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Influence of Aging Time on the Structural Changes of Cassava Thermoplastic Starch

Published online by Cambridge University Press:  31 January 2012

José H. Mina ,
Alex Valadez ,
Pedro J. Herrera-Franco  and
Tanit Toledano
José H. Mina
Affiliation:
Facultad de Ingeniería de la Universidad del Valle, Escuela de Ingeniería de Materiales. Grupo de Materiales Compuestos. Email: josemina1@hotmail.com
Alex Valadez
Affiliation:
Unidad de Materiales, Centro de Investigación Científica de Yucatán A.C. (CICY) Calle 43# 130, Chuburná de Hidalgo, Mérida Yucatán México.
Pedro J. Herrera-Franco
Affiliation:
Unidad de Materiales, Centro de Investigación Científica de Yucatán A.C. (CICY) Calle 43# 130, Chuburná de Hidalgo, Mérida Yucatán México.
Tanit Toledano
Affiliation:
Unidad de Materiales, Centro de Investigación Científica de Yucatán A.C. (CICY) Calle 43# 130, Chuburná de Hidalgo, Mérida Yucatán México.
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Abstract

In this work the change in the structural properties of cassava (manihot sculenta Crantz) thermoplastic starch (TPS) under controlled environment (humidity and temperature) was studied. Fourier Transform Infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results showed an evident increasing in the amorphous phase of the TPS regarding the native starch. There was a relative decrease of the band at 1047 cm-1 associated to crystalline structure of starch compared to the amorphous peak at 1022 cm-1. The X-ray diffraction patterns confirmed the increment of the amorphous phase in the TPS samples. Likewise the X-ray diffraction patterns shows evidence of residual type C crystallinity and the formation of a new crystalline phase type VH due to the orientation induced in plasticization process. In first stage of conditioning the tensile yield stress drops from 7.5 drops to 0.5 MPa and the break strain increases 1000%. At the same time it seems that the crystallinity of the samples increases as was evidenced by the gradually increasing of the FTIR band at 1047 cm-1. In a second stage, the yield stress increases, the break strain drops and the crystallinity continue growing steadily. These findings suggest that coexist two phenomena simultaneously in the samples. A phenomenon of re-crystallization (retrogradation) that tends to make the material more stiff and a process of plasticization that tends to softening it. It seems that the latter mechanism predominates in the first stage, at short times, and the former in the second stage, at older times.

Keywords

PolymerMacromolecular structureX-ray diffraction (XRD)Scanning electron microscopy (SEM)Stress/strain relationship
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1372: Symposium S3 – Structural and Chemical Characterization of Metal Alloys and Compounds—2011 , 2012 , imrc-1372-s3-p86
Copyright
Copyright © Materials Research Society 2012

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References

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