About Levan: Technical Sheet
PROPERTIES DISTINGUISHING LEVAN: Unlike polysaccharides used as emulsifiers and thickeners, levan does not swell in water and has an unusually low intrinsic viscosity at 0.14 dl/gm. Levan-based films are good oxygen barriers. For a bio-based material, levan is relatively acid stable. Dissolved in 1 N HCl and held at 70°C, over an hour is needed for complete hydrolysis. For a biobased material, it has good heat stability melting with decomposition at 225°C. The glass transition temperature is 133°C. Levan absorbs UV radiation, particularly in the UV-C range. Levan does not form a gel. Levan-based films are clear to white, depending on the thickness. Some of the properties are listed below.
- Film former
- Water "soluble"
- Molecular weight > 107
- Low intrinsic viscosity
- Produced by non-GMO
- Does not swell in water
- No skin or ocular irritation
- Film is excellent O2 barrier
- 50-200 nm diameter spheres
- Resistant to organic solvents
- Long term storage in dry form
- No allergic contact sensitization
- 133°C Glass transition temperature
HISTORY: Levan was first identified over 100 years ago. Properties distinguishing levan from other polysaccharides have long interested researchers. Its value in medical applications has been demonstrated repeatedly. But levan has only been available in small quantities and its potential has been unrealized because of the high cost. A method has been developed for large scale production, making levan economically viable.
PRODUCTION: The Montana Polysaccharides levan is produced by a species of Bacillus in a tightly controlled fermentation of sugar. The organism is NOT genetically modified. Production is at Cathay Biotechnology (www.cathaybiotech.com) and is sold under the trade name Levana™.
NO OCULAR IRRITANCY: Ocular irritancy tests have shown levan is safe for use near the eye.
Chorioallantoic Membrane Vascular Assay (CAMVA 14 day)
- RC50 >3.0% = Non-irritant
- RC50 >1.0% <3.0% = Indeterminate
- RC50 <1.0% = Irritant
Interpretation: CAMVA tests are conducted on egg chorioallantoic membranes. A higher number denotes less irritation. At 87% (well above the 3% threshold for a non-irritant), the CAMVA test indicates levan is not causing irritation.
Bovine Corneal Opacity and Permeability Test (BCOP)
- 0-25 = Mild irritant
- 25.1 - 55 = Moderate irritant
- 55.1 and above = Severe irritant
Interpretation: For this test, a lower number points to less irritation. The BCOP score of minus 0.94, indicates marginally less irritation for corneas treated with levan than the saline controls.
NO DERMAL IRRITATION OR ALLERGIC CONTACT SENSITIZATION: A Human Repeat Insult Patch Test (HRIPT) on 50 people had zero scores, indicating that levan does not cause dermal irritation. Upon administration of challenge doses there was no indication of allergic contact sensitization.
NO CYTOTOXICITY: Levan is not cytotoxic in the Agar Diffusion Test.
OXYGEN BARRIER & WATER VAPOR TRANSMISSION: Levan-based films with 10% montmorillonite and 5% PEG were tested as a barrier to oxygen in a MOCON Ox-Tran permeation unit at 0% relative humidity and 23°C. Prior to testing, the films were conditioned at 25% relative humidity. Results on 110 micron films showed an oxygen permeability of 0. The lower limit of the L-type module using masked film samples is 0.05 cc/m2-day. The average water vapor transmission rate for this film was 123 g/m2-day.
SOLUBILITY: Levan is considered to be water "soluble". Technically, it would be more accurate to refer to levan in water as a suspension that does not readily settle out. Large flakes require several hours to dissolve in cold water. Powdered levan will solubilize more rapidly as will solutions made with hot water. A thin film of levan will dissolve quickly in warm water.
Levan may be made water insoluble by tying up a portion of the available
hydroxyl groups. The most successful approach found to date has involved
cross-linking. One method uses an emulsifiable diphenylmethane diisocyanate
(MDI) such as one sold by Huntsman called Rubinate. A hexamethylene
diisocyanate (HDI) will also cross-link levan but there is considerable
foaming and the open time is very short. Another avenue is to derivatize
levan for increased water resistance.
Levan does not dissolve in most organic solvents including the following:
- Methanol, ethanol, isopropanol, n-propanol
- Acetone, methylethylketone, toluene
- Ethyl lactate
- N, N-dimethyloctanamide, N, N-dimethyl-decanamide
- Methyl caprylate/caprate, methylpalmitate/oleate
- Propylene carbonate, ethylene carbonate
- Methoxypolyethylene glycol, polyethylene glycol
- Kerosene, gasoline
- Dimethyl formamide
- Ethoxyethyl acetate, acetic anhydride
- Furfuryl alcohol
Powdered levan will dissolve slowly in DMSO (dimethyl sulfoxide). The adhesive strength of levan is not affected by soaking in gasoline, jet fuel, d-limonene, methylethylketone or toluene for several days.
VISCOSITY: Levan has an unusually low intrinsic viscosity at 0.14 dl/gm. By way of comparison it may be noted that the intrinsic viscosity of dextrose is around 1 dl/gm and for thickeners like CMC, it approaches 100 dl/gm.
The following graph shows the dependency of viscosity on concentration. In practice, formulations generally include less than 25% levan, where the polymer has a very low viscosity. It is only in the 45-55% range when branches become entangled that the viscosity rises dramatically. At 55% solids, levan has the consistency of chewing gum.
See paper in Rheology section for detailed description of graph.
MICROBIAL GROWTH NOT ENCOURAGED: Unlike some natural products, levan does not encourage growth of fungi and bacteria. Cultures of Aspergillus sp., Cladosporium sp., Brevibacillus sp., Staphylococcus epidermidis, and Micrococcus sp. were grown on levan coated agar plates and on treated construction materials. Organism growth was not visibly different from that of most untreated controls. Although levan did not enhance microbial growth, neither did it hinder the growth of existing bacteria and fungi.
ADHESIVE PROPERTIES: Levan has good adhesive strength. The following table shows the tensile strength of levan compared with other natural polymers when used to bond bare aluminum coupons. It should be noted that these tests used levan dissolved in water with no additives. It may be anticipated that formulated glues based on levan would have a superior performance.
Tensile strength is average of 9 or 10 replicates using bare aluminum coupons.
Levan can be used as a wood adhesive where the wood often fails before the adhesive bond. The low viscosity may necessitate formulation with a thickener for rough surfaces. Levan is sensitive to water, so is most useful for applications where a temporary bond is desired or for a product that will not be exposed to water such as furniture. Cross-linked levan makes a water-insoluble bond and has been found useful for certain plastics.
FILMS: Levan is a film former. With no additives, levan films are brittle. Adding clay such as 10-50% montmorillonite or 2% Laponite® produces a film that is flexible, translucent, not sticky and water resistant. Glycerol may be included at a rate of 0.2-5% to increase film flexibility. Other suitable plasticizers are PEG and sorbitol. Plasticizers tend to negate the water resistance effect of clay.
BIODEGRADABLE: In a marine biodegradation test, it was found that 60% of levan was mineralized in 10 days.
RAW MATERIAL: Levan is sold under the trade name Levana™ as a powder. It has an extended shelf life as long as it remains dry. To obtain the desired concentration, levan is simply dissolved in water. Levan can be applied as a fine spray, drying to a hard coating. As long as the coating retains some moisture it will remain flexible. Plasticizers will also help maintain flexibility. Adhesive applications generally require 20-30% solutions while cosmetic applications typically incorporate 1-10% levan. This levan is a raw material; no attempt has been made to formulate a finished product. Levan is both the INCI and scientific name. The CAS number for levan is 9013-95-0.