1.5. Determination of extractives
Solvent extraction (60 ml acetone for 1 g of dried biomass sample) was used, and the temperature was
held at 90 °C for 2 h. After that, the sample was dried at 105 °C until a constant weight was obtained. The
weight difference before and after the extraction is the amount of extractives.
1.6. Holocellulose extraction
The procedure used for preparing holocellulose involves the treatment of the biomass samples (4 g)
with an acid solution (160 cm3 sodium acetate solution) at 75 °C for 5 h. Sodium chlorite (4 cm3
) was
added every hour during 4 h. The mixture is then cooled down and the residue was filtered and washed
with water first (1 dm3
) and with acetone (15 cm3
). The residue was dried at room temperature; an aliquot
was weighted and dried at 105 °C for the determination of the holocellulose content [15].
1.7. Hemicellulose extraction
10 mL of 0.5 mol/L sodium hydroxide was added to 1 g of extractive-free dried biomass, and the
temperature was held at 80 °C for 3.5 h. The samples were then washed using DI water until the pH value
of the solution approach 7, and then they were dried to a constant weight. The difference between the
sample weight before and after this treatment is hemicelluloses content [16]. The cellulose content was
calculated by subtracting the determined hemicelluloses content from the known holocellulose content.
1.8. Calorific value
A bomb calorimeter (Leco AC-350) equipped with water bath and oxygen controller was used to
obtain the heating value.
1.9. Extraction of oil
Oil from RSS and RSK were extracted from the 10g of samples by soxhlet extraction using hexane as
solvent at 60 °C for 6 hours [5]. All resulted supernatants were collected and evaporated in a rotary
evaporator to remove the solvent. The oil yield (oil content) of the rubber seed were calculated as below