Study On Thinning Of Multi-stage Draft Fibers Assisted By Hot Airflow In Polymer Melt Differential Electrospinning

The thinner diameter and the larger the specific surface area of the polymer fiber,the function of the unit weight of the polymer material is stronger.Therefore,fiber thinning has always been a research hotspot in the field of fiber manufacturing.The masks that have been widely used in the recent epidemic of new coronaviruses rely on finer polymer fibers and electrostatic adsorption effects to achieve aerogel filtration,but the fiber fineness of masks on the market is still a few microns.It is significant to achieve fiber from from micrometers to nanometers.Electrospinning technology has opened up a new way for industrialized manufacturing of fibers from micrometers to nanometers.In recent years,it has attracted a lot of attention from academia and industry.In connection with the problems of low efficiency,solvent pollution,and easy clogging of traditional capillary solution electrospinning technology,my team had proposed a new method of melt differential electrospinning.PP with an average fiber diameter of 990 nm and micron grade PLA fiber had been prepared.How to make the fiber fineness within 800 nm and close to the 300 nm of solution electrospinning is challenging.Auxiliary airflow helps to further draw down the differential multiple jets,and auxiliary hot airflow helps the drawing process to keep the jets in a molten state.Previous studies in world had conducted studies on airflow-assisted electrospinning,but they were not matched with melt differential electrospinning system,and the researches were not thorough enough.This subject is based on melt differential electrospinning technology and equipment,and it is proposed to change the auxiliary air temperature and air flow loading method to further refine the fiber.The specific research content is as follows:A new technology of multi-stage draft fiber assisted by two-stage loading airflow assisted melt differential electrospinning was introduced,and innovatively led into two airflows simultaneously in melt differential electrospinning technology.A heated air flow was led out from the central air intake pipe inside the spray head,and a normal temperature air flow led to the air flow ejector under the spray head.Multistage stretching and thinning process of differential multi-jet flow was formed by the first-stage heating air flow,the second-level normal temperature air flow at the entrance of the ejector,the second-level normal temperature air flow and the high-pressure electrostatic.It was studied the relationship between the diameter and distribution of the fiber and velocity and temperature of first-stage heating airflow.The results showed that the increase of the temperature and speed of the first-stage heating air flow would reduce the average fiber diameter and improved the uniformity of fiber diameter.The best spinning process parameter range was the first-stage heating air temperature is 120?160?,and the air speed is 78.6?117.8 m/s(air flow rate is 8?12 m3/h),and it successfully made PLA fibers with an average diameter of 610 nm and PP fibers with 810 nm.It was proposed that a new technology of multi-stage drafting fibers by melt differential electrospinning assisted by negative pressure hot air flow.This research innovatively introduced heated airflow into the airflow ejector under the nozzle.It was formed a multi-stage drafting effect on the jet that the electric field between the nozzle and the ejector,the local negative pressure air flow formed by the hot air flow at the nozzle of the ejector,and the hot air flow ejected by the ejector.And the research expounded the relationship between the airflow temperature,the spinning distance and diameter and uniformity of the fiber,and studied the effect of airflow temperature on the porosity and pore size distribution of fiber membranes.It was concluded that the optimal spinning interval parameters were heating air temperature 80?120?,spinning distance 5?7 cm,and PLA fiber with an average diameter of 400 nm was successfully prepared.Finally,the above process parameters were applied to the development of thermoplastic TPU ultrafine fibers.The TPU fiber with an average diameter of 1.21 ?m was successfully made by using the negative pressure hot air flow assisted multi-stage drafting process.Compared with the TPU fiber made by capillary melt electrospinning process(above 10 ?m),the TPU fiber diameter was reduced by more than 80%.It was equivalent to the diameter of laser-heated electrospun TPU fiber(0.9?1.7?m),and the study had improved the preparation efficiency by 40 times.In summary,it was proposed that a new technology that two-stage loading airflow-assisted melt differential electrospinning multistage drafting fiber and hot airflow-assisted melt differential electrospinning multistage drafting fiber in this paper,which realized the reduction of PP and PLA fiber diameter and improved the fiber diameter distribution uniformity;further based on hot air flow assisted multi-stage drafting optimization process for TPU melt differential electrospinning new material development,made TPU fiber preparation efficiency and fineness ahead of other melt spinning techniques.This article provided a new method for the exploration and development of the melt electrospinning fiber refinement process.This research result is expected to be applied to industrial production.