Research On The Rheological Behaviors And Mechanisms Of Polypropylene Composites Filled With Multi-walled Carbon Nanotubes

As the most widely used and the fastest growing general plastic in the world,Polypropylene(PP)has advantages in sources,easy processing and excellent comprehensive performance.However,it has restrictions of low strength,poor cold resistance and flame retardant and so on in the use,which limit application of PP in some areas.Since carbon nanotubes(CNTs)is found,it has been paid attention by scientific community due to its unique structure and excellent performance.It has great prospect and important theoretical significance if we can use carbon nanotubes to modify polymer.In this work,three types of multi-walled nanotubes were chosen to prepare via melt blending with PP to get three types of PP/MWNTs composites.And rheological behavior s of PP/MWNTs composites were studied by capillary rheometer and rotational rheometer,thus could provide theoretical guidance for polymer processing.The results of capillary extrusion rheological experiment showed that flowing curve of PP/MWNTs was basically linear,which conformed to the power law.And melt apparent viscosity decreased with the increase of apparent shear rate.Moreover,adding MWNTs would hinder the mo vement of molecular chain effectively in the process of extrusion flow.Therefore,the apparent viscosity of composite materials got increased.Besides,obstacle ability of chain motion would increase with the increase of MWNTs aspect ratio.According to Arrhenius equation,it was concluded that with the increase of MWNTs aspect ratio,the viscous flow activation energy of PP/MWNTs composite got higher.Rheological datas were calibrated by Bagley theory and the results showed that total and entrance pressure drop of the PP/MWNTs composite got increased with the increase of MWNTs content.It mainly because that the mo vement of chain got slow due to addition of MWNTs,and parts of MWNTs would be stretched with storage and dissipation of energy.Besides,the increase of MWNTs aspect ratio was helpful to improve rheological elastic storage of PP/MWNTs composites,resulting in total and entrance pressure drop increased for PP/MWNTs composites.This result was attributed to coil degree and agglomeration of MWNTs in the PP matrix.The dynamic rheological test results showed that complex viscosity of PP/MWNTs composites got increased with the increase of MWNTs content.However,when the MWNTs content is too much,MWNTs would form three-dimensional network structure in the PP matrix,making PP/MWNTs composites showing obvious shear thinned behavior in low frequency area.Moreover,the increase of MWNTs content or MWNTs aspect ratio was helpful to increase energy storage modulus and loss modulus of PP/MWNTs composite.Howe ver,adding MWNTs would lead to appearing loss factor peak,and with increase of MWNTs content or MWNTs aspect ratio,network structure would get steady and loss factor peak of PP/MWNTs mo ved to high frequency area.At the same time,according to Cole-Cole curve,it was found that with the increase of MWNTs content or MWNTs aspect ratio,filler dispersion got worse due to agglomeration of MWNTs in PP matrix.The extrusion swell ratio test results was consistent with the rheological test.And value of the first normal stress difference was predicted by using Tanner model,Bagley model,Graessley model and Liang model.The predicted value kept same trend with shear stress change,and predicted value between Bagley model and Liang model had remained close.The end pressure drop was predicted according to several classic model and predicted value kept same trend with measured value.And minimum error was 5.8 % while maximum error was 17.6 %.For the medium long extrusion die,the prediction of extrusion swell ratio by Liang formula was much bigger than measured value due to gravity action.After correction,predicted value and measured value kept close,and error could be controlled within 5 %.