This work describes flax fibre reinforced polymeric composites with recent developments. The properties of flax fibres, as well as advanced fibre treatments such as mercerization, silane treatment, acylation, peroxide treatment and coatings for the enhancement of flax/matrix incompatibility are presented. The characteristic properties and characterizations of flax composites on various polymers including polypropylene (PP) and polylactic acid, epoxy, bio-epoxy and bio-phenolic resin are discussed. A brief overview is also given on the recent nanotechnology applied in flax composites.

The disposal of large amounts of waste from daily use polymers is among one of the foremost concerns in the current era. Effective utilization of bio-renewable materials procured from natural sources has been proposed as a potential solution to this problem. Among such different polymers, Poly lactic acid (PLA) which is a bio-degradable polymer, resembles quite promotable features, which can be polymerized from sustainable sources as chips sugarcane, starch and corn. Ring-opening polymerization (ROP) of Lactide (LA) monomer considering catalysts such as Al, Sn or Zn is one of the efficient methods for the PLA synthesis. However, the PLA polymerized through this type of catalysts may contain trace elements of the catalyst. Due to their carcinogenic nature, the traces of such catalysts should be (ideally) removed from the synthesis process. The use of alternative energy (AE- UV, Microwave) sources could be a potential route. Alternative development of non-metal catalysts is best alternatives for the processing of PLA through ROP. PLA layer based composite materials are gaining huge interest due to their multiple application (food, medical etc.) as eco-friendly material. In this article, we review on the implementation of AE sources for PLA processing and to populate the current state-of-the-art associated with the PLA research, especially application in nanocomposite materials field

Due to the inherent environmental benefits of using renewable materials, mimosa tannin resin (a natural phenolic resin) reinforced by flax fibres could offer desirable characteristics (lightweight, economic and low environmental impact) aiming at reducing carbon footprint of superlight electric vehicles. The non-woven flax mats were chemically treated (alkali, acetylation, silane and enzymatic treatment) to prepare tannin composites through compression moulding (130 °C/35 min/1.5 MPa). The change in fibre morphology was seen in SEM (scanning electronic microscope) images. The treatments (except enzymatic) showed significant improvement in tensile properties, along with enhancement (acetylation) in flexural properties, but little effect on impact resistance for all treatments. APS (aminopropyl triethoxy siloxane) treated composites showed highest tensile strength of 60 MPa and modulus of 7.5 GPa. BTCA (butanetetracarboxylic acid) treatment led to the highest flexural strength of up to 70 MPa. NaOH treatment retained the impact failure force of about 0.5 kN and sustained the saturation energy (4.86 J) compared to untreated composites (4.80 J)

PLA is one of the most promising bio-compostable and bio-degradable thermoplastic polymers made from renewable sources. PLA is generally produced by ring opening polymerization (ROP) of lactide using the metallic/bimetallic catalyst (Sn, Zn, and Al) or other organic catalysts in a suitable solvent. In this work, reactive extrusion experiments using stannous octoate Sn(Oct)₂ and tri-phenyl phosphine (PPh)₃ were considered to perform ROP of lactide. Ultrasound energy source was used for activating and/or boosting the polymerization as an alternative energy (AE) source. Ludovic^® software, designed for simulation of the extrusion process, had to be modified in order to simulate the reactive extrusion of lactide and for the application of an AE source in an extruder. A mathematical model for the ROP of lactide reaction was developed to estimate the kinetics of the polymerization process. The isothermal curves generated through this model were then used by Ludovic software to simulate the “reactive” extrusion process of ROP of lactide. Results from the experiments and simulations were compared to validate the simulation methodology. It was observed that the application of an AE source boosts the polymerization of lactide monomers. However, it was also observed that the predicted residence time was shorter than the experimental one. There is potentially a case for reducing the residence time distribution (RTD) in Ludovic^® due to the ‘liquid’ monomer flow in the extruder. Although this change in parameters resulted in validation of the simulation, it was concluded that further research is needed to validate this assumption.