Simulation And Experimental Study On Centrifugal Melt Electrospinning

Centrifugal melt electrospinning,as a technology for preparing ultrafine fibers,has attracted wide attention from researchers because of its high yield,low cost,no solvent,and green environmental protection.However,the centrifugal melt electrospinning has severe experimental conditions such as high pressure,high speed and high temperature,which limits the research and development of this technology.In addition,the centrifugal force and the electric field force in the centrifugal melt electrospinning are the main driving forces for promoting molecular chain orientation and fiber refinement.The movement of polymer molecular segments during centrifugal electrospinning is critical to the performance of the prepared fibers,but little research has been done on them.This phenomenon seriously hinders the exploration of the trajectory and performance of the fiber during the centrifugal melt electrospinning,and limits the industrialization of the centrifugal melt electrospinning.In order to solve the above problems,this thesis carried out simulation and experimental research on the process of centrifugal melt electrospinning and the properties of its fibers.The aim is to obtain the influence of centrifugal force and electric field force on the movement of molecular chains during the spinning process through in-depth research,and promote the development of ultrafine fiber technology by centrifugal melt electrospinning.The main research contents are as follows:Firstly,the dispersive particle dynamics(DPD)simulation of the centrifugal melt electrospinning process was carried out,and the motion state of the fiber was observed by visualization software.The study explores the dynamic state of fibers and fiber properties through two types of electric fields.The first explores the effects of rotational speed,temperature,and electric field force coefficients in an ordinary electrostatic field.The second explores the effects of duty ratio and frequency under a pulsed electric field.It can be seen from the simulation that in the ordinary electrostatic field,the appropriate increase of the rotational speed,temperature and electric field force coefficient can refine the fiber to a certain extent,and increase the fiber yield and the degree of disentanglement of the fiber molecular chain.However,if the three parameters are too high,the opposite effect will occur.In addition,by observing the fiber trajectories of the three spinning parameters,it can be found that the influence of temperature on the stability of the jet is the greatest.When the temperature is too high,there will be messy fibers.In the pulsed electric field,when the duty ratio is 70%,the fiber diameter is the smallest.When the duty ratio is 100%,the degree of untangling of the fiber molecular chains is the highest.The frequency is inversely proportional to the fiber diameter and proportional to the degree of untangling.Secondly,the effect of polymer molecular weight(molecular chain length)on the spinning process and basic properties of fibers were studied by DPD simulation.At the same time,centrifugal melt electrospinning and straight barrel melt electrospinning were used to prepare L-polylactic acid(PLLA)fibers with different molecular weights.The morphology,crystallization properties,molecular chain orientation and mechanical properties of the fibers were characterized.The number of spring-to-particle spring bonds,i.e.the length of the molecular chain,was simulated using C++programming.The results show that when the length of the molecular chain is too large,it will hinder the disentanglement of the molecular chain inside the fiber,and the orientation becomes weak,so that the fiber diameter becomes larger.In the experimental part,three relative molecular mass PLLA fibers were prepared by straight barrel melt electrospinning and centrifugal melt electrospinning,respectively.The experimental results show that the fiber properties prepared by centrifugal melt electrospinning are better than the straight barrel melt electrospinning.Besides,the fiber diameter is only 1/3 of the straight barrel melt electrospinning,and the fiber morphology is evenly distributed.The results of differential scanning calorimetry(DSC)and polarization infrared spectroscopy(P-FTIR)test show that the preparation process of centrifugal melt electrospinning promotes the movement of molecular segments,and the entanglement between adjacent molecular chains makes the orientation of fiber molecular chains obvious.Scanning electron microscopy(SEM)images and mechanical test show that PLLA fibers prepared by straight barrel melt electrospinning have a large area of fracture and poor mechanical properties.By testing the performance of PLLA fibers of different relative molecular weights,the fiber diameter decreases as the relative molecular mass decreases.Analysis of P-FTIR and polarized light microscopy(POM)images shows that the fiber with a relatively small molecular weight has a higher degree of orientation of the internal molecular chain,and the tensile strength and Young’s modulus of the fiber are greatly improved.By comparison,the experimental results are consistent with the DPD simulation.Finally,different ratios of polylactic acid-polyvinyl alcohol(PLLA-PVA)composite fiber membranes were prepared by centrifugal melt electrospinning.The fibers were tested and characterized by SEM,thermogravimetric analysis(TGA),micro-commercial thermogravimetric analysis(DTG),water contact angle,gas permeability and biodegradability.Compared to pure PLLA fibers,PLLA-PVA composite fibers are smaller in diameter and can be as thin as 5.11 μm.Compared with pure PVA,the thermal stability of the PLLA-PVA composite fiber membrane is improved.At the same time,the application of PLLA-PVA composite fiber membrane in biomedical field was explored.The experimental results show that the PLLA-PVA composite fiber membrane has excellent wettability,gas permeability and biodegradability.Therefore,it basically meets the requirements for the use of wound dressings.In summary,this thesis uses DPD simulation and experimental characterization.By studying the influence of spinning parameters,process conditions of polymer raw materials with relative molecular mass on the.properties of centrifugally electrospun fibers,the optimal spinning conditions and molecular chain motion were explored.At the same time,the PLLA-PVA composite fiber membrane was prepared by centrifugal melt electrospinning and its application in the field of wound dressing was studied.