Valida - Fibrillated cellulose for stabilisation and rheology modification

Blog Archive | 5 minutes  | Author: Erin White , BSc.

SAPPI is the market-leading pulp and paper company but has diversified in order to offer new woodfibre technologies that meet the ever-evolving demands of the market. As sustainability has become a greater concern to consumers and driven product development, SAPPI saw an opportunity to provide a sustainable rheology modifier that can match and often outperform its less sustainable counterparts and so developed Valida.

In this technical article:

What is Valida?

Valida is made from the most abundant organic material on earth, natural cellulose. In wood, cellulose fibres form a matrix that provides the strength associated with the material. Through a process known as fibrillation, these cellulose fibres can be separated from each other, giving a much larger surface area. This process provides their name, fibrillated cellulose. When dispersed in a liquid, the long spindly fibrils form an extensive network through both hydrogen bonding and mechanical entanglement. Depending on the width of the fibrils, they can be further specified as either microfibrillated cellulose (MFC) or nanofibrillated cellulose (NFC).

 

Benefits of Valida

In comparison to conventional thickeners like cellulose ethers or xantham gum, fibrillated cellulose has a number of unique benefits including broad pH stability from pH 1 to 13 and high tolerance to salts whilst also providing reinforcement and enhanced open time due to their water retention properties.

Valida Improves Thixotropy

The extensive network that is formed means that Valida exhibits extremely shear thinning properties. High shear will break down the hydrogen bonds and entanglement so that the fibrils will align giving low viscosity and allowing easy flow. Upon removing the shear, the network can reform (these interactions are energetically favourable), so the viscosity will return to the pre-sheared state.

 

Valida is stable in pH 1 to 13

Conventional thickeners like Alkai-Swellable Emulsions (ASE) or Hydrophobic Alkai-Swellable Emulsions (HASE) acrylics often rely solely on hydrogen bonding for their network are often broken down at extreme pHs as their ability to make these bonds is inhibited. As Valida also uses entanglement, the effect on pH can be minimised as the network can be preserved even without access to free H+ ions for H bonding. The minimal effects of pH ranges of 1-13 on Valida can be seen in Figure 1.

 

Viscosity of Valida at different pH levels.

Figure 1: The viscosity of Valida is not significantly reduced by high pH as it does not solely rely on H bonding but also entanglement.

 

Valida has a high tolerance to salts

Valida also has excellent stability towards electrolytes and salts. A higher concentration of salt will mean a higher ratio of Valida to water and so increase the viscosity allowing it to be present in a range of formulations.

 

A bar chart showing viscosity of a formulation at 100 / s at different salt concentrations of 0 - 20 %. As the salt concentration is increased, the viscsoity is also seen to increase. This is shown with both NaCl and CaCl2

Figure 2: Valida is stable in high salt concentrations so it can be used in a range of formulations.

 

Valida is stable in polar solvents

The H-bonding in the Valida network gives a strong synergy with polar solvents that can also hydrogen bond. This however only happens when the solvent is at a high percentage; Having 10% of solvent presence doesn't influence the viscosity but Valida is stable either way.

 

Valida has water retention properties

Valida is a hydrophilic substance and has a high surface area meaning the water retention properties are high. This is particularly notable for cosmetics and personal care where a nice skin feel is achieved and in coatings applications where Valida can help prolong the open time.

 

Valida stabilises oil-in-water emulsions

Oil-in-water emulsions are notoriously difficult to stabilise due to the difference in polarity between the two. As such emulsifiers are often added to aid this process where one end shares the polarity of the water and the other of the oil. These, however, often get bad-press in both food and cosmetics. Here, Valida can reduce or completely remove the need for emulsifiers depending on the oil content (at less than 10% the emulsifier can be removed entirely). This works as the oil droplets are stabilised by the Valida network allowing them to stay distributed throughout the water.

 

Two side by side images of oil in water through a microscope. One shows this without Valida, the other shows the oil suspended evenly throughout in the presence of Valida.

Figure 3: When Valida is incorporated into an oil-in-water emulsion, the oil droplets can be stabilised and distributed within the water via the network of hydrogen bonds and entanglement.

 

Valida is biodegradable

As a natural product made from cellulose, Valida is biodegradable as well as being sustainably sourced. It is also approved for use in wash away cosmetics products.

 

Valida has higher resistance to microbial attack

Cellulose ethers, such as HEC, CMC and HPMC, are chemically modified cellulose and are often used as thickeners. When left in the same conditions for a month, Valida and HEC exhibit different responses. This is because Valida is more resistant to microbial degradation and so remains active.

 

4 test tubes, 2 using HEC and 2 using Valida. One of each is a before and shows particles well suspended. The other of each is after 1 month, the HEC one shows the particles sunk to the bottom while Valida's ones are still well suspended.

Figure 4: Suspension of particles can be seen even after a month with Valida showing the resistance to microbial degradation and attack. Both solutions were prepared with 0.5% active content and stored at room temperature for 1 month.

 

Valida Applications

Due to Valida's unique properties, it finds use in a number of applications including Personal Care, Coatings, Adhesives, and Cementitious formulations.

Coatings

In paints and coatings, rheology is a factor that must be largely considered. Throughout the storage, application and lifetime of the paint, different properties and viscosities are preferable. As such thixotropic behaviour, where the viscosity is dependent on the shear, is often the go-to. During the application of paint, low viscosity is wanted to ensure good coverage and easy application however once on the surface, high viscosity is necessary to prevent sagging and drippage. With Valida, this can be achieved with a high shear application method, such as spraying which will break down the network and offer a low viscosity until the product is left at rest on the surface without the shear when the network will immediately reform and offer high viscosity. The in can stability of the product is also important as customers want a homogenous coating even if it has been left a while.

 

White paint being poured into a tray for rolling

Figure 4: Valida offers thixotropic behaviour that gives the ideal rheology at all stages of paint storage, application and lifetime.

 

Cosmetics and Personal Care

Valida is being used in personal care products to stabilise formulations without thickening them and to suspend particles evenly throughout the product. It also has the advantage of resulting in a nice skin feel and being easily sprayable and spreadable. Valida has excellent synergy with Xanthum gum meaning it can either replace or reduce the need for it. Valida offers similar properties as a thickener or rheology modifier but without the greasy and sticky feel that is often associated with Xanthum gum. Depending on the Valida percentages it can then be used as a thickener (high percentage) or have minimal impact of viscosity (low percentage).

 

Look out for further articles going into more detail on the many different Valida applications soon. If you need advice incorporating Valida into your formulation or you would like a sample, please get in touch with us and one of our technical team will be happy to answer any questions and discuss your specific requirements. 

Author: Erin White , BSc.

Erin studied at the University of York where she earned a BSc in Chemistry and has just completed a MSc in Atmospheric Chemistry. She has recently joined us and will be covering areas across all markets.