Structure And Properties Researching Of Poly(L-Lactic Acid)/Poly(Propylene Carbonate)

The paper introduced the structure and properties researching of poly(L-lactic acid)(PLLA)/poly(propylene carbonate)(PPC) blend using solution blends method and melting blend methods. The crystallization? compatibility?phase structure?mechanical properties and orientation have been investigated with FTIR?SEM and POM in detail in this work. Main achievements are as follows:1. The PLLA/PPC blend film was prepared via solution casting method in this work. The crystallization of PLLA/PPC blend film was investigated with FTIR. The results showed that PLLA crystallized in its a'form at low crystallization temperature(<80?), while in its a form at high crystallization temperature(> 100?). The temperature at which PLLA grown in its a form was influenced by the PPC. It decreased with increasing content of the PPC. This reason is that blending with PPC leads to an increase in molecular mobility, which is in favor of crystallization of PLLA in the a form. And also the result of FTIR in situ showed that, ?' form would change to a form in the process of temperature increased.2. The PLLA/PPC blend sheet was prepared via melting method in this work. The relationship between phase structure and mechanical properties was investigated with SEM and material testing machine. DSC results suggested that PLLA and PPC were partially miscible while were compatible to some extent. The SEM results showed that PLLA/PPC blends were typical "sea-island" structure, when PLLA content was less than 55%, the PLLA acted as dispersed phase and PPC was continuous phase, when PLLA content increased to 55%, phase reversal acted, PLLA played continuous phase and PPC was dispersed phase. Mechanical testing results showed that, addition of a little amount of PPC can be effective in improving the tensile strength and elongation at break was increased. Combining with SEM results, the relationship between phase and mechanical properties could be found that, when crystalline condition was changed, phase reversal was occurred in the blend system, PLLA from dispersed phase to continuous phase, and mechanical testing results showed that with the phase reversal, the tensile strength of blend sheet was increased and the elongation at break was decreased.3. The orientation and cold crystallization of PLLA/PPC blend film was investigated by POM and material testing machine. POM results showed that blend film was oriented after drawing at the temperature above the Tg of PLLA. Mechanical testing results showed that, the tensile strength of parallel direction was increased and vertical direction was decreased. After annealing at the oriented condition, the mechanical properties of oriented blend film had changed, that the tensile strength of parallel direction had no change and vertical direction had a significant increasing. The results showed the mechanical properties at low temperature(70?) and high temperature(130?) were different,and the reason is crystallization of PLLA increases the tensile strength.