JOURNAL OF MATERIALS SCIENCE LETTERS 20, 2 0 0 1, 2095 – 2096 The determination of porosity and cellulose content of plant fibers by density methods L. Y. MWAIKAMBO Department of Engineering and Applied Science, University of Bath, Bath BA2 7AY, UK E-mail: msplym@materials.bath.ac.uk M. P. ANSELL Department of Engineering and Applied Science, University of Bath, Bath BA2 7AY, UK Plant fibers often arranged in fiber bundles, for exam- ple hemp and jute are comprised of four main chemical components namely cellulose, hemicelluloses, lignin and pectin. These are chemical components, which make the solid morphological structure of plant fibers together with the air filled lumen. In some cases the lu- men contains protoplasm for example in cotton single fibers [1]. The absolute diameter of plant fibers excludes the lumen but includes the pores trapped between the fib- rils and lamellae. The absolute density excludes all the pores and lumen and is therefore a measure of the solid matter of the fibers. The bulk (apparent) density on the other hand includes all the solid material and the pores of the fibers. The bulk density is always less than that without pores hence less than the absolute density due to the buoyancy effect caused by the trapped air. The abso- lute density of pure cellulose is reported as 1592 kg/m 3 and that of regenerated cellulose as 1583 kg/m 3 [2]. The absolute density of most plant fibers is between 1400–1500 kg/m 3 . This slight drop of density in plant fibers is due to the presence of porosity including the lumen and impurities such as waxes and oils. The quantification of the plant fibers’ constituents has traditionally been carried out by chemical methods using established standard methods such as the ASTM, BS and ISO standards. Sun et al. [3] used 6%NaOH and 17.5%NaOH to extract hemicellulose and produced a scheme for the fractionation of polysaccharides and lignin from oil palm trunk and empty fruit bunch (EFB). Mitchel and Winandy [4] used ethanol, acidic chlorite and then an alkaline to extract hemicellulose from holo- cellulose. Sugars, residual acid and Klason lignin were determined by Pettersen and Schmidt [5] to determine α-cellulose. The literature available gives different cellulose con- tents for the same fiber and sometimes the difference T A B L E I Some physical properties of hemp, sisal, jute and kapok fibers Fiber Diameter Absolute density Bulk density Porosity Non-cellulose Non-cellulose P + X [( P + X ) - Y ] Cellulose content type (μm) ρ a (kg/m 3 ) ρ b (kg/m 3 ) P (%) X (%) + air Y (%) Y ′ (%) T air (%) Z (%) Hemp 67.84 1505 1468 2.46 5.46 7.79 7.92 0.13 91.95 Sisal 167.85 1428 1273 10.85 10.30 20.04 21.15 1.11 77.74 Jute 45.44 1532 1358 11.36 3.77 14.70 15.13 0.43 84.44 Kapok 22.65 1474 384 73.95 7.41 75.88 81.36 5.48 13.16 between one result and the other can be of the or- der of 12% difference [6, 7]. In this work combining the Archimedes method with the technique of helium pycnometry makes unique accurate measurements of porosity and cellulose content. The densities of hemp, sisal, jute and kapok fibers have been measured as part of a programme of work on plant fiber composites [8]. Kapok fibers are single seed fibers and the three other fibers are fiber bundles. Average diameter for 50 fibers evaluated by scanning electron microscope (SEM) and image analysis (IA) are presented in Table I. Benzene with a density of 875 kg/m 3 was used as a solvent for the measurement of the bulk density of fibers and an electronic balance was used to weigh fibers. Weights were measured to the nearest 0.001 g. A tuft of fibers was first weighed on the pan and its weight recorded as W fa . The fiber was then immersed in the benzene and made to rest on the weighing pan submerged in the solvent. The weight in kg of the im- mersed fiber was then recorded as W fs . The bulk density (ρ b ) of the fibers was calculated using Equation 1. ρ b = ρ s W fa W fa - W fs (1) Where ρ s = the density of the solvent (benzene) (kg/m 3 ). All measurements were determined at 19 ◦ C. Helium pycnometer model AccuPyc 1330 acquired from Micrometrics Instrument Corporation (USA) was used to measure the absolute density of fibers. The sample was placed into the pycnometry sample holder and weighed. The sample and container were then placed into the cell chamber. The sample identifi- cation number was given and its weight recorded. The helium gas was then admitted into the cell chamber filling the open lumen and pores. This procedure was 0261-8028 C  2001 Kluwer Academic Publishers 2095