The Chemistry of Indigenous Technology; Application of the Aqueous Extract of Parkia Biglobosa Fruit Husk in Formulation of Mud Wall Plaster

Parkia biglobosa belongs to the family Leguminosae and the subfamily Mimosoideae. The aqueous extract of its fruit husk is well mixed with a sandy loam soil to obtain a uniform paste, and this is applied as a mud wall plaster on the walls of mud buildings to protect the walls against erosion by rain water. Methods used in the project were Sohxlet extraction, TLC, HPLC, UV, IR, AAS, Flame photometry and X-ray analyses. To determine the chemical interactions of the constituents of a plastering material a simulated sample of the mud wall plaster was prepared and analysed. The water and ethanol extracts of the husk as well as the soil were separately analysed. The mass of extractable material from samples of husk harvested and stored for about a year (old husk) was compared with that of dry freshly harvested husk (new husk). Some organic constituents of the extract were identified and their interaction with metal constituents of the soil discussed. The average weight recovery yield of dry extractable material from the husk by water was 37.77% compared to that by ethanol which was 30.83 %. Based upon quantitative extractable material, and neglecting the differences in extraction temperature, water was found to be a more efficient solvent than ethanol for the extraction of Parkia biglobosa fruit husk. Also water is generally cheaper and more accessible than ethanol hence recommended for extraction of the husk. The storage duration of the husk (after harvesting) was practicably irrelevant to the amount of extractable material. Husks that have been harvested and kept for about a year produced almost the same yield of extractable material as freshly harvested husk. The respective amounts were: 38.31% / 37.22% weight recovered for old / new husk extracted by water and 30.70% / 30.95% for old / new husk extracted by ethanol. Fractionation of the aqueous extract produced four components: weak acid, strong acid, basic and neutral fractions. From the AAS and Flame analysis, the soil was found to contain: K (556.351 mg/Kg), Mg (230.054 mg/Kg), Fe (419.499 mg/Kg), Ca (336.315 mg/Kg) and Si (1400.564 mg/Kg) as well as Na (97.585 mg/Kg), Ni (103.220 mg/Kg), Pb (17.531 mg/Kg) and Zn (58.050 mg/Kg). In addition, the husks were found to have substantial amounts of Fe (144.248 mg/Kg), K (962.832 mg/Kg) and Mg (246.018 mg/Kg). Phenolics, anthraquinone glycosides, flavonoids, alkaloids and saponins were indicated in the aqueous extract by phytochemical screening and verified by indication of their functional groups in UV, HPLC and IR analyses. The functional groups present included -OH, C=0, -CH3, -NH and OC/ON. The UV analysis indicated the presence of conjugated systems in the aqueous husk extract. The crude water extract as well as the weak acid and the basic fractions all absorbed predominantly in the visible region whilst the strong acid fraction absorbed mostly in the UV region. The IR of the formulated plaster using the crude water extract indicated that the plaster contains a number of organic complexes and organometallic compounds such as methoxides, ethoxides and n-butoxides complicated by C-O and C-C coupling of Fe, Co, Al, Si and Zn. There were also SiPh4 at 1100 cm"1, Si(CH3)4 at 800-600 cm'1, Si-CH3 between 1280-1255 cm*1, trialkoxy silanes [(RO)3SiH] between 840-800 cm*1 as well as tetraoxides of silicon indicated around 880-720 cm"1. These were confirmed by associated absorption due to CH2-rocking which occurred at 725 and 720 cm1 (w).From the spectra of the plasters of all the fractions, those of the acidic fractions were predominated by bands due to organometallic compounds very similar to those of the plaster formulated using the crude water extract. The plaster of the weak acid fraction had more identical bands with the plaster of the water extract. Therefore, the organic components of the acidic fractions were identified to have played key roles in the reactions leading to the formation of relevant organometalloids. IR spectra of the formulated plaster attributable to aluminum complexes and trialkylboranes which are unaffected by water at ambient temperatures have also been observed at 1170, 1135 and 1120 cm"1.

Source: KNUST