| Calcium sulfate whisker is a kind of polymer material reinforcement with excellent performance.It is cheap and has a wide range of sources.However,its surface polarity is high and its compatibility with polymer materials is poor.The current modification is mainly focuses on coupling agent and surfactant with low molecular weight.The winding and van der Waals forces produced by low molecular weight modifiers in polymer materials and polymer segments are limited,which limits the compatibility of calcium sulfate whiskers and polymer materials.In-situ graft polymerization modification has shown good effects in the modification of other inorganic powders.However,there are few studies on in-situ graft polymerization modification of calcium sulfate whiskers at present,so in-situ polymerization modification is applied It is of great significance to calcium sulfate whiskers.Using sodium oleate containing-C=C-as modifier,calcium sulfate whisker was modified in aqueous phase,and-C=C-was introduced to the surface of calcium sulfate whisker.Then PMMA was successfully grafted on the surface of the modified whisker by in-situ dispersion polymerization.Finally,the calcium sulfate whisker grafted and coated with PMMA was added to PP to prepare composite materials.（1）The modification effect and modification mechanism were characterized by sedimentation method,XRD,drift,XPS,SEM,TEM and other methods.The effect of sodium oleate dosage on the precipitation height of modified whiskers was that the sedimentation height of modified whiskers decreased slightly to 3.1 with a small amount of sodium oleate compared with unmodified whiskers when the modification time was 10 min and the modification temperature was 50℃.When the amount of modifier increased to 0.1 g,the settlement height increased to 10.6 cm,and then changed little.The modification time had little effect on the settlement height.Under the condition of modification time of 10 min and sodium oleate dosage of 0.2 g,the influence of modification temperature on the precipitation height of modified whiskers is that when the temperature reaches 70℃and 90℃from 30℃and 50℃,the sedimentation height of modified whiskers decreases rapidly from 10.5 cm and 10.0 cm to 3.1 cm and 3.2 cm.The critical amount of sodium oleate increased with the increase of temperature.Drift and XPS showed that oleic acid was adsorbed on the surface of whisker after modification,and two forms of oleate were adsorbed on the surface of whisker during modification.（2）In the process of in-situ grafting polymerization,the higher the reaction temperature is,the lower the grafting degree is.The highest grafting degree reaches0.61%at the modification temperature of 60℃.The grafting degree increases with the increase of initiator dosage.When the amount of initiator is 0.2g,the grafting degree reaches the maximum of 0.63%.The increase of the amount of initiator has no obvious effect on the grafting degree.When the temperature was 60℃,the amount of initiator was 0.2 g,the grafting degree first increased and then decreased with the increase of the amount of PVP.When the dosage of PVP was 0.3 g,the grafting degree reached the maximum of 0.65%.TEM showed that the calcium sulfate whisker grafted with PMMA was needle like core-shell structure,and the surface of calcium sulfate whisker was grafted with PMMA successfully.The contact angle of calcium sulfate whisker grafted with PMMA with water was 88.70°through contact angle test,which proved that the surface hydrophobic effect of PMMA grafted whisker was obvious,and it was expected to be an excellent reinforcement of polymer materials.Then the influence of whisker shape on the grafting degree was studied.The shorter the whisker was,the higher the grafting degree was.（3）The calcium sulfate whiskers modified by PMMA graft coating were added to the PP material.The results show that the tensile strength and bending strength of the material can be improved by adding 4%PMMA grafted and coated calcium sulfate whisker,reaching 17.49 MPa and 18.72 MPa,respectively,which are 7.2%and 6.9%higher than that of unmodified whiskers.Calcium sulfate whiskers grafted with PMMA can significantly increase the impact strength of PP to 48.9 kJ·m-2,which is 29.9%higher than that of pure PP.The cross-section of the composite material shows that the calcium sulfate whiskers grafted with PMMA can be tightly combined with the PP matrix.The whiskers grafted with PMMA on the surface can be entangled with the polymer chain of PP in PP,and the composite material can better transmit stress when it is broken under force,thereby improving the impact strength of PP material. |
