Chapter 4 - Production of composite filaments for fused deposition modeling

Abstract

The key pre-requisite for a material to be printable by fused deposition modeling (FDM, aka fused filament fabrication, FFF) is that it must be easily processed into a filament with a round cross-section having a consistent diameter of 1.75 or 2.85 mm, which are the standard sizes in the marketplace. Whereas extruding neat polymer filaments is a well-established procedure, composite materials bring about new technical challenges because the presence of the filler modifies the thermal and rheological properties of the thermoplastic matrix. Specific applications may require a selective filler distribution, however, oftentimes the filler should be uniformly dispersed, which is usually accomplished by solvent mixing or by hot-melt compounding. Potential filler agglomerates should be carefully eliminated. The composite material must then be extruded into a filament with closely controlled geometry. Surface modification of the filler is often necessary to strengthen the interface bonding with the thermoplastic matrix, whilst surfactants and plasticizers may improve the workability, especially for high filler loadings. This chapter explores the effect that a filler may have on the extrudability of thermoplastic-based materials, compares different mixing strategies and introduces the functioning mechanisms of single screw and twin-screw extruders. Suggestions are provided to tackle common issues such as filler agglomeration, poor distribution or weak interaction with the polymer matrix.