A NATURAL FIT FOR SUSTAINABLE DEVELOPMENT
|
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) |
|
| NEWS HARVEST |
 |
|
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
material, 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. Breakers often require an activator (or catalyst) to increase the viscosity reduction rate. There is a need to improve the efficiency and environmental friendliness of these activators. A recent patent discloses the use of an activator for an oxidation-based breaker which is effective at moderate temperatures (<100 °C) and which is composed of a relatively innocuous Fe(II)-protein complex (“Methods for reducing the viscosity of treatment fluids,” RE Hanes Jr, RW Pauls, DE Griffin, KA Frost, and JM Terracina [Halliburton Energy Services, Inc], US Patent 7,334,640; 2008 [full text]).
I'm sure if we really tried, we could find a polysaccharide that complexed Fe(II) and worked as well as this protein. Polysaccharides rule!
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 (“Xyloglucan in
cellulose modification,” Q Zhou, MW Rutland,
TT Teeri, and H Brumer, Cellulose 2007, 14, 625-641 [abstract].
The strong absorptive association between XG and cellulose in aqueous solution provides a very mild and versatile mechanism to append useful functionality to the surface of recalcitrant cellulose fibers. Following are methods which have been recently demonstrated:
- Activation of XG to form carboxyl groups, followed by coupling with proteins (enzyme or antibody). The resulting protein-polysaccharide conjugate was then absorbed onto cellulose powder in water. The gentle binding conditions maintain the biological activity of the protein.
- Derivatization of oligomeric XG (prepared by enzymatic hydrolysis of native XG) by reductive amination to introduce a terminal amine group. Various functional groups (R), such as fluorescent dyes, proteins, thiols, and initiators for graft polymerizations, can be linked via the amine. The functionalized XG-R oligomer was then transferred onto high molecular weight XG via a biomimetic enzymatic transglycosylation reaction and the resulting high mass XG-R finally absorbed onto cellulose. The great utility of this method lies in its aqueous, environmentally friendly processing conditions and ease of attachment of a wide range of functional groups.
- Grafting of hydrophobic polymers onto the hydrophilic cellulose surface was achieved by using the cellulose-anchored XG which was derivatized with graft polymerization initiator as prepared in method 2. Styrenic, acrylic, and aliphatic polyester polymer branchs were grafted and a hydrophobic surface was formed. The method is milder than alternate cellulose grafting methods and the polymer product was also biodegradable by common industrial enzymes.
- Coupling of carboxy-terminated hydrophobic polymer (polystyrene) to amino-XG to form an amphiphilic compatibilizer for the preparation of nanocomposites of cellulose nanofillers in a nonpolar matrix.
Cellulose is a valuable industrial material due to its low cost, sustainable production, biodegradability, and material properties but is not easily modified in its native state. However, XG has the unique ability to mediate surface modification processes to produce new functional properties for cellulose while also maintaining its environmentally friendly features.
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 synthetic, 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.
There is much recent patent activity in the highly competitive LCD market which is being driven by needs for increased performance and lower costs. Many patents describe improvements in the use of CA as a protective, isotropic film for use on the polarizing plate components. Another important performance need is the ability to improve the view of the the display from oblique angles which has been one of the drawbacks of LCDs compared with CRTs. If you are viewing this webpage on a LCD display, this effect should be apparent by looking at the display from different angles. In addition to the properties that have made CA useful as a protective film, it has another potentially useful functional property: when a film is stretched at a temperature near its softening point it develops an optical anisotropy due to the alignment of the polymer molecules. This property can be utilized in an “optical compensation film” to improve the viewing angle of the display. In addition, a recent patent application describes how the anisotropy can be tuned by altering the substitution pattern of the ester groups on the cellulose backbone which exhibit slightly different refractive index contributions. That is, varying the ester groups (acetate, propionate, butyrate, benzoyl), or presumably any other functional group, and their degrees of substitution will affect the optical properties of the polymer film. An equation has been developed which correlates the optical anisotropy with the cellulose ester composition (“Cellulose Compound Film, Optical Compensation Sheet, Polarizing Plate, and Liquid Crystal Display Device,” Y Nozoe, T Omatsu (Fujifilm Corp), US Patent Application 20070259134; 2007 [full text]). It's fair to say that modern polymer science, as in this example, is making its greatest advances today by taking "old" polymers where they have never been before.
November 2007 - If you could dissolve wood in a solvent what could you do with that solution?
Maybe ...
... Regenerate the
wood in a different form that isn't possible by
conventional methods, such as fibers, films, composites, or less
ordered material that could be more easily converted to
glucose for ethanol production.
... Modify
its chemical structure and properties, homogeneously, with
chemical reactions.
... Analyze it to study the
wood's composition without having to
first separate the components.
These are just some of the ideas that are being explored now that wood and other lignocellulosic materials have been found to be soluble in ionic liquids (ILs).
Wood is primarily composed of lignin and the polysaccharides, cellulose and hemicellulose. Hemicellulose is a class of relatively complex polysaccharides, i.e., containing multiple monosaccharide repeat unit structures and with side chains/branching, and whose structure varies with plant species. Lignin is a network (crosslinked) polymer with oxygenated phenylpropane repeat units. Wood, and other lignocellulosic biomass, are renewable and CO2-neutral resources, however processing of wood into other products is inefficient and often involves hazardous and environmentally unfriendly processes (e.g., production of paper, or purified cellulose and its derivatives). Recently, many biopolymers in their purified forms have been found to be soluble in highly polar ionic liquids. These include polysaccharides such as cellulose and chitin which otherwise are only soluble in certain relatively hazardous solvents. Wood itself has just recently been found to be soluble in certain ionic liquids. more...
October 2007 - "Molecular engineering" of alginate's structure leads to improved properties
Alginate is a versatile polysaccharide produced commercially from seaweed (20,000 tons/yr). It is primarily used as a thickener or gelling agent for aqueous mixtures (other applications). It thus affects the flow properties of a solution – its rheology. These properties are valuable in food preparations, pharmaceutical formulations, and specialized medical applications such as cell encapsulation. Alginate forms strong gels in the presence of divalent cations, particularly calcium, by way of ionic crosslinks between the polyanionic alginate chains. Thus, when an aqueous solution containing sodium alginate is mixed with a water-soluble calcium salt, the mixture forms a gel with elastic properties. Alginate's unique gelling properties result from its primary chemical structure. The polymer backbone is composed of two monosaccharide repeating units, mannuronate (M) and guluronate (G), which are isomers differing in configuration at the C-5 position (see figure). They can be present in different ratios and in different sized blocks of M or G units. The G-blocks form especially strong interchain crosslinks with calcium ions and are a large factor in the gel properties. Alginate from different seaweed sources has different M/G ratios and different M and G block lengths and, as commonly occurs with natural products, has additional heterogeneity due to varying growth conditions. Recently, researchers have developed a method to synthesize alginate compositions in a controlled fashion with relatively long G-blocks at varying M/G ratios and an absence of M-blocks. These materials formed gels which showed markedly improved performance over native alginates.
Figure. (Top) Mannuronate (M) and guluronate (G) structures. Note different configurations at C-5. (Bottom) Synthetic conversion of all-M backbone structure to alternating M-G and then G-blocks.
The structure of alginate was optimized to produce gel beads, or capsules, specifically for medical applications (cell encapsulation, tissue engineering) where strength, stability, and controlled, uniform porosity are important. It is very likely that lessons learned in this study will be valuable in alginate's industrial applications as well. more...
September 2007 - Orally-dissolving strips for delivery of drugs and flavors
Maybe you've seen them in your drug store – small packages
containing thin
strips of material that dissolve quickly in your mouth and deliver a
dose of drug, breath
freshener,
or vitamin. The base material is a water
soluble polymer that can be formed into a film of sufficient strength
and
flexibility, and most importantly, is safe to ingest. What
type of materials can do all this? You guessed it ...
polysaccharides. Some examples of film-forming, water-soluble,
ingestible polysaccharides are hydroxypropyl methylcellulose (HPMC),
carboxymethylcellulose (CMC), and pullulan.
Active ingredients, flavors, and colors can be absorbed into the polysaccharide film which provides a convenient means for packaging, dispensing, and ingestion. When contacted with saliva in the mouth, the film dissolves rapidly, releasing the ingredients. This form of delivery offers many advantages, especially for children and elderly people who have difficulty swallowing conventional pills. more...
July 2007 – A more sustainable process to produce regenerated cellulose
As industry seeks sustainable and more environmentally friendly polymeric materials, cellulose comes to the forefront. That is a result of its abundance in nature, low cost, useful properties, as well as its biodegradability and other green features. Cellulose exhibits good mechanical properties and possesses an affinity for water yet is insoluble in it. Unfortunately, cellulose cannot be melt-processed into the many forms and shapes needed in industrial applications like conventional plastics due to thermal decomposition. However, it can be processed, or regenerated, via solvent-based processes to afford the commercial cellulose fibers such as rayon and films such as cellophane - even filtration membranes. The solvent-based processes used to regenerate cellulose require volatile and/or toxic solvents and relatively complex (costly) operations. Finding alternative solvents for these processes is not a simple matter – the strong interchain forces that give cellulose its unique structure and properties prevent its dissolution in all but the most polar solvents, such as N-methylmorpholine oxide (Lyocell process) or require derivatizing solvents (carbon disulfide, Viscose process).
A new regeneration process which employs an environmentally friendly solvent system consisting of aqueous NaOH and urea offers great potential. more...
June 2007 – An extruded form of xanthan gum rapidly disperses in water
Xanthan gum is one of the most important polysaccharides in commercial use. It is used as a thickener, suspending agent, and emulsion stabilizer in food products, personal care formulations, and oil drilling. It is produced industrially by microbial fermentation and is classified as an extracellular polysaccharide as it is produced in the cell and then released into its surrounding aqueous medium (more on xanthan structure and properties). Its exceptional rheological properties include: high viscosity at low shear rates (when the liquid is barely moving), greatly reduced viscosity at high shear rates (when the liquid is stirred or poured – called shear thinning or pseudoplastic behavior), and low sensitivity to changes in pH and ionic strength. These properties are attributed to the high molecular weight chains which form rigid helical structures in aqueous solution. Shear thinning occurs as relatively weak, noncovalent intermolecular associations and chain entanglement are disrupted (more on rheology of hydrocolloids).
Xanthan gum is produced commercially as a solid powder which must be redissolved in water prior to use in its various applications. Being a high molecular weight polymer, this is a relatively slow process and requires high-shear agitation to achieve homogeneous dispersion. Recently a new method has been developed which produces a form of xanthan gum that is rapidly and homogeneously dispersed in water. In this method a concentrated xanthan-water mixture is extruded in a twin screw extruder at 85 °C, followed by drying and grinding. more...
May 2007 – Hydroxypropyl cellulose films for packaging
A BIG market for plastics is in packaging. Articles and materials such as food must be contained and/or protected during shipment and storage. In general, the plastic in which they are packaged must be flexible, tough, strong, transparent, inexpensive, and sometimes provide other functions such as barrier to oxygen, carbon dioxide, and water vapor. Consider the many types of plastic packaging you encounter during a walk through a grocery store. However, with our growing human population, these materials make an increasing impact on our environment. Because most plastics are based on nonrenewable petrochemical resources and contribute to environmental and health problems over their life-cycle, biobased materials are being developed to alleviate their impact. In general, polysaccharide materials do not make good packaging materials because they are relatively brittle, unless plasticized with additives, and have limited moisture resistance. Regarding the former property, there have been efforts recently to identify and develop polysaccharide-based thermoplastics which are inherently tougher.
Thus, in the context of packaging applications, researchers have recently shown that some commercially available polysaccharides, in particular, derivatives such as hydroxypropyl cellulose, do possess a high strength and toughness at ambient conditions. more...
April 2007 - Ophthalmic drug delivery based on controlled gelation of guar gum solutions
Polysaccharides
have shown great value in drug delivery systems – one key reason is
their hydrophilicity – which makes them compatible with the aqueous
environments in living things. Water-soluble polysaccharides, or
hydrocolloids, have an additional extremely valuable feature – an
ability to be crosslinked in aqueous solution. Crosslinking transforms
the initial
liquid of relatively low viscosity, depending on polymer concentration,
to
a highly swollen semisolid, or hydrogel, with elastic properties, or
points in between with intermediate degrees of visco-elastic
properties. Crosslinking can
occur under a variety of conditions depending on the particular
polysaccharide. In a previous highlight,
the crosslinking of
alginate was exploited for commercial, non-drug
applications.
Crosslinkable hydrocolloids are used for delivery of ophthalmic drugs
(such as glaucoma treatment). Thus, a low-viscosity, aqueous solution
of a drug and polysaccharide is topically administered to the eye
where the liquid immediately forms a gel due to different pH and ionic
strength conditions. The drug is thereby able
to be
administered accurately and diffuse from the semisolid hydrogel in a
controlled fashion. A recent invention using guar gum and a borate
crosslinking agent has improved delivery
performance. more...
March 2007 – Maintaining the quality of oils in food products during storage with polysaccharide-based antioxidants
Food
is more than an energy and nutrient source that gets us through the
day: from another perspective, it is an industrial product for
mass distribution that delivers energy and nutrients in an
appetizing way. “Industrial” and “appetizing” in the same
sentence? ... Sure, why not? In fact, certain biobased,
polysaccharide additives help make modern foods more appealing and
storage-stable. Water-soluble polymers increase the viscosity and
modify other flow properties of solutions (their rheology) in
different
ways. In food applications, where modification and control
of product properties are important and nontoxicity is essential,
water-soluble polysaccharides (PSs) are employed. These PSs, also
known as hydrocolloids, are of great commercial value as thickeners,
gelling agents, emulsifiers, and emulsion stabilizers, providing
desirable sensory properties for the consumer. Some polysaccharide
hydrocolloids occur naturally in foods and are responsible for the
food's distinctive properties. Think yogurt. Commercial examples
of food hydrocolloids are starch, cellulose derivatives, such as
carboxymethyl cellulose and methyl cellulose, alginate and its
derivatives, carrageenans, gum arabic, guar gum, gum tragacanth,
locust bean gum, other plant gums, xanthan gum, gellan, welan,
rhamnsan, and curdlan. As a result of their different chemical
structures, each polysaccharide can impart unique viscoelastic
properties to aqueous solutions or mixtures.
In addition to their effects on the rheological properties of food, polysaccharide hydrocolloids have recently been found to inhibit air oxidation of lipids (e.g., vegetable oils) in aqueous emulsions which are commonly found in food products. Degradation of taste and flavor results from lipid oxidation. Synthetic small-molecule antioxidant compounds, such as BHT (butylated hydroxytoluene) and TBHQ (t-butylhydroquinone), are frequently used to inhibit oxidation, however there is some concern about their safety, so the ability to use nontoxic PSs is of great interest. more...
February 2007 – A cleaner world with the help of polysaccharides: mineral scale control and particle dispersion
In everyday life we see crusty mineral scale deposits around water faucets and films or stains on dishware cleaned in automatic dishwashers. On a much larger scale (no pun intended), equipment surfaces that are used in water-containing industrial processes can become fouled by mineral salts. Examples of situations where scale formation is a very important commercial problem include boilers, cooling water systems, desalination systems, fabric and dishware cleaning, and oil and water wells. Thus, products that can prevent scale formation or improve the dispersability of precipitated solids are of great value. Currently, some synthetic water-soluble polymers which bear polar/ionizable functional groups have been commercialized for this purpose, for example, polyacrylic acids. Due to increasing costs associated with the petrochemical-based products, there is renewed interest in developing polysaccharides for scale control. Recently, researchers at National Starch and Chemical Company have discovered that partially oxidized polysaccharides, primarily starchs, which contain relatively low amounts of carboxylic acid and aldehyde functionality were effective at prevention of scale formation and dispersion of solid particles. more...
January 2007 - Biofilm control with polysaccharides: fight slime with slime!
Wherever
there is water, there is the potential for microbial growth and often
in our human society that becomes a real problem. In 
particular,
industrial equipment such as heat exchangers and cooling towers can
lose their effectiveness due to excessive microbial growth on their
surfaces. In addition, medical implants can develop persistent
microbial growths on their surfaces and threaten the health of the
human host. Microorganisms exist in nature predominantly in the form
of these slimy surface-attached colonies, called biofilms,
which
provide protection from stress (e.g., desiccation, pH changes),
biocides (chlorine, antibiotics), and host immunological defenses.
Recent research indicates that certain naturally occurring
polysaccharides could lead to new products for controlling
biofilms. more...
