**4. Effect of fillers on the properties of thermoplastic elastomers based on maleated EPDM**

Fillers are used to improve some properties of thermoplastic compositions. It is well known that the fillers interact with ionic elastomers leading to the formation of ionic, covalent or hydrogen bonds with them. The appearance of these bonds determines a reinforcing effect of rubber composition and the improving of modulus, tear strength or of tensile strength (Zuga et al., 2004).

The filler nature (carbon black, precipitated silica or chalk) will influence the properties of ionic thermoplastic elastomers and it is very important to select the type of filler and optimum quantity which must be incorporated in a composition designated to be utilized in light industry.


Table 5. Formulations and characteristics of rubber blends based on EPDM-g-MA (Royaltuf 485)

Some formulations and properties of rubber blends based on EPDM-g-MA are given in Tab. 5 and 6 in order to reveal the influence of filler nature on the resulting compositions. From these tables it can be seen that the hardness of composition increases together with filler incorporation due to the reinforcing effect of fillers. This improvement of hardness is more

Fillers are used to improve some properties of thermoplastic compositions. It is well known that the fillers interact with ionic elastomers leading to the formation of ionic, covalent or hydrogen bonds with them. The appearance of these bonds determines a reinforcing effect of rubber composition and the improving of modulus, tear strength or of tensile strength

The filler nature (carbon black, precipitated silica or chalk) will influence the properties of ionic thermoplastic elastomers and it is very important to select the type of filler and optimum quantity which must be incorporated in a composition designated to be utilized in

Ingredients/Sample O1 U11 U12 U13 C11 C12 C13 F11 F12 F13

Zinc oxide, g 20 20 20 20 20 20 20 20 20 20 Stearic acid, g 2 2 2 2 2 2 2 2 2 2 Zinc stearate, g 20 20 20 20 20 20 20 20 20 20

Chalk, g - - - - 30 60 90 - - - Carbon black HAF, g - - - - - - - 30 60 90

Hardness, ºShA 63 72 81 89 66 67 72 67 77 84 Elasticity, % 34 34 36 34 36 32 30 32 30 26

Elongation at break, % 767 580 273 100 567 473 473 633 490 420 Residual elongation, % 83 61 24 9.3 59 49 53 75 60 60 Tear strength, N/mm 36 43.5 46 48 37.5 41 44 53 60 74 Specific weight, g/cm3 1.07 1.12 1.16 1.23 1.14 1.25 1.35 1.11 1.16 1.22

Table 5. Formulations and characteristics of rubber blends based on EPDM-g-MA (Royaltuf

Some formulations and properties of rubber blends based on EPDM-g-MA are given in Tab. 5 and 6 in order to reveal the influence of filler nature on the resulting compositions. From these tables it can be seen that the hardness of composition increases together with filler incorporation due to the reinforcing effect of fillers. This improvement of hardness is more

100 100 100 100 100 100 100 100 100 100


10 10 10 10 10 10 10 10 10 10

1 1 1 1 1 1 1 1 1 1

8.8 8.2 5.2 4.7 7 6.9 5.8 9.3 9.6 11

102 135 182 246 165 176 196 149 162 161

**4. Effect of fillers on the properties of thermoplastic elastomers based on** 

**maleated EPDM** 

(Zuga et al., 2004).

light industry.

485, g

g

1010, g

N/mm2

mm3

485)

EPDM-g-AM Royaltuf

Precipitated silica Perkasil, g

Paraffin oil Texpar 22,

Antioxidant Irganox

Characteristics

Tensile strength,

Abrasion resistance,

pronounced for compositions with active fillers (carbon black, silica) as compared to compositions containing inactive fillers (chalk). For the compositions containing Royaltuf 485 the increase of filler level determines an increase of hardness of 41 % for compositions having precipitated silica and of 33 % for compositions with carbon black, respectively. The same effect was observed for compositions containing Royaltuf 498, where the hardness increase with 34.8% introducing precipitated silica and with 28.8 % for compositions having carbon black as filler. The introducing of chalk determines a lower increase of hardness (about 15 %, Tab. 5).

The elasticity decreases by introducing fillers in composition. For compositions containing Royaltuf 485 the elasticity was diminished from 34 to 26 % in the case of carbon black utilization and lower decrease together with the increase of chalk level (from 34 to 30 %). The elasticity shows a nonuniform variation in compositions with silica or chalk and it decreases till 28% in compositions with carbon black (compositions with Royaltuf 498).


Table 6. Formulations and characteristics of rubber blends based on EPDM-g-MA (Royaltuf 498)

Tensile strength also decreases together with the increase of silica and chalk levels for the both compositions. In case of compositions containing carbon black the tensile strength

New Thermoplastic Ionic Elastomers Based on MA-g-EPDM with Advanced Characteristics 383

Figure 10 shows that adding the plasticizer (paraffin oil) for polymer chains has resulted in a decreased hardness (by 12oShA) but adding the ionic plasticizer (zinc stearate) has resulted in an increased hardness as the last one plasticizes the ionic groups at a temperature above the its melting point (128oC) and at the room temperature it acts like a filler (increases by 1oShA up to 11oShA). Hardness changes as a result of adding zinc stearate are more marked with the blend

An increase in elasticity with the increase in the amount of paraffin oil added to the blends was found out (Fig. 11); but the elasticity decreases as the amount of the added ionic plasticizer is increased and this decrease is more marked with blends containing EPDM and 1 % maleic anhydride. The blends containing EPDM and 1 % maleic anhydride show a higher elasticity with the decreasing in crystalline phase to the favour of amorphous phase.

0 10 20 30 40 50 60

 20 phr zinc stearate 40 phr zinc stearate

> 20 phr zinc stearate 40 phr zinc stearate

Paraffin oil level, phr

0 10 20 30 40 50 60

Paraffin oil level, phr

(a) (b) Fig. 11. Changes in elasticity according to the added plasticizer amounts: (a) for blends with

Elasticity, %

(a) (b) Fig. 10. Changes in hardness according to the added plasticizer amounts. (a) for blends with

> 20 phr zinc stearate 40 phr zinc stearate

Hardness, ShA

containing EPDM and 1 % maleic anhydride because of the enlarged ionic ranges.

 20 phr zinc stearate 40 phr zinc stearate

0 10 20 30 40 50 60

Paraffin oil level, phr

Royaltuf 485; (b) for blends with Royaltuf 498

0 10 20 30 40 50 60

Paraffin oil level, phr

Royaltuf 485 (b) for blends with Royaltuf 498

Elasticity, %

Hardness, ShA

increases with 25% as the filler level increases, while in compositions containing Royaltuf 498 the tensile strength increases with 37.7 % for carbon black level of 30 phr and then it decreases untill 22.6 %. The elongation at break decreases together with the increase of filler level. The most increase was observed in compositions containing precipitated silica. Tear strength increases against filler level for all compositions, the high values were obtained for compositions containing carbon black.

Also, the specific weight and abrasion resistance increase as the filler level becomes higher. However, the values of specific weight for compositions containing more than 60 phr of filler are very high and inadequate for use in shoes fabrication. The values of abrasion resistance confirm that these compounds can be used to manufacture "every day" shoes.

From Tabs. 5 and 6, the best characteristics of the compositions based EPDM-g-MA were obtained using as fillers carbon black and silica, occurring an increase of hardness, tensile strength and tear strength. Taking into account that a higher filler level leads to the decrease of melt composition viscosity and to the increase of specific weight and abrasion resistance, a rubber composition containing 30 phr carbon black or 30 phr precipitated silica could be selected in order to utilize in EPDM-g-MA compounds (Zuga et al., 2004).
