Polyethylenes having faster crystallization rate and improved environmental stress cracking resistance

Abstract

Disclosed is a polyethylene composition having faster crystallization rate and improved environmental stress cracking resistance. The polyethylene composition comprises a multimodal polyethylene and a nucleating agent. The multimodal polyethylene comprises from 25 to 50 wt % of a low molecular weight ethylene homopolymer component, from 25 to 50 wt % of a medium molecular weight ethylene copolymer component and from 25 to 50 wt % of a high molecular weight ethylene copolymer component. The polyethylene composition has an environmental stress cracking resistance (ASTM D1693, Condition B in 100% Igepal) greater than or equal to 40 days and a crystallization half time less than or equal to 70% of the crystallization half time of the multimodal polyethylene without nucleating agent.

I claim: 
     
         1 . A polyethylene composition comprising:
 (i) a nucleating agent, and   (ii) a multimodal polyethylene having:
 a. from 25 to 50 wt % of a low molecular weight ethylene homopolymer component, 
 b. from 25 to 50 wt % of a medium molecular weight ethylene copolymer component, and 
 c. from 25 to 50 wt % of a high molecular weight ethylene copolymer component; 
   
       wherein the polyethylene composition has an environmental stress cracking resistance measured according to ASTM D1693, Condition B in 100% Igepal greater than or equal to 40 days, and a crystallization half time less than or equal to 70% of the crystallization half time of the multimodal polyethylene without the nucleating agent. 
     
     
         2 . The polyethylene composition of  claim 1  having a crystallization half time less than or equal to 60% of the crystallization half time of the multimodal polyethylene. 
     
     
         3 . The polyethylene composition of  claim 1  having a crystallization half time less than or equal to 50% of the crystallization half time of the multimodal polyethylene. 
     
     
         4 . The polyethylene composition of  claim 1  having a crystallization half time less than or equal to 12 minutes at 124° C. 
     
     
         5 . The polyethylene composition of  claim 1  having a crystallization half time less than or equal to 9 minutes at 124° C. 
     
     
         6 . The polyethylene composition of  claim 1  having a crystallization half time less than or equal to 6 minutes at 124° C. 
     
     
         7 . The polyethylene composition of  claim 1 , wherein the nucleating agent is selected from the group consisting of zinc glycerolate, calcium glycerolate, calcium hexahydrophthalate, zinc hexahydrophthalate, and mixtures thereof. 
     
     
         8 . The polyethylene composition of  claim 7 , comprising from 10 ppm to 10,000 ppm of the nucleating agent. 
     
     
         9 . The polyethylene composition of  claim 8 , comprising from 20 ppm to 5,000 ppm of the nucleating agent. 
     
     
         10 . The polyethylene composition of  claim 9 , comprising from 50 ppm to 1,000 ppm of the nucleating agent. 
     
     
         11 . The polyethylene composition of  claim 1 , wherein the multimodal polyethylene has a density from of 0.942 g/cm 3  to 0.959 g/cm 3  and MI 2  from 0.2 dg/min to 30 dg/min. 
     
     
         12 . The polyethylene composition of  claim 1 , wherein the multimodal polyethylene comprises from 30 to 40 wt % of the low molecular weight ethylene homopolymer component, from 30 to 40 wt % of the medium molecular weight ethylene copolymer component and from 20 to 30 wt % of the high molecular weight ethylene copolymer component. 
     
     
         13 . The polyethylene composition of  claim 1 , wherein the low molecular weight ethylene homopolymer component has a density within the range of 0.965 g/cm 3  to 0.973 g/cm 3  and a melt index MI 2  within the range of 100 dg/min to 250 dg/min, the medium molecular weight ethylene copolymer component has a density within the range of 0.950 g/cm 3  to 0.962 g/cm 3  and a melt index MI 2  within the range of 10 dg/min to 30 dg/min, and the high molecular weight ethylene copolymer component has a density within the range of 0.905 g/cm 3  to 0.935 g/cm 3  and a melt index MI 2  within the range of 0.01 dg/min to 0.1 dg/min. 
     
     
         14 . An article comprising the polyethylene composition of  claim 1 . 
     
     
         15 . A single-piece bottle cap comprising the polyethylene composition of  claim 1 .