Linear polyethylenes stabilized against melt index drop with aromatic sulfonhydrazides
BACKGROUND OF THE INVENTION 
     Linear polymers of ethylene such as high density polyethylene (HDPE) and linear low density polyethylene (LLDPE) exhibit melt index (MI) drop during melt processing, for example, during extrusion. Compositions of this invention are stabilized to reduce the drop in melt index normally experienced. 
     SUMMARY OF THE INVENTION 
     This invention relates to compositions comprising a linear polymer of ethylene such as high density polyethylene or linear low density polyethylene copolymers and an amount of an aromatic toluene sulfonhydrazide which is effective to stabilize the composition against a drop in melt index during melt processing. 
     The aromatic sulfonhydrazide is preferably a benzene or substituted-benzene sulfonhydrazide. Para-toluene sulfonhydrazide has been found to be particularly effective. 
     The aromatic sulfonhydrazide is incorporated into the composition in effective amounts generally range from about 0.01 to 2 weight percent. The aromatic sulfonhydrazide can be introduced into the composition in any convenient manner, such as by direct addition or by introduction with a master batch containing an ethylene polymer and a higher concentration of the aromatic sulfonhydrazide. The master batches then can be diluted with additional virgin ethylene polymer to achieve the necessary concentration in the composition as disclosed herein. 
     The compositions can also contain conventional ingredients, such as fillers, antioxidants, stabilizers and the like. 
     As indicated, the ethylene polymer can be a high density polymer of ethylene or a linear low density polymer of ethylene. Linear low density ethylene polymers are copolymers of ethylene and a higher olefin and contain a sufficient amount of the higher olefin so that the copolymer has a density in the range of about 0.90 to about 0.94, preferably 0.91 to 0.93. The higher olefin is commonly 1-butene, 1-hexene, 4-methyl-1-pentene, or 1-octene. Such materials are disclosed in U.S. Pat. No. 4,076,698, which is incorporated herein by reference in entirety, and are widely available. 
     The invention is illustrated by the following examples in which all parts are by weight. 
    
    
     EXAMPLES 1-4 
     Para-toluenesulfonhydrazide (PTSH) 97%, was added to two different resins a linear low density polyethylene (LLDPE) and a high density polyethylene (HDPE) to determine the effect on melt index. Blends were passed through a Brabender twin screw extruder three times successively at 275° C. and 70 rpm. Residence time was 40 seconds. Enough resin was retained after each pass for melt index (MI) determinations which are summarized in Table 1 below. 
     
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EXAMPLE  C-1    1         2      C-2   3    4                             
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LLDPE    400 g  400     g   400  g   --    --   --                        
HDPE     --     --        --     400   400  400                           
PTSH     --     0.4     g   0.8  g   --    0.4  0.8                       
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 LLDPE -- ethylenehexene copolymer, density 0.925                         
 HDPE -- ethylene homopolymer density 0.952                               
 
    
     
                       TABLE 1                                                     
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          M.I.    M.I.       M.I.  M.I.                                   
Example   Pass 0  Pass 1     Pass 2                                       
                                   Pass 3                                 
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C-1       0.93    0.35       0.23  0.15                                   
1         --      0.62       0.56  0.71                                   
2         --      0.63       0.62  0.75                                   
C-2       0.74    0.40       0.14  0.09                                   
3         --      0.50       0.38  0.28                                   
4         --      0.61       0.41  0.44                                   
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     EXAMPLES 5-6 
     In a manner similar to that described in Examples 1-4 a LLDPE copolymer of ethylene and butene was blended with 0.1% PTSH in the Brabender extruder at 186° C. The Melt Index of the blends was measured and reported in Table 2. 
     
                       TABLE 2                                                     
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With LLDPE Alone   LLDPE With PTSH                                        
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Pass 0       1      2     3    0     1    2     3                         
MI   1.75    1.38   1.02  0.67 1.75  1.64 1.63  1.36                      
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     Although the present invention has been described with preferred embodiments, it is to be understood that modifications and variations may be restored to, without departing from the spirit and scope of this invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the appended claims.