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

More documents

Recommendations

Info

a Composite stiffness E cp [GPa] b Composite stiffness E cp [GPa] 60 50 40 30 20 10 0 60 50 40 30 20 10 0 P.rad. treated hemp, long P.rad. treated hemp, short C.sub. treated hemp, short Hemp yarn, Wound Hemp yarn, Lay up 0 10 20 30 40 50 60 Fibre content [% v/v] Water retted hemp Raw hemp bast 0 10 20 30 40 50 60 Fibre content [% v/v] Figure 7. Effect of composite fabrication (a), fibre length (a), fungal defibration (a) and water retting (b) on composite stiffness after correction for porosity plotted as a function of fibre volume fraction. 136 Risø-PhD-11
DISCUSSION The defibration of hemp fibres by cultivation of P. radiata resulted in fibres with higher cellulose content than water retted hemp and pectinase treated hemp (Thygesen et al., 2002) due to increased degradation of pectin and lignin. The cellulose crystallinity tended to decrease with the cellulose content obtained by the fungal treatments (Figure 3) showing that during processing part of the crystalline cellulose is converted into its amorphous form. A similar chemical composition to P. radiata defibrated hemp has been obtained by wet oxidation (Thygesen et al., 2002; Thomsen et al., 2005), which is also an oxidative process resulting in decreased cellulose crystallinity (Thygesen, 2006). The machine winding and hand lay-up techniques resulted in roughly the same composite strength (Figure 6a), showing that the hand lay-up technique results in the same optimal fibre alignment generally obtained by machine (Madsen & Lilholt, 2003). The fibre length was an important parameter for both calculation of the fibre strength and stiffness due to the high risk of composite failure near the fibre ends, when these are located in the strained specimen section. Therefore, the calculated fibre strength decreased by 1.23 times for composites based on the short fibre length (Figure 6a) and further reduction might occur if the fibre ends are not at random positions. The fibre strength and stiffness were in general compared based on back calculation from composite data since this involves identical test specimens, accurate measurement of the force and accurate measurement of the strain. However this will cause inaccuracy due to the effect of fibre length and fibre-matrix interface. The advantage with the fibre bundle tensile test is that the fibre strength is measured in a more direct manner. However since the test samples are small and of variable size and geometry it was decided to rely on the composite data. The composite strength for the laminate with 35% v/v hemp yarn (230 MPa; Figure 6a), was slightly lower than for flax yarn based composites (251 MPa; Vf = 43% v/v) (Madsen & Lilholt, 2003). However the calculated fibre strength was lowest in the flax yarn (575 MPa). The lower strength in composites with P. radiata defibrated hemp fibres (174 MPa, Figure 6a) was due to the lower cellulose content, the lower fibre content (32 % v/v) and the lower failure strain of the fibres resulting in lower matrix stress of 25 MPa compared with 39 – 43 MPa (Table 4). Investigations reported by Hepworth et al. (2000b) with raw hemp bast and water retted hemp in epoxy-composites have shown much lower composite strength (80 – 90 MPa) using 20% v/v fibres leading to a fibre strength of 290 – 340 MPa, which can be due to incomplete fibre alignment. The composite stiffness has been found to 27 GPa in composites containing 43 % v/v flax fibres (Madsen & Lilholt, 2003). This corresponds to a fibre stiffness of 58 GPa, which is close to the stiffness for hemp yarn that was calculated in this study (60 GPa). Even though the hemp fibres were handled with mild methods like hand peeling and fungal defibration, a higher calculated fibre strength than 643 MPa was not obtained, which is similar to the strength of traditionally produced hemp yarn (677 MPa). The similar results are surprising and indicate that the final fibre strength is not very dependent on the defibration method applied (Table 4). Risø-PhD-11 137
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 and 44:
a b c Composition [% w/w] 100 Compo
Page 45 and 46:
8 Fibre strength in hemp The streng
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 83 and 84:
Risø-PhD-11 83
Page 85 and 86: Risø-PhD-11 85
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
Page 97 and 98: 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.
Page 119 and 120: Paper IV Comparison of composites m
Page 121 and 122: ABSTRACT Aligned epoxy-matrix compo
Page 123 and 124: the calculation of volume fractions
Page 125 and 126: solution (pH 4) for 4 h at 85°C. L
Page 127 and 128: E ⎛ dσ c ⎞ = ⎜ ⎟ ⎝ dε
Page 129 and 130: Table 2. Chemical composition, stru
Page 131 and 132: transverse section of the small hem
Page 133 and 134: Long fibres that pass through the e
Page 135: Figure 6. Effect of composite fabri
Page 139 and 140: This investigation showed that the
Page 141 and 142: Bos, H.L., Molenveld, K., Teunissen
Page 143 and 144: Thygesen, A., 2006. Properties of h
Page 147: Risø’s research is aimed at solv
show all

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

Create successful ePaper yourself

Delete template?

Save as template?