**1. Introduction**

370 Thermoplastic Elastomers

Zhao, F., Ping, Z., Zhao, S., Jian, Y. & Kuhn, W. (2007) Characterization of Elastomer

685 - 688

Networks by NMR Parameters Part II. *Kautsch. Gummi Kunstst.,* Vol. 60, No. 12, pp.

Ionic thermoplastic elastomers or ionomers are copolymers involving a major non-polar constituent (which can be crystallized or not) and a minor ionizable constituent, partly or entirely neutralized with mono- and divalent inorganic ions as a salt at a concentration not exceeding 10 mol % (Andrei & Dobrescu, 1987; Stelescu, 2011).

In order to obtain ionic thermoplastic elastomers, one or more of the techniques listed bellow can be used:


The ionic elastomer compounds resemble highly with the traditional rubber compounds but there are some differences. Because the former are thermoplastics, there is no curing stage and, therefore, no sulfur and vulcanization accelerators or peroxides are added. Another significant difference is the use of an ionizing agent - ionic plasticizer in preparing ionic thermoplastic elastomers. It plays the role of promoting the ionic break-up of the ionic interactions at high temperatures to enable the shearing flow of the compound; at room

<sup>\*</sup> Corresponding Author

New Thermoplastic Ionic Elastomers Based on MA-g-EPDM with Advanced Characteristics 373

has been converted into a thermoplastic ionic elastomer by adding various percentages of ionic plasticizer to the blend. The behaviour of the thermoplastic ionic elastomers resulted by adding fillers like as precipitated silica and carbon black in various percentages was assessed. The extent of the neutralization agent, ionic and non-ionic plasticizers, filler, polyolefin's which influence the characteristics of the resulting products was determined with the purpose of selecting the best types of ionic thermoplastic elastomer based on EPDM-g-AM. All the laboratory prepared compounds were tested for the physicomechanical characteristics; based on the results, three thermoplastic ionic elastomers with

To obtain better characteristics, the creation of nanocomposites from a selected EPDM-g-AM compound and organically modified montmorillonite clay (OMMT) was targeted. Nanocomposites based on maleated ethylene propylene diene terpolymer and organically modified montmorillonite (OMMT) has been prepared by melt intercalation procedure. The materials were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic scanning calorimetry (DSC) and mechanical tests. XRD data show the increase of the distance between the silicate layers indicating the intercalation of polymer chains in the montmorillonite galleries. The incorporation of OMMT in composites determines the increase of melting peak temperature (Tm) and heat of fusion (ΔHf) suggesting a supplementary nucleation increase due to the OMMT presence. The mechanical properties were analyzed as a function of the OMMT level in the composite and the results reveal

Ionic thermoplastic elastomer compounds can be used in many applications such as: to manufacture a wide range of consumer goods (hoses, soles etc), as modifier for other materials, to make adhesives, to obtain impermeable flexible thin membranes such as cover membranes etc. (Swapan et al., 2001; Zhao-Hua et al., 2002; Einsenbach et al., 1998; Piere,

The new types of thermoplastic elastomers can be processed by specific techniques for thermoplastic materials, thus removing the vulcanization stage involving high power expenditure and release of noxious products, improved characteristics (higher values for elasticity, ageing resistance, abrasive resistance, acid and alkali fastness) of these materials

The potential users of the new rubber materials will be economic operators processing rubber and plastics, footwear and car component manufactures etc. They can be used in the manufacture of a large range of products like as hoses, gaskets, rubber shoes, protective

Ionic thermoplastic elastomers can be obtained by processing of ethylene propylene diene elastomers (EPDM) grafted with maleic anhydride (EPDM-g-MA) having different contents of maleic anhydride. The compositions of thermoplastic elastomers contain besides EPDMg-MA the following elements: neutralizing agents of the ionic groups (zinc oxide in the presence of stearic acid), ionic plasticizers (zinc stearate), nonionic plasticizers (paraffin oil), fillers (precipitated silica, carbon black, chalk), polyolefins (high density polyethylene

the best characteristics were selected and the applications of these were set up.

remarkable improvement relative to the conventional composite.

2002; Ronatti, 1990; Nachmias & Sera, 2002).

can be assured.

equipment etc.

**2. Preparation** 

temperature it behaves like a filler. Zinc stearate is the most largely used ionic plasticizer but some others can be also used, like calcium stearate, zinc acetate, stearamide (Nahmias & Marco Serra, 2002; Zuga et. al, 2009; Stelescu et al., 2011).

A formulation of ionic thermoplastic elastomer compound consists generally of a neutralized ionomer, ionic plasticizer, non-ionic plasticizer, filler, antioxidants, other polymers, etc. (Zuga & Cincu, 2006a). A significant increase of vitrifying point by incorporating ions into polymers was prouved (Eisenberg, 1977). This increase depends on the nature of the basic ion, the effect being stronger as the ionic forces are larger. They have also shown that the nature of the basic ion influences not only the value of Tg (glass transition temperature), but also the position and shape of the module – temperature curve. The increase of ion content leads to an increase of the module and the increase of the specific plateau of vulcanized rubber.

An important contribution to establishing the relation between properties and the ion content in ionomers has been brought by research on carboxylated elastomers. Ionomer-rubbers have remarkable properties such as: high module, large elongation at break and a constant plateau in the module – temperature curve. This constant plateau can be explained through the presence of a small concentration of stable interchain bonds, called multiplets. Elongation at break has been attributed to the loosening of ionic bonds by exchange reactions between crosslinking bridges of various chains, thus hindering an excessive strain. Finally, due to the presence of ionic aggregates which may act as "filling materials", of reinforcement and of quasi-crosslinking, the initial high module of materials can be explained.

Rheological studies on ionomers in melt (Szymczyk & Roslaniec, 1999) have highlighted a remarkably large increase of melt viscosity, as a result of introducing ions into polymers. This increase depends on the ion concentration or on the neutralization degree and less on the nature of ions. Also, the non-Newtonian character of ionomers in melt is noticed, probably due to the fact that the movement of chain segments and chains implies dissociation of ion pairs in cluster aggregates. This dissociation certainly has a determining influence on rheological properties in melt. In partially neutralized ionomers, hydrogen bonds between the carboxyl functional groups may also have a significant effect on flow properties.

There are a few studies (Zuga & Cincu, 2006b, 2006c; Datta & Kharagpur, 1997; Paeglis & O'Shea, 1988) on ionomers based on maleated and/or sulphonate EPDM rubber indicating the fact that, by introducing neutralization agents (zinc oxide, sodium hydroxide etc.) when a metal base is obtained, modifications of physico-mechanical properties which take place in system are assumed to be due to the rigid phase resulted from the restriction of chain mobility in the ionic aggregate area and a reduction of crystallinity compared to that existing in the initial elastomer is noticed (Stelescu, 2010).

This review gives an overview about our research on ionic thermoplastic elastomers based on maleated ethylene propylene diene terpolymer (EPDM-g-MA). The investigations were aimed to obtain some new generations of ionic thermoplastic elastomers with high technical and processing characteristics intended to be processed on the injection moulding machines, resulting in high quality products complying with the international market requirements. Two types of maleated ethylene propylene terpolymer elastomers (EPDM-g-MA) with various levels (0.5 and 1.0 %) of maleic anhydride were used. The EPDM-g-MA rubbers were modified by neutralizing them with zinc oxide and stearic acid, and then the ionomer has been converted into a thermoplastic ionic elastomer by adding various percentages of ionic plasticizer to the blend. The behaviour of the thermoplastic ionic elastomers resulted by adding fillers like as precipitated silica and carbon black in various percentages was assessed. The extent of the neutralization agent, ionic and non-ionic plasticizers, filler, polyolefin's which influence the characteristics of the resulting products was determined with the purpose of selecting the best types of ionic thermoplastic elastomer based on EPDM-g-AM. All the laboratory prepared compounds were tested for the physicomechanical characteristics; based on the results, three thermoplastic ionic elastomers with the best characteristics were selected and the applications of these were set up.

To obtain better characteristics, the creation of nanocomposites from a selected EPDM-g-AM compound and organically modified montmorillonite clay (OMMT) was targeted. Nanocomposites based on maleated ethylene propylene diene terpolymer and organically modified montmorillonite (OMMT) has been prepared by melt intercalation procedure. The materials were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic scanning calorimetry (DSC) and mechanical tests. XRD data show the increase of the distance between the silicate layers indicating the intercalation of polymer chains in the montmorillonite galleries. The incorporation of OMMT in composites determines the increase of melting peak temperature (Tm) and heat of fusion (ΔHf) suggesting a supplementary nucleation increase due to the OMMT presence. The mechanical properties were analyzed as a function of the OMMT level in the composite and the results reveal remarkable improvement relative to the conventional composite.

Ionic thermoplastic elastomer compounds can be used in many applications such as: to manufacture a wide range of consumer goods (hoses, soles etc), as modifier for other materials, to make adhesives, to obtain impermeable flexible thin membranes such as cover membranes etc. (Swapan et al., 2001; Zhao-Hua et al., 2002; Einsenbach et al., 1998; Piere, 2002; Ronatti, 1990; Nachmias & Sera, 2002).

The new types of thermoplastic elastomers can be processed by specific techniques for thermoplastic materials, thus removing the vulcanization stage involving high power expenditure and release of noxious products, improved characteristics (higher values for elasticity, ageing resistance, abrasive resistance, acid and alkali fastness) of these materials can be assured.

The potential users of the new rubber materials will be economic operators processing rubber and plastics, footwear and car component manufactures etc. They can be used in the manufacture of a large range of products like as hoses, gaskets, rubber shoes, protective equipment etc.
