Preparation And Applications Of High Processable Poly(P-Phenylene Terephthalamide) Solution

Poly（p-phenylene terephthalamide）（PPTA）with excellent thermal properties,chemical stability,electrical insulation properties and wear resistance is widely used in aerospace,national defense,military industry,transportation,personal protection.Due to the strong hydrogen bonding between the PPTA molecular chains,however,the high polymerization degree PPTA chains are easily gelled during the reaction,which are insoluble in common organic solvents.Meanwhile,the melting point of PPTA is higher than its decomposition temperature,hence,it can only be dissolved in concentrated sulfuric acid for liquid crystal spinning.In concluding,the higher cost and complicated process greatly limits the application of PPTA in other aspects.（1）In chapter 2,the LMW-PPTA solutions with different end group which could exist in organic solvent for a certain period of time were synthesized by low temperature copolymerization.Then,the possibility of one-step method processing for PPTA fiber was studied by investigating the polymerization degree and gel time of secondary copolymerization under different situations.Significantly,the one-step method processing for PPTA fiber is not only free from the dependence on concentrated sulfuric acid,but also procides a facile,lower-cost and environmental way for the manufacture of PPTA fiber.（2）In view of the poor dimensional thermal stability of lithium battery separators,it is easy to cause safety hazards.In chapter 3,the low molecular weight poly（p-phenylene terephthalamide）（PPTA）was introduced into the surface of integral PE network by a dip-coating and phase separation process,and a thermally stable separator with thermal-shutdown function was prepared.The pore structure of PE separator was primely retained by controlling the concentration of the casting solution.Furthermore,it can be observed that the initial modulus was greatly improved compared to that of pristine PE separator,which indicated that the p-PE separators had superior ability to resist against the puncturing from the branched crystal.The ionic conductivities of PE,p-PE-1separators were calculated as 4.67′10^-3 S/cm,7.46′10^-3 S/cm,respectively.In addition,the p-PE-1-150separator also showed similar lower bulk resistance,which meant that p-PE-1 separator heated at150℃ for 0.5 h still possesses superior ionic conductivity(3.73′10^-3 S/cm)while PE separator has been melted.After the same heated treatment,it is found that the bulk resistance of the p-PE-1-180separator was hundreds of times higher than that of p-PE-1 separator.The observation can be explained by the phenomenon that the pore of p-PE-1 separator had begun to shut down.The composite separator was proved to combine thermal shutdown function and exceptional thermal stability higher than 240℃.The polar PPTA coating and remained pore structure endowed composite separator with superior wettability,ionic conductivity and cell performance.Remarkably,the facile procedure,lower cost and excellent properties can satisfy the stringent demand of industrialization for high-performance lithium ion batteries.（3）In chapter 4,limited processability of high molecular weight poly（p-phenylene terephthalamide）（PPTA）results in complex,time-consuming,and high-cost procedure of preparing PPTA aerogel.In this study,a facile scale-manufacture PPTA and c-PPTA aerogels with adjustable thermal conductivity,great thermal stability and superior mechanical properties were fabricated.The obtained aerogels were endowed with extraordinary pore structure and porosity which accordingly could be applied in aerogel/PCM composite materials.Herein,the chopped PPTA fiber reinforced PPTA aerogel was prepared by spontaneous low molecular weight PPTA（LMW-PPTA）gel.The pore structure and thermal insulation characteristics of composite PPTA aerogel were effectively controlled by varying the concentration of LMW-PPTA solution.Then,the PPTA/phase-change composite（PPTA/PCM）was obtained by dipping process.It was confirmed that the composite PPTA aerogel acquired superior thermal insulation,mechanical properties and great thermal stability above 500°C.Furthermore,the infrared stealth property of PPTA/PCM composite material was also studied systematically.Significantly,the facile-procedure and lower-cost PPTA aerogel and its composites may have a great potential to be applied as thermal insulation and infrared stealth materials in industrial applications.（4）In chapter 5,the facile and low-cost gelation process was proposed to fabricate PPTA paper.The LMW-PPTA solution was injected into non-woven PPTA fabric consisted of chopped PPTA which was used as a substrate.Then,the PPTA gel was prepared by gelation and washing processes,in which the PPTA nanonetwork not only formed the stable homogeneous structure,but also served as vital adhesive between chopped PPTA fibers.Finally,the PPTA paper was obtained by slow-pressing and hot-pressing procedures,which was proved with high tear strength,great mechanical properties,thermal stability and dielectric breakdown strength.To further enhance the hydrophobicity of entire PPTA paper,the poly（vinylidene fluoride）（PVDF）was doped into LMW-PPTA solution to fabricate hydrophobic PPTA（h-PPTA）paper.In addition,the lacking addition of PVDF still endowed h-PPTA paper with superior hydrophobicity benefited from its special structure.The phenomenon suggested that the gelation process and PPTA paper not only could be served as ideal candidate in terms of fabricating insulating materials and honeycomb materials,but also had far reaching application potential in composite materials.（5）In chapter 6,the PPTA gel was made by unstable low molecular weight PPTA solution without any cross-linking agent.Then,the PPTA cellular material was prepared by solvent replacement and freeze drying.Subsequently,the lightweight and flexible PPTA membrane was obtained by pressing process at room temperature.It is believed that its rigid and strong molecular chain structure would endow PPTA membrane with minor CTE,superior thermal stability and electrical insulation.Herein,the PPTA cellular material has great processability,and it is achievable for the conductive materials to be embedded into PPTA cellular material and form circuits.Ultimately,the one-piece FPC was obtained by pressing.Particularly,the one-piece PPTA FPC not only exhibited minor CTE,but was also equipped with great thermal stability,facile procedure,lower cost and superior transfer characteristics.Therefore,the one-piece PPTA FPC demonstrated in this study illustrated great potential of application in the wearables,robotics,and biocompatible implantable devices.In this paper,low molecular weight PPTA solution with high processability was successfully prepared.Its applications in different fields was studied and discussed,which provided a new processing method and direction for the wider application of high performance PPTA polymer.