18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS 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 not only eliminate the need for introduction of twist 1 Introduction in yarns for textile processability, it can also act as a Low-cost renewable natural fibres [1] have, almost film-former, lubricant, surfactant and binder in the exclusively, been used as short fibre randomly production of aligned fabrics. Moreover, distributed reinforcements in non-structural hydrophobic modification of HEC can enhance its thermoplastic applications [2] (and references performance as a surfactant and even as a therein). Through this study, the potential of compatibiliser to create a better fibre-matrix biofibres as reinforcements in load-bearing interface. applications is assessed by evaluating the 2 Methodology performance of vacuum infused thermoset unidirectional (UD) plant bast fibre composites 2.1 Materials (PFCs) against E-glass composites (GFCs). For this study, four commercially available plant However, the development of structural PFCs bast fibre ring spun yarns were chosen (Table 1). requires specific consideration over traditional J250 (jute) and H285 (hemp) yarns were obtained in composites. Firstly, the lack of composites- high twist. F250 is a low twist flax commingled with applicable biofibres is apparent noting that they a polyester binder yarn while F400 is low twist require specific consideration over textile industry roving of flax. The three numbers denote datasheet requirements [3]; where textile yarns are twisted for (nominal) linear density in tex. The deviation of the processability, employing twisted yarns as true linear density from the nominal linear density is reinforcements hinders impregnation and also presented in Table 1. The significant difference compromises orientation efficiency of the resulting for J250 may be attributable to the 7 – 10 % composite. This study highlights the significance of moisture content of plant fibres [5], particularly as reinforcement plant fibre yarn construction (twist J250 is produced in humid Bangladesh. The and compaction) in composite manufacturing (fill measured fibre density, mean yarn twist angle and time, void content) and mechanical properties. yarn packing fraction are also presented in Table 1. Secondly, current research trends highlight the importance of interface engineering in the 2.2 Production of plant fibre UD fabric development of PFCs due to their shortcomings A simplified drum-winding facility is used to associated with poor fibre-matrix adhesion. produce UD mats (Fig. 1). The process involves the Although conventional fibre surface modification automatic winding of a yarn (from a single bobbin) techniques improve the interface and composite around a rotating and traversing metal drum. To mechanical properties, they i) are an additional step minimize inter-yarn spacing, periodic manual in PFC manufacture, ii) require expensive or toxic adjustments are necessary. Once the drum length is chemicals, and iii) reduce the reinforcing fibre covered, the monolayer winding is uniformly hand tensile strength by up to 50% (if unoptimised) [4]. painted with 0.6 wt% aqueous HEC solution and This study investigates the use of a cheap, dried at 60 °C for 30 mins. The UD mat is recovered commercially applicable, non-toxic, novel fibre upon drying. HEC was purchased from the Dow surface treatment technique: hydroxyethylcellulose Chemical Company under the trade name Cellosize (HEC) sizing of plant fibre yarns. HEC sizing may HEC QP-52000H.
2.3 Manufacture of UD composites W W f f c c v ; v 1 ; f m Four layers of UD mat were used to produce 250 W W f c f c mm square 3-3.5 mm thick composite plaques. Resin 1 v v v (1) injection was achieved by vacuum infusion. To v f m observe the flow regime, the mould tool included a 2.4.3 Composite mechanical testing clear acrylic top face. Reduced race tracking and Tensile tests were conducted according to ISO 527- improved impregnation was achieved by line-gate 4:1997 using an Instron 5985 testing machine injection with resin flow perpendicular to the UD equipped with a 100 kN load cell and an mat. extensometer. Six 250 mm long and 25 mm wide For composite manufacture, two standard specimens were tested for each type of composite at thermosetting resin systems were used: i) a a cross-head speed of 2 mm/min. The ultimate Reichhold Norpol orthophthalic unsaturated tensile strength (UTS) σ T , tensile modulus E T (in the polyester (UP) type 420-100 and ii) a Gurit UK Ltd. strain range of 0.025 - 0.10 %) and the failure strain low viscosity Epoxy Prime 20LV. For both resin ε T of the composite samples were measured. systems, post cure was carried out at 50 °C for 6 h From the composite properties, fibre tensile strength after ambient curing for 16 h. σ f , and modulus E f were back-calculated using the UD and random E-glass composites were also rule of mixtures in (2). The reinforcement efficiency manufactured for comparative purposes. factor (η) for UD composites was assumed to be 1. 2.4 Experimental For E-glass random (R) composites, an efficiency factor of 3/8 was used. 2.4.1 Yarn tensile properties E v E v E T m m ; T m m (2) To observe the effect of HEC treatment on the f f v v mechanical properties of the yarns, tensile properties f f of the untreated and HEC treated yarns were Three-point bending flexural tests were performed measured with an Instron 5969 testing machine set according to ISO 178:1997 using a Hounsfield up with a 2 kN load cell. Single yarns with a gauge testing machine equipped with a three-point bending length of 250 mm were tested at a cross-head speed fixture and 2 kN load cell to determine the flexural of 200 mm/min. Ten specimen were tested for each strength σ F and flexural modulus E F of the yarn, as deemed sufficient by several researchers [3, composites. Six specimens (80 mm long and 15 mm 6, 7]. Yarn tenacity (cN/tex), stiffness (N/tex) and wide) were tested for each type of composite at a failure strain (%) were determined from the tensile cross-head speed of 2 mm/min. tests. Finally, the impact properties of the composites were determined using an Avery Denison pendulum 2.4.2 Composite physical properties Charpy testing machine according to ISO 179:1997. The fibre volume fraction (v f ), matrix volume The un-notched specimens were loaded flatwise fraction (v m ) and void volume fraction (v v ) of the with weighted hammers at a point perpendicular to manufactured composites were determined using the direction of the UD fabric plane; a 2.7 J hammer (1), where W and ρ represent mass and density, was used for PFCs while a 5 J hammer was used for respectively while the subscripts f, m and c denote E-glass UD composites. A striking velocity of 3.46 ms -1 was used. Six specimens (100 mm long and 10 fibres, matrix and composite, respectively. Composite density was determined using helium mm wide) were tested for each type of composite. pycnometry. Optical microscopy was used to 3 Results qualitatively investigate the types of porosity in the composites. Mould fill times during laminate 3.1 Effect of HEC treatment on yarn tensile manufacture were also recorded. properties Although statistically insignificant (at α = 0.05), HEC treatment has a detrimental effect on the tenacity and stiffness of high twist yarns (Fig. 2).
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