Thermal, rheological, and mechanical properties of polypropylene/phosphate ore composites

Abstract

A low-cost and abundantly available calcareous phosphate ore can be used as an inorganic filler to fabricate various geopolymers and concreate composites based on plastics. However, the synergistic effect between this ore and polypropylene (PP) has not been thoroughly studied. This work describes the addition of phosphate ore as a reinforcement to PP, resulting in geopolymer composites through melt mixing and injection molding techniques. The purpose is to achieve value addition with this low-cost material and to establish structure–property relationships of the resulting geopolymer through analysis of the compatibility between the filler and the matrix. Differential scanning calorimetry analysis shows that the crystallinity for the PP/ore composites decreases from 43% to 37% compared with that of neat PP. The decrease in crystallinity is also confirmed by X-ray diffraction analysis. Thermogravimetric analysis shows that the composites’ thermal stability increased by 50 to 70℃. The increase in size of the ore particles from ~ 25 to 100 µm led to an increase in the Young's modulus from 1479 to 1749 MPa. The sample with small ore particles exhibits high complex viscosity in the entire angular frequency range. The complex viscosity of this sample at 0.01, 0.1, 1, 10, and 100 rad/s frequency is 2220, 1811, 1758, 961.5, and 376.5 Pa·s, respectively, which is the highest amongst the investigated samples. The linear dynamic viscoelasticity shows a greater increase in the storage modulus (G’) for smaller ore particles than for larger ones at lower frequencies. The storage modulus for the sample with a small particle size is 20 Pa, whereas that of the sample with large particles is 3 Pa. The morphological analysis shows a relatively weak interaction between the fillers and the matrix, which could adversely affect the tensile and impact strengths.