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Upgrading of pilot lines for the processing of bionanocomposites

Author: Natalia Ortuno, ITENE

In Bionanopolys project, the objective of work package 4 is to upgrade the pilot lines involved in the development of bionanocomposites from the use of the nanomaterials synthesized in WP3, solvents, and organic compounds, extracted from different biomass sources. These pilot plants are part of the network 2 and once upgraded they will propose their services in the Bionanopolys OITB.

This work package, led by ITENE (Instituto Tecnológico del Embalaje, Transporte y Logística), gather all the following european partners in charge of pilot plants or providing technical support to the pilot plants: ITENE, CTP, AITEX, CENTI, CIDAUT, CEA, IRIS and PARTICULA.

The network 2 is composed of three pilot plants:

Pilot plant 6: Modification and functionalization of nanomaterials in liquid and gaseous medium

This pilot plant will be used to change the nature and properties of nanoadditives by incorporating organic compounds into their structure. This will improve the degree of dispersion in polymeric matrices and binders, mainly to obtain better barrier and mechanical properties. On the other hand, these modifications can also be used to confer specific functions to the nanoadditives, such as water-repellent, antimicrobial and flame-retardant properties, to name a few.

Industrial partners of the consortium, as well as the users of the OITB, will have the opportunity to use nanoadditives obtained in the pilot plants involved in WP3 i.e. cellulose nanofibers, cellulose nanocrystals, nanolignin, but also other nanoadditives like nanoclays, silica, metallic nanoparticles etc. After their modification these nanoadditives can confer promising properties to their products.

The small size and high specific surface area of nanoadditives, as well as the improvement in chemical compatibility after their modification, help to improve the interaction with the polymer matrix or binders into which they are incorporated, without the need to add high levels. However, one of the main disadvantages of using nanoadditives is their high production cost compared to other additives. For this reason, the BIONANOPOLYS consortium in WP4 is focusing on improving the pilot plants involved in the modification/functionalisation processes in order to obtain more cost-effective nanoadditives.

One of the upgrades was the purchase of new reactors capable of working with wider temperature and pressure ranges for both aqueous and organic solvent-based systems. These reactions are controlled through the use of in-line monitoring devices to measure parameters such as pH and conductivity. A faster and automatic feeding of the nanoadditives was implemented to achieve more efficient processes from a safety point of view. Finally, an ultra-high shear mixing system was installed at the bottom of the plant to improve the dispersion grade in the reaction medium. This increases the yield of the reaction and reduces the amount of reagents, mixing time and energy required.

For drying the modified/functionalised nanoadditives, pilot plant 6 has a spray drying system to remove water and obtain the nanoadditives in powder form, which are then used in pilot plants 7 and 8 to produce bionanocomposites and bionanodispersions, respectively. In addition to this type of modification, it is also possible to carry out gas-solid reactions with the nanoadditives as well as on cellulose-based substrates without the need for organic solvents and successive post-treatment steps to obtain environmentally friendly materials.

Two different types of equipment are available for these types of modification. On a smaller scale, a tubular furnace able to work at temperature of up to 1200 ºC can be used to anchor organic compounds in a gaseous state on the nanoadditives. On the other hand, and for a larger scale, a patented and continuous process based on a solvent-free reaction is used to confer water resistance to cellulose nanofibres while maintaining the convertibility, recyclability and biodegradability of these substrates.

Pilot plant 7: Nanocomposites compounding. Thermoplastics.

The dispersion of nanoadditives plays an important role in getting the best bionanocomposites, as their final properties strongly depend on the interaction between the surface of the nanoadditives and the polymer matrix. If these interactions are unfavourable, instead of a nanocomposite you get a microcomposite (micrometre scale dimensions) and the properties of the reinforced material are significantly deminished.

The aim of pilot plant 7 is to significantly improve the performance of nanocomposites as an additive to bioplastics in order to obtain high-performance bionanoproducts. For this purpose, two approaches can be followed:

The first is about increasing the contact area between the nanoadditives and the polymer matrix during the compounding process to improve the interaction between them. Increasing dispersion can be done by designing a specific screw configuration and selecting optimal process parameters to break the binding forces that cause the nanoadditive particles to form agglomerates and distribute them properly in the polymer matrix. However, assessing dispersion is not an easy task and therefore determining the optimal screw configuration and processing parameters can be very time consuming. To overcome these drawbacks, disruptive monitoring techniques for in-process control of dispersion, such as inline rheology and inline spectroscopy, have been introduced in the WP4 pilot lines. In addition, the use of advanced simulation software for the compounding process enables the prediction of dispersion during the process.

The second approach to improving the performance of biopolymers is to use what is known as reactive extrusion technology. This involves using an extruder to chemically modify the biopolymer, which can then be combined with the functionalized nanoadditive to boost its properties. By applying all these approaches to the production of bionanocomposites, it is expected that the properties of a wide range of products for a variety of applications can be improved in a more sustainable way.

The knowledge gained in the field of bionanocomposites will enable the pilot plants involved to offer innovative solutions for processing advanced polymer materials with improved properties for a wide range of applications. Simulation and monitoring tools can significantly shorten the lead time for new material developments and reduce costs, as certain properties are achieved through fewer tests and trials.

In this pilot plant 7, mathematical modelling is also offered to predict the final properties of the developed bionanocomposites by studying the physical and chemical properties of the nanoadditives and the polymer matrices. With this service, the experimental work can be better defined to obtain the most promising results without having to perform a large number of tests.

The work carried out in this pilot plant will enable the industry to better understand the dispersion behavior of nanoadditives in thermoplastic matrices and predict their properties during processing through disruptive modelling and in-line monitoring tools. In this way, it will be possible to easily adjust and optimize compounding parameters and screw configurations depending on the nanoadditive and polymer matrix, and maximise the performance of the resulting nanocomposite.

Pilot plant 8: Biobased nanodispersion

The output of pilot plant 6 will also be used to develop bio-based nanodispersions in this pilot plant. The plant will be upgraded with reactors with a larger capacity (from 10 to 100 L) and considering different dispersion methods (i.e. stirrers, homogenizers, ultrasonic tips). The aim is to increase the dispersibility of nanomaterials in liquid media (polymer resins dissolved in water or solvent-based systems) and to achieve significant savings in power consumption due to the reduction in mixing and dissolution times.

The final distribution of nanomaterials in liquid media is crucial to guarantee their effectiveness. Therefore, in this pilot plant, the type of dispersion and a number of parameters are offered for optimization to adapt the best properties and avoid agglomeration and incompatibilities that do not improve the materials. Batches from 10 to 100 L and adjustment of speed, time, temperature, pH and stirrer type can be selected to design the preparation of bio-based nanodispersions. The reactor with the largest capacity also has a recirculation pump to reduce time and solvent volume during the cleaning stages.

The obtained bio-based nanodispersion will be stable and homogenized to be suitable for common coating applications such as flexographic, gravure, slot-die, and spray coating. Thus, improved barrier, mechanical and antimicrobial properties of coated materials can be achieved in the Bionanopolys pilot plant 14.

Pilot plant 8 can also be used to develop bionanocomposites through in-situ polymerization reactions. The aim of in-situ polymerisation is to insert the nanoparticles into the polymer matrix during the polymer synthesis process. This method can be performed in a single step while the polymer chains are growing, increasing the compatibility and dispersion of the nanoparticles in the polymer matrix. The BIONANOPOLYS project will use this technology, better known for petroleum-based systems, to produce alternative bionanocomposites for industrial partners and OITB users. The upgrade of this pilot line includes modifications to the solids and gas feed systems, as well as the stirring systems, which will allow tight control of the polymerization environment to improve the dispersion of the nanoadditives in the polymer matrix. These improvements will enable an increase in production rate and provide a wider range of services with different products and knowledge for the production of bionanocomposites in situ.