A NATURAL FIT FOR SUSTAINABLE DEVELOPMENT
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Polysaccharides are biologically produced (bio-based) materials that have a unique combination of functional properties and environmentally friendly features. Polysaccharides are also polymers and their long chain structures, as in man-made polymers, provide good mechanical properties for applications such as fibers, films, adhesives, melt processable plastics, thickeners, rheology modifiers, hydrogels, drug delivery agents, emulsifiers, etc. They are renewable materials, produced from other biological compounds, and generally are non-toxic and biodegradable. These features make polysaccharide materials a natural fit for sustainable development. Commercially available products include starch, cellulose and its derivatives (such as cellulose acetate, carboxymethyl cellulose, and methyl cellulose), sodium alginate, xanthan gum, dextran, carrageenan, and hyaluronic acid. Research continues to bring us new materials with improved performance and lower costs. This website is dedicated to promoting the commercial development of polysaccharide materials. Explore this website and learn more about the chemical and physical properties of polysaccharides, their applications and markets, and commercial sources. Featured below are highlights of recent articles about exciting developments with polysaccharide materials. “From ophthalmic drug delivery to inexpensive thermoplastics, biomaterials made
from polysaccharide[s] offer sometimes surprising solutions to modern problems.
Visitors will learn a lot from this site.” |
 Polysaccharide sources: wood (cellulose), seaweed (alginate), bacteria (xanthan gum) |
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| NEWS HARVEST |
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January 2010 - Microencapsulation by coacervation
Microencapsulation is a process that provides a structured coating around small 
liquid droplets or solid particles. This can be very useful in order to protect
the core materials from other reactive compounds, like oxygen; to improve their
handling characteristics, for example to give a liquid the properties of a
solid; or to provide a controlled-release mechanism to an active ingredient,
such as pharmaceuticals, flavors and fragrances. Different microencapsulation
processes have evolved for different needs, such as coacervation. In
coacervation, an aqueous
polymer solution is induced to deposit a coating, or shell, around a dispersed,
immiscible phase of liquid droplets. After separation of the remaining water
phase, the coated particles may be dried or otherwise treated to form hardened
particles. The coacervation of the polymer coating can be induced by different
mechanisms. In the simplest system, coacervation is induced by changes in
temperature or salt concentration, or addition of a non-solvent or an
incompatible polymer to the solution. Polysaccharides are well suited to this
application due to their water solubility and functional groups that can be
exploited for coacervation.
In practice, microencapsulation by coacervation involves three steps:
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Droplet formation – agitation and dispersion of an immiscible liquid in an aqueous polymer solution
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Coacervate formation - conversion of the mixture into 3 immiscible phases (dispersed core, shell/coating, and continuous aqueous phase)
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Microcapsule isolation - drying or crosslinking
Recently, progress on a new method for microencapsulation has been reported (“Microencapsulation of oil by polymer mixture-ionic surfactant interaction induced coacervation,” JM Katona, VJ Sovilj, LB Petrovic, Carbohydrate Polymers 2010, 79, 563-70 [abstract]). Microcapsules of vegetable oil were prepared by coacervation with aqueous solutions of two polysaccharide materials induced by addition of a surfactant. The resulting microcapsules were spray dried to form powders and their properties were studied. The following components were used: 0.7% aqueous hydroxypropyl methylcellulose (HPMC, a slightly hydrophobic nonionic polysaccharide), 0.3% sodium carboxymethylcellulose (NaCMC, an anionic polysaccharide), 0-2% sodium dodecylsulfate (SDS, an anionic surfactant). The interactions of these three materials in water are complex and depend on relative concentration. HPMC and NaCMC are compatible in water forming a homogeneous mixture. However, upon addition of the anionic surfactant SDS, it associates with HPMC through hydrophobic interactions. This association results in an increased negative charge in the complex which causes unfavorable interactions with NaCMC and ultimately separation of an HPMC/SDS coacervate phase. Various properties of the coacervate and the final microcapsule were evaluated.
This work is a good example of how subtle hydrophobic, hydrogen-bonding, and ionic interactions between polysaccharides and with small molecules in water solution can lead to very useful materials.
October 2009 - Specialty adhesive for dentures
Polysaccharides can be very useful adhesives. The two key characteristics of a good adhesive
are a strong adhesion to surfaces and a sufficent cohesive strength within the cured adhesive itself to hold the bond
together when exposed to pulling (tensile) or shearing forces. As with most polymers, their high molecular weight
affords good cohesive strength. Adhesion of the polymer to different surfaces is generally a property of the individual
materials. Generally polar, hydrophilic polymers like polysaccharides adhere well to similar high surface energy surfaces,
as evidenced by easy wetting by water.
One interesting application of polysaccharide adhesives is for dentures. This application requires that the adhesive be non-toxic, non-irritating, easily applied and removed, and the adhesive formulation should remain homogeneous in its packaging over time. In addition, it should be able to form an effective thin film so that it not displace the dentures while in use, a neutral or basic pH so as not to promote demineralization of tooth enamel, and resistance to fermentation which leads to acid formation by oral microbes.
The first denture adhesives were actually comprised of polysaccharide gums (water-soluble polysaccharides). However current products utilize synthetic polymers comprised of polyvinylmethylether maleate or polyvinylalcohol-methyl acrylate copolymer. These materials have performed better than the polysaccharide gums however they suffer from a difficulty in complete removal after use and have a tendency to separate into low and high viscosity components in their packaging leading to premature hardening of the formulation and, as a result, product waste.
A new patent application [JC Sunnucks, “Water Erodible Denture Adhesive,” US Patent Applic. 2009/0205534 (8/09) [full text] discloses a denture adhesive comprised of high amylose corn starch and glucomannan, both commercially available polysaccharides. The high amylose corn starch is resistant to intra-oral fermentation and thus acid formation. Glucomannan is derived from aloe or konjac plants and produces desirable thin films. When mixed with water the material forms a composite in which the continuous high-amylose starch phase is dispersed in the aqueous glucomannan. The mixture exhibits a higher shear strength than either component separately. The shear strength of this adhesive is only about 1 psi but this is all that is required in this application - sufficient but not too strong so that it can be removed when needed. The new adhesive had comparable strength to the commercial denture adhesives derived from synthetic polymers. It is not clear if the adhesive sets, or builds strength, after application or whether it has sufficient strength and adhesion to the denture and oral surfaces right out of the tube.
Isn't a bit ironic that certain foods that you put in your mouth to eat - plant polysaccharides - can cause your teeth to go bad, but also be used to help hold your replacement choppers in place??
June 2009 - The goal: competitively priced microbial polysaccharides
A number of polysaccharides are commercially produced by fermentation of renewable resources – for example,
xanthan gum, gellan, dextran, and pullulan. 
They generally find use in higher value
applications such as thickeners and rheology modifiers in food and medical applications. Pullulan is a water-soluble,
colorless material that makes strong films with high adhesion and oxygen barrier properties. In addition, it is edible
and sold in food applications, such as protective coatings and packaging. A large market is also in capsules for
pharmaceuticals. Chemically, pullulan is a polymer of glucose repeat units with α-(1,4) linkages, much like starch,
but with a portion of 1,6-linkages. This is enough to disrupt the regular structure and render the polymer with properties
that produce amorphous, flexible films and greater water solubility. Thus it has very attractive physical and mechanical
properties. However the cost to produce it is still significantly greater than similar polymeric materials produced from
petrochemical sources. However, with a driving force to production of more sustainable and environmentally friendly
materials, efforts continue to improve the production cost of pullulan. These improvements should be applicable to
other microbial polysaccharides and help their overall commercial development and broader utility.
In a recent publication, researchers described improvements to the pullulan production process. Key challenges in the production process lie in the product isolation after the fermentation is complete - in particular, separation of proteins, color bodies, and other impurities. Currently proteins are separated by selective precipitation of the polysaccharide from an aqueous solution by dilution with ethanol. Much but not all of the protein contaminant remains in solution. Color is conventionally removed by carbon absorption although separation of the resulting carbon from the viscous solution is difficult and leads to product losses. New improvements which optimized the recovery of pullulan have been demonstrated and involve separating cell mass by centrifugation, heating the broth at 80 C to denature and precipitate protein, decolorization by treatment with hydrogen peroxide, concentration by vacuum distillation of water, and then ethanol precipitation. The final pullulan product was obtained with a high recovery and in higher purities than commercial material (“Downstream processing of pullulan from fermentation broth,” S Wu, Z Jin, JM Kim, Q Tong, and H Chen, Carbohydrate Polymers 2009, 77, 750-753 [abstract]).
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February 2009 - Biodegradable, polysaccharide based scale inhibitor for industrial water treatment
The average person is largely unaware of the industrial water treatment business. Yet it is very
important for the efficient workings of industry today. Water is used in many industrial operations, for example in
cooling towers or geothermal systems for heat transfer, or in oilfield operations to maximize recovery of oil. The tanks, pipes,
heat exchangers, etc. all must be kept clean of fouling by inorganic and organic materials which is a continual challenge.
One class of chemicals employed for this purpose are scale inhibitors. They work by inhibiting crystal formation and deposition
on equipment surfaces. Commercial products are phosphonates and low molecular weight polyacrylates and polymaleates. Although
effective, they are lacking in biodegradability which is desirable considering that the environmental fate of these materials
often is discharge into water bodies.
This is where polysaccharides come in ... water soluble, polymeric, biodegradable, economical, and as a bonus, produced from renewable resources. By suitable modification of the polysaccharide structure, the required scale inhibition properties can be achieved. more...
October 2008 - Using the polysaccharide triple helix to produce functional one-dimensional nanocomposites
We all are aware of the elegant and powerful double-stranded helix structure of DNA which is the basis of the life
reproduction process. Another helix structure with amazing properties is found in some polysaccharide materials and it
is being exploited to generate new composite materials for nanotechnology. β-1,3-Glucans, as found in biologically
produced and commercially available polysaccharides such as curdlan, schizophyllan, and scleroglucan, exist in triple
stranded helix structures. The interior of the helix structure is hydrophobic and the exterior is hydrophilic. This
structure might be considered to be an extended version of a cyclodextrin. The triple helix structure is favored in
aqueous mixtures but it can be denatured to a random coil structure by dissolution in polar aprotic solvents. The helix
can be reassembled by exchanging the solvent back to water and it is this reversable process which has been recently
employed to wrap the polysaccharide around other materials which are hydrophobic and fibrous (one dimensional) and thus
modify their properties. In addition, this “sugar-coating” should improve biocompatibility.
Also note that the β-1,3-glucan structure is stable in the human system
due to a lack of enzymes available to degrade it and offers utility in medical/health applications.
Carbon nanotubes have very impressive mechanical properties and electrical conductivity and are at the forefront of new materials in nanotechnology. Processing and use of carbon nanotubes is limited by their hydrophobicity and agglomeration. A hydrophilic character can be incorporated onto the surfaces of the nanosized fibers by co-assembling, or wrapping, them with a β-1,3-glucan. more...
August 2008 - Controlled-release systems based on a hydrophilic matrix
Too much of a good thing can have unintended consequences. This is true in pharmaceutical applications and in applications
involving herbicides, biocides, personal care products, fragrances, even toilet cleaning products, where a large dose of the
product can be 
harmful, expensive, or produce some other undesirable sensory effects. Thus, controlled, or sustained, release
technology has evolved. Polymeric materials play an important part in these products due to their physical and mechanical
properties which facilitate the holding and then releasing of active ingredients in a controlled fashion. Biobased,
polysaccharide materials, such as cellulose ethers, have proven to be especially useful and a large commercial market
continues to grow. Cellulose ethers are produced in many structural variations: different alkyl ether substituents
(methyl, hydroxypropyl, hydroxyethyl, ethyl, and carboxymethyl being the most commercially important) in homogeneous or
mixed compositions, of varying degrees of substitution and molecular weights. Although the most important materials are
semi-synthetic (produced by derivatization of cellulose with alkyl halides or epoxides), a large fraction of the material
nevertheless is derived from naturally occurring, renewable cellulose.
Recent progress in the understanding of controlled release processes is seen in a study of the diffusion mechanism of active ingredients in cellulose ether-based tablets. more...
June 2008 - Improving the biocompatibility of synthetic polymers by incorporation of hyaluronic acid
Synthetic polymer chemistry continues to provide us with amazing materials for just about every application imaginable. One of the current frontiers in which synthetic materials are being employed is at the interface with biological systems, that is, to replace damaged or failing tissues in living organisms, especially humans. Often the desired functional properties, such as strength and flexibility have been achieved, however longer term biocompatibility remains to be a challenge. For example, articles made from synthetic polymers which are used in the blood stream, such as vascular grafts, develop thrombosis in which platelets and red blood cells adhere to the unnatural material and form clots. Similarly, contact lenses made from synthetic materials can be fouled by adsorption of proteins that occur in tear fluids and cause discomfort to the wearer. There are many naturally occurring polymers that do not suffer these biocompatibility problems however they are not easily produced, especially in a “tailorable” way with a range of properties or with the facile processability of synthetic materials. Recently, researchers have achieved hybrid materials with the best features of both biological and synthetic polymers. more...
Ultimately, articles used in biological applications may be produced entirely by biological means. But until we are able to meet that awesome challenge, careful engineering of hybrids of biological and synthetic polymers like those described above will provide valuable materials for these needs.
April 2008 - Environmentally friendly aqueous viscosified treatment fluids and breakers for oil drilling
A large market for polysaccharides is in the oil drilling industry.
Seems like an odd combination ... Isn't it ironic that renewable
materials, polysaccharides, are used to facilitate production of a
depleting material, petroleum? What makes polysaccharides so valuable
in this application is the high viscosity of their aqueous 
solutions
and the ability to crosslink them to form shear-thinning gels (high
viscosity when the solution is at rest and low viscosity when being
pumped). Such viscous and visco-elastic treatment fluids are useful in
underground oil well operations for drilling, fracturing, diverting,
and gravel packing. That is, the treatment solutions are effective for
suspension of solids in drilling muds, removal of drill cuttings, and
placement of gravel packs and proppants (particulate materials that
bridge pores in the rock formations to maintain oil flow). The high
viscosity also facilitates transfer of hydraulic pressure throughout
the formation and prevents undesired loss of the fluid into the
formation. Thus, the aqueous polysaccharide solutions provide a
spectrum of engineered well treatment fluids. In addition to these
valuable functional properties, other benefits are derived from the
green features of polysaccharides, such as their renewability, very low
toxicity, and biodegradability. Examples of polysaccharides that are
used in oil drilling are guar gum (and its derivatives, hydroxypropyl
guar and carboxymethyl guar), xanthan gum, scleroglucan,
carboxymethylcellulose, and other galactomannans, such as locust bean
gum. Whereas, the much higher purity grades of these polysaccharides
are used for more high valued products, such as food and personal care,
the lower purity grades are well suited for the oil industry and thus
allow full usage of all materials from polysaccharide production.
In many of the applications of well treatment fluids described above, it is also necessary to reduce the viscosity of the fluid when that property is no longer needed prior to oil production. Various methods have been developed to depolymerize the polysaccharide and thus reduce the viscosity by incorporation of “breakers”, such as acids, oxidants, and enzymes. more...
February 2008 - Surface modification of cellulose mediated by xyloglucan
Like teammates, xyloglucan and cellulose have complementary abilities and work together to achieve something that neither could do alone. In naturally occurring wood, xyloglucan binds tightly and specifically to cellulose fibers. Cellulose fibers by themselves have very impressive strength, but an even greater composite strength is achieved when the fibers are “glued” together with xyloglucan. Xyloglucan's interaction with cellulose has also been employed in industrial applications to improve the performance of textiles and paper. Recently xyloglucan has been exploited as a vector or anchor to introduce new functional groups to cellulose surfaces and alter its properties under mild and environmentally friendly conditions.
Xyloglucan (XG) is widespread in nature in plants but is most commonly
isolated from tamarind kernel powder (~60% XG) which is produced
commercially on a large scale. XG actually is a group of
polysaccharides defined generally as neutral, unbranched polymers of
glucose with xylose pendent groups. This chemical structure (see
Figure) is very similar to that of cellulose in that they both have the
same poly(b-1,4-glucopyranose) backbone. The xylose substitution
pattern along the backbone varys depending on the
natural source. Certain other monosaccharides are also
typically found attached to the xylose units. Whereas cellulose is
highly crystalline and water-insoluble, XG is readily water soluble.
However when XG is associated with cellulose as in wood, a strong
complex results as evidenced by the fact that XG cannot be extracted
from it with water. The complex can be broken however by extraction
with strong aqueous base. Details of the XG-cellulose relationship are
reviewed in a recent article along with creative new methods which
make use of XG as an anchor to introduce new chemical functional groups
to cellulose surfaces and modify its properties. more...
December 2007 - Cellulose acetate - an important biobased material in liquid crystal displays
It's very apparent that liquid crystal display (LCD) devices are
popular and
finding their way into more products everyday. Examples are displays
for computers, televisions, appliances, portable devices like
phones, GPS devices, and the original application .... watches. The
advantages of LCDs are light weight, 
compact size and low power
consumption - vast improvements over the previous cathode ray tube
(CRT) displays. LCDs have a complex construction and are a truly
amazing triumph of science and engineering [read more].
Within an LCD, light is transmitted through a liquid crystal cell
which is sandwiched between two polarizing plates. The polarizing
plates are protected by a transparent film which is composed of
cellulose acetate (more specifically cellulose triacetate or
triacetyl cellulose in which all three of the hydroxyl groups on each
glucose repeat unit is fully acetylated). It's ironic that
cellulose acetate, one of the oldest commercial polymers, plays a
crucial part in this high-tech electronics appication.
Cellulose acetate (CA) is produced by the synthetic derivatization
of
biologically produced cellulose. As such, it is one of the first
synthetically modified, biobased polymers and has found wide utility. Acetylation
of cellulose causes a dramatic change in properties. Cellulose is
hydrophilic, highly crystalline, can't be melt processed due
decomposition before
its high melting point, and is poorly soluble in common solvents. CA is
a hydrophobic,
amorphous material that can be dissolved in common solvents or
melted, especially after mixing with plasticizers, and can be readily
processed into different forms for many applications. Its
functional properties include: moisture
resistance, optical clarity, high heat resistance (softening
temperature), melt processability, high mechanical strength and
toughness. These properties have made CA valuable in the following
commercial applications: plastic articles (tool handles, eyeglass
frames), cigarette filter material, water purification membranes,
textile fibers (known as “acetate”), optical films. The latter
application, specifically its use in LCDs, is becoming an especially
important market for CA and driving increased production of this
biobased material. Its combination of high clarity, isotropic
transmittance (passes light equally in each direction), good moisture
and temperature resistance, low cost, adhesion to high surface-energy
polarizing films, and also its renewable raw material source make CA
the material of choice. more...