Preparation And Performance Study Of PP/SEBS Foamed Cable Material

With the development of society and technology,robots have been widely used in industry,agriculture,service industry,high-tech and other fields,liberating people from tedious,dangerous and high-intensity labor.In order to meet the needs of underwater work,more underwater robots have come into people’s view.It is important to prepare a floating foam wire and cable for underwater robots with light material,small density,good mechanical properties and insulation properties.Polypropylene（PP）is a kind of polymer material with low density,excellent mechanical properties and insulation properties,and is the preferred resin matrix material for manufacturing floating foamed wires and cables.However,the melt strength of pure PP material is low,and its foaming property is poor,which is difficult to meet the use requirements,limiting its application in floating foamed wires and cables.Therefore,the melt strength of modified polypropylene material has become a research hotspot.In this paper,the melt strength of PP was modified by Styrene Ethylene Butylene Styrene（SEBS）.At the same time,the foaming system with Ethylene Vinyl Acetate Copolymer（EVA）as the carrier of the foaming masterbatch was studied to determine the optimal formula and process of the foaming masterbatch,and then the PP/SEBS foaming cable compound with excellent performance was prepared to meet the requirements of floating foaming wires and cables for underwater robots.In this paper,foaming masterbatch was prepared.The effects of blending process of foaming masterbatch and the content of EVA carrier on the mechanical properties,electrical properties,rheological properties and micro morphology of PP were studied.The effects of co foaming agent,foaming agent and nucleating agent on the foaming effect of PP were emphatically studied.The results showed that the best blending process of foaming masterbatch was temperature 140℃,rotational speed 40 r/min and time 8 min.With the increase of EVA content,the storage modulus,loss modulus and complex viscosity of PP/EVA materials decreased first and then increased,the breaking elongation increased first and then decreased,the tensile strength decreased all the time,the bulk resistance increased first and then decreased,and the breakdown field strength showed a downward trend.When the EVA content was 10 wt%,the performance was optimal.With the increase of the content of auxiliary blowing promotor,the decomposition temperature of foaming agent decreased gradually,the cell size of foaming material increased all the time,and the cell density increased first and then decreased;With the increase of the content of foaming agent and nucleating agent,the cell size first decreases and then increases,and the cell density first increases and then decreases.When the content of blowing promotor is 3 wt%,the content of foaming agent is 1.5 wt%,and the content of nucleating agent calcium carbonate is 1 wt%,the prepared PP foaming material has the best performance,and the cell size is 80μm.Cell density is 1.16×10⁴（pieces/cm³）,tensile strength 11.64 MPa,elongation at break 218.47%.The optimum foaming masterbatch formula was obtained as follows:EVA content 68.9 wt%,blowing promotor 20.7 wt%,foaming agent content 10.3 wt%,nucleating agent content 6.9 wt%.At this time,the amount of foaming masterbatch in the foaming system was 14.5 wt%.Then PP/SEBS foam matrix was prepared.The effects of different SEBS contents on the rheological properties,micromorphology,mechanical and electrical properties of PP/SEBS foam matrix were studied.The results showed that with the increase of SEBS content,the storage modulus,loss modulus and complex viscosity of PP/SEBS foam matrix materials were increasing.At the angular frequency of0.119 rad/s,when the content of SEBS in PP/SEBS composites was 30 wt%,the storage modulus and loss modulus of the composites were 179 Pa and 581 Pa,respectively,The complex viscosity is 5100 Pa·s,which is 275%,22%and 27%higher than that of pure PP respectively;The elongation at break shows a trend of first increasing and then decreasing,the tensile strength has been decreasing,the volume resistance first increases and then decreases,the breakdown field strength shows a downward trend,and the Shore hardness A gradually decreases.Further,PP/SEBS and foaming masterbatch were blended and extruded to prepare foamed cable materials.The foaming characteristics,mechanical and electrical properties of PP/SEBS foamed cable materials were studied and compared with the matrix materials.The results showed that the tensile strength of PP/SEBS foamed cable material first decreased,then increased,and finally decreased.The breakdown field strength first decreased,then increased.The density of the foamed material showed a downward trend.Other property changes were consistent with those of the above foamed matrix materials;When the content of SEBS is 30 wt%,the comprehensive performance of foamed PP/SEBS cable compound is the best,and the cell size is 65μm.Compared with pure PP foamed material,the foam cell density decreased by 18.75%and was 2.7×10⁴（pieces/cm³）,133%higher than that of pure PP foamed material,and the distribution is the most uniform,with breaking elongation of 876.28%,tensile strength of 13.17 MPa,and volume resistivity of7.5×10¹³Ω·m,the breakdown field strength is 18.54 k V/mm,which is 13.71%,41.04%,33.6%and 24.54%lower than that of the base material respectively,with the smallest drop.The Shore hardness A and density of the foam cable material are 79 and 0.4 g/cm³respectively.Finally,the extrusion process of PP/SEBS foamed cable compound was studied.The results showed that the cell size of PP/SEBS foamed cable material increased gradually with the increase of mold temperature,and the cell density increased first and then decreased.When the mold temperature was 180℃,the cell structure was the best;With the increase of screw speed,the cell size of PP/SEBS foamed cable material decreased,while the cell density gradually increased.When the screw speed was 50 r/min,the cell structure was the best.The optimum extrusion process was obtained as follows:the temperature of the extruder body I,II and III areas were160℃,165℃and 170℃respectively,the die temperature was 180℃,and the screw speed was 50 r/min.