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. A C C E P T E DACCEPTED MANUSCRIPT 2 ROP of Monomers through Metal/ ROP of Monomers through Metal/ ROP of Monomers through Metal/ ROP of Monomers through Metal/metal metal metal metal----free free free free Catalyst Catalyst Catalyst CatalystThe basis of the ROP process starts with opening the cyclic ring of monomers like amides (lactams), esters (lactones) and a cyclic ether. Then the opened ring acts as an active centre where other monomers join to create a longer polymer chain via ionic propagation consisting of initiation/ propagation as well as termination reactions [12]. In last two decades, several different classes of catalysts were implemented to synthesis PLA however, metal-based catalysts are the most common [7][8][9][10][11]. Apart from metal, organic and enzyme-based catalysts were also tried but with regards to the efficiency and reaction time, metal based catalysts show a more promising effect than non-metal based catalysts. Among many, Sn(Oct) 2 was a highly approved catalyst by United State food and drugs association (USFDA) for catalysis of LA. Once the monomer gets activated by the initiator (catalyst), the active site attracts other monomers to attach and increase the chain length. Thermodynamic and reaction kinetic are key factors for the suitability of polymerization of cyclic monomers [12], [13].

Flax reinforced tannin-based composites have a potential to be used in vehicle applications due to the environmental advantages and good mechanical properties. In this paper, the effects of fibre configuration on mechanical properties of flax/tannin composites were investigated for nonwoven and woven fabric lay-up angles (UD, [0°, 90°] 2 and [0°, +45°, 90°, -45°] 2 ). The tannin/flax composites were prepared by compression moulding. The manufactured specimens were then characterized for quasi-static tensile properties, dynamic mechanical properties and low-energy impact performance. Failure mechanism was further investigated using microscopy and demonstrated the need for further adhesion improvements.The study shows that the UD fabric reinforced composite performs better in tensile strength and modulus whereas [0°, +45°, 90°, -45°] 2 composite provides the best impact energy absorption performance.

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 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/35min/1.5MPa). The change in fibre morphology was seen in SEM (scanning electronic images). The treatments showed significant improvement in tensile properties, along with enhancement in flexural properties, but little effect on impact resistance. APS treated composites showed highest tensile strength of 60 MPa and modulus of 7.5 GPa. BTCA 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).

The reported research work was a multi-disciplinary, collaborative effort. Author SPD is the lead researcher and author of this manuscript. A detailed literature review and information regarding the ROP of lactide in the literature was conducted by author SPD as part of his doctoral thesis. Authors SPD, VM, HAA, JLB and KB contributed to the development of detailed study for the state-of-the art in the field of chronological development in the field of PLA processing. The author's contributed equally for making the manuscript more scientific and meaningful in terms of English language.

Innovation is often driven by changes in government policies regulating the industries, especially true in case of the automotive. Except weight savings, the strict EU regulation of 95% recyclable material-made vehicles drives the manufactures and scientists to seek new 'green materials' for structural applications. With handing at two major drawbacks (production cost and safety), ECHOSHELL is supported by EU to develop and optimise structural solutions for superlight electric vehicles by using bio-composites made of highperformance natural fibres and resins, providing enhanced strength and bio-degradability characteristics. Flax reinforced tannin-based composite is selected as one of the candidates and were firstly investigated with different fabric lay-up angles (non-woven flax mat, UD, [0, 90°] 4 and [0, +45°, 90°,-45°] 2) through authors' work. Some of the obtained results, such as tensile properties and SEM micrographs were shown in this conference paper. The UD flax reinforced composite exhibits the best tensile performance, with tensile strength and modulus of 150 MPa and 9.6 MPa, respectively. It was observed that during tension the oriented-fabric composites showed some delamination process, which are expected to be eliminated through surface treatment (alkali treatment etc.) and nanotechnology, such as the use of nano-fibrils. Failure mechanism of the tested samples were identified through SEM results, indicating that the combination of fibre pull-out, fibre breakage and brittle resins failure mainly contribute to the fracture failure of composites.

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.

Mechanical and impact performance of three-phase polyamide 6 nanocomposites AbstractIn this work, three-phase nanocomposites using multiscale reinforcements were studied to evaluate the influence of nanofillers on static and dynamic mechanical properties at varying temperature conditions. In particular, short-fibres reinforced polyamide 6 (30 wt.%) composites with various weight fractions of montmorillonite (OMMT) and nanosilica (SiO 2 ), manufactured and investigated. Quasi-static tensile properties were investigated at room temperature and also at 65 o C just above the polyamide 6 (PA6) glass transition temperature.The low velocity impact tests were conducted on the manufactured cone-shaped structures to evaluate the crash behaviour and energy absorption capability. The study results shows that the increase of the weight percentage level of OMMT in PA6/glass fibre (30 wt.%) composite made the nanocomposites more brittle and simultaneously deteriorated the tensile properties.SiO 2 nanofiller at 1 wt.% was found to be the optimum ratio for improving tensile properties in silica-based nanocomposites studied. It was further noted that for both types of nanofillers, the crashing behaviour and energy absorption in dynamic properties were improved with increase in nanofillers weight percentage in the composites. The study also shows that the brittleness behaviour of the nanocomposites investigated is associated to the fibre/matrix interaction which is dependent on the nanofiller type and has significant effect on crash modes observed.