Preparation of ultrafine polypropylene/iron composite powders through pan-milling

A novel pan-milling technique was developed to prepare ultrafine polypropylene/iron composite powders, in which the average grain size of the iron particles attain a nanoscale level. The mechanical action of size reduction is attributed to the compression, stretching and fracture of cracks during pan-milling, pulverization and agglomeration which occur simultaneously and reach an equilibrium state at a certain milling stage. An average grain size of iron below 100 nm was obtained and reached 28 nm after 30 milling cycles while co-milling with polypropylene (PP). X-ray diffraction and TEM analyses indicate that iron oxide is formed on the outer layer of iron particles due to infiltration of air during milling. Ultrafine polypropylene/iron composite powders were prepared by pan-milling, crystalline structure of polypropylene is not found. The experimental results show that co-milling is more effective for the size reduction both for PP and iron, and retards the occurrence of counter-grinding process due to the agglomeration of fine particles, PP and Fe form intimate mixing state during pulverization.