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. 2021 Mar 18;7(3):e06482.
doi: 10.1016/j.heliyon.2021.e06482. eCollection 2021 Mar.

Manufacturing of starch-based materials using ultrasonic compression moulding (UCM): toward a structural application

M Teil  1   2 , A Regazzi  1   2 , B Harthong  1 , P J J Dumont  2 , D Imbault  1 , J-L Putaux  3 , R Peyroux  1
Affiliations

Manufacturing of starch-based materials using ultrasonic compression moulding (UCM): toward a structural application

M Teil et al. Heliyon. .

Abstract

An experimental study of the ultrasonic compression moulding (UCM) to manufacture biobased composites made of semicrystalline starch powders and softwood fibres is described. The main objective was to assess the potential of using this fast and economical processing technique to elaborate a 100% biobased composite which might substitute more usual polymer materials for structural applications. The starch powder was chosen as raw material for the matrix while the reinforcement was made of softwood fibres. Tablets made of starch only and composite beams were processed under different conditions and characterised by several techniques. Three types of starch powders and two types of fibres were used as raw materials. A morphological and crystalline analysis was carried out by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The native semicrystalline structure of starch granules was not totally preserved so as to obtain a homogeneous material. Diametral compression tests on tablets were performed to improve the processing route and obtain the materials with the best properties. Bending tests were used on composite beams to quantify the mechanical properties and study the effects of the processing parameters. The optimum processing parameters were defined and allowed obtaining a matrix for which the flexural strength reached 21 MPa. Mechanical properties were improved when fibres were added into the matrix: three-points bending tests showed a Young's modulus of 6 GPa, a flexural strength of 75 MPa and a flexural strain at break of 6% for a bulk density of 1.25. Considering these results, UCM appears to be a promising process to design a 100% biobased composite with mechanical properties comparable to those of classical discontinuous fibre composites.

Keywords: Biobased composites; Starch granules; Ultrasonic moulding; Wood fibres.

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Conflict of interest statement

The authors declare the following conflict of interests: Pierre Dumont; [is an Associate Editor for the Materials Science section at Heliyon].

Figures

Figure 1
Figure 1
(a) Scanning electron microscopy image and (b) X-ray radiography of waxy maize starch powder.
Figure 2
Figure 2
Optical micrographs of (a) chemically bleached fibres and (b) mechanical fibres in aqueous suspensions.
Figure 3
Figure 3
The main steps to process a composite material from fibres and starch powders.
Figure 4
Figure 4
(a) The ultrasonic welder with (b) the three sonotrodes and (c) the two moulds (CAD views) used to process starch powder (cylindrical mould) and composites (oblong mould).
Figure 5
Figure 5
Principle of the diametral compression test, typical curve definitions of the extracted properties.
Figure 6
Figure 6
Plots of the electrical generating power and displacement of the sonotrode and tablets appearance for different processing times. Here, E2 was chosen to be very close to Em,0.
Figure 7
Figure 7
Different kinds of morphology were observed by SEM for pure starch tablets on the breaking patterns depending on the location and the energy (A area for porous material; C area for dense and homogeneous material; and B area as transition between A and C areas). Similar results were observed in the work of Regazzi et al. where thermal compression was studied on the same material.
Figure 8
Figure 8
X-ray diffraction profiles of (a) native and (b) processed starch samples presenting some of the best properties: best yield stress (standard dry maize starch - decreasing waves amplitude of 60 μm - pressure of 17.8 MPa), highest density (standard hydrated maize starch - decreasing waves amplitude of 60 μm - pressure of 17.8 MPa) and best strength (standard hydrated maize starch - decreasing waves amplitude of 60 μm - pressure of 7.6 MPa). These two graphs have the same vertical scale. The profile of amylose complexes with palmitic acid has been added in panel (a) for comparison.
Figure 9
Figure 9
SEM image of breaking patterns of 50 %wt reinforced (a) chemical fibres - waxy starch composite and (b) mechanical fibres - waxy starch composite (arrows show the interfaces between layers). The welding time is 0.70 s, pressure is 15 MPa with the highest amplitude.
Figure 10
Figure 10
(a) Bulk density and (b) Young's modulus of composites as a function of the fibre content and the nature of starch and fibres. The welding time is 0.70 s, pressure is 15 MPa with the highest amplitude. “CB”, “CTMP” and “Amylo” refer to chemical pulp, mechanical pulp and amylose-extender starch, respectively.
Figure 11
Figure 11
Typical curves obtained from three-point bending tests for various composites and fibre contents of (a) 30 wt% and (b) 50 wt%. The welding time is 0.70 s, pressure is 15 MPa with the highest amplitude. “CB”, “CTMP” and “Amylo” refer to chemical pulp, mechanical pulp and amylose-extender starch, respectively.
Figure 12
Figure 12
(a) Bulk density and (b) Young's modulus of composites as a function of pressure, amplitude and welding time. The composite is made of amylose-extender maize starch and chemical pulp with a reinforcement of 50%.
See this image and copyright information in PMC

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