The Surface Modification Of Anhydrite Whisker And Its Surface Modification Mechanism

Anhydrite whisker has good thermal stability,chemical resistance,low cost,high strength and great stiffness.It can be as a promising reinforcing agent in rubber,plastic,paint and so on.However,the small dimension with high surface free energy and low thermodynamic stability lead to readily aggregation.As filler,anhydrite whisker has low compatibility with organic matrix due to its hydrophilic and oleophobic properties.Surface modification is utilized as an efficient way to overcome the aforementioned drawbacks.In our study,surface modification of anhydrite whisker and its mechanism are studied intensively.Influences of the technical factors such as surfactant dosage,modification time,modification temperature were studied respectively.The products are investigated by X-ray powder diffraction(XRD),scanning electron microscope(SEM),Transmission electron microscopy(TEM),Fouier transform infrared(FT-IR)spectroscopy and X-ray photoelectron spectroscopy(XPS)to reveal the surface modification mechanism.The main contents of this paper are shown as follows:1.Anhydrite whisker was modified with inorganic-organic surface modification method.Trisodium phosphate was used to active the anhydrite whisker surface.Stearic acid as organic modifier was applied to modify the surface of anhydrite whisker.The inorganic-organic modifier is uniformly distributed on anhydrite whisker surface.The thickness of coating is 20 nm-50 nm.Anhydrite whisker surface character is changed from hydrophilicity to hydrophobicity.The contact angle of modified anhydrite whisker reaches up to 108°.2.Anhydrite whisker was modified with mono alkyl phosphate ester directly.The contact angle of modified anhydrite whisker reaches up to 97°.The thickness of alkyl phosphate layer is 20 nm-50 nm.FT-IR and XPS results show that the phosphate headgroup of mono-alkyl phosphate react with Ca on anhydrite whisker surface through forming chemical bonds.-Ca-SO4 and-Ca-O-PO2K-O-R coexiston anhydrite whisker surface.3.Hydrophobic anhydrite whisker was prepared via the hydrolysis and condensation process of tetraethyl orthosilicate followed by octadecyl trichlorosilane modification.The results indicate that anhydrite whisker surface character is changed from hydrophilicity to hydrophobicity after modification,which contact angle reached up to 123°.The modifier is absorbed on anhydrite whisker surface by hydrogen bond interaction.The thickness of surface modification layer is 10 nm-20 nm.