Compatibilized thermoplastic vulcanizate compositions
Disclosed is the preparation of compatibilized thermoplastic vulcanizates with reduced crosslinked rubber dispersion sizes and dispersity. A cross-linkable ethylene-propylene-diene terpolymer with majority propylene (PEDM) is used to compatibilize a plastic and rubber blend of a polypropylene (PP) and an ethylene-propylene-diene terpolymer rubber, where the propylene content is less than 50 wt % (EPDM), in dynamic vulcanization and preparation of PP/EPDM thermoplastic vulcanizates. The resulting PP/EPDM thermoplastic vulcanizates typically exhibit a weight average equivalent dispersion diameter of less than 3 microns and a particle size polydispersity index (PSDI), or weight average over number average dispersion diameter, of less than 5. This reduction in crosslinked rubber dispersion size in a PP/EPDM TPV by using PEDM compatibilizers enhances the toughness of the vulcanizate product by raising both elongation to break and break stress.
1. A thermoplastic vulcanizate comprising an isotactic polypropylene matrix phase in which a cross-linked ethylene-propylene-diene terpolymer (EPDM) is dispersed, the vulcanizate comprising the reaction product of:
a) 35 to 55 wt % of an ethylene-propylene-diene terpolymer (EPDM), wherein the EPDM comprises 50 to 80 wt% ethylene;
b) 20 to 30 wt % of isotactic polypropylene (iPP);
c) 10 to 25 wt % of a diluent;
d) 0.5 to 15 wt % of a propylene-ethylene-diene terpolymer (PEDM) compatibilizer, wherein the PEDM comprises 2 to 25 wt% ethylene and a diene content of 1 to 21 wt%; and
e) 1.5 to 3.0 wt % of curatives;
each weight percent is by weight of the combined components.
2. The thermoplastic vulcanizate of claim 1 , in which the EPDM comprises 55 to 75 wt % ethylene and 2 to 10 wt % ethylene norbornene.
3. The thermoplastic vulcanizate of claim 1 , in which the amount of PEDM is from 3 to 25 wt % of the amount of EPDM.
4. The thermoplastic vulcanizate of claim 1 , in which the MFR 2.16 at 230° C. of the PEDM is from 0.5 to 20 g/10 min.
5. The thermoplastic vulcanizate of claim 1 , in which the PEDM comprises 5 to 20 wt % ethylene and 2 to 15 wt % ethylene norbornene.
6. The thermoplastic vulcanizate of claim 1 , wherein the particle size dispersity index (PSDI) is less than 3.