Bimodal pipe resin and products made therefrom

Abstract

Disclosed is a bimodal Ziegler-Natta catalyzed polyethylene, having a density of from 0.930 g/cc to 0.960 g/cc, and a molecular weight distribution of from 10 to 25, wherein an article formed therefrom has a PENT of at least 1500. Also disclosed is a method of preparing a tubular article including obtaining a bimodal polyethylene having a density of from 0.930 g/cc to 0.960 g/cc and a molecular weight distribution of from 10 to 25, and processing the polyethylene under conditions where a specific energy input (SEI) is less than 300 kW.h/ton, and wherein the article has a PENT of at least 1500. Further disclosed is a method for controlling the degradation of polyethylene including polymerizing ethylene monomer, recovering polyethylene, extruding the polyethylene, and controlling the degradation of polyethylene by measuring the SEI to the extruder and adjusting throughput and/or gear suction pressure keep SEI less than 300 kW.h/ton, and forming an article.

1 . A bimodal polymer comprising Ziegler-Natta catalyzed polyethylene, having a density of from 0.930 g/cc to 0.960 g/cc, and a molecular weight distribution of from 10 to 25, wherein an article formed from the polymer has a PENT of at least 1500 using test ASTM F 1473.  
   
   
       2 . The bimodal polyethylene of  claim 1 , wherein the polyethylene is a copolymer.  
   
   
       3 . The bimodal polyethylene of  claim 1 , wherein the polyethylene has a density of from 0.946 g/cc to 0.951 g/cc.  
   
   
       4 . The bimodal polyethylene of  claim 1 , wherein a polyethylene fluff is extruded into pellets using a specific energy input (SEI) of less than 300 kW.h/ton.  
   
   
       5 . The bimodal polyethylene of  claim 1 , wherein the polyethylene is produced by contacting ethylene with a Ziegler-Natta catalyst produced by: 
 contacting an alkyl magnesium compound with an alcohol to form a magnesium dialkoxide compound;    contacting said magnesium dialkoxide compound with a first agent selected from ClTi(O i Pr) 3 , ClSi(Me) 3  and combinations thereof, to form a reaction product “A”;    contacting said reaction product “A” with a second agent comprised of TiCl 4 /Ti(OBu) 4  to form reaction product “B”;    contacting said reaction product “B” with a third agent comprised of TiCl 4  to form reaction product “C”;    contacting said reaction product “C” with a fourth agent comprised of TiCl 4  to form reaction product “D”; and    contacting said reaction product “D” with a fifth agent selected from TMA, TIBAl, TEAl, n-octyl aluminum, n-hexyl aluminum and combinations thereof, to form said catalyst.    
   
   
       6 . The bimodal polyethylene of  claim 1 , wherein the polyethylene is produced in one or more slurry phase reactors.  
   
   
       7 . The bimodal polyethylene of  claim 1 , wherein the polyethylene is produced in one or more gas phase reactors.  
   
   
       8 . The bimodal polyethylene of  claim 1 , wherein the polyethylene is produced in one or more solution phase reactors.  
   
   
       9 . An article formed from the bimodal polyethylene of  claim 1 .  
   
   
       10 . A method of preparing a pipe or tubing, comprising: 
 obtaining a bimodal polyethylene, having a density of from 0.930 g/cc to 0.960 g/cc, and a molecular weight distribution of from 10 to 25;    processing the polyethylene under conditions in which a specific energy input (SEI) is less than 300 kW.h/ton; and    forming a pipe or tubing article, wherein said article has a PENT of at least 1500.    
   
   
       11 . The method of  claim 10 , wherein the pipe or tubing has a PENT of at least 3000.  
   
   
       12 . The method of  claim 10 , wherein the polyethylene is processed under conditions in which a specific energy input (SEI) is from 150 to 250 kW.h/ton.  
   
   
       13 . The method of  claim 10 , wherein the polyethylene is processed under conditions in which a specific energy input (SEI) is from 150 to 200 kW.h/ton.  
   
   
       14 . The method of  claim 10 , further comprising the step of controlling a suction pressure and a throughput of an extruder so that the Mz of the polyethylene in a pellet or tubing is with 10% of the Mz before the processing of a polyethylene fluff.  
   
   
       15 . The method of  claim 10 , further comprising the step of using Ziegler-Natta catalyst to produce said polyethylene  
   
   
       16 . The method of  claim 15 , wherein the Ziegler-Natta catalyst is produced by a process comprising: 
 contacting an alkyl magnesium compound with an alcohol to form a magnesium dialkoxide compound;    contacting said magnesium dialkoxide compound with a first agent selected from ClTi(O i Pr) 3 , ClSi(Me) 3  and combinations thereof, to form a reaction product “A”;    contacting said reaction product “A” with a second agent comprised of TiCl 4/ Ti(OBu) 4 .to form reaction product “B”;    contacting said reaction product “B” with a third agent comprised of TiCl 4  to form reaction product “C”;    contacting said reaction product “C” with a fourth agent comprised of TiCl 4  to form reaction product “D”; and    contacting said reaction product “D” with a fifth agent selected from TMA, TIBAl, TEAl, n-octyl aluminum, n-hexyl aluminum and combinations thereof, to form said catalyst.    
   
   
       17 . A method for controlling the degradation of polyethylene comprising: 
 polymerizing ethylene monomer;    recovering polyethylene;    extruding the polyethylene and controlling the degradation of the polyethylene during extrusion by: 
 measuring the specific energy input (SEI) to the extruder and  
 adjusting a process parameter selected from the group consisting of throughput, gear suction pressure, and a combination thereof to control SEI to less than 300 kW.h/ton; and  
 forming an article.  
   
   
   
       18 . The method of  claim 17 , wherein the article comprises pellets.  
   
   
       19 . The method of  claim 17 , wherein the article comprises a tubular member or pipe.  
   
   
       20 . The method of  claim 19 , wherein the article has a PENT of at least 1500 using test ASTM F 1473.  
   
   
       21 . The method of  claim 17 , wherein is PENT is increased as compared to a method otherwise identical except that the SEI is not controlled to less than 300 kW.h/ton.  
   
   
       22 . The method of  claim 17 , further comprising of the step of measuring Mz and controlling the SEI to minimize the change in Mz of the polymer to less than 10% of an Mz of the polymer before extrusion.