In Situ FTIR Study Of The Relationship Between Mechanical Properties And Evolution Of Structure In The Drawing Process For PLA Film

This topic was studied the relationship between structure and mechanicalproperties of polylactic acid film stretching process and the effect of temperature onthe evolution of the structure and mechanical properties of polylactic acid filmcorresponds to the process of stretching using in situ FTIR. The melt-quenchedamorphous polylactic acid film sample was obtained by the solution method, theinitial samples was characterized by DSC and WAXD, combined with Fouriertransform infrared spectroscopy (FTIR) and stretching the heat station situ tensile tostretch the samples, through processing and analysis of data to obtained true strainstrain curve and real polarized infrared spectra corresponding tensile samples,thespecific findings are as follows:(1) The polylactic acid stretched film in the amorphous glass transitiontemperature Tg higher than the tensile strain induces opposite amorphous polylacticacid crystal phase transition, and also induce the polylactic acid-induced α’-to-αsolid-solid phase transition. As the tensile strain increases the internal amorphouspolylactic acid decreases, the crystal phase increases. As the polylactic acid stretchedin the amorphous phase as the strain increases an intermediate phase is formed, as thestrain is increased when it reaches the critical crystallization began strain α’crystalline phase, the true strain continues increase α ’ orderly crystalline meet andgradually improve gradually occurs α’-to-α solid-solid phase transition, eventuallyforming α crystalline phase (corresponding to1293cm-1characteristic band).(2) When amorphous polylactic acid stretched at different temperatures criticalstrain of strain-induced crystallization of different sizes, corresponding to thetemperature of58℃,63℃,73℃situ stretched polylactic acid film of amorphouscrystalline critical strain are: ε=1.1, ε=1.0, ε=0.7, which shows that as thecrystallization temperature increases the critical strain decreases, this reasons may beas the temperature rises, and the motion of molecular chains of the molecular chaincapacity increases, the more ordered structure of the molecular chains and thus it is easier to form into crystalline phase. At58℃,63℃,73℃stretched polylactic acidfilm when the critical strain corresponding to the crystallization of dichroic ratio areR956=1.25, R956=1.187, R956=1.07as the temperature increases the critical crystalstrain corresponding dichroic ratio decreases, i.e., the crystallization temperatureincreases with the degree of orientation decrease, while at lower temperatures agreater degree of crystalline orientation of the corresponding, at higher crystallizationtemperatures corresponding the smaller the degree of orientation, which may bestretched along with the molecular chain orientation, but due to the temperature riseof the solution on the one hand the stretching orientation of molecular chains in theprocess of increasing the tensile strain of the same orientation as compared lowactivity other polymer chains in the stretching process, to enhance the molecularchain is more readily into the crystal lattice of the crystal.(3) Simultaneously stretching the polylactic acid (PLA) is the evolution of theinternal structure of the mechanical properties corresponding to change in thetemperature of58℃,63℃,73℃amorphous polylactic acid stretched film in situ,the corresponding the true strain was ε=1.1, ε=1.0, ε=0.7tensile specimen strainhardening phenomenon began to appear, this time appeared crystalline phasecorresponding to disguise the true should coincide with different temperaturesstretched polylactic acid.