# Liquid Deposition Modeling of Biobased Epoxy Composites: Natural Fillers as Rheology Modifiers and Reinforcements

## TL;DR

This paper explores using natural fillers to improve the properties of biobased epoxy composites for 3D printing.

## Contribution

The study introduces a method to optimize biobased composites for 3D printing using natural fillers as rheology modifiers.

## Key findings

- Microfibrillated cellulose (MFC) enhanced rheological and mechanical properties but caused shrinkage at high loadings.
- A combination of microcrystalline cellulose (MCC) and MFC improved viscosity and mechanical strength without losing structural recovery.
- An optimized formulation with 22 vol% MCC and 1 vol% MFC showed suitable properties for 3D printing with good extrusion and shape fidelity.

## Abstract

In this work, aimed
at developing biomass-based composite pastes
for liquid deposition modeling (LDM) 3D printing, we investigated
the tuning of the rheological properties of a cardanol-based epoxy
resin through the incorporation of various fillers: microcrystalline
cellulose (MCC), microfibrillated cellulose (MFC), and nanoclay (MMT).
The thermal cross-linking of the amine-cured composite pastes was
monitored by ATR-FTIR and DSC analyses, confirming complete conversion
of epoxy functionalities. The rheological behavior of the uncured
composites was studied in view of LDM 3D printing. Viscosity data
were fitted with the Herschel–Bulkley model to determine yield
stress (τ0), consistency index (K), and flow behavior index (n). Shear-thinning behavior
with solid-like to liquid-like transition at relatively low strain
(0.5–5%) was induced by the addition of fillers, with adequate
structural recovery. MFC proved to be the most effective rheological
and mechanical property enhancer but could not be used alone due to
curing-induced shrinkage at high loadings. Partial substitution of
MCC with MFC, instead, drastically increased viscosity and reinforced
shear thinning while retaining solid-like behavior at rest and yielded
the highest tensile mechanical properties. In contrast, partial substitution
of MCC with MMT slightly improved the tensile properties without significantly
changing the rheology. Overall, increasing the filler content improved
the mechanical properties of the composites to an extent that depended
on the type and amount of filler. An optimized formulation containing
22 vol % of MCC and 1 vol % of MFC showed promising properties for
LDM 3D printing, exhibiting proper extrusion (τ0 =
281.54 Pa, K = 855.43 Pa·s
n
, and n = 0.57), good shape fidelity, and,
after curing, tensile modulus and strength equal to 5.34 and 1.31
MPa, respectively.