Applications Of Deep Eutectic Solvents In Polymer Processing And Their Hygroscopicity

As a new green solvent,the deep eutectic solvent(DES)are showing promising applications in material processing,reaction,extraction,and electrochemistry due to its advantages of low vapor pressure,good biodegradability,non-toxicity,low cost,easy synthesis and recycling,and tunable properties.Although most DESs can not dissolve polymers efficiently,they can still be used in polymer processing as dispersion media oe antisolvent.With the applications of DES in polymer processing and determination of its hygroscopicity as research background,the applications of novel DES emulsions in solvent extraction and electrospraying/electrospinning processes were investigated to extend these two traditional methods to fabricate polymer nano-/micro-particles and capsules.At the same time,a novel unit process: droplet drying of polymer solution was proposed to control morpghology of the product particles through the analysis of a series of solution processing based processes for preparing the polymer nano-/microparticles and capsules.The peclet number was applied in the solvent evaporation of emulsion to properly organize the study of affecting factors of this process,to improve this traditional and mature method by preliminarily entrusting it with new function of morphological control over its product particle.Finally,the hygroscopicity data of the DES were determined experimentally by using the homemade in-situ measuring apparatus.In detail,the research is consisted of three sections:(1)The preparation of polymer micro-particles and capsules from solvent extraction of O/DES emulsion,(2)Morhpoogical control over micro-particles from solvent evaporation of O/W emulsion,(3)Electrosraying and electrospinning of DES emulsion,(4)Study on hygroscopicity of DES.In the section of “The preparation of polymer micro-particles and capsules from solvent extraction of O/DES emulsion”,the micro-particles of PLGA,and PMMA,and microcapsules of ibuprofen-PLGA,PLA,and PMMA were successfully prepared using the solvent extraction of O/DES emulsion.The replacement of water phase in W/O emulsion and continuous phase in the O/O emulsion with DES provided an opportunity to achieve surfactant-free anhydrous route or to reduce the use of harmful organic solvent,respectively.The stability term of the O/DES emulsions was determined to be60 and 72 hours according to the measurements of viscosity and electric conduxctivity,which satisfied the requirement for preparing the polymer microparticles and microcapsules.At the same time,the solvent of the oil phase was found to be of great importance in determining the morphology of the product microparticles and microcapsules.When the DCM was used,the spherical solid particles and capsules were obtained;when the EA was used,the particles and capsules with irregular shapes were fabricated.The EEs and DLEs were in the ranges of 14.5-16.5% and 87.1-98.9%,respectively,while the release term was aroud 150 hours accrding to the in vitro tests.In the section of “Morhpoogical control over micro-particles from solvent evaporation of O/W emulsion”,the single factor method was used to investigate the effects of PMMA concentration,molecular weight of PMMA,type of polymer,vaporation temperature,and type of oil solvent on the morphology of the product micro-particles with the variation of Peclet number as criterion.The results showed that(1)No pronounced morphological change was observed with increase in polymer molecular weight,however,the diameter of microparticles increased.(2)The PCL particles were inclined to be spherical particles with coarse surface while the PMMA particles were bowl-like particles or microporous particles with smooth surface.Meanwhile,the connection among PCL particles was more serious than PMMA,which might be due to the difference in glass transition temperature(Tg).(3)With the incease in polymer concentration,the diameter of polymer particles increased but the morphology did not change.(4)With the increase in EA concentration of the mixed solvent,polymer particles with relatively large cavity were proned to be prepared due to the easier structural collapse.Meanwhile,the particles were getting more irregular and their surfaces were getting coarser.(5)With the increase in homogenization rate,morphology of the product particles did not change but the diameter decreased.In the section of “Electrosraying and electrospinning of DES emulsion”,the PCL microparticles and ChCl/Vitamin C-PCL microcapsules were successfully prepared uing electrospraying and electrospinning of DES emulsions.For a series of[PCL/DCM]/[ChCl/MA] DES,although the PCL concentration in its solution reached10 wt%,the product was micro-particles instead of fibers.The EEs of ChCl and VC in the microcapsules prepared from [ChCl/VC]/[PCL/DCM] emulsions were in the ranges of 53.7-78.9% and 62.2-96.2%,respectively.And the DLEs of ChCl and VC were in the ranges of 20.7-32.2% and 16.0-24.8%,respectively.In the section of “Study on hygroscopicity of DES”,for the first time the hygroscopicity data of [ChCl][EG],[ChCl][PEG400] and so on were experimentally determined in the temperature range of 303-353 K and relative humity range of 10-40%by using the homemade apparatus that was self designed and built to measure the hygroscopicity of liquid in-situ based on gravitic method.The effects of temperature,relative humity,and molar ratio of HBA and HBD in the DES on the hygroscopicity were investigated.The results showed,(1)For the DES of [ChCl][EG](molar ratio of1:4),the higher relative humity and/or temperature led to higher equilibrium hygroscopicity.(2)For the DES of [ChCl][EG] with different molar ratios,the increase in EG content resulted in decrease of equilibrium hygroscopicity.(3)For the common DESs such as [ChCl][EG],[ChCl][urea],and [ChCl][PEG400],[ChCl][EG] displayed the highest equilibrium hygroscopicity while [ChCl][PEG400] showed the lowest equilibrium hygroscopicity.