Effect Of Dispersion On The Properties Of PP/nano-CaCO₃ Composites

Nanometer calcium carbonate?nano-CaCO₃?is one of the few nanopowders synthesis at industrial-scale production.It has obvious advantages as a filler material for polymers,which can improve the toughness of the polymer without impairing the rigidity.Nano-CaCO₃ is also a kind of environment-frindly material and helps to ameliorate enviromental pollution.Due to its potential economic benefits and huge market prospects,the research on application of nano-CaCO₃ has been gaining attention in the last few decades for the plastic industry and the study on the various types of polymer/nano-CaCO₃ composites has been reported.Polypropylene?PP?is an important universal plastic which has a wide range of applications in many fields,such as automotive industry,household appliances,packaging and building materials.However,its toughness is poor at low temperature and its aging resistance is not good.Therefore,the research of modified PP with nano-CaCO₃ has received widespread attention.It is well known that the uniform dispersion of nano-CaCO₃ in the matrix has decisive influence on the properties of composite material,furthermore,the proper surface modification of nano-CaCO₃ is the key factor for the excellent performance.Considering the actual production process and cost,it's relatively difficult to use laboratory methods to implement surface modification in industrial production.Therefore,using the industrial equipment and process directly to implement surface modification has more important practical significance and application prospect.In addition,the studies on nano-CaCO₃ filled polymers were always concentrated on low filling content?1-10 wt%?in the past,and research of high filling content is conducive to the expansion of its application.In view of the problems above,the following work is done in this paper: the PP/nanoCaCO₃ composites are prepared by twin screw extrusion using several kinds of modified nanoCaCO₃.The morphology,mechanical properties,thermal properties,crystallization behavior and rheological behavior of the composites are studied systematically.The effect of nano-CaCO₃ dispersion on the mechanical properties of the composites is investigated significantly.The results and conclusions are as follows:?1?Some small molecules,such as coupling agents,dispersants,may become a defect in the system and reduce the mechanical properties of composites once it can not react with the active hydroxyl groups on the surface of nanoCaCO₃.?2?In the process of blending,the shape of the needle-like or cluster-like nano-CaCO₃ is broken by the screw shearing and the nano-CaCO₃ is completely dispersed in the form of granular or granular agglomeration.The dispersion and distribution of the particles are extremely uneven,which may seriously deteriorate the mechanical properties of the composites.?3?The addition of nano-CaCO₃ has a function of heterogeneous nucleation,which can make PP grow around the nano particles.Spherulites become smaller,spherical interface gets blurred,the melting and crystallization enthalpy of the composites decrease.With the increase of the filling amount,crystalline and thermal behavior of the composites shows the increase trend.?4?The nano-CaCO₃ modified by stearic acid is well dispersed in the PP matrix.Under the high filling capacity,the agglomeration size is below 0.5?m and the distribution is uniform.When the content of nano-CaCO₃ is 30 wt%,the impact strength of PP/nanoCaCO₃ composites increases by 81.6%,the flexural strength increased by 22%,the tensile strength decreased by 17.4%,and the flexural modulus increased by 27.8%.That is to say,the composites can obtain a greater increase in toughness with little loss of rigidity.?5?The fracture is ductile fracture for the composites with good dispersion of the nano particles in the matrix.There are a large amount of plastic deformation such as yield that can be observed at the fracture.Under the action of impact force,the submicron agglomeration can be partially deblocked to form crack holes which can prevent the development of cracks.