Structural evolution of palygorskite for reinforcing the performance of polypropylene

Raw palygorskite (RPal) and its structural evolution products (OPal) were modified with silane coupling agent KH-570 to form silanized KRPal and KOPal nanorods, which were used as eco-friendly nanofillers to prepare polypropylene/KRPal (PP/KRPal) and polypropylene/KOPal (PP/KOPal) organic–inorganic composites. Structure characterization results revealed that moderate oxalic acid (OA) leaching process can break Si-O-M bonds (M represents Mg, Al, etc.) of RPal nanorods to produce more active silanol groups, thereby improving the dispersibility, surface reactivity and surface silanization modification efficiency of RPal nanorods. After 24 h of OA leaching and silanization, the KOPal-24 h nanorod has the highest silane grafting rate of 4.05 %, which is significantly higher than that of KRPal (only 0.61 %). As a result, KOPal (especially KOPal-24 h) as a potential nanofiller improved the mechanical properties of PP/Pal composites more effectively than KRPal (tensile strength reaches 56.77 MPa for the PP/KOPal-24 h composite), which results from the large aspect ratio and relatively higher surface activity of OPal nanorods. In short, the reinforcing performance of Pal nanorods towards PP can be improved significantly by a simple acid leaching treatment, which would provide a universal and effective method to expand the potential application of natural nanoclays as nanofillers for the production of high-performance polymer composites.