Properties of hemp fibre polymer composites -An optimisation of ...

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7.3 The treatment procedures effect on cellulose crystallinity Wet oxidation of corn stover resulted in increased content of crystalline cellulose in the fibres. The content of crystalline cellulose appeared to reach a level of 38-42% w/w for obtained cellulose contents of 50-60% w/w. Crystalline cellulose is thereby converted into its amorphous form at the high temperature applied during the treatment (190°C). For the fungal defibrated hemp fibres, the cellulose crystallinity tended to decrease versus the obtained cellulose content showing that some crystalline cellulose was converted into amorphous form (Figure 27). Hemp yarn had even lower cellulose crystallinity and a sample crystallinity similar to water retted hemp fibres. The cellulose crystallinity remained constant during water retting of hemp, which was presumably due to the low lignin degradation, compared with the lignin degradation during defibration with P. radiata Cel 26 (Paper IV). Sample crystallinity [% w/w] 100 80 60 40 20 0 Corn stover Barley straw Hemp fibres WO corn stover C.sub. treat hemp P.rad. treat hemp Water-rett. hemp Hemp yarn Norway spruce 0 20 40 60 80 100 Cellulose content [% w/w] Figure 27. Sample crystallinity determined by Rietveld refinement versus the cellulose content determined by the comprehensive fibre analysis. The full drawn line shows the relationship for non-woody fibres. The grey line shows the effect of wet oxidation on corn stover. The effect of fungal treatment is shown by the dotted line (Paper III; Paper IV). 44 Risø-PhD-11
8 Fibre strength in hemp The strength and the composition of hemp fibres depends on parameters like weather conditions, soil type, fertilization and defibration type (Hoffmann, 1961). Even the fibres within a single stem vary in strength with the weakest ones at the base of the stem presumably due to differences in chemical composition. The sensitivity to harvest year seems to vary between hemp cultivars with highest variation for Uniko B and lowest variation with Uso 11 and Felina 34 (Figure 28; Sankari, 2000). Low variation in the fibre strength indicates low sensitivity to weather conditions resulting in similar fibre properties each year. 8.1 Effect of hemp cultivar and the Weibull distribution Hemp cultivars have bast fibres with different mechanical properties due to differences in the chemical composition of the fibres (Table 3). Based on cultivation experiments in Finland, the fibre strength with lowest standard deviation (100-200 MPa) was obtained with the cultivars Futura, Fedora and Felina with fibre bundle strength varying between 650 MPa and 1050 MPa (Sankari, 2000). Fibres from the cultivars Uniko B and Secuieni had higher fibre strength (550-1400 MPa) and higher standard deviation. Thereby lower effective strength will be obtained as explained by the Weibull distribution (Lilholt, 2002; Figure 28). The Weibull effect is determined by a statistical procedure for calculation of the overall tensile strength of many fibres from the terms σ0 and m, which depend on the average single fibre strength and the standard deviation. Increasing standard deviation (decreasing m) results in decreasing fibre bundle strength at constant average single fibre strength. Thus, raw Felina hemp fibres had a single fibre strength of 1200±400 MPa (Figure 29) and a fibre bundle strength of 950±230 MPa (Figure 30) which is 20% lower than the single fibre strength. According to the Weibull distribution the average fibre bundle strength is calculated as − 1 m 1 σ = σ ⋅V ⋅ Γ 1+ ) and V = e × m av 0 ( m where σ0 is a normalized stress term and Γ is the gamma function. The fibre bundle efficiency is the ratio between the overall fibre bundle strength and the average single fibre strength: σ = 1 − 1 ( e × m) × ( Γ( 1+ ) ) av m σ b m Risø-PhD-11 45
Page 1 and 2: Risø-PhD-11(EN) Properties of hemp
Page 3 and 4: Contents Preface 6 1 Resumé 7 2 Li
Page 5 and 6: PhD thesis: Properties of hemp fibr
Page 7 and 8: 1 Resumé Karakterisering af hampef
Page 9 and 10: 2.4 Oral presentations Anders Thyge
Page 11 and 12: 4 Introduction Hemp (Cannabis sativ
Page 13 and 14: 4.2 The outline of the thesis The f
Page 15 and 16: The only fertilizer used was 360/48
Page 17 and 18: Temperature [ o C] 35 30 25 20 15 1
Page 19 and 20: A B Figure 7. A: Model of transvers
Page 21 and 22: Figure 8. Lignin (a), pectin (b) an
Page 23 and 24: Figure 11. Microfibril angles (MFA)
Page 25 and 26: Teleman, 1997). The crystal structu
Page 27 and 28: to the computing effort and the sub
Page 29 and 30: Figure 15. The structure of hemicel
Page 31 and 32: fibre mats, which are made by air-d
Page 33 and 34: Figure 18. From fibre filament to a
Page 35 and 36: A B C D Figure 20. Chemical structu
Page 37 and 38: water vapour and air are removed fr
Page 39 and 40: 7 Defibration methods Defibration m
Page 41 and 42: Table 5. Fibre yield and cellulose
Page 43: a b c Composition [% w/w] 100 Compo
Page 47 and 48: 8.2 Effect of pre-treatment of hemp
Page 49 and 50: E-modulus [GPa] 90 80 70 60 50 40 3
Page 51 and 52: Second mode: Failure is controlled
Page 53 and 54: structure, which made much higher f
Page 55 and 56: Table 7. Porosity factors determine
Page 57 and 58: Thereby, the effective fibre streng
Page 59 and 60: a b Composite tensile strength σcu
Page 61 and 62: Table 9. Mechanical properties in a
Page 63 and 64: a σ c/ρ c [10 3 m 2 /s 2 ] b Ec/
Page 65 and 66: Fibre strength σ f [MPa] Fibre sti
Page 67 and 68: 11 References Andersen TL, Lilholt
Page 69 and 70: Kaar WE, Cool LG, Merriman MM, Brin
Page 71 and 72: Stowell EZ, Liu TS, 1961. On the Me
Page 73 and 74: Appendix A: Comprehensive composite
Page 75 and 76: The porosity constants can now be d
Page 77 and 78: Appendix D: Density and mechanical
Page 79 and 80: Paper I Changes in chemical composi
Page 81 and 82: Risø-PhD-11 81
Page 89 and 90: Paper II Hemp fiber microstructure
Page 91 and 92: ABSTRACT Characterization of hemp f
Page 93 and 94: METHODS AND TECHNIQUES Treatment of
Page 95 and 96:
2000) and their orientation gave th
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By TEM microscopy, the single fiber
Page 99 and 100:
Table 1. Chemical composition of th
Page 101 and 102:
Table 2. Tensile strength (σ) and
Page 103 and 104:
Morvan, C., Jauneau, A., Flaman, A.
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Risø-PhD-11 105
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Risø-PhD-11 117
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Paper IV Comparison of composites m
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ABSTRACT Aligned epoxy-matrix compo
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the calculation of volume fractions
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solution (pH 4) for 4 h at 85°C. L
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E ⎛ dσ c ⎞ = ⎜ ⎟ ⎝ dε
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Table 2. Chemical composition, stru
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transverse section of the small hem
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Long fibres that pass through the e
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Figure 6. Effect of composite fabri
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DISCUSSION The defibration of hemp
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This investigation showed that the
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Bos, H.L., Molenveld, K., Teunissen
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Thygesen, A., 2006. Properties of h
Page 145 and 146:
Risø-PhD-11 145
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Risø’s research is aimed at solv
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