18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS 1 Introduction Low-cost renewable natural fibres [1] have, almost exclusively, been used as short fibre randomly distributed reinforcements in non-structural thermoplastic applications [2] (and references therein). Through this study, the potential of biofibres as reinforcements in load-bearing applications is assessed by evaluating the performance of vacuum infused thermoset unidirectional (UD) plant bast fibre composites (PFCs) against E-glass composites (GFCs). However, the development of structural PFCs requires specific consideration over traditional composites. Firstly, the lack of composites- applicable biofibres is apparent noting that they require specific consideration over textile industry requirements [3]; where textile yarns are twisted for processability, employing twisted yarns as reinforcements hinders impregnation and compromises orientation efficiency of the resulting composite. This study highlights the significance of reinforcement plant fibre yarn construction (twist and compaction) in composite manufacturing (fill time, void content) and mechanical properties. Secondly, current research trends highlight the importance of interface engineering in the development of PFCs due to their shortcomings associated with poor fibre-matrix adhesion. Although conventional fibre surface modification techniques improve the interface and composite mechanical properties, they i) are an additional step in PFC manufacture, ii) require expensive or toxic chemicals, and iii) reduce the reinforcing fibre tensile strength by up to 50% (if unoptimised) [4]. This study investigates the use of a cheap, commercially applicable, non-toxic, novel fibre surface treatment technique: hydroxyethylcellulose (HEC) sizing of plant fibre yarns. HEC sizing may not only eliminate the need for introduction of twist in yarns for textile processability, it can also act as a film-former, lubricant, surfactant and binder in the production of aligned fabrics. Moreover, hydrophobic modification of HEC can enhance its performance as a surfactant and even as a compatibiliser to create a better fibre-matrix interface. 2 Methodology 2.1 Materials For this study, four commercially available plant bast fibre ring spun yarns were chosen (Table 1). J250 (jute) and H285 (hemp) yarns were obtained in high twist. F250 is a low twist flax commingled with a polyester binder yarn while F400 is low twist roving of flax. The three numbers denote datasheet (nominal) linear density in tex. The deviation of the true linear density from the nominal linear density is also presented in Table 1. The significant difference for J250 may be attributable to the 7 – 10 % moisture content of plant fibres [5], particularly as J250 is produced in humid Bangladesh. The measured fibre density, mean yarn twist angle and yarn packing fraction are also presented in Table 1. 2.2 Production of plant fibre UD fabric A simplified drum-winding facility is used to produce UD mats (Fig. 1). The process involves the automatic winding of a yarn (from a single bobbin) around a rotating and traversing metal drum. To minimize inter-yarn spacing, periodic manual adjustments are necessary. Once the drum length is covered, the monolayer winding is uniformly hand painted with 0.6 wt% aqueous HEC solution and dried at 60 °C for 30 mins. The UD mat is recovered upon drying. HEC was purchased from the Dow Chemical Company under the trade name Cellosize HEC QP-52000H. YARN OPTIMISATION AND PLANT FIBRE SURFACE TREATMENT USING HYDROXYETHYLCELLULOSE FOR THE DEVELOPMENT OF STRUCTURAL BIO-BASED COMPOSITES D.U. Shah *, P.J. Schubel, M.J. Clifford, P. Licence, N.A. Warrior Faculty of Engineering, University of Nottingham, Nottingham, UK * Corresponding author (eaxds1@nottingham.ac.uk) Keywords: natural fibres, structural composites, physical properties, surface modification, vacuum infusion, mechanical properties