A colored cholesteric phase of cellulose nanocrystals is encapsulated in a polysaccharide/proteinaceous shell that guarantees the stability and usability of the colorant.

About

As a result of the growing demand for biodegradable materials over the past decade, the application of environmental friendly approaches to nanotechnology and nanomaterials is likely to appeal to consumers and unlock new business potential and opportunities for renewable materials for advanced applications. Cellulose nanocrystals (CNC) are bio-sustainable materials which are able to self-assemble into cholesteric liquid crystalline phases, Ch, where the vivid structural color originates from the interaction of light with nanoscale structural properties. The Ch is made of layers, where CNCs are aligned in a particular average orientation (i.e. the director). Among these layers the directors’ orientations are distributed in a helical fashion with a specific pitch, P, of around 1 μm. Surprisingly, for CNC this Ch organization is kept in the dry solid film. Here a structural color is developed as the helical P shrinks to a value comparable to the wavelength of visible light (200 -700 nm).
During the past years, many studies were devoted to the control and improvement of this color. Unfortunately, this severely limits the application of Ch-CNC in coatings or photonic films. However, in our opinion, the exploitation of Ch-CNC as colorant will be beneficial for several reasons. Firstly, there is a large availability of raw materials. Secondly, there are different methods of recovering CNC in biomasses or food waste, making the process sustainable. Thirdly, the fastness of the color is greatly improved compared to biodegradable organic dyes. Finally, and most importantly, the material is fully biodegradable and there is no risk of accidental exposure.
Until now, the development of the Ch-CNC ordered organization has not been obtained in different geometries, such as spherical particles, if not in very limited situations (WO 2018/033584 A1). This is mainly due to the fact that a drying spherical drop undergoes surface buckling and disruption of the cholesteric organization. A simple solution to avoid this issue was proposed in WO 2014/118466. However, the obtained colorant has poor stability in particular in water, thus limiting its actual application.
The present innovation is still based on a top-down approach, but it guarantees the stability and usability of the colorant by encapsulating layered Ch-CNC films in biopolymeric shell. This very simple and intuitive concept will open the possibility of the encapsulation of different type of liquid crystalline phases, based on a variety of biodegradable nanoparticles (keratin, chitin, and so on). Despite being very straightforward, the proposed solution is challenging and it requires investigation on the physical and chemical aspects of the microencapsulation process.
The assembly of a structurally-colored CNC film is quite straightforward. However, the encapsulation process will be the critical step for the completion of this concept innovation. Before encapsulation, it will be necessary to destroy the film into fine grinded platelet-like particles. Subsequently, these particles should be dispersed in appropriate medium for the encapsulation process. In this step, it is important that the particles maintain their structure avoiding any swelling or re-dissolution in the medium. This will require the investigation of a number of different physical and chemical parameters (salt content, pH, temperature, time). These investigations will be crucial to define a strategy also to scale up and automatize the process. It will be considered the utilization of lab-scale microencapsulator for a continuous production of the above biodegradable colorants.

Key Benefits

The key benefits of our innovation are:
- Large availability of raw materials;
- Sustainability of the whole process, raw materials can be recycled from biomasses with simple methods;
- Our system is fully biocompatible and biodegradable;
- Our concept allows complete protection and therefore utilisation of the color in a wide range of applications;
- Structural colours are insensitive to light-induced degradation;
- No dye synthesis process and additional purification costs are required;
- Safe upon accidental exposure.

Applications

Our innovation can be easily applied in several fields, since encapsulation is able to preserve the integrity of the color by the action of external molecules. Among the various applications, the use of our invention in dishwashing products (gels and liquid formulation) and liquid laundry detergents will be of particular interest. Indeed, nowadays it is difficult to include biodegradable dyes in these media, since they can easily undergo degradation processes. In the course of the implementation, our product would be also integrated in powder-type samples.

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