(2019) 1:6
Omer et al. BMC Chemical Engineering
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earlier than that in Ethiopia, some other reports consid- ered India as center of origin [3 – 6].The estimated an- nual production in the world was about 4.8 million tons; and the share of India (4.528 million tons), Nigeria (0.826 million tons), Sudan (0.249 million tons), Pakistan (0.116 million tons), Cote d ’ Iviore (0.115 million tons), Egypt (0.100 million tons) and Iraq (0.153 million tons) [7]. Okra is important food supplement in tropical regions and has nutritional and medicinal values, it is used traditionally in treating diseases as diabetes, pyretic syndrome, and spasmodic [7 – 11]. Stalk fiber of okra is characterized by high lignin, low α -cellulose, and shorter fiber length, while bast fiber is characterized by low lignin, high α -cellulose, and longer fiber length [12] the pulps obtained from okra stalks is good enough [13] with a high carbohydrates content (65.0%), low lignin contents (20.5%) and similar to chemical components of non-woody plants indicating okra stalks as promising source for papermaking utilization, in addition to that okra fibers can be applied as reinforcement in polymer composites [14 – 16]. The Anthraquinone (AQ) acts as redox catalyst during alkaline pulping, reduce aldehyde end groups of the carbohydrates, forming carboxylic acid, inhibits the alka- line depolymerization results in an increased yield. The soda-AQ cooking suitable for pulping non-woody plants and agricultural residues from economic and environ- mental points of views [17, 18]. The present study focused in evaluation the character- istics of Sudanese Abelmoschus esculentus okra stalks in terms of fiber morphological properties, chemical com- position, Soda-AQ pulping and papermaking character- istics and therefore indicate their suitability for paper pulp production. Methods Abelmoschus esculentus okra (Fig. 1) stalks were selected randomly according to TAPPI Standards [19] from Marenjan area in Gezira state, central Sudan is charac- terized with clay soil with low to moderate annual rain- fall. The length of stalks was 2. 5-3 m tall and 2-2.5 cm in diameter. The prepared raw materials were packed in plastic bags and transported by bus to National Centre for Research (NCR) in Khartoum state. Leaves and steams were separated manually, and then stalks were chopped into 2-4 cm length. Chips were left for air dry- ing according to TAPPI standard (T 257-cm- 02) [19]. The air dry samples of core and bark of okra were manually separated and chopped to 3 – 5 cm length. Fiber dimension evaluation done after maceration with a mix- ture of 30% hydrogen peroxide and acetic acid (1:1) for core and bark parts separately and was carried out microscopically at 300x and 400x magnifications accord- ing to (TAPPI-232 cm-01) after staining with aqueous
Fig. 1 Abelmoschus esculentus okra plant
safranin [20, 21]. The raw materials was characterized chemically in accordance with applicable TAPPI stan- dards for different components, namely: preparation for chemical analysis (TAPPI-264-cm-97) sampling and test- ing for moisture (TAPPI-210 cm-93) lignin (TAPPI-222), alpha cellulose (TAPPI-203 OS-61), hot water soluble (TAPPI-T- 207), Pentosans (TAPPI-223-cm-01) solvent ex- traction of wood (TAPPI-204), and ash (TAPPI-212) [22]. According to the suggestions of other authors, the op- eration conditions used during soda-anthraquinone cooking of okra were selected, as follows: maximum temperature 165C 0 , time to maximum temperature 60 min, time at temperature 120 min, anthraquinone con- centration 0.1% and liquid/okra stalks ratio was 5. Representative sample of a portion prepared chips for pulping trails was ground in a star mill and the 40X60 mesh fraction was used for chemical analysis according to TAPPI standards and Obolenskaya [23]. All the conditions were constant except for soda concentration as (NaOH, 15-21% on oven dry weight of okra stalks) for optimization of cooking and the concen- tration of alkali was the most effective variable. After pulping, the cooked material was washed with water at room temperature to remove the residual cooking liquor and was fiberized in a disintegrator at 1200 rpm for 30 min, at room temperature and l0% consistency. The pulp was then beaten in Valley beater according to TAPPI- 200-sp-01 freeness of pulp (Canadian standard method TAPPI 227om-99), Kappa number (TAPPI-236 om-99), viscosity (TAPPI-230om − 99), physical testing of pulp sheets (TAPPI-220-sp-01). Conditioning of testing atmosphere (TAPPI-402-sp-98), Burst strength (TAPPI- 403om-97), Tensile (TAPP-404-cm-92), tearing resist- ance (TAPPI-414 om-98), folding endurance (TAPPI- 423 cm-98) and density (TAPPI258-om-02) and ISO standards [24]. The chemical charges for all cooks at different active alkali levels were calculated as NaOH on oven dry raw
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