Reduction of hygroscopicity of PLA filament for 3D printing by introducing nano silica as filler

Abstract

3D (three dimensional) printing is also known as additive manufacturing technology that is one of the most rapidly growing technologies in present world. It is capable of producing a physical prototype in a way lesser time and cost as compared to conventional methods like injection molding. One of the most popular choices of material in 3D printing, via Fused Deposition Modelling (FDM) method, is Polylactic Acid (PLA). Studies have found that PLA is highly hygroscopic, and this is a great setback to such an important biodegradable polymer. Water-swollen PLA produces poor finished product, short shelf life, poor bonding adhesion, bubbles forming and etc. Meanwhile, silica gel and fumed silicas are found to be frequently used as desiccant due to its excellence characteristic in preventing moisture that prevents spoilage of filaments. Therefore, the aim of this study is to reduce the hygroscopicity of PLA filament for 3D printing by incorporating nano-silica - silanol treated and untreated, as a filler. Extruded samples of PLA nanocomposites were tested in moisture uptake test. PLA nanocomposites with nano-silicas ranging from 0, 1, and 3 wt % (weight percentage) were prepared using high speed mixer and subsequently extruded into filaments in a single screw extruder. Moisture uptake performance was then confirmed by TGA (thermal-gravitational analyzer). Incorporating treated nano silica at 1 wt % yield the highest reduction in hygroscopicity by 40 %. Furthermore, its thermal stability was found to be improved compared to pure PLA and another nanocomposites composition. 3 wt% Nanocomposites recorded highest tensile strength, Young’s modulus and elongation at break gains. However, its hygroscopicity stood by just 19 %, which is inferior to the 1 wt% nanocomposites. This may be due to excessive content of nano-silica that had accumulated in the PLA matrix and causes non-uniform filler distribution. Agglomeration may as well create more void spaces which in turn could allow moisture or air bubble to reside in the sample. Nevertheless, untreated nano silica had shown improvements in tensile test but in terms of hygroscopicity was just about 10 % and lower. Scanning electron microscope (SEM) confirmed the finding on dispersions of the nanosilicas within the matrix of PLA. As a conclusion, silanol treated nano-silica has successfully improve the PLA matrix, specifically for 1% treated nano-silica filled PLA which showing greatest improvement on hygroscopicity reduction while outperform plain PLA in tensile properties.