The direct polycondensation has 3 main steps:
1. Removal of water.
2. Polycondensation of oligomer.
3. Melt condensation that makes PLA with high molecular weight.
Direct polycondensation of lactic acid is the modest reaction that forms lactide simultaneously by the decomposition processes and it is not used for the large production of PLA [19-22]. Back in the days, the direct polycondensation was assumed as the reaction that produces inadequate polymers with low molecular weight. But with the development of the condensation reaction, it can produce polymers with significantly high molecular weight [23-25].
The lactic acid does the condensation reaction by itself by the both -OH and -COOH …show more content…
Enzymatic polymerization is one of the best alternative methods that can be used in synthesize PLA with better physical and chemical properties. This is an eco-friendly process, which can synthesize PLA in mild conditions. Polymerization process can be adjusted and controlled in this method .
Materials and Methods for PLA synthesis
85 wt% of purity Lactic acid was used in the polymerization process, and Stannous octoate (Sn(Oct)2) was used as the catalyst. The polymerization process was carried out in a bench top system (Fig. xxxx ), consists with two flasks of 0.5 L, a mechanical stirrer, temperature control system, condenser connected to a vacuum pump. The reaction was conducted with and without nitrogen gas to control the system innert atmosphere. Differential Scanning Calorimetric (DSC) was used to obtain thermal transitions and properties of products .This procedure was performed using a first heating ramp to reach 200°C followed by a cooling to 25°C to erase the thermal history, then a second heating was made to 200°C. Heating and cooling rate was always of 10°C/min under nitrogen flow of 40 ml/min. The functional groups of PLA and LA can be analyzed by Fourier Transform Infrared Spectroscopy