The Preparation And Fiber Formation Mechanism Of Centrifugally Spun Starch-based Fibers From Amylopectin Rich Starches

As a kind of important bio-based fibers,researchers had paid attention to prepare starch-based fibers for a long time.However,the traditional melt,dry,wet spinning teniques,and even electrospinning were difficult in preparing pure starch-based fibers from native starches,which due to the high ratio of amylopectin in many native starches.In this thesis,we tried to prepared starch-based fibers from amylopectin rich native starches by using centrifugal spinning.The formation mechanism of fibers was analyzed.The obtained results would provide theoretical and experimental basis for further exploring and utilizing of starch-based fibers,and preparing fiber from other branched polymers or polymers with branch chains as well.This thesis includes the following three parts:(1)The spinnability of amylose roch corn starch,native corn starch,waxy corn starch,and potato starch were investigated by using self-made centrifugal spinning setup.The effect of amylopectin on the spinnability of starches was analyzed.And the formation mechanism of surface morphology for native starch-based fibers and the controlling methods were studied.Resulted showed that starch-based fibers could be prepared from amylose rich corn starch with amylose content of 77.87%,native corn starch with amylopectin content of 68.89%,and native potato starch with amylopectin content of 73.35%,which by adjusting the solution concentration,nozzle diameter,rotational speed,nozzle to collector distance,and by supplementing hot air.The obtained fibers had narraw diameter distributions and with average diameters below 2?m.The critical entanglement concentration(c_e)of the starch solution decreased with the increase of amylopectin content.Waxy corn starch with amylopectin content of 90.58%had no critical entanglement concentration,and therefore was failure in fiber preparation.The results for surface morpsologies formation mechanism of fibers indicated that"needle-shaped"nanostructures on the surface of starch-based fibers were formed by the rearrangement of short-branch chains in the amylopectin at an angle along the jet axis during centrifugal spinning,and shown on fiber surface by prompting the phase separation of amylopectin and amylose.Therefore,the surface morphology of the fibers could be controlled by changing the hot air temperature and the ratio of amylopectin/amylose.(2)The initial jet and jet trajectory of the starch solution during the centrifugal spinning proceeding were captured by the SLR camera,and compared with jet evolution of PVP solution and electrospun starch solution,which in orded to observe the characteristics of jet evolution.Resulted indicated that initial jets were always moving toward the reverse direction of spinneret rotation and including initial thinning.The initial jets and its initial thinning were affected by the solution concentration,nozzle diameter and rotational speed.The jets formed by starch solution were always including steady-state and unstable jets.Among these,the unstable jets contained traveling wave disturbance and Rayleigh-Taylor instability,and were easily broken into droplets.By contrast,polyvinylpyrrolidone(PVP)solution could form steady-state jets to form fibers at the spinning concentration.The relationship between radius of jet trajectory and the jet arc length indicated that the radius of jet trajectory increased exponentially with the increase of the arc length with the trend gradually slow down,and this relationship was not affected by solution type and spinning parameters.The results of spinnability test for starch and PVP solution at different concentrations showed that the fiber formed by the starch solution always containing some of beads,while the beads on the PVP fiber webs were decreased significantly or even expected to eliminate with the increase of concentration.This could be due to the linear macromolecular chain structure of PVP had stronger chain entanglement at the spinning concentration,and was easily to move and rearrange along with jet axis during jet stretching process,which improved the jet stability.In addition,the jet breakup arc length could be decreased by increasing the amylopectin content,while pure amylopectin solution could form jets with certain arc length in the centrifugal spinning system as well.In the electrospinning system,only the native starch and amylose could form jets with a certain arc length,but could hardly form a jet from the amylopectin solution.(3)The water stability of starch-based fiber was improved by cross-linking method.Poorly water soluble ibuprofen and ketoprofen were chosen as model drugs to prepare the drug-loaded fibers,and the release properties of fibers were investigated.We found that the water stability of corn starch-based fibers could be improved obviously after treating with 4%(w/w)citric acid ethanol solution at165°C for 10 min,while the potato starch-based fibers were better to treat with 8%(w/w)citric acid ethanol solution under the same treatment conditions.Neverthless,the harsh treatment temperature for this method might limit the application of fibers in the temperature sensitive fields.Therefore,we also investigated the effect of glutaraldehyde/acetate solution on water stability of fibers in the form of vapor phase.Results indicated that the water stability could be improved after treating fibers at40°C for 12 h.The mild processing conditions of this method made up for the shortcomings of the former method.By adding a small amount of polyethylene oxide(PEO),the tensile strength of fibers could be effectively improved,and drug-loaded fibers with starch/drug/PEO ratio of 40/20/1 could be successfully prepared.The release properties of drug-loaded fibers indicated that more than 75%of loaded drugs could be released from fibers and the release time cuold reach 48 h in the absence of burst release(drug release?80%within 2 hours).