Properties of hemp fibre polymer composites -An optimisation of ...
Properties of hemp fibre polymer composites -An optimisation of ...
Properties of hemp fibre polymer composites -An optimisation of ...
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aw <strong>hemp</strong> bast, water retted <strong>hemp</strong> or P. radiata Cel 26 defibrated <strong>hemp</strong>, as<br />
reinforcement was 20 GPa, 26 GPa and 30 GPa, respectively without consideration <strong>of</strong><br />
porosity (Ec). Cultivation <strong>of</strong> P. radiata Cel 26 for defibration <strong>of</strong> <strong>hemp</strong> <strong>fibre</strong>s resulted<br />
thereby both in the highest composite strength and highest composite stiffness.<br />
Based on obtainable composite strength and stiffness, the best defibration method was<br />
cultivation <strong>of</strong> P. radiata Cel 26 followed by water retting and at last by cultivation <strong>of</strong> C.<br />
subvermispora. It was determined that the <strong>hemp</strong> <strong>fibre</strong>s tensile strength and stiffness were<br />
affected by the investigated defibration methods at 90% probability using analysis <strong>of</strong><br />
variance (F-test with number <strong>of</strong> samples = 4 and number <strong>of</strong> repetitions = 23 for F0.1)<br />
(Paper IV).<br />
The curve for composite strength for E-glass <strong>fibre</strong>s had about twice the slope <strong>of</strong> the<br />
curves for <strong>hemp</strong> yarn and defibrated <strong>hemp</strong> <strong>fibre</strong>s. That is due to the high strength <strong>of</strong><br />
glass <strong>fibre</strong>s (1200 – 1500 MPa) compared with <strong>hemp</strong> <strong>fibre</strong>s (535 – 677 MPa). The<br />
<strong>composites</strong> reinforced with glass <strong>fibre</strong>s with a maximum strength <strong>of</strong> 770 MPa could get<br />
much stronger than the <strong>hemp</strong> <strong>fibre</strong> reinforced <strong>composites</strong> (230 MPa) due to the higher<br />
obtainable <strong>fibre</strong> content. The curve for composite stiffness for E-glass <strong>fibre</strong>s had similar<br />
slope to the curve for raw <strong>hemp</strong> bast. That is due to the moderate stiffness <strong>of</strong> glass <strong>fibre</strong>s<br />
(71 – 77 GPa) compared with the defibrated <strong>hemp</strong> <strong>fibre</strong>s (88 – 94 GPa). The <strong>composites</strong><br />
reinforced with glass <strong>fibre</strong>s had a maximum stiffness <strong>of</strong> 40 GPa, which is not much<br />
higher than obtained with <strong>hemp</strong> <strong>fibre</strong>s (30 GPa).<br />
The curve for composite strength for barley straw had about four times lower slope than<br />
the curves for defibrated <strong>hemp</strong> <strong>fibre</strong>s. That is due to the low strength <strong>of</strong> barley straw<br />
(240 MPa) compared with the <strong>hemp</strong> <strong>fibre</strong>s (535-677 MPa) and the higher porosity<br />
content. The <strong>composites</strong> reinforced with barley straw with a maximum strength <strong>of</strong> 19<br />
MPa were up to 10 times weaker than the <strong>hemp</strong> <strong>fibre</strong> reinforced <strong>composites</strong> (230 MPa)<br />
due to the low obtainable <strong>fibre</strong> content and the very high porosity content (up to 44%<br />
v/v). The curve for composite stiffness had 15 times lower slope than the curves for the<br />
<strong>hemp</strong> based <strong>fibre</strong>s. That is due to the low <strong>fibre</strong> stiffness (22 GPa) and high porosity<br />
content. The <strong>composites</strong> were therefore not much stiffer than the epoxy matrix (3 GPa).<br />
58 Risø-PhD-11
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