Browsing by Author "Siriwardhana, M.W.H.N.M."

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    Effect of Residual Diammonium Hydrogen Phosphate (Dahp) Content on Natural Rubber Centrifuged Latex Properties Development and its Effect on Latex Film Properties
    (Uva Wellassa University of Sri Lanka, 2016) Siriwardhana, M.W.H.N.M.
    Natural rubber particle, a polyisoprene core is surrounded by a shell of non-rubber components, proteins and phospholipids. Natural PO43- are added to ammonia preserved latex due to the hydrolysis of phospholipid layer around the rubber particle. Although this process contribute for the stability of the latex this could produce a waste sludge; a precipitate of magnesium with phosphate. In centrifuged latex (CL) manufacturing process PO43- are added as diammonium hydrogen phosphate (DAHP) before centrifugation in order to remove residual Mg2+ present in field latex (F-NRL) to the level of 80-100 ppm. In most cases, added DAHP will leave excess PO43- in latex as most manufacturers added it without estimating the remaining Mg2+ present in latex. It results in high amount of PO43- in latex as considerable amount of PO43- are released from the • natural hydrolysis process with storage time. This study, aimed to determine the effect of residual DAHP content on properties of latex and films. A series of CL samples were prepared by adding 0 g (control sample), 3, 6, 9, 12 and 15 g of 15% DAHP. Changes of the latex characteristics such as mechanical (MST) and chemical stability time (CST), PO43- and Mgt} content, viscosity and mechanical properties of latex films were determined with time according to ISO procedures. High ammonia preserved CL showed a considerable amount of natural PO43" of about 350-250 ppm which fluctuate with storage time. The excess PO43- in the latex lead to decrease in viscosity and stability due to colloidal destabilization. The control sample showed highest MST (315 seconds) and CST (97 seconds) with storage time. Higher PO43- content in latex causes increase in tensile strength but not more than 23 M Pa. The highest tensile strength of 25 M Pa was achieved by control sample with time. Elongation at break of all the samples are greater than 750% and control sample showed the highest value. Finally concluded that, no need to add DAHP in manufacturing CL if the Mg2+ content of F-NRL is below 100 ppm. Key words: - colloidal; destabilization; diammonium; magnesium; rubber latex; phosphate
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    Effect of Residual Diammonium Hydrogen Phosphate Content on Properties of Natural Rubber Centrifuged Latex
    (Uva Wellassa University of Sri Lanka, 2021) Siriwardhana, M.W.H.N.M.; Attanayake, A.; Lochana, E.A.L.; Senevirathna, A.M.W.K.
    Natural rubber particle, a polyisoprene core is surrounded by a shell of non-rubber components, proteins and phospholipids. Natural PO43- are added to ammonia preserved latex due to the hydrolysis of phospholipid layer around the rubber particle. Although this process contributes to the stability of the latex this could produce a waste sludge; a precipitate of magnesium with phosphate. In centrifuged latex (CL) manufacturing process PO43- are added as diammonium hydrogen phosphate (DAHP) before centrifugation in order to remove residual Mg2+ present in field latex to the level of 80-100 ppm. In most cases, added DAHP will leave excess PO43- in latex as most manufacturers added it without estimating the remaining Mg2+ present in latex. It results in a high amount of PO43- in latex as a considerable amount of PO43- are released from the natural process of hydrolysis with storage time. This study aimed to determine the variation of residual PO43- content of CL with storage time and its ultimate effect on latex property development. A series of centrifuged latex samples were prepared by adding 0 g (control sample), 3 g, 6 g, 9 g, 12 g, and 15 g of 15% DAHP. Changes of the latex characteristics such as mechanical (MST) and chemical stability time (CST), PO43- and Mg2+ concentration, viscosity were determined with time. All the testing were carried out according to ISO procedures. High ammonia preserved CL showed a considerable amount of natural PO43- of about 300-200 ppm with storage time. The PO43- content of latex is not a stable amount and showed several fluctuations with time due to several chemical reactions within the latex sample. The excess amount of PO43- in the latex leads to a decrease in viscosity and stability of latex due to colloidal destabilization. The control sample showed the highest MST (315 seconds) and CST (97 seconds) with storage time than other samples revealing that there is no need for the addition of DAHP if the Mg2+ content of field latex is below 100 ppm in manufacturing CL. Keywords: Latex; Diammonium; Phosphate; Magnesium; Destabilization; Colloidal