Study On Extrusion And Processing Parameters Of Polymeric Microtubes With Rectangular Microchannels

Rectangular channels are widely used in microfluidics,biological detection,micro-heat transfer and other fields because of their unique high-aspect-ratio channels with parallel walls and high specific surface area.However,at present,most of the rectangular channels are fabricated through the two-step method,which uses soft lithography or micro-injection molding technology to cut micro-scale rectangular grooves and then bond to substrate to encapsulate the grooves.This method has complicated process and high cost,but it is still difficult to achieve a high aspect ratio for the rectangular channel.In this study,based on the technology and experiences of extrusion of circular microtubes,rectangular microtubes with high aspect ratio are produced in one step by micro-extrusion.The effects of multi-factors are studied by numerical simulations and extrusion experiments.The research results can be apapted to direct the production of non-circular microtubes by micro-extrusion.The main researches and results are as following:(1)The numerical modeling is carried on for the extrusion process of single-channel rectangular tubes.The effects of the process parameters,the dimensions of extrusion dies and the material parameters on the aspect ratio and the morphology of rectangular microtubes are studied.the feasibility of producing rectangular microtubes with high-aspect-ratio channel by micro-extrusion is proved.According to the analysis of the deformation process of the extruded products,the inequality of extrusion swelling at the long sides and the shorts sides of the rectangular microtubes are the fundamental reson for the change of aspect ratio of microchannels,while the viscosity of polymer melt,the dimensions of the extrusion dies and the air flow rate are dominant factors for the aspect ratio of the rectangular channels.(2)Based on the results of numerical simulations,a specially designed extrusion die which can be connected to the air system is fabricated and LDPE with low viscosity is used to produce the single-channel rectangular microtube in one step.The results show that the actual air flow rate is effected by the polymer flow rate and hauling speed.By adjusting the processing parameters,the highest aspect ratio of rectangular channels achieved is 87,and the shape of the channel is still quite regular.In order to develop the potential applications of rectangular microtubes,they are used to observe and measure microdroplets inside the channel.Since the polymeric microtubes are easy to be secondary processed,they are also used to fabricate the integrated divece for preparation of large flux droplet.(3)According to the numerical and experimental results of single-channel rectangular microtubes,the effects of multi factors in the extrusion process of multi-channel rectangular microtubes are investigated by numerical simulations,especially for the resons of the non-uniformity of different channels.By modifying the dimensions of the extrusion die and using gas-assisted technology,the uniformity among the channels of the multi-channel rectangular microtubes is effectively improved.