Study On The Preparation And Properties Of PA6/Anhydrite Composites

As a kind of inorganic filler, anhydrite(AII type) possesses the characteristics of sound and heat insulation, flame retardant, good abrasion resistance, etc. It has been investigated for numerous applications especially composites. However, the application of AII is largely impeded by its surface hydrophilicity as well as poor compatibility with other matrix materials. In order to change its surface hydrophilicity and improve the interactions between matrix and anhydrite for taking full advantage of anhydrite in composites, the activation treatment of anhydrite is an effective approach. In this research, the AII was activated by two approaches of high temperature calcination and surface modification. Based on previous step, the activated AII was used to modify nylon 6(PA6), then the PA6/AII composites were prepared. Subsequently, the influence of AII contents, activation approaches and coupling agent contents on the properties of the composites was investigated. The main contributions are as follows:(1)The AII was activated by two approaches of high temperature calcination and surface modification. Afterhigh temperature calcination, XRD results confirms the crystallization water in AII has been removed; results of SEM show that the dispersion of calcined anhydrite(c-AII) in ethanol solventis improved compared with AII. After surface modification, FTIR and XPS results reveal that KH560 has been attached to AII via covalent bonding; results of SEM display that the dispersion of surface modifiedanhydrite(AIIg) in ethanol solventhas been greatly improvedto the best dispersionstatus.(2)Based on(1), the anhydrite before and after activation was added to the PA6 matrix to prepare PA6/anhydrite composites and specimens by extrusion and injection molding. The influence of anhydrite contents and activation approaches on the properties of the composites was studied. The results of mechanical tests show that the best tensile strength and bending strength of composites are achieved when the content of anhydrite is 15 phr, and the surface modification is more conducive to the improvement of mechanical properties of composites than high temperature calcination. The results of XRD and DSC demonstrate that the addition of different anhydrite could promote the transformation of PA6 crystal type from ? phase to the less stable ? phase, and the content of ? phase of PA6 increases with the increasing anhydrite content. TGA results show that the there is little influence of AIIg contents on the thermal stability of the composites; the activation of anhydrite is beneficial to improve the thermal properties of the composites. SEM images display that, when the content of AIIg is below 20 phr, the AIIg particles disperse uniformly in the PA6 matrix and the interface combination between AIIg and PA6 matrix is good.(3)The AII was modified with different amounts of silane coupling agent, and then added to PA6 matrix to prepare composites. The effect of silane coupling agent amount on the properties of composites was investigated. The results of XRD and DSC indicate that the addition of anhydrite modified with different silane coupling agent amounts could promote the transformation of PA6 crystal type from ? phase to the less stable ? phase, and when the amount of silane coupling agent is below 1.5 wt.%, the content of ? phase of PA6 increases with the increasing silane coupling agent amount. In addition, the crystallinity of composites is increased to maximal value when the silane coupling agent amount is 1 wt.%. TGA results illustrate that the there is little influence of coupling agent amounton the thermal stability of the composites. SEM images show that the dispersion of anhydrite in the matrix and the interface combination between anhydrite and PA6 matrix are improved to the best when coupling agent amount is 1-1.5 wt.%.