| Poly(L-lactide)(PLLA)and Poly(D-lactide)(PDLA)can form stereocomplex crystal(sc-PLA)with high melting temperature,heat resistance and anti-hydrolysis performance,etc.It has attracted much attention because it can enhance melt strength,heat distortion temperature and mechanical properties of polylactic.The mechanism of sc-PLA formation is due to the tight packing of molecular chains caused by the intermolecular hydrogen bonding between chiral polymers.Constructing interfacial sc-PLA in polylactic based composite material and blend will improve the interfacial strength between the two phases,which affects the formation and evolution of the aggregate structure as well as other macro physical properties.However,crystalline properties and mechanism of polyurethane elastomer with soft and hard block structures are still unclear.This paper is to synthesis bio-based polyurethane elastomers containing PDLA soft segment,which was used as CNC-filled modified substrates and commercial PLLA toughener,respectively.By constructing sc-PLA at the interface,the interfacial strength is improved to achieve compatibilization.The factor affecting the formation of sc-PLA and the internal mechanism of the influence of the sc-PLA interfacial compatibilization on the performance of blend material is revealed.The main research contents of the paper are as follows:First,bio-based polyurethane elastomer containing PDLA as soft segment(D-PU)and nanocellulose grafted PLLA(CNC-g-L)were synthesized.The effect of sc-PLA on the dispersion of CNC,melt strength,mechanical properties,and oxygen barrier performance with different blending ratio was studied.The results show that the interfacial sc-PLA improves the compatibilization between D-PU and CNC-g-L,which significantly enhances the melt strength and mechanical properties.Young's modulus and yield strength was increased by 7%,21%,respectively.The dispersion of nanocellulose were improved by sc-PLA,increasing the gas diffusion path to enhance oxygen barrier performance.Next,D-PU/PLLA blend was obtained via melt blending between D-PU and commercial PLLA.The effect of different D-PU content on the aggregate structure and mechanical performance of blend by the construction of interfacial sc-PLA were investigated.The results show that the characteristic crystalline diffraction peaks of sc-PLA gradually became apparent,and the melt strength and tensile strength of the blend increased along with more D-PU content.The interfacial sc-PLA can increase the two-phase interfacial strength between D-PU and PLLA,which promotes the formation of the banded structure of the dispersed phase.When the D-PU content is 15 wt%,the elongation at break and notched impact strength of the blended reach 164%and 27 KJ/m~2,which are 13 and 16 times higher than pure PLLA,respectively.Finally,the compatibilization mechanism of the interfacial sc-PLA was studied based on comparing bio-based polyurethane elastomer containing PLLA(L-PU)and PLLA blend.The contact angle test results show that the theoretical calculation value of the interfacial tension between polyurethane elastomer and PLLA matrix is not significantly different due to the similar chemical structure of L-PU and D-PU.However,sc-PLA is a hydrogen bond between enantiomers,which shows higher compatibilization and enhances the melt strength of the blend as well as achieves uniform distribution of the toughened phase,improving the impact strength.Thermal annealing experiment shows that the interfacial sc-PLA serves as nucleation site,which increases the number of crystals and reduces their size.The notched impact strength of the annealed sample reaches 50.5 KJ/m~2. |
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