Production of cellulose fibres from different resources and in different dimensions and physical properties
Cellulose and pulp
Wood is the main source (>90%) to produce plant-derived cellulose.
While in theory any tree can be used for pulp-making, coniferous trees (softwood) are preferred because the cellulose fibers in the pulp of these species are longer, and therefore make stronger paper. Some of the most commonly used trees are spruce and pine. Other trees (hardwood) used for cellulose production are eucalyptus, aspen, birch and beech. Non-wood alternatives like wheat straw, miscanthus and bagasse are gaining more and more interest.
Wood and other plant materials used to make pulp contain three main components (apart from water): cellulose fibers, lignin and hemicelluloses. The aim of pulping is to break down the bulk structure of the fibre source, be it chips, stems or other plant parts, into the constituent fibres.
Chemical pulping achieves this by degrading the lignin and hemicellulose into small, water-soluble molecules which can be washed away from the cellulose fibres without depolymerizing and weakening the cellulose fibres.
The kraft (sulfate) process is the dominant chemical pulping method. It entails treatment of wood chips with a hot mixture of water, sodium hydroxide, and sodium sulfide, known as white liquor, that breaks the bonds that link lignin, hemicellulose, and cellulose. The technology consists of several steps, both mechanical and chemical. Alternative methods are the sulfite and organosolv process.
Most of the produced wood pulp is used to make paper and cardboard.
Micro- and nano-cellulose
After further mechanical treatment, e.g. milling, sieving, compacting and pelletizing cellulose fibers can be used in a lot of other industries such as food, pharma and filtration. They work as fillers, binders, stabilizers, disintegrants and dietary fibers.
It is possible to produce a powdered cellulose with a particle size of 20 µm with mechanical milling.
Through high-pressure, high temperature and high velocity impact homogenization, grinding or microfluidization it is possible to rip the larger cellulose fibers apart into nanofibers. These fibrils are called cellulose nanofibers (CNF) or nanofibrillated cellulose (NFC). Typical fibril widths are 5–20 nanometers with a wide range of lengths, typically several micrometers.
Cellulose consists of fibrils with crystalline and amorphous regions. By an acid hydrolysis process it is possible to isolate the insoluble crystalline part from the amorphous part and you obtain a microcrystalline cellulose (MCC).
MCC is a valuable additive in pharmaceutical (tableting powder), food (texturizer, fat substitute), cosmetic (abrasive, anti-caking agent) and other industries (extender, emulsifier, bulking agent).
With chemical substitution reactions it is possible to turn cellulose into a variety of derivatives, eg. carboxymethyl cellulose, ethyl cellulose, methyl cellulose, hydroxypropyl cellulose and combinations of those. The cellulose derivatives can have water and organic solubility. They are used as excipients, lubricants, emulsifiers, binders, thickeners in all kind of different industries.
The thermoplastic all-cellulose-based materials developed in the project contain cellulose derivatives, cellulose powders and bio-based plasticizers. The mechanical properties of the materials are comparable to commercially available PLA-based composite materials, but have improved temperature resistance.
Specialty cellulose pulp: ASPA ECF (Elementary Chlorine Free) is a bleached long fibre sulphate pulp based on pine and spruce, bleached with oxygen, peroxide and chlorine-dioxide. This pulp has very good strength properties and low conductivity.
Microcrystalline cellulose: Arbocel UFC 100 is a MCC with an average particle size of 8 µm.
Cellulose derivative: VTT MMCC-C16 is a thermoplastic cellulose ester and works as a plasticizer in the formulation.
For more details about the 3D printing formulation please go to novumproject.eu.