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Abstract
The article presents results regarding the use of the melt flow index method (MFIM) in estimating the rheological properties of polylactic acid (PLA) and PLA-based materials, as tool in the selection of the operating conditions at their shaping into filaments and for 3D printing with thus obtained filaments. Based on the MFIM, the molecular weight of various PLA grade commonly used in melt processing techniques, including printing, were qualitatively compared. It was found that PLA for printing has the lowest molecular weight as compared with the PLA melt processed through injection, extrusion, thermoforming. It has been also shown that the MFIM can be used to verify the efficiency of drying, pre-treatment always needed to be done, before filaments obtaining and/or printing, especially in case of renewable polyesters. By simulating the printing at the indexer, via depositing successive layers, one over the other, it was possible to estimate the optimal flow conditions that ensure a good adhesion between the deposited layers. The estimation of the condition which ensure the needed adhesion between the deposited layers with the help of the MFIM was verified with good results on a grade of high loaded PLA achieved according to an original formulation.
Highlights
It is well known that the subtractive manufacturing technique uses blocks of material from which the unnecessary parts are removed until the shape of the desired item is obtained
In order to identify the most appropriate polylactic acid (PLA) grade that can be used in 3D / 4D printing and in subsequent modification researchers for getting new materials for printing technologies, the molecular weights were estimated, qualitatively, based on the rheological properties of the melts for several types of PLAs designed for melt processing into finished product both by classical techniques and by 3D/4D printing
The found qualitative order of the increasing of the molecular weight for the PLA grades processable in finished product by several melting techniques are described by equation (2): Mw 3D printing < Mw blow film extrusion < Mw injection < Mw thermoforming
Summary
It is well known that the subtractive manufacturing technique uses blocks of material from which the unnecessary parts are removed until the shape of the desired item is obtained Unlike this technique, in the 3D procedures, the three-dimensional object is acquired under the computer’s control, by successive deposition of layers of approx.0.15 mm thickness, one over the other, until the desired shape is achieved. In the 3D procedures, the three-dimensional object is acquired under the computer’s control, by successive deposition of layers of approx.0.15 mm thickness, one over the other, until the desired shape is achieved That is why this technique is called "additive /cumulative manufacturing" [1,2] or 3D printing [3]. Nowadays the 3D printing is considered a revolutionary process which can become the third technical revolution of the mankind
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