Solid state modification of propylene polymers
A process for improving the melt characteristics of propylene-ethylene random block and impact copolymers is provided. The process involves contacting a powder of the copolymer with a low level of free radical initiator followed by heating at a temperature below the melting point of the copolymer and above the free radical initiation temperature.
1. A process for modifying the melt properties of propylene-ethylene copolymers comprising contacting a propylene-ethylene copolymer resin powder having an average particle size from 5 to 2500 microns with 0.5 to 500 ppm of a free radical initiator selected from the group consisting of organic peroxides, organic hydroperoxides and azo compounds at a temperature above the initiation temperature of the free radical initiator and below the melting point of the copolymer, said propylene-ethylene copolymers containing 55 to 99.5 wt. % propylene and 0.5 to 45 wt. % ethylene and selected from the group consisting of random copolymers, block copolymers and impact copolymers.
2. The process of claim 1 wherein the free radical initiator is an organic peroxide utilized in an amount from 1 to 250 ppm.
3. The process of claim 2 wherein the free radical initiator is selected from the group consisting of dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and t-amyl peroxypivalate.
4. The process of claim 1 wherein the powder has an average particle size from 75 to 2000 microns, the free radical initiator is an organic peroxide and the powder and organic peroxide are contacted at a temperature from 40° C. to 160° C.
5. The process of claim 4 wherein the propylene-ethylene copolymer is a random copolymer containing 65 to 99.5 wt. % propylene and 0.5 to 35 wt. % ethylene.
6. The process of claim 4 wherein the propylene-ethylene copolymer is an impact copolymer containing 65 to 99.5 wt. % propylene and 0.5 to 35 wt. % ethylene.
7. A process for modifying the melt characteristics of propylene-ethylene copolymers containing 55 to 99.5 wt. % propylene and 0.5 to 45 wt. % ethylene comprising adsorbing 0.5 to 500 ppm of a free radical initiator selected from the group consisting of organic peroxides, organic hydroperoxides and azo compounds on a powder of said copolymer having an average particle size from 5 to 2500 microns to uniformly distribute the free radical initiator throughout the entire powder volume and heating the powder at a temperature from 40° C. to 160° C. but below the melting point of the propylene-ethylene copolymer for a period of time sufficient to decompose substantially all of the free radical initiator and increase the ER of the copolymer at least 5 percent.
8. The process of claim 7 wherein the free radical initiator is an organic peroxide.
9. The process of claim 8 wherein the powder has an average particle size of 75 to 2000 microns, the organic peroxide is utilized in an amount from 1 to 250 ppm and the powder is heated at a temperature from 50° C. to 140° C.
10. The process of claim 9 wherein the organic peroxide is selected from the group consisting of dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and t-amyl peroxypivalate.
11. The process of claim 9 wherein the organic peroxide is utilized in an amount from 2 to 100 ppm and the powder is heated at a temperature from 75° C. to 130° C.
12. The process of claim 8 wherein the ER of the copolymer is increased by at least 10 percent.