Development of innovative processes for the transformation of polymeric thermoplastic materials based on compression molding at high rates

Poly(lactic acid) possesses many desirable properties, above all biodegradability an compostability. PLA can be either amorphous or semicrystalline depending on its stereochemistry and thermal history. A high crystallinity degree is desirable to increase the heat resistance of PLA but it is rather difficult to reach high values during injection and compression moulding due to its very slow crystallization kinetics. Therefore, two different approaches can be carried out. The first concerns the synthesis and use of a PLA stereocomplex by mixing PLLA and PDLA, because this blend has shown higher crystallization rates and higher melting temperature than the single homopolymers. The second approach regards the adding of a nucleating agent that favours the formation of the PLA spherulites. In my thesis project, funded by SACMI Imola, an innovative process for the processing of PLA by compression moulding was developed. The study was focused on two different aspects. The first regarded the formation and crystallization of the stereocomplex by means a Rheo-Raman instrument. The second aspect regarded the investigation of some operative parameters for the compression moulding process for the production of coffee-pods. The results regarding the stereocomplex have shown that its formation is strongly affected from two different parameters that are the temperature of the experiment and the shear rate applied. By means the Rheo-Raman analysis it was also possible to monitor on line the formation and crystallization of the stereocomplex, that takes place in relatively short time (1-2 minutes). As far as the processing of PLA by means compression moulding is concerned, the attention was focused on the thermal treatments after the formation of the coffee pod. This thermal treatment, carried out by means a post-mould device, favours the post crystallization process of the polymer leading to reach the target value requested for the application in the coffee machines.