Preparation and Characterization of Electrically Conductive Films from Native Sago Starch

Lisa Sim Siew Onn

Bachelor of Science with Honours (Resource Chemistry)

2013

Faculty of Resource Science and Technology

Preparation and Characterization of Electrically Conductive Films from Native Sago Starch

Lisa Sim Siew Onn (26757)

A final project report submitted in the fulfilment of the requirements for the degree of Bachelor of Science with Honours (Resource Chemistry)

Supervisor: Assoc. Prof. Dr. Pang Suh Cem Co-Supervisor: Dr. Chin Suk Fun

Resource Chemistry Department of Chemistry

Faculty of Resource Science and Technology Universiti Malaysia Sarawak

2013

I

Acknowledgement

First of all, I would like to thank The Department of Chemistry, Universiti Malaysia Sarawak

for giving me an opportunity to fulfil my Final Year Project.

I would like to express my deepest gratitude to my supervisor, Associate Professor Dr. Pang

Suh C em f or hi s g uidance, e ncouragement a nd advice t hroughout t he p roject. H e ha s be en

patiently giving me ideas and information on my project and report writing.

Besides that, I would also like to thank the master students of Physical Chemistry Laboratory,

Kak Fiona and Kak Ainn for their help and guidance in my laboratory work. They have eased

my burden and helped me to solve problem that arised in my project.

Last but not least, I would like to express my appreciation to all my friends that have guided

and supported me in completing my Final Year Project.

II

TABLE OF CONTENTS

Acknowledgement .................................................................................................................. I

Table of content………………………………………………………………………....II-III

List of Tables and Figures ................................................................................................... IV

Abstract .................................................................................................................................. 1

1.0 Introduction .................................................................................................................. 2-3

1.1 Objectives of Study ............................................................................................... 3

2.0 Literature Review ............................................................................................................ 4

2.1 Types of biopolymer and biopolymer films ....................................................... 4-7

2.2 Methods of Preparation and Characterization ....................................................... 7

2.2.1 Preparation of Biopolymer Films ................................................................... 7

2.2.2 Preparation of Electrically Conductive Polymer Films ......................... 8-9

2.2.3 Characterization of biopolymer films .................................................. 9-10

2.3 Application of biopolymers and biopolymer films ........................................ 10-11

3.0 Methodology .................................................................................................................. 12

3.1 Sample Preparation ............................................................................................. 12

3.2 Preparation of Native Sago Starch Solution Mixture. ......................................... 12

3.3 Preparation of Copper (II) Sulfide Dispersion. .............................................. 12-13

3.4 Preparation of Electrically Conductive CuS/Starch-Based Films .................. 13-14

3.5 Flow Chart of Methodology ........................................................................... 15-16

III

4.0 Results and Discussion .................................................................................................. 17

4.1 Physical Properties of CuS/Starch-based Films ............................................. 17-18

4.2 Electrical Conductivity of CuS/starch Films ................................................. 19-23

4.3 Scanning Electron Microscopy (SEM) .......................................................... 24-25

4.4 Characterization by Fourier Transform Infra-Red (FTIR) Spectroscopy ...... 26-27

5.0 Conclusion and Recommendation ................................................................................. 28

6.0 Reference .................................................................................................................. 29-31

IV

List of Tables and Figures

Table 1: Mass of CuSO4·5H2O and Na2S2O3·5H2O required to prepare various concentration of CuS solutions.

Tables

Table 2: Resistivity of CuS/starch films at various concentrations of CuS solutions.

Table 3: E lectrical c onductivity of C uS/starch-based f ilm on v arious concentrations of C uS dispersions.

Table 4: Mean concentrations of copper in CuS/starch films.

Table 5: Calculated mass of copper, sulfide and copper (II) sulphide

Figure 1: Points of measurement for resistivity of electrically conductive CuS/starch films

Figures

Figure 2: O verview of methodology us ed f or t he c oating of s tarch-based films w ith C uS dispersion.

Figure 3: Overview of methodology used for the direct incorporation of CuS dispersion into starch solution mixture.

Figure 4: Photographs of starch based film (a) without CuS (b) with CuS.

Figure 5: Photograph of CuS/starch films with various concentration of CuS solution (a) 0.025 mol dm-3, (b) 0.05 mol dm-3, (c) 0.075 mol dm-3, (d) 0.10 mol dm-3

Figure 6: Photograph of flexible CuS/starch film

Figure 7: Starch film coated with CuS solution

Figure 8: Resistivity and conductivity of starch-based films on va rious concentrations of CuS solutions.

Figure 9: Effect of mass of CuS and concentration of CuS dispersion on electrical conductivity of CuS/starch films.

Figure 10: S EM m icrograph of s tarch-based f ilms ( a) w ithout i ncorporation of c opper (II) sulfide (CuS), (b) with 0.025 mol dm-3 of CuS, (c) 0.05 m ol dm-3 CuS, (d) 0.075 mol dm-3 CuS and (e) 0.10 mol dm-3 CuS.

Figure 11: FTIR spectra of starch-based film (a) without CuS and (b) with CuS (0.10 mol dm-3)

1

Preparation and Characterization of Electrically Conductive Films from Native Sago

Starch

Lisa Sim Siew Onn

Department of Resource Chemistry

Faculty of Resource Science and Technology

Universiti Malaysia Sarawak

ABSTRACT

In t his s tudy, electrically conductive bi opolymer f ilm ha ve been de veloped us ing na tive

sago starch as t he m ain precursor m aterial. Native s ago starch is a l ocally pr oduced

biopolymer w hich is eas ily av ailable, cheap, non-toxic a nd bi odegradable. T he

morphology and chemical structures of the starch-based films was characterized by using

Scanning E lectron M icroscopy ( SEM), F ourier T ransformed Infrared S pectroscopy

respectively and Atomic Absorption S pectroscopy. T he e lectrical conductivity o f s tarch-

based films w as de termined by a mul timeter. The pot ential a pplications of the se

electrically conductive starch-based films were evaluated.

Key Words: starch-based film, Copper(II) sulfide, conductive biopolymers

ABSTRAK

Dalam kajian ini, filem biopolimer elektrik konduktif telah dihasilkan dengan

menggunakan kanji sagu asli sebagai bahan pelopor utama. Kanji sagu asli adalah

biopolimer keluaran tempatan yang mudah didapati, murah, tidak toksik dan mesra alam.

Morfologi dan kimia struktur filem yang berasaskan kanji dicirikan dengan menggunakan

Scanning Electron Microscopy (SEM), Fourier Transformed Infrared Spectroscopy dan

Atomic Absorption Spectroscopy. Pengaliran elektik filem berasaskan kanji telah

ditentukan oleh multimeter. Aplikasi potensi filem-filem berasaskan kanji elektrik konduktif

telah dinilai.

Kata Kunci: filem berasaskan kanji, Copper (II) sulfide, biopolimer konduktif

2

1.0 Introduction

In t he pr esent s tudy, n ative s ago s tarch i s chosen as t he pr ecursor material f or t he

preparation of e lectrically c onductive f ilms be cause s ago s tarch i s c heap, a bundant,

biodegradable and environmentally benign and locally available (Pang et al., 2011b). Sago,

also known as food starch, is prepared from the carbohydrate materials stored in the trunks

of pa lms s uch a s Metroxylon rumphii and M. sagu. Sago s tarch i s c ommonly us ed f or

making noodles, bread, biscuits and so on. Starch film is the thin sheet of flexible material

derived mainly from starch and lesser amount of plasticizer. Electrically conductivity of a

substance is a measure of its ability to conduct an electric current.

According t o T haranathan ( 2005), s tarch i s a macromolecular c omplex of a t l east t wo

polymeric components, namely a l inear and a highly branched α-D-glucan present in the

ratio of ~1:3, r espectively, bot h of w hich are essentially 1,4 -linked, with the la tter in

addition t o ha ve 4 -linked br anches a ttached t o t he m ain c hain b y 1,6 -linkages. T hese

polymeric species are amylase and amylopectin (Ahmad & Arof, 2009).

The purpose of using natural polymers to develop electrically conductive films is because

it i s bi odegradable a nd possesses pot entials t o be de veloped i nto s ustainable m aterials,

while s imultaneously r educing e nvironmental impact. Such films r epresent pot ential

industrial and value-added ut ilization of local resources. Currently, native s tarch is being

widely us ed i n va rious i ndustrial a pplications s uch a s c oating a nd sizing i n pa per

industries, t extiles, bi nder a nd adhesives, absorbent, dr ug de livery carriers, a nd i mplants

(Chin et al., 2011) . A ccording t o A hmad a nd A rof ( 2009), s tarch h as be en i ncorporated

into s ynthetised pol ymer m atrix s ince t he 1970s a nd s everal e fforts ha ve be en m ade t o

convert starch into thermoplastic materials in the past decades. However, native starch has

limited utilization due to several factors such as poor mechanical properties, insolubility in

3

water, and high viscosity. Many researchers have modified native starch to further improve

its properties for more diverse applications. The properties of modified starch are affected

by several factors, such as source of starch, the degree of substitution (DS), and types of

substituent. Lu et al. (2009) stated that possible ways to improve the properties of starch

are t hrough physical o r che mical m odifications s uch a s bl ending, de rivation a nd graft

copolymerization. S tarch unde rgoes pl asticization a nd dopi ng pr ocess t o f orm hi ghly

conductive f ilms ( Lu et al., 2009) . T he a im of pl asticization is t o de crease t he glass

transition temperature and increase the deformation rupture for a lower s tress in order to

change a rigid material at a certain temperature into a malleable material eas ier to shape

and process. Water, glycerol and diethylene glycol are examples of plasticizers used.

The process of making starch films does not require sophisticated equipments or apparatus

which will not incur a high cost for the production. The thickness of starch-based films can

be easily controlled and are conformal to desirable shapes of any devices. Lu et al. (2009)

reported t hat s tarch shows pr operties w hich are s uitable as el ectrode/electrolyte cont act,

and it has both mechanical and adhesive qualities to be made into different forms.

1.1 Objectives of Study

The objectives of this study include:

(i) to develop electrically conductive films from native sago starch.

(ii) to characterize and optimize the electrical conductivity of sago starch film.

4

2.0 Literature Review

2.1 Types of biopolymer and biopolymer films

Biopolymers are generally polymers that occurred in nature, and so it is biodegradable and

renewable. Examples o f biopolymers in the human bod y are carbohydrates and proteins.

Many di fferent t ypes of bi opolymer f ilms a re pr oduced du e t o t heir di verse yet

environmentally friendly properties.

Biopolymers can also be produced into biopolymer plastics by converting plant sugars into

plastic, pr oducing pl astic i nside m icroorganism, a nd gr owing pl astic i n c orn a nd ot her

crops ( Ontario Bioauto Council, n.d.) . T oday, many companies a nd o rganizations a re

conducting research and de veloping p rojects t o e xplore t he bi opolymer i ndustry. T he

advantage of biopolymer i s t hat i s can be extruded, blown, moulded, i njection-moulded,

foamed, thermoformed, and coated onto other materials (Ontario Bioauto Council, n.d.).

Polyhydroxyalkanoates ( PHA) ar e pol yesters t hat accum ulate i n a w ide va riety of

microorganism. A ccording t o O ntario B ioauto C ouncil ( n.d.), P HA c an i mitate

polypropylene, polystyrene, and polyethylene, while exhibiting properties similar to many

synthetic polymers and are considered to be the broadest biopolymer because they are their

own class and can have many different chemical s tructures. These polymers have a w ide

range of properties ranging from stiff and brittle plastics to rubberlike materials. Currently,

there are 100 different monomer types of PHA that have been discovered. PHAs are able to

fully de grade i nto c arbon di oxide a nd w ater, l eaving no e nvironmentally ha rming w aste

behind. PHA’s desirable properties such as good tensile strength, printability, flavour and

odour barriers, heat sealability, grease and oil resistance and temperature stability has made

a m ark i n t he f ood pa ckaging i ndustry ( Ontario B ioauto C ouncil, n.d. ). F ermentation

5

process us ed t o produce P HAs l eads t o pr oduction of pol ymers w ith m any di fferent

combinations of properties.

Polyhydroxybutyrate ( PHB) i s one of t he f ew monomeric uni ts of P HA t hat ha ve be en

introduced into the market in relatively large quantities. It accumulates as energy reserves

in many different types of organisms. PHB has the lowest molecular weight out of all the

PHA monomers. PHB possesses properties similar to polypropylene such as; stiff, highly

crystalline, brittle, has a hi gh melting poi nt, and low mol ecular w eight. Its hi gh melting

point makes processing difficult (Ontario Bioauto Council, n.d.). PHB’s water insolubility

and relatively resistant to hydrolytic d egradation is w hat di fferentiate it f rom ot her

bioplastics. PHB shows good oxygen permeability. It has good ultra-violet resistance but

has poor resistance to acids and bases. It is biocompatible and hence is suitable for medical

applications (Ontario Bioauto Council, n.d.). PHB accumulates as energy reserves in many

different types of organisms.

Many adv antages a re realized when hydroxyvalerate ( HV) i s add ed to produce t he

copolymer P oly ( 3-Hydroxybutyrate-co-3-Hydroxyvalerate) P HBV ( Ontario B ioauto

Council, n.d.). PHBV copolymer is less stiff, tougher, and easier to process than PHB. It is

water resistant and impermeable to oxygen. Depending on the percentage of HV added, the

melting point of PHBV is between 100°C-160°C. For example, P (3HB-co-10%3HV) has

a tensile s trength (Mpa) of 36, 69% crystallinity and a 10% elongation at break (Ontario

Bioauto Council, n.d.).

Poly(lactic acid) (PLA) A i s a t hermoplastic and compostable pol ymer made f rom l actic

acid which can degrade in an aerobic or anaerobic environment in six months to five years.

PLA has similar properties of polyethylene in terms of tensile strength, printability, grease-

resistance, modulus, flavour and odour barrier; the temperature stability and processability

6

of pol ystyrene (Ontario B ioauto C ouncil, n.d.) . P LA can b e pr ocessed b y i njection

moulding, sheet extrusion, blow moulding, thermoforming and film forming. PLA can be

recycled by ch emical c onversion back to lactic aci d and then repolymerized (Ontario

Bioauto C ouncil, n.d. ). Unmodified P LA h as l imitations s uch a s b rittleness, a l ow he at

distortion temperature, and slow crystallization rates. Current applications of PLA include

food pa ckaging, di sposable bot tles, f loral w raps, di sposable ut ensils, di shes, f ast f ood

service ware, medical devices and grocery bags (Ontario Bioauto Council, n.d.).

Tanabe et al. (2002) had developed a keratin-chitosan composite film. The keratin alone is

very f ragile a nd s o c hitosan i s a dded t o s trengthen t he f ilm ( Tanabe et al., 2002) .

Nascimento et al. (2012), reported the development of a film from passion fruit mesocarp

flour (MF) p roduced b y industrial processing o f j uices. M F f ilms a re f ound to be more

hydrophilic, t ougher a nd m ore f lexible t han f ilms m ade f rom s tarch. A lso, F lores et al.

(2010) ha d d eveloped t apioca s tarch-glycerol b ased e dible films w ith x anthan g um or

potassium s orbate added to test its e ffect on the tensile s trength, solubility in water and

elasticity of the films formed.

Wang et al. (2004) reported the development of films prepared from wheat glutens which

were modi fied by mic robial tr ansglutaminase to improve the ph ysical a nd barrier

properties of the films with added glycerol as a plasticizer. The addition of glycerol greatly

improved the water vapour barrier and mechanical properties of the films. Almeida et al.

(2010) had successfully developed chitosan-cellulose films. The blending of cellulose with

chitosan is one of the methods to improve the mechanical properties of chitosan which is

water-sensitive and poor in tensile strength after wetting in water (Almeida et al., 2010).

Cha et al. (2002) h ave de veloped N a-alginate- and k -carrageenan-based films w ith

incorporated antimicrobial a gents f or pot ential f ood pa ckaging pur poses. B esides that,

Emmambux et al. (n.d.) had also reported on t he production of edible coatings and films

7

from c ereal bi opolymers s uch a s pr oteins a nd pol ysaccharides as t hey h ave good

mechanical properties and excellent gas and grease barriers.

2.2 Methods of Preparation and Characterization

2.2.1 Preparation of Biopolymer Films

Wang et al. ( 2006) pr epared t he film-forming s olutions b y s olubilising the s tarch using

distilled water a nd glycerol w as added as a pl asticizer to the te st s olution at a c onstant

glycerol:starch pow der r atio of 1: 2 ( w/w). T he i ncorporation o f pl asticizers r educes t he

crystallinity and glass tr ansition temperature of s tarch while e nhancing t he i onic

conductivity by reducing ionic aggregation (Lopes et al., 2002). The solutions were stirred

continuosly us ing a m agnetic s tirrer hot plate a nd he ld f or 30 m inutes a t temperature of

(60–80) °C then subsequently cooled to 40°C (Wang et al., 2006). Any remaining bubbles

were removed via pipette and left to rest. The films were formed by casting the solution in

a level circular Teflon-coated Perspex plates, transferred to a controlled room and dried for

24 h at 50 ± 5% RH (relative humidity) and 23h ± 2°C. The formed films were peeled from

the casting plates (Wang et al., 2006).

Arrieta et al. (2011) stated that the electrically conductive starch film could be developed

through the casting process with a condition of pH 9.0 and a controlled temperature of 70

ºC for 15 minutes. The sago starch are mixed with glycerol (GLY), glutaraldehyde (GLU),

polyethyleneglycol (PEG) and lithium perchlorate (LP) at room temperature with constant

stirring ( Arrieta et al., 2011 ). T he s olution w as l eft s itting f or 48 ho urs at 70 ºC on

polytetrafluoroethylene trays (Arrieta et al., 2011). Seven days after making of films, the

films are stabilized and were assessed on its physical consistency and conductivity.

8

2.2.2 Preparation of Electrically Conductive Polymer Films

Yamamoto et al. (1993) had developed electrically conductive poly(ethylene terephthalate)

(PET) and poly(vinyl alcohol) (PVA) films by depositing copper (II) sulfide on the surface

of the films. As reported by Inoue et al. (1992), CuS is precipitated instantaneously when a

readily di ssociated water-soluble c opper c ompound, r eacts w ith s odium s ulfide. Ionic

copper compound has a faster rate of formation when used in the preparation of CuS, as

compared to the us e of a s table coppe r ch elate which might l ead to the f ormation of a

different pr oduct. T he P ET f ilm w as i mmersed i n a m ethanol s olution ( 1%) of

poly(ethyleneimine) (PEI) for 48h a t room temperature and dried for 2-3h (Yamamoto et

al., 1993) . T he P EI-treated f ilm w as c onnected t o a w ire a nd di pped i n a s olution o f

CuSO4·5H2O (0.10M) and Na2S2O3 (0.10M) in a beaker and heated at 70°C by an oil bath

with magnetic stirring (Yamamoto et al., 1993).

According t o Y amamoto et al. ( 1993), i n t he f irst 0.5h, t he c olor of the s olution t urned

from yellow green to yellow brown, then dark b rown to black. After 2h, the black color

solution turned colorless while the film turned green and the resulting film was rinsed with

water several times before being dipped in water under ultrasonification for 0.5h and dried

in the air (Yamamoto et al., 1993).

Yamamoto et al. (1993) stated that the copper (II) sulfide coated PET film shows a surface

resistivity of 55Ω/square. According to Inoue et al. ( 1992), t he c opper i n c opper (II)

sulfides, C uxS, has m ixed valence s tates t hat at tributes to its c omplicated structures a nd

leads t o i nteresting c hemical pr operties. C opper s ulfide (CuxS) us ually e xhibits s emi-

metallic properties, intrinsic semi-conductivities and in some cases, ductility (Chen, 2011).

CuS c an be e xploited in t he f abrication of electronic de vices due s t o its m etal-like

electrical behaviour (Inoue et al., 1992). According to Chen (2011), copper sulfide (CuxS)

9

thin films have been found to have very useful electrical and optical properties which have

attracted great interest for their potential use in energy application, such as applications in

achievement of s olar c ells a nd i n pho tochemical c onversion of s olar e nergy a s s olar

absorber coating, as selective radiation filters on architectural windows for solar control in

warm climates and as electroconductive coatings deposited on organic polymers. Although

PET is not a biopolymer, there is a possibility of copper (II) sulfide incorporated to starch

films to produce an electrically conductive film.

2.2.3 Characterization of biopolymer films

The Four-Point P robe i s us ed t o m easure t he film t hickness a nd r esistivity of t he s tarch

film (Chan, 1994). It consists of four equally spaced tungsten metal tips with finite radius.

To m inimize s ample da mage dur ing pr obing, e ach t ip i s s upported by s prings. T he f our

metal tips will automatically travels up and down during the measurement as it is a part of

an auto-mechanical stage (Chan, 1994). According to Bautista (2004), the film resistivity is

determined by the voltmeter which measures the voltage across the inner two probes as a

high impedance current source is used to supply current through the outer two probes. A

typical probe spacing (s) is ~1mm. Only a thickness of 100’s of Angstroms up to 1 micron

can be measured (Bautista, 2004). Acccording to Gutierrez et al. (2002), surface resistivity

could be defined as the material’s inherent surface resistance to current flow multiplied by

that r atio of s pecimen s urface di mensions ( width of e lectrodes di vided b y t he di stance

between electrodes) w hich t ransforms t he m easured r esistance t o t hat obt ained i f t he

electrodes had formed the opposite sides of a square. For low resistive material such as the

starch film, a maximum current is needed to achieve a reading on the display but has to be

restricted to a cer tain number due t o heating ef fects and excessive cur rent density at t he

probe tips (Chan, 1994). Surface resistivity does not depend on the physical dimensions of

the material.

10

The m orphology a nd pa rticles s ize of t he s tarch f ilm a re i nvestigated by us ing s canning

electron m icroscope (SEM) ( Chin et al., 2011) . Images a re t aken on a J EOL J SM-820

model S EM a t a m agnification of 5000x . T he starch f ilms a re pr e-coated with a thi n

platinum la yer to minimize the c hanging e ffect. Noraini Binti ( 2011) reported that the

optimum temperature that was used to dry the starch films was at 60°C because the drying

process was rapid enough to prevent the formation of bubbles on the surface of the starch

films. Almeida et al. (2010) reported that FTIR Spectroscopy is used in the examination of

the chemical composition of the starch film to determine any changes had occurred in the

molecular structure between 400 and 4000cm-1. The starch films were mixed with KBr and

compressed t o f orm pe llets f or i nfrared m easurement. The s tarch films ha ve w avelength

peak of 3436c m-1 for –OH bond and w avelength pe ak o f 2930c m-1 while t he s tarch-

glycerol f ilms ha ve w avelength pe aks o f 2935c m-1 for –CH bond, 1412 cm-1 for –C-OH

bond a nd 1079c m-1 for C -O bond ( Noraini B inti, 2011) . B esides, t he pe rcentage

composition of c arbon, h ydrogen a nd ni trogen a re de termined b y us ing CHN E lemental

Analyzer (Pang et al., 2011a), where the samples were combusted at high temperatures in a

stream of oxygen and the products of combustion of carbon, hydrogen and nitrogen were

measured in a single analysis.

2.3 Application of biopolymers and biopolymer films

According t o O chubiojo a nd R odrigues ( 2012), s tarch ha s t aken a ne w pot ential

biomaterial f or pha rmaceutical a pplications be cause of i ts uni que ph ysiochemical and

functional characteristic. Starch can act as tablet disintegrant where by they are generally

employed for i mmediate r elease t ablet f ormulations w hen t he dr ug s hould be a vailable

within short span of t ime to the absorptive area (Ochubiojo & Rodrigues, 2012) . On the

other hand, starches that have undergone modification such as Graft, acetylation and ester

phosporylation have been extensively evaluated for sustaining the release of drug for better

11

patient compliances. Acetylated and hydroxyethyl s tarch are now mainly used as pl asma

volume e xpanders f or t he t reatment of pa tients s uffering f rom t rauma, he avy bl ood l oss

and cancer (Ochubiojo & Rodrigues, 2012).

According to Lu et al. (2009), starch based biopolymers films can be applied in the area of

food i ndustries a nd a griculture. T raditional f ood pa ckaging m aterial s uch a s l ow de nsity

polyethylene (LDPE) has affected the environment due to its non-biodegradability which

leads t o a p roblem i n i ts di sposal. B y h aving n on-toxic and antimicrobial b iodegradable

films for food packaging, food product protection would improve immensely. Emambux et

al. (n.d.) reported that the use of edible coatings/biofilms and polymeric packaging f ilms

can be as effective as refrigeration, use of chemical additives and irradiation in extending

the shelf life of minimally processed food fruits and vegetables. Edible coatings and films

can be applied on fresh and minimally processed fruits and vegetables to extend their shelf

life by creating a modified atmosphere and preventing water loss (Emmambux et al., n.d.).

Emmambux et al. (n.d.) also reported that the white discoloration, a physiological defect,

in minimally processed carrots was reduced by the use of a cellulose based coating.

Lu et al. ( 2009) a lso m entioned t hat t he a bundant c onsumption of a griculture f ilms ha s

lead to non-economic and time-consuming methods of disposal such as landfill, recycling

or bur ning w hich c auses ha rm t o t he e nvironment. T he de velopment of s tarch-based

biodegradable polymers has three major applications in the agriculture area which are; the

covering o f greenhouse, mulch film and fertilizer controlled release materials (Lu et al.,

2009) w hich w ill ove rcome t he pr oblems m entioned. A s m entioned b y A lmeida et al.

(2010), c hitosan-cellulose b iopolymer f ilm is a pot ential s ubstitute f or c ommon

thermoplastic which readily pollutes the environment.

12

3.0 Methodology

3.1 Sample Preparation

Native Sago starch powder was purchased from the local store and stored in the desiccator

filled with anhydrous silica gel to reduce the moisture content. The sago starch was used

without f urther pur ifications i n t he e xperiment. C opper ( II) s ulfide ( CuS) w as us ed t o

induce e lectrical conductivity in the s tarch-based f ilms. CuS was prepared b y di ssolving

Copper S ulfate P entahydrate ( CuSO4·5H2O) a nd S odium T hiosulfate P entahydrate

(Na2S2O3·5H2O) in Ultra Pure water.

3.2 Preparation of Native Sago Starch Solution Mixture.

1.9212g of sago starch was dispersed into 62.5 ml of Ultra Pure water and heated at 100°C

for 1 ½ hours in a water bath to gelatinize the starch. The starch mixture was stirred slowly

to avoid trapping or the formation of air bubbles and was covered with aluminium foil to

avoid c ontamination b y dus t a nd e xcessive e vaporation. T hen, 0.38m l of glycerol and

0.10g of sodium sulphate (Na2SO4) salt was added into the solution. The solution mixture

was then stirred for at least 1 hour until mixed homogeneously.

3.3 Preparation of Copper (II) Sulfide Dispersion.

To prepare the CuS dispersion, CuSO4·5H2O and Na2S2O3·5H2O were dissolved in 250ml

of ultra pure water in a beaker. The ratio of CuSO4·5H2O to Na2S2O3·5H2O used was 1:1 in

the pr eparation of 2 electrically conductive s tarch-based f ilms. T he s olution ha d a bl ue-

green colour as the solids starts to dissolve. The solution was heated at around (50-60) °C

for at least ½ hour until black precipitate were formed. The final solution consists of a clear

transparent solution at the top and black precipitate at the bot tom of the beaker. The top

clear solution was removed. 10ml of Ultra Pure water was added into t he bl ack mixture

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remained i n t he b eaker a nd put i nto a s onicator a nd s onicated f or 1 0 m inutes. F our

different concentrations of C uS s olutions w ere pr epared t o m ake t he s tarch-based films

electrically c onductive. T able 1 s hows t he w eights of C uSO4·5H2O a nd Na 2S2O3·5H2O

used to prepare various concentrations of CuS solutions.

Table 1 : Mas s o f CuSO4·5H2O a nd Na 2S2O3·5H2O r equired t o p repare v arious co ncentration o f C uS

solutions.

Concentration of CuS solution (mol dm-3)

Mass of CuSO4·5H2O used (g)

Mass of Na2S2O3·5H2O used (g)

0.025 0.7803 0.7753

0.050 1.5605 1.5510

0.075 2.3408 2.3260

0.100 3.1210 3.1014

3.4 Preparation of Electrically Conductive CuS/Starch-Based Films

In this study, two different approaches were carried out to prepare electrically conductive

starch-based films:

(a) The pr e-formed s tarch film w as di pped i n 0.10 M of c opper ( II) s ulfide ( CuS)

solution and then dried in the oven at 55 °C.

(b) CuS dispersion was added directly into the starch solution mixture and dried in the

oven at 55 °C.

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In method (a), the pre-formed starch film was dipped into 10ml of CuS dispersion and then

dried in an oven at 55 ° C until the the films were completely dry. In method (b), 10ml of

CuS di spersion was poured into t he beaker containing 62.5ml of s tarch solution mixture

and left to stir for another ½ hour. 30ml of the CuS/starch dispersion was poured into each

Petri dish and dried at 55°C in the oven for 26 hour s to form the CuS/starch-based film.

The resulting films were stored in the desiccators to prevent absorption of moisture before

further an alysis. Duplicate s amples w ere pr epared for di fferent con centrations of C uS

dispersion.

The electrical conductivity of the starch-based films was tested using a multimeter based

on their resistance. The lower the resistivity, the higher the e lectrical conductivity of the

CuS/starch-based film. For e ach concentration of t he el ectrically cond uctive C uS/starch

films, two films are prepared; film A and film B. The resistivity for film A and Film B for

each concentration was taken based on three points on a given film as shown in Figure 1.

Figure 1: Points of measurement for resistivity of electrically conductive CuS/starch films.

Point 1

Point 2

Point 3

CuS/starch film

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3.5 Flow Chart of Methodology

Figure 2 shows the flow chart of an overview of methodology used in the study.

Figure 2: Overview of methodology used for the coating of starch-based films with CuS dispersion.

1.9212g of native sago starch powder was dispersed in

62.5ml of Ultra Pure water. CuSO4·5H2O and

Na2S2O3·5H2O are dissolved in 250ml Ultra Pure water

Heated at 100 °C for 1 ½ hrs.

Gelatinized starch solution Heated at (50-60) °C for ½ hr. Glycerol and Na2SO4

was added and solution stirred for 1 hr.

CuS precipitate. Sago starch/ glycerol solution

Poured in Petri dishes and dried in oven at 55 °C for 26 hrs.

Sonicated in Ultra Pure water

Starch-based films CuS Dispersion

Coated with CuS dispersion and dried in oven at 55 °C

CuS/starch films

Electrical conductivity measurement of CuS/starch films by using a multimeter.

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3.5 Flow Chart of Methodology

Figure 3 shows the flow chart of an overview of methodology used in the study.

Figure 3: Overview of methodology used for the direct incorporation of CuS dispersion into starch solution mixture.

CuSO4·5H2O and Na2S2O3·5H2O are dissolved

in 250ml Ultra Pure water

1.9212g of native sago starch powder was dispersed in

62.5ml of Ultra Pure water.

Heated at 100 °C for 1 ½ hrs.

CuS precipitate. Gelatinized starch solution

Glycerol and Na2SO4 was added and solution stirred for 1 hr.

CuS Dispersion Sago starch/ glycerol solution

CuS/starch solution mixture

CuS/starch films

Electrical conductivity measurement of CuS/starch films by using a multimeter.

Heated at (50-60) °C for ½ hr.

Sonicated in Ultra Pure water.

Dried in oven at 55 °C for 26 hrs.

Stirred for ½ hr.

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4.0 Results and Discussion

4.1 Physical Properties of CuS/Starch-based Films

Figure 4 s hows two s tarch-based f ilms with and without t he i ncorporation of copper ( II)

sulfide. CuS/starch f ilms were black in colour due to the CuS layers which was bl ack in

colour. The surface appearance of starch based films without CuS were transparent with a

smooth and shiny surface surface morphology whereas CuS/starch films showed a rougher

surface morphology. This was probably due to the presence of tiny CuS particles deposited

on the surface of the films.

Figure 4: Photographs of starch based film (a) without CuS (b) with CuS. Figure 5 shows the CuS/starch films with various concentrations. As the concentration of

CuS dispersion increase, t he C uS/starch f ilms t end t o s how a m ore r ubbery and r ough

texture, probably attributed to the thick layer of CuS. The CuS/starch films still possessed

the flexibility of starch-based films without the addition of any CuS layer. The CuS/starch

film could be bent or rolled without cracking. Figure 6 shows a rolled up CuS/starch film.

Figure 7 s hows a s tarch f ilm t hat ha d be en c oated w ith C uS di spersion b y di p-coating.

During the coating pr ocess, the s tarch films be came s oft w ith a slight ge latinous

(b) (a)

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consistency due t o t he adsorption of w ater. In this c ase, t he dr ied C uS/starch f ilm w as

brittle and the coating of CuS on the starch-based film was not uniform.

Figure 5: Photograph of CuS/starch films with various concentration of CuS dispersion (a) 0.025 mol dm-3,

(b) 0.05 mol dm-3, (c) 0.075 mol dm-3, (d) 0.10 mol dm-3

Figure 6: Photograph of flexible CuS/starch film Figure 7: Starch film coated with CuS dispersion

(b) (a)

(c) (d)