ABSTRACT
Biosourced and biodegradable materials will gradually replace the currently existing family of oil-based polymers as they become costand performance-wise competitive. Polylactic acid or polylactide (PLA) is becoming the most important bio-based polymer due to its favorable properties widely investigated. Polylactic acid, also known as polylactide, is an aliphatic polyester produced from renewable sources. It has attracted huge attention due to its biodegradability and mechanical properties similar to polyethylene terephthalate (PET), polystyrene (PS) and other common petrol-based plastics. It has a wide range of applications in medical devices, food packaging, electronics, and engineering devices. Production of PLA with low molecular weight (LMW) through direct polycondensation (PC) is known since 1932. Water is the byproduct of the reaction, which
has to be removed from the reaction in order to shift the chemical equilibrium to the product side and enhance the polycondensation reaction to increase the polymerization degree. Reacting mixture viscosity increases during polymerization that makes the water removal very dificult, thus only LMW polymers can be produce by PC. The most effective method to manufacture high-molecularweight PLA is through ring opening polymerization (ROP) of lactide [1]. Like ROP of ε-caprolactam [2, 3], this reaction requires strict purity of the lactide monomer, obtained by dimerization of the lactic acid monomer [4]. PLA is obtained by heating a catalyst/ monomer mixture under vacuum or an inert atmosphere. Tin (II)- based catalysts, tin octoate in particular, are the most widely used catalysts for the ring-opening polymerization of lactide. They have been shown to give a controlled and living polymerization of lactide via coordination-insertion mechanism. High-molecular-weight polymer with monomer conversion above 95%, good reaction rate, and low levels of racemization can be obtained using tin (II) compounds and Sn(Oct)2 in particular [5]. The existing PLA production processes mainly employ a series of batch reactors, which are time-, energy-, and cost consuming. Since high-molecular-weight PLA can be obtained in a short time in the presence of a co-catalyst, e.g., triphenyl phosphate, through ROP, the reactive extrusion of lactide has recently attracted many researchers. This method allows the production of ready-to-use PLA parts in a shorter and costeffective process [6].
