Restricted Crystallization Of Poly(Lactic Acid) Racemic Blends In Porous Materials And Their Application

The stereocomplex crystal（SC）formed by blending L-polylactic acid（PLLA）and D-polylactic acid（PDLA）has a melting point nearly 50°C higher than that of the homogeneous crystal（HC）formed by PLLA（or PDLA）.Stereocomplex crystals are also becoming a prominent focus in the field of PLA research due to higher thermal stability and better mechanical properties.In addition to intermolecular interactions,the diffusivity of molecular chains is also considered to be an important factor for the stereocomplex crystallization of polylactic acid racemic blends.In this thesis,AAO and MOFs are used as the confinement environment of PLLA/PDLA to realize the regulation of the diffusion behavior of molecular chains by changing the confinement manner and degree of molecular chains,and by examining the blending of PLLA/PDLA under different confinement conditions of molecular chains changes in crystallization behavior.At the same time,the specific capacitance properties of NH₂-MIL-88/PLLA/PDLA materials were explored,and the addition of polymers to other MOFs materials could be used as a reference for supercapacitors to improve their capacitance properties.Firstly,in this thesis,PLLA/PDLA with different molecular weights was penetrationed into anodic alumina templates（AAO）with different pore sizes to explore the changes in crystallization behavior of PLLA/PDLA under restricted conditions.The infiltration template was characterized and analyzed,and it was found that the larger pore size was more likely to infiltrate,and the higher the molecular weight,the worse the infiltration effect.After removing the continuous phase interference on the surface of the AAO template,the AAO templates with different pore sizes have different degrees of penetration.The analysis of XRD and DSC results shows that in the smaller pore size AAO template,the degree of restriction is greater,and it is more difficult to penetrate and crystallize,resulting in the shift of T_mand T_cto the low temperature direction.As the molecular weight increases,the degree of confinement also increases.Subsequently,PLLA/PDLA with a molecular weight of 20 kg/mol was composited with two MOFs,MIL-88 and NH₂-MIL-88,prepared by hydrothermal reaction.The characterization analysis showed that the particle structure of MOFs did not change significantly before and after compounding,and it also proved that the compounding of PLLA/PDLA and MOFs was successful.The changes in BET and pore size after compounding confirmed the entry of PLLA/PDLA into the nanopores of NH₂-MIL-88.XRD and FTIR results shows that only SC crystals were formed in PLLA/PDLA after compounding.DSC and Flash DSC results showed that when PLLA/PDLA was confined in porous MOF with smaller nano-pore size and more complex structure,the degree of restriction was greater,and molecular chain diffusion was more difficult,so crystal formation was more difficult.The overall relationship between the semi-crystallization time and the isothermal crystallization temperature shows a trend of first decreasing and then increasing,which is a two-stage inverted bell diagram.Finally,in this thesis,the specific capacitance properties of NH₂-MIL-88 and NH₂-MIL-88/PLLA/PDLA as electrode materials before and after carbonization were investigated experimentally,and the experimental results were compared and analyzed.It can be seen from the CV and GCD curves that the composite high-temperature carbonization of NH₂-MIL-88 and PLLA/PDLA in a ratio of 1:1 shows better performance than other samples,with a current density of 63.57 F/g specific capacitance at 3 A/g.Due to the limited diffusion in the micropores,the voltage drop increases.With the gradual increase of the current density,the specific capacitance decreases,and the capacitance retention rate is 68.2%,which is the highest among all samples,indicating the layered microstructure of NM₁P₁after carbonization.The pore structure is more suitable for the fast transport of ions.