Bast fibres are defined as those obtained from the outer cell layers of the stems of various plants. The fibres find use in textile applications and are increasingly being considered as reinforcements for polymer matrix composites as they are perceived to be "sustainable". The fibres are composed primarily of cellulose which potentially has a Young's modulus of ~140 GPa (being a value comparable with man-made aramid [Kevlar/Twaron] fibres). The plants which are currently attracting most interest are flax and hemp (in temperate climates) or jute and kenaf (in tropical climates). This review paper will consider the growth, harvesting and fibre separation techniques suitable to yield fibre of appropriate quality. The text will then address characterisation of the fibre as, unlike man-made fibres, the cross section is neither circular nor uniform along the length.

a b s t r a c tBast fibres are defined as those obtained from the outer cell layers of the stems of various plants. The fibres find use in textile applications and are increasingly being considered as reinforcements for polymer matrix composites as they are perceived to be ''sustainable". The fibres are composed primarily of cellulose which potentially has a Young's modulus of $140 GPa (being a value comparable with man-made aramid [Kevlar/Twaron] fibres). The plants which are currently attracting most interest are flax and hemp (in temperate climates) or jute and kenaf (in tropical climates). Part 2 of this review will consider the prediction of the properties of natural fibre reinforced composites, manufacturing techniques and composite materials characterisation using microscopy, mechanical, chemical and thermal techniques. The review will close with a brief overview of the potential applications and the environmental considerations which might expedite or constrain the adoption of these composites.Ó 2010 Elsevier Ltd. All rights reserved. Prediction of mechanical propertiesThe elastic modulus of a composite material can normally be predicted using the standard rule-of-mixtures (Eq. (1)) [1]:where g l is the fibre length distribution factor, g o is the fibre orientation distribution factor, E f is the elastic modulus of the fibre (Vincent [2] has estimated a modulus of up to 140 Gpa for cellulose fibres), E m is the elastic modulus of the matrix, V f is the fibre volume fraction and V m is the matrix volume fraction (assuming V f + V m = 1, i.e. no voids or other inclusions). At this stage in the review, we have neglected the void which occurs within the fibre on the expectation that it will not influence the above. There is an interdependency within V f E f given that the fibre cross-section and modulus could be calculated on the gross area or the net area after taking the lumen into consideration. The previous assumption would then become V f + V m + V v + V l = 1, where V v is the volume fraction of voids in the matrix and at the interface and V l is the volume fraction of lumen as a proportion of the whole composite. Effect of voidsMadsen et al. [3] have developed a model to predict the volumetric composition (volume fractions of fibres, matrix and porosity) and density of composites as a function of the fibre weight fraction. The model is particularly aimed at plant fibre composites, but is also valid for all other composites. The porosity is initially divided into three parts associated with the fibre, the interface and the matrix. Madsen et al. [4] have presented a modified rule-ofmixtures to include the influence of porosity on the composite stiffness. The model (Eq. (2)) integrates the volumetric composition of the composites with their mechanical properties.where V p is the volume fraction of porosity derived from weight fractions of the other components and n is a porosity efficiency exponent quantifying the effect of porosity which gives rise to stress concentrations in the composites. When n = 0,...

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The ISO 14040 series of standards describe the principles and framework for the conduct of life cycle assessment (LCA). The system defines four phases: (i) definition of the goal and scope of the LCA, (ii) the life cycle inventory analysis (LCI), (iii) the life cycle impact assessment (LCIA), and (iv) the life cycle interpretation. The standards do not describe the LCA technique in detail, nor do they specify methodologies for the individual phases of the LCA. Dependent of the goal and scope, there can be very different outcomes from the analysis. This paper considers how the outcomes might change for the specific case of flax fibres for the reinforcement of composites. The study compares allocation of environmental burdens to two different primary products: (i) flax seed as a nutritional supplement with fibre generated from the waste stream, or (ii) flax fibre as the primary product.