Dispersion of nano-clay at higher levels into polypropylene with carbon dioxide in the presence of maleated polypropylene
The use of supercritical carbon dioxide (scCO2) has proven to be beneficial for surface modified montmorillonite (MMT) nano-clay dispersion up to 6.6 wt% in a polypropylene (PP) matrix and lead to improved material mechanical properties in our earlier research. Our further modifications of the processing procedure including a sequential mixing technique successfully extended the technique to PP composites with as much as 10 wt% of clays and continuously increasing mechanical properties. In order to obtain additional enhancements of the composite properties at this clay level, polypropylene grafted with maleic anhydride (PP-g-MA) is included in this work. The results from the studies of the mechanical properties, rheological properties, and transmission electron microscopy (TEM) show that PP-g-MA is greatly beneficial in generating an exfoliated nano-clay morphology. Greater enhancements in the mechanical properties and nano-clay dispersion in the polymer matrix are observed when PP-g-MA is combined with the scCO2 and sequential mixing techniques. The PP-g-MA based nano-clay composites have a high degree of exfoliated structure even with the addition of up to approximately 10 wt% nano-clay when using this technique, with mechanical properties such as yield strength and Young's modulus being increased by as much as 12 and 88%, respectively, relative to the polymer matrix. It is believed that the modulus reported here is the highest reported in the literature for conventional PP's.