Abstract
In this work, an extrusion-based 3D printing technique was employed for processing of biobased blends of Poly(Lactic Acid) (PLA) with low-cost kraft lignin. In Fused Filament Fabrication (FFF) 3D printing process, objects are built in a layer-by-layer fashion by melting, extruding and selectively depositing thermoplastic fibers on a platform. These fibers are used as building blocks for more complex structures with defined microarchitecture, in an automated, cost-effective process, with minimum material waste. A sustainable material consisting of lignin biopolymer blended with poly(lactic acid) was examined for its physical properties and for its melt processability during the FFF process. Samples with different PLA/lignin weight ratios were prepared and their mechanical (tensile testing), thermal (Differential Scanning Calorimetry analysis) and morphological (optical and scanning electron microscopy, SEM) properties were studied. The composition with optimum properties was selected for the production of 3D-printing filament. Three process parameters, which contribute to shear rate and stress imposed on the melt, were examined: extrusion temperature, printing speed and fiber’s width varied and their effect on extrudates’ morphology was evaluated. The mechanical properties of 3D printed specimens were assessed with tensile testing and SEM fractography.
Highlights
In the last decade, issues concerning environmental pollution and the increasing awareness of limited resources, have motivated the scientific community to study and optimize renewable alternatives to traditional petroleum-derived plastics, like biobased composite materials that are sourced from carbon-neutral feedstocks [1]
At 5 wt.% lignin content, the morphology mainly consists of a uniform dispersion of lignin aggregates of small size (
Other authors have explained double melting behavior with a melt-recrystallization model, where the low-temperature and high-temperature peaks in the Differential Scanning Calorimetry (DSC) curve are attributed to the melting of some amount of the original crystals and to the melting of crystals formed through a melt-recrystallization process during the heating scan, respectively [33]
Summary
Issues concerning environmental pollution and the increasing awareness of limited resources, have motivated the scientific community to study and optimize renewable alternatives to traditional petroleum-derived plastics, like biobased composite materials that are sourced from carbon-neutral feedstocks [1]. The formation of bonds among individual fibers in the FFF process consists of complicated heat and mass transfer phenomena coupled with thermal and mechanical stress accumulation and phase changes. The strength of these bonds depends on the growth of the neck formed between adjacent fibers and on the molecular diffusion and randomization at the interface [11]. In most CAM programs for lower end FFF 3D printers, VFR is a function of the linear feed velocity of the filament and of several design parameters related to the toolpath (e.g. the width and height of individual fibers, defined by extrusion width and layer height parameters) [14]. A qualitative assessment of the filler’s dispersion and agglomeration into the polymeric matrix, as well as its effect on surface morphology and diameter of individual fibers was made with optical microscopy
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