Polymer Composite With Oriented Nano Particles And Their Microcellular Foaming

Polymeric foams have been widely used in the fields of automobile,aviation,packaging and construction because of its light weight,low cost,good elasticity and cushioning performance.Some properties of the polymeric foams need to be achieved by the addition of nanoparticles,and the addition of nano particles could also play a good heterogeneous nucleation and produce more nucleation point of the foam,which results in the formation of larger cell density and smaller cell size.Meanwhile,different dispersed forms of nanoparticles had great influence on the cell structure and even the polymer properties.In this paper,we focus on the effect of the dispersion and orientational dispersion of nanoparticles on the foaming properties of the polymer,thermoplastic polyurethane was used as the polymer matrix to prepare nanocomposites with graphene（G）and carbon nanotubes（MWNT）,respectively.Mainly to carry out the following aspects of the work:Polymer nanocomposites with different contents of nano particles were prepared by a combination of solution and melt blending,from which TPU composite fibers with different diameter sizes were fabricated via melt spinning with different drawing rate.Subsequently,foamed TPU composite fibers were prepared by a batch foaming process using supercritical carbon dioxide（ScCO₂）as foaming agent.The dispersion of nano particles in the composite fibers was characterized by TEM.The results showed that nano particles could be dispersed uniformly in the TPU matrix,showing good dispersion morphology and interfacial compatibility.The cross section of the foamed fiber was scanned by SEM to investigate the cell structure,the cell size and the density.The results showed that the expansion portion of the fibers of 200 μm was great increased by the presence of nano particles and the range of foaming increases significantly.By adding 5.0 wt% nano particles into the composite fibers of 500 μm,the cell size and cell density were decreased and increased from ³.8 μm and 4.93×109 cells/cm3 in pristine TPU foam to ².0 μm and 2.42×1010 cells/cm3.In view of the mechanical traction spinning process leading to the process of nano particles along the tensile force in the direction of partical orientation,nano composites with different compression ratios were prepared by pressure induced flow processed with different content of nano particles,in which could further investigate the effect of orientation dispersion of nano particles on the foaming properties of the polymer.The results showed that different compression ratios have little effect on the cell size and density of pure TPU.For TPU composites,the larger compression ratio made the nano particles more closely packed in the polymer,and improved the polymer melt strength when the compression ratio reached 1:4,the cell size decreased to the maximum,which decreased from 1.86 μm to 1.43 μm with 5 wt% nano particles added.In addition,tensile strength of TPU composites at 300% strain was conducted.The results showed that the tensile strength of TPU was increased from 33 MPa to 47.5 MPa,and the tensile stress increased by 43.9% when the nano particles were incorporated of 3 wt%.The dynamic rheological analysis of the TPU composites was carried out by using the super expanding rheometer.The result showed that the storage modulus and loss modulus of the TPU composites increased with the increase of the nanofiller content.