The aim of this research paper is to study the behaviour of a common used biopolymer (Poly(Lactic Acid) (PLA)) after several reprocesses and how two different types of additives (a melt strength enhancer and a nanoadditive) affect its mechanical and rheological properties. Systematic extraction of extrudate samples from a twin-screw compounder was done in order to study the effect in the properties of the reprocessed material. Detailed rheological tests on a capillary rheometer as well as mechanical studies on a universal tensile machine after preparation of injected specimens were carried out. Results evidenced that PLA and reinforced PLA materials can be reprocessed and recycled without a remarkable loss in their mechanical properties. Several processing restrictions and specific phenomena were identified and are explained in the present manuscript.

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Owing to the depletion of oil based resources, new environmentally friendly materials are in continuous development. Poly(lactic acid) (PLA), a thermoplastic polymer obtained from renewable resources, is being seriously considered as a replacement for petroleum based products. The aim of the present study is to enhance the mechanical properties of this biopolymer with the addition of a natural based filler, a functionalised sepiolite, and to ensure a good dispersion by applying ultrasonic waves throughout the compounding process. A good affinity between the polymer and the silicate filler is essential in the nanocomposite to attain the optimal reinforcement. Nanocomposites of PLA/sepiolite were processed by extrusion compounding containing different weight percentages of nanoreinforcement. An ultrasonic homemade device developed by the authors was coupled at die position and used to improve the dispersion of the nanoclays in the molten polymer. Nanocomposite materials were later injected to produce different specimens that were characterised. The effect on the mechanical properties of PLA reinforced with sepiolite was analysed by conducting flexural tests. Strain-stress curves were obtained, and their stiffness and toughness were compared for the different specimens. Micrographs (SEM) were examined to demonstrate the effectiveness of using ultrasounds to improve the dispersion of the nanoclays within the polymeric matrix. Viscosity under low shear rates was measured with a rotational parallel plate rheometer in order to monitor the changes induced on the rheological behaviour of the composites. It was demonstrated that the application of ultrasonic waves in composite compounding improves nanoclay dispersion, which results in an enhancement of the reinforcement of the fillers and decreases the viscosity of the composites during the process. These effects become more significant for high loads of reinforcement, especially for 10 wt-% sepiolite specimens.

The manufacturing of medium-sized hollow parts using a foamed high density polyethylene was studied using a conventional accumulator blow extrusion machine and a systematic capture of pictures during the parison formation. To fully monitor the parison formation, several experiments were carried out varying the chemical foaming agent content from 0 wt.% to 2 wt.% and increasing the push extrusion speed. Results pointed out greater wall thickness, diameter, and length of parisons with higher weight percentage of blowing agent and extrusion speed. A full experimental characterisation of parison dimensions was essential to assure a proper prediction of the blowing step. Information was used as input for modelling and simulations of the blowing phase of an industrial container. To validate the proposed methodology, a blow moulding process of a generic container was simulated using Ansys Polyflow v13 software and its finite element analysis which provided an accurate approximation of the wall thickness expected. Further real tests on the simulated container also demonstrated that, in those parisons with a 1 wt.% CFA concentration and higher blowing pressure, there was remarkable improvement on their packaging properties such as decreasing of the total weight of the container and an enhancement of its surface quality.