476, 552 and 560 volts in floor material fitted by four, five and six strips. These values were higher than that observed in Fig. 4 using ungrounded strips. Al-though ESC increased by increasing the number of grounded stainless steel

strips in Fig. 8, friction coefficient de-creased slightly to 0.77 compared to the data shown in Fig. 6.

ESC slightly decreased down to 401, 420 and 486 volts in floor material fitted by four, five and six strips respectively, Fig. 9. These values were lower than that noticed in Fig. 4, because the electrical resistance of floor material (A) is higher than material (B) as illustrated in table 1. Consequently, the friction coefficient de-creased also from 0.8057 in Fig. 6 to 0.74 in Fig. 10. Grounding increased also ESC by in-creasing the number of strips, as illus-trated in Fig. 7. The maximum value was 516 volts in floor material (B) fitted by six strips while it was 308 volts in specimen free of strips as illustrated in Fig. 11. On the other hand, it was observed that ESC

increased by 3 % while friction coeffi-cient decreased by 5 % as observed in Fig. 12.

Figure 13 shows that, presence of wa-ter/chlorine dilution wet surface de-creased ESC to 67, 81 and 98 volts in floor material fitted by four, five and six strips respectively. Those values were lower than that generated in dry sliding in Fig. 4. This behavior is attributed to the good conductivity of water which facilitates leaking the generated charge out of the contact area. Consequently friction coef-ficient decreased down to 0.79 in the specimen fitted by six strips, while it was 0.82 in the specimen free of strips at the same condition, Fig. 14. That behavior confirms the necessity of adding stain-less steel strips, in the back of floor mate-rial, to enhance friction coefficient dur-



ing walking against water/chlorine wet floor.

ESC increased by increasing the num-ber of grounded strips due to charging by induction, Fig. 15. When the strips were grounded, some of their electrons leave through the ground wire and the strips have excess positive charge. The voltage was 77, 98 and 117 in floor material (A) fitted by four, five and six grounded strips besides, this values were higher than that noticed in Fig. 13. On other hand, the friction coefficient increased by increasing grounded strips to (0.753) and (0.817) in floor material fitted by six and without strips respectively, as illus-trated in Fig. 16.

The floor material (B) generated ESC lower than that observed in material (A), Fig. 17, where ESC was 47, 52 and 65 volts in floor material fitted by four, five and six stainless steel strips respectively. These values were lower than that ob-served in Fig. 13. This reduction influ-enced also friction coefficient which de-creased to 0.7 and 0.8 in floor material fitted by six and without strips respec-tively, Fig. 18.

At water/chlorine dilution wet sur-face, the voltage decreased to 72 volts, Fig. 20, which was lower than that ob-served in Fig. 11. The voltage was 516 volts in floor material fitted by grounded six strips. This behavior is attributed to the presence of water film which leaks amount of generated ESC. On the other hand, the voltage increased up to 72 volts in the floor material fitted by six grounded strips, Fig. 19, due to charging by induction.

Friction coefficient decreased down to 0.67 in floor material fitted by six grounded strips, Fig. 20, which was lower than that displayed in Fig. 18.

Conclusions1. ESC increased by increasing the num-

ber of strips, where the double layer of the ESC generated on the sliding sur-faces causes an E-field which generat-ed extra amount of ESC.

2. Increasing ESC has a pronounced ef-fect on adhesion force between the contact surfaces leading to an increase in the friction coefficient and conse-quently increases safety of walking.

3. ESC increased by 3 % in the presence of grounded stainless steel strips, while friction coefficient decreased by 4 - 5 %.

4. Floor material (B) generated ESC lower than that observed in floor material (A).

5. At dry sliding, ESC was higher than

that generated at water/chlorine dilu-tion wet sliding. On the other hand, the friction coefficient decreases only by 5 %, confirming the increased abili-ty of the tested floor to avoid slip ac-cidents due to excessive movement, especially at wet sliding.

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Fig. 20: Effect of num-ber of ungrounded strips on friction coef-ficient on material (B) at wet chlorine sliding.

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Reducing electrostatic Charge · 2018. 7. 31. · ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS 54 KGK · 7-8 2018 Electrostatic charge (ESC) polyvinyl chloride (PVC) floor