Composite compositions from graft polymerized rigid fillers

DETAILED DESCRIPTION OF THE INVENTION In prior art methods of preparing filled thermoplastics, the thermoplastic matrix and the filler (either ungrafted or graft polymerized with a small amount of polymer to improve compatibility of the two components and strength of the final product) are intimately mixed in a separate step and the mixture processed under conditions stringent enough to give a completely homogeneous mixture of filler and matrix.
In practice, the loading level of filler (either grafted or ungrafted) in a thermoplastic matrix polymer will depend on a variety of factors.
With spherical filler particles, an upper loading limit will be set by the geometry of packing.
This will depend on both particle size and size distribution.
For example, Leidner and Woodhams [J.
Appl.
Polym.
Sci.
18: 2637 (1974)] used glass beads in a polyester resin at volume percentages ranging from 0-45%.
Needle-shaped filler particles, on the other hand, can be used at higher loading levels; if the particles are aligned and closely packed.
Often the loading limit will be determined by the processability of the filled system.
Graft polymerized fillers in the prior art have been surface grafted (as opposed to grafting within the filler matrix) and thus usually contain only about 5% grafted polymer [Bixler et al.
, U.
S.
Pat.
No.
3,471,439 and Mod.
Plast.
45: 143 (1968)].
Due to the low synthetic polymer content, loading levels of graft polymerized fillers and the mixing and processing requirements for the filled plastics are about the same as for ungrafted fillers.
We were surprised when we discovered that certain rigid fillers, when graft polymerized with thermoplastic polymers to give a synthetic polymer content of about 40-50%, could be processed by conventional methods, such as extrusion, in the total absence of any added matrix polymer, to give useful composite plastics.
We were further surprised when we found that our new plastic composites had mechanical properties comparable to those exhibited by conventional composite materials