SAGO PALM 22: 1−5 (2014)

Preparation of biodegradable foam from sago residue
Aldilla Sari Utami1, Titi Candra Sunarti2, Naoto Isono1,*,
Makoto Hisamatsu1 and Hiroshi Ehara1
12

Graduate School of Bioresources, Mie University, Tsu 514-8507, Japan

Department of Agroindustrial Technology, Bogor Agricultural University, Kampus IPB Darmaga, Bogor 16002, Indonesia* Corresponding author

Abstract: We prepared biodegradable foam by pressing and baking a mixture containing native sago residue,cellulose, polyvinyl alcohol, magnesium stearate, and water. The foam was opaque and brown; it had a roughsurface and a porous internal structure. The foam was denser than commercial polystyrene foam. However, themodulus of elasticity and modulus of rupture in flexure of the foam prepared from native sago residue werehigher than those of polystyrene foam, indicating that the foam from sago residue was stiff, had high strength,
and would be suitable for holding and protecting heavy materials. We also prepared another foam using acidtreated sago residue instead of native sago residue. The foam from the acid-treated residue was thinner and moreporous than the foam from the native residue. A higher modulus of elasticity in flexure of the foam from theacid-treated residue was also observed. Thus, we found that partial acid hydrolysis of starch in sago residue
modifies the structural and physico-mechanical properties of the resulting foam.
Keywords: acid treatment, biodegradable foam, packaging, physico-mechanical properties, porous structure,sago residue
Introduction

Sago palm is an important crop for the starchindustry in Southeast Asia and Oceania (Singhal et al.,2008; Awg-Adeni et al., 2013). A large amount ofsago pith waste (sago residue) is produced after starch
extraction and is usually discarded nearby, generating

environmental problems (Awg-Adeni et al., 2010).
The utilization of sago residue is expected not only toreduce the disposal of waste, but also to produce otherbeneficial materials. Many studies have attempted toutilize sago residue for producing beneficial materials,
e.g., fermentable sugar, enzymes, adsorbents, andbioethanol (Singhal et al., 2008; Linggang et al.,2012; Awg-Adeni et al., 2013). However, foammaterial for packaging has not yet been produced
from sago residue.

In the packaging industry, researchers attempt todesign alternative biomaterials to replace synthetic
polymers in view of environmental and economical

considerations. Biodegradable foam is one of theinventions expected to be used for ordinary packaging
that can be degraded by microorganisms. Somestudies have shown that it is possible to prepare

biodegradable foam from starches, natural fibers, andwater (Benezet et al., 2012). Fibers adhere to thestarch matrix and act as reinforcements (Shogren etal., 2002), while water acts as a foaming agent and aplasticizer (Bergeret and Benezet, 2011). In somecases, other polymers such as polyvinyl alcohol(PVA) and additives are also added to improve theproperties of the foam (Shogren et al., 2002; Cinelli etal., 2006; Benezet et al., 2012). PVA is abiodegradable synthetic polymer that improves thestrength, flexibility, and water resistance of foam

(Shogren et al., 1998). Foam is generally prepared byeither the extrusion process or the pressing and baking
process (Glenn and Orts, 2001). In the extrusion

process, materials are fed into a rotating screw

A. S. Utami et.al.

2

extruder with gradual heating. The pressing and

2. Preparation of acid-treated sago residue

preparation of biodegradable foam from cassava

incubated at 37°C for 10 days with daily shaking. The

baking process, on the other hand, involves theSago residue (83 g, dry weight basis) was

casting of materials in a closed heated mold. The

suspended in 1.5 L of 2.0 M sulfuric acid andal., 2007), and potato starch (Cinelli et al., 2006) has

hydroxide and filtered under vacuum using filter

starch (Salgado et al., 2008), wheat starch (Zhou etbeen extensively studied. Biodegradable foam wasalso prepared from sago starch (Pimpa et al., 2007).
However, foam prepared from sago residue has notbeen reported.

In this study, we prepared biodegradable foam fromsago residue and characterized it. The physicomechanical properties were determined, and themicrostructure of the foam was observed. We also
prepared foam from acid-treated sago residue.
Materials and Methods
1. Sago residue

Sago residue, after the extraction of starch, wasobtained from a sago producer in West Java,
Indonesia, and was sun dried for 2 days. The contentof cellulose, hemicellulose, and lignin in the residue

was determined according to Linggang et al. (2012).

Briefly, the content of cellulose was determined bysubtracting the weight of lignin from the weight of theinsoluble material after treating the sago residue witha dilute-acid detergent solution (0.5 M sulfuric acidcontaining 0.05 M cetrimonium bromide). The
content of hemicellulose was the difference between

the insoluble material after treatment of the sago
residue with a dilute-acid detergent solution and thatwith a neutral detergent solution containing 0.1 M

sodium dodecyl sulfate. The content of lignin wasmeasured by weighing the insoluble material afterhydrolysis of the insoluble material after treatment of
the sago residue with a dilute-acid detergent solution

using 13 M sulfuric acid. The starch content wasdetermined by quantifying reducing sugars in acidhydrolysates of starch using the method ISO

5377:1981 (http://www.iso.org).

mixture was then neutralized using 2.0 M sodium
paper. The solid particulates were washed with

distilled water repeatedly and dried at 37 ° C for 3days.

3. Preparation of foam from sago residue

Sago residue (2 g; native residue or acid-treatedresidue), cellulose (0.5 g), PVA (2 g; degree ofhydrolysis of 99.4-99.8 mol%; PT Tirta Marta,

Cikupa Tangerang, Indonesia), water (9 g), andmagnesium stearate (0.5 g) were homogenized using ahigh-speed mixer with a wire whisk attachment(CucinaHR

1530/8,Philips,Amsterdam,Netherlands) for 10 min. Cellulose was prepared fromsago residue by the method described by Hisyam(2012). Magnesium stearate was used as a moldrelease agent (Salgado et al., 2008). The sago residue
mixture was cast by pressing and baking at 170° C for
3 min using a baking machine. This equipment,

consisting of a steel insert and a steel cavity mold,
was made according to Glenn and Orts (2001) withminor modifications of the mold sizes as follows: theinside dimensions of the insert mold are 200 mm inlength, 122 mm in width, and 13 mm in height; while

the inside dimensions of the cavity mold are 203 mmin length, 119 mm in width, and 13 mm in height.
Both molds were preheated before casting, and theinsert (top) mold was moved downward to mate withthe cavity (bottom) mold.

4. Physico-mechanical characterization of the foam

The foam was cut into small square pieces, andtheir length, width, and thickness were measured

using a micrometer screw. Samples were thenweighed, and their densities were calculated.

To evaluate the flexural properties of foam, themodulus of elasticity (MoE) in flexure and thePreparation of foam from sago residue

3

modulus of rupture (MoR) in flexure were determined

The foam was opaque and brown. Scanning electron

method D790-91 (1991). All measurements werefoam (Fig. 2B). Some physico-mechanical properties ofusing a universal testing machine (Model 4500,Instron, Canton, MA, USA) according to ASTM

performed in duplicate or triplicate, and the averagevalues were reported.

5. Scanning electron microscopy

The surface and a cross section of the foam wereobserved using an S-4000 scanning electron

microscopy showed that the surface of the foam wasrough (Fig. 2A), and some cavities existed inside thethe foam were determined (Table 1). The thickness ofthe foam was 3.05 mm. The density (0.286 g/cm3) of thefoam from the native sago residue was greater than thatAB

microscope (Hitachi Science Systems, Hitachinaka,Japan) with an accelerating voltage of 5 kV, as
described previously (Srichuwong et al., 2005b).

200 µm

C

100 µmDResults

1. Characteristics of the foam prepared fromnative sago residue

Sago residue used in this study consisted of starch(63%), cellulose (11%), hemicellulose (7.6%), lignin

Fig. 2. Scanning electron micrographs of foam preparedfrom sago residue A, Surface of foam from native
sago residue; B, cross section of foam from native
sago residue; C, surface of foam from acid-treatedsago residue; D, cross section of foam from acidtreated sago residue(12%), and minor components (e.g., ash andminerals). The composition of this sago residue wassimilar to that reported by Abd-Aziz (2002).
To prepare the foam, native

sago residue, cellulose, water,PVA, and magnesium stearate
were mixed and baked in a pairof molds. Tray-like foam wasobtained by pressing and baking
the sago residue mixture (Fig. 1).

100 µm

100 µmTable 1. Physico-mechanical characteristics of foam prepared from sago residue
Thickness

DensityMoE

MoR(mm)(g/cm3)

(MPa)

(MPa)

Foam from native sago residue

3.05

0.286

387

16.3

Foam from acid-treated sago residue

2.15

0.362

705

17.6

Commercial polystyrene foama

0.68

0.063

105

1.3a

Glenn et al. (2001)

of commercial polystyrene foam (0.063 g/cm3; Glenn etal., 2001). The MoE (387 MPa) and MoR (16.3 MPa) ofthe foam from the native sago residue were high. TheMoE represents the stiffness of a material, while theMoR reflects its strength.

2. Characteristics of the foam prepared fromacid-treated sago residue

We prepared another foam using acid-treated sago

5 cmFig. 1. Foam prepared from native sago residue

residue instead of native sago residue. Shogren et al.
(2002) described that the use of modified starchaffects the structure and properties of the foam. Acid

A. S. Utami et.al.

4hydrolysis has been used for a long time to modify

preferentially hydrolyzed and dissolved; however, thethinner than that from the native residue (Table 1).

of acid-treated sago residue would modify thestarch properties (LeCorre, 2010). The thickness ofthe foam from the acid-treated residue (2.15 mm) was
The density (0.362 g/cm ) and MoR (17.6 MPa) of the3foam from the acid-treated residue were almost thesame as those from the native residue. However, ahigher MoE (705 MPa) was observed in the foamfrom the acid-treated residue. As was the foam fromthe native residue, the surface of the foam from theacid-treated residue was rough (Fig. 2C). However,the foam was more porous than that from the nativeresidue (Fig. 2D).
Discussion

Sago residue is considered suitable for making

biodegradable foam for packaging because it contains
a considerable amount of starch and fibers. In thisstudy, we demonstrated that foam is prepared fromsago residue by pressing and baking with a pair ofmolds. Preparing the foam by the pressing and baking

method has an advantage, in that shapes of foam areeasily modified by using different types of molds(Glenn and Orts, 2001). The MoE and MoR of thefoam from the native sago residue were high,indicating that the foam had a mechanically strong

structure (Table 1) and that it would be practicallyuseful for packaging. During baking of the sago
residue mixture, starch is gelatinized and water is

evaporated, resulting in the formation of foam
(Salgado et al., 2008). Fibers adhere to the starchmatrix and act as reinforcements (Shogren et al.,2002). Starch and fibers have similar chemicalstructures, which might facilitate the formation ofhydrogen bonds between them (Bergeret and Benezet,2011). Cavities existing inside the sago residue foam
(Fig. 2B) might be formed due to water evaporation
during the pressing and baking (Salgado et al., 2008).

Partial hydrolysis of starch using dilute acidgenerates thin-boiling starches (e.g., Naegeli

amylodextrin and Lintner starch). During acidhydrolysis, the amorphous parts of starches aremain crystalline structures (acid-resistant residues)
remain intact (Srichuwong, 2005a). Therefore, the use
structural and physico-mechanical properties of theresulting foam. The thickness of the foam preparedfrom the acid-treated residue was low. Because theswelling power of the starch was reduced by partialhydrolysis, the foam could not expand sufficiently atthe baking step. The water-retaining capacity of starchdecreased with hydrolysis of the amorphous region ofstarch, which might result in the generation of morecavities inside the foam (Fig. 2D). Furthermore, theMoE (i.e., stiffness) of the foam from the acid-treatedresidue was higher than that from the native residue,
which might be attributed to the fact that the acidtreated residue was less amorphous (Table 1). In

contrast, the density and MoR of the foam from theacid-treated residue were similar to those of the foamfrom the native residue. This does not conflict withthe observation by Glenn and Orts (2001) that MoR
tends to be increased by the density of a starch-basedfoam.

The foam prepared from sago residue in this study

has at least two disadvantages. First, the density of thefoam is several times higher than that of commercial
polystyrene foam, which would affect transportation

costs in practical use. Second, the foam from sago
residue readily absorbs a significant amount of waterand becomes fragile (data not shown). Therefore, thefoam can be applied only to low moisture materials(e.g., electronic equipment). Improving the density andwater resistance of the foam is needed for low-cost andwidespread use.

In conclusion, we succeeded in preparing

biodegradable foam from sago residue. The foam wasstiffer and had greater strength than commercial

polystyrene foam. The use of acid-treated sago
residue alters the microstructure and the physico-mechanical properties of foam. Biodegradable foamfrom sago residue would be suitable for holding andprotecting heavy materials.

Preparation of foam from sago residue

References

Abd-Aziz, S 2002 Sago starch and its utilisation. Journalof Bioscience and Bioengineering 94: 526-529.

American Society for Testing and Materials (ASTM)
1991 Method D790-91: Standard test methods for

flexural properties of unreinforced and reinforced
plastics and electrical insulating materials. In:

Annual Book of ASTM Standards. ASTM
(Philadelphia).

Awg-Adeni, D.S., S. Abd-Aziz, K. Bujang and M.A.

Hassan 2010 Bioconversion of sago residue intovalue added products. African Journal ofBiotechnology 9: 2016-2021.

Awg-Adeni, D.S., K.B. Bujang, M.A. Hassan and S.

51139-1153.

Linggang, S., L.Y. Phang, M.H. Wasoh and S. Abd-Aziz2012 Sago pith residue as an alternative cheap
substrate for fermentable sugars production. Applied
Biochemistry and Biotechnology 167: 122-131.

Pimpa, B., K. Muhammad, Z. Ghazali, K. Hashim,

M.A. Hassan and D.M. Hashim 2007 Optimizationof conditions for production of sago starch-based
foam. Carbohydrate Polymers 68: 751-760.

Salgado, P.R., V.C. Schmidt, S.E. Molina Ortiz, A.N.
Mauri and J.B. Laurindo 2008 Biodegradable

foams based on cassava starch, sunflower proteinsand cellulose fibers obtained by a baking process.
Journal of Food Engineering 85: 435-443.

Abd-Aziz 2013 Recovery of glucose from residual

Shogren, R.L., J.W. Lawton and K.F. Tiefenbacher

Benezet, J.C., A. Stanojlovic-Davidovic, A. Bergeret,properties. Industrial Crops and Products 16: 69-79.

starch of sago hampas for bioethanol production.
BioMed Research International 2013: 935852.

L. Ferry and A. Crespy 2012 Mechanical andphysical properties of expanded starch, reinforcedby natural fibres. Industrial Crops and Products 37:435-440.

2002 Baked starch foams: starch modifications andadditives improve process parameters, structure andShogren, R.L., J.W. Lawton, K.F. Tiefenbacher andL. Chen 1998 Starch-poly(vinyl alcohol) foamed
articles prepared by a baking process. Journal ofApplied Polymer Science 68: 2129-2140.

Bergeret, A. and J.C. Benezet 2011 Natural fibre-Singhal, R.S., J.F. Kennedy, S.M. Gopalakrishnan, A.

Cinelli, P., E. Chiellini, J.W. Lawton and S.H. Imamsago palm-derived products. Carbohydrate

reinforced biofoams. International Journal ofPolymer Science 2011: 569871.

2006 Foamed articles based on potato starch, corn

Kaczmarek, C.J. Knill and P.F. Akmar 2008

Industrial production, processing, and utilization ofPolymers 72: 1-20.

fibers and poly(vinyl alcohol). Polymer

Srichuwong, S., N. Isono, T. Mishima, and M.

based foam formed by compression/explosion

susceptibility to acid and enzyme hydrolysis ofDegradation and Stability 91: 1147-1155.

Glenn, G.M. and W.J. Orts 2001 Properties of starchprocessing. Industrial Crops and Products 13: 135-143.

Glenn, G.M., W.J. Orts and G.A.R. Nobes 2001

Hisamatsu 2005a Structure of lintnerized starch isrelated to X-ray diffraction pattern andstarch granules. International Journal of Biological
Macromolecules 37: 115-121.

Starch, fiber and CaCO 3 effects on the physical

Srichuwong, S., T. Sunarti, T. Mishima, N. Isono andHisyam 2012 Isolation of cellulose from sago waste

fine structure to thermal properties and enzyme

properties of foams made by a baking process.
Industrial Crops and Products 14: 201-212.

by using hydrogen peroxide delignification.

Undergraduate thesis, Bogor Agricultural
University (Bogor).

Le Corre, D., J. Bras and A. Dufresne 2010 Starchnanoparticles: a review. Biomacromolecules 11:

M. Hisamatsu 2005b Starches from different
botanical sources I: Contribution of amylopectin
digestibility. Carbohydrate Polymers 60: 529-538.

Zhou, J., J. Song and R. Parker 2007 Microwaveassisted moulding using expandable extruded

pellets from wheat flours and starch. Carbohydrate
Polymers 69: 445-454.