biodegradable polymers from corn’s starch
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BIODEGRADABLE POLYMERS FROM CORN’S STARCH
NIK ABD HAFIIDZ BIN NIK ABDUL MALEK
(2014688106)
KHAIRUL IZWAN BIN AHMAD ROBERT
(2014472518)
MOHD ARSHAD BIN ABDUL RASHID
(2014683386)
FARIS AZRI BIN ASWANDI
(2014679658)
TIMOTHY ALVIN
(2014696804)
PREPARED FOR
DR. NIK RAIKHAN BINTI NIK HIM
FACULTY OF CHEMICAL ENGINEERING
UNIVERSITI TEKNOLOGI MARA
SHAH ALAM
2014
1
TABLE OF CONTENTS
PAGE
Introduction 3
1.1 Biodegradable Polymers 4
1.2 Polysaccharides 5
1.3 Starch 5
1.3.1 Amylose 6
1.3.2 Amylopectin 7
1.3.4 Minor Components 7
1.4 Starch-Based Biodegradable Polymers 8
1.5 Preparation of Starch-Based Biodegradable Polymers 8
1.5.1 Physical blends 9
1.5.1.1 Blend with Synthetic Degradable Polymers 9
1.5.1.2 Blend with Biopolymers 11
1.5.2 Chemical Derivatives. 11
1.6 Thermoplastic Starch Products. 12
1.6.1 Starch Reactions And Modifications 13
1.7 Starch – Aliphatic Polyester Blends 13
1.8 Starch Based Superabsorbent Polymers 15
1.9 Polylactic Acid or Polylactide 18
1.10 1,4:3,6-Dianhydrohexitols-Based Polymers 19
1.11 Isosorbide 20
1.11.1 Isosorbide Synthesis 22
1.11.2 Isosorbide In Plastic Production 22
1.11.3 Isosorbide in UV Absorption 24
Conclusion 25
References 26
2
Introduction
Our dependence on plastic in our daily life is very high, almost 100 million
tons annually (Anonymous, n.d). Plastic which is derived from petroleum has some
future constraints due to limited resource and difficulty in degrading so it can cause
environmental problems. In addition, the migration of monomers from the plastic
packaging into food products can cause various health problems.
One of the most studied and promising raw materials for the production of
biodegradable plastics is starch and cellulose which is natural renewable carbohydrate
polymer obtained from a great variety of crops. Starch and lignocellulose are low cost
material in comparison to most synthetic plastics. Starch has been investigated widely
for the potential manufacture of products such as water soluble pouches for detergents
and insecticides, flushable liners and bags, and biomedical delivery systems and
devices (Fishman et al., 2000). Large scale corn productions in Malaysia have to be
expanded in order to meet the growing demand parallel to the expansion of the swine
and poultry industry. The annual import of corn worth 400 million ringgit is expected
to increase to one billion ringgit by the year 2020 (Index mundi, n.d). This versatile,
natural, biodegradable, and renewable resource has many commercial applications. As
a raw material, it is replacing petroleum in many industrial applications, from plastic
containers to clean-burning ethanol. The development of biodegradable polymers is a
high priority from the standpoint of environmental preservation; biodegradable
polymers from corn chemistry have a number of advantages over other synthetic
materials. Starch based biodegradable polymers has many its types of production
which is thermoplastic-starch products, starch-aliphatic polyester blends, starch and
pbs/pbsa polyester blends, starch-based superabsorbent polymers, polylactic acid or
polylactide, 1,4:3,6-Dianhydrohexitols-based polymers, and Isosorbide.
Polymers derived from starch (a component of corn) or other carbohydrates
made from entirely renewable resources have been used in the manufacture of quality
plastics, packaging materials, and fabrics (Koch and Röper, 1988), as well a variety of
biomedical materials for example bioMEMs, biochips, and bioscaffolds. Utilization of
corn starch for biodegradable polymer, will provide greater added value and also
decrease the environmental problem.
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1.1 Biodegradable Polymers
Biodegradable polymers are a specific type of polymer that breaks down after its
intended purpose to result in natural byproducts such as gases (CO2, N2), water,
biomass, and inorganic salts. (Avérous & Pollet, 2012). These polymers are found both
naturally and synthetically made, and largely consist of ester, amide, and ether
functional groups. A polymer based on a C-C backbone tends to resist degradation,
whereas heteroatom-containing polymer backbones confer biodegradability.
Biodegradability can, therefore, be engineered into polymers by the judicious addition
of chemical linkages such as anhydride, ester, or amide bonds, among others. (Maung,
2004).
The usual mechanism for degradation is by hydrolysis or enzymatic cleavage of
the labile heteroatom bonds, resulting in a scission of the polymer backbone.
Macroorganisms can eat and, sometimes, digest polymers, and also initiate a
mechanical, chemical, or enzymatic aging (sigmaaldrich.com, N.D). Different
classifications of various biodegradable polymers have been proposed from previous
studies and our focus is biodegradibles plolymers from starch and more specific is
from corn starch.
Figure 1: Classification of the main biodegradable polymers (Luc Avérous & Eric
Pollet, 2012)
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1.2 Polysaccharides
Polysaccharides are the most abundant macromolecules in the biosphere.
These complex carbohydrates constituted of glycosidic bonds are often one of the
main structural elements of plants and animals exoskeleton such as cellulose,
carrageenan, and chitin. The polysaccharides presented in this chapter are starch.
1.3 Starch
Depending on the botanical origin of the plant, starch grains can have different
shapes and size (from 0.5 to 175 lm). These granules are composed of two a-D-
glucopyranose homopolymers, the amylose and the amylopectin (Guilbot,1985).
Their proportions in the grains depend directly on the botanical source. The amylose
is a mostly linear α-D(1, 4’)-glucan and branched amylopectin, having the same
backbone structure as amylose but with many α-1, 6’-linked branch points (figure )
Figure 2: Molecular structure of starch (Avérous & Pollet, 2012)
5
There are a lot of hydroxyl groups on starch chains, two secondary hydroxyl
groups at C-2 and C-3 of each glucose residue, as well as one primary hydroxyl group
at C-6 when it is not linked. Evidently, starch is hydrophilic. The available hydroxyl
groups on the starch chains potentially exhibit reactivity specific for alcohols. In other
words, they can be oxidized and reduced, and may participate in the formation of
hydrogen bonds, ethers and esters (Tomasik et al., 2004) Starch has different
proportions of amylose and amylopectin ranging from about 10–20% amylose and
80–90% amylopectin depending on the source.
Amylose is soluble in water and forms a helicalstructure. Starch occurs
naturally as discrete granules since the short branched amylopectin chains are able to
form helical structures which crystallize. Starch granules exhibit hydrophilic
properties and strong inter-molecular association via hydrogen bonding formed by the
hydroxyl groups on the granule surface. The starch granule organization consists in
alternation of crystalline and amorphous areas leading to a concentric structure. The
amorphous areas are mainly constituted of amylose chains and amylopectin branching
points. The crystalline parts are mainly composed of amylopectin side chains
(Avérous, Pollet, 2012).
Because of numerous intermolecular hydrogen bonds existing between the
chains, the melting temperature (Tm) of starch is higher than its degradation
temperature. Consequently, to elaborate a plastic-like material, it is necessary to
introduce high water content or/and some non-volatile plasticizers which decrease the
glass transition temperature (Tg) and the Tm (Stepto, 2003). These plasticized
materials are currently named ‘‘thermoplastic starch’’ or ‘‘plasticized starch”. To be
transformed, the starch granular structure has to be disrupted. The disruption can be
obtained either by a solvent-casting process or by a melting process where starch and
plasticizers are mixed under thermo-mechanical treatment.
1.3.1 Amylose
Amylose is defined as a linear molecule of D-glucopyranosyl units joined by α
(1-4) linkage, but it is today well established that some molecules are slightly
branched by α (1-6) linkages Amylose solutions can be easily characterized by size-
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exclusion chromatography coupled on-line to multi-angle laser light scattering (SEC–
MALLS). It is the smaller of the two polysaccharides making up starch molecule. The
amylose is essentially linear but not purely and its solution properties are generally
regarded as typical for those of a linear polymer. (Tomasik et al., 2004) Amylose is
located in the granule as bundles between amylopectin clusters and or randomly
dispersed. They could be located therefore among the amorphous and crystalline
regions of the amylopectin clusters. In starch granules, the amylose chain displays a
natural twist in a helical conformation with six anhydroglucose units per turn
(Guilbot,1985). Amylose is probably the first biopolymer for which a helical structure
was proposed. The ability of amylose to form complexes with butanol provides a
method for separating amylose from amylopectin by selective precipitation according
to Avérous & Pollet, (2012).
1.3.2 Amylopectin
Amylopectin is the highly branched component of starch and it is formed
through chains of α -D glucopyranosyl residues linked together mainly by α (1.4)
linkages but with 5–6% of α (1,6) bonds at the branch points. Thus, the outer chains
(A) are glycosidically linked at their potential reducing group through C6 of a glucose
residue to an inner chain (B); such chains are in turn defined as chains bearing other
chains as branches. The single C chain per molecule likewise carries other chains as
branches but contains the sole reducing terminal residue. The ratio of A-chains to B-
chains is an important parameter which is also referred to as the degree of multiple
branching.
1.3.4 Minor Components
Minor components associated with starches correspond to three categories of
materials: (i) particulate material, composed mainly of cell-wall fragments; (ii)
surface components, removable by extraction procedures; and (iii) internal
components. Lipids represent the most important fraction associated with the starch
granules. Starch quality is also influenced by the presence of lipids, proteins and
phosphorous. Lipid levels are lower in tuber than in cereal starches.
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1.4 Starch-Based Biodegradable Polymers
Starch, a major component of corn, is a linear polysaccharide made up of
repeating glucose groups with glycosidic linkages in the 1-4 carbon positions with
chain lengths of 500 to 2000 glucose units. There are two major polymer molecules in
starch which are amylose and amylopectin. Amylose, which has alpha linkage, is both
flexible and digestible. (Sanjay et al., 2007)
There are three types of biodegradable materials which are agricultural
polymers used alone or blended with biodegradable synthetic polymers, microbial
polymers produced from the fermentation of agricultural products used as substract
and monomers or oligomers polymerized by means of conventional chemical
processes and obtained from the fermentation of agricultural raw materials used as
substract. (Guilbert, 2000)
Starch-based blends present an enormous potential to be widely used in the
biomedical and the environmental fields, as they are totally biodegradable,
inexpensive (when compared to other biodegradable polymers) and available in large
quantities. (Glover, 1993)
1.5 Preparation Of Starch-Based Biodegradable Polymers
Various physical or chemical modifications of starch have been investigated to
improve the properties of starch such as blending and graft polymerization.
8
Figure 3: Molecular structure of amylase and amylopectin(starch) (Lu et al., 2009).
1.5.1 Physical blends
1.5.1.1 Blend With Synthetic Degradable Polymers
Griffin (1977) first started to adopt starch as a filler of polyolefin and its
concentrations is as low as 6-15%. Bikiaris et al. (1998) attempted to enhance
biodegradability of the vinyl polymers by incorporating starch to a carbon-carbon
backbone matrix. The starch granules were used to increase the surface area available
for attack by microorganisms but the system is partially biodegradable and not
acceptable from an ecological point of view. (Lu et al. 2009).
Biodegradable polymers are introduced to prepare completely biodegradable
starch-based composites. Aliphatic polyesters, polyvinyl alcohol (PVA) and
biopolymers were usually used to blend with starch. Poly(β-hydroxyalkanoates)
(PHA) that was obtained by microbial synthesis, and polylactide(PLA) or poly(ε-
caprolactone) (PCL) that were derived from chemical polymerization are the
commonly used polyesters. (Lu e. al. 2009). The blending of starch with degradable
polyesters was done in order to improve its cost competitiveness while maintaining as
well as improving other properties such as mechanical properties.
PLA is one of the most important biodegradable polyesters with many
excellent properties and has been widely applied in many fields, especially for
biomedical one. PLA possesses good biocompatibility and process ability, as well as
high strength and modulus. However, PLA is very brittle under tension and bend
loads and develops serious physical aging during application. Moreover, PLA is a
much more expensive material than the common industrial polymers. (Jun, 2000)
Many efforts have been made to develop PLA/starch blends to reduce total
raw materials cost and enhance their degradability. The major problem of this blend
system is the poor interfacial interaction between hydrophilic starch granules and
hydrophobic PLA. Mechanical properties of blends of PLA and starch using
conventional processes are very poor because of incompatibility. (Wang et al. , 2008)
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Glycerol, formamide, and water are used alone or combined as plasticizers to
enhance the dispersion and the interfacial affinity in thermoplastic starch (TPS)/PLA
blends. This is to improve the compatibility between hydrophilic starch granules and
hydrophobic PLA. The strong intermolecular and intramolecular hydrogen bonds in
starch can be weakened in the presence of water and other plasticizers. (Wang et al. ,
2008) A suitable compatibilizer is needed to enhance the compatibility between PLA
and starch. Another way to enhance the interfacial affinity is by using gelatinization
of starch. Starch is gelatinized to disintegrate granules and overcome the strong
interaction of starch molecules in the presence of water and other plasticizers, which
leads to well dispersion. (Park et al. , 2000)
PCL is a synthetic biodegradable polymer which is linear, hydrophobic,
partially crystalline polyester, and can be slowly degraded by microbes. (Scott and
Gilead 1995) The weakness of pure starch materials including low resilience, high
moisture sensitivity and high shrinkage has been overcome by adding PCL to starch
matrix even at low PCL concentration. Blending with PCL, the impact resistance and
the dimensional stability of native starch is improved significantly. The glass
transition temperature and mechanical properties of TPS/PCL blend are varied with
its composition and the content of plasticizer. TPS/PCL blend is similar to TPS/PLA
blend in both the compatibility and the role of components. (Averous et al., 2000)
PCL/starch blends can be further reinforced with fiber (Franco. et al., 2004) and nano-
clay respectively which results in hydrolytic stability, degradation rate, and
compatibilization between PCL and starch are improved. (Vertuccio. et al., 2009)
1.5.1.2 Blend With Biopolymers
Natural polymers such as chitosan and cellulose and their derivatives are
naturally biodegradable, and exhibit unique properties. A number of researches have
been devoted to study the blend of them with starch. Starch and chitosan are abundant
naturally occurring polysaccharide. Both of them are cheap, renewable, non-toxic, and
biodegradable. The starch/chitosan blend exhibits good film forming property, which
is attributed to the inter- and intra-molecular hydrogen bonding that formed between
amino groups and hydroxyl groups on the backbone of two components. The
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mechanical properties, water barrier properties, and miscibility of biodegradable
blend films are affected by the ratio of starch and chitosan (Bourtoom & Chinnan,
2008)
Extrusion of the mixture of corn starch and microcrystalline cellulose in the
presence or absence of plasticizers (polyols) is used to produce edible films. By
increasing the content of the cellulose component, the rupture strength is increased,
whereas the elongation at break and the permeability of films for water vapor are
decreased. Starch can form thermodynamically compatible blend films with water-
soluble carboxymethylcellulose (CMC) when the starch content is below 25 mass%.
Such films are biodegradable in presence of microorganisms. (Lu et al. 2009).
1.5.2 Chemical Derivatives.
The problem that occurs for starch-based blends is that starch and many
polymers are immiscible. This results in poor mechanical properties of starch/polymer
blends. Therefore, chemical modifications are applied to the starch/polymer blends.
Chemical modifications of starch are generally carried out via the reaction with
hydroxyl groups in the starch molecule. (Bao et al., 2003) Graft copolymerization is
an often used powerful means to modify the properties of starch. Moreover, starch-g-
polymer can be used as an effective compatibilizer for starch-based blends.
(Kiatkamjornwong et al., 2002)
PCL and PLA are chemically bonded onto starch and can be used directly as
thermoplastics or compatibilizer. The graft-copolymers starch-g-PCL and starch-g-
PLA can be completely biodegraded under natural conditions and exhibit improved
mechanical performances. To introduce PCL or PLA segments onto starch, the ring
opening graft polymerization of ε-caprolactone or L-lactide with starch is carried out.
(Dubois et al., 1999) (Choi. et al., 1999)
Starch-g-poly(vinyl alcohol) can be prepared via the radical graft
copolymerization of starch with vinyl acetate and then the saponification of the
starch-g-poly(vinyl acetate). Starch-g-PVA behaves good properties of both
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components such as processability, hydrophilicity, biodegradability and gelation
ability. (Fanta et al., 1979) (Samaha et al., 2005)
1.6 Thermoplastic Starch Products.
When biodegradable thermoplastic-starch plastics, which have a starch
(amylose) content of more than 70 percent, are combined with specific plasticizing
solvents, they produce thermoplastic materials with good performance properties and
inherent biodegradability. The hydrophilic nature of high-starch content plastics,
which readily disintegrate on contact with water, can be overcome by blending and
chemically modifying the material by acetylation, esterification, or etherification.
Starch-based polymers are often plasticized, destructured, and/or blended with other
high-performance polymers (e.g., aliphatic polyesters and polyvinyl alcohols) to
provide useful mechanical properties for different packaging applications. (Sanjay et
al., 2007)
Thermoplastic starch has gradually increased in commercialization. However,
there are still a lot of challenges needed to be overcome to make commercially viable
biodegradable and compostable starch polymers. Thermoplastic starch films generally
need to have starch content greater than 70% to have biodegradable or compostable
action. High amylose starch is preferred for thermoplastic film formation. (Nolan,
2002)
Myllarinen et al. (2002) showed that, while glycerol plasticised amylose films
do retrograde and display slight B and V type diffraction patterns, their crystallinity
remains stable over time and changes in humidity. Conversely, glycerol plasticised
amylopectin films were initially amorphous, but over weeks displayed a steady
increase in B type crystallinity. Interestingly, amylopectin films without plasticiser
remained amorphous during ageing. From both researchers, it can be concluded that
the functional properties of amylose films are in general slightly better than those of
amylopectin films regarding both film strength and barrier properties.
1.6.1 Starch Reactions And Modifications
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The modification of starch has been attracting researchers for applications as
biodegradable packaging materials. Hydroxypropylation is the most important
reactive process in starch film processing where the chemically modified starch which
is Hydroxypropyl (HP) starch has wide range of applications.
HP starches have enhanced solubility, low gelatinisation temperatures, low
retrogradation and crystallinity and superior mechanical properties when compared
with native starches. (Lafargue, et al., 2007) HP starches are completely
biodegradable, and are commonly found in food packaging and film industries. (Kim,
2003) The amylose content and HP modification of native starches have been
demonstrated to have a significant effect on their extrusion characteristics.
(Chaudhary,. et al., 2009)
1.7 Starch – Aliphatic Polyester Blends
Among the natural polymers, starch is of interest. It is regenerated from
carbon dioxide and water by photosynthesis in plants. Owing to its complete
biodegradability, low cost and renewability, starch is considered as a promising
candidate for developing sustainable materials (Lu et al., 2009). Synthetic aliphatic
polyesters have also been developed. Polylactic acid (PLA) is an example of such
polymers. In this case, the monomer used, lactic acid, is a natural product, which
could be obtained from microorganisms through fermentation. Many species of
bacteria, such as those belonging to the genus Lactobacilli, are used to mass-produce
lactic acid.
Organisms such as L. amylophilus produce predominantly the L isomer of
lactic acid, while others, produce mainly the D isomer or a mixture. Synthesis of
polylactic acid usually proceeds through cyclic dimers of lactic acid, also known as
lactides.Two polymerization methods are possible. Condensation polymerization
involves removal of water as esters are formed. This route, however, cannot be used
to produce high molecular weight polymers, unless additives, such as chain extenders,
are added. The additives must later be removed, adding to the cost of production.
13
As a result, condensation is more expensive to perform. To obtain higher chain
lengths without the use of additives, Mitsui Chemicals in Japan has developed
azeotropic condensation methods. As the name implies, the water is removed
azetropically, increasing the efficiency of polymerizatioin. Unfortunately, this method
requires a high quantity of toxic catalysts, which may remain in the polymer. Another
method of PLA production involves ring-opening polymerization (ROP) of lactides.
High molecular weight polymers can be produced using this method. The mechanism
may be either ionic or coordination-insertion, where the latter involves a catalyst.
Ionic ROP may suffer from high levels of racemization, transesterification and
impurities. Various copolymers can be produced to modify the characteristics of the
final product. Examples of monomers that can be used to produce copolymers include
glycolide and valerolactone. Due to its intrinsic brittle nature, plasticizers are
necessary to produce PLA thermoplastic.
Figure 4: Core structure of poly(lactic acid) (source :
http://www.writework.com/uploads/5/57417/skeletal-formula-poly-lactic-acid.png)
Aliphatic polyesters are odorless and can be used for trash bags, diapers, and
cosmetic and beverage bottles. They can be processed on conventional processing
equipment at 140-260 °C, in blown and extruded films, foams, and injection moulded
products. Aliphatic polyesters are biodegradable but often lack in good thermal and
mechanical properties. Vice versa, aromatic polyesters, have excellent material
properties, but are resistant to microbial attack.
1.8 Starch Based Superabsorbent Polymers
14
Superabsorbent polymer (SAP) materials are hydrophilic networks that can
absorb and retain huge amounts of water or aqueous solutions. They can uptake water
as high as 100,000% (Zohuriaan-Mehr, et al., 2008). They are lightly cross-linked
networks of hydrophilic polymer chains. The network can swell in water and hold a
large amount of water while maintaining the physical dimension structure. It was
known that commercially used water-absorbent polymeric materials employed are
partial neutralization products of cross-linked polyacrylic acids, partial hydrolysis
products of starch–acrylonitrile copolymers and starch–acrylic acid graft copolymers.
At present, the material’s biodegradability is an important focus of the research in this
field because of the renewed attention towards environmental protection issues (Lenzi
et al., 2003). The half life is in general in the range 5 - 7 years, and they degrade into
ammonium, carbon dioxide and water.
SAPs are widely used in personal hygiene products. Recent research is
focused in other application areas of SAPs, viz., biosensing, soft actuators/valves,
catalysis, concentration of viruses, vitamin, bovine serum albumin and controlled
drug delivery. SAPs or hydrogels have been also studied for the concentration of
macromolecules. SAPs are used in soil to create a water reserve, near the rhizosphere
zone (roots) and benefit agriculture.
SAPs as hydrogels, relative to their own mass can absorb and retain
extraordinary large amounts of water or aqueous solution. These ultrahigh absorbing
materials can imbibe deionized water as high as 1,000-100,000% (10-1000 g/g)
whereas the absorption capacity of common hydrogels is not more than 100% (1 g/g).
The SAP particle shape (granule, fibre, film,etc.) has to be basically preserved
after water absorption and swelling, i.e., the swollen gel strength should be high
enough to prevent a loosening, mushy, or slimy state. This is a major practical feature
that discriminates SAPs from other hydrogels (Zohuriaan-Mehr,.et al., 2008)
15
Figure 5: A visual comparison of the SAP single particle in dry (right) and swollen
state (left) (Zohuriaan-Mehr,.et al., 2008)
Graft copolymerization of starch with vinyl monomers (viz.
acrylamide, acrylonitrile, acrylic acid) has gained importance in improving some
properties of synthetic absorbent polymers. Moreover, the graft products have
received considerable attention because of their immense industrial potential with
their biodegradability, low cost, and renewability. However, so far more attention has
been put only in the graft products of original starch. Compared with anionic or
cationic graft copolymers, amphoteric absorbent polymers have potential salt-tolerant
swelling character (Li‐Qin et al., 2005).
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The earliest commercial SAPs were produced from starch and AN monomer
by the first mentioned method without employing a cross-linker (Zohuriaan-Mehr, et
al., 2008). The starch-g-PAN copolymer (SPAN) was then treated in alkaline medium
to produce a hybrid SAP, hydrolyzed SPAN (H-SPAN) while an in-situ cross-linking
occurred simultaneously
1.9 Polylactic Acid or Polylactide
The terms Polylactide (PLA) can be defined as biodegradable polymer
production based on renewable resources with a range of applications which is similar
to Polyethylene terephthalate (PET) (R.Hagen, 2012). Uhde Inventa-Fisher, a
German-based company, has been developing a Polylactide (PLA) process for the last
10 years (http://www.uhde-inventa-fischer.com), and Cargill in the United States and
Teijin in Japan are investing in large scale production facilities for the manufacture of
Polylactide (PLA).
Glucose is a common feedstock for the process of Polylactide (PLA), which
can be produced by the hydrolysis of starch. The production of sodium lactate and
some impurities, such as proteins, cellular mass, and so on by the fermentation of
glucose. The sodium lactate is transformed into lactic acid after done a number of
purification steps, which is then concentrated to remove residual water (Chaniga,
2012).
Thermal polymerization or known as self-condensation which yields a low-
molecular weight Polylactide (PLA) pre-polymer, then a distillable cyclic dimmer
(dilactide, or simply lactide) produced by thermally depolymerised. Among these
methods, cross-linking seems to be a particularly good method to improve the thermal
stability of Polylactide (PLA) while maintaining its biodegradability (Quynh et al.,
2007; Mitomo et al., 2006).
High-molecular weight Polylactide (PLA) by the ring-opening polymerization
of the purified dilactide with a suitable catalyst, often a tin salt such as stannous
octoate. The final polymer is then granulated and further processed for the desired
application. The Polylactide (PLA) has good mechanical properties such as it is used
17
as packaging material (e.g., film, sheet, or bottles), textiles (e.g., filaments or fibers),
engineering plastics, and medical polymers (e.g, surgical thread or implants), (Reis et
al., 1997).
1.10 1,4:3,6-Dianhydrohexitols-Based Polymers
It is difficult to incorporate the simple carbohydrates directly into polymer
structures because both primary and secondary hydroxyl functionalities interfere with
the synthesis of well defined products in carbohydrates (Fenouillot, 2009). Then, the
1, 4:3, 6-dianhydrohexitols had been used to circumvent the problem.
Dianhydrohexitols are well documented by-products of the starch industry obtained
by dehydration of D-hexitols, which are made by a simple reduction of hexose sugars
(Stross and Hemmer, 1991). There is about 650,000 tons of Dianhydrohexitols are
produced annually worldwide (Sheldon, 1993).
The chiral biomass derived products transforms or exists as three main
isomers (isosorbide, isomannide, and isoidide), in which depending on the
configuration of the two hydroxyl functions (derived from D-glucose, D-mannose,
and L-fructose, respectively) (Rousseau, 2009). The most widely available
Dianhydrohexitol is Isosorbide in which produced from glucose via sorbitol (Pascault.
1995).
18
Figure 6: The Uhde Inventa-Fisher process of making polylactide from starch.
Source: www.udhe-inventa-fisher.com.
1.11 Isosorbide
Isosorbide is a non-toxic biodegradable diol derived from bio-based feedstock. It can
be used for preparing thermoplastic starch through a semi-industrial process of
extrusion. Isosorbide allows some technological advantages with respect to classical
plasticizers: namely, direct mixing with starch, energy savings for the low processing
temperature required and lower water uptake.(Battegazzore, Bocchini, Nicola,
Martini, & Frache, 2014)
Figure 7:isosorbide (source: google image)
With molecular formula C6H10O4 (Molecular weight = 146.14), it is chiral, large
and bulky, making it look like white crystalline powder, very hygroscopic (~8
kilo/liter of water). Its melting point is around 61-64°C and boiling point of 1600C
(10mm Hg). It is soluble in water, alcohol, dioxane, ketones but almost insoluble in
19
hydrocarbons, esters, ethers. Aside from that, it is very heat stable, non-toxic and
generally recognized as safe. It is difunctional, reactivity of hydroxyl groups not
equivalent. It is a renewable, sustainable and biodegradable resource because it is
derived from sorbitol, a low cost product made from corn.(Michael Jaffe & Friedhoff,
2008)
1.11.1 Isosorbide Synthesis
Figure 8 : isosorbide synthesis
1.11.2 Isosorbide In Plastic Production
The chemistry of isosorbide is highly flexible with the ability to be
manipulated for specific polymer backbones. It can be tailored by different methods
of esterification and develop a proprietary technology platform. The compounds can
have performance similar to dioctyl pthalate in PVC applications. Isosorbide is an
innovative renewable solid plasticizer for thermoplastic starch and is much more
feasible than using petroleum resins. Crystallinity and mechanical properties do not
change in the course of time using isosorbide. (Michael Jaffe & Friedhoff, 2008).
Early work that focused on isosorbide used it as a constituent for the development of
20
thermoplastic polymers for coatings applications (Noordover, 2007)These studies
showed that adding isosorbide in increasing concentrations increased the mechanical
properties of otherwise poor materials, and isosorbide could increase the Tg of their
materials by as much as 73% depending on concentration (Jasinska, 2010). The
temperature profile necessary for the processing is about 20°C lower than that
employed for the classic glycerol plasticization, allowing energy savings. The
obtained TPS is easily processable and film production from compression molding
was proven. The collected data by thermogravimetry have shown that the plasticized
starch is stable up to 200°C in nitrogen as well as oxygen atmosphere like a common
starch plasticized with glycerol. The mechanical properties and oxygen permeability
of starch plasticized with isosorbide are dependent from water content related to the
air relative humidity.
Thermoplastic starch plasticized with isosorbide is not subjected to
retrogradation. Retrogradation is a reaction that takes place in gelatinized starch when
the amylose and amylopectin chains realign themselves, causing the liquid to gel.
(Battegazzore et al., 2014)
Figure 9:
21
Figure 10: PVC Plastic
1.11.3 Isosorbide in UV Absorption
Isosorbide based UV stabilizers like isosorbide bis ferulate ester and related
compounds could be synthesized using a carbodiimide route. Isosorbide enables the
creation of a biodegradable UV stabilizer derived from natural sources. It can absorb
UV light strongly between 230-360 nm, hence suitable to be applied by both plastics
and cosmetics industries. The fact that isosorbide is an antioxidant also incline to the
application in cosmetics. (Michael Jaffe & Friedhoff, 2008)
Conclusion
Studies of biodegradable polymers are very important in ensuring a greener
and more sustainable future. A common misunderstanding is that all biodegradable
polymers are made from renewable resources but they can be produced via synthetic
and biotechnological means for example from petroleum. In order to slow down the
declination of non-renewable resource, high quality polymers can be produced from
alternative, cheaper renewable resources like corn and maize.
There are many advantages in using biodegradable polymers from corn starch
such as biodegradable plastics applies to environmental properties, primarily when it
comes to the handling of waste plastics and the effects of their decomposition on the
22
environment. When biodegradable plastics decompose biologically, the resulting
natural components do not affect the environment in any harmful way. Even though
the ordinary, non-biodegradable plastics do not release harmful substances into the
environment, they are relatively durable and although the threat posed by plastics is
not removed completely, the damage that could be done is significantly lower.
The uses of biodegradeable polymers are wide. Making use of the easily obtained
isosorbide, we can improve the production of multiple industries. In plastic
production, isosorbide reduces production cost while simultaneously improving the
mechanical properties of the plastic. The plastics produced from isosorbide also will
not retrograde (Battegazzore et al., 2014). Meanwhile in the cosmetic industries, the
polymer can be used in improving skin protection against harmful UV rays.
Another advantage of biodegradable polymers is that they decompose into natural
substances and do not require separate collection, sorting, recycling or any other final waste
solution like landfills as is the case with non-biodegradable plastics. While these measures
reduce the environmental impact of waste they cannot eliminate it or establish the state of
natural processes as can be done with biodegradable polymers. Their natural degradation
allows artificial materials-bioplastics to enter the natural cycle and be reused.
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