Characterization of different starch types for their application in ceramic processing

doi:10.1016/j.jeurceramsoc.2005.02.015

Journal of the European Ceramic Society

Volume 26, Issue 8, 2006, Pages 1301-1309

https://doi.org/10.1016/j.jeurceramsoc.2005.02.015 Get rights and content

Abstract

Starch is a frequently used pore-forming agent in ceramic technology. Moreover, it can take over the function of a body-forming agent in a recently developed process, called starch consolidation casting. Upon firing the starch polymers are burnt out without residues and leave a pore structure determined by the type of starch applied. In this paper, five commonly available starch types (potato, wheat, tapioca, corn and rice starch) are characterized with respect to size and shape. Size distributions are measured via laser diffraction and microscopic image analysis. Rice starch is found to be the smallest type (median size 4.4–4.8 μm), potato starch the largest (median size 46–49 μm) and the other types intermediate (median size 12–21 μm). The distribution is narrow for corn and tapioca starch (span approximately 1.1), while potato, wheat and rice starch are relatively polydisperse (span approximately 1.35–1.65). The shape of the starch granules is most anisometric for potato starch (average aspect ratio 1.3–1.4). All other starch types, although possibly of polyhedral shape (tapioca, corn and rice starch), are more isometric, i.e. very close to an average aspect ratio of 1.

Introduction

Starch is one of the frequently used pore-forming agents in ceramic technology.1, 2 Due to its chemical composition (a polysaccharide consisting essentially of C, H and O only) this natural biopolymer is easily burnt out during firing without residues in the final ceramic body. In a recently developed process, called starch consolidation casting (SCC), starch can additionally take the role of a body-forming agent.3, 4, 5, 6, 7, 8, 9 This process exploits the ability of starch granules to swell in aqueous media at elevated temperature and enables ceramic green bodies to be formed from starch-containing aqueous ceramic suspensions by casting into non-porous molds (e.g. polymer or metal molds). Principles, processing details and modeling issues concerning the SCC process as well as microstructure–property characterization of final ceramics prepared by SCC can be found in Refs. 10, 11, 12, 13, 14, 15. Of course, also the SCC process results in porous ceramics with a microstructure determined by the type of starch used. However, optimization of the SCC process is a highly complex task, which is complicated by the intricate time–temperature behavior of starch in aqueous media and the non-equilibrium nature of phase transitions (e.g. gelatinization and retrogradation).16, 17 Although starch granules can generally change their size (and volume) and possibly shape during swelling, the initial size and shape will determine the characteristics of the pore space of the final ceramics to a large degree.

In any case, as a first step towards efficient microstructural control by the SCC process, it is necessary to know the initial size, shape and size distribution of the starch type used. In particular, concerning size distribution, it is desirable to dispose of a characterization in terms of laser diffraction (LD) data and in terms of microscopic image analysis (MIA) data. The former (LD) is a convenient modern standard method that can be routinely applied in process optimization and production control, while the latter (MIA) is a method that can be conveniently applied for the characterization of fired ceramic bodies. In other words, only by MIA it is possible to relate the particle size distribution of the pore-forming agent directly to the pore size distribution in the fired ceramics. In spite of the immense literature on starch science and technology, it seems that a systematic comparison between LD data and MIA data from the viewpoint of particle statistics is not available. The purpose of this paper to provide such a comparison and to present the individual characteristics for five native starch types which are commercially available in the world market: potato, wheat, tapioca, corn and rice.

The size and shape information provided in this paper should be helpful to realistically delimit the potential microstructural goals that can be attacked with starch as a pore-forming agent (in conventional ceramic shaping technologies or in the SCC process) and may serve as a guideline in selecting the appropriate starch type for a concrete application in mind. The comparison between LD and MIA results is a necessary precondition for future process optimization and improved microstructural control.

Section snippets

Starch types

Starches are complex biopolymers of natural origin, occurring in the form of granules in plant tissue. Chemically, they consist essentially of two types of polysaccharides (glucose polymers), amylose and amylopectin, cf. Table 1. For a detailed characterization of composition, structure and properties of starch, including the time–temperature behavior in aqueous media (with or without additional solutes), the reader can refer to several excellent reviews.18, 19, 20 What is of primary interest

Measurement details and evaluation procedure

All five starch types (potato, tapioca, wheat, corn, and rice) have been characterized by LD and MIA. The reader can refer to standard monographs21, 22 for measurement principles of these methods. Laser diffraction was carried out in a standard way23, 24 on the particle sizer Analysette 22 (Fritsch Laborgeratebau GmbH, Germany) using a He–Ne laser (wavelength approximately 0.6 μm) and performing a model-independent evaluation via Fraunhofer theory. No sample preparation was necessary prior to

Results and discussion

Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7 show micrographs of potato, wheat, tapioca, corn and rice starch, respectively. It is evident that potato starch exhibits the largest and most anisometric granules (Fig. 3). The deviation from sphericity is clearly towards prolate shapes. Polydispersity is a common feature of all starch types, but wheat starch shows a large amount of small grains beside many large grains, while intermediate sizes are apparently missing (Fig. 4). Most wheat starch granules

Summary and conclusions

Five starch types, all commercially available on the world market, have been characterized with respect to size and shape. Size distributions have been measured by LD and MIA. The latter, although much more operator-intensive and time-consuming, was necessary in order to verify the possibility to replace MIA by LD in routine measurements and to justify the future use of LD (and not MIA) results for a direct comparison with resulting pore-size distributions measured by MIA. In particular, good

Acknowledgement

This work was part of the project “Preparation and properties of advanced materials—modelling, characterization, technology”, supported by the Czech Ministry of Education, Youth and Sports (Grant No. MSM 223100002). The support is gratefully acknowledged.

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Characterization of different starch types for their application in ceramic processing

Abstract

Introduction

Section snippets

Starch types

Measurement details and evaluation procedure

Results and discussion

Summary and conclusions

Acknowledgement

J. Eur. Ceram. Soc.

J. Eur. Ceram. Soc.

J. Eur. Ceram. Soc.

Mater. Res. Bull.

Mater. Sci. Eng.

J. Eur. Ceram. Soc.

J. Eur. Ceram. Soc.

Novel water-based shaping of ceramic components

Br. Ceram. Proc.

Porous ceramics formed using starch consolidation

Key Eng. Mater.

New trends in shaping of ceramics (in Czech)

Sklář a keramik

Gelatin casting and starch consolidation of alumina ceramics

Starch consolidation casting of alumina ceramics—body formation and microstructural characterization

Key Eng. Mater.

A model for the body formation in starch consolidation casting

J. Mater. Sci. Lett.

Zirconia and alumina-zirconia composites ceramics prepared by starch consolidation

Influence of the starch type on microstructure and properties of oxide ceramics prepared by starch consolidation (in Czech)