Heat stability of asbestos-filled polypropylene

Abstract

Polyester forming reactants of low volatility including an organic acid or anhydride such as trimellitic anhydride, and a polyhydric alcohol, such as dipentaerythritol or pentaterythritol, are admixed at a temperature above 400° F. with partially stabilized polypropylene and asbestos filler to provide a heat stabilized, asbestos-filled polypropylene composition.

What is claimed is: 
     
       1. A process of producing an asbestos reinforced, heat-stabilized polypropylene article comprising: (a) admixing at a temperature above about 400° F. a mixture comprising, in parts by weight .[.per 100 parts by weight of polypropylene.]., 1 to 2 parts of polyester forming organic acid of acid anhydride having a melting point of 250°-550° F.; 1 to 2 parts of a polyhydric alcohol having a melting point of from 250°-550° F.; 10 to 40 parts of asbestos fiber; and .Iadd.sufficient .Iaddend.polypropylene resin .Iadd.to make a total of 100 parts of admixture.Iaddend.; and   (b) molding the admixture to produce a stabilized article.   
     
     
       2. The process of claim 1 including the step of prefluxing at a temperature above 400° F. the ingredients of said mixture other than said asbestos fiber before the admixing step. 
     
     
       3. The process of claim 2 in which the asbestos fiber is chrysotile and including the step of drying the chrysotile asbestos fiber at a temperature above about 350° F. before the prefluxing step to remove moisture from the fiber which would otherwise distill from the mixture. 
     
     
       4. The process of claim 1 in which the organic acid or anhydride is trimellitic anhydride and the polyhydric alcohol is dipentaerythritol. 
     
     
       5. The process of claim 4 in which said mixture includes about two parts by weight of trimellitic anhydride, two parts by weight dipentaerythritol and 35 to 40 parts by weight of asbestos fiber. 
     
     
       6. The process of claim 1 in which 0.5-2.0 parts by weight of a free radical inhibitor selected from the group consisting of hindered phenols and organic phosphites is admixed with the asbestos fiber and polypropylene resin. 
     
     
       7. A heat-stabilized filler-reinforced polypropylene composition comprising, in parts by weight .[.per 100 parts by weight of polypropylene.]., 35 to 40 parts of asbestos fiber, .[.polypropylene, and.]. the product of compounding 1 to 2 parts of an organic acid or anhydride and 1 to 2 parts of a polyhydric alcohol, the organic acid or anhydride and the polyhydric alcohol having a melting point of from 250°-550° F., in the presence of the asbestos fiber and polypropylene at a temperature above about 400° F..Iadd., and sufficient polypropylene resin to make a total of 100 parts of composition.Iaddend.. 
     
     
       8. The composition of claim 7 in which approximately equal parts by weight of trimellitic anhydride and the polyhydric alcohol are present. 
     
     
       9. The composition of claim 8 in which the polyhydric alcohol is dipentaerythritol. 
     
     
       10. The composition of claim 8 in which asbestos is chrysotile asbestos.