Additive Manufacturing of Biodegradable Hemp-Reinforced Polybutylene Succinate (PBS) and Its Mechanical Characterization

Abstract

The additive manufacturing of natural fibre-reinforced polymers is a pivotal method in developing sustainable engineering solutions. Using the fused filament fabrication method, the current study investigates the additive manufacturing of hemp-reinforced polybutylene succinate (PBS) alongside its mechanical characterization. Two types of hemp reinforcement are considered: short fibres (max. length smaller than 2 mm) and long fibres (max. length smaller than 10 mm), which are compared against non-reinforced (pure) PBS. A detailed analysis is performed regarding the determination of suitable 3D printing parameters (overlap, temperature, nozzle diameter). In a comprehensive experimental study, additionally to general analyses regarding the influence of hemp reinforcement on the mechanical behaviour, the effect of printing parameters is determined and discussed. Introducing an overlap in the additive manufacturing of the specimens results in improved mechanical performance. The study highlights that the Young's modulus of PBS can be improved by 63% by introducing hemp fibres in conjunction with overlap. In contrast, hemp fibre reinforcement reduces the tensile strength of PBS, while this effect is less pronounced considering overlap in the additive manufacturing process.

Keywords: FFF printing; PBS; additive manufacturing; biopolymer; experiment; hemp; natural fibre reinforcement; printing parameters; stiffness; tensile strength.

Figure 1

Hemp particles used in the present study; (a) short fibres (SF)–maximum length ≤ 2 mm (b) long fibres (LF)–maximum length ≤ 10 mm.

Figure 2

Schematic of FFF 3D printing process according to the Prusa i3MK3s.

Figure 3

Schematic of the test specimens following ASTM D3039; cross-hatched areas ($L_2$) indicate the area of the tabs.

Figure 4

Detailed view of test specimen, number of layers and printing paths.

Figure 5

(a) Raster bed orientation (b) 3D printer Prusa i3 MK3S+ used for printing the specimens, (c) testing machine ZwickRoell Z2.5 used for testing the specimens.

Figure 6

(a) First pre-tests printed with different nozzle temperatures: short fibre-reinforced PBS (SF-PBS) with 180, 190 and 200 °C printing temperature, long fibre-reinforced PBS (LF-PBS) with 180, 190 and 200 °C printing temperature and a failed print of long fibre-reinforced PBS at 175 °C. (b) Pre-tests printed with different overlap of the printing paths at a temperature of 180 °C: short fibre-reinforced PBS (SF-PBS) with 0, 5, 10 and 20% overlap, long fibre-reinforced PBS (LF-PBS) with with 0, 5, 10 and 20% overlap.

Figure 7

Theoretical overlap from slicing.

Figure 8

Overview of additively manufactured specimen types: ‘pure PBS’ (PBS, PBS OL), short fibre-reinforced PBS (SF-PBS, SF-PBS OL), long fibre-reinforced PBS (LF-PBS, LF-PBS OL), OL–overlap of 5% used in printing, specimens printed at $180{}^{°}$C (specimens printed at a higher temperature of 200 ${}^{°}\mathrm{C}$ (‘HT’) are not shown).

Figure 9

Stress–strain behaviour of PBS and hemp fibre-reinforced PBS; SF—short fibre, LF—long fibre, OL—overlap (5%), HT—higher printing temperature ($200{}^{°}$C instead $180{}^{°}$C) [24].

Figure 10

Comparison of the stress–strain behaviour of hemp-reinforced PBS for changing fibre size (SF, LF) and overlap printing parameter (OL).

Figure 11

Comparison of stress–strain behaviour of hemp-reinforced PBS for changing fibre size (SF, LF) and printing parameter temperature (HT). (a) SF-PBS OL ($180{}^{°}$C) and SF-PBS OL HT ($200{}^{°}$C). (b) LF-PBS OL ($180{}^{°}$C) and LF-PBS OL HT ($200{}^{°}$C).

Figure 12

Stress–strain behaviour comparison of nozzle sizes 0.8 mm and 1.0 mm.

Figure 13

Overview of characteristic material parameters for all types tested.