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Natural Rubber (NR) And Ethylene-Propylene-Diene Monomer (EDPM) Blends
The development of blends of NR with EPDM combines the superior physical properties and competitive price of NR with the excellent resistance to weathering, in particular to attack by ozone of EPDM. However, NR and EPDM blends are heterogeneous dispersion of fast curing NR phase and a slow curing EPDM phase. The overall result is that the blend vulcanisate is composed of overcured NR and undercured EPDM, and these would adversely affect the properties of the blend.

In order to achieve improved co-curability throughout the NR/EPDM blends, a procedure has been developed whereby NR is cross-blended with a modified EPDM to give a blend which is able to meet the above properties. The approach used is to increase the cure rate of EPDM by modifying the EPDM phase to make it more reactive towards curatives, using commercially available sulphur donors such as bis-alkylphenoldisulphide (BAPD), in combination with dithiocaprolactam (DTDC) and/or dithiomorpholine (DTDM). This approach is termed as 'reactive mixing'.

Products in general

The technology of making the NR/modified EPDM blends has been shown to be suitable for a number of applications such as extruded profile weatherstrips for automotive and moulded products like grommet and washing machine gasket. These products typically use 100% EPDM, hence, the inclusion of a certain percentage of NR would reduce the products cost without affecting the products quality and performance.

  Automotive Weatherstrips
Automotive Weatherstrips

Washing Machine Gaskets
Washing Machine Gaskets

Manufacturing process
  • Preparation of compound

  • Reactive mixing can only be achieved effectively in an internal mixer which has good temperature control and monitoring facilities. The most critical approach to the preparation of the NR/modified blends is the mixing procedure itself particularly for the modification of the EPDM phase whereby the dump temperature of mixing is to exceed 1650C. Two separate NR and EPDM masterbatches are first prepared. The separate masterbatches are then cross-blended (according to the ratio required) in a second stage mix and then curatives are added in a final stage mix on a two-roll mill. The separate masterbatch and cross-blending approach ensures that the sulphur donors used in the EPDM modification stage act primarily in the EPDM phase of the blend as well as ensuring that both phases of the blend have the correct filler loading and are well mixed.

  • Determination of scorch time, cure characteristics and physical testing (e.g., hardness, tensile properties, tear resistance, rebound resilience, compression set and ozone resistance)
    The above properties are necessary before the blend compounds can proceed to the subsequent fabrication processes such as extrusion and moulding.

    The physical properties will also depend on product(s) application(s).

  • Fabrication and vulcanisation of products
    Weatherstrips are prepared by extrusion with vulcanisation carried out in a continuous vulcanisation system such as using Liquid Curing medium (LCM) or a microwave. Grommet and washing machine gasket are prepared by injection moulding technique.

  • Products performance - depend on the type of products and where they are to be used
Other Info
  Processing Flow Chart
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