Nomenclature
Chapter 3 Materials and experimental methodology
3.2 Material properties
3.2.1 Fiber
Percentages of cellulose, lignin, hemicellulose and ash of each type of natural fiber (coir, jute and WH) were determined as per the procedures given by Jenkins (1930), TAPPI Test Methods (1996), Goering and Van Soest (1970) and ASTM E1755-01 (2007), respectively.
Moisture content of the fibers was determined using oven-drying method (at 50◦C for 12 h) as per Methacanon et al. (2010) to avoid any biomass loss. Mean tensile strength at breakage, Young’s modulus and specific gravity of tested fibers were determined according to IS-1670-(1991) and IS-2720-Part 3-(1980), respectively. The specific gravity for coir, jute and WH was found to be 1.24 ± 0.10, 1.12 ± 0.05 and 0.7 ± 0.03 (Mean ± standard error of mean) respectively. The average diameter of the fibers used was 0.4 ± 0.1 mm for jute and coir, while WH has a diameter of 2 ± 0.8 mm for maintaining the same fiber aspect ratio.
Fig. 3.1. Surface morphology of jute, coir and water hyacinth fibers at different magnifications
Table 3.1 summarizes some physical and biochemical properties of each fiber type expressed in mean and standard error of mean. Jute has the highest cellulose content and thus show
highest tensile strength among tested fibers. On the other hand, coir has the highest percentage of lignin and it is the most ductile fiber (i.e., the highest elongation at break). Jute and WH, which have the highest hemicellulose content, showcases higher moisture absorbing ability. Figure 3.1 shows the Field Emission Scanning Electron Microscope (FE-SEM) images of jute, coir and WH, highlighting the surface morphology of the tested fibers at two magnification levels. WH is a monofilament fiber and each individual fiber is constituted by fibrils that would not be dissociated during mixing with soil. On the contrary, jute and coir have multifilament fibers segregate into finer fibers upon mixing with soil. The individual coir fiber shows a rougher surface at 1000X as compared to the other fibers.
Table 3.1. Properties of fibers used in this study
Physical properties Bio-chemical composition
Natural moisture
content (%)
Elastic Young’s modulus
Breaking tensile strength
(MPa)
Moisture Absorption
Capacity (%)
Elongation at break
(%)
Cellulo se (%)
Hemice llulose (%)
Lignin (%)
Ash (%) Coir
7 ± 1.2 7.2 ± 2.2 150 ± 3 12.6 ± 1.5 26 ± 2.2 43 ± 2.3
15 ± 1.1
38 ± 2.2
2 ± 0.8 Jute
14 ± 1.3 17 ± 3 500 ± 11 40 ± 1.4 10 ± 1.8 60 ± 3.4
22 ± 1.9
16 ± 1.6
1 ± 0.9 Water hyacinth
12 ± 2.1 12 ± 1.8 313 ± 8 95 ± 3.4 14 ± 1 46 ± 2.6
21 ± 2
11 ± 0.9
11 ± 1.5
3.2.2 Soil
Two soils were used in this study, sourced from north-east India and another from Shantou, China. The soil from India (Soil 1) was mostly used in all of the investigation. The soil from China (Soil 2) was used only in those sections where biochar was investigated. The soil index properties of soils used in this study are tabulated in Table 3.2.
Table 3.2. Soil index properties
Soil Property Standard Soil 1 Soil 2
Specific Gravity ASTM D 854 2.63 2.65
Particle size distribution (%)
Coarse Sand (4.75mm-2mm) Medium Sand (2mm-0.425mm) Fine Sand (0.425mm-0.075mm) Silt (0.075mm-0.002mm) Clay (<0.002mm)
ASTM D 422
0 7 28 40 25
0 37 21 37 5 Atterberg Limits (%)
Liquid Limit Plastic Limit Shrinkage Limit
ASTM D 4318
42 24 19
43 26 16 Compaction properties
Optimum Moisture Content (%) Maximum Dry Density (kN/m3)
ASTM D 698
17 16.5
16.5 15.8
Fig.3.2 Surface morphology of the two soils studied at 2K X magnification by FE-SEM
The surface morphology of the two soils has been presented at 2K X magnifications. It is seen that soil 1 has more fine particles as compared to soil 2 which is in accordance with the particle gradation listed in Table 3.2.
3.2.3 Biochar
The biochar feedstock was WH stems sourced from Deepor Lake in North-east India to avoid any genetic variability. The stems were chopped evenly and fed in a pyrolysis chamber at 350-400 ℃ based on thermo-gravimetric analysis (TGA; Fig. 3.3) of the sample. An automatic crusher was adopted to crush the coarse BC acquired from pyrolysis which was then sieved through 2mm sieves. The basic and engineering properties of the BC are tabulated in Table 3.3 and Table 3.4. The Atterberg limits and compaction characteristics of pure WH BC could not be determined as it is cohesionless when not mixed with soil. The elemental analyzer (Bird et al. 2017) was used to measure the carbon, hydrogen, nitrogen and oxygen content in the biochar produced. The ash content and cation exchange capacity is measured by ASTM E1755-01 (2007) and the ammonium acetate method (Thomas 1982). The surface morphology of BC particles is compared with that of the soil and soil-WH BC using FE-SEM images as shown in Fig. 3.4(a-b). The FE-SEM was performed using ZEISS SIGMA microscope analysis setup. It can be evidently viewed that a majority of the BC particles are smaller in size as compared to soil particles and consists mostly silt sized particles (<75 micron). The change in the pore structure of soil-BC composite occurs means resulting from its mixture with soil (Fig. 3.4c). Also, the BC appears to have inherent intra- pores with its matrix (Fig. 3.4d) which makes it susceptible to absorb additional water as compared to only bare soil. These intra-pores are developed due to WH being a lingo-cellulose material and upon pyrolysis leads to pores due to hemicellulose and cellulose degrading first followed by lignin (Lehmann and Joseph 2015, Pardo et al. 2018). The relevance of intra-pores of biochar in retaining additional water will be discussed chapter 5. The Fourier-transform infrared spectroscopy (FTIR) analysis was done by LT-4100 device (LABTRONICS instruments ltd) to analyze the surface
functional groups. The functional groups are majorly hydrophilic with OH- hydroxyl group as well as COOH- carboxyl group and is also presented in Fig. 3.5.
Fig. 3.3. Thermo-gravimetric analysis (TGA) of water hyacinth used in the current study
Table. 3.3 Basic properties of WH BC
Soil properties Standard WH BC
Particle size distribution ASTM D 422
Coarse Sand (2 – 4.75 mm) 0.00
Medium Sand (0.425 - 2 mm) 000
Fine Sand (0.075 – 0.425 mm) 30.48
Silt (<0.075 mm) 68.52
Clay (<0.002 mm 1
Atterberg limits ASTM D 4318
Liquid limit (LL) ND
Plastic limit (PL) ND
Plastic Index (PI) ND
Max. Dry Density (kN/m3) ASTM D 698 ND
OMC (%) ASTM D 698 ND
Specific gravity ASTM D 854 0.8
pH ASTM D 4972 7.69
ND-Cannot be determined
Fig. 3.4 FE-SEM images of (a) Soil, (b) WH-BC, (c) Soil-WH BC composite (5% BC) at 2K X magnification and BC intra-pore morphology
Table 3.4 Basic properties of water hyacinth biochar Feedstock Pyrolysis
process
Pyrolysis temperature
(℃)
Elemental analysis Ash content
(%)
CEC (cmol
kg-1) WH stem
sourced from Deepor lake,India
Slow
pyrolysis 350-400
C (%)
H (%)
O (%)
N (%)
39 21.95 53.39 42.80 1.99 1.82
Fig. 3.5 FTIR response of water hyacinth biochar used in the study