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A growing trend in coatings formulation and the chemical industry in general is the adoption of plant-based raw materials. There are numerous drivers for this including regulatory requirements, voluntary certifications and an emerging consumer demand for sustainable products. Sourcing raw materials from plants, also known as bio-based or renewable materials, moves away from non-renewable petrochemical sources of ingredients.<\/p>\n
When trying to meet a certain threshold of plant-based content all formulation components should be considered. Prioritizing the highest percentage content\u00a0 components first for replacement is the sensible approach but a wholistic view might be needed to achieve bio-based content goals.<\/p>\n
In most waterborne coating formulations the components with the highest contents by weight are usually water, binder and pigments. While there are some bio-based organic pigments available, binders are the usually the first components a formulator would investigate for incorporation of plant-based raw materials. For an introduction to plant-based resins for coatings see \u201cBio-based Resins\u2019 Important Role in Coatings and Sustainability\u201d posted August 16, 2019 in the ULProspector Knowledge Center.<\/p>\n
While additives generally are a relatively small percentage of most waterborne coatings formulations their contribution to the overall bio-based content can be significant. This can make the difference between meeting requirements for an eco-label or sustainability standard or falling short. Raw material suppliers offer a broad variety of plant-based additives serving the same functions as the petrochemical based alternatives.<\/p>\n
One of the most common groups of additives utilized in coatings are surfactants. Short for \u201csurface active agents\u201d surfactants form bridges at the interface of dissimilar materials or phases. Surfactants perform many essential functions in waterborne coating formulations. Pigment dispersion and substrate wetting are functions served by surfactants.<\/p>\n
The generic description of a surfactant includes a \u201chead\u201d with an affinity for a particular phase, such as a fatty acid, which would make it lipophilic. On the other end the generic surfactant would feature a group with an affinity towards a phase opposite of the head. If the head was lipophilic the \u201ctail\u201d would be hydrophilic so the surfactant can form a bridge between the two phases. This is how a surfactant can disprove the old adage \u201coil and water don\u2019t mix\u201d.<\/p>\n
Pigment dispersion is one of the most critical parts of paint formulation. Without proper\u00a0 dispersion of the pigments a paint cannot perform as expected whether it is a multi-stage thermosetting OEM automotive coating or a low cost interior wall paint. Poor pigment dispersion can lead to problems in color matching, non-uniformity of gloss or sheen, and inconsistent colorant acceptance.<\/p>\n
By definition, pigments are materials that are insoluble in the continuous phase of the paint formulation. These solid particles must be distributed (dispersed) evenly throughout the coating and remain stable under the storage, application and curing conditions the coating could reasonably experience . Pigment dispersing agents or dispersants aid this process by working at the liquid\/solid interface between the pigment and the continuous phase.<\/p>\n
Dispersants are structured so that they form bridges from the pigment to the polymers and solvents in the liquid coating enabling a stable distribution. One portion of the dispersant (the \u201chead\u201d) has affinity for the pigment and orients to the pigment surface while another portion of the dispersant (the \u201ctail\u201d) is attracted to the continuous phase. Since these structural elements vary with the natures of the pigments and the polymers\/solvents comprising the coating system dispersants are often optimized for use in specific applications.<\/p>\n
Lankem offers a line of bio-based dispersants developed for use with different pigment types in waterborne coatings. The BioLoop pigment dispersing agent offerings include products targeted to inorganic pigments and Titanium Dioxide, one specially formulated to disperse organic pigments and a specific dispersing agent for hard to disperse pigments which are prone to flocculation.<\/p>\n
Surface wetting is a universally important property of coatings. Coatings adhere to substrates predominantly through physical interactions and weak chemical forces such as hydrogen bonding or Van der Waals forces. Proper surface wetting is the first step to maximize the interactions which enable adhesion. Several companies offer wetting agents made from bio-based raw materials.<\/p>\n
Neutralizing agents play important roles in the stability, surface wetting and film forming properties of waterborne coatings. They can also be a source of Volatile Organic Compounds (VOCs) in a formulation. Often combinations of neutralizing agents are used to balance properties and optimize a formula for a specific purpose.<\/p>\n
Clariant offers a unique plant-base neutralizing agent made from glucose called Genamin Gluco 50. With a 75% renewable content, a high degree of biodegradability, zero VOC content and no requirements for human or environmental hazard warnings, this material is ideal for use in eco label coatings. Genamin Gluco 50 enhances storage stability of coatings, improves color acceptance and imparts flash rust resistance to formulations.<\/p>\n
Rheology modifiers are one of the most important class of additives for waterborne coatings. Latex polymers are generally very high in molecular weight but lack the long chain entanglements which give solvent borne coatings viscosity profiles providing expected application properties such as sheer thinning and sag resistance. Waterborne coatings don\u2019t have these inherent viscosity properties and rheology modifiers are used to impart them to the formulation.<\/p>\n
Recently several raw material suppliers have offered rheology modifiers based on nano-cellulose. Several materials fall within the definition of nano- cellulose including cellulose nano-fibers,, microfibrilated cellulose, cellulose nano-crystals\u00a0 and bacterial cellulose.\u00a0 Nano-cellulose materials are a byproduct of wood processing, chiefly paper manufacturing, and do not use plants intended for human or domestic animal food sources.<\/p>\n
As rheology modifiers nano-cellulose derivatives impart high viscosity at low shear rates to waterborne paints. This prevents settling of high density pigments like Titanium Dioxide and ceramic beads. Upon the application of moderate to high shear rates during paint application the nano-cellulose structure temporarily breaks down and the viscosity drops rapidly. This allows atomization in a spray gun or paint to flow from a roller to a wall. When the shear is no longer applied, the nano-cellulose structure recovers and viscosity increases. The high viscosity prevents the coating from flowing or sagging.<\/p>\n
Defoamers are an essential component for waterborne coatings. Waterborne coatings tend to form foam due to the variety of components in the formula. Unfortunately additives such as surfactants can stabilize foam in coatings. This can lead to a situation where one additive must be used to correct a defect partially caused by another.<\/p>\n
Alfa Chemicals offers Foamstop VF 35 N based on renewable plant-based raw materials. This defoamer is suitable of low-VOC pigmented paints and high gloss emulsion based clear coatings.<\/p>\n
Italian manufacturer Siliconi Commerciale SpA is offering WS 941 bio-based defoamer for use in waterborne coatings. Based on natural oils, this product is suitable for architectural paints and water-based adhesives.<\/p>\n
Additives are often the \u201csecret sauce\u201d of a waterborne coating formulation which makes it possible to meet the customers expectations. They enhance the storage stability, color acceptance, surface wetting and application properties of the coating. Almost every waterborne coating formula uses additives and the selection of plant-based additives will only continue to grow.<\/p>\n","protected":false},"excerpt":{"rendered":"