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RSC Advances Review results in poor mechanical performance composites absorbing water depending on processing temperature, bre volume fraction, orientation of reinforcement, permeability nature of bre, area of exposed surfaces, diffusivity, reaction between water and matrix and surface protection.46 Among the conven- tional techniques for the production of biocomposites parts, stratication, hand lay-up and vacuum bagging methods are the most popular.172 Composite materials can be made of layers fabricated with a thickness between 0.1 and 0.5 mm when laminated but even thicker when it comes to low cost applica- tions.173–175 Moreover, laminate composites perform better when bres are oriented according to a main loading direction. Multidirectional loading conditions require stratication manufacturing techniques that vary the distribution/direction of the reinforcement, layer by layer. Long-bre laminate composites show superior mechanical performances, but the ease of processability of short and fragmented bres compos- ites is more convenient thanks to automated workows that even contemplate material reuse. Of all the fabrication methods, the hand lay-up laminating is probably the earliest technique employed in the production of composite materials, particularly in the marine industry. This technique allows for the production of solid laminates and sandwich composite structures. It is well suited to the production of large parts such as boat hulls. Reinforcement bres are laid on a mould where a resin is then poured and squeezed with a roller to remove trapped air. A vacuum effect is necessary before the catalyst is activated to harden the resin and reinforcement into the nal composite. Lastly, lamination pressurizing and vacuum bagging methods can be applied during the curing stage to further remove the air interlayer, increasing interfacial stress transfer thanks to an optimized bre-to-resin ratio in the composite part.176 The application of nanotechnology has been introduced in some research areas and has further potential to improve the behaviour of biocomposites. The use of nanoscale llers such as inorganic pigments,177 minerals,178 ceramics,179 nanocellulose180 and nanoclays181 were recently considered in the production of composite coatings for paper. Moreover, antimicrobial paper,182 and self-healing properties for cotton fabric183 are desirable properties that would be of interest for the case of biocomposite material manufacturing. In the specic case of the manufacturing process of sustainable bio- composites the available technologies are listed as follow: spray- up process, lament winding, pultrusion process, compression moulding, resin transfer moulding, pre-preggers, compounding and extrusion and injection moulding processes. Resin winding and pultrusion are interesting processes that use laments of uninterrupted bres. Resin winding blends together the rein- forcement thanks to a bath of resin into which bres are continuously fed at varying speed or twisting angle. The pul- trusion method is preferred in the fabrication of continuous, constant cross-section products, especially for the high productive nature of the process. Compression moulding forms composites made of dry bres and resins applying high pres- sure in rigid moulds placed in hydraulic presses, whereas resin transfer moulding is a process more related to cold pressing.184 Pre-pregs are compounds made of bre, resin, llers and catalyst produced in sheet or dough for sheet moulding and dough moulding compound respectively. The former forms the nal product via compression moulding, whereas the dough can also be injected before the catalyst is activated by heat.185 Compounding and extrusion are processes widely used with varieties of materials such as blend bre composites that can be extruded into pellets for injection moulding. Finally, injection moulding forces the preheated composite into closed moulds to be cooled and removed aer solidication of the part.186 Three-dimensional 3DP printing, also known as Additive Manufacturing (AM), is also currently offering a wide range of different materials solutions. Polymers, ceramics, organics and reinforced biobased materials can be extruded, cured, bound and sintered from micro- to meter-scale. Advantages are currently under evaluation aiming at understanding technology drawbacks and possible improvements and developments.187–189 However, virtual 3D geometries with almost arbitrary shape and complexity, can be produced adding material where needed.190 On the biocomposite side, multi-material printers are fostering additive processes for their ability to combine different mate- rials with transfer of interfacial activation mechanisms from biological to engineering composites. Furthermore, advanced manufacturing can rely on Computed Aided Design (CAD) coupled to algorithm modelling and imaging technologies to exploit the complexities enabled by 3DP using multiple mate- rials. Algorithm modelling and 3DP are now providing the possibility to create complex topologies with resolutions approaching several length scales.191–194 Several kinds of 3D printing process exist, but most can be placed into one of three distinct categories.195,196 First, there are printers that form object layers extruding a semi-liquid material from a computer- controlled print head nozzle. Secondly, there are printers that use photo polymerisation to selectively solidify a liquid with a laser beam or light source. And nally, there are devices that 3D print by adhering particles of powder to achieve some form of granular materials binding. Direct tools allow the creation of architectural forms taking advantage of the intuitive interaction between user and 3D modeller. Freedom in designing complex shapes is gained, possibly made of multiple parts leading to the manufacturing of multi-material assemblies. Therefore control can be reached not only on the hierarchical disposition of materials, but also on their chemical and physical functionality.196,197 5.4 Surface treatments and coatings So far, the use of biobased composites has been restricted to interior and moderate loading applications. The poor outdoor resistance of the natural bres, especially in wet conditions, implies the need of developing coatings, surface treatments and additives to reduce the tendency of the composite to absorb moisture over time. Moreover, the matrix/reinforcement system is based on a mechanical interplay that, for the case of biobased composites, weakens due to the opposing nature of hydrophilic matrix and hydrophobic reinforcement.198 Therefore, surface treatments can be crucial in the attempt to preserve mechanical 32934 | RSC Adv., 2021, 11, 32917–32941 © 2021 The Author(s). 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