Process for dispersing a thermally sensitive additive into a melt
A continuous process for incorporating a thermally sensitive additive into a polymer melt of virgin polymer at a temperature at least 10° C. below a temperature at which the virgin polymer is typically processed. The virgin polymer is first processed in an apparatus which extensively shear-thins the polymer until its normally entangled molecules are substantially disentangled. This is preferably done in a TekFlow® processor. The additive is then added to the resulting modified melt which is then processed in a high-shear apparatus, e.g. a co-rotating, twin-screw extruder, but more preferably in a second TekFlow® processor. This novel process allows making concentrates having a level of additive which could not be made to date and yet have the additive substantially uniformly dispersed. In particular a concentrate of polypropylene having a 30% by wt concentration of an organoclay in which the platelets are substantially uniformly dispersed, at least 10% more strongly intercalated than prior to treatment, and substantially fully exfoliated, is made with this process.
1. A process for incorporating an additive into a fluid virgin polymer melt comprising:
providing a polymer melt comprising virgin polymer to a first stress-fatiguing means;
stress-fatiguing the polymer melt to obtain a stress-fatigued polymer melt;
adding a thermally sensitive particulate additive to the stress-fatigued polymer melt, the stress-fatigued polymer melt being at a temperature at least 10° C. lower than the fluidization temperature of the virgin polymer, to yield an additive-rich melt, and the fluidization temperature being above the degradation temperature of the additive;
feeding the additive-rich melt into a feed-inlet of a mixing means; and
providing sufficient energy of mixing in the mixing means to disperse the additive substantially uniformly throughout the additive-rich melt without raising the temperature of the additive-rich melt by more than 10° C.
2. The process of claim 1 wherein the additive comprises particles in a size range from about 10 nm to 212 μm.
3. The process of claim 2 wherein the temperature of the polymer melt entering the first stress-fatiguing means is at least 10° C. below the temperature of the polymer melt leaving the first stress-fatiguing means.
4. The process of claim 3 wherein the mixing means is a second stress-fatiguing means.
5. The process of claim 3 wherein the additive is selected from the group consisting of flame retardant, conductive polymers, light stabilizers, thermal stabilizers, antistatic agents, biocides, coupling agents, peroxides, blowing agents, pigments, nanoclays, and a combination of one with another.
6. The process of claim 3 wherein the virgin polymer is selected from the group consisting of a substantially crystalline polymer, a substantially amorphous polymer and a partially crystalline polymer, and the melt is essentially free of a dispersing agent.
7. The process of claim 3 wherein the additive is selected from the group consisting of alumina trihydrate, wood flour, polyaniline polymer and an organoclay.
8. The process of claim 3 wherein the additive comprises nanoparticles in a concentration between about 1% to 40% by weight.
9. The process of claim 3 wherein the additive comprises micron-sized particles in a concentration between about 1% to 50% by weight.