Study Of Flexible/Rigid Chain Polymer Solutions And The Aggregation Structure Of The Resultant Fiber

As polymer fiber are getting used in industry and aerospace,national defense and other advanced science,the application of fiber expands sharply,so the performance of synthetic fiber need to cover every possible range of practical applications.In this thesis,we studied different systems of polymer,flexible and rigid molecular chains,to get the information of the aggregation structures,solutions,amorphous and crystal states.Also,we did quantitative analysis of the orientation structures of crystal/amorphous phase under heat treatment.High performance fiber with rigid chain can only dissolve in strong acid and the processing condition is rigorous.Therefore,a new kind of soluble polyarylether was selected in this paper,using conventional solution processing method,the feasibility for new high performance fiber and the fiber structure was systematically analyzed.For rigid chain system,the apparent viscosity of PPEK/NMP solution increased dramatically along the mass concentration and molecular weight of polymer.PPEK solution obeyed Newtonian behaviour when mass concentration under 30 wt%,while deviated when concentration over 40 wt%.The solution showed sensibility to temperature,by which we could control the viscosity effectively.PPEK fibers were fabricated by dry spinning of 40 wt%solution.The X ray result indicated that no crystal structure in PPEK fiber,even under hot stretching for several times.But there is certain sufficient intermolecular force in fiber forming through dry spinning.PET has similar chemical structure with PPEK,but molecular orientation will trigger crystallization easily for PET.To investigate the orientation mode for perfectly amorphous polymer chains of PPEK quantitatively,the radian distribution function(RDF)for undrawn PPEK film and PET film were calculated.The most probable distance for neighbor chains for PPEK random system was 0.481 nm,which was larger than that of PET(0.471 nm).Because of the benzene-naphthalene twist structure of PPEK,even there was orientation for molecules,it will never crystallize.On the opposite,neighbor PET chains will form zig-zag formation,and crystallize easily.Most probable distance between adjacent molecular chains was evaluated as the first trial for oriented amorphous polymer PPEK,using the two-dimensional radial distribution function formulated by a series expansion of Bessel and Legendre functions of coherent X-ray intensity curves.Additionally,the strain between adjacent PPEK chains under external stress along the fiber axis was measured by a homemade instrument in relation to the chain orientation degree.These results indicated that the amorphous chains were connected with strong intermolecular force between adjacent PPEK chains,and the force could achieve fiber spinning.A series of UH blend gels were made using paraffin oil as solvent,and systematic rheological measurements were conducted to investigate the effect of introducing HDPE to the pure UPE gel.Adding several times of solid content of HDPE to the UPE gel would enlarge neither the apparent viscosity nor the moduli of the previous system.The UH blend gel also showed excellent compatibility during measurement,which is good for the resultant gel-spun fibers.Nascent fiber underwent hot stretching after spinning to different draw ratios to study the drawing-property relationship.The orientations of PE crystal become better along hot drawing.Due to the transforming from folded chain into extended chain,Lfibril went lager when ? ? 45,while Lfibril decreased under further drawing when ?>45,which is because of the breakage of fibril and recrystallization.The tensile strength of fiber went the same evolution as fibril length,indicating Lfibril would definitely affect the mechanical property of fiber.Tensile strength of UH55-45 fiber was 15.6 cN/dtex,of which would fulfill the demand in industrial use,and this could provide another option for fiber development.Situation becomes a little different when it comes to UHMWPE/LDPE system.UL gels were made with the mass fraction of U/L fixed to 1/1,but the total mass content varied form 2 wt%(sample name UL-2)to 10 wt%(UL-10).The UL-10 sample presented an obvious shear thinning behavior,and exhibited a lower apparent viscosity than that of UPE-5 gel,in spite of the twice solid content of the latter one.The UL gels had a high solid content but a lower viscosity,which permits the gel good spinnability and high efficiency.Also,according to the rheological results,no obvious phase separation was found during spinning temperature.At the same time,UL gels showed much shear thinning than UPE gel,due to the more branch structure of LDPE compared to the liner structure of HDPE,which also caused the lower orientation degree of Lfibril in UL fiber than UH fiber.GR was selected as improvement filler to UPE fiber.UPE/GR blend gels were made by adding 1%or 5%GR based to polymer weight.The viscosity increased a little as adding 5%GR content,which would not affect the spinning process.The crystallinity and orientation degree of PE both decreased as the present of GR,while tensile strength and elongation at break of blend fibers both increased on the contrary.The result indicated that,GR has strong interrelation with polymer chains,which could help bearing the stress when stretching.That is why the tensile property improved.In conclusion,relevant issues should be noticed since it has different sensitivities to external condition when the polymer chains are flexible or rigid structures.Spinning and follow-up processing should be carefully conducted on fabricating fibers aiming at relatively high performance materials.