EcoSphere® is a new biobased material that is an alternative to petroleum-based latex. It can broadly substitute for oil-based latex in diverse applications, such as paper and paperboard, architectural coatings, carpet backing, engineered wood products, insulation and roofing, cosmetics, textiles, nonwovens and drilling fluids. Much like the Intel™ microchip powers many different brands of computer, the “EcoSphere Inside” concept enables our partners to power their own sustainability initiatives. In the paper industry, EcoSphere biolatex™ binders represent a new family of commercially available products for the manufacture of coated paper and paperboard, providing a traditional industry an alternative to non-renewable petroleum chemicals. These products result from the transformation of annually renewable crop resources via the company’s patented processes into a dry biopolymer nanoparticle agglomerate powder that can be used dry or pre-dispersed in water.

This family of EcoSphere products exhibit excellent ultra-high shear rheology, shear-thinning behavior similar to petrochemical-based colloids such as carboxylated styrene butadiene (SB), styrene acrylate (SA) and polyvinyl acetate (PVAc or “acetate”) latex.

EcoSphere market — a new raw material for many markets:

• The global emulsion polymer market is >15 billion pounds and growing at 3-5% per year.
• Styrene butadiene emulsions and the paper market are the largest segments.
• EcoSphere can be designed to participate in all other major end use markets.

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SB and SA Latex are the dominant petrochemical-based binders used in coated paper and paperboard manufacturing processes. The advent of synthetic latex is one of the major discoveries in polymer science to date. Instead of the need to dissolve the relatively large (high molecular weight) polymers in a solvent, which limits the maximum % solids for a given target viscosity, polymer colloids or waterborne latexes consist of high molecular weight polymers “hidden” within the colloid particles.

Similarly, starch is a very high molecular weight polymer. However, starch must be jet cooked before it can be used as a component in paper binder recipes. In unmodified form, jet cooked starches are limited to 5-10% solids solutions. These jet cooked solutions need to be kept warm and are stable only for hours due to retrogradation (a process of re-crystallization and gelation that causes the cooked starch to irreversibly thicken and gel). This is why industrial starches are typically reduced in molecular weight (acid thinned, hydroxyethylated, oxidized, phosphorylated, enzyme treated, or thermo-chemically modified, or other), in order for them to be able to be used at higher solids levels (typically up to ~30% maximum, and even higher for severely degraded starches). The reduction in molecular weight of industrial starches is required in order to ensure paper coating recipes are not too dilute. However, the lower molecular weight decreases performance and binder strength. Similar to the advent of latex paints and paper coating binders, the creation of our biopolymer colloid or biolatex enables the production of higher solids dispersions and much improved paper binder performance. Hopefully, the above explanation helps to put into perspective the significance of the biolatex innovation.

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Figure 1: Bottom Up Emulsion Polymerization Process for Petroleum Latex Compared to Top Down Reactive Extrusion Process for Biolatex

The fundamental design of the biolatex is similar to that of synthetic latexes, although the process for producing them is completely different. While synthetic latex is produced by polymerization of petroleum-based monomers in an aqueous emulsion process (“bottom up approach”), EcoSphere biolatex is produced from starch particles (see Figure 1a) via a “top down approach” using a proprietary reactive extrusion process. The process converts starch into a thermoplastic melt that is transformed into an agglomerate of dry crosslinked biopolymer nanoparticles (Figure 1b). The dry product is shipped directly to the customer, where it is readily dispersed in water to form the EcoSphere biolatex dispersion. This therefore eliminates the cost of shipping water. Figure 1c, for a freeze-dried biolatex sample, illustrates the nano-particular form of the biolatex.

EcoSphere is unique because its discrete particles are insoluble and thus form an aqueous polymer colloid. EcoSphere containing coating formulations can reach high solids levels of up to ~70% or higher, depending on the recipe. The end result is that EcoSphere biolatex behaves more like a synthetic latex and not a cooked starch solution.

Figure 2 illustrates the typical particle size ranges for oil-derived synthetic latexes, such as polyvinyl acetate (PVAc) used in adhesives (typically > 1 mm or 1000 nm), polyacrylics (typically 300-500 nm) and SB Latex (typically 150-250 nm). Generally great efforts are made to ensure SB and SA Latex binder particles approach 150 nm to ensure enhanced binder strength (because the smaller the particle, the higher the surface area and the higher the binder strength). The smaller the particle, the more surfactant is required, and the more expensive that type of SB or SA Latex binder system becomes. The biolatex by comparison (Figure 2) is smaller in size (50-150 nm) than the synthetic latexes and requires no surfactant for its colloidal stabilization.

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Figure 2: Particle Size Measurements for Oil-Derived Synthetic Latexes Compared with Native Corn Starch Granules and Biolatex

Instead, the biolatex has been designed with “protective colloid” stabilization mechanism, in which a very small fraction of water-soluble “hairy” starch polymers provide steric stabilization (Figure 3). This provides excellent high shear rheological characteristics that are essential for high speed paper coating processes (while this is not the case for the common jet cooked industrial starches). In addition, the small particle size provides for excellent binder strength. Fundamental lab studies have established a number of key fundamental differences and advantages of the biolatex technology over the synthetic latex binders. This can be summarized as follows:

1. While petroleum-based synthetic SB Latex binders typically consist of colloids with a non-swollen core with minor swelling of anionic repulsion layer, biolatex binders consist of crosslinked water-swollen nanoparticles that are sterically stabilized.
2. Synthetic latex and pigment particles tend to be non-deformable and dilatent under high shear-high solids conditions (under the blade they dewater quickly and can cause blade instability); instead, biolatex colloids are “shear deformable” (self-lubricating) and exhibit unique high shear rheology: less dilatancy.
3. The biolatex can replace SB and SA Latex on a 1:1 basis, while industrial starches are typically used at a 2:1 replacement level.
4. The biolatex exhibits less binder migration, quicker immobilization, more open coating structure, and smoother coating surfaces.
5. The biolatex appears to resist shrinkage upon drying, which explains the favorable results on gloss and other paper and print properties.

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Figure 3: Hypothesized Structure of the Biolatex Colloid Particle

This model helps explain the favorable “on-machine” paper coating performance at the mill, as well as the excellent coated paper and paperboard properties (such as gloss, opacity, etc.). While conventional industrial starches are known to lead to a reduction in paper properties relative to the synthetic SB and SA Latex binders, the performance of the biolatex can be explained as illustrated in Figure 4.

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Figure 4: Illustration of the Drying Process of Biopolymer Nanoparticles

Shrinkage leads to rougher paper coating surfaces which can reduce critical properties such as gloss. Unlike industrial starches, petroleum-based binders such as SB and SA Latex are subject to little shrinkage upon drying, and are known to deliver good optical properties. EcoSphere biolatex binders can be used in premium paper and paperboard grades because they perform favorably when compared to SB and SA Latex binders.  Successful pilot plant and mill trials have shown that EcoSphere biolatex products do not exhibit conventional starch-like qualities. This is because the crosslinked starch nanoparticles that make up the EcoSphere biolatex maintain their swollen or expanded structures upon drying (Figure 4).

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