Industrial Crops and Products 11 2000 217 – 225
Biodegradable plastic made from bean products
E.M. Salmoral
a,
, M.E. Gonzalez
b
, M.P. Mariscal
a
a
Department of Chemistry, Engineering Faculty, Buenos Aires Uni6ersity, Paseo Colon
850
C.P.
1063
, Buenos Aires, Argentina
b
Technological and Agricultural Unit, Ezeiza Atomic Center, National Atomic Energy Commission, Argentina Accepted 8 October 1999
Abstract
The aim of the present work was to explore the suitability of two kinds of bean with typical protein quality and different starch structure to produce moulded specimens by compression. In this work we analysed the possibility of
forming new plastic materials from two kinds of bean preparations; with different protein content, in the presence or absence of inherent cellulose material and other biopolymer such as starch. Significant differences were determined in
the fine structure of glucopolysaccharides isolated from the different types of bean. Complete moulding of the specimens took place at 20 MPa at a temperature not higher than 140°C, for 7 min. The mechanical properties of the
moulded plastics based on soluble protein black bean BP were superior in elongation, tensile strength and low water absorption than the soluble protein white bean WP variety. However, the addition of boric acid 3 ww, in total
batch basis to white bean plastic materials was effective in improving slightly the mechanical properties in the case of their whole flours products WWF. The gamma radiation was effective to reduce water absorption only in plastics
materials with cellulose – starch content BWF, WWF and improved their mechanical properties. The gelatinization process of the moulded material was influenced by the predominant lineal structure of the carbohydrate content.
© 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Biodegradable plastics; Agricultural plastics; Bean protein; Gamma-irradiation www.elsevier.comlocateindcrop
1. Introduction
The use of renewable natural polymers in the manufacture of plastics grows in impulse and
importance in the last years of the 20th century. Many major chemical companies are becoming
increasingly interested in developing technologies for the manufacturing of products from crops.
Among the products derived from the legumi- nous studied for manufacturing plastics, are the
soy isolate prepared by precipitation at pH 4.5, with 90 protein; the soy concentrate, prepared
by eluting soluble components from defatted soy flour with 70 protein and about 18 carbohy-
drate and soy flour with lower protein content, from 50 to about 34 Kinsella 1979; Salt et al.,
1982.
In the present work we employed as raw mate- rial two leguminous varieties like Phaseolus 6ul-
Corresponding author. Tel.: + 54-11-43430891; fax: + 54- 11-43121191.
E-mail addresses
:
esalmorfi.uba.ar E.M. Salmoral, mae- gonzcnea.gov.ar M.E. Gonzalez
0926-669000 - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 6 - 6 6 9 0 9 9 0 0 0 5 7 - 6
garis L., from which there is evidence about their prehistoric existence in South America. Their
greatest production is in the North West of Argentina.
The black bean used is a cultivar noticeable for its high resistance to viral diseases of warm areas
and it is eventually of high yield Vizgarra, 1995. We have utilised the white bean cultivar be-
cause it is commercially important and has also been submitted to phyto-improvement by agro-
nomic experiments. The seeds, which are typical of Argentina, were
defatted; their polysaccharides, proteins and fiber isolated, purified and quantified.
Starch is a mixture of two polysaccharides: amylose in which predominates linear a-1,4 glu-
can, and amylopectin highly branched a-1,6 glu- can with branching points occurring through
a -1,6 linkages.
The two components: amylose and amylopectin are present in varied ratios, depending on the
vegetal source Salmoral et al., 1993. In our case, the starch was used in addition to glycerol as
plasticizers and was selected in order not to re- duce the biodegradability of biopolymers.
Boric acid is reported to be able to react with glycerol and starch forming a network among
starch chains and glycerol molecules. It has been suggested the existence of crosslinks among
starch, glycerol and boric acid. Crosslinks be- tween OH- of the components caused by boric
acid would enlarge the molecules and so prevent the segments for easy moving Yu et al., 1998.
In the present work, the addition of boric acid to the blend in a dose non toxic was studied. We
examined the effect of gamma radiation on blends of proteins and defatted whole flour with respect
to the mechanical properties and the water ab- sorption of the molded plastics.
Gamma radiation has been reported to be use- ful in the crosslinking of proteins Ressouany et
al., 1998, which would mean an increase in the tensile strength of the product.
On the other hand, ionizing radiation acts on polysaccharides by breaking C – C bonds and
forming acid and reductive groups Pruzinek and Hola, 1987
The objective was to compare two different varieties of crop products of legumes of Phaseolus
6 ulgaris L.
2. Materials and methods
